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Nanoelectronics refers to the use ofnanotechnology inelectronic components. The term covers a diverse set of devices and materials, with the common characteristic that they are so small that inter-atomic interactions andquantum mechanical properties need to be studied extensively. Some of these candidates include: hybrid molecular/semiconductor electronics, one-dimensionalnanotubes/nanowires (e.g.carbon nanotube orsilicon nanowires) or advancedmolecular electronics.
Nanoelectronic devices have critical dimensions with a size range between1 nm and100 nm.[1] RecentsiliconMOSFET (metal–oxide–semiconductor field-effect transistor, or MOS transistor) technology generations are already within this regime, including22 nanometersCMOS (complementary MOS)nodes and succeeding14 nm,10 nm and7 nmFinFET (fin field-effect transistor) generations. Nanoelectronics is sometimes considered asdisruptive technology because present candidates are significantly different from traditionaltransistors.
In 1965,Gordon Moore observed that silicon transistors were undergoing a continual process of scaling downward, an observation which was later codified asMoore's law. Since his observation, transistor minimum feature sizes have decreased from 10 micrometers to the 10 nm range as of 2019. Note that thetechnology node doesn't directly represent the minimum feature size. The field of nanoelectronics aims to enable the continued realization of this law by using new methods and materials to build electronic devices with feature sizes on thenanoscale.
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Thevolume of an object decreases as the third power of its linear dimensions, but thesurface area only decreases as its second power. This somewhat subtle and unavoidable principle has significant ramifications. For example, thepower of adrill (or any other machine) is proportional to the volume, while thefriction of the drill'sbearings andgears is proportional to their surface area. For a normal-sized drill, the power of the device is enough to handily overcome any friction. However, scaling its length down by a factor of 1000, for example, decreases its power by 10003 (a factor of a billion) while reducing the friction by only 10002 (a factor of only a million). Proportionally it has 1000 times less power per unit friction than the original drill. If the original friction-to-power ratio was, say, 1%, that implies the smaller drill will have 10 times as much friction as power; the drill is useless.
For this reason, while super-miniature electronicintegrated circuits are fully functional, the same technology cannot be used to make working mechanical devices beyond the scales where frictional forces start to exceed the available power. So even though you may see microphotographs of delicately etched silicon gears, such devices are currently little more than curiosities with limited real world applications, for example, in moving mirrors and shutters.[2] Surface tension increases in much the same way, thus magnifying the tendency for very small objects to stick together. This could possibly make any kind of"micro factory" impractical: even if robotic arms and hands could be scaled down, anything they pick up will tend to be impossible to put down. The above being said,molecular evolution has resulted in workingcilia,flagella, muscle fibers and rotary motors in aqueous environments, all on the nanoscale. These machines exploit the increased frictional forces found at the micro or nanoscale. Unlike a paddle or a propeller which depends on normal frictional forces (the frictional forces perpendicular to the surface) to achieve propulsion, cilia develop motion from the exaggerated drag or laminar forces (frictional forces parallel to the surface) present at micro and nano dimensions. To build meaningful "machines" at the nanoscale, the relevant forces need to be considered. We are faced with the development and design of intrinsically pertinent machines rather than the simple reproductions of macroscopic ones.
All scaling issues therefore need to be assessed thoroughly when evaluating nanotechnology for practical applications.
For example, electron transistors, which involve transistor operation based on a single electron.Nanoelectromechanical systems also fall under this category.Nanofabrication can be used to construct ultradense parallel arrays ofnanowires, as an alternative to synthesizingnanowires individually.[3][4] Of particular prominence in this field,silicon nanowires are being increasingly studied towards diverse applications in nanoelectronics, energy conversion and storage. SuchSiNWs can be fabricated bythermal oxidation in large quantities to yield nanowires with controllable thickness.
Besides being small and allowing more transistors to be packed into a single chip, the uniform and symmetrical structure ofnanowires and/ornanotubesallows a higherelectron mobility (faster electron movement in the material), a higherdielectric constant (faster frequency), and a symmetricalelectron/hole characteristic.[5]
Also,nanoparticles can be used asquantum dots.
Single-molecule electronic devices are extensively researched. These schemes would make heavy use ofmolecular self-assembly, designing the device components to construct a larger structure or even a complete system on their own. This can be very useful forreconfigurable computing, and may even completely replace presentFPGA technology.
Molecular electronics[6] is a technology under development brings hope for future atomic-scale electronic systems. A promising application of molecular electronics was proposed by the IBM researcher Ari Aviram and the theoretical chemistMark Ratner in their 1974 and 1988 papersMolecules for Memory, Logic and Amplification (seeunimolecular rectifier).[7][8]
Manynanowire structures have been studied as candidates for interconnecting nanoelectronic devices:nanotubes of carbon and other materials,metal atom chaines,cumulene orpolyyne carbon atom chains,[9] and many polymers such aspolythiophenes.
Nanoionics studies the transport of ions rather than electrons in nanoscale systems.
Nanophotonics studies the behavior of light on the nanoscale, and has the goal of developing devices that take advantage of this behavior.
Current high-technology production processes are based on traditional top down strategies, where nanotechnology has already been introduced silently. The critical length scale ofintegrated circuits is already at the nanoscale (50 nm and below) regarding the gate length of transistors inCPUs orDRAM devices.
Nanoelectronics holds the promise of makingcomputer processors more powerful than are possible with conventionalsemiconductor fabrication techniques. A number of approaches are currently being researched, including new forms ofnanolithography, as well as the use ofnanomaterials such asnanowires orsmall molecules in place of traditionalCMOS components.Field-effect transistors have been made using both semiconductingcarbon nanotubes[10] and with heterostructured semiconductornanowires (SiNWs).[11]
Electronic memory designs in the past have largely relied on the formation of transistors. However, research intocrossbar switch based electronics have offered an alternative using reconfigurable interconnections between vertical and horizontal wiring arrays to create ultra high density memories. Two leaders in this area areNantero which has developed a carbon nanotube based crossbar memory calledNano-RAM andHewlett-Packard which has proposed the use ofmemristor material as a future replacement of Flash memory.[citation needed]
An example of such novel devices is based onspintronics. The dependence of the resistance of a material (due to the spin of the electrons) on an external field is calledmagnetoresistance. This effect can be significantly amplified (GMR - Giant Magneto-Resistance) for nanosized objects, for example when two ferromagnetic layers are separated by a nonmagnetic layer, which is several nanometers thick (e.g. Co-Cu-Co). The GMR effect has led to a strong increase in the data storage density of hard disks and made the gigabyte range possible. The so-called tunneling magnetoresistance (TMR) is very similar to GMR and based on the spin dependent tunneling of electrons through adjacent ferromagnetic layers. Both GMR and TMR effects can be used to create a non-volatile main memory for computers, such as the so-called magnetic random access memory orMRAM.[citation needed]
In the modern communication technology traditional analog electrical devices are increasingly replaced by optical oroptoelectronic devices due to their enormous bandwidth and capacity, respectively. Two promising examples arephotonic crystals andquantum dots.[citation needed] Photonic crystals are materials with a periodic variation in the refractive index with a lattice constant that is half the wavelength of the light used. They offer a selectable band gap for the propagation of a certain wavelength, thus they resemble a semiconductor, but for light orphotons instead ofelectrons. Quantum dots are nanoscaled objects, which can be used, among many other things, for the construction of lasers. The advantage of a quantum dot laser over the traditional semiconductor laser is that their emitted wavelength depends on the diameter of the dot. Quantum dot lasers are cheaper and offer a higher beam quality than conventional laser diodes.
The production of displays with low energy consumption might be accomplished usingcarbon nanotubes (CNT) and/orsilicon nanowires. Such nanostructures are electrically conductive and due to their small diameter of several nanometers, they can be used as field emitters with extremely high efficiency forfield-emission displays (FED). The principle of operation resembles that of thecathode-ray tube, but on a much smaller length scale.[citation needed]
Entirely new approaches for computing exploit the laws of quantum mechanics for novel quantum computers, which enable the use of fast quantum algorithms. The Quantum computer has quantum bit memory space termed "Qubit" for several computations at the same time. In nanoelectronic devices, the qubit is encoded by the quantum state of one or more electrons spin. The spin are confined by either a semiconductor quantum dot or a dopant.[12]
Nanoradios have been developed structured aroundcarbon nanotubes.[13]
Research is ongoing to usenanowires and other nanostructured materials with the hope to create cheaper and more efficientsolar cells than are possible with conventional planar silicon solar cells.[14] It is believed that the invention of more efficient solar energy would have a great effect on satisfying global energy needs.
There is also research into energy production for devices that would operatein vivo, called bio-nano generators. A bio-nano generator is ananoscaleelectrochemical device, like afuel cell orgalvanic cell, but drawing power fromblood glucose in a living body, much the same as how the body generatesenergy fromfood. To achieve the effect, anenzyme is used that is capable of stripping glucose of itselectrons, freeing them for use in electrical devices. The average person's body could, theoretically, generate 100watts ofelectricity (about 2000 food calories per day) using a bio-nano generator.[15] However, this estimate is only true if all food was converted to electricity, and the human body needs some energy consistently, so possible power generated is likely much lower. The electricity generated by such a device could power devices embedded in the body (such aspacemakers), or sugar-fednanorobots. Much of the research done on bio-nano generators is still experimental, withPanasonic's Nanotechnology Research Laboratory among those at the forefront.
There is great interest in constructing nanoelectronic devices[16][17][18] that could detect the concentrations ofbiomolecules in real time for use as medical diagnostics,[19] thus falling into the category ofnanomedicine.[20]A parallel line of research seeks to create nanoelectronic devices which could interact with singlecells for use in basic biological research.[21]These devices are callednanosensors. Such miniaturization on nanoelectronics towards in vivo proteomic sensing should enable new approaches for health monitoring, surveillance, and defense technology.[22][23][24]
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