Structural and Stoichiometry Change in NiO with a Thin IrO2 Layer

An IrO2 layer has been proposed as the material for minimizing dispersion of several memory switching parameters of resistance-change random access memory devices using NiO. We present Raman scattering and ellipsometry measurements on NiO films with and without an IrO2 layer. Our Raman measurements on the NiO films show that the addition of an IrO2 layer enhances the local crystalline quality, which is completely consistent with previous results. Moreover, we found an IrO2 layer to be associated with the changing stoichiometry in the NiO film. This can also be related to an abrupt change in the optical transition near 2.7 eV with IrO2, which is known to reflect the NiO stoichiometry.