Implications of Burn-In Stress on NBTI Degradation

Burn-in is accepted as a way to evaluate ageing effects in an accelerated manner. It has been suggested that burn-in stress may have a significant effect on the Negative Bias Temperature Instability (NBTI) of subthreshold CMOS circuits. This paper analyses the effect of burn-in on NBTI in the context of a Digital to Analogue Converter (DAC) circuit. Analogue circuits require matched device pairs; NBTI may cause mismatches and hence circuit failure. The NBTI degradation observed in the simulation analysis indicates that under severe stress conditions, a significant voltage threshold mismatch in the DAC beyond the design specification of 2 mV limit can result. Experimental results confirm the sensitivity of the DAC circuit design to NBTI resulting from burn-in.