Piezoelectric micromechanical transducer, piezoelectric micromechanical transducer array and method for manufacturing same

Abstract

A piezoelectric micromechanical transducer, a piezoelectric micromechanical transducer array, and a method for manufacturing the same. The method for manufacturing the piezoelectric micromechanical transducer includes forming a device cavity on a substrate; forming a sacrificial layer in the device cavity, a surface of the sacrificial layer being flush with a surface of the substrate; forming a piezoelectric structure on the substrate and the sacrificial layer, the piezoelectric structure including a first electrode, a piezoelectric layer, and a second electrode stacked, a normal projection of the piezoelectric structure on the substrate overlapping a normal projection of the device cavity on the substrate; forming a release hole, the release hole penetrating the piezoelectric structure and contacting the sacrificial layer; and etching the sacrificial layer through the release hole to remove at least part of the sacrificial layer. Thus, the method for manufacturing the piezoelectric micromechanical transducer can make the resonant frequency, amplitude response, capacitance value, and acoustic performance of the piezoelectric micromechanical transducer differ very little.

Description

Technical Field

[0001] This disclosure relates to a piezoelectric micromechanical transducer, a piezoelectric micromechanical transducer array, and a method for fabricating the same. Background Technology

[0002] Ultrasound, with its advantages of non-invasiveness, high penetration, and high detection accuracy, is widely used in industrial non-destructive testing, medical imaging, and consumer electronics. Piezoelectric micromechanical ultrasonic transducers (PMUTs), as a new type of ultrasonic transducer, offer advantages such as high processing precision, good CMOS compatibility, high sensitivity, and low driving voltage, and have great application potential in future ultrasonic imaging scenarios. Summary of the Invention

[0003] This disclosure provides a piezoelectric micromechanical transducer, a piezoelectric micromechanical transducer array, and a method for fabricating the same. The method for fabricating the piezoelectric micromechanical transducer involves first forming a device cavity on a substrate, ensuring high consistency in the shape, size, and depth of the cavity. This results in minimal differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method reduces residual stress, thereby improving product yield.

[0004] At least one embodiment of this disclosure provides a method for fabricating a piezoelectric micromechanical transducer, comprising: forming a device cavity on a substrate; forming a sacrificial layer in the device cavity, the surface of the sacrificial layer being flush with the surface of the substrate; forming a piezoelectric structure on the substrate and the sacrificial layer, the piezoelectric structure including a first electrode, a piezoelectric layer and a second electrode stacked thereon, the orthographic projection of the piezoelectric structure on the substrate overlapping the orthographic projection of the device cavity on the substrate; forming a release hole, the release hole penetrating the piezoelectric structure and contacting the sacrificial layer; and etching the sacrificial layer through the release hole to remove at least a portion of the sacrificial layer.

[0005] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the orthogonal projection of the release hole on the substrate is located within the range of the orthogonal projection of the device cavity on the substrate.

[0006] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the release hole penetrates at least through the piezoelectric layer and the first electrode in the piezoelectric structure.

[0007] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the method further includes: forming a first isolation trench at the edge of the piezoelectric structure, wherein the orthographic projection of the first isolation trench on the substrate is located outside the orthographic projection of the device cavity on the substrate.

[0008] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the first isolation trench at least penetrates the piezoelectric layer in the piezoelectric structure.

[0009] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the method further includes: forming a second isolation trench from the side of the substrate away from the piezoelectric structure, wherein the orthographic projection of the second isolation trench on the substrate is located outside the orthographic projection of the device cavity on the substrate.

[0010] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, before forming a piezoelectric structure on the substrate and the sacrificial layer, the method further includes forming a seed layer on the substrate and the sacrificial layer.

[0011] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, after forming a piezoelectric structure on the substrate and the sacrificial layer, the fabrication method further includes: forming a passivation layer on the side of the piezoelectric structure away from the substrate to protect the piezoelectric structure, wherein the release hole also penetrates the passivation layer.

[0012] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, forming the piezoelectric structure on the substrate and the sacrificial layer includes: forming a first electrode pad disposed in the same layer as the first electrode; and forming a second electrode pad disposed in the same layer as the second electrode.

[0013] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the method further includes: patterning the passivation layer and the piezoelectric layer to form a first window and a second window, wherein the first window exposes the first electrode pad and the second window exposes the second electrode pad.

[0014] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the method further includes: forming a first auxiliary electrode and a second auxiliary electrode on the first electrode pad and the second electrode pad respectively through the first window and the second window, wherein the conductivity of the first auxiliary electrode is greater than the conductivity of the first electrode pad, and the conductivity of the second auxiliary electrode is greater than the conductivity of the second electrode pad.

[0015] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the method further includes: forming an acoustic matching layer on the piezoelectric structure, which is configured to perform acoustic impedance matching on the ultrasonic waves generated by the piezoelectric structure.

[0016] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, forming a sacrificial layer in the device cavity includes: forming a sacrificial material layer on one side of the substrate where the device cavity is formed, the sacrificial material layer filling the device cavity, the thickness of the sacrificial material layer being greater than the depth of the device cavity; and planarizing the sacrificial material layer using a planarization process and exposing the substrate, the sacrificial material layer located in the device cavity filling the device cavity to form the sacrificial layer.

[0017] For example, in a method for fabricating a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, the planarization process includes a chemical mechanical polishing process or an etch-back process.

[0018] At least one embodiment of this disclosure also provides a method for fabricating a piezoelectric micromechanical transducer array, which includes: forming a plurality of piezoelectric micromechanical transducers arranged in an array, wherein each of the piezoelectric micromechanical transducers is fabricated using the piezoelectric micromechanical transducer fabrication method described in any one of the above claims.

[0019] At least one embodiment of this disclosure also provides a piezoelectric micromechanical transducer, comprising: a substrate including a device cavity; a piezoelectric structure located on the substrate and covering the device cavity, the piezoelectric structure including a first electrode, a piezoelectric layer and a second electrode stacked thereon; and a release hole penetrating the piezoelectric structure and communicating with the device cavity.

[0020] For example, in a piezoelectric micromechanical transducer provided in one embodiment of this disclosure, a sacrificial residual layer is further included, located within the device cavity and on the side of the piezoelectric structure near the substrate.

[0021] For example, in a piezoelectric micromechanical transducer provided in one embodiment of this disclosure, the orthogonal projection of the release hole on the substrate is located within the range of the orthogonal projection of the device cavity on the substrate.

[0022] For example, in a piezoelectric micromechanical transducer provided in an embodiment of this disclosure, a first isolation trench is further included, located at the edge of the piezoelectric structure, wherein the orthographic projection of the first isolation trench on the substrate is outside the orthographic projection of the device cavity on the substrate.

[0023] For example, in a piezoelectric micromechanical transducer provided in one embodiment of this disclosure, the first isolation trench penetrates at least the piezoelectric layer in the piezoelectric structure.

[0024] For example, in a piezoelectric micromechanical transducer provided in one embodiment of this disclosure, a second isolation trench is further included, located on the side of the substrate away from the piezoelectric structure, wherein the orthographic projection of the second isolation trench on the substrate is outside the orthographic projection of the device cavity on the substrate.

[0025] For example, in a piezoelectric micromechanical transducer provided in one embodiment of this disclosure, a seed layer is further included, located between the substrate and the piezoelectric structure.

[0026] At least one embodiment of this disclosure also provides a piezoelectric micromechanical transducer array, including a plurality of piezoelectric micromechanical transducers arranged in an array, wherein the plurality of piezoelectric micromechanical transducers include the piezoelectric micromechanical transducers according to any one of the preceding claims. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of this disclosure and are not intended to limit this disclosure.

[0028] Figure 1 A schematic flowchart illustrating a method for fabricating a piezoelectric micromechanical transducer according to an embodiment of this disclosure; Figures 2-15 This is a schematic diagram illustrating the steps of a method for fabricating a piezoelectric micromechanical transducer according to an embodiment of the present disclosure; Figure 16 A schematic diagram of another piezoelectric micromechanical transducer provided in an embodiment of this disclosure; and Figure 17 This is a schematic diagram of a piezoelectric micromechanical transducer array provided in one embodiment of the present disclosure. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the described embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0030] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0031] Unless otherwise defined, the features such as "parallel," "perpendicular," and "identical" used in the embodiments of this invention include the strictly defined cases of "parallel," "perpendicular," and "identical," as well as cases involving a certain degree of error, such as "approximately parallel," "approximately perpendicular," and "approximately identical." For example, the aforementioned "approximately" may indicate that the difference between the compared objects is within 10% or 5% of the average value of the compared objects. Unless otherwise specified in the following embodiments of this invention, the quantity of a component or element is implied to mean that the component or element may be one or more, or can be understood as at least one. "At least one" refers to one or more, and "more" refers to at least two. In the embodiments of this invention, "same-layer arrangement" refers to the relationship between multiple film layers formed from the same material after undergoing the same step (e.g., a patterning process). Here, "same-layer" does not always mean that the multiple film layers have the same thickness or that the multiple film layers have the same height in a cross-sectional view.

[0032] Currently, high-resolution ultrasound imaging with large imaging areas requires large-aperture PMUT arrays. However, large-scale ultrasound transducer arrays face problems such as low yield and poor consistency. This leads to a reduction in the effective array area, decreased image resolution and contrast, and increased side lobes and artifacts. Simultaneously, it increases manufacturing costs and reduces system reliability. These problems severely limit the practicality and commercialization of PMUT arrays.

[0033] Common PMUT creation methods include the following: 1. Fabrication method based on deep reactive ion etching (DRIE) PMUT fabrication based on deep reactive ion etching (DRIE) is a common bottom-up fabrication method. This method first deposits or grows various functional layers (including piezoelectric layers, electrodes, etc.) on a silicon substrate, and then uses DRIE technology to etch cavities from the back or front of the silicon substrate, allowing the aforementioned functional layers to form a thin film structure that can vibrate freely. This fabrication method offers high processing flexibility, enabling the creation of cavities of arbitrary shapes and sizes, and also has fewer process steps and lower costs.

[0034] However, the cyclic etching and passivation steps in the DRIE etching process described above can easily produce wavy or sawtooth textures in the etched sidewall structure, which may lead to stress concentration in the thin film structure and reduce the mechanical properties and stability of the structure. At the same time, the DRIE etching rate fluctuates greatly with process conditions, and the aspect ratio of the etching increases with the cavity depth, which may result in a decrease in etching rate or severe side etching. This leads to poor consistency in cavity size and depth on the same wafer, affecting the consistency of the device's resonant frequency and sensitivity.

[0035] 2. Fabrication method based on cavity SOI

[0036] The PMUT fabrication method based on Cavity SOI utilizes an SOI wafer with a pre-formed cavity as the starting substrate. First, a piezoelectric layer and electrodes are grown or deposited on the device layer; then, the buried oxide layer (BOX layer) is removed to form a suspended vibrating structure. The greatest advantage of this fabrication method is that the cavity size, depth, and location are precisely defined in advance by the wafer manufacturer, thus providing excellent array consistency, high yield, and lower processing complexity.

[0037] However, Cavity SOI wafers are expensive, and the cavity size and structural parameters are determined during the wafer fabrication stage, resulting in poor flexibility. This method requires bonding to fabricate Cavity SOI wafers, so the device fill rate is also low.

[0038] 3. Fabrication method based on wafer bonding

[0039] PMUT fabrication methods based on wafer bonding typically involve bonding two or more wafers together to achieve the device structure. For example, wafers with pre-fabricated piezoelectric layers and electrode structures can be bonded to wafers with pre-prepared cavities to form PMUT arrays. This fabrication method allows for precise control of film thickness, cavity size, and array structure consistency, offering excellent fabrication flexibility and high device uniformity.

[0040] However, precise alignment and high-quality bonding interfaces are required during wafer bonding. Bubbles, voids, or impurities may occur during bonding, leading to defects that may affect film stress. Differences in thermal expansion coefficients and material mismatch during bonding can also cause residual stress. These issues can affect device consistency and reliability. In addition, the equipment and process costs for wafer bonding are very high.

[0041] 4. Fabrication method based on etched sacrificial layer

[0042] The fabrication method based on the etched sacrificial layer typically involves pre-defining the sacrificial layer region and structure on the substrate wafer, sequentially constructing the film structure layer, bottom electrode, piezoelectric layer and top electrode on the sacrificial layer, and completing the wiring and passivation, while opening release holes in the non-effective vibration region; then, the sacrificial layer is removed by selective etching on the front side, forming an air cavity under the film and releasing the suspended film structure, thereby obtaining a PMUT device with high consistency, high fill factor and easy large-scale array integration.

[0043] However, the sacrificial layer process requires the introduction of release holes to allow etching gas / liquid to enter the sacrificial layer material. Currently used sacrificial layer processes all have release holes in non-effective vibration regions, resulting in the PMUT cavity shape not being strictly square or circular, causing distortion of vibration modes. At the same time, due to the irregular shape, additional stress is introduced, affecting key indicators such as device performance, array consistency, and yield.

[0044] To address this, this disclosure provides a method for fabricating a piezoelectric micromechanical transducer, comprising: forming a device cavity on a substrate; forming a sacrificial layer in the device cavity, the surface of the sacrificial layer being flush with the surface of the substrate; forming a piezoelectric structure on the substrate and the sacrificial layer, the piezoelectric structure including a first electrode, a piezoelectric layer, and a second electrode stacked thereon, the orthographic projection of the piezoelectric structure on the substrate overlapping the orthographic projection of the device cavity on the substrate; forming a release hole, the release hole penetrating the piezoelectric structure and contacting the sacrificial layer; and etching the sacrificial layer through the release hole to remove at least a portion of the sacrificial layer. Thus, this method for fabricating a piezoelectric micromechanical transducer, by first forming the device cavity on the substrate, ensures high consistency in the shape, size, and depth of the device cavity, thereby minimizing differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method can reduce residual stress, thereby improving product yield.

[0045] This disclosure also provides a method for fabricating a piezoelectric micromechanical transducer array, comprising: forming a plurality of piezoelectric micromechanical transducers arranged in an array; each piezoelectric micromechanical transducer being fabricated using the method described in any of the preceding embodiments. Therefore, when the piezoelectric micromechanical transducer array is formed using this method, the entire array can generate an ideal beam during operation, greatly improving the ultrasonic focusing accuracy, spatial resolution, and imaging contrast, avoiding imaging defects such as sidelobes and artifacts, and improving image quality and measurement accuracy.

[0046] This disclosure also provides a piezoelectric micromechanical transducer, comprising: a substrate including a device cavity; a piezoelectric structure located on the substrate and covering the device cavity, the piezoelectric structure including a first electrode, a piezoelectric layer, and a second electrode stacked thereon; and a release hole penetrating the piezoelectric structure and communicating with the device cavity. Thus, the piezoelectric micromechanical transducer forms a device cavity within the substrate, thereby enabling the shape, size, and depth of the device cavity to have high consistency, resulting in minimal differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer.

[0047] This disclosure also provides a piezoelectric micromechanical transducer array, comprising a plurality of piezoelectric micromechanical transducers arranged in an array, wherein the plurality of piezoelectric micromechanical transducers include any of the piezoelectric micromechanical transducers described above. Thus, the entire array can generate an ideal beam during operation, greatly improving ultrasonic focusing accuracy, spatial resolution, and imaging contrast, avoiding imaging defects such as sidelobes and artifacts, and enhancing image quality and measurement accuracy.

[0048] The piezoelectric micromechanical transducer and its fabrication method, as well as the piezoelectric micromechanical transducer array and its fabrication method, provided in the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings.

[0049] Figure 1 This is a schematic flowchart illustrating a method for fabricating a piezoelectric micromechanical transducer according to an embodiment of this disclosure. Figure 1 As shown, the fabrication method of this piezoelectric micromechanical transducer includes the following steps S101 to S105: Step S101: Form a device cavity on the substrate.

[0050] For example, a silicon wafer substrate is provided, and then an etching process can be used to etch a device cavity onto the substrate. The shape and diameter of the etched device cavity define the shape and size of the device cavity in the subsequently formed piezoelectric micromechanical transducer. It should be noted that the substrate described above can also be other substrates, such as a sapphire substrate; in addition, because the direct etching process described above has high precision, the device cavity has high precision.

[0051] Step S102: A sacrificial layer is formed in the device cavity, the surface of which is flush with the surface of the substrate.

[0052] For example, a deposition process can be used to form a sacrificial layer in the device cavity.

[0053] Step S103: A piezoelectric structure is formed on the substrate and the sacrificial layer. The piezoelectric structure includes a first electrode, a piezoelectric layer, and a second electrode stacked together. The orthographic projection of the piezoelectric structure on the substrate overlaps with the orthographic projection of the device cavity on the substrate. It should be noted that, because the surface of the sacrificial layer is flush with the surface of the substrate, the piezoelectric structure formed on the substrate and the sacrificial layer has high quality.

[0054] Step S104: Form a release hole that penetrates the piezoelectric structure and contacts the sacrificial layer.

[0055] For example, the aforementioned release holes can be formed through an etching process.

[0056] Step S105: Etch the sacrificial layer through the release hole to remove at least a portion of the sacrificial layer.

[0057] In the fabrication method of the piezoelectric micromechanical transducer provided in this disclosure, by first forming a device cavity on the substrate, the shape, size, and depth of the device cavity are highly consistent, thereby minimizing the differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method can reduce residual stress, thereby improving product yield.

[0058] In some examples, in step S104 above, the orthogonal projection of the formed release hole onto the substrate lies within the range of the orthogonal projection of the device cavity onto the substrate. Therefore, the release hole does not disrupt the shape of the device cavity, allowing it to maintain a regular shape, such as a square or circle. It should be noted that the commonly used sacrificial layer process creates the release hole outside the device cavity and then forms a horizontal groove or hole to connect the release hole to the device cavity. This results in the device cavity shape of the piezoelectric micromechanical transducer not being strictly square or circular, leading to distortion of the vibration modes. Furthermore, the irregular shape of the device cavity introduces additional stress, affecting key indicators such as device performance, array consistency, and yield.

[0059] In some examples, the first and second electrodes described above may be molybdenum layers. Of course, embodiments of this disclosure include, but are not limited to, the first and second electrodes described above may be replaced with metals or metal stacks such as Ti / Mo (titanium / molybdenum), Ti / Pt (titanium / platinum), W (tungsten), Ru (ruthenium), and Al (aluminum) to balance resistance, adhesion, stress, and subsequent etching selectivity.

[0060] In some examples, in step S104 above, the formed release hole penetrates at least the piezoelectric layer and the first electrode in the piezoelectric structure. It should be noted that the size of the second electrode in the piezoelectric structure can be smaller than the size of the first electrode. In this case, the release hole can penetrate the piezoelectric layer and the first electrode to connect the device cavity to the outside world for etching and removal of the sacrificial layer. Of course, the formed release hole can also penetrate the piezoelectric layer, the first electrode, and the second electrode in the piezoelectric structure.

[0061] In some examples, the fabrication method of the aforementioned piezoelectric micromechanical transducer further includes forming a first isolation trench at the edge of the piezoelectric structure, wherein the orthographic projection of the first isolation trench onto the substrate is outside the orthographic projection of the device cavity onto the substrate. Thus, the first isolation trench can isolate adjacent piezoelectric structures (array elements), thereby avoiding acoustic crosstalk between adjacent piezoelectric structures. On the other hand, the first isolation trench can also release accumulated stress, thereby preventing buckling deformation of the piezoelectric material layer, thus improving product yield and stability.

[0062] In some examples, the first isolation trench described above penetrates at least through the piezoelectric layer in the piezoelectric structure, thereby effectively avoiding acoustic crosstalk between adjacent piezoelectric structures.

[0063] In some examples, the fabrication method of the piezoelectric micromechanical transducer described above further includes forming a second isolation trench from the side of the substrate away from the piezoelectric structure, wherein the orthographic projection of the second isolation trench on the substrate is outside the orthographic projection of the device cavity on the substrate. Thus, the second isolation trench can also prevent vibration crosstalk between device cavities. On the other hand, the second isolation trench can also release accumulated stress.

[0064] In some examples, the above-described method for fabricating a piezoelectric micromechanical transducer further includes: filling the first isolation trench with a low-modulus polymer to form a first isolation structure; and / or filling the second isolation trench with a low-modulus polymer to form a second isolation structure.

[0065] In some examples, prior to step S103 described above, i.e., before forming the piezoelectric structure on the substrate and sacrificial layer, the fabrication method further includes forming a seed layer on the substrate and sacrificial layer. This seed layer can thus improve the growth quality of each film layer in the subsequently formed piezoelectric structure and reduce residual stress.

[0066] For example, the seed layer described above can be an aluminum nitride layer. Of course, the embodiments disclosed herein include, but are not limited to, the seed layer described above can also be replaced with a transition layer such as AlN / AlON / SiN (aluminum nitride / aluminum oxynitride / silicon nitride) or a multilayer gradient stress buffer layer to achieve the same crystal orientation induction and residual stress control.

[0067] In some examples, after step S103 described above, i.e., after forming the piezoelectric structure on the substrate and the sacrificial layer, the fabrication method further includes forming a passivation layer on the side of the piezoelectric structure away from the substrate to protect the piezoelectric structure. In this case, the aforementioned release hole also penetrates the passivation layer.

[0068] In some examples, forming a piezoelectric structure on a substrate and a sacrificial layer includes: forming a first electrode pad disposed in the same layer as the first electrode; and forming a second electrode pad disposed in the same layer as the second electrode.

[0069] For example, the first electrode and the first electrode pad described above can be formed through the same conductive layer and the same patterning process; the second electrode and the second electrode pad described above can be formed through the same conductive layer and the same patterning process.

[0070] In some examples, the fabrication method of the piezoelectric micromechanical transducer described above further includes: patterning the passivation layer and the piezoelectric layer to form a first window and a second window, wherein the first window exposes a first electrode pad and the second window exposes a second electrode pad.

[0071] In some examples, the fabrication method of the piezoelectric micromechanical transducer described above further includes: forming a first auxiliary electrode and a second auxiliary electrode on the first electrode pad and the second electrode pad respectively through a first window and a second window, wherein the conductivity of the first auxiliary electrode is greater than that of the first electrode pad, and the conductivity of the second auxiliary electrode is greater than that of the second electrode pad. Thus, the first and second auxiliary electrodes can improve conductivity on the one hand, and reduce the difficulty of wire bonding on the other.

[0072] In some examples, the above-mentioned method for fabricating piezoelectric micromechanical transducers further includes forming an acoustic matching layer on the piezoelectric structure, which is configured to perform acoustic impedance matching on the ultrasonic waves generated by the piezoelectric structure, thereby both sealing the device and achieving matching of sound velocity and acoustic impedance.

[0073] In some examples, in the fabrication method of a piezoelectric micromechanical transducer, forming a sacrificial layer in the device cavity includes: forming a sacrificial material layer on one side of the substrate where the device cavity is formed, the sacrificial material layer filling the device cavity, the thickness of the sacrificial material layer being greater than the depth of the device cavity; and planarizing the sacrificial material layer using a planarization process to expose the substrate; the sacrificial material layer located in the device cavity fills the device cavity to form a sacrificial layer. Thus, this fabrication method enables the surface of the sacrificial layer to be flush with the surface of the substrate.

[0074] In some examples, the planarization process described above includes chemical mechanical polishing or etching back.

[0075] For example, planarization can be replaced by spin-coating self-planarization with etch-back, multiple coating-curing-etch-back, or selective filling assisted by local hard masks to reduce particles / defects introduced by CMP and improve yield.

[0076] Figures 2-15 This is a schematic diagram illustrating the steps of a method for fabricating a piezoelectric micromechanical transducer according to an embodiment of this disclosure.

[0077] like Figure 2 As shown, a device cavity 112 is formed on the substrate 110; the device cavity 112 is a groove or recess that is recessed from the surface of the substrate 110; the device cavity 112 does not penetrate the substrate 110.

[0078] For example, the substrate 110 described above can be a silicon wafer substrate, and then an etching process can be used to etch device cavities 112 into the substrate 110. The shape and diameter of the etched device cavity define the shape and size of the device cavity in the subsequently formed piezoelectric micromechanical transducer. Of course, the substrate described above can also be made of common substrate materials such as alumina, silicon nitride, and sapphire.

[0079] For example, the etching process described above can be wet anisotropic etching (such as KOH / TMAH) to obtain specific sidewall morphology and stress distribution. Of course, the embodiments disclosed herein include, but are not limited to, the etching process described above can also be a dry etching process (DRIE / ICP).

[0080] like Figure 3 As shown, a sacrificial material layer 1200 is formed on one side of the substrate 110 where the device cavity 112 is formed. The sacrificial material layer 1200 fills the device cavity 112. The thickness of the sacrificial material layer 1200 is greater than the depth of the device cavity 112, thereby ensuring that the device cavity 112 is completely filled by the sacrificial material layer.

[0081] For example, the sacrificial material layer described above can be silicon oxide or silicon nitride. Of course, the embodiments disclosed herein include, but are not limited to, other materials, such as monocrystalline silicon, polycrystalline silicon, silicon-germanium (SiGe), aluminum (Al), polymers (PI / PR / BCB), and other different systems.

[0082] like Figure 4 As shown, a planarization process is used to planarize the sacrificial material layer 1200 and expose the substrate 110; the sacrificial material layer 1200 located in the device cavity 112 fills the device cavity 112 to form the sacrificial layer 120. Thus, this fabrication method can achieve that the surface of the sacrificial layer is flush with the surface of the substrate.

[0083] For example, chemical mechanical polishing (CMP) can be used to smooth out the deposited excess sacrificial material layer, exposing the substrate so that the sacrificial material layer just fills the device cavity.

[0084] like Figure 5 As shown, a seed layer 150 is formed on the substrate 110 and the sacrificial layer 120 to improve the growth quality of subsequent film layers and reduce residual stress.

[0085] For example, the seed layer 150 described above can be aluminum nitride (AlN); the seed layer can be formed using a deposition process. Of course, the embodiments disclosed herein include, but are not limited to, the seed layer described above can also be replaced with a transition layer such as AlN / AlON / SiN (aluminum nitride / aluminum oxynitride / silicon nitride) or a multilayer gradient stress buffer layer to achieve the same crystal orientation induction and residual stress control.

[0086] like Figure 6 As shown, a first electrode 131 and a first electrode pad 181 are formed on the seed layer 150.

[0087] For example, a molybdenum metal layer can be deposited on a seed layer and patterned using an etching process to form the first electrode and the first electrode pad described above. Of course, embodiments of this disclosure include, but are not limited to, the first and second electrodes described above can be replaced with metals or metal stacks such as Ti / Mo (titanium / molybdenum), Ti / Pt (titanium / platinum), W (tungsten), Ru (ruthenium), and Al (aluminum) to balance resistance, adhesion, stress, and subsequent etching selectivity.

[0088] like Figure 7 As shown, a piezoelectric layer 133 is formed on the seed layer 150 and the first electrode 131.

[0089] For example, the piezoelectric layer described above can be made of aluminum scandium nitride (AlScN), thus exhibiting a high piezoelectric coefficient. It should be noted that the scandium concentration in aluminum scandium nitride can be adjusted as needed. Of course, the embodiments disclosed herein include, but are not limited to, other piezoelectric materials, such as aluminum nitride, lead zirconate titanate (PZT), zinc oxide (ZnO), lithium niobate (LN), lead magnesium niobate-lead titanate (PMN-PT), or polyvinylidene fluoride (PVDF). Furthermore, the piezoelectric layer described above can achieve the same goals of enhanced coupling and stress reduction by adjusting the deposition process (sputtering / sol-gel / chemical methods, etc.) and deposition parameter window.

[0090] like Figure 8 As shown, a second electrode 132 and a second electrode pad 182 are formed on the piezoelectric layer 133. The orthographic projection of the second electrode 132 on the piezoelectric layer 133 overlaps with the orthographic projection of the first electrode 131 on the piezoelectric layer 133, thereby forming a piezoelectric structure 130.

[0091] For example, a molybdenum metal layer can be deposited on the piezoelectric layer first, and then patterned using an etching process to form the second electrode and the second electrode pads described above. It should be noted that the material of the second electrode can be replaced with Al (aluminum), Au (gold), Pt (platinum), W (tungsten), or a stack thereof; the patterning process can be replaced with a lift-off process (metal stripping process), or a "hard mask + segmented etching" method can be used to reduce damage to the piezoelectric layer and improve uniformity.

[0092] like Figure 9 As shown, a passivation layer 170 is formed on the above-mentioned film layer to protect the formed device and can also serve as a passive layer to improve the performance of the PMUT device.

[0093] For example, the passivation layer described above can be a single-layer structure or a stacked structure of multiple materials selected from silicon nitride (SiN), silicon oxide (SiO2), aluminum oxide (Al2O3), and parylene. A stress compensation layer (symmetrical stack) can be introduced to further reduce warpage and residual stress, thereby improving the uniformity of the array elements. In addition, the passivation layer described above can also be disposed between the first electrode and the substrate.

[0094] like Figure 10 As shown, the passivation layer 170 is etched to form a first window W1 exposing the first electrode pad 181 and a second window W2 exposing the second electrode pad 182.

[0095] like Figure 11 As shown, a first auxiliary electrode 191 and a second auxiliary electrode 192 are formed on the first electrode pad 181 and the second electrode pad 182 respectively through the first window W1 and the second window W2. Therefore, the first and second auxiliary electrodes can improve conductivity and reduce the difficulty of wire bonding.

[0096] For example, the first auxiliary electrode 191 and the second auxiliary electrode 192 described above can be formed using a lift-off process (metal stripping process); the materials of the first auxiliary electrode 191 and the second auxiliary electrode 192 can be materials with high conductivity such as aluminum, gold, silver, and copper, thereby improving conductivity.

[0097] For example, the first and second auxiliary electrodes described above can also employ electroplated Ni / Au (nickel / gold), electroplated Cu (copper), or sputtered / evaporated multilayer metal stacks (e.g., Ti / Au (titanium / gold), Ti / Cu / Au (titanium / copper / gold)) to reduce contact resistance and improve wire bonding / bonding reliability. Alternatively, the first and second auxiliary electrodes can also employ a UBM (Under-Bump Metallization) structure to meet subsequent flip-chip or bump interconnect requirements.

[0098] like Figure 12 As shown, a first isolation trench 201 is formed around the piezoelectric structure 130, and the orthographic projection of the first isolation trench 201 on the substrate 110 is outside the orthographic projection of the device cavity 112 on the substrate 110. Thus, the first isolation trench can isolate adjacent piezoelectric structures (array elements), thereby avoiding acoustic crosstalk between adjacent piezoelectric structures. On the other hand, the first isolation trench can also release accumulated stress, thereby preventing buckling deformation of the piezoelectric material layer, thus improving product yield and stability.

[0099] like Figure 13 As shown, within the area of ​​the device cavity 112, the passivation layer 170, the piezoelectric layer 133 and the first electrode 131 are etched to form a release hole 140; the release hole 140 connects the sacrificial layer 120 in the device cavity 112 to the outside.

[0100] like Figure 14 As shown, the sacrificial layer 120 is etched and removed through the release hole 140, thereby forming a hollow cavity 112. The orthogonal projection of the formed release hole 140 onto the substrate 110 lies within the range of the orthogonal projection of the device cavity 112 onto the substrate 110. Thus, the release hole does not disrupt the shape of the device cavity, allowing the device cavity to maintain a regular shape, such as a square or a circle.

[0101] For example, the shape of the orthographic projection of the release hole 140 onto the substrate 110, i.e., the cross-sectional shape of the release hole 140, can be rectangular, triangular, or circular. Of course, embodiments disclosed herein include, but are not limited to, these.

[0102] For example, the sacrificial layer can be made of different materials such as monocrystalline silicon, polycrystalline silicon, silicon dioxide, silicon germanium, metallic aluminum, or polymers (polyimide (PI), polymeric resin (PR), or benzocyclobutene (BCB)). When the sacrificial layer is a silicon-based material, the etching process can employ XeF2 (xenon difluoride) vapor phase etching, HF (hydrogen fluoride) liquid phase etching, or vapor phase etching. When the sacrificial layer is a polymer sacrificial layer, the etching process can employ O2 plasma ashing, or a segmented / multiple release and cleaning process to improve the release uniformity and yield of large-area arrays.

[0103] like Figure 15 As shown, an acoustic matching layer 160 is formed on the above structure and is configured to perform acoustic impedance matching on the ultrasonic waves generated by the piezoelectric structure 130, thereby both sealing the device and achieving matching of sound velocity and acoustic impedance.

[0104] For example, the aforementioned acoustic matching layer can be formed by bonding / spin-coating / drop-coating a matching material (such as PDMS, epoxy resin, etc.).

[0105] For example, the above-mentioned acoustic matching layer formation process can also be replaced with polyurethane / thermoplastic polyurethane (PU / TPU), silicone gel, parylene, or multilayer composite matching layer (gradient impedance layer). Alternatively, wafer-level capping / low-temperature deposition sealing can be used to achieve cavity sealing, and then an external matching layer can be superimposed to simultaneously meet the requirements of reliable sealing and acoustic matching.

[0106] In the fabrication method of the piezoelectric micromechanical transducer provided in this disclosure, by first forming a device cavity on the substrate, the shape, size, and depth of the device cavity are highly consistent, thereby minimizing the differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method can reduce residual stress, thereby improving product yield.

[0107] It should be noted that the above-mentioned method for fabricating piezoelectric micromechanical transducers is not limited to piezoelectric micromechanical ultrasonic transducers (PMUTs), but can also be applied to the production of any device containing a cavity structure, such as capacitive micromechanical ultrasonic transducers (CMUTs), that requires high consistency and high yield.

[0108] In some examples, the piezoelectric structure described above is configured to generate ultrasonic or electromagnetic waves. When the piezoelectric structure is configured to generate ultrasonic waves, the piezoelectric micromechanical transducer can be a piezoelectric micromechanical ultrasonic transducer (PMUT); when the piezoelectric structure is configured to generate electromagnetic waves, the piezoelectric micromechanical transducer can be a magnetoelectric antenna or a magnetic sensor. Additionally, when the piezoelectric structure is configured to generate electromagnetic waves, the piezoelectric micromechanical transducer may also include a magnetic layer located on a passivation layer. Furthermore, the piezoelectric structure described above can also be configured to process and compute optical signals. In this case, the piezoelectric micromechanical transducer can be an optical modulator, an optical switch, or an optical processor.

[0109] This disclosure provides a method for fabricating a piezoelectric micromechanical transducer array. The method includes forming a plurality of piezoelectric micromechanical transducers arranged in an array, each transducer being fabricated using the method described in any of the above examples. Therefore, after forming the piezoelectric micromechanical transducer array using this method, the entire array can generate an ideal beam during operation, greatly improving ultrasonic focusing accuracy, spatial resolution, and imaging contrast, avoiding imaging defects such as sidelobes and artifacts, and improving image quality and measurement accuracy. Furthermore, this fabrication method can also reduce crosstalk between adjacent piezoelectric micromechanical transducers.

[0110] One embodiment of this disclosure also provides a piezoelectric micromechanical transducer. For example... Figure 15 As shown, the piezoelectric micromechanical transducer 100 includes: a substrate 110, a piezoelectric structure 130, and a release hole 140; the substrate 110 includes a device cavity 112; the piezoelectric structure 130 is located on the substrate 110 and covers the device cavity 112, and the piezoelectric structure 130 includes a first electrode 131, a piezoelectric layer 133, and a second electrode 132 stacked together; the release hole 140 penetrates the piezoelectric structure 130 and communicates with the device cavity 112.

[0111] In the piezoelectric micromechanical transducer provided in this embodiment, by forming a device cavity in the substrate, the shape, size, and depth of the device cavity can be made highly consistent, thereby minimizing the differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method can reduce residual stress, thereby improving product yield.

[0112] In some examples, such as Figure 15 As shown, the orthographic projection of the release hole 140 on the substrate 110 lies within the range of the orthographic projection of the device cavity 112 on the substrate 110. Therefore, the release hole does not disrupt the shape of the device cavity, allowing it to maintain a regular shape, such as a square or circle. It should be noted that the commonly used sacrificial layer process creates the release hole outside the device cavity and then forms a horizontal groove or hole to connect the release hole to the device cavity. This results in the device cavity shape of the piezoelectric micromechanical transducer not being strictly square or circular, leading to distortion of the vibration modes. Furthermore, the irregular shape of the device cavity introduces additional stress, affecting key indicators such as device performance, array consistency, and yield.

[0113] In some examples, such as Figure 15As shown, the piezoelectric micromechanical transducer 100 also includes a first isolation trench 201 located at the edge of the piezoelectric structure 130; the orthographic projection of the first isolation trench 201 on the substrate 110 is outside the orthographic projection of the device cavity 112 on the substrate 110. Thus, the first isolation trench can isolate adjacent piezoelectric structures (array elements), thereby avoiding acoustic crosstalk between adjacent piezoelectric structures. On the other hand, the first isolation trench can also release accumulated stress, thereby preventing buckling deformation of the piezoelectric material layer, thus improving product yield and stability.

[0114] In some examples, such as Figure 15 As shown, the first isolation trench 201 penetrates at least the piezoelectric layer 133 in the piezoelectric structure 130, thereby ensuring good isolation performance. It should be noted that the size of the second electrode in the piezoelectric structure can be smaller than the size of the first electrode. In this case, a release hole can penetrate through the piezoelectric layer and the first electrode to connect the device cavity to the outside world for etching and removal of the sacrificial layer. Alternatively, the formed release hole can penetrate through the piezoelectric layer, the first electrode, and the second electrode in the piezoelectric structure.

[0115] In some examples, such as Figure 15 As shown, the first isolation trench 201 described above can be filled with air or a low-modulus polymer to form a first isolation structure 211.

[0116] In some examples, such as Figure 15 As shown, the piezoelectric micromechanical transducer 100 further includes a seed layer 150 located between the substrate 110 and the piezoelectric structure 130. The seed layer 150 can improve the growth quality of subsequent film layers and reduce residual stress.

[0117] For example, the seed layer 150 described above can be aluminum nitride (AlN); the seed layer can be formed using a deposition process. Of course, the embodiments disclosed herein include, but are not limited to, the seed layer described above can also be replaced with a transition layer such as AlN / AlON / SiN (aluminum nitride / aluminum oxynitride / silicon nitride) or a multilayer gradient stress buffer layer to achieve the same crystal orientation induction and residual stress control.

[0118] Figure 16 This is a schematic diagram of another piezoelectric micromechanical transducer provided in an embodiment of this disclosure. (See attached diagram.) Figure 16 As shown, the piezoelectric micromechanical transducer 100 includes: a substrate 110, a piezoelectric structure 130, and a release hole 140; the substrate 110 includes a device cavity 112; the piezoelectric structure 130 is located on the substrate 110 and covers the device cavity 112, and the piezoelectric structure 130 includes a first electrode 131, a piezoelectric layer 133, and a second electrode 132 stacked together; the release hole 140 penetrates the piezoelectric structure 130 and communicates with the device cavity 112.

[0119] and Figure 15 Unlike the piezoelectric micromechanical transducer shown, such as Figure 16 As shown, the piezoelectric micromechanical transducer 100 also includes a sacrificial residual layer 125, which is located within the device cavity 112 and on the side of the piezoelectric structure 130 near the substrate 110.

[0120] In the piezoelectric micromechanical transducer provided in this embodiment, by forming a device cavity in the substrate, the shape, size, and depth of the device cavity can be made highly consistent, thereby minimizing the differences in the resonant frequency, amplitude response, capacitance, and acoustic performance of the piezoelectric micromechanical transducer. Furthermore, by forming the device cavity first and then removing the sacrificial layer, this fabrication method can reduce residual stress, thereby improving product yield.

[0121] In some examples, such as Figure 16 As shown, the piezoelectric micromechanical transducer 100 also includes a second isolation trench 202 located on the side of the substrate 110 away from the piezoelectric structure 130; the orthographic projection of the second isolation trench 202 on the substrate 110 is outside the orthographic projection of the device cavity 112 on the substrate 110. Therefore, the second isolation trench can also prevent vibration crosstalk between device cavities. On the other hand, the second isolation trench can also release accumulated stress.

[0122] In some examples, such as Figure 16 As shown, the second isolation trench 202 described above can be filled with air or a low-modulus polymer to form a second isolation structure 212.

[0123] One embodiment of this disclosure also provides a piezoelectric micromechanical transducer array. Figure 17 This is a schematic diagram of a piezoelectric micromechanical transducer array provided as an embodiment of this disclosure. Figure 17 As shown, the piezoelectric micromechanical transducer array 300 includes a plurality of piezoelectric micromechanical transducers 100 arranged in an array; the plurality of piezoelectric micromechanical transducers 100 include the piezoelectric micromechanical transducers 100 provided in any of the examples described above. Therefore, the entire array can generate an ideal beam during operation, greatly improving the ultrasonic focusing accuracy, spatial resolution, and imaging contrast, avoiding imaging defects such as side lobes and artifacts, and improving image quality and measurement accuracy.

[0124] The following points need to be explained: (1) The accompanying drawings of the embodiments of this disclosure only involve the structures involved in the embodiments of this disclosure, and other structures can be referred to the general design.

[0125] (2) Where there is no conflict, features of the same embodiment and different embodiments of this disclosure may be combined with each other.

[0126] The above description is merely an exemplary embodiment of this disclosure and is not intended to limit the scope of protection of this disclosure, which is determined by the appended claims.

Claims

1. A method for fabricating a piezoelectric micromechanical transducer, comprising: Form device cavities on the substrate; A sacrificial layer is formed in the device cavity, and the surface of the sacrificial layer is flush with the surface of the substrate. A piezoelectric structure is formed on the substrate and the sacrificial layer. The piezoelectric structure includes a first electrode, a piezoelectric layer and a second electrode stacked together. The orthographic projection of the piezoelectric structure on the substrate overlaps with the orthographic projection of the device cavity on the substrate. A release hole is formed, which penetrates the piezoelectric structure and contacts the sacrificial layer; as well as The sacrificial layer is etched through the release hole to remove at least a portion of the sacrificial layer.

2. The method for fabricating a piezoelectric micromechanical transducer according to claim 1, wherein, The orthographic projection of the release hole on the substrate is within the range of the orthographic projection of the device cavity on the substrate.

3. The method for fabricating a piezoelectric micromechanical transducer according to claim 1, wherein, The release hole penetrates at least through the piezoelectric layer and the first electrode in the piezoelectric structure.

4. The method for manufacturing the piezoelectric micromechanical transducer according to any one of claims 1-3 further includes: A first isolation trench is formed at the edge of the piezoelectric structure, and the orthographic projection of the first isolation trench on the substrate is outside the orthographic projection of the device cavity on the substrate.

5. The method for fabricating a piezoelectric micromechanical transducer according to claim 4, wherein, The first isolation trench penetrates at least the piezoelectric layer in the piezoelectric structure.

6. The method for manufacturing the piezoelectric micromechanical transducer according to any one of claims 1-3 further includes: A second isolation trench is formed from the side of the substrate away from the piezoelectric structure, and the orthographic projection of the second isolation trench on the substrate is outside the orthographic projection of the device cavity on the substrate.

7. The method for fabricating a piezoelectric micromechanical transducer according to any one of claims 1-3, wherein before forming the piezoelectric structure on the substrate and the sacrificial layer, the method further comprises: A seed layer is formed on the substrate and the sacrificial layer.

8. The method for fabricating a piezoelectric micromechanical transducer according to any one of claims 1-3, wherein after forming the piezoelectric structure on the substrate and the sacrificial layer, the method further comprises: A passivation layer is formed on the side of the piezoelectric structure away from the substrate to protect the piezoelectric structure. The release hole also penetrates the passivation layer.

9. The method for fabricating a piezoelectric micromechanical transducer according to claim 8, wherein, Forming the piezoelectric structure on the substrate and the sacrificial layer includes: A first electrode pad is formed in the same layer as the first electrode; A second electrode pad is formed in the same layer as the second electrode.

10. The method for manufacturing a piezoelectric micromechanical transducer according to claim 9 further includes: The passivation layer and the piezoelectric layer are patterned to form a first window and a second window. The first window exposes the first electrode pad, and the second window exposes the second electrode pad.

11. The method for manufacturing a piezoelectric micromechanical transducer according to claim 10 further includes: A first auxiliary electrode and a second auxiliary electrode are formed on the first electrode pad and the second electrode pad respectively through the first window and the second window. Wherein, the conductivity of the first auxiliary electrode is greater than the conductivity of the first electrode pad, and the conductivity of the second auxiliary electrode is greater than the conductivity of the second electrode pad.

12. The method for manufacturing the piezoelectric micromechanical transducer according to any one of claims 1-4, further comprising: An acoustic matching layer is formed on the piezoelectric structure and configured to perform acoustic impedance matching on the ultrasonic waves generated by the piezoelectric structure.

13. The method for manufacturing the piezoelectric micromechanical transducer according to any one of claims 1-4, wherein, Forming a sacrificial layer in the device cavity includes: A sacrificial material layer is formed on one side of the substrate where the device cavity is formed. The sacrificial material layer fills the device cavity, and the thickness of the sacrificial material layer is greater than the depth of the device cavity. The sacrificial material layer is planarized using a planarization process, exposing the substrate. The sacrificial material layer located in the device cavity fills the device cavity to form the sacrificial layer.

14. The method for fabricating a piezoelectric micromechanical transducer according to claim 13, wherein, The planarization process includes chemical mechanical polishing or etching back.

15. A method for fabricating a piezoelectric micromechanical transducer array, comprising: Multiple piezoelectric micromechanical transducers are arranged in an array. The piezoelectric micromechanical transducers described herein are manufactured using the piezoelectric micromechanical transducer manufacturing method according to any one of claims 1-14.

16. A piezoelectric micromechanical transducer, comprising: Substrate, including device cavities; A piezoelectric structure is located on the substrate and covers the device cavity, the piezoelectric structure comprising a first electrode, a piezoelectric layer and a second electrode stacked together; as well as A release hole penetrates the piezoelectric structure and communicates with the cavity of the device.

17. The piezoelectric micromechanical transducer according to claim 16, further comprising: A sacrificial residue layer is located within the cavity of the device and on the side of the piezoelectric structure closest to the substrate.

18. The piezoelectric micromechanical transducer according to claim 16, wherein, The orthographic projection of the release hole on the substrate is within the range of the orthographic projection of the device cavity on the substrate.

19. The piezoelectric micromechanical transducer according to any one of claims 16-18, further comprising: The first isolation trench is located at the edge of the piezoelectric structure. Wherein, the orthographic projection of the first isolation trench on the substrate is located outside the orthographic projection of the device cavity on the substrate.

20. The piezoelectric micromechanical transducer according to claim 19, wherein, The first isolation trench penetrates at least the piezoelectric layer in the piezoelectric structure.

21. The piezoelectric micromechanical transducer according to any one of claims 16-18, further comprising: The second isolation trench is located on the side of the substrate away from the piezoelectric structure. Wherein, the orthographic projection of the second isolation trench on the substrate is located outside the orthographic projection of the device cavity on the substrate.

22. The piezoelectric micromechanical transducer according to any one of claims 16-18, further comprising: A seed layer is located between the substrate and the piezoelectric structure.

23. A piezoelectric micromechanical transducer array, comprising a plurality of piezoelectric micromechanical transducers arranged in an array, wherein, The plurality of piezoelectric micromechanical transducers include the piezoelectric micromechanical transducers according to any one of claims 16-22.

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