Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1997-12-11
2002-09-03
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C257S242000
Reexamination Certificate
active
06445414
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a solid-state image pick-up device and a method of controlling a solid-state image pick-up device and, more particularly, to a solid-state image pick-up device having resistive gate vertical charge transfer units and a method of controlling thereof.
DESCRIPTION OF THE RELATED ART
An inter-line type charge coupled device is a typical example of the solid state image pick-up device. The inter-line type charge coupled device comprises a photo-diode array, vertical shift registers and a horizontal shift register. The photo-diode array has a plurality of columns of photo-diodes, and the vertical shift registers are interposed between the columns of photo-diodes. A charge transfer region and transfer electrodes over the charge transfer region form the vertical shift register, and a charge transfer signal is supplied to the transfer electrodes so as to sequentially change the potential level under the transfer electrodes, and the vertical shift registers convey all the charge packets or every other charge packet from the associated photo-diode columns to the horizontal shift register.
The vertical shift register transfers the charge packets from the stage to stage, and is expected to accumulate all the charge packets supplied from the associated photo diode column. However, when the cell is shrunk, it becomes impossible to give sufficient capacitance to thereto.
One of the approaches to solve the problem is disclosed by Hendric Heyns et. al. in “The Resistive Gate CTD Area-Image Sensor”, IEEE Transaction on Electron Devices, vol. ED-25, No. 2, pages 135 to 139, February 1978. According to the paper, a constant potential difference is applied between both ends of the resistive gate so as to create a gradient charge transfer channel along the resistive gate, and a charge packet is transferred through the gradient charge transfer channel. The charge transfer is carried out for each row of photo diodes, and each vertical charge transfer element is expected to transfer the charge packet from one photo diode. For this reason, it is possible to decrease the area assigned to the vertical charge transfer element. This results in enlargement of the area assigned to the photo-diode.
FIGS. 1 and 2
illustrate the prior art area image sensor having the resistive gate charge transfer devices or elements, and
FIGS. 3 and 4
illustrates the vertical charge transfer elements and photo diodes. A photo-shield plate is removed from the layout shown in
FIGS. 1 and 3
and the structure shown in
FIG. 2
for better understanding. The prior art area image sensor is fabricated on a p-type semiconductor chip
1
, and photo diodes
2
and n-type charge transfer regions
3
are formed in the surface portion of the p-type semiconductor chip
1
. The photo diodes
2
have a MOS (Metal-Oxide-Semiconductor) structure, and the photo diodes
2
are arranged in rows and columns. The columns of photo diodes
2
and the n-type charger transfer regions
3
are alternately arranged, and each columns of photo-diodes
2
is associated with one of the n-type charge transfer regions
3
. The n-type charge transfer regions
3
are hatched in FIG.
3
. Heavily doped p-type channel stoppers
4
electrically isolate the photo diodes
2
from non-associated n-type charge transfer regions
3
, and provide p-n junctions for generating photo charge. The channel potential is designed to be or the order of 2 volts.
The major surface of the p-type semiconductor substrate
1
is covered with an insulating layer
5
, and a resistive gate electrode
6
of highly resistive polysilicon is patterned on the insulating layer
5
. The resistive gate electrode
6
has gradient potential electrode portions
6
a
superposed over the n-channel charge transfer regions
3
and common electrode portions
6
b
/
6
c
connected between the gradient potential electrode portions
6
a
and constant potential sources
7
a
/
7
b.
The constant potential source
7
a
applies high potential level through the common electrode portion
6
b
to the gradient potential electrode portions
6
a,
and the other constant potential source
7
b
applies low potential level through the other common electrode portion
6
c
to the other ends of the gradient potential electrode portions
6
a.
As a result, gradient potential takes place along the gradient potential electrode portions
6
a.
The gradient potential electrode portion
6
a,
the insulating layer
5
and the n-type charge transfer region
3
form in combination each vertical charge transfer element.
The resistive gate electrode
6
is covered with an insulating layer
8
, and accumulation electrodes
9
are patterned over the insulating layer
8
. The accumulation electrodes
9
extend in perpendicular to the gradient potential electrode portions
6
a,
and are respectively associated with the rows of photo diodes
2
. Each of the accumulation electrodes
9
is held in contact with the insulating layer
5
over the photo diodes
2
of the associated row at intervals, and image-carrying light is incident onto the depletion regions of the photo diodes
2
. The incident light generates charge packets, and the charge packets are accumulated in potential wells under the accumulation electrodes
9
held in contact with the insulating layer
5
.
The accumulation electrodes
9
are connected to a vertical shift register
10
, and are selectively driven to a read-out potential level. When the vertical shift register
10
changes one of the accumulation electrodes
9
to the read-out potential level, charge packets are read out from the photo diodes
2
of the associated row to the n-type charge transfer regions
3
, respectively, and the gradient potential in the electrode portions
6
a
moves the charge packets toward a horizontal charge transfer element
11
.
Transfer gate electrodes
12
a
/
12
b
extend over the n-type charge transfer regions
3
in the vicinity of the horizontal charge transfer element
11
, and an accumulation electrode
13
extends between the transfer gate electrodes
12
a
/
12
b.
The accumulation electrode
13
is covered with the insulating layer
8
, and is spaced from the gradient potential electrode portion
6
a,
and the transfer electrodes
12
a
/
12
b
are provided on both sides of the accumulation electrode
13
.
The accumulation electrodes
9
and the transfer electrodes
12
a
/
12
b
are covered with a transparent insulating layer
14
(see FIG.
4
), and a photo shield layer
15
of aluminum is patterned on the transparent insulating layer
14
. The photo shield layer
15
has openings
15
a,
and the photo diodes
2
are exposed to the openings
15
a.
The photo shield layer
15
prevents the n-type charge transfer regions
3
from the incident light.
The n-type charge transfer regions
3
are connected to anti-blooming drain regions
16
, and an anti-blooming electrode
17
sweeps excess photo charge from the n-type charge transfer regions
3
to the anti-blooming drain region
16
. The horizontal charge transfer element
11
is connected to an output circuit
18
, and an image signal is output from the circuit
18
.
The potential difference between the common electrode portions
6
c
and
6
b
produces a gradient potential along the gradient potential electrode portion
6
a,
and the gradient potential makes the potential well gradually high toward the transfer gate
12
a.
A charge packet CP is transferred from a photo diode
2
to the n-type charge transfer region
3
, and is transferred along the n-type charge transfer region
3
due to the gradient potential level. The transfer gate
12
a
firstly makes the potential level thereunder high, and the charge packet CP is accumulated in the potential well under the accumulation electrode
13
. Thereafter, the transfer gate
12
b
makes the potential level thereunder high, and the accumulation electrode
13
makes the potential level thereunder lower than the potential level under the transfer gate
12
b.
Then, the charge packet CP flows into the horizontal charge transfer element
11
Foley & Lardner
Garber Wendy R.
Tillery Rashawn N
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