Design and Optimization of Base-Profile for the Thermal Stability of SiGe HBT Over Wide Temperature Range

To improve the thermal stability of curvent gain β and cut-off frequency f_T in SiGe heterojunction bipolur transistors(HBTs),the impacts of doping profile in the base of SiGe HBT with the box Ge profile on the temperature sensitivity of current gain β and cut-off frequency f_T are investigated firstly.It can be found that with the doping peak concentration in the base gradually approaching to the collector,β and f_T of HBT decrease slowly as temperature increases.Then the impacts of Ge profile across the base of SiGe HBT with the base peak concentration approaching to the collector on the temperature sensitivity of current gain β and cut-off frequency f_T are investigated.It can be found that reducing Ge fraction at the emitter end of the base and increasing grading of the Ge across the base can weaken the sensitivity of β to temperature,and reducing grading of the Ge across the base and increasing Ge fraction at the emitter end of the base can weaken the sensitivity of f_T to temperature.Based on these results,a novel segmented step box(SSB) Ge profile is proposed,which possesses modest β and f_T,and weak temperature sensitivity of current gain and cut-off frequency.