Fabrication of highly crystalline oxide thin films on plastics: Sol–gel transfer technique involving high temperature process

• Sol–gel transfer technique for fabricating oxide films on plastics was modified.
• The technique involves gel film firing on polymeric layers on silicon substrates.
• Films fired at temperatures as high as 1000 °C were transferred to plastic substrates.
• The crystallinity was improved thanks to the high temperature firing process.
• Rutile thin films could be realized on polycarbonate substrates.

Si(100) substrates were coated with a polyimide (PI)–polyvinylpyrrolidone (PVP) mixture film, and an alkoxide-derived TiO2 gel film was deposited on it by spin-coating. The gel films were fired under various conditions with final annealing at 600–1000 °C. The PI–PVP layer was completely decomposed at such high temperatures while the TiO2 films survived on Si(100) substrates without any damages. When the final annealing temperature was raised, the crystalline phase changed from anatase to rutile, and the crystallite size and the refractive index of the films tended to increase. The TiO2 films thus fired on Si(100) substrates were transferred to polycarbonate (PC) substrates by melting the surface of the plastic substrate either in a near-infrared image furnace or on a hot plate under a load. Cycles of deposition and firing were found to be effective in achieving successful transfer even for the films finally annealed at 1000 °C. X-ray photoelectron spectroscopic analyses on the film/Si(100) interface suggested that the residual carbon or carbides at the interface could be a possible factor, but not a necessary and decisive factor that allows the film transfer.