EFFECTS OF RELIABILITY SCREENS ON MOS CHARGE TRAPPING

The effects of pre-irradiation elevated-temperature bias stresses on t he radiation hardness of field-oxide transistors have been investigate d as a function of stress temperature, time, and bias. Both the stress temperature and time are found to have a significant impact on radiat ion-induced charge buildup in these transistors. Specifically, an incr ease in either the stress temperature or; time causes a much larger ne gative shift (towards depletion) in the I-V characteristics of the n-c hannel field-oxide transistors. This increased shift in the transistor I-V characteristics with stress temperature and time suggests that th e mechanisms responsible for the stress effects are thermally activate d. An activation energy of similar to 0.38 eV was measured. The stress bias was found to have no impact on radiation-induced charge buildup in these transistors. The observed stress temperature, time, and bias dependencies appears to be consistent with the diffusion of molecular hydrogen during a given stress period. These results have important im plications for the development of hardness assurance test methods.