A vertical structure GaN acoustic sensor and a preparation method thereof

Abstract

The application relates to the technical field of semiconductor devices, and discloses a vertical structure GaN acoustic sensor and a preparation method thereof. The GaN acoustic sensor comprises a substrate, a bottom electrode, a piezoelectric layer and a top electrode which are sequentially arranged on one side of the substrate; the substrate has a cavity; the bottom electrode, the piezoelectric layer and the top electrode jointly form a suspended multilayer composite film and completely cover the cavity; and the piezoelectric layer is a GaN film which is peeled off from a preset substrate by an electrochemical peeling technology and is transferred to the substrate. The electrochemical peeling technology of the GaN epitaxial film is combined with the design of the vertical structure micro-electro-mechanical system acoustic sensor, ideal transduction materials are provided for high-performance acoustic detection, a solid foundation is laid for the high consistency and stability of the device, and the conversion efficiency and receiving sensitivity of the acoustic signal are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a vertical GaN acoustic sensor and its fabrication method. Background Technology

[0002] Acoustic sensors are energy conversion devices that convert external sound wave signals (such as air pressure fluctuations and mechanical vibrations) into processable electrical signals. As a crucial means of modern information acquisition, they have extremely wide applications in environmental noise monitoring, industrial structural health monitoring, biomedical imaging, consumer electronics, military reconnaissance, and microelectromechanical systems (MEMS) integration. With the rapid development of the Internet of Things, artificial intelligence, and wearable devices, the demand for high-performance, miniaturized, low-power, and integrable acoustic sensors is increasing. In particular, piezoelectric MEMS acoustic sensors, due to their advantages such as simple structure, fast response speed, high sensitivity, low power consumption, and ease of miniaturization and mass production, have become an important development direction for current acoustic sensing technology.

[0003] However, as MEMS technology evolves towards high-density arraying and system-level integration, traditional piezoelectric acoustic sensors are gradually revealing numerous bottlenecks in material and structural design. From a materials perspective, existing MEMS piezoelectric acoustic sensors primarily use materials such as aluminum nitride (AlN), zinc oxide (ZnO), or lead zirconate titanate (PZT) as the piezoelectric layer. While AlN possesses good compatibility with complementary metal-oxide-semiconductor (CMOS) processes, high thermal stability, and mechanical strength, its low piezoelectric coefficient results in low electromechanical coupling efficiency, limiting its sensitivity in detecting weak acoustic signals. ZnO, although possessing certain piezoelectric properties, suffers from poor chemical and thermal stability, making it prone to degradation in complex environments. PZT, despite its excellent piezoelectric performance, not only poses environmental pollution problems due to its lead content but also is incompatible with standard silicon-based CMOS processes, making monolithic integration with backend circuits difficult and limiting its application potential in high-end intelligent sensing systems. From a structural design perspective, traditional piezoelectric acoustic sensors are mostly fabricated using bulk micromachining or surface micromachining processes. The piezoelectric thin film is usually directly deposited or bonded onto a relatively thick substrate, or connected to the substrate through a support layer. This structure subjects the vibrating diaphragm to strong mechanical constraints, resulting in limited displacement amplitude under sound pressure and reduced energy conversion efficiency. Especially in high-frequency or broadband applications, the acoustic impedance matching problem of the substrate and the mechanical coupling effect will further deteriorate the frequency response characteristics and array consistency of the device, affecting the overall performance of the sensor.

[0004] In recent years, gallium nitride (GaN), as a third-generation wide-bandgap semiconductor material, has shown broad application prospects in radio frequency devices, power electronics, and optoelectronics due to its excellent piezoelectric properties, high electron mobility, good mechanical strength, and chemical stability. Its potential in acoustic sensing has also gradually attracted attention from academia and industry. However, GaN typically needs to be obtained through epitaxial growth on heterogeneous substrates such as sapphire, silicon carbide, or silicon. The presence of these substrates not only restricts the vibrational freedom of the piezoelectric film but also increases the overall thickness and manufacturing cost of the device. More importantly, how to non-destructively and efficiently peel and transfer high-quality GaN epitaxial films from the original growth substrate to the target substrate has always been a key technical challenge restricting its widespread application in MEMS acoustic sensors. Traditional methods such as laser peeling and mechanical polishing often damage the film, affecting its crystal quality and piezoelectric properties.

[0005] Therefore, there is an urgent need to develop a GaN acoustic sensor that possesses excellent piezoelectric properties, good process compatibility, and can achieve low-damage transfer and high-performance suspension structure design. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a gallium nitride acoustic sensor.

[0007] The second objective of this invention is to provide a method for fabricating such a gallium nitride acoustic sensor.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a gallium nitride acoustic sensor, including a substrate, and a bottom electrode, a piezoelectric layer and a top electrode sequentially disposed on one side of the substrate; The substrate has a cavity; the bottom electrode, the piezoelectric layer, and the top electrode together constitute a suspended multilayer composite film and completely cover the cavity; the piezoelectric layer is a gallium nitride film peeled off from a preset substrate and transferred to the substrate by electrochemical stripping technology.

[0009] In some embodiments of the present invention, the piezoelectric layer completely covers the opening of the cavity; the vertical projection of the top electrode is completely located within the opening of the cavity, and a gap is left between the edge of the top electrode and the edge of the cavity.

[0010] In some embodiments of the present invention, the cavity may be cylindrical in shape.

[0011] In some embodiments of the present invention, the geometry of the top electrode is circular or polygonal; the driving method of the top electrode is single-ended driving or differential driving.

[0012] In some embodiments of the present invention, the gallium nitride thin film is prepared by a method comprising the following steps: A core layer, a buffer layer, a sacrificial layer, and a target layer are sequentially grown on a preset substrate. The sacrificial layer is selectively electrochemically etched with an electrochemical etching solution to peel off the epitaxial film located above the sacrificial layer from a preset substrate, thereby obtaining the gallium nitride film. The nucleation layer is made of gallium nitride; the buffer layer and the sacrificial layer are made of silicon-doped gallium nitride, with the silicon doping concentration of the sacrificial layer being greater than that of the buffer layer; and the target layer is made of a nitride epitaxial film.

[0013] In some embodiments of the present invention, the gallium nitride thin film is prepared in which the silicon doping concentration of the buffer layer is 1.0 × 10⁻⁶. 18 cm -3 -8.0×10 18 cm -3 The silicon doping concentration of the sacrificial layer is 1.0 × 10⁻⁶. 19 cm -3 -2.0×10 19 cm -3 .

[0014] In some embodiments of the present invention, the thickness of the nucleation layer is 300 nm to 1.5 μm.

[0015] In some embodiments of the present invention, the thickness of the buffer layer is 300 nm-3 μm.

[0016] In some embodiments of the present invention, the thickness of the sacrificial layer is 0.5-1.5 μm.

[0017] In some embodiments of the present invention, the electrochemical corrosion process conditions include at least one of the following: the concentration of the electrochemical corrosion solution is 0.1-0.5 mol / L; the corrosion voltage is 13-19 V; the corrosion temperature is 25-35 °C; and the corrosion time is 1-3 h.

[0018] In some preferred embodiments of the present invention, the electrochemical corrosion process conditions include at least one of the following: the concentration of the electrochemical corrosion solution is 0.2-0.4 mol / L; the corrosion voltage is 15-17V; the corrosion temperature is 25-35℃; and the corrosion time is 1-2h.

[0019] In some embodiments of the present invention, the electrochemical corrosion solution is an oxalic acid solution.

[0020] In some embodiments of the present invention, the preset substrate is selected from a silicon substrate, a sapphire substrate, or a gallium nitride substrate.

[0021] In some embodiments of the present invention, the growth methods of the nucleation layer, buffer layer, sacrificial layer and target layer are independently selected from metal-organic vapor phase epitaxy, molecular beam epitaxy, physical vapor phase epitaxy or ion beam epitaxy.

[0022] In some embodiments of the present invention, the substrate is made of a material selected from monocrystalline silicon, mica, or a flexible polymer.

[0023] In some preferred embodiments of the present invention, the flexible polymer comprises polyethylene terephthalate (PET).

[0024] In some embodiments of the present invention, the materials of the bottom electrode and the top electrode are independently selected from at least one of indium, doped single-crystal silicon, molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, and composites or alloys formed from the above materials.

[0025] Specifically, the doped single-crystal silicon refers to highly conductive silicon with improved conductivity obtained by doping ultrapure single-crystal silicon with trace amounts of Group IIIA elements (such as boron) or Group VA elements (such as phosphorus or arsenic).

[0026] A second aspect of the present invention provides a method for fabricating the gallium nitride acoustic sensor described in the first aspect of the present invention, comprising the following steps: S1. A cavity is formed on the substrate, and then a bottom electrode is deposited on the substrate to obtain the target substrate; S2. Transfer the gallium nitride thin film onto the target substrate, cover the bottom electrode, and heat-bond it to form a piezoelectric layer; S3. Deposit and pattern a top electrode on the piezoelectric layer to form a top electrode; S4. Etch a portion of the piezoelectric layer to expose the bottom electrode, and deposit lead electrode pads for the top and bottom electrodes to obtain the gallium nitride acoustic sensor.

[0027] In some embodiments of the present invention, the cavity is formed by laser perforation or etching.

[0028] In some embodiments of the present invention, the deposition methods of the top electrode and the bottom electrode are independently selected from sputtering, electron beam evaporation, thermal evaporation or electrochemical deposition.

[0029] In some embodiments of the present invention, the patterning method of the top electrode is selected from photolithography or etching.

[0030] In some embodiments of the present invention, the temperature for heat bonding is 120-180°C and the time is 8-12 minutes.

[0031] In some preferred embodiments of the present invention, the temperature for heat bonding is 135-165°C and the time is 9-11 min.

[0032] In some embodiments of the present invention, the preparation method further includes establishing a physical field simulation model of the gallium nitride acoustic sensor and determining the structural geometric parameters and / or electromechanical performance parameters of the gallium nitride acoustic sensor through numerical calculation.

[0033] In some embodiments of the present invention, the structural geometric parameters include at least one of the cavity lateral dimension, piezoelectric layer thickness, and top electrode lateral dimension.

[0034] In some embodiments of the present invention, the electromechanical performance parameters include at least one of resonant frequency and receiving sensitivity.

[0035] In some embodiments of the present invention, establishing a physical field simulation model of the gallium nitride acoustic sensor and determining the structural geometric parameters and / or electromechanical performance parameters of the gallium nitride acoustic sensor through numerical calculation specifically includes: 1) Determine the layer structure and material of each layer of the gallium nitride acoustic sensor; 2) Establish a three-dimensional finite element simulation model of the gallium nitride acoustic sensor; 3) Investigate the influence of structural geometric parameters on electromechanical performance using parametric scanning; 4) Determine the structural dimension parameters based on the analysis results of step 3) and the actual process; 5) Based on the structural dimensional parameters determined in step 4), establish a three-dimensional finite element simulation model again; 6) Optimize the structural geometric parameters to obtain the electromechanical performance parameters.

[0036] In some embodiments of the present invention, the study of the influence of structural geometric parameters on electromechanical performance includes the use of solid mechanics and electrostatic field and multiphysics coupling.

[0037] Compared with the prior art, the beneficial effects of the present invention are: 1) The gallium nitride acoustic sensor provided by this invention combines the electrochemical lift-off technology of gallium nitride epitaxial thin films with the design of a vertical microelectromechanical system acoustic sensor. At the material level, by utilizing the excellent piezoelectric properties and mechanical strength of gallium nitride itself, the problems of low piezoelectric coefficient of traditional aluminum nitride and lead-containing lead zirconate titanate and process incompatibility are solved, providing an ideal transducer material for high-performance acoustic detection. At the process level, by pre-setting a heavily doped sacrificial layer and performing selective electrochemical wet etching, large-area, low-damage lift-off of high-quality gallium nitride thin films is achieved. The root mean square roughness of the film surface after lift-off is as low as 3.17 nm, and the crystal quality is well maintained, laying a solid foundation for the high consistency and stability of the device. At the structural level, the lift-off gallium nitride thin film is transferred and bonded to a target substrate with a cavity to form a suspended composite thin film structure consisting of a bottom electrode, a piezoelectric layer, and a top electrode. This significantly reduces the mechanical constraint of the substrate on the vibrating diaphragm and enhances the effective bending deformation under acoustic excitation, thereby greatly improving the conversion efficiency and receiving sensitivity of the acoustic signal. 2) The method for fabricating gallium nitride acoustic sensors provided by this invention further reduces parasitic capacitance and optimizes signal-to-noise ratio by simulating and optimizing electrode size. While improving device performance, it reduces the cost and process difficulty of array chip integration. It can cover a wide frequency range of detection from infrasound to ultrasound and has broad engineering application prospects in environmental monitoring, biomedical imaging, wearable devices and industrial inspection. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of the gallium nitride acoustic sensor in the embodiment.

[0039] Figure 2 This is a schematic diagram of the epitaxial structure during the preparation of the gallium nitride thin film in the example; Figure 3 This is a schematic diagram of the electrochemical stripping method for gallium nitride thin films in the embodiments; Figure 4 This is a schematic diagram illustrating the transfer of a gallium nitride thin film to a target substrate in an embodiment. Figure 5 This is a schematic diagram of the fabrication process of the gallium nitride acoustic sensor in the embodiment; Figure 6 The simulation results show the receiving sensitivity of the gallium nitride acoustic sensor under a sound pressure of 1 Pa in the example. Wherein, 1-substrate; 2-bottom electrode; 3-piezoelectric layer; 4-top electrode; 5-cavity; 6-target layer; 7-sacrificial layer; 8-buffer layer; 9-nucleation layer; 10-preset substrate. Detailed Implementation

[0040] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0041] Example This embodiment prepares a gallium nitride acoustic sensor, and the steps are as follows: S11. The gallium nitride acoustic sensor is composed of a substrate, a bottom electrode, a piezoelectric layer and a top electrode stacked in sequence. The materials of each layer are single crystal silicon, indium, gallium nitride thin film and nickel / gold composite, respectively. A cylindrical cavity is provided on the substrate. The top electrode is a differential driving electrode, which includes a circular inner electrode and an annular outer electrode. S12. Use COMSOL simulation software to establish a three-dimensional finite element simulation model; S13. The influence of important geometric parameters (piezoelectric layer thickness, cavity cross-sectional radius, and top electrode radius) on the electromechanical performance (resonant frequency and sensitivity) of the device is studied by parametric scanning. Solid mechanics, electrostatic field, and multi-physics coupling are used. The cavity cross-sectional radius, cavity longitudinal depth, piezoelectric layer thickness, top electrode thickness, bottom electrode thickness, and top electrode radius are determined by analysis results. S14. Determine the structural dimension parameters based on the analysis results of step S13 and the actual process. S15. Establish a more accurate three-dimensional finite element simulation model based on the structural dimension parameters determined in step S14. S16. Optimize the structural geometry parameters. The final structural dimensions are as follows: the cross-sectional radius of the cavity is 400 μm, and the depth is 400 μm to ensure that the diaphragm has sufficient mechanical compliance and structural strength. The thickness of the indium layer of the bottom electrode is 200 nm as a conductive layer. The thickness of the gallium nitride piezoelectric layer is 1 μm. The thickness of the nickel layer in the top electrode is 15 nm as an adhesion layer. The thickness of the gold layer is 50 nm as a conductive layer. The radius of the inner circular electrode of the top electrode is 250 μm. The radius of the small circle of the outer annular electrode is 280 μm. The radius of the large circle of the outer annular electrode is 400 μm. The ring width of the annular electrode is 120 μm. The receiving sensitivity display device calculated under these structural geometry parameters has high receiving performance. S17. Referring to the gallium nitride acoustic sensor design in steps S16-S17, a cavity of the corresponding size is prepared on the substrate by laser perforation so that the final cavity depth reaches the target depth. Then, the bottom electrode is deposited on the substrate by electron beam evaporation process to obtain the target substrate. S21. A nucleation layer, a buffer layer, a sacrificial layer, and a target layer are sequentially grown on a sapphire substrate using metal-organic vapor phase epitaxy to form an epitaxial structure. The nucleation layer is made of gallium nitride and has a thickness of 1 μm. The buffer layer is made of silicon-doped gallium nitride with a silicon doping concentration of 5.0 × 10⁻⁶. 18 cm -3 The thickness is 2μm, and the sacrificial layer is made of silicon-doped gallium nitride with a silicon doping concentration of 1.5×10⁻⁶. 19 cm -3 The thickness is 1μm, and the target layer is a nitride epitaxial film. S22. Inject a 0.3 mol / L oxalic acid solution into the electrochemical reaction cell. Use a diamond glass cutter to cut through the target layer on the surface of the epitaxial structure in step S21 to expose the sacrificial layer. Apply silver paste evenly to this area and connect the side with the silver paste to the anode of the electrochemical cell. Immerse the remaining 2 / 3 area in the oxalic acid solution and apply a 16V etching voltage. Perform selective electrochemical etching of the sacrificial layer at 30°C for 2 hours. Then peel the epitaxial film above the sacrificial layer from the preset substrate to obtain a gallium nitride film. S23. Transfer the gallium nitride thin film onto the target substrate, completely covering the bottom electrode, and place it on a 150°C hot stage for 10 minutes to perform high-temperature bonding and form a piezoelectric layer. S31. A top electrode is deposited on the piezoelectric layer by sputtering, and patterned by photolithography and etching to form the top electrode. S41. Selective etching of the piezoelectric layer is performed using inductively coupled plasma etching to form a bottom electrode via, exposing the pad area of ​​the bottom electrode. Then, lead pad metal is deposited by sputtering and patterned by photolithography and stripping processes to form the lead pads of the top and bottom electrodes, thus obtaining a gallium nitride acoustic sensor.

[0042] Figure 1 This is a schematic diagram of the gallium nitride acoustic sensor in the embodiment. Figure 1 It is known that the gallium nitride acoustic sensor consists of a substrate 1, a bottom electrode 2, a piezoelectric layer 3, and a top electrode 4 stacked sequentially. The substrate 1 has a cylindrical cavity 5 extending upward from its center. The bottom electrode 2, the piezoelectric layer 3, and the top electrode 4 together form a suspended multilayer composite film. The piezoelectric layer 3 completely covers the opening of the cavity 5, and the vertical projection of the top electrode 4 is completely within the opening of the cavity 5. A gap is left between the edge of the top electrode 4 and the edge of the cavity 5. This size design can ensure optimal reception performance.

[0043] Figure 2 This is a schematic diagram of the epitaxial structure during the preparation of the gallium nitride thin film in the examples. Figure 2It can be seen that the epitaxial structure includes, from bottom to top, a preset substrate 10, a nucleation layer 9, a buffer layer 8, a sacrificial layer 7, and a target layer 6.

[0044] Figure 3 This is a schematic diagram of the electrochemical stripping method for gallium nitride thin films in the embodiments. Figure 3 As can be seen, in this embodiment, the heavily doped gallium nitride sacrificial layer is selectively electrochemically wet-etched by immersing the epitaxial structure in oxalic acid solution to achieve the peeling of the gallium nitride film. The surface morphology of the electrochemically peeled and transferred gallium nitride film onto the target substrate is characterized by atomic force microscopy (AFM). The results show that the root mean square roughness (RMS) of the gallium nitride film is about 3.17 nm, indicating that it has extremely high surface flatness. This means that the peeling and transfer process of the present invention causes minimal damage to the gallium nitride crystal structure and can perfectly maintain the crystal quality and surface characteristics of the epitaxial film.

[0045] Figure 4 This is a schematic diagram illustrating the transfer of a gallium nitride thin film to a target substrate in this embodiment. Figure 4 It is known that a piezoelectric layer can be fabricated by transferring a gallium nitride thin film to a target substrate and heating it to bond the gallium nitride thin film to the bottom electrode.

[0046] Figure 5 This is a schematic diagram of the fabrication process of the gallium nitride acoustic sensor in the embodiment. Figure 5 As can be seen, in this embodiment, a cavity is first formed on the substrate 1, and then a bottom electrode 2 is deposited on the substrate 1 to obtain the target substrate; then, a gallium nitride thin film 3 is transferred to the target substrate to completely cover the bottom electrode 2, and a piezoelectric layer is formed by heat bonding; a top electrode is deposited on the piezoelectric layer and patterned to form the top electrode 4; finally, part of the piezoelectric layer is etched to expose the bottom electrode, and lead electrode pads of the top electrode and the bottom electrode are deposited to complete the fabrication of the gallium nitride acoustic sensor.

[0047] Figure 6 The simulation results of the gallium nitride acoustic sensor's receiving sensitivity under 1 Pa sound pressure are presented in the examples. Figure 6 It is known that the gallium nitride acoustic sensor prepared in this embodiment has a significant resonance peak at approximately 53.6 Hz. At this frequency, the receiving sensitivity is the highest, approximately 5.5 mV / Pa. This means that the gallium nitride acoustic sensor prepared in this embodiment also has high sensitivity in the low-frequency band below 100 Hz, and has the potential to be applied to infrasound detection (such as earthquake monitoring and environmental noise monitoring). Furthermore, by changing the key dimensions of the device, this invention can enable its acoustic detection frequency range to cover the frequency bands from infrasound to ultrasound.

Claims

1. A gallium nitride acoustic sensor, characterized in that, It includes a substrate, and a bottom electrode, a piezoelectric layer and a top electrode sequentially disposed on one side of the substrate; The substrate has a cavity; the bottom electrode, the piezoelectric layer, and the top electrode together constitute a suspended multilayer composite film and completely cover the cavity; the piezoelectric layer is a gallium nitride film peeled off from a preset substrate and transferred to the substrate by electrochemical stripping technology.

2. The gallium nitride acoustic sensor according to claim 1, characterized in that, The piezoelectric layer completely covers the opening of the cavity; the vertical projection of the top electrode is completely within the opening of the cavity, and a gap is left between the edge of the top electrode and the edge of the cavity.

3. The gallium nitride acoustic sensor according to claim 1, characterized in that, The gallium nitride thin film is prepared by a method comprising the following steps: A core layer, a buffer layer, a sacrificial layer, and a target layer are sequentially grown on a preset substrate. The sacrificial layer is selectively electrochemically etched with an electrochemical etching solution to peel off the epitaxial film above the sacrificial layer from a preset substrate, thereby obtaining the gallium nitride film. The nucleation layer is made of gallium nitride; the buffer layer and the sacrificial layer are made of silicon-doped gallium nitride, with the silicon doping concentration of the sacrificial layer being greater than that of the buffer layer; and the target layer is made of a nitride epitaxial film.

4. The gallium nitride acoustic sensor according to claim 3, characterized in that, The gallium nitride thin film obtained has a silicon doping concentration of 1.0 × 10⁻⁶ in the buffer layer. 18 cm -3 -8.0×10 18 cm -3 The silicon doping concentration of the sacrificial layer is 1.0 × 10⁻⁶. 19 cm -3 -2.0×10 19 cm -3 .

5. The gallium nitride acoustic sensor according to claim 3, characterized in that, The electrochemical corrosion process conditions include at least one of the following: the concentration of the electrochemical corrosion solution is 0.1-0.5 mol / L; the corrosion voltage is 13-19 V; the corrosion temperature is 25-35 °C; and the corrosion time is 1-3 h.

6. The gallium nitride acoustic sensor according to claim 1, characterized in that, The substrate is made of a material selected from monocrystalline silicon, mica, or flexible polymer.

7. The gallium nitride acoustic sensor according to claim 1, characterized in that, The materials of the bottom electrode and the top electrode are independently selected from at least one of indium, doped single crystal silicon, molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, and composites or alloys formed from the above materials.

8. A method for fabricating a gallium nitride acoustic sensor according to any one of claims 1-7, characterized in that, Includes the following steps: S1. A cavity is formed on the substrate, and then a bottom electrode is deposited on the substrate to obtain the target substrate; S2. Transfer the gallium nitride thin film onto the target substrate, cover the bottom electrode, and heat-bond it to form a piezoelectric layer; S3. Deposit and pattern a top electrode on the piezoelectric layer to form a top electrode; S4. Etch a portion of the piezoelectric layer to expose the bottom electrode, and deposit lead electrode pads for the top and bottom electrodes to obtain the gallium nitride acoustic sensor.

9. The preparation method according to claim 8, characterized in that, The heating bonding temperature is 120-180℃, and the time is 8-12 minutes.

10. The preparation method according to claim 8, characterized in that, The preparation method also includes establishing a physical field simulation model of the gallium nitride acoustic sensor and determining the structural geometric parameters and / or electromechanical performance parameters of the gallium nitride acoustic sensor through numerical calculation.

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