Breakdown-Voltage Degradation Under AC Stress of Thick SiO2 Capacitors for Galvanic Insulation

High-voltage dielectric breakdown of thick amorphous silicon-dioxide capacitors for galvanic insulation have been recently investigated showing a significant difference under dc and ac stresses. The impact-ionization generation is expected to be the dominant mechanism for thicknesses from about 1 to
${15} \mu \text{m}$
. Significant degradation of the breakdown voltage is observed for ac stress, which requires a focused TCAD-based investigation to fully understand the involved physical mechanisms. Accurate TCAD predictions of the measured leakage current allow us to validate the proposed model gaining a detailed understanding of the device breakdown regime.