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SXRD TM Creates Previously Unknown Smooth, Realistic Images
Reflective Liquid Crystal Display Technology for Use in Projection System |
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Extremely high contrast:
3000:1 or higher |
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Realistic high resolution
that supports full HD |
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High aperture ratio: 92% |
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High-speed response
time: under 5 ms |
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Superlative light resistance
reliability provided
by inorganic alignment
film |
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0.78-Type Full HD Resolution
2M-pixel SXRD |
1.55-Type 4K Resolution
8.85M-pixel SXRD |
In March 2005, Sony released the
largest*1 Japanese-market consumer TV
set, the 70V QUALIA 006 Projection TV
“KDS-70Q006”. (See photograph 1.) At
the same time as providing the first full
HD support*2 in a projection TV (with a
fixed pixel system) and faithfully reproducing
dark scenes with its high contrast,
this product achieves photograph-like
smooth high picture quality images.
This
product adopts 0.78-type full HD SXRD
(Silicon X-tal*3 Reflective Display) for
each of the red, blue, and green color channels
in the optical engine that forms the
heart of this product.
The high picture quality of the QUALIA 006 is created by
the high resolution, high aperture ratio,
high contrast, and high-speed response,
which are the features of the SXRD technology.
*1: According to a Sony survey on February 9,
2005.
*2: According to a Sony survey on February 9,
2005 of fixed pixel system projection TVs in
the Japanese market.
*3: X-tal means “crystal.” |
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SXRD Device Technology |
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SXRD devices are reflective LCD devices
that use the LCOS (Liquid Crystal on Silicon)
silicon drive devices independently
developed by Sony.
These are projection
display devices that enlarge and project
an image onto a screen with an optical
system and are included in front projectors
and projection TV sets.
Currently, Sony has developed two
devices, a diagonal 0.78-type full HD
resolution (1920H × 1080V) panel and a
diagonal 1.55 type with an 8.85M pixel
resolution (4096H × 2160V) panel.
These
devices are already in the mass production
stage.
Table 1 presents the specifications
of these panels and photograph 2
shows the products.
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Device Structure that
Supports High Picture Quality |
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Figure 1 shows the structure of the SXRD
device. The pixel pitch is 9 µm in the 0.78-
type panel and 8.5 µm in the 1.55-type
panel.
Since the inter-pixel space is an
extremely small 0.35 µm in both panels,
they have high aperture ratios of 92% or
higher.
The features of the SXRD devices
are smooth images made possible by the
high aperture ratio and the high resolution
that exceeds 2M pixels (full HD
(1920H × 1080V)), the high device contrast
of over 3000:1, the high-speed response
time of under 5 ms, and the superlative
light resistance reliability due to the
inorganic alignment film. |
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High Resolution |
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Sony took advantage of the structural
features of the reflective type devices and
silicon fine fabrication technologies and
achieved a 9 µm pixel pitch by embedding
the drive circuits in the back side of
the reflective mirror, and was able to lay
out 2 million pixels in an area with a
diagonal of about 2 cm.
Furthermore, by
achieving the industry’s smallest class of
0.35 µm for the space between adjacent
pixels in a reflective LCD device, Sony
was able to minimize the “mesh effect”
(the perception of looking at a scene
through a screen door) and create devices
that can provide smooth and natural
images. |
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High Contrast and High-Speed
Response |
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The performance of these devices is based
on Sony’s unique vertical aligned liquid
crystal material and a device structure that
has a narrow (2 µm or less) liquid crystal
cell gap.
Sony was able to minimize light
leakage when black areas are displayed
by using a vertical aligned liquid crystal
that features normally black operation (the
device displays black when no voltage is
applied) and thus increase the device contrast
characteristics.
Sony increased the
contrast even further by making the thickness
of the liquid crystal section (liquid
crystal cell) between the silicon drive substrate
and the opposing glass substrate be
2 µm or less.
Since the spacers normally
introduced into the display area to keep
the thickness of the liquid crystal cells
even disrupt the alignment of the liquid
crystal material and lead to light leakage that reduces contrast, Sony created a structure
in which no spacers whatsoever are
introduced into the display area.
By developing
this kind of optimal device structure,
Sony was able to implement a practical
device that achieves the contrast performance
inherent to the vertical liquid
crystal material.
While it is commonly known that the liquid
crystal response speed is proportional
to the thickness of the liquid crystal cell,
in the SXRD device, Sony was able to
make the cell the extremely thin 2 µm or
less, and thus achieve a rise time of 2.2
ms and a fall time of 2.3 ms.
Thus these
devices achieve the high-speed response
of a total time under 5 ms.
For video with
a frame frequency of 60 Hz, a single frame
has a period of about 16 ms.
Since SXRD
devices can be driven with a period that
is sufficiently short relative to that time,
they can provide crisp image quality even
for video. |
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High Reliability |
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Normally, a polyimide organic alignment
film is used for aligning (determining the
direction that the liquid crystal molecules
will tilt when a voltage is applied) the
liquid crystal material.
For the SXRD
technology, Sony developed an inorganic
alignment technology that matches the
vertical liquid crystal material.
Projection
devices normally require the use of an
unthinkably bright light to enlarge and
project brightly an image created on a
small area with a diagonal of about 2 cm.
It is known that inorganic materials generally
are highly reliable with respect to
exposure to light, and in the SXRD
devices as well, Sony was able to achieve
superlative light resistance by developing
an inorganic alignment technology.
At the
same time, Sony adopted a high-efficiency
cooling structure that uses the feature of
the reflective type LCD that allows it to
be cooled from the back. |
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Sony’s Unique Process
Technologies |
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Sony developed the panel assembly technology
shown in figure 2 that uses wafer
unit superposition as a mass production
technology to create narrow gap cells
without using spacers as described previously.
For normal projection devices, it is
common to use a process in which the
drive substrate and opposing glass are both
cut into small sections with a diagonal of
about 2 cm and then stacked together in
individual units.
However, if this method
is used to manufacture liquid crystal cells
with a thickness of 2 µm or less, various
problems occur.
These problems include
an increased probability that the cell thickness
will become uneven due to dust getting
into the devices and an increased
difficulty in controlling the cell thickness
precision, since no spacers whatsoever are
used in the display area.
Compared to
conventional processes in which panels
are assembled after the chips are cut apart,
this newly-developed 200 mm wafer unit
process has the features that dust cannot get trapped in the panels when the chips
are cut apart and the precision can be controlled
evenly in the narrow gap created
without the use of spacers by controlling
the thickness across the whole wafer.
This
achieves an extremely high production
efficiency.
There were several technologies whose
development were keys to actually implementing
this process: silicon wafer
planarization technology, inorganic alignment
film uniform growth technology,
high-precision superposition technology,
and high-efficiency scribing technology.
Current Sony mass production is at the
level of achieving a ±3% gap precision
for 1.5 to 2 µm thickness narrow gap
panels. |
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Future Developments |
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Sony’s SXRD technology was first used
in the industry’s first full HD home use
front projector, the QUALIA 004 (photograph
3) in December 2003.
Following
that, it was next used in the QUALIA 006
projection TV described here. Furthermore,
the 8.85M-pixel 1.55-type 4K
SXRD with a resolution over four times
that of full HD was included in the “SRX-R110”
(photograph 4) and the “SRX-R105”,
which were released as products
targeted mainly for use in digital cinemas.
With the rapid progress in the switch to
high definition in satellite and terrestrial
digital broadcasting and the market
penetration of high picture quality media
such as the next generation of large-capacity
optical discs, there are strong
demands for not only high resolution but
for high picture quality displays that can
reproduce content without picture
quality degradation. To respond to these
demands, at the same time as releasing
more SXRD high picture quality products
that target even wider markets, Sony will
also continue to advance the development
of technologies that strive for even higher
picture quality. |
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See
all articles with figures and tables.  |
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Vol.41 |
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