Effect of room air exposure on the field emission performance of UV light irradiated Si-gated field emitter arrays

Abstract

Field emission cathodes are promising candidates in nanoscale vacuum channel transistors and are used in microwave vacuum electron devices. Prior research has shown that UV light exposure as well as 350 °C vacuum bake can desorb water vapor from Si field emission tips, resulting in lower work function and improved emission performance. However, after long exposure to room air (greater than 24 h), the improved performance is lost as water adsorbs on the tips. In this study, experiments were carried on two sets of 1000 × 1000 Si-gated field emitter arrays to determine the length of time that emitters can be exposed to room air without degradation. First, the samples were exposed to UV light irradiation in vacuum, and the I–V curves were measured. Then, the samples were exposed to room air with a relative humidity ranging from 30% to 40% for varying times (5, 6, 8, 12, 24, and 48 h) and then tested again under high vacuum. It was found that the emission current did not degrade after room air exposure of 5 h. However, at 6 h of exposure, degradation started to occur, and after 24 h, the emission current went back to the original, pre-UV exposure case. In a separate experiment, UV irradiated samples were stored in nitrogen for 72 h, with a 10% degradation in current. These results demonstrate that field emission devices with improved performance resulting from water desorption can be handled in air up to 5 h, depending upon humidity and stored in nitrogen for 72 h while maintaining improved performance.