Characterization of defects in aluminum nitride substrates through partial discharge measurements

Partial discharge (PD) characteristics in aluminum nitride (AlN) insulating substrates at sinusoidal and switched voltages have been investigated. The substrates were tested in silicone liquid. PDs we observed both at sharp edges of the copper conductor and inside the ceramic. Phase-resolved PD patterns at sinusoidal voltage were analyzed for both defects. Optical measurement with a photomultiplier tube (PMT) was used to characterize discharges occurring at the surface of the substrates at switched voltages. The average PD inception voltage (PDIV) at sinusoidal voltage counted 8.5 $\mathrm{kV}_{\mathrm{p}}$ in contrast to 5 $\mathrm{kV}_{\mathrm{p}}$ and 6 $\mathrm{kV}_{\mathrm{p}}$ at negative and positive unipolar square pulses respectively. As shown with bipolar pulse tests the PD inception was determined by the peak-to-peak voltage.