US20080189933A1 - Photoetched Ultrasound Transducer Components - Google Patents

Abstract

A photoetchable glass ceramic is used to form a three dimensional structure for a transducer component. This photostructurable material allows generation of various shapes or structures. For example, a matching layer is formed, in part, using photoetchable glass ceramics with an anechoic-shaped gradient structure. The gradient structures are then filled with materials having desired impedance properties. By allowing generation of desired structures within the matching layer, a desired acoustic impedance property may be provided. As another example, a hollow column is photo etched and used for providing air backing in a backing layer. As yet another example, a transducer layer is formed within a framework of photostructurable material. A plurality of holes with associated shelves is provided for pick-and-place locating of transducer elements within an array. The photostructurable material assists in manufacturing.

Description

RELATED APPLICATIONS
• The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 60/559,134, filed Apr. 1, 2004, which is hereby incorporated by reference.
BACKGROUND
• The present invention relates to ultrasound transducers. In particular, three dimensional structures are formed for components in an ultrasound transducer.
• Medical diagnostic ultrasound transducers include a stack of layers. For example, a transducer layer is sandwiched between one or more matching layers and a backing layer. The transducer stack is relatively small, such as supporting an array of elements with a sub-millimeter pitch and thickness. Due to the small size of the transducer, the complexity of structures useable within a transducer stack is limited. For example, various matching layer structures for graduated or desired acoustical impedance have been proposed but are costly or difficult to manufacture.
BRIEF SUMMARY
• By way of introduction, the preferred embodiments described below include improvements to ultrasound transducers and methods for manufacturing ultrasound transducers. A photoetchable glass ceramic is used to form a three dimensional structure for a transducer component. This photostructurable material allows generation of various shapes or structures. For example, a matching layer is formed, in part, using photoetchable glass ceramics with an anechoic-shaped gradient structure. The gradient structures are then filled with materials having desired impedance properties. By allowing generation of desired structures within the matching layer, a desired acoustic impedance property may be provided. As another example, a hollow column is photo etched and used for providing air backing in a backing layer. As yet another example, a transducer layer is formed within a framework of photostructurable material. A plurality of holes with associated shelves is provided for pick-and-place location of transducer elements within an array. The photostructurable material assists in manufacturing.
• In a first aspect, an improvement is provided for an ultrasound transducer with a matching layer, transducer layer and backing layer. The improvement includes using a photoetchable glass ceramic component within the ultrasound transducer.
• In a second aspect, a method is provided for manufacturing an ultrasound transducer. A component of the ultrasound transducer is microfabricated from a photoetchable glass ceramic. The component is stacked in a transducer stack.
• In a third aspect, an ultrasound transducer is provided with a three dimensional structure. A transducer layer is positioned adjacent to a matching layer. A backing layer is positioned adjacent to the transducer layer. At least one of the matching layer, transducer layer and backing layer includes the three dimensional structure formed in a photostructurable material.
• The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
• The components and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.
• FIG. 1 is a side view of one embodiment of a transducer stack;
• FIG. 2 is a partial cut-away view of a matching layer in one embodiment;
• FIG. 3 shows processing steps for forming a transducer layer using photostructurable material in one embodiment;
• FIG. 4 is a perspective view of one embodiment of a backing layer formed from photostructurable material; and
• FIG. 5 shows one embodiment of a method for manufacturing an ultrasound transducer.
DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS
• A photoetchable glass-ceramic, such as Shott Foturan®, is used to create 3-D structure for components of an ultrasound transducer. Matching or backing layers for specialized transducer applications are created. Example applications include very low density and low impedance matching layers, backing materials with uniaxial electrical conductors in the Z direction, and structures for configuring graded-impedance matching layers.
• FIG. 1 shows one embodiment of anultrasound transducer10. Theultrasound transducer10 is used for medical diagnostic imaging. For example, theultrasound transducer10 is a one or two dimensional array of elements for phased array imaging. Theultrasound transducer10 includes a plurality of layers, such as amatching layer12,transducer layer14 andbacking layer16. Additional, different or fewer layers may be provided. For example, two or threematching layers12 are provided. As another example, a grounding plane, electrode layer or a flex circuit or other signal conductor layers are provided within the stack of theultrasound transducer10.
• Thelayers12,14,16 are any now known or later developed structure or material. Theultrasound transducer10 includes at least one component of photoetchable glass ceramic. Photoetchable glass ceramics include lithium aluminosilicate glass-ceramic. Other photostructurable materials may be provided. In one embodiment, Foturan® from Shott is provided. Photostructurable material allows writing or forming of a boundary on or under a surface of the material. An ultraviolet or other laser is focused to areas or volumes of desired removal to form a three dimensional boundary. A chemical etch is then used to remove or allow separation of material to expose the boundary. Such photostructurable materials may provide for large aspect ratios, square profiles, moving parts, or other three dimensional structures with a desired profile. For example, structures formed with a more complex surface, such as a tapered surface, than can be generated with a drill or dicing saw may be provided. Since the laser may be focused within the photostructurable material, the formed surface or structure has a three dimensional configuration as opposed to a simple two dimensional configuration.
• The matchinglayer12 is a solid material or a composite material. As a composite, a photoetchable glass ceramic component is filled with or mated to other material. Cast filler of silicone, epoxy, or other material with the desired acoustical impedance is used. Filler material otherwise unsuitable for bonding or dicing, yet yielding lower impedance, may be provided since the photoetchable glass ceramic provides structure of thematching layer12.
• The photoetchable glass ceramic is used to form any of various desired three dimensional structures within thematching layer12.FIG. 2 shows four differentpossible structures20. Tapered divots, tapered holes, tapered grooves, combinations thereof or other three dimensional structures may be provided. In one embodiment, a same threedimensional structure20 is provided throughout thematching layer12. In alternative embodiments,different structures20 are provided within thesame matching layer12. The tapering may be a linear or non-linear taper. Any now known or later developed three dimensional structure within thematching layer12 for filling or maintaining free of filler to provide a desired acoustic impedance matching layer characteristic may be used.
• Thematching layer12 has a desired acoustic impedance or a desired variation in acoustic impedance from one surface to another surface. Holes through theentire matching layer12 or within thematching layer12 may provide desired acoustic impedance properties. Divots extending partially into but not through thematching layer12 may also provide desired acoustic impedance properties. Anechoic-shaped gradient structures may more likely avoid acoustic reflections by more gradually matching acoustic impedance of the transducer to a skin or patient surface.
• FIG. 2 shows thematching layer12 formed out of a structure of photoetchable class ceramic. In alternative embodiments, the photoetchable glass ceramic is used to form a mold. The filler or other casting material is then molded for forming the actual matching layer. Mated molds may be provided for forming different portions of thematching layer12 for combination together for asingle matching layer12. The use of the photostructurable material may minimize or avoid multiple dicing, filling and plating steps.
• Thematching layer12 is electrically conductive or an electrical insulator. Where electrical signals, such as a ground or transmit and receive signals, are to be passed through thematching layer12, electrically conductive plating or filler may be provided in through-holes or threedimensional structures20 passing through theentire matching layer12. Alternatively, the threedimensional structures20 used for tailoring the acoustic impedance are plated prior to filling for providing uniaxial electrical conductivity from the top to the bottom of thematching layer12. Non conductive fillers may be used.
• Alternatively or additionally, the photostructurable material is used as part of thetransducer layer14. For example, the photoetchable glass ceramic is used as a frame for holding a plurality of elements.FIG. 3 shows one embodiment of photoetchable glassceramic block30 being used as a frame for a multi-dimensional array of elements. Thephotoetchable glass ceramic30 is of any desired dimension, such as ½ a millimeter to 10 millimeters thickness with a width and length dimension associated with the desired array and array shape. A plurality ofholes32 is formed within theblock30 of photoetchable glass ceramic. Theholes32 are square, hexagonal, round, triangular or other shape. Hexagonal shaping may minimize generation of grating lobes. Each of theholes32 is sized and shaped for insertion of a piezoelectric or other transducer element.
• The photoetchable glass ceramic is metalized or plated with ametal layer34. For example, electrolysis, evaporation, sputtering or another technique is used to provide gold or other material in a desired pattern within theholes32 or on other surfaces of theblock30. For example, one or more electrically isolated conductors are formed within each of theholes32 for routing signals to the top or bottom of theholes32. Etching, grinding, masking or other techniques may be used to remove or prevent any undesired metallization.
• Individual elements are picked and placed within theholes32. Alternatively, a slab or linear extent of elements are picked and placed within grooves formed within the photoetchable glassceramic block30. Dicing then separates the elements along an additional dimensional. For a multi-dimensional transducer array, the elements are single or multi-layer PZT elements. For example, elements with three to five layers of PZT are pre-formed with inter-connected electrodes. The elements may include matching layers or matching layers may be formed after placement of the elements within thephotostructurable material block30.
• When theholes32 are formed, shelves are formed in each of theholes32. The shelf may be a bump, protrusion, narrowing of thehole32 or other structures for mechanically supporting the elements within theholes32. Photoetching allows formation of three dimensional shapes, allowing the shelves for maintaining position of the elements. Metalized plating34 extends upward from the shelves for connecting a bottom electrode to a top surface or downward from the shelves for connecting bottom electrode, top electrode or both bottom and top electrodes to a back surface of thephotostructurable material block30. Metalizing thus provides for a Z-axis or uniaxially conductive routing of signal or ground traces.
• To maintain elements within theholes32, a cast backer may be formed on a top or bottom of theholes32 after the elements are positioned. For example, a non-conductive silicone is provided. Alternatively, electrically conductive filler is provided. In yet other alternative embodiments, the filler is positioned within theholes32 prior to placement of the elements. Theexcess filler36 is then ground or otherwise removed to isolate the elements in each of the associated holes32. Where conductive matching layers are provided, the elements may be positioned within theholes32 to extend above thephotostructurable material block30, and grinding may be avoided. Thefiller36 is controlled such that the filler does not extend above the electrically conductive matching layers.
• Any additional matching layers, grounding electrodes orother materials38 are formed on each of the elements within theholes32 or across the entire frame provided by thephotostructurable material30.
• In yet another alternative or additional embodiment, the photoetchable glass ceramic is used for the backing layer16 (seeFIGS. 1 and 4). For example, the frame provided by thephotostructurable material block30 ofFIG. 3 has sufficient height that a portion of theholes32 beneath the shelves serves as an air backing. Any metallization within theholes32 is routed through the air backing for Z-axis or uniaxial conductivity within the backing. Flip chip technology using bump or polymer bump bonding or other circuit connection is then provided on the bottom on thephotostructurable material block30 and associated air backing for routing signals to and from the elements. In one embodiment, the circuit board for bump bonding to the back of thephotostructurable block30 acting as Z-axis backing block routes the signals laterally away from the array. A multiple level board is provided for a staggered exposure of different conductors routed to different elements. The staggered exposure, such as providing 3, 4 or 5 or more levels in the same board, more efficiently routes the many traces for a two dimensional array. Alternatively, flexible circuits or other materials on the top or bottom of thephotostructurable material block30 route signals to or from the elements. Alternatively, signal traces are formed within or onbacking layer16. Using photostructurable material, different routes or tunnels may be provided for metallizing within thebacking layer16. Electrical traces may be provided for Z-axis backing or other electrical routing to the side surfaces of thebacking layer16 for a more spread exposure of different signal lines.
• FIG. 4 shows an additional oralternative backing layer16 formed from photoetchable glass ceramic. A hollow column is formed from a single or plurality of pieces of photoetchable glass ceramic. The hollow portion is sized or shaped to provide air backing or other backing for a portion or the entire array of elements. Atransducer layer14 is positioned over the hollow column of thebacking layer16. In one embodiment, the hollow column is filled with additional acoustic absorbing material other than air. Further structures for absorbing acoustic energy may be provided within the backing layer, such as pyramidal shapes formed on the surface within the hollow portion of thebacking layer16. Other sound reflecting, deflecting or absorbing structures may be formed.
• FIG. 5 shows one embodiment of a method for manufacturing an ultrasound transducer using photoetchable glass ceramic. The method is performed to form the same or different structures than described inFIGS. 1 through 4. Any of the matching layer, transducer layer or backing layer is formed from the photoetchable glass ceramic.
• Inact50, a component of the ultrasound transducer is manufactured from a photoetchable glass ceramic. The photoetchable glass ceramic is used as a mold to form a component or is used as an actual piece of the component. The microfabrication is performed by transmitting ultraviolet light or other light to change a crystal structure of the photoetchable glass ceramic in a three dimensional volume within or on the photostructurable material. The photostructurable material is then exposed to a chemical etch. The altered crystalline structure is weakened or removed by the chemical etch. As a result, the structure with the desired three dimensional shape is formed by material removal.
• Inact52, various layers of the transducer are stacked. One or more of the layers includes at least one component formed from the photoetchable glass ceramic. For example, one or more of the layers includes a photoetchable glass ceramic. As another example, one or more of the layers includes a structure molded from a mold made of photoetchable glass ceramic. The stacked ultrasound transducer is used for generating and receiving acoustic energy. Medical diagnostic imaging is performed using an array formed from the transducer stack. The transducer stack may be used in other types of sonography.
• While the invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.

Claims (7)

1-10. (canceled)

11. A method for manufacturing an ultrasound transducer, the method comprising:

microfabricating a component of the ultrasound transducer from a photoetchable glass ceramic; and

stacking the component in a transducer stack.

12. The method ofclaim 11 wherein microfabricating comprises:

forming an anechoic-shaped gradient structure; and

filling the anechoic-shaped gradient structure;

wherein the component comprises a matching layer.

13. The method ofclaim 11 wherein microfabricating comprises forming a tapered hole, a tapered divot, a tapered groove or combinations thereof in the photoetchable glass ceramic, wherein the component comprises a matching layer.

14. The method ofclaim 11 wherein microfabricating comprises forming a plurality of holes each with a shelf; and further comprising:

positioning transducer elements within the component, the shelves operable to support the transducer elements;

wherein the component comprises a frame for a transducer layer.

15. The method ofclaim 11 wherein microfabricating comprises forming a hollow column and wherein the component comprises a backing layer for air backed elements.

16-20. (canceled)

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