Substrate Current Based Avalanche Multiplication Measurement in 120 GHz SiGe HBTs

A new substrate current-based technique for measuring the avalanche multiplication factor (M - 1) in high-speed SiGe heterojunction bipolar transistors (HBTs) is proposed. The technique enables M - 1 measurement at high operating current densities required for high-speed operation, where conventional techniques fail because of self-heating. Using the proposed technique, M - 1 was measured up to 10 mA/mum(2) on SiGe HBTs featuring 120 GHz peak f(T) which occurs at J(c) about 7 mA/mum(2) Implications for circuit applications are also discussed.