U.S. patent application number 15/671750 was filed with the patent office on 2018-02-22 for display device, electronic device, and mobile information terminal.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Ryo HATSUMI, Satoshi SEO, Shunpei YAMAZAKI.
Application Number | 20180052363 15/671750 |
Document ID | / |
Family ID | 61191487 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180052363 |
Kind Code |
A1 |
YAMAZAKI; Shunpei ; et
al. |
February 22, 2018 |
DISPLAY DEVICE, ELECTRONIC DEVICE, AND MOBILE INFORMATION
TERMINAL
Abstract
A display device capable of displaying images with wide color
gamut is provided. A display device capable of displaying images
with wide color gamut and capable of relaxing contrast made by
narrow spectra is provided. The display device includes a liquid
crystal element and a light-emitting element. Light obtained from
the liquid crystal element through a color filter has an NTSC area
ratio of more than or equal to 20 percent and less than or equal to
60 percent and light emitted by the light-emitting element has a
BT.2020 area ratio of more than or equal to 80 percent and less
than or equal to 100 percent.
Inventors: |
YAMAZAKI; Shunpei; (Tokyo,
JP) ; SEO; Satoshi; (Sagamihara, JP) ;
HATSUMI; Ryo; (Hadano, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
61191487 |
Appl. No.: |
15/671750 |
Filed: |
August 8, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 1/6058 20130101;
H01L 27/3232 20130101; G02F 1/133514 20130101; H01L 27/322
20130101; G02F 1/1343 20130101; G02F 2201/44 20130101; G02F 1/13718
20130101; H01L 27/3244 20130101; H01L 51/504 20130101; G02F
1/133553 20130101; G02F 1/133621 20130101; H04N 1/6066
20130101 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; H04N 1/60 20060101 H04N001/60; G02F 1/1343 20060101
G02F001/1343; G02F 1/137 20060101 G02F001/137 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2016 |
JP |
2016-159793 |
Claims
1. A display device comprising: a liquid crystal element; and a
light-emitting element, wherein light obtained from the liquid
crystal element through a color filter has an NTSC area ratio of
more than or equal to 20% and less than or equal to 60%, and
wherein light emitted by the light-emitting element has a BT.2020
area ratio of more than or equal to 80% and less than or equal to
100%.
2. The display device according to claim 1, wherein the liquid
crystal element is a reflective liquid crystal element, and wherein
the light-emitting element comprises an EL layer between a
reflective electrode and a semi-transmissive and semi-reflective
electrode.
3. The display device according to claim 1, wherein the liquid
crystal element overlaps with the light-emitting element.
4. A display device comprising: a liquid crystal element; and a
light-emitting element, wherein light obtained from the liquid
crystal element through a color filter has an NTSC coverage of more
than or equal to 20% and less than or equal to 60%, and wherein
light emitted by the light-emitting element has a BT.2020 coverage
of more than or equal to 75% and less than or equal to 100%.
5. The display device according to claim 4, wherein the liquid
crystal element overlaps with the light-emitting element.
6. The display device according to claim 4, wherein the liquid
crystal element is a reflective liquid crystal element, and wherein
the light-emitting element comprises an EL layer between a
reflective electrode and a semi-transmissive and semi-reflective
electrode.
7. An electronic device comprising: the display device according to
claim 4; and an operation key, a speaker, a microphone, or an
external connection portion.
8. A mobile phone comprising: the display device according to claim
4; and an operation key, a speaker, a microphone, or an external
connection portion.
9. A mobile information terminal comprising: the display device
according to claim 4; and an operation key, a speaker, a
microphone, or an external connection portion.
10. A display device comprising: a liquid crystal element; and a
first light-emitting element, wherein light obtained from the
liquid crystal element has an NTSC coverage of more than or equal
to 20% and less than or equal to 60%, and wherein light emitted by
the first light-emitting element has CIE 1931 chromaticity
coordinates (x1, y1) where x1 is more than or equal to 0.130 and
less than or equal to 0.250 and y1 is more than 0.710 and less than
or equal to 0.810.
11. The display device according to claim 10, wherein the liquid
crystal element overlaps with the first light-emitting element.
12. The display device according to claim 10, wherein the liquid
crystal element is a reflective liquid crystal element, and wherein
the first light-emitting element comprises an EL layer between a
reflective electrode and a semi-transmissive and semi-reflective
electrode.
13. The display device according to claim 10, further comprising, a
second light-emitting element, wherein light emitted by the second
light-emitting element has CIE 1931 chromaticity coordinates (x2,
y2) where x2 is more than 0.680 and less than or equal to 0.720 and
y2 is more than or equal to 0.260 and less than or equal to
0.320.
14. The display device according to claim 13, wherein the liquid
crystal element overlaps with the second light-emitting
element.
15. The display device according to claim 10, further comprising, a
third light-emitting element, wherein light emitted by the third
light-emitting element has CIE 1931 chromaticity coordinates (x3,
y3) where x3 is more than or equal to 0.120 and less than or equal
to 0.170 and y3 is more than or equal to 0.020 and less than
0.060.
16. The display device according to claim 15, wherein the liquid
crystal element overlaps with the third light-emitting element.
Description
TECHNICAL FIELD
[0001] One embodiment of the present invention relates to a display
device and an electronic device. Note that one embodiment of the
present invention is not limited thereto. That is, one embodiment
of the present invention relates to an object, a method, a
manufacturing method, or a driving method. In addition, one
embodiment of the present invention relates to a process, a
machine, manufacture, and a composition of matter. As specific
examples, a semiconductor device, a display device, a liquid
crystal display device, a lighting device, and the like can be
given.
BACKGROUND ART
[0002] As display devices, liquid crystal display devices including
a liquid crystal element as their display element, light-emitting
devices including a light-emitting element (EL element) as their
display element, and the like are known. For example, in a liquid
crystal display device, a liquid crystal element including a liquid
crystal material is interposed between a pair of electrodes facing
each other with alignment films provided between the liquid crystal
element and the electrodes, and the liquid crystal display device
displays images by utilizing the optical modulation action of the
liquid crystal. A light-emitting device includes a light-emitting
element in which an EL layer is interposed between a pair of
electrodes, and displays images by utilizing light emission
obtained from the light-emitting element when voltage is applied
between the pair of electrodes.
[0003] In order to perform full-color display with the use of the
display elements, in the case of the liquid crystal element, a
color filter is used in combination with the liquid crystal
element, whereby full-color display can be performed. In the case
of the light-emitting element, a plurality of light-emitting
elements in which EL layers include light-emitting materials for
different light emission colors are formed, whereby full-color
display can be performed. Alternatively, the light emitting element
can also be used in combination with a color filter.
[0004] As specific methods for displaying full-color images with
light-emitting elements, so-called side-by-side patterning in which
light-emitting elements which emit light of different colors are
separately formed, a white-color filter method in which a white
color light-emitting element is combined with a color filter, and a
color conversion method in which a light-emitting element which
emits monochromatic light such as a blue light-emitting element is
combined with a color conversion filter can be given.
REFERENCE
Patent Document
[Patent Document 1] Japanese Published Patent Application No.
2007-53090
DISCLOSURE OF INVENTION
[0005] In order to make such a display device display full-color
images, the chromaticities (x, y) of emission colors of
light-emitting elements are set within desired ranges, so that
images with wide color gamut can be displayed.
[0006] However, although light emitted by a light-emitting element
has an excellent chromaticity, the light has extremely narrow
spectra, such that the display has strong contrast, and thus is too
intense for the viewers and likely to tire them.
[0007] Then, one embodiment of the present invention provides a
display device capable of displaying images with wide color gamut.
Another embodiment of the present invention provides a display
device capable of displaying images with wide color gamut and
capable of relaxing contrast made by narrow spectra. Another
embodiment of the present invention provides a display device
capable of displaying eye-friendly images with wide color gamut.
Another embodiment of the present invention provides a novel
light-emitting element. Another embodiment of the present invention
provides a light-emitting element with excellent color purity.
[0008] Note that the descriptions of these objects do not preclude
the existence of other objects. In one embodiment of the present
invention, there is no need to achieve all the objects. Other
objects will be apparent from and can be derived from the
description of the specification, the drawings, the claims, and the
like.
[0009] One embodiment of the present invention is a display device
including a liquid crystal element and a light-emitting element. In
the display device, light obtained from the liquid crystal element
through a color filter has an NTSC area ratio of more than or equal
to 20% and less than or equal to 60% and light emitted by the
light-emitting element has a BT.2020 area ratio of more than or
equal to 80% and less than or equal to 100%. Note that the light
emitted by the light-emitting element preferably has a BT.2020 area
ratio of more than or equal to 90% and less than or equal to
100%.
[0010] Another embodiment of the present invention is a display
device including a liquid crystal element and a light-emitting
element. In the display device, light obtained from the liquid
crystal element through a color filter has an NTSC coverage of more
than or equal to 20% and less than or equal to 60% and light
emitted by the light-emitting element has a BT.2020 coverage of
more than or equal to 75% and less than or equal to 100%. Note that
the light emitted by the light-emitting element preferably has a
BT.2020 coverage of more than or equal to 75% and less than or
equal to 100%.
[0011] Another embodiment of the present invention is a display
device including a liquid crystal element and a light-emitting
element. In the display device, light obtained from the liquid
crystal element has an NTSC coverage of more than or equal to 20%
and less than or equal to 60% and light emitted by the
light-emitting element has CIE 1931 chromaticity coordinates (x,
y), where x is more than or equal to 0.130 and less than or equal
to 0.250 and y is more than 0.710 and less than or equal to
0.810.
[0012] Another embodiment of the present invention is a display
device including a liquid crystal element and a light-emitting
element. In the display device, light obtained from the liquid
crystal element has an NTSC coverage of more than or equal to 20%
and less than or equal to 60% and light emitted by the
light-emitting element has CIE 1931 chromaticity coordinates (x,
y), where x is more than 0.680 and less than or equal to 0.720 and
y is more than or equal to 0.260 and less than or equal to
0.320.
[0013] Another embodiment of the present invention is a display
device including a liquid crystal element and a light-emitting
element. In the display device, light obtained from the liquid
crystal element has an NTSC coverage of more than or equal to 20%
and less than or equal to 60% and light emitted by the
light-emitting element has CIE 1931 chromaticity coordinates (x,
y), where x is more than or equal to 0.120 and less than or equal
to 0.170 and y is more than or equal to 0.020 and less than
0.060.
[0014] Note that, in each of the above structures, the liquid
crystal element is a reflective liquid crystal element and the
light-emitting element is a light-emitting element including an EL
layer between a reflective electrode and a semi-transmissive and
semi-reflective electrode.
[0015] In the above structures, the EL layer included in the
light-emitting element preferably emits white light. The EL layer
includes at least a light-emitting layer. A plurality of EL layers
may be provided. The EL layers may be stacked with a charge
generation layer provided therebetween.
[0016] Another embodiment of the present invention is an electronic
device that includes the display device of one embodiment of the
present invention and an operation key, a speaker, a microphone, or
an external connection portion.
[0017] Another embodiment of the present invention is a mobile
information terminal that includes the display device of one
embodiment of the present invention and an operation key, a
speaker, a microphone, or an external connection portion.
[0018] One embodiment of the present invention includes, in its
category, in addition to a display device including a display
element, an electronic device including the display device
(specifically, an electronic device including the display element
or the display device and a connection terminal or an operation
key) and a lighting device including the display device
(specifically, a lighting device including the display element or
the display device and a housing). Accordingly, a display device in
this specification means an image display device or a light source
(including a lighting device). Furthermore, the display device
includes the following modules in its category: a module in which a
connector such as a flexible printed circuit (FPC) or a tape
carrier package (TCP) is attached to a display device; a module
having a TCP whose end is provided with a printed wiring board; and
a module in which an integrated circuit (IC) is directly mounted on
a display element by a chip on glass (COG) method.
[0019] According to one embodiment of the present invention, a
display device capable of displaying images with wide color gamut
can be provided. According to another embodiment of the present
invention, a display device capable of displaying images with wide
color gamut and capable of relaxing contrast made by narrow spectra
can be provided. According to another embodiment of the present
invention, a display device capable of displaying eye-friendly
images with wide color gamut can be provided. According to another
embodiment of the present invention, a novel light-emitting element
can be provided. According to another embodiment of the present
invention, a light-emitting element with excellent color purity can
be provided.
[0020] Note that the description of these effects does not preclude
the existence of other effects. One embodiment of the present
invention does not necessarily achieve all the effects listed
above. Other effects will be apparent from and can be derived from
the description of the specification, the drawings, the claims, and
the like.
BRIEF DESCRIPTION OF DRAWINGS
[0021] In the accompanying drawings:
[0022] FIGS. 1A and 1B are diagrams illustrating a display device
of one embodiment of the present invention;
[0023] FIGS. 2A to 2C are diagrams each illustrating a display
device of one embodiment of the present invention;
[0024] FIGS. 3A to 3D are diagrams each illustrating a display
device of one embodiment of the present invention;
[0025] FIGS. 4A to 4E are diagrams each illustrating a display
device of one embodiment of the present invention;
[0026] FIGS. 5A, 5B1, and 5B2 are diagrams each illustrating a
display device of one embodiment of the present invention;
[0027] FIG. 6 is a diagram illustrating a display device of one
embodiment of the present invention;
[0028] FIGS. 7A to 7D, 7D'-1, 7D'-2, and 7E are diagrams each
illustrating an electronic device;
[0029] FIGS. 8A to 8C are diagrams illustrating an electronic
device;
[0030] FIGS. 9A and 9B are diagrams illustrating an automobile;
[0031] FIG. 10 is a diagram showing an NTSC coverage-reflectance
characteristic (simulated values) of a liquid crystal panel;
[0032] FIG. 11 is a diagram showing an NTSC coverage-reflectance
characteristic (actual values) of a liquid crystal panel;
[0033] FIG. 12 is a diagram showing an NTSC coverage-reflectance
characteristic of a liquid crystal panel (corrected values);
[0034] FIG. 13 is a diagram illustrating a light-emitting
element;
[0035] FIG. 14 shows transmission spectra of color filters;
[0036] FIG. 15 is a diagram showing a luminance-current density
characteristic of light-emitting elements 1 to 4;
[0037] FIG. 16 is a diagram showing a luminance-voltage
characteristic of light-emitting elements 1 to 4;
[0038] FIG. 17 is a diagram showing a current efficiency-luminance
characteristic of light-emitting elements 1 to 4;
[0039] FIG. 18 is a diagram showing a current-voltage
characteristic of light-emitting elements 1 to 4;
[0040] FIG. 19 shows light emission spectra of light-emitting
elements 1 to 4;
[0041] FIG. 20 is a diagram showing a luminance-current density
characteristic of light-emitting elements 5 to 8;
[0042] FIG. 21 is a diagram showing a luminance-voltage
characteristic of light-emitting elements 5 to 8;
[0043] FIG. 22 is a diagram showing a current efficiency-luminance
characteristic of light-emitting elements 5 to 8;
[0044] FIG. 23 is a diagram showing a current-voltage
characteristic of light-emitting elements 5 to 8; and
[0045] FIG. 24 shows light emission spectra of light-emitting
elements 5 to 8.
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] Embodiments of the present invention will be described below
with reference to the drawings. However, the present invention is
not limited to the following description, and the mode and details
can be variously changed unless departing from the scope and spirit
of the present invention. Thus, the present invention should not be
construed as being limited to the description in the following
embodiments.
[0047] Note that the position, the size, the range, or the like of
each structure illustrated in the drawings and the like are not
accurately represented in some cases for easy understanding.
Therefore, the disclosed invention is not necessarily limited to
the position, size, range, or the like as disclosed in the drawings
and the like.
[0048] In describing the structures of the invention with reference
to the drawings in this specification and the like, common
reference numerals are used for the same portions in different
drawings.
Embodiment 1
[0049] In this embodiment, a display device of one embodiment of
the present invention will be described with reference to FIGS. 1A
and 1B.
[0050] FIG. 1A illustrates a structure of a display device of one
embodiment of the present invention, which includes a liquid
crystal element 100L and a light-emitting element 100E.
[0051] The liquid crystal element 100L includes a liquid crystal
layer 103L and alignment films 104 between a first electrode 101L
and a second electrode 102L. The first electrode 101L is a
reflective electrode which can reflect ambient light. The second
electrode 102L is a transparent electrode that has a
light-transmitting property and is capable of transmitting visible
light.
[0052] A color filter (also referred to as a coloring layer) 105L
and a polarizing layer 106 are provided on the side where light
transmitted through the second electrode 102L exits to the outside.
Accordingly, the light transmitted through the second electrode
102L is transmitted through the color filter 105L and the
polarizing layer 106 to become light 107L.
[0053] The light-emitting element 100E includes an EL layer 103E
between a first electrode 101E and a second electrode 102E. Note
that at least one of electrodes included in the light-emitting
element, the second electrode 102E, is a transparent electrode that
has a light-transmitting property and is capable of transmitting
visible light. The EL layer 103E can contain a light-emitting
material from which a desirable light emission color can be
obtained or can contain a plurality of light-emitting materials of
different light emission colors in combination. A color filter
(also referred to as a coloring layer) 105E is provided as needed
on the side where light transmitted through the second electrode
102E is emitted outward.
[0054] The light emitted by the EL layer 103E is transmitted
through the second electrode 102E and transmitted through the color
filter 105E, if the color filter 105E is provided, to become light
107E.
[0055] The display device in this embodiment includes the liquid
crystal element 100L and the light-emitting element 100E; thus,
light obtained from the display device is light 108 including the
light 107L exiting from the liquid crystal element 100L and the
light 107E emitted by the light-emitting element 100E.
[0056] Note that light exiting from the liquid crystal element 100L
(the light 107L) in the display device in this embodiment meets the
National Television System Committee (NTSC) standard among quality
indicators for full-color display. The NTSC standard is a color
gamut standard for analog television and was established by the
NTSC. The NTSC standard color gamut is shown in FIG. 1B.
Specifically, the light 107L has a full-color display quality that
meets chromaticity coordinates (x, y), in the CIE 1931 chromaticity
coordinates (xy chromaticity coordinates), of red (R) at (0.670,
0.330); green (G), (0.210, 0.710); and blue (B), (0.140, 0.080).
The CIE 1931 chromaticity coordinates are provided by the
International Commission on Illumination (CIE). Note that an NTSC
area ratio is obtained in the following manner: an area P of a
triangle formed by connecting the CIE 1931 chromaticity coordinates
of R, G, and B which fulfill the NTSC standard (the above xy
chromaticity coordinates) and an area Q of a triangle formed by
connecting the CIE chromaticity coordinates (x, y) of the liquid
crystal elements (R, G, and B) of one embodiment of the present
invention are calculated and then the area ratio (Q/P) is
calculated. An NTSC coverage is a value which represents how much
percentage of the NTSC standard color gamut (the inside of the
above triangle) can be reproduced using a combination of the CIE
chromaticity coordinates (x, y) of the liquid crystal elements (R,
G, and B) of one embodiment of the present invention.
[0057] In this embodiment, a reflective liquid crystal element is
preferably used as the liquid crystal element 100L included in the
display device. In the liquid crystal element 100L, an NTSC area
ratio or an NTSC coverage is preferably more than or equal to 20%
and less than or equal to 60%. This is because a reflectance of
more than or equal to 15% can be obtained in a panel including a
reflective liquid crystal element when the NTSC area ratio or an
NTSC coverage of the liquid crystal element 100L is more than or
equal to 20% and less than or equal to 60%. The display device in
this embodiment is a panel including a light-emitting element
capable of meeting BT.2020 and a liquid crystal element. Therefore,
when the liquid crystal element has an NTSC area ratio or an NTSC
coverage of more than or equal to 20% and less than or equal to 60%
and a panel including the liquid crystal element is so bright as to
have a reflectance of more than or equal to 15%, the display
device, as a whole, can display eye-friendly images with wide color
gamut and high visibility. Note that to examine the relation of the
reflectance to the NTSC area ratio or coverage in the panel
including a reflective liquid crystal element, simulation results
will be described in Examples.
[0058] When a reflective liquid crystal element is used as the
liquid crystal element 100L included in the display device,
eye-friendly images can be displayed because the viewers seeing
images displayed by the liquid crystal element do not directly see
the light source of the element (the light source is an indirect
light source). Note that when the viewers can see the display
without directly seeing the light source in the above manner, a
transmissive liquid crystal element, a MEMS element, or the like
can also be used.
[0059] As a driving mode for the liquid crystal element 100L, a
vertical alignment (VA) mode, a twisted nematic (TN) mode, an
in-plane-switching (IPS) mode, a fringe field switching (FFS) mode,
an optically compensated birefringence (OCB) mode, a blue phase, or
the like can be used. Note that as a specific example of the VA
mode, a multi-domain vertical alignment (MVA) mode, a patterned
vertical alignment (PVA) mode, an electrically controlled
birefringence (ECB) mode, a continuous pinwheel alignment (CPA)
mode, an advanced super view (ASV) mode, or the like can be
given.
[0060] As the liquid crystal used for the liquid crystal element
100L, a thermotropic liquid crystal, a low-molecular liquid
crystal, a high-molecular liquid crystal, a polymer dispersed
liquid crystal (PDLC), a ferroelectric liquid crystal, an
anti-ferroelectric liquid crystal, or the like can be used. Such a
liquid crystal exhibits a cholesteric phase, a smectic phase, a
cubic phase, a chiral nematic phase, an isotropic phase, or the
like depending on conditions. In addition, either a positive liquid
crystal or a negative liquid crystal may be used, and an
appropriate liquid crystal material can be used depending on the
mode or design to be used.
[0061] For materials used for the electrodes of the liquid crystal
element 100L (the first electrode 101L and the second electrode
102L), any of the materials below can be used in an appropriate
combination as long as the above functions (e.g., a
light-transmitting property) can be fulfilled. For example, a
metal, an alloy, an electrically conductive compound, a mixture of
these, and the like can be appropriately used. Specifically, an
In--Sn oxide (also referred to as ITO), an In--Si--Sn oxide (also
referred to as ITSO), an In--Zn oxide, an In--W--Zn oxide, or the
like can be used. In addition, it is possible to use a metal such
as aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn),
iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga),
zinc (Zn), indium (In), tin (Sn), zirconium (Zr), molybdenum (Mo),
tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum
(Pt), silver (Ag), yttrium (Y), or neodymium (Nd) or an alloy
containing an appropriate combination of any of these metals. It is
also possible to use a Group 1 element or a Group 2 element in the
periodic table, which is not described above (e.g., lithium (Li),
cesium (Cs), calcium (Ca), or strontium (Sr)), a rare earth metal
such as europium (Eu) or ytterbium (Yb), an alloy containing an
appropriate combination of any of these elements, graphene, or the
like.
[0062] The color filter 105E and the color filter 105L are each a
filter that transmits visible light in a specific wavelength range
and blocks visible light in a specific wavelength range. Thus, when
the color filters 105E and 105L transmitting only light in a
desired wavelength range are provided appropriately, colors of
light exiting from the liquid crystal element can be adjusted. Note
that the color filters 105E and 105L can be formed by a staining
method, a pigment dispersion method, a printing method, an
evaporation method, and the like.
[0063] The polarizing layer 106 is a filter that lets light having
limited vibration directions pass through the polarizing layer 106.
The polarizing layer 106 may be provided on the inner side of the
substrate placed outside the electrodes of the liquid crystal
element 100L (the first electrode 101L and the second electrode
102L) (on the side close to the electrodes) or may be provided on
the outer side of the substrate. Although not illustrated in FIG.
1A, a retardation layer may be provided.
[0064] In addition, light emitted by the light-emitting element
100E (the light 107E) in the display device of one embodiment of
the present invention preferably has a chromaticity (x, y) that
meets a standard established by Japan Broadcasting Corporation
(NHK) and used for ultra high definition television (UHDTV, also
referred to as Super Hi-Vision television) among quality indicators
for full-color display. The standard is so-called BT.2020 standard.
The BT.2020 standard color gamut is shown in FIG. 1B. Specifically,
the BT.2020 standard meets a full-color display quality that meets
chromaticity coordinates (x, y), in the CIE 1931 chromaticity
coordinates (xy chromaticity coordinates), of red at (0.708,
0.292); green, (0.170, 0.797); and blue, (0.131, 0.046). The CIE
1931 chromaticity coordinates are established by the International
Commission on Illumination (CIE).
[0065] For materials used for the electrodes of the light-emitting
element 100E (the first electrode 101E and the second electrode
102E), the materials described above as the materials used for the
electrodes of the liquid crystal element 100L (the first electrode
101L and the second electrode 102L) can be used in an appropriate
combination as long as the above functions (e.g., transmittance)
can be fulfilled.
[0066] The light-emitting elements meeting the BT.2020 standard
include a light-emitting element (red) 200R which emits red light,
a light-emitting element (green) 200G which emits green light, and
a light-emitting element (blue) 200B which emits blue light as
illustrated in FIG. 2A. These light-emitting elements can include
respective EL layers (203R, 203G, and 203B) which include different
light-emitting materials. Note that stack structures and materials
of the EL layers are preferably selected such that the chromaticity
(x, y) of the light-emitting element (red) 200R is (0.708, 0.292),
the chromaticity of the light-emitting element (green) 200G is
(0.170, 0.797), and the chromaticity of the light-emitting element
(blue) 200B is (0.131, 0.046).
[0067] Note that the light-emitting elements (200R, 200G, and 200B)
in FIG. 2A each include a first electrode 201 and a second
electrode 202. In the case of the light-emitting elements (200R,
200G, and 200B) in FIG. 2A, a transparent electrode which transmits
visible light is used at least as the second electrode 202. In
addition, red light 207R is emitted by the EL layer 203R in the
light-emitting element (red) 200R, green light 207G is emitted by
the EL layer 203G in the light-emitting element (green) 200G, and
blue light 207B is emitted by the EL layer 203B in the
light-emitting element (blue) 200B.
[0068] Light-emitting elements having the structures illustrated in
FIG. 2B are also formed so as to meet the BT.2020 standard. Each of
the light-emitting elements in FIG. 2B is identical to each of the
light-emitting elements in FIG. 2A in the structure of the first
electrode 201 and the second electrode 202, and is different in
that a light-emitting element (red) 200R', a light-emitting element
(green) 200G', and a light-emitting element (blue) 200B' includes a
common EL layer 203W which emits white light. Note that red light
207R' is obtained from the light-emitting element (red) 200R' by
passing through a color filter (red) 204R having a function of
transmitting red light. In addition, green light 207G' is obtained
from the light-emitting element (green) 200G' by passing through a
color filter (green) 204G having a function of transmitting green
light. Furthermore, blue light 207B' is obtained from the
light-emitting element (blue) 200B' by passing through a color
filter (blue) 204B having a function of transmitting blue
light.
[0069] Light-emitting elements having the structures illustrated in
FIG. 2C are also formed so as to meet the BT.2020 standard. The
light-emitting elements having the structures illustrated in FIG.
2C are preferable for forming light-emitting elements meeting the
BT.2020 standard because the light-emitting elements in FIG. 2C
have a micro optical resonator (microcavity) structure having a
function of strengthening light emission depending on colors of the
light to be obtained from the light-emitting elements. Accordingly,
in the light-emitting elements in FIG. 2C, the first electrode 201
is a reflective electrode and a second electrode 202' is a
semi-transmissive and semi-reflective electrode. Note that even
light-emitting elements including the separately formed EL layers
as illustrated in FIG. 2A can be combined with a micro optical
resonator (microcavity) structure.
[0070] In FIG. 2C, a light-emitting element (red) 200R'' is a
light-emitting element which emits red light; thus, it is
preferable that a light-transmitting conductive film 208R be
stacked over the first electrode 201 and an optical path length
between the first electrode 201 and the second electrode 202' be
adjusted so as to be an optical path length a, which is suitable
for strengthening red light emission. In addition, a light-emitting
element (green) 200G'' is a light-emitting element which emits
green light; thus, it is preferable that a light-transmitting
conductive film 208G be stacked over the first electrode 201 and
the optical path length between the first electrode 201 and the
second electrode 202' be adjusted so as to be an optical path
length b, which is suitable for strengthening green light emission.
Furthermore, a light-emitting element (blue) 200B'' is a
light-emitting element which emits blue light; therefore, the EL
layer 203W is formed such that the optical path length between the
first electrode 201 and the second electrode 202' becomes an
optical path length c, which is suitable for strengthening blue
light emission. As needed, a light-transmitting conductive film can
be stacked over the first electrode 201 to adjust the optical path
length.
[0071] When white light is emitted from the EL layer 203W as
illustrated in FIGS. 2B and 2C, it is desirable that red, green,
and blue light emission, which compose white light emission, each
have an independent light emission spectrum. The spectra desirably
do not overlap with each other in order to prevent the decrease in
the color purity. The spectra of specifically green light emission
and red light emission have peak wavelengths close to each other
and are likely to overlap with each other. In order to prevent such
overlap of light emission spectra, a favorable light-emitting
material is used for the EL layer included in the EL layer 203W and
a specific stack structure is employed in the light-emitting
element described in this embodiment. Thus, overlap of different
light emission spectra can be prevented, so that light-emitting
elements which show excellent color chromaticities for every color
can be obtained.
[0072] As the light-emitting element 100E included in the display
device in this embodiment, light-emitting elements which cover
chromaticity ranges (a region A, a region B, and a region C)
represented in the chromaticity coordinates in FIG. 1B are
preferably used. As specific chromaticity ranges for the
light-emitting elements, the light-emitting element (red) (200R,
200R', or 200R'') covers a chromaticity range represented by the
region A, the light-emitting element (green) (200G, 200G', or
200G'') covers a chromaticity range represented by the region B,
and the light-emitting element (blue) (200B, 200B', or 200B'')
covers a chromaticity range represented by the region C. In the CIE
1931 chromaticity coordinates, the region A has x of more than
0.680 and less than or equal to 0.720 and y of more than or equal
to 0.260 and less than or equal to 0.320, the region B has x of
more than or equal to 0.130 and less than or equal to 0.250 and y
of more than 0.710 and less than or equal to 0.810, and the region
C has x of more than or equal to 0.120 and less than or equal to
0.170 and y of more than or equal to 0.020 and less than 0.060.
[0073] Note that the peak wavelength of the light emission spectrum
of each of the light-emitting elements (red) (200R, 200R', and
200R'') in FIGS. 2A to 2C is preferably more than or equal to 620
nm and less than or equal to 680 nm. In addition, the peak
wavelength of the light emission spectrum of each of the
light-emitting elements (green) (200G, 200G', and 200G'') is
preferably more than or equal to 500 nm and less than or equal to
530 nm. Furthermore, the peak wavelength of the light emission
spectrum of each of the light-emitting elements (blue) (200B,
200B', and 200B'') is preferably more than or equal to 430 nm and
less than or equal to 460 nm. The half widths of the light emission
spectra of the light-emitting element (red) (200R, 200R', or
200R''), the light-emitting element (green) (200G, 200G', or
200G''), and the light-emitting element (blue) (200B, 200B', or
200B'') are preferably more than or equal to 5 nm and less than or
equal to 45 nm, more than or equal to 5 nm and less than or equal
to 35 nm, and more than or equal to 5 nm and less than or equal to
25 nm, respectively.
[0074] In one embodiment of the present invention, light emitted by
the light-emitting element preferably meets the above chromaticity,
and the area ratio thereof to the BT.2020 color gamut in the CIE
chromaticity coordinates (x, y) is preferably more than or equal to
80% or the coverage of the BT.2020 color gamut is preferably more
than or equal to 75%. Further preferably, the area ratio is more
than or equal to 90% or the coverage is more than or equal to
85%.
[0075] Accordingly, in the display device in this embodiment, light
exiting from the liquid crystal element through a color filter has
an NTSC area ratio or an NTSC coverage of more than or equal to 20%
and less than or equal to 60%, and light emitted by the
light-emitting element has a BT.2020 area ratio of more than or
equal to 80% and less than or equal to 100% or a BT.2020 coverage
of more than or equal to 75% and less than or equal to 100%. Note
that the light emitted by the light-emitting element further
preferably has a BT.2020 area ratio of more than or equal to 90%
and less than or equal to 100% or a BT.2020 coverage of more than
or equal to 85% and less than or equal to 100%.
[0076] Note that in order to calculate the chromaticity, any of a
luminance colorimeter, a spectroradiometer, and an emission
spectrometer may be used, and it is sufficient that the above
chromaticity be met by any one of the measuring methods. However,
it is further preferable that the above chromaticity be met by all
of the measuring methods.
[0077] Note that the structure described in this embodiment can be
used in an appropriate combination with any of the structures
described in the other embodiments.
Embodiment 2
[0078] In this embodiment, an example of a light-emitting element
which can be applied to a display device of one embodiment of the
present invention will be described.
<<Basic Structure of Light-Emitting Element>>
[0079] A basic structure of a light-emitting element will be
described. FIG. 3A illustrates a light-emitting element in which an
EL layer including a light-emitting layer is provided between a
pair of electrodes. Specifically, an EL layer 303 is provided
between a first electrode 301 and a second electrode 302.
[0080] FIG. 3B illustrates a light-emitting element that has a
stacked-layer structure (tandem structure) in which a plurality of
EL layers (two EL layers 303a and 303b in FIG. 3B) are provided
between a pair of electrodes and a charge generation layer 304 is
provided between the EL layers. Such a tandem light-emitting
element can be driven at low voltage.
[0081] The charge generation layer 304 has a function of injecting
electrons into one of the EL layers (303a or 303b) and injecting
holes into the other of the EL layers (303b or 303a) when a voltage
is applied between the first electrode 301 and the second electrode
302. Thus, in FIG. 3B, when a voltage is applied between the first
electrode 301 and the second electrode 302 such that the potential
of the first electrode 301 is higher than that of the second
electrode 302, the charge generation layer 304 injects electrons
into the EL layer 303a and injects holes into the EL layer
303b.
[0082] Note that in terms of light extraction efficiency, the
charge generation layer 304 preferably has a property of
transmitting visible light (specifically, the charge generation
layer 304 has a visible light transmittance of 40% or higher).
Furthermore, the charge generation layer 304 functions even if it
has lower conductivity than the first electrode 301 or the second
electrode 302.
[0083] FIG. 3C illustrates the EL layer 303 of the light-emitting
element having a stacked-layer structure. In this case, the first
electrode 301 is regarded as functioning as an anode. The EL layer
303 has a structure in which a hole-injection layer 311, a
hole-transport layer 312, a light-emitting layer 313, an
electron-transport layer 314, and an electron-injection layer 315
are stacked in this order over the first electrode 301. Even in the
case where a plurality of EL layers are provided as in the tandem
structure illustrated in FIG. 3B, the layers in each EL layer are
sequentially stacked from the anode side as described above. When
the first electrode 301 is a cathode and the second electrode 302
is an anode, the stacking order of the layers is reversed.
[0084] The light-emitting layer 313 included in the EL layers (303,
303a, and 303b) contains an appropriate combination of a
light-emitting material and a plurality of materials, so that
fluorescence or phosphorescence of a desired light emission color
can be obtained. The light-emitting layer 313 may include a
stacked-layer structure having different light emission colors. In
that case, the light-emitting material and other materials are
different between the stacked light-emitting layers. Alternatively,
the plurality of EL layers (303a and 303b) in FIG. 3B may exhibit
the respective light emission colors. Also in that case, the
light-emitting material and other materials are different between
the light-emitting layers.
[0085] As one embodiment of the present invention, the
light-emitting element in FIG. 3C has, for example, a micro optical
resonator (microcavity) structure in which the first electrode 301
is a reflective electrode and the second electrode 302 is a
semi-transmissive and semi-reflective electrode, whereby light
emission from the light-emitting layer 313 in the EL layer 303 can
be resonated between the electrodes. Thus, light emission obtained
through the second electrode 302 can be intensified.
[0086] Note that when the first electrode 301 of the light-emitting
element is a reflective electrode with a structure in which a
reflective conductive material and a light-transmitting conductive
material (a transparent conductive film) are stacked, optical
adjustment can be performed by controlling the thickness of the
transparent conductive film. Specifically, when the wavelength of
light from the light-emitting layer 313 is .lamda., the distance
between the first electrode 301 and the second electrode 302 is
preferably adjusted to around m.lamda./2 (m is a natural
number).
[0087] To amplify desired light (wavelength: .lamda.) obtained from
the light-emitting layer 313, the optical path length from the
first electrode 301 to a region in the light-emitting layer 313
emitting the desired light (light-emitting region) and the optical
path length from the second electrode 302 to the region in the
light-emitting layer 313 emitting the desired light (light-emitting
region) are each preferably adjusted to around (2m'+1).lamda./4 (m'
is a natural number). Here, the light-emitting region means a
region where holes and electrons are recombined in the
light-emitting layer 313.
[0088] By such optical adjustment, the spectrum of specific
monochromatic light from the light-emitting layer 313 can be
narrowed and light emission with a high color purity can be
obtained.
[0089] In that case, the optical path length between the first
electrode 301 and the second electrode 302 is, to be exact,
represented by the total thickness from a reflective region in the
first electrode 301 to a reflective region in the second electrode
302. However, it is difficult to precisely determine the reflective
region in the first electrode 301 or the second electrode 302;
therefore, it is presumed that the above effect can be sufficiently
obtained when appropriate positions in the first electrode 301 and
the second electrode 302 are assumed to be the reflective regions.
Furthermore, the optical path length between the first electrode
301 and the light-emitting layer emitting desired light is, to be
exact, the optical path length between the reflective region in the
first electrode 301 and the light-emitting region in the
light-emitting layer emitting desired light. However, it is
difficult to precisely determine the reflective region in the first
electrode 301 or the light-emitting region in the light-emitting
layer emitting desired light; therefore, it is presumed that the
above effect can be sufficiently obtained when appropriate
positions in the first electrode 301 are assumed to be the
reflective regions and appropriate positions in the light-emitting
layer emitting desired light are assumed to be the light-emitting
regions.
[0090] The light-emitting element in FIG. 3C has a microcavity
structure, so that light (monochromatic light rays) with different
wavelengths can be extracted even if the same EL layer is employed.
Thus, separate coloring aimed at plural light emission colors
(e.g., R, G, and B) is not necessary. Therefore, higher-resolution
display can be easily achieved. Note that a combination with color
filters is also possible. Furthermore, light emission intensity
with a specific wavelength in the front direction can be increased,
whereby power consumption can be reduced.
[0091] In the above light-emitting element, at least one of the
first electrode 301 and the second electrode 302 is a
light-transmitting electrode (a transparent electrode, a
semi-transmissive and semi-reflective electrode, or the like). In
the case where the light-transmitting electrode is a transparent
electrode, the transparent electrode has a visible light
transmittance of more than or equal to 40%. In the case where the
light-transmitting electrode is a semi-transmissive and
semi-reflective electrode, the semi-transmissive and
semi-reflective electrode has a visible light reflectance of more
than or equal to 20% and less than or equal to 80%, preferably more
than or equal to 40% and less than or equal to 70%. These
electrodes preferably have a resistivity of 1.times.10.sup.-2
.OMEGA.cm or less.
[0092] Furthermore, when one of the first electrode 301 and the
second electrode 302 is a reflective electrode in the above
light-emitting element, the visible light reflectance of the
reflective electrode is more than or equal to 40% and less than or
equal to 100%, preferably more than or equal to 70% and less than
or equal to 100%. This electrode preferably has a resistivity of
1.times.10.sup.-2 .OMEGA.cm or less.
<<Specific Structure and Forming Method of Light-Emitting
Element>>
[0093] Next, a specific structure and a specific forming method of
the light-emitting element will be described. Here, a
light-emitting element having the tandem structure in FIG. 3B and
microcavity structures is described with reference to FIG. 3D. In
the light-emitting element in FIG. 3D, a reflective electrode is
formed as the first electrode 301 and a semi-transmissive and
semi-reflective electrode is formed as the second electrode 302.
Therefore, a single-layer structure or a stacked-layer structure
can be formed using one or more kinds of desired electrode
materials. Note that the second electrode 302 is formed with the
use of a material selected as described above after the EL layer
303b is formed. These electrodes can be formed by a sputtering
method or a vacuum evaporation method.
<First Electrode and Second Electrode>
[0094] For materials used for the first electrode 301 and the
second electrode 302, any of the materials below can be used in an
appropriate combination as long as the functions of the electrodes
described above can be fulfilled. For example, a metal, an alloy,
an electrically conductive compound, a mixture of these, and the
like can be appropriately used. Specifically, an In--Sn oxide (also
referred to as ITO), an In--Si--Sn oxide (also referred to as
ITSO), an In--Zn oxide, an In--W--Zn oxide, or the like can be
used. In addition, it is possible to use a metal such as aluminum
(Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe),
cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn),
indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten
(W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium
(Y), or neodymium (Nd) or an alloy containing an appropriate
combination of any of these metals. It is also possible to use a
Group 1 element or a Group 2 element in the periodic table, which
is not described above (e.g., lithium (Li), cesium (Cs), calcium
(Ca), or strontium (Sr)), a rare earth metal such as europium (Eu)
or ytterbium (Yb), an alloy containing an appropriate combination
of any of these elements, graphene, or the like.
[0095] In the light-emitting element in FIG. 3D, when the first
electrode 301 is an anode, a hole-injection layer 311a and a
hole-transport layer 312a of the EL layer 303a are sequentially
stacked over the first electrode 301 by a vacuum evaporation
method. After the EL layer 303a and the charge generation layer 304
are formed, a hole-injection layer 311b and a hole-transport layer
312b of the EL layer 303b are sequentially stacked over the charge
generation layer 304 in a similar manner.
<Hole-Injection Layer and Hole-Transport Layer>
[0096] The hole-injection layers (311a and 311b) inject holes from
the first electrode 301 that is an anode to the EL layers (303a and
303b) and each contain a material with a high hole-injection
property.
[0097] As examples of the material with a high hole-injection
property, transition metal oxides such as molybdenum oxide,
vanadium oxide, ruthenium oxide, tungsten oxide, and manganese
oxide can be given. Alternatively, it is possible to use any of the
following materials: phthalocyanine-based compounds such as
phthalocyanine (abbreviation: H.sub.2Pc) and copper phthalocyanine
(abbreviation: CuPc); aromatic amine compounds such as
4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl
(abbreviation: DPAB) and
N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1-
'-biphenyl)-4,4'-diamine (abbreviation: DNTPD); high molecular
compounds such as
poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)
(abbreviation: PEDOT/PSS); and the like.
[0098] Alternatively, as the material with a high hole-injection
property, a composite material containing a hole-transport material
and an acceptor material (an electron-accepting material) can also
be used. In that case, the acceptor material extracts electrons
from a hole-transport material, so that holes are generated in the
hole-injection layer 311, and the holes are injected into the
light-emitting layers (313a and 313b) through the hole-transport
layers (312a and 312b). Note that each of the hole-injection layers
(311a and 311b) may be formed to have a single-layer structure
using a composite material containing a hole-transport material and
an acceptor material (an electron-accepting material), or a
stacked-layer structure in which a layer including a hole-transport
material and a layer including an acceptor material (an
electron-accepting material) are stacked.
[0099] The hole-transport layers (312a and 312b) transport the
holes, which are injected from the first electrode 301 by the
hole-injection layers (311a and 311b), to the light-emitting layers
(313a and 313b). Note that the hole-transport layers (312a and
312b) each contain a hole-transport material. It is particularly
preferable that the HOMO level of the hole-transport material
included in the hole-transport layers (312a and 312b) be the same
as or close to that of the hole-injection layers (311a and
311b).
[0100] Examples of the acceptor material used for the
hole-injection layers (311a and 311b) include an oxide of a metal
belonging to any of Group 4 to Group 8 of the periodic table.
Specifically, molybdenum oxide, vanadium oxide, niobium oxide,
tantalum oxide, chromium oxide, tungsten oxide, manganese oxide,
and rhenium oxide can be given. Among these, molybdenum oxide is
especially preferable since it is stable in the air and its
hygroscopic property is low and is easily treated. Alternatively,
organic acceptors such as a quinodimethane derivative, a chloranil
derivative, and a hexaazatriphenylene derivative can be used.
Specifically, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane
(abbreviation: F.sub.4-TCNQ), chloranil,
2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene
(abbreviation: HAT-CN), or the like can be used.
[0101] The hole-transport materials used for the hole-injection
layers (311a and 311b) and the hole-transport layers (312a and
312b) are preferably materials with a hole mobility of more than or
equal to 10.sup.-6 cm.sup.2/Vs. Note that other materials may be
used as long as the materials have a hole-transport property higher
than an electron-transport property.
[0102] Preferred hole-transport materials are .pi.-electron rich
heteroaromatic compounds (e.g., carbazole derivatives and indole
derivatives) and aromatic amine compounds, examples of which
include compounds having an aromatic amine skeleton, such as
4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB
or .alpha.-NPD),
N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine
(abbreviation: TPD),
4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl
(abbreviation: BSPB),
4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:
BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine
(abbreviation: mBPAFLP),
4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBA1BP),
3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:
PCPPn),
N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-am-
ine (abbreviation: PCBiF),
N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimeth-
yl-9H-fluoren-2-amine (abbreviation: PCBBiF),
4,4'-diphenyl-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBBi1BP),
4-(1-naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBANB),
4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBNBB),
9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-am-
ine (abbreviation: PCBAF),
N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluoren-2-am-
ine (abbreviation: PCBASF),
4,4',4''-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA),
4,4',4''-tris(N,N'-diphenylamino)triphenylamine (abbreviation:
TDATA),
4,4',4''-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine
(abbreviation: MTDATA), and
4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl
(abbreviation: BSPB); compounds having a carbazole skeleton, such
as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),
4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP),
3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP),
3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP),
3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole
(abbreviation: PCzPCA1),
3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole
(abbreviation: PCzPCA2),
3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole
(abbreviation: PCzPCN1), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene
(abbreviation: TCPB), and
9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:
CzPA); compounds having a thiophene skeleton, such as
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II),
2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene
(abbreviation: DBTFLP-III), and
4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene
(abbreviation: DBTFLP-IV); and compounds having a furan skeleton,
such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran)
(abbreviation: DBF3P-II) and
4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran
(abbreviation: mmDBFFLBi-II).
[0103] A high molecular compound such as poly(N-vinylcarbazole)
(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation:
PVTPA),
poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)meth-
acrylamide](abbreviation: PTPDMA), or
poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine]
(abbreviation: Poly-TPD) can also be used.
[0104] Note that the hole-transport material is not limited to the
above examples and one of or a combination of various known
materials may be used as the hole-transport material for the
hole-injection layers (311a and 311b) and the hole-transport layers
(312a and 312b).
[0105] Next, in the light-emitting element in FIG. 3D, the
light-emitting layer 313a is formed over the hole-transport layer
312a of the EL layer 303a by a vacuum evaporation method. After the
EL layer 303a and the charge generation layer 304 are formed, the
light-emitting layer 313b is formed over the hole-transport layer
312b of the EL layer 303b by a vacuum evaporation method.
<Light-Emitting Layer>
[0106] The light-emitting layers (313a and 313b) each contain a
light-emitting material. Note that as the light-emitting material,
a material whose light emission color is blue, violet, bluish
violet, green, yellowish green, yellow, orange, red, or the like is
appropriately used. When the plurality of light-emitting layers
(313a and 313b) are formed using different light-emitting
materials, different light emission colors can be exhibited (for
example, complementary light emission colors are combined to
achieve white light emission). Furthermore, a stacked-layer
structure in which one light-emitting layer contains two or more
kinds of light-emitting materials may be employed.
[0107] The light-emitting layers (313a and 313b) each may contain
one or more kinds of organic compounds (a host material and an
assist material) in addition to a light-emitting material (a guest
material). As the one or more kinds of organic compounds, one or
both of the hole-transport material and the electron-transport
material described in this embodiment can be used.
[0108] In one embodiment of the present invention, it is preferable
that a light-emitting material which emits blue light (a
blue-light-emitting material) be used as a guest material in one of
the light-emitting layers (313a and 313b) in the light-emitting
element and a material which emits green light (a
green-light-emitting material) and a material which emits red light
(a red-light-emitting material) be used in the other light-emitting
layer. This manner is effective in the case where the
blue-light-emitting material (the blue-light-emitting layer) has a
lower light emission efficiency or a shorter lifetime than the
materials (layers) which emit other colors. Here, it is preferable
that a light-emitting material that converts singlet excitation
energy into emission of light in the visible light range be used as
the blue-light-emitting material and light-emitting materials that
convert triplet excitation energy into emission of light in the
visible light range be used as the green- and red-light-emitting
materials, whereby the spectrum balance between R, G, and B is
improved.
[0109] There is no particular limitation on the light-emitting
materials that can be used for the light-emitting layers (313a and
313b), and a light-emitting material that converts singlet
excitation energy into emission of light in the visible light range
or a light-emitting material that converts triplet excitation
energy into emission of light in the visible light range can be
used. Examples of the light-emitting material are given below.
[0110] As an example of the light-emitting material that converts
singlet excitation energy into light emission, a material emitting
fluorescence (a fluorescent material) can be given. Examples of the
material emitting fluorescence include a pyrene derivative, an
anthracene derivative, a triphenylene derivative, a fluorene
derivative, a carbazole derivative, a dibenzothiophene derivative,
a dibenzofuran derivative, a dibenzoquinoxaline derivative, a
quinoxaline derivative, a pyridine derivative, a pyrimidine
derivative, a phenanthrene derivative, and a naphthalene
derivative. A pyrene derivative is particularly preferable because
it has a high light emission quantum yield. Specific examples of
the pyrene derivative include
N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyre-
ne-1,6-diamine (abbreviation: 1,6mMemFLPAPm),
N,N'-diphenyl-N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diam-
ine (abbreviation: 1,6FLPAPm),
N,N'-bis(dibenzofuran-2-yl)-N,N'-diphenylpyrene-1,6-diamine
(abbreviation: 1,6FrAPrn),
N,N'-bis(dibenzothiophen-2-yl)-N,N'-diphenylpyrene-1,6-diamine
(abbreviation: 1,6ThAPm),
N,N'-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-6-amine](-
abbreviation: 1,6BnfAPrn),
N,N'-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine]
(abbreviation: 1,6BnfAPm-02), and
N,N'-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-ami-
ne] (abbreviation: 1,6BnfAPm-03). In addition, the pyrene
derivative is a group of compounds effective for meeting the
chromaticity of blue (the chromaticity range represented by the
region C) in one embodiment of the present invention.
[0111] In addition, it is possible to use
5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2'-bipyridine
(abbreviation: PAP2BPy),
5,6-bis[4'-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2'-bipyridine
(abbreviation: PAPP2BPy),
N,N'-bis[4-(9H-carbazol-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine
(abbreviation: YGA2S),
4-(9H-carbazol-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine
(abbreviation: YGAPA),
4-(9H-carbazol-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine
(abbreviation: 2YGAPPA),
N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine
(abbreviation: PCAPA),
4-(10-phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBAPA),
4-[4-(10-phenyl-9-anthryl)phenyl]-4'-(9-phenyl-9H-carbazol-3-yl)triphenyl-
amine (abbreviation: PCBAPBA), perylene,
2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP),
N,N'-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphe-
nyl-1,4-phenylenediamine] (abbreviation: DPABPA),
N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine
(abbreviation: 2PCAPPA),
N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediam-
ine (abbreviation: 2DPAPPA), or the like.
[0112] As examples of a light-emitting material that converts
triplet excitation energy into light emission, a material emitting
phosphorescence (a phosphorescent material) and a thermally
activated delayed fluorescence (TADF) material that exhibits
thermally activated delayed fluorescence can be given.
[0113] Examples of a phosphorescent material include an
organometallic complex, a metal complex (a platinum complex), and a
rare earth metal complex. These materials exhibit the respective
light emission colors (light emission peaks) and thus, any of them
is appropriately selected according to need.
[0114] As examples of a phosphorescent material which emits blue or
green light and whose light emission spectrum has a peak wavelength
of greater than or equal to 450 nm and less than or equal to 570
nm, the following materials can be given.
[0115] For example, organometallic complexes having a 4H-triazole
skeleton, such as
tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-.-
kappa.N2]phenyl-.kappa.C}iridium(III) (abbreviation:
[Ir(mpptz-dmp).sub.3]),
tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)
(abbreviation: [Ir(Mptz).sub.3]),
tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)
(abbreviation: [Ir(iPrptz-3b).sub.3]), and
tris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazolato]iridium(III)
(abbreviation: [Ir(iPr5btz).sub.3]); organometallic complexes
having a 1H-triazole skeleton, such as
tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III-
) (abbreviation: [Ir(Mptz1-mp).sub.3]) and
tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)
(abbreviation: [Ir(Prptz1-Me).sub.3]); organometallic complexes
having an imidazole skeleton, such as
fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)
(abbreviation: [Ir(iPrpmi).sub.3]) and
tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridiu-
m(III) (abbreviation: [Ir(dmpimpt-Me).sub.3]); organometallic
complexes in which a phenylpyridine derivative having an
electron-withdrawing group is a ligand, such as
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium(III)
tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium(III)
picolinate (abbreviation: FIrpic), bis
{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C.sup.2'}iridium(III)
picolinate (abbreviation: [Ir(CF.sub.3ppy).sub.2(pic)]),
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium(III)
acetylacetonate (abbreviation: FIr(acac)); and the like can be
given.
[0116] As examples of a phosphorescent material which emits green
or yellow light and whose light emission spectrum has a peak
wavelength of greater than or equal to 495 nm and less than or
equal to 590 nm, the following materials can be given.
[0117] For example, organometallic iridium complexes having a
pyrimidine skeleton, such as
tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:
[Ir(mppm).sub.3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(tBuppm).sub.3]),
(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(mppm).sub.2(acac)]),
(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(tBuppm).sub.2(acac)]),
(acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III)
(abbreviation: [Ir(nbppm).sub.2(acac)]),
(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iri-
dium(III) (abbreviation: [Ir(mpmppm).sub.2(acac)]),
(acetylacetonato)bis
{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-N3]phenyl-.kappa.C}-
iridium(III) (abbreviation: [Ir(dmppm-dmp).sub.2(acac)]), and
(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)
(abbreviation: [Ir(dppm).sub.2(acac)]); organometallic iridium
complexes having a pyrazine skeleton, such as
(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)
(abbreviation: [Ir(mppr-Me).sub.2(acac)]) and
(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)
(abbreviation: [Ir(mppr-iPr).sub.2(acac)]); organometallic iridium
complexes having a pyridine skeleton, such as
tris(2-phenylpyridinato-N, C.sup.2')iridium(III) (abbreviation:
[Ir(ppy).sub.3]), bis(2-phenylpyridinato-N,C.sup.2')iridium(III)
acetylacetonate (abbreviation: [Ir(ppy).sub.2(acac)]),
bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation:
[Ir(bzq).sub.2(acac)]), tris(benzo[h]quinolinato)iridium(III)
(abbreviation: [Ir(bzq).sub.3]), tris(2-phenylquinolinato-N,
C.sup.2')iridium(III) (abbreviation: [Ir(pq).sub.3]), and
bis(2-phenylquinolinato-N,C.sup.2')iridium(III) acetylacetonate
(abbreviation: [Ir(pq).sub.2(acac)]); organometallic complexes such
as bis(2,4-diphenyl-1,3-oxazolato-N,C.sup.2')iridium(III)
acetylacetonate (abbreviation: [Ir(dpo).sub.2(acac)]),
bis{2-[4'-(perfluorophenyl)phenyl]pyridinato-N,C.sup.2'}iridium(III)
acetylacetonate (abbreviation: [Ir(p-PF-ph).sub.2(acac)]), and
bis(2-phenylbenzothiazolato-N, C.sup.2')iridium(III)
acetylacetonate (abbreviation: [Ir(bt).sub.2(acac)]); and rare
earth metal complexes such as tris(acetylacetonato)
(monophenanthroline)terbium(III) (abbreviation:
[Tb(acac).sub.3(Phen)]) can be given.
[0118] Among the above, an organometallic complex having a pyridine
skeleton (particularly, a phenylpyridine skeleton) or a pyrimidine
skeleton is a group of compounds effective for meeting the
chromaticity of green (the chromaticity range represented by the
region B) in one embodiment of the present invention.
[0119] As examples of a phosphorescent material which emits yellow
or red light and whose emission spectrum has a peak wavelength of
greater than or equal to 570 nm and less than or equal to 750 nm,
the following materials can be given.
[0120] For example, organometallic complexes having a pyrimidine
skeleton, such as
(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]ir-
idium(III) (abbreviation: [Ir(5mdppm).sub.2(dibm)]),
bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)
(abbreviation: [Ir(5mdppm).sub.2(dpm)]), and
bis[4,6-di(naphthalen-1-yl)pyrimidinato]
(dipivaloylmethanato)iridium(III) (abbreviation:
[Ir(d1npm).sub.2(dpm)]); organometallic complexes having a pyrazine
skeleton, such as
(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)
(abbreviation: [Ir(tppr).sub.2(acac)]),
bis(2,3,5-triphenylpyrazinato) (dipivaloylmethanato)iridium(III)
(abbreviation: [Ir(tppr).sub.2(dpm)]), bis
{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-.kappa.N-
]phenyl-.kappa.C}(2,6-dimethyl-3,5-heptanedionato-.kappa..sup.2O,O')iridiu-
m(III) (abbreviation: [Ir(dmdppr-P).sub.2(dibm)]),
bis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-
-2-pyrazinyl-.kappa.N]phenyl-.kappa.C}(2,2,6,6-tetramethyl-3,5-heptanedion-
ato-.kappa..sup.2O,O')iridium(III) (abbreviation:
[Ir(dmdppr-dmCP).sub.2(dpm)]),
(acetylacetonato)bis[2-methyl-3-phenylquinoxalinato-N,C.sup.2']iridium(II-
I) (abbreviation: [Ir(mpq).sub.2(acac)]),
(acetylacetonato)bis(2,3-diphenylquinoxalinato-N,C.sup.2')iridium(III)
(abbreviation: [Ir(dpq).sub.2(acac)]), and
(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)
(abbreviation: [Ir(Fdpq).sub.2(acac)]); organometallic complexes
having a pyridine skeleton, such as
tris(1-phenylisoquinolinato-N,C.sup.2')iridium(III) (abbreviation:
[Ir(piq).sub.3]) and
bis(1-phenylisoquinolinato-N,C.sup.2')iridium(III) acetylacetonate
(abbreviation: [Ir(piq).sub.2(acac)]); platinum complexes such as
2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)
(abbreviation: [PtOEP]); and rare earth metal complexes such as
tris(1,3-diphenyl-1,3-propanedionato)
(monophenanthroline)europium(III) (abbreviation:
[Eu(DBM).sub.3(Phen)]) and
tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(-
III) (abbreviation: [Eu(TTA).sub.3(Phen)]) can be given.
[0121] Among the above, an organometallic complex having a pyrazine
skeleton is a group of compounds effective for meeting the
chromaticity of red (the chromaticity range represented by the
region A) in one embodiment of the present invention. In
particular, an organometallic complex containing a cyano group
(e.g., [Ir(dmdppr-dmCP).sub.2(dpm)]) is preferable because it is
stable.
[0122] Note that as the blue-light-emitting material, a material
whose photoluminescence peak wavelength is greater than or equal to
430 nm and less than or equal to 470 nm, preferably greater than or
equal to 430 nm and less than or equal to 460 nm may be used. As
the green-light-emitting material, a material whose
photoluminescence peak wavelength is greater than or equal to 500
nm and less than or equal to 540 nm, preferably greater than or
equal to 500 nm and less than or equal to 530 nm may be used. As
the red-light-emitting material, a material whose photoluminescence
peak wavelength is greater than or equal to 610 nm and less than or
equal to 680 nm, preferably greater than or equal to 620 nm and
less than or equal to 680 nm may be used. Note that the
photoluminescence may be measured with either a solution or a thin
film.
[0123] With the parallel use of such compounds and microcavity
effect, the above chromaticity can be more easily met. Here, a
semi-transmissive and semi-reflective electrode (a metal thin film
portion) that is needed for obtaining microcavity effect preferably
has a thickness of more than or equal to 20 nm and less than or
equal to 40 nm, further preferably more than 25 nm and less than or
equal to 40 nm. However, the thickness of more than 40 nm possibly
reduces the efficiency.
[0124] As the organic compounds (the host material and the assist
material) used in the light-emitting layers (313a and 313b), one or
more kinds of materials having a larger energy gap than the
light-emitting material (the guest material) are used.
[0125] When the light-emitting material is a fluorescent material,
it is preferable to use an organic compound that has a high energy
level in a singlet excited state and has a low energy level in a
triplet excited state. For example, an anthracene derivative or a
tetracene derivative is preferably used. Specific examples include
9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole
(abbreviation: PCzPA),
3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:
PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole
(abbreviation: CzPA),
7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c, g]carbazole
(abbreviation: cgDBCzPA),
6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan
(abbreviation: 2mBnfPPA),
9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4'-yl}anthracene
(abbreviation: FLPPA), 5,12-diphenyltetracene, and
5,12-bis(biphenyl-2-yl)tetracene.
[0126] In the case where the light-emitting material is a
phosphorescent material, an organic compound having triplet
excitation energy (energy difference between a ground state and a
triplet excited state) which is higher than that of the
light-emitting material is preferably selected. In that case, it is
possible to use a zinc- or aluminum-based metal complex, an
oxadiazole derivative, a triazole derivative, a benzimidazole
derivative, a quinoxaline derivative, a dibenzoquinoxaline
derivative, a dibenzothiophene derivative, a dibenzofuran
derivative, a pyrimidine derivative, a triazine derivative, a
pyridine derivative, a bipyridine derivative, a phenanthroline
derivative, an aromatic amine, a carbazole derivative, and the
like.
[0127] Specific examples include metal complexes such as
tris(8-quinolinolato)aluminum(III) (abbreviation: Alq),
tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation:
Almq.sub.3), bis(10-hydroxybenzo[h]quinolinato)beryllium(II)
(abbreviation: BeBq.sub.2), bis(2-methyl-8-quinolinolato)
(4-phenylphenolato)aluminum(III) (abbreviation: BAlq),
bis(8-quinolinolato)zinc(II) (abbreviation: Znq),
bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and
bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);
heterocyclic compounds such as
2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
(abbreviation: PBD),
1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene
(abbreviation: OXD-7),
3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole
(abbreviation: TAZ),
2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)
(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen),
bathocuproine (abbreviation: BCP),
2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline
(abbreviation: NBphen), and
9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole
(abbreviation: CO11); and aromatic amine compounds such as NPB,
TPD, and BSPB.
[0128] In addition, condensed polycyclic aromatic compounds such as
anthracene derivatives, phenanthrene derivatives, pyrene
derivatives, chrysene derivatives, and dibenzo[g,p]chrysene
derivatives can be used. Specifically, 9,10-diphenylanthracene
(abbreviation: DPAnth),
N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine
(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine
(abbreviation: DPhPA), YGAPA, PCAPA,
N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-am-
ine (abbreviation: PCAPBA), 2PCAPA,
6,12-dimethoxy-5,11-diphenylchrysene, DBC1,
9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:
CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole
(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene
(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation:
DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation:
t-BuDNA), 9,9'-bianthryl (abbreviation: BANT),
9,9'-(stilbene-3,3'-diyl)diphenanthrene (abbreviation: DPNS),
9,9'-(stilbene-4,4'-diyl)diphenanthrene (abbreviation: DPNS2),
1,3,5-tri(1-pyrenyl)benzene (abbreviation: TPB3), or the like can
be used.
[0129] In the case where a plurality of organic compounds are used
for the light-emitting layers (313a and 313b), it is preferable to
use compounds that form an exciplex in combination with each other.
In that case, although any of various organic compounds can be
combined appropriately to be used, to form an exciplex efficiently,
it is particularly preferable to combine a compound that easily
accepts holes (a hole-transport material) and a compound that
easily accepts electrons (an electron-transport material). As the
hole-transport material and the electron-transport material,
specifically, any of the materials described in this embodiment can
be used.
[0130] Note that the TADF material is a material that can
up-convert a triplet excited state into a singlet excited state
(i.e., reverse intersystem crossing is possible) using a little
thermal energy and efficiently exhibits light emission
(fluorescence) from the singlet excited state. The TADF is
efficiently obtained under the condition where the difference in
energy between the triplet excitation level and the singlet
excitation level is greater than or equal to 0 eV and less than or
equal to 0.2 eV, preferably greater than or equal to 0 eV and less
than or equal to 0.1 eV. Note that "delayed fluorescence" exhibited
by the TADF material refers to light emission having the same
spectrum as normal fluorescence and an extremely long lifetime. The
lifetime is 10.sup.-6 seconds or longer, preferably 10.sup.-3
seconds or longer.
[0131] Examples of the TADF material are fullerene, a derivative
thereof, an acridine derivative such as proflavine, eosin, and the
like. Other examples include a metal-containing porphyrin, such as
a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin
(Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of
the metal-containing porphyrin include a protoporphyrin-tin
fluoride complex (SnF.sub.2(Proto IX)), a mesoporphyrin-tin
fluoride complex (SnF.sub.2(Meso IX)), a hematoporphyrin-tin
fluoride complex (SnF.sub.2(Hemato IX)), a coproporphyrin
tetramethyl ester-tin fluoride complex (SnF.sub.2(Copro III-4Me)),
an octaethylporphyrin-tin fluoride complex (SnF.sub.2(OEP)), an
etioporphyrin-tin fluoride complex (SnF.sub.2(Etio I)), and an
octaethylporphyrin-platinum chloride complex (PtCl.sub.2OEP).
[0132] Alternatively, a heterocyclic compound having a
.pi.-electron rich heteroaromatic ring and a .pi.-electron
deficient heteroaromatic ring, such as
2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1-
,3,5-triazine (PIC-TRZ),
2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-
-1,3,5-triazine (PCCzPTzn),
2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine
(PXZ-TRZ),
3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-tria-
zole (PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one
(ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone
(DMAC-DPS), or
10-phenyl-10H,10'H-spiro[acridin-9,9'-anthracen]-10'-one (ACRSA)
can be used. Note that a substance in which the .pi.-electron rich
heteroaromatic ring is directly bonded to the .pi.-electron
deficient heteroaromatic ring is particularly preferable because
both the donor property of the .pi.-electron rich heteroaromatic
ring and the acceptor property of the .pi.-electron deficient
heteroaromatic ring are increased and the energy difference between
the singlet excited state and the triplet excited state becomes
small.
[0133] Note that a TADF material can also be used in combination
with another organic compound.
[0134] Next, in the light-emitting element in FIG. 3D, the
electron-transport layer 314a is formed over the light-emitting
layer 313a of the EL layer 303a by a vacuum evaporation method.
After the EL layer 303a and the charge generation layer 304 are
formed, the electron-transport layer 314b is formed over the
light-emitting layer 313b of the EL layer 303b by a vacuum
evaporation method.
<Electron-Transport Layer>
[0135] The electron-transport layers (314a and 314b) transport the
electrons, which are injected from the second electrode 302 by the
electron-injection layers (315a and 315b), to the light-emitting
layers (313a and 313b). Note that the electron-transport layers
(314a and 314b) each contain an electron-transport material. It is
preferable that the electron-transport materials included in the
electron-transport layers (314a and 314b) be materials with an
electron mobility of higher than or equal to 1.times.10.sup.-6
cm.sup.2/Vs. Note that other materials may also be used as long as
the materials have an electron-transport property higher than a
hole-transport property.
[0136] Examples of the electron-transport material include metal
complexes having a quinoline ligand, a benzoquinoline ligand, an
oxazole ligand, and a thiazole ligand; an oxadiazole derivative; a
triazole derivative; a phenanthroline derivative; a pyridine
derivative; and a bipyridine derivative. In addition, a
.pi.-electron deficient heteroaromatic compound such as a
nitrogen-containing heteroaromatic compound can also be used.
[0137] Specifically, it is possible to use metal complexes such as
Alq.sub.3, tris(4-methyl-8-quinolinolato)aluminum (abbreviation:
Almq.sub.3), bis(10-hydroxybenzo[h]quinolinato)beryllium
(abbreviation: BeBq.sub.2), BAlq, Zn(BOX).sub.2, and
bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:
Zn(BTZ).sub.2), heteroaromatic compounds such as
2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
(abbreviation: PBD),
1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene
(abbreviation: OXD-7),
3-(4'-tert-butylphenyl)-4-phenyl-5-(4''-biphenyl)-1,2,4-triazole
(abbreviation: TAZ),
3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole
(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),
bathocuproine (abbreviation: BCP), and
4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs), and
quinoxaline derivatives and dibenzoquinoxaline derivatives such as
2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline
(abbreviation: 2mDBTPDBq-II),
2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline
(abbreviation: 2mDBTBPDBq-II),
2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline
(abbreviation: 2CzPDBq-III),
7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline
(abbreviation: 7mDBTPDBq-II), and
6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline
(abbreviation: 6mDBTPDBq-II).
[0138] Further alternatively, a high molecular compound such as
poly(2,5-pyridinediyl) (abbreviation: PPy),
poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)]
(abbreviation: PF-Py) or
poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)]
(abbreviation: PF-BPy) can be used.
[0139] Each of the electron-transport layers (314a and 314b) is not
limited to a single layer, but may be a stack of two or more layers
each containing any of the above materials.
[0140] Next, in the light-emitting element in FIG. 3D, the
electron-injection layer 315a is formed over the electron-transport
layer 314a of the EL layer 303a by a vacuum evaporation method.
Subsequently, the EL layer 303a and the charge generation layer 304
are formed, the components up to the electron-transport layer 314b
of the EL layer 303b are formed and then, the electron-injection
layer 315b is formed thereover by a vacuum evaporation method.
<Electron-Injection Layer>
[0141] The electron-injection layers (315a and 315b) each contain a
material having a high electron-injection property. The
electron-injection layers (315a and 315b) can each be formed using
an alkali metal, an alkaline earth metal, or a compound thereof,
such as lithium fluoride (LiF), cesium fluoride (CsF), calcium
fluoride (CaF.sub.2), or lithium oxide (LiOx). A rare earth metal
compound like erbium fluoride (ErF.sub.3) can also be used.
Electride may also be used for the electron-injection layers (315a
and 315b). Examples of the electrode include a material in which
electrons are added at high concentration to calcium oxide-aluminum
oxide. Any of the materials for forming the electron-transport
layers (314a and 314b), which are given above, can also be
used.
[0142] A composite material in which an organic compound and an
electron donor (donor) are mixed may also be used for the
electron-injection layers (315a and 315b). Such a composite
material is excellent in an electron-injection property and an
electron-transport property because electrons are generated in the
organic compound by the electron donor. The organic compound here
is preferably a material excellent in transporting the generated
electrons; specifically, for example, the electron-transport
materials for forming the electron-transport layers (314a and 314b)
(e.g., a metal complex or a heteroaromatic compound) can be used.
As the electron donor, a material showing an electron-donating
property with respect to the organic compound may be used.
Preferable examples are an alkali metal, an alkaline earth metal,
and a rare earth metal. Specifically, lithium, cesium, magnesium,
calcium, erbium, ytterbium, and the like can be given. Furthermore,
an alkali metal oxide and an alkaline earth metal oxide are
preferable, and a lithium oxide, a calcium oxide, a barium oxide,
and the like can be given. Alternatively, Lewis base such as
magnesium oxide can be used. Further alternatively, an organic
compound such as tetrathiafulvalene (abbreviation: TTF) can be
used.
[0143] In the case where light obtained from the light-emitting
layer 313b is amplified, for example, the optical path length
between the second electrode 302 and the light-emitting layer 313b
is preferably less than one fourth of the wavelength .lamda. of
light emitted by the light-emitting layer 313b. In that case, the
optical path length can be adjusted by changing the thickness of
the electron-transport layer 314b or the electron-injection layer
315b.
<Charge Generation Layer>
[0144] The charge generation layer 304 has a function of injecting
electrons into the EL layer 303a and injecting holes into the EL
layer 303b when a voltage is applied between the first electrode
(anode) 301 and the second electrode (cathode) 302. The charge
generation layer 304 may have either a structure in which an
electron acceptor (acceptor) is added to a hole-transport material
or a structure in which an electron donor (donor) is added to an
electron-transport material. Alternatively, both of these
structures may be stacked. Note that by formation of the charge
generation layer 304 with the use of any of the above materials, it
is possible to suppress the increase in drive voltage caused when
the EL layers are stacked.
[0145] In the case where the charge generation layer 304 has a
structure in which an electron acceptor is added to a
hole-transport material, any of the materials described in this
embodiment can be used as the hole-transport material. As the
electron acceptor, it is possible to use
7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:
F.sub.4-TCNQ), chloranil, and the like. In addition, an oxide of
metals that belong to Group 4 to Group 8 of the periodic table can
be given. Specifically, vanadium oxide, niobium oxide, tantalum
oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese
oxide, rhenium oxide, or the like is used.
[0146] In the case where the charge generation layer 304 has a
structure in which an electron donor is added to an
electron-transport material, any of the materials described in this
embodiment can be used as the electron-transport material. As the
electron donor, it is possible to use an alkali metal, an alkaline
earth metal, a rare earth metal, metals that belong to Groups 2 and
13 of the periodic table, or an oxide or carbonate thereof.
Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium
(Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate,
or the like is preferably used. Alternatively, an organic compound
such as tetrathianaphthacene may be used as the electron donor.
<Substrate>
[0147] The light-emitting element described in this embodiment can
be formed over a variety of substrates. Note that the type of the
substrate is not limited to a certain type. Examples of the
substrate include a semiconductor substrate (e.g., a single crystal
substrate or a silicon substrate), an SOI substrate, a glass
substrate, a quartz substrate, a plastic substrate, a metal
substrate, a stainless steel substrate, a substrate including
stainless steel foil, a tungsten substrate, a substrate including
tungsten foil, a flexible substrate, an attachment film, paper
including a fibrous material, and a base material film.
[0148] Examples of the glass substrate include a barium
borosilicate glass substrate, an aluminoborosilicate glass
substrate, and a soda lime glass substrate. Examples of a flexible
substrate, an attachment film, and a base material film include
plastics typified by polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), and polyether sulfone (PES); a synthetic resin
such as acrylic; polypropylene; polyester; polyvinyl fluoride;
polyvinyl chloride; polyamide; polyimide; aramid; epoxy; an
inorganic vapor deposition film; and paper.
[0149] For formation of the light-emitting element in this
embodiment, a vacuum process such as an evaporation method or a
solution process such as a spin coating method or an ink-jet method
can be used. When an evaporation method is used, a physical vapor
deposition method (PVD method) such as a sputtering method, an ion
plating method, an ion beam evaporation method, a molecular beam
evaporation method, or a vacuum evaporation method, a chemical
vapor deposition method (CVD method), or the like can be used.
Specifically, the functional layers (the hole-injection layers
(311a and 311b), the hole-transport layers (312a and 312b), the
light-emitting layers (313a and 313b), the electron-transport
layers (314a and 314b), the electron-injection layers (315a and
315b)) included in the EL layers and the charge generation layer
304 of the light-emitting element can be formed by an evaporation
method (e.g., a vacuum evaporation method), a coating method (e.g.,
a dip coating method, a die coating method, a bar coating method, a
spin coating method, or a spray coating method), a printing method
(e.g., an ink-jet method, screen printing (stencil), offset
printing (planography), flexography (relief printing), gravure
printing, or micro-contact printing), or the like.
[0150] Note that materials that can be used for the functional
layers (the hole-injection layers (311a and 311b), the
hole-transport layers (312a and 312b), the light-emitting layers
(313a and 313b), the electron-transport layers (314a and 314b), and
the electron-injection layers (315a and 315b)) that are included in
the EL layers (303a and 303b) and the charge generation layer 304
in the light-emitting element described in this embodiment are not
limited to the above materials, and other materials can be used in
combination as long as the functions of the layers are fulfilled.
For example, a high molecular compound (e.g., an oligomer, a
dendrimer, or a polymer), a middle molecular compound (a compound
between a low molecular compound and a high molecular compound with
a molecular weight of 400 to 4000), an inorganic compound (e.g., a
quantum dot material), or the like can be used. The quantum dot may
be a colloidal quantum dot, an alloyed quantum dot, a core-shell
quantum dot, a core quantum dot, or the like.
[0151] The structure described in this embodiment can be used in an
appropriate combination with any of the structures described in the
other embodiments.
Embodiment 3
[0152] In this embodiment, a display device of one embodiment of
the present invention which has a first element layer including a
liquid crystal element and a second element layer including a
light-emitting element and in which the display elements can
perform the respective kinds of display is described. Note that
such a display device can also be referred to as an emission and
reflection hybrid display or an emission/reflection hybrid display
(ER-hybrid display) or the like.
[0153] The display device in this embodiment, which can perform
both display using the liquid crystal element and display using the
light-emitting element, can be driven with extremely low power
consumption in the outdoors and other bright places where ambient
light is intense when a reflective liquid crystal element is used
as the liquid crystal element because the display can be performed
with the reflective liquid crystal element utilizing the ambient
light. In the case where the ambient light is too intense resulting
in surface reflection, images can be displayed with the use of both
the liquid crystal element and the light-emitting element at the
same time. On the other hand, the display device can perform image
display with a wide viewing angle and a high color reproducibility
and can be driven with low power consumption in the nighttime or in
the indoors and other dark places where ambient light is weak when
the light-emitting element, which does not need a light source, is
used. Alternatively, a structure can be employed in which a
transmissive (or a semi-transmissive and semi-reflective electrode)
liquid crystal element is used as the liquid crystal element and
the light-emitting element is used as both the light source of the
liquid crystal element and a display element. Thus, a combination
of the liquid crystal element and the light-emitting element can
display images with high color reproducibility at low power
consumption as compared to conventional display panels.
[0154] The display device in FIG. 4A has a structure in which a
first element layer (display element layer) 410 including a
reflective liquid crystal element 401, a second element layer
(display element layer) 411 including a light-emitting element 402,
a third element layer (driving element layer) 412 including
transistors (425 and 426) which drive these elements (the liquid
crystal element 401 and the light-emitting element 402) are
stacked. In FIG. 4A, the third element layer (driving element
layer) 412 is positioned between the first element layer (display
element layer) 410 and the second element layer (display element
layer) 411. However, the present invention is not limited thereto.
When the structure in FIG. 4A is simplified and illustrated like
the structure in FIG. 4B, the display device can have the stacked
layer structures in FIGS. 4C to 4E as the other variations.
[0155] In each of the display devices in FIGS. 4A to 4E, the liquid
crystal element 401 included in the first element layer (display
element layer) 410 and the light-emitting element 402 included in
the second element layer (display element layer) 411 can be driven
in the following modes: display is performed with the liquid
crystal element 401 by reflection of visible light on the
conductive layer 403 serving as a first electrode (reflective
electrode) in a first mode; and display is performed by emission of
light from the light-emitting element 402 through an opening 404 in
the conductive layer 403 in a second mode, for example.
[0156] Note that the first element layer 410 including the liquid
crystal element 401, the second element layer 411 including the
light-emitting element 402, and the third element layer 412
including the transistors (driving elements) (425 and 426) can be
stacked by a technique in which the layers are formed separately,
peeled, and bonded to each other. Note that in the case where the
stacked-layer structure is formed by bonding in the above manner,
the element layers are stacked with insulating layers provided
therebetween. The elements (the liquid crystal element 401, the
light-emitting element 402, the transistors (425 and 426), and the
like) formed in the element layers can be electrically connected
via conductive films (wirings) formed in the insulating layers that
insulate the elements from one another.
[0157] The liquid crystal element 401 included in the first element
layer 410 is a reflective liquid crystal element. The conductive
layer 403 serves as a reflective electrode, and is thus formed
using a material with high reflectivity. Note that the conductive
layer 403 includes the opening 404. Furthermore, a conductive layer
407 serves as a transparent electrode, and is thus formed using a
material that transmits visible light. The conductive layer 403 and
the conductive layer 407 are in contact with each other and
function as one electrode of the liquid crystal element 401. A
conductive layer 408 functions as the other electrode of the liquid
crystal element 401. Alignment films 415 and 416 are provided on
the conductive layers 407 and 408, respectively and in contact with
the liquid crystal layer 409. An insulating layer 419 formed in
contact with a color filter 418 serves as an overcoat. Note that
the alignment films 415 and 416 are not necessarily provided when
not needed.
[0158] In addition, it is preferable that a spacer which has a
function of preventing the electrodes of the liquid crystal element
401 from being too close to each other (a function of keeping a
cell gap) be provided, though not illustrated here.
[0159] The light-emitting element 402 included in the second
element layer 411 has a stacked-layer structure in which an EL
layer 422 is provided between a conductive layer 420 serving as one
electrode and a conductive layer 421 serving as the other
electrode. Note that the conductive layer 421 includes a material
transmitting visible light and the conductive layer 420 includes a
material reflecting visible light. Thus, light emitted from the
light-emitting element 402 which is transmitted through the
conductive layer 420 is emitted to the outside of the substrate 405
such that the light is transmitted through a color filter 423,
transmitted through the liquid crystal element 401 via the opening
404, and then transmitted through a polarizing layer 424.
[0160] One of a source and a drain of the transistor 426, which is
one of the transistors (425 and 426) included in the third element
layer 412, is electrically connected to the conductive layer 403
and the conductive layer 407 of the liquid crystal element 401
through a terminal portion 427. Note that the transistor 426
corresponds to a transistor SW1 in FIG. 6 that will be described
later. One of a source and a drain of the transistor 425 is
electrically connected to the conductive layer 420 in the
light-emitting element 402. For example, the transistor 425
corresponds to a transistor M in FIG. 6.
[0161] Note that the transistors (425 and 426) are electrically
connected to the outside via an FPC or the like, though not
illustrated here.
[0162] FIG. 5A is a block diagram illustrating a display device. A
display device includes a circuit (G) 501, a circuit (S) 502, and a
display portion 503. In the display portion 503, a plurality of
pixels 504 are arranged in an R direction and a C direction in a
matrix. A plurality of wirings G1, wirings G2, wirings ANO, and
wirings CSCOM are electrically connected to the circuit (G) 501.
These wirings are also electrically connected to the plurality of
pixels 504 arranged in the R direction. A plurality of wirings S1
and wirings S2 are electrically connected to the circuit (S) 502,
and these wirings are also electrically connected to the plurality
of pixels 504 arranged in the C direction.
[0163] Each of the plurality of pixels 504 includes a liquid
crystal element and a light-emitting element. The liquid crystal
element and the light-emitting element include portions overlapping
with each other.
[0164] FIG. 5B1 shows the shape of a conductive film 505 serving as
a reflective electrode of the liquid crystal element included in
the pixel 504. Note that an opening 507 is provided in a position
506 which is part of the conductive film 505 and which overlaps
with the light-emitting element. That is, light emitted from the
light-emitting element is emitted through the opening 507.
[0165] The pixels 504 in FIG. 5B1 are arranged such that the pixels
504 adjacent in the R direction exhibit different colors.
Furthermore, the openings 507 are provided so as not to be arranged
in a line in the R direction. Such arrangement has an effect of
suppressing crosstalk between the light-emitting elements of
adjacent pixels 504. Furthermore, there is an advantage that
element formation is facilitated.
[0166] The opening 507 can have a polygonal shape, a quadrangular
shape, an elliptical shape, a circular shape, a cross shape, a
stripe shape, or a slit-like shape, for example.
[0167] FIG. 5B2 illustrates another example of the arrangement of
the conductive films 505.
[0168] The ratio of the opening 507 to the total area of the
conductive film 505 (excluding the opening 507) affects the display
of the display device. That is, a problem is caused in that as the
area of the opening 507 is larger, the display using the liquid
crystal element becomes darker; in contrast, as the area of the
opening 507 is smaller, the display using the light-emitting
element becomes darker. Furthermore, in addition to the problem of
the ratio of the opening, a small area of the opening 507 itself
also causes a problem in that extraction efficiency of light
emitted from the light-emitting element is decreased. The ratio of
the opening 507 to the total area of the conductive film 505
(excluding the opening 507) is preferably 5% or more and 60% or
less because the visibility can be maintained even when the liquid
crystal element and the light-emitting element are used in a
combination.
[0169] Next, an example of a circuit configuration of the pixel 504
is described with reference to FIG. 6. FIG. 6 illustrates two
adjacent pixels 504.
[0170] The pixel 504 includes the transistor SW1, a capacitor C1, a
liquid crystal element 510, a transistor SW2, the transistor M, a
capacitor C2, a light-emitting element 511, and the like. Note that
these components are electrically connected to any of the wiring
G1, the wiring G2, the wiring ANO, the wiring CSCOM, the wiring S1,
and the wiring S2 in the pixel 504. The liquid crystal element 510
and the light-emitting element 511 are electrically connected to a
wiring VCOM1 and a wiring VCOM2, respectively.
[0171] A gate of the transistor SW1 is connected to the wiring G1.
One of a source and a drain of the transistor SW1 is connected to
the wiring Si, and the other of the source and the drain is
connected to one electrode of the capacitor C1 and one electrode of
the liquid crystal element 510. The other electrode of the
capacitor C1 is electrically connected to the wiring CSCOM. The
other electrode of the liquid crystal element 510 is connected to
the wiring VCOM1.
[0172] A gate of the transistor SW2 is connected to the wiring G2.
One of a source and a drain of the transistor SW2 is connected to
the wiring S2, and the other of the source and the drain is
connected to one electrode of the capacitor C2 and a gate of the
transistor M. The other electrode of the capacitor C2 is connected
to one of a source and a drain of the transistor M and the wiring
ANO. The other of the source and the drain of the transistor M is
connected to one electrode of the light-emitting element 511.
Furthermore, the other electrode of the light-emitting element 511
is connected to the wiring VCOM2.
[0173] Note that the transistor M includes two gates between which
a semiconductor is provided and which are electrically connected to
each other. With such a structure, the amount of current flowing
through the transistor M can be increased.
[0174] The on/off state of the transistor SW1 is controlled by a
signal from the wiring G1. A predetermined potential is applied
from the wiring VCOM1. Furthermore, orientation of liquid crystals
of the liquid crystal element 510 can be controlled by a signal
from the wiring Si. A predetermined potential is applied from the
wiring CSCOM.
[0175] The on/off state of the transistor SW2 is controlled by a
signal from the wiring G2. By the difference between the potentials
applied from the wiring VCOM2 and the wiring ANO, the
light-emitting element 511 can emit light. Furthermore, the
conduction state of the transistor M is controlled by a signal from
the wiring S2.
[0176] In the above structure, in the case of the first mode, for
example, the liquid crystal element 510 is controlled by the
signals applied from the wiring G1 and the wiring S1 and optical
modulation is utilized, whereby display can be performed. In the
case of the second mode, the light-emitting element 511 emits light
when the signals are applied from the wiring G2 and the wiring S2,
whereby display can be performed. In the case where both modes are
performed at the same time, desired display can be performed by the
liquid crystal element 510 and the light-emitting element 511 on
the basis of the signals from the wiring G1, the wiring G2, the
wiring Si, and the wiring S2.
[0177] Note that the structure described in this embodiment can be
used in an appropriate combination with any of the structures
described in the other embodiments.
Embodiment 4
[0178] In this embodiment, an example of the transistor formed in
the driving element layer included in the element layer of the
display device of one embodiment of the present invention is
described. As the transistor, for example, a planar transistor, a
staggered transistor, an inverted staggered transistor, or the like
can be used. A top-gate or bottom-gate transistor structure can be
employed. Gate electrodes may be provided above and below a
channel. Thus, there are no particular limitations on the structure
of any of the transistors.
[0179] As a semiconductor material used for the semiconductor layer
of the transistor, an element of Group 14 (e.g., silicon or
germanium), a compound semiconductor, or an oxide semiconductor can
be used, for example. A semiconductor containing silicon, a
semiconductor containing gallium arsenide, an oxide semiconductor
containing indium, or the like can be typically used.
[0180] There is no particular limitation on the crystallinity of a
semiconductor material used for the semiconductor layer of the
transistor, and an amorphous semiconductor or a semiconductor
having crystallinity (a microcrystalline semiconductor, a
polycrystalline semiconductor, a single crystal semiconductor, or a
semiconductor partly including crystal regions) may be used. A
semiconductor having crystallinity is preferably used, in which
case deterioration of the transistor characteristics can be
suppressed.
[0181] Among the above semiconductor materials used for the
semiconductor layer of the transistor, it is particularly
preferable to use a metal oxide.
[0182] In this specification and the like, a metal oxide means an
oxide of metal in a broad sense. Metal oxides are classified into
oxide insulators, oxide conductors (including transparent oxide
conductors), oxide semiconductors (also simply referred to as OS),
and the like. For example, a metal oxide used in an active layer of
a transistor is called an oxide semiconductor in some cases. In
other words, an OS FET can mean a transistor including a metal
oxide or an oxide semiconductor.
[0183] In this specification and the like, a metal oxide including
nitrogen is also called a metal oxide in some cases. Moreover, a
metal oxide including nitrogen may be called a metal
oxynitride.
[0184] Next, an oxide semiconductor which is a metal oxide will be
described.
[0185] An oxide semiconductor is a semiconductor material having a
wider band gap and a lower carrier density than silicon and thus
can reduce the off-state current of a transistor. It is
particularly preferable to use an oxide semiconductor having an
energy gap of 2 eV or more, further preferably 2.5 eV or more, and
still further preferably 3 eV or more.
[0186] When a transistor has a reduced off-state current, charge
accumulated in a capacitor that is connected in series to the
transistor can be held for a long time. Accordingly, when such a
transistor is used for a pixel, operation of a driver circuit can
be stopped while a gray scale of an image displayed in each display
region is maintained. As a result, a display device with extremely
low power consumption can be obtained.
[0187] In this specification and the like, "c-axis aligned crystal
(CAAC)" or "cloud-aligned composite (CAC)" may be stated. CAAC
refers to an example of a crystal structure, and CAC refers to an
example of a function or a material composition.
[0188] In this specification and the like, CAC-OS or CAC-metal
oxide has a function of a conductor in a part of the material and
has a function of a dielectric (or insulator) in another part of
the material; as a whole, CAC-OS or CAC-metal oxide has a function
of a semiconductor. In the case where CAC-OS or CAC-metal oxide is
used in an active layer of a transistor, the conductor has a
function of letting electrons (or holes) serving as carriers flow,
and the dielectric has a function of not letting electrons serving
as carriers flow. By the complementary action of the function as a
conductor and the function as a dielectric, CAC-OS or CAC-metal
oxide can have a switching function (on/off function). In the
CAC-OS or CAC-metal oxide, separation of the functions can maximize
each function.
[0189] In this specification and the like, CAC-OS or CAC-metal
oxide includes conductor regions and dielectric regions. The
conductor regions have the above-described function of the
conductor, and the dielectric regions have the above-described
function of the dielectric. In some cases, the conductor regions
and the dielectric regions in the material are separated at the
nanoparticle level. In some cases, the conductor regions and the
dielectric regions are unevenly distributed in the material. The
conductor regions are observed to be coupled in a cloud-like manner
with their boundaries blurred, in some cases.
[0190] In other words, CAC-OS or CAC-metal oxide can be called a
matrix composite or a metal matrix composite.
[0191] Furthermore, in the CAC-OS or CAC-metal oxide, the conductor
regions and the dielectric regions each have a size of more than or
equal to 0.5 nm and less than or equal to 10 nm, preferably more
than or equal to 0.5 nm and less than or equal to 3 nm and are
dispersed in the material, in some cases.
[0192] Next, the above-mentioned CAC-OS will be described in
detail.
[0193] The CAC-OS has, for example, a composition in which elements
included in an oxide semiconductor are unevenly distributed.
Materials including unevenly distributed elements each have a size
of greater than or equal to 0.5 nm and less than or equal to 10 nm,
preferably greater than or equal to 1 nm and less than or equal to
2 nm, or a similar size. Note that in the following description of
an oxide semiconductor, a state in which one or more elements are
unevenly distributed and regions including the element(s) are mixed
is referred to as a mosaic pattern or a patch-like pattern. The
region has a size of greater than or equal to 0.5 nm and less than
or equal to 10 nm, preferably greater than or equal to 1 nm and
less than or equal to 2 nm, or a similar size.
[0194] Note that an oxide semiconductor preferably contains at
least indium. In particular, indium and zinc are preferably
contained. In addition, an element M (one or more kinds of elements
selected from aluminum, gallium, yttrium, copper, vanadium,
beryllium, boron, silicon, titanium, iron, nickel, germanium,
zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium,
tantalum, tungsten, magnesium, and the like) may be contained.
[0195] For example, of the CAC-OS, an In--Ga--Zn oxide with the CAC
composition (such an In--Ga--Zn oxide may be particularly referred
to as CAC-IGZO) has a composition in which materials are separated
into indium oxide (InO.sub.X1, where X1 is a real number greater
than 0) or indium zinc oxide (In.sub.X2Zn.sub.Y2O.sub.Z2, where X2,
Y2, and Z2 are real numbers greater than 0), and gallium oxide
(GaO.sub.X3, where X3 is a real number greater than 0), gallium
zinc oxide (Ga.sub.X4Zn.sub.Y4O.sub.Z4, where X4, Y4, and Z4 are
real numbers greater than 0), or the like, and a mosaic pattern is
formed. Then, InO.sub.X1 or In.sub.X2Zn.sub.Y2O.sub.Z2 forming the
mosaic pattern is evenly distributed in the film. This composition
is also referred to as a cloud-like composition.
[0196] That is, the CAC-OS is a composite oxide semiconductor with
a composition in which a region including GaO.sub.X3 as a main
component and a region including In.sub.X2Zn.sub.Y2O.sub.Z2 or
InO.sub.X1 as a main component are mixed. Note that in this
specification, for example, when the atomic ratio of In to an
element M in a first region is greater than the atomic ratio of In
to an element M in a second region, the first region has higher In
concentration than the second region.
[0197] Note that a compound including In, Ga, Zn, and O is also
known as IGZO. Typical examples of IGZO include a crystalline
compound represented by InGaO.sub.3(ZnO).sub.m1, (m1 is a natural
number) and a crystalline compound represented by
In.sub.(1+x0)Ga.sub.(1-x0)O.sub.3(ZnO).sub.m0
(-1.ltoreq.x0.ltoreq.1; m0 is a given number).
[0198] The above crystalline compounds have a single crystal
structure, a polycrystalline structure, or a CAAC structure. Note
that the CAAC structure is a crystal structure in which a plurality
of IGZO nanocrystals have c-axis alignment and are connected in the
a-b plane direction without alignment.
[0199] On the other hand, the CAC-OS relates to the material
composition of an oxide semiconductor. In a material composition of
a CAC-OS including In, Ga, Zn, and O, nanoparticle regions
including Ga as a main component are observed in part of the CAC-OS
and nanoparticle regions including In as a main component are
observed in part thereof. These nanoparticle regions are randomly
dispersed to form a mosaic pattern. Therefore, the crystal
structure is a secondary element for the CAC-OS.
[0200] Note that in the CAC-OS, a stacked-layer structure including
two or more films with different atomic ratios is not included. For
example, a two-layer structure of a film including In as a main
component and a film including Ga as a main component is not
included.
[0201] A boundary between the region including GaO.sub.X3 as a main
component and the region including In.sub.X2Zn.sub.Y2O.sub.Z2 or
InO.sub.X1 as a main component is not clearly observed in some
cases.
[0202] In the case where one or more of aluminum, yttrium, copper,
vanadium, beryllium, boron, silicon, titanium, iron, nickel,
germanium, zirconium, molybdenum, lanthanum, cerium, neodymium,
hafnium, tantalum, tungsten, magnesium, and the like are contained
instead of gallium in a CAC-OS, nanoparticle regions including the
selected metal element(s) as a main component(s) are observed in
part of the CAC-OS and nanoparticle regions including In as a main
component are observed in part thereof, and these nanoparticle
regions are randomly dispersed to form a mosaic pattern in the
CAC-OS.
[0203] The CAC-OS can be formed by a sputtering method under
conditions where a substrate is intentionally not heated, for
example. In the case of forming the CAC-OS by a sputtering method,
one or more selected from an inert gas (typically, argon), an
oxygen gas, and a nitrogen gas may be used as a deposition gas. The
ratio of the flow rate of an oxygen gas to the total flow rate of
the deposition gas at the time of deposition is preferably as low
as possible, and for example, the flow ratio of an oxygen gas is
preferably higher than or equal to 0% and less than 30%, further
preferably higher than or equal to 0% and less than or equal to
10%.
[0204] The CAC-OS is characterized in that no clear peak is
observed in measurement using .theta./2.theta. scan by an
out-of-plane method, which is an X-ray diffraction (XRD)
measurement method. That is, X-ray diffraction shows no alignment
in the a-b plane direction and the c-axis direction in a measured
region.
[0205] In an electron diffraction pattern of the CAC-OS which is
obtained by irradiation with an electron beam with a probe diameter
of 1 nm (also referred to as a nanometer-sized electron beam), a
ring-like region with high luminance and a plurality of bright
spots in the ring-like region are observed. Therefore, the electron
diffraction pattern indicates that the crystal structure of the
CAC-OS includes a nanocrystal (nc) structure with no alignment in
plan-view and cross-sectional directions.
[0206] For example, energy dispersive X-ray spectroscopy (EDX) is
used to obtain EDX mapping, and according to the EDX mapping, the
CAC-OS of the In--Ga--Zn oxide has a composition in which the
regions including GaO.sub.X3 as a main component and the regions
including In.sub.X2Zn.sub.Y2O.sub.Z2 or InO.sub.X1 as a main
component are unevenly distributed and mixed.
[0207] The CAC-OS has a structure different from that of an IGZO
compound in which metal elements are evenly distributed, and has
characteristics different from those of the IGZO compound. That is,
in the CAC-OS, regions including GaO.sub.X3 or the like as a main
component and regions including In.sub.X2Zn.sub.Y2O.sub.Z2 or
InO.sub.X1 as a main component are separated to form a mosaic
pattern.
[0208] The conductivity of a region including
In.sub.X2Zn.sub.Y2O.sub.Z2 or InO.sub.X1 as a main component is
higher than that of a region including GaO.sub.X3 or the like as a
main component. In other words, when carriers flow through regions
including In.sub.X2Zn.sub.Y2O.sub.Z2 or InO.sub.X1 as a main
component, the conductivity of an oxide semiconductor is exhibited.
Accordingly, when regions including In.sub.X2Zn.sub.Y2O.sub.Z2 or
InO.sub.X1 as a main component are distributed in an oxide
semiconductor like a cloud, high field-effect mobility (t) can be
achieved.
[0209] In contrast, the insulating property of a region including
GaO.sub.X3 or the like as a main component is higher than that of a
region including In.sub.X2Zn.sub.Y2O.sub.Z2 or InO.sub.X1 as a main
component. In other words, when regions including GaO.sub.X3 or the
like as a main component are distributed in an oxide semiconductor,
leakage current can be suppressed and favorable switching operation
can be achieved.
[0210] Accordingly, when a CAC-OS is used for a semiconductor layer
of a transistor, the insulating property derived from GaO.sub.X3 or
the like and the conductivity derived from
In.sub.X2Zn.sub.Y2O.sub.Z2 or InO.sub.X1 complement each other,
whereby high on-state current (Ion) and high field-effect mobility
(pt) can be achieved.
[0211] When a CAC-OS is used for a semiconductor layer of a
transistor, the transistor can have increased reliability.
[0212] It is preferable that the atomic ratio of metal elements of
a sputtering target used for depositing the In-M-Zn-based oxide
satisfy In.gtoreq.M and Zn.gtoreq.M. As the atomic ratio of metal
elements of such a sputtering target, In:M:Zn=1:1:1,
In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:4.1 and the like are
preferable. Note that the atomic ratio of metal elements in the
formed film varies from the atomic ratio of those in the
above-described sputtering target, within a range of .+-.40%.
[0213] The formed film preferably has a low carrier density. An
oxide semiconductor with a low carrier density has a low impurity
concentration and a low density of defect states and can be
regarded as an oxide semiconductor with stable characteristics. For
example, for an oxide semiconductor film with a low carrier
density, it is desirable to use an oxide semiconductor whose
carrier density is lower than or equal to
1.times.10.sup.17/cm.sup.3, preferably lower than or equal to
1.times.10.sup.15/cm.sup.3, further preferably lower than or equal
to 1.times.10.sup.13/cm.sup.3, still further preferably lower than
or equal to 1.times.10.sup.11/cm.sup.3, even further preferably
lower than 1.times.10.sup.10/cm.sup.3, and higher than or equal to
1.times.10.sup.-9/cm.sup.3.
[0214] Note that without limitation to the compositions and
materials described above, a material with an appropriate
composition can be used depending on required semiconductor
characteristics and electrical characteristics (e.g., field-effect
mobility and threshold voltage) of a transistor. To obtain the
required semiconductor characteristics of the transistor, it is
preferable that the carrier density, the impurity concentration,
the defect density, the atomic ratio between a metal element and
oxygen, the interatomic distance, the density, and the like of the
semiconductor layer be set to appropriate values.
[0215] Alkali metal and alkaline earth metal might generate
carriers when bonded to an oxide semiconductor, in which case the
off-state current of the transistor might be increased. Therefore,
the concentration of alkali metal or alkaline earth metal of the
semiconductor layer, which is measured by secondary ion mass
spectrometry, is lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, preferably lower than or equal to 2.times.10.sup.16
atoms/cm.sup.3.
[0216] When an oxide semiconductor is used, the crystal structure
thereof may be a non-single-crystal structure. Examples of the
non-single-crystal structure include the above-described CAAC-OS, a
polycrystalline structure, a microcrystalline structure, and an
amorphous structure. Among the non-single-crystal structures, the
amorphous structure has the highest density of defect states,
whereas a CAAC-OS has the lowest density of defect states. The
amorphous structure has disordered atomic arrangement or an
absolutely amorphous structure and no crystal portion.
[0217] Note that the semiconductor layer may be a mixed film
including two or more of the following: a region having an
amorphous structure, a region having a microcrystalline structure,
a region having a polycrystalline structure, a region of CAAC-OS,
and a region having a single-crystal structure. The mixed film has,
for example, a single-layer structure or a stacked-layer structure
including two or more of the above regions in some cases.
[0218] When a transistor in the driving element layer included in
the element layer of the display device of one embodiment of the
present invention is the transistor described in this embodiment,
the display device can have high reliability.
[0219] Note that the structure described in this embodiment can be
used in an appropriate combination with any of the structures
described in the other embodiments.
Embodiment 5
[0220] In this embodiment, examples of a variety of electronic
devices and an automobile manufactured using a display device of
one embodiment of the present invention are described.
[0221] Examples of the electronic device including the display
device are television devices (also referred to as TV or television
receivers), monitors for computers and the like, digital cameras,
digital video cameras, digital photo frames, mobile phones (also
referred to as cellular phones or portable telephone devices),
portable game consoles, goggle-type displays (e.g., VR goggles),
mobile information terminals, audio playback devices, large game
machines such as pachinko machines, and the like. Specific examples
of these electronic devices are illustrated in FIGS. 7A, 7B, 7C,
7D, 7D'-1, 7D'-2, and 7E, and FIGS. 8A to 8C.
[0222] FIG. 7A illustrates an example of a television device. In a
television device 7100, a display portion 7103 is incorporated in a
housing 7101. The display portion 7103 can display images and may
be a touch panel (an input/output device) including a touch sensor
(an input device). Note that the display device of one embodiment
of the present invention can be used for the display portion 7103.
In addition, here, the housing 7101 is supported by a stand
7105.
[0223] The television device 7100 can be operated by an operation
switch of the housing 7101 or a separate remote controller 7110.
With operation keys 7109 of the remote controller 7110, channels
and volume can be changed and images displayed on the display
portion 7103 can be controlled. Furthermore, the remote controller
7110 may be provided with a display portion 7107 for displaying
data output from the remote controller 7110.
[0224] Note that the television device 7100 is provided with a
receiver, a modem, and the like. With the use of the receiver,
general television broadcasts can be received. Moreover, when the
television device is connected to a communication network with or
without wires via the modem, one-way (from a sender to a receiver)
or two-way (between a sender and a receiver or between receivers)
information communication can be performed.
[0225] FIG. 7B illustrates a computer, which includes a main body
7201, a housing 7202, a display portion 7203, a keyboard 7204, an
external connection port 7205, a pointing device 7206, and the
like. Note that this computer can be manufactured using the display
device of one embodiment of the present invention for the display
portion 7203. The display portion 7203 may be a touch panel (an
input/output device) including a touch sensor (an input device).
Note that the computer can be especially suitable for outdoor use
by including the display device of one embodiment of the present
invention because a reduction in visibility due to reflection of
ambient light can be prevented in the display device.
[0226] FIG. 7C illustrates a smart watch, which includes a housing
7302, a display portion 7304, operation buttons 7311 and 7312, a
connection terminal 7313, a band 7321, a clasp 7322, and the
like.
[0227] The display portion 7304 mounted in the housing 7302 serving
as a bezel includes a non-rectangular display region. The display
portion 7304 can display an icon 7305 indicating time, another icon
7306, and the like. The display portion 7304 may be a touch panel
(an input/output device) including a touch sensor (an input
device). Note that the smart watch can be especially suitable for
outdoor use by including the display device of one embodiment of
the present invention because a reduction in visibility due to
reflection of ambient light can be prevented in the display
device.
[0228] The smart watch illustrated in FIG. 7C can have a variety of
functions, such as a function of displaying a variety of
information (e.g., a still image, a moving image, and a text image)
on a display portion, a touch panel function, a function of
displaying a calendar, date, time, and the like, a function of
controlling processing with a variety of software (programs), a
wireless communication function, a function of being connected to a
variety of computer networks with a wireless communication
function, a function of transmitting and receiving a variety of
data with a wireless communication function, and a function of
reading program or data stored in a recording medium and displaying
the program or data on a display portion.
[0229] The housing 7302 can include a speaker, a sensor (a sensor
having a function of measuring force, displacement, position,
speed, acceleration, angular velocity, rotational frequency,
distance, light, liquid, magnetism, temperature, chemical
substance, sound, time, hardness, electric field, current, voltage,
electric power, radiation, flow rate, humidity, gradient,
oscillation, odor, or infrared rays), a microphone, and the like.
Note that the smart watch can be manufactured using the display
device for the display portion 7304.
[0230] FIG. 7D illustrates an example of a mobile phone (e.g., a
smartphone). A mobile phone 7400 includes a housing 7401 provided
with a display portion 7402, a microphone 7406, a speaker 7405, a
camera 7407, an external connection portion 7404, an operation
button 7403, and the like. In the case where a display device is
manufactured in the manner that the liquid crystal element and
light-emitting element of one embodiment of the present invention
are formed over a flexible substrate, the display device can be
used for the display portion 7402 having a curved surface as
illustrated in FIG. 7D.
[0231] When the display portion 7402 of the mobile phone 7400
illustrated in FIG. 7D is touched with a finger or the like, data
can be input into the mobile phone 7400. Furthermore, operations
such as making a call and composing an e-mail can be performed by
touch on the display portion 7402 with a finger or the like.
[0232] The display portion 7402 has mainly three screen modes. The
first mode is a display mode mainly for displaying images. The
second mode is an input mode mainly for inputting data such as
text. The third mode is a display-and-input mode in which two modes
of the display mode and the input mode are combined.
[0233] For example, in the case of making a call or composing an
e-mail, a text input mode mainly for inputting text is selected for
the display portion 7402 and text input operation can be performed
using characters displayed on the screen. In this case, it is
preferable to display a keyboard or number buttons on almost the
entire screen of the display portion 7402.
[0234] When a detection device such as a gyroscope sensor or an
acceleration sensor is provided inside the mobile phone 7400,
display on the screen of the display portion 7402 can be
automatically changed by determining the orientation of the mobile
phone 7400 (whether the mobile phone is placed horizontally or
vertically).
[0235] The screen modes are changed by touch on the display portion
7402 or operation with the operation button 7403 of the housing
7401. Alternatively, the screen modes can be switched depending on
kinds of images displayed on the display portion 7402. For example,
when a signal of an image displayed on the display portion is a
signal of moving image data, the screen mode is switched to the
display mode. When the signal is a signal of text data, the screen
mode is switched to the input mode.
[0236] Moreover, in the input mode, when input by touching the
display portion 7402 is not performed within a specified period
while a signal detected by an optical sensor in the display portion
7402 is detected, the screen mode may be controlled so as to be
switched from the input mode to the display mode.
[0237] The display portion 7402 may also function as an image
sensor. For example, an image of a palm print, a fingerprint, or
the like is taken by touch on the display portion 7402 with the
palm or the finger, whereby personal authentication can be
performed. In addition, when a backlight or a sensing light source
that emits near-infrared light is provided in the display portion,
an image of a finger vein, a palm vein, or the like can be taken.
Note that the mobile phone can be especially suitable for outdoor
use by including the display device of one embodiment of the
present invention in the display portion 7402 because a reduction
in visibility due to reflection of ambient light can be prevented
in the display device.
[0238] Furthermore, the display device can be used for a mobile
phone having a structure illustrated in FIG. 7D'-1 or FIG. 7D'-2,
which is another structure of the mobile phone (e.g.,
smartphone).
[0239] Note that in the case of the structure illustrated in FIG.
7D'-1 or FIG. 7D'-2, text data, image data, or the like can be
displayed on second screens 7502(1) and 7502(2) of housings 7500(1)
and 7500(2) as well as first screens 7501(1) and 7501(2). Such a
structure enables the user to easily see text data, image data, or
the like displayed on the second screens 7502(1) and 7502(2) while
the mobile phone is placed in user's breast pocket.
[0240] FIG. 7E shows a goggle-type display (a head-mounted
display), which includes a main body 7601, a display portion 7602,
and an arm 7603. Note that the goggle-type display can be
especially suitable for outdoor use by including the display device
of one embodiment of the present invention in the display portion
7602 because a reduction in visibility due to reflection of ambient
light can be prevented.
[0241] Another electronic device including the display device is a
foldable mobile information terminal illustrated in FIGS. 8A to 8C.
FIG. 8A illustrates a mobile information terminal 9310 which is
opened. FIG. 8B illustrates the mobile information terminal 9310
which is being opened or being folded. FIG. 8C illustrates the
mobile information terminal 9310 which is folded. The mobile
information terminal 9310 is highly portable when folded and is
highly browsable when opened because of a seamless large display
region.
[0242] A display portion 9311 is supported by three housings 9315
joined together by hinges 9313. Note that the display portion 9311
may be a touch panel (an input/output device) including a touch
sensor (an input device). When the display portion 9311 is bent at
a connection portion between two housings 9315 with the use of the
hinges 9313, the mobile information terminal 9310 can be reversibly
changed in shape from an opened state to a folded state. A display
region 9312 in the display portion 9311 is a display region that is
positioned at a side surface of the mobile information terminal
9310 that is folded. On the display region 9312, information icons,
file shortcuts of frequently used applications or programs, and the
like can be displayed, and confirmation of information and start of
application can be smoothly performed. Note that the mobile
information terminal can be especially suitable for outdoor use by
including the display device of one embodiment of the present
invention in the display portion 9311 because a reduction in
visibility due to reflection of ambient light can be prevented in
the display device.
[0243] FIGS. 9A and 9B illustrate an automobile including the
display device. The display device can be incorporated in the
automobile, and specifically, can be included in lights 5101
(including lights of the rear part of the car), a wheel 5102 of a
tire, a part or whole of a door 5103, or the like on the outer side
of the automobile which is illustrated in FIG. 9A. The display
device can also be included in a display portion 5104, a steering
wheel 5105, a gear lever 5106, a seat 5107, an inner rearview
mirror 5108, or the like on the inner side of the automobile which
is illustrated in FIG. 9B, or in a part of a glass window. Note
that the display device of one embodiment the present invention
which is provided in part of the automobile can be especially
suitable for outdoor use because a reduction in visibility due to
reflection of ambient light from the display device can be
prevented.
[0244] As described above, the electronic devices and automobiles
can be obtained using the display device of one embodiment of the
present invention. Note that the display device can be used for
electronic devices and automobiles in a variety of fields without
being limited to the electronic devices and automobiles described
in this embodiment.
[0245] Note that the structure described in this embodiment can be
used in an appropriate combination with any of the structures
described in the other embodiments.
Example 1
[0246] Simulations were performed to examine the relation between
the brightness (reflectance) and the NTSC coverage in a display
including a reflective liquid crystal element (a reflective
display) and the results are described in this example.
[0247] The light source of a reflective display is ambient light,
and it is difficult to adjust the luminance of the light source as
appropriate. The outside light is transmitted twice through a color
filter when entering a display and exiting from the display; thus,
it can be said that the reflectivity is largely affected by the
color filter. That is, the reflectivity can be controlled as the
thickness of the color filter is adjusted.
[0248] Then, the reflectivity of a display was changed as the
thickness of the color filter was adjusted, and the relation
between the reflectance and the NTSC coverage was estimated by
liquid crystal alignment simulation. For the calculation, LCD
Master 1D manufactured by SHINTECH, Inc. was used. The calculation
conditions are shown in Table 1 below. Note that the incident light
was set to 100% on the assumption that the reflectance was specular
reflection.
TABLE-US-00001 TABLE 1 Algorithm 2x2 (Single reflection) Light
source D65 Polar angle 0 LC mode Twisted ECB LC ZLI-4792 Gap 2
.mu.m Twist 70 Applied Voltage 0/6 V
[0249] FIG. 10 shows the simulation results.
[0250] Next, the NTSC area ratio and the NTSC coverage as a
function of the reflectance were measured using an actual
reflective display. The measurement was performed in the manner
that light was incident at a polar angle of 30.degree. and received
at 0.degree.. Specular reflection is not employed; thus, the
reflectance of a standard white plate is set to 100%. Note that the
conditions of a reflective display panel used for this measurement
are shown in Table 2 below.
TABLE-US-00002 TABLE 2 LC mode Twisted ECB Pixel density 212 ppi
Aperture ratio 83.4% Dn 0.100 De 3.56 Gap 2 .mu.m Twist 70 Applied
Voltage 0/6 V
[0251] FIG. 11 shows the measurement results.
[0252] Here, the simulation results in FIG. 10 and the measurement
results (actual measurement results) in FIG. 11 were corrected so
as to be comparable with each other because the reflectance in the
simulation and the reflectance in the measurement are differently
defined. Specifically, the reflectance when the light source was
100% was multiplied by a constant such that a curve of the NTSC
coverage with respect to the reflectance obtained by simulation was
fitted to the plots of the measurement results. FIG. 12 shows the
results.
[0253] The results in FIG. 12 indicate that a reflectance of more
than or equal to 16% and less than or equal to 26% can be obtained
in the panel including a reflective liquid crystal element when the
NTSC area ratio or the NTSC coverage is set to more than or equal
to 20% and less than or equal to 60%. That is, it is apparent that
brightness (reflectance) required for the display including a
reflective liquid crystal element (reflective display) can be
obtained when the NTSC area ratio or the NTSC coverage is more than
or equal to 20% and less than or equal to 60%.
Example 2
[0254] In this example, an element structure, a forming method, and
properties of a light-emitting element used in the display device
of one embodiment of the present invention will be described. Note
that FIG. 13 illustrates an element structure of a light-emitting
element described in this example, and Table 3 shows specific
structures. Table 3 also shows color filters (CF) combined with
light-emitting elements. A light-emitting element 1 is combined
with a CF-R; a light-emitting element 2, a CF-G; and each of
light-emitting elements 3 and 4, a CF-B. FIG. 14 shows transmitting
properties of these CFs. Chemical formulae of materials used in
this example are shown below.
TABLE-US-00003 TABLE 3 First hole- Light- First hole- transport
emitting First First electrode injection layer layer layer (A)
electron-transport layer Symbol in FIG. 13 901 911a 912a 913a 914a
Light-emitting Ag--Pd--Cu ITSO PCPPn:MoOx PCPPn *1 cgDBCzPA NBphen
element 1(R) (200 nm) (110 nm) (1:0.5 10 nm) (10 nm) (10 nm) (15
nm) Light-emitting ITSO PCPPn:MoOx element 2(G) (45 nm) (1:0.5 20
nm) Light-emitting ITSO PCPPn:MoOx element 3(B1) (10 nm) (1:0.5
12.5 nm) Light-emitting ITSO PCPPn:MoOx element 4(B1.5) (110 nm)
(1:0.5 16 nm) First Light-emitting layer (B) electron- Charge
Second hole- First light- Second injection generation Second
hole-injection transport emitting light-emitting layer layer layer
layer layer layer Symbol in FIG. 13 915a 904 911b 912b 913(b1)
913(b2) (Reference) Light-emitting Li.sub.2O CuPc DBT3P-II:MoOx
BPAFLP *2 *3 Light-emitting element 1(R) (0.1 nm) (2 nm) (1:0.5 10
nm) (15 nm) element 1(R) Light-emitting Light-emitting element 2(G)
element 2(G) Light-emitting Llight-emitting element 3(B1) element
3(B1) Light-emitting Light-emitting element 4(B1.5) element 4(B1.5)
Second Second electron-transport electron- layer injection layer
Second electrode Symbol in FIG. 13 914b 915b 903 CF Light-emitting
2mDBTBPDBq-II Nbphen LiF Ag:Mg ITO CF-R Light-emitting element 1(R)
(25 nm) (15 nm) (1 nm) (1:0.1 25 nm) (70 nm) element 1(R)
Light-emitting CF-G Light-emitting element 2(G) element 2(G)
Light-emitting CF-B Light-emitting element 3(B1) element 3(B1)
Light-emitting CF-B Light-emitting element 4(B1.5) element 4(B1.5)
*1 cgDBCzPA:1,6BnfAPrn-03 (1:0.03 25 nm) *2
2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm).sub.3] (0.8:0.2:0.06 20 nm) *3
2mDBTBPDBq-II:[Ir(dmdppr-P).sub.2(dibm)] (1:0.04 20 nm)
##STR00001## ##STR00002## ##STR00003## ##STR00004##
<<Formation of Light-Emitting Element>>
[0255] A light-emitting element in this example has a structure
illustrated in FIG. 13 in which a first electrode 901 is formed
over a substrate 900, a first EL layer 902a is formed over the
first electrode 901, a charge generation layer 904 is formed over
the first EL layer 902a, a second EL layer 902b is formed over the
charge generation layer 904, and a second electrode 903 is formed
over the second EL layer 902b. Note that the light-emitting element
1 in this example is a light-emitting element emitting mainly red
light and referred to as a light-emitting element 1(R). The
light-emitting element 2 is a light-emitting element emitting
mainly green light and referred to as a light-emitting element
2(G). The light-emitting element 3 and the light-emitting element 4
are each a light-emitting element emitting mainly blue light and
are also referred to as a light-emitting element 3(B1) and a
light-emitting element 3(B1.5), respectively.
[0256] First, the first electrode 901 was formed over the substrate
900. The electrode area was set to 4 mm.sup.2 (2 mm.times.2 mm). A
glass substrate was used as the substrate 900. The first electrode
901 was formed in the following manner: a 200-nm-thick alloy film
of silver (Ag), palladium (Pd), and copper (Cu) (the alloy is also
referred to as Ag--Pd--Cu) was formed by a sputtering method, and
an ITSO was formed by a sputtering method. The ITSO was formed such
that the thickness was 110 nm in the case of the light-emitting
element 1(R), the thickness was 45 nm in the case of the
light-emitting element 2(G), the thickness was 10 nm in the case of
the light-emitting element 3(B1), and the thickness was 110 nm in
the case of the light-emitting element 4(B1.5). In this example,
the first electrode 901 functions as an anode. The first electrode
901 is a reflective electrode having a function of reflecting
light. In this example, both the light-emitting element 3(B1) and
the light-emitting element 4(B1.5) emit blue light but have
different optical path lengths between their electrodes. The
light-emitting element 3(B1) has an adjusted optical path length
between its electrodes of 1 wavelength and the light-emitting
element 4(B1.5) has an adjusted optical path length between its
electrodes of 1.5 wavelengths.
[0257] As pretreatment, a surface of the substrate was washed with
water, baking was performed at 200.degree. C. for one hour, and
then UV ozone treatment was performed for 370 seconds. After that,
the substrate was transferred into a vacuum evaporation apparatus
where the pressure had been reduced to approximately 10.sup.-4 Pa,
and was subjected to vacuum baking at 170.degree. C. for 60 minutes
in a heating chamber of the vacuum evaporation apparatus, and then
the substrate was cooled down for about 30 minutes.
[0258] Next, a first hole-injection layer 911a was formed over the
first electrode 901. After the pressure in the vacuum evaporation
apparatus was reduced to 10.sup.-4 Pa, the hole-injection layer
911a was formed by co-evaporation such that the weight ratio of
3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:
PCPPn) to molybdenum oxide was 1:0.5, and such that the thickness
was 10 nm in the case of the light-emitting element 1(R), the
thickness was 20 nm in the case of the light-emitting element 2(G),
the thickness was 12.5 nm in the case of the light-emitting element
3(B1), and the thickness was 16 nm in the case of the
light-emitting element 4(B1.5).
[0259] Then, a first hole-transport layer 912a was formed over the
first hole-injection layer 911a. As the first hole-transport layer
912a, PCPPn was deposited by evaporation to a thickness of 10 nm.
Note that the same applies to the first light-emitting element, the
second light-emitting element, the third light-emitting element,
and the fourth light-emitting element. When the same applies to all
the light-emitting elements, there is no description
hereinafter.
[0260] Next, a light-emitting layer (A) 913a was formed over the
first hole-transport layer 912a.
[0261] The light-emitting layer (A) 913a was formed to a thickness
of 25 nm by co-evaporation using
7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole
(abbreviation: cgDBCzPA) as a host material and using
N,N'-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-ami-
ne] (abbreviation: 1,6BnfAPrn-03) as a guest material (a
fluorescent material), such that the weight ratio of cgDBCzPA to
1,6BnfAPrn-03 was 1:0.03.
[0262] Next, a first electron-transport layer 914a was formed over
the light-emitting layer (A) 913a. The first electron-transport
layer 914a was formed in the following manner: cgDBCzPA and
2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline
(abbreviation: NBphen) were sequentially deposited by evaporation
to thicknesses of 10 nm and 15 nm, respectively.
[0263] Next, a first electron-injection layer 915a was formed over
the first electron-transport layer 914a. The first
electron-injection layer 915a was formed to a thickness of 0.1 nm
by evaporation of lithium oxide (Li.sub.2O).
[0264] Then, the charge generation layer 904 was formed over the
first electron-injection layer 915a. The charge generation layer
904 was formed by evaporation of copper phthalocyanine
(abbreviation: CuPc) to a thickness of 2 nm.
[0265] Next, a second hole-injection layer 911b was formed over the
charge generation layer 904. The second hole-injection layer 911b
was formed to a thickness of 10 nm by co-evaporation such that the
weight ratio of 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene)
(abbreviation: DBT3P-II) to molybdenum oxide was 1:0.5.
[0266] Then, a second hole-transport layer 912b was formed over the
second hole-injection layer 911b. The hole-transport layer 912b was
formed to a thickness of 15 nm by evaporation of
4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:
BPAFLP).
[0267] A light-emitting layer (B) 913b was formed over the second
hole-transport layer 912b. The light-emitting layer (B) 913b had a
stacked-layer structure of a first light-emitting layer (B1)
913(b1) and a second light-emitting layer (B2) 913(b2).
[0268] The first light-emitting layer (B1) 913(b1) was formed to a
thickness of 20 nm by co-evaporation using
2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline
(abbreviation: 2mDBTBPDBq-II) as a host material, using
N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimeth-
yl-9H-fluoren-2-amine (abbreviation: PCBBiF) as an assist material,
and using tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(tBuppm).sub.3]) as a guest material (a
phosphorescent material) such that the weight ratio of
2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm).sub.3] was 0.8:0.2:0.06. The
second light-emitting layer (B2) 913(b2) was formed to a thickness
of 20 nm by co-evaporation using 2mDBTBPDBq-II as a host material
and using bis
{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-.kappa.N]phe-
nyl-.kappa.C}(2,6-dimethyl-3,5-heptanedionato-.kappa..sup.2O,O')iridium(II-
I) (abbreviation: [Ir(dmdppr-P).sub.2(dibm)]) as a guest material
(a phosphorescent material), such that the weight ratio of
2mDBTBPDBq-II to [Ir(dmdppr-P).sub.2(dibm)] was 1:0.04.
[0269] Next, a second electron-transport layer 914b was formed over
the second light-emitting layer (B2) 913(b2). The second
electron-transport layer 914b was formed in the following manner:
2mDBTBPDBq-II and NBphen were sequentially deposited by evaporation
to thicknesses of 10 nm and 15 nm, respectively.
[0270] Then, a second electron-injection layer 915b was formed over
the second electron-transport layer 914b. The second
electron-injection layer 915b was formed to a thickness of 1 nm by
evaporation of lithium fluoride (LiF).
[0271] Then, the second electrode 903 was formed over the second
electron-injection layer 915b. The second electrode 903 was formed
in the following manner: a film of silver (Ag) and magnesium (Mg)
was formed to a thickness of 15 nm by co-evaporation at a volume
ratio of Ag:Mg=1:0.1, and then indium tin oxide (ITO) was formed to
a thickness of 70 nm by a sputtering method. In this example, the
second electrode 903 functions as a cathode. Moreover, the second
electrode 903 is a semi-transmissive and semi-reflective electrode
having functions of transmitting light and reflecting light.
[0272] Through the above steps, the light-emitting element in which
the EL layers are provided between the pair of electrodes was
formed over the substrate 900. The first hole-injection layer 911a,
the first hole-transport layer 912a, the light-emitting layer 913a,
the first electron-transport layer 914a, the first
electron-injection layer 915a, the second hole-injection layer
911b, the second hole-transport layer 912b, the light-emitting
layer (B) 913b, the second electron-transport layer 914b, and the
second electron-injection layer 915b that are described above are
functional layers forming the EL layers of one embodiment of the
present invention. Furthermore, in all the evaporation steps in the
above forming method, evaporation was performed by a
resistance-heating method.
[0273] The light-emitting element formed in this example is sealed
between the substrate 900 and a substrate 905 as illustrated in
FIG. 13. The substrate 905 is provided with a color filter 906. The
sealing between the substrate 900 and the substrate 905 was
performed in such a manner that the substrate 905 was fixed to the
substrate 900 with a sealing material in a glove box containing a
nitrogen atmosphere, a sealant was applied to surround the
light-emitting element formed over the substrate 900, and then
irradiation with 365-nm ultraviolet light at 6 J/cm.sup.2 was
performed and heat treatment was performed at 80.degree. C. for 1
hour for sealing.
[0274] The light-emitting elements formed in this example each have
a structure in which light is emitted in the direction indicated by
the arrow from the second electrode 903 side of the light-emitting
element.
<<Operation Characteristics of Light-Emitting
Elements>>
[0275] Operation characteristics of the formed light-emitting
elements were measured. Note that the measurement was performed at
room temperature (in an atmosphere kept at 25.degree. C.). The
results are shown in FIG. 15, FIG. 16, FIG. 17, and FIG. 18. FIG.
19 shows light emission spectra when current at a current density
of 2.5 mA/cm.sup.2 was applied to the light-emitting elements. The
light emission spectra were measured with a multi-channel
spectrometer (PMA-12 produced by Hamamatsu Photonics K.K.). As
shown in FIG. 19, the light emission spectrum of the light-emitting
element 1(R) which emits red light has a peak around 635 nm, the
light emission spectrum of the light-emitting element 2(G) which
emits green light has a peak around 521 nm, and the light emission
spectra of the light-emitting elements 3(B1) and 4(B1.5) which emit
blue light each have a peak around 453 nm. The spectrum shapes were
narrowed. In this example, the results of measuring light emission
obtained from a combination of light-emitting elements and color
filters are shown.
[0276] FIG. 14 shows transmission spectra of the color filter (red)
(CF-R) used in combination with the light-emitting element 1(R),
the color filter (green) (CF-G) used in combination with the
light-emitting element 2(G), and the color filter (blue) (CF-B)
used in combination with the light-emitting elements 3(B1) and
4(B1.5). FIG. 14 shows that the transmittance of the CF-R at 600 nm
is lower than or equal to 60% and is 52%, whereas the transmittance
of the CF-R at 650 nm is higher than or equal to 70% and is 89%. In
addition, the transmittance of the CF-G at 480 nm and at 580 nm are
lower than or equal to 60% and are 26% and 52%, respectively,
whereas the transmittance of the CF-G at 530 nm is higher than or
equal to 70% and is 72%. Furthermore, the transmittance of the CF-B
at 510 nm is lower than or equal to 60% and is 60%, whereas the
transmittance of the CF-B at 450 nm is higher than or equal to 70%
and is 80%.
[0277] The results of measuring the chromaticities (x, y) of the
light-emitting elements formed in this example (the light-emitting
element 1(R), the light-emitting element 2(G), and the
light-emitting element 3(B1)) with a luminance colorimeter (BM-5A
manufactured by TOPCON CORPORATION) are shown in Table 4 below. The
chromaticity of the light-emitting element 1(R) was measured at a
luminance of approximately 730 cd/m.sup.2. The chromaticity of the
light-emitting element 2(G) was measured at a luminance of
approximately 1800 cd/m.sup.2. The chromaticity of the
light-emitting element 3(B1) was measured at a luminance of
approximately 130 cd/m.sup.2. Note that white light emission close
to D65 can be obtained by summing the luminance of R, the luminance
of G, and the luminance of B.
TABLE-US-00004 TABLE 4 x y Light-emitting 0.697 0.297 element 1(R)
Light-emitting 0.186 0.778 element 2(G) Light-emitting 0.142 0.046
element 3(B1)
[0278] On the basis of the results in Table 4, the BT.2020 area
ratio and the BT.2020 coverage were calculated using these
chromaticities (x, y) and were 93% and 91%, respectively. Note that
the BT.2020 area ratio was obtained in such a manner that an area A
of a triangle formed by connecting the CIE chromaticity coordinates
(x, y) of RGB which fulfill the BT.2020 standard and area B of a
triangle formed by connecting the CIE chromaticity coordinates (x,
y) of the three light-emitting elements described in this example
were calculated and the area ratio (B/A) was calculated. The
BT.2020 coverage is a value which represents how much percentage of
the BT.2020 standard color gamut (the inside of the above triangle)
can be reproduced using a combination of the chromaticities of the
three light-emitting elements described in this example.
[0279] The results of measuring the chromaticities (x, y) of the
light-emitting element 1(R), the light-emitting element 2(G), and
the light-emitting element 4(B1.5)) with a luminance colorimeter
among the light-emitting elements formed in this example are shown
in Table 5 below. The chromaticity of the light-emitting element
1(R) was measured at a luminance of approximately 550 cd/m.sup.2.
The chromaticity of the light-emitting element 2(G) was measured at
a luminance of approximately 1800 cd/m.sup.2. The chromaticity of
the light-emitting element 4(B1.5) was measured at a luminance of
approximately 130 cd/m.sup.2. Note that white light emission close
to D65 can be obtained by summing the luminance of R, the luminance
of G, and the luminance of B.
TABLE-US-00005 TABLE 5 x y Light-emitting 0.697 0.297 element 1(R)
Light-emitting 0.186 0.778 element 2(G) Light-emitting 0.156 0.042
element 4(B1.5)
[0280] On the basis of the results in Table 5, the BT.2020 area
ratio and the BT.2020 coverage were calculated using the
chromaticities (x, y) and were 92% and 90%, respectively. Even such
a structure having improved blue light emission efficiency can
achieve extremely wide-range color reproducibility.
[0281] The above results shows that, in this example, the
chromaticity of the light-emitting element 1(R) falls within a
chromaticity range in which x is more than 0.680 and less than or
equal to 0.720 and y is more than or equal to 0.260 and less than
or equal to 0.320, the chromaticity of the light-emitting element
2(G) falls within a chromaticity range in which x is more than or
equal to 0.130 and less than or equal to 0.250 and y is more than
0.710 and less than or equal to 0.810, and the chromaticity of the
light-emitting element 3(B1) falls within a chromaticity range in
which x is more than or equal to 0.120 and less than or equal to
0.170 and y is more than or equal to 0.020 and less than 0.060. The
light-emitting element 1(R) has x of more than 0.680, and thus
particularly has a better red chromaticity than the Digital Cinema
Initiatives (DCI-P3) standard, in which the chromaticity
coordinates (x, y) of red (R) are (0.680, 0.320); green (G),
(0.265, 0.690); and blue (B), (0.150, 0.060). The light-emitting
element 2(G) has y of more than 0.71, and thus particularly has a
better green chromaticity than the DCI-P3 standard and the NTSC
standard. In addition, the light-emitting elements 3(B1) and
4(B1.5) each have y of less than 0.06, and thus particularly has a
better blue chromaticity than the DCI-P3 standard.
[0282] Note that the chromaticities (x, y) of the light-emitting
elements 1(R), 2(G), 3(B1), and 4(B1.5) calculated using the values
of the light emission spectra shown in FIG. 19 are (0.693, 0.303),
(0.202, 0.744), (0.139, 0.056), and (0.160, 0.057), respectively.
Therefore, when the chromaticities of a combination of the
light-emitting elements 1(R), 2(G), and 3(B1) are calculated using
the light emission spectra, the BT.2020 area ratio is 86% and the
BT.2020 coverage is 84%. In addition, when the chromaticities of a
combination of the light-emitting elements 1(R), 2(G), and 4(B1.5)
are calculated using the light emission spectra, the BT.2020 area
ratio is 84% and the BT.2020 coverage is 82%.
Example 3
[0283] In this example, an element structure, a forming method, and
properties of a light-emitting element used in a display device of
one embodiment of the present invention will be described. Note
that FIG. 13 illustrates an element structure of a light-emitting
element described in this example, and Table 6 shows specific
structures. Chemical formulae of materials used in this example are
shown below. The color filters whose transmission spectra are shown
in FIG. 14 were used.
TABLE-US-00006 TABLE 6 First hole- Light- First hole- transport
emitting First First electrode injection layer layer layer (A)
electron-transport layer Symbol in FIG. 13 901 911a 912a 913a 914a
Light-emitting Ag--Pd--Cu ITSO PCPPn:MoOx PCPPn *1 cgDBCzPA NBphen
element 5(R) (200 nm) (110 nm) (1:0.5 10 nm) (10 nm) (10 nm) (15
nm) Light-emitting ITSO PCPPn:MoOx element 6(G) (45 nm) (1:0.5 20
nm) Light-emitting ITSO PCPPn:MoOx element 7(B1) (10 nm) (1:0.5
12.5 nm) Light-emitting ITSO PCPPn:MoOx element 8(B1.5) (110 nm)
(1:0.5 19 nm) First Light-emitting layer (B) electron- Charge
Second hole- First light- Second injection generation Second
hole-injection transport emitting light-emitting layer layer layer
layer layer layer Symbol in FIG. 13 915a 904 911b 912b 913(b1)
913(b2) (Reference) Light-emitting Li.sub.2O CuPc DBT3P-II:MoOx
BPAFLP *2 *3 Light-emitting element 5(R) (0.1 nm) (2 nm) (1:0.5 10
nm) (15 nm) element 5(R) Light-emitting Light-emitting element 6(G)
element 6(G) Light-emitting Light-emitting element 7(B1) element
7(B1) Light-emitting Light-emitting element 8(B1.5) element 8(B1.5)
Second Second electron-transport electron- layer injection layer
Second electrode Symbol in FIG. 13 914b 915b 903 CF Light-emitting
2mDBTBPDBq-II Nbphen LiF Ag:Mg ITO CF-R Light-emitting element 5(R)
(25 nm) (15 nm) (1 nm) (1:0.1 30 nm) (70 nm) element 5(R)
Light-emitting CF-G Light-emitting element 6(G) element 6(G)
Light-emitting CF-B Light-emitting element 7(B1) element 7(B1)
Light-emitting CF-B Light-emitting element 8(B1.5) element 8(B1.5)
*1 cgDBCzPA:1,6BnfAPrn-03 (1:0.03 25 nm) *2
2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm).sub.3] (0.8:0.2:0.06 20 nm) *3
2mDBTBPDBq-II:[Ir(dmdppr-P).sub.2(dibm)] (1:0.04 20 nm)
##STR00005## ##STR00006## ##STR00007## ##STR00008##
<<Formation of Light-Emitting Element>>
[0284] A light-emitting element in this example has the structure
illustrated in FIG. 13 in which the first electrode 901 is formed
over the substrate 900, the first EL layer 902a is formed over the
first electrode 901, the charge generation layer 904 is formed over
the first EL layer 902a, the second EL layer 902b is formed over
the charge generation layer 904, and the second electrode 903 is
formed over the second EL layer 902b as in Example 2. Note that a
light-emitting element 5 in this example is a light-emitting
element emitting mainly red light and referred to as a
light-emitting element 5(R). A light-emitting element 6 is a
light-emitting element emitting mainly green light and referred to
as a light-emitting element 6(G). A light-emitting element 7 and a
light-emitting element 8 are each a light-emitting element emitting
mainly blue light and are also referred to as a light-emitting
element 7(B1) and a light-emitting element 8(B1.5),
respectively.
[0285] In the light-emitting elements in this example, the
thicknesses of the layers formed at the time of forming the
elements are different from each other. However, the layers can be
formed using the same material and in the same manner as in Example
2; therefore, Example 2 can be referred to and description is
omitted in this example.
<<Operation Characteristics of Light-Emitting
Elements>>
[0286] Operation characteristics of the formed light-emitting
elements were measured. Note that the measurement was performed at
room temperature (in an atmosphere kept at 25.degree. C.). The
results are shown in FIG. 20, FIG. 21, FIG. 22, and FIG. 23. FIG.
24 shows light emission spectra when current at a current density
of 2.5 mA/cm.sup.2 was applied to the light-emitting elements. The
light emission spectra were measured with a multi-channel
spectrometer (PMA-12 produced by Hamamatsu Photonics K.K.). As
shown in FIG. 24, the light emission spectrum of the light-emitting
element 5(R) which emits red light has a peak around 635 nm, the
light emission spectrum of the light-emitting element 6(G) which
emits green light has a peak around 530 nm, and the light emission
spectra of the light-emitting elements 7(B1) and 8(B1.5) which emit
blue light have peaks around 464 nm and 453 nm, respectively. The
spectrum shapes were narrowed. In this example, the results of
measuring light emission obtained from a combination of
light-emitting elements and color filters are shown.
[0287] Next, the results of measuring the chromaticities (x, y) of
the light-emitting elements formed in this example (the
light-emitting element 5(R), the light-emitting element 6(G), and
the light-emitting element 7(B1)) with a luminance colorimeter
(BM-5A manufactured by TOPCON CORPORATION) are shown in Table 7
below. The chromaticity of the light-emitting element 5(R) was
measured at a luminance of approximately 650 cd/m.sup.2. The
chromaticity of the light-emitting element 6(G) was measured at a
luminance of approximately 1900 cd/m.sup.2. The chromaticity of the
light-emitting element 7(B1) was measured at a luminance of
approximately 140 cd/m.sup.2. Note that white light emission close
to D65 can be obtained by summing the luminance of R, the luminance
of G, and the luminance of B.
TABLE-US-00007 TABLE 7 x y Light-emitting 0.700 0.294 element 5(R)
Light-emitting 0.175 0.793 element 6(G) Light-emitting 0.142 0.039
element 7(B1)
[0288] On the basis of the results in Table 7, the BT.2020 area
ratio and the BT.2020 coverage were calculated using the
chromaticities (x, y) and were 97% and 95%, respectively.
[0289] The results of measuring the chromaticities (x, y) of the
light-emitting element 5(R), the light-emitting element 6(G), and
the light-emitting element 8(B1.5)) among the light-emitting
elements formed in this example with a luminance colorimeter are
shown in Table 8 below. The chromaticity of the light-emitting
element 5(R) was measured at a luminance of approximately 650
cd/m.sup.2. The chromaticity of the light-emitting element 6(G) was
measured at a luminance of approximately 1900 cd/m.sup.2. The
chromaticity of the light-emitting element 8(B1.5) was measured at
a luminance of approximately 170 cd/m.sup.2. Note that white light
emission close to D65 can be obtained by summing the luminance of
R, the luminance of G, and the luminance of B.
TABLE-US-00008 TABLE 8 x y Light-emitting 0.700 0.294 element 5(R)
Light-emitting 0.175 0.793 element 6(G) Light-emitting 0.153 0.046
element 8(B1.5)
[0290] On the basis of the results in Table 8, the BT.2020 area
ratio and the BT.2020 coverage were calculated using the
chromaticities (x, y) and were 95% and 93%, respectively. Even such
a structure having improved blue light emission efficiency can
achieve extremely wide-range color reproducibility.
[0291] The above results shows that, in this example, the
chromaticity of the light-emitting element 5(R) falls within a
chromaticity range in which x is more than 0.680 and less than or
equal to 0.720 and y is greater than or equal to 0.260 and less
than or equal to 0.320, the chromaticity of the light-emitting
element 6(G) falls within a chromaticity range in which x is more
than or equal to 0.130 and less than or equal to 0.250 and y is
more than 0.710 and less than or equal to 0.810, and the
chromaticity of the light-emitting element 7(B1) falls within a
chromaticity range in which x is more than or equal to 0.120 and
less than or equal to 0.170 and y is more than or equal to 0.020
and less than 0.060. The light-emitting element 6(G) has y of more
than 0.71, and thus particularly has a better green chromaticity
than the DCI-P3 standard and the NTSC standard. In addition, the
light-emitting elements 7(B1) and 8(B1.5) each have y of less than
0.06, and thus particularly has a better blue chromaticity than the
DCI-P3 standard.
[0292] Note that the chromaticities (x, y) of the light-emitting
elements 5, 6, 7, and 8 calculated using the values of the light
emission spectra shown in FIG. 24 are (0.696, 0.300), (0.185,
0.760), (0.140, 0.048), and (0.154, 0.056), respectively.
Therefore, when the chromaticities of a combination of the
light-emitting elements 5(R), 6(G), and 7(B1) are calculated using
the light emission spectra, the BT.2020 area ratio is 91% and the
BT.2020 coverage is 89%. In addition, when the chromaticities of a
combination of the light-emitting elements 5(R), 6(G), and 8(B1.5)
are calculated using the light emission spectra, the BT.2020 area
ratio is 88% and the BT.2020 coverage is 86%.
Reference Example
[0293] In this reference example, a synthesis method of bis
{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2--
pyrazinyl-N]phenyl-.kappa.C}(2,2,6,6-tetramethyl-3,5-heptanedionato-.kappa-
..sup.2O,O')iridium(III) (abbreviation:
[Ir(dmdppr-dmCP).sub.2(dpm)]) (Structural formula (100)), which is
an organometallic complex and a light-emitting material that can be
used for the light-emitting layer in the light-emitting element of
one embodiment of the present invention, is described. The
organometallic complex has a peak of a light emission spectrum at
more than or equal to 600 nm and less than or equal to 700 nm. The
structure of [Ir(dmdppr-dmCP).sub.2(dpm)] is shown below.
##STR00009##
Step 1: Synthesis of 5-hydroxy-2,3-(3,5-dimethylphenyl)pyrazine
[0294] First, 5.27 g of 3,3',5,5'-tetramethylbenzyl, 2.61 g of
glycinamide hydrochloride, 1.92 g of sodium hydroxide, and 50 mL of
methanol were put into a three-necked flask equipped with a reflux
pipe, and the air in the flask was replaced with nitrogen. After
that, the mixture was stirred at 80.degree. C. for 7 hours to cause
a reaction. Then, 2.5 mL of 12M hydrochloric acid was added thereto
and stirring was performed for 30 minutes. Then, 2.02 g of
potassium bicarbonate was added, and stirring was performed for 30
minutes. After the resulting suspension was subjected to suction
filtration, the obtained solid was washed with water and methanol
to give an objective pyrazine derivative as milky white powder in a
yield of 79%. A synthesis scheme of Step 1 is shown in (a-1).
##STR00010##
Step 2: Synthesis of 5,6-bis(3,5-dimethylphenyl)pyrazin-2-yl
trifluoromethanesulfonate
[0295] Next, 4.80 g of 5-hydroxy-2,3-(3,5-dimethylphenyl)pyrazine
which was obtained in Step 1, 4.5 mL of triethylamine, and 80 mL of
dehydrated dichloromethane were put into a three-necked flask, and
the air in the flask was replaced with nitrogen. The flask was
cooled down to -20.degree. C. Then, 3.5 mL of
trifluoromethanesulfonic anhydride was dropped therein, and
stirring was performed at room temperature for 17.5 hours. After
that, the flask was cooled down to 0.degree. C. Then, 0.7 mL of
trifluoromethanesulfonic anhydride was further dropped therein, and
stirring was performed at room temperature for 22 hours to cause a
reaction. To the reaction solution, 50 mL of water and 5 mL of 1M
hydrochloric acid were added and then, dichloromethane was added,
so that a substance contained in the reaction solution was
extracted in the dichloromethane. A saturated aqueous solution of
sodium hydrogencarbonate and saturated saline were added to this
dichloromethane for washing. Then, magnesium sulfate was added
thereto for drying. After being dried, the solution was filtered,
and the filtrate was concentrated and the obtained residue was
purified by silica gel column chromatography using
toluene:hexane=1:1 (volume ratio) as a developing solvent, to give
an objective pyrazine derivative as yellow oil in a yield of 96%. A
synthesis scheme of Step 2 is shown in (a-2).
##STR00011##
Step 3: Synthesis of
5-(4-cyano-2,6-dimethylphenyl)-2,3-bis(3,5-dimethylphenyl)pyrazine
(abbreviation: Hdmdppr-dmCP)
[0296] Next, 2.05 g of 5,6-bis(3,5-dimethylphenyl)pyrazin-2-yl
trifluoromethanesulfonate which was obtained in Step 2, 1.00 g of
4-cyano-2,6-dimethylphenylboronic acid, 3.81 g of tripotassium
phosphate, 40 mL of toluene, and 4 mL of water were put into a
three-necked flask, and the air in the flask was replaced with
nitrogen. The mixture in the flask was degassed by being stirred
under reduced pressure, 0.044 g of
tris(dibenzylideneacetone)dipalladium(0) and 0.084 g of
tris(2,6-dimethoxyphenyl)phosphine were then added thereto, and the
mixture was refluxed for 7 hours. Water was added to the reaction
solution, and then toluene was added, so that the material
contained in the reaction solution was extracted in the toluene.
Saturated saline was added to the toluene solution, and the toluene
solution was washed. Then, magnesium sulfate was added thereto for
drying. After being dried, the solution was filtered, and the
filtrate was concentrated and the obtained residue was purified by
silica gel column chromatography using hexane:ethyl acetate=5:1
(volume ratio) as a developing solvent, to give an objective
pyrazine derivative Hdmdppr-dmCP as white powder in a yield of 90%.
A synthesis scheme of Step 3 is shown in (a-3).
##STR00012##
Step 4: Synthesis of
di-.mu.-chloro-tetrakis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3--
(3,5-dimethylphenyl)-2-pyrazinyl-.kappa.N]phenyl-.kappa.C}diiridium(III)
(abbreviation: [Ir(dmdppr-dmCP).sub.2Cl].sub.2)
[0297] Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.74 g of
Hdmdppr-dmCP (abbreviation) which was obtained in Step 3, and 0.60
g of iridium chloride hydrate (IrCl.sub.3.times.H.sub.2O) (produced
by FURUYA METAL Co., Ltd.) were put into a recovery flask equipped
with a reflux pipe, and the air in the flask was replaced with
argon. After that, microwave irradiation (2.45 GHz, 100 W) was
performed for an hour to cause a reaction. The solvent was
distilled off, and then the obtained residue was suction-filtered
and washed with hexane to give a dinuclear complex
[Ir(dmdppr-dmCP).sub.2Cl].sub.2 as brown powder in a yield of 89%.
A synthesis scheme of Step 4 is shown in (a-4).
##STR00013##
<Step 5: Synthesis of bis
{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2--
pyrazinyl-N]phenyl-.kappa.C}(2,2,6,6-tetramethyl-3,5-heptanedionato-.kappa-
..sup.2O,O')iridium(III) (abbreviation:
[Ir(dmdppr-dmCP).sub.2(dpm)])>
[0298] Furthermore, 30 mL of 2-ethoxyethanol, 0.96 g of
[Ir(dmdppr-dmCP).sub.2Cl].sub.2 that is the dinuclear complex
obtained in Step 4, 0.26 g of dipivaloylmethane (abbreviation:
Hdpm), and 0.48 g of sodium carbonate were put into a recovery
flask equipped with a reflux pipe, and the air in the flask was
replaced with argon. After that, microwave irradiation (2.45 GHz,
100 W) was performed for 60 minutes. Moreover, 0.13 g of Hdpm was
added thereto, and the reaction container was subjected to
microwave irradiation (2.45 GHz, 120 W) for 60 minutes to cause a
reaction. The solvent was distilled off, and the obtained residue
was purified by silica gel column chromatography using
dichloromethane and hexane as a developing solvent in a volume
ratio of 1:1. The obtained residue was further purified by silica
gel column chromatography using dichloromethane as a developing
solvent, and then recrystallization was performed with a mixed
solvent of dichloromethane and methanol to give
[Ir(dmdppr-dmCP).sub.2(dpm)] which is the organometallic complex as
red powder in a yield of 37%. By a train sublimation method, 0.39 g
of the obtained red powder was purified. The sublimation
purification was carried out at 300.degree. C. under a pressure of
2.6 Pa with a flow rate of an argon gas at 5 mL/min. After the
purification by sublimation, a red solid, which was an objective
substance, was obtained in a yield of 85%. A synthetic scheme of
Step 5 is shown in (a-5).
##STR00014##
[0299] Note that results of the analysis of the red powder obtained
in Step 5 by nuclear magnetic resonance spectrometry (1H-NMR) are
given below. These results revealed that
[Ir(dmdppr-dmCP).sub.2(dpm)], which is the organometallic complex
represented by Structural Formula (100), was obtained in this
synthesis example.
[0300] .sup.1H-NMR. .delta. (CD.sub.2Cl.sub.2): 0.91 (s, 18H), 1.41
(s, 6H), 1.95 (s, 6H), 2.12 (s, 12H), 2.35 (s, 12H), 5.63 (s, 1H),
6.49 (s, 2H), 6.86 (s, 2H), 7.17 (s, 2H), 7.34 (s, 4H), 7.43 (s,
4H), 8.15 (s, 2H).
EXPLANATION OF REFERENCE
[0301] 100L: liquid crystal element, 100E: light-emitting element,
101L, 101E: first electrode, 102L, 102E: second electrode, 103L:
liquid crystal layer, 103E: EL layer, 104: alignment film, 105L:
color filter, 105E: color filter, 106: polarizing layer, 107L,
107E, 108: light, 200R, 200R', 200R'': light-emitting element
(red), 200G, 200G', 200G'': light-emitting element (green), 200B,
200B', 200B'': light-emitting element (blue), 201: first electrode,
202, 202': second electrode, 203R, 203G, 203B, 203W: EL layer,
204R, 204G, 204B: EL layer, 207R, 207R', 207R'': light emission
(red), 207G, 207G', 207G'': light emission (green), 207B, 207B',
207B'': light emission (blue), 301: first electrode, 302: second
electrode, 303: EL layer, 303a, 303b: EL layer, 304: charge
generation layer, 311, 311a, 311b: hole-injection layer, 312, 312a,
312b: hole-transport layer, 313, 313a, 313b: light-emitting layer,
314, 314a, 314b: electron-transport layer, 315, 315a, 315b:
electron-injection layer, 401: liquid crystal element, 402:
light-emitting element, 403: conductive layer, 404: opening, 405:
second substrate, 407: conductive layer, 408: conductive layer,
409: liquid crystal layer, 410: first element layer (display
element layer), 411: second element layer (display element layer),
412: third element layer (driving element layer), 415: alignment
film, 416: alignment film, 418: color filter, 419: insulating
layer, 420: conductive layer, 421: conductive layer, 422: EL layer,
423: color filter, 424: polarizing layer, 425: transistor, 426:
transistor, 427: terminal portion, 501: circuit (G), 502: circuit
(S), 503: display portion, 504: pixel, 505: conductive film, 506:
position, 507: opening, 510: liquid crystal element, 511:
light-emitting element, 900: substrate, 901: first electrode, 902a:
first EL layer, 902b: second EL layer, 903: second electrode, 904:
charge generation layer, 905: substrate, 906: color filter, 911a:
first hole-injection layer, 911b: second hole-injection layer,
912a: first hole-transport layer, 912b: second hole-transport
layer, 913a: light-emitting layer (A), 913b: light-emitting layer
(B), 913(b1): first light-emitting layer (B1), 913(b2): second
light-emitting layer (B2), 914a: first electron-transport layer,
914b: second electron-transport layer, 915a: first
electron-injection layer, 915b: second electron-injection layer,
5101: light, 5102: wheel, 5103: door, 5104: display portion, 5105:
steering wheel, 5106: gear lever, 5107: seat, 5108: inner rearview
mirror, 7100: television device, 7101: housing, 7103: display
portion, 7105: stand, 7107: display portion, 7109: operation key,
7110: remote controller, 7201: main body, 7202: housing, 7203:
display portion, 7204: keyboard, 7205: external connection port,
7206: pointing device, 7302: housing, 7304: display portion, 7305:
icon indicating time, 7306: another icon, 7311: operation button,
7312: operation button, 7313: connection terminal, 7321: band,
7322: clasp, 7400: mobile phone, 7401: housing, 7402: display
portion, 7403: operation button, 7404: external connection portion,
7405: speaker, 7406: microphone, 7407: camera, 7500(1), 7500(2):
housing, 7501(1), 7501(2): first screen, 7502(1), 7502(2): second
screen, 7601: main body, 7602: display portion, 7603: arm, 9310:
mobile information terminal, 9311: display portion, 9312: display
region, 9313: hinge, 9315: housing
[0302] This application is based on Japanese Patent Application
serial No. 2016-159793 filed with Japan Patent Office on Aug. 17,
2016, the entire contents of which are hereby incorporated by
reference.
* * * * *