A high-performance, low-insertion-loss filter and its design method

Abstract

This disclosure provides a high-performance, low-insertion-loss filter and its design method, belonging to the field of resonator and filter technology. The filter includes at least one series resonator and at least one parallel resonator; reflective structures are disposed on both sides of the interdigital transducer and at the tips of multiple interdigital strips. The type of reflective structure is determined based on the impedance response characteristics of the series and parallel resonators. In series or parallel resonators with stray modes, the reflective structure is an embedded reflective grating in the piezoelectric layer or a convex reflective grating on the piezoelectric layer, used to selectively suppress the leakage of acoustic wave energy in the main resonant mode. In series or parallel resonators without stray modes, the reflective structure is a reflective groove disposed in and penetrating the piezoelectric layer, used to suppress the leakage of acoustic wave energy. This disclosure can reduce the probability of generating large in-band ripple while reducing passband insertion loss, thereby improving filter performance.

Description

Technical Field

[0001] This disclosure relates to the field of resonator and filter technology, and in particular to a high-performance, low-insertion-loss filter and its design method. Background Technology

[0002] 5G communication technology has gradually matured and become commercialized. With the explosive growth of mobile data traffic, the demand for future 6G communication technology is becoming increasingly strong. This requires the core radio frequency (RF) front-end module to have superior performance. Among these components, the RF filter is the most critical component determining the bandwidth of wireless communication. Bulk acoustic wave resonators (BARs) have become the best choice for implementing 5G RF filters due to their unique characteristics such as high frequency and miniaturization.

[0003] In related technologies, the leakage of acoustic wave energy is suppressed by setting identical reflective grooves penetrating the piezoelectric layer on both sides of the interdigital transducer in a series-parallel resonator, thereby improving the quality factor (Q) of the resonator and reducing the passband insertion loss of the filter.

[0004] However, the reflective groove penetrating the piezoelectric layer, as a total reflection boundary, does not selectively suppress the leakage of acoustic energy. When there are stray modes in the series-parallel resonators, the reflective groove will suppress the leakage of acoustic energy of both the main resonant mode and the stray mode. That is, it will enhance the stray mode while enhancing the main resonant mode, resulting in a large in-band ripple in the passband of the filter and degrading the filter performance. Summary of the Invention

[0005] This disclosure provides a high-performance, low-insertion-loss filter and its design method, which can reduce passband insertion loss while decreasing the probability of generating large in-band ripple, thereby improving filter performance. The technical solution includes at least the following:

[0006] On one hand, a filter is provided, including at least one series resonator and at least one parallel resonator. Both the series and parallel resonators include a support structure, a piezoelectric layer, an interdigital transducer, and a reflective structure. The support structure has a cavity. The piezoelectric layer is disposed on the support structure and covers the cavity. The interdigital transducer is disposed on the piezoelectric layer and includes multiple interdigital strips located in the region of the cavity. The reflective structure is disposed on both sides of the interdigital transducer and at the tips of the multiple interdigital strips. The type of reflection structure is determined based on the impedance response characteristics of the series resonator and the parallel resonator. In the series resonator or the parallel resonator with stray modes, the reflection structure is an embedded reflection grating in the piezoelectric layer or a convex reflection grating on the piezoelectric layer, used to selectively suppress the leakage of acoustic wave energy of the main resonant mode. In the series resonator or the parallel resonator without stray modes, the reflection structure is a reflection groove in the piezoelectric layer and penetrating the piezoelectric layer, used to suppress the leakage of acoustic wave energy.

[0007] Optionally, the material of the embedded reflective grating is different from the material of the piezoelectric layer. The material of the embedded reflective grating includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, air, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride.

[0008] Optionally, the material of the convex reflective grating includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride.

[0009] Optionally, the interdigitated strip is provided with at least one scattering hole, which is filled with a scattering medium to suppress the formation of standing waves in the region where the interdigitated transducer is located.

[0010] Optionally, the interdigitated strip is provided with a plurality of scattering holes, which are arranged along the length direction of the interdigitated strip and are located in the area where the plurality of interdigitated strips intersect and overlap.

[0011] Optionally, the interdigital transducer includes a first electrode layer and a second electrode layer stacked sequentially in a direction away from the piezoelectric layer, the scattering hole is located in the first electrode layer and penetrates the first electrode layer, the second electrode layer also serves as the scattering medium filling the scattering hole, and the acoustic impedance of the first electrode layer is different from that of the second electrode layer.

[0012] Optionally, the material of the first electrode layer includes at least one of Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag, and the material of the second electrode layer includes at least one of Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag.

[0013] Optionally, the material of the piezoelectric layer includes at least one of AlN, ScAlN, PMN-PT, ZnO, LiNbO3, LiTaO3, PZT, and PVDF.

[0014] Optionally, the series resonator and the parallel resonator further include a ground electrode, which is disposed on the piezoelectric layer and located on both sides of the interdigital transducer.

[0015] On the other hand, a filter design method is provided, the filter including at least one series resonator and at least one parallel resonator. Both the series and parallel resonators include a support structure, a piezoelectric layer, an interdigital transducer, and a reflective structure. The support structure has a cavity, the piezoelectric layer is disposed on the support structure and covers the cavity, the interdigital transducer is disposed on the piezoelectric layer, and the interdigital transducer includes multiple interdigital strips located in the region of the cavity. The reflective structure is disposed on both sides of the interdigital transducer and at the tips of the multiple interdigital strips. The design method includes: determining the type of the reflection structure based on the impedance response characteristics of the series resonator and the parallel resonator; in the series resonator or the parallel resonator with stray modes, the reflection structure is an embedded reflection grating in the piezoelectric layer or a convex reflection grating on the piezoelectric layer, used to selectively suppress the leakage of acoustic energy of the main resonant mode; in the series resonator or the parallel resonator without stray modes, the reflection structure is a reflection groove in the piezoelectric layer and penetrating the piezoelectric layer, used to suppress the leakage of acoustic energy.

[0016] The beneficial effects of the technical solutions provided in this disclosure include at least the following:

[0017] In this embodiment, by setting reflection structures on both sides of the interdigital transducer and at the tips of multiple interdigital strips, the probability of acoustic energy leakage from the sides of the interdigital transducer or the tips of the interdigital strips can be effectively reduced, and the acoustic energy can be better confined in the area where multiple interdigital strips intersect and overlap, thereby effectively reducing the passband insertion loss of the filter. The type of reflection structure is determined according to the impedance response characteristics of the series resonator and the parallel resonator. In the series resonator or the parallel resonator with stray modes, the reflection structure is an embedded reflection grating embedded in the piezoelectric layer or a convex reflection grating disposed on the piezoelectric layer. As one-dimensional phononic crystals, the embedded reflection grating and the convex reflection grating can control the position of the bandgap by adjusting the structural size, selectively suppressing the leakage of acoustic energy of the main resonant mode, while allowing the acoustic energy of the stray mode to leak out, thus enhancing only the main resonant mode without enhancing the stray mode. In spurious-mode-free series or parallel resonators, the reflection structure is a reflective groove disposed within and extending through the piezoelectric layer. This reflective groove suppresses acoustic energy leakage, and since there are no spurious modes, it does not amplify them. This reduces passband insertion loss while decreasing the probability of generating significant in-band ripple, thereby improving filter performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a filter provided in an embodiment of this disclosure;

[0020] Figure 2 This is a partial structural schematic diagram of a resonator provided in an embodiment of this disclosure;

[0021] Figure 3 This is a partial structural schematic diagram of another resonator provided in an embodiment of this disclosure;

[0022] Figure 4 This is a partial structural schematic diagram of another resonator provided in the embodiments of this disclosure;

[0023] Figure 5 This is a simulation diagram of a filter provided in an embodiment of this disclosure;

[0024] Figure 6 This is a simulation diagram of an embedded reflective grating provided in an embodiment of this disclosure;

[0025] Figure 7These are simulation effect comparison diagrams of an embedded reflective grating provided in the embodiments of this disclosure;

[0026] Figure 8 This is a schematic diagram of another filter structure provided in an embodiment of this disclosure;

[0027] Figure 9 This is a schematic diagram of the structure of another filter provided in this embodiment;

[0028] Figure 10 This is a schematic diagram of the structure of another filter provided in this embodiment;

[0029] Figure 11 This is a schematic diagram of the filter fabrication process in Example 1;

[0030] Figure 12 This is a schematic diagram of the filter fabrication process in Example 2;

[0031] Figure 13 This is a schematic diagram of the filter fabrication process in Example 3;

[0032] Figure 14 This is a schematic diagram of the filter fabrication process in Example 4.

[0033] Figure label:

[0034] 1: Series resonator; 2: Parallel resonator; 10: Support structure; 101: Cavity; 11: Substrate; 12: Dielectric layer; 20: Piezoelectric layer; 201: Groove; 30: Interdigital transducer; 31: Interdigital strip; 311: Scattering aperture; 32: First electrode layer; 33: Second electrode layer; 40: Reflection structure; 41: Embedded reflective grating; 42: Convex reflective grating; 43: Reflective groove; 50: Ground electrode. Detailed Implementation

[0035] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the element or object preceding “comprising” or “including” encompasses the element or object listed following “comprising” or “including” and its equivalents, and do not exclude other elements or objects. The terms “connected” or “linked” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. “Up,” “down,” “left,” “right,” etc., are used only to indicate relative positional relationships, which may change accordingly when the absolute position of the described object changes. A and / or B indicates the presence of three cases: A, B, and A and B.

[0036] To make the objectives, technical solutions, and advantages of this disclosure clearer, the embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0037] Example 1:

[0038] Figure 1 This is a schematic diagram of the structure of a filter provided in an embodiment of this disclosure. Figure 1 The diagram shows a top view of the filter and a schematic cross-sectional view at section line AA. Figure 1 As shown, the filter includes at least one series resonator 1 and at least one parallel resonator 2. Both the series resonator 1 and the parallel resonator 2 include a support structure 10, a piezoelectric layer 20, an interdigital transducer 30, and a reflection structure 40.

[0039] The support structure 10 has a cavity 101. A piezoelectric layer 20 is disposed on the support structure 10 and covers the cavity 101. An interdigital transducer 30 is disposed on the piezoelectric layer 20, and the interdigital transducer 30 includes multiple interdigital strips 31 located in the region where the cavity 101 is located. A reflection structure 40 is disposed on both sides of the interdigital transducer 30 and at the tips of the multiple interdigital strips 31. The type of the reflection structure 40 is determined according to the impedance response characteristics of the series resonator 1 and the parallel resonator 2.

[0040] Figure 2 This is a partial structural schematic diagram of a resonator provided in an embodiment of this disclosure. Figure 2 A partial top view of a resonator and a schematic diagram of the cross-sectional structure at section lines BB and CC are shown. Figure 3This is a partial structural schematic diagram of another resonator provided in an embodiment of this disclosure. Figure 3 A partial top view of another resonator and a schematic diagram of the cross-sectional structure at section line BB are shown. Figure 4 This is a partial structural schematic diagram of another resonator provided in the embodiments of this disclosure. Figure 4 A partial top view of another type of resonator and a schematic diagram of its cross-sectional structure at section line BB are shown. See also Figures 1 to 4 In the series resonator 1 or parallel resonator 2 with stray modes, the reflection structure 40 is an embedded reflection grating 41 embedded in the piezoelectric layer 20 or a convex reflection grating 42 disposed on the piezoelectric layer 20, used to selectively suppress the leakage of acoustic wave energy of the main resonant mode. In the series resonator 1 or parallel resonator 2 without stray modes, the reflection structure 40 is a reflection groove 43 disposed in the piezoelectric layer 20 and penetrating the piezoelectric layer 20, used to suppress the leakage of acoustic wave energy.

[0041] In this embodiment, by providing reflection structures 40 on both sides of the interdigital transducer 30 and at the fingertips of the multiple interdigital strips 31, the probability of acoustic energy leakage from the sides of the interdigital transducer 30 or the fingertips of the interdigital strips 31 can be effectively reduced, and the acoustic energy can be better confined in the area where the multiple interdigital strips 31 intersect and overlap, thereby effectively reducing the passband insertion loss of the filter. The type of reflection structure 40 is determined according to the impedance response characteristics of the series resonator 1 and the parallel resonator 2. In the series resonator 1 or the parallel resonator 2 with stray modes, the reflection structure 40 is an embedded reflection grating 41 embedded in the piezoelectric layer 20 or a convex reflection grating 42 disposed on the piezoelectric layer 20. As one-dimensional phononic crystals, the embedded reflection grating 41 and the convex reflection grating 42 can control the position of the bandgap by adjusting the structural size, selectively suppressing the leakage of acoustic energy of the main resonant mode, while allowing the acoustic energy of the stray mode to leak out, thus enhancing only the main resonant mode without enhancing the stray mode. In the spurious-mode-free series resonator 1 or parallel resonator 2, the reflection structure 40 is a reflection groove 43 disposed in and penetrating the piezoelectric layer 20. The reflection groove 43 can suppress the leakage of acoustic wave energy. Since there are no spurious modes, the reflection groove 43 will not enhance spurious modes either. In this way, the probability of generating large in-band ripple can be reduced while reducing passband insertion loss, thereby improving the performance of the filter.

[0042] Furthermore, the embedded reflective grating 41 and convex reflective grating 42, which selectively suppress the leakage of acoustic wave energy in the main resonant mode, generally require high manufacturing precision and are therefore costly. In contrast, the reflective groove 43, serving as the boundary of total reflection, does not exhibit selectivity in suppressing acoustic wave energy leakage, thus requiring lower manufacturing precision and being less expensive. Therefore, determining the type of the reflective structure 40 as an embedded reflective grating 41, a convex reflective grating 42, or a reflective groove 43 based on the impedance response characteristics of the series resonator 1 and the parallel resonator 2 can reduce the passband insertion loss of the filter, improve its performance, and ensure lower manufacturing costs.

[0043] It should be noted that simulations can be performed in advance to determine the impedance response characteristics of series and parallel resonators, i.e., whether stray modes exist, based on the simulation results, and then the type of reflection structure can be determined.

[0044] The principles of reflective grooves, embedded reflective gratings, and convex reflective gratings are explained below. When setting a reflective groove, the sound wave reflection coefficient can be calculated according to the following formulas (1) to (3):

[0045] (1)

[0046] (2)

[0047] (3)

[0048] Among them, Z Air ρ represents the acoustic impedance of air. Air E represents the density of air. Air Z represents the Young's modulus of air. Pie ρ represents the acoustic impedance of the piezoelectric layer. Pie E represents the density of the piezoelectric layer. Pie R represents the Young's modulus of the piezoelectric layer, and R is the acoustic reflection coefficient.

[0049] According to the formulas (1) to (3) above, the acoustic impedance of air is close to 0 and can be ignored. Therefore, the sound wave reflection coefficient is 1. When the sound wave propagates from the piezoelectric layer into the air of the reflector, the sound wave is totally reflected and the energy is effectively confined. It is independent of the frequency. The reflector does not have selectivity in suppressing the leakage of sound wave energy.

[0050] Embedded and convex reflective gratings, as one-dimensional phononic crystals, form acoustic band gaps through periodically arranged structural units, effectively suppressing the propagation of sound waves within a specific frequency range. This band gap characteristic originates from Bragg scattering or local resonance mechanisms. Bragg scattering type: When the wavelength of the sound wave is close to the lattice constant, the scattering effect of the periodic structure leads to the superposition of sound wave reflections, forming a band gap. Local resonance type: Through the resonance characteristics of a single scatterer coupled with the matrix, band gaps can be generated at lower frequency bands (such as the 100 Hz level).

[0051] Figure 5 This is a simulation diagram of a filter provided in an embodiment of this disclosure. Figure 5 As shown, the impedance response characteristics of series resonators and parallel resonators in a filter can be determined in advance based on COMSOL three-dimensional finite element simulation. Figure 5 Parts (a) and (b) represent the impedance response characteristics of the parallel resonator and series resonator in the filter, respectively. Figure 5 As shown in part (a), the admittance curve of the parallel resonator exhibits a significant peak at approximately 4.8 GHz and a significant trough at approximately 5.35 GHz. These peaks and troughs directly reflect the frequencies of the primary resonant mode. Additionally, at the elliptical dashed box near approximately 5.6 GHz, there are smaller peaks and troughs, indicating the presence of stray modes in the parallel resonator. If the reflective structure is set to a reflective groove, it will simultaneously suppress the leakage of acoustic energy from both the primary resonant mode and the stray mode, resulting in significant in-band ripple within the filter's passband. Therefore, the reflective structure can be configured as an embedded reflective grating or a convex reflective grating to selectively suppress the leakage of acoustic energy from the primary resonant mode. Figure 5 As shown in part (b), the admittance curve of the series resonator has a significant peak at a frequency of approximately 5.48 GHz and a significant trough at a frequency of approximately 6.07 GHz. These peaks and troughs directly reflect the frequency of the main resonant mode. Furthermore, there are no additional significant peaks or troughs in other parts of the admittance curve, which means that there are no stray modes in the series resonator. Therefore, the reflection structure can be set as a non-selective reflection groove, which can suppress the leakage of acoustic energy while ensuring low manufacturing costs.

[0052] like Figure 1 As shown, in this embodiment, the reflection structure 40 in the series resonator 1 is a reflection groove 43, and the reflection structure 40 in the parallel resonator 2 is an embedded reflection grating 41.

[0053] Figure 6 This is a simulation diagram of an embedded reflective grating provided in an embodiment of this disclosure. Figure 6As shown, the width and depth of the embedded reflector grating can be designed using COMSOL 3D finite element simulation software to adjust the bandgap width. The overall dimensions of the embedded reflector grating can be designed to adjust the position of the bandgap, ensuring that the dominant resonant mode is within the bandgap range while stray modes remain outside it. This selectively suppresses the leakage of acoustic energy from the dominant resonant mode, allowing the stray mode's energy to leak out, thus enhancing only the dominant resonant mode without enhancing stray modes. Here, the smaller the structural unit size of the embedded reflector grating, the higher the frequency of the bandgap.

[0054] Figure 6 In this design, by adjusting the structural dimensions of the embedded reflector grating, it can be made to exhibit distinct bandgap characteristics. Specifically, the first bandgap is from 5.8933 GHz to 6.0950 GHz, the second bandgap is from 5.2473 GHz to 5.5266 GHz, and the third bandgap is from 4.4874 GHz to 4.8225 GHz. This allows for... Figure 5 In part (a), the main resonant modes are located within the second and third band gaps, while the stray modes are located outside the band gap range.

[0055] In other embodiments, when the reflective structure is selected to be a convex reflective grating, the width and height of the convex reflective grating can be designed to adjust the width of the bandgap, and the overall size of the convex reflective grating can be designed to adjust the position of the bandgap, so as to selectively suppress the leakage of acoustic energy of the main resonant mode, while allowing the acoustic energy of the stray mode to leak out, thus enhancing only the main resonant mode and not the stray mode.

[0056] like Figure 1 As shown, optionally, the support structure 10 includes a substrate 11 and a dielectric layer 12 stacked sequentially along the direction close to the piezoelectric layer 20, and the cavity 101 penetrates the substrate 11 and the dielectric layer 12.

[0057] Alternatively, the substrate 11 may be made of silicon.

[0058] Alternatively, the dielectric layer 12 may be made of silicon dioxide.

[0059] It should be noted that the materials of substrate 11 and dielectric layer 12 are only examples. In other embodiments, the materials of substrate 11 and dielectric layer 12 can be adjusted according to actual needs, and this disclosure does not limit them.

[0060] For example, in the series resonator 1, the piezoelectric layer 20 has a groove 201 located in the region where the cavity 101 is located, the interdigital strip 31 of the interdigital transducer 30 is located in the groove 201, and the reflective structure 40 disposed on both sides of the interdigital transducer 30 is located on both sides of the groove 201 and in the region where the cavity 101 is located.

[0061] In this embodiment, the series resonator 1 and the parallel resonator 2 are arranged from right to left, and the groove 201 is disposed in the series resonator 1 on the right side.

[0062] Optionally, the material of the piezoelectric layer 20 includes at least one selected from AlN, ScAlN, lead magnesium niobate-lead titanate (PMN-PT), ZnO, LiNbO3, LiTaO3, lead zirconate titanate (PZT), and polyvinylidene fluoride (PVDF). This ensures that the piezoelectric properties of the piezoelectric layer 20 are good. For example, the material of the piezoelectric layer 20 can be one of AlN, ScAlN, LiNbO3, or PZT, or the material of the piezoelectric layer 20 can include sequentially stacked AlN and ScAlN layers, etc. In other embodiments, the material of the piezoelectric layer 20 can also be other piezoelectric materials as needed, and this disclosure does not limit this.

[0063] For example, the piezoelectric layer 20 can be X-cut, Y-cut, or Z-cut, or the material orientation obtained by rotating different Euler angles.

[0064] For example, the shape of the piezoelectric layer 20 can be a polygon such as a quadrilateral, pentagon, or hexagon, or a curved surface such as a circle or ellipse, or an irregular shape.

[0065] For example, the interdigital transducer also includes a busbar connected to a plurality of interdigital bars 31.

[0066] For example, both the interdigitated bar 31 and the busbar can be rectangular. In other embodiments, the interdigitated bar 31 and the busbar can also be trapezoidal or other polygonal or irregular shapes. For example, both the interdigitated bar 31 and the busbar can be rectangular, with the length direction of the interdigitated bar 31 perpendicular to the length direction of the busbar.

[0067] See Figures 1 to 3 Optionally, at least one scattering hole 311 is provided in the interdigital strip 31, and the scattering hole 311 is filled with a scattering medium to suppress the formation of standing waves in the region where the interdigital transducer 30 is located. By providing the scattering hole 311 and the scattering medium, the transverse higher-order modes propagating in the region where the interdigital transducer 30 is located can be suppressed. The transverse higher-order spurious modes formed by the coherence of standing waves in the region where the interdigital transducer 30 is located can be suppressed by scattering destruction, which is beneficial to improving the performance of the filter.

[0068] Optionally, the interdigitated strip 31 is provided with a plurality of scattering holes 311, which are arranged along the length of the interdigitated strip 31 and located in the area where the interdigitated strip 31 intersects and overlaps. This can further effectively suppress the formation of standing waves.

[0069] For example, the scattering aperture 311 is a circular aperture. In other embodiments, the shape of the scattering aperture 311 can also be adjusted according to actual needs. For example, the scattering aperture 311 can also be an elliptical aperture or a polygonal aperture, etc., and this disclosure does not limit it.

[0070] Optionally, the interdigital transducer 30 includes a first electrode layer 32 and a second electrode layer 33 stacked sequentially in a direction away from the piezoelectric layer 20. A scattering aperture 311 is located in and penetrates the first electrode layer 32. The second electrode layer 33 also serves as a scattering medium filling the scattering aperture 311. The acoustic impedance of the first electrode layer 32 is different from that of the second electrode layer 33. By forming a scattering structure consisting of a scattering aperture 311 and a scattering medium through the first electrode layer 32 and the second electrode layer 33, the formation of standing waves can be suppressed, and the fabrication process can be simplified, reducing costs.

[0071] Optionally, the first electrode layer 32 and the second electrode layer 33 are made of metallic materials. Exemplarily, the material of the first electrode layer 32 includes at least one selected from Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag, and the material of the second electrode layer 33 includes at least one selected from Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag. The materials of the first electrode layer 32 and the second electrode layer 33 are different. For example, the material of the first electrode layer 32 can be Mo, and the material of the second electrode layer 33 can be Au.

[0072] Optionally, the reflective groove 43 is rectangular or rounded rectangular in shape. In other embodiments, the shape of the reflective groove 43 can also be adjusted according to actual needs, and this disclosure does not limit it.

[0073] For example, the reflective groove 43 is a rounded rectangular strip. Reflective grooves 43 are provided on both sides of the arrangement direction of the multiple interdigital strips 31 of the interdigital transducer 30 and at the fingertips of the multiple interdigital strips 31. The length direction of the reflective grooves 43 located on both sides of the arrangement direction of the multiple interdigital strips 31 is parallel to the length direction of the interdigital strips 31, while the length direction of the reflective grooves 43 located at the fingertips of the multiple interdigital strips 31 is perpendicular to the length direction of the interdigital strips 31. The reflective grooves 43 located on both sides of the arrangement direction of the multiple interdigital strips 31 and the reflective groove 43 located at the fingertips of the outermost interdigital strip 31 can communicate with each other.

[0074] Optionally, the embedded reflective grating 41 is rectangular in shape. In other embodiments, the shape of the embedded reflective grating 41 can also be adjusted according to actual needs, and this disclosure does not limit it.

[0075] For example, the embedded reflective grating 41 is rectangular in shape, embedded in the piezoelectric layer 20 but not penetrating the piezoelectric layer 20. Embedded reflective gratings 41 are provided on both sides of the arrangement direction of the multiple interdigital strips 31 of the interdigital transducer 30 and at the finger tips of the multiple interdigital strips 31. Each embedded reflective grating 41 includes two or three rectangular structural units arranged periodically. The length direction of the embedded reflective gratings 41 located on both sides of the arrangement direction of the multiple interdigital strips 31 is parallel to the length direction of the interdigital strips 31, and the length direction of the embedded reflective gratings 41 located at the finger tips of the multiple interdigital strips 31 is perpendicular to the length direction of the interdigital strips 31.

[0076] Optionally, the material of the embedded reflective grating 41 is different from that of the piezoelectric layer 20. The material of the embedded reflective grating 41 includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, air, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride. Choosing a material with a significantly different acoustic impedance from that of the piezoelectric layer 20 for the embedded reflective grating 41 ensures a better selective suppression of acoustic wave energy leakage in the main resonant mode.

[0077] For example, the material of the embedded reflective grating 41 can be air. That is, the embedded reflective grating 41 can be formed by directly creating periodically arranged reflective grating grooves that do not penetrate the piezoelectric layer 20 in the piezoelectric layer, so that air serves as the reflective medium. In other embodiments, the material of the embedded reflective grating 41 can also be adjusted according to actual needs. For example, reflective media such as gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, silicon dioxide, aluminum oxide, aluminum nitride, or scandium-doped aluminum nitride can be embedded in the piezoelectric layer 20 to form the embedded reflective grating 41. This disclosure does not limit this.

[0078] like Figure 1 As shown, optionally, the series resonator 1 and the parallel resonator 2 also include a ground electrode 50, which is disposed on the piezoelectric layer 20 and located on both sides of the interdigital transducer 30. The ground electrode 50 is located outside the reflective structure 40. The use of the ground electrode 50 helps to reduce test errors.

[0079] For example, the ground electrode 50 may be in the shape of a bracket with a notch facing the interdigital transducer 30.

[0080] For example, the ground electrode 50 is co-layered with the interdigital transducer 30. Here, co-layered means formed by the same patterning process, or in contact with the same surface of the same film layer. This simplifies the fabrication process and reduces fabrication costs. For example, the ground electrode 50 may also include a first electrode layer 32 and a second electrode layer 33 sequentially stacked in a direction away from the piezoelectric layer 20.

[0081] The following is a comparative explanation of the effects of embedded reflective gratings. Figure 7 This is a comparison diagram of the simulation effect of an embedded reflective grating provided in the embodiments of this disclosure. Figure 7 Part (a) shows the simulation effect of the embedded reflective grating. Figure 7 Part (b) shows the partial three-dimensional structure of the embedded reflective grating at the dashed box in part (a). Figure 7 Section (c) shows the simulation effect without the embedded reflector grating. Figure 7 In the process, the embedded reflective grating 41 is made of air, with a width W of 0.7 μm and a depth H of 0.28 μm, as shown below. Figure 7 As shown, in the resonator with embedded reflector grating 41, the acoustic wave energy is significantly confined within the region between the embedded reflector gratings 41 within the reflection bandgap range, with an amplitude of 1.64 × 10⁻⁶. -12 μm to 7.28×10 -6 Between μm, in a resonator without an embedded reflector grating 41, acoustic energy leaks to various regions, with amplitudes between 3.48 × 10⁻⁶. -10 μm to 6.19×10 -6 Between μm. That is, the embedded reflective grating 41 can effectively suppress the leakage of acoustic wave energy in the main resonant mode.

[0082] Example 2:

[0083] Figure 8 This is a schematic diagram of another filter structure provided in an embodiment of this disclosure. Figure 8 The diagram shows a top view of the filter and a schematic cross-sectional view at section line AA. Figure 8 As shown, the only difference between this embodiment and Embodiment 1 is the type of the reflective structure 40.

[0084] In this embodiment, the series resonator 1 and the parallel resonator 2 are arranged from right to left, and the groove 201 is disposed in the series resonator 1 on the right side. The reflection structure 40 in the series resonator 1 is a reflection groove 43, and the reflection structure 40 in the parallel resonator 2 is a convex reflection grating 42.

[0085] See Figure 4 and Figure 8 Optionally, the convex reflective grating 42 is rectangular in shape. In other embodiments, the shape of the convex reflective grating 42 can also be adjusted according to actual needs, and this disclosure does not impose any limitations on it.

[0086] For example, the convex reflective grating 42 is rectangular in shape and protrudes from the piezoelectric layer 20. Convex reflective gratings 42 are provided on both sides of the arrangement direction of the multiple interdigital strips 31 of the interdigital transducer 30 and at the finger tips of the multiple interdigital strips 31. Each convex reflective grating 42 includes two or three rectangular structural units arranged periodically. The length direction of the convex reflective gratings 42 located on both sides of the arrangement direction of the multiple interdigital strips 31 is parallel to the length direction of the interdigital strips 31, and the length direction of the convex reflective gratings 42 located at the finger tips of the multiple interdigital strips 31 is perpendicular to the length direction of the interdigital strips 31.

[0087] Optionally, the material of the convex reflector grating 42 includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride. This ensures that the convex reflector grating 42 effectively suppresses the leakage of acoustic wave energy in the main resonant mode.

[0088] In other embodiments, the material of the convex reflective grating 42 may also be adjusted according to actual needs, and this disclosure does not limit it.

[0089] For example, the convex reflective gate 42 is co-layered with the first electrode layer 32. This allows for the simultaneous fabrication of the first electrode layer 32 and the convex reflective gate 42, simplifying the fabrication process and reducing costs. For instance, the material of the convex reflective gate 42 can be Mo.

[0090] Example 3:

[0091] Figure 9 This is a schematic diagram of the structure of another filter provided in an embodiment of this disclosure. Figure 9 The diagram shows a top view of the filter and a schematic cross-sectional view at section line AA. Figure 9 As shown, the only difference between this embodiment and embodiment 1 is the arrangement of the series resonator 1 and the parallel resonator 2 and the type of the reflection structure 40.

[0092] In this embodiment, the series resonator 1 and the parallel resonator 2 are arranged from left to right, and the groove 201 is disposed in the series resonator 1 on the left side. The reflection structure 40 in the series resonator 1 is a convex reflection grating 42, and the reflection structure 40 in the parallel resonator 2 is a reflection groove 43.

[0093] Example 4:

[0094] Figure 10 This is a schematic diagram of the structure of another filter provided in an embodiment of this disclosure. Figure 10 The diagram shows a top view of the filter and a schematic cross-sectional view at section line AA. Figure 10As shown, the only difference between this embodiment and embodiment 1 is the arrangement of the series resonator 1 and the parallel resonator 2 and the type of the reflection structure 40.

[0095] In this embodiment, the series resonator 1 and the parallel resonator 2 are arranged from left to right, and the groove 201 is disposed in the series resonator 1 on the left side. The reflection structure 40 in the series resonator 1 is an embedded reflection grating 41, and the reflection structure 40 in the parallel resonator 2 is a reflection groove 43.

[0096] This disclosure also provides a filter design method. The filter includes at least one series resonator and at least one parallel resonator. Both the series and parallel resonators include a support structure, a piezoelectric layer, an interdigital transducer, and a reflective structure. The support structure has a cavity. The piezoelectric layer is disposed on the support structure and covers the cavity. The interdigital transducer is disposed on the piezoelectric layer and includes multiple interdigital strips located in the region where the cavity is located. The reflective structure is disposed on both sides of the interdigital transducer and at the tips of the multiple interdigital strips. The design method includes:

[0097] The type of reflection structure is determined based on the impedance response characteristics of series and parallel resonators. In series or parallel resonators with stray modes, the reflection structure is an embedded reflection grating in the piezoelectric layer or a convex reflection grating on the piezoelectric layer, used to selectively suppress the leakage of acoustic energy in the main resonant mode. In series or parallel resonators without stray modes, the reflection structure is a reflection groove in the piezoelectric layer that penetrates the piezoelectric layer, used to suppress the leakage of acoustic energy.

[0098] It should be noted that the design method embodiments are based on the same inventive concept as the above embodiments 1 to 4. The beneficial effects of the embodiments disclosed herein can be found in the above embodiments 1 to 4, and will not be repeated here.

[0099] Optionally, after determining that the reflective structure is an embedded reflective grating disposed in the piezoelectric layer or a convex reflective grating disposed on the piezoelectric layer, the design method may further include the following steps:

[0100] The structural dimensions of the embedded or convex reflector grating are determined based on the impedance response characteristics. The bandgap width is adjusted by designing the width and depth of the embedded reflector grating or the width and height of the convex reflector grating. The position of the bandgap is adjusted by designing the overall dimensions of the embedded or convex reflector grating, ensuring that the dominant resonant mode is within the bandgap range while stray modes are outside it. This achieves selective suppression of acoustic energy leakage from the dominant resonant mode, while allowing stray mode acoustic energy to leak out, thus enhancing only the dominant resonant mode without enhancing stray modes. The design process can be found in the previous section. Figure 5 and Figure 6Related embodiments are omitted in detail here.

[0101] Figure 11 This is a schematic diagram of the filter fabrication process in Example 1. See also... Figure 1 and Figure 11 Optionally, the method for fabricating the filter includes the following steps:

[0102] The first step is to form a piezoelectric layer on the support structure without a cavity.

[0103] For example, a piezoelectric material can be deposited on a support structure without a cavity first, and then the piezoelectric material can be etched to form a piezoelectric layer 20 with grooves 201.

[0104] The second step is to form the first electrode layer on the piezoelectric layer.

[0105] For example, the first electrode layer 32 can be formed on the piezoelectric layer 20 by deposition and photolithography lift-off processes.

[0106] The third step is to form a reflective structure.

[0107] For example, the piezoelectric layer 20 can be etched to form a reflective groove 43 and an embedded reflective grating 41 with air as the reflective medium, respectively, to obtain a reflective structure 40.

[0108] It should be noted that since the reflective groove 43 penetrates the piezoelectric layer 20, while the embedded reflective gate 41 does not penetrate the piezoelectric layer 20, that is, the etching depths of the reflective groove 43 and the embedded reflective gate 41 are different. Therefore, the reflective groove 43 and the embedded reflective gate 41 can be formed by two-step etching.

[0109] The fourth step is to form a second electrode layer on the first electrode layer to obtain an interdigital transducer and a ground electrode.

[0110] For example, a second electrode layer 33 can be formed on the first electrode layer 32 by deposition and photolithography lift-off processes to obtain an interdigital transducer 30 and a ground electrode 50.

[0111] The fifth step is to form a cavity.

[0112] For example, the surface of the support structure away from the piezoelectric layer 20 without a cavity can be etched to form a cavity 101, thereby obtaining a support structure 10 with a cavity 101.

[0113] Figure 12 This is a schematic diagram of the filter fabrication process in Example 2. See also... Figure 8 and Figure 12 Optionally, the method for fabricating the filter includes the following steps:

[0114] The first step is to form a piezoelectric layer on the support structure without a cavity.

[0115] For example, a piezoelectric material can be deposited on a support structure without a cavity first, and then the piezoelectric material can be etched to form a piezoelectric layer 20 with grooves 201.

[0116] The second step is to form the first electrode layer on the piezoelectric layer.

[0117] For example, the first electrode layer 32 can be formed on the piezoelectric layer 20 by deposition and photolithography lift-off processes.

[0118] The third step is to form a reflective structure.

[0119] For example, the piezoelectric layer 20 can be etched to form a reflective groove 43, and a convex reflective gate 42 can be formed on the piezoelectric layer 20 by deposition and photolithography lift-off processes to obtain a reflective structure 40.

[0120] It should be noted that when the convex reflective gate 42 is made of the same material as the first electrode layer 32, the first electrode layer 32 and the convex reflective gate 42 can also be formed in the second step by the same deposition and photolithography lift-off process.

[0121] The fourth step is to form a second electrode layer on the first electrode layer to obtain an interdigital transducer and a ground electrode.

[0122] For example, a second electrode layer 33 can be formed on the first electrode layer 32 by deposition and photolithography lift-off processes to obtain an interdigital transducer 30 and a ground electrode 50.

[0123] The fifth step is to form a cavity.

[0124] For example, the surface of the support structure away from the piezoelectric layer 20 without a cavity can be etched to form a cavity 101, thereby obtaining a support structure 10 with a cavity 101.

[0125] Figure 13 This is a schematic diagram of the filter fabrication process in Example 3. See also... Figure 9 and Figure 13 Optionally, the method for fabricating the filter includes the following steps:

[0126] The first step is to form a piezoelectric layer on the support structure without a cavity.

[0127] For example, a piezoelectric material can be deposited on a support structure without a cavity first, and then the piezoelectric material can be etched to form a piezoelectric layer 20 with grooves 201.

[0128] The second step is to form the first electrode layer on the piezoelectric layer.

[0129] For example, the first electrode layer 32 can be formed on the piezoelectric layer 20 by deposition and photolithography lift-off processes.

[0130] The third step is to form a reflective structure.

[0131] For example, the piezoelectric layer 20 can be etched to form a reflective groove 43, and a convex reflective gate 42 can be formed on the piezoelectric layer 20 through deposition and photolithography lift-off processes to obtain a reflective structure 40. When the convex reflective gate 42 is made of the same material as the first electrode layer 32, the first electrode layer 32 and the convex reflective gate 42 can also be formed in the second step through the same deposition and photolithography lift-off processes.

[0132] The fourth step is to form a second electrode layer on the first electrode layer to obtain an interdigital transducer and a ground electrode.

[0133] For example, a second electrode layer 33 can be formed on the first electrode layer 32 by deposition and photolithography lift-off processes to obtain an interdigital transducer 30 and a ground electrode 50.

[0134] The fifth step is to form a cavity.

[0135] For example, the surface of the support structure away from the piezoelectric layer 20 without a cavity can be etched to form a cavity 101, thereby obtaining a support structure 10 with a cavity 101.

[0136] Figure 14 This is a schematic diagram of the filter fabrication process in Example 4. See also... Figure 10 and Figure 14 Optionally, the method for fabricating the filter includes the following steps:

[0137] The first step is to form a piezoelectric layer on the support structure without a cavity.

[0138] For example, a piezoelectric material can be deposited on a support structure without a cavity first, and then the piezoelectric material can be etched to form a piezoelectric layer 20 with grooves 201.

[0139] The second step is to form the first electrode layer on the piezoelectric layer.

[0140] For example, the first electrode layer 32 can be formed on the piezoelectric layer 20 by deposition and photolithography lift-off processes.

[0141] The third step is to form a reflective structure.

[0142] For example, the piezoelectric layer 20 can be etched to form a reflective groove 43 and an embedded reflective grating 41 with air as the reflective medium, respectively, to obtain a reflective structure 40. The reflective groove 43 and the embedded reflective grating 41 can be formed by two etching steps.

[0143] The fourth step is to form a second electrode layer on the first electrode layer to obtain an interdigital transducer and a ground electrode.

[0144] For example, a second electrode layer 33 can be formed on the first electrode layer 32 by deposition and photolithography lift-off processes to obtain an interdigital transducer 30 and a ground electrode 50.

[0145] The fifth step is to form a cavity.

[0146] For example, the surface of the support structure away from the piezoelectric layer 20 without a cavity can be etched to form a cavity 101, thereby obtaining a support structure 10 with a cavity 101.

[0147] It should be noted that in the above preparation method embodiments, the markings of each film material are only for indication. Figure 1 , Figure 8 , Figure 9 or Figure 10 The corresponding film structure states during the fabrication process, and the structure, shape, material, and positional relationships of each film layer in the final filter can be found in [reference needed]. Figure 1 , Figure 8 , Figure 9 or Figure 10 Detailed descriptions of related structural embodiments are omitted here.

[0148] The above description is merely an optional embodiment of this disclosure and is not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A filter, characterized in that, It includes at least one series resonator and at least one parallel resonator, each of which includes a support structure, a piezoelectric layer, an interdigital transducer, and a reflective structure; The supporting structure has a cavity; The piezoelectric layer is disposed on the support structure and covers the cavity; The interdigital transducer is disposed on the piezoelectric layer, and the interdigital transducer includes a busbar and multiple interdigital bars located in the region where the cavity is located; The reflective structure is disposed on both sides of the arrangement direction of the plurality of interdigitated bars and in the region between the busbar and the fingertips of the plurality of interdigitated bars. The type of the reflective structure is determined according to the impedance response characteristics of the series resonator and the parallel resonator. In the series resonator or the parallel resonator with stray modes, the reflective structure is an embedded reflective grating embedded in the piezoelectric layer or a convex reflective grating disposed on the piezoelectric layer, used to selectively suppress the leakage of acoustic wave energy of the main resonant mode. In the series resonator or the parallel resonator without stray modes, the reflective structure is a reflective groove disposed in the piezoelectric layer and penetrating the piezoelectric layer, used to suppress the leakage of acoustic wave energy.

2. The filter according to claim 1, characterized in that, The material of the embedded reflective grating is different from the material of the piezoelectric layer. The material of the embedded reflective grating includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, air, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride.

3. The filter according to claim 1, characterized in that, The material of the convex reflective grating includes at least one of gold, copper, silver, aluminum, titanium, tungsten, chromium, molybdenum, platinum, graphene, diamond, silicon carbide, silicon dioxide, aluminum oxide, aluminum nitride, and scandium-doped aluminum nitride.

4. The filter according to any one of claims 1 to 3, characterized in that, At least one scattering hole is provided in the interdigital strip, and the scattering hole is filled with a scattering medium to suppress the formation of standing waves in the region where the interdigital transducer is located.

5. The filter according to claim 4, characterized in that, The interdigitated strip is provided with a plurality of scattering holes, which are arranged along the length of the interdigitated strip and are located in the area where the plurality of interdigitated strips intersect and overlap.

6. The filter according to claim 4, characterized in that, The interdigital transducer includes a first electrode layer and a second electrode layer stacked sequentially in a direction away from the piezoelectric layer. The scattering aperture is located in the first electrode layer and penetrates the first electrode layer. The second electrode layer also serves as the scattering medium and fills the scattering aperture. The acoustic impedance of the first electrode layer is different from that of the second electrode layer.

7. The filter according to claim 6, characterized in that, The material of the first electrode layer includes at least one of Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag, and the material of the second electrode layer includes at least one of Mo, Al, Cu, Au, Ti, Cr, W, In, and Ag.

8. The filter according to any one of claims 1 to 3, characterized in that, The material of the piezoelectric layer includes at least one of AlN, ScAlN, PMN-PT, ZnO, LiNbO3, LiTaO3, PZT, and PVDF.

9. The filter according to any one of claims 1 to 3, characterized in that, The series resonator and the parallel resonator also include ground electrodes, which are disposed on the piezoelectric layer and located on both sides of the interdigital transducer.

10. A filter design method, characterized in that, The filter includes at least one series resonator and at least one parallel resonator. Both the series and parallel resonators include a support structure, a piezoelectric layer, an interdigital transducer, and a reflective structure. The support structure has a cavity. The piezoelectric layer is disposed on the support structure and covers the cavity. The interdigital transducer is disposed on the piezoelectric layer and includes a busbar and multiple interdigital strips located in the region of the cavity. The reflective structure is disposed on both sides of the arrangement direction of the multiple interdigital strips and in the region between the busbar and the fingertips of the multiple interdigital strips. The design method includes: The type of the reflection structure is determined based on the impedance response characteristics of the series resonator and the parallel resonator. In the series resonator or the parallel resonator with stray modes, the reflection structure is an embedded reflection grating in the piezoelectric layer or a convex reflection grating on the piezoelectric layer, used to selectively suppress the leakage of acoustic wave energy of the main resonant mode. In the series resonator or the parallel resonator without stray modes, the reflection structure is a reflection groove in the piezoelectric layer and penetrating the piezoelectric layer, used to suppress the leakage of acoustic wave energy.

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