The Influence of Parasitic Resistances on the f_T-Optimisation of High-Speed SiGe-HBTs

摘要

We study the influence of parasitic series resistances on the cut-off frequency of high-speed SiGe hetero-junction bipolar transistors. Due to coupling of the parasitic resistances with the internal collector-base capacitance significant extra delay time is introduced. This extra delay will cause saturation, or even a decrease, of f_T at higher collector doping levels. In addition, we study the optimisation of an n-cap emitter profile, which is only possible when the collector delay is reduced to a minimum, and the series resistances are properly included.