Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-05-11
2004-07-13
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S904000, C345S080000
Reexamination Certificate
active
06762735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic display (electro optical device) formed by fabricating an EL (electro luminescence) on a substrate. In particular, the present invention relates to a display device using a semiconductor element (an element which uses a semiconductor thin film). Further, the present invention relates to an electronic device using an EL display in a display portion and the method of detecting the EL display.
The EL element herein refers to both an element that utilizes light emission from a singlet exciton (fluorescence) and an element that utilizes light emission from a triplet exciton (phosphorescence).
2. Description of the Related Art
Recently, a technique for forming a thin film transistor (hereinafter, referred to as TFT) on a substrate has been remarkably developed, and a development of its application to an active matrix display device has been continuously made. In particular, TFTs using a polysilicon film can operate at high speed, because such TFTs have a higher field effect mobility than TFTs using a conventional amorphous silicon film. Therefore, the control of pixels, which has been conventionally conducted by a driver circuit provided outside a substrate, can be performed by a driver circuit provided on the same substrate on which the pixels are provided.
Such an active matrix display device includes various circuits and elements formed on the same substrate. With this structure, the active matrix display device provides various advantages such as reduced manufacturing cost, reduced size of a display device, an increased yield, and a reduced throughput.
Furthermore, an active matrix EL display device including an EL element as a self-luminescent element has been actively studied. The EL display device is also called Organic EL Display (OELD) or Organic Light Emitting Diode (OLED).
In contrast with the liquid crystal display device, the EL display device is selfluminescent. The EL element has such a structure that an EL layer is sandwiched between a pair of electrodes (anode and cathode). However, the EL layer has normally a lamination structure. As a typical example of the lamination structures, a lamination structure “hole transport layer/light emitting layer/electron transport layer” proposed by Tang et al. of Eastman Kodak Company is cited. This structure has an extremely high light emitting efficiency. For this advantage, most light emitting devices, which are currently under study and development, employ this structure.
Furthermore, the light emitting device may have such a lamination structure that a hole injection layer, a hole transport layer, a light emitting layer and an electron transport layer are deposited on an anode or a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are deposited on an anode in this order. Moreover, the light emitting layer may be doped with a fluorescent pigment or the like.
All layers formed between a cathode and an anode are referred to generically as EL layers within this specification. The above stated hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer, electron injecting layer, and the like are therefore all contained within the EL layer.
A predetermined voltage is then applied to the EL layer having the above structure by a pair of electrodes, thus recombination of a carrier thus occurs in the light emitting layer, and light is emitted. Note that the emission of light by the EL element is referred to as driving the EL element throughout this specification. Further, an EL element formed by an anode, an EL layer, and a cathode is referred to as an EL element throughout this specification.
As a method of driving an EL display device, an analog driving method (analog drive) can be given. The analog drive of an EL display device is described with reference to
FIGS. 10 and 11
.
FIG. 10
shows a structure of a pixel portion of an EL display device that is driven in an analog manner. Gate signal lines (G1 through Gy) to which a gate select signal from a gate signal line driver circuit is input are connected to a gate electrode of a switching TFT
1801
included in each pixel. One of a source region and a drain region of the switching TFT
1801
included in each pixel is connected to source signal lines (also referred to as data signal lines) S1 to Sx to which an analog video signal is input, whereas the other is connected to a gate electrode of an EL driver TFT
1804
included in each pixel and a capacitor
1808
included in each pixel.
A source region and a drain region of the driver TFT
1804
included in each pixel are connected to power source supply lines V1 through Vx and to an EL element
1806
, respectively. An electric potential of the power source supply lines V1 through Vx is referred to as an power source electric potential. The power source supply lines V1 through Vx are connected to the capacitors
1808
included in the respective pixels.
The EL element
1806
includes an anode, a cathode and an EL layer sandwiched between the anode and the cathode. If the anode of the EL element
1806
is connected to the source or the drain region of the driver TFT
1804
, the anode and the cathode of the EL element
1806
become a pixel electrode and an opposing electrode, respectively. On the other hand, if the cathode of the EL element
1806
is connected to the source or the drain region of the driver TFT
1804
, the anode and the cathode of the EL element
1806
become an opposing electrode and a pixel electrode, respectively.
Note that the electric potential of the opposing electrode is referred to as an opposing electric potential in this specification. Note also that an power source for imparting the opposing electric potential to the opposing electrode is referred to as an opposing electric power supply. The electric potential difference between the electric potential of the pixel electrode and the electric potential of the opposing electrode is an EL driver voltage, and the EL driver voltage is applied to the EL layer.
FIG. 11
shows a timing chart in the case where the EL display device shown in
FIG. 10
is driven in an analog manner. The period from the selection of one gate signal line until the selection of a next gate signal line is called one line period (L). The period from the display of one image to another image corresponds to one frame period (F). In the case of the EL display device shown in
FIG. 10
, since there are y gate signal lines, y line periods (L1 to Ly) are provided within one frame period.
With the enhancement in resolution, the number of line periods within one frame period increases. As a result, the driver circuit must be driven at a high frequency.
An power source electric potential at the power source supply lines (V1 through Vx) is held constant, and an opposing electric potential at the opposing electrodes is also held constant. The opposing electric potential has a potential difference with the power source electric potential to such a degree that a EL element
1806
emits light.
The gate signal line G1 is selected in the first line period L1 by a gate signal input to the gate signal line G1 from the gate signal line driver circuit. Then an analog video signal is then input in order to the source signal lines S1 to Sx. All of the switching TFTs
1801
connected to the gate signal line G1 are in an ON state, and therefore the analog video signal input to the source signal lines S1 to Sx is input to gate electrodes of the driver TFTs
1804
through the switching TFTs
1801
.
The description here takes as an example a timing chart of the case where the switching TFT
1801
and the driving TFT
1804
are both n-channel TFTs. The switching TFT and the driving TFT may instead be p-channel TFTs, or one of them may be an n-channel TFT while the other is a p-channel TFT.
In this specification, the TFT being turned ON means that the gate voltage of the TFT is changed such that the source-
Mengistu Amare
Semiconductor Energy Laboratory Co,. Ltd.
Sheng Tom
LandOfFree
Electro luminescence display device and method of testing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electro luminescence display device and method of testing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electro luminescence display device and method of testing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3215581