Pulse-induced alternation from bipolar resistive switching to unipolar resistive switching in the Ag/AgOx/Mg0.2Zn0.8O/Pt device

Electric field-induced resistive switching (RS) and related effects are studied for the ZnO-based device Ag/AgOx/Mg0.2Zn0.8O/Pt. The system exhibits a bipolar resistive switching (BRS) for the current (I)-voltage (V) cycles, with the set/reset voltage distributing in a narrow region around 0.15 V/0.16 V. The high to low resistance ratio is similar to 10, and the resistive state is well retainable. However, the RS becomes unipolar (unipolar resistive switching-URS) when electric pulses are applied, with a fairly wide distribution of the set/reset voltages, though the resistive state is still well retainable. It was further found that a backward transition from the URS to the BRS state can be occasionally triggered by simply performing I-V cycling in the negative branch, which shows the strong competition of the BRS and URS states. Both the BRS and URS states were stable and reproducible over 90 cycles. Possible mechanisms for the BRS and URS state and their mutual transition were discussed.