In this thesis a look beyond the basic semiconductor equations in the context of reliability issues is taken because not only the performance of unstressed devices is important. Due to the constant geometric shrinking and the use of new materials, many degradation mechanisms which were formerly of minor importance, are now coming to the forefront of interest. In this work, two of those degradation mechanisms, namely the dielectric leakage currents of highly degraded dielectrics and negative bias temperature instability (NBTI), have been investigated. Through implementing the models in a numerical device and circuit simulator and coupling them to the semiconductor device equations, self-consistent simulations become possible. The device engineer can not only evaluate the normal operation of an improved or newly designed device concept, he can also investigate the susceptibility to those two degradation mechanisms in the same simulation run. By having insight into the device and the physical quantities causing the degradation he can optimize the structure not only for fast but also for reliable operation.
Especially NBTI, where the main focus of this work lies upon, has obtained tremendous scientific and industrial interest in recent years. As the exact physical mechanisms responsible for the degradation are still not completely identified and researchers are doing their best to promote the understanding, considerable progress has been made and new insights are gained nearly every month. Thus, it might be interesting to have another look at the topic in one or two years and further improve the available models.