Formation and properties of proton-exchanged and annealed LiNbO/sub 3/ waveguides for surface acoustic wave

The proton-exchanged (PE) and annealed PE (APE) z-cut LiNbO/sub 3/ waveguides were fabricated using H/sub 4/P/sub 2/O/sub 7/. The positive strain, c-axis lattice constant change (/spl Delta/c/c), was calculated to be about +0.43%, which was almost independent of the exchanged conditions. The penetration depth of H measured by secondary ion mass spectrometry (SIMS) exhibited a step-like profile, which was assumed to be equal to the waveguide depth (d). The surface acoustic wave (SAW) properties of PE and APE z-cut LiNbO/sub 3/ samples were investigated. The phase velocity (V/sub p/) and electromechanical coupling coefficient (K/sup 2/) of PE samples were significantly decreased by the increase of kd, where k was the wavenumber (2/spl pi///spl lambda/). The insertion loss (IL) of PE samples was increased by the increase of kd and became nearly constant at kd>0.064. The temperature coefficient of frequency (TCF) of PE samples allowed an apparent increase with kd, reaching a maximum at kd=0.292, then slightly decreased at higher kd. The effects of annealing resulted in a restoration of V/sub p/ and an improvement of IL.