(a) Dependence of resistance on applied voltage for a test Ge2Sb2Te5 memory cell. The pulse width was kept constant at100 ns. (b) The slope of the plot in (a) as a function of applied voltage. In this plot, troughs indicate regions where the cell resistance changes little with applied voltage, indicating a (meta)stable state.
Evolution of the percentage of atoms involved in fourfold rings during annealing of a 63-atom model of amorphous Ge2Sb2Te5 at 300, 500, and 700 K. Representative snapshots of the 300 K (a), 500 K (b), and 700 K (c) models are shown below. In these models, atoms involved in fourfold rings are coloured red. The snapshot images were created using the VMD software.20
Schematic probability distribution functions for crystal nucleation (solid line) and growth (dashed line) as a function of temperature. In our proposed model, intermediate states would be formed in a range of temperatures in which nucleation was fast, but growth relatively is slow, as marked by the shaded region in the figure.
Thermal stability of the three states. (a) Evolution of the percentage of atoms involved in fourfold rings during extended annealing at 300, 500, and 700 K. (b) Structure of the intermediate state model after approx. 2.5 ns of annealing—cf. Figure 2(a). This image was created using the VMD software.20
Temperature-dependent chemical ordering. (a) Proportion of fourfold rings in 63-atom models of Ge2Sb2Te5 which contain only chemically correct bonds and which contain one or more types of wrong bonds. (b) Proportions of chemically incorrect rings containing each of the four possible types of wrong bonds in GST-225.
Snapshots of 99-atom models of amorphous Ge2Sb2Te5 after annealing at 300 (a), 500 (b), and 700 K (c). As in Figure 2, atoms involved in fourfold rings are coloured red. These images were created using the VMD software.20
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