Principle of Operation

Figure A shows the cross-sectional structure of a conventional IGBT and the carrier distribution in the N-base region. The carrier concentration decreases monotonically across the N-base region from the collector electrode to the emitter electrode. In order to increase the collector-emitter voltage of an IGBT, a deep N-base region is necessary between the collector and emitter electrodes. However, a deep N-base region leads to an area with lower carrier concentration. The consequent increase in electrical resistance results in an increase in voltage drop and thus an increase in on-state voltage.

Figure B shows the cross-sectional structure of and the carrier distribution in an IEGT. The IEGT has an IGBT-like structure with deeper and wider trench gates than the IGBT. This structure increases the gate-to-emitter resistance, preventing carriers from passing through the emitter side. Consequently, carrier concentration is enhanced near the emitter electrode in the N-base region. As this phenomenon has the same effect as carrier injection and accumulation, it is called the injection enhancement (IE) effect. This trench-gate structure helps reduce an increase in voltage drop even at high collector-emitter voltage rating.