Bulk acoustic wave resonator, filter, and multiplexer

Abstract

The application discloses a bulk acoustic wave resonator, a filter and a multiplexer, and belongs to the technical field of bulk acoustic wave resonators, and comprises a piezoelectric layer and an electrode structure, wherein a region covered by the electrode structure on the piezoelectric layer serves as a resonance region; two acoustic structure regions with different topological phases are arranged in the piezoelectric layer; a closed topological phase transition interface is formed at the junction of the two acoustic structure regions and is distributed around the edge of the electrode structure so as to completely surround the resonance region; the two acoustic structure regions are both composed of periodically arranged structure units, and there is an angle deviation in the arrangement direction of the structure units between the two regions. The bulk acoustic wave resonator aims to solve the technical problems of the conventional thin film bulk acoustic wave resonator, such as transverse acoustic wave energy leakage, reduced quality factor, parasitic coupling, sensitivity of the conventional microstructure to geometric parameters, influence of manufacturing deviation on performance, loss caused by edge bending strain and acoustic backscattering at a complex boundary and the like, and significantly improves the performance and reliability of the resonator.

Description

Technical Field

[0001] This invention belongs to the field of bulk acoustic resonator technology, and specifically relates to a bulk acoustic resonator, filter and multiplexer. Background Technology

[0002] Thin-film bulk acoustic resonators (FBARs) are core filtering components in modern wireless communication RF front-ends, and their performance directly determines signal quality and efficiency. FBARs utilize the inverse piezoelectric effect of piezoelectric thin films to convert electrical energy into mechanical energy, forming stable bulk acoustic resonance. However, traditional FBAR structures inherently suffer from lateral acoustic energy leakage: at the edge of the resonant region, due to drastic changes in acoustic impedance, some acoustic energy is scattered laterally instead of being completely confined within the effective resonant body of the electrode region. This leakage leads to two main negative effects: first, it reduces the filter's quality factor (Q value), thereby increasing the filter's insertion loss and worsening out-of-band rejection; second, it causes parasitic coupling between adjacent filters, creating unnecessary spurious modes in complex filter networks.

[0003] To suppress lateral leakage, existing technologies typically employ Bragg reflector layers or air gap structures. These methods confine sound waves to a specific region by creating an acoustic bandgap. However, these traditional microstructures are extremely sensitive to geometric parameters; even minor deviations during manufacturing can weaken their bandgap performance, leading to a decrease in energy confinement capability. Furthermore, at the rigid boundaries of the filter edges, the amplitude of sound wave vibrations is forced to zero, inducing strong bending strain, which becomes one of the main sources of intrinsic material loss. More critically, traditional structures struggle to avoid backscattering of sound waves at complex boundaries such as electrode apexes, further exacerbating energy dissipation.

[0004] Therefore, existing technologies need to be improved and developed. Summary of the Invention

[0005] The purpose of this invention is to provide a bulk acoustic resonator, filter, and multiplexer, which aims to solve the technical problems of traditional thin-film bulk acoustic resonators, such as transverse acoustic energy leakage, reduced quality factor, parasitic coupling, sensitivity of traditional microstructures to geometric parameters, performance impact of manufacturing deviations, loss caused by edge bending strain, and acoustic backscattering at complex boundaries, thereby significantly improving the performance and reliability of the resonator.

[0006] In a first aspect, the present invention provides a bulk acoustic resonator, including a piezoelectric layer and an electrode structure disposed on the surface of the piezoelectric layer, wherein the area covered by the electrode structure on the piezoelectric layer is a resonant region. The piezoelectric layer has a first acoustic structure region and a second acoustic structure region, and the first acoustic structure region and the second acoustic structure region have different topological phases. A closed topological phase transition interface is formed at the junction of the first acoustic structure region and the second acoustic structure region. The topological phase transition interface is distributed around the edge of the electrode structure so as to completely surround the resonant region. Both the first acoustic structure region and the second acoustic structure region are composed of periodically arranged structural units, and there is a preset angular deviation in the arrangement of the structural units between the two regions.

[0007] The bulk acoustic resonator provided by this invention can strictly limit acoustic energy using a topological phase change interface, effectively suppress transverse acoustic energy leakage, improve the quality factor of the resonator, and reduce parasitic coupling. At the same time, it overcomes the problems of traditional microstructures being sensitive to geometric parameters, manufacturing deviations affecting performance, and acoustic backscattering at complex boundaries.

[0008] Furthermore, the first acoustic structure region and the second acoustic structure region are composed of a periodic arrangement of piezoelectric material lattice.

[0009] Furthermore, the arrangement orientation of the structural units corresponds to the lattice orientation of the piezoelectric material.

[0010] Furthermore, the angular deviation is the lattice orientation difference of the structural units between the first acoustic structural region and the second acoustic structural region, and is an integer multiple of 60°.

[0011] Furthermore, the piezoelectric material is AlN material.

[0012] Furthermore, the electrode structure is a polygonal structure.

[0013] Furthermore, the polygonal structure is a pentagonal structure.

[0014] Furthermore, the electrode structure includes a top electrode and a bottom electrode, and the piezoelectric layer is disposed between the top electrode and the bottom electrode; the first acoustic structure region is located in the piezoelectric layer surrounding the polygonal structure, and the second acoustic structure region is located in the piezoelectric layer within the projection range of the polygonal structure along the vertical direction.

[0015] Secondly, the present invention provides a filter including the aforementioned bulk acoustic resonator.

[0016] Thirdly, the present invention provides a multiplexer, including the aforementioned bulk acoustic resonator.

[0017] As can be seen from the above, the bulk acoustic resonator provided by this invention, by setting a first acoustic structure region and a second acoustic structure region with different topological phases within the piezoelectric layer, and forming a closed topological phase transition interface at the junction of the two regions, is distributed around the edge of the electrode structure to completely surround the resonant region. This topological phase transition interface can support the propagation of boundary states protected by topology, thereby strictly confining the acoustic wave energy to the vicinity of the electrode structure edge. Due to the topological protection characteristics, the acoustic wave has backscattering suppression capability when propagating along the boundary, and can maintain transmission stability even at the apex of the electrode structure, effectively reducing mode scattering and energy leakage at traditional boundaries. In addition, by breaking the spatial symmetry to achieve the difference in topological phases, the sensitivity of traditional microstructures to geometric parameters is avoided, and the manufacturing tolerance is improved. Therefore, the bulk acoustic resonator of this application can effectively solve the problems of transverse acoustic wave energy leakage, reduced quality factor, parasitic coupling, sensitivity of traditional microstructures to geometric parameters, performance impact of manufacturing deviations, loss caused by edge bending strain, and acoustic wave backscattering at complex boundaries in the prior art, significantly improving the performance and reliability of the resonator.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of a bulk acoustic resonator provided in an embodiment of the present invention.

[0020] Figure 2 This is a top view of a bulk acoustic resonator provided in an embodiment of the present invention.

[0021] Label Explanation: 100, Piezoelectric layer; 110, First acoustic structure region; 120, Second acoustic structure region; 130, Topological phase transition interface; 140, Structural unit; 200, Top electrode; 300, Bottom electrode. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0026] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0027] In practical applications of thin-film bulk acoustic resonators (FCARs), abrupt changes in acoustic impedance at the edges of the resonant region cause transverse acoustic wave energy scattering, preventing the acoustic waves from being completely confined within the effective resonant body of the electrode region. This energy leakage directly reduces the filter's quality factor, leading to increased insertion loss and deterioration of out-of-band rejection. Furthermore, the scattered acoustic waves form parasitic coupling between adjacent filters, inducing spurious modes that interfere with signal transmission stability and affect the RF front-end's ability to guarantee signal quality and efficiency.

[0028] For example, in the RF front-end module of a 5G communication base station, multiple thin-film bulk acoustic resonators are densely integrated to achieve multi-band filtering. When the resonators operate at high frequencies, the acoustic energy leakage at the edges of the resonant region becomes particularly significant, specifically manifested as unintended vibrational coupling between adjacent resonators caused by the leaked acoustic waves. This leads to increased phase noise in the received signal and a decrease in the steepness of the filter's passband edge, resulting in the inability to accurately separate the target frequency band. In complex filter networks, this problem further causes resonant frequency drift and signal distortion, increasing the bit error rate of the communication link and constraining the overall system reliability.

[0029] If the problem of transverse acoustic energy leakage is not addressed, the performance of the filter will continue to degrade, and the signal processing capabilities of the RF front-end will be unable to meet the demands of modern wireless communication. Spurious modes caused by parasitic coupling will accumulate, eventually leading to the failure of the filter network and affecting the stability of communication quality. Furthermore, energy loss due to mode scattering will exacerbate the uneven distribution of mechanical stress within the resonator, accelerating the aging process of the device and shortening its service life. Therefore, it is essential to seek a structural design that can effectively suppress energy leakage and optimize the localization of acoustic modes.

[0030] For reference, see the appendix. Figure 1 and attached Figure 2 The present invention provides a bulk acoustic resonator, including a piezoelectric layer 100 and an electrode structure disposed on the surface of the piezoelectric layer 100, wherein the area covered by the electrode structure on the piezoelectric layer 100 is a resonant region. The piezoelectric layer 100 has a first acoustic structure region 110 and a second acoustic structure region 120, and the first acoustic structure region 110 and the second acoustic structure region 120 have different topological phases. A closed topological phase transition interface 130 is formed at the junction of the first acoustic structure region 110 and the second acoustic structure region 120. The topological phase transition interface 130 is distributed around the edge of the electrode structure so that it completely surrounds the resonant region. Both the first acoustic structure area 110 and the second acoustic structure area 120 are composed of periodically arranged structural units 140, and there is a preset angular deviation in the arrangement of the structural units 140 between the two areas.

[0031] For ease of understanding, the following explains some key terms in this embodiment: Piezoelectric layer 100: Piezoelectric layer 100 is a material layer capable of converting mechanical energy and electrical energy into each other. When mechanical stress is applied, piezoelectric layer 100 generates an electric charge; conversely, when an electric field is applied, piezoelectric layer 100 deforms. In a bulk acoustic resonator, piezoelectric layer 100 is the core component for generating and receiving sound waves.

[0032] Electrode structure: The electrode structure is typically made of conductive material and is disposed on the surface of the piezoelectric layer 100 to apply an electric field or collect charge. The area covered by the electrode structure on the piezoelectric layer 100 is defined as the resonant region, which is the region where sound wave energy is mainly concentrated and resonance occurs.

[0033] Topological phase: A topological phase is a macroscopic physical property of a material or structure, characterized by its robustness to local disturbances or defects. In the field of acoustics, regions with different topological phases can support the propagation of topologically protected boundary states at their boundaries, allowing sound wave energy to be transmitted stably along the boundary without being affected by scattering.

[0034] Topological phase transition interface 130: The topological phase transition interface 130 is the boundary line or interface between two regions with different topological phases. This interface can support the propagation of boundary states protected by topology. The acoustic energy is strictly confined to the vicinity of the electrode structure edge. Due to the topological protection characteristics, the acoustic waves have backscattering suppression capability when propagating along the boundary, and can maintain transmission stability even at the apex of the electrode structure, effectively reducing mode scattering and energy leakage at traditional boundaries.

[0035] Structural unit 140: Structural unit 140 is the basic repeating unit that constitutes the periodic acoustic structure. By changing the geometry, size, or arrangement of structural unit 140, the acoustic properties of the material can be controlled, thereby achieving different topological phases.

[0036] This embodiment provides a bulk acoustic wave resonator, which includes a piezoelectric layer 100 and an electrode structure disposed on the surface of the piezoelectric layer 100. The area covered by the electrode structure on the piezoelectric layer 100 serves as the resonant region. To address the problem of transverse acoustic wave energy leakage in conventional bulk acoustic wave resonators, and to improve acoustic wave energy confinement capability and reduce mode scattering and energy leakage, this embodiment provides a first acoustic structure region 110 and a second acoustic structure region 120 within the piezoelectric layer 100. The first acoustic structure region 110 and the second acoustic structure region 120 have different topological phases.

[0037] Specifically, the piezoelectric layer 100 can be made of various piezoelectric materials, such as aluminum nitride (AlN), zinc oxide (ZnO), or lithium niobate (LiNbO3). The electrode structure can be made of various conductive materials, such as metallic aluminum, molybdenum, or tungsten. The electrode structure can be designed in various geometries, such as circular, square, rectangular, or polygonal, to meet different application requirements. For example, the electrode structure can be designed as circular, and the area it covers on the piezoelectric layer 100 is the circular resonant region.

[0038] A closed topological phase transition interface 130 is formed at the boundary between the first acoustic structure region 110 and the second acoustic structure region 120. The topological phase transition interface 130 is distributed around the edge of the electrode structure to completely surround the resonant region. The topological phase transition interface 130 supports topologically protected boundary state propagation, and the acoustic wave energy is strictly confined to the vicinity of the electrode structure edge. Due to the topological protection characteristics, the acoustic wave has backscattering suppression capability when propagating along the boundary, maintaining transmission stability even at the apex of the electrode structure, effectively reducing mode scattering and energy leakage at traditional boundaries. For example, when the electrode structure is circular, the topological phase transition interface 130 can form a closed ring structure concentric with the edge of the circular electrode. When the electrode structure is square, the topological phase transition interface 130 can form a closed square ring structure parallel to the edge of the square electrode.

[0039] Both the first acoustic structural region 110 and the second acoustic structural region 120 are composed of periodically arranged structural units 140, and there is a predetermined angular deviation in the arrangement of the structural units 140 between the two regions, so as to achieve a difference in topological phase by breaking the spatial symmetry. For example, the structural units 140 can be an array of micropillars or an array of holes formed by etching piezoelectric material. By changing the arrangement direction of these micropillars or holes, the symmetry of the acoustic structure can be changed, thereby inducing different topological phases. For example, the structural units 140 of the first acoustic structural region 110 can be arranged along the 0° direction, while the structural units 140 of the second acoustic structural region 120 can be arranged along the 30° direction, thereby producing a predetermined angular deviation and thus achieving a difference in topological phase.

[0040] The following example will provide a more detailed explanation of the above technical solution: Suppose we need to design a high-performance thin-film bulk acoustic (FBAR) filter to address the transverse acoustic energy leakage problem at the resonant region edge of a conventional FBAR. At the resonant region edge, due to the abrupt change in acoustic impedance, some acoustic energy is scattered laterally rather than being completely confined within the effective resonant body of the electrode region. This leakage reduces the filter's quality factor (Q value), thereby increasing the filter's insertion loss and deteriorating out-of-band rejection. It also causes parasitic coupling between adjacent filters, creating unwanted stray modes in complex filter networks.

[0041] To address this issue, this application proposes a thin-film bulk acoustic filter with topological acoustic boundaries. The core of this design lies in suppressing lateral energy leakage by constructing a topologically protected acoustic wave transmission path. The filter employs a standard sandwich structure, including a bottom electrode 300, a piezoelectric layer 100, and a top electrode 200. The top electrode 200 is designed as a pentagonal structure. A first acoustic structure region 110 is formed in the piezoelectric layer 100 surrounding the pentagonal electrode 200, and a second acoustic structure region 120 is formed in the piezoelectric layer 100 within the vertical projection range of the pentagonal electrode 200. The first acoustic structure region 110 and the second acoustic structure region 120 are composed of a periodically arranged lattice of piezoelectric material, and there is a predetermined angular deviation in the arrangement of the structural units 140 between the two regions. Specifically, the first acoustic structure region 110 is composed of a periodically arranged structural units 140 with a first lattice orientation, and the second acoustic structure region 120 is composed of a periodically arranged structural units 140 with a second lattice orientation. The lattice orientation difference between the two regions is an integer multiple of 60°, thereby breaking the structural symmetry and generating a non-trivial topological phase transition.

[0042] Because the first acoustic structure region 110 and the second acoustic structure region 120 have different topological phases, a closed topological phase transition interface 130 is formed at their boundary. This topological phase transition interface 130 is precisely distributed along the boundary of the pentagonal electrode 200, forming a closed topological boundary that completely surrounds the resonant region. When an electrical signal is applied to the piezoelectric layer 100 through the top electrode 200 and the bottom electrode 300, the piezoelectric layer 100 generates mechanical vibrations, forming bulk acoustic waves. These acoustic waves propagate within the resonant region. When the acoustic waves propagate to the edge of the resonant region, due to the presence of the topological phase transition interface 130, the acoustic wave energy is strictly confined to the vicinity of the interface at the edge of the pentagonal electrode 200. The topological phase transition interface 130 can support the propagation of topologically protected boundary states, and the acoustic waves have backscattering suppression capability when propagating along the boundary, maintaining transmission stability even at the pentagonal vertices, effectively reducing mode scattering and energy leakage at traditional boundaries. By transforming the traditional scattering boundary into a guiding boundary with topological protection characteristics, effective confinement of transverse acoustic wave energy is achieved.

[0043] Through the above technical solution, the bulk acoustic wave resonator of this embodiment can significantly improve the quality factor and out-of-band rejection performance of the filter. Compared with the traditional method of suppressing lateral leakage by constructing a Bragg reflector layer or air gap structure, this embodiment utilizes a topological protection mechanism, making the localization of acoustic wave energy more robust to small deviations in the manufacturing process, and avoiding the problem of high requirements for geometric parameters in traditional microstructures. In addition, since the topological boundary can support stable boundary state propagation, it avoids the strong bending strain caused by the forced reduction of acoustic wave vibration amplitude to zero at the traditional "hard" boundary, thereby reducing intrinsic material loss. Therefore, the bulk acoustic wave resonator of this embodiment has significant technical progress and innovation in solving the problem of lateral acoustic wave energy leakage.

[0044] In some embodiments, the first acoustic structure region 110 and the second acoustic structure region 120 are composed of a periodic arrangement of piezoelectric material lattice; the arrangement orientation of the structural unit 140 is the lattice orientation of the piezoelectric material; the angular deviation is the difference in lattice orientation between the structural unit 140 and the first acoustic structure region 110 and the second acoustic structure region 120, and is an integer multiple of 60°.

[0045] To better understand the above technical solution, the key technical features involved will be explained in detail below.

[0046] The periodic lattice arrangement of piezoelectric materials refers to the highly ordered and repeating geometric structure of the basic atoms or molecules constituting the piezoelectric material in space. This periodic arrangement is an inherent property of piezoelectric materials, determining their macroscopic physical properties and providing a periodic medium for the propagation of sound waves. As one method of realization, piezoelectric thin films with specific crystal orientations can be directly grown on suitable substrates using crystal growth techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or molecular beam epitaxy (MBE), thereby forming acoustic structure regions with periodic lattice arrangements. Alternatively, micro-nano fabrication techniques, such as electron beam etching or ion beam etching, can be used to precisely depict periodic microstructures on amorphous or polycrystalline piezoelectric thin films, enabling them to exhibit the acoustic characteristics of periodic lattice arrangements macroscopically, thus forming the first acoustic structure region 110 and the second acoustic structure region 120.

[0047] The orientation of the structural units 140 refers to the spatial orientation of the smallest repeating units constituting the first acoustic structural region 110 and the second acoustic structural region 120. Setting their orientation to match the lattice orientation of the piezoelectric material means that the geometric axes or symmetry axes of these structural units 140 are aligned with the specific crystal axis direction of the piezoelectric material crystal. This alignment ensures a high degree of coupling between the acoustic structural region and the crystal structure of the material itself, thereby more effectively utilizing the piezoelectric properties and acoustic anisotropy of the material. Specifically, during the fabrication of the piezoelectric thin film, the crystal orientation of the film can be precisely controlled to match the preset orientation of the structural units 140. Alternatively, in subsequent microfabrication steps, photolithography or etching techniques can be used to precisely align the pattern of the structural units 140 with the lattice direction of the piezoelectric material to achieve a correspondence between the orientation of the structural units 140 and the lattice orientation.

[0048] Angular deviation refers to the angle between the lattice orientation of structural unit 140 in the first acoustic structural region 110 and the lattice orientation of structural unit 140 in the second acoustic structural region 120. Setting it to an integer multiple of 60° utilizes the six-fold symmetry of the crystal structure of many piezoelectric materials (e.g., aluminum nitride, AlN). This specific angular difference can effectively break the spatial symmetry between the two regions, thereby generating a non-trivial topological phase difference between the first acoustic structural region 110 and the second acoustic structural region 120. During fabrication, the angle between the lattice orientations of the first acoustic structural region 110 and the second acoustic structural region 120 can be preset to integer multiples such as 60° and 120° by rotating the mask or adjusting the crystal growth direction. Furthermore, during the design phase, the optimal angular deviation that can produce a stable topological phase transition can be determined through theoretical calculations and numerical simulations, and applied to the design of the photolithographic mask to achieve a precise lattice orientation difference, thereby ensuring the stable formation of the topological phase transition interface 130.

[0049] Based on the aforementioned technical features, the solution of this application achieves its intended function and solves the technical problem in the following manner. This solution utilizes the inherent crystal structure characteristics of piezoelectric materials by designing the first acoustic structure region 110 and the second acoustic structure region 120 as being composed of a periodic arrangement of piezoelectric material lattices, and ensuring that the orientation of the structural unit 140 is consistent with the lattice orientation of the piezoelectric material. This design ensures that the acoustic structure regions have a stable periodic basis and makes the acoustic properties closely related to the crystal symmetry of the material. Furthermore, by introducing a precise angular deviation between the first acoustic structure region 110 and the second acoustic structure region 120, which is equal to the lattice orientation difference of the structural unit 140 and an integer multiple of 60°, the spatial symmetry between the two regions is intentionally broken. This controlled symmetry breaking is a key mechanism for generating nontrivial topological phase differences. Specifically, the periodic lattice arrangement of the piezoelectric material provides a natural periodic potential field for the propagation of sound waves, and the alignment of the arrangement of the structural units 140 with the lattice orientation allows these periodic potential fields to be precisely defined and controlled. When the lattice orientations of two adjacent regions (i.e., the first acoustic structure region 110 and the second acoustic structure region 120) differ by an integer multiple of 60°, although they are both composed of the same piezoelectric material, their acoustic band structure will undergo a fundamental change, resulting in a difference in topological phase. This topological phase transition mechanism based on lattice orientation difference utilizes the intrinsic symmetry of crystal materials, making the formation of the topological phase transition interface 130 more stable and controllable, and less susceptible to the influence of minor geometric deviations during manufacturing. Through the above technical solution, the first acoustic structure region 110 and the second acoustic structure region 120 with different topological phases are formed within the piezoelectric layer 100, and a closed topological phase transition interface 130 is constructed at their boundary. This topological phase transition interface 130 supports topologically protected boundary state propagation, thus strictly confining acoustic wave energy to the vicinity of the electrode structure edge. Due to the topological protection characteristics, acoustic waves exhibit backscattering suppression capabilities as they propagate along the boundary, maintaining propagation stability even at the apex of the electrode structure, effectively reducing mode scattering and energy leakage at traditional boundaries. This method fundamentally solves the problem of acoustic wave energy leakage at the edge of the resonant region in traditional FBARs, significantly improving the resonator's quality factor and out-of-band rejection capability.

[0050] The following specific example further clarifies the implementation of this application. As a specific implementation, the piezoelectric material can be aluminum nitride (AlN), which has a hexagonal crystal structure and naturally possesses six-fold symmetry. In this case, both the first acoustic structural region 110 and the second acoustic structural region 120 are composed of a periodic arrangement of AlN crystals. The arrangement orientation of the structural units 140 can be designed to align with a specific crystal axis direction of the AlN crystal, for example, parallel to the a-axis or c-axis direction of the AlN crystal. Furthermore, to achieve a difference in topological phase, the lattice orientation of the structural units 140 in the first acoustic structural region 110 can be aligned with a reference direction of the AlN crystal. The lattice orientation of the structural units 140 in the second acoustic structural region 120 can be rotated by 60° or 120° relative to this reference direction, thereby forming a 60° or 120° lattice orientation difference. This precise 60° integer multiple angular deviation can effectively break the spatial symmetry between the two regions, thereby generating a non-trivial topological phase transition between the first acoustic structure region 110 and the second acoustic structure region 120, and thus forming a stable topological phase transition interface 130.

[0051] Through the above technical solution, this application solves the problem of ensuring that the arrangement of structural units can accurately achieve topological phase difference by utilizing the inherent periodic lattice arrangement and precisely controlled lattice orientation difference of piezoelectric materials, thereby avoiding manufacturing deviations and improving stability. This topological phase transition mechanism based on crystal symmetry breaking makes the formation of the topological phase transition interface 130 more stable and controllable, significantly reducing the sensitivity to manufacturing precision. Therefore, the formed topological phase transition interface 130 can more reliably support the propagation of topologically protected boundary states, thereby ensuring that acoustic wave energy is strictly confined to the vicinity of the electrode structure edge and effectively suppressing backscattering. This not only improves the quality factor and out-of-band rejection capability of the bulk acoustic resonator, but also enhances the robustness and reliability of the device in practical applications, providing a solid foundation for the design of high-performance RF filters.

[0052] In some embodiments, the piezoelectric material is AlN.

[0053] In some embodiments, the electrode structure is a polygonal structure.

[0054] In some embodiments, the polygonal structure is a pentagonal structure.

[0055] In some embodiments, reference is made to the appendix. Figure 1 The electrode structure includes a top electrode 200 and a bottom electrode 300, and a piezoelectric layer 100 is disposed between the top electrode 200 and the bottom electrode 300; the first acoustic structure region 110 is located in the piezoelectric layer 100 on the periphery of the polygonal structure, and the second acoustic structure region 120 is located in the piezoelectric layer 100 within the projection range of the polygonal structure along the vertical direction.

[0056] The top electrode 200 and bottom electrode 300 are key conductive components of the bulk acoustic wave resonator, used to apply an electric field to the piezoelectric layer 100 to excite sound waves and to detect the electrical signals generated by the sound wave vibrations from the piezoelectric layer 100. They are typically made of metallic materials with good conductivity and acoustic properties, such as molybdenum, tungsten, aluminum, or gold. Their thickness and geometry significantly influence the resonant frequency and quality factor of the resonator. The top electrode 200 and bottom electrode 300 can be fabricated using microfabrication processes such as physical vapor deposition (PVD) or chemical vapor deposition (CVD) combined with photolithography and etching. The piezoelectric layer 100 is the core functional layer of the bulk acoustic wave resonator, responsible for the conversion between electrical energy and mechanical energy (sound waves). This layer is typically composed of materials with piezoelectric effects, such as aluminum nitride (AlN), zinc oxide (ZnO), or lithium niobate (LiNbO3). The thickness of the piezoelectric layer 100 directly determines the fundamental frequency of the resonator, while its crystal quality and orientation are crucial to the resonator's performance. The piezoelectric layer 100 can be grown on the bottom electrode 300 using techniques such as magnetron sputtering or molecular beam epitaxy, followed by the formation of the top electrode 200. The first acoustic structure region 110 is a region within the piezoelectric layer 100 with a specific topological phase, where the arrangement of its periodic structural units 140 differs from that of the second acoustic structure region 120. This region is precisely positioned around the periphery of the electrode structure (polygonal structure), together with the second acoustic structure region 120, defining a closed topological phase transition interface 130. The formation of the first acoustic structure region 110 can be achieved through local lattice engineering, etching, or growth of periodic microstructures with specific crystal orientations within the piezoelectric layer 100. The second acoustic structure region 120 is also a region within the piezoelectric layer 100 with a specific topological phase, where the arrangement of its periodic structural units 140 differs from that of the first acoustic structure region 110. This region lies within the vertical projection range of the electrode structure (polygonal structure), i.e., within the resonant region covered by the electrode structure. The second acoustic structure region 120 is formed in a similar manner to the first acoustic structure region 110, and is intended to work together with the first acoustic structure region 110 to construct a topological phase transition interface 130 in order to effectively limit the sound wave energy inside the resonant region.

[0057] The solution of this application designs the electrode structure as a sandwich structure including a top electrode 200 and a bottom electrode 300, and on this basis, precisely positions the first acoustic structure region 110 and the second acoustic structure region 120 within the piezoelectric layer 100. Specifically, the first acoustic structure region 110 is arranged on the periphery of the polygonal electrode structure, while the second acoustic structure region 120 is located within the projection range of the polygonal electrode structure in the vertical direction. This ingenious layout allows the topological phase transition interface 130 between the first acoustic structure region 110 and the second acoustic structure region 120 to be distributed tightly and completely around the edge of the polygonal electrode structure, thereby ensuring that the topological protection mechanism is fully and effectively applied throughout the resonant region edge, especially at the polygonal vertices where sound wave scattering and energy leakage are traditionally prone to occur. In this way, the sound wave energy is strictly confined to the vicinity of the electrode structure edge, and due to the topological protection characteristics, the sound wave has backscattering suppression capability when propagating along the boundary, maintaining transmission stability even at the vertices of the polygonal electrode, thereby effectively reducing mode scattering and energy leakage at the traditional boundary and solving the inherent problems at the vertices of the polygonal electrode structure.

[0058] The present invention provides a filter, including the bulk acoustic resonator in the above embodiments.

[0059] The present invention provides a multiplexer, including the bulk acoustic resonator in the above embodiments.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A bulk acoustic wave resonator, comprising a piezoelectric layer (100) and an electrode structure disposed on the surface of the piezoelectric layer (100), wherein the area covered by the electrode structure on the piezoelectric layer (100) serves as a resonant region, characterized in that: The piezoelectric layer (100) is provided with a first acoustic structure region (110) and a second acoustic structure region (120), and the first acoustic structure region (110) and the second acoustic structure region (120) have different topological phases; A closed topological phase change interface (130) is formed at the junction of the first acoustic structure region (110) and the second acoustic structure region (120). The topological phase change interface (130) is distributed around the edge of the electrode structure so that it completely surrounds the resonant region. Both the first acoustic structure region (110) and the second acoustic structure region (120) are composed of periodically arranged structural units (140), and there is a preset angular deviation in the arrangement of the structural units (140) between the two regions.

2. The bulk acoustic resonator according to claim 1, characterized in that, The first acoustic structure region (110) and the second acoustic structure region (120) are composed of a periodic arrangement of piezoelectric material lattice.

3. The bulk acoustic resonator according to claim 2, characterized in that, The arrangement orientation of the structural unit (140) is the lattice orientation of the piezoelectric material.

4. The bulk acoustic resonator according to claim 3, characterized in that, The angular deviation is the lattice orientation difference of the structural unit (140) between the first acoustic structural region (110) and the second acoustic structural region (120), and is an integer multiple of 60°.

5. The bulk acoustic resonator according to claim 2, characterized in that, The piezoelectric material is AlN.

6. The bulk acoustic resonator according to claim 1, characterized in that, The electrode structure is a polygonal structure.

7. The bulk acoustic resonator according to claim 6, characterized in that, The polygonal structure is a pentagonal structure.

8. The bulk acoustic resonator according to claim 6, characterized in that, The electrode structure includes a top electrode (200) and a bottom electrode (300), and the piezoelectric layer (100) is disposed between the top electrode (200) and the bottom electrode (300); the first acoustic structure region (110) is located in the piezoelectric layer (100) on the periphery of the polygonal structure, and the second acoustic structure region (120) is located in the piezoelectric layer (100) within the projection range of the polygonal structure along the vertical direction.

9. A filter, characterized in that, Includes the bulk acoustic resonator as described in any one of claims 1-8.

10. A multiplexer, characterized in that, Includes the bulk acoustic resonator as described in any one of claims 1-8.

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