Analysis and modeling of a digital CMOS circuit operation and reliability after gate oxide breakdown: A case study

A CMOS ring oscillator circuit is observed to operate even after a number of its FET's have undergone a hard gate oxide breakdown. The first breakdown is identified with emission microscopy and statistical tools to most likely occur in the circuit's nFET's. A physical model and an equivalent electrical circuit for an nFET after hard gate oxide breakdown are constructed and used to confirm the understanding of the impact of FET gate oxide breakdown on the ring oscillator. The observations are generalized to conclude that, provided stable soft breakdowns are the only gate oxide failures occurring at operating conditions, large parts of digital CMOS circuits will be unaffected by these failures.