n-MOS transistor impact ionization boosted by cumulative stress degradation in a 250 nm SiGe BiCMOS technology

We introduce experimental observations of impact ionization boosting in n-type MOSFET of a 250 nm SiGe BiCMOS technology, when operated under aging test conditions. The electrical characteristics of the transistor, such as drain current capability, transconductance, and threshold voltage degrade with the stress time following a power law as expected. However, the impact ionization measured as the hot-carrier bulk current enhances with the aging process. By comparison with numerical simulations, we corroborate that such an impact ionization boosting is attributed to an enhancement of the longitudinal electric field at the drain side.