Capacitive effects in IGBTs limiting their reliability under short circuit

The short-circuit oscillation mechanism in IGBTs is investigated in this paper by the aid of semiconductor device simulation tools. A 3.3-kV IGBT cell has been used for the simulations demonstrating that a single IGBT cell is able to oscillate together with the external circuit parasitic elements. The work presented here through both circuit and device analysis, confirms that the oscillations can be understood with focus on the device capacitive effects coming from the interaction between carrier concentration and the electric field. The paper also shows the 2-D effects during one oscillation cycle, revealing that the gate capacitance changes according with the shape of the electric field due to the charge distribution in the n-base. It has been identified that the time-varying capacitance leads to parametric oscillations together with the stray gate inductance, which limit the reliability of the IGBT.