Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-03-19
2002-04-16
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S113000, C349S044000
Reexamination Certificate
active
06373540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reflective guest-host-liquid-crystal display devices, and in particular, to techniques for improving efficiency of the use of incident light by using a quarter-wavelength-plate layer and a light-reflection layer, both built into a reflective guest-host-liquid-crystal display device. In more particular, the present invention relates to the structure of a black matrix for shielding light in the peripheries of pixels.
2. Description of the Related Art
A reflective guest-host-liquid-crystal display device including a quarter-wavelength-plate and a light-reflection layer is disclosed in, for example, Japanese Unexamined Patent Publication No. 6-222351, and its section view is shown in FIG.
4
. The reflective guest-host-liquid-crystal display device
101
includes a pair of upper and lower substrate
102
and
103
, guest-host liquid crystal
104
, a dichroic dye
105
, a pair of upper and lower transparent electrodes
106
and
110
, a pair of upper and lower alignment layers
107
and
111
, a light-reflection layer
108
, and a quarter-wavelength-plate layer
109
. The pair of substrates
102
and
103
is composed of insulating material such as glass, quartz or plastic. At least, the upper substrate
102
is transparent. The guest-host liquid crystal
104
, which includes the dichroic dye
105
, is held between the pair of substrates
102
and
103
. The guest-host liquid crystal
104
includes nematic liquid crystal molecules
104
a.
The dichroic dye
105
is so-called “p-type dye” having transition dipole moments almost parallel to the major axes of its molecules. On the inner surface
102
a
of the upper substrate
102
are formed switching devices (not shown). The transparent substrates
106
are patterned in a matrix to form pixel electrodes, which are driven by the corresponding switching devices. The outer surface of the upper substrate
102
is coated with the alignment layer
107
, which is composed of polyimide resin. The surface of the alignment layer
107
is processed, for example, by rubbing, and horizontally aligns the nematic liquid crystal molecules
104
a.
In addition, the light-reflection layer
108
, which is composed of aluminum, and the quarter-wavelength-plate layer
109
, which is composed of high-molecular liquid crystal, are formed in the order given on the surface
103
a
of the lower substrate
103
. The transparent electrodes
110
and the alignment layer
111
are formed in the order given on the quarter-wavelength-plate layer
109
.
Subsequently, the operation of the reflective guest-host-liquid-crystal display device
101
when performing monochrome display will be briefly described.
When no voltage is applied, the nematic liquid crystal molecules
104
a
align horizontally, and the dichroic dye
105
aligns similarly. When light incident from the upper substrate
102
travels into the guest-host liquid crystal
104
, components of the incident light having an oscillating plane parallel to the major axes of the molecules of the dichroic dye
105
are absorbed by the dichroic dye
105
. Other components having an oscillating plane vertical to the major axes of the molecules of the dichroic dye
105
pass through the guest-host liquid crystal
104
, and are circularly polarized by the quarter-wavelength-plate layer
109
formed over the inner surface
103
a
of the lower substrate
103
. The circularly polarized components are reflected by the light-reflection layer
108
. At this time, the reflected light is polarized in the reverse direction, and passes through the quarter-wavelength-plate layer
109
again to form components having a polarizing plane parallel to the major axes of the molecules of the dichroic dye
105
. The formed components are absorbed in the dichroic dye
105
, which generates almost completely black display.
In addition, when a voltage is applied, the nematic liquid crystal molecules
104
a
align vertically along the direction of the electric field, and the dichroic dye
105
aligns similarly. Light incident from the upper substrate
104
passes through the guest-host liquid crystal
104
without being absorbed in the dichroic dye
105
, and is reflected by the light-reflection layer
108
without being substantially affected by the quarter-wavelength-plate layer
109
. The reflected light passes through the quarter-wavelength-plate layer
109
again to be emergent without being absorbed in the guest-host liquid crystal
104
, which generates white display.
According to the conventional structure shown in
FIG. 4
, the switching devices for driving the pixels are formed on the emergent-side substrate. The switching devices consist of thin film transistors. The switching devices shield the incident light, which reduces the aperture ratio of the pixels by the amount of the shielding. To cope with this point, there has been developed a structure in which switching devices are formed on the reflection-side substrate, whose example is shown in FIG.
5
. As shown in
FIG. 5
, an upper substrate
201
has a counter electrode
203
a
totally formed thereon, which consists of a transparent electrode, and a lower substrate
202
has pixel electrodes
204
a
consisting of a matrix of segmented reflector electrodes. In other words, this example is an active matrix type. On the outer surface of the lower substrate
202
, the pixel electrodes
204
a,
which are patterned in a matrix, and the thin film transistors (TFTs) corresponding thereto are formed. The TFTs are used as switching devices for respectively driving the pixel electrodes
204
a.
In other words, by selectively switching the TFTs, a signal voltage can be written into the corresponding TFTs. The drain region D of each TFT is connected to the pixel electrode
204
a.
The source region S thereof is connected to a signal interconnection
221
. The gate electrode G thereof is connected to a gate interconnection. An auxiliary capacitor Cs is formed to correspond to each pixel electrode
204
a.
The pixel electrode
204
a
is electrically separated by a planarizing layer
222
from the TFT, the auxiliary capacitor Cs and the signal interconnection
221
. On the outer surface of the upper substrate
201
is totally formed the counter electrode
203
a.
An electro-optical material
205
is held between both substrates
201
and
202
, which are opposed, with a predetermined gap provided therebetween. The electro-optical material
205
has a layered structure including guest-host liquid crystal
206
and a quarter-wavelength-plate layer
207
. The guest-host liquid crystal
206
contains nematic liquid crystal molecules
209
and dichroic dye
208
, and are horizontally aligned by upper and lower alignment layers
210
and
211
. The quarter-wavelength-plate layer
207
is formed along the pixel electrode
204
a.
Writing the signal voltage to the pixel electrode
204
a
generates an electric field between it and the opposing counter electrode
203
a,
which changes the guest-host liquid crystal
206
between its absorbing condition and its transparent condition. This optical change is generated for each pixel electrode, which enables the displaying of the desired image. Below the pixel electrode
204
a
are positioned the TFT, the auxiliary capacitor Cs and the signal interconnection
221
. There are not these component parts in the incident optical path, which does not affect the pixel aperture ratio. In other words, the area of the pixel electrode
204
a
can be totally used as the pixel aperture, which enables bright display.
The above-described reflective guest-host-liquid-crystal display device uses exterior light like natural light without using a backlight for back lighting. Thus, in order to obtain the bright image, the aperture ratio of pixels needs to be increased. Concerning this point, the structure shown in
FIG. 5
enables a sufficient pixel aperture ratio, as described above. In addition, when color display is performed in the structure shown in
FIG. 5
, three-primary-color fil
Qi Mike
Sikes William L.
Sonnenschein Nath & Rosenthal
Sony Corporation
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