US20110165337A1 - Method and system for printing aligned nanowires and other electrical devices - Google Patents

Abstract

Methods and systems for applying nanowires and electrical devices to surfaces are described. In a first aspect, at least one nanowire is provided proximate to an electrode pair. An electric field is generated by electrodes of the electrode pair to associate the at least one nanowire with the electrodes. The electrode pair is aligned with a region of the destination surface. The at least one nanowire is deposited from the electrode pair to the region. In another aspect, a plurality of electrical devices is provided proximate to an electrode pair. An electric field is generated by electrodes of the electrode pair to associate an electrical device of the plurality of electrical devices with the electrodes. The electrode pair is aligned with a region of the destination surface. The electrical device is deposited from the electrode pair to the region.

Description

• This application is a divisional of allowed U.S. application Ser. No. 12/114,446, filed on May 2, 2008, which claims the benefit of U.S. Provisional Application No. 60/916,337, filed on May 7, 2007, both of which are incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to nanostructures, and more particularly, to the deposition of aligned nanostructures and electrical devices.
• 2. Background of the Invention
• Nanostructures, such as nanowires, have the potential to facilitate a whole new generation of electronic devices. A major impediment to the emergence of this new generation of electronic devices based on nanostructures is the ability to effectively align and deposit the nanostructures on various surfaces, such as substrates. Electric fields enable the alignment of nanowires suspended in suspension, but current techniques pose stringent constraints on the scalability to large area substrates. Likewise, current techniques for depositing electrical devices, such as integrated circuits, dies, optical components, etc., do not scale well to large area substrates.
• What are needed are systems and methods for achieving a high quality deposition of nanostructures and other electrical devices that are suitable for manufacturing large arrays of nanostructure-enabled electronic devices.
SUMMARY OF THE INVENTION
• Methods and systems for applying nanowires to surfaces are described. In an example aspect, nanowires are provided proximate to an electrode pair. An electric field is generated by electrodes of the electrode pair to associate the nanowires with the electrodes. The electrode pair is aligned with a region of the destination surface. The nanowires are deposited from the electrode pair to the region.
• The nanowires may be deposited to the region in a variety of ways. For example, a passive or active force, or combination of such forces, may be used to move the nanowires from the electrodes to the destination surface. Example forces include an electric field (AC and/or DC), a vacuum force, an electrostatic force, gravity, and/or other forces.
• In a first example, the electrode pair may be formed on a transfer surface. The transfer surface is configured to have a first electric charge. The first electric charge applies a repulsive electrostatic force to the nanowires (e.g., the nanowires may have the same charge as the first electric charge). The electric field generated by the electrodes attracts the nanowires to the transfer surface against the repulsive electrostatic force. In one instance, the electric field may be biased with an alternating current (AC) field to attract the nanowires to the transfer surface. The electric field may be reduced (including entirely removed) to enable the nanowires to be moved toward the destination surface by the repulsive electrostatic force of the first electric charge.
• In another example, the destination surface has a second electric charge that is opposite the first electric charge. An attractive electrostatic force of the second electric charge attracts the nanowires to the destination surface. A distance between the nanowires and the destination surface may be reduced to increase this attraction.
• In another example, the transfer surface is vibrated (e.g., ultrasonically) to enable the attractive electrostatic force of the second electric charge to attract the nanowires toward the destination surface.
• In another example, a vacuum is applied from the destination surface to the transfer surface to move the nanowires toward the destination surface. For example, the vacuum may draw a solution in which the nanowires reside towards the destination surface. The solution flow draws the nanowires toward the destination surface.
• In another example, a second electric field associated with the destination surface is generated to attract the nanowires toward the destination surface.
• In another aspect of the present invention, a system for applying nanowires to a destination surface is described. The system includes a body having a transfer surface, an electrode pair formed on the transfer surface, a suspension that includes a plurality of nanowires provided proximate to the electrode pair, a signal generator, and an alignment mechanism. The signal generator is coupled to the electrode pair. The signal generator is configured to supply an electric signal to enable electrodes of the electrode pair to generate an electric field to associate nanowires of the plurality of nanowires with the electrodes. The alignment mechanism is configured to align the electrode pair with a region of the destination surface to enable the nanowires to be deposited from the electrode pair to the region.
• In another aspect of the present invention, electrical devices are transferred to surfaces in a similar manner as described elsewhere herein for nanowires. In aspects, one or more electrical devices are provided proximate to an electrode pair on a transfer surface. The electrode pair is energized, whereby an electrical device becomes associated with the electrode pair. Subsequently, the electrical device is deposited from the electrode pair to a destination surface.
• In another aspect of the present invention, nanostructures, such as nanowires, are transferred to a destination surface. A transfer surface of a print head is positioned adjacent to a destination surface. A nanowire is associated with the transfer surface. A distance between the transfer surface and the destination surface is reduced. A fluid is received in one or more openings in the transfer surface from between the transfer surface and the destination surface during the reducing of the distance between the transfer and destination surfaces. Receiving the fluid in the opening(s) reduces a shear force on the nanowire. The nanowire is deposited from the transfer surface to the destination surface.
• In still another aspect of the present invention, nanostructures, such as nanowires, are transferred to a destination substrate. A nanowire transfer system includes an association station, a printing station, and a cleaning station. The association station is configured to receive a plurality of print heads, and to associate nanostructures with a transfer surface of each of the received plurality of print heads. The printing station is configured to receive a destination substrate and at least one of the print heads, and to transfer the nanostructures from the received print head(s) to a plurality of regions of a surface of the destination substrate. The cleaning station is configured to receive the plurality of print heads from the printing station, and to clean the received plurality of print heads.
• In aspects, the printing station may be configured to perform the transfer of the nanostructures as a “wet” transfer or a “dry” transfer.
• In a further aspect, the nanowire transfer system may include an inspection station. The inspection station is configured to perform an inspection of the transfer surfaces of the plurality of print heads, and to select at least one print head of the plurality of print heads based on the inspection. The printing station may be configured to transfer the nanostructures from the selected at least one print head.
• In a still further aspect, the nanowire transfer system may include a repair station. The repair station is configured to perform an inspection of the nanostructures transferred to the plurality of regions of the surface of the destination substrate. If the repair station determines an arrangement of nanostructures in need of repair, the repair station is configured to repair the arrangement of nanostructures.
• In a still further aspect, the nanowire transfer system may include a print head drying station and a repair station. The print head drying station is configured to dry the nanostructures associated with the transfer surfaces of the plurality of print heads. The repair station is configured to perform an inspection of the dried transfer surfaces. If the repair station determines an arrangement of nanostructures associated with a transfer surface in need of repair, the repair station is configured to repair the determined arrangement of nanostructures. The print head drying station enables a dry transfer of the nanowires to be performed at the printing station.
• In a still further aspect, the nanowire transfer system may include a panel drying station. The panel drying station is configured to dry the nanostructures transferred to the plurality of regions of the surface of the destination substrate (e.g., if a wet transfer of the nanowires is performed by the printing station)
• Further embodiments, features, and advantages of the invention, as well as the structure and operation of the various embodiments of the invention are described in detail below with reference to accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
• The invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The drawing in which an element first appears is indicated by the left-most digit in the corresponding reference number.
• FIG. 1A is a diagram of a single crystal semiconductor nanowire.
• FIG. 1B is a diagram of a nanowire doped according to a core-shell (CS) structure.
• FIG. 1C is a diagram of a nanowire doped according to a core-shell-shell (CSS) structure.
• FIG. 2 shows a block diagram of a nanostructure transfer system, according to an example embodiment of the present invention.
• FIG. 3 shows a flowchart providing example steps for transferring nanostructures, according to example embodiments of the present invention.
• FIGS. 4-6 show block diagram views of the nanostructure transfer system ofFIG. 2 during different phases of operation, according to example embodiments of the present invention.
• FIG. 7 shows a nanowire print head, according to an embodiment of the present invention.
• FIGS. 8 and 9 show portions of example nanowire transfer systems, according to embodiments of the present invention.
• FIG. 10 shows a block diagram of a nanowire solution flow system, according to an example embodiment of the present invention.
• FIGS. 11 and 12 show views of an example print head having cantilevers, according to an example embodiment of the present invention.
• FIG. 13 shows an electric field generation system for a transfer system, according to an example embodiment of the present invention.
• FIG. 14 shows a transfer system, where an electric field is generated to associate nanowires with an electrode pair, according to an example embodiment of the present invention.
• FIG. 15 shows the transfer system ofFIG. 14, with an associated nanowire, according to an example embodiment of the present invention.
• FIG. 16 shows forces acting upon a nanowire in a transfer system, according to an example embodiment of the present invention.
• FIGS. 17 and 18 show plan and side views of the print head ofFIG. 11, with associated nanowires, according to example embodiment of the present invention.
• FIG. 19 shows an alignment system, according to an example embodiment of the present invention.
• FIG. 20 shows a print head having been aligned with a surface region by alignment mechanism, according to an embodiment of the present invention.
• FIGS. 21 and 22 show the print head in solution ofFIG. 9 being aligned with a destination surface, according to an example embodiment of the present invention.
• FIG. 23 shows an example print head with spacers, according to an embodiment of the present invention.
• FIGS. 24 and 25 show side views of the print head ofFIG. 11 in alignment with a destination surface, according to an example embodiment of the present invention.
• FIG. 26 shows a nanowire transfer system with a vacuum source, according to an example embodiment of the present invention.
• FIG. 27 shows an example plan view of a transfer surface with vacuum ports, according to an example embodiment of the present invention.
• FIGS. 28,29,31A,31B,32, and33 show example nanowire transfer systems configured to deposit nanowires, according to example embodiments of the present invention.
• FIG. 30 shows a plot of potential energy levels for a transfer surface having an oxide layer and for a destination surface having a nitride layer, according to an embodiment of the present invention.
• FIG. 31C shows a plot of the inertial motion of nanowires in isopropyl alcohol, according to an embodiment of the present invention.
• FIG. 34 shows a nanowire transfer system that includes a print head having two electrode pairs, according to an embodiment of the present invention.
• FIG. 35 shows a flowchart providing example steps for transferring electrical devices, according to example embodiments of the present invention.
• FIGS. 36-39 show block diagram views of an electrical device transfer system during different phases of operation, according to example embodiments of the present invention.
• FIG. 40 shows a cross-sectional view of a nanostructure transfer system, according to an example embodiment of the present invention.
• FIG. 41 shows a view of a transfer surface of the print head shown inFIG. 40, according to an example embodiment of the present invention.
• FIG. 42 shows a cross-sectional view of a nanostructure transfer system, according to an example embodiment of the present invention.
• FIG. 43 show a view of a transfer surface of the print head shown inFIG. 42, according to an example embodiment of the present invention.
• FIG. 44 shows a flowchart for transferring nanostructures to a destination surface, according to an example embodiment of the present invention.
• FIG. 45 shows a cross-sectional view of the nanostructure transfer system ofFIG. 42, illustrating a nanowire being deposited to the destination surface, according to an example embodiment of the present invention.
• FIG. 46 shows a nanostructure transfer system, according to an embodiment of the present invention.
• FIG. 47 shows a cross-sectional view of a print head, according to an example embodiment of the present invention.
• FIG. 48 shows a block diagram of a nanostructure printing system, according to an example embodiment of the present invention.
• FIG. 49 shows a flowchart for a print head pipeline portion of the system ofFIG. 48, according to an example embodiment of the present invention.
• FIG. 50 shows a flowchart for a panel pipeline portion of the system ofFIG. 48, according to an example embodiment of the present invention.
• FIGS. 51 and 52 show views of an example association station, according to embodiments of the present invention.
• FIG. 53 shows an example inspection station, according to an embodiment of the present invention.
• FIGS. 54-56 show views of a printing station during a nanostructure transfer process, according to an example embodiment of the present invention.
• FIG. 57 shows an example cleaning station, according to an embodiment of the present invention
• FIGS. 58 and 59 show views of a panel repair station, according to example embodiments of the present invention.
• FIG. 60 shows an example panel drying station, according to an embodiment of the present invention.
• FIG. 61 shows a block diagram of a nanostructure printing system, according to an example embodiment of the present invention.
• FIG. 62 shows a flowchart for a print head pipeline portion of the system ofFIG. 61, according to an example embodiment of the present invention.
• FIG. 63 shows a flowchart for a panel pipeline portion of the system ofFIG. 61, according to an example embodiment of the present invention.
• FIGS. 64,66,68, and70 show views of a nanostructure transfer system during a nanostructure transfer process, according to example embodiments of the present invention.
• FIGS. 65,67,69, and71 show respective images captured using a microscope of the nanostructure transfer system shown inFIGS. 64,66,68, and70, according to example embodiments of the present invention.
• The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
DETAILED DESCRIPTION OF THE INVENTION
• It should be appreciated that the particular implementations shown and described herein are examples of the invention and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional electronics, manufacturing, semiconductor devices, and nanowire (NW), nanorod, nanotube, and nanoribbon technologies and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail herein. Furthermore, for purposes of brevity, the invention is frequently described herein as pertaining to nanowires.
• It should be appreciated that although nanowires are frequently referred to, the techniques described herein are also applicable to other nanostructures, such as nanorods, nanotubes, nanotetrapods, nanoribbons and/or combinations thereof. It should further be appreciated that the manufacturing techniques described herein could be used to create any semiconductor device type, and other electronic component types. Further, the techniques would be suitable for application in electrical systems, optical systems, consumer electronics, industrial electronics, wireless systems, space applications, or any other application.
• As used herein, an “aspect ratio” is the length of a first axis of a nanostructure divided by the average of the lengths of the second and third axes of the nanostructure, where the second and third axes are the two axes whose lengths are most nearly equal to each other. For example, the aspect ratio for a perfect rod would be the length of its long axis divided by the diameter of a cross-section perpendicular to (normal to) the long axis.
• The term “heterostructure” when used with reference to nanostructures refers to nanostructures characterized by at least two different and/or distinguishable material types. Typically, one region of the nanostructure comprises a first material type, while a second region of the nanostructure comprises a second material type. In certain embodiments, the nanostructure comprises a core of a first material and at least one shell of a second (or third etc.) material, where the different material types are distributed radially about the long axis of a nanowire, a long axis of an arm of a branched nanocrystal, or the center of a nanocrystal, for example. A shell need not completely cover the adjacent materials to be considered a shell or for the nanostructure to be considered a heterostructure. For example, a nanocrystal characterized by a core of one material covered with small islands of a second material is a heterostructure. In other embodiments, the different material types are distributed at different locations within the nanostructure. For example, material types can be distributed along the major (long) axis of a nanowire or along a long axis of arm of a branched nanocrystal. Different regions within a heterostructure can comprise entirely different materials, or the different regions can comprise a base material.
• As used herein, a “nanostructure” is a structure having at least one region or characteristic dimension with a dimension of less than about 500 nm, e.g., less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm. Typically, the region or characteristic dimension will be along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, branched nanocrystals, nanotetrapods, tripods, bipods, nanocrystals, nanodots, quantum dots, nanoparticles, branched tetrapods (e.g., inorganic dendrimers), and the like. Nanostructures can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g., heterostructures). Nanostructures can be, for example, substantially crystalline, substantially monocrystalline, polycrystalline, amorphous, or a combination thereof. In one aspect, each of the three dimensions of the nanostructure has a dimension of less than about 500 nm, for example, less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm.
• As used herein, the term “nanowire” generally refers to any elongated conductive or semiconductive material (or other material described herein) that includes at least one cross-sectional dimension that is less than 500 nm, and preferably, equal to or less than less than about 100 nm, and has an aspect ratio (length:width) of greater than 10, preferably greater than 50, and more preferably, greater than 100. Exemplary nanowires for use in the practice of the methods and systems of the present invention are on the order of 10's of microns long (e.g., about 10, 20, 30, 40, 50 microns, etc.) and about 100 nm in diameter.
• The nanowires of this invention can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g., nanowire heterostructures). The nanowires can be fabricated from essentially any convenient material or materials, and can be, e.g., substantially crystalline, substantially monocrystalline, polycrystalline, or amorphous. Nanowires can have a variable diameter or can have a substantially uniform diameter, that is, a diameter that shows a variance less than about 20% (e.g., less than about 10%, less than about 5%, or less than about 1%) over the region of greatest variability and over a linear dimension of at least 5 nm (e.g., at least 10 nm, at least 20 nm, or at least 50 nm). Typically the diameter is evaluated away from the ends of the nanowire (e.g., over the central 20%, 40%, 50%, or 80% of the nanowire). A nanowire can be straight or can be e.g., curved or bent, over the entire length of its long axis or a portion thereof. In certain embodiments, a nanowire or a portion thereof can exhibit two- or three-dimensional quantum confinement. Nanowires according to this invention can expressly exclude carbon nanotubes, and, in certain embodiments, exclude “whiskers” or “nanowhiskers”, particularly whiskers having a diameter greater than 100 nm, or greater than about 200 nm.
• Examples of such nanowires include semiconductor nanowires as described in Published International Patent Application Nos. WO 02/17362, WO 02/48701, and WO 01/03208, carbon nanotubes, and other elongated conductive or semiconductive structures of like dimensions, which are incorporated herein by reference.
• As used herein, the term “nanorod” generally refers to any elongated conductive or semiconductive material (or other material described herein) similar to a nanowire, but having an aspect ratio (length:width) less than that of a nanowire. Note that two or more nanorods can be coupled together along their longitudinal axis so that the coupled nanorods span all the way between electrodes. Alternatively, two or more nanorods can be substantially aligned along their longitudinal axis, but not coupled together, such that a small gap exists between the ends of the two or more nanorods. In this case, electrons can flow from one nanorod to another by hopping from one nanorod to another to traverse the small gap. The two or more nanorods can be substantially aligned, such that they form a path by which electrons can travel between electrodes.
• A wide range of types of materials for nanowires, nanorods, nanotubes and nanoribbons can be used, including semiconductor material selected from, e.g., Si, Ge, Sn, Se, Te, B, C (including diamond), P, B—C, B—P(BP₆), B—Si, Si—C, Si—Ge, Si—Sn and Ge—Sn, SiC, BN, BP, BAs, MN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, Cul, AgF, AgCl, AgBr, Agl, BeSiN₂, CaCN₂, ZnGeP₂, CdSnAs₂, ZnSnSb₂, CuGeP₃, CuSi₂P₃, (Cu, Ag)(Al, Ga, In, Tl, Fe)(S, Se, Te)₂, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂(S, Se, Te)₃, Al₂CO, and an appropriate combination of two or more such semiconductors.
• The nanowires can also be formed from other materials such as metals such as gold, nickel, palladium, iradium, cobalt, chromium, aluminum, titanium, tin and the like, metal alloys, polymers, conductive polymers, ceramics, and/or combinations thereof. Other now known or later developed conducting or semiconductor materials can be employed.
• In certain aspects, the semiconductor may comprise a dopant from a group consisting of: a p-type dopant from Group III of the periodic table; an n-type dopant from Group V of the periodic table; a p-type dopant selected from a group consisting of: B, Al and In; an n-type dopant selected from a group consisting of: P, As and Sb; a p-type dopant from Group II of the periodic table; a p-type dopant selected from a group consisting of: Mg, Zn, Cd and Hg; a p-type dopant from Group IV of the periodic table; a p-type dopant selected from a group consisting of: C and Si; or an n-type dopant selected from a group consisting of: Si, Ge, Sn, S, Se and Te. Other now known or later developed dopant materials can be employed.
• Additionally, the nanowires or nanoribbons can include carbon nanotubes, or nanotubes formed of conductive or semiconductive organic polymer materials, (e.g., pentacene, and transition metal oxides).
• Hence, although the term “nanowire” is referred to throughout the description herein for illustrative purposes, it is intended that the description herein also encompass the use of nanotubes (e.g., nanowire-like structures having a hollow tube formed axially therethrough). Nanotubes can be formed in combinations/thin films of nanotubes as is described herein for nanowires, alone or in combination with nanowires, to provide the properties and advantages described herein.
• It should be understood that the spatial descriptions (e.g., “above”, “below”, “up”, “down”, “top”, “bottom,” “vertical,” “horizontal,” etc.) made herein are for purposes of illustration only, and that devices of the present invention can be spatially arranged in any orientation or manner.
• FIG. 1A illustrates a single crystal semiconductor nanowire core (hereafter “nanowire”)100.FIG. 1A shows ananowire100 that is a uniformly doped single crystal nanowire. Such single crystal nanowires can be doped into either p- or n-type semiconductors in a fairly controlled way. Doped nanowires such asnanowire100 exhibit improved electronic properties. For instance, such nanowires can be doped to have carrier mobility levels comparable to bulk single crystal materials.
• FIG. 1B shows ananowire110 having a core-shell structure, with ashell112 around the nanowire core. Surface scattering can be reduced by forming an outer layer of the nanowire, such as by the passivation annealing of nanowires, and/or the use of core-shell structures with nanowires. An insulating layer, such as an oxide coating, can be formed on a nanowire as the shell layer. Furthermore, for example, for silicon nanowires having an oxide coating, the annealing of the nanowires in hydrogen (H₂) can greatly reduce surface states. In embodiments, the core-shell combination is configured to satisfy the following constraints: (1) the shell energy level should be higher than the core energy level, so that the conducting carriers are confined in the core; and (2) the core and shell materials should have good lattice match, with few surface states and surface charges. Other more complex NW core-shell structures may also be used to include a core of single crystal semiconductor, an inner-shell of gate dielectric, and an outer-shell of conformal gate, such as shown inFIG. 1C.FIG. 1C shows ananowire114 having a core-shell-shell structure, with aninner shell112 andouter shell116 around the nanowire core. This can be realized by depositing a layer of TaAlN, WN, or highly-doped amorphous silicon around the Si/SiO_xcore-shell structure (described above) as the outer-gate shell, for example.
• The valence band of the insulating shell can be lower than the valence band of the core for p-type doped wires, or the conduction band of the shell can be higher than the core for n-type doped wires. Generally, the core nanostructure can be made from any metallic or semiconductor material, and the one or more shell layers deposited on the core can be made from the same or a different material. For example, the first core material can comprise a first semiconductor selected from the group consisting of: a Group II-VI semiconductor, a Group III-V semiconductor, a Group IV semiconductor, and an alloy thereof. Similarly, the second material of the one or more shell layers can comprise an oxide layer, a second semiconductor, the same as or different from the first semiconductor, e.g., selected from the group consisting of: a Group II-VI semiconductor, a Group III-V semiconductor, a Group IV semiconductor, and an alloy thereof. Example semiconductors include, but are not limited to, CdSe, CdTe, InP, InAs, CdS, ZnS, ZnSe, ZnTe, HgTe, GaN, GaP, GaAs, GaSb, InSb, Si, Ge, AlAs, AlSb, PbSe, PbS, and PbTe. As noted above, metallic materials such as gold, chromium, tin, nickel, aluminum etc. and alloys thereof can be used as the core material, and the metallic core can be overcoated with an appropriate shell material such as silicon dioxide or other insulating materials, which may in turn may be coated with one or more additional shell layers of the materials described above to form more complex core-shell-shell nanowire structures.
• Nanostructures can be fabricated and their size can be controlled by any of a number of convenient methods that can be adapted to different materials. For example, synthesis of nanocrystals of various composition is described in, e.g., Peng et al. (2000) “Shape Control of CdSe Nanocrystals”Nature404, 59-61; Puntes et al. (2001) “Colloidal nanocrystal shape and size control: The case of cobalt”Science291, 2115-2117; U.S. Pat. No. 6,306,736 to Alivisatos et al. (Oct. 23, 2001) entitled “Process for forming shaped group III-V semiconductor nanocrystals, and product formed using process”; U.S. Pat. No. 6,225,198 to Alivisatos et al. (May 1, 2001) entitled “Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process”; U.S. Pat. No. 5,505,928 to Alivisatos et al. (Apr. 9, 1996) entitled “Preparation of III-V semiconductor nanocrystals”; U.S. Pat. No. 5,751,018 to Alivisatos et al. (May 12, 1998) entitled “Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers”; U.S. Pat. No. 6,048,616 to Gallagher et al. (Apr. 11, 2000) entitled “Encapsulated quantum sized doped semiconductor particles and method of manufacturing same”; and U.S. Pat. No. 5,990,479 to Weiss et al. (Nov. 23, 1999) entitled “Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes.”
• Growth of nanowires having various aspect ratios, including nanowires with controlled diameters, is described in, e.g., Gudiksen et al (2000) “Diameter-selective synthesis of semiconductor nanowires”J. Am. Chem. Soc.122, 8801-8802; Cui et al. (2001) “Diameter-controlled synthesis of single-crystal silicon nanowires”Appl. Phys. Lett.78, 2214-2216; Gudiksen et al. (2001) “Synthetic control of the diameter and length of single crystal semiconductor nanowires”J. Phys. Chem. B105, 4062-4064; Morales et al. (1998) “A laser ablation method for the synthesis of crystalline semiconductor nanowires”Science279, 208-211; Duan et al. (2000) “General synthesis of compound semiconductor nanowires”Adv. Mater.12, 298-302; Cui et al. (2000) “Doping and electrical transport in silicon nanowires”J. Phys. Chem. B104, 5213-5216; Peng et al. (2000) “Shape control of CdSe nanocrystals”Nature404, 59-61; Puntes et al. (2001) “Colloidal nanocrystal shape and size control: The case of cobalt”Science291, 2115-2117; U.S. Pat. No. 6,306,736 to Alivisatos et al. (Oct. 23, 2001) entitled “Process for forming shaped group III-V semiconductor nanocrystals, and product formed using process”; U.S. Pat. No. 6,225,198 to Alivisatos et al. (May 1, 2001) entitled “Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process”; U.S. Pat. No. 6,036,774 to Lieber et al. (Mar. 14, 2000) entitled “Method of producing metal oxide nanorods”; U.S. Pat. No. 5,897,945 to Lieber et al. (Apr. 27, 1999) entitled “Metal oxide nanorods”; U.S. Pat. No. 5,997,832 to Lieber et al. (Dec. 7, 1999) “Preparation of carbide nanorods”; Urbau et al. (2002) “Synthesis of single-crystalline perovskite nanowires composed of barium titanate and strontium titanate”J. Am. Chem. Soc.,124, 1186; and Yun et al. (2002) “Ferroelectric Properties of Individual Barium Titanate Nanowires Investigated by Scanned Probe Microscopy”Nanoletters2, 447.
• Growth of branched nanowires (e.g., nanotetrapods, tripods, bipods, and branched tetrapods) is described in, e.g., Jun et al. (2001) “Controlled synthesis of multi-armed CdS nanorod architectures using monosurfactant system”J. Am. Chem. Soc.123, 5150-5151; and Manna et al. (2000) “Synthesis of Soluble and Processable Rod-,Arrow-,Teardrop-,and Tetrapod-Shaped CdSe Nanocrystals” J. Am. Chem. Soc.122, 12700-12706.
• Synthesis of nanoparticles is described in, e.g., U.S. Pat. No. 5,690,807 to Clark Jr. et al. (Nov. 25, 1997) entitled “Method for producing semiconductor particles”; U.S. Pat. No. 6,136,156 to El-Shall, et al. (Oct. 24, 2000) entitled “Nanoparticles of silicon oxide alloys”; U.S. Pat. No. 6,413,489 to Ying et al. (Jul. 2, 2002) entitled “Synthesis of nanometer-sized particles by reverse micelle mediated techniques”; and Liu et al. (2001) “Sol-Gel Synthesis of Free-Standing Ferroelectric Lead Zirconate Titanate Nanoparticles”J. Am. Chem. Soc.123, 4344. Synthesis of nanoparticles is also described in the above citations for growth of nanocrystals, nanowires, and branched nanowires, where the resulting nanostructures have an aspect ratio less than about 1.5.
• Synthesis of core-shell nanostructure heterostructures, namely nanocrystal and nanowire (e.g., nanorod) core-shell heterostructures, are described in, e.g., Peng et al. (1997) “Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility”J. Am. Chem. Soc.119, 7019-7029; Dabbousi et al. (1997) “(CdSe)ZnS core-shell quantum dots: Synthesis and characterization of a size series of highly luminescent nanocrysallites”J. Phys. Chem. B101, 9463-9475; Manna et al. (2002) “Epitaxial growth and photochemical annealing of graded CdS/ZnS shells on colloidal CdSe nanorods”J. Am. Chem. Soc.124, 7136-7145; and Cao et al. (2000) “Growth and properties of semiconductor core/shell nanocrystals with InAs cores”J. Am. Chem. Soc.122, 9692-9702. Similar approaches can be applied to growth of other core-shell nanostructures.
• Growth of nanowire heterostructures in which the different materials are distributed at different locations along the long axis of the nanowire is described in, e.g., Gudiksen et al. (2002) “Growth of nanowire superlattice structures for nanoscale photonics and electronics”Nature415, 617-620; Bjork et al. (2002) “One-dimensional steeplechase for electrons realized”Nano Letters2, 86-90; Wu et al. (2002) “Block-by-block growth of single-crystalline Si/SiGe superlattice nanowires”Nano Letters2, 83-86; and U.S. patent application 60/370,095 (Apr. 2, 2002) to Empedocles entitled “Nanowire heterostructures for encoding information.” Similar approaches can be applied to growth of other heterostructures.
Example Embodiments for Transferring Nanowires
• Embodiments for applying nanostructures such as nanowires to surfaces are described in this section. In embodiments, one or more nanowires are provided proximate to an electrode pair on a transfer surface. The electrode pair is energized, whereby the nanowires become associated with the electrode pair. Subsequently, the nanowires are deposited from the electrode pairs to a destination surface.
• The term “positioning” as used throughout refers to the alignment and association, as well as the deposition or coupling, of nanowires onto a surface, for example, an electrode pair. Positioning includes nanowires that are both aligned and non-aligned. The term “aligned” nanowires as used throughout refers to nanowires that are substantially parallel or oriented in the same or substantially same direction of one another (i.e. the nanowires are aligned in the same direction, or within about 45° of one another). The nanowires of the present invention are aligned such that they are all substantially parallel to one another and substantially perpendicular to each electrode of an electrode pair (e.g., aligned parallel to an axis through both electrodes) (though in additional embodiments, they can be aligned parallel to an electrode). Positioning of nanowires onto an electrode pair includes positioning the nanowires such that the nanowires span the electrode pair. In embodiments in which the nanowires are longer than the distance separating two electrodes of an electrode pair, the nanowires may extend beyond the electrodes.
• Methods for providing nanowires for use in the methods and systems of the present invention are well known in the art. In an embodiment, the nanowires are provided in a suspension, which is a plurality of nanowires suspended in a liquid. In an embodiment, the liquid is an aqueous media, such as water or a solution of water, ions (including salts), and other components, for example surfactants. Additional examples of liquids suitable for preparing nanowire suspensions include, but are not limited, organic solvents, inorganic solvents, alcohols (e.g., isopropyl alcohol) (IPA), etc.
• As used herein the phrase “proximate to an electrode pair” as it relates to providing the nanowires means that the nanowires are provided or positioned such that they can be acted upon by an electric field generated at the electrode pair. This is a distance from the electrode pair such that they can be associated with the electrodes. In example embodiments, the nanowires are provided such that they are at distance of less than about 10 mm from the electrode pairs. For example, the nanowires may be provided such that they are less than about 100 μm, less than about 50 μm, or less than about 1 μm from the electrode pair.
• In embodiments, the present invention provides a system or apparatus for nanostructure alignment and deposition. For example,FIG. 2 shows ananostructure transfer system200, according to an example embodiment of the present invention. As shown inFIG. 2,transfer system200 includes ananostructure print head202, nanostructure(s)204, and adestination substrate212.Nanostructure print head202 is a body configured to receive nanostructure(s)204, and to transfer nanostructure(s)204 tosubstrate212. As shown inFIG. 2,nanostructure print head202 has atransfer surface206 and includes anelectrode pair208.Substrate212 has asurface210, referred to as a “destination surface” for receiving nanostructure(s)204.Electrode pair208 is located ontransfer surface206. Nanostructure(s)204 are received byelectrode pair208 oftransfer surface206, for transfer todestination surface210. Nanostructure(s)204 can include any of the nanostructure types mentioned elsewhere herein, including one or more nanowires. Further description of the components oftransfer system200 is provided further below.
• FIG. 3 shows aflowchart300 providing example steps for transferring nanostructures, according to example embodiments of the present invention. For example,nanostructure print head202 ofFIG. 2 can be used to transfer nanostructure(s)204 according toflowchart300. For illustrative purposes,flowchart300 is described as follows with respect to FIGS.2 and4-6, which show various block diagrams of embodiments of the present invention. Other structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. Not all steps offlowchart300 are necessarily performed in all embodiments.
• Flowchart300 begins withstep302. Instep302, at least one nanostructure is provided proximate to an electrode pair. For example, as shown inFIG. 2, nanostructure(s)204 are provided proximate toelectrode pair208. For instance, nanostructure(s)204 may be present in a solution which flows in contact withelectrode pair208, to enable nanostructure(s)204 to be positioned proximate toelectrode pair208. Alternatively, nanostructure(s)204 may be provided proximate toelectrode pair208 in other ways.
• Instep304, an electric field is generated by electrodes of the electrode pair to associate one or more nanostructures with the electrodes. For instance, an electrical potential may be coupled toelectrode pair208 to generate the electric field. The electric field generated byelectrode pair208 may be used to associate nanostructure(s)204 withelectrode pair208 that are proximately located toelectrode pair208. As shown inFIG. 4,nanostructures204 are associated withelectrode pair208. In an embodiment, associated nanostructure(s)204 are held suspended at a distance fromtransfer surface206 by the electric field. Example embodiments for generating an electric field by an electrode pair to associate nanostructures are described in further detail below.
• Instep306, the electrode pair is aligned with a region of the destination surface. For example, as shown inFIG. 5,electrode pair208 is aligned withdestination surface210, bynanostructure print head202, which is moved towards destination surface210 (e.g., in a direction shown by a dotted arrow inFIG. 5). In an embodiment,electrode pair208 is aligned in contact withdestination surface210. In another embodiment,electrode pair208 is aligned adjacent todestination surface210, a short distance away fromdestination surface210.Electrode pair208 may be aligned with any region ofsurface210, including a generally open region (i.e., no contacts onsurface210 are required), a region having electrical contacts corresponding toelectrode pair208, or other region.Electrode pair208 is aligned with a region ofsurface210 on which nanostructure(s)204 are to be positioned.
• Instep308, the one or more nanostructures are deposited from the electrode pair to the region. Nanostructure(s)204 may be deposited ondestination surface210 in a variety of ways. Various example embodiments for depositing nanostructures on a surface are described in detail below.
• Instep310, the electrode pair is removed from alignment with the region of the surface. For example, as shown inFIG. 6,nanostructure print head202 is moved away from destination surface210 (e.g., in a direction shown by dotted arrow inFIG. 6). Nanostructure(s)204 remain deposited onsurface210.Nanostructure print head202 can subsequently be used to repeat performingflowchart300 for the same region ofsurface210, a different region ofsurface210, and/or a surface of a structure other thansubstrate212, to deposit further nanostructures.
• Detailed example embodiments fornanostructure transfer system200 and for performingflowchart300 are described as follows. The embodiments are described below with respect to nanowires. These embodiments are provided for illustrative purposes, and are not intended to be limiting. It will be understood by persons skilled in the relevant art(s) that these embodiments may be used to transfer other types of nanostructures than just nanowires. Furthermore, these various embodiments may be adapted and/or combined in a variety of ways, as would be known to persons skilled in the relevant art(s) from the teachings herein.
• FIG. 7 shows ananowire print head702, which is an example ofnanostructure print head202 shown inFIG. 2, according to an embodiment of the present invention. As shown inFIG. 7,nanowire print head702 includeselectrode pair208 ontransfer surface206.Transfer surface206 may be a surface of a substrate or other structure ofprint head702 onto whichelectrode pair208 is formed (e.g., patterned, plated, etc.).Electrode pair208 includes afirst electrode704 and asecond electrode706.Transfer surface206 may be formed of any suitable material, such as a semiconductor wafer or dielectric material. Example suitable materials include, but are not limited to Si, SiO₂, GaAs, InP, and other semiconductor materials described herein. Exemplary materials for use as first andsecond electrodes704 and706 include, but are not limited to, Al, Mo (Moly electrodes), Cu, Fe, Au, Ag, Pt, Cr/Au, doped polysilicon, etc. Electrodes for use in the practice of the present invention can also further comprise an oxide coating or other layer on their surface, if desired. Any suitable orientation or pattern of first andsecond electrodes704 and706 can be used. Note that in embodiments, one or more additional electrodes may be positioned on print head702 (e.g., betweenelectrodes704 and706). Such additional electrodes may be configured to modify an attractive or repulsive force (e.g., an electrostatic force) between the nanowires associated withprint head702 andtransfer surface206 and/or a destination surface.
• Nanowires may be provided proximate to first andsecond electrodes704 and706 in a variety of ways according to step302 offlowchart300. For example,FIG. 8 shows a portion of ananowire transfer system800, according to an embodiment of the present invention. As shown inFIG. 8,transfer system800 includesprint head702 and asolution container802.Container802 contains asolution804 that includes a plurality ofnanowires806, which may be referred to as a “nanowire suspension.” In the embodiment ofFIG. 8,transfer surface206 ofprint head702 is temporarily moved (e.g., “dipped”) intosolution804 to enablenanowires806 to become proximate toelectrode pair208, according to step302 offlowchart300.
• FIG. 9 shows a portion of ananowire transfer system900, according to an alternative embodiment of the present invention. As shown inFIG. 9,transfer system900 includesprint head702 andsolution container802.Container802 containssolution804 that includes plurality ofnanowires806. In the embodiment ofFIG. 9, transfer surface206 (and the rest of print head702) resides insolution804, to enablenanowires806 to become proximate toelectrode pair208, according to step302 offlowchart300.
• Note that althoughelectrode pair208 is shown inFIG. 9 as facing upward insolution804, and is shown inFIG. 8 as facing downward,print head702 may be oriented in other ways so thatelectrode pair208 may face in other directions, including upwards, downwards or sideways.
• Nanowires806 may be any suitable nanowire type described herein or otherwise known. For example,nanowires806 may have a semiconductor core and one or more shell layers disposed about the core (i.e., the shell layers surround the core) (such as shown inFIGS. 1B and 1C). Examples semiconductor materials and shell materials include those described elsewhere herein. In an example embodiment, the core includes silicon (Si) and at least one of the shell layers, such as the outermost shell layer (i.e., the shell layer that is in contact with the external environment) includes a metal, such as TaAlN or WN. Additional examples of metal shell layers include those described elsewhere herein. Further exemplary nanowires include core:shell (CS) nanowires (e.g., SiO₂), core:shell:shell (CSS) nanowires (e.g., SiO₂:metal), and core:no oxide shell:metal shell nanowires (CNOS) (e.g., Si:metal).
• In an embodiment,container802 receives a flow ofsolution804 containingnanowires806. For instance,FIG. 10 shows a block diagram of a nanowiresolution flow system1000, according to an example embodiment of the present invention. As shown inFIG. 10,flow system1000 includes a nanowiresuspension source reservoir1002,container802, and a nanowiresuspension collection chamber1004. Nanowiresuspension source reservoir1002 is a tank or other type of reservoir that contains a supply ofsolution804.Nanowires806 may be introduced intosolution804 inreservoir1002 to form the suspension, if desired.Solution804 may be any suitable type of liquid for containingnanowires806, including water, isopropyl alcohol (IPA), other liquids described herein, etc.
• As shown inFIG. 10, nanowiresuspension source reservoir1002 outputs ananowire suspension flow1006 that is received bycontainer802.Nanowire suspension flow1006 may be supplied byreservoir1002 tocontainer802 by one or more flow channels, pipes, valves, etc. After enabling the suspension to interact withprint head702,container802 outputs a residualnanowire suspension flow1008 that is received by nanowiresuspension collection chamber1004. Nanowiresuspension collection chamber1004 is a tank or other type of reservoir. The residual nanowire suspension flow received inchamber1004 may be filtered and/or supplied back tosource reservoir1002 for recirculation throughsystem1000, may have residual nanowires recovered therefrom, may be discarded, etc.
• Thus, in the embodiments described above, one ormore nanowires806 are provided by providing a suspension of nanowires (e.g., a nanowire “ink”) toelectrode pair208. As represented inFIG. 10, a nanowire suspension is provided by flowing a solution containing nanowires against an electrode pair on a transfer surface. Asnanowires806 are provided, the suspension flow helps to align the nanowires in the direction of the flow.
• In an embodiment,container802 can be stirred, vibrated, or otherwise moved to maintain a homogeneous suspension ofnanowires806. In another embodiment, where a stratified suspension of nanowires is desired, gravity, electric fields and/or an overflow by a nanowire-free solvent of similar or lower density can be used to create stratification. A stratified suspension of nanowires may be used in a variety of ways. For example,print head702 may be positioned in a high nanowire-density region of the stratified suspension for deposition of nanowires, and subsequently positioned in a lower density, “clean solvent” region for removal of excess nanowires.
• Additional methods for providing nanowires to an electrode pair are well known in the art, and include, but are not limited to, spray coaters, spray painting, meniscus coater, dip-coater, bar-coater, gravure coater, Meyer rod, doctor blade, extrusion, micro-gravure, web coaters, doctor blade coaters, in-line or ink jet printers.
• As described above, a variety of configurations forelectrode pair208 may be used in embodiments. For example,electrode pair208 may be fixed position electrodes. In another embodiment,electrode pair208 may be configured to enable compliance with a destination surface to which they may be applied. For instance,FIG. 11 shows a plan view of anexample print head1100, according to an embodiment of the present invention.Print head1100 has atransfer surface1102 having first andsecond cantilevers1104 and1106 that mountelectrode pair208.FIG. 12 shows a side cross-sectional view ofprint head1100. As shown inFIGS. 12 and 13, first andsecond cantilevers1104 and1106 are generally coplanar and coaxial bodies, having adjacently positioned movable ends, and oppositely positioned fixed ends.First cantilever1104 has a raisedend portion1112 on its movable end, andsecond cantilever1106 has a raisedend portion1114 on its movable end.First electrode704 is formed on raisedend portion1112 offirst cantilever1104, andsecond electrode706 is formed on raisedend portion1114 ofsecond cantilever1106. A first electrical conductor1108 (e.g., a metal trace) is formed onfirst cantilever1104 to electrically couplefirst electrode704 to an external circuit, and a second electrical conductor1110 (e.g., a metal trace) is formed onsecond cantilever1106 to electrically couplesecond electrode706 to an external circuit. For example, first and secondelectrical conductors1110 may electrically couple first andsecond electrodes704 and706 to a DC and/or AC electrical signal source.
• First andsecond cantilevers1104 and1106 are not substantially flexible in the plane oftransfer surface1102, but are flexible in a direction normal to the plane of transfer surface1102 (shown as a Z-axis inFIG. 12). Thus, when first andsecond electrodes704 and706 are positioned in contact with a surface (e.g., destination surface210), the free ends of first andsecond cantilevers1104 and1106 can flex into agap1202 below their free ends, to provide compliance to protect first andsecond electrodes704 and706 from damage, and to aid in complying with a non-level destination surface.
• Cantilevers1104 and1106 may be any type and configuration of cantilever. In an embodiment,cantilevers1104 and1106 are micro-electromechanical system (MEMS) cantilevers.
• According to step304 of flowchart300 (FIG. 3), an electric field is generated by electrodes of an electrode pair to associate nanostructures with the electrodes.FIG. 13 shows ananowire transfer system1300 that can be used to performstep304 of flowchart300 (FIG. 3), according to an example embodiment of the present invention. As shown inFIG. 13,system1300 includes avoltage source1302.Voltage source1302 is a signal/waveform generator coupled toelectrode pair208 byelectrical signal1304.Voltage source1302 generateselectrical signal1304 as a direct current (DC) and/or alternating current (AC) signal to causeelectrode pair208 to generate an electric field. For example,FIG. 14 showstransfer system800 ofFIG. 8, where an electric field, represented between first andsecond electrodes704 and706 byarrow1402, is generated by application of a voltage toelectrode pair208.Electric field1402 is generated betweenelectrodes704 and706 ofelectrode pair208 by energizing electrode pair withelectrical signal1304 to associate at least some ofnanowires806 withelectrode pair208. It should be noted thatelectric field1402 can be generated before, after, or during the period of nanowire producing/introduction intocontainer802. As used herein, the terms “electric field” and “electromagnetic field” are used interchangeably and refer to the force exerted on charged objects in the vicinity of an electric charge. As used herein, “energizing the electrode pair” refers to any suitable mechanism or system for providing an electric current to the electrodes such that an electric field is generated between electrodes of an electrode pair.
• Energizingelectrode pair208 to generateelectric field1402 can be performed during part or all of a nanowire alignment and deposition process. For example,electrode pair208 may remain energized duringstep306 of flowchart300 (alignment of print head) and during a portion or all ofstep308 of flowchart300 (deposition of nanowires). In an example embodiment,electric field1402 is generated by coupling (e.g., using wires or other connection)first electrode704 to a positive electrode terminal ofvoltage source1302, and couplingsecond electrode706 to a negative electrode terminal ofvoltage source1302. When an electric current is switched on and supplied byelectrical signal1304, the negative and positive terminals transfer charge toelectrodes704 and706 positioned ontransfer surface206, thereby generatingelectric field1402 betweenelectrodes704 and706 ofelectrode pair208. In embodiments,electric field1402 can be constant electric field, a pulsed electric field such as a pulsed AC electric field, or other electric field type.
• The energizing ofelectrode pair208 to createelectric field1402 can also be caused by supplying an electromagnetic wave toelectrode pair208. As is well known in the art, waveguides of various dimensions and configurations (e.g., cylindrical, rectangular) can be used to direct and supply an electromagnetic wave (see e.g., Guru, B. S. et al., “Electromagnetic Field Theory Fundamentals,” Chapter 10, PWS Publishing Company, Boston, Mass. (1998)). Operation frequencies of waveguides for use in the practice of the present invention are readily determined by those of skill in the art, and may be in the range of about 100 MHz to 10 GHz, about 1 GHz-5 GHz, about 2-3 GHz, about 2.5 GHz, or about 2.45 GHz, for example.
• As is further described below, asnanowires806 encounter an ACelectric field1402 generated betweenelectrodes704 and706, a field gradient results. A net dipole moment is produced in proximate nanowires806 (e.g., nanowire806ainFIG. 14), and the AC field exerts a torque on the dipole, such that proximate nanowires align parallel to the direction of the electric field. For example,FIG. 15 shows nanowire806ahaving been aligned byelectric field1402 parallel toelectric field1402 in association withelectrode pair208.
• In embodiments, first andsecond electrodes704 and706 are separated by a distance that is less than, equal to, or greater than a long axis length ofnanowires806.Nanowires806 of any length can be aligned and positioned using the methods of the present invention. In an embodiment, the distance between electrodes of an electrode pair is such that the nanowires extend just beyond the first edge of the electrode. In an embodiment,nanowires806 extend just beyond a first edge and into a middle of each electrode, with tens of nanometers to several microns overlapping the electrode material at the end of ananowire806.Nanowires806 that are shorter than the distance betweenelectrodes704 and706 may be able to couple to only one electrode in a pair (if they couple at all), and thus may be removed during subsequent removing phases if desired. Similarly,nanowires806 that are substantially longer than the distance betweenelectrodes704 and706 hang over one or more ofelectrodes704 and706, and may be removed during subsequent removing phases (larger exposed surface area). Thus, this embodiment additionally provides a way to preferentially selectnanowires806 of a particular length from a suspension of a range of nanowire sizes, and align and deposit them onto anelectrode pair208. Embodiments may also associate andcouple nanowires806 that are “straight” rather than bent or crooked. Hence, such embodiments provide an added benefit of depositing preferablystraight nanowires806, rather than less preferred bent orcrooked nanowires806.
• In addition to aligning the nanowires parallel to an AC electric field, the field gradient exerts a dielectrophoretic force onproximate nanowires806, attracting them towardelectrode pair208.FIG. 16 shows aforce1602 attractingnanowire806atowardselectrode pair208 ofprint head702. In an embodiment,force1602 is a dielectrophoretic force. The gradient is highest atelectrode pair208, exerting an increasing attraction toward the electrodes. An electric double-layer is produced at the surface of each electrode ofelectrode pair208, such that oppositely charged ions are present at each electrode. In the presence ofelectric field1402, the ions migrate away from each electrode and initially towardnanowire806ahovering proximately nearby (e.g., above or below). As ions approach oppositely chargednanowire806a, the ions are repulsed by the like charge and then directed back toward the respective electrode resulting in a circulating pattern of ions. Liquid that is present (i.e., the nanowire suspension) is also circulated, generating an electro-osmotic force that opposes the dielectrophoreticforce attracting nanowire806ato the electrodes. Thus, in an embodiment, aforce1606 shown inFIG. 16 may be an osmotic force. Asforces1602 and1606 reach an equilibrium (or relative equilibrium),nanowire806ais held in place such that it becomes associated withelectrode pair208. As used herein the terms “associated” and “pinned” are used to indicate that nanowires (such asnanowire806a) are in such a state that the electro-osmotic force and the dielectrophoretic force are at equilibrium, such that there is no or little net movement of the nanowires away from electrode pair208 (i.e., normal or substantially normal to transfersurface206 and electrode pair208). This is also called the “association phase” throughout.
• Furthermore, in an embodiment, charge values ofnanowires806 andtransfer surface206 affect association or pinning of nanowires toelectrode pair208. For example,FIG. 16 showsprint head702 having associatednanowire806a(additional nanowires not shown may also be associated). As shown inFIG. 16,transfer surface206 may have alayer1604 that provides a surface charge to transfersurface206, such as an oxide layer. The charge polarity oflayer1604 can be selected to attract or repelnanowire806a, as desired. For example,layer1604 can provide a negative surface charge to transfersurface206 that results in a repulsive force onnanowire806a, which may also have a negative surface charge (e.g., in isopropyl alcohol). Thus,force1606 repellingnanowire806ainFIG. 16 may include an electrostatic repulsive force that results from a same charge polarity ofnanowire806aandlayer1604.
• In the associated, or pinned state, the nanowires are aligned parallel to the electric field, but are sufficiently mobile along the electrode edges (i.e. in a plane just above the surface of the electrodes). For example,FIGS. 17 and 18 show plan and side cross-sectional views, respectively, ofelectrode pair208 oncantilevers1104 and1106 ofFIG. 11. As shown inFIGS. 17 and 18, a plurality ofnanowires1702 is associated, or pinned, with first andsecond electrodes704 and706.Nanowires1702 are pinned at adistance1802 fromelectrode pair208. The amount ofdistance1802 depends on a variety of factors, including a strength of the appliedelectric field1402, a frequency ofelectric field1402, a strength of charge ofnanowires1702, a strength of charge oflayer1604, etc.
• In the associated or pinned state,nanowires1702 are free to rearrange, migrate and/or align along the length of theelectrodes704 and706.Nanowires1702 that are already substantially aligned withelectric field1402 will tend to migrate alongelectrode pair208 until contacting, and/or being repelled by, a nearest neighbor nanowire.Nanowires1702 that are not substantially aligned will tend to migrate such that they become aligned as they contact, and/or are repelled by, nearest neighbor nanowires and, an equilibrium between the various forces acting onnanowires1702 is reached. The lateral mobility (i.e., along electrode pairs208, perpendicular to a direction of electric field1402) ofnanowires1702 allows them to accommodate a chronological sequence of alignment and association events without giving rise to nanowire clumping. That is, as nanowires are continuously supplied to electrode pair208 (i.e., from a suspension) additional nanowires are able to associate with the electrodes, as the nanowires that are previously associated are freely mobile such that they move out of the way to accommodate additional nanowires.
• For further example description regarding the association of nanowires with electrode pairs, various nanowire densities, alternating current frequencies, modulating of the electric field, “locking” nanowires to an electrode pair, etc., refer to co-pending U.S. Appl. No. 60/857,765, filed Nov. 9, 2006, titled “Methods for Nanowire Alignment and Deposition,” which is incorporated by reference herein in its entirety.
• Following the associating ofnanowires1702 withelectrodes704 and706, uncoupled nanowires can then be removed fromelectrode pair208 so as to substantially eliminate nanowires that are not fully aligned, not fully coupled, overlapped, crossing, or otherwise not ideally coupled toelectrode pair208. Nanowires that are to be removed following the coupling phase are described herein as “uncoupled nanowires.” Any suitable method for removing uncoupled nanowires can be used. For example, the uncoupled nanowires can be removed using tweezers (e.g., optical tweezers, see, e.g., U.S. Pat. Nos. 6,941,033, 6,897,950 and 6,846,084, the disclosures of each of which are incorporated herein by reference in their entireties) or similar instrument, or by shaking or physically dislodging the uncoupled nanowires. Suitably, uncoupled nanowires are removed by flushing away the nanowires. As used herein, the term “flushing away” includes processes where a fluid (either gaseous or liquid phase) is flowed over or around the nanowires so as to remove them from the electrode pairs. Nanowires that are crossed can be uncrossed using a suitably modulated electric field, and a third electrode can be used to remove “uncoupled nanowires,” such as dielectrophoretically or electroosmotically. Uncoupled nanowires can also be removed inertially, and by other techniques.
• According to step306 of flowchart300 (FIG. 3), the electrode pair is aligned with a region of the destination surface.FIG. 19 shows a printhead alignment system1900 that can be used to performstep306 for a nanowire transfer system, according to an example embodiment of the present invention. As shown inFIG. 19,system1900 includes analignment mechanism1902 that is coupled toprint head702.Alignment mechanism1902 is configured to moveprint head702 such thatelectrode pair208 is aligned with a designatednanowire transfer region1904 ondestination surface210 ofsubstrate212.Alignment mechanism1902 may be configured to moveprint head702 so thatelectrode pair208 is adjacent to but not in contact withregion1904, and/or to moveprint head702 so thatelectrode pair208contacts region1904. For example,alignment mechanism1902 may include a motor (e.g., a linear motor) or other movement mechanism for movingprint head702 toregion1904. Furthermore,alignment mechanism1902 may include position detecting sensors for detecting a position ofprint head702 and/orsubstrate212 to accurately positionprint head702 with respect toregion1904. Example position detecting sensors may include optical sensors (e.g., vision systems), proximity sensors, mechanical sensors, etc., to detect relative position.
• Substrate212 may be any type of structure suitable for placement of nanostructures. For example,substrate212 may be formed of a variety of materials, including a semiconductor material (e.g., silicon, GaAs, etc.), a polymer (e.g., a plastic material), glass, a ceramic material, a composite material, a printed circuit board (PCB), etc.
• Note thatFIG. 19 shows an embodiment whereelectrode pair208 and a plurality of associatednanowires1702 are covered in afluid membrane1906. For example,print head702 may have been dipped insolution804, as shown inFIG. 8, to havenanowires1702 associated withelectrode pair208, as shown inFIGS. 14 and 15. Subsequently,print head702 is withdrawn fromsolution804. However,fluid membrane1906 remains ontransfer surface206 to keepnanowires1702 wet. In this manner,nanowires1702 remain associated withelectrode pair208, including being aligned and positioned relative to first andsecond electrodes704 and706. For example,transfer surface206 may be coated with a hydrophilic material that enablesfluid membrane1906 to stick to transfersurface206. In embodiments,region1904 ondestination surface210 may also be coated with a solution or may alternatively be relatively dry.
• FIG. 20 showsprint head702 having been aligned withregion1904 by alignment mechanism1902 (e.g., in the direction of the downward dotted arrow shown inFIG. 20). As shown inFIG. 20, first andsecond electrodes704 and706 physically holdnanowires1702 in contact withregion1904. Furthermore,nanowires1702 substantially retain their alignment and position onelectrode pair208 while making contact withregion1904 due to the action ofelectric field1402 and other forces acting onnanowires1702.
• FIGS. 21 and 22show print head702 ofFIG. 9 being aligned withdestination surface210, according to an example embodiment of the present invention.Nanowires806 are shown removed fromsolution804 inFIGS. 21 and 22, although they may alternatively still be present insolution804. As shown inFIG. 21,substrate212 andprint head702 are both submerged insolution804.Nanowires1702 are shown associated withelectrodes704 and706 (e.g., according to step304 of flowchart300). As shown inFIG. 22,print head702 has been aligned with region1904 (e.g., byalignment mechanism1902, not shown inFIGS. 21 and 22). First andsecond electrodes704 and706 physically holdnanowires1702 in contact withregion1904 inFIG. 22. Furthermore,nanowires1702 substantially retain their alignment and position onelectrode pair208 while making contact withregion1904, as described above.
• Note that in an embodiment, as shown inFIG. 23, one or more spacers orspacing members2302 may be present on transfer surface206 (and/or on destination surface210) to holdtransfer surface206/electrode pair208 at a predetermined distance fromdestination surface210, and/or to reduce an impact betweenelectrodes704 and706 anddestination surface210 when making contact. This may further be useful in aiding associatednanowires1702 from losing their alignment and position whentransfer surface206 is being aligned withdestination surface210 according tostep306. Spacingmembers2302 may be used in combination with any embodiment described herein. Spacingmembers2302 may have any height, as determined for a particular application. For example, in an embodiment, aspacing member2302 has a height of approximately 100 μm.
• FIGS. 24 and 25 show examples of print head alignment for the configuration ofprint head1100 ofFIGS. 11,17, and18. As shown inFIG. 24,print head1100 has been aligned with region1904 (e.g., byalignment mechanism1902, not shown inFIGS. 24 and 25). First andsecond electrodes704 and706 physically holdnanowire1702 in contact withregion1904 inFIG. 22. Furthermore,nanowires1702 substantially retain their alignment and position onelectrode pair208 while making contact withregion1904, as described above.
• InFIG. 25,substrate212 is not planar, but instead has an uneven surface. A portion ofregion1904 corresponding tosecond electrode706 is higher than a portion ofregion1904 corresponding tofirst electrode704. Thus,second cantilever1106 ofprint head1100 flexes (e.g., in an upward direction indicated by a dotted arrow) in order forsecond electrode706 to maintain contact withregion1904. Furthermore, bysecond cantilever1106 flexing,first electrode704 is able to maintain holding its respective ends ofnanowires1702 onregion1904.
• Note that in an embodiment where a print head is aligned with a destination surface in solution, the solution between the print head and destination surface will be displaced during alignment. If the solution is displaced laterally, this may cause problems with displacing associated nanowires, with increasing an area of the print head, and/or further problems.FIG. 26 shows ananowire transfer system2600, according to an example embodiment of the present invention.System2600 is similar tosystem1300 shown inFIG. 13, with the addition of avacuum source2602. Furthermore,transfer surface206 includes one ormore vacuum ports2604 coupled tovacuum source2602.Vacuum source2602 applies a vacuum orsuction2606 throughvacuum port2604 to the volume betweentransfer surface206 andsubstrate212 to remove excess solution. Thus, astransfer surface206 andsubstrate212 approach each other, excess solution can be removed to prevent displacement of associated nanowires, etc.
• FIG. 27 shows an example plan view oftransfer surface206, according to an example embodiment of the present invention. As shown inFIG. 27,transfer surface206 includes first andsecond electrodes704 and706, and a plurality ofvacuum ports2604a-2604c. In the example ofFIG. 27, threevacuum ports2604a-2604care shown.First vacuum port2604ais positioned ontransfer surface206 adjacent tofirst electrode704.Second vacuum port2604bis positioned ontransfer surface206 between first andsecond electrodes704 and706.Third vacuum port2604cis positioned ontransfer surface206 adjacent tosecond electrode706. Any number ofvacuum ports2604 may be present, and may be distributed ontransfer surface206 as desired. In the example ofFIG. 27,vacuum ports2604a-2604care rectangular shaped. In other embodiments,vacuum ports2604 may have other shapes, including round, square, etc.
• According to step308 of flowchart300 (FIG. 3), one or more nanostructures are deposited from the electrode pair to the region. Nanowires may be deposited ondestination surface210 in a variety of ways. Various example embodiments for depositing nanowires on a surface are described as follows.
• For example,FIG. 28 shows ananowire transfer system2800, according to an embodiment of the present invention. As shown inFIG. 28,nanowires2802 are deposited onregion1904 fromelectrode pair208. In the embodiment ofFIG. 28, aforce2802 is present (which may include one or more forces) that attractednanowires1702 fromprint head702 todestination surface210 while they are aligned, and/or repellednanowires1702 fromprint head702, overcoming any force(s) that attractednanowires1702 to transfersurface206 ofprint head702. Example forces that may be present inforce2802 include an electric field (AC and/or DC), a vacuum force, an electrostatic force, gravity, ultrasonic excitation, and/or other forces. These and other passive and active forces may be used to attract/repelnanowires1702, as would be known to persons skilled in the relevant art(s). Example embodiments for utilizing some of these forces are described as follows.
• For example,FIG. 29 shows atransfer system2900, according to an embodiment of the present invention.Transfer system2900 is generally similar totransfer system2800 ofFIG. 28. However, as shown inFIG. 29,transfer surface206 has negatively chargedlayer2902 formed thereon. Negatively chargedlayer2902 results in a negative surface charge fortransfer surface206, and thus a DC repulsive force on nanowires1702 (which may be negatively charged). For example,layer2902 may be an oxide layer. An electric field generated by electrode pair208 (e.g., electric field1402) is biased with an AC field condition to previously capturenanowires1702 from solution, according to step304 offlowchart300 described above.
• Furthermore, as shown inFIG. 29,destination surface210 has a positively chargedlayer2904 formed thereon. For example, positively chargelayer2904 may be an alumina layer. Positively chargedlayer2904 results in a positive surface charge fordestination surface210, and thus a DC attractive force onnanowires1702. Whentransfer surface206 anddestination surface210 are sufficiently close (e.g., in the range of 1 μm to 4 μm), including when they are in contact with each other,nanowires1702 transfer ontodestination surface210, as shown inFIG. 29, because the DC attractive force oflayer2904 overcomes the attractive force (dielectrophoretic force) caused by the AC electric field generated byelectrode pair208. In an embodiment, to enable transfer, the AC electric field may be reduced (e.g., by voltage source1302) or entirely removed to reduce or remove the dielectrophoretic force.
• FIG. 30 shows aplot3000 of nanowire potential energy as a function of distance from eithertransfer surface206 ordestination surface210.Transfer surface206 can have a negatively chargedlayer2902 as an oxide layer anddestination surface210 can have a positively chargedlayer2904 as a nitride layer, according to an embodiment of the present invention. Aplot line3002 represents the potential energy of nanowires suspended in solution overtransfer surface206 and aplot line3004 represents the potential energy of nanowires suspended in solution overdestination surface210.
• As shown inFIG. 30, at afirst plot region3006 representing a first potential minimum onplot line3002 fortransfer surface210,nanowires1702 are associated (pinned) withelectrode pair208. The pinned nanowires remain relatively rigid/aligned without being in contact with a transfer surface. In the current example, first plot region (first potential minimum)3006 occurs whentransfer surface206 anddestination surface210 are approximately 1 μm-4 μm apart. At a second plot region (second potential minimum)3008 representing a potential minimum onplot line3004 fordestination surface210,nanowires1702 are attracted todestination surface210 due to the electrostatic attraction by the nitride layer.Nanowires1702 may be “locked” ondestination surface210 in this manner.Second plot region3008 occurs when nanowires anddestination surface210 are spaced approximately 0.1 μm-0.4 μm apart.
• The transfer ofnanowires1702 fromtransfer surface206 ontodestination surface210 is achieved by first “weakly” pinningnanowires1702 ontransfer surface206 at low electric fields and low frequencies, “strongly” pinningnanowires1702 ontransfer surface206 using low electric fields and high frequencies, movingtransfer surface206 to close proximity withdestination surface210, and finally releasingnanowires1702 frompotential minimum3006 oftransfer surface206 by reducing the AC field onelectrodes704 and706 oftransfer surface206. Due to the electrostatic repulsion represented by a potential maximum3010 betweennanowires1702 and transfer surface206 (e.g. layer2902 on transfer surface206)nanowires1702 move away fromtransfer surface206 after reduction of the AC attractive field. Within the rotational diffusion time (i.e. time required for nanowires to be rotated by an angle θ from a pre-aligned direction while subjected to gravity and Brownian motion)nanowires1702 maintain the desired alignment determined by the AC field acrosselectrodes704 and706 ontransfer surface206. The close proximity (e.g., ˜1 μm) of thepre-aligned nanowires1702 in solution todestination surface210 enables a transfer ontodestination surface210 due to the electrostatic attraction represented by potential minimum3008 (e.g. layer2904 on destination surface210). An efficient transfer ofnanowires1702 is enabled when the rotational diffusion time is large compared to the translational diffusion time for motion of nanowires from potential minimum3006 topotential minimum3008. Functional layers onnanowires1702 and ondestination surface210 can be used to minimize the translational diffusion time without affecting the rotational diffusion time.
• Note that in an embodiment, ultrasonic excitation/vibration can be used to enhance the process just described. For example,FIG. 31A shows atransfer system3100, according to an embodiment of the present invention.Transfer system3100 is generally similar totransfer system2900 ofFIG. 29, with the addition ofultrasonic vibration source3102.Ultrasonic vibration source3102 includes a piezoelectric transducer or other ultrasonic vibration source to ultrasonically vibrateprint head702 andtransfer surface206. In an embodiment, ultrasonic vibration ofprint head702 causes nanowires to be separated from the transfer head up to approximately 100 μm, which enables the distance betweentransfer surface206 anddestination surface210 to be larger while still allowingnanowires1702 to be deposited ondestination surface210. The rate at whichprint head702 moves towarddestination surface210 may be high initially and reduced gradually asprint head702 moves close todestination surface210. For example,ultrasonic vibration source3102 can be activated when transfer surface206 approaches within 100 μm ofdestination surface210. This enables depositing ofnanowires1702 to destination surface210 (e.g., by gravity, electrostatic attraction, etc.) sooner (at a larger distance) while better maintaining the alignment ofnanowires1702 withelectrode pair208 than whenelectrode pair208 is moved closer or evencontacts destination surface210.
• FIG. 31B shows atransfer system3150, according to an embodiment of the present invention.Transfer system3150 is generally similar totransfer system3100 ofFIG. 31A, except that anultrasonic vibration source3152 is coupled tosubstrate212, rather thanultrasonic vibration source3102 being associated withprint head702. Although shown coupled to a bottom surface ofsubstrate212,ultrasonic vibration source3152 can be coupled tosubstrate212 in any manner, including being coupled to the top surface, or being embedded insubstrate212Ultrasonic vibration source3152 may be secured in an ultrasonic chuck, or other application mechanism.
• Ultrasonic vibration source3152 includes a piezoelectric transducer or other ultrasonic vibration source to ultrasonically vibratesubstrate212, and thus to ultrasonically vibratedestination surface210. Furthermore, whentransfer surface206 anddestination surface210 are brought near each other, spacers2302 (onprint head702 and/or substrate212)contact print head702 anddestination surface210 together. Thus,ultrasonic vibration source3152 also vibratesprint head702 andtransfer surface206. Becauseultrasonic vibration source3152 vibrates bothtransfer surface206 anddestination surface210, they vibrate synchronously, such that they both vibrate in the same direction simultaneously. This causes less turbulence than when only one oftransfer surface206 anddestination surface210 vibrate, and thusnanowires1702 are better able to retain their alignment while being transferred (e.g., by gravity, electrostatic attraction, etc.) fromtransfer surface206 todestination surface210.
• FIG. 31C shows aplot3170 of an inertial motion of nanowires in isopropyl alcohol (IPA) solution, according to an embodiment of the present invention. AnX-axis3172 ofplot3170 is a displacement amplitude, in centimeters, ofdestination surface210 andtransfer surface206 caused byultrasonic vibration source3152. A Y-axis3174 ofplot3170 is a displacement frequency caused byultrasonic vibration source3152. A Z-axis3176 ofplot3170 shows a resulting displacement amplitude ofnanowires1702 in μm. Aplot surface3178 indicates generally that as surface displacement amplitude increases (on X-axis3172), nanowire displacement amplitude (on Z-axis3176) also increases. Likewise, as displacement frequency (on Y-axis3174) increases, nanowire displacement amplitude (on Z-axis3176) also increases.
• In an example embodiment,transfer surface206 and/ordestination surface210 may be ultrasonically vibrated at relatively high frequency, such as 10 KHz, with a low amplitude, such as 50-100 microns, to effectively transfernanowires1702 fromtransfer surface206 todestination surface210. A variety of other combinations of displacement amplitude (X-axis3172) and displacement frequency (Y-axis3174) combinations are apparent fromplot3170, and may be used to cause wire displacement (Z-axis3176) to transfer nanowires, as desired for a particular application.
• FIG. 32 shows anexample transfer system3200, according to another embodiment of the present invention.Transfer system3200 is similar totransfer system2800 ofFIG. 28, with the addition of avacuum source3202 that applies avacuum force3204 throughvacuum ports3206 insubstrate212 to attractnanowires1702 todestination surface210. For example, usingvacuum force3204,vacuum source3202 draws asolution surrounding nanowires1702 in throughvacuum ports3206. The resulting solution flow exerts a pull onnanowires1702 towarddestination surface210.
• FIG. 33 shows anexample transfer system3300, according to another embodiment of the present invention.Transfer system3300 is similar totransfer system2800 ofFIG. 28, with the addition of anelectric field source3302 that generates anelectric field3304 to attractnanowires1702 todestination surface210. For example, in an embodiment,electric field source3302 may generate a DC electric field forelectric field3304. The DC electric field (e.g., a positive charge) exerts an attractive force onnanowires1702 due to the opposite charge of nanowires1702 (e.g., a negative charge), causingnanowires1702 to move. Such movement ofnanowires1702 enablesnanowires1702 to be attracted todestination surface210 byelectric field3304 and/or other force. In another embodiment,electric field source3302 may generate an AC electric field forelectric field3304 which operates in an analogous fashion to movenanowires1702, to enablenanowires1702 to be attracted todestination surface210. In still another embodiment, a combination of DC and AC electric fields may be used. In an embodiment,electric field source3302 is a signal generator, voltage supply, or other component or device capable of generating an electric field.
• It is noted that the above described embodiments for depositing nanowires on a destination surface according to step308 of flowchart300 (FIG. 3) may be combined in any manner, as would be understood by persons skilled in the relevant art(s) from the teachings herein.
• According to step310 of flowchart300 (FIG. 3), the electrode pair is removed from alignment with the region of the surface. For example, as shown inFIG. 28,print head702 may be moved in the upward direction (shown by dotted arrow) to be removed from alignment withregion1904. For example, alignment mechanism1902 (shown inFIG. 19) may be used to moveprint head702 from alignment withregion1904. In an embodiment, a fluid can be supplied (e.g., throughports2604 ofFIG. 26 and/orports3206 ofFIG. 32) betweentransfer surface206 anddestination surface210 to provide pressure to move the surfaces apart (e.g., gas or liquid pressure). In this manner,flowchart300 ofFIG. 3 may be repeated byprint head702, to associate and deposit further nanowires onregion1904, on other region(s) ofsubstrate212, and/or on alternative surfaces.
• Furthermore,flowchart300 is adaptable to using multiple electrode pairs on a single transfer surface to deposit groups of nanowires on substrates in parallel. For example,FIG. 34 shows ananowire transfer system3400 that includes aprint head3402 having two electrode pairs, according to an embodiment of the present invention. As shown inFIG. 34,print head3402 has atransfer surface3404 having afirst electrode pair208aand asecond electrode pair208b.First electrode pair208ais shown having associatednanowires1702a, andsecond electrode pair208bis shown having associatednanowires1702b.Nanowires1702aare designated for deposit onfirst region1904aofdestination surface210, andnanowires1702bare designated for deposit onsecond region1904bofdestination surface210.
• Thus, in an embodiment, each step offlowchart300 shown inFIG. 3 may be performed for both of first and second electrode pairs208aand208bin parallel. Instep302, in parallel with providingnanowires1702aproximate tofirst electrode pair208a,nanowires1702bcan be provided proximate tosecond electrode pair208b. Instep304, in parallel with generating a first electric field (e.g.,electric field1402 inFIG. 14) usingfirst electrode pair208a, a second electric field can be generated usingsecond electrode pair208btoassociate nanowires1702bwithsecond electrode pair208b. In embodiments, a same electrical signal (e.g., electrical signal1304) can be provided to both of first and second electrode pairs208aand208b, or different electrical signals can be generated and provided.
• Instep306, in parallel with aligningfirst electrode pair208awithfirst region1904a,second electrode pair208bcan be aligned withsecond region1904b. Instep308, in parallel with depositingnanowires1702afromfirst electrode pair208atofirst region1904a,nanowires1702bcan be deposited fromsecond electrode pair208btosecond region1904b. Instep310, first and second electrode pairs208aand208bcan be removed from alignment with their respective regions in parallel, by withdrawingprint head3402 fromdestination surface210.
• Note that any number of electrode pairs may be formed on a transfer surface to be used to transfer any number of corresponding sets of nanowires in parallel, in a similar fashion to the configuration ofFIG. 34. By increasing the size oftransfer surface206, to enable additional electrode pairs, increasing numbers of simultaneous nanowire transfers may be performed in parallel, increasing a rate of fabrication. The spacing ofelectrodes704 and706 of electrode pairs on print heads may be varied to associate and deposit different types of nanowires, including different lengths, dopings, shell materials, etc.
Example Embodiments for Transferring Electrical Devices
• Embodiments are described in this section for applying electrical devices, such as integrated circuits, electrical components, semiconductor die, optical devices, etc., to surfaces in a similar manner as described above for nanowires. In embodiments, one or more electrical devices are provided proximate to an electrode pair on a transfer surface. The electrode pair is energized such that an electrical device becomes associated with the electrode pair. Subsequently, the electrical device is deposited from the electrode pair to a destination surface.
• FIG. 35 shows aflowchart3500 providing example steps for transferring electrical devices, according to example embodiments of the present invention. For example,print head702 ofFIG. 7 can be used to transfer electrical devices according toflowchart3500. For illustrative purposes,flowchart3500 is described as follows with respect toFIGS. 36-39, which show block diagrams of an electricaldevice transfer system3600, according to an embodiment of the present invention. Other structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. Not all steps offlowchart3500 are necessarily performed in all embodiments.
• Flowchart3500 begins withstep3502. Instep3502, at least one electrical device is provided proximate to an electrode pair. For example, as shown inFIG. 36,electrical devices3602 are provided proximate toelectrode pair208. InFIG. 36,electrical devices3602 are present insolution804, which flows in contact withelectrode pair208, to enableelectrical devices3602 to be positioned proximate toelectrode pair208. Alternatively,electrical devices3602 may be provided proximate toelectrode pair208 in other ways. In embodiments,electrical devices3602 may all be the same type of electrical device, or may include different types.
• Instep3504, an electric field is generated by electrodes of the electrode pair to associate an electrical device with the electrodes. For instance, an electrical potential may be coupled toelectrode pair208 to generate the electric field. The electric field generated byelectrode pair208 may be used to associate one ofelectrical devices3602 withelectrode pair208 that is proximately located toelectrode pair208. As shown inFIG. 37,electrical device3602ais associated withelectrode pair208. In an embodiment, associatedelectrical device3602ais held suspended at a distance fromtransfer surface206 by the electric field.
• The example embodiments described above for generating an electric field by an electrode pair to associate nanostructures are adaptable to associating electrical devices. For example, as described with respect toFIG. 14, anelectric field1402 is generated betweenelectrodes704 and706 ofelectrode pair208.Electric field1402 can be used to align electrical deviceelectrical device3602a, and to positionelectrical device3602abetweenelectrodes704 and706. Whenelectrical device3602aencounters an AC electric field generated betweenelectrodes704 and706, a field gradient results. A net dipole moment is produced in proximateelectrical devices3602, and the AC field exerts a torque on the dipole, such that proximateelectrical device3602aaligns parallel to the direction of the electric field.
• Furthermore, in an embodiment, the field gradient exerts a dielectrophoretic force on proximateelectrical device3602a, attracting it towardelectrode pair208, as described above for nanowires with respect toFIG. 16. An electro-osmotic force may also be generated, as described above, that opposes the dielectrophoretic force attractingelectrical device3602ato the electrodes. As these forces reach an equilibrium (or relative equilibrium),electrical device3602ais held in place such that it becomes associated, or “pinned,” withelectrode pair208.
• As mentioned above,electrical devices3602 inFIG. 36 may all be the same type of electrical device or may include different electrical device types. When different electrical device types are present,electrodes704 and706 may be sized and/or positioned to generate the electric field in a manner to only attract a designated type of electrical device. In an embodiment,electrical device3602amay have a metal (or other material) patterned thereon to enhance the attraction ofelectrical device3602atoelectrodes208.
• Instep3506, the electrode pair is aligned with a region of the destination surface. For example, as shown inFIG. 38,electrode pair208 is aligned withdestination surface210, byprint head702, which is moved towardsdestination surface210. In an embodiment,electrode pair208 is aligned in contact withdestination surface210. In another embodiment,electrode pair208 is aligned adjacent todestination surface210, a short distance away fromdestination surface210.Electrode pair208 may be aligned with any region ofsurface210, including a generally open region (i.e., no contacts onsurface210 are required), a region having electrical contacts corresponding toelectrode pair208, or other region.Electrode pair208 is aligned with a region ofsurface210 on whichelectrical device3602ais to be positioned.
• Instep3508, the electrical device is deposited from the electrode pair to the region.Electrical device3602amay be deposited ondestination surface210 in a variety of ways. Various example embodiments for depositing nanostructures on a surface are described in detail above. For example, the embodiments described above with respect toFIGS. 28-33 for depositing nanostructures may be used to depositelectrical device3602a. For example, inFIG. 28, aforce2802 is present (which may include one or more forces) that attractednanowires1702 fromprint head702 todestination surface210 and/or repellednanowires1702 fromprint head702.Force2802 may also be used to depositelectrical device3602atodestination surface210 fromprint head702. Example forces that may be present inforce2802 include an electric field (AC and/or DC), a vacuum force, an electrostatic force, gravity, ultrasonic excitation, and/or other forces. These and other passive and active forces may be used to attract/repelelectrical device3602a, as would be known to persons skilled in the relevant art(s). Furthermore, ultrasonic vibration may be used, as described above with respect toFIGS. 31A-31C, to aid in freeingelectrical device3602afromprint head702, to transfer to destination surface210 (e.g., via a force such as gravity, an electrostatic force, etc.).
• Instep3510, the electrode pair is removed from alignment with the region of the surface. For example, as shown inFIG. 39,print head702 is moved away fromdestination surface210.Electrical device3602aremains deposited onsurface210.Print head702 can subsequently be used to repeat performingflowchart3500 for the same region ofsurface210, a different region ofsurface210, and/or a surface of a structure other thansubstrate212, to deposit further electrical devices. Furthermore, in an embodiment,print head702 may be used to simultaneously transfer nanostructures and electrical devices.
• Using the techniques described herein, complex electrical circuits can be formed, by using print heads to transfer nanostructures and electrical devices to substrates.
Further Print Head Embodiments
• Further embodiments are described in this section for applying nanostructures to surfaces using print heads. Print heads used to “print” nanowires onto a substrate in the presence of a fluid, as described above, may cause a shear force that is orthogonal to the motion of the print head as the print head approaches the substrate. As a result, the fluid is forced out of the region between the print head and the substrate due. This fluid shear can displace the nanowires laterally, causing the nanowires to be misplaced in the printing process.
• For example,FIG. 40 shows a cross-sectional view of ananostructure transfer system4000, according to an embodiment of the present invention. As shown inFIG. 40,system4000 includesprint head702 andsubstrate212.FIG. 41 shows a view oftransfer surface206 ofprint head702.Print head702 is configured to transfer nanostructures, such as a nanowire1702 (shown end-on inFIG. 40), fromelectrodes704 and706 todestination surface210 in aliquid solution4004.
• During the transfer process,print head702 is moved towardssubstrate212 in the direction ofarrow4002, reducing a distance betweentransfer surface206 anddestination surface210.Arrows4006 indicate directions of flow ofsolution4004 asprint head4002 is moved towardssubstrate212, assolution4004 is forced out of the region betweentransfer surface206 anddestination surface210. Referring toFIG. 40, the relative lengths ofarrows4006 indicate a relative flow velocity at the locations ofarrows4006. For instance, a flow velocity is lower forsolution4004 close to one oftransfer surface206 anddestination surface210 relative tosolution4004 midway betweentransfer surface206 anddestination surface210. Referring toFIG. 41,arrows4006 indicate thatsolution4004 is forced outwardly in all directions from a central region of transfer surface2006.
• As indicted inFIG. 41,solution4004 is forced to flow acrossnanowire1702 whenprint head702 is moved towardssubstrate212. This fluid exerts a shear force onnanowire1702, which may undesirably displacenanowire1702 laterally, causingnanowire1702 to be misplaced in the printing process.
• In embodiments, drain holes are formed in a print head to remove fluid from the region between the print head and the destination surface as the print head approaches the destination surface. The drain holes reduce a shear force on the nanowires, to enable the nanowires to be more reliably transferred from the print head to the destination surface. For exampleFIG. 42 shows ananostructure transfer system4200, according to an example embodiment of the present invention. As shown inFIG. 42,system4200 includes aprint head4202 andsubstrate212.FIG. 43 shows a view oftransfer surface206 ofprint head4202. As shown inFIGS. 42 and 43,transfer surface206 includes first andsecond openings4204aand4204b(also referred to as “drain holes”). First andsecond openings4204aand4204breceivesolution4004 from the region betweentransfer surface206 anddestination surface210 whenprint head4202 is moved towardsubstrate210. Removal ofsolution4004 due to first andsecond openings4204aand4204breduces a shear force onnanowire1702 while being deposited fromtransfer surface206 todestination surface210.
• FIG. 44 shows aflowchart4400 for transferring nanostructures to a destination surface, according to an example embodiment of the present invention.System4200 may performflowchart4400, for example.Flowchart4400 is described as follows. Other structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion.
• Instep4402, a transfer surface of a print head is positioned adjacent to a destination surface. For instance, as shown inFIG. 42,transfer surface206 ofprint head4202 is positioned adjacent todestination surface210 ofsubstrate212.
• Instep4404, a distance between the transfer surface and the destination surface is reduced. Referring toFIG. 42,print head4202 is moved in the direction ofarrow4002 to reduce adistance4208 betweentransfer surface206 anddestination surface210.
• Instep4406, a fluid is received through at least one opening in the transfer surface from between the transfer surface and the destination surface duringstep4404. As indicated byarrows4206 inFIGS. 42 and 43,solution4004 betweentransfer surface206 anddestination surface210 flows outward from a central region of transfer surface2006 due totransfer surface206 moving towarddestination surface210. Furthermore, as indicated byarrows4210 shown inFIG. 42,solution4004 flows intoopenings4204aand4204bintransfer surface206.Openings4204aand4204brelieve at least a portion of the shear force received bynanowire1702 by receivingsolution4004.
• Instep4408, a nanowire associated with the transfer surface is deposited to the destination surface. For instance,FIG. 45 shows a view ofsystem4200 ofFIG. 42, wheretransfer surface206 is proximate todestination surface210, such thatnanowire1702 may be deposited todestination surface210.Nanowire1702 may be deposited fromtransfer surface206 todestination surface210 in any manner described elsewhere herein, including as described above with respect toflowchart300 shown inFIG. 3. Subsequent to the deposition ofnanowire1702,print head4202 andsubstrate212 may be moved apart.
• Although two openings4204 (openings4204aand4204b) are shown inFIGS. 42 and 43, any number of openings4204 may be present intransfer surface206. For example, instead of a pair of openings4204 (as shown inFIGS. 42 and 43), an array of openings4204 of any number may be present at the locations ofopenings4204aand4204b. Such openings may have any shape, including being round, rectangular, or any other shape.
• Furthermore, openings4204 may have any distribution/geometry relative toelectrodes704 and706 to further reduce the shear force. For example, as shown inFIG. 43,openings4204aand4204bmay be located relative toelectrodes704 and706 so thatnanowire1702 is located midway betweenopenings4204aand4204b. In this manner, a “dead zone” for flow ofsolution4004 at the location ofnanowire1702 is created (e.g., a flow stream is parted at nanowire1702), so that the shear force experienced bynanowire1702 may be brought close to none. In the embodiment ofFIG. 43, openings4204 can be holes and/or slots that are positioned symmetrically along either side of the long axis ofnanowire1702.
• Furthermore, as shown inFIG. 43,openings4202 may have lengths that are longer than a long axis length ofnanowire1702. Alternatively,openings4202 may have a length that is the same or less than a long axis length ofnanowire1702. A width ofopenings4204aand4204bmay be selected so that a substantial amount ofsolution4004 betweenopenings4204aand4204bon either side ofnanowire1702 may exit throughopenings4204aand4204b.
• Although openings4204 are shown inFIG. 42 as being located along the length ofnanowire1702, alternatively or additionally, openings4204 may be located ontransfer surface206 adjacent to one or both ends ofnanowire1702. Furthermore, althoughopenings4204aand4204bare shown inFIG. 42 as penetrating all the way throughprint head4202, alternatively, openings4204 may penetrate partially through print head4204 (e.g., may be recessed areas intransfer surface206, of any suitable depth).
• In the example ofFIGS. 42 and 43,solution4004 is enabled to passively flow into openings4204. In another embodiment,solution4004 may be actively drawn into openings4204. For instance, a piston/cylinder arrangement, a corkscrew, vacuum suction, and/or further mechanisms may be used to actively drawsolution4004 into openings4204. For example,FIG. 46 shows ananostructure transfer system4600, according to an embodiment of the present invention.System4600 is generally similar tosystem4200 shown inFIG. 42, with the addition of first andsecond pistons4602aand4602b.Pistons4602aand4602bare located inopenings4204aand4204b, respectively.First piston4602aandopening4204aform a first piston/cylinder arrangement, andsecond piston4602bandopening4204bform a second piston/cylinder arrangement. First andsecond pistons4602aand4602bmay be configured to move in the directions ofarrows4604 duringstep4404 offlowchart4400, to enablesolution4004 to be drawn intoopenings4204aand4204baccording to step4406 offlowchart4400.
Example Electrode Embodiments
• Nanostructures and/or contaminants may become attached to transfer surfaces of print heads, causing degradation in performance. In embodiments, the transfer surface of nanostructure print heads may be treated to prevent contaminants from sticking, and/to increase a durability of the transfer surface. Such embodiments may be particularly useful to extend a lifetime of a print head/transfer surface when print heads/transfer surfaces are expensive to replace. For example, a coating may be applied to the transfer surface, such as a coating of a non-stick material. In an embodiment, the coating may be removable. In this manner, the coating may be removed and reapplied as needed when a coating wears out, rather than having to dispose of the print head completely.
• For instance,FIG. 47 shows a cross-sectional view of aprint head4700, according to an example embodiment of the present invention. As shown inFIG. 47, anon-stick material layer4702 is formed ontransfer surface206 ofprint head4700.Non-stick material layer4702 is a coating of a non-stick material that is configured to reduce nanowire and contaminate adhesion. In addition,non-stick material layer4702 may be removed (e.g., stripped) fromtransfer surface206, and reapplied to transfersurface206, to provide a longer lifespan to printhead4700.
• Example advantages ofnon-stick material layer4702 ontransfer surface206 include preventing nanowire adhesion and sticking, enabling the use of a higher nanowire capture voltage (e.g., duringstep304 offlowchart300 inFIG. 3) so that nanowires are not lost due to shear forces during the nanowire transfer process (e.g., as described above with respect toFIGS. 41 and 42), enhancing nanowire transfer efficiency, and/or reducing contamination and corrosion ofprint head4700 to increase a lifetime ofprint head4700.
• Non-stick material layer4702 may be formed ontransfer surface206 in any manner, including by coatingtransfer surface206 from a solution (i.e., spin coating or dip coating) or by a vapor phase deposition process.Non-stick material layer4702 may be configured to have weak adhesion properties, such as adhesion properties characterized through van der Waals forces.Transfer surface206 may be treated with adhesion promoters to preventnon-stick material layer4702 from delaminating fromtransfer surface206. Example materials fornon-stick material layer4702 include materials that have very low van der Waals force attraction with inorganic materials (contamination and nanowires), such as organic molecules or fluorinated organics (e.g., Teflon). A fluorinated organic material, such as Teflon, can have van der Waals forces3 orders of magnitude lower than a typical oxide surface, thus making the strength of adhesion of contaminants to transfersurface206 relatively weak. A thickness and/or chemistry ofnon-stick material layer4702 may be selected as desired for the particular application.
• In addition, as described above,non-stick material layer4702 may be removable. For instance, if nanowires and/or other contamination does adhere to transfersurface206 after one or more uses,non-stick material layer4702 may be removed using solvents, plasma, thermal decomposition, or other removal material or technique. After removal ofnon-stick material layer4702, a fresh replacement coating ofnon-stick material layer4702 may be formed ontransfer surface206. This replacement process is simpler and less expensive than manufacturing areplacement print head4700, which may be relatively expensive.
• For instance, another type of non-stick material that may be applied to transfersurface206, is a film of a material such as SiO₂or Si₃N₄. Such a film may be deposited ontransfer surface206 according to a plasma enhanced chemical vapor deposition (PECVD) process or other process. Such a film may prevent nanowires from sticking to transfersurface206 by static charge. Furthermore, such a film may be removed after use, and reapplied to transfersurface206, as needed, which may enable a lifespan oftransfer surface206 to be increased.
Example Nanostructure Printing Processes and Systems
• Example embodiments are described in this section for nanostructure printing processes and systems. Embodiments are described for fabricating devices that incorporate nanostructures. These embodiments are provided for illustrative purposes, and are not intended to be limiting.
• For example,FIG. 48 shows a block diagram of ananostructure printing system4800, according to an example embodiment of the present invention. As shown inFIG. 48,system4800 includes anassociation station4802, aninspection station4804, aprinting station4806, acleaning station4808, apanel repair station4812, and apanel drying station4814.Association station4802,inspection station4804,printing station4806, andcleaning station4808 form a print head pipeline portion ofsystem4800, andprinting station4806,panel repair station4812, andpanel drying station4814 form a panel pipeline portion ofsystem4800.
• System4800 is described with respect toflowcharts4900 and5000 shown inFIGS. 49 and 50, respectively.Flowchart4900 shows a process for the print head pipeline portion ofsystem4800, andflowchart5000 shows a process for the panel pipeline ofsystem4800, according to example embodiments of the present invention. For illustrative purposes,flowcharts4900 and5000 are described as follows with respect tosystem4800. Other structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. Not all elements ofsystem4800 shown inFIG. 48 need be present in all embodiments, and not all steps offlowcharts4900 and5000 are necessarily performed in all embodiments.
• Flowchart4900 is first described. Instep4902 offlowchart4900, nanostructures are associated with transfer surfaces of print heads. For example, as shown inFIG. 48,association station4802 receives a plurality ofprint heads4818, including aprint head4810.Association station4802 is configured to associate nanostructures with a transfer surface of each print head of the received plurality ofprint heads4818. The association of nanostructures withprint heads4818 may be performed in any manner described elsewhere herein, such as described above with respect toflowchart300 inFIG. 3, or in other ways known to persons skilled in the relevant art(s). As shown inFIG. 48,association station4802 outputs a plurality of print heads and associatednanostructures4820.
• For example,FIG. 51 illustrates nanostructures being associated with transfer surfaces ofprint head4810 in solution (e.g., in a liquid environment) atassociation station4802. In an embodiment,print head4810 is one of a plurality of print heads received atassociation station4802. In another embodiment, asingle print head4810 is received. In the example ofFIG. 51,print head4810 has sixtransfer surfaces206a-206f. In other embodiments,print head4810 may have other numbers of transfer surfaces206, including a two-dimensional array of transfer surfaces206.Transfer surfaces206a-206fare submerged in a nanowire solution5106 (e.g., a nanowire ink) contained by areservoir5104. As shown inFIG. 51,print head4810 has five through-holes or openings5108a-5108e, with each opening5108 being positioned between a corresponding adjacent pair of transfer surfaces206. Openings5108 may be configured similarly to openings4204 described above with respect toFIG. 42. In embodiments,print head4810 may include any number and configuration of openings5108.
• Although not shown inFIG. 51, in the current example, eachtransfer surface206a-206fincludes a respective pair of electrodes (e.g.,electrode pair208 ofFIG. 2, which may includeelectrodes704 and706 shown inFIG. 7). The electrodes generate an electric field (e.g.,electric field1402 shown inFIG. 14) to associate one or more nanowires5110 innanowire solution5106 with therespective transfer surface206. For example,FIG. 51 shows afirst nanowire5110ainsolution5106 that is not associated with any oftransfer surfaces206a-206b. Asecond nanowire5110bis shown associated withsecond transfer surface206b. Athird nanowire5110cis nearby but not associated withfirst transfer surface206a.
• During or afterstep4902,print head4810 ofFIG. 48 may optionally be configured to flush excess nanostructures fromtransfer surfaces206 of plurality ofprint heads4818 atassociation station4802. For example,FIG. 52 shows excess nanowires being flushed fromtransfer surfaces206a-206fofprint head4810. In the example ofFIG. 51, a fluid (e.g., solution5106) is shown being flowed through openings5108a-5108e(as indicated by arrows5202) to flush excess nanowires5110 fromtransfer surface206a-206f. A fluid source (not shown inFIG. 52) configured to produce a suitable fluid pressure may be coupled to aninlet5102 ofprint head4810, or may be otherwise coupled toprint head4810, to provide the fluid to flow through openings5108a-5108e. A fluid velocity and flush time provided by the fluid source may be determined for a particular application. For example, fluid velocities in the range of 1-100 μm/s may be used, during a flush time of 60 minutes or less (e.g., 1 minute or less), in embodiments.
• Excess nanowires5110, such asnanowire5110c, which may be desired to be flushed fromtransfer surfaces206, are nanowires that may be weakly associated with atransfer surface206, that may have become entangled with other nanowires5110 that are associated, and/or that may have become otherwise attached to (but not associated with) a surface ofprint head4810. For example,nanowire5110cis shown inFIG. 52 as having been flushed fromtransfer surface206a.
• Referring back toflowchart4900, instep4904, an inspection of the print heads is performed. For example, as shown inFIG. 48,inspection station4804 receives plurality of print heads and associatednanostructures4820.Inspection station4804 is configured to perform an inspection of transfer surfaces206 of the received plurality of print heads, and to select at least one print head of received plurality of print heads based on the inspection. As shown inFIG. 48,inspection station4804 outputs at least one selected print head and associatednanostructures4822.
• For instance,FIG. 53 shows an example ofinspection station4804, according to an embodiment of the present invention. As shown inFIG. 53,inspection station4804 has received a plurality ofprint heads4810a-4810c. Each ofprint heads4810a-4810chas a respective plurality oftransfer surfaces206a-206f. Aninspection device5302 is present that is configured to inspect arrangements of nanowires5110 associated withtransfer surfaces206 ofprint heads4810a-4810c.Inspection device5302 may be an optical inspection device (e.g., a microscope, a camera, and/or other optical inspection device), an electrical inspection device, a mechanical inspection device, and/or further type of inspection device.Inspection device5302 may be configured to determine whether a sufficient number of nanostructures is present at eachtransfer surface206, to determine whether an unsuitable arrangement of nanostructures is present at a transfer surface206 (e.g., determine whether sufficient contact between electrodes is made by the present nanostructures), and/or to otherwise determine the suitability and/or unsuitability of an arrangement of nanostructures at transfer surfaces206 ofprint heads4810a-4810c.
• For example, inFIG. 53,inspection device5302 may determine that an insufficient number of nanowires5110 (e.g., no nanowires) is present attransfer surface206cofprint head4810a, while all transfer surfaces ofprint heads4810band4810chave sufficient numbers and arrangements of nanowires5110. Becauseinspection device5302 determined thattransfer surface206cofprint head4810 does not have a sufficient number of associated nanowires5110,print head4810amay be indicated as having failed inspection, whileprint heads4810band4810cmay be indicated as having passed inspection.
• Instep4906, one or more print heads are selected based on the inspection. One or more print heads that passed inspection instep4904 may be selected. In the current example, becauseinspection device5302 determined thatprint heads4810band4810cpassed inspection, whileprint head4810afailed inspection,print heads4810band4810cmay be selected for further processing insystem4800. Note that in an embodiment, an arrangement of nanowires5110 at aprint head4810 that failed inspection may be repaired. For example, in the current example, aftertransfer surface206cwas determined (in step4904) to be lacking a sufficient number of nanowires, one or more additional nanowires5110 may be associated withtransfer surface206c. Subsequently,print head4810amay be re-inspected (repeat step4904). Ifprint head4810apasses the re-inspection,print head4810amay be selected instep4906. Example embodiments for repairing arrangements of nanostructures on surfaces (e.g., transfer surfaces, destination surfaces) are described in detail further below.
• Instep4908, the nanostructures are transferred from the selected print head(s) to a destination surface. For example, as shown inFIG. 48,printing station4806 receives at least one selected print head and associatednanostructures4822. In the current example, at least one selected print head and associatednanostructures4822 includesprint heads4810band4810c.Printing station4806 also receives apanel4816, which is an example ofdestination substrate212 shown inFIG. 2.Printing station4806 is configured to transfer the nanostructures from the received at least one of the plurality of print heads to a plurality of regions of a surface ofpanel4816. As shown inFIG. 48,printing station4806 outputs a plurality ofprint heads4824 and a panel with depositednanostructures4828.
• In embodiments,printing station4806 may be configured to transfer nanostructures fromprint heads4810 topanel4816 in any manner described elsewhere herein, such as described above with respect toflowchart300 inFIG. 3, or in other ways known to persons skilled in the relevant art(s). For instance,FIGS. 54-56 show views ofprinting station4806 during a nanostructure transfer process, according to an example embodiment of the present invention. In an example embodiment, transfer surfaces206 ofprint heads4802 anddestination surface210 may be coated with molecules that interact via a lock and key mechanism. One oftransfers surfaces206 orprint heads4802 may be coated with a first molecule, and the other of transfer surfaces206 orprint heads4802 may be coated with a second molecule. The first and second molecules interact according to a molecular binding process that occurs in biological systems. This type of molecular recognition could be used to perform more sophisticated multi step depositions of nanowires5110. Such a molecular coating may be used on transfer surfaces and destination surfaces in conjunction with other nanostructure transfer embodiments described elsewhere herein.
• FIG. 54 showsprint head4810bandpanel4816 insolution5106. InFIG. 54, one or more nanowires5110 are associated with each oftransfer surfaces206a-206fofprint head4810b. InFIG. 55,print head4810bis moved adjacent topanel4816, so that each oftransfer surfaces206a-206fis aligned with a corresponding one ofregions1902a-1902fofpanel4816. InFIG. 56,print head4810bhas deposited nanowires5110 onpanel4816, and has withdrawn frompanel4816. For instance, as shown inFIG. 56,nanowire5110bis deposited fromtransfer surface206btoregion1904bofdestination surface210 ofpanel4816.
• Instep4910, the print heads are cleaned. For example, as shown inFIG. 48,cleaning station4808 receives plurality ofprint heads4824. In the current example, plurality ofprint heads4824 includesprint heads4810a-4810c.Cleaning station4808 is configured to clean the received plurality ofprint heads4824.Cleaning station4808 may be configured to cleanprint heads4824 in any manner, to remove any remaining nanostructures (e.g., nanostructures that were not deposited from a print head at printing station4806) and/or to remove any further contaminants.
• For instance,FIG. 57 shows an example of cleaningstation4808, according to an embodiment of the present invention. InFIG. 57, afluid source5702 may be present that outputs and/or directs a fluid to transfersurfaces206a-206f, as indicated byarrows5704, to remove/dislodge contaminants fromtransfer surfaces206a-206f.Fluid source5702 may be any mechanism for providing a fluid flow of a suitable pressure. The fluid output/directed byfluid source5702 may besolution5106 and/or other fluid, such a fluid configured to cleantransfer surfaces206a-206f.
• As shown inFIG. 48,cleaning station4808 outputs plurality ofprint heads4818. Plurality ofprint heads4818 may be received byassociation station4802 for a next cycle of nanostructure printing to be performed bysystem4800. In an embodiment, a single set of print heads may proceed from station to station insystem4800, such that at any particular time, all print heads are at the same station. In another embodiment, at any particular time, each station may be operating on a corresponding set of print heads, which shift to a next station at predetermined time intervals.
• Flowchart5000, which relates to a pipeline of destination panels, is now described. Instep5002 offlowchart5000, the nanostructures are received on the destination surface. For example, as shown inFIGS. 54-56 and described above (with respect to step4908 of flowchart4900), nanowires5110 are transferred todestination surface210 ofpanel4816.
• Instep5004, the placement of received nanostructures on the destination surface is repaired.Step5004 is optional. For example, as shown inFIG. 48,panel repair station4812 receives panel with depositednanostructures4828.Panel repair station4812 is configured to perform an inspection of the nanostructures transferred to the plurality of regions of the surface of the received panel. For instance,FIGS. 58 and 59 show views of an examplepanel repair station4812, according to embodiments of the present invention. InFIG. 58, aninspection device5802 is present that is configured to inspect arrangements of nanowires5110 atregions1904 ofpanel4816.Inspection device5802 may be an optical inspection device (e.g., a microscope, a camera, and/or other optical inspection device), an electrical inspection device, a mechanical inspection device, and/or further type of inspection device.Inspection device5802 may be configured to determine whether a sufficient number of nanostructures is present at eachregion1904, to determine whether an unsuitable arrangement of nanostructures is present at a region1904 (e.g., sufficient contact with electrical conductors onsurface210 is not made by the present nanostructures), and/or to otherwise determine the suitability and/or unsuitability of an arrangement of nanostructures atregions1904 ofdestination surface210.
• For example, inFIG. 58,inspection device5802 may determine that an insufficient number of nanowires5110 (e.g., no nanowires) is present atregion1904cofpanel4816. Becauseinspection device5802 determined thatregion1904cdoes not have a sufficient number of nanowires5110,region1904cmay be indicated for repair.
• FIG. 59 shows a repair of the arrangement of nanostructures atregion1904cbeing performed. In the example ofFIG. 59, aprint head5902 is shown repairingregion1904c, by depositing one or more nanostructures, including ananowire5110c, onregion1904c. Thus, in an embodiment,print head5902 may be configured to add one or more nanostructures to aregion1904 in need of repair. Alternatively or additionally, if nanostructures are present in aregion1904 in need of repair,print head5902 may be configured to rearrange the present nanostructures (e.g., move nanostructures into contact with desired electrical conductors of the region1904), and/or to remove one or more present nanostructures, to create a sufficient nanostructure arrangement.
• As shown inFIG. 48,panel repair station4812 outputs a panel with depositednano structures4830.
• Instep5006, the destination surface is dried. For example, as shown inFIG. 48,panel drying station4814 receives panel with depositednanostructures4830.Panel drying station4814 is configured to dry the deposited nanostructures onpanel4814. For instance,FIG. 60 shows an example ofpanel drying station4814, according to an embodiment of the present invention. As shown inFIG. 60, adryer6002 is present.Dryer6002 is configured to dry nanowires5110 onpanel4814.Dryer6002 may be configured to dry nanowires5110 onpanel4814 in any suitable manner, including by radiating electromagnetic energy (e.g., infrared heat), by blowing air6004 (as shown inFIG. 60), and/or in any other manner.
• As shown inFIG. 48,panel drying station4814outputs panel4816 with depositednanostructures4826.Panel4816 may receive further processing, such as receiving a coating for environmental protection of the deposited nanostructures.Panel4816 withnanostructures4826 may be an electronic device, such as a display, and/or may be incorporated into an electronic device. Examples of such electronic devices are described further below.
• Nanostructure printing system4800 includesprinting station4806, which in the example ofFIGS. 54-56, performs a “wet” nanostructure transfer process (e.g., nanowires5110 are transferred inFIGS. 54-56 inreservoir5104 containing solution5106) (also referred to as “wet stamping”). In an alternative embodiment, a nanostructure printing system may perform a “dry” nanostructure transfer process. For example,FIG. 61 shows ananostructure printing system6100, according to an example embodiment of the present invention.Nanostructure printing system6100 includes anassociation station6102, a dryingstation6104, a printhead repair station6106, aprinting station6108, acleaning station6110, and apanel repair station6114.Printing station6108 ofsystem6100 is configured to perform a dry nanostructure transfer process.Association station6102, dryingstation6104, printhead repair station6106,printing station6108, andcleaning station6110 form a print head pipeline portion ofsystem6100, andprinting station6108 andpanel repair station6114 form a panel pipeline portion ofsystem6100.
• System6100 is described with respect toflowcharts6200 and6300 shown inFIGS. 62 and 63, respectively.Flowchart6200 shows a process for the print head pipeline portion ofsystem6100, andflowchart6300 shows a process for the panel pipeline ofsystem6100, according to example embodiments of the present invention. For illustrative purposes,flowcharts6200 and6300 are described as follows with respect tosystem6100. Other structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. Not all elements ofsystem6100 shown inFIG. 61 need be present in all embodiments, and not all steps offlowcharts6200 and6300 are necessarily performed in all embodiments.
• Flowchart6200 is first described. Instep6202 offlowchart6200, nanostructures are associated with transfer surfaces of print heads. For example, as shown inFIG. 61,association station6102 receives a plurality ofprint heads6118, including aprint head6112.Association station6102 is configured to associate nanostructures with a transfer surface of each print head the received plurality ofprint heads6118. The association of nanostructures withprint heads6118 may be performed in any manner described elsewhere herein, such as described above with respect toflowchart300 inFIG. 3, or in other ways known to persons skilled in the relevant art(s). For instance,association station6102 may associate nanostructures with print heads in a similar manner as described above forassociation station4802 ofFIG. 48. As shown inFIG. 61,association station6102 outputs a plurality of print heads and associatednanostructures6120.
• Instep6204, the print heads are dried. For example, as shown inFIG. 61, dryingstation6104 receives plurality of print heads and associatednanostructures6120.Drying station6104 is configured to dry the transfer surfaces and associated nanostructures of the received plurality of print heads. For instance, dryingstation6104 may include a dryer similar todryer6002 shown inFIG. 60, and described above, to perform drying. As shown inFIG. 61, dryingstation6104 outputs a dried plurality of print heads and associatednanostructures6122.
• Instep6206, placement of nanostructures on one or more print heads is repaired.Step6206 is optional. For example, as shown inFIG. 61, printhead repair station6106 receives dried plurality of print heads and associatednanostructures6122. Printhead repair station6106 may be configured to inspect and repair the nanostructures associated with the print heads in a similar manner aspanel repair station4812 ofFIG. 48, and described above. For instance, printhead repair station6106 may include an inspection device similar toinspection device5802 shown inFIG. 58, to determine nanostructure arrangements on print heads in need of repair. Furthermore, printhead repair station6106 may include a print head or other repair device, such asprint head5902 shown inFIG. 59, which may be used repair the determined nanostructure arrangements in need of repair, in a wet or dry manner. As shown inFIG. 61,panel repair station6106 outputs a plurality of print heads and associatednanostructures6124.
• Instep6208, the nanostructures are transferred from one or more of the print heads to a destination surface. For example, as shown inFIG. 61,printing station6108 receives plurality of print heads and associatednanostructures6124.Printing station6108 also receives apanel6116, which is an example ofdestination substrate212 shown inFIG. 2.Printing station6108 is configured to transfer the nanostructures from the received plurality of print heads to a plurality of regions of a surface ofpanel6116. Nanostructures may be transferred from all of the received print heads, or from a selected portion of the print heads (e.g., selected in a similar manner as described above with respect to step4906 of flowchart4900). In embodiments,printing station6108 may be configured to transfer nanostructures topanel6116 according to any dry transfer process described elsewhere herein, such as described above with respect toflowchart300 inFIG. 3, or in other ways known to persons skilled in the relevant art(s). For example, a difference in adhesion properties of the transfer surface of the print head and of the destination surface may be used to enable a transfer of nanostructures. The destination surface may be configured to have greater adhesion (to the nanostructures) than the transfer surface. In this manner, the nanostructures associated with the transfer surface may be brought into contact with the destination surface. As the transfer surface is moved away from the destination surface, the greater adhesion of the destination surface may cause the nanostructure to remain on the destination surface.
• In an embodiment,printing station6108 may be configured similarly toprinting station4806 shown inFIGS. 54-56, but without the presence ofreservoir5104 andsolution5106. As shown inFIG. 61,printing station6108 outputs a plurality ofprint heads6126 and a panel with depositednanostructures6130.
• Instep6210, the print heads are cleaned. For example, as shown inFIG. 61,cleaning station6110 receives plurality ofprint heads6126.Cleaning station6110 is configured to clean the received plurality ofprint heads6126.Cleaning station6110 may be configured to cleanprint heads6126 in any manner, to remove any remaining nanostructures (e.g., nanostructures that were not deposited from a print head at printing station6108) and/or to remove any further contaminants. For instance, cleaningstation6110 may be configured to clean print heads in a similar fashion as cleaningstation4808 shown inFIG. 48. In an example embodiment, cleaningstation6110 may include a fluid source, such asfluid source5702 shown inFIG. 57, to clean the transfer surfaces ofprint heads6126. As shown inFIG. 61,cleaning station6110 outputs plurality ofprint heads6118. Plurality ofprint heads6118 may be received byassociation station6102 for a next cycle of nanostructure printing to be performed bysystem6100. In an embodiment, a single set of print heads may proceed from station to station insystem6100, such that at any particular time, all print heads are at the same station. In another embodiment, at any particular time, each station may be operating on a corresponding set of print heads, which shift forward to the next station at predetermined time intervals.
• Flowchart6300, which relates to a pipeline of destination panels forsystem6100, is now described. Instep6302 offlowchart6300, the nanostructures are received on the destination surface. For example, as described above (with respect to step6208 of flowchart6200), nanostructures are transferred topanel6116 byprinting station6108.
• Instep6302, placement of the received nanostructures is repaired on destination surface.Step6302 is optional. For example, as shown inFIG. 61,panel repair station6114 receives panel with depositednanostructures6130.Panel repair station6114 is configured to perform an inspection of the nanostructures transferred to the plurality of regions of the surface of the received panel. For instance,panel repair station6114 may be configured similarly topanel repair station4812 described above with respect toFIG. 48, including being configured as shown inFIGS. 58 and 59.
• As shown inFIG. 61,panel repair station6114outputs panel6116 with depositednanostructures6128.Panel6116 may receive further processing, such as receiving a coating for environmental protection ofnanostructures6128.Panel6116 withnanostructures6128 may be an electronic device, such as a display, and/or may be incorporated into an electronic device. Examples of such electronic devices are described further below.
Example Captured Images of a Nanostructure Transfer Process
• This section describes images captured during a nanostructure transfer process performed according to an embodiment of the present invention.FIG. 64 shows ananostructure transfer system6400 used to perform the nanostructure transfer and to capture the images of the transfer. As shown inFIG. 64,system6400 includesprint head702,destination substrate212, and animage capturing microscope6402.Transfer surface206 ofprint head702 includes first andsecond electrodes704 and706 and a plurality ofspacing members2302. InFIG. 64,electrodes704 and706 hold an associatedfirst nanowire1702a(and asecond nanowire1702b, not visible inFIG. 64). First andsecond nanowires1702aand1702bmay have been associated with first andsecond electrodes704 and706 in any manner described elsewhere herein, such as described above with respect tosteps302 and304 of flowchart300 (FIG. 3).FIG. 65 shows afirst image6500 captured bymicroscope6402 ofsystem6400.First image6500 shows first andsecond nanowires1702aand1702bassociated with first andsecond electrodes704 and706 ontransfer surface206 ofprint head702. Note that in the current example,destination substrate212 is transparent tomicroscope6402, and thusmicroscope6402 may capture images ofnanowires1702aand1702bthroughsubstrate212.
• FIG. 66 shows another view ofnanostructure transfer system6400, whereprint head702 is moved into contact with destination substrate212 (e.g., according to step306 offlowchart300 ofFIG. 3). Spacingmembers2302 ontransfer surface206 ofprint head702 are in contact withdestination surface210 ofsubstrate212, to maintainprint head702 at a predetermined distance (a height of spacing members2302) fromsubstrate212.FIG. 67 shows asecond image6700 captured bymicroscope6402 of first andsecond nanowires1702aand1702bassociated with first andsecond electrodes704 and706, withprint head702 in contact with destination surface210 (as inFIG. 66).
• FIG. 68 shows another view ofnanostructure transfer system6400. InFIG. 68,print head702 remains in contact with destination substrate212 (as inFIG. 66). Furthermore, inFIG. 68,nanowire1702a(andnanowire1702b, not visible inFIG. 68) is transferred todestination surface210 ofsubstrate212.Nanowires1702aand1702bmay be transferred todestination surface210 in any manner described elsewhere herein, such as according to step308 of flowchart300 (FIG. 3) described above. For example, an electric field generated by first andsecond electrodes704 and706 (e.g., step304 of flowchart300) may be removed to release first andsecond nanowires1702aand1702b. Furthermore,destination surface210 may have been configured to have a charge that is opposite to a charge of first andsecond nanowires1702aand1702b, to attractnanowires1702aand1702b.FIG. 69 shows athird image6900 captured bymicroscope6402 of first andsecond nanowires1702aand1702b, where first andsecond nanowires1702aand1702bare transferred to destination surface210 (as inFIG. 68).
• FIG. 70 shows another view ofnanostructure transfer system6400. InFIG. 70,print head702 is moved away from destination substrate212 (e.g., according to step310 offlowchart300 inFIG. 3).Nanowire1702a(andnanowire1702b, not visible inFIG. 68) remains deposited ondestination surface210 ofsubstrate212.FIG. 71 shows afourth image7100 captured bymicroscope6402 of first andsecond nanowires1702aand1702b, where first andsecond nanowires1702aand1702bare ondestination surface210, andprint head702 has been moved away from destination surface210 (as inFIG. 70). Note that in each ofFIGS. 65,67,69,71,microscope6402 is focused onnanowires1702aand1702b. Thus, inFIG. 71, first andsecond nanowires1702aand1702bremain in focus, while focus is diminished with respect to transfersurface206 ofprint head702 due to the increased separation betweennanowires1702aand1702bandtransfer surface206.
• Example electronic devices and systems that can be formed according to embodiments of the present invention are described below.
Use of Nanowires and Electrical Devices Deposited According to the Present Invention in Exemplary Devices and Applications
• Numerous electronic devices and systems can incorporate semiconductor or other type devices with thin films of nanowires and/or electrical devices deposited according the methods of the present invention. Some example applications for the present invention are described below or elsewhere herein for illustrative purposes, and are not limiting. The applications described herein can include aligned or non-aligned thin films of nanowires, and can include composite or non-composite thin films of nanowires.
• Semiconductor devices (or other type devices) can be coupled to signals of other electronic circuits, and/or can be integrated with other electronic circuits. Semiconductor devices can be formed on large substrates, which can be subsequently separated or diced into smaller substrates. Furthermore, on large substrates (i.e., substrates substantially larger than conventional semiconductor wafers), semiconductor devices formed thereon can be interconnected.
• The nanowires deposited by the processes and methods of the present invention can also be incorporated in applications requiring a single semiconductor device, and in multiple semiconductor devices. For example, the nanowires deposited by the processes and methods of the present invention are particularly applicable to large area, macro electronic substrates on which a plurality of semiconductor devices are formed. Such electronic devices can include display driving circuits for active matrix liquid crystal displays (LCDs), organic LED displays, field emission displays. Other active displays can be formed from a nanowire-polymer, quantum dots-polymer composite (the composite can function both as the emitter and active driving matrix). The nanowires deposited by the processes and methods of the present invention are also applicable to smart libraries, credit cards, large area array sensors, and radio-frequency identification (RFID) tags, including smart cards, smart inventory tags, and the like.
• The nanowires deposited by the processes and methods of the present invention are also applicable to digital and analog circuit applications. In particular, the nanowires deposited by the processes and methods of the present invention are useful in applications that require ultra large-scale integration on a large area substrate. For example, a thin film of nanowires deposited by the processes and methods of the present invention can be implemented in logic circuits, memory circuits, processors, amplifiers, and other digital and analog circuits.
• The nanowires deposited by the processes and methods of the present invention can be applied to photovoltaic applications. In such applications, a clear conducting substrate is used to enhance the photovoltaic properties of the particular photovoltaic device. For example, such a clear conducting substrate can be used as a flexible, large-area replacement for indium tin oxide (ITO) or the like. A substrate can be coated with a thin film of nanowires that is formed to have a large bandgap, i.e., greater than visible light so that it would be non-absorbing, but would be formed to have either the HOMO or LUMO bands aligned with the active material of a photovoltaic device that would be formed on top of it. Clear conductors can be located on two sides of the absorbing photovoltaic material to carry away current from the photovoltaic device. Two different nanowire materials can be chosen, one having the HOMO aligned with that of the photovoltaic material HOMO band, and the other having the LUMO aligned with the LUMO band of the photovoltaic material. The bandgaps of the two nanowires materials can be chosen to be much larger than that of the photovoltaic material. The nanowires, according to this embodiment, can be lightly doped to decrease the resistance of the thin films of nanowires, while permitting the substrate to remain mostly non-absorbing.
• Hence, a wide range of military and consumer goods can incorporate the nanowires and electrical devices deposited by the processes and methods of the present invention. For example, such goods can include personal computers, workstations, servers, networking devices, handheld electronic devices such as PDAs and palm pilots, telephones (e.g., cellular and standard), radios, televisions, electronic games and game systems, home security systems, automobiles, aircraft, boats, other household and commercial appliances, and the like.
• Exemplary embodiments of the present invention have been presented. The invention is not limited to these examples. These examples are presented herein for purposes of illustration, and not limitation. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope and spirit of the invention.
• All publications, patents and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference.
Example Embodiments
• In an embodiment, a method for transferring nanowires to a destination surface includes providing at least one nanowire proximate to an electrode pair, generating an electric field with electrodes of the electrode pair to associate the at least one nanowire with the electrodes, aligning the electrode pair with a region of the destination surface, and depositing the at least one nanowire from the electrode pair to the region.
• The transfer surface may be configured to have a first electric charge.
• The first electric charge may apply a repulsive electrostatic force to the at least one nanowire, and the electric field may be configured to attract the at least one nanowire to the transfer surface against the repulsive electrostatic force.
• The electric field may be biased with an alternating current (AC) field to attract the at least one nanowire to the transfer surface.
• The electric field may be biased with a second AC field to enable the at least one nanowire to move toward the destination surface.
• The destination surface may be configured to have a second electric charge that is opposite the first electric charge.
• The at least one nanowire may be enabled to be attracted to the destination surface by an attractive electrostatic force of the second electric charge by reducing a distance between the at least one nanowire and the destination surface.
• The at least one nanowire may be attracted toward the destination surface with the second electric charge.
• The transfer surface may be ultrasonically vibrated to enable an attractive electrostatic force of the second electric charge to attract the at least one nanowire toward the destination surface.
• Both the transfer surface and destination surface may be ultrasonically vibrated.
• The transfer surface and destination surface may be ultrasonically vibrated synchronously.
• A vacuum may be applied from the destination surface to the transfer surface to move the at least one nanowire toward the destination surface.
• A second electric field associated with the destination surface may be generated to attract the at least one nanowire toward the destination surface.
• Generation of the electric field may be ceased.
• The destination surface may be configured to have a hydrophilic property to attract a solution containing the at least one nanowire toward the destination surface.
• The transfer surface may be configured to have a hydrophobic property to repel a solution containing the at least one nanowire.
• A solution containing the at least one nanowire may be flowed on the electrode pair.
• A rate of flow of the solution on the electrode pair may be varied.
• The electrode pair may include a first electrode and a second electrode, and the at least one nanowire may include a first nanowire. A first end of the first nanowire may be caused to be positioned adjacent to a surface of the first electrode, and a second end of the first nanowire may be caused to be positioned adjacent to a surface of the second electrode.
• The at least one nanowire may be caused to align substantially in parallel with an axis through the first and second electrodes.
• The at least one nanowire may be positioned such that the first and second ends are not in contact with the first and second electrodes.
• The region may include an electrical contact pair. The electrode pair may be contacted with the electrical contact pair.
• The electrode pair may be contacted with the destination surface.
• A cantilever that mounts a first electrode of the electrode pair may be caused to flex due to the contacting.
• A pair of cantilevers that mount the electrode pair may be caused to flex due to the contacting.
• The electrode pair may be positioned adjacent to the surface.
• The electrode pair may be removed from alignment with the region of the destination surface.
• A second at least one nanowire may be provided proximate to the electrode pair.
• A second electric field may be generated with the electrodes of the electrode pair to associate the second at least one nanowire with the electrodes. The electrode pair may be aligned with a second region of the surface. The at least one nanowire may be deposited from the electrode pair to the second region.
• The first electrode pair and a second electrode pair may be on a common transfer surface. In parallel with the providing the first at least one nanowire proximate to the first electrode pair, a second at least one nanowire proximate may be provided to the second electrode pair. In parallel with the generating the first electric field, a second electric field may be generated with second electrodes of the second electrode pair to associate the second at least one nanowire with the second electrodes. In parallel with the aligning the first electrode pair with the first region of the surface, the second electrode pair may be aligned with a second region of the surface. In parallel with the depositing the first at least one nanowire from the first electrode pair to the first region, the second at least one nanowire may be deposited from the second electrode pair to the second region.
• Uncoupled nanowires may be removed from the electrode pair.
• In another embodiment, a system for transferring nanowires to a destination may include a body having a transfer surface, an electrode pair on the transfer surface, a suspension that includes a plurality of nanowires provided proximate to the electrode pair, a signal generator coupled to the electrode pair, wherein the signal generator is configured to enable electrodes of the electrode pair to generate an electric field to associate at least one nanowire of the plurality of nanowires with the electrodes, and an alignment mechanism configured to align the electrode pair with a region of the destination surface to enable the associated at least one nanowire to be deposited from the electrode pair to the region.
• The transfer surface may have a first electric charge.
• The first electric charge may apply a repulsive electrostatic force to the at least one nanowire, and the electric field may attract the at least one nanowire to the transfer surface against the repulsive electrostatic force.
• The signal generator may bias the electric field with an alternating current (AC) field to attract the at least one nanowire to the transfer surface.
• The signal generator may bias the electric field with a second AC field to enable the associated at least one nanowire to move toward the destination surface.
• The destination surface may have a second electric charge that is opposite the first electric charge.
• The alignment mechanism may be configured to reduce a distance between the at least one nanowire and the destination surface to enable the associated at least one nanowire to be attracted to the destination surface by an attractive electrostatic force of the second electric charge.
• The associated at least one nanowire may be attracted toward the destination surface by the second electric charge.
• The system may further include an ultrasonic vibration source configured to vibrate the transfer surface to enable an attractive electrostatic force of the second electric charge to attract the associated at least one nanowire toward the destination surface.
• The ultrasonic vibration source may be configured to vibrate both the transfer surface and destination surface.
• The ultrasonic vibration source may be configured to vibrate the transfer surface and destination surface synchronously.
• The system may further include a vacuum source configured to apply a vacuum from the destination surface to the transfer surface to move the associated at least one nanowire toward the destination surface.
• The system may further include an electric field source configured to generate a second electric field associated with the destination surface to attract the associated at least one nanowire toward the destination surface.
• The signal generator may be configured to reduce an intensity of the electric field to enable the associated at least one nanowire to be attracted toward the destination surface.
• The destination surface may be configured to have a hydrophilic property to attract a fluid containing the associated at least one nanowire toward the destination surface.
• The transfer surface may be configured to have a hydrophobic property to repel the fluid containing the associated at least one nanowire.
• The system may further include a container that contains the suspension and the electrode pair.
• The suspension may be flowed over the electrode pair.
• The electrode pair may include a first electrode and a second electrode, and the at least one nanowire may include a first nanowire. The electric field may cause a first end of the first nanowire to be positioned adjacent to a surface of the first electrode, and a second end of the first nanowire to be positioned adjacent to a surface of the second electrode.
• The electric field may align the at least one nanowire substantially in parallel with an axis through the first and second electrodes.
• The electric field may position the at least one nanowire such that the first and second ends are not in contact with the first and second electrodes.
• The region may include an electrical contact pair. The alignment mechanism may be configured to contact the electrode pair with the electrical contact pair.
• The alignment mechanism may be configured contact the electrode pair with the destination surface.
• The transfer surface may have a cantilever that mounts a first electrode of the electrode pair. The cantilever is configured to flex if the electrode pair contacts the destination surface.
• The transfer surface may have a pair of cantilevers that mount first and second electrodes of the electrode pair. The pair of cantilevers is configured to flex if the electrode pair contacts the destination surface.
• The alignment mechanism may be configured to position the electrode pair adjacent to the surface.
• The system may further include a plurality of spacers on the transfer surface.
• The alignment mechanism may be configured to remove the electrode pair from alignment with the region of the destination surface after the associated at least one nanowire is deposited.
• A second electrode pair may be on the transfer surface.
• In another embodiment, a method for applying nanowires to a destination surface may include aligning an electrode pair having an associated at least one nanowire with a region of the destination surface, and depositing the at least one nanowire from the electrode pair to the region.
• In another embodiment, a system for transferring electrical devices to a destination surface may include a body having a transfer surface, an electrode pair on the transfer surface, a suspension that includes a plurality of electrical devices provided proximate to the electrode pair, a signal generator coupled to the electrode pair, wherein the signal generator is configured to enable electrodes of the electrode pair to generate an electric field to associate an electrical device of the plurality of electrical devices with the electrodes, and an alignment mechanism configured to align the electrode pair with a region of the destination surface to enable the associated electrical device to be deposited from the electrode pair to the region.
• The system may further include an ultrasonic vibration source configured to vibrate the transfer surface to enable an attractive electrostatic force to attract the associated electrical device toward the destination surface.
• The ultrasonic vibration source may be configured to vibrate both the transfer surface and destination surface.
• The ultrasonic vibration source may be configured to vibrate the transfer surface and destination surface synchronously.
• The system may further include an ultrasonic vibration source configured to vibrate the transfer surface to enable an attractive electrostatic force to attract the associated electrical device toward the destination surface.
• The ultrasonic vibration source may be configured to vibrate both the transfer surface and destination surface.
• The ultrasonic vibration source may be configured to vibrate the transfer surface and destination surface synchronously.
• In another embodiment, a method for transferring nanowires to a destination surface may include positioning a transfer surface of a print head adjacent to a destination surface, wherein a nanowire is associated with the transfer surface, reducing a distance between the transfer surface and the destination surface, receiving a fluid in at least one opening in the transfer surface from between the transfer surface and the destination surface during the reducing, and depositing the nanowire from the transfer surface to the destination surface.
• The fluid may be received in first and second openings in the transfer surface, the nanowire being associated with the transfer surface at a location substantially midway between the first and second openings.
• The first and second openings may each have a length that is greater than a length of a long axis of the nanowire.
• The lengths of the first and second openings may be positioned in the transfer surface in parallel with the long axis of the nanowire.
• A piston may be moved within each of the first and second openings to draw the fluid from between the transfer surface and the destination surface into the first and second openings.
• In another embodiment, a system for transferring nanowires to a destination surface may include a body having a transfer surface, at least one opening in the transfer surface, and an electrode pair formed on the transfer surface. The electrode pair may be configured to generate an electric field to associate a nanowire with the electrode pair. The at least one opening may be configured to receive a fluid from between the transfer surface and the destination surface.
• The at least one opening may be configured to receive the fluid from between the transfer surface and the destination surface when the transfer surface is being moved toward the destination surface.
• The at least one opening may include a first opening and a second opening. The electrode pair may be configured to associate the nanowire with the transfer surface at a location substantially midway between the first and second openings.
• The first and second openings may each have a length that is greater than a length of a long axis of the nanowire.
• The first and second openings may be positioned in the transfer surface such that the lengths of the first and second openings are configured to be parallel with the long axis of the nanowire.
• The system may further include a first piston in the first opening and a second piston in the second opening. The first and second pistons may be configured to draw the fluid from between the transfer surface and the destination surface into the first and second openings.
• In another embodiment, a method for transferring nanowires to a destination substrate may include associating nanostructures with transfer surfaces of a plurality of print heads, performing an inspection of the transfer surfaces of the plurality of print heads, selecting at least one print head of the plurality of print heads based on the inspection, and transferring the nanostructures from the selected at least one print head to a plurality of regions of a surface of a destination substrate.
• Excess nanostructures may be flushed from the transfer surfaces of the plurality of print heads.
• The selected at least one print head may be cleaned after the transferring.
• An inspection may be performed of the nanostructures transferred to the plurality of regions of the surface of the destination substrate.
• An arrangement of nanostructures transferred to a region of the surface of the destination substrate in need of repair may be determined, and the determined arrangement of nanostructures may be repaired.
• The transfer surfaces may be positioned in a suspension containing a plurality of nanostructures, and an electric field may be generated with electrodes of an electrode pair of each transfer surface to associate nanostructures with the electrode pair of each transfer surface.
• The associated nanostructures may be deposited from at least one electrode pair of the selected at least one print head to the surface of the destination substrate.
• In another embodiment, a method for transferring nanowires to a destination substrate may include associating nanostructures with transfer surfaces of a plurality of print heads, drying the transfer surfaces having associated nanostructures, performing an inspection of the dried transfer surfaces having associated nanostructures, and transferring the nanostructures from the dried transfer surfaces to a plurality of regions of a surface of the destination substrate.
• An arrangement of nanostructures associated with a transfer surface of a print head in need of repair may be determined, and the determined arrangement of nanostructures may be repaired.
• Excess nanostructures may be flushed from the transfer surfaces of the plurality of print heads prior to the drying.
• The plurality of print heads may be cleaned after the transferring.
• An inspection of the nanostructures transferred to the plurality of regions of the surface of the destination substrate may be performed.
• An arrangement of nanostructures transferred to a region of the surface of the destination substrate in need of repair may be determined, and the determined arrangement of nanostructures may be repaired.
• The transfer surfaces may be positioned in a suspension containing a plurality of nanostructures, and an electric field may be generated with electrodes of an electrode pair of each transfer surface to associate nanostructures with the electrode pair of each transfer surface.
• The associated nanostructures may be deposited from at least one electrode pair of the selected at least one print head to the surface of the destination substrate.
• In another embodiment, a system for transferring nanowires to a destination substrate may include an association station configured to receive a plurality of print heads, and to associate nanostructures with a transfer surface of each of the received plurality of print heads, a printing station configured to receive a destination substrate and at least one of the plurality of print heads, and to transfer the nanostructures from the received at least one of the plurality of print heads to a plurality of regions of a surface of the destination substrate, and a cleaning station configured to receive the plurality of print heads from the printing station, and to clean the received plurality of print heads.
• The association station may be configured to flush excess nanostructures from the transfer surfaces of the plurality of print heads.
• The system may further include a repair station configured to receive the destination substrate, and to perform an inspection of the nanostructures transferred to the plurality of regions of the surface of the destination substrate.
• The repair station may be configured to determine an arrangement of nanostructures transferred to a region of the surface of the destination substrate in need of repair based on the inspection, and to repair the determined arrangement of nano structures.
• The printing station may be configured to perform a wet transfer of the nano structures.
• The system may further include an inspection station configured to receive the plurality of print heads from the association station, to perform an inspection of the transfer surfaces of the plurality of print heads, and to select at least one print head of the plurality of print heads based on the inspection. The printing station may be configured to transfer the nanostructures from the selected at least one print head to the plurality of regions of the surface of the destination substrate.
• The system may further include a panel drying station configured to receive the destination substrate, and to dry the nanostructures transferred to the plurality of regions of the surface of the destination substrate.
• The printing station may be configured to perform a dry transfer of the nano structures.
• The system may further include a print head drying station configured to receive the plurality of print heads, and to dry the transfer surfaces and the nanostructures associated with the transfer surfaces of the plurality of print heads.
• The system may further include a repair station configured to perform an inspection of the dried transfer surfaces having associated nanostructures, to determine an arrangement of nanostructures associated with a transfer surface of a print head in need of repair based on the inspection, and to repair the determined arrangement of nano structures.

Claims (21)

1. A system for transferring nanowires to a destination surface, comprising:

a body having a transfer surface;

an electrode pair on the transfer surface;

a suspension that includes a plurality of nanowires provided proximate to the electrode pair;

a signal generator coupled to the electrode pair, wherein the signal generator is configured to enable electrodes of the electrode pair to generate an electric field to associate at least one nanowire of the plurality of nanowires with the electrodes; and

an alignment mechanism configured to align the electrode pair with a region of the destination surface to enable the associated at least one nanowire to be deposited from the electrode pair to the region.

2. A system for applying nanowires to a destination surface, comprising:

a body having a transfer surface; and

an electrode pair formed on the transfer surface;

wherein the electrode pair is configured to generate an electric field to associate a proximate at least one nanowire with the electrode pair; and

wherein the electrode pair is configured to be aligned with a region of the destination surface to enable the associated at least one nanowire to be deposited from the electrode pair to the region.

3. A method for transferring electrical devices to a destination surface, comprising:

providing at least one electrical device proximate to an electrode pair;

generating an electric field with electrodes of the electrode pair to associate an electrical device with the electrodes;

aligning the electrode pair with a region of the destination surface; and

depositing the electrical device from the electrode pair to the region.

4. The method ofclaim 3, wherein the electrical device is an integrated circuit die, wherein said depositing comprises:

depositing the integrated circuit die from the electrode pair to the region.

5. The method ofclaim 3, wherein the electrical device is one of an integrated circuit, an electrical component, or an optical device, wherein said depositing comprises:

depositing the one of the integrated circuit, the electrical component, or the optical device from the electrode pair to the region.

6. The method ofclaim 3, wherein said depositing comprises:

ultrasonically vibrating the transfer surface to enable an attractive electrostatic force to attract the electrical device toward the destination surface.

7. The method ofclaim 6, wherein said ultrasonically vibrating the transfer surface comprises:

ultrasonically vibrating both the transfer surface and destination surface.

8. The method ofclaim 7, wherein said ultrasonically vibrating the transfer surface further comprises:

ultrasonically vibrating the transfer surface and destination surface synchronously.

9. A system for transferring electrical devices to a destination surface, comprising:

a body having a transfer surface;

an electrode pair on the transfer surface;

a suspension that includes a plurality of electrical devices provided proximate to the electrode pair;

a signal generator coupled to the electrode pair, wherein the signal generator is configured to enable electrodes of the electrode pair to generate an electric field to associate an electrical device of the plurality of electrical devices with the electrodes; and

an alignment mechanism configured to align the electrode pair with a region of the destination surface to enable the associated electrical device to be deposited from the electrode pair to the region.

10. The system ofclaim 9, wherein the electrical device is an integrated circuit die.

11. The system ofclaim 9, wherein the electrical device is one of an integrated circuit, an electrical component, or an optical device.

12. A system for applying electrical devices to a destination surface, comprising:

a body having a transfer surface; and

an electrode pair formed on the transfer surface;

wherein the electrode pair is configured to generate an electric field to associate a proximate electrical device with the electrode pair; and

wherein the electrode pair is configured to be aligned with a region of the destination surface to enable the associated electrical device to be deposited from the electrode pair to the region.

13. The system ofclaim 12, wherein the electrical device is an integrated circuit die.

14. The system ofclaim 12, wherein the electrical device is one of an integrated circuit, an electrical component, or an optical device.

15. A method for transferring nanowires to a destination surface, comprising:

positioning a transfer surface of a print head adjacent to a destination surface, wherein a nanowire is associated with the transfer surface;

reducing a distance between the transfer surface and the destination surface;

receiving a fluid in at least one opening in the transfer surface from between the transfer surface and the destination surface during said reducing; and

depositing the nanowire from the transfer surface to the destination surface.

16. A system for transferring nanowires to a destination surface, comprising:

a body having a transfer surface;

at least one opening in the transfer surface; and

an electrode pair formed on the transfer surface;

wherein the electrode pair is configured to generate an electric field to associate a nanowire with the electrode pair; and

wherein the at least one opening is configured to receive a fluid from between the transfer surface and the destination surface.

17. A method for transferring nanowires to a destination substrate, comprising:

associating nanostructures with transfer surfaces of a plurality of print heads;

performing an inspection of the transfer surfaces of the plurality of print heads;

selecting at least one print head of the plurality of print heads based on the inspection; and

transferring the nanostructures from the selected at least one print head to a plurality of regions of a surface of a destination substrate.

18. A method for transferring nanowires to a destination substrate, comprising:

associating nanostructures with transfer surfaces of a plurality of print heads;

drying the transfer surfaces having associated nanostructures;

performing an inspection of the dried transfer surfaces having associated nanostructures; and

transferring the nanostructures from the dried transfer surfaces to a plurality of regions of a surface of the destination substrate.

19. A system for transferring nanowires to a destination substrate, comprising:

an association station configured to receive a plurality of print heads, and to associate nanostructures with a transfer surface of each of the received plurality of print heads;

a printing station configured to receive a destination substrate and at least one of the plurality of print heads, and to transfer the nanostructures from the received at least one of the plurality of print heads to a plurality of regions of a surface of the destination substrate; and

a cleaning station configured to receive the plurality of print heads from the printing station, and to clean the received plurality of print heads.

20. A system for applying nanowires to a destination surface, comprising:

a body having a transfer surface;

a non-stick coating formed on the transfer surface; and

an electrode pair formed on the transfer surface;

wherein the electrode pair is configured to generate an electric field to associate a proximate at least one nanowire with the electrode pair; and

wherein the electrode pair is configured to be aligned with a region of the destination surface to enable the associated at least one nanowire to be deposited from the electrode pair to the region.

21. A method for transferring nanowires to a destination substrate, comprising:

associating nanostructures with transfer surfaces of a plurality of print heads;

performing an inspection of the transfer surfaces of the plurality of print heads;

determining an arrangement of nanostructures associated with a transfer surface of a print head of the plurality of print heads in need of repair;

repairing the determined arrangement of nanostructures; and

transferring the repaired arrangement of nanostructures from the transfer surface of the print head to a destination substrate.

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