Analysis of NBTI effects on high frequency digital circuits

This paper analyzes some of the secondary effects in estimating negative bias temperature instability (NBTI) induced threshold voltage shift on high frequency digital circuits. Therefore, a circuit model is developed to be used for statistical estimation of the threshold voltage shift. Making use of this model as well as technology computer aided design (TCAD) and SPICE simulations, a methodology is developed to estimate NBTI induced threshold voltage shift. Simulation results reveal that commonly made assumptions on digital circuits, such as: square signal assumption and ignorable effect of drain bias, may yield overestimation of the NBTI induced threshold voltage shift by more than 10% after five years of operation, which may lead to a severe underestimation of a circuit's reliability.