The impact and implication of BTI/HCI decoupling on ring oscillator

In this study, a novel RO test structure is proposed and demonstrated to decouple the impact of BTI and HCI effect in RO degradation. The frequency dependence of RO degradation is also investigated with wide frequency range (5.5MHz to 700MHz). Detail characterizations of RO degradation revealed that the impact of NBTI on RO degradation is frequency independent. It is found that NBTI lifetime difference is prominent under different stress frequencies on discrete device. However, NBTI induced I_D degradation (ΔI_D) between sub-GHz range is not significant to show a notable frequency dependency feature. On the other hand, nHCI induced RO degradation increases monotonically as frequency goes higher. The more HCI degradation is in RO, the more notable frequency dependence of RO. Even though nHCI becomes severe under high bias, NBTI is still the dominant degradation mechanism of RO. Due to the huge recovery of NBTI, the frequency shift of RO is not as severe as we expected. It further implies time exponent failed to reflect the dominant degradation mechanism of RO.