This paper reports a direct observation of resistive switching occurring on the nanoscale within NiO layers deposited on top of a tungsten pillar bottom electrode. Filamentary conduction was evidenced by atomic force microscopy using a conductive tip that enabled performing electroforming and reset operations at nanoscale. In the low resistive state, it is shown that the current is driven by multiple conductive nanometric regions in agreement with the filamentary conduction models. In the high resistive state, conduction originates from weak residual conductive regions remaining after reset operation. Finally, retention measurements performed at the nanoscale demonstrated the persistence of localized conductive regions after more than 30 days.

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