.
The ETM has been based on the concept that electrons tunneling into and out of
a defect have the same energy. This implies that the corresponding trap
level remains at the same energy within the oxide bandgap regardless of
whether the defect has captured a charge or not. However, as pointed out in
Section 2.3, this level is subject to a shift after each charging or discharging
event. This is due to the fact that the defect undergo structural relaxation,
which involves strengthening, weakening, or even disrupting bonds. With this
deformation, the defect orbitals change which is accompanied by a shifts of the
corresponding defect levels. This concept of the level shift has not received much
attention so far but has important implications for the tunneling kinetics in
.
In the first part of this chapter it will be demonstrated that the charging and
discharging of defects involves a non-negligible structural relaxation, which results in
an appreciable level shift and thus impacts the trapping dynamics. Using DFT, the
corresponding switching levels will be determined for a number of defects suspected
to be present in 
. Based on the position of these levels, the defects will be
tentatively classified according to their expected trapping behavior in NBTI
experiments. In order to allow for quantitative predictions, a new model
accounting for the level shift will be developed in the second part of this
chapter. This model will then be tested whether it can explain the NBTI
experiments.
Center and Variants