Surface acoustic wave filter and forming method thereof

Abstract

The invention relates to a surface acoustic wave filter and a forming method thereof. The surface acoustic wave filter comprises a piezoelectric substrate and an interdigital transduction layer. The piezoelectric substrate includes a base layer and a piezoelectric layer. The interdigital transduction layer comprises a plurality of finger electrodes which are arranged at intervals in the first direction, the area where each finger electrode and the adjacent finger electrode are overlapped in the first direction comprises an interdigital area and suppression areas, the suppression areas are located on the two sides of the interdigital area in the second direction, and the first direction and the second direction intersect and are both parallel to the surface of the piezoelectric layer. Each finger electrode comprises a first part and a second part, the first part is located in the interdigital area, the second part is located in the suppression area, and the thickness of the second part is larger than that of the first part. Compared with the interdigital region, the suppression region has lower sound velocity, and the sound wave encounters a low-speed region when propagating in the second direction (transverse direction) to form a boundary condition with mismatched wave resistance, so that the transverse clutter mode is difficult to maintain or propagate, and the influence of the transverse clutter mode is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a surface acoustic wave filter and a forming method thereof. Background Art

[0002] Surface acoustic wave (SAW) filters are electronic components that utilize the piezoelectric effect and the propagation characteristics of acoustic waves to filter signals. Compared to traditional passive filters (such as those composed of capacitors and inductors), SAW filters offer advantages such as miniaturization, low insertion loss, and a high quality factor (Q factor). They are widely used in mobile phone base stations, RF communication modules, satellite communications, and other fields.

[0003] Ideally, the acoustic wave propagation of a surface acoustic wave filter should strictly follow the direction pointed by the IDT at the input. However, because surface acoustic waves are affected by factors such as boundary effects, substrate material properties, and structural inhomogeneities when propagating on the surface of piezoelectric materials, in addition to propagating along the main propagation direction, surface acoustic waves also propagate transversely, that is, acoustic wave modes propagating in directions perpendicular to the main propagation direction. These transversely propagating surface acoustic waves cannot be effectively guided to the IDT at the output end. Instead, they reflect and interfere within the filter, forming so-called transverse clutter modes. The presence of transverse clutter modes disperses some of the acoustic wave energy from the main propagation path, resulting in a reduction in the energy of the main mode, thereby increasing insertion loss and reducing the filter's energy conversion efficiency. At the same time, additional resonance peaks are formed within and near the passband. These peaks correspond to clutter signals, making it impossible for the filter to effectively distinguish between target signals and interference signals, thereby reducing the filter's frequency selectivity and affecting the filter's stability and consistency. Summary of the Invention

[0004] The embodiments of the present application provide a surface acoustic wave filter and a method for forming the same, which are intended to suppress lateral clutter modes, reduce the insertion loss of the surface acoustic wave filter, and improve the stability and consistency of the surface acoustic wave filter.

[0005] In order to achieve the above-mentioned object, according to a first aspect of the present application, there is provided a surface acoustic wave filter, comprising: A piezoelectric substrate comprising a base layer and a piezoelectric layer located on the base layer; an interdigital transduction layer, located on a surface of the piezoelectric layer facing away from the substrate layer, comprising a plurality of finger electrodes spaced apart along a first direction, wherein an area where each finger electrode overlaps with an adjacent finger electrode in the first direction comprises an interdigital region and an inhibition region, wherein the inhibition region is located on both sides of the interdigital region in a second direction, and the first direction and the second direction intersect and are both parallel to the surface of the piezoelectric layer; Each of the finger electrodes includes a first portion and a second portion connected to each other, the first portion is located in the interdigital region, the second portion is located in the inhibition region, and the thickness of the second portion is greater than that of the first portion.

[0006] Optionally, in the second direction, the second part has a first connecting side wall on a side close to the first part, the first connecting side wall connecting a side surface of the second part facing away from the piezoelectric layer and a side surface of the first part facing away from the piezoelectric layer, and the first connecting side wall is inclined relative to the side surface of the first part facing away from the piezoelectric layer.

[0007] Optionally, a plane where a surface of the first portion facing away from the piezoelectric layer is located is a first plane, a first angle α is formed between the first connecting side wall and the first plane, and a tangent value of the first angle α is in a range of [0.35, 12].

[0008] Optionally, a surface of the second portion facing away from the piezoelectric layer has a first height difference relative to a surface of the first portion facing away from the piezoelectric layer, and a value range of the first height difference is [20 nm, 80 nm].

[0009] Optionally, a protective layer is further included, which is located on a side of the interdigital transduction layer away from the piezoelectric layer and covers the interdigital transduction layer and the piezoelectric layer exposed between two adjacent finger electrodes.

[0010] Optionally, the protective layer includes a third portion and a fourth portion connected to each other, the third portion covers the first portion, the fourth portion covers the second portion, and the thickness of the fourth portion is the same as that of the third portion.

[0011] Optionally, in the second direction, the fourth part has a second connecting side wall on a side close to the third part, and the second connecting side wall connects a side surface of the fourth part facing away from the second part and a side surface of the third part facing away from the first part, and the second connecting side wall is inclined relative to a side surface of the third part facing away from the piezoelectric layer.

[0012] Optionally, a plane where a surface of a side of the third portion faces away from the first portion is located is a second plane, a second angle β is formed between the second connecting side wall and the second plane, and a tangent value of the second angle β is in the range of [0.35, 12].

[0013] Optionally, a surface of the fourth portion facing away from the second portion has a second height difference relative to a surface of the third portion facing away from the first portion, and a value range of the second height difference is [5 nm, 20 nm].

[0014] Optionally, the interdigital transduction layer further includes a first bus bar and a second bus bar respectively located on both sides of the finger electrodes in the second direction, the first bus bar and the second bus bar extend along the first direction, and the finger electrodes extend along the second direction. In the first direction, one of two adjacent finger electrodes is connected to the first bus bar, and the other is connected to the second bus bar. There is a second gap between one end of the finger electrode connected to the first bus bar and the second bus bar, and there is a first gap between one end of the finger electrode connected to the second bus bar and the first bus bar.

[0015] Optionally, the finger electrode further includes a connecting portion, wherein the connecting portion connects the second portion of the finger electrode and a corresponding bus bar; The thickness of the connecting portion is the same as that of the second portion, and the thickness of the connecting portion is also the same as that of the connected bus bar.

[0016] Optionally, the protective layer further includes a fifth portion covering the connecting portion, the first bus bar and the second bus bar, and a thickness of the fifth portion is the same as a thickness of the fourth portion.

[0017] Optionally, the protective layer further includes a spacer portion filled in the first space and the second space, and a distance from a surface of the spacer portion facing away from the piezoelectric layer to the piezoelectric layer is smaller than a distance from the fifth portion to the piezoelectric layer.

[0018] Optionally, it includes two third bus bars arranged opposite to each other along the second direction, and the third bus bars extend along the first direction. In the third direction, the projection of one of the two third bus bars overlaps with the projection of the first interval, and the projection of the other overlaps with the projection of the second interval. The third direction is perpendicular to the side surface of the piezoelectric layer facing away from the base layer.

[0019] According to a second aspect of the present application, a method for forming a surface acoustic wave filter includes: forming a piezoelectric substrate, the piezoelectric substrate comprising a base layer and a piezoelectric layer stacked together; An interdigital transduction layer is formed on a surface of the piezoelectric layer facing away from the substrate layer, the interdigital transduction layer includes a plurality of finger electrodes arranged at intervals along a first direction, and the area where each finger electrode overlaps with an adjacent finger electrode in the first direction includes an interdigital region and an inhibition region, the inhibition region is located on both sides of the interdigital region in a second direction, the first direction and the second direction intersect and are both parallel to the surface of the piezoelectric layer facing away from the substrate layer, each finger electrode includes a first portion and a second portion connected to each other, the first portion is located in the interdigital region, the second portion is located in the inhibition region, and the thickness of the second portion is greater than the thickness of the first portion.

[0020] Optionally, it also includes: forming a protective layer on the side of the interdigital transduction layer away from the piezoelectric layer, the protective layer covering the interdigital transduction layer and the piezoelectric layer exposed between two adjacent finger electrodes, the protective layer including a third part and a fourth part connected to each other, the third part covering the first part, the fourth part covering the second part, and the thickness of the fourth part being equal to the thickness of the third part.

[0021] In the surface acoustic wave filter of the embodiment of the present application, in the interdigital transduction layer, the area where each finger electrode overlaps with the adjacent finger electrode in the first direction is the main excitation and conversion area of the acoustic wave. This area includes the interdigital region and the suppression region located on both sides of the interdigital region in the second direction. The thickness of the finger electrodes in the interdigital region is relatively small (i.e., the thickness of the first part is relatively small). Due to the light mass of the finger electrodes, the mass loading effect on the piezoelectric layer is relatively weak, so the local wave velocity in this area is relatively high. In contrast, the thickness of the finger electrodes in the suppression region (the area on both sides of the interdigital region) is relatively large (i.e., the thickness of the second part is relatively large). The thicker finger electrodes increase the local mass loading effect, which reduces the effective elastic wave velocity in this area, so the local wave velocity in this area is relatively low. Because the suppression region has a lower acoustic velocity, the acoustic wave will encounter a low-speed region when propagating in the second direction (transverse direction), forming a boundary condition of wave impedance mismatch, making it difficult for transverse noise modes to maintain or propagate, thereby reducing the impact of transverse noise modes.

[0022] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS To more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0023] In order to more completely understand the present application and its beneficial effects, the following description will be given in conjunction with the accompanying drawings, wherein the same drawing numbers represent the same parts in the following description.

[0024] Figure 1 This is a schematic diagram of a top view of a surface acoustic wave filter provided in an embodiment of the present application. Figure 1 ; Figure 2 This is a surface acoustic wave filter provided by the embodiment of the present application. Figure 1 Cross-sectional view at AA in the middle; Figure 3 yes Figure 2 An enlarged view of position C of the surface acoustic wave filter shown; Figure 4 yes Figure 2 The sound velocity variation diagram of the surface acoustic wave filter shown; Figure 5 This is a schematic diagram of a top view of a surface acoustic wave filter provided in an embodiment of the present application. Figure 2 ; Figure 6 This is a surface acoustic wave filter provided by the embodiment of the present application. Figure 5 Cross-sectional view at DD in the middle; Figure 7 yes Figure 6 The sound velocity variation diagram of the surface acoustic wave filter shown; Figure 8 This is a characteristic diagram showing how the real part of the admittance of the surface acoustic wave filter changes with frequency when the thickness of the first part and the second part are the same; Figure 9 This is a characteristic diagram of the admittance of the surface acoustic wave filter changing with frequency when the thickness of the first part and the second part are the same; Figure 10 The characteristic of the real part of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 1 ; Figure 11 The characteristic of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 1 ; Figure 12 The characteristic of the real part of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 2 ; Figure 13 The characteristic of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 2 ; Figure 14 The characteristic of the real part of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 3 ; Figure 15 The characteristic of the admittance of the surface acoustic wave filter provided by the embodiment of the present application changing with frequency is Figure 3 ; Figure 16 This is a surface acoustic wave filter provided by the embodiment of the present application. Figure 1 Cross-sectional view at the middle BB.

[0025] Description of reference numerals: 100, piezoelectric substrate; 101, base layer; 1011, substrate; 1012, temperature compensation structure; 102, piezoelectric layer; 200, interdigital transduction layer; 201, finger electrode; 2011, first portion; 20121, first connecting sidewall; 2012, second portion; 2013, connecting portion; 202, first bus bar; 203, second bus bar; 204, third bus bar; 300, protective layer; 301, third portion; 302, fourth portion; 3021, second connecting side wall; 303, fifth portion; 304, spacer; 10. Interdigital region; 11. Inhibitory region; 12. First interval; 13. Second interval; 20. First plane; 21. Second plane. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0027] The present invention provides a surface acoustic wave filter. Figure 1 and Figure 2 The surface acoustic wave filter disclosed in the present application includes a piezoelectric substrate 100 and an interdigital transduction layer 200. The piezoelectric substrate 100 includes a base layer 101 and a piezoelectric layer 102 located on the base layer 101. The interdigital transduction layer 200 is located on the surface of the piezoelectric layer 102 on the side away from the base layer 101, and includes a plurality of finger electrodes 201 spaced apart along a first direction. The area where each finger electrode 201 overlaps with the adjacent finger electrode 201 in the first direction includes an interdigital region 10 and an inhibition region 11. The inhibition region 11 is located on both sides of the interdigital region 10 in the second direction. The first and second directions intersect and are both parallel to the surface of the piezoelectric layer 102. Each finger electrode 201 includes a first portion 2011 and a second portion 2012 connected to each other. The first portion 2011 is located in the interdigital region 10, and the second portion 2012 is located in the inhibition region 11. The thickness of the second portion 2012 is greater than that of the first portion 2011.

[0028] In a surface acoustic wave filter, when the acoustic wave excited by the interdigital transduction layer 200 propagates along a first direction (the main propagation direction), some of the energy propagates along a second direction (the transverse direction), forming transverse noise modes. Transverse noise modes disperse the acoustic wave energy, increase insertion loss, and form additional resonance peaks, affecting the frequency selectivity of the surface acoustic wave filter. In the embodiment disclosed in this application, in the interdigital transduction layer 200, the region where each finger electrode 201 overlaps with the adjacent finger electrode 201 in the first direction is the primary excitation and conversion region for the acoustic wave. This region includes the interdigital region 10 and the suppression region 11 located on either side of the interdigital region 10 in the second direction. The finger electrodes 201 in the interdigital region 10 are thinner (i.e., the thickness of the first portion 2011 is thinner). Due to the light mass of the finger electrodes 201, the mass loading effect on the piezoelectric layer 102 is weaker, resulting in a higher local wave velocity in this region. In contrast, the finger electrodes 201 in suppression region 11 (the area on either side of interdigital region 10) are thicker (i.e., the thickness of second portion 2012 is greater). This thicker finger electrode 201 increases the local mass loading effect, reducing the effective elastic wave velocity in this region, resulting in a lower local wave velocity. Because suppression region 11 has a lower acoustic velocity, acoustic waves propagating in the second (lateral) direction encounter low-velocity regions, creating a wave impedance mismatch boundary condition. This makes it difficult for transverse clutter modes to maintain or propagate, thereby reducing their impact.

[0029] In the embodiments disclosed in the present application, the interdigital transduction layer 200 can be a single-layer metal structure or a multi-layer metal structure. Any metal structure of the interdigital transduction layer 200 can be made of a single metal or made of multiple metal doping. When the interdigital transduction layer 200 is a multi-layer metal structure, the materials of the metal structures of each layer can be the same or different. Specific metal materials can be selected from: aluminum (Al), copper (Cu), silver (Ag), gold (Au), tungsten (W), chromium (Cr), titanium (Ti), molybdenum (Mo) or a combination thereof or doped metals. In some embodiments, such as Figure 2The base layer 101 includes a substrate 1011 and a temperature-compensating structure 1012 stacked in sequence. The piezoelectric layer 102 is located on the side of the temperature-compensating structure 1012 facing away from the substrate 1011. The substrate 1011 is typically made of a high-acoustic-velocity material, specifically polycrystalline silicon or single-crystalline silicon. The piezoelectric layer 102 can be made of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). Furthermore, the performance of a surface acoustic wave filter (such as resonant frequency, bandwidth, etc.) typically drifts with temperature. The material of the piezoelectric layer 102 typically has a positive temperature coefficient. By covering the substrate 1011 with a temperature-compensating structure 1012 having a negative temperature coefficient, the effect of temperature changes on the performance of the surface acoustic wave filter can be effectively offset. Specifically, the temperature compensation structure 1012 is usually made of silicon dioxide (SiO2) or tantalum dioxide (Ta2O5). Both silicon dioxide (SiO2) and tantalum dioxide (Ta2O5) have negative temperature coefficients and stable material properties. They can balance the temperature coefficient of the surface acoustic wave filter, thereby stabilizing the performance of the surface acoustic wave filter and maintaining consistent operating characteristics at different temperatures.

[0030] In order to further reduce the interference of the lateral clutter mode on the sound waves in the main propagation direction (first direction), refer to Figure 2 and Figure 3 In the embodiment disclosed in the present application, in the second direction, the side of the second portion 2012 close to the first portion 2011 has a first connecting sidewall 20121. The first connecting sidewall 20121 connects the side surface of the second portion 2012 facing away from the piezoelectric layer 102 and the side surface of the first portion 2011 facing away from the piezoelectric layer 102. The first connecting sidewall 20121 is inclined relative to the side surface of the first portion 2011 facing away from the piezoelectric layer 102. Conventional vertical sidewalls may cause sound waves to reflect at the thickness mutation point, while the inclined setting of the first connecting sidewall 20121 can reduce the reflection and scattering of sound waves between regions of different thicknesses, facilitate the smooth transition of sound waves between the interdigital region 10 and the suppression region 11, reduce discontinuities in the sound wave propagation path, and thus improve the transmission efficiency of the sound waves. At the same time, in the traditional vertical sidewall design, sound waves are prone to form standing waves at the interface, which will enhance the lateral noise mode. The inclined arrangement of the first connecting side wall 20121 can destroy the formation conditions of the standing wave, making it more difficult to maintain the transverse clutter mode, thereby enhancing the suppression effect on the transverse clutter mode.

[0031] In some embodiments, the surface acoustic wave filter further includes a protective layer 300. The protective layer 300 is located on a side of the interdigital transduction layer 200 facing away from the piezoelectric layer 102, covering the interdigital transduction layer 200 and the portion of the piezoelectric layer 102 exposed between two adjacent finger electrodes 201. Specifically, the protective layer 300 may be made of silicon nitride. The protective layer 300 can prevent the interdigital transduction layer 200 from physical damage from the external environment, such as scratches, abrasion, or mechanical impact. Furthermore, the protective layer 300 has sufficient chemical stability to prevent moisture, chemicals, and other corrosive environments from corroding the interdigital transduction layer 200 and the piezoelectric layer 102.

[0032] The protective layer 300 includes a third portion 301 and a fourth portion 302 connected to each other. The third portion 301 covers the first portion 2011, and the fourth portion 302 covers the second portion 2012. The thickness of the fourth portion 302 is the same as that of the third portion 301. The uniform thickness of the protective layer 300 covering the finger electrodes 201 ensures consistent propagation characteristics of sound waves across the entire surface, preventing the speed of sound waves from being affected by thickness differences. This ensures that the speed of sound waves passing through the area where the second portion 2012 is located is lower than the speed of sound waves passing through the area where the first portion 2011 is located.

[0033] Specifically, in the second direction, the side of the fourth portion 302 proximal to the third portion 301 has a second connecting sidewall 3021. The second connecting sidewall 3021 connects a surface of the fourth portion 302 facing away from the second portion 2012 and a surface of the third portion 301 facing away from the first portion 2011. The second connecting sidewall 3021 is inclined relative to a surface of the third portion 301 facing away from the piezoelectric layer 102. The principle of the inclined configuration of the second connecting sidewall 3021 is the same as that of the first connecting sidewall 20121 and will not be repeated here. In some embodiments, the plane on which the surface of the first portion 2011 facing away from the piezoelectric layer 102 lies is the first plane 20. A first angle α is formed between the first connecting sidewall 20121 and the first plane 20, and the tangent of the first angle α is in the range of [0.35, 12]. In some embodiments, the surface of the third portion 301 facing away from the first portion 2011 is located on a second plane 21. A second angle β is formed between the second connecting sidewall 3021 and the second plane 21, and the tangent of the second angle β is in the range of [0.35, 12]. It is worth mentioning that to prevent the protective layer 300 from affecting the change in the speed of sound waves, the first angle α and the second angle β are generally set to the same angle. In some embodiments, the surface of the second portion 2012 facing away from the piezoelectric layer 102 has a first height difference relative to the surface of the first portion 2011 facing away from the piezoelectric layer 102, and the value of the first height difference is in the range of [20nm, 80nm]. In some embodiments, the surface of the fourth portion 302 facing away from the second portion 2012 has a second height difference relative to the surface of the third portion 301 facing away from the first portion 2011, and the value of the second height difference is in the range of [5nm, 20nm].

[0034] Reference Figure 8 and Figure 9 , Figure 8 2 is a characteristic diagram showing how the real part of the admittance of the surface acoustic wave filter changes with frequency when the thickness of the first portion 2011 and the second portion 2012 are the same. Figure 9 The characteristic diagram of the admittance of the surface acoustic wave filter changing with frequency when the thickness of the first part 2011 and the second part 2012 are the same. Figure 8 and Figure 9 The frequency range of the resonance (sound wave propagating in the second direction) is [846MHZ, 869MHZ], and the observation Figure 8 and Figure 9 It can be seen that when the thickness of the first portion 2011 and the second portion 2012 is the same, the real part of the admittance of the surface acoustic wave filter fluctuates greatly with the frequency near the resonant frequency, and the fluctuation of the admittance is also large. Figure 10 and Figure 11 、 Figure 12 and Figure 13 、 Figure 14 and Figure 15 ( Figure 10 、 11 The unit of the horizontal axis frequency of 12, 13, 14, and 15 is HZ). Figure 10 The characteristic diagram of the real part of the admittance of the surface acoustic wave filter with the first angle α being 1.7, the second angle β being 1.7, the first height difference being 80nm, and the second height difference being 10nm, is shown. The characteristic diagram of the admittance of the surface acoustic wave filter with the same structural parameters being shown is shown in FIG. Figure 11 ; Figure 12 The characteristic diagram of the real part of the admittance of the surface acoustic wave filter with the first angle α being 1.5, the second angle β being 1.5, the first height difference being 70nm, and the second height difference being 15nm, is shown. The characteristic diagram of the admittance of the surface acoustic wave filter with the same structural parameters being shown is shown in FIG. Figure 13 ; Figure 14 The characteristic diagram of the real part of the admittance of the surface acoustic wave filter with the first angle α being 1, the second angle β being 1, the first height difference being 65nm, and the second height difference being 20nm, is shown. The characteristic diagram of the admittance of the surface acoustic wave filter with the same structural parameters being shown in FIG. Figure 15 It can be clearly seen that, compared with the surface acoustic wave filter in which the first portion 2011 and the second portion 2012 have the same thickness, the surface acoustic wave filter disclosed in the present application in which the thickness of the first portion 2011 is smaller than that of the second portion 2012 has a smaller fluctuation of the real part of the admittance with frequency near the resonant frequency, a smoother curve of the real part of the admittance with frequency, a smaller fluctuation of the admittance with frequency, and a smoother curve of the admittance with frequency, which can effectively suppress the lateral clutter mode.

[0035] Continue to refer Figure 1 and Figure 2 The interdigitated transduction layer 200 further includes a first bus bar 202 and a second bus bar 203 located on either side of the finger electrode 201 in the second direction. The first bus bar 202 and the second bus bar 203 extend along the first direction, while the finger electrode 201 extends along the second direction. In the first direction, one of two adjacent finger electrodes 201 is connected to the first bus bar 202, and the other is connected to the second bus bar 203. A second gap 13 is formed between the end of the finger electrode 201 connected to the first bus bar 202 that faces away from the first bus bar 202 and the second bus bar 203, and a first gap 12 is formed between the end of the finger electrode 201 connected to the second bus bar 203 that faces away from the second bus bar 203 and the first bus bar 202. Furthermore, the finger electrode 201 further includes a connecting portion 2013, specifically, the connecting portion 2013 connects the second portion 2012 of the finger electrode 201 to the corresponding bus bar. The thickness of the connecting portion 2013 is the same as that of the second portion 2012, and the thickness of the connecting portion 2013 is also the same as that of the connected busbar. The protective layer 300 also includes a fifth portion 303 covering the connecting portion 2013, the first busbar 202, and the second busbar 203, and a spacer portion 304 that fills the first and second gaps 12 and 13. The thickness of the fifth portion 303 is the same as that of the fourth portion 302. The distance from the side of the spacer portion 304 facing away from the piezoelectric layer 102 to the piezoelectric layer 102 is shorter than the distance from the fifth portion 303 to the piezoelectric layer 102. With this arrangement, the speed of sound waves at the first and second gaps 12 and 13 is greater than the speed of sound waves at the first gap 12 on both sides of the second direction, and greater than the speed of sound waves at the second gap 13 on both sides of the second direction. This results in a sound velocity difference interface between the first busbar 202 and the first gap 12, and a sound velocity difference interface between the first gap 12 and the second portion 2012. The sound velocity difference interface will scatter the sound waves. When the sound waves propagate to these sound velocity difference interfaces, part of the energy will be scattered to other directions instead of continuing to propagate in the lateral direction (the second direction), thereby suppressing the formation of lateral clutter patterns. Figure 4 It can be clearly seen that the sound speed of the sound wave at the first interval 12 and the second interval 13 is significantly higher than that at the two sides thereof, and the second portion 2012 located on both sides of the first portion 2011 can effectively reduce the sound speed of the sound wave. Figure 16 It is worth mentioning that the spacer 304 of the protection layer 300 is also filled in the space between two adjacent finger electrodes 201 to cover the exposed piezoelectric layer 102 between the two adjacent finger electrodes 201 .

[0036] Reference Figure 5 and Figure 6In some embodiments, the surface acoustic wave filter further includes two third bus bars 204 arranged opposite to each other along the second direction. The third bus bar 204 extends along the first direction. The third bus bar 204 is located on the side of the interdigital transduction layer 200 facing away from the piezoelectric substrate 100. In the third direction, the projection of one of the two third bus bars 204 overlaps with the projection of the first gap 12, and the projection of the other overlaps with the projection of the second gap 13. The third direction is perpendicular to the surface of the piezoelectric layer 102 facing away from the base layer 101. Specifically, the third bus bar 204 is connected to the spacer portion 304 when it is above the first gap 12 and the second gap 13, and is connected to the side of the connection portion 2013 facing away from the piezoelectric layer 102 when it is above the connection portion 2013. Refer to Figure 7 After the third bus bar 204 is introduced, the sound velocity of the sound wave in the first interval 12 and the second interval 13 will increase, decrease, and then increase again. When the sound wave enters the first interval 12 and the second interval 13, and leaves the first interval 12 and the second interval 13, the increase in sound velocity can change the propagation direction of the sound wave propagating in the second direction, so that the sound wave is more concentrated in the finger electrode 201 area, reducing the leakage of the sound wave in the second direction; the sound velocity is reduced in the first interval 12 and the second interval 13, which can consume the sound wave propagating in the second direction and suppress the propagation of the lateral noise mode. Accordingly, the present invention also provides an embodiment of a method for forming a surface acoustic wave filter. Please refer to Figure 2 , forming a piezoelectric substrate 100, which includes a stacked base layer 101 and a piezoelectric layer 102. The structures, positions, and materials of the piezoelectric substrate 100, base layer 101, and piezoelectric layer 102 have been described in the previous embodiments and will not be repeated here.

[0037] Continue to refer to Figure 2 An interdigital transduction layer 200 is formed on the surface of the piezoelectric layer 102 facing away from the substrate layer 101. The interdigital transduction layer 200 includes a plurality of finger electrodes 201 spaced apart along a first direction. The region where each finger electrode 201 overlaps with an adjacent finger electrode 201 in the first direction includes an interdigital region 10 and an inhibition region 11. The inhibition region 11 is located on either side of the interdigital region 10 in a second direction. The first and second directions intersect and are both parallel to the surface of the piezoelectric layer 102 facing away from the substrate layer 101. Each finger electrode 201 includes a first portion 2011 and a second portion 2012 connected to each other. The first portion 2011 is located in the interdigital region 10, and the second portion 2012 is located in the inhibition region 11. The thickness of the second portion 2012 is greater than that of the first portion 2011. The structure and position of the first portion 2011 and the second portion 2012 have been described in the previous embodiment and will not be repeated here.

[0038] Continue to refer to Figure 2A protective layer 300 is formed on the side of the IDT layer 200 facing away from the piezoelectric layer 102. The protective layer 300 covers the IDT layer 200 and the piezoelectric layer 102 exposed between two adjacent finger electrodes 201. The protective layer 300 includes a third portion 301 and a fourth portion 302 connected to each other. The third portion 301 covers the first portion 2011, and the fourth portion 302 covers the second portion 2012. The thickness of the fourth portion 302 is equal to that of the third portion 301. The structure and position of the third portion 301 and the fourth portion 302 have been described in the previous embodiment and will not be repeated here.

[0039] In some embodiments, the formed interdigital transduction layer 200 further includes a first bus bar 202 and a second bus bar 203, respectively, located on either side of the finger electrode 201 in the second direction. The first bus bar 202 and the second bus bar 203 extend along the first direction, while the finger electrode 201 extends along the second direction. In the first direction, one of two adjacent finger electrodes 201 is connected to the first bus bar 202, and the other is connected to the second bus bar 203. A second gap 13 is formed between the end of the finger electrode 201 connected to the first bus bar 202 that faces away from the first bus bar 202 and the second bus bar 203, and a first gap 12 is formed between the end of the finger electrode 201 connected to the second bus bar 203 that faces away from the second bus bar 203 and the first bus bar 202. Furthermore, the finger electrode 201 further includes a connecting portion 2013, specifically, connecting the second portion 2012 of the finger electrode 201 to the corresponding bus bar. The thickness of the connecting portion 2013 is the same as that of the second portion 2012, and the thickness of the connecting portion 2013 is also the same as that of the connected busbar. Based on this, in some embodiments, the protective layer 300 formed further includes a fifth portion 303 covering the connecting portion 2013, the first busbar 202, and the second busbar 203, and a spacer portion 304 filling the first and second spacers 12 and 13. The thickness of the fifth portion 303 is the same as that of the fourth portion 302. The distance from the surface of the spacer portion 304 facing away from the piezoelectric layer 102 to the piezoelectric layer 102 is less than the distance from the fifth portion 303 to the piezoelectric layer 102.

[0040] Furthermore, in some embodiments, before forming the protective layer 300, the method for forming a surface acoustic wave filter further includes forming two third bus bars 204, disposed opposite each other along a second direction, on a side of the IDT layer 200 facing away from the piezoelectric substrate 100. The third bus bars 204 extend along the first direction. In the third direction, the projection of one of the two third bus bars 204 overlaps with the projection of the first gap 12, and the projection of the other overlaps with the projection of the second gap 13. The third direction is perpendicular to the surface of the piezoelectric layer 102 facing away from the base layer 101. After forming the third bus bars 204, the protective layer 300 is formed, i.e., on the side of the IDT layer 200 facing away from the piezoelectric substrate 100. The formed protective layer 300 wraps around the third bus bars 204.

[0041] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0042] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0043] The embodiments, implementation methods and related technical features of the present application can be combined and replaced with each other without conflict.

[0044] The above are merely preferred embodiments of the present application and do not constitute any form of limitation to the present application. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A surface acoustic wave filter, characterized in that: include: A piezoelectric substrate comprising a base layer and a piezoelectric layer located on the base layer; an interdigital transduction layer, located on a surface of the piezoelectric layer facing away from the substrate layer, comprising a plurality of finger electrodes spaced apart along a first direction, wherein an area where each finger electrode overlaps with an adjacent finger electrode in the first direction comprises an interdigital region and an inhibition region, wherein the inhibition region is located on both sides of the interdigital region in a second direction, and the first direction and the second direction intersect and are both parallel to the surface of the piezoelectric layer; Each of the finger electrodes includes a first portion and a second portion connected to each other, the first portion is located in the interdigital region, the second portion is located in the inhibition region, and the thickness of the second portion is greater than that of the first portion.

2. The surface acoustic wave filter according to claim 1, wherein In the second direction, the second part has a first connecting side wall on a side close to the first part, and the first connecting side wall connects the side surface of the second part facing away from the piezoelectric layer and the side surface of the first part facing away from the piezoelectric layer. The first connecting side wall is inclined relative to the side surface of the first part facing away from the piezoelectric layer.

3. The surface acoustic wave filter according to claim 2, wherein A plane where a surface of the first portion facing away from the piezoelectric layer is located is a first plane, a first angle α is formed between the first connecting side wall and the first plane, and a tangent value of the first angle α is in a range of [0.35, 12].

4. The surface acoustic wave filter according to claim 1, wherein A surface of the second portion facing away from the piezoelectric layer has a first height difference relative to a surface of the first portion facing away from the piezoelectric layer, and a value range of the first height difference is [20 nm, 80 nm].

5. The surface acoustic wave filter according to claim 1, wherein The device further comprises a protective layer, which is located on a side of the interdigital transduction layer away from the piezoelectric layer and covers the interdigital transduction layer and the piezoelectric layer exposed between two adjacent finger electrodes.

6. The surface acoustic wave filter according to claim 5, wherein The protective layer includes a third portion and a fourth portion connected to each other, the third portion covers the first portion, the fourth portion covers the second portion, and a thickness of the fourth portion is the same as a thickness of the third portion.

7. The surface acoustic wave filter according to claim 6, wherein In the second direction, the fourth part has a second connecting side wall on the side close to the third part, and the second connecting side wall connects the side surface of the fourth part facing away from the second part and the side surface of the third part facing away from the first part. The second connecting side wall is inclined relative to the side surface of the third part facing away from the piezoelectric layer.

8. The surface acoustic wave filter according to claim 7, wherein A plane where a surface of a side of the third portion facing away from the first portion lies is a second plane, a second angle β is formed between the second connecting side wall and the second plane, and a tangent value of the second angle β is in a range of [0.35, 12].

9. The surface acoustic wave filter according to claim 6, wherein A surface of the fourth portion facing away from the second portion has a second height difference relative to a surface of the third portion facing away from the first portion, and a value range of the second height difference is [5 nm, 20 nm].

10. The surface acoustic wave filter according to claim 6, wherein The interdigital transduction layer further includes a first bus bar and a second bus bar respectively located on both sides of the finger electrodes in the second direction, the first bus bar and the second bus bar extending along the first direction, and the finger electrodes extending along the second direction. In the first direction, one of two adjacent finger electrodes is connected to the first bus bar, and the other is connected to the second bus bar; There is a second gap between one end of the finger electrode connected to the first bus bar and the second bus bar, and there is a first gap between one end of the finger electrode connected to the second bus bar and the first bus bar.

11. The surface acoustic wave filter according to claim 10, wherein The finger electrode further includes a connecting portion, the connecting portion connecting the second portion of the finger electrode and the corresponding bus bar; The thickness of the connecting portion is the same as that of the second portion, and the thickness of the connecting portion is also the same as that of the connected bus bar.

12. The surface acoustic wave filter according to claim 11, wherein The protective layer further includes a fifth portion covering the connecting portion, the first bus bar, and the second bus bar, and a thickness of the fifth portion is the same as a thickness of the fourth portion.

13. The surface acoustic wave filter according to claim 12, wherein The protection layer further includes a spacer portion filled in the first space and the second space, and a distance from a surface of the spacer portion facing away from the piezoelectric layer to the piezoelectric layer is smaller than a distance from the fifth portion to the piezoelectric layer.

14. The surface acoustic wave filter according to claim 12, wherein It includes two third bus bars arranged opposite to each other along a second direction, and the third bus bars extend along the first direction. In the third direction, the projection of one of the two third bus bars overlaps with the projection of the first interval, and the projection of the other overlaps with the projection of the second interval. The third direction is perpendicular to the side surface of the piezoelectric layer facing away from the base layer.

15. A method for forming a surface acoustic wave filter, characterized in that: include: forming a piezoelectric substrate, the piezoelectric substrate comprising a base layer and a piezoelectric layer stacked together; An interdigital transduction layer is formed on a surface of the piezoelectric layer facing away from the substrate layer, the interdigital transduction layer includes a plurality of finger electrodes arranged at intervals along a first direction, and the area where each finger electrode overlaps with an adjacent finger electrode in the first direction includes an interdigital region and an inhibition region, the inhibition region is located on both sides of the interdigital region in a second direction, the first direction and the second direction intersect and are both parallel to the surface of the piezoelectric layer facing away from the substrate layer, each finger electrode includes a first portion and a second portion connected to each other, the first portion is located in the interdigital region, the second portion is located in the inhibition region, and the thickness of the second portion is greater than the thickness of the first portion.

16. The method for forming a surface acoustic wave filter according to claim 15, wherein: Also includes: A protective layer is formed on the side of the interdigital transduction layer facing away from the piezoelectric layer, the protective layer covers the interdigital transduction layer and the piezoelectric layer exposed between two adjacent finger electrodes, the protective layer includes a third portion and a fourth portion connected to each other, the third portion covers the first portion, the fourth portion covers the second portion, and the thickness of the fourth portion is equal to the thickness of the third portion.

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