Physical and memory characteristics of the atomic-layer-depositedRuOxmetal nanocrystal capacitors in an n-Si/SiO2/HfO2/RuOx/Al2O3/Pt structure with different postdeposition annealing temperatures from 850–1000°C have been investigated. TheRuOxmetal nanocrystals with an average diameter of 7 nm and a highdensity of 0.7 × 1012/cm2are observed by high-resolution transmission electron microscopy after a postdeposition annealing temperature at 1000°C. The density ofRuOxnanocrystal is decreased (slightly) by increasing the annealing temperatures, due to agglomeration of multiple nanocrystals. The RuO3nanocrystals and Hf-silicate layer at the SiO2/HfO2interface are confirmed by X-ray photoelectron spectroscopy. For post-deposition annealing temperature of 1000°C, the memory capacitors with a small equivalent oxide thickness of ~9 nm possess a large hysteresis memory window of >5 V at a small sweeping gate voltage of ±5 V. A promising memory window under a small sweeping gate voltage of ~3 V is also observed due to charge trapping in theRuOxmetal nanocrystals. The program/erase mechanism is modified Fowler-Nordheim (F-N) tunneling of the electrons and holes from Si substrate. The electrons and holes are trapped in theRuOxnanocrystals. Excellent program/erase endurance of 106cycles and a large memory window of 4.3 V with a small charge loss of ~23% at 85°C are observed after 10 years of data retention time, due to the deep-level traps in theRuOxnanocrystals. The memory structure is very promising for future nanoscale nonvolatile memory applications.
On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals
