Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-06-17
2001-05-01
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S046000, C349S048000, C349S149000, C349S152000, C257S059000, 43
Reexamination Certificate
active
06226059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor substrate, especially, a thin film transistor substrate of, for example a liquid crystal display device of active matrix type using thin film transistors, a liquid crystal display panel and a liquid crystal display device.
2. Description of Related Art
In a liquid crystal display device of active matrix type, non-linear elements (e.g., switching elements) are disposed in a manner to correspond to a plurality of pixel electrodes arranged in matrix, respectively. The liquid crystal in each pixel is always driven, in principle, (at a duty ratio of 1.0). Therefore, in comparison with the so-called “simple matrix type” which employs a time division driving system, the active system has better contrast and has become an indispensable technique particularly in a color liquid crystal display device. A typical example of the switching element is a thin film transistor (TFT).
In a conventional thin film transistor substrate of a liquid crystal display device of active matrix type, pure Al, Al—Pd or Al—Si is used as a material of a scanning signal line and a gate electrode, and an anodized oxide layer of Al is formed on the scanning signal line and gate electrode.
Here, the liquid crystal display device of active matrix type using the thin film transistors is known in JP-A-2-85826 or on pp. 193 to 210 of Nikkei Electronics entitled “Active Matrix Type Color Liquid Crystal Display of 12.5 Type Adopting Redundant Construction” and issued on Dec. 15, 1986 by NIKKEI McGRAW-HILL, for example.
Available as prior arts are U.S. Pat. No. 5,132,820 (Someya et al), U.S. Pat. No. 4,786,148 (Sekimura et al) and JP-A-62-269120. None of them, however, give a description “a scanning signal line and a gate electrode are made of an alloy of Al and an insulating film formed of an anodized oxide film of the scanning signal line or the gate electrode is formed on the surface of at least one of the scanning signal line and the gate electrode”.
U.S. Pat. No. 5,028,122 (Hamada et al) and JP-A-2-106723 (Nagase) resemble the present invention in point of a description “a gate electrode is made of Ta and an insulating film formed of an anodized oxide film of the gate electrode is formed on the surface of the gate electrode” but fail to give a description “an alloy of Al and Ta is used in a gate electrode to provide a higher insulating property of the anodized oxide film than that obtained when Ta is used”. In the present invention one of the features is represented in the description that “a scanning signal line and a gate electrode are made of an Al and Ta alloy and an anodized oxide film of the scanning signal line or the gate electrode is formed on the surface of at least one of the scanning signal line and the gate electrode” to thereby obtain a higher anodized oxide film insulating characteristic than that obtained with Ta, as shown in FIG.
17
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In a thin film transistor substrate using pure Al as a material of a scanning signal line and a gate electrode, a hillock takes place; in a thin film transistor substrate using Al—Pd as a material of a scanning signal line and a gate electrode, a hillock takes place and besides an anodized oxide film has a low breakdown voltage; and in a thin film transistor substrate using Al—Si as a material of a scanning signal line and a gate electrode, a residue is generated after etching. Accordingly, in any of the above thin film transistor substrates, the fabrication yield and reliability are degraded and the production process becomes complicated for the purpose of improving the fabrication yield, thus raising the cost of production.
SUMMARY OF THE INVENTION
The present invention is achieved to solve the aforementioned problems and it is an object of this invention to provide high-fabrication yield and highly reliable thin film transistor substrate, liquid crystal display panel and liquid crystal display device.
To accomplish the above object, according to the present invention, in a thin film transistor substrate in which an anodized oxide film of Al is formed on at least one of a scanning signal line and a gate electrode, Al—Ta or Al—Ti is used as a material of the scanning signal line and the gate electrode. The breakdown voltage of the anodized oxide film is important. As a result of experiments conducted in connection with the breakdown voltage, the present inventor had a knowledge of the fact that when a material which cannot be anodized (for example, Pd or Si) is used as a material to be added to Al, a resulting oxide film has a low breakdown voltage but when a material which can be anodized (for example, Ta or Ti) is added, a resulting oxide film has a remarkably high breakdown voltage. The thickness of the anodized oxide film is set to 1,000 angstroms or more.
In this case, a material containing Cr is used for a gate terminal connected to the scanning signal line.
Al—Ta or Al—Ti is used as a material of the gate terminal connected to the scanning signal line, the side of the gate terminal is covered with an insulating film and the top of the gate terminal is covered with another conductive film.
The additive amount of Ta or Ti in the Al—Ta or Al—Ti is 0.5 to 2.5 at % (atomic percentage; a ratio of the number of added atoms to the number of total atoms in a certain volume).
A different insulating film is formed on the anodized oxide film formed on the gate electrode.
In this case, a silicon nitride film is used as the different insulating film.
Al—Ta or Al—Ti is used as a material of the video signal line.
Amorphous silicon hydride is used as a material of an active layer of the thin film transistor.
The anodized oxide film, a different insulating film and an amorphous silicon hydride film are formed between the scanning signal line and the video signal line.
The anodized oxide film and different insulating film are used as a dielectric film of a latching capacitor.
The anodized oxide film is used as the dielectric film of the latching capacitor.
In a liquid crystal display panel having a thin film transistor substrate in which an anodized oxide film of Al is formed on at least one of a scanning signal line and a gate electrode, Al—Ta or Al—Ti is used as a material of the scanning signal line and gate electrode and the thickness of the anodized oxide film is set to 1,000 angstroms or more.
There are provided a liquid crystal display panel having a thin film transistor substrate in which an anodized oxide film of Al is formed on at least one of a scanning signal line and a gate electrode, Al—Ta or Al—Ti is used as a material of the scanning signal line and gate electrode and the thickness of the anodized oxide film is set to 1,000 angstroms or more, a video signal driving circuit for applying a video signal to the liquid crystal display panel, a scanning circuit for applying a scanning signal to the liquid crystal display panel, and a control circuit for applying information for the liquid crystal display panel to the video signal driving circuit and the scanning circuit.
In the thin film transistor substrate, liquid crystal display panel and liquid crystal display device, no hillock takes place, no residue is generated after etching, the anodized oxide film has a high breakdown voltage, and the production process does not become complicated for the sake of improving the fabrication yield.
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Matsumaru Haruo
Nakatani Mitsuo
Oikawa Saburo
Oritsuki Ryoji
Sasano Akira
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Ngo Julie
Sikes William L.
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