Nonvolatile memory properties of thin oxides with single- and multi-layered Si nanocrystals obtained by ion beam sputtering

Single-, double-, and 50- period SiO _x/SiO ₂ have been prepared on Si wafers by ion beam sputtering deposition and subsequently annealed to form Si nanocrystals (NCs) in the SiO _x layer. For 50-period SiO _x/SiO ₂ multilayers, the flat-band voltage shift (ΔV _FB) of the C-V curves is found to be inversely proportional to the photoluminescence peak wavelength and intensity, which indicates that larger-sized and more dense Si NCs will exhibit a stronger nonvolatile memory. In single-layer devices, a reduction in the tunnel-oxide thickness strongly enhances ΔV _FB, and an asymmetry exists between electron and hole storage. The retention time is improved by increasing the thickness of the tunnel oxide rather than the control oxide. The defect states in these devices are considerably reduced by hydrogenation passivation, enhancing ΔV _FB in the hole storage. ΔV _FB is enhanced on both polarities by reducing the thickness of the center oxide in doubly-stacked devices, A longer retention time is found in the doubly-stacked memory, which seems to result from suppressed charge leakage between the upper NC layer and the substrate due to an energy barrier in the lower NC layer.