Alternative field electron emission characteristics from graphite-insulator composite layers

A novel type of emitter for a FED, the pFED is being developed for the past ten years. This emitter is formed from micron-sized silica coated with a nano-scale silica insulator. Of the commercially available graphites tested, the best performance was obtained from a 6 mum grade material. When printing such a material a coverage of ~15% cannot be exceeded without forming large clusters that disrupt subsequent processing, thus limiting the density of potential emission sites. In addition, many flakes lie flat on the surface and are unlikely to contribute to emission. In order to improve the density of emitters a thick ink approach has been investigated where the flakes are supported in a mixture of nanoparticle silica (or other insulating particles such as TiO₂ or Al₂O₃) and submicron graphite. The resulting structure is some 1-2 mum thick with the graphite flakes and the underlying cathode connected by a semi-resistive pathway of conducting and insulating particles. The emission properties of these thick inks were comparable with those of the thin inks except that in some cases a second type of emission (Type II emission) was observed