Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-06-05
2004-07-06
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S074100, C345S014000, C345S076000, C345S077000, C345S078000, C345S079000, C345S092000, C345S100000, C345S204000, C345S205000, C345S211000, C345S212000, C315S169100, C315S169300
Reexamination Certificate
active
06760004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic display device which is formed having an EL (electroluminescent) element on a substrate. More particularly, it relates to a display device which employs a semiconductor element (an element including a semiconductor thin film). Also, it relates to an electronic equipment whose display portion includes an EL display device.
2. Description of the Related Art
In recent years, EL display devices each having an EL element as a self-emission type element have been vigorously developed. The EL display device is also called the “organic EL display (OELD)” or “organic light emitting diode (OLED)”.
Unlike a liquid crystal display device, the EL display device is of self-emission type. The EL element has a construction wherein an EL layer is sandwiched in between a pair of electrodes (an anode and a cathode), and wherein the EL layer has a multilayer structure ordinarily. Typically mentioned is the multilayer structure of “hole transporting layer/light emitting layer/electron transporting layer” proposed by Tang et al., Eastman Kodak Company. The multilayer structure exhibits a very high emission efficiency, and most of the EL display devices being currently under researches and developments adopt this structure.
Alternatively, the multilayer structure may be so formed that the anode is successively overlaid with a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer, or a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer/an electron injecting layer. The light emitting layer may well be doped with a fluorescent coloring matter or the like.
In this specification, all layers interposed between the cathode and the anode shall be generally termed the “EL layer”. Accordingly, the hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer and electron injecting layer mentioned above are all included in the “EL layer”.
Herein, a predetermined voltage is applied to the EL layer of the above structure by the pair of electrodes, whereby light is emitted by the recombination of carriers taking place in the light emitting layer. In this specification, the light emission of the EL element shall be called the “drive of the EL element”. Also in this specification, a light emitting element which is constituted by the anode, EL layer and cathode shall be called the “EL element”.
Here, in this specification, the “EL element” shall cover both light emission (fluorescence) from a singlet exciton and light emission (phosphorescence) from a triplet exciton.
The driving systems of EL display devices include a passive system and an active system.
The passive type EL display device has a structure wherein stripe-like anodes (transparent electrodes) formed on an insulating substrate, organic EL layers, and stripe-like cathodes formed so as to intersect orthogonally to the anodes are stacked in succession. The equivalent circuit of the passive type EL display device is shown in FIG.
2
. According to the passive system, one of scanning lines is selected, and among pixels lying on the selected scanning line, only ones whose signal lines are ON states emit light.
Signals to be inputted to the signal lines are created in such a way that a data signal (video signal) externally inputted is edited by a signal line driving circuit. Here in the passive type EL display device, the signal line driving circuit is disposed in such a way that an IC chip is mounted on the display device by TAB (Tape Automated Bonding), or that the IC chip is assembled in the display device by bonding it directly onto the pixel substrate. The IC chip is so constructed that a circuit is formed on a semiconductor substrate such as silicon chip. In the case of bonding the IC chip directly onto the pixel substrate, accordingly, the semiconductor substrate is bonded onto the insulating substrate used as the pixel substrate.
On the other hand, the active type EL display device is constructed of EL elements, and gate signal lines, source signal lines, power supply lines, transistors and capacitors which are formed on an insulating substrate. One of the capacitors and two of the transistors are disposed for each of the pixels of the display device.
In general, the active type EL display device has a structure wherein two or more transistors are disposed for each pixel.
In the active type EL display device, the pixel is formed in such a way that the transistors are fabricated on the insulating substrate by employing semiconductor thin films. Here, the transistors formed by employing the semiconductor thin films are called the “thin film transistors (hereinbelow, abbreviated to “TFTs”).
The circuit diagram of the pixel of the active type EL display device is shown in FIG.
3
.
The gate electrode of the switching TFT is connected to the gate signal line. One of the source region and drain region of the switching TFT is connected with the source signal line, while the other is connected with the gate electrode of the EL driving TFT and one electrode of the capacitor. One of the source region and drain region of the EL driving TFT is connected with the anode or cathode of the EL element, while the other is connected with the power supply line. That electrode of the capacitor which is not connected with the switching TFT, is connected with the power supply line.
In the pixel for which both the gate signal line and the source signal line have turned ON, charges are stored in the capacitor through the switching TFT. During a time period for which the capacitor continues to apply a voltage to the gate electrode of the EL driving TFT, current continues to flow from the power supply line to the EL element through the EL driving TFT, and the EL element continues to emit light.
Signals to be inputted to the source signal lines are created in such a way that a data signal externally inputted is edited by a source signal line driving circuit. In the active type EL display device, the source signal line driving circuit can be fabricated of TFTs on the insulating substrate simultaneously with the circuits of the pixel portion of the display device.
An analog driving method (analog drive) is mentioned as the driving method of the active type EL display device. The analog drive will be explained with reference to
FIGS. 4 and 5
.
FIG. 4
shows the structure of the pixel portion of the active type EL display device conforming to the analog drive. Gate signal lines (G
1
-Gy) to which selection signals from a gate signal line driving circuit are respectively inputted, are connected to the gate electrodes of switching TFTs
1801
included in individual pixels. Besides, either regions of the source regions and drain regions of the switching TFTs
1801
included in the individual pixels are connected to source signal lines (also called “data signal lines”) (S
1
-Sx) to which analog signals are respectively inputted, while the other regions are connected to the gate electrodes of EL driving TFTs
1804
included in the individual pixels and also to capacitors
1808
included in the individual pixels.
Either regions of the source regions and drain regions of the EL driving TFTs
1804
included in the individual pixels are connected to power supply lines (V
1
-Vx), while the other regions are connected to EL elements
1806
. The potentials of the power supply lines (V
1
-Vx) are called “power source potentials”. Besides, the power supply lines (V
1
-Vx) are connected to the capacitors
1808
included in the individual pixels.
Each of the EL elements
1806
includes an anode, a cathode, and an EL layer which is interposed between the anode and the cathode. In a case where the anode of the EL element
1806
is connected with the source region or drain region of the EL driving TFT
1804
, this anode of the EL element
1806
serves as a pixel electrode, and the cathode thereof serves as a counter electrode. To the contrary, in a case where the cathode
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