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Nat Mater. 2008 May;7(5):399-405. doi: 10.1038/nmat2157. Epub 2008 Mar 23.

Microscopic origin of the fast crystallization ability of Ge-Sb-Te phase-change memory materials.

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1
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.

Abstract

Ge-Sb-Te materials are used in optical DVDs and non-volatile electronic memories (phase-change random-access memory). In both, data storage is effected by fast, reversible phase changes between crystalline and amorphous states. Despite much experimental and theoretical effort to understand the phase-change mechanism, the detailed atomistic changes involved are still unknown. Here, we describe for the first time how the entire write/erase cycle for the Ge(2)Sb(2)Te(5) composition can be reproduced using ab initio molecular-dynamics simulations. Deep insight is gained into the phase-change process; very high densities of connected square rings, characteristic of the metastable rocksalt structure, form during melt cooling and are also quenched into the amorphous phase. Their presence strongly facilitates the homogeneous crystal nucleation of Ge(2)Sb(2)Te(5). As this simulation procedure is general, the microscopic insight provided on crystal nucleation should open up new ways to develop superior phase-change memory materials, for example, faster nucleation, different compositions, doping levels and so on.

PMID:
18362909
DOI:
10.1038/nmat2157
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