Preparation And Performance Research Of Low-dimensional Nanomaterial Field Emission Arrays

Vacuum electronic devices have the advantages of high frequency and high power,and play an irreplaceable role in modern military,information communication,aerospace,social life and other fields.The electronic source is the core component of vacuum electronic device,and its performance directly determines the whole performance of the device.Compared with the traditional hot cathode,the cold field emission cathode has the advantages of instantaneous response,room temperature operation and high monochromatism of electron beam.In order to further improve the current density,stability,life and other properties of the field emission cathode,the preparation and field emission performance of different nanomaterials were explored in this paper,aiming to obtain excellent electronic source materials and structures,and meet the strategic needs of the country in military,aerospace and other fields.The research of field emission cathode has successively experienced Spindt cathode,silicon tip array,thin film cathode represented by diamond,low dimensional nanometer material cathode represented by carbon nanotube.Carbon nanotubes have excellent field emission performance due to their advantages of high conductivity,high mechanical strength and large aspect ratio.For example,the opening electric field and threshold electric field are low,but the current density still needs to be further increased to meet the needs of high-power devices.Spindt cathode is considered to be the most ideal electron source structure due to the emitter position,morphology,number,controllable integration,low driving current,small shielding effect between emitters and other advantages.Therefore,while optimizing the field emission performance of carbon nanotube array,this paper also explored the preparation process of Spindt cathode,including the preparation of silicon tip and metal cone tip as well as the preliminary test of the field emission performance of silicon tip,laying a foundation for the construction of Spindt cathode based on carbon tube.Specific research contents are as follows:1.Growth and field emission properties of carbon nanotube arrays.In this paper,carbon nanotube arrays were grown vertically on silicon substrates by plasma enhanced chemical vapor deposition(PECVD).In order to further enhance the field emission performance of carbon nanotubes,low work function titanium carbide was coated on the surface of carbon nanotubes,and the preparation parameters of titanium carbide were optimized.The results show that compared with the carbon tube,the field emission performance of the optimized opening electric field is improved obviously.The opening electric field of the optimized sample decreases from about 2.4V/?m to about 1.8V/?m,and the maximum current increases from 0.782mA to 1.577mA.2.Research on the field emission properties of silicon tip Spindt cathode.In this paper,the silicon tip field emission arrays with different emission areas are obtained on the silicon substrate by dry etching using silica as a mask.In order to reduce the tip radius of etched silicon tip,a silicon tip array with a tip radius of about 10nm was successfully prepared by multiple thermal oxidation process.In order to reduce the operating voltage,a silicon tip field emission array with gate control structure was prepared.The test results show that the average current of a single silicon tip is about 10nA when the gate voltage is 60V and the anode voltage is 2200V.In order to obtain larger emission current,the silicon tip array density can be increased.3.Metal taper tip Spindt cathode.In order to prepare metal micro-tip field emission array with more uniform morphology,an inverted mold process was developed in this paper.First,the inverted pyramid grooves were obtained on the silicon substrate surface by lithography and wet etching.The grooves are then filled with metal by magnetron sputtering and a new substrate is formed by a nickel plating process.Finally,the silicon substrate was etched by wet method to obtain the tip field emission arrays of molybdenum and nickel respectively.This technology not only obtained the uniform morphology of the emitting tip array,but also laid a technological foundation for the subsequent preparation of heterojunction Spindt cathode.