Base-profile optimization for minimum noise figure in advanced UHV/CVD SiGe HBT´s

We investigate the base-profile design issues associated with optimizing ultrahigh vacuum/chemical vapor deposition (UHV/CVD) silicon-germanium (SiGe) heterojunction bipolar transistors (HBT´s) for minimum broad-band noise. Using the simulator for cryogenic research and SiGe bipolar device optimization (SCORPIO), the impact of Ge profile, base doping level, and base thickness on minimum noise figure (NF_min) are quantitatively examined across the -55°C-125°C temperature range. We introduce a novel Ge profile for optimum NF_min, which allows independent control of current gain (β) and achieves maximum f_T while maintaining thermodynamic stability. Simulations show that this profile can achieve a β of ~200, a peak f_T>50 GHz, a peak f _max>60 GHz, and an NF_min<0.5 dB at 2 GHz and <1 dB at 10 GHz using a conservative base width of ~90 nm. We predict that a 45-nm base-width/0.5-μm emitter-width device with a thermodynamically stable flat Ge profile, manufacturable using an UHV/CVD growth technique, should be able to achieve an NF_min<0.4 dB at 2 GHz and ~0.8 dB at 10 GHz along with a β of ~300, a peak f_T>70 GHz, and a peak f_max >90 GHz. These 300-K performance values improve as the temperature is reduced