Patent Application
20070007863
The present invention relates to multi-layer ultrasound transducer arrays. In particular, electrical interconnection of different electrodes of a multi-layer structure is provided.
In multi-layer ultrasound transducer arrays, a plurality of layers of transducer material is stacked together. Electrodes separate each layer of transducer material. Every other electrode is connected with the signal source and the remaining electrodes are connected with a ground potential. Providing for electrical interconnections between the different electrodes of the layers may be difficult. For example, multi-dimensional transducer arrays provide limited access to the electrodes of interior layers of interior elements.
U.S. Pat. No. 6,664,717 discloses one embodiment of a multi-layer, multi-dimensional transducer array. By forming different layers with a same or similar electrode configuration, the layers may be stacked together to provide the desired electrical interconnections. Electrical contact is made through an asperity contact.
Other approaches use vias. For example, tape cast sheets of piezoelectric material are screen printed. An electrode pattern is printed on the sheets. The sheets are then stacked. The stack is fired or sintered. Vias are then formed through the stack for electrical interconnection. However, tape casting and associated sintering have poor dimensional control. The electrode pattern may be warped or shifted to undesired locations, causing misalignment with the later formed vias.
By way of introduction, the preferred embodiments described below include elements, arrays and methods of manufacturing ultrasound transducer arrays. Vias are formed on each of a plurality of layers of transducer material prior to stacking. Using a desired electrode pattern or removal of strips, pairs of electrodes associated with each layer of transducer material are provided in coplanar arrangements on each side of the layer. The smaller of the electrode structures on a given side is routed through or connects with the vias. When the layers are stacked, the vias and coplanar arrangement are used for interconnecting the electrodes between various layers. The electrical connection is provided through asperity contact.
In a first aspect, an element is provided for use in an ultrasound transducer array. A plurality of electrodes is stacked with a plurality of layers of transducer material in asperity contact. At least one via for electrically connecting an electrode of the plurality of electrodes on a first layer of the plurality of layers extends through a second layer of the plurality of layers.
In a second aspect, a multi-dimensional ultrasound transducer array is provided. A plurality of elements in a multi-dimensional distribution each has at least two layers of transducer material. A first electrode arrangement electrically separates or is electrically separate from a second electrode arrangement. The two arrangements are provided on each of the elements and, at least in part, are coplanar on a same side of at least one of the two layers of transducer material. A via includes at least part of the first electrode arrangement.
In a third aspect, a method is provided for manufacturing a multi-dimensional ultrasound transducer array. A plurality of vias is formed on different layers of transducer material. At least one conductor is formed on each of the layers of transducer material. The layers of transducer material are stacked after forming the plurality of vias.
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.
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.
A transducer array of one or more elements has one or more discrete multi-layered piezo-ceramic elements. The array is formed by stacking drilled, metallized and patterned piezoelectric plates. The plates are aligned relative to each other and bonded together. Electrical continuity between plates is achieved by asperity contact of mating electrodes and vias, and maintained by a polymeric layer, such as epoxy adhesive, disposed between the plates. With or without an additional conductive matching layer for connection to a common ground, the stack of plates is diced in orthogonal directions to define and electrically isolate individual elements from each other. Electrical connectivity to one or both electrode arrangements may be provided on the top or bottom of the stack. Coplanar presentation of the hot and neutral electrodes is provided on the top or bottom surfaces of the stack. Different layers may be associated with different hot electrodes or arrangements, allowing the use of different receive or transmit signals for different layers.
In act 12, a plurality of vias is formed on each of at least two layers of transducer material. The transducer material includes a piezoelectric or composite piezoelectric plate. Each layer of transducer material corresponds to an entire array of elements, but may correspond to just a portion of the array. The layer 22 of transducer material is ground or otherwise formed for flatness or to a shape such that the layers 22 mate with asperity contact.
The vias are through holes extending entirely through each plate. The vias are formed by drilling, such as with a mechanical or laser drill, such as a very short wavelength laser. In one embodiment, the transducer plate 22 is formed with the vias 28 by injection molding. Alternatively, chemical etching is provided to form the vias.
The vias are formed with a spacing of about twice an element pitch.
In act 14, a conductor is formed on each of the layers of transducer material. For example, each plate of piezoelectric material is completely coated with a conductive material, such as a copper, silver, aluminum or other electrically conductive material. The coating is performed with sputtering, electro-less deposition, electroplating or other now known or later developed techniques. The coating covers the top and bottom surfaces of each plate as well as the sidewalls of the vias 28. The vias 28 have an aspect ratio of about 1:1.5, and may be easily coated with an electrode. Different aspect ratios may be provided. Alternatively, the coating fills the vias 28 with conductive material. The side edges of the layer 22 may or may not be coated. Once separated or isolated in act 16, the conductor forms two or more electrodes on the layer 22 of transducer material. Different ones of the vias 28 may be used or associated with different ones of the electrodes on given transducer layer 22.
In act 16, isolation gaps are formed. As shown in
The isolation gaps 32 leave a portion of a first electrode 30 adjacent to the via 28 and extending into and through the via 28. Another portion of a different electrode 34 covers the remaining surface area of the piezoelectric plate 22. Since the first portion 30 of one electrode is on a same surface as the other electrode 34, both electrodes 30, 34 are coplanar or provided on a same surface. As shown in
After formation of the isolation gaps 16, a plurality of separate layers 22 of transducer material have corresponding vias 28 and isolation gaps 32. Each layer 22 is separately manufactured. To avoid destruction of the layers 22, a carrier or other plate is used for supporting the layer 22, during processing and transport. After forming the isolation gap 32 in act 16, each layer 22 includes two different electrodes 34, 30. Each of the electrodes 30, 34 are exposed on both top and bottom surfaces 36, 38. The portions of each electrode 30, 34 are connected between the surfaces 36, 38 by one or more vias 28. Before or after dicing or kerfing, the electrodes 30, 34 are electrically isolated from each other.
In one embodiment, each of the layers 22 for a given transducer stack has a similar or identical structure. In alternative embodiments, one or both of the top and bottom layers 22 to be used in the transducer stack has a different arrangement of isolation gaps 32. For example, isolation gaps 32 are formed to prevent exposure of one electrode on one of the surfaces. As a result, a flexible circuit used for connecting signals to the transducer array may connect with only one electrode arrangement. For use on a top surface, a grounding plane may connect with only one of the two electrodes 30, 34 on the layer. In one embodiment, both the top and bottom layers 22 have only one pole or type of electrode 30, 34 showing, such as a ground electrode for the top surface of the top layer 22 and a signal electrode for the bottom surface of the bottom layer 22. In another embodiment, the top layer 22, the bottom layer 22 or both the top and bottom layer 22 have electrodes 30, 34 of both poles exposed on both top and bottom surfaces of the layer 22. In yet another embodiment, one or more of the layers 22 within the stack or between other layers 22 are formed to avoid interconnection of the signal electrodes between the layers 22. For example, a stack of six layers 22 has two different signal electrodes, one formed for the upper three layers 22 and another formed for the lower three layers 22. The junction between the middle two layers provides connection of grounding electrodes but not signal electrodes.
In act 18, the layers 22 formed as described above are stacked. The stacking occurs after forming the vias 28 and isolation gaps 32. The vias 28 or electrodes 30, 34 of each of the layers 22 are aligned. By aligning, the first type of electrode 30, 34 of different layers 22 is mated to the same type of electrode 30, 34 of other layers 22.
To maintain the asperity contact of the layers of transducer material, the stacked layers 22 are bonded together. With strong electrode adhesion and bonding under pressure, interlayer 22 electrical connections are formed and held or maintained with asperity contact.
In an alternative embodiment than shown in
The stacked layers 22 may also be stacked with a backing block and one or more matching layers before or after bonding. The matching layers may be conductive or non-conductive. A flexible circuit for signal connection and a ground plane connection are also stacked adjacent to a top surface, bottom surface or both top and bottom surfaces of the transducer stack.
In one embodiment, the backing block is a Z-axis conducting backing block. For example, a plurality of conductors route along the Z-axis to one or more pads or bumps provided on the top of the backing block for connecting with different ones of the elements 48. Alternatively, a flexible circuit extends to the side to route electrical signals from the various elements without the Z-axis backing. In one embodiment of the Z-axis backer, a plurality of plates of backing material has grooves formed at an element pitch. The grooves are then metallized. The metallized grooves act as the Z-axis conductors. By stacking the plates along an elevation or an azimuth dimension, the plurality of Z-axis conductors at the element pitch for the array are provided. Electrodes or bumps are then formed on the exposed ends of the Z-axis conductors for connection with flexible circuits and the elements of the transducer.
In act 20, the layers of transducer material 22 are diced.
The electrodes 30, 34 are stacked with the layers 22 of transducer material in asperity contact. The stacking is performed along a range or Z-axis. Each layer 22 of transducer material is sandwiched between two majority electrodes, such as one grounding electrode 30 and a one-signal electrode 34. Between each layer 22 of transducer material is one or more electrodes 30, 34. For example, a separate electrode 30 is formed on each of the layers 22. When stacked, the two electrodes 30 are in contact. The layers 22, such as from transducer layer 22 to an electrode 30, 34 or between pairs of electrodes 30, 34, are positioned in asperity contact. Bonding material holds the stack together, providing electrical conductivity between the layers.
One or more vias 28 electrically connect the electrodes 30, 34 of the layers 22 together. For example, the conductors 40 positioned in a via 28 connect an electrode of one layer 22 through a second layer 22. The element 48 includes two arrangements of electrodes 30, 34 where each arrangement 30, 34 includes a majority electrode between every other layer 22.
The conductors 40, 42 are positioned for the electrical interconnections in different vias 28. The vias 28 are an entire cylinder or only a portion of a cylinder, such as a quarter or less of via 28 due to dicing into the via 28 along orthogonal lines. Greater or lesser portions of an entire via 28 may be used for each conductor 40, 42 for interconnecting layers 22. Since two electrode arrangements 30, 34 are provided, two different vias 28 and associated interconnecting electrodes 40, 42 are used in each element 48. The vias 28 are on opposite sides of the element 48, such as at opposite corners. To provide or more likely assure electrical interconnection through the vias 28, at least a minority electrode is formed separated from a majority electrode by the isolation gap 32 between the layers 22 of transducer material. The majority and minority electrodes are coplanar, allowing contact for electrical conductivity through asperity contact. The top of the top layer 22 or the bottom of the bottom layer 22 or both surfaces also include majority and minority electrodes. Alternatively, the top or bottom of the stacks is associated with a single electrode arrangement 30, 34.
A plurality of the elements 48 are positioned adjacent to each other in at least one dimension or spaced apart for a sparse array. For example,
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.
