Frequency dependence of NBTI in high-k/metal-gate technology

In this paper, frequency dependency of the Negative Bias Temperature Instability (NBTI) in a wide frequency range (10kHz ~ 500MHz) is investigated using on-chip test structure. The designed test structure allows measurement in AC and DC mode. Statistically meaningful AC/DC lifetime ratios are extracted after accelerated reliability stress and show a non-monotonic behavior. Random Telegraph Noise (RTN) trap analysis of a single defect is also carried out which reveals that trap located near interface with time constant 10^-10~10^-4s are responsible for such behavior. A model from trap occupancy of individual defects point of view is also proposed to justify with plausible reasons the non-monotonic behavior of AC/DC ratio in wide frequency range.