Resistance switching characteristics of CeO2/Ti/CeO2 tri-layered films sandwiched between Pt bottom electrode and two different top electrodes (Ti and TaN) with different work functions have been investigated. RRAM memory cells composed of TaN/CeO2/Ti/CeO2/Pt reveal better resistive switching performance instead of Ti/CeO2/Ti/CeO2/Pt memory stacks. As compared to the Ti/CeO2 interface, much better ability of TaN/CeO2 interface to store and exchange plays a key role in the RS performance improvement, including lower forming/SET voltages, large memory window (~102) and no significant data degradation during endurance test of >104 switching cycles. The formation of TaON thinner interfacial layer between TaN TE and CeO2 film is found to be accountable for improved resistance switching behavior. Partial charge density of states is analyzed using density functional theory. It is found that the conductive filaments formed in CeO2 based devices is assisted by interstitial Ti dopant. Better stability and reproducibility in cycle-to-cycle (C2C) resistance distribution and Vset/Vreset uniformity were achieved due to the modulation of current conduction mechanism from Ohmic in low field region to Schottky emission in high field region.

By introducing a thin non-stoichiometric CeO2-x switching layer between the high oxygen affinity metal TaN top electrode and the TiO2 layer in a TaN/CeO2-x/TiO2/Pt bilayer (BL) device, it is possible to enhance the endurance characteristics and overcome the reliability issue. Compared with a single layer device, a BL device significantly enhances the number of direct current overswitching cycles to >1.2 × 104, non-destructive retention (>104 s), and switching uniformity. A TaON interface layer is formed which served as a reservoir of oxygen ions (O2−) in the SET-process and acts as an O2− supplier to refill the oxygen vacancies in the RESET-process and so plays a key role in the formation and rupture of conductive filaments. This study demonstrates that simply introducing a thin non-stoichiometric CeO2-x switching layer into TiO2-based devices can facilitate the enhancement of the endurance property for future nonvolatile memory applications.

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Memory devices with bilayer CeO2−x/ZnO and ZnO/CeO2−x heterostructures sandwiched between Ti top and Pt bottom electrodes were fabricated by RF-magnetron sputtering at room temperature. N-type semiconductor materials were used in both device heterostructures, but interestingly, change in heterostructure and electroforming polarity caused significant variations in resistive switching (RS) properties. Results have revealed that the electroforming polarity has great influence on both CeO2−x/ZnO and ZnO/CeO2−x heterostructure performance such as electroforming voltage, good switching cycle-to-cycle endurance (~ 102), and ON/OFF ratio. A device with CeO2−x/ZnO heterostructure reveals good RS performance due to the formation of Schottky barrier at top and bottom interfaces. Dominant conduction mechanism of high resistance state (HRS) was Schottky emission in high field region. Nature of the temperature dependence of low resistance state and HRS confirmed that RS is caused by the formation and rupture of conductive filaments composed of oxygen vacancies.