Variability in Total-Ionizing-Dose Response of Fourth-Generation SiGe HBTs

Statistical analysis is performed on the totalionizing-dose (TID) response of fourth-generation silicon-germanium heterojunction bipolar transistors, revealing an increasing variance in base current with increasing dose. A 10-fold increase is observed after 2 Mrad(SiO ₂ ) of radiation exposure. The postirradiation performance is shown to be poorly correlated with initial performance, revealing potential difficulties for radiation hardness assurance testing. Simple analytical theory is used to demonstrate how TID exacerbates performance variations due to preexisting process-induced variations. Then, technology computer-aided design (TCAD) simulations are used to investigate the fundamental mechanisms driving these statistical changes, particularly process variations associated with the doping profiles. Simulation results reveal potential methods to both predict TID response and mitigate it at the process level. Finally, implications for hardness assurance testing and radiation-tolerant device and circuit design are discussed, especially the need to consider postirradiation variability in the design process for radiation-intense applications.