Direct evidence of phase separation in Ge₂ Sb₂ Te₅ in phase change memory devices

Phase change materials in phase change random access memory (PRAM) undergo very high electrical stress as well as thermal stress during operation. These can cause intrinsic problems in stability of the PRAM devices. We investigate the stability of Ge₂ Sb₂ Te₅, the most common phase change material for PRAM, under electrical stress. After multiple programming cycles, cross-sectional transmission electron microscopy and energy dispersive analysis show that electromigration as well as incongruent melting causes phase separation by mass movement by which the peak position of Sb and Ge lies shifted toward the cathode and that of Te toward the anode.