Developments in Ceramic Materials Research

Field Emission Display on Ceramic 245
diameter and several microns in length in 1993 [27], extensive studies of carbon nanotubes’
material and physical properties began. Today, carbon nanotubes are driving scientific
research. The basic research field has several important directions including chemistry,
electronic transport, mechanical and field emission properties.
A carbon nanotube is a very small piece of graphite, a derivative of carbon, rolled up into
a very small tube. It is not a metal, but a very strong structure built entirely out of covalent
bonds with field emission properties. Carbon nanotubes are high in aspect ratio and whiskerlike
in shape, which is favourable for field emission. Even for moderate voltages, a strong
electric field develops at the free end of supported carbon nanotubes because of their
sharpness. This was observed by de Heer and co-workers at EPFL in 1995 [28]. Carbon
nanotubes are chemically stable, therefore they only react under extreme conditions such as
extremely high temperatures (2500°C) with oxygen or hydrogen; consequently, the problems
of reacting with resident gases, overheating, or tip deformation are not serious with carbon
nanotubes as compared with micro tip field emitters. It was realized immediately that these
nanotube field emitters must be superior to conventional electron sources and might find their
way into all kind of applications, most importantly flat panel displays [29, 30]. It is
remarkable that after only five years Samsung actually realized a very bright colour field
emission display, which will be shortly commercialised using this technology. Carbon
nanotube based FED research is very active in the USA, Europe and Asia. Big companies
such as Motorola Inc [31], Samsung Group [32], and Sony Group are aggressively pursuing
FED technology using carbon nanotubes.
Apart from the well known electrical power saving advantage, another major advantage
of the FED technology is that the display is thin and light. Although it has the optical quality
of a CRT, it does not produce X-rays since the voltage applied to phosphor screen is no more
than 6 to 8 kV as compared to the voltage of 15 to 30 kV required to apply to phosphor screen
in the case of CRT. FEDs are not sensitive to magnetic fields or large temperature variations.
For all of these reasons it can find wide range of applications in industrial and automobile
applications, or as a monitor for scientific and medical instruments such as mass
spectrometers or oscilloscopes. Versions have also been developed for avionics and this
technology could possibly be considered for manned space systems. FED is emerging as a
potential threat to the big TFT-LCD dominant display market. In general, FEDs offer the
prospect of flat panel displays which are superior to TFT-LCD screens in brightness, colour
rendition, response time and operating temperature range. FED has demonstrated its
advantages: high contrast ratio, great brightness, consuming low power, wide viewing angle,
excellent colour gamut, can be used in harsh environment such as in wider range of operating
temperature, and in radiation condition.
Nowadays, the most popular substrate material on which FEDs are fabricated is the sodalime
glass, which is compatible to the TFT-LCD technology. There are many advantages of
using the soda-lime glass over other materials for display application. For example, soda-lime
glass is vacuum compatible, the material cost is inexpensive, the mature technique enable the
soda-lime glass to be made very flat over a relatively large area, and it can be coated with a
variety of materials using Very Large Scale Integration (VLSI) thin film technology [33].
However, the fabrication of the Spindt type micro tips, using micro fabrication technique, has
difficulties to produce large area field emitters with acceptable uniformity [34]. So far, FEDs
constructed with the Spindt type micro field emitters, as well as the carbon nanotubes have
only been produced on small and medium size substrates.