Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2002-04-04
2004-12-14
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S051000, C349S052000
Reexamination Certificate
active
06831728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of manufacturing a nonlinear element, a method of manufacturing an electrooptic device, an electrooptic device, and an electronic apparatus. More specifically, the present invention relates to a technique for forming an insulating film which constitutes a nonlinear element.
2. Description of Related Art
Electrooptic devices, such as a liquid crystal device and an EL (electroluminescence) display panel, have been recently popularized as display sections of electronic apparatuses, such as a cell phone, a portable computer, a video camera, etc.
A known example of liquid crystal devices among such electrooptic devices uses a thin film diode (TFD) element as a pixel switching nonlinear element for active matrix driving.
Such a liquid crystal device can include a pair of substrates which hold a liquid crystal therebetween, TFD elements and pixel electrodes formed on one of the substrates, and stripe-shaped counter electrodes (signal electrodes) formed on the other substrate. Each of the TFD elements is formed by, for example, forming a first metal film such as a Ta film or a Ta alloy film on the surface of the substrate, forming an insulating film on the surface of the first metal film by anodization, and then forming a second metal film on the surface of the insulating film.
SUMMARY OF THE INVENTION
In a liquid crystal device using the TFD elements as nonlinear elements, when the current-voltage characteristics of the TFD elements have high nonlinearity, the driving voltage of the liquid crystal device can be set to a low value, and a high-contrast display can be realized. Based on this view, a method of annealing an insulating film in a water vapor atmosphere to modify the insulating film has been studied as a technique for improving the characteristics of the TFD elements, as disclosed in, for example, Japanese Unexamined Patent Publication No. 08-830953. However, further improvement is required.
In order to suppress the difference (polar difference) in quantity between the currents flowing through a TFD element with the positive and negative applied voltages, a back-to-back structure is generally used, in which two TFD elements are connected in series. In the back-to-back structure, the step of depositing an insulating film by anodization requires power feed to an element portion, and thus anodization must be effected in a state in which a portion constituting a TFD element is connected to wiring for passing an anodization current through a bridge portion. Therefore, after the insulating film is formed by anodization, the bridge portion for connecting the TFD element portion and the feed wiring for anodization must be cut, thereby causing the problem of increasing the number of manufacturing steps.
In consideration of the above problem, an object of the present invention is to provide a method of manufacturing a nonlinear element capable of further improving electrical properties, such as nonlinearity of a TFD element, a method of manufacturing an electrooptic device, an electrooptic device, and an electronic apparatus.
Another object of the present invention is to provide a method of manufacturing a nonlinear element capable of decreasing the number of steps for manufacturing a nonlinear element to permit the manufacture of a nonlinear element at low cost.
In order to achieve the objects of the present invention, a method of manufacturing a nonlinear element having a first metal film, an insulating film, and a second metal film, which are laminated in this order, can include the first metal film forming step of forming the first metal film, the second metal film forming step of forming the second metal film, and the high-pressure annealing step of performing annealing in a predetermined atmosphere under a high pressure between the first metal film forming step and the second metal film forming step.
In the present invention, in order to modify the insulating film formed by anodization, high-pressure annealing is performed in an inert gas atmosphere, a nitrogen gas atmosphere or an atmosphere containing water vapor. In order to oxidize the surface of a metal film, high-pressure annealing is performed in an atmosphere containing water vapor. In this way, high-pressure annealing in a predetermined atmosphere can further improve the nonlinearity of the current-voltage characteristics of a nonlinear element, as compared with normal-pressure annealing in a water vapor atmosphere. Therefore, in a liquid crystal device, the driving voltage can be set to a low value, and a display of high quality such as improved contrast or the like can be realized.
In the present invention, the first metal film can include, for example, a metal film containing at least Ta.
For example, the present invention may include the first metal film forming step, an insulating film forming step of forming the insulating film on the surface of the first metal film by anodization, the high-pressure annealing step of performing annealing in an inert gas atmosphere, a nitrogen gas atmosphere or an atmosphere containing water vapor, and the second metal film forming step for forming the second metal film on the surface of the insulating film. In this case, high-pressure annealing is performed, for example, under the conditions including a temperature of 100° C. to 600° C., and a pressure of 0.5 MPa to 3 MPa, and preferably the conditions including a temperature of 150° C. to 300° C., and a pressure of 0.5 MPa to 2 MPa. In this construction, the insulating film formed by anodization can be modified to improve the nonlinearity of the current-voltage characteristics of a nonlinear element. Also, high-pressure annealing can obtain the same effect as conventional annealing at a lower annealing temperature than the conventional annealing, thereby preventing deformation of a substrate.
For example, in experiment for manufacturing a TFD element having the back-to-back structure, an anodic oxide film was formed on a Ta film by anodization with a voltage set to each of 10 V, 15 V and 20 V, and then high-pressure annealing for 1 hour at 200° C. in an atmosphere containing water vapor under a high pressure of 1 MPa, high-pressure annealing for 1 hour at 300° C. in an atmosphere containing water vapor under a high pressure of 1 MPa, and high-pressure annealing for 1 hour at 350° C. in a nitrogen atmosphere under a high pressure of 1 MPa were performed for studying nonlinearity &bgr; of a nonlinear element. As a result, the results shown by solid line C, point B and solid line D in FIG.
1
(
a
) were obtained. As shown in
FIG. 1
(
a
), good nonlinearity &bgr; can be obtained by high-pressure annealing. According to the experimental results shown in the graph, and other experimental results obtained, high-pressure annealing at a temperature of 200° C. and a pressure of about 1 MPa produces a nonlinear element having good nonlinearity &bgr;.
For example, the present invention can include the first metal film forming step, the high-pressure annealing step performing high-pressure annealing in an atmosphere containing water vapor to oxidize the surface of the first metal film, the insulating film forming step of forming the insulating film on the surface of the first metal film by anodizing the surface of the first metal film, and the second metal film forming step for forming the second metal film on the surface of the insulating film. In this case, high-pressure annealing is performed, for example, under the conditions including a temperature of 100° C. to 600° C. and a pressure of 0.5 MPa to 3 MPa, and preferably the conditions including a temperature of 150° C. to 300° C. and a pressure of 0.5 MPa to 2 MPa. In this construction, the insulating film formed by high-pressure annealing, and the insulating film formed by anodization can be used as the insulating film of the nonlinear element, thereby improving the nonlinearity of the current-voltage characteristics of the nonlinear element.
For example, the present invention can include the
Naono Hideaki
Seki Takumi
Taguchi Satoshi
Watanabe Yoshihiro
Duong Tai
Seiko Epson Corporation
Ton Toan
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