Various types of displays have become
common in the every day life. The displays are used in televisions, computers
etc. They also have wide use in laboratories and in medical applications. The
displays are those devices by which we can view moving objects. The displays
are manufactured depending upon their application.
One of the hottest markets driving physics research is
the demand for a perfect visual display. People want, for example, large, thin,
lightweight screens for high-definition TV and outside displays and very high
resolution flat computer monitors that are robust and use little power. Several
types of flat display are competing for these applications. Not surprisingly, the research departments of
universities and the big electronics companies around the world are bustling
with exciting ideas and developments. New university spinout companies are
developing many new devices. The different types displays
available are:
·
Liquid crystal displays
·
Plasma displays
·
Electro luminescent displays
·
Field emission displays
·
Projection displays
Liquid crystal displays
Even the
liquid crystal display (LCD), which has
85 per cent of the flat-screen market, is still a young technology and the
subject of very active research. LCDs depend on arrays of cells (pixels)
containing a thin layer of molecules which naturally line up (liquid crystals);
their orientation can be altered by applying a voltage so as to control the
amount of light passing through. Their main drawbacks have been poor viewing characteristics
when seen from the side and in bright light, and a switching speed too slow for
video. Electrically sensitive materials called ferroelectric and
antiferroelectric liquid crystals show potential. These work slightly
differently and are bistable so should use less power. They can respond 100 to
1000 times faster than current displays, and should give brighter images from
all angles. One solution to the drawbacks of LCDs is to combine them with
another technology. Indeed, the latest, high quality LCDs on the market
incorporates a tiny electronic switch (a thin film transistor, TFT) in each
pixel to drive the display.
Plasma displays
Although LCDs up to a 42-inch
diagonal have been demonstrated, for larger flat TV screens, companies have
instead turned to plasma display panels. These employ gas discharges (as in a
fluorescent tube) controlled by an electrical signal. The ionized gas, or plasma, emits ultraviolet light which stimulates red, green and
blue phosphors inside each pixel making up the display panel to produce colored light. The images on the latest displays are very clear and bright.
Unfortunately they are still expensive.
Electro luminescent displays
One of the most promising emerging display
technologies exploits ultra thin films of organic compounds, either small
molecules or polymers, which emit light (luminescence) when subjected to a
voltage. These organic light-emitting diodes (OLEDs) produce bright,
lightweight displays.
Field emission displays
The other major technology competing for the flat
screen, market is the field emission display. This works a bit like a
cathode-ray tube, except that electrons are emitted from thousands of metal
‘micro-tips’, or even a diamond film, when an electric field is applied between
the tips and a nearby phosphor coated screen. Printable Field Emitters, based
at the Rutherford Appleton Laboratory near Oxford, has come up with a novel
idea employing low-cost composite materials deposited and patterned using
screen printing and simple photo-lithography This technology could produce
affordable large displays in the 20 to 40-inch diagonal range suitable for TVs.
Projection displays
Finally, a completely different
approach showing potential is to direct light from an image source using
wave-guides through a glass or plastic sheet onto a screen. A clever variation
of this is ‘the Wedge’ developed by Cambridge 3D Display. Light rays pass up a
thin wedge-shaped glass plate and emerge at right angles at various points
depending on the angle of entry. The beauty of this device is that it could be
used to project any kind of micro-display – LCD or OLED, for example – onto a
large screen.
All of the technologies described
here still have drawbacks and no one yet knows which will win the big prize of
flat screen TVs. It is likely that all of them will find niche markets. The
next five years will certainly see a revolution in flat screen development.
FED Technology
The FED
screen mainly contains three parts:
1.
Low-voltage phosphors.
2.
A field emission cathode using a thin carbon sheet as
an edge emitter.
3. FED
packaging, including sealing and vacuum processing.
