Total dose effects on a fully-depleted SOI NMOSFET and its lateral parasitic transistor

Abstract

The dose induced threshold voltage shift of fully-depleted NMOS transistors is strongly correlated with charge trapping in the buried oxide. Thinner buried oxides, which are less dose sensitive than thicker ones, not necessarily improve the radiation hardness of fully-depleted transistors because of the higher coupling effect. The lateral parasitic transistor is more affected by the buried oxide charge trapping than the main active transistor. The lateral and back surface conduction in the thin part of the mesa edge, increases with ionizing dose and adds to the front surface conduction. Body tie is the only lateral isolation immune to dose effects.