In high voltage direct current (HVDC) converters, a series connection of semiconductor devices is often used to achieve the desired blocking voltage. In such configuration, an unequal voltage sharing may drive one or more devices into avalanche breakdown, eventually causing the failure of the entire group of devices. This paper presents the experimental evaluation of SiC MOSFETs from different manufacturers operated in avalanche. A setup was developed to test the devices under such condition. The reliability of SiC MOSFETs have been compared. To correlate the experimental results with the failure mechanism, the MOSFETs were decapsulated to identify the failure sites on the SiC dies. Examination results show that for some tested devices, the failure occurs at the metallization source of the die, and results in a short circuit between all three terminals of the MOSFETs. Furthermore, it has been found that the parasitic BJT latch up and the intrinsic temperature limit are the main failure mechanisms for these devices.

The failure mode of press-pack-type packages dedicated to SiC devices is experimentally analyzed in order to investigate their use for HVDC applications. Single SiC Schottky diode samples have been submitted to short-circuit conditions and continuous current flow test. The samples have been then characterized with optical and scanning electronic microscopy. Results from the experiments reveal that the press-pack structure offers a short-circuit failure mode with SiC devices, as it does for Si devices. The metallurgy involved is, however, quite different. Cu, Ni, Ag or Al foils are found to be suitable interface material between the package and the die to achieve a stable a short-circuit failure mode, providing the die is properly attached to a substrate.

Reliability is one of the key issues for the application of Silicon carbide (SiC) diode in high power conversion systems. For instance, in high voltage direct current (HVDC) converters, the devices can be submitted to high voltage transients which yield to avalanche. This paper presents the experimental evaluation of SiC diodes submitted to avalanche, and shows that the energy dissipation in the device can increase quickly and will not be uniformly distributed across the surface of the device. It has been observed that failure occurs at a fairly low energy level (<0.3 J/cm²), on the edge of the die, where the electrical field intensity is the greatest. The failure results in the collapse of the voltage across the diode (short-circuit failure mode). If a large current is maintained through the diode after its failure, then the damage site is enlarged, masking the initial failure spot, and eventually resulting in a destruction of the device and an open circuit.

No abstract

No abstract