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A finite element model consisting of a conducting filament with or without a gap was used to reproduce the behavior of TaOx-based resistive switching devices. The specific goal was to explore the range of possible filament parameters such as filament diameter, composition, gap width, and composition to reproduce the conductance and shape of I–V while keeping the maximum temperature within the acceptable range allowing for ion motion and preventing melting. The model solving heat and charge transport produced a good agreement with experimental data for the oxygen content in the filament below TaO1.3, the filament diameter range between 6 and 22 nm, and the gap oxygen content between TaO1.7 and TaO1.85. Gap width was not limited to either low or high sides according to the criteria considered in this report. The obtained filament composition corresponds to oxygen deficiency an order of magnitude higher than one estimated by other modeling efforts. This was in large part due to the use of recent experimental values of conductivity as a function of composition and temperature. Our modeling results imply that a large fraction of atoms leaves and/or accumulates within the filament to produce a large relative concentration change. This, in turn, necessitates the inclusion of strain energy in the filament formation modeling. In addition, the results reproduce non-linear I–V without the necessity of assuming the Poole–Frenkel type of electrical conduction or the presence of a barrier at the oxide/metal interface. 

33rd USENIX Security Symposium (USENIX Security 24)