Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-10-13
2002-02-26
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000, C313S505000, C313S503000
Reexamination Certificate
active
06351066
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescence element, which will be referred to as “an organic EL element” in this specification hereinafter, used as an element of an organic electroluminescence display. More particularly, the present invention relates to an organic EL element and a manufacturing method thereof in which patterning can be easily conducted when an organic thin film is laminated on an anode and a cathode is formed on the organic thin film.
The organic EL element is used for a back light of a liquid crystal display, a display applied to various types of display units and a light source of an optical communication system. By changing a luminescent material or layer structure, it is possible for the organic EL element to obtain various luminescent wave length including blue luminescence, which is difficult to obtain by a conventional inorganic EL element. Therefore, the organic EL element is widely used in the fields of various luminescent devices and color displays.
According to the basic method of manufacturing an organic EL element, it is manufactured as follows. For example, ITO film (Indium Tin Oxide), 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. An organic thin film is laminated on this ITO film. Further, a cathode, which includes a pair electrodes together with the anode formed by ITO film, is formed on this organic thin film by means of metallic vapor deposition. Recently, a method of manufacturing an organic electroluminescence element has been adopted for the purpose of enhancing the insulating property when the cathode is formed by means of vapor deposition and also for the purpose of preventing a short circuit between the cathode and ITO film formed as an anode. The manufacturing method includes a process in which an upper end portion of an electrically insulating bulkhead provided between the organic thin film and the laminated body of the cathode and also provided between the cathodes is formed into a T-shape in the longitudinal cross-sectional shape.
The above method of manufacturing an organic electroluminescence element, in which the overhang portion is formed in the manufacturing process, is disclosed in, for example, JP-A (Japanese Unexamined Patent Publication No.) 8-315981 and others. The essential concept of the above manufacturing method is shown in
FIGS. 4A-4F
.
As shown in
FIG. 4A
, an anode is made of a transparent electrode
52
on a glass substrate
51
by means of patterning, wherein an electrically conductive transparent ITO is subjected to patterning for forming the transparent electrode
52
. In this case, a plurality of rows of transparent electrodes
52
are provided in parallel to each other on a glass substrate
51
in the uniform thickness. A film of polyimide
53
, which is an unphotosensitive and electrically insulating material, is formed by, for example, the method of spin coating. This film of polyimide
53
is formed on both the glass substrate
51
and the transparent electrode
52
in parallel to them in a direction perpendicular to the arranging direction of the transparent electrode
52
. This film of polyimide
53
is finally formed as an insulating bulkhead. Next, as shown in
FIG. 4B
, an SiO
2
film
54
used as material to form an overhang portion is formed by the method of spattering so that an appropriate film thickness can be obtained. After that, as shown in
FIG. 4C
, a photoresist pattern
55
is formed by the method of photolithography on the SiO
2
film
54
.
Further, as shown in
FIG. 4D
, the SiO
2
film
54
is etched so as to be the same pattern as that of the photoresist pattern
55
while the photoresist pattern
55
is used as a mask in the process of etching. Next, as shown in
FIG. 4E
, the film of polyimide
53
is vertically etched by the method of reactive etching in which O
2
is used as an etching gas. Then, as shown in
FIG. 4F
, the sides of polyimide
53
are equally subjected to side etching by the method of wet etching in which an alkali solution is used. Due to the foregoing, the overhang portion can be formed, in which the SiO
2
film
54
protrudes to the transverse direction from the sides of polyimide
53
.
After the process in which the overhang portion is formed, an organic thin film is formed on the upper surface of the transparent electrode
52
. Further, a cathode is formed on this organic thin film by the method of vapor deposition. In the process of vapor deposition of the cathode, metallic vapor is incident upon the glass substrate
51
from above, so that metallic vapor can not come round to the side of the transparent electrode
52
and a short circuit of the transparent electrode
52
with the cathode formed by vapor deposition can be prevented.
However, according to the manufacturing method described above, the SiO
2
film
54
must be etched and then polyimide
53
must be successively etched in the process until the overhang portion is formed. Even after the above two etching processes, an etching process is required in which polyimide
53
is etched in an alkaline solution. Accordingly, it is necessary to conduct the etching processes three times in total. Even if polyimide
53
is subjected to wet etching in an alkaline solution at the beginning, it is necessary to go through two etching processes, which affect the yield of products. Since the SiO
2
film
54
in which plastic deformation tends to occur is formed on polyimide
53
in which elastic deformation tends to occur and the thickness of which is relatively large, cracks are easily caused in the SiO
2
film
54
by the influence of heat, and there is a possibility that the reliability is deteriorated.
As described above, when the conventional organic EL element is manufactured, it is necessary to conduct etching at least twice in the process until the overhang portion is formed so that the anode made of ITO formed on the glass substrate can not be short-circuited with the cathode. Therefore, the working process becomes complicated and the productivity is affected. Since hard SiO
2
is formed on soft polyimide, cracks tend to be caused on the SiO
2
film
54
, and the reliability is deteriorated.
JP-A No. 8-315981 discloses a manufacturing method in which a reversely tapered portion is formed by resist. However, it is impossible in principle to form a reversely tapered portion with the positive type resist. When negative type resist is used, it is easy to form a reversely tapered portion. However, it is impossible to form an acute angle in the gate portion. Therefore, metallic vapor must be incident upon the substrate after the formation of the cathode. Accordingly, various devices are required, which reduce the yield of products. When resist for image rehearsal, for example, AZ5214, which is the brand name of Hekisuto K.K., is used, it is easily possible to form a bulkhead, the taper angle of which is small. However, it has poor adhesion to the substrate, and further the profile is greatly affected by the exposure and development. Therefore, it is impossible to form a reversely tapered portion while the yield of products is maintained high.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an organic EL element, the structure of which is simple, the manufacturing cost of which is low, and the reliability of which is high. It is another object of the present invention to provide a method of manufacturing the organic EL element. It is still another object of the present invention to optimize an image generation on a display on which the organic EL element is used.
The present invention provides an organic electroluminescence element comprising: a first electrode provided on a substrate; an insulating bulkhead from which a portion of the first electrode is exposed, the insulating bulkhead being formed into a thickness so that the insulating bulkhead can be protruded to the above of the first electrode; an organic thin film formed on the first el
Gyoutoku Akira
Komatsu Takahiro
Matsushita Electric - Industrial Co., Ltd.
Patel Nimeshkumar D.
Pearne & Gordon LLP
Santiago Mariceli
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