Active matrix liquid crystal display apparatus

Details Active matrix liquid crystal display apparatus Active matrix liquid crystal display apparatus

1999-07-14

2004-12-14

Wu, Shean C (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299010, C428S001300

Reexamination Certificate

active

06830787

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display apparatus, in which an electric field is applied, mainly parallel to the substrates, and in which a broad visual field and a large numerical aperture are realized.
In a conventional liquid crystal display apparatus, the electrodes for driving the liquid crystal layer are formed on the surface of two substrates, and transparent electrodes are used, the electrodes facing each other. This is because what is used is a twisted nematic display method (TN method) in which the liquid crystal layer is driven by applying an electric field in a direction vertical to the surface of the substrate. On the other hand, a display method in which an electric field is applied in a direction almost parallel to the surface of the substrate using comb-type electrodes has been disclosed in the Japanese Patent publication No. 63-21907 (1988) and U.S. Pat. No. 4,345,249. In this case, the electrodes are not necessarily selected to be transparent, but non-transparent and metallic electrodes with a higher electric conductivity are used. However, in the above-mentioned prior art, for the display method in which the electric field is applied in a direction substantially parallel to the surface of the electrode, which is designated as a “horizontal electric field method”, specifically used in the active matrix drive mode, the material property required to realize a high numerical aperture is not described in detail.
In the conventional active matrix type liquid crystal display apparatus, typically using the twisted nematic method, a transparent electrode is used. It is, therefore, possible to make the numerical aperture relatively wide, which is the area that the light per unit pixel passes through. However, in the horizontal electric field method, an opaque metal electrode is used. It is, therefore, impossible to realize a large numerical aperture. In this regard, there is an essential problem in that the opaque portion of the electrode can not be used as part of the area that light passes through. Further, the brightness of the display apparatus also depends upon the magnitude of the numerical aperture. Even if the intensity of the background light is increased in an effort to alleviate this problem, the problem arises that the power consumption is increased extremely.
Accordingly, in order to realize a large numerical aperture when employing the horizontal electric field method, it is necessary to enlarge the gap between the electrodes. However a new problem arises due to the enlargement of the gap. First, a disturbance of the orientation occurs due to static electricity, because the volume of the liquid crystal decreases further. Generally, the electrode in the horizontal electric field method is different in configuration from the one in the other type. Therefore, the volume of the liquid crystal is not so large. If the volume becomes smaller by enlarging the gap between the electrodes, the liquid crystal is susceptible to the effects of static electricity. As a result, the disturbance of the orientation due to static electricity increases. Secondly, if the gap between the electrodes becomes large, a problem arises in that the display method driven by the electric field requires a large drive voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an active matrix type liquid crystal display apparatus using the horizontal electric field method, in which a broad visual field and a large numerical aperture are realized.
In the present invention, the following features are used for solving the above mentioned problems and attaining the above objective.
According to a first aspect of the present invention; the present invention comprises a pair of substrates, at least one of which is transparent; a liquid crystal layer inserted between the substrates; an orientation film provided between the liquid crystal layer and at least one of the pair of substrates and on an inner side of said at least one substrate; a scanning signal electrode, an image signal electrode, a pixel electrode and an active device, each provided between the liquid crystal layer and the at least one substrate; and polarization means provided on the outer side of the substrates, for changing a optical characteristic according to an orientation state of the liquid crystal; each of said electrodes being constructed so as to apply an electric field, mainly parallel to said substrates, against said liquid crystal layer, and being connected to an external control means for controlling optionally the applied electric field according to the display pattern; wherein said electrode lies between at least two dielectric layers disposed above and below the electrode, and wherein the resistivity of said liquid crystal is higher than or equal to 1×10
9
&OHgr;.cm and lower than or equal to 1×10
13
&OHgr;.cm.
According to a second aspect of the present invention, the present invention comprises a pair of substrates, at least one of which is transparent; a liquid crystal layer inserted between the substrates; an orientation film provided between the liquid crystal and at least one of the pair of substrates and on an inner side of said at least one substrate; a scanning signal electrode, an image signal electrode, a pixel electrode and an active device, each provided between the liquid crystal layer and the at least one substrate; and polarization means provided on the outer side of the substrates, for changing a optical characteristic according to an orientation state of the liquid crystal; each of said electrodes being constructed so as to apply an electric field, mainly parallel to said substrates, against said liquid crystal layer, and being connected to an external control means for controlling optionally the applied electric field according to the display pattern; wherein a ratio 1/d of a gap 1 between said electrodes to a cell gap d is greater than or equal to 2.0, and the relation between an elasticity constant K
2
and a dielectric anisotropy be satisfies the following equation (1):
K
2
/&Dgr;&Dgr;&egr;<9.0×10
−8
[dyn],  (1).
According to a third aspect of the present invention, in the arrangement of the second aspect, the gap between the substrates facing each other is made to be less than or equal to 6 mm, the gap between the electrodes is made to be more than or equal to 10 mm, and the drive voltage is made to be lower than or equal to 5V.
According to a fourth aspect of the present invention, in the arrangement of the first and second aspects, the liquid crystal composite material is made to include a liquid crystal chemical compound represented by a general chemical formula (I), in which a cyano group, trifluoromethyl group, trifluoromethoxyl group or nitro group is included as an end group:
(In the formula (I), X
1
, X
2
and X
3
are a fluoro group, cyano group, trifluoromethyl group, trifluoromethoxyl group, nitro group or hydrogen atom; R is an alkyl group or alkoxyl group having a carbon number 1 to 10 which can be substituted; Ring A is a cyclohexane ring, benzene ring, dioxane ring, pyrimidine ring, or [2,2,2]-bicyclohexane ring; Z is a single bonding, ester bonding, ether bonding, or methylene; or ethylene; and n is an integer, 1 or 2.)
According to a fifth aspect of the present invention, in the arrangement of the first and second aspects, the liquid crystal composite material is made to include a liquid crystal chemical compound represented by a general chemical formula (II), in which a cyano group, trifluoromethyl group, trifluoromethoxyl group, or nitro group is included in a transverse axis of the molecule of the liquid crystal chemical compound:
(In the formula (II), X
1
and X
2
are a fluoro group, cyano group, trifluoromethyl group, trifluoromethoxyl group, nitro group or hydrogen atom; R is an alkyl group or alkoxyl group having a carbon number 1 to 10 which can be substituted; Ring A is a cyclohexane ring, benzene ring, dioxane ring,

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