A comprehensive understanding of conductive mechanism of RRAM: from electron conduction to ionic dynamics

Resistive random access memories (RRAMs) have been highlighted for being the potential candidate of the next generation nonvolatile memory devices in last decades, since Moore's law is going to the end and the size of the traditional transistor almost reaches the physical limitation. Lots of previous studies on the conductive mechanism of RRAMs are intended to optimal the functionality of RRAMs. However, the classification of these mechanisms is very complex, which is not conducive to targeted function optimization. In this review, the electrons transition mode is described in detail, the classification of electrochemical metallization (ECM) is redefined, and the conductive mechanism of valence change memory (VCM) systems, which is often overlooked, is also discussed. At last, a prospective of RRAM relate to synapses then making wildly application is stated. In general, the review aims to understand conductive mechanisms of RRAMs systematically and provide a guidance for optimal the switching properties.