Piezoelectric device with pillar structure and method of manufacture

Abstract

A piezoelectric device (100) and a method of manufacturing. A first substrate (10) is provided having an array of pillars (11) comprising a piezoelectric material (M). A second substrate (20) is provided having a piezoelectric layer (21) facing respective ends of the pillars (11). While the piezoelectric layer (21) is at least partially liquid, respective ends of the pillars (11) are pushed (P) into the piezoelectric layer (21). The piezoelectric layer (21) is hardened to form an integral connection between the piezoelectric layer (21) and the pillars (11). Thus, the piezoelectric layer (21) can form a bridge structure between respective ends of the pillars (11). The integral piezoelectric structure can be polarized by a high voltage (HV). The bridge structure can be used as a platform for depositing electrical contacts (23). The piezoelectric device (100) can be used for generating or detecting acoustic waves, for example in medical imaging.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to devices comprising pillar structures of piezoelectric material, such as acoustic wave transducers, and methods of manufacturing such devices. BACKGROUND

[0002] For example, pillar structures can be advantageous for reducing acoustic and / or mechanical cross-coupling between acoustic wave device elements. In one document, Chen et al. [DOI: 10.1039 / C5NR01746G] describe a high performance P(VDF-TrFE) nanogenerator with self-connected and vertically integrated fibers by patterned EHD pulling. In another document, Chen et al. [DOI: 10.1002 / smll.201604245] describe high-performance piezoelectric nanogenerators with imprinted P(VDF-TrFE) / BaTiO3 nanocomposite micropillars for self-powered flexible sensors. In another document, Xu et al. [DOI: 10.1117 / 12.817028] describe the design and microfabrication of a PVDF acoustic sensor.

[0003] There remains a need for further improvements in the manufacture and use of piezoelectric devices, such as piezoelectric devices having robust structures that are compatible with various manufacturing and subsequent processing steps. SUMMARY

[0004] This disclosure relates to piezoelectric devices and manufacturing methods. As described herein, a piezoelectric device comprises an array of pillars, each pillar comprising a piezoelectric material. Typically, the pillars are disposed on a substrate. A piezoelectric layer can be integrally connected to the pillars at their respective ends relative to the substrate. For example, the piezoelectric layer forms a bridging structure that serves as a platform for the piezoelectric material between the respective ends of the pillars. Such a device can be manufactured by pressing a substrate having an array of piezoelectric pillars into a layer of liquefied piezoelectric material, which can be provided on another substrate. When the piezoelectric material hardens, an integral connection can be formed therebetween. Thus, a hardened piezoelectric layer can form a bridging structure between the respective ends of the pillars. Advantageously, the bridging structure of the piezoelectric material can serve as a platform for easy placement of additional electrical components and structures. By using the same or similar materials for the pillars and the bridging layer, the structure can form an integral structure with uniform electromechanical properties. Attached Figure Description

[0005] These and other features, aspects, and advantages of the apparatus, system, and method of this disclosure will become more readily understood from the following description, the appended claims, and the accompanying drawings, in which:

[0006] Figure 1 to FIG. 6 The steps for manufacturing a piezoelectric device are shown.

[0007] FIG. 7A Various sizes of piezoelectric devices are shown;

[0008] FIG. 7B An image of a piezoelectric device made by the method described herein is shown;

[0009] FIG. 8A to FIG. 8E A piezoelectric device with an anchoring structure is shown to improve the adhesion of piezoelectric materials. Detailed Implementation

[0010] The terminology used to describe particular embodiments is 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 or all combinations of one or more of the associated listed items. It should be understood that the terms “comprising” and / or “including” indicate the presence of a described feature, but do not exclude the presence or addition of one or more other features. It should be further understood that when a particular step of a method is indicated to follow another step, that particular step may directly follow that other step, or one or more intermediate steps may be performed before performing that particular step, unless otherwise indicated. Similarly, it should be understood that when describing a connection between structures or components, such connection may be established directly or via intermediate structures or components, unless otherwise indicated.

[0011] The application is more fully described in the following description with reference to the drawings, in which several embodiments of the application are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions can be exaggerated for clarity. Embodiments can be described with reference to schematic and / or cross-sectional illustrations of possibly idealized embodiments and intermediate structures of the application. Similar numbers refer to similar components throughout the specification and drawings. Relative terms, and terms of derivation thereof, should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are intended to encompass different orientations of the system in addition to the orientation depicted in the figures, unless otherwise specified or unless it can be readily apparent from the figure number or the figure description that the orientation is not intended to be a limiting feature. Moreover, terms such as "front" and "back," "lower" and "upper," and the like can be used herein for ease of description and are not intended to be limiting.

[0012] FIG. 1A and FIG. 1B Forming the array of pillars 11 by molding (F) is shown. In one embodiment, e.g. as shown, this forming includes pushing a mold structure 30 having mold openings 31 into the lead layer 1 on the first substrate 10. Although the mold openings 31 are shown in the figures as extending through the mold structure 30, the openings can of course also be closed at the top. Thereby, the piezoelectric material "M" of the lead layer 1 can be pushed into the respective mold openings 31 to form the respective pillars 11. In some embodiments, the piezoelectric material "M" in the lead layer 1 is softened, e.g. by heating before and / or during molding. This can help to shape the material into the pillars. The material of the pillars can be hardened, e.g. by active or passive cooling before the mold is removed.

[0013] Other ways of forming the array of piezoelectric pillars as described herein can also be envisaged. For example, in some embodiments (not shown), the piezoelectric material "M" of the lead layer 1 is cut away according to a grid line to form pillars 11 therebetween. For example, the material can be cut by a physical cutting tool, a laser or other exposure, selective etching. It is also envisaged to create the pillars by additive manufacturing. Further methods of creating the pillars can include electrohydrodynamic stretching.

[0014] In some embodiments, e.g. as shown, the first substrate 10 forms a support structure below the array of pillars 11. Typically, the material of the first substrate 10 is different from the material of the pillars, e.g. a non-piezoelectric material. For example, the first substrate 10 comprises a plastic, glass or silicon substrate. Alternatively, the first substrate 10 can itself comprise the piezoelectric material "M" formed substantially only by the lead layer 1. By using a flexible substrate as the first substrate 10, it can be easier to separate the mold structure 30 from the pillars 11 after shaping. Alternatively, or in addition, the mold structure 30 can also be flexible.

[0015] In a preferred embodiment, the length of the pillars 11 has a direction perpendicular to the plane of the first substrate 10 and the respective end is facing away from the first substrate 10 (towards the piezoelectric layer 21), as for example shown in the figures. Alternatively, or in addition, it is conceivable that some or all pillars are oriented at an angle with respect to the surface normal of the first and / or second substrate.

[0016] In a preferred embodiment, the electrical connections and / or components are comprised in or on the first substrate 10. For example, these can be formed in a lithographic manner, for example on a silicon substrate or a substrate of another material. In some embodiments, one or more further layers are formed between the lead layer 1 and the first substrate 10. For example, the additional layers can have electrical or other functions. Preferably, at least the first electrode 13 is formed between the pillars 11 and the first substrate 10 to apply an electrical potential (voltage) to the piezoelectric material "M". For example, the first electrode 13 comprises an electrically conductive layer, for example a metal, which can or can not be patterned. In some embodiments, the first electrode 13 is a common electrode to apply the same voltage to all pillars. For example, the first electrode 13 is a continuous metal layer laid underneath all pillars. In other or further embodiments, the first electrode 13 is subdivided to address (apply a respective voltage to) individual pillars or groups of pillars, for example a subset of all pillars. For example, one electrode can cover a collection or group of adjacent pillars.

[0017] In other or further embodiments, the first substrate 10 is removed using similar methods as described herein with respect to the second substrate 20. For example, as shown in the figures, the residual part of the lead layer 1 after molding can form a second piezoelectric layer 12. The second piezoelectric layer 12 can also be formed in other ways, for example as a separate layer or added later similar to the first piezoelectric layer 21. If the first substrate 10 is removed, this can serve as another platform between the pillars 11, similar to the piezoelectric layer 21 on the other side. Accordingly, the electrical connections can also be formed after removal of the first substrate 10, or an intermediate layer with the electrical connections can be left on the second piezoelectric layer 12 when the substrate is removed. Alternatively, or in addition to serving as a platform, the second piezoelectric layer 12 can also have other functions, independent of whether the first substrate 10 is removed or not. For example, the second piezoelectric layer 12 can help to stabilize the construction of the pillars 11, and / or to stabilize the connection of the pillars 11 to the first substrate 10 or to an intermediate layer, for example the first electrode 13.

[0018] FIG. 2A and FIG. 2BApplication of piezoelectric layer 21 to array of piezoelectric pillars 11 is shown. In one preferred embodiment, first substrate 10 is provided with an array of pillars 11 comprising piezoelectric material "M", and second substrate 20 is provided with piezoelectric layer 21 facing respective ends of pillars 11. In another or further preferred embodiment, respective ends of pillars 11 are pressed (P) into piezoelectric layer 21, while piezoelectric layer 21 is at least partially liquid. In some embodiments, piezoelectric layer 21 is hardened to form a unitary connection between piezoelectric layer 21 and pillars 11. In this regard, piezoelectric layer 21 can form a bridging structure between respective ends of pillars 11.

[0019] Various ways can be contemplated to create the bridging structure or platform. In one preferred embodiment, the pillars are pressed slightly onto a substrate comprising a thin film bridge that is "wet", e.g., is a liquid having a relatively low viscosity. For example, the viscosity of piezoelectric layer 21, which is at least partially liquid, can be less than (e.g., can be comparable to peanut butter), or less than (e.g., can be comparable to honey) or less than (e.g., such as olive oil), down to (water), or less. For example, piezoelectric layer 21 can be "wet" or liquid because the bridging layer is in solution, uncrosslinked (unhardened), or softened due to being near its melting (or glass transition) temperature. This can depend on the type of piezoelectric material "M".

[0020] When the pillars are pressed in, the layer can be allowed to dry, harden, or cool to form a permanent bridging structure. For example, this can cause the viscosity to increase by several hundred-fold, several thousand-fold, or more, most preferably so that piezoelectric layer 21 acts as a solid. By hardening the layer as the pillars 11 are pressed into the piezoelectric layer 21, which is at least partially liquid, a permanent (or at least sufficiently durable) connection can be formed therebetween. Thereafter, pillars 11 and piezoelectric layer 21 can essentially form a single or unitary piece of piezoelectric material "M".

[0021] Depending on the viscosity and thickness of the "wet" piezoelectric layer 21, the pillars can be pressed into the layer with a certain amount of force. Generally, a volume of the wet film can move into the space between the pillars. This can effectively reduce the height of the pillars. To some extent, this effect can be desirable because it promotes adhesion between the pillars and the bridging layer. In some embodiments, e.g., when the film is relatively thin compared to the height of the pillars, the pillars can even be pressed down completely, to the point where they touch the substrate of the wet film. At this point, for example, no further movement can occur and the wet film does not further enter the space between the pillars. In other or further embodiments, e.g., when it is not desirable to reduce the effective pillar height, a limited amount of pressure can be applied, depending on the viscosity of the wet film. In some cases, the weight of first substrate 10, e.g., a glass plate, comprising the pillars can be sufficient.

[0022] In a preferred embodiment, the piezoelectric layer 21 essentially comprises the same piezoelectric material "M" as the pillars 11. By using the same material, the piezoelectric layer 21 and the pillars 11 can have similar properties and / or the connection between them can be improved. For example, when the combined structure is actuated by applying an electric field, the resulting deformation of the piezoelectric material "M" can be the same or similar for the respective parts of the piezoelectric layer 21 and the pillars 11. The connection can also be fully integrated.

[0023] In a preferred embodiment, the piezoelectric material "M" of each of the pillars 11 and the piezoelectric layer 21 comprises (or essentially consists of) a piezoelectric polymer. Most preferably, the piezoelectric material comprises (or essentially consists of) a polymeric material or a composite polymeric / ceramic material. Examples of polymeric piezoelectric materials can include polyvinylidene fluoride (PVDF) and its copolymers, polyamides, liquid crystal polymers, polyacetamides, and polyvinylidene chloride PVDC. Examples of composite polymeric / ceramic materials can include BaTi03, PZT, ZnO or PMN-PT within a polymeric medium such as PVDF, epoxy, SU8 and PDMS.

[0024] In a preferred embodiment, the piezoelectric layer 21 is melted by applying heat (H) until the piezoelectric layer 21 is at least partially liquefied. Most preferably, the heat H is applied to the piezoelectric layer 21 but not to the pillars 11. In this way, the structural integrity of the piezoelectric layer 21 can be better maintained. Most preferably, the heat H is applied to the piezoelectric layer 21 before, but not during, the step of pushing the pillars 11 into the piezoelectric layer 21.

[0025] In some embodiments, an internal heat source (not shown, e.g. as part of the second substrate) can be used to heat the piezoelectric layer 21. In other and further embodiments, the heat H is applied by an external heat source (also not shown). For example, the second substrate 20 (only) with the piezoelectric layer 21 is placed in an oven to apply the heat H (e.g. while the first substrate 10 is maintained unheated). Alternatively, or in addition, the heat H is applied by a (directed) radiation source, e.g. by irradiating the piezoelectric layer 21 with infrared or other radiation. In one embodiment, the heat H is applied exclusively or predominantly to the piezoelectric layer 21.

[0026] In one embodiment, for example as FIG. 2BAs shown, the molten piezoelectric layer 21 is hardened (C) after being connected with the pillars 11 by cooling to form an integral connection with the pillars 11. For example, the material of the piezoelectric layer 21 can be hardened by active or passive cooling. Alternatively, or in addition to melting, in some embodiments the at least partially liquid or wet piezoelectric layer 21 comprises an un-solidified (un-crosslinked) piezoelectric material "M". For example, the pillars 11 are pushed into the un-solidified piezoelectric layer 21, after which the piezoelectric layer 21 is hardened by solidification. For example, the piezoelectric layer 21 is solidified by heat and / or electromagnetic radiation, for example by ultraviolet light to promote crosslinking in the piezoelectric material "M". In other or further embodiments, the at least partially liquid or wet piezoelectric layer 21 comprises or is formed from a solution with the piezoelectric material "M". For example, the pillars 11 are pushed into the liquid solution of the piezoelectric layer 21, after which the solution is hardened by drying. For example, the piezoelectric layer 21 is actively or passively dried, leaving a solid structure when the solvent is removed. A combination of drying and solidification is also conceivable, for example when the solution comprises an un-solidified piezoelectric material "M" which is solidified after the solvent is removed. It is also conceivable to apply the piezoelectric material "M" in a solution, and to melt the material after drying.

[0027] In a preferred embodiment, the respective end portions of the pillars 11 are arranged in a face-down position when being pushed P into the at least partially molten piezoelectric layer 21. By hanging the pillars 11 upside down (in the direction of gravity) from the first substrate 10, the pillars can better maintain their shape, even if the pillars have started to melt, for example by indirect heating from the piezoelectric layer 21. In another or further embodiment, the piezoelectric layer 21 is preferably arranged on top of the second substrate 20 in a face-up position or face-up orientation. Advantageously, in this orientation, molten material of the piezoelectric layer 21 can remain on the second substrate 20 without dripping between the pillars 11. After the piezoelectric layer 21 is sufficiently hardened, the connected structure can be flipped over, for example for subsequent processing.

[0028] FIG. 3A and FIG. 3BAn embodiment is shown in which the second substrate 20 is removed. In one embodiment, the second substrate 20 is removed (R) leaving the hardened piezoelectric layer 21 as a platform for the respective end of the bridge pillar 11. This can, for example, reveal a uniform and flat surface on top of the platform. In some embodiments, subsequent electrical connections can be placed directly on the piezoelectric layer 21 and then form an integral part with the pillar 11. The use of a flexible, e.g. bendable, substrate as the second substrate can facilitate the removal of the second substrate. For example, a plastic or other flexible material is used. In addition to removal, it is conceivable that the second substrate 20 remains attached to the piezoelectric layer 21. For example, the second substrate 20 can include electrical connections and / or layers (not shown) between the second substrate 20 and the piezoelectric layer 21. These integrated connections on the second substrate 20 can then be used, for example, to apply a respective voltage to the pillar 11. For example, the second substrate 20 can have integrated second electrodes that cooperate with the first electrodes 13 on the first substrate 10 to apply an electric field between the two electrodes.

[0029] FIG. 4A and FIG. 4B An embodiment is shown in which the circuitry is applied to the platform formed by the piezoelectric layer 21. In some embodiments, electrical contacts 23 and / or interconnects 25 are provided on the piezoelectric layer 21 of the bridge pillar 11. These contacts and / or interconnects can be used, for example, to apply a respective voltage to the piezoelectric material "M" or receive a respective voltage from the piezoelectric material "M". It will be appreciated that the platform formed by the integration of the piezoelectric layer 21 with the pillar 11 can greatly facilitate the deposition of the contacts 23 and / or interconnects 25.

[0030] In some embodiments, after the piezoelectric layer 21 on the second substrate 20 is hardened, the first substrate 10 is flipped over (e.g. the first substrate 10 is turned back to the bottom). In this way, the piezoelectric layer 21 can form a platform on top of the pillars 11 facing up, on which subsequent connections or components are deposited. By providing a horizontal platform on top of the pillars 11, various subsequent deposition methods can be facilitated. In one preferred embodiment, the electrical contacts 23 (or other components and structures) are deposited on the piezoelectric layer 21 by photolithography. This can include, for example, depositing a further layer of material on top of the piezoelectric layer 21 and exposing to a light pattern to selectively form or remove structures, e.g. by wet or dry etching techniques. Other or further deposition techniques can also be used, such as printing or other transfer techniques, e.g. light-induced forward transfer techniques (LIFT) that transfer structures or components from a donor substrate (not shown).

[0031] A piezoelectric device as described herein can be used to transmit and / or receive acoustic signals, e.g. ultrasound. For example, a voltage can be applied to generate an electric field via the piezoelectric material "M" of the pillars 11 to actuate their vibrations. Alternatively, or in addition, a voltage can be measured from vibrations of the pillars 11 caused, e.g. by an external source. In some embodiments, e.g. as shown, a respective one or more pillars 11 are connected via respective electrodes 13, 23 to an electrical device 50 configured to transceive electrical signals therebetween. For example, the electrical device 50 comprises a signal generator and / or a sensor device. Further components, e.g. a controller, can also be connected to determine which one or more pillars 11 are addressed.

[0032] FIG. 5A and FIG. 5B Polarization of the piezoelectric material in the pillars 11, the bridge structure formed by the piezoelectric layer 21 and, optionally, the second piezoelectric layer 12 at the bottom is shown. In one embodiment, the second piezoelectric layer 12 is also integrally connected to the pillars 11. Accordingly, the first piezoelectric layer 21, the pillars 11 and the second piezoelectric layer 12 can all be integrally connected. In a preferred embodiment, the piezoelectric material "M" in the array of pillars 11 is polarized by applying a (high) voltage "HV", while an electrically insulating material "I" is provided in the spacing between the pillars 11 inside the array. Advantageously, during polarization, the electrically insulating material "I" can be used to prevent short-circuit sparks that can damage the device. In some embodiments, the electrically insulating material "I" comprises a fluid, e.g. a liquid. Solid insulating materials can also be used. In some embodiments, the electrically insulating material "I" is provided in the spacing between the pillars 11 after the pillars are connected to the piezoelectric layer 21. For example, a liquid or gas can be pumped into the spacing between the pillars. Most preferably, the electrically insulating material "I" is removed after polarization. In this way, the insulating material need not affect the mechanical properties of the array.

[0033] In a preferred embodiment, e.g. as shown in FIG. 5A the pillars 11 are polarized by corona polarization after the pillars 11 are connected to the piezoelectric layer 21. Without being bound by theory, the electric charge can be spread across the piezoelectric layer 21 to cause a more uniform electric field along the length of the pillars (as opposed to an open structure, where the electric charge can also reach the sides of the pillars). Other ways of polarizing the piezoelectric material can also be envisaged, preferably polarizing along the length of the pillars, e.g. by applying a high voltage "HV" across respective electrodes 13, 23 on both sides of the ends of the pillars, as shown in FIG. 5B Accordingly, it will be appreciated that polarization can occur at different stages of manufacture, e.g. before or after applying the electrodes.

[0034] FIG. 6A preferred sequence of steps for manufacturing the piezoelectric device 100 described herein is shown. Of course other sequences are also contemplated, e.g. adding further steps, removing optional steps, rearranging steps, etc. For example, the array of pillars 11 can be manufactured by other methods than molding F. For example, the pillars can be face down when molded, or kept face up when connected to the wet piezoelectric layer 21 (adhered upside down from the second substrate 20). For example, instead of heat H, a solution or unhardened material can be used to wet or liquefy the piezoelectric layer 21. For example, the pillars 11 can be actively pushed into the piezoelectric layer 21, e.g. only by gravity or by active pushing, and vice versa. For example, the second substrate 20 can be left on the hardened piezoelectric layer 21. For example, the piezoelectric layer material can be polarized before, during or after the assembled structure. For example, the electrical connections can be integrated in the respective substrates and / or applied afterwards.

[0035] FIG. 7A Piezoelectric devices 100 of various dimensions are shown. FIG. 7B Images of piezoelectric devices made by the methods described herein are shown. The left images represent cross-sectional views. The images on the right represent top views, the top right corner images focus on the piezoelectric bridging layer, and the bottom right corner images focus on the pillars / pockets.

[0036] Irrespective of the manufacturing method, the present disclosure can provide advantageous structures and devices. In one embodiment, a piezoelectric device 100 comprises a first substrate 10 having an array of pillars 11 comprising piezoelectric material "M", and a piezoelectric layer 12 integrally connected with the pillars 11 on respective end portions of the pillars relative to the first substrate 10. Preferably, the piezoelectric layer 21 forms a bridging structure serving as a platform of piezoelectric material "M" between respective end portions of the pillars 11.

[0037] In some embodiments, the piezoelectric device 100 includes electrical contacts (not shown here) on top of the platform formed by the piezoelectric layer 21. In other or further embodiments, the piezoelectric device 100 includes a second piezoelectric layer 12 between the pillars 11 and the first substrate 10. In a preferred embodiment, the piezoelectric device 100 includes a first electrode (not indicated here) between the second piezoelectric layer 12 and the first substrate 10. In some embodiments, the piezoelectric device 100 includes or is coupled to an electrical device (not shown here) configured to transmit and receive electrical signals. For example, signals are transmitted to and / or received from respective electrodes on both ends of the pillars 11, e.g. via one or more piezoelectric layers 12, 22. The piezoelectric device 100 as manufactured and / or configured as described herein can be used for many purposes, most preferably for generating or detecting acoustic waves, e.g. in the ultrasonic frequency range. For example, the piezoelectric device 100 can be part of a medical diagnostic and / or imaging device. Other uses are also conceivable.

[0038] In a preferred embodiment, the pillars 11 have a pillar height "Z1" which is an integer multiple of half the wavelength of the (longitudinal) acoustic wave in the pillars. The pillar height is preferably chosen such that the natural resonance frequency along the length (height) of the pillars matches the frequency of the acoustic wave to be transmitted or received. In this way, the wave can resonate in the pillars, thereby increasing the efficiency. For example, the resonance frequency can be determined by factors such as material stiffness, pillar shape, condition of the substrate (which can give a λ / 2 or λ / 4 resonator). As an example, a one hundred micron PVDF-TrFE pillar is used which, in combination with the substrate, has a resonance frequency of about ten million hertz. Other dimensions, materials and frequencies are of course also possible. For example, the pillar height "Z1" can typically vary between five and three hundred microns, preferably between ten and two hundred microns. For example, the piezoelectric device is used for ultrasonic applications.

[0039] In a preferred embodiment, the pillars 11 have a pillar height "Z1" and a pillar width "X1", wherein the pillar height "Z1" is at least twice as large as the pillar width "X1". The higher the aspect ratio, the more the pillars can be used as a kind of one-dimensional structure. For example, this can improve the separation between transverse and axial resonance modes. On the other hand, preferably the length is chosen to be equal to half the wavelength, while the thickness or width of the pillars is preferably not so small as to jeopardize the structural integrity. The manufacturing method can also limit the minimum width. For example, the ratio "Z1" / "X1" is typically between one and a half and ten, preferably more than three or four.

[0040] In a preferred embodiment, the pillars 11 are separated by gaps 11g between the pillars. In principle, a gap 11g of a few microns, e.g., greater than five microns, is sufficient to provide sufficient damping between the pillars for coupling. Typically, the distance "X2" between the pillars is similar to the pillar width "X1", e.g., differing by less than a factor of three, preferably less than a factor of two or less than fifty percent. By way of example, both the pillar width "X1" and the distance "X2" are in a typical range of between five microns and one hundred microns. In some embodiments, the distance "X2" is chosen so that Lamb waves (e.g., A0 surface waves) via the piezoelectric layer 21 do not constructively interfere with the next pillar, so the pillars can be independent. In some embodiments, e.g., for imaging, the spacing between the pillars (X1+X2) is preferably less than half the wavelength of the ultrasound waves. The spacing can also be larger, e.g., for other applications.

[0041] Depending on the distribution of the pillars, the total surface size "X3" of the piezoelectric layer 21 is typically much larger than the spacing ("X1"+ "X2"). By way of example, "X3" can be at least five or ten times larger than ("X1"+ "X2"). In some embodiments, the array includes at least ten pillars, preferably at least twenty, at least fifty, at least one hundred, at least one thousand, e.g., up to a million or more pillars. By way of example, a piezoelectric device includes an array of two hundred by two hundred pillars at a spacing of fifty microns distributed over a one square centimeter surface.

[0042] Preferably, the thickness "Z2" of the piezoelectric layer 21 is thick enough on the one hand to allow the pillars 11 to be immersed in the layer at least some distance for connection and / or to provide a sufficient platform structure for subsequent processing, and on the other hand not so thick as to interfere with the actuation of the pillars or the desired one-dimensional behavior of the assembled structure. Typically, the length "Z1" of the pillars 11 is at least two or three times, preferably at least five times, more preferably, e.g., up to ten times, twenty times or more, larger than the thickness "Z2" of the piezoelectric layer 21.

[0043] Typically, the thickness "Z2" of the piezoelectric layer 21 is about ten percent of the pillar height "Z1". In some embodiments, the thinner the thickness of the piezoelectric layer 21 compared to the pillar height "Z1", the less cross-talk between the pillars can be expected. In other or further embodiments, a thicker piezoelectric layer 21 can be used to allow surface waves to pass along a bridge or platform formed by the piezoelectric layer 21, e.g., for interference. In addition, the mechanical stability of the bridge can be better when the piezoelectric layer 21 is thicker. By way of example, the thickness "Z2" of the piezoelectric layer 21 is between one micron and thirty microns, preferably between five microns and twenty microns.

[0044] In some embodiments, the structure of the pillars can be supported by a second piezoelectric layer 12 located on the other end portion. The thickness Z3 of this second piezoelectric layer 12 can generally be similar or identical to the thickness "Z2" of the first piezoelectric layer 21, for example within a factor of two or three, and most preferably as symmetric as possible.

[0045] Typically, the first substrate 10 has a thickness "Z4" that is greater than the thickness of the piezoelectric layer 21, greater than the length "Z1" of the pillars, or even greater than the thickness of the combined structure. For example, the first substrate 10 has a thickness of at least half a millimeter, greater than one millimeter, for example up to half a centimeter, or more. The second substrate (not shown here) can have a similar thickness to the first substrate 10, or a different thickness, for example less than the thickness of the first substrate 10.

[0046] FIG. 8A to FIG. 8E Another embodiment for manufacturing the piezoelectric device 100 described herein is shown.

[0047] In some embodiments, for example as shown in FIG. 8B The first substrate 10 is provided with an anchoring structure 10a. For example, the anchoring structure 10a can be used to help or improve the adhesion of subsequent layers deposited onto the first substrate 10. In one embodiment, the anchoring structure 10a is formed by etching a series of cavities into the first substrate 10. For example, the first substrate 10 comprises or is formed substantially from a polymer material that can be etched away. Other materials can also be used. Typically, the etching process is guided by an etch mask. For example, as shown in FIG. 8A Advantageously, the etch mask can be formed at least in part by the pattern of the bottom electrode 13. In addition, electrical and / or other locations on the first substrate 10, for example other or further etch mask structures adjacent to the bottom electrode 13 can be used. In a preferred embodiment, the series of cavities undercut the etch mask at least in part, for example travel partially under the electrode. This can further improve adhesion, in particular allowing subsequent layers to remain adhered to the first substrate 10 in the case of significant bending. Alternatively, or in addition to etching, the anchoring structure 10a can also be formed by other means, for example by the structure of the bottom electrode itself, or by providing another structure on the first substrate 10 and connected to the first substrate to help maintain adhesion of subsequent layers.

[0048] In some embodiments, for example as shown in FIG. 8CAs shown, a subsequent layer is provided on the first substrate 10 after the anchoring structure 10a is formed. Preferably, the subsequent layer is initially provided in (partly) liquid form. In this way, the subsequent layer can flow or be more easily pushed into the anchoring structure 10a. When the material of the subsequent layer has flowed and / or been pushed into the cavities, it can at least partly harden, e.g. cure. Most preferably, the subsequent layer comprises a piezoelectric material M, which can form the lead layer 1, as previously described, e.g. with reference to FIG. 1A The lead layer 1 comprises or is formed by a polymer piezoelectric material, e.g. P(PVDF-TrFE), which is initially applied in liquid form. In one embodiment, the lead layer 1 is molded to form the pillars 11 of piezoelectric material M, e.g. as shown in FIG. 8D The molding process can involve pushing a mold structure 30 into the lead layer 1. This can also help to push the piezoelectric material M (further) into the anchoring structure 10a. Other ways of forming the pillars 11 are also conceivable. In other or further embodiments, e.g. as shown in FIG. 8E The piezoelectric layer 21 is integrally connected to the pillars 11, e.g. forming a bridge structure between respective end portions of the pillars. For example, as described with reference to FIG. 2A to FIG. 3B The piezoelectric layer 21 can be provided.

[0049] For the purpose of clarity and brevity of explanation, features described herein are part of the same or different embodiments, however, it is understood that the scope of the invention can include embodiments having combinations of all or some of the described features. For example, while embodiments show various layers and components forming a piezoelectric device, one skilled in the art can also conceive alternative ways of achieving similar functions or results, with the advantages of the present disclosure. For example, layers and structures can be combined or split into one or more alternative components. Different elements of the discussed and shown embodiments provide certain advantages, e.g. manufacturing and using a piezoelectric device having a rigid structure and being compatible with different manufacturing and subsequent processing steps.

[0050] In some embodiments, piezoelectric devices as described herein are used for non-contact mixing of liquids, e.g. by acoustic streaming, to achieve low shear high mass flow. In one embodiment, the piezoelectric device comprises a flexible substrate. By way of example, the flexible substrate can form part of or be applied to a flexible bag containing the liquids to be mixed. By way of example, the bag comprises a flexible (bio)reactor and / or the liquids comprise biological liquids, e.g. medical liquids, in particular vaccines which can benefit from (continuous or batch) mixing. Advantageously, a large area flexible ultrasonic transducer or substrate can be monolithically formed or patchable, e.g. the flexible acoustic device can be conformal to the bag, ensuring good coupling. Furthermore, the bag with integrated acoustic device can be easily packaged, e.g. substantially flat (when the bag is empty) without sharp / hard objects inside the bag. In addition to use in flexible containers, rigid or flexible piezoelectric devices can also form part of or be integrated in the walls of rigid containers for mixing or other purposes, e.g. sensing. Other flexible and / or rigid piezoelectric material / substrate applications are also envisaged. Of course, it will be appreciated that any of the foregoing embodiments or processes can be combined with one or more other embodiments or processes to provide further improvements in design and advantages sought and matched. It will be appreciated that the present disclosure provides particular advantages for piezoelectric transducers for sensing or actuating relatively large and / or flexible surfaces, which can generally be applied to any application using piezoelectric devices.

[0051] In the interpretation of the appended claims, it is to be understood that the word "comprising" does not exclude the presence of other elements than those listed in a given claim; the word "a" or "an" preceding the citation of a element does not exclude the presence of a plurality of such elements; any reference signs in the claims should not be construed as limiting the scope; the use of the expressions "first", "second" and the like do not imply any order but rather are used to distinguish one claim from another; any device or part thereof can be combined with another device or part thereof to form a further device, unless specifically mentioned otherwise. When a claim refers to "another" or "an" preceding an element, this refers to a different claim than the one in which this element is found. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The disclosure encompasses all possible combinations of the individual aspects, operations and features recited in the claims.

Claims

1. A method for manufacturing a piezoelectric device (100), the method comprising: -supply ο First substrate (10), having an array of several pillars (11) comprising piezoelectric material (M), and ο A second substrate (20) having a piezoelectric layer (21) facing the respective end of the pillar (11); - When the piezoelectric layer (21) is at least partially liquid, the corresponding end of the support (11) is pushed (P) into the piezoelectric layer (21); and - Harden the piezoelectric layer (21) to form an integral connection between the piezoelectric layer (21) and the pillar (11), wherein the piezoelectric layer (21) forms a bridging structure between the respective ends of the pillar (11).

2. The method of claim 1, wherein, The piezoelectric layer (21) essentially comprises the same piezoelectric material (M) as the support (11).

3. The method of claim 1 or 2, wherein, The piezoelectric material (M) of each of the pillars (11) and the piezoelectric layer (21) comprises a piezoelectric polymer.

4. The method according to claim 1 or 2, wherein, The piezoelectric layer (21) is melted by applying heat (H) until the piezoelectric layer is at least partially liquefied, wherein the heat (H) is applied to the piezoelectric layer (21) but not to the pillar (11).

5. The method according to claim 1 or 2, wherein, When the corresponding end of the support column is pushed (P) into at least partially molten piezoelectric layer (21), the corresponding end of the support column (11) is arranged in a downward orientation.

6. The method according to claim 1 or 2, wherein, The second substrate (20) is removed (R), leaving a hardened piezoelectric layer (21) as a platform bridging the respective ends of the pillar (11).

7. The method according to claim 1 or 2, wherein, A plurality of electrical contacts (23) and / or a plurality of interconnects (25) are disposed on the piezoelectric layer (21) bridging the pillar (11) for applying a corresponding voltage to the piezoelectric material (M) or receiving a corresponding voltage from the piezoelectric material (M).

8. The method according to claim 1 or 2, wherein, After the piezoelectric layer (21) on the second substrate (20) is hardened, the first substrate (10) is flipped over, so that the piezoelectric layer (21) forms a platform on top of the upward-facing pillar (11), on which subsequent connections or components are deposited.

9. The method according to claim 1 or 2, wherein, Electrical contacts (23) are deposited on the bridging structure formed by the piezoelectric layer (21) by photolithography.

10. The method according to claim 1 or 2, wherein, A first electrode (13) is formed between the pillar (11) and the first substrate (10) for applying a potential to the piezoelectric material (M).

11. The method according to claim 1 or 2, wherein, The piezoelectric material (M) in the array of pillars (11) is polarized by applying a voltage (HV), while an electrically insulating material (I) is disposed in the spacing between the pillars (11) inside the array, wherein the electrically insulating material (I) is removed after polarization.

12. The method according to claim 1 or 2, wherein, After the pillar (11) is connected to the piezoelectric layer (21), the pillar (11) is polarized by corona polarization.

13. Use of a piezoelectric device (100) for generating or detecting sound waves, the piezoelectric device (100) comprising: A first substrate (10) having an array of a plurality of pillars (11) comprising a piezoelectric material (M); a first piezoelectric layer (12) integrally connected to the pillars (11) between the first substrate (10) and the pillars (11) at respective first ends of the pillars (11), wherein the first piezoelectric layer (12) forms a substrate structure between the respective first ends of the pillars (11); and a second piezoelectric layer (21) integrally connected to the pillars (11) at respective second ends of the pillars relative to the first substrate (10), wherein the second piezoelectric layer (21) forms a bridging structure that serves as a platform comprising the piezoelectric material (M) between the respective second ends of the pillars (11).

14. A piezoelectric device (100), comprising: A first substrate (10) having an array of a plurality of pillars (11) comprising a piezoelectric material (M); a first piezoelectric layer (12) integrally connected to the pillars (11) between the first substrate (10) and the pillars (11) at respective first ends of the pillars (11), wherein the first piezoelectric layer (12) forms a substrate structure between the respective first ends of the pillars (11); and a second piezoelectric layer (21) integrally connected to the pillars (11) at respective second ends of the pillars relative to the first substrate (10), wherein the second piezoelectric layer (21) forms a bridging structure that serves as a platform comprising the piezoelectric material (M) between the respective second ends of the pillars (11).

15. The piezoelectric device according to claim 14, comprising: - A first electrode (13) is located between the first piezoelectric layer (12) and the first substrate (10). - A plurality of electrical contacts (23), which form at least one second electrode on the top of the platform formed by the second piezoelectric layer (21), and - An electrical device (50) configured to transmit and receive electrical signals from the first electrode and the second electrode (13, 23) for generating and / or measuring sound waves.

16. The piezoelectric device according to claim 14, wherein, The second piezoelectric layer (21) has a first thickness (Z2) between 1 micrometer and 30 micrometers.

17. The piezoelectric device according to claim 16, wherein, The first piezoelectric layer (12) has a second thickness (Z3), which is similar to or the same as the first thickness (Z2) of the second piezoelectric layer (21), with a difference of up to three times.

18. The piezoelectric device according to claim 14, wherein, The first substrate (10) has a third thickness (Z4), which is at least 0.5 mm.

19. The piezoelectric device according to claim 14, wherein, The support (11) has a support height (Z1) between 5 micrometers and 300 micrometers.

20. The piezoelectric device according to claim 14, wherein, The support column (11) has a support column height (Z1) and a support column width (X1), wherein the support column height (Z1) is at least twice as large as the support column width (X1).

Images