Exploring No Man's Land-Arrhenius Crystallization of Thin-Film Phase Change Material at 1 000 000 K s-1 via Nanocalorimetry

Non-volatile phase-change memory (PCM) devices are based on phase-change materials such as Ge2Sb2Te5 (GST). PCM requires critically high crystallization growth velocity (CGV) for nanosecond switching speeds, which makes its material-level kinetics investigation inaccessible for most characterization methods and remains ambiguous. In this work, nanocalorimetry enters this no-man's land with scanning rate up to 1 000 000 K s(-1) (fastest heating rate among all reported calorimetric studies on GST) and smaller sample-size (10-40 nm thick) typical of PCM devices. Viscosity of supercooled liquid GST (inferred from the crystallization kinetic) exhibits Arrhenius behavior up to 290 degrees C, indicating its low fragility nature and thus a fragile-to-strong crossover at approximate to 410 degrees C. Thin-film GST crystallization is found to be a single-step Arrhenius process dominated by growth of interfacial nuclei with activation energy of 2.36 +/- 0.14 eV. Calculated CGV is consistent with that of actual PCM cells. This addresses a 10-year-debate originated from the unexpected non-Arrhenius kinetics measured by commercialized chip-based calorimetry, which reports CGV 10(3)-10(5) higher than those measured using PCM cells. Negligible thermal lag (<1.5 K) and no delamination is observed in this work. Melting, solidification, and specific heat of GST are also measured and agree with conventional calorimetry of bulk samples.

Automated summary

This research utilizes nanocalorimetry to investigate phase-change material Ge2Sb2Te5 and discovers its low fragility nature and fragile-to-strong temperature crossover. The crystallization process of thin-film Ge2Sb2Te5 is also studied. The findings resolve the debate regarding crystallization growth velocity in phase-change memory and provide measurements for the melting, solidification, and specific heat of Ge2Sb2Te5.