Stress reduction during phase change in Ge2Sb2Te5 by capping TiN film

It has been one of the most important issues to minimize the stress reduction during phase change in GST (Ge₂Sb₂Te₅) alloy for PRAM (Phase-change Random Access Memory) applications, because the alloy has been reported to face the significant stress during the phase change. We fabricated GST/oxide/substrate as a basic structure, and then added two more structures by capping an adhesion layer (Ti) or a barrier metal (TiN) on GST layer, respectively. We report that TiN-capped structure shows about 40% stress reduction during the phase change compared with that of the basic structure. The stress reduction is considered to be due to the intrinsic compressive stress in TiN film itself.