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 arc a large electromechanical coupling coefficient (k²), small temperature coefficient of frequency (TCP) and low propagation loss. The LiNbO₃ and LiTaO₃ have good properties as the SAW substrates with a large size. Unfortunately, these possess the defect of having large values of TCP. In this paper, SAW-bonded composite substrates with a large k², small TCP, 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 TCP on LiNbO₃/SiO₂ substrates. The experimental results for LiNbO₃/glass substrates revealed a TCP of [-19 ppm/°C]. The propagation properties were almost the same as those of the single crystal.