Bipolar Resistive Switching in Oxides for Memory Applications

Abstract

Resistance change Random Access Memory (RRAM) devices in which at least two resistance states are used are a top candidate for future nonvolatile data storage. Simple Metal-Insulator-Metal (MIM) structures form the memory element which can be easily incorporated in large arrays. In particular, in the so-called Valence Change Memories (VCM) the drift of anions, typically oxygen, is considered as the key step to explain the bistable resistive switching behavior. A first-order classification of the observed material changes is related to the geometrical location. In “filamentary” type switching the formation and rupture of a thin filament is responsible for the resistance change. In the “distributed” systems the switching can be traced back to modifications at interfaces. Oxygen ion migration into thin tunnel oxides in high electric fields and Schottky barrier engineering with metals and complex perovskites are two mechanisms under discussion for the distributed systems. In the filamentary type of switching fast oxygen ion transport along extended defects is demonstrated to be the key step for the formation of the conducting filaments. The bistable resistance characteristics with switching induced by voltage pulses is a promising approach for future nonvolatile memory technologies. Excellent scaling behavior to sizes below 20 nm has been demonstrated.