Design graphs for the intrinsic alpha cut-off parameters ωα, ωTandmof bipolar transistors

Abstract

Design graphs are developed for the intrinsic alpha cut-off frequencies ωα, and ωT, and for the excess phase m of bipolar transistors. The Kroemer equation giving the base transport factor in single-diffused transistors (constant aiding field in the base) is extended to cover double-diffused transistors (constant aiding and retarding fields in the base). The base retarding held is found to have an important degradation effect on the cut-off frequencies: a 2 kT/q retarding voltage extended along 20% of the base width diminishes ωα,to about half the value corresponding to a single-diffused transistor. A practical design criterion is given for optimizing the impurity-concentration profiles of double-diffused transistors.