Effect of SiO2 protective layer on LiNbO3 structured SAW resonators and temperature characteristics study

Abstract

In this paper, using LiNbO3 as the piezoelectric substrate, Pt as the electrode and SiO2 as the protective layer, a multi-physics field coupled finite element model was used to investigate the effect of the protective layer thickness on the Rayleigh wave propagation characteristics, and the relationship between the protective layer thickness and the frequency–temperature coefficient TCF and electromechanical coupling coefficient K 2 is established. The frequency characteristics of the device and the microscopic changes of the electrode and substrate structures under high temperature were analyzed experimentally. The results show that no acoustic mode shift occurs when the normalized thickness is less than 31.25%. As the thickness of the protective layer increases, the vibration displacement in the direction of L wave, SH wave and SV wave decreases, and the thickness of the protective layer can be increased appropriately to reduce the interference of SH wave to Rayleigh wave; |TCF| decreases with increasing thickness of the protective layer. Changes in the thickness of the protective layer at different temperatures lead to fluctuations in K 2; the protective layer structure leads to a slight decrease in Q value. As the temperature increases, the fluctuation of the resonant frequency of the SAW resonator increases. The SiO2 protective layer can effectively protect LiNbO3 materials while improving the high-temperature working stability of Pt electrodes.