Staggered thickness type surface acoustic wave resonator, filter and manufacturing method thereof

Abstract

The invention discloses a staggered thickness type surface acoustic wave resonator, a filter and a manufacturing method thereof, and relates to the technical field of resonators / filters, the resonator comprises a substrate, a first electrode finger film layer and a second electrode finger film layer, the first electrode finger film layer is arranged on the substrate, one part of the second electrode finger film layer is arranged on the substrate, and the other part of the second electrode finger film layer is arranged on the substrate. The other part covers the first electrode finger film layer to form an overlapping area, and the first electrode finger film layer, the second electrode finger film layer and the overlapping area form a grid structure with the thickness changing in a staggered mode; according to the resonator, the filter and the manufacturing method thereof, the formed staggered grid structure forms different sound velocity regions between the interdigital electrode region and the bus bar, the propagation of a transverse mode is influenced, the transverse mode suppression effect is improved, the structure avoids the problem of large impedance caused by a thin metal film layer, and the performance of the resonator is improved. And a device with high resonant frequency has normal performance.

Description

Technical Field

[0001] The present invention relates to the technical field of resonators / filters, and particularly to an interleaved thickness surface acoustic wave resonator, filter and manufacturing method thereof. Background Art

[0002] Surface Acoustic Wave (SAW) filters are widely used in the field of radio frequency communication due to their small size and suitability for mass production. And as the application scenarios of communication systems become more and more complex, the industry has gradually adopted SAW filters with composite film substrates (bonded substrates / multilayer thin film substrates) and LiNbO3 piezoelectric thin films to meet the market demands of high Q, high isolation, low loss performance, and high temperature stability.

[0003] However, products realized based on the manufacturing technology of composite film substrates and LiNbO3 piezoelectric thin films will result in serious transverse mode ripples. These transverse modes will generate spurious responses, increase the insertion loss of SAW resonators / filters, cause fluctuations in the passband, reduce the device sensitivity, and have a greater impact on the device performance. Therefore, transverse mode suppression is a pain point in the industry and an urgent problem to be solved.

[0004] In the comparison form of products under the existing technology, the transverse mode appears in the curve graph between the resonant frequency and the anti-resonant frequency, as Figure 18 shown. Disadvantages: For SAW surface acoustic wave products of products realized based on the manufacturing technology of composite film substrates and LiNbO3 piezoelectric thin films in semiconductor processes, there will be strong transverse mode ripples ( Figure 18 R1 - R6 in the figure) when the acoustic wave propagates in a typical interdigital structure, resulting in unevenness in the filter passband, unstable performance, and large fluctuations in insertion loss.

[0005] According to the resonator performance curve graph of the existing double-layer film suppression structure at high frequencies as Figure 19 shown, disadvantages: The thickness of the metal film layer is related to the resonant frequency of the device. When the resonant frequency of the device is at high frequencies, the required metal film layer becomes significantly thinner, resulting in a relatively large impedance of the film layer. Compared with the operation at medium and low frequencies, it not only fails to achieve the effect of transverse mode suppression but also causes a significant decline in device performance. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes an interleaved thickness surface acoustic wave resonator, filter and manufacturing method thereof, which suppresses the propagation of transverse modes, not only improves the suppression effect of transverse mode ripples of the surface acoustic wave resonator, but also solves the problem of relatively large impedance caused by the thin thickness at high frequencies in the multilayer film structure.

[0007] An interleaved thickness type surface acoustic wave resonator proposed by the present invention includes a substrate, a first electrode finger film layer, and a second electrode finger film layer. The first electrode finger film layer is disposed on the substrate. A part of the second electrode finger film layer is disposed on the substrate, and the other part covers the first electrode finger film layer to form an overlapping region. The first electrode finger film layer, the second electrode finger film layer, and the overlapping region form a grid structure with interleaved thickness changes, and different sound velocity regions are formed between the interdigital electrode region and the bus bar by the grid structure.

[0008] Further, the thickness of the first electrode finger film layer is less than that of the second electrode finger film layer.

[0009] Further, the thickness of the first electrode finger film layer is 2%λ - 4%λ, and the thickness of the second electrode finger film layer is 5%λ - 12%λ.

[0010] Further, in the different sound velocity regions formed by the grid structure, the sound velocity decreases as the film layer thickness increases.

[0011] Further, the surface of the resonator is divided into multiple regions according to different functions: functional region A is the bus bar, functional region B is the interleaved sound velocity region, functional region C is the transverse connection region, functional region D is the double-layer film region, and functional region E is the interdigital electrode region, where functional regions A, B, and C together form the grid structure.

[0012] Further, in functional region B, the first electrode finger film layer and the overlapping region are interleaved.

[0013] Further, the grid structure has interleaved thickness changes in the finger bar direction to form different sound velocity regions.

[0014] Further, the grid structure has interleaved thickness changes in the direction perpendicular to the finger bar to form different sound velocity regions.

[0015] An interleaved thickness type filter includes a housing and a resonator disposed in the housing, and the resonator is the resonator described above.

[0016] Further, it includes the following steps:

[0017] On the selected substrate, the first electrode finger film layer is formed by photolithography, evaporation, degluing / etching or photolithography, degluing, evaporation, and stripping, and the thickness of the first electrode finger film layer is 2%λ - 4%λ;

[0018] On the substrate on which the first electrode finger film layer has been formed, the second electrode finger film layer is formed by photolithography, evaporation, degluing / etching or photolithography, degluing, evaporation, and stripping, and the thickness of the second electrode finger film layer is 5%λ - 12%λ.

[0019] The advantages of an interleaved thickness type surface acoustic wave resonator, filter and manufacturing method thereof provided by the present invention are as follows: The formed interleaved grid structure forms different sound velocity regions between the interdigital electrode region and the bus bar, which affects the propagation of the transverse mode and thus improves the effect of transverse mode suppression. And this structure avoids the problem of too large impedance caused by the thin metal film layer, enabling the device with a resonant frequency in the high frequency range to have normal performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of the present invention;

[0021] Figure 2 is a schematic structural diagram of the first electrode finger film layer

[0022] Figure 3 is a schematic structural diagram of the second electrode finger film layer;

[0023] Figure 4 is a schematic structural diagram formed by covering the second electrode finger film layer on the substrate and the first electrode finger film layer;

[0024] Figure 5 is Figure 1 a schematic diagram of different sound velocity regions formed by various film thicknesses along the finger bar direction in

[0025] Figure 6 is Figure 1 a schematic diagram of a grid structure with alternating thickness formed on the substrate in the direction perpendicular to the finger bar in

[0026] Figure 7 is a schematic structural diagram of a multi-layer thin film substrate;

[0027] Figure 8 is a schematic structural diagram of a bonded substrate;

[0028] Figure 9 is a schematic structural diagram of a LiNbO3 piezoelectric substrate;

[0029] Figure 10 is a real part curve graph of the admittance characteristics of three structures at medium frequency in a comparison example of simulation results of a resonator with the prior art and the structure of the present invention;

[0030] Figure 11 is a graph of the admittance characteristics of three structures at high frequency in a comparison example of simulation results of a resonator with the prior art and the structure of the present invention;

[0031] Figure 12 is the first type of Figure 1 schematic diagram of a film layer scheme with alternating film thickness changes in the transverse or longitudinal direction formed in a

[0032] Figure 13For the second type of similarity Figure 1 Schematic diagram of a film layer solution with an alternating film thickness change in the horizontal or vertical direction

[0033] Figure 14 For the third type of similarity Figure 1 Schematic diagram of a film layer solution with an alternating film thickness change in the horizontal or vertical direction

[0034] Figure 15 For the fourth type of similarity Figure 1 Schematic diagram of a film layer solution with an alternating film thickness change in the horizontal or vertical direction

[0035] Figure 16 For the fifth type of similarity Figure 1 Schematic diagram of a film layer solution with an alternating film thickness change in the horizontal or vertical direction

[0036] Figure 17 For the sixth type of similarity Figure 1 Schematic diagram of a film layer solution with an alternating film thickness change in the horizontal or vertical direction

[0037] Figure 18 In the comparison form of the product under the existing technology, the curve graph where the horizontal mode appears between the resonance frequency and the anti-resonance frequency

[0038] Figure 19 Resonator performance curve graph of the existing double-layer film suppression structure at high frequencies

[0039] Among them, 1. Substrate, 2. First electrode finger film layer, 3. Second electrode finger film layer, 4. Substrate, 5. High-resistance film, 6. Bonding material layer, 7. Piezoelectric layer, 8. LiNbO3 piezoelectric layer, 2 - 3. Overlap region Specific implementation mode

[0040] Next, the technical solution of the present invention will be described in detail through specific embodiments. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below

[0041] Such as Figures 1 to 19As shown in the figure, a staggered-thickness surface acoustic wave resonator proposed by the present invention includes a substrate 1, a first electrode finger film layer 2, and a second electrode finger film layer 3. The first electrode finger film layer 2 is disposed on the substrate 1. A part of the second electrode finger film layer 3 is disposed on the substrate 1, and the other part covers the first electrode finger film layer 2 to form an overlapping region 2-3. The first electrode finger film layer 2, the second electrode finger film layer 3, and the overlapping region 2-3 form a grid structure with staggered thickness changes. The grid structure forms different sound velocity regions between the interdigital electrode region and the bus bar.

[0042] Based on the prior art, in this embodiment, a first metal film layer is first evaporated on the substrate to form a grid structure on the substrate 1, and then a second metal film layer 3 is evaporated on the substrate 1 and the first metal layer 2. Finally, a grid structure with staggered thickness changes is formed on the substrate 1. This staggered grid structure forms different sound velocity regions between the interdigital electrode region and the bus bar, affecting the propagation of the transverse mode and thus improving the effect of transverse mode suppression. And this structure avoids the problem of too large impedance caused by thin metal film layers, enabling devices with high resonant frequencies to have normal performance.

[0043] In this embodiment, according to the formula for the propagation velocity of the medium v = λ×f0, that is, the wave velocity is equal to the product of the wavelength and the vibration frequency. It can be seen that for the sound wave propagating in a piezoelectric crystal with a specified tangential direction (the same tangential direction, the same propagation velocity), at different device operating frequencies, the wavelength will be different due to different frequencies. And the design of the filter device is different according to different operating frequency requirements, using different λ. Therefore, the material parameters in this embodiment are all in a proportional relationship with λ, that is, in an inverse proportional relationship with the operating frequency.

[0044] To more conveniently understand the resonator of this embodiment, the surface of the resonator is divided into multiple regions according to different functions: functional region A is the bus bar, functional region B is the staggered sound velocity region, functional region C is the transverse connection region, functional region D is the double-layer film region, and functional region E is the interdigital electrode region. Among them, functional regions A, B, and C together form the grid structure.

[0045] Functional region A is the bus bar, which is respectively connected to two signal ports; functional region E is the interdigital electrode region, including a plurality of electrode fingers, which extend in a comb shape from the transverse connection region towards each other. For the specific division of functional regions A and E, reference can be made to Patent CN117713738 A (Resonator, Filter, and Forming Method with the Function of Suppressing Hybrid Mode Ripples).

[0046] Functional region B is the staggered sonic velocity region: It is the part connecting the bus bar and the lateral connection region. Among them, the grid corresponding to the end of the finger bar in the overlapping region 2-3 has the thickness of the first electrode finger film layer, and the grid corresponding to the virtual finger film of the first electrode finger film layer is in the overlapping region 2-3 (i.e., thick-thin & thin-thick). Its main function is to adjust the sonic velocity and suppress the propagation of the lateral hybrid mode in the direction of the finger bar;

[0047] Functional region C is the lateral connection region: It is used to connect the finger bar and the grid structure;

[0048] Functional region D is the double-layer film region: It includes the virtual finger film, the end of the directly connected finger bar, and the front end of the adjacent finger bar. The thickness of the virtual finger film is the thickness of the first electrode finger film layer, the thickness of the end of the directly connected finger bar is the overlapping region 2-3, and the thickness of the front end of the adjacent finger bar is the thickness of the second electrode finger film layer. Its main function is to adjust the sonic velocity and suppress the propagation of the lateral hybrid mode in the direction of the finger bar.

[0049] The grid structure of this embodiment has the following structural characteristics (a1) to (a3):

[0050] (a1) The thickness changes staggered in the direction of the finger bar, forming different sonic velocity regions, effectively restricting the surface acoustic wave energy in the interdigital electrode region of functional region E and suppressing the propagation of the lateral mode in the direction of the finger bar;

[0051] (a2) The thickness also changes staggered in the direction perpendicular to the finger bar, forming different sonic velocity regions, reducing the leakage of the lateral mode energy in the bus bar region and further suppressing the energy loss caused by the cross-mode propagation;

[0052] (a3) Functional region B also connects the finger bar and the bus bar region through a thicker metal film layer (i.e., the overlapping region 2-3), avoiding the problem of too large impedance due to too thin bottom metal in the double-layer film structure at high frequencies and reducing the insertion loss.

[0053] It should be noted that the thickness of the first electrode finger film layer is 2%λ to 4%λ, the thickness of the second electrode finger film layer is 5%λ to 12%λ, and the thickness of the second electrode finger film layer is greater than that of the first electrode finger film layer.

[0054] In this embodiment, the substrate is preferably a composite substrate and a LiNbO3 piezoelectric substrate. Among them, the composite substrate is preferably a bonded substrate and a multi-layer thin film substrate. The composite substrate is preferably a bonded substrate and a multi-layer thin film substrate, as Figures 7 to 9 shown. As in Figure 7In the multi-layer thin film substrate, it includes a substrate 4, a high-resistance film 5, a bonding material layer 6, and a piezoelectric layer 7. The high-resistance film 5 is preferably polycrystalline silicon (Poly-Si) with a thickness of (100 nm to 1000 nm); the bonding material layer 6 is preferably SiO2 with a thickness of (0.2λ to 0.6λ, 100 nm to 4500 nm); the substrate 4 is preferably high-resistance silicon (Si) with a resistivity of 100 Ω·cm or more, more preferably 1000 Ω·cm or more, and further preferably 4000 Ω·cm or more. The preferred crystal phase is (001) / (100) / (010), the preferred crystal plane is (100) / (110) / (111), and the thickness is greater than 100 μm; the elastic wave propagation direction ψ of the piezoelectric layer 7 is defined by the Euler angles (Φ, θ, ψ) of the piezoelectric single crystal, preferably (35 - 60)-degree Y-X cut LiTaO3, and the thickness is preferably (0.2λ to 0.5λ, 100 nm to 4000 nm).

[0055] As shown Figure 8 in the figure, the bonded substrate is composed of the substrate 4 and the piezoelectric layer 7. As shown Figure 9 in the figure, in the LiNbO3 piezoelectric substrate, the substrate 1 includes a LiNbO3 piezoelectric layer 8. In the LiNbO3 piezoelectric substrate as shown Figure 9 like this, the cutting angle of LiNbO3 in the Euler angle expression is a piezoelectric material with θ = 38 ± 10°; or a piezoelectric material with θ = -85 ± 15°; or θ = 131 ± 15° or a piezoelectric material with θ = -90 ± 10°, ψ = -90 ± 10°, and the thickness is greater than 100 μm.

[0056] As an example:

[0057] The electrode finger crossing width of the IDT electrode: 20λ, where λ is the wavelength determined by the electrode finger spacing, λ = 1.5 μm;

[0058] The duty cycle η in the IDT electrode = 0.4;

[0059] The film thickness of the first electrode finger: 2%λ;

[0060] The film thickness of the second electrode finger: 10%λ;

[0061] Substrate: Composite substrate

[0062] The film thickness of the LiTaO3 film: 0.3λ;

[0063] Piezoelectric thin film: A Y-X cut LiTaO3 film with a cutting angle of 42° and a thickness of 430 nm;

[0064] The film thickness of the SiO2 film that constitutes the bonding material layer: 400 nm;

[0065] The thickness of the high-resistance film Poly-Si layer is 1000 nm;

[0066] The thickness of the high-resistance silicon (Si) is 500 um.

[0067] The implementation steps of the technical solution based on the above design parameters are as follows:

[0068] S1. On the selected substrate 1, form the first electrode finger film layer 2 through photolithography, evaporation, resist stripping / etching or photolithography, resist stripping, evaporation, and lift-off. The thickness of the first electrode finger film layer 2 is 2%λ - 4%λ, as Figure 2 shown;

[0069] S2. On the substrate 1 after forming the first electrode finger film layer 2, form the second electrode finger film layer 3 through photolithography, evaporation, resist stripping / etching or photolithography, resist stripping, evaporation, and lift-off. Part of the second electrode finger film layer 3 will directly cover the substrate 1, and the other part will cover the first electrode finger film layer 2. The top view of the morphology of the second electrode finger film layer 3 is as Figure 3 shown, and the top view of the morphology of the second electrode finger film layer 3 covering the substrate and the first electrode finger film layer is as Figure 4 shown.

[0070] After the first electrode finger film layer 2 and the second electrode finger film layer 3 are formed, there are three film thicknesses in the metal film layer on the substrate 1, namely the first electrode finger film thickness, the second electrode finger film thickness, and the overlapping area 2 - 3 formed by the superposition of the first electrode finger and the second electrode finger, as Figure 5 shown in the cross-sectional view. The design of multiple film thicknesses along the finger bar direction forms different sound velocity regions. The position with a thicker film thickness has a lower sound velocity, and the position with a thinner film thickness has a higher sound velocity. The multiple sound velocity regions suppress the propagation of the transverse mode along the finger bar direction and reduce the influence of the transverse mode on the device performance.

[0071] In the functional area B, perpendicular to the finger bar direction, a grid structure with alternating thicknesses is formed on the substrate, as Figure 6 shown. The alternating grid structure forms different sound velocity regions perpendicular to the finger bar direction, further reducing the energy leakage caused by the transverse mode.

[0072] Finally, this grid structure also makes the metal connection between the finger bar region and the bus bar region thicker. Compared with the existing double-layer film or similar structures where the connection region is too thin at high frequencies, resulting in a large impedance, this structure ensures the reliability and low loss of the connection.

[0073] This embodiment provides a method for enhancing the suppression effect of the lateral mode ripple of surface acoustic waves and solving the problem of large impedance caused by the thin thickness of the multi-layer film structure at high frequencies, which is applicable to SAW resonator / filter devices TFSAW / TCSAW. At the same time, this embodiment is applicable to a variety of substrates, including but not limited to: composite substrates and LiNbO3 piezoelectric substrates, where the composite substrate is preferably a bonded substrate and a multi-layer thin film substrate.

[0074] In addition, this embodiment proposes a grid structure with staggered thicknesses. This grid structure is formed by making a first electrode finger film layer 2 on the substrate 1 and then making a second electrode finger film layer 3 covering the substrate or the first electrode finger film layer 2. On this basis, more electrode finger film layers can be added, such as Figures 12 to 17 shown, not limited to the double-layer film structure described above in this embodiment, but this embodiment preferably uses a double-layer film structure.

[0075] It should be understood that the specific construction process of the grid structure is not limited to the method described above, and the overlapping area is not limited to the positional relationship described above. A film layer scheme with lateral or longitudinal alternating film thickness changes formed in other similar forms is essentially the same. Such as Figures 12 to 17 ; only through experiments, it is shown that the grid structure set above is the optimal scheme.

[0076] In order to verify that the resonator of this embodiment has the effect of suppressing the lateral mode ripple, such as Figure 10 and 11 are comparison examples of the simulation results of the resonator of the prior art and the structure of this embodiment, where Figure 10 is the real part curve of the admittance characteristic at medium frequency, Figure 11 are the admittance characteristic curves of the three structures at high frequencies. The red solid line is the transverse mode suppression structure, the blue dashed line is the structure of this embodiment, and the green dotted line is the existing double-layer film suppression structure. From Figure 10 it can be clearly seen that both the structure of this embodiment and the existing double-layer film structure can effectively suppress the lateral mode, and the lateral mode ripple after suppression by the structure of this embodiment is smoother, that is, the suppression effect of the transverse mode is better; from Figure 11 it can be clearly seen that due to the thin film thickness at high frequencies, the impedance of the thin layer metal in the double-layer film is too large, seriously affecting the performance of the device itself and causing the admittance curve to collapse. In contrast, the device performance of the structure of this embodiment is still normal and has a good transverse mode suppression effect, indicating the effectiveness of the structure of this embodiment in the transverse mode suppression function.

[0077] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. An interleaved thickness type surface acoustic wave resonator, characterized in that, It includes a substrate (1), a first electrode finger film layer (2), and a second electrode finger film layer (3). The first electrode finger film layer (2) is disposed on the substrate (1). A part of the second electrode finger film layer (3) is disposed on the substrate (1), and the other part covers the first electrode finger film layer (2) to form an overlapping region (2-3). The first electrode finger film layer (2), the second electrode finger film layer (3), and the overlapping region (2-3) form a grid structure with staggered thickness changes, and different sound velocity regions are formed between the interdigital electrode region and the bus bar by the grid structure.

2. The interleaved thickness type surface acoustic wave resonator according to claim 1, wherein The thickness of the first electrode finger film layer (2) is less than that of the second electrode finger film layer (3).

3. The interleaved thickness type surface acoustic wave resonator according to claim 1, wherein The thickness of the first electrode finger film layer (2) is 2%λ to 4%λ, and the thickness of the second electrode finger film layer (3) is greater than 5%λ to 12%λ.

4. The interleaved thickness type surface acoustic wave resonator according to claim 1, characterized in that, In the different sound velocity regions formed by the grid structure, the sound velocity decreases as the film layer thickness increases.

5. The interleaved thickness type surface acoustic wave resonator according to claim 1, characterized in that, The surface of the resonator is divided into multiple regions according to different functions: functional region A is the bus bar, functional region B is the staggered sound velocity region, functional region C is the transverse connection region, functional region D is the double-layer film region, and functional region E is the interdigital electrode region. Among them, functional regions A, B, and C together form the grid structure.

6. The interleaved thickness type surface acoustic wave resonator according to claim 1, wherein In functional region B, the first electrode finger film layer (2) and the overlapping region (2-3) are arranged alternately.

7. The interleaved thickness type surface acoustic wave resonator according to claim 1, wherein The grid structure has staggered thickness changes in the finger bar direction to form different sound velocity regions.

8. The interleaved thickness type surface acoustic wave resonator according to claim 1, characterized in that, The grid structure has staggered thickness changes in the direction perpendicular to the finger bar to form different sound velocity regions.

9. An interleaved thickness type filter, characterized in that, It includes a housing and a resonator disposed in the housing. The resonator is the resonator according to any one of claims 1 to 6.

10. The manufacturing method of the interleaved thickness type surface acoustic wave resonator according to claim 1, wherein It includes the following steps: On the selected substrate (1), the first electrode finger film layer (2) is formed by photolithography, evaporation, degluing / etching or photolithography, degluing, evaporation, and stripping. The thickness of the first electrode finger film layer (2) is 2%λ to 4%λ; On the substrate (1) on which the first electrode finger film layer (2) has been formed, the second electrode finger film layer (3) is formed by photolithography, evaporation, degluing / etching or photolithography, degluing, evaporation, and stripping. The thickness of the second electrode finger film layer (3) is 5%λ to 12%λ.

Images