Design method of 13gxbar filter based on lithium niobate thin film
By optimizing the crystal cut and structural parameters of the lithium niobate thin-film XBAR filter and combining acoustic-electric-magnetic joint simulation, the problems of long design time, high cost and poor robustness of existing design methods are solved, and an efficient and low-cost design process is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI UNIV
- Filing Date
- 2026-02-09
- Publication Date
- 2026-05-12
AI Technical Summary
Existing lithium niobate thin-film XBAR filter design methods rely on manufacturing processes, which are time-consuming, costly, have poor robustness, and are difficult to adapt to changes in materials.
Finite element simulation software is used to optimize crystal cutting and structural parameters. Combined with acoustic-electric-magnetic joint simulation, the design process is optimized through the equivalent dielectric constant method, realizing a design method of simulation before process.
It significantly improves design efficiency, shortens the R&D cycle, reduces costs, enhances model robustness and design accuracy, and adapts to different materials and structural changes.
Smart Images
Figure CN121706503B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of radio frequency filter technology, and more specifically, to a design method for a 13GXBAR filter based on lithium niobate thin film. Background Technology
[0002] With the rapid development of wireless communication systems, from the early 2G, 3G, and 4G networks to today's new generation of mobile communication networks, communication spectrum resources are becoming increasingly scarce, frequency band allocation is becoming more and more complex, and the performance requirements for radio frequency front-end filters are constantly increasing. High-frequency, large-bandwidth radio frequency acoustic filters have become a research hotspot in this field.
[0003] XBAR resonators have attracted widespread attention in acoustic resonator design due to their combination of the advantages of bulk acoustic waves and surface acoustic waves. Lithium niobate (LiNbO3), through a novel thin-film transfer technique involving ion cutting, possesses a stronger piezoelectric effect and a higher coupling coefficient than aluminum nitride (AlN), making it a promising candidate for ultra-wideband filters. Furthermore, by utilizing the modal isolation and energy confinement characteristics of its release mechanism, high quality factors can be achieved. Therefore, XBAR resonators based on lithium niobate thin films have become an important research direction in wireless communication RF front-ends.
[0004] Existing filter design methods have significant drawbacks: the design process relies on manufacturing processes, requiring extensive fabrication and testing to establish a resonator model parameter library covering different film materials, thicknesses, structures, and operating frequencies. This is not only time-consuming and inefficient, but also involves high manufacturing costs. Furthermore, filters manufactured using equivalent models are only reliable for filters made with the same materials, exhibiting poor robustness. Once the materials are changed, extensive refitting work is required. Summary of the Invention
[0005] The purpose of this invention is to provide a design method for a 13GXBAR filter based on lithium niobate thin film, so as to solve the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention aims to provide a design method for a 13GXBAR filter based on lithium niobate thin film, including: step S1, crystal cutting optimization: in finite element simulation software, the Euler angle of the lithium niobate thin film is parametrically scanned and optimized, and the crystal cutting direction is determined based on obtaining the optimal electromechanical coupling coefficient and complete suppression of stray modes in the target frequency band.
[0007] Step S2, Structural Parameter Determination: Based on the determined crystal orientation, a three-dimensional model of the XBAR resonator is established in the finite element simulation software. Parametric simulations are performed on the electrode material, interdigital structure parameters, and thin film thickness to determine the optimal combination of structural parameters that meets the target center frequency requirement.
[0008] Step S3, Finite Element Modeling and Verification: Using the optimal combination of structural parameters, a three-dimensional force-electric coupling finite element model of the XBAR resonator is constructed. The complex impedance data of the XBAR resonator as a function of frequency is obtained by solving in the frequency domain, and the accuracy of the model is verified.
[0009] Step S4, Acoustic-Electro-Magnetic Joint Simulation: The complex impedance data of the resonator obtained in Step S3 is used to calculate the equivalent relative permittivity as a function of frequency using the equivalent permittivity formula; a layout model of the XBAR filter is constructed in the three-dimensional electromagnetic simulation software, and the calculated equivalent permittivity is imported into the piezoelectric layer material properties in the model to perform acoustic-electro-magnetic joint simulation, obtain the S-parameters of the filter, and verify and optimize the design based on the simulation results.
[0010] As a further improvement to this technical solution, the finite element simulation software is COMSOL Multiphysics.
[0011] As a further improvement to this technical solution, the Euler angles are determined as follows: The X-axis is rotated to the N-axis using the original crystal axis Z as the rotation axis; the Z-axis is rotated to the x3-axis using the N-axis as the rotation axis; and the N-axis is rotated to the x1-axis using the x3-axis as the rotation axis. At this point, the Y-axis reaches the x2-axis position, resulting in a new crystal coordinate system (x1, x2, x3). In the finite element simulation software, the Euler angles are parametrically scanned within a preset range to simulate and obtain the admittance frequency response curve of the XBAR resonator under each Euler angle combination. The series resonant frequency and parallel resonant frequency are extracted from each admittance curve, and the corresponding effective electromechanical coupling coefficient is calculated according to the formula to determine candidate Euler angles. From the candidate Euler angles, the combination with the largest electromechanical coupling coefficient is selected as the optimal Euler angle.
[0012] As a further improvement to this technical solution, the electromechanical coupling coefficient is calculated using the following formula:
[0013]
[0014] in, Represents the electromechanical coupling coefficient. Indicates the parallel resonant frequency. This represents the series resonant frequency.
[0015] As a further improvement to this technical solution, the preset condition is specifically as follows: for the admittance frequency response curve corresponding to each Euler angle combination, within the target frequency band, the amplitude of all stray resonant modes is lower than the amplitude of the main resonant peak by a preset suppression threshold.
[0016] As a further improvement to this technical solution, the interdigitated structure parameters include interdigitated finger width, interdigitated finger spacing, number of interdigitated finger pairs, and metallization rate.
[0017] As a further improvement to this technical solution, the three-dimensional force-electric coupling finite element model includes solid mechanical physical fields, electrostatic physical fields, and piezoelectric effect modules.
[0018] As a further improvement to this technical solution, the three-dimensional force-electric coupling model is constructed by selecting aluminum as the electrode material and lithium niobate film as the piezoelectric material. The material density, relative permittivity, coupling matrix, elastic matrix, Poisson's ratio, and Young's modulus are exported from the material library of the finite element simulation software, and the elastic matrix of lithium niobate is manually input. At the same time, the boundary conditions of the solid mechanical field, electrostatic field, and piezoelectric effect module are set.
[0019] As a further improvement to this technical solution, the three-dimensional electromagnetic simulation software is ANSYS HFSS.
[0020] As a further improvement to this technical solution, the formula for the equivalent dielectric constant is:
[0021] ;
[0022] in, Represents the equivalent relative permittivity. Indicates the area of the active region. Indicates the thickness of the piezoelectric layer. Represents the vacuum permittivity. Indicates impedance, Represents angular frequency. It represents the imaginary unit.
[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0024] 1. Significantly improve design efficiency and shorten the R&D cycle: Adopt a forward design process of "simulation first, then process". Before tape-out, device performance can be accurately predicted through finite element simulation, completely eliminating the reliance on multiple trial and error processes and shortening the design cycle from "months" to "days or weeks".
[0025] 2. Significantly reduce R&D costs: By greatly reducing or even avoiding the number of repeated tape-outs in the early stages, it directly saves expensive process manufacturing costs and lowers the threshold for technology development.
[0026] 3. Enhanced Model Robustness and Universality: This method uses intrinsic physical parameters of materials (such as piezoelectric constant and elastic constant) for simulation. The established model reflects the inherent physical laws of the device, rather than the accidental result of a specific process. Therefore, the model has stronger robustness, can adapt to changes in different material parameters and structural dimensions, and has better universality.
[0027] 4. Improved Design Accuracy and Reliability: Through finite element analysis involving multi-physics coupling of force, electricity, and acoustics, combined with acoustic-electric-magnetic joint simulation achieved by the equivalent dielectric constant method, the complex physical effects of devices can be simulated with high fidelity. This results in simulation results that closely match the final measured performance, and the design accuracy is far superior to that of traditional equivalent circuit models. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.
[0029] Figure 1 This is a schematic diagram of the implementation steps of the method of the present invention;
[0030] Figure 2 A schematic diagram of the rotary cutting of LiNbO3 crystal;
[0031] Figure 3 The admittance response of the XBAR resonator under different lithium niobate film thicknesses;
[0032] Figure 4 This is a flowchart of the finite element simulation analysis method.
[0033] Figure 5 A 3D simulation model of the XBAR resonator;
[0034] Figure 6 It is an XBAR resonator grid structure;
[0035] Figure 7 Comparison of the cascaded XBAR resonator and the experimental data from its fabrication;
[0036] Figure 8 Comparison of parallel XBAR resonators and experimental data;
[0037] Figure 9 Port 1 is the dielectric constant curve;
[0038] Figure 10 Port 2 is the dielectric constant curve;
[0039] Figure 11 For electromagnetic simulation model;
[0040] Figure 12 The S-parameters are those of a 13GXBAR filter with lithium niobate thin film. Detailed Implementation
[0041] 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.
[0042] Example: Please refer to Figure 1 As shown, a design method for a 13GXBAR filter based on lithium niobate thin film is provided, including: Step S1, crystal cutting optimization: In the finite element simulation software, the Euler angle of the lithium niobate thin film is parametrically scanned and optimized to determine the crystal cutting direction based on obtaining the optimal electromechanical coupling coefficient and complete suppression of stray modes in the target frequency band.
[0043] In one specific embodiment, the finite element simulation software is COMSOL Multiphysics.
[0044] In one specific embodiment, the Euler angles are determined as follows: The X-axis is rotated to the N-axis using the original crystal axis Z as the rotation axis; the Z-axis is rotated to the x3-axis using the N-axis as the rotation axis; and the N-axis is rotated to the x1-axis using the x3-axis as the rotation axis. At this point, the Y-axis reaches the x2-axis position, resulting in a new crystal coordinate system (x1, x2, x3). In the finite element simulation software, the Euler angles (…) are determined. Parametric scanning is performed within a preset range to simulate and obtain the admittance frequency response curve of the XBAR resonator under each Euler angle combination. The series resonant frequency and parallel resonant frequency are extracted from each admittance curve and the corresponding effective electromechanical coupling coefficient is calculated according to the formula to determine the candidate Euler angles. From the candidate Euler angles, the combination with the largest electromechanical coupling coefficient is selected as the optimal Euler angle.
[0045] LiNbO3 crystals have three material properties, namely piezoelectric constant ( ), elastic constant ( ) and dielectric constant ( Their initial parameters can be represented by their relative positions in a coordinate system (X, Y, Z). Figure 2 The diagram shows a schematic of a LiNbO3 crystal being rotated and cut. To make Euler angles more visually clear, the first rotation begins from the crystal axis, with the original X-axis rotating around the Z-axis by an angle. , The range is from 0° to 360°, with the X-axis rotated to the N-axis. The second rotation, using the N-axis as a reference, involves rotating the Z-axis by an angle... To the x3 axis, The range is from 0° to 180°. The third rotation is based on the x3 axis, with the N rotation axis rotating by an angle. To the x1 axis, The range is from 0° to 360°. After three rotations, the original Y-axis reaches the x2 axis position, and the original crystal coordinate system (X, Y, Z) becomes the normal crystal coordinate system (x1, x2, x3), while ( , , ) are called Euler angles, and the corresponding ( Let ω be the angular velocity of the Euler angle during rotation, proving the dynamic consistency of the coordinate system rotation. The tangential direction of the piezoelectric crystal after rotation can be represented by Euler angles. For example, the Euler angle of LiNbO3 with ZY tangential direction is (0, 0, 90°), and the Euler angle of LiNbO3 with Y128° tangential direction is (0, 38°, 0). In the subsequent finite element simulation resonator, the tangential direction of the piezoelectric material is the crystal tangential direction during rotation by default, that is, the Euler angle is (0, 0, 0). It is necessary to make corresponding transformations to the crystal coordinate axis to obtain the material properties that conform to the corresponding crystal tangential direction.
[0046] It should be noted that the crystal tangent here is Y128° tangent, its Euler angles are (0°, 38°, 0°), and the target frequency band is 13GHz.
[0047] By parametrically scanning and simulating the set of variables "Euler angles" (computer electrical coupling coefficient, checking stray suppression), the optimal crystal orientation is selected from countless possible crystal orientations. This optimal orientation is the "crystal orientation" adopted in this design method.
[0048] In one specific embodiment, the electromechanical coupling coefficient is calculated using the following formula:
[0049]
[0050] in, Represents the electromechanical coupling coefficient. Indicates the parallel resonant frequency. This represents the series resonant frequency.
[0051] In one specific embodiment, the preset condition is as follows: for the admittance frequency response curve corresponding to each Euler angle combination, within the target frequency band, the amplitude of all stray resonant modes is lower than the amplitude of the main resonant peak by a preset suppression threshold (40dB).
[0052] Step S2, Structural Parameter Determination: Based on the determined crystal orientation, a three-dimensional model of the XBAR resonator is established in the finite element simulation software. Parametric simulations are performed on the electrode material, interdigital structure parameters, and thin film thickness to determine the optimal combination of structural parameters that meets the target center frequency requirement.
[0053] The phase velocity of the resonator varies with electrode thickness. Without considering electrode load, the phase velocity is below 2500 m / s. However, the shear wave velocities of Al, Ti, and W electrodes are all greater than 2500 m / s. Therefore, when a thinner electrode covers the surface, the higher sound velocity of the electrode will increase the overall phase velocity of the resonator. At this point, the electrode mass loading effect is not significant, resulting in a slight increase in the resonator phase velocity. This phenomenon is more pronounced with higher sound velocity and lower density of the electrode material itself. As the electrode thickness increases, the mass loading effect becomes more significant, leading to a decrease in the resonator phase velocity. The resonator was simulated using COMSOL software to study the effects of duty cycle and film thickness on the resonator coupling coefficient and resonant frequency. Parametric simulations were performed on the LiNbO3 film thickness of the resonator. By changing the electrode width, the coupling coefficient of the resonator corresponding to each width and duty cycle was calculated, and the resonant frequency of the resonator corresponding to each LiNbO3 thickness was calculated. Curves showing the LiNbO3 thickness under different parameters were generated. Figure 3 It can be observed that the resonant frequency of the resonator decreases with increasing LiNbO3 thickness. Therefore, to obtain a resonant frequency of around 13 GHz, a suitable resonant frequency should be selected. The LiNbO3 thin film was then used for subsequent resonator simulation and fabrication.
[0054] In one specific embodiment, the interdigitated structure parameters include interdigitated width, interdigitated spacing, number of interdigitated pairs, and metallization rate.
[0055] Step S3, Finite Element Modeling and Verification: Using the optimal combination of structural parameters, a three-dimensional force-electric coupling finite element model of the XBAR resonator is constructed. The complex impedance data of the XBAR resonator as a function of frequency is obtained by solving in the frequency domain, and the accuracy of the model is verified.
[0056] In one specific embodiment, the three-dimensional force-electric coupling finite element model includes solid mechanical physical fields, electrostatic physical fields, and piezoelectric effect modules.
[0057] In one specific embodiment, the three-dimensional force-electric coupling model is constructed by selecting aluminum as the electrode material and lithium niobate film as the piezoelectric material. The material density, relative permittivity, coupling matrix, elastic matrix, Poisson's ratio, and Young's modulus are exported from the material library of the finite element simulation software, and the elastic matrix of lithium niobate is manually input. At the same time, boundary conditions for the solid mechanical field, electrostatic field, and piezoelectric effect module are set. In the solid mechanical field, the electrodes and the ordinary acoustic layer of the substrate are set as linear elastic materials, the longitudinal dimension is a free boundary, and the transverse dimension is a fixed constraint. The mechanical damping and dielectric loss of the piezoelectric material are defined. In the electrostatic field, a charge conservation region and a terminal region are defined, and specific voltage terminals and grounding are respectively set on the upper and lower electrode surfaces.
[0058] In one specific embodiment, the three-dimensional electromagnetic simulation software is ANSYS HFSS.
[0059] By analyzing the finite element model, the impedance characteristics of lithium niobate can be analyzed more comprehensively, and the physical field states of lithium niobate under resonant conditions can be obtained intuitively. The finite element method is based on the variational principle and partitioned interpolation. The model is discretized and an interpolation function is constructed. It is assumed that the behavior of actual points is represented by the interpolation relationship of the behavior of adjacent nodes, thereby discretizing the physical problem into a system of algebraic equations for solving unknowns at the nodes.
[0060] Finite element method (FEM) modeling can solve almost all problems related to piezoelectric transducers, such as structural stress analysis, vibration modal analysis, resonant frequency calculation, and impedance calculation. COMSOL and ANSYS are commonly used FEM software and can perform multiphysics modeling of XBAR devices. For the optimization of lithium niobate thin film structures, piezoelectric coupling analysis is mainly employed.
[0061] This design method first requires identifying the research object, then abstracting the research object to determine the task and objectives, and finally developing a specific simulation plan based on the objectives. The general steps are as follows: Figure 4 As shown.
[0062] The model building process is as follows:
[0063] First, a geometric model of the lithium niobate structure is performed in the software. To further simulate the working state of the actual device, this design method uses three-dimensional spatial modeling. Figure 5 As shown, from top to bottom, the components are interdigitated electrodes, recessed piezoelectric layers, and piezoelectric layers. Al was chosen as the electrode material, and lithium niobate film as the piezoelectric material. Most parameters of the materials involved were exported from the software's built-in material library, including material density, relative permittivity, coupling matrix, elasticity matrix, Poisson's ratio, and Young's modulus. The elasticity matrix of lithium niobate was manually input. After establishing the three-dimensional model of lithium niobate, the solid mechanical field, electrostatic field, and piezoelectric effect modules were set, i.e., the corresponding mechanical and electrical boundary conditions were set. In the solid mechanical field, the electrodes and the substrate's ordinary acoustic layer were set as linear elastic materials, defined as free boundaries in the longitudinal dimension and fixed constraints in the transverse dimension. The mechanical damping and dielectric loss of the piezoelectric material were also defined. In the electrostatic field, a charge conservation region and a termination region were defined, with a 1V termination and a 0V ground on the upper and lower electrode surfaces, respectively.
[0064] After adding the physics fields, mesh the model. For example... Figure 6As shown, the density of the mesh affects the accuracy of the final solution. Generally, the smaller the mesh size, the more fine the features of the model are displayed, and the closer the calculation results are to the true values. However, excessively fine meshes not only result in a very large computational load but also easily introduce outliers that differ significantly from experimental results. Therefore, the number of meshes must be reduced within an appropriate range of analysis.
[0065] The solution and result analysis process is as follows:
[0066] Add a frequency domain solver to analyze the frequency characteristics of the XBAR device, and set an appropriate solution range and step size.
[0067] After completing the above operations, you need to define variables, input relevant formulas, and obtain the required XBAR frequency impedance characteristic curve and phase curve through the one-dimensional plotting group.
[0068] The fitting process is as follows:
[0069] The complex impedance data of the resulting resonator is compared with the data of the target resonator. By changing the electrode thickness, the area and shape of the resonator, the final result is made to fit the target result.
[0070] In XBAR resonator design, the area configuration of the unit array directly relates to the static capacitance characteristics, thus affecting the overall impedance performance. The filter network configuration is closely related to the resonant frequency and impedance matching of the resonator; therefore, the area distribution of the array units in the topology needs to be precisely planned. As the thickness of the XBAR resonator's laminated film increases, the center resonant frequency tends to decrease. This is because the increased film thickness lengthens the sound wave propagation path, and with a constant sound velocity, the half-wavelength increases accordingly, leading to a frequency decrease. Due to the interdigitated electrode structure, XBAR resonators are prone to coupling between transverse and longitudinal modes, resulting in parasitic resonance. To address this issue, an asymmetric interdigitated electrode design can be used to reduce the series resonant frequency (…). The corresponding parasitic transverse modes are reflected multiple times at the electrode boundaries, reducing their fundamental parasitic resonant frequency. At the same time, by setting an impedance adjustment frame at the edge of the interdigital electrodes, a significant impedance mismatch and a high reflection coefficient are formed, preventing the transverse modes from leaking from the edge of the effective excitation region, thereby suppressing the parasitic response and improving the filter's in-band flatness and out-of-band suppression performance.
[0071] Using the finite element method (FEM), a three-dimensional simulation physical model of the XBAR resonator in series and parallel configuration was established in the software, and the admittance curve of the resonator was simulated. For example... Figure 7 , 8 As shown, the admittance curve of the actual fabricated XBAR resonator is compared with that of the series-parallel resonator. The admittance of the series-parallel resonator is then introduced into HFSS for first-order filter design using the dielectric constant method.
[0072] Step S4, Acoustic-Electro-Magnetic Joint Simulation: The complex impedance data of the resonator obtained in Step S3 is used to calculate the equivalent relative permittivity as a function of frequency using the equivalent permittivity formula; a layout model of the XBAR filter is constructed in the three-dimensional electromagnetic simulation software, and the calculated equivalent permittivity is imported into the piezoelectric layer material properties in the model to perform acoustic-electro-magnetic joint simulation, obtain the S-parameters of the filter, and verify and optimize the design based on the simulation results.
[0073] S-parameters (Scattering parameters) are the most critical and direct indicators used to describe the radio frequency performance of filters.
[0074] In one specific embodiment, the formula for the equivalent dielectric constant is:
[0075] ;
[0076] in, Represents the equivalent relative permittivity. Indicates the area of the active region. Indicates the thickness of the piezoelectric layer. Represents the vacuum permittivity. Indicates impedance, Represents angular frequency. It represents the imaginary unit.
[0077] XBAR resonators exhibit both acoustic and electromagnetic (EM) effects. In XBAR filters, the ohmic loss of the interdigital electrodes, the dielectric loss of the piezoelectric layer, and the acoustic loss during sound wave propagation increase the filter's passband loss; while electromagnetic effects (such as parasitic capacitance between interdigital electrodes and edge field coupling) affect the filter's out-of-band rejection performance. Therefore, joint simulation of acoustic and electromagnetic behavior is necessary for more accurate simulation of filter performance. Traditional P-matrix models can simulate the acoustic effects of XBARs, but they are difficult to fully characterize electromagnetic coupling. Therefore, it is necessary to combine the obtained acoustic characteristic simulation data with the electromagnetic (EM) effects presented by the solid model of the XBAR filter in 3D electromagnetic simulation software. The acoustic-electric-magnetic effects are jointly simulated. The results of this acoustic-electric-magnetic joint simulation can serve as a reliable method for design evaluation, making the transmission characteristics of the obtained filter closer to the measured curves of the device.
[0078] Simulated XBAR resonator The distribution characteristics can be modeled using a new approach: the acoustic behavior of XBAR is derived by formula, and its acoustic-electric coupling characteristics are characterized by the equivalent dielectric constant. This equivalent parameter is then imported into the XBAR electromagnetic model in the electromagnetic simulation software HFSS, thereby achieving a one-time acoustic-electric joint simulation.
[0079] First, the dielectric constant of the model is obtained using the equivalent dielectric constant method. The process is as follows: The force-electric coupling characteristics of the XBAR filter are obtained through finite element simulation analysis, and the impedance characteristic curve of each array unit (i.e., the relationship between the real and imaginary parts of the impedance and the frequency) is obtained.
[0080] Immediately afterwards, through get As can be seen from the formula, the dielectric constant is a complex number, and both its real and imaginary parts vary with frequency. This calculation formula can be written into a MATLAB program to obtain the real part of the dielectric constant and the loss tangent.
[0081] A 3D solid model of the same first-order XBAR filter was constructed in the HFSS simulation software, and lumped ports were added for simulation. The dielectric constant was imported into the XBAR filter model in HFSS for simulation, and its reliability was verified by comparing it with the admittance curve of the measured data. Layout design was then performed to obtain the corresponding first-order filter S-parameters.
[0082] Map Design
[0083] (1) The real part, imaginary part, and loss tangent of the filter corresponding to the three-dimensional simulation model of the XBAR resonator obtained by finite element simulation analysis method are calculated by MATLAB, such as Figure 9 , 10 As shown.
[0084] (2) Import the first-order XBAR filter structure model designed by the finite element simulation analysis method into the HFSS simulation software, make relevant settings, construct a 3-D solid model, and add lumped ports for simulation. Import the dielectric constant into the model for simulation to obtain the corresponding first-order filter S-parameters, thus completing the design of the first-order XBAR filter, such as... Figure 11 , 12 As shown.
[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A design method for a 13GXBAR filter based on lithium niobate thin film, characterized in that, include: Step S1, Crystal Cutting Optimization: In the finite element simulation software, the Euler angle of the lithium niobate thin film is parametrically scanned and optimized. The crystal tangent is determined based on obtaining the optimal electromechanical coupling coefficient and completely suppressing stray modes in the target frequency band. Step S2, Determination of structural parameters: Based on the determined crystal tangency, a three-dimensional model of the XBAR resonator is established in the finite element simulation software. Parametric simulations are performed on the electrode material, interdigital structure parameters and film thickness to determine the optimal combination of structural parameters that meets the target center frequency requirement. Step S3, Finite Element Modeling and Verification: Using the optimal combination of structural parameters, a three-dimensional force-electric coupling finite element model of the XBAR resonator is constructed. The complex impedance data of the XBAR resonator as a function of frequency is obtained by solving in the frequency domain, and the accuracy of the model is verified. Step S4, Acoustic-Electro-Magnetic Joint Simulation: The complex impedance data of the resonator obtained in Step S3 is used to calculate the equivalent relative permittivity as a function of frequency using the equivalent permittivity formula; a layout model of the XBAR filter is constructed in the three-dimensional electromagnetic simulation software, and the calculated equivalent permittivity is imported into the piezoelectric layer material properties in the model to perform acoustic-electro-magnetic joint simulation, obtain the S-parameters of the filter, and verify and optimize the design based on the simulation results.
2. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The finite element simulation software is COMSOL Multiphysics.
3. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The Euler angles are determined as follows: Rotate the X-axis to the N-axis using the original crystal axis Z as the rotation axis, rotate the Z-axis to the x3-axis using the N-axis as the rotation axis, and rotate the N-axis to the x1-axis using the x3-axis as the rotation axis. At this point, the Y-axis reaches the x2-axis position, resulting in a new crystal coordinate system (x1, x2, x3). In the finite element simulation software, parametrically scan the Euler angles within a preset range to simulate and obtain the admittance frequency response curve of the XBAR resonator under each Euler angle combination. Extract the series resonant frequency and parallel resonant frequency from each admittance curve and calculate the corresponding electromechanical coupling coefficient according to the formula. Euler angles that meet the preset conditions are selected as candidates to obtain candidate Euler angles. From the candidate Euler angles, select the combination with the largest electromechanical coupling coefficient as the optimal Euler angle.
4. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 3, characterized in that, The electromechanical coupling coefficient is calculated using the following formula: ； in, Represents the electromechanical coupling coefficient. Indicates the parallel resonant frequency. This represents the series resonant frequency.
5. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 3, characterized in that, The preset conditions are specifically as follows: For the admittance frequency response curve corresponding to each Euler angle combination, within the target frequency band, the amplitudes of all stray resonant modes are lower than the amplitude of the main resonant peak by a preset suppression threshold.
6. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The interdigitated structure parameters include interdigitated width, interdigitated spacing, number of interdigitated pairs, and metallization rate.
7. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The three-dimensional force-electric coupling finite element model includes modules for solid mechanical fields, electrostatic fields, and piezoelectric effects.
8. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The three-dimensional force-electric coupling model was constructed by selecting aluminum as the electrode material and lithium niobate film as the piezoelectric material. The material density, relative permittivity, coupling matrix, elastic matrix, Poisson's ratio, and Young's modulus were exported from the material library of the finite element simulation software, and the elastic matrix of lithium niobate was manually input. At the same time, the boundary conditions of the solid mechanical field, electrostatic field, and piezoelectric effect module were set.
9. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The three-dimensional electromagnetic simulation software is ANSYS HFSS.
10. The design method for a 13GXBAR filter based on lithium niobate thin film according to claim 1, characterized in that, The formula for the equivalent dielectric constant is: ； in, Represents the equivalent relative permittivity. Indicates the area of the active region. Indicates the thickness of the piezoelectric layer. Represents the vacuum permittivity. Indicates impedance, Represents angular frequency. It represents the imaginary unit.