Time-dependent degradation of MOSFET channel mobility following pulsed irradiation

A model is presented for the time-dependent mobility of channel carriers in MOSFETs following pulsed irradiation. It includes the effects of both trapped hole (ΔN_OT) removal (annealing) and the time-dependent buildup of interface traps (Δ N_IT). Several sets of time-resolved transconductance data beginning at 10^-4 s are examined for n-channel devices in light of the model. It is shown that, even though ΔN _IT generally dominates the change in mobility at late time, at early times (≲10^-2 s) following pulsed irradiation the effect of trapped holes can be significant and in fact is usually dominant over ΔN_IT. With increasing time, the mobility undergoes a limited recovery as the ΔN_OT effect diminishes due to the annealing of the trapped holes and the increase in tunneling distance to the nearest trapped holes. However, at t~0.1 s, there is a turnaround in the mobility recovery followed by further degradation in time as the time-dependent ΔN_IT effect becomes significant. The experimentally determined mobility degradation coefficients are found to be consistent for several samples of varying oxide thickness and to scale with temperature according to the prediction of the model