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 ΔVth varied according to the drain bias Vd, during the measurement of drain current Id. The depletion length Ldep into the channel was calculated based on a particular Vd value and the channel doping concentration. Ldep was used to extract the channel edge region length Ledge, then the center channel region length Lcen was obtained by subtracting Ledge from the gate length Lgate. We proposed an equation that uses Ldep, Lcen, Ledge and degree of ΔVth variation to calculate ΔVth according to Lgate while the p-MOSFET is under NBTI stress. Equation estimates of ΔVth at different Lgate were similar to measurements.