Memory characteristics of double-layer metal and semiconductor heterogeneous nanocrystals embedded in SiO2

MOS capacitor structure with double-layer heterogeneous nanocrystals consisting of metal and semiconductor embedded in gate oxide for the applications of nonvolatile memory have been fabricated and characterized. By combining the self-assembled Ni nanocrystals and vacuum electron-beam co-evaporated Si nanocrystals in SiO₂ matrix, the MOS capacitor with double-layer heterogeneous nanocrystals can appear large charge storage capacity and improved retention characteristics compared to that with single-layer nanocrystals. The metal nanocrystals at the lower stack enable the direct tunneling mechanism to obtain larger flat voltage shift, while the Si nanocrystals at the upper stack works as an additional charge trap layer to enhance the retention time and the flat voltage shift.