WO2007067282A2 - Transducteur ultrasonique en reseau - Google Patents

Transducteur ultrasonique en reseau Download PDF

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Publication number
WO2007067282A2
WO2007067282A2 PCT/US2006/042889 US2006042889W WO2007067282A2 WO 2007067282 A2 WO2007067282 A2 WO 2007067282A2 US 2006042889 W US2006042889 W US 2006042889W WO 2007067282 A2 WO2007067282 A2 WO 2007067282A2
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WO
WIPO (PCT)
Prior art keywords
layer
stack
ultrasonic transducer
kerf
interposer
Prior art date
Application number
PCT/US2006/042889
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English (en)
Other versions
WO2007067282A8 (fr
WO2007067282A3 (fr
Inventor
Marc Lukacs
Stuart F. Foster
Jianhua Yin
Guofeng Pang
Richard Garcia
Original Assignee
Visualsonics Inc.
Sunnybrook And Women's College Health Sciences Centre
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Visualsonics Inc., Sunnybrook And Women's College Health Sciences Centre filed Critical Visualsonics Inc.
Priority to JP2008539043A priority Critical patent/JP4807761B2/ja
Priority to CA002627927A priority patent/CA2627927A1/fr
Priority to EP06827415A priority patent/EP1951445A2/fr
Publication of WO2007067282A2 publication Critical patent/WO2007067282A2/fr
Publication of WO2007067282A3 publication Critical patent/WO2007067282A3/fr
Publication of WO2007067282A8 publication Critical patent/WO2007067282A8/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
    • B06B1/0622—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements on one surface
    • B06B1/064—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements on one surface with multiple active layers

Definitions

  • High-Frequency ultrasonic transducers made from piezoelectric materials, are used in medicine to resolve small tissue features, in the skin and eye and in intravascular imaging applications. High-frequency ultrasonic transducers are also used for imaging structures and fluid flow in small or laboratory animals.
  • the simplest ultrasound imaging system employs a fixed-focused single-element transducer that is mechanically scanned to capture a 2D-depth image. Linear-array transducers are more attractive, however, and offer features such as variable focus, variable beam steering, and permit more advanced image construction algorithms and increased frame rates.
  • linear array transducers have many advantages
  • conventional linear- array transducer fabrication requires complex procedures.
  • the piezoelectric structures of an array must be smaller, thinner and more delicate than those of low frequency array piezoelectrics.
  • conventional dice and fill methods of array production using a dicing saw, and more recent dicing saw methods such as interdigital pair bonding have many disadvantages and have been unsatisfactory in the production of high-frequency linear array transducers.
  • an ultrasonic transducer of the present invention comprises a stack having a first face, an opposed second face and a longitudinal axis extending therebetween.
  • the stack comprises a plurality of layers, each layer having a top surface and an opposed bottom surface.
  • the plurality of layers of the stack comprises a piezoelectric layer that is connected to a dielectric layer.
  • a plurality of kerf slots are defined therein the stack, each kerf slot extending a predetermined depth therein the stack and a first predetermined length in a direction substantially parallel to the axis.
  • the dielectric layer defines an opening extending a second predetermined length in a direction that is substantially parallel to the axis of the stack.
  • the first predetermined length of each kerf slot is at least as long as the second predetermined length of the opening defined by the dielectric layer. Additionally, the first predetermined length is shorter than the longitudinal distance between the first face and the opposed second face of the stack in a lengthwise direction substantially parallel to the longitudinal axis.
  • Figure 1 is a perspective view of an embodiment of an arrayed ultrasonic transducer of the invention showing a plurality of array elements, i.e., 1, 2 > 3, 4 . . . N array elements.
  • Figure 2 is a perspective view of an array element of the plurality of array elements of the arrayed ultrasonic transducer of Figure 1.
  • Figure 3 is a perspective view showing a lens mounted thereon the array element of Figure 2.
  • Figure 4 is a cross-sectional view of one embodiment of an arrayed ultrasonic transducer of the present invention.
  • Figure 5 is an exploded cross-sectional view of the embodiment shown in Figure
  • Figure 6 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first and second kerf slots extending through a first matching layer, a piezoelectric layer, a dielectric layer and into a backing layer.
  • Figure 7 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first and second kerf slots extending through a first and second matching layer, a piezoelectric layer, a dielectric layer and into a backing layer.
  • Figure 8 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first and second kerf slots extending through a first and second matching layer, a piezoelectric layer, a dielectric layer, and into a lens and a backing layer.
  • Figure 9 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first and second kerf slots extending through a first and second matching layer, a piezoelectric layer, a dielectric layer and into a lens, and a backing layer, wherein, in this example, the plurality of second kerf slots are narrower than the plurality of first kerf slots.
  • Figure 10 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first kerf slots extending through a first and second matching layer, a piezoelectric layer, a dielectric layer, and into a lens and a backing layer, and further showing a plurality of second kerf slots extending through a first and second matching layer, and into a lens, and a piezoelectric layer.
  • Figure 11 is an exemplary partial cross-sectional view of the arrayed ultrasonic transducer of Figure 1 taken transverse to the longitudinal axis Ls of the arrayed ultrasonic transducer, showing a plurality of first kerf slots extending through a first and second matching layer, a piezoelectric layer, a dielectric layer and into a lens and a backing layer, and further showing a plurality of second kerf slots extending through a dielectric layer and into a piezoelectric layer.
  • Figures 12A-G shows an exemplary method for making an embodiment of an arrayed ultrasonic transducer of the present invention.
  • Figure 13 shows a graphical illustration of the frequency response of the transducer.
  • Figure 14 shows a graphical illustration of the time response of the transducer.
  • Figure 15 is a graphical analysis of the exemplified PZT stack of Fig. 12G, showing the optimum area for the design in the red coloring. This analysis is for the exemplified PZT stack illustrated in Fig. 12G and represents a baseline for comparison of alternative stack designs.
  • Figure 16 is an elevational cross-sectional view of an alternative embodiment of a PZT stack having a bonding layer interposed therebetween an upper unpoled PZT and a lower poled PZT layer, in which the PZT layers have substantially similar acoustic impedance.
  • the pitch of the array is defined as 2x(we,>+ Wki + Wk 2 where ⁇ e (also labeled as
  • W e iement is the width of a sub-diced element and Wk 1 and Wk 2 are the widths of the first and second kerf slots respectively.
  • Figure 17 is a graphical analysis of the exemplified PZT stack of Fig. 16 having. a first kerf width W k i of 8 ⁇ m and a second kerf width W k2 of 8 ⁇ m and showing a preferred area for the design in red.
  • Figure 18 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k1 of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing a preferred area for the design in red.
  • Figure 19 is a graphical analysis of the exemplified PZT stack of Fig. 19 having a first kerf width W k1 of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing how bandwidth can be affected by the width of the element and the thickness of the upper unpoled PZT layer.
  • Figure 20 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k i of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing how pulse width can be affected by the width of the element and the thickness of the upper unpoled
  • PZT layer for a pulse response at the— 6dB threshold level.
  • Figure 21 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k1 of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing how pulse width can be affected by the width of the element and the thickness of the upper unpoled
  • PZT layer for a pulse response at the -2OdB threshold level.
  • Figure 22 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k1 of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing how center frequency can be affected by the width of the element and the thickness of the upper unpoled PZT layer.
  • Figure 23 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k1 of 8 ⁇ m and a second kerf width W k2 of 5 ⁇ m and showing how the ripple in the passband can be affected by the width of the element and the thickness of the upper unpoled PZT layer.
  • Figure 24 is a graphical analysis of the exemplified PZT stack of Fig. 16 having a first kerf width W k i of 8 ⁇ m. and a second kerf width W k2 of 5 ⁇ m and showing how the pulse sidelobe suppression can be affected by the width of the element and the thickness of the upper unpoled PZT layer.
  • Figure 25 A-C are exemplary top, bottom and cross-sectional views of an exemplary schematic PZT stack of the present invention, the top view showing, at the top and bottom of the PZT stack, portions of the ground electric layer extending outwardly from the overlying lens; the bottom view showing, at the longitudinally extending edges, exposed portions of the dielectric layer between individual signal electrode elements (as one will appreciate, not show in the center portion of the PZT stack are the lines showing the individualized signal electrode elements— one signal electrode per element of the PZT stack).
  • Figure 26A is a top plan view of an interposer for use with the PZT stack of Fig. 25 A-C, showing electrical traces extending outwardly from adjacent the central opening of the transducer and ground electrical traces located at the top and bottom portions of the interposer, showing a dielectric layer disposed thereon a portion of the surface of the interposer, the dielectric layer defining an array of staggered wells positioned along an axis parallel to the longitudinal axis of the interposer, each well communicating with an electrical trace of the interposer, and further showing a solder paste ball bump mounted therein each well in the dielectric layer such that, when a PZT stack is mounted thereon the dielectric layer and heat is applied, the solder melts to form the desired electrical continuity between the individual element signal electrodes and the individual trances on the interposer - the well helping to retain the solder within the confines of the well.
  • Figure 26B is a partial enlarged view of the staggered wells of the dielectric layer and the electrical traces of the underlying interposer of Fig. 26A, the well being configured to accept the solder paste ball bumps.
  • Figure 27A is a top plan view of the PZT stack of Fig. 25 A mounted thereon the dielectric layer and the interposer of Fig. 26 A.
  • Figure 27B is a top plan view of the PZT stack of Fig. 25 A mounted thereon the dielectric layer and interposer of Fig. 26 A, showing the PZT stack as a transparent layer to illustrate the mounting relationship between the PZT stack and the underlying interposer, the solder paste ball bumps mounted therebetween forming an electrical connection between the respective element signal electrodes and the electrical traces on the interposer.
  • Figure 28A is a schematic top plan view of an exemplary circuit board for mounting the transducer of the present invention thereto, the circuit board having a plurality of board electrical traces formed thereon, each board electrical trace having a proximal end adapted to couple to an electrical trace of the transducer and a distal end adapted to couple to a connector, such as, for example, a cable for communication of signals therethrough.
  • a connector such as, for example, a cable for communication of signals therethrough.
  • Figure 28B is a top plan view of an exemplary circuit board for mounting of an exemplary 256-element array having a 75 micron pitch.
  • Figure 28C is a top plan view of the vias of the circuit board of Fig. 28B that are in communication with an underlying ground layer of the circuit board.
  • Figure 29 is a top plan view of a portion of the exemplified circuit board showing, in Region A, the ground electrode layer of the transducer wire bonded to an electrical trace on the interposer, which is, in turn, wire bonded to ground pads of the circuit board, and further showing, in Region B, the individual electrical traces of the transducer wire bonded to individual board electrical traces of the circuit board.
  • Figure 30A is a partial enlarged cross-sectional view of Region A of Fig. 29, showing the dielectric layer positioned about the solder paste ball bumps and between the
  • Figure 3OB is a partial enlarged cross-sectional view of Region B of Fig. 29, showing the dielectric layer between the PZT stack and the interposer.
  • Figures 3 IA and 3 IB are partial cross-sectional views of an exemplified transducer mounted to a portion of the circuit board.
  • Figure 32 is an enlarged partial view Region B of an exemplified transducer mounted to a portion of the circuit board.
  • Figure 33 is a partial enlarged cross-sectional view of a transducer that does not include an interposer, showing a solder paste ball bump mounted thereon the underlying circuit board, each ball bump being mounted onto one board electrical trace of the circuit board, and showing the PZT stack being mounted thereon so that the respective element signal electrodes of the PZT stack are in electrical continuity, via the respective ball bumps, to their respective board: electrical trace of the circuit board.
  • Figure 34A is a partial enlarged cross-sectional view of Fig. 33, showing the ground electrode layer of the transducer without an interposer wire bonded to ground pads of the circuit board.
  • Figure 34B is a partial enlarged cross-sectional view of Fig. 33, showing the ball bump disposed therebetween and in electrical communication with the electrical trace of the circuit board and the element signal electrode of the PZT stack.
  • Figure 35 is a top elevational schematic view of an exemplary interposer defining a plurality of opening, therein and showing alignment means on portions of the peripheral edges of the interposer.
  • Figure 36 is a top elevational schematic view of a PZT stack showing a plurality of troughs that extend through the ground electrode layer and into the underlying PZT stack a predetermined distance and are filed with a conductive material.
  • Figure 37 is a top elevational schematic view of the PZT stack of Figure 36, showing at least one matching layer mounted thereon a portion of the top surface of the PZT stack.
  • Figure 38 is a bottom elevation schematic view of the PZT stack of Figure 37 connected to and underlying the interposer of Figure 35, showing the at least one matching layer connected to the interposer and showing the bottom surface of the PZT stack of Figure
  • Figure 39 is a bottom elevational schematic view of the PZT stack of Figure 38 after a dielectric layer is patterned on portions of the bottom surface of the PZT stack of
  • Figure 40 is a bottom elevational schematic view of the PZT stack of Figure 39 after a signal electrode layer is patterned on portions of the dielectric layer and the bottom surface of the PZT stack.
  • Figure 41 is a top elevational schematic view of the PZT stack of Figure 40 after a shield electrode is patterned on portions of the interposer surrounding the openings in the interposer, the shield electrode in this example connected to the matching layer that is exposed in the opening of the interposer.
  • Figure 42 is a bottom elevational schematic view of the PZT stack of Figure 41 after the stack has been diced into individual ultrasonic transducer arrays, and showing the exposed ends of the ground bus lines and the electrical traces of the signal electrode layer on the bottom surface of the PZT stack.
  • Figure 43 is a bottom elevational schematic view of the PZT stack of Figure 42, showings exemplary wire bond leads connecting the ground bus lines to a ground of a circuit and connecting the bond pads of the electrical traces of the signal electrode layer to signal lines of the circuit, and showing a backing covering the portions of the electrical traces that are connected to and underlie the array elements defined therein the PZT stack.
  • Figure 44 is a schematic perspective cross-sectional view of an array element of the plurality of array elements therein of the PZT stack of Figure 43 with the interposer and shield electrode removed and after the first and second kerf slots are formed in the PZT stack of Figure 43.
  • Figure 45 is a schematic perspective cross-sectional view of an array element of the plurality of array elements therein of the PZT stack of Figure 43 with the shield electrode removed and after the first and second kerf slots are formed in the PZT stack of
  • Figure 46 is a schematic perspective cross-sectional view of an array element of the plurality of array elements therein of the PZT stack of Figure 43 after the first and second kerf slots are formed in the PZT stack of Figure 43.
  • Figure 47 is a schematic perspective view of an array element of the plurality of array elements therein of the PZT stack of Figure 46 with a lens mounted therein the opening of the interposer and in contact with the shield electrode.
  • Figure 48 is a schematic perspective view of an array element of the plurality of array elements therein of the PZT stack of Figure 47 with an additional backing layer attached to the PZT stack.
  • Figure 49 is a schematic cross-sectional view of the transducer mounted with respect to and in electrical communication with a flex circuit DETAILED DESCRIPTION OF THE INVENTION
  • ranges can be expressed herein as from “about” one particular value, and/or to "about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “30” is disclosed, then “about 30" is also disclosed.
  • an ultrasonic transducer comprises a stack 100 having a first face 102, an opposed second face 104, and a longitudinal axis Ls extending therebetween.
  • the stack comprises a plurality of layers, each layer having a top surface 128 and an opposed bottom surface 130.
  • the plurality of layers of the stack comprises a piezoelectric layer 106 and a dielectric layer 108.
  • the dielectric layer is connected to and underlies the piezoelectric layer.
  • the plurality of layers of the stack can further comprise a ground electrode layer 110, a signal electrode layer 112, a backing layer 114, and at least one matching layer.
  • Additional layers cut can include, but are not limited to, temporary protective layers (not shown), an acoustic lens 302, photoresist layers (not shown), conductive epoxies (not shown), adhesive layers (not shown), polymer layers (not shown), metal layers (not shown), and the like.
  • the piezoelectric layer 106 can be made of a variety of materials.
  • materials that form the piezoelectric layer can be selected from a group comprising ceramic, single crystal, polymer and co-polymer materials, ceramic- polymer and ceramic-ceramic composites with 0-3, 2-2 and/or 3-1 connectivity, and the like.
  • the piezoelectric layer comprises lead zirconate titanate (PZT) ceramic.
  • the dielectric layer 108 can define the active area of the piezoelectric layer. At least a portion of the dielectric layer can be deposited directly onto at least a portion of the piezoelectric layer by conventional thin film techniques, including but not limited to spin coating or dip coating. Alternatively, the dielectric layer can be patterned by means of photolithography to expose an area of the piezoelectric layer.
  • the dielectric layer can be applied to the bottom surface of the piezoelectric layer.
  • the dielectric layer does not cover the entire bottom surface of the piezoelectric layer, hi one aspect, the dielectric layer defines, an opening or gap that extends a second predetermined length L2 in a direction substantially parallel to the longitudinal axis of the stack.
  • the opening in the dielectric layer is preferably aligned with a central region of the bottom surface of the piezoelectric layer.
  • the opening defines the elevation dimension of the array.
  • each element 120 of the array has the same elevation dimension and the width of the opening is constant within the area of the piezoelectric layer reserved for the active area of the device that has formed kerf slots.
  • the length of the opening in the dielectric layer can vary in a predetermined manner in an axis substantially perpendicular to the longitudinal axis of the stack resulting in a variation in the elevation dimension of the array elements.
  • the relative thickness of the dielectric layer and the piezoelectric layer and the relative dielectric constants of the dielectric layer and the piezoelectric layer define the extent to which the applied voltage is divided across the two layers. In one example, the voltage can be split at 90% across the dielectric layer and 10% across the piezoelectric layer. It is contemplated that the ratio of the voltage divider across the dielectric layer and the piezoelectric layer can be varied. In the portion of the piezoelectric layer where there is no underlying dielectric layer, then the full magnitude of the applied voltage appears across the piezoelectric layer. This portion defines the active area of the array.
  • the dielectric layer allows for the use of a piezoelectric layer that is wider than the active area and allows for kerf slots (described below) to be made in the active area and extend beyond this area in such a way that array elements (described below) and array sub-elements (described below) are defined in the active area, but a common ground is maintained on the top surface.
  • a plurality of first kerf slots 118 are defined therein the stack.
  • Each first kerf slot extends a predetermined depth therein the stack and a first predetermined length Ll in a direction substantially parallel to the longitudinal axis of the stack.
  • the "predetermined depth" of the first kerf slot can comprise a predetermined depth profile that is a function of position along the respective length of the first kerf slot.
  • the first predetermined length of each first kerf slot is at least as long as the second predetermined length of the opening defined by the dielectric layer and is shorter than the longitudinal distance between the first face and the opposed second face of the stack in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • the plurality of first kerf slots define a plurality of ultrasonic array elements 120, i.e., array elements 1, 2, 3, 4 . . . N.
  • the ultrasonic transducer can also comprise a plurality of second kerf slots 122.
  • each second kerf slot extends a predetermined depth therein the stack and a third predetermined length L3 in a direction substantially parallel to the longitudinal axis of the stack.
  • the "predetermined depth" of the second kerf slot can comprise a predetermined depth profile that is a function of position along the respective length of the second kerf slot.
  • the length of each second kerf slot is at least as long as the second predetermined length of the opening defined by the dielectric layer and is shorter than the longitudinal distance between the first face and the opposed second face of the stack in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • each second kerf slot is positioned adjacent to at least one first kerf slot.
  • the plurality of first kerf slots define a plurality of ultrasonic array elements and the plurality of second kerf slots define a plurality of ultrasonic array sub-elements 124.
  • an array of the present invention without any second kerf slots has one array sub- element per array element and an array of the present invention with one second kerf slot between two respective first kerf slots has two array sub-elements per array element.
  • the formed array elements are supported by the contiguous portion of the stack near the respective first and second faces of the stack.
  • the piezoelectric layer of the stack of the present invention can resonate at frequencies that are considered high relative to current clinical imaging frequency standards.
  • the piezoelectric layer resonates at a center frequency of about 30 MHz.
  • the piezoelectric layer resonates at a center frequency of about and between 10-200 MHz, preferably about and between, 20-150 MHz, and more preferably about and between 25-100 MHz.
  • each of the plurality of ultrasonic array sub-elements has an aspect ratio of width to height of about and between 0.2 - 1.0, preferably about and between 0.3 - 0.8, and more preferably about and between 0.4 - 0.7. In one aspect, an aspect ratio of width to height of less than about 0.6 for the cross-section of the piezoelectric elements is used. This aspect ratio, and the geometry resulting therefrom, separates lateral resonance modes of an array element from the thickness resonant mode used to create the acoustic energy. Similar cross-sectional designs can be considered for arrays of other types as understood by one skilled in the art.
  • first kerf slots are made to define a plurality of array elements.
  • 129 respective first and second kerf slots are made to produce 128 piezoelectric sub-elements that make up the 64 elements of the array. It is contemplated that this number can be increased for a larger array.
  • 65 and 257 first kerf slots can be used for array structures with 64 and 256 array elements respectively.
  • the first and/or second kerf slots can be filled with air.
  • the first and/or second kerf slots can also be filled with a liquid or a solid, such as, for example, a polymer.
  • sub-dicing using a plurality of first and second kerf slots is a technique in which two adjacent sub-elements are electrically shorted together, such that the pair of shorted sub-elements act as one element of the array.
  • element pitch which is the center to center spacing of the array elements resulting from the first kerf slots
  • sub-dicing allows for an improved element width to height aspect ratio such that unwanted lateral resonances within the element are shifted to frequencies outside of the desired bandwidth of the operation of the device.
  • the piezoelectric layer of the stack of the present invention has a pitch of about and between 7.5-30Q microns, preferably about and between 10-150 microns, and more preferably about and between 15-100 microns. In one example and not meant to be limiting, for a 30 MHz array design, the resulting pitch for a 1.5 ⁇ is about 74 microns.
  • narrowing the kerf slots can minimize the pitch of the array such that the effects of grating lobes of energy can be minimized during normal operation of the array device. Further, by narrowing the kerf slots, the element strength and sensitivity are maximized for a given array pitch by removing as little of the piezoelectric layer as possible. Using laser machining, the piezoelectric layer may be patterned with a fine pitch and maintain mechanical integrity.
  • Laser micromachining can be used to extend the plurality of first and/or second kerf slots to their predetermined depth into the stack.
  • Laser micromachining offers a non- contact method to extend or "dice” the kerf slots.
  • Lasers that can be used to "dice” the kerf slots include, for example, visible and ultraviolet wavelength lasers and lasers with pulse lengths from 100ns-lfs, and the like.
  • the heat affected zone (HAZ) is minimized by using shorter wavelength lasers in the UV range and/or picosecond-femtosecond pulse length lasers.
  • Laser micromachining can direct a large amount of energy in as small a volume as possible in as short a time as possible to locally ablate the surface of a material. If the absorption of incident photons occurs over a short enough time period, then thermal conduction does not have time to take place. A clean ablated slot is created with little residual energy, which avoids localized melting and minimizes thermal damage. It is desirable to choose laser conditions that maximize the consumed energy within the vaporized region while minimizing damage to the surrounding piezoelectric layer.
  • the energy density of the absorbed laser pulse can be maximized and the energy can be prevented from dissipating within the material via thermal conduction mechanisms.
  • Two exemplified types of lasers that can be used are ultraviolet (UV) lasers and femtosecond (fs) lasers.
  • UV lasers have a very shallow absorption depth in ceramic and therefore the energy is contained in a shallow volume.
  • Fs lasers which have a very short time pulse (about 10-15 s) and therefore the absorption of energy takes place on this time scale. In one example, any need to repole the piezoelectric layer after laser cutting is not required.
  • UV excimer lasers are adapted for the manufacturing of complex micro- structures for the production of micro-optical-electro-mechanical-systems (MOEMS) units such as nozzles, optical devices, sensors and the like.
  • MOEMS micro-optical-electro-mechanical-systems
  • Excimer lasers provide material processing with low thermal damage and with high resolution due to high peak power output in short pulses at several ultraviolet wavelengths.
  • the ablated depth for a given laser micromachining system is strongly dependent on the energy per pulse and on the number of pulses.
  • the ablation rate can be almost constant and fairly independent for a given laser fluence up to a depth beyond which the rate decreases rapidly and saturates to zero.
  • a predetermined kerf depth as a function of position can be achieved up to the saturation depth for a given laser fluence.
  • the saturation depth can be attributed to the absorption of the laser energy by the plasma plume (created during the ablation process) and by the walls of the laser trench.
  • the plasma in the plume can be denser and more absorbing when it is confined within the walls of a deeper trench; in addition, it may take longer for the plume to expand.
  • the time between the beginning of the laser pulse and the start of the plume attenuation is. generally a few nanoseconds at a high fluence. For lasers with pulse lengths of 10's of ns, this means that the later portion of the laser beam will interact with the plume.
  • picosecond - femtosecond lasers can avoid the interaction of the laser beam with the plume.
  • the laser used to extend the first or second kerf slots into or through the piezoelectric layer is a short wavelength laser such as, for example, a KrF Excimer laser system (having, for example, about a 248nm wavelength).
  • a short wavelength laser such as, for example, a KrF Excimer laser system (having, for example, about a 248nm wavelength).
  • Another example of a short wavelength laser that may be used is an argon fluoride laser (having, for example, about a 193 nm wavelength)
  • the laser used to cut the piezoelectric layer is a short pulse length laser.
  • lasers modified to emit a short pulse length on the order of ps to fs can be used.
  • a KrF excimer laser system (UV light with a wavelength of about 248nm) with a fluence range of about and between 0-20 J/cm2 (preferably about and between 0.5 - 10.0 J/cm2 for PZT ceramic) can be used to laser cut kerf slots about and between 1-30 ⁇ m wide (more preferably between 5-10 ⁇ m wide) through the piezoelectric layer about and between 1-200 ⁇ m thick (preferably between 10-150 ⁇ m thick).
  • the actual thickness of the piezoelectric layer is most commonly based on a thickness that ranges from 1 A ⁇ to 1 A ⁇ based on the speed of sound of the material and the intended center frequency of the array transducer.
  • the choice of backing layer and matching layer(s) and their respective acoustic impedance values dictate the final thickness of the piezoelectric layer.
  • the target thickness can be further fine-tuned based on the specific width to height aspect ratio of each sub-element of the array, which would also be clear to one skilled in the art.
  • the number of laser pulses per unit area can also allow for a well-defined depth control.
  • a lower fluence laser pulse i.e., less than about 1 J/cm2-10 J/cm2 can be used to laser ablate through polymer based material and through thin metal layers.
  • the plurality of layers can further include a signal electrode layer 112 and a ground electrode layer 110.
  • the electrodes can be defined by the application of a metallization layer (not shown) that covers the dielectric layer and the exposed area of the piezoelectric layer.
  • the electrode layers can comprise any metalized surface as would be understood by one skilled in the art.
  • a non-limiting example of electrode material that can be used is Nickel (Ni).
  • a metalized layer of lower resistance (at 1-100 MHz) that does not oxidize can be deposited by thin film deposition techniques such as sputtering (evaporation, electroplating, etc.).
  • a Cr/Au combination (300 / 3000 Angstroms respectively) is an example of such a lower resistance metalized layer, although thinner and thicker layers can also be used.
  • the Cr is used as an interfacial adhesion layer for the Au.
  • other conventional interfacial adhesion layers well known in the semiconductor and microfabrication fields can be used.
  • At least a portion of the top surface of the signal electrode layer is connected to at least a portion of the bottom surface of the piezoelectric layer and at least a portion of the top surface of the signal electrode layer is connected to at least a portion of the bottom surface of the dielectric layer.
  • the signal electrode is wider than the opening defined by the dielectric layer and covers the edge of the dielectric layer in the areas that are above the conductive material 404 used to surface mount the stack to the interposer, as described herein.
  • the signal electrode pattern deposited is one that covers the entire surface of the bottom surface of the piezoelectric layer or is a predetermined pattern of suitable area that extends across the opening defined by the dielectric layer.
  • the original length of the signal electrode maybe longer than the final length of the signal electrode.
  • the signal electrode may be trimmed (or etched) into a more intricate pattern that results in a shorter length.
  • a laser or other material removal techniques such as reactive ion etching (RTF,) etc.
  • RTF reactive ion etching
  • a signal electrode of simple rectangular shape, that is longer than the dielectric gap, is deposited by sputtering (300/3000 Cr/ Au respectively - although thicker and thinner layers are contemplated).
  • the signal electrode is then patterned by means of a laser.
  • a shadow mask and standard 'wet bench' photolithographic processes can also be used to directly create the same, or similar, signal electrode pattern, which is of more intricate detail.
  • the ground electrode layer is connected to at least a portion of the top surface of the piezoelectric layer. At least a portion of the top surface of the ground electrode layer is connected to at least a portion of the bottom surface of a first matching layer 116.
  • the ground electrode layer is at least as long as the second predetermined length of the opening defined by the dielectric layer in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • the ground electrode layer is at least as long as the first predetermined length of each first kerf slot in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • the ground electrode layer connectively overlies substantially all of the top surface of the piezoelectric layer.
  • the ground electrode layer is at least as long as the first predetermined length of each first kerf slot (as described above) and the third predetermined length of each second kerf slot in a lengthwise direction substantially parallel to the longitudinal axis of the stack. Tn one aspect, part of the ground electrode typically remains exposed in order to allow for the signal ground to be connected from the ground electrode to the signal ground trace (or traces) on the interposer 402 (described below).
  • the electrodes can be applied by a physical deposition technique (evaporation or sputtering) although other processes such as, for example, electroplating, can also be used.
  • a conformal coating technique is used, such as sputtering, to achieve good step coverage in the areas in the vicinity to the edge of the dielectric layer.
  • the ratio of electric potential across the dielectric layer to electric potential across the piezoelectric layer is proportional to the thickness of the dielectric layer to the thickness of the piezoelectric layer and is inversely proportional to the dielectric constant of the dielectric layer to the dielectric constant of the piezoelectric layer.
  • the plurality of layers of the stack can further comprise at least one matching layer having a top surface and an opposed bottom surface, hi one aspect, the plurality of layers comprises two such matching layers. At least a portion of the bottom surface of the first matching layer 116 can be connected to at least a portion of the top surface of the piezoelectric layer. If a second matching layer 126 is used, at least a portion of the bottom surface of the second matching layer is connected to at least a portion of the top surface of the first matching layer.
  • the matching layer(s) can be at least as long as the second predetermined length of the opening defined by the dielectric layer in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • the matching layer(s) has a predetermined acoustic impedance and target thickness.
  • a predetermined acoustic impedance and target thickness For example, powder (vol%) mixed with epoxy can be used to create a predetermined acoustic impedance.
  • the matching layer(s) can be applied to the top surface of the piezoelectric layer, allowed to cure and then lapped to the correct target thickness.
  • the matching layer(s) can have a thickness that is usually equal to about or around equal to 1 A of a wavelength of sound, at the center frequency ,of the device, within the matching layer material itself.
  • the specific thickness range of the matching layers depends on the actual choice of layers, their specific material properties, and the intended center frequency of the device, hi one example and not meant to be limiting, for polymer based matching layer materials, and at 30 MHz, this results in a preferred thickness value of about 15-25um.
  • the matching layer(s) can comprise PZT 30% by volume mixed with 301-2 Epotek epoxy having an acoustic impedance of about 8 Mrayl.
  • the acoustic impedance can be between about 8-9 Mrayl, in another aspect, the impedance can be between about 3-10 Mrayl, and, in yet another aspect, the impedance can be between about 1-33 Mrayl.
  • the preparation of the powder loaded epoxy and the subsequent curing of the material onto the top face of the piezoelectric layer such that there are substantially no air pockets within the layer is known to one skilled in the art.
  • the epoxy can be initially degassed, the powder mixed in and then the mixture degassed a second time.
  • the mixture can be applied to the surface of the piezoelectric layer at a setpoint temperature that is elevated from room temperature (20 - 200°C) with 80°C being used for 301-2 epoxy.
  • the epoxy generally cures in 2 hours.
  • the thickness of the first matching layer is about 1 A wavelength and is about 20 ⁇ m thick for 30% by volume PZT in 301-2 epoxy.
  • the plurality of layers of the stack can further comprise a backing layer 114 having a top surface and an opposed bottom surface.
  • the backing layer substantially fills the opening defined by the dielectric layer.
  • at least a portion of the top surface of the backing layer is connected to at least a portion of the bottom surface of the dielectric layer.
  • substantially all of the bottom surface of the dielectric layer is connected to at least a portion of top surface of the backing layer.
  • at least a portion of the top surface of the backing layer is connected to at least a portion of the bottom surface of the piezoelectric layer.
  • the matching and backing layers can be selected from materials with acoustic impedance between that of air and/or water and that of the piezoelectric layer.
  • an epoxy or polymer can be mixed with metal and/or ceramic powder of various compositions and ratios to create a material of variable acoustic impedance and attenuation. Any such combinations of materials are contemplated in this disclosure.
  • the choice of matching layer(s), ranging from 1-6 discrete layers to one gradually changing layer, and backing layer(s), ranging from 0-5 discrete layers to one gradually changing layer alters the thickness of the piezoelectric layer for a specific center frequency.
  • the thickness of the piezoelectric layer is between about 50 ⁇ m to about 60 ⁇ m. In other non-limiting examples, the thickness can range between about 40 ⁇ m to 75 ⁇ m. For transducers with center frequencies in the range of 25-50 MHz and for a different number of matching and backing layers, the thickness of the piezoelectric layer is scaled accordingly based on the knowledge of the materials being used and one skilled in the art of transducer design can determine the appropriate dimensions.
  • a laser can be used to modify one (or both) surface(s) of the piezoelectric layer.
  • One such modification can be the creation of a curved ceramic surface prior to the application of the matching and backing layers. This is an extension of the variable depth control methodology of laser cutting applied in two dimensions.
  • a metallization layer (not shown) can be deposited.
  • a re-poling of the piezoelectric layer can also be used to realign the electric dipoles of the piezoelectric layer material.
  • a lens 302 can be positioned in substantial overlying registration with the top surface of the layer that is the uppermost layer of the stack.
  • the lens can be used for focusing the acoustic energy.
  • the lens can be made of a polymeric material as would be known to one skilled in the art. For example, a preformed or prefabricated piece of Rexolite which has three flat sides and one curved face can be used as a lens.
  • the radius of curvature (R) is determined by the intended focal length of the acoustic lens.
  • the lens can be conventionally shaped using computerized numerical control equipment, laser machining, molding, and the like, hi one aspect, the radius of curvature is large enough such that the width of the curvature (WC) is at least as wide as the opening defined by the dielectric layer.
  • the minimum thickness of the lens substantially overlies the center of the opening or gap defined by the dielectric layer. Further, the width of the curvature is greater than the opening or gap defined by the dielectric layer. Li one aspect, the length of the lens can be wider than the length of a kerf slot allowing for all of the kerf slots to be protected and sealed once the lens is mounted on the top of the transducer device.
  • the flat face of the lens can be coated with an adhesive layer to provide for bonding the lens to the stack.
  • the adhesive layer can be a SU-8 photoresist layer that serves to bond the lens to the stack.
  • the applied adhesive layer can also act as a second matching layer 126 provided that the thickness of the adhesive layer applied to the bottom face of the lens is of an appropriate wavelength in thickness (such as, for example 1 A wavelength in thickness).
  • the thickness of the exemplified SU-8 layer can be controlled by normal thin film deposition techniques (such as, for example, spin coating).
  • a film of SU-8 becomes sticky (tacky) when the temperature of the coating is raised to about 60-85°C.
  • the surface topology of the SU- 8 layer may start to change. Therefore in a preferred aspect this process is performed at a set point temperature of 80°C. Since the SU-8 layer is already in solid form, and the elevated temperature only causes the layer to become tacky, then once the layer is attached to the stack, the applied SU-8 does not flow down the kerfs of the array. This maintains the physical gap and mechanical isolation between the formed array elements.
  • the SU-8 layer and the lens can be laser cut, which effectively extends the array kerfs (first and/or second array kerf slots), and in one aspect, the sub-diced or second kerfs, through both matching layers (or if two matching layers are used) and into the lens.
  • a pick and place machine or an alignment jig that is sized and shaped to the particular size and shape of the actual components being bonded together
  • the laser fluence of approximately 1-5 J/cm 2 can be used.
  • At least one first kerf slot can extend through or into at least one layer to reach its predetermined depth/depth profile in the stack. Some or all of the layers of the stack can be cut through or into substantially simultaneously. Thus, a plurality of the layers can be selectively cut through substantially at the same time. Moreover, several layers can be selectively cut through at one time, and other layers can be selectively cut through at subsequent times, as would be clear to one skilled in the art.
  • At least a portion of at least one first and/or second kerf slot extends to a predetermined depth that is at least 60% of the distance from the top surface of the piezoelectric layer to the bottom surface of the piezoelectric layer and at least a portion of at least one first and/or second kerf slot can extend to a predetermined depth that is 100% of the distance from the top surface of the piezoelectric layer to the bottom surface of the piezoelectric layer.
  • At least a portion of at least one first kerf slot can extend to a predetermined depth into the dielectric layer and at least a portion of one first kerf slot can also extend to a predetermined depth into the backing layer.
  • the predetermined depth into the backing layer can vary from 0 microns to a depth that is equal to or greater than the thickness of the piezoelectric layer itself.
  • Laser micromachining through the backing layer can provide a significant improvement in isolation between adjacent elements, hi one aspect, at least a portion of one first kerf slot extends through at least one layer and extends to a predetermined depth into the backing layer.
  • the predetermined depth into the backing layer may vary.
  • the predetermined depth of at least a portion of at least one first kerf slot can vary in comparison to the predetermined depth of another portion of that same respective kerf slot or to a predetermined depth of at least a portion of another kerf slot in a lengthwise direction substantially parallel to the longitudinal axis of the stack.
  • the predetermined depth of at least one first kerf slot can be deeper than the predetermined depth of at least one other kerf slot.
  • At least one second kerf slot can extend through at least one layer to reach its predetermined depth in the stack as described above for the first kerf slots.
  • the second kerf slots can extend into or through at least one layer of the stack as described above for the first kerf slots. If layers of the stack are cut independently, each kerf slot in a given layer of the stack, whether a first or second kerf slot can be in substantial overlying registration with its corresponding slot in an adjacent layer.
  • the kerf slots are laser cut into the piezoelectric layer after the stack has been mounted onto the interposer and a backing layer has been applied.
  • the ultrasonic transducer can further comprise an interposer 402 having a top surface and an opposed bottom surface.
  • the interposer defines a second opening extending a fourth predetermined length L4 in a direction substantially parallel to the longitudinal axis Ls of the stack. The second opening allows for easy application of the backing layer to the bottom surface of the piezoelectric stack.
  • a plurality of electrical traces 406 can be positioned on the top surface of the interposer in a predetermined pattern and the signal electrode layer 112 can also define an electrode pattern.
  • the stack including the signal electrode 112 with a defined electrode pattern, can be mounted in substantial overlying registration with the interposer 402 such that the electrode pattern defined by the signal electrode layer is electrically coupled with the predetermined pattern of electrical traces positioned on the top surface of the interposer.
  • the interposer can also act as a redistribution layer for electrical leads to the individual elements of the array.
  • the ground electrode 110 of the array can be connected to the traces on the interposer reserved for ground connections. These connections can be made in advance of attaching the lens, if a lens is used.
  • connection can be made after the lens is attached.
  • surface mounting can be performed using methods known in the art, for example, and not meant to be limiting, by using an electrically conducting surface mount material, including but not limited to solder, or by using wirebonding.
  • the backing material 114 can be made as described herein.
  • the backing material can be made from powder (vol%) mixed with epoxy which can be used to create a predetermined acoustic impedance.
  • PZT 30% mixed with 301-2 Epotek epoxy has acoustic impedance of 8 Mrayl, and is non-conducting.
  • the epoxy-based backing layer can be composed of other powders such as, for example, tungsten, alumina, and the like. It will be appreciated that other conventional backing materials are contemplated such as, for example and not meant to be limiting, a conductive silver epoxy.
  • a backing layer can be prefabricated and cut to an appropriate size after it has cured such that it fits through the opening defined by the interposer.
  • the top surface of the prefabricated backing can be coated with a fresh layer of backing material (or other adhesive) and be located in the second opening defined by the interposer.
  • the rigid plate can be removed after the bonding of the backing is complete.
  • the array of the present invention can be of any shape as would be clear to one of skill in the art and includes linear arrays, sparse linear arrays, 1.5 Dimensional arrays, and the like.
  • a method of fabricating an ultrasonic array comprising cutting a piezoelectric layer 106 with a laser, wherein said piezoelectric layer resonates at a high ultrasonic transmit frequency. Also provided herein, is a method of fabricating an ultrasonic array comprising cutting a piezoelectric layer with a laser, wherein the piezoelectric layer resonates at an ultrasonic transmit center frequency of about 30 MHz.
  • an ultrasonic array comprising cutting a piezoelectric layer with a laser, wherein said piezoelectric layer resonates at an ultrasonic transmit frequency of about and between 10-200 MHz, preferably about and between, 20-150 MHz, and more preferably about and between 25-100 MHz.
  • a method wherein the "dicing" of all functional layers can be achieved in one or a series of consecutive steps.
  • a method of fabricating an ultrasonic array that includes cutting a piezoelectric layer with a laser so that the piezoelectric layer resonates at a high ultrasonic transmit frequency.
  • the laser cuts additional layers other than the piezoelectric layer.
  • the piezoelectric layer and the additional layers are cut at substantially the same time, or substantially simultaneously.
  • Additional layers cut can include, but are not limited to, temporary protective layers, an acoustic lens 302, matching layers 116 and/or 126, backing layers 114, photoresist layers, conductive epoxies, adhesive layers, polymer layers, metal layers, electrode layers 110 and/or 112, and the like. Some or all of the layers can be cut through substantially simultaneously. Thus, a plurality of the layers can be selectively cut through substantially at the same time. Moreover, several layers can be selectively cut through at one time, and other layers can be selectively cut through at subsequent times, as would be clear to one skilled in the art.
  • a laser cuts first though at least a piezoelectric layer and second through a backing layer where both the top and bottom faces of the stack are exposed to air.
  • the stack 100 can be attached to a mechanical support or interposer 402 that defines a hole or opening located below the area of the stack in order to retain access to the bottom surface of the stack.
  • the interposer can also act as a
  • redistribution layer for electrical leads to the individual elements of the array in one example, after the laser cuts are made through the stack mounted onto the interposer, additional backing material can be deposited into the second opening defined by the interposer to increase the thickness of the backing layer.
  • the disclosed method is not limited to a single cut by the laser, and as would be clear to one skilled in the art, multiple additional cuts can be made by the laser, through one or more disclosed layers.
  • a method of fabricating an ultrasonic array that includes cutting a piezoelectric layer with a laser so that the piezoelectric layer resonates at a high ultrasonic transmit frequency.
  • the laser cuts portions of the
  • the laser may, for example, cut to at least one depth, or several different depths. Each depth of laser cut can be considered as a separate region of the array structure. For example, one region can require the laser to cut through the matching layer, electrode layers, the piezoelectric layer and the backing layer, and a second region can require the laser to cut through the matching layer, the electrode layers, the piezoelectric layer, the dielectric layer 108, and the like.
  • both the top and bottom surfaces of a pre- diced assembled stack are exposed and the laser machining can take place from either (or both) surface(s).
  • having both surfaces exposed allows for cleaner and straighter kerf edges to be created by laser machining.
  • ceramic polymer composite layers can be fabricated and lapped to similar thicknesses as described about using techniques known in the art such as, for example, by interdigitation methods.
  • 2-2 and 3-1 ceramic polymer composites can be made with a ceramic width and a ceramic- to-ceramic spacing on the order of the pitch required for an array.
  • the polymer filler can be removed and element-to-element cross talk of the array can be reduced.
  • the fluence required to remove a polymer material is lower than that required for ceramic, and therefore an excimer laser represents a suitable tool for the removal of the polymer in a polymer- ceramic composite to create an array structure with air kerfs.
  • the 2-2 composite within the active area of the array (where the polymer is being removed), the 2-2 composite can be used as a 1-phase ceramic.
  • one axis of connectivity of the polymer in a 3-1 composite can be removed.
  • Another approach for the 2-2 composite can be to laser micro machine the cuts perpendicular to the orientation of the 2-2 composite.
  • the result can be a structure similar to the one created using the 3-1 composite since the array elements would be a
  • the surface of the sample being laser ablated can be protected from debris being deposited on the sample during the laser process itself.
  • a protective layer can be disposed on the top surface of the stack assembly.
  • the protective layer may be temporary and can be removed after the laser processing.
  • the protective layer may be a soluble layer such as, for example, a conventional resist layer.
  • the top surface is a thin metal layer the protective layer acts to prevent the metal from peeling or flaking off.
  • other soluble layers that can remain adhered to the sample despite the high laser fluence and the high density of laser cuts and that can still be removed from the surface after laser cutting can be used.
  • FIG. 12a-12g An exemplary method for fabricating an exemplary high-frequency ultrasonic array using laser micromachining is shown in figures 12a-12g.
  • a pre-poled piezoelectric structure with an electrode on its top and bottom surfaces is provided.
  • An exemplary structure is model PZT 3203HD (part number KSN6579C), distributed by CTS Communications Components ftic (Bloomingdale, IL).
  • the electrode on the top surface of the piezoelectric becomes the ground electrode 110 of the array and the electrode on the bottom surface is removed and replaced with a dielectric layer 108.
  • An electrode can be subsequently deposited onto the bottom surface of the piezoelectric, which becomes the signal electrode 112 of the array.
  • a metalized layer of lower resistance (at 1-100 MHz) that does not oxidize is deposited by thin film deposition techniques such as sputtering, evaporation, electroplating, etc.
  • a non-limiting example of such a metalized layer is a Cr/Au combination. If this layer is used, the Cr is used as an adhesion layer for the Au.
  • the natural surface roughness of the structure form the manufacturer may be larger than desired.
  • the top surface of the piezoelectric structure maybe lapped to a smooth finish and an electrode applied to the lapped surface.
  • a first matching layer 116 is applied to top surface of the piezoelectric structure.
  • part of the top electrode remains exposed to allow for the signal ground to be connected from the top electrode to the signal ground trace (or traces) on an underlying interposer 402.
  • the matching layer is applied to the top surface of the piezoelectric structure, allowed to cure and is then lapped to the target thickness.
  • a matching, layer material used was PZT 30% mixed with 301-2 Epotek epoxy that had an acoustic impedance of about 8 Mrayl. In some examples a range of 7-9 Myral is desired for the first layer. In other examples, a range of 1-33 Mryal can be used.
  • the powder loaded epoxy is prepared and cured onto the top face of the piezoelectric structure such that there are substantially no air pockets within the first matching layer.
  • the 301-2 epoxy was first degassed, the powder was mixed in, and the mixture was degassed a second time.
  • the mixture is applied to the surface of the piezoelectric structure at a setpoint temperature that is elevated from room temperature.
  • the matching layer has a desired acoustic impedance of 7-9 Mryal and target thickness of about 1 A wavelength which is about 20 ⁇ m thick for 30% PZT in 301-2 epoxy.
  • powders of different compositions and of appropriate (vol%) mixed with different epoxies of desired viscosity can be used to create the desired acoustic impedance.
  • a metalized layer can be applied to the top of the lapped matching layer that connects to the top electrode of the piezoelectric structure. This additional metal layer serves as a redundant grounding layer that will help with electrical shielding.
  • the bottom surface of the piezoelectric structure is lapped to achieve the target thickness of the piezoelectric layer 106 suitable to create a device with the desired center frequency of operation when the stack is in its completed form.
  • the desired thickness is dependent on the choice of layers of the stack, their material composition and the fabricated geometry and dimensions.
  • the thickness of the piezoelectric layer is affected by the acoustic impedance of the other layers in the stack and by the width-to-height ratio of the array elements 120 that are defined by the combination of the pitch of the array and the kerf width of the array element kerfs 118 and of the sub-diced kerfs 122.
  • the target thickness of piezoelectric layer was about 60 ⁇ m.
  • the target thickness is about 50-70 ⁇ m.
  • the values are scaled accordingly based on the knowledge of the materials being used as would be known to one skilled in the art.
  • a dielectric layer 108 is applied to at least a portion of the bottom surface of the lapped piezoelectric layer.
  • the applied dielectric layer defines an opening in the central region of the piezoelectric layer (underneath the area covered by the matching layer).
  • the opening defined by the dielectric layer also defines the elevation dimension of the array.
  • SU-8 resist formulations MicroChem, Newton, MA
  • spin speed time of spinning and heating
  • a uniform thickness can be achieved.
  • SU-8 formulations are also photo-imageable and thus by means of standard photolithography, the dielectric layer is patterned and a gap of desired width and breath was etched out of the resist to form the opening in the dielectric layer.
  • a negative resist formulation is used such that the areas of the resist that are exposed to UV radiation are not removed during the etching process to create the opening of the dielectric layer (or any general pattern).
  • Adhesion of the dielectric layer to the bottom surface of the piezoelectric layer is enhanced by a post UV exposure.
  • the additional UV exposure after the etching process improves the cross linking within the SU-8 layer and increases the adhesion and chemical resistance of the dielectric layer.
  • a mechanical support can be used to prevent cracking of the stack 100 during the dielectric layer application process.
  • the mechanical support is applied to the first matching layer by spinning an SU-8 layer onto the mechanical support itself.
  • the mechanical support can be used during the deposition of the SU-8 dielectric, the spinning, the baking, the initial UV exposure and the development of the resist.
  • the mechanical support is removed prior to the second UV exposure as the SU-8 layer acts as a support unto itself.
  • a signal electrode layer 112 is applied to the lapped bottom surface of the piezoelectric layer and to the bottom surface of the dielectric layer.
  • the signal electrode layer is wider than the opening defined by the dielectric layer and covers the edge of the patterned dielectric layer in the areas that overlie the conductive material used to surface mount the stack to the underlying interposer.
  • the signal electrode layer is typically applied by a conventional physical deposition technique such as evaporation or sputtering, although other processes can be used such as electroplating.
  • a conventional conformal coating technique such as sputtering is used in order to achieve good step coverage in the areas in the vicinity to the edge of the dielectric layer.
  • the signal electrode layer covers the entire surface of the bottom face of the stack or forms a rectangular pattern centered across the opening defied by dielectric layer.
  • the signal electrode layer is then patterned by means of a laser.
  • the original length of the signal electrode layer is longer than the final length of the signal electrode.
  • the signal electrode is trimmed (or etched) into a more intricate pattern to form a shorter length.
  • a shadow mask or standard photolithographic process can be used to deposit a pattern of more intricate detail.
  • a laser or another material removal technique such as reactive ion etching (RIE), for example, can also be used to remove some of the deposited signal electrode to create a similar intricate pattern.
  • RIE reactive ion etching
  • the stack is mounted onto a mechanical support such that upper surface of the first matching layer is bonded to the mechanical support and the bottom face of the stack is exposed.
  • the mechanical support is larger in surface dimension than the stack.
  • markings that are used for alignment purposes during surface mounting of the stack onto an interposer.
  • the mechanical support can be, but is not limited to, an interposer.
  • an interposer is a 64-element 74 ⁇ m pitch array (1.5 lambda at 30MHz), part number
  • GK3907_3A which can be obtained from Gennum Corporation (Burlington, Ontario, Canada).
  • Gennum Corporation Gennum Corporation (Burlington, Ontario, Canada).
  • the two edges of the opening defined by the dielectric layer can be oriented perpendicular to the metal traces on the support so that the stack can be properly oriented with respect to the metal traces on the interposer during a surface mounting step.
  • any (or all) external traces on the interposer are used as alignment markings. These markings allow for the determination of the orientation of the opening defined by the dielectric layer with respect to the markings on the mechanical support in both X-Y axes.
  • the alignment markers on the mechanical support are placed on a portion of the surface of the stack itself. For example, alignment marks can be placed on the stack during the deposition of the ground electrode layer.
  • an electrode pattern is created on the bottom surface of the signal electrode layer, which is located on the bottom face of the stack, and is patterned with a laser.
  • the depth of the laser cut is deep enough to remove a portion of the electrode.
  • this laser micromachining process step is similar to the use of lasers to trim electrical traces on surface resistors and on circuit boards or flex circuits.
  • the X-Y axes of the laser beam are defined with a known relation to the opening defined by the dielectric layer.
  • the laser trimmed pattern is oriented in a manner such that the pattern can be superimposed on top of the metal trace pattern that is defined on the interposer.
  • the Y axis alignment of the trimmed signal electrode pattern to the signal trace pattern of the interposer is important and in one aspect misalignment is no more that 1 full array element pitch.
  • a KrF excimer laser used in projection etch mode with a shadow mask can be used to create a desired electrode pattern.
  • a homogenous central part of the excimer laser beam cut out by using a rectangular aperture passes through a beam
  • the attenuator, double telescopic system and a thin metal mask and imaged onto the surface of the specimen mounted on a computer controlled x-y-z stage with a 3-lens projection system ( ⁇ l .5 ⁇ m resolution) of 86.9mm effective focal length.
  • the reduction ratio of the mask projection system can be fixed to 10: 1.
  • two sets of features are trimmed into the signal electrode on the stack.
  • Leadfinger features are trimmed into the signal electrode on the stack to provide electrical continuity from the interposer to the active area of the piezoelectric layer defined by the opening defined by the dielectric layer. In the process of making these leadfmgers, the final length of the signal electrode can be created. Narrow lines are also trimmed into the signal electrode on the stack to electrically isolate each leadfinger.
  • backing material 114 is applied to the formed stack. If an epoxy based backing is used, and wherein some curing in-situ within the hole of the interposer takes place, the use of a rigid plate bonded to the top surface of the stack can be used to avoid warping of the stack. The plate can be removed once the curing of the backing layer is complete.
  • a combination of backing material properties that includes a high acoustic attenuation, and a large enough thickness, is selected such that the backing layer behaves as close to a 100% absorbing material as possible. The backing layer does not cause electrical shorting between array elements.
  • the ground electrode of the stack is connected to the traces on the interposer reserved for ground connections.
  • the traces from the interposer are connected to an even larger footprint circuit platform made from flex circuit or other PCB materials that allows for the integration of the array with an appropriate beamformer electronics necessary to operate the device in real time for generating a real time ultrasound image as would be known to one skilled in the art.
  • array elements 120 and sub-elements 124 can be formed by aligning a laser beam such that array kerf slots are oriented and aligned (in both X and Y) with respect to the bottom electrode pattern in the stack.
  • the laser cut kerfs extend into the underlying backing layer.
  • a lens 302 is positioned in substantial overlying registration with the top surface of the layer that is the uppermost layer of the stack, In another aspect ⁇ the minimum thickness of the lens substantially overlies the center of the opening defined by the dielectric layer. In a further aspect, the width of the curvature is greater than the opening defined by the dielectric layer. The length of the lens can be wider than the length of an underlying kerf slot allowing for all of the kerf slots to be protected and sealed once the lens is mounted on the top of the transducer device.
  • the bottom, flat face of the lens can be coated with an adhesive layer to provide for bonding the lens to the formed and cut stack.
  • the adhesive layer can by a SU-8 photoresist layer that serves to bond the lens to the stack.
  • the applied adhesive layer can also act as a second matching layer 126 provided that the thickness of the adhesive layer applied to the bottom face of the lens is of an appropriate wavelength in thickness (such as, for example 1 A wavelength in thickness).
  • the thickness of the exemplified SU-8 layer can be controlled by normal thin film deposition techniques (such as, for example, spin coating).
  • a film of SU-8 becomes sticky (tacky) when the temperature of the coating is raised to about 60-85 0 C. At temperatures higher than 85 0 C, the surface topology of the SU- 8 layer may start to change. Therefore, in a preferred aspect, this process is performed at a set point temperature of 8O 0 C. Since the SU-8 layer is already in solid form, and the elevated temperature only causes the layer to become tacky, then once the adhesive layer is attached to the stack, the applied SU-8 does not flow down the kerfs of the array. This maintains the physical gap and mechanical isolation between the formed array elements. To avoid trapping air in between the adhesive layer and the first matching layer, it is preferred that this bonding process take place in a partial vacuum. Ih one aspect, after the bonding has taken place, and the sample cooled to room temperature, a UV exposure of the SU-8 layer (through the attached lens) is used to cross link the SU-8, to make the layer more rigid, and to improve adhesion.
  • the SU-8 layer and the lens can be laser cut, which effectively extends the array kerfs (first and/or second array kerf slots), and in one aspect, the sub-diced or second kerfs, through both matching layers (or if two matching layers are used) and into the lens.
  • a PZT stack is disclosed that allows for a super wide bandwidth response while maintaining a relatively simple combination of layers within the stack itself.
  • one desired characteristic of transducer, or of the PZT stack design is to have a broadband frequency response (or a short time response in the time domain).
  • piezoelectric layer of the PZT stack to dampen the response of the transducer. It is further controlled by the use of a properly designed set of wave matching layers onto the top face of the piezoelectric layer.
  • a properly designed set of wave matching layers onto the top face of the piezoelectric layer.
  • the number of matching layers varies from 1-3 layers, although more layers are possible.
  • the material properties of all these layers including the acoustic impedance, speed of sound, elastic compliance and thickness play primary roles in the design of the piezoelectric stack.
  • the ability to fabricate a piezoelectric stack becomes increasingly tricky to manage as the number of layers increases and as the design centre frequency of the transducer increases.
  • the thickness of the matching layers may be in the range of 1-60 microns in thickness and depends on the particular material parameters of each selected matching layer.
  • a design for a ultrasonic transducer comprises a matching layer, disposed within a PZT stack, which has the same material parameters, such as, for example, acoustic impedance, as the piezoelectric layer itself.
  • a PZT stack having a determined acoustic impedance is provided that is connected to an unpoled PZT matching layer.
  • the acoustic impedance of the PZT stack and the unpoled PZT matching layer are substantially equal.
  • PZT-PZT stacks have previously been developed with a typical goal to create a structure that resonates at f 0 and 2f 0 .
  • both PZT layers are poled and are active.
  • the second PZT layer is unpoled (not active) and is acting as a passive interfacial layer between the active PZT layer and the ultrasound medium.
  • bandwidth refers to the passband of the transducer, or the range of frequencies that fall within 6dB of the frequency point that is the most sensitive (or demonstrates the least amount of insertion loss).
  • center frequency refers to the center frequency of the transducer and is usually defined as the mid point in the -6dB Bandwidth of the device.
  • a centre frequency of substantially 30 MHz is used.
  • the phrase "insertion loss” refers to the strength of the acoustic response from 1 array element of the PZT-PZT transducer stack with respect to the acoustic response of 1 array element of the PZT stack illustrated in Figure 12G when both respective elements are excited with the same electrical pulse.
  • the IL ⁇ 24.5dB (IL stands for insertion loss) in Figure 15 is an absolute value that refers to the response of the transducer using an absolute energy scale.
  • the term "ripple” refers to, or characterizes, the small variation in response of the transducer within the bandwidth of the device. This definition does not take into account any slope that may exist within the bandwidth of the transducer.
  • pulse response refers to the time interval for which the transducer is emitting an acoustic response above a defined threshold after it has been excited with a drive pulse.
  • the normal threshold levels quoted are usually at the -6dB and -2OdB levels.
  • the drive pulse is a broadband single cycle bipolar pulse with a center frequency equal to the centre frequency of the response of the transducer.
  • the phrase “secondary pulse suppression” refers to the suppression of the peak of the secondary lobe of a pulse response.
  • the pulse response there is usually the initial pulse (or the first lobe) response followed by secondary lobes.
  • the secondary lobes have much less amplitude than the first lobe.
  • a useful metric is to determine the peak of the secondary lobe. It is desirable to have this peak as low as possible.
  • the relative difference between the initial lobe and the second lobe has been characterized and can be kept at a level that is 2OdB below the initial peak.
  • the phrase "shift in center frequency” refers to the variation of the center frequency of the device.
  • the thickness of the piezoelectric layer remains the same for all permutations of matching and backing layers used in the simulation.
  • the variation in the layers used for the FEA simulations does cause a change in the center frequency of the device.
  • the sensitivity of this change is a useful metric for determining how reproducible a particular PZT stack design will be. This is represented as a ratio of the FEA determined F 0 over the designed F 0 value. For example, a ratio of "one" means that for a particular stack design, there is no shift in center frequency.
  • an exemplary PZT stack is shown having a backing underlying a connected PZT layer.
  • Two matching layers 126, 116 are mounted thereon an upper surface of the PZT layer 106.
  • a lens is connected to the upper surface of the top most matching layer 126.
  • the PZT stack for a transducer in one example of the alternative embodiment of the PZT stack for a transducer, as shown in cross-section in Fig. 16, two layers of PZT 502, 504 are provided and positioned in overlying relationship to each other.
  • the upper layer of PZT 502 is unpoled and the lower layer of PZT 504 is poled.
  • the unpoled and inactive upper PZT layer can be formed of the same material as the poled and active lower PZT layer.
  • the upper PZT layer could be formed from other materials having similar acoustic impedance to the lower PZT layer.
  • a bonding layer 506 formed from, for example and not meant to be limiting, tin solder, and the like, is positioned therebetween and in contact with the two opposing surfaces of the two layers of PZT.
  • the bottom surface of the lower poled layer of PZT is mounted thereon the top surface of a backing layer 508, which is formed from, for example and not meant to be limiting, PZT, epoxy, and the like.
  • a lens 512 is positioned onto the top surface of the upper layer of PZT.
  • a ground electrode layer can be interposed therebetween the lower poled piezoelectric layer and the upper unpoled piezoelectric layer.
  • a spaced series of parallel first kerf slots 520 are cut into the composite formed from the bonded two layers of PZT and extend through the substantial thickness of the composite. Further, a spaced series of second kerf slots 522 is cut into the composite, from the upper surface of the unpoled upper PZT layer through approximately 75% of the thickness of the active PZT layer. A depth of about 75% is approximately the minimum depth through the active layer of the PZT layer that is required to achieve the performance illustrated in Figures 17-24. One skilled in the art will appreciate that it is contemplated that a depth exceeding 75% is contemplated as the deeper depth can improve the performance even more than what is presented in the figures. [00176] In the embodiment shown in Figure 16, and as shown in Figs.
  • bandwidth, passband ripple, sidelobe and pulse width are controlled by structural parameters such as, for example, element width (w e ), kerf width (wki, Wk 2 ), kerf depth, thickness of the bonding layer positioned between the inactive and active PZT layers, and thickness of the inactive PZT layer (h PZ n).
  • Figs. 17 and 18 illustrate graphically the analysis of the exemplified PZT stack shown in Fig. 16. The preferred area for the transducer designs are highlighted in red coloring.
  • the first kerf width is 8 ⁇ m and the second kerf width is 8 ⁇ m.
  • the first kerf width is 8 ⁇ m and the second kerf width is 5 ⁇ m.
  • Figures 21- 24 illustrate the affect of the width of the element and the thickness of the upper unpoled PZT layer affects bandwidth, pulse width at the -6 dB and -2OdB threshold levels, center frequency, ripple in the passband, and pulse sidelobe suppression.
  • the first kerf width was constant at 8- ⁇ m and the second kerf width was constant at 5 ⁇ m.
  • the present invention further comprises a circuit board that is adapted to accept an exemplary transducer and that is further adapted to connect to at least one conventional connector.
  • the conventional connector is adapted to complementarily connect with a cable for transmission and/or supply of required signals.
  • Figure 28 shows a top view of an exemplary circuit board for a 256- element array having a 75 micron pitch.
  • FIGS 25A-27B an exemplary transducer for use with the exemplary circuit board is illustrated.
  • FIGs 25A-25C exemplary top, bottom and cross-sectional views of an exemplary schematic PZT stack of the present invention are shown.
  • Figure 25 A shows a top view of the PZT stack and illustrates portions of the ground electrode layer 600 that extend from the top and bottom portions of the PZT stack.
  • the ground electric layer extends the full width of the PZT stack.
  • Figure 25B shows a bottom view of the PZT stack.
  • the PZT stack forms exposed portions of the dielectric layer 610 between individual signal electrode elements 620.
  • the signal elements extend the full width of the PZT stack. As one will appreciate, not shown in the underlying "center portion" of the PZT stack are lines showing the individualized signal electrode elements. As one will further appreciate, there is one signal electrode per element of the PZT stack, e.g., 256 signal electrodes for a 256-element array.
  • Figure 26A is a top plan view of an interposer 650 for use with the PZT stack of Figures 25A-C, comprising electrical traces 652 extending outwardly from adjacent the central opening of the interposer.
  • the interposer further comprises ground electrical traces located at the top and bottom portions of the piece.
  • the interposer can further comprise a dielectric layer 656 disposed thereon a portion of the top surface of the interposer about the central opening of the piece.
  • the dielectric layer defines two arrays of staggered wells 660, one array being on each side of the central opening and extending along an axis parallel to the longitudinal axis of the interposer. Each well is in communication with an electrical trace of the interposer.
  • a solder paste 662 can be used to fill each of the wells in the dielectric layer such that, when a PZT stack is mounted thereon the dielectric layer and heat is applied, the solder melts to form the desired electrical continuity between the individual element signal electrodes and the individual trances on the interposer. Ih use, the well helps to retain the solder within the confines of the well.
  • Figure 27A is a top plan view of the PZT stack shown in Figure 25 A mounted thereon the dielectric layer of the interposer shown in Figure 26A.
  • Figure 27B provides a top plan view of the PZT stack shown in Figures 25A mounted thereon the dielectric layer and interposer shown in Figure 26 A, in which the PZT stack is shown as a transparency. This provides an illustration of the mounting relationship between the PZT stack and the underlying dielectric layer/interposer, the solder paste mounted therebetween forming an electrical connection between the respective element signal electrodes and the electrical traces on the interposer.
  • FIG. 28A-28C a schematic top plan view of an exemplary circuit board 680 for mounting the transducer of the present invention thereto is illustrated.
  • the circuit board comprising a bottom copper ground layer and a Kapton layer mounted to the upper surface of the bottom copper ground layer.
  • the circuit board can also comprise a plurality on underlying substantially rigid support structures, hi this aspect, a central portion surrounding a central opening in the circuit board has a rigid support structure mounted to the bottom surface of the bottom copper ground layer.
  • portions of the circuit board to which the connectors will be attached also have rigid support structures mounted to the bottom surface of the bottom copper ground layer.
  • the circuit board further comprise a plurality of board electrical traces formed thereon the top surface of the Kapton layer, each board electrical trace having a proximal end adapted to couple to an electrical trace of the transducer and a distal end adapted to couple to a connector, such as, for example, a cable for communication of signals therethrough.
  • a connector such as, for example, a cable for communication of signals therethrough.
  • the length of the circuit forming each electrical trace has a substantially constant impedance.
  • the circuit board also comprises a plurality of vias that pass though the Kapton layer and are in communication with the underlying ground layer so that signal return paths, or signal ground paths, can be formed. Further, the circuit board comprises a plurality of ground pins. Each ground pin has a proximal end that is coupled to the ground layer of the circuit board (passing through one of the vias in the Kapton layer) and a distal end that is adapted to couple to the connector.
  • Figure 28B is a top plan view of an exemplary circuit board for mounting of an exemplary 256-element array having a 75 micron pitch and
  • Figure 28C is a top plan view of the vias of the circuit board of Figure 28B that are in communication with an underlying ground layer of the circuit board.
  • Figure 28B also defines bores in the circuit board that are sized and shaped to accept pins of the connectors such that, when the connector is mounted thereon portions of the circuit board, there will be correct registration of the respective electrical traces and ground pins with the connector.
  • Figure 29 illustrates a partial enlarged top plan view of a portion of the exemplified circuit board showing, in Region A, the ground electrode layer 600 of the transducer being wire bonded to the ground electrical trace 654 on the interposer 650, which is, in turn, wire bonded to the ground pads 682 of the circuit board.
  • An enlarged exemplary connection of the ground electrode layer of the transducer is shown in Figure 3OA.
  • the ground pads of the circuit board are in communication, through vias in the Kapton layer, with the underlying bottom copper ground layer.
  • the individual electrical traces 610 of the transducer are wire bonded to individual board electrical traces 684 of the circuit board.
  • the central opening 686 of the circuit board 680 underlies the backing material of the transducer.
  • the present invention contemplates mounting a transducer, as exemplarily shown in Figure 25A, that does not include an interposer to the substantially rigid central portion of the circuit board.
  • This embodiment allows for the elimination of most of the wire bonds.
  • the exemplified PZT stack is surface mounted onto the circuit board directly by, for example, means of a series of ball bumps 690, formed, for example and without limitation, from gold.
  • the exemplified gold ball bump means is a conventional surface mounting technique and represents another type of surface mounting techniques consistent with the previously mentioned surface mounting techniques.
  • the rigidized central portion of the circuit board can optionally provide the same functionality as the interposer.
  • Figure 34A shows the ground electrode layer of the transducer (without interposer) wire bonded to the ground pads of the circuit board.
  • the wires can be covered with a protective glob top coating that protects the wire bonds.
  • a glob top dam that prevents the glob top material from flowing beyond the vicinity of the wire bonds can also be used. It is contemplated that the glob top dam can remain permanently or it can be removed once the glob top material has been properly cured.
  • the gold ball bumps are applied directly onto the circuit board.
  • Each ball bump is positioned in communication with one electrical trace of the circuit board.
  • the PZT stack is secured to the circuit board by, for example and not meant to be limiting, a) use of an underfill, such as a UV curable; b) use of an ACF tape; c) by electroplating pure Indium solder onto the electrodes of either the PZT or the circuit board and reflowing the Indium to provide a solder joint between the signal electrode on the PZT and the gold ball bump on the circuit board, and the like.
  • the exemplified transducer assembly would include an interposer 800 having an upper surface 802 and a lower surface 804 that is configured to mount to the top surface of the uppermost matching layer of the underlying PZT composite assembly.
  • the interposer further defines at least one opening 810 that extends therethrough the interposer from the upper surface to the lower surface.
  • the walls 812 that form the opening in the interposer can have a tapered shape in cross-section such that the cross-sectional area of the opening defined in the upper surface is greater than the cross-sectional area of the opening defined in the lower surface of the interposer.
  • the opening in the interposer is configured to substantially surround the active area of the underlying PZT composite assembly.
  • the opening has a longitudinal length dimension that is greater than the distance between the first and last array elements to be defined therein the PZT composite assembly and a width dimension that is greater than the length of the first kerf slot.
  • the interposer can be formed of a hard ceramic, such as, for example and not meant to be limiting, Alumina.
  • the peripheral edge 815 of the interposer can define at least one alignment means for aiding in the alignment of the interposer with an underlying PZT composite assembly.
  • each alignment means can comprise a notch 817 defined in the peripheral edge of the interposer.
  • pairs of notches 817A, 817B could be defined on the peripheral edge adjacent each of the corners of the interposer.
  • the interposer can have alignment means, such as, for example, alignment features that are provided on the lower surface of the interposer to aid in the alignment of the interposer to the underlying PZT stack.
  • alignment features can be provided on the upper surface of the interposer to aid in the alignment of a dicing assembly.
  • the PZT composite assembly 820 can comprise a commercially available PZT layer, or alternatively any of the PZT layer composite assemblies described above.
  • the PZT layer has an electrode layer 821 deposited on a top substantially planar surface of the PZT layer.
  • the electrode layer will act as the ground electrode for the resulting array transducer.
  • the PZT stack has a standard size of 2.625" X 2.625". It is not important what the thickness of the PZT layer is at this stage of the assembly.
  • each trough, bore, or vias of the pair of troughs, bores, or vias is positioned substantially parallel to each other and are spaced a predetermined distance, hi the illustrated example, two pairs of troughs are formed on the PZT composite assembly.
  • the formed pairs of troughs, bores, or vias are filed with a conductive material, such as, for example, silver epoxy, solder and the like, and, as one skilled in the art will appreciate, the filed troughs, bores, or vias form a pair of ground bus lines that are in electrical
  • At least one matching layer 830 is mounted onto a portion of the upper surface of the electrode layer.
  • the matching layer substantially covers the desired working surface of the electrode layer, i.e., the matching layer is mounted onto the upper surface of the electrode layer such that the portions of the electrode layer that will form a portion of the completed array assembly are covered.
  • the at least one matching layer can subsequently be lapped, if required, to a desired thickness.
  • the bottom surface of the interposer can subsequently be mounted to the top surface of the uppermost matching layer.
  • a conventional adhesive such as, without limitation, epoxy or an adhesive film, can be used to connect the interposer to the matching layer. It is preferred that, when the interposer is connected to the underlying matching layer, none of the adhesive is present on the portions of the matching layer that are exposed via the openings in the interposer.
  • the alignment means of the interposer can be used to aid in the positioning of the built up composite assembly and the interposer by, in this example, positioning the peripheral edges of the built up composite assembly such that they are substantially co-planar to the respective edges of the notches in the peripheral edge of the interposer.
  • the lower surface of the PZT layer is conventionally ground or lapped down to a desired thickness. The thickness can be measured with respect to the lower surface of the exposed portions of the attached interposer.
  • the lower surface of the PZT layer is lapped until the ground bus line 824 is exposed on the lower, lapped, surface of the PZT layer.
  • this aspect acts to communicate the ground from the upper surface of the PZT layer to the lower surface of the PZT layer.
  • the opening in the interposer can be temporarily filled to increase the structurally rigidity of the built up composite assembly as the lower surface of PZT layer is being lapped tQ the desired thickness.
  • the material that filled the opening of the interposer can be removed.
  • a dielectric layer 840 is conventionally deposited onto the lapped lower surface of the PZT layer.
  • the dielectric layer can be a photoresist that can be spin coated unto the lapped surface with a spin speed and spin cycle suitable for creating a dielectric layer of a desired thickness.
  • the dielectric layer can then be patterned as desired by conventional photolithography techniques.
  • the PZT stack, prior to lapping or grinding could be diced to a controlled depth and filled with epoxy such that, upon lapping of the PZT stack, the epoxy itself would form the dielectric layer.
  • the methodology would result in a substantially planar bottom surface as opposed to the initial method that would result in a dielectric step.
  • the two methods result in different surface morphology, they produce a PZT stack with a dielectric layer that performs the identical function.
  • a pair of opposing elongate strips of dielectric material 840A, 840B will be defined for each array transponder being formed in the assembly process.
  • the pairs of opposing elongate dielectric strips are positioned substantially parallel to each other and extend therebetween the exposed ends on the ground bus line on the lower surface of the PZT layer.
  • the dielectric layer is deposited such that at least a portion of the ground bus line on the lower surface of the built up composite assembly is exposed.
  • the signal electrodes 850 are formed on the lower surface of the built up composite assembly. As noted above for the previous embodiments, a signal trace or electrode is provided for each of the array element of the transducer. Further, each signal trace 850 has a portion that is connected directly to the lower surface of the PZT layer and a portion that is deposited on the dielectric layer. In one aspect, a portion of the signal trace that is deposited on the dielectric layer forms a bond pad 852.
  • the signal electrodes can be formed by any conventional means such as, for example and not meant to be limiting, sputtering to a desired depth and patterning via laser machining and/or photolithography.
  • the exposed portion of the matching layer therein the opening on the interposer can be covered with a shield electrode 860.
  • at least the wall portions of the opening can also be covered to form a portion of the shield electrode.
  • the shield electrode could extend onto the upper surface of the interposer and substantially surrounds the opening. It will be appreciated that the shield electrode is not in communication with the ground of the formed transducer, but rather is configured to be placed into electrical communication with a system or chassis ground (not shown) once the array is fully packaged into a housing with a medical cable assembly.
  • the built up composite assembly can be diced to a desired size.
  • the built up composite assembly can be diced into eight separate composite assemblies that can be subsequently formed into the eight operational
  • transducers Ih this aspect, if a conventional dicing saw is used, it is preferred that the dicing saw cut from the top of the composite assembly.
  • the first and second kerfs slots are formed in the composite assemblies to define the array elements of the transducer.
  • the first and second kerf slots can be formed as described above for the other embodiments.
  • some backing material can be applied to the lower surface of the PZT layer during the process of forming the first and second kerf slots.
  • the sequence of application of backing and of formation of the kerf slots can be performed in several different combinations to achieve the array structures that are illustrated and described herein. Two exemplary examples are described below. One skilled in the art would appreciate that several more combinations within the scope and spirit of this invention are possible.
  • laser alignment features can be laser cut from the bottom side of the PZT surface through the entire thickness of the stack in an area adjacent to the signal electrode pattern that is not part of the active array.
  • a backing can be subsequently applied to the bottom surface of the PZT that substantially covers the gap between the dielectric layers but leaves the bond pads of the signal electrodes exposed.
  • the composite assembly can be flipped over and the laser can be registered to the formed alignment features. After registration, the first and second kerf slots can be laser machined to the desired depth.
  • laser alignment features can be laser cut from the bottom side of the PZT surface through the entire thickness of the stack in an area adjacent to the signal electrode pattern that is not part of the array.
  • a portion of the first kerf slots are laser machined from the bottom surface of the PZT to a depth that is less than the full thickness of the composite PZT stack such that the first kerf slots do not break the top surface of the composite PZT stack.
  • a thin layer of backing material can then be applied to the bottom surface of the PZT that substantially covers the gap between the dielectric layers but leaves the bond pads exposed.
  • the composite assembly can be flipped over to allow the laser to be registered to the alignment features. After registration, both the first kerf and second kerf slots can be laser machined.
  • the first kerf slots were already partially formed from the bottom side, these kerfs exhibit less taper, which is intrinsic to laser machining.
  • the second kerf slots may extend to a different depth than the first kerf slots.
  • the first and second kerfs can be machined to their desired depths by the use of a laser.
  • the first kerfs can extend through the shield electrode layer, through the at least one matching layer, through the ground electrode layer, and into a least a portion of the underlying PZT layer.
  • the first and second kerfs define the array elements as described above.
  • the portions of the exposed signal traces that are positioned thereon the lower surface of the PZT layer can be covered by a backing layer 870.
  • the applied backing does not extend thereon the dielectric layer and it is more preferred that the applied backing does not cover any of the bond pads of the signal traces.
  • a substantially rigid substrate 900 is provided that defines an opening configured for receipt of the transponder.
  • the substrate can be formed of a conventional circuit board material such as, for example and not meant to be limiting, FR4 and the like.
  • the opposing ends of the flex circuit which are exemplarily described above, are attached to the substrate on opposing sides of the opening in the substrate and define a pocket 902 for operative receipt of the transponder.
  • a portion of the upper surface of the interposer of the transponder is mounted therein the formed pocket of the circuit.
  • the signal pads and ground pads of the flex circuit and the bond pads and ground bus pads of the transponder are visible and are readily accessible from that elevational perspective.
  • the relative position of the respective pads and grounds allows for the use of wire bonding to form the signal and ground wire bonds. After the wire bonding is completed, all of the bonds are covered with a conventional glob top material 904 to protect the integrity of the wire bonds.
  • a ring enclosure 910 is mounted to a portion of the flex circuit.
  • the mounted ring enclosure is configured to surround the array transducer and the glob top signal and ground wire bonds.
  • the ring can then be filed with a backing material 912 to provide a backing layer of adequate thickness behind the formed PZT stack and to further protect the assembled transducer.
  • the added backing can be made of the identical composition to the existing backing already in contact to the PZT stack.
  • a lens if used and not otherwise already mounted, can be mounted to a portion of the shield electrode that overlies the matching layer within the opening defined in the interposer.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)

Abstract

La présente invention concerne un transducteur ultrasonique qui comprend une pile ayant une première face, une seconde face opposée et un axe longitudinal se prolongeant entre deux. La pile comprend une pluralité de couches, chaque couche ayant une surface supérieure et une surface inférieure opposée ; la pluralité de couches de la pile comprend une couche piézoélectrique sans pole supérieure, une couche piézoélectrique avec pole, inférieure et sous-jacente, et une couche diélectrique. La couche diélectrique est reliée à la couche piézoélectrique et définit une ouverture se prolongeant dans une seconde longueur prédéterminée dans une direction sensiblement parallèle à l'axe de la pile. Une pluralité de premières entailles est définie dans la pile, chaque entaille s'étendant sur une profondeur prédéterminée dans la pile via la couche piézoélectrique supérieure et dans la couche piézoélectrique inférieure et sur une première longueur prédéterminée dans une direction sensiblement parallèle à l'axe.
PCT/US2006/042889 2005-11-02 2006-11-02 Transducteur ultrasonique en reseau WO2007067282A2 (fr)

Priority Applications (3)

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JP2008539043A JP4807761B2 (ja) 2005-11-02 2006-11-02 アレイ超音波トランスデューサ
CA002627927A CA2627927A1 (fr) 2005-11-02 2006-11-02 Transducteur ultrasonique en reseau
EP06827415A EP1951445A2 (fr) 2005-11-02 2006-11-02 Transducteur ultrasonique en reseau

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US73309105P 2005-11-02 2005-11-02
US60/733,091 2005-11-02

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WO2007067282A3 WO2007067282A3 (fr) 2007-08-16
WO2007067282A8 WO2007067282A8 (fr) 2008-10-02

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WO2017069701A1 (fr) * 2015-10-21 2017-04-27 Agency For Science, Technology And Research Transducteur d'ultrasons et son procédé de fabrication
US9935254B2 (en) 2008-09-18 2018-04-03 Fujifilm Sonosite, Inc. Methods for manufacturing ultrasound transducers and other components
US10596597B2 (en) 2008-09-18 2020-03-24 Fujifilm Sonosite, Inc. Methods for manufacturing ultrasound transducers and other components
EP3918886A4 (fr) * 2019-01-29 2022-11-02 Butterfly Network, Inc. Structures d'emballage et procédés d'encapsulation pour dispositifs à ultrasons sur puce

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CA2628100C (fr) 2005-11-02 2016-08-23 Visualsonics Inc. Systeme ultrasons haute frequence en reseau
US8207652B2 (en) * 2009-06-16 2012-06-26 General Electric Company Ultrasound transducer with improved acoustic performance
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JP5695350B2 (ja) * 2010-06-10 2015-04-01 国立大学法人東北大学 高周波振動圧電素子、超音波センサおよび高周波振動圧電素子の製造方法
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CN101405090A (zh) 2009-04-08
JP4807761B2 (ja) 2011-11-02

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