Optimization of Mason Model in Thin Film Bulk Acoustic Resonators with Extra Passivating Piezoelectric Structures

With the rapid development of 5G and Micro-Electro-Mechanical System (MEMS) technology, piezoelectric film bulk acoustic resonators (FBARs) have gradually become one of the hotspots of Radio Frequency (RF) filters. In this paper, the electrical impedance model of FBARs was derived based on the acoustic wave transmission characteristics in the thin film, traditional one-dimensional mason model of FBARs was improved. The finite element simulation was used to validate this modified mason model. The ADS software was used to study the influence of the thickness of the passivating piezoelectric (PAS-PZ) layer on the impedance characteristics. The simulation results show that as the thickness of the PAS-PZ layer increases, the transmission path of the acoustic wave increases, resulting in a gradual decrease in the resonant frequency; as the piezoelectric thickness increases, the k(eff)(2) (effective electromechanical coupling factor) and Q of the device basically show no changes with the thickness of the PAS-PZ layer. All the results show that FBARs with a passivating piezoelectric layer can be accurately and efficiently modeled through this modified mason model without complex finite element simulation, which lays a solid foundation for FBAR design and optimization.