This work investigates the resistive switching mechanism in the Cu/TiW/InGaZnO/Al2O3/Pt-based memristor. By introducing the Al2O3 layer, the nanoscale diameter of the Cu filament decreased from 6.51 to 0.83 nm as the current compliance decreases from 1 mA to 50 μA. The resistive switching memory characteristics, such as a large ratio of high-resistance state (HRS)/low-resistance state (LRS) (∼107), stable switching cycle stability (>9 × 102), and multilevel operation, are observed and apparently improved compared to the counterpart of the Cu/TiW/InGaZnO/Pt memory device. These results are attributed to the control of Cu formation/dissolution by introducing the Al2O3 nanolayer at the InGaZnO/Pt interface. The findings of this study can not only improve the performance of the amorphous InGaZnO memristor but also be promising for potential applications of next-generation flat-panel displays in wearable devices.