Emitter series resistance from open-collector measurements influence of the collector region and the parasitic pnp transistor

The open-collector method for determination of the emitter series resistance in integrated bipolar transistors is analyzed. Existing models do not provide the accuracy required for a correct determination of the emitter series resistance. In order to accurately describe the saturation voltage, a set of model equations is derived that provides a more accurate description of the epitaxial collector region. The measured V-CE(I-E) characteristic is found to depend on the properties of the collector region as well as the parasitic substrate transistor. Using the model developed, a consistent description of measurement results for different bias conditions of the collector-substrate junction is possible. With this new understanding of the open-collector method, an improved procedure to extract the emitter resistance from measurement data is developed, and results of the method applied to integrated bipolar transistors are presented.