Study On Performance And Nonlinearity Of Surface Acoustic Wave Devices

A technology for transmitting and processing signals by using surface acoustic waves?SAW?is called surface acoustic wave technology.Because of its simple structure,small size,light weight and strong frequency selectivity,SAW devices have been widely used in modern communication systems,mobile phones,television,radio,radar and other fields,and play an important role in the national economy and national defense construction.The development of 5G technology puts forward higher requirements for the performance of SAW devices.Many countries are investing a lot of manpower,material and financial resources to develop high-performance SAW devices.Although the theoretical study of SAW in China is not too late,the technology and market of high performance SAW devices are still monopolized by developed countries.As a result,the research on SAW devices is still of great significance.Aiming on the characteristics of acoustic surface wave,the paper focuses on the computational method,acquisition of key parameters,mechanism of temperature and nonlinear effects on the performance of surface acoustic wave devices.The main research content and results are as follow:Firstly,the several analysis methods of surface acoustic wave devices are compared:delta-function model,impulse function model,equivalent circuit model?ECM?,coupling-of-mode theory?COM?,P-matrix method and finite element method.The basic characteristics and parameters of acoustic surface waves are calculated and discussed,such as frequency response,impedance characteristics and insertion loss.These researches are helpful to intuitively understand the basic characteristics of SAW devices and lay a foundation for future research.A method of obtaining COM parameters by numerical calculation is proposed.This method skillfully utilizes the intrinsic relationship between the finite element method and the P-matrix method to establish the relationships between COM parameters and the finite element results,the COM parameters are then obtained.It is not only simple and flexible,but also has wide range of application and accurate results,and minor calculation.Moreover,with these parameters obtained from the simple model,COM method can be applied to complex structures and SAW devices.The frequency response characteristics of SAW devices,such as one-port SAW resonators,two-port filters,reflecting gratings and three-port filters,are investigated by COM method with the acquired parameters.Through the calculation and analysis of surface acoustic wave devices,the influence of model parameters on the performance of surface acoustic wave devices is clarified.The research results can provide theoretical guidance for the design of SAW devices.The piezoelectric governing equations for studying frequency shift caused by temperature are established by using the incremental Lagrangian equations.The frequency-temperature behavior of SAW devices is studied by finite element method,where lithium niobate?LiNbO₃?,aluminum nitride?AlN?and quartz?SiO₂?are taken as examples.A two-layer SAW resonator finite element model with a low frequency temperature coefficient is proposed.The frequency-temperature behavior of the resonator is investigated in detail,and the thickness of surface wave layer is also optimized.As the frequency of the device increases,the influence of temperature on device performance is becoming more and more serious.Accordingly,these results are of great significance for improving the performance of SAW devices.The definitions and properties of the third-order elastic constants,the third-order piezoelectric constants and the third-order dielectric constants are investigated from the energy equation.The relationships between the independent components and the non-independent components of the 32 kinds of point groups which belong to seven major crystal systems are calculated.These third-order material constants play an important role in describing the nonlinear behavior of SAW.Based on the nonlinear piezoelectric equations,the governing equations on the second-order harmonic effect are derived.The finite element model is established to calculate and analyze the second-order harmonic effect.The generation mechanism of non-linear behavior of surface acoustic wave devices is revealed.These studies will help to solve the problem of signal distortion of SAW devices caused by nonlinear effects.In summary,the following key issues are studied and solved:how to obtain COM parameters,how to calculate and analyze SAW devices,the temperature effect,third-order material constants and the second-order harmonic effect.Theoretical and finite element models are proposed to carry on the research related to acoustic surface wave.The research results have important theoretical significance and engineering value for the research and application of surface acoustic wave devices.