Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 3) Second breakdown. <s> A rapid type of second breakdown observed in silicon n+-p-n-n+transistors is shown to be due to avalanche injection at the collector n-n+junction. Localized thermal effects, which are usually associated With second breakdown, are shown to play a minor role in the initiation of the transition to the low voltage state. A useful tool in the analysis of avalanche injection is the n+-n-n+diode, which exhibits negative resistance at a critical voltage and current. A close correspondence between the behavior of the diode and the transistor (open base) is established both theoretically and experimentally. Qualitative agreement with the proposed model is obtained for both directions of base current flow. It is shown that transistors having thin, lightly doped collector regions are particularly susceptible to avalanche injection, which suggests that some compromise may be necessary in the design of high-frequency power transistors. <s> BIB001 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 3) Second breakdown. <s> The internal failure dynamics of the insulated gate bipolar transistor (IGBT) for unclamped inductive switching (UIS) conditions are studied using simulations and measurements. The UIS measurements are made using a unique, automated nondestructive reverse bias safe operating area (RBSOA) test system. Simulations are performed with an advanced IGBT circuit simulator model for UIS conditions to predict the mechanisms and conditions for failure. It is shown that the conditions for UIS failure and the shape of the anode voltage avalanche sustaining waveforms during turn-off vary with the IGBT temperature, and turn-off current level. Evidence of single and multiple filament formation is presented and supported with both measurements and simulations. <s> BIB002 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 3) Second breakdown. <s> 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 IC- VCE 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. <s> BIB003
Second breakdown is a kind of local thermal breakdown for transistors BIB001 due to high current stresses, which can also happen to IGBTs during on-state and turn-off. The failure mechanism of second breakdown is as follows: with the increase of current, the collector-base junction spacecharge density increases, and the breakdown voltage decreases, resulting in a further increase in the current density. This process continues until the area of the high current density region reduces down to the minimum area of a stable current filament. Then, the filament temperature increases rapidly due to self-heating and a rapid collapse in voltage across IGBT occurs. This has been comprehensively simulated and measured in BIB002 . How to improve IGBT ruggedness at high current density and prevent second breakdown is still an interesting research topic BIB003 .