Interpretations for coexistence of unipolar and bipolar resistive switching behaviors in Pt/NiO/ITO structure

In this work, a Pt/NiO/ITO memory device is fabricated and characterized. Unipolar resistive switching (URS) and bipolar resistive switching (BRS) are both observed and reproduced. Results of X-ray photoelectron spectroscopy imply the presence of oxygen vacancy (V _O) in the NiO film, and such defect is later proven to be intimated with both URS and BRS effects. Via current fitting to derive the conductive mechanisms for URS and BRS, we deduce that the impact of Schottky emission on the switching behavior could be mainly connected to the migration of oxygen anions (O^2-) and recombination between O^2- ions and V_Os. However, the fitting results of I-V curves suggest the plausible principles dominating the URS and BRS could be quite different although the device is dominated by the same mechanisms in both URS and BRS operations.