Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-09-15
2004-07-06
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S299000, C257S223000, C257S230000, C257S445000
Reexamination Certificate
active
06760073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a solid-state image sensor, and more particularly to a solid-state image sensor including an excessive charge exhausting section located adjacent to a charge transfer section for horizontally transferring electric charges therethrough.
2. Description of the Related Art
A solid-state image sensor has been conventionally used as an input device of a video-tape recorder (VTR) equipped with a camera. However, with recent need of the greater number of pixels, a solid-state image sensor has begun to be used as an input device for an electronic still camera in which optical data is converted into electric signals in place of development of a film, and the electric signals are stored in a memory to thereby make a hard copy, or the electric signals are displayed as images on a monitor screen.
Since such a solid-state image sensor as mentioned above includes a light-electricity transfer section, and charge transfer sections for vertically and horizontally transferring signal charges accumulated in the light-electricity transfer section, there might be accumulated electric charges produced by light-electricity conversion having been carried out in an unnecessary period of time, and unnecessary signal charges such as electric charges caused by a current produced at an interface between silicon and an oxide film, as well as signal charges constituting necessary image signals.
When a solid-state image sensor is used as an input device of a video-tape recorder equipped with a camera, such unnecessary signal charges are settled down to a stable level after signal charges corresponding to a couple of screens have been displayed. Hence, there is caused no serious problem.
On the other hand, when a solid-state image sensor is used as an input device of an electronic still camera, such unnecessary signal charges as mentioned above are combined with signal charges constituting image signals, causing a problem of degradation in quality of images.
In addition, if there is applied a trigger by means of a shutter button when it took much time to remove such unnecessary signal charges, there would be caused time delay until a shutter is actually open or closed from the time of application of a trigger, which might lose shutter chance.
Hence, when a solid-state image sensor is to be used as an input device of an electronic still camera, it is necessary to instantaneously remove unnecessary signal charges existing in both light-electricity transfer sections and charge transfer sections at the same time when a trigger is applied by means of a shutter, unlike when a solid-state image sensor is used as an input device of a video-tape recorder equipped with a camera.
There has been suggested many attempts for removing such unnecessary signal charges.
For instance, one of such attempts is suggested in the article “CCD Image Sensor having Vertical Overflow Structure” by Ishihara et al. in Television Institute Brochure, Vol. 37, No. 10, October 1983, pp. 782(16)-787(21). According to the article, unnecessary charges existing in light-electricity transfer sections are removed by carrying out blooming control and formation of a vertical overflow drain structure. In the blooming control, there is formed a p− semiconductor region just below an n-type semiconductor region constituting a light-electricity transfer region, and a reverse-bias voltage is applied to an n
3−
semiconductor substrate to thereby transfer excessive charges to the n
3−
semiconductor substrate. By forming the vertical overflow drain structure, it is possible to make the n-type semiconductor region depleted, and drive all signal charges into the n
3−
semiconductor substrate.
Since the charge transfer section for horizontally transferring electric charges can operate at a high rate, unnecessary charges existing in the charge transfer section are removed into a reset drain located adjacent to the horizontal charge transfer section, in an ordinary operation.
On the other hand, it is necessary to transfer unnecessary charges by a distance corresponding to at least a couple of screens in order to remove the unnecessary charges existing in charge transfer sections for vertically transferring electric charges.
Japanese Unexamined Patent Publication No. 8-256429 has suggested a method of removing such unnecessary charges existing in charge transfer sections for vertically transferring electric charges. In the suggested method, an excessive charge exhausting section is formed adjacent to the charge transfer sections. Unnecessary charges existing in the charge transfer sections are forwardly transferred, and removed into the excessive charge exhausting section.
FIG. 1
is a block diagram of a solid-state image sensor suggested in Japanese Unexamined Patent Publication No. 8-256429. The illustrated solid-state image sensor is comprised of light-electricity transfer sections
1
arranged in a plurality of lines, a plurality of first charge transfer sections
2
for vertically transferring electric charges, located adjacent to each of the light-electricity transfer sections
1
, a second charge transfer section
3
for horizontally transferring electric charges, extending at one ends of both the light-electricity transfer sections
1
and the first charge transfer sections
2
, an output circuit
4
electrically connected to the second charge transfer section
3
, a potential barrier section
5
located adjacent to the second charge transfer section
3
, an excessive charge exhausting section
6
located adjacent to the potential barrier section
5
, and an n
++
semiconductor region
7
located at one end of the excessive charge exhausting section
6
and electrically connected to a power source voltage VDD.
FIG. 2
is a plan view of the region encircled with a broken line A in
FIG. 1
, that is, the region located adjacent to the second charge transfer section
3
and including the potential barrier section
5
and the excessive charge exhausting section
6
.
As illustrated in
FIG. 2
, the region is comprised of a first charge transfer channel
11
for vertically transferring electric charges therethrough, second charge transfer sections
12
for horizontally transferring electric charges therethrough, located adjacent to the first charge transfer channel
11
and including a charge accumulating region
13
and a charge barrier region
14
, a potential barrier section
15
located adjacent to the second charge transfer sections
12
, an excessive charge exhausting section
16
located adjacent to the potential barrier section
15
, a semiconductor region
17
acting as a device isolation region and having a first electrical conductivity, first charge transfer electrodes
19
for horizontally transferring electric charges therethrough, each composed of a first layer of polysilicon, second charge transfer electrodes
20
for horizontally transferring electric charges therethrough, each composed of a second layer of polysilicon, and a final charge transfer electrode
21
for vertically transferring electric charges.
FIG. 3
is a cross-sectional view taken along the line III—III in
FIG. 2
, and shows potential of each region at the cross-section.
FIG. 4
is a cross-sectional view taken along the line IV—IV in
FIG. 2
, and shows potential of each region at the cross-section.
As illustrated in
FIGS. 3 and 4
, the solid-state image sensor is comprised of an n
3−
semiconductor substrate
31
having an impurity concentration of about 2.0E14 cm
−3
, a p-type well layer
32
formed at a surface of the n
3−
semiconductor substrate
31
and having an impurity concentration of about 1.0E16 cm
−3
, an n− type semiconductor region
33
constituting a buried channel of the charge accumulating region
13
of the first and second charge transfer sections
2
and
3
, and having an impurity concentration of about 1.3E17 cm
−3
, an n− type semiconductor region
34
constituting a buried channel of the charge barri
Garber Wendy R.
McGinn & Gibb PLLC
NEC Electronics Corporation
Rosendale Matthew L
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