Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-06-29
2004-08-24
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S509000
Reexamination Certificate
active
06781307
ABSTRACT:
This application claims the benefit of Korean Application No. P
2000-83098
, 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 electroluminescent device and a method for manufacturing the same.
2. Discussion of the Related Art
Ultra thin sized flat panel displays having a display screen with a thickness of several centimeters, especially liquid crystal display (LCD) devices, are widely used for monitors in notebook computers, spacecraft, aircraft, etc.
LCD panels are in general non-luminous and require a backlight at the rear of the liquid crystal panel as a light source. The conventional, backlight is not satisfactory because of its large weight, power consumption, and thickness. In this respect, it is desirable to replace the conventional backlight with a thinner, lighter, less-power consuming alternative. Currently, thin and light electroluminescent devices are under research and development.
Electroluminescent devices can be divided into two types: a light-emitting diode (LED) and an electroluminescent diode (ELD), depending on the operational principles. The light emission of LEDs is based on a radiant transition due to electron-hole recombination near a P-N junction. Recently, a rapid development of an LED based on an organic material is in progress.
On the other hand, the light emission of ELDs is based on luminescence that takes place when high energy electrons generated in a light-emitting layer excite a phosphor upon impact, Electrons within the light-emitting layer acquire energy from a high electric field and turn into hot electrons. The hot electrons then excite an activator to generate light.
ELDs are manufactured by thick-film printing of a mixture of resin and light-emitting powder or by thin film printing. ELDs are also divided into two types: the AC type and the DC type, depending on the driving modes.
An electroluminescent device of the related art will be described with reference to FIG.
1
.
FIG. 1
is a schematic perspective view of a related art electroluminescent device. As shown in
FIG. 1
, the related art electroluminescent device includes a substrate
11
and a transparent electrode layer
13
on the substrate
11
. The transparent electrode layer
13
is formed in a predetermined pattern, such as in a stripe pattern. The transparent electrode
13
is formed of indium tin oxide (ITO), for example. A lower insulating layer
15
of SiO
X
, SiN
X
, or BaTiO
3
is formed on the transparent electrode layer
13
, and a light-emitting layer
17
of a ZnS based light-emitting material is formed on the lower insulating layer
15
. The related art device further includes an upper insulating layer
19
made of SiO
X
, SiN
X
, or Al
2
O
3
on the light-emitting layer
17
. It further includes a metal electrode layer
21
made of a metal, such as Al, on the upper insulating layer
19
, and a surface passivation layer
23
on the metal electrode layer
21
.
In this related art electroluminescent device, when an AC voltage is applied between the transparent electrode layer
13
and the metal electrode layer
21
, a high electric field in the order of 10
6
V/cm is built within the light-emitting layer
17
. Electrons generated in the interface between the upper insulating layer
19
and the light-emitting layer
17
tunnel into the light-emitting layer
17
.
The tunneling electrons are accelerated by the high electric field in the light-emitting layer
17
. The accelerated electrons collide with activators (Cu and/or Mn) within the light-emitting layer
17
to excite electrons in the ground state to excited states. When electrons at a higher energy level transit to the vacant sites in a lower energy level state created by the excitation—e.g., when the excited electrons transit to the ground state (or to other lower energy level states), light having a wavelength corresponding to the energy difference is emitted. The color of the emitted light thus depends on the energy difference.
A method for manufacturing the related art electroluminescent device will now be described in more detail. The transparent electrode layer
13
is formed on the glass substrate
11
. Specifically, a thin ITO film having a high conductivity end a good transparent physical characteristic is deposited on the substrate
11
. The thin ITO film is then patterned by photolithography into a stripe shape to form transparent electrodes, which are collectively referred to as “transparent electrode layer
13
.”
A BaTiO
3
based lower insulating layer
15
is formed on the transparent electrode layer
13
by RF reactive sputtering. The light-emitting layer
17
is then formed on the lower insulating layer
15
. The light-emitting layer
17
may be formed via electron-beam deposition by cold pressing a powder of a Cu or Mn doped ZnS material and by generating small grains. Alternatively, the light-emitting layer
17
nay be formed by sputtering 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 sputtering or chemical vapor deposition (CVD). The metal electrode layer
21
is formed on the upper insulating layer
19
. Specifically, a thin Al or Ag film is formed on the upper insulating layer
19
by thermal deposition and is patterned into stripe-shaped metal electrodes that extend perpendicularly to the transparent electrodes of the transparent electrode layer
13
underneath. Finally, the surface passivation layer
23
is formed on the metal electrode layer
21
. This completes the manufacture of the related art electroluminescent device.
However, the related art electroluminescent device have several drawbacks. As briefly explained above because a thin film transistor (TFT) liquid crystal display (LCD) panel (TFT-LCD panel) for notebook computers and monitors has no self-luminous function, a light-emitting device such as a backlight is required. Since the conventional backlight is constructed by combining a light-guiding plate, a light-diffusion plate, and a prism with a cold cathode fluorescent lamp, the manufacturing cost is high, and the manufacturing process is undesirably complicated. Moreover, the large thickness of the backlights increases the thickness of the resultant monitor devices, which is undesirable. To substitute for such a conventional backlight, the related, art electroluminescent device has been proposed. Although the manufacturing cost and thickness of the related art electroluminescent device have been somewhat reduced recently, it is still expensive. Moreover, the related art electroluminescent device still has an insufficient luminance to be used as a light source for LCDs.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electroluminescent 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 electroluminescent device and a method for manufacturing the same, in which a sufficiently high luminance can be obtained so that the device can be used as a backlight for LCD panels.
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 scheme 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, the electroluminescent device according to a first aspect includes a lower electrode layer having a surface of a plurality of convex shapes, formed on the substrate, an insulating layer, a light-emitting layer, and an upper electrode layer sequentially formed on t
Guharay Karabi
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Patel Nimeshkumar D.
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