Preparation method of scandium-doped aluminum nitride lamb wave resonator

Abstract

The embodiment of the invention provides a preparation method of a scandium-doped aluminum nitride Lamb wave resonator, and belongs to the field of radio frequency MEMS devices. The preparation method comprises the following steps: sequentially preparing an electrode layer of a lower interdigital electrode, a middle piezoelectric layer and an electrode layer of an upper interdigital electrode on a first wafer; preparing a protective layer and forming a cavity; inversely placing the first wafer on the second wafer; removing the first wafer and performing patterning processing to form a lower interdigital electrode; etching the electrode layer and the middle piezoelectric layer to lead out an upper interdigital electrode; and preparing a bonding pad and etching the electrode layer of the upper interdigital electrode, the middle piezoelectric layer and the electrode layer of the lower interdigital electrode to form an air reflection boundary. The manufactured device structure is inverted through a wafer level transfer technology, the process sequence of interdigital electrode patterning and piezoelectric film deposition is changed, the problem of structural distortion or breakage caused by piezoelectric film deposition due to patterning of the interdigital electrode is solved, and preparation of the high-quality scandium-doped aluminum nitride lamb wave resonator is achieved.

Description

Technical Field

[0001] The invention belongs to the field of radio frequency MEMS devices, and in particular relates to a method for preparing a scandium-doped aluminum nitride Lamb wave resonator. Background Art

[0002] In recent years, the rapid development of 5G communications, the Internet of Things, and virtual reality has greatly improved the convenience of modern life, but it has also put forward more stringent requirements for high-performance filter technology and sensor technology. Resonators are the basic components of filters and sensors. Their resonant frequency (f), effective electromechanical coefficient (k t 2 ) and quality factor (Q value) directly affect the key performance indicators of filters and sensors. Lamb wave resonators based on aluminum nitride / aluminum nitride-doped piezoelectric films have the advantages of high temperature resistance, small size and on-chip multi-band integration. Their high-order resonant modes have been proven to achieve operating frequencies exceeding 20 GHz, and have great potential in the application of next-generation wireless communications and sensing technologies.

[0003] In previous studies, the interdigital electrodes are usually designed as the upper interdigital electrodes of the Lamb wave resonator, while the lower interdigital electrodes of the Lamb wave resonator are mostly suspended flat electrodes or grounded flat electrodes. The reason is that the flat electrode helps to deposit aluminum nitride / doped aluminum nitride films with higher preferential orientation by low-temperature sputtering. However, in the application of filters, setting both the upper and lower interdigital electrodes of the resonator as interdigital electrodes is conducive to achieving a more uniform vertical electric field distribution, thereby improving the effective electromechanical coupling coefficient (k) of the resonator. t 2 ) to achieve greater bandwidth to meet market demand.

[0004] In the actual manufacturing process of Lamb wave resonators, it is necessary to pattern the lower interdigital electrodes first and then deposit the piezoelectric layer. Therefore, the interdigital electrodes at the bottom of the resonator will affect the deposition quality of the aluminum nitride / aluminum nitride-doped piezoelectric film above, thereby affecting the performance and yield of the resonator. By preparing a bottom electrode with a smooth transition morphology, the crystal orientation of the aluminum nitride / aluminum nitride-doped film can be improved. However, for Lamb wave resonators with smaller electrode line widths, the edge tilt angle causes the interdigital electrodes to be triangular, which in turn excites resonant modes that are different from the longitudinal wavelength of the target mode, resulting in an increase in parasitic modes and reduced performance.

[0005] In view of this, there is an urgent need to optimize the process technology of Lamb wave resonators to solve the problem of poor deposition quality of AlN / AlN-doped piezoelectric films caused by the bottom patterned interdigital electrodes. Summary of the invention

[0006] The purpose of the present invention is to propose a method for preparing a scandium-doped aluminum nitride Lamb wave resonator, and to optimize the performance and manufacturing yield of the resonator by optimizing the process. The scandium-doped aluminum nitride Lamb wave resonator is a high-performance scandium-doped aluminum nitride Lamb wave resonator based on wafer-level transfer technology.

[0007] The present invention provides the following technical solutions:

[0008] In a first aspect, a method for preparing a scandium-doped aluminum nitride Lamb wave resonator is provided, the method comprising the following steps:

[0009] Sequentially preparing an electrode layer of a lower interdigital electrode, an intermediate piezoelectric layer, and an electrode layer of an upper interdigital electrode on a first wafer;

[0010] preparing a protective layer above the electrode layer of the upper interdigitated electrode and forming a cavity in the protective layer;

[0011] placing the first wafer with the protective layer upside down on the second wafer;

[0012] removing the first wafer until the electrode layer of the lower interdigital electrode is reached and patterning the electrode layer of the lower interdigital electrode to form the lower interdigital electrode;

[0013] etching the electrode layer and the middle piezoelectric layer of the upper interdigital electrode to lead out the upper interdigital electrode;

[0014] The pad is prepared and the electrode layer of the upper interdigital electrode, the middle piezoelectric layer and the electrode layer of the lower interdigital electrode are etched to form an air reflection boundary.

[0015] In some embodiments of the present invention, before depositing the electrode layer of the lower interdigital electrodes, a stop layer is prepared on the first wafer, and then a seed layer is deposited.

[0016] In some embodiments of the present invention, the protective layer is a three-layer structure of silicon dioxide / silicon nitride / silicon dioxide.

[0017] In some embodiments of the present invention, the preparation in step S1 is to generate a silicon oxide film on the surface of the first wafer using a wet oxidation process to form the stop layer.

[0018] In some embodiments of the present invention, a cavity is formed in the protective layer by a combination of dry and wet processes, the upper silicon dioxide and silicon nitride are removed by dry etching, and the lower silicon dioxide is removed by wet etching.

[0019] In some embodiments of the present invention, the step of placing the first wafer with the protective layer upside down on the second wafer comprises:

[0020] The surface of silicon dioxide is planarized by chemical mechanical polishing;

[0021] Aligning the first wafer and the second wafer according to the alignment mark, and pre-bonding the two by van der Waals force by vacuum adsorption;

[0022] The pre-bonded first wafer and second wafer are placed in an annealing furnace and subjected to high temperature annealing to enhance the bonding strength.

[0023] In some embodiments of the present invention, removing the first wafer until reaching the electrode layer of the lower interdigitated electrode includes removing the first wafer, a stop layer, and a seed layer.

[0024] In some embodiments of the present invention, the first wafer is removed by a thinning process;

[0025] removing the stop layer by wet etching;

[0026] The seed layer is removed by wet etching.

[0027] In some embodiments of the present invention, the stop layer is removed by wet etching with a mixed buffered oxide etchant BOE solution;

[0028] The seed layer is removed by wet etching with a KOH solution.

[0029] In some embodiments of the present invention, the substrate material of the first wafer is high-resistance silicon;

[0030] The material of the stop layer is silicon dioxide;

[0031] The material of the seed layer is aluminum nitride;

[0032] The material of the upper interdigitated electrode is molybdenum;

[0033] The material of the intermediate piezoelectric layer is scandium-doped aluminum nitride;

[0034] The material of the lower interdigital electrode is molybdenum.

[0035] A method for preparing a scandium-doped aluminum nitride Lamb wave resonator provided according to an embodiment of the present invention has at least one of the following advantages:

[0036] Through the wafer-level transfer technology of bonding silicon (Si) and silicon dioxide (SiO2), the order of bottom finger electrode patterning and AlScN film deposition was optimized, thereby solving the problem of structural distortion or fracture of the deposited piezoelectric film caused by the patterned IDT electrode, thereby improving the performance and yield of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, in which:

[0038] Figure 1 It is a schematic structural diagram after processing in step 1 of a method for preparing a scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0039] Figure 2 It is a schematic diagram of the structure after processing in step 2 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0040] Figure 3 It is a schematic diagram of the structure after processing in step 3 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0041] Figure 4 It is a schematic diagram of the structure after processing in step 4 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0042] Figure 5 It is a schematic diagram of the structure after processing in step 5 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0043] Figure 6 It is a schematic diagram of the structure after processing in step 6 of the method for preparing a scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0044] Figure 7 It is a schematic diagram of the structure after processing in step 7 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0045] Figure 8 It is a schematic diagram of the structure after processing in step 8 of the method for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0046] Fig. 9 A schematic diagram of the structure after processing in step 1 of a conventional manufacturing process preparation method of a scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0047] Fig.10 A schematic diagram of the structure after processing in step 2 of the conventional manufacturing process preparation method of scandium-doped aluminum nitride Lamb wave resonator is provided for embodiment 2 of the present invention;

[0048] Fig.11 A schematic diagram of the structure after processing in step 3 of the conventional manufacturing process preparation method of the scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0049] Fig.12 A schematic diagram of the structure after processing in step 4 of the conventional manufacturing process preparation method of the scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0050] Fig.13A schematic diagram of the structure after processing in step 5 of the conventional manufacturing process preparation method of the scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0051] Fig.14 A schematic diagram of the structure after processing in step 6 of the conventional manufacturing process preparation method of the scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0052] Fig.15 A schematic diagram of the structure after processing in step 7 of the conventional manufacturing process for preparing the scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0053] Fig.16 This is a simulation diagram of a scandium-doped aluminum nitride Lamb wave resonator with an electrode period of 2μm; Fig.16 (a) is an admittance diagram of a scandium-doped aluminum nitride Lamb wave resonator with a period of 12 μm manufactured by two different processes provided in Examples 1 and 2 of the present invention; Fig.16 (b) is the Q value, f and k t 2 The graph changes with the number of abnormally oriented grains (N);

[0054] Fig.17 This is a simulation diagram of a scandium-doped aluminum nitride Lamb wave resonator with an electrode period of 12μm; Fig.17 (a) is an admittance diagram of a scandium-doped aluminum nitride Lamb wave resonator with a period of 2 μm manufactured by two different processes provided in Examples 1 and 2 of the present invention; Fig.17 (b) is the Q value, f and k t 2 The graph changes with the number of abnormally oriented grains (N);

[0055] Fig.18 An XRD scanning swing curve diagram of a scandium-doped aluminum nitride film in a method for preparing a scandium-doped aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0056] Fig.19 An XRD scanning swing curve diagram of a scandium-doped aluminum nitride film prepared by a conventional manufacturing process for a scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention;

[0057] In the figure: 100- scandium-doped aluminum nitride Lamb wave resonator prepared by the present invention, 10-first wafer, 20-stop layer, 30-seed layer, 40-lower interdigital electrode, 50-middle piezoelectric layer, 60-upper interdigital electrode, 70-protective layer, 80-pad, 90-second wafer;

[0058] 200 - scandium-doped aluminum nitride Lamb wave resonator prepared by conventional process, 210 - substrate, 220 - stop layer, 230 - sacrificial layer, 240 - lower interdigital electrode, 250 - middle piezoelectric layer, 260 - upper interdigital electrode, 270 - cavity. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0060] In order to make the purpose, design scheme and innovation of this application clearer, the technical scheme of this application is fully described below.

[0061] It should be noted that the terms used in this application are generally terms commonly used by those skilled in the art. If there is any inconsistency with the commonly used terms, the terms in this application shall prevail.

[0062] The term "dry etching" is a process of removing unwanted materials from the surface of solid materials on the wafer surface by using plasma or reactive gas (without the participation of liquid); the term "wet etching" is a process of removing unwanted materials by immersing the etched material in a corrosive solution; the term "chemical mechanical polishing (CMP)" refers to the flattening of the wafer being processed, combining chemical action and mechanical grinding technology to achieve micron or nanometer-level material removal on the surface of the polished workpiece, making its surface highly flat; the term "annealing" is a process of heating a metal to a certain temperature, maintaining it for a sufficient time, and then cooling it at an appropriate rate; the term "bonding" is a process in which two or more adjacent atoms interact strongly, and the atoms are linked together in a "bond" manner to form a molecule; the term "patterning" refers to the generation of a nanometer-level regular surface structure in at least one dimensional direction, and patterning can be achieved using a variety of technologies, such as photolithography, scanning probe-based micromaching, microcontact printing, etc.; the term "interdigitated (IDT) electrode" refers to an electrode with a periodic pattern in the surface such as a finger or comb;

[0063] As used herein, the terms "comprises," "comprising," or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances.

[0064] The following is a detailed description of the implementation of the present application.

[0065] Example 1

[0066] In embodiment 1 of the present invention, a method for preparing a scandium-doped aluminum nitride Lamb wave resonator 100 is provided. The method for preparing the scandium-doped aluminum nitride Lamb wave resonator 100 is based on a wafer-level transfer technology. The method for preparing the scandium-doped aluminum nitride Lamb wave resonator 100 comprises:

[0067] S1 step, see Figure 1 , prepare a first wafer 10, which is generally a high-resistance Si substrate, and first deposit a stop layer 20 on the surface of the high-resistance Si substrate. The material of the stop layer 20 is SiO2, so as to avoid excessive etching in the subsequent step of removing the first wafer 10, such as step S6, which may cause damage to the lower interdigital electrode and affect the resonator performance. Then deposit a seed layer 30 with a thickness of 18nm, and the material of the seed layer 30 is, for example, AlN.

[0068] S2 step, see Figure 2 Then, a 210 nm thick Mo film is deposited on the seed layer 30 as the electrode layer of the lower interdigital electrode 40. After the Mo film is deposited, an AlScN film with a thickness of 770 nm is deposited on it without patterning as the intermediate piezoelectric layer 50. A 300 nm thick Mo film is deposited on the AlScN film, and then patterned to form interdigital electrodes as the upper interdigital electrodes 60.

[0069] Step S3, see Figure 3 , a three-layer structure of SiO2 / SiN / SiO2 with thicknesses of, for example, 300 / 120 / 1800 nm is prepared as the protective layer 70.

[0070] Step S4, see Figure 4 , etching the protective layer 70 in the effective area to form a cavity;

[0071] Step S5, see Figure 5 , transferring the device prepared in step S4 to a second wafer 90;

[0072] Step S6, see Figure 6 , removing the first wafer 10, the stop layer 20 and the seed layer 30, and patterning the electrode layer of the lower interdigital electrode 40 to form a lower interdigital electrode;

[0073] Step S7, see Figure 7 , etching the lower interdigital electrode 40 and the middle piezoelectric layer 50, and leading out the upper interdigital electrode 60;

[0074] Step S8, see Figure 8 , prepare a pad of, for example, copper and etch the upper interdigital electrode 60, the middle piezoelectric layer 50 and the lower interdigital electrode 40 to form an air reflection boundary.

[0075] In some embodiments, the first wafer 10 is a high-resistance Si substrate;

[0076] In some embodiments, the material of the stop layer 20 is SiO2. The function of the stop layer SiO2 is to prevent the lower interdigital electrodes from being damaged due to over-etching during the step of removing the substrate in step S6, thereby affecting the resonator performance.

[0077] The material of the seed layer 30 is AlN, in order to better grow the electrode layer of the lower interdigital electrode 40 in step S2.

[0078] In some embodiments, the preparation in step S1 is performed by a wet oxidation process. In some embodiments, the material of the upper interdigital electrode 60 and the lower interdigital electrode 40 is metal Mo.

[0079] In some implementations, the material of the intermediate piezoelectric layer 50 is AlScN.

[0080] In some embodiments, the three-layer structure of the protective layer SiO2 / SiN / SiO2 in step S3 helps to improve the mechanical stability of the support structure and can avoid excessive etching and damage to the upper interdigital electrode 60 in step S4.

[0081] In some embodiments, the etching in step S4 is a combination of dry and wet processes, the upper SiO2 and SiN are removed by dry etching, and the lower SiO2 is removed by wet etching to avoid excessive etching affecting the upper interdigital electrodes.

[0082] In some embodiments, the step of transferring the device to the second wafer in step S5 includes:

[0083] S51 uses chemical mechanical polishing (CMP) technology to flatten the SiO2 surface;

[0084] S52 aligns the first wafer 10 and the second wafer 90 according to the alignment mark, and uses vacuum adsorption to pre-bond the two by van der Waals force;

[0085] S53: placing the pre-bonded first wafer 10 and second wafer 90 into an annealing furnace for high temperature annealing to further enhance the bonding strength;

[0086] In some embodiments, the step of removing the first wafer 10, the stop layer 20 and the seed layer 30 in step S6 includes:

[0087] S61 removes the first wafer 10 through a thinning process;

[0088] S62: removing the stop layer 20 by wet etching with a mixed buffered oxide etchant (BOE) solution (HF and NH4F);

[0089] S63: The seed layer 30 is removed by wet etching using a KOH solution.

[0090] Example 2

[0091] Embodiment 2 of the present invention provides a method for preparing a scandium-doped aluminum nitride Lamb wave resonator 200 using a conventional manufacturing process. As shown in the figure, the preparation method comprises:

[0092] Step S1, see Fig. 9 , etching the substrate 210 to form a release cavity, and then preparing a layer of SiO2 film as a stop layer 220 to effectively prevent etching of the non-active area substrate during the release process;

[0093] Step S2, see Fig.10 , filling a Si layer as a sacrificial layer 230 on the SiO2 film, removing the Si material outside the release cavity, and facilitating the rapid completion of subsequent chemical mechanical polishing (CMP);

[0094] Step S3, see Fig.11 , depositing a layer of Mo and performing patterning to form a lower interdigital electrode 240;

[0095] Step S4, see Fig.12 , depositing an Al ScN piezoelectric film to form an intermediate piezoelectric layer 250;

[0096] Step S5, see Fig.13 , depositing a layer of Mo and performing patterning to form an upper interdigital electrode 260;

[0097] Step S6, see Fig.14 , etching the Mo / Al ScN / Mo three-layer film to form a release hole, and placing it in xenon difluoride (XeF2) gas to release the sacrificial layer to form a cavity 270;

[0098] Step S7, see Fig.15 , the lower interdigital electrode 240 and the middle piezoelectric layer 250 located above the pad area are etched, the upper interdigital electrode 260 is led out and a Cu pad is prepared.

[0099] The resonator prepared by the conventional process, because the patterned interdigital electrodes may cause cracks or other abnormally oriented grains in the AlScN piezoelectric film deposited thereon, the resonator prepared by the preparation method based on wafer-level transfer technology provided in Example 1 and the conventional manufacturing process provided in Example 2 was simulated and analyzed by COMSOL Multiphysics software to obtain the following results: Fig.16 (a)- Fig.17 (b).

[0100] In order to ensure the universality of the experimental results, Lamb wave resonators in two frequency bands, high frequency (period of 2 μm) and low frequency (period of 12 μm), were prepared. Fig.16 The effect of cracks or other abnormally oriented grains (N) on the Q value, f and k of the Lamb wave resonator (resonator period is 12μm) t 2 impact. Fig.16 Derived Q value, f and k for N pairs of Lamb wave resonators (resonator period is 2μm) t 2 The impact of Fig.16 (a) and Fig.17 (a) shows that when N = 0 (resonator prepared by wafer-level transfer technology), the frequency is the highest, the resonance peak is the sharpest, and the resonator performance is the best. When N = 40, 80, 120, 160, 200 (resonator prepared by traditional technology), the frequency slowly shifts as N increases. Fig.16 (b) and Fig.17 (b) As N increases, the effective electromechanical coupling coefficient (k t 2 ) and quality factor (Q) gradually decrease, and the resonator performance is deteriorated.

[0101] Fig.18 X-ray diffraction swing test (XRD) curve of a scandium-doped aluminum nitride film according to a method for preparing a high-performance scandium-doped aluminum nitride Lamb wave resonator based on wafer-level transfer technology provided in Example 1 of the present invention and Fig.19(X-ray diffraction swing test (XRD) curve of a scandium-doped aluminum nitride film prepared by a traditional manufacturing process for a scandium-doped aluminum nitride Lamb wave resonator provided in Example 2 of the present invention), it can be seen from the figure that the full width at half maximum (FWHM) of the scandium-doped aluminum nitride film prepared by the preparation method based on wafer-level transfer technology is 1.18, which is lower than the FWHM of 1.61 of the scandium-doped aluminum nitride film prepared by the traditional manufacturing process.

[0102] Therefore, the film deposition quality of the scandium-doped aluminum nitride Lamb wave resonator prepared based on the wafer transfer technology is better than that of the resonator prepared by the traditional manufacturing process. The problem of poor deposition quality of the scandium-doped aluminum nitride film caused by the bottom patterned interdigital electrodes is solved, and the performance of the resonator is improved.

[0103] A method for preparing a scandium-doped aluminum nitride Lamb wave resonator provided according to an embodiment of the present invention has at least one of the following advantages:

[0104] Through the wafer-level transfer technology of bonding silicon (Si) and silicon dioxide (SiO2), the order of bottom finger electrode patterning and AlScN film deposition was optimized, thereby solving the problem of structural distortion or fracture of the deposited piezoelectric film caused by the patterned IDT electrode, thereby improving the performance and yield of the resonator.

[0105] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a scandium-doped aluminum nitride Lamb wave resonator, characterized in that: The preparation method comprises the following steps: An electrode layer of a lower interdigital electrode (40), an intermediate piezoelectric layer (50) and an electrode layer of an upper interdigital electrode (60) are sequentially prepared on a first wafer (10); Preparing a protective layer (70) above the electrode layer of the upper interdigitated electrode and forming a cavity in the protective layer (70); Placing the first wafer (10) with the protective layer (70) upside down on the second wafer (90); removing the first wafer (10) until the electrode layer of the lower interdigital electrode (40) is reached and patterning the electrode layer of the lower interdigital electrode (40) to form the lower interdigital electrode (40); Etching the electrode layer of the upper interdigital electrode (60) and the intermediate piezoelectric layer (50) to lead out the upper interdigital electrode (60); A pad is prepared and the electrode layer of the upper interdigital electrode (60), the middle piezoelectric layer (50) and the electrode layer of the lower interdigital electrode (40) are etched to form an air reflection boundary.

2. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 1, characterized in that: Before depositing the electrode layer of the lower interdigital electrode (40), a stop layer (20) is prepared on the first wafer (10), and then a seed layer (30) is deposited.

3. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 1, characterized in that: The protective layer (70) is a three-layer structure of silicon dioxide / silicon nitride / silicon dioxide.

4. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 1, characterized in that: The preparation in step S1 is to generate a silicon oxide film on the surface of the first wafer using a wet oxidation process to form the stop layer (20).

5. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 3, characterized in that: A cavity is formed in the protective layer (70) by using a process combining dry and wet methods, the silicon dioxide and silicon nitride in the upper layer are removed by dry etching, and the silicon dioxide in the lower layer is removed by wet etching.

6. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 5, characterized in that: The step of placing the first wafer (10) with the protective layer (70) upside down on the second wafer (90) comprises: The surface of silicon dioxide is planarized by chemical mechanical polishing; The first wafer (10) and the second wafer (90) are aligned according to the alignment mark, and the two are pre-bonded by van der Waals force by using vacuum adsorption; The pre-bonded first wafer (10) and second wafer (90) are placed in an annealing furnace and subjected to high-temperature annealing to enhance the bonding strength.

7. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 2, characterized in that: The process of removing the first wafer (10) until reaching the electrode layer of the lower interdigitated electrode (40) comprises removing the first wafer (10), the stop layer (20) and the seed layer (30).

8. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 7, characterized in that: removing the first wafer (10) through a thinning process; removing the stop layer (20) by wet etching; The seed layer (30) is removed by wet etching.

9. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 8, characterized in that: removing the stop layer (20) by wet etching with a mixed buffered oxide etchant BOE solution; The seed layer (30) is removed by wet etching using a KOH solution.

10. The method for preparing a scandium-doped aluminum nitride Lamb wave resonator according to claim 1, characterized in that: The substrate material of the first wafer (10) is high-resistance silicon; The material of the stop layer (20) is silicon dioxide; The material of the seed layer (30) is aluminum nitride; The material of the upper interdigital electrode (40) is molybdenum; The material of the intermediate piezoelectric layer (50) is scandium-doped aluminum nitride; The material of the lower interdigital electrode (60) is molybdenum.

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