Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2000-05-01
2003-03-18
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S689000, C428S697000
Reexamination Certificate
active
06534183
ABSTRACT:
TECHNICAL FIELD
The present invention relates to sintered metal oxides of great use as blanks for transparent electroconductive films for display devices and others, to targets of the sintered products for forming transparent electroconductive films, to transparent electroconductive materials, and to transparent electroconductive glass and films formed from the targets.
BACKGROUND ART
Recently, various display devices such as liquid-crystal displays, electroluminescent displays, field emission displays and others have been introduced into office appliances and also control systems in factories. These devices all have a sandwich structure with a display member put between transparent electroconductive films.
For the transparent electroconductive films, much used is indium oxide-tin oxide (hereinafter referred to as ITO) to give ITO films. The ITO films are highly transparent and have low electric resistance, and, in addition, they are well etched and their adhesiveness to substrates is good. As having such good properties, the ITO films are widely used in the art. In general, the ITO films are formed in various methods of sputtering, ion-plating, vapor deposition, etc.
Though having such good properties, however, there still remain some problems to be solved with the ITO films when they are used, for example, as transparent electrodes for liquid-crystal display devices. The problems with the ITO films include their surface accuracy, the tapering processability of electrodes made of them, and their workability into electrodes with junctions or contact points.
Specifically, ITO itself is a crystalline metal oxide, and its crystal grains grow in the step of forming it into films. The growing crystal grains deposit on the surface of the ITO film, thereby lowering the surface accuracy of the film. In the step of etching the ITO film for forming an electrode, the intergranular boundaries in the film are first etched, and the etched surface of the electrode shall be roughened. Therefore, it is difficult to etch the ITO film with accuracy. Further, in the step of tapering the ITO film electrode, the intergranular boundaries in the film are also first etched, and the ITO grains will often remain in the etched area. In that condition, the ITO film electrode could not be well insulated from the counter electrode, thereby often causing display failure.
To solve the problem, a transparent electroconductive material comprising indium oxide and zinc oxide was proposed, for example, in Japanese Patent Laid-Open No. 234565/1994. Its workability into electrodes was improved without its transparency and electroconductivity being not sacrificed. However, the indium oxide-zinc oxide material has a bulk resistance of from 2 to 5 m&OHgr;·cm, and the electric power to be applied thereto for forming it into films is limited. Therefore, the problem with the material is that the productivity in forming it into films is low.
In an organic electroluminescent device having a film electrode of ITO, holes must be transferred from the ITO film a electrode into the light emission layer or into the hole transporting layer. For this, it is desirable that the work function of the electrode material and that of the organic compound for the light emission layer or the hole transporting layer are nearly on the same level and that the energy gap between the anode and the hole transporting layer is as small as possible. To reduce the energy gap, the difference between the work function of the anode material and the ionization potential of the organic compound for the hole transporting layer must be reduced. Various organic compounds have been proposed for hole-transporting substances usable for forming the hole transporting layer. Of those, aromatic amine compounds, especially triphenylamine derivatives have been known to have good capabilities. Triphenylamine, one of triphenylamine derivatives, has an ionization potential of from 5.5 to 5.6 electron volts. On the other hand, for transparent electroconductive films, well known is indium oxide-tin oxide (hereinafter referred to as ITO) having high transparency and low electric resistance. The work function of ITO is 4.6 electron volts. Accordingly, there shall be a relatively large energy gap between the anode and the electron transportation layer both of such ordinary materials.
In that situation, proposed was an organic, light-emitting thin-film device having an organic compound layer between an anode and a cathode, for example, in Japanese Patent Laid-Open No. 63771/1997. In this, the anode is of a thin film of a metal oxide of which the work function is larger than that of ITO. However, the thin-film anode of such a metal oxide has a light transmittance of 10% when the metal oxide is ruthenium oxide, and 20% when it is vanadium oxide. To increase the light transmittance, proposed was a two-layered structure composed of an ITO film and an ultra-thin film of the metal oxide, the ultra-thin film having a thickness of not larger than 300 angstroms. Even in this case, however, the light transmittance of the two-layered structure is still 40 to 60% or so. Therefore, the two-layered structure is still problematic in that its transparency is not satisfactory for transparent electrodes for display devices.
DISCLOSURE OF THE INVENTION
The present invention is to provide sintered metal oxides capable of being formed into films in a stable and efficient manner through sputtering or the like, targets of the sintered products, and transparent electroconductive glass and films formed from the targets. The transparent electroconductive glass and films have good transparency, good electroconductivity and good workability into electrodes, and when they are formed into transparent electrodes and used in organic electroluminescent devices, the difference between their work function and the ionization potential of the hole-transporting substances in the devices is small and therefore the transparent electrodes do not lower the light emission efficiency of the devices.
Having assiduously studied so as to solve the problems noted above, we, the present inventors have found that using sintered products of compounds, which comprise indium oxide, tin oxide and zinc oxide in a specific ratio, as transparent electroconductive materials solves the problems. On the basis of this finding, we have completed the present invention.
Specifically, the invention includes first to fourth aspects, which are summarized as follows:
[I] First Aspect of the Invention
[1] A sintered product that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and contains a hexagonal layer compound of In
2
O
3
.(ZnO)m with m indicating an integer of from 2 to 20, and a spinel-structured compound of Zn
2
SnO
4
.
[2] The sintered product of above [1], which has a specific resistance of smaller than 2 m&OHgr;·cm.
[3] A sintered product that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of an oxide of a positive tetra-valent or higher poly-valent metal, and contains a hexagonal layer compound of In
2
O
3
.(ZnO)m with m indicating an integer of from 2 to 20, and a spinel-structured compound of Zn
2
SnO
4
.
[4] The sintered product of above [3], in which the oxide of a positive tetra-valent or higher poly-valent metal is ruthenium oxide, molybdenum oxide or vanadium oxide.
[5] A sputtering target for transparent electroconductive films, which comprises the sintered product of any of above [1] to [4].
[6] An electron-beaming target for transparent electroconductiv
Idemitsu Kosan Co. Ltd.
Jones Deborah
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sperty Arden
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