Surface acoustic wave properties on various rotated Y-cut langasite crystal substrates grown by Czochralski method

A langasite crystal has been paid to much attention as a substrate for surface acoustic wave (SAW) devices recently, because it has a larger electromechanical coupling factor (k_s) than quartz and an excellent temperature coefficient of frequency (TCF) similar to quartz. A leaky SAW (LSAW) and a leaky pseudo SAW (LPSAW) of the various rotated Y cut langasite substrates grown by the Czochralski method were measured by an ultrasonic microscope. The measured results were compared with the theoretical values calculated by five kinds of material constants. The TCFs of Rayleigh SAW filters having various Al thickness of interdigital transducer (IDT) on various rotated Y plates were measured. It was clarified that (0°, 142°, 24.5°) and (0°, 143°, 24°) substrates showed turnover temperatures of 25°C and 30°C, and more excellent TCFs (1.83 and 1.63 ppm/°C) at normalized Al-IDT thickness 0.0125 compared with ones reported until now. Measured results of electromechanical coupling factor on their substrates showed almost equal values to theoretical ones