  Germanium antimony telluride has been the most used and studied phase-change
material for electronic memory due to its suitable crystallization temperature,
amorphous to crystalline resistance contrast, and stability of the amorphous
phase. In this work, the segregation of Ge in a Ge2Sb2Te5 film of 30 nm
thickness during heating inside the transmission electron microscope was
observed and characterized. The Ge2Sb2Te5 film was deposited using sputtering
on a Protochips Fusion holder and left uncapped in atmosphere for about four
months. Oxygen incorporated within the film played a significant role in the
chemical segregation observed which resulted in amorphous Ge-O grain boundaries
and Sb and Te rich crystalline domains. Such composition changes can occur when
the phase-change material interfaces insulating oxide layers in an integrated
device and would significantly impact its electrical and thermal properties.
