13GXBAR filter design method based on lithium niobate film

Abstract

The invention relates to the technical field of radio frequency filters, in particular to a 13GXBAR filter design method based on a lithium niobate film. The Euler angle of the lithium niobate thin film is subjected to simulation setting in finite element simulation software, admittance responses under different cutting angles are obtained, an admittance curve with a large electromechanical coupling coefficient and complete stray mode suppression is obtained, the tangential angle is used for simulating an electrode material, the interdigital logarithm, the interdigital distance, the thin film thickness and the metallization ratio, and an admittance curve with a large electromechanical coupling coefficient and complete stray mode suppression is obtained. The method comprises the following steps of: constructing a plurality of resonators, obtaining impedance of each resonator, obtaining material parameters of the corresponding resonator, constructing a three-dimensional force-electricity coupling model of the lithium niobate resonator, carrying out layout design on the physical model in finite element simulation software through a field-circuit coupling method, and coupling force-electricity-sound multi-physical fields to obtain an S parameter curve of the designed XBAR filter; and whether the S parameter result is consistent with the target is verified, so that the forward design of full-simulation driving is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radio frequency filter, in particular to a design method of 13G XBAR filter based on lithium niobate thin film. BACKGROUND

[0002] With the rapid development of wireless communication system, from the early 2G, 3G, 4G network to the new generation of mobile communication network today, the communication spectrum resource is more and more nervous, the frequency band allocation is more and more complex, the performance requirement of radio frequency front-end filter is continuously improved, and the radio frequency acoustic wave filter with high frequency and large bandwidth becomes the research hotspot in this field.

[0003] XBAR resonator is widely concerned in the design of acoustic wave resonator because of its advantages of combining bulk acoustic wave and surface acoustic wave. Lithium niobate (LiNbO3) has stronger piezoelectric effect and higher coupling coefficient than aluminum nitride (AlN) by means of ion cutting new film transfer technology, which is expected to realize ultra-wide bandwidth filter, and can obtain high quality factor by using its modal isolation and energy limitation characteristics of mechanical structure. Therefore, the XBAR resonator based on lithium niobate thin film becomes an important research direction of radio frequency front-end of wireless communication.

[0004] The existing filter design method has obvious defects: the design process depends on the process manufacturing, and a large number of wafer fabrication and testing are needed to establish resonator model parameter library covering different film layer materials, thickness, structure and different working frequencies, which not only takes a long time and has low design efficiency, but also has high process manufacturing cost. In addition, the filter fitted by the equivalent model of the process manufacturing has reliability only for the filter made of the same material, and has poor robustness. Once the material is changed, a large amount of fitting work needs to be done again. SUMMARY

[0005] The present application aims to provide a design method of 13G XBAR filter based on lithium niobate thin film to solve the problems in the background art.

[0006] To achieve the above-mentioned purpose, the present application aims to provide a design method of 13G XBAR filter based on lithium niobate thin film, comprising: step S1, crystal cut optimization: in the finite element simulation software, the crystal Euler angle of lithium niobate thin film is parameterized scanning and optimization, so as to obtain the optimal electromechanical coupling coefficient in the target frequency band and the complete suppression of stray mode as the judgment basis, and determine the crystal cut direction.

[0007] Step S2, structure parameter determination: based on the determined crystal cut direction, a three-dimensional model of XBAR resonator is established in the finite element simulation software, the electrode material, interdigital structure parameters and film thickness are parameterized simulation, and the optimal structure parameter combination meeting the target center frequency requirement is determined.

[0008] Step S3, finite element modeling and verification: using the optimal structure parameter combination, a three-dimensional force-electric coupling finite element model of the XBAR resonator is constructed, the complex impedance data of the resonator varying with frequency is obtained by frequency domain solving, and the accuracy of the model is verified.

[0009] Step S4, acoustic-electric-magnetic joint simulation: the complex impedance data of the resonator obtained in step S3 is used to calculate the equivalent relative permittivity varying with frequency through the equivalent permittivity formula; a layout model of the XBAR filter is constructed in the three-dimensional electromagnetic simulation software, the calculated equivalent permittivity is imported into the material properties of the piezoelectric layer in the model, acoustic-electric-magnetic joint simulation is performed, the S parameters of the filter are obtained, and the design is verified and optimized according to the simulation results.

[0010] As a further improvement of the technical solution, the finite element simulation software is COMSOL Multiphysics.

[0011] As a further improvement of the technical solution, the Euler angle determination process is as follows: rotating the X axis to the N axis with the original crystal axis Z as the rotation axis, rotating the Z axis to the x3 axis with N as the rotation axis, rotating the N axis to the x1 axis with x3 as the rotation axis, at this time the Y axis reaches the x2 axis position, obtaining a new crystal coordinate system (x1, x2, x3), in the finite element simulation software, the Euler angles in the preset range are parameterized and scanned, the admittance frequency response curves of the XBAR resonator under each Euler angle combination are simulated; the series resonance frequency and the parallel resonance frequency are extracted from each admittance curve and the corresponding effective electromechanical coupling coefficient is calculated according to the formula, and then the candidate Euler angles are determined, 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 of the technical solution, the electromechanical coupling coefficient calculation formula is:

[0013]

[0014] wherein, represents the electromechanical coupling coefficient, represents the parallel resonance frequency, represents the series resonance frequency.

[0015] As a further improvement of the technical solution, the preset condition is specifically that for the admittance frequency response curve corresponding to each Euler angle combination, the amplitude of all spurious resonance modes in the target frequency band is lower than the amplitude of the main resonance peak by a preset suppression threshold.

[0016] As a further improvement of the technical solution, the interdigital structure parameters include interdigital width, interdigital spacing, interdigital pair number and metallization rate.

[0017] As a further improvement of the technical solution, the three-dimensional force-electric coupling finite element model comprises a solid mechanics physical field, an electrostatic physical field and a piezoelectric effect module.

[0018] As a further improvement of the technical solution, when the three-dimensional force-electric coupling model is constructed, aluminum is selected as the electrode material, lithium niobate film is selected as the piezoelectric material, the density, the relative dielectric constant, the coupling matrix, the elastic matrix, the Poisson's ratio and the Young's modulus of the material are derived from the material library of the finite element simulation software, and the elastic matrix of lithium niobate is manually input; and the boundary conditions of the solid mechanics physical field, the electrostatic physical field and the piezoelectric effect module are set.

[0019] As a further improvement of the technical solution, the three-dimensional electromagnetic simulation software is ANSYS HFSS.

[0020] As a further improvement of the technical solution, the equivalent dielectric constant formula is:

[0021] ;

[0022] wherein, the equivalent relative dielectric constant is represented by, the active area is represented by, the piezoelectric layer thickness is represented by, the vacuum dielectric constant is represented by, the impedance is represented by, the angular frequency is represented by, the imaginary unit is represented by.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] 1. Greatly improving the design efficiency and shortening the research and development period: adopting the positive design process of "simulation first, process later". Before tape-out, the device performance can be accurately predicted through finite element simulation, and the dependence on repeated trial and error of physical devices is completely eliminated, and the design period is shortened from "months" to "days or weeks".

[0025] 2. Significantly reducing the research and development cost: due to the great reduction or even avoidance of the number of repeated tape-out in the early stage, the expensive process manufacturing cost is directly saved, and the threshold of technical development is reduced.

[0026] 3. Enhancing the robustness and universality of the model: the present method is based on the intrinsic physical parameters (such as piezoelectric constant and elastic constant) of the material for simulation, and the established model reflects the inherent physical law of the device, rather than the accidental result of a specific process. Therefore, the model has stronger robustness and can adapt to changes in different material parameters and structure sizes, and has better universality.

[0027] 4. Improve the design accuracy and reliability: through the "force-electricity-sound" multi-physical field coupling finite element analysis, and combined with the "equivalent dielectric constant method" to realize the sound-electricity-magnetic joint simulation, which can simulate the complex physical effect of the device with high fidelity, and the simulation result is highly consistent with the final measured performance, and the design accuracy is much higher than that of the traditional equivalent circuit model BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1 The method of the present application is implemented step flowchart; Figure 2 The LiNbO3 crystal rotary cutting schematic diagram; Figure 3 The XBAR resonator admittance response under different thicknesses of lithium niobate film; Figure 4 The finite element simulation analysis method flowchart; Figure 5 The XBAR resonator simulation three-dimensional model; Figure 6 The XBAR resonator grid structure; Figure 7 The series XBAR resonator and the preparation measured data are compared; Figure 8 The parallel XBAR resonator and the preparation measured data are compared; Figure 9 The dielectric constant curve port 1; Figure 10 The dielectric constant curve port 2; Figure 11 The electromagnetic simulation model; Figure 12 The 13GXBAR filter S parameter of lithium niobate film. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] Embodiment: please refer to Figure 1 As shown in the figure, a lithium niobate thin film-based 13GXBAR filter design method is provided, comprising: step S1, crystal cut optimization: in the finite element simulation software, the crystal Euler angle of the lithium niobate thin film is parameterized scanned and optimized, so that the optimal electromechanical coupling coefficient is obtained in the target frequency band and the completely suppressed stray mode is taken as the judgment basis to determine the crystal cut direction.

[0032] In one specific embodiment, the finite element simulation software is COMSOL Multiphysics.

[0033] In one specific embodiment, the Euler angle determination process is: rotating the X axis to the N axis with the original crystal axis Z as the rotation axis, rotating the Z axis to the x3 axis with N as the rotation axis, rotating the N axis to the x1 axis with x3 as the rotation axis, at this time the Y axis reaches the x2 axis position, obtaining a new crystal coordinate system (x1, x2, x3), in the finite element simulation software, the Euler angle ( ) is parameterized scanned in a preset range, and the admittance frequency response curve of the XBAR resonator under each Euler angle combination is simulated; the series resonance frequency and the parallel resonance frequency are extracted from each admittance curve, and the corresponding effective electromechanical coupling coefficient is calculated according to the formula, and then the candidate Euler angle is determined, and from the candidate Euler angle, the combination with the largest electromechanical coupling coefficient is selected as the optimal Euler angle.

[0034] LiNbO3 crystal has three material properties, namely piezoelectric constant ( ), elastic constant ( ) and dielectric constant ( ), and their initial parameters can be represented by the relative position of a coordinate system (X, Y, Z). Figure 2 The figure shows the schematic diagram of the rotated cut of LiNbO3 crystal. In order to make the Euler angle more visualized, the first rotation is started from the crystal axis, the X axis of the original crystal axis is rotated around the Z axis by an angle , in the range of 0° to 360°, and the X axis is rotated to the N rotation axis. The second rotation is based on the N rotation axis, and the Z rotation axis is rotated to the x3 axis by an angle , in the range of 0° to 180°. The third rotation is based on the x3 axis, and the N rotation axis is rotated to the x1 axis by an angle , in the range of 0° to 360°. After three rotations, the original Y axis reaches the x2 axis position, and the coordinate system (X, Y, Z) of the original crystal axis becomes the coordinate system (x1, x2, x3) of the normal crystal, and ( , , ) is called Euler angle, 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.

[0035] 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.

[0036] 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.

[0037] In one specific embodiment, the electromechanical coupling coefficient is calculated using the following formula:

[0038]

[0039] in, Represents the electromechanical coupling coefficient. Indicates the parallel resonant frequency. This represents the series resonant frequency.

[0040] 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).

[0041] 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.

[0042] The phase velocity of the resonator varies with the thickness of the electrode. Without considering the electrode load, the phase velocity of the resonator is below 2500 m / s, and the shear wave velocity of electrodes such as Al, Ti, and W is greater than 2500 m / s. Therefore, when a thinner electrode is covered on the surface, the electrode with a higher sound velocity will increase the overall phase velocity of the resonator, and at this time, the electrode mass load effect is not obvious, so a small upward trend of the phase velocity of the resonator will appear. The higher the sound velocity and the smaller the density of the electrode material itself, the more obvious the phenomenon. With the increase of the thickness of the electrode, the mass load effect is more obvious, and the phase velocity of the resonator. The resonator is simulated by COMSOL software. The influence of the duty cycle and the thickness of the film on the coupling coefficient and the resonant frequency of the resonator is studied. The thickness of the LiNbO3 film of the resonator is parameterized and simulated. By changing the width of the electrode of the resonator, the coupling coefficient of the resonator corresponding to each width and duty cycle is calculated. The resonant frequency of the resonator corresponding to each LiNbO3 thickness is calculated. The curve of LiNbO3 thickness under different parameters can be found from Figure 3 The resonant frequency of the resonator decreases with the increase of the thickness of LiNbO3, therefore, in order to obtain a resonant frequency of about 13 GHz, the LiNbO3 film with a thickness of is selected for subsequent resonator simulation and preparation.

[0043] In one specific embodiment, the interdigital structure parameters include interdigital width, interdigital spacing, interdigital logarithm, and metallization rate.

[0044] Step S3, finite element modeling and verification: using the optimal structure parameter combination, a three-dimensional force-electric coupling finite element model of the XBAR resonator is constructed, the complex impedance data of the resonator varying with frequency is obtained by frequency domain solving, and the accuracy of the model is verified.

[0045] In one specific embodiment, the three-dimensional force-electric coupling finite element model contains solid mechanics physical field, electrostatic physical field and piezoelectric effect module.

[0046] In one specific embodiment, when the three-dimensional force-electric coupling model is constructed, aluminum is selected as the electrode material and lithium niobate film as the piezoelectric material. The density, relative dielectric constant, coupling matrix, elastic matrix, Poisson's ratio and Young's modulus of the material are derived 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 mechanics physical field, the electrostatic physical field and the piezoelectric effect module are set. In the solid mechanics field, the electrode and the substrate acoustic layer are set as linear elastic material, the longitudinal scale is free boundary, and the transverse scale is fixed constraint, and the mechanical damping and dielectric loss of the piezoelectric material are defined. In the electrostatic field, the charge conservation area and the terminal area are defined, and the specific voltage terminal and ground are set on the upper and lower electrode surfaces respectively.

[0047] In one embodiment, the three-dimensional electromagnetic simulation software is ANSYS HFSS.

[0048] Through the analysis of the finite element model, the impedance characteristics of lithium niobate can be more comprehensively analyzed, and the state of each physical field in lithium niobate under resonance can be intuitively obtained. The finite element method is based on the variational principle and interpolation, which discretizes the model and constructs the interpolation function, and approximately considers that the behavior of the actual point is represented by the interpolation relationship of the behavior of the adjacent nodes, so as to discretize the physical problem into an algebraic equation group for solving the node unknowns.

[0049] The finite element modeling method can calculate almost all problems of piezoelectric transducers, such as structural stress analysis, vibration modal analysis, resonance frequency calculation, and impedance calculation. COMSOL and ANSYS software are currently commonly used finite element analysis software, which can realize the multi-physical field modeling of XBAR devices. For the optimization of lithium niobate thin film structure, the piezoelectric coupling analysis method is mainly used.

[0050] The design method first needs to determine the object of study, then abstract the research object, determine the task and target, and then formulate a specific simulation scheme according to the purpose. The general steps are as shown in Figure 4 .

[0051] The model is established as follows:

[0052] First, the geometric modeling of lithium niobate structure in the software is carried out. In order to further simulate the working state of the actual device, the three-dimensional modeling is selected in this design method. As shown in Figure 5 , from top to bottom, they are interdigital electrodes, recessed piezoelectric layer, and piezoelectric layer. Al is selected as the electrode material, and lithium niobate thin film is selected as the piezoelectric material. Most of the parameters of the materials involved are derived from the material library of the software, including the density, relative dielectric constant, coupling matrix, elastic matrix, Poisson's ratio, and Young's modulus of the material. The elastic matrix of lithium niobate is manually input. After establishing the three-dimensional model of lithium niobate, the setting of the solid mechanics physical field, the electrostatic physical field and the piezoelectric effect module is completed, that is, the corresponding boundary conditions of mechanics and electricity are set. In the solid mechanics field, the electrode and the substrate acoustic layer are set as linear elastic materials, and are defined as free boundary in the longitudinal dimension and fixed constraint in the transverse dimension. The mechanical damping and dielectric loss of the piezoelectric material are defined; in the electrostatic field, the charge conservation area and the terminal area are defined, and 1V terminal and 0V ground are set on the upper and lower electrode surfaces respectively.

[0053] After the physical field is added, the model is meshed. As shown in Figure 6As shown, the density of the grid size will affect the final solution accuracy. Generally, the smaller the grid size, the more subtle features of the model can be displayed, and the closer the calculation result is to the true value. However, too fine a grid will not only cause a very large amount of calculation, but also easily cause abnormal values that differ greatly from the experimental results. Therefore, the number of grids must be reduced within a suitable analysis range.

[0054] The solution and result analysis process is as follows:

[0055] An added frequency domain solver is used to analyze the frequency characteristics of the XBAR device, and a suitable solution range and step size are set.

[0056] After the above operations, variables need to be defined, relevant formulas need to be input, and the required XBAR frequency impedance characteristic curve and phase curve are obtained through a one-dimensional plotting group.

[0057] The result fitting process is as follows:

[0058] The obtained complex impedance data of the resonator are compared with the target resonator data, and the final result is fitted with the target result by changing the electrode thickness, changing the resonator area and shape.

[0059] In the design of the XBAR resonator, the area configuration of the unit array is directly related to the static capacitance characteristics, and further affects the overall impedance performance. The networking of the filter is closely related to the resonant frequency and impedance matching degree of the resonator, so the area distribution of the array unit needs to be accurately planned in the topology structure. With the increase of the thickness of the XBAR resonator laminated film, the center resonant frequency shows a decreasing trend. This is because the increase of the film thickness prolongs the sound wave propagation path. Under the condition of constant sound speed, the half wavelength correspondingly becomes larger, resulting in a decrease in frequency. Due to the structure characteristics of the interdigital electrode, the XBAR resonator is prone to coupling of the transverse mode and the longitudinal mode, thereby generating a parasitic resonance. To solve this problem, an asymmetric interdigital electrode design can be used to make the parasitic transverse mode corresponding to the series resonant frequency (f0) reflect multiple times at the electrode boundary, thereby reducing the basic parasitic resonance frequency. At the same time, by setting an impedance adjustment frame at the edge of the interdigital electrode, a significant impedance mismatch and high reflection coefficient are formed, which prevents the transverse mode from leaking from the edge of the effective excitation area, thereby suppressing the parasitic response and improving the in-band flatness and out-of-band suppression performance of the filter.

[0060] A finite element simulation method is used to establish a series-parallel three-dimensional simulation physical model of the XBAR resonator in the software, and the admittance curve of the resonator is simulated. As shown in Figure 7 , 8 the admittance of the series-parallel resonator is imported into HFSS for first-order filter design through the dielectric constant method.

[0061] ​Step S4, acoustic-electric-magnetic combined simulation: the complex impedance data of the resonator obtained in step S3 is used to calculate the equivalent relative permittivity varying with frequency through the equivalent permittivity formula; a layout model of the XBAR filter is constructed in the three-dimensional electromagnetic simulation software, the calculated equivalent permittivity is imported into the material properties of the piezoelectric layer in the model, acoustic-electric-magnetic combined simulation is performed, the S parameters of the filter are obtained, and the design is verified and optimized according to the simulation results.

[0062] The S parameters (Scattering Parameters) are the most critical and direct indicators for describing the radio frequency performance of the filter.

[0063] In one specific embodiment, the equivalent permittivity formula is:

[0064] ;

[0065] wherein, represents the equivalent relative permittivity, represents the active area, represents the piezoelectric layer thickness, represents the vacuum permittivity, represents the impedance, represents the angular frequency, represents the imaginary unit.

[0066] Both acoustic effect and electromagnetic (EM) effect exist in the XBAR resonator. In the XBAR filter, the ohmic loss of the interdigital electrode, the dielectric loss of the piezoelectric layer, and the acoustic loss in the acoustic wave propagation will increase the passband loss of the filter; while the electromagnetic effect (such as the parasitic capacitance between the interdigital electrodes, the edge field coupling) will affect the out-of-band rejection performance of the filter. Therefore, acoustic and electromagnetic behaviors need to be simulated jointly to more accurately simulate the filter performance. The traditional P matrix model can simulate the acoustic effect of the XBAR, but it is difficult to completely characterize the electromagnetic coupling, so the acoustic characteristic simulation data obtained by the P matrix model and the electromagnetic (EM) effect presented by the entity model of the XBAR filter in the three-dimensional electromagnetic simulation software need to be simulated jointly. The acoustic-electric-magnetic combined simulation result can be used as a reliable method for design evaluation, and the obtained filter transmission characteristics are closer to the actual measured curves.

[0067] The distribution characteristics of the XBAR resonator can be simulated by a new modeling method: the acoustic behavior of the XBAR is derived through a formula, and the acoustic-electric coupling characteristics are characterized by an equivalent permittivity, which is then imported into the XBAR electromagnetic model in the electromagnetic simulation software HFSS, so as to realize one-time acoustic-electric combined simulation.

[0068] ​​First, the equivalent dielectric constant method is used to obtain the model dielectric constant, the process is as follows: the force-electric coupling characteristics of the XBAR filter are obtained by finite element simulation analysis, and the impedance characteristic curve of each array unit (i.e. the relationship between the real part and the imaginary part of impedance and the frequency) is obtained.

[0069] Next, the is obtained It can be seen from the formula that the dielectric constant is a complex number, and the real part and the imaginary part of the dielectric constant change with the frequency. The real part and the loss tangent of the dielectric constant are obtained by writing the calculation formula into the MATLAB program.

[0070] A 3-D solid model of the same first-order XBAR filter is constructed in the HFSS simulation software, and a lumped port is added for simulation. The dielectric constant is imported into the XBAR filter model in HFSS for simulation, and compared with the measured admittance curve to verify its reliability, and the layout design is performed to obtain the corresponding first-order filter S parameter.

[0071] Layout design

[0072] (1) The dielectric constant real part, imaginary part and loss tangent of the XBAR resonator 3-D simulation model corresponding to the filter obtained by the finite element simulation analysis method are calculated by MATLAB, as shown in Figure 9 , 10 .

[0073] (2) The first-order XBAR filter structure model designed by the finite element simulation analysis method is imported into the HFSS simulation software, relevant settings are made, a 3-D solid model is constructed, and a lumped port is added for simulation. The dielectric constant is imported into the model for simulation to obtain the corresponding first-order filter S parameter, and the XBAR first-order filter design is completed, as shown in Figure 11 , 12 .

[0074] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only preferred examples of the present application, and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

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 finger width, interdigitated finger spacing, number of interdigitated finger 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.

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