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NiO films display unipolar resistance switching characteristics, due to the electrically induced formation and rupture of nanofilaments. While the applicative interest for possible use in highly dense resistance switching memory (RRAM) is extremely high, switching phenomena pose strong fundamental challenges in understanding the physical mechanisms and models. This work addresses the set and reset mechanisms for the formation and rupture of nanofilaments in NiO RRAM devices. Reset is described in terms of thermally-accelerated diffusion and oxidation processes, and its resistance dependence is explained by size-dependent Joule heating and oxidation. The filament is described as a region with locally-enhanced doping, resulting in an insulator-metal transition driven by structural and chemical defects. The set mechanism is explained by a threshold switching effect, triggering chemical reduction and a consequent local increase of metallic doping. The possible use of the observed resistance-dependent reset and set parameters to improve the memory array operation and variability is finally discussed.

Resistive-switching memory (RRAM) is attracting a considerable interest for the development of high-density nonvolatile memories. However, several scaling and reliability issues still affect the development path of RRAM. This work addresses random telegraph-signal noise (RTN) of the RRAM current, potentially affecting the memory stability. We show a clear resistance dependence of the RTN amplitude, and we propose a physical model describing the interaction of the localized current with a fluctuating defect. By estimating the diameter of the conductive filament, the model quantitatively accounts for the observed RTN amplitude, thus allowing for an analytical prediction of state stability in RRAM

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