Theoretical analysis and modeling of bipolar transistor operation under reversal base current conditions

A two-dimensional theoretical analysis of bipolar transistor operation under reversal base current conditions is presented. This model describes the current crowding effect occurring when the device is biased above the open-base breakdown voltage BVCEO, also known as the “pinch-in” effect. In addition, the model clarifies, for the first time, the physical origin of instability phenomena occurring under common-base operating conditions. Closed form analytical relations are derived for the conditions which define the onset of instability under forced-VBE and forced-IE conditions. Finally, we present a simple analytical model for the base current- and geometry-dependence of the base resistance. This model is suitable for being incorporated into BJT compact models to properly describe device operation above BVCEO.