Turn-off behaviour of high voltage NPT- and FS-IGBT

A simple but physical based one dimensional model is used to characterize the turn-off of high voltage IGBTs. The dependence of the overvoltage and the peak electric field on the gate driving conditions is analyzed. The transition from a triangular to a trapezoidal electric field has a major impact on the turn-off behaviour. If this transition occurs during the voltage slope, the dv/dt increases significantly. If the field-stop layer is reached during the current slope, the current snaps off which leads to a second voltage spike with a high absolute voltage but only a moderate peak field.