Properties of leaky, leaky pseudo, and Rayleigh surface acoustic waves on various rotated Y-cut langasite crystal substrates

A leaky surface acoustic wave (LSAW) and a leaky pseudo SAW (LPSAW) of various rotated Y-cut langasite substrates grown by the Czochralski method were measured by an ultrasonic microscope. The measured results agreed well with the values calculated using Ilyaeve's material constants of five kinds of material. Rayleigh SAW transversal filters, having various aluminum (Al) thicknesses of interdigital transducers (IDT), were constituted on (0 degrees, 140-150 degrees, 24-25 degrees) and (12 degrees, 150-153 degrees, 36-37 degrees) plates. A temperature coefficient of frequency (TCF) of the Rayleigh SAW filters was measured by measuring their center frequency. It was clarified that (0 degrees, 142 degrees, 14.5 degrees) and (0 degrees, 143 degrees, 24 degrees) plates at normalized Al-IDT thickness (H-Al/lambda) 0.0125, and (12 degrees, 153 degrees, 37 degrees) plates at H-Al/lambda = 0.0625 showed turnover temperatures of 25 degrees C, 30 degrees C and 26 degrees C and excellent TCFs (Delta F/F/degrees C = 1.83, 1.63, and 1.95 ppm/degrees C). Measured results of electromechanical coupling factor on their substrates showed similar values (k(s)(2) = 0.41, 0.42 and 0.46%) to the theoretical ones. The (12 degrees, 153 degrees, 37 degrees) plate having the largest coupling factor is the most suitable one for SAW devices. Furthermore, the velocity, the coupling factor, and the propagation loss of LSAW on air/various Y-X langasite plates (0 degrees, theta, 0 degrees) were also calculated.