Transient avalanche oscillation of IGBTs under high current

Under high current, a new type of high frequency oscillation is found during the turn off of 3.3 kV IGBTs with trench gate structure. Measurements and simulations indicate that the avalanche generation and transit time effect of carriers within the IGBT leads to this oscillation. The transition time effect takes place during rise of collector voltage at turn-off, especially during the dynamic avalanche phase. The range of frequencies is at several 100 MHz. As the oscillation occurs only transiently, during dynamic avalanche, it is named - Transient Avalanche Oscillation (TA-Oscillation). Both the IMPATT- and PETT-mechanisms are found to be involved in the TA-Oscillation. Detailed investigations of the TA-Oscillation on a special development version of a 3.3 kV IGBT led to measures to suppress and avoid such an oscillation. A consequence of preventing this oscillation is proved as an improvement in robustness during turn-off.