A Study of the Influence of Technology on the Negative Gate Capacitance in 1.2kV IGBTs

Due to the widespread usage of 1.2kV IGBTs for low and medium voltage applications, for the first time, this paper investigates the influence of technology on the instability effect of negative gate capacitance (NGC) in IGBT technologies - NPT (non punch-through), PT (punch-through) and FS (field stop). Due to the high density of plasma during forward conduction the p-channel inversion layer formed at the gate oxide/N-drift interface, acts as a low resistance path for holes to flow to the emitter contact. This induces negative charge on the gate electrode and NGC is said to occur when dQ_G/dV_G becomes negative. NGC can influence turn-on and short circuit performance of an IGBT due to accumulation of holes under the gate oxide at high anode voltages. This paper attempts to explain why the FS is the optimum IGBT technology in terms of NGC performance. Moreover, it is shown that the level of gate voltage overshoot can be correlated with N-drift potential under the gate oxide, due to hole- accumulation within the induced p-channel.