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

Stress induced leakage current after electrical stress and radiation induce d leakage current after irradiation have been studied on ultra-thin gate ox ides, 4 nm and 4.4 nm thick. Differences between positive and negative leak age currents, which is very large (almost one order of magnitude) if taken at a given gate-to-substrate voltage, almost disappears when currents are p lotted as a function of the oxide electric field, if this field is correctl y evaluated. We suggest that residual asymmetries are due to a non-homogene ous distribution of traps across the oxide. These asymmetries of stress ind uced leakage current and radiation induced leakage current have been studie d for electrical stresses at different polarities and for positive and nega tive gate bias voltages applied during irradiation, respectively. Electrica l stresses have been performed by using Fowler-Nordheim injection under pos itive or negative gate voltages. Radiation stresses have been performed by using an 8 MeV electron beam and devices have been biased at positive or ne gative gate-to-substrate voltages during irradiation. (C) 1999 Elsevier Sci ence B.V. All rights reserved.