Technology Scaling Effect on the Relative Impact of NBTI and Process Variation on the Reliability of Digital Circuits

The impact of negative bias temperature instability (NBTI) on circuit reliability is typically assessed without accounting for the variability associated with the manufacturing process. With technology progression, manufacturing process variability scales more aggressively than transistor NBTI lifetime. Hence, a clear link between transistor and circuit reliability that takes variability into account is imperative to analyze circuit reliability. We propose a figure of merit termed fall-out to describe the proportion of circuits whose frequencies would exceed the initial manufacturing distribution. We use fall-out to assess NBTI and process variability in tandem, and we show that the fall-out of circuit frequency (or timing delay) peaks and diminishes as technology scales. We propose that the fall-out of a ring oscillator can be used as a worst-case indicator of circuit reliability in any given technology.