Experimental Detection and Numerical Validation of Different Failure Mechanisms in IGBTs During Unclamped Inductive Switching

The physics of the different failure modes that limit the maximum avalanche capability during unclamped inductive switching (UIS) in punchthrough (PT) and not PT (NPT) insulated-gate bipolar transistor (IGBT) structures is analyzed in this paper. Both 3-D electrothermal numerical simulations and experimental evaluations support the theoretical analysis. Experimental results for UIS test show that, at low time duration (or inductance value) of the test, the UIS limit moves from energy limitation to current limitation. While the energy limitation is well known, the current-limited failures are less studied. In this paper, the current limit for UIS test is analyzed in detail, and the cause is attributed to a filamentary current conduction due to the presence of a negative differential resistance (NDR) region in the I_C- V_CE curve in breakdown. The filamentary current conduction locally increases the current density causing early device latch-up and possible device failure at a current much lower than the one dictated by energy limitations. The physical parameters that affect both the onset of NDR region and the failure current are discussed for both an NPT trench IGBT structure with a local lifetime control and a PT trench IGBT structure with a field-stop layer.