Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-03-29
2004-09-07
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S503000, C313S505000, C313S506000, C313S498000, C428S037000, C428S038000, C428S042100, C428S047000, C428S066500
Reexamination Certificate
active
06787989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a substrate with a transparent conductive film and an organic electroluminescence (hereinafter referred to as “EL”) device using the same, and more particularly to a substrate with a transparent conductive film, which is used as an electrode (anode) of an EL display device, and an organic EL device having an organic multilayer film laminated on a surface of the transparent conductive film.
2. Prior Art
The organic EL device is a display device which has an organic multilayer film comprised of a hole transport layer, a light-emitting layer, and an electron transport layer, interposed between an anode and a cathode, for carrying out an electric charge injection/recombination-based light-emitting operation. Recently, the organic EL device has been actively researched and developed in view of its advantageous features as a display device, i.e. a lower driving voltage and a wide range of possible luminescent colors which can be realized due to the variety of organic materials available therefor.
In an organic EL device of this kind, holes injected from the anode and electrons injected from the cathode travel through the hole transport layer and the electron transport layer to the light-emitting layer where the holes and the electrons are recombined to perform a light-emitting operation. As the cathode, a metal material, such as aluminum (AL) is employed, and as the anode, indium tin oxide (hereinafter referred to as “ITO”) is employed, which has an excellent transparency and a low electrical resistance.
In the organic EL device of the above-mentioned kind, when holes are injected from the anode into the light-emitting layer, the holes move from the anode to the hole transport layer across an energy barrier between the anode and the hole transport layer. The work function of an ordinary ITO film, however, is by far smaller than the ionization potential Ip of the hole transport layer (the ionization potential Ip of the hole transport layer is normally 5.5 to 5.6 eV whereas the work function of the surface of the ITO film formed by a sputtering method is 4.2 to 4.7 eV), so that the balance of injection into the light-emitting layer between injected holes and injected electrons is lost, resulting an increase in the driving voltage. Therefore, to attain a reduced driving voltage, it is necessary to enhance the efficiency of injection of holes into the hole transport layer, and to this end, the energy barrier between the anode and the hole transport layer is required to be minimized.
Further, in the organic EL device, if the transparent conductive film as the anode has a large surface roughness (difference in height between protruding portions and recessed portions), a high electric field can be concentratedly applied to protruding portions of the surface. This causes a slight electric discharge to occur at the protruding portions, and therefore makes the device prone to a breakdown to form dark points from which light is no longer emitted. In short, the durability of the organic EL device is degraded. Therefore, the transparent conductive film is required to have a minimized surface roughness, i.e. an excellent smoothness.
To meet the above requirements, there has been proposed a technique by Japanese Laid-Open Patent Publication (Kokai) No. 8-167479 (hereinafter referred to as “the first prior art”), which carries out annealing on an ITO film formed as a transparent conductive film to obtain a smooth surface on the ITO film, and then subjects the resulting surface to further annealing or plasma processing, thereby increasing the work function of the ITO film to reduce the energy barrier between the anode and the hole transport layer.
More specifically, in the first prior art, after depositing amorphous particles formed of ITO onto the substrate, annealing is carried out within a temperature range of 100 to 500° C. under a non-oxidizing atmosphere, thereby causing crystal growth of the particles such that the ITO film has a surface roughness of 10 nm or less. Further, annealing is effected on the surface within a temperature range of 100 to 500° C. under an oxidizing atmosphere or a plasma is irradiated onto the surface, to make the work function of the surface of the ITO film larger than that of an ordinary ITO film, whereby the energy barrier between the anode and the hole transport layer of the ITO film is reduced.
In the first prior art, however, although the work function of the ITO film can be increased and the surface roughness can be reduced to a level of 10 nm or less to obtain a good smoothness, the film exhibits a high specific resistance of 2×10
−4
&OHgr;·cm or higher, since the ITO film is formed by the sputtering method.
More specifically, differently from a voltage driven device, such as a crystal display device, the organic EL device, which is a current driven device, is susceptible resistance in power consumption and display quality to the wiring. To avoid this, it is necessary to reduce the resistance of the transparent conductive film (ITO film) as the anode, and to this end, it is required to minimize the specific resistance of the ITO film. However, the ITO film according to the above first prior art, which is formed by the conventional sputtering method, has a high specific resistance, which not only causes a large power loss of an organic EL device using the ITO film owing to a high wiring resistance, resulting in an increase in the power consumption, but also degrades display quality, which makes the ITO film difficult to be applied to today's EL devices of which capability of displaying high-precision images is demanded.
Further, the above first prior art is disadvantageous in that the film manufacturing process is complicated since a post treatment, such as annealing, is required.
As another conventional technique, there has been proposed a method of adding a metal oxide having a high work function, such as ruthenium oxide, molybdenum oxide or vanadium oxide, to ITO (Japanese Laid-Open Patent Publication (Kokai) No. 2000-72526; hereinafter referred to as “the second prior art”).
The second prior art adds the above-mentioned metal oxide which has a higher work function than that of the ordinary ITO, to ITO to thereby increase the work function of the surface of an ITO film as a transparent conductive film. This enables reduction of the energy barrier between the anode and the hole transport layer.
The second prior art, however, has the disadvantage of increased manufacturing costs due to the use of a special and expensive metal oxide, such as ruthenium oxide or molybdenum oxide, which is added to the ITO. Moreover, similarly to the first prior art, the second prior art employs the sputtering method in forming the ITO film, which therefore only has a specific resistance of 7×10
−4
&OHgr;·cm or higher. Similarly to the first prior art, this results in increased power consumption and degraded display quality. This makes the ITO film produced by the second prior art difficult to be put to practical use in a high-precision EL display device.
Still another conventional technique has also been proposed which forms an ITO film into a bilayer structure, whereby one ITO film at an interface side in contact with a hole transport layer has an increased work function (Japanese Laid-Open Patent Publication (Kokai) No. 2000-68073; hereinafter referred to as “the third prior art”).
The third prior art attempts to obtain an improved hole injection characteristic, by changing the oxygen partial pressure during a film forming process for forming an ITO film by the sputtering method, so that the ionization potential Ip, i.e. the work function of the interface portion of the ITO film is made closer to the ionization potential Ip of the hole transport layer.
More specifically, the third prior art changes the oxygen partial pressure during the film forming process, thereby forming an ITO film having a bilayer structure comprised of two layers having respective different ioni
Kato Yukihiro
Wada Shunji
Nippon Sheet Glass Co. Ltd.
Patel Vip
Rossi & Associates
Roy Sikha
LandOfFree
Substrate with transparent conductive film and organic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Substrate with transparent conductive film and organic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Substrate with transparent conductive film and organic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3232215