Diamond Cold-Discharge Cathodes for Discharge Lamp Application

摘要

B-doped polycrystalline diamond has been investigated as a cold-discharge cathode material for cold-cathode fluorescent lamps (CCFLs). The diamond film was synthesized by microwave plasma chemical vapor deposition (CVD) and basic cold-discharge characteristics were evaluated by open-cell measurement. The diamond showed a more than 35% smaller cathode fall, V{sub}, which is the voltage drop in front of the cathode during discharge, than the V{sub}c in the case of molybdenum (Mo). On the basis of these results, small cylindrical cathodes made of diamond thin films were prepared and tested. V{sub}c increased after the tube fabrication process, however, it recovered and was reduced by discharging in gas ambient containing hydrogen (H{sub}2). Furthermore, a fully sealed discharge tube with a CCFL-like slim outer shape (outer diameter, 4 mm; gap between cathodes, 160 mm) was fabricated by applying a cylindrical cathode and discharge gas containing H{sub}2. The sealed tube operated successfully at currents under 1 mA. Although the current was smaller than that of commercial CCFLs, the diamond-coated cathode discharge tube showed a V{sub}c that was about 1.3% smaller than that of an uncoated Mo cathode tube, which means the same percent power reduction for the discharge tube.