Modeling And Characteristics Study Of Silicon Carbide Bipolar Junction Transistors

Silicon Carbide(SiC) power devices have a better performance than Si in power electronic circuits. The SiC bipolar junction transistor(BJT) is a promising high voltage switching device, especially for high temperature environment. Compared to Si BJT, SiC BJT does not suffer from second breakdown. Compared to other bipolar devices, like IGBT and GTO, SiC BJT does not have the junction voltage needed to overcome in order to conduct current. Compared to other SiC devices, like SiC MOSFETs and SiC JFETs, SiC BJT have the advantage of no critical oxide and low on-resistance. Also the process complexity is reduced greatly as compared to SiC MOSFETs. Therefore, it is necessary to build a SiC BJT model to evaluate its potential utilization in converter systems.In this paper, the SiC BJT’s static and dynamic models have been developed based on fundamental working principles. It has been to use a mature Si BJT model to build the equivalent circuit for SiC BJTs. Considering the recombination of carriers at the surface and in the space-charge layer, two extra components should each be added to the base current. The capacitance model shows the dynamic characteristics of devices. In normal condition, both of the base-emitter junction and the base-collector junction are not forward biased heavily. Therefore, the capacitance model is based on the barrier capacitances due to the diffusion capacitances do not play a major role. The model parameters have been extracted from experimental plots at various voltage levels and temperatures. The modeling results are then implemented in a circuit simulator such as Saber to build a SiC BJT model. Validity of the model is confirmed by comparing the model with experimental static and dynamic characteristics.A SiC BJT model including quasi-saturation effects is proposed in this paper. The model limits the number of parameters required for the Gummel-Poon model. High voltage SiC BJTs have been developed as switches in power circuits. In these circuits, the device switches between the blocking state, while supporting the high collector voltage and the on-state with a low voltage drop at the quasi-saturation region. Accuracy modeling of the SiC BJT including the quasi-saturation region is very important for the switching characteristics in power circuits. In the model, quasi-saturation effects are accounted for by modeling the collector resistance which changes by voltage.