I'm anodically bonding a 0.5 mm silicon wafer to a 0.5 mm Pyrex 7740 glass wafer. My silicon wafer has a thick layer of oxide on its surface, and because it this insulating layer requires a high voltage to produce a strong bond. The setup that I constructed is illustrated below (using 1800-2000V now rather than 900V), and consists of the two wafers sandwiched between two graphite plates that act as anode and cathode. The breakdown voltage for Pyrex 7740 glass is 13 MV/m, or 6500V for a 0.5 mm thick wafer. However, once the voltage gets to around 1800V, I begin to hear an electrical fizzing noise coming from inside the oven. When bonding is finished, I see hundreds of tiny pits all over the glass surface, the same as when you hit glass with an arc of electricity. This never happens at 900V, just at the higher voltages. Can someone explain why this might be happening? I'm not an electrical engineer, nor an expert on electronics by any stretch of the imagination.