Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-11-06
2001-09-25
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000
Reexamination Certificate
active
06295107
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display apparatus and, more particularly, it relates to a liquid crystal display apparatus comprising a micro-lens array.
2. Related Background Art
Known micro-lens arrays include those that can be formed on a transparent substrate covered by a light-shielding film having a given pattern as disclosed in Japanese Patent Application Laid-Open No. 7-261164. This patent document describes a method of producing micro-lenses by utilizing the surface tension of molten resin. However, lenses produced by such a method gives rise to aberration to a considerable extent in a peripheral area of the lens. This aberration problem that occurs in a peripheral area of micro-lens is normally bypassed by using a light-shielding underlayer. However, such a technique is accompanied by problems, which will be discussed below.
FIG. 13
of the-accompanying drawings is a schematic cross sectional view of a structure comprising known micro-lenses. Such a structure is typically prepared by forming a light-shielding layer
702
on a transparent substrate
701
, applying a photosensitive resin material onto the substrate and thereafter exposing it to light and developing the latent image to leave the photosensitive material as dots only in areas corresponding to the pixel array to be used with it. The photosensitive resin left on the substrate as dots is then molten and transformed into micro-lenses by utilizing the surface tension of the resin material to produce a structure
703
as shown in FIG.
13
. While rays of light such as those denoted by
704
,
705
,
706
in
FIG. 13
that enter a micro-lens at and near the center thereof may be converged to the focal point
707
of the lens, those entering the micro-lens at a peripheral area thereof such as ray of light
708
is not accurately brought to the focal point
707
but follows the route indicated by
709
because of the aberration of the micro-lens is particularly remarkable in the peripheral area. As a result, the converged rays of light show a light spot having a relatively large diameter. While, theoretically, the ray of light
708
is supposed to be blocked by the light-shielding layer
702
after entering the corresponding micro-lens
703
, it actually passes through the corresponding aperture of the light-shielding layer
702
and leaves the substrate from the lower surface thereof as shown. When such known micro-lenses are used in a liquid crystal display apparatus designed to contain a large number of small pixels in order to display finely defined images, the rays of light entering each micro-lens have to be converged to produce a very small spot of light. Then, obviously, the above pointed out problem adversely affects the effort of improving the brightness and the contrast of the image to be displayed on the liquid crystal display apparatus.
There arises another problem as will be described below when known micro-lenses are used for liquid crystal display apparatus and photosensors. Normally, the circuit substrate of a display apparatus or a photosensor is prepared by way of a semiconductor process independently from the process of producing micro-lenses before they are bonded together in a well aligned fashion to become integral with each other. A high degree of accuracy is required for aligning them with each other particularly when small pixels are used. For instance, if each pixel is about 10 microns large in an TN type transmission liquid crystal display apparatus, each pixel electrode is required to have a size of about 9 microns in order to satisfactorily separate adjacently located pixels. A phenomenon referred to as disclination of liquid crystal occurs in a peripheral area of the pixel electrodes to make it impossible to uniformly control the orientation of the liquid crystal and therefore to effectively utilize them in a peripheral area of about 2.5 microns. The contrast and the gradation of the image displayed on the display apparatus will be degraded if the light-shielding effect is not perfect in this area. Taking additionally the above pointed out problem of the diameter of each spot of light into consideration, the allowable dimensional error for the alignment of the micro-lenses and the circuit substrate will be less than 1 micron when the spot diameter is 3 micron because 9−2.5−2.5−3=1, which may be too rigorous to the process of manufacturing liquid crystal display apparatus. While there is a known technique of forming alignment marks, utilizing the light-shielding layer, the marks formed in the light-shielding layer are used for both the operation of patterning for the micro-lenses and that of aligning the circuit substrate and the micro-lenses because the micro-lenses are subjected to the patterning operation after forming the light-shielding layer.
FIG. 14
shows alignment marks
801
in cross section. However, with the use of such alignment marks, it will be difficult to reduce the error of the alignment of the pixel electrodes and the micro-lenses to a desired level if the alignment marks are displaced relative to the micro-lenses even when the error of the alignment of the circuit substrate and the micro-lenses is reduced to less than 1 micron.
Thus, the above discussed problems have been baffling the past efforts for arranging more pixels in a liquid crystal display apparatus and improving the brightness and the contrast of the displayed image when known micro-lenses are used for a liquid crystal display apparatus.
SUMMARY OF THE INVENTION
In view of the above identified problems, it is therefore the object of the present invention to provide a liquid crystal display apparatus wherein the aberration production areas of the micro-lenses are shielded from light and the accuracy of the alignment of the circuit substrate and the micro-lenses is improved.
According to an aspect of the invention, the above object is achieved by providing a liquid crystal display apparatus comprising a light source, a transparent substrate carrying thereon a light-shielding layer adapted to selectively blocking rays of light emitted from the light source and a micro-lens array, a circuit substrate carrying thereon a plurality of pixel electrodes and liquid crystal pinched between the transparent substrate and the circuit substrate and driven by the pixel electrodes to modulate the rays of light from the light source and display optical images, characterized in that the light-shielding layer have apertures and the rays of light from the light source pass through the respective micro-lenses after passing through the corresponding apertures and before entering the liquid crystal.
Preferably, in a liquid crystal display apparatus according to the invention, each of the micro-lenses has a curved surface for converging rays of light from the light source and the rays of light from the light source pass through the respective curved surfaces of the micro-lenses after passing through the corresponding apertures of the light-shielding layer and before entering the liquid crystal.
Preferably, in a liquid crystal display apparatus according to the invention, the rays of light from the light source are made to enter the respective micro-lenses in a plurality of different directions and the pitch of arrangement of the micro-lenses is as high as an integer-fold of the pitch of arrangement of the pixel electrodes.
Preferably, in a liquid crystal display apparatus according to the invention, alignment marks are formed by using the material same as that of the micro-lenses in order to bond said transparent substrate and the circuit substrate.
Still preferably, in a liquid crystal display apparatus according to the invention, alignment marks are formed by using the material same as that of the light-shielding layer in order to bond the transparent substrate and the circuit substrate.
According to another aspect of the invention, there is provided a liquid crystal display apparatus comprising a plurality of pixel electrodes adapted
Koyama Osamu
Kurematsu Katsumi
Watanabe Takanori
Canon Kabushiki Kaisha
Chowdhury Tarifur R.
Fitzpatrick ,Cella, Harper & Scinto
Sikes William L.
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