Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-03-29
2002-01-22
Sikes, William L. (Department: 3871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S054000, C349S192000
Reexamination Certificate
active
06340998
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a thin film transistor liquid crystal display and, more particularly, to a line lay-out pattern of a thin film transistor liquid crystal display capable of providing against cut-off of lines for supplying a predetermined ‘ON’- or ‘OFF’-signal to thin film transistors and improving ‘ON’-current characteristic of the thin film transistors arranged in a parallel.
2 Description of the Prior Art
As well-known, such a liquid crystal display (LCD) device is a typical display that, depending on the dielectric anisotropy feature of liquid crystal materials, controls the amount of light to be penetrated so as to depict image pixels on a screen. Profitably, such a LCD device is employed in a lap-top computer, a word processor, a portable television set and so on.
In general, the LCD device may be fabricated in a simple matrix structure in which two strip-shaped electrodes are intersectionally formed in a matrix manner and, thus, the arranged status of liquid crystal material positioned between the electrodes is controlled by way of the voltage generated at the intersection of the electrodes, and an active matrix structure in which thin film transistors serving as switching means for driving image pixels are associated with the simple matrix structure to enhance a contrast, a drive duty ratio and a multi-gray level of the pixels.
FIG. 4
shows a typical reflection type LCD device with thin film transistors, which is employed with the aforementioned active matrix structure. The LCD device shown in the
FIG. 4
includes a upper substrate
30
, a lower substrate
50
and a liquid crystal layer
72
which are disposed in a staked structure.
In addition, a polarizing plate
36
is disposed on the upper substrate
30
while a color filter
34
and a common electrode
32
made of ITO (Indium tin oxide) are disposed at a lower side of the upper substrate
30
in order.
Typically, a thin film transistor T is designed between the lower substrate
50
and a corresponding pixel electrode
52
formed at an upper side of the lower substrate
50
. Preferably, the thin film transistor T is electrically connected to the pixel electrode
52
via a corresponding contact hole CH penetrated through an insulating layer
54
formed between the lower substrate
50
and the pixel electrode
52
. Further, the arranged direction of the liquid crystal layer
72
formed between the common electrode
32
and the pixel electrode
52
can be oriented along the rubbing direction of two orientation films
75
a
and
75
b.
FIG. 5
shows a line layout diagram of 3×3 matrix of a conventional liquid crystal display device. In the drawing, gate lines GL and source lines SL, which are connected to a corresponding drive circuit (not shown), are made of a metal film, for example Cr, Mo, Al and so on, and are intersected with each other. Furthermore, the thin film transistor T having a gate electrode G, a drain electrode D and a source electrode S is formed within a lattice defined by the intersected lines GL and SL so that the gate electrode G and the source electrode S of the thin film transistor T are electrically connected to the corresponding gate line GL and the corresponding source line SL.
According to the liquid crystal display device thus constructed, the thin film transistor T which receives a drive signal from the drive circuit through the gate line GL and the source line SL outputs an electric pixel driving signal to the pixel electrode
52
, selectively. In this way, liquid crystal molecules of the liquid crystal layer
72
positioned between the pixel electrode
52
and the common electrode
32
can be controlled to have a twisted angle that is in discord with the polarizing direction of the polarizing plate
36
.
In such a conventional liquid crystal display device, however, since the gate lines GL and the source lines SL are designed in fine line-width from the structural point of the line layout, a disadvantageous defect may be easily generated on the gate lines GL and/or the source lines SL during a photolithography process or an etching process.
In addition, if the defect is occurred on the lines GL and/or SL. unexpected problems can be also occurred as follows.
First, resistance of the defected portion of the line GL and/or SL is increased to distort the pixel driving signal. For this reason, the contrast may be partially varied on the same image screen, thereby deteriorating the quality in display of the image.
Second, since increased current flows concentrically through the defected portion of the line GL and/or SL, cut-off of the line GL and/or SL may be easily occurred by reason of movement of metal particles forming the defected line portion. If the line is partially cut-off, then a signal current can't flow to the rear of the cut-off portion of the line, thereby generating a linear blanking appearance on the image screen.
Furthermore, disadvantageous problems may be occurred from the thin film transistor T connected between the lines GL and SL and the pixel electrode
52
, as follows.
First, while an insulation of a gate insulating layer GI of the thin film transistor T is damaged or destroyed by static electricity charged before a coating process of the liquid crystal display device, or while a miss-alignment in a photo etching process of the pixel electrode
52
and the insulation layer
54
to be carried out after a formation of the electrodes of the thin film transistor T is adversely induced, satisfactory contact between the thin film transistor T and the lines GL and SL or between the thin film transistor T and the pixel electrode
52
can't be ensured. In accordance with a degradation of the thin film transistor T, spot-shaped blanks may be appeared at the portion of the image screen corresponding to the position of the pixel electrode
52
connected with the degraded thin film transistor T.
Thus, even if the rest thin film transistors can be operated normally, the LCD device including only one transistor T deteriorated in function must be abandoned inevitably.
Second, a lifetime of the LCD device depends on that of the thin film transistors T. Therefore, if any one of the transistors T arranged in the matrix structure is degraded in function, the lifetime of the LCD device is also reduced and, thus, the lifetime property of the LCD can't be assured to an extent demanded by consumers.
According to the conventional LCD device having the aforementioned unfavorable problems, as the image screen is designed to be in large size and high definition, the larger numbers of the lines and the thin film transistors are needed so as to drive the image screen to thereby deteriorate the yield and the lifetime property of the LCD device.
Additionally, as the image screen is designed to be in large size and high in definition, the length of the lines must be gradually lengthened to be thereby insufficient the voltage appeared at the end of the lines, deteriorating the display quality of the LCD device unequally.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
Accordingly, an object of the present invention is to provide a thin film transistor liquid crystal display (LCD), wherein even if any of line patterns for connecting a drive IC (Integrated Circuit), which outputs a signal necessary to drive a liquid crystal, to a plurality of thin film transistors mounted on a display panel is cut, or if any one of the thin film transistors is deteriorated in function, image pixels still can be turned on and off.
In order to achieve the above-noted object, the present invention provides a thin film transistor liquid crystal display comprising primary lines and secondary lines to supply scanning signals and data signals respectively wherein each of said primary and secondary lines are branched and a thin film transistor is electrically coupled to each of the branched lines such that at least two transistors are turned on and off simultaneously when one of primary
Choi Young Il
Kang Seung Gon
Kim Byung-Hee
Kim Sun Hwa
Shin Hyun Eok
Bushnell , Esq. Robert E.
Chandhury Tarifur R.
Samsung Display Devices Co., Ltd
Sikes William L.
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