Phase change memories rest on the ability of some chalcogenide alloys to undergo a fast and reversible transition between the crystalline and amorphous phases upon Joule heating. The fast crystallization is due to a high nucleation rate and a large crystal growth velocity which are actually possible thanks to the fragility of the supercooled liquid that allows for the persistence of a high atomic mobility at high supercooling where the thermodynamical driving force for crystallization is also high. Since crystallization in the devices occurs by rapidly heating the amorphous phase, hysteretic effects might arise with a different diffusion coefficient and viscosity on heating than on cooling. In this work, we have quantified these hysteretic effects in the phase change compound GeTe by means of molecular dynamics simulations. The atomic mobility in the overheated amorphous phase is lower than in supercooled liquid at the same temperature and the viscosity is consequently higher. Still, the simulations of the overheated amorphous phase reveal a breakdown of the Stokes-Einstein relation between the diffusion coefficient and the viscosity, similarly to what we found previously in the supercooled liquid. Evidences are provided that the breakdown is due to the emergence of dynamical heterogeneities at high supercooling.

Sosso, G., Behler, J., Bernasconi, M. (2016). Atomic mobility in the overheated amorphous GeTe compound for phase change memories. PHYSICA STATUS SOLIDI. A, APPLICATIONS AND MATERIALS SCIENCE, 213(2), 329-334 [10.1002/pssa.201532378].

Atomic mobility in the overheated amorphous GeTe compound for phase change memories

SOSSO, GABRIELE CESARE
Primo
;
BERNASCONI, MARCO
2016

Abstract

Phase change memories rest on the ability of some chalcogenide alloys to undergo a fast and reversible transition between the crystalline and amorphous phases upon Joule heating. The fast crystallization is due to a high nucleation rate and a large crystal growth velocity which are actually possible thanks to the fragility of the supercooled liquid that allows for the persistence of a high atomic mobility at high supercooling where the thermodynamical driving force for crystallization is also high. Since crystallization in the devices occurs by rapidly heating the amorphous phase, hysteretic effects might arise with a different diffusion coefficient and viscosity on heating than on cooling. In this work, we have quantified these hysteretic effects in the phase change compound GeTe by means of molecular dynamics simulations. The atomic mobility in the overheated amorphous phase is lower than in supercooled liquid at the same temperature and the viscosity is consequently higher. Still, the simulations of the overheated amorphous phase reveal a breakdown of the Stokes-Einstein relation between the diffusion coefficient and the viscosity, similarly to what we found previously in the supercooled liquid. Evidences are provided that the breakdown is due to the emergence of dynamical heterogeneities at high supercooling.
Articolo in rivista - Articolo scientifico
GeTe; Glasses; molecular dynamics simulations; phase change memories; supercooled liquids;
Glasses; molecular dynamics simulations; phase change memories; supercooled liquids; Electrical and Electronic Engineering;
English
2016
213
2
329
334
none
Sosso, G., Behler, J., Bernasconi, M. (2016). Atomic mobility in the overheated amorphous GeTe compound for phase change memories. PHYSICA STATUS SOLIDI. A, APPLICATIONS AND MATERIALS SCIENCE, 213(2), 329-334 [10.1002/pssa.201532378].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/110992
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