Multi-level resistive switching characteristics of a Cu₂O/Al₂O₃ bilayer device are presented. An oxidation state gradient in copper oxide induced by the fabrication process was found to play a dominant role in defining the multiple resistance states. The highly conductive grain boundaries of the copper oxide-an unusual property for an oxide semiconductor-are discussed for the first time regarding their role in the resistive switching mechanism.
Keywords: aluminum oxide; copper oxide; grain boundaries; multi-level cell; resistive switching memories.