An investigation of fT and fmax degradation due to device interconnects in 0.5 THz SiGe HBT technology

In this paper, the authors investigate the impact of device interconnect parasitics on the two most commonly-accepted RF small-signal figures-of-merit, the transit frequency (fT) and the maximum frequency of oscillation (fmax) in state-of-the-art SiGe HBT technology. Simulations and measurement results are provided as a guideline to design an optimum device interconnect scheme to achieve a high fmax. Test structures were characterized with de-embedding structures providing reference planes at the device level and at the top-metal level. Measurements show an fmax of 450 GHz at the device level and at the top-metal level a degradation of only 4% to 430 GHz. These results demonstrate a significant advantage of the SiGe HBT technology compared to ultra-scaled CMOS technology at device speeds approaching a terahertz, and to the best of the authors' knowledge, demonstrate the highest fmax reported at the top-metal level in any state-of-the-art silicon technology.