Enhanced Radiation Effects on Submicron Narrow-Channel NMOS

We have observed an enhanced radiation sensitivity for narrow-channel NMOS transistors. The radiation-induced threshold shift increases rapidly as the channel width decreased below 4 μm. For example, with 4.5 μm channel lengths the radiation sensitivity for 0.8 μm wide FETs is twice that for 5 μm wide devices. This geometry dependence can be explained qualitatively by two-dimensional potential calculations. These calculations show the fringing field influence on threshold voltage is reduced after radiation, leading to a larger total shift for the narrow channel devices.