FED CATHODES MATERIALS

Dr. Sheshin at the Moscow Institute of Physics and Technology is studying field emission cathodes, and has fifteen years of experience on emission from carbon-based materials. He believes that carbon emitters are the best candidates for practical field emission cathodes due to their self-healing characteristics, which lead to uniformity of emission (106 emission sites/fiber are possible). In addition, he believes that carbon cathodes will work at 10-6 Torr, and that Spindt cathodes will need 10-8 Torr for good emission and lifetime. He has some evidence that carbon cathodes will tolerate 10-4 Torr, and that a current density of 105 A/cm2 is possible. A life test was run for 7,000 hrs. Dr. Sheshin and his associates do not fabricate their fibers, but obtain them from the Graphite Institute. They have a new method of fabricating the carbon fiber cathodes that is different than the one disclosed in publications.

Patterned growth of silicon needles has been achieved at the Institute of Crystallography at the Russian Academy of Sciences in Moscow. A vapor-liquid-solid growth technique allows the growth of very sharp needles that are potentially useful for field emission tips. The growth must be performed at 900-1,000 degrees centigrade. The needles can be formed in regular arrays over an area of 1 cm2 by applying a pattern of Au dots using standard photolithography on which the needles form. Some needles were only a nanometers at the tip, and the researchers were attempting to detect quantum size effects. A second area of interest is to generate photoluminescence or electroluminescence from large areas covered by needles. Needle growth has also been demonstrated with InAs and GaAs.

The group under Dr. Givargizov has succeeded in growing diamond microspheres on the tips of the needles from an H2- CH4 plasma. The spheres shown to the WTEC team were about 2 microns in diameter. The scientists had not yet controlled the deposition process well enough to form a diamond sphere on the tip of every needle nor to prevent nucleation on the sides of the needles. The group believes it will be able to dope the diamond spheres for negative electron affinity. The testing of the diamond spheres was just beginning. [See Vacuum Fluorescent, Electroluminescent, Field Emission, and Other Emissive Displays for more recent developments in Dr. Givargizov's laboratory - Ed.]

The Volga Research and Development Institute in Saratov has a dry etching process for FEDs with Cr, SiO2, and Al for a 128 x 128 (1,000 pixel) display. The Volga Institute uses automated glass cleaning with H2O2 and NH4OH. For FED development, the institute is pursuing the Spindt approach with Mo tip emitters. However, the institute also is investigating designs with a graphite emitter edge, with a 1 mm anode-cathode separation, and razor edge. Volga scientists also demonstrated a working 4-inch-square FED with a green rastor.

At the Zelenograd Research Institute of Physical Problems, the panel saw an FED with a display area of about 2" x 2" on a 4" x 5" glass substrate. The institute's scientists used a monochrome ZnO phosphor with 40 V on the accelerating electrode and 75 V on the phosphor screen; a brightness of 3,000 cd/m2 was obtained with a phosphor efficiency of 3 lm/W. The substrates were 20 microns apart and the operating pressure was 5 x 10-4 Pa. They used wedge-shaped silicon cathodes with a packing density of 106/mm2, yielding about 103 emitters per pixel.


Published: December 1994; WTEC Hyper-Librarian