Temperature dependence and size effect of thermal conductivity of Ge2Sb2Te5 thin film

This study investigates the dependence of thermal conductivity on both ambient temperature and film thickness in Ge2Sb2Te5 (GST) thin films, the most widely used phase-change material, with thicknesses under 40 nm. The measurements are performed using the thermoreflectance method, and the thermal boundary resistances between the GST and metals are concurrently determined. The thermal conductivity of hexagonal GST (h-GST) is analyzed using a model that integrates phenomenological equations and first-principles calculations. This model quantifies the contributions of both the electron and phonon components to the thermal conductivity of h-GST and clarifies the influence of grain boundary effects. The film thickness dependence of the thermal conductivity of h-GST at room temperature (∼300 K), as a size effect, is found to be highly sensitive to sample preparation. This dependence is determined by the electrical resistivity of h-GST, which varies with annealing temperature and grain size. From the analysis, the typical grain size is estimated to be less than 10 nm. In addition, the slope of the ambient temperature dependence of the thermal conductivity is correlated with the electrical resistivity. Electrical resistivity serves as an indicator of the relative contributions of the electron and phonon components to thermal conductivity. These findings highlight the critical roles of film deposition conditions and film thickness in influencing both thermal conductivity and electrical resistivity to provide valuable insights that increase the accuracy of thermal design in phase-change memory applications.