Sol-gel Deposition of BaTiO_{3} Thin Films for Electro-optic Waveguide Modulators

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Alfred University. Faculty of Ceramic Engineering. Kazuo Inamori School of Engineering
Barium titanate thin films were deposited onto silica-clad silicon using a sol-gel spin coating process. Such films could have valuable applications as electro-optic waveguide components and devices. A large polymer, polyvinylpyrrolidone, was added to a conventional acetate-based sol-gel to increase film thickness. The effect of processing parameters on thin film properties was studied using several techniques including prism coupling. This method also was used to study the optical loss in the films. The films were heat-treated under various conditions and a rapid heating recipe (fast ramp to 500ºC then 700ºC for 30 minutes) was shown to fully crystallize the film to perovskite BaTiO_{3}. The as deposited films show desirably low loss (~1 dB/cm). However, the loss in all the fired films was very high despite the fact that the grain size in the film is on the order of 10-20nm. The results indicated that this high loss was locked into the system early during the organic removal phase, which was unexpected. Pyrolysis of the large polymeric molecules can be expected to create a new structure within the porous film consisting of isolated, but interconnected nanodomains of solid. A mechanism is proposed where clusters of the domains scatter light in the pyrolyzed films. This phenomenon evidently continues to dominate all the way to the final densified polycrystalline state.
Barium titanate, Optical properties, Waveguide modulators, Electroceramics, Thin films, Sol-gels, Deposition, Ceramics