Synthesis and charge storage properties of double-layered NiSi nanocrystals

Based on bidirectional diffusion of Ni atoms, double-layered nickel silicide (NiSi) nano-crystals (NCs) for multilevel charge storage were fabricated, and their charge storage properties were examined. The double layer was produced by long-term thermal annealing (for 4 h at 900 degrees C) of a sandwich structure comprised of a thin Ni film of 0.3 nm sandwiched between two silicon-rich oxide (SiO1.36) layers. Transmission electron microscopic image clearly exhibits a distinct NiSi nanocrystal double layer with a gap of about 7 nm between the mean positions of particle distribution in each NC layer. Capacitance-voltage measurements on the metal/oxide/semiconductor (MOS) capacitors with the double-layered NiSi nanocrystals are shown to have the apparent two plateaus of charge storage, the large memory window of about 9 V and the improved charge retention stability.