Dual-mode surface acoustic wave device and preparation method therefor

Abstract

The present application discloses a dual-mode surface acoustic wave device and a preparation method therefor. The dual-mode surface acoustic wave device comprises a substrate, a piezoelectric layer and an interdigital electrode which are sequentially stacked in a selected direction; the thickness of the interdigital electrode is 10 nm to 5 µm to excite a first-order horizontal shear wave mode, so that the dual-mode surface acoustic wave device has two acoustic wave modes, i.e., a ground-state horizontal shear wave mode and a first-order horizontal shear wave mode. By using the solution provided by the present application, a dual-mode surface acoustic wave device having two acoustic wave modes, i.e., a ground-state horizontal shear wave mode and a first-order horizontal shear wave mode, can be prepared, so that the dual-mode surface acoustic wave device provided by the present application can support filtering across more frequency bands in 5G communication, conforming to the miniaturization and broadband development trends of surface acoustic wave filters.

Description

Dual-mode surface acoustic wave device and preparation method thereof

[0001] This application is based on and claims priority from Chinese patent application number 202410009274.0 filed on January 4, 2024, entitled “Dual-mode surface acoustic wave device and its preparation method”. Technical Field

[0002] The present application relates to the field of electronic information technology, and in particular to a dual-mode surface acoustic wave device and a method for preparing the same. Background Art

[0003] Mobile devices, such as smartphones, have achieved richer functionality with the continuous advancement of mobile communication technology, greatly facilitating people's lives. However, as the number of mobile devices continues to increase, data transmission volume is exploding. To ensure uncompromised data transmission rates, the number of filters in next-generation mobile communication technologies must also increase accordingly. Furthermore, mobile devices (such as cell phones) also require portability, and increasing the number of filters inevitably increases their size. Therefore, miniaturization of filters is a technical challenge in the RF field.

[0004] Most filters in mobile phone RF front-end modules are surface acoustic wave filters, composed of piezoelectric materials and metal interdigital transducer electrode materials. In RF front-end modules, filters need to perform signal separation and selection functions for multiple discrete frequency bands. Traditional filters generally have a single passband, that is, a specific passband frequency response characteristic. Increasing the bandwidth of this passband can support more frequency bands, thereby reducing the number of filters required. In addition, multi-passband filters based on multimode resonators can use a single filter to perform filtering tasks that require multiple single-passband filters. Therefore, combining multiple passband filters is an effective way to reduce the size and number of electronic components in RF front-end modules.

[0005] Application Contents

[0006] The main purpose of this application is to provide a dual-mode surface acoustic wave device and a preparation method thereof, so as to overcome the deficiencies in the prior art.

[0007] To achieve the aforementioned application objectives, the technical solutions adopted in this application include:

[0008] On one hand, the present application provides a dual-mode surface acoustic wave device, comprising a substrate, a piezoelectric layer, and interdigital electrodes stacked in sequence along a selected direction, wherein the thickness of the interdigital electrodes is 10 nm to 5 μm, preferably 0.1 μm to 4 μm, to excite a first-order horizontal shear wave mode, thereby enabling the dual-mode surface acoustic wave device to have two acoustic wave modes: a ground-state horizontal shear wave and a first-order horizontal shear wave. For example, the thickness of the interdigital electrodes can be 10 nm, 30 nm, 50 nm, 0.1 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0009] Furthermore, the wavelength of the interdigitated electrode is 0.4μm to 20μm, preferably 0.8μm to 8μm, for example, it can be 0.4μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.2μm, 3μm, 3.8μm, 4μm, 5μm, 6μm, 8μm, 10μm, 13μm, 15μm, 19μm, 20μm, etc.

[0010] Furthermore, the width of the interdigital electrodes is 0.1 μm to 5 μm, preferably 0.2 μm to 2 μm, for example, 0.1 μm, 0.2 μm, 0.6 μm, 1 μm, 1.5 μm, 2 μm, 2.2 μm, 3 μm, 3.8 μm, 4 μm, 5 μm, etc.

[0011] Furthermore, the thickness-to-wavelength ratio of the interdigital electrodes is 0.09 to 0.4.

[0012] Furthermore, the material of the interdigital electrode has a density of 2700 kg / m 3 More metals.

[0013] Furthermore, the material of the interdigital electrode is aluminum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.17-0.4, or the material of the interdigital electrode is copper, and the thickness-to-wavelength ratio of the interdigital electrode is 0.12-0.3; or the material of the interdigital electrode is molybdenum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.2-0.3; or the material of the interdigital electrode is tungsten, and the thickness-to-wavelength ratio of the interdigital electrode is 0.15-0.3; or the material of the interdigital electrode is platinum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.09-0.28.

[0014] In some more specific embodiments, the dual-mode surface acoustic wave device further includes at least one functional layer, and the functional layer is disposed between the piezoelectric layer and the substrate.

[0015] Furthermore, the material of the functional layer includes at least one of silicon oxide, aluminum oxide, aluminum nitride, silicon nitride, hafnium oxide, zirconium oxide, titanium oxide, and polysilicon, but is not limited thereto.

[0016] Furthermore, the thickness of the functional layer is 0.1 μm to 10 μm, preferably 0.1 μm to 1 μm.

[0017] In some more specific embodiments, the dual-mode surface acoustic wave device includes at least two functional layers, the at least two functional layers are stacked in sequence, and the at least two functional layers are made of different materials.

[0018] Furthermore, the piezoelectric layer includes a rotated Y-cut LiTaO 3 single crystal film or a rotated Y-cut LiNbO 3 single crystal film.

[0019] Furthermore, the thickness of the piezoelectric layer is 0.2 μm to 5 μm.

[0020] Furthermore, the surface roughness of the piezoelectric layer is less than 1 nm.

[0021] Furthermore, the shear wave velocity of the substrate is greater than 4200 m / s.

[0022] Furthermore, the substrate is a single crystal support substrate. Specifically, the substrate can be any one of a quartz substrate, a silicon substrate, a sapphire substrate, a diamond substrate, and a silicon carbide substrate, but is not limited thereto. The shear wave velocity of the quartz substrate is lower than 4200 m / s.

[0023] Furthermore, the thickness of the substrate is 200 μm to 1000 μm, preferably 250 μm to 500 μm.

[0024] Furthermore, a buffer layer is provided between the interdigital electrodes and the piezoelectric layer. The material of the buffer layer includes at least one of titanium, nickel, chromium and zirconium, but is not limited thereto.

[0025] Furthermore, the thickness of the buffer layer is 1 nm to 20 nm.

[0026] Furthermore, the electromechanical coupling coefficient of the ground-state horizontal shear wave of the dual-mode surface acoustic wave device is above 15%, and the electromechanical coupling coefficient of the first-order horizontal shear wave is above 10%.

[0027] Furthermore, the dual-mode surface acoustic wave device may be a dual-mode surface acoustic wave resonator.

[0028] The present application also provides a method for preparing a dual-mode surface acoustic wave device, comprising:

[0029] providing a substrate;

[0030] preparing a piezoelectric layer on a substrate;

[0031] fabricating interdigital electrodes on the piezoelectric layer;

[0032] The thickness of the interdigital electrodes is 10 nm to 5 μm, preferably 0.1 μm to 4 μm, to excite a first-order horizontal shear wave mode, thereby enabling the dual-mode surface acoustic wave device to have two acoustic wave modes: a ground-state horizontal shear wave and a first-order horizontal shear wave. For example, the thickness of the interdigital electrodes can be 10 nm, 30 nm, 50 nm, 0.1 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0033] Furthermore, the width of the interdigital electrodes is 0.1 μm to 5 μm, preferably 0.2 μm to 2 μm, for example, 0.1 μm, 0.2 μm, 0.6 μm, 1 μm, 1.5 μm, 2 μm, 2.2 μm, 3 μm, 3.8 μm, 4 μm, 5 μm, etc.

[0034] Furthermore, the wavelength of the interdigitated electrode is 0.4μm to 20μm, preferably 0.8μm to 8μm, for example, it can be 0.4μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.2μm, 3μm, 3.8μm, 4μm, 5μm, 6μm, 8μm, 10μm, 13μm, 15μm, 19μm, 20μm, etc.

[0035] Furthermore, the thickness-to-wavelength ratio of the interdigital electrodes is 0.09 to 0.4.

[0036] Furthermore, the material of the interdigital electrode has a density of 2700 kg / m 3 More metals.

[0037] Furthermore, the material of the interdigital electrode is aluminum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.17-0.4, or the material of the interdigital electrode is copper, and the thickness-to-wavelength ratio of the interdigital electrode is 0.12-0.3; or the material of the interdigital electrode is molybdenum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.2-0.3; or the material of the interdigital electrode is tungsten, and the thickness-to-wavelength ratio of the interdigital electrode is 0.15-0.3; or the material of the interdigital electrode is platinum, and the thickness-to-wavelength ratio of the interdigital electrode is 0.09-0.28.

[0038] In some more specific embodiments, the preparation method may specifically include:

[0039] First, ion implantation is performed on a polished surface of the piezoelectric layer to form an ion implantation layer in the piezoelectric layer; a substrate is bonded to the polished surface of the piezoelectric layer; and then the bonded substrate and the piezoelectric layer are bonded to form a composite substrate;

[0040] Annealing the composite substrate, peeling the piezoelectric layer along the ion implantation layer, and then grinding and polishing the surface of the peeled piezoelectric layer away from the substrate using a polishing method (such as chemical mechanical polishing) to reduce the thickness to a desired thickness;

[0041] Finally, interdigital electrodes are formed on the surface of the piezoelectric layer of the composite substrate away from the substrate.

[0042] Furthermore, the temperature of ion implantation is 50-100°C, the energy of ion implantation is 1-2500keV, and the implantation dose is 1×10 15 ~9×10 17 cm -1 .

[0043] Furthermore, when the laminated substrate and the piezoelectric layer are bonded to form a composite substrate, the bonding temperature used is 20-250° C., and the bonding pressure is 100-1000N, preferably 600-1000N.

[0044] Furthermore, the above preparation method specifically includes: annealing the composite substrate at 50-900° C. for 10 minutes to 100 hours, so that the piezoelectric layer is peeled off along the ion implantation layer.

[0045] In other more specific embodiments, the above preparation method can also specifically include: first bonding the substrate and the piezoelectric layer by direct bonding to form a composite substrate, the composite substrate having two acoustic wave modes: ground state horizontal shear wave and first-order horizontal shear wave, and then making interdigitated electrodes on the piezoelectric layer.

[0046] Furthermore, the above preparation method specifically comprises: in a vacuum degree less than 10 -4 The substrate and the piezoelectric layer are directly bonded to form a composite substrate under the conditions of Pa, a bonding temperature of 20 to 250°C, and a bonding pressure of 600 to 1000N; the composite substrate is annealed at 200 to 300°C for 5 to 10 hours to enhance the bonding force; and the piezoelectric layer is polished to the required thickness before or after annealing.

[0047] Furthermore, the above preparation method specifically includes: first preparing an electrode film on the piezoelectric layer by electron beam evaporation or magnetron sputtering, and then patterning the electrode film by photolithography stripping, etching or mask coating to form an interdigitated electrode.

[0048] Furthermore, before forming the composite substrate, the above preparation method also includes: cleaning the piezoelectric layer and the substrate. The cleaning steps can be: ultrasonic cleaning for 4 to 8 minutes in the order of acetone, alcohol, and deionized water, and then drying with nitrogen.

[0049] Furthermore, the dual-mode surface acoustic wave device may also include a functional layer, and the above-mentioned preparation method may specifically include: first performing ion implantation on the polished surface of the piezoelectric layer, and stacking the piezoelectric layer, the functional layer and the substrate in sequence, so that the functional layer is located between the piezoelectric layer and the substrate, and the functional layer is bonded to the polished surface of the piezoelectric layer; then, the bonded piezoelectric layer, the functional layer and the substrate are bonded to form a composite substrate.

[0050] Furthermore, the above preparation method may specifically include: forming a functional layer on the piezoelectric layer by using a thin film preparation method such as chemical vapor deposition, physical vapor deposition or sol-gel method.

[0051] Compared with the prior art, the advantages of this application include:

[0052] 1) The dual-mode surface acoustic wave device provided in this application adopts the method of increasing the thickness of the electrode to enhance the excitation of the SH1 mode, and together with the SH0 mode, it constitutes a dual-mode surface acoustic wave resonator and filter, and the electromechanical coupling coefficients of the two acoustic wave modes are large. The electromechanical coupling coefficient of the SH0 mode can reach more than 15%, and the electromechanical coupling coefficient of the SH1 mode can reach more than 10%. Therefore, the dual-mode surface acoustic wave device provided in this application can support filtering effects in more frequency bands in 5G communications, which is in line with the development trend of miniaturization and broadband surface acoustic wave filters.

[0053] 2) The dual-mode surface acoustic wave device provided in the present application improves the temperature stability of the device, reduces temperature drift, increases the effective resistance of the substrate, and improves the Q value of the device by setting a functional layer between the piezoelectric layer and the substrate; in addition, the material of the functional layer can be silicon dioxide and aluminum nitride. The low sound velocity of silicon dioxide and the high sound velocity of aluminum nitride can form a waveguide structure, thereby further enhancing the acoustic wave energy limiting effect of the device and reducing the energy loss of the device.

[0054] 3) The preparation method of the dual-mode surface acoustic wave device provided in this application utilizes a bonding process to combine a rotated Y-cut LiTaO3 or rotated Y-cut LiNbO3 single crystal film with a substrate to form a composite piezoelectric substrate, thereby suppressing the leakage of leaky surface acoustic waves (LSAW), enhancing the acoustic wave energy limiting effect of the substrate, and converting the main resonance into a non-leaky SH0 mode, with an electromechanical coupling coefficient of more than 15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG1 is a schematic structural diagram of a dual-mode surface acoustic wave device provided by the present application;

[0056] FIG2 is another schematic structural diagram of the dual-mode surface acoustic wave filter provided by the present application;

[0057] FIG3 is a simulated admittance diagram of a large-bandwidth dual-mode surface acoustic wave filter provided in Example 1 of the present application;

[0058] FIG4 is a vibration shape diagram of the SHO mode of a wide-bandwidth dual-mode surface acoustic wave filter provided in Example 1 of the present application;

[0059] FIG5 is a vibration shape diagram of the SH1 mode of a wide-bandwidth dual-mode surface acoustic wave filter provided in Example 1 of the present application;

[0060] Figure 6 is the sound velocity v of the SH1 mode in Example 1 of the present application p Variation trend with Cu electrode thickness-wavelength ratio;

[0061] FIG7 is the electromechanical coupling coefficient K of the SH1 mode in Example 1 of the present application 2 Variation trend with Cu electrode thickness-wavelength ratio;

[0062] FIG8 is a diagram showing the sound velocity v of the SH1 mode in Example 1 of the present application. p Variation trend with Al electrode thickness-wavelength ratio;

[0063] FIG9 is the electromechanical coupling coefficient K of the SH1 mode in Example 1 of the present application 2 Variation trend with Al electrode thickness-wavelength ratio;

[0064] FIG10 shows the admittance curve test results of a wide-bandwidth dual-mode surface acoustic wave filter when the material of the interdigital electrodes is Al, the thickness is 200 nm, and the wavelengths of the interdigital electrodes are 1 μm and 1.1 μm;

[0065] FIG11 is a graph showing the S21 curve test results of a wide-bandwidth dual-mode surface acoustic wave filter when the interdigital electrodes are made of Al and have a thickness of 200 nm;

[0066] FIG12 is a schematic structural diagram of another dual-mode surface acoustic wave device provided by the present application. DETAILED DESCRIPTION

[0067] In view of the deficiencies in the prior art, the applicant of this case has proposed the technical solution of this application after long-term research and extensive practice. The following will further explain the technical solution, its implementation process and principles through specific examples. However, the examples are only used to explain this application, but this application is not limited to them. Unless otherwise specified, the thin film preparation process, patterning process, annealing process, bonding and corresponding equipment used in this application are all known to those skilled in the art. In addition, the experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0068] The applicant in this case found through research that the bandwidth of the acoustic filter is proportional to the electromechanical coupling coefficient of the corresponding resonator, and the leakage wave mode in rotated Y-cut lithium niobate (LiNbO3) is characterized by a large electromechanical coupling coefficient. Research based on piezoelectric single crystal thin film lithium tantalate (LiTaO3), LiNbO3 and high acoustic velocity substrate composite substrates found that the high acoustic velocity substrate is beneficial to reducing the leakage of leakage waves, making it a leak-free horizontal shear wave (SH0) mode with an electromechanical coupling coefficient exceeding 15%; at the same time, there is a first-order horizontal shear wave (SH1) mode in the structure, which can be enhanced and excited by increasing the electrode thickness, so that its electromechanical coupling coefficient exceeds 10%. Therefore, the structure can be used to prepare dual-mode resonators to meet the requirements of large bandwidth and miniaturization of filters in the 5G era.

[0069] In particular, the electromechanical coupling coefficient K in the following embodiment is 2 The calculation formula is as follows:

[0070] K 2 =(π / 2)×(f s / f p ) / tan[(π / 2)×(f s / f p )] (1)

[0071] Among them, f s is the resonant frequency, f p is the anti-resonance frequency, and the two are the frequencies corresponding to the highest point and the lowest point of the resonant signal of interest in the admittance curve of the resonator, respectively.

[0072] Phase velocity v p The calculation formula is as follows:

[0073] V p =(f s +f p )×λ / 2 (2)

[0074] It should be noted that the phase velocity describes the speed of sound of the acoustic wave mode in the resonator, and the speed of sound has a large range, including the intrinsic properties of the material.

[0075] Please refer to Figure 1, which is a structural schematic diagram of the dual-mode surface acoustic wave device provided by the present application. The dual-mode surface acoustic wave device simultaneously has two acoustic wave modes with large electromechanical coupling coefficients. The dual-mode surface acoustic wave device includes a substrate 5, a piezoelectric layer 2 and an interdigital electrode 1 stacked in sequence along a selected direction, and the thickness-to-wavelength ratio (h / λ) of the interdigital electrode 1 is 0.09 to 0.4; the selected direction is the longitudinal direction or thickness direction of the dual-mode surface acoustic wave device; the dual-mode surface acoustic wave device can be a dual-mode surface acoustic wave resonator, and a dual-mode surface acoustic wave filter can be prepared using the dual-mode surface acoustic wave resonator. The dual-mode surface acoustic wave filter includes at least one dual-mode surface acoustic wave resonator.

[0076] The interdigitated electrode 1 includes a plurality of spaced-apart fingers 11, and the shapes and sizes of the plurality of fingers 11 are the same. The thickness h of each finger 11 is the thickness of the interdigitated electrode, and the wavelength λ of the interdigitated electrode is 2a+2b, wherein a is the width of each finger 11, and b is the spacing between two adjacent fingers 11. It can be understood that the width of a finger 11 and the spacing between two adjacent fingers 11 are both dimensions along the radial direction of the finger 11, and the radial direction of the finger 11 is perpendicular to the selected direction.

[0077] In the structure of interdigital electrode 1 / piezoelectric layer 2 / substrate 5 with horizontal shear wave (SH wave) as the main mode, the ground state horizontal shear wave mode and the first-order horizontal shear wave mode generally coexist. However, the first-order horizontal shear wave mode is generally considered to be a stray mode because it cannot be fully excited. The present application directly controls the material and thickness of the interdigital electrode 1 so that the thickness-to-wavelength ratio of the interdigital electrode 1 reaches a specific range, changes the sound velocity and electromechanical coupling coefficient of the first-order horizontal shear wave mode, and achieves effective excitation of the two modes at the same time, thereby obtaining a dual-mode surface acoustic wave device.

[0078] The material of the interdigital electrode 1 is a material with a density of 2700 kg / m 3 For example, the material of the interdigital electrode 1 can be aluminum (Al), copper (Cu), molybdenum (Mo), tungsten (W) or platinum (Pt), etc., wherein the density of aluminum is 2700 kg / m 3 , horizontal shear modulus is 26GPa, shear wave acoustic impedance is 8.4Pa 6 ·s / m 3 ;The density of copper is 8960kg / m 3 , horizontal shear modulus is 45GPa, shear wave acoustic impedance is 20Pa 6 ·s / m 3 ; The density of molybdenum is 10200kg / m 3 , horizontal shear modulus is 119GPa, shear wave acoustic impedance is 34.9Pa 6 ·s / m 3 ; The density of platinum is 21450kg / m3 , horizontal shear modulus is 61GPa, and shear wave acoustic impedance is 36.2Pa 6 ·s / m 3 ; The density of tungsten is 19350kg / m 3 , horizontal shear modulus is 161GPa, and shear wave acoustic impedance is 55.7Pa 6 ·s / m 3 .

[0079] In a specific embodiment, the material of the interdigital electrode 1 is aluminum, and the thickness-to-wavelength ratio of the interdigital electrode 1 is 0.17-0.4; alternatively, the material of the interdigital electrode 1 is copper, and the thickness-to-wavelength ratio of the interdigital electrode 1 is 0.12-0.3, for example, it can be 0.12, 0.13, 0.15, 0.18, 0.2, 0.21, 0.25, 0.27, 0.29, 0.3, etc.; alternatively, the material of the interdigital electrode 1 is molybdenum, and the thickness-to-wavelength ratio of the interdigital electrode 1 is 0.2-0.3, for example, it can be 0.21, 0.22, 0.23, 0.25, 0.26, 0.28, 0.3, etc. ; Alternatively, the material of the interdigital electrode 1 is tungsten, and the thickness-to-wavelength ratio of the interdigital electrode 1 is 0.15 to 0.3, for example, it can be 0.15, 0.16, 0.17, 0.19, 0.2, 0.21, 0.23, 0.25, 0.27, 0.29, 0.3, etc.; Alternatively, the material of the interdigital electrode 1 is platinum, and the thickness-to-wavelength ratio of the interdigital electrode 1 is 0.09 to 0.28, for example, it can be 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.18, 0.2, 0.21, 0.22, 0.25, 0.27, 0.28, etc.

[0080] For example, when the material of the interdigital electrode 1 is aluminum and the thickness-to-wavelength ratio of the interdigital electrode 1 exceeds 0.17, the electromechanical coupling coefficient of the first-order horizontal shear wave mode of the dual-mode surface acoustic wave device exceeds 10%, and the first-order horizontal shear wave mode is effectively excited. When the material of the interdigital electrode 1 is copper and the thickness-to-wavelength ratio of the interdigital electrode 1 exceeds 0.12, the electromechanical coupling coefficient of the first-order horizontal shear wave mode exceeds 10%, and it is considered that the first-order horizontal shear wave mode is effectively excited. However, the interdigital electrode 1 cannot be infinitely thickened. An excessively thick interdigital electrode 1 will lead to increased losses. For example, when the material of the interdigital electrode 1 is aluminum and the thickness-to-wavelength ratio of the interdigital electrode 1 exceeds 0.28, the anti-resonance response of the first-order horizontal shear wave mode deteriorates, making it unsuitable for use as a filter.

[0081] Specifically, the thickness h of the interdigital electrode 1 is 10 nm to 5 μm, preferably 0.1 μm to 4 μm, for example, it can be 10 nm, 30 nm, 50 nm, 0.1 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.; the width a of the interdigital electrode 1 is 0.1 μm to 5 μm, preferably 0.2 μm to 2 μm, for example, it can be 0.1 μm, 0.2 μm, 0.6 μm, 1 μm, 1.5 μm, 2 μm, etc. μm, 2.2μm, 3μm, 3.8μm, 4μm, 5μm, etc.; the wavelength λ of the interdigitated electrode 1 is 0.4μm~20μm, preferably 0.8μm~8μm, for example, it can be 0.4μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.2μm, 3μm, 3.8μm, 4μm, 5μm, 6μm, 8μm, 10μm, 13μm, 15μm, 19μm, 20μm, etc.

[0082] Specifically, the piezoelectric layer 2 includes a rotated Y-cut LiTaO 3 single crystal thin film or a rotated Y-cut LiNbO 3 single crystal thin film. The thickness of the piezoelectric layer 2 is 0.2 μm to 5 μm, and the surface roughness is less than 1 nm.

[0083] Specifically, substrate 5 is a single crystal support substrate, specifically a high-acoustic-velocity non-piezoelectric support substrate, and the shear wave velocity of substrate 5 is greater than 4200 m / s; illustratively, the single crystal support substrate includes any one of a quartz substrate, a silicon substrate, a sapphire substrate, a diamond substrate, and a silicon carbide substrate, and the thickness of substrate 5 is 200 μm to 1000 μm.

[0084] In a specific embodiment, a buffer layer may be further provided between the interdigital electrodes 1 and the piezoelectric layer 2 . The material of the buffer layer includes at least one of titanium, nickel, chromium and zirconium, but is not limited thereto. The thickness of the buffer layer is 1 nm to 20 nm.

[0085] In another specific embodiment, the dual-mode surface acoustic wave device may further include at least one functional layer disposed between the piezoelectric layer 2 and the substrate 5. The material of the functional layer includes at least one of, but is not limited to, silicon oxide, aluminum oxide, aluminum nitride, silicon nitride, hafnium oxide, zirconium oxide, titanium oxide, and polysilicon. The thickness of the functional layer is 0.1 μm to 10 μm, preferably 0.1 μm to 1 μm. As a typical embodiment, the dual-mode surface acoustic wave device includes at least two functional layers, the at least two functional layers being stacked sequentially, and the at least two functional layers being made of different materials.

[0086] Example 1

[0087] Please refer to Figure 2, which is a cross-sectional schematic diagram of a large-bandwidth dual-mode surface acoustic wave filter based on a 32° YX-LiNbO3 / SiO2 / SiC structure (the figure only includes part of the interdigitated electrodes). The large-bandwidth dual-mode surface acoustic wave filter includes a substrate 5, a first functional layer 3, a piezoelectric layer 2 and interdigitated electrodes 1 arranged in sequence along a selected direction.

[0088] As shown in FIG2 , the piezoelectric layer 2 is a 32° YX-LiNbO 3 thin film with a thickness of 300 nm, the first functional layer 3 is a SiO 2 thin film with a thickness of 200 nm, and the substrate 5 is a SiC substrate.

[0089] The dual-mode surface acoustic wave device provided in this embodiment was tested, and the following results were obtained:

[0090] When the material of the interdigital electrode 1 is Al, the thickness of the interdigital electrode 1 is h = 180nm, and the wavelength λ = 1μm, the admittance curve of the single-ended resonator simulated in this embodiment is shown in Figure 3. It can be seen from Figure 3 that the dual-mode surface acoustic wave device can excite two acoustic wave modes, and the resonant frequencies fs of the two resonances are 3010MHz and 4930MHz respectively; the two acoustic wave modes are SH0 mode and SH1 mode, and their vibration mode diagrams are shown in Figures 4 and 5 respectively.

[0091] 2) When the material of the interdigital electrode 1 is Cu and the wavelength λ = 1 μm, the v of the SH1 mode is tested under different thickness wavelength ratios h / λ of the same electrode. p (phase velocity) and K 2 (electromechanical coupling coefficient) curves, as shown in Figures 6 and 7, show that as the thickness of the Cu electrode increases, the v of the SH1 mode increases. p Gradually decrease, K 2 It increases first and then decreases. When the thickness-wavelength ratio h / λ=0.22, K 2 Reaching a maximum of 17.53%.

[0092] 3) When the material of the interdigital electrode 1 is Al and the wavelength λ is 1 μm, the v of the SH1 mode is tested under different electrode thickness and wavelength ratio h / λ. p (phase velocity) and K 2 (electromechanical coupling coefficient) curves, as shown in Figures 8 and 9, show that as the thickness of Al increases, the v of the SH1 mode increases. p Gradually decrease, K 2 It increases first and then decreases. When the thickness-wavelength ratio h / λ=0.34, K 2 Reaching a maximum value of 22.76%.

[0093] 4) When the material of the interdigital electrode is Al and the thickness is 200 nm; when the wavelength of the interdigital electrode 1 is 1 μm and 1.1 μm, the admittance curve schematic diagram shown in Figure 10 is measured, which describes two dual-mode resonator signals without spurious modes. The red line is the admittance curve schematic diagram corresponding to the wavelength of the interdigital electrode 1 of 1 μm, and the black line is the admittance curve schematic diagram corresponding to the wavelength of the interdigital electrode 1 of 1.1 μm.

[0094] 5) When the material of the interdigital electrodes is Al and the thickness is 200 nm; FIG11 is a graph of the S21 of the dual-mode filter, the center frequency f of the low-frequency passband c The frequency of the high-frequency passband is 3065.0MHz, the insertion loss is 3.46dB, and the 3-dB bandwidth is 5.1%. c The frequency band is 4808.4MHz, the insertion loss is 2.92dB, and the 3-dB bandwidth is 5.9%.

[0095] Existing dual-channel surface acoustic wave filters generally have a structure in which two filters are connected in parallel. The dual-mode surface acoustic wave device provided in this embodiment realizes dual-channel signals in a ladder filter, which is beneficial for reducing the usage area.

[0096] Based on the high-bandwidth dual-mode surface acoustic wave device with a 32° YX-LiNbO3 / SiO2 / SiC structure in the above embodiment, the present application also provides a preparation process of the dual-mode surface acoustic wave device, which is specifically as follows:

[0097] 1) Perform standard cleaning on the piezoelectric layer and SiC substrate.

[0098] The piezoelectric layer may be a 4-inch 32° Y-cut LiNbO3 piezoelectric wafer, the thickness of the LiNbO3 piezoelectric wafer is 300 μm; the thickness of the SiC substrate is 500 μm.

[0099] 2) A 200 nm thick silicon dioxide film was prepared on a SiC substrate by radio frequency magnetron sputtering as the first functional layer.

[0100] The back vacuum degree is less than 9×10 -5 Pa, silicon dioxide target sputtering is used to deposit silicon dioxide thin film under room temperature conditions, the flow rates of Ar and O2 are controlled to be 18 sccm and 6 sccm respectively, the coating pressure is 0.5 Pa, the power is 300 w, and the time is 40 minutes.

[0101] 3) The cleaned 4-inch 32° Y-cut LiNbO3 piezoelectric wafer was ion-implanted to form an ion-implanted layer inside the 32° Y-cut LiNbO3 piezoelectric wafer. The ion implantation temperature was 200°C, the ion implantation energy was 75keV, and the implantation dose was 9×10 16 cm -1 .

[0102] 4) Bonding the SiC substrate with the silicon dioxide film to the ion-implanted surface of the LiNbO3 piezoelectric wafer to form a composite substrate at a bonding temperature of 200° C. and a bonding pressure of 500 kg.

[0103] 5) Annealing the composite substrate at 170° C. for 3 hours to peel off the LiNbO3 along the ion-implanted layer. Then, chemical mechanical polishing was used to thin and smooth the LiNbO3 piezoelectric wafer in the peeled composite substrate until the LiNbO3 piezoelectric wafer was thinned to 300 nm.

[0104] 6) A photolithography method is used to prepare an interdigital electrode mask pattern on the surface of the polished LiNbO3 piezoelectric wafer, and an Al film with a thickness of 200 nm is prepared based on the interdigital electrode mask pattern by ion beam evaporation. Then, the interdigital electrode mask pattern is peeled off to obtain the Al interdigital electrode.

[0105] The preparation method of the dual-mode surface acoustic wave device provided in this application has low process difficulty. A rotating Y-cut LiTaO3 or LiNbO3 single crystal film is combined with a substrate (which can be called a high-acoustic-speed non-piezoelectric support substrate) by a bonding process to form a composite substrate, which suppresses the leakage of leaky surface acoustic waves, enhances the acoustic wave energy limiting effect of the substrate, and converts the main resonance into a non-leaky SH0 mode. The electromechanical coupling coefficient can reach more than 15%.

[0106] Example 2

[0107] Please refer to Figure 12. A large-bandwidth dual-mode surface acoustic wave filter based on a 32° YX-LiNbO3 / SiO2 / SiC structure in this embodiment is basically the same as the structure in Example 1, except that the large-bandwidth dual-mode surface acoustic wave filter in this embodiment also includes a second functional layer 4.

[0108] The first functional layer 3 is a silicon dioxide film, which can improve the temperature stability of the device and reduce temperature drift; the second functional layer 4 is a polycrystalline silicon film, which can increase the effective resistance of the substrate and improve the Q value of the device. Alternatively, the first functional layer 3 is a silicon dioxide film and the second functional layer 4 is an aluminum nitride film. The low sound velocity of silicon dioxide and the high sound velocity of aluminum nitride enable the first functional layer and the second functional layer to form a waveguide structure, which can further enhance the acoustic wave energy limiting effect of the device and reduce the energy loss of the device. Moreover, the functional layer will not damage the filtering function of the device, and can improve the comprehensive performance of the surface acoustic wave device, thereby reducing temperature drift, improving the Q value and reducing insertion loss.

[0109] The present application provides a dual-mode surface acoustic wave device, which utilizes the rich tangential and contained acoustic wave modes in a rotated Y-cut LiTaO3 or LiNbO3 single crystal film, and adjusts the thickness-to-wavelength ratio by increasing the thickness of the interdigitated electrode to enhance the excitation of the SH1 mode, which together with the SH0 mode constitutes a dual-mode surface acoustic wave resonator and filter. The electromechanical coupling coefficients of the two acoustic wave modes are both large, the electromechanical coupling coefficient of the SH0 mode can reach more than 15%, and the electromechanical coupling coefficient of the SH1 mode can reach more than 10%. Therefore, the dual-mode surface acoustic wave device provided by the present application can support filtering effects in more frequency bands in 5G communications, which is in line with the development trend of miniaturization and broadband surface acoustic wave filters.

[0110] The relative film thickness of the traditional surface acoustic wave resonator electrode is generally around 8%. This application enhances the excitation of the SH1 mode by increasing the relative film thickness of the interdigitated electrode, and its electromechanical coupling coefficient and impedance ratio are greatly improved. At this time, the performance of the main resonance SH0 mode still remains at a high level, and the two acoustic wave modes can form a dual-mode filter.

[0111] In addition, the dual-mode surface acoustic wave device provided by the present application can also be provided with 1 to 2 functional layers between the piezoelectric layer and the substrate. For example, adding a silicon dioxide functional layer alone can improve the temperature stability of the device and reduce temperature drift; adding a polysilicon functional layer alone can increase the effective resistance of the substrate and improve the Q value of the device; when adding a silicon dioxide functional layer and an aluminum nitride functional layer at the same time, the low sound velocity of silicon dioxide and the high sound velocity of aluminum nitride can form a waveguide structure, thereby further enhancing the acoustic wave energy limiting effect of the device and reducing the energy loss of the device; and the functional layer not only does not damage the filtering function of the device, but also can improve the overall performance of the surface acoustic wave device, thereby reducing temperature drift, improving the Q value and reducing insertion loss.

[0112] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit and substance of this application shall be included within the scope of protection of this application.

Claims

1. A dual-mode surface acoustic wave device, comprising a substrate, a piezoelectric layer, and interdigital electrodes stacked in sequence along a selected direction, characterized in that, The thickness of the interdigital electrode is 10 nm to 5 μm, and the thickness-wavelength ratio of the interdigital electrode is 0.09 to 0.4 to excite the first-order horizontal shear wave mode, so that the dual-mode surface acoustic wave device has two acoustic wave modes, namely the ground-state horizontal shear wave and the first-order horizontal shear wave. In addition, the dual-mode surface acoustic wave device further includes at least one functional layer, and the functional layer is disposed between the piezoelectric layer and the substrate. The electromechanical coupling coefficient of the ground-state horizontal shear wave of the dual-mode surface acoustic wave device is more than 15%, and the electromechanical coupling coefficient of the first-order horizontal shear wave of the dual-mode surface acoustic wave device is more than 10%.

2. The dual-mode surface acoustic wave device according to claim 1, wherein: The wavelength of the interdigital electrode is 0.4 μm to 20 μm; and / or, the width of the interdigital electrode is 0.1 μm to 5 μm.

3. The dual-mode surface acoustic wave device according to claim 1 or 2, characterized in that: The material of the interdigital electrode is a metal with a density of 2700 kg / m 3 or above.

4. The dual-mode surface acoustic wave device according to claim 3, wherein: The material of the interdigital electrode is aluminum, and the thickness-wavelength ratio of the interdigital electrode is 0.17 to 0.4; or, the material of the interdigital electrode is copper, and the thickness-wavelength ratio of the interdigital electrode is 0.12 to 0.3; or, the material of the interdigital electrode is molybdenum, and the thickness-wavelength ratio of the interdigital electrode is 0.2 to 0.3; or, the material of the interdigital electrode is tungsten, and the thickness-wavelength ratio of the interdigital electrode is 0.15 to 0.3; or, the material of the interdigital electrode is platinum, and the thickness-wavelength ratio of the interdigital electrode is 0.09 to 0.

28.

5. The dual-mode surface acoustic wave device according to claim 1, characterized in that: The material of the functional layer includes at least one of silicon oxide, aluminum oxide, aluminum nitride, silicon nitride, hafnium oxide, zirconium oxide, titanium oxide, and polysilicon; and / or, the thickness of the functional layer is 0.1 μm to 10 μm; and / or, the dual-mode surface acoustic wave device includes at least two functional layers, and the at least two functional layers are stacked in sequence, and the materials of the at least two functional layers are different.

6. The dual-mode surface acoustic wave device according to claim 1, characterized in that: The piezoelectric layer includes a rotated Y-cut LiTaO3 single crystal thin film or a rotated Y-cut LiNbO3 single crystal thin film; and / or, the thickness of the piezoelectric layer is 0.2 μm to 5 μm; and / or, the surface roughness of the piezoelectric layer is less than 1 nm.

7. The dual-mode surface acoustic wave device according to claim 1, wherein The substrate is a single crystal support substrate; and / or, the shear wave velocity of the substrate is greater than 4200 m / s; and / or, the substrate includes any one of a quartz substrate, a silicon substrate, a sapphire substrate, a diamond substrate, or a silicon carbide substrate; and / or, the thickness of the substrate is 200 μm to 1000 μm.

8. The dual-mode surface acoustic wave device according to claim 1, wherein: A buffer layer is further disposed between the interdigital electrode and the piezoelectric layer, and the material of the buffer layer includes at least one of titanium, nickel, chromium, and zirconium; and / or, the thickness of the buffer layer is 1 nm to 20 nm.

9. A preparation method of a dual-mode surface acoustic wave device, characterized in that, Including: Providing a substrate; Successively preparing a functional layer and a piezoelectric layer on the substrate; Preparing an interdigital electrode on the piezoelectric layer; Among them, the thickness of the interdigital electrode is 10 nm to 5 μm, and the thickness-to-wavelength ratio of the interdigital electrode is 0.09 to 0.4 to excite the first-order horizontal shear wave mode, so that the dual-mode surface acoustic wave device has two acoustic wave modes: the ground-state horizontal shear wave and the first-order horizontal shear wave. The electromechanical coupling coefficient of the ground-state horizontal shear wave of the dual-mode surface acoustic wave device is above 15%, and the electromechanical coupling coefficient of the first-order horizontal shear wave of the dual-mode surface acoustic wave device is above 10%.

10. The manufacturing method of the dual-mode surface acoustic wave device according to claim 9, characterized in that: The wavelength of the interdigital electrode is 0.4 μm to 20 μm.

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