Thermal stability of the power SiGe HBT with non-uniform finger length

A 20-finger power SiGe heterojunction bipolar transistor (HBT) with non-uniform emitter finger length is fabricated to improve the thermal stability. For comparison, a SiGe HBT with traditional uniform emitter finger length is also fabricated. The thermal resistance (R
th
) and the regression loci of two types of HBTs at different biases are measured and compared. Experimental results show that the thermal stability of the HBT with non-uniform emitter finger length is always superior to that of the uniform one over a wide biasing range. The ability to improve R
th
is strengthened from low to high collector current. At the same time, the power level for thermal regression is increases by 48.1%. Furthermore, the measurements of two-dimensional temperature profiles in two types of HBTs are performed to directly prove the improvement of the thermal stability and the peak temperature in the device with non-uniform finger length. Because of the decrease in peak temperature and the improvement of thermal stability, power SiGe HBT with non-uniform finer length can operate at higher bias and hence has higher power handling capability.