Surface acoustic wave filter and preparation method thereof

Abstract

The invention relates to a surface acoustic wave filter and a preparation method thereof. The preparation method comprises the following steps: providing a glass substrate; a piezoelectric material layer is provided, the piezoelectric material layer comprises a bonding surface, and a sacrificial layer is formed in the portion, close to the bonding surface, of the piezoelectric material layer; bonding the bonding surface with the glass substrate; removing the piezoelectric material layer on one side, far away from the glass substrate, of the sacrificial layer, and forming a piezoelectric layer on the glass substrate; an interdigital electrode structure is formed over the piezoelectric layer. The surface acoustic wave filter and the preparation method thereof have the advantages of low cost, batch preparation, device miniaturization and high integration, and are particularly suitable for meeting the requirements on high-frequency acoustic devices in scenes such as communication technology, Internet of Things, intelligent terminals and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface acoustic wave filter, in particular to a surface acoustic wave filter and a preparation method thereof. BACKGROUND

[0002] With the development of communication technology towards 5G era, multiple-input multiple-output (MIMO) technology is rising, and acoustic filters are widely used in terminal products such as mobile phones, tablets, smart wear, Internet of Things, etc. which have strict requirements on size and performance. For example, the number of acoustic filters in a single mobile phone is more than 70 to meet the requirements of high performance and small size.

[0003] The existing acoustic filters mainly include two types of surface acoustic wave filter (SAW) and bulk acoustic wave filter (BAW). However, the standard SAW filter has a simple structure, low cost, and is suitable for frequency bands below 1.5 GHz, and has a wide application in the low frequency band. However, the standard SAW device has obvious disadvantages in the frequency region above 2 GHz, mainly in the low Q value, serious energy leakage and large frequency change with temperature (temperature drift), which makes it difficult to meet the performance requirements in high frequency, wide band and extreme temperature environment. Although BAW is suitable for high frequency applications, the process is complex and the cost is high.

[0004] In order to break through the performance bottleneck of the standard SAW, two types of improved SAW technologies have been developed in the industry: temperature compensation SAW (TC-SAW) and thin film SAW (TF-SAW, also known as IHPSAW). TF-SAW effectively suppresses the leakage of acoustic waves to the substrate by designing a complex hetero-substrate structure, such as silicon, polysilicon / nitride and silicon dioxide stacked in turn, significantly improving the Q value of the device and improving the temperature drift characteristics, making it suitable for high frequency, high power and high-low temperature alternating environment. However, due to the high cost of substrate materials and complex processing technology, TF-SAW faces high manufacturing cost pressure in large-scale commercialization.

[0005] Compared with TF-SAW, TC-SAW technology suppresses temperature drift by introducing a temperature compensation mechanism into the conventional SAW device structure. There are mainly two ways to achieve this: one is surface sputtering type, which deposits a layer of silicon dioxide film with positive frequency temperature coefficient on the surface of the SAW device to offset the negative frequency temperature coefficient of the piezoelectric material itself; the other is substrate bonding type, which bonds the thinned piezoelectric material (such as lithium niobate or lithium tantalate) with silicon, sapphire, spinel and other substrates, and improves the temperature drift characteristics of the device by taking advantage of the better thermal stability of the latter. Although both TC-SAW schemes have achieved certain results in temperature compensation and are more cost-effective than TF-SAW, they still have the following problems:

[0006] The surface sputtering type TC-SAW needs to introduce an additional thick silicon dioxide film deposition process based on multiple mask steps, which significantly increases the manufacturing complexity and material cost; the substrate bonding type TC-SAW needs to perform thermal oxidation treatment on the Si substrate to form a buffer layer silicon dioxide film, and at the same time, perform high-precision grinding (CMP) treatment on the surface of the piezoelectric layer and the substrate, which not only increases the process steps, but also puts higher requirements on the equipment and process precision; the high-quality silicon or sapphire wafer required for bonding itself has a high cost, which further weakens the cost advantage; and whether it is sputtering type or bonding type, the integration degree is still limited by the device structure, and it is difficult to realize higher integration modular design.

[0007] Therefore, on the basis of ensuring the high-frequency performance and low temperature drift characteristics of the device, further simplifying the process flow, reducing the substrate cost and improving the integration capability of the device have become the key direction for the development of the next generation of SAW filters. SUMMARY

[0008] Therefore, on the basis of ensuring the high-frequency performance and low temperature drift characteristics of the device, further simplifying the process flow, reducing the substrate cost and improving the integration capability of the device have become the key direction for the development of the next generation of SAW filters.

[0009] To achieve the above-mentioned purpose, in one aspect, the present application provides a preparation method of a surface acoustic wave filter, comprising:

[0010] providing a glass substrate;

[0011] providing a piezoelectric material layer, the piezoelectric material layer comprising a bonding surface, and the piezoelectric material layer being formed with a sacrificial layer inside near the bonding surface;

[0012] bonding the bonding surface and the glass substrate;

[0013] removing the piezoelectric material layer on the side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate;

[0014] forming an interdigital electrode structure above the piezoelectric layer.

[0015] In one embodiment, the glass substrate is an amorphous silicon dioxide material, and the glass substrate has a positive frequency temperature coefficient.

[0016] In one embodiment, the glass substrate is further doped with an adjusting component for adjusting the frequency temperature coefficient of the glass substrate.

[0017] In one embodiment, the roughness of the bonding surface is in the range of 0-1 nm, and the roughness of the surface of the glass substrate bonded with the bonding surface is in the range of 0-1 nm.

[0018] In one of the embodiments, before the bonding of the bonding surface to the glass substrate, further comprising: forming a buffer layer on the glass substrate.

[0019] In one of the embodiments, the sacrificial layer is formed in the piezoelectric material layer close to the bonding surface by an ion implantation process,

[0020] The removing of the piezoelectric material layer on the side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate comprises:

[0021] The sacrificial layer is subjected to a heat treatment, so that the piezoelectric material layer separates at the sacrificial layer, and the piezoelectric material layer on the side of the sacrificial layer away from the glass substrate is removed, and the piezoelectric material layer bonded to the glass substrate serves as the piezoelectric layer.

[0022] In one of the embodiments, after the removing of the piezoelectric material layer on the side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate, further comprising:

[0023] The sacrificial layer is removed.

[0024] In one of the embodiments, the width of the glass substrate is greater than the width of the piezoelectric layer, wherein the part of the glass substrate on which the piezoelectric layer is not formed serves as a non-bonding area, and the part of the glass substrate on which the piezoelectric layer is formed serves as a bonding area,

[0025] After the forming of the interdigital electrode structure on the piezoelectric layer, further comprising:

[0026] A connection structure is formed on the non-bonding area, the connection structure comprising a connection via and a conductive part filling the connection via, and the connection via penetrates through the glass substrate.

[0027] In one of the embodiments, after the forming of the connection structure on the non-bonding area, further comprising:

[0028] A connection electrode is formed above the non-bonding area, and a functional structure layer is formed on the side of the glass substrate away from the piezoelectric layer, wherein the conductive part electrically connects the connection electrode and the functional structure layer, and the connection electrode is electrically connected to the interdigital electrode structure.

[0029] In another aspect, the application further provides a surface acoustic wave filter prepared by the preparation method of the surface acoustic wave filter according to any one of the above embodiments.

[0030] The surface acoustic wave filter and the preparation method thereof form a sacrifice layer inside the piezoelectric material layer close to the bonding surface, bond the side of the piezoelectric material layer close to the sacrifice layer with the glass substrate, and realize the peeling and transferring of the piezoelectric layer on the glass substrate based on the sacrifice layer. The high-quality piezoelectric layer transferring process is realized, the complex process and material waste caused by traditional multilayer film deposition and grinding are avoided, and the device preparation cost is significantly reduced. Compared with the silicon substrate or other substrates with heterogeneous structures used in the traditional surface acoustic wave filter, the cost of the glass substrate with the same size is only 10%-20% of the silicon substrate, the overall material cost of device manufacturing is significantly reduced, the additional process steps such as thermal oxidation and grinding are reduced, the process is simplified and mass production is facilitated, the material acoustic performance of the glass substrate is good, the dielectric loss is low, the temperature compensation performance is excellent, the surface acoustic wave propagation with low insertion loss can be realized, and the glass substrate is particularly suitable for high-frequency and high-performance filter scenarios. In addition, the glass substrate has good microstructure processing capability and is easy to form a high-precision through-hole structure, which can realize vertical electrical connection from the piezoelectric layer to the back surface of the glass substrate, facilitate subsequent electrode lead-out, packaging interconnection and function module integration, and improve the integration and design flexibility of the device. Therefore, the preparation method of the surface acoustic wave filter has the advantages of low cost, batch production, device miniaturization and high integration on the basis of ensuring the frequency temperature stability and performance consistency of the filter, and is particularly suitable for the demand for high-frequency acoustic devices in communication technology, Internet of Things, intelligent terminals and other scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0032] Figure 1 The flow chart of the preparation method of the surface acoustic wave filter provided in an embodiment;

[0033] Figure 2 The cross-sectional structure schematic diagram of the glass substrate in the preparation method of the surface acoustic wave filter provided in an embodiment;

[0034] Figure 3 The cross-sectional structure schematic diagram of the piezoelectric material layer in the preparation method of the surface acoustic wave filter provided in an embodiment;

[0035] Figure 4 The cross-sectional structure schematic diagram of the bonding surface and the glass substrate in the preparation method of the surface acoustic wave filter provided in an embodiment;

[0036] Figure 5 A cross-sectional structure schematic diagram of a piezoelectric layer formed in a preparation method of a surface acoustic wave filter provided in an embodiment;

[0037] Figure 6 A cross-sectional structure schematic diagram of an interdigital electrode structure formed in a preparation method of a surface acoustic wave filter provided in an embodiment;

[0038] Figure 7 A cross-sectional structure schematic diagram of a non-bonding area formed after etching a piezoelectric layer in a preparation method of a surface acoustic wave filter provided in an embodiment;

[0039] Figure 8 A cross-sectional structure schematic diagram of a connection structure, a connection electrode and a functional structure layer formed in a preparation method of a surface acoustic wave filter provided in an embodiment.

[0040] BRIEF DESCRIPTION OF DRAWINGS

[0041] 1 - glass substrate, 11 - non-bonding area, 12 - bonding area, 2 - piezoelectric material layer, 21 - sacrificial layer, 22 - bonding surface, 3 - piezoelectric layer, 4 - interdigital electrode structure, 41 - finger electrode, 5 - connection structure, 51 - connection via, 52 - conductive part, 6 - connection electrode, 7 - functional structure layer, 71 - rewiring layer, 72 - passive device. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present application is more thorough and complete.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0044] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0045] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can also be oriented in the other direction, and the spatially relative terms used herein can be interpreted accordingly.

[0046] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", or the like, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

[0047] Referring to Figure 1 The present application provides a method for manufacturing a surface acoustic wave filter, comprising the following steps:

[0048] Step S1: providing a glass substrate 1;

[0049] Step S2: providing a piezoelectric material layer 2, the piezoelectric material layer 2 comprising a bonding surface 22, and a sacrificial layer 21 is formed inside the piezoelectric material layer 2 close to the bonding surface 22;

[0050] Step S3: bonding the bonding surface 22 with the glass substrate 1;

[0051] Step S4: removing the piezoelectric material layer 2 on the side of the sacrificial layer 21 away from the glass substrate 1 to form a piezoelectric layer 3 on the glass substrate 1;

[0052] Step S5: forming an interdigital electrode structure 4 above the piezoelectric layer 3.

[0053] In the above example, by forming a sacrificial layer 21 inside the piezoelectric material layer 2 close to the bonding surface 22, and bonding the side of the piezoelectric material layer 2 close to the sacrificial layer 21 with the glass substrate 1, and then achieving the peeling and transferring of the piezoelectric layer 3 based on the sacrificial layer 21, not only a high-quality piezoelectric layer 3 transferring process is achieved, avoiding the complex process and material waste brought by traditional multi-layer film deposition and grinding, but also the device preparation cost is significantly reduced. Compared with the silicon substrate or other substrates with heterogeneous structure used in traditional surface acoustic wave filters, the cost of the glass substrate 1 of the same size is only 10%-20% of that of the silicon substrate, significantly reducing the overall material cost of device manufacturing, and reducing the need for additional process steps such as thermal oxidation and grinding, which is conducive to process simplification and mass production, and the material acoustic performance of the glass substrate 1 is good, the dielectric loss is low, and the temperature compensation performance is good, which can realize low insertion loss of surface acoustic wave propagation, especially suitable for high-frequency and high-performance filter scenarios. In addition, the glass substrate 1 has good microstructure processing capability and is easy to form high-precision via structures, which can realize vertical electrical connection from the piezoelectric layer to the back of the glass substrate in the filter structure, facilitating subsequent electrode lead-out, packaging interconnection and functional module integration, and improving the integration and design flexibility of the device. Therefore, the preparation method of the above surface acoustic wave filter has the advantages of low cost, batch production, device miniaturization and high integration on the basis of ensuring the frequency temperature stability and performance consistency of the filter, which is especially suitable for the demand for high-frequency acoustic devices in communication technology, Internet of Things, smart terminals and other scenarios.

[0054] Specifically, referring to Figure 2 , step S1 is performed to provide a glass substrate 1.

[0055] Exemplarily, the glass substrate 1 is an amorphous silicon dioxide material, and compared with a polycrystalline or complex structure substrate, the acoustic velocity of amorphous silicon dioxide is relatively high (although lower than that of single crystal silicon, but generally higher than that of many piezoelectric materials), and the acoustic wave propagation loss is low in most frequency bands, which helps to realize higher frequency surface acoustic wave filter devices and lower insertion loss, and is especially suitable for high frequency applications.

[0056] Further, the glass substrate 1 also has a high melting point and good thermal stability, can withstand the heat budget required by subsequent processes such as thin film deposition, annealing, bonding, etc., avoid deformation or performance degradation caused by thermal stress, and maintain structural stability within the device operating temperature range; and the glass substrate 1 has excellent corrosion resistance to most acids (except hydrofluoric acid), bases and solvents, ensuring reliability in wet cleaning and etching processes; secondly, the glass substrate 1 also has high hardness and rigidity, which can provide good physical support for the device, enhance the anti-vibration and reliability of the overall structure, and is especially suitable for radio frequency module packaging applications that require high stability and mechanical interference resistance.

[0057] In addition, compared with the silicon substrate or other substrates with heterogeneous structures used in traditional surface acoustic wave filters, the glass substrate 1 has a significant advantage in manufacturing cost. The cost of the glass substrate 1 of the same size is only 10%-20% of the cost of the silicon substrate, significantly reducing the overall material cost of device manufacturing, while reducing the need for additional process steps such as thermal oxidation and grinding, facilitating process simplification and mass production.

[0058] In one embodiment, the glass substrate 1 has a positive frequency temperature coefficient, which can offset or reduce the negative frequency temperature coefficient of the piezoelectric material, maintain the low temperature drift or zero temperature drift characteristics of the overall filter, improve the performance stability of the filter under different temperature conditions, and adapt to a wider operating temperature range.

[0059] Further, the glass substrate 1 is also doped with an adjusting component for adjusting the temperature frequency coefficient of the glass substrate 1, and the adjusting component can be potassium, sodium, boron, etc. doping ions, or inorganic oxides such as zinc oxide, aluminum oxide, titanium dioxide, and phosphorus pentoxide. By precisely controlling the ratio of the basic component silicon dioxide of the glass substrate 1 and the different types of adjusting components introduced, the composition of the glass substrate 1 material can be precisely adjusted, and a wider range of frequency temperature coefficients can be obtained, so as to completely compensate for the frequency temperature coefficient of the piezoelectric material, and to engineer the frequency temperature coefficient of the glass substrate 1 material within a certain range, thereby more effectively matching and compensating for the temperature drift characteristics of the piezoelectric layer 3. In addition, the introduction of the adjusting component can also further affect the acoustic parameters of the glass substrate 1, such as acoustic velocity, acoustic impedance, and acoustic attenuation coefficient, providing more design dimensions for the wave mode control, spurious mode suppression, energy concentration, etc. characteristics of the device, thereby optimizing the frequency response curve and Q value of the SAW filter.

[0060] In addition, the glass substrate 1 also has excellent bonding compatibility, and can be combined with the piezoelectric material (such as LiTaO3, LiNbO3 film or wafer) through direct bonding or auxiliary bonding process to realize high-quality combination, ensure efficient transmission of acoustic waves between the glass substrate 1 and the piezoelectric layer 3, reduce interface scattering, and improve the overall performance of the device.

[0061] Specifically, referring to Figure 3 , a step S2 is performed to provide a piezoelectric material layer 2, the piezoelectric material layer 2 includes a bonding surface 22, and the piezoelectric material layer 2 is formed with a sacrifice layer 21 inside near the bonding surface 22.

[0062] Exemplarily, the material of the piezoelectric material layer 2 includes lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or other single crystal or polycrystalline materials with piezoelectric properties, and in the embodiment, the specific crystal orientation or doping state of the piezoelectric material layer 2 is not limited. The piezoelectric material layer 2 can realize efficient mutual conversion of electrical energy and surface acoustic wave energy through the piezoelectric effect, and can also provide a physical path for surface acoustic wave propagation, but since the piezoelectric material layer 2 has a negative frequency temperature coefficient, the negative frequency temperature coefficient of the piezoelectric material layer 2 needs to be eliminated to ensure that the performance of the device is not affected.

[0063] In one embodiment, the sacrifice layer 21 is formed in the piezoelectric material layer 2 near the bonding surface 22 by an ion implantation process. That is, by implanting high-energy ions into the piezoelectric material layer 2, the chemical bonds of the material layer at a target depth inside the piezoelectric material layer 2 can be destroyed, and a defect-rich layer is formed at the target depth inside the material, which serves as the sacrifice layer 21 for subsequent interlayer peeling.

[0064] Specifically, the implanted ions can include hydrogen ions (H⁺), helium ions (He⁺), or a combination of the two, or other inert or light ions can be selected according to the specific material system. By adjusting parameters such as implantation dose, implantation energy, implantation angle, and implantation temperature, the depth position (i.e. target depth), thickness range, and defect density of the sacrifice layer 21 can be precisely controlled, and the efficiency and delamination quality of the subsequent thermal peeling process can be optimized. For example, the implantation depth can be designed according to the thickness of the target piezoelectric layer 3 and the desired peeling position, and the general range is hundreds of nanometers to several microns, and the specific parameters can be adjusted according to the type of piezoelectric material layer 2 and the target device structure, which is not limited here.

[0065] Specifically, referring to Figure 4 , a step S3 is performed to bond the bonding surface 22 to the glass substrate 1.

[0066] In one embodiment, the roughness of the bonding surface 22 is in the range of 0-1 nm, and the roughness of the surface of the glass substrate 1 bonded to the bonding surface 22 is in the range of 0-1 nm. That is, in order to realize direct bonding of the bonding surface 22 to the glass substrate 1 and achieve high-quality bonding, the glass substrate 1 and the piezoelectric material layer 2 are both polished to control the surface roughness in the range of 0-1 nm, which can satisfy the direct bonding condition without an intermediate adhesive layer, significantly improving the transmission efficiency of acoustic waves at the interface and reducing additional acoustic loss.

[0067] In another embodiment, before the bonding surface 22 is bonded to the glass substrate 1, a buffer layer (not shown) is formed on the glass substrate 1. That is, the glass substrate 1 is further provided with a buffer layer, and further, the bonding surface 22 of the piezoelectric material layer 2 is bonded to the buffer layer by direct bonding, thereby forming a stable connection interface between the glass substrate 1 and the piezoelectric material layer 2.

[0068] Exemplarily, the method of forming the buffer layer includes chemical vapor deposition, physical vapor deposition or other suitable methods. The material of the buffer layer includes silicon nitride, and can also be other materials with good mechanical properties and acoustic barrier properties, such as silicon oxynitride, aluminum nitride, silicon dioxide (crystalline state), etc.

[0069] The buffer layer can further obtain excellent surface flatness and cleanliness through process selection, and introduce hydroxyl groups or other polar functional groups through surface activation treatment, thereby enhancing the direct bonding strength with the piezoelectric material layer 2 and improving the interface reliability. The buffer layer can also introduce a transition interface between the glass substrate 1 and the piezoelectric material layer 2 with a difference in thermal expansion coefficient, reduce thermal stress concentration, and avoid the risk of cracking or peeling of the device during heat treatment or operation. And by selecting a medium layer material with high acoustic impedance or sound absorption characteristics as the buffer layer, it can also have a blocking or reflecting effect on the propagation of acoustic waves within the operating frequency band, preventing acoustic energy from penetrating the glass substrate and attenuating, thereby improving the energy confinement and Q value of the surface acoustic wave filter. Therefore, the buffer layer not only enhances the bonding ability of the piezoelectric material as a structural layer, but also plays a role in regulating and optimizing the acoustic wave propagation path during the operation of the filter, thereby improving the performance stability and reliability of the overall device.

[0070] Specifically, referring to Figure 5 , step S4 is performed to remove the piezoelectric material layer 2 on the side of the sacrificial layer 21 away from the glass substrate 1 to form a piezoelectric layer 3 on the glass substrate 1.

[0071] In one embodiment, removing the piezoelectric material layer 2 on the side of the sacrificial layer 21 away from the glass substrate 1 to form a piezoelectric layer 3 on the glass substrate 1 includes:

[0072] The sacrificial layer 21 is subjected to a heat treatment, which causes the piezoelectric material layer 2 to separate at the sacrificial layer 21, and the piezoelectric material layer 2 on the side of the sacrificial layer 21 away from the glass substrate 1 is removed, and the piezoelectric material layer 2 bonded to the glass substrate 1 remains as the piezoelectric layer 3. This is because the sacrificial layer 21 is formed by ion implantation to break part of the chemical bonds in the crystal structure of the piezoelectric material layer 2, forming a cavity, bubble or stress concentration area, and thus by applying a heat treatment, the implanted ions are encouraged to gather and promote the formation and expansion of microbubbles, and thus induce the cleavage or splitting of the piezoelectric material layer 2 at the sacrificial layer 21, achieving the separation of the piezoelectric material layer 2.

[0073] In the heat treatment of the sacrificial layer 21, rapid annealing is performed at a predetermined temperature in the range of 300-600°C.

[0074] In addition, after the piezoelectric material layer 2 separates at the sacrificial layer 21, the part of the piezoelectric material layer 2 on the side of the ion implantation surface, i.e. bonded to the glass substrate 1, forms the piezoelectric layer 3 required by the device, with good thickness uniformity and surface integrity, while the remaining part in the direction away from the implantation surface remains as the base layer of the piezoelectric material layer 2, which can be selectively recycled and reused.

[0075] In one embodiment, based on the sacrificial layer 21, after the piezoelectric layer 3 is formed on the glass substrate 1, it further comprises: removing the sacrificial layer 21. After the piezoelectric layer 3 is formed, the sacrificial layer 21 still remaining on the piezoelectric layer 3 needs to be further removed to ensure the flatness of the surface of the piezoelectric layer 3 and the stability of the device performance. The method of removing the sacrificial layer 21 includes chemical mechanical polishing (CMP) or other suitable methods to effectively eliminate the potential defect layer, ion sacrificial layer or other impurity residues on the separation interface that affect the device performance, while adjusting the thickness of the piezoelectric layer 3 to achieve precise control of the acoustic wave propagation mode, improve the surface roughness and provide a high-quality substrate for the formation of the subsequent interdigital electrode structure.

[0076] Therefore, the above-mentioned method of forming a sacrificial layer 21 inside the piezoelectric material layer 2, bonding the bonding surface 22 of the piezoelectric material layer 2 to the glass substrate 1, and then based on the sacrificial layer 21 to achieve the peeling and transfer of the piezoelectric layer 3, not only realizes a high-quality piezoelectric layer 3 transfer process, without high-temperature fusion or organic glue bonding, avoids the warping or cracking problem caused by the mismatch of material thermal expansion and contraction, improves the process compatibility and reliability of the overall device, avoids the complex process and material waste brought by traditional multi-layer film deposition and polishing, and significantly reduces the cost of device preparation.

[0077] Specifically, referring to Figure 6 to Figure 8 , step S5 is performed to form an interdigital electrode structure 4 above the piezoelectric layer 3.

[0078] Exemplarily, the interdigital electrode structure 4 is a key functional structure for realizing excitation and reception of surface acoustic waves, and is used for exciting surface acoustic waves in the piezoelectric layer, receiving acoustic wave signals and converting them into electrical signals; the interdigital electrode structure 4 includes a plurality of interdigital electrodes 41 arranged in an interlaced manner, wherein the shape, period and spacing of the interdigital electrodes 41 determine the center frequency and bandwidth characteristics of the device. The material of the interdigital electrode structure 4 includes aluminum, aluminum alloy, gold, copper, molybdenum or other conductive materials.

[0079] In one embodiment, the interdigital electrode structure 4 is formed, including:

[0080] forming an interdigital electrode material layer (not shown) on the piezoelectric layer 3; the method for forming the interdigital electrode material layer includes sputtering, evaporation or other suitable methods;

[0081] forming a patterned photoresist layer (not shown) on the interdigital electrode material layer;

[0082] etching the interdigital electrode material layer based on the patterned photoresist layer to obtain a plurality of interdigital electrodes 41, i.e., the interdigital electrode structure 4.

[0083] In one embodiment, a protective layer (not shown) is further formed on the interdigital electrode structure 4 to improve the corrosion resistance and reliability of the interdigital electrode structure 4. The protective layer can be formed by metal passivation treatment or by covering a protective layer.

[0084] It should be noted that the thickness of the interdigital electrode structure 4 can be selected according to actual conditions in a case capable of balancing electrical conductivity and acoustic wave scattering, which is not limited herein. The electrode width and spacing of the interdigital electrodes 41 in the interdigital electrode structure 4 are determined according to the design frequency (f) and the acoustic velocity (v) of the piezoelectric layer 3, and generally satisfy the design rule of λ=v / f.

[0085] The interdigital electrode structure 4 formed on the piezoelectric layer 3 has a fine structure and a regular arrangement, realizes excitation and detection of surface acoustic waves in the piezoelectric layer 3, and obtains filtering performance with high frequency, high Q value and low insertion loss; and the interdigital electrode structure 4 is compatible with subsequent bonding packaging or system-level integration technology, improving the integration and reliability of the device.

[0086] In one embodiment, the width of the glass substrate 1 is greater than the width of the piezoelectric layer 3, wherein the part of the glass substrate 1 on which the piezoelectric layer 3 is not formed serves as a non-bonding area 11, and the part of the glass substrate 1 on which the piezoelectric layer 3 is formed serves as a bonding area 12; after the interdigital electrode structure 4 is formed on the piezoelectric layer 3, the method further includes:

[0087] forming a connecting structure 5 on the non-bonding area 11, the connecting structure 5 including a connecting through hole 51 and a conductive portion 52 filling the connecting through hole 51, and the connecting through hole 51 penetrating through the glass substrate 1.

[0088] In one embodiment, as shown in FIG. 1, the method further comprises, before forming the connection structure 5 in the non-bonding area 11, partially etching the piezoelectric layer 3, so that the width of the glass substrate 1 is larger than the width of the piezoelectric layer 3, and after etching, the part of the glass substrate 1 without the piezoelectric layer 3 is the non-bonding area 11, and the part of the glass substrate 1 with the piezoelectric layer 3 is the bonding area 12. Figure 7 In one embodiment, as shown in FIG. 1, the method further comprises, before forming the connection structure 5 in the non-bonding area 11, partially etching the piezoelectric layer 3, so that the width of the glass substrate 1 is larger than the width of the piezoelectric layer 3, and after etching, the part of the glass substrate 1 without the piezoelectric layer 3 is the non-bonding area 11, and the part of the glass substrate 1 with the piezoelectric layer 3 is the bonding area 12.

[0089] In another embodiment, the piezoelectric layer 3 can also be directly set to have a width smaller than that of the glass substrate 1, i.e., the width of the piezoelectric material layer 2 is smaller than that of the glass substrate 1, and then the part of the glass substrate 1 without the piezoelectric layer 3 is the non-bonding area 11, and the part of the glass substrate 1 with the piezoelectric layer 3 is the bonding area 12.

[0090] Therefore, the non-bonding area 11 provides spatial support for the subsequent formation of the connection structure 5, and the connection structure 5 is formed in the non-bonding area 11, including:

[0091] The connection through hole 51 is formed in the glass substrate 1 in the non-bonding area 11, and the method for forming the connection through hole 51 includes laser drilling, reactive ion etching (RIE), dry etching, wet etching or other suitable methods.

[0092] The conductive part 52 is formed in the connection through hole 51, and the method for forming the conductive part 52 includes physical vapor deposition, electroless plating, electroplating or other suitable methods, and the material of the conductive part 52 includes gold, silver, copper, molybdenum, tungsten, titanium or other suitable materials.

[0093] In one embodiment, after the connection structure 5 is formed in the non-bonding area 11, the method further comprises forming a connection electrode 6 above the non-bonding area 11 and forming a functional structure layer 7 on the side of the glass substrate 1 away from the piezoelectric layer 3, wherein the conductive part 52 electrically connects the connection electrode 6 and the functional structure layer 7, and the connection electrode 6 is electrically connected to the interdigital electrode structure 4. The connection electrode 6 is located on the peripheral area of the piezoelectric layer 3 or the metal extension area electrically connected to the interdigital electrode structure 4, and the connection electrode 6 can be formed by sputtering, evaporation and patterning from the same metal material (such as aluminum, molybdenum, gold) as the interdigital electrode structure 4, and the connection electrode 6 is electrically connected to the interdigital electrode structure 4 through a metal lead or a through hole metal layer, and the functional structure layer 7 includes a redistribution layer (RDL) 71 and a passive device 72, wherein the passive device 72 includes an inductor, a capacitor, a resistor or an integrated circuit module. The conductive part 52 electrically connects the connection electrode 6 and the functional structure layer 7, realizing vertical electrical connection from the piezoelectric layer 3, the interdigital electrode structure 4 to the back functional structure layer 7.

[0094] Therefore, by limiting the piezoelectric layer 3 in the local area of the glass substrate 1 and arranging the connecting structure 5 in the non-bonding area 11, not only a precise and reliable electrode lead-out channel is achieved, the overall parasitic loss of the device is reduced, but also the wiring complexity and space waste of the traditional electrode extending from the front to the side and then winding to the back are reduced, the device structure integration and packaging flexibility are improved, the miniaturization, high frequency and high reliability of the surface acoustic wave filter are realized, and a more optimal solution is provided for the 5G and subsequent communication systems.

[0095] In addition, the glass substrate 1 is used as a support substrate, and the connecting structure 5 is formed in the non-bonding area 11 of the glass substrate 1. Compared with the traditional substrate technology, the glass substrate 1 has no lattice anisotropy, and compared with crystal materials such as silicon, it has better isotropy and micron-level processing precision in processes such as laser drilling, ultrasonic-assisted drilling, mortar sandblasting, and wet etching, which is suitable for large-scale through-hole array manufacturing. The thermal expansion coefficient of the glass substrate 1 can be better matched with the piezoelectric layer through composition adjustment, which can effectively inhibit cracks, metal peeling or void problems during the metalization and heat treatment of the connecting through-hole 51. Compared with silicon or ceramic conductive or semi-conductive substrates, the glass substrate 1 is an electrically insulating material, which naturally has high resistivity, and the connecting through-hole 51 is not prone to parasitic capacitance and crosstalk after formation, which can significantly reduce radio frequency loss and improve the performance of the surface acoustic wave device in high-frequency scenarios.

[0096] In one embodiment, the application also provides a surface acoustic wave filter prepared by the preparation method of the surface acoustic wave filter described in any of the above embodiments. The surface acoustic wave filter comprises a glass substrate 1, a piezoelectric layer 3 and an interdigital electrode structure 4, wherein the piezoelectric layer 3 is bonded to the glass substrate 1, and the interdigital electrode structure 4 is formed on the piezoelectric layer 3.

[0097] In one embodiment, a buffer layer is further formed on the glass substrate 1, and the piezoelectric layer 3 is bonded to the buffer layer.

[0098] In one embodiment, the width of the glass substrate 1 is greater than the width of the piezoelectric layer 3, wherein the part of the glass substrate 1 without the piezoelectric layer 3 is the non-bonding area 11, the part of the glass substrate 1 forming the piezoelectric layer 3 is the bonding area 12, the non-bonding area 11 further forms the connecting structure 5, the connecting structure 5 includes the connecting through-hole 51 and the conductive part 52 filling the connecting through-hole 51, and the connecting through-hole 51 penetrates the glass substrate 1.

[0099] In one embodiment, a connecting electrode 6 is further formed above the non-bonding area 11, and a functional structure layer 7 is further formed on the side of the glass substrate 1 away from the piezoelectric layer 3, wherein the conductive part 52 electrically connects the connecting electrode 6 and the functional structure layer 7, and the connecting electrode 6 is electrically connected to the interdigital electrode structure 4.

[0100] It should be understood that, although Figure 1 The steps in the flowcharts of FIGS. 1-3 are shown in sequential order following arrows, but the steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specifically noted, the steps are not required to be performed in the order indicated. The steps can be performed in other orders. Figure 1 At least some of the steps in FIGS. 1-3 can include multiple steps or multiple phases, which can not necessarily be performed in the same order as shown, and can be performed at least partially concurrently or in different orders.

[0101] In the description of the specification, the description of the terms "some embodiments", "other embodiments", "certain embodiments", etc. means that the particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the present application. The illustrative description of these terms in this specification is not necessarily referring merely to the same embodiment or example.

[0102] The technical features of the above-described embodiments can be combined in any manner. For brevity, not all possible combinations of the technical features of the above-described embodiments are described, but it should be understood that any combination of the technical features is within the scope of the present application as long as the combination does not result in a contradiction.

[0103] The above-described embodiments are merely some embodiments of the present application, and the description is specific and detailed, but should not be construed as limiting the scope of the patent application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent application of the present application should be subject to the appended claims.

Claims

1. A method for preparing a surface acoustic wave filter, characterized in that: include: providing a glass substrate; Providing a piezoelectric material layer, the piezoelectric material layer comprising a bonding surface, and a sacrificial layer formed inside the piezoelectric material layer near the bonding surface; bonding the bonding surface to the glass substrate; removing the piezoelectric material layer located on a side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate; An interdigital electrode structure is formed above the piezoelectric layer.

2. The method for preparing a surface acoustic wave filter according to claim 1, wherein: The glass substrate is made of amorphous silicon dioxide material and has a positive frequency temperature coefficient.

3. The method for preparing a surface acoustic wave filter according to claim 2, wherein: The glass substrate is further doped with an adjusting component for adjusting the frequency temperature coefficient of the glass substrate.

4. The method for preparing a surface acoustic wave filter according to claim 1, wherein: The roughness of the bonding surface is in the range of 0-1 nm, and the roughness of the surface of the glass substrate bonded to the bonding surface is in the range of 0-1 nm.

5. The method for preparing a surface acoustic wave filter according to claim 1, wherein: Before bonding the bonding surface to the glass substrate, the method further includes: forming a buffer layer on the glass substrate.

6. The method for preparing a surface acoustic wave filter according to claim 1, wherein: The sacrificial layer is formed in the piezoelectric material layer near the bonding surface by an ion implantation process. The step of removing the piezoelectric material layer located on a side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate comprises: The sacrificial layer is heat-treated to separate the piezoelectric material layer at the sacrificial layer, thereby removing the piezoelectric material layer on a side of the sacrificial layer away from the glass substrate, and the piezoelectric material layer bonded to the glass substrate serves as the piezoelectric layer.

7. The method for preparing a surface acoustic wave filter according to claim 1, wherein: After removing the piezoelectric material layer located on a side of the sacrificial layer away from the glass substrate to form a piezoelectric layer on the glass substrate, the method further includes: The sacrificial layer is removed.

8. The method for preparing a surface acoustic wave filter according to claim 1, wherein: The width of the glass substrate is greater than the width of the piezoelectric layer, wherein a portion of the glass substrate where the piezoelectric layer is not formed serves as a non-bonding area, and a portion of the glass substrate where the piezoelectric layer is formed serves as a bonding area. After forming the interdigital electrode structure on the piezoelectric layer, the method further includes: A connection structure is formed in the non-bonding area, wherein the connection structure includes a connection through hole and a conductive portion filling the connection through hole, and the connection through hole passes through the glass substrate.

9. The method for preparing a surface acoustic wave filter according to claim 8, wherein: After forming the connection structure in the non-bonding area, the method further includes: A connecting electrode is formed above the non-bonding area, and a functional structure layer is formed on the side of the glass substrate away from the piezoelectric layer, wherein the conductive portion electrically connects the connecting electrode and the functional structure layer, and the connecting electrode is electrically connected to the interdigital electrode structure.

10. A surface acoustic wave filter, characterized in that: The surface acoustic wave filter is prepared by the method for preparing a surface acoustic wave filter according to any one of claims 1 to 9.

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