Acoustic stack for an ultrasonic transducer and method of manufacturing thereof

Abstract

An acoustic stack for an ultrasonic transducer and a method of manufacturing the same are provided. In one example, an acoustic stack (100) includes a piezoelectric layer (110), a matching layer (120) disposed directly on a first side of the piezoelectric layer (110), and a de-matching layer (130) disposed directly on a second side of the piezoelectric layer (110), the first side opposite the second side. One or more layers can be deposited via thermal spray deposition.

Description

Technical Field

[0001] The embodiments of the subject matter disclosed herein relate to ultrasonic transducers, and more specifically, to acoustic stacks for ultrasonic transducers and methods of manufacturing thereof. Background Technology

[0002] Ultrasound imaging systems typically include ultrasound transducers that perform various ultrasound scans. An ultrasound transducer comprises one or more acoustic stacks. The acoustic stacks emit ultrasound energy and receive ultrasound signals based on the reflected ultrasound energy. The ultrasound signals received by the acoustic stacks are used to generate images of one or more anatomical structures within the patient's body.

[0003] The acoustic stack in an ultrasonic transducer typically includes a piezoelectric material that changes shape in response to an applied voltage. Changing the potential applied to the piezoelectric material generates ultrasonic energy. Summary of the Invention

[0004] One embodiment relates to an acoustic stack for an ultrasonic transducer. The acoustic stack may include a piezoelectric layer, a matching layer disposed directly on a first side of the piezoelectric layer, and a dematching layer disposed directly on a second side of the piezoelectric layer, the first side being opposite to the second side.

[0005] On the other hand, a method is disclosed. This method involves depositing a matching layer on a first side of a piezoelectric layer via thermal spraying.

[0006] On the other hand, a method for fabricating an acoustic stack is disclosed. The method includes plasma-spraying deposition of a first layer on a substrate, the first layer comprising a composite material including aluminum, silicon, and graphite; disposing a flexible circuit on the first layer; sputtering a second layer on the flexible circuit, the second layer comprising gold; electroplating a third layer on the second layer, the third layer comprising nickel; thermally-spraying deposition of a fourth layer on the third layer, the fourth layer comprising tungsten carbide; electroplating a fifth layer on the fourth layer, the fifth layer comprising nickel; thermally-spraying deposition of a sixth layer on the fifth layer, the sixth layer comprising a piezoelectric material; plasma-spraying deposition of a seventh layer on the sixth layer, the seventh layer comprising a composite material including aluminum, silicon, and graphite; and plasma-spraying deposition of an eighth layer on the seventh layer, the eighth layer comprising polymethyl methacrylate.

[0007] This overview is merely illustrative and is not intended to be limiting in any way. Other aspects, inventive features, and advantages of the apparatus or process described herein will become apparent from the detailed description set forth herein in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements. Attached Figure Description

[0008] Figure 1 This is a cross-sectional view of the acoustic stack used for ultrasonic transducers.

[0009] Figure 2 This is a cross-sectional view of another acoustic stack used for ultrasonic transducers.

[0010] Figure 3 It is used for preparation Figure 1 A schematic diagram of the acoustic stacking process.

[0011] Figure 4 It is used for preparation Figure 1 A schematic diagram of another process of acoustic stacking in the process.

[0012] Figure 5 It is used for preparation Figure 2 A schematic diagram of the acoustic stacking process.

[0013] Figure 6 It is used for preparation Figure 2 A schematic diagram of another process of acoustic stacking in the process.

[0014] Figure 7 This is a schematic diagram of the process used to prepare cut acoustic stacks.

[0015] Figure 8 This is a schematic diagram of another process used to prepare cut acoustic stacks.

[0016] Figure 9 This is a schematic diagram of another process used to prepare cut acoustic stacks.

[0017] Figure 10 This is a cross-sectional view of an ultrasonic probe with acoustic stacking. Detailed Implementation

[0018] Referring generally to the accompanying drawings, an acoustic stack for an ultrasonic transducer is disclosed. The acoustic stack includes a piezoelectric layer, a matching layer disposed directly on one side of the piezoelectric layer, and a dematching layer disposed directly on the opposite side of the piezoelectric layer, opposite to the side with the matching layer.

[0019] Acoustic stacks are typically fabricated by bonding matching and dematching layers to a piezoelectric layer using an adhesive (e.g., epoxy resin), which may be sintered. Generally, for ease of handling and, if applicable, to accommodate sintering, thicker layers of layer material are bonded to the piezoelectric layer, and these layers are then ground or polished to a predetermined thickness to form the matching and dematching layers useful in the acoustic stack. Good matching characteristics can be achieved if the thickness of the gradient matching layer is in the range of about a quarter wavelength to about two wavelengths. For example, in the case of bonding the matching layer to the piezoelectric layer using a sintering method, the matching layer may have a thickness of about 2.5 mm or more to maintain the flatness of the layer during sintering, and the matching layer may be ground to a thickness of about 50 μm to about 250 μm. Given the stringent tolerances required for effective acoustic stacks, the grinding or polishing process complicates the large-scale fabrication of acoustic stacks. In particular, these processes can consume significant amounts of water and generate environmental waste, thus increasing cost and complexity.

[0020] To address these issues, this paper discloses acoustic stacks for ultrasonic transducers and methods for fabricating these acoustic stacks using a layer deposition process. This process deposits the layers of the acoustic stack directly onto each other, allowing the layers to be directly positioned without the use of adhesives and without the need for sintering between the layers. Avoiding the use of adhesives improves the performance of the acoustic stack by reducing acoustic impedance mismatch, thereby improving resolution and sensitivity. Furthermore, these processes can precisely deposit micron-scale layers, avoiding or substantially reducing the need for grinding or polishing to produce layers of predetermined thickness, thus avoiding the manufacturing complexities associated with grinding or polishing.

[0021] Layer deposition processes used to form the layers of the acoustic stack disclosed herein include thermal spraying deposition, which includes plasma spraying, detonation spraying, arc spraying, flame spraying, high-velocity oxygen fuel (HVOF) spraying, high-velocity air fuel (HVAF) spraying, and warm spraying. Layer deposition processes may also include cold spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), or electroplating. For example, a seed layer can be formed using spraying deposition, PVD, CVD, or electroplating methods to facilitate the formation of matching and dematching layers in thermal spraying deposition.

[0022] Figure 1This is a cross-sectional view of an acoustic stack 100 for an ultrasonic transducer. The acoustic stack 100 includes a piezoelectric layer 110, wherein a matching layer 120 is disposed on one side of the piezoelectric layer 110, and a dematching layer 130 is disposed directly on the opposite side of the piezoelectric layer 110. The matching layer 120, the dematching layer 130, and the optional piezoelectric layer 110 are deposited using the processes disclosed herein. The acoustic stack 100 may be adhesive-free between the different layers. Instead, the matching layer 120 and the dematching layer 130 may be mechanically and / or chemically bonded to the piezoelectric layer 110, wherein mechanical bonding is achieved by a layer deposition process for forming the acoustic stack layers.

[0023] Figure 2 This is a cross-sectional view of another acoustic stack 200 used for an ultrasonic transducer. The acoustic stack 200 includes a piezoelectric layer 210, a first matching layer 220 disposed on one side of the piezoelectric layer 210, and a dematching layer 230 disposed on the other side of the piezoelectric layer 210. A matching seed layer 222 is located between the piezoelectric layer 210 and the first matching layer 220 to promote the deposition of the first matching layer. A second matching layer 224 is disposed on the first matching layer 220. A dematching seed layer 232 is located between the piezoelectric layer 210 and the dematching layer 230 to promote the deposition of the dematching layer 230. A conductive metal layer 244 is disposed on the dematching layer 230, with the conductive metal seed layer 242 located between them. A flexible circuit 240 is disposed on the conductive metal layer 244. The flexible circuit 240 is disposed on a substrate 250.

[0024] In any embodiment, the piezoelectric layer may be configured to generate acoustic energy and transmit it into the body of a patient (not shown), and to receive backscattered acoustic signals from the patient to form and display images. The piezoelectric layer typically has an acoustic impedance of about 37 M ayls, while human tissue typically has an acoustic impedance of about 1.5 M ayls. As is known in the art, the piezoelectric layer may include electrodes on a top surface and a bottom surface.

[0025] The piezoelectric layer can be formed of piezoelectric ceramics, piezoelectric composites, piezoelectric single crystals, or piezoelectric polymers. Examples of piezoelectric ceramic materials include, but are not limited to, lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), magnesium-doped PIN-PMN-PT, lead magnesium niobate, lead titanate, lead indium niobate, barium titanate, lithium niobate, lithium tantalate, aluminum scandium nitride, silicon carbide, or combinations of two or more of these. The piezoelectric layer may comprise multiple layers of the aforementioned materials. The piezoelectric layer may comprise multiple layers of the same material, or it may comprise multiple layers of different materials.

[0026] The piezoelectric layer may have a thickness of about 0.01 mm to about 2 mm. Piezoelectric layers of different thicknesses can be used for low-frequency (e.g., about 1 MHz to about 5 MHz) transducers and high-frequency (e.g., about 5 MHz to about 10 MHz) transducers. Acoustic stacks for low-frequency transducers may include piezoelectric layers with a thickness of about 0.5 mm to about 2 mm (e.g., about 0.5 mm to about 1 mm, about 0.5 mm, about 0.6 mm, about 0.7 mm, about 0.8 mm, about 0.9 mm, or about 1 mm). Acoustic stacks for high-frequency transducers may include a piezoelectric layer having a thickness of about 0.01 mm to about 0.5 mm (e.g., about 0.02 mm to about 0.5 mm, about 0.05 mm to about 0.5 mm, or about 0.1 mm to about 0.5 mm, about 0.01 mm, about 0.02 mm, about 0.03 mm, about 0.04 mm, about 0.05 mm, about 0.06 mm, about 0.07 mm, about 0.08 mm, about 0.09 mm, about 0.1 mm, about 0.2 mm, about 0.3 mm, about 0.4 mm, or about 0.5 mm).

[0027] In any embodiment, one or more matching layers facilitate matching of impedance differences that may exist between the piezoelectric layer and the patient. Any number of matching layers can be provided. Each matching layer can have any acoustic impedance value, such as, but not limited to, between about 2 M Rayls and about 15 M Rayls and / or less than about 10 M Rayls. In some embodiments, each matching layer has an acoustic impedance less than that of the piezoelectric layer. In some embodiments, multiple matching layers are provided such that the acoustic impedance from the piezoelectric layer gradually decreases. For example, in some embodiments, three matching layers are provided, where the matching layer closest to the piezoelectric layer is about 15 M Rayls, the next matching layer is about 8 M Rayls, and the matching layer furthest from the piezoelectric layer is about 3 M Rayls. In some embodiments, one or more matching layers include an acoustic impedance gradient.

[0028] Each matching layer may be conductive or non-conductive. When a matching layer is non-conductive, it may include a conductive film layer thereon (not shown). As described herein, one or more matching layers (and / or conductive film layers thereon) may provide an electrical ground connection between the matching layer and the corresponding electrode of the flexible circuit.

[0029] One or more matching layers may be formed of graphite, aluminum, silicon, polymers, or combinations thereof. One or more matching layers may include metal-silicon-carbon composites (e.g., aluminum-silicon-graphite composites, aluminum-silicon-polymer composites, and combinations thereof), polymers, and combinations thereof. Exemplary polymers that may be present in the matching layers include, but are not limited to, polymethyl methacrylate (PMMA), polyester, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), and mixtures or copolymers of any two or more thereof. For example, the matching layer may include one or more layers formed of aluminum-silicon graphite disposed closer to the piezoelectric layer, and one or more polymer layers (e.g., polyester or PMMA) disposed on an aluminum-silicon graphite layer farther from the piezoelectric layer. For example, the matching layer may be formed of two layers, one comprising graphite, aluminum, silicon, polymers, or combinations thereof (e.g., aluminum-silicon-carbon composites), and the second comprising a polymer. As another example, the matching layer may be formed of two layers, one comprising an aluminum-silicon-graphite composite and the other comprising an aluminum-silicon-polymer composite.

[0030] The aluminum-silicon-carbon composite material may contain about 1% to about 20% silicon relative to the total weight of the composite material, for example about 1% to about 10% by weight, about 2% to about 8% by weight, about 1% by weight, about 2% by weight, about 3% by weight, about 4% by weight, about 5% by weight, about 6% by weight, about 7% by weight, about 8% by weight, about 9% by weight, about 10% by weight, about 15% by weight, or about 20% by weight.

[0031] The aluminum-silicon-carbon composite material may contain about 40% to about 80% aluminum relative to the total weight of the composite material, for example about 45% to about 75%, about 50% to about 70%, about 50% to about 60%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, or about 80%.

[0032] The aluminum-silicon-graphite composite material may contain about 10% to about 60% graphite relative to the total weight of the composite material, for example, about 20% to about 50% by weight, about 20% to about 30% by weight, about 40% to about 50% by weight, about 20% by weight, about 22% by weight, about 24% by weight, about 26% by weight, about 28% by weight, about 30% by weight, about 32% by weight, about 34% by weight, about 36% by weight, about 38% by weight, about 40% by weight, about 42% by weight, about 44% by weight, about 46% by weight, about 48% by weight, about 50% by weight, about 52% by weight, about 54% by weight, about 56% by weight, about 58% by weight, or about 60% by weight ± 1% by weight.

[0033] Aluminosilicate graphite can have a gradient composition, wherein the weight percentage of graphite gradually increases with distance from the piezoelectric layer, resulting in a gradual decrease in acoustic impedance from the piezoelectric layer. For example, a gradient composite may contain about 10% to about 30% of graphite on the side of the composite closer to the piezoelectric layer and about 35% to about 55% of graphite on the side of the composite farther from the piezoelectric layer, wherein the graphite concentration has a gradient variation (e.g., a linear gradient or a polynomial gradient) across the thickness of the layer.

[0034] The aluminum-silicon polymer composite material may contain about 10% to about 60% of polymer relative to the total weight of the composite material, for example about 20% to about 50% by weight, about 20% to about 30% by weight, about 40% to about 50% by weight, about 20% by weight, about 22% by weight, about 24% by weight, about 26% by weight, about 28% by weight, about 30% by weight, about 32% by weight, about 34% by weight, about 36% by weight, about 38% by weight, about 40% by weight, about 42% by weight, about 44% by weight, about 46% by weight, about 48% by weight, about 50% by weight, about 52% by weight, about 54% by weight, about 56% by weight, about 58% by weight, or about 60% by weight ± 1% by weight.

[0035] Each matching layer can have any thickness, and matching layers can have any combination of thicknesses. Examples of combination thicknesses for matching layers include, but are not limited to, thicknesses approximately relative to the wavelength (λ) at a resonant frequency of about λ / k, where k is 1, 2, or 4. Depending on the resonant frequency, the combination thickness of the matching layers can be from about 1 μm to about 1000 μm (e.g., from about 2 μm to about 20 μm, from about 5 μm to about 500 μm, from about 10 μm to about 200 μm, or from about 20 μm to about 100 μm). Any matching layer can have a thickness from about 1 μm to about 500 μm (e.g., from about 2 μm to about 20 μm, from about 4 μm to about 100 μm, from about 10 μm to about 50 μm, or from about 20 μm to about 40 μm).

[0036] A matching seed layer may exist between the piezoelectric layer and the matching layer to facilitate the deposition of the first matching layer on the piezoelectric layer, or vice versa. The seed layer may provide nucleation sites for the deposition of the matching layer on the piezoelectric layer or for the deposition of the piezoelectric layer on the matching layer. The seed layer may be formed of gold, nickel, aluminum, alumina, tungsten carbide, graphite, silicon, silicon oxide, or any combination of two or more of these. For example, the seed layer may be a silicon-aluminum-graphite composite material. The seed layer may be a continuous or discontinuous layer, depending on the layer thickness and the deposition type used to form the layer. The seed layer may have a thickness of about 0.1 μm to about 10 μm (e.g., 0.1 μm to about 5 μm, about 0.3 μm to about 5 μm, or about 0.5 μm to about 2 μm).

[0037] In cases where the acoustic stack comprises more than one matching layer, the acoustic stack may include additional seed layers between the matching layers. The additional seed layers may be formed of gold, nickel, aluminum, alumina, tungsten carbide, graphite, silicon, silicon oxide, or any combination of two or more of these. For example, the additional seed layer may be a silicon-aluminum-graphite composite material. For example, the additional seed layer may be a continuous or discontinuous layer, depending on the layer thickness and the deposition type used for the deposited layer. The seed layer may have a thickness of about 0.1 μm to about 10 μm (e.g., 0.1 μm to about 5 μm, about 0.3 μm to about 5 μm, or about 0.5 μm to about 2 μm).

[0038] A dematching seed layer may be present between the piezoelectric layer and the dematching layer to facilitate the deposition of either the dematching layer or the piezoelectric layer. The seed layer may provide nucleation sites for the deposition of the dematching layer on the piezoelectric layer or for the deposition of the piezoelectric layer on the dematching layer. The seed layer may be formed of gold, nickel, aluminum, tungsten carbide, silicon, alumina, silicon oxide, or any combination of two or more of these. The seed layer may be a continuous or discontinuous layer, depending on the layer thickness and the deposition type used to form the layer. The seed layer may have a thickness of about 0.1 μm to about 10 μm (e.g., 0.1 μm to about 5 μm, about 0.3 μm to about 5 μm, or about 0.5 μm to about 2 μm).

[0039] In any implementation, the acoustic stack may include one or more dematching layers. The dematching layer may be a layer with a higher acoustic impedance than the piezoelectric layer, disposed between the piezoelectric layer and the flexible circuit. The dematching layer reduces acoustic artifacts. For example, the acoustic impedance of the piezoelectric layer may be in the range of about 3 MRayls to about 35 MRayls, while the acoustic impedance of the dematching layer may be in the range of about 60 MRayls to about 100 MRayls (e.g., above 70 MRayls). The dematching layer may be formed of tungsten carbide, tungsten, tantalum, or other materials with similar acoustic impedance, or any combination of two or more of these. The dematching layer acts as an acoustic impedance transducer, significantly increasing the effective acoustic impedance presented (or experienced by) the back side of the piezoelectric layer to a value substantially greater than the impedance of the piezoelectric layer. Therefore, most of the acoustic energy is reflected from the front side of the piezoelectric layer.

[0040] The dematching layer may include one or more layers. The combined thickness of the dematching layers may be from about 1 μm to about 500 μm (e.g., from about 2 μm to about 20 μm, from about 4 μm to about 100 μm, from about 10 μm to about 50 μm, from about 20 μm to about 40 μm, from about 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm or 500 μm). Any dematching layer may have a thickness of about 1 μm to about 500 μm (e.g., about 2 μm to about 20 μm, about 4 μm to about 100 μm, about 10 μm to about 50 μm, about 20 μm to about 40 μm, about 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm or 500 μm).

[0041] The acoustic stack may include a conductive metal layer disposed between the dematching layer and the flexible circuitry. The conductive metal layer may be an electrode. During operation of the ultrasonic transducer, electrical waveform pulses may be applied to the electrodes, thereby inducing mechanical changes in the piezoelectric layer and generating ultrasonic waves. Non-limiting examples of metals that may be used to form the conductive metal layer include gold, platinum, silver, nickel, aluminum, copper, steel, or any combination of two or more of these. The conductive metal layer may have a thickness of about 0.05 mm to about 2 mm (e.g., about 0.05 mm to about 1 mm, about 0.05 mm, about 0.5 mm, about 0.05 mm, about 0.4 mm, about 0.05 mm, or about 0.1 mm).

[0042] The acoustic stack may include a seed layer between a conductive metal layer and a dematching layer. The seed layer may provide nucleation sites for the deposition of the dematching layer on the conductive metal layer or for the deposition of the conductive metal layer on the dematching layer. The seed layer may be formed of gold, nickel, aluminum, tungsten carbide, tungsten, silicon, silicon oxide, aluminum oxide, or any combination of two or more of these. The seed layer may be a continuous or discontinuous layer, depending on the layer thickness and the deposition type used to form the layer. The seed layer may have a thickness of about 0.1 μm to about 10 μm (e.g., 0.1 μm to about 5 μm, about 0.3 μm to about 5 μm, or about 0.5 μm to about 2 μm).

[0043] Flexible circuits can be disposed on a conductive metal layer. Flexible circuits are integrated circuits. Integrated circuits can be any type of integrated circuit, such as, but not limited to, application-specific integrated circuits (ASICs). Various components of an ultrasound system can be included within an integrated circuit. For example, an integrated circuit can include the transmitter, receiver, and beamforming electronics of an ultrasound system.

[0044] Flexible circuits can be disposed on a substrate. The substrate can facilitate the fabrication of acoustic stacks. For example, the substrate can serve as a surface on which layers of acoustic stacks are formed. The substrate can be formed from a solid material (e.g., steel, titanium, tungsten, silicon) that is stable at a temperature of at least 500°C. The substrate may include a surface layer that acts as an acoustic backing layer. The surface layer can be formed from graphite, aluminum, silicon, or a combination of two or more of these. For example, the surface layer may comprise an aluminum-silicon-graphite composite material.

[0045] Another aspect of this technology includes methods for forming acoustic stacks. These methods may use layer deposition processes, such as, but not limited to, thermal spraying deposition (e.g., plasma spraying, detonation spraying, arc spraying, flame spraying, high-velocity oxygen fuel (HVOF) spraying, high-velocity air fuel (HVAF) spraying, and warm spraying), cold spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), electroplating, and any combination of two or more thereof, to deposit the layers of the acoustic stack.

[0046] Figure 3 It is used for preparation Figure 1 A schematic diagram of the acoustic stacking process is shown. This process uses a full-stack processing method. In step 301, a dematching layer 330 is deposited on substrate 300. In step 303, a piezoelectric layer 310 is deposited on the dematching layer 330. In step 305, a matching layer 320 is deposited on the piezoelectric layer 310, thereby forming the acoustic stack. In step 307, the acoustic stack may optionally be removed from substrate 300. In other embodiments, the deposition order may be reversed, wherein the matching layer is deposited on the substrate, the piezoelectric layer is deposited on the matching layer, and the dematching layer is deposited on the piezoelectric layer.

[0047] Figure 4 It is used for preparation Figure 1 A schematic diagram of another process in the acoustic stacking. This process uses a front-end and back-end processing approach. In step 401, a dematching layer 430 is deposited on piezoelectric layer 410. In step 403, a matching layer 420 is deposited on piezoelectric layer 410. In other embodiments, the order may be reversed, wherein the matching layer is deposited on the piezoelectric layer, and then the dematching layer is deposited on the piezoelectric layer.

[0048] Figure 5 It is used for preparation Figure 2This is a schematic diagram of the acoustic stacking process. The process uses a full-stack processing method. In step 501, a backing acoustic layer 550 is deposited on the substrate 500. In step 503, a flexible circuit 540 is formed on the backing acoustic layer 550. In step 505, a conductive metal layer 544 is deposited on the flexible circuit 540. In step 507, a dematching seed layer 542 is deposited on the conductive metal layer 544. In step 509, a dematching layer 530 is deposited on the dematching seed layer 542. In step 511, a piezoelectric seed layer 532 is deposited on the dematching layer 530. In step 513, a piezoelectric layer 510 is deposited on the piezoelectric seed layer 532. In step 515, a matching seed layer 522 is deposited on the piezoelectric layer 510. In step 517, a first matching layer 520 is deposited on the matching seed layer 522. In step 519, a second matching layer 524 is deposited on the first matching layer 520. In other embodiments, Figure 5 The depositional order can be reversed.

[0049] Figure 6 It is used for preparation Figure 2 This is a schematic diagram of another process in the acoustic stacking. This process uses front-end and back-end processing methods. In step 601, a dematching seed layer 632 is deposited on the piezoelectric layer 610. In step 603, a dematching layer 630 is deposited on the dematching seed layer 632. In step 605, a conductive seed layer 642 is deposited on the dematching layer 630. In step 607, a conductive layer 644 is deposited on the conductive seed layer 642. In step 609, a matching seed layer 622 is deposited on the surface of the piezoelectric layer 610 opposite to the surface on which the dematching seed layer 632 is disposed. In step 611, a first matching layer 620 is deposited on the matching seed layer 622. In step 613, a second matching layer 624 is deposited on the first matching layer 620. In step 615, a flexible circuit 640 is disposed on the conductive layer 644. In step 617, a backing acoustic layer 650 is deposited on the flexible circuit 640. In other embodiments, Figure 6 The deposition order can be changed; for example, the matching layer can be deposited before the dematching layer.

[0050] In any embodiment of the process disclosed herein, one or more seed layers may or may not be deposited to facilitate the deposition of a matching layer, a dematching layer, a piezoelectric layer, a conductive layer, and a backing acoustic layer, depending on the type of deposition used for the deposited layers and the type of material deposited.

[0051] The acoustic stack layers can be applied, deposited, or otherwise formed using any of a variety of conventional techniques, including thermal spraying deposition methods (e.g., plasma spraying, detonation spraying, arc spraying, flame spraying, high-velocity oxygen fuel (HVOF) spraying, high-velocity air fuel (HVAF) spraying, and warm spraying), cold spraying, physical vapor deposition (PVD) (e.g., electron beam physical vapor deposition (EBPVD), plasma spraying, including air plasma spraying (APS) and vacuum plasma spraying (VPS)), chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), electroplating, or combinations of such techniques, such as, for example, a combination of thermal spraying, electroplating, and PVD or CVD techniques. For example, thermal spraying can be used to form one or more of a matching layer, a dematching layer, a piezoelectric layer, a conductive layer, a backing acoustic layer, and a seed layer. Seed layers can be formed using PVD and / or CVD. In some embodiments, the conductive layer can be formed using electroplating. One advantage of these deposition techniques is their ability to deposit layers to a predetermined thickness with little or no grinding or polishing. The advantage of thermal spray deposition techniques is that layers can be deposited under ambient conditions and do not require a vacuum or explosion-proof environment. Furthermore, curing or additional process steps may not be necessary. These deposition techniques can be used to form acoustic stacks in batch or continuous processes.

[0052] Various types of thermal spraying techniques, well known to those skilled in the art, can be used to apply or deposit one or more layers of an acoustic stack. During the thermal spraying process, the substrate temperature can advantageously be maintained within a temperature range of about 20°C to about 100°C, about 20°C to about 80°C, about 20°C to about 70°C, about 20°C to about 60°C, or about 20°C to about 50°C. Thermal spraying is particularly suitable for depositing thin films with a thickness of about 10 μm to about 10 mm.

[0053] Raw materials used in thermal spraying technology may include particles having an average diameter of about 10 μm to about 500 μm, about 10 μm to about 250 μm, or about 10 μm to about 100 μm as measured by SEM. For forming an aluminum-silicon-graphite composite mating layer by thermal spraying, the raw materials may include particles of an aluminum alloy-graphite composite powder (e.g., about 30% to about 80% by weight of aluminum, about 1% to about 20% by weight of silicon, and about 10% to about 60% by weight of graphite, or an aluminum:silicon:graphite weight ratio of about 64:7:22, 61:6:24, or 42:5:45, measured by the total weight of the composite powder). To form the aluminum-silicon-polyester composite matching layer, the raw materials may include powders of an aluminum-silicon metal matrix having a polymer (e.g., polyester) embedded as a dislocation / weakening phase (e.g., about 30% to about 80% by weight of aluminum, about 1% to about 20% by weight of silicon and about 10% to about 60% by weight of graphite, or an aluminum:silicon:polymer weight ratio of about 53:7:40, measured by the total weight of the composite powder).

[0054] Plasma spraying technology involves the formation of high-temperature plasma that generates a hot plume. See, for example, the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition, Volume 15, page 255, and the references cited therein, and U.S. Patent No. 5,332,598 (Kawasaki et al.), published July 26, 1994; U.S. Patent No. 5,047,612 (Savkar et al.), published September 10, 1991; and U.S. Patent No. 4,741,286 (Itoh et al.), published May 3, 1998, which are instructive for various aspects of plasma spraying to which this document applies. Plasma spraying technology can be used to deposit, for example, metals, metal carbides, metal oxides, silicon, silicon oxide, and metal alloys. Acoustic stacking layer materials (e.g., tungsten carbide powder for depositing tungsten carbide dematching layers, or aluminum silicon graphite powder for depositing aluminum silicon graphite matching layers) are supplied to the plume, and the high-speed plume is directed toward the surface of the piezoelectric layer. The various details of this type of plasma spraying technology will be well known to those skilled in the art, including various related steps and process parameters, such as plasma spraying parameters, including spraying distance (gun to substrate), selection of spraying times, powder feed rate, particle velocity, spray gun power, plasma gas selection, oxidation control by adjusting oxide stoichiometry, deposition angle, and post-treatment of the applied coating; etc. Spray gun power can vary from about 10 kW to about 200 kW, for example, from about 40 kW to about 60 kW. The velocity of the dematched layer coating material particles flowing into the plasma plume (or plasma “jet”) is another parameter that can be precisely controlled.

[0055] In short, a typical plasma spraying system includes a plasma gun anode having a nozzle pointing toward the coated deposition surface of the substrate. The plasma gun is typically automated, for example by a robotic mechanism capable of moving the gun in various modes across the substrate surface. A plasma plume extends axially between the outlet of the plasma gun anode and the substrate surface. A powder injection device is positioned at a predetermined desired axial location between the anode and the substrate surface. In some embodiments of such systems, the powder injection device is radially spaced from the plasma plume region, and the injector tube for the powder material is positioned such that it can guide the powder into the plasma plume at a desired angle. Powder particles entrained in a carrier gas are propelled through the injector and into the plasma plume. The particles are then heated in the plasma and pushed toward the substrate. The particles melt, impact the substrate, and rapidly cool to form an acoustically stacked layer.

[0056] Arc spraying, also known as plasma-transferred arc (PTWA) thermal spraying, is a form of plasma spraying that uses conductive wires as the raw material in a plasma spraying system. As an example, arc spraying can be used to form conductive metal layers with acoustic stacks. In short, arc spraying involves a supersonic plasma jet formed by a transfer arc between a non-consumable cathode and a metal wire, which melts and atomizes the wire. The atomized wire particles are entrained in a carrier gas and propelled toward a substrate, where the particles flatten and rapidly solidify upon impact with the substrate due to their high kinetic energy, thereby forming a layer on the surface. Various details of this type of arc spraying technology will be well known to those skilled in the art, including various related steps and process parameters, such as plasma spraying parameters including the spraying distance (gun to substrate), the selection of the number of sprays, the type and thickness of the metal wire, the particle velocity, the plasma gas selection, the deposition angle, and the post-treatment of the applied coating; etc.

[0057] Suitable thermal spraying methods for depositing thin, dense, and smooth layers of acoustic stacks are high-velocity oxygen flame (HVOF) or high-velocity air fuel spray (HVAF). HVOF and HVAF can be used to deposit, for example, metals, metal carbides, metal oxides, silicon, silicon oxide, silicon carbide, and metal alloys. For example, HVOF or HVAF can be used to deposit tungsten carbide dematching layers or aluminum-silicon-graphite composite matching layers. As another example, HVOF or HVAF can be used to deposit piezoelectric layers formed from lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), magnesium-doped PIN-PMN-PT, lead magnesium niobate, lead titanate, lead indium niobate, barium titanate, lithium niobate, lithium tantalate, aluminum scandium nitride, silicon carbide, or any combination of two or more of these. The heat source can be a flame or a thermal plume controlled by the input gas, fuel, and nozzle design. Oxygen or air fuel is supplied under high pressure, causing the flame to emerge from the nozzle at supersonic speed. Guns with tapered / divergent or straight-hole nozzles can be used to apply the dematching layer. Those skilled in the art will know how to adjust these process parameters.

[0058] An improved form of HVOF that can be used to deposit layers of acoustic stacks is thermal spraying. Thermal spraying can be used to deposit raw material powders such as metals, metal carbides, metal oxides, metal alloys, and any combination of two or more of them. By injecting a low-temperature (e.g., about 20°C to about 30°C) inert gas into the combustion gas jet of the HVOF, the temperature of the propellant gas can be controlled in the general range of about 700°C to about 2000°C, allowing many powder materials to be deposited in a thermally softened state at high impact velocities. Deposition parameters, including the amount of cryogenic gas mixed into the carrier gas, the heat source, the carrier gas velocity, the nozzle design, and the stoichiometry of the powder mixture, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0059] Another suitable thermal spraying method for depositing thin, dense, and smooth layers of acoustic stacks is flame spraying. Flame spraying can be used to deposit, for example, metals, metal carbides, metal oxides, metal alloys, polymers, and any combination of two or more of these from raw material powders, rods, or wires. For example, detonation spraying can be used to deposit tungsten carbide dematching layers. In short, in this process, a combustible gas such as acetylene or propane is ignited with oxygen to generate a high-temperature flame that melts the raw material into particles. These molten particles are then advanced onto a substrate to form a robust coating. Flame parameters, including the gas-to-oxygen mixing ratio and the material feed rate, can be adjusted to alter the deposition quality and layer properties. Those skilled in the art will know how to adjust these process parameters.

[0060] Another suitable thermal spraying method for depositing thin, dense, and smooth layers of acoustic stacks is detonation spraying. Detonation spraying can be used to deposit, for example, metals, metal carbides, metal oxides, metal alloys, silicon, silicon oxide, and any combination of two or more of these from feedstock powders. For example, detonation spraying can be used to deposit tungsten carbide dematching layers. In short, in this method, a controlled explosion of a fuel-air mixture generates high-pressure and high-temperature gases that propel feedstock particles toward the substrate at supersonic speeds. See, for example, U.S. Patent No. 2,714,563 (Poorman et al.), published August 2, 1955. This process can be fine-tuned by changing parameters such as the type of fuel, the stoichiometry of the powder mixture, and the geometry of the explosion chamber. Those skilled in the art will know how to adjust these process parameters.

[0061] Cold spraying is another spraying technique that can be used to deposit layers of acoustic stacks. Cold spraying can be used to deposit raw material powders such as metals, metal carbides, metal oxides, metal alloys, polymers, and any combination of two or more of these. For example, cold spraying can be used to deposit tungsten carbide mating layers. In short, in this process, solid powder is entrained in a carrier gas and pushed towards a substrate at a speed of about 350 m / s to about 1200 m / s, where the powder plastically deforms and bonds to the substrate, forming a layer. Unlike thermal spraying, cold spraying does not involve molten powder. Similar to thermal spraying, cold spraying is particularly suitable for depositing thin films with a thickness of about 10 μm to about 10 mm. Deposition parameters, including carrier gas, gas pressure, gas temperature, particle size, raw material, and nozzle design, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0062] In addition to thermal spraying processes used for depositing layers for acoustic stacking, thin film deposition processes can also be used to deposit such layers. Thin film deposition processes are particularly suitable for depositing seed layers and / or thin, continuous films. Thin film deposition processes include, but are not limited to, physical vapor deposition (PVD) (including electron beam physical vapor deposition (EBPVD)), plasma spraying (including air plasma spraying (APS) and vacuum plasma spraying (VPS)), chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and electroplating.

[0063] PVD processes typically utilize a vacuum chamber and surface interaction with a precursor material in the vapor phase to form thin films. PVD can be used to deposit from solid precursor materials such as metals, metal carbides, metal oxides, metal alloys, silicon, silicon oxide, and any combination of two or more of these. Specifically, the source material is physically transferred to the substrate in a vacuum without any chemical reaction. Physical vapor deposition processes include electron beam physical vapor deposition (EBPVD) and plasma spraying, including air plasma spraying (APS) and vacuum plasma spraying (VPS). PVD is particularly suitable for depositing films with thicknesses from about 0.1 μm to about 50 μm. Deposition parameters, including the pressure in the vacuum chamber, the substrate temperature, the carrier gas flow rate, the precursor material, and the predetermined layer thickness, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0064] In contrast to PVD, CVD processes involve the reaction or decomposition of precursors on a substrate surface to form a thin film. Specifically, the substrate is exposed to one or more volatile precursors that react and / or decompose on the substrate surface to produce the desired deposit. CVD can be used to deposit precursor gases such as metals, metal carbides, metal oxides, metal alloys, silicon, silicon oxide, and any combination of two or more of these. Generally, CVD is particularly suitable for depositing thin films with a thickness of about 0.1 μm to about 50 μm. Deposition parameters, including the vacuum chamber, substrate temperature, carrier gas flow rate, precursor gas, and predetermined layer thickness, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0065] Alternating Layer Deposition (ALD) is a form of CVD that involves the controlled, alternating exposure of a gaseous precursor in a series of pulses, causing the precursor to react with the surface in a self-limiting manner. ALD can be used to deposit precursor gases such as metals, metal carbides, metal oxides, metal alloys, silicon, silicon oxide, silicon nitride, and any combination of two or more of these. ALD offers more precise thickness control and conformality than other CVD processes and is particularly suitable for depositing films with thicknesses from about 0.1 nm to about 100 nm. Deposition parameters, including the vacuum chamber, substrate temperature, carrier gas flow rate, precursor gas, and predetermined layer thickness, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0066] Electroplating (also known as electrodeposition) is a process of coating a metal layer onto a substrate using an electric current. Typically, electroplating involves reducing cations from a liquid electrolyte derived from a metal using an current from an external power source, with the substrate acting as the negative electrode of the electrolytic cell. Electroplating can be used to deposit metals and metal alloys. For example, electroplating can be used to deposit conductive metal (e.g., nickel) layers in acoustic stacks. Electroplating is particularly suitable for depositing thin films with a thickness of about 10 μm to about 1000 μm. Deposition parameters, including current density, cation concentration in the electrolyte, temperature, agitation, and the pH of the electrolyte, can be varied to achieve predetermined layer characteristics. Those skilled in the art will know how to adjust these process parameters.

[0067] Another aspect of this technology includes methods for simultaneously forming an array of acoustic stacks on a substrate or forming discontinuous layers of acoustic stacks using a mask. Specifically, because thermal spraying, cold spraying, and PVD are visible processes, the mask can be a shadow mask or sacrificial layer in a lift-off process. The lift-off process can be used to pattern layers to deposit layers using non-visual processes (including CVD, ALD, and electroplating) to form an array of acoustic stacks or an array of discontinuous layers. These processes can be used to avoid or significantly reduce the amount of cutting required to fabricate an array of acoustic stacks.

[0068] Figure 7 This is a schematic diagram of a process for fabricating a patterned dematching layer on a piezoelectric layer. In step 701, a sacrificial pattern 760 is applied to the piezoelectric layer 710. In step 703, a seed layer 732 is deposited on the piezoelectric layer 710. In step 705, a dematching layer 730 is deposited on the seed layer 732. In step 707, the sacrificial pattern 760 is stripped (e.g., via etching or dissolution) to expose the patterned dematching layer 730.

[0069] Figure 8 This is a schematic diagram of another process for fabricating a cut acoustic stack. In step 801, a sacrificial pattern 860 is applied to a substrate 800. In step 803, a dematching layer 830 is deposited on the substrate 800. In step 805, a piezoelectric layer 810 is deposited on the dematching layer 830. In step 807, a matching layer 820 is deposited on the piezoelectric layer 810. In step 809, the sacrificial pattern 860 is stripped to expose an array of acoustic stacks on the substrate 800.

[0070] Figure 9This is a schematic diagram of another process for fabricating a cut acoustic stack. This process uses a shadow mask to deposit a patterned dematching layer. In step 901, a shadow mask 960 is positioned over a piezoelectric layer 910. In step 903, a seed layer 932 is deposited on the piezoelectric layer 910 using a line-of-sight technique (e.g., PVD). Because the seed layer 932 is deposited using a line-of-sight process, the shadow mask 960 applies a pattern to the seed layer 932. In step 905, a dematching layer 930 is deposited on the seed layer 932 using a line-of-sight technique (e.g., thermal spraying). Like the seed layer 932, the dematching layer 930 is deposited using a line-of-sight process such that the dematching layer 930 has the pattern applied by the shadow mask 960. In step 907, the shadow mask 960 is removed from the piezoelectric layer 910, thereby exposing the patterned dematching layer 932.

[0071] Another aspect of this technology includes an ultrasonic probe having an acoustic stack or an array of acoustic stacks as disclosed herein. Figure 10 This is a cross-sectional view of an ultrasound probe 1000 having an acoustic stack 1010. The ultrasound probe 1000 includes a housing 1030, an acoustic stack 1010 as disclosed herein, and a lens 1020. In other embodiments, the acoustic stack 1010 is disposed within the lens 1020. The ultrasound probe 1000 can be coupled to an ultrasound medical imaging system including processing circuitry and a display device. In this way, the ultrasound medical imaging system is configured to acquire ultrasound medical images of a patient using the ultrasound probe 1000 and display the images on a display device.

[0072] The embodiments described herein have been illustrated with reference to the accompanying drawings. The drawings illustrate certain details of specific embodiments providing the systems, methods, and procedures described herein. However, the use of the drawings to describe the embodiments should not be construed as imposing any limitations that may exist in the drawings on the content of this disclosure.

[0073] It should be understood that no element of any claim herein may be applied under 35 USC. The provisions of 112(f) shall be interpreted unless the element is explicitly expressed using the phrase “apparatus for…”.

[0074] As used herein, terms of degree such as “about,” “approximately,” “substantially,” and similar terms are intended to have a broad meaning consistent with common and accepted usage by one of ordinary skill in the art to which the subject matter of this disclosure pertains. Those skilled in the art who read this disclosure will understand that these terms are intended to allow for the description of certain features described and claimed, without limiting the scope of these features to any precise numerical range provided. Therefore, these terms should be interpreted as indicating that non-substantial or irrelevant modifications or alterations to the described and claimed subject matter are considered to be within the scope of the disclosure set forth in the appended claims.

[0075] It should be noted that terms such as “exemplary,” “example,” and similar terms used herein to describe various implementations are intended to indicate that such implementations are possible examples, representations, or illustrations of possible implementations, and such terms are not intended to imply that such implementations are necessarily special or excellent examples.

[0076] As used herein, the term "coupling" and its variations refer to the direct or indirect engagement of two components with each other. Such engagement can be static (e.g., permanent or fixed) or movable (e.g., removable or releasable). Such engagement can be achieved by directly coupling the two components together, by coupling the two components together using a separate intermediate component and any additional intermediate components coupled to each other, or by coupling the two components together using an intermediate component integrally formed with one of the two components. If "coupling" or its variations are modified by an additional term (e.g., direct coupling), the general definition of "coupling" provided above will be modified by the common linguistic meaning of the additional term (e.g., "direct coupling" refers to the engagement of two components without any separate intermediate component), resulting in a narrower definition of "coupling" than the general definition provided above. Such connections can be mechanical, electrical, or fluid.

[0077] As used herein, the term "or" is inclusive (not exclusive), and therefore, when used to connect lists of elements, the term "or" indicates one, some, or all of the elements in the list. Unless otherwise explicitly stated, conjunctions such as the phrase "at least one of X, Y, and Z" should be understood to mean that the elements can be X, Y, and Z; X and Y; X and Z; Y and Z; or X, Y, and Z (i.e., any element on its own or any combination of X, Y, and Z). Therefore, unless otherwise stated, such conjunctions generally do not imply that certain embodiments require at least one of X, at least one of Y, and at least one of Z to be present respectively.

[0078] References to element positions in this document (e.g., "top", "bottom", "above", "below") are used only to describe the orientation of the individual elements in the figure. It should be noted that, according to other exemplary embodiments, the orientation of the various elements may differ, and such variations are intended to be covered by this disclosure.

[0079] As used herein, terms such as “engine” or “circuit” can include hardware and machine-readable media on which instructions for configuring hardware to perform the functions described herein are stored. An engine or circuit can be embodied as one or more circuit components, including but not limited to processing circuitry, network interfaces, peripheral devices, input devices, output devices, sensors, etc. In some embodiments, an engine or circuit can take the form of one or more analog circuits, electronic circuits (e.g., integrated circuits (ICs), discrete circuits, system-on-a-chip (SoC) circuits, etc.), telecommunications circuits, hybrid circuits, and any other type of circuit. In this respect, an engine or circuit can include any type of component for implementing or facilitating the implementation of the operations described herein. For example, an engine or circuit as described herein can include one or more transistors, logic gates (e.g., NAND, AND, NOR, OR, XOR, NOT, XNOR, etc.), resistors, multiplexers, registers, capacitors, inductors, diodes, wiring, etc.

[0080] An engine or circuit may be embodied as one or more processing circuits, which include one or more processors communicatively coupled to one or more memories or memory devices. In this respect, the one or more processors may execute instructions stored in memory or instructions otherwise accessible to the one or more processors. The one or more processors may be constructed in a manner sufficient to perform at least the operations described herein. In some embodiments, the one or more processors may be shared by multiple engines or circuits (e.g., engine A and engine B, or circuit A and circuit B may include or otherwise share the same processor, which in some example embodiments may execute instructions stored or otherwise accessed via different regions of memory).

[0081] Alternatively or additionally, one or more processors may be configured to perform or otherwise perform certain operations independently of one or more coprocessors. In other example embodiments, two or more processors may be bus-coupled to enable independent, parallel, pipelined, or multithreaded instruction execution. Each processor may be provided as one or more suitable processors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or other suitable electronic data processing components configured to execute instructions provided by memory. One or more processors may take the form of a single-core processor, a multi-core processor (e.g., a dual-core processor, a triple-core processor, a quad-core processor, etc.), a microprocessor, etc. In some embodiments, one or more processors may be external to the device; for example, one or more processors may be remote processors (e.g., cloud-based processors). Alternatively or additionally, one or more processors may be internal to the device and / or local to the device. In this regard, a given engine or circuitry or its components may be deployed locally (e.g., as part of a local server, a local computing system, etc.) or remotely (e.g., as part of a remote server such as a cloud-based server). For this purpose, an engine or circuitry as described herein may include components distributed across one or more locations.

[0082] Example systems used to provide an overall system or part of the embodiments described herein may include one or more computers, including processing units, system memory, and a system bus coupling various system components, including the system memory, to the processing units. Each memory device may include a non-transitory volatile storage medium, a non-volatile storage medium (e.g., one or more volatile and / or non-volatile memories), etc. In some embodiments, the non-volatile medium may be in the form of ROM, flash memory (e.g., flash memory such as NAND, 3D NAND, NOR, 3D NOR, etc.), EEPROM, MRAM, magnetic storage devices, hard disks, optical disks, etc. In other embodiments, the volatile storage medium may be in the form of RAM, TRAM, ZRAM, etc. Combinations of the above are also included within the scope of machine-readable media. In this regard, machine-executable instructions include, for example, instructions and data that cause a general-purpose computer, a special-purpose computer, or a special-purpose processor to perform a function or a set of functions. According to the example implementation described herein, each respective memory device is operable to retain or otherwise store information relating to operations performed by one or more associated circuits, including processor instructions and related data (e.g., database components, object code components, script components, etc.).

[0083] Although the accompanying drawings may illustrate and the specification may describe a particular order and composition of method steps, the order of these steps may differ from the order depicted and described. For example, two or more steps may be performed simultaneously or partially simultaneously. Furthermore, some method steps performed as discrete steps may be combined, steps performed as combined steps may be divided into discrete steps, the order of certain processes may be reversed or otherwise altered, and the nature or number of discrete processes may be changed or varied. According to alternative embodiments, the order or sequence of any element or device may be changed or replaced. Therefore, all such modifications are intended to be included within the scope of this disclosure as defined in the appended claims. Such variations may depend, for example, on the chosen software and hardware system and the designer's choice. All such variations are within the scope of this disclosure. Similarly, software implementations of the described methods may be accomplished using standard programming techniques with rule-based logic and other logic to perform various connection steps, processing steps, comparison steps, and decision steps.

[0084] The foregoing description of embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed, and modifications and variations can be made in accordance with, or derived from, the teachings described above. These embodiments were chosen and described to explain the principles of the disclosure and its practical application, thereby enabling those skilled in the art to utilize the various embodiments and make various modifications suitable for the intended particular purpose. Other substitutions, modifications, alterations, and omissions may be made to the design, operating conditions, and arrangement of the embodiments without departing from the scope of the disclosure as set forth in the appended claims.

Claims

1. An acoustic stack (100), said acoustic stack comprising: Piezoelectric layer (110); A matching layer (120) is disposed directly on the first side of the piezoelectric layer (110); and A dematching layer (130) is disposed directly on the second side of the piezoelectric layer (110), with the first side opposite to the second side.

2. The acoustic stack (100) according to claim 1, wherein the acoustic stack (100) is free of adhesive.

3. The acoustic stack (100) according to claim 1, wherein the dematching layer (130) comprises tungsten carbide.

4. The acoustic stack (100) according to claim 3, wherein the dematching layer (130) further comprises a seed layer (732) disposed directly on the second side of the piezoelectric layer (110), the seed layer (732) comprising gold, nickel or aluminum.

5. The acoustic stack (100) according to claim 1, wherein the matching layer (120) comprises: A first matching layer (220) comprises graphite, aluminum, silicon, polymer, or a combination of two or more of the above. and The second matching layer (224) contains a polymer.

6. The acoustic stack (100) according to claim 5, wherein the matching layer (120) further comprises a seed layer (732) disposed directly on the first side of the piezoelectric layer (110), the seed layer (732) comprising gold, nickel or aluminum.

7. The acoustic stack (100) according to claim 5, wherein the first matching layer (220) comprises a composite material containing graphite, aluminum and silicon having an elemental gradient.

8. The acoustic stack (100) according to claim 1, wherein the piezoelectric layer (110) comprises lead zirconate titanate, lead magnesium niobate, lead titanate, lead indium niobate, silicon carbide, or a combination of two or more thereof.

9. A method comprising depositing a matching layer (120) on a first side of a piezoelectric layer (110) via thermal spraying.

10. The method of claim 9, wherein depositing the matching layer (120) comprises depositing the matching layer (120) directly on a first side of the piezoelectric layer (110), and the thermal spraying deposition comprises plasma spraying.

11. The method of claim 9, wherein depositing the matching layer (120) comprises: A seed layer (732) comprising gold, nickel or aluminum is deposited directly on the first side of the piezoelectric layer (110) via physical vapor deposition (PVD), chemical vapor deposition (CVD) or electroplating. A first matching layer (220) is deposited on the seed layer (732) via thermal spraying. The first matching layer (220) comprises graphite, aluminum, silicon, polymer, or a combination of two or more of these materials. A second matching layer (224) is deposited on the first matching layer (220) via thermal spraying, the second matching layer (224) comprising a polymer.

12. The method of claim 9, further comprising depositing a dematching layer (130) on a second side of the piezoelectric layer (110) via thermal spray deposition.

13. The method of claim 12, wherein depositing the de-matching layer (130) comprises: The dematching layer (130) is deposited directly on the second side of the piezoelectric layer (110); and the thermal spraying deposition includes high-speed oxygen fuel spraying (HVOF).

14. The method of claim 12, wherein depositing the dematching layer (130) comprises: A seed layer (732) comprising tungsten carbide, gold, nickel, or aluminum is deposited directly on the second side of the piezoelectric layer (110) via physical vapor deposition (PVD), chemical vapor deposition (CVD), or electroplating; and A tungsten carbide layer is deposited on the seed layer (732) via thermal spraying; and the thermal spraying deposition includes high-speed oxygen fuel spraying (HVOF).

15. The method of claim 9, further comprising depositing a dematching layer (130) on the conductive layer (644) via thermal spray deposition.

16. The method of claim 15, wherein depositing the dematching layer (130) comprises depositing the dematching layer (130) directly onto the conductive layer (644), and the thermal spraying deposition comprises high-velocity oxygen fuel spraying (HVOF).

17. The method of claim 15, wherein depositing the dematching layer (130) comprises: A seed layer (732) comprising tungsten carbide, gold, nickel, or aluminum is deposited directly on the conductive layer (644) via physical vapor deposition (PVD), chemical vapor deposition (CVD), or electroplating; and A tungsten carbide layer is deposited on the seed layer (732) via thermal spraying; and the thermal spraying deposition includes HVOF.

18. The method of claim 15, further comprising depositing the piezoelectric layer (110) on the dematching layer (130) via thermal spraying, the piezoelectric layer (110) comprising lead zirconate titanate, lead magnesium niobate, lead titanate, lead indium niobate, silicon carbide, or a combination of two or more of the above.

19. The method of claim 9, further comprising: Before depositing the matching layer (120), a patterned mask is provided on the first side of the piezoelectric layer (110) to guide the deposition of the matching layer (120).

20. A method for preparing an acoustic stack (200), the method comprising: A first layer (250) is deposited on a substrate by plasma spraying, the first layer comprising a composite material comprising aluminum, silicon and graphite; The flexible circuit (240) is disposed on the first layer; A second layer (244) comprising gold is sputtered onto the flexible circuit (240); A third layer (242) is electroplated on the second layer (244), the third layer (242) comprising nickel; A fourth layer (230) is thermally sprayed onto the third layer (242), the fourth layer (230) comprising tungsten carbide; A fifth layer (232) is electroplated on the fourth layer (230), the fifth layer (232) comprising nickel; A sixth layer (210) is thermally sprayed onto the fifth layer (230), the sixth layer (210) comprising a piezoelectric material; A seventh layer (222) is plasma-sprayed and deposited on the sixth layer (210), the seventh layer (222) comprising a composite material containing aluminum, silicon, and graphite; and An eighth layer (220) is deposited by plasma spraying on the seventh layer (222), the eighth layer (220) comprising polymethyl methacrylate.

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