Bulk acoustic wave filter and preparation method thereof

Abstract

The invention discloses a bulk acoustic wave filter and a preparation method thereof. The bulk acoustic wave filter comprises at least one bulk acoustic wave resonator and at least three release holes symmetrically arranged around the bulk acoustic wave resonator, the bulk acoustic wave resonator comprises a substrate and a piezoelectric structure, the substrate comprises a cavity, and the piezoelectric structure is located on the side, away from the substrate, of the cavity; and the release hole is communicated with the cavity. According to the technical scheme, the removal uniformity and the removal cleaning rate of the filling material in the cavity of the bulk acoustic wave filter can be improved, the preparation reliability of the cavity is improved, and then the working performance of the bulk acoustic wave resonator and the bulk acoustic wave filter is improved.

Description

Technical Field

[0001] The present invention relates to the field of filtering technology, and in particular to a bulk acoustic wave filter and a preparation method thereof. Background Art

[0002] With the rapid development of semiconductor technology, resonators made from semiconductor materials have found widespread application in communication systems. Resonators provided by related technologies include a piezoelectric layer and a resonant cavity. Release holes are typically provided to remove material originally located in the resonant cavity to form the resonant cavity.

[0003] However, the number of release holes set in the existing resonator is small or the position setting is unreasonable, resulting in incomplete release of the material originally located in the resonant cavity, forming a residual island structure, and affecting the working performance of the resonator. Summary of the Invention

[0004] The present invention provides a bulk acoustic wave filter and a preparation method thereof, which can improve the removal uniformity and removal cleanliness rate of filling material inside the cavity of the bulk acoustic wave filter, improve the preparation reliability of the cavity, and further improve the working performance of the bulk acoustic wave resonator and the bulk acoustic wave filter.

[0005] In a first aspect, the present invention provides a bulk acoustic wave filter comprising: at least one bulk acoustic wave resonator and at least three release holes symmetrically arranged around the bulk acoustic wave resonator;

[0006] The bulk acoustic wave resonator comprises:

[0007] a substrate including a cavity;

[0008] a piezoelectric structure, located on a side of the cavity facing away from the substrate;

[0009] Wherein, the release hole is communicated with the cavity.

[0010] Optionally, the geometric center of a geometric figure formed by connecting the release holes symmetrically arranged around the same BAW resonator is the resonator geometric center of the BAW resonator.

[0011] Optionally, the bulk acoustic wave resonator includes at least two series resonators and at least two parallel resonators;

[0012] Some of the series resonators are electrically connected to the parallel resonators, the series resonators are electrically connected to the series resonators, and the parallel resonators are electrically connected to the parallel resonators; the series resonators are arranged along a first direction, and the parallel resonators are arranged along a second direction; the first direction intersects with the second direction.

[0013] Optionally, some of the release holes are connected to the cavities of two adjacent series resonators; and / or some of the release holes are connected to the cavities of two adjacent parallel resonators.

[0014] Optionally, some of the release holes are connected to some of the cavities of the series resonators and some of the cavities of the parallel resonators.

[0015] Optionally, the piezoelectric structure includes: a first electrode layer, a piezoelectric layer and a second electrode layer;

[0016] The first electrode layer is located on the side of the cavity facing away from the substrate; the piezoelectric layer is located on the side of the first electrode layer facing away from the substrate; the second electrode layer is located on the side of the piezoelectric layer facing away from the substrate; the release hole passes through the first electrode layer, the piezoelectric layer and the second electrode layer.

[0017] Optionally, the aperture of the release hole is r;

[0018] Among them, 0.3μm≤r≤3μm.

[0019] Optionally, among the release holes surrounding the same bulk acoustic wave resonator, the distance between two adjacent release holes is L1;

[0020] Among them, 10μm≤L1≤100μm.

[0021] In a second aspect, the present invention provides a method for preparing a bulk acoustic wave filter, comprising:

[0022] Providing a substrate; the substrate comprising a cavity;

[0023] filling the cavity with a sacrificial layer;

[0024] preparing a piezoelectric structure on a side of the sacrificial layer facing away from the substrate;

[0025] Drilling the piezoelectric structure to form release holes; at least three release holes are symmetrically arranged around the same cavity, and the release holes are connected to the cavity;

[0026] An etching solution is introduced into the release hole to remove the sacrificial layer in the cavity to form the bulk acoustic wave filter.

[0027] Optionally, preparing a piezoelectric structure on a side of the sacrificial layer facing away from the substrate includes:

[0028] forming a first electrode layer on a side of the sacrificial layer facing away from the substrate;

[0029] preparing a piezoelectric layer on a side of the first electrode layer facing away from the substrate;

[0030] A second electrode layer is formed on a side of the piezoelectric layer facing away from the substrate.

[0031] The technical solution provided by the present invention has at least three release holes symmetrically arranged around a BAW resonator, and the release holes are connected to the cavity, so that the release holes located around the same BAW resonator have a small or equal spacing from the central area of ​​the BAW resonator. When the etching liquid or etching gas enters the cavity through the release holes, the etching liquid or etching gas reaches the center of the cavity through the release holes at a small or uniform rate. The etching liquid or etching gas reaching the central area of ​​the cavity can move toward the center of the cavity from at least three symmetrically arranged directions, thereby improving the uniformity and cleanliness of removing the filling material inside the cavity, improving the preparation reliability of the cavity, and thereby improving the working performance of the BAW resonator and the BAW filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a top view of a bulk acoustic wave filter provided by an embodiment of the present invention;

[0033] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure along the section line BB';

[0034] Figure 3 A schematic top view of another bulk acoustic wave filter provided by an embodiment of the present invention;

[0035] Figure 4 A schematic top view of another bulk acoustic wave filter provided by an embodiment of the present invention;

[0036] Figure 5 A schematic top view of the structure of another bulk acoustic wave filter provided by an embodiment of the present invention;

[0037] Figure 6 A schematic diagram of a top view of a bulk acoustic wave filter provided by an embodiment of the present invention;

[0038] Figure 7 A schematic top view of another bulk acoustic wave filter provided by an embodiment of the present invention;

[0039] Figure 8 A schematic top view of another bulk acoustic wave filter provided by an embodiment of the present invention;

[0040] Figure 9 A flowchart of a method for preparing a bulk acoustic wave filter provided by an embodiment of the present invention;

[0041] Figure 10 A schematic structural diagram of a process for preparing a bulk acoustic wave filter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0043] Figure 1 A schematic top view of a bulk acoustic wave filter provided by an embodiment of the present invention is shown. Figure 2 for Figure 1 Schematic diagram of the cross-section structure along the section line BB', refer to Figure 1 and Figure 2 As shown, the BAW filter 100 includes at least one BAW resonator 10 and at least three release holes 20 symmetrically arranged around the BAW resonator 10; the BAW resonator 10 includes a substrate 01 and a piezoelectric structure 02: the substrate 01 includes a cavity 010; the piezoelectric structure 02 is located on the side of the cavity 010 away from the substrate 01; wherein the release hole 20 is connected to the cavity 010.

[0044] The symmetrical arrangement can be symmetrical about the geometric center of the BAW resonator 10, or about the central transverse axis AA' of the BAW resonator 10, or about the central longitudinal axis BB' of the BAW resonator 10. The substrate 01 includes materials such as silicon or silicon nitride. The cavity 50 includes air or a dielectric material with high acoustic impedance. Figure 2 01 includes a groove, and a cavity 50 is formed in the groove. The cavity 50 can also be located on the surface of the substrate 01 and can be arranged according to actual needs. The apertures of the release holes 20 are the same.

[0045] In an optional embodiment, the piezoelectric structure 02 includes a first electrode layer 021, a piezoelectric layer 022, and a second electrode layer 023. The first electrode layer 021 is located on the side of the cavity 010 facing away from the substrate 01; the piezoelectric layer 022 is located on the side of the first electrode layer 021 facing away from the substrate 01; and the second electrode layer 023 is located on the side of the piezoelectric layer 022 facing away from the substrate 01. The release hole 20 penetrates the first electrode layer 021, the piezoelectric layer 022, and the second electrode layer 023.

[0046] Among them, the materials of the first electrode layer 021 and the second electrode layer 023 include molybdenum, ruthenium, gold, aluminum, magnesium, copper, tungsten, titanium, iridium, osmium, chromium, platinum or alloy materials of the above metals, and the piezoelectric layer 022 includes aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium nitride (LiNbO3), quartz (Quartz), potassium nitride (KNbO3) or lithium tantalate (LiTaO3) and other materials, and may also contain rare earth element doping materials with a certain atomic ratio of the above materials.

[0047] Specifically, when an electric signal is applied to the first electrode layer 021 or the second electrode layer 023, the piezoelectric layer 022 will produce longitudinal deformation due to the inverse piezoelectric effect, generating a bulk acoustic wave that propagates and vibrates longitudinally. The surface of the second electrode layer 023 facing away from the substrate 01 is in contact with the air, so that the bulk acoustic wave is reflected on the surface of the second electrode layer 023 facing away from the substrate 01. At the same time, a cavity 50 is provided on the surface of the first electrode layer 021 facing the substrate 01. The cavity 50 also reflects the bulk acoustic wave, so that energy does not leak to the substrate 01, thereby causing the bulk acoustic wave to reflect back and forth between the first electrode layer 021 and the second electrode layer 023, forming a standing wave in the piezoelectric layer 022 to generate resonance. The bulk acoustic wave is converted into an electrical signal by utilizing the piezoelectric effect of the piezoelectric layer 022, and then output by the other electrode to which the electrical signal is not applied. Therefore, in the direction Z perpendicular to the plane of the substrate 01, the area where the cavity 50, the first electrode layer 021, the piezoelectric layer 022 and the second electrode layer 023 overlap and the adjacent layers are in contact with each other is the active area A1, also known as the effective resonance area; the cavity 50 can reflect the bulk acoustic wave to the active area A1 and the passive area B1, and the bulk acoustic wave reflected to the active area A1 can generate resonance in the piezoelectric layer 022.

[0048] It should be noted that before fabricating the piezoelectric structure 02, to ensure the flatness of the piezoelectric structure 02, a flattening material is filled into the cavity 010 to level the surface of the cavity 010 facing away from the substrate 01 with the surface of the substrate 01. This provides a relatively flat fabrication surface for the subsequent fabrication of the piezoelectric structure 02 and improves the fabrication reliability of the piezoelectric structure 02. However, after the piezoelectric structure 02 is fabricated, the filling material in the cavity 010 needs to be removed to form the cavity 010. The present invention provides at least three release holes 20 connected to the cavity 010 and symmetrically arranged around the BAW resonator 10. The distance between each release hole 20 and the central area of ​​the BAW resonator 10 is comparable or equal. When liquid or gas for etching or removing the filling material is provided into the cavity 010 through the release holes 20, the distance or rate at which the etching liquid or etching gas reaches the central area of ​​the cavity 010 through the release holes 20 is comparable or equal. Therefore, the etching liquid or etching gas can be uniformly transmitted toward the center of the cavity 010 in at least three directions, thereby improving the uniformity and removal effect of the filling material in the central area of ​​the cavity 010, reducing the residual filling material in the central area of ​​the cavity 010, improving the preparation effect of the cavity 010, and improving the working performance of the BAW resonator and the BAW filter.

[0049] It is understandable that Figure 1 Only three release holes 20 symmetrically arranged around the BAW resonator 10 are shown. On the basis of including at least three release holes 20, the number of release holes 20 symmetrically arranged around the BAW resonator 10 can be set according to actual needs and is not specifically limited here.

[0050] The technical solution of the embodiment of the present invention is to provide at least three release holes symmetrically arranged around a BAW resonator, and the release holes are connected to the cavity, so that the release holes located around the same BAW resonator have a small or equal spacing to the central area of ​​the BAW resonator. When the etching liquid or etching gas enters the cavity through the release holes, the etching liquid or etching gas reaches the center of the cavity through the release holes at a small or uniform rate. The etching liquid or etching gas reaching the central area of ​​the cavity can move toward the center of the cavity from at least three symmetrically arranged directions, thereby improving the uniformity and cleanliness of removing the filling material inside the cavity, improving the preparation reliability of the cavity, and thereby improving the working performance of the BAW resonator and the BAW filter.

[0051] Optional, Figure 3 A schematic diagram of a top view of another bulk acoustic wave filter provided in an embodiment of the present invention is shown in FIG. Figure 3 As shown, the geometric center of the geometric figure formed by connecting the release holes 20 arranged around the same BAW resonator 10 is the resonator geometric center O′ of the BAW resonator 10 .

[0052] Specifically, the release holes 20 disposed around the same BAW resonator 10 include release hole 21, release hole 22, and release hole 23. Release hole 21 is sequentially connected to release hole 22, release hole 22 to release hole 23, and release hole 23 to release hole 21 to form a triangular geometric figure, with the center of gravity of the triangle being the geometric center. The center of gravity of the BAW resonator 10 is the resonator geometric center O'. By setting the geometric center of the geometric figure to be the resonator geometric center O' of the BAW resonator 10, the distances between each release hole 20 and the resonator geometric center O' are equal, ensuring that the etching liquid or etching gas is transmitted to the resonator geometric center O' at the same rate through each release hole 20, thereby improving the removal rate of the filling material within the cavity 010 and reducing the residual filling material within the cavity 010.

[0053] In other optional embodiments, Figure 4 A schematic diagram of a top view of another bulk acoustic wave filter provided in an embodiment of the present invention is shown in FIG. Figure 4 As shown, there are four release holes symmetrically arranged around BAW filter 10, namely release hole 21, release hole 22, release hole 23, and release hole 24. By sequentially connecting release hole 21 with release hole 22, 22 with release hole 23, 23 with release hole 24, and 24 with release hole 21, the geometric shape formed is a quadrilateral, and the center of gravity of the quadrilateral is the geometric center O' of the resonator. The number of release holes symmetrically arranged around BAW filter 10 can also be other, and the geometric shape formed by connecting the release holes 20 can be a pentagon, a hexagon, or the like, which is not specifically limited here.

[0054] Optional, Figure 5 A schematic diagram of a top view of another bulk acoustic wave filter provided in an embodiment of the present invention is shown in FIG. Figure 5 As shown, the BAW resonator 10 includes at least two series resonators 11 and at least two parallel resonators 12; some of the series resonators 11 are electrically connected to the parallel resonators 12, the series resonators 11 are electrically connected to the series resonators 11, and the parallel resonators 12 are electrically connected to the parallel resonators 12; the series resonators 11 are arranged along a first direction X, and the parallel resonators 12 are arranged along a second direction Y, and the first direction X intersects with the second direction Y.

[0055] Specifically, the series resonator 111 and the series resonator 112 are electrically connected to each other via the first electrode layer 021 in the piezoelectric structure 02, the series resonator 112 and the parallel resonator 121 are electrically connected via the first electrode layer 021 in the piezoelectric structure 02, and the parallel resonator 121 and the parallel resonator 122 are electrically connected via the first electrode layer 021 in the piezoelectric structure 02. In this way, by providing the series resonator 11 and the parallel resonator 12, the propagation path of the bulk acoustic wave can be extended, the length of the resonant cavity is increased, and the fundamental frequency and harmonic frequency distribution of the bulk acoustic wave filter 100 can be changed, thereby improving the frequency selectivity of the bulk acoustic wave filter and the passband flatness, enabling the bulk acoustic wave filter 100 to achieve more complex filtering characteristics and optimize insertion loss.

[0056] Optional, Figure 6 A schematic diagram of a top view of a bulk acoustic wave filter provided by an embodiment of the present invention is shown in FIG. Figure 6 As shown, there are some release holes 20 that are in communication with the cavities 010 of two adjacent series resonators 11 ; and / or there are some release holes 20 that are in communication with the cavities 010 of two adjacent parallel resonators 12 .

[0057] Specifically, by providing some release holes 20 in communication with the cavities 010 of two adjacent series resonators 11, when the etching liquid or etching gas is introduced into the release holes 20, the filling material in the cavities 010 of the two adjacent series resonators 11 can be removed simultaneously, so that the two adjacent series resonators 11 share the same release hole 20, reducing the number of release holes 20 provided and improving the utilization rate of the release holes 20. Correspondingly, by providing some release holes 20 in communication with the cavities 010 of two adjacent parallel resonators 12, when the etching liquid or etching gas is introduced into the release holes 20, the filling material in the cavities 010 of the two adjacent parallel resonators 12 can be removed simultaneously, so that the two adjacent parallel resonators 12 share the same release hole 20, reducing the number of release holes 20 provided and improving the utilization rate of the release holes 20. For example, Figure 6The release hole 25 is in communication with the cavities 010 of the adjacent series resonators 111 and 112, and the release hole 25 is in communication with the cavities 010 of the adjacent parallel resonators 121 and 122; the sharing of the release hole 20 in the bulk acoustic wave filter 100 can also be other, which can be set according to actual needs, and is not specifically limited here.

[0058] Optionally, Figure 7 Another top view structural schematic diagram of a bulk acoustic wave filter provided by an embodiment of the present application is shown in FIG. 6. Figure 7 As shown, there are some release holes 20 in communication with the cavities 010 of some series resonators 11 and the cavities 010 of some parallel resonators 12.

[0059] Specifically, by setting some release holes 20 in communication with the cavities 010 of some series resonators 11 and the cavities 010 of some parallel resonators 12, when etching liquid or etching gas is introduced into the release hole 20, the filling material in the cavities 010 of the two resonators 10 in communication with the release hole 20 can be removed at the same time, so that the series resonators 11 and the parallel resonators 12 share the same release hole 20, the number of release holes 20 is reduced, and the utilization rate of the release hole 20 is improved.

[0060] It can be understood that some release holes 20 are in communication with the cavities 010 of some series resonators 11 and the cavities 010 of some parallel resonators 12, and the series resonators 11 and the parallel resonators 12 in communication can be two resonators 10 adjacent and electrically connected, or two resonators 10 close to each other, for example, Figure 7 The release hole 27 is in communication with the cavities of the series resonator 111 and the parallel resonator 121, and the release hole 28 is in communication with the cavities of the series resonator 112 and the parallel resonator 121, which can also be other, which can be set according to actual needs.

[0061] Optionally, referring to Figure 1 The aperture of the release hole 20 is r, where 0.3 μm≤r≤3 μm.

[0062] Specifically, if the aperture r of the release hole 20 is less than 0.3 μm, the transmission amount of the etching liquid or etching gas through the release hole 20 is small, and the transmission rate is slow. If the aperture r of the release hole 20 is greater than 3 μm, the rate of the etching liquid entering the release hole 20 increases, but at the same time, the stability of the film layer in the piezoelectric structure 02 around the release hole 20 is affected. Therefore, by setting the aperture r of the release hole 20 in the numerical range of 0.3 μm to 3 μm, the transmission rate of the etching liquid or etching gas entering the release hole 20 can be improved, so as to improve the etching efficiency of the filling material in the cavity 010, and at the same time, the stability of the piezoelectric structure 02 around the release hole 20 can be improved, and the structural stability of the bulk acoustic wave filter 100 can be improved.

[0063] In an optional embodiment, Figure 8 A top view structural schematic diagram of another bulk acoustic wave filter provided by the embodiment of the present application is shown in FIG. 6. Figure 8 As shown in the figure, the interval L1 between the adjacent two release holes 20 around the same bulk acoustic wave resonator 10 is 10 μm≤L1≤100 μm.

[0064] Specifically, if the interval L1 between the adjacent two release holes 20 is less than 10 μm, the interval between the release holes 20 is small, and in order to ensure that the filling material in the cavity 010 of the bulk acoustic wave resonator 10 is completely removed, a large number of release holes 20 need to be set. If the interval L1 between the adjacent two release holes 20 is greater than 100 μm, the release holes 20 are dispersed in the area far away from the bulk acoustic wave resonator 10 around the bulk acoustic wave resonator 10, so that the distance of the etching liquid or etching gas through the release hole 20 to reach the cavity of the bulk acoustic wave resonator 10 is large, resulting in low removal efficiency of the filling material in the cavity. Therefore, by setting the interval L1 between the adjacent two release holes 20 around the same bulk acoustic wave resonator 10 in the numerical range of 10 μm to 100 μm, the interval between the release hole 20 and the cavity of the bulk acoustic wave resonator 10 is shortened, the transmission efficiency of the etching liquid or etching gas through the release hole 20 to the cavity of the bulk acoustic wave resonator 10 is improved, and then the removal efficiency of the filling material in the cavity is improved.

[0065] Based on the same inventive concept, the embodiment of the present application also provides a preparation method of a bulk acoustic wave filter, Figure 9 A flow chart of a preparation method of a bulk acoustic wave filter provided by the embodiment of the present application is shown in FIG. 7. Figure 10 A process structural schematic diagram of a bulk acoustic wave filter provided by the embodiment of the present application is shown in FIG. 8, which refers to Figure 9 and Figure 10 The preparation method of the bulk acoustic wave filter comprises the following steps:

[0066] S11, providing a substrate.

[0067] The substrate 01 includes a cavity 010 .

[0068] Specifically, a substrate without a cavity 010 may be provided, and etching may be performed on one surface of the substrate using an etching device, etc., to form a substrate 01 including the cavity 010. The size of the cavity 010 may be set according to actual needs, and the shape of the cavity 010 may be circular or elliptical, etc. In an exemplary embodiment, the diameter of the cavity 010 ranges from 20 μm to 100 μm.

[0069] S12, filling the cavity with a sacrificial layer.

[0070] Sacrificial layer 010 comprises a material such as silicon dioxide or silicon nitride and can be configured as needed. A plasma-enhanced chemical vapor deposition process can be used to deposit a material such as silicon dioxide into cavity 010 to fill cavity 010 and form sacrificial layer 011. This maintains a flat surface on the side of cavity 010 facing away from substrate 01, thereby improving the flatness of subsequent film layers.

[0071] S13. Prepare a piezoelectric structure on the side of the sacrificial layer facing away from the substrate.

[0072] Specifically, the piezoelectric structure 02 may include a first electrode layer 021, a piezoelectric layer 022, and a second electrode layer 023. The first electrode layer 021, the piezoelectric layer 022, and the second electrode layer 023 may be sequentially formed on the side of the sacrificial layer 011 facing away from the substrate 01 using a deposition process or other similar process to form the piezoelectric structure 02.

[0073] In an optional embodiment, a piezoelectric structure 02 is prepared on the side of the sacrificial layer 011 facing away from the substrate 01, including preparing a first electrode layer 021 on the side of the sacrificial layer 011 facing away from the substrate 01; preparing a piezoelectric layer 022 on the side of the first electrode layer 021 facing away from the substrate; and preparing a second electrode layer 023 on the side of the piezoelectric layer 022 facing away from the substrate 01.

[0074] Specifically, a material such as molybdenum or tungsten is sputter-deposited on the side of the sacrificial layer 011 facing away from the substrate 01 to form a first electrode layer 021. The thickness of the first electrode layer 021 ranges from 100 nm to 300 nm, and the shape of the first electrode layer 021 can be circular or polygonal. A material such as aluminum oxide or zinc oxide is deposited on the side of the first electrode layer 021 facing away from the substrate 01 using processes such as magnetron sensing or atomic layer deposition to form a piezoelectric layer 022. The thickness of the piezoelectric layer 022 ranges from 1 μm to 3 μm. A patterned second electrode layer 023 is formed on the side of the piezoelectric layer 022 facing away from the substrate 01 using deposition, beam etching, and ion beam etching.

[0075] S14. Drilling the piezoelectric structure to form a release hole.

[0076] There are at least three release holes symmetrically arranged around the same cavity, and the release holes are connected to the cavity.

[0077] Specifically, ion etching or other processes can be used to drill holes in the piezoelectric structure 02 located around the bulk acoustic wave resonator to form release holes 20 that penetrate the piezoelectric structure 02, and the release holes 20 are connected to the cavity 010 or the sacrificial layer 011, and the connection method can be directly overlapping with the cavity 010.

[0078] S15. Introduce an etching solution into the release hole to remove the sacrificial layer in the cavity to form a bulk acoustic wave filter.

[0079] The etching solution includes buffered oxide etchant (BOE), hydrofluoric acid, etc., and etching gas such as XeF2 gas can also be provided to the release hole 20 to remove the sacrificial layer 011 located in the cavity 010. It can be set according to actual needs.

[0080] Specifically, the time for the etchant to be introduced into the release holes 20 can be adjusted based on the thickness and overall size of the sacrificial layer 011 and the number of release holes 20 provided, to avoid etching the substrate 01 due to an excessively long etching time, thereby ensuring the stability of the substrate 01. In an optional embodiment, the etchant is hydrofluoric acid, the etching time ranges from 10 minutes to 60 minutes, and the height of the cavity 010 ranges from 0.5 μm to 2 μm.

[0081] The technical solution provided by the present invention is to provide at least three release holes symmetrically arranged around the same cavity, and the release holes are connected to the cavity, so that when an etching liquid is introduced into the release holes to remove the sacrificial layer located in the cavity, the etching liquid has a small or uniform rate of reaching the center of the cavity through each release hole. The etching liquid or etching gas reaching the central area of ​​the cavity can move toward the center of the cavity from at least three symmetrically arranged directions, thereby improving the uniformity and cleanliness of removing the filling material inside the cavity, improving the preparation reliability of the cavity, and thereby improving the working performance of the bulk acoustic wave resonator and the bulk acoustic wave filter.

[0082] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations, and substitutions are possible for those skilled in the art without departing from the scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the scope of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A bulk acoustic wave filter, characterized in that: include: at least one bulk acoustic wave resonator and at least three release holes symmetrically arranged around the bulk acoustic wave resonator; The bulk acoustic wave resonator comprises: a substrate including a cavity; a piezoelectric structure, located on a side of the cavity facing away from the substrate; Wherein, the release hole is communicated with the cavity.

2. The bulk acoustic wave filter according to claim 1, wherein The geometric center of the geometric figure formed by connecting the release holes symmetrically arranged around the same BAW resonator is the resonator geometric center of the BAW resonator.

3. The bulk acoustic wave filter according to claim 1, wherein The bulk acoustic wave resonator includes at least two series resonators and at least two parallel resonators; Some of the series resonators are electrically connected to the parallel resonators, the series resonators are electrically connected to the series resonators, and the parallel resonators are electrically connected to the parallel resonators; the series resonators are arranged along a first direction, and the parallel resonators are arranged along a second direction; the first direction intersects with the second direction.

4. The bulk acoustic wave filter according to claim 3, wherein Some of the release holes are connected to the cavities of two adjacent series resonators; and / or some of the release holes are connected to the cavities of two adjacent parallel resonators.

5. The bulk acoustic wave filter according to claim 3, wherein Some of the release holes are connected to some of the cavities of the series resonators and some of the cavities of the parallel resonators.

6. The bulk acoustic wave filter according to claim 1, wherein The piezoelectric structure includes: a first electrode layer, a piezoelectric layer and a second electrode layer; The first electrode layer is located on the side of the cavity facing away from the substrate; the piezoelectric layer is located on the side of the first electrode layer facing away from the substrate; the second electrode layer is located on the side of the piezoelectric layer facing away from the substrate; the release hole passes through the first electrode layer, the piezoelectric layer and the second electrode layer.

7. The bulk acoustic wave filter according to claim 1, wherein The aperture of the release hole is r; Among them, 0.3μm≤r≤3μm.

8. The bulk acoustic wave filter according to claim 1, wherein Among the release holes surrounding the same bulk acoustic wave resonator, the distance between two adjacent release holes is L1; Among them, 10μm≤L1≤100μm.

9. A method for preparing a bulk acoustic wave filter, characterized in that: include: providing a substrate; The substrate includes a cavity; filling the cavity with a sacrificial layer; preparing a piezoelectric structure on a side of the sacrificial layer facing away from the substrate; Drilling the piezoelectric structure to form release holes; at least three release holes are symmetrically arranged around the same cavity, and the release holes are connected to the cavity; An etching solution is introduced into the release hole to remove the sacrificial layer in the cavity to form the bulk acoustic wave filter.

10. The preparation method according to claim 9, characterized in that A piezoelectric structure is prepared on a side of the sacrificial layer facing away from the substrate, comprising: forming a first electrode layer on a side of the sacrificial layer facing away from the substrate; preparing a piezoelectric layer on a side of the first electrode layer facing away from the substrate; A second electrode layer is formed on a side of the piezoelectric layer facing away from the substrate.

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