Key criteria for the short-circuit capability of IGBTs

Abstract

Short-circuit behavior and capability are investigated and optimized during IGBT development. Thereby, knowledge about destruction and high-frequency short-circuit oscillation mechanisms is needed. For the thermal destruction mechanism, filaments are formed shortly before destruction during the thermal runaway itself, whereas for the electrical destruction mechanism strong current filaments are formed by an electrical mechanism, before the self-heating in the filaments leads to a thermal runaway. At low collector-emitter voltages, weak non-destructive filaments exist for a large current range. For both the filament formation and short-circuit oscillations (SCOs), an electric-field peak in the field-stop layer and a quasi-plasma layer beneath the MOS cells are mandatory. For SCOs, which are caused by a periodic storage and release of charge carriers inside the device, additionally, a weak electrical field at the beginning of the drift zone is necessary. Weak, non-destructive filaments and SCOs are likely to occur simultaneously. An increase of the bipolar current gain reduces the operating area with SCOs and increases the electrical short-circuit capability. A simultaneous reduction of the thermal short-circuit robustness can be avoided by advanced p-emitter concepts or (over-)compensated by an improved thermal setup.