Epitaxial CeO2 thin films for a mechanism study of resistive random access memory (ReRAM)

A thin epitaxial CeO2 film was grown on a Cu(111) single crystal in order to investigate the mechanism of resistive memory/switching devices with an ultimately thin high-k dielectric film. A small amount of Pt was deposited on the CeO2 film and the Pt/CeO2/Cu structure was characterized by conductive atomic force microscopy and X-ray photoelectron spectroscopy. It was found that the grown epitaxial CeO2 film was fully oxidized, i.e., the valence of Ce atoms in the film was completely Ce4+. However, after the deposition of a small amount of Pt, it was revealed that Ce atoms were partially reduced to Ce3+ in full thickness of the film. The Pt/CeO2/Cu structure did not show switching behavior in resistance. The observed reduction of CeO2 film is considered to be responsible to the non-switching behavior. The thermodynamics of the reduction of the CeO2 film and the kinetics of oxygen diffusion in the reduced CeO2 film are discussed.