Forming and switching mechanisms of a cation-migration-based oxide resistivememory

Abstract

We report detailed current–voltage and current–time measurements to reveal the forming and switchingbehaviors of Cu/Ta2O5/Pt nonvolatile resistive memory devices. The devices can be initially SET (fromthe OFF state to the ON state) when a low positive bias voltage is applied tothe Cu electrode. This first SET operation corresponds to the first formationof a metal filament by inhomogeneous nucleation and subsequent growth ofCu on the Pt electrode, based on the migration of Cu ions in the stableTa2O5 matrix. After the forming, the device exhibits bipolar switching behavior(SET at positive bias and RESET (from the ON state to the OFF state)at negative bias) with increasing the ON resistance from a few hundredΩ to afew kΩ. From the measurements of the temperature stability of the ON states, we concludedthat the RESET process consists of the Joule-heating-assisted oxidation of Cuatoms at the thinnest part of the metal filament followed by diffusion and driftof the Cu ions under their own concentration gradient and the applied electricfield, disconnecting the metal filament. With ON resistances of the order of a fewkΩ, the SET and RESET operations are repeated by the inhomogeneous nucleation and theJoule-heating-assisted dissolution of a small filament on a remaining filament. Thisswitching model is applicable to the operation of cation-migration-based resistive memoriesusing other oxide materials.