Surface acoustic wave resonator with multi-coefficient coupled modes

Abstract

Provided in the present disclosure is a surface acoustic wave resonator with multi-coefficient coupled modes. The surface acoustic wave resonator comprises: a substrate; a piezoelectric layer, which is arranged on the substrate; and an electrode layer, which is arranged on the piezoelectric layer and comprises at least two interdigital electrodes, wherein the piezoelectric layer is made of Y-cut lithium niobate; the piezoelectric layer jointly excites acoustic waves on the basis of the mutual coupling of a piezoelectric coefficient e15, and / or a piezoelectric coefficient e16 and / or a piezoelectric coefficient e34; and the ratio of the distance between the interdigital electrodes to the thickness of the electrode layer ranges from 0.5 to 10.

Description

Surface acoustic wave resonator with multi-coefficient coupled modes Technical Field

[0001] The present disclosure relates to the technical field of resonators, and in particular to a surface acoustic wave resonator with multiple coefficient coupling modes. Background Art

[0002] With the widespread application of mobile wireless communication devices, SAW (Surface Acoustic Wave) devices have been an important component of signal filtering in RF modules for decades. However, with the rapid development of the fifth-generation mobile communication protocol, the emerging frequency bands require larger bandwidths, which poses new challenges to traditional surface acoustic wave resonators - frequency and bandwidth. In order to address the challenges brought by the new communication protocols, some solutions have been proposed, such as AlScN bulk acoustic wave devices, Lamb wave resonators, and new solutions have been proposed, all of which are aimed at improving the electromechanical coupling coefficient k 2 This is mainly because the electromechanical coupling coefficient k 2 It is considered the most important performance indicator and directly determines the bandwidth of the filter. However, the complex manufacturing process of bulk acoustic wave devices requires individual trimming of the piezoelectric film thickness, and doping the piezoelectric film will reduce the quality factor of the resonator.

[0003] On the other hand, piezoelectric waveguides based on suspended thin films, such as Lamb wave resonators, are being developed. The thin films are made of lithium tantalate (LT) or lithium niobate (LN), both of which have been shown to have high Q values ​​or large electromechanical coupling properties. Furthermore, the use of periodically poled LN provides a way to mitigate internal charge cancellation and performance loss during frequency scaling, with preliminary results demonstrating good RF performance. However, these require precise control of the lithium niobate thickness to achieve a certain frequency and lack flexibility in the design of single-chip frequency scaling. Another issue is that the mechanical stability of suspended resonators still needs to be improved in large-scale manufacturing.

[0004] Relatively speaking, surface acoustic wave resonators are still the most economical solution. Currently, commercially prepared surface acoustic wave devices also follow the above development trend, that is, to meet higher frequency bands and larger bandwidths. So far, the more mature one is the horizontal shear mode surface acoustic wave resonator, which has a relatively large k 2 , but it mainly works below 3GHz and there are many spurious modes nearby.

[0005] Summary of the Invention

[0006] In light of this, the present application provides a multi-coefficient coupled mode surface acoustic wave resonator with improved electromechanical coupling. By varying the mass loading effect of the metal electrodes—that is, by designing the ratio of the electrode width and thickness to the piezoelectric layer thickness to alter the electric field distribution—and utilizing piezoelectric constants with both positive and negative coefficients, i.e., piezoelectric constants with similar or identical vibration directions, a high electromechanical coupling coefficient exceeding 10% is achieved in this acoustic wave resonator structure. This disclosure couples all piezoelectric coefficients vibrating in the same direction, achieving an acoustic wave resonator with an ultra-wide bandwidth.

[0007] The present invention provides a multi-coefficient coupled mode surface acoustic wave resonator, comprising: a substrate; a piezoelectric layer disposed on the substrate; an electrode layer disposed on the piezoelectric layer, comprising at least two interdigitated electrodes; wherein the piezoelectric layer is made of Y-cut lithium niobate, and the piezoelectric layer is based on the piezoelectric coefficient e 15 , and / or piezoelectric coefficient e 16 , and / or piezoelectric coefficient e 34 Mutually coupled, they jointly excite acoustic waves; the ratio of the interdigital electrode spacing to the electrode layer thickness is 0.5-10.

[0008] According to an embodiment of the present disclosure, the substrate is prepared from a material selected from any one of silicon, sapphire, gallium nitride, and silicon carbide.

[0009] According to an embodiment of the present disclosure, the thickness of the piezoelectric layer is 10 nm-30 um.

[0010] According to an embodiment of the present disclosure, the material for preparing the interdigital electrodes is selected from at least one of gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, and titanium.

[0011] According to an embodiment of the present disclosure, the number of interdigital electrodes is 2-500.

[0012] According to an embodiment of the present disclosure, the thickness of the interdigital electrode is 5-500 nm, the width is 0.001-5 um, and the length is 1-500 um.

[0013] According to an embodiment of the present disclosure, the ratio of the thickness of the interdigital electrodes to the thickness of the piezoelectric layer is less than 0.5.

[0014] According to the embodiment of the present disclosure, the piezoelectric coefficients vibrating in the same direction are coupled together by adjusting the thickness and width of the interdigital electrodes.

[0015] According to an embodiment of the present disclosure, the multi-coefficient coupled mode surface acoustic wave resonator further includes: a silicon dioxide layer disposed between the substrate and the piezoelectric layer for temperature compensation.

[0016] Optionally, a silicon dioxide layer may be deposited on the electrode layer for temperature compensation.

[0017] The electromechanical coupling coefficient of the surface acoustic wave resonator with multi-coefficient coupling modes disclosed in the present invention exceeds 20%, and can achieve higher frequencies (>5 GHz) and larger bandwidths (>400 MHz). BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1a is a schematic structural diagram of a multi-coefficient coupled mode surface acoustic wave resonator according to an embodiment of the present disclosure;

[0019] FIG1b is a flowchart of a process for preparing a multi-coefficient coupled mode surface acoustic wave resonator structure according to an embodiment of the present disclosure;

[0020] FIG2 is a diagram showing steps for preparing a multi-coefficient coupled mode surface acoustic wave resonator structure according to an embodiment of the present disclosure;

[0021] FIG3 is a cross-sectional schematic diagram of a multi-coefficient coupled mode surface acoustic wave resonator according to an embodiment of the present disclosure;

[0022] FIG4 schematically shows the multi-coefficient (e 15 、e 16 、e 34 ) 2D simulation vibration displacement diagram of the coupled mode surface acoustic wave resonator;

[0023] FIG5 schematically shows the multi-coefficient (e 15 、e 16 、e 34 ) 3D simulation vibration displacement diagram of the surface acoustic wave resonator in coupled mode;

[0024] FIG6 schematically shows the multi-coefficient (e 15 、e 16 、e 34 ) Multi-coefficient coupled admittance diagram of coupled modes of surface acoustic wave resonators;

[0025] FIG7 schematically shows a schematic structural diagram of a multi-coefficient coupled mode surface acoustic wave resonator in which a layer of silicon dioxide is added between the piezoelectric layer and the substrate as a temperature compensation layer;

[0026] FIG8 schematically shows a schematic structural diagram of a multi-coefficient coupled mode surface acoustic wave resonator in which a layer of silicon dioxide is added to the interdigital electrodes as a temperature compensation layer;

[0027] FIG9 schematically shows that the piezoelectric layer of the surface acoustic wave resonator has only a piezoelectric coefficient e 16 Admittance diagram and 3D vibration displacement diagram;

[0028] FIG10 schematically shows that the piezoelectric layer of the surface acoustic wave resonator has only a piezoelectric coefficient e 15 Admittance diagram and 3D vibration displacement diagram;

[0029] FIG11 schematically shows that the piezoelectric layer of the surface acoustic wave resonator has only a piezoelectric coefficient e 34 Admittance diagram and 3D vibration displacement diagram;

[0030] FIG12 schematically shows the piezoelectric coefficient e of the piezoelectric layer of the surface acoustic wave resonator. 15 +e 34 Admittance diagram and 3D vibration displacement diagram;

[0031] FIG13 schematically shows the piezoelectric coefficient e of the piezoelectric layer of the surface acoustic wave resonator. 15 +e 16 Admittance diagram and 3D vibration displacement diagram;

[0032] FIG14 schematically shows that the piezoelectric layer of the surface acoustic wave resonator has a piezoelectric coefficient e 16 +e 34 Admittance diagram and 3D vibration displacement diagram.

[0033] Reference numerals: 1 - substrate; 2 - piezoelectric layer; 3 - adhesive layer; 4 - electrode layer. DETAILED DESCRIPTION

[0034] This disclosure provides a multi-coefficient coupled-mode surface acoustic wave resonator. By designing the ratio of electrode width and thickness to the piezoelectric layer thickness to alter the electric field distribution, a high electromechanical coupling coefficient (ECC) exceeding 10% is achieved. Furthermore, because the ratio of electrode width and thickness to the piezoelectric layer is very small, the electric field is confined to the piezoelectric layer, confining the acoustic wave energy to the piezoelectric layer. This improves the ECC and quality factor.

[0035] Because Y-cut LN has a rich variety of piezoelectric coefficients, it can excite a variety of different acoustic wave modes under conventional surface acoustic wave conditions. The excitation of these acoustic wave modes is determined by the piezoelectric coefficients of the piezoelectric material. Furthermore, acoustic wave vibration directions excited by piezoelectric coefficients with opposite signs differ. In the prior art, stray signals are generally eliminated by changing the angle, adding cut fingers, or using false fingers. In this disclosure, the mass loading effect of the metal electrodes is adjusted to modify the electric field confined within the piezoelectric film, thereby coupling the electromechanical coupling coefficients of the same vibration direction.

[0036] Table 1 below shows the material parameters of Y-cut lithium niobate:

[0037] Table 1

[0038] From Table 1 we can see that 15 ,e 16 ,e 21 ,e 22 ,e 23 ,e 31 ,e34 The piezoelectric coefficients are all negative, only e 33 The piezoelectric coefficient is positive, and the positive and negative represent the vibration direction. That is, we can adjust the thickness and width of the designed electrodes to couple the piezoelectric constants of the same vibration direction. Here, since the interdigital electrodes are only on the top of the piezoelectric film, the coupled piezoelectric coefficient must include e 1* For e 31 (-2.54) and e 33 (2.54), since the vibrations are in opposite directions, they cancel each other out.

[0039] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0040] In an embodiment of the present disclosure, a multi-coefficient coupled mode surface acoustic wave resonator is provided. As shown in FIG1 and FIG2 , the multi-coefficient coupled mode surface acoustic wave resonator includes:

[0041] Substrate 1;

[0042] a piezoelectric layer 2 disposed on a substrate 1;

[0043] an electrode layer 4, disposed on the piezoelectric layer, comprising at least two interdigitated electrodes;

[0044] The piezoelectric layer 2 is made of Y-cut lithium niobate and has a piezoelectric coefficient e 15 , and / or piezoelectric coefficient e 16 , and / or piezoelectric coefficient e 34 The mutual coupling excites the acoustic waves together; the ratio of the distance between adjacent interdigital electrodes and the thickness of the electrode layer is 0.5-10.

[0045] According to an embodiment of the present disclosure, the substrate 1 is made of a material selected from any one of silicon, sapphire, gallium nitride, and silicon carbide.

[0046] According to an embodiment of the present disclosure, the thickness of the piezoelectric layer 2 is 10 nm-30 um.

[0047] According to an embodiment of the present disclosure, the interdigital electrodes are made of at least one material selected from the group consisting of gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, and titanium. For example, the interdigital electrodes may be alloys of titanium-gold, titanium-aluminum, titanium-copper, chromium-gold, chromium-aluminum, and chromium-copper.

[0048] According to the embodiment of the present disclosure, the number of interdigital electrodes is 2-500, which is set according to actual needs. The thickness of the interdigital electrodes is 5-500 nm, the width is 0.001-5 μm, and the length is 1-500 μm.

[0049] According to an embodiment of the present disclosure, the ratio of the thickness of the interdigital electrodes to the thickness of the piezoelectric layer is less than 0.5.

[0050] According to the embodiment of the present disclosure, the piezoelectric coefficients vibrating in the same direction are coupled together by adjusting the thickness and width of the interdigital electrodes.

[0051] According to the embodiment of the present disclosure, in combination with FIG3, FIG7, and FIG8, h e is the thickness of the interdigital electrode, W e is the width of the interdigital electrode; h LN is the thickness of the piezoelectric layer; the wavelength λ of the excited resonant acoustic wave can be four times the width of the interdigital electrode, or twice the spacing between the interdigital electrodes.

[0052] According to an embodiment of the present disclosure, as shown in FIG1 and FIG2 , the main steps involved in preparing the above-mentioned multi-coefficient coupled mode surface acoustic wave resonator include:

[0053] S1: Prepare a piezoelectric film layer on a substrate and apply electron beam photoresist, and use electron beam lithography to pattern and define interdigital electrodes;

[0054] S2: depositing electrode materials on the piezoelectric film layer to obtain interdigitated electrodes;

[0055] S3: Apply UV photoresist and use UV lithography to pattern and define metal connection lines;

[0056] S4: depositing electrode materials on the piezoelectric film layer to obtain metal connecting wires;

[0057] As shown in FIG. 1 , the photoresist coated during the preparation process serves as the coating layer 3 , is only used and appears during the preparation process, and is finally removed.

[0058] The metal connecting wires are used to realize electrical connection between the interdigital electrodes and other devices.

[0059] According to an embodiment of the present disclosure, as shown in FIG7 , the multi-coefficient coupled mode surface acoustic wave resonator further includes a silicon dioxide layer, which is disposed between the substrate and the piezoelectric layer for temperature compensation, serving as a temperature compensation layer, thereby forming a temperature compensated multi-coefficient coupled mode surface acoustic wave resonator.

[0060] According to an embodiment of the present disclosure, as shown in Figure 8, a silicon dioxide layer can also be deposited on the electrode layer. The preparation process can be PECVD, electron beam coating, thermal evaporation, magnetron sputtering, etc., covering the interdigitated electrodes and used as a temperature compensation layer to form another temperature-compensated multi-coefficient coupled mode surface acoustic wave resonator.

[0061] After experimental and simulation tests, combined with Figures 4, 5, and 6, the piezoelectric coefficient (e 15 、e16 、e 34 ) coupling state, from the two-dimensional vibration displacement diagram, the vibration at this time is mainly concentrated in the Z direction, and obvious up and down vibrations can be seen. From the three-dimensional vibration displacement diagram, the vibration also has shear and tensile vibrations in the horizontal plane between adjacent interdigitated electrodes, forming a complex form of vibration between the two electrodes approaching each other and shear contraction. It is not a vibration in a single direction, but a coupled vibration that exists in the three directions of X, Y, and Z. As shown in Figure 6, it can be seen that the admittance diagram of multi-piezoelectric coefficient coupling has an electromechanical coupling coefficient k 2 Up to 54%, frequency f s As shown in Figure 9, only the piezoelectric coefficient e 16 When combined with the three-dimensional simulation diagram, it can be seen that the vibration is mainly only in the XY plane, which is a shear vibration, and the electromechanical coupling coefficient k 2 As shown in Figure 10, only the piezoelectric coefficient e 15 When combined with the three-dimensional simulation diagram, it can be seen that the vibration displacement is mainly concentrated in the Z direction, one metal electrode is in the form of tensile vibration, and the other metal electrode is in the form of contraction vibration. The electromechanical coupling coefficient k 2 is 1.1%; as shown in Figure 11, only the piezoelectric coefficient e 34 When combined with the three-dimensional simulation diagram, it can be seen that the vibration displacement is mainly concentrated in the Y direction and the Z direction, and the electromechanical coupling coefficient k 2 As shown in Figure 12, there is a piezoelectric coefficient e 15 、e 34 When combined with the three-dimensional simulation diagram, it can be seen that there is contraction vibration between the two electrodes, and there is also shear vibration in the XY plane, but the degree of shear vibration is not very strong. The electromechanical coupling coefficient k 2 As shown in Figure 13, there is a piezoelectric coefficient e 15 、e 16 When combined with the three-dimensional simulation diagram, it can be seen that the vibration is mainly shear vibration in the XY plane, and there are also expansion and contraction vibrations in the Z direction. The electromechanical coupling coefficient k 2 As shown in Figure 14, there is a piezoelectric coefficient e 34 、e 16 When combined with the three-dimensional simulation diagram, it can be seen that the vibration is mainly the stretching vibration in the XY direction, and the electromechanical coupling coefficient has increased significantly. 2 It reached 32%, indicating that the piezoelectric coefficient e 34 and e 16 The solid curves in Figures 6, 9 to 14 represent the simulated admittance curves (COMSOL), and the dashed lines represent the equivalent circuit model fitting curves (MBVD model).

[0062] The embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that any implementations not depicted or described in the drawings or the main text of the specification are known to those skilled in the art and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the various specific structures, shapes, or methods described in the embodiments, and can be easily modified or replaced by those skilled in the art.

[0063] In summary, the present disclosure provides a multi-coefficient coupled mode surface acoustic wave resonator, which achieves higher frequency, larger bandwidth and lower loss.

[0064] The specific embodiments of the present disclosure described above do not limit the scope of protection of the present disclosure. Any other corresponding changes and modifications made based on the technical concept of the present disclosure should be included in the scope of protection of the claims of the present disclosure.

Claims

1. A multi-coefficient coupled mode surface acoustic wave resonator, comprising: substrate; a piezoelectric layer disposed on a substrate; an electrode layer, disposed on the piezoelectric layer, comprising at least two interdigitated electrodes; Wherein, the piezoelectric layer is made of Y-cut lithium niobate, and the piezoelectric layer is based on the piezoelectric coefficient e 15 , and / or piezoelectric coefficient e 16 , and / or piezoelectric coefficient e 34 Mutually coupled, they jointly excite acoustic waves; the ratio of the interdigital electrode spacing to the electrode layer thickness is 0.5-10.

2. The multi-coefficient coupled mode surface acoustic wave resonator according to claim 1, wherein the substrate is made of a material selected from any one of silicon, sapphire, gallium nitride, and silicon carbide. 3 . The multi-coefficient coupled mode surface acoustic wave resonator according to claim 1 , wherein the thickness of the piezoelectric layer is 10 nm-30 μm.

4. The multi-coefficient coupled mode surface acoustic wave resonator according to claim 1, wherein the material for preparing the interdigital electrodes is selected from at least one of gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, and titanium. 5 . The multi-coefficient coupled-mode surface acoustic wave resonator according to claim 1 , wherein the number of the interdigital electrodes is 2-500. 6 . The multi-coefficient coupled mode surface acoustic wave resonator according to claim 1 , wherein the interdigital electrodes have a thickness of 5-500 nm, a width of 0.001-5 μm, and a length of 1-500 μm. 7 . The multi-coefficient coupled-mode surface acoustic wave resonator according to claim 1 , wherein a ratio of a thickness of the interdigital electrodes to a thickness of the piezoelectric layer is less than 0.

5.

8. The multi-coefficient coupled-mode surface acoustic wave resonator according to claim 1, wherein the piezoelectric coefficients vibrating in the same direction are coupled together by adjusting the thickness and width of the interdigital electrodes.

9. The multi-coefficient coupled-mode surface acoustic wave resonator according to any one of claims 1 to 8, further comprising: A silicon dioxide layer is disposed between the substrate and the piezoelectric layer for temperature compensation.

10. The multi-coefficient coupled-mode surface acoustic wave resonator according to any one of claims 1 to 8, further comprising: A silicon dioxide layer is plated on the electrode layer for temperature compensation.

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