Optimization of characteristics related to the emitter-base junction in self-aligned SEG SiGe HBTs and their application in 72-GHz-static/92-GHz-dynamic frequency dividers

Characteristics related to the emitter-base junction of self-aligned selective-epitaxial-growth SiGe heterojunction bipolar transistors (HBTs) were optimized for use with a highly-doped base. The thickness of the Si-cap layer affected both the emitter-base junction concentration and space-charge width, so the dc and ac characteristics of the SiGe HBTs were in turn dependent on this thickness. With a 4×10¹⁹-cm^-3 boron-doped base, a 131-GHz cutoff frequency and ECL gate-delay time of 5.4 ps were achieved for the optimized SiGe HBTs. A static frequency divider with a maximum operating frequency of 72.2 GHz and a dynamic frequency divider with a maximum operating frequency of 92.4 GHz were developed for optical-fiber link and millimeter-wave communication systems of the future.