Study Of Nano Carbon Materials-based Field Emission Display And Light

Carbon nanotubes (CNTs) have been studied extensively as cold cathodes for field emission devices, such as field emission display (FED), field emission lighting, microwave amplifier, X-ray tube, due to their high aspect ratio, small tip radio of curvature, and high conductivity. These carbon nanotubes field emission devices possess many vantages such as high definition, low power consumption, high brightness, fast response time, wide work temperature range and low cost. During the CNTs application to the products, there are many problems such as the low cost, low temperature, large-scaled and controllable fabrication, the uniformity and stability of the field emission and the processing compatibility. The solution to these problems will speed up the industrialization of the field emission devices based on CNTs and raise the market competition ability. CNTs cathodes are commonly prepared in two ways: in situ CNTs growth directly on the catalyst patterned substrate by chemical vapor deposition (CVD), and screen-printing of CNTs paste on electrodes-patterned glass.In this study, the two methods are both applied to systemically study the properties of CNTs field emission cathode. The CNTs film cathodes are grown on Cu catalyst on glass substrate using chemical vapor deposition method. Screen printing and electrophoretic deposition are also used to fabricate CNTs cathode with large scale and low cost and high field emission properties. Main concludes and innovative results are listed as follow:1) Optimization of the CNT cathodes growth using CVD-Screen printing techniqueThe effects of growth temperature, flow ratio of C₂H₂ and H₂, on the growth of CNTs are systematically studied. The CNTs are then mixed with organic pastes to be screen-printed on substrate to form FE cathodes. With increasing the temperature, the diameters of CNTs become smaller and purity increases; with lower C₂H₂ flow rate, the higher purity and the better emission capacity. The results indicate that there is an optimal temperature range (600℃⁷00℃) and C₂H₂ flow ratio (20sccm-50sccm) being used as the field emission cathode. The ratio of CNTs and organic solution should be kept at 1:9 or 1:10, making the cathodes reach the best field emission performance. By adjusting these processing parameters, the growth and field emission properties of the CNTs can be controlled to some extent.2) Preparation and Optimization of field emission properties of carbon nanotubes cathodes by electrophoretic depositionCold cathodes of carbon nanotubes (CNTs) are deposited on the glass substrate by electrophoretic deposition (EPD) method. The emission characteristics of the CNTs film cathodes have as good properties as those by screen printing and better emission uniformity. The influences of the voltage and distance between electrodes, deposition time, electrolyte in the electrophoretic process of flat cold cathode fabrication on the uniformity of the CNTs film distribution are studied. The results indicate uniformity of CNTs film and optimized emission properties of the cathode have been achieved when the voltage is 25 V, deposition time is 10 min and distance between electrodes is 5 cm, and Al(NO₃)₃ is used as the electrolyte.3) The Growth and Field Emission Properties of Carbon Nanotubes on Cu film by Chemical Vapor DepositionCu catalyst films are deposited on glass substrates by DC magnetron sputtering and the CNTs are grown by CVD. Four metal (W, Ni, Cr, Ti) are sputtered prior to Cu to be barrier layers o reduce the Cu diffusion. The morphologies and the voltage current measurements are concluded that better field emission properties of CNT films can be obtained on titanium, tungsten barriered Cu, while chromium and nickel are not suitable barrier candidates for copper in CNT-FED application because of the worse emission performance. The thicknesses of barrier layer and catalyst layer are critical parameters to control the growth of CNT films. The Ti films have a wide range of thickness (5-30 nm) to prevent the Cu diffusion, while W barrier layer should be at 10nm to obtain CNTs with better emission properties. The optimal thicknesses of Cu on Ti are 25-30 nm. Due to the low catalyst activity of Cu, the growth temperature of CNT film should more than 500℃and lower than 550℃on glass substrates at the growth time of 30 min.4) Fabrication of the CNT field emission flight, display devices by three methodsCNT field emission flight, display devices have been developed utilizing CNTs as the emitter by screen printing, electrophoretic deposition and catalyst direct growth. Screen printing is a good candidate for the fabrication of large scale CNT-based field emission devices at low cost. The prototype devices have the performance of good uniformity and stability. The field emission properties of cathode by electrophoretic deposition are also studied. The effect of ball milling and solution concentration are investigated to improve the uniformity of deposited CNTs film. For lower threshold voltage of field emission, we compared the properties of "triode structure" with "diode structure". The experiment shows that electrophoretic deposition is a good approach to preparing the cold cathode of field emission. The primary studies of patterned CNT cathode directly grown on glass indicate that the method makes high emission capability and high definition, also high process cost and poor uniformity at large scale.