Method for preparing pMUT device with assistance of thinning and application of pMUT device

Abstract

The invention discloses a method for preparing a pMUT device through thinning assistance and application of the pMUT device, and belongs to the technical field of piezoelectric micromechanical ultrasonic transducers. According to the method, a piezoelectric single crystal wafer is bonded to a temporary substrate and is thinned and polished to obtain a piezoelectric single crystal film, then a lower electrode of the pMUT is deposited on the surface of the piezoelectric film wafer, and then the lower electrode face of the wafer is bonded with a silicon wafer with a pre-etched blind hole to achieve preparation of the pMUT cavity. Meanwhile, the bonding layer can be used as a structural layer of the pMUT, and finally, the preparation of the pMUT is completed after the piezoelectric film is etched and an upper electrode is deposited, so that the preparation cost of the pMUT single crystal film can be reduced, the stability and the reliability of the size of the cavity structure of the pMUT are improved, the erosion of the size and the angle of the side wall caused by the release of the sacrificial layer is also avoided, and the service life of the pMUT is prolonged. The size of the cavity is accurately controlled in advance.

Description

Technical Field

[0001] The present application relates to a method for thinning-assisted preparation of a pMUT device and its application, belonging to the technical field of piezoelectric micromechanical ultrasonic transducer technology. Background Art

[0002] Piezoelectric micromachined ultrasonic transducer (pMUT) is a micro device that generates and detects ultrasonic waves based on the inverse piezoelectric and piezoelectric effects of piezoelectric thin film materials. It has been widely used in medical ultrasonic imaging, ultrasonic ranging, non-destructive testing, biosensing, etc. The structure of pMUT usually consists of a piezoelectric film layer, a structural layer, an upper and lower electrode layer, and a support layer with a cavity. Piezoelectric film is the core structure of pMUT, and commonly used films include aluminum nitride (AlN), scandium-doped aluminum nitride (ScAlN), polycrystalline lead zirconate titanate (PZT), lithium niobate (LiNbO3), lithium tantalate (LiTaO3) and other materials. Single crystal thin film materials, such as lithium niobate and lithium tantalate, have high piezoelectric coefficients and low dielectric losses, making it easier to prepare high-performance pMUT devices. However, at present, piezoelectric single crystal thin films cannot be obtained by direct growth. They can only be prepared by the smart-cut method, which is costly and difficult to process. Therefore, obtaining thin-film single crystal piezoelectric materials has always been a difficulty in preparing high-performance pMUTs. The structural layer and the support layer usually use SOI wafers, which is convenient for the processing of MEMS structures using mature silicon processing technology. Another processing difficulty lies in the high-precision size control of the cavity. Since the frequency of the pMUT is particularly sensitive to the cavity size, slight size changes can easily cause frequency fluctuations. Dry etching has high etching accuracy and selectivity, but the process is difficult, the equipment is complex, and the cost is high. The wet etching process is simple and low-cost, but there is a problem of side etching, and it is difficult to ensure the accuracy and consistency of etching. Therefore, it is crucial to select a suitable etching process and accurately control the etching parameters. Summary of the invention

[0003] In order to solve the problems of complex, difficult to control and high cost of piezoelectric thin film manufacturing process in the prior art of pMUT device processing, the present application proposes a technical solution for thinning-assisted preparation of pMUT devices, wherein a piezoelectric single crystal wafer is bonded to a temporary substrate and thinned and polished to obtain a piezoelectric single crystal thin film, and then the lower electrode of the pMUT is deposited on the surface of the piezoelectric thin film wafer, and then the lower electrode surface of the wafer is bonded to a silicon wafer with a pre-etched blind hole to realize the preparation of the pMUT cavity. At the same time, the bonding layer can be used as the structural layer of the pMUT. Finally, the piezoelectric film is etched and the upper electrode is deposited to complete the preparation of the pMUT. This solution can reduce the preparation cost of the pMUT single crystal thin film, and at the same time, it can also improve the stability and reliability of the pMUT cavity structure size.

[0004] This application adopts the following technical solutions:

[0005] According to a first aspect of the present application, a method for thinning-assisted preparation of a pMUT device is provided, comprising the following steps:

[0006] Providing a first substrate, a second substrate, and a lithium niobate wafer;

[0007] Etching a surface of one side of the first substrate to form a blind hole to obtain component A;

[0008] Bonding one side surface of the second substrate to one side surface of the lithium niobate wafer via a bonding layer, then thinning the lithium niobate wafer to form a lithium niobate single crystal film, and depositing a lower electrode on the lithium niobate single crystal film to obtain component B;

[0009] The surface of one side of the blind hole of component A is bonded to the surface of one side of the lower electrode of component B through a structural layer, and then the second substrate and the bonding layer are etched away, and a lower electrode lead-out structure and an upper electrode are prepared on the lithium niobate single crystal film to obtain the pMUT device.

[0010] In one embodiment, the material of the bonding layer and the structural layer is independently selected from one of bonding glue and SiO2.

[0011] In one embodiment, the thickness of the lithium niobate single crystal film is 1 um to 20 um.

[0012] In one embodiment, the thickness of the bottom electrode is 300 nm to 5 um.

[0013] In one embodiment, the blind hole has a depth of 10 um to 200 um.

[0014] In one embodiment, the thickness of the upper electrode is 300 nm to 5 um.

[0015] In one embodiment, the step of preparing the lower electrode lead-out structure and the upper electrode comprises: etching a position corresponding to the lower electrode lead-out structure on the lithium niobate single crystal film to form a through hole to expose a portion of the lower electrode;

[0016] Patterned metal deposition is performed in the through hole and on the lithium niobate single crystal film to obtain the lower electrode lead-out structure and the upper electrode, respectively.

[0017] In one embodiment, the etching method for removing the second substrate and the bonding layer adopts deep reactive ion etching.

[0018] In one embodiment, the first substrate and the second substrate are independently selected from one of silicon wafer, glass, flexible polymer film, silicon carbide and sapphire.

[0019] According to a second aspect of the present application, there is provided an application of any of the above-mentioned thinning-assisted preparation methods for a pMUT device in the preparation of a sensor or an ultrasonic imaging device.

[0020] The beneficial effects of this application include:

[0021] (1) The method for preparing pMUT devices with the assistance of thinning provided in the present application prepares a lithium niobate thin film layer with a lower electrode by a thinning-assisted method, without the need for commercial thin-film lithium niobate, thereby saving costs, optimizing the preparation process, and ensuring the stability of the electrode.

[0022] (2) The thinning-assisted preparation method of the pMUT device provided in the present application prepares a cavity on a silicon wafer by means of a silicon blind hole, thereby avoiding the erosion of the side wall size and angle caused by the release of the sacrificial layer, and achieving precise control of the cavity size in advance.

[0023] (3) The thinning-assisted preparation method of the pMUT device provided in the present application does not require a wet etching process, thereby avoiding the potential safety hazards caused by acidic liquids during processing and facilitating the continuous operation of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the substrate preparation process of the silicon blind via of the present application;

[0025] Figure 2 This is a process flow chart of the thinning-assisted preparation method of lithium niobate substrate with a lower electrode of the present application;

[0026] Figure 3 This is a process flow chart of PMUT preparation assisted by thinning in this application;

[0027] Figure 4 It is a process flow chart of a PMUT using a sacrificial layer release method in comparative example 1 of the present application. DETAILED DESCRIPTION

[0028] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0029] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0030] Unless otherwise specified, conventional methods were used for testing and instrument settings were those recommended by the manufacturer.

[0031] The present application obtains a piezoelectric single crystal thin film by bonding a piezoelectric single crystal wafer to a temporary substrate and thinning and polishing it, then depositing the lower electrode of the pMUT on the surface of the piezoelectric thin film wafer, and then bonding the lower electrode surface of the wafer to a silicon wafer with a pre-etched blind hole to achieve the preparation of the pMUT cavity. At the same time, the bonding layer can be used as the structural layer of the pMUT. Finally, the piezoelectric film is etched and the upper electrode is deposited to complete the preparation of the pMUT. This scheme can reduce the preparation cost of the pMUT single crystal thin film on the one hand, and can also improve the stability and reliability of the pMUT cavity structure size on the other hand.

[0032] In one embodiment, a method for thinning-assisted preparation of a pMUT device is provided, comprising the following steps:

[0033] Providing a first substrate, a second substrate, and a lithium niobate wafer;

[0034] Etching a surface of one side of the first substrate to form a blind hole to obtain component A;

[0035] Bonding one side surface of the second substrate to one side surface of the lithium niobate wafer via a bonding layer, then thinning the lithium niobate wafer to form a lithium niobate single crystal film, and depositing a lower electrode on the lithium niobate single crystal film to obtain component B;

[0036] The surface of one side of the blind hole of component A is bonded to the surface of one side of the lower electrode of component B through a structural layer, and then the second substrate and the bonding layer are etched away, and a lower electrode lead-out structure and an upper electrode are prepared on the lithium niobate single crystal film to obtain the pMUT device.

[0037] In one embodiment, the material of the bonding layer and the structural layer is independently selected from one of bonding glue and SiO2.

[0038] The bonding method of the present application is selected from adhesive bonding or permanent bonding, preferably adhesive bonding, wherein the permanent bonding is achieved by growing SiO2 as a bonding layer.

[0039] In one embodiment, the thickness of the lithium niobate single crystal film is 1 um to 20 um.

[0040] In one embodiment, the thickness of the lithium niobate single crystal film is 2 um to 5 um.

[0041] In one embodiment, the thickness of the bottom electrode is 300 nm to 5 um.

[0042] In one embodiment, the thickness of the lower electrode is 500 nm to 1 um.

[0043] The method of depositing the lower electrode in the present application is not strictly limited, and those skilled in the art can select from the existing technologies as needed, for example, magnetron sputtering and electron beam evaporation.

[0044] In one embodiment, the material of the lower electrode is selected from at least one of Au, Cr, Ti, Ag, Al, and Cu.

[0045] In one embodiment, the material of the lower electrode is selected from Cr and Au.

[0046] In one embodiment, the blind hole has a depth of 10 um to 200 um.

[0047] In one embodiment, the blind hole has a depth of 100 um to 150 um.

[0048] In one embodiment, the step of etching to form a blind hole includes: coating a photoresist on one side surface of the first substrate, and then sequentially exposing, developing, and baking the photoresist to form a through hole on the upper side of the blind hole position of the first substrate, and then etching the first substrate to form the blind hole.

[0049] The materials and technical means used in the step of etching to form blind holes in the present application can be selected from the existing technology according to needs.

[0050] In one embodiment, the thickness of the upper electrode is 300 nm to 5 um.

[0051] In one embodiment, the thickness of the upper electrode is 500 nm to 1 um.

[0052] In one embodiment, the material of the lower electrode lead-out structure and the upper electrode is independently selected from at least one of Mo, Au, Cr, Ti, Ag, Al, and Cu.

[0053] In one embodiment, the step of preparing the lower electrode lead-out structure and the upper electrode comprises: etching a position corresponding to the lower electrode lead-out structure on the lithium niobate single crystal film to form a through hole to expose a portion of the lower electrode;

[0054] Patterned metal deposition is performed in the through hole and on the lithium niobate single crystal film to obtain the lower electrode lead-out structure and the upper electrode, respectively.

[0055] In one embodiment, the step of etching to form a through hole to expose a portion of the lower electrode includes: coating a photoresist on the lithium niobate single crystal film, and then sequentially exposing, developing, and baking the photoresist to form a through hole on the upper side of the lower electrode lead-out structure position of the lithium niobate single crystal film, and then etching the lithium niobate single crystal film to include the lower electrode.

[0056] The materials and technical means used in the step of etching to form blind holes in the present application can be selected from the existing technology according to needs.

[0057] In one embodiment, the etching method for removing the second substrate and the bonding layer is deep reactive ion etching (DRIE).

[0058] In one embodiment, the first substrate and the second substrate are independently selected from one of a silicon wafer, glass, and a flexible polymer film.

[0059] In order to more clearly describe the technical solution of the present application, in one embodiment, the present application further describes in detail a method for thinning-assisted preparation of a pMUT device, comprising the following steps:

[0060] Step 1: Cleaning

[0061] The lithium niobate wafer, the first substrate sheet and the second substrate are ultrasonically cleaned in acetone, isopropanol and deionized water in sequence, dried with nitrogen and baked.

[0062] Step 2: Bonding thinning + electrode preparation

[0063] bonding the lithium niobate wafer to a second substrate;

[0064] Thinning the unbonded surface of the lithium niobate wafer to obtain a lithium niobate single crystal film;

[0065] A layer of metal is deposited on the surface of the lithium niobate single crystal film obtained after thinning as a lower electrode.

[0066] In one embodiment, the bonding method can be selected from adhesive bonding and permanent bonding of growing SiO2, preferably adhesive bonding;

[0067] In one embodiment, the thickness of the lithium niobate single crystal film obtained after thinning is 1 um to 20 um, preferably 2 um to 5 um.

[0068] In one embodiment, the deposition method can be selected as magnetron sputtering, electron beam evaporation, etc., the metal component can be selected as Au, Cr, Ti, Ag, Al, Cu, etc., preferably a combination of Cr+Au, and the thickness of the metal layer can be selected as 300nm~5um, preferably 500nm~1um.

[0069] Step 3: Silicon blind via preparation

[0070] The photoresist is coated on the surface of the first substrate, followed by exposure, development, and baking on a hot plate to form a hard film. After the photolithography process is completed, the silicon blind hole is etched to complete the preparation of the blind hole on the silicon wafer.

[0071] In one embodiment, the thickness of the photoresist is 0.6 um to 5 um, preferably 1 um to 2 um.

[0072] In one embodiment, the exposure dose is 60 mJ / cm 2 ~200mJ / cm 2 , preferably 110 mJ / cm 2 ~130mJ / cm 2 .

[0073] In one embodiment, the temperature for hardening the film may be 90°C-120°C, preferably 100°C-110°C.

[0074] In one embodiment, the etching method is preferably dry etching, the etching depth can be selected to be 10um to 200um, preferably 100um to 150um, and the etching gas is SF6.

[0075] Step 4: Bonding

[0076] The second substrate on which the lower electrode and lithium niobate single crystal film are prepared is bonded to the first substrate on which the silicon blind hole is prepared, and the bonding surfaces are the lower electrode surface and the blind hole surface.

[0077] In one embodiment, the bonding method can be selected from adhesive bonding and permanent bonding of growing SiO2, preferably adhesive bonding.

[0078] Step 5: Remove the bonding glue

[0079] After bonding, DRIE etching is performed to ensure that the second substrate and the bonding adhesive are removed, and the termination layer is a lithium niobate single crystal film.

[0080] Step 6: LN Etching

[0081] The lithium niobate single crystal film is etched by ICP-RIE to ensure that the lithium niobate single crystal film layer is etched through and the stop layer is the lower electrode layer.

[0082] In one embodiment, the ICP power may be selected to be 200W to 2000W, preferably 1000W to 1500W.

[0083] Step 7: Depositing the top electrode

[0084] Photoresist is coated on the thin surface of lithium niobate single crystal, followed by exposure and development. After the photolithography process, electron beam evaporation is performed to deposit metal to form upper and lower electrode lead-out structures, completing the preparation of the overall PMUT device.

[0085] In one embodiment, the thickness of the photoresist is 0.6 um to 5 um, preferably 1 um to 2 um.

[0086] In one embodiment, the exposure dose is 60 mJ / cm 2 ~200mJ / cm 2 , preferably 110 mJ / cm 2 ~130mJ / cm 2 .

[0087] In one embodiment, the metal component can be selected from Mo, Au, Cr, Ti, Ag, Al, Cu, etc., preferably a combination of Al+Au.

[0088] In one embodiment, the thickness of the metal layer may be 300 nm to 5 um, preferably 500 nm to 1 um.

[0089] In the existing technology of pMUT device processing, the main processing methods are Smart-cut process and cavity sacrificial process. Among them, Smart-cut process is an important method for preparing thin-film lithium niobate based on ion implantation and wafer bonding technology. First, specific ions (such as hydrogen ions, etc.) are implanted into the lithium niobate crystal by ion implantation to form a damage layer at a certain depth. Then, the implanted lithium niobate wafer is bonded to another substrate wafer. Then, after annealing, the chemical bonds of the implanted ion layer are changed, and the lithium niobate film at the damaged layer will be peeled off from the original wafer and transferred to the substrate wafer. Then, the wafer is annealed again to reduce the damage to the crystal caused by ion implantation. Finally, a single crystal lithium niobate thin film wafer is obtained by polishing. However, although Smart-cut process is a common method for preparing thin-film lithium niobate, it also has the following constraints: (1) High equipment requirements: Smart-Cut process requires the use of high-precision semiconductor manufacturing equipment such as ion implanters and bonding equipment. These equipment are expensive and have high maintenance costs, which increases the equipment investment for preparing thin-film lithium niobate. (2) Difficulty in process control: This process involves multiple complex process steps, such as precise control of ion implantation dose and energy, precise adjustment of bonding temperature and pressure, and precise control of the splitting process. Deviations in process parameters in any link may lead to reduced film quality or preparation failure. The cavity sacrificial process is a commonly used technology for making cavity structures in piezoelectric micromechanical ultrasonic transducers (pMUTs), but it also has some disadvantages, mainly including the following aspects: (1) Process complexity: Multi-step operation: The sacrificial process usually involves multiple complex steps, such as deposition of sacrificial layers, patterning, etching, etc. Each step requires precise control and high process consistency to ensure that the final cavity structure meets the design requirements. This increases the complexity and difficulty of the manufacturing process and places high demands on the technical level of process equipment and operators. Process compatibility challenges: In the manufacture of pMUTs, the sacrificial process needs to be compatible with other process steps, such as deposition of piezoelectric materials and preparation of electrodes. There may be mutual influences between different materials and processes. For example, etching of the sacrificial layer may damage the deposited piezoelectric material or electrode, thereby affecting the performance of the pMUT. Therefore, the process parameters and sequence need to be carefully optimized to ensure good compatibility between the process steps. (2) Incomplete removal of the sacrificial layer: Residue problem: During the removal of the sacrificial layer, some sacrificial layer materials may remain inside or around the cavity. These residues will change the acoustic properties of the cavity, increase the scattering and attenuation of sound waves, and reduce the performance of the pMUT. Removal efficiency: Ensuring the complete removal of the sacrificial layer requires sufficient etching time and suitable etchants, but this may cause excessive etching or damage to other structural materials. Therefore, it is necessary to minimize the impact on other parts while ensuring the complete removal of the sacrificial layer, which requires precise process control and optimization.(3) High cost: Material cost: Some special materials used in the sacrificial process, such as high-quality sacrificial layer materials and etchants, are usually expensive. In addition, in order to ensure the stability and reliability of the process, it may be necessary to use purer and more expensive materials, which further increases the material cost. Equipment and process costs: Due to the complexity of the sacrificial process and the requirements for precision, advanced process equipment such as high-precision photolithography machines and etching machines are required. The purchase and maintenance costs of these equipment are very high, and they also consume a lot of energy and chemical reagents. In addition, the complex process also requires more process time and labor costs, which leads to an increase in the overall manufacturing cost.

[0090] In order to more clearly describe the technical improvement of the technical solution of the present application compared with the prior art, the technical solution of the present application ( Figures 1 to 3 ) and the typical solution in the prior art ( Figure 4 ) is described in further detail:

[0091] Example 1

[0092] Step 1: Cleaning

[0093] The lithium niobate wafer, the first silicon wafer and the second silicon wafer were ultrasonically cleaned in acetone, isopropanol and deionized water in sequence, dried with nitrogen and baked.

[0094] Step 2: Bonding thinning + electrode preparation

[0095] like Figure 2 As shown, the lithium niobate wafer and the cleaned second silicon wafer are bonded by adhesive coating, and the unbonded surface of the lithium niobate wafer is thinned to a thickness of 3um to obtain a lithium niobate single crystal film. A metal layer is deposited on the surface of the lithium niobate single crystal film as a lower electrode by magnetron sputtering. The metal composition is a combination of Cr+Au, and the thickness of the metal layer is 800nm.

[0096] Step 3: Silicon blind via preparation

[0097] like Figure 1 As shown, PR photoresist is coated on the surface of the first silicon wafer after cleaning, and the thickness of the PR photoresist is 1.5um. Then, exposure is performed at an exposure dose of 110mJ / cm 2 , then develop and bake the hard film on a hot plate at a temperature of 100°C. After the photolithography process is completed, the silicon blind hole is etched. The etching method is preferably dry etching, the etching depth is 130um, and the etching gas is SF6. The preparation of the blind hole on the silicon wafer is completed.

[0098] Step 4: Bonding

[0099] like Figure 3As shown, the second silicon wafer with the lower electrode and lithium niobate single crystal film prepared thereon and the first silicon wafer with the silicon blind hole prepared thereon are bonded, the bonding surfaces are the lower electrode surface and the blind hole surface, and the bonding method is glue coating bonding.

[0100] Step 5: Remove the bonding glue

[0101] like Figure 3 As shown, DRIE etching is performed after bonding to ensure that the upper second silicon wafer and the bonding adhesive are removed, and the termination layer is a lithium niobate single crystal thin film layer.

[0102] Step 6: LN Etching

[0103] like Figure 3 As shown, ICP-RIE is used to etch the lithium niobate single crystal film to ensure that the lithium niobate single crystal film layer is etched through, the termination layer is the lower electrode layer, and the ICP power is 1200W.

[0104] Step 7: Depositing the top electrode

[0105] like Figure 3 As shown, PR photoresist is coated on the surface of lithium niobate single crystal film, and the thickness of PR photoresist is 1.5um. Then it is exposed, and the exposure dose is 120mJ / cm 2 , followed by development. After the photolithography process is completed, electron beam evaporation is performed to deposit metal to form upper and lower electrode lead-out structures, respectively. The metal composition is a combination of Al+Au, and the thickness of the metal deposition is 700nm. The preparation of the overall PMUT device is completed.

[0106] Comparative Example 1

[0107] A typical example of a pMUT device including a sacrificial layer release step is shown in FIG. Figure 4 As shown, including:

[0108] Step 1: Cleaning

[0109] The first silicon wafer was ultrasonically cleaned in acetone, isopropanol and deionized water successively, dried with nitrogen and baked.

[0110] Step 2: Sacrificial layer deposition

[0111] The cleaned first silicon wafer is photolithographically etched to form a blind hole, and a SiO2 sacrificial layer is grown by PECVD (low-temperature plasma chemical vapor deposition) method with a thickness of 30 um. Subsequently, the SiO2 outside the blind hole is removed by CMP.

[0112] Step 3: pMUT structure growth

[0113] On the first silicon wafer with a sacrificial layer prepared, the lower electrode (Mo), the piezoelectric layer (AlN), and the upper electrode (Mo) are gradually grown by magnetron sputtering, with thicknesses of 1um, 3um, and 1um respectively.

[0114] Step 4: Patterning the pMUT Structure

[0115] The first step is to pattern the upper electrode layer, and use the method of photolithography and etching to etch through the upper electrode layer to expose the piezoelectric layer. The second step is to further pattern the exposed piezoelectric layer, and etching to ensure that the lower electrode is exposed.

[0116] Step 5: Lead Wires

[0117] After patterning on the wafer, a layer of Au is deposited to form a lower electrode lead-out structure to lead out the lower electrode, and an upper electrode lead-out structure to lead out the upper electrode for subsequent packaging testing.

[0118] Step 6: Sacrificial Layer Release

[0119] The wafer was immersed in BOE solution with a BOE concentration of 6:1 and an immersion time of 1 hour to ensure that the SiO2 of the sacrificial layer was completely released to form the cavity of the PMUT and complete the device preparation.

[0120] Compared with the typical case of the prior art in Comparative Example 1, the technical solution of the present application using Example 1 as a typical example can combine single crystal piezoelectric materials such as lithium niobate with pMUT by bonding and thinning, and has a higher piezoelectric coefficient and lower dielectric loss. The advantage is that the acid cleaning step avoids corrosion to processing equipment and danger to personnel, and ensures the accuracy of dimensional control.

[0121] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for thinning-assisted preparation of a pMUT device, characterized in that: The steps include: Providing a first substrate, a second substrate, and a lithium niobate wafer; Etching a surface of one side of the first substrate to form a blind hole to obtain component A; Bonding one side surface of the second substrate to one side surface of the lithium niobate wafer via a bonding layer, then thinning the lithium niobate wafer to form a lithium niobate single crystal film, and depositing a lower electrode on the lithium niobate single crystal film to obtain component B; The surface of one side of the blind hole of component A is bonded to the surface of one side of the lower electrode of component B through a structural layer, and then the second substrate and the bonding layer are etched away, and a lower electrode lead-out structure and an upper electrode are prepared on the lithium niobate single crystal film to obtain the pMUT device.

2. The method for thinning-assisted preparation of a pMUT device according to claim 1, characterized in that: The materials of the bonding layer and the structural layer are independently selected from bonding glue and SiO2.

3. The method for preparing a pMUT device by thinning-assisted method according to claim 1, characterized in that: The thickness of the lithium niobate single crystal film is 1 um to 20 um.

4. The method for thinning-assisted preparation of a pMUT device according to claim 1, characterized in that: The thickness of the lower electrode is 300nm~5um.

5. The method for thinning-assisted preparation of pMUT device according to claim 1, characterized in that: The depth of the blind hole is 10um to 200um.

6. The method for thinning-assisted preparation of a pMUT device according to claim 1, characterized in that: The thickness of the upper electrode is 300nm-5um.

7. The method for preparing a pMUT device by thinning-assisted method according to claim 1, characterized in that: The step of preparing the lower electrode lead-out structure and the upper electrode comprises: etching a position corresponding to the lower electrode lead-out structure on the lithium niobate single crystal film to form a through hole to expose a portion of the lower electrode; Patterned metal deposition is performed in the through hole and on the lithium niobate single crystal film to obtain the lower electrode lead-out structure and the upper electrode, respectively.

8. The method for thinning-assisted preparation of a pMUT device according to claim 1, characterized in that: The etching method for removing the second substrate and the bonding layer by etching is deep reactive ion etching.

9. The method for thinning-assisted preparation of a pMUT device according to claim 1, characterized in that: The first substrate and the second substrate are independently selected from one of silicon wafer, glass, flexible polymer film, silicon carbide and sapphire.

10. Application of the method for preparing pMUT devices with the aid of thinning according to any one of claims 1 to 9 in preparing sensors and ultrasonic imaging devices.

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