A practical method to extract the thermal resistance for heterojunction bipolar transistors

Self-heating of bipolar transistors can lead to a significant increase of their junction temperature. This must be correctly considered for accurate modeling and also to ensure reliability. Because of this, several measurement techniques for thermal resistance extraction were proposed in the literature. However, a drawback of most methods is that they require measurements at different ambient temperatures for each device. This is very tedious if a large number of different transistors must be investigated. Therefore, we present a new technique that allows extraction of the thermal resistance from simple measurements carried out at only one ambient temperature, based on previously determined technology-specific data. Moreover, as a byproduct, the emitter resistance is estimated. The validity of this method is demonstrated here for SiGe HBTs, but it has also been used successfully for GaAs HBTs.