U.S. patent number RE47,544 [Application Number 15/199,247] was granted by the patent office on 2019-07-30 for organic light emitting display device and method of manufacturing the same.
This patent grant is currently assigned to LG Display Co., Ltd.. The grantee listed for this patent is LG Display Co., Ltd.. Invention is credited to Byung Chul Ahn, Hong Seok Choi, Chang Wook Han, Hwa Kyung Kim, Woo Jin Nam, Yoon Heung Tak, Shinji Takasugi.
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United States Patent |
RE47,544 |
Kim , et al. |
July 30, 2019 |
Organic light emitting display device and method of manufacturing
the same
Abstract
Provided are a method of manufacturing an organic light emitting
display device and an organic light emitting display device
manufactured by the method. The method includes calculating a
peak-luminance current density for each of a red sub-pixel, a blue
sub-pixel, a green sub-pixel, and a white sub-pixel, calculating an
average use current density for each of the red sub-pixel, blue
sub-pixel, green sub-pixel, and white sub-pixel; determining a size
of each sub-pixel with the peak-luminance current density and the
average use current density, and forming the sub-pixels with the
determined sizes of the respective sub-pixels. The present
invention sets the size of each sub-pixel in consideration of a
peak-luminance current density and an average use current density,
thus easily achieving the peak luminance and enhancing the
color-coordinate life.
Inventors: |
Kim; Hwa Kyung (Gyeonggi-do,
KR), Ahn; Byung Chul (Seoul, KR), Han;
Chang Wook (Seoul, KR), Nam; Woo Jin
(Gyeonggi-do, KR), Choi; Hong Seok (Seoul,
KR), Tak; Yoon Heung (Gyeonggi-do, KR),
Takasugi; Shinji (Gyeonggi-do, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
LG Display Co., Ltd. |
Seoul |
N/A |
KR |
|
|
Assignee: |
LG Display Co., Ltd. (Seoul,
KR)
|
Family
ID: |
1000003257966 |
Appl.
No.: |
15/199,247 |
Filed: |
June 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
13706572 |
Dec 6, 2012 |
8766292 |
Jul 1, 2014 |
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Foreign Application Priority Data
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Dec 21, 2011 [KR] |
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10-2011-0139620 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
27/3216 (20130101); H01L 51/52 (20130101); H01L
51/56 (20130101); H01L 27/3216 (20130101); H01L
27/3213 (20130101); H01L 27/3213 (20130101) |
Current International
Class: |
H01L
27/32 (20060101); H01L 51/52 (20060101); H01L
51/56 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2006189475 |
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Jul 2006 |
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JP |
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20020027932 |
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Apr 2002 |
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KR |
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20050069312 |
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Jul 2005 |
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KR |
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100579171 |
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May 2006 |
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KR |
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100579549 |
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May 2006 |
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KR |
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20060106757 |
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Oct 2006 |
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KR |
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Other References
Chinese Office Action dated Aug. 5, 2014 for corresponding Chinese
patent application No. 201210548066.5. cited by applicant .
Chinese Office Action dated Apr. 13, 2015 for corresponding Chinese
patent application No. 201210548066.5. cited by applicant .
Communication from the European Patent Office dated Mar. 7, 2016
for corresponding EPO patent application No. 12 008 086.6-1552.
cited by applicant .
EPO Communication dated Apr. 3, 2013 transmitting extended European
Search Report for corresponding EPO Application No. 1200808.6.
cited by applicant .
EPO Communication dated Aug. 19, 2014 regarding corresponding EPO
Application No. 12008086.5. cited by applicant .
Korean Patent office communication dated Oct. 8, 2012 regarding
corresponding Korean Application No. 10-2011-0139620. cited by
applicant .
Korean Patent office communication dated Jun. 4, 2012 regarding
corresponding Korean Application No. 10-2011-0139620. cited by
applicant .
Li, J. et al., "White polymer light emitting diodes with
multi-layer device structure," Synthetic metals, Elsevier Sequoia,
Lausanne, CH, vol. 159. No. 1-2, Jan. 1, 2009, p. 36-40,
XP025910838, ISSN: 0379-6779, DOI: 10.1016/J. Synthmet.2008.07.010.
cited by applicant .
Communication from the European Patent Office dated Mar. 27, 2018
regarding a counterpart European patent application No. EP 12 008
086.6. cited by applicant .
Lee, B., et. al. "TFT-LCD with RGBW Color System", SID 03 Digest
(2003) pp. 1212-1215. cited by examiner .
Spindler, J., et. al. "System Considerations for RGBW OLED
Displays"J. of SID 14/1 (2006), pp. 37-48. cited by examiner .
Wei, B., et. al. "High peak luminance of molecularly dye-doped
organic light-emitting diodes under intense voltage pulses", J.
Appl. Phys. 98, (2005) p. 044506-5. cited by examiner.
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Primary Examiner: Vincent; Sean E
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
What is claimed is:
1. An organic light emitting display device, comprising: .Iadd.a
pixel including:.Iaddend. a .Iadd.single .Iaddend.red sub-pixel
.[.formed.]. on a substrate; a .Iadd.single .Iaddend.blue sub-pixel
.[.formed.]. on the substrate; a .Iadd.single .Iaddend.green
sub-pixel .[.formed.]. on the substrate; and a .Iadd.single
.Iaddend.white sub-pixel .[.formed.]. on the substrate,
.Iadd.wherein the sub-pixels are arranged in the order of the red
sub-pixel, the white sub-pixel, the green sub-pixel, and the blue
sub-pixel in one direction, and.Iaddend. wherein, in the
sub-pixels; .[.a sub-pixel having a greatest area is one of.]. a
sub-pixel having a highest peak-luminance current .[.density and a
sub-pixel having a highest average use current density.].
.Iadd.among the red, blue, green, and white sub-pixels has one of a
largest area and a second largest area among the red, blue, green,
and white sub-pixels, and has a larger area than at least one of
the other three sub-pixels.Iaddend., .Iadd.and.Iaddend. .[.a
sub-pixel having a second greatest area is the other of the
sub-pixel having the highest peak-luminance current density and the
sub-pixel having the highest average use current density,.]. the
peak-luminance current .[.density.]. .Iadd.for each sub-pixel
.Iaddend.is a current .[.density.]. necessary for the sub-pixel
.[.for realizing peak luminance that is predetermined maximum peak,
and the average use current density is a current density that is
averagely used with a use time of the sub-pixel.]. .Iadd.to realize
a predetermined maximum luminance value for the
sub-pixel.Iaddend..
2. The organic light emitting display device of claim 1, wherein,
an area of the red sub-pixel is 1.25 to 1.5 times an area of the
white sub-pixel; an area of the blue sub-pixel is 1.25 or less
times and exceeds 1.0 times an area of the white sub-pixel; and an
area of the green sub-pixel is 1.25 or less times and exceeds 1.0
times an area of the white sub-pixel.
3. The organic light emitting display device of claim 1, wherein
the sub-pixels have the same height.[., and are arranged in the
order of the red sub-pixel, the white sub-pixel, the green
sub-pixel, and the blue sub-pixel.]..
.[.4. A method of manufacturing an organic light emitting display
device, comprising: forming a TFT array; forming a 2-peak white
OLED emitting white light by combination of light emitted from
first and second emission layers (EMLs), on the TFT array; and
forming a red sub-pixel, a blue sub-pixel, a green sub-pixel and a
white sub-pixel, wherein, in the forming the sub-pixels: one of a
sub-pixel having a highest peak-luminance current density and a
sub-pixel having a highest average use current density have a
greatest area, and the other of the sub-pixel having the highest
peak-luminance current density and the sub-pixel having the highest
average use current density have a second greatest area..].
5. The method of claim .[.4.]. .Iadd.22.Iaddend., wherein the
sub-pixel having the highest .Iadd.determined
.Iaddend.peak-luminance current density is the red sub-pixel.
.[.6. The method of claim 4, wherein, in the forming the
sub-pixels: an average use current density of the sub-pixel having
the highest average use current density is 6 or less times an
average use current density of the sub-pixel having the lowest
average use current density, a peak-luminance design achievement
degree of a sub-pixel having a highest peak-luminance design
achievement degree is 2 or less times a peak-luminance design
achievement degree of a sub-pixel having the lowest peak-luminance
design achievement degree, and a color-coordinate life of the
organic light emitting display device is 20,000 hours or more, the
color-coordinate life being a time taken until reaching a
predetermined color-coordinate threshold change amount, the
predetermined color-coordinate threshold change amount calculated
by a color-coordinate change amount being 0.015, the
color-coordinate change amount being expressed as
[u'.sub.t-u'.sub.0).sup.2+(v'.sub.t-v'.sub.0).sup.2].sup.1/2, the
color-coordinate change amount being a color-coordinate difference
between initial color coordinates (u'0, v'0) and color coordinates
(u't, v't) after a certain time "t" elapses..].
.Iadd.7. The organic light emitting display device of claim 1,
wherein a sub-pixel having a highest average use current has the
other of the largest area and the second largest area, an average
use current of each sub-pixel being a current of the sub-pixel
averaged over a use time of the sub-pixel, and wherein the
sub-pixel having the highest average use current is the blue
sub-pixel..Iaddend.
.Iadd.8. The organic light emitting display device of claim 7,
wherein the blue sub-pixel has the second largest area, the second
largest area being smaller than the largest area..Iaddend.
.Iadd.9. The organic light emitting display device of claim 1,
wherein the organic light emitting display device has a spectrum
characteristic in which intensity at a wavelength corresponding to
a color of the sub-pixel having the highest peak-luminance current
among red, green, and blue is lower than intensity at wavelengths
respectively corresponding to the other two of red, green, and
blue..Iaddend.
.Iadd.10. The organic light emitting display device of claim 1, the
sub-pixel having the highest peak-luminance current is the red
sub-pixel, and wherein the red sub-pixel has the larger area than
each of the green, blue, and white sub-pixels..Iaddend.
.Iadd.11. An organic light emitting display device, comprising: a
pixel including a red sub-pixel, a blue sub-pixel, a green
sub-pixel, and a white sub-pixel arranged consecutively in one
direction on a substrate; wherein, among the red, blue, green, and
white sub-pixels, the red sub-pixel has one of a largest area and a
second largest area, and has a larger area than at least one of the
blue, green, and white sub-pixels..Iaddend.
.Iadd.12. The organic light emitting display device of claim 11,
wherein, among the red, blue, green, and white sub-pixels, the blue
sub-pixel has the other of the largest area and the second largest
area..Iaddend.
.Iadd.13. The organic light emitting display device of claim 12,
wherein the second largest area is larger than an area of the white
sub-pixel, and wherein the white sub-pixel has a smallest area
among the red, blue, green, and white sub-pixels..Iaddend.
.Iadd.14. The organic light emitting display device of claim 11,
wherein: an area of the red sub-pixel is 1.25 to 1.5 times an area
of the white sub-pixel; the area of the blue sub-pixel is 1.0 to
1.25 times the area of the white sub-pixel; and an area of the
green sub-pixel is 1.0 to 1.25 times the area of the white
sub-pixel..Iaddend.
.Iadd.15. The organic light emitting display device of claim 11,
wherein the organic light emitting display device has a spectrum
characteristic in which intensity at a wavelength corresponding to
red is lower than intensity at wavelengths respectively
corresponding to green and blue..Iaddend.
.Iadd.16. An organic light emitting display device, comprising: a
pixel including: a single red sub-pixel on a substrate; a single
blue sub-pixel on the substrate; a single green sub-pixel on the
substrate; and a single white sub-pixel on the substrate, wherein
the sub-pixels are arranged in the order of the red sub-pixel, the
white sub-pixel, the green sub-pixel, and the blue sub-pixel in one
direction, and wherein the organic light emitting display device
has a spectrum characteristic with respective intensity at
wavelengths respectively corresponding to red, green, and blue, and
wherein a sub-pixel having a color with a lowest corresponding
intensity in the spectrum characteristic among red, blue, and green
has a largest area among the red, blue, green, and white
sub-pixels, and has a larger area than at least one of the other
three sub-pixels..Iaddend.
.Iadd.17. The organic light emitting display device of claim 16,
wherein the sub-pixel having the color with the lowest
corresponding intensity in the spectrum characteristic among red,
blue, and green is red, and the red sub-pixel has the largest area
among the red, blue, green, and white sub-pixels..Iaddend.
.Iadd.18. The organic light emitting display device of claim 16,
wherein the sub-pixel having the color with the lowest
corresponding intensity in the spectrum characteristic among red,
blue, and green has a highest peak-luminance current among the red,
blue, green, and white sub-pixels..Iaddend.
.Iadd.19. The organic light emitting display device of claim 16,
wherein a sub-pixel having a highest average use current has a
second largest area among the red, blue, green, and white
sub-pixels, an average use current of each sub-pixel being a
current of the sub-pixel averaged over a use time of the
sub-pixel..Iaddend.
.Iadd.20. The organic light emitting display device of claim 19,
wherein the sub-pixel having the highest average use current is the
blue sub-pixel, and the second largest area is smaller than the
largest area..Iaddend.
.Iadd.21. The organic light emitting display device of claim 16,
wherein the white sub-pixel has a smallest area among the red,
blue, green, and white sub-pixels..Iaddend.
.Iadd.22. A method of fabricating an organic light emitting display
device having a substrate, the method comprising: determining a
peak-luminance current density for each of a red sub-pixel, a blue
sub-pixel, a green sub-pixel, and a white sub-pixel having a same
area; determining an average use current density for each of the
red, blue, green, and white sub-pixels having the same area;
determining a primary size of each of the red, blue, green, and
white sub-pixels based on the determined peak luminance current
density; determining a secondary size of each of the red, blue,
green, and white sub-pixels based on the determined average use
current density; forming on the substrate a red sub-pixel, a blue
sub-pixel, a green sub-pixel, and a white sub-pixel, each having a
respective size determined based on the primary size and the
secondary size, wherein the forming of the red, blue, green, and
white sub-pixels includes: respectively setting the size of each of
the red, blue, green, and white sub-pixels based on the primary
size and the secondary size; and forming each of the red, blue,
green, and white sub-pixels on the substrate based on the
respectively set size, and wherein: a sub-pixel having a highest
determined peak-luminance current density is formed to have a
largest size among the red, blue, green, and white sub-pixels, and
to have a greater size than at least one of the other three
sub-pixel, an average use current density of the sub-pixel having
the highest determined average use current density is 6 or less
times an average use current density of the sub-pixel having the
lowest determined average use current density, a peak-luminance
design achievement degree of a sub-pixel having a highest
peak-luminance design achievement degree is 2 or less times a
peak-luminance design achievement degree of a sub-pixel having the
lowest peak-luminance design achievement degree, and a
color-coordinate life of the organic light emitting display device
is 20,000 hours or more, the color-coordinate life being a time
taken until reaching a predetermined color-coordinate threshold
change amount, the predetermined color-coordinate threshold change
amount calculated by a color-coordinate change amount being 0.015,
the color-coordinate change amount being expressed as
[u'.sub.t-u'.sub.0).sup.2+(v'.sub.t-v'.sub.0).sup.2].sup.1/2, the
color-coordinate change amount being a color-coordinate difference
between initial color coordinates (u'0, v'0) and color coordinates
(u't, v't) after a certain time "t" elapses..Iaddend.
.Iadd.23. The method of claim 22, wherein a sub-pixel having a
highest determined average use current density is formed to have a
second largest area smaller than the largest area, and wherein the
sub-pixel having the highest determined average use current density
is the blue sub-pixel..Iaddend.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of the Korean Patent
Application No. 10-2011-0139620 filed on Dec. 21, 2011, which is
hereby incorporated by reference as if fully set forth herein.
BACKGROUND
1. Field of the Invention
The present invention relates to an organic light emitting display
device using organic light emitting diodes (OLEDs) and a method of
manufacturing the same.
2. Discussion of the Related Art
Recently, with the advancement of multimedia, the importance of
flat panel display (FPD) devices is increasing. Therefore, various
FPD devices such as liquid crystal display (LCD) devices, plasma
display panel (PDP) devices, field emission display (FED) devices,
and organic light emitting display devices are being used
practically. In such FPD devices, the organic light emitting
display devices have a fast response time of 1 ms or less and low
power consumption, and have no limitation in a viewing angle
because the organic light emitting display devices self-emit light.
Accordingly, the organic light emitting display devices are
attracting much attention as next generation FPD devices.
A related art organic light emitting display device includes a
plurality of pixels that are respectively formed in a plurality of
pixel areas defined by intersections between a plurality of gate
lines and a plurality of data lines, and each of the pixels
includes a red sub-pixel, a green sub-pixel, and a blue sub-pixel.
The related art organic light emitting display device combines red
light, green light, and blue light emitted from the respective
sub-pixels to realize a certain color in units of a pixel, thereby
displaying an image.
FIG. 1 is a diagram illustrating sub-pixels of a related art
organic light emitting display device.
As seen in FIG. 1, the related art organic light emitting display
device 10 includes a red sub-pixel 11, a blue sub-pixel 13, and a
green sub-pixel 15.
According to the organic light emitting display device 10, in a
sub-pixel which is the most used based on the frequency of use and
an accumulated use time for each sub-pixel, a current density
increases compared to the other sub-pixels, and thus, deterioration
is rapidly made, thereby shortening the service life of a
corresponding sub-pixel. As a result, a time for which the color
coordinates of the organic light emitting display device 10 are
changed is shortened, and thus, a color-coordinate life is
shortened.
To overcome such limitations, a method has been proposed in which,
by enlarging the size of a sub-pixel (for example, the blue
sub-pixel 13) having the high frequency of use and an accumulated
much use time compared to the other sub-pixels 11 and 15, the
current density of the blue sub-pixel 13 is lowered, and thus, the
service lives of the sub-pixels 11, 13 and 15 become equal, thereby
extending the color-coordinate life of the organic light emitting
display device 10.
However, as described above, when the size of a blue sub-pixel is
enlarged in order for the service lives of sub-pixels to become
similar, it is impossible to realize the peak luminance of a pure
color of each of the other sub-pixels.
SUMMARY
Accordingly, the present invention is directed to an organic light
emitting display device using organic light emitting diodes (OLEDs)
and a method of manufacturing the same that substantially obviate
one or more problems due to limitations and disadvantages of the
related art.
An aspect of the present invention is directed to an organic light
emitting display device with the consideration of both peak
luminance and a color-coordinate life, and a method of
manufacturing the same.
Additional advantages and features of the invention will be set
forth in part in the description which follows and in part will
become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from practice of the
invention. The objectives and other advantages of the invention may
be realized and attained by the structure particularly pointed out
in the written description and claims hereof as well as the
appended drawings.
To achieve these and other advantages and in accordance with the
purpose of the invention, as embodied and broadly described herein,
there is provided a method of manufacturing an organic light
emitting display device including: calculating a peak-luminance
current density for each of a red sub-pixel, a blue sub-pixel, a
green sub-pixel, and a white sub-pixel; calculating an average use
current density for each of the red sub-pixel, blue sub-pixel,
green sub-pixel, and white sub-pixel; determining a size of each
sub-pixel with the peak-luminance current density and the average
use current density; and forming the sub-pixels with the determined
sizes of the respective sub-pixels.
In another aspect of the present invention, there is provided an
organic light emitting display device including: a red sub-pixel, a
blue sub-pixel, a green sub-pixel, and a white sub-pixel formed on
a substrate, wherein each of the sub-pixels is formed in the
calculated size thereof with the calculated peak-luminance current
density and the calculated average use current density.
It is to be understood that both the foregoing general description
and the following detailed description of the present invention are
exemplary and explanatory and are intended to provide further
explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
FIG. 1 is a diagram illustrating sub-pixels of a related art
organic light emitting display device;
FIG. 2 is a diagram illustrating a schematic structure of an
organic light emitting display device according to an embodiment of
the present invention;
FIG. 3 is a diagram illustrating the area of each sub-pixel of an
organic light emitting display device according to an embodiment of
the present invention;
FIG. 4 is a diagram showing spectrum characteristic of an organic
light emitting display device according to an embodiment of the
present invention;
FIG. 5 is a diagram illustrating a method of manufacturing an
organic light emitting display device according to an embodiment of
the present invention;
FIG. 6 is a sectional view illustrating an organic light emitting
display device according to an embodiment of the present
invention;
FIG. 7 is a view illustrating a sectional surface of an organic
light emitting display device according to another embodiment of
the present invention;
FIGS. 8 to 10 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
28.5:28.5:45:34.2;
FIGS. 11 to 13 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
35:35:35:35;
FIGS. 14 to 16 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
45.5:38.5:39.8:16.3;
FIGS. 17 to 19 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
45:35:35:30; and
FIG. 20 is a graph showing a comparison result of current densities
based on an area ratio of sub-pixels which are described in FIGS. 8
to 19.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to the exemplary embodiments
of the present invention, examples of which are illustrated in the
accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts.
Hereinafter, embodiments of the present invention will be described
in detail with reference to the accompanying drawings.
In description of embodiments of the present invention, when a
structure is described as being formed at an upper portion/lower
portion of another structure or on/under the other structure, this
description should be construed as including a case where the
structures contact each other and moreover a case where a third
structure is disposed therebetween.
FIG. 2 is a diagram illustrating a schematic structure of an
organic light emitting display device according to an embodiment of
the present invention.
As seen in FIG. 2, the organic light emitting display device
according to an embodiment of the present invention includes a gate
lines GL, a data line DL, a power line PL, a red sub-pixel R, a
white sub-pixel W, a green sub-pixel G, and a blue sub-pixel B.
The gate line GL is formed to be extended in a first direction, on
a substrate. The data line DL is formed to intersect the gate line
GL and to be extended in a second direction, on the substrate. The
power line PL may be formed apart from and in parallel to the data
line DL.
A plurality of the gate lines GL and a plurality of the data lines
DL are cross-arranged to define the red sub-pixel R, the white
sub-pixel W, the green sub-pixel G, and the blue sub-pixel B.
A thin film transistor (TFT) and an OLED are formed in each of a
plurality of sub-pixel areas.
The TFT includes a switching TFT and a driving TFT. The switching
TFT is connected to the gate line GL and the data line DL, and
receives a gate signal and a data signal. One end of the switching
TFT is connected to the driving TFT. The TFT driving transistor is
connected to the power line PD and the OLED.
The OLED is formed on the TFT, and includes a cathode electrode, an
organic light emitting layer, and an anode electrode. The organic
light emitting layer includes an electron injection layer (EIL), an
electron transport layer (ETL), an emission layer (EML), a hole
transport layer (HTL), and a hole injection layer (HIL), and has a
structure in which the layers are stacked in a multilayer.
When a driving voltage is applied to the anode electrode and the
cathode electrode, a hole passing through the HTL and an electron
passing through the ETL move to the EML to generate an exciton, and
thus, the EML emits visible light.
In an embodiment of the organic light emitting display device
according to the present invention, the OLED is formed as a white
OLED (WOLED). Therefore, a color filter that converts white light,
emitted from the WOLED, into red light, green light, or blue light
is formed such that the red sub-pixel R, the white sub-pixel W, the
green sub-pixel G, and the blue sub-pixel B express respective
colors. In this case, the color filter may not be formed in an area
in which the white sub-pixel is disposed.
The combination of the red sub-pixel R, the white sub-pixel W, the
green sub-pixel G, and the blue sub-pixel B forms a unit pixel to
express various colors.
FIG. 3 is a diagram illustrating the area of each sub-pixel of an
organic light emitting display device according to an embodiment of
the present invention.
As seen in FIG. 3, in the organic light emitting display device
according to an embodiment of the present invention, the sub-pixels
are designed to have different areas.
In one scheme that differently designs the areas of the sub-pixels,
the red sub-pixel R, the white sub-pixel W, the green sub-pixel G,
and the blue sub-pixel B may have the same height H, and respective
lengths L1 to L4 of the sub-pixels may be differently changed,
specifically, the respective lengths L1 to L4 of the sub-pixels may
differ. In this case, by only adjusting a interval between the data
lines DL, the respective areas of the sub-pixels are differently
changed. However, the present invention is not limited thereto. As
another example, the respective heights H of the sub-pixels may be
differently set, and may be differently designed by various
schemes.
According to an embodiment of the present invention, in designing
the areas of the red, white, green, and blue sub-pixels, the
peak-luminance current density of each of the sub-pixels and the
average use current density of each sub-pixel are considered.
The peak luminance denotes the maximum luminance that is shown at a
color temperature reference satisfying the design spec of the
organic light emitting display device. In an RGB structure, when
realizing the peak luminance, the peak luminance is achieved by a
combination satisfying a color temperature of a product by pure
color of red, green, and blue. In a WRGB structure, there are two
methods, which include a method that realizes the peak luminance
with the red, green, blue, and white sub-pixels and a method that
realizes the peak luminance by using only the red, green, and blue
sub-pixels with no white sub-pixel. In all of the two methods, only
when it is possible to realize the peak luminance, image quality
equal to the image-quality level of the RGB structure is realized
in expressing a pure color.
A color filter is generally used for realizing red, green, and blue
with the WOLED, in which case the efficiency of red, green, and
blue light passing through the color filter is reduced to less than
the efficiency of the WOLED. Therefore, in the WRGB structure, a
high current needs to flow in each of the red, green, and blue
sub-pixels for realizing the peak luminance with only the green,
and blue sub-pixels, and thus, the current density of each of the
green, and blue sub-pixels increases.
To design the area of each sub-pixel in consideration of the
peak-luminance current density and average use current density of
each sub-pixel, the peak luminance current density of each
sub-pixel is calculated, and a sub-pixel having a high
peak-luminance current density is relatively greater designed,
thereby enabling the peak luminance of each sub-pixel to be
achieved more easily. Also, by calculating the average use current
density of each sub-pixel and relatively greater designing a
sub-pixel having a high average use current density, a
deterioration speed difference between the sub-pixels is minimized,
and thus, a color-coordinate life is extended.
As a result, the optimal area of each sub-pixel is designed in
consideration of both the peak-luminance current density and the
average use current density of each sub-pixel, and thus, a peak
luminance achievement rate of each sub-pixel increases and a
deterioration speed difference between the sub-pixels is
minimized.
First, the reason and method that calculates the peak-luminance
current density of each sub-pixel and relatively greater designs a
sub-pixel having a high peak-luminance current density will now be
described.
The peak luminance, as described above, denotes the maximum
luminance value that is predetermined in the organic light emitting
display device. When the peak luminance is set, each sub-pixel is
formed to realize peak luminance for each color. To realize the
peak luminance in this way, a current density necessary for each of
the red, green, blue, and white sub-pixels is defined as a
peak-luminance current density.
Performing comparison based on the same pixel area, the WRGB
sub-pixel structure that further includes a white sub-pixel
compared to the RGB sub-pixel structure is relatively reduced in
area of each of RGB sub-pixels thereof.
Therefore, to show the peak luminance of the same pure color as
that of the RGB sub-pixel structure, the WRGB sub-pixel structure
needs to increase the current density of each of the red, green,
and blue sub-pixels. Especially, some and all of the sub-pixels
have different peak-luminance current densities, and, in an
embodiment of the present invention, the area of a sub-pixel
requiring the highest peak-luminance current density is formed
greater than those of the other sub-pixels.
As a result, by enlarging the area of a sub-pixel requiring the
highest peak-luminance current density, the peak luminance can be
achieved even though the current density of the sub-pixel is
relatively lowered.
Hereinafter, a method according to an embodiment that sets a
peak-luminance current density for achieving the peak luminance for
each sub-pixel will be described with reference to FIG. 4.
FIG. 4 is a diagram showing spectrum characteristic of an organic
light emitting display device according to an embodiment of the
present invention.
As seen in FIG. 4, it can be seen that the organic light emitting
display device according to an embodiment of the present invention
includes a 2-peak WOLED, and particularly, intensity near a
wavelength of about 650 nm displaying red is relatively low.
As seen in the spectrum characteristic of an OLED in which the
intensity of red is low, in the red sub-pixel, it is required to
set the highest peak-luminance current density for achieving the
peak luminance. In this case, therefore, the area of the red
sub-pixel may be formed greater than those of the other sub-pixels
so as to more easily achieve the peak luminance.
On the other hand, in the white sub-pixel, since the white
sub-pixel uses an entire wavelength range of visible light, the
lowest peak-luminance current density may be set for achieving the
peak luminance. In this case, therefore, the area of the white
sub-pixel may be formed greater than those of the other
sub-pixels.
In this way, the peak-luminance current density may be set in
consideration of the spectrum characteristic of the OLED, and, when
the 2-peak WOLED of FIG. 4 is applied, the area of the red
sub-pixel may be relatively greater formed. However, when the
spectrum characteristic of the OLED is changed, the area of a
sub-pixel other than the red sub-pixel may be relatively greater
formed.
Next, the reason and method that calculates the average use current
density of each sub-pixel and relatively greater designs a
sub-pixel having a high average use current density will now be
described.
As the OLED is used, the OLED is deteriorated, and thus, a
sub-pixel emits light having color coordinates different from the
original color coordinates thereof. For this reason, a time taken
until reaching a predetermined color-coordinate threshold change
amount is measured and defined as the color-coordinate life of the
OLED.
A color-coordinate life is construed using the amount of changed
color coordinates (hereinafter referred to as a color-coordinate
change amount).
The color-coordinate change amount is defined as a color-coordinate
difference between initial color coordinates (u'0, v'0) and color
coordinates (u't, v't) after a certain time "t" elapses, according
to the Commission Internationale de I'Eclairage (CIE) 1931 standard
colorimetric system (u', v'). The color-coordinate change amount is
expressed as Equation (1). color-coordinate change
amount=[u'.sub.t-u'.sub.0).sup.2+(v'.sub.t-v'.sub.0).sup.2].sup.1/2
(1)
As the color-coordinate change amount increases, a time taken until
reaching the predetermined color-coordinate threshold change amount
becomes shorter. Accordingly, as a color-coordinate life becomes
shorter and a color-coordinate change amount becomes lower, the
color-coordinate life may be construed as being long.
As a factor affecting the color-coordinate life, there is an
average use current density based on an accumulated use time and
the frequency of use of a sub-pixel. That is, when a sub-pixel is
used for a long time at a high current density, the
color-coordinate life of an OLED is shortened. Accordingly, by
appropriately designing an average use current density, the
color-coordinate life is extended.
Here, the average use current density is defined as current density
that is averagely required according to an accumulated use time and
the frequency of use of each sub-pixel, in reproducing general
images.
When the average use current density of each sub-pixel is measured
by reproducing general images, it can be seen that a sub-pixel
having the highest average use current density is a blue sub-pixel,
a sub-pixel having the second highest average use current density
is a white sub-pixel, and red and green sub-pixels have the third
highest average use current density.
Accordingly, in the present invention, the area of the blue
sub-pixel having the highest average use current density is formed
greater than those of the other sub-pixels. As the area of the blue
sub-pixel having the highest average use current density increases,
the average use current density becomes lower, and thus, the
color-coordinate life of the blue sub-pixel is enhanced.
Image sticking occurs in an initial driving stage of the organic
light emitting display device. Image sticking denotes that a
specific image is stuck and shown due to a sub-pixel whose a
service life has been intensively shortened, in driving a panel.
Image sticking has correlation with the area, color-coordinate
life, and image-sticking life of each sub-pixel. A method of
decreasing image sticking is matched with a condition that
maximizes the color-coordinate life. Therefore, in an operation of
determining the area of a sub-pixel, when a color-coordinate life
is considered, an image-sticking life is not separately considered.
However, depending on the case, the image-sticking life may be
considered in an operation of determining the area of a
sub-pixel.
The image-sticking life is defined as a time taken until an average
luminance reduction ratio becomes a certain ratio, and the certain
ratio may be set to 5%. RGBW sub-pixels have different luminance
reduction ratios, and thus, the average luminance reduction ratio
of each sub-pixel is used in analyzing image sticking.
Here, the multiplication of the luminance ratio and luminance
reduction ratio of each sub-pixel is calculated, the average
luminance reduction ratio is defined as the sum of the
multiplications for the respective sub-pixels.
The present invention enhances the color-coordinate life, and
thereby improves the image-sticking life, thus decreasing image
sticking.
As described above, the peak-luminance current density of each
sub-pixel is calculated, and the area of a sub-pixel having a high
peak-luminance current density is relatively greater set. Also, the
average use current density of each sub-pixel is calculated, and
the area of a sub-pixel having a high average use current density
is relatively greater set. In overall consideration of the two
factors, the area of each sub-pixel may be designed.
Therefore, depending on the case, even though a specific sub-pixel
has the highest peak-luminance current density, the area of the
specific sub-pixel may be set relatively less than those of the
other sub-pixels in the optimally designed state. Similarly, even
though a specific sub-pixel has the highest average use current
density, the area of the specific sub-pixel may be set relatively
less than those of the other sub-pixels in the optimally designed
state.
Referring again to FIG. 3, according to an embodiment of the
present invention, the width L1 of the red sub-pixel, the width L2
of the white sub-pixel, the width L3 of the green sub-pixel, and
the width L4 of the blue sub-pixel are designed to meet a condition
of "L1>L4.gtoreq.L3>L2".
That is, the area of the red sub-pixel is the greatest, the area of
the white sub-pixel is the least, and the area of the blue
sub-pixel is equal to or greater than that of the green
sub-pixel.
In more detail, the area of the red sub-pixel may be 1.25 to 1.5
times that of the white sub-pixel. Also, the area of the blue
sub-pixel may be 1.25 or less times that of the white sub-pixel.
Also, the area of the green sub-pixel may be 1.25 or less times
that of the white sub-pixel.
In an embodiment when the sub-pixels are designed under the
conditions, an area ratio of the red, blue, green, and white
sub-pixels may be 40:35:35:30.
The sub-pixels may be arranged in a stripe type. In this case, the
arrangement order of the sub-pixels may be set as the order of the
red, blue, green, and white sub-pixels. Also, a sub-pixel in which
a high current flows and a sub-pixel in which a low current flows
may be designed to share a Vdd line.
The reason is because the drop of a voltage (IR drop) is caused by
a local current difference of a power line because a high current
flows in the blue and white sub-pixels, and decreases the overall
luminance uniformity of the organic light emitting display device,
causing the reduction in reliability of the organic light emitting
display device. Also, the reason is because a local temperature
difference occurs due to a current difference.
Accordingly, the blue and white sub-pixels in which the highest
current flows are arranged apart from each other, and thus, the
overall luminance uniformity of the organic light emitting display
device is enhanced. Therefore, a temperature difference becomes
uniform, and reliability is enhanced.
In a type in which the sub-pixels are arranged, there is a quad
type in which the sub-pixels are arranged in a checkered shape, in
addition to the stripe type. However, the arrangement type of the
sub-pixels is not limited to the stripe type.
FIG. 5 is a diagram illustrating a method of manufacturing an
organic light emitting display device according to an embodiment of
the present invention. The method of manufacturing the organic
light emitting display device uses the above-described method that
sets the sizes of the sub-pixels. In the following description, a
repetitive description on the same elements as the above-described
elements is not provided.
First, the peak-luminance current density and average use current
density of each sub-pixel having the same area are calculated in
operation S100.
The peak luminance current density, as described above, is
calculated in consideration of the spectrum characteristic of an
OLED, and more specifically, the spectrum characteristic of an
organic light emitting layer.
The average use current density is calculated as a current density
that is averagely required according to an accumulated use time and
the frequency of use of each sub-pixel in reproducing general
images.
Subsequently, the size of each sub-pixel is primarily set with the
calculated peak luminance current density in operation S200. For
example, in a 2-peak white organic light emitting layer, and thus,
the size of the red sub-pixel is greatest set.
Subsequently, the size of each sub-pixel is secondarily set with
the calculated average use current density in operation S300. For
example, when the average use current density of each sub-pixel is
measured by reproducing general images, a sub-pixel having the
highest average use current density may be the blue sub-pixel.
There is no predetermined order between operation S200 (which
primarily sets the size of each sub-pixel with the calculated peak
luminance current density) and operation S300 that secondarily sets
the size of each sub-pixel with the calculated average use current
density. Therefore, after operation S300 that secondarily sets the
size of each sub-pixel, operation S200 that primarily sets the size
of each sub-pixel may be performed.
Subsequently, the optimal size of each sub-pixel is determined with
the setting value (which has been calculated in the operation of
primarily setting the size of each sub-pixel) and the setting value
that has been calculated in the operation of secondarily setting
the size of each sub-pixel, in operation S400.
That is, the optimal size of each sub-pixel is determined with the
primarily set size of each sub-pixel and the secondarily set size
of each sub-pixel.
In this case, an average use current density of a sub-pixel having
the highest average use current density may be 6 or less times that
of a sub-pixel having the lowest average use current density, and
moreover, a peak-luminance design achievement degree of a sub-pixel
having the highest peak-luminance design achievement degree may be
2 or less times that of a sub-pixel having the lowest
peak-luminance design achievement degree, in which case a luminance
deviation between the sub-pixels is reduced. Also, the
color-coordinate life of the organic light emitting display device
may be 20,000 hours or more.
Subsequently, each sub-pixel is formed according to the determined
sub-pixel sizes in operation S500.
A process of forming each sub-pixel may include a process that
forms a TFT array, a process that forms an OLED (including an
organic light emitting layer formed on the TFT array) emitting
white light, and a process that forms a color filter converting
light, emitted from the OLED, into light having a certain
color.
The process that forms the TFT array includes a process that forms
the gate line GL, data line DL, and power line PL of FIG. 2, and a
process that forms the switching TFT and the driving TFT in each
sub-pixel area defined by the gate line GL and the data line
DL.
The process of forming the OLED and the process of forming the
color filter may be differently performed for the respective
sub-pixels. Specifically, a process of forming the red sub-pixel
may include the process of forming the OLED and a process of
forming a red color filter, a process of forming the blue sub-pixel
may include the process of forming the OLED and a process of
forming a blue color filter, a process of forming the green
sub-pixel may include the process of forming the OLED and a process
of forming a green color filter, and a process of forming the white
sub-pixel may include the process of forming the OLED.
The detailed structure of each sub-pixel may be the structure of
FIGS. 6 and 7 to be described below.
FIG. 6 is a sectional view illustrating an organic light emitting
display device according to an embodiment of the present
invention.
As seen in FIG. 6, the organic light emitting display device
according to an embodiment of the present invention includes a
substrate 101, a gate electrode 103, a gate insulator 110, a
semiconductor layer 131, an etch stopper 132, a source electrode
135, a drain electrode 137, a first passivation layer 140, a color
filter 150, a second passivation layer 160, an anode electrode 170,
a bank layer 175, an organic light emitting layer 180, and a
cathode electrode 190.
The substrate 101 may be formed of glass or transparent
plastic.
The gate electrode 103 is formed on the substrate 101, and
connected to the gate line GL. The gate electrode 103 may be a
multilayer formed of one selected from the group consisting of Mo,
Al, Cr, Au, Ti, Ni, Nd, and Cu, and an alloy thereof.
The gate insulator 110 is formed on the gate electrode 103, and may
be silicon oxide (SiOx), silicon nitride (SiNx), or a multilayer
thereof. However, the gate insulator 110 is not limited
thereto.
The semiconductor layer 131 is formed on the gate insulator 110,
and may include amorphous silicon or polycrystalline silicon in
which the amorphous silicon is crystallized.
The etch stopper 132 may be formed on the semiconductor layer 131,
and protect the semiconductor layer 131. However, the etch stopper
132 may not be provided depending on the case.
The source electrode 135 and the drain electrode 137 may be formed
on the semiconductor layer 131. The source electrode 135 and the
drain electrode 137 may be formed in a single layer or a
multilayer. The source electrode 135 and the drain electrode 137
may be formed of one selected from the group consisting of Mo, Al,
Cr, Au, Ti, Ni, Nd, and Cu, and an alloy thereof.
The first passivation layer 140 may be formed on the source
electrode 135 and the drain electrode 137, and may be SiOx, SiNx,
or a multilayer thereof. However, the first passivation layer 140
is not limited thereto.
The color filter 150 is formed in a red sub-pixel area, a blue
sub-pixel area, and a green sub-pixel area, on the first
passivation layer 140. The color filter 150 converts white light,
emitted from an OLED, into red, blue, and green light.
The second passivation layer 160 may be formed on the color filter
150, and may be acryl-based resin, polyimide resin, SiOx, SiNx, or
a multilayer thereof. However, the second passivation layer 160 is
not limited thereto.
A light compensation layer (not shown) may be formed on the second
passivation layer 160. The light compensation layer may be formed
of SiOx or SiNx, or in a multilayer thereof, for enhancing the
color viewing angle characteristic of the organic light emitting
display device.
The anode electrode 170 may be formed on the second passivation
layer 160, and formed of transparent indium tin oxide (ITO) or
indium zinc oxide (IZO). However, the anode electrode 170 is not
limited thereto. The anode electrode 170 is electrically connected
to the source electrode 135. To this end, a contact hole is formed
in a certain region of the first passivation layer 140, and a
contact hole is formed in a certain region of the second
passivation layer 160.
The bank layer 175 may be formed on the anode electrode 170, and
include an organic material such as benzocyclobutene (BCB)-based
resin, acryl-based resin, or polyimide resin. The bank layer 175 is
formed on the anode electrode 170 to have a certain opening such
that light emitted from the organic light emitting layer 180 is
transmitted.
The organic light emitting layer 180 is formed on the bank layer
175, and emits white light. The organic light emitting layer 180
may include an EIL, an ETL, an EML, an HTL, and an HIL, and may be
formed in a multilayer.
When a driving voltage is applied to the anode electrode 170 and
the cathode electrode 190, a hole passing through the HTL and an
electron passing through the ETL move to the EML to generate an
exciton, and thus, the EML emits visible light.
The emitted white light passes through the color filter 150 and is
externally transferred toward the substrate 101. At this point,
light passing through a red color filter 151 is converted into red
light, light passing through a blue color filter 155 is converted
into blue light, and light passing through a green color filter 153
is converted into green light.
The cathode electrode 190 may be formed on the organic light
emitting layer 180, and may use a metal material such as Al, Ca, or
Mg, or a transparent material such as ITO or IZO.
The organic light emitting display device of FIG. 6 relates to an
example of a bottom-emission type, and the present invention may be
applied to various examples of the bottom-emission type known to
those skilled in the art. Also, the present invention may be
applied to a top-emission type, in addition to the bottom-emission
type.
FIG. 7 is a view illustrating a sectional surface of an organic
light emitting display device according to another embodiment of
the present invention.
As seen in FIG. 7, an organic light emitting layer 180 is formed
between an anode electrode 170 and a cathode electrode 190, and
includes a first stack 181, a charge generation layer (CGL) 183,
and a second stack 185.
The first stack 181 may include an EIL, an ETL, a first EML, an
HTL, and an HIL. The first EML may be formed as an emission layer
emitting blue light.
Then second stack 185 may include an EIL, an ETL, a second EML, an
HTL, and an HIL. The second EML may be formed as an emission layer
emitting yellow-green light.
The CGL 183 is formed between the first and second stacks 181 and
185, and formed of a material having low optical loss
characteristic and low electrical loss characteristic.
The organic light emitting layer 180 having the above-described
structure emits white light by combination of the first EML
(emitting blue light) and the second EML (emitting yellow-green
light). Therefore, the organic light emitting layer 180 having the
structure of FIG. 7 may be easily applied to the organic light
emitting display device of FIG. 6.
In addition to the organic light emitting layer 180 including the
two EMLs and emitting white light, an organic light emitting layer
including three or more EMLs and emitting white light may be
applied to the organic light emitting display device of FIG. 6.
Hereinafter, experiment data for determining area ratios by
sub-pixel will be described in detail with reference to graphs.
Comparative Example 1
FIGS. 8 to 10 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
28.5:28.5:45:34.2.
That is, the comparative example 1 is a case in which the area of
the blue sub-pixel is greatest formed. As seen in FIG. 10, since
the area of the blue sub-pixel which is frequently used in
realizing a standard moving image is greatest formed, it can be
seen that the color-coordinate life is good.
However, the comparative example 1 does not consider a
peak-luminance current density, and thus, as seen in FIG. 9, it can
be seen that a peak-luminance design achievement degree of the red
sub-pixel having the highest peak-luminance current density is
58.15% and is very low. That is, it is very difficult to achieve
the peak luminance.
Comparative Example 2
FIGS. 11 to 13 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
35:35:35:35.
That is, the comparative example 2 is a case in which the areas of
all sub-pixels are formed equally. As seen in FIG. 13, it can be
seen that the color-coordinate life is slightly shortened compared
to the comparative example 1.
Moreover, as seen in FIG. 12, in the peak-luminance design
achievement degree, it can be seen that an achievement ratio of the
white sub-pixel is excessively high.
Comparative Example 3
FIGS. 14 to 16 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
45.5:38.5:39.8:16.3.
The comparative example 3 is a case in which the red sub-pixel is
formed to have the greatest area, the blue sub-pixel is formed to
have the second greatest area, the green sub-pixel is formed to
have the third greatest area, and the white sub-pixel is formed to
have the least area.
As seen in FIG. 15, it can be seen that the sub-pixels are formed
to have an overall equal peak-luminance design achievement degree,
and thus, the peak luminance is easily achieved.
However, as seen in FIG. 16, it can be seen that the
color-coordinate life is relatively shortened compared to the
comparative examples 1 and 2. Also, as seen in FIG. 20, it can be
seen that an average current density difference between the green
sub-pixel and the white sub-pixel is large. That is, the average
current density of the white sub-pixel exceeds 6 times that of the
green sub-pixel.
FIG. 20 is a graph showing a comparison result of current densities
based on an area ratio of sub-pixels which are described in FIGS. 8
to 19.
Example 1
FIGS. 17 to 19 are graphs showing peak-luminance current density
requirements, peak-luminance design achievement degree, and
color-coordinate life when an area ratio of a red sub-pixel, a
green sub-pixel, a blue sub-pixel, and a white sub-pixel is
45:35:35:30.
The example 1 is a case in which the red sub-pixel is formed to
have the greatest area, the blue and green sub-pixels are formed to
have the second greatest area, and the white sub-pixel is formed to
have the least white sub-pixel.
As seen in FIG. 18, the example 1 shows an achievement ratio lower
than the peak-luminance design achievement degree of the
comparative example 3, but, as seen in FIG. 19, it can be seen that
the color-coordinate life is enhanced compared to the comparative
example 3. Also, as seen in FIG. 20, it can be seen that the
average current density deviation of each sub-pixel is reduced
compared to the comparative example 3.
As described above, the present invention fundamentally uses a
white sub-pixel having good light emission efficiency, in addition
to red, green, and blue sub-pixels, thus improving the luminance
characteristic of the organic light emitting display device.
Especially, the present invention sets the size of each sub-pixel
in consideration of a peak-luminance current density and an average
use current density, thus easily achieving the peak luminance and
enhancing the color-coordinate life.
The present invention enhances the color-coordinate life, and
thereby improves the image-sticking life, thus decreasing image
sticking.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the inventions. Thus,
it is intended that the present invention covers the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *