Aging in Phase Change Materials: Getting Insight from Simulation

Aging is one of the effects limiting the advent of phase change materials as acting components in non-volatile memories. This paper presents a review of recent simulation works allowing to describe the underlying microscopic mechanisms that are responsible for the aging of the semiconductor glass and the accompanying resistance drift. In comparison with other systems, the fragile character of phase change materials imposes the use of different methods to sample the space of configurations and the chemical ordering. The emerging picture is that both the evolution of coordination defects and of the underlying network are responsible for the evolution of the electronic properties. The advantage of simulations is that they allow to determine the relation between chemical ordering, the local geometry of atoms, and the nature of electronic states. From these correlations, one can extrapolate to obtain the structure of the “ideal” amorphous state and the relation between bonding in this phase and that of the more conductive crystalline phase. This understanding of microscopic phenomena is crucial to interpret experimental results, but also paves the way to the design of optimized glasses, that are less prone to aging, while preserving the unique properties that place phase change materials among the best candidates for high performance and scalable non-volatile memories.