Low-field current on thin oxides after constant current or radiation stresses

Stress induced leakage current after electrical stress and radiation induced leakage current after irradiation have been studied on ultra-thin gate oxides, 4 nm and 4.4 nm thick. Differences between positive and negative leakage currents, which is very large (almost one order of magnitude) if taken at a given gate-to-substrate voltage, almost disappears when currents are plotted as a function of the oxide electric field, if this field is correctly evaluated. We suggest that residual asymmetries are due to a non-homogeneous distribution of traps across the oxide. These asymmetries of stress induced leakage current and radiation induced leakage current have been studied for electrical stresses at different polarities and for positive and negative gate bias voltages applied during irradiation, respectively. Electrical stresses have been performed by using Fowler–Nordheim injection under positive or negative gate voltages. Radiation stresses have been performed by using an 8 MeV electron beam and devices have been biased at positive or negative gate-to-substrate voltages during irradiation.