Realibility Assessment, Condition Monitoring and Lifetime Estimation of Silicon Carbide Mosfets
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The reliability of power semiconductors is a highly critical topic due to their widespread industrial applications such as aerospace, oil and gas, transportation, and power grid. In recent years, Silicon Carbide (SiC) MOSFET is proofed to be a strong alternative to conventional Silicon-based counterparts. Being a relatively new device type with limited field data and potential uncertainties, SiC MOSFET should be investigated from reliability and ruggedness aspects exhaustively to guarantee the long-term robustness of SiC-based power electronic systems. This dissertation comprehensively evaluates commercial SiC MOSFETs’ reliability under various accelerated lifetime tests, develops on-board condition monitoring circuits, and proposes lifetime estimation solutions. An overview of SiC MOSFET aging mechanisms and up-to-date accelerated lifetime tests is first presented as a guideline for accelerated aging and aging assessment tests. By means of various accelerated lifetime tests, SiC MOSFETs are aged under different electrical, thermal, and mechanical stress patterns, and their corresponding aging mechanisms are investigated. Specifically, high electric field tests, active channel gate bias tests, and widely adopted power cycling tests are employed to trigger the device’s degradation at both chip and package levels. Throughout the tests, SiC MOSFETs are characterized by static electrical parameters and switching transients. Further, the device’s aging impact on system-level performance is evaluated. Under the light of evaluated aging precursors, on-board condition monitoring methods are proposed, developed, and implemented. In terms of SiC MOSFET lifetime estimation, a MATLAB toolbox is designed and developed based on the system mission profile. By using the device’s electro-thermal model and lifetime model, the accumulated damage and estimated consumable lifetime of certain SiC MOSFET is extrapolated. This dissertation intends to comprehensively study reliability issues of SiC MOSFETs from both aspects including test for reliability and design for reliability.