Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2003-04-23
2004-12-07
Vu, David (Department: 2821)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000
Reexamination Certificate
active
06828723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a display device, especially to an electroluminescent display device.
2. Description of the Related Art
An EL display device with an electroluminescent (referred to as EL hereinafter) element has been gathering attention as a display device substituting a CRT or an LCD. The development effort for the EL display device with a thin film transistor (referred to as TFT hereinafter) as a switching element for driving the EL element has been made accordingly.
FIG. 9
is a plan view of a pixel portion of an organic EL display device.
FIG. 10A
is a cross-sectional view of the display device along with the A—A line, and
FIG. 10B
is a cross-sectional view of the display device along with the B—B line shown in FIG.
9
.
A pixel portion
115
is formed in the area surrounded with a gate signal line
51
and a drain signal line
52
as shown in
FIGS. 9
,
10
A and
10
B. The pixel portions are disposed in a matrix configuration.
An organic EL element
60
, which is a light emitting element, a switching TFT
30
for controlling the timing when to supply electric current to the organic EL element
60
, a driving TFT
40
for supplying electric current to the organic EL element
60
, and a storage capacitance element are disposed in the pixel portion
115
. The organic El element
60
is configured from an anode layer
61
, an emissive element layer made of light emitting material, and a cathode layer
65
.
The first TFT
30
, the TFT used for switching, is disposed near the crossing of the two signal lines
51
,
52
. The source
33
s
of the TFT
30
works also as a capacitance electrode
55
, which forms capacitance with a storage capacitance electrode line
54
. The source
33
s
is also connected to the gate
41
of the second TFT
40
, the TFT for driving the EL element. The source
43
s
of the second TFT
40
is connected to the anode layer
61
of the organic El element
60
, and the drain
43
d
of the second TFT
40
is connected to a driving source line
53
, which supplies electric current to the organic EL element
60
.
The storage capacitance electrode line
54
is disposed parallel to the gate signal line
51
. The storage capacitance electrode line
54
is made of chrome and forms capacitance by accumulating electric charge between itself and the capacitance electrode
55
connected to the source
33
s
of the TFT through a gate insulating film
12
. This storage capacitance
56
is disposed in order to keep the voltage applied to the gate electrode
41
of the second TFT
40
.
The organic EL display device is configured by forming the TFT and the organic EL element consecutively on a substrate
10
, which is made of a glass, a synthetic resin, a conductive material, or a semiconductor, as shown in
FIGS. 10A and 10B
. When the conductive substrate or the semiconductor substrate is used as the substrate
10
, an insulating film made of SiO
2
or SiN should be first disposed on the substrate. Then, the first and second TFTs and the organic EL element are formed. Both TFTs should have a top-gate configuration, where the gate electrode is located above an active layer with the gate insulating film between them.
Next, the first TFT
30
for switching will be explained.
An amorphous silicon film (referred to as a-Si film hereinafter) is formed through a CVD method on the insulating substrate
10
, which is made of quartz glass or non-alkaline glass as shown in FIG.
10
A. The a-Si film is irradiated by a laser beam for recrystallization from melt, forming a poly-crystalline silicon film (referred to as a p-Si film, hereinafter). This functions as the active layer
33
. Single layer or multiple layers of a SiO
2
film and a SiN film are formed on the p-Si film as the gate insulating film
12
, on which the gate signal line
51
, also working as the gate electrode
31
, made of a metal with a high-melting point such as Cr and Mo as well as the drain signal line
52
made of Al are disposed.
A SiO
2
film, a SiN film and a SiO
2
film are sequentially disposed to form an interlayer insulating film
15
on the entire surface of the gate insulating film
32
and the active layer
33
. A drain electrode
36
, which is formed by filling a contact hole formed at the location corresponding to the drain
33
d
with a metal such as Al, is disposed, and a planarization film
17
made of organic resin for flattening the surface is formed on the entire surface.
Next, the second TFT
40
, the TFT for driving the organic El element will be explained. An a-Si film is formed on the insulating substrate
10
. The a-Si film is irradiated by a laser beam for forming a poly-crystalline silicon film functioning as the active layer
43
. The gate insulating film
12
, and the gate electrode
41
made of a metal with a high-melting point such as Cr and Mo are deposited on the active layer
43
. A channel
43
c
is formed in the active layer
43
. A source
43
s
and a drain
43
d
are also formed at both sides of the channel
43
c
. A SiO
2
film, a SiN film and a SiO
2
film are sequentially disposed to form the interlayer insulating film
15
on the entire surface of the gate insulating film
12
and the active layer
43
. The driving source line
53
, which is connected to the driving source by filling a contact hole formed at the location corresponding to the drain
43
d
with a metal such as Al, is disposed. Furthermore, the planarization film
17
made of organic resin for flattening the surface is formed on the entire surface. A contact hole is formed in the planarization film
17
at the location corresponding to the source
43
s
. The anode layer
61
of the organic El element, which is a transparent electrode made of ITO making contact with the source
43
s
through the contact hole described above, is formed on the planarization film
17
. The anode layer
61
is disposed forming an island for each of the pixel portions.
The organic EL element
60
includes the anode layer
61
, a hole transportation layer
62
having a first hole transportation layer made of MTDATA (4,4-bis (3-mathylphenylphenylamino) biphenyl) and a second hole transportation layer made of TPD (4,4,4-tris (3-methylphenylphenylamino) triphenylanine), an emissive layer
63
made of Bebq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) including quinacridone derivative, an electron transportation layer
64
made of Bebq2, and the cathode layer
65
made of either magnesium-indium alloy, aluminum, or aluminum alloy.
The holes inputted from the anode layer
61
and the electrons inputted from the cathode layer
65
are re-combined in the emissive layer of the organic EL element
60
, activating organic molecules of the emissive layer. When the activated molecules are deactivated, light is emitted from the emissive layer, and passes through the transparent anode layer
61
and the transparent insulating substrate to escape outside the display devie as illuminating light. The above technology is described in, for example, Japanese Laid-Open Patent Publication No. H-11 283182.
The cathode layer
65
is disposed covering the entire pixel portion
115
in the above organic EL display device.
FIG. 11
shows the layout of one of the pixels of the display device. The pixel portion
200
, which is the same as the pixel portion
115
of
FIG. 9
, has an organic emissive portion
201
that includes the organic EL element
60
and a circuit portion
202
that includes the switching and driving TFTs. The cathode layer
1
C of the organic El element is disposed on the entire pixel portion
200
.
The wiring materials such as aluminum used for the cathode layer is only utilized as the cathode layer, and they are not used for other wiring in the conventional organic EL display device. Therefore, the open aperture of this display device decreases when new signal lines and new source lines are formed in the display panel, leading to lowered luminescence of the organic EL display device.
SUMMARY OF THE INVENTION
The invention provide a display device having
Anzai Katsuya
Matsumoto Shoichi
Morrison & Foerster / LLP
Sanyo Electric Co,. Ltd.
Vu David
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