A high-Q bulk acoustic resonator, filter, duplexer, and their fabrication method

Abstract

The application provides a high-Q bulk acoustic resonator, a filter, a duplexer and a preparation method thereof, and relates to the technical field of bulk acoustic resonators. In the high-Q bulk acoustic resonator, the bottom electrode and the top electrode form a high-low acoustic impedance transverse impedance mismatch structure in the transverse direction, and also form a high-low acoustic impedance longitudinal impedance mismatch structure in the longitudinal direction. The high-Q bulk acoustic resonator aims to solve the problems that the single-protrusion and double-protrusion frame structures have poor inhibition effect on Lamb wave leakage or have greater processing difficulty, ensures simple process and effectively inhibits the leakage of Lamb wave transverse energy, and thus improves the Q value.

Description

Technical Field

[0001] This invention relates to the field of bulk acoustic wave resonator technology, and more specifically, to a high-Q bulk acoustic wave resonator, filter, duplexer, and its fabrication method. Background Technology

[0002] Acoustic resonators utilize the inverse piezoelectric effect to convert electrical signals into vibration (sound) signals. Due to the inherent characteristics of the resonator, vibrations (sound) at a specific frequency resonate and output only that signal. Bulk acoustic resonators, fabricated using the longitudinal resonance of a piezoelectric thin film in the thickness direction, have become indispensable radio frequency devices in the field of high-frequency mobile communications.

[0003] Bulk acoustic wave filters / duplexers offer superior filtering characteristics, such as low insertion loss, which often places high Q-value requirements on the resonator.

[0004] However, Lamb waves inevitably exist in bulk acoustic resonators. These Lamb waves are generated by the free surface under transverse stress and radiate outward from the active region (i.e., transverse leakage), resulting in energy loss. Therefore, effectively suppressing Lamb wave energy leakage is an important guarantee for improving the Q value.

[0005] In existing technologies, a single-protrusion frame structure is often used. On the one hand, it requires adding another layer of protrusion frame structure, and the width of the protrusion needs to be precisely measured, which is quite difficult. On the other hand, its ability to suppress lateral leakage is also limited. In addition, a double-protrusion frame structure is used, which has a better ability to prevent leakage, but it requires adding multiple layers of processes, which is more complex. Furthermore, the width of the protrusion needs to be precisely measured, which is also quite difficult.

[0006] Therefore, there is an urgent need for a technical solution that is simple to manufacture, does not have high size requirements, and can ensure that Lamb wave energy does not leak. Summary of the Invention

[0007] The purpose of this invention is to provide a high-Q bulk acoustic resonator, filter, duplexer, and its fabrication method, aiming to solve the problems of poor Lamb wave leakage suppression effect or high processing difficulty of existing single-protrusion and double-protrusion frame structures, ensuring simple process and effective suppression of Lamb wave transverse energy leakage, thereby improving Q value.

[0008] In a first aspect, the present invention provides a high Q-value bulk acoustic resonator, comprising a substrate, a bottom electrode, a piezoelectric layer and a top electrode stacked longitudinally, wherein a cavity is provided between the substrate and the bottom electrode, and a first lateral impedance mismatch structure is provided on both sides of the bottom electrode in the lateral direction. The first lateral impedance mismatch structure includes a first impedance part and a second impedance part alternately connected in the lateral direction, wherein the acoustic impedance of the first impedance part is lower than the acoustic impedance of the second impedance part.

[0009] The top electrode has a second transverse impedance mismatch structure on both sides of its transverse direction. The second transverse impedance mismatch structure includes a third impedance part and a fourth impedance part that are alternately connected in the transverse direction. The acoustic impedance of the third impedance part is lower than that of the fourth impedance part.

[0010] The longitudinal projection of the third impedance part is misaligned with the longitudinal projection of the first impedance part and overlaps with the longitudinal projection of the second impedance part, forming a first longitudinal impedance mismatch structure.

[0011] The longitudinal projection of the fourth impedance part is misaligned with the longitudinal projection of the second impedance part and overlaps with the longitudinal projection of the first impedance part, forming a second longitudinal impedance mismatch structure.

[0012] The high-Q bulk acoustic wave resonator provided by this invention effectively suppresses Lamb wave energy leakage by setting a transverse impedance mismatch structure at the transverse edges of the bottom and top electrodes and forming a longitudinal impedance mismatch structure by utilizing longitudinal projection misalignment and overlap. This improves the Q value of the bulk acoustic wave resonator, while simplifying the manufacturing process and reducing the requirements for dimensional accuracy.

[0013] Furthermore, both sides of the bottom electrode in the lateral direction are set as bevels so that the cross-sectional shape of the bottom electrode is a trapezoid with a narrow top and a wide bottom.

[0014] Furthermore, it also includes a frequency modulation layer stacked longitudinally on the top electrode.

[0015] Furthermore, both the first impedance section and the third impedance section are made of molybdenum material.

[0016] Furthermore, both the second impedance section and the fourth impedance section are made of tungsten material.

[0017] Secondly, the present invention provides a filter including the high Q-value bulk acoustic resonator described above.

[0018] Thirdly, the present invention provides a duplexer, including the high-Q bulk acoustic resonator described above.

[0019] Fourthly, the present invention provides a method for fabricating the aforementioned high-Q bulk acoustic resonator, comprising the following steps:

[0020] S1. Using photolithography, grooves are etched on the substrate, and then CVD coating is performed on the grooves to obtain a sacrificial layer that fills the grooves;

[0021] S2. Using a coating process, a patterned first impedance portion is obtained by performing a first coating on the sacrificial layer;

[0022] S3. Using a coating process, a second coating is performed on the sacrificial layer to obtain a patterned second impedance portion, and the second impedance portion and the first impedance portion are alternately connected laterally to form the bottom electrode;

[0023] S4. A piezoelectric layer is grown on the bottom electrode using PVD technology;

[0024] S5. Using a coating process, a patterned third impedance portion is obtained by performing a first coating on the piezoelectric layer, and the longitudinal projection of the third impedance portion is misaligned with the longitudinal projection of the first impedance portion and overlaps with the longitudinal projection of the second impedance portion.

[0025] S6. Using a coating process, a second coating is performed on the piezoelectric layer to obtain the patterned fourth impedance part, and the third impedance part and the fourth impedance part are alternately connected in the transverse direction to form the top electrode, and the longitudinal projection of the fourth impedance part is misaligned with the longitudinal projection of the second impedance part and overlaps with the longitudinal projection of the first impedance part.

[0026] S7. The cavity is obtained by releasing the sacrificial layer.

[0027] Furthermore, the steps between step S1 and step S2 include:

[0028] The sacrificial layer is smoothed using CMP technology.

[0029] Furthermore, the steps between steps S6 and S7 include:

[0030] A frequency modulation layer is grown on the top electrode using PVD technology.

[0031] As can be seen from the above, the high Q-value bulk acoustic resonator provided by the present invention can effectively solve the problem of poor insertion loss of bulk acoustic filters / duplexers. Compared with the existing single-protrusion frame structure, the present invention can better suppress the lateral leakage of Lamb waves. Compared with the existing double-protrusion frame structure, it has a simpler processing technology, effectively reducing the processing difficulty and improving product performance and customer user experience.

[0032] 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

[0033] Figure 1 This is a schematic diagram of the first structure of a high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of a second structure of a high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of a third structure of a high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the fourth structure of a high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the upper part of the fabrication process of the high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0038] Figure 6 This is a schematic diagram of the lower half of the fabrication process of the high-Q bulk acoustic resonator provided in an embodiment of the present invention.

[0039] Figure 7 This is a flowchart of a preparation method provided in an embodiment of the present invention.

[0040] Label Explanation:

[0041] 100, Substrate; 200, Bottom electrode; 210, First impedance section; 220, Second impedance section; 300, Piezoelectric layer; 400, Top electrode; 410, Third impedance section; 420, Fourth impedance section; 500, Cavity; 600, Frequency modulation layer; 700, Sacrificial layer. Detailed Implementation

[0042] 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.

[0043] 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., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limitations on this invention.

[0044] 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.

[0045] 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.

[0046] 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 in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. 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. Also, in the description of this invention, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0049] It should be noted that the terms "vertical direction" and "lateral direction" mentioned below are in conjunction with the appendix. Figure 1 and attached Figure 2 The arrows are for reference.

[0050] Reference Appendix Figure 1 Appendix Figure 2 Appendix Figure 3 and attached Figure 4 The present invention provides a high Q-value bulk acoustic resonator, comprising a substrate 100, a bottom electrode 200, a piezoelectric layer 300 and a top electrode 400 stacked longitudinally. A cavity 500 is provided between the substrate 100 and the bottom electrode 200. A first lateral impedance mismatch structure is provided on both sides of the bottom electrode 200 in the lateral direction. The first lateral impedance mismatch structure includes a first impedance part 210 and a second impedance part 220 alternately connected in the lateral direction. The acoustic impedance of the first impedance part 210 is lower than the acoustic impedance of the second impedance part 220.

[0051] The top electrode 400 has a second transverse impedance mismatch structure on both sides of its transverse direction. The second transverse impedance mismatch structure includes a third impedance part 410 and a fourth impedance part 420 that are alternately connected in the transverse direction. The acoustic impedance of the third impedance part 410 is lower than that of the fourth impedance part 420.

[0052] The longitudinal projection of the third impedance section 410 is misaligned with the longitudinal projection of the first impedance section 210 and overlaps with the longitudinal projection of the second impedance section 220, forming a first longitudinal impedance mismatch structure.

[0053] The longitudinal projection of the fourth impedance section 420 is misaligned with the longitudinal projection of the second impedance section 220 and overlaps with the longitudinal projection of the first impedance section 210, forming a second longitudinal impedance mismatch structure.

[0054] This application effectively suppresses Lamb wave energy leakage by setting a transverse impedance mismatch structure at the transverse edges of the bottom electrode 200 and the top electrode 400, and forming a longitudinal impedance mismatch structure by utilizing longitudinal projection misalignment and overlap. This improves the Q value of the bulk acoustic resonator, while simplifying the process and reducing the requirements for dimensional accuracy.

[0055] The high-Q bulk acoustic resonator proposed in this application is based on a clever structural design to suppress Lamb wave energy leakage, thereby improving the resonator's quality factor (Q value). The substrate 100 is the basic supporting structure of the resonator, typically made of materials such as silicon, glass, or ceramic, providing stable support for subsequent layered structures. The bottom electrode 200 and top electrode 400 are key components for converting electrical signals into acoustic signals. They sandwich the piezoelectric layer 300, and by applying an electric field, the piezoelectric layer 300 undergoes mechanical deformation, thereby exciting acoustic waves. The piezoelectric layer 300 is the core functional layer of the resonator, typically made of piezoelectric materials such as aluminum nitride (AlN), zinc oxide (ZnO), or lead zirconate titanate (PZT), and its thickness determines the resonant frequency. The cavity 500 is designed to provide an acoustic isolation region, reducing acoustic wave leakage to the substrate 100, thereby improving the resonator's performance.

[0056] Specifically, a first lateral impedance mismatch structure is provided on both sides of the bottom electrode 200 in the lateral direction. This first lateral impedance mismatch structure includes a first impedance section 210 and a second impedance section 220 alternately connected in the lateral direction. The acoustic impedance of the first impedance section 210 is lower than that of the second impedance section 220. For example, the first impedance section 210 can be made of a material with lower acoustic impedance, such as molybdenum (Mo), while the second impedance section 220 can be made of a material with higher acoustic impedance, such as tungsten (W). This alternating connection structure can create a periodic change in acoustic impedance in the lateral direction, thereby reflecting and scattering transversely propagating Lamb waves.

[0057] Similarly, a second lateral impedance mismatch structure is provided on both sides of the top electrode 400 in the lateral direction. This second lateral impedance mismatch structure includes a third impedance section 410 and a fourth impedance section 420 alternately connected in the lateral direction. The acoustic impedance of the third impedance section 410 is lower than that of the fourth impedance section 420. For example, the third impedance section 410 can be made of the same material as the first impedance section 210, such as molybdenum, while the fourth impedance section 420 can be made of the same material as the second impedance section 220, such as tungsten. By also providing a similar lateral impedance mismatch structure at the edges of the top electrode 400, the suppression effect on Lamb waves can be further enhanced.

[0058] In the longitudinal direction, the projection of the third impedance section 410 is misaligned with the projection of the first impedance section 210 and overlaps with the projection of the second impedance section 220, forming a first longitudinal impedance mismatch structure. Simultaneously, the projection of the fourth impedance section 420 is misaligned with the projection of the second impedance section 220 and overlaps with the projection of the first impedance section 210, forming a second longitudinal impedance mismatch structure. This misaligned and overlapping arrangement introduces a discontinuity in acoustic impedance in the longitudinal direction, thereby affecting the longitudinally propagating sound waves.

[0059] The high-Q bulk acoustic wave resonator proposed in this application operates by using acoustic impedance mismatch to suppress Lamb wave energy leakage. When the bulk acoustic wave resonator is working, the piezoelectric layer 300 generates longitudinal vibration in the thickness direction under the action of an electric field, exciting acoustic waves. However, due to the presence of transverse stress free surfaces, Lamb waves are inevitably generated and radiated outward from the active region, resulting in energy loss and thus affecting the Q value of the resonator.

[0060] To address this issue, this application incorporates a first lateral impedance mismatch structure and a second lateral impedance mismatch structure at the lateral edges of the bottom electrode 200 and the top electrode 400, respectively. These lateral impedance mismatch structures, by alternately connecting materials with different acoustic impedances along the lateral direction, create a periodic variation in acoustic impedance. When a Lamb wave propagates in the lateral direction and encounters these interfaces of acoustic impedance discontinuity, some energy is reflected back, and some energy is scattered, effectively preventing the Lamb wave from leaking outward.

[0061] Furthermore, this application introduces impedance mismatch in the longitudinal direction. Specifically, the projection of the third impedance section 410 is misaligned with the projection of the first impedance section 210 and overlaps with the projection of the second impedance section 220, forming a first longitudinal impedance mismatch structure. Simultaneously, the projection of the fourth impedance section 420 is misaligned with the projection of the second impedance section 220 and overlaps with the projection of the first impedance section 210, forming a second longitudinal impedance mismatch structure. This longitudinal misalignment and overlap design results in a periodic change in acoustic impedance in the longitudinal direction as well. When sound waves propagate in the longitudinal direction, they are also affected by these impedance mismatch structures, further restricting the lateral propagation of the sound waves and better confining their energy within the active region of the resonator.

[0062] Thus, through the dual impedance mismatch structure in both the transverse and longitudinal directions, the energy of the Lamb wave is effectively confined within the resonator, reducing energy leakage to the outside. This effective energy confinement directly leads to a significant increase in the resonator's Q value.

[0063] Compared to traditional methods that use single or double protrusion frame structures to suppress Lamb wave energy leakage, the high-Q bulk acoustic resonator proposed in this application has significant advantages and innovations. Traditional methods require additional protrusion frame layers, which not only increases the complexity of the fabrication process but also demands high precision in the width dimensions of the protrusions, making it difficult to achieve. Furthermore, single-protrusion frame structures have limited ability to suppress lateral leakage, while double-protrusion frame structures, although offering better suppression, further increase the fabrication difficulty due to the complexity of their multi-layered fabrication process.

[0064] The core innovation of this application lies in the use of lateral impedance mismatch structures formed by alternating connections of different acoustic impedance materials at the lateral edges of the bottom electrode 200 and the top electrode 400, and the clever utilization of the longitudinal projection misalignment and overlap of these structures to form a longitudinal impedance mismatch structure. This design eliminates the need for an additional raised frame layer, achieving periodic changes in acoustic impedance directly within the electrode layers. This significantly simplifies the fabrication process and reduces the stringent requirements for dimensional accuracy.

[0065] This application achieves effective suppression of Lamb wave energy leakage without increasing additional process complexity through an innovative dual impedance mismatch structure in both the lateral and longitudinal directions, thereby significantly improving the Q value of the bulk acoustic resonator. This design not only solves the problems of complex processes, high precision requirements, and limited suppression effects in existing technologies, but also provides a higher-performance radio frequency device for the high-frequency mobile communication field, demonstrating significant technological advancement and practical value.

[0066] In some embodiments described above, the high-Q bulk acoustic resonator improves its Q value by incorporating an impedance mismatch structure at the lateral edges of the bottom electrode 200 and the top electrode 400. However, in practical implementation, if the electrode edges are too steep or perpendicular, unwanted reflection or scattering of acoustic energy at the edges may occur, introducing parasitic modes or reducing the resonator's Q value. Without addressing these issues, the resonator's performance may not be optimal, especially in high-frequency applications where parasitic mode suppression and Q value enhancement are crucial.

[0067] Further, see attached document. Figure 3 and attached Figure 4 The third impedance portion 410 and the fourth impedance portion 420 in the second transverse impedance mismatch structure on both sides of the top electrode 400 in the transverse direction are arranged in a stepped shape.

[0068] In some embodiments, reference is made to the appendix. Figure 1 Appendix Figure 2 Appendix Figure 3 and attached Figure 4The two edges of the bottom electrode 200 in the lateral direction are both set as bevels so that the cross-sectional shape of the bottom electrode 200 is a trapezoid with a narrow top and a wide bottom.

[0069] During the fabrication process, the anisotropy of the etching process can be controlled, or techniques such as angled evaporation and etching back can be used to make the sidewalls of the bottom electrode 200 no longer vertical, but inclined inward or outward. When both sides are set as bevels, the top width of the bottom electrode 200 will be different from the bottom width, thus forming a trapezoidal cross-section.

[0070] The solution in this application effectively alters the propagation and reflection characteristics of sound waves at the electrode edge by setting the lateral edge of the bottom electrode 200 as a slope. Traditional right-angled edges tend to create abrupt changes in acoustic impedance, leading to strong reflection of sound wave energy at the edge and potentially exciting edge modes or parasitic modes. In contrast, a trapezoidal cross-section, especially a sloped edge, provides a smoother acoustic impedance transition region, allowing sound wave energy to be more effectively confined within the resonant region in the lateral direction, reducing outward leakage. This increases the concentration of sound wave energy and suppresses the generation of unwanted modes.

[0071] Through the above technical solution, the trapezoidal cross-section design of the bottom electrode 200 significantly improves the acoustic energy confinement effect of the resonator, effectively suppressing the generation of edge modes and parasitic modes. This not only helps to improve the Q value of the resonator and reduce insertion loss, but also improves the frequency response characteristics of the resonator, enabling it to exhibit higher performance stability and reliability in practical applications.

[0072] In some embodiments, reference is made to the appendix. Figure 1 Appendix Figure 2 Appendix Figure 3 and attached Figure 4 It also includes a frequency modulation layer 600 stacked longitudinally on the top electrode 400, so as to achieve effective adjustment of the resonant frequency by stacking the frequency modulation layer 600 on the top electrode 400.

[0073] In some embodiments, both the first impedance section 210 and the third impedance section 410 are made of molybdenum material.

[0074] In some embodiments, both the second impedance section 220 and the fourth impedance section 420 are made of tungsten material.

[0075] The present invention provides a filter, including the high Q value bulk acoustic resonator in the above embodiments.

[0076] The present invention provides a duplexer, including the high Q value bulk acoustic resonator in the above embodiments.

[0077] Reference Appendix Figure 5 Appendix Figure 6 and attached Figure 7 The present invention provides a method for fabricating the high-Q bulk acoustic resonator in the above embodiments, comprising the following steps:

[0078] S1. Using photolithography, grooves are etched on the substrate, and then CVD coating is performed on the grooves to obtain a sacrificial layer that fills the grooves;

[0079] S2. Using a coating process, a patterned first impedance section is obtained by performing a first coating on the sacrificial layer;

[0080] S3. Using a coating process, a patterned second impedance part is obtained by performing a second coating on the sacrificial layer, and the second impedance part and the first impedance part are alternately connected in the transverse direction to form a bottom electrode;

[0081] S4. A piezoelectric layer is grown on the bottom electrode using PVD technology;

[0082] S5. Using a coating process, a patterned third impedance part is obtained by first coating on the piezoelectric layer, and the longitudinal projection of the third impedance part is misaligned with the longitudinal projection of the first impedance part and overlaps with the longitudinal projection of the second impedance part.

[0083] S6. Using a coating process, a patterned fourth impedance part is obtained by performing a second coating on the piezoelectric layer, and the third impedance part and the fourth impedance part are alternately connected in the transverse direction to form a top electrode, and the longitudinal projection of the fourth impedance part is misaligned with the longitudinal projection of the second impedance part and overlaps with the longitudinal projection of the first impedance part.

[0084] S7. A cavity is obtained by releasing the sacrificial layer.

[0085] In step S1, the substrate 100 is typically made of materials such as silicon, sapphire, or glass, on which grooves of predetermined shape and depth are precisely etched using a photolithography process. Subsequently, a chemical vapor deposition (CVD) technique is used to fill these grooves with a material that can be selectively removed later (i.e., a sacrificial layer 700). This sacrificial layer 700 will be removed in a subsequent step to form the cavity 500.

[0086] In step S2, a patterned first impedance portion 210 is formed on the substrate 100 filled with the sacrificial layer 700 by a first coating process (e.g., physical vapor deposition PVD or chemical vapor deposition CVD), combined with photolithography and etching techniques, and a lift-off process. The material of the first impedance portion 210 is selected to have a low acoustic impedance.

[0087] In step S3, immediately following the first impedance portion 210 and the sacrificial layer 700, a patterned second impedance portion 220 is formed through a second coating process. The material of the second impedance portion 220 is selected to have a high acoustic impedance. Through precise patterning, the first impedance portion 210 and the second impedance portion 220 are alternately connected in the lateral direction, together forming the bottom electrode 200.

[0088] In step S4, a piezoelectric layer 300 is grown on the formed bottom electrode 200 using a physical vapor deposition (PVD) process, such as sputtering or evaporation. The piezoelectric layer 300 is typically made of piezoelectric materials such as aluminum nitride (AlN), zinc oxide (ZnO), or lead zirconate titanate (PZT), and its thickness is crucial to the resonant frequency of the resonator.

[0089] In step S5, a patterned third impedance portion 410 is formed on the piezoelectric layer 300 through a first coating process. The material of the third impedance portion 410 is selected to have a low acoustic impedance. In this step, it is crucial to ensure that the projection of the third impedance portion 410 is misaligned with the projection of the first impedance portion 210 in the longitudinal direction, while overlapping with the projection of the second impedance portion 220, thereby forming a first longitudinal impedance mismatch structure.

[0090] In step S6, a patterned fourth impedance portion 420 is formed on the third impedance portion 410 and the piezoelectric layer 300 through a second coating process. The material of the fourth impedance portion 420 is selected to have a high acoustic impedance. Through precise patterning, the third impedance portion 410 and the fourth impedance portion 420 are alternately connected in the lateral direction to jointly form the top electrode 400. At the same time, in this step, it is ensured that the projection of the fourth impedance portion 420 is misaligned with the projection of the second impedance portion 220 in the longitudinal direction, while overlapping with the projection of the first impedance portion 210, thereby forming a second longitudinal impedance mismatch structure.

[0091] In step S7, a cavity 500 is formed between the substrate 100 and the bottom electrode 200 by selectively releasing (e.g., wet etching or dry etching) the sacrificial layer 700 formed in step S1. The formation of the cavity 500 is key to achieving a high Q value for the bulk acoustic wave resonator.

[0092] The solution in this application employs a step-by-step patterned deposition process for the first impedance section 210, the second impedance section 220, the third impedance section 410, and the fourth impedance section 420. By strictly controlling the alternating lateral connections and the misalignment and overlap of their longitudinal projections, the precise formation of the lateral impedance mismatch structure, as well as the first and second longitudinal impedance mismatch structures, of the bottom electrode 200 and the top electrode 400 is ensured. This step-by-step deposition and patterning strategy makes the precise arrangement of different acoustic impedance materials possible, thereby effectively limiting the propagation of acoustic wave energy within the resonator, reducing energy leakage to the outside, and ultimately improving the Q value of the resonator.

[0093] The above technical solutions significantly improve manufacturing precision and process stability, effectively reducing acoustic energy loss caused by structural inaccuracies, thus contributing to the acquisition of resonators with higher Q values. Furthermore, this fabrication method exhibits good repeatability and mass production potential, effectively improving production yield and reducing manufacturing costs, providing a reliable manufacturing pathway for the industrial application of high-performance bulk acoustic wave resonators.

[0094] In some embodiments, a further step is included between step S1 and step S2:

[0095] The sacrificial layer is smoothed using CMP technology.

[0096] CMP, or Chemical Mechanical Polishing, is a technique that combines chemical etching with mechanical abrasion to planarize the surface of a material. This process effectively removes excess material from the surface of the sacrificial layer 700 and eliminates surface irregularities, resulting in a highly flat surface. In practical applications, specific parameters of the CMP process, such as the slurry formulation, polishing pressure, polishing speed, and polishing time, can be adjusted according to the material properties of the sacrificial layer 700 and the required flatness to ensure that the surface of the sacrificial layer 700 is uniformly smoothed.

[0097] The reason why the CMP process is introduced after the formation of the sacrificial layer 700 in this application is that the sacrificial layer 700 formed by photolithography and CVD deposition in step S1, especially when filling the grooves, often has a surface that is difficult to achieve ideal flatness. This uneven surface will directly affect the deposition quality of the first impedance portion 210 in the subsequent step S2, for example, causing uneven thickness of the first impedance portion 210, or forming defects in the uneven area. It is precisely because the CMP process can precisely planarize the surface of the sacrificial layer 700 and eliminate surface undulations that the subsequent deposition of the first impedance portion 210 and the second impedance portion 220 can be carried out on a highly flat substrate, thereby ensuring the uniformity and structural integrity of the electrode layer.

[0098] In some embodiments, a further step is included between step S6 and step S7:

[0099] A frequency modulation layer is grown on the top electrode using PVD technology.

[0100] Among them, PVD, or Physical Vapor Deposition, is a commonly used thin film deposition technique. Its key feature is its ability to precisely control the thickness and uniformity of the thin film, thereby ensuring the quality of the grown frequency modulation layer 600. The frequency modulation layer 600 is grown on the surface of the top electrode 400, and its function is to fine-tune the resonant frequency of the resonator by changing its effective mass or stress state. The introduction of this step allows for precise pre-adjustment of the resonant frequency before the cavity 500 is fully formed—that is, when the resonator structure is basically complete but the stress has not yet been fully released—providing a crucial process window for subsequent performance optimization.

[0101] This application's solution effectively addresses the potential deviation in the resonant frequency by introducing a step between steps S6 and S7: growing a frequency-tuning layer 600 on the top electrode 400 using a PVD process. Specifically, the resonant frequency of a resonator is closely related to its effective mass and elastic constant. By precisely depositing a frequency-tuning layer 600 on the top electrode 400, the total effective mass of the resonator can be finely adjusted. Since the PVD process enables nanometer-level precise control of the film thickness, the thickness of the frequency-tuning layer 600 can be precisely adjusted based on the deviation between the actual measured resonant frequency and the target frequency, thereby achieving fine compensation and calibration of the resonant frequency. This frequency tuning operation, performed before the cavity 500 is released, avoids complex and potentially damaging post-processing after the resonator is fully formed, improving the efficiency and accuracy of frequency tuning.

[0102] In this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations.

[0103] The use of terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refers to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of the present 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.

[0104] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of manufacture for fabricating a bulk acoustic wave resonator having a high Q-value, characterized by, A high-Q bulk acoustic resonator includes a substrate (100), a bottom electrode (200), a piezoelectric layer (300), and a top electrode (400) stacked in sequence in the longitudinal direction, a cavity (500) is arranged between the substrate (100) and the bottom electrode (200), characterized in that the bottom electrode (200) is provided with a first lateral impedance mismatch structure on both sides of the lateral direction, the first lateral impedance mismatch structure includes first impedance parts (210) and second impedance parts (220) connected alternately in the lateral direction, the acoustic impedance of the first impedance part (210) is lower than that of the second impedance part (220); the top electrode (400) is provided with a second lateral impedance mismatch structure on both sides of the lateral direction, the second lateral impedance mismatch structure includes third impedance parts (410) and fourth impedance parts (420) connected alternately in the lateral direction, the acoustic impedance of the third impedance part (410) is lower than that of the fourth impedance part (420); the longitudinal projection of the third impedance part (410) is offset from the longitudinal projection of the first impedance part (210) and overlaps the longitudinal projection of the second impedance part (220), forming a first longitudinal impedance mismatch structure; the longitudinal projection of the fourth impedance part (420) is offset from the longitudinal projection of the second impedance part (220) and overlaps the longitudinal projection of the first impedance part (210), forming a second longitudinal impedance mismatch structure; the preparation method comprises the following steps: S1. After etching a groove on the substrate by using a photolithography process, the groove is coated by CVD to obtain a sacrificial layer filling the groove; S2. By using a coating process, the first impedance part is patterned by performing first coating on the sacrificial layer; S3. By using a coating process, the second impedance part is patterned by performing second coating on the sacrificial layer, and the second impedance part and the first impedance part are alternately connected in the lateral direction to form the bottom electrode; S4. By using a PVD process, the piezoelectric layer is grown on the bottom electrode; S5. By using a coating process, the third impedance part is patterned by performing first coating on the piezoelectric layer, and the longitudinal projection of the third impedance part is offset from the longitudinal projection of the first impedance part and overlaps the longitudinal projection of the second impedance part; S6. By using a coating process, the fourth impedance part is patterned by performing second coating on the piezoelectric layer, and the third impedance part and the fourth impedance part are alternately connected in the lateral direction to form the top electrode, and the longitudinal projection of the fourth impedance part is offset from the longitudinal projection of the second impedance part and overlaps the longitudinal projection of the first impedance part; S7. The cavity is obtained by releasing the sacrificial layer.

2. The production method according to claim 1, characterized by, between step S1 and step S2, further comprising the step of: using a CMP process to polish the sacrificial layer.

3. The preparation method according to claim 1, characterized in that, between step S6 and step S7, further comprising the step of: using a PVD process to grow a frequency modulation layer on the top electrode.

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