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Ring Oscillators (RO) have traditionally been utilized to assess the effect NBTI transistor degradation on operating frequency. RO stress results are difficult to interpret for technologies with metal gates and high-k dielectrics, since the circuit degrades from both NBTI in PFETs and PBTI in NFETs. We have successfully designed and tested specialized circuits that separate the contribution of each BTI mechanism on RO frequency degradation. Because of their simplicity, these structures are suitable for early learning in the development cycle.