4.3 Conclusion

In this chapter, several peculiarities of the ETM have been analyzed and compared to the experimental findings of NBTI. It has been pointed out that this model predicts a logarithmic time behavior over several decades during stress and relaxation. However, the ETM fails to explain NBTI for several reasons:

• saturates within or even before the experimental time window for devices with thin gate dielectrics as applied in modern semiconductor devices. This problem becomes even more severe if charge injection from the gate is considered.
• The asymmetry between stress and recovery cannot be reproduced by this model.
• The ETM shows the wrong temperature and field dependence, which are both inherent to the model and therefore cannot be improved by suitably chosen fitting parameters.

The above arguments summarized in Table 4.1 are a strong evidence that the NBTI degradation cannot be described by hole trapping according to the ETM. As a consequence, this model is discarded from the list of possible NBTI models, and other capture processes must be considered.

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Table 4.1: Checklist for an NBTI model. This table contains the most important features of the NBTI stress and relaxation curves. The above features must be viewed as criteria which have to be fulfilled by an NBTI model candidate.

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