Effect of deposition temperature and niobium doping on resistive switching properties of the polycrystalline NiO_x films

In this work, we investigated the effect of growth temperature and doping of Nb, with a valence different from that of Ni, on the resistance switching behavior of NiO_x films. Reactive dc magnetron sputtering was used to fabricate Pt/ NiO_x /Pt metal-insulator-metal (MIM) stacks on Ti/ SiO₂ /Si substrates with Nb doping at various substrate temperatures. The crystallinity, surface morphology, and chemical bonding states of NiO _x were also characterized in conjunction with the resistance switching. Deposition at 400°C improved the resistance switching endurance, and Nb doping of up to 3.5% at 400°C produced a higher endurance for the SET/RESET processes with a narrower distribution of V_SET as compared to the undoped NiO_x films. X-ray diffraction showed that sputtering at 400°C made the (111) textures pronounced with the reduced full width at half-maximum of the (111) peak as compared to the NiO_x films deposited at room temperature. X-ray photoemission spectroscopy showed that the Nb doping of NiO_x films produced a higher density in the metallic Ni⁰ than in the undoped NiO_x films deposited at the same temperature. This work shows that resistive switching behavior of NiO _x can be enhanced by doping it with Nb of different oxidation valences.