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Previously Unknown Superb
Picture Quality |
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| Table 1 presents the specifications of the
organic EL panel used in the CLIE. This
panel achieves high brightness (150 cd/m2), high contrast (1000:1), and high resolution
(151 ppi). Furthermore, its color
reproducibility greatly exceeds that of
conventional organic EL panels. (See figure
1.) While the color gamut of conventional
panels had an area only approximately
70% of that of standard CRT
monitors, this panel achieves a gamut that
is 147% of the CRT gamut, roughly twice
that of the conventional panels. Taken
together, these picture quality characteristics
mean that this panel creates strikingly
beautiful images.
At the same time, this panel holds the per
unit area of screen power consumption to
levels lower than those of conventional
panels. This was achieved by using unique
Sony-developed device structures. |
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Panel Structure that Gets the Best Performance from the Technology |
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Light extraction methods
While conventional panels adopted a
method called bottom emission, this panel
uses top emission. The method in which
the light generated by EL is extracted from
the TFT substrate side is called bottom
emission. Since the EL drive pixel circuits
are present on the TFT substrate, the area
from which light can be extracted is limited
and the efficiency with which the light
generated by EL is used is reduced. In
contrast, light is extracted from the sealing
substrate side in top emission and the
light generated by EL can be extracted
efficiently.
No circular polarizer is
required
In conventional panels, a circular polarizer
(retardation film and polarizer) was
installed on the panel surface. While this
was provided to prevent the reflection of
ambient light, it also reduced the amount
of EL light emitted. This panel does not
use a circular polarizer, but rather uses the
microcavity structure described later in
this article and color filters. At the same
time as preventing the reflection of ambient
light, the microcavity structure and
color filters achieve an increase in color
purity. The ability to use color filters relatively
easily is a feature of top emission.
In bottom emission panels, the color filters
(OCCF*) are formed on the TFT circuit,
and furthermore, the organic film is
formed on top of those filters, thus increasing
the technical difficulty of manufacturing
the panels.
It is the combination of top emission, the
microcavity structure, and these color filters
that allow this panel to achieve its
superb picture quality with low power
consumption.
* OCCF: On-chip Color Filter
Fully fixed sealing
Previously, CAN sealing, in which an inert
gas is enclosed, was used. More recently,
glass substrates that have been
carved out from the inside and the edge
sections retained (see figure 2) have been
used for sealing. These are sealing methods
that avoid as much as possible damage
to the organic films by the sealing
process.
In this panel, the problem of damage to
the organic films by the sealing process
has been resolved and a fully fixed structure
that can better withstand external
mechanical shocks has been created. This
has allowed Sony to reduce the thickness
of the sealing glass and make the panel
even thinner. Furthermore, it opens the
way to creating ultrathin panels using
plastic film sealing. |
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Sony's Unique "Super Top
Emission" Technology |
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As we described in the previous section,
this panel represents a significant technological
leap over conventional panels and
shows the way for the future of organic
EL technology. It is Sony's unique “Super
Top Emission” technology (figure 3
shows its logo) that makes this leap possible.
Microcavity structure
Figure 4 shows the device structure. One
of the features of this panel is that the
thicknesses of the organic films differ for
the RGB colors. This is because the film
thickness is selected to match the optical
path length between the cathode and anode
electrodes to the EL spectral peak
wavelength for each color (microcavity
structure).
Another feature is the point that the cathode
electrode is a semitransparent film.
The light whose wavelength matches the
optical path length between the electrodes
repeatedly reflects and interferes (multiple
reflectance interference) between the
cathode semitransparent film and the (reflective
film) anode electrode. As a result
the spectrum of the extracted light is
sharpened (see figure 5) and the color
purity is increased.
Microcavity structure and
color filters
Figure 6 shows the effect of reducing
ambient light reflection provided by the
microcavity structure and the color filters.
When the organic film optical path length
is matched to the wavelength of the green
EL light, the green component of the ambient
reflected light is cut. At the same
time, the ambient reflected light with colors
other than green is cut by the green
filter. That is, when a color filter is combined
with the microcavity structure, essentially
all ambient reflected light can be
cut. This allows high contrast to be
achieved without the use of a circular
polarizer.
While this figure shows this effect for
green, red and blue operate in the same
manner.
Color filter color selection
white EL technique
In addition to the technique used in the
panel included in the CLIE and described
previously in this article, Sony has also
developed a microcavity structure color
filter color selection white EL technique.
In this technique, the whole panel is manufactured
using an EL film that generates
white light emission and color filters are
used for RGB color selection. Figure 7
shows the cross section of a panel using
this technique. Sony exhibited a 12.5-type
prototype panel using this technique at
SID 2004*. (See photograph 2.)
*: SID 2004: Display technology related to
conference and exhibition held on May 25 to
27, 2004 in Seattle, Washington. |
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Photograph 2
Sony Color Filter Color
Selection White EL Panel
(12.5 type) Displayed at SID
2004
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Future Developments |
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| Sony has developed the unique "Super
Top Emission" technology that takes
maximum advantage of the features of
organic EL technology and supports mass
production. Sony is committed to providing
the highest performance organic EL
panels and maintaining their commanding
lead over those of other manufacturers
in this area.
Keep your eye on Sony for the best in
organic EL panels. |
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See
all articles with figures and tables.  |
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Vol.39 |
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