Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-11-06
2004-07-20
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S076000, C315S169300
Reexamination Certificate
active
06765549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an EL (electro-luminescence) display formed by preparing an EL element on a substrate. More particularly, the invention relates to an EL display using a semiconductor element (an element using a semiconductor thin film). Furthermore, the present invention relates to an electronic device in which the EL display is used in a display portion thereof. The EL devices referred to in this specification may includes triplet-based light emission devices and/or singlet-based light emission devices.
2. Description of the Related Art
In recent years, technology for forming a TFT on a substrate has been largely improved, and an application development of the TFT to an active matrix type display device has been carried out. In particular, the TFT using a polysilicon film has a higher electric field effect mobility than the TFT using a conventional amorphous silicon film, and therefore, the TFT may be operated at a high speed. Thus, the pixel control which has been conducted at a driver circuit outside of the substrate may be conducted at the driver circuit which is formed on the same substrate as the pixel.
Such an active matrix type display device can, by preparing various circuits and elements on the same substrate, obtain various advantages such as a decrease in the manufacturing cost, a decrease in the size of the display device, an increase in the yield, and a decrease in the throughput.
Further, research on the active matrix type EL display having an EL element as a self-light-emitting device (hereafter referred to as an EL display) is becoming more and more active. The EL display is referred to as an organic EL display (OELD) or an organic light-emitting diode (OLED).
The EL display is a self-light-emitting type unlike a liquid crystal display device. The EL element is constituted in such a manner that an EL layer is sandwiched between a pair of electrodes. However, the EL layer normally has a lamination structure. Typically, the lamination structure of a “positive hole transport layer/a luminous layer/an electron transport layer” proposed by Tang et al. of the Eastman Kodak Company can be cited. This structure has a very high light-emitting efficiency, and this structure is adopted in almost all the EL displays which are currently subjected to research and development.
In addition, the structure may be such that on the pixel electrode, a positive hole injection layer/a positive hole transport layer/a luminous layer/an electron transport layer, or a positive hole injection layer/a positive hole transport layer/a luminous layer/an electron transport layer/an electron injection layer may be laminated in order. Phosphorescent dye or the like may be doped into the luminous layer.
In this specification, all the layers provided between the pixel electrode and an opposite electrode are generally referred to as EL layers. Consequently, the positive hole injection layer, the positive hole transport layer, the luminous layer, the electron transport layer, the electron injection layer and the like are all included in the EL layers.
Then, a predetermined voltage is applied to the EL layer having the above structure from the pair of the electrodes, so that a recombination of carriers is generated in the luminous layer and light is emitted. Incidentally, in this specification, the fact that the EL element emits a light is described as the fact that the EL element is driven. Furthermore, in this specification, the light-emitting element formed of the anode, the EL layer and the cathode is referred to as an EL element.
Conventionally, the pixel structure of an active matrix type EL display device has generally been like that shown in FIG.
18
. Reference numeral
1701
in
FIG. 18
denotes a TFT functioning as a switching element (hereafter referred to as a switching TFT), reference numeral
1702
denotes a TFT functioning as an element for controlling the electric current supplied to an EL element
1703
(hereafter referred to as an EL driver TFT), reference numeral
1703
denotes the EL element, and reference numeral
1704
denotes a capacitor (storage capacitor).
Gate signal lines (G
1
to Gy) for inputting gate signals are connected to gate electrodes of the switching TFTs
1701
of each pixel. Further, one set of regions of source regions and drain regions of the switching TFTs
1701
of each pixel are connected to source signal lines, also referred to as data signal lines (S
1
to Sx) for inputting digital data signals, and the other set of regions is connected to gate electrodes of the EL driver TFTs
1702
of each pixel and to the capacitors
1704
of each pixel, respectively. Note that the digital data signal refers to a digital video signal.
One of the source regions of the EL driver TFTs
1702
of each pixel is connected to one of electric power supply lines (V
1
to Vx), and the drain region is connected to the EL element
1703
. The electric potential of the electric power supply lines (V
1
to Vx) is referred to as an electric power supply potential. Further, the electric power supply lines (V
1
to Vx) are connected to the capacitor
1704
of each pixel.
The EL element
1703
is composed of an anode, a cathode, and an EL layer formed between the anode and the cathode. When the anode is connected to the drain region of the EL driver TFT
1702
, namely when the anode is a pixel electrode, the cathode becomes an opposing electrode. Conversely, when the cathode is connected to the drain region of the EL driver TFT
1702
, namely when the cathode is the pixel electrode, the anode becomes the opposing electrode. The electric potential of the opposing electrode is referred to as an opposing electric potential throughout this specification. The electric potential difference between the electric potential of the opposing electrode and the electric potential of the pixel electrode is an EL driver voltage, and the EL driver voltage is applied to the EL layer.
A conventional method of driving an EL display is explained next. First, all of the switching TFTs
1701
having their gate electrode connected to the signal line G
1
turn on in accordance with a gate signal input to the gate signal line G
1
. Note that the fact that all of the switching TFTs having their gate electrode connected to the signal line turn on in accordance with the gate signal is referred to as a gate signal line selection in this specification.
The digital data signal is then input into the source signal lines (S
1
to Sx) in order. The opposing electric potential is maintained at the same level as the electric power supply potential of the electric power supply lines (V
1
to Vx). The digital data signal has “0” or “1” information, and the “0” and “1” digital data signals specify signals having either high or low voltage.
The digital data signal input to the source signal lines (S
1
to Sx) is then input to the gate electrode of the EL driver TFT
1702
through the on-state switching TFT
1701
. Further, the digital data signal is also input to the capacitor
1704
and stored.
The gate signal lines G
2
to Gy are then selected in order in accordance with the gate signal, and the above operations are repeated. Note that the input of the digital data signal to the gate electrode of the EL driver TFT through the switching TFT is referred to as inputting the digital data signal to the pixel throughout this specification. A period until the digital data signal is input to all of the pixels is referred to as a write-in period.
When the digital data signal is input to all of the pixels, all of the switching TFTs
1701
are turned off. The opposing electric potential is then given an electric potential difference to the electric power supply potential at a level in which the EL elements emit light. The digital data signal stored in the capacitor
1704
is then input to the gate electrode of the EL driver TFT
1702
.
When the digital data signal has “0” information, the EL driver TFT
1702
is set to the off state and the EL element
1703
does n
Koyama Jun
Yamazaki Shunpei
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Semiconductor Energy Laboratory Co,. Ltd.
Shalwala Bipin
Sheng Tom
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