Theoretical Analysis of Solidly Mounted Film Bulk Acoustic Resonator with Nanocrystalline Diamond as High Impedance Material of Bragg Reflector

In this paper, a solidly mounted resonator (SMR) was designed with nanocrystalline diamond (NCD) as the high acoustic impedance material of Bragg reflector to improve the quality. We used Mathcad to investigate the effect of the Bragg reflector on the performance of the SMR, as well as the influence of different materials and the number of layers of Bragg reflector on the quality factor Q. Results show that the Bragg reflector could reduce energy loss effectively, and the higher the impedance of the high acoustic impedance layer, the better the SMR. The parasitic factors of the SMR using two high acoustic impedance materials, tungsten (W) and NCD, were also simulated by an Advanced Design System (ADS) using the Mason model. It was found that the parasitic effect caused by metal would significantly decrease the Q factor of the SMR. In the frequency range below 6 GHz, within which the SMR works normally, NCD performed better than W. Therefore, NCD is a better choice of high acoustic impedance material in the design of the SMR, with improved quality at high frequency and low loss. The optimum number of layers of Bragg reflector is 6.