Lanthanum Hexaboride Field Emitter Array Cathode Preparation Process And Testing

Vacuum microelectronic devices based on field emission theory have received extensive attention due to their small size, low power consumption, low voltage, high speed, anti-radiation and large range of working temperature. The whole performance of the device is critically depended on the capability of field emission cathodes, which have received large improvement in the structure, material and fabrication through the researchers'efforts.The choice of cathode material is very important in the fabrication of field emission cathodes. The work function, conductance, density, thermal reliability and chemical stability of the material must be considered, as well as the requirement for machining. Recently, a lot of kinds of materials have developed, most of which have disadvantages including high work function, low emission stability, low uniformity, and poor emission performance. Compared with these common field emitter materials, lanthanum hexaboride (LaB6) is an excellent material for use as field emission cathode due to its high chemical stability, low work function, high conductance, and active surface. At present, molybdenum tip-emitters prepared by Spindt Lab and silicon tip-emitters using oxide-sharpening process are the most widely used. Both of them are fabricated on silicon substrate, which leads to the compatibility with VLSI technology and mass production.In experiment, bird-beak-LaB6 field emission cathodes with sub-micron gate aperture are fabricated by modifying the conventional Spindt process. The gate-insulating layer is formed by local oxidation of silicon, and the gate hole size is decreased due to the lateral encroachment of oxide. Aluminum is deposited at a grazing angle to form sacrificial layer by thermal evaporation. At last, LaB6 material is deposited subsequently by electron beam evaporation, resulting in the formation of LaB6 emitters with 25nm in tip radius. The most serious problem existing in this technology is the short circuit between the gate and cathode. Some possible methods are developed to solve this problem. First, a number of experiments are processed with the same structure. In result, the short circuit phenomenon can be overcome between times, but the repeatability is poor and short circuit may occur during the subsequent measurement. In the second method, the conventional Spindt technology is introduced to form LaB6 field emission arrays and the emitters are packaged and measured in the subsequent experiments.Research in my paper is mainly concentrated on the fabricating technology of field emission cathodes, including the etching process, film deposition, package, seasoning and measurement. The test equipment and circuit are designed for the field emission characteristics measurement of LaB6 emitters. Further more, the test results are discussed and some impossible methods are proposed to improve the performance of LaB6 field emission cathodes.