A new method to extract HBT thermal resistance and its temperature and power dependence

This paper introduces a new technique for the measurement of the thermal resistance of HBTs. The method is very simple, because it requires only standard dc I_C-V_CE measurements taken at different baseplate temperatures, but it is able to account for the dependence of the thermal resistance on both the baseplate temperature and the dissipated power (under the simplifying assumption that the thermal resistance increases linearly with the dissipated power). We have obtained and shown consistent results extracted from devices with an emitter area ranging from 90 μm² (1 finger) to 1080 μm² (12 fingers). The thermal-resistance values extracted with a standard and well-known technique are seen to fall inside the range of our results. We have also applied an alternative method that assumes a linear dependence between thermal resistance and junction temperature, and we have shown that both models lead to similar results, which points to the consistency and robustness of our extraction technique.