InGaP/GaAs HBT Safe Operating Area and Thermal Size Effect

Deeply understanding HBT thermal characteristics and safe operating area (SOA) is critical to the improvement of the ruggedness and reliability of power amplifiers. In this work, we investigate the device size effect of SOA and thermal resistance by means of experimental measurement, analytical modeling and 3dimensional simulation. For HBTs with a factor of ten variations in emitter area, the SOAs are characterized under extremely high current density, and the thermal simulations are performed and the thermal resistances are measured with a thermal-electrical method. It is found that with increasing device size, the SOA in terms of current density shrinks and thermal resistance per unit area increases, which is demonstrated by both simulation and measurement.