Bulk acoustic wave resonators, filters and electronic devices

Abstract

The present invention discloses a bulk acoustic wave resonator, comprising: a substrate; an acoustic mirror; a bottom electrode having a bottom electrode pin; a top electrode having a top electrode pin; a piezoelectric layer arranged between the bottom electrode and the top electrode, wherein: there is a first gap between a sandwich structure composed of the bottom electrode, the top electrode and the piezoelectric layer and the upper surface of the substrate, and the first gap makes the main resonant structure of the resonator formed by the bottom electrode, the piezoelectric layer and the top electrode have no contact with the substrate; a contact area reduction structure is arranged between the lower side of the sandwich structure and the upper surface of the substrate. The present invention also discloses a filter having the resonator and an electronic device having the filter or the resonator.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and in particular to a bulk acoustic wave resonator, a filter, and an electronic device having the resonator or the filter. Background Art

[0002] As the basic elements of electronic devices, electronic devices have been widely used, including mobile phones, automobiles, household appliances, etc. In addition, technologies such as artificial intelligence, the Internet of Things, and 5G communications that will change the world in the future still need to rely on electronic devices as a foundation.

[0003] Film Bulk Acoustic Resonator (FBAR, also known as BAW) as an important member of piezoelectric devices is playing an important role in the communication field, especially FBAR filters have an increasingly larger market share in the field of radio frequency filters. FBAR has excellent characteristics such as small size, high resonant frequency, high quality factor, large power capacity, and good roll-off effect. Its filters are gradually replacing traditional surface acoustic wave (SAW) filters and ceramic filters, playing a huge role in the field of wireless communication radio frequency. Its high sensitivity advantage can also be applied to biological, physical, medical and other sensing fields.

[0004] The main structure of the film bulk acoustic wave resonator is a "sandwich" structure consisting of electrode-piezoelectric film-electrode, that is, a layer of piezoelectric material is sandwiched between two layers of metal electrode layers. By inputting a sinusoidal signal between the two electrodes, FBAR uses the inverse piezoelectric effect to convert the input electrical signal into mechanical resonance, and then uses the piezoelectric effect to convert the mechanical resonance into an electrical signal output.

[0005] High-frequency resonators with high quality factors and low dynamic impedance are the best choice for integrated oscillators. In recent years, as the size of resonator packages decreases, the frequency drift caused by external stress on the resonator becomes more and more serious, seriously affecting the performance and stability of the oscillator.

[0006] With the rapid development of integrated circuit technology, the frequency stability of FBAR resonators is becoming more and more important. In order to adapt to the development trend of miniaturization, it is necessary to solve or alleviate the frequency stability problem of FBAR resonators. Summary of the invention

[0007] In order to alleviate or solve the above problems in the prior art, the present invention proposes a bulk acoustic wave resonator whose frequency is not affected by external stress.

[0008] According to one aspect of an embodiment of the present invention, a bulk acoustic wave resonator is provided, comprising:

[0009] substrate;

[0010] Acoustic mirror;

[0011] A bottom electrode having a bottom electrode pin;

[0012] a top electrode having a top electrode pin;

[0013] A piezoelectric layer is disposed between the bottom electrode and the top electrode,

[0014] in:

[0015] There is a first gap between the sandwich structure consisting of the bottom electrode, the top electrode and the piezoelectric layer and the upper surface of the substrate, wherein the first gap makes the main resonant region of the resonator formed by the bottom electrode, the piezoelectric layer and the top electrode have no contact with the substrate;

[0016] A contact area reducing structure is disposed between the lower side of the sandwich structure and the upper surface of the substrate.

[0017] Optionally, the resonator also includes a protective structural layer, the protective structural layer includes a first part and a second part, the first part is connected to the upper surface of the substrate, the outer end of the second part is connected to the inner end of the first part, the second part extends along the piezoelectric layer to above the piezoelectric layer and at least a part of the second part forms a second gap with the piezoelectric layer in the thickness direction, and the second part is spaced apart from the top electrode in the lateral direction.

[0018] An embodiment of the present invention further relates to a filter, comprising the above-mentioned BAW resonator.

[0019] An embodiment of the present invention also relates to an electronic device, comprising the above-mentioned filter or the above-mentioned resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following description and accompanying drawings may better help understand these and other features and advantages of various embodiments disclosed by the present invention, in which the same reference numerals always represent the same components, wherein:

[0021] Figure 1A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 1B or Figure 1C BB direction);

[0022] Figure 1B According to an exemplary embodiment of the present invention Figure 1A Schematic top view of the BAW resonator in FIG.

[0023] Figure 1C According to an exemplary embodiment of the present invention Figure 1A Schematic top view of the BAW resonator in FIG.

[0024] Figure 2A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 2B BB direction);

[0025] Figure 2B According to an exemplary embodiment of the present invention Figure 2A Schematic top view of the BAW resonator in FIG.

[0026] Figure 2C is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 2B CC direction);

[0027] Figure 2D is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 2B DD direction);

[0028] Figure 3 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 1B or Figure 1C BB direction);

[0029] Figure 4A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 4B BB direction);

[0030] Figure 4B According to an exemplary embodiment of the present invention Figure 4A Schematic top view of the BAW resonator in FIG.

[0031] Figure 5A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 5B BB direction in the middle);

[0032] Figure 5B is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0033] Figure 5C for Figure 5B An enlarged schematic diagram of part A in FIG.

[0034] Fig. 6A is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0035] Figure 6B for Fig. 6A An enlarged schematic diagram of part A in FIG.

[0036] Fig. 7A is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0037] Figure 7B for Fig. 7A An enlarged schematic diagram of part A in FIG.

[0038] Fig. 8A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 5B BB direction in the figure), wherein the contact area reduction structure is a convex structure;

[0039] Figure 8B for Fig. 8A An enlarged schematic diagram of part A in FIG.

[0040] Figure 8C is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 5B BB direction in the figure), wherein the contact area reduction structure is a convex structure;

[0041] Fig.9A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Fig. 9C BB direction in the middle);

[0042] Fig. 9B for Fig.9A An enlarged schematic diagram of part A in FIG.

[0043] Fig. 9C is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0044] Fig.9D for Fig. 9C An enlarged schematic diagram of part A in FIG. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0046] Figure 1A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 1B or Figure 1C BB direction). Figure 1B According to an exemplary embodiment of the present invention Figure 1A Schematic top view of the BAW resonator in Figure 2. Figure 1C A top view schematic diagram of the bulk acoustic wave resonator in Figure 1A an exemplary embodiment according to the present invention.

[0047] In Figures 1A-1C it, the reference numerals represent as follows:

[0048] 101: Substrate, such as silicon, etc.

[0049] 103: Cavity, which can also be other acoustic mirror structures such as a Bragg reflector layer

[0050] 105: Bottom electrode, there is no contact between the bottom electrode and the substrate 101, and there is an air gap

[0051] 107: Piezoelectric layer, the part of the piezoelectric layer outside the bottom electrode (the part within the main resonance region) has no contact with the substrate 101, and there is an air gap

[0052] 109: Top electrode

[0053] 111: Passivation layer, aluminum nitride (AlN), silicon nitride, etc.

[0054] 113: Air gap, separating the bottom electrode 105 and the substrate 101, the piezoelectric layer 107 and the substrate 101, and the protection structure 115 and the piezoelectric layer 107

[0055] 115: Protection structure, which consists of two parts: the part connected to the substrate is the first part 115a, and the suspended part not connected to other layers is the second part 115b, and 115b is a suspended structure. The end point of the second part is horizontally located between the bottom electrode and the top electrode. The material of the protection structure 115 can be metal, such as gold, molybdenum, aluminum, etc., alloy, other materials. If it is a material that is not easily oxidized, only one layer of the protection structure 115 is required. If it is a material that is easily oxidized, a passivation layer should be added above the protection structure 115.

[0056] W1: The distance between the bottom electrode 105 and the top electrode 109. In the embodiment shown in Fig. 1, the horizontal distance between the second end point (inner end, in the present invention, the end or side close to the center of the effective region of the resonator is the inner; correspondingly, the first end point is the outer end, in the invention, the end or side far from the center of the effective region of the resonator is the outer) of the protection structure 115 and the top electrode 109 is W, 0 < W ≤ W1, and its specific range is not more than 15 μm.

[0057] W2: The distance between the bottom electrode 105 and the end on the same side of the piezoelectric layer 107. Its specific range is: 3 - 50 μm.

[0058] H1: The distance between the protection structure 115 and the piezoelectric layer 107. Its specific range is: Optionally

[0059] H2: The distance between the piezoelectric layer 107 and the substrate 101. Its specific range is: Optional

[0060] In the present invention, the numerical range mentioned may be not only the endpoint values, but also the median values ​​or other values ​​between the endpoint values, all of which are within the protection scope of the present invention.

[0061] It should be pointed out that in the embodiments given in the present invention, a protective structure 115 is provided. However, as can be understood by those skilled in the art, in the case where there is a gap between the main resonance region of the sandwich structure of the resonator and the upper surface of the substrate, the protective structure 115 may not be provided. Here, the main resonance structure refers to the sandwich structure region of the resonator excluding the top and bottom electrode lead portions. In the present invention, the overlapping region of the bottom electrode, the piezoelectric layer, the top electrode and the acoustic mirror in the thickness direction of the resonator constitutes the effective region of the resonator. In the present invention, the situation where there is a gap between the main resonator structure and the upper surface of the substrate particularly refers to the situation where there is a gap between the main resonance structure and the upper surface of the substrate except for the effective region or the acoustic mirror region. Because a gap is formed between the main resonance region of the sandwich structure of the resonator and the substrate, the frequency of the resonator is not affected by the stress of the substrate. This is conducive to the stability of the resonator frequency.

[0062] When the protective structure 115 is provided, if the resonator is deformed during operation, the protective structure 115 can limit the deformation of the resonator, so that the resonator is not easily deformed or broken.

[0063] Figure 1B and Figure 1C The situations where the electrode pins are arranged on different sides and the situations where the electrode pins are arranged on the same side are respectively shown.

[0064] exist Figure 1B In the embodiment, the electrode pins 117 and 119 are located on different sides, and the protection structure 115 is divided into two parts. Figure 1C In the embodiment, the electrode pins 117 and 119 are located on the same side, which is beneficial to the continuity of the protection structure, and the protection structure is a whole, so the protection effect is better.

[0065] Figure 2A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 2B BB direction). Figure 2B According to an exemplary embodiment of the present invention Figure 2A Schematic top view of the BAW resonator in Figure 2. Figure 2C and 2Dis a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (respectively along Figure 2B CC direction and DD direction).

[0066] exist Figures 2A-2D In the embodiment shown in the figure and the subsequent embodiments, a passivation layer 116 is provided on the protection structure 115. The material of the protection structure 115 may be, for example, molybdenum, and the material of the protection structure 115 may be the same as or different from that of the top electrode. The material of the passivation layer 116 may be the same as that of the passivation layer 111, for example, both may be AlN, or they may be different.

[0067] exist Figures 2A-2D In FIG. 1 , it can be seen that the protection structure 115 is located outside the bottom electrode in the lateral direction. Figure 1A This avoids the inner end of the protection structure 115 and the bottom electrode from overlapping in the thickness direction of the resonator, thereby avoiding the formation of a small sandwich structure. Figures 2A-2D In the illustrated embodiment, the protection structure 115 is not present to affect the performance of the resonator due to the additional sandwich structure.

[0068] Figure 3 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 1B or Figure 1C In order to further reduce the impact of the protection structure on the performance of the resonator, Figure 3 In the embodiment, the bottom electrode is arranged so that in the projection in the thickness direction of the resonator, the bottom electrode is located inside the acoustic mirror.

[0069] Figure 4A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the

[0070] Figure 4B BB direction). Figure 4B According to an exemplary embodiment of the present invention Figure 4A Schematic top view of the BAW resonator in Figure 2.

[0071] like Figure 4A-4B As shown, the inner end of the second part of the protection structure 115 is directly connected to the piezoelectric layer, so compared with the previous embodiment in which the protection structure 115 is a suspended structure, Figure 4A and 4B The protective structure in the embodiment shown in FIG. 1 is a semi-suspended structure.

[0072] In a further embodiment, Figure 4A As shown, the connection portion between the inner end of the second portion of the protection structure 115 and the piezoelectric layer is located outside the edge of the bottom electrode in the lateral direction of the resonator.

[0073] Although there is a first gap between the bottom side of the sandwich structure of the resonator and the upper side of the substrate, in practice, the bottom side of the sandwich structure and the upper side of the substrate still contact each other. In order to reduce the influence of external stress on the performance of the resonator in this case, a contact area reduction structure is provided between the bottom side of the sandwich structure and the upper side of the substrate, so that when the edge of the sandwich structure contacts the substrate, it will not be completely attached, thereby reducing the influence of external stress. Figures 5A-9D Specific instructions.

[0074] Figure 5A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Figure 5B BB direction in the middle). Figure 5B FIG. 4 is a schematic top view of a BAW resonator according to an exemplary embodiment of the present invention. Figure 5C for Figure 5B An enlarged schematic diagram of part A in FIG.

[0075] exist Figures 5A-5C In the figure, a small cavity 121 is arranged outside the cavity 103 (corresponding to the substructure constituting the contact area reduction structure, which can also be considered as a depression). The small cavity 121 can be etched at the same height as the cavity 103, or can be etched at different times with different heights. When the resonator device is deformed due to stress, the edge position will not be completely in contact with the substrate, thereby reducing the influence of external stress. It should be pointed out that in the present invention, the "small" in the small cavity only means that it is smaller in size relative to the acoustic mirror cavity. For example, the length and width of the small cavity can be in the range of 1-30um.

[0076] like Figure 5B As shown, the small cavity 121 can be arranged in a ring shape along the edge of the cavity 103, or can be arranged vertically. Figure 5B Shown is a ring arrangement.

[0077] Fig. 6A FIG. 4 is a schematic top view of a BAW resonator according to an exemplary embodiment of the present invention. Fig. 6A The embodiment shown is Figure 5A The embodiment shown in -C is substantially the same, except that the extension direction of the small cavity 121 is arranged perpendicular to the edge of the cavity 103. Figure 6B for Fig. 6A The enlarged schematic diagram of part A in FIG. 1 specifically shows the relationship between the small cavity 121 and the cavity 103, the bottom electrode 105, and the piezoelectric layer 107.

[0078] Fig. 7A FIG. 4 is a schematic top view of a BAW resonator according to an exemplary embodiment of the present invention. Figure 7B for Fig. 7AThe enlarged schematic diagram of the A part in FIG. Figure 7A-7B As shown, the small cavity 121 is vertically arranged along the edge of the cavity 103, and the cavity 103 can be directly arranged as a structure with a protrusion. Figure 7B The cavity 103 is shown as being configured as a structure with a protrusion.

[0079] Fig. 8A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 5B BB direction in the middle); Figure 8B for Fig. 8A An enlarged schematic diagram of part A in FIG. Figure 8C is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (similar to the cross-sectional view of Figure 5B BB direction in the figure), wherein the contact area reduction structure is a convex structure. Fig. 8A and Figure 8B In FIG. 1 , it is shown that a plurality of protrusions are provided outside the cavity 103 below the bottom electrode and the piezoelectric layer, and the plurality of protrusions serve as contact area reduction structures. Figure 8C In the embodiment, the protrusion is on the substrate, which can be formed by etching on the substrate or can be a new layer structure.

[0080] Fig.9A is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention (along the Fig. 9C BB direction in the middle). Fig. 9B for Fig.9A A magnified schematic diagram of part A in FIG. Figures 9A-9B In the embodiment, a plurality of bumps are used as contact area reduction structures.

[0081] Fig. 9C is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, Fig.9D for Fig. 9C The enlarged schematic diagram of the A portion in FIG. The plurality of protrusions may be arranged discretely or in an array.

[0082] As those skilled in the art will appreciate, although Figures 5A-9D In the example, the electrode pins are arranged on the same side, but Figures 5A-9D The contact area reduction structure can also be used in resonators where electrode pins are arranged on different sides.

[0083] As will be appreciated by those skilled in the art, the BAW resonator according to the present invention may be used to form a filter.

[0084] Based on the above, the present invention proposes the following technical solutions:

[0085] 1. A bulk acoustic wave resonator, comprising:

[0086] substrate;

[0087] Acoustic mirror;

[0088] A bottom electrode having a bottom electrode pin;

[0089] a top electrode having a top electrode pin;

[0090] A piezoelectric layer is disposed between the bottom electrode and the top electrode,

[0091] in:

[0092] There is a first gap between the sandwich structure consisting of the bottom electrode, the top electrode and the piezoelectric layer and the upper surface of the substrate, wherein the first gap makes the main resonant region of the resonator formed by the bottom electrode, the piezoelectric layer and the top electrode have no contact with the substrate;

[0093] A contact area reducing structure is disposed between the lower side of the sandwich structure and the upper surface of the substrate.

[0094] 2. The resonator according to item 1, further comprising:

[0095] A protective structural layer, the protective structural layer comprising a first part and a second part, the first part is connected to the upper surface of the substrate, the outer end of the second part is connected to the inner end of the first part, the second part extends along the piezoelectric layer to above the piezoelectric layer and at least a part of the second part forms a second gap with the piezoelectric layer in the thickness direction, and the second part is spaced apart from the top electrode in the lateral direction.

[0096] 3. The resonator according to 2, wherein:

[0097] The top electrode pin and the bottom electrode pin are located on opposite sides of the resonator in a lateral direction;

[0098] The protection structure layer is arranged along the periphery of the resonator effective area, and includes a first circumferential portion and a second circumferential portion separated by a top electrode pin and a bottom electrode pin in a circumferential direction.

[0099] 4. The resonator according to 2, wherein:

[0100] The top electrode pin and the bottom electrode pin are located on the same side of the resonator in the lateral direction;

[0101] The protection structure layer is arranged along the periphery of the effective area of ​​the resonator, and in the top view of the resonator, the top electrode pin and the bottom electrode pin are located at the gap of the protection structure layer in the circumferential direction.

[0102] 5. The resonator according to 2, wherein:

[0103] The second gap extends over an entire portion of the second portion, and an inner end of the second portion is spaced apart from the piezoelectric layer in a thickness direction of the resonator.

[0104] 6. The resonator according to 2, wherein:

[0105] An inner end of the second portion is connected to the piezoelectric layer.

[0106] 7. The resonator according to 6, wherein:

[0107] An inner end of the second portion and a projection of the bottom electrode in a thickness direction of the resonator are spaced apart from each other.

[0108] 8. The resonator according to 2, wherein:

[0109] The first gap communicates with the second gap.

[0110] 9. The resonator according to 8, wherein:

[0111] The acoustic mirror is an acoustic mirror cavity, and the first gap is communicated with the acoustic mirror cavity.

[0112] 10. A resonator according to any one of 1 to 9, wherein:

[0113] The contact area reducing structure is arranged on the outer side of the acoustic mirror.

[0114] 11. A resonator according to any one of 1 to 9, wherein:

[0115] The contact area reducing structure is arranged in a ring shape as a whole along the circumferential direction of the effective area of ​​the resonator; or

[0116] The contact area reducing structure includes a plurality of structural units that are arranged spaced apart from each other in a circumferential direction of an effective region of a resonator.

[0117] 12. A resonator according to any one of 1 to 9, wherein:

[0118] The contact area reduction structure includes a plurality of substructures, and the plurality of substructures are arranged discretely or in an array.

[0119] 13. A resonator according to any one of 1 to 12, wherein:

[0120] The contact area reducing structure is disposed on the substrate.

[0121] 14. The resonator according to 13, wherein:

[0122] The acoustic mirror is an acoustic mirror cavity; and

[0123] The contact area reducing structure includes a plurality of depressions disposed outside the cavity.

[0124] 15. The resonator according to 14, wherein:

[0125] The depth of the recess is the same as the depth of the acoustic mirror cavity, or is smaller than the depth of the acoustic mirror cavity.

[0126] 16. The resonator according to 14 or 15, wherein:

[0127] The recess extends in length direction parallel to the edge of the acoustic mirror cavity; or

[0128] The recess extends in a length direction perpendicular to an edge of the acoustic mirror cavity.

[0129] 17. The resonator according to 13, wherein:

[0130] The acoustic mirror is an acoustic mirror cavity, the contact area reducing structure comprises a plurality of strip-shaped protrusions arranged on a base, gaps between the plurality of strip-shaped protrusions are communicated with the acoustic mirror cavity, the plurality of strip-shaped protrusions extend perpendicularly to a side wall of the acoustic mirror cavity and end surfaces of the plurality of strip-shaped protrusions are flush with the side wall of the acoustic mirror cavity, and top surfaces of the plurality of strip-shaped protrusions are flush with an upper surface of the base; or

[0131] The contact area reducing structure includes a plurality of protrusions disposed on an upper side of a substrate.

[0132] 18. A resonator according to any one of 1 to 12, wherein:

[0133] The contact area reducing structure is disposed at a lower side of the sandwich structure.

[0134] 19. The resonator according to 18, wherein:

[0135] The contact area reducing structure includes protrusions or bumps protruding toward the substrate.

[0136] 20. The resonator according to 19, wherein:

[0137] The acoustic mirror is an acoustic mirror cavity;

[0138] The contact area reducing structure is adjacent to an edge of the acoustic mirror cavity in a lateral direction of the resonator.

[0139] 21. A filter comprising the BAW resonator according to any one of 1-20.

[0140] 22. An electronic device comprising the filter according to 21 or the BAW resonator according to any one of 1-20.

[0141] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bulk acoustic wave resonator, comprising: substrate; Acoustic mirror; A bottom electrode having a bottom electrode pin; a top electrode having a top electrode pin; A piezoelectric layer is disposed between the bottom electrode and the top electrode, in: There is a first gap between the sandwich structure composed of the bottom electrode, the top electrode and the piezoelectric layer and the upper surface of the substrate, and the first gap makes the main resonant structure of the resonator formed by the bottom electrode, the piezoelectric layer and the top electrode have no contact with the substrate; A contact area reducing structure is provided between the lower side of the sandwich structure and the upper surface of the substrate; It also includes: a protective structural layer, the protective structural layer includes a first part and a second part, the first part is connected to the upper surface of the substrate, the outer end of the second part is connected to the inner end of the first part, the second part extends along the piezoelectric layer to above the piezoelectric layer and at least a part of the second part forms a second gap with the piezoelectric layer in the thickness direction, and the second part is spaced apart from the top electrode in the lateral direction.

2. The resonator according to claim 1, wherein: The top electrode pin and the bottom electrode pin are located on opposite sides of the resonator in a lateral direction; The protection structure layer is arranged along the periphery of the resonator effective area, and includes a first circumferential portion and a second circumferential portion separated by a top electrode pin and a bottom electrode pin in a circumferential direction.

3. The resonator of claim 1, wherein: The top electrode pin and the bottom electrode pin are located on the same side of the resonator in the lateral direction; The protection structure layer is arranged along the periphery of the effective area of ​​the resonator, and in the top view of the resonator, the top electrode pin and the bottom electrode pin are located at the gap of the protection structure layer in the circumferential direction.

4. The resonator of claim 1, wherein: The second gap extends over an entire portion of the second portion, and an inner end of the second portion is spaced apart from the piezoelectric layer in a thickness direction of the resonator.

5. The resonator of claim 1, wherein: An inner end of the second portion is connected to the piezoelectric layer.

6. The resonator of claim 5, wherein: An inner end of the second portion and a projection of the bottom electrode in a thickness direction of the resonator are spaced apart from each other.

7. The resonator of claim 1, wherein: The first gap communicates with the second gap.

8. The resonator of claim 7, wherein: The acoustic mirror is an acoustic mirror cavity, and the first gap is communicated with the acoustic mirror cavity.

9. The resonator according to any one of claims 1 to 8, wherein: The contact area reducing structure is arranged on the outer side of the acoustic mirror.

10. The resonator according to any one of claims 1 to 8, wherein: The contact area reducing structure is arranged in a ring shape as a whole along the circumferential direction of the effective area of ​​the resonator; or The contact area reducing structure includes a plurality of structural units that are arranged spaced apart from each other in a circumferential direction of an effective region of a resonator.

11. The resonator according to any one of claims 1 to 8, wherein: The contact area reduction structure includes a plurality of substructures, and the plurality of substructures are arranged discretely or in an array.

12. The resonator according to any one of claims 1 to 8, wherein: The contact area reducing structure is disposed on the substrate.

13. The resonator of claim 12, wherein: The acoustic mirror is an acoustic mirror cavity; and The contact area reducing structure includes a plurality of depressions disposed outside the cavity.

14. The resonator of claim 13, wherein: The depth of the recess is the same as the depth of the acoustic mirror cavity, or is smaller than the depth of the acoustic mirror cavity.

15. A resonator according to claim 13 or 14, wherein: The recess extends in length direction parallel to the edge of the acoustic mirror cavity; or The recess extends in a length direction perpendicular to an edge of the acoustic mirror cavity.

16. The resonator of claim 12, wherein: The acoustic mirror is an acoustic mirror cavity, the contact area reducing structure comprises a plurality of strip-shaped protrusions arranged on a base, gaps between the plurality of strip-shaped protrusions are communicated with the acoustic mirror cavity, the plurality of strip-shaped protrusions extend perpendicularly to a side wall of the acoustic mirror cavity and end surfaces of the plurality of strip-shaped protrusions are flush with the side wall of the acoustic mirror cavity, and top surfaces of the plurality of strip-shaped protrusions are flush with an upper surface of the base; or The contact area reducing structure includes a plurality of protrusions disposed on an upper side of a substrate.

17. The resonator according to any one of claims 1 to 8, wherein: The contact area reducing structure is disposed at a lower side of the sandwich structure.

18. The resonator of claim 17, wherein: The contact area reducing structure includes protrusions or bumps protruding toward the substrate.

19. The resonator of claim 18, wherein: The acoustic mirror is an acoustic mirror cavity; The contact area reducing structure is adjacent to an edge of the acoustic mirror cavity in a lateral direction of the resonator.

20. A filter comprising the BAW resonator according to any one of claims 1 to 19.

21. An electronic device comprising the filter according to claim 20 or the BAW resonator according to any one of claims 1 to 19.

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