Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-13
2003-03-04
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C315S169300
Reexamination Certificate
active
06529178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current driving type emissive display apparatus such as an organic electro luminescence (hereinafter referred to as an “organic EL”) device having a thin-film transistor and a method for driving the apparatus, and more particularly, to a technique for realizing a reduction in deterioration over time or a reduction in both deterioration over time and electric power consumption simultaneously.
2. Description of Related Art
An operation of a conventional current driving type emissive apparatus such as an organic EL having thin-film transistors will be described with reference to
FIGS. 16
,
17
, and
18
.
FIG. 16
is an equivalent circuit diagram of one pixel of the conventional organic EL display device having thin-film transistors,
FIG. 17
is an equivalent circuit diagram showing a matrix construction of the conventional organic EL display device having thin-film transistors, and
FIG. 18
is a driving voltage diagram of the conventional organic EL display device having thin-film transistors.
Provided are: a data line
112
; a first switching element
121
(hereinafter referred to as a “switching thin-film transistor”) in which the source-terminal side is connected to the data line
112
and a gate electrode is connected to a scanning line
111
; a holding electrode
113
for storage capacity, in which one terminal is connected to the drain terminal side of the switching thin-film transistor
121
; a second switching element
122
(hereinafter referred to as a “current thin-film transistor”), in which a gate terminal is connected to the drain terminal of the switching thin-film transistor and the source terminal is connected to a first feeder
114
; and an organic EL device
135
, one terminal of which is connected to the drain terminal of the current thin-film transistor and the other terminal of which is connected to a second feeder.
The switching thin-film transistor
121
controls the conduction between the data line
112
and the holding electrode
113
by the potential of the scanning line
111
. That is, a scanning potential
211
controls the conduction between a signal potential
212
and a holding potential
213
. Although an n-channel type thin-film transistor is employed. as the switching thin-film transistor
121
in this example, a p-channel type thin-film transistor may also be employed. In such an example the high-potential-side of the scanning potential
211
and the low-potential-side thereof are reverse to those of this embodiment.
In a pixel in a displaying condition, the signal potential
212
is high and the high potential is held at the holding potential
213
. In a pixel in a non-displaying condition, the signal potential
212
is low and the low potential is held at the holding potential
213
.
The current thin-film transistor
122
controls the conduction between the first feeder
114
and a pixel electrode
115
by the potential. of the holding electrode
113
. That is, the holding potential
213
controls the conduction between a first feed potential
214
and a pixel potential
215
. Although an n-channel type thin-film transistor is employed as the current thin-film transistor
122
in this example, a p-channel type thin-film transistor may also be employed. In such an example the high-potential-side of the signal potential
212
and the low potential thereof are reverse to those of this embodiment.
In a pixel in a displaying condition, the holding potential
213
is high, so the first feeder
114
and the pixel electrode
115
are electrically connected. In a pixel in a non-displaying condition, the holding potential
213
is low, so the conduction between the first feeder
114
and the pixel electrode
115
is interrupted.
In a pixel in a displaying condition, the current flows from the first feeder
114
through the current thin-film transistor
122
and the pixel electrode
115
to a second feeder
116
, and the organic EL device
135
emits light. In a pixel in a non-displaying condition, no current flows, and the organic EL device will not emit light.
Since the first feed potential
214
is higher than a second feed potential
216
, the current flows from the first feeder
114
, through the current thin-film transistor
122
, the pixel electrode
115
, and the organic EL device
135
to the second feeder
116
.
The actual operation of organic EL display apparatuses with thin-film transistors is not as simple as that described above and the devices operate under more complex relationships of voltages and currents. Similarly and qualitatively, however, the above description holds true.
FIG. 19
is a sectional view of the organic EL display apparatus having a conventional thin-film transistor.
FIG. 20
is a plan view of the organic EL display apparatus having the conventional thin-film transistor. A section taken along the line A—A of
FIG. 19
corresponds to a section taken along the line A-A′ of FIG.
20
.
In the organic EL device
135
, a current flows from a high-electric-potential-side electrode
165
of the organic EL device through a luminescent material
155
for the organic EL device to a low-electric-potential electrode
175
of the organic EL device. Although PPV, ITO, and Al are respectively employed as the luminescent material for the organic EL device
155
, the material for the high electric potential side electrode
165
of the organic EL device, and the material for the low-electric-potential electrode
175
of the organic EL device in this example, other materials may also be used.
In the conventional example, in which an AC voltage is applied between the source terminal and the drain terminal of the switching thin-film transistor
121
, to cause an alternating current to flow, a DC voltage is applied between the source terminal and the drain terminal of the current thin-film transistor
122
to disadvantageously cause a direct current to flow. This is due to an asymmetric configuration optimizing the materials of the high and low-potential-side in order to improve the luminous efficiency of the organic EL device
135
; the organic EL device emits light because of the DC voltage being applied causing the direct current to flow. However, when a DC voltage is applied not only to the organic EL device but also to the thin-film transistor or a direct current flows, a rapid deterioration of the thin-film transistor over time will be caused.
On the other hand, an AC voltage may also be applied between the source terminal and the drain terminal of the current thin-film transistor
122
. In this case, an alternating current will not flow through the organic EL device
135
, but only a one-way current flow, because of the rectification of the organic EL device
135
. In other words, the organic EL device
135
emits light in one direction, while it does not emit light in the other direction, so that the luminous efficiency deteriorates. Thus it requires an increase in power consumption to obtain the same amount of light emission as in the case in which a DC voltage is applied to cause a direct current to flow.
SUMMARY OF THE INVENTION
Thus, an object of this invention is to reduce deterioration over time of a switching element such as a thin-film transistor in a current driving type emissive apparatus such as an organic EL display device having a thin-film transistor. Another object of this invention is to reduce in deterioration over time of a switching element such as a thin-film transistor, and to simultaneously achieve both improvement in luminous efficiency and reduction in power consumption.
To solve the above problems, a first aspect of this invention consists of a plurality of scanning lines, a plurality of data lines, and thin-film transistors and a luminescent element formed in a manner such that they correspond to each intersection of the scanning lines and the data lines, wherein an AC voltage is applied between source and drain terminals of the thin-film transistors and wherein a DC voltage is applied between first and second
Eisen Alexander
Oliff & Berridg,e PLC
Seiko Epson Corporation
LandOfFree
Current-driven emissive display device, method for driving... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Current-driven emissive display device, method for driving..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current-driven emissive display device, method for driving... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3046017