Table 5.2: Checklist for an NBTI model validation. Since the LSM does not
fulfill all of the criteria established in Section 1.4, it must be discarded as a
possible model for NBTI.
In this chapter, the concept of the level shift has been incorporated in the ETM. The resulting LSM has been tested whether it is capable of explaining the NBTI phenomenon. By means of DFT simulations it has been proven that the structural relaxation after a tunneling process occurs for a series of defects suspected to be responsible for NBTI. Therefore, the ETM has been modified to account for the unquestionable occurrence of the level shift. This involves more complicated trapping dynamics but, for instance, allows for a temperature activation, missing in the ETM, as well as the asymmetry between stress and recovery. However, as pointed out in Table 5.2, the LSM is not capable of reproducing all of the essential NBTI features, such as the field and temperature dependence. As a consequence, it must be ruled out as an adequate model for charge trapping in NBTI.