This paper presents the first investigation of the physical origins of the observed variable proton tolerance in multiple SiGe HBT BiCMOS technology generations. We use the combination of an extensive set of newly measured proton data on distinct SiGe HBT BiCMOS technology generations, detailed calibrated 2-D MEDICI simulations for both the SiGe HBT and Si CMOS devices, as well as reverse-bias emitter-base and forward-bias electrical stress data to aid the analysis. We find that the scaling-induced increase in the emitter-base electric field under the spacer oxide in the SiGe HBT is primarily responsible for the degraded radiation tolerance with technology scaling, while the decrease in shallow-trench thickness is largely responsible for the improved nFET radiation tolerance with technology scaling.

An investigation of the origins of the variable proton tolerance in multiple SiGe HBT BiCMOS technology generations