Junction capacitance models of SiGe HBT

When SiGe HBT is in the case of normal operation, depleted approximation is not suited, and the influence of movable charge should be taken into account when c onsideri ng of their junction capacitance. Based on the analysis and study of the carr ier tr ansport of SiGe HBT, emitter junction capacitance model is developed by consider ing the carrier distribution, and the collector junction capacitance model is al so established for different current densities including base extending eff ect. The junction capacitance models are used to simulate frequency characteristics. The results of simulation show good agreements with the experimental data.