Transmission line model of base spreading resistance at high currents

Abstract

The base resistance of a bipolar transistor at high currents has been analyzed using a transmission-line model and taking the current-crowding effect into account. A closed-form solution has been obtained and shows that the collector current dependency on V/sub B,E/ is proportional to exp(V/sub B,E//2V/sub T/). This ideology factor of 2 for collector current is usually attributed to conductivity modulation at high currents. Analysis shows that the current crowding can also contribute to the nonunity ideology factor. The analysis is in agreement with experimental results.<>