Atomistic Simulations of the Decomposition Pathways of Ge-Rich GeSbTe Alloys for Phase Change Embedded Memories

The prototypical Ge₂Sb₂Te₅ phase change compound displays a crystallization temperature too<br/>low for embedded phase change memories of interest for applications in the automotive sector.<br/>Ge-rich GeSbTe (GST) alloys are emerging as promising materials for embedded memories<br/>thanks to the higher thermal stability of their amorphous phase. Upon crystallization Ge-rich<br/>GST alloys undergo a phase separation into Ge and a less Ge-rich GST alloy. This phase<br/>separation enhances the crystallization temperature, but it also gives rise to some drawbacks<br/>such as a high cell-to-cell variability and a drift of the electrical resistance with time in the set<br/>state. The details of the decomposition process are, however, largely unknown. In this work, we<br/>report on high-throughput calculations based on Density Functional Theory on the<br/>decomposition pathways of Ge-rich GST alloys. We first calculated the formation free energy of<br/>GST alloys in the central region of Ge-Sb-Te ternary phase diagram and their distance from the<br/>convex hull. These data allowed us to estimate the decomposition propensity of Ge-rich GST<br/>alloys which suggested a possible strategy to minimize phase separation by still keeping a high<br/>crystallization temperature.