Surface acoustic wave properties on rotated Y-cut langasite single crystal substrates

The langasite substrate has been expected to have a large electromechanical coupling factor and an excellent temperature coefficient of frequency (TCF) in surface acoustic wave (SAW) properties. A large size langasite single crystal was grown by the Czochralski method. A leaky SAW (LSAW) and a leaky pseudo SAW (LPSAW) of the various rotated Y cut langasite substrates were measured by an ultrasonic microscope. Of them, their measured results on Euler angle (0°,150°,0~180°) and (0°,10~170°,0°) of the substrates were compared with the theoretical values calculated by five kinds of material constants. They were similar to calculated values using Ilyaev´s material constants. Variations of LPSAW velocities on Z-cut plates having defects called core, were also measured and evaluated by the ultrasonic microscope. The substrates showed large variations of LPSAW velocities. The TCFs of the Rayleigh SAW were measured by measuring the center frequency of a transversal filter taking account of AI-IDT thickness. It was clarified that (0°,142~143°,24~25°) substrates showed excellent TCF´s at normalized AI-IDT thickness 0.0125