On the frequency limits of SiGe HBTs for TeraHertz applications
Yuan Jiahui, Ram Krithivasan, et al.
BCTM 2007
We present a detailed examination of the dc design considerations associated with optimizing epitaxial Si- and SiGe-base bipolar transistors for the 77 K environment. Transistors and circuits were fabricated using four different vertical profiles, three with a graded-bandgap SiGe base, and one with a Si base for comparison. All four epitaxial-base profiles yield transistors with dc properties suitable for high-speed logic applications in the 77 K environment. The differences between the low-temperature dc characteristics of Si and SiGe transistors are highlighted both theoretically and experimentally. We discuss the profile design constraints of epitaxial Si and SiGe-base devices that are unique to low-temperature operation. In particular, we identify a performance tradeoff associated with the use of an intrinsic spacer layer to reduce parasitic leakage at low temperatures and the consequent base resistance degradation due to enhanced carrier freeze-out. In addition, we provide evidence that a collector-base heterojunction barrier effect severely degrades the current drive and transconductance of SiGe-base transistors operating at low temperatures. Due to its thermally activated nature, this SiGe-barrier effect is important at low temperatures even when unobservable at room temperature. © 1993 IEEE
Yuan Jiahui, Ram Krithivasan, et al.
BCTM 2007
Maurizio Arienzo, James H. Comfort, et al.
ESSDERC 1992
John D. Cressler, James H. Comfort, et al.
IEEE Electron Device Letters
Anuj Madan, Jiong Jiong Mo, et al.
RADECS 2009