The effect of the hole current on the channel inversion in trench insulated gate bipolar transistors (TIGBT)

Abstract

It has been found that the hole current flowing vertically through the MOS substrate of a Trench IGBT (TIGBT) contributes significantly to a reduction in channel resistance. Compared to a classical IGBT the potential developed by the hole current is distributed in the p region, which acts as the substrate for the MOS, in parallel with the channel and no longer gives rise to the latch-up of the cathode junction. An analytical model which includes the effect of the potential distribution in the MOS substrate on the carrier inversion in the channel is presented. Numerical simulation and analytical modeling demonstrate a positive feedback effect created by the hole current which improves the I-V characteristics of the TIGBT. The analysis has been extended for different doping profiles of the (ftp) base. In the case of a diffused p layer with a Gaussian profile the physical behaviour of the MOS channel in the presence of a substrate current has been found to be different from a classical MOS channel