An Evaluation of Extraction Methods for the External Collector Resistance for InP DHBTs

The external collector resistance, while less important for the DC characteristics of a device, influences the RF behavior and associated figures-of-merit such as the power gain. From a modeling point of view, a badly chosen value for rCx often leads to wrong values for time constants or maximum junction capacitance values. Various methods have been published in the past that attempt to determine rCx as accurately and independently of other extraction steps as possible. However, a given method is often based on assumptions that are not valid for all technologies. This paper compares the most suitable methods specifically for InP DHBTs, using measured and simulated data for three different process technologies and relying on compact models for a fair comparison in terms of accuracy.