Tungsten nanocrystals embedded in high-k materials for memory application

Abstract

The formation of tungsten nanocrystals (W-NCs) on atomic-layer-deposited HfAlO∕Al2O3 tunnel oxide was demonstrated for application in a memory device. It was found that the density and size distribution of W-NCs are not only controlled by the initial film thickness, annealing temperature, and time, but also by the metal∕tunnel oxide interface structure. Well-isolated W-NCs with an average diameter of 5 nm and a surface density of 5×1011cm−2 were obtained by applying a thin Al2O3 wetting layer onto HfAlO tunneling oxide. A large flatband voltage shift of 5.7 V was observed from capacitance–voltage measurement when a bias voltage up to ±4V was applied.