LOW-VOLTAGE FIELD EMITTER ARRAY CATHODE FOR HIGH-FREQUENCY APPLICATIONS

The composite-based low voltage field emitter cathode offers distinct advantages for high-frequency applications. It is based on a c directionally solidified ZrO2.Y2O3-W eutectic composite containing aligned, single-crystal tungsten fibers, almost-equal-to 500 nm in diameter, with spatial densities of 2-50 X 10(6)/cm2. The composite can be etched to form fibers of virtually any length with tip radii of 5-10 nm. A gridded structure can be formed around the fibers using a line-of-sight vapor deposition process. Because of the thickness of the composite chips used as the substrate (0.5 mm) and the high resistivity of the oxide matrix, the insulator film can be made extremely thin, thereby reducing the extractor aperture radius. Emission tests have verified this configuration results in measurably higher field enhancement values for the arrays.