Crystallization Kinetics of GeSbTe Phase-Change Nanoparticles Resolved by Ultrafast Calorimetry

Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime. Therefore, we present here an innovative exploration of the crystallization kinetics of Ge₂Sb₂Te₅ (GST) nanoparticles (NPs) exploiting differential scanning calorimetry with ultrafast heating up to 40 000 K s^-1. Our results demonstrate that the non-Arrhenius thermal dependence of viscosity at high temperature becomes an Arrhenius-like behavior when the glass transition is approached, indicating a fragile-to-strong (FS) crossover in the as-deposited amorphous GST NPs. The overall crystal growth rate of the GST NPs is unraveled as well. This unique feature of the FS crossover is favorable for memory applications as it is correlated to improved data retention. Furthermore, we show that methane incorporation during NP production enhances the stability of the amorphous NP phase (and thereby data retention), while a comparable maximum crystal growth rate is still observed. These results offer deep insight into the crystallization kinetics of nanostructured GST, paving the way for designing nonvolatile memories with PCM dimensions smaller than 20 nm.