Thickness dependence of the amorphous-cubic and cubic-hexagonal phase transition temperatures of GeSbTe thin films on silicon nitride

The crystallization temperature of GeSbTe thin films with thicknesses between 11 and 87nm on silicon nitride was studied through resistance versus temperature measurements. The amorphous-cubic phase transition occurs at ~150°C for all films thicknesses, whereas the cubic-hexagonal phase transition temperature increases with film thickness, from ~200°C for the 20nm film to ~250°C for the 87nm film. The cubic-hexagonal transition occurs gradually for the 11nm film. Implications for phase-change memory devices are discussed.