Introduction: why are ceramic materials (when compared to organic materials) necessary for the purpose of electric isolation in power modules, especially for medium voltage applications

1. Comparison of dielectric properties of bare ceramic substrates (AlN, Al2O3, Si3N4 without metallization)

• Dielectric breakdown strength of ceramic substrates: impact of thickness and temperature (RT to 400°C)
• Broadband dielectric spectroscopy results
• Electrical conductivity in temperature (dc and surface potential measurement results)
• Conclusion: AlN ceramic is the most suitable material for medium voltage applications (when compared to other ceramic grades like Al2O3, Si3N4)

2. Dielectric properties of metallized AlN ceramic substrates

• Different ways to metallize AlN ceramic (DBC, AMB)
• Impact of metallization on electric field strength / dielectric breakdown (theory / simulation / measurement results)
• Conclusion: next to the ceramic material itself, the metallization has a significant impact on the dielectric properties of the substrates.

3.  Current development for medium voltage applications

• Partial discharge measurement methods in dynamic conditions (as already performed in the past for inductive loads). Open questions: can it be duplicated under high du/dt for ceramic substrates?? Is it possible? Does it make sense? Is partial discharge in ceramic substrate under high du/dt expected to be the main degradation mode in power module?
• Examples of possible new substrate materials for medium voltage applications
• Conclusion: still many efforts / activities are necessary both at academic and industrial levels but some technology solutions that could satisfy the needs / fulfil the requirements have been identified

4. Conclusion + outlook in future works (optional)

Olvier Mathieu, Lionel Laudebat, Zarel Valdez, Marie-Laure Locatelli, Sorin dinculescu, Hugo Reynes, Cyril Buttay