I 1111111111111111 11111 111111111111111 IIIII IIIII IIIII IIIII IIIIII IIII IIII IIII
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`US007636142B2
`
`c12) United States Patent
`Aota et al.
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 7,636,142 B2
`Dec. 22, 2009
`
`(54) LIQUID CRY STAL DISPLAY DEVICE
`
`(56)
`
`References Cited
`
`(75)
`
`Inventors: Masaaki Aota, Ogaki (JP); Yasuo
`Segawa, Kitagata-cho (JP); Tomohide
`Onogi, Anpachi-cho (JP)
`
`(73) Assignee: Epson Imaging Devices Corporation,
`Azumino (JP)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 176 days.
`
`(21) Appl. No.: 12/010,843
`
`(22) Filed:
`
`Jan.30, 2008
`
`(65)
`
`Prior Publication Data
`
`US 2008/0204614 Al
`
`Aug. 28, 2008
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 26, 2007
`
`(JP)
`
`............................. 2007-045969
`
`(51)
`
`Int. Cl.
`
`G02F 11133
`
`(2006.01)
`(2006.01)
`G02F 111335
`(52) U.S. Cl. ......................................... 349/114; 349/33
`(58) Field of Classification Search ....................... None
`See application file for complete search history.
`
`U.S. PATENT DOCUMENTS
`
`2006/0203157 Al*
`2006/0215081 Al*
`
`9/2006 Ozawa et al. ............... 349/114
`9/2006 Song et al. .................. 349/107
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`
`A 2005-107535
`
`4/2005
`
`* cited by examiner
`
`Primary Examiner-Tina M Wong
`(74) Attorney, Agent, or Firm-Oliff & Berridge, PLC
`
`(57)
`
`ABSTRACT
`
`A liquid crystal display device includes an upper electrode
`and a lower electrode interposing an insulation layer therebe­
`tween, wherein an electric field opening part for passing an
`electric field is formed in the upper electrode and liquid
`crystal molecules are driven by applying a voltage between
`the lower electrode and the upper electrode, wherein a win­
`dow-shaped opening part formed by partially removing the
`lower electrode for connecting an upper electrode wiring and
`the upper electrode, which interpose an interlayer insulation
`film there between, together is disposed in a lower part of the
`lower electrode, and wherein one end portion of the electric
`field opening part in the longitudinal direction around the
`window-shaped opening part is disposed to be overlapped
`with the window-shaped opening part in a plan view.
`
`9 Claims, 7 Drawing Sheets
`
`62
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`64
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`.tf=-......-20
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`30
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`32
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`36
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`34
`
`22
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`Page 1 of 15
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`Tianma Exhibit 1001
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`

`

`U.S. Patent
`
`Dec. 22, 2009
`
`Sheet 1 of 7
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`US 7,636,142 B2
`
`FIG. 1
`
`62
`
`64
`
`~20
`
`22
`
`FIG. 2
`
`20
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`28
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`43
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`38
`
`Page 2 of 15
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`

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`U.S. Patent
`
`Dec. 22, 2009
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`Sheet 2 of 7
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`US 7,636,142 B2
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`FIG. 3
`
`38
`
`FIG. 4
`
`L
`
`L
`
`D
`
`43
`
`_____ 42
`
`43
`
`43
`
`R
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`Page 3 of 15
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`

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`U.S. Patent
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`Dec. 22, 2009
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`Sheet 3 of 7
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`US 7,636,142 B2
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`29~ - - - - - -....
`L ________ _j
`
`FIG. 6
`rr-=--=,-----7
`I I r1 1
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`Page 4 of 15
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`

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`U.S. Patent
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`Dec. 22, 2009
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`Sheet 4 of 7
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`US 7,636,142 B2
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`FIG. 7
`35
`
`34
`
`94
`
`FIG. 8
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`Page 5 of 15
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`U.S. Patent
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`Dec. 22, 2009
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`Sheet 5 of 7
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`US 7,636,142 B2
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`FIG. 9
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`32
`
`100
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`38
`
`FIG. 10
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`Page 6 of 15
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`

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`U.S. Patent
`US. Patent
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`Dec. 22, 2009
`Dec. 22, 2009
`
`Sheet 6 of 7
`Sheet 6 of7
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`US 7,636,142 B2
`US 7,636,142 B2
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`FIG. 11
`FIG. 11
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`100
`
`102
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`43
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`42
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`Page 7 of 15
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`Page 7 of 15
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`

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`U.S. Patent
`
`Dec. 22, 2009
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`Sheet 7 of 7
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`US 7,636,142 B2
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`FIG. 12
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`43
`
`FIG. 13
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`FIG. 14
`
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`
`42
`
`42
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`100
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`FIG. 15
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`43
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`102
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`43
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`43
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`43
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`Page 8 of 15
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`

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`US 7,636,142 B2
`
`1
`LIQUID CRYSTAL DISPLAY DEVICE
`
`BACKGROUND
`
`1. Technical Field
`The present invention relates to a liquid crystal display
`device, and more particularly, to a liquid crystal display
`device having upper and lower electrodes interposing an insu(cid:173)
`lation layer therebetween in which an electric field opening
`part for passing an electric field is formed in the upper elec(cid:173)
`trode and liquid crystal molecules are driven by applying a
`voltage between the upper and lower electrodes.
`2. Related Art
`As a display method for liquid crystal displays, generally,
`a TN (Twisted Nematic) mode has been widely used. How(cid:173)
`ever, there is a limitation on the viewing angle according to
`the display principle of the TN mode. As a method for solving
`this problem, a horizontal electric field method in which a
`pixel electrode and a common electrode are formed on a same
`substrate as a pair of electrodes for driving liquid crystal
`molecules, a voltage is applied between the pixel electrode
`and the common electrode so as to generate an electric field
`approximately parallel to the substrate, and the liquid crystal
`molecules are driven within a plane substantially parallel to
`the substrate surface has been known.
`As the horizontal electric field method, an IPS (In Plane
`Switching) type and an FFS (Fringe Field Switching) type
`have been known. In the IPS type, a pixel electrode having a
`comb-teeth shape and a common electrode having a comb- 30
`teeth shape are combined to be disposed. The comb-teeth
`shape is formed in a configuration in which one end portion of
`an opening part, formed for passing an electric field, in the
`longitudinal direction is closed, the other end portion of the
`opening part is opened, and the one end portions of each
`opening part are connected together in a case where a plural(cid:173)
`ity of the opening parts is disposed.
`On the other hand, in the FFS type, an upper electrode and
`a lower electrode interposing an insulation layer therebe(cid:173)
`tween are formed, one between the upper and lower elec(cid:173)
`trodes is assigned as a common electrode, the other is
`assigned as a pixel electrode, and an opening part, for
`example, having a slit shape is formed in the upper electrode.
`Here, as an opening part used for passing an electric field, a
`thin and long groove shaped opening part in which both end 45
`portions of the opening part in the longitudinal direction are
`closed is formed. When a plurality of the groove-shaped
`opening parts is disposed, the opening parts are separately
`disposed.
`The opening part is formed by etching an electrode layer 50
`thin film. When the opening part is formed, for example, to
`have a thin and long groove shape, there are many cases that
`edge portions of the opening part which are end portions in
`the longitudinal direction are formed to have a round shape or
`an arc shape. For example, in the FFS type, since an electric 55
`field that comes from the lower electrode, passes through the
`opening part, and progresses toward the upper electrode flows
`along the pattern of this opening part, and thus, a horizontal
`electric field is formed along the pattern of the arc shape.
`Accordingly, when the initial alignment of the liquid crystal 60
`molecules are set to be substantially parallel to a long side of
`the opening part, for example, by using a rubbing process or
`the like, the liquid crystal molecules are driven by applying a
`horizontal electric field, liquid crystal molecules located in a
`straight line portion of the long side of the opening part rotates 65
`in a direction perpendicular to the long side from the initial
`alignment state. However, liquid crystal molecules located in
`
`5
`
`2
`the edge portions of the opening part rotates in a direction
`perpendicular to the arc shape from the initial alignment state.
`When the liquid crystal molecules rotate along the arc
`shape of the edge portions from its initial disposition state,
`there is a case where the rotation direction of the liquid crystal
`molecules is reversed and there is a case where the rotation
`direction of the liquid crystal molecules changes depending
`on locations. This phenomenon in which the rotation direc(cid:173)
`tion changes depending on the locations is called disclination.
`10 In a boundary in which the rotation direction changes, since
`the liquid crystal molecules may rotate in an undesired direc(cid:173)
`tion or cannot rotated, there is a case where the transmittance
`is lowered and the boundary is visually recognized. The case
`is referred to as a rotating tilt line, a rotation tilt defect, or
`15 simply disclination.
`For example, in JP-A-2005-107535, it is described that,
`when a configuration in which a black matrix of an upper
`substrate and an edge portion of a pixel electrode of a lower
`substrate is overlapped in a predetermined area and a liquid
`20 crystal is interposed between the two substrates is used, the
`twist angle ofliquid crystal molecules becomes almost 90° to
`be aligned in a vertical direction due to the interference of the
`electric field between the black matrix and the pixel electrode
`as the location ofliquid crystal molecules moves from the end
`25 portion of the edge portion of the pixel electrode to a center
`portion. However, in JP-A-2005-107535, it is indicated that
`the edge portion has a curve shape due to limitation of the
`exposure process and thus a trace of rubbing, that is, discli-
`nation ( a rotating tilt line) occurs in a white gray scale level.
`The disclination will be described later in more detail, in
`comparison with embodiments of the invention.
`As described above, when the disclination occurs in a part,
`transmittance in the part is lowered. Generally, when the
`disclination occurs, display quality may be judged to be low-
`35 ered. As described above, the end portion of the opening part
`of the upper electrode in the longitudinal direction has an arc
`shape for improving the capacity of a process such as an
`etching process, and the electric field between the lower and
`upper electrodes passing through the opening part is formed
`40 along the pattern of the arc shape, and whereby the disclina(cid:173)
`tion occurs. Accordingly, in order to suppress the occurrence
`of disclination, it is needed to consider the shape, disposition,
`and the like of the opening part disposed in the upper elec-
`trode in relation with the lower electrode.
`In addition, since a wiring for supplying a predetermined
`electric potential to the upper electrode is disposed on a lower
`layer side relative to the upper electrode, it is needed to
`remove the lower electrode, an insulation layer, and the like
`for connecting the wiring to the upper electrode. Accordingly,
`while a contact hole for connecting the wiring, which is used
`for supplying the electric potential, and the upper electrode
`together is provided, an area around the contact hole has a
`multi-level structure, and thus it is needed to consider the
`effect of the level difference when the opening part of the
`upper electrode is disposed.
`As described above, although there are limitations such as
`disclination, the contact hole, and the level difference around
`the contact hole on the disposition of the opening part in the
`upper electrode, the disposition of the opening part has an
`effect on the display quality of the liquid crystal display.
`
`SUMMARY
`
`An advantage of some aspects of the invention is that it
`provides a liquid crystal display device, which has a configu(cid:173)
`ration that an upper electrode and lower electrode interposing
`an insulation layertherebetween are included, an electric field
`
`Page 9 of 15
`
`

`

`US 7,636,142 B2
`
`5
`
`4
`FIG. 5 is a diagram showing a state in which a gate elec(cid:173)
`trode and a common electrode wiring are formed in a produc(cid:173)
`tion process of a liquid crystal display device according to an
`embodiment of the invention.
`FIG. 6 is a diagram showing a state in which contact holes
`are formed in a source-drain portion of a switching element
`and a portion of a common electrode wiring, in a case where
`the process proceeds further from the state shown in FIG. 5.
`FIG. 7 is a diagram showing a state in which source-drain
`10 wirings and a common electrode connection part are formed
`in a case where the process proceeds further from the state
`shown in FIG. 6.
`FIG. 8 is a diagram showing a state in which an insulation
`film is formed and contact holes are formed in positions
`corresponding to the common electrode connection part and
`a drain wiring in a case where the process proceeds further
`from the state shown in FIG. 7.
`FIG. 9 is a diagram showing a state in which a common
`electrode having a window-shaped opening part is formed in
`20 a case where the process proceeds further from the state
`shown in FIG. 8.
`FIG. 10 is a diagram showing a state in which an FFS
`insulation film is formed and a contact hole is formed in a
`position corresponding to the window-shaped opening part in
`25 a case where the process proceeds further from the state
`shown in FIG. 9.
`FIG. 11 is a diagram showing a state in which a pixel
`electrode having a slit is formed in a case where the process
`proceeds further from the state shown in FIG. 10.
`FIG. 12 is a diagram of a slit around the window-shaped
`opening part according to an embodiment of the invention.
`FIG. 13 shows an example of different disposition for
`comparison with FIG. 12.
`FIG. 14 shows another example of different disposition for
`comparison with FIG. 12.
`FIG. 15 shows still another example for comparison with
`FIG. 12 and is a diagram for describing disposition of the
`window-shaped opening part.
`
`35
`
`3
`opening part for passing an electric field is formed in the
`upper electrode, and liquid crystal molecules are driven by
`applying a voltage between the upper and lower electrodes,
`capable of improving display quality.
`According to a first aspect of the invention, there is pro-
`vided a liquid crystal display device including an upper elec(cid:173)
`trode and a lower electrode interposing an insulation layer
`therebetween. An electric field opening part for passing an
`electric field is formed in the upper electrode and liquid
`crystal molecules are driven by applying a voltage between
`the lower electrode and the upper electrode. A window(cid:173)
`shaped opening part formed by partially removing the lower
`electrode for connecting an upper electrode wiring and the
`upper electrode, which interpose an interlayer insulation film 15
`there between, together is disposed in a lower part of the lower
`electrode. One end portion of the electric field opening part in
`the longitudinal direction around the window-shaped open(cid:173)
`ing part is disposed to be overlapped with the window-shaped
`opening part in a plan view.
`By using the above-described configuration, the electric
`field opening part is disposed to be overlapped with the win(cid:173)
`dow-shaped opening part in a plan view, and this the electric
`field opening part can be disposed in a large area, and thereby
`it is possible to improve the display quality. In addition, since
`the lower electrode is removed below the one end portion of
`the electric field opening part, the electric field between the
`upper and lower electrodes is not applied to an arc shape
`portion even in a case where the end portion has the arc shape, 30
`and accordingly, it is possible to suppress the occurrence of
`the disclination and improve the display quality.
`In the liquid crystal device, the window-shaped opening
`part may be disposed on an inner side relative to an outer
`circumferential end portion of the upper electrode. Since an
`area around the window-shaped opening part has a multi(cid:173)
`level structure, the upper electrode becomes thin in the multi(cid:173)
`level portion. In particular, when the window-shaped opening
`part in which the lower electrode is removed is formed on the
`outer circumferential end portion of the upper electrode, a 40
`boundary of the cut face of the level difference directly
`appears in the outer circumferential end portion. Accordingly,
`for example, an etching liquid or the like permeates from the
`boundary of the cut face of the level difference along the level
`difference, and thereby there is a possibility that the upper 45
`electrode forms a short circuit along the level difference. In
`addition, according to the configuration of the upper portion,
`since the window-shaped opening part is disposed on the
`inner side relative to the outer circumferential end portion of
`the upper electrode, it is possible to suppress the effect of 50
`formation of a short circuit due to the level difference of the
`window-shaped opening part or the like.
`
`DESCRIPTION OF EXEMPLARY
`EMBODIMENTS
`
`Hereinafter, embodiments of the present invention will be
`described in detail with reference to the accompanying draw(cid:173)
`ings. As a liquid crystal display device having upper and
`lower electrodes interposing an insulation layer there between
`and driving liquid crystal molecules by forming an electric
`field opening part on the upper electrode for passing an elec-
`tric field and applying a voltage between the upper and lower
`electrodes, a liquid crystal device having upper and lower
`electrodes disposed in a component substrate and interposing
`an insulation layertherebetween in which the upper and lower
`electrodes are configured as pixel and common electrodes
`55 will now be described. However, a reverse configuration, that
`is, a configuration in which the lower electrode is configured
`as the pixel electrode and the upper electrode is configured as
`the common electrode may be used.
`In addition, a case where the electric field opening part
`having a slit shape in which both ends of the electric field
`opening in the longitudinal direction are closed is used will be
`described. However, the electric field opening part may have
`a comb teeth-like shape in which one end of the electric
`opening part in its longitudinal direction is opened.
`Furthermore, in an FFS mode described below, although
`the lower electrodes are divided for each pixel, however, the
`lower electrodes may not be divided for each pixel.
`
`60
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention will be described with reference to the
`accompanying drawings, wherein like numbers reference like
`elements.
`FIG. 1 is a sectional view of a liquid crystal display device
`for describing declination.
`FIG. 2 is a plan view corresponding to the sectional view
`shown in FIG. 1.
`FIG. 3 is a diagram showing the form of an electric field
`applied between a common electrode and a pixel electrode.
`FIG. 4 is a diagram showing the form of occurrence of
`disclination in an edge portion of a slit.
`
`Page 10 of 15
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`

`

`US 7,636,142 B2
`
`5
`Before the embodiments of the invention are described, a
`mechanism of occurrence of disclination in a horizontal elec(cid:173)
`tric field driving mode will be described with reference to
`FI GS. 1 to 4, together with the configuration ofa liquid crystal
`device.
`FIG. 1 is a partly sectional view of one sub pixel of a color
`liquid crystal display device using an FFS mode. FIG. 2 is a
`plan view corresponding to the sectional view shown in FIG.
`1 and shows three sub pixels corresponding to one pixel. FIG.
`3 is a diagram showing a form of an electric field driving 10
`liquid crystal molecules in using the FFS mode. FIG. 4 is a
`diagram showing a state in which disclination occurs.
`FIG. 1, as described above, shows one sub pixel part in the
`sectional view of the liquid crystal display device 10. Here, a
`sub pixel, for example, is a display part corresponding to R, G, 15
`or B when color display is performed by using R, G, and B. In
`this example, one pixel is constituted by three sub pixels of an
`R sub pixel, a G sub pixel, and a B sub pixel.As shown in FIG.
`1, the liquid crystal display 10 includes a component substrate
`20, an opposing substrate 60, and liquid crystal molecules 50 20
`pinched between the component substrate 20 and the oppos(cid:173)
`ing substrate 60.
`The opposing substrate 60 is a side of the liquid crystal
`display 10 that faces a user. The opposing substrate 60 has a
`configuration in which several films are stacked. In the 25
`example shown in FIG. 1, the opposing substrate 60 includes
`a glass substrate 62, a black matrix 64, and a color filter 66, in
`the sequence from the side facing the user toward the com(cid:173)
`ponent substrate 20 side. In the sectional view shown in FIG.
`1, since the black matrix 64 is hidden behind the color filter 66 30
`or disposed below the color filter 66, it is denoted by a dotted
`line. The materials, the size, a forming method, and the like of
`the opposing substrate 60 which are known in a general
`method of manufacturing a liquid crystal display of an active
`matrix type can be employed, and thus detailed descriptions 35
`thereof are omitted here.
`The component substrate 20 is also referred to as a TFT
`substrate or a TFT side substrate. The component substrate 20
`is a substrate disposed on a side on which a TFT element used
`as a switching element 80 is disposed and faces the opposing
`substrate 60. Here, in the component substrate 20, a pair of
`electrodes for driving the liquid crystal molecules 50 is dis(cid:173)
`posed. On the component substrate 20, a plurality of films
`patterned as a multi-layer structure is stacked by using known
`film forming technology and pattern forming technology.
`In the example shown in FIG. 1, in the component substrate
`20, a glass substrate 22, a semiconductor layer 24, a gate
`insulation film 26, gate and common electrode wirings 28 and
`29 formed by using a same process, an interlayer insulation
`film 30, source and drain wirings 32 and 33 formed by a same
`process, a common electrode connecting part 34, an insula(cid:173)
`tion film 36, a common electrode 38, an FFS insulation film
`40, and a pixel electrode 42 are sequentially formed from the
`side not facing the user toward the liquid crystal molecule 50
`side. The materials, the size, a forming method, and the like of
`the component substrate 20 which are known in a general
`method of manufacturing a liquid crystal display of an active
`matrix type can be employed, and thus detailed descriptions
`thereof are omitted here.
`Although not shown in FIG. 1, an alignment film is formed
`on the pixel electrode 42. An alignment film is disposed on a
`side of the opposing substrate 60 which faces the liquid crys(cid:173)
`tal molecules 50, similarly.
`FIG. 2 is a plan view corresponding to the sectional view
`shown in FIG. 1. In the figure, one pixel constituted by three
`sub pixels is shown. In addition, FIG. 1 corresponds to a
`
`6
`sectional view taken along line A-A shown in FIG. 2. Like
`reference numerals in FIGS. 1 and 2 denote like elements.
`In each sub pixel, a gate line, a part of which becomes the
`gate electrode 28 and a data line 35 are disposed to be per-
`5 pendicular to each other. In an intersection between the gate
`and data lines, the TFT element serving as a switching ele(cid:173)
`ment 80 is disposed. The gate line becomes the gate electrode
`28 shown in FIG. 1 around the switching element 80, and the
`data line 35 is connected to the source-drain wiring 33 shown
`in FIG. 1. As described above, the liquid crystal device 10 has
`TFT elements serving as switching elements 80 in the inter-
`sections of a plurality of gate lines and a plurality of data lines
`31 and is so-called an active matrix display device. The gate
`line is also referred to as a scan line or a scan signal line. The
`data line 35 is also referred to as a signal line, a video signal
`line, or the like.
`The TFT element serving as a switching element 80 is a
`transistor element having the gate insulation film 26 formed
`on the semiconductor layer 24 shown in FIG. 1, the gate
`electrode 28 formed on the gate insulation film 26, and the
`source and the drain connected to the source and drain wirings
`32 and 33. TFT is an abbreviation for Thin Film Transistor.
`Between the source and drain of the TFT element serving as
`a switching element 80, one, for example, the drain is con(cid:173)
`nected to the data line 31, and the other, for example, the
`source is connected to the pixel electrode 42. Since the drain
`and the source are compatible with each other, it may be
`configured that the source is connected to the data line 35 and
`the drain is connected to the pixel electrode 42. The drain and
`source of the TFT element serving as a switching element 80
`are conducted by selecting the gate line, and in the example
`described above, a video signal transmitted from the data line
`35 connected to the drain is supplied to the pixel electrode 42.
`Here, the pixel electrode 42 is represented to have the same
`size as the common electrode 38. In other words, the pixel
`electrode 42 and the common electrode 38 are formed sepa(cid:173)
`rately for each one sub pixel and are disposed on the whole
`area of the sub pixel except for the data line 35. In the example
`shown in FIG. 2, although the common electrode 38 is rep-
`40 resented to be separately formed for each sub pixel, the com(cid:173)
`mon electrode 38 may be formed over sub pixels in some
`cases.
`In the pixel electrode 42, a slit 43 is formed. The slit 43, as
`shown in FIG. 1, is an electric field opening part for driving
`liquid crystal molecules using an electric field by applying a
`voltage between the pixel electrode 42, which is an upper
`electrode, and the common electrode 38, which is a lower
`electrode, having the FFS insulation film 40 interposed ther(cid:173)
`ebetween. In FIG. 2, a plurality of the slits 43 is disposed in
`50 the pixel electrode 42 and the slits 43 are disposed to be
`spaced apart from one another and be parallel to a longitudi(cid:173)
`nal direction of the opening part. The slit 43 is an opening part
`having a thin and long groove shape in which both ends in the
`longitudinal direction are closed, and thus the end portions in
`55 the longitudinal direction are formed to be round in an etching
`process. Hereinafter, the round end portion is referred to an
`edge portion. The disclination occurs in this edge portion.
`FIG. 3 is a schematic diagram showing the form of an
`electric field E applied between the pixel electrode 42 and the
`60 common electrode 38. In the figure, the electric field E pass(cid:173)
`ing through the slit 43 disposed in the pixel electrode 42 and
`progressing toward the common electrode 38 through the FFS
`insulation film 40 is shown. On the other hand, there is a case
`where the electric field is formed in the opposite direction,
`65 that is, the electric field passes through the slit 43 from the
`common electrode 38 and progresses toward the pixel elec(cid:173)
`trode 42.
`
`45
`
`Page 11 of 15
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`

`

`US 7,636,142 B2
`
`7
`FIG. 4 is an enlarged diagram of portion IV shown in FIG.
`2 and is a schematic diagram showing the form of occurrence
`of the disclination in the edge portion that is an end portion of
`the slit 43. Here, the slit 43 is disposed horizontally in the
`left-to-right direction on the surface of the figure, and the
`rubbing direction R-R is slightly tilted toward the upper right
`side with respect to the horizontal direction on the surface of
`the figure. The tilt angle can be set to a specific angle, for
`example, an angle between 3 ° and 5° degrees. In other words,
`in a state that the electric field is not applied, the liquid crystal
`molecule L is tilted toward a slightly upper right side with
`respect to the slit 43. However, this rubbing direction is only
`an example for a description, and thus, a different direction or
`a different tilt angle may be configured.
`The slit 43 is formed on a transparent conduction material
`film that forms the pixel electrode 42, for example, by using
`etching technology. Thus, as described above, the edge por(cid:173)
`tion of the slit is quite or less round, and, as shown in FIG. 4,
`has an arc shape close to a half circle.
`When the electric field E is not applied, a liquid crystal 20
`molecule L located in the edge portion of the slit 43 is in its
`initial disposition state and is adjusted in the rubbing direc(cid:173)
`tion. In other words, although the liquid crystal molecule is
`slightly tilted from the edge of the slit 43, the liquid crystal
`molecule is adjusted in a substantially parallel direction. 25
`When the electric field E is applied in this state, the liquid
`crystal molecule rotates along the direction of the electric
`field E to be almost perpendicular to the edge of the slit 43.
`Since the electric field is applied to the arc-shaped portion in
`a direction perpendicular to the edge of the slit 43, the arc 30
`shape rotates in the counterclockwise direction by a half
`circle along the edge of the slit 43, and accordingly, the
`direction of the electric field changes by 180° along the arc
`shape. For example, when an electric field is applied to a slit
`43 located on the upper left side shown in FIG. 4, a liquid 35
`crystal molecule Lon the upper long side on the slit 43 rotates
`in the counterclockwise direction. Similarly, a liquid crystal
`molecule L located on the lower long side of the slit 43 rotates
`in the counterclockwise direction. However, in a portion hav(cid:173)
`ing an arc shape of a half circle, while a liquid crystal mo!- 40
`ecule L located in an upper quadrant portion of the arc shape
`rotates in the counterclockwise direction, a liquid crystal
`molecule L located in an lower quadrant portion of the arc
`shape rotates in the clockwise direction.
`As described above, when the liquid crystal molecule L is 45
`to be rotated in a desired direction by applying an electric
`field, in the lower right quadrant of the arc shaped portion of
`the edge of the slit 43 on the right side, there is a case where
`the liquid crystal molecule L rotates in a direction opposite to
`the desired direction. In other words, there is a case where the 50
`liquid crystal molecule does not rotate in the desired direc(cid:173)
`tion. As described above, when a horizontal electric field is
`applied, there is a case where the rotation direction of the
`liquid crystal molecule Lin the edge portion changes depend(cid:173)
`ing on its location. As described above, a phenomenon in 55
`which the rotation direction is different depending on the
`location is disclination. In a boundary in which the rotation
`direction changes, since the liquid crystal molecule L may be
`rotated in an undesired direction or cannot be rotated, there is
`a case where the transmittance is lowered and the boundary is 60
`visually recognized. The case is referred to as a rotating tilt
`line, a rotation tilt defect, or simply disclination. FIG. 4 shows
`a region denoted as D in which the disclination occurs.
`In FIG. 4, the area Dis an edge portion of a fringe of the slit
`43. In particular, the area D is in the range from a place in 65
`which the direction of the normal line of the slit 43 coincides
`with the initial alignment direction of the liquid crystal mo!-
`
`8
`ecule L, that is, the rubbing direction R-R to a place in which
`the direction of the normal line of the slit 43 forms an angle of
`90° in the clockwise direction with respect to the rubbing
`direction. When an electric field is applied, in this range
`5 shown in FIG. 4, the liquid crystal molecule L rotates in the
`clockwise direction to be perpendicular to the fringe of the
`edge portion. On the other hand, in areas other then this area,
`the liquid crystal molecule L rotates in the counterclockwise
`direction to be perpendicular to the fringe of the slit 43. In
`10 other words, the area Din which the disclination in the edge
`portion of the slit 43 occurs is a range from a place in which
`the direction of the normal line of the slit 43 coincides with
`the rubbing direction R-R to a place forming 90° in the
`15 clockwise direction with respect to the rubbing direction.
`In other words, as shown in FIG. 4, when the end portion of
`the opening part has an arc shape like the slit 43, an area Din
`which disclination occurs is the second and fourth quadrants
`of a circle having an x axis in the direction in which the slits
`43 extend in the longitudinal direction and a Y axis perpen(cid:173)
`dicular to the x axis when a tilt angle formed by a direction in
`which the end portion of the slit 43 in the longitudinal direc(cid:173)
`tion extends with respect to a rubbing direction R-R is in the
`positive direction, that is, an angle formed in the clockwise
`direction. On the other hand, when the tilt angle is in the
`negative direction, that is, an angle formed in a counterclock(cid:173)
`wise direction, the area in which disclination occurs are the
`first and third quadrants of the circle.
`In addition, unlike FIG. 4, when the common electrode has
`a comb-teeth shape and the transparent conduction mate