Cryogenic Operation of Third-Generation, 200-GHz Peak-fT , Silicon–Germanium Heterojunction Bipolar Transistors

We present a comprehensive investigation of the
cryogenic performance of third-generation silicon–germanium
(SiGe) heterojunction bipolar transistor (HBT) technology.
Measurements of the current–voltage (dc), small-signal ac, and
broad-band noise characteristics of a 200-GHz SiGe HBT were
made at 85 K, 120 K, 150 K, 200 K, and 300 K. These devices
show excellent behavior down to 85 K, maintaining reasonable dc
ideality, with a peak current gain of 3800, a peak cut-off frequency
( ) of 260 GHz, a peak max of 310 GHz, and a minimum
noise figure (NFmin) of approximately 0.30 dB at a frequency of
14 GHz, in all cases representing significant improvements over
their corresponding values at 300 K. These results demonstrate
that aggressively scaled SiGe HBTs are inherently well suited
for cryogenic electronics applications requiring extreme levels of
transistor performance.