Coexistence of unipolar and bipolar switching in nanocrystalline spinel ferrite ZnFe2O4 thin films synthesized by sol-gel method

In this letter, we report the coexistence of unipolar and bipolar switching in a solution-based nano-crystalline spinel ferrite ZnFe2O4 thin film prepared by the sol-gel method. It is seen that the Au/ZnFe2O4/Pt device could be activated between unipolar and bipolar switching modes just by choosing RESET-voltage polarity. Conversions between unipolar to bipolar switching modes are reversible and controllable. The results show that the SET-voltage of unipolar switching is smaller than that of bipolar switching, while memory windows (ON/OFF ratio) are identical. Furthermore, filaments are induced by the migration of oxygen vacancies (VOs), which are responsible for reducing variations in SET voltages of unipolar switching. By analyzing the current transport conduction mechanism, the electrode-limited Schottky emission mechanism is dominated in the high field region. Temperature dependence of low and high resistance states indicates that conductive filaments are composed of VOs and metallic Zn atoms, involving Joule heating and electrochemical redox reaction effects. Investigation on coexisting both unipolar and bipolar switching modes in a single Au/ZnFe2O4/Pt memory cell would open a pathway for spinel ferrite based low-cost nonvolatile memory. Published by AIP Publishing.