Small-signal modeling of the lateral NQS effect in SiGe HBTs

Detailed formulations for DC and AC emitter current crowding are presented in view of developing an extended π-equivalent circuit (EC) model to accurately predict the lateral non-quasi-static effects in silicon germanium heterojunction bipolar transistors. Under negligible DC current crowding, the EC reduces to a simple π-model. The implementation-suitable versions of the models are also developed. Compared to state-of-the-art model formulations, the extended π-model shows better accuracy in predicting device simulated data. If desired, the high level of accuracy obtained by the extended π-model can be traded with the required extra simulation time due to one extra node.