Thermal-gradient-driven elemental segregation in Ge2Sb2Te5 phase change memory cells

Abstract

Thermal gradients have been predicted to play a large role in compositional segregation leading to failure in phase change memories. We have developed a methodology for isolating thermal-gradient driven segregation effects without interference from the electric field. In Ge2Sb2Te5 functional layers, Sb and Te move along the temperature gradient, while Ge segregates in the opposite direction. The direction of segregation is consistent for devices that were repeatedly melted, as well as for devices that were never melted and remained in the polycrystalline state. The results have implications for the reliability of phase change memories.