Detrimental effects of O² and CO² on the cathode performance of flat‐matrix CRTs used for large‐scale flat displays

Abstract

Abstract— The detrimental effects of O2 and CO2 on the cathode emissions of a flat‐matrix (FM) CRT and some methods which increase its life are described. Cathode emission gradually decreases over long‐term operation when an FM‐CRT is used as a tiling element in a large‐scale flat display. It is necessary that for the FM‐CRT the reduction of the emission current be within 10% in order to keep the operational life longer than 10,000 hours. The reason for the degradation of the cathode emission was clarified by experiments using high‐vacuum equipment. It was found from experiments that O2 and CO2, which are produced by the dissolution and activation of the oxide‐coated cathodes, are very harmful to emissions. It is, therefore, very important to lower the partial pressure of O2 and CO2 in the FM‐CRT in order to reduce their harmful influence on the oxide cathodes. Two methods were used to reduce their partial pressure in the FM‐CRT. One was to make the diameter of the evacuation tube larger and the other was to increase the quantity of the getters. It was found that the adoption of twice as many getters in the FM‐CRT was most useful in lowering the partial pressure of O2 and CO2. This has ensured that the life of an FM‐CRT is longer than 10,000 hours.