Low-temperature operation of SiGe p-n-p HBTs

SiGe-base p-n-p transistors with good current gain (100-200) and high cutoff frequency (>50 GHz) were operated from room temperature down to 85 K with no degradation in either current gain or cutoff frequency. This demonstrates that proper device design can alleviate the performance degradation associated with the large valence-band discontinuity in the base-collector junction (valence-band barrier effects). A peak cutoff frequency of 61 GHz for V/sub bc/=2 V was obtained at 85 K compared to 59 GHz at 298 K.