Liquid crystal display device

Details Liquid crystal display device Liquid crystal display device

1999-10-14

2002-01-22

Ton, Toan (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S180000, C349S181000

Reexamination Certificate

active

06341002

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a reflection/transmission type liquid crystal display device capable of performing a display both in a reflection mode and a transmission mode.
2. Description of the Related Art
Conventionally, there have been a reflection type liquid crystal display device utilizing ambient light, a transmission type liquid crystal display device utilizing backlight, and a semi-transmission type liquid crystal display device equipped with a half mirror and a backlight.
In a reflection type liquid crystal display device, a display becomes less visible under dim environment, whereas in a transmission type liquid crystal display device, a display becomes hazy under strong ambient light (e.g., under outdoor sunlight). As a liquid crystal display device capable of functioning in both modes so as to perform a satisfactory display under any environment, a semi-transmission type liquid crystal display device is disclosed by Japanese Laid-Open Publication No. 7-333598.
However, the above-mentioned conventional semi-transmission type liquid crystal display device has the following problems.
The conventional semi-transmission type liquid crystal display device uses a half mirror in place of a reflective plate used in a reflection type liquid crystal display device, and has a minute transmission region (e.g., minute holes in a metal thin film) in a reflection region, thereby performing a display by utilizing transmitted light as well as reflected light. Since reflected light and transmitted light used for a display pass through the same liquid crystal layer, an optical path of reflected light becomes twice that of transmitted light, which causes a large difference in retardation of the liquid crystal layer with respect to reflected light and transmitted light. Thus, a satisfactory display cannot be obtained. Furthermore, a display in a reflection mode and a display in a transmission mode are superimposed on each other, so that the respective displays cannot be separately optimized. This results in difficulty in performing a color display, and causes a blurred display.
SUMMARY OF THE INVENTION
A liquid crystal display device according to the present invention, includes: a first substrate, a second substrate, a liquid crystal layer interposed between the first substrate and the second substrate, and a plurality of pixel regions defined by a pair of electrodes for applying a voltage to the liquid crystal layer, wherein each of the plurality of pixel regions includes a reflection region and a transmission region, and the liquid crystal layer is made of a liquid crystal material having positive dielectric anisotropy, the device further including: a first polarizing element provided on the first substrate opposite to the liquid crystal layer; a second polarizing element provided on the second substrate opposite to the liquid crystal layer; a first phase difference compensator provided between the first polarizing element and the liquid crystal layer; and a second phase difference compensator provided between the second polarizing element and the liquid crystal layer, a twist angle &thgr;
t
of the liquid crystal layer being in a range of 0° to 90°, wherein retardation Rd and the twist angle &thgr;
t
in a visible light region of the liquid crystal layer in the reflection region are in ranges within curves respectively represented by the following Formulae (1) and (2), and Formulae (3) and (4), in ranges within curves respectively represented by the following Formulae (5) and (6) and Formulae (7) and (8) at the twist angle &thgr;
t
in a range of 0°≦&thgr;
t
≦54.3°, and in ranges within curves respectively represented by the following Formulae (5) and (8) at the twist angle &thgr;
t
in a range of 54.3°<&thgr;
t
≦90°, and wherein the retardation Rd and the twist angle &thgr;
t
in a visible light region of the liquid crystal layer in the transmission region are in ranges within curves respectively represented by the following Formulae (9) and (10) and Formulae (11) and (12):
Rd=−0.0043·&thgr;
t
2
−0.065·&thgr;
t
+1011.8  (1)
Rd=−0.0089·&thgr;
t
2
+0.1379·&thgr;
t
+914.68  (2)
Rd=−0.0015·&thgr;
t
2
−0.1612·&thgr;
t
+737.29  (3)
Rd=−0.0064·&thgr;
t
2
−0.0043·&thgr;
t
+640.65  (4)
Rd=−0.0178·&thgr;
t
2
+0.2219·&thgr;
t
+458.92  (5)
Rd=−0.0405·&thgr;
t
2
+0.4045·&thgr;
t
+364.05  (6)
Rd=0.0347·&thgr;
t
2
−0.4161·&thgr;
t
+186.53  (7)
Rd=0.0098·&thgr;
t
2
−0.1912·&thgr;
t
+89.873  (8)
 Rd=−0.0043·&thgr;
t
2
−0.065·&thgr;
t
+995.66  (9)
Rd=−0.0058·&thgr;
t
2
−0.0202·&thgr;
t
+665.8  (10)
Rd=−0.0248·&thgr;
t
2
+0.6307·&thgr;
t
+439.58  (11)
Rd=0.0181·&thgr;
t
2
−0.6662·&thgr;
t
+109.51  (12)
In one embodiment of the present invention, the retardation Rd is in a range within the curves respectively represented by Formulae (7) and (8) at the twist angle &thgr;
t
in the reflection region in a range of 0°≦&thgr;
t
≦54.3°, and in a range within the curves respectively represented by Formulae (5) and (8) at the twist angle &thgr;
t
in the reflection region in a range of 54.3°<&thgr;
t
≦90°, and the retardation is in a range within the curves respectively represented by Formulae (11) and (12) at the twist angle &thgr;
t
in the transmission region in a range of 0°≦&thgr;
t
≦90°.
In another embodiment of the present invention, the reflection region and the transmission region include a liquid crystal layer made of the same liquid crystal material, and a thickness of the liquid crystal layer in the reflection region is smaller than a thickness of the liquid crystal layer in the transmission region.
In another embodiment of the present invention, the first phase difference compensator has a first phase difference plate, the twist angle &thgr;
t
of the liquid crystal layer is 0°, the retardation Rd of the reflection region is 90 nm≦Rd≦187 nm, the retardation Rd of the transmission region is 110 nm≦Rd≦440 nm, and the retardation Rd of the first phase difference plate is 30 nm≦Rd≦250 nm.
In another embodiment of the present invention, the first phase difference compensator further has a second phase difference plate, and the retardation Rd of the second phase difference plate is in a range of 220 nm≦Rd≦330 nm.
In another embodiment of the present invention, the second phase difference compensator has a third phase difference plate, and the retardation Rd of the third phase difference plate is in a range of 120≦Rd≦150 nm.
In another embodiment of the present invention, the second phase difference compensator further has a fourth phase difference plate, and the retardation Rd of the fourth phase difference plate is in a range of 240≦Rd≦310 nm.
Hereinafter, the function of the present invention will be described. First, the terms used herein will be described. In a reflection/transmission liquid crystal display device, a region where a display is performed by using transmitted light is referred to as a transmission region, and a region where a display is performed by using reflected light is referred to as a reflection region. The transmission region and the reflection region respectively include a transparent electrode region and a reflective electrode region formed on a substrate and a liquid crystal layer interposed between a pair of substrates. The transparent electrode region and the reflective electrode region on the substrate respectively define two-dimensional areas of the reflection region and the transmission region. The transparent electrode region is typically defined by a transparent electrode. The reflective electrode region is

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