Modeling mixed-mode DC and RF stress in SiGe HBT power amplifiers

The degradation of SiGe HBTs due to mixed-mode DC and RF stress (simultaneous application of high current and voltage) has been modeled for the first time. State-of-the-art 200 GHz SiGe HBTs were first characterized, and then DC and RF stressed. Using TCAD simulations and calculations based upon a reaction-diffusion model, the excess base current due to stress was modeled as a function of the stress current and voltage. This physics-based stress model was then designed as a sub-circuit in Cadence, and incorporated into a cascode SiGe PA design to predict the DC and RF stress-induced excess base current. Predicted degradation is in agreement with RF stress results.