Switching of nanosized filaments in NiO by conductive atomic force microscopy

Resistive switching in binary metal oxides consists of conductivity changes originating from the electrical creation/dissolution of conductive filaments (CFs) at nanoscale. The investigation of CF local properties can only be achieved through physical and electrical studies at the scale of 10 nm or less, that is, the characteristic size of CFs. This work reports on the direct manipulation of individual CFs formed through insulating NiO films by conductive atomic force microscopy (CAFM) and the comparison between forming/reset processes induced by CAFM and those observed in large-area devices with the same NiO film. The switching variability due to local defects, such as grain boundaries and dislocations, is directly evidenced by CAFM during electroforming process. Our results also indicate that the forming voltage under CAFM can be significantly smaller than the one observed in large-area devices, thus providing evidence for the electric-field enhancement underneath the CAFM tip. Filament deactivation, or reset, at extremely low currents close to 100 nA is demonstrated and described in terms of electrode-limited CF. These results suggest that device engineering and CF size limitation may allow for a significant reduction of forming voltage and reset current in resistive switching random-access memory switching.