Chapter 3
Previous Modeling Attempts

In the 1960’s, the investigations of the Si- interface revealed a close-coupling of the increase of surface traps sitting at the interface and a phenomenon which will be later on known as the bias temperture instability. Both effects were known to cause a negative shift of the threshold voltage [3, 4, 53]. Though this phenonmenon was already known not to cause real device failure as for example time dependent dielectric breakdown (TDDB) [35, 54], the creeping shift of alerted the industry and the scientific community to develop a model which is capable of describing the mechanisms behind BTI. In order to judge such a model as functional, clear definitions of its applicability but also potential limits have to be listed. The following review summarizes the existing modeling efforts, including their advantages and disadvantages.