High-coupling leaky SAWs on LiTaO₃ thin plate bonded to quartz substrate

The propagation properties and resonance characteristics of leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) on a LiTaO3 (LT) thin plate bonded to an AT-cut quartz substrate were investigated. For the LSAWs and LLSAWs, the bonded structures of 36°Y-cut X-propagating LT (36°YX-LT)/AT-cut X-propagating quartz (ATX-quartz) and X-cut 31°Y-propagating LT (X31°Y-LT)/AT-cut 45°X-propagating quartz (AT45°X-quartz) were fabricated, respectively, and the electromechanical coupling factor (K²) was determined from the measured admittance properties of an interdigital transducer. For the LSAW on 36°YX-LT/ATX-quartz, K² of 11.8% was obtained experimentally at an LT thin-plate thickness of 0.25 wavelength, whereas K² for a single LT substrate was measured to be 5.9%. For the LLSAW on X31°Y-LT/AT45°X-quartz, K² increased from 2.5% for the single LT substrate to 6.2% at an LT thin-plate thickness of 0.28 wavelength. In both the LSAWs and LLSAWs on the bonded substrate, the improvements of resonance characteristics and the temperature coefficient of frequency (TCF) were observed as compared with those of the single LT substrate. Furthermore, K² of approximately 12% and TCF of 0 ppm/°C were theoretically obtained simultaneously for the LSAW on 36°YX-LT/AT-cut 90°X-propagating quartz at a certain thin-plate thickness.