Physical mechanism and temperature acceleration of relaxation effects in phase-change memory cells

The main reliability issues of phase change memory (PCM) cells are related to the metastable nature of the amorphous phase in the chalcogenide material. The amorphous phase spontaneously evolves during time by crystallization and structural relaxation, that is the short range ordering in the amorphous phase to minimize the defect concentration and free energy. Crystallization physics has been studied by almost 60 years, and application of the standard nucleation theory has been successfully applied to provide extrapolation methodologies for PCM reliability estimation. On the other hand, structural relaxation and its impact on carrier transport in the amorphous chalcogenide are not completely understood yet. The purpose of this paper is to study structural relaxation effects in PCM cells, focusing on a) the physical interpretation of the relaxation and b) the temperature acceleration of the phenomenon, which is essential to provide extrapolation techniques and analytical compact models for prediction of PCM reliability.