Comparison of low frequency noise evolution with oxide trapped charge in irradiated n-MOS transistors

The threshold voltage shift and the low frequency channel noise of n-MOS transistors have been measured after X-ray radiation at different total 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 ΔN_ot or the interface-state density ΔN_it) and the excess noise evolution, as each of these parameters increases with the dose. One of the way to distinguish which of those defects is involved in the increase of the 1/f low frequency noise, is to observe the n-MOS transistors behavior at different times after irradiation. These post-irradiation-effects were investigated after a biased storage time (at room temperature) at constant step times on a logarithmic scale (from 10 to 1000 hours). They revealed a close correlation between the excess channel noise and the density of oxide trapped charge ΔN _ot