Phase Diagram of GeTe-Sb2Te3 Phase Change Memory Materials
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Phase Diagram of GeTe-Sb2Te3 Phase Change Memory Materials: In-situ High
Pressure-Temperature X-ray Diffraction Study
B. Kalkan1, S. M. Clark1 and S. Sen2
1Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA94720,
USA.
2Dept. of Chemical Eng. & Materials Science UC Davis, One Shields Avenue, Davis, CA
95616, USA.
Crystalline and amorphous Ge-Sb-Te alloys have recently received significant attention
due to their extraordinary technological importance in rewritable optical and electronic
memory applications (e.g. DVD-RW, Blue-Ray disc). These alloys have been aptly
termed phase-change materials as they show rapid thermal or electrical switching
between crystalline and glassy/amorphous phases under suitable conditions. The three
key properties that distinguish the phase-change materials from other chalcogenides are
(1) their ultrafast crystallization kinetics over a timescale of tens of nanoseconds at
elevated temperatures, (2) their strongly contrasting optical and/or electrical properties
between amorphous and crystalline phases and (3) stable, repeatable switching (multimillion
cycles) between the crystalline and amorphous phases.
Unfortunately, in spite of their key importance in the phase change phenomena, the
atomic scale mechanisms and the thermodynamics of these complex structural
transformations between the amorphous and various crystalline polymorphic GST phases
are not well understood. In this study, the results of a synchrotron X-ray diffraction
(XRD) study of the pressure and temperature dependent phase transformations in c-
GST124 phase at pressures up to 44 GPa and temperatures up to 838 K will be presented.
Our main focus is placed on the demonstration of P-T phase diagram where the
Clapeyron slope for melting transition and pressure induced amorphization is negative
and change of the molar volumes and densities of GST phases in the studied pressure and
temperature region.