CHARGE BUILDUP AND OXIDE WEAR-OUT DURING FOWLER-NORDHEIM ELECTRON INJECTION IN IRRADIATED MOS STRUCTURES

The degradation phenomena and charge build-up during high-field Fowler -Nordheim stress in silicon dioxide layers of MOS structures, pre-degr aded by ionizing radiation, has been studied from the point of view of dielectric strength wear-out and long-term reliability. External bias of both polarities was applied to the structures during irradiation t o separate generated carriers, force the current flow, and to enhance or inhibit radiation-induced degradation. It has been found that break down and wear-out properties of the oxides remain unchanged after the irradiation regardless of irradiation conditions. On the other hand, w hile the rate of electron trap generation during the prolonged stress has not been found sensitive to irradiation, we have found that the in itial voltage transients during constant-current stress may be strongl y affected by the changes in the radiation-induced hole trap occupancy . The character of the initial transient may indicate both net positiv e or negative charge build-up, depending on the hole trap occupancy pr ior to he high-filed degradation.