Mitigation of High Frequency Spurious Responses in Rayleigh SAW Resonators on LiNbO3 Substrate

This paper describes the behavior of a higher-order mode spurious response on the low acoustic velocity (LAV)-Rayleigh surface acoustic wave (SAW) structure, which realizes remarkable miniaturization of temperature compensated SAW (TC-SAW) devices. In multilayered SiO2/LiNbO3 (LN) TC-SAW structures including the LAV-Rayleigh SAW, it is well known that a higher-order mode propagating in the SiO
₂
layer causes a spurious response above the frequency of the main response, and its suppression is highly required. First, we calculated impedance characteristics of several configurations of Pt electrode thickness and cut angle of LN since the LAV-Rayleigh SAW is different in them from the conventional Rayleigh SAW. The results showed that the LAV-Rayleigh SAW has the following advantages of higher-order mode; 1) larger frequency difference between the main and spurious responses, 2) smaller response size. Next, we made additional calculations of acoustic velocity, electromechanical coupling factor (K
²
), and field distribution of the spurious mode. As a result, we validated that the first advantage is due to dependency of acoustic velocity of the modes on Pt thickness, and the second advantage is induced by both the decrease of K
²
and the increase of acoustic radiation with the variation of Pt thickness and cut angle. Finally, one port resonators were fabricated to confirm the validity of the calculation results, and the superiority of the LAV-Rayleigh SAW is demonstrated.