Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Reexamination Certificate
1998-09-15
2003-12-16
King, Roy (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
C205S124000, C205S234000, C205S322000
Reexamination Certificate
active
06663760
ABSTRACT:
TECHNICAL FIELD
This invention relates to a non-aqueous electrolyte for fabricating a two-terminal nonlinear element that is used as a switching element, a method of fabricating a two-terminal nonlinear element by using this non-aqueous electrolyte, a two-terminal nonlinear element obtained by this fabrication method, and a liquid crystal display panel using that element.
BACKGROUND ART
In an active matrix type of liquid crystal display device, a liquid crystal fills a space between an active matrix substrate, which is formed as a matrix array with a switching element provided for each pixel region, and a facing substrate provided with a color filter or the like. Predetermined image information can be displayed by controlling the alignment of the liquid crystal in each pixel region. In general, a three-terminal element such as a thin-film transistor (TFT) or a two-terminal element such as a metal-insulator-metal (MIM) type of nonlinear element (hereinafter called a “MIM element”) is used as each of these switching elements. A switching element using a two-terminal element is considered to be better than a three-terminal element in that there is no cross-over shorting and the fabrication thereof can be simplified.
To implement a liquid crystal display panel with a high image quality that has good contrast, and also no discernible display unevenness, after-image, or image persistence within a liquid crystal display device using MIM elements, it is important to ensure that the characteristics of the MIM elements satisfy the following conditions:
(1) The capacitance of each MIM element must be sufficiently smaller than the capacitance of the liquid crystal display panel,
(2) Changes with time in the voltage-current characteristic of the MIM element must be sufficiently small,
(3) The symmetry of the voltage-current characteristic of the MIM element must be good,
(4) The steepness of the voltage-current characteristic of the MIM element must be sufficiently high, and
(5) The resistance of the MIM element must be sufficiently uniform over a wide area.
In other words, to increase the contrast, it is necessary to make the capacitance of the MIM component sufficiently small with respect to the capacitance of the liquid crystal display panel, and also ensure that the steepness of the voltage-current characteristic of the MIM component is sufficiently large. To ensure there is no discernible display unevenness, it is necessary to make the resistance of the MIM component sufficiently uniform over a wide area. To ensure there is no discernible after-image, it is necessary to make sure that the changes with time in the voltage-current characteristic of the MIM element are sufficiently small. Furthermore, to ensure there is no discernible image sticking, it is necessary to make sure that the changes with time in the voltage-current characteristic of the MIM element are sufficiently small, and also that the symmetry of the voltage-current characteristic of the MIM element is good.
In this case, “after-image” is a phenomenon that occurs when another image is displayed after a certain image has been displayed for several minutes, in which case the previous image can still be discerned. Similarly, “image sticking” is a phenomenon that occurs when another image is displayed after a certain image has been displayed for several hours, in which case the previous image can still be discerned. The phrase “the symmetry of the voltage-current characteristic is good” means that, when a current flows from the first conductive film to the second conductive film under a certain voltage and when a current flows from the second conductive film to the first conductive film, the difference in absolute values of these currents is sufficiently small.
Examples of documents that disclose techniques for MIM elements are listed below.
(a) Japanese Patent Application Laid-Open No. 52-149090 discloses an MIM element that is fabricated from a first conductive film of tantalum, an insulated film that is a metal oxide film formed by anodic oxidation of this first conductive film, and a second conductive film of chromium formed on a surface of this insulated film. The insulated film is formed to a uniform thickness without pinholes, by forming it by anodic oxidation of the surface of the first conductive film. Japanese Patent Application Laid-Open No. 57-122478 disclosed the use of a dilute aqueous solution of citric acid as the electrolyte for anodic oxidation.
These techniques do not necessarily ensure sufficient quality for the above characteristics (2) to (5) of the resultant MIM element. In other words, they are unsatisfactory from the viewpoints of changes with time, symmetry, and steepness of the voltage-current characteristic, and also the resistance of the element is not sufficiently uniform over a wide area. This means that it would be difficult to ensure a high level of contrast over a wide temperature range in a liquid crystal display device using such MIM elements, and there will be problems such as a tendency towards unevenness in the display.
(b) The international application PCT/JP94/00204 (International Publication No. WO94/18600) discloses a configuration in which is used a film of an alloy of tantalum to which tungsten is added, as the first conductive film of the MIM element.
Since the first conductive film of the MIM element produced by this technique is a film of an alloy comprising tantalum and a specific element such as tungsten, instead of tantalum alone, this provides an improvement over the techniques disclosed in the documents of (a) with respect to characteristics (2) and (3), in other words, the changes with time and the symmetry of the voltage-current characteristic of the MIM element, so it is capable of improving quality to a level at which after-images cannot be discerned, and also of maintaining a good contrast over a wide temperature range. However, this technique has a problem concerning insufficient margin in the contrast characteristics required of such an element at high temperatures.
(c) Jpn. J. Appl. Phys, 31,4582 (1992) discloses the use of a dilute aqueous solution of phosphoric acid or ammonium borate as the electrolyte for the anodic oxidation used for forming the insulated film of an MIM element.
This technique provides an improvement over the techniques disclosed in the documents of (a) with respect to characteristics (2) and (3), in other words, the changes with time and the symmetry of the voltage-current characteristic of the MIM element, so it is capable of improving quality to a level at which after-images cannot be discerned, and also of maintaining a good contrast over a wide temperature range. However, this also has problems in that the reliability of the resultant elements is low, they are likely to be destroyed by short-circuiting, and display unevenness easily occurs.
(d) Japanese Patent Application Laid-Open No. 2-93433 discloses a configuration in which a film of an alloy of tantalum and silicon is used as the first conductive film of the MIM element.
This technique made it possible to improve the steepness of the voltage-current characteristic in comparison with the techniques of the documents of (a), and also provide sufficient margin over a wide temperature range to ensure a high contrast. However, this technique also has problems in that the reliability of the element is low and thus it can easily be destroyed, and display unevenness can easily occur.
DISCLOSURE OF THE INVENTION
An objective of this invention is to provide a two-terminal nonlinear element that satisfies all the characteristics (1) to (5) required of the above described MIM element, particularly a capacitance that is sufficiently small, a voltage-current characteristic with a sufficiently large steepness, and a resistance that is sufficiently uniform over a wide area; and also a liquid crystal display panel that uses this two-terminal nonlinear element and has a high image quality with a good contrast and no display unevenness.
Another objective of this invention is to provide a non-aqueous e
Inoue Takashi
Mizutani Fumikazu
Seki Takumi
Takeuchi Sachie
Ue Makoto
King Roy
Leader William T.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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