Modeling total dose effects in narrow-channel devices

Exposure of MOSFET's to large doses of ionizing radiation causes bulk oxide charging and an increase in interface state density. The former shifts device operation thresholds. The latter degrades channel mobility gmand increases subthreshold leakage. The degree of damage introduced depends on oxide electric fields. Making gate dimensions smaller complicates modeling a number of ways. Some of these complications are addressed in this paper. Specifically, problems associated with narrowing the width of the device channel are investigated. It is shown that differential charging of the field and gate regions leads to an effective widening of the channel. For typical n-channel MOSFET's used in very-large-scale integrated circuits, this widening may amount to 0.3 µm after a 10-krad:SiO2dose of ionizing radiation. A model incorporating channel widening and radiation-induced mobility degradation is proposed.