Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-21
2001-11-13
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000
Reexamination Certificate
active
06317187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal light valve apparatus, and in particular to a liquid crystal light valve apparatus which improves a contrast to thereby improve an image quality.
2. Description of the Related Art
A liquid crystal light valve (LCLV) apparatus is an optical to optical image converter. A light valve is such an apparatus adapted to being capable of receiving a light which is low in light intensity, reading out its optical image on real time by using a light fed from another light source, and output the image. Hereafter, a liquid crystal light valve apparatus is also referred to simply as a liquid crystal light valve.
The liquid crystal light valves are classified into a transmission type and a reflection type.
In the reflection type, there is used an active matrix scheme in which a signal is supplied from an output terminal to each pixel to turn on or off each pixel, and a light writing-in scheme in which light writing is conducted on a photoconductive layer from a rear face side opposite to its output.
On the other hand, in the transmission type, only the active matrix scheme is used.
The fact common to the above described three schemes is that a liquid crystal layer is interposed between opposed electrodes.
In order to make birefringence of the liquid crystal layer in these liquid crystal light valves constant in a pixel area, therefore, the spacing between both substrates having electrodes opposed to each other via the liquid crystal layer needs to be kept constant.
For the purpose of keeping the spacing between the substrates constant, a spacer is provided.
Heretofore, a method shown in
FIG. 1
has been used. On a first substrate
51
having function elements such as a transistor or the like formed thereon, globular beads
53
having uniform diameters are scattered. A second substrate
52
having an opposed electrode formed thereon is stuck to the scattered beads
53
.
In this method, however, the beads
53
serving as the spacer are scattered also on pixel electrodes
55
. Therefore, shadows of the beads
53
appear in a projected image. In addition, random distribution of the shadows of the beads
53
causes conspicuousness. This results in a problem of degraded image quality.
In order to eliminate the shadows of the beads
53
, therefore, there is widely used such a method that the spacers
53
are not disposed in the image display area. According to the method, when adhering the peripheral portions of the substrates, spacers are added to the bonding agent thereof t o form the spacing.
In this case, the surface flatness of both substrates on the side contacting the liquid crystal layer needs to be limited to, for example, 0.3 &mgr;m or less over the whole image display area.
As a matter of fact, however, a glass substrate, a semiconductor substrate or the like having a thickness of 1.1 mm or less widely used as a liquid crystal glass substrate is easily bent by stress of a thin film electrode layer such as metal or the like, a semiconductor film such as amorphous silicon or the like, and an insulation film or the like formed thereon.
Therefore, the above described method of forming the spacer only around the periphery of glass has been put to practical use only in the case where the liquid crystal light valve apparatus is small with a surface area comprised of the above described pixel display area and a peripheral portion thereof being equal to or less than 30 mm in each side length and in addition the error allowance of the substrate spacing is comparatively large, such as in the case of the so-called twist pneumatic oriented normally white mode of transmission type.
In other words, in the case where the error allowance of the spacing is small as in a liquid crystal light valve having many pixels and a large display area, a liquid crystal light valve of reflection type using an electrically controlled birefringence (ECB) mode and so on, it is difficult to apply the above described method of forming the spacers only in the periphery of glass and it becomes necessary to dispose spacers in the display area.
In order to dispose the spacers so as not to make the shadows of the spacers inconspicuous, therefore, it is made necessary to dispose the spacers selectively only the portion between pixels.
And there is being studied a method of forming a so-called pillar-shaped spacer
54
by using registering a as self alignment with respect to pixel electrodes
55
forming pixels, for example, as shown in FIG.
2
.
FIG. 3
shows a schematic sectional view of a conventional liquid crystal light valve of transmission type.
This liquid crystal light valve of transmission type has the following configuration. A first substrate
51
is formed by forming pixel electrodes
55
divided so as to be associated with respective pixels, on an internal surface of a base substrate
50
made of, for example, glass and forming an orientation film
61
over the entire internal surface so as to cover the pixel electrodes
55
. A second substrate
52
is formed by forming opposed electrodes
60
on an internal surface of a base substrate
50
made of, for example, glass and forming an orientation film
62
over the entire internal surface so as to cover the opposed electrodes
60
. The first substrate
51
and the second substrate
52
are disposed so as to be opposed to each other via pillar-shaped spacers
54
. In addition, the peripheral portions of the substrates
51
and
52
are hermetically sealed, and a liquid crystal layer
58
is formed between the substrates
51
and
52
. The liquid crystal light valve of transmission type has thus been formed.
If in
FIG. 3
the pixel electrodes
55
of the first substrate
51
are made of a material having a high light reflection factor such as Al, Cr, W or the like, or alternatively a dielectric multi-layer reflection film or the like is disposed between the pixel electrodes
55
and the liquid crystal layer
58
, then a liquid crystal light valve of reflection type is directly obtained.
Especially, in order to sink the wholly black state, i.e., make the wholly black state blacker in the liquid crystal light valve of
FIG. 3
, for example, a polarization plate
56
and a analyzer plate
57
are respectively disposed on the first and second substrates
51
and
52
so as to satisfy the orthogonal Nicol relation. Directions of the orientation films
61
and
62
respectively provided on the pixel electrodes
55
and the opposed electrodes
60
which are in turn provided on opposed sides respectively of the substrates
51
and
52
are made the same as those of the polarization plate
56
and the analyzer plate
57
, respectively. Between the orientation films
61
and
62
, a liquid crystal is injected.
Operation of this liquid crystal light valve is shown in
FIGS. 4A and 4B
.
In a state of
FIG. 4A
in which any voltage is not applied between both the electrodes
55
and
60
in the above described configuration, incident light
64
applied to the liquid crystal panel passes through the polarization plate
56
, becomes a linearly polarized light
65
, optically rotates along the twist of liquid crystal molecules
59
, and passes through the analyzer plate
57
as it is. This results in a bright state.
On the other hand, in a state of
FIG. 4B
in which a voltage is applied between the electrodes
55
and
60
, the liquid crystal molecules
59
are oriented vertically. Irrespective of its wavelength, therefore, the linearly polarized light
65
through the polarization plate
56
cannot pass through the analyzer plate
57
disposed perpendicular to the polarization plate
56
. As a result, the wholly black state can be implemented.
The configuration conducting the above described operation is in the bright state when no voltage is applied, and hence its operation mode is called a normally white mode. Since the wholly black state can be implemented irrespective of the light wavelength, this configuration recently tends to be adopted in many cases.
When the above descri
Nakajima Hideharu
Oohata Toyoharu
Parker Kenneth
Qi Mike
Sonnenschein Nath & Rosenthal
Sony Corporation
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