Modeling and characterization of SiGe HBT low-frequency noise figures-of-merit for RFIC applications

We present the first systematic experimental and modeling results of noise corner frequency (f_C) and noise corner frequency to cutoff frequency ratio (f_C/f_T) for SiGe heterojunction bipolar transistors (HBTs) in a commercial SiGe RF technology. The f_C and f_C/f_T ratio are investigated as a function of operating collector current density, SiGe profile, breakdown voltage, and transistor geometry. We demonstrate that both the f_C and f_C/f_T ratio can be significantly reduced by careful SiGe profile optimization. A comparison of the f_C and f_C/f_T ratio for high breakdown and standard breakdown voltage devices is made. Geometrical scaling data show that the SiGe HBT with A_E=0.5×2.5 μm² has the lowest f_C and f_C/f_T ratio compared to other device geometries. An f_C reduction of nearly 50% can be achieved by choosing this device as the unit cell in RF integrated-circuit design.