A method for preparing a resonant cavity of a bulk acoustic wave filter

Abstract

The present application provides a method for preparing a resonant cavity of a bulk acoustic wave filter, the preparation method comprising: forming a piezoelectric layer group; providing a substrate; bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein a through hole is preset on the polymer film, and after bonding is completed, a resonant cavity formed by the polymer film isolation layer, the piezoelectric layer group and the substrate is formed at the through hole. The present application scheme abandons the traditional scheme of first depositing USG / PSG and then digging holes to deposit POLY / SIN in the prior art, and instead adopts a method of bonding a polymer film isolation layer to form a resonant cavity, which can effectively improve product quality and yield, and can reduce production costs.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor devices, and in particular to a method for preparing a resonant cavity of a bulk acoustic wave filter. Background Art

[0002] This section is intended to provide a background or context for the embodiments of the present application. The description herein is not admitted to be prior art by inclusion in this section.

[0003] BAW (Bulk Acoustic Wave) filter is a filter based on the piezoelectric effect, which is usually used in wireless communication, radio frequency and microwave fields. Its working principle is to use the piezoelectric properties of piezoelectric crystals to convert electrical signals into mechanical vibration signals, and then convert the mechanical vibration signals into electrical signals to achieve filtering of signals of different frequencies.

[0004] The resonant cavity is an important component of the BAW filter. Figure 1 The schematic cross-sectional view of the resonant cavity of a BAW resonator provided by the prior art is shown. The conventional method for preparing a BAW resonator in the prior art is: first, a silicate USG (Undoped Silicate Glass) or PSG (Phosphosilicate Glass) is deposited on a substrate, and then a cavity is formed by etching on the USG / PSG. In order to improve the isolation effect, after the cavity is formed, a layer of POLY (polycrystalline silicon) or SIN (silicon nitride) needs to be deposited in the cavity. This conventional method has at least the following problems:

[0005] 1) The temperature is too high during POLY / SIN deposition, which increases the stress of the piezoelectric layer, causing the film layer to deform after the cavity is released, affecting the quality of the finished product;

[0006] 2) USG / PSG has high stress, which can easily cause the substrate to warp up significantly and break easily in the subsequent process, thus reducing the product yield;

[0007] 3) The formation of USG / PSG requires multiple deposition and polishing processes, resulting in high production costs;

[0008] 4) There is a cavity filling layer and a corresponding release process is required, resulting in higher production costs.

[0009] In view of the above problems, it is necessary to provide a method for preparing a bulk acoustic wave filter resonant cavity that can improve product quality and yield and reduce production costs. Summary of the invention

[0010] Various aspects of the present application provide a method for preparing a bulk acoustic wave filter resonant cavity, so as to improve product quality and yield and reduce production costs.

[0011] In one aspect of the present application, a method for preparing a resonant cavity of a bulk acoustic wave filter is provided, comprising:

[0012] forming a piezoelectric layer group;

[0013] providing a substrate;

[0014] A polymer film is bonded between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein the polymer film is preset with a through hole, and after bonding is completed, a resonant cavity surrounded by the polymer film isolation layer, the piezoelectric layer group and the substrate is formed at the through hole.

[0015] Optionally, bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer includes:

[0016] Bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer;

[0017] The substrate is bonded based on the polymer film isolation layer being away from the piezoelectric layer group.

[0018] Optionally, forming a piezoelectric layer group includes:

[0019] forming a piezoelectric layer group on a substrate;

[0020] After bonding the substrate based on the polymer film isolation layer away from the side of the piezoelectric layer group, the method further includes:

[0021] The substrate is removed.

[0022] Optionally, the piezoelectric layer group includes: a first electrode layer, a piezoelectric layer and a second electrode layer;

[0023] The step of forming a piezoelectric layer group on a substrate comprises:

[0024] forming a first electrode layer, a piezoelectric layer and a second electrode layer covering the entire surface on the substrate in sequence;

[0025] The second electrode layer is etched to form a second electrode layer that partially covers the piezoelectric layer.

[0026] Optionally, the step of bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer includes:

[0027] A polymer film is bonded to the second electrode layer to form a polymer film isolation layer, wherein the polymer film is bonded to the piezoelectric layer in a partial area of ​​the piezoelectric layer not covered by the second electrode layer.

[0028] Optionally, after removing the substrate, the method further comprises:

[0029] The first electrode layer is etched to form a first electrode layer that partially covers the piezoelectric layer, a first projection of the first electrode layer on the piezoelectric layer and a second projection of the second electrode layer on the piezoelectric layer partially overlap, and a working area of ​​the resonant cavity is formed in the overlapping area.

[0030] Optionally, before bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, the method further includes:

[0031] Provide polymer films;

[0032] A plurality of through holes are formed in the polymer film.

[0033] Optionally, after forming the through hole on the polymer film, the line width of the remaining part is greater than 10 micrometers, and / or the area proportion of the remaining part is greater than 10%.

[0034] Optionally, bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer includes:

[0035] A polymer film is bonded between the piezoelectric layer group and the substrate by melt bonding to form a polymer film isolation layer. The glass transition temperature of the polymer film is greater than 250 degrees Celsius, and the stress after bonding is less than 100 MPa.

[0036] Optionally, the polymer film includes a polyimide film.

[0037] The solution provided in the embodiment of the present application is to form a piezoelectric layer group and provide a substrate, and then bond a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein a through hole is preset on the polymer film, so that a resonant cavity formed by the polymer film isolation layer, the piezoelectric layer group and the substrate can be formed at the through hole after the bonding is completed. The solution abandons the traditional solution of first depositing USG / PSG and then digging a hole to deposit POLY / SIN in the prior art, and instead adopts the method of bonding polymer films to form a resonant cavity. Since the bonding temperature is much lower than the deposition temperature in the traditional solution, the bonding process has little effect on the piezoelectric layer and will not cause the problem of increased stress in the piezoelectric layer, thereby effectively improving the product quality. Since the polymer film will not bring additional stress during bonding and will not cause the substrate to warp significantly, the product yield can be effectively improved compared with the traditional solution. In addition, the solution of the present application does not require multiple complicated deposition, polishing, etching and other process steps, which can effectively reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0039] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0040] Figure 1 A schematic cross-sectional view of a resonant cavity of a bulk acoustic wave resonator provided in the prior art;

[0041] Figure 2 A flow chart of a method for preparing a resonant cavity of a bulk acoustic wave resonator provided in one embodiment of the present application;

[0042] Figure 3 A cross-sectional diagram of a process for forming a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application Figure 1 ;

[0043] Figure 4 A cross-sectional diagram of a process for forming a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application Figure 2 ;

[0044] Figure 5 A cross-sectional diagram of a process for forming a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application Figure 3 ;

[0045] Figure 6 A cross-sectional diagram of a process for forming a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application Figure 4 ;

[0046] Figure 7 A cross-sectional diagram of a process for forming a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application Figure 5 ;

[0047] Figure 8 A schematic diagram of a working area of ​​a bulk acoustic wave resonator provided in one embodiment of the present application;

[0048] The same or similar reference numerals in the drawings represent the same or similar components. DETAILED DESCRIPTION

[0049] 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, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] Unless otherwise defined, the technical terms or scientific terms used in this application should be understood by people with ordinary skills in the field to which this application belongs. "First", "second" and similar words used in this application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and other similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and other similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0051] In the embodiments of the present application, the terms "upper", "lower", "inner", "middle", "outer", "front", "back" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings. These terms are mainly intended to better describe the embodiments of the present application, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition to the orientations shown in the accompanying drawings, the spatially relative terms are intended to cover different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative terms used herein may also be interpreted accordingly. Moreover, in addition to being used to indicate an orientation or positional relationship, some of the above terms may also be used to indicate other meanings, such as the term "upper" may also be used to indicate a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] Considering that the main reason why the traditional solution causes excessive stress and substrate warping is that materials such as POLY, SIN, USG, PSG need to be deposited by high-temperature deposition methods such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), among which the deposition temperature of PVD generally needs to be greater than 500 degrees Celsius, and the deposition temperature of CVD generally needs to be greater than 700 degrees Celsius. Therefore, the present application considers using a lower temperature process to prepare the resonant cavity, and bonding is a more ideal method. On this basis, it is also necessary to select suitable materials to make the isolation layer, and comprehensively select the polymer film according to the bonding temperature, stress performance, insulation performance, dielectric loss, stability, cost and other characteristics of the material to achieve the purpose of the embodiment of the present application. In addition, for the problem of how to form a resonant cavity on a polymer film, it is proposed to pre-open a through hole, and then bond the piezoelectric layer group and the substrate on both sides of the polymer film to enclose the resonant cavity. For details, please refer to the following embodiment description for understanding.

[0053] Please refer to Figure 2 , which is a flow chart of a method for preparing a bulk acoustic wave resonator resonant cavity provided in an embodiment of the present application, such as Figure 2 As shown, a method for preparing a resonant cavity of a bulk acoustic wave resonator provided in an embodiment of the present application may include the following steps:

[0054] Step S101: forming a piezoelectric layer group,

[0055] Among them, the piezoelectric layer group is the core structure of the bulk acoustic wave filter, which can use the piezoelectric characteristics to convert electrical signals into mechanical vibration signals, and then convert the mechanical vibration signals into electrical signals to achieve filtering of signals of different frequencies.

[0056] It should be noted that the above-mentioned piezoelectric layer group can be formed on a substrate, or on an intermediate component after other structures of the BAW filter are formed. The embodiments of the present application are not limited thereto, and those skilled in the art can flexibly adjust and change the implementation according to the overall process flow.

[0057] Step S102: providing a substrate,

[0058] The material of the substrate preferably includes silicon, silicon on insulator (SOI), glass, silicon carbide (SiC) or gallium arsenide (GaAs), etc., which is not limited in the embodiments of the present application, and those skilled in the art can flexibly select or change the implementation according to actual needs.

[0059] Step S103: bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein the polymer film is preset with a through hole, and after bonding is completed, a resonant cavity surrounded by the polymer film isolation layer, the piezoelectric layer group and the substrate is formed at the through hole.

[0060] The solution provided in the embodiment of the present application is to form a piezoelectric layer group and provide a substrate, and then bond a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein a through hole is preset on the polymer film, so that a resonant cavity formed by the polymer film isolation layer, the piezoelectric layer group and the substrate can be formed at the through hole after the bonding is completed. The solution abandons the traditional solution of first depositing USG / PSG and then digging a hole to deposit POLY / SIN in the prior art, and instead adopts the method of bonding polymer films to form a resonant cavity. Since the bonding temperature is much lower than the deposition temperature in the traditional solution, the bonding process has little effect on the piezoelectric layer and will not cause the problem of increased stress in the piezoelectric layer, thereby effectively improving the product quality. Since the polymer film will not bring additional stress during bonding and will not cause the substrate to warp significantly, the product yield can be effectively improved compared with the traditional solution. In addition, the solution of the present application does not require multiple complicated deposition, polishing, etching and other process steps, which can effectively reduce the production cost.

[0061] Among them, when implementing the above-mentioned step S103, it can be implemented through a single bonding process or a secondary bonding process, wherein the single bonding process refers to aligning the piezoelectric layer group, the polymer film and the substrate and then bonding them once to bond the three together, and the secondary bonding process refers to first bonding the piezoelectric layer group to the polymer film and then bonding it to the substrate, or first bonding the substrate to the polymer film and then bonding it to the piezoelectric layer group, so as to bond the three together. Technical personnel in this field can flexibly choose to implement it according to equipment conditions and bonding accuracy requirements. In the following exemplary description, the secondary bonding process of first bonding the piezoelectric layer group to the polymer film and then bonding it to the substrate is mainly described, but the description of materials, parameters, and structures is also applicable to the other two processes mentioned above, and can also be used to describe the other two processes mentioned above. For the sake of simplicity, some contents will not be repeated. Please refer to and learn from each implementation method.

[0062] In some modified implementations of the embodiments of the present application, bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer includes:

[0063] Bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer;

[0064] The substrate is bonded based on the polymer film isolation layer being away from the piezoelectric layer group.

[0065] Since the through holes on the polymer film need to be aligned with the working area in the piezoelectric layer group in order to realize the function of the resonant cavity, in order to improve the process accuracy, it is preferred to bond the piezoelectric layer group to the polymer film first. Since the substrate does not need to be precisely aligned, the bonding with the polymer film can be completed in the second bonding. Through this implementation, the alignment of the through holes and the working area in the piezoelectric layer group can be effectively achieved, which helps to improve the process accuracy and thus improve product quality and yield.

[0066] Based on the above implementation, in some modified implementations, the step S101 of forming a piezoelectric layer group may include: forming a piezoelectric layer group on a substrate;

[0067] Correspondingly, after bonding the substrate based on the polymer film isolation layer away from the piezoelectric layer group, the method may further include: removing the base.

[0068] The substrate plays a role in assisting attachment, fixation and shaping, and can be removed after the resonant cavity is formed.

[0069] In some modified implementations, the piezoelectric layer group may include: a first electrode layer, a piezoelectric layer, and a second electrode layer;

[0070] The forming of a piezoelectric layer group on the substrate may include:

[0071] forming a first electrode layer, a piezoelectric layer and a second electrode layer covering the entire surface on the substrate in sequence;

[0072] The second electrode layer is etched to form a second electrode layer that partially covers the piezoelectric layer.

[0073] Among them, the material of the first electrode layer and the second electrode layer is preferably Al, Cu, Mo, Au or Pt; the embodiment of the present application preferably adopts the PVD method to prepare the first electrode layer and the second electrode layer. In the embodiment of the present application, the material of the piezoelectric layer preferably includes AlN, scandium-doped aluminum nitride (AlxSc1-xN), lithium niobate (LiNbO3), lithium tantalate (LiTaO3) or quartz, and the material of the piezoelectric layer can be polycrystalline or single crystal; the embodiment of the present application preferably adopts PVD or metal organic chemical vapor deposition (MOCVD) method to prepare the piezoelectric layer. The method used for etching the second electrode layer preferably includes wet etching or dry etching, which is not limited in the embodiment of the present application.

[0074] The effect of forming a fully covered first electrode layer, a piezoelectric layer and a second electrode layer on the substrate in sequence can be referred to Figure 3 For understanding, the effect of etching the second electrode layer to form a second electrode layer that partially covers the piezoelectric layer can be referred to Figure 4 To understand.

[0075] The above-mentioned piezoelectric layer group has the advantages of simple structure and easy production. The cavity structure for bulk acoustic wave filter in the present application is prepared based on the piezoelectric layer group, which has the advantages of high efficiency, high yield rate and low cost, and is particularly suitable for the production of D-BAW filters.

[0076] Based on the above-mentioned implementation manner, in some modified implementation manners, the step of bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer may include: bonding a polymer film based on the second electrode layer to form a polymer film isolation layer, wherein the polymer film is bonded to the piezoelectric layer in a partial area of ​​the piezoelectric layer not covered by the second electrode layer.

[0077] The effect of bonding the polymer film to form a polymer film isolation layer based on the piezoelectric layer group can be referred to Figure 5 For understanding, the effect of bonding the substrate on the side of the polymer film isolation layer away from the piezoelectric layer group in the subsequent steps can be referred to Figure 6 To understand, such as Figure 6As shown, after the substrate is bonded to the polymer film isolation layer, a resonant cavity surrounded by the polymer film isolation layer, the second electrode layer, the piezoelectric layer and the substrate can be formed at the through hole.

[0078] In some modified implementations, after removing the substrate, the method further comprises:

[0079] The first electrode layer is etched to form a first electrode layer that partially covers the piezoelectric layer, a first projection of the first electrode layer on the piezoelectric layer and a second projection of the second electrode layer on the piezoelectric layer partially overlap, and a working area of ​​the resonant cavity is formed in the overlapping area.

[0080] The method for etching the first electrode layer preferably includes wet etching or dry etching, which is not limited in the present embodiment. The effect of etching the first electrode layer to form a first electrode layer that partially covers the piezoelectric layer can be referred to. Figure 7 To understand.

[0081] Based on this embodiment, the first electrode layer and the second electrode layer both partially cover the piezoelectric layer, and the first projection of the first electrode layer on the piezoelectric layer and the second projection of the second electrode layer on the piezoelectric layer are misaligned but partially overlapped, and the area corresponding to the overlapping portion is the working area of ​​the bulk acoustic wave filter resonant cavity, and the working area can refer to Figure 8 To understand.

[0082] Regarding the problem of how to form a resonant cavity on a polymer film, the embodiment of the present application proposes a method of pre-opening a through hole, and then respectively bonding a piezoelectric layer group and a substrate on both sides of the polymer film to enclose and form a resonant cavity. Accordingly, in some modified implementations, before bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer, the method further includes:

[0083] Provide polymer films;

[0084] A plurality of through holes are formed in the polymer film.

[0085] Among them, forming a plurality of through holes on the polymer film can be formed by using processes such as dry etching, wet etching, laser engraving, etc., which is not limited in the embodiments of the present application.

[0086] In addition, in some modified implementations, through holes can also be formed in the process of manufacturing the polymer film. For example, when the polymer film is manufactured by the casting method, a plurality of micro-protrusions are provided on the substrate or base tape used for casting, and a polymer film with through holes can be formed after curing. Those skilled in the art can flexibly change the implementation based on the exemplary description of the embodiments of the present application, which should all be within the scope of protection of the present application.

[0087] Based on the aforementioned embodiment, in some modified embodiments, after forming the through hole in the polymer film, the line width of the remaining part is greater than 10 microns, and / or the area proportion of the remaining part is greater than 10%.

[0088] Since the remaining part after the through hole is formed in the polymer film is used to constitute the cavity wall of the resonant cavity, the thickness of the cavity wall of the resonant cavity corresponds to the line width or area ratio of the above-mentioned remaining part on the film plane. If the line width is too narrow or the area ratio is too small, it means that the cavity wall of the resonant cavity is too small, which will affect the isolation effect. Therefore, in the embodiment of the present application, it is necessary to ensure that the line width of the remaining part after the through hole is formed on the polymer film is greater than 10 microns, and / or the area ratio of the remaining part is greater than 10%, so as to ensure that the cavity wall of the resonant cavity formed subsequently has sufficient isolation capability.

[0089] In addition, it should be noted that the polymer film isolation layer in the embodiment of the present application is pre-formed with the above-mentioned through hole before bonding. The larger the through hole, the smaller the line width and area of ​​the above-mentioned remaining part, and deformation or even breakage and other abnormalities are prone to occur during the bonding process, affecting product quality and yield. Therefore, through this embodiment, it can also be ensured that the through hole will not be too large, which can reduce the probability of deformation or breakage of the polymer film, thereby improving product quality and yield.

[0090] In some modified implementations, bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer includes:

[0091] A polymer film is bonded between the piezoelectric layer group and the substrate by melt bonding to form a polymer film isolation layer. The glass transition temperature of the polymer film is greater than 250 degrees Celsius, and the stress after bonding is less than 100 MPa.

[0092] Among them, the glass transition temperature is an inherent property of polymer films. Different polymer films have different glass transition temperatures. For example, although they are all polyimide (PI) films, PI films of different types and produced by different manufacturers will also have different glass transition temperatures, for example, 280°C, 385°C and 500°C, etc. Technical personnel in this field can flexibly choose according to actual needs.

[0093] In practical applications, the temperature of melt bonding needs to be greater than the glass transition temperature of the polymer film isolation layer, and in order to achieve the purpose of low-temperature bonding, the temperature of melt bonding generally needs to be lower than 400 degrees Celsius, preferably lower than 300 degrees Celsius. Too low a temperature will lead to poor curing after bonding, and too high a temperature will lead to excessive stress after bonding. Based on the above explanation of the melt bonding temperature, the embodiment of the present application preferably uses a PI film with a glass transition temperature of 280 degrees Celsius to realize the polymer film isolation layer. It should be noted that the above critical parameters such as 250 degrees Celsius, 400 degrees Celsius, and 300 degrees Celsius are the preferred parameters provided by the embodiments of the present application, which can obtain relatively ideal effects. Those skilled in the art can further optimize on this basis in combination with actual needs to obtain better results.

[0094] In addition, different polymer films will also produce different stress performances after bonding. Those skilled in the art can flexibly choose to use them according to the stress performance of various polymer films, and the embodiments of the present application are not limited thereto.

[0095] Since one of the purposes of the present application is to solve the problem of substrate warping and increased stress, compared with the traditional solution using PVD, CVD and other deposition methods for high temperature (above 500 degrees Celsius) deposition, the low temperature (less than 400 degrees Celsius) bonding process can effectively reduce the problem of substrate warping and increased stress. At the same time, considering the isolation effect of the isolation layer around the resonant cavity and the ease of bonding, the embodiment of the present application selects a polymer film to make the isolation layer. The polymer film is a film made of organic high molecular polymers. Although there are many types of polymer films, they all have good electrical insulation. Those skilled in the art can select a suitable polymer film according to actual needs, combined with the bonding temperature, stress performance, insulation performance, dielectric loss, stability, cost and other characteristics of various polymer films to achieve the purpose of the embodiment of the present application. For example, polyimide PI film, polyphenylene sulfide PPS film, polyetheretherketone PEEK film, etc. can be used in the embodiment of the present application to achieve the purpose of the present application.

[0096] In some preferred embodiments, the present application has undergone a large number of experiments and comprehensively considered the above-mentioned various factors to select a polyimide film to implement the polymer film isolation layer. Accordingly, based on any of the aforementioned embodiments, in some modified embodiments, the polymer film includes a polyimide film.

[0097] Polyimide (PI) is a high-performance polymer of imide monomers, which has the advantages of excellent mechanical strength, bending performance, continuous stability, heat resistance, insulation properties, low cost, etc. The use of polyimide film to make the isolation layer of the embodiment of the present application can effectively achieve the purpose of improving product quality and yield and reducing production costs.

[0098] In addition, in order to meet the transmission path requirements of the bulk acoustic wave filter for the resonant sound waves, the size of the resonant cavity also needs to meet the preset conditions to meet the product application requirements. Therefore, in some modified embodiments, the thickness of the polymer film isolation layer after bonding is between 5 microns and 20 microns.

[0099] In addition, based on any embodiment of the present application, in some modified embodiments, after bonding, the distance between the edge of the through hole on the polymer film isolation layer and the working area of ​​the bulk acoustic wave filter is greater than 2 microns.

[0100] Please refer to Figure 8 It is understood that there should be a necessary distance between the working area and the edge of the through hole on the polymer film isolation layer. In practical applications, in order to meet application requirements, the distance needs to be greater than 2 microns.

[0101] In some preferred embodiments, the bulk acoustic wave filter is a D-BAW filter. The D-BAW filter can be used to make wireless communication modules (such as WiFi modules), microcontroller units (MCUs) and field programmable gate arrays (FPGAs), etc., and has excellent filtering capabilities.

[0102] There are a few points to note:

[0103] (1) The drawings of the embodiments of the present application only involve structures related to the embodiments of the present application, and other structures may refer to the general design;

[0104] (2) Unless there is a conflict, the features of the same embodiment or different embodiments of the present application may be combined with each other.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a bulk acoustic wave filter resonant cavity, characterized in that: include: forming a piezoelectric layer group, wherein the piezoelectric layer group comprises a first electrode layer, a piezoelectric layer and a second electrode layer, wherein the first electrode layer and the second electrode layer are respectively arranged on both sides of the piezoelectric layer; providing a substrate; A polymer film is provided, and a plurality of through holes are formed on the polymer film; wherein the polymer film with through holes is manufactured by a tape casting method, the through holes are formed based on micro protrusions on a tape casting substrate or a base tape, and after the through holes are formed on the polymer film, the line width of the remaining part is greater than 10 microns, and / or the area of ​​the remaining part accounts for more than 10%; The polymer film having a plurality of through holes is bonded between the piezoelectric layer group and the substrate to form a polymer film isolation layer, wherein the polymer film is preset with through holes before bonding, and after bonding is completed, a resonant cavity surrounded by the polymer film isolation layer, the piezoelectric layer group and the substrate is formed at the through holes, the through holes on the polymer film are aligned with the working area in the piezoelectric layer group, and there is a gap between the working area and the edge of the through holes, and the thickness of the polymer film isolation layer after bonding is between 5 microns and 20 microns.

2. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 1, characterized in that: The step of bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer comprises: Bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer; The substrate is bonded based on the polymer film isolation layer being away from the piezoelectric layer group.

3. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 2, characterized in that: The forming of the piezoelectric layer group comprises: forming a piezoelectric layer group on a substrate; After bonding the substrate based on the polymer film isolation layer away from the side of the piezoelectric layer group, the method further includes: The substrate is removed.

4. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 3, characterized in that: The step of forming a piezoelectric layer group on a substrate comprises: forming a first electrode layer, a piezoelectric layer and a second electrode layer covering the entire surface on the substrate in sequence; The second electrode layer is etched to form a second electrode layer that partially covers the piezoelectric layer.

5. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 4, characterized in that: The method of bonding a polymer film based on the piezoelectric layer group to form a polymer film isolation layer comprises: A polymer film is bonded to the second electrode layer to form a polymer film isolation layer, wherein the polymer film is bonded to the piezoelectric layer in a partial area of ​​the piezoelectric layer not covered by the second electrode layer.

6. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 4, characterized in that: After removing the substrate, the method further comprises: The first electrode layer is etched to form a first electrode layer that partially covers the piezoelectric layer, a first projection of the first electrode layer on the piezoelectric layer and a second projection of the second electrode layer on the piezoelectric layer partially overlap, and a working area of ​​the resonant cavity is formed in the overlapping area.

7. The method for preparing a bulk acoustic wave filter resonant cavity according to claim 1, characterized in that: The step of bonding a polymer film between the piezoelectric layer group and the substrate to form a polymer film isolation layer comprises: A polymer film is bonded between the piezoelectric layer group and the substrate by melt bonding to form a polymer film isolation layer. The glass transition temperature of the polymer film is greater than 250 degrees Celsius, and the stress after bonding is less than 100 MPa.

8. The method for preparing a bulk acoustic wave filter resonant cavity according to any one of claims 1 to 7, characterized in that: The polymer film includes a polyimide film.

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