Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-11-09
2001-01-09
Malinowski, Walter (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S113000
Reexamination Certificate
active
06172723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection type liquid crystal display device which forms an image by modulating light reflected from a reflection type matrix substrate with liquid crystals.
2. Related Background Art
Liquid crystal display devices are presently used as thin display devices for various industrial and commercial apparatuses. Projection type display devices for projecting and magnifying light modulated with liquid crystals are widely used for large screen display devices. A reflection type liquid crystal display device which has a high efficiency of light utilization is expected as a device capable of displaying an image of high precision and brightness.
FIG. 14A
is a cross sectional view showing a typical example of a conventional reflection type liquid crystal color display device. The display device has a pair of a transparent substrate
1
and an active matrix substrate
2
between which liquid crystals
3
are sandwiched. Incident light indicated by an arrow to modulated at each pixel with liquid crystals driven on the active matrix substrate, reflected by a reflection electrode
10
, projected and magnified to obtain a desired image.
The transparent substrate
1
has a glass substrate
4
on which a color filter array
5
of R (red), G (green), and B (blue) is formed. At the interface with liquid crystals, there are a transparent electrode
8
for applying a voltage and an orientation film
9
laminated with the transparent electrode
8
. A microlens array
7
is formed on the color filter array
5
in order to improve the efficiency of light utilization. Each lens has a radius of curvature which makes incident parallel light focus generally upon the reflection electrode
10
. In order to cut stray light between pixels, a black matrix
6
is formed to fill the space between adjacent color filters of the color filter array
5
.
The above-described conventional display device is, however, associated with the problem that light components not focussed upon the reflection electrode
10
because of aberration of the microlens array
7
and stray light components incident upon the microlens array
7
are mixed with light reflected from the reflection electrode
10
and this mixed light lowers the quality of a projected image.
FIG. 14B
shows the details of optical paths of one pixel. Light
20
generally vertically incident upon the substrate
1
is refracted by a microlens
7
, focussed upon an approximately central area
26
of the reflection electrode
10
, reflected by the reflection electrode
10
, again becomes incident upon the microlens
7
, and is output as vertical light
21
. If the microlens provides incident light of different wavelengths with the same refraction and has a perfect parabolic shape, light of different wavelengths can be focussed upon one focal point
26
. However, in practice, the parabolic shape is imperfect and the focal length changes with wavelength (aberration). Therefore, for example, some light propagates along a path
22
and is reflected at a position shifted from the focal point so that it is output along a direction
22
shifted from the vertical direction. Further, light incident along a direction
24
is reflected at a position
28
and output along a is direction
25
. Such phenomena are superposed upon at a number of pixels. In addition, there is a variation of shapes of microlenses of respective pixels. Output unnecessary light components are mixed with a normal image so that the contrast and image quality may be lowered by these noise components.
If the size of the reflection electrode is made small in order to solve the above problem, a space between adjacent pixels becomes large so that an electric field in this space does not become vertical to the substrate plane and orientation of liquid crystals may be disturbed. From this reason, the contrast is lowered and defects in an image increase.
SUMMARY OF THE INVENTION
In order to solve the above problem, the invention provides a reflection type liquid crystal display device, comprising: a first substrate having an array of a plurality of light reflecting pixel electrodes; a second substrate having an array of a plurality of microlenses; and liquid crystals sandwiched between the first and second substrates for modulating incident light entering between the first and second substrates and reflected by the pixel electrodes to form an optical display, wherein each of the light reflecting pixel electrodes includes a high reflectivity region formed near at a focal point upon which light incident upon a microlens is focussed, the high reflectivity region reflecting the incident light, and a low reflectivity region formed surrounding the high reflectivity region, the low reflectivity region limiting a reflection of incident light components of stray light to be caused by aberration among light passed through the microlens.
According to the invention, the high reflectivity region reflects main image signal components of the incident light, and the low reflectivity region hardly reflects light components not focussed because of aberration and stray light components, because it has a low reflectivity. Accordingly, the project image has high contrast and high quality and does not contain unnecessary light components other than essential image signals. Since the size of the reflection electrode is the same as that of the conventional reflection electrode, disturbance of orientations of liquid crystals and lowered contrast can be prevented.
According to the present invention, most of light converged by the microlens is applied to the high reflectivity region, light components caused by lens aberration and stray light components among light converged by the microlens are applied to the low reflectivity region.
According to the present invention, light components having the main wavelength incident upon the microlens are focussed upon the high reflectivity region of the reflection electrode, and noise components such as lens aberration light components and stray light components are reflected slightly by the low reflectivity region. Therefore, the contrast of a projected image can be improved and the image quality can be improved.
According to an embodiment of the invention, the high reflectivity region is provided in a central area of each pixel electrode and two-dimensionally surrounded by the low reflectivity region.
According to another embodiment, light components having the main wavelength incident upon the microlens are focussed upon the high reflectivity region near in generally the central area of the reflection electrode, and aberration light components and stray light components are incident upon the nearby area of the reflection electrode which surrounds the high reflectivity region. Accordingly, without changing the size of the pixel electrode, noise components can be cut, which contributes to improve the contrast of a projected image and the image quality.
According to a further embodiment, the high reflective region is made of a high reflectivity conductive material and the low reflectivity region is made of a low reflectivity conductive material.
According to a still further embodiment, the high and low reflectivity regions are made of conductive materials having different reflectivities. A large difference between two reflectivities allows the contrast of a projected image to be improved.
According to a still further embodiment, the high reflectivity region is made of a conductive material and the low reflectivity region is made of a material laminated on the conductive material, the material having a reflectivity lower than the conductive material.
According to a still further embodiment, the low reflectivity region is made of low reflection material formed in the surface layer of the high reflectivity region. Accordingly, the size of the reflection electrode can be maintained same as the high reflectivity region, while the low reflectivity region with a lowered reflectivity is formed in the surface layer.
A
Inoue Shunsuke
Koyama Osamu
Kurematsu Katsumi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Malinowski Walter
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