SiGe-HBTs with high fT at moderate current densities

Silicon-germanium heterojunction bipolar transistors (HBTs) have been developed with regard to high cutoff frequencies within a wide collector current range. Unity current gain frequencies f_T high as 116 GHz were obtained at a collector current density of 2×10⁵ A/cm². In addition, the FWHM of cutoff frequency f_T 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