The Study Of Silicon Nanowire Electrode Discharge Characteristics

Gas discharge research, especially the discharge under small gap, has outstanding academic values. On one hand, in the fields of integrated circuits and MEMS devices, discharge breakdown is harmful and should be avoided; the other hand, in the areas of new gas sensors, electrostatic precipitators, ion propulsions, discharge breakdown is becoming an important means of analysis and application. Therefore, the electrical breakdown of the material and the discharge behavior of the system are very necessary. The discharge behavior research of nanomaterials under the small electrode distance and low-voltage, is still in its infancy, and is becoming into one of the hotspots. In this thesis, silicon nanowires (SiNWs) were studied as the research object. The nanostructures fabrication and modification, as well as its application in electron emission, corona discharge and gas ionization were analyzed. The main contents and results are as follows:Firstly, the preparation and optimization of SiNWs electrodes were carried out and the gold nanoparticles decorated SiNWs electrodes were fabricated. SiNWs were first prepared by metal-assisted wet chemical etching. The vertically aligned silicon nanowire arrays with the average diameter of100nm were obtained and have high field enhancement factor. The influence of the process parameters such as etchant solution concentration, temperature, doping type on the nanowires appearance was studied. Gold nanoparticles(AuNPs), prepared by reduction of chloroauric acid, with the average diameter of10nm, were assembled onto the surface of SiNWs with APTMS as coupling agent to form the Au/SiNWs nanocomposite electrode. And the AuNPs were single crystal with content of7.26%.Secondly, the field emission (FE) behaviors of SiNWs and Au/SiNWs composites were studied and the ultra-low turn-on electric field was obtained. First, the FE performance of SiNWs, made from wafers with different doping types and doping concentrations, was investigated. And the study indicated that lightly-doped n-type SiNWs has the higher FE perfromance. Next, the FE characteristics of Au/SiNWs nanocomposite were studied. It is found that by introduction of AuNPs, the FE performance of SiNWs can be improved remarkably:the turn-on field can be reduced from1.76V/μm (SiNWs) to0.17V/(.μm (Au/SiNWs). On this foundation, the variable temperature field emission characteristics, i.e., the field emission properties of SiNWs and Au/SiNWs under different temperatures, had also been studied. The FE performance of the SiNWs increased slightly with temperature, the current density at various temperatures are different. For Au/SiNWs, the FE characteristics increased obviously with temperature. At last, in view of the existence of silicon dioxide, we proposed the MIS-Schottky band model for SiNWs and analyzed the possible FE mechanism.Thirdly, under the atmospheric pressure, with SiNWs electrodes as needle electrode and metal as plane electrode, the positive corona and negative corona discharge characteristics of SiNWs was been studied. According to the mechanism of needle-to-plane corona discharge, the corona discharge electrode was designed. The onset voltage of positive corona discharge is about700V voltage, and the stable working voltage range of the corona discharge is700-1600V. The onset voltage of negative corona discharge is about400V voltage, and the stable working voltage range of the corona discharge is400-1700V.Fourthly, the micro-gap, l-20μm, ionization behavior of micromachined SiNWs electrodes at atmospheric under room temperature were investigated, and the departure from the classical Paschen’s curve was found. First, two kinds of micromachined ionization devices with controllable micron level electrode gap were fabricated. Both of them consist of SiNWs electrode and glass electrode. The first one is that glass is etched to form the concaved-glass/SiNW structure. And the second one is to selectively to fabricate SiNW to form the concaved-SiNW/glass structure. The homemade ionization testing system was used. Ionization devices were tested and the corresponding I-V characteristics of the air ionization at atmospheric were recorded and analyzed. The obtained breakdown voltage in air is only about21V, which is smaller than other similar structures with one-dimensional nanomaterials. The effects of two parameters, pressure P and electrode gap distance d, were discussed respectively. When the pressure reduced logarithmically, both the current and the gas breakdown voltage linearly decreased accordingly. When the electrode gap is less than7μm, breakdown voltage showed strong linear relation with the gap distance d, departure from the Paschen’s curve. The influence of parameters, e.g., electrode polarities, doping type and doping concentration of SiNWs, on gas ionization were also been studied. The results as following:the breakdown voltage of n-type low doped SiNWs is less than p-type low doped, but on the contrary of the breakdown current. And the breakdown voltage and current of p-type low doped SiNWs were both below p-type high doped SiNWs.