Effect of Ge composition on the ballasting resistor of RF power SiGe HBTs

摘要

A new expression for the thermal stability factor S of power HBTs is presented in this paper, considering the temperature dependence of collector saturation current. Based on the expression, the accurate minimum emitter ballasting resistance (REmin) of the HBTs that is necessary in the thermal stability condition is determined. It is found that for SiGe HBTs, the REmin decreases with the increasing operating temperature in the high temperature region due to the existence of Ge composition in SiGe base whereas for Si BJTs, the REmin increases monotonously with the operation temperature. Hence for high-temperature-operation SiGe HBTs, the additional emitter ballasting resistance can be decrease so as to minimize adverse effect of the ballasting resistance as possible. These results provide a good guide to design emitter ballasting resistance of power HBTs and high-temperature-operation HBTs.