Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-05-06
2003-11-25
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
Reexamination Certificate
active
06653780
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a luminescent display device including a transparent substrate, particularly formed of resin substrate, and a transparent electrode, an auxiliary electrode and a luminescent layer which are laminated on the substrate and also relates to a method of manufacturing such a luminescent display device.
In general, there is known an organic EL (electro-luminescent or electroluminescent) display element, which is composed of a transparent electrode in shape of stripe laminated on a transparent substrate formed of, for example, glass, a luminescent layer made of an organic compound and laminated on the transparent electrode, and a metal electrode in shape of stripe laminated on the luminescent layer so as to be perpendicular to the transparent electrode. The transparent electrode is formed as an anode and the metal electrode is formed as a cathode, and when direct current (DC) field is applied between the transparent electrode and the metal electrode, the current passes through the organic compound and, hence, the luminescent layer is emitted. The light emitted from the luminescent layer is taken out from the transparent electrode side.
A resin substrate is used in place of the glass substrate for the purpose of making the thickness of the organic EL display device thin. The use of the resin substrate can make the thickness of the substrate itself thin and hardly cracked. And an organic EL display device utilizing the resin substrate can be bent, thus being advantageous.
However, in the case of using the resin substrate, it is necessary to form a moisture-proof layer on the resin substrate because the luminescent layer formed of an organic compound is weak to moisture (water content) and the water content passes through the resin substrate.
Further, electric current passes through the organic compound laminated on the resin substrate, and when the current passes, it becomes necessary to pay attention to a resistance of the transparent electrode. That is, the metal electrode has a low resistance and, on the other hand, the transparent electrode made of an oxide has a resistance higher than that of the metal electrode. Accordingly, the resistance of the transparent electrode becomes significant as the current passes the organic compound.
When the resistance increases, there may cause a case that the adequate field is not applied to the organic compound as being apart from a connection portion to a circuit, which results in an uneven luminescence between a plurality of organic compounds, thus being inconvenient and defective. In order to solve such defect, there is provided a technology for disposing an auxiliary electrode. That is, a metal auxiliary electrode is disposed on the side of the transparent electrode so as to be conductive thereto to reduce wiring resistance on an anode side.
FIG. 6
represents steps for preparing an organic EL element on a resin substrate as a substrate. That is, a resin substrate
1
is prepared and a moisture-proof
5
is laminated on one surface of the resin substrate
1
(step S
1
). A transparent electrode
2
as anode is formed, in form of film, on the moisture-proof layer
5
(step S
2
), and the thus laminated transparent electrode
2
is then subjected to a patterning treatment or process (step S
3
). Next, a metal thin film is formed as an auxiliary electrode
3
on the transparent electrode
3
(step S
4
). This metal thin film is thereafter subjected to the patterning treatment (step S
5
).
It will easily be assumed that the formation of the auxiliary electrode is needed at a time of manufacturing a luminescent display device using the resin substrate. The following problem or defect will be caused, however, at the time of forming the metal thin film on the resin substrate
1
as the auxiliary electrode
3
.
That is, since the resin substrate
1
is softer in material than the glass substrate (i.e. smaller Young's module), the resin substrate
1
was largely bowed, as shown in step S
4
in
FIG. 6
, at the time of forming the metal thin film, which adversely influences a subsequent processes or steps including the patterning treatment of the metal thin film.
Furthermore, when the metal thin film is formed on the resin substrate
1
, there may cause a case that crack
9
is formed to the moisture-proof layer
5
or the layer of the transparent electrode
2
, which may then be damaged of broken. In the case of breaking the moisture-proof layer
5
, harmful water content will intrude into the luminescent layer, and hence, it may become difficult to preserve the luminescent layer in good state.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a luminescent display device in which, at a time of forming an auxiliary electrode on a resin substrate, a warpage or bowing of the resin substrate can be prevented and the moisture-proof layer and/or transparent electrode is free from being damaged, and also provide a method of manufacturing such luminescent display device.
In order to achieve the above and other objects, the inventors viewed a point that inner stress always remains in a thin film formed on the resin substrate through vacuum evaporation, spattering, epitaxial growth or like process or treatment, and the warpage of the resin substrate and/or damage of the moisture-proof layer is resulted from the remaining inner stress. The inner stress &sgr;(dyn/cm
2
) in the metal film is a force, per unit sectional area, which is applied from one side of the sectional area to the other side thereof. The inventors also found that the above defect or damage at the time of forming the auxiliary electrode on the resin substrate could be solved by reducing the total stress S=&sgr;×d(dyn/cm) (&sgr;: inner stress; d: film thickness) to a predetermined value.
Taking the above matters into consideration, inventors of the subject application achieved the above and other objects according to the present invention by providing, in one aspect, a luminescent display device comprising a resin substrate having one and another surfaces, and a transparent electrode, a metal auxiliary electrode disposed to be conductive to the transparent electrode and a luminescent layer composed of an organic compound, the transparent electrode, the auxiliary electrode and the luminescent layer being laminated in form of layers on the one surface of the resin substrate,
wherein the auxiliary electrode has a total stress of {(inner stress)×(film thickness thereof)} of not more than 1.3×10
5
dyn/cm.
Hereunder, the reason why the total stress of the auxiliary electrode was decided to be not more than 1.3×10
5
dyn/cm in the above aspect of the present invention will be explained.
The relationship between the inner stress &sgr; of the auxiliary electrode and a radius of curvature r of the warpage of the resin substrate is expressed by the following equation (1) in view of balancing between a force and moment of a minute (fine) portion of the substrate:
r=E·b
2
/{6(1−&ngr;)
d·&sgr;}
&sgr;=
E·b
2
/{6(1−&ngr;)
d·r}
(1)
(r: radius of curvature of warpage of substrate; E: Young's modulus of substrate; b: thickness of substrate; &ngr;: Poisson's ratio of substrate; d: film thickness of auxiliary electrode; &sgr;: stress of auxiliary electrode)
In the case of the resin substrate, though being different in materials which form the substrates, approximately, Young's modulus=10000 to 20000 kgf/cm
2
and Poisson's ratio=0.4 to 0.5. The inventors of the subject application evaluated warpage amount and cracks of barrier layer (moisture-proof layer) at a time of forming chromium films of the thicknesses described in the following Table 1 by using a usual resin substrate having a thickness of 0.2 mm and length of 100 mm.
TABLE 1
Evaluation of
Film Thickness
Crack to Barrier
Total Stres
Miyadera Toshiyuki
Miyaguchi Satoshi
Nagayama Kenichi
Sugimoto Akira
Yoshida Ayako
Patel Vip
Pioneer Corporation
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