Electrode dependence of resistance switching in polycrystalline NiO films

We investigated resistance switching in top-electrode/$\mathrm{Ni}\mathrm{O}∕\mathrm{Pt}$ structures where the top electrode was Au, Pt, Ti, or Al. For $\mathrm{Pt}∕\mathrm{Ni}\mathrm{O}∕\mathrm{Pt}$ and $\mathrm{Au}∕\mathrm{Ni}\mathrm{O}∕\mathrm{Pt}$ structures with ohmic contacts, the effective electric field inside the film was high enough to induce trapping or detrapping at defect states and thus resistance switching. For a $\mathrm{Ti}∕\mathrm{Ni}\mathrm{O}∕\mathrm{Pt}$ structure with well-defined Schottky contact at $\mathrm{Ti}∕\mathrm{Ni}\mathrm{O}$ interface accompanied by an appreciable voltage drop, the effective electric field inside the NiO film was not enough to induce resistance switching. For an $\mathrm{Al}∕\mathrm{Ni}\mathrm{O}∕\mathrm{Pt}$ structure with a low Schottky barrier at the $\mathrm{Al}∕\mathrm{Ni}\mathrm{O}$ interface, resistance switching could be induced at a higher voltage since the voltage drop at the $\mathrm{Al}∕\mathrm{Ni}\mathrm{O}$ interface was not negligible but small.