Electromechanical Coupling Constants of Surface Acoustic Waves on Lithium Niobate Covered with Silicon Dioxide

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Abstract
The coupling constant of 128°-rotated y-cut x-propagating LiNbO3 covered with SiO2 was measured. SiO2 was deposited on LiNbO3 before forming SAW transducers, and was used as a nonpiezoelectric film to control the coupling constant of the piezoelectric substrate. The coupling constant decreased as the film became thicker. The admittance of SAW transducers formed on the film was then measured, and the coupling constant was derived from the measured admittance. The measured coupling constant was 0.047, 0.038, 0.034 and 0.029 when the ratio of the film thickness to the SAW wavelength was 0.005, 0.01, 0.015 and 0.02, respectively. The coupling constant of the LiNbO3 substrate without the SiO2 film was 0.057, which agrees with the value of 0.056 reported previously.