Investigation of Continuous Turn-Off Characteristics of IGBT Devices Under Overload Conditions

This study investigates the repetitive overload turn-off behavior of a 1200 V/15 A trench field-stop IGBT using a clamped inductive load circuit. The DC-link voltage is set to 600, 800, and 1000 V, while the external circuit configuration and the 2 ms pulse interval remain unchanged. The displayed sequences at 600 and 800 V exhibit no destructive failure. Under the 1000 V condition, 24 of 30 devices fail, and the cycle-to-failure ranges from 6 to 27. Before failure, the peak VCE, turn-off current, and Eoff reach 1248.1 V, 80.2 A, and 12.87 mJ, respectively. During the final destructive event, VCE first recovers to approximately 1.16 kV and then collapses toward zero, while IC re-grows to approximately 106.8 A. A statically validated two-dimensional simulation model shows pulse-to-pulse temperature accumulation, mobility reduction, expansion of the high-field and impact-ionization regions, and persistence of an electron-rich transport path near the trench-gate active region. Post-failure SEM reveals a filament-like damage trace, emitter-side Al damage, damaged trench-gate structures, and contiguous multi-cell ablation. The combined evidence indicates that repetitive heating progressively strengthens the coupling among carrier transport, electric-field concentration, avalanche generation, current localization, and self-heating, which leads to delayed localized electrothermal instability. An auxiliary RC-IGBT comparison further confirms that the repetitive overload turn-off boundary depends on the device technology and operating conditions.