O 2 /Ar ratio and growth temperature during the deposition process of HfO x thin film have the significant effect on the OFF-state current of Al/HfO x /ITO devices. In order to enhance the quality of HfO x layer, HfO x thin film was sputtered at 300-700 K in a mixed ambient of Ar and oxygen. For HfO x thin films deposited at 500 K with O 2 /Ar ratio of 0.2, the resistive switching ratio is enhanced by five orders of magnitude. The resistive switching I-V characteristics at 120-300 K were investigated. Using temperature-dependent transport in HfO x thin film, two transport mechanisms cocontribute to the high resistance state current: the correlated barrier hopping conduction and the weak metallic filamentary conduction.Index Terms-Hafnium oxide, resistive random access memory (ReRAM), temperature dependence of the off-state and the on-state.