Abstract:
A double-sided flexible circuit is used to provide interconnection to a piezoelectric ultrasonic transducer array. The ultrasonic crystal is covered with first and second electrode layers having an insulation gap provided therebetween. The flexible circuit material is then bonded to the first and second electrode layers so that one side of the double sided flexible circuit makes contact to one set of transducer electrodes and the other side of the flexible circuit makes contact to the second set of transducer electrodes. The ultrasonic transducer desirably includes a concave acoustic lens having an acoustic velocity greater than water.

Description:
This application claims benefit to U.S. provisional application Ser. No. 60/142,059, filed Jul. 2, 1999. 
    
    
     FIELD OF INVENTION 
     The present application is generally directed to the field of linear or curvilinear ultrasonic transducers, particularly those used in medical imaging. 
     BACKGROUND OF THE INVENTION 
     Ultrasonic imaging has been utilized for a number of years in the medical field. Linear and curvilinear ultrasonic transducers are used to produce visual images of features within a patient&#39;s body. Such ultrasonic imaging transducers are also used in other fields. However, medical imaging is perhaps the best known use of such transducers. 
     Typically, an ultrasonic transducer for producing visual images of features inside the body includes an array of ultrasonic elements which may be driven by a desired excitation and/or receive ultrasonic reflections obtained from various features of interest. 
     As technology progresses, there has been an increasing need to produce ultrasonic images having enhanced resolution. There is also, of course, a desire to produce ultrasonic transducers producing not only better images, but exhibiting greater reliability and ease of manufacture. 
     In a typical ultrasonic transducer array, a piezoelectric crystal is driven by a voltage applied across first and second piezoelectric electrodes. Such an ultrasonic transducer is generally formed of a piezoelectric crystal that is provided with first and second piezoelectric electrodes to form a electrode crystal assembly. This electrode crystal assembly is then fastened to a backing, and the piezoelectric crystal with its associated piezoelectric electrodes is then cut transversely into individual electrode elements extending along a longitudinal direction. 
     One of the limiting factors in manufacturing such piezoelectric ultrasonic transducers is that, as transducer elements size decreases, the difficulty in affixing contact wiring to the transducer increases. Such contact wiring is needed to connect the acoustic transducer with its associated drive or sensing circuitry. 
     SUMMARY OF THE INVENTION 
     According to the teachings of the present application, a double sided flexible circuit, flex circuit or connector is used to contact both of the electrodes used to drive or sense a vibration within the piezoelectric crystal. According to the teachings of the present application, the first and second piezoelectric electrodes are connected to the flexible double sided circuit or connector either by soldering the flexible double sided connector to the piezoelectric electrodes or alternatively through the use of anisotropic conductive adhesive. When the flexible double sided connector is bonded to the piezoelectric electrodes, a fillet in the bonding material is used to strengthen the connection. In the case of a soldering method, this fillet would of course be a solder. However, this fillet could additionally be formed of a conductive epoxy by screen printing or another process. Anisotropic conductive adhesive may also be used to connect the flexible connector to the transducer. 
     In one preferred embodiment, one of the first and second connector conductors is a common conductor commonly connected to all of either the first and second piezoelectric electrodes. The second connector conductor is, in this case, however, constructed of a plurality of individual conductors each connected to an individual piezoelectric transducer element. In an alternative embodiment, individual grounds are used and accessed to individually drive or sense from each of the piezoelectric transducer elements. Thus, both sides of the flexible double sided connector contains individual electrodes for connecting to each of the piezoelectric elements. 
     In yet another embodiment, piezoelectric transducer element density can be increased by utilizing two flexible double sided connectors, connecting to the piezoelectric electrodes of the piezoelectric crystal from two sides. This enables each connector conductor of the double sided flexible connector to access only every other piezoelectric transducer element, thereby increasing the spacing or pitch of the conductive wirings provided on the flexible double sided connector to enable the pitch of the individual conductors on each flexible double sided connector to be reduced. Thus, the relative spacing of each connector wire as compared to its transducer element is increased. This can be done in two ways. Registration can be maintained between the first and second conductive contacts so that the two contacts of a single piezoelectric element are addressed from a single flexible circuit or double sided connector. Alternatively, it may be desirable to offset the first and second sides from each other in a single flexible double sided connector, so that each circuit element is contacted using a first flexible double sided connector and the second terminal is contacted using a second flexible double sided connector. 
     Through the use of individual grounds in accordance with the teachings of the present application, alternative piezoelectric elements may desirably have their grounds on opposite planes of the piezoelectric crystal. This may serve to reduce noise, for example, depending upon the driving system employed. 
     There are several other features of the present application which result in improved transducer. A concave lens having a transmission velocity substantially greater than water may be used to focus the transducer, particularly in the transverse direction. This lens is constructed in the preferred embodiment of an epoxy having a transmission velocity of greater than 1700 m/sec. In contrast, water has a transmission velocity of about 1500 m/sec. A shielding layer is desirably deposited outside of the piezoelectric crystal, associated matching layers, and acoustic lens. This shielding layer reduces electromagnetic interference as well as electrically shielding the patient from the sensor. By properly sizing the thickness of the shielding layer, the shield may attenuate electromagnetic radiation interference without substantially attenuating ultrasonic signal sensitivity. Desirably, this shield layer is vapor deposited to provide 100% coverage of the top surface and side walls of the transducer. The transducer of the present application further includes distended portions of the acoustical element, shielding layer and protective cover which extend over the side walls of the piezoelectric crystal and matching layers to protect the seams there between, including the adhesive binding the piezoelectric crystal to the backing and matching layer. 
     It should be apparent that the above features and advantages of the present invention filed from the preferred embodiments set forth here and below, as may be understood from the following description and accompanied drawings which illustrate exemplary embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section of an exemplary transducer produced according to the teachings of the present invention. 
     FIG. 1A is a schematic illustration of a linear ultrasonic transducer used to explain the nomenclature used in such devices. 
     FIG. 1B is an alternative construction of the piezoelectric crystal  12  and piezoelectric electrode  18 ,  20  otherwise usable in the embodiment of FIG.  1 . 
     FIG. 2 is an enlargement of a portion of the FIG. 1 illustration, better illustrating the connection of the flexible double sided connector to the piezoelectric crystal in accordance with the teachings of the present application. 
     FIG. 3 is a partial plan view of the underside of the piezoelectric crystal  12  and piezoelectric electrodes  18 ,  20 , illustrating one example of the connection of the flexible double sided connector thereto. 
     FIG. 4 is an alternative embodiment showing another example of the connection of the flexible double sided connector to the piezoelectric crystal and its associated piezoelectric crystal elements. 
     FIG. 5 is still another embodiment of the connection of the flexible double sided connector  22  to the piezoelectric crystal and its associated elements. In this embodiment, two double sided flexible connectors are utilized so that the pitch or separation between the wirings of adjacent connectors can be increased. 
     FIG. 6 is a schematic illustration of a plurality of piezoelectric crystal transducer elements connected to plural wires of the first connector conductor, further illustrating the voltage pluralities supplied to the first and second piezoelectric electrodes of each piezoelectric crystal transducer element. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1A is a schematic illustration of a linear ultrasonic transducer including plural ultrasonic transducer elements  10   a-k . This figure is primarily provided in the specification of the present application in order to define the terms longitudinal and transverse as used throughout the specification of the present applications. The term longitudinal is used to describe the direction along the length of the linear or curvilinear ultrasonic transducer  10  while the transverse direction is orthogonal thereto. While this figure illustrates a linear ultrasonic transducer, the transducer, within the contemplation of the present application, may curve in either the transverse or longitudinal direction to produce a curvilinear array. 
     Referring now to FIG. 1 of the present application, a piezoelectric crystal  12  is coated with a suitable conductor, for example copper, to produce a conductive coating  14 . This conductive coating  14  is formed into first and second piezoelectric electrodes  18 ,  20  in order to produce a piezoelectric crystal  12  sandwiched by first and second piezoelectric electrodes  18 ,  20 . Insulative gaps  16  are provided to divide the conductive coating  14  into the first and second piezoelectric electrodes  18 ,  20 . Insulative gaps  16 ,  17  may be formed by any suitable process including dicing or etching. 
     In the embodiment of FIG. 1, the first and second piezoelectric electrodes  18 ,  20  are formed by completely coating the four sides of the piezoelectric crystal  12  with conductive material separated only at the ends in the longitudinal direction and divided by first and second insulation gaps  16 ,  17  by any substitute process. As an alternative, referencing FIG. 1B, only a single insulative gap  16  may be used, the first and second electrodes being otherwise separated by omitting a conductive coating from one side  19  to produce an insulative gap. 
     According to the teachings of the present application, a flexible double sided circuit or connector  22  is used to connect the piezoelectric transducer elements  10   a-k  to suitable drive or sensing circuitry as would occur to one of ordinary skill in the art. As may be better seen in FIGS. 3-5, the piezoelectric crystal  12  and its conductive coating  14  are typically diced to formed dicing gaps  15  which in turn produce the plural ultrasonic transducers elements  10   a-k  extending along the longitudinal axis of the transducer  10 . This technique is generally well known in the art and is normally performed after the conductively coated piezoelectric crystal  12  is bonded to a backing  30  by a suitable adhesive  31  or alternating to a matching layer  32 ,  33 . 
     In accordance with the teachings of the present application, prior to the bonding of the conductively coated piezoelectric crystal to the backing, a flexible double sided connector  22  is affixed to the piezoelectric crystal  12  and its associated electrodes  18 ,  20  as will be described below. After this bonding step is completed, a suitable adhesive  31  is used to bond the conductively coated piezoelectric crystal  12  to the backing  30 . 
     The structure of the transducer of the present application further includes an inner matching layer  32  and outer matching layer  33 . A acoustical focusing element  34  is further provided, the acoustical focusing element  34  including lamination protecting portions  34 P extending around the periphery of the inner and outer matching layer  32 , the conductively coated piezoelectric crystal  12 , and all or part of the backing layer  30 . In this way, the lamination protecting portion  34 P of the acoustical focusing element  34  provides mechanical and moisture protection to the transducer structure to prevent layer separation. 
     The acoustical focusing element  34  of the present application is a concave lens having a acoustical velocity greater than that of water. In the preferred embodiment, the acoustical focusing element  34  is a concave lens formed of an epoxy or urethane having a transmission velocity of greater than 1700 m/sec and preferably about 2000 m/sec. This is compared to a typical acoustical transmission velocity of 1500 m/sec for water. Since the acoustical transmission velocity of the concave lens is greater than that of water, the concave lens will have the effect of focusing the acoustical energy to a focal point defined by the concave lens curvature. 
     According to the teachings of the present application, a shielding layer  36  is provided by vapor deposition of a suitable metallic electromagnetic shield on the top surface side walls and end walls of the transducer array. This shielding layer  36  improves sensing accuracy by reducing the transducers sensitivity to electro-magnetic interference and further isolates the patient from the transducer array. The shielding layer  36  also provides an effective moisture barrier to prevent delamination or other moistures related damage to the transducer layer structure. 
     A protective cover  38  is further laminated over the shielding layer  36 . The protective cover  38  also covers the layering of the transducer, providing further moisture and mechanical protection thereto. 
     The specific details of the flexible double sided connector used in accordance with the teachings of the present application are better illustrated with reference to FIG. 2 which is a magnified partial view of the structure of FIG.  1 . The flexible double sided connector or circuit  22  is preferably formed of a flexible non-conductive substrate  24 , in the preferred embodiment a polyimide film such as that marketed under the trademark Kapton by E. I. Dupont Co., or an equivalent film. Suitable first and second connector conductors  26 ,  28  are provided on opposed sides of the flexible insulated substrate  24 . In the preferred embodiment, a suitable wiring pattern, as described in further detail with reference to the remainder of the specification, is provided on one or both sides of this flexible double sided connector. 
     Prior to fastening the flexible double sided connector  22  to the conductively coated piezoelectric crystal  12 , the end of the flexible double sided connector  22  is prepared for affixing through stepping the respective first connector conductor  26 , flexible insulated substrate  24 , and second connector conductor  28  so that a portion of each of these layers is presented on a single side of the flexible double sided connector  22 . As can be seen from FIG. 2, a portion of the second connector conductor  28  extends beyond both the first connector conductor  26  and the flexible insulative substrate  24  to form an exposed second contact  28 E. In similar fashion, the flexible insulative substrate  24  along with the second connector conductor  28  extend beyond the first connector conductor  26  to form an exposed gap insulating portion  241 . Naturally, a portion of the first connector conductor  26  remains exposed and forms an exposed first contact  26 E. 
     The flexible double sided connector  22  is then conductively affixed to the first and second piezoelectric electrodes  18 ,  20  by any suitable conductive bonding material. This is accomplished by aligning the exposed gap insulating portion  241  with one of the insulative gaps  16 . The exposed first contact  26 E is then bonded to the first piezoelectric electrode  18  with a first conductive contact bond  40  while the exposed second contact  28 E is bonded to the second piezoelectric electrode  20  with a second conductive contact bond  41 . 
     In accordance with one preferred embodiment of the present application, the first and second conductive contact bonds  40 , 41  are accomplished by use of a metallic solder. However, according to an alternative embodiment of the present applications, an anisotropic conductive adhesive can be used to produce the first and second conductive contact bonds  40 ,  41 . It should be noted that the first conductive contact bond  40  preferably includes a connection strengthening fillet  42  which, in a solder construction extends up at least a major portion of the side wall of the conductively coated piezoelectric crystal  12 . This fillet provides a strengthening to the connection between the flexible double sided connector  22  and the conductive coating  14 . 
     The flexible double sided connector  22  is normally fastened to the conductively coated piezoelectric crystal prior to assembly of the remainder of the device. The piezoelectric crystal is then attached to the backing  30  by a suitable adhesive  31  and the remainder of the transducer is formed as would occur to one of ordinary skill in the art. Of course, the formation of the linear ultrasonic transducer requires the construction of plural ultrasonic transducer elements  10   a-k  as shown in FIG.  1 . Typically this is produced by dicing the piezoelectric crystal after mounting to the backing. Thus, individual electrodes formed as part of the first or second connector conductors are aligned to connect to specific ultrasonic transducer elements  10   a-k . Dicing is normally performed after the flexible double-sided connector  22  is attached. Thus, the end of the double sided flexible connector  22  is normally also diced. 
     The use of a flexible double-sided connector  22  allows considerable flexibility in the manner in which connections to the linear ultrasonic transducer  10  are arranged. FIG. 3 illustrates a first example of connection to the individual ultrasonic transducer elements  10   a - 10   d  through the use of a flexible double-sided connector  22 . FIG. 3, as well as FIGS. 4 and 5, illustrate the underside of the conductively coated piezoelectric crystal and the manner in which the flexible double-sided connector  22  and its individual conductors are affixed thereto. 
     In the example of FIG. 3, the first connector conductor  26  is commonly connected to all of the ultrasonic transducer elements  10   a-d  as a first common or ground conductor  26 C which is, in turn, connected to each of the first transducer element electrodes  18   a-d . Thus, in this embodiment, the first transducer element electrodes  18   a-d  are commonly connected. The second connector conductor  28  then uses individual second individual connector conductors  28   a-d  to connect to the second transducer electrode elements  20   a-d . Note that the insulative gap  16  is bridged by a exposed insulating portion  241  of the flexible insulative substrate  24 . In this manner, individual second transducer electrode elements  20   a-d  are individually accessed while the first transducer element electrodes  18   a-d  are commonly connected. Of course, this arrangement could be reversed, in accordance with the teachings of the present application, and individual first transducer element electrodes  28   a-d  could be used to access the first transducer element electrodes  18   a-d  while a common ground conductor could be used to collectively contact the second transducer element electrodes  20   a-d.    
     Note that the FIG. 3 embodiment contemplates that the flexible double-sided connector  22  will access the ultrasonic transducer from its edge, enabling the generation of a connection strengthening fillet  42 . However, it is also possible for the flexible double-sided connector  22  to approach the gap  16  from the other direction, from the direction of the center of the transducer array, within the teachings of the present application. 
     FIG. 4 illustrates an alternative embodiment where both the first and second individual connector conductors  26   a-d  and  28   a-d  each individually contact individual first and second transducer element electrodes  18   a-d ,  20   a-d . Thus, in the embodiment of FIG. 4 no common electrode is used for certain advantageous reasons. Otherwise, the embodiment of FIG. 4 is substantially identical to the embodiment of FIG.  3 . 
     FIG. 5 illustrates another alternative embodiment of the transducer connection of the present application. In FIG. 5, first and second flexible double sided connectors  22   a ,  22   b  are collectively used to access the individual ultrasonic transducer elements  20   a-e . As the size of individual ultrasonic transducer elements decreases, the size of the individual connector conductors  26   a-k ,  28   a-k  creates increasing problems, not only due to shrinkage of the connector lithography, but also due to registration problems. These problems can be greatly reduced by only connecting to every other ultrasonic transducer element using a single flexible double sided conductor  22   a  or  22   b . Thus, in the embodiment of FIG. 5, the first connector conductor  26  of the first double sided conductor  22   a  connects only to odd first individual connector conductors  26   a ,  26   c ,  26   e , while the second connector conductor  28  of the first double sided conductor  26   a  connects to only even first individual connector conductors  26   b ,  26   d . Similarly, the first connector conductor  26  of the second double sided conductor  22   b  connects only to even first individual connector conductors  26   b ,  26   d , while the second connector conductor  28  of the second double sided conductor  22   b  connects to only odd first individual connector conductors  26   a ,  26   c ,  26   e.    
     In a two double sided conductor embodiment, there are two principal alternatives. In the embodiment shown in FIG. 5, the second connector conductor connects to different ultrasonic transducer elements than are connected to by the first connector conductor  26 . Thus, whereas the first connector conductor  26  of the first flexible double sided conductor  26   a  connects to odd ultrasonic transducer elements  10   a ,  10   c ,  10   e , the second connector conductor in the embodiment of FIG. 5 connects to even ultrasonic transducer elements  10   b ,  10   d . The same is true of the second flexible double sided connector  22   b  in which the second connector conductor  28  connects to odd second individual connector conductors  28   a ,  28   c ,  28   e . Of course, the relationship between the first and second connector conductors  26 ,  28  may be reversed in accordance with the teachings of the present invention so that the first flexible double sided connector  28   a  has first and second connector conductors  26 ,  28  which both connect to odd ultrasonic transducer elements  10   a ,  10   c ,  10   e  while the corresponding first and second connector conductors  26 ,  28  of the second flexible double sided conductor  28   b  connect to even ultrasonic transducer elements  10   b ,  10   d . Either of these solutions provides substantial advantages in increasing transducer element density, thereby enabling increased imaging resolution. 
     FIG. 6 shows a further alternative embodiment of the present application where the first connector conductors  26  and second connector conductors  28  drive alternate ultrasonic transducer elements with reversed polarity, driving the first transducer element electrodes  18   a ,  18   c , and  18   e  with one polarity while driving the first transducer element electrodes  18   b ,  18   d  with the reversed polarity. This results in reduction of noise in the overall device. 
     Although, for simplicity, the embodiments illustrated in the present application are linear, one dimensional arrays, the principals of the present application may also be applied to curvilinear otherwise transducers. Such curvilinear transducers may be curved in the longitudinal or transverse direction to accomplish various focusing objectives as would occur to one of ordinary skill in the art. However, the principals of the present application are equally applicable to such curvilinear transducer arrays. 
     It is apparent from the foregoing description that applicants have invented an improved transducer array. It should be apparent from the foregoing that there are various modifications which would be made within the contemplation of one or ordinary skill in the art. The scope of the present application should include such modifications and is defined solely by the appended claims.