Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-03-12
2001-07-17
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S111000, C349S113000
Reexamination Certificate
active
06262783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective liquid crystal display device preferably used as display means for an information terminal device such as a personal computer, a mobile computer, and a word processor, as well as a portable telephone, an electronic still camera, a VTR, a car navigating device, a liquid crystal television, or the like; and a method for fabricating the same.
2. Description of the Related Art
In recent years, reflective liquid crystal display devices have been widely used, especially as information display means for a portable information terminal device, because the reflective liquid crystal display device can be made thin and light-weight and it consumes low electricity.
In such a reflective liquid crystal display device, the development of a diffuse reflection plate has been vigorously conducted in order to realize a paper white display. For example, Japanese Laid-open Publication No. 6-27481 describes the technique for a diffuse reflection plate employing a photosensitive resin.
According to the above-described Publication, when concave and convex portions are patterned using a photosensitive resin, exposure is performed using a stepper exposure device with a photomask. However, in the case where the stepper exposure device is employed, an area which can be exposed at one time is limited to approximately a 5 inch sized area. As a result, in the case where an area greater than a 5 inch area is exposed, it is necessary to change exposure sites more than once so as to cover entire area to be exposed.
When more than one exposure is conducted during the fabrication process of a diffuse reflection plate with an area greater than 5 inches, for example, it is necessary to perform delicate alignment work with a mask, a substrate, and a stepper for every exposure, resulting in a significantly degraded working efficiency. Even if the alignment is accurately performed, due to a natural light-quantity distribution in the stepper or distortion in light rays (i.e., differences in the degree of light parallelization, or the like), exposure conditions differ for every region bounded by a joint (i.e., a boundary of a region exposed at one time). As a result, the shape of unevenness (concave and convex) suddenly changes at the joint area, thereby influencing optical characteristics of the reflective electrode. Consequently, joint or non-uniformity in display is observed.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a reflective liquid crystal display device includes a pair of transparent plates; a liquid crystal layer interposed between the pair of plates; a light-shielding layer provided on one of the plates, the light-shielding layer having a light-transmitting portion and a light-shielding portion; a storage capacitor electrode; an insulating layer covering the light-shielding layer and the storage capacitor electrode, the insulating layer having concave and convex surfaces; and a reflective pixel electrode provided on the concave and convex surfaces of the insulating layer.
In one embodiment of the invention, the light-shielding layer has a common signal line; the storage capacitor electrode overlaps the common signal line via an insulating layer interposed therebetween so as to form a storage capacitor.
In another embodiment of the invention, the reflective liquid crystal display device further includes a plurality of pixel regions arranged in a matrix of N rows and M columns, where N and M are positive integers; a plurality of capacitor electrodes, each of which correspond to respective pixel region; and N gate signal lines, each of which correspond to a respective row of pixel regions. A storage capacitor electrode in Ith row overlaps an (I+1)th or (I−1)th gate signal lines with an insulating layer interposed therebetween so as to form a storage capacitor, where I is a integer greater than 0 and less than and equal to N.
In another embodiment of the invention, a part of the Ith gate signal line extends into a pixel region so as to overlap the storage capacitor electrodes in the (I+1)th or (I−1)th row with the insulating layer interposed therebetween.
In another embodiment of the invention, the storage capacitor electrode has an opening at a position corresponding to the light-transmitting portion of the light-shielding layer.
In another embodiment of the invention, a shape of the light-transmitting portion of the light-shielding layer is approximately round. A distance between two adjacent light-transmitting portions is in a range of about 3 to about 50 microns.
In another embodiment of the invention, the storage capacitor electrode is a transparent electrode.
According to another aspect of the invention, a method for fabricating a reflective liquid crystal display device including a liquid crystal layer interposed between two substrates, includes the steps of forming a light-shielding layer having a light-transmitting portion on a plate of one of the two substrates; forming a storage capacitor electrode made of a conductive material; forming an insulating layer covering the light-shielding layer and the storage capacitor electrode; and exposing the substrate from a side opposite to the side where the insulating layer is formed.
In one embodiment of the invention, the storage capacitor electrode is a transparent electrode.
Hereinafter, effects of the above-described structures according to the present invention will be described.
According to the reflective liquid crystal display device of the present invention, when the insulating layer having holes is patterned, it becomes possible to realize self-alignment by performing exposure from the bottom side of the substrate with the light-shielding region below the insulating layer used as a mask pattern. Accordingly, no photomask is required, and full plate exposure by a large exposure device becomes possible. As a result, joints and non-uniformity in display, both of which are caused by the stepper exposure, can be overcome. In addition, since the storage capacitor electrode is provided, a storage capacitor for driving a liquid crystal molecule can be formed. As a result, the reflective liquid crystal display device having a satisfactory display quality is obtained.
According to the reflective liquid crystal display device of the present invention, the concave and convex portions on the surface of the reflective electrode are formed by self-alignment due to the bottom-side exposure utilizing the common signal line for forming a storage capacitor. As a result, it becomes possible to provide, with a simple process, the reflective liquid crystal display device generating neither joints nor non-uniformity in display and having excellent display quality which is realized by the storage capacitor.
According to the reflective liquid crystal display device of the present invention, the storage capacitor electrode formed above the light-shielding film overlaps the gate signal line. As a result, the storage capacitor can be easily formed.
According to the reflective liquid crystal display device of the present invention, the gate signal line is overlapped with the storage capacitor electrode so as to form the storage capacitor at a position between an overlapped portion of the extended gate signal line and the storage capacitor electrode and the storage capacitor electrode. As a result, the storage capacitor can be formed without providing the common electrode line.
According to the reflective liquid crystal display device of the present invention, the holes in the light-shielding film are disposed so as to approximately correspond to holes in the storage capacitor electrode. As a result, it becomes possible to form concave and convex portions for giving excellent light scattering characteristics to the surface of the pixel electrode located above the holes. In the case where a reflective liquid crystal display device does not have such a structure, the following defects may occur. For example, when exposure is conducted fro
Ban Mariko
Tanaka Tomoko
Tsuda Kazuhiko
Nixon & Vanderhye P.C.
Parker Kenneth
Sharp Kabushiki Kaisha
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