Extrapolated fmax of heterojunction bipolar transistors

TitleExtrapolated fmax of heterojunction bipolar transistors
Publication TypeJournal Article
Year of Publication1999
AuthorsVaidyanathan, M., and D. L. Pulfrey
JournalElectron Devices, IEEE Transactions on
Pagination301 -309
Date Publishedfeb.
Keywordsbase resistance, collector-base junction capacitance, common-emitter unity-current-gain frequency, dynamic resistance, effective base-resistance-collector-capacitance product, extrapolated fmax, extrapolation, general time constant, heterojunction bipolar transistors, parameter estimation, parasitic collector resistance, parasitic emitter resistance, semiconductor device models

It is shown that the extrapolated fmax of heterojunction bipolar transistors (HBT's) can be written in the form f max= radic;fT/8 pi;(RC)eff, where fT is the common-emitter, unity-current-gain frequency, and where (RC)eff is a general time constant that includes not only the effects of the base resistance and collector-base junction capacitance, but also the effects of the parasitic emitter and collector resistances, and the dynamic resistance 1/gm, where gm is the transconductance. Simple expressions are derived for (RC) eff, and these are applied to two state-of-the-art devices recently reported in the literature. It is demonstrated that, in modern HBT's, (RC)eff can differ significantly from the effective base-resistance-collector-capacitance product conventionally assumed to determine fmax


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