  Memory devices based on resistive switching (RS) have not been fully realised
due to lack of understanding of the underlying switching mechanisms. Nature of
ion transport responsible for switching and growth of conducting filament in
transition metal oxide based RS devices is still in debate. Here, we
investigated the mechanism in Niobium oxide based RS devices, which shows
unipolar switching with high ON/OFF ratio, good endurance cycles and high
retention times. We controlled the boundary conditions between low-conductance
insulating and a high-conductance metallic state where conducting filament (CF)
can form atomic point contact and exhibit quantized conductance behaviour.
Based on the statistics generated from quantized steps data, we demonstrated
that the CF is growing atom by atom with the applied voltage sweeps. We also
observed stable quantized states, which can be utilized in multistate
switching.
