Thermodynamic Origin of Nonvolatility in Resistive Memory

Resistive memory or memristor is a highly potential memory and computing unit for next-generation information storage, in-memory computing, and neuromorphic computing. Valence change memory (VCM) is a promising memristor that stores information through the distribution of oxygen vacancy point defects in transition metal oxides.<br/><br/>The ability to store and retain information is a critical function of nonvolatile memory. It is widely believed non-volatility in resistive memory is a result of the slow diffusion kinetics of oxygen vacancies. In this work, we combine materials characterization, device measurements, ab initio, and continuum modeling and show instead that information retention results from phase separation that results from materials thermodynamics. We definitively show for the first time that the amorphous refractory metal oxides undergo spinodal decomposition into two phases with different metal to oxygen ratios. Moreover, the stability of this spinodal decomposition controls whether a resistive memory cell will be able to retain information over time.<br/><br/>By applying phase separation, a foundational principle of materials science, to the field of resistive memory, we explain for the first time why these materials are able to function as nonvolatile memory. We further highlight the critical importance of considering nonideal thermodynamic interactions such as phase separation for future electronic materials dominated by point defects.