A TCAD-Based Analysis of Substrate Bias Effect on Asymmetric Lateral SiGe HBT for THz Applications

Abstract

In this work, a new asymmetric lateral silicon germanium heterojunction bipolar transistor (SiGe HBT) is proposed. This asymmetric structure allows one to modulate the carrier densities in the collector region by the application of substrate bias, which causes significant improvements in device performance. The open base breakdown voltage can be tuned from 2.2 to 3.6 V and the transit frequency ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <inline-formula> <tex-math notation="LaTeX">$ \textit{f}_{{\sf T}} $</tex-math> </inline-formula> </i> ) is improved up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 90% by varying the substrate bias. The bias-dependent variation in transit time is elaborately discussed using regional analysis. This work, for the first time, demonstrates an oscillation frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ \textit{f}_{\text{MAX}} $</tex-math> </inline-formula> ) of 2.7 THz achievable by tuning the substrate bias in an asymmetric silicon-on-insulator (SOI) lateral SiGe HBT.