Novel method to determine base resistance in SiGe HBT HICUM based on rational function fitting

An accurate and efficient base resistance (R_B) extraction methodology for SiGe HBT HICUM model is developed in this paper. Differing from previous methods, the proposed technique is based on the rational function fitting. Two formulas are used to determine the lower and upper limits of R_B, and then R_B is confined to a very narrow range and can be estimated analytically only from S-parameter data, without any special structures or numerical optimization. The proposed method is successfully applied to SiGe HBTs with different device geometries. Results demonstrate that the average error for extracted R_B is less than 2.5% over a wide range of bias points. Therefore, we believe that the proposed technique is a reliable routine applicable to estimation of the base resistance for SiGe HBT HICUM model.