Research Of New Bulk Acoustic Wave Resonator

The bulk acoustic resonator is a new MEMS device,which has the advantages of small size,good performance and integration,and has been widely concerned in the field of radio frequency communication and sensor.The advent of the 5G communication era and the development of flexible electronics have put forward higher requirements for bulk acoustic wave resonators.High frequency,miniaturization,and flexibility have become the future development direction of bulk acoustic wave resonators.In this paper,the piezoelectric materials,electrode structure and preparation technology of the bulk acoustic resonator are studied creatively.The single crystal acoustic resonator based on Z-cut lithium niobate and flexible body acoustic resonator based on P(VDF-TrFE)are designed and prepared.Two new electrode structures are proposed.The specific research contents and achievements are as follows:1.Single crystal lithium niobate is used to replace the traditional polycrystalline piezoelectric materials.Through theoretical calculation,the acoustic transmission characteristics of Li Nb O₃ with different tangential directions are obtained,and the feasibility of using Z-cut single crystal Li Nb O₃ as bulk acoustic resonator is proved.The equivalent circuit of piezoelectric layer and common acoustic material is obtained.On this basis,the Mason equivalent circuit model of single crystal Li Nb O₃ bulk acoustic resonator is established.The influence of the thickness of piezoelectric layer,electrode and Bragg reflector on the device performance is analyzed by ADS simulation software.2.The surface roughness of Z-cut single crystal lithium niobate was obtained by ion implantation stripping method.A solid-state assembled solid-state acoustic resonator based on Z-cut single crystal lithium niobate was designed.The complete device preparation technology is explored,including electrode preparation,Bragg reflection layer preparation and lithium niobate etching.The solid state assembly device was successfully prepared and tested in laboratory.The results show that the frequency of the resonator is more than 3 GHz.3.The process simplification and structure optimization of the single crystal lithium niobate acoustic resonator are carried out.The back etched cavity is used to replace Bragg reflector,and the back etched bulk acoustic resonator is designed and prepared.A silicon back etching scheme is proposed,which combines the two-way hole lithium niobate etching with dry wet etching.The improved device frequency increased to 5 GHz,and the quality factor increased to more than 600.In addition,in order to further improve the performance of the device,innovative designs are also made for the electrode structure.Two new electrode structures of block metal electrode and graphene composite electrode are proposed to effectively solve the problem of parasitic clutter and temperature rise during operation.4.Choose P(VDF-TrFE)flexible piezoelectric material for the preparation of bulk acoustic wave resonator.The P(VDF-TrFE)film with high crystallinity and good surface condition was prepared by multiple spin coating method.Based on the problems that the prepared piezoelectric film is not resistant to high temperature and is soluble in acetone,a new electrode preparation process was explored that baked glue at a low temperature of 60?and stripped off the developer with full exposure.The P(VDF-TrFE)bulk acoustic wave resonator was successfully prepared under laboratory conditions.The series resonance frequency is 40.87 MHz,the parallel resonance frequency is 43.87 MHz,and the effective electromechanical coupling coefficient exceeds 10%.