Threshold switching of a NbOx device prepared by DC reactive sputtering

Threshold switching devices based on insulator-metal transition (IMT) are expected to overcome the reduction of sneak current and studies of their use for self-oscillators attract much attention. In this study, we observed threshold switching caused by IMT in a cross-point Pt/Ti/NbO_x/Pt/Ti/SiO₂ device after annealing at 400 °C, annealing assisted formation of stable stoichiometric NbO. The diffusion of Ti atoms of thetop electrode to the NbO_x layer was observed. It is suggested that Ti oxidation caused scavenging of oxygen from NbO_x, and valence number of Nb ion is reduced to form stoichiometric metallic NbO. With applying negative voltage to the upper Pt/Ti electrode, a NbO₂ layer was formed by diffusion of oxygen ions from the TiO_x layer. Then threshold switching has become easy to occur in the succeeding positive voltage sweeping.