Controversial issues in negative bias temperature instability

In spite of 50 years of history, there is still no consensus on the basic physics of Negative Bias Temperature Instability. Two competing models, Reaction-Diffusion and Defect-Centric, currently vie for dominance. The differences appear fundamental: one model holds that NBTI is a diffusion-limited process and the other holds that it is reaction-limited. Basic issues of disagreement are summarized and the main controversial aspects of each model are reviewed and contrasted.