Increasing emission current from MIM cathodes by using an Ir-Pt-Au multilayer top electrode

We investigated the effect of the top electrode materials on the electron emission and durability of metal-insulator-metal (MIM) cathode. The durability is improved when high sublimation-enthalpy material, such as Ir, Mo, or W, are used; however, the emission current, and the transfer ratio, decrease. The material dependence of the transfer ratio is shown to be dominated hy the scattering probability of hot electrons in the metal. The scattering probability was estimated from the metal's density-of-states, or more simply, from the number of d-electrons. We found that the multilayer top electrode consisting of Ir, Pt, and Au provides the best top electrode combination for MIM cathodes. The high sublimation-enthalpy Ir layer, which is in contact with the insulator, acts as a barrier metal and improves the durability, whereas the surface Au layer maintains the transfer ratio at a high value. With this top electrode structure, emission current density is increased to 5.8 mA/cm(2), which is sufficient for field-emission displays. We demonstrated a display consisting of a 30 x 30-dot MIM cathode-array with the multilayer top electrodes.