Designing Multiple Crystallization in Superlattice-like Phase-Change Materials for Multilevel Phase-Change Memory

A multilevel phase-change memory device was successfully designed, which was fabricated using a Ge₄₀Te₆₀/Cr superlattice-like (SLL) structure. In the SLL films, a two-step phase change process is observed at elevated temperatures, which reveals the crystallization of Ge₄₀Te₆₀ (GT) and an interface-dominated formation of Cr₂Ge₂Te₆ (CrGT). The bonding of Cr-Te and Ge-Ge is accompanied by the breaking of a Ge-Te bond, which is mainly in the Ge-rich GeTe_4-Ge units. The formation of CrGT is related to the breaking apart of the edge-sharing octahedron in GT and Cr replacement at Ge sites. The crystalline GT acts as the crystallization precursors in the formation of the CrGT phase. The stable reversible two-step phase change can guarantee the reliability of the multilevel storage. The present work may shed light on the possible mechanism of the CrGT phase transition-based interfacial dynamic process. The designed multiple crystallization system demonstrates a potential for multilevel storage.