Very High Field Emission from a Carbon Nanotube Array With Isolated Subregions and Balanced Resistances

Field-emission electron sources can be used in microwave amplifiers, microthrusters, field-emission lamps, and X-ray tubes. However, both large cathode areas (multiple square millimeters) and large total currents (> 10 mA) are required in these devices. It has been reported that the average field-emission current density can be very high when the emission area is quite small. However, the current density decreases a lot when the emission area is large. The nonuniform field emission from a large field emitter array and its influences on the total emission current are analyzed in this paper. From the results of the numerical simulations, the relations between the average field-emission current density and the size of the carbon nanotube (CNT) array are found. Due to the standard height deviation of CNTs in an array, some CNTs may be quite high if the array is large. To avoid the current overload from the highest CNT, the total field-emission current has a nonlinear relation with the area of the CNT array. Therefore, the field-emission current is limited even if the emission area is large. According to the results of the theoretical studies, a new way is proposed to enhance the field-emission current. In this method, the field emitter array is divided into a few isolated subregions. After the measurement of the field-emission characteristics of different isolated subregions, the balanced resistances are attached to these regions to improve emission uniformity. Finally, the field-emission current increases from 5 to 13.8 mA after the adoption of isolated subregions and balanced resistances, and the average current density is 1.76 A/cm(2).