Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-07-22
2004-03-16
Qi, Zhi Qiang (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000, C349S113000
Reexamination Certificate
active
06707521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the structure of an electronic device such as personal computers and word processors, and more specifically, to a liquid crystal display (LCD) device equipped with the electronic device and a method of manufacturing a reflection layer in the liquid crystal display device. The present invention may also be applied to an electro-optical device having the liquid crystal display device.
A “semiconductor device” as used herein refers to a general device activated by a semiconductor. Therefore, the above-noted liquid crystal display device and the electro-optical device also fall within a category of semiconductor device. For clarification, the terms of “liquid crystal display device” and “electro-optical device” are separately used herein.
2. Description of Related Arts
Typically, a reflection type liquid crystal display device is known. The reflection type liquid crystal display device is more advantageous than a transmission type liquid crystal display device in that a lower power consumption may be achieved since no back light is used. Incidentally, the reflection type liquid crystal display device has been increasingly required for a direct-vision type display for mobile computers and video cameras.
FIG. 11
is a schematic view showing an example of a conventional structure. Referring to
FIG. 11
, between a substrate
10
and an opposing substrate
17
are provided switching elements
11
such as thin film transistors, an interlayer insulating film
12
, pixel electrodes
13
, an orientated layer
14
, a liquid crystal layer
15
, another orientated layer
14
, and an opposite electrode
16
in the stated order from the top surface of the substrate
10
. Incident light
20
is reflected by the pixel electrodes
13
to generate a reflection light
21
. It is to be noted that although all components are not shown in
FIG. 11
, which is a schematic view, a number of switching elements and a number of pixel electrodes are formed in a matrix on the surface of the substrate
10
.
The reflection type liquid crystal display device utilizes an optical modulating action of the liquid crystal to select the state where the incident light is reflected by the pixel electrodes to be outputted to the outside of the device and the state where the incident light is not outputted to the outside of the device, thereby allowing for the light or dark indication, and a combination thereof would allow an image to be displayed. Each pixel electrode is made of a metal with a high refractive index such as aluminum, and is electrically connected to a switching element such as a thin film transistor.
Such an operational principle causes a phenomenon in which in such a displaying state as a light display, that is, the state where the incident light from the external is reflected by the pixel electrodes to be outputted to the external of the device, the display attained by reflecting the incident light by the pixel electrodes as it is, like a mirror, may glare or darken depending upon a viewing angle. In other words, there occurs a phenomenon that the angle of vision may be narrowed.
This is caused by the fact that the reflection state of the incident light differs depend on its viewing angle of the user. In order to avoid such a problem, a need arises to devise the incident light so as to be reflected diffusely on the pixel electrode.
In general, to obtain a diffused reflection, the surface of the pixel electrode made of a metal material is subjected to light etching to form a fine concave or convex portion thereon.
Hitherto, such a problem has been arisen in which the reflectivity of the refection layer is lowered due to the formation of an orientated layer with a high refractive index on the reflection layer (pixel electrodes made of a metal material). For example, in the case where an orientated layer (having the reflectivity of 1.6) is formed on a vapor-deposited aluminum layer (having the reflectivity of 91.6%), the reflectivity is lowered to 87.4% in calculation, or is lowered to approximately 85% to 86% according to an actual experiment.
In addition, conventionally, formation of a concave or convex portion on the reflection layer causes a reflectivity to be reduced in nature.
The conventional method of forming the reflection layer on which the concave or convex portion is formed by etching encountered a limitation in terms of the depth of the concave or convex portion to be made deep. Accordingly, there was a problem with the conventional reflection layer (pixel electrode) in terms of brightness applicable to a liquid crystal display device (particularly, to a direct viewing reflection-type liquid crystal panel), since the reflection and diffused reflection of light (including diffusion and scattering) were not sufficient.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems, and therefore has an object of the present invention to provide a structure of a liquid crystal display device comprising a reflection layer in which an incident light is reflected and reflected diffusely more efficiently compared to a prior art, and a method of manufacturing the same.
According to a first aspect of the present invention disclosed in this specification, there is provided a liquid crystal display device comprising:
a pixel electrode made of a metal material, which is formed over a substrate; and
a reflection layer formed of a dielectric multi-layer film, which is formed on the pixel electrode,
characterized in that a concave or convex portion is formed on the surface of the pixel electrode.
In the foregoing structure, it is characterized in that the dielectric multi-layer film comprises a structure in which a thin film with a low reflective index and a thin film with a higher reflective index are laminated,
film thickness d
1
of the thin film with a lower reflective index is so adjusted as to satisfy 400 nm≦&lgr;
1
≦500 nm (&lgr;
1
=4 n
1
d
1
), where the film thickness and the reflective index of the thin film with a low reflective index are d
1
and n
1
, respectively, and
a film thickness d
2
of the thin film with a high reflective index is so adjusted as to satisfy 450 nm≦&lgr;
1
≦700 nm (&lgr;
2
=4 n
2
d
2
), where the film thickness and the reflective index of the thin film with a high reflective index are d
2
and n
2
, respectively.
In the foregoing structure, it is characterized in that the pixel electrode is made of aluminum, a material containing aluminum as a main component, silver, or a material containing silver as a main component.
In the foregoing structure, it is characterized in that the pixel electrode is formed on an interlayer insulating film in contact therewith, the interlayer insulating film being provided with a concave or convex portion formed on its surface.
In any one of the foregoing structure, it is characterized in that a liquid crystal is sealed between a pair of substrates, the liquid crystal display device comprising the pixel electrode arranged in a matrix manner on one substrate, a thin film transistor connected to the pixel electrode, and a reflection layer.
According to another aspect of the present invention disclosed in the present specification, there is provided a method of manufacturing a liquid crystal display device, characterized by comprising the steps of:
forming a switching element on a substrate;
forming a pixel electrode connected to the switching element, the pixel electrode being provided with a concave or convex portion on its surface; and
forming a dielectric multi-layer film formed of a dielectric film on the top surface of the pixel electrode.
In the foregoing structure, it is characterized in that the step of forming the pixel electrode having the concave or convex portion on its surface comprises a step of forming a pixel electrode on an interlayer insulating film having the concave or convex portion on its surface.
Further, in the foregoing structure, it is characterized in that the step of forming t
Hirakata Yoshiharu
Nishi Takeshi
Satake Rumo
Yamazaki Shunpei
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Qi Mike
Qi Zhi Qiang
Semiconductor Energy Laboratory Co,. Ltd.
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