Study On Spurious Mode Suppression Of Bulk Acoustic Wave Resonators Based On Lithium Niobate

The rapid development of 5G communication technology has brought a series of challenges to RF filters.The market urgently needs high-performance RF filters with high frequency,large bandwidth,small size,and low insertion loss.Among many filters,bulk acoustic wave(BAW)filters have gradually become the mainstream due to their small size and high operating frequency.The BAW resonator is the basic unit of the BAW filter,and various structures have been derived in the process of development.among them,the laterally-excited bulk acoustic wave(XBAR)adopts the interdigital transducer structure of the surface acoustic wave(SAW)resonator and obtains excellent characteristics.In order to design a high-performance XBAR filter,it is necessary to design an excellent XBAR resonator,but the spurious response is a serious problem that often occurs in the design of XBAR resonators,which will greatly affect the insertion loss of the filter.Therefore,the research on spurious mode suppression of the XBAR resonator is particularly important.This thesis studies the spurious mode suppression method of XBAR resonator based on lithium niobate.The basic idea is to realize high frequency and high electromechanical coupling coefficient XBAR resonator by using the piezoelectric material lithium niobate film with high electromechanical coupling coefficient.In this thesis,finite element analysis method is used to analyze XBAR resonators and the spurious mode response encountered in the design,and then analyze the sources and suppression methods for different spurious mode responses.Based on the simulation and analysis of the XBAR resonator,the Bragg reflection grating structure is adopted to improve the feasibility of the manufacturing process,and then the XBAR resonator with high frequency and high electromechanical coupling coefficient is fabricated.Finally,the test results of the resonator are obtained.The series resonance frequency of the resonator is 3.723 GHz,and the electromechanical coupling coefficient is 13.03%,which does not reach the expected design specification.Then,the test data is fitted by the equivalent circuit model,and the problems and solutions in the process of design and manufacturing test are discussed through the fitting results.Finally,although the XBAR resonator designed this time did not reach expectations,it still has a high resonant frequency and a considerable electromechanical coupling coefficient,showing the great potential of XBAR resonators in high frequency,high electromechanical coupling coefficient resonators field.In addition,this thesis provides explanations and solutions for the shortcomings of this design and process,which provide a reference for subsequent design and manufacturing.