Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-01-12
2004-09-07
Chung, David Y. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S156000
Reexamination Certificate
active
06788372
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal panel for use in a liquid crystal display such as a transmissive or reflective liquid crystal display or ferroelectric liquid crystal display, a manufacturing method for the liquid crystal panel, a liquid crystal display using the liquid crystal panel, and a liquid crystal projector using the liquid crystal panel.
A liquid crystal panel used in a related art liquid crystal display has such a structure that a pair of substrates formed of glass or the like are opposed to each other with a given spacing (gap) defined therebetween, and a liquid crystal layer is formed so as to fill the given gap and provide numerous pixels in the form of matrix. One of the pair of substrates has one surface on the liquid crystal layer side formed with a switching element such as a thin-film transistor (TFT) and a pixel electrode for each pixel. The other substrate has one surface on the liquid crystal layer side formed with an opposing electrode opposed to the pixel electrode. In some case, the other substrate is provided with color filters and/or microlenses, for example.
The characteristics of such a liquid crystal panel, such as response speed, contrast, and viewing angle, are closely related with the size of the above gap between the opposed substrates, which size is equal to the thickness of the liquid crystal layer. Therefore, precise control of the gap to a required size is important to obtain a high display quality. Further, if the gap size is nonuniform, there occurs display nonuniformity due to Newton's rings, causing a degradation in viewability. Conventionally, the gap size is adjusted by dispersing rod-like or spherical spacers formed of glass, plastic, etc. between the pair of substrates. The spacers are dispersed by randomly applying them over the surface of any one of the pair of substrates, for example. Further, the display nonuniformity in a related art liquid crystal projector using such a liquid crystal panel is also prevented by a similar method.
However, the gap adjustment using the spacers as mentioned above has the following problems. The above-mentioned gap adjustment is effective in a liquid crystal panel having a large pixel size (e.g., about 200 &mgr;m×200 &mgr;m pitch) fabricated by using a thin-film transistor (TFT) of amorphous silicon (a-Si) or polysilicon (poly-Si) deposited under low-temperature conditions for a semiconductor layer constituting the switching element. However, in a liquid crystal panel having a small pixel size (e.g., about 20 &mgr;m×20 &mgr;m pitch or less) fabricated by using a TFT of poly-Si deposited under high-temperature conditions for the semiconductor layer of the switching element, a bright spot or the like is generated, for example, causing a reduction in display quality.
That is, because the spacers are applied over the surface of any one of the pair of substrates and accordingly located also in an effective pixel portion composed of a large number of pixels in the form of a matrix, there occurs an alignment disorder of liquid crystal molecules due to the spacers present in the effective pixel portion in a liquid crystal panel having a small pixel size. Such alignment disorder of liquid crystal molecules has a profound effect on the display quality.
Furthermore, the density of the spacers cannot be adjusted in applying the spacers in the related art technology, so that the gap size tends to be nonuniform in any liquid crystal panel irrespective of the kind of the semiconductor layer, thus readily inviting a reduction in display quality. Accordingly, in a three-panel type liquid crystal projector using such liquid crystal panels, color matching of all the liquid crystal panels used is very difficult because of nonuniformity of the gap size.
In the case of carrying out the gap adjustment by using the spacers, not only the step of applying the spacers to one of the substrates, but also the step of applying a conductive paste for a common electrode portion is necessary. The common electrode portion is provided in a peripheral region of the liquid crystal panel at a position outside of the effective pixel portion, so as to take a common potential between the substrates on the switching element side and the opposing electrode side. Accordingly, these individual process steps and devices to be used in these steps are necessary, so that the manufacturing steps become complicated to cause a reduction in productivity and an increase in manufacturing cost.
In a liquid crystal panel using a ferroelectric liquid crystal in a reflective liquid crystal display utilizing birefringence, the gap adjustment by application of the spacers without occurrence of alignment fault is difficult because the ferroelectric liquid crystal has a layered structure. Further, in the liquid crystal panel using the ferroelectric liquid crystal, very-high-accuracy adjustment of the gap size is required, and this requirement cannot be satisfied even by the use of the spacers.
In the case that the liquid crystal panel has microlenses or the like formed of a material having a coefficient of thermal expansion different from that of the material of the pair of substrates, e.g., glass, there occurs distortion or the like different from each other between the substrates due to heat applied in manufacturing the liquid crystal panel, causing a difficulty of high-accuracy setting of the gap size.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a liquid crystal panel of any type such as transmissive or reflective which is improved in display quality by adjusting the gap size with high accuracy and uniformity.
It is another object of the present invention to provide a manufacturing method for the liquid crystal panel at a low cost with high productivity.
It is a further object of the present invention to provide a liquid crystal display using the liquid crystal panel.
It is a still further object of the present invention to provide a liquid crystal projector using the liquid crystal panel.
In accordance with a first aspect of the present invention, there is provided a liquid crystal panel including a first substrate, a second substrate opposed to the first substrate with a given gap defined therebetween, and a liquid crystal layer filling the given gap. The first substrate has one surface formed with a planarizing film having a flat surface on the liquid crystal layer side. A plurality of pixels in the form of a matrix are formed on the flat surface of the planarizing film, and a light shielding region is formed between any adjacent ones of the pixels. A projection for defining the given gap between the first and second substrates is formed on the flat surface of the planarizing film at a position in the light shielding region so as to abut against an innermost surface of the second substrate adjacent to the liquid crystal layer.
In accordance with a second aspect of the present invention, there is provided a manufacturing method for the above liquid crystal panel, having the steps of forming the planarizing film on one surface of a dielectric substrate, forming the projection on the flat surface of the planarizing film at a position in the light shielding region to thereby obtain the first substrate, and bonding the first substrate and the second substrate opposed to each other so that the projection abuts against the innermost surface of the second substrate.
In accordance with another aspect of the present invention, there is provided a liquid crystal display having the above liquid crystal panel. In accordance with a further aspect of the present invention, there is provided a liquid crystal projector (e.g., three-panel type liquid crystal projector) having the above liquid crystal panel.
In the liquid crystal panel according to the present invention, the projection for defining the given gap between the first and second substrates is formed on the flat surface of the planarizing film at a position in the light shielding region so as to abut agains
Kaise Kikuo
Shima Syuichi
Chung David Y.
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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