Thermal Performance Characterization of Multi-Finger Si/SiGe Heterojunction Bipolar Transistors Considering Parallel-Mode Heat Spreading

In this work, the thermal performance of multi-finger SiGe Heterojunction Bipolar Transistors (HBTs) implemented in a 0.13 µm BiCMOS9MW process is analyzed through coupled semiconductor–Heat Transfer in Solids (HTS) simulations in COMSOL Multiphysics. Devices with emitter counts ranging from one to twelve fingers are studied to quantify the influence of parallel-mode heat spreading on self-heating. The extracted results indicate a significant reduction in total thermal resistance RTOT, from approximately 1.13 × 104 K/W for a single-finger layout to 4.64 × 103, 2.53 × 103, and 1.36 × 103 K/W for three-, six-, and twelve-finger configurations, respectively. This improvement corresponds to a decrease in peak junction temperature from 467 to 440 K, 428, and 414 K. The effective heat transfer coefficient h0 also exhibits a clear dependence on emitter geometry, varying from 2.28 × 107 W K–1 m–2 for a single finger to 1.85 × 107, 1.69 × 107, and 1.58 × 107 W K–1 m–2 for the three-, six-, and twelve-finger layouts. Furthermore, the analysis highlights that central emitter fingers undergo higher temperature rises due to mutual thermal coupling, which can impact device reliability. The findings provide practical guidelines for the thermal optimization of high-frequency SiGe HBT layouts in advanced BiCMOS technologies.