On the transit time of polysilicon emitter transistors

Abstract

Polysilicon emitter transistors are now being widely used in high speed bipolar circuits because of their extremely low emitter transit time τ E. A model has been developed here to predict the relative contributions of the neutral polysilicon and monosilicon regions of the emitter to τ E, for various device parameters. Studies have been made for both uniform and exponential doping profiles in the mono-emitter region. Relative contributions of τ E and base transit time τ B towards the total forward transit time τ F for various device parameters have also been studied.