Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-07
2004-11-30
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S083000
Reexamination Certificate
active
06825820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an EL (electroluminescence) display device (a light emitting device or a light emitting diode or OLED (Organic Light Emission Diode) formed by fabricating semiconductor elements (elements using a thin semiconductor film) on a substrate, and to an electronic device which uses the EL display device for a display unit thereof. The EL devices referred to in this specification include triplet-based light emission devices and/or singlet-based light emission devices, for example.
2. Related Art
In recent years, technology for forming TFTs on a substrate has greatly advanced and study has been forwarded to apply the technology to the active matrix-type display devices. In particular, study has been vigorously forwarded concerning the active matrix-type EL display device using EL elements as spontaneously light-emitting elements among the active matrix type display devices. The EL display device is also called organic EL display (OELD) or organic light-emitting diode (OLED).
Unlike liquid crystal display devices, the EL display device is the one that spontaneously emits light. The EL element has a structure in which an EL layer is held between a pair of electrodes, the EL layer being, usually, of a laminated layer structure. The laminated-layer structure can be represented by a “positive hole-transporting layer/light emitting layer/electron-transporting layer” proposed by Tang et al. of Eastman Kodak Co. This structure features a very high light-emitting efficiency, and almost all of the EL display devices that have now been studied and developed are employing this structure.
Luminescence of the organic EL material stems from the emission of light (fluorescence) of when a singlet excited state returns back to the ground state or stems from the emission of light (phosphorescence) of when a triplet excited state returns back to the ground state. The EL element of this invention may utilize either one of the above-mentioned type of light emission or may utilize both of the above-mentioned types of light emission.
In addition to the above, there can be further employed a lamination of positive hole-injection layer/positive hole-transporting layer/light-emitting layer/electron transporting layer or a lamination of positive hole-injection layer/positive hole-transporting layer/light-emitting layer/electron-transporting layer/electron-injection layer on the pixel electrode. The EL layer may be doped with a fluorescent coloring matter.
A predetermined voltage is applied to the thus constituted EL layer from a pair of electrodes, whereby the carriers are recombined together in the light-emitting layer to emit light. In this specification, the EL element is called to have been driven when it emits light.
In this specification, the light-emitting element formed by an anode, an EL layer and a cathode is called EL element.
FIG. 14
illustrates the structure of a representative active matrix-type EL display device (hereinafter referred to as EL display device), wherein FIG.
14
(A) shows the arrangement of a pixel unit of the EL display device and a drive circuit therefor. Reference numeral
901
denotes a pixel unit,
902
denotes a source signal line drive circuit,
903
denotes a gate signal line drive circuit, and
905
denotes draw-out terminals.
The pixel unit
901
includes plural pixels
906
. Reference numeral
904
denotes power source feed lines formed on the pixel unit
901
to apply a potential to the pixel electrodes of the EL elements possessed by all pixels
906
. Power source feed lines
904
are connected to detour wirings
907
which are connected to an external power source via draw-out terminals
905
.
Pixels
906
are selected by select signals input to gate signal lines
913
from the gate signal line drive circuit
903
. The potential of the power source feed lines
904
is given to the selected pixels
906
due to video signals input to the source signal line
912
from the source signal line drive circuit
902
, and the pixels
906
display part of the picture.
FIG.
14
(B) is a circuit diagram of pixels corresponding to R (red), G (green) and B (blue) among the pixels
906
shown in FIG.
14
(A).
In FIG.
14
(B), a pixel
906
r
for R, a pixel
906
g
for G and a pixel
906
b
for B have a common gate signal line
913
. Further, the pixel
906
r
for R has a source signal
912
r
for R, the pixel
906
g
for G has a source signal line
912
g
for G, and the pixel
906
b
for B has a source signal line
912
b
for B.
The pixel
906
r
for R, the pixel
906
g
for G and the pixel
906
b
for B have a switching TFT
910
and an EL drive TFT
911
, respectively. Further, the pixel
906
r
for R has an EL element
915
r
for R, the pixel
906
g
for C has an EL element
915
g
for G, and the pixel
906
b
for B has an EL element
915
b
for B.
When a select signal is input to the gate signal line
913
, the switching TFTs
910
connected at their gate electrodes to the gate signal line
913
are all turned on. In this specification, this state is referred to as that the gate signal line
913
is selected.
Video signals input to the source signal line
912
r
for R, to the source signal line
912
g
for G and to the source signal line
912
b
for B, are further input to the EL element
915
r
for R, to the EL element
915
g
for G and to the EL element
915
b
for B through the switching TFTs
910
which have been turned on, so as to be input to the gate electrodes of the EL drive TFTs
911
.
When the video signals are input to the gate electrodes of the EL drive TFTs
911
, the potential of the power source feed line
914
r
for R is applied to the pixel electrode of the EL element
915
r
for R, the potential of the power source feed line
914
g
for G is applied to the pixel electrode of the EL element
915
g
for G, and the potential of the power source feed line
914
b
for B is applied to the pixel electrode of the EL element
915
b
for B. As a result, the EL element
915
r
for R, the EL element
915
g
for G and the EL element
915
b
for B emit light, and a display is produced by the pixel
906
r
for R, by the pixel
906
g
for G and by the pixel
906
b
for B.
The EL display devices can be roughly divided into those of the four color display systems, such as those of the system shown in
FIG. 14
forming EL elements of three kinds of organic EL materials corresponding to R (red), G (green) and B (blue), those of the system in which white light-emitting EL elements and color filters are combined together, those of the system in which blue or bluish green light-emitting EL elements and a fluorescent material (fluorescent color-conversion layer: CCM) are combined together, and those of the system in which EL elements corresponding to RGB are stacked by using transparent electrodes for the cathodes (opposing electrodes).
In general, even when the same voltage is applied to the EL layer, the light-emitting brightness of the EL layer differs depending upon the organic EL material used for the EL layer.
FIG. 15
illustrates voltage—brightness characteristics of the EL layers of each of the colors. As shown in
FIG. 15
, the light-emitting brightness of the EL layer to the applied voltage, varies depending upon the organic EL materials used for the EL elements of each of the colors. This is because the current density of when the same voltage is applied differs depending upon the organic EL materials.
Even when the current density remains the same, the light-emitting brightness differs depending upon the organic EL materials.
In the EL display device, therefore, the potentials of the power source feed lines for the pixels of each of the colors are usually adjusted to maintain a balance in the light-emitting brightness of the EL elements of three colors.
The magnitude of electric current flowing into the pixel unit through the detour wiring is determined by the number of pixels producing a white display in the pixel unit. The pixels producing the white display stand for those pixel elements havi
Inukai Kazutaka
Koyama Jun
Osame Mitsuaki
Yamazaki Shunpei
Mengistu Amare
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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