Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-05
2003-07-15
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S138000, C349S187000, C430S020000
Reexamination Certificate
active
06593983
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display substrate and a fabricating method thereof and a liquid crystal display, in particular to a reflection type liquid crystal display which can realize a low consumption electric power by reflecting an external light and displaying images and a liquid crystal display substrate used therefor and a fabricating method thereof.
2. Description of the Related Art
Among reflection type displays using a light valve for a light modulation, a projection type display using a liquid crystal light valve what is so called a liquid crystal projector can display a very high definition and a large image display, thereby having a possibility to replace CRTs in near future. The projection type display displays images using a transmission type or reflection type liquid crystal light valve. Among them, the conventional reflection type liquid crystal display described in Japanese Laid-open Patent Application No. 8-248425 and the U.S. counterpart Pat. No. 5,739,890 is described with reference to FIG.
9
.
FIG. 9
shows a schematic cross sectional view of the conventional reflection type liquid crystal light valve. A transistor
104
, a detailed picture thereof is omitted, is formed on a silicon substrate
100
. A silicon oxide film
102
is formed on the silicon substrate
100
and the transistor
104
, and a reflection preventing film
106
using titanium nitride (TiN) is formed on the silicon oxide film
102
.
A metal layer
111
is formed on the reflection preventing film
106
as an inter-wire layer via the silicon oxide film
108
. A silicon oxide film
102
′ is formed on the metal layer
111
as the first insulating film and a reflection preventing film
106
′ using TiN is formed on the silicon oxide film
102
′. A silicon oxide film
108
′ is formed on the reflection preventing film
106
′ as the second insulating film and a display electrode
112
which is made of aluminum (Al) and also functions as a light reflecting film is formed thereon.
The display electrode
112
is connected to the metal layer
111
by a connecting conductor
110
′ working as a plug electrode, for example, made of tungsten (W) and embedded in a through-hole formed at the silicon oxide film
102
′ and silicon oxide film
108
′. Further, the metal layer
111
is connected to a source electrode (not shown) of the transistor
104
by a connecting conductor
110
of tungsten embedded in a through-hole formed at the silicon oxide film
102
and silicon oxide film
108
. An Al layer is not formed between the adjacent display electrodes
112
, and the reflection preventing film
106
′ is arranged at least at a lower layer between the display electrodes
112
. A glass substrate
116
as an opposing substrate is arranged via a spacer not shown. An opposing electrode
114
is formed on the whole surface of the display electrode
112
side of the glass substrate
116
. Furthermore, a liquid crystal
120
is sealed between the opposing electrode
114
and the display electrode
112
at a predetermined cell gap.
The transistor
104
is a FET (field effect transistor) in which, other than the source electrode, a drain electrode connected to data lines and a gate electrode (these are not shown) connected to scanning lines are formed, and the transistor
104
functions as a switching element which applies a voltage applied to data lines when a gate is in the ON state to the display electrode
112
.
By changing a transmissivity of the light by changing the direction of liquid crystal molecules
122
in response to a voltage applied between the display electrode
112
and the opposing electrode
114
when the transistor
114
is ON, an incident light from the glass substrate
116
side is reflected by the display electrode
112
and then re-emits from the glass substrate
116
or the light is prevented from reaching to the display electrode
112
, thereby a gradation display being performed.
In
FIG. 9
, though a connection between the display electrode
112
and a source electrode (not shown) of the transistor
104
is made by a drawing-around of the metal layer or the like as a inter-wire layer, an arrangement of this inter-wire layer is not required as long as the relationship of arrangement of the connection between the transistor
104
and the light reflection film
112
coincides.
Further, the silicon oxide films
102
,
102
′,
108
′ and the like which are interlayer insulating films are HDP films formed by a high density plasma (HDP) CVD method and their upper surfaces are performed a planarization process by a polishing process such as a CMP (Chemical Mechanical Polishing) method thereon. In the reflection type liquid crystal display, the planarization of the interlayer insulating film which is a lower layer of the display electrode
112
is important and the surface of the display electrode
112
can be planarized by the planarization of the interlayer insulating film, thereby improving the reflectance of the external light.
Further, the conventional reflection type liquid crystal display shown in
FIG. 9
uses TiN as a forming material for the reflection preventing films
106
and
106
′. Since TiN has a light absorption function, TiN can prevent the generation of deterioration of the color tone and the like which occurs due to the reflection of the incident light from the gap between the display electrodes
112
. It should be noted that in case of the conventional reflection type liquid crystal display, the reflection preventing film
106
is also arranged between the display electrode
112
and the inter-wire layer other than the gap between the display electrodes
112
.
In the meantime, TiN used as the forming material for the reflection preventing films
106
and
106
′ has a conductivity. Therefore, when the contact holes which connect between the display electrode
112
and the metal layer
111
and between the metal layer
111
and the transistor
104
are directly formed at the reflection preventing films
106
and
106
′, TiN which is the forming material for the reflection preventing films
106
and
106
′ exposes on the inner faces of the contact holes, so the embedding of the contact holes by the connecting conductors
110
and
110
′ results in a problem for shortage of all display electrodes.
Therefore, opening the windows having a diameter larger than a diameter of the contact holes at predetermined positions of the reflection preventing films
106
and
106
′, the contact holes are formed in the windows so that the contact holes do not contact to the rims of the windows. For this reason, a patterning for forming the windows at the reflection preventing films
106
and
106
′ are required. Further, with respect to the formation of the contact holes, an alignment is required so that the contact holes do not contact with the rims of the windows formed to the reflection preventing films
106
and
106
′. At this time, when the windows with the larger diameter are formed at the reflection preventing films
106
and
106
′ having an alignment margin to assure the insulation between the connecting conductors
110
and
110
′ and the reflection preventing films
106
and
106
′, the gap between the display electrodes
112
overlaps the windows of the reflection preventing films
106
and
106
′, thereby causing a problem that the incident light from the gap between the display electrodes
112
can not be absorbed at the reflection preventing films
106
and
106
′.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display substrate and a fabricating method thereof and a liquid crystal display which can prevent a color tone of a reflection light and the like from deterioration by surely absorbing an incident light from a gap between display electrodes.
The above object is achieved by a fabricating method of a liquid crystal disp
Ohashi Makoto
Okuda Shoji
Chowdhury Tarifur R.
Fujitsu Limited
Greer Burns & Crain Ltd.
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