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Sony "Exmor R" CMOS Image
Sensors Achieve a Dramatic
Increase in Performance
Consumer CMOS Image Sensors Achieve High Sensitivity and Low Noise |
 |
Adoption of a back-illuminated structure |
|
Sensitivity characteristics approximately
twice those of current image sensors
achieved |
|
Improved vignetting |
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Wafer thinning technology |
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Unique Sony photodiode structure |
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* “Exmor R” is a trademark of Sony Corporation.
The “Exmor R” is a Sony’s CMOS image
sensor with significantly enhanced imaging
characteristics including sensitivity and low
noise by changing fundamental structure of
“Exmor” pixel adopted column-parallel A/D
converter to back-illuminated type. |
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 Responding to Growing Market Needs |
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. |
In the consumer digital cameras, the way
digital still cameras are owned is changing
from being shared by the whole family to being
owned by the individual, and the number of
consumer digital camera shipped worldwide
will soon exceed 100 million units. Along with
the increase in individual ownership, the ways
cameras are being used is expanding beyond
simply recording special events to capturing all
sorts of scenes in their users' daily lives. For
example, there are now needs for taking pictures
in situations where there may not be adequate
light, such as photographs of children or pets
at play, taking natural appearing photographs
without flash, or taking clear photographs in dark
locations without using a tripod. There are also
increasing user needs for taking photographs of
subjects that are moving rapidly. However the
continuous high-speed imaging and S/N ratio
of the miniature CCD image sensors used in
current digital still cameras are not adequate
to meet these needs. Given this background,
Sony developed the "Exmor R" CMOS image
sensor.
The "Exmor R" CMOS image sensor, in addition
to supporting high-speed imaging due to the
adoption of column-parallel A/D conversion,
achieves sensitivity characteristics that are improved by approximately a factor of two
from current front-illuminated image sensors by
adopting a newly-developed back-illuminated
structure. This structure significantly improves
picture quality for photographing subjects
that are moving or for taking pictures in dark
locations. |
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Sensitivity Characteristics Improved by
Approximately a Factor of Two by
the
Back-Illuminated Structure |
| . |
. |
Since the incident light entering current CMOS
image sensors passes through gaps in the metal
wiring layer, the light is obstructed by that metal
wiring layer and cannot be delivered efficiently
to the photodiodes. In particular, since light
that comes in at an angle is reflected back,
problems such as the outer areas of the image
being darker or the sensitivity not increasing as
the aperture is opened wider occur. Also, when
combined with a zoom lens, the sensitivity and
color balance of the outer areas of the image
may change with the zoom setting.
Sony has now developed a back-illuminated
structure that differs from the current pixel
structure (the front-illuminated structure) in
that the metal wiring layer is placed below the
photodetectors. In the back-illuminated structure, light is projected onto the rear surface of the
silicon substrate (the back side) and as a result,
the amount of light entering each unit pixel is
increased since it is not affected by the metal
wirings and other circuits. This also allows the
change in sensitivity with the angle of incidence
to be minimized. This structure increases the
light collecting efficiency even under imaging
conditions where high angles of incidence are
common, and achieves sensitivity characteristics
that are increased by approximately a factor of
two over current image sensors. (See figures
1 and 2.) |
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Figure 1 : Cross-Sectional Structures
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 Wafer Thinning Technology |
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See
all articles with figures and tables.  |
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Vol.59 |
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