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A Low Loss Trench IGBT with Variable Doping Layer in P-base for Improving Turn-off Capability

A low loss trench Insulated Gate Bipolar Transistor (IGBT) with n-type variable doping layer (VDL) buried in P-base is proposed. Firstly, in the central of the cell between two gates, the VDL is thin and lightly doped. It can be fully depleted during the off-state thus clamping the potential of the floating-P region at a low value, avoiding premature breakdown caused by the layer introduced in P-base. Secondly, the doping concentration of VDL increases steadily towards the gate to form high hole barrier. Therefore, it enhances the conductivity modulation effect and obtains low forward voltage drop (VON). Lastly, due to the different hole barrier formed by VDL, hole current path can be modulated. Fewer holes flow underneath the N+-emitter thus suppressing dynamic latch-up during the turn-off process. Numerical simulation results show that, under the same VON, the turn-off loss (Eoff) can be reduced by 57% and 26% compared with the Carrier Stored Trench-Gate Bipolar Transistor (CSTBT) and the advanced IGBT structure which features super body layer (SBL), respectively. By finely design the doping concentration gradient of the VDL, the turn-off capability can be improved by 117% compared with that of SBL-IGBT.