Colloidal Syntheses of Novel Sb₂S₃ and Bi₂S₃ Cubic Phases for Phase Change Memory Applications

Phase change memory (PCM) is a developing technology that is set to position itself as the bridge between fast, volatile, dynamic random-access memory (DRAM) and slow, non-volatile, NAND flash storage which have become the workhorses of device architecture. To store non-volatile information, PCM typically utilizes the difference in resistance between the amorphous and metastable cubic phases of pseudo-binary GeTe-Sb₂Te₃ which undergoes a fast and reversible phase transformation. This phase change, which can occur in nanoseconds in thin films, allows for access times that can be a full order of magnitude faster than NAND flash. Despite seeming stoichiometrically imbalanced, the metastable cubic phase in Sb₂Te₃ and its alloys do not fall immediately into the more stable layered orthorhombic phase due to stabilization from a high concentration of cation site specific defects (&gt;30%) which decreases the antibonding characteristics around the Fermi level. These defects are also responsible for the unique disorder-induced localization of states which accounts for a majority of the phase’s resistance. A noteworthy computational study by Xu et al. has predicted several other metal chalcogenides that could theoretically share a similar metastable cubic phase.¹ Here, we present a direct, scalable, colloidal synthesis route for two of these previously undiscovered defect rich cubic phases for Sb₂S₃ and Bi₂S₃ nanocrystals. Solution syntheses such as these will prove invaluable for studying these and other metastable phases for use in PCM technology that would be otherwise inaccessible by other synthetic routes.<br/><br/>(1) Xu, Y.; Wang, X.; Zhang, W.; Schäfer, L.; Reindl, J.; vom Bruch, F.; Zhou, Y.; Evang, V.; Wang, J.; Deringer, V. L.; Ma, E.; Wuttig, M.; Mazzarello, R. Materials Screening for Disorder Controlled Chalcogenide Crystals for Phase Change Memory Applications. <i>Adv. Mater.</i> <b>2021</b>, <i>33</i> (9), 2006221.