10-05-2014, 10:44 AM
Field Emission Display Screen
[attachment=63090]
Introduction
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.
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 ionised gas, or plasma, emits ultraviolet light which stimulates red, green and blue phosphors inside each pixel making up the display panel to produce coloured 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 photolithography. 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.
Low voltage phosphors
The low voltage phosphors are the screens in which the images are displayed. In the display technology the phosphor screens act as anode, which receives the electrons emitted from the cathode. The phosphor glows when the electrons bombards with it to show the images. The phosphors are made up of layers of three primary colours -green, red and blue. These colour phosphors are displayed by the “field sequential colour” in which the green information is read first then redrawn with red information and finally with blue colour. The FED may have pixel pitches of about 0.2mm.
Field emission cathode
In the field emission display screen the cathode are electron guns that emit electrons. Here there are about 200-million electron guns called “micro tips”. The emission of electrons is called “cold cathode emission”. Each of these micro tips is smaller than one micrometer and they are deposited into a dense grid. They are made up of materials such as molybdenum.
FED packaging
The field emission display screens are comprised of a thin sandwich. In this the back is a sheet of glass or silicon that contains millions of tiny field emitters which is the cathode. The front is a sheet of glass coated with phosphor dots, which is the anode. The anode and cathode are a fraction of millimeter apart.
WORKING
The field emission display works a bit like the cathode ray tube except that electrons are emitted from thousands of metal micro tips or even from a diamond film. This emission of electron occurs from the cold cathode when a voltage is applied between the cathode and anode. These electrons propagate from cathode to anode. They bombard with the phosphor, which is the anode and causes it to glow. This reproduces the image on the screen by the mixing of colours present in the screen.
Conclusion
CRT technology has already reached its technological and marketing limits and will likely be replaced in 10 years. The modern world needs substances that are small in size. This shows that the cathode ray tube do not have much to do anything in the market in future. And it would die already, if Field Emission Display (FED) technology or any other displays would bring anything to the market.
[attachment=63090]
Introduction
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.
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 ionised gas, or plasma, emits ultraviolet light which stimulates red, green and blue phosphors inside each pixel making up the display panel to produce coloured 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 photolithography. 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.
Low voltage phosphors
The low voltage phosphors are the screens in which the images are displayed. In the display technology the phosphor screens act as anode, which receives the electrons emitted from the cathode. The phosphor glows when the electrons bombards with it to show the images. The phosphors are made up of layers of three primary colours -green, red and blue. These colour phosphors are displayed by the “field sequential colour” in which the green information is read first then redrawn with red information and finally with blue colour. The FED may have pixel pitches of about 0.2mm.
Field emission cathode
In the field emission display screen the cathode are electron guns that emit electrons. Here there are about 200-million electron guns called “micro tips”. The emission of electrons is called “cold cathode emission”. Each of these micro tips is smaller than one micrometer and they are deposited into a dense grid. They are made up of materials such as molybdenum.
FED packaging
The field emission display screens are comprised of a thin sandwich. In this the back is a sheet of glass or silicon that contains millions of tiny field emitters which is the cathode. The front is a sheet of glass coated with phosphor dots, which is the anode. The anode and cathode are a fraction of millimeter apart.
WORKING
The field emission display works a bit like the cathode ray tube except that electrons are emitted from thousands of metal micro tips or even from a diamond film. This emission of electron occurs from the cold cathode when a voltage is applied between the cathode and anode. These electrons propagate from cathode to anode. They bombard with the phosphor, which is the anode and causes it to glow. This reproduces the image on the screen by the mixing of colours present in the screen.
Conclusion
CRT technology has already reached its technological and marketing limits and will likely be replaced in 10 years. The modern world needs substances that are small in size. This shows that the cathode ray tube do not have much to do anything in the market in future. And it would die already, if Field Emission Display (FED) technology or any other displays would bring anything to the market.