Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-09-10
2004-11-16
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S498000
Reexamination Certificate
active
06819043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to an electroluminescent device (hereinafter, “ELD”) and method of manufacturing the same. More particularly, it relates to an electroluminescent device and method of manufacturing the same, capable of reducing the loss of light propagated along the lateral side of the device and increasing the amount of light propagated to the front of the display to improve the brightness and efficiency of the device, in such a way that a transparent conductive film or a luminescent layer is made of materials having crystallographic anisotropy and is then etched to make the transparent conductive film or the luminescent layer with a protrusion shaped or textured surface feature.
2. Description of the Prior Art
An electroluminescence device (hereinafter, “ELD”) is one using an electroluminescent phenomena occurring when an electric field is applied to materials such as ZnS, CaS, and the like. SHARP (Japan) announced a thin ELD having a high brightness and a long life (1974). Since then, many researches have been made on the ELD. In particular, C. W. Tang in Eastman Kodak manufactured a thin film ELD using an organic material and reported that a green luminescence of high brightness is possible. As the result, researches have been actively made on an organic ELD having a low driving voltage and being advantageous in the process.
The structure of the ELD may mainly includes an alternating-current thin film type structure, an alternating-current thick film type structure, a direct-current thin film type structure and a direct-current thick film type structure. In detail, the structure of the alternating-current thin film type structure usually includes upper and lower insulating layers with a luminescent layer intervened between them, and the alternating-current thick film type structure including an luminescent material mixed with insulating binder and an insulating layer. Also, the structure of the direct-current type structure includes a thin film type structure having a single insulating layer and a luminescent layer, and a thick film type structure having a luminescent layer.
A structure of a conventional ELD
10
will be described by reference to FIG.
1
.
As shown in
FIG. 1
, the alternating-current thin film ELD
10
includes a transparent substrate such as glass
11
, or semiconductor single crystal substrates such as silicon
11
or a flexible substrate
11
. A lower electrode
12
as a transparent electrode is formed on the substrate
11
. A lower insulating layer
13
formed on the lower electrode
12
. A luminescent layer
14
is formed on the lower insulating layer
13
. An upper insulating layer
15
is formed on the luminescent layer
14
. An upper electrode
16
made of a transparent electrode or a metal electrode is formed on the upper insulating layer
15
.
FIG.
10
and
FIG. 11
show schematic diagram of the crystal structure and the surface atom arrangement for II-VI and III-V compounds, respectively. III-V group compounds have a cubic or hexagonal structure. In
FIG. 10
, A/A′ indicate II group or III group atoms and B/B′ indicate VI group or V group atoms. Also, the direction of the arrows is (111) in case of the cubic system and (0001) in case of the hexagonal system. Also,
FIG. 11
shows the electron arrangement of A and B atoms each constituting {0001} or {111} crystal surfaces of II-VI group or III-V group compound. In
FIG. 11
, A indicates II group or III group atoms and B indicates VI group or V group atoms.
However, the conventional ELD
10
having this structure did not have the brightness and efficiency sufficient to be applicable to the display requiring a high brightness and efficiency. Therefore, there is an urgent need for a new ELD having a high brightness and efficiency.
In order to solve this problem, many researches haven been made on a new ELD having these high brightness and efficiency characteristics. For example, the crystallinity of phosphor materials constituting the ELD, the degree of activation for activator ions, the number of accelerated electrons, and the energy and its distribution must be controlled. For this, a method of manufacturing various phosphor materials and an annealing method for the purpose of an improved crystal property of the phosphor materials and an effective activation of the activator ions. Also, there has been proposed a method of using an insulating material having high dielectric constant in order to generate accelerated electrons having high energy of narrow energy distribution.
Meanwhile, in order to manufacture a ELD of a high brightness and a high efficiency as described above, a solution by which the amount of light emitted toward the lateral side of the ELD display is promising. As the surface and flatness of the film adopted in the conventional ELD is usually smooth and good, 80~90% of emitted lights from activator ions actually propagate along the interface between the insulating layer and the luminescent layer or the interface between the insulating layer and the electrode layer and can not emitted to front side due to so called “Light-Piping” or “Waveguide” effect. Due to this, the light traveling toward the front of the display that can contribute an actual optical efficiency is only 10~20% of the total.
SUMMARY OF THE INVENTION
The present invention is contrived to solve the above problems and an object of the present invention is to increase the scattering of light by deforming the surface of a film constituting an ELD in order to manufacture the ELD having a high brightness and high efficiency.
Further, another object of the present invention is to simplify the process by applying ZnO that can be relatively easily etched as compared to the transparent electrode made of conventional indium tin oxide (hereinafter, “ITO”) to a process of forming the transparent electrode.
In order to accomplish the above object, an electroluminescent device according to the present invention is characterized in that it comprises a substrate, a first electrode formed on the substrate, a luminescent layer formed on the first electrode, and a second electrode formed on the luminescent layer, wherein at least one of the first electrode, the luminescent layer and the second electrode is formed to have a protrusion or texture at its surface.
Preferably, the electroluminescent device further includes a first insulating layer formed between the first electrode and the luminescent layer; and a second insulating layer formed between the luminescent layer and the second electrode.
REFERENCES:
patent: 4737684 (1988-04-01), Seto et al.
Etching of Crystals; Theory, Experiment, and Application by K. Sangwal; Institute of Physics, Poland 1987 pp. 425, 432.
A tunnel thin film electroluminescent device; C.J. Summers et al; Appl. Phys. Lett. Jan. 13, 1997 pp. 234-236.
Texture etched ZnO:Al coated glass substrates for silicon based thin film solar cells; by O. Kluth et al. Thin Solid Films (1999) pp. 247-253.
The effect of despition temperature on the properties of Al-doped zinc oxide thin films; J.F. Chang et al. Thin Solid Films 386 (2001) pp. 79-86.
Optical and electrical properties of direct-current magnetron-sputtered ZnO; Al films vol. 90, No. 7, Journal of applied physics Oct. 1, 2001 pp. 3432-3436.
Synthesis and optelectronic characterization of gallium doped zinc oxide transparent electrodes; GA Hirata et al.; Thin Solid Films 288 (1996) pp. 29-31.
Kim Yong Shin
Lee Yong Eui
Park Sang Hee
Yun Sun Jin
Blakely , Sokoloff, Taylor & Zafman LLP
Electronics and Telecommunications Research Institute
Patel Vip
LandOfFree
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