Study On Cathode Emission And Strucyure Desigh Of High-Frequency Devices

During the past tens of years, countries from the whole world funded to develop solid-state devices. Although solid-state devices replaced parts of low frequency microwave tubes in low frequency range, development since 1980s indicated that the frequency of solid-state devices was limited and it cannot meet the requirements of next era of weapons. Micro-vacuum devices have both the advantages of solid-state devices and vacuum devices, so it becomes to be a focus to study.As an important type of cold cathode material, carbon nanotube has been widely studied to apply in Field Emission Display (FED). These years, emission performance of carbon nanotube is improving, so it has potential to apply in high frequency devices.The thesis studied application of carbon nanotube to high frequency devices. Presently, the first main problems need to solve were the emission uniformity and the emission current density. The thesis studied for these problems in Chapter 3. Carbon nanotubes lined in different shape were calculated and result showed that the uniformity of carbon nanotubes lined in cirque shape was the best. Secondly, in Chapter 3 the cathode emission current density was studied from the respect of cathode structure. The fringe field effect was used to improve the emission current density. To enlarge the fringe used the method of dividing the cathode into several elements. Results showed that the emission current density could be improved by optimizing some parameters of the structure. Furthermore, results also showed that the uniformity of cathode emission could be improved by dividing cathode into several elements.To apply carbon nanotubes to high frequency devices, another important problem need to solve was how to get well shaped electron beam. Chapter 4 studied and designed different electrical chunnel to shape the electron beam. During designing, two aspects were considered, one was the transverse velocity of electrons emitted from exit of chunnel, and the other was the range of electrons distributed. Designs were based on the converted funnel shaped chunnel with insulating material inside. Four different structures were calculated and we got one type of structure with good electron beam shape.Ion bombardment was one of the important factors resulting in failure of field emission. Getters used in vacuum devices cannot remove the inert gases of residual gas. Chapter 5 studied the ion bombardment damage induced by inert gases to field emission cathode (including silicon and molybdenum). From the calculation results, damages to silicon were larger than molybdenum under the same ion bombardment. Damages by different inert gases to the same cathode material were also compared. Results showed that larger the atomicity of gas, larger destroy it will induced to cathode.