Resonance phase operation of a SiGe HBT

A novel operation mode-the so-called resonance phase operation-is demonstrated using a SiGe HBT (hetero-bipolar transistor). Transit time effects and coherent transport lead by proper design of the transistor to a phase shift larger than π. In this resonance phase mode, a current gain above 0 dB is achieved at frequency bands well above the transit frequency. We have designed and fabricated SiGe HBTs in order to investigate the resonance phase effect at frequencies below 50 GHz due to easier measurement technique. The transistors were fabricated using a low-temperature process. They showed a rather high breakthrough voltage of up to 20 V. The RF measurement showed the typical HBT behaviour up to the transit frequency fT. At higher frequencies the current gain H21 rose again above 0 dB. We have thus demonstrated the existence of the resonance phase effect in a SiGe HBT.