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.