Measuring, modeling, and minimizing capacitances in heterojunction bipolar transistors

We demonstrate methods to separate junction and pad capacitances from on-wafer S-parameter measurements of HBTs with different areas and layouts. The measured junction capacitances are in good agreement with models, indicating that large-area devices are suitable for monitoring vendor epi-wafer doping. Measuring open HBTs does not give the correct pad capacitances. Finally, a capacitance comparison for a variety of layouts shows that bar-devices consistently give smaller base-collector values than multiple dot HBTs. Copyright (C) 1996 Elsevier Science Ltd.