Oxidation kinetics of Ni metallic films: Formation of NiO-based resistive switching structures

Resistive switching controlled by external voltage has been reported in many Metal/Resistive oxide/Metal (MRM) structures in which the resistive oxide was simple transition metal oxide thin films such as NiO or TiO2 deposited by reactive sputtering. In this paper, we have explored the possibility to form NiO-based MRM structures from the partial oxidation of a blanket Ni metallic film using a Rapid Thermal Annealing route, the remaining Ni layer being used as bottom electrode. X-ray diffraction was used to apprehend the Ni oxidation kinetics while transmission electron microscopy enabled investigating local microstructure and film interfaces. These analyses have especially emphasized the predominant role of the as-deposited Ni metallic film microstructure (size and orientation of crystallites) on (i) oxidation kinetics, (ii) NiO film microstructural characteristics (crystallite size, texture and interface roughness) and (iii) subsequent electrical behavior. On this latter point, the as-grown NiO films were initially in the low resistance ON state without the electro-forming step usually required for sputtered films. Above the threshold voltage varying from 2 to 5 V depending on oxidation conditions, the Pt/NiO/Ni MRM structures irreversibly switched into the high resistance OFF state. This irreversibility is thought to originate in the microstructure of the NiO films that would cause the difficulty to re-form conductive paths.