Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-06
2003-02-18
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06522375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a reflection type liquid crystal display, and more specifically to a reflection type liquid crystal display having a reflection electrode with bumps and a method for fabricating the same.
2. Description of the Related Art
Generally, a cathode ray tubes (CRT) used for displays like monitors of televisions or computers is not easy to install or move due to its bulky volume, heavy weight, and enormous power consumption. To overcome such disadvantages, liquid crystal displays (LCDs), plasma display panels, or flat panel displays using an electroluminescence element have been proposed and widely used.
High definition and multicolor display driven at a lower voltage with less power consumption makes the LCDs considered as one of most leading display device. In addition, LCDs are easy to manufacture, and therefore, are widely used for various electronic devices. There are two types of LCDs: a projection type display using an external light source; and a reflection type display using ambient lights.
The reflection type display is thin and light. It consumes less power because backlight devices are not necessary. It shows an excellent display outdoors. Thus, the reflection type displays are widely used for a portable device.
However, the current reflection type LCD has a dark screen and fails to show high definition and multicolor images. Therefore, the reflection type LCDs are employed for a low price product that requires a simple pattern display, such as numbers.
To use reflection type LCD for a portable information device, such as a document viewer and an internet viewer, a high definition and multicolor display with an enhanced reflection luminance is necessary. Such an enhancement in reflection luminance and high definition is also necessary to easily look at the monochromatic LCDs that mainly display character information. However, such an enhancement requires an active matrix substrate having a switching element, for example, thin film transistors. In practice, a device using a monochromatic LCD are sold at a lower price. Therefore, it cannot use thin film transistor LCDs of a high price.
In the long run, the portable information devices would provide a multicolor display function. The monochromatic LCDs will fade away, and the reflection type LCD devices with a multicolor display function are under development.
Despite the developing panel technologies and the expanding market, the reflection type multicolor LCDs are rarely available commercially. This is because the reflection type multicolor LCD devices have shown a poor performance in brightness, contrast, and a response time.
Two techniques are combined to obtain an improved brightness. One is enhancing a reflectivity of a reflection electrode, and the other is achieving a high aperture ratio. The reflectivity enhancement has been used for a conventional guest-host liquid crystal displays. Maximizing a reflectivity by allowing minute bumps to a reflection electrode is disclosed in U.S. Pat. No. 5,408,345 entitled “Reflection type liquid crystal display device wherein the reflector has bumps”.
However, the ideal reflectivity has not yet been achieved, always requiring a reflectivity enhancement for the reflection type liquid crystal displays.
FIG. 1
is a simplified plan view showing the surface of a reflection electrode described in the prior art.
Referring to
FIG. 1
, a reflection electrode
10
has a surface that a plurality of microlenses
2
of convex semi-spheres are irregularly arranged and a plurality of ravines
4
are arranged between the microlenses
2
, the ravines having different areas depending on their respective positions. Such surface structure allows the microlenses
2
of the reflection electrode
10
to have different heights, resulting in low and irregular reflectivity from place to place.
Moreover, the low and irregular reflectivity makes liquid crystal molecules aligned non-homogeneously, and causes a very low contrast ratio during display of pictures.
In addition, since the ravine width is different from place to place, it is difficult to precisely form the microlenses in accordance with its design dimension.
Moreover, the prior art has a drawback that requires two photolithography processes: a first photolithography process for forming microlenses using a first mask; and a second photolithography process for forming a contact hole for the contact with the drain electrode of thin film transistor using a second mask. In other words, light exposing processes are required twice.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to make a reflection electrode have more enhanced reflectivity and contrast ratio.
It is another object of the invention to precisely form microlens of a reflection electrode as designed.
It is still another object of the invention to simplify the formation of microlenses and contact holes.
To achieve the above objects and other advantages, a reflection type liquid crystal display according to one aspect of the present invention includes a reflection electrode of which surface has a plurality of irregular and convex polygons, widths of respective ravines between the convex polygons being constant. The irregular sizes and heights of the convex polygons in various directions and much reduced flat regions maximize the reflectivity and also minimizes non-homogeneous alignment.
In order to enhance the reflectivity at the front side, a dimple can be formed at the apex of the convex polygon to a certain depth.
A method for fabricating such a reflection type liquid crystal display is also disclosed
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Jang Yong-Kyu
Joo Young-Kuil
Kang Myeon-Koo
Kwag Jih-Oh
Shin Jong-Eup
Hae-Chan Park
McGuireWoods LLP
Nguyen Hoan
Samsung Electronics Co,. Ltd.
Ton Toan
LandOfFree
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