SiGe HBTs With Normal High-Speed Emitter-Up and Reverse Low-Power Collector-Up Operation

SiGe heterojunction bipolar transistors (HBTs) are usually optimized to obtain best performance in the forward operation mode. In this paper, we demonstrate that a simultaneous excellent performance in the reverse mode of operation can be obtained as well. A f_T / f_max combination of 50/100 GHz is obtained, which is, to our knowledge, the best value reported for a Si-based HBT operating in the reverse mode. This excellent performance is analyzed and explained by studying the different delay components of the device in the reverse operation mode. It is shown that the extrinsic SiGe base region plays a crucial role. Additionally, good low-power performance in the reverse operation mode is obtained as well, which is attributed to a reduction in the device parasitic contributions. The simultaneous availability of a high-speed performance in the forward mode and a low-power performance in the reverse mode offers additional flexibility to optimize circuit performance in terms of speed, power, and area.