Film bulk acoustic resonator and preparation method thereof

Abstract

The invention provides a film bulk acoustic resonator and a preparation method thereof, and relates to the technical field of semiconductors. The film bulk acoustic resonator comprises a substrate, a lower electrode, a piezoelectric layer and an upper electrode, wherein the lower electrode, the piezoelectric layer and the upper electrode are sequentially arranged on the substrate; 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 side faces of the first thickening layer and the second thickening layer are attached to the upper electrode, a first gap is formed between the surface, away from the piezoelectric layer, of the first thickening layer and the wing structure, and the first gap is filled with air or provided with a first sacrificial layer. A second gap is formed between the surface, away from the piezoelectric layer, of the second thickening layer and the bridge structure, and the second gap is filled with air or provided with a second sacrificial layer. According to the film bulk acoustic resonator, a non-longitudinal electric field introduced by lifting of the wing structure and the bridge structure is effectively inhibited, and transverse acoustic waves excited by the non-longitudinal electric field in the piezoelectric layer are avoided, so that the performance is improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a thin film bulk acoustic wave resonator and a method for preparing the same. Background Art

[0002] RF filters are the cornerstone of wireless communications. Film bulk acoustic resonator (FBAR) has become one of the core components for building RF filters due to its high quality factor, low loss, high reliability, miniaturization, and compatibility with IC processes. With the rapid development of 5G wireless communications, FBAR is required to have a small 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] The traditional film bulk acoustic wave resonator is a typical sandwich structure of upper electrode-piezoelectric layer-lower electrode. Ideally, by applying alternating current to the surface of the upper and lower electrodes, the piezoelectric effect is used to excite the longitudinal wave (longitudinal wave) propagating in the height direction. However, due to the defects in the film material and the limitations of the boundary conditions on the structure, there are also transverse waves in the FBAR perpendicular to the height direction of the film, such as Rayleigh-Lamb waves. The presence of transverse waves interferes with the vibration of the main mode, thereby affecting the performance of the resonator, such as reducing the K value, Q value and FOM value.

[0004] Therefore, how to optimize the boundary conditions of FBAR, limit and utilize the shear waves existing in FBAR, and further improve the K value, Q value and FOM value of the resonator is one of the imminent issues. Summary of the invention

[0005] The purpose of the present application is to provide a thin film bulk acoustic wave resonator and a preparation method thereof, which can improve the performance of the resonator, in view of the above-mentioned deficiencies in the prior art.

[0006] To achieve the above purpose, the technical solution adopted in the embodiment of the present application is as follows:

[0007] According to one aspect of an embodiment of the present application, a thin film bulk acoustic wave resonator is provided, comprising: a substrate, a lower electrode, a piezoelectric layer and an upper electrode arranged in sequence on the substrate, wherein a wing structure and a bridge structure are provided at the edge of the upper electrode; a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure are also provided on the piezoelectric layer, and the side surfaces of the first thickening layer and the second thickening layer are respectively bonded to the upper electrode, a first gap is provided between a surface of the first thickening layer facing away from the piezoelectric layer and the wing structure, the first gap is filled with air or a first sacrificial layer is provided, and a second gap is provided between a 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 a second sacrificial layer is provided.

[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 in contact with the upper electrode, the side of the first thickened region facing away from the piezoelectric layer is in contact with the side of the upper electrode facing the piezoelectric layer, and a first gap is formed between the side of the second thickened region facing away from the piezoelectric layer and 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 in contact with the upper electrode, the side of the third thickened region facing away from the piezoelectric layer is in contact with the side of the upper electrode facing the piezoelectric layer, and a second gap is formed between the side of the fourth thickened region facing away from the piezoelectric layer and the bridge structure.

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

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

[0012] Optionally, it further includes a seed layer disposed on the substrate, and the lower electrode covers the seed layer.

[0013] Optionally, a passivation layer is further included, the passivation layer covers the upper electrode, the wing structure and the bridge structure, and an annular groove is provided on a side of the passivation layer away from the upper electrode, and the annular groove is located above the upper electrode.

[0014] According to another aspect of an embodiment of the present application, a method for preparing a thin film bulk acoustic wave resonator is provided, including: 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 forming a second sacrificial layer on the second thickening layer; forming a wing structure on the first sacrificial layer, forming 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 an upper electrode between the wing structure and the bridge structure, it also 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 orthographic 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] The present application provides a thin film bulk acoustic wave resonator, comprising: a substrate, a lower electrode, a piezoelectric layer and an upper electrode arranged on the substrate in sequence, the edge of the upper electrode is provided with a wing structure and a bridge structure; the piezoelectric layer is also 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 fitted with the upper electrode, a first gap is provided 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, a second gap is provided 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. The thin film bulk acoustic wave resonator utilizes 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 to effectively suppress the non-longitudinal electric field introduced by the lifting of the wing structure and the bridge structure, and avoids the transverse acoustic waves excited by the non-longitudinal electric field in the piezoelectric layer, thereby improving the performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 One of the structural schematic diagrams of the thin film bulk acoustic resonator provided in the embodiment of the present application;

[0023] Figure 2The second structural schematic diagram of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0024] Figure 3 The third structural schematic diagram of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0025] Figure 4 A fourth structural diagram of a thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0026] Figure 5 A potential diagram of a thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0027] Figure 6 A fifth structural diagram of a thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0028] Figure 7 The sixth structural diagram of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0029] Figure 8 A graph showing the relationship between the width of the second thickened region and the electromechanical coupling coefficient in the thin film bulk acoustic resonator provided in an embodiment of the present application;

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

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

[0032] Fig.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 an embodiment of the present application;

[0033] Fig.12 One of the flow charts of the method for preparing a thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0034] Fig.13 One of the schematic diagrams of the preparation process of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0035] Fig.14 The second schematic diagram of the preparation process of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0036] Fig.15 The third schematic diagram of the preparation process of the thin film bulk acoustic wave resonator provided in the embodiment of the present application;

[0037] Fig.16A fourth schematic diagram of the preparation process of the thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0038] Fig.17 A fifth schematic diagram of the preparation process of the thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0039] Fig.18 Flow chart 2 of the method for preparing a thin film bulk acoustic wave resonator provided in an embodiment of the present application;

[0040] Fig.19 The sixth schematic diagram of the preparation process of the thin film bulk acoustic wave resonator provided in the embodiment of the present application.

[0041] Icon: 10-thin film bulk acoustic wave 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 thickening layer; 171-first thickening region; 172-second thickening region; 18-second thickening layer; 181-third thickening region; 182-fourth thickening 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-transverse; Y-longitudinal. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0044] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0045] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0046] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0047] In one aspect of the embodiment of the present application, referring 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 arranged in sequence on the substrate 11, and a wing structure 15 and a bridge structure 16 are provided at the edge of the upper electrode 14. The overlapping area of ​​the upper electrode 14, the piezoelectric layer 13 and the lower electrode 12 in the longitudinal direction Y is the active area of ​​the thin film bulk acoustic wave resonator 10. The wing structure 15 and the bridge structure 16 are lifted up and separated from the piezoelectric layer 13.

[0048] The piezoelectric layer 13 is also provided with 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, so as to achieve electrical connection with the upper electrode 14. At least a part of the first thickening layer 17 corresponds to the position of the wing structure 15 in the longitudinal direction Y, that is, it is located below the wing structure 15. At least a part of the second thickening layer 18 corresponds to the position of the bridge structure 16 in the longitudinal direction Y, that is, it is located below the bridge structure 16. Please refer to Figure 3 and Figure 4There is a first gap 19 between the surface of the first thickened layer 17 facing away from the piezoelectric layer 13 (i.e., the upper surface) and the wing structure 15, and the first gap 19 is filled with air or provided with a first sacrificial layer 20. There is a second gap 21 between the surface of the second thickened layer 18 facing away from the piezoelectric layer 13 (i.e., the upper surface) and the bridge structure 16, and the second gap 21 is filled with air or provided with 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 flat, curved, or stepped.

[0049] Please refer to Figure 5 , after the first thickened layer 17 is connected to the upper electrode 14, it extends to the bottom of 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 area, which can effectively reflect transverse sound 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. The first gap 19 is used to form a low acoustic impedance region, resulting in an acoustic impedance mismatch between the active area and the low acoustic impedance region, which is also beneficial for reflecting transverse waves and suppressing the leakage of energy in the active area, further improving the Q value of the resonator. In addition, the first gap 19 makes the electric potential 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 can avoid the transverse sound waves excited by the non-longitudinal electric field inside the piezoelectric layer 13, thereby improving the performance of the thin film bulk acoustic wave 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 other side and the bridge structure 16. At the same time, the non-longitudinal electric field introduced by the lifting of the bridge structure 16 is suppressed, thereby improving the performance of the thin film bulk acoustic wave resonator 10. In addition, by adjusting the width (dimension in the horizontal direction X) and height (dimension in the vertical direction Y) of the first thickened layer 17, the Q value and K value of the resonator can also be adjusted.

[0050] Since the first thickening layer 17 and the second thickening layer 18 will not cause a non-longitudinal electric field, the inclination angles of the first thickening layer 17 and the second thickening layer 18 can be any angle, so the setting of the first gap 19 and the second gap 21 also reduces the process cost. It should be noted that the inclination angle of the first thickening layer 17 refers to the angle between the lower surface of the first thickening layer 17 and the side surface of the first thickening layer 17 that is in contact with the upper electrode 14, and the inclination angle of the second thickening layer 18 refers to the angle between the lower surface of the second thickening layer 18 and the side surface of the second thickening 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 respectively, the electric potential of the first thickened layer 17 and the second thickened layer 18 is equal to the electric 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, and between the second thickened layer 18 and the upper electrode 14.

[0052] Optionally, see 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 in contact with the upper electrode 14, and the side of the first thickened region 171 facing away from the piezoelectric layer 13 is in contact with the side of the upper electrode 14 facing the piezoelectric layer 13. A first gap 19 is formed between the side of the second thickened region 172 facing away from the piezoelectric layer 13 and the wing structure 15.

[0053] One side of the first thickened region 171 is in contact with the upper electrode 14, and the other side thereof is in contact with the second thickened region 172. The lower surface of the first thickened region 171 is in contact with the piezoelectric layer 13, and the upper surface is in contact with the upper electrode 14. The lower surface of the second thickened region 172 is in contact with 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 lifted upward to form a first step, and the gap between the first step and the piezoelectric layer 13 is smaller and is completely filled by the first thickened region 171. The gap between the wing structure 15 as the second step and the piezoelectric layer 13 is larger and 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 in contact with the upper electrode 14, the side of the third thickened region 181 facing away from the piezoelectric layer 13 is in contact with the side of the upper electrode 14 facing the piezoelectric layer 13, and a second gap 21 is formed between the side of the fourth thickened region 182 facing away from the piezoelectric layer 13 and the bridge structure 16.

[0056] One side of the third thickened region 181 is in contact with the upper electrode 14, and the other side thereof is in contact with the fourth thickened region 182. The lower surface of the third thickened region 181 is in contact with the piezoelectric layer 13, and the upper surface is in contact with the upper electrode 14. The lower surface of the fourth thickened region 182 is in contact with 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 lifted upward to form a third step, and the gap between the third step and the piezoelectric layer 13 is smaller and is completely filled by the third thickened region 181. The gap between the bridge structure 16 as the fourth step and the piezoelectric layer 13 is larger and 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 of equal height to facilitate processing.

[0059] Optionally, see Figure 6 and Figure 7 A third gap 23 is provided between the piezoelectric layer 13 and the wing structure 15 . The third gap 23 and the first gap 19 are both filled with air or are both provided with a first sacrificial layer 20 .

[0060] By adjusting the width of the first thickened layer 17, a third gap 23 can be provided 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, the third gap 23 and the first gap 19 are both filled with air, or the third gap 23 and the first gap 19 are both 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 the fourth gap 24 and the second gap 21 are both filled with air, or are both provided with a second sacrificial layer 22 .

[0062] By adjusting the width of the second thickened layer 18, a fourth gap 24 can be provided 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, the fourth gap 24 and the second gap 21 are both filled with air, or the fourth gap 24 and the second gap 21 are both filled with the second sacrificial layer 22.

[0063] In order to make the lower electrode 12 and the piezoelectric layer 13 have a better lattice orientation, optionally, the FBAW resonator 10 further includes 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 wave resonator 10 also includes a passivation layer 26, which covers the upper electrode 14, the wing structure 15 and the bridge structure 16. An annular groove 261 is provided on the side of the passivation layer 26 facing away from the upper electrode 14, and the orthographic 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 the parasitic of the series resonator frequency of the Type II dispersive FBAR 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 position of the active region of the FBAR 10 in the longitudinal direction Y. The cavity 111 is used to reflect sound waves.

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

[0068] Furthermore, the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262 are filled with a protection layer 27 to protect the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262 .

[0069] by Figure 1 Taking the thin film bulk acoustic wave resonator 10 as an example, Figure 8 shows the relationship between the width of the second thickened region 172 and the electromechanical coupling coefficient, Fig. 9 shows the relationship between the height of the second thickened region 172 and the electromechanical coupling coefficient, Fig.10 shows the relationship between the width of the second thickened region 172 and the quality factor, Fig.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 the electromechanical coupling coefficient (K value) and the quality factor (Q value) of the FBAR 10 can be adjusted by adjusting the width and height of the second thickened region 172 .

[0070] Figure 1 The quality factor of the thin film bulk acoustic wave resonator 10 shown is about 900. In the prior art, the quality factor of the thin film bulk acoustic wave resonator with a sandwich structure is about 300, and the quality factor of the thin film bulk acoustic wave resonator with a sandwich structure + wing structure + bridge structure is about 450. It can be seen that the quality factor of the thin film bulk acoustic wave resonator 10 with a sandwich structure + wing structure + bridge structure + thickened layer structure provided in the embodiment of the present application is significantly higher than that of the thin film bulk acoustic wave resonator in the prior art.

[0071] Please refer to Fig.12 This embodiment also provides a method for preparing a thin film bulk acoustic wave resonator, comprising:

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

[0073] Please refer to Fig.13, the lower electrode 12 covers part of the substrate 11, and the piezoelectric layer 13 covers the lower electrode 12 and the piezoelectric layer 13 exposed by the lower electrode 12. The material of the substrate 11 can be a silicon wafer, such as high-resistance silicon, or a special substrate 11. The material of the lower electrode 12 is generally Mo, Al, Pt, Cu, Au, etc. The material of the piezoelectric layer 13 is generally AlN and common piezoelectric materials such as doped AlN, PZT, LiNbO3, LiTaO3, etc., and can also be a composite piezoelectric material, such as AlN / ScAlN, etc.

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

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

[0076] By way of example, sequentially forming a lower electrode 12 and a piezoelectric layer 13 on a substrate 11 includes: uniformly depositing a layer of 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 layer of piezoelectric material on the lower electrode 12 and the exposed substrate 11 to form a piezoelectric layer 13.

[0077] S200: forming a first thickening layer and a second thickening layer on the piezoelectric layer.

[0078] Please refer to Fig.14 The first thickening layer 17 and the second thickening layer 18 respectively cover a portion of the piezoelectric layer 13. The material 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 layer of thickening material on the piezoelectric layer 13; patterning the thickening material to remove part of the thickening material, and forming a first thickening layer 17 and a second thickening layer 18 on the piezoelectric layer 13.

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

[0081] Please refer to Figure 3 , Figure 4 and Fig.15, the first sacrificial layer 20 covers the first thickening layer 17, and the second sacrificial layer 22 covers the second thickening layer 18. The first sacrificial layer 20 can completely cover the first thickening layer 17, or can cover part of the first thickening layer 17. The second sacrificial layer 22 can completely cover the second thickening layer 18, or can cover part of the second thickening layer 18. The materials of the first sacrificial layer 20 and the second sacrificial layer 22 can be silicon dioxide or the like.

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

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

[0084] Please refer to Fig.16 , the edges of the upper electrode 14 are respectively connected to the wing structure 15 and the bridge structure 16. 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 can be composite thin film materials. The material of the upper electrode 14 can be the same as that of the lower electrode 12, or different.

[0085] By way of example, a wing structure 15 is formed on a first sacrificial layer 20, a bridge structure 16 is formed on a second sacrificial layer 22, and an upper electrode 14 is formed between the wing structure 15 and the bridge structure 16, including: uniformly depositing a layer of upper electrode 14 material on the piezoelectric layer 13, the first sacrificial layer 20, and the second sacrificial layer 22; patterning the upper electrode 14 material to remove part of the upper electrode 14 material to form 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 preparation method of the above-mentioned thin film bulk acoustic wave resonator 10 forms a first thickening layer 17 and a second thickening layer 18 above the piezoelectric layer 13, and uses the first sacrificial layer 20 to lift the wing structure 15 upward and separate it from the first thickening layer 17, and the second thickening layer 18 lifts the bridge structure 16 upward and separates it from the second thickening layer 18, thereby adding a low-frequency structure that can effectively reflect transverse sound waves at the edge of the active area, thereby improving the Q value of the resonator. At the same time, the wing structure 15, the first sacrificial layer 20 and the first thickening layer 17, the bridge structure 16, the second sacrificial layer 22 and the second thickening layer 18 also respectively constitute a low acoustic impedance region, resulting in an acoustic impedance mismatch between the active area and the low acoustic impedance region, which is also conducive to reflecting transverse waves and suppressing the leakage of energy in the active area, further improving the Q value of the resonator.

[0087] In addition, the first sacrificial layer 20 and the second sacrificial layer 22 are provided to make the electric 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, thereby avoiding the introduction of a non-longitudinal electric field to excite transverse acoustic waves inside the piezoelectric layer 13, thereby improving the performance of the resonator. By adjusting the width and height of the first thickened layer 17 and the second thickened layer 18, the Q value and K value of the resonator can also be adjusted.

[0088] Optionally, see 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 will affect the coverage area of ​​the first sacrificial layer 20 on the first thickened layer 17 and the coverage area of ​​the second sacrificial layer 22 on the second thickened layer 18, thereby forming thin film bulk acoustic wave 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, the first sacrificial layer 20 covers the area on the upper surface of the first thickened layer 17 where the upper electrode 14 does not need to be formed. When the second sacrificial layer 22 covers a portion of the second thickened layer 18, the second sacrificial layer 22 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] Optionally, see Figure 7 The first sacrificial layer 20 further covers the piezoelectric layer 13 outside the first thickening layer 17 , and / or the second sacrificial layer 22 further covers the piezoelectric layer 13 outside the second thickening layer 18 .

[0091] Optionally, please refer again to Fig.12 After forming the upper electrode 14 between the wing structure 15 and the bridge structure 16, the method for preparing the thin film bulk acoustic wave resonator 10 further includes:

[0092] S500: forming a passivation layer on the wing structure, the upper electrode and the bridge structure.

[0093] Please refer to Fig.17 The material of the passivation layer 26 can be AlN, SiC, SiO2, SiN, etc. The passivation layer 26 is generally made of a material that is not easy to absorb moisture, which can prevent the underlying film from being oxidized, thereby protecting the underlying film.

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

[0095] S600: forming an annular groove on the passivation layer, wherein an orthographic projection of the annular groove on the piezoelectric layer is located between the first thickened layer and the second thickened layer.

[0096] Illustratively, forming the 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 again to Fig.12 After forming an upper electrode between the wing structure and the bridge structure, the method for preparing the thin film bulk acoustic wave resonator further includes:

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

[0099] Please refer to Figure 1 There is air between the first thickened layer 17 and the wing structure 15, and between the second thickened layer 18 and the bridge structure 16, which can also form a low acoustic impedance area and make the electric 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 thickening layer 17 and the wing structure 15 and a second gap between the second thickening 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 by a dry method or a wet method.

[0101] To form a sound reflection structure, optionally, refer to Fig.18 , providing a substrate 11, and sequentially forming a lower electrode 12 and a piezoelectric layer 13 on the substrate 11, including:

[0102] S110: providing a substrate, forming a cavity on a surface of the substrate, and filling the cavity with a sacrificial layer material.

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

[0104] S130: forming a lower electrode and a piezoelectric layer in sequence on the substrate.

[0105] Please refer to Fig.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 upper electrode 14, the piezoelectric layer 13 and the lower electrode 12 formed subsequently in the longitudinal direction Y should be located above the cavity 111. The sacrificial layer material located outside the cavity 111 can be ground and removed by chemical mechanical polishing (CMP). At the end of the preparation of the thin film bulk acoustic resonator 10, the third sacrificial layer needs to be released so that the cavity 111 is filled with air.

[0106] Please refer to Fig.13 Generally speaking, in order to provide the lower electrode 12 and the piezoelectric layer 13 with a better lattice orientation, before forming the lower electrode 12, a layer of seed layer material is uniformly deposited 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] In order to lead out the lower electrode 12 and the upper electrode 14, it is also necessary to prepare a lower electrode lead-out structure and an upper electrode lead-out structure. At this time, after forming the piezoelectric layer 13, the piezoelectric layer 13 needs to be etched to form a lower electrode lead-out hole 131 on the piezoelectric layer 13, and the lower electrode lead-out hole 131 exposes a part of the lower electrode 12. Figures 14 to 17 When the first thickening layer 17, the upper electrode 14 and the passivation layer 26 are subsequently formed, the material used will also cover the lower electrode lead-out hole 131 layer by layer. Fig.19 After forming the passivation layer 26, the passivation layer 26 needs to be etched to form an upper electrode lead-out hole 262 on the passivation layer 26, and the upper electrode lead-out hole 262 exposes a portion of the upper electrode 14. A protective material may also be filled in the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262 to form a protective layer 27 to protect the lower electrode lead-out hole 131 and the upper electrode lead-out hole 262.

[0108] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present 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 sequentially arranged on the substrate, wherein a wing structure and a bridge structure are provided at an edge of the upper electrode; The piezoelectric layer is also provided with a first thickening layer corresponding to the wing structure and a second thickening layer corresponding to the bridge structure. The side surfaces of the first thickening layer and the second thickening layer are respectively in contact with the upper electrode. A first gap is formed between a 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 provided with a first sacrificial layer. A second gap is formed between a 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 provided with a second sacrificial layer.

2. The thin film bulk acoustic wave resonator according to 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 in contact with the edge of the upper electrode, the side of the first thickened region facing away from the piezoelectric layer is in contact with the side of the upper electrode facing the piezoelectric layer, and the first gap is formed between the side of the second thickened region facing away from the piezoelectric layer and the wing structure.

3. The thin film bulk acoustic wave resonator according to 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 in contact with the edge of the upper electrode, the side of the third thickened region facing away from the piezoelectric layer is in contact with the side of the upper electrode facing the piezoelectric layer, and the second gap is formed between the side of the fourth thickened region facing away from the piezoelectric layer and the bridge structure.

4. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: A third gap is provided between the piezoelectric layer and the wing structure, and the third gap and the first gap are both filled with the air or are both provided with the first sacrificial layer.

5. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: A fourth gap is provided between the piezoelectric layer and the bridge structure, and the fourth gap and the second gap are both filled with the air or are both provided with the second sacrificial layer.

6. The thin film bulk acoustic wave 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 according to any one of claims 1 to 5, characterized in that: It also includes a passivation layer, which covers the upper electrode, the wing structure and the bridge structure. The passivation layer is provided with an annular groove on the side away from the upper electrode, and the positive projection of the annular groove on the piezoelectric layer is located between the first thickened layer and the second thickened layer.

8. A method for preparing a thin film bulk acoustic wave resonator, characterized in that: include: 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 thickened layer, and forming a second sacrificial layer on the second thickened layer; 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.

9. The method for preparing a thin film bulk acoustic wave resonator according to claim 8, characterized in that: After forming the upper electrode between the wing structure and the bridge structure, the method further includes: The first sacrificial layer and the second sacrificial layer are released 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 preparing a thin film bulk acoustic wave resonator according to 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 preparing a thin film bulk acoustic wave resonator according to claim 8, characterized in that: The first sacrificial layer further covers the piezoelectric layer outside the first thickening layer, and / or the second sacrificial layer further covers the piezoelectric layer outside the second thickening layer.

12. The method for preparing a thin film bulk acoustic wave resonator according to 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: forming a passivation layer on the wing structure, the upper electrode and the bridge structure; An annular groove is formed on the passivation layer, wherein an orthographic projection of the annular groove on the piezoelectric layer is located between the first thickened layer and the second thickened layer.

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