A procedure for characterizing the BJT base resistance and Early voltages utilizing a dual base transistor test structure

The pinched-base extraction technique is investigated in detail. The separation of extrinsic and intrinsic base resistances utilizing the dependence of these resistances on transistor geometry is discussed. Uncertainties in extracted parameter values and deviations between nominal and real device geometry are shown to be two major problems associated with separation of the base resistance components. Also, the use of the extracted resistances in compact transistor modeling for circuit simulation is discussed. It is shown that the intrinsic base resistance obtained using the pinched-base technique does not necessarily translate directly into a compact model parameter. The dual base test structure used for resistance extraction is also used for extraction of the voltage dependent Early voltages. In contrast to previous methods which require the extrinsic base resistance, the method presented here does not require this parameter which, as shown here, can be difficult to extract. By using the new extraction method on transistors with different emitter widths, it was observed that the Early voltages decrease as the emitter width is increased and saturates at some value for very wide emitters. An explanation to the observed behavior, supported by device structure simulations, is also given.