Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-07
2002-06-04
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S190000
Reexamination Certificate
active
06400439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and a process for producing the same. In particular, the present invention relates to a liquid crystal display device having excellent mechanical strength as well as sealing property without any poor display caused by a sealing material, and a process for producing the same.
2. Description of the Related Art
A liquid crystal display device comprises a pair of insulating substrates (typically, glass substrates)
101
and
102
, and a liquid crystal layer
110
as a display medium which is disposed between the substrates, as illustrated in FIG.
36
. On the glass substrate
101
, an active element (typically, thin film transistor (TFT)) which controls the electro-optical characteristics of the liquid crystal, and a scanning line and a signal line which give a gate signal and a source signal, respectively to the active element are provided. This substrate
101
is designated as a TFT substrate (or an active matrix substrate). On the glass substrate
102
, color layers
106
,
107
and
108
which constitute color filters, and a black matrix
105
which is a light-shading layer are formed. This substrate
102
is designated as a color filter substrate.
Ordinarily, the TFT substrate
101
and the color filter substrate
102
are adhered together by a sealing material
103
to form a cell. In adhering these substrates, the TFT substrate
101
and the color filter substrate
102
are adhered together by using an intra-sealing spacer
304
and a liquid crystal layer spacer
303
at a certain gap (a cell gap). The cell gap is approximately 4 &mgr;m to 6 &mgr;m and its variation is ±10% in the conventional TN-type liquid crystal display device.
The intra-sealing spacer
304
is included in the sealing material
103
. Usually, the diameter of the intra-sealing spacer is about 5 &mgr;m. The sealing materials that can be used include thermosetting resins and ultraviolet curable resins. The sealing material is coated on either the TFT substrate or the color filter substrate in the prescribed pattern by a screen printing method, a letterpress printing method or a dispenser coating method. According to each coating method, the viscosity of the sealing material is adjusted at a level optimal for the coating. The viscosity is usually adjusted by the addition of a filler (for example, silicon oxide or alumina having a particle size of 1 &mgr;m to 3 &mgr;m). The liquid crystal layer spacer
303
is sprinkled in a portion of the substrates on which the sealing material is not coated. Usually, the diameter of the liquid crystal layer spacer is also about 5 &mgr;. The liquid crystal layer spacer is sprinkled in an amount of about 100 pieces/mm
2
.
In adhering the substrates, the TFT substrate and the color filter substrate are aligned, and then a sufficient load applied so that the prescribed cell gap is retained, and heated or irradiated with ultraviolet ray at that state. The heating and ultraviolet ray irradiation conditions may be varied depending upon the hardening characteristics of the sealing material, and the load may be varied depending upon the sizes of the substrates, and the area and viscosity of the sealing material, and the like. Then, a liquid crystal material is injected into the cell from an inlet formed in a portion of the sealing material
103
by, for example, a vacuum injection method, and further the inlet is sealed by, for example, an ultraviolet curable resin. Thus, the liquid crystal-display device is completed.
Such a liquid crystal display device provides display information on the screen by selecting a display pixel arranged in a matrix shape. For example, an active matrix-type liquid crystal display device (a type using a switching element (an active element) such as TFT for each pixel electrode as a selective procedure of the display pixel) is capable of providing a high contrast display, and has been widely used for liquid crystal televisions, notebook-type personal computers, and the like. The switching element of the active matrix-type liquid crystal display device has the function of turning on and off a signal voltage applied between the pixel electrode and a transparent electrode (counter electrode) formed opposite to said pixel electrode through the liquid crystal layer, and displays an image information by the optical variation of the liquid crystal layer caused by the potential difference between the pixel electrode and the counter electrode.
A gate bus line which is a scanning line operating the pixel electrode and the switching element, and a source bus line which is a signal line for applying a signal voltage are usually formed through, for example, a silicon nitride insulating film of several hundreds to one thousand and several hundreds angstroms, and formed at a gap of several microns to ten and several microns.
A liquid crystal display device comprising an interlayer insulating film made from for example silicon nitride and having a thickness of several thousands angstroms which is formed on the gate bus line and the source bus line, and pixel electrodes further formed thereon has been proposed (e.g., Japanese Laid-open Publication No. 58-172685). According to this liquid crystal display device, since it is possible to form a pixel electrode also on each bus line, the area of the pixel electrodes can be enlarged to provide the increased light transmittance (i.e., aperture ratio) of the liquid crystal display device.
The following illustrates one example of the structure of an active matrix substrate used for this liquid crystal display device.
FIGS. 37 and 38
are a schematic plan view and a schematic cross-sectional view of the active matrix substrate, respectively. The active matrix substrate comprises a gate electrode
609
, a gate insulating film
610
, a semiconductor layer
611
, an n
+
-Si layer
612
which constitutes a source and drain electrode, a metal layer
613
which constitutes a source signal line, an interlayer insulating film
607
, and a transparent conductive layer
603
which constitutes a pixel electrode, all of which are formed in this order on a transparent insulating-substrate
608
. The pixel electrode is electrically connected to the drain electrode of the TFT through a contact hole
614
penetrating the interlayer insulating f film
607
. Since the interlayer insulating film is formed between the pixel electrode and the scanning and signal lines in the active matrix substrate illustrated in the figures, it is possible to form the pixel electrode as overlapping with the signal line.
On the effective display portion of the finished active matrix substrate, an alignment film made from a polyimide or the like is formed to provide an alignment function by a treatment such as rubbing, UV irradiation, and the like. Also, a transparent counter common electrode is formed using ITO (indium tin oxide) or the like on the counter substrate, and thereafter its effective display portion is subjected to the same treatment. A sealing material is coated on the periphery portion of the panel by a printing procedure or the like in such a manner that the panel is surrounded by the sealing material. An inlet is formed in a part of the sealing material. Moreover, a conductive material is attached to the signal input terminal for the counter electrode located on the active matrix substrate. Then, a spacer is sprinkled so as to provide a uniform cell gap of the liquid crystal layer, the liquid crystal layer and the counter electrode are aligned, and the sealing material is heated and cured. Thereafter, a liquid crystal is injected from the liquid crystal inlet which is then closed with a sealing material to complete the glass portion of the active matrix-type liquid crystal display device. Since a flat surface is obtained according to the liquid crystal display device using such an active matrix substrate, there is a benefit that the orientation disturbance of the liquid crystal molecules inside the display region can b
Fujioka Kazuyoshi
Miyamoto Kazushige
Nagata Hisashi
Narutaki Yozo
Shimada Takayuki
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