Fabrication of ultrathin IrO2 top electrode for improving thermal stability of metal-insulator-metal field emission cathodes

Thermal stability and interfacial charge trap properties of the multi-metal (Ir/Pt/Au) top electrode of a metal-insulator-metal cathode for field emission display applications were examined. The thin (∼5 nm) multi-metal electrode did not show sufficient thermal stability during the post-annealing stage, which is needed to obtain good emission properties of the cathode, due to inter-diffusion and agglomeration of the layers. Reactively sputtered IrO2 thin films as the top electrode were examined considering their excellent thermal stability and low work function. However, the proper sputtering conditions of thin IrO2 (<10 nm) films were different from those of thick films (>100 nm) and should be optimized again due to the serious resputtering of the substrate at the initial deposition stage. Increasing the oxygen concentration (25%) during sputtering, which is the condition that results in a non-uniform film when the film is thick (>100 nm), was essential to ensure that the film was a well oxidized IrO2 when the film was very thin (<10 nm). Excellent thermal stability in terms of the non-varying resistivity and surface roughness of the 8-nm-thick IrO2 films compared to the multi-metal electrode film were confirmed.