Ruthenium oxide metal nanocrystal capacitors with high-κ dielectric tunneling barriers for nanoscale nonvolatile memory device applications

The ruthenium oxide metal nanocrystals embedded in high-κ HfO2/Al2O3 dielectric tunneling barriers prepared by atomic layer deposition in the n-Si/SiO2/HfO2/ruthenium oxide (RuOx)/Al2O3/Pt memory capacitors with a small equivalent oxide thickness of 8.6 ± 0.5 nm have been investigated. The RuOx metal nanocrystals in a memory capacitor structure observed by high-resolution transmission electron microscopy show a small average diameter of ∼7 nm with high-density of >1.0 × 1012/cm2 and thickness of ∼3 nm. The ruthenium oxide nanocrystals composed with RuO2 and RuO3 elements are confirmed by X-ray photoelectron spectroscopy. The enhanced memory characteristics such as a large memory window of ΔV ≈ 12.2 V at a sweeping gate voltage of ±10 V and ΔV ≈ 5.2 V at a small sweeping gate voltage of ±5 V, highly uniform and reproducible, a large electron (or hole) storage density of ∼1 × 1013/cm2, low charge loss of <7% (ΔV ≈ 4.2 V) after 1 × 104 s of retention time are observed due to the formation of RuOx nanocrystals after the annealing treatment and design of the memory structure. The charge storage in the RuOx nanocrystals under a small voltage operation (∼5 V) is due to the modified Fowler–Nordheim tunneling mechanism. This memory structure can be useful for future nanoscale nonvolatile memory device applications.