THERMAL TRANSPORT IN PHASE CHANGE MEMORY MATERIALS
Phase change memory uses brief pulses of electrical current to induce phase transitions in chalcogenide material regions with dimensions near or even far below 50 nm. The strongly differing electrical conductivities of the crystalline and amorphous phases allow data storage at densities in excess of terabits per square inch. Nanoscale conduction heat transfer governs the figures of merit in these devices, which include the energy and time required for switching, and has received much attention through both measurements and simulations over the last two decades. This chapter reviews the recent progress on thermal conduction phenomena relevant for phase change memory, including a summary of the physical mechanisms involved as well as the most useful simulation and measurement techniques. Experimental work has focused on separating the intrinsic and boundary resistances of thin film phase change materials, as well as the individual contributions of electrons and phonons to the effective conductivity of the hexagonal crystalline phase. Simulations have focused on improving device geometries and switching characteristics, and continue to need improvements in the areas of crystallization modeling and the impact of phase distribution on electrical and thermal transport. Future research requires a more detailed understanding of electron-phonon coupling and its impact on electrical and thermal conduction in the crystalline phase, as well as greater insight into thermoelectric transport and its impact on device behavior. This progress will be critical for the development of innovative memory strategies including multibit storage.
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