An analytic expression for the HBT extrinsic base-collector capacitance derived from S-parameter measurements

Abstract

Direct extraction is the most accurate method for the determination of equivalent-circuits of heterojunction bipolar transistors (HBTs). However, previous work lacks an exact expression for the extrinsic base-collector capacitance, which models the distributed nature of the base. This paper gives the derivation of an exact expression for this capacitance. As a result, each intrinsic equivalent-circuit parameter is determined using a simple exact expression at each measured frequency. The expression is valid for both the hybrid- /spl pi/ and the physics-based T-topology equivalent circuits. Extraction results for InP- and GaAs-HBTs are given.