SiGe power HBT's for low-voltage, high-performance RF applications

Silicon-Germanium (SiGe) power heterojunction bipolar transistors (HBT's) are fabricated by using two or ten device unit cells with an emitter area of 5×0.5×16.5 μm2each. The large power transistor features 1 W RF output power at 3-dB gain compression, 3.5 V bias, and 2.4 GHz with a maximum power-added-efficiency (PAE) of 48% for class A/B operation. At a supply voltage of 1.5 V, the transistor delivers a 3-dB RF output power of 150 mW with a PAE of 47%. It is shown that a high collector doping level is advantageous for low-voltage operation. Further, by using special bias sense ports, the interconnect losses are found to degrade the device performance to a considerable degree.