Understanding the coexistence of unipolar and bipolar resistive switching in NiFe2O4 resistive memory devices

In this Letter, spinel ferrite NiFe2O4 films prepared through pulsed laser deposition are used to fabricate Pt/NiFe2O4/Pt devices with the coexistence of unipolar resistive switching (URS) and bipolar resistive switching (BRS). The device demonstrated nonvolatile and stable resistive switching (RS) properties under URS and BRS modes. The current–voltage (I–V) fitting analysis and temperature dependence measurements suggested that one Pt/NiFe2O4/Pt RRAM cell follows two significantly different RS and carrier transport mechanisms under URS and BRS modes. Under URS mode, the carrier mechanism alternates between the high resistance state (HRS) with Schottky emission and low resistance state (LRS) with the Ohmic mechanism. In contrast, under BRS mode, carrier transport at HRS and LRS is dominated by space-charge-limited current and nearest-neighboring hopping, respectively. Finally, a physical model, combining oxygen ion (O2−) migration and electric field distribution simulated by COMSOL Multiphysics, is proposed to further clarify the coexistence of two distinct RS and carrier transport mechanisms in the single Pt/NiFe2O4/Pt RRAM device.