n-MOS Transistor Impact Ionization Boosted by Cumulative Stress Degradation in a 250-nm SiGe BiCMOS Technology

We introduce experimental observations of impact ionization in an n-type MOSFET of a 250 nm SiGe BiCMOS technology when operated under an aging test setup at room temperature. As expected, the electrical basic parameters of the transistor, such as drain current drivability, transconductance, and threshold voltage degrades following a power law. However, impact ionization measured as bulk current enhances as degradation evolves with stress time. Through numerical simulations we prove that impaction ionization gets boosted because an enhancement of the longitudinal electric field peak at the drain side, where most of the hot carriers are generated.