The onset of crystallization in phase-change memory devices is studied by simulating an initially amorphous sample through a disordered network of localized states. The transport of charge and electron energy is self-consistently coupled to the Poisson and the Fourier heat equations, so that crystallization sites are found at the nanoscale. Results show how Ovonic switching and crystallization are both correlated to the formation of hot-carrier conduction paths, and the conditions for the occurrence of these phenomena are investigated. The model is then validated against data from ultra-scaled carbon-nanotube-contacted devices. Device-to-device variability of macroscopically identical devices is also analyzed.
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