Investigation on safe-operating-area degradation and failure modes of SiC MOSFETs under repetitive short-circuit conditions

Abstract

• Repetitive short circuits cause thermal runaway failure of SiC MOSFETs • Safe operating area reduces after repetitive short-circuit conditions • Repetition frequency and duration affect degradation of SiC MOSFETs • Hole traps in gate oxides induce degradation of SiC MOSFETs The safe operating area is an operating area with high reliability for SiC MOSFET, and its degradation may cause power electronic system failure. The safe-operating-area degradation and the failure modes of 1200V/66A SiC MOSFET caused by repetitive short-circuit stress with different short-circuit times and short-circuit time intervals are investigated. A short circuit test platform with circuit protection is configured to degrade DUT(device under test), and the safe operating area is characterized after repetitive short circuit stress is applied. The degradation mechanism of the safe operating area is explained by the 1-D electro-thermal coupling model based on Sentaurus TCAD. When the critical short-circuit duration is 12μs, the single short-circuit failure mode of DUT with 400V dc-bus voltage is a gate-source short-circuit failure. From the short circuit test result, the failure modes under repetitive short-circuit conditions include gate-source short-circuit failure and thermal runaway, depending on the repetitive short-circuit time intervals. For the same short-circuit time interval, when the short-circuit duration is 10μs, the weakest boundary of the safe operating area is the blocking voltage. When the short-circuit duration is 2μs, all three boundaries of the safe operating area are contracted. These results are confined to 400V dc-bus voltage, 25°C case temperature, and 18V/-3V gate-source voltage. Schematic diagram of the degradation of the safe operating area of the device under long-term operating conditions. (a) Small margin, failure (b) Large margin, high cost (c) Optimal design