PhD Quentin MOLIN

“High Voltage SiC MOSFET Robustness study: threshold voltage shift and short-circuit behaviour”

This manuscript is a contribution to reliability and robustness study of MOSFET components on silicon carbide “SiC”, wide band gap semiconductor with better characteristics compared to silicon “Si” material. Those new power switches can provide better switching frequencies or voltage withstanding for example in power converter. SiC MOSFET are the results of approximately 10 years of research and development and can provide increased performances and weight to some converter topology for high voltage direct current networks.

Others power switches available are still introduced and an introduction to reliability is explaining why such work on this new power switches is important. Transition from Si technologies to SiC ones require a lot of work regarding its robustness.

Before showing reliability and robustness results is presented I give a lot of details regarding to the measurement and monitoring of key parameters used in the next chapters. The results of our tests on the threshold voltage instability are presented and how we validated an empirical model on this drift. This was used to propose an enhanced measurement protocol on the threshold voltage.

Static and dynamic experimental results presented next will show if the voltage drift during ageing is significant or not. Further analysis is proposed to add more insight on the understanding of the oxide degradation mechanisms through C-V and charge pumping measurements.

Finally, the ageing results presented on 1.7 kV SiC MOSFET are focused on the short-circuit and repetitive short-circuit behavior of the same components. Drain to source voltage influence on critical energy during this particular and stressful operation mode is studied. This time, the results are worrying.

The last chapter is confidential.

Thesis director: Hervé Morel