Phase-Change Behavior of Stoichiometric Ge[sub 2]Sb[sub 2]Te[sub 5] in Phase-Change Random Access Memory

We observed the atomic structures for each reset and set state in a phase-change random access memory fabricated using stoichiometric crystalline . The reset state clearly showed a mixture of dome-shaped amorphous and crystal structure surrounding amorphous, but the set state showed abnormally grown large grains due to recrystallization of the amorphous structure. The crystal structure of the recrystallized grain was face-centered cubic. The element analysis indicated that the atomic composition changes to nonstoichiometric phase in the active regions of the reset and the set state, which is Sb-rich and Te-deficient compared to the pristine stoichiometric composition. Analysis showed that thermal interdiffusion of Sb and Te caused nonstoichiometric nature of the material to reach the energetically stable state in the active region.