Cantilever beam structure containing piezoelectric single crystal film, laser modification auxiliary preparation method of cantilever beam structure and MEMS device

Abstract

The invention discloses a cantilever beam structure containing a piezoelectric single crystal film, a laser modification auxiliary preparation method of the cantilever beam structure and an MEMS device, and belongs to the technical field of MEMS. Laser modification and a wet etching process are combined to accurately and quickly etch a single crystal lithium niobate or lithium tantalate substrate sheet to obtain a cantilever beam structure containing a piezoelectric single crystal film, a cavity is formed in an internal area of the substrate sheet, the piezoelectric single crystal film is arranged on the surface layer of one surface of the substrate sheet relatively close to the cavity and covers the cavity, and the piezoelectric single crystal film is arranged on the surface layer of the other surface of the substrate sheet. At least one micropore is formed in the position, opposite to the edge of the cavity, of the edge of the piezoelectric single crystal film, and the cavity is communicated with the outside of the base piece through the micropore. According to the invention, the single crystal lithium niobate or lithium tantalate film and the cantilever beam structure are prepared at the same time and are used in the MEMS device, and the same material structure design of the cavity layer and the piezoelectric single crystal film layer can effectively solve the problems of stress matching and compensation of the cavity layer and the piezoelectric single crystal film layer; and the problem that the performance of the device is reduced due to internal lattice mismatch caused by a traditional piezoelectric single crystal film deposition method is solved.

Description

Technical Field

[0001] The present application relates to a cantilever beam structure containing a piezoelectric single crystal film and a laser modification-assisted preparation method thereof, and a MEMS device, belonging to the field of MEMS technology. Background Art

[0002] Lithium niobate wafers and lithium tantalate wafers are widely used in the preparation of many devices due to their excellent properties: for example, their excellent piezoelectric and ferroelectric effects are widely used in the preparation of sensors and detectors; their acoustic properties are widely used in MEMS devices such as surface acoustic wave devices and thin film bulk acoustic wave resonator devices; their outstanding electro-optical and nonlinear optical effects play a key role in the development and application of optical devices such as optical waveguides, electro-optic modulators, optical phase modulators, and electro-optic Q-switches. Under the current development trend of device integration and miniaturization, higher requirements are also placed on the micro-nano processing technology of single-crystal lithium niobate or lithium tantalate materials.

[0003] Single crystal lithium niobate or lithium tantalate has stable chemical properties, good corrosion resistance and high temperature resistance, and is a hard and brittle material that is difficult to process. Currently, the commonly used etching methods are mainly dry etching and wet etching. Dry etching mainly uses the method of directly etching on the surface of lithium niobate film to prepare waveguides. However, this method has high cost, complex equipment, poor etching selectivity for underlying materials, and device damage caused by plasma during the etching process. Wet etching mainly uses chromium as a mask, and directly places the lithium niobate film in a hydrofluoric acid solution to etch the surface not covered by the chromium mask. Compared with dry etching, wet etching has low cost and is suitable for mass production, but the etching product lithium fluoride will be deposited on the surface of lithium niobate, which not only affects the etching speed, but also causes isotropic etching due to the flow characteristics of the liquid. Therefore, it is extremely difficult to process single crystal lithium niobate or lithium tantalate using only wet etching, and the selectivity is not high. In addition, laser processing technology is a processing technology that uses the characteristics of the interaction between laser beams and matter to cut, weld, surface treat, punch holes and micro-process materials. This technology is a practical method for wafer etching with high efficiency and low production cost. However, due to the limitations of laser diffraction limits and thermal effects, the resolution of laser ablation cutting is limited and the etching accuracy is not high, which cannot meet the needs of high-precision and high-quality processing of piezoelectric single crystal films. Summary of the invention

[0004] Based on this, the present application provides a cantilever beam structure containing a piezoelectric single crystal film and its laser modification assisted preparation method and MEMS device, which uses laser assisted wet etching to solve the problem of balancing the etching rate and etching accuracy of single crystal lithium niobate or lithium tantalate and the cost in the existing MEMS technology. Based on this, a method for preparing a cantilever beam structure containing a piezoelectric single crystal film is provided, which solves the stress matching and compensation problems of the cavity layer and the piezoelectric single crystal film layer, as well as the problem of internal lattice mismatch caused by traditional single crystal piezoelectric film deposition methods, resulting in reduced device performance.

[0005] According to a first aspect of the present application, there is provided a cantilever beam structure containing a piezoelectric single crystal film, comprising a substrate sheet, wherein the substrate sheet is made of single crystal lithium niobate or single crystal lithium tantalate;

[0006] A cavity is provided inside the substrate sheet, in an area close to a surface layer of one side of the substrate sheet;

[0007] The portion covering the cavity on the surface of one side of the substrate sheet relatively close to the cavity is a piezoelectric single crystal film;

[0008] At least one microhole is arranged on the edge of the piezoelectric single crystal film at a position opposite to the edge of the cavity, and the cavity is connected with the outside of the substrate sheet through the microhole.

[0009] In one embodiment, the micropores have a pore size of 5 μm to 20 μm.

[0010] In one embodiment, the piezoelectric single crystal film has a thickness of 0.3 μm to 10 μm.

[0011] According to a second aspect of the present application, a laser modification-assisted preparation method of the cantilever beam structure containing a piezoelectric single crystal film is provided, comprising:

[0012] Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet;

[0013] Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region;

[0014] The modified solid substrate sheet with deposited electrodes and structural layers and opened holes is placed in an etching solution and immersed until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film, thereby obtaining the cantilever beam structure containing the piezoelectric single crystal film.

[0015] In one embodiment, the opening is selected from laser modified etched opening or direct laser ablation opening.

[0016] In one embodiment, the laser modification and etching of the openings is: using laser to irradiate the microporous region of the solid substrate sheet to modify the material of the region to form the same material as the modified region, thereby forming closed micropores.

[0017] In one embodiment, the direct laser ablation opening is performed by irradiating a microporous region of a solid substrate sheet with a laser so that open micropores are directly formed in the region.

[0018] In one embodiment, the laser irradiation conditions include: laser pulse width of 150fs to 500ps, laser wavelength of 780nm to 1100nm, and laser frequency of 1kHz to 1MHz.

[0019] In one embodiment, the etching solution is selected from a hydrogen fluoride solution having a hydrogen fluoride content of 2% to 49%.

[0020] In the present application, there is no strict limitation on the components other than hydrogen fluoride in the hydrogen fluoride-containing solution, and those skilled in the art can select the components according to the requirements.

[0021] In one embodiment, the hydrogen fluoride-containing solution is selected from hydrofluoric acid or BOE solution.

[0022] According to the third aspect of the present application, a MEMS device is provided, comprising the above-mentioned cantilever beam structure containing a piezoelectric single crystal film, or a cantilever beam structure containing a piezoelectric single crystal film after the side of its substrate sheet relatively away from the cavity is thinned to expose the cavity.

[0023] In one embodiment, the MEMS device is selected from a piezoelectric ultrasonic transducer, a resonator, a pressure sensor, and an acoustic wave filter.

[0024] In one embodiment, the piezoelectric ultrasonic transducer includes at least two electrodes, a structural layer, and a substrate;

[0025] The electrode is arranged on the surface of the piezoelectric single crystal film away from the cavity;

[0026] The structural layer covers the surface of one side of the piezoelectric single crystal film of the cantilever beam structure containing the piezoelectric single crystal film;

[0027] The positions of the structural layer corresponding to the micropores are provided with through holes connecting the micropores with the outside;

[0028] The thickness of the structural layer is greater than the thickness of the electrode;

[0029] The substrate is formed by thinning a side of the base sheet relatively far from the cavity to expose the cavity and then leaving a portion surrounding the piezoelectric single crystal film.

[0030] In one embodiment, the structural layer is provided with openings for accommodating the electrodes at positions corresponding to the electrodes.

[0031] In one embodiment, the piezoelectric ultrasonic transducer is prepared by a method comprising the following steps:

[0032] Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet;

[0033] Depositing an electrode on a surface of the modified solid substrate sheet corresponding to the piezoelectric single crystal film;

[0034] Depositing a structural layer on one side of the modified solid substrate sheet where the electrode is deposited;

[0035] Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region;

[0036] Placing the modified solid substrate sheet with deposited electrodes and structural layers and having holes therein into an etching solution, and immersing the substrate until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film;

[0037] The piezoelectric ultrasonic transducer is obtained by thinning a side of the substrate sheet that is relatively far from the cavity until the cavity is exposed.

[0038] In one embodiment, the preparation of the piezoelectric ultrasonic transducer further includes the following step: etching and removing a portion of the structural layer corresponding to the electrode until an opening is formed to expose the electrode.

[0039] In one embodiment, the thickness of the electrode is 0.05 μm to 3 μm.

[0040] In one embodiment, the material of the electrode is selected from at least one of Mo (molybdenum), Pt (platinum), Cr (chromium), and Al (aluminum).

[0041] In one embodiment, the thickness of the structural layer is 5 μm to 20 μm.

[0042] In one embodiment, the material of the structural layer is selected from silicon dioxide, polysilicon, and silicon nitride.

[0043] The beneficial effects of this application include:

[0044] 1. The cantilever beam structure containing a piezoelectric single crystal film prepared by the technical solution of the present application directly etches a cavity structure in the lithium niobate or lithium tantalate piezoelectric material through a special etching process, and retains the piezoelectric film layer, thereby ensuring that the piezoelectric layer and the cavity layer are made of the same material, and can effectively solve the stress matching and compensation problems of the cavity layer and the piezoelectric single crystal film layer.

[0045] 2. The laser modification-assisted preparation method of the cantilever beam structure containing the piezoelectric single crystal film in the technical solution of the present application uses laser irradiation to modify the crystal properties of lithium niobate or lithium tantalate in a specific area to amorphous properties. The modified material is easy to remove, and its etching rate is much higher than that of single crystal lithium niobate or lithium tantalate crystals that have not been irradiated by laser. The difference in wet etching rates between the two is used to achieve precise etching of specific areas. This method has high modification efficiency and greatly improves the preparation efficiency of lithium niobate or lithium tantalate crystal micro-nano structures. In addition, it is possible to prepare a cavity inside a lithium niobate or lithium tantalate substrate sheet by laser modification-assisted wet etching, and simultaneously prepare a single crystal lithium niobate or lithium tantalate film and a cantilever beam structure.

[0046] 3. The MEMS device based on the cantilever beam structure containing piezoelectric single crystal film in the technical solution of this application can prepare a variety of high-performance MEMS devices by utilizing the high piezoelectric coefficient, high electromechanical coupling coefficient and low dielectric loss of the single crystal lithium niobate or lithium tantalate film in the prepared structure. For example, a piezoelectric ultrasonic transducer with low power consumption, high signal-to-noise ratio, high emission sound pressure level and full-frequency response can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the laser modification-assisted preparation method of the cantilever beam structure containing a piezoelectric single crystal film of the present application, wherein (a) is the state after laser irradiation to form a modified area, (b) is the state after opening a hole, and (c) is the state after etching to remove the modified area.

[0048] Figure 2 It is a schematic diagram of the laser modification-assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film using a laser modification etching and hole opening method in Example 1 of the present application.

[0049] Figure 3 It is a schematic diagram of the laser modification-assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film by direct laser ablation hole opening in Example 2 of the present application.

[0050] Figure 4 This is a process flow chart of the manufacturing process of the piezoelectric ultrasonic transducer of Example 3 of the present application, wherein (a) is depositing electrodes, (b) is depositing structural layers, (c) is opening holes and etching to remove modified areas, and (d) is thinning the substrate sheet to expose the cavity.

[0051] Figure 5It is a schematic diagram of the structure of the piezoelectric ultrasonic transducer of Example 3 of the present application.

[0052] Figure ID

[0053] 1. Modified region; 2. Micropore; 3. Cavity; 4. Piezoelectric single crystal film; 5. Substrate; 6. Electrode; 7. Structural layer. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0056] In order to solve the problem that it is difficult to balance the etching rate and etching accuracy of single-crystal lithium niobate or lithium tantalate, the wet etching process in the prior art is relatively simple, high-precision and low-cost, but it is usually not very selective for different materials. While removing the target material, it may also cause unnecessary corrosion to the underlying or adjacent materials, affecting the performance and yield of the device. Due to the uneven distribution of the fluidity of the solution and the concentration of the reactants, the etching rate may be inconsistent at different positions on the wafer surface, affecting the uniformity of the etching. There are also problems such as sidewall erosion, residual pollution, and environmental safety. The laser ablation technology in the prior art has high efficiency and low production cost, but it is limited by the laser diffraction limit and thermal effects. The resolution of laser ablation cutting is limited and cannot meet the needs of high-precision and high-quality processing of piezoelectric single crystal films. The inventors found that combining laser modification in laser processing technology with wet etching technology can have the advantages of both technologies and achieve accurate and rapid etching of single-crystal lithium niobate or lithium tantalate.

[0057] In view of the intrinsic stress caused by the traditional piezoelectric single crystal film deposition method of the cantilever beam structure used in MEMS devices, which causes the internal lattice mismatch problem, a special processing technology in the prior art etches a cavity structure in lithium niobate or lithium tantalate material and simultaneously obtains a piezoelectric single crystal film layer. The inventors have found that the method of forming a single crystal film and a cavity structure at the same time and the integrated structure can solve the stress matching and compensation problem of the cavity layer and the piezoelectric single crystal film layer.

[0058] In order to solve the stress matching and compensation problem between the cavity layer and the piezoelectric single crystal film layer, in one embodiment, the present application provides a cantilever beam structure containing a piezoelectric single crystal film, the structural schematic diagram is as follows: Figure 1 As shown in c, it includes a substrate sheet, and the material of the substrate sheet is single crystal lithium niobate or single crystal lithium tantalate;

[0059] A cavity is provided inside the substrate sheet, in an area close to a surface layer of one side of the substrate sheet;

[0060] The portion covering the cavity on the surface of one side of the substrate sheet relatively close to the cavity is a piezoelectric single crystal film;

[0061] At least one microhole is arranged on the edge of the piezoelectric single crystal film at a position opposite to the edge of the cavity, and the cavity is connected with the outside of the substrate sheet through the microhole.

[0062] In one embodiment, the piezoelectric single crystal film has a thickness of 0.3 μm to 10 μm.

[0063] In one embodiment, the micropores have a pore size of 5 μm to 20 μm.

[0064] In one embodiment, the pore size of the micropores is preferably 10 μm.

[0065] In one embodiment, the substrate wafer is a single crystal lithium niobate wafer or a single crystal lithium tantalate wafer.

[0066] In the present application, the shape and size of the cavity are not strictly limited in the present application, and technical personnel in this field can select the size according to their needs. Accordingly, the number of micropores depends on the target volume of the cavity and the target etching speed. At the same etching speed, the larger the volume of the cavity, the more micropores are required; at the same cavity volume, the more micropores, the faster the etching speed.

[0067] In the present application, the shape of the micropores is not strictly limited, and the etching solution can be introduced into the modified area for contact. The cross-sectional shape and size of the micropores are considered to be equivalent to a circle for size limitation.

[0068] In order to realize the rapid integration of a piezoelectric single crystal film and a cantilever beam structure, the present application provides a laser modification-assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film. The preparation process diagram is shown in FIG. Figure 1 As shown, laser irradiation is performed on a specific area on the surface of a lithium niobate or lithium tantalate wafer, and amorphous transformation crystal modification occurs inside the irradiated area. Holes are opened from top to bottom at the edge of the modified layer to achieve wet etching with a hydrofluoric acid-containing etchant, and the selective etching characteristic that the etching rate of the modified layer is much higher than that of the unmodified area is used to achieve the engraving of the three-dimensional structure of the lithium niobate or lithium tantalate wafer.

[0069] In one embodiment, a laser modification-assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film comprises:

[0070] Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet;

[0071] Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region;

[0072] The modified solid substrate sheet with deposited electrodes and structural layers and opened holes is placed in an etching solution and immersed until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film, thereby obtaining the cantilever beam structure containing the piezoelectric single crystal film.

[0073] In one embodiment, the cleaning comprises ultrasonically cleaning the solid substrate sheet in acetone, ethanol and deionized water in sequence, drying with nitrogen, and baking.

[0074] In one embodiment, the laser is a femtosecond laser or a picosecond laser.

[0075] In one embodiment, the laser irradiation conditions include: laser pulse width of 150fs to 500ps, laser wavelength of 780nm to 1100nm, and laser frequency of 1kHz to 1MHz.

[0076] In the present application, the laser irradiation conditions can be selected within the above range according to the actual structural requirements so as to complete the modification of the target area inside the substrate sheet.

[0077] In one of the embodiments, the present application does not impose strict limitations on the scanning rate and number of scans of laser irradiation, and those skilled in the art may make selections based on their needs. In a specific embodiment of the present application, the scanning rate and number of scans are preferably selected based on the depth requirements of the target modified cavity structure. The lower the scanning rate of the laser irradiation and the greater the number of scans, the greater the depth of the modified cavity and the greater the subsequent etching depth.

[0078] In one embodiment, a designated area on the surface of a clean lithium niobate wafer or lithium tantalate wafer is locally irradiated with laser to form a modified area inside. The wafer surface absorbs laser energy and transmits it to the inside to form an amorphous transformation to form a modified area. The etching rate of the modified area is much higher than that of the unmodified area, thereby obtaining a selective etching characteristic.

[0079] In one embodiment, the opening is selected from a laser modified etched opening or a direct laser ablated opening;

[0080] In one embodiment, the laser modification and etching of the openings is: using laser to irradiate the microporous region of the solid substrate sheet to modify the material of the region to form the same material as the modified region, thereby forming closed micropores.

[0081] Closed micropores refer to micropores that are still filled with the amorphous material part of the substrate sheet after laser irradiation modification, while the original crystalline state of the substrate sheet is maintained around the micropores. In the subsequent etching process, the amorphous material part in the micropores will be etched away first to form through micropores, and then the etching liquid will be introduced from the micropores to contact the modified area inside the substrate sheet.

[0082] In one embodiment, the direct laser ablation opening is performed by irradiating a microporous region of a solid substrate sheet with a laser so that open micropores are directly formed in the region.

[0083] Open micropores refer to micropores formed by directly removing the substrate sheet material by laser etching. In the subsequent etching process, etching liquid can be directly introduced to contact the modified area inside the substrate sheet.

[0084] In one embodiment, the opening is used to introduce an etching solution into the modified region to etch and remove the modified region.

[0085] In one embodiment, the etching solution is selected from a hydrogen fluoride solution having a hydrogen fluoride content of 2% to 49%;

[0086] The hydrogen fluoride-containing solution is selected from at least one of a hydrofluoric acid solution and a BOE solution.

[0087] In one embodiment, during the immersion etching process, the substrate sheet is taken out for observation at regular intervals until the modified layer is completely removed.

[0088] In one embodiment, the etching solution is preferably dilute hydrofluoric acid. In the process of wet etching lithium niobate or lithium tantalate using a hydrofluoric acid solution, dilute hydrofluoric acid is difficult to react with lithium niobate or lithium tantalate. However, due to laser modification, the crystal bond structure of lithium niobate or lithium tantalate is amorphized, and the bond length is compressed. Therefore, the bond dissociation energy is greatly reduced, resulting in the preferential etching of the amorphous phase due to the easy dissociation of its atoms. The concentration of the hydrofluoric acid solution can be adjusted according to the desired etching rate.

[0089] In one embodiment, the immersion etching process also includes using ultrasound to assist in accelerating the removal efficiency of the patterned mask. The conditions of the ultrasonic treatment are not strictly limited and can be adjusted by those skilled in the art as needed.

[0090] In one embodiment, after the modified area is completely etched away to form a cavity and a piezoelectric single crystal film, the surface of the substrate is polished and cleaned to obtain the cantilever beam structure containing the piezoelectric single crystal film. The present application preferably uses a chemical mechanical polishing (CMP) process to polish and clean the surface layer of the substrate.

[0091] In order to solve the intrinsic stress caused by the traditional piezoelectric single crystal film deposition method, which causes the internal lattice mismatch problem, as well as the stress matching and compensation problem between the cavity layer and the piezoelectric single crystal film layer. The present application also provides a MEMS device, including the cantilever beam structure containing the piezoelectric single crystal film, or the cantilever beam structure containing the piezoelectric single crystal film after the side of the substrate sheet relatively far from the cavity is thinned to expose the cavity.

[0092] In one embodiment, the MEMS device is selected from a piezoelectric ultrasonic transducer, a resonator, a pressure sensor, and an acoustic wave filter.

[0093] In one embodiment, the piezoelectric ultrasonic transducer includes at least two electrodes, a structural layer, and a substrate;

[0094] The electrode is arranged on the surface of the piezoelectric single crystal film away from the cavity;

[0095] The structural layer covers the surface of one side of the piezoelectric single crystal film of the cantilever beam structure containing the piezoelectric single crystal film;

[0096] The positions of the structural layer corresponding to the micropores are provided with through holes connecting the micropores with the outside;

[0097] The thickness of the structural layer is greater than the thickness of the electrode;

[0098] The substrate is formed by thinning a side of the substrate sheet relatively far from the cavity to expose the cavity and then leaving a portion surrounding the piezoelectric single crystal film;

[0099] Preferably, the piezoelectric ultrasonic transducer is prepared by a method comprising the following steps:

[0100] Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet;

[0101] Depositing an electrode on a surface of the modified solid substrate sheet corresponding to the piezoelectric single crystal film;

[0102] Depositing a structural layer on one side of the modified solid substrate sheet where the electrode is deposited;

[0103] Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region;

[0104] Placing the modified solid substrate sheet with deposited electrodes and structural layers and opened holes in an etching solution, and immersing until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film;

[0105] The piezoelectric ultrasonic transducer is obtained by thinning a side of the substrate sheet that is relatively far from the cavity until the cavity is exposed.

[0106] In one embodiment, the thickness of the electrode is 0.05 μm to 3 μm.

[0107] In one embodiment, the material of the electrode is selected from at least one of Mo (molybdenum), Pt (platinum), Cr (chromium), and Al (aluminum).

[0108] In one embodiment, the material of the electrode is preferably Mo (molybdenum).

[0109] In one embodiment, the deposited electrode is prepared on a lithium niobate or lithium tantalate substrate using a vacuum evaporation device or a sputtering device, and the electrode thickness is.

[0110] In one embodiment, the number of the electrodes is preferably 2.

[0111] In one embodiment, the thickness of the structural layer is 5 μm to 20 μm.

[0112] In one embodiment, the material of the structural layer is selected from silicon dioxide, polysilicon, and silicon nitride.

[0113] In one embodiment, the material of the structural layer is preferably silicon dioxide.

[0114] In one embodiment, the deposited structural layer is deposited on the surface of the substrate using a chemical vapor deposition device.

[0115] The specific processes and parameters for depositing electrodes and depositing structural layers are not strictly limited in the present application, and those skilled in the art may select and adjust them as needed to achieve deposition of electrodes and structural layers.

[0116] In the technical solution of the present application, the MEMS device based on the cantilever beam structure containing the piezoelectric single crystal film can prepare a variety of high-performance MEMS devices by utilizing the high voltage electric coefficient, high electromechanical coupling coefficient and low dielectric loss of the single crystal lithium niobate or lithium tantalate film in the prepared structure. The special processing technology of the present application is associated with the high voltage electric coefficient, high electromechanical coupling coefficient and low dielectric loss. The high voltage electric coefficient, high electromechanical coupling coefficient and low dielectric loss are the characteristics of lithium niobate or lithium tantalate itself. Although lithium niobate or lithium tantalate has excellent characteristics, it is difficult to etch a perfect cavity structure by itself. Therefore, the excellent characteristics are difficult to be reflected in the MEMS device. However, the present application can show the high voltage electric coefficient, high electromechanical coupling coefficient and low dielectric loss of lithium niobate or lithium tantalate in the device through the aforementioned special processing technology.

[0117] Example 1

[0118] Schematic diagram of the laser modification assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film by laser modification etching and opening a hole. Figure 2 As shown, the specific steps are:

[0119] Step 1: Cleaning;

[0120] Take a single crystal lithium niobate wafer, immerse it in acetone, ethanol and deionized water for ultrasonic cleaning twice, then blow dry the lithium niobate wafer with nitrogen, and bake it in a drying oven (90°C) to form a solid substrate.

[0121] Step 2: Laser modification;

[0122] The cleaned solid substrate sheet is placed on a moving stage, and the laser is moved to the target irradiation area of ​​the solid substrate sheet. The laser is used to irradiate the internal irradiation area of ​​the solid substrate sheet to form a modified area, wherein the laser parameters used for laser irradiation are: laser pulse width is 200ps, laser wavelength is 800nm, and laser frequency is 5kHz. The irradiation area directly includes the micropore area (about 5μm in diameter) and the internal cavity area. The crystal properties of lithium niobate in the irradiation area change from crystal to amorphous to form a modified area, and a modified solid substrate sheet is obtained. At this time, the micropore area is still filled with the amorphous material part of the substrate sheet after laser irradiation modification, while the original crystal state of the substrate sheet is maintained around the micropore. In the subsequent etching process, the amorphous material part in the micropore will be etched away first to form a through micropore.

[0123] Step 3: wet etching;

[0124] The modified solid substrate sheet was placed in an etching solution (a 5% by mass hydrofluoric acid solution) and immersed at 30°C. The sample was taken out and observed every 5 minutes. The results showed that the laser-irradiated lithium niobate modified area was obviously etched, while the unmodified area was etched at a very slow rate or even basically not etched, until the modified area was completely etched away to form a cavity and a piezoelectric single crystal film, thereby obtaining a cantilever beam structure containing a piezoelectric single crystal film.

[0125] Step 4: Surface treatment;

[0126] The surface of the substrate sheet with the cantilever beam structure containing the piezoelectric single crystal film is subjected to chemical mechanical polishing and cleaning to obtain a cantilever beam structure device containing the piezoelectric single crystal film. The structural schematic diagram is shown in FIG. Figure 1 As shown in c, it includes a substrate sheet, the material of which is single-crystal lithium niobate or single-crystal lithium tantalate; a cavity is arranged in the interior of the substrate sheet, in an area close to the surface of one side of the substrate sheet; a portion of the surface of one side of the substrate sheet relatively close to the cavity that covers the cavity is a piezoelectric single crystal film; at least one micropore is arranged on the edge of the piezoelectric single crystal film at a position relative to the edge of the cavity, and the cavity is connected to the outside of the substrate sheet through the micropore.

[0127] Example 2

[0128] Schematic diagram of the laser modification-assisted preparation method of a cantilever beam structure containing a piezoelectric single crystal film by direct laser ablation hole opening Figure 3 As shown, the specific steps are:

[0129] Step 1: Cleaning;

[0130] Take a single crystal lithium tantalate wafer and immerse it in acetone, ethanol and deionized water for ultrasonic cleaning twice each. Then use nitrogen to blow dry the lithium niobate wafer, and then bake it in a drying oven (90°C) to form a solid substrate.

[0131] Step 2: Laser modification;

[0132] The cleaned solid substrate sheet is placed on a moving stage, and the laser is moved to the target irradiation area of ​​the solid substrate sheet. The internal irradiation area of ​​the solid substrate sheet is irradiated with a laser to form a modified area, wherein the laser parameters used for laser irradiation are: laser pulse width of 200fs, laser wavelength of 1100nm, and laser frequency of 8kHz. The irradiation area is the internal cavity area, and the properties of the lithium tantalate crystal in the irradiation area are transformed from crystal to amorphous to form a modified area, thereby obtaining a modified solid substrate sheet.

[0133] Step 3: Drill holes;

[0134] A laser drilling process is adopted, and the output pulse laser beam power is selected to be 50W and the frequency is 500kHz. A hole is made on the surface of the modified solid substrate sheet close to the modified area at a position corresponding to the edge of the modified area until the area where the micropores are formed is connected to the modified area, with a diameter of about 5μm.

[0135] Step 4: wet etching;

[0136] The modified solid substrate sheet with holes opened was placed in an etching solution (a hydrofluoric acid solution with a mass fraction of 5%) and immersed at 30°C. The sample was taken out and observed every 5 minutes. The results showed that the laser-irradiated lithium tantalate modified area was obviously etched, while the etching rate of the unmodified area was extremely slow or even basically not etched, until the modified area was completely etched away to form a cavity and a piezoelectric single crystal film, thereby obtaining a cantilever beam structure containing a piezoelectric single crystal film.

[0137] Step 5: Surface treatment;

[0138] The surface of the substrate sheet with the cantilever beam structure containing the piezoelectric single crystal film is subjected to chemical mechanical polishing and cleaning to obtain a cantilever beam structure device containing the piezoelectric single crystal film. The structural schematic diagram is shown in FIG. Figure 1 c, which is the same structure as that prepared in Example 1.

[0139] Example 3

[0140] The manufacturing process flow chart of piezoelectric ultrasonic transducer is as follows Figure 4 As shown, the specific steps are:

[0141] The preparation process of lithium niobate or lithium tantalate piezoelectric ultrasonic transducer is as follows:

[0142] Step 1: Substrate preparation;

[0143] A single crystal solid substrate sheet (single crystal lithium niobate wafer or single crystal lithium tantalate wafer) is cleaned and laser modified to obtain a modified solid substrate sheet, wherein the cleaning method and laser modification method are consistent with Example 1 or Example 2.

[0144] Step 2: Electrode preparation;

[0145] The two electrodes are prepared on the modified solid substrate using vacuum evaporation equipment or sputtering equipment. The thickness is 0.05 μm and the preparation material is Mo (molybdenum). The specific operation method is as follows:

[0146] Vacuum evaporation: Place the molybdenum electrode sample to be plated in a vacuum evaporation machine and use a vacuum pump to evacuate the film to a vacuum degree of 1.3x10 -2 ~1.3x10 -3Pa, the crucible is heated to melt the high-purity molybdenum wire at 1800℃~2000℃ and evaporate into gaseous molybdenum. The gaseous molybdenum particles are deposited on the surface of the moving film substrate, and after cooling and reduction, a continuous and bright metallic molybdenum layer is formed.

[0147] Magnetron sputtering: Install the molybdenum target and place the molybdenum electrode sample on the sample stage of the magnetron sputtering coating machine. The target-substrate distance is 80 mm. Vacuum the sample by introducing Ar gas to make the vacuum degree reach 3.0×10 -6 mbar, power 500 W, substrate temperature at room temperature, and sputtering time 60 s.

[0148] Step 3: Structural layer growth;

[0149] A chemical vapor deposition device deposits silicon dioxide with a thickness of 10 μm as a structural layer on the front side of the modified solid substrate sheet.

[0150] Step 4: Laser-assisted wet etching of the cavity;

[0151] The laser drilling process is adopted, the output pulse laser beam power is selected to be 40-60W, the frequency is 450-550kHz, and holes are made in the surface layer of the modified solid substrate sheet near the modified area and the position corresponding to the edge of the modified area of ​​the structural layer until the area where the micropores are formed is connected with the modified area, and the diameter is about 5μm. The modified solid substrate sheet after the holes are opened is placed in an etching solution (a hydrofluoric acid solution with a mass fraction of 2%), immersed at 30°C, and the sample is taken out and observed every 5 minutes. The results show that the laser irradiated lithium tantalate modified area is obviously etched, while the etching rate of the unmodified area is extremely slow or even basically not etched, until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film, and a cantilever beam structure containing a piezoelectric single crystal film is obtained.

[0152] Step 5: Back thinning;

[0153] The piezoelectric ultrasonic transducer is obtained by thinning the side of the cantilever beam structure substrate sheet containing the single crystal film that is relatively far away from the cavity until the cavity structure is completely exposed.

[0154] The structure of the obtained piezoelectric ultrasonic transducer is as follows: Figure 5 As shown, it includes two electrodes, a structural layer, and a substrate; the electrode is arranged on the surface of the piezoelectric single crystal film away from the cavity; the structural layer covers the surface of the piezoelectric single crystal film on the cantilever beam structure containing the piezoelectric single crystal film; the position of the structural layer corresponding to the micropore is provided with a through hole connecting the micropore with the outside; the thickness of the structural layer is greater than the thickness of the electrode; the position of the structural layer corresponding to the electrode is provided with an opening for accommodating the electrode; the substrate is formed by the side of the substrate sheet relatively away from the cavity after being thinned to expose the cavity and the remaining part surrounding the piezoelectric single crystal film.

[0155] It can be seen from the above embodiments that the method provided in the present application can realize the efficient preparation of lithium niobate or lithium tantalate cantilever beam structure, and solves the processing problems of cumbersome preparation steps and low efficiency of traditional methods. The cantilever beam structure with a single-crystal lithium niobate or lithium tantalate thin film is prepared by this method. Through the thin film deposition process, the preparation of piezoelectric lithium niobate or lithium tantalate piezoelectric ultrasonic transducers can be realized, which solves the problems that traditional piezoelectric acoustic transducers are limited by the performance of polycrystalline piezoelectric materials, have low sensitivity and emission sound pressure level, and poor high-frequency response, and single-crystal piezoelectric materials have excellent performance, but the processing technology is cumbersome and the cost is high.

[0156] 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 cantilever beam structure containing a piezoelectric single crystal film, characterized in that: It includes a substrate sheet, wherein the substrate sheet is made of single crystal lithium niobate or single crystal lithium tantalate; A cavity is provided inside the substrate sheet, in an area close to a surface layer of one side of the substrate sheet; The portion covering the cavity on the surface of one side of the substrate sheet relatively close to the cavity is a piezoelectric single crystal film; At least one microhole is arranged on the edge of the piezoelectric single crystal film at a position opposite to the edge of the cavity, and the cavity is connected with the outside of the substrate sheet through the microhole.

2. The cantilever beam structure containing a piezoelectric single crystal film according to claim 1, characterized in that: The pore diameter of the micropores is 5 μm to 20 μm.

3. The cantilever beam structure containing a piezoelectric single crystal film according to claim 1, characterized in that: The thickness of the piezoelectric single crystal film is 0.3 μm to 10 μm.

4. The laser modification-assisted preparation method of the cantilever beam structure containing a piezoelectric single crystal film according to any one of claims 1 to 3, characterized in that: include: Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet; Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region; The modified solid substrate sheet with deposited electrodes and structural layers and opened holes is placed in an etching solution and immersed until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film, thereby obtaining the cantilever beam structure containing the piezoelectric single crystal film.

5. The laser modification assisted preparation method according to claim 4, characterized in that: The opening is selected from laser modified etching opening or direct laser ablation opening; Preferably, the laser modification and etching of the openings is: using laser to irradiate the microporous region of the solid substrate sheet to modify the material of the region to form the same material as the modified region, thereby forming closed micropores; Preferably, the direct laser ablation opening of holes is performed by irradiating a microporous region of a solid substrate sheet with laser light so that open micropores are directly formed in the region.

6. The laser modification assisted preparation method according to claim 4, characterized in that: The conditions of the laser irradiation include: a laser pulse width of 150 fs to 500 ps, ​​a laser wavelength of 780 nm to 1100 nm, and a laser frequency of 1 kHz to 1 MHz.

7. The laser modification assisted preparation method according to claim 4, characterized in that: The etching solution is selected from a hydrogen fluoride solution having a hydrogen fluoride content of 2% to 49%; Preferably, the solution containing hydrogen fluoride is selected from hydrofluoric acid or BOE solution.

8. A MEMS device, characterized in that: A cantilever beam structure comprising a piezoelectric single crystal film as claimed in any one of claims 1 to 3, or a cantilever beam structure comprising a piezoelectric single crystal film after a side of a substrate sheet relatively away from the cavity is thinned to expose the cavity.

9. The MEMS device according to claim 8, characterized in that: The MEMS device is selected from one of a piezoelectric ultrasonic transducer, a resonator, a pressure sensor, and an acoustic wave filter.

10. The MEMS device according to claim 8, characterized in that: The piezoelectric ultrasonic transducer includes at least two electrodes, a structural layer, and a substrate; The electrode is arranged on the surface of the piezoelectric single crystal film away from the cavity; The structural layer covers the surface of one side of the piezoelectric single crystal film of the cantilever beam structure containing the piezoelectric single crystal film; The positions of the structural layer corresponding to the micropores are provided with through holes connecting the micropores with the outside; The thickness of the structural layer is greater than the thickness of the electrode; The substrate is formed by thinning a side of the substrate sheet relatively far from the cavity to expose the cavity and then leaving a portion surrounding the piezoelectric single crystal film; Preferably, the piezoelectric ultrasonic transducer is prepared by a method comprising the following steps: Placing the cleaned solid substrate sheet on a moving stage, and using a laser to irradiate the interior of the solid substrate sheet to form a modified region, thereby obtaining a modified solid substrate sheet; Depositing an electrode on a surface of the modified solid substrate sheet corresponding to the piezoelectric single crystal film; Depositing a structural layer on one side of the modified solid substrate sheet where the electrode is deposited; Opening holes at positions corresponding to the edge of the modified region on the surface of the modified solid substrate sheet close to the modified region until the area where micropores are formed is connected to the modified region; Placing the modified solid substrate sheet with deposited electrodes and structural layers and having holes therein into an etching solution, and immersing the substrate until the modified area is completely etched away to form a cavity and a piezoelectric single crystal film; The piezoelectric ultrasonic transducer is obtained by thinning a side of the substrate sheet that is relatively far from the cavity until the cavity is exposed.

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