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For PMOSFET devices, negative bias temperature instability (NBTI) is a serious reliability concern. Because of recovery effects, careful stress and measurement methods must be used to determine threshold voltage degradation. These methods typically assume that mobility and subthreshold slope (SubSlp) degradation are minimal. Recent papers have pointed out that this assumption may not be valid. This paper discusses for the first time a unique fast-switching NBTI measurement technique that alternates between two VGS measurement conditions to determine the SubSlp versus stress time. From these measurements, the effect of SubSlp degradation on VT degradation can be accurately determined, and results are compared to the standard techniques.
Device and Materials Reliability, IEEE Transactions on (Volume:9 , Issue: 2 )
Date of Publication: June 2009