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Correlation between BTI-induced degradations and process variations by measuring frequency of ROs

We analyze the correlation between BTI (Bias Temperature Instability)-induced degradations and process variations. BTI shows a strong effect on highly scaled LSIs in the same way as the process variations. It is necessary to predict the combinational effects. We should analyze both aging-degradations and process variations of MOSFETs to explain the correlation. We measure initial frequencies and the aging-degradations of ROs (ring oscillators) of 65-nm process test circuits. The initial frequencies of ROs follow gaussian distributions. The degradations can be approximated by logarithmic function of stress time. The degradation at the “fast” condition of the variations has a higher impact on the frequency than the “slow” one. The correlation coefficient is 0.338. In this case, we can reduce the design margin for BTI-induced degradations because the degradation at the “slow” conditon on the variations is smaller than the average.