U.S. patent application number 11/080539 was filed with the patent office on 2005-09-22 for photoelectric converting film stack type solid-state image pickup device.
This patent application is currently assigned to FUJI PHOTO FILM CO., LTD.. Invention is credited to Fukunaga, Toshiaki.
Application Number | 20050205879 11/080539 |
Document ID | / |
Family ID | 34985300 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050205879 |
Kind Code |
A1 |
Fukunaga, Toshiaki |
September 22, 2005 |
Photoelectric converting film stack type solid-state image pickup
device
Abstract
A photoelectric converting film stack type solid-state image
pickup device comprising: a semiconductor substrate in which a
signal read circuit is formed; and at least one photoelectric
converting film interposed between two electrode films, said at
least one photoelectric converting film being stacked above the
semiconductor substrate, wherein a signal corresponding to an
intensity of incident light is read outside by the signal read
circuit, the signal being generated by photoelectric conversion
with the photoelectric converting film, wherein the photoelectric
converting film comprises: a first layer comprising: an ultrafine
particle including (i) a quantum dot contributing to the
photoelectric conversion and (ii) a material having a band gap
larger than that of the quantum dot, the quantum dot being coated
with the material; and a hole transport layer stacked on the first
layer.
Inventors: |
Fukunaga, Toshiaki;
(Kanagawa, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJI PHOTO FILM CO., LTD.
|
Family ID: |
34985300 |
Appl. No.: |
11/080539 |
Filed: |
March 16, 2005 |
Current U.S.
Class: |
257/80 ;
257/E27.135 |
Current CPC
Class: |
H01L 27/14647 20130101;
B82Y 10/00 20130101 |
Class at
Publication: |
257/080 |
International
Class: |
H01L 027/15 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2004 |
JP |
P.2004-076068 |
Claims
What is claimed is:
1. A photoelectric converting film stack type solid-state image
pickup device comprising: a semiconductor substrate in which a
signal read circuit is formed; and at least one photoelectric
converting film interposed between two electrode films, said at
least one photoelectric converting film being stacked above the
semiconductor substrate, wherein a signal corresponding to an
intensity of incident light is read outside by the signal read
circuit, the signal being generated by photoelectric conversion
with the photoelectric converting film, wherein the photoelectric
converting film comprises: a first layer comprising: an ultrafine
particle including (i) a quantum dot contributing to the
photoelectric conversion and (ii) a material having a band gap
larger than that of the quantum dot, the quantum dot being coated
with the material; and a hole transport layer stacked on the first
layer.
2. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 1, wherein the hole transport
layer comprises a semiconductor having a bad gap larger than that
of the quantum dot.
3. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 2, wherein the semiconductor of
the hole transport layer is doped with an impurity.
4. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 1, wherein the hole transport
layer comprises an organic film.
5. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 1, wherein the first layer
further comprises an electron transport layer, and the ultrafine
particle is dispersed in the electron transport layer.
6. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 1, wherein the quantum dot
comprises CdSe or CdS and the material coated on the quantum dot is
ZnSe or ZnS.
7. The photoelectric converting film stack type solid-state image
pickup device as claimed claim 1, wherein said at least one
photoelectric converting film comprises three photoelectric
converting film layers which are stacked through a transparent
insulating film, each of said at least one photoelectric converting
film being interposed between two transparent electrode films.
8. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 7, wherein an average particle
diameter of the ultrafine particle in each of said photoelectric
converting films is determined such that first one of the three
photoelectric converting film layers has a light absorption maximum
at a wavelength of 400 to 500 nm, second one of the three
photoelectric converting film layers has a light absorption maximum
at a wavelength of 500 to 560 nm, and third one of the three
photoelectric converting film layers a light absorption maximum at
a wavelength of 560 to 640 nm.
9. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 1, wherein said at least one
photoelectric converting film comprises four photoelectric
converting film layers which are stacked through a transparent
insulating film, each of said at least one photoelectric converting
film being interposed between two transparent electrode films.
10. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 9, wherein an average particle
diameter of the ultrafine particle in each of said photoelectric
converting films is determined such that first one of the four
photoelectric converting film layers has a light absorption maximum
at a wavelength of 420 to 480 nm, second one of the four
photoelectric converting film layers has a light absorption maximum
at a wavelength of 480 to 520 nm, third one of the four
photoelectric converting film layers a light absorption maximum at
a wavelength of 520 to 560 nm, and fourth one of the four
photoelectric converting film layers a light absorption maximum at
a wavelength of 560 to 620 nm.
11. The photoelectric converting film stack type solid-state image
pickup device as claimed in claim 10, wherein a red color signal
amount is determined by subtracting a second amount of signals
detected by the second photoelectric converting film layer from a
fourth amount of signals detected by the fourth photoelectric
converting film layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a photoelectric converting
film stack type solid-state image pickup device fabricated by
stacking a photoelectric converting film on a semiconductor
substrate having formed on the surface thereof a signal read
circuit.
[0003] 2. Description of the Related Art
[0004] As for the photoelectric converting film stack type
solid-state image pickup device, a prototype device is described,
for example, in JP-A-58-103165. In this solid-state image pickup
device, three photosensitive layers are stacked on a semiconductor
substrate, and electrical signals of red (R), green (G) and blue
(B) detected by respective photosensitive layers are read out by
MOS circuits formed on the semiconductor substrate surface.
[0005] Solid-state image pickup devices having such a constitution
were proposed in the past and thereafter, CCD-type image sensors or
CMOS-type image sensors where a large number of light-receiving
parts (photodiodes) are collectively stacked on the semiconductor
substrate surface part and color filters of red (R), green (G) and
blue (B) are stacked on respective light-receiving parts have made
remarkable progress. At present, an image sensor where hundreds of
light-receiving parts (pixels) are clustered on one chip is mounted
on a digital still camera.
[0006] However, CCD-type image sensors or CMOS-type image sensors
are reaching the limit of their technical progress and come to
encounter a problem of bad production yield because the opening
size of one light-receiving part is about 2 .mu.m and approximated
to the wavelength order of incident light.
[0007] Furthermore, the upper limit of the quantity of
photoelectric charges accumulated in one minute light-receiving
part is as small as about 3,000 electrons and with this number of
electrons, it is difficult to clearly express 256 gradations.
Therefore, CCD-type or CMOS-type image sensors can be hardly
expected to be more enhanced in view of pictorial quality or
sensitivity.
[0008] As a solid-state image pickup device capable of solving
these problems, the solid-state image pickup device proposed in
JP-A-58-103165 is taken notice of, and image sensors described in
Japanese Patent No. 3,405,099 and JP-A-2002-83946 are newly
proposed.
[0009] In the image sensor described in Japanese Patent No.
3,405,099, a medium having dispersed therein ultrafine silicon
particles is used for the photoelectric converting layer and by
stacking three photoelectric converting layers differing in the
particle diameter of the ultrafine particle on a semiconductor
substrate, electrical signals according to respective intensities
of red, green and blue lights received are generated by respective
photoelectric converting layers.
[0010] In the image sensor described in JP-A-2002-83946, similarly,
three nanosilicon layers differing in the particle diameter are
stacked on a semiconductor substrate, and electrical signals of
red, green and blue colors detected by respective nanosilicon
layers are each read out into an accumulation diode formed on the
surface part of the semiconductor substrate.
[0011] However, since the ultrafine particle used is silicon in
both of Japanese Patent No. 3,405,099 and JP-A-2002-83946, an
electron-hole pair generated upon receiving light cannot be
satisfactorily prevented from recombining on the ultrafine particle
surface and this causes a problem that the performance as a
solid-state image pickup device is not satisfied.
[0012] On the other hand, studies of ultrafine particles are
introduced in B. O. Dabbousi et al., "(CdSe)ZnS Core-Shell Quantum
Dots: Synthesis and Characterization of a Size Series of Highly
Luminescent Nanocrystallites", J. Phys. Chem. B 1997, 101,
9463-9475, though this is not related to a solid-state image pickup
device. "(CdSe)ZnS Core-Shell Quantum Dots: Synthesis and
Characterization of a Size Series of Highly Luminescent
Nanocrystallites" describes an ultrafine particle obtained by
coating the periphery of a CdSe quantum dot with ZnS. This CdSe
quantum dot with ZnS shell is advantageous in that the
electron-hole pair can be prevented from surface recombination as
compared with an ultrafine silicon particle.
[0013] In order to practically use the photoelectric converting
film stack type solid-state image pickup device, what material is
used to form the photoelectric converting film is present as a
problem. This problem can be overcome by using a CdSe quantum dot
with ZnS shell introduced in B. O. Dabbousi et al., "(CdSe)ZnS
Core-Shell Quantum Dots: Synthesis and Characterization of a Size
Series of Highly Luminescent Nanocrystallites", J. Phys. Chem. B
1997, 101, 9463-9475 in place of the ultrafine silicon particle
described in Japanese Patent No. 3,405,099 and JP-A-2002-83946.
[0014] However, it is necessary to solve another problem that even
when a CdSe quantum dot with an ZnS shell is merely dispersed in a
medium and formed into a film and the film (photoelectric
converting film) is interposed between upper and lower transparent
electrode films and applied with a voltage, the photoelectric
charges (signal charges) cannot be efficiently taken out.
SUMMARY OF THE INVENTION
[0015] An object of the present invention is to provide a
photoelectric converting film stack type solid-state image pickup
device where when a photoelectric converting film, for example,
using a CdSe quantum dot with ZnS shell is used to fabricate the
solid-state image pickup device, the photoelectric charges can be
efficiently taken out from the photoelectric converting film.
[0016] According to the invention, there is provided a
photoelectric converting film stack type solid-state image pickup
device comprising: a semiconductor substrate in which a signal read
circuit is formed; and at least one photoelectric converting film
interposed between two electrode films, said at least one
photoelectric converting film being stacked above the semiconductor
substrate, wherein a signal corresponding to an intensity of
incident light is read outside by the signal read circuit, the
signal being generated by photoelectric conversion with the
photoelectric converting film, wherein the photoelectric converting
film comprises: a first layer comprising: an ultrafine particle
including (i) a quantum dot contributing to the photoelectric
conversion and (ii) a material having a band gap larger than that
of the quantum dot, the quantum dot being coated with the material;
and a hole transport layer stacked on the first layer.
[0017] By virtue of this constitution, the signal charges generated
upon entering of light into the quantum dot can be efficiently read
out from the photoelectric converting film.
[0018] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein the hole transport layer comprises a semiconductor
having a bad gap larger than that of the quantum dot.
[0019] By virtue of this constitution, the signal charges can be
more efficiently taken out from the photoelectric converting
film.
[0020] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein the semiconductor of the hole transport layer is
doped with an impurity.
[0021] By virtue of this constitution, the signal charges can be
more easily read out from the photoelectric converting film.
[0022] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein the hole transport layer comprises an organic
film.
[0023] By virtue of this constitution, a conventionally developed
organic film can be used.
[0024] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein the first layer further comprises an electron
transport layer, and the ultrafine particle is dispersed in the
electron transport layer.
[0025] By virtue of this constitution, the signal charges can be
more easily and efficiently read out from the photoelectric
converting film.
[0026] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein the quantum dot comprises CdSe or CdS and the
material coated on the quantum dot is ZnSe or ZnS.
[0027] By virtue of this constitution, the electron-hole pair
generated upon entering of light is prevented from recombining.
[0028] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein said at least one photoelectric converting film
comprises three photoelectric converting film layers which are
stacked through a transparent insulating film, each of said at
least one photoelectric converting film being interposed between
two transparent electrode films.
[0029] By virtue of this constitution, a color image can be picked
up.
[0030] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein an average particle diameter of the ultrafine
particle in each of said photoelectric converting films is
determined such that first one of the three photoelectric
converting film layers has a light absorption maximum at a
wavelength of 400 to 500 nm, second one of the three photoelectric
converting film layers has a light absorption maximum at a
wavelength of 500 to 560 nm, and third one of the three
photoelectric converting film layers a light absorption maximum at
a wavelength of 560 to 640 nm.
[0031] By virtue of this constitution, image data separated into
three primary colors of red (R), green (G) and blue (B) can be
taken out.
[0032] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein said at least one photoelectric converting film
comprises four photoelectric converting film layers which are
stacked through a transparent insulating film, each of said at
least one photoelectric converting film being interposed between
two transparent electrode films.
[0033] By virtue of this constitution, the signals can be variously
processed and a color image with good color reproducibility can be
picked up.
[0034] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein an average particle diameter of the ultrafine
particle in each of said photoelectric converting films is
determined such that first one of the four photoelectric converting
film layers has a light absorption maximum at a wavelength of 420
to 480 nm, second one of the four photoelectric converting film
layers has a light absorption maximum at a wavelength of 480 to 520
nm, third one of the four photoelectric converting film layers a
light absorption maximum at a wavelength of 520 to 560 nm, and
fourth one of the four photoelectric converting film layers a light
absorption maximum at a wavelength of 560 to 620 nm.
[0035] By virtue of this constitution, a color image with more
excellent color reproducibility can be picked up.
[0036] According to the invention, there is provided the
photoelectric converting film stack type solid-state image pickup
device, wherein a red color signal amount is determined by
subtracting a second amount of signals detected by the second
photoelectric converting film layer from a fourth amount of signals
detected by the fourth photoelectric converting film layer.
[0037] By virtue of this constitution, the red color can be
reproduced according to the human luminous efficacy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a cross-sectional schematic view of one pixel
portion in the photoelectric converting film stack type solid-state
image pickup device having a three-layer structure according to one
embodiment of the present invention;
[0039] FIG. 2 is a cross-sectional schematic view of one pixel
portion in the photoelectric converting film stack type solid-state
image pickup device having a four-layer structure according to one
embodiment of the present invention;
[0040] FIG. 3 is a graph showing the human luminous efficacy;
[0041] FIG. 4 is a circuitry view of the signal read circuit
comprising MOS circuits;
[0042] FIG. 5 is a cross-sectional schematic view of the
photoelectric converting film according to one embodiment of the
present invention; and
[0043] FIG. 6 is a cross-sectional schematic view of the
photoelectric converting film according to another embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0044] One embodiment of the present invention is described below
by referring to the drawings.
[0045] FIG. 1 is a cross-sectional schematic view of one pixel
portion of the photoelectric converting film stack type solid-state
image pickup device according to one embodiment of the present
invention. This embodiment takes a constitution such that
photoelectric converting films are stacked in three layers to take
out electrical signals corresponding to three primary colors of red
(R), green (G) and blue (B), namely, a constitution of picking up a
color image, but a constitution of picking up a monochromatic
image, for example, a black-and-white image, by providing only one
photoelectric converting film layer may also be employed.
[0046] In FIG. 1, a high-concentration impurity region 2 for
accumulating the red color signal, an MOS circuit 3 for reading out
the red color signal, a high-concentration impurity region 4 for
accumulating the green signal, an MOS circuit 5 for reading out the
green signal, a high-concentration impurity region 6 for
accumulating the blue signal, and an MOS circuit 7 for reading out
the blue signal are formed on the surface part of a P-well layer
formed on an n-type silicon substrate.
[0047] The MOS circuits 3, 5 and 7 each comprises impurity regions
for source and drain formed on the semiconductor substrate surface
and a gate electrode formed through a gate insulating film 8. The
upper part of these gate insulating film 8 and gate electrodes is
flattened by stacking an insulating film 9 thereon. A
light-shielding film is sometimes formed on the insulating film 9,
but when a light-shielding film is formed, an insulating film 10 is
further stacked thereon so as to insulate the light-shielding film,
because the light-shielding film is a metal thin film in many
cases. In the case of not providing a light-shielding film there,
the insulating films 9 and 10 may be an integrated film.
[0048] The signals according to the signal charge amount, which are
accumulated in the high-concentration impurity regions 2, 4 and 6
for accumulating the above-described color signals, are read out by
the MOS circuits 3, 5 and 7 and further taken outside by read-out
electrodes (not shown) formed on the semiconductor substrate, and
the constitution thereof is the same as that of the related-art
CMOS-type image sensors.
[0049] This example takes a constitution such that the signal
according to the signal charge amount is read out by the MOS
circuit, but a constitution where the electric charges accumulated
in the high-concentration impurity regions 2, 4 and 6 for
accumulating the color signals are, similarly to the related-art
CCD-type image sensors, moved along a vertical transfer path and
read outside along a horizontal transfer path may also be
employed.
[0050] The above-described constitutions are fabricated by the
semiconductor process for the related-art CCD-type image sensors or
CMOS-type image sensors, and a photoelectric converting film stack
type solid-state image pickup device is produced by adding the
following constitutions.
[0051] A transparent electrode film 11 is formed on the insulating
film 10 shown in FIG. 1. This transparent film 11 is energized by
an electrode 12 and conducted to the high-concentration impurity
region 2 for accumulating the red signal. The electrode 12 is
electrically connected only to the transparent electrode film 11
and the high-concentration impurity region 2, but is insulated from
others. Thereafter, a photoelectric converting film 13 for red
color detection is formed on the transparent electrode film 11 and
a transparent electrode film 14 is further formed thereon. That is,
in this constitution, a photoelectric converting film 13 is
interposed between a pair of transparent electrode films 11 and 14.
Incidentally, the electrode film 11 as the lowermost layer may be
made opaque to serve also as a light-shielding film.
[0052] A transparent insulating film 15 is formed on the
transparent electrode film 14 and a transparent electrode film 16
is formed thereon. This transparent electrode film 16 is energized
by an electrode 17 and conducted to the high-concentration impurity
region 4 for accumulating the green signal. The electrode 17 is
electrically connected only to the transparent electrode film 16
and the high-concentration impurity region 4, but is insulated from
others. Thereafter, a photoelectric converting film 18 for green
color detection is formed on the transparent electrode film 16 and
a transparent electrode film 19 is formed thereon. That is, in this
constitution, a photoelectric converting film 18 is interposed
between a pair of transparent electrode films 16 and 19.
[0053] A transparent insulating film 20 is formed on the
transparent electrode film 19 and a transparent electrode film 21
is formed thereon. This transparent electrode film 21 is energized
by an electrode 22 and conducted to the high-concentration impurity
region 6 for accumulating the blue signal. The electrode 22 is
electrically connected only to the transparent electrode film 21
and the high-concentration impurity region 6, but is insulated from
others. Thereafter, a photoelectric converting film 23 for blue
color detection is formed on the transparent electrode film 21 and
a transparent electrode film 24 is formed thereon. That is, in this
constitution, a photoelectric converting film 23 is interposed
between a pair of transparent electrode films 21 and 24.
[0054] A transparent insulating film 25 is formed as an uppermost
layer and in this embodiment, a light-shielding film 26 of limiting
the incidence area of incident light into this pixel is provided in
the transparent insulating film 25. The reason why the
light-shielding film 26 is provided in the uppermost layer in this
embodiment is because color mixing between pixels can be more
decreased. As for the homogeneous transparent electrode film, a
thin film of tin oxide (SnO.sub.2), titanium oxide (TiO.sub.2),
indium oxide (InO.sub.2), indium oxide-tin (ITO), indium oxide-zinc
(IZO) or InGaO.sub.3(ZnO).sub.5(IGZO) is used, but the present
invention is not limited thereto. Examples of the method for
forming this film include a laser ablation method and a sputtering
method.
[0055] The photoelectric converting films 23, 18 and 13 have
fundamentally the same constitution but are differing in the
particle diameter of the CdSe quantum dot with ZnS shell provided
in the film. The CdSe quantum dot with ZnS shell in the
photoelectric converting film 23 for blue color detection has a
smallest particle diameter, the CdSe quantum dot with ZnS shell in
the photoelectric converting film 18 for green color detection has
an intermediate particle diameter, and the CdSe quantum dot with
ZnS shell in the photoelectric converting film 33 for red color
detection has a largest particle diameter. These particle diameters
all are on the nanometer order.
[0056] For example, the average particle diameter of the CdSe
quantum dot for blue color detection is preferably on the order of
1.7 to 2.5 nm, the average particle diameter of the CdSe quantum
dot for green color detection is preferably on the order of 2.5 to
5 nm, and the average particle diameter of the CdSe quantum dot for
red color detection is preferably on the order of 5 to 10 nm.
[0057] These particle diameters each is selected to give large
light absorption at the corresponding wavelength and generate a
great number of electron-hole pairs. More specifically, the
particle size is selected in the photoelectric converting film 23
for blue color detection to give a light absorption maximum of 400
to 500 nm, in the photoelectric converting film 18 for green color
detection to give a light absorption maximum of 500 to 560 nm, and
in the photoelectric converting film 13 for red color detection to
give a light absorption maximum of 560 to 640 nm.
[0058] The embodiment shown in FIG. 1 is an example of the
photoelectric converting film stack type solid-state image pickup
device for detecting three primary colors of red, green and blue,
but a constitution of detecting four colors may also be employed.
FIG. 2 is a cross-sectional schematic view of one pixel portion in
a photoelectric converting film stack type solid-state image pickup
device for detecting four colors, where in addition to the
constitution of FIG. 1, a layer comprising transparent electrodes
32 and 33 having interposed therein a photoelectric converting film
31 of detecting an intermediate color (GB: emerald color) between
green (G) and blue (B) is provided between the layer for green
color detection and the layer for blue color detection. That is,
photoelectric converting films 23, 31, 18 and 13 are sequentially
provided from the top in the order of increasing the wavelength of
light to be detected.
[0059] In this example, the particle diameter of the quantum dot is
determined such that the light absorption maximum in the
photoelectric converting film 23 becomes from 420 to 480 nm, the
light absorption maximum in the photoelectric converting film 31
becomes from 480 to 520 nm, the light absorption maximum in the
photoelectric converting film 18 becomes from 520 to 560 nm, and
the light absorption maximum in the photoelectric converting film
13 becomes from 580 to 620 nm.
[0060] A high-concentration impurity region 36 for accumulating the
signal charges of intermediate color is formed on the semiconductor
substrate, an electrode 35 for energizing the high-concentration
impurity region 36 and the transparent electrode 32, which is
electrically insulated from other constituent portions, is
provided, and an MOS circuit 37 for reading out the signal charges
in the high-concentration impurity region 36 is provided on the
semiconductor substrate. Of course, a transparent insulating film
34 is provided between the transparent electrode film 31 and the
upper transparent electrode film 21.
[0061] The detection of intermediate color at a wavelength of 480
to 520 nm is advantageous to correct the red color according to the
human luminous efficacy. The human luminous efficacy has, as shown
by .alpha., .beta., .gamma. in FIG. 3, negative sensitivities in
green (G), red (R) and blue (B) colors. Due to these negative
sensitivities, even when only positive sensitivities of R, G and B
are detected by a solid-state image pickup device to perform color
reproduction, the image viewed by a human being cannot be
reproduced. Therefore, the largest negative sensitivity .beta.,
that is, negative sensitivity of red, is detected by the
photoelectric converting film 31, and a signal processing of
subtracting this negative sensitivity portion from the red
sensitivity detected by the photoelectric converting film 13 is
performed in the same manner as the signal processing described in
Japanese Patent No. 2,872,759, whereby the human sensitivity to red
color can be reproduced.
[0062] FIG. 4 is a circuitry view of the MOS circuits 3, 5 and 7
shown in FIG. 1. The MOS circuits for R, G and B each comprises
three FET elements, and the circuit constitution thereof is the
same as that of the circuit used for the related-art CMOS-type
image sensors. The difference in the solid-state image pickup
device of FIG. 2 is only to add three FET elements for intermediate
color (GB) per one pixel portion.
[0063] In the related-art CMOS-type image sensors, a
"light-receiving part" must be provided on the semiconductor
surface and therefore, when producing those MOS circuits on the
semiconductor surface, they should be produced in a narrow space so
as to assure the space for a wide light-receiving part. However, in
the photoelectric converting film stack type solid-state image
pickup device of this embodiment, the "light-receiving part" need
not be provided on the semiconductor surface and the production of
MOS circuits is facilitated. Furthermore, the wiring space can
afford room and therefore, wiring connection to allow for reading
of R, G and B together is also facilitated unlike the constitution
of FIG. 4 where R, G and B are sequentially read out while
selecting one of these by a selection signal. The same applies also
to the case where the read-out circuit is not an MOS circuit but a
type of providing an electric charge transfer path as in CCD-type
image sensors.
[0064] In FIGS. 1 and 2, the structure of one pixel portion is
shown. These pixels are vertically and horizontally arranged in an
array manner on the surface side of a semiconductor substrate. The
photoelectric converting film need not be stacked every each pixel,
but one sheet of a photoelectric converting film may be stacked on
the entire surface of the semiconductor substrate and in this case,
individual pixels can be divided by forming one of the paired
transparent electrodes having interposed therein each photoelectric
converting film, on one pixel separately from another pixel.
[0065] When light enters into the photoelectric converting film
stack type solid-state image pickup device of FIG. 1 or 2 from a
subject, blue light out of the incident light is absorbed by the
photoelectric converting film 23, green light is absorbed by the
photoelectric converting film 18, and red light is absorbed by the
photoelectric converting film 13. In the case of FIG. 2, emerald
light as the intermediate color (GB) between blue and green is
absorbed by the photoelectric converting film 31.
[0066] In the quantum dot (ultrafine particle) constituting the
photoelectric converting film 23, the incident light is absorbed
and an electron-hole pair is produced. This electron-hole pair
recombines and emits blue light with the elapse of time, but when a
voltage is applied between the transparent electrodes 24 and 21,
the electron of the electron-hole pair penetrates the transparent
electrode 21 and flows into the high-concentration impurity region
6 through the electrode 22.
[0067] Similarly, the electron produced in the photoelectric
converting film 18 according to the quantity of green incident
light flows into the high-concentration impurity region 4, the
electron produced in the photoelectric converting film 13 according
to the quantity of red incident light flows into the
high-concentration impurity region 2, and the electron according to
the quantity of emerald incident light flows into the
high-concentration impurity region 36 (FIG. 2). Then, the electrons
of electric charges corresponding to respective colors are read
outside by the MOS circuits 3, 5, 7 and 37.
[0068] FIG. 5 is a cross-sectional schematic view of the
photoelectric converting films 23, 18, 13 and 31. The photoelectric
converting film 23 (the same applies to 18, 13 and 31 which are
differing only in the particle size of the quantum dot) provided
between the transparent electrode films 24 and 21 comprises
numerous deposited CdSe quantum dots 41 with ZnS shell and a hole
transport layer 42 stacked thereon. The hole transport layer 42 is
formed of a material having a band gap larger than that of the
quantum dot 41.
[0069] In this example, the hole transport layer 42 is suitably
constituted by a ZnS layer, but the present invention is not
limited thereto. For example, as long as the hole transport layer
42 is an organic film and the constituent molecule thereof can
transport a hole from the photosensitive molecular film, there is
no particular limitation. Examples of the molecule which can be
used include organic molecules having a skeleton such as
p-phenylenediamine, o-phenylenediamine, m-phenylenediamine,
tetrathiafulvalene, diselenadithiafulvalene, tetraselena-fulvalene,
tetraselenotetracene, quinoline, acridine, ferrocene, benzidine,
diaminopyrene, polydiacetylene, hydroquinone, dimethoxybenzene,
diazobenzene and phenothiazine.
[0070] FIG. 6 is a cross-sectional schematic view of the
photoelectric converting films 23, 18, 13 and 31 according to
another embodiment. The difference from the embodiment shown in
FIG. 5 is in that a layer obtained by depositing numerous CdSe
quantum dots 41 with ZnS shell is provided in FIG. 5, whereas
numerous CdSe quantum dots 41 with ZnS shell are dispersed in an
electron transport layer 43 in this embodiment.
[0071] The molecule constituting the electron transport layer 43 is
not particularly limited as long as it can transport an electron
from the photosensitive molecular film, and examples of the
molecule which can be used include organic molecules having a
skeleton such as tetracyanoquinodimethane, benzoquinone,
naphthoquinone, anthraquinone, dinitrobenzene, trinitrobenzene,
tricyanobenzene, hexacyanobenzene, trinitrofluolenone,
chlorobenzoquinone, dichlorobenzoquinone, trichlorobenzo-quinone,
dichlorodicyanobenzoquinone, cyanobenzoquinone,
dicyanobenzoquinone, tricyanobenzoquinone,
N,N1-dicyano-quinonediimine, N,N'-disulfonylquinonediimine,
N-carbonyl-N'-cyanoquinonediimine,
N-carbonyl-N'-sulfonylquinone-diimine,
N-sulfonyl-N'-cyanoquinonediimine, N-sulfonyl-quinoneimine,
N-cyanoquinoneimine and dithienylene copper complex. Also, such an
organic molecule may be dispersed in a polymer working out to the
electron transport layer.
[0072] The photoelectric converting film 23 and the like can be
produced as follows. Numerous CdSe quantum dots overcoated with ZnS
are produced and dispersed in an organic solvent, and the
dispersion is coated on the transparent film 21 by spin coating or
the like and dried. The drying is preferably performed in vacuum.
Thereafter, the hole transport layer 42 is formed by vacuum
deposition, sputtering or the like, and then the transparent
electrode film 24 is formed by vapor deposition, sputtering or the
like, thereby completing the photoelectric converting film 23
interposed between transparent electrode films 24 and 21. In this
case, ZnS preferably contains a p-type impurity.
[0073] The production method of the CdSe quantum dot 41 with ZnS
shell is not particularly limited and the method described in B. O.
Dabbousi et al., "(CdSe)ZnS Core-Shell Quantum Dots: Synthesis and
Characterization of a Size Series of Highly Luminescent
Nanocrystallites", J. Phys. Chem. B 1997, 101, 9463-975 may be
used. That is, a sulfide shell such as zinc sulfide (ZnS) or CdS is
formed by a reaction method of contacting a semiconductor ultrafine
particle with water, such as reverse micelle process or aqueous
solution reaction. The formation of a ZnS shell on a CdS core is
reported in B. S. Zou et al., International Journal of quantum
Chemistry, Vol. 72, 439-450 (1999), and the formation of a CdS
shell on a CdSe core is reported in L. Xu et al., J. Mater. Sci.,
Vol. 35, 1375-1378 (2000).
[0074] If the CdSe quantum dot with ZnS shell is merely used as the
photoelectric converting film, it is difficult to efficiently take
out electrons according to the color signals, but as in this
embodiment, when the CdSe quantum dot with ZnS shell is used
together with a hole transport film 42, electrons according to the
color signals can be efficiently taken out. Furthermore, as shown
in FIG. 6, when an electron transport layer 43 is provided, the
color signals can be more easily taken out.
[0075] As for the thickness of the thus-formed photoelectric
converting film 23, for example, in the case of a photo-electric
converting film of photoelectrically converting blue light, the
thickness is preferably large enough to allow for satisfactory
absorption of blue light and no entering of the blue light into the
next layer. If the blue light enters into the next photoelectric
converting film layer for green light and causes photoexcitation,
bad color separation results.
[0076] In order to move the signal charges to the corresponding
high-concentration impurity region 2 or the like from the
photoelectric converting film, a technique of taking out signals
from a light-receiving element of normal CCD-type image sensors or
CMOS-type image sensors may be applied. Examples thereof include a
method of injecting a constant amount of bias charges into the
high-concentration impurity region 2 or the like (accumulation
diode) (refresh mode) and after accumulating a predetermined amount
of electric charges (photoelectric conversion mode), reading out
the signal charges. The photoelectric converting film itself may be
used as the accumulation diode, or an accumulation diode may be
separately provided.
[0077] For reading out the signal charges moved to the
high-concentration impurity region 2 or the like, a read-out
technique in normal CCD-type image sensors or CMOS-type image
sensors can be applied as-is.
[0078] In the related art, the solid-state image pickup device such
as CCD comprises a light-receiving element having a photoelectric
conversion function and is imparted with functions of, for example,
accumulating the converted signals, reading out the accumulated
signals and selecting the pixel position. The signal charges or
signal currents resulting from photoelectric conversion in the
light-receiving part are accumulated in the light-receiving part
itself or in a capacitor provided separately, and the electric
charges accumulated are read out simultaneously with selection of
the pixel position by the technique of so-called charge coupled
device (CCD) or MOS-type image pickup device (so-called CMOS
sensor) using an X-Y address system.
[0079] The CCD-type image sensor comprises a charge transfer part
of transferring the pixel charge signals to an analogue shift
register by a transfer switch, and a method of sequentially reading
out the signals to the output terminal by the operation of register
is used. For example, a line address-type system, a frame
transfer-type system, an interline transfer-type system and a frame
interline transfer-type system are known. Also, a two-phase
structure, a three-phase structure, a four-phase structure, an
embedded channel structure and the like are known for CCD, and an
arbitrary structure thereof may be employed for the vertical
transfer path in the photoelectric converting film stack type
solid-state image pickup device of the present invention.
[0080] The address selection system includes a system of
sequentially selecting each one of the pixels by a multiplexer
switch and a digital shift register, and reading it out as a signal
voltage (or electric charge) to a common output line. The image
pickup device using a two-dimensionally arrayed X-Y address
scanning system is known as a CMOS sensor. In this system, a switch
provided in a pixel connected to the X-Y intersection is connected
to a vertical shift register, and the signal read out from the
pixel provided in the same row as that where the switch is turned
on by a voltage from the vertical scanning shift register, is read
out to the output line in the column direction. These signals are
sequentially read out from the output terminal through a switch
driven by the horizontal scanning shift register.
[0081] The output signal can be read out by using a floating
diffusion detector or a floating gate detector. Also, the S/N
property may be enhanced by providing a signal amplification
circuit in the pixel portion or using a correlated double sampling
technique.
[0082] As for the signal processing, gamma correction by an ADC
circuit, digitization by an AD converter, luminance signal
processing, or color signal processing can be applied. Examples of
the color signal processing include white balance processing, color
separation processing and color matrix processing. In the case of
using an NTSC signal, a processing of converting RGB signals into
YIQ signals can be applied. These are the same as those used in the
related-art CCD-type image sensors or CMOS-type image sensors.
[0083] In the above-described embodiment, a CdSe quantum dot with
ZnS shell is used, but the ultrafine particle material is not
limited thereto and may be sufficient if it is an ultrafine
particle obtained by coating a core with a material having a band
gap larger than the band gap of a quantum dot working out to the
core. For example, an ultrafine particle using an InN quantum dot
as the core may be used. And, by forming the electron transport
layer and the hole transport layer each from a GaN quantum dot, the
signal charge after photoelectric conversion can be efficiently
taken out from the photoelectric converting film. The same applies
to the case where the core is CdS and the material coated on the
core is ZnS.
[0084] In the above-described embodiment, a microlens, an infrared
cut filter and an ultraviolet cut filter are not referred to, but
in the constitutions of FIGS. 1 and 2, an infrared cut filter may
be provided on the lowermost or uppermost layer, or a microlens may
be used to elevate the degree of light condensation. Also, an
ultraviolet cut filter may be provided on the uppermost layer or
interposed at an appropriate portion between the lens and the
photoelectric converting film.
[0085] Furthermore, in the photoelectric converting film stack type
solid-state image pickup device of this embodiment, when the
photoelectric converting film is constituted in a three-layer or
four-layer structure, various advantageous effects can be obtained.
For example, the image picked up can be free from generation of
moire, one pixel can detect R, G and B together to eliminate the
use of an optical low pass filter and realize high resolution, both
luminance and color can be satisfactorily resolved without color
bleeding, good reproducibility of hair and the like can be attained
by virtue of simple signal processing and no generation of
pseudo-signal, the mixing or partial reading of pixels can be
facilitated, a numerical aperture of 100% can be obtained even
without using a microlens, and shading does not occur due to no
restriction in the eye point distance to the image pickup lens,
thereby ensuring suitability for lens-interchangeable cameras and
contributing to thinning of the lens. In this way, the problems of
the related-art CCD-type or CMOS-type image sensors can be
overcome.
[0086] According to the present invention, a photoelectric
converting film stack type solid image pickup device capable of
efficiently taking out the photoelectric charges (signal charges)
from the photoelectric converting film can be provided.
[0087] The photoelectric converting film stack type solid-state
image pickup device of the present invention can be used in place
of the related-art CCD-type or CMOS-type image sensors and is
useful when mounted on a digital camera and the like because one
pixel can be made larger than in the related-art techniques and
therefore, the sensitivity can be elevated.
[0088] The entire disclosure of each and every foreign patent
application from which the benefit of foreign priority has been
claimed in the present application is incorporated herein by
reference, as if fully set forth.
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