Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-06-29
2003-06-17
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S403000, C428S917000, C313S502000, C313S505000, C313S509000, C427S066000, C427S212000
Reexamination Certificate
active
06579631
ABSTRACT:
The present invention claims the benefit of Korean Patent Application No. P2000-83099 filed in Korea on Dec. 27, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device, and more particularly, to an electroluminescence device and a method for manufacturing the same.
2. Discussion of the Related Art
Ultra thin flat panel display devices, especially liquid crystal display (LCD) devices, are widely used in monitors for notebook computers, spacecrafts, and aircrafts.
Of such LCDs, a passive luminescence LCD device includes a back light provided at the rear of a liquid crystal panel and used as a light source. The back light adds additional weight, power consumption, and thickness to the LCD device. In this respect, it is expected that the back light will eventually be replaced by an advanced high efficiency self-luminescence display device. Currently, a thin and light electroluminescence device is being researched and developed.
Electroluminescence devices can be divided into light-emitting diodes (LEDs) and electroluminescence diodes (ELDs) depending on the application principles. A LED is based on radiant transition course of electron-hole recombinations near a P-N junction. Recently, rapid development of LEDs using an organic material is in progress.
An ELD is based on luminescence generated when high energy electrons generated within a light-emitting layer excite a phosphor layer by impact. Basically, the electrons within the light-emitting layer obtain energy under a high electric field, thereby generating hot electrons. The hot electrons then excite and release an activator, thereby generating light.
ELDs are generally manufactured by a thick film printing process by using a mixture of resin and light-emitting powder. Alternatively, a thin film printing process may be used. Also, ELDs are divided into an AC type and a DC type depending on different driving modes.
A related art electroluminescence device will now be described with reference to the accompanying drawings.
FIG. 1
is a schematic view of a related art electroluminescence device. As shown in
FIG. 1
, the related art electroluminescence device includes a substrate
11
, a transparent electrode layer
13
formed on the substrate
11
in a predetermined pattern such as a stripe pattern, a lower insulating layer
15
of SiO
x
, SiN
x
, or BaTiO
3
formed on the transparent electrode layer
13
, a light-emitting layer
17
of ZnS based light-emitting material formed on the lower insulating layer
15
, and an upper insulating layer
19
of SiO
x
, SiN
x
, or Al
2
O
3
formed on the light-emitting layer
17
. It further includes a metal electrode layer
21
of a metal, such as Al, formed on the upper insulating layer
19
, and a surface passivation layer
23
formed on the metal electrode layer
21
.
In the aforementioned related art electroluminescence device, when an AC voltage is applied to the transparent electrode layer
13
and the metal electrode layer
21
, a high electric field of ~10
6
V/cm is formed within the light-emitting layer
17
. Electrons generated in the interface between the upper insulating layer
19
and the light-emitting layer
17
are tunneled into the light-emitting layer
17
.
The tunneled electrons are accelerated by the high electric field within the light-emitting layer
17
. The accelerated electrons come into collision, with an activator (Cu or Mn) within the light-emitting layer
17
so that electrons are excited from the ground state. When the excited electrons are again transited to the ground state, a unique light equivalent to the energy difference is emitted. At this time, the color of the emitted light depends on the energy difference.
A method for manufacturing the aforementioned related art electroluminescence device will now be described. As shown in
FIG. 1
, the transparent electrode layer
13
is formed on the glass substrate
11
. In more detail, an indium tin oxide (ITO) thin film having a high conductivity and transparent physical characteristic is deposited on the substrate
11
. The ITO thin film is then patterned by a photolithography process to form a stripe shape, thereby forming transparent electrodes.
Afterwards, the BaTiO
3
based lower insulating layer
15
is formed on the transparent electrode layer
13
by a RF reactive sputtering process. The light-emitting layer
17
is then formed on the lower insulating layer
15
.
The light-emitting layer
17
may be formed by an electron-beam deposition, e.g., by cold pressing a powder in which Cu or Mn is doped on ZnS and generating small grains. Alternatively, the light-emitting layer
17
may be formed by a sputtering method using a target.
The upper insulating layer
19
of SiO
x
, SiN
x
, or Al
2
O
3
is formed on the light-emitting layer
17
by a sputtering process or chemical vapor deposition (CVD) process.
The metal electrode layer
21
is formed on the upper insulating layer
19
. An Al or Ag thin film is formed on the upper insulating layer
19
by a thermal deposition method and then stripe shaped metal electrodes are formed to cross the transparent electrodes of the transparent electrode layer
13
. The surface passivation layer
23
is finally formed on the metal electrode layer
21
. Thus, the related art process for manufacturing an electroluminescence device is completed.
However, the related art electroluminescence device and the method for manufacturing the same have several problems. Since the electroluminescence device requires a high electric field, an insulating layer is required both above and below the light-emitting layer to prevent a short circuit resulting from any defect. The insulating layer limits the maximum current flowing to the device to a range corresponding to the discharge and charge displacement of the insulating layer.
In case where the light-emitting layer is formed by either a vacuum deposition method according to the sputtering method or a thick film printing method using a powder, the insulating layer is normally formed by screen printing using an organic binder. This increases the required process steps and the manufacturing cost.
Furthermore, since the insulating layer is respectively formed above and below the light-emitting layer, a voltage drop occurs as a result. For this reason, a threshold voltage required to drive the device becomes higher. In other words, an undesirably high driving voltage is required.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electroluminescence device and a method for manufacturing the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electroluminescence device and a method for manufacturing the same that minimize the process steps and the manufacturing cost.
Another object of the present invention is to provide an electroluminescence device and a method for fabricating the same that can obtain a sufficiently high light-emitting effect under a low driving voltage.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electroluminescence device according to the present invention includes a substrate, a lower electrode layer formed on the substrate, a light-emitting layer formed directly on the lower electrode layer, an upper electrode layer formed on the light-emitting layer, and a passivation layer formed on the upper electrode layer.
In another aspect of the present invention, an electroluminescence device including a
Garrett Dawn
Kelly Cynthia H.
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
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