A field emission display (FED) refers to a device in which electrons emitted from a cathode panel are irradiated on a fluorescent substance of an anode panel to display an image. The field emission display operates in a similar manner to a cathode ray tube (CRT) but has a flat shape. Just like the cathode ray tube, the field emission display is operated by emission of cathode rays and therefore provides a high light-emitting efficiency, a wide viewing angle, an increased operating speed and a reduced production cost. Among major components of the field emission display are an anode panel and a cathode panel. The anode and cathode panels are spaced apart from each other by a spacer with a vacuum space left therebetween. The anode panel includes a transparent panel, a transparent conductive anode attached to the transparent panel and a fluorescent substance coated on the transparent panel. The cathode panel includes a plurality of field emission arrays (FEA) each having a cathode and an electron emitter. A triode type cathode and a diode type cathode are used as the cathode. The triode type cathode is extensively used in recent years because it has an ability to easily control an emission current with a low voltage and to realize a gray scale with ease.
The electron emitter as a key element of the field emission display is classified into a tip-type and a flat-type. The tip-type electron emitter has a gate hole of reduced diameter and therefore can work at a low voltage. In addition, the tip-type electron emitter is effective in increasing the number of electron emitters within a pixel and increasing the emission current. The tip-type electron emitter is divided into a silicon tip and a metal tip depending on the material thereof. The metal tip is made of a metal such as tungsten, molybdenum or the like and requires a high voltage to emit electrons. Thus, the metal tip suffers from severe dry corrosion, which leads to a problem of shortened lifespan. The silicon tip offers such advantages as ease of shape change, increased homogeneity, and good compatibility with a semiconductor manufacturing process. However, the silicon tip is accompanied by such disadvantages as an unstable emission current, a high risk of damage, presence of an oxide film and limited panel size.
In recent years, attention is paid to an electron emitter made of a carbon material such as diamond, carbon nano tube, diamond-like carbon or unshaped carbon. The carbon material is low in the work function value for determination of an electron emission voltage, exceptionally resistant to corrosion and highly conductive. In particular, the carbon nano tube is advantageous in that electrons are concentrated on the pointed end thereof and can be emitted with ease. Moreover, the carbon nano tube has some features of diamond-based materials. In addition, the carbon nano tube shows a feature of high aspect ratio. If the carbon nano tube is vertically arranged on a substrate, it is possible to greatly increase the electron emission efficiency.
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