U.S. patent application number 10/879489 was filed with the patent office on 2005-01-13 for light-emitting device.
Invention is credited to Abe, Hiroko, Nomura, Ryoji, Yamazaki, Shunpei, Yukawa, Mikio.
Application Number | 20050008052 10/879489 |
Document ID | / |
Family ID | 33562309 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050008052 |
Kind Code |
A1 |
Nomura, Ryoji ; et
al. |
January 13, 2005 |
Light-emitting device
Abstract
The conventional light-emitting element formed by an
electroluminescent material has a problem due to poor color purity
of light emission. Accordingly, it is an object of the present
invention to provide a high luminance and high efficiency
light-emitting device formed by an organic compound material. The
invention provides a light-emitting device in which an organic
compound layer that emits light having an emission peak with a
half-band width of at most 10 nm upon applying current is
interposed between a pair of electrodes is provided. The variation
of emission peak intensity depending on a current density can be
sorted by two linear regions with different gradients. A region of
a sharp gradient is at a higher current density side compared to a
region of a slow gradient. TFTs are provided to each pixel in order
to perform active matrix driving.
Inventors: |
Nomura, Ryoji; (Yamato,
JP) ; Abe, Hiroko; (Tokyo, JP) ; Yukawa,
Mikio; (Atsugi, JP) ; Yamazaki, Shunpei;
(Tokyo, JP) |
Correspondence
Address: |
ERIC ROBINSON
PMB 955
21010 SOUTHBANK ST.
POTOMAC FALLS
VA
20165
US
|
Family ID: |
33562309 |
Appl. No.: |
10/879489 |
Filed: |
June 30, 2004 |
Current U.S.
Class: |
372/39 ;
257/79 |
Current CPC
Class: |
H01L 27/322 20130101;
H01L 27/3244 20130101; H01L 51/5265 20130101; H01L 2251/558
20130101; H01L 2251/533 20130101; H01L 2251/5315 20130101 |
Class at
Publication: |
372/039 ;
257/079 |
International
Class: |
H01S 003/14; H01L
033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2003 |
JP |
2003-189914 |
Claims
What is claimed is:
1. A light-emitting device comprising an organic compound layer
capable of emitting non coherent light and coherent light.
2. A light-emitting device comprising an organic compound layer
capable of emitting luminescence and laser light.
3. A light-emitting device comprising an organic compound layer
interposed between a pair of electrodes, wherein the organic
compound layer emits light having an emission peak with a half-band
width of at most 10 nm.
4. A light-emitting device comprising an organic compound layer
formed between a pair of substrates, wherein the organic compound
layer emits light with an emission spectrum having a plurality of
peaks, and the organic compound layer is formed to have a thickness
of a half wavelength or integral multiple of the half wavelength in
order to form a stationary wave with respect to light at a
specified wavelength in the emission spectrum.
5. A light-emitting device comprising: light-emitting elements
arranged in a matrix form, each comprising an organic compound
layer capable of emitting coherent light and non coherent light;
and a transistor connected to one of the light-emitting elements
for controlling light emission from said one of the light-emitting
elements.
6. A light-emitting device comprising: light-emitting elements
arranged in a matrix form, each comprising an organic compound
layer capable of emitting luminescence and laser light; and a
transistor connected to one of the light-emitting elements for
controlling light emission from said one of the light-emitting
elements.
7. A light-emitting device comprising: light-emitting elements
arranged in a matrix form, each comprising a pair of electrodes and
an organic compound layer disposed therebetween; and a transistor
connected to one of the light-emitting elements for controlling
light emission from said one of the light-emitting elements,
wherein the organic compound layer emits light having an emission
peak with a half-band width of at most 10 nm.
8. A light-emitting device comprising: light-emitting elements
arranged in a matrix form, each comprising an organic compound
layer; and a transistor connected to one of the light-emitting
elements for controlling light emission from said one of the
light-emitting elements, wherein the light-emitting elements are
formed between a pair of substrates, the organic compound layer
emits light with an emission spectrum having a plurality of peaks,
and the organic compound layer is formed to have a thickness of a
half wavelength or integral multiple of the half wavelength in
order to form a stationary wave with respect to light at a
specified wavelength in the emission spectrum.
9. The light-emitting device according to claim 1, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
10. The light-emitting device according to claim 2, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
11. The light-emitting device according to claim 3, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
12. The light-emitting device according to claim 4, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
13. The light-emitting device according to claim 5, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
14. The light-emitting device according to claim 6, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
15. The light-emitting device according to claim 7, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
16. The light-emitting device according to claim 8, wherein the
light-emitting device is used for a display portion of an
electronic apparatus selected from the group consisting of TV set,
video camera, computer, sound reproduction device, digital camera,
and cellular phone.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a light-emitting device including
an organic compound material as a light emitting medium used for
displaying images, a lighting, and the like.
[0003] 2. Related Art
[0004] As a light-emitting device available in full color image
display by arranging a plurality of light-emitting pixels in a
matrix configuration (rows and columns), a light-emitting device
available in full color display by combining electroluminescent
(EL) elements, each of which emits light in different emission
color (typically, red (R), green (G), and blue (B)) per pixel is
well known. However, there has been a problem that emission
lifetime varies by emission color. Further, there has been a
problem that a precision technique for patterning is required.
[0005] As another method, a method of combining a blue
light-emitting element and a color conversion layer can be
nominated. There has been also a problem that high practical color
conversion efficiency cannot be obtained according to this method.
In addition, it has been problematic that a high efficiency blue
light-emitting element has been required.
[0006] There is also a method that a white light-emitting element
and a color filter are combined; however, there has been a problem
that the usability of light emission is deteriorated, and so a high
luminance white light-emitting element is required.
SUMMARY OF THE INVENTION
[0007] The problem in the above mentioned conventional techniques
is caused by poor color purity of light emission of a
light-emitting element formed by an electroluminescent material. In
view of the foregoing, it is an object of the present invention to
provide a high luminance and high efficiency light-emitting device
formed by organic compound materials.
[0008] The present invention is to provide a light-emitting device
having a feature that an organic compound material is used as a
light emitting medium, and coherent light and non coherent light
from the organic compound material, in other words, luminescence
and laser light are coupled out simultaneously or respectively.
According to the invention, a material that produces
electroluminescence is used. In order to emit laser light in
addition to the electroluminescence, a plurality of different
organic compound materials is used to be stacked in consideration
of the wavelength. The thickness of each layer and the lamination
configuration are determined for different purposes.
[0009] As used in the following, the term "organic compound layer"
is a generic term used to refer to a thin film containing mainly
organic compounds interposed between a pair of electrodes. An
organic compound layer is formed to be interposed between a pair of
electrodes. An organic compound layer is preferably formed by a
plurality of layers, each of which has different carrier
transportation properties. Moreover, a light-emitting layer is
included in the organic compound layer. An organic compound layer
is preferably formed to have a resonator structure interposed
between reflective layers.
[0010] In a light-emitting device according to the present
invention, a plurality of layers are stacked as an organic compound
layer so as to emit both coherent light and non coherent light by
applying current through the organic compound layer interposed
between a pair of electrodes.
[0011] The light-emitting device is preferably formed to have a
so-called resonator structure, in which a reflector is provided to
either or both of surfaces of the organic compound layer inside the
pair of electrodes. That is, a reflector is preferably provided to
either or both of surfaces of the organic compound layer inside the
pair of electrodes so that a stationary wave is produced with
respect to light at a specified wavelength emitted from the organic
compound layer. Moreover, the organic compound layer is preferably
formed to have a thickness of 1/2 time as a wavelength of laser
oscillation (half wavelength) or integral multiple of the same.
[0012] A light-emitting device used in the invention has a
plurality of emission peaks. In the light-emitting device, an
organic compound layer emitting light having an emission peak with
a half-band width of at most 10 nm is interposed between a pair of
electrodes.
[0013] Further, the light-emitting device is preferably formed to
have a so-called resonator structure, in which a reflector is
provided to either or both of surfaces of the organic compound
layer inside the pair of electrodes. That is, a reflector is
preferably provided to either or both of surfaces of the organic
compound layer inside the pair of electrodes so that a stationary
wave is produced with respect to light at the wavelength determined
by the film thickness. Moreover, the organic compound layer is
preferably formed to have a thickness of 1/2 time of a wavelength
of laser oscillation, that is, half wavelength, or integral
multiple of the same.
[0014] An organic compound layer used in the invention has the
configuration composed of a hole injecting layer, a hole
transporting layer, a light-emitting layer, an electron
transporting layer, an electron injecting layer, and the like. A
material having hole transportation properties such as hole
mobility is referred to a hole injecting layer or a hole
transporting layer. A material having electron transportation
properties such as electron mobility is referred to as an electron
injecting layer. Though the hole transporting layer and the hole
injecting layer are described respectively, they are the same in
terms that they have the common property of hole transportation as
most important property. As a matter of convenience, a layer
adjacent to an anode is referred to as a hole injecting layer, and
a layer adjacent to a light-emitting layer is referred to as a hole
transporting layer. Further, a layer adjacent to a cathode is
referred to as an electron injecting layer, a layer adjacent to a
light-emitting layer is referred to as an electron transporting
layer. The light-emitting layer may serve as the electron
transporting layer, and so it can be referred to as a
light-emitting electron transporting layer. In addition, the
light-emitting layer may serve as a hole injecting layer, a hole
transporting layer, an electron injecting layer, an electron
transporting layer, and the like. Further, the light-emitting layer
can be formed by metal complexes, organic dye materials, various
derivatives, or the like in order to vary emission color.
[0015] In a lamination configuration of such an organic compound
layer, electrons injected from a cathode and holes injected from an
anode are recombined to form an exciton in the light-emitting
layer, and the exciton radiates light while they are back to the
ground state. Light emission is obtained by so-called
electroluminescence from the exciton. In a light-emitting device
according to the invention, a hole transporting layer is formed on
a light-emitting layer so as to emit light having an emission peak
with a half-band width of at most 10 nm at a central wavelength in
a shorter wavelength side than a wavelength band of the light that
is generated in the light-emitting layer upon applying current.
Thus, it is possible to induce laser light.
[0016] The invention is to provide a light-emitting device in which
an organic compound layer that emits light having an emission peak
with a half-band width of at most 10 nm upon applying current is
interposed between a pair of electrodes. The variation of emission
peak intensity depending on a current density can be sorted by two
linear regions with different gradients. A region of a sharp
gradient is at a higher current density side compared to a region
of a slow gradient in the two linear regions with different
gradients.
[0017] The invention is to provide a light-emitting device in which
light-emitting elements provided with the above mentioned organic
compound layer are arranged in a matrix configuration to form a
pixel portion, and transistors for controlling light generated in
the light-emitting elements are connected to the light-emitting
elements.
[0018] According to the invention, a high luminance and high
efficiency light-emitting device can be provided that couples out
coherent light and non coherent light, in other words, luminescence
and laser light in order to utilize the out-coupled light.
[0019] These and other objects, features and advantages of the
present invention will become more apparent upon reading of the
following detailed description along with the accompanied
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A is a perspective view, and FIGS. 1B and 1C are
longitudinal cross-sectional views for showing a structure of a
light-emitting device according to Embodiment mode of the present
invention;
[0021] FIG. 2 is an explanatory top view for showing a structure of
a light-emitting device according to Embodiment mode of the
invention;
[0022] FIG. 3 is an explanatory cross-sectional view for showing a
structure of a light-emitting device according to Embodiment mode
of the invention;
[0023] FIG. 4 is an explanatory cross-sectional view for showing a
structure of a light-emitting device according to Embodiment mode
of the invention;
[0024] FIG. 5 is an explanatory cross-sectional view for showing a
structure of a light-emitting device according to Embodiment mode
of the invention;
[0025] FIG. 6 is an explanatory cross-sectional view for showing a
structure of a light-emitting device according to Embodiment of the
invention;
[0026] FIGS. 7A and 7B are graphs for showing a current density
dependency, which is normalized by a maximum value of emission
intensity, of emission spectra of a light-emitting element
manufactured according to Embodiment;
[0027] FIG. 8 is a graph for showing an emission spectrum at
current density of 120 mA/cm.sup.2 of a light-emitting element
manufactured according to Embodiment; and
[0028] FIGS. 9A to 9G are views for showing examples of electric
appliances completed by using a light-emitting device according to
the invention.
DESCRIPTION OF THE INVENTION
EMBODIMENT MODE
[0029] Embodiment Mode of the invention is a light-emitting device
in which an organic compound layer having a plurality of emission
peaks is interposed between a pair of electrodes. One feature of
the light-emitting device is producing light emission having at
least one emission peak with a half-band width of at most 10 nm. An
emission peak with a narrow half band width can be realized by
utilizing an organic compound material and a lamination
configuration as follows.
[0030] In an organic electroluminescent element, a large number of
carriers are supplied to an organic thin film. When applying
current, the number of carriers presented in the element and the
number of molecules presented in the element becomes approximately
the same, or the number of carriers becomes larger than that of
molecules. Therefore, the number of molecules with no carriers,
that is, the number of molecules in a ground state, is smaller than
that of molecules with carriers. When an excitation state is
produced due to carrier recombination in this state, it becomes
possible to create the state that the number of molecules in the
excitation state is relatively larger than that of molecules in a
ground state. Hence, it can be expected that population inversion
can be sufficiently produced by applying a small amount of current.
When the thickness of an organic film serving as a resonator for
the element is formed to be integral multiple of a half wavelength,
it can be expected that laser oscillation can be realized by light
amplification due to induced radiation and resonation generated
from the state of population inversion.
[0031] FIG. 4 shows a structure of a top emission type
light-emitting element in which laser light is emitted from a top
surface of a substrate. In FIG. 4, reference numeral 41 denotes a
substrate, which is formed by any materials. For example, not only
glass, quartz, plastic, but also a flexible substrate such as paper
or cloth can be used. Of course, the substrate is not required to
be transparent.
[0032] An anode 42 has a function of injecting holes to an organic
compound layer. In addition, the anode 42 serves as a reflecting
mirror. Therefore, a material that has poor absorption properties
of visible light, high reflectivity, and large work functions (at
least 4.0 eV) is required. As a material that meets the foregoing
conditions, Ag, Pt, Au, or the like can be used. In addition, since
the electrode is used as a reflecting mirror, the electrode is
required to have the thickness that does not transmit visible
light. Specifically, the electrode may be formed to have a
thickness of from several ten nm to several hundreds nm.
[0033] An organic compound layer which emits light by applying
current is formed over the anode 42. Specifically, a hole injecting
layer 43, a hole transporting layer 44, a light-emitting layer 45,
and an electron transporting layer 46 and an electron injecting
layer 47 are formed.
[0034] As the hole injecting layer 43, materials having small
ionization potential, which are classified broadly into metal
oxides, low molecular organic compounds, and high molecular
compounds are used. As examples of the metal oxides, vanadium
oxides, molybdenum oxides, ruthenium oxides, aluminum oxides, and
the like can be used. As examples of the low molecular organic
compounds, starburst amine typified by m-MTDATA,
metallophthalocyanine, and the like can be used. As examples of the
high molecular compounds, conjugated polymer such as polyaniline or
polythiophene derivatives can be nominated. By using the foregoing
materials as a hole injecting layer, a hole injecting barrier is
reduced to inject holes effectively.
[0035] As a typical example of the hole transporting layer 44,
known materials such as aromatic amine can be preferably used. For
example, 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl
(abbreviated .alpha.-NPD),
4,4',4"-tris(N,N-diphenyl-amino)-triphenyl amine (abbreviated
TDATA), or the like can be used. As high molecular materials,
poly(vinyl carbazole) having excellent hole transportation
properties can be used.
[0036] As the light-emitting layer 45, a metal complex such as
tris(8-quinolinolate) aluminum (abbreviated Alq.sub.3),
tris(4-methyl-8-quinolinolate)aluminum (abbreviated Almq.sub.3),
bis(10-hydroxybenzo[.eta.]-quinolinato)beryllium (abbreviated
BeBq.sub.2),
bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminu- m
(abbreviated BAlq), bis [2-(2-hydroxyphenyl)-benzooxazolate]zinc
(abbreviated Zn(BOX).sub.2), bis
[2-(2-hydroxyphenyl)-benzothiazolate]zin- c (abbreviated
Zn(BTZ).sub.2), or the like can be used. Alternatively, various
types of fluorescent dye can be used. Further, phosphorescent
materials such as a platinum octaethylporphyrin complex, a
tris(phenylpyridine)iridium complex, or a
tris(benzylidene-acetonato)phen- anthrene europium complex can be
efficiently used. Since phosphorescent materials have longer
excitation lifetime than that of fluorescent materials, population
inversion, that is, the state in which the number of molecules in
an excited state is larger that that in a ground state, becomes to
be formed easily, which is essential to laser oscillation.
[0037] In addition, light-emitting materials can be used as dopant
in the foregoing light-emitting layer. Therefore, a material having
larger ionization potential and band gap than those of the
light-emitting material can be used as a host material, and a small
amount of the foregoing light-emitting material (approximately from
0.001 to 30%) can be mixed into the host material.
[0038] As the electron transporting layer 46, a metal complex
having a quinoline skeleton or a benzoquinoline skeleton, or a
mixed ligand complex thereof typified by
tris(8-quinolinolate)aluminum (abbreviated Alq.sub.3) is preferably
used. Alternatively, an oxadiazole derivative such as
2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviated
PBD), or 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-y-
l]benzene (abbreviated OXD-7), a triazole derivative such as
3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole
(abbreviated TAZ), or
3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphe-
nylyl)-1,2,4-triazole (abbreviated p-EtTAZ), phenanthroline
derivatives such as bathophenanthroline (abbreviated BPhen), or
bathocuproin (abbreviated BCP) can be used.
[0039] As the electron injecting layer 47, an alkali metal or
alkaline earth metal salt such as calcium fluoride, lithium
fluoride, or cesium bromide can be used. The cathode 48 is formed
thereover. The cathode 48 may be formed by a metal having small
work functions, an alloy, an electrical conductive compound, and
mixture of the foregoing materials, each of which is used for the
general organic electroluminescent elements. As specific examples
of the cathode material, an element of group 1 or 2 in the periodic
table, that is, an alkali metal such as Li, Cs, or the like; alkali
earth metal such as Mg, Ca, Sr, or the like; an alloy containing
the foregoing materials (Mg/Ag, Al/Li); or a transition metal
containing a rare earth metal can be used. Alternatively, the
cathode 48 can be formed by stacking a metal such as Al, Ag, or ITO
(including alloys) with the foregoing materials. In addition, a
resonator structure is required between the anode and the reflector
over the cathode in order to resonate light emission obtained from
a light-emitting layer in this embodiment mode. Therefore, as a
cathode material, a metal having poor absorption of visible light
and high reflectance is preferably used. Specifically, Al, Mg, or
an alloy of Al or Mg is preferably used.
[0040] The foregoing organic materials can be applied with either
wet or dry process. In case of using high molecular materials, spin
coating, ink jetting, dip coating, printing, or the like can be
appropriately used. On the other hand, in case of using low
molecular materials, not only dip coating or spin coating, but also
vapor deposition can be used. The anode material and the cathode
material may be applied with vapor deposition, sputtering, or the
like.
[0041] The most important thing is an interval between the cathode
and the reflecting mirror over the anode. The interval is required
to be integral multiple of a half wavelength for forming a
stationary wave to amplify light. For example, in order to amplify
light at 400 nm, an interval at least 200 nm is required.
Similarly, in order to amplify light at 800 nm, an interval of 400
nm is required. The emission wavelength of the foregoing organic
light-emitting materials is mainly in a visible light region.
Therefore, in order to amplify the visible light defined as from
400 to 800 nm, the interval between the reflector mirror and the
cathode 48, that is, the thickness of a functional layer is
required to have a thickness of at least 200 nm. In addition, since
it should consider that light speed is less for the refraction
index of a material, it is required that the value obtained by
multiplying the thickness by refraction index is at least 200
nm.
[0042] The cathode 48 is formed to have transmittance of from 50 to
95% for the wavelength of laser oscillation. The cathode 48 may be
formed to have a thickness of from 5 to 20 nm in case of being
formed by MgAg alloys. Alternatively, MgAg alloys having excellent
electron injection properties can be stacked directly instead of
forming the electron injecting layer 47. In this instance, since
laser light is emitted from a top surface, the cathode 48 serves as
an output mirror. Accordingly, the cathode is formed to have
transmittance of from 50 to 95% for the wavelength of laser
oscillation. For example, an MgAg alloy is formed to have a
thickness of from 5 to 20 nm.
[0043] FIG. 5 shows the state that a reflecting mirror is located
over the underside of a transparent electrode. Therefore, the
thickness of an organic compound layer can be reduced and laser
light can be oscillated from the top surface of a substrate by the
structure in which the transparent electrode is incorporated into a
part of a resonator.
[0044] In FIG. 5, a substrate 51 can be formed by any materials.
For example, not only glass, quartz, plastic, but also a flexible
substrate such as paper or cloth can be used. Of course, the
substrate is not required to be transparent. A reflecting mirror 52
is provided over the substrate 51. As the reflecting mirror 52, a
material that has high reflectivity and poor absorption properties
for visible light is selected. Specifically, metals such as Al, Ag,
or the like; alloys containing mainly the foregoing metals; or a
laminated film of derivatives such as SiO.sub.2, TiO.sub.2, or the
like can be used. In a derivative laminated film, the thickness of
each layer is determined so as to reflect selectively light with an
oscillation wavelength. The derivative laminated film is formed by
stacking some layers required for total reflection. An electrode 53
is formed over the reflecting mirror 52. The electrode 53 is
required to inject holes to an organic compound layer and have high
transparency. For the electrode 53, a transparent electrode such as
ITO, TiN, or the like is preferably used.
[0045] Over the electrode 53, the same structure as that of an
organic electroluminescent element that emits light upon applying
current. That is, a hole injecting layer 54, a hole transporting
layer 55, a light-emitting layer 56, and an electron transporting
layer 57 are formed. These layers may be formed by the foregoing
materials. In the hole injecting layer 54, the hole transporting
layer 55 and the electron transporting layer 57, a layer that does
not contribute light emission is not necessarily formed. The
electron injecting layer 58 is generally formed over the electron
transporting layer 57. An organic compound doped with an alkali
metal such as Li, Ce, or the like is preferably used. Thereafter, a
cathode 59 is formed. The cathode 59 may be formed by the foregoing
materials. Alternatively, MgAg alloys having excellent electron
injection properties can be stacked directly instead of forming the
electron injecting layer 58. In this instance, since laser light is
emitted from a top surface, the cathode 59 serves as an output
mirror. Accordingly, the cathode is formed to have transmittance of
from 50 to 95% for the wavelength of laser oscillation. For
example, an MgAg alloy is formed to have a thickness of from 5 to
20 nm.
[0046] By applying current to thus formed light-emitting element, a
part of light amplified from the organic compound layer resonates
between the cathode and the anode, and a stationary wave is formed.
Here, the resonator is formed to have a thickness including the
thickness of the transparent electrode. Accordingly, the thickness
of the organic compound layer can be reduced. Hence, light can be
emitted at low voltage. Accordingly, laser can be oscillated at low
voltage and electroluminescence can be emitted simultaneously.
[0047] A light-emitting device using the above described
light-emitting element is explained with reference to FIGS. 1 and
2. A light-emitting device according to this embodiment mode uses
the above described light-emitting element to create a display by
using non coherent laser light and coherent laser light due to
fluorescence and phosphorescence upon applying an electric field.
FIG. 1A is a perspective view for showing the structure of the
light-emitting device without an external circuit or the like. FIG.
1B is a cross-sectional view of FIG. 1A taken along the line A-A'.
FIG. 1C is a cross-sectional view of FIG. 1A taken along the line
B-B'.
[0048] The light-emitting device has a element substrate 10
installed with an image display portion 12, a scanning line drive
circuit 13, a data line drive circuit 14, an input terminal unit
15, and the like. The element substrate 10 is fixed to an opposing
substrate 11 provided with a color filter 18 by sealing agent
19.
[0049] As the element substrate 10, glass, quartz, plastic,
semiconductor, or the like is used. As the opposing substrate 11,
glass, quartz, plastic, or the like transmitting at least visible
light is used as a member. The substrate can be formed into any
shape such as a plate, a film, or a sheet in a single layer
structure or a laminated layer structure. As glass, a transparent
glass such as a commercially available non-alkali glass is
preferably used. As a glass substrate, an alkali glass coated with
a silicon oxide film can be used. In case of using plastic,
polyethylenenaphthalate (PEN), polyethylene terephthalate (PET),
polyether sulfone (PES), transparent polyimide, or the like can be
used. In addition, transparent ceramic such as transparent alumina
or ZnS sintered body can be used.
[0050] The sealing agent 19 is formed along with the edge of the
opposing substrate 11. The sealing agent 19 is formed to overlap
with the scanning line drive circuit 13 and the data line drive
circuit 14 via an interlayer insulating film 16. The interlayer
insulating film 16 is formed with a flatness surface, and a top
surface and a side portion of the interlayer insulating film 16 are
formed by silicon nitride or silicon oxynitride. In the image
display portion 12, a matrix is formed with data lines and scanning
lines extended from the scanning line drive circuit 13 or the data
line drive circuit 14. A pixel matrix is composed of a crop of
switching elements located appropriately in various places and a
crop of light-emitting elements 17 connected electrically to the
crop of switching elements. The scanning line drive circuit 13 is
driven from both sides of the image display portion 12; however,
the scanning line drive circuit 13 may be driven from only either
side of the image display portion 12 in case that the problem of
signal delay is vanishingly small.
[0051] Color filters 18 corresponding to the crop of light-emitting
elements 17 capable of displaying multicolor are provided. The
color filters 18 are appropriately composed of a filter for
transmitting a specified wavelength corresponding to each pixel, a
sharp cut filter for cutting a wavelength of at most limited
transmittance, and a color correction filter. Alternatively, a
color conversion layer can be used with the foregoing filters.
[0052] Here, the crop of light-emitting elements 17 is composed of
light-emitting elements emitting specific light having at least one
emission peak with a half-band width of at most 10 nm. In this
instance, a band path filter for specified light and a filter
transmitting a specific wavelength as the color filters 18 are
located corresponding to each pixel.
[0053] The input terminal unit 15 is formed at the periphery of the
element substrate 10. The input terminal unit 15 receives various
signals from an external circuit and connects to a power source.
Space surrounded by the element substrate 10, the opposing
substrate 11, and the sealing agent 19 is filled with an inert gas.
By filling the inert gas, the crop of light-emitting elements 17 is
protected from corrosion. Drying agent such as barium oxide may be
provided in the space.
[0054] FIG. 2 is a top view of the element substrate 10 for showing
the structure thereof in detail. The structure of the element
substrate 10 shows the arrangement of the scanning line drive
circuit 13 enclosing the two sides of the image display portion 12
and the data line drive circuit 14 adjacent to other side of the
image display portion 12 and the input terminal unit 15.
[0055] In FIG. 2, compartmentalized one pixel region 23 is arranged
in rows and in columns to compose the image display portion 12. A
first auxiliary wiring 20 is formed in stripe parallel to columns.
The both ends or the either end of the first auxiliary wiring 20 is
extended to outside of the image pixel portion. The first auxiliary
wiring 20 is formed to prevent from overlapping with the one pixel
region 23 so as not to interfere with an opening ratio. A second
auxiliary wiring 21 connected electrically to the first auxiliary
wiring 20 is extended in parallel to rows. The both ends or either
end of the second auxiliary wiring 21 connects electrically to a
wiring 22 extended from the input terminal unit 15. Constant
potential or alternation potential may be applied to the wiring 22
depending on the drive method of the organic electroluminescent
element.
[0056] The auxiliary wiring is preferably formed by a material
having resistivity of at most 1.times.10.sup.-5 .omega.cm. The
value of resistance of the auxiliary wiring per 1 cm is preferably
at most 100 .OMEGA.. Needless to say, the value of resistance of
the auxiliary wiring is determined by a line width and a thickness
besides a material to be formed. For, example, in case that the
pitch between pixel rows is 200 .mu.m, the first auxiliary wiring
formed over a bank layer is appropriately formed to have a width of
from 20 to 40 .mu.m given that the width of the pixel electrode is
approximately 120 .mu.m. In case that the auxiliary wiring is
formed by aluminum alloys having resistivity of 4.times.10.sup.-6
.OMEGA.cm to have a thickness of 0.4 .mu.m, the value of resistance
becomes 50 .OMEGA.per 1 cm when the line width is 20 .mu.m.
[0057] FIG. 3 is a cross-sectional view showing the structure of a
light-emitting device. A pixel (A), a pixel (B), and a pixel (C)
are formed over the element substrate 10. A light-emitting element
251 connected to a thin film transistor (hereinafter, TFT) 201 is
provided to the pixel (A). A light-emitting element 252 connected
to a TFT 202 is provided to the pixel (B). A light-emitting element
253 connected to a TFT 203 is provided to the pixel (C). The TFTs
and the light-emitting elements are formed via an interlayer
insulating film 204.
[0058] Each electrodes 205a to 205c is formed over the interlayer
insulating film 204 to connect electrically to the TFT of each
pixel.
[0059] The light-emitting element is formed to sandwich an organic
compound layer between the electrode 205a and other electrode 210.
The structure of the organic compound layer can be varied depending
on the emission color of each pixel. Other than a light-emitting
layer, that is, a hole injecting layer, a hole transporting layer,
an electron injecting layer, and an electron transporting layer,
may be shared by each pixel.
[0060] In FIG. 3, a hole transporting layer 206 and an electron
transporting layer 209 are formed by one layer to be shared by each
pixel. A light-emitting layer 207 is shared by the pixels (A), (B).
A light-emitting layer 208 formed by another material is provided
to the pixel (C).
[0061] As in the present invention, in case that a light-emitting
element that emits light having a plurality of emission peaks and
having an emission spectrum distributed throughout a specified
wavelength band is used, light can be coupled out selectively by a
coloring layer of a color filter 18 provided corresponding to the
pixel. A pixel that can couple out coherent light by locating a
coloring layer serving as a band path filter can be provided to a
light-emitting element capable of emitting non coherent light
(electroluminescence) and coherent light (laser light). Therefore,
a pixel portion that can display an image by coupling out
respectively non coherent light (electroluminescence) and coherent
light (laser light) using an optical filter can be provided.
[0062] The space between the opposing substrate 11 and the element
substrate 10 may be filled with light-transmitting resin or a dried
inert gas, or depressurized in order to seal the light-emitting
element.
[0063] In this embodiment mode, a transistor provided to a pixel is
formed by a TFT; however, the invention is not limited thereto. A
TFT composed of a MOS transistor formed over a single crystalline
semiconductor substrate or a SOI (Silicon On Insulator), or an
amorphous semiconductor film such as silicon can be formed.
EMBODIMENT
[0064] Hereinafter, an example of a light-emitting element capable
of being applied for the present invention will be explained with
reference to FIG. 6.
[0065] As a substrate for forming a film such as an electrode or a
light-emitting layer, a glass substrate 101 such as commercially
available alumino silicate glass, barium borosilicate glass, and
the like are preferably used. Over the glass substrate, an ITO film
is formed by sputtering to have a thickness of from 30 to 100 nm as
the first electrode (anode) 102.
[0066] As the hole transporting layer 103,
4,4'-bis[N-(1-naphthyl)-N-pheny- l-amino]-biphenyl (NPB) is
deposited by vacuum vapor deposition to have a thickness of 135 nm.
As the light-emitting layer 104, 4,4'-bis(N-carbazolyl)-biphenyl
(CBP) as a host material and an iridium complex,
Ir(tpy).sub.2(acac) as a triplet light-emitting material are
deposited to have a thickness of 30 nm by co-evaporation. The
weight ratio of the CBP and the iridium complex is 10:1. The
electron transporting layer 105 is formed thereover by bathocuproin
(BCP) to have a thickness of 105 nm. The electron injecting layer
106 is formed by calcium fluoride (CaF.sub.2). The second electrode
107 is formed by Al (aluminum) by vapor deposition.
[0067] The film thickness of each layer formed by organic materials
is determined so as to amplify light generated in an organic
compound layer. Therefore, the light emission from the Ir complex,
which is added to the light-emitting layer 104, or the light
emission from the hole transporting layer 103 preferably form a
stationary wave by repeating reflection at the interface between
the first electrode 102 and the hole transporting layer 103, the
interface between the electron transporting layer 105 and the
electron injecting layer 106, or the interface between the electron
injecting layer 106 and the second electrode 107.
[0068] Materials capable of emitting light are the Ir complex and
the NPB in the organic compound materials used here. These
materials give light emission in a visible light region (400 to 800
nm). In order to form a stationary wave, the intervals between
reflective surfaces are required to be the integral multiple of a
half wavelength. For example, in order to form a stationary wave of
400 nm, the intervals are required to be 200 nm or the integral
multiple thereof. That is, the thicknesses are required to be
integral multiple of 200 nm, such as 200, 400, or 600 nm.
Similarly, in order to form a stationary wave of light at 800 nm,
the intervals between the reflective surfaces, that is, the
thicknesses are required to be integral multiple of 400 nm, such as
400, 800, or 1200 nm.
[0069] By way of embodiment, the hole transporting layer 103 is
formed to have a thickness of 135 nm, the light-emitting layer 104
is formed to have a thickness of 30 nm, and the electron
transporting layer 105 is formed to have a thickness of 105 nm. As
a result, the organic compound layer is formed to have a thickness
of 270 nm in total. In this case, given that the refractive index
of organic compound layer is 1.7, the wavelength of light capable
of forming a stationary wave is the one that is divided 920 nm by
integer, that is, 460 nm in a visible light region.
[0070] FIGS. 7A and 7B show an emission spectrum of a thus obtained
light-emitting element. Light emission is obtained by applying
direct voltage to a pair of electrodes with the first electrode
serving as an anode and the second electrode serving as a cathode.
Light emission can be observed at an applied voltage of around 6 V.
Light emission of tens of thousands candela (Cd) is obtained at an
applied voltage of 24 V.
[0071] In both spectra shown in FIGS. 7A and 7B, normalized
emission intensity is shown. FIG. 7A shows an emission spectrum of
a face emission observed from the side of the first electrode. FIG.
7B shows an emission spectrum of an edge emission observed from a
lateral side of the substrate provided with a laminated organic
compound layer. As shown in FIG. 7A, intense emission is observed
in a wavelength band of from 475 to 650 nm. The emission is
produced from the Ir complex. Another emission is observed at
around 400 to 475 nm. The emission is produced from the NPB.
[0072] The measurement shows that carriers (holes and electrons)
are recombined each other almost always in the light-emitting layer
104 to excite the light emission from the Ir complex; however, some
carriers are recombined in the hole transporting layer 103. In case
of the face emission, emission intensity varies depending on the
variation of a current density. Therefore, the spectra at any
current density become to have identical forms, and only the
intensity is increased linearly in proportion to the increase of a
current density.
[0073] Compared to the spectrum shown in FIG. 7A, the spectrum of
the edge emission has two features. The first feature is that the
waveform of an emission spectrum in the wavelength band of from 475
to 650 nm is different from that in FIG. 7A. The second feature is
that a sharp emission spectrum is observed around 460 nm in FIG.
7B. The reason of the former is not clear. On the contrary, the
reason of the latter may be considered that a stationary wave is
formed by the organic compound layer 102, and only the light
emission at the wavelength is amplified. Actually, as mentioned
above, the wavelength which allows stationary wave is 460 nm in the
organic compound layer 102 with the thickness. As the most
characteristic feature, the intensity of the emission in the
wavelength band of from 475 to 600 nm varies in proportion to the
increase of a current density, on the contrary, the intensity of
another emission spectrum having a peak at around 460 nm further
increases than the increase of a current density. Therefore, in the
normalized intensity shown in FIG. 7B, only emission at 460 nm is
relatively increased.
[0074] Therefore, the measurement shows that the structure of the
light-emitting device serves as a resonator of light at 460 nm to
amplify the light. FIG. 8 shows a result of increasing a current
density. As shown in FIG. 8, a spectrum shape of face emission is
not varied at all at a current density of 120 mA/cm.sup.2. On the
contrary, the intensity of edge emission is increased at 460 nm;
therefore sharp emission intensity is obtained.
[0075] Table 1 shows laser oscillation characteristics of a sample
manufactured according to Embodiment. Table 1 is the measurement
result of the sample in three pieces showing a peak wavelength of
from 462 to 464 nm, a half-band width of at most 10 nm, and a
threshold of from 10 to 12.5 mA/cm.sup.2 and presenting a good
repeatability. These characteristics are measured at room
temperature.
1TABLE 1 threshold peak wavelength half-band width.sup.[1] sample
No. (mA/cm.sup.2) (nm) (nm) 1 12.5 464 8.0 2 10.0 462 8.0.sup.[2] 3
11.0 463 9.1 .sup.[1]half-band width of 50 mA/cm.sup.2,
.sup.[2]half-band width of 60 mA/cm.sup.2
[0076] Accordingly, the light-emitting device has a resonator
structure for light emission around 460 nm to form a stationary
wave of light at the wavelength. Further, light emission of 460 nm
denotes threshold to a current density. The behavior is similar to
that of a solid laser. In case that the threshold indicates that
what is called population inversion is started, laser light is
oscillated at a further large current density.
[0077] The invention can be practiced by utilizing another
lamination structure formed by another material, in case that the
invention is not limited to the foregoing structure of the
light-emitting element, and that electroluminescence and laser
light can be coupled out simultaneously or respectively.
[0078] In a light-emitting device according to the invention shown
in FIG. 3, the case that a light-emitting element according to this
embodiment will be explained. A light-emitting layer 207 is shared
by a light-emitting elements 251, 252 to use an organic compound
layer according to this embodiment. When a coloring layer 211 is
formed by a blue filter corresponding to the light-emitting element
251, laser light having an emission peak at 460 nm. A coloring
layer 212 is formed by a green filter for the light-emitting
element 252. In a light-emitting element 253, a light-emitting
layer 208 is formed into a red light-emitting layer by using
different materials and by doping red emission dye into Alq.sub.3
or TPD. The color purity of emission color of the light-emitting
element 253 can be improved by using a red color filter as a
coloring layer 213. A blue filter may be used as a coloring layer
211 for the light-emitting element 251. A blue cut filter may be
used as a coloring layer 212 for the light-emitting element
252.
[0079] Accordingly, a light-emitting device available in full color
display (red (R), green (G), blue (B)) can be thus
manufactured.
[0080] Various electric appliances can be completed by using the
above mentioned light-emitting device according to the invention,
such as a personal digital assistant (an electronic book, a mobile
computer, a cellular phone, and the like), video camera, digital
camera, computer, a liquid crystal TV set, cellular phone, and the
like.
[0081] FIG. 9A illustrates an example of a TV set applied with the
invention composed of a housing 301, a support 302, a display
portion 303, and the like. The TV set can be completed by using a
light-emitting device according to the invention as a display
portion 303.
[0082] FIG. 9B illustrates an example of a video camera applied
with the invention composed of a main body 311, a display portion
312, a sound input unit 313, operation switches 314, a battery 315,
an image reception portion 316, and the like. The video camera can
be completed by using a light-emitting device according to the
invention as a display portion 312.
[0083] FIG. 9C illustrates an example of a computer applied with
the invention composed of a main body 321, a housing 322, a display
portion 323, a key board 324, and the like. The computer can be
completed by using a light-emitting device according to the
invention as a display portion 323.
[0084] FIG. 9D illustrates an example of a PDA (Personal Digital
Assistant) applied with the invention composed of a main body 331,
a stylus 332, a display portion 333, operation buttons 334, an
external interface 335, and the like. The PDA can be completed by
using a light-emitting device according to the invention as a
display portion 333.
[0085] FIG. 9E illustrates an example of a sound reproduction
device applied with the invention, in specific, an in-car audio
system composed of a main body 341, a display portion 342,
operation switches 343, 344, and the like. The sound reproduction
device can be completed by using a light-emitting device according
to the invention as a display portion 342.
[0086] FIG. 9F illustrates an example of a digital camera applied
with the invention composed of a main body 351, a display portion
(A) 352, an eye-piece portion 353, operation switches 354, a
display portion (B) 355, a battery 356, and the like. The digital
camera can be completed by using a light-emitting device according
to the invention as display portions 352, 355.
[0087] FIG. 9G illustrates an example of a cellular phone applied
with the invention composed of a main body 361, a sound output
portion 362, a sound input portion 363, a display portion 364,
operation switches 365, an antenna 366, and the like. The cellular
phone can be completed by using a light-emitting device according
to the invention as the display portion 364.
[0088] These electric appliances are illustrative only. A
light-emitting device according to the invention is not limited
thereto, but can be used as a means for displaying images in a
washing machine, a refrigerator, a land line, a game machine, a
microwave oven, a radio, and the like.
[0089] Although the present invention has been fully described by
way of examples with reference to the accompanying drawings, it is
to be understood that various changes and modifications will be
apparent to those skilled in the art. Therefore, unless otherwise
such changes and modifications depart from the scope of the present
invention hereinafter described, they should be construed as being
included therein.
* * * * *