5.2.4 Consequences

The two described extraction schemes of the FPM-method, namely the avg  - and the avg+  ITH   -extraction, have shown that fully automated handling of a dataset helps to consistently compare experimental results. However, the performed measurements also underlined the fact that even with proper fitting/smoothing methods to avoid noise as much as possible, the practicability of the measurement routine has to be checked first, especially when dealing with different pulse polarities for NBTI and PBTI.

In the case of PBTI a detailed characterization via FPM is simply not possible because the pulse settings are not suitable for both PBTI stress and recovery characterization in a single measurement. The settings are usually a compromise between maximizing the data range for the ID (VG)  -characteristics on the one hand and preventing the device from undesired NBTI stress on the other hand. The latter case occurs when the device is driven too far into inversion. Despite these drawbacks the trend of the degradation can be determined, cf. Fig. 5.5 and Fig. 5.6. It features a negative shift of the threshold voltage, comparable to NBTI but smaller. So far this refutes the existence of electron tunneling as stated in [24], but unfortunately the actual type of defects contributing to BTI still remains unclear. Therefore the measurement technique proposed at the beginning of this chapter using charge pumping will be investigated next. Special emphasis is again put on the measurement method itself.