Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-11-29
2004-05-04
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S059000, C257S072000
Reexamination Certificate
active
06730966
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an EL (electro-luminescence) display formed by incorporating an EL element on a substrate. More particularly, the invention relates to an EL display (electric device) using a semiconductor element (an element using a semiconductor thin film). Furthermore, the present invention relates to an electronic apparatus (EL display device) in which the EL display is used in a display portion thereof.
2. Description of the Related Art
In recent years, technology for forming a thin film transistor (hereinafter, TFT) on a substrate has been largely improved, and an application development of the TFT to an active matrix 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 former 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 display device can, by incorporating various circuits and elements on the same substrate, obtain various advantages such as decrease in manufacturing costs, decrease in sizes of the display devices, increase in its yields, and decrease in its throughputs.
Further, research on the active matrix EL display device having an EL element as a self-light-emitting device (hereinafter referred to as 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 “hole transport layer/a light emitting/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, it may have a structure such that on the pixel electrode, a hole injection layer/a hole transport layer/a light emitting/ an electron transport layer, or a hole injection layer/a hole transport layer/a light emitting/an electron transport layer/an electron injection layer may be laminated in the stated order. Phosphorescent dye or the like may be doped into the light emitting.
In this specification, all of the layers provided between the pixel electrode and an opposite electrode are generally referred to as EL layers. Consequently, the hole injection layer, the hole transport layer, the light emitting, the electron transport layer, the electron injection layer and the like are all included in the EL layers.
A predetermined voltage is applied from a pair of electrodes to the EL layer of the above structure, with the result that recombination of carriers occurs in the light emitting layer to emit light. Note that in the present specification, emitting light by an EL element is referred to as driving the EL element. Besides, in the present specification, a light emitting element formed of an anode, an EL layer, and a cathode, is referred to as an EL element. Besides, a potential difference generated between an anode and a cathode of an EL element is referred to as an EL driver voltage.
FIG. 23
is a block diagram of a conventional multi gradation system EL display. The EL display shown in
FIG. 23
uses TFTs formed on a substrate and includes a pixel portion
101
, and a source signal side driver circuit
102
and a gate signal side driver circuit
103
which are disposed at the periphery of the pixel portion. An external switch
116
for controlling an EL driver voltage is connected to the pixel portion
101
.
The source signal side driver circuit
102
fundamentally contains a shift register
102
a
, a latch (A)
102
b
, and a latch (B)
102
c
. Further, clock signals CK and start pulses SP are input to the shift register
102
a
, digital data signals are input to the latch (A)
102
b
, and latch signals are input to the latch (B)
102
c.
The digital data signal input to the pixel portion
101
is formed by a time-division gradation data signal generation circuit
114
. A video signal consisting of an analog signal or digital signal (a signal containing image information) is converted into a digital data signal for performing time-division gradation in the time-division gradation data signal generation circuit
114
. At the same time, timing pulses necessary for performing time-division gradation display are generated in this circuit.
Specifically, the time-division gradation data signal generation circuit
114
contains means for: dividing one frame period into a plurality of subframe periods corresponding to n-bit (where n is an integer equal to or greater than 2) gradations; selecting write-in periods and display periods in the plurality of subframe periods; and setting the length of the display periods.
As the structure of the pixel portion
101
, what is shown in
FIG. 18
has been general. In
FIG. 18
, gate signal lines (G
1
to Gn) for inputting gate signals and source signal lines (also referred to as data signal lines) (S
1
to Sn) for inputting digital data signals are provided in the pixel portion
101
. Note that the digital data signal means a digital video signal.
Besides, power source supply lines (V
1
to Vn) are provided in parallel with the source signal lines (S
1
to Sn). The potential of the power source supply line (V
1
to Vn) is referred to as a power source potential. Besides, wiring lines (Vb
1
to Vbn) are provided in parallel with the gate lines (G
1
to Gn). The wiring lines (Vb
1
to Vbn) are connected to the external switch
116
.
A plurality of pixels
104
are arranged in matrix form in the pixel portion
101
.
FIG. 19
is an enlarged view of the pixel
104
. In
FIG. 19
, reference numeral
1701
designates a TFT (hereinafter referred to as a switching TFT) functioning as a switching element;
1702
, a TFT (hereinafter referred to as an EL driving TFT) functioning as an element (current control element) for controlling a current supplied to an EL element
1703
; and
1704
, a capacitor (holding capacitance).
A gate electrode of the switching TFT
1701
is connected to a gate signal line
1705
of one of the gate signal lines (G
1
to Gn) for inputting gate signals. One of a source region and a drain region of the switching TFT
1701
is connected to a source signal line
1706
of one of the source signal lines (S
1
to Sn) for inputting digital data signals, and the other is connected to a gate electrode of the EL driving TFT
1702
and the capacitor
1704
, respectively.
One of a source region and a drain region of the driving TFT
1702
is connected to a power source supply line
1707
of one of the power source supply lines (V
1
to Vn), and the other is connected to the EL element
1703
. The capacitor
1704
is connected to the power source supply line
1707
of one of the power source supply lines (V
1
to Vn).
The EL element
1703
is formed of an anode, a cathode, and an EL layer provided between the anode and the cathode. In the case where the anode is connected to the source region or the drain region of the EL driving TFT
1702
, in other words, in the case where the anode is a pixel electrode, the cathode becomes an opposite electrode. On the contrary, in the case where the cathode is connected to the source region or the drain region of the EL driving TFT
1702
, in other words, in the case where the cathode is a pixel electrode, the anode becomes an opposite electrode. In the present specification, the potential of the opposite electrode is referred to as an opposite potential. A potential difference between the potential of the opposite electrode an
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Ngo Ngan V.
Semiconductor Energy Laboratory Co,. Ltd.
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