Toward Understanding the Wide Distribution of Time Scales in Negative Bias Temperature Instability

Abstract

Difficulties with evaluating Negative Bias Temperature Instability (NBTI) are linked to fast effects occurring at microsecond or possibly faster time scales. The wide distribution of time scales involved in NBTI relaxation suggests participation of some sort of dispersion in the underlying NBTI mechanism. A universal behavior of the relaxation is observed and used to benchmark several models incorporating dispersion. The impact of the boundary condition on the model based on dispersive transport is also briefly discussed. Furthermore, on-chip circuits are designed and fabricated to measure the effect of AC NBTI up to 2 GHz on individual devices. The results on both single pFET's and inverters indicate that AC NBTI is independent of the frequency in the entire 1 Hz - 2 GHz range. This suggests that any characteristic time scale of the NBTI mechanism must be below 1 ns.