Electrical studies on new generations of oxide cathodes for CRT applications.

A systematic study has been made of two novel types of BaO/SrO oxide cathode with 5% and 2.5% addition of Ni powder by weight on a Ni cap containing an activating impurity. The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this thesis the electrical properties of these new types of oxide cathodes, supplied by LG Philips Displays, have been investigated in relation to the different activation processes. Scanning electron microscopic techniques were employed to study the surface morphological changes of the oxide cathodes and nickel caps as a result of cathode activation extending over periods of 1-12 hrs. Elemental analysis of barium, strontium, tungsten, magnesium and aluminum was obtained from the energy dispersion x-ray spectroscopy.The conductivity and the electron activation energy were studied as a function of temperature in the range 300-1200K after conversion and activation of the cathode at 1200 for one hour and accelerated up to 600hrs at a temperature of 1100K. Experimental results yield three values for the electron activation energy of 1.49, 2.38 eV and 3.3eV. The conduction mechanisms observed a metallic conduction at low temperature (300-500)K after operation for several hundred hours due to improvements in the Ba coverage layer on the grains of oxide layer. The influence of different durations on the activation process has been investigated at three activation temperatures (1125K, 1200K, 1425K). SEM and EDX analysis show a structural phase transformation in the oxide material. The activator agents W and Al are shown to penetrate the BaO\SrO layer in two different ways.The formation of compounds associated with the diffusion of reducing elements (Mg, Al and W) to the Ni cap surface of oxide cathode through hundreds of cathode acceleration hours has been studied by a new method. This method used two cathodes, one of them is coated and the other is uncoated, in an attach-contact configuration mounted in a dummy tube. The D.C electrical characteristics show a very strong rectifying behavior through the Metal-Semiconductor junction (M-S junction) due to the I/V curves. The characteristics are found to be reversible and reproducible, and gave a rectification ratio (r) of 100. The calculated value of ideality factor indicated n = 9.6, which is evidence of tunnelling conduction.