Thermal simulation and design of GaAs HBTs

GaAs based hetero-junction bipolar transistors (HBTs) offer high speed and good device matching characteristics that are attractive for many high-speed circuits. However, thermal behaviors with multi-fingers can significantly affect HBTs performance. In this paper, three dimensional (3-D) finite-element modeling (FEM) approaches are built up to analyze the maximum temperature region and temperature distribution of GaAs based HBTs devices. The thermal performance for two different types of unit cell including the standard cell and emitter thermal shunt cell were simulated and compared. As a result of generated heat from emitter fingers transfers to the substrate through the metal bridge, unit cell with emitter thermal shunt reduced the junction temperature significantly. The thermal effects of metal bridge thickness and various substrate thermal conductivity values are also discussed.