Resistive switching random access memory (RRAM) with oxygen ion drift under electric (E)-field has been intensively studied. However, the findings are insufficient because redox reaction by oxygen ion drift occurs beneath the top electrode, and it is difficult to analyze with a nondestructive method. Therefore, an effective method to circumvent this difficulty is suggested in this study with a Pt/Al2O3/TiO2/Pt device using a single layer graphene (SLG) top electrode. Based on results from spectroscopic analyses, the SLG serves as not only an interface free electrode, but also as a highly effective indicator for proving O- ion drift motion in response to the E-field in RRAM. The origin of asymmetric resistive switching is due to a redox reaction at the interface by oxygen ion drift. The endurance and operation-current distribution are significantly improved with increased thickness of the Al2O3 insertion layer, which provides carrier tunneling barrier height. The resistance ratio of the high resistance state (HRS) to the low resistance state (LRS) is greater than one order of magnitude in a log scale within 1800 cycles. This result demonstrates that control of a localized charge tunneling barrier is a key factor for reliable resistive switching of the scaled-down RRAM.