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Doping is an effective way to improve the performance of conventional phase-change materials. We introduced an alkaline element calcium (Ca) in GeTe films and studied their crystallization kinetics by using flash DSC. It was found that a small amount of Ca doping (4.0 at. %) can significantly enhance the thermal stability, but the maximum crystal growth rate does not decrease significantly. Moreover, no any Ca-related crystalline phase and Ca-related chemical bond can be found in Ca-doped GeTe, implying that Ca atoms are in free state in GeTe matrix.

Elemental antimony (Sb) has been carried out recently as a phase-change material to overcome composition segregation in a heavily cycled memory cell. Explosive crystal growth of Sb is desirable for fast operation speed in memory; however, poor thermal stability, i.e., fast spontaneous crystallization at room temperature, significantly impedes its applications. In this work, we designed a thermal stability enhanced “monatomic” Sb in a specific confined structure of [Sb(3 nm)/SiO2(5 nm)]32 and investigated its crystallization kinetics by using the ultrafast differential scanning calorimetry method. It was found that this nanoscale Sb exhibits appealing amorphous thermal stability with a crystallization activation energy of 2.68 eV and the temperature for 10-year data retention more than 361 K. Moreover, strong non-Arrhenius crystallization behavior with a high fragility index of 90 was unrevealed in Sb supercooled liquids, which has the maximum crystal growth rate of 2.17 m s−1 at 785 K. Thanks to the fast crystal growth rate and attractive thermal stability of this monatomic Sb, it could be one of the most important candidates for high-integrated on-chip memory without any composition segregation.

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