Short Circuit Ruggedness of New Generation 1.2 kV SiC MOSFETs

Abstract

New generations of silicon carbide (SiC) based MOSFETs are commercially available from manufacturers featuring smaller chip size with higher power density demonstrating performance improvement compared to their previous generation counterparts. As the size of the chip is small, the volume available to dissipate energy during short-circuit (SC) like conditions is reduced, leading to increased self-heating of the device. Therefore, the short circuit withstand time (SCWT) is reduced. As a reliability aspect, ruggedness to extreme operating conditions like SC needs to be analyzed for these devices, to improve the design or to design better detection and protection circuits for these MOSFETs when used in specific SC vulnerable applications. In this work, the new third generation 1.2 kV SiC MOSFET from Wolfspeed in a TO-247-4 pin package having a smaller chip size is measured for SC ruggedness. The causes for device failure under different DC-link voltages, gate bias voltages, SC pulse durations and self-heating behavior are analyzed based on the destructive SC tests performed. The device is measured to have an SCWT of 2 µs at a DC-link voltage of 800 V compared to SCWT of 4.5 µs for the second generation 1.2 kV devices with larger chip size and TO-247-3 pin package. The presence of the Kelvin source contact demonstrates higher peak SC currents compared to the same devices without Kelvin source.

Time-Resolved Short Circuit Failure Analysis of SiC MOSFETs

“…In the event of a short circuit, the high power density quickly leads to extreme temperatures. This rapid heating above 1000 • C leads to an often catastrophic failure within less than 10 µs at typical operating voltages [1]. It also makes understanding the process difficult, as any measurement needs to be very fast.…”

Investigation of Repetitive Short Circuit Stress as a Degradation Metric in Symmetrical and Asymmetrical Double-Trench SiC Power MOSFETs

“…The dc-link voltage is selected to be lower, which is 400 V, since the purpose is to extend the cycle to observe the degradation patterns and avoid destructive failure. The SC time is chosen to be 10 µs, the typical required time for Si IGBT [12], [13]. For each cycle, the period is set to be 5 s to enable enough time to dissipate the heat.…”

Review of Methodologies for Evaluating Short-Circuit Robustness and Reliability of SiC Power MOSFETs

“…Upon that happening, three terminals are shorted, and the surface of the die is expected to change significantly. For example, in [93], [117], a visible burn mark has been seen at the source pad, and in [118], [119], a cross-sectional image of the damaged die has revealed severe damages within the SiC material. In [30], observation with a scanning-electron microscope (SEM) has also confirmed the wide melting of the aluminum layer above the source pad of a 1200V die burdened by thermal runaway.…”