5.2.1 Determination of the Fitting Region

It is a challenge to determine the range of measurement data within the FPM pulse, which is further used to extract VTH   . This is because on the one hand side the noisy subthreshold region should be avoided, but at the same time a preferably large range of data points is required for the fitting algorithm. This balancing act is illustrated in Fig. 5.9. A good compromise is found by using all data points between VG = − 0.32V  , where the signal-to-noise ratio is still reasonable high, and the stress level of NBTI at VG = − 3.0V  . This range provides the best possible agreement of the manual fitting and the two proposed extraction schemes, avg  and avg + ITH   .


PIC


Figure 5.9: Changes of the threshold voltage of the SPICE level 1 model fit to FPM after [2451]. The VG   -range used to extract VTH   properly is restricted by the noise in the subthreshold regime on the one hand and by the maximally accessible inversion regime on the other hand. The optimum VG   -range goes from − 0.32V  to − 3.0V  .