Theory And Fabrication Of Bulk Acoustic Wave Resonator Based On Phononic Crystal

With the continuous advancement of informatization and the rapid development of mobile technology—from smart homes to autonomous vehicles—there are an ever-growing demand for advanced radio frequency(RF)communication systems.The filter is an indispensable component of assorted RF systems;the performance of the filters determines the overall quality of the communication systems.With the advent of the 5g communication era,the frequency band supported by smartphones and various small mobile terminals is increasing,and its communication frequency is also gradually increasing,which brings some challenges to the traditional RF front-end devices.The traditional RF filter cannot meet the current market demand because of its performance and size constraints.As the best option to integrate with RF circuit or microwave circuit,bulk acoustic wave filter has great development and application prospects in modern RF communication systems.This paper will focus on the solidly assembled resonator based on the one-dimensional phononic crystal(Bragg structure)and two-dimensional phononic crystal,study the influence and variation law of four phononic crystal structures on the performance of bulk acoustic wave devices,then explore the main loss mechanism in SMR devices,and put forward improvement schemes,it lays a foundation for the application of solid assembly resonator in today's RF front-end.The research contents of this paper are as follows:(1)Firstly,the working principle of bulk acoustic wave resonator and the energy band characteristics of phononic crystals are theoretically analyzed,and the energy band characteristics of four kinds of phononic crystals and their corresponding transmission losses are obtained by COMSOL finite element software simulation.Using the characteristics of phononic crystals in the forbidden band,a design scheme of bulk acoustic wave resonator based on phononic crystals is proposed,Then the feasibility of the scheme is proved by the finite element method.(2)The main loss mechanism of the traditional quarter wavelength solid-state assembled resonator is analyzed,and the shear wave leakage problem which is easy to be ignored is emphatically analyzed.Then,based on the thin film optical theory,an improved Bragg design scheme is proposed,which can have high reflection coefficients for longitudinal wave and shear wave at the same time.The two-dimensional and three-dimensional finite element simulation models are established by using the finite element method.The simulation results prove the feasibility of the optimized Bragg scheme design.In addition,the thermal properties of FBAR and SMR devices are analyzed utilizing piezoelectric solid heat transfer multi-physical field coupling.(3)Finally,according to the theoretical results analyzed in the previous chapters,complete traditional and optimized SMR devices are prepared through MEMS processing technology and tested by a vector network analyzer.Finally,the series resonant frequency of the device is 3.055 ghz,the Q value of the device parallel resonator is 572,and the Q value of the optimized device is 40%higher than that of the traditional device,it is proved that the Bragg design can improve the performance of SMR resonator.