Irreversible modification of Ge2Sb2Te5 phase change material by nanometer-thin Ti adhesion layers in a device-compatible stack

The authors report on an interaction between chalcogenide phase-change material Ge2Sb2Te5 and a thin Ti adhesion layer considered for integration into a structure of a memory cell. Segregation of Te atoms in the chalcogenide film to the interface drives an interaction between Ti and Te atoms and formation of Ti–Te binary phases. This reaction has distinct signatures in the film-stack stress even for a nanometer-thin Ti layer. The irreversible Te segregation and modification of Ge2Sb2Te5 change the crystallization process, completely suppressing the final transformation into an otherwise stable hcp phase, and thus impacts the ultimate life cycle of such a phase-change based memory cell.