A bulk acoustic resonator, its manufacturing method, and a filter

Abstract

This invention provides a method for manufacturing a bulk acoustic wave resonator, including a substrate provision step, an acoustic reflection structure formation step, and a stacked structure formation step. The stacked structure formation step includes: sequentially forming a lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode from bottom to top on the substrate or the acoustic reflection structure. The upper electrode, the second piezoelectric layer, the first piezoelectric layer, the lower electrode, and the acoustic reflection structure have an overlapping region in the device thickness direction, which constitutes the resonant region of the bulk acoustic wave resonator. The first piezoelectric layer is implemented using a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is implemented using an undoped piezoelectric material. Correspondingly, this invention also provides a bulk acoustic wave resonator and a filter. Implementing this invention can yield a bulk acoustic wave resonator that balances electromechanical coupling coefficient and quality factor, has low parasitic modes, and exhibits stress balance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a bulk acoustic wave resonator, its manufacturing method, and a filter. Background Technology

[0002] Bulk acoustic resonators are currently the most widely used type of resonator. Please refer to [reference needed]. Figure 1 , Figure 1 This is a cross-sectional schematic diagram of a common bulk acoustic wave resonator in the prior art. As shown in the figure, the existing bulk acoustic wave resonator includes a substrate 10, a stacked structure formed on the substrate 10, and a cavity 11 formed between the substrate 10 and the stacked structure for sound wave reflection. The stacked structure further includes a lower electrode 12, a piezoelectric layer 13, and an upper electrode 14 from bottom to top. The upper electrode 14, the piezoelectric layer 13, the lower electrode 12, and the cavity 11 have an overlapping region in the thickness direction of the device. This overlapping region is the resonant region of the bulk acoustic wave resonator.

[0003] Aluminum nitride (ANT) is the preferred material for piezoelectric layers due to its good piezoelectric properties and thermal stability. However, ANT suffers from a low electromechanical coupling coefficient, which limits the bandwidth of filters based on bulk acoustic wave (BAW) resonators. To address this, a common approach is to dope ANT with rare-earth elements (such as scandium) to improve the electromechanical coupling coefficient. While this effectively increases the electromechanical coupling coefficient, it also leads to a decrease in the BAW resonator's quality factor. Furthermore, increasing the electromechanical coupling coefficient results in a thinner piezoelectric layer, which in turn reduces the resonant region area of ​​the BAW resonator. This smaller resonant region area leads to larger parasitic modes. Especially with high rare-earth element doping concentrations, the resonant region area can shrink excessively, resulting in an overabundance of parasitic modes in the BAW resonator. Moreover, rare-earth-doped ANT also suffers from stress imbalance. Summary of the Invention

[0004] To overcome the aforementioned deficiencies in the prior art, the present invention provides a method for manufacturing a bulk acoustic resonator. This method includes a substrate provision step, an acoustic reflection structure formation step, and a stacked structure formation step. The acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure. The stacked structure formation step includes:

[0005] A lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode are formed sequentially from bottom to top on the substrate or the acoustic reflection structure. The upper electrode, the second piezoelectric layer, the first piezoelectric layer, the lower electrode, and the acoustic reflection structure have an overlapping region in the thickness direction of the device. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0006] The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material.

[0007] According to one aspect of the invention, in this manufacturing method, the impurity element is a rare earth element.

[0008] According to another aspect of the invention, in this manufacturing method, the doping concentration of the rare earth element is 5% to 50%.

[0009] According to another aspect of the invention, in this manufacturing method, the doped piezoelectric material is scandium-doped aluminum nitride, and the undoped piezoelectric material is aluminum nitride.

[0010] According to another aspect of the invention, the manufacturing method further includes: forming a first acoustic reflection portion in the first piezoelectric layer, the first acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed; and / or forming a second acoustic reflection portion in the second piezoelectric layer, the second acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed.

[0011] According to another aspect of the present invention, in the manufacturing method, the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: after forming the first piezoelectric layer and before forming the second piezoelectric layer, etching a first region of the first piezoelectric layer to form a first groove structure, the first region being located outside and close to or adjacent to the resonant region to be formed; filling the first groove structure with a first sacrificial material; after forming the second piezoelectric layer and before forming the upper electrode, etching a second region of the second piezoelectric layer to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and removing the first sacrificial material after forming the upper electrode; wherein the first groove structure constitutes the first acoustic reflection portion, and the second groove structure constitutes the second acoustic reflection portion.

[0012] According to another aspect of the invention, in the manufacturing method, the first groove structure penetrates the first piezoelectric layer, and the second groove structure penetrates the second piezoelectric layer.

[0013] According to another aspect of the invention, in the manufacturing method, the first groove structure is a whole groove or a plurality of first groove units arranged at intervals along the edge of the resonant region to be formed; the second groove structure is a whole groove or a plurality of second groove units arranged at intervals along the edge of the resonant region to be formed.

[0014] According to another aspect of the invention, in the manufacturing method, the horizontal projections of the first groove structure and the second groove structure surround the entire outer periphery of the horizontal projection of the resonant region to be formed, wherein there is no overlapping region or partial overlap between the horizontal projections of the first groove structure and the second groove structure.

[0015] According to another aspect of the present invention, the manufacturing method further includes: forming a first connection portion connected to the lower electrode on the substrate; the horizontal projection of the resonant region to be formed and the horizontal projection of the lower electrode are polygons with the same shape and corresponding sides, wherein the first side in the horizontal projection of the lower electrode corresponds to the side of the lower electrode that is connected to the first connection portion, and the second side in the horizontal projection of the resonant region to be formed corresponds to the first side; the horizontal projection of the first groove structure surrounds the other sides of the horizontal projection of the resonant region to be formed except for the second side, and the horizontal projection of the second groove structure surrounds the second side in the horizontal projection of the resonant region to be formed.

[0016] According to another aspect of the present invention, the manufacturing method comprising the steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer includes: forming a first protrusion structure on the structure obtained after forming the lower electrode and before forming the first piezoelectric layer, the first protrusion structure being located below a first region to be formed of the first piezoelectric layer, the first region being located outside and close to or adjacent to the resonant region to be formed; forming a second protrusion structure on the first piezoelectric layer after forming the first piezoelectric layer and before forming the second piezoelectric layer, the second protrusion structure being located below a second region to be formed of the second piezoelectric layer, the second region being located outside and close to or adjacent to the resonant region to be formed; and after forming the upper electrode, removing the first protrusion structure to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and removing the second protrusion structure to form a second air bridge structure in the second region of the second piezoelectric layer; wherein the first air bridge structure constitutes the first acoustic reflector and the second air bridge structure constitutes the second acoustic reflector.

[0017] According to another aspect of the invention, the step of forming the acoustic reflection structure includes: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; the step of forming the lower electrode includes: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below a first region to be formed of the first piezoelectric layer is not covered by the lower electrode, the first region being located outside and close to or adjacent to the resonant region to be formed; the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer... Before forming the first piezoelectric layer, the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is etched to form a fourth groove structure; after forming the first piezoelectric layer and before forming the second piezoelectric layer, a second protrusion structure is formed on the first piezoelectric layer, the second protrusion structure being located below the second region to be formed of the second piezoelectric layer, the second region being located outside and close to or adjacent to the resonant region to be formed; after forming the upper electrode, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and while forming the cavity, a downwardly recessed first air bridge structure is formed in the first region of the first piezoelectric layer; wherein, the first air bridge structure constitutes the first acoustic reflection portion, and the second air bridge structure constitutes the second acoustic reflection portion.

[0018] According to another aspect of the present invention, the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer, forming a first protrusion structure and a second protrusion structure on the structure obtained after forming the lower electrode, the first protrusion structure being located below a first region where the first piezoelectric layer is to be formed, and the second protrusion structure being located below a second region where the second piezoelectric layer is to be formed, wherein the first region and the second region are both located outside and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projection of the first region and the horizontal projection of the second region; after forming the first piezoelectric layer and before forming the second piezoelectric layer, forming a first protrusion structure and a second protrusion structure on the structure obtained after forming the lower electrode, the first protrusion structure being located below a first region where the first piezoelectric layer is to be formed, ... the first protrusion structure being located below the first region where the second piezoelectric layer is to be formed, the second protrusion structure being located below a second region where the second piezoelectric layer is to be formed, the first protrusion structure being located outside and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projection of the first region and the horizontal projection The portion above the second protrusion structure is etched to form a first groove structure penetrating the first piezoelectric layer; after forming the second piezoelectric layer and before forming the upper electrode, the portion of the second piezoelectric layer above the first protrusion structure is etched to form a second groove structure penetrating the second piezoelectric layer; and after forming the upper electrode, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer; wherein the first groove structure and the first air bridge structure together constitute the first acoustic reflection portion, and the second groove structure and the second air bridge structure together constitute the second acoustic reflection portion.

[0019] According to another aspect of the invention, in the manufacturing method, the step of forming the acoustic reflection structure includes: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; the step of forming the lower electrode includes: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below a first region to be formed of a first piezoelectric layer is not covered by the lower electrode. The region is located outside and close to or adjacent to the resonant region to be formed; the steps of forming a first acoustic reflection portion in the first piezoelectric layer and a second acoustic reflection portion in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer, etching the portion of the third sacrificial material located below the first region of the first piezoelectric layer to form a fourth groove structure; after forming the first piezoelectric layer and before forming the second piezoelectric layer, etching a third region of the first piezoelectric layer to form a first groove structure, the third region being located outside and close to or adjacent to the resonant region to be formed. A resonant region is formed, wherein the horizontal projection of the third region does not overlap with the horizontal projection of the first region; and the first groove structure is filled with a first sacrificial material; a second protrusion structure is formed on the structure obtained by filling the first groove structure, the second protrusion structure being located below the second region to be formed of the second piezoelectric layer, the second region being located outside and close to or adjacent to the resonant region to be formed; after forming the second piezoelectric layer and before forming the upper electrode, a fourth region of the second piezoelectric layer is etched to form a second groove structure, the fourth region being located outside and close to or adjacent to the resonant region to be formed, the horizontal projection of the fourth region not overlapping with the horizontal projection of the second region; after forming the upper electrode, the first sacrificial material is removed, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and a downwardly recessed first air bridge structure is formed in the first piezoelectric layer while forming the cavity; wherein the first groove structure and the first air bridge structure together constitute the first acoustic reflection part, and the second groove structure and the second air bridge structure together constitute the second acoustic reflection part.

[0020] According to another aspect of the present invention, the manufacturing method comprising the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer includes: forming a first protrusion structure on the structure obtained after forming the lower electrode and before forming the first piezoelectric layer, the first protrusion structure being located below a first region to be formed of the first piezoelectric layer, the first region being located outside and close to or adjacent to the resonant region to be formed; etching a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer to form a second groove structure after forming the second piezoelectric layer and before forming the upper electrode, the second region being located outside and close to or adjacent to the resonant region to be formed; and removing the first protrusion structure after forming the upper electrode to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer; wherein the portion of the first air bridge structure and the portion of the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection portion, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflection portion.

[0021] According to another aspect of the present invention, in the manufacturing method, the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: forming a first piezoelectric layer on the substrate after forming the lower electrode and before forming the second piezoelectric layer; etching a first region of the first piezoelectric layer to form a first groove structure penetrating the first piezoelectric layer, the first region being located outside and close to or adjacent to the resonant region to be formed; filling the first groove structure with a first sacrificial material; and forming a second piezoelectric layer on the first piezoelectric layer, the second piezoelectric layer... The first piezoelectric layer is formed by the first piezoelectric layer and the first piezoelectric layer; after the formation of the second piezoelectric layer and before the formation of the upper electrode, a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer is etched to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and the first sacrificial material is removed after the formation of the upper electrode; wherein the portion of the first groove structure and the portion of the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection portion, and the portion of the second groove structure located in the second piezoelectric layer together constitutes the second acoustic reflection portion.

[0022] The present invention also provides a bulk acoustic resonator, the bulk acoustic resonator comprising:

[0023] Substrate;

[0024] A stacked structure is formed on the substrate and includes, from bottom to top, a lower electrode, a first piezoelectric layer, a second piezoelectric layer and an upper electrode. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material.

[0025] An acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure, and the acoustic reflection structure overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer and the upper electrode in the thickness direction of the device, and the overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0026] According to one aspect of the invention, in the bulk acoustic resonator, the impurity element is a rare earth element.

[0027] According to another aspect of the invention, the doping concentration of the rare earth element in the bulk acoustic resonator is 5% to 50%.

[0028] According to another aspect of the invention, in the bulk acoustic resonator, the doped piezoelectric material is scandium-doped aluminum nitride, and the undoped piezoelectric material is aluminum nitride.

[0029] According to another aspect of the invention, in the bulk acoustic resonator, the first piezoelectric layer further includes a first acoustic reflection portion located outside the resonant region and close to or adjacent to the resonant region; and / or the second piezoelectric layer further includes a second acoustic reflection portion located outside the resonant region and close to or adjacent to the resonant region.

[0030] According to another aspect of the present invention, in the bulk acoustic resonator, the first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein the first acoustic reflection portion is a first groove structure formed by etching the upper surface of the first piezoelectric layer, and the second acoustic reflection portion is a second groove structure formed by etching the upper surface of the second piezoelectric layer.

[0031] According to another aspect of the invention, in the bulk acoustic resonator, the first groove structure penetrates the first piezoelectric layer, and the second groove structure penetrates the second piezoelectric layer.

[0032] According to another aspect of the invention, in the bulk acoustic resonator, the first groove structure is a single groove or a plurality of first groove units spaced apart along the edge of the resonant region; the second groove structure is a single groove or a plurality of second groove units spaced apart along the edge of the resonant region.

[0033] According to another aspect of the invention, in the bulk acoustic resonator, the horizontal projections of the first groove structure and the second groove structure surround the entire outer periphery of the horizontal projection of the resonant region, wherein there is no overlapping region or partial overlap between the horizontal projections of the first groove structure and the second groove structure.

[0034] According to another aspect of the invention, the bulk acoustic resonator further includes a first connection portion formed on the substrate and connected to the lower electrode; the horizontal projection of the resonant region and the horizontal projection of the lower electrode are polygons with the same shape and corresponding sides, wherein a first side in the horizontal projection of the lower electrode corresponds to the side of the lower electrode that is connected to the first connection portion, and a second side in the horizontal projection of the resonant region corresponds to the first side; the horizontal projection of the first groove structure surrounds the other sides of the horizontal projection of the resonant region except for the second side, and the horizontal projection of the second groove structure surrounds the second side in the horizontal projection of the resonant region.

[0035] According to another aspect of the invention, in the bulk acoustic resonator, the first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein the first acoustic reflection portion is an upwardly convex first air bridge structure and the second acoustic reflection portion is an upwardly convex air bridge structure.

[0036] According to another aspect of the invention, in the bulk acoustic resonator, the acoustic reflection structure is a cavity formed by a third groove structure formed on the substrate and the stacked structure; the first piezoelectric layer includes the first acoustic reflection portion and the second piezoelectric layer includes the second acoustic reflection portion, wherein the first acoustic reflection portion is a first air bridge structure formed in the cavity and recessed downwards, and the second acoustic reflection portion is a second air bridge structure protruding upwards.

[0037] According to another aspect of the present invention, in the bulk acoustic resonator, the first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein the first acoustic reflection portion includes a first groove structure and an upwardly protruding first air bridge structure, and the second acoustic reflection portion includes a second groove structure and an upwardly protruding second air bridge structure.

[0038] According to another aspect of the invention, in the bulk acoustic resonator, the acoustic reflection structure is a cavity surrounded by a third groove structure formed on the substrate and the stacked structure; the first piezoelectric layer includes the first acoustic reflection portion and the second piezoelectric layer includes the second acoustic reflection portion, wherein the first acoustic reflection portion includes the first groove structure and the first air bridge structure formed in the cavity and recessed downwards, and the second acoustic reflection portion includes the second groove structure and the second air bridge structure protruding upwards.

[0039] According to another aspect of the present invention, in the bulk acoustic resonator, the first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein an upwardly protruding first air bridge structure is formed in the first piezoelectric layer, and a second groove structure is formed in the structure formed by the second piezoelectric layer and the first piezoelectric layer, the portions of the first air bridge structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection portion, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflection portion.

[0040] According to another aspect of the present invention, in the bulk acoustic resonator, the first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein the first piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer from bottom to top, a first groove structure penetrating the first piezoelectric layer is formed in the first piezoelectric layer, a second groove structure is formed in the structure formed by the second piezoelectric layer and the first piezoelectric layer, the portions of the first groove structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection portion, and the portions of the second groove structure located in the second piezoelectric layer together constitute the second acoustic reflection portion.

[0041] The present invention also provides a filter comprising a bulk acoustic resonator formed by the aforementioned manufacturing method, or the aforementioned bulk acoustic resonator.

[0042] The method for manufacturing a bulk acoustic wave resonator provided by the present invention forms two piezoelectric layers in a stacked structure (from bottom to top, the first piezoelectric layer and the second piezoelectric layer). The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material. Compared with the prior art, the present invention has the following advantages: (1) In the prior art, the piezoelectric layer of the bulk acoustic wave resonator is only made of a single doped piezoelectric material. Although this can effectively improve the electromechanical coupling coefficient of the piezoelectric layer and thus help to broaden the bandwidth of the filter formed based on the bulk acoustic wave resonator, it will at the same time lead to a decrease in the quality factor of the bulk acoustic wave resonator. That is, the electromechanical coupling coefficient of the piezoelectric layer and the quality factor of the bulk acoustic wave resonator cannot be balanced. The present invention improves the electromechanical coupling coefficient through the doped first piezoelectric layer, and at the same time improves the quality factor of the bulk acoustic wave resonator through the undoped second piezoelectric layer, so as to compensate for the decrease in the device quality factor caused by the doped first piezoelectric layer to a certain extent. In other words, implementing this invention can effectively balance the electromechanical coupling coefficient of the piezoelectric layer and the quality factor of the device. (2) In the prior art, the piezoelectric layer of the bulk acoustic wave resonator is only made of a single layer of doped piezoelectric material. Although this can effectively improve the electromechanical coupling coefficient of the piezoelectric layer, it will also lead to a reduction in the area of ​​the device's resonant region, especially when the doping concentration is high, which will lead to an excessive reduction in the area of ​​the device's resonant region. In this invention, an undoped second piezoelectric layer is formed on the doped first piezoelectric layer. In this case, not only can the electromechanical coupling coefficient be improved, but the presence of the second piezoelectric layer also makes the area of ​​the device's resonant region appropriately larger, thereby effectively avoiding the situation where the area of ​​the device's resonant region is too small, and thus effectively avoiding the problem of excessive parasitic modes in the device caused by the small area of ​​the resonant region. (3) The second piezoelectric layer can also balance the stress of the first piezoelectric layer, thereby making the device stress more balanced. Accordingly, the bulk acoustic wave resonator formed based on the manufacturing method provided by this invention has the characteristics of balancing the electromechanical coupling coefficient and quality factor, small parasitic modes, and balanced stress. Furthermore, the filter formed based on the bulk acoustic resonator provided by this invention has excellent performance characteristics. Attached Figure Description

[0043] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1 This is a schematic cross-sectional view of a bulk acoustic resonator in the prior art;

[0045] Figure 2 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to a specific embodiment of the present invention;

[0046] Figures 3(a) to 3(h) According to Figure 2 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0047] Figures 4(a) and 4(b) are top views of the structures shown in Figures 3(d) and 3(g), respectively.

[0048] Figure 5 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to a preferred embodiment of the present invention;

[0049] Figures 6(a) to 6(f) According to Figure 5 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0050] Figures 7(a) and 7(b) are top views of the structures shown in Figures 6(a) and 6(d), respectively, where the first groove structure and the second groove structure are both a single groove.

[0051] Figures 8(a) and 8(b) are top views of the structures shown in Figures 6(a) and 6(d), respectively, wherein the first groove structure and the second groove structure are both composed of multiple groove units;

[0052] Figures 9(a) and 9(b) are top views of the structures obtained after the formation of the first groove structure and the second groove structure according to a preferred embodiment of the present invention.

[0053] Figure 10 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0054] Figures 11(a) to 11(g) According to Figure 10 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0055] Figure 12 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0056] Figures 13(a) to 13(g) According to Figure 12 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0057] Figure 14 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0058] Figures 15(a) to 15(g) According to Figure 14 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0059] Figure 16 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0060] Figures 17(a) to 17(g) According to Figure 16 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0061] Figure 18 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0062] Figures 19(a) to 19(f) According to Figure 18 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0063] Figure 20 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention;

[0064] Figures 21(a) to 21(h) According to Figure 20 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0065] The same or similar reference numerals in the accompanying drawings represent the same or similar parts. Detailed Implementation

[0066] To better understand and explain the present invention, a further detailed description of the invention will be provided below in conjunction with the accompanying drawings.

[0067] This invention provides a method for manufacturing a bulk acoustic resonator, the method comprising a substrate provision step, an acoustic reflection structure formation step, and a stacked structure formation step, wherein the acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure, wherein the stacked structure formation step includes:

[0068] A lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode are formed sequentially from bottom to top on the substrate or the acoustic reflection structure. The upper electrode, the second piezoelectric layer, the first piezoelectric layer, the lower electrode, and the acoustic reflection structure have an overlapping region in the thickness direction of the device. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0069] The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material.

[0070] The manufacturing method provided by this invention is applicable to air-gap type bulk acoustic wave resonators (i.e., the acoustic reflection structure is a cavity), Bragg reflection type bulk acoustic wave resonators (i.e., the acoustic reflection structure is a Bragg reflection layer), and reverse-etched type bulk acoustic wave resonators (i.e., the acoustic reflection structure is an opening penetrating the substrate). The manufacturing method of the bulk acoustic wave resonator provided by this invention will be described below using a bulk acoustic wave resonator with a cavity acoustic reflection structure as an example. Please refer to... Figure 2 , Figure 2 This is a flowchart illustrating a method for manufacturing a bulk acoustic resonator according to a specific embodiment of the present invention. As shown, the manufacturing method includes:

[0071] In step S101, a substrate is provided;

[0072] In step S102, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0073] In step S103, a lower electrode is formed on the substrate;

[0074] In step S104, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0075] In step S105, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0076] In step S106, an upper electrode is formed on the second piezoelectric layer;

[0077] In step S107, the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. This cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0078] Below, we will combine Figures 3(a) to 3(h) The steps S101 to S107 described above will be explained in detail.

[0079] Specifically, in step S101, as shown in FIG3(a), a substrate 100 is provided. In this embodiment, the material of the substrate 100 includes, but is not limited to, semiconductor materials such as silicon, germanium, and germanium-silicon. All existing materials suitable for bulk acoustic wave resonator substrates are applicable to this invention; for the sake of simplicity, not all possible materials for the substrate 100 will be listed here. Furthermore, this invention does not impose any limitation on the thickness of the substrate 100, which can be determined according to actual design requirements.

[0080] In step S102, firstly, as shown in FIG3(b), the upper surface of the substrate 100 (i.e., the surface used to form the device) is etched to form a groove structure 100a (hereinafter referred to as the third groove structure 100a). Next, as shown in FIG3(c), the third groove structure 100a is filled with a sacrificial material 101 (hereinafter referred to as the third sacrificial material 101). In this embodiment, the step of filling the third groove structure 100a with the third sacrificial material 101 includes: firstly, depositing the third sacrificial material 101 on the structure shown in FIG3(b), wherein the thickness of the third sacrificial material 101 is greater than the depth of the third groove structure 100a; then, planarizing the third sacrificial material 101 until the upper surface of the substrate 100 is exposed, in which case the upper surface of the third sacrificial material 101 in the third groove structure 100a is flush with the upper surface of the substrate 100. The term "flush" here means that the height difference between the two is within the allowable range of process tolerance. The present invention does not limit the third sacrificial material 101 in any way. Existing conventional sacrificial materials such as phosphosilicate glass (PSG), borosilicate glass (BPSG), and intrinsic silicon dioxide (USG) are all applicable to the present invention.

[0081] In step S103, as shown in FIG3(d), a lower electrode metal material (not shown) is deposited on the upper surface of the substrate 100, and the lower electrode metal material is patterned to form the lower electrode 102a. Please refer in conjunction with FIG4(a), which is a top view of the structure shown in FIG3(d), and FIG3(d) is a cross-sectional view of the structure shown in FIG4(a) along line AA'. In this embodiment, as shown, the lower electrode 102a falls within the opening range of the third groove structure 100a. In this way, after the third sacrificial material 101 in the third groove structure is subsequently removed to form a cavity below the lower electrode 102a, there is no contact between the edge region of the lower electrode 102a and the substrate 100. This helps to reduce the energy loss caused by sound waves entering the substrate 100 through the edge region of the lower electrode 102a, thereby effectively improving the quality factor of the device. Those skilled in the art will understand that (1) in other embodiments, the lower electrode may also completely cover the third groove structure, that is, the edge region of the lower electrode is formed on the substrate. After the third sacrificial material in the third groove structure is subsequently removed to form a cavity below the lower electrode, the substrate provides support for the edge region of the lower electrode, which is beneficial to improving the reliability of the device. Whether the lower electrode completely covers the third groove structure can be determined according to the actual design requirements. (2) The hexagonal shape of the lower electrode 102a in Figure 4(a) is only an illustrative example. In other embodiments, the lower electrode 102a may also be designed as a regular pentagon, rectangle, circle, or even an irregular shape. This document does not impose any limitations on this.

[0082] Furthermore, as shown in Figure 4(a), in this embodiment, in addition to forming the lower electrode 102a, a first connection portion 102b connected to the lower electrode 102a is also formed on the substrate 100. This first connection portion 102b is used for signal connection of the bulk acoustic wave resonator. The lower electrode 102a and the first connection portion 102b are formed simultaneously; that is, after depositing the lower electrode metal material on the upper surface of the substrate 100, it is patterned to simultaneously form the lower electrode 102a and the first connection portion 102b. It should be noted that in this embodiment, the lower electrode 102a and the first connection portion 102b are formed simultaneously and are an integrated structure. The division of the lower electrode 102a and the first connection portion 102b into two parts in Figure 4(a) is merely a deliberate distinction. The same drawing method will be used for both in subsequent figures, and this will not be further explained below. The materials for the lower electrode 102a and the first connection portion 102b can be conventional electrode metals such as molybdenum (Mo). The thickness of the lower electrode 102a and the first connecting part 102b can be set according to actual design requirements.

[0083] In step S104, as shown in FIG3(e), a piezoelectric material is deposited on the upper surface of the substrate 100, and planarization is performed to form a first piezoelectric layer 103 covering the upper surface of the structure shown in FIG3(d). The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements that can improve the electromechanical coupling coefficient of the first piezoelectric layer. This invention does not limit the impurity elements; any element that can improve the electromechanical coupling coefficient of the piezoelectric material after being doped into it is applicable to this invention. For example, the impurity elements can be one or any combination of rare earth elements, including but not limited to scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, magnesium, and titanium. In this embodiment, the doped piezoelectric material is scandium-doped aluminum nitride. Those skilled in the art will understand that, in other embodiments, the doped piezoelectric material may also be zinc oxide, lithium niobate, lead titanate, etc., which are doped with impurity elements, and the present invention does not limit it in any way.

[0084] Furthermore, it should be noted that (1) the doping concentration of impurity elements is determined according to the specific type of impurity element and the design requirements of the bulk acoustic wave resonator, and this invention does not impose any limitations on it. For rare earth elements, the preferred doping concentration range is 5%-50%. (2) This invention does not impose any limitations on the thickness of the first piezoelectric layer 103, and it can be set according to actual design requirements. Preferably, the thickness range of the first piezoelectric layer 103 is 10nm-2μm. (3) In this embodiment, the planarization treatment of the upper surface of the first piezoelectric layer 103 is beneficial to improving the growth quality of subsequent layers. In other embodiments, the first piezoelectric layer 103 can also be formed directly by depositing doped piezoelectric materials.

[0085] In step S105, as shown in FIG3(f), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, wherein the second piezoelectric layer 104 is implemented using an undoped piezoelectric material. In this embodiment, the second piezoelectric layer 104 is implemented using undoped aluminum nitride. Those skilled in the art will understand that in other embodiments, the second piezoelectric layer 104 can also be implemented using undoped zinc oxide, lithium niobate, lead zirconate titanate, etc., which will not be listed here for the sake of brevity. Furthermore, the present invention does not impose any limitation on the thickness of the second piezoelectric layer 104, which can be set according to actual design requirements. Preferably, the thickness range of the second piezoelectric layer 104 is 10 nm-2 μm.

[0086] In step S106, as shown in FIG3(g), an upper electrode metal material (not shown) is deposited on the first piezoelectric layer 104, and the upper electrode metal material is patterned to form an upper electrode 105a. Please refer to FIG4(b) in conjunction with FIG4(g), which is a top view of the structure shown in FIG3(g), and FIG3(g) is a cross-sectional view of the structure shown in FIG4(b) along line AA'. In this embodiment, the upper electrode 105a falls within the opening range of the third groove structure 100a, and its projection in the horizontal direction coincides with that of the lower electrode 102a. It should be noted that (1) since the third groove structure 100a and the first connecting part 102b cannot be directly seen from the top view, the opening edge of the third groove structure 100a and the edge of the first connecting part 102b are represented by dashed lines in FIG4(b). (2) The fact that the upper electrode 105a and the lower electrode 102a project exactly coincide in the horizontal direction is only a preferred embodiment. In other embodiments, their projections in the horizontal direction may not coincide, and this is not a limitation. (3) The fact that the upper electrode 105a and the lower electrode 102a have the same shape in Figure 4(b) is only a preferred embodiment. In other embodiments, the upper electrode 105a may be designed in other shapes according to actual design requirements, and this is not a limitation.

[0087] Furthermore, as shown in Figure 4(b), in this embodiment, in addition to forming the upper electrode 105a, a second connection portion 105b connected to the upper electrode 105a is also formed on the second piezoelectric layer 104. This second connection portion 105b is used for signal connection of the bulk acoustic resonator. The upper electrode 105a and the second connection portion 105b are formed simultaneously; that is, after depositing the upper electrode metal material on the second piezoelectric layer 104, it is patterned to simultaneously form the upper electrode 105a and the second connection portion 105b. It should be noted that in this embodiment, the upper electrode 105a and the second connection portion 105b are formed simultaneously, and they are an integrated structure. The division of the upper electrode 105a and the second connection portion 105b into two parts in Figure 4(b) is merely a deliberate distinction; the same drawing method will be used for both in subsequent figures, and this will not be further explained below. The materials of the upper electrode 105a and the second connection portion 105b can be conventional electrode metals such as molybdenum (Mo), and can be the same as or different from the materials of the lower electrode 102a and the first connection portion 102b. Furthermore, the thickness of the upper electrode 105a and the second connecting part 105b can be set according to actual design requirements.

[0088] In the following text, the structure consisting of the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a will be referred to as a stacked structure. Thus, the stacked structure is formed.

[0089] Furthermore, it should be noted that, depending on actual design requirements, a seed layer (not shown) may be formed between the substrate 100 and the lower electrode 102a, a passivation layer (not shown) may be formed on the upper electrode 105a, and an air bridge / air wing may be formed at the edge of the upper electrode 105a, etc. This article does not impose any limitations on these.

[0090] In step S107, as shown in FIG3(h), the third sacrificial material 101 within the third groove structure 100a of the substrate 100 is removed to form a cavity 101a between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction (the area between the two dashed lines in the figure). This overlapping area constitutes the resonant region of the bulk acoustic wave resonator. Correspondingly, other regions in the bulk acoustic wave resonator located outside the resonant region are referred to as the non-resonant region of the bulk acoustic wave resonator. In this embodiment, the stacked structure is etched to form a release hole (not shown) exposing the third sacrificial material 101, and the third sacrificial material 101 is removed through this release hole using an etching solution. In other embodiments, the release hole may also be formed in other locations, such as below the third sacrificial material 101, penetrating the substrate 100, etc., which is not limited herein. The bulk acoustic wave resonator fabrication is thus completed.

[0091] As mentioned earlier, the manufacturing method provided by this invention is also applicable to Bragg reflector-type bulk acoustic wave resonators and reverse-etched bulk acoustic wave resonators. The main difference between these two and air-gap type bulk acoustic wave resonators lies in the formation steps of the acoustic reflection structure. For the Bragg reflector-type bulk acoustic wave resonator, the manufacturing process is as follows: First, a substrate is provided; then, a Bragg reflector layer composed of alternating layers of high acoustic impedance material and low acoustic impedance material is formed on the substrate; finally, a stacked structure is formed on the Bragg reflector layer, which consists of a lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode from bottom to top, and the upper electrode, the second piezoelectric layer, the first piezoelectric layer, the lower electrode, and the Bragg reflector layer have overlapping areas in the device thickness direction. For a reverse-etched bulk acoustic wave resonator, the manufacturing process is as follows: First, a substrate is provided; then, a stacked structure is formed on the substrate, which consists of a lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode from bottom to top; finally, the back side of the substrate is etched to form an opening penetrating the substrate, and the opening overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the thickness direction of the device. It should be noted that (1) the formation of the Bragg reflection layer in the Bragg reflection type bulk acoustic wave resonator and the formation of the back side opening of the substrate in the reverse-etched bulk acoustic wave resonator are both conventional techniques in the field, and will not be described again here for the sake of brevity. (2) The steps for forming the stacked structure in the Bragg reflection type bulk acoustic wave resonator and the reverse-etched bulk acoustic wave resonator can refer to the steps for forming the stacked structure in the air gap type bulk acoustic wave resonator described above, and will not be repeated here for the sake of brevity.

[0092] The method for manufacturing a bulk acoustic wave resonator provided by the present invention forms two piezoelectric layers in a stacked structure (from bottom to top, the first piezoelectric layer and the second piezoelectric layer). The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material. Compared with the prior art, the present invention has the following advantages: (1) In the prior art, the piezoelectric layer of the bulk acoustic wave resonator is only made of a single doped piezoelectric material. Although this can effectively improve the electromechanical coupling coefficient of the piezoelectric layer and thus help to broaden the bandwidth of the filter formed based on the bulk acoustic wave resonator, it will at the same time lead to a decrease in the quality factor of the bulk acoustic wave resonator. That is, the electromechanical coupling coefficient of the piezoelectric layer and the quality factor of the bulk acoustic wave resonator cannot be balanced. The present invention improves the electromechanical coupling coefficient through the doped first piezoelectric layer, and at the same time improves the quality factor of the bulk acoustic wave resonator through the undoped second piezoelectric layer, so as to compensate for the decrease in the device quality factor caused by the doped first piezoelectric layer to a certain extent. In other words, implementing this invention can effectively balance the electromechanical coupling coefficient of the piezoelectric layer and the quality factor of the device. (2) In the prior art, the piezoelectric layer of the bulk acoustic resonator is only made of a single layer of doped piezoelectric material. Although this can effectively improve the electromechanical coupling coefficient of the piezoelectric layer, it will also lead to a reduction in the area of ​​the device's resonant region, especially when the doping concentration is high, which will lead to an excessive reduction in the area of ​​the device's resonant region. In this invention, an undoped second piezoelectric layer is formed on the doped first piezoelectric layer. In this case, not only can the electromechanical coupling coefficient be improved, but the presence of the second piezoelectric layer also makes the area of ​​the device's resonant region appropriately larger, thereby effectively avoiding the situation where the area of ​​the device's resonant region is too small, and thus effectively avoiding the problem of excessive parasitic modes in the device caused by the small area of ​​the resonant region. (3) The second piezoelectric layer can also balance the stress of the first piezoelectric layer, thereby making the device stress more balanced.

[0093] Preferably, the manufacturing method provided by the present invention further includes: forming an acoustic reflection portion capable of reflecting sound waves in at least one of a first piezoelectric layer and a second piezoelectric layer, wherein the acoustic reflection portion is located outside and close to or adjacent to the resonant region to be formed. Specifically, in one embodiment, a first acoustic reflection portion is formed in the first piezoelectric layer, the first acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed; and a second acoustic reflection portion is formed in the second piezoelectric layer, the second acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed. In another embodiment, the first acoustic reflection portion is formed only in the first piezoelectric layer, the first acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed. In yet another embodiment, the second acoustic reflection portion is formed only in the second piezoelectric layer, the second acoustic reflection portion being located outside and close to or adjacent to the resonant region to be formed. In this embodiment, when the first acoustic reflector is formed in the first piezoelectric layer, it can be a groove structure, an air bridge structure, or a combination of both. Similarly, the second acoustic reflector can be a groove structure, an air bridge structure, or a combination of both. Those skilled in the art will understand that the first and second acoustic reflectors are not limited to the aforementioned groove structures, air bridge structures, or combinations thereof. Other structures capable of acoustic wave reflection also fall within the scope of this invention. For the sake of brevity, not all possible structures of the first and second acoustic reflectors will be listed here. Forming an acoustic reflector in the first and / or second piezoelectric layers can provide acoustic impedance mismatch, which helps reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0094] The following explanation uses the example of forming a first acoustic reflector in a first piezoelectric layer and forming a second acoustic reflector in a second piezoelectric layer.

[0095] In a preferred embodiment, the steps of forming a first acoustic reflector in a first piezoelectric layer and forming a second acoustic reflector in a second piezoelectric layer include: etching a first region of the first piezoelectric layer after forming the first piezoelectric layer and before forming the second piezoelectric layer to form a first groove structure, the first region being located outside and close to or adjacent to the resonant region to be formed; filling the first groove structure with a first sacrificial material; etching a second region of the second piezoelectric layer after forming the second piezoelectric layer and before forming the upper electrode to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and removing the first sacrificial material after forming the upper electrode; wherein the first groove structure constitutes the first acoustic reflector and the second groove structure constitutes the second acoustic reflector.

[0096] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 5 , Figure 5 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to a preferred embodiment of the present invention. As shown, the manufacturing method includes:

[0097] In step S201, a substrate is provided;

[0098] In step S202, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0099] In step S203, a lower electrode is formed on the substrate;

[0100] In step S204, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0101] In step S205, the first region of the first piezoelectric layer is etched to form a first groove structure, the first region being located outside and close to or adjacent to the resonant region to be formed; and the first groove structure is filled with a first sacrificial material.

[0102] In step S206, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0103] In step S207, the second region of the second piezoelectric layer is etched to form a second groove structure. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0104] In step S208, an upper electrode is formed on the second piezoelectric layer;

[0105] In step S209, the first sacrificial material is removed, and the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0106] Below, we will combine Figures 6(a) to 6(f) The steps S201 to S209 described above will be explained in detail.

[0107] Specifically, steps S201 to S204 can be referred to the aforementioned steps S101 to S104, and will not be repeated here for the sake of brevity. The structure obtained after performing step S204 can be referred to Figure 3(e). The subsequent steps S205 to S209 will be explained based on the structure shown in Figure 3(e).

[0108] In step S205, firstly, the first region of the first piezoelectric layer is etched to form a first groove structure, wherein the first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0109] Please refer to Figures 6(a) and 7(a) in conjunction. Figure 7(a) is a top view of the structure shown in Figure 6(a), and Figure 6(a) is a cross-sectional view of the structure shown in Figure 7(a) along line AA'. As shown, in this embodiment, the lower electrode 102a falls within the opening range of the third groove structure formed on the substrate 100 and coincides exactly with the horizontal projection of the resonant region to be formed (the area shown by the dashed line in the figure), that is, the lower electrode 102a precisely defines the range of the resonant region to be formed. Those skilled in the art will understand that in other embodiments, the lower electrode 102a may also completely cover the third groove structure, that is, the edge region of the lower electrode 102a is formed on the substrate 100. In this embodiment, as shown, the first piezoelectric layer 103 is etched to form a first groove structure 103a penetrating the first piezoelectric layer 103. Those skilled in the art will understand that it is a preferred embodiment for the first groove structure 103a to penetrate the first piezoelectric layer 103; in other embodiments, the first groove structure 103a may not penetrate the first piezoelectric layer 103. In this embodiment, as shown in the figure, the first groove structure 103a surrounds a portion of the outer periphery of the resonant region to be formed. Here, "the first groove structure 103a surrounding the portion of the outer periphery of the resonant region to be formed" refers to the horizontal projection (i.e., the projection in the horizontal direction) of the first groove structure 103a surrounding a portion of the horizontal projection of the resonant region to be formed. In other embodiments, the first groove structure 103a may also surround the entire resonant region to be formed, i.e., the horizontal projection of the first groove structure 103a surrounds the entire edge of the horizontal projection of the resonant region to be formed. Furthermore, in this embodiment, as shown in the figure, the edge of the portion of the horizontal projection of the resonant region to be formed that is adjacent to the resonant region to be formed, i.e., the edge surrounded by the horizontal projection of the first groove structure 103a, coincides with the inner edge of the horizontal projection of the first groove structure 103a. For the case where the first groove structure 103a is adjacent to and surrounds the entire resonant region to be formed, the inner edge of the horizontal projection of the first groove structure 103a coincides with the entire edge of the horizontal projection of the resonant region to be formed. The term "coincidentally" here means that the distance difference between them is within the allowable range of process error. Those skilled in the art will understand that it is a preferred embodiment that the first groove structure 103a is located close to the resonant region to be formed. In other embodiments, the first groove structure 103a may also be formed at a position close to the resonant region to be formed.

[0110] It should be noted that (1) in this embodiment, as shown in FIG7(a), the first groove structure 103a is a single groove. In other embodiments, as shown in FIG8(a), the first groove structure 103a may also be composed of multiple first groove units, which are arranged at intervals along the edge of the resonant region to be formed. (2) in this embodiment, as shown in FIG6(a) and FIG7(a), the outer edge of the horizontal projection of the first groove structure 103a coincides with the corresponding edge of the horizontal projection of the opening of the third groove structure. Those skilled in the art will understand that this should not be construed as a limitation on the size of the first groove structure 103a. In other embodiments, the outer edge of the horizontal projection of the first groove structure 103a may fall within the horizontal projection of the opening of the third groove structure or be located outside the horizontal projection of the opening of the third groove structure.

[0111] Next, as shown in FIG6(b), the first groove structure 103a is filled with the first sacrificial material 103b. Preferably, the first sacrificial material 103b is the same as the third sacrificial material 101 filled in the third groove structure of the substrate 100, so as to facilitate its removal in one go later. Those skilled in the art will understand that in other embodiments, the first sacrificial material 103b and the third sacrificial material 101 may also be different.

[0112] In step S206, as shown in FIG6(c), a second piezoelectric layer 104 is formed on the upper surface of the structure shown in FIG6(b), the second piezoelectric layer 104 being implemented using an undoped piezoelectric material.

[0113] In step S207, the second region of the second piezoelectric layer is etched to form a second groove structure, wherein the second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0114] Please refer to Figures 6(d) and 7(b) in conjunction. Figure 7(b) is a top view of the structure shown in Figure 6(d), and Figure 6(d) is a cross-sectional view of the structure shown in Figure 7(b) along line AA'. As shown, in this embodiment, the second piezoelectric layer 104 is etched to form a second groove structure 104a penetrating the second piezoelectric layer 104. Those skilled in the art will understand that it is a preferred embodiment for the second groove structure 104a to penetrate the second piezoelectric layer 104; in other embodiments, the second groove structure 104a may not penetrate the second piezoelectric layer 104. In this embodiment, as shown, the second groove structure 104a surrounds a portion of the outer periphery of the resonant region to be formed. Here, the portion of the outer periphery of the resonant region to be formed by the second groove structure 104a refers to the portion of the edge of the horizontal projection of the second groove structure 104a surrounding the horizontal projection of the resonant region to be formed. In other embodiments, the second groove structure 104a may also surround the entire resonant region to be formed, that is, the horizontal projection of the second groove structure 104a surrounds the entire edge of the horizontal projection of the resonant region to be formed. Furthermore, in this embodiment, as shown in the figure, the second groove structure 104a is adjacent to the resonant region to be formed, that is, the edge of the portion surrounded by the horizontal projection of the resonant region to be formed coincides with the inner edge of the horizontal projection of the second groove structure 104a. In the case where the second groove structure 104a is adjacent to and surrounds the entire resonant region to be formed, the inner edge of the horizontal projection of the second groove structure 104a coincides with the entire edge of the horizontal projection of the resonant region to be formed. Those skilled in the art will understand that the second groove structure 104a being adjacent to the resonant region to be formed is a preferred embodiment; in other embodiments, the second groove structure 104a may also be formed close to the resonant region to be formed.

[0115] It should be noted that (1) in this embodiment, as shown in FIG7(b), the second groove structure 104a is a single groove. In other embodiments, as shown in FIG8(b), the second groove structure 104a may also be composed of multiple second groove units, which are arranged at intervals along the edge of the resonant region to be formed. (2) in this embodiment, as shown in FIG6(d) and FIG7(b), the outer edge of the horizontal projection of the second groove structure 104a coincides exactly with the corresponding edge of the horizontal projection of the opening of the third groove structure. Those skilled in the art will understand that this should not be construed as a limitation on the size of the second groove structure 104a. In other embodiments, the outer edge of the horizontal projection of the second groove structure 104a may fall within the horizontal projection of the opening of the third groove structure or be located outside the horizontal projection of the opening of the third groove structure.

[0116] In step S208, as shown in FIG6(e), an upper electrode 105a and a second connection portion connected to the upper electrode 105a are formed on the second piezoelectric layer 104.

[0117] It should be noted that in this embodiment, after forming the second groove structure 104a in step S207, the upper electrode 105a is directly formed on the second piezoelectric layer 104. In other embodiments, after forming the second groove structure 104a in step S207, the second groove structure 104a can be filled with a second sacrificial material (preferably the same as the third sacrificial material 101 and the first sacrificial material 103b) before step S208 is performed to form the upper electrode 105a.

[0118] In step S209, as shown in FIG6(f), the first sacrificial material 103b and the third sacrificial material 101 can be removed, for example, by means of a release hole (not shown). Specifically, when the first sacrificial material 103b and the third sacrificial material 101 are the same, both can be removed at once. After the removal of the third sacrificial material 101, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic wave resonator. After the removal of the first sacrificial material 103b, the space originally occupied by the first sacrificial material 103b (i.e., the space where the first groove structure is located) is released. At this point, the bulk acoustic wave resonator is manufactured, wherein the first groove structure in the first piezoelectric layer constitutes the first acoustic reflection part, and the second groove structure in the second piezoelectric layer constitutes the second acoustic reflection part. It should be noted that if the second groove structure 104a is filled with a second sacrificial material, the second sacrificial material needs to be removed. This second sacrificial material can be removed directly using a corrosive solution. After the second sacrificial material is removed, the space originally occupied by it (i.e., the space where the second groove structure is located) is released.

[0119] In existing bulk acoustic wave (BAW) resonators, the entire piezoelectric layer is continuous. When the BAW resonator is operating, some sound waves in the resonant region leak through the piezoelectric layer into the non-resonant region, resulting in lateral sound wave leakage and affecting the performance of the BAW resonator. In this invention, the first and second piezoelectric layers have groove structures formed near or adjacent to the resonant region. These groove structures can reflect sound waves propagating outward from the resonant region back into the resonant region, thereby reducing lateral sound wave leakage and improving the performance of the BAW resonator.

[0120] For cases where the first groove structure penetrates the first piezoelectric layer and the second groove structure penetrates the second piezoelectric layer, preferably, as shown in Figures 7(a) and 7(b), the horizontal projections of the first groove structure 103a and the second groove structure 104a surround the entire outer periphery of the horizontal projection of the resonant region to be formed. Simultaneously, there is no overlap between the horizontal projections of the first groove structure 103a and the second groove structure 104a. That is, the horizontal projections of the first groove structure 103a and the second groove structure 104a form a ring that completely surrounds the horizontal projection of the resonant region to be formed. The advantage of this design is that, since there is no overlap between the horizontal projections of the first groove structure 103a and the second groove structure 104a, there are no groove structures penetrating the entire piezoelectric structure composed of the first piezoelectric layer 103 and the second piezoelectric layer 104. This effectively reduces lateral acoustic leakage while ensuring the structural stability of the bulk acoustic resonator.

[0121] It should be noted that the layout of the first groove structure 103a and the second groove structure 104a in Figures 7(a) and 7(b) is merely illustrative. Those skilled in the art will understand that the present invention does not limit the specific layout of the first and second groove structures, as long as their horizontal projections do not overlap and surround the entire periphery of the horizontal projection of the resonant region to be formed. Below, a preferred layout of the first and second groove structures is described using the example that the horizontal projection of the resonant region to be formed and the horizontal projection of the lower electrode are polygons of the same shape with corresponding edges. Specifically, the first edge in the horizontal projection of the lower electrode is defined as the edge connecting the lower electrode and the first connecting portion, and the second edge in the horizontal projection of the resonant region to be formed is defined as the first edge in the horizontal projection of the lower electrode. Based on this, the first groove structure is arranged so that its horizontal projection surrounds all edges of the horizontal projection of the resonant region to be formed except for the second edge. Correspondingly, the horizontal projection of the second groove structure surrounds the second edge of the horizontal projection of the resonant region to be formed, thus ensuring that the horizontal projections of the first and second groove structures do not overlap and surround the entire periphery of the horizontal projection of the resonant region to be formed. This arrangement of the first and second groove structures is beneficial to the structural stability of the bulk acoustic wave resonator. Let's take the example of the lower electrode defining the area to be formed (i.e., the horizontal projection of the lower electrode coincides with the horizontal projection of the area to be formed), and the horizontal projection of the area to be formed being a regular hexagon. Referring to Figures 9(a) and 9(b), as shown, the horizontal projection of the first groove structure 103a surrounds the other five sides of the horizontal projection of the area to be formed, excluding the second side. The horizontal projection of the second groove structure 104a surrounds the second side of the horizontal projection of the area to be formed. The horizontal projections of the first groove structure 103a and the second groove structure 104a do not overlap, and their horizontal projections precisely form a regular hexagonal ring that completely surrounds the horizontal projection of the area to be formed.

[0122] Those skilled in the art will understand that the absence of overlap between the horizontal projections of the first and second groove structures, and the fact that the horizontal projections of the first and second groove structures surround the entire outer periphery of the horizontal projection of the resonant region to be formed, is only a preferred embodiment. In other embodiments, the horizontal projections of the first and second groove structures may surround the entire outer periphery of the horizontal projection of the resonant region to be formed, while the horizontal projections of the first and second groove structures partially overlap; or the horizontal projections of the first and second groove structures may only surround a portion of the outer periphery of the horizontal projection of the resonant region to be formed, while the horizontal projections of the first and second groove structures may or may not overlap. This invention does not impose any limitations on these embodiments.

[0123] In another preferred embodiment, after forming the lower electrode and before forming the first piezoelectric layer, a first protrusion structure is formed on the structure obtained after forming the lower electrode. The first protrusion structure is located below a first region where the first piezoelectric layer is to be formed, and the first region is located outside and close to or adjacent to the resonant region to be formed. After forming the first piezoelectric layer and before forming the second piezoelectric layer, a second protrusion structure is formed on the first piezoelectric layer. The second protrusion structure is located below a second region where the second piezoelectric layer is to be formed, and the second region is located outside and close to or adjacent to the resonant region to be formed. After forming the upper electrode, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and the second protrusion structure is removed to form a second air bridge structure in the second region of the second piezoelectric layer. The first air bridge structure constitutes a first acoustic reflection portion, and the second air bridge structure constitutes a second acoustic reflection portion.

[0124] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 10 , Figure 10 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown, the manufacturing method includes:

[0125] In step S301, a substrate is provided;

[0126] In step S302, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0127] In step S303, a lower electrode is formed on the substrate;

[0128] In step S304, a first protrusion structure is formed on the structure obtained after forming the lower electrode. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0129] In step S305, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0130] In step S306, a second protrusion structure is formed on the first piezoelectric layer. The second protrusion structure is located below the second region where the second piezoelectric layer is to be formed. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0131] In step S307, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0132] In step S308, an upper electrode is formed on the second piezoelectric layer;

[0133] In step S309, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, the second protrusion structure is removed to form a second air bridge structure in the second region of the second piezoelectric layer, and the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. The overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0134] Below, we will combine Figures 11(a) to 11(g) The steps S301 to S309 described above will be explained in detail.

[0135] Specifically, steps S301 to S302 can be referred to the aforementioned steps S101 to S102, and will not be repeated here for the sake of brevity. The structure obtained after performing step S302 can be referred to Figure 3(c). The subsequent steps S303 to S309 will be explained based on the structure shown in Figure 3(c).

[0136] In step S303, as shown in FIG11(a), a lower electrode 102a is formed on the structure shown in FIG3(c). In this embodiment, the lower electrode 102a completely covers the third groove structure. In other embodiments, the lower electrode 102a may also fall within the opening range of the third groove structure. For example, in the structure shown in FIG3(d), the lower electrode 102a falls within the opening range of the third groove structure and precisely defines the range of the resonant region to be formed.

[0137] In step S304, as shown in FIG11(b), a first protrusion structure 106 is formed on the structure shown in FIG11(a). The first protrusion structure 106 is located below the first region where the first piezoelectric layer is to be formed, wherein the first region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed. In this embodiment, a sacrificial material (not shown, referred to as the fourth sacrificial material below) is deposited on the structure shown in FIG11(a), and the fourth sacrificial material is patterned to form the first protrusion structure 106 below the first region where the first piezoelectric layer is to be formed. It should be noted that (1) in this embodiment, the first protrusion structure 106 is formed on the lower electrode 102a. In other embodiments, for the case where the lower electrode 102a falls within the opening range of the third groove structure, the first protrusion structure 106 may also be formed on the substrate 100 filled with the third sacrificial material 101. (2) The fourth sacrificial material is preferably the same as the third sacrificial material 101 to facilitate subsequent one-time removal.

[0138] In step S305, as shown in FIG11(c), a first piezoelectric layer 103 is formed on the substrate 100, which covers the upper surface of the structure shown in FIG11(b). The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer.

[0139] In step S306, as shown in FIG11(d), a second protrusion structure 107 is formed on the first piezoelectric layer 103. The second protrusion structure 107 is located below the second region where the second piezoelectric layer is to be formed, wherein the second region is located outside and close to or adjacent to the resonant region to be formed. In this embodiment, a sacrificial material (not shown, hereinafter referred to as the fifth sacrificial material) is deposited on the structure shown in FIG11(c), and the fifth sacrificial material is patterned to form the second protrusion structure 107 below the second region where the second piezoelectric layer is to be formed. The fifth sacrificial material is preferably the same as the third sacrificial material 101 and the fourth sacrificial material to facilitate subsequent one-time removal. It should be noted that the present invention does not limit the specific formation position of the first protrusion structure 106 and the second protrusion structure 107. In a preferred embodiment, the horizontal projection of the first protrusion structure 106 and the horizontal projection of the second protrusion structure 107 surround the entire outer periphery of the horizontal projection of the resonant region to be formed, and there is no overlapping area between the horizontal projection of the first protrusion structure 106 and the horizontal projection of the second protrusion structure 107.

[0140] In step S307, as shown in FIG11(e), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, and the second piezoelectric layer 104 covers the first piezoelectric layer 103 and the second protrusion structure 107. The second piezoelectric layer 104 is implemented using an undoped piezoelectric material.

[0141] In step S308, as shown in FIG11(f), an upper electrode 105a is formed on the second piezoelectric layer 104.

[0142] In step S309, as shown in FIG11(g), the first protrusion structure 106, the second protrusion structure 107, and the third sacrificial material 101 are removed, for example, through a release hole (not shown). After the first protrusion structure 106 is removed, the space originally occupied by it is released to form a first air gap 106a. Correspondingly, a suspended and upwardly protruding first air bridge structure 106b (i.e., the portion of the first piezoelectric layer 103 above the first air gap 106a) is formed in the first region of the first piezoelectric layer 103. After the second protrusion structure 107 is removed, the space originally occupied by it is released to form a second air gap 107a. Correspondingly, a suspended and upwardly protruding second air bridge structure 107b (i.e., the portion of the second piezoelectric layer 104 above the second air gap 107a) is formed in the second region of the second piezoelectric layer 104. After the third sacrificial material 101 is removed, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic wave resonator. The bulk acoustic wave resonator is now manufactured. The first air bridge structure 106b in the first piezoelectric layer 103 constitutes the first acoustic reflection part, and the second air bridge structure 107b in the second piezoelectric layer 104 constitutes the second acoustic reflection part.

[0143] The air bridge structure formed in the first and second piezoelectric layers, close to or adjacent to the resonant region, can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0144] In another preferred embodiment, the step of forming the acoustic reflection structure includes: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; the step of forming the lower electrode includes: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below a first region to be formed of the first piezoelectric layer is not covered by the lower electrode, the first region being located outside and close to or adjacent to the resonant region to be formed; the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: after forming the lower electrode and before forming the upper electrode, the lower electrode is formed by etching the substrate to form a third groove structure and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; the step of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer includes ...; and the step of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer. Before forming the first piezoelectric layer, the portion of the third sacrificial material located below the first region where the first piezoelectric layer is to be formed is etched to form a fourth groove structure; after forming the first piezoelectric layer and before forming the second piezoelectric layer, a second protrusion structure is formed on the first piezoelectric layer, the second protrusion structure being located below the second region where the second piezoelectric layer is to be formed, the second region being located outside and close to or adjacent to the resonant region where the resonant region is to be formed; after forming the upper electrode, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and while forming the cavity, a downwardly recessed first air bridge structure is formed in the first region of the first piezoelectric layer; wherein, the first air bridge structure constitutes a first acoustic reflection portion, and the second air bridge structure constitutes a second acoustic reflection portion.

[0145] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 12 , Figure 12 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown in the figure, the manufacturing method includes:

[0146] In step S401, a substrate is provided;

[0147] In step S402, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0148] In step S403, a lower electrode metal material is deposited on the substrate and patterned to form a lower electrode. The portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is not covered by the lower electrode. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0149] In step S404, the portion of the third sacrificial material located below the first region where the first piezoelectric layer is to be formed is etched to form a fourth groove structure;

[0150] In step S405, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0151] In step S406, a second protrusion structure is formed on the first piezoelectric layer. The second protrusion structure is located below the second region where the second piezoelectric layer is to be formed. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0152] In step S407, a second piezoelectric layer is formed on the first piezoelectric layer, the second piezoelectric layer being implemented using an undoped piezoelectric material;

[0153] In step S408, an upper electrode is formed on the second piezoelectric layer;

[0154] In step S409, the second protrusion structure is removed to form a second air bridge structure in the second region of the second piezoelectric layer, the third sacrificial material is removed to form a cavity between the stacked structure and the substrate, and a downwardly recessed first air bridge structure is formed in the first region of the first piezoelectric layer. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0155] Below, we will combine Figures 13(a) to 13(g) The steps S401 to S409 described above will be explained in detail.

[0156] Specifically, steps S401 to S402 can be referred to the aforementioned steps S101 to S102, and will not be repeated here for the sake of brevity. The structure obtained after performing step S402 can be referred to Figure 3(c). The subsequent steps S403 to S409 will be explained based on the structure shown in Figure 3(c).

[0157] In step S403, as shown in FIG13(a), a lower electrode metal material is deposited on the substrate 100 and patterned to form a lower electrode 102a. In this embodiment, the lower electrode 102a falls within the opening range of the third groove structure formed on the substrate 100 and coincides exactly with the horizontal projection of the resonant region to be formed, that is, the lower electrode 102a precisely defines the range of the resonant region to be formed. The portion of the third sacrificial material 101 located below the first region to be formed of the first piezoelectric layer (the portion circled in the figure) is not covered by the lower electrode. This first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0158] In step S404, as shown in FIG13(b), the portion of the third sacrificial material 101 located below the first region where the first piezoelectric layer is to be formed is etched to form a fourth groove structure 101b. The fourth groove structure 101b may be a whole groove or a plurality of fourth groove units arranged at intervals along the edge of the resonant region to be formed.

[0159] In step S405, as shown in FIG13(c), a first piezoelectric layer 103 is formed on the substrate 100, which covers the upper surface of the structure shown in FIG13(b). The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer.

[0160] In step S406, as shown in FIG13(d), a second protrusion structure 107 is formed on the first piezoelectric layer 103. The second protrusion structure 107 is located below the second region where the second piezoelectric layer is to be formed. The second region is located outside and close to or adjacent to the resonant region to be formed. The material of the second protrusion structure 107 is preferably the same as the third sacrificial material 101. It should be noted that the present invention does not limit the specific formation position of the fourth groove structure 101b and the second protrusion structure 107. In a preferred embodiment, the horizontal projection of the fourth groove structure and the horizontal projection of the second protrusion structure 107 surround the entire outer periphery of the horizontal projection of the resonant region to be formed, and there is no overlapping area between the horizontal projection of the fourth groove structure and the horizontal projection of the second protrusion structure 107.

[0161] In step S407, as shown in FIG13(e), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, and the second piezoelectric layer 104 covers the first piezoelectric layer 103 and the second protrusion structure 107. The second piezoelectric layer 104 is implemented using an undoped piezoelectric material.

[0162] In step S408, as shown in FIG13(f), an upper electrode 105a is formed on the second piezoelectric layer 104.

[0163] In step S409, as shown in FIG13(g), the second protrusion structure 107 and the third sacrificial material 101 are removed by means of, for example, a release hole (not shown). After the removal of the second protrusion structure 107, the space originally occupied by the second protrusion structure 107 is released to form a second air gap 107a. Correspondingly, a suspended and upwardly protruding second air bridge structure 107b (i.e., the portion of the second piezoelectric layer 104 located above the second air gap 107a) is formed in the second region of the second piezoelectric layer 104. After the removal of the third sacrificial material 101, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic resonator. Furthermore, while removing the third sacrificial material 101 to form the cavity 101a, a suspended and downwardly recessed first air bridge structure 106b is formed in the first region of the first piezoelectric layer 103, and the first air bridge 106b is located in the cavity 101a. At this point, the bulk acoustic resonator is manufactured, wherein the first air bridge structure 106b in the first piezoelectric layer 103 constitutes the first acoustic reflection part, and the second air bridge structure 107b in the second piezoelectric layer 104 constitutes the second acoustic reflection part.

[0164] The air bridge structure formed in the first and second piezoelectric layers, close to or adjacent to the resonant region, can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0165] In another specific embodiment, the steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer, forming a first protrusion structure and a second protrusion structure on the structure obtained after forming the lower electrode, wherein the first protrusion structure is located below the first region where the first piezoelectric layer is to be formed, and the second protrusion structure is located below the second region where the second piezoelectric layer is to be formed, wherein both the first region and the second region are located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projections of the first region and the horizontal projections of the second region; after forming the first piezoelectric layer and before forming the second piezoelectric layer... Previously, the portion of the first piezoelectric layer above the second protrusion structure was etched to form a first groove structure penetrating the first piezoelectric layer; after the second piezoelectric layer was formed and before the upper electrode was formed, the portion of the second piezoelectric layer above the first protrusion structure was etched to form a second groove structure penetrating the second piezoelectric layer; and after the upper electrode was formed, the first protrusion structure was removed to form an upwardly protruding first air bridge structure in a first region of the first piezoelectric layer, and an upwardly protruding second air bridge structure in a second region of the second piezoelectric layer; wherein the first groove structure and the first air bridge structure together constitute a first acoustic reflector, and the second groove structure and the second air bridge structure together constitute a second acoustic reflector.

[0166] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 14 , Figure 14 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown in the figure, the manufacturing method includes:

[0167] In step S501, a substrate is provided;

[0168] In step S502, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0169] In step S503, a lower electrode is formed on the substrate;

[0170] In step S504, a first protrusion structure and a second protrusion structure are formed on the structure obtained after forming the lower electrode. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed, and the second protrusion structure is located below the second region where the second piezoelectric layer is to be formed. The first region and the second region are both located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projection of the first region and the horizontal projection of the second region.

[0171] In step S505, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0172] In step S506, the portion of the first piezoelectric layer located above the second protrusion structure is etched to form a first groove structure penetrating the first piezoelectric layer.

[0173] In step S507, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0174] In step S508, the portion of the second piezoelectric layer located above the first protrusion structure is etched to form a second groove structure penetrating the second piezoelectric layer;

[0175] In step S509, an upper electrode is formed on the second piezoelectric layer;

[0176] In step S510, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. The overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0177] Below, we will combine Figures 15(a) to 15(g) The steps S501 to S510 described above will be explained in detail.

[0178] Specifically, steps S501 to S503 can be referred to the aforementioned steps S101 to S103, and will not be repeated here for the sake of brevity. The structure obtained after performing step S503 can be referred to Figure 3(d). The subsequent steps S504 to S510 will be explained based on the structure shown in Figure 3(d).

[0179] In step S504, as shown in FIG15(a), a first protrusion structure 106 and a second protrusion structure 107 are formed on the structure shown in FIG3(d). The first protrusion structure 106 is located below the first region where the first piezoelectric layer 103 is to be formed, and the second protrusion structure 107 is located below the second region where the second piezoelectric layer 104 is to be formed. The first region and the second region are both located outside the resonant region to be formed and are close to or adjacent to the resonant region to be formed. In addition, there is no overlap between the horizontal projection of the first region and the horizontal projection of the second region. The simultaneous formation of the first protrusion structure 106 and the second protrusion structure 107 is beneficial to the simplification of the manufacturing process. It should be noted that (1) in this embodiment, the first protrusion structure 106 and the second protrusion structure 107 are formed on the substrate 100 filled with the third sacrificial material 101. In other embodiments, for the case where the lower electrode 102a completely covers the third groove structure, the first protrusion structure 106 and the second protrusion structure 107 may also be formed on the lower electrode 102a. (2) The present invention does not limit the specific formation position of the first protrusion structure 106 and the second protrusion structure 107. In a preferred embodiment, the horizontal projection of the first protrusion structure 106 and the horizontal projection of the second protrusion structure 107 surround the entire outer periphery of the horizontal projection of the resonant region to be formed. (3) The materials of the first protrusion structure 106 and the second protrusion structure 107 are preferably the same as the third sacrificial material 101.

[0180] In step S505, as shown in FIG15(b), a first piezoelectric layer 103 is formed on the substrate 100, which covers the upper surface of the structure shown in FIG15(a). The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer.

[0181] In step S506, as shown in FIG15(c), the portion of the first piezoelectric layer 103 located above the second protrusion structure 107 is etched to form a first groove structure 103a penetrating the first piezoelectric layer 103.

[0182] In step S507, as shown in FIG15(d), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, and the second piezoelectric layer 104 covers the first piezoelectric layer 103 and the second protrusion structure 107. The second piezoelectric layer 104 is implemented using an undoped piezoelectric material.

[0183] In step S508, as shown in FIG15(e), the portion of the second piezoelectric layer 104 located above the first protrusion structure 106 is etched to form a second groove structure 104a penetrating the second piezoelectric layer 104.

[0184] In step S509, as shown in FIG15(f), an upper electrode 105a is formed on the second piezoelectric layer 104.

[0185] In step S510, as shown in FIG15(g), the first protrusion structure 106, the second protrusion structure 107, and the third sacrificial material 101 are removed, for example, through a release hole (not shown). After the first protrusion structure 106 is removed, the space originally occupied by it is released to form a first air gap 106a. Correspondingly, a suspended and upwardly protruding first air bridge structure 106b (i.e., the portion of the first piezoelectric layer 103 above the first air gap 106a) is formed in the first region of the first piezoelectric layer 103. After the second protrusion structure 107 is removed, the space originally occupied by it is released to form a second air gap 107a. Correspondingly, a suspended and upwardly protruding second air bridge structure 107b (i.e., the portion of the second piezoelectric layer 104 above the second air gap 107a) is formed in the second region of the second piezoelectric layer 104. After the third sacrificial material 101 is removed, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic wave resonator. The bulk acoustic wave resonator is now manufactured. The first groove structure and the first air bridge structure 106b in the first piezoelectric layer 103 together constitute the first acoustic reflection part, and the second groove structure 104a and the second air bridge structure 107b in the second piezoelectric layer 104 together constitute the second acoustic reflection part.

[0186] Both the first and second piezoelectric layers have groove structures and air bridge structures formed near or adjacent to the resonant region. These groove structures and air bridge structures can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0187] In another specific embodiment, the steps of forming the acoustic reflection structure include: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; the steps of forming the lower electrode include: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is not covered by the lower electrode, the first region being located outside and close to or adjacent to the resonant region to be formed; the steps of forming a first acoustic reflection portion in the first piezoelectric layer and forming a second acoustic reflection portion in the second piezoelectric layer include: etching the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer to form a fourth groove structure after forming the lower electrode and before forming the first piezoelectric layer; etching a third region of the first piezoelectric layer to form a first groove structure after forming the first piezoelectric layer and before forming the second piezoelectric layer, the third region being located outside and close to or adjacent to the resonant region to be formed. A resonant region is to be formed, wherein the horizontal projection of the third region does not overlap with the horizontal projection of the first region; and the first groove structure is filled with a first sacrificial material; a second protrusion structure is formed on the structure obtained by filling the first groove structure, the second protrusion structure being located below the second region where the second piezoelectric layer is to be formed, the second region being located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed; after forming the second piezoelectric layer and before forming the upper electrode, the fourth region of the second piezoelectric layer is etched to form a second groove structure, the fourth region being located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed, the horizontal projection of the fourth region and the horizontal projection of the second region not overlapping; after forming the upper electrode, the first sacrificial material is removed, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and a downwardly recessed first air bridge structure is formed in the first piezoelectric layer while forming the cavity; wherein the first groove structure and the first air bridge structure together constitute the first acoustic reflection part, and the second groove structure and the second air bridge structure together constitute the second acoustic reflection part.

[0188] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 16 , Figure 16 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown in the figure, the manufacturing method includes:

[0189] In step S601, a substrate is provided;

[0190] In step S602, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0191] In step S603, a lower electrode metal material is deposited on the substrate and patterned to form a lower electrode. The portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is not covered by the lower electrode. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0192] In step S604, the portion of the third sacrificial material located below the first region where the first piezoelectric layer is to be formed is etched to form a fourth groove structure;

[0193] In step S605, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0194] In step S606, the third region of the first piezoelectric layer is etched to form a first groove structure. The third region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed. There is no overlap between the horizontal projection of the third region and the horizontal projection of the first region. The first groove structure is filled with a first sacrificial material.

[0195] In step S607, a second protrusion structure is formed on the structure obtained by filling the first groove structure. The second protrusion structure is located below the second region where the second piezoelectric layer is to be formed. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0196] In step S608, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is implemented using an undoped piezoelectric material;

[0197] In step S609, the fourth region of the second piezoelectric layer is etched to form a second groove structure. The fourth region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed. There is no overlap between the horizontal projection of the fourth region and the horizontal projection of the second region.

[0198] In step S610, an upper electrode is formed on the second piezoelectric layer;

[0199] In step S611, the first sacrificial material is removed, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, the third sacrificial material is removed to form a cavity between the stacked structure and the substrate, and a downwardly recessed first air bridge structure is formed in the first region of the first piezoelectric layer. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer and the upper electrode in the device thickness direction. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0200] Below, we will combine Figures 17(a) to 17(g) The steps S601 to S611 above will be described in detail.

[0201] Specifically, steps S601 to S605 can be referred to the aforementioned steps S401 to S405, and will not be repeated here for the sake of brevity. The structure obtained after performing step S605 can be referred to Figure 13(c). The subsequent steps S606 to S611 will be explained based on the structure shown in Figure 13(c).

[0202] In step S606, firstly, as shown in FIG17(a), the third region of the first piezoelectric layer 103 is etched to form a first groove structure 103a. This third region is located outside and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projection of the third region and the horizontal projection of the first region. Next, as shown in FIG17(b), the first groove structure is filled using the first sacrificial material 103b.

[0203] It should be noted that: (1) In this embodiment, the first groove structure 103a penetrates the first piezoelectric layer 103. In other embodiments, the first groove structure 103a may not penetrate the first piezoelectric layer 103; (2) In this embodiment, the horizontal projections of both the first region and the third region surround the entire outer periphery of the horizontal projection of the resonant region to be formed. In other embodiments, the horizontal projections of both the first region and the third region may only surround a portion of the outer periphery of the horizontal projection of the resonant region to be formed.

[0204] In step S607, as shown in FIG17(c), a second protrusion structure 107 is formed on the structure obtained by filling the first groove structure (i.e., on the structure shown in FIG17(b)). The second protrusion structure 107 is located below the second region of the second piezoelectric layer to be formed, and the second region is located outside and close to or adjacent to the resonant region to be formed. In this embodiment, the horizontal projections of the second region of the second piezoelectric layer and the third region of the first piezoelectric layer coincide exactly, so the second protrusion structure 107 is formed exactly on the first sacrificial material 103b. Those skilled in the art will understand that the horizontal projection of the second region of the second piezoelectric layer may not coincide with or may partially coincide with the horizontal projection of the third region of the first piezoelectric layer (i.e., the second protrusion structure 107 may also be formed on the first piezoelectric layer 103, or partially formed on the first sacrificial material 103b and the remainder formed on the first piezoelectric layer 103).

[0205] In step S608, as shown in FIG17(d), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, and the second piezoelectric layer 104 covers the first piezoelectric layer 103 and the second protrusion structure 107. The second piezoelectric layer 104 is implemented using an undoped piezoelectric material.

[0206] In step S609, as shown in FIG17(e), the fourth region of the second piezoelectric layer 104 is etched to form a second groove structure 104a. The fourth region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed. There is no overlap between the horizontal projection of the fourth region and the horizontal projection of the second region.

[0207] It should be noted that: (1) In this embodiment, the second groove structure 104a penetrates the second piezoelectric layer 104. In other embodiments, the second groove structure 104a may not penetrate the second piezoelectric layer 104; (2) In this embodiment, the horizontal projections of both the fourth region and the second region surround the entire outer periphery of the horizontal projection of the resonant region to be formed. In other embodiments, the horizontal projections of both the fourth region and the second region may only surround a portion of the outer periphery of the horizontal projection of the resonant region to be formed; (3) Preferably, the materials of the first sacrificial material 103b, the third sacrificial material 101, and the second protrusion structure 107 are the same; (4) In other embodiments, the second groove structure 104a may also be filled with the second sacrificial material (preferably the same as the materials of the first sacrificial material 103b, the third sacrificial material 101, and the second protrusion structure 107).

[0208] In step S610, as shown in FIG17(f), an upper electrode 105a is formed on the second piezoelectric layer 103.

[0209] In step S611, as shown in FIG17(g), the first sacrificial material 103b, the third sacrificial material 101, and the second protrusion structure 107 are removed by means of, for example, a release hole (not shown).

[0210] After the first sacrificial material 103b is removed, the space originally occupied by the first sacrificial material 103b (i.e., the space where the first groove structure is located) is released. After the second protrusion structure 107 is removed, the space originally occupied by the second protrusion structure 107 is released to form the second air gap 107a. Correspondingly, a suspended and upwardly protruding second air bridge structure 107b (i.e., the part of the second piezoelectric layer 104 located above the second air gap 107a) is formed in the second region of the second piezoelectric layer 104. After the third sacrificial material 101 is removed, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic resonator. Furthermore, while removing the third sacrificial material 101 to form the cavity 101a, a suspended and downwardly recessed first air bridge structure 106b is formed in the first region of the first piezoelectric layer 103, and the first air bridge 106b is located in the cavity 101a. At this point, the bulk acoustic resonator is manufactured. The first air bridge structure 106b and the first groove structure 103a in the first piezoelectric layer 103 together constitute the first acoustic reflection part, and the second air bridge structure 107b and the second groove structure 104a in the second piezoelectric layer 104 together constitute the second acoustic reflection part. It should be noted that if the second groove structure 104a is filled with the second sacrificial material, the second sacrificial material needs to be removed. The second sacrificial material can be directly removed using an etching solution. After the second sacrificial material is removed, the space originally occupied by the second sacrificial material (i.e., the space where the second groove structure is located) is released.

[0211] Both the first and second piezoelectric layers have groove structures and air bridge structures formed near or adjacent to the resonant region. These groove structures and air bridge structures can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0212] In another specific embodiment, the steps of forming a first acoustic reflector in a first piezoelectric layer and a second acoustic reflector in a second piezoelectric layer include: after forming a lower electrode and before forming the first piezoelectric layer, forming a first protrusion structure on the structure obtained after forming the lower electrode, the first protrusion structure being located below a first region where the first piezoelectric layer is to be formed, the first region being located outside and close to or adjacent to the resonant region to be formed; after forming the second piezoelectric layer and before forming the upper electrode, etching a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and after forming the upper electrode, removing the first protrusion structure to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer; wherein the portions of the first air bridge structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflector, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflector.

[0213] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 18 , Figure 18 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown in the figure, the manufacturing method includes:

[0214] In step S701, a substrate is provided;

[0215] In step S702, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0216] In step S703, a lower electrode is formed on the substrate;

[0217] In step S704, a first protrusion structure is formed on the structure obtained after forming the lower electrode. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0218] In step S705, a first piezoelectric layer is formed on the substrate. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements for improving the electromechanical coupling coefficient of the first piezoelectric layer.

[0219] In step S706, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0220] In step S707, the second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer is etched to form a second groove structure. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0221] In step S708, an upper electrode is formed on the second piezoelectric layer;

[0222] In step S709, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. The overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0223] Below, we will combine Figures 19(a) to 19(f) The steps S701 to S709 described above will be explained in detail.

[0224] Specifically, steps S701 to S703 can be referred to the aforementioned steps S101 to S103, and will not be repeated here for the sake of brevity. The structure obtained after performing step S703 can be referred to Figure 3(d). The subsequent steps S704 to S709 will be explained based on the structure shown in Figure 3(d).

[0225] In step S704, as shown in FIG19(a), a first protrusion structure 106 is formed on the structure obtained by forming the lower electrode 103a (i.e., the structure shown in FIG3(d)). The first protrusion structure 106 is located below the first region where the first piezoelectric layer is to be formed. The first region is located outside and close to or adjacent to the resonant region to be formed. The material of the first protrusion structure 106 is preferably the same as the third sacrificial material 101.

[0226] In step S705, as shown in FIG19(b), a first piezoelectric layer 103 is formed on the substrate 100, which covers the upper surface of the structure shown in FIG19(a). The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. In this embodiment, the upper surface of the first piezoelectric layer 103 undergoes a planarization operation. Those skilled in the art will understand that in other embodiments, the planarization operation may not be performed.

[0227] In step S706, as shown in FIG19(c), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, the second piezoelectric layer 104 being implemented using an undoped piezoelectric material.

[0228] In step S707, as shown in FIG19(d), the second region of the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103 is etched to form a second groove structure 104a. The second region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed.

[0229] It should be noted that (1) in this embodiment, the second groove structure 104a penetrates the second piezoelectric layer 104 and extends into the first piezoelectric layer 103, but does not penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. In other embodiments, the second groove structure 104a may also be formed only by etching the second piezoelectric layer 104 (it may penetrate the second piezoelectric layer 104 or not), or it may penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. The present invention does not limit this. (2) Preferably, the horizontal projections of the first region and the second region surround the entire outer periphery of the horizontal projection of the resonant region to be formed, and there is no overlapping area between the horizontal projections of the first region and the second region. Those skilled in the art will understand that the horizontal projections of the first region and the second region may also only surround a portion of the outer periphery of the horizontal projection of the resonant region to be formed. (3) In other embodiments, the second groove structure 104a may also be filled with a second sacrificial material (preferably the same material as the third sacrificial material 101 and the first protrusion structure 106).

[0230] In step S708, as shown in FIG19(e), an upper electrode 105a is formed on the second piezoelectric layer 104.

[0231] In step S709, as shown in FIG19(f), the first protrusion structure 106 and the third sacrificial material 101 are removed by means of, for example, a release hole (not shown).

[0232] After the first protrusion structure 106 is removed, the space originally occupied by the first protrusion structure 106 is released to form the first air gap 106a. Correspondingly, a suspended and upwardly protruding first air bridge structure 106b (i.e., the portion of the first piezoelectric layer 103 located above the first air gap 106a) is formed in the first region of the first piezoelectric layer 103. After the third sacrificial material 101 is removed, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping region is the resonant region of the bulk acoustic wave resonator. At this point, the bulk acoustic wave resonator is manufactured. The first air bridge structure 106b and the portion of the second groove structure 104a located in the first piezoelectric layer 103 together constitute the first acoustic reflection part, and the portion of the second groove structure 104a located in the second piezoelectric layer 104 constitutes the second acoustic reflection part. It should be noted that if the second groove structure 104a is filled with a second sacrificial material, the second sacrificial material needs to be removed. This second sacrificial material can be removed directly using a corrosive solution. After the second sacrificial material is removed, the space originally occupied by it (i.e., the space where the second groove structure is located) is released.

[0233] The first piezoelectric layer has a groove structure and an air bridge structure that are close to or adjacent to the resonant region, and the second piezoelectric layer has a groove structure that is close to or adjacent to the resonant region. The groove structure and the air bridge structure can provide acoustic impedance mismatch, which is beneficial to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0234] In another specific embodiment, the steps of forming a first acoustic reflection portion in a first piezoelectric layer and a second acoustic reflection portion in a second piezoelectric layer include: forming a first piezoelectric layer on a substrate after forming a lower electrode and before forming the second piezoelectric layer; etching a first region of the first piezoelectric layer to form a first groove structure penetrating the first piezoelectric layer, the first region being located outside and close to or adjacent to the resonant region to be formed; filling the first groove structure with a first sacrificial material; forming a second piezoelectric layer on the first piezoelectric layer, the second piezoelectric layer and the first piezoelectric layer constituting the first piezoelectric layer; etching a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer after forming the second piezoelectric layer and before forming the upper electrode to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and removing the first sacrificial material after forming the upper electrode; wherein the portions of the first groove structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection portion, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflection portion.

[0235] The following section will continue to use an air-gap type bulk acoustic resonator as an example to describe the steps of the specific embodiment described above in detail. Please refer to... Figure 20 , Figure 20 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to another preferred embodiment of the present invention. As shown in the figure, the manufacturing method includes:

[0236] In step S801, a substrate is provided;

[0237] In step S802, a third groove structure is formed on the substrate and the third groove structure is filled with a third sacrificial material;

[0238] In step S803, a lower electrode is formed on the substrate;

[0239] In step S804, a first piezoelectric layer is formed on a substrate, and a first region of the first piezoelectric layer is etched to form a first groove structure penetrating the first piezoelectric layer. The first region is located outside and close to or adjacent to the resonant region to be formed. The first groove structure is filled with a first sacrificial material. A second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer and the first piezoelectric layer constitute a first piezoelectric layer. Both the first and second piezoelectric layers are implemented using doped piezoelectric materials, which are doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer.

[0240] In step S805, a second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer is made of an undoped piezoelectric material;

[0241] In step S806, the second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer is etched to form a second groove structure. The second region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed.

[0242] In step S807, an upper electrode is formed on the second piezoelectric layer;

[0243] In step S808, the first sacrificial material is removed, and the third sacrificial material is removed to form a cavity between the stacked structure and the substrate. The cavity overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer, and the upper electrode in the device thickness direction. This overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0244] Below, we will combine Figures 21(a) to 21(h) The steps S801 to S807 described above will be explained in detail.

[0245] Specifically, steps S801 to S803 can be referred to the aforementioned steps S101 to S103, and will not be repeated here for the sake of brevity. The structure obtained after performing step S803 can be referred to Figure 3(d). The subsequent steps S804 to S808 will be explained based on the structure shown in Figure 3(d).

[0246] In step S804, firstly, as shown in FIG21(a), a first piezoelectric layer 103-1 is formed on the substrate 100, which covers the upper surface of the structure shown in FIG3(d). In this embodiment, the upper surface of the first piezoelectric layer 103-1 is planarized. It will be understood by those skilled in the art that in other embodiments, the planarization operation may not be performed. Next, as shown in FIG21(b), a first region of the first piezoelectric layer 103-1 is etched to form a first groove structure 103a penetrating the first piezoelectric layer 103-1, the first region being located outside and close to or adjacent to the resonant region to be formed. Next, as shown in FIG21(c), the first groove structure 103a is filled with a first sacrificial material 103b. Next, as shown in Figure 21(d), a second piezoelectric layer 103-2 is formed on the first piezoelectric layer 103-1, wherein the second piezoelectric layer 103-2 and the first piezoelectric layer 103-1 together constitute the first piezoelectric layer. In this embodiment, both the first piezoelectric layer 103-1 and the second piezoelectric layer 103-2 are made of doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. It should be noted that: (1) the materials of the first piezoelectric layer 103-1 and the second piezoelectric layer 103-2 can be the same or different; (2) the thickness of the first piezoelectric layer 103-1 and the second piezoelectric layer 103-2 can be determined according to the actual design requirements.

[0247] In step S805, as shown in FIG21(e), a second piezoelectric layer 104 is formed on the first piezoelectric layer 103, the second piezoelectric layer 104 being implemented using an undoped piezoelectric material.

[0248] In step S806, firstly, as shown in FIG21(f), the second region of the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103 is etched to form a second groove structure 104a. The second region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed.

[0249] It should be noted that (1) in this embodiment, the second groove structure 104a penetrates the second piezoelectric layer 104 and extends into the first piezoelectric layer 103, but does not penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. In other embodiments, the second groove structure 104a may also be formed only by etching the second piezoelectric layer 104 (it may penetrate the second piezoelectric layer 104 or not), or it may penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. The present invention does not limit this in any way. (2) Preferably, the horizontal projections of the first region and the second region surround the entire outer periphery of the horizontal projection of the resonant region to be formed, and there is no overlapping region or partial overlap between the horizontal projections of the first region and the second region. Those skilled in the art will understand that the horizontal projections of the first region and the second region may also only surround a portion of the outer periphery of the horizontal projection of the resonant region to be formed. In view of the overlap between the horizontal projections of the first region and the second region, it is preferable that the second groove structure 104a and the first groove structure 103a do not penetrate each other, so as to ensure that there is no groove structure that penetrates the entire piezoelectric structure, which is beneficial to ensuring the structural stability of the bulk acoustic resonator. (3) In other embodiments, the second groove structure 104a can also be filled with a second sacrificial material (preferably the same as the third sacrificial material 101 and the first sacrificial material 103b).

[0250] In step S807, as shown in FIG21(g), an upper electrode 105a is formed on the second piezoelectric layer 104.

[0251] In step S808, as shown in FIG21(h), the first sacrificial material 103a and the third sacrificial material 101 are removed by means of, for example, a release hole (not shown).

[0252] After the first sacrificial material 103b is removed, the space originally occupied by the first sacrificial material 103b (i.e., the space where the first groove structure is located) is released. After the third sacrificial material 101 is removed, a cavity 101a is formed between the stacked structure and the substrate 100. This cavity 101a overlaps with the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a in the device thickness direction. This overlapping area is the resonant region of the bulk acoustic wave resonator. The bulk acoustic wave resonator is thus completed. The portion of the first groove structure 103a and the portion of the second groove structure 104a located in the first piezoelectric layer 103 together constitute the first acoustic reflection part, and the portion of the second groove structure 104a located in the second piezoelectric layer 104 constitutes the second acoustic reflection part. It should be noted that if the second groove structure 104a is filled with the second sacrificial material, the second sacrificial material also needs to be removed. The second sacrificial material can be directly removed using an etching solution. After the second sacrificial material is removed, the space originally occupied by the second sacrificial material (i.e., the space where the second groove structure is located) is released.

[0253] Both the first and second piezoelectric layers have groove structures formed near or adjacent to the resonant region. These groove structures can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0254] It should be noted that (1) for cases where the acoustic reflection portion is formed only in the first or second piezoelectric layer, the operation steps for the corresponding layer described above can be referred to, and will not be repeated here for the sake of brevity. (2) The case where the acoustic reflection portion is an air bridge structure that is recessed downward in the cavity also applies to the reverse-etched bulk acoustic resonator. In the manufacturing method of the air gap type bulk acoustic resonator, the third sacrificial material in the third groove structure of the substrate is etched to form the fourth groove structure, and in subsequent steps, the third sacrificial material is removed to form a cavity, and an air bridge structure that is suspended and recessed downward in the cavity is formed in the first piezoelectric layer. As for the manufacturing method of the reverse-etched bulk acoustic resonator, after the lower electrode is formed on the substrate, the substrate is etched to form the fourth groove structure, and after the upper electrode is formed, the back side of the substrate is etched to form an opening that penetrates the substrate, and an air bridge structure that is suspended and recessed downward in the opening is formed in the first piezoelectric layer. The same applies to Bragg reflector-type bulk acoustic resonators and reverse-etched bulk acoustic resonators as well as those with grooved or upward-protruding air bridge structures. The main difference between these two and air-gap bulk acoustic resonators in their manufacturing methods lies in the steps for forming the acoustic reflector structure, which will not be elaborated here for the sake of simplicity.

[0255] Accordingly, the present invention also provides a bulk acoustic resonator, which includes:

[0256] Substrate;

[0257] A stacked structure is formed on the substrate and includes, from bottom to top, a lower electrode, a first piezoelectric layer, a second piezoelectric layer and an upper electrode. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material.

[0258] An acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure, and the acoustic reflection structure overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer and the upper electrode in the thickness direction of the device, and the overlapping region constitutes the resonant region of the bulk acoustic resonator.

[0259] The components of the bulk acoustic resonator described above will be explained in detail below with reference to Figure 3(h).

[0260] Specifically, as shown in the figure, the bulk acoustic wave resonator provided by the present invention includes a substrate 100. The material and thickness of the substrate 100 can be referred to the relevant part of the bulk acoustic wave resonator manufacturing method above. For the sake of brevity, it will not be repeated here.

[0261] As shown in the figure, the bulk acoustic wave resonator provided by the present invention further includes a stacked structure formed on a substrate 100, and from bottom to top, includes a lower electrode 102a, a first piezoelectric layer 103, a second piezoelectric layer 104, and an upper electrode 105a. The first piezoelectric layer 103 is implemented using a doped piezoelectric material, which is doped with impurity elements that can improve the electromechanical coupling coefficient of the first piezoelectric layer. The present invention does not limit the impurity elements; any element that can improve the electromechanical coupling coefficient of the piezoelectric material after being doped into it is applicable to the present invention. For example, the impurity elements can be one or any combination of rare earth elements, including but not limited to scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, magnesium, and titanium. In this embodiment, the doped piezoelectric material is scandium-doped aluminum nitride. Those skilled in the art will understand that in other embodiments, the doped piezoelectric material can also be zinc oxide, lithium niobate, lead titanate zirconate, etc., doped with impurity elements, and the present invention does not limit this in any way. Furthermore, for the impurity element being a rare earth element, its doping concentration is preferably in the range of 5%-50%. The second piezoelectric layer 104 is implemented using an undoped piezoelectric material. In this embodiment, the second piezoelectric layer 104 is implemented using undoped aluminum nitride. Those skilled in the art will understand that in other embodiments, the second piezoelectric layer 104 can also be implemented using undoped zinc oxide, lithium niobate, lead titanate zirconate, etc., and for the sake of brevity, they will not be listed here. It should be noted that (1) the materials and thicknesses of the lower electrode 102a and the upper electrode 105a, the thicknesses of the first piezoelectric layer 103 and the second piezoelectric layer 104, etc. can be referred to the relevant parts of the previous description of the bulk acoustic wave resonator manufacturing method. For the sake of brevity, they will not be repeated here; (2) In this embodiment, the bulk acoustic wave resonator also includes a first connection portion formed on the substrate 100 and connected to the lower electrode 102a, and a second connection portion formed on the second piezoelectric layer 104 and connected to the upper electrode 105a. The first connection portion and the second connection portion are both used for signal connection of the bulk acoustic wave resonator.

[0262] The bulk acoustic wave resonator provided by the present invention also includes an acoustic reflection structure. As shown in the figure, in this embodiment, the bulk acoustic wave resonator is an air gap type bulk acoustic wave resonator, and the corresponding acoustic reflection structure is a cavity 101a. The cavity 101a is surrounded by a third groove structure and a stacked structure formed on the surface of the substrate 100. The cavity 101a, the lower electrode 102a, the first piezoelectric layer 103, the second piezoelectric layer 104, and the upper electrode 105a have an overlapping area in the thickness direction of the device. This overlapping area constitutes the resonant region of the bulk acoustic wave resonator. It should be noted that (1) as shown in the figure, in this embodiment, the lower electrode 102a falls within the opening range of the cavity 101a. In other embodiments, the lower electrode 102a can also completely cover the cavity 101a, that is, the edge region of the lower electrode 102a is formed on the substrate 100 and contacts the substrate 100. (2) In other embodiments, the bulk acoustic resonator may also be a Bragg reflection type bulk acoustic resonator, and the corresponding acoustic reflection structure is a Bragg reflection layer formed between the substrate and the stacked structure; or the bulk acoustic resonator may also be a reverse etching type bulk acoustic resonator, and the corresponding acoustic reflection structure is an opening formed on the back side of the substrate and penetrating the substrate.

[0263] The bulk acoustic wave resonator provided by this invention comprises two piezoelectric layers (from bottom to top: a first piezoelectric layer and a second piezoelectric layer). The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material. Compared with existing bulk acoustic wave resonators where the piezoelectric layer is made of only one layer of doped piezoelectric material, the bulk acoustic wave resonator provided by this invention has the advantages of balancing the electromechanical coupling coefficient of the piezoelectric layer and the device quality factor, having small parasitic modes, and balanced stress.

[0264] Preferably, a first acoustic reflector is formed in the first piezoelectric layer, the first acoustic reflector being located outside and close to or adjacent to the resonant region; and / or a second acoustic reflector is formed in the second piezoelectric layer, the second acoustic reflector being located outside and close to or adjacent to the resonant region. In the case where the first acoustic reflector is formed in the first piezoelectric layer, the first acoustic reflector can be a groove structure, an air bridge structure, or a combination of a groove structure and an air bridge structure; similarly, the second acoustic reflector can be a groove structure, an air bridge structure, or a combination of a groove structure and an air bridge structure. Those skilled in the art will understand that the first acoustic reflector and the second acoustic reflector are not limited to the aforementioned groove structure, air bridge structure, and combinations of groove and air bridge structures. Other structures capable of achieving sound wave reflection also fall within the scope of this invention. For the sake of brevity, not all possible structures of the first and second acoustic reflectors will be listed here. An acoustic reflection portion is formed in the first piezoelectric layer and / or the second piezoelectric layer. This acoustic reflection portion can provide acoustic impedance mismatch, which helps to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator.

[0265] The following explanation uses the example of a first acoustic reflector formed in a first piezoelectric layer and a second acoustic reflector formed in a second piezoelectric layer.

[0266] In a preferred embodiment, the first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector. The first acoustic reflector is a first groove structure formed by etching the upper surface of the first piezoelectric layer, and the second acoustic reflector is a second groove structure formed by etching the upper surface of the second piezoelectric layer. The following description uses an air-gap type bulk acoustic resonator as an example, with reference to FIG. 6(f). Those skilled in the art will understand that Bragg reflection type bulk acoustic resonators and reverse-etched type bulk acoustic resonators are also applicable.

[0267] In this embodiment, as shown in the figure, the first groove structure 103a is formed in the first piezoelectric layer 103, specifically located outside and adjacent to the resonant region. In this embodiment, as shown in the figure, the first groove structure 103a penetrates the first piezoelectric layer 103. In other embodiments, the first groove structure 103a may not penetrate the first piezoelectric layer 103. In this embodiment, the first groove structure 103a surrounds a portion of the outer periphery of the resonant region, that is, the horizontal projection of the first groove structure 103a surrounds a portion of the edge of the horizontal projection of the resonant region. In other embodiments, the first groove structure 103a may also surround the entire resonant region. In this embodiment, the first groove structure 103a is adjacent to the resonant region, that is, the edge of the portion of the horizontal projection of the resonant region surrounded by the horizontal projection of the first groove structure 103a coincides with the inner edge of the horizontal projection of the first groove structure 103a. In the case where the first groove structure 103a is adjacent to and surrounds the entire resonant region, the inner edge of the horizontal projection of the first groove structure 103a coincides with the entire edge of the horizontal projection of the resonant region. Those skilled in the art will understand that it is a preferred embodiment that the first groove structure 103a is located adjacent to the resonant region. In other embodiments, the first groove structure 103a may also be formed near the resonant region. Furthermore, in this embodiment, the first groove structure 103a is a single groove. In other embodiments, the first groove structure 103a may also be composed of multiple first groove units, which are arranged at intervals along the edge of the resonant region.

[0268] In this embodiment, as shown in the figure, the second groove structure 104a is formed in the second piezoelectric layer 104, specifically located outside and adjacent to the resonant region. In this embodiment, as shown in the figure, the second groove structure 104a penetrates the second piezoelectric layer 104. In other embodiments, the second groove structure 104a may not penetrate the second piezoelectric layer 104. In this embodiment, the second groove structure 104a surrounds a portion of the outer periphery of the resonant region, that is, the horizontal projection of the second groove structure 104a surrounds a portion of the edge of the horizontal projection of the resonant region. In other embodiments, the second groove structure 104a may also surround the entire resonant region. In this embodiment, the second groove structure 104a is adjacent to the resonant region, that is, the edge of the portion of the horizontal projection of the resonant region surrounded by the horizontal projection of the second groove structure 104a coincides with the inner edge of the horizontal projection of the second groove structure 104a. For the case where the second groove structure 104a is adjacent to and surrounds the entire resonant region, the inner edge of the horizontal projection of the second groove structure 104a coincides with the entire edge of the horizontal projection of the resonant region. Those skilled in the art will understand that it is a preferred embodiment that the second groove structure 104a is located adjacent to the resonant region. In other embodiments, the second groove structure 104a may also be formed near the resonant region. Furthermore, in this embodiment, the second groove structure 104a is a single groove. In other embodiments, the second groove structure 104a may also be composed of multiple second groove units, which are arranged at intervals along the edge of the resonant region.

[0269] The first and second piezoelectric layers have groove structures formed near or adjacent to the resonant region. These groove structures can reflect sound waves propagating outward from the resonant region back into the resonant region, thereby reducing the lateral leakage of sound waves and improving the performance of the bulk acoustic resonator.

[0270] For cases where the first groove structure penetrates the first piezoelectric layer and the second groove structure penetrates the second piezoelectric layer, preferably, the horizontal projections of the first and second groove structures surround the entire outer periphery of the horizontal projection of the resonant region, while there is no overlapping area between the horizontal projections of the first and second groove structures. That is, the horizontal projections of the first and second groove structures form a ring that completely surrounds the horizontal projection of the resonant region. The advantage of this design is that it effectively reduces lateral acoustic leakage while ensuring the structural stability of the bulk acoustic resonator. Those skilled in the art will understand that the present invention does not limit the specific layout of the first and second groove structures, as long as their horizontal projections do not overlap and surround the entire outer periphery of the horizontal projection of the resonant region. Below, a preferred layout of the first and second groove structures is described using the example of the horizontal projections of the resonant region and the lower electrode being polygons of the same shape with corresponding sides. Specifically, the first side in the horizontal projection of the lower electrode is defined as the side that forms a connection between the lower electrode and the first connecting part, and the second side in the horizontal projection of the resonant region is defined as the first side in the horizontal projection of the lower electrode. Based on this, the first groove structure is arranged so that its horizontal projection surrounds the other sides in the horizontal projection of the resonant region except for the second side. Correspondingly, the horizontal projection of the second groove structure surrounds the second side in the horizontal projection of the resonant region, so that the horizontal projections of the first groove structure and the second groove structure do not overlap and surround the entire outer periphery of the horizontal projection of the resonant region.

[0271] In another preferred embodiment, as shown in FIG11(g), the first acoustic reflector is a first air bridge structure 106b that protrudes upward and is suspended in the first piezoelectric layer 103, and the second acoustic reflector is a second air bridge structure 107b that protrudes upward and is suspended in the second piezoelectric layer 104. It should be noted that the present invention does not limit the specific formation positions of the first air bridge structure 106b and the second air bridge structure 107b. Preferably, the horizontal projections of the first air bridge structure 106b and the second air bridge structure 107b surround the entire outer periphery of the horizontal projection of the resonant region, and there is no overlapping area between the horizontal projections of the first air bridge structure 106b and the second air bridge structure 107b. The air bridge structures formed in the first and second piezoelectric layers near or adjacent to the resonant region can provide acoustic impedance mismatch, which is beneficial for reducing the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. Furthermore, those skilled in the art will understand that the structure shown in Figure 11(g) is an air gap type bulk acoustic resonator, but the Bragg reflection type bulk acoustic resonator and the reverse etching type bulk acoustic resonator are also applicable.

[0272] In another preferred embodiment, as shown in FIG13(g), the acoustic reflection structure is a cavity 101a formed by a third groove structure and a stacked structure formed on the substrate 100; the first acoustic reflection part is a first air bridge structure 106b formed in the cavity 101a, recessed downward and suspended, and the second acoustic reflection part is a second air bridge structure 107b formed in the second piezoelectric layer 104, protruding upward and suspended. It should be noted that the present invention does not limit the specific formation position of the first air bridge structure 106b and the second air bridge structure 107b. Preferably, the horizontal projection of the first air bridge structure 106b and the horizontal projection of the second air bridge structure 107b surround the entire outer periphery of the horizontal projection of the resonant region, and there is no overlapping area between the horizontal projection of the first air bridge structure 106b and the horizontal projection of the second air bridge structure 107b. The air bridge structures formed in the first piezoelectric layer and the second piezoelectric layer that are close to or adjacent to the resonant region can provide acoustic impedance mismatch, which is beneficial to reducing the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. Furthermore, those skilled in the art will understand that the structure shown in Figure 13(g) is an air gap type bulk acoustic resonator, but the reverse etched type bulk acoustic resonator is also applicable.

[0273] In another preferred embodiment, as shown in FIG15(g), the first acoustic reflector includes a first groove structure formed in the first piezoelectric layer 103 and an upwardly protruding and suspended first air bridge structure 106b, and the second acoustic reflector includes a second groove structure 104a formed in the second piezoelectric layer 104 and an upwardly protruding and suspended second air bridge structure 107b. It should be noted that (1) in this embodiment, the horizontal projections of the second air bridge structure 107b and the first groove structure coincide exactly, and the horizontal projections of the first air bridge structure 106b and the second groove structure coincide exactly. In other embodiments, they may not coincide. (2) The present invention does not limit the specific formation position of the first air bridge structure 106b and the first groove structure 103a, preferably their horizontal projections surround the entire outer periphery of the horizontal projection of the resonant region (or only surround a portion of the outer periphery of the horizontal projection of the resonant region). Similarly, the present invention does not limit the specific formation positions of the second air bridge structure 107b and the second groove structure 104a. Preferably, their horizontal projections surround the entire outer periphery of the horizontal projection of the resonant region (or only a portion of the outer periphery of the horizontal projection of the resonant region). The groove structure and air bridge structure formed in the first piezoelectric layer and the second piezoelectric layer, close to or adjacent to the resonant region, can provide acoustic impedance mismatch, which is beneficial to reducing the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. Furthermore, those skilled in the art will understand that the structure shown in FIG15(g) is an air gap type bulk acoustic resonator, but Bragg reflection type bulk acoustic resonators and reverse etching type bulk acoustic resonators are also applicable.

[0274] In another preferred embodiment, as shown in FIG17(g), the acoustic reflection structure is a cavity 101a formed by a third groove structure and a stacked structure formed on the substrate 100; the first acoustic reflection part includes a first groove structure 103a formed in the first piezoelectric layer 103 and a first air bridge structure 106b formed in the cavity 101a that is recessed downward and suspended; the second acoustic reflection part includes a second groove structure 104a formed in the second piezoelectric layer 104 and a second air bridge structure 107b that is protruding upward and suspended. It should be noted that the present invention does not limit the specific formation position of the first air bridge structure 106b and the first groove structure 103a, preferably their horizontal projections surround the entire outer periphery of the horizontal projection of the resonant region (or they may only surround a portion of the outer periphery of the horizontal projection of the resonant region). Similarly, the present invention does not limit the specific formation position of the second air bridge structure 107b and the second groove structure 104a, preferably their horizontal projections surround the entire outer periphery of the horizontal projection of the resonant region (or they may only surround a portion of the outer periphery of the horizontal projection of the resonant region). The groove and air bridge structures formed in the first and second piezoelectric layers, close to or adjacent to the resonant region, can provide acoustic impedance mismatch, which helps reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. Furthermore, those skilled in the art will understand that while the structure shown in Figure 17(g) is an air-gap type bulk acoustic resonator, the reverse-etched type bulk acoustic resonator is equally applicable.

[0275] In another preferred embodiment, as shown in FIG19(f), a first air bridge structure 106b protruding upward and suspended is formed in the first piezoelectric layer 103, and a second groove structure 104a is formed in the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. The portions of the first air bridge structure 106b and the second groove structure 104a located in the first piezoelectric layer 103 together constitute the first sound reflection part, and the portion of the second groove structure 104a located in the second piezoelectric layer 104 constitutes the second sound reflection part. It should be noted that (1) in this embodiment, the second groove structure 104a penetrates the second piezoelectric layer 104 and extends into the first piezoelectric layer 103, but does not penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. In other embodiments, the second groove structure 104a may be formed only in the second piezoelectric layer 104 (it may penetrate the second piezoelectric layer 104 or not), or it may penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer 103. (2) Preferably, the horizontal projections of the first air bridge structure 106b and the second groove structure 104a surround the entire outer periphery of the horizontal projection of the resonant region. The groove structure and air bridge structure formed in the first piezoelectric layer and the second piezoelectric layer that are close to or adjacent to the resonant region can provide acoustic impedance mismatch, which is beneficial to reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. In addition, those skilled in the art will understand that the structure shown in FIG19(f) is an air gap type bulk acoustic resonator, but the Bragg reflection type bulk acoustic resonator and the reverse etching type bulk acoustic resonator are also applicable.

[0276] In another preferred embodiment, as shown in FIG21(h), the first piezoelectric layer comprises, from bottom to top, a first piezoelectric layer 103-1 and a second piezoelectric layer 103-2. A first groove structure 103a is formed in the first piezoelectric layer 103-1, penetrating the first piezoelectric layer 103-1. A second groove structure 104a is formed in the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer. The portions of the first groove structure 103a and the second groove structure 104a located in the first piezoelectric layer together constitute a first acoustic reflection portion. The portion of the second groove structure 104a located in the second piezoelectric layer 104 constitutes a second acoustic reflection portion. It should be noted that, (1) in this embodiment, the second groove structure 104a penetrates the second piezoelectric layer 104 and extends into the first piezoelectric layer, but does not penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer. In other embodiments, the second groove structure 104a may be formed only in the second piezoelectric layer 104 (it may penetrate the second piezoelectric layer 104 or not), or it may penetrate the structure formed by the second piezoelectric layer 104 and the first piezoelectric layer. (2) Preferably, the horizontal projections of the first groove structure 103a and the second groove structure 104a surround the entire outer periphery of the horizontal projection of the resonant region, and there is no overlapping area or partial overlap between the horizontal projections of the first groove structure 103a and the second groove structure 104a. Those skilled in the art will understand that the horizontal projections of the first groove structure 103a and the second groove structure 104a may also only surround a portion of the outer periphery of the horizontal projection of the resonant region. In the case where there is an overlap between the horizontal projections of the first groove structure 103a and the second groove structure 104a, it is preferable that the second groove structure 104a and the first groove structure 103a do not penetrate, so as to ensure that there is no groove structure that penetrates the entire piezoelectric structure, which is beneficial to ensuring the structural stability of the bulk acoustic resonator. The groove structure formed in the first and second piezoelectric layers, close to or adjacent to the resonant region, can provide acoustic impedance mismatch, which helps reduce the lateral propagation of sound waves, thereby improving the performance of the bulk acoustic resonator. Furthermore, those skilled in the art will understand that the structure shown in Figure 21(h) is an air-gap type bulk acoustic resonator, but Bragg reflection type bulk acoustic resonators and reverse-etched type bulk acoustic resonators are also applicable.

[0277] Accordingly, the present invention also provides a filter comprising a bulk acoustic wave resonator, wherein the bulk acoustic wave resonator is formed using the aforementioned manufacturing method or implemented using the aforementioned bulk acoustic wave resonator. Considering that the specific structure of the bulk acoustic wave resonator can be referred to the corresponding section above, it will not be repeated here for the sake of brevity. Since the bulk acoustic wave resonator provided by the present invention has the characteristics of balancing electromechanical coupling coefficient and quality factor, low parasitic modes, and stress balance, the filter formed based on this bulk acoustic wave resonator has correspondingly superior performance characteristics.

[0278] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other components, units, or steps, and the singular does not exclude the plural. Multiple components, units, or devices recited in the system claims may also be implemented by a single component, unit, or device in software or hardware.

[0279] The above-disclosed embodiments are merely some preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for manufacturing a bulk acoustic resonator, characterized in that, The manufacturing method includes: The process includes a substrate provision step, an acoustic reflection structure formation step, and a stacked structure formation step, wherein the acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure, and the stacked structure formation step includes: A lower electrode, a first piezoelectric layer, a second piezoelectric layer, and an upper electrode are formed sequentially from bottom to top on the substrate or the acoustic reflection structure. The upper electrode, the second piezoelectric layer, the first piezoelectric layer, the lower electrode, and the acoustic reflection structure have an overlapping region in the thickness direction of the device. This overlapping region constitutes the resonant region of the bulk acoustic resonator. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer; the second piezoelectric layer is made of an undoped piezoelectric material. Wherein, a first acoustic reflector is formed in the first piezoelectric layer, the first acoustic reflector being located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed; and / or A second acoustic reflection portion is formed in the second piezoelectric layer, the second acoustic reflection portion being located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed.

2. The manufacturing method according to claim 1, characterized in that, in, The impurity element is a rare earth element.

3. The manufacturing method according to claim 2, characterized in that, in, The doping concentration of the rare earth element is 5% to 50%.

4. The manufacturing method according to claim 2, characterized in that, in, The doped piezoelectric material is scandium-doped aluminum nitride, and the undoped piezoelectric material is aluminum nitride.

5. The manufacturing method according to claim 1, characterized in that, in, The steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: After the first piezoelectric layer is formed and before the second piezoelectric layer is formed, a first region of the first piezoelectric layer is etched to form a first groove structure, the first region being located outside and close to or adjacent to the resonant region to be formed; and the first groove structure is filled with a first sacrificial material. After the formation of the second piezoelectric layer and before the formation of the upper electrode, a second region of the second piezoelectric layer is etched to form a second groove structure, the second region being located outside and close to or adjacent to the resonant region to be formed; and The first sacrificial material is removed after the upper electrode is formed; The first groove structure constitutes the first acoustic reflection part, and the second groove structure constitutes the second acoustic reflection part.

6. The manufacturing method according to claim 5, characterized in that, in: The first groove structure penetrates the first piezoelectric layer, and the second groove structure penetrates the second piezoelectric layer.

7. The manufacturing method according to claim 5 or 6, characterized in that, in: The first groove structure is either a single groove or multiple first groove units arranged at intervals along the edge of the resonant region to be formed. The second groove structure is either a single groove or multiple second groove units arranged at intervals along the edge of the resonant region to be formed.

8. The manufacturing method according to any one of claims 5 to 6, characterized in that, in: The horizontal projections of the first groove structure and the second groove structure surround the entire outer periphery of the horizontal projection of the resonant region to be formed, wherein there is no overlapping area or partial overlap between the horizontal projections of the first groove structure and the second groove structure.

9. The manufacturing method according to claim 5 or 6, characterized in that, in: The manufacturing method further includes: forming a first connection portion on the substrate that is connected to the lower electrode; The horizontal projection of the resonant region to be formed and the horizontal projection of the lower electrode are polygons with the same shape and corresponding sides. The first side of the horizontal projection of the lower electrode corresponds to the side of the lower electrode that is connected to the first connecting part, and the second side of the horizontal projection of the resonant region to be formed corresponds to the first side. The horizontal projection of the first groove structure surrounds all sides of the horizontal projection of the resonant region to be formed except for the second side, and the horizontal projection of the second groove structure surrounds the second side of the horizontal projection of the resonant region to be formed.

10. The manufacturing method according to claim 5, characterized in that, in, The steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: After the lower electrode is formed and before the first piezoelectric layer is formed, a first protrusion structure is formed on the structure obtained after the lower electrode is formed. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed. After the formation of the first piezoelectric layer and before the formation of the second piezoelectric layer, a second protrusion structure is formed on the first piezoelectric layer. This second protrusion structure is located below a second region where the second piezoelectric layer is to be formed, and this second region is located outside and close to or adjacent to the resonant region to be formed. After the upper electrode is formed, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and the second protrusion structure is removed to form a second air bridge structure in the second region of the second piezoelectric layer. The first air bridge structure constitutes the first sound reflection part, and the second air bridge structure constitutes the second sound reflection part.

11. The manufacturing method according to claim 5, characterized in that, in: The steps for forming the acoustic reflection structure include: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; The step of forming the lower electrode includes: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is not covered by the lower electrode, and the first region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed. The steps of forming a first acoustic reflector in the first piezoelectric layer and a second acoustic reflector in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer, etching the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer to form a fourth groove structure; after forming the first piezoelectric layer and before forming the second piezoelectric layer, forming a second protrusion structure on the first piezoelectric layer, the second protrusion structure being located below the second region to be formed of the second piezoelectric layer, the second region being located outside and close to or adjacent to the resonant region to be formed; after forming the upper electrode, removing the second protrusion structure to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and forming a downwardly recessed first air bridge structure in the first region of the first piezoelectric layer while forming the cavity; wherein the first air bridge structure constitutes the first acoustic reflector and the second air bridge structure constitutes the second acoustic reflector.

12. The manufacturing method according to claim 5, characterized in that, in, The steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: After the lower electrode is formed and before the first piezoelectric layer is formed, a first protrusion structure and a second protrusion structure are formed on the structure obtained after the lower electrode is formed. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed, and the second protrusion structure is located below the second region where the second piezoelectric layer is to be formed. The first region and the second region are both located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed, and there is no overlap between the horizontal projection of the first region and the horizontal projection of the second region. After the first piezoelectric layer is formed and before the second piezoelectric layer is formed, the portion of the first piezoelectric layer located above the second protrusion structure is etched to form a first groove structure penetrating the first piezoelectric layer. After the formation of the second piezoelectric layer and before the formation of the upper electrode, the portion of the second piezoelectric layer located above the first protrusion structure is etched to form a second groove structure penetrating the second piezoelectric layer; and After forming the upper electrode, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer, and the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer; The first groove structure and the first air bridge structure together constitute the first sound reflection part, and the second groove structure and the second air bridge structure together constitute the second sound reflection part.

13. The manufacturing method according to claim 5, characterized in that, in: The steps for forming the acoustic reflection structure include: etching the substrate to form a third groove structure after the substrate provision step and before forming the lower electrode, and filling the third groove structure with a third sacrificial material; and removing the third sacrificial material to form a cavity after forming the upper electrode; The step of forming the lower electrode includes: depositing a lower electrode metal material on the substrate and patterning it to form the lower electrode, wherein the portion of the third sacrificial material located below the first region to be formed of the first piezoelectric layer is not covered by the lower electrode, and the first region is located outside the resonant region to be formed and close to or adjacent to the resonant region to be formed. The steps of forming a first acoustic reflector in the first piezoelectric layer and a second acoustic reflector in the second piezoelectric layer include: after forming the lower electrode and before forming the first piezoelectric layer, etching the portion of the third sacrificial material located below the first region of the first piezoelectric layer to be formed to form a fourth groove structure; after forming the first piezoelectric layer and before forming the second piezoelectric layer, etching a third region of the first piezoelectric layer to form a first groove structure, the third region being located outside and close to or adjacent to the resonant region to be formed, and the horizontal projection of the third region not overlapping with the horizontal projection of the first region; filling the first groove structure with the first sacrificial material; and forming a second protrusion structure on the structure obtained by filling the first groove structure, the second protrusion structure being located below the second region of the second piezoelectric layer to be formed, the second region... Located outside and close to or adjacent to the resonant region to be formed; after forming the second piezoelectric layer and before forming the upper electrode, a fourth region of the second piezoelectric layer is etched to form a second groove structure, the fourth region being located outside and close to or adjacent to the resonant region to be formed, and the horizontal projection of the fourth region and the horizontal projection of the second region not overlapping; after forming the upper electrode, the first sacrificial material is removed, the second protrusion structure is removed to form an upwardly protruding second air bridge structure in the second region of the second piezoelectric layer, and a downwardly recessed first air bridge structure is formed in the first piezoelectric layer while forming the cavity; wherein, the first groove structure and the first air bridge structure together constitute the first acoustic reflection part, and the second groove structure and the second air bridge structure together constitute the second acoustic reflection part.

14. The manufacturing method according to claim 5, characterized in that, in, The steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: After the lower electrode is formed and before the first piezoelectric layer is formed, a first protrusion structure is formed on the structure obtained after the lower electrode is formed. The first protrusion structure is located below the first region where the first piezoelectric layer is to be formed. The first region is located outside the resonant region to be formed and is close to or adjacent to the resonant region to be formed. After the formation of the second piezoelectric layer and before the formation of the top electrode, a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer is etched to form a second groove structure. This second region is located outside and close to or adjacent to the resonant region to be formed. After the upper electrode is formed, the first protrusion structure is removed to form an upwardly protruding first air bridge structure in the first region of the first piezoelectric layer; The first air bridge structure and the portion of the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection part, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflection part.

15. The manufacturing method according to claim 5, characterized in that, in, The steps of forming a first acoustic reflector in the first piezoelectric layer and forming a second acoustic reflector in the second piezoelectric layer include: After the lower electrode is formed and before the second piezoelectric layer is formed, a first piezoelectric layer is formed on the substrate, and a first region of the first piezoelectric layer is etched to form a first groove structure penetrating the first piezoelectric layer. The first region is located outside and close to or adjacent to the resonant region to be formed. The first groove structure is filled with a first sacrificial material. A second piezoelectric layer is formed on the first piezoelectric layer, and the second piezoelectric layer and the first piezoelectric layer constitute the first piezoelectric layer. After the formation of the second piezoelectric layer and before the formation of the top electrode, a second region of the structure formed by the second piezoelectric layer and the first piezoelectric layer is etched to form a second groove structure. This second region is located outside and close to or adjacent to the resonant region to be formed. The first sacrificial material is removed after the upper electrode is formed; The first groove structure and the portion of the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflection part, and the portion of the second groove structure located in the second piezoelectric layer together constitutes the second acoustic reflection part.

16. A bulk acoustic resonator, characterized in that, The bulk acoustic resonator includes: Substrate; A stacked structure is formed on the substrate and includes, from bottom to top, a lower electrode, a first piezoelectric layer, a second piezoelectric layer and an upper electrode. The first piezoelectric layer is made of a doped piezoelectric material, which is doped with impurity elements to improve the electromechanical coupling coefficient of the first piezoelectric layer. The second piezoelectric layer is made of an undoped piezoelectric material. An acoustic reflection structure is formed within the substrate or between the substrate and the stacked structure, and the acoustic reflection structure overlaps with the lower electrode, the first piezoelectric layer, the second piezoelectric layer and the upper electrode in the thickness direction of the device, and the overlapping region constitutes the resonant region of the bulk acoustic resonator. The first piezoelectric layer further includes a first acoustic reflector, which is located outside the resonant region and close to or adjacent to the resonant region; and / or The second piezoelectric layer also includes a second acoustic reflector located outside the resonant region and close to or adjacent to the resonant region.

17. The bulk acoustic resonator according to claim 16, characterized in that, in, The impurity element is a rare earth element.

18. The bulk acoustic resonator according to claim 17, characterized in that, in, The doping concentration of the rare earth element is 5% to 50%.

19. The bulk acoustic resonator according to claim 18, characterized in that, in, The doped piezoelectric material is scandium-doped aluminum nitride, and the undoped piezoelectric material is aluminum nitride.

20. The bulk acoustic resonator according to claim 16, characterized in that, in: The first piezoelectric layer includes a first acoustic reflection portion and the second piezoelectric layer includes a second acoustic reflection portion, wherein the first acoustic reflection portion is a first groove structure formed by etching the upper surface of the first piezoelectric layer, and the second acoustic reflection portion is a second groove structure formed by etching the upper surface of the second piezoelectric layer.

21. The bulk acoustic resonator according to claim 20, characterized in that, in: The first groove structure penetrates the first piezoelectric layer, and the second groove structure penetrates the second piezoelectric layer.

22. The bulk acoustic resonator according to claim 20 or 21, characterized in that, in: The first groove structure is a single groove or a plurality of first groove units arranged at intervals along the edge of the resonant region; The second groove structure is either a single groove or a plurality of second groove units spaced apart along the edge of the resonant region.

23. The bulk acoustic resonator according to any one of claims 20 to 21, characterized in that, in: The horizontal projections of the first groove structure and the second groove structure surround the entire outer periphery of the horizontal projection of the resonant region, wherein there is no overlapping area or partial overlap between the horizontal projections of the first groove structure and the second groove structure.

24. The bulk acoustic resonator according to claim 20, characterized in that, in: The bulk acoustic resonator further includes a first connection portion formed on the substrate and connected to the lower electrode; The horizontal projection of the resonant region and the horizontal projection of the lower electrode are polygons with the same shape and corresponding sides. The first side of the horizontal projection of the lower electrode corresponds to the side of the lower electrode that forms a connection with the first connecting part, and the second side of the horizontal projection of the resonant region corresponds to the first side. The horizontal projection of the first groove structure surrounds all sides of the horizontal projection of the resonant region except for the second side, and the horizontal projection of the second groove structure surrounds the second side of the horizontal projection of the resonant region.

25. The bulk acoustic resonator according to claim 16, characterized in that, in: The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector, wherein the first acoustic reflector is an upwardly convex first air bridge structure and the second acoustic reflector is an upwardly convex second air bridge structure.

26. The bulk acoustic resonator according to claim 16, characterized in that, in: The acoustic reflection structure is a cavity formed by a third groove structure formed on the substrate and the stacked structure. The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector, wherein the first acoustic reflector is a first air bridge structure formed in the cavity and recessed downwards, and the second acoustic reflector is a second air bridge structure protruding upwards.

27. The bulk acoustic resonator according to claim 16, characterized in that, in: The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector. The first acoustic reflector includes a first groove structure and an upwardly protruding first air bridge structure, and the second acoustic reflector includes a second groove structure and an upwardly protruding second air bridge structure.

28. The bulk acoustic resonator according to claim 16, characterized in that, in: The acoustic reflection structure is a cavity formed by a third groove structure formed on the substrate and the stacked structure. The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector. The first acoustic reflector includes a first groove structure and a first air bridge structure formed in the cavity and recessed downwards. The second acoustic reflector includes a second groove structure and a second air bridge structure protruding upwards.

29. The bulk acoustic resonator according to claim 16, characterized in that, in: The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector. The first piezoelectric layer has an upwardly protruding first air bridge structure, and the structure formed by the second piezoelectric layer and the first piezoelectric layer has a second groove structure. The portions of the first air bridge structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflector, and the portion of the second groove structure located in the second piezoelectric layer constitutes the second acoustic reflector.

30. The bulk acoustic resonator according to claim 16, characterized in that, in: The first piezoelectric layer includes a first acoustic reflector and the second piezoelectric layer includes a second acoustic reflector. The first piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer from bottom to top. A first groove structure is formed in the first piezoelectric layer, and a second groove structure is formed in the structure formed by the second piezoelectric layer and the first piezoelectric layer. The portions of the first groove structure and the second groove structure located in the first piezoelectric layer together constitute the first acoustic reflector, and the portions of the second groove structure located in the second piezoelectric layer together constitute the second acoustic reflector.

31. A filter, characterized in that, The filter includes: A bulk acoustic resonator formed by the manufacturing method as described in any one of claims 1 to 15, or a bulk acoustic resonator as described in any one of claims 16 to 30.

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