Cavity structure for bulk acoustic wave filter, bulk acoustic wave filter and electronic device

Abstract

The present application provides a cavity structure for a bulk acoustic wave filter, a bulk acoustic wave filter, and an electronic device, wherein the cavity structure includes a piezoelectric layer group, a polymer film isolation layer, and a substrate; wherein the polymer film isolation layer is bonded between the piezoelectric layer group and the substrate, and is provided with a through hole, at which the polymer film isolation layer, the piezoelectric layer group, and the substrate together surround a resonant cavity. The present application scheme abandons the traditional scheme of forming a resonant cavity based on inorganic substances such as POLY / SIN in the prior art, and instead uses a polymer film isolation layer to form a resonant cavity by bonding, 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 cavity structure for a bulk acoustic wave filter, a bulk acoustic wave filter, and an electronic device. 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 cross-sectional schematic diagram of the BAW resonator resonant cavity provided by the prior art is shown. In the prior art, the BAW resonator resonant cavity is mainly formed by a vapor deposition process based on inorganic materials such as POLY (polycrystalline silicon) or SIN (silicon nitride). The traditional scheme for preparing the BAW resonator resonant cavity 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. The BAW filter cavity structure prepared by this traditional scheme 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 bulk acoustic wave filter cavity structure with higher quality and yield and lower cost. Summary of the invention

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

[0011] In one aspect of the present application, there is provided a cavity structure for a bulk acoustic wave filter, comprising: a piezoelectric layer group, a polymer film isolation layer and a substrate;

[0012] The polymer film isolation layer is bonded between the piezoelectric layer group and the substrate, and is provided with a through hole. At the through hole, the polymer film isolation layer, the piezoelectric layer group and the substrate are surrounded together to form a resonant cavity.

[0013] Optionally, the piezoelectric layer group includes a first electrode layer, a piezoelectric layer and a second electrode layer; wherein,

[0014] The piezoelectric layer is disposed between the first electrode layer and the second electrode layer;

[0015] The second electrode layer partially covers the piezoelectric layer, and the resonant cavity is connected to both the second electrode layer and the piezoelectric layer on one side of the piezoelectric layer group.

[0016] Optionally, the polymer film isolation layer is realized by using a polyimide film.

[0017] Optionally, the thickness of the polymer film isolation layer is between 5 microns and 20 microns.

[0018] Optionally, the distance between the edge of the through hole on the polymer film isolation layer and the working area of ​​the BAW filter is greater than 2 microns.

[0019] Optionally, the glass transition temperature of the polyimide film is greater than 250 degrees Celsius.

[0020] Optionally, the projected area of ​​the polymer film isolation layer on the substrate accounts for more than 10%.

[0021] Optionally, a projection line width of the polymer film isolation layer on the substrate is greater than 10 microns.

[0022] Another aspect of the present application provides a bulk acoustic wave filter, wherein the bulk acoustic wave filter has the cavity structure for a bulk acoustic wave filter provided in the present application.

[0023] Another aspect of the present application provides an electronic device, wherein the electronic device is provided with the bulk acoustic wave filter provided by the present application.

[0024] The solution provided in the embodiment of the present application abandons the traditional solution of forming a resonant cavity based on inorganic substances such as POLY / SIN in the prior art, and instead uses a polymer film isolation layer to form a resonant cavity by bonding. 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. Furthermore, since the polymer film will not bring additional stress during bonding and will not cause a large amount of warping of the substrate, the product yield can be effectively improved compared with the traditional solution. In addition, the resonant cavity structure of the present application is simple, and there is no need to perform multiple complicated deposition, polishing, etching and other process steps for production, which can effectively reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] 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:

[0027] Figure 1 A schematic cross-sectional view of a resonant cavity of a bulk acoustic wave resonator provided in the prior art;

[0028] Figure 2 A schematic cross-sectional view of a resonant cavity of a bulk acoustic wave resonator provided in one embodiment of the present application;

[0029] Figure 3 A schematic diagram of a working area of ​​a bulk acoustic wave resonator provided in one embodiment of the present application;

[0030] The same or similar reference numerals in the drawings represent the same or similar components. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Figure 2 A schematic cross-sectional view of a bulk acoustic wave resonator resonant cavity provided in an embodiment of the present application is shown. As shown in the figure, the cavity structure for a bulk acoustic wave filter comprises: a piezoelectric layer group 11, a polymer film isolation layer 12 and a substrate 13; wherein,

[0035] The polymer film isolation layer 12 is bonded between the piezoelectric layer group 11 and the substrate 13, and is provided with a through hole. At the through hole, the polymer film isolation layer 12, the piezoelectric layer group 11 and the substrate 13 are surrounded together to form a resonant cavity.

[0036] The above-mentioned cavity structure for bulk acoustic wave filter provided in the embodiment of the present application abandons the traditional scheme of forming a resonant cavity based on inorganic substances such as POLY / SIN in the prior art, and instead uses a polymer film isolation layer to form a resonant cavity by bonding. Since the bonding temperature is much lower than the deposition temperature in the traditional scheme, 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 a large amount of warping of the substrate, the product yield can be effectively improved compared with the traditional scheme. In addition, the resonant cavity structure of the present application is simple, and there is no need to perform multiple complicated deposition, polishing, etching and other process steps for production, which can effectively reduce the production cost.

[0037] Please continue to refer to Figure 2 It is understood that in some modified implementations, the piezoelectric layer group 11 includes a first electrode layer 111, a piezoelectric layer 112, and a second electrode layer 113; wherein,

[0038] The piezoelectric layer 112 is disposed between the first electrode layer 111 and the second electrode layer 113;

[0039] The second electrode layer 113 partially covers the piezoelectric layer 112 , and the resonant cavity is connected to both the second electrode layer 113 and the piezoelectric layer 112 on one side of the piezoelectric layer group 11 .

[0040] Since the second electrode layer 113 partially covers the piezoelectric layer 112, the projections of the second electrode layer 113 and the first electrode layer 111 on the piezoelectric layer 112 also partially overlap, and the overlapping portion is the working area of ​​the BAW filter. In practical applications, the first electrode layer 111 can also be designed to partially cover the piezoelectric layer 112, and its first projection on the piezoelectric layer 112 and the second projection of the second electrode layer 113 on the piezoelectric layer 112 are misaligned. In this case, the overlapping portion of the first projection and the second projection is the working area of ​​the BAW filter, and the working area can be referred to Figure 3 To understand.

[0041] The piezoelectric layer group 11 has the advantages of simple structure and easy production. The cavity structure for the bulk acoustic wave filter formed based on the piezoelectric layer group 11 has the advantages of high efficiency, high yield, low cost, etc., and is particularly suitable for the production of D-BAW filters.

[0042] 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 13 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.

[0043] In some preferred embodiments, the present application has selected a polyimide film to implement the polymer film isolation layer 12 after a large number of experiments and taking into account the above-mentioned various factors.

[0044] 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.

[0045] Based on any embodiment of the present application, in some modified embodiments, the polymer film isolation layer 12 is solidified between the piezoelectric layer group 11 and the substrate 13 by melt bonding, the glass transition temperature of the polymer film isolation layer 12 is greater than 250 degrees Celsius, and the stress after bonding is less than 100 MPa.

[0046] Among them, the glass transition temperature is an inherent property of polymer films. Different polymer films have different glass transition temperatures. Even if they are all polyimide films, PI films of different types and produced by different manufacturers will 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.

[0047] In practical applications, the temperature of melt bonding needs to be greater than the glass transition temperature of the polymer film isolation layer 12, 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 a more ideal effect. Those skilled in the art can further optimize on this basis in combination with actual needs to obtain better results.

[0048] 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.

[0049] 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 preset conditions to meet product application requirements. Therefore, in some modified embodiments, the thickness of the polymer film isolation layer 12 after curing is between 5 microns and 20 microns.

[0050] In addition, please refer to Figure 3 As shown, based on any embodiment of the present application, in some modified embodiments, the distance between the edge of the through hole on the polymer film isolation layer 12 and the working area of ​​the BAW filter is greater than 2 microns.

[0051] The overlapping portion of the first projection of the first electrode layer 111 on the piezoelectric layer 112 and the second projection of the second electrode layer 113 on the piezoelectric layer 112 is the working area of ​​the BAW filter. Figure 3 As shown, the working area should have a necessary distance from the edge of the through hole on the polymer film isolation layer 12. In practical applications, in order to meet application requirements, the distance needs to be greater than 2 microns.

[0052] In addition, in order to ensure the isolation effect of the polymer film isolation layer 12, based on any embodiment of the present application, in some modified embodiments, the projected area of ​​the polymer film isolation layer 12 on the substrate 13 accounts for more than 10%.

[0053] Since too small an area may lead to poor isolation effect, based on this embodiment, the isolation effect of the polymer film isolation layer 12 can be effectively ensured.

[0054] 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 above-mentioned projected area, and deformation or even breakage and other abnormalities are prone to occur during the bonding process, affecting product quality and yield. Therefore, by limiting the projected area of ​​the above-mentioned polymer film isolation layer 12 to a proportion greater than 10%, it can be ensured that the through hole will not be too large, reducing the probability of deformation or breakage of the polymer film, thereby improving product quality and yield.

[0055] In addition, in order to ensure the isolation effect of the polymer film isolation layer 12 and reduce the probability of deformation or fracture of the polymer film, in other modified implementations, the projection line width of the polymer film isolation layer 12 on the substrate 13 is greater than 10 microns. The requirement that the projection line width is greater than 10 microns is also set to ensure the isolation effect of the polymer film isolation layer 12 and reduce the probability of deformation or fracture of the polymer film, so as to obtain a more stable isolation effect and higher product quality and yield.

[0056] Based on the same inventive concept, a bulk acoustic wave filter is also provided in an embodiment of the present application. The bulk acoustic wave filter has a cavity structure for a bulk acoustic wave filter provided in the present application.

[0057] In some preferred embodiments, the bulk acoustic wave filter is a D-BAW filter.

[0058] The BAW filter provided in the embodiment of the present application is based on the same inventive concept as the cavity structure for the BAW filter provided in the aforementioned embodiment of the present application and has the same beneficial effects.

[0059] Based on the same inventive concept, an electronic device is also provided in an embodiment of the present application. The electronic device is provided with the bulk acoustic wave filter provided in the present application.

[0060] Exemplarily, the electronic device may be a semiconductor device provided with the above-mentioned bulk acoustic wave filter or may include but is not limited to a wireless communication module (such as a WiFi module), a microcontroller unit (MCU) and a field programmable gate array (FPGA), etc., which is not limited in the embodiments of the present application.

[0061] The electronic device provided in the embodiment of the present application is based on the same inventive concept as the cavity structure and bulk acoustic wave filter for a bulk acoustic wave filter provided in the aforementioned embodiment of the present application, and has the same beneficial effects.

[0062] There are a few points to note:

[0063] (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;

[0064] (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.

[0065] 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 cavity structure for a bulk acoustic wave filter, characterized in that: include: A piezoelectric layer group, a polymer film isolation layer and a substrate; wherein, The piezoelectric layer group includes a first electrode layer, a piezoelectric layer, and a second electrode layer; The polymer film isolation layer is bonded between the piezoelectric layer group and the substrate, and is provided with a through hole. At the through hole, the polymer film isolation layer, the piezoelectric layer group and the substrate together surround to form a resonant cavity, wherein the through hole is pre-formed before the polymer film isolation layer is bonded; The overlapping portion of 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 is the working area of ​​the BAW filter; There is a necessary gap between the working area and the edge of the through hole on the polymer film isolation layer; The projected area of ​​the polymer film isolation layer on the substrate accounts for more than 10%.

2. The cavity structure for a bulk acoustic wave filter according to claim 1, characterized in that: The piezoelectric layer is disposed between the first electrode layer and the second electrode layer; The second electrode layer partially covers the piezoelectric layer, and the resonant cavity is connected to both the second electrode layer and the piezoelectric layer on one side of the piezoelectric layer group.

3. The cavity structure for a bulk acoustic wave filter according to claim 1, characterized in that: The polymer film isolation layer is realized by using a polyimide film.

4. The cavity structure for a bulk acoustic wave filter according to claim 3, characterized in that: The thickness of the polymer film isolation layer is between 5 micrometers and 20 micrometers.

5. The cavity structure for a bulk acoustic wave filter according to claim 3, characterized in that: 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.

6. The cavity structure for a bulk acoustic wave filter according to claim 3, characterized in that: The glass transition temperature of the polyimide film is greater than 250 degrees Celsius.

7. The cavity structure for a bulk acoustic wave filter according to claim 3, characterized in that: The projection line width of the polymer film isolation layer on the substrate is greater than 10 microns.

8. A bulk acoustic wave filter, characterized in that: The bulk acoustic wave filter has the cavity structure for a bulk acoustic wave filter according to any one of claims 1 to 7.

9. An electronic device, characterized in that: The electronic device is provided with the bulk acoustic wave filter according to claim 8.

Images