A low-temperature-drift surface acoustic wave filter and a method for manufacturing the same

Abstract

The application discloses a low-temperature drift surface acoustic wave filter and a preparation method thereof. The low-temperature drift surface acoustic wave filter comprises a substrate and a plurality of interdigital electrodes which are arranged on the substrate in a spaced manner, wherein the substrate has a piezoelectric effect; the interdigital electrode comprises a compensation layer arranged on the substrate and a metal layer in contact with the compensation layer, wherein the material of the compensation layer is silicon dioxide; and the sidewall of the interdigital electrode is plated with a protective film, and the Young's modulus of the material of the protective film is greater than the Young's modulus of the material of the metal layer. Thus, the technical problem that the surface acoustic wave filter in the prior art is damaged and fails due to the drift of the working frequency and the damage of the interdigital electrode caused by the temperature rise under high input power is solved.

Description

Technical Field

[0001] This application relates to the field of radio frequency front-end technology, and in particular to a low-temperature drift surface acoustic wave filter and its fabrication method. Background Technology

[0002] Surface acoustic wave (SAW) filters, with their small size, low cost, and excellent performance, have become one of the core components of mobile communication radio frequency (RF) front-end modules. As wireless communication technology evolves towards 5G and future 6G, spectrum resources are becoming increasingly scarce, placing more stringent demands on the frequency selectivity and passband stability of SAW filters in RF systems.

[0003] However, the piezoelectric materials used in the substrates of surface acoustic wave (SAW) filters (such as lithium tantalate or lithium niobate) exhibit significant temperature drift coefficients. When the SAW filter is under high input power, alternating stress and Joule heating occur. Changes in ambient temperature at this time can alter the propagation speed of SAW waves. This causes the operating frequency of the SAW filter to drift, potentially exceeding its effective bandwidth, and ultimately leading to filter failure.

[0004] Meanwhile, because interdigitated electrodes have low resistivity, they typically use metals with low Young's modulus and are relatively soft. Therefore, the temperature rise and high-frequency alternating stress caused by high input power can lead to plastic flow and diffusion of metal atoms on the sidewalls of the interdigitated electrodes, gradually forming mounds or cavities, ultimately resulting in damage to the interdigitated electrodes. Consequently, damage to the interdigitated electrodes can lead to the failure of the surface acoustic wave filter.

[0005] The publication number is CN116915211A, and the title is "An Ultra-Wideband Zero-Temperature-Drift Surface Acoustic Wave Filter". It includes a first filter, a second filter, ..., an nth filter connected in parallel between the input and output terminals. The transmission curves of each filter are partially superimposed to form an ultra-wideband transmission curve. Both the first filter and the nth filter are provided with a temperature compensation layer. The frequencies corresponding to the left and right roll-off points of the ultra-wideband transmission curve are selected as the frequencies f1 and fn of the first filter and the nth filter, respectively, and the wavelengths λ1 and λn of the first filter and the nth filter are obtained. From the normalized relationship curve of temperature drift coefficient with the thickness of the piezoelectric crystal layer and the temperature compensation layer relative to the wavelength, the thicknesses h1' and hn' of the temperature compensation layer that are close to or equal to zero temperature drift are selected as the thicknesses of the temperature compensation layer of the first filter and the nth filter.

[0006] The publication number is CN120498407A, entitled "Warm-Conditioned Surface Acoustic Wave Filter and its Fabrication Method." The method involves selecting a piezoelectric substrate and forming a first and second trench on its upper surface; depositing polycrystalline silicon on the upper surface of the piezoelectric substrate to completely fill the trenches; grinding the polycrystalline silicon until the piezoelectric substrate is exposed; implanting ions into the polycrystalline silicon to form n-type and p-type thermocouple pairs; fabricating a first dielectric layer on the upper surface of the silicon substrate; fabricating a first thermocouple pair interconnection layer, a second thermocouple pair interconnection layer, and a third thermocouple pair interconnection layer in the first, second, and third trenches formed in the first dielectric layer, respectively; fabricating a second dielectric layer on the upper surface of the first dielectric layer; and fabricating an interdigitated structure and a third dielectric layer on the lower surface of the piezoelectric substrate to obtain a warm-conditioned surface acoustic wave filter.

[0007] There is currently no effective solution to the technical problem in the existing technology of surface acoustic wave (SAW) filters that causes temperature rise under high input power, resulting in operating frequency drift and damage to interdigital electrodes, thus leading to filter failure. Summary of the Invention

[0008] This disclosure provides a low-temperature drift surface acoustic wave filter and its fabrication method, which at least solves the technical problem in the prior art that surface acoustic wave filters fail due to temperature rise under high input power, which causes operating frequency drift and interdigital electrode damage.

[0009] According to one aspect of this application, a low-temperature drift surface acoustic wave filter is provided, comprising: a substrate and a plurality of interdigitated electrodes spaced apart on the substrate, wherein the substrate has a piezoelectric effect; the interdigitated electrodes include a compensation layer disposed on the substrate and a metal layer in contact with the compensation layer, wherein the material of the compensation layer is silicon dioxide; and the sidewalls of the interdigitated electrodes are coated with a protective film, wherein the material of the protective film has a Young's modulus greater than the Young's modulus of the material of the metal layer.

[0010] According to another aspect of this application, a method for fabricating a low-temperature drift surface acoustic wave filter is provided, comprising: providing a substrate; depositing a silicon dioxide layer on the substrate, coating the silicon dioxide layer with photoresist and patterning it; etching the silicon dioxide layer according to the patterned photoresist to form a compensation layer, and removing the photoresist; depositing a metal film on the substrate and the compensation layer, coating the metal film with photoresist and patterning it; etching the metal film according to the patterned photoresist to form a metal layer, and removing the photoresist to obtain interdigitated electrodes and busbars; and depositing a film on the substrate and the interdigitated electrodes, and etching to form a protective film encapsulating the sidewalls of the interdigitated electrodes, thereby obtaining a low-temperature drift surface acoustic wave filter.

[0011] To address the aforementioned technical problems, this application provides a low-temperature drift surface acoustic wave (SAW) filter. In the low-temperature drift SAW filter, multiple interdigitated electrodes are spaced apart on a substrate. Further, a compensation layer for the interdigitated electrodes is disposed on the substrate and contacts a metal layer. The compensation layer is made of silicon dioxide. Furthermore, a protective film is deposited on the sidewalls of the interdigitated electrodes, and the Young's modulus of the protective film material is greater than that of the metal layer material.

[0012] Because the piezoelectric material used in the substrate has a large temperature drift coefficient, changes in ambient temperature can cause the operating frequency of the surface acoustic wave (SAW) filter to drift, and may even exceed the effective bandwidth of the SAW filter, leading to the failure of the SAW filter.

[0013] Therefore, this application provides a compensation layer made of silicon dioxide on the substrate, utilizing the positive resonant frequency temperature coefficient of silicon dioxide to offset the negative resonant frequency temperature coefficient of the substrate material. Thus, the compensation layer reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter, preventing filter failure due to operating frequency drift.

[0014] Furthermore, the interdigitated electrodes with low resistance have a lower Young's modulus and are relatively softer. Under the repeated action of alternating stress and thermal stress caused by high input power, the atoms on the sidewalls of the interdigitated electrodes are prone to plastic flow and diffusion, gradually forming mounds or cavities, which eventually leads to damage to the interdigitated electrodes and causes the low-temperature drift surface acoustic wave filter to fail.

[0015] Therefore, this application coats the sidewalls of the interdigital electrodes with a protective film, and the Young's modulus of the protective film material is greater than that of the interdigital electrode material (including the compensation layer and the metal layer). In other words, under high input power conditions, the protective film directly bears most of the stress, reducing the stress intensity on the interdigital electrodes and preventing the softer internal interdigital electrodes from undergoing severe volume expansion, contraction, or creep. This prevents damage to the sidewalls of the interdigital electrodes and avoids failure of the low-temperature drift surface acoustic wave filter.

[0016] Furthermore, this solves the technical problem in the existing technology where surface acoustic wave (SAW) filters experience temperature rise under high input power, which causes the operating frequency to drift and the interdigitated electrodes to be damaged, leading to the failure of the SAW filter.

[0017] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments of this application in conjunction with the accompanying drawings. Attached Figure Description

[0018] The following sections will describe some specific embodiments of this application in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic diagram of the structure of the low-temperature drift surface acoustic wave filter according to the embodiments of this application; Figure 2 This is a schematic diagram of another low-temperature drift surface acoustic wave filter according to an embodiment of this application; Figure 3 This is a schematic diagram of a low-temperature drift surface acoustic wave filter with a protective film coated on the sidewalls and upper surface of the interdigitated electrodes according to an embodiment of this application. Figure 4 This is a schematic diagram of the structure of a low-temperature drift surface acoustic wave filter with an equal width of compensation layer and metal layer according to an embodiment of this application; Figure 5 This is a schematic diagram of the structure of a low-temperature drift surface acoustic wave filter with a compensation layer width greater than the metal layer width, according to an embodiment of this application. Figure 6 This is a schematic diagram of the structure of the low-temperature drift surface acoustic wave filter located on the compensation layer in the first part according to the embodiments of this application; Figure 7 This is a schematic diagram of the structure of a low-temperature drift surface acoustic wave filter with a compensation layer height equal to the metal layer height, according to an embodiment of this application. Figure 8 This is a schematic diagram of the silicon dioxide layer according to the embodiments of this application; Figure 9 This is a schematic diagram of photoresist coating on a silicon dioxide layer according to an embodiment of this application; Figure 10 This is a schematic diagram of the photoresist on the patterned silicon dioxide layer according to the embodiments of this application; Figure 11 This is a schematic diagram of the etching of the silicon dioxide layer according to the embodiments of this application; Figure 12 This is a schematic diagram of the compensation layer according to an embodiment of this application; Figure 13 This is a schematic diagram of the metal film according to an embodiment of this application; Figure 14 This is a schematic diagram of the photoresist on the patterned metal film according to the embodiments of this application; and Figure 15 This is a schematic diagram of the etching of a metal film according to an embodiment of this application. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other. This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] To enable those skilled in the art to better understand the present disclosure, the technical solutions of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present disclosure.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Figure 1 This is a schematic diagram of the structure of the low-temperature drift surface acoustic wave filter according to the embodiments of this application. Figure 2 This is a schematic diagram of another low-temperature drift surface acoustic wave filter according to an embodiment of this application. According to one aspect of this embodiment, a low-temperature drift surface acoustic wave filter 10 is provided, comprising: a substrate 100 and a plurality of interdigitated electrodes 200 spaced apart on the substrate 100, wherein the substrate 100 has a piezoelectric effect; the interdigitated electrodes 200 include a compensation layer 210 disposed on the substrate 100 and a metal layer 220 in contact with the compensation layer 210, wherein the material of the compensation layer 210 is silicon dioxide; and the sidewalls of the interdigitated electrodes 200 are coated with a protective film 300, wherein the Young's modulus of the material of the protective film 300 is greater than the Young's modulus of the material of the metal layer 220.

[0024] As described in the background section, surface acoustic wave (SAW) filters have become one of the core components of mobile communication radio frequency (RF) front-end modules due to their small size, low cost, and excellent performance. With the evolution of wireless communication technology towards 5G and future 6G, spectrum resources are becoming increasingly scarce, placing more stringent requirements on the frequency selectivity and passband stability of SAW filters in RF systems.

[0025] However, the piezoelectric materials used in the substrates of surface acoustic wave (SAW) filters (such as lithium tantalate or lithium niobate) exhibit significant temperature drift coefficients. When the SAW filter is under high input power, alternating stress and Joule heating occur. Changes in ambient temperature at this time can alter the propagation speed of SAW waves. This causes the operating frequency of the SAW filter to drift, potentially exceeding its effective bandwidth, and ultimately leading to filter failure.

[0026] Meanwhile, because interdigitated electrodes have low resistivity, they typically use metals with low Young's modulus and are relatively soft. Therefore, the temperature rise and high-frequency alternating stress caused by high input power can lead to plastic flow and diffusion of metal atoms on the sidewalls of the interdigitated electrodes, gradually forming mounds or cavities, ultimately resulting in damage to the interdigitated electrodes. Consequently, damage to the interdigitated electrodes can lead to the failure of the surface acoustic wave filter.

[0027] In view of this, this application provides a low-temperature drift surface acoustic wave filter 10. (Reference) Figure 1 and Figure 2 As shown, in the low-temperature drift surface acoustic wave filter 10, a plurality of interdigitated electrodes 200 are spaced apart on the substrate 100. Further, a compensation layer 210 of the interdigitated electrodes 200 is disposed on the substrate 100 and contacts the metal layer 220. The compensation layer 210 is made of silicon dioxide. Furthermore, a protective film 300 is deposited on the sidewalls of the interdigitated electrodes 200, and the Young's modulus of the material of the protective film 300 is greater than the Young's modulus of the material of the metal layer 220.

[0028] Because the piezoelectric material used in substrate 100 has a large temperature drift coefficient, changes in ambient temperature can cause the operating frequency of the surface acoustic wave filter to drift, and may even exceed the effective bandwidth of the surface acoustic wave filter, leading to the failure of the surface acoustic wave filter.

[0029] Therefore, this application provides a compensation layer 210 made of silicon dioxide on the substrate 100, utilizing the positive resonant frequency temperature coefficient of silicon dioxide to offset the negative resonant frequency temperature coefficient of the substrate 100 material. Thus, the compensation layer 210 reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10, preventing the low-temperature drift surface acoustic wave filter 10 from failing due to operating frequency drift.

[0030] Furthermore, the interdigitated electrode 200, with its low resistance, has a relatively low Young's modulus and is relatively soft. Under the repeated action of alternating stress and thermal stress caused by high input power, the atoms on the sidewalls of the interdigitated electrode 200 are prone to plastic flow and diffusion, gradually forming mounds or cavities, which eventually leads to damage to the interdigitated electrode 200 and causes the low-temperature drift surface acoustic wave filter 10 to fail.

[0031] Therefore, this application coats the sidewalls of the interdigital electrode 200 with a protective film 300, and the Young's modulus of the material of the protective film 300 is greater than that of the material of the interdigital electrode 200 (including the compensation layer 210 and the metal layer 220). In other words, under high input power conditions, the protective film 300 directly bears most of the stress, reducing the stress intensity on the interdigital electrode 200 and preventing the softer internal interdigital electrode 200 from undergoing severe volume expansion, contraction, or creep. This prevents damage to the sidewalls of the interdigital electrode 200 and avoids failure of the low-temperature drift surface acoustic wave filter 10.

[0032] Furthermore, this solves the technical problem in the existing technology where surface acoustic wave (SAW) filters experience temperature rise under high input power, which causes the operating frequency to drift and the interdigitated electrodes to be damaged, leading to the failure of the SAW filter.

[0033] also, Figure 1 and Figure 2 The two different cross sections of the interdigitated electrodes 200 shown are only different in design, and both are suitable for the structure of the above-mentioned low-temperature drift surface acoustic wave filter 10.

[0034] Preferably, the material of the substrate 100 may be, for example, lithium tantalate or lithium niobate.

[0035] Optionally, the upper surface of the interdigital electrode 200 is coated with a protective film 300.

[0036] Specifically, Figure 3 This is a schematic diagram of a low-temperature drift surface acoustic wave filter with a protective film coated on the sidewalls and top surface of the interdigitated electrodes according to an embodiment of this application. (Reference) Figure 3 As shown, the sidewalls and top surface of the interdigital electrode 200 are coated with a protective film 300.

[0037] Therefore, under high input power, the protective film 300 can withstand most of the stress, reducing the stress intensity inside the interdigital electrode 200 and preventing the formation of voids on the upper surface and sidewalls of the interdigital electrode 200. Furthermore, it can prevent the failure of the low-temperature drift surface acoustic wave filter 10 caused by damage to the interdigital electrode 200.

[0038] Optionally, the metal layer 220 surrounds the outer periphery of the compensation layer 210 and contacts the substrate 100.

[0039] Specifically, refer to Figures 1-3 As shown, the compensation layer 210 is surrounded by a metal layer 220, and the metal layer 220 is in contact with the substrate 100.

[0040] Thus, the interdigitated electrodes 200 can be electrically connected to the substrate 100 through the metal layer 220, achieving efficient conversion between electrical signals and surface acoustic waves. Furthermore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. This reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10, preventing its failure due to operating frequency drift.

[0041] Optionally, the metal layer 220 is disposed on the compensation layer 210, and the width of the compensation layer 210 is equal to the width of the metal layer 220.

[0042] Specifically, Figure 4 This is a schematic diagram of a low-temperature drift surface acoustic wave filter with equal width of compensation layer and metal layer according to an embodiment of this application. (Reference) Figure 4 As shown, a metal layer 220 of equal width is provided on the compensation layer 210.

[0043] Therefore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. Consequently, the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10 can be reduced, thus preventing the low-temperature drift surface acoustic wave filter 10 from failing due to operating frequency drift.

[0044] Optionally, the metal layer 220 is disposed on the compensation layer 210, and the width of the compensation layer 210 is greater than the width of the metal layer 220.

[0045] Specifically, Figure 5 This is a schematic diagram of a low-temperature drift surface acoustic wave filter with a compensation layer width greater than the metal layer width, according to an embodiment of this application. (Reference) Figure 5 As shown, a non-uniform width metal layer 220 is provided on the compensation layer 210, and the width of the compensation layer 210 is greater than the width of the metal layer 220.

[0046] Therefore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. Consequently, the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10 can be reduced, thus preventing the low-temperature drift surface acoustic wave filter 10 from failing due to operating frequency drift.

[0047] Optionally, the metal layer 220 includes a first portion 221 and a second portion 222, wherein the first portion 221 is formed on the second portion 222; and the second portion 222 passes through the compensation layer 210 and contacts the substrate 100.

[0048] Specifically, Figure 6 This is a schematic diagram of the structure of the low-temperature drift surface acoustic wave filter located on the compensation layer in the first part according to the embodiments of this application. Figure 7 This is a schematic diagram of a low-temperature drift surface acoustic wave filter with a compensation layer height equal to the metal layer height, according to an embodiment of this application. (Reference) Figure 6 and Figure 7 As shown, a first portion 221 of the metal layer 220 is formed on a second portion 222, and the second portion 222 passes through the compensation layer 210 and contacts the substrate 100.

[0049] Thus, the interdigitated electrodes 200 can be electrically connected to the substrate 100 through the metal layer 220, achieving efficient conversion between electrical signals and surface acoustic waves. Furthermore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. This reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10, preventing its failure due to operating frequency drift.

[0050] Optionally, the width of the first portion 221 is equal to the sum of the width of the compensation layer 210 and the width of the second portion 222.

[0051] Specifically, refer to Figure 6 As shown, the compensation layer 210 is disposed under the first part 221, and the width of the first part 221 is equal to the sum of the width of the compensation layer 210 and the width of the second part 222.

[0052] Thus, the interdigitated electrodes 200 can be electrically connected to the substrate 100 through the metal layer 220, achieving efficient conversion between electrical signals and surface acoustic waves. Furthermore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. This reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10, preventing its failure due to operating frequency drift.

[0053] Optionally, the height of the metal layer 220 is equal to the height of the compensation layer 210; the first portion 221 passes through the compensation layer 210; and the width of the first portion 221 is greater than the width of the second portion 222.

[0054] Specifically, refer to Figure 7 As shown, the height of the metal layer 220 is equal to the height of the compensation layer 210. That is, the sum of the height of the first part 221 and the height of the second part 222 is equal to the height of the compensation layer 210.

[0055] Furthermore, the width of the first portion 221 is greater than the width of the second portion 222. While the second portion 222 passes through the compensation layer 210, the first portion 221 also passes through the compensation layer 210. That is, the metal layer 220 passes through the compensation layer 210, and the compensation layer 210 wraps around the sidewall of the metal layer 220.

[0056] Thus, the interdigitated electrodes 200 can be electrically connected to the substrate 100 through the metal layer 220, achieving efficient conversion between electrical signals and surface acoustic waves. Furthermore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. This reduces the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10, preventing its failure due to operating frequency drift.

[0057] It is important to note that, in cases such as Figures 4-7 In the low-temperature drift surface acoustic wave filter 10 shown, the protective film 300 can either only cover the sidewalls of the interdigital electrode 200, or cover both the sidewalls and the top surface of the interdigital electrode 200 (e.g., Figure 3 (As shown).

[0058] Optionally, it also includes: a busbar 400 disposed on both sides of the plurality of interdigitated electrodes 200, wherein the busbar 400 includes a compensation layer 210 and a metal layer 220, and the width of the compensation layer 210 is equal to the width of the metal layer 220.

[0059] Specifically, refer to Figures 1-7 As shown, a busbar 400 is also disposed on the substrate 100, and the busbar 400 is disposed opposite to both sides of the plurality of interdigitated electrodes 200. The busbar 400 includes a compensation layer 210 and a metal layer 220, and the width of the compensation layer 210 is equal to the width of the metal layer 220.

[0060] Therefore, the positive resonant frequency temperature coefficient of the compensation layer 210 is used to offset the negative resonant frequency temperature coefficient of the substrate 100. Consequently, the temperature drift coefficient of the low-temperature drift surface acoustic wave filter 10 can be reduced, thus preventing the low-temperature drift surface acoustic wave filter 10 from failing due to operating frequency drift.

[0061] According to another aspect of this embodiment, a method for fabricating a low-temperature drift surface acoustic wave filter 10 is provided, comprising: providing a substrate 100; depositing a silicon dioxide layer on the substrate 100, coating the silicon dioxide layer with photoresist and patterning it; etching the silicon dioxide layer according to the patterned photoresist to form a compensation layer 210, and removing the photoresist; depositing a metal film on the substrate 100 and the compensation layer 210, coating the metal film with photoresist and patterning it; etching the metal film according to the patterned photoresist to form a metal layer 220, and removing the photoresist to obtain interdigitated electrodes 200 and busbars 400; and depositing a film on the substrate 100 and the interdigitated electrodes 200, and etching to form a protective film 300 encapsulating the sidewalls of the interdigitated electrodes 200, thereby obtaining the low-temperature drift surface acoustic wave filter 10.

[0062] Specifically, Figure 8 This is a schematic diagram of the silicon dioxide layer according to an embodiment of this application. Figure 9 This is a schematic diagram of photoresist coating on a silicon dioxide layer according to an embodiment of this application. Figure 10 This is a schematic diagram of the photoresist on the patterned silicon dioxide layer according to the embodiments of this application. Figure 11 This is a schematic diagram of the etching of the silicon dioxide layer according to the embodiments of this application. Figure 12 This is a schematic diagram of the compensation layer according to an embodiment of this application. Figure 13 This is a schematic diagram of the metal film according to an embodiment of this application. Figure 14 This is a schematic diagram of photoresist on a patterned metal film according to an embodiment of this application. Figure 15 This is a schematic diagram of the etching of a metal film according to an embodiment of this application.

[0063] refer to Figure 5 and Figures 8-15 As shown, firstly, a substrate 100 is provided, and silicon dioxide is sputtered on the substrate 100. The substrate is then planarized using a chemical mechanical polishing (CMP) process, and finely adjusted using a trimming process to obtain a silicon dioxide layer.

[0064] Next, photoresist is uniformly coated onto the silicon dioxide layer. Using a photolithography machine, ultraviolet light is passed through a patterned mask and irradiated onto the photoresist-coated silicon dioxide layer. Then, a developer is used to develop the silicon dioxide layer, revealing the pattern to be used in subsequent etching steps. Furthermore, the silicon dioxide layer is etched according to the pattern to form a compensation layer 210, and the photoresist is then stripped off.

[0065] Furthermore, a metal film is obtained by evaporation on the substrate 100 and the compensation layer 210, planarization by chemical mechanical polishing (CMP), and fine adjustment by trimming.

[0066] Furthermore, photoresist is uniformly coated onto the metal film. Using a photolithography machine, ultraviolet light is passed through a patterned mask and irradiated onto the photoresist-coated metal film. Then, a developer is used to develop the metal film, revealing the pattern to be used in subsequent etching steps. The metal film is then etched according to the pattern to form a metal layer 220, and the photoresist is stripped off. This results in multiple interdigitated electrodes 200 and busbars 400 disposed opposite each other on both sides of the multiple interdigitated electrodes 200.

[0067] Finally, a film is deposited on the substrate 100 and the interdigitated electrode 200 using a sputtering process. Then, a protective film 300 is formed by argon ion etching, ultimately encapsulating the sidewalls of the interdigitated electrode 200. Thus, a low-temperature drift surface acoustic wave filter 10 is obtained.

[0068] Therefore, the low-temperature drift surface acoustic wave filter 10 prepared through the above steps can improve the temperature drift coefficient and protect the interdigital electrode 200. Furthermore, it can prevent the failure of the low-temperature drift surface acoustic wave filter 10 caused by operating frequency drift and damage to the interdigital electrode 200.

[0069] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of this disclosure. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0070] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0071] In the description of this disclosure, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing this disclosure and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this disclosure; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0072] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A low-temperature drift surface acoustic wave filter (10), characterized in that, include: A substrate (100) and a plurality of interdigitated electrodes (200) spaced apart on the substrate (100), wherein the substrate (100) has a piezoelectric effect; The interdigitated electrode (200) includes a compensation layer (210) disposed on the substrate (100) and a metal layer (220) in contact with the compensation layer (210), wherein the material of the compensation layer (210) is silicon dioxide; and The sidewalls and upper surface of the interdigitated electrode (200) are coated with a protective film (300), and the material of the protective film (300) has a Young's modulus greater than that of the material of the metal layer (220).

2. The low-temperature drift surface acoustic wave filter (10) according to claim 1, characterized in that, The metal layer (220) wraps around the outer periphery of the compensation layer (210) and is in contact with the substrate (100).

3. The low-temperature drift surface acoustic wave filter (10) according to claim 1, characterized in that, The metal layer (220) is disposed on the compensation layer (210), and the width of the compensation layer (210) is equal to the width of the metal layer (220).

4. The low-temperature drift surface acoustic wave filter (10) according to claim 1, characterized in that, The metal layer (220) is disposed on the compensation layer (210), and the width of the compensation layer (210) is greater than the width of the metal layer (220).

5. The low-temperature drift surface acoustic wave filter (10) according to claim 1, characterized in that, The metal layer (220) includes a first portion (221) and a second portion (222), and the first portion (221) is formed on the second portion (222); as well as The second part (222) passes through the compensation layer (210) and contacts the substrate (100).

6. The low-temperature drift surface acoustic wave filter (10) according to claim 5, characterized in that, The first portion (221) is disposed on the compensation layer (210), and the width of the first portion (221) is equal to the sum of the width of the compensation layer (210) and the width of the second portion (222).

7. The low-temperature drift surface acoustic wave filter (10) according to claim 5, characterized in that, The height of the metal layer (220) is equal to the height of the compensation layer (210); The first portion (221) passes through the compensation layer (210); and The width of the first part (221) is greater than the width of the second part (222).

8. The low-temperature drift surface acoustic wave filter (10) according to claim 1, characterized in that, It also includes: a busbar (400) disposed on both sides of the plurality of interdigitated electrodes (200), wherein the busbar (400) includes the compensation layer (210) and the metal layer (220), and the width of the compensation layer (210) is equal to the width of the metal layer (220).

9. A method for fabricating a low-temperature drifting surface acoustic wave filter (10), characterized in that, include: Substrate (100) is provided; A silicon dioxide layer is deposited on the substrate (100), and a photoresist is coated and patterned on the silicon dioxide layer; Based on the patterned photoresist, the silicon dioxide layer is etched to form a compensation layer (210), and the photoresist is stripped off; A metal film is deposited on the substrate (100) and the compensation layer (210), and a photoresist is coated and patterned on the metal film; Based on the patterned photoresist, the metal film is etched to form a metal layer (220), and the photoresist is stripped to obtain interdigitated electrodes (200) and busbars (400). as well as A protective film (300) is deposited on the substrate (100) and the interdigitated electrode (200) and etched to form a protective film (300) that wraps around the sidewall of the interdigitated electrode (200) to obtain a low-temperature drift surface acoustic wave filter (10).

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