Highly crystalline metal oxide thin films on plastic substrates prepared via firing and transfer: key role of the “lost” organic underlayer

Abstract

Our sol–gel transfer technique realizes highly crystalline metal oxide thin films on plastic substrates. In that technique a precursor gel film is fired at temperatures as high as 700 °C on an organic underlayer that is deposited beforehand on a single crystal silicon substrate. The resultant crystalline oxide film is transferred to a plastic substrate by heating the film on a hot plate and pressing a plastic substrate on it. The organic underlayer, which is completely lost during firing, critically facilitates the oxide film delamination from the silicon substrate. In order to answer the question how such a “lost” organic underlayer could be the key for the transfer, the effect of the underlayer thickness on the oxide film transferrability was investigated. Titania and zinc oxide precursor films were prepared by spin-coating on polyimide-polyvinylpyrrolidone and polyimide layers on Si(100) substrates, respectively, followed by firing and transfer to polycarbonate (PC) substrates. Quantitative evaluation based on image analysis demonstrated that thicker “lost” underlayers result in larger area fractions of the successfully transferred oxide films. Depth profile analyses by X-ray photoelectron spectroscopy excluded the residual carbon at the film/Si(100) interface as the delamination facilitator. On the other hand, atomic force microscopic observations demonstrated that thicker “lost” underlayers create larger surface roughness on both sides of the oxide films. It was concluded that such an increase in roughness decreased the contact area and brought the anchoring effect, reducing and increasing the film/Si(100) and film/PC adhesions, respectively, which facilitates the film transfer.