In this paper, we reported a coexistence of bipolar and unipolar characteristics in Cu/NiO/Pt RRAM cells. We studied the unipolar resistive switching firstly. The Cu/NiO/Pt exhibits an extensibility performance in low power consumption. The reset current is higher than 1 mA when the current compliance is above 1 mA. However, the reset current can decrease to 300 μA when the current compliance decreases to 50 μA. Furthermore, the Cu/NiO/Pt device also shows a bipolar behavior. However, the decreasing reset current phenomenon and bipolar behavior were not observed in Pt/NiO/Pt structure. Then we compared the temperature dependence of the LRS resistance. The two structures showed positive temperature coefficients (α) in low resistance state (LRS), suggesting metallic filaments controlling the LRS. The temperature coefficient (α) of Cu/NiO/Pt structure is lower than that in Pt/NiO/Pt structure, which indicates different metal filaments are formed in the Cu/NiO/Pt structure. It is suggested that the coexistence of bipolar and unipolar and low power consumption is ascribed to the application of Cu electrode to NiO dielectric.
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