Collector-up SiGe heterojunction bipolar transistors

SiGe heterojunction bipolar transistors (HBT's) in collector-up version hav e been built. This configuration has the advantage of a very low collector- base capacitance. In addition, because the substrate is the emitter, extrem ely low emitter series inductances may be achieved, e.g., in the case of pa ckaged discrete devices. This is particularly interesting for RF power ampl ifiers. Transistors fabricated on MBE-grown layers with an emitter size of 1.6 mu m showed near-ideal Gummel plots, de current gains of up to 485, an S-21 gain of 20 dB at 2 GHz and an f(max) of 33 GHz. A problem to be solved is the large parasitic C-BE capacitance which degrades the transit frequen cy.