This study aims to characterize the oxide based Resistive Random Access Memory memory cell at the nanoscale. Resistive memory stacks were characterized by conductive atomic force microscopy (C-AFM) under vacuum. The AFM tips served as the top electrode. The effect of different tip materials, polarities, bottom electrodes, and compliance currents on resistive switching is described and compared with the results obtained for devices at the micrometric scale. The experimental results are then interpreted by a filament based model. An interpretation in terms of conductive filament geometry is finally given.