Theoretical analysis of SAW propagation characteristics under the strained medium and applications for high temperature stable high coupling SAW substrates

The important properties required for SAW substrates are a large electromechanical coupling coefficient (k²), small temperature coefficient of frequency (TCF), low propagation loss, etc. LiNbO₃ and LiTaO₃ have good properties as SAW substrates with a large size. Unfortunately these possess the disadvantage of large values of TCF. In this paper, SAW bonded composite substrates with a large k², small TCF, low propagation loss and no dispersion using conventional bonders are investigated theoretically and experimentally. The propagation characteristics of SAW under the strained piezoelectric crystal using the higher-order elasticity theory have been analyzed. The theoretical results show zero TCF on LiNbO₃/SiO₂ substrates. The experimental results of LiNbO₃/glass substrate showed TCF of 19 pptn/°C. The propagation properties were almost the same as those of the single crystal