Controllable crystallization of Ge2Sb2Te5 phase-change memory thin films driven by multiple femtosecond laser pulses

•Controllable crystallization of Ge2Sb2Te5 films by multiple fs laser pulses.•Real-time reflectivity measurement and two-temperature model calculation were used.•Different crystallization processes and mechanisms at low, medium, and high fluences. In this study, controllable crystallization processes of as-deposited amorphous Ge2Sb2Te5 phase-change memory thin films driven by multiple femtosecond laser pulses were investigated in detail. The threshold effects of pulse fluence and the number of pulses were analyzed comprehensively using real-time reflectivity measurements and two-temperature model calculations. The different optical transients indicated three kinds of crystallization processes at low, medium, and high fluences. These results may provide further insights into the ultrafast phase-transition mechanics and are useful in the design of programmable multi-level logic devices based on phase change memory materials.