Enhancing Electron-Emission Efficiency of MIM Tunneling Cathodes by Reducing Insulator Trap Density

Metal–insulator–metal (MIM) tunneling cathodes demonstrate electron-emission efficiency $(\alpha )$ of 9 $%$ to 11 $%$ . This threefold increase in $\alpha$ from that previously reported is achieved by reducing trap density in the cathodes\´ insulator, thereby enabling tunneling electrons to accelerate with fewer scatterings in the insulator. Life tests show that the high $\alpha$ is maintained for a 19 000-h operation in sealed display panels containing a ZnS-based phosphor. The reduction of trap density also suppresses long-term drifts in emission and diode currents to a satisfactory level. These emission characteristics are sufficient for realizing a large-sized field-emission display with MIM cathodes. In addition, an effective method for measuring trap density in the insulator of MIM devices is devised. This method adopts low-stress $I$ – $V$ measurement following charge-injection stress. Measurement by this method reveals that trap density is proportional to neodymium concentration in the anodized insulator. The trap density is therefore reduced by lowering the neodymium content in the precursor Al–Nd alloy film. Moreover, the robustness of the MIM cathodes to charge-injection stress is demonstrated.