High‐performance Si/SiGe heterojunction bipolar transistors grown by molecular‐beam epitaxy

Si/SiGe heterojunction bipolar transistors have been fabricated by growing the complete layer structure with molecular‐beam epitaxy. The precise control of composition and thickness of the different layers have yielded excellent device performance with high Early voltage and current gains. The best measured transit frequency was 73 GHz. The low base sheet resistance of about 1 kΩ per square led to an fmax of 55 GHz. Noise figures were 1.2 dB at 2 GHz and 2 dB at 10 GHz. In a first application a hybrid mm wave 24‐GHz oscillator was built with a phase noise of -92 dB at 100 kHz off carrier.