Structure optimization of trench-isolated SiGe HBTs for simultaneous improvements in thermal and electrical performances

The current level in the modern high-speed SiGe heterojunction bipolar transistors (HBTs) continues to increase for operation speed enhancement, but the resultant self-heating and elevated junction temperature emerge as a growing concern for device reliability as well as performance. To address such thermal issues, the optimization of SiGe HBT structures to achieve simultaneous improvements in thermal and electrical performance is carried out in this study. As a foundation for the study, an Rth measurement method and a geometry-based fast analytic thermal model were first developed for trench-isolated SiGe HBTs. Based on the method and model, a set of device design points for lowered Rth without compromising the RF performance have been successfully proposed and experimentally verified on IBM's 200-GHz SiGe HBTs. The details of the proposed structures and acquired results will be described in detail in the paper. The results obtained in this study shed a light on the possibility of the simultaneous optimization of thermal and electrical performance of SiGe HBTs.