J. Phys. IV France 08 (1998) Pr3-95-Pr3-98
Extraction of collector-base resistance of UHV/CVD SiGe HBTs operating at low temperaturesU. Gogineni, G. Niu and J.D. Cressler
Alabama Microelectronics Science and Technology Center, Department of Electrical Engineering, 200 Broun Hall, Aubum University, Aubum AL 36849, U.S.A.
The neutral base recombination (NBR) induced collector-base resistance (rµ) determines the upper limit of the output resistance attainable with the cascode configuration in analog design. We present here the extraction of the collector-base resistance in cryogenically operated SiGe HBTs using a new general purpose equivalent circuit. The new equivalent circuit is better suited for devices with significant NBR where rµ is comparable to ro. A general technique for extracting rµ in terms of the ac voltage-drive and the ac current-drive Early voltages is proposed which facilitates measurement and circuit modeling. Measurements on state-of-the-art SiGe HBTs indicate that the rµ/ro ratio decreases with cooling because of an increase in the ratio of the two Early voltages.
© EDP Sciences 1998