Negative bias temperature instability: Recoverable versus permanent degradation

The analysis of negative bias temperature instability (NBTI) conventionally focuses on the stress phase where features like the power-law exponent, the temperature-dependence, and saturation of the observed threshold voltage shift have been extensively studied. As soon as the stress is removed, however, relaxation sets in, restoring at least some of the degradation. Although some studies on the relaxation phase have been presented, few authors have acknowledged the importance of the relaxation phase as a means of deepening our understanding of NBTI. We present a detailed analysis of NBTI relaxation, show that even at lower stressing voltages a permanent/slowly relaxing component is present, and demonstrate how this initially less dominant component might eventually determine the device lifetime.