U.S. patent application number 12/408298 was filed with the patent office on 2010-03-25 for display device and method of driving the same.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Young-Jin Chang, In-Do Chung, Ji-Hye Eom, Seong-Hyun Jin, Young-ll Kim, Hyung-Don NA, Doo-Hyung Woo.
Application Number | 20100073266 12/408298 |
Document ID | / |
Family ID | 42037113 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100073266 |
Kind Code |
A1 |
NA; Hyung-Don ; et
al. |
March 25, 2010 |
DISPLAY DEVICE AND METHOD OF DRIVING THE SAME
Abstract
The present invention provides a display device and a method of
driving the same. The display device includes: a light-emitting
device; a first capacitor connected between a first contact point
and a second contact point; a driving transistor including an input
terminal connected to a first voltage, an output terminal, and a
control terminal connected to the second contact point; a first
switching transistor controlled by a first control signal and
connected between a data voltage and the first contact point; a
second switching transistor controlled by a second control signal
and connected between a second voltage and the first contact point;
a third switching transistor controlled by a third control signal
and connected between the second contact point and the second
voltage; a fourth switching transistor controlled by the first
control signal and connected between the second contact point and
the output terminal of the driving transistor; and a fifth
switching transistor controlled by the second control signal and
connected between the light-emitting device and the output terminal
of the driving transistor.
Inventors: |
NA; Hyung-Don; (Seoul,
KR) ; Kim; Young-ll; (Suwon-si, KR) ; Woo;
Doo-Hyung; (Anyang-si, KR) ; Chang; Young-Jin;
(Yongin-si, KR) ; Eom; Ji-Hye; (Suwon-si, KR)
; Chung; In-Do; (Yongin-si, KR) ; Jin;
Seong-Hyun; (Incheon, KR) |
Correspondence
Address: |
H.C. PARK & ASSOCIATES, PLC
8500 LEESBURG PIKE, SUITE 7500
VIENNA
VA
22182
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon-si
KR
|
Family ID: |
42037113 |
Appl. No.: |
12/408298 |
Filed: |
March 20, 2009 |
Current U.S.
Class: |
345/76 |
Current CPC
Class: |
G09G 2300/0819 20130101;
G09G 2310/0262 20130101; G09G 2300/043 20130101; H01L 27/3248
20130101; G09G 2320/0223 20130101; G09G 2320/0261 20130101; H01L
27/3262 20130101; H01L 29/78672 20130101; G09G 2300/0842 20130101;
G09G 3/3233 20130101; G09G 2320/043 20130101; H01L 27/3258
20130101; G09G 2300/0861 20130101 |
Class at
Publication: |
345/76 |
International
Class: |
G09G 3/30 20060101
G09G003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2008 |
KR |
10-2008-0092133 |
Claims
1. A display device, comprising: a light emitting element; a first
capacitor connected between a first contact point and a second
contact point; a driving transistor comprising an input terminal
connected to a first voltage, an output terminal, and a control
terminal, the control terminal connected to the second contact
point; a first switching transistor controlled by a first control
signal and connected between a data voltage and the first contact
point; a second switching transistor controlled by a second control
signal and connected between a second voltage and the first contact
point; a third switching transistor controlled by a third control
signal and connected between the second contact point and the
second voltage; a fourth switching transistor controlled by the
first control signal and connected between the second contact point
and the output terminal of the driving transistor; and a fifth
switching transistor controlled by the second control signal and
connected between the light emitting element and the output
terminal of the driving transistor.
2. The display device of claim 1, wherein the first switching
transistor, the third switching transistor, and the fourth
switching transistor respectively comprise a different channel-type
electric field effect transistor from the second switching
transistor, the fifth switching transistor, and the driving
transistor.
3. The display device of claim 2, wherein the first switching
transistor, the third switching transistor, and the fourth
switching transistor are n-channel electric field effect
transistors.
4. The display device of claim 3, wherein the second switching
transistor, the fifth switching transistor, and the driving
transistor are p-channel electric field effect transistors.
5. The display device of claim 4, wherein the first switching
transistor, the second switching transistor, the third switching
transistor, the fourth switching transistor, and the fifth
switching transistor and the driving transistor comprise
polysilicon.
6. The display device of claim 1, wherein, in a first period, a
second period, a third period, a fourth period, and a fifth period,
the periods being sequentially formed: the first switching
transistor, the second switching transistor, the third switching
transistor, the fourth switching transistor, and the fifth
switching transistor are turned off for the first period; the first
switching transistor, the third switching transistor, and the
fourth switching transistor are turned on, and the second switching
transistor and the fifth switching transistor are turned off for
the second period; the first switching transistor and the fourth
switching transistor are turned on, and the second switching
transistor, the third switching transistor, and the fifth switching
transistor are turned off for the third period; the first switching
transistor, the second switching transistor, the third switching
transistor, the fourth switching transistor, and the fifth
switching transistor are turned off for the fourth period; and the
second switching transistor and the fifth switching transistor are
turned on, and the first switching transistor, the third switching
transistor, and the fourth switching transistor are turned off for
the fifth period.
7. The display device of claim 6, wherein the light emitting
element does not emit light for the first period, the second
period, the third period, and the fourth period, and the light
emitting element emits light for the fifth period.
8. The display device of claim 7, wherein the sum of the first
period, the second period, the third period, the fourth period, and
the fifth period is one frame.
9. The display device of claim 8, wherein the fifth period is half
the one frame.
10. The display device of claim 1, wherein each of the third
switching transistor and the fourth switching transistor comprise a
control terminal, an output terminal, and an input terminal, and
the control terminals of the third switching transistor and the
fourth switching transistor respectively comprise a plurality of
protruding portions.
11. The display device of claim 1, wherein each of the first
switching transistor and the second switching transistor comprise a
control terminal, an output terminal, and an input terminal, and
the control terminals of the first switching transistor, the second
switching transistor, and the driving transistor respectively
comprise a plurality of protruding portions.
12. The display device of claim 11, wherein the fifth switching
transistor comprises a control terminal, an output terminal, and an
input terminal, and the control terminal of the fifth switching
transistor comprises a plurality of protruding portions.
13. A method of driving a display device comprising a light
emitting element, a capacitor connected between a first contact
point and a second contact point, and a driving transistor
comprising an input terminal, an output terminal, and a control
terminal, the control terminal connected to the second contact
point, the method comprising: disconnecting the output terminal of
the driving transistor, the second contact point, and the light
emitting element from each other; connecting a data voltage to the
first contact point and connecting the second contact point to the
output terminal of the driving transistor; connecting a second
voltage to the second contact point; disconnecting the second
contact point from the second voltage; disconnecting the output
terminal of the driving transistor from the second contact point
and disconnecting the first contact point from the data voltage;
and connecting the second voltage to the first contact point and
connecting the light emitting element to the output terminal of the
driving transistor.
14. The method of claim 13, wherein connecting the second voltage
to the first contact point and connecting the light emitting
element to the output terminal of the driving transistor is
performed for half a frame.
15. A display device, comprising: a substrate; a first
semiconductor, a second semiconductor, a third semiconductor, a
fourth semiconductor, a fifth semiconductor, and a sixth
semiconductor arranged on the substrate; a gate insulating layer
arranged on the first semiconductor, the second semiconductor, the
third semiconductor, the fourth semiconductor, the fifth
semiconductor, and the sixth semiconductor; a first control
terminal, a second control terminal, a third control terminal, a
fourth control terminal, a fifth control terminal, a sixth control
terminal, and a sustain electrode arranged on the gate insulating
layer; an interlayer insulating film arranged on the first control
terminal, the second control terminal, the third control terminal,
the fourth control terminal, the fifth control terminal, and the
sixth control terminal; an electrode member opposite to a first
input terminal, a second input terminal, a third input terminal, a
fourth input terminal, a fifth input terminal, and a sixth input
terminal, a first output terminal, a second output terminal, a
third output terminal, a fourth output terminal, a fifth output
terminal, a sixth output terminal, and the sustain electrode, which
are respectively arranged on the interlayer insulating film; a
passivation layer arranged on the first input terminal, the second
input terminal, the third input terminal, the fourth input
terminal, the fifth input terminal, and the sixth input terminal
and the first output terminal, the second output terminal, the
third output terminal, the fourth output terminal, the fifth output
terminal, and the sixth output terminal; a pixel electrode arranged
on the passivation layer and connected to the fifth output
terminal; a partition arranged on the pixel electrode, the
partition comprising an opening exposing a portion of the pixel
electrode; a light emitting member arranged in the opening; a
common electrode arranged on the light emitting member and the
partition; and a capacitor connected between a first contact point
and a second contact point, wherein the first output terminal and
the second output terminal are connected to each other at the first
contact point, and the third output terminal, the fourth input
terminal, and the sixth control terminal are connected to each
other at the second contact point, and at least one of the first
control terminal and the second control terminal comprise a
plurality of protruding portions.
16. The display device of claim 15, wherein at least one of the
third control terminal, the fourth control terminal, and the fifth
control terminal comprise a plurality of protruding portions.
17. The display device of claim 15, wherein the first control
terminal and the fourth control terminal are connected to each
other, and the second control terminal and the fifth control
terminal are connected to each other.
18. The display device of claim 15, wherein the fourth output
terminal, the fifth input terminal, and the sixth output terminal
are connected to each other.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from and the benefit of
Korean Patent Application No. 10-2008-0092133, filed on Sep. 19,
2008, which is hereby incorporated by reference for all purposes as
if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a display device and a
method of driving the same, and more particularly, to an organic
light emitting device (OLED) and a method of driving the same.
[0004] 2. Discussion of the Background
[0005] A pixel of an organic light emitting device includes an
organic light emitting element, and a thin film transistor (TFT)
and a capacitor that drive the OLED.
[0006] The TFT is classified into a polysilicon TFT and an
amorphous silicon TFT according to the kind of active layer.
[0007] Because amorphous silicon forms a thin film by depositing at
a low temperature, amorphous silicon may be used for a
semiconductor layer of a switching element of a display device that
uses glass having a low melting point as a substrate.
[0008] However, because the amorphous silicon TFT has low electron
mobility, it may be difficult to form a display element in a large
size.
[0009] Further, in the amorphous silicon TFT, because a direct
current (DC) voltage is continuously applied to a control terminal,
a threshold voltage may be transited and thus the amorphous silicon
TFT may be deteriorated.
[0010] Thus, deterioration of the amorphous silicon TFT may shorten
a life-span of an OLED.
[0011] Therefore, application of a polysilicon TFT having high
electron mobility, good high frequency operation characteristics,
and a low leakage current is desired.
[0012] Particularly, when using a backplane of low temperature
polycrystalline silicon (LTPS), a shortened life-span of the OLED
may be avoided.
[0013] However, a laser shot mark formed when crystallizing the
polysilicon TFT with a laser may cause a deviation in a threshold
voltage of driving transistors within one panel and thus uniformity
of a screen may be deteriorated.
[0014] In order to solve this problem, the OLED may include a
compensation circuit.
[0015] The compensation circuit includes a plurality of TFTs.
A TFT that is included in the compensation circuit and a driving
transistor of an OLED may generate a leakage current according to
the characteristics thereof. Accordingly, luminance of the OLED may
be lowered, or a function of the compensation pixel may not be
appropriately performed.
[0016] A hold type of flat panel display device such as an organic
light emitting device displays a fixed image for a predetermined
time period, for example for one frame, regardless of whether it is
a still picture or a motion picture.
[0017] For example, when displaying some object that continuously
moves, the object stays at a specific position for a frame and
stays at a position to which the object moves after a time period
of a frame in a next frame, and thus a motion of the object may be
discretely displayed.
[0018] Because a time period of a frame is a time period in which
an afterimage is sustained, even if motion of the object is
displayed in this way, motion of the object may be continuously
viewed.
[0019] However, when viewing a continuously moving object through a
screen, because a line of sight of a person continuously moves
along a motion of the object, the line of sight of a person
collides with a discrete display method of the display device and
thus a blurring phenomenon of a screen may occur.
[0020] For example, it is assumed that the display device displays
as an object stays at a position A in a first frame and at a
position B in a second frame. In the first frame, a line of sight
of a person moves from the position A to the position B along an
estimated movement path of the object.
[0021] However, the object is not actually displayed at an
intermediate position between the positions A and B.
[0022] Finally, because luminance that is recognized by a person
for the first frame is an integrated value of luminance of pixels
in a path between the position A and the position B, i.e., an
average value between luminance of an object and luminance of a
background, an object may be blurredly viewed.
[0023] Because a degree to which an object is blurredly viewed in a
hold type of display device is proportional to a time period in
which the display device sustains the display, a so-called impulse
driving method has been suggested in which an image is displayed
for only a partial time period within one frame and a black color
is displayed for the remaining time period.
[0024] In this way, because a time period for displaying an image
is shortened and luminance is thus decreased, a method of further
increasing luminance for a display time period, or a method of
displaying intermediate luminance of adjacent frames instead of a
black color, has been suggested.
[0025] However, in this method, power consumption may increase and
driving the display device may be complicated.
SUMMARY OF THE INVENTION
[0026] The present invention provides a display device having
advantages of reducing a blurring phenomenon of an image of an
organic light emitting device, compensating a deviation in a
threshold voltage of an organic light emitting device having a
polysilicon TFT, and sustaining reliability of each TFT.
[0027] Additional features of the invention will be set forth in
the description which follows, and in part will be apparent from
the description, or may be learned by practice of the
invention.
[0028] The present invention discloses a display device including:
a light-emitting device; a first capacitor connected between a
first contact point and a second contact point; a driving
transistor including an input terminal connected to a first
voltage, an output terminal, and a control terminal, the control
terminal connected to the second contact point; a first switching
transistor controlled by a first control signal and connected
between a data voltage and the first contact point; a second
switching transistor controlled by a second control signal and
connected between a second voltage and the first contact point; a
third switching transistor controlled by a third control signal and
connected between the second contact point and the second voltage;
a fourth switching transistor controlled by the first control
signal and connected between the second contact point and the
output terminal of the driving transistor; and a fifth switching
transistor controlled by the second control signal and connected
between the light-emitting device and the output terminal of the
driving transistor.
[0029] The present invention also discloses a method of driving a
display device including a light-emitting device, a capacitor
connected between a first contact point and a second contact point,
and a driving transistor including an input terminal, an output
terminal, and a control terminal, the control terminal connected to
the second contact point, the method including: disconnecting the
output terminal of the driving transistor, the second contact
point, and the light-emitting device from each other; connecting a
data voltage to the first contact point and connecting the second
contact point to the output terminal of the driving transistor;
connecting a second voltage to the second contact point;
disconnecting the second contact point from the second voltage;
disconnecting the output terminal of the driving transistor from
the second contact point and disconnecting the first contact point
from the data voltage; and connecting the second voltage to the
first contact point and connecting the light-emitting device to the
output terminal of the driving transistor.
[0030] The present invention also discloses a display device
including: a substrate; a first semiconductor, a second
semiconductor, a third semiconductor, a fourth semiconductor, a
fifth semiconductor, and a sixth semiconductor arranged on the
substrate; a gate insulating layer arranged on the first
semiconductor, the second semiconductor, the third semiconductor,
the fourth semiconductor, the fifth semiconductor, and the sixth
semiconductor; a first control terminal, a second control terminal,
a third control terminal, a fourth control terminal, a fifth
control terminal, a sixth control terminal, and a sustain electrode
arranged on the gate insulating layer; an interlayer insulating
film arranged on the first control terminal, the second control
terminal, the third control terminal, the fourth control terminal,
the fifth control terminal, and the sixth control terminal; an
electrode member opposite to a first input terminal, a second input
terminal, a third input terminal, a fourth input terminal, a fifth
input terminal, and a sixth input terminal, a first output
terminal, a second output terminal, a third output terminal, a
fourth output terminal, a fifth output terminal, a sixth output
terminal, and the sustain electrode, arranged on the interlayer
insulating film; a passivation layer arranged on the first input
terminal, the second input terminal, the third input terminal, the
fourth input terminal, the fifth input terminal, and the sixth
input terminal and the first output terminal, the second output
terminal, the third output terminal, the fourth output terminal,
the fifth output terminal, and the sixth output terminal; a pixel
electrode arranged on the passivation layer and connected to the
fifth output terminal; a partition arranged on the pixel electrode,
the partition comprising an opening exposing a portion of the pixel
electrode; a light emitting member arranged in the opening; and a
common electrode arranged on the light emitting member and the
partition, wherein each of the first control terminal, the second
control terminal, the third control terminal, the fourth control
terminal, the fifth control terminal, and the sixth control
terminal respectively includes a plurality of protruding portions,
and wherein the first output terminal and the second output
terminal are connected to each other, the first control terminal
and the fourth control terminal are connected to each other, the
second control terminal and the fifth control terminal are
connected to each other, the third output terminal, the fourth
input terminal, and the sixth control terminal are connected to
each other, and the fourth output terminal, the fifth input
terminal, and the sixth output terminal are connected to each
other.
[0031] Therefore, a blurring phenomenon of an image of an organic
light emitting device can be reduced and a deviation of a threshold
voltage can be compensated.
[0032] Further, by sustaining reliability of each of TFTs that are
included in the organic light emitting device, display quality can
be improved.
[0033] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention, and together with the description serve to explain
the principles of the invention.
[0035] FIG. 1 is a block diagram of an organic light emitting
device according to an exemplary embodiment of the present
invention.
[0036] FIG. 2 is an equivalent circuit diagram of a pixel in an
organic light emitting device according to an exemplary embodiment
of the present invention.
[0037] FIG. 3 shows an example of a waveform diagram showing a
driving signal that is applied to one row of pixels in an organic
light emitting device according to an exemplary embodiment of the
present invention.
[0038] FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are equivalent
circuit diagrams of a pixel in each period that is shown in FIG.
3.
[0039] FIG. 9 is a layout view of an organic light emitting device
according to an exemplary embodiment of the present invention.
[0040] FIG. 10 and FIG. 11 are cross-sectional views of the organic
light emitting device taken along lines X-X and XI-XI,
respectively, of FIG. 9.
[0041] FIG. 12 is a graph showing a magnitude of a current
according to the difference between an input voltage and an output
voltage of a driving transistor in an organic light emitting device
in a conventional art.
[0042] FIG. 13 is a graph showing a magnitude of a current
according to the difference between an input voltage and an output
voltage of a driving transistor in an organic light emitting device
according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0043] The invention is described more fully hereinafter with
reference to the accompanying drawings, in which embodiments of the
invention are shown. This invention may, however, be embodied in
many different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure is thorough, and will fully convey
the scope of the invention to those skilled in the art. In the
drawings, the size and relative sizes of layers and regions may be
exaggerated for clarity. Like reference numerals in the drawings
denote like elements.
[0044] It will be understood that when an element or layer is
referred to as being "on" or "connected to" another element or
layer, it can be directly on or directly connected to the other
element or layer, or intervening elements or layers may be present.
In contrast, when an element is referred to as being "directly on"
or "directly connected to" another element or layer, there are no
intervening elements or layers present.
[0045] An organic light emitting device according to an exemplary
embodiment of the present invention is described with reference to
FIG. 1 and FIG. 2.
[0046] FIG. 1 is a block diagram of an organic light emitting
device according to an exemplary embodiment of the present
invention, and FIG. 2 is an equivalent circuit diagram of a pixel
in an organic light emitting device according to an exemplary
embodiment of the present invention.
[0047] Referring to FIG. 1, the organic light emitting device
includes a display panel 300, a scanning driver 400, a data driver
500, and a signal controller 600.
[0048] The display panel 300 includes a plurality of signal lines
G.sub.1-G.sub.n and D.sub.1-D.sub.m, a plurality of voltage lines
(not shown), and a plurality of pixels PX that are connected
thereto and that are arranged in an approximate matrix form.
[0049] The signal lines G.sub.1-G.sub.n and D.sub.1-D.sub.m include
a plurality of scanning signal lines G.sub.1-G.sub.n that transfer
a scanning signal and a plurality of data lines D.sub.1-D.sub.m
that transfer a data signal.
[0050] The scanning signal lines G.sub.1-G.sub.n respectively
include first scanning signal lines G.sub.a1, G.sub.a2, . . . ,
G.sub.an that transfer a first scanning signal Vga, second scanning
signal lines G.sub.bl, G.sub.b2, . . . , G.sub.bn that transfer a
second scanning signal Vgb, and third scanning signal lines
G.sub.c1, G.sub.c2, G.sub.cn that transfer a third scanning signal
Vgc.
[0051] The scanning signal lines G.sub.1-G.sub.n extend in a row
direction and are substantially parallel to each other, and the
data lines D.sub.1-D.sub.m extend in a column direction and are
substantially parallel to each other.
[0052] The voltage lines include a driving voltage line (not shown)
that transfers a driving voltage and a sustain voltage line (not
shown) that transfers a sustain voltage. As shown in FIG. 2, each
pixel PX includes an organic light emitting element LD, a driving
transistor Qd, a capacitor Cst, and five switching transistors
Qs1-Qs5.
[0053] The driving transistor Qd has an output terminal, an input
terminal, and a control terminal.
[0054] The control terminal of the driving transistor Qd is
connected to the capacitor Cst at a contact point N2, the input
terminal thereof is connected to a driving voltage Vdd, and the
output terminal thereof is connected to the switching transistor
Qs5.
[0055] One end of the capacitor Cst is connected to the driving
transistor Qd at the contact point N2 and is connected to the
switching transistors Qs1 and Qs2 at a contact point N1.
[0056] The switching transistors Qs1-Qs5 may be included in three
switching units SU1, SU2, and SU3.
[0057] The switching unit SU1 selects one of a data voltage Vdat
and a sustain voltage Vsus in response to first and second scanning
signals Vgai and Vgbi (i=1, 2, . . . , N), connects the selected
voltage to the contact point N1, and includes two switching
transistors Qs1 and Qs2.
[0058] The switching transistor Qs1 operates in response to the
first scanning signal Vgai and is connected between the contact
point N1 and the data voltage Vdat.
[0059] The switching transistor Qs2 operates in response to the
second scanning signal Vgbi and is connected between the contact
point N1 and the sustain voltage Vsus.
[0060] The switching unit SU2 intermits a connection between the
sustain voltage Vsus and the contact point N2 in response to the
third scanning signal Vgci, and includes the switching transistor
Qs2 that is connected between the sustain voltage Vsus and the
contact point N2.
[0061] The switching unit SU3 selects one of the contact point N2
and the light-emitting device LD in response to the first and
second scanning signals Vgai and Vgbi, connects the selected one to
the output terminal of the driving transistor Qd, and includes two
switching transistors Qs4 and Qs5.
[0062] The switching transistor Qs4 operates in response to the
first scanning signal Vgai, is connected between the output
terminal of the driving transistor Qd and the contact point N2, and
the switching transistor Qs5 operates in response to the second
scanning signal Vgbi and is connected between the output terminal
of the driving transistor Qd and the organic light emitting element
LD.
[0063] The switching transistors Qs1, Qs3, and Qs4 are n-channel
electric field effect transistors, and the switching transistors
Qs2 and Qs5 and the driving transistor Qd are p-channel electric
field effect transistors.
[0064] The electric field effect transistor includes, for example,
a TFT, and the TFT may include polysilicon or amorphous
silicon.
[0065] Channel types of the switching transistors Qs1-Q5 and the
driving transistor Qd may be reversed, and in this case, waveforms
of a signal for driving them may also be reversed.
[0066] An anode and a cathode of the organic light emitting element
LD are connected to the switching transistor Qs5 and the common
voltage Vss, respectively.
[0067] The organic light emitting element LD emits light with
different intensity according to the magnitude of a current
I.sub.LD that is supplied by the driving transistor Qd through the
switching transistor Qs5, thereby displaying an image, and the
magnitude of the current I.sub.LD depends on the magnitude of a
voltage between the control terminal and the input terminal of the
driving transistor Qd.
[0068] Referring again to FIG. 1, the scanning driver 400 is
connected to the scanning signal lines G.sub.1-G.sub.n of the
display panel 300 and applies a scanning signal consisting of a
combination of a high voltage Von and a low voltage Voff to each of
the scanning signal lines G.sub.1-G.sub.n.
[0069] The high voltage Von may electrically connect the switching
transistors Qs1, Qs3, and Qs4, or turn off the switching
transistors Qs2 and Qs5, and the low voltage Voff may turn off the
switching transistors Qs1, Qs3, and Qs4, or electrically connect
the switching transistors Qs2 and Qs5.
[0070] The sustain voltage Vsus is a lower than the driving voltage
Vdd.
[0071] The sustain voltage Vsus is applied through a sustain
voltage line (not shown), and the driving voltage Vdd is applied
through a driving voltage line (not shown).
[0072] The data driver 500 is connected to data lines
D.sub.1-D.sub.m of the display panel 300 and applies a data voltage
Vdat representing an image signal to the data lines
D.sub.1-D.sub.m.
[0073] The signal controller 600 controls operations of the
scanning driver 400 and the data driver 500.
[0074] Each of the driving devices 400, 500, and 600 may be
directly mounted on the display panel 300 in at least one
integrated circuit (IC) chip form, may be mounted on a flexible
printed circuit film (not shown) to be attached to the display
panel 300 in a tape carrier package (TCP) form, or may be mounted
on a separate printed circuit board (PCB) (not shown).
[0075] Alternatively, the driving devices 400, 500, and 600
together with the signal lines G.sub.1-G.sub.n and D.sub.1-D.sub.n
and the transistors Qs1 through Qs5 and Qd may be integrated with
the display panel 300.
[0076] Further, the driving devices 400, 500, and 600 may be
integrated into a single chip, and in this case, at least one of
the driving devices 400, 500, and 600, or at least one circuit
element constituting them may be formed outside of the single
chip.
[0077] A display operation of the organic light emitting device
will now be described in detail with reference to FIG. 1, FIG. 2,
FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8.
[0078] FIG. 3 shows an example of a waveform diagram of a driving
signal that is applied to one row of pixels in an organic light
emitting device according to an exemplary embodiment of the present
invention, and FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are
equivalent circuit diagrams of a pixel in each period that is shown
in FIG. 3.
[0079] The signal controller 600 receives an input image signal Din
and an input control signal ICON that controls the display of the
input image signal Din from an external graphics controller (not
shown).
[0080] The input image signal Din includes luminance information of
each pixel PX, and luminance thereof has grays of a given quantity,
for example, 1024=2.sup.10, 256=2.sup.8, or 64=2.sup.6.
[0081] The input control signal ICON includes, for example, a
vertical synchronization signal, a horizontal synchronization
signal, a main clock signal, and a data enable signal. The signal
controller 600 appropriately processes the input image signal Din
to correspond to an operating condition of the display panel 300
based on the input image signal Din and the input control signal
ICON, and generates a scan control signal CONT1, a data control
signal CONT2, and an output image signal Dout.
[0082] The signal controller 600 sends the scan control signal
CONT1 to the scanning driver 400 and sends the data control signal
CONT2 and an output image signal Dout to the data driver 500.
[0083] The scan control signal CONT1 may include a scanning start
signal STV that instructs the scanning start of a high voltage Von
for the scanning signal lines G.sub.1-G.sub.n, at least one clock
signal that controls an output period of a high voltage Von, and an
output enable signal OE that limits a sustain time period of the
high voltage Von.
[0084] The data control signal CONT2 includes a horizontal
synchronization start signal that notifies the transmission start
of a digital image signal Dout for one row of pixels PX, and a data
clock signal HCLK and a load signal that apply an analog data
voltage to the data lines D.sub.1-D.sub.m.
[0085] The scanning driver 400 sequentially changes a scanning
signal that is applied to the scanning signal lines G.sub.1-G.sub.n
to a high voltage Von and then to a low voltage Voff according to a
scan control signal CONT1 from the signal controller 600.
[0086] According to the data control signal CONT2 from the signal
controller 600, the data driver 500 receives a digital output image
signal Dout for each row of pixels PX, converts the output image
signal Dout to an analog data voltage Vdat, and then applies the
analog data voltage Vdat to the data lines D.sub.1-D.sub.m.
[0087] The data driver 500 outputs a data voltage Vdat for one row
of pixels PX for one horizontal period 1 H.
[0088] Hereinafter, a specific row of pixel, for example an i-th
row of pixels, is described.
[0089] Referring to FIG. 3, the scanning driver 400 changes the
second scanning signal Vgbi that is applied to a second scanning
signal line G.sub.bi to a high voltage Von according to a scan
control signal CONT1 from the signal controller 600, and sustains
scanning signals Vgai and Vgci that are applied to the first and
third scanning signal lines G.sub.ai and G.sub.ci, respectively, at
a low voltage Voff.
[0090] Accordingly, as shown in FIG. 4, the first, third, and
fourth switching transistors Qs1, Qs3, and Qs4 are turned off, and
the second and fourth switching transistors Qs2 and Qs5 sustain a
turned-off state.
[0091] Because the switching transistor Qs5 is turned off, the
organic light emitting element LD does not emit light, and this is
called a first period T1.
[0092] Thereafter, the scanning driver 400 changes a voltage of the
scanning signals Vgai and Vgci that are applied to the first and
third scanning signal lines G.sub.ai and G.sub.ci from a low
voltage Voff to a high voltage Von according to the scan control
signal CONT1 from the signal controller 600, and sustains the
second scanning signal Vgbi that is applied to the second scanning
signal line G.sub.bi at a high voltage Von.
[0093] Accordingly, as shown in FIG. 5, the switching transistors
Qs1, Qs3, and Qs4 are turned on and the switching transistors Qs2
and Qs5 sustain a turned-off state, and this is called a second
period T2.
[0094] In the second period T2, the data voltage Vdat is applied to
the contact point N1, the sustain voltage Vsus is applied to the
contact point N2, and a voltage difference between the two contact
points N1 and N2 is stored in the capacitor Cst.
[0095] Therefore, the driving transistor Qd is turned on to flow a
current, but because the switching transistor Qs5 is turned off,
the organic light emitting element LD does not emit light.
[0096] Thereafter, the scanning driver 400 changes a voltage of a
scanning signal Vgci that is applied to the third scanning signal
line G.sub.ci from a high voltage Von to a low voltage Voff
according to the scan control signal CONT1 from the signal
controller 600, and sustains the first and second scanning signals
Vgai and Vgbi that are applied to the first and second scanning
signal lines G.sub.ai and G.sub.bi, respectively, at a high voltage
Von.
[0097] Accordingly, as shown in FIG. 6, the first and fourth
switching transistors Qs1 and Qs4 are turned on, and the second,
third, and fifth switching transistors Qs2, Qs3, and Qs5 sustain a
turned-off state, and this is called a third period T3.
[0098] In the third period T3, the contact point N2 is separated
from the sustain voltage Vsus.
[0099] Because the driving transistor Qd sustains a turned-on
state, charges that have been charged to the capacitor Cst are
discharged through the driving transistor Qd.
[0100] The discharge stops when a voltage difference between the
control terminal and the input terminal of the driving transistor
Qd becomes a threshold voltage Vth of the driving transistor
Qd.
[0101] Therefore, a voltage V.sub.N2 of the contact point N2
converges on the following voltage value.
V.sub.N2=Vdd+Vth (Equation 1)
[0102] In this case, because a voltage V.sub.N1 of the contact
point N1 sustains a data voltage Vdat, a voltage that is stored in
the capacitor Cst is represented by Equation 2.
V.sub.N1-V.sub.N2=Vdat-(Vdd+Vth) (Equation 2)
[0103] Thereafter, the scanning driver 400 changes a voltage of the
first scanning signal Vgai that is applied to the first scanning
signal line G.sub.ai from a high voltage Von to a low voltage Voff
according to the scan control signal CONT1 from the signal
controller 600, sustains a voltage of the second scanning signal
Vgbi that is applied to the second scanning signal line G.sub.bi at
a high voltage Von, and sustains the third scanning signal Vgci
that is applied to the third scanning signal line G.sub.ci at a low
voltage Voff.
[0104] Thereafter, as shown in FIG. 7, the first and fourth
switching transistors Qs1 and Qs4 are turned off, and the second,
third, and fifth switching transistors Qs2, Qs3, and Qs5 sustain a
turned-off state.
[0105] This is called a fourth period T4.
[0106] In the fourth period T4, because a voltage that is stored in
the capacitor Cst is sustained, the driving transistor Qd is
electrically connected to flow a current, but because the switching
transistor Qs5 is turned off, the organic light emitting element LD
does not emit light.
[0107] Thereafter, the scanning driver 400 changes a voltage of the
second scanning signal Vgbi that is applied to the second scanning
signal line G.sub.bi from a high voltage Von to a low voltage Voff
according to the scan control signal CONT1 from the signal
controller 600, and sustains the first and third scanning signals
Vgai and Vgci that are applied to the first and third scanning
signal lines G.sub.ai and G.sub.ci, respectively, at a low voltage
Voff.
[0108] Accordingly, as shown in FIG. 8, the second and fifth
switching transistors Qs2 and Qs5 are turned on, and the first,
third, and fourth switching transistors Qs1, Qs3, and Qs4 sustain a
turned-off state, and this is called a fifth period T5.
[0109] In the fifth period T5, the contact point N1 is separated
from the data voltage Vdat to be connected to the sustain voltage
Vsus, and the control terminal of the driving transistor Qd is
floated.
[0110] Therefore, the voltage V.sub.N2 of the contact point N2 is
represented by Equation 3.
V.sub.N2=Vdd+Vth-Vdat+Vsus (Equation 3)
[0111] As the switching element Qs5 is turned on, the output
terminal of the driving transistor Qd is connected to the
light-emitting device LD, and the driving transistor Qd flows an
output current I.sub.LD that is controlled by a voltage difference
Vgs between the control terminal and the input terminal of the
driving transistor Qd.
I LD = 1 / 2 .times. K .times. ( Vgs - Vth ) 2 = 1 / 2 .times. K
.times. ( V N 2 - Vdd - Vth ) 2 = 1 / 2 .times. K .times. ( Vdd +
Vth - Vdat + Vsus - Vdd - Vth ) 2 = 1 / 2 .times. K .times. ( Vdat
- Vsus ) 2 ( Equation 4 ) ##EQU00001##
[0112] where K is a constant according to characteristics of the
driving transistor Qd, K=.mu.CiW/L, .mu. is electric field effect
mobility, Ci is capacity of a gate insulation layer, W is a channel
width of the driving transistor Qd, and L is a channel length of
the driving transistor Qd.
[0113] According to Equation 4, the output current I.sub.LD in the
light emitting period T3 is determined by only the data voltage
Vdat and the sustain voltage Vsus.
[0114] Therefore, the output current I.sub.LD is not influenced by
a threshold voltage Vth of the driving transistor Qd.
[0115] The output current I.sub.LD is supplied to the organic light
emitting element LD, and the organic light emitting element LD
emits light with different intensity according to a magnitude of
the output current I.sub.LD, thereby displaying an image.
[0116] Therefore, even if there is a deviation in a threshold
voltage Vth between the driving transistors Qd, or even if a
magnitude of a threshold voltage Vth of each driving transistor Qd
sequentially changes, a uniform image can be displayed.
[0117] The fifth period T5 is sustained until a first period T1 for
an i-th row of pixels PX starts again in a next frame, and an
operation in each of the periods T1-T5 is equally repeated in a
next row of pixels PX.
[0118] However, for example, a first period T1 of an (i+1)th row
starts after a fifth period T5 of an i-th row ends.
[0119] In this way, as all scanning signal lines G.sub.1-G.sub.n
sequentially perform a control of the periods T1-T5, the
corresponding images are displayed in all pixels PX.
[0120] As described above, in the first to fourth periods T1-T4,
because the fifth switching transistor Qs5 is turned off, the
light-emitting device LD does not emit light, and in the fifth
period T5, because the fifth switching transistor Qs5 is turned on,
the light-emitting device LD emits light.
[0121] Here, the first period T1 secures a portion of a period in
which the light-emitting device does not emit light, and the fourth
period T4 functions as a buffer before a time period in which the
light-emitting device emits light.
[0122] In this way, if one frame is divided into periods T1-T4 in
which the light-emitting device LD does not emit light and a period
T5 in which the light-emitting device LD emits light, a screen
displays black for the periods T1-T4 in which the light-emitting
device LD does not emit light, and thus an impulse driving effect
may be obtained.
[0123] Therefore, blurring of an image may be prevented.
[0124] The sum of the first to fourth periods T1-T4 may be
identical to a length of the fifth period T5.
[0125] Therefore, the sum of the first to fourth periods T1-T4 and
the fifth period T5 may be about half a frame.
[0126] However, the length of each of the periods T1-T5 may be
adjusted as needed.
[0127] Now, an organic light emitting device according to an
exemplary embodiment of the present invention will be described in
detail with reference to FIG. 9, FIG. 10, and FIG. 11.
[0128] FIG. 9 is a layout view of an organic light emitting device
according to an exemplary embodiment of the present invention, and
FIG. 10 and FIG. 11 are cross-sectional views of the organic light
emitting device taken along lines X-X and XI-XI, respectively, of
FIG. 9.
[0129] A blocking layer 111 that is made of silicon oxide or
silicon nitride is formed on a substrate 110 that is made of
transparent glass, etc.
[0130] The blocking layer 111 may have a dual-layer structure.
[0131] A plurality of first, second, third, fourth, fifth, and
sixth semiconductor islands 154s1, 154s2, 154s3, 154s4, 154s5, and
154d that are made of polysilicon, etc., are formed on the blocking
layer 111.
[0132] Each of the first, third, and fourth semiconductor islands
154s1, 154s3, and 154s4 includes a plurality of extrinsic regions
including n-type conductive impurities and at least one intrinsic
region that includes a very small amount of conductive
impurities.
[0133] Each of the second, fifth, and sixth semiconductor islands
154s2, 154s5, and 154d includes a plurality of extrinsic regions
including p-type conductive impurities and at least one intrinsic
region that includes a very small amount of conductive
impurities.
[0134] The p-type conductive impurities may include boron (B),
gallium (Ga), etc., and the n-type conductive impurities may
include phosphorus (P), arsenic (As), etc.
[0135] In the sixth semiconductor island 154d, an extrinsic region
includes a source region 153d, a drain region 155d, and an
intermediate region 152d, and these regions are doped with p-type
impurities and are separated from each other.
[0136] The intrinsic region includes a pair of channel regions
156d1 and 156d2 that are positioned between the extrinsic regions
152d, 153d, and 155d.
[0137] The extrinsic regions may further include a lightly doped
region (not shown) that is positioned between the channel regions
156d1 and 156d2 and the source and drain regions 153a, 153d, and
155d.
[0138] The lightly doped region may be replaced with an offset
region that includes very few impurities.
[0139] The first to fifth semiconductors 154s1-154s5 also include
source and drain regions, an intermediate region, and a channel
region (not shown), as in the sixth semiconductor 154d.
[0140] A gate insulating layer 140 that is made of silicon oxide or
silicon nitride is formed on the semiconductors 154s1-5 and 154d
and the blocking layer 111.
[0141] A plurality of gate conductors including first, second, and
third gate lines 121a, 121b, and 121c, first and second electrode
members 124d and 128, a sustain voltage line 126, a common voltage
line 127, and a first driving voltage line 176a are formed on the
gate insulating layer 140.
[0142] The first, second, and third gate lines 121a, 121b, and 121c
transfer a gate signal and extend substantially in a horizontal
direction.
[0143] The first gate line 121a includes first and fourth control
electrodes 124s1 and 124s4, the second gate line 121b includes
second and fifth control electrodes 124s2 and 124s5, and the third
gate line 121c includes a third control electrode 124s3.
[0144] The second electrode member 124d forms a sixth control
electrode 124d.
[0145] Each of the first to sixth control electrodes 124s1-5 and
124d respectively includes two protruding portions 124s1a and 124s
1b, 124s2a and 124s2b, 124s3a and 124s3b, 124s4a and 124s4b, 124s5a
and 124s5b, and 124da and 124db that are opposite to each
other.
[0146] In FIG. 9, the protruding portions 124s1a, 124s1b, 124s2a,
124s2b, 124s3a, 124s3b, 124s4a, 124s4b, 124s5a, 124s5b, 124da, and
124db are shown in pairs, but the quantity of the protruding
portions is not limited thereto and the protruding portions may be
formed in a quantity of more than pairs.
[0147] The first to sixth control electrodes 124s1-5 and 124d
intersect the first to sixth semiconductor islands 154s1-5 and 154d
and overlap each of the channel regions 156d1 and 156d2.
[0148] Each of the gate lines 121a-c includes wide end parts 129a,
129b and 129c, in order to connect to other layers or an external
driving circuit.
[0149] When a gate driving circuit for generating a gate signal is
integrated with the substrate 110, the gate lines 121a-c are
extended to be directly connected to the gate driving circuit.
[0150] The second electrode member 128 forms a storage electrode
128.
[0151] A sustain voltage Vsus is applied to the sustain voltage
line 126 and extends in a horizontal direction.
[0152] A driving voltage Vdd is applied to the first driving
voltage line 176a and extends in a horizontal direction.
[0153] An interlayer insulating film 160 is formed on the gate
conductors 121a-c, 124d, and 128.
[0154] Contact holes 162a and 162b that expose the sustain voltage
line 126, contact holes 163s1, 165s1, 163s2, 165s2, 163s3, 165s3,
163s4, 165s4, 163s5, 165s5, 163d, and 165d that expose each of
source and drain regions of the first to sixth semiconductor
islands 154s1-5 and 154d, a contact hole 164 that exposes some of
the storage electrode 128, a contact hole 166 that exposes some of
the sixth control electrode 124d, and contact holes 167a and 167b
that expose some of the first driving voltage line 176a are formed
in the interlayer insulating film 160 and the gate insulating layer
140.
[0155] A plurality of data conductors including a data line 171, a
second driving voltage line 176b, and third to eighth electrode
members 177a, 177b, 177c, 177d, 177e, and 177f are formed on the
interlayer insulating film 160.
[0156] The data line 171 transfers a data signal and mainly extends
in a vertical direction to intersect the gate lines 121a-c.
[0157] Each data line 171 includes a first input electrode 173s1
that is connected to a source region of the first semiconductor
154s1 through the contact hole 163s1, and may include a wide end
part 179 in order to connect to other layers or an external driving
circuit.
[0158] When a data driving circuit for generating a data signal is
integrated with the substrate 110, the data line 171 is extended to
be directly connected to a data driving circuit.
[0159] The third electrode member 177a includes a first output
electrode 175s1 that is connected to a drain region of the first
semiconductor island 154s1 through the contact hole 165s1, a second
output electrode 175s2 that is connected to a drain region of the
second semiconductor 154s2 through the contact hole 165s2, and a
wide part 178 that forms a capacitor Cst by overlapping with the
storage electrode 128.
[0160] The fourth electrode member 177b includes a second input
electrode 173s2 that is connected to a source region of the second
semiconductor island 154s2 through the contact hole 163s2, and the
second input electrode 173s2 is connected to the sustain voltage
line 126 through the contact hole 162a.
[0161] The fifth electrode member 177c includes a third input
electrode 173s3 that is connected to a source region of the third
semiconductor island 154s3 through the contact hole 163s3, and the
third input electrode 173s3 is connected to the sustain voltage
line 126 through the contact hole 162b.
[0162] The sixth electrode member 177d includes a third output
electrode 175s3 that is connected to a drain region of the third
semiconductor 154s3 through the contact hole 165s3 and a fourth
input electrode 173s4 that is connected to a source region of the
fourth semiconductor island 154s4 through the contact hole
163s4.
[0163] The sixth electrode member 177d is connected to the first
and second output electrodes 175s1 and 175s2 through the contact
hole 164 and is connected to the sixth control electrode 124d
through the contact hole 166.
[0164] The seventh electrode member 177e includes a fourth output
electrode 175s4 that is connected to a drain region of the fourth
semiconductor island 154s4 through the contact hole 165s4, a fifth
input electrode 173s5 that is connected to a source region of the
fifth semiconductor island 154s5 through the contact hole 163s5,
and a sixth output electrode 175d that is connected to a drain
region of the sixth semiconductor 154d through the contact hole
165d.
[0165] The eighth electrode member 177f includes a fifth output
electrode 175s5 that is connected to a drain region of the fifth
semiconductor 154s5 through the contact hole 165s5.
[0166] The second driving voltage line 176b transfers a driving
voltage and extends substantially in a vertical direction to cross
the gate lines 121a-c.
[0167] The second driving voltage line 176b includes a plurality of
sixth input electrodes 173d that are connected to a source region
of the sixth semiconductor 154d through the contact hole 163d.
[0168] The second driving voltage line 176b is connected to the
first driving voltage line 176a through the contact holes 167a and
167b.
[0169] A passivation layer 180 is formed on the data conductors
171, 172, 175a, and 175b.
[0170] The passivation layer 180 includes a lower layer 180p that
is made of an inorganic material and an upper part 180q that is
made of an organic material.
[0171] A plurality of contact holes 185 that expose the fifth
output electrode 175s5 are formed in the passivation layer 180.
[0172] A plurality of contact holes 182 that expose an end part of
the data line 171 may also be formed in the passivation layer 180,
and a plurality of contact holes 181a-c that respectively expose an
end part of the gate lines 121a-c may be formed in the passivation
layer 180 and the interlayer insulating film 160.
[0173] A reflection layer 192 is formed on the passivation layer
180, and a plurality of pixel electrodes 191 are formed on the
reflection layer 192.
[0174] Each pixel electrode 191 is physically and electrically
connected to a fifth output electrode 175s5 through a contact hole
185.
[0175] A plurality of contact assistants 81a, 81b, 81c and 82 may
also be formed on the passivation layer 180, and they are connected
to an exposed end part of the gate lines 121a-c and the data line
171.
[0176] A partition 360 is formed on the passivation layer 180.
[0177] The partition 360 encloses a periphery of an edge of the
pixel electrode 191 like a bank to define an opening, and is made
of an organic insulator or an inorganic insulator.
[0178] The partition 360 may also be made of a photoresist
including a black pigment, and in this case, the partition 360
performs a function of a light blocking member and has a simple
forming process.
[0179] An organic light emitting member 370 is formed in a region
on the pixel electrode 191 that is surrounded by the partition
360.
[0180] The organic light emitting member 370 is made of an organic
material that emits light of any one of three primary colors of
red, green, and blue.
[0181] A common electrode 270 is formed on the organic light
emitting member 370.
[0182] The common electrode 270 receives a common voltage and is
made of a reflective metal including calcium (Ca), barium (Ba),
magnesium (Mg), aluminum, silver, etc., or a transparent conductive
material such as indium tin oxide (ITO) or indium zinc oxide
(IZO).
[0183] The common electrode 270 is connected to a common voltage
line 127 through a contact hole (not shown), thereby lowering
resistance of the common electrode 270.
[0184] In the organic light emitting device, the
first/second/third/fourth/fifth semiconductor islands 154s1-5, the
first/second/third/fourth/fifth control electrodes 124s1-5, the
first/second/third/fourth/fifth input electrodes 173s1-5, and the
first/second/third/fourth/fifth output electrodes 175s1-5
respectively constitute first/second/third/fourth/fifth switching
TFTs Qs1/Qs2/Qs3/Qs4/Qs5, and channels of the
first/second/third/fourth/fifth switching TFTs Qs1/Qs2/Qs3/Qs4/Qs5
are formed in channel regions of the
first/second/third/fourth/fifth semiconductor islands 154s1-5.
[0185] The sixth semiconductor island 154d, the sixth control
electrode 124d, the sixth input electrode 173d, and the sixth
output electrode 175d constitute a driving TFT Qd, and a channel of
the driving TFT Qd is formed in a channel region of the sixth
semiconductor 154d.
[0186] Here, one electrode of each of the first to fourth switching
transistors Qs1, Qs2, Qs3, and Qs4 and the driving transistors Qd
is connected to a capacitor Cst that is formed by the storage
electrode 128 and a wide part 178 of the third electrode
member.
[0187] As described above, because each of the control electrodes
124s1-4 and 124d of the first to fourth switching transistors Qs1-4
and the driving transistor Qd respectively has two protruding
portions 124s1a and 124s1b, 124s2a and 124s2b, 124s3a and 124s3b,
124s4a and 124s4b, and 124da and 124db that are opposite to each
other, a channel thereof is divided into two parts.
[0188] Accordingly, because a leakage current of each of the
transistors Qs1-4 and Qd decreases, a current flowing to each of
the transistors Qs1-4 and Qd according to an external environment
such as time and temperature factors is uniformly sustained.
[0189] Therefore, reliability of each of the transistors Qs1-4 and
Qd can be secured.
[0190] Particularly, reliability of the transistors Qs1, Qs2, Qs3,
Qs4, and Qd that are connected to the capacitor Cst to influence on
capacitance of the capacitor Cst is secured, and thus luminance of
the display device sustain can be sustained at a desired level.
[0191] The pixel electrode 191, the organic light emitting member
370, and the common electrode 270 constitute an organic light
emitting diode, and the pixel electrode 191 becomes an anode and
the common electrode 270 becomes a cathode, or the pixel electrode
191 becomes a cathode and the common electrode 270 becomes an
anode.
[0192] An effect of an organic light emitting device according to
an exemplary embodiment of the present invention is now described
with reference to FIG. 12 and FIG. 13.
[0193] FIG. 12 is a graph showing a magnitude of a current
according to the difference between an input voltage and an output
voltage of a driving transistor in an organic light emitting device
in a conventional art, and FIG. 13 is a graph showing a magnitude
of a current according to the difference between an input voltage
and an output voltage of a driving transistor in an organic light
emitting device according to an exemplary embodiment of the present
invention.
[0194] FIG. 12 shows a case where a control terminal of the driving
transistor includes one protruding portion, and FIG. 13 shows a
case where a control terminal of the driving transistor includes
two or more protruding portions according to an exemplary
embodiment of the present invention.
[0195] For convenience, only a control terminal of the driving
transistor was changed and an experiment was performed.
[0196] Referring to FIG. 12, a curved line of a current I.sub.LD
according to the difference Vgs between an input voltage and an
output voltage of the driving transistor sequentially has different
forms.
[0197] That is, a current I.sub.LD according to the same voltage
difference Vgs decreases to some degree and then again
increases.
[0198] Therefore, it can be seen that a current I.sub.LD according
to a voltage difference Vgs may be sequentially unstable.
[0199] In contrast, referring to FIG. 13, a curved line of a
current I.sub.LD according to the difference Vgs between an input
voltage and an output voltage of the driving transistor
sequentially has the same form.
[0200] Therefore, as a constant current I.sub.LD flows regardless
of a driving time period, reliability of the transistor may be
improved.
[0201] It will be apparent to those skilled in the art that various
modifications and variation can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *