Analysis of Vₜₕ Variations in IGBTs Under Thermal Stress for Improved Condition Monitoring in Automotive Power Conversion Systems

Today, power conversion in automotive industry depends heavily on the reliable operation of insulated-gate bipolar transistors (IGBTs). Condition monitoring of IGBTs and reporting imminent faults to driver dashboard are critical for avoiding any fatal accidents. In this study, first, a comprehensive comparison is carried out between on-state collector-emitter drop (V_{ce,on}) with gate threshold voltage (Vₜₕ), as two reliable aging precursors. In order to enrich current understanding of IGBT aging prognosis, accelerated aging methods are applied under a wide variety of thermal stresses. Aging mechanisms and physical phenomena responsible for variation in both V_{ce,on} and Vₜₕ have been methodically investigated. These explanations are also supported by detailed failure analysis. Based on the extensive result sets for tested samples from different manufacturers with different structural types, it is found that V_{ce,on} show different trends at different stress levels, whereas under the same test conditions Vₜₕ provides more consistent and robust state-of-health information. Finally, an example experiment has been performed in which continuous V_{ce,on} measurements coupled with Vₜₕ information has been used to provide more insight about the device aging as well as faults in an automobile's sub-systems.