Simulation and modeling of the low-frequency base resistance of bipolar transistors and its dependence on current and geometry

The current and geometry dependence of the low-frequency base resistance of high-speed bipolar transistors was investigated by means of quasi-three-dimensional numerical device simulations. It is shown that the total base resistance can be separated into a current- and geometry-dependent internal part and an only geometry-dependent external part. Both of these parts can be accurately approximated by simple analytical formulas which are well suited for compact transistor modeling. The investigations are based on sheet resistances and dimensions the values of which are typical for self-aligned double-polysilicon technology