Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2003-07-17
2004-12-14
Tran, Thien F (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S072000, C257S088000, C257S098000
Reexamination Certificate
active
06831298
ABSTRACT:
The present invention claims the benefit of Korean Patent Application No. P2002-041939 filed in Korea on Jul. 18, 2002, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic electroluminescent display device, and more particularly, to a dual panel-type organic electroluminescent display device.
2. Discussion of the Related Art
Among flat panel displays, liquid crystal display (LCD) devices have been commonly used due to their thin profile, light weight, and low power consumption. However, the LCD devices are not self-luminescent and suffer from low brightness, low contrast ratios, narrow viewing angles, and large overall sizes.
Organic electroluminescent display (OELD) devices have wide viewing angles and excellent contrast ratios because of their self-luminescence. In addition, since the OELD devices do not require additional light sources, such as a backlight, the OELD devices have relatively small sizes, are light weight, and have low power consumption, as compared the LCD devices. Furthermore, the OELD devices can be driven by low voltage direct current (DC) and have short microsecond response times. Since the OELD devices are solid state devices, the OELD devices sufficiently withstand external impact and have greater operational temperature ranges. In addition, the OELD devices may be manufactured at low cost since only deposition and encapsulation apparatus are necessary for manufacturing the OELD devices, thereby simplifying manufacturing processes.
The OELD devices are commonly categorized as top emission-type and bottom emission-type according to a direction of the emitted light. Furthermore, the OELD devices may be categorized as one of passive matrix-type OELD devices and active matrix-type OELD devices depending upon methods of driving the devices. The passive matrix-type OELD devices are commonly used because of their simplicity and ease of fabrication. However, the passive matrix-type OELD devices have scanning lines and signal lines that perpendicularly cross each other in a matrix configuration. Since a scanning voltage is sequentially supplied to the scanning lines to operate each pixel, an instantaneous brightness of each pixel during a selection period should reach a value resulting from multiplying an average brightness by the number of the scanning lines to obtain a required average brightness. Accordingly, as the number of the scanning lines increases, the applied voltage and current also increase. Thus, the passive matrix-type OELD devices are not adequate for high resolution display and large-sized displays since the devices easily deteriorate during use, and power consumption is high.
Since the passive matrix-type OELD devices have many disadvantages with regard to image resolution, power consumption, and operational lifetime, the active matrix-type OELD device have been developed to produce high image resolution in large area displays. In the active matrix-type OELD devices, thin film transistors (TFTs) are disposed at each sub-pixel to function as a switching element to turn each sub-pixel ON and OFF. Accordingly, a first electrode connected to the TFT is turned ON/OFF by the sub-pixel, and a second electrode facing the first electrode functions as a common electrode. In addition, a voltage supplied to the pixel is stored in a storage capacitor, thereby maintaining the voltage and driving the device until a voltage of next frame is supplied, regardless of the number of the scanning lines. As a result, since an equivalent brightness is obtained with a low applied current, an active matrix-type OELD device has low power consumption and high image resolution over a large area.
FIG. 1
is a schematic circuit diagram of a pixel structure of an active matrix-type OELD device according to the related art. In
FIG. 1
, a scanning line
1
is arranged along a first direction, and a signal line
2
and a power line
3
that are spaced apart from each other are arranged along a second direction perpendicular to the first direction. The signal line
2
and the power line
3
cross the scanning line
1
, thereby defining a pixel area. A switching thin film transistor (TFT) T
S
, i.e., an addressing element, is connected to the scanning line
1
and the signal line
2
, and a storage capacitor C
ST
is connected to the switching TFT T
S
and the power line
3
. A driving thin film transistor (TFT) T
D
, i.e., a current source element, is connected to the storage capacitor C
ST
and the power line
3
, and an organic electroluminescent (EL) diode D
EL
is connected to the driving TFT T
D
. When a forward current is supplied to the organic EL diode D
EL
, an electron and a hole are recombined to generate an electron-hole pair through the P(positive)-N(negative) junction between an anode, which provides the hole, and a cathode, which provides the electron. Since the electron-hole pair has an energy that is lower than the separated electron and hole, an energy difference exists between the recombination and the separated electron-hole pair, whereby light is emitted due to the energy difference.
FIG. 2
is a cross sectional view of a bottom emission-type organic electroluminescent display (OELD) device according to the related art. In
FIG. 2
, first and second substrates
10
and
30
are bonded together by a seal pattern
40
, wherein one pixel region is shown to include red, green, and blue sub-pixel regions. A thin film transistor (TFT) T is formed at each sub-pixel region P
sub
on an inner surface of the first substrate
10
, and a first electrode
12
is connected to the TFT T. An organic electroluminescent layer
14
includes luminescent materials of red, green, and blue and is formed on the TFT T. In addition, the first electrode
12
and a second electrode
16
are formed on the organic electroluminescent layer
14
, whereby the first and second electrodes
12
and
16
induce an electric field to the organic electroluminescent layer
14
. A desiccant (not shown) is formed in an inner surface of the second substrate
30
to shield an internal portion of the OELD device from external moisture. The desiccant is attached to the second substrate
30
by an adhesive (not shown), such as semi-transparent tape.
In the bottom emission-type OELD device, for example, the first electrode
12
functions as an anode and is made of a transparent conductive material, and the second electrode
16
functions as a cathode and is made of a metallic material of low work function. Accordingly, the organic electroluminescent layer
14
is composed of a hole injection layer
14
a
, a hole transporting layer
14
b
, an emission layer
14
c
, and an electron transporting layer
14
d
formed over the first electrode
12
. The emission layer
14
c
has a structure where emissive materials of red, green, and blue are alternately disposed at each sub-pixel region P
sub
.
FIG. 3
is a cross sectional view of a sub-pixel region of a bottom emission-type organic electroluminescent display device according to the related art. In
FIG. 3
, a TFT T having a semiconductor layer
62
, a gate electrode
68
, and source and drain electrodes
80
and
82
is formed on a substrate
10
. The source electrode
80
of the TFT T is connected to a storage capacitor C
ST
, and the drain electrode
82
is connected to an organic electroluminescent (EL) diode D
EL
. The storage capacitor C
ST
includes a power electrode
72
and a capacitor electrode
64
that face each other with an insulating layer interposed between the power electrode
72
and the capacitor electrode
64
, wherein the capacitor electrode
64
is made of the same material as the semiconductor layer
62
. The TFT T and the storage capacitor C
ST
are commonly referred to as array elements A. The organic EL diode D
EL
includes first and second electrodes
12
and
16
that face each other with an organic EL layer
14
interposed therebetween. The source electrode
80
of the TFT T is connected to the power electrode
72
of the storage capacitor C
ST
Kim Kwan-Soo
Kim Ock-Hee
Lee Nam-Yang
Park Jae-Yong
Yoo Choong-Keun
LG.Philips LCD Co. , Ltd.
Morgan & Lewis & Bockius, LLP
Tran Thien F
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