An MOS (metal oxide semiconductor) capacitor structure with double-layer heterogeneous nanocrystals consisting of semiconductor and metal embedded in a gate oxide for nonvolatile memory applications has been fab-ricated and characterized.By combining vacuum electron-beam co-evaporated Si nanocrystals and self-assembled Ni nanocrystals in a SiO2 matrix,an MOS capacitor with double-layer heterogeneous nanocrystals can have larger charge storage capacity and improved retention characteristics compared to one with single-layer nanocrystals.The upper metal nanocrystals as an additional charge trap layer enable the direct tunneling mechanism to enhance the flat voltage shift and prolong the retention time.
The Si2Sb2Te5 phase change material has been studied by applying a nano-tip(30 nm in diameter) on an atomic force microscopy system.Memory switching from a high resistance state to a low resistance state has been achieved,with a resistance change of about 1000 times.In a typical I-V curve,the current increases significantly after the voltage exceeds～4.3 V.The phase transformation of a Si2Sb2Te5 film was studied in situ by means of in situ X-ray diffraction and temperature dependent resistance measurements.The thermal stability of Si2Sb2Te5 and Ge2Sb2Te5 was characterized and compared as well.
