Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-01-07
2004-09-21
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S111000, C349S155000
Reexamination Certificate
active
06795141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap to substantially reduce the Mura defect.
2. Description of the Related Art
A liquid crystal display device typically includes a pair of substrates which are maintained in a spaced apart, yet parallel relationship with one another. The space between the substrates is commonly referred to as the cell gap. Interposed between the substrates, within the cell gap, is a liquid crystal material which changes its optical characteristics in response to an applied electrical signal.
A plurality of electrodes are disposed upon the inner surface of the substrates in order to control and apply the desired electrical signals to the liquid crystal material. Some LCD devices will have an electrode arrangement which allows a predetermined set of characters or symbols to be generated, while other LCD devices have a matrix of electrodes that form a display comprised of a great plurality of individually accessible pixel elements, each of which may be selectively activated to form an infinite variety of images.
Due to the electro-optical characteristics inherent the liquid crystal material, it will typically assume one state when no electrical signal is applied and will assume another different state when an electrical signal is applied. For example, some liquid crystal materials will assume a reflective state when no electrical signal is applied, and will assume a transmissive state under the influence of an applied electrical signal. Some new liquid crystal materials provide performance with a variety of different gray levels as well.
In order to assure the proper operation of a liquid crystal display device, it is critical that the cell gap is maintained uniformly and precisely throughout the entire display. Even slight deviations in the cell gap will result in a noticeable and defective appearance in the display (so-called Mura defect). This can readily be seen with a conventional LCD display panel when even slight pressure is applied by a fingertip. In response to the pressure, the cell gap in the affected area will be reduced slightly, resulting a dark spot, degradation of contrast or other undesirable defect in the displayed image.
In a conventional technology, the LCD device, as shown in
FIG. 1
, includes a TFT substrate
61
, a color filter substrate
71
and liquid crystal material sandwiched therebetween. The cell gap is maintained by providing a plurality of spacers
79
between the substrates
61
and
71
. The spacers
79
, which are of a uniform height, are disposed usually randomly within the cell gap, such as by a spraying technique. This generally results in an uneven distribution of spacers. To ensure that an adequate concentration of spacers to maintain the proper cell gap is disposed in all areas of the display, a superfluity of spacers must be used. In addition, according to such conventional techniques for placement of the spacers, they are placed in both “inactive” and “active” areas of the display. The “active” areas are those areas of the liquid crystal material which may be selectively activated because they are located between opposed electrodes disposed upon the substrates. The “inactive” areas are those areas of the liquid crystal material that cannot be selectively activated because of the absence of opposed electrodes on the substrates.
Inherently, there are several undesirable deficiencies in the structure and performance of the liquid crystal display panel existing in such conventional spacer techniques. Spacers which are disposed in the active display areas, particularly due to the superfluity of spacers, cause defects, such as the degradation of contrast or the undesirable emission of light around the edges of the spacers therein.
Therefore, European Patent 1030211 A2, incorporated herein by reference, discloses a liquid crystal display, shown in
FIG. 2
, which can omit the step of scattering spacers and thus avoiding deviations in cell thickness due to the uneven distribution of spacers. This LCD generally includes a TFT (Thin Film Transistor) substrate
30
, a CF (Color Filter) substrate
40
and a liquid crystal material layer
49
sealed therebetween. As shown in
FIG. 2
, the projection patterns
45
formed on the CF substrate
40
have a height of about 4.0 &mgr;m to keep the uniform cell gap.
However, the spacer in the both liquid crystal displays of the conventional technology and the above mentioned European patent is deposited on the glass substrate and the color filter layer is disposed between the spacer and the substrate.
Now referring to
FIG. 4
, it depicts a stress-strain diagram of the post spacer of 20
&PHgr;
&mgr;m deposited directly on a glass substrate at room temperature and with a color filter layer interposed between the post spacer and the glass substrate. It will be appreciated that the spacer deposited directly on the glass substrate is substantially elastic, shown as the curve A, but the spacer deposited on the glass substrate with the color filter layer interposed therebetween is partial elastic, shown as the curve B, in which a permanent strain remains after the load is released. Thus, if a pressure (or stress) loaded on the LCD is big enough to result in the permanent strain, the total height of the spacer with the color filter layer deposited on the glass substrate will be changed. In other words, the cell gap may be uneven and the Mura defect may be generated after the LCD panel is loaded with a substantial pressure.
European Patent 1030211 A2 further discloses another structure of the LCD, as shown in the
FIG. 3
, wherein a black matrix
52
is formed on the glass substrate
51
on the side of a color filter substrate
50
to coincide with a gate bus lines
33
b
, a drain bus lines
33
a
, TFTs and auxiliary capacitance electrodes on a TFT substrate
30
. This black matrix
52
is formed of black resin to have a thickness of about 4 &mgr;m. The color filters
53
(red, green, and blue) are formed at opening portions of the black matrix
52
with a thickness of 1.5 &mgr;m. Then, an opposing electrode
54
formed of ITO (Indium-tin Oxide) is formed on the black matrix
52
and the color filters
53
. A projection pattern
55
of about 1.5 &mgr;m height is formed on the opposing electrode
54
in a zigzag fashion. In the result, the black matrix
52
together with the projection pattern
55
forms a spacing structure for keeping the uniform cell gap with respect to the other substrate, thereby replacing the conventional spacer. However, the black matrix
52
formed of black resin still fails to prevent a permanent strain remaining after the load is released.
Accordingly, there exist needs for providing a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap to substantially reduce the Mura defect.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap of the LCD device even though the LCD device is loaded with a pressure or a force.
It is another object of the present invention to provide a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap of the LCD device, thereby substantially reducing the Mura defect.
In order to achieve the objects mentioned hereinabove, the present invention provides a color filter substrate for an LCD device. The color filter substrate comprises a transparent substrate having a substantially flat surface, a black matrix, a plurality of color filters, an electrode, a plurality of spacers, and an alignment film. The black matrix is formed on predetermined regions of the substrate. The plurality of color filters are formed between the regions of the black matrix with overlapping porti
Chi Mei Optoelectronics
Chowdhury Tarifur R.
Gilman & Berner LLP
Hauptman Lowe
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