Chemical Design Principles for Cache-Type Sc-Sb-Te Phase-Change Memory Materials

Enhanced crystal nucleation in a Sc-Sb-Te phase-change material has enabled subnanosecond switching in phase-change memory devices, making cache-type nonvolatile memory feasible. However, the microscopic mechanisms remain to be further explored. In this work, we present a systematic ab initio study of the relevant parent compounds, namely, Sc₂Te₃ and Sb₂Te₃. Despite similar bond lengths and angles in the amorphous phases of the two compounds, Sc₂Te₃ displays a much more ordered amorphous network without homopolar bonds. As a result, the local structural order in amorphous Sc₂Te₃ is dominated by square motifs, remarkably similar to those of the metastable rocksalt-like phase. Chemical bonding analysis indicates more robust Sc-Te bonds compared with Sb-Te bonds in the amorphous phase, as well as a substantial role of electrostatic interactions in Sc₂Te₃ but not in Sb₂Te₃. The robustness of Sc-Te bonds explains the enhanced nucleation in Sc-Sb-Te compounds. Finally, we discuss an alloying strategy of Sc₂Te₃ and Sb₂Te₃ for cache-type Sc-Sb-Te-based phase-change memory.