COMPARISON OF THE LOW-FREQUENCY NOISE EVOLUTION WITH THE OXIDE TRAPPED CHARGE IN IRRADIATED N-MOS TRANSISTORS

The threshold voltage shift and the low frequency channel noise of n-M OS transistors have been measured after X-ray radiation at different t otal doses. From the measurements performed just after the irradiation stage, any clear relation could not be established between one of the defects (known as the oxide trapped charge density DELTAN(ot) or the interface-state density DELTAN(it)) and the excess noise evolution, as each of these parameters increases with the dose. One of the way to d istinguish which of those defects is involved in the increase of the 1 /f low frequency noise, is to observe the n-MOS transistors behavior a t different times after irradiation. These Post-Irradiation-Effects (P IE) were investigated after a bi~ased storage time (at room temperatur e) at constant step times on a logarithmic scale (from 10 to 1000 hour s). They revealed a close correlation between the excess channel noise and the density of oxide trapped charge DELTAN(ot).