Quantitative characterization of proton-exchanged layers in LiTaO3 optoelectronic devices by line-focus-beam acoustic microscopy

Application of line-focus-beam (LFB) acoustic microscopy is extended to quantitative characterization of proton-exchanged/annealed layers employed in LiTaO3 optical waveguides. Several specimens of Z-cut LiTaO3 substrates, processed under the fabrication conditions for second-harmonic generation (SHG) optoelectronic devices, were prepared for measurements of the leaky surface acoustic wave (LSAW) velocities. Remarkable decreases in LSAW velocity due to the processes of proton exchange and annealing were observed, providing very useful information on the proton concentration and depth in diffusion layer, and on the process temperature distribution. It is found that measurement sensitivity is highest in the Y-axis wave propagation direction and the resolution to the optical waveguide parameters of diffusion depth and refractive index is much greater than the conventional techniques. It is suggested that this ultrasonic method should be adopted as a new analytical technique for development and evaluation of device fabrication processes and systems destined for future mass production.