A Robust On-Chip Sensor for Online Monitoring of BTI-Induced Aging in Integrated Circuits

Bias Temperature Instability(BTI) is an aging phenomenon in MOS transistors which is increasingly becoming one of the critical concerns for reliability of analog, digital and mixed-signal circuits, especially in deeply scaled technologies. This paper presents a robust integrated sensor that allows for the direct monitoring of the BTI-induced threshold voltage change of MOS transistors that have been subjected to stress. We achieve this by comparing a MOS transistor or device-under-test(DUT) which is stressed and is likely to suffer from BTI aging with a reference MOS device for which measures have been taken to ensure that it experiences negligible aging during its lifetime. The mixed-signal nature of the proposed sensor architecture allows for a direct physical-to-digital conversion of the BTI-induced threshold voltage change, as well as, fast measurements which is crucial because of the recovery effects of BTI. We also discuss a potential use case of proposed sensor for the online monitoring of an analog circuit.