Electric Fields and Interfacial Phase-Change Memory Structures

Phase-change memory (PCM), a nonvolatile electrical memory based upon the local structure of chalcogenide compounds such as (Formula presented.), is playing an ever increasing role in society. In PCM, information is stored via structure, specifically crystalline or amorphous phases. As generation of the amorphous state requires a melt-quench process, the energy required for switching is relatively large. Interfacial PCM (iPCM) is a form of PCM that greatly improves energy efficiency consisting of a short-period (Formula presented.) superlattice. Unlike conventional PCM, iPCM is believed to switch between two crystalline states. The large energy reduction to switch iPCM and the absence of a melt-quenched phase has led to speculation that electrical fields may play a role in the switching process. Herein, ab initio molecular dynamics is employed to explore electric field effects on proposed iPCM structures. Structures are terminated by van der Waals (vdW)-bonded layers to avoid dangling bonds. Unlike previous speculation in the literature, the effect of electrical fields on Ge atoms is minimal with Te–Te vdW gaps experiencing the largest change. The electric-field-induced rearrangements vary; however, for all structures, a dilation in the vdW gap is observed possibly facilitating the proposed switching mechanisms.