UC Riverside

This work is devoted to investigating the feasibility of engineering nanocrystals and tunnel oxide layer with a novel structure. Several novel devices are demonstrated to improve the performance of the novel nanocrystal memories.

A novel TiSi2 nanocrystal memory was demonstrated. TiSi2 nanocrystals were synthesized on SiO2 by annealing Ti covered Si nanocrystals. Compared to the reference Si nanocrystal memory, both experiment and simulation results show that TiSi2 nanocrystal memory exhibits larger memory window, faster writing and erasing, and longer retention lifetime as a result of the metallic property of the silicide nanocrystals. Due to thermally stable, CMOS compatible properties, TiSi2 nanocrystals are highly promising for nonvolatile memory device application.

Metal/high-k dielectric core-shell nanocrystal memory capacitors were proposed. This kind of MOS memory shows good performance in charge storage capacity, programming and erasing speed. A self-assembled di-block co-polymer is used to align the NCs to improve the scalability of the overall sample.

An ordered Co/Al2O3 core-shell nanocrystal (NC) nonvolatile memory device was also fabricated. Self-assembled di-block co-polymer process aligned the NCs with uniform size. Co/Al2O3 core-shell NCs were formed using atomic layer deposition of Al2O3 before and after the ordered Co NC formation. Compared to Co NC memory, Co/Al2O3 core-shell NC memory shows improved retention performance without sacrificing writing and erasing speeds.

Another new discrete NiSi nanocrystals (NCs) were synthesized by rapid thermal oxygen annealing (RTO) of very thin Si/Ni/Si films on SiO2 tunneling layer. The RTO process resulted in smooth surface of the NC floating layer, in turn, uniform thickness of subsequent control oxide layer. Metal-oxide-semiconductor capacitor memory was fabricated. Electrical properties of the memory device such as programming, erasing and retention were characterized and good performance was achieved, which is due to the reduction of the leakage paths in the smooth device structure.

Therefore, it is concluded that metallic nanocrystal with aligned core-shell structure memory is a very promising candidate to replace Si nanocrystal for future generation nonvolatile flash memory devices.