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On Correction of A Delay Value Using Ring-Oscillators for Aging Detection and Prediction

On-chip delay measurement in field is effective for aging detection and prediction of a logic circuit. On the other hand, circuit delay is affected by not only aging but also environment such as temperature and voltage. When comparing a value of measured circuit delay with another value measured in different time to check the progress of aging, we need to correct the measured delay value to allow a fair comparison by eliminating the influence of environmental variations from the delay values. In this paper, we propose a method to convert circuit delay values measured in field into ones measured under the same environment i.e., predetermined temperature and voltage condition. The proposed method, which employs a digital temperature and voltage sensor with ring-oscillators, uses not temperature and voltage values but ROs frequency in the sensor. Furthermore, we also introduce a calibration method for reducing correction errors due to process variation. In evaluation for TEG chips in 65nm CMOS process, the proposed method can improve the correction accuracy for from 83.91ps to 39.78ps. The corrected delay values correspond to 317-day of aging and the prediction accuracy improves 48-day compared with correction using temperature and voltage values.