Zero Temperature Coefficient of Frequency Surface Acoustic Wave Resonator for Narrow-Duplex-Gap Application on SiO₂/Al/LiNbO₃Structure

Abstract

In this paper, we describe a zero temperature coefficient of frequency (TCF) surface acoustic wave (SAW) resonator on a SiO2/Al/LiNbO3 structure. We studied the dependence of TCF and electromechanical coupling factor (K2) of shear-horizontal (SH) SAW on SiO2 thickness, where the SiO2 shape control technique is applied to suppress spurious responses caused by the Rayleigh mode. As a result, we could realize a high performance SAW resonator having moderate K2 (8%) and zero TCF with complete suppression of the Rayleigh-mode spurious response. We demonstrated that the SiO2 shape control technique is effective for suppression of the Rayleigh-mode spurious response in the SAW resonator using the SiO2/Al/LiNbO3 structure for a wide range of SiO2 thicknesses. We also revealed the applicability of the SiO2/Al/LiNbO3 structure to SAW duplexers with a narrow duplex gap.