Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-12-26
2004-01-06
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C257S298000, C257S296000, C257S308000, C257S300000, C345S048000, C345S084000
Reexamination Certificate
active
06674245
ABSTRACT:
This application claims the benefit of the Korean Patent Application No. P2001-088544 filed on Dec. 29, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to an active matrix organic electroluminescence display (ELD) device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for increasing a luminance and securing a storage capacitance at the same time.
2. Discussion of the Related Art
As information technologies develop rapidly, a necessity for flat panel displays, which have advantages of thinness, light weight, and low power consumption, has been increased. Accordingly, various flat panel display devices, such as a liquid crystal display (LCD) device, a plasma display panel (PDP), a field emission display device, and an electroluminescence display (ELD) device, have been researched and developed. The electro-luminescence display (ELD) device makes use of an electro-luminescence phenomenon, in which light is generated when an electric field of a certain intensity is applied to a fluorescent substance.
The electroluminescence display (ELD) devices can be classified into an inorganic electroluminescence display (ELD) device and an organic electroluminescence display (ELD) device depending upon a source material for exciting carriers. The organic electroluminescence display (ELD) device has drawn attention as an efficient display device for natural colors because it can display all colors from the entire visible light range, and has a high brightness and a low driving voltage. In addition, because the organic electroluminescence display (ELD) device is self-luminescent, it has a high contrast ratio and is suitable for an ultra-thin type display device. Moreover, due to its simple manufacturing process, a level of environmental contamination may become relatively low. Besides, the organic electroluminescence display (ELD) device has a response time of only a few microseconds (&mgr;s), so that it is suitable for displaying moving images. The organic electroluminescence display (ELD) device has no limit in a viewing angle and is stable at low temperature conditions. Because it is driven with a relatively low voltage in the range of about 5V and 15V, manufacturing and design of a driving circuit are easy.
A structure of the organic electroluminescence display (ELD) device is similar to that of the inorganic electroluminescence display (ELD) device, except for that a light-emitting principle is different from that of the inorganic electroluminescence display (ELD) device. More specifically, the organic electroluminescence display (ELD) device emits light on a recombination of an electron and a hole, and thus being referred to as an organic light emitting diode (OLED). Recently, an active matrix type, in which a plurality of pixels are arranged in a matrix form, and a thin film transistor is connected thereto, has been widely applied to the flat panel display devices. The active matrix type is also applied to the organic electro-luminescence display (ELD) device, which is referred to as an active matrix organic electroluminescence display (ELD) device.
FIG. 1
is a circuit diagram illustrating a pixel of a related art active matrix organic electroluminescence display device. As shown in
FIG. 1
, a pixel of the active matrix organic electro-luminescent display device has a switching thin film transistor
4
, a driving thin film transistor
5
, a storage capacitor
6
, and a light emitting diode (LED)
7
. The switching thin film transistor
4
and the driving thin film transistor
5
are formed of p-type polycrystalline silicon thin film transistors. A gate electrode of the switching thin film transistor
4
is connected to the gate line
1
, and a source electrode is connected to the data line
2
. A drain electrode of the switching thin film transistor
4
is connected to a gate electrode of the driving thin film transistor
5
. A drain electrode of the driving thin film transistor
5
is connected to an anode electrode of the light emitting diode (LED)
7
. A source electrode of the driving thin film transistor
5
is connected to a power line
3
, and a cathode electrode of the light emitting diode (LED)
7
is grounded. A storage capacitor
6
is connected to the gate electrode and the source electrode of the driving thin film transistor
5
.
When a signal is applied to the gate line
1
, the switching thin film transistor
4
is turned on, and an image signal from the data line
2
is stored into the storage capacitor
6
through the switching thin film transistor
4
. When the image signal is applied to the gate electrode of the driving thin film transistor
5
, the driving thin film transistor
5
is turned on, thereby allowing the light emitting diode (LED)
7
to emit light. A luminance of the light emitting diode (LED)
7
is controlled by varying a current of the light emitting diode (LED)
7
. The storage capacitor
6
keeps a gate voltage of the driving thin film transistor
5
constant even when the switching thin film transistor
4
is turned off. More specifically, since the driving thin film transistor
5
can be driven by a stored voltage in the storage capacitor
6
, even when the switch thin film transistor is turned off, the electric current may continue to flow into the light emitting diode (LED)
7
, therby allowing the light emitting diode (LED) to emit light until the next image signal comes in.
FIG. 2
is a plane view of the related art active matrix organic electroluminescence display (ELD) device. As shown in
FIG. 2
, a gate line
21
and a data line
22
cross each other and define a pixel region “P”. A switching thin film transistor T
S
is formed at each crossing point of the gate and data lines
21
and
22
and connected to the gate and data line
21
and
22
. A driving thin film transistor T
D
, which is connected to the switching thin film transistor T
S
, is formed in the pixel region “P”. A gate electrode
41
of a driving thin film transistor T
D
is connected to a drain electrode
31
of a switching thin film transistor T
S
. A source electrode
42
of the driving thin film transistor T
D
is connected to a power line
51
, which is parallel to the data line
22
. A drain electrode
43
of the driving thin film transistor T
D
is formed in the pixel region “P” and connected to a pixel electrode
61
, which is formed of a transparent conductive material. A first capacitor electrode
52
, which is connected to the power line
51
, is formed in the pixel region “P”. A second capacitor electrode
71
and
72
is formed of polycrystalline silicon and connected to the gate electrode
41
of the driving thin film transistor T
D
. The second capacitor electrode
71
and
72
overlaps the power line
51
and the first capacitor electrode
52
to form a storage capacitor.
However, since the power line
51
and the first capacitor electrode
52
are formed of an opaque metal material, in the above-described active matrix organic electroluminescence display device, an aperture ratio is decreased. Accordingly, an area of the storage capacitor in the pixel region “P” must be reduced in order to increase the aperture ratio. However, when the area of the storage capacitor is reduced, a storage capacitance of the storage capacitor is decreased, thereby increasing a kick-back voltage. In addition, a leakage of a signal cannot be prevented. Furthermore, in the related art active matrix organic electro-luminescence display (ELD) device, resistances of the power line are electrically connected in series, thereby resulting in a relatively high resistance. Accordingly, an image of low picture quality is displayed due to the heat generated by the high resistance of the power line. This problem becomes more serious as the active matrix organic electroluminescence display (ELD) device becomes larger in size.
SUMMARY OF THE INVENTION
Accordingl
Ahn Tae-Joon
Ko Doo-Hyun
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Philogene Haissa
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