An experimental and numerical study on the forward biased SOA of IGBTs

Thermal and electrical destructions of n-ch 600 V punchthrough type IGBTs in F.B.SOA are investigated by experiments and simulations, The cause of the thermal destruction is the thermal disappearance of built-in potential of p-n junction between the n⁺ emitter and the p base of the IGBT integral DMOSFET occurring at the critical temperature of ~650 K. Experiment and simulation results for the critical temperature show a good agreement. The cause of the electrical destruction is impact ionization at the n^- drift/n⁺ buffer junction in addition to the n^- drift/p base junctions. That triggers a positive feedback mechanism of increasing IGBT integral pnp transistor current which causes the device to lose gate controllability. The experimentally obtained critical power dissipation is ~2000 kW/cm². This value is ten times greater than BJTs. It was also found that emitter ballast resistance (EBR) plays an important role in describing the F.B.SOA of IGBTs