Cavity type bulk acoustic wave resonator and preparation method thereof

Abstract

The invention discloses a cavity type bulk acoustic wave resonator and a preparation method thereof, and relates to the field of semiconductor radio frequency devices. The preparation method comprises the following steps: (1) forming a piezoelectric layer on a temporary substrate; (2) forming and patterning a lower electrode layer; (3) a filling layer is formed and patterned, and the projection of the patterned lower electrode layer covers the patterned filling layer; (4) forming a wrapping layer to wrap the patterned lower electrode layer and the patterned filling layer; (5) bonding with a transfer substrate; (6) removing the temporary substrate; (7) forming an upper electrode layer on the piezoelectric layer, and patterning to enable the projection of the patterned filling layer to cover the patterned upper electrode layer; and (8) removing the filling layer to form a cavity. Wherein the filling layer is made of silicon dioxide, phosphorus-containing silicon dioxide or resin, and the wrapping layer is made of silicon or ceramic; according to the invention, various performances of the cavity type body wave resonator can be improved, and the process cost and the process difficulty of the cavity type body wave resonator are reduced.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor radio frequency devices, and in particular to a cavity type bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] With the rapid development of the fifth generation of mobile communication technology (5G), higher requirements are placed on the performance of RF front-end filters. Large bandwidth and high frequency are the two major characteristics of 5G filters. At present, the most widely used acoustic filters are surface acoustic wave filters (SAW) and bulk acoustic wave filters (BAW). Among them, the surface acoustic wave filter (SAW) is limited by the size of the interdigitated electrodes due to its frequency increase, and is relatively weak for frequency bands above 3GHz. Therefore, the 5G bulk acoustic wave filter is mainly based on the technical route of polycrystalline aluminum nitride piezoelectric thin film materials, and polycrystalline aluminum nitride needs to achieve a larger bandwidth (>200MHz) through scandium doping and other means, which is costly and difficult to implement.

[0003] In addition, the existing acoustic wave resonator is generally divided into three structures, back-etched type, solid-state assembly type and cavity type structure type, among which the back-etched type has poor mechanical firmness and is difficult to mass-produce. Although the solid-state assembly type has strong mechanical properties, its Bragg reflection layer has limited effect in limiting the sound wave, resulting in a low quality factor. The cavity type structure does not need to remove a large amount of substrate material, so it has strong mechanical stability and a high quality factor. At present, there are generally two preparation processes for the cavity type structure, so that a concave cavity is formed on the substrate, and then the lower electrode, piezoelectric film and upper electrode are prepared. This process has a poor supporting effect on the piezoelectric film, and the film is prone to cracks. The other is to first form a supporting layer with high hardness on the substrate, set a sacrificial layer at the bottom of the supporting layer, and then remove the sacrificial layer to form a cavity. Although this process has a strong supporting effect on the piezoelectric film, it also means that the piezoelectric layer must grow on the surface of the lower electrode and / or the supporting layer, which makes it difficult to grow in the form of epitaxy, and the crystal quality is poor, which affects the various performances of the bulk acoustic wave resonator. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a cavity-type bulk acoustic wave resonator and a preparation method thereof, which can reduce process cost and process difficulty and improve various performances thereof.

[0005] In order to solve the above problems, the present invention discloses a method for preparing a cavity type bulk acoustic wave resonator, which comprises the following steps:

[0006] (1) forming a piezoelectric layer on a temporary substrate;

[0007] (2) forming a lower electrode layer on the piezoelectric layer and patterning it;

[0008] (3) forming a filling layer on the temporary substrate obtained in step (2), and patterning the filling layer so that the projection of the patterned lower electrode layer covers the patterned filling layer; wherein the filling layer is made of silicon dioxide, phosphorus-containing silicon dioxide or resin;

[0009] (4) forming a wrapping layer on the temporary substrate obtained in step (3) to wrap the patterned lower electrode layer and the patterned filling layer and cover other areas of the temporary substrate; wherein the wrapping layer is made of silicon or ceramic;

[0010] (5) bonding the temporary substrate obtained in step (4) to the transfer substrate;

[0011] (6) removing the temporary substrate to expose the piezoelectric layer;

[0012] (7) forming an upper electrode layer on the piezoelectric layer and patterning the layer so that a projection of the patterned filling layer covers the patterned upper electrode layer;

[0013] (8) The filling layer is removed to form a cavity, thereby obtaining a cavity-type bulk acoustic wave resonator.

[0014] As an improvement of the above technical solution, the distance between the outer edge of the patterned filling layer and the outer edge of the projection of the patterned lower electrode layer is ≤3 μm; and / or

[0015] The distance between the outer edge of the patterned upper electrode layer and the outer edge of the projection of the patterned filling layer is ≤3 μm.

[0016] As an improvement of the above technical solution, the patterned filling layer, the patterned upper electrode layer, and the patterned lower electrode layer are all pentagonal;

[0017] The distance between the outer edge of the patterned filling layer and the outer edge of the projection of the patterned lower electrode layer is 2.2 μm to 2.8 μm;

[0018] The distance between the outer edge of the patterned upper electrode layer and the outer edge of the projection of the patterned filling layer is 2.2 μm to 2.8 μm.

[0019] As an improvement of the above technical solution, the temporary substrate is selected from one or more of a sapphire substrate, a silicon carbide substrate, a silicon nitride substrate or a silicon substrate; and / or

[0020] The transfer substrate is selected from one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate or a diamond substrate.

[0021] As an improvement of the above technical solution, the piezoelectric layer is made of single crystal aluminum nitride and / or single crystal ε-gallium oxide, and has a thickness of 200nm to 1000nm; and / or

[0022] The lower electrode layer is made of one or more of tungsten, molybdenum and aluminum, and has a thickness of 100 nm to 500 nm; and / or

[0023] The thickness of the filling layer is 100nm to 2000nm; and / or

[0024] The upper electrode layer is made of one or more of tungsten, molybdenum and aluminum, and has a thickness of 50nm to 500nm.

[0025] As an improvement of the above technical solution, the thickness of the wrapping layer is D, the total thickness of the filling layer and the lower electrode layer is d, and Dd≥300nm.

[0026] As an improvement of the above technical solution, in step (5), the encapsulation layer is polished and flattened, and then bonded to the transfer substrate;

[0027] Wherein, after grinding and flattening, the surface roughness of the wrapping layer is ≤0.3 nm, the uniformity is ≤1%, and the TTV is ≤20 μm.

[0028] As an improvement of the above technical solution, in step (6), the temporary substrate is firstly ground and thinned to 5 μm to 50 μm, and then the remaining temporary substrate is removed by dry etching to expose the piezoelectric layer.

[0029] As an improvement of the above technical solution, the piezoelectric layer is made of single crystal ε-gallium oxide.

[0030] Correspondingly, the present invention also discloses a cavity-type bulk acoustic wave resonator, which is prepared by the above-mentioned preparation method of the cavity-type bulk acoustic wave resonator.

[0031] The implementation of the present invention has the following beneficial effects:

[0032] In the preparation method of the cavity type bulk acoustic wave resonator in one embodiment of the present invention, the piezoelectric layer is first epitaxially grown on a temporary substrate, and then the lower electrode layer, the filling layer, and the wrapping layer are prepared, and then the substrate is bonded to transfer, the temporary substrate is removed, the piezoelectric layer is exposed, and then the upper electrode layer is formed. Based on this preparation method, not only the crystal quality of the piezoelectric layer is effectively improved by epitaxial growth, but also the upper electrode layer and the lower electrode layer are formed by bonding, which reduces the difficulty of production and provides a solution for the preparation of the cavity type bulk acoustic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic cross-sectional structural diagram of a temporary substrate after step S2 in one embodiment of the present invention;

[0034] Figure 2 is a schematic cross-sectional structural diagram of a temporary substrate after step S3 in one embodiment of the present invention;

[0035] Figure 3 is a schematic cross-sectional structural diagram of a temporary substrate after step S4 in one embodiment of the present invention;

[0036] Figure 4 is a schematic cross-sectional structural diagram of a temporary substrate after step S5 in one embodiment of the present invention;

[0037] Figure 5 is a schematic cross-sectional structural diagram of a transferred substrate after step S7 in one embodiment of the present invention;

[0038] Figure 6 is a schematic diagram of a top view of the transferred substrate after step S7 in one embodiment of the present invention;

[0039] Figure 7 Schematic diagram of the structure of the through hole in step S8 in one embodiment of the present invention;

[0040] Figure 8 is a schematic cross-sectional structural diagram of a cavity-type bulk acoustic wave resonator in one embodiment of the present invention;

[0041] In the figure, 1 is a temporary substrate, 2 is a piezoelectric layer, 3 is a lower electrode layer, 4 is a filling layer, 5 is a wrapping layer, 6 is a transfer substrate, 7 is an upper electrode, 8 is a cavity, and 9 is a through hole. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. In addition, it should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0043] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "left", "right", "horizontal", "top", "bottom", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0044] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0045] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0046] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, and does not indicate the relationship between the various embodiments and / or settings discussed in itself. In addition, the present application provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use scenarios of other materials.

[0047] See also Figure 1 to Figure 7 In one embodiment of the present invention, a method for preparing a cavity-type bulk acoustic wave resonator is provided, which comprises the following steps:

[0048] S1: forming a piezoelectric layer on a temporary substrate;

[0049] The temporary substrate 1 may be a sapphire substrate, a silicon substrate, a quartz substrate, a silicon carbide substrate, a silicon nitride substrate, or a gallium arsenide substrate, but is not limited thereto. Preferably, the temporary substrate 1 is a sapphire substrate, a silicon carbide substrate, a silicon nitride substrate, or a silicon substrate, more preferably a silicon substrate.

[0050] The piezoelectric layer 2 is made of one or more of polycrystalline aluminum nitride, single crystal aluminum nitride or single crystal ε-gallium oxide, but is not limited thereto. Preferably, the piezoelectric layer 2 is made of single crystal aluminum nitride and / or single crystal ε-gallium oxide. More preferably, the piezoelectric layer 2 is made of single crystal ε-gallium oxide, and is prepared by epitaxy, and its piezoelectric coefficient is twice that of single crystal aluminum nitride, which has advantages in large bandwidth and low loss.

[0051] The thickness of the piezoelectric layer 2 is 100 nm to 1000 nm, exemplarily 150 nm, 300 nm, 450 nm, 600 nm, 750 nm or 900 nm but not limited thereto, preferably 200 nm to 1000 nm.

[0052] Specifically, a polycrystalline material layer may be grown by PVD, or a single crystal material layer may be grown by MOCVD, MBE or PLD, as the piezoelectric layer 2, but is not limited thereto. Preferably, in this embodiment, a single crystal ε-gallium oxide layer is grown by MOCVD, which has high preparation efficiency and good piezoelectric performance.

[0053] S2: forming a lower electrode layer on the piezoelectric layer and patterning it;

[0054] The lower electrode layer 3 is made of one or more of tungsten, molybdenum, and aluminum, but not limited thereto. The thickness of the lower electrode layer 3 is 100 nm to 800 nm, and is exemplarily 150 nm, 200 nm, 300 nm, 450 nm, 600 nm, or 700 nm, but not limited thereto. Preferably, the lower electrode layer 3 is 100 nm to 500 nm, and more preferably 100 nm to 300 nm.

[0055] The lower electrode layer 3 may be grown by PVD, evaporation, or the like, but is not limited thereto. Preferably, in this embodiment, the lower electrode layer 3 is grown by PVD. After the lower electrode layer 3 is grown, it is patterned by a photolithography etching process, wherein the etching may be dry etching or wet etching. Preferably, the lower electrode layer 3 is etched by a dry etching process.

[0056] Specifically, the cross section of the patterned lower electrode layer 3 is circular, triangular, rectangular or pentagonal, but not limited thereto. Figure 1 and Figure 6 , the cross section of the patterned lower electrode layer 3 is a regular pentagon.

[0057] S3: forming a filling layer on the temporary substrate obtained in step S2, and patterning it so that the projection of the patterned lower electrode layer covers the patterned filling layer;

[0058] The filling layer 4 is made of silicon dioxide, phosphorus-containing silicon dioxide or resin, but is not limited thereto. The filling layer 4 of these materials is convenient for later removal. Preferably, the filling layer 4 is made of phosphorus-containing silicon dioxide, that is, phosphorus silicon glass.

[0059] The thickness of the filling layer 4 is 100nm to 2000nm to form a larger cavity 8 and improve the various performances of the cavity-type bulk acoustic wave resonator. Exemplarily, the thickness of the filling layer 4 is 400nm, 800nm, 1200nm, 1500nm or 1800nm, but is not limited thereto. Preferably, the thickness of the filling layer 4 is 500nm to 1000nm.

[0060] Specifically, the filling layer 4 can be formed by MOCVD, PECVD, spin coating, etc., but is not limited thereto. After the filling layer 4 is formed, it is patterned by a photolithography etching process, wherein the etching can be dry etching or wet etching. Preferably, the filling layer 4 is etched by a dry etching process.

[0061] Specifically, the filling layer 4 is formed above the lower electrode layer 3, and its size after patterning is smaller than the size of the patterned lower electrode layer 3, that is, the projection of the patterned lower electrode layer 3 on the surface where the filling layer 4 is located completely covers the patterned filling layer 4. Specifically, the cross-section of the patterned filling layer 4 is circular, triangular, rectangular or pentagonal, but not limited thereto. Preferably, see Figure 2 and Figure 6 , the patterned filling layer 4 is a regular pentagon.

[0062] Specifically, the sizes of the patterned filling layer 4 and the patterned lower electrode layer 3 refer to their cross-sectional sizes. Specifically, when the cross section is circular, the size is the diameter; when the cross section is rectangular, the size is the length of the long side; when the cross section is triangular, the size is the length of the longest side; when the cross section is a pentagon, the size is the maximum value of the height of the pentagon; when the cross section is other polygons, the size is the maximum value of the height of the polygon, but is not limited to this.

[0063] Specifically, the cross-sectional shapes of the patterned filling layer 4 and the patterned lower electrode layer 3 are the same or different. Preferably, in one embodiment, the cross-sectional shapes of the patterned filling layer 4 and the lower electrode layer 3 are both regular pentagons, and the five sides of the two cross-sectional shapes are parallel.

[0064] Among them, see Figure 6 The distance L between the outer edge of the patterned filling layer 4 and the outer edge of the projection of the patterned lower electrode layer 3 is ≤ 3 μm, exemplarily 0.8 μm, 1.2 μm, 2 μm or 2.4 μm, but not limited thereto, preferably 2.2 μm to 2.8 μm.

[0065] S4: forming a wrapping layer on the temporary substrate obtained in step S3 to wrap the patterned lower electrode layer and the patterned filling layer, and cover other areas of the temporary substrate;

[0066] The wrapping layer 5 is made of a high-hardness material to provide good support for the piezoelectric layer 2, the upper electrode layer 7, and the lower electrode layer 3 after the cavity 8 is formed later. Specifically, the wrapping layer 5 can be made of silicon or ceramic, but is not limited thereto.

[0067] For details, see Figure 3 In order to form a good support, the thickness D of the wrapping layer 5 should be controlled to be greater than the total thickness d of the filling layer 4 and the lower electrode layer 3, that is, the wrapping layer 5 completely wraps the lower electrode layer 3, the filling layer 4 and the exposed surface of the temporary substrate 1. Preferably, Dd should be controlled to be ≥ 300nm. More specifically, the thickness of the wrapping layer 5 is 1000nm to 3000nm, exemplarily 1200nm, 1400nm, 1800nm, 2200nm, 2600nm or 2800nm, but not limited thereto.

[0068] The encapsulating layer 5 may be prepared by chemical vapor deposition (such as MOCVD or PECVD) or physical vapor deposition (such as PVD), but is not limited thereto.

[0069] S5: bonding the temporary substrate obtained in S4 to the transfer substrate;

[0070] The transfer substrate 6 may be a sapphire substrate, a silicon substrate, a quartz substrate, a silicon carbide substrate, a silicon nitride substrate, or a gallium arsenide substrate, but is not limited thereto. Preferably, the temporary substrate 1 is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, or a diamond substrate, and more preferably a silicon substrate. Preferably, in order to facilitate bonding, a silicon layer, a silicon dioxide layer, or other non-metallic insulating material layer may also be formed on the transfer substrate 6, but is not limited thereto, and these materials are convenient for direct bonding with the encapsulation layer 5.

[0071] The temporary substrate 1 obtained in step S4 can be bonded to the transfer substrate 6 by eutectic bonding, anodic bonding, thermocompression bonding or direct bonding, but is not limited thereto. Preferably, the temporary substrate 1 is bonded by direct bonding.

[0072] Preferably, in some embodiments, before bonding, the wrapping layer 5 is ground and polished by chemical mechanical polishing (CMP) to make it flat for subsequent bonding. Specifically, after grinding and polishing, the surface roughness of the wrapping layer 5 is ≤0.3nm, the uniformity is ≤1%, and the TTV is ≤20μm. The determination methods of surface roughness, uniformity, and TTV can refer to GB / T32814-2016.

[0073] S6: removing the temporary substrate to expose the piezoelectric layer;

[0074] The temporary substrate 1 can be removed by chemical grinding, etching or laser lift-off. Preferably, in one embodiment, the temporary substrate 1 is first ground and thinned to 5 μm to 50 μm, and then the remaining temporary substrate 1 is removed by dry etching to expose the piezoelectric layer 2.

[0075] S7: forming an upper electrode layer on the piezoelectric layer and patterning it;

[0076] The upper electrode layer 7 is made of one or more of tungsten, molybdenum, and aluminum, but not limited thereto. The thickness of the upper electrode layer 7 is 50 nm to 800 nm, and is exemplarily 80 nm, 150 nm, 200 nm, 300 nm, 450 nm, 600 nm, or 700 nm, but not limited thereto. Preferably, the upper electrode layer 7 is 50 nm to 500 nm, and more preferably 100 nm to 300 nm.

[0077] The upper electrode layer 7 may be grown by PVD, evaporation, or the like, but is not limited thereto. Preferably, in this embodiment, the upper electrode layer 7 is grown by PVD. After the upper electrode layer 7 is grown, it is patterned by a photolithography etching process, wherein the etching may be dry etching or wet etching. Preferably, the upper electrode layer 7 is etched by a dry etching process.

[0078] Specifically, the upper electrode layer 7 is formed above the patterned filling layer 4, and its size after patterning is smaller than the size of the patterned filling layer 4, that is, the projection of the patterned filling layer 4 on the surface where the upper electrode layer 7 is located completely covers the patterned upper electrode layer 7. Specifically, the cross section of the patterned upper electrode layer 7 is circular, triangular, rectangular or pentagonal, but not limited thereto. Preferably, see Figure 5 and Figure 6 , the cross section of the patterned upper electrode layer 7 is a regular pentagon.

[0079] Specifically, the sizes of the patterned filling layer 4 and the patterned upper electrode layer 7 refer to their cross-sectional sizes. Specifically, when the cross section is circular, the size is the diameter; when the cross section is rectangular, the size is the length of the long side; when the cross section is triangular, the size is the length of the longest side; when the cross section is a pentagon, the size is the maximum height of the pentagon; when the cross section is other polygons, the size is the maximum height of the polygon, but is not limited to this.

[0080] Specifically, the cross-sectional shapes of the patterned filling layer 4 and the patterned upper electrode layer 7 are the same or different. Preferably, in one embodiment, the cross-sectional shapes of the patterned filling layer 4 and the upper electrode layer 7 are both regular pentagons, and the five sides of the two cross-sectional shapes are parallel.

[0081] Among them, see Figure 6The distance l between the outer edge of the patterned upper electrode layer 7 and the outer edge of the projection of the patterned filling layer 4 is ≤ 3 μm, exemplarily 0.8 μm, 1.2 μm, 2 μm or 2.4 μm, but not limited thereto, preferably 2.2 μm to 2.8 μm.

[0082] S8: removing the filling layer to form a cavity, thereby obtaining a cavity-type bulk acoustic wave resonator.

[0083] The through hole 9 can be formed by etching the piezoelectric layer 2 (see Figure 7 ), and then the filling layer 4 is removed by etching to form a cavity 8, thereby obtaining a cavity-type bulk acoustic wave resonator.

[0084] In the preparation method of the cavity-type bulk acoustic wave of the present invention, the piezoelectric layer 2 is first epitaxially grown on the temporary substrate 1, and then the lower electrode layer 3, the filling layer 4, and the wrapping layer 5 are prepared, and then the transfer substrate 6 is bonded, the temporary substrate 1 is removed, the piezoelectric layer 2 is exposed, and then the upper electrode layer 7 is formed. Based on this preparation method, not only the crystal quality of the piezoelectric layer 2 is effectively improved by epitaxial growth, but also the upper electrode layer 7 and the lower electrode layer 3 are formed by bonding, which reduces the production difficulty and provides a solution for the preparation of the cavity-type bulk acoustic wave resonator. It should be noted that although the epitaxial growth of the piezoelectric layer 2 can improve its crystal quality, it also determines that there can be no other layers (such as the lower electrode layer 3) between the substrate and the piezoelectric layer 2, which makes it impossible to prepare the lower electrode layer 3 in advance below the piezoelectric layer 2, resulting in high process difficulty and difficulty in implementation. The present invention solves this problem through a specific preparation process.

[0085] Accordingly, an embodiment of the present invention further provides a cavity type BAW resonator, which is manufactured by the above manufacturing method. Preferably, the cavity type BAW resonator in this embodiment may also include a Bragg reflection layer commonly used in the art, but is not limited thereto.

[0086] The above is a preferred embodiment of the invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the invention. These improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A method for preparing a cavity type bulk acoustic wave resonator, characterized in that: The following steps are involved: (1) forming a piezoelectric layer on a temporary substrate; (2) forming a lower electrode layer on the piezoelectric layer and patterning it; (3) forming a filling layer on the temporary substrate obtained in step (2), and patterning the filling layer so that the projection of the patterned lower electrode layer covers the patterned filling layer; wherein the filling layer is made of silicon dioxide, phosphorus-containing silicon dioxide or resin; (4) forming a wrapping layer on the temporary substrate obtained in step (3) to wrap the patterned lower electrode layer and the patterned filling layer and cover other areas of the temporary substrate; wherein the wrapping layer is made of silicon or ceramic; (5) bonding the temporary substrate obtained in step (4) to the transfer substrate; (6) removing the temporary substrate to expose the piezoelectric layer; (7) forming an upper electrode layer on the piezoelectric layer and patterning the layer so that a projection of the patterned filling layer covers the patterned upper electrode layer; (8) The filling layer is removed to form a cavity, thereby obtaining a cavity-type bulk acoustic wave resonator.

2. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: The distance between the outer edge of the patterned filling layer and the outer edge of the projection of the patterned lower electrode layer is ≤ 3 μm; and / or The distance between the outer edge of the patterned upper electrode layer and the outer edge of the projection of the patterned filling layer is ≤3 μm.

3. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: The patterned filling layer, the patterned upper electrode layer, and the patterned lower electrode layer are all pentagonal; The distance between the outer edge of the patterned filling layer and the outer edge of the projection of the patterned lower electrode layer is 2.2 μm to 2.8 μm; The distance between the outer edge of the patterned upper electrode layer and the outer edge of the projection of the patterned filling layer is 2.2 μm to 2.8 μm.

4. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: The temporary substrate is selected from one or more of a sapphire substrate, a silicon carbide substrate, a silicon nitride substrate or a silicon substrate; and / or The transfer substrate is selected from one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate or a diamond substrate.

5. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: The piezoelectric layer is made of single crystal aluminum nitride and / or single crystal ε-gallium oxide, and has a thickness of 200 nm to 1000 nm; and / or The lower electrode layer is made of one or more of tungsten, molybdenum and aluminum, and has a thickness of 100 nm to 500 nm; and / or The thickness of the filling layer is 100nm to 2000nm; and / or The upper electrode layer is made of one or more of tungsten, molybdenum and aluminum, and has a thickness of 50nm to 500nm.

6. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: The thickness of the wrapping layer is D, the total thickness of the filling layer and the lower electrode layer is d, and Dd≥300nm.

7. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: In step (5), the encapsulation layer is polished and flattened, and then bonded to the transfer substrate; Wherein, after grinding and flattening, the surface roughness of the wrapping layer is ≤0.3 nm, the uniformity is ≤1%, and the TTV is ≤20 μm.

8. The method for preparing a cavity type bulk acoustic wave resonator according to claim 1, characterized in that: In step (6), the temporary substrate is firstly ground and thinned to 5 μm to 50 μm, and then the remaining temporary substrate is removed by dry etching to expose the piezoelectric layer.

9. The method for preparing a cavity type bulk acoustic wave resonator according to any one of claims 1 to 8, characterized in that: The piezoelectric layer is made of single-crystalline ε-gallium oxide.

10. A cavity type bulk acoustic wave resonator, characterized in that: The cavity type bulk acoustic wave resonator is prepared by the preparation method of any one of claims 1 to 9.

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