Microscopic Hot-Carrier Degradation Modeling of SiGe HBTs Under Stress Conditions Close to the SOA Limit

Abstract

We present and validate a physics-based model to describe the underlying mechanisms of hot-carrier degradation in bipolar transistors. Our analysis is based on a deterministic solution of the coupled system of Boltzmann transport equations for electrons and holes. The full-band transport model provides the energy distribution functions of the charge carriers interacting with the passivated Si-H bonds along the oxide interface. The simulation results assert the dominant role of hot holes along the emitter-base spacer oxide interface in the long-term degradation of an n-p-n SiGe heterojunction bipolar transistor under low and high-current conditions at the border of the safe-operating area. The interface trap density is calculated by incorporating an energy driven paradigm for the microscopic mechanisms of defect creation into a reaction-limited model with dispersive reaction rates. These interface traps increase the forward-mode base current via Shockley-Read-Hall recombination and degrade the overall device performance. The Gummel characteristics of a degraded device and time evolution of the excess base current for different stress conditions are verified versus the experimental data obtained for a state-of-the-art toward-terahertz SiGe HBT.