Microstructure dependence on processing temperature in sol-gel derived thin ferroelectric films of LiNbO₃ on SiO₂/Si substrate

In this paper, we report our sol-gel derived thin films of LiNbO₃ on silica-on-silicon, a potential substrate for integrated optics. The dependence of the microstructure of these films on the processing temperature is presented. The films are studied by means of X-ray diffraction, atomic force microscopy, Raman spectroscopy, and variable angle spectroscopic ellipsometry. We find that the smoothness of the films can be improved by continuously annealing the films in several steps. The experimental results show that the 500°C annealed films have a nanocrystalline nature with the grain size ranging from 39nm to 109nm. The ultrafine crystalline structure and the pure trigonal phase of the film material make it suitable for E-O and A-O waveguide applications.