Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing... – Defect correction or compensation
Reexamination Certificate
2003-04-22
2004-06-08
Vo, Tuyet T. (Department: 2821)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
Defect correction or compensation
C349S039000, C313S504000, C313S503000
Reexamination Certificate
active
06747728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a luminescent display in which an organic electroluminescent (organic EL) element is preferably used as a luminescent element, and also to a method of producing it.
2. Description of the Related Art
Conventionally, an organic EL element is known which is enabled to luminesce by causing a current to flow through a phosphor member formed on a glass plate or a translucent organic film.
FIG. 4
diagrammatically shows a sectional structure of a luminescent display in which an organic EL element is used as a luminescent element. As shown in
FIG. 4
, the luminescent display of the conventional art is configured by sequentially stacking a transparent electrode (layer)
302
, an organic layer
303
, and a metal electrode (layer)
304
on a transparent substrate
301
.
Usually, an organic EL element is seemed to be a capacitive luminescent element which is equivalently expressed by a circuit resistance component, a capacitance component, and a luminescence component. When a voltage is applied across the transparent electrode
302
and the metal electrode
304
, therefore, charges corresponding to the electric capacitance of the element flow into the electrodes as a displacement current to be accumulated therein. When the voltage exceeds a fixed level (barrier voltage), a current flows into the organic layer
303
configured by an organic EL element, via the electrodes
302
and
304
, and luminescence is started in proportion to the current.
FIG. 5
shows an example of an arrangement of transparent electrodes and metal electrodes in a luminescent display of simple matrix driving.
As shown in
FIG. 5
, a luminescent display in which the above-mentioned organic EL element is used as a luminescent element is formed by, on a transparent glass substrate
101
, sequentially stacking: plural parallel stripe-like transparent electrodes
102
which are made of ITO or the like and arranged at predetermined intervals; a luminescent portion
103
configured by an organic layer; and plural parallel stripe-like metal electrodes
104
which are perpendicular to the transparent electrodes
102
and arranged at predetermined intervals. In order to attain moisture proofing, a protective film which is not shown is formed over the whole face of the substrate
101
on which the metal electrodes
104
and the organic layer
103
are formed.
In the luminescent display, formed are luminescent pixels each configured by setting, as one unit, one of regions of the organic layer
103
where paired ones of the transparent electrodes
102
and the metal electrodes
104
intersect and face each other with interposing the respective regions. A required number of the pixels are arranged into a matrix form, thereby forming a luminescent display of simple matrix driving.
In the thus formed luminescent display, a driving source which scan-drives the transparent electrodes
102
and the metal electrodes
104
adequately applies a voltage across the transparent electrode
102
and the metal electrode
104
that correspond to an appropriate pixel, and a current flows through the organic layer
103
of the corresponding pixel, so that light is emitted.
In production of such a luminescent display, the possibility of occurrence of a damage or deposition of particles is higher as the area of the display screen is larger. This is a great factor of a reduced yield in the production.
When a flaw
10
is produced in the transparent electrode
302
or a particle
20
is deposited onto the transparent electrode
302
as shown in
FIG. 4
, the organic layer
303
is insufficiently grown in the corresponding portion of the surface of the transparent electrode
302
. A defect
30
may be caused in the organic layer
303
by any reason.
As a result, in the part where the organic layer
303
is insufficiently grown, the metal electrode layer
304
may be directly grown on the transparent electrode layer
302
, so that the transparent electrode layer
302
serving as an anode may be short-circuited with the metal electrode layer
304
serving as a cathode.
Even when such a defect does not result in a short circuit, the organic layer
303
between the transparent electrode
302
and the metal electrode
304
is grown so as to be very thin, and the current for luminescence is concentrated into the thinned part. As a result, the current hardly flows through the peripheral region of the part, thereby producing a problem in that the pixel fails to luminesce. This problem is the greatest factor of a failure in production, and largely lowers the production yield.
Therefore, a countermeasure such as that a substrate is elaborately washed has been taken. However, such washing requires much labor. Furthermore, it is impossible to completely eliminate particles or flaws in the transparent electrode
302
, or irregularity of the surface of the transparent electrode
302
by washing.
As described above, in a luminescent display in which an organic EL element is used as a luminescent element, when a concave flaw exists or dust is deposited onto the transparent electrode
302
, the film growth is insufficiently performed in the part, and the organic layer
303
which is stacked on the transparent electrode
302
is formed so as to be thin. In the case where the film growth is performed by vapor deposition, particularly, when a convex part is formed by dust or the like, vapor deposition is hardly performed on side faces of the convex part, and hence the film growth is insufficiently performed.
In the thinned part of the organic layer
303
, the distance between the cathode and the anode is shorter than that in another part, and therefore the current is easily concentrated to cause a problem in that the cathode and the anode are short-circuited. Even when such a defect does not result in a short circuit, the current for luminescence is concentrated into the thinned part of the grown film. As a result, the current hardly flows through the peripheral region of the part, thereby producing a problem in that the pixel fails to luminesce.
SUMMARY OF THE INVENTION
The invention has been conducted in view of the above-discussed problems. It is an object of the invention to provide a luminescent display in which a defect due to a short circuit between a transparent electrode and a metal electrode is repaired and the yield can be improved, and also a method of producing such a luminescent display.
According to a first aspect of the invention, in a luminescent display in which a first electrode, a luminescent portion, and a second electrode are sequentially stacked on a substrate, when a part of the luminescent portion is defective, only a part of the second electrode and corresponding to the defective part is removed away, a remaining part of the second electrode is left, and the defective luminescent pixel is enabled to luminesce by the first electrode and the remaining part of the second electrode.
According to a second aspect of the invention, in luminescent display in which plural first electrodes that are arranged at predetermined intervals, a luminescent portion, and plural second electrodes that are perpendicular to the first electrodes, and that are arranged at predetermined intervals are sequentially stacked on a substrate, a luminescent pixel is formed by using, as a unit, a region where one of the first electrodes and one of the second electrodes face and intersect with each other with interposing the region, and a predetermined number of such luminescent pixels are arranged in a matrix form, when an arbitrary one of the luminescent pixels which are arranged in a matrix form is defective, only a part of the second electrode and corresponding to the defective luminescent pixel is removed away, a remaining part of the second electrode is left, and the defective luminescent pixel is enabled to luminesce by the first electrode and the remaining part of the second electrode.
According to a third aspect of the invention, in the luminescent display of the second aspect of the
Tohoku Pioneer Corporation
Vo Tuyet T.
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