Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-02-23
2004-04-20
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S505000
Reexamination Certificate
active
06724149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an emissive display device using emissive elements, such as electroluminescence elements, which employs thin film transistors for controlling such elements.
2. Description of the Related Art
In recent years, electroluminescence (referred to hereinafter as “EL”) display devices comprising EL elements have gained attention as potential replacements for CRTs and LCDS. Research has been directed to the development of EL display devices using, for example, thin film transistors (referred to hereinafter as “TFT”) as switching elements to drive the EL elements.
FIG. 1
is a plan view showing one display pixel of an organic EL display device.
FIG. 2
illustrates an equivalent circuit for a plurality of display pixels in an organic EL display device.
FIG. 3A
shows a cross-sectional view taken along line A—A of
FIG. 1
, while
FIG. 3B
shows a cross-sectional view taken along line B—B of FIG.
1
.
As shown in
FIGS. 1
,
2
,
3
A, and
3
B, each display pixel is formed in a region surrounded by gate signal lines
151
and drain signal lines
152
. A first TFT serving as a switching element is disposed near a intersection of those signal lines. The source
131
s
of the TFT simultaneously functions as a capacitor electrode
155
such that, together with the opposing storage capacitor electrode
154
described later, it forms a capacitor. The source
131
s
is connected to a gate electrode
142
of a second TFT
140
that drives the organic EL element. The source
141
s
of the second TFT
140
contacts with the anode
161
of the organic EL element. The drain
141
d
is connected to a power source line
153
.
Near the TFT
130
, a storage capacitor electrode
154
is disposed in parallel with a gate signal line
151
. The storage capacitor electrode
154
is made of a material such as chromium. The storage capacitor electrode
154
contacts the capacitor electrode
155
via a gate insulating film
112
and together stores charges, forming a capacitor. The capacitor electrode
155
is connected to the source
131
s
of the first TFT
130
. This storage capacitor is provided for retaining voltage applied to the gate
142
of the second TFT
140
.
The first TFT
130
, or the switching TFT, will now be explained.
As shown in
FIGS. 1 and 3A
, gate signal lines
151
made of refractory metal such as chromium (Cr) or molybdenum (Mo), which also serve as gate electrodes
132
, are formed on an insulator substrate
110
made of quartz glass, non-alkali glass, or a similar material. Also disposed on the substrate
110
are drain signal lines
152
composed of aluminum (Al) and power source lines
153
also composed of Al and serving as the power source for the organic EL elements.
After forming gate signal lines
151
on the substrate
110
, a gate insulating film
112
and an active layer
131
composed of poly-silicon (referred to hereinafter as “p-Si”) film are sequentially formed. The active layer
131
is of a so-called LDD (Lightly Doped Drain) structure. Specifically, low-concentration regions
131
LD are formed on both sides of each gate
132
. The source
131
s
and the drain
131
d
, which are high-concentration regions, are further disposed on the outboard sides of the low-concentration regions
131
LD.
An interlayer insulating film
115
formed by sequential lamination of a SiO
2
film, a SiN film, and a SiO
2
film is provided on the entire surface over the gate insulating film
112
, the active layer
131
, and stopper insulating films
114
. A contact hole formed in a position corresponding to the drain
141
d
is filled with metal such as Al, forming a drain electrode
116
. Further, a planarizing insulating film
117
made of an organic resin or a similar material is formed over the entire surface for planarization.
The second TFT
140
, or the TFT for driving the organic EL element, will next be described.
As shown in
FIG. 3B
, gate electrodes
142
composed of refractory metal such as Cr or Mo are formed on the insulator substrate
110
made of quartz glass, non-alkali glass, or a similar material. Further on top, a gate insulating film
112
and an active layer
141
composed of p-Si film are sequentially formed. The active layer
141
is provided with intrinsic or substantially intrinsic channels
141
c
formed above the gate electrodes
142
, and the source
141
s
and drain
141
d
are formed on respective sides of these channels
141
c
by ion doping using p-type impurities, thereby constituting a p-type channel TFT.
An interlayer insulating film
115
formed by sequential lamination of a SiO
2
film, a SiN film, and a SiO
2
film is provided on the entire surface over the gate insulating film
112
and the active layer
141
. A contact hole formed in a position corresponding to the drain
141
d
is filled with metal such as Al, forming a power source line
153
connected to a power source. Further, a planarizing insulating film
117
made of an organic resin or a similar material is formed over the entire surface for planarization. A contact hole is formed in the planarizing insulating film
117
in a position corresponding to the source
141
s
. A transparent electrode made of ITO (indium tin oxide) that contacts the source
141
s
through this contact hole, namely, the anode
161
of the organic EL element, is formed on the planarizing insulating film
117
.
The organic EL element
160
is formed by laminating, in order, the anode
161
constituted by a transparent electrode made of ITO or similar material, an emissive element layer
166
which is composed with materials including an organic compound and comprises an emissive layer, and a cathode
167
made of a magnesium-indium alloy. The cathode
167
is disposed over the entire surface of the organic EL display element shown in
FIG. 1
, that is covering the entire sheet of the figure.
In an organic EL element, holes injected from the anode and electrons injected from the cathode recombine in the emissive layer. As a result, organic molecules constituting the emissive layer are excited, generating excitons. Through the process in which these excitons undergo radiation until deactivation, light is emitted from the emissive layer. This light radiates outward through the transparent anode via the transparent insulator substrate, resulting in light emission.
In this way, electric charge applied via the source
131
s
of the first TFT
130
is accumulated in the storage capacitor
170
and applied to the gate
142
of the second TFT
140
. According to this voltage, the organic EL element emits light.
As shown in
FIG. 2
, each power source line connected to the power source for driving the organic EL elements is connected with a power source input terminal
180
disposed outside the display pixel region. The power source lines are arranged and connected with each vertical array of display pixels. With such an arrangement, at positions more distant from the power source input terminal
180
resistance of each power source line increases along with its length. The organic EL elements
160
located in display pixels distant from the power source input terminal
180
are therefore not adequately provided with necessary current, causing a disadvantage that the display in such area is dim.
SUMMARY OF THE INVENTION
The present invention was created in light of the above existing disadvantage. The purpose of the present invention is to provide an EL display device which prevents decrease in power source current due to resistance of power source lines, and adequately provides EL elements with current that should actually be supplied, accomplishing bright display.
To achieve the above purpose, the present invention provides an electroluminescence display device comprising a plurality of display pixels arranged in a matrix within a display pixel region, said display pixels having electroluminescence elements including an emissive layer between first and second electrodes, wherein, within said display pixel region, power source line for supp
Komiya Naoaki
Nishikawa Ryuji
Yamada Tsutomu
Yokoyama Ryoichi
Cantor & Colburn LLP
Dinh Trinh Vo
Sanyo Electric Co,. Ltd.
Wong Don
LandOfFree
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