Gated carbon-based cold cathode for high current applications

We have developed a gated carbon-based cold cathode capable of operating at high current densities for use in applications such as cathode-ray tubes, microwave devices, and x-ray sources. The carbon-based electron-emitting material is a good choice for these applications as it does not readily form a native oxide when exposed to atmosphere. Cathodes can thus be pretested in a vacuum chamber before insertion into the final device. Given that carbon has a low sputtering yield and is relatively inert, this material is an ideal candidate for long-lived applications in moderate vacuum environments. Our present 500-μm-diam cold cathode array contains approximately 5000 individual microtips and emits 0.1–500 μA for a gate voltage of 70–118 V. The average current density over the array is about 0.25 A/cm2 at 500 μA emission current. Long-term testing of individual cold cathodes at current densities of 0.10 A/cm2 in cathode-ray tubes has shown lifetimes in excess of 5000 h. Peak currents exceeding 10 mA (current densities of 5 A/cm2) have been achieved.