Temperature Compensated SiC Base Simulation Study Of SAW Devices

The rapid development of 5G communication technology requires higher performance RF front-end surface acoustic wave（SAW）filters.As a widely used core device,the operating frequency and temperature stability of SAW devices have become an important measure of device quality.SiC is widely used in commercial high-frequency devices due to its high sound velocity.At the same time,lithium niobate（Li Nb O₃）single crystal film has a large electromechanical coupling coefficient（K²）,and SiO₂ has a frequency temperature coefficient（TCF）compensation characteristic.Therefore,this dissertation uses finite element method to simulate and analyze the characteristics of temperature compensated SAW devices based on SiC multilayer structure,in order to provide design and implementation schemes for developing SAW devices with high temperature stability and high frequency.The dissertation mainly carried out the following work:（1）For two different temperature compensation structures,TC-SAW（Temperature compensated SAW）structure and I.H.P（Incremental High Performance）temperature compensation structure.The three-dimensional finite element simulation model of SiO₂/Al/（0°,-53°,47°）Li Nb O₃/6H-SiC and Al/（0°,-53°,47°）Li Nb O₃/SiO₂/6H-SiC multilayer film structure was established using COMSOL multi physical field simulation tool.Calculate the characteristic frequency of the structure in the frequency domain,and the phase velocity,electromechanical coupling coefficient,frequency temperature coefficient and other parameters of longitudinal surface acoustic wave（L-SAW）excited by the structure were calculated,The effects of electrode thickness and film thickness on the propagation characteristics of two different temperature compensation structures are analyzed.Two L-SAW resonators with excellent performance were obtained,wherein of TC-SAW temperature compensation structure resonator K²=9.49%,TCF=0 ppm/℃;I.H.P temperature compensation structure resonator K²=10.958%,TCF=-0.122ppm/℃;（2）In order to further select the device performance,the two kinds of unit period resonators are compared,and the 2.5-D finite length resonator model is established using COMSOL software to optimize the design of I.H.P temperature compensation structure single ended resonator.By comparing different interdigital electrode pairs,reflective grating pairs,and their acoustic field displacement,the transverse modes appearing in the periodic three-dimensional structure design are analyzed.Then,by comparing different gap lengths（L_G）,aperture lengths（L_A）,and pseudo finger electrode lengths（L_D）,as well as their acoustic field displacement,when L_D=0,L_A=15λ,L_G=0.5λL-SAW single ended resonator with good stability.（3）Finally,using the simulation results of L-SAW single ended resonator,the MBVD（Modified Butterworth-Van Dyke）equivalent model is extracted through MATLAB self programming,and it is cascaded in ADS to form a trapezoidal SAW filter.The relationship between the order of the filter and the S parameter is explored,and finally a high-order SAW trapezoidal RF filter with a center frequency of 5.1GHz,a bandwidth of 400MHz,an insertion loss of less than 2d B,and an out of band rejection of more than 20d B is obtained.In addition,the MBVD equivalent model and component parameters,which have certain guiding significance for the actual design of high-order SAW ladder filters,are obtained.In conclusion,the research in this dissertation proves that the I.H.P temperature compensation structure Al/（0°,-53°,47°）Li Nb O₃/SiO₂/6H-SiC has a good prospect in 5G mobile communication.