U.S. patent application number 09/849975 was filed with the patent office on 2001-11-08 for close contact type sensor.
Invention is credited to Kimura, Hajime.
Application Number | 20010038065 09/849975 |
Document ID | / |
Family ID | 18643354 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038065 |
Kind Code |
A1 |
Kimura, Hajime |
November 8, 2001 |
Close contact type sensor
Abstract
To provide a close contact type sensor promoting a light
utilizing efficiency, there is provided a close contact type sensor
featured in that in a close contact type sensor having a sensor
circuit portion and an irradiation window portion, a plurality of
the irradiation windows are arranged and positions and sizes of the
irradiation windows are matched to positions and sizes of opening
portions of LCD utilized as a light source.
Inventors: |
Kimura, Hajime; (Kanagawa,
JP) |
Correspondence
Address: |
JOHN F. HAYDEN
Fish & Richardson P.C.
601 Thirteenth Street, NW
Washington
DC
20005
US
|
Family ID: |
18643354 |
Appl. No.: |
09/849975 |
Filed: |
May 8, 2001 |
Current U.S.
Class: |
250/208.1 ;
257/E27.111; 257/E27.132; 257/E27.134 |
Current CPC
Class: |
H01L 27/12 20130101;
H01L 27/14645 20130101; H01L 27/14609 20130101; H01L 27/1214
20130101 |
Class at
Publication: |
250/208.1 |
International
Class: |
H01L 027/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2000 |
JP |
2000-135239 |
Claims
What is claimed is:
1. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions.
2. A scanner using the close contact type sensor according to claim
1.
3. A portable information terminal using the close contact type
sensor according to claim 1.
4. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: an optical fiber plate between the sensor circuit
portion and a reading object; wherein an area of any of the
plurality of irradiation window portions is larger than an area of
a half of a section of a single piece of an optical fiber in the
optical fiber plate.
5. A scanner using the close contact type sensor according to claim
4.
6. A portable information terminal using the close contact type
sensor according to claim 3.
7. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; and a backlight; wherein the
liquid crystal display is arranged below the backlight, the sensor
circuit portion and the plurality of irradiation widow portions are
arranged below the liquid crystal display and the plurality of
irradiation window portions are arranged on inner sides of opening
portions of the liquid crystal display.
8. A scanner using the close contact type sensor according to claim
7.
9. A portable information terminal using the close contact type
sensor according to claim 7.
10. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; a backlight; and an optical
fiber plate; wherein the liquid crystal display is arranged below
the backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, the optical fiber plate is arranged below the sensor
circuit portion and the plurality of irradiation window portions
and the plurality of irradiation window portions are arranged on
inner sides of opening portions of the liquid crystal display.
11. A scanner using the close contact type sensor according to
claim 10.
12. A portable information terminal using the close contact type
sensor according to claim 10.
13. A close contact type sensor arranged with a plurality of pixels
each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; and a backlight; wherein in
the liquid crystal display, a single piece of a unit pixel is
constituted by one pixel for red, one pixel for green and one pixel
for blue, the liquid crystal display is arranged below the
backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display and a size of the unit pixel of the liquid crystal display
is a size of the unit pixel of the close contact type sensor
multiplied by an integer or a factor of an integer thereof.
14. A scanner using the close contact type sensor according to
claim 13.
15. A portable information terminal using the close contact type
sensor according to claim 13.
16. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; a backlight; and an optical
fiber plate; wherein in the liquid crystal display, a single piece
of a unit pixel is constituted by one pixel for red, one pixel for
green and one pixel for blue, the liquid crystal display is
arranged blow the backlight, the sensor circuit portion and the
plurality of irradiation window portions are arranged below the
liquid crystal display, the optical fiber plate is arranged below
the sensor circuit portion and the plurality of irradiation window
portions and a size of the unit pixel of the liquid crystal display
is a size of the unit pixel of the close contact type sensor
multiplied by an integer or a factor of an integer thereof.
17. A scanner using the close contact type sensor according to
claim 16.
18. A portable information terminal using the close contact type
sensor according to claim 16.
19. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; and a backlight; wherein in
the liquid crystal display, a single piece of a unit pixel is
constituted by one pixel for red, one pixel for green and one pixel
for blue, the liquid crystal display is arranged blow the
backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, and light of the backlight successively transmits through
the pixel for red, the pixel for green and the pixel for blue of
the liquid crystal display at every respective subframe period.
20. A scanner using the close contact type sensor according to
claim 19.
21. A portable information terminal using the close contact type
sensor according to claim 19.
22. A close contact type sensor arranged with a plurality of unit
pixels each comprising a sensor circuit portion and a plurality of
irradiation window portions, said close contact type sensor
comprising: a liquid crystal display; a backlight; and an optical
fiber plate; wherein in the liquid crystal display, a single piece
of a unit pixel is constituted by one pixel for red, one pixel for
green and one pixel for blue, the liquid crystal display is
arranged blow the backlight, the sensor circuit portion and the
plurality of irradiation window portions are arranged below the
liquid crystal display, the optical fiber plate is arranged below
the sensor circuit portion and the plurality of irradiation window
portions and light of the backlight successively transmits through
the pixel for red, the pixel for green and the pixel for blue of
the liquid crystal display at every subframe period.
23. A scanner using the close contact type sensor according to
claim 22.
24. A portable information terminal using the close contact type
sensor according to claim 22.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a close contact type
sensor. More in details, the present invention relates to an MOS
type sensor apparatus formed by using TFT above a glass
substrate.
[0003] 2. Description of the Related Art
[0004] In recent years, information apparatus such as personal
computers have spread widely and there has been an increase in
request of reading various information by a personal computer as
electronic information. Therefore, a digital still camera as a
substitute for a conventional silver film camera and a scanner as
means for reading printed matter printed on paper, considerably
attract attention.
[0005] In a digital still camera, there is used an area sensor in
which pixels in an image sensor portion are arranged
two-dimensionally. In a scanner or a copy machine, there is used a
line sensor in which pixels in an image sensor portion are arranged
one-dimensionally.
[0006] Scanners are generally classified grossly into three types
in accordance with a reading system. That is, scanners can grossly
be classified into three types of (1) sheet feed type, (2) flat bed
type and (3) pen type (handy type). (1) Sheet feed type is a system
of fixing an image sensor portion of a scanner and reading draft by
moving the draft by sheet feeding. (2) Flat bed type is a system of
fixing draft on glass and reading the draft by moving an image
sensor portion below glass. (3) Pen type is a system of reading
draft by moving an image sensor portion above the draft by an
operator. In this way, a line sensor is frequently used in a
scanner.
[0007] In the above-described three scanner types, optical systems
used therefor are substantially determined. In a scanner of (2)
flat bed type, there is frequently adopted a reduction type optical
system for finely reading an image. A lens used for the reduction
type optical system is provided with a long focal length and
accordingly, a distance between an object for reading and an image
sensor portion is lengthened and the apparatus is large-sized.
[0008] It is necessary to downsize the apparatus in the case of (1)
sheet feed type or (3) pen type (handy type). Therefore, there is
adopted an optical system complying therewith. That is, there is
frequently adopted a close contact type optical system. According
to a close type optical system, there is arranged a rod lens array
between an image sensor and an object for reading. A rod lens array
is bundled with a number of distributed refractive index type
lenses in a rod like shape. A rod lens array focuses an image in a
one-to-one relationship and a distance between an object for
reading and an image sensor portion is shorter than that of a
reduction optical system.
[0009] As an optical system aiming at further downsizing of the
apparatus by further shortening a distance between an object for
reading and an image sensor portion, there is provided a completely
close contact type. This is an optical system for reading an object
for reading by bringing the object and an image sensor portion
substantially into close contact with each other without arranging
a lens therebetween. A protective film, thin protective glass or an
optical fiber plate is arranged between the object for reading and
the image sensor portion. The optical fiber plate is constituted by
bundling a number of optical fibers and slicing the bundle in a
shape of a plate.
[0010] There is introduced the above-described classification of
optical systems in "A close contact image sensor infiltrating
facsimiles, expels a reduction type with easiness-to-use as an
arm?" in Nikkei Electronics: 1989.4.3 (No. 470): p.159. There is
introduced a rod lens array using a distributed reflective index
type lens in "Mass production of a lens array made of plastic for
close contact sensors of facsimiles" in Nikkei Electronics:
1989.11.13 (No. 486): p.122. There is introduced an example of a
completely close contact type in "Development of a CdS-CdSe image
sensor of a completely close contact type" in Nikkei Electronics:
1990.2.19 (No.493): p.112. There is introduced an example of
completely close contact type using an optical fiber plate in
"Development of a completely close contact type image sensor of a
multiple tips system" Nikkei Electronics: 1992.9.14 (No. 563):
p.80.
[0011] As an image sensor element, there is frequently used a
sensor of a CCD type or a single crystal CMOS type. FIG. 2 shows a
sectional view in the case of adopting a close contact type optical
system by using these elements. There is arranged an optical system
10002 such as a rod lens array above an image sensor 10001 of a CCD
type (CMOS type). The optical system 10002 is used for projecting
an image on a draft onto the image sensor 10001. The relationship
between the image and the sensor is constituted by an equal
magnification system. Alight source 10003 is arranged at a position
capable of irradiating light to a reading object 10004. LED or a
fluorescent lamp is used as a kind of the light source used.
Further, glass 10005 is arranged at the topmost portion. The
reading object 10004 is arranged on the glass 10005. The operation
is as follows. First, light emitted from the light source 10003
passes through the glass 10005 and is incident on draft. Further,
the light is reflected by the reading object 10004, passes through
the glass 10005 and is incident on the optical system 10002. The
light incident on the optical system 10002 is incident on the image
sensor 10001 and is photoelectrically converted at the image sensor
10001. Further, a signal converted into electricity is read to
outside. After reading signals of one column by the image sensor, a
scanner 10006 is moved and similar operation is repeated again.
[0012] As a constitution of using other image sensor element, there
is provided a sensor formed with TFTs and photodiodes by using a-Si
or p-Si above glass. FIG. 3 shows a sectional view of a line sensor
when a completely close contact type optical system is adopted by
using these elements. According to a completely close contact type,
it is necessary to efficiently irradiate light to a reading object
304. Therefore, it is preferable that a substrate per se is
transparent. Therefore, in a completely close contact type, not a
single crystal substrate which does not transmit light but
transparent glass is frequently used. In FIG. 3, a light receiving
portion 306 is formed at glass 305 and a vicinity of the light
receiving portion 306 is formed with an irradiation window 307 for
transmitting light. Light emitted from a light source 303 is
incident on a rear face of the glass 305, passes through the
irradiation window 307, passes through an optical system 302 and is
incident on a reading object 304. Light incident on the reading
object 304, is reflected thereby, passes through the optical system
302 again and is incident on the light receiving portion 306. A
light shielding window is frequently formed between the glass 305
and the light receiving portion 306 at portions other than the
irradiation window 307 to prevent influence of light incident on
the rear face of the glass 305 from being effected.
[0013] FIGS. 4A and 4B show views viewing from above a pixel of a
sensor fabricated on glass. In FIG. 4A, a single piece of the
irradiation window 307 is arranged at the center of one pixel of
the light receiving portion 306. In FIG. 4B, a single piece of the
irradiation window 307 is arranged contiguous to one pixel of the
light receiving portion 306. These are published also in "A close
contact image sensor infiltrating facsimiles, expel the reduction
type with easiness-to-use as an arm?" in Nikkei Electronics:
1989.4.3 (No. 470): p.159. In this way, conventionally, a single
piece of pixel is arranged with only a single piece of irradiation
window.
[0014] FIGS. 5A and 5B show simple constitution views each for a
single piece of pixel. In FIG. 5A, there is a single piece of the
irradiation window 307 and there is the light receiving portion 306
for carrying out photoelectric conversion contiguous thereto. There
is arranged therebelow, a circuit portion 502 of a switching
transistor, a resetting transistor, am amplifying transistor and
the like for resetting the light receiving portion 306 or
amplifying a signal produced at the light receiving portion 306.
The light receiving portion 306 and the circuit portion 502 in
combination, is referred to as a sensor circuit portion. That is, a
single piece of a pixel 501 is constituted by the sensor circuit
portion and the irradiation window portion 307 and a plurality of
the pixels 501 are arranged to thereby constitute a line sensor or
an area sensor.
[0015] FIG. 5B is basically the same as FIG. 5A and is a
constitution view when the light receiving portion 306 and the
circuit portion 502 are arranged to overlap. It is necessary that
the irradiation window 307 is transparent since light needs to
transmit therethrough. Therefore, the irradiation window 307 and
the circuit portion 502 are not arranged to overlap. Meanwhile, the
light receiving portion 306 and the circuit portion 502 can be
arranged to overlap since there is not such a restriction.
[0016] A description has been given of the case of using a line
sensor. However,when a two-dimensional reading object is read by a
line sensor, it is necessary to move the sensor or the reading
object. Therefore, the apparatus is large-sized, reading speed is
retarded or mechanical strength is weakened. Hence, researches have
been carried out also on a close contact type area sensor arranged
with pixels two-dimensionally. In order to make light incident on a
reading object, a substrate needs to transmit light and therefore,
the substrate needs to be transparent, for example, the substrate
comprises glass. According to an area sensor, the pixels are
arranged two-dimensionally and therefore, it is not necessary to
move the area sensor in reading. Such a close contact type area
sensor is published in "Amorphous Silicon Two-Dimensional Image
Sensor and Its Application" Television Society Technical Report:
1993.3.4: p.25 or "Two-Dimensional Contact-Type Image Sensor Using
Amorphous Silicon Photo-Transistor" Jpn. J. Appli. Phys. vol.32
(1993) pp.458-461.
[0017] Further, a description is given of a close contact type area
sensor also in Japanese Patent Laid-Open No. 219823/1997 and there
is published a view of a single pixel, that is, a view arranged
with a single piece of irradiation window at a side of a light
receiving portion. In this way, also in a close contact type area
sensor, a single piece of pixel is arranged with only a single
piece of irradiation window.
[0018] Next, a description will be given of a case of reading a
reading object by color. When a color image is intended to read, a
special method needs to use. Color formation methods are grossly
classified into three types of (a) light source switching type, (b)
filter switching type and (c) type for using color image sensor.
According to (a) light source switching type, three colors of light
sources (fluorescent lamp, LED etc.) are successively winked and
image information of draft is successively read by monochromatic
image sensors to thereby provide signal outputs of red, green and
blue. According to (b) filter switching type, there are provided
color filters of red, green and blue between a while color light
source and monochromatic image sensors. Further, image information
is successively read by switching the filters to thereby provide
signal outputs of red, green and blue. According to (c) color image
sensor type, color disintegration and reading are simultaneously
carried out by a color image sensor integrated with three line
image sensors and color filters in one package.
[0019] Next, a description will be given of a sensor portion for
carrying out photoelectric conversion. Normally, light is converted
into electricity by using a PN type photodiode. Otherwise, there is
a PIN type diode, an avalanche type diode, an npn embedded type
diode, a schottky type diode or a phototransistor. Other than
these, there are a photoconductor for X-ray and a sensor for
infrared ray. Concerning these, there is a description in "A Basis
of a Solid Image Taking Element--a Mechanism of an Electronic Eye"
written by Takao Ando, Hirohito Komobuchi: Nippon Ricoh Suppan
Kai.
[0020] According to the conventional irradiation window 307, a
single piece thereof is arranged for one pixel. Therefore, the
light utilizing efficiency is not high, as a result, the signal is
also weak. Further, since light irradiated also to portions other
than the irradiation window 307, the light utilizing efficiency is
not high and more power consumption is needed. Further, depending
on a light source, light is not irradiated to a total of the
irradiation window 307 and therefore, the light utilizing
efficiency is not high and more power consumption is needed.
[0021] Here, in order to describe the light utilizing efficiency,
firstly, a description will be given of Lambert's cosine law.
Lambert's cosine law describes a reflection characteristic of light
at a diffusing face. A diffusing face following Lambert's cosine
law is referred to as a completely diffusing face and diffused
light thereof is referred to as completely diffused light. Normal
paper is near to a completely diffusing face and may approximately
be regarded as a completely diffusing face with no problem.
[0022] Suppose that as shown by FIG. 6, incident light 601 is
incident on a reflecting face 603 from an arbitrary direction.
Then, when the reflecting face 603 is a completely diffusing face,
the incident light is diffused and reflected in all of directions.
A description will be given of an intensity of reflected light 602
at this occasion. First, an intensity of light reflected in a
direction perpendicular to the reflecting face 603, that is, in a
direction of a normal line or a perpendicular line, is designated
by notation I.sub.0. And an angle made by the normal line of the
reflecting face 603 and reflected light is defined as a reflection
angle. An optical intensity I(.theta.) having a reflection angle of
.theta. is given by I(.theta.)=I.sub.0*cos.theta.. The optical
intensity is not dependent on an angle of incidence of incident
light. In this way, Lambert's cosine law states that the optical
intensity of reflected light is the optical intensity I.sub.0
multiplied by cosine of the reflection angle.
[0023] Further, the light intensity described here is an intensity
of light energy, that is, luminous intensity or luminous flux. When
considered in term of brightness, in the case of complete
diffusion, the brightness remains unchanged by an angle of viewing
the reflecting face 603.
[0024] In this way, according to a completely diffusing face,
regardless of an incident angle of incident light, reflected light
is reflected in all of directions and reflected light in a
direction of a normal line (perpendicular line) of the face is
provided with the strongest optical intensity. Further, as the
reflection angle is increased, the intensity of the reflected light
is weakened. Normal paper may be regarded as a completely diffusing
face as an approximation with excellent accuracy.
[0025] Based on Lambert's cosine law as mentioned above, a
consideration will be given of the light utilizing efficiency of a
case in which a single piece of irradiating window is arranged.
Here, for simplicity, a consideration will be given of a case in
which an optical system is not arranged. Even when an optical
system is arranged, similar consideration can be given thereto.
[0026] Suppose that as shown by FIG. 7, there is a single piece of
pixel formed with the light receiving portion 306 and the
irradiation window 307 at the glass 305, above the reading object
304 constituting a completely diffusing face. Suppose that the
irradiated light is irradiated from above. The irradiated light
transmits through the irradiation window 307 and reaches the
reading object 304.
[0027] First, when light is incident from the irradiation window
307 at a vicinity of the light receiving portion 306, reflected
light from the reading object 304 is easy to be incident on the
light receiving portion 306. Further, a reflection angle of the
reflected light at the reading object 304 is small and therefore,
an optical intensity thereof is strong as is known from Lambert's
cosine law. That is, a large amount of light reflected by the
reading object 304 is incident on the light receiving portion 306
and therefore, the light utilizing efficiency is high.
[0028] Meanwhile, when light is incident from the irradiation
window 307 remote from the light receiving portion 306, reflected
light from the reading object 304 hardly enters the light receiving
portion and is transmitted again to the irradiation window 307.
That is, the reflected light is wasted. Only light having a large
reflection angle is incident on the light receiving portion.
However, light having the large reflection light is provided with a
small optical intensity as is known from Lambert's cosine law.
Therefore, a large amount of light is not incident on the light
receiving portion 306 and the light utilizing efficiency is
low.
[0029] Next, a consideration will be given of a positional
dependency of a light receiving rate of the light receiving portion
306.
[0030] First, reflected light from the reading object 304 is easy
to be incident on the light receiving portion 306 at a vicinity of
the irradiation window 307. Further, the optical intensity is also
high since the reflection angle is small. That is, the light
receiving rate is high at the light receiving portion 306 at a
vicinity of the irradiation window 307.
[0031] Meanwhile, reflected light from the reading object 304 is
difficult to be incident on the light receiving portion 306 remote
from the irradiation window 307. Further, even when the reflected
light is incident on the light receiving portion 306, the optical
intensity is low since the reflection angle is large as is known
from Lambert's cosine law. That is, the light receiving rate is low
at the light receiving portion 306 remote from the irradiation
window 307.
[0032] The above-described is summarized as follows. That is, even
when single pieces of the large light receiving portion 306 and the
large irradiation window 307 are arranged, light is utilized
actually effectively only at a vicinity of a boundary between the
light receiving portion 306 and the irradiation window 307.
Therefore, even when the light receiving portion 306 is arranged at
a location remote from the irradiation window 307, light is wasted.
Further, even when the irradiation window 307 is arranged at a
location remote from the light receiving portion 306, light is not
utilized effectively. That is, when single pieces of the large
light receiving portion 306 and the large irradiation window 307
are arranged, the light utilizing efficiency is very poor. When
reflected light from the reading object 304 is not so much incident
on the light receiving portion 306, a signal of the light receiving
portion 306 is also weakened. As a result, a characteristic of the
sensor such as sensitivity is deteriorated.
[0033] Next, a consideration will be given of a portion of light
emitted from the light source 303 which is incident on the rear
face of the glass 305 and transmits through the irradiation window
307. When light emitted from the light source 303 is irradiated to
an entire face of the glass 305, light is irradiated also to a
portion other than the irradiation window 307. A consideration will
be given of the light utilizing efficiency in that case.
[0034] As shown by FIG. 7, light is irradiated to the irradiation
window 307 from a side opposed to the reading object 304. Further,
the irradiated light transmits through the irradiation window 307
and is irradiated to the reading object 304. The light is reflected
by the reading object 304 and is incident on the light receiving
portion 306. In the above-described procedure when light is
irradiated to an entire face of the glass 305 from the side opposed
to the reading object 304 in the direction of the irradiation
window 307, light is irradiated also to the light receiving portion
306 and a sensor circuit portion such as other circuit portion
(normally, a light shielding film is formed at portions other than
the irradiation window 307, for example, between the light
receiving portion 306 or the circuit portion and the glass 305 and
only light reflected by the reading object 304 is incident on the
light receiving portion 306). However, only light irradiated to the
irradiation window 307 is actually utilized. That is, light
irradiated to the sensor circuit portion is totally wasted. As a
result, the light utilizing efficiency is lowered. Therefore, an
increase in power consumption is caused for irradiating stronger
light to the reading object 304.
[0035] Further, in the case in which light emitted from the light
source 303 is irradiated only to a portion of the face, when
positions of the region and the irradiation window 307 are shifted
from each other, there is produced a region in which light is not
incident on the irradiation window 307. That is, an amount of light
which transmits through the irradiation window 307 and is
irradiated to the reading object 304 is reduced. As a result, the
light utilizing efficiency is lowered. Therefore, an increase in
power consumption is caused for irradiating stronger light to the
reading object 304.
SUMMARY OF THE INVENTION
[0036] It is an object of the present invention to resolve the
above-described problem of the conventional technology. Further
specifically, it is a problem of the present invention to provide a
close contact type sensor having high light utilizing
efficiency.
[0037] First, a plurality of irradiation windows are provided to
one pixel. According to an irradiation window, only an irradiation
window at a vicinity of a light receiving portion constitutes a
region in which light is effectively utilized. Further, according
to a light receiving portion, only a light receiving portion at a
vicinity of an irradiation window constitutes a region on which
light is easy to be incident. That is, light is effectively
utilized only at regions of portions of a light receiving portion
and an irradiation window at a vicinity of a boundary
therebetween.
[0038] In a single pixel, by providing a large number of
irradiation windows by reducing a size of a single irradiation
window, regions of portions of a light receiving portion and an
irradiation window at a vicinity of a boundary therebetween can be
increased. Further, a region of an irradiation window remote from a
light receiving portion and a region of a light receiving portion
remote from an irradiation window are reduced. Therefore, the light
utilizing efficiency is promoted. As a result, a magnitude of an
output signal from a pixel of a sensor is increased. Therefore,
image quality read by a sensor is promoted. Further, power
consumption of a light source can be reduced since the light
utilizing efficiency is high.
[0039] Next, when light is irradiated from a side opposed to a
reading object to an irradiation window, light is made to irradiate
to only an irradiation window portion as much as possible and light
is prevented from irradiating to a sensor circuit portion as less
as possible. Or, the irradiation window portion is made to arrange
at a region irradiated with light. As a result, light which does
not reach the reading object, that is, wasteful light is reduced
and the light utilizing efficiency is promoted. Further, power
consumption of a light source can be reduced since the light
utilizing efficiency is high.
[0040] Further, when light is irradiated from a side opposed to a
reading object to an irradiation window, it is not necessarily
needed to simultaneously carry out irradiation of light to an
irradiation window portion as much as possible, arrangement of the
irradiation window portion to a region irradiated with light and
provision of a plurality of irradiation windows to a single pixel.
These may be carried out respectively individually or may be
carried out simultaneously.
[0041] Constitutions of the present invention will be shown as
follows.
[0042] According to an aspect of the present invention, there is
provided a close contact type sensor arranged with a plurality of
unit pixels each comprising a sensor circuit portion and a
plurality of irradiation window portions.
[0043] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0044] an optical fiber plate between the sensor circuit portion
and a reading object;
[0045] wherein an area of any of the plurality of irradiation
window portions is larger than an area of a half of a section of a
single piece of an optical fiber in the optical fiber plate.
[0046] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0047] a liquid crystal display; and
[0048] a backlight;
[0049] wherein the liquid crystal display is arranged below the
backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display and the plurality of irradiation window portions are
arranged on inner sides of opening portions of the liquid crystal
display.
[0050] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0051] a liquid crystal display;
[0052] a backlight; and
[0053] an optical fiber plate;
[0054] wherein the liquid crystal display is arranged below the
backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, the optical fiber plate is arranged below the sensor
circuit portion and the plurality of irradiation window portions
and the plurality of irradiation window portions are arranged on
inner sides of opening portions of the liquid crystal display.
[0055] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0056] a liquid crystal display; and
[0057] a backlight;
[0058] wherein in the liquid crystal display, a single piece of a
unit pixel is constituted by one pixel for red, one pixel for green
and one pixel for blue, the liquid crystal display is arranged
below the backlight, the sensor circuit portion and the plurality
of irradiation window portions are arranged below the liquid
crystal display and a size of the unit pixel of the liquid crystal
display is a size of the unit pixel of the close contact type
sensor multiplied by an integer or a factor (fraction) of an
integer thereof.
[0059] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0060] a liquid crystal display;
[0061] a backlight; and
[0062] an optical fiber plate;
[0063] wherein in the liquid crystal display, a single piece of a
unit pixel is constituted by one pixel for red, one pixel for green
and one pixel for blue, the liquid crystal display is arranged blow
the backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, the optical fiber plate is arranged below the sensor
circuit portion and the plurality of irradiation window portions
and a size of the unit pixel of the liquid crystal display is a
size of the unit pixel of the close contact type sensor multiplied
by an integer or a factor of an integer thereof.
[0064] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0065] a liquid crystal display; and
[0066] a backlight;
[0067] wherein in the liquid crystal display, a single piece of a
unit pixel is constituted by one pixel for red, one pixel for green
and one pixel for blue, the liquid crystal display is arranged blow
the backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, and light of the backlight successively transmits through
the pixel for red, the pixel for green and the pixel for blue of
the liquid crystal display at every respective subframe period.
[0068] According to another aspect of the present invention, there
is provided a close contact type sensor which is a close contact
type sensor arranged with a plurality of unit pixels each
comprising a sensor circuit portion and a plurality of irradiation
window portions, the close contact type sensor comprising:
[0069] a liquid crystal display;
[0070] a backlight; and
[0071] an optical fiber plate;
[0072] wherein in the liquid crystal display, a single piece of a
unit pixel is constituted by one pixel for red, one pixel for green
and one pixel for blue, the liquid crystal display is arranged blow
the backlight, the sensor circuit portion and the plurality of
irradiation window portions are arranged below the liquid crystal
display, the optical fiber plate is arranged below the sensor
circuit portion and the plurality of irradiation window portions
and light of the backlight successively transmits through the pixel
for red, the pixel for green and the pixel for blue of the liquid
crystal display at every subframe period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0073] FIG. 1 is a sectional view of a completely close contact
type sensor according to the invention;
[0074] FIG. 2 is a sectional view of a scanner using a conventional
close contact type optical system;
[0075] FIG. 3 is a sectional view of a conventional completely
close contact type sensor;
[0076] FIGS. 4A and 4B are views showing irradiation windows of
conventional completely close contact type sensors;
[0077] FIGS. 5A and 5B are views showing constitutions of
conventional completely close contact type sensors.
[0078] FIG. 6 is a view showing Lambert's cosine law;
[0079] FIG. 7 is a sectional view of a conventional completely
close contact type sensor;
[0080] FIG. 8 is a view showing an irradiation window of a
completely close contact type sensor according to the
invention;
[0081] FIG. 9 is a sectional view of a completely close contact
type sensor according to the invention;
[0082] FIG. 10 is a sectional view of a conventional completely
close contact type sensor;
[0083] FIG. 11 is a circuit diagram of a circuit of a pixel
according to the invention;
[0084] FIGS. 12A and 12B are layout views of a pixel according to
the invention;
[0085] FIG. 13 is a sectional view of a pixel according to the
invention;
[0086] FIG. 14 is a view showing an optical fiber plate;
[0087] FIG. 15 is a sectional view of a completely close contact
type sensor according to the invention;
[0088] FIG. 16 is a perspective view of a completely close contact
type sensor according to the invention and a liquid crystal
display;
[0089] FIG. 17 is a perspective view of a completely close contact
type sensor according to the invention and a pixel portion of a
liquid crystal display;
[0090] FIG. 18 is a block diagram of an area sensor according to
the invention;
[0091] FIG. 19 is a circuit diagram of a pixel of an active sensor
according to the invention;
[0092] FIG. 20 is a circuit diagram of a pixel of an active sensor
according to the invention;
[0093] FIG. 21 is a circuit diagram of a signal processing circuit
according to the invention;
[0094] FIG. 22 is a circuit diagram of a final output amplifying
circuit according to the invention;
[0095] FIG. 23 is a circuit diagram of a final output amplifying
circuit according to the invention;
[0096] FIG. 24 is a timing chart of an area sensor according to the
invention;
[0097] FIG. 25 is a timing chart of an area sensor according to the
invention;
[0098] FIGS. 26A, 26B, 26C and 26D are views showing steps of
fabricating an image sensor according to the invention;
[0099] FIGS. 27A, 27B, 27C and 27D are views showing steps of
fabricating an image sensor according to the invention;
[0100] FIGS. 28A, 28B and 28C are views showing steps of
fabricating an image sensor according to the invention;
[0101] FIGS. 29A and 29B are views showing steps of fabricating an
image sensor according to the invention;
[0102] FIGS. 30A and 30B are views of an electronic apparatus using
an image sensor according to the invention; and
[0103] FIGS. 31A and 31B are views o f an electronic apparatus
using an image sensor according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0104] FIG. 8 shows a view viewing, from above, a case in which a
plurality of irradiation windows 807 are provided in a single
pixel. FIG. 9 shows a sectional view of FIG. 8 taken along a
section line 801. The number of the irradiation windows 807 may be
any number so far as the number is a plural number. Glass 805 is
formed with light receiving portions 806, circuit portions and the
irradiation windows 807. The irradiation window 807 is made to be
transparent for transmitting light. According to the light
receiving portion 806, a light shielding film is frequently formed
between the light receiving portion 806 and the glass 806 such that
influence is not effected thereon even when light is incident
thereon from a side opposed to a reading object 804. Further, the
light receiving portion 806 and the circuit portion may be arranged
to overlap.
[0105] Further, although in FIG. 9, for simplicity, only the light
receiving portions 806 and the irradiation windows 807 are
illustrated on the glass 805, actually, circuit portions or light
shielding films may be formed thereon.
[0106] Further, although in FIG. 9, for simplicity, nothing is
illustrated between the light receiving portion 806 and the reading
object 804, actually, an optical system, a protective film or a
glass may be arranged therebetween. As an optical system, an
optical fiber plate may be used or a rod lens array may be
used.
[0107] Further, in FIG. 9, light is irradiated from a glass face
which is not formed with the light receiving portion. However, the
light receiving portion 806, the glass 805 formed with the light
receiving portion and the reading object 804 may be arranged in
this order by turning the glass 805 upside down.
[0108] By arranging the plurality of irradiation windows 807 to a
single pixel in this way, regions of portions of the light
receiving portion and the irradiation window at a vicinity of a
boundary therebetween can be increased. As a result, light can
effectively be utilized. Therefore, a magnitude of an output signal
from a pixel of a sensor is increased and quality of image read by
the sensor is promoted. Further, power consumption of a light
source can be reduced since the light utilizing efficiency is
high.
Embodiment 2
[0109] FIG. 1 shows a sectional view of a close contact type sensor
when a liquid crystal display and a backlight are used as a light
source for a sensor. A backlight 101 is provided at the topmost
position, a liquid crystal display 103 is provided therebelow, the
light receiving portions 806 and the irradiation windows 807 are
provided therebelow and the reading object 804 are provided
therebelow.
[0110] The glass 805 is formed with the light receiving portions
806, circuit portions and the irradiation windows 807. The
irradiation window 807 is made to be transparent for transmitting
light. According to the light receiving portion 806, a light
shielding film is frequently formed between the light receiving
portion 806 and the glass 805 such that influence is not effected
thereto even when light is incident from a side opposed to the
reading object 804. Further, the light receiving portion 806 and
the circuit portion may be arranged to overlap.
[0111] Further, although in FIG. 1, for simplicity, only the light
receiving portions 106 and the irradiation windows 807 are
illustrated on the glass 805, actually, circuit portions or light
shielding films may be formed thereon.
[0112] Further, although in FIG. 1, for simplicity, nothing is
illustrated between the light receiving portion 806 and the reading
object 804, actually, an optical system, a protective film or glass
may be arranged therebetween. As an optical system, an optical
fiber plate may be used or a rod lens array may be used.
[0113] Further, in FIG. 1, light is irradiated from a glass face
which is not formed with the light receiving portions. However, the
light receiving portions 806, the glass 805 formed with the light
receiving portions and the reading object 804 may be arranged in
this order by turning the glass 805 upside down.
[0114] The operation is as follows. First, light 102 is irradiated
to a side of the liquid crystal display 103. At the liquid crystal
display 103, there are present regions which can transmit the light
102, that is, opening portions 105. The light 102 cannot transmit
through regions other than the opening portions 105. Light 104
which has transmitted through the opening portions 105 of the
liquid crystal display 103 is irradiated to sides of the light
receiving portions 806 and the irradiation windows 807. That is,
the light is not irradiated to the sides of the light receiving
portions 806 and the irradiation windows 807 over entire faces
thereof but only the light 104 which has transmitted through the
opening portions 105 is irradiated to the sides of the light
receiving portions 806 and the irradiation windows 807.
[0115] Meanwhile, on the side of the light receiving portion 806,
reflected light of light irradiated to the reading object 804 is
read by the light receiving portion 806. The irradiation windows
807 are provided for irradiating light to the reading object 804.
That is, only light irradiated to portions of the irradiation
windows 807 constitutes light 106 transmitting through the
irradiation windows. Even when light is irradiated from the liquid
crystal display 103 to a location other than the irradiation window
807, the light is wasted.
[0116] Hence, in order to effectively utilize light, with respect
to the opening portion 105 and the irradiation window 807,
positions, sizes or shapes of the both members are matched. That
is, a large amount of the light 104 which has transmitted through
the liquid crystal display is made to be the light 106 for passing
through the irradiation window by completely overlapping the
irradiation window 807 and a portion of the opening portion 105. As
a result, the light utilizing efficiency is promoted.
[0117] When with respect to the opening portion 105 and the
irradiation window 807, the positions or the sizes or the shapes
are deviated from each other, as shown by FIG. 10, a large amount
of light irradiated to the portion of the irradiation window 807 is
wasted and the light 106 for passing through the irradiation window
106 is reduced.
[0118] Further, Embodiment 1 and Embodiment 2 can freely be
combined.
EXAMPLES
Example 1
[0119] Next, a description will be given of an example when a
plurality of irradiation windows are provided to a single pixel.
FIG. 11 shows a circuit diagram of a pixel. In FIG. 11, there is
used a photodiode 1104 as a photoelectric conversion element which
is an active type sensor. A P-channel side terminal of the
photodiode 1104 is connected to a power source reference line 1112
and an N-channel side terminal 1113 thereof is connected to a gate
terminal of an amplifying transistor 1106. A drain terminal and a
source terminal of the amplifying transistor 1106 are connected to
a power source line 1109 and a drain terminal of a switching
transistor 1101. A gate terminal of the switching transistor 1101
is connected with a gate signal line 1102 and a source terminal
thereof is connected with a signal output line 1103. A gate
terminal of a resetting transistor 1107 is connected to a reset
signal line 1105. A source terminal and a drain terminal of the
resetting transistor 1107 are connected to the power source line
1109 and the gate terminal of the amplifying transistor 1106.
[0120] Further, with regard to a sensor portion for carrying out
photoelectric conversion, other than a normal PN type photodiode, a
PIN type diode, an avalanche type diode, an npn embedded type
diode, a Schottky type diode, a phototransistor, a photoconductor
for X-ray or a sensor for infrared ray can also be used. Further,
after converting X-ray into light by a fluorescent member or a
sintilator, the light may be read.
[0121] Further, although in FIG. 11, there is provided the active
type sensor mounted with the signal amplifying element, a passive
type sensor which is not mounted with the signal amplifying element
can also be used.
[0122] FIGS. 12A and 12B show layout views realizing the circuit
diagram of FIG. 11 and FIG. 13 shows a sectional view taken along a
section line 1204. FIG. 12A is a layout view before the N-channel
side terminal 1113 and FIG. 13B is a layout view after the
N-channel side terminal 1113.
[0123] The gate signal line 1102, the reset signal line 1105 and
the gate electrodes of the respective transistors are formed by
using a first wiring. Wirings for connecting the signal output line
1103, the power source line 1109 and the transistors are formed by
using a second wiring. The N-channel side terminal 1113 is formed
by using a third wiring.
[0124] The N-channel side terminal 1113 is constituted by a
material which is not transparent and accordingly, as apparent from
FIGS. 12A and 12B, portions which are not covered by the N-channel
side terminal 1113 and other wirings, constitute irradiation
windows 1201. Portions which are covered by the wirings of the
N-channel side terminal 1113 constitute light receiving portions. A
circuit portion is arranged to overlap portions covered by wirings
of the N-channel side terminal 1113. As is apparent from FIG. 13,
irradiation light is incident from a rear face of glass 1301,
transmits through the irradiation window 1201 and is irradiated to
a side of a reading object. Light reflected by the reading object
is incident on the photodiode 1104. A portion formed with the
photodiode 1104 sandwiched between the N-channel side terminal 1113
and the power source reference line 1112, constitutes a light
receiving portion 1302.
[0125] As shown by FIGS. 12A and 12B and FIG. 13, a plurality of
the irradiation windows 1201 are arranged to one pixel and
accordingly, regions of the light receiving portions 1302 and the
irradiation window 1201 at the vicinities of boundaries
therebetween are increased and the light utilizing efficiency is
promoted.
[0126] Further, although in FIG. 13, for simplicity, nothing is
illustrated between the photodiode 1104 and the reading object,
actually, an optical system, a protective film or glass may be
arranged therebetween. As an optical system, an optical fiber plate
may be used and a rod lens array may be used.
[0127] Further, in FIG. 13, light is irradiated from a glass face
which is not formed with a circuit such as a light receiving
portion. However, light may be irradiated from a face formed with a
circuit by turning the glass 1301 upside down. According to an
arrangement at that occasion, circuits of the light receiving
portion and the like (constituted by the N-channel side terminal
1113, the photodiode 1104, the power source reference line 1112, a
second contact 1203, the power source line 1109, a first contact
1202, and the resetting transistor 1107 followed by the glass
1301), the glass 1301 and the reading object may be arranged in
this order.
Example 2
[0128] Next, a description will be given of an embodiment when an
optical fiber plate is arranged between a light receiving portion
and a reading object as an optical system.
[0129] First, FIG. 14 shows an optical fiber plate, an enlarged
view thereof and a sectional view of one piece of an optical fiber.
An optical fiber plate 1401 is constituted by bundling a number of
optical fibers and slicing the bundle in a shape of plate. One
piece of the optical fiber is constituted by a core 1402 and a clad
1403. The core 1402 is disposed at the center of the optical fiber
and is provided with higher refractive index. A surrounding of the
core 1402 is covered with the clad 1403 and refractive index
thereof is lower than that of the core 1402. As a result, light
incident on a section of the optical fiber is propagated while
being totally reflected in the core 1402. A surrounding of the clad
1403 is frequently provided with an absorbing layer 1404 for
absorbing extra light.
[0130] The optical fiber plate 1401 per se is not provided with a
function of focusing light. Light is only propagated at inside of
the core 1402 of the respective piece of the optical fiber. When
light is incident on a section of one piece of the optical fiber,
light having a large angle of incidence is absorbed by the
absorbing layer 1402 since the light cannot be totally reflected at
inside of the core 1402. That is, light incident on the core 1402
of one piece of the optical fiber by a small angle of incidence, is
propagated as it is and the other light, for example, light
incident on the core 1402 by a large angle of incidence or light
incident on the clad 1403 is not propagated. As a result, when the
optical fiber plate 1401 is arranged between a light receiving
portion and a reading object, an image read by a sensor can be
prevented from being blurred.
[0131] FIG. 15 shows a sectional view when the optical fiber plate
1401 is arranged between the light receiving portion 806 and the
reading object 804. The glass 805 is formed with the light
receiving portion 806, the circuit portion and the irradiation
window 807. The irradiation window 807 is transparent for
transmitting light. The light receiving portion 806 is frequently
formed with a light shielding film between the light receiving
portion 806 and the glass 805 such that adverse influence is not
effected even when light is incident on a side thereof opposed to
the reading object 804. Further, the light receiving portion 806
and the circuit portion may be arranged to overlap.
[0132] Further, in FIG. 15, for simplicity, although there are
illustrated only the light receiving portion 806 and the
irradiation window 807 on the glass 805, actually, the circuit
portion or the light shielding film may be formed thereon.
[0133] Further, in FIG. 15, for simplicity, although there is
illustrated only the optical fiber plate between the light
receiving portion 806 and the reading object 804, actually, there
may be arranged other optical system, a protective system or
glass.
[0134] Further, light is irradiated from a glass face which is not
formed with the light receiving portion. However, there may be
constituted an arrangement in which the light receiving portion
806, the glass 805 formed with the light receiving portion and the
reading object 804 are arranged in this order by turning the glass
805 upside down.
[0135] The optical fiber can pertinently transmit light incident on
the core 1402 by a small angle of incidence. However, it is
difficult to propagate light other than thereof. In FIG. 15, a size
(diameter) of the core 1402 is larger than a size of the
irradiation window. In such a case although at a certain one of the
irradiation window, light can be made to be incident on the core
1402, at other of the irradiation window, light capable of being
made to be incident on the core 1402 is reduced. As a result, even
with the irradiation window 807 having the same size, an intensity
of light capable of being transmitted to the reading object 804
therefrom, differs. Then, by a positional relationship between the
irradiation window 807 and the core 1402, the intensity of light
irradiated to the reading object 804, differs. That is, the
intensity of light irradiated to the reading object 804, differs
depending on the pixel.
[0136] In consideration of the above-described, the size of the
irradiation window 807 needs to be larger than the size (diameter)
of the core 1402. In reality, in consideration also of sizes of the
core 1402 and the clad 1403 and in consideration of the fact that
there are a plurality of the irradiation windows 807 for one pixel,
when an area of the irradiation window 807 is equal to or larger
than a half of an area of a section of one piece of the optical
fiber of the optical fiber plate 1401, no problem is posed
actually. An upper limit of the area of the irradiation window 807
is automatically restricted since the upper limit cannot be made to
be larger than the pixel size.
[0137] Further, Example 2 may freely be combined with Example
Example 3
[0138] Next, a description will be given of a case of using a
liquid crystal display (including backlight or a front light) as a
light source for irradiation. When a light source is constituted by
a liquid crystal display, as described in Example 2, it is
preferable to align positions of an opening portion of the liquid
crystal display and an irradiation window.
[0139] FIG. 16 shows a perspective view when a liquid crystal
display is used as a light source for irradiation. First, a liquid
crystal display 1601 is arranged at the topmost position as a light
source (however, irradiation of a backlight or a front light is
omitted). Glass 1603 formed with a light receiving portion is
arranged therebelow. A reading object 1605 is arranged below the
glass 1603 formed with the light receiving portion. Light emitted
from the liquid crystal display 1601 is irradiated toward the glass
1603 formed with the light receiving portion. Further, light
transmits through an irradiation window formed at the glass 1603
formed with the light receiving portion and is irradiated to the
reading object 1605. Further, light reflected by the reading object
1605 is incident on the light receiving portion formed at the glass
1603 formed with the light receiving portion and is read as a
signal.
[0140] Here, the liquid crystal display 1601 may be an STN type
liquid crystal display or maybe a TFT type liquid crystal display
and is not particularly limited. Further, a material of liquid
crystal may be TN liquid crystal, STN liquid crystal, liquid
crystal for an IPS mode or ferroelectric liquid crystal and is not
particularly limited. Further, the liquid crystal display 1601 may
be of a transmission type or a reflection type and is not
particularly limited so far as light is irradiated therefrom.
[0141] Further, the liquid crystal display 1601 may include a
polarizer, a phase difference plate or a color filter as a
constitution thereof other than a backlight or a front light.
[0142] Further, in FIG. 16, for simplicity, although nothing is
illustrated between the glass 1603 formed with the light receiving
portion and the reading object 1605, actually, there may be
arranged an optical system, a protective film or glass. As an
optical system, an optical fiber plate may be used or a rod lens
array may be used.
[0143] Here, a description will be given of a positional
relationship between a unit pixel 1602 of the liquid crystal
display and a unit pixel 1604 constituted by the light receiving
portion and irradiation windows. FIG. 17 shows an enlarged view
thereof. In FIG. 17, in order to align positions of the opening
portion of the liquid crystal display and the irradiation window of
the sensor, a size of the unit pixel 1602 of the liquid crystal
display and a size of the unit pixel 1604 constituted by the light
receiving portion and irradiation windows are made the same.
Further, positions of the opening portion of the liquid crystal
display and the irradiation window are aligned. Thereby, light
emitted from the liquid crystal display 1601 is hardly wasted and
therefore, the light utilization efficiency is promoted.
[0144] FIG. 17 illustrates a color liquid crystal display as an
object. That is, the unit pixel 1602 is arranged with an opening
portion 1701 of red color, an opening portion 1702 of green color
and an opening portion 1703 of blue color. At surroundings of the
opening portions, there is arranged a black matrix 1704. Further, a
single one of the unit pixel 1602 is constituted by the three
colors.
[0145] Irradiation windows 1705 are formed to align with the
opening portions of the liquid crystal display. By matching
positions and sizes thereof, the light utilization efficiency can
be promoted.
[0146] However, it is not necessarily needed that the irradiation
windows 1705 are completely matched with the opening portions of
the liquid crystal display in positions and sizes thereof but may
be matched therewith as much as possible.
[0147] When the size of the unit pixel 1602 of the liquid crystal
display and the size of the unit pixel 1604 constituted by the
light receiving portion and the irradiation windows are made the
same, the positions of the opening portion and irradiation window
are easy to align. Further, when the positions are the same,
numbers of the pixels are easy to be made the same and therefore,
when an image read by the sensor is displayed on the liquid crystal
display, processings of data are easy to execute. Therefore, it is
preferable that the size of the unit pixel 1602 of the liquid
crystal display and the size of the unit pixel 1604 constituted by
the light receiving portion and the irradiation windows are made
the same.
[0148] However, when the size of the unit pixel 1602 of the liquid
crystal display is the size of the unit pixel 1604 constituted by
the light receiving portion and the irradiation windows multiplied
by an integer or a factor (fraction) of an integer there of, the
positions of the opening portion and the irradiation window are
easy to align, which is preferable.
[0149] Next, a description will be given of color formation of the
sensor. When a color liquid crystal display is used as a light
source, a color image can easily be read. Color liquid crystal
display can emit three colors of light by switching respectives
thereof and accordingly, a color image can be read by using
monochromatic sensors.
[0150] Hence, a description will be given of a method of reading a
color image. First, a color liquid crystal display irradiates light
of only red color to the sensor. Further, in the meantime, an-image
of an entire screen is read by the sensor. Thereafter, the color
liquid crystal display irradiates light of only green color to the
sensor. Further, in the meantime, an image of the entire screen is
read by the sensor. Finally, the color liquid crystal display
irradiates light of only blue color to the sensor. Further, in the
meantime, an image of the entire screen is read by the sensor.
Thereafter, signals are synthesized.
[0151] That is, when a period of reading all of image information
is defined as one frame period, the one frame period is divided
into three subframe periods. Further, in the respective subframe
period, the color liquid crystal display irradiates only a single
color. Further, the color is successively switched. In the
respective subframe period, the sensor reads the image of the
entire screen. Further, after finishing the one frame period,
images of the respective colors are synthesized to thereby form an
image in color. By the above-described operation, the color image
can be read.
[0152] Further, when the sensor in this case is an area sensor, in
comparison with a case of using a conventional CCD type line
sensor, various advantages are achieved. First, it is not necessary
to move a line sensor and therefore, an image can be read at high
speed. Further, in the case of the line sensor, it is necessary to
repeat an operation of making light impinge, storing signals and
reading an image for respective line. Therefore, it is necessary to
switch a light source at high speed. Therefore, it is necessary to
use LED as alight source. Further, since it is necessary to repeat
the operation of making light impinge, storing signals and reading
an image for respective line, a time period of reading is retarded.
However, according to an area sensor, color of light is switched
only at respective subframe and therefore, it is not necessary to
switch the color of light at high speed. Therefore, a normal
fluorescent lamp can be used as a light source. Actually, only a
pixel (color) for transmitting light by a liquid crystal display
may be switched while a light source stays to be of white color
light. Further, while storing signals at one line by making light
impinge thereto, an image of other line can be read and
accordingly, the image can be read at high speed.
[0153] Further, although in the example, a description has been
given of the case in which the liquid crystal display is
constituted by color, a monochromatic liquid crystal display may be
used.
[0154] Further, Example 3 may freely be combined with Example 1 or
Example 2.
Example 4
[0155] Next, a description will be given of an example of an area
sensor mounted with a drive circuit at a periphery thereof and
arranged with pixels two-dimensionally. FIG. 18 shows a circuit
diagram of a total thereof. First, there is provided a pixel
arrangement portion 1805 arranged with pixels two-dimensionally.
Further, there are arranged drive circuits for driving a gate
signal line and a reset signal line of respective pixel on the left
and on the right of the pixel arrangement portion 1805. In FIG. 18,
a drive circuit 1806 for a gate signal line is arranged on the left
side and a drive circuit 1807 for a reset signal line is arranged
on the right side.
[0156] Further, on an upper side of the pixel arrangement portion
1805, there are arranged circuits for signal processing. In FIG.
18, a biasing circuit 1803 is arranged on the upper side of the
pixel arrangement portion 1805. The biasing circuit 1803
constitutes a source follower circuit by being paired with an
amplifying transistor of respective pixel. On the upper side of the
biasing circuit 1803, there is arranged a circuit 1802 for sampling
and holding and signal processing. In the circuit, there are
arranged circuits for temporarily holding a signal, executing
analog to digital conversion and reducing noise. On the upper side
of the sampling and holding and signal processing circuit 1802,
there is arranged a drive circuit 1801 for a signal output line.
The drive circuit 1801 for a signal output line outputs a signal
for successively outputting the temporarily held signal. Further,
there is arranged a circuit 1804 for amplifying a final output
before outputting a signal to outside. In the circuit, a signal
which is successively outputted by the sampling and holding and
signal processing circuit 1802 and the drive circuit 1801 for a
signal output line, is amplified before being outputted to outside.
Therefore, the circuit is not needed when the signal is not
amplified, however, the circuit is frequently arranged in
reality.
[0157] Next, circuit diagrams of respective portions will be shown.
First, FIG. 19 shows a circuit diagram of a circuit 1808 of an i-th
row and j-th column pixel portion as an example in the pixel
arrangement portion 1805 which is arranged with pixels
two-dimensionally. In FIG. 19, the circuit 1808 is constituted by a
P-channel type resetting transistor 1907, a P-channel type
switching transistor 1901, an N-channel type amplifying transistor
1906 and a photoelectric conversion element (here, a photodiode
1904 which is most representative). In the photodiode 1904, a
P-channel side terminal thereof is connected to a power source
reference line 1912 and an N-channel side terminal thereof is
connected to a gate terminal of the amplifying transistor 1906. A
gate terminal of the resetting transistor 1907 is connected with an
i-th row reset signal line 1905 and a source terminal and a drain
terminal thereof are connected to a j-th column power source line
1909 and the gate terminal of the amplifying transistor 1906. A
gate terminal of the switching transistor 1901 is connected to an
i-th row gate signal line 1902 and a source terminal and a drain
terminal thereof are connected to the j-th column power source line
1909 and the amplifying transistor 1906. A source terminal and a
drain terminal of the amplifying transistor 1906 are connected to a
j-th column signal output line 1903 and the switching transistor
1901.
[0158] In FIG. 19, p-channel type is used in the resetting
transistor 1907. However, the resetting transistor may be of an
N-channel type. However, in the case of the N-channel type, in
resetting operation, voltage between the gate and the source cannot
be made large. Therefore, the resetting transistor is operated in a
saturated region and the photodiode 1904 cannot be charged
sufficiently. Therefore, although the resetting transistor can be
operated with the N-channel type, the P-channel type is more
preferable.
[0159] It is preferable that the switching transistor 1901 is
arranged between the j-th column power source line 1909 and the
amplifying transistor 1906 and the P-channel type is used therefor.
However, an N-channel type may be used therefor since the switching
transistor 1901 is operated even with the N-channel type similar to
the conventional case and maybe arranged between the j-th column
signal output line 1903 and the amplifying transistor 1906.
However, the N-channel type one is difficult to correctly output a
signal and accordingly, it is preferable that the switching
transistor 1901 is arranged between the j-th column power source
line 1909 and the amplifying transistor 1906 and the P-channel type
is used therefor.
[0160] In FIG. 19, the N-channel type is used for the amplifying
transistor 1906. However, a P-channel type can be used therefor.
However, in that case, when the amplifying transistor 1906 is
operated as a source follower circuit by being combined with a
biasing transistor, it is necessary to change a method of
connecting the circuit. That is, the amplifying transistor 1906 is
not operated by simply changing the polarity of the amplifying
transistor 1906 in the circuit diagram of FIG. 19.
[0161] Hence, FIG. 20 shows an example of a circuit constitution
when the amplifying transistor of the P-channel type is used. A
difference of constitution from that of FIG. 19 resides in that the
polarity of an amplifying transistor 2006 is of the P-channel type,
a direction of a photodiode is reversed and a power source line and
a power source reference line are switched. When the P-channel type
is used for the amplifying transistor, it is necessary to use the
P-channel type in a biasing transistor. Because the biasing
transistor needs to operate as a constant current source.
Therefore, in Fig.20,for reference, a biasing transistor 2011 is
also illustrated. The i-th row and j-th column pixel portion
circuit 1808 shown in FIG. 20 is constituted by an N-channel type
resetting transistor 2007, an N-channel type switching transistor
2001, a P-channel type amplifying transistor 2006 and a
photoelectric conversion element (here, a photodiode 2004 which is
most representative). An N-channel side terminal of the photodiode
2004 is connected to a power source line 2009 and a P-channel side
terminal thereof is connected to a gate terminal of the amplifying
transistor 2006. A gate terminal of the resetting transistor 2007
is connected with an i-th row reset signal line 2005 and a source
terminal and a drain terminal thereof are connected to a j-th
column power source reference line 2012 and the gate terminal of
the amplifying transistor 2006. A gate terminal of the switching
transistor 2001 is connected to an i-th row gate signal line 2002
and a source terminal and a drain terminal thereof are connected to
the j-th column power source reference line 2012 and the amplifying
transistor 2006. A source terminal and a drain terminal of the
amplifying transistor 2006 are connected to a j-th row signal
output line 2003 and the switching transistor 2001. A gate terminal
of the biasing transistor 2001 is connected with a bias signal line
2010 and a source terminal and a drain terminal thereof are
connected to the j-th column signal output line 2003 and the power
source line 2009.
[0162] In FIG. 20, the N-channel type is used for the resetting
transistor 2007. However, the resetting transistor may be of a
P-channel type. However, in the case of the P-channel type, in
resetting operation, voltage between the gate and the source cannot
be made large. Therefore, the resetting transistor is operated in a
saturated region and the photodiode 2004 cannot be charged
sufficiently. Therefore, although the resetting transistor is
operated by the P-channel type, the N-channel type is
preferable.
[0163] In FIG. 20, it is preferable that the switching transistor
2001 is arranged between the j-th column power source reference
line 2012 and the amplifying transistor 2006 and the N-channel type
is used therefor. However, the switching transistor 2001 is
operated also by a P-channel type and accordingly, the P-channel
type may be used therefor and may be arranged between the j-th
column signal output line 2003 and the amplifying transistor 2006.
However, it is difficult to correctly output a signal and
therefore, it is preferable that switching transistor 2001 is
arranged between the j-th column power source reference line 2009
and the amplifying transistor 2006 and the N-channel type is used
therefor.
[0164] In this way, as is apparent by comparing FIG. 19 and FIG.
20, when the polarity of the amplifying transistor is changed, an
optimum constitution of the transistor and the direction of the
photodiode are also changed.
[0165] In FIG. 19, current is supplied from a single piece of the
power source line to both of the switching transistor 1901 and the
resetting transistor 1907. In FIG. 20, current is supplied from a
single piece of the power source reference line to both of the
switching transistor 2001 and the resetting transistor 2007. In
this way, by matching the direction of the photodiode and the
polarity of the amplifying transistor, wirings can be shared.
[0166] Next, FIG. 21 shows a circuit diagram of a j-th column
peripheral portion circuit 1809 as a circuit for one column from
the biasing circuit 1803 and the sampling and holding signal
processing circuit 1802. The biasing circuit 1803 is arranged with
a biasing transistor 2111. The polarity is the same as the polarity
of the amplifying transistor of respective pixel. Therefore, when
the amplifying transistor of pixel is of an N-channel type, the
biasing transistor is also of the N-channel type. In Fig. 21, the
biasing transistor 2111 is of the N-channel type. A gate terminal
of the biasing transistor 2111 is connected with a bias signal line
2110 and a source terminal and a drain terminal thereof are
connected to a j-th column signal output line 2103 and a power
source reference line 2112 (when the biasing transistor is of a
P-channel type, a power source line is used in place of the power
source reference line). The biasing transistor 2111 is operated as
a source follower circuit by being paired with the amplifying
transistor of respective pixel. A gate terminal of a transferring
transistor 2113 is connected with a transfer signal line 2114 and a
source terminal and a drain terminal thereof are connected to a
j-th column signal output line 2103 and a storage capacitor 2115.
The transferring transistor is operated when potential of the
signal output line 2103 is transferred to the storage capacitor
2115. Therefore, a transferring transistor of a P-channel type may
be added and connected in parallel with the N-channel type
transferring transistor 2113. The storage capacitor 2115 is
connected to the transferring transistor 2113 and a power source
reference line 2112. The role of the storage capacitor 2115 resides
in temporarily storing a signal out putted from the signal output
line 2103. A gate terminal of a discharging transistor 2116 is
connected to a predischarge signal line 2117 and a source terminal
and a drain terminal thereof are connected to the storage capacitor
2115 and the power source reference line 2112. The discharging
transistor 2116 is operating to temporarily discharge electric
charge stored in the storage capacitor 2115 before inputting the
potential of the signal output line 2103 to the storage capacitor
2115.
[0167] Further, an analog to digital signal conversion circuit or a
noise reducing circuit can also be arranged.
[0168] Further, a finally selecting transistor 2119 is connected
between the storage capacitor 2115 and a final output line 2120. A
source terminal and a drain terminal of the finally selecting
transistor 2119 are connected to the storage capacitor 2115 and the
final output line 2120. and a gate terminal thereof is connected to
a j-th column final selection line 2118. The final selection line
is scanned successively from a first column. Further, when the j-th
column final selection line 2118 is selected and the finally
selecting transistor 2119 is brought into a conductive state,
potential of the storage capacitor 2115 and potential of the final
output line 2120 become equal to each other. As a result, a signal
stored in the storage capacitor 2115 can be outputted to the final
output line 2120. However, when electric charge is stored in the
final output line 2120 before outputting the signal to the final
output line 2120, the potential in outputting the signal to the
final output line 2120 is influenced by the electric charge.
Therefore, before outputting the signal to the final output line
2120, the potential of the final output line 2120 must be
initialized to a certain potential value. In FIG. 21, a final
resetting transistor 2122 is arranged between the final output line
2120 and a power source reference line 2112. Further, a gate
terminal of the finally resetting transistor 2122 is connected with
a j-th column final reset line 2121. Further, before selecting the
j-th final selecting line 2118, the j-th column final reset line
2121 is selected and the potential of the final output line 2120 is
initialized to potential of the power source reference line 2112.
Thereafter, the J-th column final selection line 2118 is selected
and the signal stored to the storage capacitor 2115 is outputted to
the final output line 2120.
[0169] The signal outputted to the final output line 2120 may be
outputted to outside as it is. However, the signal is frequently
amplified before being outputted to outside since the signal is
very weak. FIG. 22 shows a circuit of a final portion circuit 1810
as a circuit therefor. There are various circuits for amplifying a
signal such as an operational amplifier. Although any circuit may
be used so far as the circuit is a circuit for amplifying a signal,
in this case, as the simplest circuit constitution, a source
follower circuit is shown. FIG. 22 shows a case of an N-channel
type. A final output line 2202 is constituted in inputting a signal
to the final output amplifying circuit 1804. The final output line
2202 is outputted with a signal successively from a first column.
The signal is amplified by the final output amplifying circuit 1804
and is outputted to outside. The final output line 2202 is
connected to a gate terminal of an amplifying transistor 2204 for
amplifying final output. A drain terminal of the amplifying
transistor 2204 for amplifying final output is connected to a power
source line 2206 and a source terminal thereof constitutes an
output terminal. A gate terminal of a biasing transistor 2203 for
amplifying final output is connected to a bias signal line 2205 for
amplifying final output. A source terminal and a drain terminal
thereof are connected to a power source reference line 2207 and a
source terminal of the amplifying transistor 2204 for amplifying
final output.
[0170] FIG. 23 shows a circuit diagram when a source follower
circuit in the case of a P-channel type is used. A difference
between FIG. 22 and FIG. 23 resides in that the power source line
and the power source reference line are reversed. A final output
line 2302 is connected to a gate terminal of an amplifying
transistor 2304 for amplifying final output. A drain terminal of
the amplifying transistor 2304 for amplifying final output is
connected to a power source reference line 2307 and a source
terminal thereof constitutes an output terminal. A gate terminal of
a biasing transistor 2303 for amplifying final output is connected
to a bias signal line 2305 for amplifying final output. A source
terminal and a drain terminal thereof are connected to a power
source line 2306 and the source terminal of the amplifying
transistor 2304 for amplifying final output. Values of potential of
the bias signal line 2305 for amplifying final output and potential
of the biasing signal 2205 for amplifying final output in the case
of using the N-channel type, differ from each other.
[0171] In FIG. 22 and FIG. 23, the source follower circuit of only
one stage is constituted. However, source follower circuits of a
plurality of stages may be constituted. For example, when source
follower circuits of two stage are constituted, an output terminal
of a first stage may be connected to an input terminal of a second
stage thereof. Further, in the respective stage, either of the
N-channel type and the P-channel type may be used.
[0172] The drive circuit 1806 for a gate signal line, the drive
circuit 1807 for a reset signal line and the drive circuit 1801 for
a signal output line are circuits simply outputting pulse signals.
Therefore, the circuits can be implemented by using a
publicly-known technology.
[0173] Next, a description will be given of timing charts of
signals. First, FIG. 24 shows timing charts of the circuits of FIG.
18 and FIG. 19. The reset signal lines are successively scanned
from the first row. For example, an (i-1)-th row is selected,
successively, an i-th row is selected and successively, an (i+1)-th
row is selected. A period until selecting the same row again
corresponds to the frame period. The gate signal lines are
similarly scanned successively from the first row. However, a
timing of starting to scan the gate signal line is later than a
timing of starting to scan the reset signal line. For example, when
attention is paid to a pixel of the i-th row, the reset signal line
of the i-th row is selected and thereafter, the gate signal line of
the i-th row is selected. When the gate signal line of the i-throw
is selected, a signal is outputted from the pixel of the i-th row.
A time period from when the pixel is reset until the signal is
outputted constitutes a storage time period. During the storage
time period, the photodiode stores electric charge generated by
light. In the respective row, a timing of resetting and a timing of
outputting the signal, differ from each other. Therefore, although
the storage time period is equal in the pixels of all the rows,
storage time differs.
[0174] Next, FIG. 25 shows timing charts of signals in FIG. 21.
Since the operation is repeated, as an example, a consideration
will be given of the case of selecting the gate signal line of the
i-th row. First, after selecting the gate signal line 1902 of the
i-th row, the predischarge signal line 2117 is selected and the
discharging transistor 2116 is brought into a conductive state.
Thereafter, the transfer signal line 2114 is selected. Then, a
signal of respective row is outputted from the pixel of the i-th
row to the storage capacitor 2115 of the respective row.
[0175] After storing signals of all of the pixels at the i-th row
in the storage capacitors 2115 of the respective columns, signals
of the respective columns are successively outputted to the final
output line 2120. During a time period after the transfer signal
line 2114 is not selected until the gate signal line is selected,
all the columns are scanned by the drive circuit 1801 for a signal
output line. First, the final reset line of the first column is
selected, the finally resetting transistor 2122 is brought into a
conductive state and the final output line 2120 is initialized to
the potential of the power source reference line 2112. Thereafter,
the final selection line 2118 of the first column is selected, the
finally selecting transistor 2119 is brought into a conductive
state and a signal of the storage charge 2115 of the first column
is outputted to the final output line 2120. Next, the final reset
line of a second column is selected, the final resetting transistor
2122 is brought into a conductive state and the final output line
2120 is initialized to potential of the power source reference line
2112. Thereafter, the final selection line 2118 of the second
column is selected, the finally selecting transistor 2119 is
brought into a conductive state and a signal of the storage
capacitor 2115 at the second column is outputted to the final
output line 2120. Thereafter, similar operation is repeated. In the
case of a j-th column, the final reset line of the j-th column is
selected, the finally resetting transistor 2122 is brought into a
conductive state and the final output line 2120 is initialized to
the potential of the power source reference line 2112. Thereafter,
the final selection line 2118 of the j-th column is selected, the
finally selecting transistor 2119 is brought into a conductive
state and a signal of the storage capacitor 2115 of the j-th column
is outputted to the final output line 2120. Successively, the final
reset line of a (j+1)-th column is selected, the finally resetting
transistor 2122 is brought into a conductive state and the final
output line 2120 is initialized to potential of the power source
reference line 2112. Thereafter, the final selection line 2118 of
the (j+1)-th column is selected, the final selecting transistor
2119 is brought into a conductive state and a signal of the storage
capacitor 2115 of the (j+1) -th column is outputted to the final
output line 2120. Thereafter, similar operation is repeated and
signals of all the columns are successively outputted to the final
output line. During the time period, the potential of the bias
signal line 2110 stays to be constant. The signal outputted to the
final output line 2120 is amplified by the circuit 1804 for
amplifying final output and is outputted to outside.
[0176] Next, the gate signal line of a (i+1)-th row is selected.
Then, the operation is carried out similar to that in selecting the
gate signal line of the i-th row. Further, the gate signal line of
a successive row is selected and similar operation is repeated.
[0177] Further, the sensor portion for executing photoelectric
conversion may be a diode of a PIN type, an avalanche type diode,
an npn embedded type diode, a Schottky type diode, a photoconductor
for X-ray or a sensor for infrared ray other than the normal photo
diode of a PN type. Further, after converting X-ray into light by a
fluorescent member or a sintilator, the light may be read.
[0178] As has been described above, the photoelectric conversion
element is frequently connected to an input terminal of a source
follower circuit. However, a switch may be interposed therebetween
as in a photo gate type. Or, as in a logarithmic conversion type, a
signal after having been processed to constitute a logarithmic
value of optical intensity may be inputted to the input
terminal.
[0179] Although according to the example, a description has been
given of an area sensor arranged with pixels two-dimensionally, a
line sensor arranged with pixels one-dimensionally can also be
realized.
[0180] Further, Example 4 can be freely combined with Example 1
through Example 3.
Example 5
[0181] A method of manufacturing a sensor of this invention on a
glass using a TFT is explained with reference to FIGS. 26 to
29.
[0182] First, as shown in FIG. 26A, a base film 201 is formed to a
thickness of 300 nm on a glass substrate 200. A silicon oxinitride
film is laminated as the base film 201 in Example 5. At this point,
it is appropriate to set the nitrogen concentration to between 10
and 25 wt % in the film contacting the glass substrate 200. In
addition, it is effective that the base film 201 has a thermal
radiation effect, and a DLC (diamond-like carbon) film may also be
provided.
[0183] Next, an amorphous silicon film (not shown in the figure) is
formed with a thickness of 50 nm on the base film 201 by a known
deposition method. Note that it is not necessary to limit to the
amorphous silicon film, and a semiconductor film containing an
amorphous structure (including a microcrystalline semiconductor
film) may be used. In addition, a compound semiconductor film
containing an amorphous structure, such as an amorphous silicon
germanium film, may also be used. Further, the film thickness may
be made from 20 to 100 nm.
[0184] The amorphous silicon film is then crystallized by a known
technique, forming a crystalline silicon film (also referred to as
a polycrystalline silicon film or a poly-silicon film) 202. Thermal
crystallization using an electric furnace, laser annealing
crystallization using a laser light, and lamp annealing
crystallization using an infrared light as known crystallization
methods. Crystallization is performed in Example 5 using an excimer
laser light, which uses XeCl gas.
[0185] Note that pulse emission excimer laser light formed into a
linear shape is used in Example 5, but a rectangular shape may also
be used. Continuous emission type argon laser light and continuous
emission type excimer laser light can also be used.
[0186] In this Example, although the crystalline silicon film is
used as the active layer of the TFT, it is also possible to use an
amorphous silicon film as the active layer.
[0187] Note that it is effective to form the active layer of a
resetting transistor, in which there is a necessity to reduce the
off current, by the amorphous silicon film, and to form the active
layer of an amplifying transistor by the crystalline silicon film.
Electric current flows with difficulty in the amorphous silicon
film because the carrier mobility is low, and the off current does
not easily flow. In other words, the most can be made of the
advantages of both the amorphous silicon film, through which
current does not flow easily, and the crystalline silicon film,
through which current easily flows.
[0188] Next, as shown in FIG. 26B, a protective film 203 is formed
on the crystalline silicon film 202 with a silicon oxide film
having a thickness of 130 nm. This thickness may be chosen within
the range of 100 to 200 nm (preferably between 130 and 170 nm).
Furthermore, another films such as insulating films containing
silicon may also be used. The protective film 203 is formed so that
the crystalline silicon film is not directly exposed to plasma
during addition of an impurity, and so that it is possible to have
delicate concentration control of the impurity.
[0189] Resist masks 204a, 204b, and 204c are then formed on the
protective film 203, and an impurity element, which imparts n-type
conductivity (hereafter referred to as an n-type impurity element),
is added through the protective film 203. Note that elements
residing in periodic table group 15 are generally used as the
n-type impurity element, and typically phosphorous or arsenic can
be used. Note that a plasma doping method is used, in which
phosphine (PH.sub.3) is plasma-excited without separation of mass,
and phosphorous is added at a concentration of 1.times.10.sup.18
atoms/cm.sup.3 in Example 5. An ion implantation method, in which
separation of mass is performed, may also be used, of course.
[0190] The dose amount is regulated such that the n-type impurity
element is contained in n-type impurity regions (b) 205a, 205b thus
formed by this process, at a concentration of 2.times.10.sup.16 to
5.times.10.sup.19 atoms/cm.sup.3 (typically between
5.times.10.sup.17 and 5 10.sup.18 atoms/cm.sup.3)
[0191] Next, as shown in FIG. 26C, the protective film 203 and the
resist masks 204a, 204b, and 204c are removed, and an activation of
the added n-type impurity elements is performed. A known technique
of activation may be used as the means of activation, but
activation is done in Example 5 by irradiation of excimer laser
light (laser annealing). Of course, a pulse emission excimer laser
and a continuous emission excimer laser may be used, and it is not
necessary to place any limits on the use of excimer laser light.
The goal is the activation of the added impurity element, and it is
preferable that irradiation is performed at an energy level at
which the crystalline silicon film does not melt. Note that the
laser irradiation may also be performed with the protective film
203 in place.
[0192] The activation of impurity elements by heat treatment
(furnace annealing) may also be performed along with activation of
the impurity element by laser light. When activation is performed
by heat treatment, considering the heat resistance of the
substrate, it is good to perform heat treatment at about 450 to
550.degree. C.
[0193] A boundary portion (connecting portion) with end portions of
the n-type impurity regions (b) 205a, 205b, namely regions, in
which the n-type impurity element is not added, on the periphery of
the n-type impurity regions (b) 205a, 205b, is delineated by this
process. This means that, at the point when the TFTs are later
completed, extremely good connecting portion can be formed between
LDD regions and channel forming regions.
[0194] Unnecessary portions of the crystalline silicon film are
removed next, as shown in FIG. 26D, and island-shape semiconductor
films (hereinafter referred to as active layers) 206 to 210 are
formed.
[0195] Then, as shown in FIG. 27A, a gate insulating film 211 is
formed, covering the active layers 206 to 210. An insulating film
containing silicon and with a thickness of 10 to 200 nm, preferably
between 50 and 150 nm, may be used as the gate insulating film 211.
A single layer structure or a lamination structure may be used. A
110 nm thick silicon oxinitride film is used in Example 5.
[0196] Thereafter, a conductive film having a thickness of 200 to
400 nm is formed and patterned to form gate electrodes 212 to 216.
In Example 5, the gate electrodes and wirings (hereinafter referred
to as gate wirings) electrically connected to the gate electrodes
for providing conductive paths are formed of the same materials. Of
course, the gate electrode and the gate wiring may be formed of
different materials from each other. More specifically, the gate
wirings are made of a material having a lower resistivity than the
gate electrodes. This is because a material enabling fine
processing is used for the gate electrodes, while the gate wirings
are formed of a material that can provide a smaller wiring
resistance but is not suitable for fine processing. The wiring
resistance of the gate wiring can be made extremely small by using
this type of structure, and therefore a sensor portion having a
large surface area can be formed. Namely, the above described pixel
structure is extremely effective when an area sensor with a sensor
portion having a screen size of a 10 inch diagonal or larger (in
addition, a 30 inch or larger diagonal) is realized.
[0197] Although the gate electrode can be made of a single-layered
conductive film, it is preferable to form a lamination film with
two layers or three layers, if necessary. Any known conductive
films can be used for the gate electrodes 212 to 216.
[0198] Typically, it is possible to use a film made of an element
selected from the group consisting of aluminum (Al), tantalum (Ta),
titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), and
silicon (Si), a film of nitride of the above element (typically a
tantalum nitride film, tungsten nitride film, or titanium nitride
film), an alloy film of combination of the above elements
(typically Mo--W alloy or Mo--Ta alloy), or a silicide film of the
above element (typically a tungsten silicide film or a titanium
silicide film). Of course, the films may be used as a single layer
or a laminate layer.
[0199] In Example 5, a laminate film of a tungsten nitride (WN)
film having a thickness of 30 nm and a tungsten (W) film having a
thickness of 370 nm is used. This may be formed by sputtering. When
an inert gas such as Xe or Ne is added as a sputtering gas, film
peeling due to stress can be prevented.
[0200] The gate electrodes 213 and 216 are respectively formed at
this time so as to overlap a portion of the n-type impurity regions
(b) 205a and 205b through the gate insulating film 211. This
overlapping portion later becomes an LDD region overlapping the
gate electrode.
[0201] Next, an n-type impurity element (phosphorous is used in
Example 5) is added in a self-aligning manner with the gate
electrodes 212 to 216 as masks, as shown in FIG. 27B. The addition
is regulated such that phosphorous is added to n-type impurity
regions (c) 217 to 224 thus formed at a concentration of {fraction
(1/10)} to 1/2 that of the n-type impurity regions (b) 205a and
205b (typically between 1/4 and 1/3). Specifically, a concentration
of 1.times.10.sup.16 to 5.times.10.sup.18 atoms/cm.sup.3 (typically
3.times.10.sup.17 to 3.times.10.sup.18 atoms/cm.sup.3) is
preferable.
[0202] Resist masks 225a to 225c are formed next, with a shape
covering the gate electrodes 212, 214 and 215, as shown in FIG.
27C, and an n-type impurity element (phosphorous is used in Example
5) is added, forming impurity regions (a) 226 to 233 containing
phosphorous at high concentration. Ion doping using phosphine
(PH.sub.3) is also performed here, and the phosphorous
concentration of these regions is regulated so as to be set to from
1.times.10.sup.20 to 1.times.10.sup.21 atoms/cm.sup.3 (typically
between 2.times.10.sup.20 and 5.times.10.sup.21
atoms/cm.sup.3).
[0203] A source region or a drain region of the n-channel TFT is
formed by this process, and in the n-channel TFT, a portion of the
n-type impurity regions (c) 217, 218, 222, and 223 formed by the
process of FIG. 27B is remained. These remaining regions correspond
to LDD regions.
[0204] Next, as shown in FIG. 27D, the resist masks 225a to 225c
are removed, and new resist masks 234a and 234b are formed. A
p-type impurity element (boron is used in Example 5) is then added,
forming p-type impurity regions 235 and 236 containing boron at
high concentration. Boron is added here at a concentration of
3.times.10.sup.20 to 3.times.10.sup.21 atoms/cm.sup.3 (typically
between 5.times.10.sup.20 and 1.times.10.sup.21 atoms/cm.sup.3) by
ion doping using diborane (B.sub.2H.sub.6).
[0205] Note that phosphorous has already been added to the impurity
regions 235 and 236 at a concentration of 1.times.10.sup.20 to
1.times.10.sup.21 atoms/cm.sup.3, but boron is added here at a
concentration of at least 3 times or more that of the phosphorous.
Therefore, the n-type impurity regions already formed completely
invert to p-type, and function as p-type impurity regions.
[0206] Next, after removing the resist masks 234a and 234b, the
n-type or p-type impurity elements added to the active layer at
respective concentrations are activated. Furnace annealing, laser
annealing or lamp annealing can be used as a means of activation.
In Example 5, heat treatment is performed for 4 hours at
550.degree. C. in a nitrogen atmosphere in an electric furnace.
[0207] At this time, it is important to eliminate oxygen from the
surrounding atmosphere as much as possible. This is because an
exposed surface of the gate electrode is oxidized, which results in
an increased resistance if only a small amount of oxygen exists.
Accordingly, the oxygen concentration in the surrounding atmosphere
for the activation process is set at 1 ppm or less, preferably at
0.1 ppm or less.
[0208] A first interlayer insulating film 237 is formed next, as
shown in FIG. 28A. A single layer insulating film containing
silicon is used as the first interlayer insulating film 237, or a
lamination film may be used. Further, a film thickness of between
400 nm and 1.5 .mu.m may be used. A lamination structure of a
silicon oxide film having a thickness of 800 nm on a silicon
oxinitride film having a thickness of 200 nm thick is used in
Example 5.
[0209] In addition, heat treatment is performed for 1 to 12 hours
at 300 to 450.degree. C. in an atmosphere containing between 3 and
100% hydrogen, performing hydrogenation. This process is one of
hydrogen termination of dangling bonds in the semiconductor film by
hydrogen, which is thermally excited. Plasma hydrogenation (using
hydrogen excited by plasma) may also be performed as another means
of hydrogenation.
[0210] Note that the hydrogenation processing may also be inserted
during the formation of the first interlayer insulating film 237.
Namely, hydrogen processing may be performed as above after forming
the 200 nm thick silicon oxinitride film, and then the remaining
800 nm thick silicon oxide film may be formed.
[0211] Next, a contact hole is formed in the gate insulating film
211 and the first interlayer insulating film 237, and source
wirings 238 to 242 and drain wirings 243 to 247 are formed. In this
Example, this electrode is made of a laminate film of three-layer
structure in which a titanium film having a thickness of 100 nm, an
aluminum film containing titanium and having a thickness of 300 nm,
and a titanium film having a thickness of 150 nm are continuously
formed by sputtering. Of course, other conductive films may be
used.
[0212] A first passivation film 248 is formed next with a thickness
of 50 to 500 nm (typically between 200 and 300 nm). A 300 nm thick
silicon oxinitride film is used as the first passivation film 248
in Example 5. This may also be substituted by a silicon nitride
film. Note that it is effective to perform plasma processing using
a gas containing hydrogen such as H.sub.2 or NH.sub.3 before the
formation of the silicon oxinitride film. Hydrogen activated by
this preprocess is supplied to the first interlayer insulating film
237, and the film quality of the first passivation film 248 is
improved by performing heat treatment. At the same time, the
hydrogen added to the first interlayer insulating film 237 diffuses
to the lower side, and the active layers can be hydrogenated
effectively.
[0213] Reference numeral 270 shows an amplifying TFT, 271 shows a
switching TFT, 272 shows a resetting TFT, 273 shows a biasing TFT
and 274 shows a discharge TFT.
[0214] In Example 5, the amplifying TFT 270 and the biasing TFT 273
are n-channel TFTs, and both of source region side and drain region
side have LDD regions 281 to 284. Note that the LDD regions 281 to
284 do not overlap with the gate electrodes 212 and 215 through the
gate insulating film 211. The above constitution of the amplifying
TFT 270 and the biasing TFT 273 can reduce the hot carrier
injection as much as possible.
[0215] The formation of the LDD regions 283 and 286 on only the
drain region side is in consideration of reducing the hot carrier
injection and not causing the operating speed to drop. Further, it
is not necessary to be too concerned with the value of the off
current for the switching TFT 271 and the discharge TFT 274, and
more importance may be placed on the operating speed. It is
therefore preferable for the LDD regions 283 and 286 to completely
overlap with the gate electrodes 213 and 216, and to reduce
resistive components as much as possible. Namely, the so-called
offset should be eliminated. In particular, when the source signal
line driver circuit or the gate signal line driving circuit is
driven at 15V to 20V, the above constitution of the discharge TFT
274 of the Example 5 is effective to reduce the hot carrier
injection and also not to drop the operation speed.
[0216] Furthermore, in Example 5, are setting TFT 272 is p-channel
TFT and has no LDD region. Degradation due to hot carrier injection
is almost of no concern for the p-channel TFTs, and therefore LDD
regions do not have to be formed in particular. It is also
possible, of course, to form an LDD region similar to that of an
n-channel TFT to take action against hot carriers. Further, the
resetting TFT 272 may be an n-channel type TFT.
[0217] Further, by attaching a connector (flexible printed circuit,
FPC) for connecting terminals pulled around from the elements or
circuits formed on the substrate with external signal terminals,
the sensor is completed.
[0218] Note that it is possible to freely combine Example 5 with
Examples 1 to 4.
Example 6
[0219] The sensor formed by implementing the present invention can
be used in various electronic apparatus. As such electronic
apparatus of the invention, there are pointed out a scanner, a
digital still camera, an X-ray camera, a portable information
terminal (a mobile computer, a portable telephone, a portable game
machine), a note-type personal computer, a game machine and a
television telephone.
[0220] FIG. 30A shows a scanner 3001 using the close contact type
sensor and including a sensor portion 3002. The scanner 3001 is
arranged above a reading object 3003. As light therefor, light in
the room is utilized. Thereby, an exclusive light source is not
needed. The present invention can be used in the sensor portion
3002.
[0221] In FIG. 30B, in contrast to FIG. 30A, an exclusive light
source 3007 is arranged. When positions of a reading region and a
sensor portion 3005 are aligned, the light source 3007 is lifted
thereabove. Further, positions thereof are aligned by viewing a
reading object 3006 via an irradiation window of the sensor portion
3005. In reading an image, the light source 3007 and a scanner 3004
are overlapped and used. The present invention can be used in the
sensor portion 3005.
[0222] FIG. 31A shows a portable information terminal 3101
including a liquid crystal display 3102, a scanner 3103 using the
close contact type sensor and a sensor portion 3104. When the
scanner is used, as shown by a sectional view of FIG. 31B, the
liquid crystal display 3102 and the scanner 3103 are overlapped,
the scanner 3001 is arranged above a reading object 3005 and the
liquid crystal display 3102 is arranged thereabove. As irradiation
light, light of the liquid crystal display 3102 is utilized.
Thereby, an exclusive light source is not needed. The present
invention can be used in the sensor portion 3002.
[0223] According to the present invention, light incident on a
light receiving portion can be increased. Therefore, a signal is
enlarged and image quality of a sensor is promoted. Further, light
can be transmitted through an irradiation window efficiently and
therefore, wasteful light is reduced. As a result, the light
utilizing efficiency is promoted.
* * * * *