Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-06-04
2004-06-15
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S152000
Reexamination Certificate
active
06750938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device used for displaying characters and images, and a liquid crystal display apparatus incorporating the same.
2. Description of the Background Art
Liquid crystal display apparatuses, being thin and light in weight, are used in a wide variety of applications such as displays for personal digital assistance devices. Such a liquid crystal display apparatus includes a panel-shaped liquid crystal display device and other components.
A passive matrix type liquid crystal display device will now be described with reference to
FIG. 10
, as an example of a liquid crystal display device.
FIG. 10
schematically illustrates a cross section of a liquid crystal display device
101
.
The liquid crystal display device
101
includes a first substrate
102
, a second substrate
103
opposing the first substrate
102
, and a liquid crystal layer
106
provided between the substrates
102
and
103
that are sealed together along the periphery thereof by a sealant
104
containing spherical beads
104
. The liquid crystal display device
101
has a display area in which characters and shapes are displayed, and a non-display area surrounding the display area. In the display area, a plurality of strip-shaped first display electrodes
109
a
are provided on one side of the first substrate
102
that is closer to the liquid crystal layer
106
, and a plurality of strip-shaped second display electrodes
111
a
are provided on one side of the second substrate
103
that is closer to the liquid crystal layer
106
. The first display electrodes
109
a
extend in a direction vertical to the sheet of the figure and are spaced apart from one another. The second display electrodes
111
a
extend in the left-right direction in the figure and are spaced apart from one another. A rectangular pixel is defined by these electrodes
109
a
and
111
a
at each intersection therebetween, whereby a plurality of such pixels are arranged in a lattice-shaped matrix pattern. In the non-display area, first peripheral electrodes
109
b
are provided with substantially no interval therebetween on one side of the first substrate
102
that is closer to the liquid crystal layer
106
so as to surround the first display electrodes
109
a
. The first peripheral electrodes
109
b
include, for example, wiring electrodes that are connected to the first display electrodes
109
a
, and dummy electrodes that are provided so that the non-display area is occupied by electrodes as is the display area. First electrodes
109
include the first peripheral electrodes
109
b
and the first display electrodes
109
a
in the display area. A first alignment film
110
and a second alignment film
112
for regulating the orientation direction of the liquid crystal molecules are provided respectively on one side of the first display electrodes
109
a
that is closer to the liquid crystal layer
106
and on one side of the second display electrodes
111
a
that is closer to the liquid crystal layer
106
. For each pixel of the liquid crystal display device
101
, the voltage to be applied across the liquid crystal layer
106
between one first display electrode
109
a
and one second display electrode
111
a
that define the pixel is controlled so as to change the orientation of the liquid crystal molecules in the liquid crystal layer
106
and to adjust the amount of light to be transmitted therethrough, thus displaying characters and images in the display area.
The display quality of the liquid crystal display device
101
is substantially influenced by variations in the thickness of the liquid crystal layer
106
, i.e., variations in the cell gap. As the variations increase, the display quality decreases, causing a display non-uniformity, or the like. Therefore, in order to achieve a good display quality, it is necessary to achieve a uniform cell gap.
In order to address the problem, a large number of spherical spacers are provided between the first and second substrates in the prior art. However, such spherical spacers are easily collapsed by an external force because they support the substrates by point contact, and the particle diameter thereof is in conformity with the normal distribution, whereby it is not possible to achieve a highly uniform cell gap with such spherical spacers. Moreover, spherical spacers have small contact areas with the substrates because they support the substrates by point contact as described above. Therefore, even if the spherical spacers are fixed by providing a fixing layer or an attachment layer, they are moved in the liquid crystal layer by an external force such as a vibration or a shock applied thereto, thereby causing a change in the spacer distribution, which in turn influences the cell gap variations.
In view of this, a different type of liquid crystal display device has been proposed and put into practical use, in which a large number of columnar spacers are provided so as to be spaced apart from one another between the opposing surfaces of the first substrate and the second substrate.
For example, Japanese Laid-Open Patent Publication No. 6-222370 discloses a method for fixing columnar spacers along gaps in a transparent electrode by forming a transparent electrode pattern on a surface of a substrate by using a photoresist, baking the photoresist remaining on the pattern to convert it into a lift-off mask, forming a photosensitive film having a predetermined thickness on the surface of the substrate, exposing and developing the photosensitive film from the reverse surface of the substrate via the lift-off mask so as to form the columnar spacers that are aligned with the gaps in the transparent electrode pattern.
Moreover, Japanese Laid-Open Patent Publication No. 2000-298282 discloses a liquid crystal display apparatus including a pair of substrates with a liquid crystal layer being interposed therebetween, a first electrode provided on one of the substrates in a pixel region, a second electrode provided on the other substrate in a pixel region, and a columnar spacer provided on one of the substrates in the pixel region, the columnar spacer being covered by one of the first and second electrodes that is provided on the one of the substrates. Japanese Laid-Open Patent Publication No. 2000-298282 discloses that with such a configuration, the direction of an electric field produced between a portion of the electrode that is formed on the side surface of the columnar spacer and the other electrode is different from that of an electric field produced between another portion of the electrode and the other electrode, thereby providing a so-called “multi-domain” effect in this area.
Such columnar spacers are formed by applying and pre-baking a material obtained by adding a photosensitizer to an acrylic resin liquid, or the like, on the first substrate on which an electrode pattern has been formed, subjecting the material to a UV exposure/development process using a photomask, and then baking the material.
The cell gap uniformity is required not only in the display area in which characters and images are displayed, but also in the non-display area surrounding the display area, because it substantially influences the display quality in the peripheral portion of the display area. Particularly, in an STN (Super Twisted Nematic) liquid crystal display device, in which an image is displayed by controlling not only the optical rotatory of the liquid crystal material but also the birefringence thereof, the retardation is sensitive to variations in the cell gap, thereby imposing very high requirements as to the uniformity of the cell gap in the display area and in the non-display area. Liquid crystal display devices using ferroelectric liquid crystal materials also impose such high requirements because of their very small cell gaps. In order to address such requirements, columnar spacers are usually provided not only in the display area but also in the non-display area.
However, the provision of columnar s
Chung David
Daley, Jr. William J.
Edwards & Angell LLP
Kim Robert H.
Sharp Kabushiki Kaisha
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