Lithium niobate single crystal thin film based love wave phononic crystal resonator

Abstract

This invention relates to the field of surface acoustic wave (SAW) device technology and discloses a Love wave phononic crystal resonator based on a lithium niobate single-crystal thin film. The resonator includes a functional substrate and a piezoelectric thin film layer on the upper surface of the functional substrate. An interdigital transducer is disposed in the middle region of the upper surface of the piezoelectric thin film layer, and phononic crystals are disposed on both sides of the interdigital transducer. The piezoelectric thin film layer is a lithium niobate single-crystal thin film, and the tangential direction of the lithium niobate single-crystal thin film is any one of the X-cut directions, including the X-cut and the Y direction from -15° to 15°. This invention utilizes phononic crystals to replace the reflector grating in traditional SAW resonators. By combining the functional substrate and the lithium niobate single-crystal thin film to construct a material system, it achieves higher sound velocity and lower longitudinal loss. It features a simple structure, small size, and ease of fabrication and integration, and exhibits a higher Q value compared to a Bragg grating resonator of the same size.

Description

Technical Field

[0001] This invention relates to the field of surface acoustic wave (SAW) device technology, and in particular to a Love wave phononic crystal resonator based on a lithium niobate single-crystal thin film. Background Technology

[0002] Phononic crystals are novel artificially synthesized periodic materials used to control and manipulate the propagation of sound waves. They can be formed by periodically arranging scatterers embedded in a medium. These periodically arranged scatterers can be made of any material other than the substrate, including air slots / holes. Phononic crystals possess unique properties such as band gaps and anisotropic propagation. The band gap is the frequency range in which sound waves cannot propagate, exhibiting strong impediment and localization of acoustic signals. This characteristic has been observed in bulk acoustic waves, surface acoustic waves (SAWs), and Lamb waves in various phononic crystal structures. In recent years, based on the band gap characteristics of phononic crystals, researchers have proposed SAW devices such as filters and resonators.

[0003] Surface acoustic wave (SAW) devices possess advantages such as low transmission loss, high energy conversion efficiency, and compact structure, making them key components in modern high-frequency, high-speed communication systems and sensing applications. SAW primarily includes Rayleigh waves and Love waves. With the development of multilayer piezoelectric composite substrates, various high-performance SAW devices based on Love waves have been researched and applied. One of the key performance indicators of SAW resonators is the quality factor (Q), which determines the rectangularity and insertion loss of the filter, the phase noise of the oscillator, and the sensitivity of the sensor. Therefore, resonators with higher Q values ​​have always been a goal pursued by researchers. Existing Bragg grating resonators require numerous metal reflectors, while phononic crystals, which have strong acoustic wave impedimentation capabilities, can replace the reflectors in traditional SAW resonators. This enhances the energy localization effect of the resonator (i.e., reduces the mode volume of the resonator), thereby reducing the energy loss of the resonator (i.e., increasing the Q value of the SAW resonator). Simultaneously, replacing the reflectors in traditional SAW resonators with phononic crystals can reduce the device area, facilitating the realization of more compact and highly integrated SAW resonators and filters.

[0004] Furthermore, among the piezoelectric materials used in surface acoustic wave (SAW) devices, lithium niobate exhibits significant advantages, including a high electromechanical coupling coefficient, high temperature stability, a wide frequency range, and a relatively mature fabrication process, making it of great application value in SAW devices.

[0005] In summary, how to improve surface acoustic wave resonators based on the advantages of lithium niobate and phononic crystals has become an important research topic in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a Love wave phononic crystal resonator based on a lithium niobate single crystal thin film. By using a phononic crystal to replace the reflector grating in a traditional surface acoustic wave resonator, and by combining a functional substrate with a lithium niobate single crystal thin film to construct a material system, higher sound velocity and lower longitudinal loss are achieved. It has the characteristics of simple structure, small size, and easy fabrication and integration. Compared with a Bragg reflector grating resonator of the same size, it has a higher Q value.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A Love wave phononic crystal resonator based on a lithium niobate single crystal thin film, the Love wave phononic crystal resonator includes a functional substrate and a piezoelectric thin film layer located on the upper surface of the functional substrate, an interdigital transducer is disposed in the middle region of the upper surface of the piezoelectric thin film layer, and phononic crystals are disposed on both sides of the interdigital transducer.

[0009] The piezoelectric thin film layer is a lithium niobate single crystal thin film, and the tangential direction of the lithium niobate single crystal thin film is any one of the X-cut, including the X-cut and the Y direction from -15° to 15°.

[0010] Furthermore, the material of the functional substrate is one or more of silicon carbide, sapphire, quartz, diamond, silicon dioxide, polycrystalline silicon, and monocrystalline silicon.

[0011] Furthermore, the thickness of the lithium niobate single crystal thin film is 0-10 micrometers.

[0012] Furthermore, the phononic crystal is formed by etching periodic or aperiodic holes or grooves on the surface of the lithium niobate single crystal film, or by growing periodic or aperiodic pillar structures on the surface of the lithium niobate single crystal film.

[0013] Furthermore, the cross-sectional shape of the hole or groove structure and the column structure is one or more combinations of circular, elliptical, triangular, polygonal or other irregular shapes.

[0014] Furthermore, the material of the column structure is lithium niobate, silicon, silicon dioxide, silicon nitride, or a metal material, wherein the metal material includes aluminum, copper, nickel, and chromium; the height of the column structure is 0-1000 micrometers.

[0015] Furthermore, the lattice of the phononic crystal is one of a triangular lattice, a tetragonal lattice, a honeycomblattice, a kagome lattice, or other lattices with symmetry, and the lattice period ranges from 0 to 1000 micrometers.

[0016] Furthermore, the spacing between the interdigital transducer and the phononic crystal is greater than 1 / 2 times the electrode period.

[0017] Furthermore, the interdigital transducer includes at least two pairs of interdigital electrodes, the thickness of which is 0-5000 nanometers, and the material of which is an alloy of one or more combinations of gold, silver, aluminum, titanium, nickel, and chromium; the electrode period of which is 0-1000 micrometers, and the electrode width of which is 0-250 micrometers.

[0018] According to specific embodiments provided by the present invention, the Love wave phononic crystal resonator based on lithium niobate single crystal thin film disclosed by the present invention has the following technical effects:

[0019] (1) Replacing the reflection grating in the traditional surface acoustic wave resonator with a phononic crystal can enhance the energy localization effect of the resonator (i.e. reduce the mode volume of the resonator), thereby reducing the energy loss of the resonator (i.e. increasing the Q value of the surface acoustic wave resonator). At the same time, it can reduce the device area, which is conducive to realizing a more compact and more integrated Love wave phononic crystal resonator.

[0020] (2) By combining a functional substrate with a lithium niobate single crystal thin film, a material system can be constructed to achieve higher sound speed and lower longitudinal loss. The Love wave based on lithium niobate is a horizontal shear wave, which lacks a displacement component perpendicular to the substrate surface, which can significantly reduce energy transmission loss and achieve a larger electromechanical coupling coefficient. This is beneficial for exploring Love wave phononic crystal resonators with ultra-large bandwidth and small temperature drift.

[0021] In summary, the Love wave phononic crystal resonator provided by this invention has a relatively simple structure, small size, and is easy to fabricate and integrate. The phononic crystal has a wide directional bandgap for Love waves. Without affecting the heat dissipation and operating bandwidth of surface acoustic wave devices, the quality factor of the Love wave phononic crystal resonator fabricated based on this phononic crystal is significantly improved compared to a Bragg grating resonator of the same size. This is of great significance for realizing high-performance, miniaturized next-generation microwave acoustic devices. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a top view schematic diagram of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film of the present invention;

[0024] Figure 2 This is a schematic cross-sectional view of the Love aperture type phononic crystal resonator along section line A-A' in Embodiment 1 of the present invention;

[0025] Figure 3 This is a schematic cross-sectional view of the Love wave column type phononic crystal resonator along section line A-A' in Embodiment 2 of the present invention;

[0026] Figure 4 The image shows the surface acoustic wave bandgap structure of the Love wave phononic crystal resonator in the -5°Y direction in Embodiment 1 of the present invention. (a) is a schematic diagram of the Love mode bandgap along the Г-X direction of the phononic crystal lattice, and (b) and (c) are the top view and front view of the sound field distribution in the phononic crystal cell, respectively.

[0027] Figure 5 The figures show a comparison of the energy field distribution at the main resonance peak of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the conventional reflective grating resonator in Embodiment 1 of the present invention, and a comparison of their respective admittances. In the figures, (a) and (b) are the energy field distribution at the main resonance peak of the conventional reflective grating resonator and the Love wave phononic crystal resonator based on lithium niobate single crystal thin film, respectively; and (c) and (d) are the admittances at the main resonance peak of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the conventional reflective grating resonator, respectively.

[0028] Figure 6 This is a schematic cross-sectional view of the Love aperture type phononic crystal resonator of Embodiment 3 of the present invention along section line A-A';

[0029] Figure 7 This is a cross-sectional schematic diagram of the Love wave column type phononic crystal resonator along section line A-A' in Embodiment 4 of the present invention;

[0030] Figure 8 The image shows the surface acoustic wave bandgap structure of the Love wave phononic crystal resonator in the -5°Y direction in Embodiment 3 of the present invention. (a) is a schematic diagram of the Love mode bandgap along the Г-X direction of the phononic crystal lattice, and (b) and (c) are the top view and front view of the sound field distribution in the phononic crystal cell, respectively.

[0031] Figure 9 The above are comparison diagrams of the admittance of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the traditional reflective gate resonator in Embodiment 3 of the present invention. Among them, (a) and (b) are the admittance diagrams at the main resonance peak of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the traditional reflective gate resonator, respectively.

[0032] Figure 10 This is a schematic cross-sectional view of the Love aperture type phononic crystal resonator along section line A-A' in Embodiment 5 of the present invention;

[0033] Figure 11 This is a schematic cross-sectional view of the Love wave column type phononic crystal resonator along section line A-A' in Embodiment 6 of the present invention;

[0034] Figure 12 The image shows the surface acoustic wave bandgap structure of the Love wave phononic crystal resonator in the -5°Y direction in Embodiment 5 of the present invention. (a) is a schematic diagram of the Love mode bandgap along the Г-X direction of the phononic crystal lattice, and (b) and (c) are the top view and front view of the sound field distribution in the phononic crystal cell, respectively.

[0035] Figure 13 The diagram shows a comparison of the admittance of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the traditional reflective gate resonator in Embodiment 5 of the present invention. (a) and (b) are the admittance diagrams of the Love wave phononic crystal resonator based on lithium niobate single crystal thin film and the traditional reflective gate resonator, respectively.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1, Phononic crystal region; 1', Microporous phononic crystal; 1", Micropillar phononic crystal; 2, Interdigitated transducer; 3, Piezoelectric thin film layer; 4, 5, 6, 7, Functional substrate. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] In the description of an invention patent, it is important to understand the terms "upper," "lower," "front," and "rear."

[0040] The terms "left," "right," "top," "bottom," "inner," "outer," "center," "longitudinal," "lateral," "vertical," and "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the purpose of facilitating and simplifying the description of the invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. When an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there may be an intermediate element present.

[0041] The purpose of this invention is to design a Love wave phononic crystal resonator with a relatively simple structure and small size, in order to address the issue that existing Bragg grating resonators require a large number of metal reflectors. This device is easy to fabricate and integrate, and has a higher Q value compared to Bragg grating resonators of the same size.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] like Figure 1 , Figure 2 , Figure 3 , Figure 6 , Figure 7 , Figure 10 , Figure 11 As shown, the present invention provides a Love wave phononic crystal resonator based on a lithium niobate single crystal thin film, comprising a functional substrate (one or more layers) and a piezoelectric thin film layer 3 located on the upper surface of the functional substrate. An interdigital transducer 2 is disposed in the middle region of the upper surface of the piezoelectric thin film layer 3, and phononic crystals are disposed in phononic crystal regions 1 on both sides of the interdigital transducer 2. The frequencies of the main resonance peak and the anti-resonance peak of the Love wave phononic crystal resonator are both within the phononic crystal bandgap.

[0044] Preferably, the piezoelectric thin film layer 3 is a lithium niobate single crystal thin film, and the tangential direction of the lithium niobate single crystal thin film is any one of the X-cut, including the X-cut and the Y direction from -15° to 15°. Among them, the lithium niobate single crystal thin film in the -10° Y direction has a larger electromechanical coupling coefficient, and the lithium niobate single crystal thin film in the -5° to -3° Y direction has a higher quality factor.

[0045] For example, the lithium niobate single crystal thin film has an X-shaped tangent and a -5° Y-direction, with the electrode periodic direction parallel to the -5° Y-direction.

[0046] For example, the material of the functional substrate is one (one layer) or more (multilayers) of silicon carbide (4-H, 6-H or 3-C), sapphire, (AT-cut, BT-cut or SC-cut) quartz, diamond, silicon dioxide, polycrystalline silicon, and monocrystalline silicon.

[0047] For example, the thickness of the lithium niobate single crystal thin film is 0-10 micrometers.

[0048] For example, the phononic crystal is formed by etching periodic or aperiodic holes or grooves on the surface of the lithium niobate single-crystal thin film (i.e., the holes or grooves are located within the lithium niobate single-crystal thin film itself), or by growing periodic or aperiodic pillar structures on the surface of the lithium niobate single-crystal thin film (i.e., the pillar structures are located on the upper surface of the lithium niobate single-crystal thin film). The depth of the etched holes or grooves may be less than, equal to, or greater than the thickness of the lithium niobate single-crystal thin film (i.e., the phononic crystal structure is located not only in the lithium niobate single-crystal thin film but also in the functional substrate material).

[0049] The cross-sectional shape of the hole or groove structure and the column structure is one or more combinations of circular, elliptical, triangular, polygonal, or other irregular shapes. The polygons include quadrilaterals (squares, rhombuses, rectangles), pentagons, hexagons, etc.

[0050] For example, the material of the pillar structure is lithium niobate (of the same origin as the piezoelectric thin film layer), silicon, silicon dioxide, silicon nitride, or a metal material, wherein the metal material includes aluminum, copper, nickel, and chromium; for example, the height of the pillar structure is 0-1000 micrometers.

[0051] The phononic crystal has a lattice that is one of a triangular lattice, a tetragonal lattice, a honeycomb lattice, a kagome lattice, or other lattices with symmetry, and the lattice period ranges from 0 to 1000 micrometers.

[0052] For example, the spacing between the interdigital transducer and the phononic crystal is greater than 1 / 2 times the electrode period.

[0053] Specifically, the interdigital transducer includes at least two pairs of interdigital electrodes, which are metal electrodes with a thickness of 0-5000 nanometers. The material of the interdigital electrodes is an alloy of one or more combinations of gold, silver, aluminum, titanium, nickel, and chromium. The electrode period of the interdigital electrodes is 0-1000 micrometers, and the electrode width is 0-250 micrometers.

[0054] Example 1

[0055] Figure 1This is a top view of a Love wave phonon crystal resonator provided in Embodiment 1 of the present invention. In Embodiment 1, the phonon crystal is formed by etching periodic or non-periodic holes or grooves on the surface of the lithium niobate single-crystal thin film. The phonon crystal lattice is a tetragonal lattice with C4 symmetry and a lattice period of 1.5 micrometers. The etched hole structure forms a micro-hole phonon crystal 1', with the micro-holes being circular in shape, i.e., circular holes, with a diameter of 1 micrometer and a depth of 300 nanometers, thus forming a Love wave aperture type phonon crystal resonator. A cross-sectional view of the Love wave aperture type phonon crystal resonator along section line A-A' is shown below. Figure 2 As shown. In this embodiment, a functional substrate 4 is provided, and the substrate 4 can be 4-H, 6-H, or 3-C silicon carbide.

[0056] In this embodiment 1, the interdigitated electrodes are gold electrodes with an electrode period of 2.05 micrometers, an electrode thickness of 45 nanometers, and an effective electrode aperture of 70 lattice periods, or 105 micrometers. The interdigitated electrode region can excite Love waves that vibrate in the horizontal plane perpendicular to the propagation direction.

[0057] The Love aperture type phononic crystal resonator in this embodiment of the invention has a Love mode bandgap along the Γ-X direction of the phononic crystal lattice, with a bandgap range of 1.99 GHz to 2.32 GHz. Figure 4 As shown in (a), the Love wave is a horizontal shear wave, with its acoustic energy mainly distributed on the surface of the piezoelectric substrate, and the wave vibration direction is perpendicular to the wave propagation direction. In this embodiment, the top view and front view of the sound field distribution in the phononic crystal cell are shown below. Figure 4 As shown in (b) and (c).

[0058] The distance between the electrode area and the reflection area is one of the important factors affecting the quality factor. In this embodiment of the invention, the distance between the electrode area and the reflection area is defined as the distance L between the center of the outermost metal electrode and the center of the innermost circular hole, such as... Figure 2 As shown, the spacing L is preferably 3 / 4 times the electrode period, i.e., 1.5375 micrometers.

[0059] The Love wave phononic crystal resonator based on lithium niobate single-crystal thin film provided in Embodiment 1 of this invention has significant technical advantages compared with traditional reflective gate resonators:

[0060] like Figure 5As shown in (a) and (b), the energy field distribution of the Love wave phononic crystal resonator at the main resonant peak frequency of 2.032 GHz is mainly concentrated in the interdigitated electrode region, indicating that the phononic crystal has a very strong localization effect on energy. In contrast, the energy of the traditional reflective grating resonator will have a more serious energy leakage in the direction of Love wave propagation. It can be seen that the Love wave phononic crystal resonator provided by the present invention has a stronger energy localization effect than the traditional reflective grating resonator.

[0061] The admittances of Love wave phononic crystal resonators and traditional reflective grating resonators are as follows: Figure 5 As shown in (c) and (d), the main resonant peak frequency (2.032 GHz) and anti-resonant peak frequency (2.265 GHz) of the Love wave phononic crystal resonator are both within the phononic crystal bandgap (1.99 GHz - 2.32 GHz). Clearly, compared with the admittance of a traditional reflective grating resonator, the main resonant peak of the Love wave phononic crystal resonator is sharper. According to the formula for calculating the quality factor of the main resonant peak, Q = f... s / f 3dB , where f s The main resonant peak frequency, f 3dB Given a 3dB bandwidth at the resonance peak, the Q value of the main resonance peak of the Love wave phononic crystal resonator in this embodiment of the invention is 1847.0, while the Q value of the main resonance peak of the traditional reflective grating resonator is only 701.9, accompanied by higher-order spurious modes. This indicates that the Love wave phononic crystal resonator provided by this invention has a higher quality factor than the traditional reflective grating resonator while keeping the electromechanical coupling coefficient unchanged.

[0062] Example 2

[0063] In this embodiment 2, the phononic crystal is formed by growing periodic or non-periodic pillar structures on the surface of the lithium niobate single-crystal thin film. The pillar structures form micropillar phononic crystals 1", where each pillar is a cylinder with a height of 50 nanometers, made of aluminum, with a lattice period of 1.5 micrometers and a diameter of 1 micrometer, forming a Love wave pillar-type phononic crystal resonator. The cross-sectional view of the Love wave pillar-type phononic crystal resonator along section line A-A' is shown below. Figure 3 As shown. In this embodiment, the functional base 4 is provided with one layer.

[0064] Example 3

[0065] In Embodiment 3 of the present invention, the phononic crystal is formed by etching periodic or non-periodic holes or grooves on the surface of the lithium niobate single-crystal thin film. The phononic crystal lattice is a tetragonal lattice with C4 symmetry and a lattice period of 1.5 micrometers. The etched hole structure forms a micro-hole phononic crystal 1', the micro-holes being circular in shape, i.e., circular holes, with a diameter of 1 micrometer and a depth of 300 nanometers, forming a Love wave aperture type phononic crystal resonator. The cross-sectional view of the Love wave aperture type phononic crystal resonator along section line A-A' is shown below. Figure 6 As shown. In this embodiment, the functional substrate has three layers: 5-silicon dioxide, 6-polycrystalline silicon, and 7-monocrystalline silicon. Other materials can also be used.

[0066] In this embodiment 3, the interdigitated electrodes are gold electrodes with an electrode period of 1.3 micrometers, an electrode thickness of 135 nanometers, and an effective electrode aperture of 70 lattice periods, or 91 micrometers. The interdigitated electrode region can excite Love waves that vibrate in the horizontal plane perpendicular to the propagation direction.

[0067] The Love aperture type phononic crystal resonator in Embodiment 3 of the present invention has a Love mode bandgap along the Γ-X direction of the phononic crystal lattice, with a bandgap range of 1.22 GHz to 1.63 GHz. Figure 8 As shown in (a), the Love wave is a horizontal shear wave, with its acoustic energy mainly distributed on the surface of the piezoelectric substrate, and the wave vibration direction is perpendicular to the wave propagation direction. In this embodiment, the top view and front view of the sound field distribution in the phononic crystal cell are shown below. Figure 8 As shown in (b) and (c).

[0068] The distance between the electrode area and the reflection area is one of the important factors affecting the quality factor. In this embodiment of the invention, the distance between the electrode area and the reflection area is defined as the distance L between the center of the outermost metal electrode and the center of the innermost circular hole, such as... Figure 6 As shown, the spacing L is preferably 3 / 4 times the electrode period, i.e. 0.975 micrometers.

[0069] The Love wave phononic crystal resonator based on lithium niobate single-crystal thin film provided in Embodiment 3 of the present invention has significant technical advantages compared with the traditional reflective gate resonator:

[0070] The admittances of Love wave phononic crystal resonators and traditional reflective grating resonators are as follows: Figure 9 As shown in (a) and (b), the main resonant peak frequency (1.365 GHz) and anti-resonant peak frequency (1.52 GHz) of the Love wave phononic crystal resonator are both within the phononic crystal bandgap (1.22 GHz - 1.63 GHz). Clearly, compared with the admittance of a traditional reflective grating resonator, the main resonant peak of the Love wave phononic crystal resonator is sharper. According to the formula for calculating the quality factor of the main resonant peak, Q = f...s / f 3dB In this embodiment of the invention, the Q value of the main resonance peak of the Love wave phononic crystal resonator is 341, while the Q value of the main resonance peak of the traditional reflective grating resonator is only 221. This indicates that the Love wave phononic crystal resonator provided by this invention has a higher quality factor than the traditional reflective grating resonator while keeping the electromechanical coupling coefficient unchanged.

[0071] Example 4

[0072] In this embodiment 4, the phononic crystal is formed by growing periodic or non-periodic pillar structures on the surface of the lithium niobate single-crystal thin film. The pillar structures form micropillar phononic crystals 1", where each pillar is a cylinder with a height of 50 nanometers, made of aluminum, with a lattice period of 1.5 micrometers and a diameter of 1 micrometer, forming a Love wave pillar-type phononic crystal resonator. The cross-sectional view of the Love wave pillar-type phononic crystal resonator along section line A-A' is shown below. Figure 7 As shown. In this embodiment, the functional substrate is provided with three layers, namely 5, 6, and 7, which can be made of different materials.

[0073] Example 5

[0074] In Embodiment 5 of the present invention, the phononic crystal is formed by etching periodic or non-periodic holes or grooves on the surface of the lithium niobate single-crystal thin film. The phononic crystal lattice is a tetragonal lattice with C4 symmetry and a lattice period of 1.5 micrometers. The etched hole structure forms a micro-hole phononic crystal 1', with the micro-holes being circular in shape, i.e., circular holes, with a diameter of 1 micrometer and a depth of 300 nanometers, forming a Love wave aperture type phononic crystal resonator. The cross-sectional view of the Love wave aperture type phononic crystal resonator along section line A-A' is shown below. Figure 10 As shown. In this embodiment, the functional substrate has two layers, namely 5-silicon dioxide and 7-monocrystalline silicon, but other different materials can also be used.

[0075] In this embodiment 5, the interdigitated electrodes are gold electrodes with an electrode period of 1.3 micrometers, an electrode thickness of 135 nanometers, and an effective electrode aperture of 70 lattice periods, or 91 micrometers. The interdigitated electrode region can excite Love waves that vibrate in the horizontal plane perpendicular to the propagation direction.

[0076] The Love aperture type phononic crystal resonator in Embodiment 5 of the present invention has a Love mode bandgap along the Γ-X direction of the phononic crystal lattice, with a bandgap range of 1.22 GHz to 1.63 GHz. Figure 12 As shown in (a), the Love wave is a horizontal shear wave, with its acoustic energy mainly distributed on the surface of the piezoelectric substrate, and the wave vibration direction is perpendicular to the wave propagation direction. In this embodiment, the top view and front view of the sound field distribution in the phononic crystal cell are shown below. Figure 12 As shown in (b) and (c).

[0077] The distance between the electrode area and the reflection area is one of the important factors affecting the quality factor. In this embodiment of the invention, the distance between the electrode area and the reflection area is defined as the distance L between the center of the outermost metal electrode and the center of the innermost circular hole, such as... Figure 2 As shown, the spacing L is preferably 3 / 4 times the electrode period, i.e. 0.975 micrometers.

[0078] The Love wave phononic crystal resonator based on lithium niobate single-crystal thin film provided in Embodiment 5 of the present invention has significant technical advantages compared with the traditional reflective gate resonator:

[0079] The admittances of Love wave phononic crystal resonators and traditional reflective grating resonators are as follows: Figure 13 As shown in (a) and (b), the main resonant peak frequency (1.365 GHz) and anti-resonant peak frequency (1.52 GHz) of the Love wave phononic crystal resonator are both within the phononic crystal bandgap (1.24 GHz - 1.68 GHz). Clearly, compared with the admittance of a traditional reflective grating resonator, the main resonant peak of the Love wave phononic crystal resonator is sharper. According to the formula for calculating the quality factor of the main resonant peak, Q = f... s / f 3dB In this embodiment of the invention, the main resonance peak Q value of the Love wave phononic crystal resonator is 455, while the main resonance peak Q value of the traditional reflective grating resonator is only 207. This indicates that the Love wave phononic crystal resonator provided by this invention has a higher quality factor than the traditional reflective grating resonator while keeping the electromechanical coupling coefficient unchanged.

[0080] Example 6

[0081] In this embodiment 6, the phononic crystal is formed by growing periodic or non-periodic pillar structures on the surface of the lithium niobate single-crystal thin film. The pillar structures form micropillar phononic crystals 1", where each pillar is a cylinder with a height of 50 nanometers, made of aluminum, with a lattice period of 1.5 micrometers and a diameter of 1 micrometer, forming a Love wave pillar-type phononic crystal resonator. The cross-sectional view of the Love wave pillar-type phononic crystal resonator along section line A-A' is shown below. Figure 11 As shown. In this embodiment, the functional substrate has two layers, 5 and 7, which can be made of different materials.

[0082] In summary, the Love wave phononic crystal based on a functional substrate and a lithium niobate single-crystal thin film provided by this invention has a wider Love wave directional bandgap. Without affecting the heat dissipation and operating bandwidth of the surface acoustic wave device, the quality factor of the Love wave phononic crystal resonator invented based on the phononic crystal is significantly improved compared with the Bragg reflector resonator of the same size. This is of great significance for realizing a new generation of high-performance and miniaturized microwave acoustic devices.

[0083] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A Love wave phononic crystal resonator based on a lithium niobate single crystal thin film, characterized in that, The Love wave phononic crystal resonator includes a functional substrate and a piezoelectric thin film layer located on the upper surface of the functional substrate. An interdigital transducer is disposed in the middle region of the upper surface of the piezoelectric thin film layer, and phononic crystals are disposed on both sides of the interdigital transducer. The piezoelectric thin film layer is a lithium niobate single crystal thin film, and the tangential direction of the lithium niobate single crystal thin film is any one of the X-cut, including the X-cut and the Y direction from -15° to 15°. The phononic crystal is formed by etching periodic or aperiodic holes or grooves on the surface of the lithium niobate single-crystal thin film, or by growing periodic or aperiodic pillar structures on the surface of the lithium niobate single-crystal thin film; the cross-sectional shape of the holes or grooves and the pillar structures is one or more combinations of circular, elliptical, triangular, polygonal or other irregular shapes; the lattice of the phononic crystal is one of triangular lattice, tetragonal lattice, honeycomb lattice, kagome lattice or other symmetrical lattices, and the lattice period ranges from 0 to 1000 micrometers; The spacing between the interdigital transducer and the phononic crystal is greater than 1 / 2 times the electrode period.

2. The lithium niobate single crystal thin film based Love wave phononic crystal resonator according to claim 1, wherein The material of the functional substrate is one or more of silicon carbide, sapphire, quartz, diamond, silicon dioxide, polycrystalline silicon, and monocrystalline silicon.

3. The Love wave phononic crystal resonator based on a lithium niobate single-crystal thin film according to claim 1, characterized in that, The thickness of the lithium niobate single crystal thin film is 0-10 micrometers.

4. The Love wave phononic crystal resonator based on a lithium niobate single-crystal thin film according to claim 1, characterized in that, The column structure is made of lithium niobate, silicon, silicon dioxide, silicon nitride, or a metal, including aluminum, copper, nickel, and chromium; the height of the column structure is 0-1000 micrometers.

5. The Love wave phononic crystal resonator based on a lithium niobate single-crystal thin film according to claim 1, characterized in that, The interdigital transducer includes at least two pairs of interdigital electrodes, the thickness of which is 0-5000 nanometers, and the material of which is an alloy of one or more combinations of gold, silver, aluminum, titanium, nickel, and chromium; the electrode period of which is 0-1000 micrometers, and the electrode width of which is 0-250 micrometers.

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