Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-19
2001-12-04
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S138000, C349S187000
Reexamination Certificate
active
06327009
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection-type liquid crystal display panel and a method of fabricating the same. More particularly, the present invention relates to a reflection-type liquid crystal display panel suitable for use as a display unit for OA apparatus including note-size lap top personal computers and word processors, video apparatus including pocketable television sets, and game machines, and a method of fabricating the same.
2. Description of the Related Art
The application of liquid crystal display panels to pocketable liquid crystal television sets, lap top personal computers and word processors has rapidly developed in recent years. Particularly, reflection-type liquid crystal displays, which reflect incident external light to display images, are being watched with keen interest because reflection-type liquid crystal display panels do not need any backlight unit, are capable of operating at a low power consumption rate and of being powered by batteries; and are thin and of lightweight.
Generally known reflection-type liquid crystal display panels are TN liquid crystal display panels in which a liquid crystal is driven in a twisted nematic (TN) mode, and STN liquid crystal display panels in which a liquid crystal is driven in a super twisted nematic (STN) mode. The TN liquid crystal display panel displays monochromatic images by using the optical properties of a liquid crystal display panel, namely, an optically rotatory characteristic which is exhibited when no voltage is applied thereto and a polarization canceling characteristic which is exhibited when a voltage is applied thereto.
A dichromatic dye is added to a known amorphous chiral nematic guest-host liquid crystal, and the orientation of the liquid crystal is controlled by voltage to control the orientation of the dichromatic dye for displaying images. A liquid crystal display panel employing such a mixture of an amorphous chiral nematic guest-host liquid crystal and a dichromatic dye does not need any polarizing plate, and has a high luminance and a wide viewing angle.
A color liquid crystal display has a liquid crystal display panel provided with an R-, a G- and a B-filter therein, and displays multicolor or full-color images by utilizing an optical switching characteristic. Currently, TN reflection-type liquid crystal display panels are employed in portable liquid crystal television sets, namely, pocketable liquid crystal television sets, driven in an active matrix driving mode or a passive matrix driving mode.
Referring to
FIG. 14
showing a conventional monochromatic reflection-type liquid crystal display panel
20
in a typical sectional view, the liquid crystal display panel
20
has a back glass substrate
20
a,
a front glass substrate
20
b
disposed opposite to the back glass substrate
20
a,
an insulating layer
22
formed on the inner surface of the back glass substrate
20
a,
first electrodes
23
a
for forming pixels, formed on the insulating layer
22
in the pattern of stripes, an alignment film
24
a
formed on the insulating layer
22
so as to cover the first electrodes
23
a,
second electrodes
23
b
formed on the inner surface of the front glass substrate
20
b
in the pattern of stripes so as to extend perpendicularly to the first electrodes
23
a,
and an alignment film
24
b
formed on the inner surface of the front glass substrate
20
b
so as to cover the second electrodes
23
b.
The second electrodes
23
b
formed on the front glass substrate
20
b
are transparent electrodes, and the first electrodes
23
a
formed on the back glass substrate
20
a
are reflective electrodes of a conductive metal. The electrodes
23
a
and
23
b
of the glass substrates
20
a
and
20
b
are scanned in a passive matrix driving mode to display images on the liquid crystal display panel.
Referring to
FIG. 15
showing a conventional monochromatic reflection-type liquid crystal display panel
20
in a typical sectional view, the liquid crystal display panel
20
has a back glass substrate
20
a,
a front glass substrate
20
b
disposed opposite to the back glass substrate
20
a,
an insulating layer
22
formed on the inner surface of the back glass substrate
20
a,
thin-film transistors (TFTs)
21
forming pixels and formed on the insulting layer
22
, a matrix of electrodes
23
a
formed on the insulating layer
22
, an alignment film
24
a
covering the TFTs and the electrodes
23
a,
a planar common electrode
23
b
formed on the inner surface of the front glass substrate
20
b,
and an alignment film
24
b
formed on the common electrode
23
b.
The common electrode
23
b
formed on the front glass substrate
20
b
is a transparent electrode, and the electrodes
23
a
formed on the back glass substrate
20
a
are reflective electrodes of a conductive metal.
The back glass substrate
20
a
and the front glass substrate are spaced a predetermined distance apart by a spacer, not shown, so as to form a space therebetween, and a liquid crystal, such as a guest-host liquid crystal, is filled in the space between the glass substrates
20
a
and
20
b
to form a liquid crystal layer
25
, and the liquid crystal layer
25
is sealed in the space by a sealing member
26
attached to the peripheral parts of the glass substrates
20
a
and
20
b.
The conventional reflection-type liquid crystal display panel is provided on its back surface with a reflecting plate of a metal, such as an aluminum plate, having a surface finished by grinding to provide the same with a light scattering property or a reflecting plate formed by depositing a metal, such as aluminum, by evaporation on a roughened surface of a base plate to provide the roughened surface with a light scattering property to secure a wide visual angle. Usually, the reflecting plate attached to the back surface of the liquid crystal display panel is omitted if reflective electrodes are employed. The reflection-type liquid crystal display panels
20
shown in
FIGS. 14 and 15
are not provided with any reflecting plate on their back surfaces.
The foregoing conventional reflection-type liquid crystal display panel provided with the reflective electrodes having mirror surfaces reflects images of matters in front of the reflection-type liquid crystal display panel in a specular reflection mode and thereby the visibility of the screen of the reflection-type liquid crystal display panel is deteriorated.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to improve the visibility of a reflection-type liquid crystal display panel provided with electrodes having reflective surfaces by suppressing the reflection of matters in front of the reflection-type liquid crystal display panel in the reflective surfaces of the electrodes of the reflection-type liquid crystal display panel.
The image displaying performance of the foregoing conventional reflection-type liquid crystal display panel provided with the insulating layer over the entire inner surface of the glass substrate is deteriorated due to current leakage across the pixel electrodes if the insulating layer has a low surface resistivity.
Accordingly, it is a second object of the present invention to improve the image displaying performance of a reflection-type liquid crystal display panel provided with electrodes formed on an insulating layer.
According to a first aspect of the present invention, a reflection-type liquid crystal display panel comprises a flat, smooth substrate, an insulating layer formed on the inner surface of the substrate, and reflective electrodes formed on the insulating layer, in which the minute irregularities are formed in the surfaces of the insulating layer, the reflective electrodes are formed on the surface of the insulating layer so as to conform to the minute irregularities.
According to a second aspect of the present invention, a reflection-type liquid crystal display panel comprises a flat, smooth substrate, an insulating layer formed on the inner surface of the substrate, an
Dai Nippon Printing Co. Ltd.
Morgan & Finnegan L.L.P.
Ton Toan
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