Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-10-13
2002-07-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S503000, C313S505000, C257S091000, C257S099000
Reexamination Certificate
active
06416886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroluminescence device, which will be referred to as “an organic EL device” in this specification hereinafter, used as an element of an organic electroluminescence display. More particularly, the present invention relates to an organic EL device in which resistance of ITO (Indium Tin Oxide) film is reduced by increasing the thickness of ITO film when a transparent conductive film such as ITO film is formed as an anode so that short circuit between the anode and the cathode can be effectively prevented. Also, the present invention relates to a method of manufacturing the organic EL device.
2. Description of the Related Art
Concerning the organic EL device used for a back light of a liquid crystal display, a display applied to various types of display units and a light source of optical communication, by controlling its luminescent material and layer structure, it is possible to obtain various luminescent wave length including blue luminescence, which is difficult to obtain by a conventional inorganic EL device. Therefore, the organic EL device is widely used in the fields of various luminescent devices and color displays.
According to the basic method of manufacturing an organic EL device, it is manufactured as follows. For example, ITO film, which is known as a transparent conductive film, is formed on the surface of a glass substrate so that ITO film can be used as a transparent anode. Organic thin film is laminated on this ITO film. Further, a cathode, which composes a pair together with the anode formed by ITO film, is formed on this organic thin film by means of metallic vapor deposition.
When the size of a display composed of pixels of the above organic EL devices is increased, the following problems may be encountered. The overall ITO film is formed in a wide range. Therefore, resistance of ITO film is increased. As a result, it is impossible to avoid an increase in applied voltage. Also, when it is necessary to provide a higher resolution, the pattern width is reduced, and resistance is increased. Therefore, voltage is increased in the same manner as that described above. For the above reasons, in order to apply the organic EL devices to an image plane of a large size, it is necessary to reduce specific resistance of ITO to be used, or alternatively, it is effective to increase the film thickness of ITO film. This is owing to a reason that the larger the thickness of ITO film is, the lower the resistance is.
However, according to the physical property of ITO film, specific resistance of ITO film can be reduced to a predetermined value (p=150 to 200 &mgr;&OHgr;·cm) Therefore, in order to apply the organic EL device to an image plane of a large size, the countermeasure which has been taken up to this time is not sufficient. And also in order to increase the resolution of an image plane, the countermeasure which has been taken up to this time is not sufficient.
On the other hand, by increasing the thickness of ITO film, it is possible to reduce the resistance sufficiently. However, when the thickness of ITO film is increased, the transmittance is deteriorated. Therefore, it is difficult to obtain a sufficiently high intensity of light because of the deterioration of transmittance. Further, the following new problem may be caused. Since the organic thin film formed on ITO film is thinner than ITO film, when the thickness of ITO film is increased, an anode composed of this ITO film is short-circuited with a metallic cathode formed on the organic thin film.
FIG. 3
is a schematic illustration showing an arrangement of a conventional example in which there is a possibility that the anode is electrically communicated (short-circuited) with the cathode when the thickness of ITO film is increased. In the above arrangement, ITO film
52
is formed on a transparent glass substrate
51
by depositing step and patterning step. On this ITO film
52
, there is formed an organic thin film
53
which is an organic EL medium. Further, on this organic thin film
53
, there is formed a metallic cathode
54
by means of vapor-deposition.
An upper limit of the thickness of the organic thin film
53
is approximately 200 nm at most. When the thickness of the organic thin film
53
is increased to a value higher than that, problems are caused in the characteristics of the organic thin film
53
. On the other hand, in order to apply ITO film
52
to an image plane of a large size and high resolution, it is preferable that the thickness of ITO film is not less than 300 nm. For the above reasons, it is difficult for the organic thin film, which is an insulating material (semiconductor), to cover ITO film
52
completely. Especially, in an edge portion of an upper end of ITO film, a defective coverage of the organic thin film
53
tends to occur. In the case of occurrence of a defective coverage of the organic thin film
53
, ITO film
52
and the cathode
54
are short-circuited with each other, and the characteristic is deteriorated. That is, when the thickness of ITO film
52
is increased, an increase in the resistance can be suppressed. Therefore, it is possible to apply it to an image plane of a large size. However, due to the above short circuit, a local luminescent trouble is caused, and further a cross talk is caused by a leakage of electrical current.
As described above, the increase in the thickness of ITO film
52
is effective to maintain resistance low, however, a difference in level between ITO film
52
and a surface of the glass substrate
51
is made, which causes a new problem. For the above reasons, instead of the above manufacturing method, there is provided a manufacturing method shown in
FIGS. 4A-4D
.
Processes according to manufacturing method are shown in
FIGS. 4A-4D
First, ITO film
52
is deposited on the glass substrate
51
and patterned to anode patterns by photolithography (FIG.
4
A). After that, SiO
2
film
55
is formed on the anode patterns of ITO film
52
(FIG.
4
B). A resist
56
is coated on the SiO
2
film
55
and patterned by photolithography (FIG.
4
C). Further, when the SiO
2
film
55
is etched by using the resist
56
as a mask and then the resist
56
is removed. Therefore SiO
2
film
55
is embedded between the anode patterns of ITO film
52
as shown in FIG.
4
D. In this way, a difference in level of the surface of the anode patterns of ITO film
52
from that of other area on the glass substrate
51
can be suppressed.
When SiO
2
55
is embedded between the anode patterns of ITO film
52
, although it is impossible to make the entire surface flat, it is possible to suppress the occurrence of a defective coverage of the organic thin film
54
at the edge portion of the anode patterns of ITO film
52
. Due to the foregoing, when the cathode
54
is formed as shown in
FIG. 3
, it is possible to prevent a short circuit between anode patterns of ITO film
52
and the cathode
54
. Therefore, not only it becomes possible to reduce resistance by increasing the thickness of ITO film
52
, but also the occurrence of cross talk caused by short circuit after the formation of films can be suppressed.
However, according to the above manufacturing method, the following processes are required. After ITO film
52
is subjected to etching on the glass substrate
51
by using a resist pattern as the mask, SiO
2
55
is formed on the overall surface, and then patterning is conducted in accordance with the mask pattern for patterning the ITO film
52
. After that, SiO
2
55
is subjected to etching, so that SiO
2
55
can be embedded only into a clearance (an interval region) between the anode patterns of ITO film
52
. That is, it is necessary to conduct patterning not less than twice for the formation anode patterns of ITO film
52
and embedded patterns of SiO
2
55
. Further, it is necessary to conduct patterning of SiO
2
55
in accordance with anode patterns of ITO film
52
. For the above reasons, a high accuracy is required for the mask alignment, wh
Gyoutoku Akira
Iwanaga Hideaki
Garrett Dawn
Kelly Cynthia H.
Pearne & Gordon LLP
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