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 (>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.

(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. Adv. Mater. 2021, 33 (9), 2006221.