Ion beam induced charge (IBIC) studies of silicon germanium heterojunction bipolar transistors (HBTs)

SiGe HBTs are strong candidates for space communication applications because of their resistance to total dose effects and their overall high performance. However, they seem to be sensitive to single event upsets (SEUs). These devices were designed using deep trench isolation geometry to reduce charge collection due to ion hits outside the active area. Using four electrode (base, emitter, collector, and substrate) IBIC measurements at the Sandia Nuclear Microprobe Facility, we found that the largest fraction of the induced charge occurred on the collector and on the substrate; significantly less induced charge was found on the base electrode, and practically no induced charge was detected on the emitter. These devices showed a very well defined, high charge collection area enclosed by the deep trench. There was a sudden drop of induced charge at the trench but a long tail was present outside of the active area extending several tens of microns. The charge collection mechanisms inside and outside of the deep trench will be discussed and first results of Time Resolved IBIC in SiGe HBTs will be presented.