Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-01-29
2004-02-24
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S099000, C349S096000, C349S117000, C349S076000
Reexamination Certificate
active
06697134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective-type liquid crystal display (LCD) and a method for manufacturing a same and more particularly to the reflective-type LCD having a layer-stacked type ¼ wavelength plate formed by combining a ½ wavelength phase difference film with a ¼ wavelength phase difference film placed on one side opposite to another side being in contact with a liquid crystal in a facing substrate on the obverse side of a display and opposing to a thin film transistor (TFT) substrate, and to the method for manufacturing the above reflective-type LCD.
The present application claims priority of Japanese Patent Application No.2001-022485 filed on Jan. 30, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
An LCD is widely used as a display unit for a variety of information devices or a like. Such the LCD is basically configured so that a liquid crystal is sandwiched between a thin film transistor (TFT) substrate on which a TFT operating as a switching element adapted to drive the liquid crystal and which serves as a liquid crystal driving element forming substrate is formed and a facing substrate placed so as to be opposed to the TFT substrate. The LCD is broadly classified into two types, one type being a transmission-type LCD in which a desired display is achieved by observing, from a side of the facing substrate, light incident on the liquid crystal from a side of the TFT substrate and another being a reflective-type LCD in which a desired display is achieved by having light incident on the liquid crystal from the side of the facing substrate reflect on the side of the TFT substrate and by causing the light to be emitted from the side of the facing substrate.
When the transmission-type LCD is compared with the reflective-type LCD, the former is inferior, in a point of reduction in power consumption, to the latter, since the former requires a light source such as a backlight to have light enter the liquid crystal from the side of the TFT substrate and also since a ratio of the power consumption of the entire LCD to that of the light source is as large as several ten percent. Therefore, in applications in which reduction in the power consumption is required, in particular, the reflective-type LCD is mainly employed.
However, the reflective-type LCD configured without use of a polarizer on the side of the facing substrate has a shortcoming in that, an actual value of retardation of a phase difference film placed on the side of the liquid crystal or on the side of the facing substrate changes due to a shift in a viewing angle when a display is observed from the side of the facing substrate and, as a result, a yellowish glare develops on the display, causing discomfort when viewing to users.
In an attempt to solve the above problem, a reflective-type LCD is disclosed, for example, in Japanese Patent No.3095005. The disclosed reflective-type LCD includes, as shown in
FIG. 7
, a TFT substrate
101
on which a TFT (not shown) operating as a driving element to drive a liquid crystal is formed, a facing substrate
102
, and a liquid crystal
103
sandwiched between the TFT substrate
101
and the facing substrate
102
.
The TFT substrate
101
has a first transparent insulating substrate
104
made up of glass or a like, on which the TFT (not shown) is formed on the side of the liquid crystal
103
, a reflective electrode
105
formed on the side of the liquid crystal
103
on the first transparent insulating substrate
104
and operating as a pixel electrode and also serving as a reflective plate and a first oriented film
106
formed in a manner so as to cover the reflective electrode
105
and to be in contact with the liquid crystal
103
. The facing substrate
102
includes a second transparent insulating substrate
108
made up of glass or a like, a polarizer
109
formed on a side opposite to a side being in contact with the liquid crystal
103
on the second transparent insulating substrate
108
, a layer-stacked type ¼ wavelength plate
110
formed between the polarizer
109
and the second transparent insulating substrate
108
and constructed by combining a ½ wavelength phase difference film
111
with a ¼ wavelength phase difference film
112
, both being made from a polycarbonate polymer or a polysulfone polymer, a common electrode
113
on a side of the liquid crystal
103
on the second transparent insulating substrate
108
, and a second oriented film
114
formed in a manner so as to cover the common electrode
113
and to be in contact with the liquid crystal
103
. Moreover, as the liquid crystal
103
, a Twisted Nematic (TN) type liquid crystal is used.
Here, a twisted direction of the liquid crystal
103
occurring when the liquid crystal
103
is traced from the side of the facing substrate
102
to the side of the TFT substrate
101
relative to an oriented direction on the side of the facing substrate
102
on the liquid crystal
103
is defined as being “positive”, the polarizer
109
is formed so that an angle “&agr;” formed by its polarized light absorbing axis and by the oriented direction is set to be within a range of 5 degrees to 35 degrees, the ½ wavelength phase difference film
111
is placed so that an angle “&bgr;” formed by its optical axis and by the oriented direction is set to be within a range of −15 degrees to 15 degrees and the ¼ wavelength phase difference film
112
is placed so that an angle “&ggr;” formed by its optical axis and by the oriented direction is set to be within a range of −75 degrees to −45 degrees (refer to FIG.
2
). Moreover, a twisted angle of the liquid crystal
103
employed in the example is set to be within a range of 66 degrees to 74 degrees and a product “&Dgr; nd” of a refractive index anisotropy (angle) of the liquid crystal
103
and a thickness of a layer of the liquid crystal
103
is set to be within a range of 0.21 &mgr;m to 0.31 &mgr;m.
In the conventional reflective-type LCD having configurations described above, since a change in retardation caused by a shift in a viewing angle of the liquid crystal
103
and a change in retardation caused by a shift in viewing angles of the phase difference films
111
and
112
can totally cancel each other out, development of unwanted colors on a display due to the change in the viewing angle can be resolved.
However, the conventional reflective-type LCD has another problem. That is, since the conventional reflective-type LCD uses, as the phase difference film to be formed on the side of the facing substrate
102
, a material exhibiting great wavelength dispersion in anisotropy of the refractive index in a visible light region, other colors develop at the same time when a black color is displayed. In the conventional reflective-type LCD, a polycarbonate polymer or polysulfone polymer is used as the ½ wavelength phase difference film
111
and as the ¼ wavelength phase difference film
112
both making up the layer stacked-type ¼ wavelength plate
110
placed on a side opposite to a side being in contact with the liquid crystal
103
in the facing substrate
102
, however, since these materials exhibit great wavelength dispersion in anisotropy of the refractive index, other colors develop at the same time when a black color is displayed.
FIG. 3
is a diagram explaining the wavelength dispersion in anisotropy of the refractive index occurring when the ½ wavelength phase difference film
111
and ¼ wavelength phase difference film
112
both being made from the polycarbonate polymer are used in the conventional reflective-type LCD, in which a ratio of the wavelength dispersion is plotted as ordinate and a wavelength of light in a visible range as abscissa. The degree of the wavelength dispersion is indicated by a ratio of the refractive index anisotropy “&Dgr; n (&lgr;)” in an arbitrary wavelength “&lgr;” to a refractive index anisotropy “&Dgr; n (550)” in a refere
Inoue Daisuke
Watanabe Takahiko
Duong Thoi V.
Kim Robert H.
McGinn & Gibb PLLC
NEC LCD Technologies Ltd.
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