Electrical Characteristic Investigation On SiC Power MOSFET

SiC MOSFET which is made of the third generation WBG semiconductor-Silicon Carbide-is gradually replacing Si IGBT in the high-power facility of EV,HEV,photovoltaic inverter and locomotive traction,etc.owing to its unique performance such as higher breakdown voltage,higher frequency,lower switching loss and the ability to work under high temperature and irradiation.In recent years,the commercial products of SiC MOSFET are booming.The products cover from the rated breakdown voltage from600V to 1700V.In order to gain a better understanding of the dynamic characteristics of SiC MOSFET,two dynamic experimental platforms were designed and built in this paper,the planar type and the new double-trench type of SiC MOSFET with the same rated voltage,current and R_on is compared through experiments.Further investigations and analyses are carried through Sentaurus TCAD simulations.The dynamic characteristics including switching characteristic and robustness of 1200V SiC MOSFET are studied in depth in this paper,which has guiding significance for design and application of SiC MOSET.Firstly,a double-pulse switching platform for 1200V SiC MOSFET is designed and built.Waveforms and switching losses of two types of SiC MOSFETs were studied under different load voltage,load current,gate resistance and gate turn-off voltage.The results show that the larger gate resistance can suppress the oscillation caused by parasitic parameters but also significantly reduce the dv/dt and di/dt thus increasing the switching loss.Furthermore,the more negative turn-off voltage can reduce the turn-off loss.Under different experimental conditions,the switch-on losses of the trench type MOSFETs are close to that of the planar type MOSFETs,while the switch-off losses of the trench type MOSFETs are greater than that of the planar type MOSFETs.The effects of three lumped parasitic inductance and the parasitic capacitance on the switching characteristics of SiC MOSFET are simulated and analyzed.The result indicates that the common source parasitic inductance L_s increases the total switching loss.L_d of the power loop intensifies the oscillation of the drain-to-source voltage and current.L_g of the gate loop has the least influence on switching loss and the oscillation of waveforms.The parasitic inductance C_j has the greatest influence on the drain-to-source current overshoot and undershoot during the switching transient.Secondly,an unclamped inductive switching platform for 1200V SiC MOSFET is designed and built.Avalanche capability and the static electrical characteristics of both the planar and the trench type SiC MOSFET is assessed through UIS test under three different loads.The single avalanche energy of the planar and the trench type MOSFET under the load of 3.6mH is 0.91J and 0.32J,respectively.The avalanche energy decreases as the load decreases.The failure mechanism of both SiC MOSFETs is revealed and analysed through experiments and TCAD simulations.The planar type SiC MOSFET is invalid by the source metal melting caused by the lattice temperature soaring.For the trench type SiC MOSFET,new failure behaviors and mechanism different from those of planar type ones are uncovered:The trench type SiC MOSFET is invalid by the breakdown of the gate oxide layer at the bottom and corner of the trench.