SiGe-HBTs with high <i> f _T </i> at moderatecurrentdensities

Abstract

Silicon-germanium heterojunction bipolar transistors (SiG-HBTs) have been developed with regard to high cutoff frequencies within a wide collector current range. Unity current gain frequencies fT as high as 116 GHz were obtained at a collector current density of 2 × 105 A/cm2. In addition, the FWHM of cutoff frequency fT against collector current exceeds one and a half decades. Calculations indicate that the ratio of the collector to emitter area essentially determines the current density range of a high frequency HBT.