Base-region optimization of SiGe HBTs for high-frequency microwave power amplification

The base-region optimization of SiGe power heterojunction bipolar transistors (HBTs) for high-frequency microwave power amplification is investigated. It is found that employing a heavily doped base region in conjunction with a high Ge content of proper profile can effectively improve the large-signal power-gain values of SiGe HBTs while maintaining their high breakdown voltages and thus allow them to be efficiently operated with high power at higher microwave frequencies. More importantly, with such a base-region optimization, not only lateral-scaling requirements can be relaxed but also a common-base configuration for power amplification using these devices can be favored, which further enhances the power-gain values of SiGe power HBTs at high frequencies. Load-pull experimental results are presented to show the highest figure-of-merit power performance of SiGe power HBTs with an optimized base region. The power performance of SiGe power HBTs operated at X-band with different base-region designs was also compared to illustrate the significant benefits that result from the base-region optimization.