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`US006580487Bl
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`
`(12)United States Patent
`Kim et al.
`
`(10)Patent No.:
`US 6,580,487 Bl
`
`Jun.17,2003
`(45)Date of Patent:
`
`(54)FRING E FIELD SWITCHING LIQUID
`CRYSTAL DISPLAY
`
`Eun Sik Kim, Kyoungki-do (KR);
`
`(75)Inventors:
`JP
`
`Young Keun Lee, Kyoungki-do (KR)
`JP
`JP
`
`JP
`
`Boe-Hydis Technology Co., Ltd.,
`
`
`(73)Assignee:
`
`Kyoungki-do (KR)
`
`JP
`
`JP
`
`FOREIGN PATENT DOCUMENTS
`
`
`55138922 10/1980
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`57069281 4/1982
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`58083478 5/1983
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`60222825 11/1985
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`02071616 3/1990
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`11167120 6/1999
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`11282427 10/1999
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`JP
`*cited by examiner
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`
`
`( *) Notice: Subject to any disclaimer, the term of this
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`
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`patent is extended or adjusted under 35
`Primary Examiner-Toan Ton
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`
`
`U.S.C. 154(b) by O days.
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`
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`(21)Appl. No.: 09/606,731
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`(57)
`
`ABSTRACT
`
`(74) Attorney, Agent, or Firm-Ladas & Parry
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`Disclosed is a fringe field switching liquid crystal display
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`capable of improving picture quality by minimizing vertical
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`components in a fringe field. The fringe field liquid crystal
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`display includes: a lower substrate; a gate bus line extended
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`Jun. 29, 1999 (KR) ............................................ 99-25223
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`on the lower substrate in a selected direction; a data bus line
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`disposed to cross the gate bus line, thereby defining a sub
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`(51)Int. Cl.7 .............................................. G02F 1/1343
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`pixel; a thin film transistor disposed at an intersection of the
`349/143 (52)U.S. Cl. ........................................ 349/141;
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`gate bus line and the data bus line; a counter electrode
`(58)Field of Search ..................................
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`349/141, 143
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`formed at each sub pixel and formed in shape of a rectan­
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`gular plate, the counter electrode to which a common signal
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`is continuously transmitted; and a pixel electrode electrically
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`connected to the thin film transistor and comprising a
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`plurality of teeth which are overlapped with the counter
`
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`4,542,960 A 9/1985 Yang
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`electrode so as to form a fringe field with the counter
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`
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`4,643,533 A 2/1987 Armitage
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`
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`electrode, wherein the counter comprises a plurality of slits,
`
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`5,309,264 A 5/1994 Lien et al.
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`and the slits are disposed between the teeth of the pixel
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`
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`5,576,862 A 11/1996 Sugiyama et al.
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`electrode, and the counter electrode and the pixel electrode
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`5,914,762 A * 6/1999 Lee et al. ................... 349/141
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`5,959,708 A 9/1999 Lee et al.
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`are made of a transparent conductor.
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`6,233,034 Bl * 5/2001 Lee et al. ................... 349/141
`1 Claim, 5 Drawing Sheets
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`6,256,081 Bl * 7/2001 Lee et al. ................... 349/141
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`(22) Filed:Jun.29,2000
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`(30)Foreign Application Priority Data
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`(56)
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`References Cited
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`U.S. PATENT DOCUMENTS
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`Page 1 of 8
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`Tianma Exhibit 1009
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`U.S. Patent
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`Jun. 17, 2003
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`Sheet 1 of 5
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`US 6,580,487 B1
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`FIG. 1
`(PRIOR ART)
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`TFT 7
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`•
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`[VI] [7 ]----
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`È=` N
`|----------------------------------------------
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`Page 2 of 8
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`U.S. Patent
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`Jun. 17, 2003
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`Sheet 2 of 5
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`US 6,580,487 B1
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`FIG.2
`(PRIOR ART)
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`FA
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`FIG.3
`(PRIOR ART)
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`- Psy's
`Z (2\\\ Z-9a
`NN
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`FA
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`Page 3 of 8
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`U.S. Patent
`US. Patent
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`Jun. 17, 2003
`Jun. 17, 2003
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`Sheet 3 of 5
`Sheet 3 0f 5
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`US 6,580,487 B1
`US 6,580,487 B1
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`FIG.4
`FICA
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`Page 4 of 8
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`Page 4 of 8
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`U.S. Patent
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`Jun. 17, 2003
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`Sheet 4 of 5
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`US 6,580,487 B1
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`FIG.5
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`12O
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`12
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`Page 5 of 8
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`U.S. Patent
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`Jun. 17, 2003
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`Sheet 5 of 5
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`US 6,580,487 B1
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`FIG. 6
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`190
`14
`12
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`11
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`12d
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`12O
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`Page 6 of 8
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`

`

`1
`FRINGE FIELD SWITCHING LIQUID
`CRYSTAL DISPLAY
`
`2
`However, the conventional FFS-LCD has following prob
`lems.
`
`US 6,580,487 B1
`
`FIELD OF THE INVENTION
`The present invention relates to a fringe field Switching
`liquid crystal display(“LCD), and more particularly to a
`fringe field Switching LCD reducing vertical components of
`a fringe field that is generated between a counter electrode
`and a pixel electrode.
`BRIEF DESCRIPTION OF THE INVENTION
`Generally, the fringe field Switching liquid crystal display
`(“FFS-LCD’) is proposed to substitute a general in-plane
`switching liquid crystal display(“IPS-LCD”) having low
`aperture ratio and transmittance, a corresponding patent
`application has been filed in the Rep. of Korea in application
`number of 98-9243.
`The foregoing FFS-LCD includes upper and lower Sub
`Strates being Separated with a Selected cell gap, a liquid
`crystal layer, and counter and pixel electrodes formed at an
`inner Surface of the lower Substrate. The counter and the
`pixel electrodes are made of transparent conductor, a dis
`tance between the counter electrode and the pixel electrode
`is Smaller than the cell gap. As a result, fringe fields are
`formed between electrodes and on the electrodes.
`FIG. 1 is a plane view of a lower Substrate structure of the
`FFS-LCD
`Referring to FIG. 1, a gate bus line 3 and a data bus line
`7 are disposed on a lower Substrate 1 in a croSS or a matrix
`type, thereby defining a sub pixel Pix. A thin film transistor
`TFT is disposed adjacent to an interSection of the gate bus
`line 3 and the data bus line 7. A counter electrode 2 is made
`of transparent conductor and is formed at each Sub pixel Pix.
`Here, the counter electrode 2 is in shape of a rectangular
`plate or a comb. A common Signal line 30 for continuously
`providing common Signals to the counter electrode 2, is
`disposed in contact with the counter electrode 2. Herein, the
`common signal line 30 is made of a metal layer having
`excellent Signal transmittance property, generally a metal
`layer for gate bus line. In addition, the common Signal line
`30 includes a first part 30a being parallel to the gate bus line
`3 and being in contact with a Selected portion of the counter
`electrode 2, and a second part 30b being extended from the
`first part 30a parallel to the data bus line 7 and being
`disposed between the counter electrode 2 and the data bus
`line 7. A pixel electrode 9 is formed at the Sub pixel Pix so
`that the pixel electrode 9 overlaps with the counter electrode
`2. At this time, the pixel electrode 9 is electrically insulated
`from the counter electrode 2. The pixel electrode 9 is formed
`in shape of a comb, and includes a tooth part 9a having a
`plurality of teeth which are disposed parallel to the data bus
`line 7 and arranged with a uniform distance from each other,
`and a bar 9b contacting one end of the tooth part 9a and
`being in contact with a Selected portion of the thin film
`transistor TFT. Meanwhile, although not shown in drawings,
`an upper Substrate opposing the lower Substrate 1 is opposed
`with a greater distance than that of the pixel electrode 9 and
`the counter electrode 5.
`Operation of the foregoing FFS-LCD is as follows. When
`an electric field is formed between the counter electrode 5
`and the pixel electrode 9, the distance between the counter
`electrode 5 and the pixel electrode 9, i.e. the thickness of
`gate insulating layer is greater than that of the upper and the
`lower Substrates, thereby generating a fringe field between
`and on the electrodes. The fringe field influences over the
`entire counter electrode 5 and the pixel electrode 9, thereby
`driving all liquid crystal molecules on the electrodes.
`Accordingly, high aperture ratio and high transmittance are
`realized.
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`First, since the distance between the tooth part 9a of the
`pixel electrode 9 and the counter electrode 5 is smaller than
`the cell gap, i.e. the distance between upper and lower
`Substrates, Vertical components exist in the fringe field.
`These vertical components of the fringe field are only
`generated on upper region of the electrodes, and long axes
`of the liquid crystal molecules which should be parallel to
`the Substrates are disposed almost vertical to the Substrates.
`Therefore, mis-alingment of the liquid crystal molecules
`results and there is found Some defects in the picture quality.
`Moreover, the vertical components FA of the fringe field
`are shown in the different types, as shown in FIGS. 2 and 3,
`with respect to the (+) frame of LCD and (-) frame of LCD.
`Accordingly, arrangements of liquid crystal molecules 10a
`in the (+) frame in the (-) frame are different from each
`other, a difference in the brightneSS occurs. Due to the
`difference in the brightness, a DC bias is applied to the liquid
`crystal layer thereby degrading the liquid crystal molecules.
`AS a result, the defect in the picture quality occurs.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, the object of the present invention is to
`provide an FFS-LCD capable of minimizing the vertical
`components of the fringe field and improving picture quality.
`To accomplish the foregoing object, one embodiment of
`the present invention provides an FFS-LCD including: a
`lower Substrate; a gate bus line extended on the lower
`Substrate in a Selected direction; a data bus line disposed to
`croSS the gate bus line, thereby defining a Sub pixel, a thin
`film transistor disposed at an interSection of the gate bus line
`and the data bus line; a counter electrode formed at each Sub
`pixel and formed in Shape of a rectangular plate, the counter
`electrode to which a common Signal is continuously trans
`mitted; and a pixel electrode electrically connected to the
`thin film transistor and comprising a plurality of teeth which
`are overlapped with the counter electrode So as to form a
`fringe field with the counter electrode, wherein the counter
`comprises a plurality of Slits, and the Slits are disposed
`between the teeth of the pixel electrode, and the counter
`electrode and the pixel electrode are made of a transparent
`conductor.
`
`Further, another embodiment of the present invention
`provides an FFS-LCD including: a lower Substrate; a gate
`bus line extended on the lower Substrate in a Selected
`direction; a data bus line disposed to croSS the gate bus line,
`thereby defining a Sub pixel; a thin film transistor disposed
`at an interSection of the gate bus line and the data bus line;
`a counter electrode formed at each Sub pixel and formed in
`shape of a rectangular plate, the counter electrode to which
`a common signal is continuously transmitted; and a pixel
`electrode electrically connected to the thin film transistor
`and comprising a plurality of teeth which are overlapped
`with the counter electrode So as to form a fringe field and the
`teeth are parallel with the data bus line, wherein the counter
`comprises a plurality of Slits, and the Slits are disposed
`between the teeth of the pixel electrode, and the counter
`electrode and the pixel electrode are made of a transparent
`conductor.
`
`Page 7 of 8
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`

`

`US 6,580,487 B1
`
`3
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a plane view of a general FFS-LCD.
`FIG. 2 is a cross-sectional view taken along the line II-II'
`of FIG. 1, for illustrating the arrangement of liquid crystal
`molecules in case of (+) frame.
`FIG. 3 is a cross-sectional view taken along the line II-II'
`of FIG. 1, for illustrating the arrangement of liquid crystal
`molecules in case of (-) frame.
`FIG. 4 is a plane view for showing the FFS-LCD accord
`ing to the present invention.
`FIG. 5 is a plane view for showing a counter electrode of
`the FFS-LCD according to the present invention.
`FIG. 6 is a cross-sectional view taken along the line
`VI-VI' of FIG. 4, for illustrating the arrangement of liquid
`crystal molecules in case of (+) frame.
`FIG. 7 is a cross-sectional view taken along the line
`VI-VI' of FIG. 4, for illustrating the arrangement of liquid
`crystal molecules in case of (-) frame.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`First, referring to FIG. 4, a gate bus line 13 is extended to
`an upper portion of a lower Substrate 11 in a direction of X
`shown in drawings, a data bus line 17 is extended in a
`direction of y which is Substantially perpendicular to the
`gate bus line 13, thereby defining a Sub pixel pix of a
`rectangular shape in the lower Substrate 11 Herein, as known
`in the art, the gate bus line 13 and the data bus line 17 are
`insulated from each other by a gate insulating layer (not
`shown). A thin film transistor TFT is disposed adjacent to an
`Intersection of the gate bus line 13 and the data bus line 17.
`The counter electrode 12 is formed at each sub pixel. The
`counter electrode 12 is made of a transparent conductive
`layer, for example ITO materials, and formed in the shape of
`a plate, preferably a rectangular plate. Further, the counter
`electrode 12 includes a plurality of Slits 12a. Here, long axes
`of the silts 12a are parallel to the data bus line 17 and the
`respective Slits 12a are disposed parallel to each other and
`Separated with a uniform distance. Only the counter elec
`trode 12 as described above is illustrated in FIG. 5.
`Meanwhile, a common signal line 130 is in contact with a
`Selected portion of the counter electrode 12 and transmits
`common signals to the counter electrode 12. The common
`signal line 130 includes a first 130a being parallel to the gate
`bus line 13 and being in contact with a Selected portion of
`the counter electrode 12, and a second part 130b being
`extended from the first part 130a parallel to the data bus line
`17 and being disposed between the counter electrode 12, and
`a second part 130b being extended from the first part 130a
`parallel to the data bus line 17 and being disposed between
`the counter electrode 12 and the data bus line 17. A pixel
`electrode 19 is formed at each sub pixel pix to overlap the
`counter electrode 12. The pixel electrode 19 includes a
`plurality of teeth 19a parallel to the data bus line 14 and
`being disposed between the slits 12a, and a bar 19b con
`necting one end of the teeth 19a and being in contact with
`a drain electrode of the thin film transistor TFT. At this time,
`distances between the teeth 19a is greater than the width of
`the slits 12a. As a result, the Slits 12a are exposed through
`spaces between the teeth 19a. Additionally, the pixel elec
`trode 19, similar to the counter electrode 12, is made of a
`transparent conductor, for example an ITO material. Further,
`a distance between the teeth 19a of the pixel electrode 19
`and the counter electrode 12 is Smaller than that of the upper
`and lower Substrates. In addition, the width of the teeth 19a
`of the pixel electrode 19 and the width of the exposed
`counter electrode 12 are determined Such that a fringe field
`can influence to the upper region of those electrodes.
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`4
`Operation of the foregoing FFS-LCD of the present
`invention is as follows. When a voltage difference exists
`between the counter electrode 12 and the pixel electrode 19,
`there is generated a fringe field F between the counter
`electrode 12 and the teeth 19a of the pixel electrode 19.
`Herein, the fringe field F is formed between the exposed
`counter electrode 12 of both ends of the slit 12a and the teeth
`19a of the pixel electrode 19, therefore no vertical compo
`nent is needed. That is, a certain portion of the fringe field
`which has been shown as the vertical component is curved
`toward the outside of the slit 12a by the slit 12a. As a result,
`the defect in picture quality is eliminated. Herein, the
`reference numeral 14 in the drawing Signifies a gate insu
`lating layer.
`Moreover, as described in the present invention, when the
`Slit 12a is formed at the exposed counter electrode 12, no
`voltage difference is occurred as shown in FIGS. 6 and 7
`Since an identical electric field is formed at the (+) frame and
`at the (-) frame respectively. Additionally, because no
`Voltage difference is occurred, application of DC bias to the
`liquid crystal molecules also reduced, thereby preventing
`degrading of liquid crystal molecules. As a result, the defect
`in picture quality is eliminated.
`As discussed above in detail, in the FFS-LCD according
`to the present invention, Slits are formed in the counter
`electrode exposed by the teeth of the pixel electrode, and
`have the width Smaller than the distance between the teeth.
`As a result, the vertical components of the FFS-LCD are
`removed between the teeth of the pixel electrode and the
`counter electrode, thereby preventing the mis-alignment of
`liquid crystal molecules. Additionally, the fringe fields of the
`(+) frame and the (-) frame are formed in the same
`configuration, thereby reducing differences of the arrange
`ment of liquid crystal molecules. Therefore, picture quality
`of the liquid crystal display is greatly enhanced.
`Various other modifications will be apparent to and can be
`readily made by those skilled in the art without departing
`from the Scope and Spirit of the present invention.
`What is claimed is:
`1. A fringe field switching liquid crystal display (FFS
`LCD) comprising:
`a lower Substrate;
`a gate bus line extended on the lower Substrate in a
`Selected direction;
`a data bus line disposed to croSS the gate bus line, thereby
`defining a Sub pixel,
`a thin film transistor disposed at an interSection of the gate
`bus line and the data bus line;
`a counter electrode formed at each Sub pixel and formed
`in the shape of a plate, the counter electrode having a
`common Signal continuously transmitted thereto, and
`a pixel electrode electrically connected to the thin film
`transistor and comprising a plurality of teeth which
`Overlap an upper part of the counter electrode So as to
`form a fringe field with the counter electrode,
`wherein the counter electrode comprises a plurality of
`slits, the minor axis of the Slit having a width Smaller
`than the distance between the teeth of the pixel elec
`trode and the major axis of the Slit having a width
`parallel with the major axis of the teeth, and Said slits
`are fully exposed through Spaces between the teeth; and
`the counter electrode and the pixel electrode are made of
`a transparent conductor.
`
`k
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