Excellent resistive memory characteristics and switching mechanism using a Ti nanolayer at the Cu/TaO_x interface

Excellent resistive switching memory characteristics were demonstrated for an Al/Cu/Ti/TaO_x/W structure with a Ti nanolayer at the Cu/TaO_x interface under low voltage operation of ± 1.5 V and a range of current compliances (CCs) from 0.1 to 500 μA. Oxygen accumulation at the Ti nanolayer and formation of a defective high-κ TaO_x film were confirmed by high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photo-electron spectroscopy. The resistive switching memory characteristics of the Al/Cu/Ti/TaO_x/W structure, such as HRS/LRS (approximately 10⁴), stable switching cycle stability (>10⁶) and multi-level operation, were improved compared with those of Al/Cu/TaO_x/W devices. These results were attributed to the control of Cu migration/dissolution by the insertion of a Ti nanolayer at the Cu/TaO_x interface. In contrast, CuO_x formation at the Cu/TaO_x interface was observed in an Al/Cu/TaO_x/W structure, which hindered dissolution of the Cu filament and resulted in a small resistance ratio of approximately 10 at a CC of 500 μA. A high charge-trapping density of 6.9 × 10¹⁶ /cm² was observed in the Al/Cu/Ti/TaO_x/W structure from capacitance-voltage hysteresis characteristics, indicating the migration of Cu ions through defect sites. The switching mechanism was successfully explained for structures with and without the Ti nanolayer. By using a new approach, the nanoscale diameter of Cu filament decreased from 10.4 to 0.17 nm as the CC decreased from 500 to 0.1 μA, resulting in a large memory size of 7.6 T to 28 Pbit/sq in. Extrapolated 10-year data retention of the Ti nanolayer device was also obtained. The findings of this study will not only improve resistive switching memory performance but also aid future design of nanoscale nonvolatile memory.