Temperature-Dependent Physical and Memory Characteristics of Atomic-Layer-Deposited RuO_x Metal Nanocrystal Capacitors

摘要

Physical and memory characteristics of the atomic-layer-deposited RuO_x metal nanocrystal capacitors in an n-Si/SiO_2/HfO_2/ RuO_x/Al_2O_3/Pt structure with different postdeposition annealing temperatures from 850-1000℃ have been investigated. The RuO_x metal nanocrystals with an average diameter of 7 nm and a highdensity of 0.7 x 10~(12)/cm~2 are observed by high-resolution transmission electron microscopy after a postdeposition annealing temperature at 1000℃. The density of RuO_x nanocrystal is decreased (slightly) by increasing the annealing temperatures, due to agglomeration of multiple nanocrystals. The RuO_3 nanocrystals and Hf-silicate layer at the SiO_2/HfO_2 interface are confirmed by X-ray photoelectron spectroscopy. For post-deposition annealing temperature of 1000℃, 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 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 10~6 cycles and a large memory window of 4.3 V with a small charge loss of ～23% at 85℃ 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.