Impact of Surface Roughness and Material Properties of Inert Electrodes on the Threshold Voltages and Their Distributions of ReRAM Memory Cells

Abstract

The paper explores the impact of the surface roughness (SR) and other material properties of metal electrodes on the statistical distributions of the switching threshold voltages, Vform, Vset, and Vreset, of a resistive memory (ReRAM) cell. The surface roughness of Pt, Ru, Co, and Cu in Cu/TaOx/Pt, Cu/TaOx/Ru, and Cu/TaOx/Co devices is extensively characterized and related to the switching characteristics of the devices. We find that SF has both impacts on the mean and on the standard deviation of the Vform, Vset, and partly also on the Vreset distributions. The surface roughness of free metal surfaces of Pt, Ru, and Co when annealed at 600 °C and 900 °C is found to increase significantly, but this increase is substantially suppressed when passivated by the thin switching layer of the solid electrolyte, such as TaOx or SiO2. The increase of SR of those metals with increasing temperature correlates well with their melting temperature. Overall, we find that the differences in surface roughness along with material properties such as the thermal conductivity and work function explain well the differences between the distributions of the threshold voltages of the ReRAM devices with Pt, Ru, and Co serving as the inert electrode.