ReRAM (resistance random access memory) has been receiving attention as the next-generation memory owing to advantages such as fast switching-speed, low power consumption, and simple structure. However, in order to improve the properties of the candidate materials that show resistive switching phenomenon, it is essential to understand the resistive switching mechanism. This study was conducted to investigate the switching mechanism of a ReRAM device with Pt/a-IGZO (amorphous InGa-Zn-O)/TaOx/Al2O3/W structure that exhibits useful properties such as forming free and self-rectifying properties in addition to the general memory properties of existing ReRAM devices. Based on a series of designed experiments and analysis, it was found that the current hysteresis in this device is based on the oxygen vacancy exchange between a-IGZO and TaOx. The movement of positively charged oxygen vacancy according to the relative polarity of applied voltage between the two oxides induces the resistance change of TaOx layer, which in turn results in the resistive switching. (C) 2014 Elsevier B.V. All rights reserved.