Fabrication of TiO ₂ /SiO ₂ multilayer film structure by the sol-gel process with efficient thermal treatment methods

Multilayer structure of thin films by the sol-gel process attracts great attention for versatile applications. However, the multilayer structure often shows undesirable morphologies such as cracks or delaminations resulted from non-wettability of the coating solution with the pre-deposited hydrophobic layer, especially in the case of SiO ₂ layers. The hydrophobic surface is originated from residual alkoxy groups in the layer after sintering step. For the sintering process, introducing the heating-up period from the room temperature to the target temperature is very effective in removing residual alkoxy groups from the SiO ₂ film by hydrolysis with remaining water molecules. The well-defined TiO ₂ /SiO ₂ multilayer structure is successfully fabricated at a sintering temperature of 300 °C by forming a hydrophilic SiO ₂ layer with the heating-up period.