21-11-2012, 11:43 AM
OLED: An emerging display technology
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Introduction
An exciting technology has been available in many small devices
such as cell phones and digital camera displays for the last 13
years. Soon it may available for use in larger standard office and
home entertainment displays. The technology is organic light
emitting diode (OLED). It is possible that in the next 2-3 years
you may see an 80” OLED in your living room or board room that
only requires 10 or less volts of power to operate.
OLED display devices use organic carbon-based films, sandwiched
together between two charged electrodes. One is a metallic
cathode and the other a transparent anode, which is usually
glass. Online encyclopedia, Wikipedia, defines an organic compound
as “any member of a large class of chemical compounds
whose molecules contain carbon, with the exception of carbides,
carbonates, carbon oxides and gases containing carbon.”
1. Vacuum Deposition or Vacuum Thermal Evaporation (VTE).
In a vacuum chamber, the organic molecules are evaporated
through a slow heat process and then allowed to condense as
thin films onto a cooled substrate. This is a very inefficient and
expensive process.
2. Organic Vapor Phase Deposition (OVPD). This process employs
an inert carrier gas (such as nitrogen) to precisely transfer
films of organic material onto a cooled substrate in a hot-walled,
low-pressure chamber. The precise transfer and ability to better
control film thickness translates to lower material cost and higher
production throughput.
3. Inkjet Printing. OLEDs are sprayed onto the substrate the same
way our desktop inkjet printer sprays ink onto paper. This greatly
reduces the cost of manufacturing OLEDs and allows for printing
on very large films. This allows for a much lower cost and larger
home displays and PIPD products.
One of the major benefits of OLEDs is their low power consumption
when compared to traditional LEDs or LCDs. OLEDs also do
not require backlighting to function, which in addition to using
less power, also lowers manufacturing costs.
Even with all the layers that make up an OLED, this is an emissive
technology – meaning it generates its own light. An OLED
display is very thin and compact, typically has a viewing angle of
160 degrees and will operate on as little as 2 volts.
Imagine today’s typical 60” flat-screen display, but instead of
an 8-in. thick, 250-lb. plasma display or a 65-lb. LCD, your 60”
OLED display is only 1/2” thick and weighs roughly 30 lbs.!
How do OLEDs work?
As previously mentioned, OLEDs are an emissive technology,
which means they emits light instead of diffusing or reflecting
a secondary source, as LCDs and LEDs currently do. Below is a
graphic explanation of how the technology works.
remain off. Again, the brightness of each pixel is proportional to
the amount of applied current.
PMOLEDs are easy to make, but they consume more power than
other types of OLED, mainly due to the power needed for the
external circuitry. PMOLEDs are most efficient for text and icons
and are best suited for small screens (2- to 3-inch diagonal) such
as those you find in cell phones, PDAs and MP3 players. Even
with the external circuitry, PMOLEDs consume less battery power
than the LCDs that are currently used in these devices.
OLED Advantages
The LCD is currently the display of choice in small devices and
is also popular in large-screen TVs. Regular LEDs often form the
digits on digital clocks and other electronic devices. OLEDs offer
many advantages over both LCDs and LEDs, including:
• The plastic, organic layers of an OLED are thinner, lighter
and more flexible than the crystalline layers in an LED or LCD.
• Because the light-emitting layers of an OLED are lighter,
the substrate of an OLED can be flexible instead of rigid.
OLED substrates can be plastic rather than the glass used for
LEDs and LCDs.
• OLEDs are brighter than LEDs. Because the organic layers
of an OLED are much thinner than the corresponding inorganic
crystal layers of an LED, the conductive and emissive
layers of an OLED can be multi-layered. Also, LEDs and LCDs
require glass for support, and glass absorbs some light.
OLEDs do not require glass.
• OLEDs do not require backlighting like LCDs. LCDs work by
selectively blocking areas of the backlight to make the images
that you see, while OLEDs generate light themselves.
Because OLEDs do not require backlighting, they consume
much less power than LCDs (most of the LCD power goes to
the backlighting). This is especially important for battery-operated
devices such as cell phones.
• OLEDs are easier to produce and can be made to larger sizes.
Because OLEDs are essentially plastics, they can be made
into large, thin sheets. It is much more difficult to grow and
lay down so many liquid crystals.
OLED Applications
OLED technology was invented by Eastman Kodak in the early
1980s and, currently, OLEDs are used in small-screen devices
such as cell phones, PDAs and digital cameras. In March 2003,
the company introduced the world’s first digital camera with an
OLED display. In September 2004, Sony Corporation announced
that it was beginning mass production of OLED screens for its
CLIE PEG-VZ90 model of personal-entertainment handhelds.
Several companies have already built prototype computer monitors
and large-screen TVs. In May 2005, Samsung Electronics
announced that it had developed the first 40” OLED-based, ultraslim
TV.
OLED Research and development is moving forward at a rapid
pace and may soon lead to applications in heads-up displays
(HUD), automotive dashboards, billboard-type displays, home
and office lighting, and flexible displays. OLEDs refresh approximately
1000 times faster than LCDs. Although a device with an
OLED display could change information in real time, the eye cannot
perceive changes to video faster than about 13ms. Refresh
rate is also not the end-all in display products. Many of the highend
monitors take advantage of advanced engineering in scalers
and other components to make the view more pleasing to the eye.