Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-16
2004-02-03
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000
Reexamination Certificate
active
06686981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection type liquid crystal display.
2. Description of the Prior Art
A number of reflection type liquid crystal displays that create a recognizable image by reflecting incident light originating from the observer's side have been proposed.
FIG. 1
is a sectional view of a conventional reflection type liquid crystal display.
As shown in
FIG. 1
, such a conventional reflection type liquid crystal display includes gate electrodes
11
made of a refractory metal, such as chromium (Cr) or molybdenum (Mo), a gate insulating film
12
, and active layers
13
made of polysilicon formed successively on an insulating substrate of quartz glass or non-alkali glass or the like.
Each active layer
13
includes channels
13
c
formed above the gate electrodes
11
, and a source
13
s
and a drain
13
d
that are formed on both sides of the channels
13
c
by ion implantation using stopper insulating films
14
on the channels
13
c
as masks.
An inter-layer insulating film
15
, which includes a SiO
2
film, a SiN film and a SiO
2
film deposited in succession, is formed over the entire surfaces of the gate insulating film
12
, the active layer
13
and the stopper insulating films
14
. A drain electrode
16
is formed by filling a contact hole, which is formed to correspond to the drain
13
d
, with a metal, such as Al. Then, a planarization insulating film
17
, which consists of an organic resin, for example and serves to flatten the surface, is formed over the entire surface. A contact hole is formed at a location of the planarization insulating film corresponding to the source
13
s
. A display electrode
19
as a transparent electrode, which consists of ITO (Indium Thin Oxide) in contact with the source
13
s
through this contact hole and serves also as the source electrode
18
, is formed on the planarization insulating film
17
. An alignment film
20
consisting of an organic resin, such as polyimide, and aligns liquid crystal elements
21
, is formed on the display electrode
19
.
A polarizer
40
and a reflector
42
to reflect incident light are arranged on the surface of an insulating substrate having TFTs fabricated as described (a TFT substrate)
10
which is opposite the surface where there is the TFT.
On the side of a counter electrode substrate
30
facing the TFT substrate
10
, are provided a color filter
31
including primary colors, red (R), green (G), and blue (B) and a black matrix
32
with a function to shield light; a protective film
33
of a resin formed on the color filter
31
; and a counter electrode
34
and an alignment film
35
formed over the entire surface of the protective film
33
. On the side not facing the insulating substrate
10
, a polarizer
41
is located. The insulating substrate
10
and the counter electrode substrate
30
are bonded together with their peripheries sealed with a sealing bond, thus forming a space inside, and this space is filled with a twisted nematic (TN) liquid crystal
21
with positive dielectric constant anisotropy.
The propagation of light when a user views reflection type liquid crystal display as above is described below with reference to FIG.
1
.
As indicated by a broken line with an arrow, an external light
100
, such as natural light, coming from outside enters from the polarizer
40
on the side of an observer
101
, and passes through the counter electrode substrate
30
, the color filter
31
, the protective film
33
, the counter electrode
34
, the alignment film
35
, the TN liquid crystal
21
, the alignment film
20
on the TFT substrate
10
, the display electrode
19
, the planarization insulating film
17
, the inter-layer insulating film
15
, the gate insulating film
12
, the glass substrate
10
and the polarizer
40
. The light is reflected by the reflector
42
, goes through the layers in a direction opposite to the direction of incidence, emerges from the polarizer
41
of the counter electrode substrate
30
and enters the eyes of the observer.
However, after the incident light
100
passes through the display electrode
19
a
and is reflected by the reflector
42
, the reflected light passes between the display electrode
19
a
and the display electrode
19
b
and enters the observer's eyes. More specifically, the fact that the reflected light does not enter to the display electrode
19
a
gives rise to parallax, and the observer is unable to see an intrinsic image of the display electrode
19
a
, but rather a disparity. This is a disadvantage.
When a color display is viewed through a color filter as shown in
FIG. 1
, instead of the proper color of the display electrode, a color disparity due to parallax is viewed.
Another drawback of the conventional reflection type liquid display is that the use of TN liquid crystal results in a very narrow viewing angle for both display and observation.
SUMMARY OF THE INVENTION
The present invention has been made to rectify the disadvantages described above and has as its object to provide a reflection type liquid crystal display that offers display without parallax and a wider angle of view.
According to one aspect of the present invention, there is provided a reflection type liquid crystal display, which comprises first and second substrates disposed facing each other and holding a liquid crystal exhibiting a negative dielectric constant anisotropy therebetween; a switching element, a reflective display electrode formed of a conductive reflective material and connected to the switching element, and an alignment film to align the liquid crystal molecules, disposed on the side of the surface of a first substrate facing the second substrate; a counter electrode having an alignment control window for controlling the alignment of the liquid crystal molecules and an alignment film, disposed on the side of a second substrate facing the first substrate; and a phase plate and a polarizer disposed on the side of the second substrate not facing the first substrate.
According to another aspect of the present invention, the reflection type liquid crystal display comprises first and second substrates disposed facing each other and holding therebetween a liquid crystal exhibiting a negative dielectric constant anisotropy; a switching element, a reflective display electrode formed of a conductive reflective material and connected to the switching element, and an alignment film to align the liquid crystal molecules, disposed on the side of the surface of a first substrate facing the second substrate; a counter electrode having an alignment control window for controlling the alignment of the liquid crystal molecules and an alignment film, disposed on the side of a second substrate facing the first substrate; and a phase plate and a polarizer on the side of the second substrate not facing the first substrate, wherein the side of the second substrate not facing the first substrate is viewing side of the display.
According to yet another aspect of the present invention, a light diffusing layer is formed on either one of the sides of the second substrate which faces or does not face the first substrate.
As mentioned above, according to the present invention, the adoption of the reflective display electrodes more effectively reduces the occurrence of parallax by thickness of glass, for example, than when the reflector was provided on the outer side of the TFT substrate.
By the use of a liquid crystal with a negative dielectric constant anisotropy and by the provision of the alignment control windows, it becomes possible to produce a reflection type display with a wider viewing angle for observation from any direction—from above or below or left or right. The addition of the diffusing layer ensures the diffusion of an incident light into the display device or an emerging light from it, so that a bright screen image can be obtained in any direction.
A polarizer used to be mounted in each substrate, but according to the present invention, only one polarizer is mounted. The
Noritake Kazuto
Ogawa Shinji
Cantor & Colburn LLP
Parker Kenneth
Sanyo Electric Co,. Ltd.
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