Nonpolar resistance switching of metal/binary-transition-metal oxides/metal sandwiches: Homogeneous/inhomogeneous transition of current distribution

Exotic features of a metal/oxide/metal sandwich, which will be the basis for a drastically innovative nonvolatile memory device, is brought to light from a physical point of view. Here the insulator is one of the ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe₂O₃, NiO, and CoO. The sandwich exhibits a resistance that reversibly switches between two states: one is a highly resistive off state and the other is a conductive on state. Several distinct features were universally observed in these binary TMO sandwiches: namely, nonpolar switching, nonvolatile threshold switching, and current-voltage duality. From the systematic sample-size dependence of the resistance in on and off states, we conclude that the resistance switching is due to the formation of ``electric faucet'' at the interface, which shows up as a homogeneous to inhomogeneous transition of the current distribution.