High-level injection influence on the high frequency performance of polycrystalline silicon emitter bipolar transistors

Abstract

This paper reports high-level injection influence on the high frequency performance in the polycrystalline silicon emitter bipolar transistors. Under high-level injection, the transconductance is not proportional to collector current. From the analysis, both the base resistance and the cutoff frequency are functions of terminal voltage, i.e. applied bias, and the maximum oscillation frequency is also a function of terminal voltage. By comparing these results obtained from the self-consistent high-level injection model considering injected charge storage (i.e. injected electron and hole concentrations comparable to doping concentrations in the base and emitter region) and base resistance with those results obtained from models which neglect the injected charge storage effect and/or the base resistance, it is found that both the injected charge storage effect and the base resistance must be considered to get accurate aforementioned device parameters.