The interaction between chemisorbed oxygen adatoms (O2(ad)−) and oxygen vacancies associated with the formation/rupture of conductive filaments dominates the switching yield of ZnO, which is also confirmed by the fact that the reduction of SET/RESET voltage with the temperature. The pronounced surface effect-induced conductivity lowering due to O2(ad)− chemisorption leads to increased resistance of high resistance state (HRS). The current decay of the HRS with increased temperatures/times is owing to the severe O2(ad)− chemisorption as Joule heating is continuously applied. The statistical analysis for over 400 cells provides essential evidence for evaluating the surface effect on resistive switching.

This letter investigates the unipolar resistive switching behaviors of sputtered ZnO thin films by changing the electrode combinations of Pt and Ru, creating four sandwich structures of Pt/ZnO/Pt, Pt/ZnO/Ru, Ru/ZnO/Pt, and Ru/ZnO/Ru. Only the Pt/ZnO/Ru devices in this letter achieved favorable resistive switching characteristics, including good endurance performance, narrow distributions in switching parameters, high ON/OFF ratio (> 150), and clear difference between the set and reset voltages (∼1 V). This may be attributed to the low oxygen affinity of Pt electrodes and the strong c-axis texture of ZnO thin films grown on Ru electrodes.