Improved Nonlinear Self-Heating Compact Modeling in SiGe HBTs Using Mextram

The linear and nonlinear SH models in the latest versions of Mextram are evaluated, with an emphasis on high-power biases and ambient temperature scalability. The Mextram nonlinear SH model is shown to have limitations in fitting high-power regions at all temperatures. An investigation of the dynamic thermal resistance r TH reveals that it is only a function of T junc , which limits the fitting capability of the current nonlinear SH model. A new nonlinear SH model is proposed based on analysis of the r TH characteristics to improve high-power region fitting at multiple ambient temperatures. The model is demonstrated on a SiGe HBT from −25 ◦ C to 125 ◦ C.