Bipolar tri-state resistive switching characteristics in Ti/CeO_x/Pt memory device

Highly repeatable multilevel bipolar resistive switching in Ti/CeO_x/Pt nonvolatile memory device has been demonstrated. X-ray diffraction studies of CeO₂ films reveal the formation of weak polycrystalline structure. The observed good memory performance, including stable cycling endurance and long data retention times (>10⁴ s) with an acceptable resistance ratio (～ 10²), enables the device for its applications in future non-volatile resistive random access memories (RRAMs). Based on the unique distribution characteristics of oxygen vacancies in CeO_x films, the possible mechanism of multilevel resistive switching in CeO_x RRAM devices has been discussed. The conduction mechanism in low resistance state is found to be Ohmic due to conductive filamentary paths, while that in the high resistance state was identified as Ohmic for low applied voltages and a space-charge-limited conduction dominated by Schottky emission at high applied voltages.