Piezoelectric device having a pillar structure and method for manufacturing the same

Abstract

A piezoelectric device (100) and a method for fabricating the same are disclosed. A first substrate (10) includes an array of pillars (11) comprising a piezoelectric material (M). A second substrate (20) includes a piezoelectric layer (21) facing each end of the pillars (11). While the piezoelectric layer (21) is at least partially liquid, each end of the pillars (11) is pressed (P) into the piezoelectric layer (21). The piezoelectric layer (21) solidifies, forming an integral connection between the piezoelectric layer (21) and the pillars (11). This allows the piezoelectric layer (21) to form a bridge structure between each end of the pillars (11). The integral piezoelectric structure can be polarized by a high voltage (HV). The bridge structure can serve as a platform for depositing electrical contacts (23). The piezoelectric device (100) can be used to generate or detect acoustic waves, for example, in medical imaging.

Description

Technical Field

[0001] The present disclosure relates to devices such as acoustic transducers having a pillar structure of a piezoelectric material and methods of manufacturing such devices.

Background Art

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

[0003] There remains a need for further improvement in the manufacture and use of piezoelectric devices, such as having a robust structure that is compatible with various manufacturing and post-processing steps, for example.

Summary of the Invention

[0004] Aspects of the present disclosure relate to piezoelectric devices and methods of manufacturing the same. As described herein, a piezoelectric device includes an array of pillars that include a piezoelectric material. Typically, the pillars are disposed on a substrate. A piezoelectric layer can be integrally connected to each of the pillars at each end of the pillar facing the substrate. For example, the piezoelectric layer can form a bridging structure that functions as a platform for the piezoelectric material between each end of each of the pillars. Such a device can be manufactured by pressing a substrate having an array of piezoelectric pillars against a layer of a liquid piezoelectric material provided on another substrate. When the piezoelectric materials solidify, an integral connection can be formed therebetween. Thus, the solidified piezoelectric layer can form a bridging structure between each end of each of the pillars. Advantageously, the bridging structure of the piezoelectric material can be used as a platform for easily disposing additional electrical components and structures. By using the same or similar materials for both the pillars and the bridging layer, the structure can form a monolithic structure having uniform electromechanical properties.

[0005] These and other features, aspects, and advantages of the devices, systems, and methods of the present disclosure will be understood in more detail from the following detailed description, the appended claims, and the accompanying drawings.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0007] The terms used to describe specific embodiments are not intended to limit the present 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" identify the presence of the described features, but do not preclude the presence or addition of one or more other features. If a particular step of a method is described as following another step, unless otherwise specified, the particular step may follow directly after the other step or one or more intermediate steps may be performed before the particular step is executed. Similarly, when a connection between structures or components is described, it will be understood that this connection can be established directly or through intermediate structures and components, unless otherwise specified.

[0008] Hereinafter, the present invention will be more fully described with reference to the accompanying drawings showing embodiments of the invention. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional views of perhaps idealized embodiments of the present invention and intermediate structures. In this specification and the drawings, like numbers refer to like elements throughout. Relative terms and their derivatives are to be construed as referring to the orientation as then described or as shown in the drawings being described. These relative terms are for convenience of description and do not require the system to be constructed or operated in a particular orientation, unless otherwise specified.

[0009] Figures 1A and 1B show the formation of an array of pillars 11 by a mold (F). In one embodiment, for example as shown in the figures, this formation includes pushing a mold structure 30 having mold openings 31 into a precursor layer 1 on a first substrate 10. The openings 31 are shown as extending through the mold structure 30, but of course it is also possible to close these upper portions. Thus, the piezoelectric material "M" of the precursor layer 1 can be pushed into each mold opening 31 to form each pillar 11. In some embodiments, the piezoelectric material "M" in the precursor layer 1 is softened, for example by heating, before and / or during the molding. This may facilitate deforming the material into the shape of the pillars. The pillar material may be solidified, for example by active or passive cooling, before the mold is removed.

[0010] Also, other methods of forming an array of piezoelectric pillars as described herein may be envisioned. For example, in some embodiments (not shown), the piezoelectric material "M" of the precursor layer 1 is cut along the lines of a grid, and pillars 11 are formed between those lines. For example, the material can be cut by a physical cutting tool, a laser, or other exposure, and optionally etched thereafter. It is also conceivable to manufacture the pillars by additive manufacturing. Yet another method for manufacturing the pillars can include electro-hydrodynamic pulling.

[0011] In some embodiments, as illustrated for example, the first substrate 10 forms a support structure under an array of pillars 11. Typically, the first substrate 10 is made of a material different from that of the pillars, for example, not a piezoelectric material. For example, the first substrate 10 includes a plastic, glass, or silicon substrate. Alternatively, the first substrate 10 may itself include a piezoelectric material "M" formed substantially only by the precursor layer 1. By using a flexible substrate as the first substrate 10, it may be easier to separate the mold structure 30 from the pillars 11 after formation. Alternatively or additionally, the mold structure 30 may be flexible.

[0012] In a preferred embodiment, as illustrated for example, the length of the pillar 11 has a direction perpendicular to the plane of the first substrate 10, and each end faces away from the first substrate 10 (in the direction of the piezoelectric layer 21). Alternatively or additionally, it is conceivable that some or all of the pillars are oriented at an angle with respect to the surface normal of the first substrate and / or the second substrate.

[0013] In a preferred embodiment, the electrical connections and / or components are incorporated within or on the first substrate 10. For example, these can be formed by lithography, for example on a substrate of silicon or other material. In some embodiments, one or more additional layers are formed between the precursor layer 1 and the first substrate 10. For example, the additional layer may have an electrical function or other function. Preferably, at least a first electrode 13 for applying a potential (voltage) to the piezoelectric material "M" is formed between the pillar 11 and the first substrate 10. For example, the first electrode 13 includes a conductive layer (e.g., metal) which may or may not be patterned. In some embodiments, the first electrode 13 is a common electrode for applying the same voltage to all the pillars. For example, the first electrode 13 is a continuous metal layer passing under all the pillars. In other or further embodiments, the first electrode 13 is subdivided to individually address (apply respective voltages to) one pillar or a plurality of pillars (e.g., a subset of all the pillars). For example, one electrode may cover an aggregate or cluster of adjacent pillars.

[0014] In other embodiments or further embodiments, the first substrate 10 is removed in a manner similar to that described herein with respect to the second substrate 20. For example, as shown, the remaining portion of the precursor layer 1 after molding can form the second piezoelectric layer 12. The second piezoelectric layer 12 can also be formed by other methods, for example, it can be formed as a separate layer, or it can be added later in the same manner as the first piezoelectric layer 21. When the first substrate 10 is removed, the second piezoelectric layer 12 can function as another platform between the pillars 11, similar to the piezoelectric layer 21 on the opposite side. Thus, an electrical connection can be formed even after the first substrate 10 is removed, or an intermediate layer having an electrical connection can remain on the second piezoelectric layer 12 while the substrate is removed. Alternatively, or in addition to functioning as a platform, the second piezoelectric layer 12 can also have other functions regardless of whether the first substrate 10 is removed. For example, the second piezoelectric layer 12 can help stabilize the structure of the pillars 11 and / or the connection of the pillars 11 to the first substrate 10 or the intermediate layer (such as the first electrode 13).

[0015] Figures 2A and 2B show the provision of the piezoelectric layer 21 on an array of piezoelectric pillars 11. In a preferred embodiment, the first substrate 10 comprises an array of pillars 11 containing the piezoelectric material "M", and the second substrate 20 comprises a piezoelectric layer 21 facing each end of the pillars 11. In other embodiments or further embodiments, each end of the pillars 11 is pushed (P) into the piezoelectric layer 21 while the piezoelectric layer 21 is at least partially liquid. In some embodiments, the piezoelectric layer 21 is solidified to form an integral connection between the piezoelectric layer 21 and the pillars 11. Thereby, the piezoelectric layer 21 can form a bridge structure between each end of the pillars 11.

[0016] Various methods can be considered to form a bridge structure or a platform. In a preferred embodiment, the pillar is lightly pressed onto a substrate that includes a "wet" thin film bridge (e.g., a liquid having a relatively low viscosity). For example, the viscosity of the at least partially liquid piezoelectric layer 21 is less than 10 6 mPa·s (equivalent to peanut butter), or less than 10 4 mPa·s (equivalent to honey), or less than 10 2 mPa·s (e.g., olive oil-like), and preferably 1 mPa·s or less (water). For example, the piezoelectric layer 21 can be "wet" or liquid because the bridge layer is in a solution state, uncrosslinked (uncured), or near its melting (or glass transition) temperature, which can depend on the type of piezoelectric material "M".

[0017] When the pillar is pushed in, the piezoelectric layer 21 can dry, cure, or cool to form a persistent bridge structure. For example, this can dramatically increase the viscosity by 100-fold, 1000-fold, or more, most preferably to a viscosity at which the piezoelectric layer 21 acts as a solid. A permanent (or at least sufficiently durable) connection can be formed between them by solidifying the at least partially liquid piezoelectric layer 21 while the pillar 11 is being pushed into the piezoelectric layer 21. Thereafter, the pillar 11 and the piezoelectric layer 21 can form an essentially monolithic or integral piece of the piezoelectric material "M".

[0018] Depending on the viscosity and thickness of the "wet" piezoelectric layer 21, the pillars can be pushed into the piezoelectric layer 21 with a specific force. Typically, a certain volume of the wet thin film can move into the spacing between the pillars. As a result, the height of the pillars can be reduced. This effect can be desirable to some extent as it promotes the adhesion between the pillars and the bridge layer. In some embodiments, for example, when the film is relatively thin compared to the height of the pillars, the pillars can even be completely pushed down until they contact the substrate on which the wet thin film is formed. For example, at this point, no further movement may occur and the wet thin film may not penetrate further into the space between the pillars. In other or further embodiments, for example, when it is not desired to reduce the effective pillar height, a limited pressure can be applied depending on the viscosity of the wet film. In some cases, the weight of the first substrate 10 (e.g., a glass plate) containing the pillars is sufficient.

[0019] In a preferred embodiment, the piezoelectric layer 21 comprises the same piezoelectric material "M" as the pillars 11 substantially. 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 operating the composite structure by applying an electric field, the deformation occurring in the piezoelectric material "M" can be the same or similar in each part of the piezoelectric layer 21 and the pillars 11. Also, the connection part can be completely integrated.

[0020] In a preferred embodiment, the piezoelectric material "M" of the pillars 11 and the piezoelectric layer 21 each comprises (or consists essentially of) a piezoelectric polymer. Most preferably, the piezoelectric material comprises or consists essentially of a polymeric material or a polymer / ceramic composite material. Examples of polymeric piezoelectric materials include PVDF and its copolymers, polyamides, liquid crystal polymers, polyimides, and polyvinylidene chloride PVDC. Examples of polymer / ceramic composite materials include those containing BaTiO3, PZT, ZnO, or PMN-PT in a polymeric medium such as PVDF, epoxy, SU8, and PDMS.

[0021] In a preferred embodiment, the piezoelectric layer 21 is melted by applying heat (H) until it is at least partially liquefied. Most preferably, the heat H is applied to the piezoelectric layer 21 but not to the pillar 11. Thereby, the structural integrity of the piezoelectric layer 21 can be maintained better. Most preferably, the heat H is applied to the piezoelectric layer 21 before the step of pushing (P) the pillar 11 into the piezoelectric layer 21, rather than during the pushing step.

[0022] In some embodiments, an internal heat source (for example, as part of a second substrate not shown) can be used to heat the piezoelectric layer 21. In other or further embodiments, the heat H is applied by an external heat source (also not shown). For example, only the second substrate 20 having the piezoelectric layer 21 is placed in an oven to apply the heat H (while, for example, the first substrate 10 remains unheated). Alternatively or additionally, the heat H is applied by a (directional) radiation source, for example, by irradiating the piezoelectric layer 21 with infrared rays or other radiation. In one embodiment, the heat H is applied only to the piezoelectric layer 21 or mainly to the piezoelectric layer 21.

[0023] In one embodiment, for example, as shown in FIG. 2B, the melted piezoelectric layer 21 is solidified by performing cooling (C) after being connected to the pillar 11, thereby forming a connection integrated with the pillar 11. For example, the material of the piezoelectric layer 21 can be solidified by active or passive cooling. Instead of or in addition to melting, in some embodiments, the at least partially liquid or wet piezoelectric layer 21 includes an uncured (non-crosslinked) piezoelectric material "M". For example, the pillar 11 is pushed into the uncured piezoelectric layer 21, and then the piezoelectric layer 21 is solidified by curing. For example, the piezoelectric layer 21 is cured by heat and / or electromagnetic radiation, such as ultraviolet light, to promote crosslinking in the piezoelectric material "M". In still other embodiments or further embodiments, the at least partially liquid or wet piezoelectric layer 21 includes or is formed by a solution having the piezoelectric material "M". For example, the pillar 11 is pushed into the solution of the piezoelectric layer 21, and then the solution is solidified by drying. For example, the piezoelectric layer 21 is actively or passively dried leaving a solid structure when the solvent is removed. Also, a combination of drying and curing is conceivable, for example, when the solution contains the uncured piezoelectric material "M" and the uncured piezoelectric material "M" is cured after the solvent is removed. It is also conceivable to apply the piezoelectric material "M" as a solution and melt the material after drying.

[0024] In a preferred embodiment, each end of the pillar 11 is arranged in a downward posture when the pillar 11 is pushed into the at least partially melted piezoelectric layer 21. By suspending the pillar 11 from the first substrate 10 (in the direction of gravity), the pillar 11 can maintain its shape better even when the pillar 11 begins to melt, for example, by indirect heat from the piezoelectric layer 21. In other embodiments or further embodiments, the piezoelectric layer 21 is preferably arranged on the second substrate 20 in an upward posture or direction. Advantageously, in this orientation, the melted 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 solidified, the connection structure can be turned over, for example, for subsequent processing.

[0025] Figures 3A and 3B illustrate an embodiment of removing the second substrate 20. In one embodiment, the second substrate 20 is removed (R), and the solidified piezoelectric layer 21 remains as a platform bridging each end of the pillar 11. For example, this may result in a uniform and flat surface on top of the platform. In some embodiments, electrical connections can be placed directly on top of the piezoelectric layer 21 later, after which the piezoelectric layer 21 forms an integral part with the pillar 11. By using a flexible (e.g., bendable) substrate as the second substrate, the removal of the second substrate can be facilitated. For example, a flexible material such as plastic is used. Instead of removing, it is conceivable to leave the second substrate attached to the piezoelectric layer 21. For example, the second substrate 20 may already include electrical connections and / or layers between the second substrate 20 and the piezoelectric layer 21 (not shown). These integrated electrical connections on the second substrate 20 can then be used to apply respective voltages to the pillar 11, for example. For example, the second substrate 20 can have an integrated second electrode that applies an electric field between the first electrode 13 on the first substrate 10.

[0026] Figures 4A and 4B illustrate providing an electrical circuit on the platform formed by the piezoelectric layer 21. In some embodiments, electrical contacts 23 and / or interconnects 25 are disposed on the piezoelectric layer 21 bridging the pillar 11. For example, these can be used to apply respective voltages to the piezoelectric material "M" or to receive respective voltages from the piezoelectric material "M". As will be appreciated, the platform formed by the piezoelectric layer 21 integrated with the pillar 11 can make the deposition of the contacts 23 and / or interconnects 25 very easy.

[0027] In some embodiments, after the piezoelectric layer 21 on the second substrate 20 has solidified, the first substrate 10 is turned over (e.g., the first substrate 10 is returned to the bottom). In this way, the piezoelectric layer 21 can form a platform on top of the upward pillars 11, on which subsequent connections or components can be formed. By providing a horizontal platform on top of the pillars 11, various subsequent film-forming methods can be facilitated. In a preferred embodiment, the electrical contact 23 (or other components and structures) is formed on the piezoelectric layer 21 by lithography. For example, this can include depositing a further layer of material on the piezoelectric layer 21 and exposing it to a light pattern for selective formation or removal of structures, for example by wet or dry etching techniques. It is also possible to use other film-forming techniques or additional film-forming techniques, such as printing or other transfer, for example light induced forward transfer (LIFT) of structures or components from a donor substrate (not shown).

[0028] Piezoelectric devices as described herein can be used to transmit and / or receive acoustic signals (e.g., ultrasonic waves). For example, a voltage can be applied to generate an electric field through the piezoelectric material "M" of the pillars 11 and activate the vibrations within the pillars. Alternatively or additionally, a voltage can be measured in response to vibrations within the pillars 11 caused, for example, by external factors. In some embodiments, as shown, for example, one or more of each of the pillars 11 are connected to an electrical device 50 configured to exchange electrical signals therebetween via respective electrodes 13, 23. For example, the electrical device 50 includes a signal generator and / or a sensor device. Also, other components or additional components, such as a controller for determining which one or more of the pillars 11 to address, can be connected.

[0029] Figures 5A and 5B show the polarization of the piezoelectric material in pillar 11, the bridge structure formed by the piezoelectric layer 21, and an optional second piezoelectric layer 12 below. In one embodiment, the second piezoelectric layer 12 is also integrally connected to the pillar 11. Thereby, the first piezoelectric layer 21, the pillar 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 the electrical insulating material "I" is provided in the array in the gaps between the pillars 11. Advantageously, the electrical insulating material "I" can be used during polarization to prevent short - circuit sparks that could damage the device. In some embodiments, the electrical insulating material "I" includes a fluid (e.g., a liquid). Also, a solid insulating material can be used. In some embodiments, the electrical insulating material "I" is provided in the gap 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 gap between the pillars. Most preferably, the electrical insulating material "I" is removed after polarization. Thus, the insulating material need not affect the mechanical properties of the pillar array.

[0030] In a preferred embodiment, as shown in FIG. 5A for example, the pillar 11 is polarized by corona polarization after the piezoelectric layer 21 is connected to the pillar 11. Without being bound by theory, the charge can spread throughout the piezoelectric layer 21, creating a more uniform electric field along the length of the pillar (as opposed to an open structure where the charge can also reach the sides of the pillar). Also, preferably other methods of polarizing the piezoelectric material along the length of the pillar are conceivable, for example, by applying a high voltage "HV" between each of the electrodes 13, 23 on both sides of the pillar ends, as shown in FIG. 5B. Thus, it will be understood that the polarization can be performed at various stages of manufacture, for example, before or after providing the electrodes.

[0031] FIG. 6 shows a preferred series of steps in manufacturing the piezoelectric device 100 described herein. Of course, other sequences are possible, such as adding additional steps, removing any step, swapping steps, etc. For example, the array of pillars 11 can be manufactured by methods other than the mold (F). For example, the pillars may already be downward in the mold, or may remain upward while connecting to the wet piezoelectric layer 21 (protruding upside down from the second substrate 20). For example, instead of heating H, the piezoelectric layer 21 can be wetted or liquefied using a solution or uncured material. For example, the pillar 11 can be actively pushed into the piezoelectric layer 21, or the piezoelectric layer 21 can be actively pushed into the pillar 11, by gravity alone or by active pushing. For example, the second substrate 20 can be left on the solidified piezoelectric layer 21. For example, the piezoelectric material can be polarized before, during, or after bonding the structures. For example, the electrical connections can be integrated into each substrate and / or provided afterwards.

[0032] FIG. 7A shows piezoelectric devices 100 having various dimensions. FIG. 7B shows a photograph of a piezoelectric device manufactured by the method as described herein. The left image represents a cross-sectional view. The right image represents a top view, with the piezoelectric bridge layer in focus at the upper right and the pillars / pockets in focus at the lower right.

[0033] Regardless of the manufacturing method, the present disclosure can provide advantageous structures and devices. In one embodiment, the piezoelectric device 100 includes a first substrate 10 having an array of pillars 11 including a piezoelectric material “M”, and a piezoelectric layer 21 integrally connected to the pillars 11 at each end of the pillars facing the first substrate 10. Preferably, the piezoelectric layer 21 forms a bridge structure between each end of the pillars 11 that functions as a platform for the piezoelectric material “M”.

[0034] In some embodiments, the piezoelectric device 100 comprises an electrical contact (not shown here) on top of the platform formed by the piezoelectric layer 21. In other or further embodiments, the piezoelectric device 100 comprises a second piezoelectric layer 12 between the pillar 11 and the first substrate 10. In a preferred embodiment, the piezoelectric device 100 comprises a first electrode (not shown here) between the second piezoelectric layer 12 and the first substrate 10. In some embodiments, the piezoelectric device 100 comprises 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 each electrode at either end of the pillar 11 via one or more piezoelectric layers 12, 22. The piezoelectric device 100 manufactured and / or structured as described herein can be used for many purposes, most preferably, for example, to generate or detect acoustic waves in the ultrasonic frequency range. For example, the piezoelectric device 100 can be used as part of a medical diagnostic device and / or a medical imaging device. Also, other uses are contemplated.

[0035] In a preferred embodiment, the pillar 11 has a pillar height "Z1" that is an integer multiple of the half wavelength of the (longitudinal) acoustic wave in the pillar. The pillar height is preferably selected such that the natural resonance frequency along the length (height) of the pillar matches the frequency of the sound emitted or received. Thereby, the acoustic wave resonates within the pillar and is amplified. For example, the resonance frequency may be determined by circumstances such as the stiffness of the material, the shape of the pillar, the substrate, etc. (this can give a λ / 2 or λ / 4 resonator). As an example, when using a 100-micron PVDF-TrFE pillar, a resonance frequency of around 10 megahertz is achieved in combination with the substrate. Of course, other dimensions, materials, and frequencies are also adoptable. For example, the dimension of the pillar height "Z1" can typically vary between 5 micrometers and 300 micrometers, preferably between 10 micrometers and 200 micrometers. For example, the piezoelectric device is used in ultrasonic applications.

[0036] In a preferred embodiment, the pillar 11 has a pillar height "Z1" and a pillar width "X1", and the pillar height "Z1" is at least twice as large as the pillar width "X1". The higher the aspect ratio, the more the pillar can function as a one-dimensional structure. For example, this can improve the separation between the lateral resonance mode and the axial resonance mode. On the other hand, the length of the pillar may preferably be selected to be equal to half of the wavelength, but the thickness or width of the pillar is preferably not so small as to impair the structural integrity. Also, the minimum width may be limited by the manufacturing method. For example, the ratio "Z1" / "X1" is typically from 1 / 2 to 10, preferably greater than 3, or greater than 4.

[0037] In a preferred embodiment, the pillars 11 are arranged with a gap 11g therebetween. In principle, a gap of several micrometers, for example greater than 5 micrometers, may be sufficient to provide sufficient attenuation of the coupling between the pillars. Typically, the distance "X2" between the pillars is of the same order as the pillar width "X1", for example, less than a difference of 3 times the pillar width "X1", preferably less than a difference of 2 times, or less than a difference of 50%. For example, both the pillar width "X1" and the distance "X2" are in a typical range between 5 micrometers and 100 micrometers. In some embodiments, the distance "X2" is selected such that the Lamb wave (e.g., A0 surface wave) passing through the piezoelectric layer 21 does not structurally interfere with adjacent pillars, so they can be independent. In some embodiments, for example, for imaging, the pitch (X1 + X2) between the pillars is preferably less than half of the ultrasonic wavelength. The pitch can be made larger, for example, in other applications.

[0038] The total surface dimension "X3" of the piezoelectric layer 21 is typically much larger than the pitch ("X1" + "X2") over which the pillars extend. For example, "X3" can be at least 5 times larger, or 10 times larger or more, than "X1" + "X2". In some embodiments, the array includes at least 10 pillars, preferably 20 or more, 50 or more, 100 or more, 1000 or more, 10,000 or more, for example up to 1 million or more pillars. For example, the piezoelectric device comprises an array of 200×200 pillars that extends over an area of 1 square centimeter at a pitch of 50 microns.

[0039] Preferably, the thickness "Z2" of the piezoelectric layer 21 is, on the one hand, sufficient to allow the pillar 11 to sink into the piezoelectric layer 21 by 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 impede the operation of the pillar or the desired one-dimensional behavior of the composite structure. Typically, the length "Z1" of the pillar 11 is at least 2 times or 3 times or more larger than the thickness "Z2" of the piezoelectric layer 21, preferably at least 5 times or more larger, more preferably, for example, up to 10 times or more, 20 times or more, or more.

[0040] Typically, the thickness "Z2" of the piezoelectric layer 21 is about 10 percent of the pillar height "Z1". In some embodiments, it can be expected that the thinner the piezoelectric layer 21 compared to the pillar height "Z1", the less crosstalk between the pillars. In other embodiments or further embodiments, if the piezoelectric layer 21 is thick, surface waves can be passed along the bridge or platform formed by the piezoelectric layer 21, for example, which can be useful for interference. Also, when the piezoelectric layer 21 is thicker, the mechanical stability of the bridge can also be better. For example, the thickness "Z2" of the piezoelectric layer 21 is 1 to 30 micrometers, preferably 5 to 20 micrometers.

[0041] In some embodiments, the structure of the pillar may be supported by the second piezoelectric layer 12 at the other end. The thickness Z3 of this second piezoelectric layer 12 can typically be the same as or identical to the thickness "Z2" of the first piezoelectric layer 21, for example, within a difference of three times the thickness "Z2", or within a difference of two times the thickness "Z2", and most preferably, as symmetric as possible within the feasible range.

[0042] Typically, the first substrate 10 has a thickness "Z4", and the thickness "Z4" of the first substrate 10 is greater than the thickness of the piezoelectric layer 21, greater than the length "Z1" of the pillar, or greater than the thickness of the composite structure. For example, the thickness of the first substrate 10 is 0.5 millimeters or more, greater than 1 millimeter, for example, up to 0.5 centimeters or more at most. The second substrate (not shown here) may have the same thickness as the first substrate 10, or may have a different thickness from the first substrate 10 (for example, a thickness smaller than the first substrate 10).

[0043] Figures 8A - 8E show another embodiment for manufacturing the piezoelectric device 100 described herein.

[0044] In some embodiments, for example, as shown in FIG. 8B, the first substrate 10 includes an anchor structure 10a. For example, the anchor structure 10a can be used to promote or improve the adhesion of subsequent layers formed on the first substrate 10. In one embodiment, the anchor structure 10a is formed by etching a group of cavities into the first substrate 10. For example, the first substrate 10 includes or is substantially formed of an etch-removable polymeric material. Other materials can also be used. Typically, the etching process is guided by an etching mask. For example, as shown in FIG. 8A, the etching mask can advantageously be at least partially formed by the pattern of the lower electrode 13. Also, other or additional etching mask structures can be used at the location of the electrodes and / or other locations on the first substrate 10 (e.g., locations adjacent to the lower electrode 13). In a preferred embodiment, the group of cavities at least partially undercuts the etching mask and, for example, extends partially under the electrodes. This can further improve the adhesion and, in particular, enable the subsequent layer to remain attached to the first substrate 10 even when substantially curved. Instead of or in addition to etching, the anchor structure 10a can also be formed in other ways, for example, formed by the structure of the lower electrode itself or by another structure disposed on and connected to the first substrate 10 that helps maintain the subsequent layer in an adhered state.

[0045] In some embodiments, for example, as shown in FIG. 8C, after forming the anchor structure 10a, a subsequent layer is provided on the first substrate 10. Preferably, the subsequent layer is first provided (partially) in a liquid form. In this way, the subsequent layer can flow into or be more easily pushed into the anchor structure 10a. When the material of the subsequent layer has flowed into and / or been pushed into the cavity, the material can be at least partially solidified, for example cured. Most preferably, the subsequent layer includes a piezoelectric material M that can form the precursor layer 1 as described above with reference to FIG. 1A. For example, the precursor layer 1 includes a polymeric piezoelectric material such as P (PVDF-TrFE) that is initially applied in a liquid form or is substantially formed from a polymeric piezoelectric material. In one embodiment, the precursor layer 1 is molded to form pillars 11 of the piezoelectric material M, for example, as shown in FIG. 8D. For example, the molding process can include pushing a mold structure 30 into the precursor layer 1. This can also help to further push the piezoelectric material M into the anchor structure 10a. Also, other methods of forming the pillars 11 are conceivable. In other or further embodiments, for example, as shown in FIG. 8E, a piezoelectric layer 21 is integrally connected to the pillars 11 to form a bridge structure, for example, between each end of the pillars. For example, the piezoelectric layer 21 can be provided as described with reference to FIGS. 2A - 3B.

[0046] For clarity and brevity of description, features are described herein as part of the same or separate embodiments, but it will be understood that the scope of the invention may include embodiments having combinations of all or some of the features described. For example, although embodiments for forming various layers and components of a piezoelectric device are shown, alternative methods may also be envisioned by those skilled in the art having the benefit of this disclosure to achieve similar functions and results. For example, layers and structures can be combined or divided into one or more alternative components. The various elements of the described and illustrated embodiments provide certain advantages, such as in the manufacture and use of a piezoelectric device having a robust structure adapted to various manufacturing and post - processing steps.

[0047] In some embodiments, the piezoelectric devices described herein are used for non-contact mixing of liquids, such as enabling low shear high mass flow by acoustic streaming. In one embodiment, the piezoelectric device includes a flexible substrate. For example, the flexible substrate can form or be applied to a part of a flexible bag containing the liquid to be mixed. For example, the bag can include a flexible (bio)reactor, and / or the liquid can include a biological liquid that can benefit from (continuous or intermittent) mixing, such as a pharmaceutical solution, particularly a vaccine. Advantageously, a large-area flexible ultrasonic transducer or substrate can be integrated or patched (reusable). For example, a flexible acoustic device can be adapted to the bag to ensure good coupling. Also, a bag having an integrated acoustic device can be easily packaged, for example, substantially flat (when empty), without sharp / rigid objects inside the bag. Instead of use in a flexible container, a rigid or flexible piezoelectric device can form or be integrated into a part of the wall of a rigid container for mixing or other purposes (e.g., sensing). Other uses of flexible and / or rigid piezoelectric devices / substrates are also contemplated. Of course, it should be understood that any one of the above embodiments or processes can be combined with one or more other embodiments or processes to provide further improvements in finding, adapting designs and advantages. It is understood that the present disclosure provides specific advantages for piezoelectric transducers used to sense or actuate relatively large and / or flexible surfaces and can generally be applied to any application where piezoelectric devices are used.

[0048] In the interpretation of the appended claims, the term "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; the articles "a" or "an" preceding an element do not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; a plurality of "means" may be represented by the same or different items or implemented structures or functions; any of the disclosed devices or parts thereof can, unless otherwise specified, be combined together or further separated into other parts; should be understood. When one claim refers to another claim, this may indicate synergistic advantages obtained by combinations of each feature. However, the fact that certain means are described in different claims does not indicate that combinations of these means cannot be used advantageously. Therefore, the present embodiment can include all practical combinations of the claims, provided that each claim can, in principle, refer to any preceding claim, unless explicitly excluded by the context.

Claims

1. A method of manufacturing a piezoelectric device (100), comprising: providing a first substrate (10) having an array of pillars (11) containing a piezoelectric material (M), and a second substrate (20) having a piezoelectric layer (21) facing each end of the pillars (11); pushing (P) each end of the pillars (11) into the piezoelectric layer (21) while the piezoelectric layer (21) is at least partially liquid; solidifying the piezoelectric layer (21) to form an integral connection between the piezoelectric layer (21) and the pillars (11), such that the piezoelectric layer (21) forms a bridge structure between each end of the pillars (11). A method comprising the above steps.

2. The method according to claim 1, wherein the piezoelectric layer (21) contains substantially the same piezoelectric material (M) as the pillars (11).

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

4. The method according to any one of claims 1 to 3, wherein the piezoelectric layer (21) is melted by applying heat (H) until it is at least partially liquefied, and the heat (H) is applied to the piezoelectric layer (21) but not to the pillars (11).

5. The method according to any one of claims 1 to 4, wherein each end of the pillars (11) is arranged in a downward direction when being pushed (P) into the at least partially melted piezoelectric layer (21).

6. The method according to any one of claims 1 to 5, wherein the second substrate (20) is removed (R), leaving the solidified piezoelectric layer (21) as a platform bridging each end of the pillars (11).

7. The method according to any one of claims 1 to 6, wherein electrical contacts (23) and / or interconnections (25) are arranged on the piezoelectric layer (21) bridging the pillars (11) to apply respective voltages to, or receive respective voltages from, the piezoelectric material (M).

8. The first substrate (10) is turned over after the piezoelectric layer (21) on the second substrate (20) has solidified, and the piezoelectric layer (21) forms a platform on top of the upward-facing pillars (11), and subsequent connections or components are formed on the platform. The method according to any one of claims 1 to 7.

9. An electrical contact (23) is formed by lithography on the bridge structure formed by the piezoelectric layer (21). The method according to any one of claims 1 to 8.

10. A first electrode (13) for applying a potential to the piezoelectric material (M) is formed between the pillar (11) and the first substrate (10). The method according to any one of claims 1 to 9.

11. While an electrical insulating material (I) is provided in the array in the gaps between the pillars (11), the piezoelectric material (M) in the array of the pillars (11) is polarized by applying a voltage (HV), and the electrical insulating material (I) is removed after the polarization. The method according to any one of claims 1 to 10.

12. The pillar (11) is polarized by corona polarization after the piezoelectric layer (21) is connected to the pillar (11). The method according to any one of claims 1 to 11.

13. A piezoelectric device (100) for generating or detecting acoustic waves, A first substrate (10) comprising an array of pillars (11) containing a piezoelectric material (M), A first piezoelectric layer (12) provided between the first substrate (10) and the pillar (11) and integrally connected to the pillar (11) at each first end of the pillar (11), the first piezoelectric layer (12) forming a base structure between each of the first ends of the pillar (11). A second piezoelectric layer (21) integrally connected to the pillar (11) at each second end of the pillar (11) on the side opposite to the first substrate (10), the second piezoelectric layer (21) forming a bridge structure functioning as a platform for the piezoelectric material (M) between each of the second ends of the pillar (11). A piezoelectric device (100) comprising.

14. A first substrate (10) comprising an array of pillars (11) containing a piezoelectric material (M), A first piezoelectric layer (12) provided between the first substrate (10) and the pillar (11) and integrally connected to the pillar (11) at each first end of the pillar (11), the first piezoelectric layer (12) forming a base structure between the respective first ends of the pillar (11). A second piezoelectric layer (21) integrally connected to the pillar (11) at each second end of the pillar (11) on the side opposite to the first substrate (10), the second piezoelectric layer (21) forming a bridge structure that functions as a platform for the piezoelectric material (M) between the respective second ends of the pillar (11). A piezoelectric device (100) comprising the above.

15. A first electrode (13) provided between the first piezoelectric layer (12) and the first substrate (10). An electrical contact (23) for forming at least one second electrode on the platform formed by the second piezoelectric layer (21). An electrical device (50) configured to transmit and receive electrical signals of the first electrode and the second electrode (13, 23) for generating and / or measuring acoustic waves. The piezoelectric device according to claim 14, comprising the above.

16. The piezoelectric device according to claim 14, wherein the second piezoelectric layer (21) has a first thickness (Z2) in the range of 1 to 30 micrometers.

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

18. The piezoelectric device according to claim 14, wherein the first substrate (10) has a third thickness (Z4) of 0.5 millimeter or more.

19. The piezoelectric device according to claim 14, wherein the pillar (11) has a pillar height (Z1) in the range of 5 micrometers to 300 micrometers.

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

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