FEOL/BEOL wear-out estimator using stress-to-frequency conversion of voltage/temperature-sensitive ring oscillators for 28nm automotive MCUs

We propose wear-out estimator of remaining lifetime, which consists of two types of custom ring oscillators (ROs) and cumulative stress counters only. This on-chip estimator operates independently without disruption of MCU main operations and is aimed for advanced automotive MCUs, which demand sufficient reliability and real-time response along with high performance in cutting-edge applications such as ADAS. One of the custom ROs is temperature sensitive RO, which achieves the count-up speed proportional to exp(-Ea/kT), thus enabling estimation of the accumulated electro-migration (EM) stress that the die has experienced thus far. The other RO is voltage and temperature sensitive RO, which achieves the count-up speed proportional to V n *exp(-Ea/kT) for use in TDDB stress estimation. The test chip of the custom ROs was fabricated by using 28nm HKMG process. The measured result successfully emulates more than one order of magnitude difference between 125C and 85C EM stress and 10× combinational accentuation of TDDB stress under simultaneous high voltage and temperature.