Physics‐Based Electro‐Thermal Modeling and Analysis of Self‐Heating Effects in 55‐nm SiGe HBTs

This work investigates spatially resolved electrothermal behavior in scaled SiGe HBTs under self‐heating conditions, emphasizing its impact on temperature distribution and RF performance. Unlike conventional lumped thermal resistance approaches assuming uniform temperature rise, the present analysis resolves the internal temperature field to capture nonuniform heat propagation effects. A physics‐based electrothermal framework combining drift–diffusion transport, temperature‐dependent semiconductor properties, and heat conduction equations is used to study hotspot formation and thermal confinement in a 55 nm SiGe HBT structure. Three operating conditions are considered: nominal operation at 300 K, self‐heating at 300 K ambient temperature, and elevated ambient temperature of 320 K. The results reveal localized hotspot formation near the base–collector junction due to current crowding and geometrical confinement, leading to RF performance degradation. The cutoff frequency decreases from 320 to 285 GHz, while the maximum oscillation frequency reduces from 486 to 458.5 GHz. The current gain decreases from 2000 to 1500, and the maximum junction temperature reaches 417 K under the highest thermal stress condition. These findings highlight the importance of spatial thermal effects in governing RF limitations of SiGe HBTs and provide insight into the coupling between heat propagation and electrical performance in BiCMOS technologies.