Do NBTI-induced interface states show fast recovery? A study using a corrected on-the-fly charge-pumping measurement technique

Data obtained by the recently developed on-the-fly charge-pumping technique has suggested a fast initial degradation and recovery of interface states during negative and/or bias temperature stress, contrary to previously published results. By revising the analysis of the measurement setup, fast interface state creation and recovery are revealed as artifact due to a different amount of oxide traps seen during the stress and relaxation phases. From this analysis we conclude that data gathered during stress and recovery phases must not be directly compared. By properly taking the contribution of (slow) oxide charges into account, which leads to a spurious increase of the charge-pumping current during the stress phase, we demonstrate that no fast initial degradation and no fast recovery of interface states occurs. Nevertheless, the charge-pumping signal is sensitive to the continuous switching of the gate voltage into accumulation, which also accelerates interface state recovery, albeit at a slower rate. We finally conclude that both the fast initial degradation and the fast initial recovery seem to be due to oxide charges. Therefore these oxide charges need to be considered. By performing simulations with our device simulator Minimos-NT using a modified Shockley-Read-Hall model it was possible to reproduce the effect of these oxide charges. For this purpose a temperature and field activated tunneling process is assumed and results in proper agreement of measurement and simulation. A correction scheme for the on-the-fly charge-pumping measurement technique is then presented.