Phase separation behavior of $Ge2Sb2Te5$ line structure during electrical stress biasing

We report the breakdown behavior of a patterned $Ge2Sb2Te5$ multiline structure during the voltage-driven electric stress biasing. Scanning Auger microscope analysis shows that the breakdown process accompanies with a phase separation of $Ge2Sb2Te5$ into an Sb, Te-rich phase and a Ge-rich phase. The phase separation is explained by the incongruent melting of $Ge2Sb2Te5$ based on the pseudobinary phase diagram between $Sb2Te3$ and GeTe. It is claimed that this phase separation behavior by incongruent melting provides one of the plausible mechanisms of the device failure in a phase change memory.