Partial Discharge Characteristics of SiO₂/Si₃N₄ Electret Incorporated AlN Substrates

Partial discharge (PD) is one of the main reasons for the degradation of dielectric material and insulation of power semiconductors and systems they drive. Subsequently, it is a challenge for the electrification of transportation systems, including ships. In recent years, electret, which can generate an electric field without an external voltage source, has been used to mitigate PD. Research on electrets shows fabricating and using electrets to counteract locally concentrated high electric fields and mitigate PD under recurrent, steep voltage pulses generated by wide bandgap (WBG) power semiconductors. In most of the studies that used electret material to mitigate PD, it was coated on a metal substrate. However, in our study, we used a thin 520-nm SiO2/Si3N4 double-layer electret on a ceramic substrate made of aluminum nitride (AlN) instead of metal. PD was measured under steep square voltage pulses with slew rates as high as 131.25 V/ns and at temperatures as high as $180~^{\circ }$ C. We measured PD magnitude and PD inception voltage (PDIV). The results indicate that AlN substrates coated with SiO2/Si3N4 thin-film electrets can reduce PD magnitude and increase PDIV in harsh electrical and thermal conditions.