Investigation on the Degradation Mechanism of Si/SiC Cascode Device Under Repetitive Short-Circuit Tests

The Si/SiC Cascode device has been widely accepted in various applications, however, its reliability issue still remains a major concern and needs to be extensively investigated. In this paper, the degradation of a 750 V Si/SiC Cascode device under repetitive short-circuit (SC) tests is investigated at 400 V DC-link voltage. Static and dynamic characteristics are measured before and after the repetitive SC cycles. As the SC cycle increases, the degradation of the device becomes gradually significant. By linking changes in electrical properties to metallization degradation, the physical mechanism of device degradation has been uncovered in depth. Experimental results show that the continuous stress under repetitive SC cycle leads to an increase in the on-state resistance of Si/SiC Cascode device. Finite-element-model (FEM) simulations show that due to the pad current crowding in the source region, the source Al metallization temperature of the SiC JFET rapidly increases to the melting point and undergoes reconstruction, resulting in a significant increase in the source Al metallization resistance. In addition, it is found by scanning electron microscopy (SEM) that the gate metal aluminum of SiC JFET chip also undergoes reconstruction, which is the reason for the degradation of the dynamic characteristics. The research in this paper will provide useful evidences for device manufactures to design Si/SiC Cascode device with high reliability.