Physical framework for NBTI: Insight from ultra-fast switching measurement of NBTI recovery

Using an ultra-fast switching measurement method, the mechanism of NBTI recovery in the first few seconds after stress termination is systematically studied. Results show: (1) A component of the fast |DeltaVt| recovery increases with stress temperature; (2) the amount of |DeltaVt| recovery is (i) independent of stress time under a negative gate recovery voltage, but (ii) increases with stress time for a positive gate recovery voltage. These observations suggest the following physical framework for NBTI: (1) Dynamic balance of rapid inelastic trapping and detrapping of holes in a narrow energy band above Si valence band edge, which accounts for the fast recovery observed, independent of stress time and (2) generation of interface states and interfacial deep-level positive trap states (above Si mid-gap) which exhibit time-dependent recovery under a positive gate recovery voltage.