Bulk acoustic wave filter

Abstract

The utility model discloses a bulk acoustic wave filter, and relates to the technical field of micro electro mechanical systems, the bulk acoustic wave filter comprises a substrate and a plurality of resonators arranged on the substrate in a cascade connection mode, the plurality of resonators comprise at least one front end resonator and one tail end resonator, the front-end resonator comprises a lower electrode, a piezoelectric layer and an upper electrode which are sequentially arranged on the substrate, the periphery of the upper electrode extends in the direction away from the upper electrode in the hierarchy direction to form a lifting part, an air gap is formed between the lifting part and the piezoelectric layer, and a capacitance compensation structure is formed between the lifting part and the upper electrode or between the lifting part and the lower electrode. According to the bulk acoustic wave filter provided by the invention, capacitance of other resonators can be compensated, so that passband pits of the filter are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of micro-electromechanical systems, and in particular to a bulk acoustic wave filter. Background Art

[0002] At present, 5G communication technology has gradually matured and commercialized. With the explosive growth of mobile data traffic, the demand for the development of future 6G communication technology is becoming increasingly strong. This requires the core RF front-end module to have better performance, among which the RF filter is the most core component that determines the wireless communication bandwidth. As a type of RF filter, the bulk acoustic wave filter has better frequency selectivity, lower loss and higher operating frequency capability, and is very suitable for high-frequency wireless communication applications.

[0003] In order to improve the nonlinearity of BAW filters and increase their power handling capacity, at least two BAW resonators are often cascaded. In the cascade process, at least two BAW resonators are arranged on a substrate and connected, wherein the end resonator is grounded through an electrode lead and a through hole arranged on the substrate. During the connection process, the electrode lead and the through hole will introduce parasitic capacitance, which will cause the parallel resonant frequency (Fp) of the end resonator to shift, resulting in inconsistent Fp of each resonator on the cascade branch, thereby causing a pit in the passband of the filter, affecting the overall performance of the filter. Utility Model Content

[0004] The object of the present application is to provide a bulk acoustic wave filter that can compensate for the capacitance of other resonators, thereby reducing the filter passband notch.

[0005] On the one hand, an embodiment of the present application provides a bulk acoustic wave filter, including a substrate and a plurality of resonators cascaded on the substrate, the plurality of resonators including at least one front-end resonator and one end resonator, the front-end resonator including a lower electrode, a piezoelectric layer and an upper electrode sequentially arranged on the substrate, the outer periphery of the upper electrode extending in a hierarchical direction away from the upper electrode to form a raised portion, an air gap is formed between the raised portion and the piezoelectric layer, and a capacitance compensation structure is formed between the raised portion and the upper electrode or between the raised portion and the lower electrode.

[0006] As an implementable manner, the elevated portion includes an air wing, and a capacitance compensation structure is formed between the air wing and the upper electrode or the lower electrode.

[0007] As an implementable manner, the air wing extends away from the center of the upper electrode, the upper electrode extends away from the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air wing, and between the extension portion and the lower electrode.

[0008] As an implementable manner, the air wing extends toward the center of the upper electrode, and a capacitance compensation structure is formed between the upper electrode and the air wing.

[0009] As an implementable manner, the elevated portion includes an air bridge, the other end of the air bridge is connected to the piezoelectric layer, and a capacitance compensation structure is formed between the air bridge and the upper electrode or the lower electrode.

[0010] As an implementable manner, the upper electrode extends in a direction away from the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air bridge.

[0011] As an implementable manner, the lower electrode extends along the hierarchical direction in a direction away from the piezoelectric layer to form a gap wing, and a capacitance compensation structure is formed between the gap wing and the air bridge.

[0012] As an implementable manner, the portion where the air bridge is connected to the piezoelectric layer is a connecting portion, and the connecting portion extends toward the space enclosed by the air bridge and the piezoelectric layer to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air bridge.

[0013] As an implementable manner, the air bridge extends toward the center of the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the upper electrode.

[0014] As an implementable method, the part where the air bridge is connected to the piezoelectric layer is a connecting part, and the air bridge protrudes from the connecting part, a cavity is formed between the lower electrode and the substrate so that the lower electrode, the piezoelectric layer and the upper electrode are bent upward at the cavity, and two support columns are arranged between the air bridge and the piezoelectric layer, and a capacitance compensation structure is formed between the two support columns.

[0015] The beneficial effects of the embodiments of the present application include:

[0016] The bulk acoustic wave filter provided by the present application includes a substrate and a plurality of resonators cascaded on the substrate, the plurality of resonators include at least one front-end resonator and one end resonator, the end resonator and the substrate are connected by leads or through holes to introduce parasitic capacitance, the front-end resonator includes a lower electrode, a piezoelectric layer and an upper electrode sequentially arranged on the substrate, a cavity is formed between the lower electrode and the substrate, the outer periphery of the upper electrode extends in the hierarchical direction away from the upper electrode to form an elevated portion, an air gap is formed between the elevated portion and the piezoelectric layer, and there is a certain gap between the elevated portion and the upper electrode or between the elevated portion and the lower electrode, and the elevated portion, the lower electrode and the upper electrode are all conductors, so that a capacitance compensation structure is formed between the elevated portion and the upper electrode or between the elevated portion and the lower electrode, with a certain capacitance value, so that a capacitance compensation structure is set in the front-end resonator to introduce a compensation capacitor. When the compensation capacitor is equal to the parasitic capacitor, the Fp of the front-end resonator and the end resonator are the same, thereby avoiding pits in the filter passband. When the compensation capacitor is less than or greater than the parasitic capacitor, the compensation capacitor compensates for part of the parasitic capacitor, thereby reducing the filter passband pit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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.

[0018] Figure 1 One of the structural schematic diagrams of a front-end resonator provided in an embodiment of the present application;

[0019] Figure 2 is an equivalent circuit diagram of a bulk acoustic wave filter in the prior art;

[0020] Figure 3 is an equivalent circuit diagram of a bulk acoustic wave filter according to an embodiment of the present application;

[0021] Figure 4 A second structural schematic diagram of a front-end resonator provided in an embodiment of the present application;

[0022] Figure 5 A third structural diagram of a front-end resonator provided in an embodiment of the present application;

[0023] Figure 6 A fourth structural diagram of a front-end resonator provided in an embodiment of the present application;

[0024] Figure 7 A fifth structural diagram of a front-end resonator provided in an embodiment of the present application;

[0025] Figure 8 A sixth structural diagram of a front-end resonator provided in an embodiment of the present application;

[0026] Fig. 9 A seventh structural diagram of a front-end resonator provided in an embodiment of the present application;

[0027] Fig.10 This is a performance comparison chart of the BAW filter provided in the embodiment of the present application and the BAW filter in the prior art.

[0028] Icons: 100-bulk acoustic wave filter; 110-substrate; 111-front end resonator; 112-end resonator; 121-lower electrode; 122-piezoelectric layer; 123-upper electrode; 124-elevation portion; 125-air wing; 126-air bridge; 131-extension portion; 132-extension portion; 133-gap wing; 134-connection portion; 135-extension portion; 136-support column; 140-cavity; 150-capacitance compensation structure. DETAILED DESCRIPTION

[0029] 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.

[0030] 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 which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0031] 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.

[0032] In the description of the present application, it should be noted that the terms "center", "vertical", "horizontal", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations 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 orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0033] The BAW filter in the prior art includes a plurality of cascaded resonators, wherein the end resonators of the plurality of resonators are connected through electrode leads and through holes, and these electrode leads and through holes introduce parasitic capacitance, so that the equivalent circuit diagram of the BAW filter is as follows: Figure 2 As shown, these parasitic capacitors will cause the parallel resonant frequency of the end resonator to shift. Specifically, the parasitic capacitors will cause the capacitance value of the end resonator to increase. According to the formula for the parallel resonant frequency (Fp), the Fp of the end resonator will be reduced, resulting in different Fp values ​​for each resonator in the BAW filter, which will cause a pit in the passband of the filter.

[0034] The present application embodiment provides a bulk acoustic wave filter 100, such as Figure 1 As shown, it includes a substrate 110 and a plurality of resonators cascaded on the substrate 110, the plurality of resonators include at least one front resonator 111 and an end resonator 112, the front resonator 111 includes a lower electrode 121, a piezoelectric layer 122 and an upper electrode 123 sequentially arranged on the substrate 110, a cavity 140 is formed between the lower electrode 121 and the substrate 110, the periphery of the upper electrode 123 extends along the hierarchical direction in a direction away from the upper electrode 123 to form a raised portion 124, an air gap is formed between the raised portion 124 and the piezoelectric layer 122, and a capacitance compensation structure 150 is formed between the raised portion 124 and the upper electrode 123 or between the raised portion 124 and the lower electrode 121.

[0035] The BAW filter 100 provided in the embodiment of the present application forms a capacitance compensation structure 150 in the front-end resonator 111, so that the capacitance of the end resonator 112 is the same as that of the front-end resonator 111, thereby making the Fp of the front-end resonator 111 and the end resonator 112 the same, thereby avoiding the occurrence of a pit in the passband of the filter. Specifically, the BAW filter 100 provided in the embodiment of the present application includes a substrate 110 and a plurality of resonators cascadedly arranged on the substrate 110, one of the plurality of resonators is connected to the outside world through the substrate 110, and the resonator connected to the outside world serves as the end resonator 112, and the remaining resonators are all the front-end resonator 111, such as Figure 3 As shown, the end resonator 112 is connected to the substrate 110 through a lead or a through hole to introduce a parasitic capacitor, and a capacitor compensation structure 150 is set in the front resonator 111 to introduce a compensation capacitor. When the compensation capacitor is equal to the parasitic capacitor, the Fp of the front resonator 111 and the end resonator 112 are the same, thereby avoiding a pit in the filter passband. When the compensation capacitor is less than or greater than the parasitic capacitor, the compensation capacitor compensates for part of the parasitic capacitor, thereby reducing the filter passband pit.

[0036] Specifically, the front-end resonator 111 in the embodiment of the present application includes a lower electrode 121, a piezoelectric layer 122 and an upper electrode 123 sequentially arranged on a substrate 110, wherein the outer periphery of the upper electrode 123 extends in a hierarchical direction in a direction away from the upper electrode 123 to form an elevated portion 124, and since the elevated portion 124 extends in a direction away from the upper electrode 123, an air gap is formed between the elevated portion 124 and the piezoelectric layer 122, and a certain gap exists between the elevated portion 124 and the upper electrode 123 or between the elevated portion 124 and the lower electrode 121, and the elevated portion 124, the lower electrode 121 and the upper electrode 123 are all conductors, so that a capacitor is formed between the elevated portion 124 and the upper electrode 123 or between the elevated portion 124 and the lower electrode 121, and has a certain capacitance value, serving as a capacitor compensation structure 150. Due to the setting of the capacitor compensation structure 150, a compensation capacitor is introduced into the front-end resonator 111, so that the filter passband pit can be reduced.

[0037] The distance between the height-adjusting portion of the capacitance compensation structure 150 and the piezoelectric layer 122 is not limited in the embodiment of the present application, and those skilled in the art can adjust it according to the actual parasitic capacitance.

[0038] In practical applications, an acoustic reflection structure is formed between the lower electrode 121 and the substrate 110 to reflect the acoustic wave propagating to the side of the lower electrode 121. Specifically, it can be as follows: Figure 1 The cavity 140 shown may also be a stack of materials with high and low acoustic impedance alternately arranged, wherein the top of the cavity 140 may extend out of the surface of the substrate or may be flush with the surface of the substrate.

[0039] The bulk acoustic wave filter 100 provided in the present application includes a substrate 110 and a plurality of resonators cascaded on the substrate 110, wherein the plurality of resonators include at least one front resonator 111 and an end resonator 112, wherein the end resonator is connected to the substrate 110 through a lead or a through hole to introduce a parasitic capacitor, and the front resonator 111 includes a lower electrode 121, a piezoelectric layer 122 and an upper electrode 123 sequentially arranged on the substrate 110, a cavity 140 is formed between the lower electrode 121 and the substrate 110, and the outer periphery of the upper electrode 123 is away from the upper electrode 123 along the hierarchical direction. 23 direction to form an elevated portion 124, an air gap is formed between the elevated portion 124 and the piezoelectric layer 122, a certain gap is formed between the elevated portion 124 and the upper electrode 123 or between the elevated portion 124 and the lower electrode 121, and the elevated portion 124, the lower electrode 121 and the upper electrode 123 are all conductors, so that a capacitor compensation structure 150 is formed between the elevated portion 124 and the upper electrode 123 or between the elevated portion 124 and the lower electrode 121, which has a certain capacitance value, so that the capacitor compensation structure 150 is set in the front end resonator 111 to introduce a compensation capacitor. When the compensation capacitor is equal to the parasitic capacitance, the Fp of the front end resonator 111 and the end resonator 112 are the same, thereby avoiding pits in the filter passband. When the compensation capacitor is less than or greater than the parasitic capacitance, the compensation capacitor compensates for part of the parasitic capacitance, thereby reducing the filter passband pit.

[0040] Optional, such as Figure 1 and Figure 4 As shown, the raised portion 124 includes an air wing 125 , and a capacitance compensation structure 150 is formed between the air wing 125 and the upper electrode 123 or the lower electrode 121 .

[0041] The raised portion 124 includes an air wing 125, which is formed by extending the end of the upper electrode 123 upward. The air wing 125 is at a certain distance from the piezoelectric layer 122, so that the air wing 125 and the upper electrode 123 and the lower electrode 121 are at a certain distance. In this way, a capacitance compensation structure 150 is formed between the air wing 125 and the upper electrode 123 or the lower electrode 121, which is used to form a compensation capacitor in the front end resonator 111, so as to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0042] In one possible implementation of the present application, Figure 1 As shown, the air wing 125 extends in a direction away from the center of the upper electrode 123 , and the upper electrode 123 extends in a direction away from the upper electrode 123 to form an extension portion 131 , and a capacitance compensation structure 150 is formed between the extension portion 131 and the air wing 125 , and between the extension portion 131 and the lower electrode 121 .

[0043] The extension portion 131 extends out of the upper electrode 123 and is located below the air wing 125, so that the air wing 125 and the extension portion 131 are arranged opposite to each other and have a certain gap, thereby forming a capacitance compensation structure 150 between the extension portion 131 and the air wing 125. In addition, the extension portion 131 and the lower electrode 121 are arranged opposite to each other and have a certain gap, thereby forming a capacitance compensation structure 150 between the extension portion 131 and the lower electrode 121. Both parts of the capacitance compensation structure 150 introduce compensation capacitors in the front end resonator 111 to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband pit.

[0044] Optional, such as Figure 4 As shown, the air wing 125 extends toward the center of the upper electrode 123 , and a capacitance compensation structure 150 is formed between the upper electrode 123 and the air wing 125 .

[0045] The air wing 125 extends toward the center of the upper electrode 123, so that the air wing 125 and a portion of the upper electrode 123 are arranged opposite to each other with a certain gap, thereby forming a capacitance compensation structure 150 between the upper electrode 123 and the air wing 125. The capacitance compensation structure 150 introduces a compensation capacitor into the front end resonator 111 to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0046] In one possible implementation of the present application, Figures 5 to 9 As shown, the elevated portion 124 includes an air bridge 126 , the other end of the air bridge 126 is connected to the piezoelectric layer 122 , and a capacitance compensation structure 150 is formed between the air bridge 126 and the upper electrode 123 or the lower electrode 121 .

[0047] The raised portion 124 includes an air bridge 126, which is an arched component formed by extending the end of the upper electrode 123 upward and then downward to contact the piezoelectric layer 122. The air bridge 126 is at a certain distance from the piezoelectric layer 122, so that there is a certain distance between the air bridge 126 and the upper electrode 123 and the lower electrode 121. In this way, a capacitance compensation structure 150 is formed between the air bridge 126 and the upper electrode 123 or the lower electrode 121, which is used to form a compensation capacitor in the front end resonator 111, so as to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband pit.

[0048] Optional, such as Figure 5 As shown, the upper electrode 123 extends in a direction away from the upper electrode 123 to form an extension portion 131 , and a capacitance compensation structure 150 is formed between the extension portion 131 and the air bridge 126 .

[0049] The extension portion 131 extends out of the upper electrode 123 and is located below the air bridge 126, so that the air bridge 126 and the extension portion 131 are arranged opposite to each other with a certain gap, thereby forming a capacitance compensation structure 150 between the extension portion 131 and the air bridge 126. The capacitance compensation structure 150 introduces a compensation capacitor into the front-end resonator 111 to reduce the capacitance difference between the front-end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0050] In one possible implementation of the present application, Figure 6 As shown, the lower electrode 121 extends along the hierarchical direction in a direction away from the piezoelectric layer 122 to form a gap wing 133 , and a capacitance compensation structure 150 is formed between the gap wing 133 and the air bridge 126 .

[0051] There is a certain gap between the gap wing 133 and the lower electrode 121, and there is a certain gap between the air bridge 126 and the upper electrode 123, so that the gap wing 133 and the air bridge 126 are arranged opposite to each other and have a certain gap, thereby forming a capacitance compensation structure 150 between the gap wing 133 and the air bridge 126. The capacitance compensation structure 150 introduces a compensation capacitor into the front-end resonator 111 to reduce the capacitance difference between the front-end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0052] Optional, such as Figure 7 As shown, the portion where the air bridge 126 connects to the piezoelectric layer 122 is a connecting portion 134 , which extends into the space enclosed by the air bridge 126 and the piezoelectric layer 122 to form an extension portion 132 , and a capacitance compensation structure 150 is formed between the extension portion 132 and the air bridge 126 .

[0053] From the above, it can be seen that the air bridge 126 is an arched component formed by the end of the upper electrode 123 extending upward and then downward to contact the piezoelectric layer 122, wherein the part where the air bridge 126 is connected to the piezoelectric layer 122 is the connecting portion 134, and the connecting portion 134 extends to the space enclosed by the air bridge 126 and the piezoelectric layer 122 to form an extension portion 132, and there is a certain gap between the extension portion 132 and the air bridge 126, and they are arranged relative to each other, so that a capacitance compensation structure 150 is formed between the extension portion 132 and the air bridge 126, which is used to form a compensation capacitor in the front end resonator 111, and is used to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband pit.

[0054] In one possible implementation of the present application, Figure 8 As shown, the air bridge 126 extends toward the center of the upper electrode 123 to form an extension portion 135 , and a capacitance compensation structure 150 is formed between the extension portion 135 and the upper electrode 123 .

[0055] The extension portion 135 is arranged opposite to a portion of the upper electrode 123 and has a certain distance therebetween, so that a capacitance compensation structure 150 is formed between the air bridge 126 and the upper electrode 123, which is used to form a compensation capacitor in the front end resonator 111, and is used to reduce the capacitance difference between the front end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0056] In one possible implementation of the present application, Fig. 9 As shown, the portion where the air bridge 126 is connected to the piezoelectric layer 122 is a connecting portion 134, and the air bridge 126 protrudes from the connecting portion 134, a cavity 140 is formed between the lower electrode 121 and the substrate 110 so that the lower electrode 121, the piezoelectric layer 122 and the upper electrode 123 are bent upward at the cavity 140, and two support columns 136 are arranged between the air bridge 126 and the piezoelectric layer 122, and a capacitance compensation structure 150 is formed between the two support columns 136.

[0057] Two support columns 136 are arranged between the air bridge 126 and the piezoelectric layer 122. The two support columns 136 are arranged opposite to each other and have a certain gap, so that a capacitance compensation structure 150 is formed between the two support columns 136. The capacitance compensation structure 150 introduces a compensation capacitor into the front-end resonator 111 to reduce the capacitance difference between the front-end resonator 111 and the end resonator 112, thereby reducing the filter passband notch.

[0058] In order to further demonstrate the beneficial effects of the present application, the applicant simulated the passband of the prior art and the embodiment of the present application and obtained Fig.10 ,Depend on Fig.10 It can be seen that the prior art has two pits in the passband, while the curve in the passband of the present application is relatively smooth. Therefore, the BAW filter 100 provided in the present application can reduce the pits in the passband.

[0059] 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 bulk acoustic wave filter, characterized in that: It includes a substrate and a plurality of resonators cascaded on the substrate, the plurality of resonators include at least one front-end resonator and one end resonator, the front-end resonator includes a lower electrode, a piezoelectric layer and an upper electrode sequentially arranged on the substrate, the outer periphery of the upper electrode extends along the hierarchical direction in a direction away from the upper electrode to form a raised portion, an air gap is formed between the raised portion and the piezoelectric layer, and a capacitance compensation structure is formed between the raised portion and the upper electrode or between the raised portion and the lower electrode.

2. The bulk acoustic wave filter according to claim 1, characterized in that The raised portion includes an air wing, and a capacitance compensation structure is formed between the air wing and the upper electrode or the lower electrode.

3. The bulk acoustic wave filter according to claim 2, characterized in that The air wing extends in a direction away from the center of the upper electrode, and the upper electrode extends in a direction away from the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air wing, and between the extension portion and the lower electrode.

4. The bulk acoustic wave filter according to claim 2, characterized in that The air wing extends in a direction close to the center of the upper electrode, and a capacitance compensation structure is formed between the upper electrode and the air wing.

5. The bulk acoustic wave filter according to claim 1, wherein: The raised portion includes an air bridge, the other end of the air bridge is connected to the piezoelectric layer, and a capacitance compensation structure is formed between the air bridge and the upper electrode or the lower electrode.

6. The bulk acoustic wave filter according to claim 5, characterized in that The upper electrode extends in a direction away from the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air bridge.

7. The bulk acoustic wave filter according to claim 5, characterized in that The lower electrode extends along the layer direction in a direction away from the piezoelectric layer to form a gap wing, and a capacitance compensation structure is formed between the gap wing and the air bridge.

8. The bulk acoustic wave filter according to claim 5, characterized in that The portion where the air bridge is connected to the piezoelectric layer is a connecting portion, and the connecting portion extends toward the space enclosed by the air bridge and the piezoelectric layer to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the air bridge.

9. The bulk acoustic wave filter according to claim 5, characterized in that The air bridge extends toward the center of the upper electrode to form an extension portion, and a capacitance compensation structure is formed between the extension portion and the upper electrode.

10. The bulk acoustic wave filter according to claim 9, characterized in that The part where the air bridge is connected to the piezoelectric layer is a connecting part, a cavity is formed between the lower electrode and the substrate so that the lower electrode, the piezoelectric layer and the upper electrode are bent upward at the cavity, the air bridge protrudes from the connecting part, two support columns are arranged between the air bridge and the piezoelectric layer, and a capacitance compensation structure is formed between the two support columns.

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