Method to predict length dependency of negative bias temperature instability degradation in p-MOSFETs

Abstract

We propose a method to predict the length dependency of the magnitude of degradation caused by negative bias temperature instability (NBTI) stress applied to a p-MOSFET. Threshold voltage degradation ΔV th varied according to the drain bias V d, during the measurement of drain current I d. The depletion length L dep into the channel was calculated based on a particular V d value and the channel doping concentration. L dep was used to extract the channel edge region length L edge, then the center channel region length L cen was obtained by subtracting L edge from the gate length L gate. We proposed an equation that uses L dep, L cen, L edge and degree of ΔV th variation to calculate ΔV th according to L gate while the p-MOSFET is under NBTI stress. Equation estimates of ΔV th at different L gate were similar to measurements.