BA2SI2TIO8 FOR SURFACE-ACOUSTIC-WAVE DEVICES

Characteristics of piezoelectric fresnoite (Ba2Si 2TiO8) for surface-acoustic-wave (SAW) devices are calculated. In general, the SAW characteristics of this material are located between those of LiNbO3 and LiTaO3. It always has nonzero temperature coefficients of delay (TCD's). The lowest TCD is approximately 38×10-6/K, corresponding to the Bleustein-Gulyaev wave on the Z-axis cylinder cuts. A layered structure of Ba2Si 2TiO8 thin film deposited on a fused-quartz substrate is expected to have excellent SAW characteristics, e.g., k2a (electromechanical coupling factor when the interdigital transducers are formed on the surface of the layer) =0.0158-0.0165, and TCD=0-25×10-6/K for kh (where k is the wave number and h is the layer thickness) =2.0-3.2. A comment is made in the Appendix on an additional contribution to the formula for the power flow, and this contribution is taken into account in the present calculation.