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

Abstract

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 °C, indicating its low fragility nature and thus a fragile-to-strong crossover at ≈410 °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 103−105 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.