Transit time of high-speed bipolar transistors in dependence on operating point, technological parameters, and temperature

The dependence of the transition time, tau /sub f/, of bipolar transistors on operating point, technological parameters (like thickness and doping concentration of the epitaxial collector) and temperature is investigated. A previously proposed analytical model for tau /sub f/ is extended to take temperature dependence into account. The critical collector current density, J/sub CK/, which defines the boundary to the high-current region, is an important quantity in the model. The physical background of the formulas for tau /sub f/ and J/sub ck/ are described, and their applicability within a wide range of parameters is demonstrated. The necessity for close-tolerance, thin, highly doped epitaxial collectors for future very-high-speed ICs is shown.<>