Thin-film Field Emission Cathode

In the present dissertation, both stack-type and coplanar-type thin-film field emission cathodes are studied using simple device structure and cost-effective manufacturing process, aiming at stable and uniform electron emission for large-size display.For the stack-type field emision cathode with a structure of Metal-Insulator-Semiconductor-Metal (MISM), Zn_0.75Mg_0.25O thin film with a lower electron affinity than that of ZnS is adopted as the semiconductor layer to facilitate the electron emission. Discontinuous metal layer is used to introduce electron energy levels at the interface between insulator and semiconductor. Stable and uniform electron emission is obtained, and the maximum emission efficiency is 0.055% with a gold interlayer and a Pt-Au-Ag multilayer top electrode. This value is higher than the best result which has ever been obtained by using ZnS as the semiconductor layer.Two typies of coplanar emitters made of discontinuous island-like films with novel structure are proposed and demonstrated. For these emitters, it is critical to fabricate and control the structure of discontinuous film, including both the size and distribution of islands, using simple process and low cost materials. One of them is based on etched porous alumina and carbon-gold-carbon compound film. The alumnia film surface is composed of rows of valleys with diameter of about 300 nm, and is realized by etching porous alumina in diluted phosphorous acid. After carbon-gold-carbon compound film is deposited onto the surface, the film at the ridges of the valleys is supposed to be thinner than that at the centers of the valleys, and the electron emission is obtained at the ridges under the action of grid voltage. To simplify the fabrication process, coplanar emitter based on discontinuous amorphous carbon film is fabricated. The carbon film is composed of nano-size islands distributed between larger ones, and is realized by etching as-deposited carbon film in oxygen plasma, using a discontinuous island-like bismuth film as the mask. The nano-size islands are supposed to be necessary for uniform and stable electron emission. The structure of the carbon film can be modified to improve the emission characteristics by changing the deposition condition of the bismuth film-mask and the etching process.Stable and uniform electron emission is obtained from coplanar emitters based on above discontinuous films, and the transient fluctuation of emission current is no higher than 5%, which is very close to the requirement for large-size display. The maximum efficiency is above 2% and 2.5%, respectively, with a grid voltage of about 45 V and an anode voltage of 3 kV. If the anode voltage is 10 kV, emission efficiency will increase to 5%, which is five times of the basic requirement value for large-size display. Finally, the impact of ambient atmosphere on the characteristics of emitter is studied, and the quantum size effect and tunnel effect are used to explain the emission mechanism of the emitter.