The surface acoustic wave propagation characteristics of 64/spl deg/ Y-X LiNbO/sub 3/ and 36/spl deg/ Y-X LiTaO/sub 3/ substrates with thin-film SiO/sub 2/

The SAW characteristics of thin-film sputtered silicon dioxide (SiO/sub 2/) on substrates of 64/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) and 36/spl deg/ Y-X lithium tantalate (LiTaO/sub 3/) have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon dioxide films in the 500 nm to 2000 nm thickness range were deposited by RF diode sputtering. The SAW velocity, propagation loss, capacitance ratio (C/sub m//C/sub 0/), and temperature coefficient of frequency (TCF), were measured using thin-film aluminum interdigital electrodes patterned on the upper film surface. The presence of the SiO/sub 2/ initially stiffened the substrate surfaces before softening the surface with increasing thickness. The SAW propagation loss values showed a minimum at film-thickness to acoustic-wavelength ratios (t//spl lambda/) in the 0.02 to 0.08 region. The TCF improved but C/sub m//C/sub 0/ decreased with increasing t//spl lambda/ ratio.