Reverse Active Operation of 200 GHz SiGe HBTs

The analysis of the HBTs operating in the reverse active mode ("reverse mode" for short), with emitter and collector terminals swapped, has largely been ignored until recently (Khater et al., 2004). However, it is important to understand the device behavior in the reverse mode because these high-performance HBTs can operate inadvertently in the reverse mode under certain circuit-relevant conditions. Moreover, in historically important merged-transistor logic (MTL) or integrated injection logic (I
²
L), the npn bipolar transistors are intentionally operated in the reverse mode to achieve high gate density (Berger et al., 1972). The reverse mode operation of 0.12 times 1.0 mum
²
SiGe HBTs in a 200 GHz technology (Jagannathan et al., 2002) is investigated in this work, including, for the first time, the reverse mode ac characteristics. The schematic cross-section of the 200 GHz SiGe HBTs featuring raised extrinsic base is shown