Improved resistive switching memory characteristics using core-shell IrO _x nano-dots in Al ₂O ₃WO _x bilayer structure

Improved resistive switching memory characteristics in an IrO _xAl ₂O ₃IrO _x-NDAl ₂O ₃WO _xW structure are investigated in this study. Core-shell iridium-oxide (IrO _x) nano-dots (NDs) with a small diameter (∼2 nm) and high-density (0.7 × 10 ¹³cm ²⁺) are observed by high-resolution transmission electron microscopy (HRTEM). The IrO _x-NDs, Al ₂O ₃, and WO _x layers are also confirmed by both HRTEM and X-ray photo-electron spectroscopy (XPS) analyses. Large number of electrons (with density of 8.9 × 10 ¹⁸cm ³⁺) in the core-region and holes (with density of 7.1 × 10 ¹⁸cm ³⁺) in the shell-region can be trapped in the IrO _x-NDs under a small sweeping gate voltage of 5 V. The IrO _x-NDs in an Al ₂O ₃WO _x bilayer structure have an excellent uniformity of the SET and RESET voltages, an applicable ratio of highlow resistance state (>50), a long read endurance of 10 ⁵ times and an extrapolated 10 years data retention at 85C. Owing to the high charge-trapping density and nano-filament formation through the small size of the core-shell IrO _x-NDs, the improvement of resistive switching performance is evident in comparison to that of the pure Al ₂O ₃ film in an IrO _xAl ₂O ₃WO _xW structure. This study is not only important for improving the performance of IrO _x-ND ReRAM devices but also helpful for designing a low power nanoscale nonvolatile memory in future.