Surface acoustic wave properties of proton-exchanged LiNbO/sub 3/ waveguides with SiO/sub 2/ film

Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO/sub 3/) waveguides with silicon dioxide (SiO/sub 2/) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO/sub 2/ film was deposited on z-cut LiNbO/sub 3/ waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (V/sub p/), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO/sub 2/ film surface. The experimental results showed that the V/sub p/ of SAW decreased slightly with the increase of h//spl lambda/, where h was the thickness of SiO/sub 2/ films and /spl lambda/ was the wavelength. The IL of SAW increased with increased h//spl lambda/. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h//spl lambda/. The TCF for PE z-cut LiNbO/sub 3/ was measured to be about -54.72 ppm//spl deg/C at h//spl lambda/ = 0.08. It revealed that the SiO/sub 2/ films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO/sub 2/ film.