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Benefits of SiGe for by Charles W. Rodriguez, Manager,
SiGe is a process technology that introduces germanium into the base layer of an otherwise all-silicon bipolar transistor. IBM’s SiGe process technology works in concert with multilayer glass-ceramic packaging. SiGe creates significant improvements in operating frequency (fT up to 50 GHz), current, noise (1/f-noise corner frequency at 373 Hz), and power. The results are circuits with the speed of more esoteric and expensive technology, such as gallium arsenide, with the integration and cost benefits that come from silicon. To create the device properties of III-V heterojunction bipolar transistors (HBTs) using mature silicon process technology, germanium is selectively introduced into the base region of the transistor. With a smaller base bandgap, the SiGe produces a higher current gain than a Si device for the same base doping level. Doping the base more heavily lowers total base resistance even more. Germanium content can be graded across the base, introducing a carrier drift field that improves frequency response. The result is a faster device with improved frequency response and circuit delay. High-performance ATE benefits from SiGe because the technology lets designers build integrated chips with more functions. With SiGe technology, designers can develop systems with high-performance mixed-signal capability, low supply voltages, and low power.
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