Influence of solvent concentration on the microstructure of SiO2-TiO2 sol-gel films

Spin-coating is one of the possible methods for the fabrication of optical planar waveguides. These have several applications in integrated optical devices, provided that their optical losses are below similar to 1 dB/cm. The attenuation is caused in part by surface and bulk scattering. The latter depends on the microstructure of the films and, more particularly, the porosity, which is studied here. A series of SiO2-TiO2 films were prepared from solutions containing different concentrations of ethanol. The influence of the ethanol/(Si + Ti)alkoxides volume ratio on the porosity was investigated by Ellipsometry, Infrared Spectroscopy, and Scanning Electron Microscopy. The porosity volume fraction was found to reach a minimum when the ethanol volume ratio is near 4.