Liquid crystal display and manufacture thereof with...

Details Liquid crystal display and manufacture thereof with... Liquid crystal display and manufacture thereof with...

2000-10-18

2003-10-28

Kim, Robert H. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S187000

Reexamination Certificate

active

06639644

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for producing a liquid crystal display device and to a liquid crystal display device.
BACKGROUND ART
Liquid crystal display devices are widely used in personal computers, portable electronic apparatus and the like. Generally, a liquid crystal display device comprises, as shown in
FIG. 36
, a liquid crystal layer
7
sandwiched between two substrates
1
, on which color filters
4
, a black matrix
5
, transparent electrodes
3
, an alignment layer
9
and so on are formed.
A TFT (thin film transistor) type liquid display device, as shown in
FIG. 37
, comprises a liquid crystal layer
7
sandwiched between a substrate
1
a
, which comprises a glass substrate
1
with transparent electrodes
3
, color filters
4
, a conductive black matrix
5
, an overcoat layer
6
, an alignment layer
9
and so on formed thereon, and a substrate
1
b
, which comprises a glass substrate
1
with transparent electrodes
3
each comprising a source electrode
14
a
, a drain electrode
14
and so on, insulating films
23
, semiconductor films
16
, gate electrodes
13
, an alignment layer
9
and so on formed thereon.
In these liquid crystal display devices, it is spacers that regulate the distance between the two substrates and maintain the thickness of the liquid crystal layer at an appropriate level.
According to the prior art methods of liquid crystal display device production, spacers are sprayed and dispersed randomly but uniformly over the substrate on which pixel electrodes are formed. Therefore, as shown in FIG.
36
and FIG.
37
, spacers are disposed also at the sites of some pixel electrodes, namely at some display sites of the liquid crystal display device. Spacers are generally made of a synthetic resin, glass or a like material and, when a spacer is disposed on a pixel electrode, its depolarizing action causes light leakage at the spacer site. Further, the liquid crystal alignment is disturbed on the spacer surface, causing a bright defect, hence the contrast and color tone are decreased and the display quality is deteriorated.
To solve such problems as mentioned above, spacers should be disposed only in spaces among neighboring electrodes, which are not display sites, namely only at sites covered by the black matrix, which is a light shield layer. The black matrix is provided for the purpose of improving the contrast of display of a liquid crystal display device or, in the case of a TFT type liquid crystal display device, for the purpose of preventing error operation of elements due to external light.
A technology of disposing spacers at sites corresponding to the black matrix, namely at sites other than display pixel sites, of a TFT type liquid crystal display device is disclosed in Japanese Kokai Publication Hei-04-256925 which comprises maintaining the gate electrode and drain electrode at the same electric potential in the step of spraying spacers. Further, Japanese Kokai Publication Hei-05-53121 discloses a method comprising applying a voltage to the circuit electrodes in the step of spacer spraying, while Japanese Kokai Publication Hei-05-61052 discloses a method comprising applying a positive voltage to the circuit electrodes and charging spacers negatively and spraying them by the dry method.
The inventions described in the references cited above use a substrate having thin film transistors (TFTs) formed thereon and control the spacer disposition by applying a voltage to the circuits of these thin film transistors.
However, they have a problem. Namely, application of a voltage to the substrate having thin film transistors (TFTS) formed thereon, for the purpose of controlling the spacer disposition may lead to destruction of elements by that voltage, hence to failure to function as a liquid crystal display device.
There is another problem. Namely, such technologies as mentioned above cannot be employed in STN type liquid display devices since the sites corresponding to the black matrix are spaces among transparent electrodes.
On the other hand, as a technology of disposing spacers in spaces between stripe-form transparent electrodes constituted by disposing a plurality of linear transparent electrodes in parallel on a substrate, as in STN type liquid crystal display devices, there is disclosed, in Japanese Kokai Publication Hei-04-204417, a method of producing liquid crystal display devices which comprises charging spacers either positively or negatively and applying a voltage of the same polarity to the linear transparent electrodes on the substrate in the step of spacer spraying.
This production method is intended to dispose spacers in interelectrode spaces by applying a voltage of the same polarity as the spacer charge polarity to the linear transparent electrodes to thereby cause spacer-electrode repulsion. However, mere application of a voltage of the same polarity as the spacer charge to the linear transparent electrodes cannot attain a sufficient reduction in electric potential between the transparent electrodes but leads to such a state as shown in FIG.
9
. Thus, any electric field suited for spacer disposition is not formed, hence the precision of spacer disposition is very poor. It is therefore impossible to improve the contrast of the product liquid crystal display device to a satisfactory extent.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for producing a liquid display device by which the above problems are solved and which enables spacer disposition in interelectrode spaces where there is no electrode, namely at black matrix sites, in STN type and TFT type liquid crystal display devices and further enables even spacer disposition to attain a uniform cell thickness all over the substrate to thereby produce liquid crystal display devices of high contrast and high display uniformity stably and in good yields, with a reduced spray step tact time, as well as liquid crystal display devices produced by such method.
In a first aspect, the present invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, disposing the substrate in close contact with an earthed conductive stage having a volume resistance of not more than 10
10
&OHgr;cm,
and a voltage of 200 V to 5 kV having the same polarity as the spacer charge polarity is applied to the transparent electrodes.
In a second aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes, a conductive black matrix and an overcoat layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, a voltage (V
1
) is applied to the conductive black matrix and a voltage (V
2
) to the transparent electrodes,
both the voltages V
1
and V
2
being positive ones and satisfying the relation V
1
<V
2
when the spacer charge polarity is positive,
or both V
1
and V
2
being negative voltages and satisfying the relation V
1
>V
2
when the spacer charge polarity is negative.
In a third aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes, an alignment layer and one or more display areas and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively cha

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