Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2000-02-09
2002-11-05
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S071000, C345S076000, C345S092000
Reexamination Certificate
active
06476419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device comprising an emissive element such as an electroluminescence element and thin film transistors.
2. Description of Related Art
Electroluminescence (EL) display devices using an electroluminescence element have recently attracted interest as potential replacements for devices such as CRT or LCD displays. For example, an EL display device having a thin film transistor (TFT) as a switching element for driving the EL element has been studied and developed.
FIG. 1
shows, in a plan view, one display pixel of a related organic EL display device.
FIG. 2
is an equivalent circuit diagram of an organic EL display device corresponding to one display pixel.
FIGS. 3A and 3B
are cross sections taken along lines A—A and B—B in
FIG. 1
, respectively.
Referring to
FIGS. 1 and 2
, a display pixel is formed in a region enclosed by a gate signal line
151
and a drain signal line
152
. Around the intersection of both signal lines is formed a first TFT
130
as a switching TFT. A source
131
s of the first TFT
130
also functions as a storage capacitor electrode
155
constituting a capacitor between the source
131
s
and a storage capacitor electrode
154
which will be described later, and is connected to a gate
142
of a second TFT
140
which drives an organic EL element. A source
141
s
of the second TFT
140
is connected to an anode
161
of the organic EL element-while a drain
141
d
is connected to a power supply line
153
for driving the organic EL element.
The storage capacitor electrode
154
is disposed in parallel to the gate signal line
151
in the vicinity of the first TFT. The storage capacitor electrode
154
comprises chromium or the like and forms a capacitor
170
for accumulating charges between the storage capacitor electrode
154
and the storage capacitor electrode
155
connected to the source
131
s
of the first TFT
130
via a gate insulating film
112
. The storage capacitor
170
is provided so as to hold a voltage to be applied to the gate
142
of the second TFT
140
.
The first TFT
130
, which is a switching TFT, will now be described.
Referring to
FIG. 3A
, on an insulating substrate
110
comprising a quartz glass, non-alkali glass, or the like, are provided the gate signal line
151
including gate electrodes
132
and comprising a refractory metal with a high melting point such as chromium (Cr), molybdenum (Mo), or the like, and the storage capacitor electrode
154
.
Subsequently, the gate insulating film
112
, and an active layer
131
comprising a poly-silicon (hereinafter referred to as “p-Si”) film are sequentially formed, such that the active layer
131
has a so-called LDD (Lightly Doped Drain) structure. More specifically, low concentration regions
131
LD are formed at both sides of the pair of channel regions
131
c
opposing to gate electrodes
132
, and a source
131
s
and a drain
131
d
of high concentration regions are further formed to the outsides of the low concentration regions.
Further, over the entire surface covering the gate insulating film
112
, the active layer
131
, and stopper insulating films
114
, an interlayer insulating film
115
having a multi-layer structure is provided, and a metal such as Al or the like is used to fill a contact hole formed in the position in the interlayer insulating film
115
corresponding to the drain
131
d
to form a drain electrode
116
. Then, a planarization insulating layer
117
comprising an organic resin is provided on the entire surface to planarize the surface.
Next, the second TFT
140
, which is an organic EL element driving TFT, will be described.
Referring to
FIG. 3B
, on the insulating substrate
110
comprising a quartz glass, non-alkali glass, or the like, the gate electrodes
142
each comprising a refractory metal (metal having a high melting point) such as Cr, Mo, or the like are formed, and the gate insulating film
112
and an active layer
141
comprising a p-Si film are sequentially formed thereon. In the active layer
141
, channels
141
c
which are intrinsic or substantially intrinsic are formed at the positions above the respective gate electrodes
142
, and the source
141
s
and the drain
141
d
are formed by doping p-type impurities at each side of the channel pair to thereby constitute a p-type channel TFT.
The interlayer insulating film
115
of a multi-layer structure is then provided over the entire surface on the gate insulating film
112
and the active layer
141
. A contact hole provided in the interlayer insulating film
115
so as to correspond to the drain
141
d
is filled with a metal such as Al to form the power supply line
153
connected to the power supply
150
. Further, the planarization insulating film
117
comprising an organic resin to planarize the surface is provided over the entire surface. On the planarization insulating film
117
, a transparent electrode, in this case the anode
161
of the organic EL element, which comprises ITO is provided to make contact with the source
141
s
via a contact hole formed at the position of the planarization insulating film
117
and the interlayer insulating film
115
corresponding to the source
141
s.
The organic EL element
160
comprises the anode
161
comprising ITO (Indium Tin Oxide) or the like and connected to the source
141
s
of the second TFT
140
, an emissive element layer
166
comprising an organic compound, and a cathode
167
using magnesium-indium alloy, formed in that order. In the organic EL element
160
, holes injected from the anode
161
and electrons injected from the cathode
167
are recombined inside the emissive element layer
166
to excite organic molecules forming the emissive element layer
166
for causing exciton. In the process of radiation and deactivation by the exciton, the emissive element layer
166
produces light which is emitted from the transparent anode
161
through the transparent insulating substrate
110
.
As shown in
FIG. 3B
, the anode
161
forms an individual pattern corresponding to each display pixel, and the emissive element layer
166
which is somewhat larger than the anode
161
is formed so as to entirely cover the anode
161
. On the other hand, the cathode
167
, which can be commonly used electrically, is formed as a common electrode.
In each pixel, charges applied from the source
131
s
of the selected first TFT
130
are accumulated and held in the storage capacitor
170
and are also applied to the gates
142
of the second TFT
140
. A current in accordance with a voltage applied to the gates
142
is applied from the power supply
150
to the organic EL element which then emits light.
In the EL display device, however, if the aperture ratio of the display pixel is small, light is irradiated from a small area of the emissive layer of the organic EL element, which results in an extremely dark display.
To cope with the foregoing disadvantage, increase of the aperture ratio may be considered. However, to increase the aperture ratio, the area of a storage capacitor which constitutes the non-emissive region within a display pixel must be decreased, which leads to problems. Especially, decrease in the storage capacitor area will reduce the storage capacity, which in turn makes it impossible for only the storage capacitor
170
to sufficiently hold the drain signal supplied from the first TFT
130
until next time the first TFT
130
is selected. As a result, the gates
142
of the second TFT
140
cannot be put into a sufficient on-state to cause the organic EL element to emit light for a sufficient period to provide a bright display.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above described problems of the related art and aims to provide an EL display device which can hold sufficient charge to produce a bright display without decreasing the aperture ratio.
In accordance with one aspect of the present invention, there is provided an electroluminescence display device comprising an ele
Lee Eddie
Lee Eugene
Sanyo Electric Co,. Ltd.
LandOfFree
Electroluminescence display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electroluminescence display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electroluminescence display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2958704