Influence of base resistance on extracting thermal resistance for SiGe HBTs

In this article, the influence of base resistance on extracting thermal resistance for SiGe heterojunction bipolar transistors is studied and an improved approach for determining the junction temperature and thermal resistance is presented. The proposed method for extracting thermal resistance is based on the temperature sensitivity of the base-emitter (B-E) voltage when the device is biased with a fixed emitter current density. This approach not only takes into account the self-heating during the different ambient temperature measurement but also revises the empirical equation of B-E voltage due to the influence of base resistance during the power dissipation increment measurement. Results are obtained for devices with different emitter lengths and fingers. Compared with the conventional method, the thermal resistance is about up to 15% improvement for the device with 0.3 × 1.9 μm ² emitter area and 13.8% for the device with 0.3 × 13.9 μm ² emitter area. The accurate thermal resistance implemented in HICUM model has resulted in better fit for transistor output characteristics.