Acoustic resonator and preparation method therefor

Abstract

The present disclosure provides an acoustic resonator and a preparation method therefor. The acoustic resonator comprises: a substrate; a piezoelectric layer, prepared on the substrate; a release region, formed between the substrate and the piezoelectric layer and configured for suspended release of the acoustic resonator; a silicon dioxide layer, prepared on the piezoelectric layer and forming a dielectric layer together with the piezoelectric layer; and a metal electrode layer, configured to generate an electric field for exciting Lamb waves to induce acoustic vibration modes in the piezoelectric layer. The thickness of the silicon dioxide layer is adjusted to improve the stress-mode distribution in the piezoelectric layer, thereby enhancing the electromechanical coupling coefficient.

Description

Acoustic resonators and their fabrication methods Technical Field

[0001] This disclosure relates to the field of high-frequency piezoelectric acoustic resonators, and more particularly to an acoustic resonator with a high frequency and high electromechanical coupling coefficient. Background Technology

[0002] With the advent of the 5G / 6G era, the demand for mobile communication, especially cellular phone applications, is constantly increasing, and the Sub-6GHz frequency band has been fully allocated. The ever-evolving wireless communication industry needs to shift to higher frequency bands and wider bandwidths to achieve faster data rates. In 5G / 6G wireless communication systems, radio frequency (RF) front-end technology is considered a key technology, and the performance of RF filters, as the core component of the RF front-end, directly determines the anti-interference capability and signal-to-noise ratio of the communication system. Existing acoustic resonators are insufficient to meet these requirements.

[0003] Therefore, how to achieve high-performance filters and acoustic resonators at higher frequencies will be an important research goal for the academic and industrial communities in the future.

[0004] Summary of the Invention

[0005] To address the aforementioned problems, this disclosure provides an acoustic resonator and its fabrication method, thereby alleviating the technical issues described above in the prior art.

[0006] One aspect of this disclosure provides an acoustic resonator, comprising: a substrate; a piezoelectric layer formed on the substrate; a release region formed between the substrate and the piezoelectric layer, configured for suspending release of the acoustic resonator; a silicon dioxide layer formed on the piezoelectric layer, forming a dielectric layer together with the piezoelectric layer; and a metal electrode layer configured to generate an electric field for exciting Lamb waves to excite the piezoelectric layer to generate acoustic vibration modes; and improving the stress mode distribution in the piezoelectric layer by adjusting the thickness of the silicon dioxide layer to increase the electromechanical coupling coefficient.

[0007] According to embodiments of this disclosure, the substrate is made of silicon, sapphire, gallium nitride, or silicon carbide.

[0008] According to embodiments of this disclosure, the material used to prepare the piezoelectric layer is selected from lithium niobate (LN), lithium tantalate (LT), or a composite material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.

[0009] According to embodiments of this disclosure, the tangential orientation of the piezoelectric layer film is 110°Y to 130°Y cut and 10°Z to 30°Z cut.

[0010] According to embodiments of this disclosure, the metal electrode layer is prepared on the upper or lower surface of the dielectric layer, or a portion thereof is located in the silicon dioxide layer.

[0011] According to an embodiment of this disclosure, the metal electrode layer includes N metal electrodes, where 2 ≤ N ≤ 600, and the spacing between two adjacent metal electrodes is half a wavelength; the width of each metal electrode is one-sixth of a wavelength, one-quarter of a wavelength, or one-eighth of a wavelength; and the length is ten wavelengths or ten half wavelengths.

[0012] According to embodiments of this disclosure, the thickness of the piezoelectric layer is 10-1000 nm.

[0013] According to embodiments of this disclosure, when the thickness of the silicon dioxide layer is 0.5 to 1.7 times the thickness of the piezoelectric layer, k is excited. 2 >20% S2 mode Lamb wave; when the silicon dioxide layer thickness is 1.5 to 2.8 times the piezoelectric layer thickness, the excitation k 2 >20% A3 mode Lamb wave; when the silicon dioxide layer thickness is 2.6 to 3.5 times the piezoelectric layer thickness, the excitation k 2 >20% of the S4 mode Lamb wave.

[0014] According to an embodiment of this disclosure, a method for fabricating an acoustic resonator is provided, comprising:

[0015] Provide a substrate and a piezoelectric layer;

[0016] Growing metal electrodes on a piezoelectric layer;

[0017] Graphically define silicon dioxide regions;

[0018] Growth of a silicon dioxide layer;

[0019] Graphically define the mask etching area;

[0020] Inductively coupled plasma etching of piezoelectric thin films;

[0021] Isotropic dry etching of silicon substrate releases piezoelectric thin film to form release region, resulting in the final acoustic resonator.

[0022] According to an embodiment of this disclosure, another method for fabricating an acoustic resonator is provided, comprising:

[0023] Provide a substrate and a piezoelectric layer;

[0024] Growing a silicon dioxide layer in a piezoelectric layer

[0025] Deposit metal electrodes on a silicon dioxide layer;

[0026] Graphically define the mask etching area;

[0027] Inductively coupled plasma etching of piezoelectric thin films;

[0028] Isotropic dry etching of silicon substrate releases piezoelectric thin film to form release region, resulting in the final acoustic resonator.

[0029] The acoustic resonator and its fabrication method disclosed herein can achieve a resonant frequency of 17.77 GHz and an electromechanical coupling coefficient as high as 46.96%, breaking through the limitation of the electromechanical coupling coefficient of high-order Lamb waves in traditional single-layer membrane structures, and bringing a better solution for the design of high-frequency broadband filters. Attached Figure Description

[0030] Figure 1 is a schematic diagram of the stress distribution of different Lamb wave modes in the acoustic resonator disclosed herein.

[0031] Figure 2 is a schematic diagram of an acoustic resonator structure provided in Embodiment 1 of this application.

[0032] Figure 3 shows the admittance simulation curve of the acoustic resonator of Embodiment 1 of this disclosure when the thickness ratio of the piezoelectric layer to the silicon dioxide layer is 1:1.

[0033] Figure 4 shows the top view and cross-sectional schematic diagram of the device when the acoustic resonator provided in Example 1 excites the S2 mode with a high electromechanical coupling coefficient.

[0034] Figure 5 is a diagram showing the fabrication steps of the acoustic resonator structure in Embodiment 1 of this disclosure.

[0035] Figure 6 is a flowchart of the fabrication process of the acoustic resonator structure in Embodiment 1 of this disclosure.

[0036] Figure 7 is a schematic diagram of an acoustic resonator structure provided in Embodiment 2 of this disclosure.

[0037] Figure 8 shows the admittance simulation curve of the acoustic resonator of Embodiment 2 of this disclosure when the thickness ratio of the piezoelectric layer to the silicon dioxide layer is 1:1.

[0038] Figure 9 is a diagram showing the fabrication steps of the acoustic resonator structure in Embodiment 2 of this disclosure.

[0039] Figure 10 is a process flow diagram of the fabrication of the acoustic resonator structure of Embodiment 2 of this disclosure.

[0040] Figure 11 is a schematic diagram of the core area of ​​another upper and lower electrode structure provided in this disclosure.

[0041] [Explanation of key component symbols in the accompanying drawings of this disclosure embodiment]

[0042] 1-Substrate; 2-Release region; 3-Piezoelectric layer; 4-Metal electrode; 5-Silicon dioxide; 6-Mask layer. Detailed Implementation

[0043] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0044] To make the above-mentioned objectives, features and advantages of this disclosure more apparent and understandable, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] This disclosure provides an acoustic resonator and its fabrication method. By depositing silicon dioxide on a piezoelectric thin film layer, the stress field distribution is improved, and a high-order Lamb wave motion mode is excited at a specific thickness ratio, thereby realizing an acoustic resonator structure with a high electromechanical coupling coefficient.

[0046] Electromechanical coupling coefficient (k) 2 As a crucial indicator of filter and resonator performance, a high electromechanical coupling coefficient ensures a sufficiently large passband bandwidth, enabling the transmission of larger amounts of data. Therefore, achieving a resonator with a high electromechanical coupling coefficient at high frequencies is key to realizing wideband filters.

[0047] Currently, the piezoelectric materials used in acoustic resonators mainly include PZT, aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN), lithium niobate (LiNbO3 / LN), and lithium tantalate (LiTaO3 / LT). Among them, lithium niobate has a large piezoelectric coefficient (e), which can well meet the requirements of high quality factor (Q) and large electromechanical coupling coefficient in the 5G / 6G frequency band, so it has gradually become a popular material for the fabrication of acoustic resonators. At the same time, lithium niobate thin films can excite a variety of high-order acoustic modes, providing a more flexible solution for the design of filters in different frequency bands. This disclosure provides an acoustic resonator and its fabrication, which excites high-order Lamb wave motion modes with high electromechanical coupling coefficients, providing a flexible solution for the design of high-frequency broadband filters.

[0048] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0049] In this embodiment of the disclosure, an acoustic resonator is provided. As shown in Figures 2, 4, 6, 7, 10, and 11, the acoustic resonator includes:

[0050] Substrate 1;

[0051] Piezoelectric layer 3 is fabricated on the substrate;

[0052] Release region 2, formed between the substrate and the piezoelectric layer, is configured for the suspended release of the acoustic resonator;

[0053] A silicon dioxide layer 5 is prepared on the piezoelectric layer, and together with the piezoelectric layer, constitutes a dielectric layer; and

[0054] The metal electrode layer 4 is configured to generate an electric field that excites Lamb waves to excite the piezoelectric layer to generate acoustic vibration modes.

[0055] The electromechanical coupling coefficient can be improved by adjusting the thickness of the silicon dioxide layer to improve the stress mode distribution in the piezoelectric layer.

[0056] The metal electrode layer is prepared on the upper or lower surface of the dielectric layer, or a portion thereof is located in the silicon dioxide layer.

[0057] The metal electrode layer comprises N metal electrodes, where 2 ≤ N ≤ 600, and the spacing between two adjacent metal electrodes is half a wavelength; the width of each metal electrode is one-sixth of a wavelength, one-quarter of a wavelength, or one-eighth of a wavelength; and the length is ten wavelengths or ten half wavelengths.

[0058] In some embodiments, the substrate may be one of the following materials: silicon, sapphire (Al2O3), gallium nitride (GaN), and silicon carbide (SiC).

[0059] In some embodiments, the piezoelectric layer material comprises one of the following: lithium niobate (LN), lithium tantalate (LT), or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.

[0060] In some embodiments, the tangential orientation of the piezoelectric layer film is 110°Y to 130°Y cut and 10°Z to 30°Z cut;

[0061] In some embodiments, the thickness of the piezoelectric layer is 10-1000 nm.

[0062] In some embodiments, the metal electrode comprises one of the following: gold, aluminum, molybdenum, platinum, copper, or an alloy composed of titanium gold, titanium aluminum, titanium copper, chromium gold, chromium aluminum, or chromium copper.

[0063] In some embodiments, the thickness of the metal electrode is 10–250 nm.

[0064] In some embodiments, the number of metal electrodes is N, where N ranges from 2 to 50.

[0065] In some embodiments, the spacing between two adjacent metal electrodes is half a wavelength, and the width of each metal electrode is one-sixth of a wavelength, one-quarter of a wavelength, or one-eighth of a wavelength.

[0066] In some embodiments, the length of the metal electrode is ten wavelengths or ten and a half wavelengths.

[0067] In some embodiments, the metal electrode can be grown on the upper surface of the silicon dioxide layer, or on both the upper and lower surfaces.

[0068] In some embodiments, metal electrodes can be fabricated on the piezoelectric thin film first, and then silicon dioxide can be deposited between the metal electrodes; alternatively, a silicon dioxide layer can be deposited on the piezoelectric thin film first, and then metal electrodes can be grown on the silicon dioxide layer.

[0069] In some embodiments, when the thickness of the silicon dioxide layer is 0.5 to 1.7 times the thickness of the piezoelectric layer, k is excited. 2 >20% S2 mode Lamb wave; 1:1 is preferred in Example 1.

[0070] In some embodiments, when the thickness of the silicon dioxide layer is 1.5 to 2.8 times the thickness of the piezoelectric layer, k is excited. 2 >20% of A3 mode Lamb waves.

[0071] In some embodiments, when the thickness of the silicon dioxide layer is 2.6 to 3.5 times the thickness of the piezoelectric layer, k is excited. 2 >20% of the S4 mode Lamb wave.

[0072] This disclosure further describes the fabrication method of the aforementioned acoustic resonator. The fabrication method includes: depositing a metal electrode on a piezoelectric thin film; depositing a mask layer on the electrode surface and defining a silicon dioxide deposition region; depositing a silicon dioxide layer; depositing the mask layer and defining an etching region; releasing the resonator from the substrate and suspending it; exciting a higher-order Lamb wave mode by a transverse electric field to obtain a high electromechanical coupling coefficient (k...). 2 The high-frequency acoustic resonator perfectly meets the performance requirements of high frequency and high bandwidth filters in the current 5G and 6G frequency bands.

[0073] This disclosure effectively excites higher-order Lamb wave modes by improving the stress field distribution, thereby significantly increasing the electromechanical coupling coefficient (k) of the acoustic resonator while maintaining high frequency and quality factor. 2 Finally, a high-frequency acoustic resonator with a high electromechanical coupling coefficient (>20%) under the S2, A3, and S4 vibration modes was obtained.

[0074] This disclosure provides a structure and fabrication method for a high-frequency acoustic resonator with a high electromechanical coupling coefficient, which excites higher-order vibration modes such as S2 / A3 / S4 when the thickness of the piezoelectric thin film and silicon dioxide are in a fixed ratio.

[0075] Figure 1 shows the stress (mode) distribution of the Lamb wave motion modes in the acoustic resonator. It can be seen that the piezoelectric effect generated by the Lamb wave resonator in the medium is related to the stress wave mode vector induced by the piezoelectric component in the medium. More specifically, the electromechanical coupling coefficient (k) is calculated using the Berlincourt formula. 2 ) Calculation yields k 2 ∝Um∝∫(E·d·T)dV, where Um is the coupling energy, E is the electric field strength, d is the piezoelectric coefficient, T is the stress, and V is the volume of the piezoelectric material. This illustrates the importance of the overlap between the applied electric field and the stress distribution of the resonant modes within the piezoelectric material along the thickness direction.

[0076] The acoustic resonator disclosed herein comprises: 1-substrate; 2-release region; 3-piezoelectric layer; 4-metal electrode; 5-silicon dioxide; 6-mask layer. The release region is used to suspend the device, making the lower boundary condition of the resonator electrically open; the mask layer is used in two steps to define the silicon dioxide deposition region and the etching region, respectively; the metal electrode is grown on the surface of the piezoelectric layer or the surface of the silicon dioxide layer, generating a transverse electric field to excite different acoustic vibration modes; the silicon dioxide layer is used to improve the stress mode distribution in the resonator. When the thickness of the piezoelectric layer is in a fixed ratio to the thickness of the silicon dioxide layer, the stress mode in the piezoelectric layer is a semi-sine curve, maximizing the integral of E and T, thereby achieving a high electromechanical coupling coefficient.

[0077] According to embodiments of this disclosure, the piezoelectric layer material comprises one of the following: lithium niobate (LN), lithium tantalate (LT), or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide;

[0078] According to Embodiment 1 of this disclosure, metal electrodes are grown on a piezoelectric layer, and silicon dioxide is deposited on the non-metallized region between the metal electrodes.

[0079] According to Embodiment 2 of this disclosure, silicon dioxide is deposited on a piezoelectric layer, and then a metal electrode is grown on the silicon dioxide.

[0080] According to embodiments of this disclosure, the thickness of the piezoelectric layer can be 10 to 1000 nm.

[0081] According to embodiments of this disclosure, the thickness of the metal electrode can be 10–250 nm.

[0082] According to embodiments of this disclosure, the number of metal electrodes is N, and the value of N ranges from 2 to 50.

[0083] According to embodiments of this disclosure, the spacing between two adjacent metal electrodes is half a wavelength, and the width of each metal electrode is one-sixth of a wavelength, one-quarter of a wavelength, or one-eighth of a wavelength. For example, in embodiment 1, the electrode width is selected as 5 μm.

[0084] According to embodiments of this disclosure, the length of the metal electrode is ten wavelengths or ten half wavelengths. For example, in Embodiment 1, the electrode length is selected as 120 μm, 200 μm, or 240 μm.

[0085] Example 1

[0086] Figure 2 shows a structural diagram of an acoustic resonator proposed in this disclosure, in which metal electrodes are grown on a piezoelectric layer and silicon dioxide is deposited between the metal electrodes. When the thickness of the silicon dioxide layer is in a certain proportion to the thickness of the piezoelectric layer, a high-order Lamb wave motion mode with a high electromechanical coupling coefficient is excited.

[0087] In this embodiment, when the piezoelectric layer is selected as 128° Y-cut lithium niobate and the metal electrode is selected as aluminum, the ratio of silicon dioxide thickness to piezoelectric film thickness is 0.5–1.7:1, which excites k 2 With an S2 Lamb wave content >20% and a silica thickness to piezoelectric film thickness ratio of 1.5–2.8:1, the excitation k 2 For A3 mode Lamb waves with >20% A3 mode content, when the ratio of silicon dioxide thickness to piezoelectric film thickness is 2.6–3.5:1, the excitation k 2 >20% of S4 Lamb wave.

[0088] Figure 3 shows the two-dimensional simulated admittance curves when the silicon dioxide thickness is 1:1 with the piezoelectric layer thickness. Under the vibration mode of the S2 mode Lamb wave, the resonant frequency (fs) reaches as high as 17.77 GHz, and the electromechanical coupling coefficient (k) is also high. 2 The efficiency is as high as 46.96%, and the anti-resonant frequency (fp) is 20.88 GHz. This breaks through the limitation of the electromechanical coupling coefficient of high-order Lamb waves in traditional single-layer film structures, and brings a better solution for the design of high-frequency broadband filters.

[0089] As shown in the top view and interface diagram of the resonator in Figure 4, when the thickness ratio of the piezoelectric layer to the silicon dioxide layer is 1:1, the S2 Lamb wave mode is excited in the dielectric layer, and its stress mode is a sinusoidal periodic curve. However, the stress in the piezoelectric layer only has a sinusoidal half-wave, which maximizes the integral of stress and electric field in the piezoelectric layer, thereby achieving a high electromechanical coupling coefficient.

[0090] This disclosure also provides a method for fabricating an acoustic resonator. Figure 5 is a flowchart of the fabrication steps of the acoustic resonator in Embodiment 1 of this disclosure. The process fabrication flow chart is shown in Figure 6.

[0091] Step S1: Provide a bilayer structure consisting of a substrate and a piezoelectric layer. The substrate can be a silicon substrate, a sapphire substrate, a gallium nitride substrate, or a silicon carbide substrate. The piezoelectric layer can be lithium niobate (LN), lithium tantalate (LT), or a composite material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.

[0092] Step S2: Electrode patterns are obtained by photolithography on the piezoelectric thin film, and the electrodes of the acoustic resonator are obtained by coating technology;

[0093] Step S3: Use masking technology to graphically define the silica deposition area;

[0094] Step S4: Deposit a silicon dioxide layer, wherein the thickness of the silicon dioxide layer depends on the Lamb wave motion mode to be excited;

[0095] Step S5: Use hard mask technology to create a mask layer above the electrode for mask protection during piezoelectric thin film etching; and further define the etching area of ​​the acoustic resonator by overlay.

[0096] Step S6: Etch the piezoelectric thin film using inductively coupled plasma etching;

[0097] Step S7: Dry etch the substrate to release the resonator from the substrate.

[0098] Example 2

[0099] Another acoustic resonator structure proposed in this disclosure is shown in Figure 7. In this structure, a silicon dioxide layer is deposited on the entire piezoelectric layer, and then a metal electrode is grown on the silicon dioxide layer to generate a transverse electric field for exciting Lamb waves. Figure 8 shows the two-dimensional simulated admittance curve of the resonator when the thickness ratio of the silicon dioxide layer to the piezoelectric layer is 1:1, where the resonant frequency (fs) is 17.83 GHz and the electromechanical coupling coefficient (k) is... 2 The harmonic response rate is as high as 45.98%, and the anti-resonant frequency (fp) is 20.89 GHz.

[0100] The working principle of this structure is similar to that described in Example 1. The core idea is to improve the stress mode distribution in the resonator by depositing a silicon dioxide layer, so that the stress and electric field intensity integral in the piezoelectric layer can be maximized. Based on this idea, the ratio of silicon dioxide layer thickness to piezoelectric layer thickness when exciting higher-order modes such as A3, S4, and A5 is not derived, but these are also within the scope of protection of this patent.

[0101] This disclosure also provides another method for fabricating an acoustic resonator. Figure 9 shows the fabrication steps of this structure, and the process fabrication flow is shown in Figure 10.

[0102] S11: Provides a substrate and a piezoelectric layer;

[0103] S12: Growing a silicon dioxide layer in a piezoelectric layer

[0104] S13: Deposit a metal electrode on the silicon dioxide layer;

[0105] S14: Graphically define the mask etching area;

[0106] S15: Using inductively coupled plasma etching to etch piezoelectric thin films;

[0107] S16: Isotropic dry etching of the silicon substrate releases the piezoelectric thin film to form the release region, resulting in the final acoustic resonator.

[0108] The masking technology, silicon dioxide deposition technology, and resonator release technology are all similar to those in Example 1, and will not be described again here.

[0109] Referring to the design of FBAR resonators, the structure proposed in this disclosure is also applicable to the upper and lower electrode structure. Figure 11 shows a diagram of the core region of the upper and lower electrode structure (excluding the substrate and release cavity). Based on the above theory, by controlling the thickness ratio of the silicon dioxide layer to the piezoelectric layer, high-order Lamb wave motion modes with high electromechanical coupling coefficients can also be excited.

[0110] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and are not described in detail. Furthermore, the definitions of the various elements and methods described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

[0111] Based on the above description, those skilled in the art should have a clear understanding of the acoustic resonator and its fabrication method disclosed herein.

[0112] In summary, this disclosure provides an acoustic resonator and its fabrication method, based on a high electromechanical coupling coefficient (k) of a piezoelectric substrate and a silicon dioxide bilayer film structure. 2 A Lamb wave acoustic resonator is disclosed. By adjusting the thickness ratio of the silicon dioxide layer to the piezoelectric layer, various higher-order modes (S2, A3, etc.) are excited, achieving an electromechanical coupling coefficient of over 40%. The resonator includes: a substrate; a release region; a piezoelectric layer; a metal electrode; a silicon dioxide layer; and a mask layer. The thickness ratio of the silicon dioxide layer to the piezoelectric layer follows a specific pattern, thereby improving the stress distribution for Lamb wave excitation and increasing the electromechanical coupling coefficient of the resonator. This disclosure also provides a method for fabricating the aforementioned acoustic resonator.

[0113] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Any other corresponding changes and modifications made based on the technical concept of this disclosure should be included within the scope of protection of the claims of this disclosure.

Claims

1. An acoustic resonator, comprising: a substrate; a piezoelectric layer fabricated on the substrate; a release region formed between the substrate and the piezoelectric layer configured for a suspended release of the acoustic resonator; a silicon dioxide layer fabricated on the piezoelectric layer, together with the piezoelectric layer, configured for a dielectric layer; and a metal electrode layer configured for generating an electric field to excite a Lamb wave to excite the piezoelectric layer to generate an acoustic wave vibration mode; a stress mode profile in the piezoelectric layer is improved by tuning the thickness of the silicon dioxide layer to increase an electromechanical coupling coefficient.

2. The acoustic resonator of claim 1, wherein the substrate is fabricated from a material selected from a group consisting of silicon, sapphire, gallium nitride, or silicon carbide.

3. The acoustic resonator of claim 1, wherein the piezoelectric layer is fabricated from a material selected from a group consisting of lithium niobate, lithium tantalate, or a composite of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, zinc oxide.

4. The acoustic resonator of claim 1, wherein a cut of the piezoelectric layer is 110°Y ~ 130°Y cut, 10°Z ~ 30°Z cut.

5. The acoustic resonator of claim 1, wherein the metal electrode layer is fabricated on an upper surface or a lower surface of the dielectric layer, or a portion of the metal electrode layer is located in the silicon dioxide layer.

6. The acoustic resonator of claim 1, wherein the metal electrode layer includes N metal electrodes, 2 ≤ N ≤ 600, a spacing between two adjacent metal electrodes is a half wavelength; a width of each metal electrode is a sixth wavelength or a quarter wavelength or an eighth wavelength; a length of each metal electrode is ten wavelengths or ten half wavelengths.

7. The acoustic resonator of claim 1, wherein a thickness of the piezoelectric layer is 10-1000 nm.

8. The acoustic resonator of claim 1, wherein: The thickness of the silicon dioxide layer is 0.5-1.7 times the thickness of the piezoelectric layer, and the S2 mode Lamb wave is excited 2 >20%. The thickness of the silicon dioxide layer is 1.5 to 2.8 times the thickness of the piezoelectric layer, and the A3 mode Lamb wave is excited 2 > 20% of the A3 mode Lamb wave; The thickness of the silicon dioxide layer is 2.6-3.5 times the thickness of the piezoelectric layer, and the S4 mode Lamb wave is excited 2 >20%.

9. A method of fabricating the acoustic resonator of any one of claims 1-8, comprising: providing a substrate and a piezoelectric layer; growing a metal electrode on the piezoelectric layer; patterning a silicon dioxide region; growing a silicon dioxide layer; patterning a mask etching region; inductively coupled plasma etching the piezoelectric film; isotropically dry etching the silicon substrate to release the piezoelectric film to form a release region to obtain a final acoustic resonator.

10. A method of fabricating the acoustic resonator of any one of claims 1-8, comprising: providing a substrate and a piezoelectric layer; growing a silicon dioxide layer on the piezoelectric layer depositing a metal electrode on the silicon dioxide layer; patterning a mask etching region; inductively coupled plasma etching the piezoelectric film; isotropically dry etching the silicon substrate to release the piezoelectric film to form a release region to obtain a final acoustic resonator.

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