Revisiting the Vertical Superjunction in SiGe HBT Performance Optimization

We numerically investigate a new asymmetric superjunction (SJ) collector profile implemented in the context of high-speed 90-nm silicon-germanium heterojunction bipolar transistors (SiGe HBTs). After reviewing past results on vertical SJ SiGe HBT collector design, we present a new SJ profile, which was generated using Bayesian optimization techniques. This new design provides improvements over both a standard collector profile and a standard SJ profile. The new profile provides a substantial increase in maximum cutoff frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{T}$ </tex-math></inline-formula>), with a slight increase in open-base-collector–emitter breakdown voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {BV}_{\text {CEO}}$ </tex-math></inline-formula>). Then, we demonstrate, via hydrodynamic (HD) simulations and numerically solving the Boltzmann transport equation (BTE), that the simulated results are physically grounded. Finally, we address control and manufacturing concerns.