Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-10-22
2002-01-15
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S504000, C313S500000, C313S505000, C313S506000, C445S024000
Reexamination Certificate
active
06339288
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a substrate for an organic electroluminescence display element, which is a light emission type display for a domestic television receiver and a terminal display device for a high information processing, a method of manufacturing the same, and an organic electroluminescence display element.
In the following description, the “electro-luminescence” element is often referred to as “EL” element.
BACKGROUND ART
An organic EL display element, which is one of flat panel type display devices, is constructed basically such that an organic EL medium layer is sandwiched between a first electrode (anode or cathode) and a second electrode (cathode or anode). Light is emitted by allowing an electric current to flow between the two electrodes. The organic EL display element is of a self-light emission type and, thus, exhibits a high brightness and a wide viewing angle. In addition, the display element can be driven under a low voltage. In general, each of the first and second electrodes consists of a plurality of electrode lines that are arranged such that the first electrode lines and the second electrode lines cross each other to form a matrix structure. That portion of the organic EL medium layer which is positioned at the intersection between the first electrode line and the second electrode line constitutes a pixel.
In order to manufacture a large capacity and high precision organic EL display element having a matrix electrode structure, a very fine patterning treatment must be applied to the electrode line.
In general, a photolithography method or a masked vapor deposition method is known as a method for forming a fine pattern of a thin film.
However, if the second electrode layer is patterned by the photolithography method, the solvent of the photoresist or the developing solution permeates into the underlying layer of the organic EL medium layer so as to bring about rupture or deterioration of the element.
On the other hand, in the case of the masked vapor deposition method, it is important to pay attentions to the bonding strength between the vapor deposition mask and the substrate. If the bonding strength is unsatisfactory, the evaporated material is partly deposited on the back side of the vapor deposition mask pattern so as to lower the resolution. If the vapor deposition mask is forcedly bonded to the substrate in an attempt to avoid the difficulty noted above, the organic EL medium layer itself is scratched.
A method for finely patterning the second electrode line without imparting damage to the organic EL medium layer is disclosed in Japanese Patent Disclosure (Kokai) No. 5-258859 and Japanese Patent Disclosure No. 5-258860. Specifically, disclosed is a technology of oblique vapor deposition of an organic EL medium and a metal using a plurality of partition walls. In this method, a plurality of partition walls are formed to cross the anode pattern, followed by obliquely applying vapor deposition for forming the organic EL medium layer and the cathode in the order mentioned. In this method, lamination and patterning of the organic EL medium and the cathode material are carried out simultaneously. In this method, however, it is difficult to carry out the vapor deposition while rotating the substrate and to control uniformly the directions of the vapor deposition beams over a large area. In addition, the anode pattern is limited to a linear pattern.
An improvement of the partition wall oblique or slant vapor deposition method outlined above is disclosed in Japanese Patent Disclosure No. 8-315981 and Japanese Patent Disclosure No. 9-102393. In the method disclosed in these prior arts, used is a partition wall having an overhanging structure (inversely tapered partition wall or a partition wall having a T-shaped cross section). The particular partition wall is mounted to the substrate having a first electrode line formed thereon. These conventional partition wall methods make it possible in principle to carry out the vapor deposition and patterning of the organic EL medium and the second electrode line simultaneously by utilizing the presence of the partition wall. It should be noted that, since the partition wall has an overhanging structure, the patterning can be performed by the vapor deposition in a direction perpendicular to the substrate, with the result that the vapor deposition can be performed while rotating the substrate.
However, in the case of using an inversely tapered partition wall, it is possible for the incident angle of the vapor deposition beam to be smaller than the tapered angle. In this case, deposition takes place also on the side wall of the partition wall, leading to possibility of short-circuiting between the two electrodes. It follows that the method using an inversely tapered partition wall is not adapted for the vapor deposition on a substrate having a large area. On the other hand, complex steps are required for forming a partition wall having a T-shaped cross section. Further, since there is a clearance between the partition wall and the organic EL medium layer, a difficulty is brought about if vapor deposition of the organic EL medium and the second electrode material are carried out by using the partition wall. Specifically, the second electrode material is also deposited on the region where the organic EL medium layer is not present. As a result, the second electrode is brought into direct contact with the first electrode, leading to short-circuiting that impairs the normal operation of the device. Even if the second electrode material is selectively deposited on the organic EL medium so as to prevent the short-circuiting, electric field is concentrated in the vicinity of the end portion of the second electrode in which the organic EL medium is laminated thin or in the edge portion of the second electrode line so as to bring about deterioration caused by insulation breakdown or Joule heat. For preventing these problems, it is proposed to form an electric insulating layer in the base portion of the partition wall. However, formation of the insulating layer makes the manufacturing process complex. Further, since the edge portion of the organic EL medium layer/second electrode line is exposed to the outside, deterioration tends to take place from the edge portion. In addition, since a clearance is provided between the partition wall and the organic EL medium layer/second electrode line, or since light is transmitted through the partition wall, the light coming from the back surface of the substrate runs through the clearance or the partition wall to reach the display surface so as to inhibit the display.
A second problem relating to the organic EL display element is that the resistance of the anode line is increased as the anode line is made finer. If the resistance of the anode line is increased, the voltage drop caused by the resistance of the anode line is increased in the case where a current required for obtaining a sufficient brightness is allowed to flow through the anode line. As a result, a high driving voltage is required. Even in the voltage driving type device such as a liquid crystal display device or an AC type inorganic EL display element, it is necessary to decrease the resistance of the electrode line including a transparent conductor film in order to make the display characteristics uniform over the entire display panel. When it comes to a current driving type element such as a organic EL display element, it is more necessary to decrease the resistance.
Various techniques for decreasing the resistance of the anode line are disclosed in, for example, Japanese Patent Disclosure No. 10-106751 and Japanese Patent Disclosure No. 9-230318. Specifically, Japanese Patent Disclosure No. 10-106751 teaches that conductive metal lines are formed in contact with both side surfaces of a transparent electrode line so as to decrease the resistance of the anode line. In this case, however, the height of the conductive metal line is limited by the height of the transparent electrode line, making it diff
Ishizaki Mamoru
Ito Yuichi
Itoi Takeshi
Kai Teruhiko
Minato Takao
Burns Doane , Swecker, Mathis LLP
Patel Nimeshkumar D.
Santiago Mariceli
Toppan Printing Co. Ltd.
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