DC extraction of the base and emitter resistances in polysilicon-emitter npn BJTs

Abstract

Five DC techniques of extracting the base and emitter resistances of polysilicon-emitter npn bipolar junction transistors (BJTs) are presented and compared. The five techniques include three previously published techniques and two new techniques, constant base current and IB–IE plane fitting. Application of the five methods to a 0.8 × 16 μm2 npn BJT shows that all but the method of impact ionization yield comparable Rc and Rbb values at high currents. The impact ionization method, which extracts Rc and Rbb in the impact ionization region and at low base currents, yields markedly different Rc and Rbb values, indicating that the values of the parasitic resistances depend on the current range over which the extraction is performed. Thus the choice of which method is best to use depends on the current range over which Rc and Rbb are to be measured, and the validity of the assumptions used in the method when applied to the device.