Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Patent
1994-10-04
1999-01-19
Saadat, Mahshid D.
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
257761, 257764, H01L 2348, H01L 2352, H01L 2940
Patent
active
058616721
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a nonlinear resistance element (in particular, to an MIM element) that is suitable for use as a pixel-switching element of a liquid crystal display device of a laptop computer, engineering workstation (EWS), or liquid crystal TV, and a method of manufacturing such a nonlinear resistance element.
BACKGROUND ART
Recently, there have been many attempts to replace the prior art CRTs used in laptop computers, EWSs, mini-TVs and the like with liquid crystal display devices, to reduce the dimensions, weight, and power consumptions of such equipment.
Various types of element are used as pixel-switching elements in these liquid crystal display devices, such as a three-terminal thin film transistor (TFT) using polysilicon or amorphous silicon, or a two-terminal nonlinear resistance element of a metal-insulator-metal (MIM) structure. Since the manufacture of TFT and other similar three-terminal elements necessitates the repeated formation of thin films on the structure, these manufacturing processes are complicated and, for reasons such as the presence of intersections between signal lines on the substrate, element defects can easily occur, causing the problem of deteriorated yield. In contrast, a two-terminal element such as an MIM element has a simpler manufacturing process than a three-terminal element, so that yield is increased, and, since there are no intersections between signal lines, it is attracting attention because it can be made less expensively with a larger area, and so it is currently being improved on and developed.
An MIM element has a structure of two electrically conductive thin films sandwiching an insulator thin film, and the voltage-current characteristic between the electrically conductive thin films is nonlinear. A typical MIM element has a tantalum(Ta)--tantalum oxide(Ta.sub.2 O.sub.5)--chromium(Cr) structure and is usually manufactured by the method described below. First, after a thin Ta film has been formed by sputtering on a glass substrate, it is etched to leave timing signal lines and MIM element portions. Next, a Ta.sub.2 O.sub.5 insulating layer is formed on the surface of the thin Ta film by an anodization method. Anodization is a favorable method in forming an insulating layer that is finer than sputtering or chemical vapor deposition (CVD), with few pinholes. Next, a Cr thin film is formed by sputtering and is then patterned, and then an electrode pattern for driving the liquid crystal is formed of a transparent conductive film of indium tin oxide (ITO).
In order to achieve a high level of image quality in a liquid crystal panel that uses this type of MIM element, it is generally important to ensure that the following characteristics are satisfied: liquid crystal, degree of nonlinearity, such that the ratio of the ON current to the OFF current is sufficiently large, and voltage-current characteristic of the element must be symmetrical.
One technique used to simplify the manufacturing process is disclosed in, for example, Japanese Patent Application Laid-Open No. 57-122476. In this technique, a transparent conductive film formed of ITO is used as an upper electrode. Forming the upper electrode of a transparent conductive film in this manner ensures that the upper electrode can be formed at the same time as a transparent electrode layer of a pixel electrode, thus the steps of forming and etching the upper electrode film can be omitted, enabling a further decrease in the number of steps. However, the positive voltage side and negative voltage side of the voltage-current characteristic of an MIM element that has an upper electrode formed of ITO differ greatly, and thus it is difficult to obtain a good current characteristic. This asymmetry of the voltage-current characteristic due to positive and negative applied voltages is a cause of flicker in the screen of the liquid crystal display device and also deterioration of the liquid crystal material.
Various techniques have been proposed in order to adapt an MIM element that use
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Katsumi AOTA, "Full-Color LCD Using MIM Diodes with Two-Mask Process" SID 91 Digest, pp. 219-222, 1991.
Inami Takashi
Inoue Takashi
Takahara Kenichi
Saadat Mahshid D.
Seiko Epson Corporation
Wilson Allan R.
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