Investigation on the Breakdown Failure in Stripe Trench-Gate Field-Stop Insulated Bipolar Transistor With Low-Saturation Voltage

In this paper, we designed a 1.5-kV trench-gate field-stop IGBT (FS-IGBT) and its on-state saturation voltage, which is smaller than 1.6 V. However, during the avalanche test, when the current limiting value of the tester is large, we have found a breakdown failure phenomenon in the designed IGBT structure although the breakdown voltage in the termination is higher than that in the cell region. The failure mechanism is investigated. It is illustrated that a filament is triggered due to some hole carriers, which can flow beneath the trenches from the cell region and then accumulate in the transition region if the trenches are ending at the deep p- well region in the termination, which is different from that in the VDMOS. To improve the avalanche reliability, a new termination structure with segregated deep p-well regions and the isolated trench is proposed and verified by numerous measurements. This paper has a significant meaning for the design of the termination of the trench-gate FS-IGBT with very low saturation voltage.