Temperature-dependent physical and memory characteristics of atomic-layer-deposited RuO_x Metal Nanocrystal Capacitors

Physical and memory characteristics of the atomic-layer-deposited RuO x metal nanocrystal capacitors in an n-Si/SiO2/HfO2/ RuO x /Al2O3/Pt structure with different postdeposition annealing temperatures from 8501000()C have been investigated. The RuO x metal nanocrystals with an average diameter of 7nm and a highdensity of 0.710¹²/cm² are observed by high-resolution transmission electron microscopy after a postdeposition annealing temperature at 1000()C. The density of RuO x nanocrystal is decreased (slightly) by increasing the annealing temperatures, due to agglomeration of multiple nanocrystals. The RuO3 nanocrystals and Hf-silicate layer at the SiO2/HfO2 interface 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 ∼9nm possess a large hysteresis memory window of 5V at a small sweeping gate voltage of 5V. A promising memory window under a small sweeping gate voltage of ∼3V is also observed due to charge trapping in the RuO x metal 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 the RuO x nanocrystals. Excellent program/erase endurance of 10⁶ cycles and a large memory window of 4.3V 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 the RuO x nanocrystals. The memory structure is very promising for future nanoscale nonvolatile memory applications.