Memory programming of TiO_2−x films by Conductive Atomic Force Microscopy evidencing filamentary resistive switching

Highlights: • We correlate RRAM performance with C-AFM measurements. • We demonstrate resistive switching through C-AFM process. • We present evidence of filament formation. • We demonstrate resistive switching in nanoscale area. - Abstract: Resistive Random Access Memory (RRAM) with a structure Au/Ti/TiO_2−x/Au demonstrated a clear bipolar resistive switching behavior without the necessity of an initial electroforming process. The titanium oxide (TiO_2−x) thin film was deposited by reactive RF magnetron sputtering at room temperature in a controlled oxygen/argon ambient. The high density of oxygen vacancies within the film (induced by the low oxygen content) is an essential component for the formation of conducting filaments and demonstration of DC or nanosecond pulsed resistance switching, but also impose limitations for the conduction behavior of the high resistance state. Conductive Atomic Force Microscopy (C-AFM) was then employed in order to investigate the nanoscale electrical properties of our device. In situ current distribution during the SET process disclosed possible formation of conducting filaments while DC sweeping bias voltage revealed an OFF/ON switching ratio of about 200. We have also demonstrated that by using C-AFM both a low resistance state and a high resistance state can be written by bipolar voltage application imaged by corresponding patterns on the TiO_2−x current image, suggesting that oxygen ions movement at the Pt-Ir coated tip/TiO_2−x interface plays a critical role in the resistive switching phenomenon and thus correlating the macroscopic characteristics of our device with its microscopic origins. Nanoscale resistance switching is also demonstrated by programming distinct patterns on the device's current image