U.S. patent number RE40,409 [Application Number 10/927,656] was granted by the patent office on 2008-07-01 for photoelectric converter having a light receiving portion with an improved readout gate.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Satoshi Kitayama, Kazushige Nigawara, Tsuyoshi Sasaki.
United States Patent |
RE40,409 |
Kitayama , et al. |
July 1, 2008 |
Photoelectric converter having a light receiving portion with an
improved readout gate
Abstract
A photoelectric converter with improved charge transfer
efficiency from a light receiving portion. The photoelectric
converter includes a light receiving portion having an output end
and a gate portion having a first side and a second side that both
define a readout gate width for the light receiving portion, where
the first side of the gate portion confronts the output end of the
light receiving portion. The photoelectric converter also includes
a charge transfer portion formed to confront the second side of the
gate portion, where the readout gate width of said gate portion is
wider at the first side confronting said light receiving portion
than at the second side confronting said charge transfer
portion.
Inventors: |
Kitayama; Satoshi (Kanagawa,
JP), Nigawara; Kazushige (Tokyo, JP),
Sasaki; Tsuyoshi (Kagoshima, JP) |
Assignee: |
Sony Corporation (Tokyo,
JP)
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Family
ID: |
18377417 |
Appl.
No.: |
10/927,656 |
Filed: |
August 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09453592 |
Dec 3, 1999 |
06515268 |
Feb 4, 2003 |
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Foreign Application Priority Data
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Dec 4, 1998 [JP] |
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P10-345559 |
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Current U.S.
Class: |
250/214.1;
257/240; 257/243; 257/466; 348/315 |
Current CPC
Class: |
H01L
27/14812 (20130101) |
Current International
Class: |
H01L
31/00 (20060101) |
Field of
Search: |
;250/214.1,208.1
;348/315 ;257/221,224,240,243,465,466 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Luu; Thanh X.
Assistant Examiner: Yam; Stephen
Attorney, Agent or Firm: Sonnenschein Nath & Rosenthal
LLP
Parent Case Text
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No.
P10-345559 filed Dec. 4, 1998 which application is incorporated
herein by reference to the extent permitted by law.
Claims
What is claimed is:
1. A photoelectric converter comprising: a .[.light receiving
portion.]. .Iadd.photodiode portion .Iaddend.having an output end;
a gate portion having a first side and a second side .[.that both
define.]. .Iadd., said gate portion having .Iaddend.a readout gate
width .Iadd.that varies between said first and second
sides.Iaddend., the first side confronting the output end of the
.[.light receiving portion.]. .Iadd.photodiode portion and the
second side being opposite the first side, the gate portion
corresponding to a single photodiode.Iaddend.; and a charge
transfer portion formed to confront the second side of the gate
portion, wherein the readout gate width of said gate portion is
wider at the first side confronting said .[.light receiving
portion.]. .Iadd.photodiode portion .Iaddend.than at the second
side confronting said charge transfer portion.
2. The photoelectric converter according to claim 1, wherein said
readout gate width narrows linearly .Iadd.proceeding .Iaddend.from
said .[.light receiving portion.]. .Iadd.photodiode portion
.Iaddend.toward said charge transfer portion.
3. The photoelectric converter according to claim 1, wherein said
gate portion comprises a first gate portion having a first readout
gate width .[.of.]. which .[.is narrower.]. .Iadd.narrows
proceeding .Iaddend.from said .[.light receiving portion.].
.Iadd.photodiode portion .Iaddend.toward said transfer portion, and
a second gate portion having a second readout gate width that is
constant .Iadd.proceeding .Iaddend.from said first gate portion
.[.towards.]. .Iadd.toward .Iaddend.said charge transfer
portion.
4. The photoelectric converter according to claim 1, wherein said
photoelectric converter is constructed as an imaging apparatus
.[.in which said light receiving portion includes.]. .Iadd.having
.Iaddend.a plurality of pixels and .[.said charge transfer portion
includes.]. a plurality of charge coupled devices.
5. The photoelectric converter according to claim 1, .[.wherein
said light receiving portion includes.]. .Iadd.comprising a
plurality of .Iaddend.photodiodes.
6. The photoelectric converter according to claim 1, wherein said
readout gate width narrows curvedly .Iadd.proceeding .Iaddend.from
said .[.light receiving portion.]. .Iadd.photodiode portion
.Iaddend.toward said charge transfer portion.
7. The photoelectric converter according to claim 1, wherein said
readout gate width narrows gradually .Iadd.proceeding .Iaddend.from
said .[.light receiving portion.]. .Iadd.photodiode portion
.Iaddend.toward said charge transfer portion.
8. The photoelectric converter according to claim 1, wherein said
charge transfer portion includes charge coupled devices
electrically connected along a vertical axis of the photoelectric
converter and disposed adjacent to the gate portion.
9. The photoelectric converter according to claim 1, wherein said
gate portion comprises a barrier gate portion and a readout gate
portion having the first and the second sides of the gate portion,
the barrier portion is disposed between said charge transfer
portion and said .[.light receiving portion.]. .Iadd.photodiode
portion .Iaddend.and has a tapered side defined by the readout gate
width of the readout gate portion.
10. The photoelectric converter according to claim 1, wherein said
gate portion substantially prevents leaking of a charge held by the
.[.light receiving portion.]. .Iadd.photodiode portion
.Iaddend.when said gate portion is in an OFF state.
.Iadd.11. A photoelectric converter comprising: a photodiode
portion having an output end; and a gate portion having a first
side and a second side, the gate portion having a readout gate
width that varies between the first and second sides, the first
side confronting the output end of the photodiode portion and the
second side being opposite the first side, the gate portion
corresponding to a single photodiode; wherein the readout gate
width of the gate portion is wider at the first side than at the
second side..Iaddend.
.Iadd.12. The photoelectric converter according to claim 11,
wherein said readout gate width of the gate portion narrows
linearly proceeding from the first side toward the second
side..Iaddend.
.Iadd.13. The photoelectric converter according to claim 11,
comprising a plurality of pixels..Iaddend.
.Iadd.14. The photoelectric converter according to claim 11,
wherein the photodiode portion includes photodiodes..Iaddend.
.Iadd.15. The photoelectric converter according to claim 11,
wherein the readout gate width of the gate portion narrows curvedly
proceeding from the first side toward the second side..Iaddend.
.Iadd.16. The photoelectric converter according to claim 11,
wherein the readout gate width of the gate portion narrows
gradually proceeding from the first side toward the second
side..Iaddend.
.Iadd.17. The photoelectric converter according to claim 11,
wherein said gate portion substantially prevents leaking of a
charge held by the photodiode portion when the gate portion is in
an OFF state..Iaddend.
.Iadd.18. The photoelectric converter according to claim 11,
wherein the first side has same width as a width of the photodiode
portion..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric converter such as
an imaging apparatus employing photoelectric conversion devices
such as photodiodes.
2. Description of Related Art
An imaging apparatus has a number of pixels formed in an imaging
area (a light receiving portion) thereof receive light signals from
a subject, photoelectrically converts the light signals into signal
charges, transfers the converted electric signals, thereby imaging
the subject.
FIG. 7 shows a CCD imaging apparatus as an example of an imaging
apparatus.
Light incident on a photodiode 1 is photoelectrically converted
into a signal charge, the signal charge is read out to a vertical
CCD portion 3 via a readout gate 12A, the signal charge is
transferred by supplying transfer clocks of, e.g. .phi.V1 to
.phi.V4 to the vertical CCD 3, and the signal charge is directed to
an output portion in a horizontal CCD portion to which transfer
clocks of, e.g. .phi.H1 and .phi.H2 are supplied, where charge
voltage conversion and the like are performed to produce an image
signal.
By the way, recent imaging apparatuses, particularly a CCD (charge
coupled device) imaging apparatus and the like, tend to have more
compact unit cells and increase the amount of charges stored in a
sensor to improve sensitivity.
For this reason, it is becoming difficult to read out charges into
a vertical CCD, which is a charge transfer portion, from a
photodiode comprising a light receiving portion (pixel portion) via
a gate portion.
Particularly, as shown in FIGS. 4A and 4B, in the case of an
imaging apparatus in which the horizontal size of a unit cell
comprising a photodiode portion 1 and a gate portion 2 is longer
than the vertical size, it is more difficult to read out charges
into a vertical CCD portion 3. FIG. 4A shows a schematic layout of
the unit cell from which the vertical CCD portion is excluded, and
FIG. 4B shows a schematic layout of the unit cell including the
vertical CCD portion (hereinafter the same is also true of other
drawings). L.sub.2-1 or W.sub.1 in the drawings is the width of a
readout gate 2A and L.sub.1-1 is the width of a gate 2B which is
not related to readout. The reference numeral 4 designates a
channel stopper for separating unit cells.
To solve such a problem, the following two measures are taken. One
is, as shown in FIGS. 5A and 5B, to enlarge the readout gate width
(gate length in a direction orthogonal to a carrier travel
direction: the same is true of the following descriptions)
L.sub.2-2 or W.sub.2 of a readout gate portion 2A (indicated by
white background or oblique lines) of the gate portion 2. The other
is, as shown in FIGS. 6A and 6B, to reduce a readout gate length
(gate length in a carrier travel direction: the same is true of the
following descriptions) l.sub.1-3.
However, in the layouts of FIGS. 5A and 5B, a ratio between the two
gates of the vertical CCD portion 3, that is, a gate 2A to read out
charges and a gate 2B which is not related to readout, is
different. Consequently, the charge capacity of the vertical CCD
portion is liable to become small or charges are liable to be
unsuccessfully transferred.
In the layouts of FIGS. 6A and 6B, the gate 2 itself fails to play
the role of a barrier during off operation, with the result that
charges leak from the photodiode portion 1 to the vertical CCD
portion 3 or light passes between a silicon film and a shielding
film (both are not shown) below the gates, and photoelectric
conversion may occur within the vertical CCD portion 3.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation,
and its object is to provide a photoelectric converter such as an
imaging apparatus which smoothly reads out charges without
influencing the charge capacity and charge transfers of a charge
transfer portion and can reduce power consumption by reducing a
readout voltage.
Specifically, a photoelectric converter of the present invention
comprises a light receiving portion, a gate portion, and a charge
transfer portion, wherein the gate width of the gate portion is
wider at the light receiving portion side than at the transfer
portion side.
Thus making a gate width wider at a light receiving portion side
than at a charge transfer portion side helps to enlarge an area of
an electric field applied to the gate in an area to admit charges
from the light receiving portion (accordingly, the electric field
of the gate area can be intensified), with the result that charges
can be easily read, and if a readout capacity is the same, a charge
readout voltage can be reduced to reduce power consumption. Yet,
since such an effect can be achieved without changing a gate width
at the charge transfer portion side, no influence is exerted on the
charge capacity and charge transfers of the charge transfer portion
and other characteristics also do not deteriorate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B show main portions of an imaging apparatus in a
first embodiment of the present invention; FIG. 1A is a layout
diagram centered on a gate portion, and FIG. 1B is a layout diagram
of a unit cell.
FIGS. 2A and 2B show main portions of an imaging apparatus in
another embodiment of the present invention; FIG. 2A is a layout
diagram centered on a gate portion, and FIG. 2B is a layout diagram
of a unit cell.
FIGS. 3A and 3B show main portions of an imaging apparatus in yet
another embodiment of the present invention; FIG. 3A is a layout
diagram centered on a gate portion, and FIG. 3B is a layout diagram
of a unit cell.
FIGS. 4A and 4B show main portions of a conventional imaging
apparatus; FIG. 4A is a layout diagram centered on a gate portion,
and FIG. 4B is a layout diagram of a unit cell.
FIGS. 5A and 5B show main portions of another conventional imaging
apparatus; FIG. 5A is a layout diagram centered on a gate portion,
and FIG. 5B is a layout diagram of a unit cell.
FIGS. 6A and 6B show main portions of yet another conventional
imaging apparatus; FIG. 6A is a layout diagram centered on a gate
portion, and FIG. 6B is a layout diagram of a unit cell.
FIG. 7 shows a CCD imaging apparatus as an example of an imaging
apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is preferably constructed as an imaging
apparatus in which the light receiving portion has pixels
comprising photodiodes and the like, and the charge transfer
portion comprises charge coupled devices.
As to the shape of the gate portion, although there are no special
limitations thereon, preferably, the gate width is narrower from
the light receiving portion toward the transfer portion straightly,
curvedly, or gradually.
Furthermore, preferably, the gate portion comprises a first gate
portion the gate width of which is narrower from the light
receiving portion toward the transfer portion, and a second gate
portion provided with an identical gate width from the first gate
portion further toward the charge transfer portion.
Hereinafter, the present invention will be described more
specifically based on an embodiment of the present invention
applied to a CCD imaging apparatus.
FIGS. 1A and 1B show main portions of a CCD imaging apparatus; FIG.
1A is a layout diagram primarily showing a configuration of a gate
portion, and FIG. 1B is a layout diagram primarily showing a
configuration of a light receiving portion including a vertical CCD
portion (hereinafter, the same is also true of other drawings).
In FIGS. 1A and 1B, the numeral number 1 designates a photodiode
portion surrounded by a channel stopper portion 4, interpixel
portions 5, and a gate portion 12, 3 and the gate portion is
adjacent to a vertical CCD portion 3.
In this embodiment, the CCD imaging apparatus is constructed so
that a part of a gate 12B of the gate 12 which is not related to
charge readout is cut in a slanted line form from a corner of the
photodiode portion 1 to the vertical CCD portion 3, as opposed to
the gate portion 2 of FIGS. 4A and 4B, whereby the width L.sub.2-5
or W.sub.4 of a gate portion 12a of a readout gate 12A adjacent to
the photodiode portion 1 is widened up to the same width as that of
the photodiode portion 1 and the width L.sub.2-4 or W.sub.4' of a
gate portion 12b of the readout gate 12A and the gate length
l.sub.1-4 at the vertical CCD portion 3 side is unchanged
(l.sub.1-4=l.sub.1-1).
Light from a subject is photoelectrically converted in the
photodiode portion 1 and thereby (signal) charges are generated.
Applying a voltage to the gate portion 12 (the gate portion 12A
goes on) causes the charges of the photodiode portion 1 to be read
out to the vertical CCD portion 3 by the readout gate portions 12a
and 12b.
The CCD imaging apparatus employs two types of gates, gate portions
12A and 12B. One of them is a gate used during charge readout, and
the other is a gate not used for charge readout, placed below the
former. In a portion where the two gate overlap, the gate not
related to readout is dominant.
This embodiment is characterized in that a gate not related to
charge readout is cut in a slanted line form as described above and
the width L.sub.2-5 or W.sub.4 of the readout gate portion 12a
adjacent to the photodiode portion 1 is widened, so that an
electric field applied to that portion is intensified during
activation so that charges within the photodiode portion 1 can be
easily read out.
Owing to the gate pattern, the gate width L.sub.2-4 or W.sub.4' at
the vertical CCD portion 3 side is the same as conventional ones.
Therefore, a gate width adjacent to the vertical CCD portion 3 can
be maintained to an optimum width for the charge capacity and
charge transfer efficiency of the vertical CCD portion 3 without
influencing the charge capacity and charge transfers of the
vertical CCD portion 3 and deteriorating other characteristics.
Also, since a charge readout voltage is reduced by widening a gate
width as described above, power consumption can be reduced. Yet,
since the read gate length l.sub.1-4 is unchanged, the gate serves,
during off operation, as an adequate barrier against charges so
that there is no leak of charges from the photodiode portion 1 to
the vertical CCD portion 3 and no leak of light to the vertical CCD
portion 3.
The embodiment shown in FIGS. 2A and 2B is is characterized in that
although the entrance gate width W.sub.4 of the readout gate
portion 12a and the exit gate width W.sub.4' of the readout gate
portion 12b are the same as those in FIG. 1, the gate width becomes
gradually smaller from the photodiode portion 1 toward the vertical
CCD portion 3.
The embodiment shown in FIGS. 3A and 3B is characterized in that
the gate width W.sub.4 of the readout gate portion 12a becomes
curvedly narrower from the photodiode portion 1 toward the vertical
CCD portion 3.
It will be appreciated that any of these embodiments can bring
about almost the same effect as in FIGS. 1A and 1B.
Although the present invention preferably applies to the above CCD
imaging apparatus, without being limited to it, the present
invention is widely applicable to other photoelectric converters
used for optical communications or other purposes if they are
constructed with a light receiving portion, a gate portion, and a
charge transfer portion. The patterns of the readout gate portion
can be changed to various ones, and layouts including the shapes
and sizes of the portions, and devices constituting the light
receiving portion are not limited to the above ones.
* * * * *