Fig. 1: Prototypical phase-change materials and their characteristics, application-driven interest of PCMs since 1960.

a Application-driven interest of PCMs since 1960: from terrestrial to spaceborne applications. b Switching the crystalline phase into the amorphous phase involves heating above T_melt (melting point) and then rapidly quenching the PCM. Switching the amorphous phase into a crystalline phase involves heating above T_crys (crystallization temperature) for sufficient time to crystallize the PCM. PCM devices are programmable via the “SET” state (akin to writing a logic “1”) and “RESET” state (writing a logic “0”). c Ge–Sb–Te ternary phase diagram showing popular GeSbTe (GST)-based PCMs include Ge₂Sb₂Te₅, Ge₁Sb₄Te₇, and Ge₁Sb₂Te₄. d Crystallization temperature as a function of composition in the Ge–Sb–Te ternary phase diagram. The optimal compositional region for high-performance embedded phase change memories is highlighted in green. Adapted from Liang Sun et al. paper¹⁴.