Temperature stable SAW devices using directly bonded LiTaO/sub 3//glass substrates

Abstract

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/spl deg/ Y-X LiTaO/sub 3/ substrate to 30 /spl mu/m 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 LiTaO/sub 3//glass thickness ratio, the temperature coefficient of frequency (TCF) of the SAW devices was maintained at approximately -6 ppm//spl deg/C from -30/spl deg/C to 80/spl deg/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/spl deg/ Y-X LiTaO/sub 3/ substrate.