Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2000-12-28
2002-03-19
Lebentritt, Michael (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S059000
Reexamination Certificate
active
06358765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing an organic electroluminescence (EL) display device having organic EL elements, and more particularly to a method for forming a low-resistance conductive layer on one of electrodes of an organic EL element.
2. Description of the Prior Art
An organic electroluminescence (EL) element utilizes a phenomenon in which holes injected from an anode and electrons injected from a cathode are recombined in a light-emission layer having a luminescence capability and light is emitted when they are deactivated from an excited state. These studies are improving the efficiency of light emission by making a light-emission layer be of a multilayer structure and started from paying attention to a high luminescence quantum efficiency and a molecular structure capable of being variously designed of organic compounds, but have only provided too low brightness and efficiency of light emission to put their organic EL elements to practical use.
After that, however, Tang and others found that the performance was remarkably improved by adopting a layered structure combined with a material having an excellent capability for transporting holes (hereinafter referred to as a hole transport layer) instead of a conventional structure having only a light-emission layer interposed between electrodes (Applied Physics Letter, Vol. 51, pp. 913, 1987).
Taking this opportunity, the studies have been concentrated in techniques based on fully separating functions into a layer having a role of injecting holes (a hole injection layer) and a layer having a role of transporting electrons (an electron transport layer) and the like, and the techniques are spurred to be put to practical use as display devices in conjunction with organic materials more improved in performance. In recent years, materials providing emission of the three primary colors, namely, red, green and blue required for a full color display device in high brightness and in high efficiency can be obtained and carrier transport materials suitable for the respective materials are being selected.
A method for driving an organic EL element capable of being used for a unit or pixel of a display device of various kinds of industrial equipment can follow a liquid crystal driving method. That is to say, a passive (matrix) driving method depending on the multiplex performance of elements, an active matrix driving method to arrange and attach a switching element for each pixel, and the like can be mentioned.
However, since an organic EL element has a property which emits light by passing carriers, namely, flowing current inside it, its electric characteristics are particularly more important in comparison with a liquid crystal display device. The reason is described in the following.
FIG. 1
shows a process of luminescence of a general organic EL element. In
FIG. 1
, an anode
1
, a hole injection layer
22
, a hole transport layer
21
, a light-emission layer
20
and an electron transport layer
23
are stacked in order, and holes and electrons injected by an intense electric field from the anode and cathode must hop over several organic functional layers having some potentials before they are recombined.
It is desirable that each organic layer has a band structure partitioned by ideal potentials as shown in
FIG. 1
, but since actually each organic layer includes a film being liable to crystallize or put its structure out of order due to change in temperature, a current leak path is generated and a leak current is taken out to the outside as an abnormal current in the element.
And from the same reason, an abnormal current is generated also when the element is driven by an inverse bias. This means that so long as an electric field is applied to an element, a leak current is generated regardless of whether or not the element emits light, and this becomes a cause to remarkably degrade the quality of the element as a display device.
As a method for suppressing such an abnormal current, Japanese Patent Laid-Open Publication No. Hei 9-102,395 discloses a method of using aluminum as a material for a cathode. However, this method has an insufficient effect on suppression of an abnormal current. And Japanese Patent Laid-Open Publication No. Hei 9-245,965 discloses a technique related to an anode characterized in that its surface roughness is a maximum of 5 nm or less, but this technique reveals a problem of a high cost required for polishing the surface of an anode and a problem of reproducibility.
SUMMARY OF THE INVENTION
As a result of diligent studies in consideration of the above-mentioned problems, an object of the present invention is to find and provide a method for manufacturing an organic EL display device to generate neither abnormal current nor short circuit in an organic EL element of it when a voltage is applied to it.
In order to attain the above object, the present invention provides a method for manufacturing an organic EL display device having an organic EL element having an organic layer which is composed of at least one layer on a substrate and which is interposed between a first electrode provided on said substrate side and a second electrode provided on the other side, said method being characterized by forming a metal layer or a metal oxide layer in a state where the substrate is cooled in an area including at least the second electrode of the organic EL element on the second electrode.
And in the above method for manufacturing an organic EL display device, as the structure of an organic EL element comprising a first electrode, a second electrode and a low-resistance conductive layer of a metal layer or a metal oxide layer, the following structures (
1
) to (
7
) obtained by combining the respective layers can be conceived.
The above organic EL element is characterized by one of the following structures:
(1) first electrode/light-emission layer/second electrode/low-resistance conductive layer;
(2) first electrode/hole transport layer/light-emission layer/second electrode/low-resistance conductive layer;
(3) first electrode/hole injection layer/light-emission layer/second electrode/low-resistance conductive layer;
(4) first electrode/hole injection layer/hole transport layer/light-emission layer/second electrode/low-resistance conductive layer;
(5) first electrode/light-emission layer/electron transport layer/second electrode/low-resistance conductive layer;
(6) first electrode/hole injection layer/light-emission layer/electron transport layer/second electrode/low-resistance conductive layer;
(7) first electrode/hole injection layer/hole transport layer/light-emission layer/electron transport layer/second electrode/low-resistance conductive layer.
The first feature of the present invention described above is in that a process of manufacturing an organic EL display device includes a process of forming as a film an organic EL element at a room temperature of 15 to 30° C. or at a temperature of 1 to 14° C. not higher than the room temperature and additionally a process of forming a low-resistance conductive layer on the surface including the second electrode of the organic EL element as keeping the substrate cooled to a low temperature not higher than the freezing point. It is desirable that the substrate is cooled to a temperature of 0 to −60 ° C.
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Lebentritt Michael
NEC Corporation
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