Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-07-06
2003-07-22
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S504000, C428S917000
Reexamination Certificate
active
06597109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic EL device using an organic compound, and more particularly to structure of an organic layer for preventing occurrence or current leakage and a method for production thereof.
2. Prior Art
Recently, active research works have been made on organic EL devices. As a basic configuration, the organic EL device includes a thin film of hole transporting material such as triphenyldiamine (TPD) or the like formed by evaporation on a hole injecting electrode, a light emitting layer made of aluminum quinolinol complex (Alq3) or the like laminated thereon, and a metal electrode (electron injecting electrode) formed thereon from a metal having a low work function such as magnesium. Such organic EL devices are watched with interest because they can achieve so high a luminance as ranging from several 100 to several 10,000 cd/m
2
with a drive voltage of approximately 10 volts.
In the manufacture of displays using such an organic EL device, it is an important problem how to lower the proportion of defective product. That is, there can arise various troubles such as uneven lamination of organic layers, damaging of organic layers in the lamination of functional thin films such as electron injecting electrode or the like, contamination of electron injecting electrode itself by impurities or oxidation thereof which cause the so-called irregular luminance or defective dot or unevenness in quality. Especially, the occurrence of leakage current is an important problem. A current of reverse direction (leakage current), if ever, brings about deterioration of display quality such as cross talk, uneven luminance, etc. and further-energy consumption not contributing to light emission such as unnecessary heating of device, and thereby a reduction of light emission efficiency.
SUMMARY OF THE INVENTION
Object of the Invention
The object of the present invention consists in realizing an organic EL device capable of preventing current leakage and retaining a long lifetime, a high luminance, a high efficiency and a high display quality.
Means for Solution of the Problem
The present inventors have conducted extensive studies on the mechanism of occurrence of leakage current. As a result, it has bee found that one of the predominant causes is the existence of minute dusts. Further, it has also been found that another cause participating in the leakage is the fine protrusions present on the hole injecting electrode. Based on these findings, the present invention has been accomplished.
The object mentioned above can be achieved by the following constructions (1)-(6):
(1) An organic EL device comprising a hole injecting electrode, an electron injecting electrode and at least one organic layer located between said electrodes, wherein at least one of the organic layers has a thickness of no less than 100 nm and a hole mobility or electron mobility of 0.5-5×10
−3
cm
2
/V.s.
(2) The organic EL device of (1), wherein one of the organic layers is located at the lowermost position, and it is any of hole injecting layer, hole transporting layer, hole injecting and transporting layer and light emitting layer, and thickness thereof is 100-400 nm.
(3) A method for preparing an organic EL device, which comprises forming a film of hole injecting electrode on a substrate, and then forming thereon at least one organic layer so that thickness of said organic layer comes to no less than 20% of average particle diameter of dusts.
(4) The method of (3), wherein said average particle diameter of dusts is an average particle diameter or dusts having a particle diameter of 0.3-1 &mgr;m and floating in the film-making chamber.
(5) The method of (3) or (4), wherein said organic layer is any of hole injecting layer, hole transporting layer, hole injecting and transporting layer and light emitting layer.
(6) The method of (3) to (5) for obtaining an organic EL device of (1) or (2).
Functions
Prior organic EL devices exhibit the so-called diode characteristics, namely a nature of not readily passing a current of reverse direction. Further, in prior EL devices, thickness of the organic layer and electron injecting electrode, except for hole injecting electrode, is about 100-200 nm. Since light is emitted at such a small layer thickness, the display can exhibit quite excellent performance. But, if dusts exist at the time of forming the organic layer, leakage current readily arises. That is, as shown in
FIG. 3
, when dust
2
is attached to the surface of picture elements after film formation of hole injecting electrode
1
and if the organic layer
3
is formed by evaporation method, shadowing takes place, due to which straightforwardly advancing vapor particles do not adhere to the shadow of dusts and there appears a gap between the formed organic layer
3
and dust
2
in the part of shadow.
If electron injecting electrode is formed by sputtering as shown in
FIG. 4
, the sputtered particles
4
a
having a high throwing power are thrown into the shadow area to form electron injecting electrode even in the shadow area. Thus, in the shadow area, the hole injecting electrode
1
and the electron injecting electrode
4
are directly connected to each other without interception by organic layer
3
, due to which a leakage current arises.
Further, as shown in
FIG. 5
, hole injecting electrode
1
can sometimes have thereon protrusions
5
formed by deformation of electrode-constituting material or abnormal crystal growth thereof. When such protrusion
5
is present, the protrusion can pierce through the laminated organic layer
3
. Even if it does not pierce, the protrusion causes a breakage of insulation when the position of protrusion
5
is close to electron injecting electrode
4
, due to which short circuit arises between hole injecting electrode
1
and electron injecting electrode or a leakage current
6
arises. Especially since hole injecting electrode
1
is made of a conductor, protrusion
5
readably causes leakage current
6
.
The occurrence of leakage current can be prevented by, as shown in
FIG. 2
, adjusting film thickness of organic layer
3
to a value allowing no existence of gap with dust
2
, or by increasing the film thickness to a value sufficiently larger than the height of protrusion
5
. By such means, the sputtered particle
4
a
becomes unable to enter the shadow part or the thickness of organic layer can be made to exceed the height of protrusion
5
sufficiently, so that occurrence of leakage current can be prevented.
REFERENCES:
patent: 5216331 (1993-06-01), Hosokawa et al.
patent: 5766779 (1998-06-01), Shi et al.
patent: 5811833 (1998-09-01), Thompson
patent: 5958609 (1999-09-01), Ueda et al.
patent: 4-85389 (1992-03-01), None
patent: 05-121168 (1993-05-01), None
patent: 6-93256 (1994-04-01), None
patent: 8-239657 (1996-09-01), None
Arai Michio
Inoue Tetsushi
Nakaya Kenji
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
TDK Corporation
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