Real-time imaging of light-induced transformations in phase-change materials

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In this digital age, we rely on computers in many aspects of our daily life. Their performance not only influences how we communicate and work, but also the efficacy of our banks and medical care. It is then in the best interest of Canada to invest in their development to maintain a strategic advantage in this sector. This Discovery Grant (DG) contributes to this goal by studying the dynamics of phase-change materials that are important for computer memory devices and have the potential to enable more efficient computer architectures. Today's computers follow a von Neumann architecture, where data must be moved between physically separate processing and memory units. As the speed of processors has outpaced that of memory, the bottle neck is now the time it takes to shuttle data back and forth. This can be overcome by performing both actions in a single device, referred to as in-memory computing. However, practical realization of such devices requires materials that can both rapidly and irreversibly switch between states for combined fast processing and non-volatile memory functionality. Phase-change materials based on chalcogenide alloys have been largely investigated for this purpose, and are already used in the computer industry for optical data storage - the composition Ge2Sb2Te5 is used in DVDs, and Ge8Sb2Te11 is used in Blue-ray disks. Data can be written in these devices using a laser or electric current to locally heat a small region, and switch it between an insulating amorphous glass phase and a conductive crystalline phase. The resultant phase is determined by the amount of heat absorbed in the process that is controlled by the incident laser power or electric current. However, the maximum data writing speed is currently limited by the amorphous to crystalline phase transformation time. It is then the goal of this DG to explore ways to increase this transformation speed and track the corresponding material structural evolution in real time using the dynamic transmission electron microscope (DTEM) at INRS. This unique microscope has the capability to capture a sequence of nanosecond images of irreversible transformations with near-atomic resolution. Specifically, this DG will address critical outstanding questions about the crystallization of phase-change materials by exploring the following research directives: (1) imaging rapidly cooled transformations, (2) tracking precursors in the amorphous phase, and (3) ultra-localized nano-plasmonic heating. This research is expected to lead to a deeper understanding of this technologically important transformation, which can impact the future design of computers. Furthermore, the expertise gained by highly qualified personnel trained in this program is widely transferable to other sectors of the Canadian technology industry.