03-03-2011, 09:56 AM
PRESENTED BY:
Tapan kumar choudhury
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FIELD EMISSION DISPLAY
What is Field emission?
Definition:
The emission of electrons stripped from parent atoms by a high electric field via quantum mechanical tunneling.
It is also called as Fowler-Nordheim tunneling because they explained the basic principles in 1928.
FED Principles
In Field emission display, electrons coming from millions of tiny micro-tips pass through gates and light up pixels on a screen.
This principle is similar to that of cathode-ray tubes in television sets. The difference: Instead of just one "gun" spraying electrons against the inside of the screens face, there are as many as 500 million of them (micro tips).
Pixels
Faceplate picture elements (pixels) are formed by depositing and patterning a black matrix, standard red, green, and blue TV phosphors and a thin aluminum layer to reflect colored light forward to the viewer.
Pixels are lightened by electrons coming from cathode.
Cathode
The cathode/back-plate is a matrix of row and column traces. Each crossover lays the foundation for an cathode emitter.
Each crossover has up to 4,500 emitters, 150 nm in diameter. This emitter density assures a high quality image.
Emitters generate electrons when a small voltage is applied to both row (base layer) and column (top layer).
Metal Tips
Typical field emission characteristics of the FED pixel with an area of 240 mm x 240 mm containing 1.4x10 6 tips.
The first generation of FED is not really compatible with large area (40”)
• The technological steps are troublesome:
Gate hole lithography Tip growth
Carbon Nanotube
Characterized by
• Superior mechanical strength.
• Low weight.
• Good heat conductance even higher than diamond.
• Ability to emit a cold electron at relatively low voltages due to high aspect ratio (h/r) and nanometer size tips (300nm).
Why Carbon NanoTube as emitters?
The threshold voltage for field emission is very low
In place of one emitter, a large no. of emitters are present
Properties of CNTs
1. Electrical Conductivity
Conductivity has been shown to be a function of their degree of twist as well as their diameter.
Carbon nanotubes with a small diameter are either
semi-conducting or metallic depending on their degree of twist
2. Mechanical Properties
Carbon nanotubes are all-carbon molecules composed of concentric graphitic shells with extremely strong covalent bonding of atoms with shells.
This property makes them one of the strongest materials known, both in terms of tensile strength and elastic modulus.
They tend to undergo buckling when placed under compressive or bending stress.
