Transistor design and application considerations for >200-GHz SiGe HBTs

SiGe HBT transistors achieving over 200 GHz f_T and f_MAX are demonstrated in this paper. Techniques and trends in SiGe HBT design are discussed. Processing techniques available to silicon technologies are utilized to minimize parasitic resistances and capacitances and thereby establish raw speeds exceeding III-V devices despite the higher mobility in those materials. Higher current densities and greater avalanche currents, which are required for establishing such high performance, are discussed as they relate to device self-heating and reliability and the degradation of the devices. Simple circuit results are shown, demonstrating 4.2-ps ring-oscillator delays.