IGBT negative gate capacitance and related instability effects

For high collector voltages, Insulated Gate Bipolar Transistors (IGBTs) exhibit a negative gate capacitance. In this condition, a p-channel inversion layer is formed on the N-base surface. The positive charges in the p-channel induce negative charges in the MOS gate electrode. This results in a negative gate capacitance. As a consequence of this negative capacitance, IGBT operation is inherently unstable, leading to current redistribution between cells or even chips