Raman scattering studies of resistance-changing NiO films with and without IrO$_{2}$ buffer layers*

NiO films are known to exhibit resistive memory switching behavior and inserting thin IrO$_{2}$ layers between electrodes and the NiO film is claimed to minimize the dispersion of memory switching parameters, thus greatly improving the device properties. We present Raman scattering results of a NiO film, a NiO film with a 20 nm-thick IrO$_{2}$ layer, and a NiO film with a 50 nm-thick IrO$_{2}$ layer. We discuss the microscopic structural changes in the three different films and their relations to the switching behavior changes. We also discuss the role of IrO$_{2}$ buffer layers in the device structures.