Theoretical Analysis of Surface Acoustic Wave Propagation Characteristics under Strained Media and Applications for High Temperature Stable High Coupling Surface Acoustic Wave Substrates

Among the important properties required for surface acoustic waves (SAW) substrates are a large electromechanical coupling coefficient ( k 2 ), small temperature coefficient of frequency (TCF) and low propagation loss. The LiNbO 3 and LiTaO 3 have good properties as the SAW substrates with a large size. Unfortunately, these possess the defect of having large values of TCF. In this paper, SAW-bonded composite substrates with a large k 2 , small TCF, low propagation loss and no dispersion using conventional bonders are investigated theoretically and experimentally. The propagation characteristics of SAWs under strained piezoelectric crystals using the higher-order elasticity theory have been analyzed. The theoretical results show zero TCF on LiNbO 3 /SiO 2 substrates. The experimental results for LiNbO 3 /glass substrates revealed a TCF of [-19 ppm/°C]. The propagation properties were almost the same as those of the single crystal.