Extraction of DC base parasitic resistance of bipolar transistors based on impact-ionization-induced base current reversal

A new method for the evaluation of the dc base parasitic resistance of bipolar transistors is described. The method is based on impact-ionization-induced base current reversal and enables the base resistance to be evaluated independently from the emitter parasitic resistance in a wide range of emitter current and collector-base voltage, without requiring any special device structure. The method can also extract the base resistance in impact-ionization regime, where current crowding due to negative base current induces an increase in base resistance at increasing emitter current.