Improved 2-D regional transit time analysis for optimized scaling of SiGe HBTs

A new method for two-dimensional (2-D) regional transit time analysis in SiGe HBTs is presented, using a commercially-available TCAD suite with hydrodynamic device simulations. The quasi-static 2-D transit time analysis is first used to determine the cutoff frequency of a well-calibrated 200 GHz SiGe HBT and then applied to the design of hypothetical SiGe HBTs with peak cutoff frequencies of 375 GHz and 450 GHz. These results are benchmarked against full frequency-domain simulations. The new regional analysis is then demonstrated at each scaling node and used to illuminate the 2-D nature of the onset of the Kirk effect and heterojunction barrier effect. These techniques enable the cutoff frequency and transit time components to be determined at lower computational complexity and in greater detail than traditional frequency-domain simulations, and are very useful for optimized scaling.