Self-assembly of metal nanocrystals on ultrathin oxide for nonvolatile memory applications

The self-assembly of metal nanocrystals including Au, Ag, and Pt on ultrathin oxide for nonvolatile memory applications are investigated. The self-assembly of nanocrystals consists of metal evaporation and selective rapid-thermal annealing (RTA). By controlling process parameters, such as the thickness of the deposited film, the post-deposition annealing temperatures, and the substrate doping concentration, metal nanocrystals with density of 2–4 × 1011 cm−2, diameter less than 8.1 nm, and diameter deviation less than 1.7 nm can be obtained. Observation by scanning-transmission electron microscopy (STEM) and convergent-beam electron diffraction (CBED) shows that nanocrystals embedded in the oxide are nearly spherical and crystalline. Metal contamination of the Si/SiO2 interface is negligible, as monitored by STEM, energy dispersive x-ray spectroscopy (EDX), and capacitance-voltage (C-V) measurements. The electrical characteristics of metal, nanocrystal nonvolatile memories also show advantages over semiconductor counterparts. Large memory windows shown by metal nanocrystal devices in C-V measurements demonstrate that the work functions of metal nanocrystals are related to the charge-storage capacity and retention time because of the deeper potential well in comparison with Si nanocrystals.