Ir-coated dispenser cathodes for CRTs

Strong demand exists for the development of high-current-density and long-life cathodes for use in CRTs. In response to this demand the authors have developed and implemented the mass production of two types of Ir-coated 411 type dispenser cathodes having a heater power of 1.31 W and 0.76 W, respectively. These cathodes were designed by computer simulation, and have a structure that allows them to be assembled in electron guns configured for conventional oxide cathodes. The following three types of life tests were carried out in order to confirm the reliability of the cathodes: (1) To investigate temperature changes during the life of the cathodes, a life test of approximately 40,000 h was conducted. The resultant temperature change was small, confirming that the reliability of the cathodes is satisfactory. (2) To investigate emission life, a 32,000 h life test was conducted. The stability of the emission current was thereby confirmed. (3) To investigate heater life, 39,000 h life tests were conducted at several heater temperature levels with a voltage of 300 V applied between the heater and the cathode. From the results of these tests, the minimum life of the heater is estimated to be 80,000 h. The results obtained in the above tests confirm that these cathodes possess good reliability.