Research On Performance And Q Value Optimization Of S-band FFBR

In recent years,with the rapid development of mobile phones,satellite communications,cloud services,and various other forms of wireless data communications,communication systems have become increasingly diversified.Traditional RF filters cannot meet the demands of miniaturization,high frequency,integration and broadband in new-generation communication due to the lack of structure.The running frequency of FBAR can reach GHz or even higher frequency due to the advantages of the structure.It is easy to achieve device integration since the device manufacturing process is compatible with semiconductor process.It is considered to be the best method for the filters of fifth-generation communication and even higher frequency band one.In order to improve the performance of FBAR filter,the performance optimization of FBAR and the fabrication of related devices are also the research hotspot in recent years.In this paper,based on the basic theory of FBAR,performance of FBAR was simulated by using finite element simulation method,and then the device was fabricated and tested.To improve the performance of FBAR,it is necessary to study single-layer and multi-layer converged structures through analyzing its spurious mode.Firstly,the model was used to analyze the influence of the thickness of piezoelectric layer and electrode layer,electrode area,and electrode shape on the performance of FBAR established with COMSOL Multiphysics software.It is found that the effective electromechanical coupling coefficient of FBAR firstly increases and then decreases as the thickness of the piezoelectric layer increases through the simulation.With the increase in the ratio of the piezoelectric layer to the electrode layer,the effective electromechanical coupling coefficient firstly increases and then gradually leveled off when other structural parameters are constant.The apodized electrode changes the reflection direction of shear Lamb wave,and increases the propagation distance of shear Lamb wave.It reduces the probability of Lamb wave forming standing wave,and then weakens the spurious mode.The simulation results show that the irregular pentagon electrode has the best suppression effect on parasitic vibration.Secondly,these works were carried out including frequency response analysis of FBAR,device manufacturing and performance testing.The test results of microwave probe show that frequency has a small drift on series resonant frequency and parallel resonant frequency of FBAR.The effective electromechanical coupling coefficient of test data is 0.1% lower than the simulation results.Finally,to analyze the main spurious modes causing the energy loss of FBAR,it is necessary to study the energy collection effect of single-layer and multi-layer converged structures based on the finite element simulation of FBAR and Fourier transform.The simulation results show that the two structures can effectively suppress the energy leakage caused by Rayleigh Lamb mode.The multi-layer structure has a good effect on suppressing the energy leakage applied to the upper and lower electrodes of FBAR.The quality factor of FBAR reaches 2384.Compared with the similar structure of FBAR devices in other papers,quality factor and the effective electromechanical coupling coefficient of the converged structure are better in this research,which has a certain reference value for researchers involved.