Methods for Determining the Emitter Resistance in SiGe HBTs: A Review and an Evaluation Across Technology Generations

For the experimental determination of the emitter resistance of bipolar junction transistors and HBTs, many methods exist in the literature, which yield quite different results though. In this paper, the most widely used methods are reviewed and applied to SiGe HBTs of different technologies and generations, including different device types (i.e., high-speed and high-voltage transistors). First, the accuracy of the methods is evaluated based on simulated data using a compact model. Explanations for causes of observed inaccuracy or failure are given and discussed. Second, suitable methods are applied to experimental data. In both cases, the results are compared for a large variety of device sizes. This paper and its results provide insight into each method's accuracy; its application limits with respect to a technology, device size, and operating range; as well as its requirements in terms of equipment and extraction effort. A guideline for extracting the emitter resistance is also given.