Flashover performance of thin-wall spacers in field emission displays

This paper reports for the first time the electrical conduction and breakdown characteristics of thin-wall ceramic spacers bridging two thin-film electrodes, which represent the FEA cathode and the phosphor anode in a field emission display (FED). Techniques to set up a high aspect-ratio thin-wall spacer were specially developed, without use of glue. An extra-low light detection 3D-imaging system using an intensified CCD camera was developed which was able to identify the location of any light activity in the stressed vacuum-gap, indicative of imminent device failure. Thin wall spacers made of MACOR((R)) machinable glass ceramic, Wesgo AL-300 and Coors AD-96 Alumina, and Coors YTZP and AMZIROX Zirconia were extensively investigated in this study. SEM surface investigation showed that both Zirconia spacers exhibited a surface superior to all materials studied; however, their breakdown voltages were very low because of their large surface leakage current. The breakdown voltages of Alumina spacers were severely limited by a triple junction effect, either due to grain pullout or the machining method causing the absence of an intimate contact between the spacer and electrode. The results revealed a saturation phenomenon of breakdown voltage vs. vacuum gap spacing, which was due to the breakdown at the edge of the thin-film electrode (edge breakdown). The spacer breakdown voltage is expected to improve by eliminating the electrode edge-breakdown phenomenon. The results of this work are highly encouraging in that an similar to 1000 mu m tall spacer can support similar to 18 kV (DC), at least 80% above the expected operational voltage of high voltage FEDs. However, it is likely that the breakdown strength can degrade in the presence of electron bombardment from the field emitter array in an FED - a subject for future investigations in our laboratory.