Sol-gel derived titania/ORMOSIL composite thin films for optical waveguide applications

We report the preparation of sol-gel waveguide films based on a newly developed recipe to incorporate organic molecules into the inorganic sol-gel glass matrix. The film was derived from a sol that has a higher titanium content in an organically modified silane (ORMOSIL), namely, y-Glycidoxypropyltrimethoxysilane. We have shown that using spin-coating and low temperature baking, a single coating layer can have a thickness of more than 1.5 μm. When such a single layer film is deposited on a microscope glass slide or a piece of silicon with a buffer-cladding layer, it is able to support the guiding of optical waves. We have characterized the film using scanning electron microscopy, atomic force microscopy, X-ray diffractometry, thermal gravimetric analysis, differential thermal analysis and Fourier transform infrared spectroscopy and have studied the properties of the waveguide film, including the microstructural properties, the chemical bonding properties, and the optical properties. Based on these experimental results, we found that a heat-treatment at a temperature slightly below 200 °C is necessary to attain a dense pore-free film. It has also been noted that a purely inorganic and crack-free silica-titania film can be obtained after baking the titania-ORMOSIL composite film at 500 °C or higher.