Bipolar resistance switching in Pt/CuO_x/Pt via local electrochemical reduction

The local changes in copper oxidation state and the corresponding resistance changes in Pt/CuO_x/Pt nanoscale heterostructures have been investigated using x-ray nanoprobe spectro-microscopy and current-voltage characterization. After gentle electroforming, during which the current-voltage behavior remains non-linear, the low resistance state was reached, and we observed regions of 160 nm width that show an increase in Cu K-alpha fluorescence intensity, indicative of partial reduction of the CuO_x. Analysis of the current voltage curves showed that the dominant conduction mechanism is Schottky emission and that the resistance state is correlated with the Schottky barrier height. We propose that the reversible resistivity change in these Pt/CuO_x/Pt heterostructures occurs through local electrochemical reduction leading to change of the Schottky barrier height at the interface between Pt and the reduced CuO_x layers and to change of the CuO_x resistivity within laterally confined portions of the CuO_x layer. These experiments reveal important insights into the mechanism of resistance switching of Pt/CuO_x/Pt performed in a current and voltage regime that does not create a metallic conduction path.