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.