On the Frequency Limits of SiGe HBTs for TeraHertz Applications

We report record f_max for a silicon-based transistor, and the first combined set of f₁+ f_max above one-terahertz for silicon-germanium heterojunction bipolar transistors (SiGe HBTs). Peak f_max of 618 GHz and f_rfloor of 463 GHz at 4.5 K (chuck temperature) were measured for a scaled 0.12 times 2.5 mum-SiGe HBT (343 / 309 GHz at 300 K), at a breakdown voltage BV_CEO of 1.62 V (1.70 at 300 K), yielding a record f_T x BV_CEO product of 750 GHz-V (510 GHz-V at 300 K). An examination of base transport in these devices at low temperatures suggests non-equilibrium effects are operative.