An Accurate Determination of Thermal Resistance of HBT Based on Pulsed Current I-V Measurement

A method to determine the thermal resistance (Rth) of HBT´s is proposed and presented in this paper. The principle of this method is based on the current gain (ß) decrease of HBT´s either from ambient temperature rise or internal DC power dissipation. The conventional pulsed I-V setup is modified to pulsed current I-V setup, where the input port of the device is stimulated by constant current rather than constant voltage. By using this setup, two main mechanisms causing the current gain decrease were effectively separated, which was not apparent in the previous methods. The proposed method was applied to find Rth´ s of various HBT´ s with different number of emitter fingers. The data agree very well with the predicted thermal resistances of larger emitter area devices by scaling with the total emitter area. Also the measurements with different pulse widths were employed to extract thermal time constant of HBT.