Influence of impact-ionization-induced instabilities on the maximum usable output voltage of Si-bipolar transistors

The onset of impact-ionization-induced instabilities limits the operating range of Si-bipolar transistors, especially in power stages. Therefore, analytical relations which characterize the onset of instabilities are derived for different driving conditions (mainly V_BE=const. and I_E=const.) and arbitrary transistor geometries. They allow the designer and technologist to calculate the maximum usable dc output voltage in dependence on transistor dimensions and technological parameters. As a consequence, the voltage range above BV_CE0 can now be more intensively and reliably used and thus the performance potential of a given technology can be better exploited. However, the reduction of the maximum tolerable output voltage with increasing emitter (or collector) current must be carefully considered. The presented theory and analytical results are verified by three-dimensional (3-D) transistor simulations and by measurements