8.6 Conclusion

Based on the SRH theory, many models have been developed in order to describe hole capture in oxide defects. Unfortunately, most attempts fail for bias temperature instability, be it because of the missing field dependence or because of the weak temperature dependence. By using a thermally activated barrier in the capture and emission rates of the SRH model, Kirton and Uren already identified that structural relaxation might play an important role to explain the large timescales observed in -noise. Their approach is further developed in the NMP model, where the strong electron-phonon interaction is used to not only explain the temperature dependence of BTI, but also its field dependence. Unfortunately not all effects of BTI can be modeled with the simple rates given by the NMP model. The field dependence experimentally observed exhibits a stronger than linear dependence and furthermore no full decorrelation between the capture and emission time constants is obtained by the simple NMP model. For this reason the NMP model will be extended to so-called metastable defect states in the next chapter.