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/μm
²
on SiGe HBTs featuring 120 GHz peak f
_T
which occurs at J/sub C/ about 7 mA/μm
²
. Implications for circuit applications are also discussed.