Reliability monitoring ring oscillator structures for isolated/combined NBTI and PBTI measurement in high-k metal gate technologies

Ring oscillator (RO) structures that separate NBTI and PBTI effects are implemented in a high-k metal gate technology. The measurement results clearly show significant RO frequency degradation from PBTI as well as NBTI. For comparison, RO structures with the same principle are also implemented in a SiO 2 /poly-gate technology, where PBTI is negligible. Experimental results show noticeable frequency degradation under NBTI-only stress mode but negligible degradation under PBTI-only mode, which illustrates the validity of the proposed principle and structures.