Acoustic piezoelectric membrane transducer array with localized membrane vibrations.

Abstract

The acoustic device (100) comprises an array of acoustic transducers (10a, 10b) formed by a patterned stack (12-15) on a flexible substrate (11). The stack comprises a piezoelectric layer (13) sandwiched between respective bottom electrode layers (12) and top electrode layers (15), and a patterned insulating layer (14) formed by a pattern of insulating material (14m). The pattern comprises insulating areas (A14) where the insulating material (14m) is disposed between one of the electrodes (12, 15) and the piezoelectric layer (13), and contact areas (A10) where the insulating material (14m) is absent and where both electrodes (12, 15) contact the piezoelectric layer (13).

Description

[Technical field]

[0001] The present disclosure relates to acoustic devices having arrays of acoustic transducers and methods of manufacture. [Background technology]

[0002] Typically, when fabricating an array of piezoelectric vibrating membranes on plastic for acoustic / ultrasonic applications, the piezoelectric material is electrically polarized at the location of the membrane by applying an electric field via electrodes, and in operation, the vibration of the membrane preferably travels laterally through the array (plate waves) and should not affect adjacent devices. Such acoustic crosstalk can adversely affect the quality and level of the generated acoustic field, resulting, for example, in poor image quality, poorly defined measurement areas, or a larger-than-expected focus for acoustic tactile feedback.

[0003] By way of background, US Patent Publication No. 2013 / 0293065 describes a piezoelectric micromachined ultrasonic transducer (pMUT) array. In one example, the coupling strength within a population of transducer elements provides splitting degenerate mode shapes for a wide bandwidth overall response, while the weaker coupling strength between adjacent populations of elements provides sufficiently small crosstalk between the populations of elements. In another example, the different membrane sizes within a population of transducer elements provide different frequency responses for a wide bandwidth overall response, while the layout of the different membrane sizes between adjacent populations of elements provides sufficiently small crosstalk between the populations of elements. In another example, the close packing of the membranes within a population of transducer elements provides improved efficiency for wide bandwidth embodiments. In another example, an elliptical piezoelectric membrane provides multiple resonant modes for a wide bandwidth overall response and high efficiency, while the orthogonality of the semi-principal axes between adjacent populations of elements provides sufficiently small crosstalk between the populations of elements. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2013 / 0293065 Summary of the Invention [Problem to be solved by the invention]

[0005] There remains a need to further improve the manufacturability and design freedom of acoustic devices having transducer arrays with minimal crosstalk. [Means for solving the problem]

[0006] Aspects of the present disclosure relate to an acoustic device and a method for manufacturing the same. Preferably, the acoustic device comprises an array of acoustic transducers formed by a patterned stack on a flexible substrate. The stack comprises a piezoelectric layer sandwiched between respective bottom and top electrode layers. A patterned insulating layer is formed by a pattern of insulating material. The pattern comprises insulating areas where insulating material is disposed between one of the electrodes and the piezoelectric layer, and contact areas where there is no insulating material, where both electrodes contact the piezoelectric layer.

[0007] As will be appreciated, the insulating material can act as an electrical insulator to separate or form transducer arrays by electrically isolating the contacts between the electrodes and the piezoelectric layer in the insulating areas around and between the transducers. In this way, arrays of acoustic transducers can be more easily manufactured. Additionally, the insulating material can act as acoustic insulation between the transducers. In this way, acoustic interference or crosstalk can be mitigated.

[0008] These and other features, aspects, and advantages of the apparatus, systems, and methods of the present disclosure will become better understood from the following description, appended claims, and accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 2 is a cross-sectional view of adjacent acoustic transducers. [Figure 1B] FIG. 1 illustrates further details of one of the converters. [Figure 2A] FIG. 13 is a cross-sectional view of an acoustic device in which an insulating material is added between the bottom electrode and the piezoelectric layer. [Figure 2B] FIG. 1 is a cross-sectional view of an acoustic device having an intermediate protective layer. [Figure 3A] 1A-1D illustrate a method of manufacturing an acoustic device. [Figure 3B] 1A-1D illustrate a method of manufacturing an acoustic device. [Figure 3C] 1A-1D illustrate a method of manufacturing an acoustic device. [Figure 3D] 1A-1D illustrate a method of manufacturing an acoustic device. [Figure 4A] FIG. 1 illustrates an acoustic device having a flexible substrate secured to a support structure. [Figure 4B] FIG. 1 illustrates an acoustic device having a flexible substrate secured to a support structure. [Figure 5A] FIG. 2 is a diagram of an array of transducers according to an example layout. [Figure 5B] 1 is a photograph of a device with a similar layout. [Figure 6] FIG. 5C illustrates measurements of deflection across the surface of an acoustic device such as that shown in FIG. 5B when the transducer is actuated. [Figure 7A] FIG. 1 illustrates another layout of an acoustic transducer. [Figure 7B] FIG. 1 illustrates another layout of an acoustic transducer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The terms used to describe specific embodiments are not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of a referenced feature but do not exclude the presence or addition of one or more other features. Unless otherwise specified, when a particular step of a method is referred to as following another step, it will be further understood that the particular step may directly follow said other step, or one or more intermediate steps may be performed prior to performing the particular step. Similarly, unless otherwise specified, when a connection between structures or components is described, it will be understood that this connection may be established directly or through an intermediate structure or component.

[0011] As described herein, an additional (insulating) layer can be used to achieve merely local poling of the piezoelectric material, preventing acoustic crosstalk through the lateral substrate. The lateral dimensions of the membrane can be determined by the overlap between the top and bottom electrodes that sandwich the effective piezoelectric polymer. By inserting an additional dielectric between locally patterned electrodes, the effective device area is determined by the shape of the additional dielectric rather than the shape of the metal electrodes. In some embodiments, an additional dielectric film can be deposited directly before or after the piezoelectric film. The additional dielectric film is patterned.

[0012] In some embodiments, a structured metal electrode is fabricated on top of a plastic substrate. A large area piezoelectric layer is deposited on the structured electrode. The resonant frequency of the membrane scales with the diameter, and at higher frequencies smaller membranes can be used. Polymers such as P(VDF-TrFE) are preferred because of the ease of manufacturing large areas of piezoelectric material compared to the small membrane dimensions. By first adding a thicker dielectric layer, for example with a thick photoresist, on top of the piezoelectric material, the membrane dimensions can be mechanically defined (pinned) to the edges of this structured layer. This means that the membrane dimensions can remain fixed even during large deflections of the membrane during vibration (high drive voltage and / or at resonance). As a final step, a second electrode can be added. This electrode can be configured per device or a common electrode shared between devices can be configured. Both electrodes contact the piezoelectric only at designated contact locations in the holes of the configured stabilizing intermediate layer.

[0013] In some embodiments, a configuration with the following layer sequence can be used: electrode / piezoelectric / patterned insulator / electrode. In other embodiments, the following sequence can be used: electrode / patterned insulator / piezoelectric / electrode. Yet further embodiments are similar, but can add a thin patterned protective layer between the patterned insulator and the piezoelectric (e.g., SiN, SiO2, AlOx) to avoid contamination and subsequent degradation of the piezoelectric material due to the patterned insulator. In some embodiments, the flexible substrate / support layer can be part of the vibrating membrane. To prevent in-plane acoustic crosstalk through this support layer, the membrane can be mechanically isolated, for example, by providing an insulating region with a much higher bending stiffness (flexural stiffness) compared to the contact area.

[0014] The present invention will now be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. The embodiments may be described with reference to schematic and / or cross-sectional illustrations of idealized embodiments and intermediate configurations of the invention, in some cases. Like numbers refer to like elements throughout the description and drawings. Relative terms and their derivatives should be construed to refer to an orientation as described in the present case or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation, unless otherwise specified.

[0015] FIG. 1A illustrates a cross-sectional view of adjacent acoustic transducers 10a, 10b, and FIG. 1B illustrates further details of one of the transducers 10a.

[0016] In a preferred embodiment, for example as shown, acoustic device 100 comprises an array of acoustic transducers 10a, 10b. In alternative or further embodiments, the array is formed by a patterned stack 12-15 on a flexible substrate 11. In some embodiments, the stack comprises a piezoelectric layer 13 sandwiched between respective bottom electrode layers 12 and top electrode layers 15. In other or further embodiments, the stack comprises an insulating layer 14. Preferably, insulating layer 14 is patterned. For example, the patterned insulating layer 14 is formed by a pattern of insulating material 14m.

[0017] In a preferred embodiment, for example as shown, the patterned insulating layer (14) comprises insulating areas A14 where the insulating material 14m is disposed between one of the electrodes 12, 15 and the piezoelectric layer 13 (in the direction Z across the substrate 11). In another or further preferred embodiment, the patterned insulating layer (14) comprises contact areas A10 where both electrodes 12, 15 contact the piezoelectric layer 13 and are free of insulating material 14m. More preferably, the acoustic transducers 10a, 10b are formed in the contact areas A10. For example, the acoustic transducers 10a, 10b are formed between the insulating areas A14. Most preferably, the insulating areas A14 surround and / or separate the respective contact areas A10. In other words, the pattern of insulating material 14m can define a boundary around the acoustic transducers 10a, 10b, where the contact areas A10 are formed in the gaps in the pattern without the insulating material 14m between the piezoelectric layer 13 and either of the electrodes 12, 15.

[0018] In a preferred embodiment, for example as shown, the active surface of the acoustic transducers 10a, 10b includes a portion of the flexible substrate 11 at the contact area A10. In other words, each acoustic transducer 10a may be formed by a stack comprising the flexible substrate 11, the piezoelectric layer 13 sandwiched between the respective bottom electrode layer 12 and top electrode layer 15, but without the insulating material 14m in that area, i.e. the contact area A10.

[0019] Preferably, the substrate 11 has a relatively high flexibility, at least sufficient to bend or flex the piezoelectric layer 13, for example to generate the acoustic wave W as intended. Typically, the first flexural stiffness of the substrate 11 (by itself without the stack) may be of the same order of magnitude as the second flexural stiffness of the stack of layers provided on the substrate 11 as part of the transducer (i.e. excluding the insulating material 14m). For example, the first flexural stiffness is between 0.1 and 10 times the second flexural stiffness. Alternatively or additionally, this can be quantified as the (first) flexural stiffness (of the substrate) constituting less than 90 percent of the total flexural stiffness Fa of the device, i.e. the sum of the first and second flexural stiffnesses, in the contact area A10.

[0020] In a preferred embodiment, the substrate 11 does not need to be removed and can remain part of the acoustic device 100. In another embodiment (not shown), the stack can be removed from the substrate on which it is fabricated, which can be a flexible substrate or another supporting substrate. For example, the patterned insulating material 14m can provide sufficient structural integrity to support the device without a substrate. This can also allow for example to use a relatively rigid substrate so that the configuration remains fixed during fabrication.

[0021] In a preferred embodiment, the acoustic device 100 is relatively flat, for example formed as a sheet. Therefore, preferably, the total thickness Z100 across the plane of the acoustic device 100 is relatively small compared to the order of its (smallest) in-plane dimension (diameter or length / width). For example, the in-plane dimension is at least 10 times, 20 times, 50 times, 100 times, 1000 times, or more than the thickness. For example, the total thickness (Z100) of the substrate 11, the piezoelectric layer 13 with the electrodes 12, 15, and the insulating area A14 may be less than 1 millimeter, less than 0.5 millimeter, for example between 100 and 200 micrometers.

[0022] To effectively mitigate crosstalk, e.g., in-plane waves Wi, between the acoustic transducers 10a, 10b, it is desirable to decouple and / or damp the vibrations of each of the acoustic transducers. For example, decoupling can be achieved by providing areas of the substrate that separate transducers having different wave propagation characteristics from areas that form the transducers. For example, damping can be achieved by providing more and / or different (e.g., dissipative) types of material in the areas between the transducers.

[0023] One way to characterize different regions of a relatively flat acoustic device 100 is by the bending stiffness (F) or flexural rigidity of each of the acoustic devices 100. For example, the bending stiffness (F) of a layer or stack can depend on its Young's modulus (E), Poisson's ratio (v), and thickness (Z). Typically, this is expressed as F=[E·Z 3 ] / [12·(1-v 2 ) In a preferred embodiment, the bending stiffness Fx in the insulating area A14 including the insulating layer 14 is at least 10 times, more preferably at least 20 times, most preferably at least 50 times, e.g., between 60 and 200 times, higher than the bending stiffness Fa in the contact area A10 forming the acoustic transducers 10a, 10b. The higher the relative bending stiffness of the insulating area, the better the in-plane crosstalk between adjacent transducers can be mitigated.

[0024] The relatively high bending stiffness of the insulating area A14 can be achieved by using an insulating material 14m having a relatively high Young's modulus, for example higher than the Young's modulus of the flexible substrate 11. Alternatively or additionally, the thickness Z14 of the layer of the insulating material 14m may be relatively thick. In a preferred embodiment, the insulating area A14 achieves a locally increased thickness Z14 for the stack compared to the contact area A10. For example, the thickness Z100 of the stack in the insulating area A14 (for example equal to Z11+Z13+Z14) is at least two times, preferably at least three times, thicker than the thickness Z10 of the stack in the contact area A10 (for example equal to Z11+Z13).

[0025] In the exemplary fabricated device, the substrate 11 was formed by a polyimide (PI) substrate having a thickness Z11=13.5 μm. On the substrate, the piezoelectric layer 13 was formed by a PVDF stack having a thickness Z13=20 μm. The bending stiffness of the device 100 in the area A10 (i.e., substrate+piezoelectric layer) was Fa=1.35E-5 N·m (=Pa·m 3) In the insulating area A14, before adding the top electrode 15, an additional layer of insulating material 14m was deposited. In particular, the insulating material 14m was formed by a layer of photoresist (SU8) having a thickness Z14=125 μm. Including this additional layer, the bending stiffness of the device 100 in the area A14 is estimated at Fi=1.19E-3 N·m, i.e. 88 times higher than in the area A10.

[0026] FIG. 2A illustrates a cross-sectional view of an acoustic device 100 in which an insulating material 14m is added between the bottom electrode 12 and the piezoelectric layer 13. This is in contrast to the embodiment of FIGS. 1A and 1B, in which the insulating material 14m is added between the piezoelectric layer 13 and the top electrode 15, for example. In a preferred embodiment, the insulating material is formed from a photoresist material. Such a material can further improve manufacturability, for example providing a simple way of defining the pattern of the insulating material 14m by a corresponding light pattern / mask for developing the photoresist. In some embodiments, it can be envisaged that the patterning of the insulating material 14m may affect the piezoelectric layer 13. For example, a method of (selectively) removing the photoresist in the contact area A10 by a process such as a photoresist material and / or wet etching. In some embodiments, this can be mitigated by adding the insulating material 14m before the piezoelectric layer 13, for example as shown.

[0027] FIG. 2B illustrates a cross-sectional view of an acoustic device 100 with an intermediate protective layer 14p. In some embodiments, the intermediate protective layer 14p is disposed between the piezoelectric layer 13 and the insulating material 14m. The intermediate protective layer 14p can alternatively or additionally be used to protect the piezoelectric layer 13 from exposure to, for example, the insulating material 14m (photoresist) and / or its removal method as shown. In this way, the piezoelectric layer 13 can also be applied before patterning the layer of insulating material 14m. Typically, the protective layer 14p can have a different material than the insulating material 14m. For example, the protective layer 14p can be more resistant to the etching process for removing the insulating material 14m. Preferably, the intermediate protective layer 14p is then locally removed in the contact area A10 using another process (than that used to remove the photoresist), such as, for example, dry etching (gas). In principle, the protective layer 14p can act in addition to the insulating material 14m as part of the electrical insulation between the electrodes and the piezoelectric layer respectively and / or as part of the acoustic insulation between adjacent transducers, and in that sense both layers 14m and 14p can be considered as parts of a patterned insulating material.

[0028] 3A-3D illustrate a method of manufacturing acoustic device 100. FIG.

[0029] In one embodiment, the method includes providing a stack formed on a flexible substrate 11, for example as shown in FIG. 3A. Preferably, the stack (initially) comprises at least a bottom electrode 12. In some embodiments, for example as shown in FIGS. 3A and 3B, a layer of insulating material 14m is deposited on the stack and selectively removed. The locations where the insulating material 14m is removed will form contact areas A10 for making electrical contact with the bottom electrode 12 through the stack. Instead of removing material after deposition, a pre-patterned layer of insulating material, for example a foil with openings, can be added to the stack (for example as shown in FIG. 7A).

[0030] In some embodiments, for example as shown in FIG. 3D , the top electrode 15 on the stack forms an array of acoustic transducers 10a, 10b in a contact area A10, where both the top and bottom electrodes are in contact with the piezoelectric layer 13 between them, and the piezoelectric layer 13 is deposited on the stack before or after a step of depositing a layer of insulating material 14m, where the acoustic transducers 10a, 10b are separated by an insulating area A14, and the insulating material 14m is disposed between one of the electrodes 12, 15 and the piezoelectric layer 13.

[0031] In some embodiments, the insulating material 14m comprises a photoresist material. In other or further embodiments, the patterned insulating layer 14 is formed by a lithographic process. For example, an unpatterned layer of insulating material 14m is exposed to a pattern of light that matches the shape of the contact areas A10 or the shape of the insulating areas A14. For example, a mask is used to achieve the patterned exposure. It will be appreciated that lithography can be used to easily form the desired high precision pattern of acoustic transducers, for example, in relatively small dimensions and / or in large numbers.

[0032] In some embodiments, a protective layer 14p is provided between the piezoelectric layer 13 and the insulating layer 14, as shown, for example, in FIG. 3A. For example, as shown in FIG. 3B, the protective layer 14p can remain when removing the insulating material 14m to protect the piezoelectric layer 13 against a removal process for patterning the insulating layer 14, such as wet etching. In some embodiments, as shown, for example, in FIG. 3C, the protective layer 14p can be removed at the contact area A10 by a separate process, such as dry etching. Thus, as shown, for example, in FIG. 3D, the top electrode layer 15 can be deposited on the piezoelectric layer 13 without the protective layer 14p therebetween.

[0033] 4A and 4B illustrate an acoustic device 100 having a flexible substrate 11 secured to a support structure 20. As shown in FIG.

[0034] In some embodiments, for example as shown, flexible substrate 11 is secured, e.g., laminated, or otherwise disposed on a relatively rigid support substrate 20. For example, substrate 11 can be laminated and / or otherwise attached to support substrate 20. The securing between the flexible substrate and the support substrate or other rigid structure can occur, for example, during and / or after manufacturing. The support substrate can be relatively flat, similar to flexible substrate 11, or can be thicker compared to flexible substrate 11. Preferably, support substrate 20 has a relatively high bending stiffness, e.g., at least 2 times, 3 times, 5 times, 10 times, or more, compared to flexible substrate 11. Thus, support substrate 20 can provide additional structural integrity.

[0035] Preferably, the support substrate 20 comprises openings 20a-20c at positions corresponding to the acoustic transducers 10a-10c, i.e. at least partially overlapping the contact area A10. For example, the flexible substrate 11 abuts the support structure at the insulating area A14, while not connecting to the support structure 20 at the contact area A10. In some embodiments, the openings 20a-20c can extend through the support substrate 20, for example as shown in FIG. 4A. In other or further embodiments, the openings 20a-20c can be formed by cavities that extend concavely from the direction of the flexible substrate 11, but do not penetrate the support substrate 20 completely. The openings can allow a relatively free movement of the transduction surface, while still achieving a rigid support. Additionally, the fixing of the insulating area A14 to the support structure can help to achieve even more acoustic isolation between the transducers 10a, 10b. In some embodiments (not shown), the support substrate can be provided on the top side, for example after the stack has been deposited and completed. Also possible is a combination with a support structure on one or both sides, preferably having through openings such as those shown in FIG. 4A on at least one side for transmitting the acoustic waves W.

[0036] Figure 5A illustrates an array of transducers according to an example layout, and Figure 5B shows a photograph of a device with a similar layout.

[0037] In some embodiments, for example as shown, the centers of the transducers can be arranged along multiple concentric circles. Thus, each of the transducers along each circle can have the same distance to a point along the central axis of the circle in a direction transverse to the plane of the device. By activating a first set of transducers along each first circle in phase, their acoustic waves can constructively interfere at a point along the central axis. By additionally activating a second set of transducers along each second circle, also in phase within the first set but with a predefined phase difference relative to the first set, a specific point can be selected above the face of the device where constructive interference between the sets occurs. This can be further improved with additional sets. In one embodiment, the device shown can be used to create a tactile feedback device that creates a tactile dot in the air by constructive interference between many transducers. For example, the location of the dot can be controlled by controlling the relative phase between the sets of transducers (along the central axis) or within each set (to move the dot off-axis). Of course, other layouts, for example a grid layout, can be used to create similar or other acoustic devices.

[0038] It will be appreciated that with effective decoupling as described herein, the lateral spacing or distance Xab between adjacent transducers 10a, 10b in any layout may be relatively small, for example of the order of magnitude of the (maximum or average) diameter Xa, Xb of the transducers 10a, 10b. For example, the (minimum) distance Xab between the transducers may be between 0.1 and 10 times, preferably between 0.2 and 5 times, and more preferably between half and 2 times, the (constant or average) diameter Xa, Xb of the transducers. In some embodiments, the density of the transducers over the surface of the device may be relatively high, for example, the transducers may cover at least 10 percent, preferably at least 20 percent, more preferably at least 30 percent, or even more than 50 percent of the surface (the remaining surface formed by the area between the transducers). The operation of the device may be more effective if a larger surface can be covered by the transducers.

[0039] Figure 6 illustrates the measurement of deflection ΔZ (in nanometers) across the surface X, Y of an acoustic device as shown in Figure 5B when the transducer is actuated. The measurement was performed using a laser vibrometer. As shown, the deflection ΔZ is confined to the contact area of ​​the transducers, while there is virtually no noticeable deflection in the insulating area between the transducers, e.g., the deflection in the insulating area is at least 1 / 10 less than the deflection in the contact area.

[0040] Figures 7A and 7B illustrate alternative layouts of acoustic transducers 10a, 10b. In one embodiment, the insulating layer 14 is pre-patterned before being added to the stack, as shown, for example, in Figure 7A. Alternatively, the insulating layer 14 shown in Figure 7B can be patterned by selective removal of material, as described, for example, with reference to Figures 3A-3D.

[0041] In a preferred embodiment, the piezoelectric layer 13 is a continuous layer extending between the different transducers 10a, 10b. Advantageously, it may be much easier to deposit piezoelectric material as a continuous layer. Preferably, a polymer-based piezoelectric material is used for the piezoelectric layer 13. For example, a polymer-based piezoelectric material can be easily applied as a continuous layer. In some embodiments, the deposited piezoelectric material may initially have randomly oriented regions. Preferably, these are aligned by "poling" the piezoelectric material, i.e., a process in which a strong electric field is applied across the material, usually at high temperature. Most preferably, the piezoelectric layer 13 is exclusively (or mainly) poled in the contact area A10. For example, a strong electric field for poling is applied via the bottom electrode 12 and the top electrode (not visible here). Due to the patterned insulating layer 14, the potential difference between the electrodes can result in a stronger electric field across the piezoelectric layer 13 in the contact area A10 than across the larger gap in the insulating area A14. As will be appreciated, selective poling can also help improve functionality, for example, to further prevent actuation of the piezoelectric layer 13 in the unpoled regions of the insulating area A14.

[0042] In some embodiments, at least one of the bottom and top electrodes is a continuous layer extending between the different transducers 10a, 10b. In other or further embodiments, at least one of the electrodes 12, 15 is patterned. In one embodiment, a combination of patterned and unpatterned electrode layers is used. Preferably, the patterning of the electrodes is such that a subset of one or more of the acoustic transducers 10a, 10b can be selectively activated. In one embodiment, a first set of one or more transducers 10a is activated by applying a voltage to a first line 12a of the bottom electrode, and a second set of a different one or more transducers 10b is activated by applying a voltage to a second line 12a of the different bottom electrode. In some embodiments, the lines 12a, 12b can comprise contact pads shaped to cover at least the contact area A10, for example as shown. Instead of or in addition to the bottom electrode being patterned, the top electrode can be patterned (not shown). In some embodiments (not shown), the pattern of the top electrode can, for example, form vertical grid lines to complement the pattern of the bottom electrode. In other or further embodiments, a grid of electrode lines can be formed on one side of the piezoelectric layer 13, for example as shown. For example, the grid can comprise thin film transistors (TFTs).

[0043] For clarity and conciseness of description, features are described herein as part of the same or separate embodiments, but it will be understood that the scope of the present invention can include embodiments having all or a combination of the described features. For example, while an embodiment is shown with a particular order of layers, alternative methods may also be envisioned by one skilled in the art having the benefit of this disclosure to achieve similar functions and results. For example, some layers can be combined or split into one or more alternative layers. The various elements of the present embodiment discussed and shown provide certain advantages, such as isolating lateral vibrations. Of course, it will be understood that in discovering and matching ideas and advantages, any one of the above embodiments or processes can be combined with one or more other embodiments or processes to achieve further improvements. It will be understood that the present disclosure provides particular benefits for acoustic transducer arrays and can be generally applied to form other electrical components between selective contact areas formed by insulating layers selectively isolating electrode layers.

[0044] In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or acts other than those listed in a given claim, the word "a" or "an" before an element does not exclude the presence of a plurality of such elements, any reference sign in a claim does not limit the scope of the claim, several "means" can be represented by the same or different items or structures or functions implemented, any of the disclosed devices or parts thereof can be combined together or divided into further parts unless otherwise specified. When one claim refers to another claim, this can indicate the advantage of the synergy achieved by the combination of their respective features. However, the mere fact that certain measures are mentioned in mutually different claims does not indicate that the combination of these measures cannot also be used to advantage. The present embodiment can thus include all operative combinations of claims, and each claim can in principle refer to any previous claim unless clearly excluded by the context. [Explanation of symbols]

[0045] 10a Acoustic transducer 10b Acoustic transducer 10c Acoustic transducer 11 Flexible substrate 12 stack, bottom electrode layer 12a 1st line, 2nd line 12b Line 13 stack, piezoelectric layer 14 stacks, insulating layers 14m Insulating material 14p intermediate protective layer 15 stack, top electrode layer 20 Support structure, support substrate 20a opening 20b opening 20c opening 100 Acoustic Devices A10 Contact area A14 Insulated area Fa Flexural stiffness Fx flexural stiffness W acoustic wave X surface Xa diameter Xb diameter Xab Distance Y surface Z10 Stack Thickness Z11 Thickness Z13 Thickness Z14 Thickness Z100 Stack Thickness ΔZ deflection

Claims

1. An acoustic device (100) comprising an array of acoustic transducers (10a, 10b) formed by a patterned stack (12-15) on a flexible substrate (11), said stack comprising: a continuous piezoelectric layer (13) extending between the different transducers (10a, 10b) and sandwiched between respective bottom electrode layers (12) and top electrode layers (15); a patterned insulating layer (14) formed by a pattern of insulating material (14m); wherein the pattern comprises: an insulating area (A14) in which the insulating material (14m) is disposed between one of the electrodes (12, 15) and the piezoelectric layer (13); a contact area (A10) where both electrodes (12, 15) are in contact with the piezoelectric layer (13) and where there is no insulating material (14m); An acoustic device (100).

2. 2. An acoustic device according to claim 1, wherein the active surfaces of the acoustic transducers (10a, 10b) comprise portions of the flexible substrate (11) in the contact areas (A10).

3. 3. An acoustic device as claimed in claim 1 or 2, wherein the total thickness (Z100) of the flexible substrate (11), the piezoelectric layer (13) with the electrodes (12, 15) and the insulating area (A14) is less than 1 millimeter.

4. 4. An acoustic device according to claim 1, wherein the thickness (Z100) of the stack in the insulating area (A14) is at least twice as thick as the thickness (Z10) of the stack in the contact area (A10).

5. 5. An acoustic device according to claim 1, wherein the flexural stiffness (Fx) in the insulating area (A14) comprising the insulating layer (14) is at least 10 times higher than the flexural stiffness (Fa) in the contact area (A10) forming the acoustic transducer (10a, 10b).

6. 6. An acoustic device according to any one of the preceding claims, wherein the insulating material (14m) is arranged between the piezoelectric layer (13) and the top electrode layer (15).

7. 7. An acoustic device according to any one of the preceding claims, wherein the insulating material (14m) comprises a photoresist material.

8. 8. An acoustic device according to claim 1, wherein an intermediate protective layer (14p) is disposed between the piezoelectric layer (13) and the insulating material (14m), the protective layer (14p) being resistant to an etching process for removing the insulating material (14m).

9. 9. An acoustic device according to any one of claims 1 to 8, wherein the distance (Xab) between nearest neighboring transducers (10a, 10b) is between half and twice the diameter (Xa, Xb) of the nearest neighboring transducers (10a, 10b).

10. 10. Acoustic device according to any one of the preceding claims, wherein the piezoelectric layer (13) is exclusively poled in the contact area (A10).

11. 11. An acoustic device according to any one of claims 1 to 10, wherein one of the electrodes (15) is a continuous layer extending between different transducers (10a, 10b) and the other of the electrodes (12) is patterned to controllably actuate different subsets of the transducers (10a, 10b).

12. 12. The acoustic device of claim 1, wherein the acoustic device (100) forms a haptic feedback device and the transducers are arranged along a plurality of concentric circles configured to create a tactile spot in the air above the device along a centerline of the concentric circles by constructive interference between acoustic waves (W) emitted by the transducers of different concentric circles.

13. 13. An acoustic device according to any one of claims 1 to 12, wherein the flexible substrate (11) is fixed on a rigid support substrate (20), and the bending stiffness of the rigid support substrate (20) is at least twice as high as the bending stiffness of the flexible substrate (11).

14. The acoustic device according to claim 13, wherein the support substrate (20) is provided with openings (20a to 20c) at positions corresponding to the acoustic transducers (10a to 10c).

15. A method of manufacturing an acoustic device (100), comprising the steps of: Providing a stack formed on a flexible substrate (11), said stack comprising at least a bottom electrode (12); depositing a layer of insulating material (14m) on said stack and selectively removing said insulating material (14m) to form contact areas (A10) for making electrical contact with said bottom electrode (12) through said stack; depositing a top electrode (15) on the stack to form an array of acoustic transducers (10a, 10b) in the contact areas (A10), both the top electrode and the bottom electrode being in contact with a piezoelectric layer (13) between them, the piezoelectric layer (13) being deposited on the stack before or after the step of depositing the layer of insulating material (14m), the acoustic transducers (10a, 10b) being separated by insulating areas (A14), the insulating material (14m) being disposed between one of the electrodes (12, 15) and the piezoelectric layer (13), the piezoelectric layer (13) being a continuous layer extending between the different transducers (10a, 10b); A method comprising:

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