A Critical Review of Techniques for the Experimental Extraction of the Thermal Resistance of Bipolar Transistors from DC Measurements—Part III: Approaches Exploiting the Base Current

This work constitutes Part III of a comprehensive three-part study that critically reviews techniques for the indirect extraction of the thermal resistance in bipolar transistors using simple DC current/voltage measurements. While Part I focused on thermometer-based methods and Part II examined approaches relying on intersection points between characteristics, this paper mainly investigates techniques exploiting the base current. Their accuracy is assessed by applying them to DC electrothermal characteristics obtained through circuit simulations of an in-house transistor model incorporating nonlinear thermal effects and comparing the extracted thermal resistance data with the formulation embedded in the model. An InGaP/GaAs HBT and a Si/SiGe HBT for high-frequency applications are considered as case studies. The analysis highlights the accuracy, advantages, and limitations of the examined approaches, discussing the impact of theoretical approximations and physical mechanisms. In addition, the analytical method proposed by Menozzi et al. is critically evaluated within the same simulation framework. Overall, the results show that none of the examined techniques provides a universally applicable, straightforward, and robust extraction procedure, since each involves theoretical assumptions and/or practical constraints that restrict its range of validity, numerical robustness, or ease of application. Finally, the findings from all three parts of this study are summarized, and practical guidelines are provided to support the selection and correct application of extraction techniques.