Nanostructures Fabricated by Anodic Aluminum Oxide (AAO) Templation Method for Electron Field Emission Applications
|關鍵字:||電子場發射;矽奈米尖錐;陽極氧化鋁;electron field emission;Silicon nanocone;Anodic Aluminum Oxide|
For the past two decades, electron field emission devices have attracted much attention because of their potential applications for cold cathode flat panel display and vacuum microwave devices. Among various electron field emitters, the Spindt type microfabricated emitter has been extensively investigated for applications of the cold cathode field emitter. In this study, we fabricated highly ordered nanostructured field emitter array using porous anodic aluminum oxide (AAO) as the template. Two types of nanostructured field emitters were prepared: the titanium nitride (TiN) nanopillar emitter array and the iridium oxide (IrO2) coated Si nanocone emitter array. In order to fabricate ordered emitter array, a TiOx nanodot array was first prepared as the nanomask for subsequent fabrication of nanoemitters. The AAO template was used to regulate the formation arrangement of the TiOx nanomaks, with which nanoemitters were then fabricated using conventional integrated circuit process technology. For fabrication of the TiN nanopillar emitter array, TiN and Al were sequentially sputter-deposited on the Si substrate followed by electrochemical anodization of the film stack, thereby the TiOx nanodot array was produced. After reactive-ion-etching the underlying TiN layer using the TiOx nanodots as the mask, TiN nanopillars can be formed with a pattern arrangement in compliant with the AAO pattern. The TiN nanopillars had a ridge-shaped edge on the top after the removal of the TiOx nanomasks. Field emission characteristics of the TiN nanopillar array were studied under a vacuum condition of 10-6 torr. The TiN nanopillars emitters had a very low turn-on voltage while the Fowler-Nordheim plot showed a nonlinear field-emission behavior. The nonlinearity was ascribed to that the ridge-shaped top edge produced field emission before the rest of the emitting area. For fabrication of Si nanocone emitters, similar processes were performed as the fabrication processes of the TiN nanopillars excepted for the thinner thickness of the TiN film. After removal of the AAO template, the TiOx nanodots and the remanent TiN thin film were subject to reactive-ion-etching processes, and the formed TiN nanopillars were used as the mask to prepare the Si nanocone array in a high-density-plasma-reactive-ion-etching (HDP-RIE) system. In order to obtain chemically stable field emitters with a high field-emission efficiency, IrO2 was deposited on the Si nanocones by pulsed anodic electrodeposition. The tip radius and the sharpness of the field emitter were highly dependent on the electrodeposition conditions, such as the pulse waveform, period and the applied current. Field emission characteristics of the IrO2 coated Si nanocone array were also studied, and showed a better field emission performance than that of the bare Si nanocone emitter array.