U.S. patent application number 13/326924 was filed with the patent office on 2012-04-05 for method of manufacturing organic light emitting device.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Naoto FUKUDA, Seiji MASHIMO, Manabu OTSUKA, Yuzo TOKUNAGA, Toshiaki YOSHIKAWA.
Application Number | 20120083062 13/326924 |
Document ID | / |
Family ID | 38139705 |
Filed Date | 2012-04-05 |
United States Patent
Application |
20120083062 |
Kind Code |
A1 |
OTSUKA; Manabu ; et
al. |
April 5, 2012 |
METHOD OF MANUFACTURING ORGANIC LIGHT EMITTING DEVICE
Abstract
Provided is a method of manufacturing an organic light emitting
device including the step of forming an electron injection layer.
The step of forming the electron injection layer includes the steps
of: vaporizing in a container a dopant material as a raw material
of a dopant; causing the vaporized dopant material to pass a heated
medium between the container and the substrate; and forming the
organic compound into the electron injection layer. According to
the method the organic light emitting device which has high
electron injection efficiency and can be driven at a low voltage
can be obtained.
Inventors: |
OTSUKA; Manabu; (Tokyo,
JP) ; TOKUNAGA; Yuzo; (Yokohama-shi, JP) ;
MASHIMO; Seiji; (Yokohama-shi, JP) ; YOSHIKAWA;
Toshiaki; (Yokohama-shi, JP) ; FUKUDA; Naoto;
(Funabashi-shi, JP) |
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
38139705 |
Appl. No.: |
13/326924 |
Filed: |
December 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11610022 |
Dec 13, 2006 |
|
|
|
13326924 |
|
|
|
|
Current U.S.
Class: |
438/46 ;
257/E33.062 |
Current CPC
Class: |
H01L 51/002 20130101;
H01L 51/5092 20130101; C23C 14/243 20130101; C23C 14/24 20130101;
H01L 51/001 20130101; H01L 51/56 20130101 |
Class at
Publication: |
438/46 ;
257/E33.062 |
International
Class: |
H01L 33/36 20100101
H01L033/36 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2005 |
JP |
2005-360025 |
Dec 1, 2006 |
JP |
2006-325113 |
Claims
1. A method of manufacturing an organic light emitting device, the
organic light emitting device comprising: a substrate; an anode and
a cathode provided on the substrate; a light emitting layer
provided between the anode and the cathode; and an electron
injection layer provided on a side of the cathode with respect to
the light emitting layer, the electron injection layer comprising
an organic compound and a dopant, the method comprising the step of
forming the electron injection layer, wherein the step of forming
the electron injection layer comprises the steps of: vaporizing in
a container a dopant material as a raw material of the dopant;
causing the vaporized dopant material to pass a heated medium
between the container and the substrate; and forming the organic
compound into the electron injection layer.
2. The method of manufacturing an organic light emitting device
according to claim 1, wherein the medium is heated by
energization.
3. The method of manufacturing an organic light emitting device
according to claim 1, wherein the medium is spaced apart from the
dopant material.
4. The method of manufacturing an organic light emitting device
according to claim 1, wherein a temperature of the medium is equal
to or higher than the vaporizing temperature of the dopant material
under vacuum.
5. The method of manufacturing an organic light emitting device
according to claim 1, wherein a temperature of the medium is equal
to or higher than 200.degree. C. and equal to or lower than
2000.degree. C.
6. The method of manufacturing an organic light emitting device
according to claim 1, wherein the medium comprises a metal.
7. The method of manufacturing an organic light emitting device
according to claim 6, wherein the metal comprises tungsten.
8. The method of manufacturing an organic light emitting device
according to claim 1, wherein the dopant material comprises an
alkali metal compound or an alkaline earth metal compound.
9. The method of manufacturing an organic light emitting device
according to claim 8, wherein the dopant material comprises cesium
carbonate.
10. The method of manufacturing an organic light emitting device
according to claim 1, wherein the step of causing the vaporized
dopant material to pass a heated medium comprises the step of
accelerating decomposition of the dopant material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 11/610,022, filed Dec. 13, 2006, which claims
the benefit of JP 2005-360025, filed Dec. 14, 2005 and JP
2006-325113, filed Dec. 1, 2006, which are incorporated by
reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of manufacturing
an organic light emitting device and vapor deposition system.
[0004] 2. Description of the Related Art
[0005] An organic light emitting device is generally formed of a
laminated structure including a substrate, an anode, a hole
transport layer, a light emitting layer, an electron transport
layer, an electron injection layer, and a cathode. In order to make
lower the voltage of such an organic light emitting device, it is
important to improve electron injectability from the cathode. More
specifically, in order to improve electron injection efficiency, a
metal, a metal compound, a metal salt, or the like having a low
work function is used as a dopant. An organic layer containing such
a dopant is used as the electron injection layer, and the dopant
functions as a donor (electron donative) dopant.
[0006] In an organic film of the electron injection layer, a metal
having a low work function donates electrons to put organic
molecules in a radical anion state. This makes it possible for
adjoining molecules to donate or accept electrons smoothly, and an
injection barrier from the cathode is lowered to improve the
electron injectability. Further, electron transportability by a
hopping mechanism in the organic layer can also be improved.
[0007] Japanese Patent Application Laid-Open Nos. 2000-182774,
2004-311403, and 2005-123094 disclose lowering of an electron
injection barrier by forming an electron injection layer so as to
contain a metal compound and reducing the metal compound in the
electron injection layer.
[0008] However, according to the technology disclosed in Japanese
Patent Application Laid-Open Nos. 2000-182774, 2004-311403, and
2005-123094, when the metal compound is not reduced and remains in
an organic film, it does not sufficiently function as a donor
dopant, and even if a doping concentration is improved, drive
voltage is not lowered. On the contrary, there is a possibility
that the drive voltage may rise.
SUMMARY OF THE INVENTION
[0009] In view of the above, an object of the present invention is
to provide a method of manufacturing an organic light emitting
device which has high electron injection efficiency and can be
driven at a low voltage, and to provide a vapor deposition
system.
[0010] That is, according to an aspect of the present invention,
there is provided a method of manufacturing an organic light
emitting device, the organic light emitting device including: a
substrate; an anode and a cathode provided on the substrate; a
light emitting layer provided between the anode and the cathode;
and an electron injection layer provided on a side of the cathode
with respect to the light emitting layer, the electron injection
layer including an organic compound and a dopant, the method
including the step of forming the electron injection layer in which
the step of forming the electron injection layer includes the steps
of: vaporizing in a container a dopant material as a raw material
of the dopant; causing the vaporized dopant material to pass a
heated medium between the container and the substrate; and forming
the organic compound into the electron injection layer.
[0011] Further, according to another aspect of the present
invention, there is provided a vapor deposition system including: a
container for containing a vapor deposition material therein;
heating means for vaporizing the vapor deposition material
contained in the container; a medium provided in a position between
the container and a base material to be vapor-deposited where the
vaporized vapor deposition material passes; and a shielding member
provided between the medium and the base material to be
vapor-deposited, for shielding heat generated by the medium.
[0012] According to the present invention, the electron-injecting
dopant in the electron injection layer can be caused to function
more efficiently. As a result, the organic light emitting device
manufactured according to the present invention has high electron
injection efficiency and can be driven at a low voltage. Further,
according to the present invention, continuous production over a
long period of time without deteriorating device characteristics
can be carried out.
[0013] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic view of an exemplary laminated
structure of an organic light emitting device manufactured
according to the present invention.
[0015] FIG. 2 is a schematic view of an exemplary vapor depositing
source used in the present invention.
[0016] FIG. 3 is a schematic view of another exemplary vapor
depositing source used in the present invention.
[0017] FIG. 4 is a schematic view of still another exemplary vapor
depositing source used in the present invention.
[0018] FIG. 5 is a schematic view of yet another exemplary vapor
depositing source used in the present invention.
[0019] FIG. 6 is a schematic view of still another exemplary vapor
depositing source used in the present invention.
[0020] FIG. 7 is a schematic view of yet another exemplary vapor
depositing source used in the present invention.
[0021] FIG. 8 is a schematic view of still another exemplary vapor
depositing source used in the present invention.
[0022] FIG. 9 is a schematic view of yet another exemplary vapor
depositing source used in the present invention.
[0023] FIG. 10 is a schematic view of still another exemplary vapor
depositing source used in the present invention.
[0024] FIG. 11 is a schematic view of yet another exemplary vapor
depositing source used in the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0025] Embodiments of the present invention are now described in
detail in the following.
[0026] The present invention relates to a method of manufacturing
an organic light emitting device having an organic layer as an
electron injection layer, which contains a dopant material
(electron-injecting dopant material) which functions as a donor
(electron donative) dopant for improving electron injection
efficiency as, for example, illustrated in FIG. 1. The
manufacturing method according to the present invention is a method
of manufacturing an organic light emitting device having a
substrate, an anode and a cathode provided on the substrate, a
light emitting layer provided between the anode and the cathode,
and an electron injection layer provided on a side of the cathode
with respect to the light emitting layer, the electron injection
layer including an organic compound and a dopant. In FIG. 1,
reference numerals 10, 11, 12, 13, 14, 15, and 16 designate the
substrate, the anode, a hole transport layer, the light emitting
layer, an electron transport layer, the electron injection layer,
and the cathode, respectively. The electron transport layer 14 is
preferably formed only of an organic compound.
[0027] In the manufacturing method according to the present
invention, the step of forming the electron injection layer
includes the step of vaporizing in a container the dopant material
which is a raw material of the dopant, the step of causing the
vaporized dopant material to pass a heated medium between the
container and the substrate, and the step of forming an organic
compound into the electron injection layer.
[0028] More specifically, when the electron injection layer 15 is
formed, a substance directly heated by energization or a substance
indirectly heated by a heat source is used as the medium.
Alternatively, a substance heated by induction heating may be used
as the medium. Induction heating make unnecessary wiring for
feeding and terminal section which come to be a high temperature,
enables to suppress thermal effect to the substrate and the
circumference, and enables to design the vapor depositing source
compactly. The inventors considers that by causing the vaporized
dopant material to pass the heated medium between the container and
the substrate, decomposition of the dopant material is accelerated
and more active state where electrons are likely to be given is
obtained,
[0029] As a result, an organic light emitting device which can be
driven at a low voltage can be manufactured. It is to be noted that
the vaporized state refers not only to a state where the dopant
material itself is vaporized but also to a state where a product of
the decomposition of the dopant material is vaporized. Although, in
the following, the present invention is specifically described in
the context of forming the electron injection layer 15 by vapor
deposition, the present invention is not limited thereto.
[0030] FIG. 2 illustrates an exemplary vapor depositing source used
in the present invention. In FIG. 2, a medium 1 is a coiled
tungsten filament heated by energization. A heat source 2 heats a
container (crucible) 3. Reference numerals 4 and 5 denote a
shielding member (upper lid) and an electron-injecting dopant
material, respectively. It is to be noted that in FIGS. 3, 4, 5, 6,
and 7, like reference numerals designate like members illustrated
in FIG. 2.
[0031] For the electron-injecting dopant material 5, for example,
alkali metal compounds, alkaline earth metal compounds, or the like
can be used. In order to improve electron injection efficiency, it
is preferable that a metal having a low work function or a compound
thereof is used as the dopant. Exemplary metals having a low work
function include alkali metals. However, alkali metals react
vigorously with moisture in the air and thus, it is difficult to
handle them in the atmosphere. It follows that, in the present
invention, it is preferable to use an alkali metal compound or an
alkaline earth metal compound which are relatively easily handled
in the atmosphere, and more preferably an alkali metal compound.
Exemplary alkali metal compounds include Na.sub.2O, K.sub.2O,
Rb.sub.2O, Cs.sub.2O, Na.sub.2CO.sub.3, K.sub.2CO.sub.3,
Rb.sub.2CO.sub.3, and Cs.sub.2CO.sub.3, and exemplary alkaline
earth metal compounds include MgO, CaO, SrO, MgCO.sub.3,
CaCO.sub.3, and SrCO.sub.3. Among them, cesium carbonate is more
preferable, because cesium carbonate is stable in the atmosphere
and is easily handled, and the atomic radius of cesium is large and
therefore diffusion into an adjoining layer is less liable to
occur.
[0032] While an alkali metal alone may be used as the electron
injection layer, an alkali metal compound and an alkaline earth
metal compound have, differently from a metal, low conductivity.
Therefore, the electron injection layer manufactured according to
the present invention is a layer where an electron-injecting dopant
material is doped in an organic compound which transports
electrons. For the organic compound which transports electrons, a
well-known material such as an alumiquinolinol complex and a
phenanthroline compound may be used.
[0033] Although the substance used as the medium 1 is not
particularly limited, a metal which decomposes the
electron-injecting dopant material by chemical reaction with the
electron-injecting dopant material is preferable, because, in
addition to decomposition due to heat, decomposition due to
chemical reaction such as reduction reaction can also be
expected.
[0034] The medium 1 is preferably provided at a location where it
is in contact with the vaporized electron-injecting dopant material
5. By bringing the vaporized electron-injecting dopant material 5
into contact with the medium 1, secondary decomposition of the
electron-injecting dopant material 5 can be accelerated. Further,
the location where the medium 1 is provided is not necessarily
limited to the inside of the container 3, and, as illustrated in
FIG. 3, the medium 1 may be provided immediately above the
container 3.
[0035] Further, it is preferable that the medium 1 is apart from
the electron-injecting dopant material 5. In other words, it is
preferable that the medium 1 is provided so as not to be in contact
with the electron-injecting dopant material 5. For example, when
the medium 1 is made of a metal which causes decomposition of the
electron-injecting dopant material by chemical reaction with the
electron-injecting dopant material, direct contact of the medium 1
with the electron-injecting dopant material 5 changes the contact
area, which may result in variations. Further, if the surface of
the medium is covered with a by-product or a residue formed by
direct reaction, the medium may be deteriorated or the effect may
be lowered. If the medium 1 is provided at a location where it is
not in contact with the solid electron-injecting dopant material 5
but is in contact with the vaporized electron-injecting dopant
material 5, the surface of the medium is less liable to be covered
with a residue or a by-product of the reaction, so even after vapor
deposition over a long period of time, decomposition by the
chemical reaction is expected, and the characteristics of the
device can be maintained.
[0036] The shape of the medium 1 is not limited to the coiled
filament, and is preferably formed in a shape in accordance with
the vapor depositing source. For example, the shape may be
spherical (FIG. 4), plate-like (FIG. 5), mesh-like (FIG. 6), or
rod-like (FIG. 7). Further, because the medium 1 can accelerate the
decomposition more efficiently by increasing the contact area
thereof, it is also preferable that a plurality of the medium 1 are
provided as illustrated in, for example, FIGS. 4 and 5.
[0037] From the viewpoint of preventing precipitation of the
electron-injecting dopant material 5, the temperature of the medium
1 is preferably equal to or higher than the vaporizing temperature
of the electron-injecting dopant material 5 under vacuum, and more
preferably 200.degree. C. or higher. Further, although it is
preferable that the temperature of the medium 1 is high from the
viewpoint of accelerating the decomposition, taking into
consideration the adverse effect of radiant heat on the organic
light emitting device and on a region around the vapor depositing
source, the temperature is preferably 2000.degree. C. or lower.
More preferably, the temperature is in the neighborhood of
1000.degree. C., where the effect of the present invention is
adequate and, at the same time, the adverse effect of radiant heat
can be suppressed relatively easily.
[0038] Further, the present invention provides a vapor deposition
system having a container for containing a vapor deposition
material therein, heating means for vaporizing the vapor deposition
material contained in the container, a medium provided between the
container and a base material to be vapor-deposited where the
vaporized vapor deposition material passes, and a shielding member
provided between the medium and the base material to be
vapor-deposited, for shielding heat generated by the medium. FIGS.
8, 10, and 11 are schematic views each illustrating an exemplary
vapor deposition system according to the present invention. In
FIGS. 8, 10, and 11, reference numerals 21, 22, 23, 24, 25, 26, and
27 denote a medium, a heat source, a container, a shielding member
(upper lid), a dopant material, another shielding member, and a
reflector, respectively.
[0039] Because provision of the shielding member 24 prevents the
base material to be formed in film from being directly exposed to
radiant heat from the medium 21, the adverse effect of heat on the
base material to be formed in film and on the region around the
vapor depositing source can be further suppressed. Therefore, when
the organic light emitting device is manufactured, deterioration of
performance of the device due to adverse effect on the organic
compound forming the device and the like can be suppressed.
[0040] The shielding member 24 is provided at an opening of the
container 23. The medium 21 is preferably provided in a space
defined by the shielding member 24 and the container 23. By
providing and confining the medium 21 in the space, the vaporized
dopant material 25 can be positively brought into contact with the
medium 21. In this case, the shielding member 24 functions as a lid
of the container 23. It is to be noted that the shielding member 24
has the opening such that the vaporized dopant material 25 moves
toward the base material to be vapor-deposited.
[0041] Further, as illustrated in FIGS. 8 and 11, it is preferable
that another shielding member (middle lid) 26 is provided between
the dopant material 25 and the medium 21. Provision of the
shielding member 26 more positively brings the vaporized dopant
material 25 into contact with the medium 21. As a result, the light
emitting performance of the organic light emitting device can be
further improved.
[0042] Further, when there is no shielding member 24 or another
shielding member, the dopant material 25 is likely to be formed as
a film as a clod (hereinafter "cluster"). The cluster leads to
generate non-luminous points, resulting that there is a possibility
that deterioration of device properties and defects of device
occur. However, provision of the shielding member 24 or another
shielding member 26 enables to suppress generation of cluster.
[0043] Although examples of the present invention are described in
the following, the present invention is not limited thereto.
Example 1
[0044] A device illustrated in FIG. 1 was manufactured. In this
example, chromium (Cr) which functions as a reflecting electrode
was used as the anode 11 and indium tin oxide (ITO) which functions
as a transparent electrode for taking out emitted light was used as
the cathode 16 to manufacture a top emission type device.
[0045] A chromium (Cr) film was formed on the substrate 10 by
sputtering in a thickness of 200 nm to obtain the anode 11. After
that, the substrate was cleaned with UV/ozone.
[0046] Then, the cleaned substrate and the material were loaded on
a vacuum vapor deposition system (manufactured by ULVAC KIKO,
Inc.). After exhausting air such that the pressure inside becomes
1.times.10.sup.-6 Torr, an N, N'-.alpha.-dinaphthylbenzidine
(.alpha.-NPD) film was formed on the anode 11 in a thickness of 60
nm to form the hole transport layer 12. Further, a co-deposited
film of coumarin 6 (1.0 wt %) and tris (8-hydroxyquinolinato)
aluminum (Alq.sub.3) was formed thereon in a thickness of 30 nm to
form the light emitting layer 13. Then, as the electron transport
layer 14, a phenanthroline compound film was formed in a thickness
of 10 nm.
[0047] Then, a film formed of a phenanthroline compound and cesium
carbonate as the electron-injecting dopant material was formed on
the electron transport layer 14 in a thickness of 40 nm to
constitute the electron injection layer 15. As the vapor depositing
source of cesium carbonate, the one illustrated in FIG. 2 was used.
More specifically, an alumina crucible was used as the container 3,
a tungsten filament as the medium 1 was provided in the container 3
which is in contact with the vaporized cesium carbonate most, and
vapor deposition was carried out with the tungsten filament being
heated by energization. A covered thermocouple was welded to
several arbitrarily chosen points on the tungsten filament to
measure the temperature. The lowest temperature was about
700.degree. C. while the highest temperature was about 1000.degree.
C.
[0048] It is to be noted that a single film was separately formed
on a silicon wafer under the same conditions as those for the
electron injection layer 15 and the concentration of cesium ions
was determined by ICP-MS analysis. It was confirmed that the
concentration of cesium in the electron injection layer 15 was
about 2 wt %.
[0049] Finally, an indium tin oxide (ITO) film was formed on the
electron injection layer 15 by sputtering in a thickness of 150 nm
to obtain the transparent cathode 16 for taking out emitted light.
After that, the substrate was moved into a glove box, and the
device was encapsulated using a glass cap having a desiccant
provided therein in an atmosphere of nitrogen.
[0050] Direct current voltage was applied to the obtained organic
light emitting device with the voltage varied from V in increments
of 0.1 V, and light emitting characteristics were examined. As a
result, the current density of the device when the applied voltage
was 5.0 V was calculated to be 80.5 mA/cm2 and the light emitting
efficiency when the applied voltage was 5.0 V was calculated to be
4.2 cd/A.
[0051] Further, after vapor deposition of cesium carbonate of the
electron injection layer 15 was continuously carried out, the
organic light emitting device was manufactured by the same
manufacturing procedure. The current density of the device when the
applied voltage was 5.0 V was calculated to be 80.0 mA/cm.sup.2 and
the light emitting efficiency when the applied voltage was 5.0 V
was calculated to be 4.3 cd/A. It was confirmed that there was
almost no change.
Comparative Example 1
[0052] A device was manufactured by a method similar to that of
Example 1 except that vapor deposition of cesium carbonate was
carried out without using a tungsten filament, and evaluation was
made. The result is shown in Table 1.
Comparative Example 2
[0053] A device was manufactured by a method similar to that of
Comparative Example 1 except that vapor deposition was carried out
such that the concentration of cesium in the electron injection
layer 15 was about 4 wt %, and evaluation was made. The result is
shown in Table 1.
[0054] As shown in Table 1, even though the doping concentration
was higher than that in Example 1, the characteristics of the
device were inferior to those of the device in Example 1.
Example 2
[0055] As a vapor depositing source of cesium carbonate, one
illustrated in FIG. 3 was used. More specifically, a tungsten
filament as the medium 1 was provided above the alumina crucible 3,
and vapor deposition was carried out with the tungsten filament
heated by energization.
[0056] A device was manufactured by a method similar to that of
Example 1 except for the above, and evaluation was made. The result
is shown in Table 1.
Example 3
[0057] As a vapor depositing source of cesium carbonate, one
illustrated in FIG. 4 was used. More specifically, spherical
tungsten as the medium 1 was provided in the alumina crucible 3,
and vapor deposition was carried out with the spherical tungsten
indirectly heated by heat from the heat source 2. A thermocouple
was attached to a bottom surface of the crucible 3 to measure the
temperature, and the temperature was about 700.degree. C.
[0058] A device was manufactured by a method similar to that of
Example 1 except for the above, and evaluation was made. The result
is shown in Table 1.
[0059] It is to be noted that, after vapor deposition of cesium
carbonate was continuously carried out, the color of the spherical
tungsten was changed to black, and the surface was covered with a
residue. However, as shown in Table 1, although the initial value
could not be maintained, it was confirmed that the characteristics
could be continuously maintained.
Example 4
[0060] A device was manufactured by a method similar to that of
Example 1 except that vapor deposition of cesium carbonate was
carried out with less electric current for energizing the tungsten
filament, and evaluation was made. The result is shown in Table
1.
[0061] It is to be noted that, similarly to the case of Example 1,
the temperature was measured at arbitrarily chosen points on the
tungsten filament. The lowest temperature was about 500.degree. C.
at a point near the top of the crucible 3 while the highest
temperature was about 700.degree. C. at a point near the center of
the filament.
Example 5
[0062] A device was manufactured by a method similar to that of
Example 2 except that vapor deposition of cesium carbonate was
carried out with less electric current for energizing the tungsten
filament, and evaluation was made. The result is shown in Table
1.
[0063] It is to be noted that, similarly to the case of Example 1,
the temperature was measured at arbitrarily chosen points on the
tungsten filament. The lowest temperature was about 200.degree. C.
at a point near the top of the crucible 3 while the highest
temperature was about 500.degree. C. at a point near the center of
the filament.
[0064] After vapor deposition of cesium carbonate was continuously
carried out, the color of the tungsten filament was slightly
changed to brown. However, as shown in Table 1, although
deterioration proceeded more than that in Example 1, it was
confirmed that the effect was maintained.
Comparative Example 3
[0065] A device was manufactured by a method similar to that of
Example 2 except that vapor deposition of cesium carbonate was
carried out without energizing the tungsten filament, and
evaluation was made. The result is shown in Table 1.
TABLE-US-00001 TABLE 1 Heater Characteristics Characteristics
Material Result of where after Location for Heater Cesium 5.0 V was
Continuous Provision Temperature Detection applied Production
Example 1 Tungsten 700-1000.degree. C. 2 wt % 80.5 mA/cm.sup.2 80.0
mA/cm.sup.2 Filament 4.2 cd/A 4.3 cd/A in Crucible Comparative No
Heater Crucible 2 wt % 43.2 mA/cm.sup.2 -- Example 1 Material
Temperature 4.0 cd/A 600-700.degree. C. Comparative No Heater
Crucible 4 wt % 60.8 mA/cm.sup.2 -- Example 2 Material Temperature
4.1 cd/A 600-700.degree. C. Example 2 Tungsten 800-1100.degree. C.
2 wt % 79.6 mA/cm.sup.2 80.3 mA/cm.sup.2 Filament 4.3 cd/A 4.2 cd/A
above Crucible Example 3 Spherical 700.degree. C. 2 wt % 62.3
mA/cm.sup.2 55.4 mA/cm.sup.2 Tungsten 4.4 cd/A 4.6 cd/A in Crucible
Example 4 Tungsten 500-700.degree. C. 2 wt % 68.9 mA/cm.sup.2 65.3
mA/cm.sup.2 Filament 4.5 cd/A 4.4 cd/A in Crucible Example 5
Tungsten 200-500.degree. C. 2 wt % 55.8 mA/cm.sup.2 50.3
mA/cm.sup.2 Filament 4.4 cd/A 4.0 cd/A above Crucible Comparative
Tungsten No 2 wt % 43.8 mA/cm.sup.2 -- Example 3 Filament
Energization 4.1 cd/A above Crucible
[0066] From the results shown above, it is assumed that, at least
by heating, the dopant can be made to function more efficiently.
Further, even at a temperature equal to or higher than 1000.degree.
C., effects comparable to or greater than those of Example 1 can be
expected.
Example 6
[0067] A device illustrated in FIG. 1 was manufactured. In the
present example, chromium (Cr) which functions as a reflecting
electrode was used as the anode 11 and indium tin oxide (ITO) which
functions as a transparent electrode for taking out emitted light
was used as the cathode 16 to manufacture a top emission type
device.
[0068] A chromium (Cr) film was formed on the substrate 10 by
sputtering in a thickness of 200 nm to obtain the anode 11. After
that, the substrate was cleaned with UV/ozone.
[0069] Then, the cleaned substrate and the material were loaded on
a vacuum vapor deposition system (manufactured by ULVAC KIKO,
Inc.). After exhausting air such that the pressure inside becomes
1.times.10.sup.-6 Torr, an N, N'-.alpha.-dinaphthylbenzidine
(.alpha.-NPD) film was formed on the anode 11 in a thickness of 60
nm to form the hole transport layer 12. Further, a co-deposited
film of coumarin 6 (1.0 wt %) and tris (8-hydroxyquinolinato)
aluminum (Alq.sub.3) was formed thereon in a thickness of 30 nm to
form the light emitting layer 13. Then, as the electron transport
layer 14, a phenanthroline compound film was formed in a thickness
of 10 nm.
[0070] Then, a film formed of a phenanthroline compound and cesium
carbonate as the electron-injecting dopant material was formed on
the electron transport layer 14 in a thickness of 40 nm to
constitute the electron injection layer 15. As the vapor depositing
source of cesium carbonate, the one illustrated in FIG. 8 was used.
More specifically, alumina was used for the container 23, the
shielding member (upper lid) 24, and the other shielding member
(middle lid) 26, and the medium 21 was provided between the upper
lid 24 and the middle lid 26 in the container 23.
[0071] The middle lid 26 preferably has a plurality of openings
formed therein, and the locations of the openings are preferably
vertically offset from the opening in the upper lid 24. Further, it
is preferable that the conductance of the openings in the middle
lid 26 is larger than that of the opening in the upper lid 24. The
diameter .phi. of the opening in the upper lid 24 used here was 2
mm. The diameter .phi. of the openings in the middle lid 26 was 1
mm and there were six openings in the middle lid 26 around the
periphery.
[0072] The numbers and diameters of the openings in the upper lid
24 and the middle lid 26 are not limited thereto.
[0073] This structure allows positive contact of the medium 21
provided between the upper lid 24 and the middle lid 26 with the
vaporized cesium carbonate to improve the device characteristics.
Further, because cesium carbonate undergoes vapor deposition
through the middle lid 26 and the upper lid 24, the number of
clusters is decreased and device defects are decreased.
[0074] The vapor depositing source was used to carry out vapor
deposition of cesium carbonate with the tungsten filament heated by
energization.
[0075] A covered thermocouple was welded to several arbitrarily
chosen points on the tungsten filament to measure the temperature.
The lowest temperature was about 700.degree. C. while the highest
temperature was about 1000.degree. C.
[0076] It is to be noted that a single film was separately formed
on a silicon wafer under the same conditions as those for the
electron injection layer 15 and the concentration of cesium ions
was determined by ICP-MS analysis. It was confirmed that the
concentration of cesium in the electron injection layer 15 was
about 2 wt % The concentration distribution of cesium within a
diameter of 75 mm of a film formed 250 mm above the vapor
depositing source was .+-.2.3%.
[0077] The substrate temperature 250 mm above the vapor depositing
source was 43.degree. C.
[0078] With regard to the number of clusters of Cs.sub.2CO.sub.3, a
single film was separately formed on a cleaned silicon wafer under
the same conditions as those for the electron injection layer 15
and an aluminum film was formed in a thickness of 300 nm so as to
cover the film. Ten such samples were manufactured, and the surface
where the film was formed was observed with a microscope under dark
field illumination, and the number of bright spots within a
diameter of 10 mm was counted. When the vapor depositing source for
Cs.sub.2CO.sub.3in the present example was used, no bright spots
were recognized.
[0079] Finally, an indium tin oxide (ITO) film was formed on the
electron injection layer 15 by sputtering in a thickness of 150 nm
to obtain the transparent cathode 16 for taking out emitted light.
After that, the substrate was moved into a glove box, and the
device was encapsulated using a glass cap having a desiccant
provided therein in an atmosphere of nitrogen.
[0080] Direct current voltage was applied to the obtained organic
light emitting device with the voltage varied from 0 V in
increments of 0.1 V, and light emitting characteristics were
examined. As a result, the current density of the device when the
applied voltage was 5.0 V was calculated to be 83.0 mA/cm.sup.2 and
the light emitting efficiency when the applied voltage was 5.0 V
was calculated to be 4.7 cd/A.
[0081] Further, after vapor deposition of cesium carbonate of the
electron injection layer 15 was continuously carried out, the
organic light emitting device was manufactured by the same
manufacturing procedure. The current density of the device when the
applied voltage was 5.0 V was calculated to be 82.8 mA/cm.sup.2 and
the light emitting efficiency when the applied voltage was 5.0 V
was calculated to be 4.7 cd/A. It was confirmed that there was
almost no change.
Example 7
[0082] A device was manufactured using a vapor depositing source
structure similar to that of Example 6 but without the middle lid
and the upper lid (FIG. 9) under the same conditions as those for
Example 6, and characteristics were evaluated. In FIG. 9, like
reference numerals designate like members illustrated in FIG. 8.
The result is shown in Table 2. It is assumed that, because there
was no middle lid and no upper lid, the tungsten filament and
cesium carbonate were not sufficiently in contact with each other,
and thus, even though the amount of cesium in the film was the
same, the amount of cesium effective for the device characteristics
was small, and thus, the characteristics were inferior to those of
Example 6.
[0083] Further, the concentration distribution of cesium within a
diameter of 75 mm of a film formed 250 mm above the vapor
depositing source was .+-.10.6%.
[0084] When the vapor depositing source was used, because the
substrate was directly exposed to radiant heat generated by the
tungsten filament, the substrate temperature 250 mm above the vapor
depositing source was 108.degree. C.
[0085] Further, the number of clusters of Cs.sub.2CO.sub.3 counted
in the same way as in Example 6 was 518 on average of the ten
samples.
Example 8
[0086] As the vapor depositing source of cesium carbonate, one
illustrated in FIG. 10 was used.
[0087] A device was manufactured using a vapor depositing source
similar to that of Example 6, but without the middle lid under the
same conditions as those for Example 6, and evaluation was made.
The result is shown in Table 2.
[0088] The concentration distribution of cesium within a diameter
of 75 mm of a film formed 250 mm above the vapor depositing source
and the substrate temperature 250 mm above the vapor depositing
source were substantially equal to those of Example 6.
[0089] The number of clusters of Cs.sub.2CO.sub.3counted was 1.6 on
average of the ten samples.
Example 9
[0090] As the vapor depositing source of cesium carbonate, one
illustrated in FIG. 11 was used. More specifically, spherical
tungsten as the medium 21 was provided in the alumina crucible 23
between the middle lid 26 and the upper lid 24, and vapor
deposition was carried out with the spherical tungsten indirectly
heated by heat from the heat source 22. A device was manufactured
by a method similar to that of Example 6 except for the above, and
evaluation was made. The result is shown in Table 2.
Example 10
[0091] A device was manufactured by a method similar to that of
Example 6 except that vapor deposition was carried out such that
the concentration of cesium in the electron injection layer 15 was
about 1 wt %, and evaluation was made. The result is shown in Table
2.
TABLE-US-00002 TABLE 2 Substrate Number of temperature Clusters
Characteristics Characteristics Concentration 250 mm (.phi.10 mm,
where after Distribution above Vapor Average 5.0 V was Continuous
of Cs.sub.2CO.sub.3 Depositing of Ten Applied Production (.phi.75
mm) Source Samples) Example 6 83.0 mA/cm.sup.2 82.8 mA/cm.sup.2
.+-.2.3% 43.degree. C. 0 4.7 cd/A 4.7 cd/A Example 7 76.2
mA/cm.sup.2 75.2 mA/cm.sup.2 .+-.10.6% 108.degree. C. 518 4.1 cd/A
4.1 cd/A Example 8 80.5 mA/cm.sup.2 80.0 mA/cm.sup.2 .+-.2.5%
44.degree. C. 1.6 4.2 cd/A 4.3 cd/A Example 9 62.3 mA/cm.sup.2 55.4
mA/cm.sup.2 .+-.2.5% 48.degree. C. 0 4.4 cd/A 4.6 cd/A Example 10
81.2 mA/cm.sup.2 80.8 mA/cm.sup.2 .+-.2.4% 41.degree. C. 0 4.4 cd/A
4.4 cd/A
[0092] By using the vapor depositing source according to the
present invention, cesium carbonate and the tungsten filament are
more positively brought into contact with each other, and thus,
even if the concentration of cesium is low, a device with excellent
characteristics can be manufactured.
[0093] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
* * * * *