Thermal stress effects of Ge₂Sb₂Te₅ phase change material: Irreversible modification with Ti adhesion layers and segregation of Te

Abstract

This paper reviews material properties of chalcogenide phase change material Ge2Sb2Te5 under thermal anneal treatments. Stress evolutions of pure Ge2Sb2Te5 films and stacks of Ge2Sb2Te5 integrating with Ti adhesion layers are investigated. Segregation of Te atoms in the Ge2Sb2Te5 film to the interface drives an interaction between Ti and Te atoms and formation of Ti-Te binary phases. The irreversible phase segregation and modification of Ge2Sb2Te5 change the crystallization process, completely suppress the final transformation into otherwise stable hcp phase, and thus impact the ultimate life-cycle of such a phase change based memory cell. Since the adhesion layer is required in cell applications, the optimization of adhesion layer material and thickness may improve the life-cycles and reliability of devices. © 2008 Elsevier B.V. All rights reserved.