A film bulk acoustic resonator and a method of manufacturing the same

Abstract

This application provides a thin-film bulk acoustic wave resonator and its fabrication method, relating to the field of semiconductor technology. The thin-film bulk acoustic wave resonator includes: a substrate, a lower electrode, a piezoelectric layer, and an upper electrode sequentially disposed on the substrate. The upper electrode has a wing structure and a bridge structure at its edge. The piezoelectric layer also has a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure. The sides of the first and second thickening layers are respectively attached to the upper electrode. A first gap exists between the surface of the first thickening layer facing away from the piezoelectric layer and the wing structure, and the first gap is filled with air or has a first sacrificial layer. A second gap exists between the surface of the second thickening layer facing away from the piezoelectric layer and the bridge structure, and the second gap is filled with air or has a second sacrificial layer. This thin-film bulk acoustic wave resonator effectively suppresses the non-longitudinal electric field introduced by the lifting of the wing structure and bridge structure, avoiding transverse acoustic waves excited by the non-longitudinal electric field inside the piezoelectric layer, thereby improving performance.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more specifically, to a thin-film bulk acoustic resonator and its fabrication method. Background Technology

[0002] Radio frequency (RF) filters are the cornerstone of wireless communication. Thin-film bulk acoustic resonators (FBARs), with their high quality factor, low loss, high reliability, miniaturization, and compatibility with IC processes, have become one of the core components for building RF filters. With the rapid development of 5G wireless communication, FBARs are required to have smaller size and higher performance: such as a larger effective electromechanical coupling coefficient (K), a higher quality factor (Q), fewer spurious modes, and a larger figure of merit (FOM).

[0003] Traditional thin-film bulk acoustic resonators (FBARs) are typically sandwich structures consisting of an upper electrode, a piezoelectric layer, and a lower electrode. Ideally, by applying alternating current to the surfaces of the upper and lower electrodes, the piezoelectric effect excites longitudinal waves propagating along the height direction. However, due to defects in the thin-film material and limitations imposed by structural boundary conditions, transverse waves, such as Rayleigh-Lamb waves, also exist in FBARs, perpendicular to the film height direction. The presence of transverse waves interferes with the vibration of the dominant mode, thus affecting the resonator's performance, such as reducing the K-value, Q-value, and FOM value.

[0004] Therefore, optimizing the boundary conditions of FBAR, limiting and utilizing the transverse waves present in FBAR, and further improving the K-value, Q-value, and FOM-value of the resonator is one of the urgent issues. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of the prior art by providing a thin-film bulk acoustic resonator and its fabrication method, which can improve the performance of the resonator.

[0006] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:

[0007] One aspect of this application provides a thin-film bulk acoustic resonator, comprising: a substrate, a lower electrode, a piezoelectric layer, and an upper electrode sequentially disposed on the substrate, wherein the upper electrode has a wing structure and a bridge structure at its edge; the piezoelectric layer is further provided with a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure, the sides of the first thickening layer and the second thickening layer are respectively attached to the upper electrode, a first gap is formed between the surface of the first thickening layer away from the piezoelectric layer and the wing structure, the first gap is filled with air or provided with a first sacrificial layer, and a second gap is formed between the surface of the second thickening layer away from the piezoelectric layer and the bridge structure, the second gap is filled with air or provided with a second sacrificial layer.

[0008] Optionally, the first thickened layer is divided into a first thickened region and a second thickened region. The side of the first thickened region is attached to the upper electrode, the side of the first thickened region away from the piezoelectric layer is attached to the side of the upper electrode facing the piezoelectric layer, and the side of the second thickened region away from the piezoelectric layer forms a first gap with the wing structure.

[0009] Optionally, the second thickened layer is divided into a third thickened region and a fourth thickened region. The side of the third thickened region is attached to the upper electrode, the side of the third thickened region away from the piezoelectric layer is attached to the side of the upper electrode facing the piezoelectric layer, and the side of the fourth thickened region away from the piezoelectric layer forms a second gap with the bridge structure.

[0010] Optionally, a third gap exists between the piezoelectric layer and the wing structure, and both the third gap and the first gap are filled with air, or both are provided with a first sacrificial layer.

[0011] Optionally, a fourth gap exists between the piezoelectric layer and the bridge structure, and both the fourth gap and the second gap are filled with air, or both are provided with a second sacrificial layer.

[0012] Optionally, it also includes a seed layer disposed on the substrate, with the lower electrode covering the seed layer.

[0013] Optionally, it also includes a passivation layer covering the upper electrode, the wing structure, and the bridge structure, with an annular groove on the side of the passivation layer facing away from the upper electrode, the annular groove being located above the upper electrode.

[0014] Another aspect of this application provides a method for fabricating a thin-film bulk acoustic resonator, comprising: providing a substrate and sequentially forming a lower electrode and a piezoelectric layer on the substrate; forming a first thickening layer and a second thickening layer on the piezoelectric layer; forming a first sacrificial layer on the first thickening layer and a second sacrificial layer on the second thickening layer; forming a wing structure on the first sacrificial layer and a bridge structure on the second sacrificial layer, and forming an upper electrode between the wing structure and the bridge structure.

[0015] Optionally, after forming the upper electrode between the wing structure and the bridge structure, the method further includes: releasing the first sacrificial layer and the second sacrificial layer to form a first gap between the first thickened layer and the wing structure, and a second gap between the second thickened layer and the bridge structure.

[0016] Optionally, the first sacrificial layer covers a portion of the first thickened layer, and / or the second sacrificial layer covers a portion of the second thickened layer.

[0017] Optionally, the first sacrificial layer further covers the piezoelectric layer outside the first thickened layer, and / or the second sacrificial layer further covers the piezoelectric layer outside the second thickened layer.

[0018] Optionally, after forming the upper electrode between the wing structure and the bridge structure, the method further includes: forming a passivation layer on the wing structure, the upper electrode, and the bridge structure; forming an annular groove on the passivation layer, wherein the orthogonal projection of the annular groove on the piezoelectric layer is located between the first thickening layer and the second thickening layer.

[0019] The beneficial effects of this application include:

[0020] This application provides a thin-film bulk acoustic resonator, comprising: a substrate, a lower electrode, a piezoelectric layer, and an upper electrode sequentially disposed on the substrate. The upper electrode has a wing structure and a bridge structure at its edge. The piezoelectric layer also has a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure. The sides of the first and second thickening layers are respectively attached to the upper electrode. A first gap exists between the surface of the first thickening layer facing away from the piezoelectric layer and the wing structure, and the first gap is filled with air or has a first sacrificial layer. A second gap exists between the surface of the second thickening layer facing away from the piezoelectric layer and the bridge structure, and the second gap is filled with air or has a second sacrificial layer. This thin-film bulk acoustic resonator effectively suppresses the non-longitudinal electric field introduced by the lifting of the wing structure and the bridge structure by utilizing the first gap between the first thickening layer and the wing structure and the second gap between the second thickening layer and the bridge structure, thus avoiding the transverse acoustic waves excited by the non-longitudinal electric field inside the piezoelectric layer, thereby improving performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is one of the structural schematic diagrams of a thin-film bulk acoustic resonator provided in the embodiments of this application;

[0023] Figure 2This is a second schematic diagram of the structure of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0024] Figure 3 This is the third schematic diagram of the structure of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0025] Figure 4 Fourth schematic diagram of the structure of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0026] Figure 5 Potential diagram of a thin-film bulk acoustic resonator provided in an embodiment of this application;

[0027] Figure 6 Fifth schematic diagram of the structure of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0028] Figure 7 Sixth schematic diagram of the structure of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0029] Figure 8 A diagram showing the relationship between the width of the second thickened region and the electromechanical coupling coefficient in a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0030] Figure 9 A graph showing the relationship between the height of the second thickened region and the electromechanical coupling coefficient in a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0031] Figure 10 A graph showing the relationship between the width of the second thickened region and the quality factor in a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0032] Figure 11 A graph showing the relationship between the height of the second thickened region and the quality factor in the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0033] Figure 12 This is one of the flowcharts for a method of fabricating a thin-film bulk acoustic resonator provided in the embodiments of this application;

[0034] Figure 13 This is one of the schematic diagrams illustrating the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0035] Figure 14 This is the second schematic diagram illustrating the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application.

[0036] Figure 15 The third schematic diagram illustrating the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0037] Figure 16Fourth schematic diagram of the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0038] Figure 17 Fifth schematic diagram of the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0039] Figure 18 A second flowchart illustrating the fabrication method of the thin-film bulk acoustic resonator provided in the embodiments of this application;

[0040] Figure 19 This is the sixth schematic diagram illustrating the fabrication process of the thin-film bulk acoustic resonator provided in the embodiments of this application.

[0041] Icons: 10-Thin-film bulk acoustic resonator; 11-Substrate; 111-Cavity; 12-Lower electrode; 13-Piezoelectric layer; 131-Lower electrode lead-out hole; 14-Upper electrode; 15-Wing structure; 16-Bridge structure; 17-First thickened layer; 171-First thickened region; 172-Second thickened region; 18-Second thickened layer; 181-Third thickened region; 182-Fourth thickened region; 19-First gap; 20-First sacrificial layer; 21-Second gap; 22-Second sacrificial layer; 23-Third gap; 24-Fourth gap; 25-Seed layer; 26-Passivation layer; 261-Annular groove; 262-Upper electrode lead-out hole; 27-Protective layer; 28-Release hole; X-Lateral direction; Y-Longitudinal direction. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. It should be noted that, unless otherwise specified, the various features in the embodiments of this application can be combined with each other, and the combined embodiments are still within the protection scope of this application.

[0044] It should be noted that similar labels 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.

[0045] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application 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 on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" 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 or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0047] One aspect of the embodiments of this application refers to... Figure 1 and Figure 2 A thin-film bulk acoustic wave resonator 10 is provided, comprising: a substrate 11, a lower electrode 12, a piezoelectric layer 13, and an upper electrode 14 sequentially disposed on the substrate 11. The upper electrode 14 has a wing structure 15 and a bridge structure 16 at its edge. The overlapping region of the upper electrode 14, the piezoelectric layer 13, and the lower electrode 12 in the longitudinal Y direction constitutes the active region of the thin-film bulk acoustic wave resonator 10. The wing structure 15 and the bridge structure 16 are raised upwards and separated from the piezoelectric layer 13.

[0048] The piezoelectric layer 13 also has a first thickening layer 17 corresponding to the wing structure 15 and a second thickening layer 18 corresponding to the bridge structure 16. The sides of the first thickening layer 17 and the second thickening layer 18 are respectively attached to the upper electrode 14, thereby achieving electrical connection with the upper electrode 14. At least a portion of the first thickening layer 17 corresponds to the position of the wing structure 15 in the longitudinal Y direction, i.e., it is located below the wing structure 15. At least a portion of the second thickening layer 18 corresponds to the position of the bridge structure 16 in the longitudinal Y direction, i.e., it is located below the bridge structure 16. Please refer to the reference. Figure 3 and Figure 4The surface of the first thickened layer 17 facing away from the piezoelectric layer 13 (i.e., the upper surface) has a first gap 19 between it and the wing structure 15. The first gap 19 is filled with air or has a first sacrificial layer 20. The surface of the second thickened layer 18 facing away from the piezoelectric layer 13 (i.e., the upper surface) has a second gap 21 between it and the bridge structure 16. The second gap 21 is filled with air or has a second sacrificial layer 22. The surfaces of the first thickened layer 17 and the second thickened layer 18 facing away from the piezoelectric layer 13 can be planar, curved, or stepped, etc.

[0049] Please refer to the reference. Figure 5 After being connected to the upper electrode 14, the first thickened layer 17 extends downwards towards the wing structure 15. A low-frequency structure is added to one side of the first thickened layer 17 at the edge of the active region, which can effectively reflect transverse acoustic waves and improve the Q value of the resonator. A first gap 19 is formed between the other side of the first thickened layer 17 and the wing structure 15. This gap 19 creates a low acoustic impedance region, resulting in an acoustic impedance mismatch between the active region and this low acoustic impedance region. This also helps to reflect transverse waves and suppress energy leakage in the active region, further improving the Q value of the resonator. Furthermore, the first gap 19 makes the potentials between the wing structure 15 and the first thickened layer 17 equal, effectively suppressing the non-longitudinal electric field introduced by the lifting of the wing structure 15. Suppressing the non-longitudinal electric field avoids transverse acoustic waves excited within the piezoelectric layer 13, thereby improving the performance of the thin-film bulk acoustic resonator 10. Similarly, a low-frequency structure is added to one side of the second thickened layer 18 at the edge of the active region, and a low acoustic impedance region is formed between the second side and the bridge structure 16. At the same time, it also suppresses the non-longitudinal electric field introduced by the lifting of the bridge structure 16, thus improving the performance of the thin-film bulk acoustic resonator 10. In addition, the Q value and K value of the resonator can be adjusted by adjusting the width (dimension in the horizontal X direction) and height (dimension in the vertical Y direction) of the first thickened layer 17.

[0050] Since the first thickened layer 17 and the second thickened layer 18 do not cause a non-longitudinal electric field, the tilt angles of the first thickened layer 17 and the second thickened layer 18 can be arbitrary. Therefore, the setting of the first gap 19 and the second gap 21 also reduces the manufacturing cost. It should be noted that the tilt angle of the first thickened layer 17 refers to the angle between the lower surface of the first thickened layer 17 and the side of the first thickened layer 17 that is in contact with the upper electrode 14, and the tilt angle of the second thickened layer 18 refers to the angle between the lower surface of the second thickened layer 18 and the side of the second thickened layer 18 that is in contact with the upper electrode 14.

[0051] In addition, since the first thickened layer 17 and the second thickened layer 18 are electrically connected to the upper electrode 14, the potentials of the first thickened layer 17 and the second thickened layer 18 are equal to the potential of the upper electrode 14 (both are positive). Therefore, there will be no corresponding interference between the first thickened layer 17 and the upper electrode 14, or between the second thickened layer 18 and the upper electrode 14.

[0052] Alternatively, please refer to Figure 1 The first thickened layer 17 is divided into a first thickened region 171 and a second thickened region 172. One side of the first thickened region 171 is attached to the upper electrode 14, and the side of the first thickened region 171 away from the piezoelectric layer 13 is attached to the side of the upper electrode 14 facing the piezoelectric layer 13. The side of the second thickened region 172 away from the piezoelectric layer 13 forms a first gap 19 with the wing structure 15.

[0053] One side of the first thickened region 171 is attached to the upper electrode 14, and the opposite side is attached to the second thickened region 172. The lower surface of the first thickened region 171 is attached to the piezoelectric layer 13, and the upper surface is attached to the upper electrode 14. The lower surface of the second thickened region 172 is attached to the piezoelectric layer 13, and a first gap 19 is formed between the upper surface and the wing structure 15.

[0054] For example, the first thickened region 171 and the second thickened region 172 have the same height. That is, the edge region of the upper electrode 14 is raised to form a first step, and the gap between the first step and the piezoelectric layer 13 is small and is completely filled by the first thickened region 171. The wing structure 15, as the second step, has a larger gap with the piezoelectric layer 13, which is partially filled by the second thickened region 172. After filling, there is a first gap 19 between the second thickened region 172 and the second step.

[0055] Optionally, the second thickened layer 18 is divided into a third thickened region 181 and a fourth thickened region 182. The side of the third thickened region 181 is attached to the upper electrode 14, and the side of the third thickened region 181 away from the piezoelectric layer 13 is attached to the side of the upper electrode 14 facing the piezoelectric layer 13. The side of the fourth thickened region 182 away from the piezoelectric layer 13 forms a second gap 21 with the bridge structure 16.

[0056] One side of the third thickened region 181 is attached to the upper electrode 14, and the opposite side is attached to the fourth thickened region 182. The lower surface of the third thickened region 181 is attached to the piezoelectric layer 13, and the upper surface is attached to the upper electrode 14. The lower surface of the fourth thickened region 182 is attached to the piezoelectric layer 13, and a third gap 23 is formed between the upper surface and the bridge structure 16.

[0057] For example, the third thickened region 181 and the fourth thickened region 182 have the same height. That is, the edge region of the upper electrode 14 is raised to form a third step, and the gap between the third step and the piezoelectric layer 13 is small and is completely filled by the third thickened region 181. The bridge structure 16, as the fourth step, has a larger gap with the piezoelectric layer 13, which is partially filled by the fourth thickened region 182. After filling, there is a third gap 23 between the fourth thickened region 182 and the fourth step.

[0058] Furthermore, the first thickened region 171, the second thickened region 172, the third thickened region 181, and the fourth thickened region 182 are all of equal height to facilitate processing.

[0059] Alternatively, please refer to Figure 6 and Figure 7 There is a third gap 23 between the piezoelectric layer 13 and the wing structure 15. Both the third gap 23 and the first gap 19 are filled with air, or both are provided with a first sacrificial layer 20.

[0060] By adjusting the width of the first thickening layer 17, a third gap 23 can be formed between the wing structure 15 and the piezoelectric layer 13, and the third gap 23 is connected to the first gap 19. For ease of processing, both the third gap 23 and the first gap 19 are filled with air, or both the third gap 23 and the first gap 19 are filled with the first sacrificial layer 20.

[0061] Optionally, a fourth gap 24 is provided between the piezoelectric layer 13 and the bridge structure 16, and both the fourth gap 24 and the second gap 21 are filled with air, or both are provided with a second sacrificial layer 22.

[0062] By adjusting the width of the second thickening layer 18, a fourth gap 24 can be formed between the bridge structure 16 and the piezoelectric layer 13, and the fourth gap 24 is connected to the second gap 21. For ease of processing, both the fourth gap 24 and the second gap 21 are filled with air, or both the fourth gap 24 and the second gap 21 are filled with the second sacrificial layer 22.

[0063] In order to give the lower electrode 12 and the piezoelectric layer 13 better lattice orientation, the thin film bulk acoustic resonator 10 may optionally include a seed layer 25 disposed on the substrate 11, and the lower electrode 12 covers the seed layer 25.

[0064] Optionally, the thin-film bulk acoustic resonator 10 further includes a passivation layer 26, which covers the upper electrode 14, the wing structure 15 and the bridge structure 16. The passivation layer 26 has an annular groove 261 on the side opposite to the upper electrode 14. The orthogonal projection of the annular groove 261 on the piezoelectric layer 13 is located between the first thickening layer 17 and the second thickening layer 18.

[0065] The annular groove 261 is projected onto the piezoelectric layer 13 along the longitudinal direction Y, and the projection of the annular groove 261 is located between the first thickened layer 17 and the second thickened layer 18. The annular groove 261 can eliminate parasitic frequencies of the series resonators in the Type II dispersive thin film bulk acoustic resonator 10.

[0066] Optionally, a cavity 111 is provided on the upper surface of the substrate 11, and at least a portion of the cavity 111 corresponds to the active region of the thin-film bulk acoustic resonator 10 in the longitudinal Y direction. The cavity 111 is used to reflect sound waves.

[0067] Optionally, the piezoelectric layer 13 is provided with a lower electrode lead-out hole 131, and the passivation layer 26 is provided with an upper electrode lead-out hole 262, so as to lead out the lower electrode 12 and the upper electrode 14 respectively.

[0068] Furthermore, a protective layer 27 is filled inside the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262 to protect them.

[0069] by Figure 1 Taking the thin-film bulk acoustic resonator 10 shown as an example, Figure 8 The relationship between the width of the second thickened region 172 and the electromechanical coupling coefficient is shown. Figure 9 The relationship between the height of the second thickened region 172 and the electromechanical coupling coefficient is shown. Figure 10 The relationship between the width of the second thickened region 172 and the quality factor is shown. Figure 11 The relationship between the height of the second thickened region 172 and the quality factor is shown. Figures 8 to 11 It can be seen that by adjusting the width and height of the second thickened region 172, the electromechanical coupling coefficient (K value) and quality factor (Q value) of the thin-film bulk acoustic resonator 10 can be adjusted.

[0070] Figure 1 The quality factor of the thin-film bulk acoustic wave resonator 10 shown is approximately 900. In the prior art, the quality factor of a sandwich-structured thin-film bulk acoustic wave resonator is approximately 300, and the quality factor of a sandwich-structure + wing-structure + bridge-structure thin-film bulk acoustic wave resonator is approximately 450. Therefore, it is evident that the quality factor of the thin-film bulk acoustic wave resonator 10 with the sandwich-structure + wing-structure + bridge-structure + thickened layer structure provided in this embodiment is significantly higher than that of existing thin-film bulk acoustic wave resonators.

[0071] Please refer to Figure 12 This embodiment also provides a method for fabricating a thin-film bulk acoustic resonator, including:

[0072] S100: Provides a substrate, and sequentially forms a lower electrode and a piezoelectric layer on the substrate.

[0073] Please refer to the reference. Figure 13The lower electrode 12 covers a portion of the substrate 11, and the piezoelectric layer 13 covers both the lower electrode 12 and the portion of the piezoelectric layer 13 exposed by the lower electrode 12. The substrate 11 can be a silicon wafer, such as high-resistivity silicon, or a special substrate. The lower electrode 12 is typically made of materials such as Mo, Al, Pt, Cu, or Au. The piezoelectric layer 13 is typically made of AlN and common piezoelectric materials such as doped AlN, PZT, LiNbO3, or LiTaO3, or it can be a composite piezoelectric material, such as AlN / ScAlN.

[0074] For example, the lower electrode 12 has an angle, which is the angle between the inclined side of the lower electrode 12 and the substrate 11.

[0075] The growth of the piezoelectric layer 13 depends on a flat surface. The smaller the tilt angle of the lower electrode 12, the higher the crystal quality of the piezoelectric layer 13 at the tilt angle. Preferably, the tilt angle is between 0° and 30°.

[0076] For example, forming a lower electrode 12 and a piezoelectric layer 13 sequentially on a substrate 11 includes: uniformly depositing a lower electrode 12 material on the substrate 11; patterning the lower electrode 12 material to remove a portion of the lower electrode 12 material to form a lower electrode 12, wherein the lower electrode 12 covers a portion of the substrate 11; and uniformly depositing a piezoelectric material on the lower electrode 12 and the exposed substrate 11 to form a piezoelectric layer 13.

[0077] S200: A first thickening layer and a second thickening layer are formed on the piezoelectric layer.

[0078] Please refer to the reference. Figure 14 The first thickening layer 17 and the second thickening layer 18 respectively cover a portion of the piezoelectric layer 13. The materials of the first thickening layer 17 and the second thickening layer 18 can be metal or non-metal.

[0079] For example, forming a first thickening layer 17 and a second thickening layer 18 on the piezoelectric layer 13 includes: uniformly depositing a thickening material on the piezoelectric layer 13; patterning the thickening material to remove a portion of the thickening material, thereby forming the first thickening layer 17 and the second thickening layer 18 on the piezoelectric layer 13.

[0080] S300: A first sacrificial layer is formed on the first thickened layer, and a second sacrificial layer 22 is formed on the second thickened layer.

[0081] Please refer to the reference. Figure 3 , Figure 4 and Figure 15A first sacrificial layer 20 covers the first thickened layer 17, and a second sacrificial layer 22 covers the second thickened layer 18. The first sacrificial layer 20 may completely cover the first thickened layer 17 or partially cover it. The second sacrificial layer 22 may completely cover the second thickened layer 18 or partially cover it. The materials of the first sacrificial layer 20 and the second sacrificial layer 22 may be silicon dioxide, etc.

[0082] For example, forming a first sacrificial layer 20 on the first thickened layer 17 and forming a second sacrificial layer 22 on the second thickened layer 18 includes: uniformly depositing a sacrificial material on the piezoelectric layer 13, the first thickened layer 17 and the second thickened layer 18; patterning the sacrificial material to remove part of the sacrificial material, forming a first sacrificial layer 20 covering the first thickened layer 17 and a second sacrificial layer 22 covering the second thickened layer 18.

[0083] S400: A wing structure is formed on the first sacrificial layer, a bridge structure is formed on the second sacrificial layer, and an upper electrode is formed between the wing structure and the bridge structure.

[0084] Please refer to the reference. Figure 16 The edges of the upper electrode 14 are connected to the wing structure 15 and the bridge structure 16, respectively. The materials of the upper electrode 14, the wing structure 15, and the bridge structure 16 can be Mo, Al, Pt, Cu, Au, etc., or composite thin film materials. The material of the upper electrode 14 can be the same as or different from the material of the lower electrode 12.

[0085] For example, forming a wing structure 15 on a first sacrificial layer 20, forming a bridge structure 16 on a second sacrificial layer 22, and forming an upper electrode 14 between the wing structure 15 and the bridge structure 16 includes: uniformly depositing an upper electrode 14 material on a piezoelectric layer 13, a first sacrificial layer 20, and a second sacrificial layer 22; patterning the upper electrode 14 material to remove a portion of the upper electrode 14 material, forming a wing structure 15 covering the first sacrificial layer 20, a bridge structure 16 covering the second sacrificial layer 22, and an upper electrode 14 connecting the wing structure 15 and the bridge structure 16.

[0086] The fabrication method of the aforementioned thin-film bulk acoustic resonator 10 involves forming a first thickening layer 17 and a second thickening layer 18 above the piezoelectric layer 13. A first sacrificial layer 20 is used to lift the wing structure 15 upwards, separating it from the first thickening layer 17. Similarly, the second thickening layer 18 lifts the bridge structure 16 upwards, separating it from the bridge structure 16. This adds a low-frequency structure capable of effectively reflecting transverse acoustic waves at the edge of the active region, improving the Q value of the resonator. Simultaneously, the wing structure 15, the first sacrificial layer 20, and the first thickening layer 17, as well as the bridge structure 16, the second sacrificial layer 22, and the second thickening layer 18, each constitute a low acoustic impedance region. This creates an acoustic impedance mismatch between the active region and this low acoustic impedance region, which also helps reflect transverse waves and suppress energy leakage in the active region, further improving the Q value of the resonator.

[0087] Furthermore, the arrangement of the first sacrificial layer 20 and the second sacrificial layer 22 ensures that the potentials between the first thickened layer 17 and the wing structure 15, and between the second thickened layer 18 and the bridge structure 16, are equal. This avoids the introduction of a non-longitudinal electric field that would excite transverse acoustic waves within the piezoelectric layer 13, thereby improving the resonator's performance. By adjusting the width and height of the first thickened layer 17 and the second thickened layer 18, the Q and K values ​​of the resonator can also be adjusted.

[0088] Alternatively, please refer to Figure 3 and Figure 4 The first sacrificial layer 20 covers a portion of the first thickened layer 17, and / or the second sacrificial layer 22 covers a portion of the second thickened layer 18.

[0089] The difference in width between the first sacrificial layer 20 and the second sacrificial layer 22 affects the coverage area of ​​the first sacrificial layer 20 over the first thickened layer 17 and the coverage area of ​​the second sacrificial layer 22 over the second thickened layer 18, thus forming thin-film bulk acoustic resonators 10 with different structures. It can be understood that when the first sacrificial layer 20 covers a portion of the first thickened layer 17, it covers the area on the upper surface of the first thickened layer 17 where the upper electrode 14 does not need to be formed. Similarly, when the second sacrificial layer 22 covers a portion of the second thickened layer 18, it also covers the area on the upper surface of the second thickened layer 18 where the upper electrode 14 does not need to be formed.

[0090] Alternatively, please refer to Figure 7 The first sacrificial layer 20 also covers the piezoelectric layer 13 outside the first thickened layer 17, and / or the second sacrificial layer 22 also covers the piezoelectric layer 13 outside the second thickened layer 18.

[0091] Optionally, please refer to again Figure 12 After forming the upper electrode 14 between the wing structure 15 and the bridge structure 16, the fabrication method of the thin-film bulk acoustic resonator 10 further includes:

[0092] S500: A passivation layer is formed on the wing structure, upper electrode, and bridge structure.

[0093] Please refer to the reference. Figure 17 The material of the passivation layer 26 can be AlN, SiC, SiO2, SiN, etc. The passivation layer 26 is generally selected from materials that do not easily absorb moisture, which can prevent the oxidation of the underlying film and thus protect the underlying film.

[0094] For example, forming a passivation layer 26 on the wing structure 15, the upper electrode 14 and the bridge structure 16 includes uniformly depositing a passivation material on the wing structure 15, the upper electrode 14 and the bridge structure 16 to form the passivation layer 26.

[0095] S600: An annular groove is formed on the passivation layer, wherein the orthogonal projection of the annular groove on the piezoelectric layer is located between the first thickening layer and the second thickening layer.

[0096] For example, forming an annular groove 261 on the passivation layer 26 includes etching the upper surface of the passivation layer 26 to form the annular groove 261.

[0097] Optionally, please refer to again Figure 12 After forming the upper electrode between the wing structure and the bridge structure, the fabrication method of the thin-film bulk acoustic resonator also includes:

[0098] S700: Release the first and second sacrificial layers to form a first gap between the first thickened layer and the wing structure, and a second gap between the second thickened layer and the bridge structure.

[0099] Please refer to the reference. Figure 1 The space between the first thickened layer 17 and the wing structure 15, and between the second thickened layer 18 and the bridge structure 16, is filled with air, which can also form a low acoustic impedance region and make the potential between the first thickened layer 17 and the wing structure 15, and between the second thickened layer 18 and the bridge structure 16 equal.

[0100] For example, releasing the first sacrificial layer 20 and the second sacrificial layer 22 to form a first gap between the first thickened layer 17 and the wing structure 15, and to form a second gap between the second thickened layer 18 and the bridge structure 16, includes: etching a release hole 28, wherein the release hole 28 passes through or extends to the first sacrificial layer 20 and / or the second sacrificial layer 22; and releasing the sacrificial material using a dry or wet method.

[0101] To form an acoustic reflection structure, optionally, please refer to... Figure 18 Providing a substrate 11, and sequentially forming a lower electrode 12 and a piezoelectric layer 13 on the substrate 11, includes:

[0102] S110: Provide a substrate, form a cavity on the surface of the substrate, and fill the cavity with sacrificial layer material.

[0103] S120: Remove the sacrificial layer material outside the cavity to form a third sacrificial layer.

[0104] S130: A lower electrode and a piezoelectric layer are sequentially formed on the substrate.

[0105] Please refer to the reference. Figure 13 and Figure 1 The sacrificial material can be silicon dioxide, phosphate glass (PSG), etc. The cavity 111 can be formed on the upper surface of the substrate 11 by etching. The overlapping area of ​​the subsequently formed upper electrode 14, piezoelectric layer 13, and lower electrode 12 in the longitudinal Y direction should be located above the cavity 111. The sacrificial layer material outside the cavity 111 can be removed by chemical mechanical polishing (CMP). Finally, in the fabrication of the thin-film bulk acoustic resonator 10, a third sacrificial layer needs to be released to fill the cavity 111 with air.

[0106] Please refer to Figure 13 Generally, in order to achieve better lattice orientation for the lower electrode 12 and the piezoelectric layer 13, a seed layer material is uniformly deposited before forming the lower electrode 12 to form a seed layer 25 on the surface of the substrate 11, and then the lower electrode 12 is formed on the seed layer 25. The seed layer material is generally aluminum nitride.

[0107] To bring out the lower electrode 12 and the upper electrode 14, it is necessary to fabricate lower electrode lead-out structures and upper electrode lead-out structures. At this time, after forming the piezoelectric layer 13, it is necessary to etch the piezoelectric layer 13 to form a lower electrode lead-out hole 131 on the piezoelectric layer 13, exposing a portion of the lower electrode 12 through the lower electrode lead-out hole 131. Please refer to the reference. Figures 14 to 17 Subsequently, during the formation of the first thickened layer 17, the upper electrode 14, and the passivation layer 26, the materials used will further cover the lower electrode lead-out hole 131 layer by layer. Please refer to... Figure 19 After the passivation layer 26 is formed, it needs to be etched to form the upper electrode lead-out hole 262 on the passivation layer 26, which exposes a portion of the upper electrode 14. A protective material can also be filled into the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262 to form a protective layer 27 to protect them.

[0108] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A thin-film bulk acoustic resonator, characterized in that, include: A substrate, a lower electrode, a piezoelectric layer and an upper electrode are sequentially disposed on the substrate, and the edge of the upper electrode is provided with a wing structure and a bridge structure; The piezoelectric layer is further provided with a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure. The sides of the first thickening layer and the second thickening layer are respectively attached to the upper electrode. There is a first gap between the surface of the first thickening layer away from the piezoelectric layer and the wing structure. The first gap is filled with air or provided with a first sacrificial layer. There is a second gap between the surface of the second thickening layer away from the piezoelectric layer and the bridge structure. The second gap is filled with air or provided with a second sacrificial layer.

2. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, The first thickened layer is divided into a first thickened region and a second thickened region. The side of the first thickened region is attached to the edge of the upper electrode. The side of the first thickened region away from the piezoelectric layer is attached to the side of the upper electrode facing the piezoelectric layer. The side of the second thickened region away from the piezoelectric layer forms the first gap with the wing structure.

3. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, The second thickened layer is divided into a third thickened region and a fourth thickened region. The side of the third thickened region is attached to the edge of the upper electrode. The side of the third thickened region away from the piezoelectric layer is attached to the side of the upper electrode facing the piezoelectric layer. The side of the fourth thickened region away from the piezoelectric layer forms the second gap with the bridge structure.

4. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, There is a third gap between the piezoelectric layer and the wing structure. Both the third gap and the first gap are filled with air, or both are provided with the first sacrificial layer.

5. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, There is a fourth gap between the piezoelectric layer and the bridge structure. Both the fourth gap and the second gap are filled with air, or both are provided with the second sacrificial layer.

6. The thin-film bulk acoustic resonator according to any one of claims 1 to 5, characterized in that, It also includes a seed layer disposed on the substrate, and the lower electrode covers the seed layer.

7. The thin-film bulk acoustic resonator as described in any one of claims 1 to 5, characterized in that, It also includes a passivation layer that covers the upper electrode, the wing structure and the bridge structure. The passivation layer has an annular groove on the side opposite to the upper electrode. The orthogonal projection of the annular groove on the piezoelectric layer is located between the first thickening layer and the second thickening layer.

8. A method for fabricating a thin-film bulk acoustic resonator, characterized in that, The method for fabricating a thin-film bulk acoustic resonator as described in any one of claims 1 to 7 comprises: A substrate is provided, and a lower electrode and a piezoelectric layer are sequentially formed on the substrate; A first thickening layer and a second thickening layer are formed on the piezoelectric layer; A first sacrificial layer is formed on the first thickened layer, and a second sacrificial layer is formed on the second thickened layer; A wing structure is formed on a first sacrificial layer, a bridge structure is formed on a second sacrificial layer, and an upper electrode is formed between the wing structure and the bridge structure.

9. The method for fabricating a thin-film bulk acoustic resonator as described in claim 8, characterized in that, After forming the upper electrode between the wing structure and the bridge structure, the method further includes: Release the first sacrificial layer and the second sacrificial layer to form a first gap between the first thickened layer and the wing structure, and a second gap between the second thickened layer and the bridge structure.

10. The method for fabricating a thin-film bulk acoustic resonator as described in claim 8, characterized in that, The first sacrificial layer covers a portion of the first thickened layer, and / or the second sacrificial layer covers a portion of the second thickened layer.

11. The method for fabricating a thin-film bulk acoustic resonator as described in claim 8, characterized in that, The first sacrificial layer also covers the piezoelectric layer outside the first thickened layer, and / or the second sacrificial layer also covers the piezoelectric layer outside the second thickened layer.

12. The method for fabricating a thin-film bulk acoustic resonator as described in any one of claims 8 to 11, characterized in that, After forming the upper electrode between the wing structure and the bridge structure, the method further includes: A passivation layer is formed on the wing structure, the upper electrode, and the bridge structure; An annular groove is formed on the passivation layer, wherein the orthogonal projection of the annular groove on the piezoelectric layer is located between the first thickening layer and the second thickening layer.

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