Understanding the phase-change mechanism of rewritable optical media

Abstract

Phase-change materials experience unusually large changes in material properties between amorphous and crystalline phases allowing them to be used as a form of memory. In this paper, we directly measure the local structure of the amorphous and crystalline phases using x-ray absorption spectroscopy. We demonstrate that the prototypical phase-change alloy Ge2Sb2Te5, the material of choice in optical and electrical phase-change memory, does not possess the rocksalt structure but likely consists of well-defined rigid building blocks that are randomly oriented in space consistent with cubic symmetry. Amorphization leads to a drastic shortening of covalent bonds and a decrease in the mean-square relative displacement, demonstrating a substantial increase in the degree of short-range ordering, in sharp contrast to the amorphization of typical covalently bonded solids.

Paul Fons

Professor of Electronics and Electrical Engineering, School of Integrated Design and Engineering

My research interests include the use of computational material science and synchrotron radiation techniques to design and develop new materials.