Abstract
The non-volatile memory characteristics of metal-oxide-semiconductor (MOS) structures embedded with Au nanocrystals in the gate oxide were studied in this thesis. The Au nanocrystals with a narrow size distribution can be self-assembed from the agglomeration of an ultrathin Au layer inserted in the gate oxide by annealing at a suitable temperature. A clear hysteresis loop is found in the capacitance-voltage (C-V) relation, indicating its significant charge storage effect. Moreover, different charging rate for two kinds of trapped carriers (electron and hole) was found from C-V measurement under various scan rates. With the use of high-k materials, the performance of Au-nanocrystals-based non-volatile memory can be improved. Among them, we have demonstrated that the use of Al2O3 as control oxide prepared by atomic-layer-deposition enhances the erase speed of the memory cells. In addition, the use of (Ba0.5Sr0.5)TiO3 (BST) as the control oxide in a Au-nanocrystals-based memory structure was also investigated. The Au nanocrystals, surrounded with a core shell of Au-doped BST, were self-assembled in the BST/SiO2 stack. The leakage of the gate oxide is reduced due to the partial dissolution of Au into the BST matrix, which enlarges the energy band-gap of BST. Moreover, direct tunneling through the tunnel oxide is suppressed because the internal field induced by the charges in the Au nanocrystals can be screened by the ultrahigh-k shell of BST. Therefore, the retention property of the Au-nanocrystals-based memory structure is improved. The charge storage characteristics of MOS structures containing Au nanocrystals in atomic-layer-deposited high-k gate dielectrics were also studied in this thesis. A satisfactory charge retention characteristic was obtained for the sample employing Al2O3 as the gate dielectric compared to that using Hf2AlOx as the gate dielectric. Moreover, a saturation of electron storage in the MOS capacitors was also observed.