Toshiharu Higuchi

Emission and life characteristics of thin film top-layer scandate cathode and diffusion of Sc2O3 and W

We investigated top-layer scandate cathodes, which are the most promising of scandate cathodes. Among the cathodes which we prepared with a layer of various thickness, the best pulse emission of 80 A/cm2 at 1300 K was recorded with cathodes having a top layer consisting of a Sc2O3 layer 2 nm thick on a W layer 8 nm thick. The emission variation of these cathodes was evaluated in life tests. The life characteristics were good in both diode and triode evaluation. We also determined diffusion coefficients of W and Sc2O3 with unporous W pellets covered with a Sc2O3 and W layer. Variations of surface concentrations of these pellets during life tests were measured using Auger electron spectroscopy. The diffusion coefficients were 6.4×10−19, 1.0×10−18, and 1.6×10−18 cm2/s at 1220 K, 1300 K, and 1370 K. Chemical states of O, Sc, and W are discussed based on detailed analysis of Auger electron spectra.

Pore geometry of dispenser cathode surface vs. emission characteristics, and Ba recovery characteristics after ion bombardment

Abstract A study was conducted to investigate the emission characteristics and barium recovery characteristics after ion bombardment of two types of Ir-coated dispenser cathodes having a pore density on the surface layer of the cathodes of 4×10 4 and 1.3×10 4 pores/mm 2 . Cathode current was measured under pulse operation in a range of 0.1–9% duty cycle. When the duty cycle dependence of emissions was examined, the current densities of both cathodes were the same in the case of 0.1% duty cycle, delivering about 12 A/cm 2 . The work functions also showed the same value. However, evaluations of 4% duty cycle and 9% duty cycle found that the cathode with a higher pore density showed emission characteristics higher by 50% and 70%. Regarding the recovery time of barium and oxygen after argon ion bombardment with Auger electron spectroscopy (AES), the low-pore-density cathode required as long as 3 min for recovery, whereas the high-pore-density cathode recovered in 1.1 min. From the above experiments, it was clarified that emission characteristics under high duty and barium recovery characteristics after ion bombardment can be improved by increasing the pore density of the surface layer. The basic mechanisms leading to these results were also theoretically considered by solving surface diffusion equations.

Long-life high-reliability Ir-coated dispenser cathode

A long-life high-reliability Ir-coated dispenser cathode has been developed. To study the life characteristics of Ir-coated dispenser cathode, which is provided with a surface alloy layer of εII, extended life tests were conducted over 10,000h. From this life data, this cathode was estimated to have a 200,000h life at 920°Cb with 0.8A/cm2, and to have a 100,000h life at 980°Cb with 2.5A/cm2before emission decreases by 4%. Further, the experiment equation for surface Ir concentration of the cathodes was deduced from the results of surface analysis. Using this equation, the surface alloy layer was evaluated as extremely stable without substantial degradation during cathode life. Thus, the Ir-coated dispenser cathode has been proved to be exceedingly durable and highly reliable.

Emission characteristics of dispenser cathodes with a fine-grained tungsten top layer

Abstract In order to improve the emission stability of the Ir-coated dispenser cathode under ion bombardment, a fine-grained tungsten top layer was applied on the substrate porous tungsten plug before Ir coating. The emission characteristics were studied after being assembled in a CRT gun. Cathode current was measured under pulse operation in a range of 0.1–9% duty. Remarkable anti-ion bombardment characteristics were observed over the range of 1–6% duty. The improved cathode showed 1.5 times higher emission current than that of a conventional Ir-coated dispenser cathode at 4% duty. AES analysis showed that the recovering rates of surface Ba and O atoms after ion bombardment were 2.5 times higher. From these results it is confirmed that the Ir coated cathode with a fine-grained tungsten top layer is provided with a good tolerance against the ion bombardment.

Modeling of life deterioration by ion bombardment of a dispenser cathode coated with an Ir/W film

We have developed the calculation method for ion bombardment traces. When an M type dispenser cathode is operated in a cathode ray tube (CRT), the surface coating film is subjected to ion bombardment due to ionized residual gas. With long-time use, the coating film is dissipated and a change to an S type occurs. This occurrence of an S type causes a deterioration of emission and focus characteristics. A method for calculating the life time dependency of the shape of ion bombardment traces using the degree of vacuum in the tube, the grid voltage, and the cathode current was studied. The calculated results and measured results were in close agreement. As a result, it was confirmed that modeling is possible using (1) an electron and ion beam trajectory calculation program, and (2) formulas for calculating the ionization cross-section and sputtering yield.

Life estimation of Ir-coated dispenser cathodes and heaters for cathode ray tubes

Two types of Ir-coated dispenser cathode for cathode ray tubes (CRTs) have been developed and their practical application has been realized. The heater powers of these cathodes are 1.31 W and 0.76 W. Life tests up to 42,000 h were conducted at two levels of cathode temperature. Based on the emission residual ratio, stability of the Ir layer and the size of ion-bombardment nicks, it was found that the minimum life expectancy was more than 70,000 h. A heater for CRTs is used in conditions where a voltage of about 200 V is normally applied between the heater and the cathode. Therefore, it is important to design such a heater so as to lower the heater temperature and to develop a coating layer with high dielectric strength. In order to solve this problem, a new coating layer has been developed. A life test has been conducted for 39,000 h with a voltage of 300 V applied between the heater and the cathode, at several heater temperature levels. From the results obtained, the minimum life of the newly developed heater is estimated to be more than 80,000 h.

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.

Emission life expectancy of Ir-coated dispenser cathodes for CRTs

A compact Ir-coated dispenser cathode was developed for CRT (cathode ray tube) use. To study the emission life of the cathode, an accelerated life test was conducted, using 111% heater voltage. Oxide cathodes were also tested for comparison. The test indicated that the emission of the oxide cathodes decreased to 50% of normal after about 5000 hours. In comparison, after approximately 10000 hours, the emission of Ir-coated dispenser cathodes had decreased less than 5%. The 10000-hour-plus life expectancy of the Ir-coated dispenser cathode was modeled, with the results projecting a life expectancy of approximately 24000 hours at 111% heater voltage. It was estimated that, under normal conditions, the life expectancy of this Ir-coated dispenser cathode would be approximately 100000 hours.<<ETX>>