Exciting materials that could phase out flash memories
Despite the fact that NAND technology has penetrated virtually the entire non-volatile memory market for data storage, it is not likely to scale below 20 nm. It is also inherently limited in speed and endurance (set/reset cycles). All the nanodevices poised for commercialisation will require something new. PCMs have lower latencies and higher endurance. They rely primarily on chalcogenide glass that is rapidly heated, shifting between its crystalline and amorphous state. The crystalline state (like binary 1) has very little resistance to current flow, whereas the amorphous state (binary 0) is highly resistive. Scientists launched the EU-funded project SYNAPSE (Synthesis and functionality of chalcogenide nanostructures for phase change memories) to explore the potential of novel nano-structured chalcogenide PCMs to reduce volume, power consumption and costs. The team focused on the use of metal organic chemical vapour deposition (MOCVD) for control over material composition, purity, fast deposition rates and industrial scalability. MOCVD on different substrates was done using two different bottom-up methods: selective area growth and vapour-liquid-solid. The target was phase-change nanowires, either of single materials (core) or two materials (core-shell structure). Materials of interest were indium-based and germanium-based chalcogenides. Extensive modelling and simulation work provided critical insight into the materials' structures and behaviours. Finite element model simulations enabled scientists to thoroughly study the impact of thermal transport and nanowire shape on memory cells. Processing and growth techniques for the nanowires were experimentally investigated, with a focus on germanium-antimony-telluride (one of the most commonly used chalcogenide for PCMs), as well as on the In-Ge-Te and In-Ge-Te deposition, featured by a higher thermal stability. As solid-state memory approaches theoretical limits, designing storage systems that can leverage PCMs is a way to overcome flash limitations. Improvements in manufacturing techniques, improved precursors useful for forming memory device structures, power consumption control and effective solutions for higher data retention are key factors for the competitiveness of PCM technology.
Keywords
Phase-change memory, Ge-Sb-Te, In-Sb-Te, In-Ge-Te nanowires, MOCVD self-assembly, phase transition simulations.
