Temperature stable SAW devices using directly bonded LiTaO3 /glass substrates

We have developed temperature stable SAW devices by using a direct-bonding technique. Temperature stability approximating that of quartz was achieved by thinning a 36° Y-X LiTaO₃ substrate to 30 μm on a glass substrate. The temperature compensated SAW devices were fabricated using a stacking procedure based on the direct bonding of a piezoelectric single crystalline layer onto a glass substrate. Because the thermal expansion coefficient (TEC) of the glass substrate is smaller than that of the piezoelectric layer, the piezoelectric layer experiences thermal stress. As a result, the temperature dependence of the SAW devices could be improved. By using a glass substrate with small TEC and minimizing the LiTaO₃/glass thickness ratio, the temperature coefficient of frequency (TCF) of the SAW devices was maintained at approximately -6 ppm/°C from -30°C to 80°C. The SAW propagation characteristics (velocity and electromechanical coupling factor) and the frequency response of the SAW devices were almost the same as those of SAW devices using a 36° Y-X LiTaO₃ substrate