61061421 Field Emission Display Screen Seminar Report
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Transcript of 61061421 Field Emission Display Screen Seminar Report
Field Emission Display Screen Seminar Report ‘03
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. 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
Dept. of ECE MESCE Kuttippuram-1-
Field Emission Display Screen Seminar Report ‘03
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.
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Field Emission Display Screen Seminar Report ‘03
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.
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.
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Field Emission Display Screen Seminar Report ‘03
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.
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Field Emission Display Screen Seminar Report ‘03
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.
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Field Emission Display Screen Seminar Report ‘03
The micro tips can be of different types:
1. Wedge type emitter using silicon.
2. Silicon tips with continuous coating of diamond particles.
3. Single-crystal diamond particle on silicon tips.
4. Planar diode emitter.
5. Metal-insulator-semiconductor type planar
emitter
Wedge type emitter using silicon
The out standing features of wedge type emitter using silicon are
its brightness and low vacuum requirements. It has a packaging density of 106
emitters per mm2 at the rate of 103 emitters per pixel. It has an accelerating
electrode potential of 40V and low power consumption. However this display
has to go miles in the case of price and mass production status.
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Field Emission Display Screen Seminar Report ‘03
Silicon tips with continuous coating of diamond particles
These cone-shaped blunt emitters have a radii of curvature ranging from
0.3 to 3 pm. The low work function can offer considerable current at low
voltage field emission.
Single-crystal diamond particle on silicon tips .
Instead of plating the polycrystalline diamond particles on silicon tips,
diamond particles can be placed on the tips of silicon needle to form a field
emitter. The only drawback is the expenditure involved in placing diamond
particles on the tips of silicon needle.
Dept. of ECE MESCE Kuttippuram-7-
Field Emission Display Screen Seminar Report ‘03
Planar diode emitter.
The planar diode emitter configuration uses a diamond like carbon
emitter. They are easy to fabricate and much suited for mass production. One
disadvantage for this type of displays is that once failed, the display will have
to work with out that pixel.
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Field Emission Display Screen Seminar Report ‘03
Metal-insulator-semiconductor type planar emitter
A new type of field emission display (FED) based on an edge-enhance
electron emission from metal-insulator-semiconductor (MIS) thin film
structure is proposed. The electrons produced by an avalanche breakdown in
the semiconductor near the edge of a top metal electrode are initially injected
to the thin film of an insulator with a negative electron affinity (NEA), and
then are injected into vacuum in proximity to the top electrode edge. The
condition for the deep-depletition breakdown near the edge of the top metal
electrode is analytically found in terms of ratio of the insulator thickness to the
maximum (breakdown) width of the semiconductor depletition region: this
ratio should be less than 2/(3 \pi - 2) = 0.27. The influence of a neighboring
metal electrode and an electrode thickness on this condition are analyzed.
Different practical schemes of the proposed display with a special reference to
M/CaF_2/Si structure are considered.
Dept. of ECE MESCE Kuttippuram-9-
Field Emission Display Screen Seminar Report ‘03
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.
The final packaging of the field emission display screen is as shown in
the figure above. The front portion here is the Phosphor and the back
represents the emitter or micro tips.
Dept. of ECE MESCE Kuttippuram-10-
Field Emission Display Screen Seminar Report ‘03
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.
Dept. of ECE MESCE Kuttippuram-11-
Field Emission Display Screen Seminar Report ‘03
There are two basic ways in which working of an FED can be explained:
1. Low voltage anode
2. High voltage anode
LOW VOLTAGE ANODE
The low voltage approach uses the “field sequential colour” method as I
mentioned earlier. In this method the entire screen is individually painted in
each of the three primary colours, one at a time. As each of the colours are
painted separately only that colour phosphor is grounded, so that all the
electrons can strike that particular colour. This prevents any of the electrons to
strike accidentally the other colours present in the screen. This may be a
problem in the case of the low voltage approach.
HIGH VOLTAGE ANODE
In the high voltage approach the emission from micro tip radiate in a
roughly 600 cone. When these tips are very close to anode, the spread to
emitted stream of electron is small enough to result in a spot size of nearly
0.33mm diameter. When the anode voltage is increased further greater
phosphor efficiency is required and also the distance between anode and
cathode should be increased to prevent arcing. Also focusing will be required
in this case.
Dept. of ECE MESCE Kuttippuram-12-
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The light emitting principle of the field emission display screen is as
shown in the figure below.
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Field Emission Display Screen Seminar Report ‘03
FED CHARACTERISTICS
In the world of miniaturization, Cathode ray tube (CRT) is giant
dinosaurs waiting for extinction. A CRT uses a single-point hot electron source
that is scanned across the screen to produce an image. Comparing with the
CRT displays the field emission displays has many advantages. They are:
1. Brightness
2. Speed
3. Compact and lightweight
4. Display size
5. Low driving voltage
6. Wider viewing angle
7. High illumination
8. Wide temperature extremes
9. Colour Quality
BRIGHTNESS
Most displays are adequate in normal (50–100 fc) room lighting.
However, in dimly lit situations, such as a patient bedside at night, dim
(reflective) displays are difficult to read. Most alarming, a dim display may be
deceptively easy to misread.
Because an FED is an emissive display that produces its own light, it
can be dimmed continuously from full brightness to less than 0.05 fL. In direct
sunlight applications there will be a problem of low contrast This often
requires the use of special contrast enhancement filters, such as 3M micro
louver filters to generate contrast.
Dept. of ECE MESCE Kuttippuram-14-
Field Emission Display Screen Seminar Report ‘03
SPEED
Display speed is the rate at which the image can be changed while
maintaining image detail. Displays with inadequate response times will create
image "smear" that can be confused with defective blood flow, or will hide
jitter that can indicate instability or electrical interference. With a response
time of 20 nanoseconds, FED technology produces smear-free video images.
COMPACT AND LIGHTWEIGHT FLAT PANEL DISPLAYS
Far less bulky than the CRT or plasma emission based displays, and are
also significantly brighter than back lit LCDs.
DISPLAY SIZE
This technology could produce affordable large displays in the 20 to 40-
inch diagonal range suitable for TVs.
LOW DRIVING VOLTAGE
As discussed earlier the field emission displays can be made to work in
extremely low voltage conditions with some limitations.
WIDER VIEWING ANGLE
A main advantage of the field emission display screens when compared
with the ordinary cathode ray tube display is its wider viewing angles. The
FED s can attain a viewing angle of 1600.
Dept. of ECE MESCE Kuttippuram-15-
Field Emission Display Screen Seminar Report ‘03
HIGH ILLUMINATION
The FED glows by itself by the bombarding of the electrons on the
phosphor screen. So the FEDs can attain high illumination.
WIDE TEMPERATURE EXTREMES
Unlike CRTs, FEDs have no cathode heater, no deflection system, and
no shadow mask. Because of the cold cathode emission, instant-on is available
at wide temperature extremes (–40 to 85°C).
COLOUR QUALITY
FEDs use conventional TV phosphors. This is of particular importance
in such areas as telemedicine. The ability of a display to show true flesh tones
depends in large part on the colorimetry of the display. TV phosphors have
been fine-tuned for decades to provide the most natural skin tones possible,
and, although not yet widely used, are unchanged in some FEDs.
FED technology provides a wide color gamut with continuous dimming
and 8-bit gray scale. Its image is equally bright from any viewing angle, and
power efficiency is high (from 3 to 40 lm/W, depending on voltage and
phosphor).
FEDs produce gray scale by a number of different methods.
a. Frame Rate Control
b. Pulse Width Modulation (PWM)
c. Voltage Modulation
d. Current or Charge Control
e. Mixed-Mode Modulation
Dept. of ECE MESCE Kuttippuram-16-
Field Emission Display Screen Seminar Report ‘03
Frame Rate Control
Running at, for example 400 Hz, a 50% gray level can be obtained by
alternating a white and a black field every other frame. A 25% gray level can
be achieved by alternating one of four frames to white, or one out of 400
frames. This method is simple, allowing the use of digital on/off drivers, but
the FED runs into flicker at low, and capacitive switching problems at high,
frequency.
Pulse Width Modulation (PWM)
PWM requires the column to switch off earlier than the row time to
decrease the pixel brightness level. The advantage to this method is that when
on, the tips are always operated at maximum voltage, but rate control delays
can add up at short switching rates.
Voltage Modulation
This is the classic analog method of producing grey levels and gives a
luminance response similar to that of a CRT. However, it requires accurate
low-power drivers and very uniform tip response.
Current or Charge Control
This method corrects for tip nonuniformity but requires complex
drivers to control the emitted charge.
Dept. of ECE MESCE Kuttippuram-17-
Field Emission Display Screen Seminar Report ‘03
Mixed-Mode Modulation
This is the method most display integrators use. Some gray scale is
obtained from partial use of two or more of the above modes, thus avoiding the
extreme conditions of any one method.
FED technology offers an array of display characteristics, ranging from
efficient high-voltage focused versions to cost-effective low-voltage proximity
focused iterations. Extracting electrons from microtips and modulating them
with a G-2 gate provides flexibility and allows display designers to specify
visual performance. Because of the simpler assembly, custom performance and
special sizes are less costly to produce
View
angles
Brightness Contrast Speed Colour
1600 To 3500 fL <100:1 20 ns TV
colours
Table I. Field emission display characteristics
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Field Emission Display Screen Seminar Report ‘03
DRAWBACKS
Even though the field emission display screens has many advantages as
mentioned above it also have some disadvantages which may be listed below:
1. Vacuum tubes do require maintenance.
2. Current FEDs often suffer from variation in screen brightness across the
display, and also within each pixel.
3. Durability due to electrical discharge in the small gaps everywhere in
FED prototypes.
4. The killing problem was durability: the tips couldn’t survive under
severe conditions of arcing (i.e. electrical discharge) due to the small gaps
everywhere in FED prototypes.
5. Another big problem for the FED concept is the cathode driver. For big
screen applications, such as HDTV, it is difficult (if not impossible) to build a
feasible high voltage (several hundred of switching voltage) driver for operating
multiple (thousands) cathodes – power consumption will exceed several
kilowatts for such a driver (note that modern TV set consumes only ~20-150
Watts of energy).
Dept. of ECE MESCE Kuttippuram-19-
Field Emission Display Screen Seminar Report ‘03
Since the FED uses the vacuum tubes like the cathode ray tubes it
requires frequent maintenance. This drawback cannot be eliminated under any
conditions.
The second, third and fourth drawbacks can be eliminated by using
ballast resistors. The ballast resistors are those resistors that form a thin layer
below the electron guns or micro tips. They are highly resistive in nature and it
restricts the amount of current flowing through the micro tips.
Dept. of ECE MESCE Kuttippuram-20-
Field Emission Display Screen Seminar Report ‘03
FAQS
1. What is field of view?
Field of View (FOV) describes how large the virtual image can appear
to be to the viewer and is measured in degrees. >50 degree FOV per eye is
possible using OLED micro displays.
2. Why didn't the FED industry already take over?
The short answer is that the fundamental FED idea was not supported
by some advanced decision making technologies, such as the Ideality
Approach As a result of that, the FED industry has been depressed for many
years.
3. What is display speed?
Display speed is the rate at which the image can be changed while
maintaining image detail.
4. Why can it be used in Laptop computers?
The FED promises full colour at low power consumption in a form
factor that is compatible with laptop computers. Also it will be attractive.
Dept. of ECE MESCE Kuttippuram-21-
Field Emission Display Screen Seminar Report ‘03
5. Is there any radiation for the field emission display screen?
Since the field emission display screen uses the vacuum tubes and the
phosphor screens there will be some radiation for it. The radiation effect of the
FED screen will be similar to that of the cathode ray tube (CRT) display.
6. Is there any interference among the electrons while it propagates?
At a time the cathode emits electrons that will hit the phosphor screen on
only one colour. So even when the electrons interfere among themselves there
will not be any loss of information.
7. What is display size?
Display size is the total size of the display in which the information can be
obtained. For the field emission display screen the display size is about 40-inches
diagonally.
Dept. of ECE MESCE Kuttippuram-22-
Field Emission Display Screen Seminar Report ‘03
FED APPLICATIONS
1. Sonographs
2. X-ray imaging
3. Heart-rate monitors
4. Laptop computers
5. Hang-on-the-wall televisions
6. Big screen and PC monitors
7. High-definition TV
Dept. of ECE MESCE Kuttippuram-23-
Field Emission Display Screen Seminar Report ‘03
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.
Dept. of ECE MESCE Kuttippuram-24-
Field Emission Display Screen Seminar Report ‘03
BIBLIOGRAPHY
BOOKS
ELECTRONICS FOR YOU, JUNE 2002
ELECTRONICS FOR YOU, JULY 2002
WEB
WWW.SHARPWORLD.COM
WWW.WTEC.ORG
WWW.VIRTUALVISION.COM
WWW.EOFOUNDRY.COM
WWW.ISIS-INNOVATION.COM
WWW.ATIP.ORG
Dept. of ECE MESCE Kuttippuram-25-
Field Emission Display Screen Seminar Report ‘03
ACKNOWLEDGEMENT
I extend my sincere thanks to Prof. P.V.Abdul Hameed, Head of
the Department for providing me with the guidance and facilities for the
Seminar.
I express my sincere gratitude to Seminar coordinator
Mr. Manoj K, Staff in charge, for his cooperation and guidance for
preparing and presenting this seminar.
I also extend my sincere thanks to all other faculty members of
Electronics and Communication Department and my friends for their
support and encouragement.
Radheesh M
Dept. of ECE MESCE Kuttippuram-26-
Field Emission Display Screen Seminar Report ‘03
ABSTRACT
With a 100-year head start over more modern screen technologies, the
CRT is still a formidable technology. It’s based on universally understood
principles and employs commonly available materials. The result is cheap-to-
make monitors capable of excellent performance, producing stable images in
true colour at high display resolutions. But in the world of miniaturization,
Cathode ray tubes (CRT) are giant dinosaurs waiting for extinction. A CRT
uses a single-point hot electron source that is scanned across the screen to
produce an image.
The CRT’s most obvious shortcomings are well known:
• It uses too much electricity.
• Its single electron beam design is prone to misfocus, misconvergence and
colour variations across the screen.
• Its clunky high-voltage electric circuits and strong magnetic fields create
harmful electromagnetic radiation.
• It’s physically too large.
Attempts to replace bulky Cathode ray tubes resulted in the
introduction of the field emission display screens (FED) screens. It will be the
biggest threat to CRT’s dominance in the panel display arena. Instead of using
a single bulky tube, FEDs use tiny ‘mini tubes’ for each pixel, and the display
can be built in the same size as a CRT screen.
The FED screens are lightweight, low power consuming and compact.
The FEDs can be used instead of some other technologies are gaining market
share in big screen and PC monitors, such as Projection TV, Plasma Displays,
Liquid Crystal, and Organic Transistor Displays.
Dept. of ECE MESCE Kuttippuram-27-
Field Emission Display Screen Seminar Report ‘03
CONTENTS
INTRODUCTION 01
FED TECHNOLOGY 04
WORKING 11
CHARACTERISTICS 14
DRAWBACKS 19
FAQS 21
APPLICATIONS 23
CONCLUSION 24
BIBLIOGRAPHY 25
Dept. of ECE MESCE Kuttippuram-28-