Abstract
The chalcogenide Ge2Sb2Te5 (GST) is of interest for use in phase-change memory. Crystallization is the rate-limiting step for memory operation, and can be accelerated by the prior application of a “priming” heating pulse. There is characteristic fading of the priming effect if there is a time interval between the priming pulse and the main heating pulse to achieve crystallization. We apply classical nucleation theory to interpret these effects, based on a fitting of nucleation kinetics (steady-state and transient) over the full temperature range of the supercooled liquid. The input data come from both physical experiments and atomistic simulations. Prior studies of conventional glass-formers such as lithium disilicate preclude any possibility of fading; the present study shows, however, that fading can be expected with the particular thermodynamic parameters relevant for GST and, possibly, other phase-change chalcogenides. We also use the nucleation analysis to highlight the distinction between GST and the other archetypical chalcogenide system (Ag,In)-doped Sb2Te. Classical nucleation theory appears to be applicable to phase-change chalcogenides, and to predict performance consistent with that of actual memory cells. Nucleation modeling may therefore be useful in optimizing materials selection and performance in device applications.
Highlights
IntroductionChalcogenide phase-change (PC) materials, exemplified by Ge2Sb2Te5 (GST) and (Ag,In)-doped Sb2Te (AIST), have been widely studied for their use in optical (DVD, Blu-rayTM) and electrical (phase-change random-access memory, PC-RAM) data recording [1]
Chalcogenide phase-change (PC) materials, exemplified by Ge2Sb2Te5 (GST) and (Ag,In)-doped Sb2Te (AIST), have been widely studied for their use in optical (DVD, Blu-rayTM) and electrical data recording [1]
Annealing effects saturate when the steady-state cluster size distribution is established [25]; These microscopical observations are complemented (i) by kinetic studies [24,30] and (ii) by atomistic simulations of ordering and the onset of crystallization in liquid chalcogenides [19,31e35]. These studies provide support for interpretations of phase-change kinetics based on classical models of crystal nucleation and growth
Summary
Chalcogenide phase-change (PC) materials, exemplified by Ge2Sb2Te5 (GST) and (Ag,In)-doped Sb2Te (AIST), have been widely studied for their use in optical (DVD, Blu-rayTM) and electrical (phase-change random-access memory, PC-RAM) data recording [1]. Comparing cluster size distributions in GST and AIST in various states, it is found that: subcritical size distributions can be detected and can be altered by annealing, laser treatment or melt-quenching [26]; pre-existing larger (smaller) cluster populations are associated with shorter (longer) nucleation incubation times [25e27]; annealing effects (larger population, shorter incubation) saturate when the steady-state cluster size distribution is established [25]; These microscopical observations are complemented (i) by kinetic (rate-equation) studies [24,30] and (ii) by atomistic simulations of ordering and the onset of crystallization in liquid chalcogenides [19,31e35] Together, these studies provide support for interpretations of phase-change kinetics based on classical models of crystal nucleation and growth. We analyze GST in detail, and contrast with the nucleation behavior in AIST
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