Search for: All records

Owing to their ability for fast switching and the large property contrast between the crystalline and amorphous states that permits multi-level data storage, in-memory computing and neuromorphic computing, the investigation of phase change materials (PCMs) remains a highly active field of research. Yet, the continuous increase in electrical resistance (called drift) observed in the amorphous phase has so far hindered the commercial implementation of multi-level data storage. It was recently shown that the resistance drift is caused by aging-induced structural relaxation of the glassy phase, which is accompanied by a simultaneous decrease in enthalpy and fictive temperature. This implies that resistance is related to enthalpy relaxation. While the resistance is known to drift even at room temperature and below, evidence for enthalpy relaxation at room temperature in amorphous PCMs is still missing. Here, we monitor changes in enthalpy induced by long-term room-temperature aging in a series of PCMs. Our results demonstrate the simultaneity of resistance drift and enthalpy relaxation at room temperature, and thus provide further insights into the mechanism of resistance drift and its possible remediation. 

While fast-switching rewritable nonvolatile memory units based on phase-change materials (PCMs) are already in production at major technology companies such as Intel (16–64 GB chips are currently available), an in-depth understanding of the physical factors that determine their success is still lacking. Recently, we have argued for a liquid-phase metal-to-semiconductor transition (M-SC), located not far below the melting point, T m , as essential. The M-SC is itself a consequence of atomic rearrangements that are involved in a fragile-to-strong viscosity transition that controls both the speed of crystallization and the stabilization of the semiconducting state. Here, we review past work and introduce a new parameter, the “metallicity” (inverse of the average Pauling electronegativity of a multicomponent alloy). When T m -scaled temperatures of known M-SCs of Group IV, V, and VI alloys are plotted against their metallicities, the curvilinear plot leads directly to the composition zone of all known PCMs and the temperature interval below T m , where the transition should occur. The metallicity concept could provide guidance for tailoring PCMs.