Ulllted States Patent [19]
`Morii et al.
`
`US006141078A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,141,078
`*Oct. 31, 2000
`
`[54] IPS TYPE LIQUID CRYSTAL DISPLAY
`APPARATUS HAVING IN_PLANE
`RETARDATION VALUE OF LESS THAN
`ZERO AND NOT MORE THAN 20
`
`4/1998 Ogura et al. .......................... .. 349/153
`5,739,888
`7/1999 Kataoka et al.
`349/117
`5,926,242
`5,982,471 11/1999 Hirakata et al. ...................... .. 349/155
`FOREIGN PATENT DOCUMENTS
`
`[75] Inventors: Yasuhiro Morii; Fumio Matsukawa;
`Akira Tsumura; Shin Tahata; Masaya
`Mizunuma; Akira Tamatani;
`Masayuki Fujii, all of Tokyo; Yasuo
`Fu'ita Kumamoto all of Ja an
`J
`>
`>
`P
`
`[73] Assignees: Mitsubishi Denki Kabushiki Kaisha,
`Tokyo; Advanced Display, Inc,’
`Kumamoto, both of J apan
`
`[ * ]
`
`Notice:
`
`This patent issued on a continued pros-
`ecution application ?led under 37 CFR
`1.53(d), and is subject to the tWenty year
`Patent term Provlslons of 35 USC-
`154(21)(2)-
`
`[21] Appl. No.: 09/237,664
`.
`_
`Jan‘ 27’ 1999
`Flled'
`[22]
`Int. c1.7 ...................... .. G02F 1/1339; G02F 1/1343
`[51]
`[52] us. Cl. ......................... .. 349/155; 349/141; 349/156
`[58] Field of Search
`349/155 156
`"""""""""""""""""" " 349/141’ 153’
`’
`
`[56]
`
`References Cited
`
`5 078 475
`5,220,446
`5,493,429
`5,537,235
`5,615,031
`
`US PATENT DOCUMENTS
`349/155
`1/1992 Sekimura et al
`349/155
`'''''''''''''''
`6/1993 Rho .............. .:
`359/68
`2/1996 Kanemoto et al. ..
`.. 359/81
`7/1996 Ishihara et al. .... ..
`3/1997 Saiuchi et al. ........................ .. 349/149
`
`2-220032 9/1990 Japan.
`4453625 5/1992 Japan -
`6460278 2/1994 Japan '
`94” 48
`/ 1997 Japan'
`9446108 6/1997 Japan '
`9-152625
`6/1997 Japan .
`9-171194 6 1997 J
`.
`/
`apa“
`Primary Examiner—William L. Sikes
`Assistant Examiner—Tarifur R. ChoWdhury
`Attorney, Agent, or Firm—Oblon, Spivak, McClelland,
`Maier & Neustadt, P.C.
`
`ABSTRACT
`[57]
`The liquid crystal display apparatus of present invention
`includes a TFT array substrate on Which there are formed
`scanning signal lines, image signal lines, thin ?lm
`transistors, liquid crystal driving electrodes, common elec
`trodes and common signal lines, a counter substrate Which
`opposes the TFT array substrate, primary spacers for main
`raining a gap between both substrates Constant, secondary
`Spacers for maintaining a gap in peripheral portions of both
`substrates constant, a seal member Which is interposed in the
`gap betWeen both substrates together With the secondary
`spacers and Which adhere peripheral portions of both
`substrates, and a liquid crystal layer, Wherein the in-plane
`retardation of the display apparatus (An)~(dmg_x—dmin) is not
`less than 0 nm and not more than 20 nm, Whereby variations
`in colors occurring in liquid crystal display apparatuses of
`IPS type which are due to unevenness of liquid Crystal layers
`can be eliminated
`
`11 Claims, 14 Drawing Sheets
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`U.S. Patent
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`FIG.13
`PRIORART
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`Page 14 of 23
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`0a. 31, 2000
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`
`1
`IPS TYPE LIQUID CRYSTAL DISPLAY
`APPARATUS HAVING IN-PLANE
`RETARDATION VALUE OF LESS THAN
`ZERO AND NOT MORE THAN 20
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to an in-plane switching
`type liquid crystal display apparatus. More particularly, the
`present invention relates to an in-plane response type liquid
`crystal display apparatus Which is obtained by adhering tWo
`substrates of Which at least electrodes on one side thereof are
`of a comb-like shape on at least one side thereof and
`enclosing liquid crystal therein, Wherein it is arranged such
`that irregularities in colors can be eliminated and display
`property improved.
`In contrast to tWisted nematic display methods Wherein an
`electric ?eld is applied on liquid crystal in a direction
`vertical With respect to a substrate, developments are being
`made in these years employing display methods in Which an
`electric ?eld is applied in a direction substantially parallel
`With respect to a substrate. For instance, Japanese Unexam
`ined Patent Publication No. 225388/1995 discloses an
`example of a liquid crystal display apparatus employing
`such a display method in Which an electric ?eld is applied in
`a direction substantially parallel With respect to a substrate,
`in Which it is referred to that the gap betWeen substrates is
`set to be not more than 6 pm or that the retardation, Which
`Will be described beloW in details, to be not less than 0.21
`pm and not more than 0.36 pm in order to improve the
`response speed.
`The inventors of the present invention have de?ned the
`above described liquid crystal display apparatus employing
`a display method in Which an electric ?eld is impressed in
`a direction substantially parallel With respect to a substrate
`as an in-plane sWitching liquid crystal display apparatus
`(hereinafter referred to as “IPS panel”).
`FIG. 11 is a partial sectional explanatory vieW of a
`conventional in-plane sWitching type liquid crystal display
`apparatus. In the draWings, only tWo pixels have been
`partially shoWn for ease of explanation (and this also applies
`to all draWings hereafter). FIG. 12 is a plan explanatory vieW
`of one pixel in a conventional IPS panel. FIG. 13 is a
`sectional explanatory vieW taken along line X-Y of FIG. 11.
`In FIG. 11, FIG. 12, and FIG. 13, numeral 1 denotes a TFT
`array substrate, numeral 2 pixel electrodes, numeral 3 TFT
`portions, and numeral 4 a counter substrate. The surface of
`the TFT array substrate 1 is provided With electrodes Which
`are of comb-like shape. Each of the pixel electrodes 2 is
`comprised of a comb-like liquid crystal driving electrode 21
`and a comb-like common electrode 22 at least a part of
`Which is formed to oppose the liquid crystal driving elec
`trode. TFT portion 3 is a generic term for thin ?lm transistors
`(hereinafter referred to as “TFT”) 14 for Writing image
`signals to the liquid crystal driving electrodes 21, and signal
`cables for supplying image signal cables 12, scanning signal
`cables 11, or common electrodes 22 With signals. The
`counter substrate 4 is arranged to oppose the TFT array
`substrate 1. Materials for forming the pixel electrodes 2 may
`be any one selected from among chrome, aluminum, indium
`tin oxide (hereinafter referred to as “ITO”). Numeral 25
`denotes an insulating ?lm. The counter substrate 4 is not
`required to be provided to be With electrodes on the surface
`thereof in case of IPS panels performing colored display, and
`is generally provided With a ?ag portion (not shoWn) formed
`of metal or resin and a color ?lter substrate With coloring
`layers 18 of red, green and blue. In order to prevent the
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`coloring layers 18 from melting to the exterior, a protecting
`?lm 24 is formed on the counter substrate 4. Numeral 17
`denotes electrodes for Writing in image signals, scanning
`signals or common signals from the substrate exterior.
`Numeral 7 denotes liquid crystal, and the thickness thereof
`is represented as d. Further, numeral 15 in FIG. 13 denotes
`one molecule Within the liquid crystal layer. Numeral 9 is a
`seal member for connecting the TFT array substrate 1 to the
`opposing substrate 4, numeral 10 secondary spacers con
`tained in the seal member, and numerals 5 and 6 polariZer.
`Numeral 23 denotes an alignment layer for aligning the
`liquid crystal 7. Further, in FIG. 13, IO denotes incident light,
`I outgoing transmitted light, T transmittance axis, D aligning
`direction, and E electric ?eld.
`The basic arrangement of the IPS panel Will be explained
`With reference to FIG. 11. In the basic arrangement of the
`IPS panel, the TFT array substrate 1 and counter substrate 4
`are opposed in a parallel manner, connected by seal member
`9, and liquid crystal 7 is interposed betWeen the TFT array
`substrate 1 and the counter substrate 4. Alignment treat
`ments have been performed for the orientation ?lm 23
`(detailed descriptions thereof Will be described later). Pri
`mary spacers 8 are dispersed Within the seal surface for
`maintaining the gap d betWeen the TFT array substrate 1 and
`the counter substrate 4 constant, and secondary spacers 10
`are disposed by mixing them into the seal member 9.
`While it has been de?ned in the prior art as disclosed in
`the above mentioned Japanese Unexamined Patent Publica
`tion No. 225388/1995 that the gap betWeen the substrates
`shall not be more than 6 pm, there is made neither any
`reference to secondary spacers 10 as shoWn in FIG. 11 Which
`are knoWn in the art by the inventors of the present invention
`nor to making the gap betWeen the substrates constant. This
`is considered to be due to the fact that it had not been
`recogniZed of the connection of these With improving irregu
`larities in colors of display Which is a subject of the present
`invention as it Will be described in details hereafter.
`The operational theory of the IPS panel Will noW be
`explained With reference to FIG. 13. As noted in the above
`explanation of the basic arrangement, the TFT array sub
`strate 1 and counter substrate 4 are opposed in a parallel
`manner. In case the liquid crystal 7 is liquid crystal of
`positive anisotropy of dielectric constant, liquid crystal
`molecules 15 are disposed such that the longitudinal axes
`thereof are parallel With respect to the substrate surface and
`such that they are also substantially parallel With respect to
`the electrodes. For this disposing method, knoWn rubbing
`methods are generally used, and in case rubbing is per
`formed for the alignment layer 23 in a direction substantially
`parallel to the electrodes, the liquid crystal molecules 15
`assume the above described alignment. In this manner, the
`polariZer 5 is disposed such that the transmission axis
`thereof is parallel With respect to the aligning direction, and
`the polariZer 6 as to be orthogonal to the transmission axis
`of the polariZer 5.
`In case the electric ?eld is OFF, light that has passed
`through the polariZer 5 reaches the second polariZer 6 along
`the alignment of the liquid crystal molecules 15. Light can
`not path through since, as noted above, the transmission axis
`of the polariZer 6 is orthogonal to the transmission axis of
`the polariZer 5. In case the electric ?eld is ON, that is, an
`electric ?eld has been generated in a horiZontal direction
`With respect to the substrate betWeen the liquid crystal
`driving electrodes 21 and common electrodes 22 Which have
`been formed to as to oppose the former, the longitudinal axis
`of the liquid crystal molecules rotates in a parallel manner
`With respect to the substrates along a direction of the electric
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`?eld Which is due to the anisotropy of dielectric constant of
`the liquid crystal. At this time, the transmitted light changes
`from a linear polarized light to an elliptical polariZation (the
`elliptical polariZation is schematically shoWn on the counter
`substrate 4 in FIG. 13 on the right-hand side thereof due to
`birefringence effects, and passes through the polariZer 6.
`In this manner, the IPS panel employs the birefringence
`effect. The birefringence effect is generally called an ECB
`(electrically controlled birefringence) effect (hereinafter
`referred to as “IPS mode”). Since the liquid crystal mol
`ecules comprise a refractive index of ordinary light no and
`a refractive index of extraordinary light ne, there exists an
`anisotropy of refractive index An=ne—no. The presence of An
`in the liquid crystal molecules causes birefringence effects.
`In the ISP panel, the liquid crystal molecules 15 are
`aligned as to be uniformly directed in one direction parallel
`to the substrate as shoWn in FIG. 13. Such a condition of
`alignment is called a homogeneous alignment. The intensity
`of transmission light I of light outgoing from polariZer 6 in
`case the polariZers 5, 6 have been disposed as shoWn in FIG.
`11 by employing homogeneous alignment is given by the
`folloWing equation.
`
`Where I0 represents intensity of light incident on the
`polariZer 5, )t represents Wavelength, and R represents
`retardation Which is obtained by multiplying an optical
`path difference betWeen ordinary light and extraordi
`nary light by thickness of the liquid crystal ((An)~d).
`That is, the intensity of light Which is outgoing from the
`polariZer 6 is given by a function of wavelength A, of
`incident light and retardation R. Thus, variations in
`thickness d of the liquid crystal 7 cause variations in
`outgoing light intensity, that is, transmission light I.
`In the theory of a conventional IPS mode as described
`above, variations occur in outgoing transmission light oWing
`to variations in thickness of the liquid crystal layer. Varia
`tions in outgoing transmission light I causes variations in
`colors of display (hereinafter referred to as “irregularities of
`colors”). Measures had already been taken in the prior art for
`eliminating variations in thickness of liquid crystal layers,
`one of Which is disclosed in Japanese Unexamined Publi
`cation No. 286176/ 1996, Wherein a planation layer of trans
`parent resin 17 is provided on the color ?lter for planation
`of the surface, and also Japanese Unexamined Patent Pub
`lication No. 225388/1995 discloses such a provision of a
`?atting layer on the color ?lter, and it is considered that such
`a ?atting layer is effective in making the thickness of the
`liquid crystal layer uniform.
`HoWever, the inventors of the present invention have
`found out, as it Will be discussed in details hereafter, that it
`is impossible to decrease variations in thickness of a liquid
`crystal layer even in a conventional arrangement in Which
`spacers have been provided betWeen tWo substrates, and
`much less is it possible to accurately make the thickness of
`the liquid crystal layer uniform by using a planation layer as
`disclosed in the above publications (Japanese Unexamined
`Patent Publication No. 286176/ 1996 and Japanese Unexam
`ined Patent Publication No. 225388/ 1995). Problematic
`points of conventional IPS panels Will noW be explained
`based on FIG. 14.
`There are cases in Which the primary spacers 8 are either
`arranged on the TFT portions 3 or alternatively, on the pixel
`electrodes 2. Generally, the volumetric ratio of TFT portions
`3 and pixel electrodes 2 of a TFT array substrate 1 is
`approximately 7:3. Therefore, it is often the case that pri
`
`4
`mary spacers 8 on the pixel electrodes 2 determine the
`thickness of the liquid crystal 7. Thus, it is often the case that
`dmax and dmin exist Within a single IPS panel in Which the
`thickness of liquid crystal 7 is uniform as shoWn in FIG. 14.
`FIG. 14 is a sectional explanatory vieW shoWing problematic
`points of a conventional IPS panel, and reference numerals
`as used therein are identical With those of FIGS. 11, 12 and
`13. In this description, the thickness of the liquid crystal
`layer of pixel portions Which are governed by the primary
`spacers 8 in convex portion of uneveness on the TFT
`portions 3 is de?ned as dmax (indicating pixels on both sides
`of the convex portion and the larger one is de?ned as dmax),
`and the thickness of the liquid crystal layer of pixel portions
`Which are governed by the primary spacers 8 in a concave
`portion of uneveness on the pixel electrodes 2 is de?ned as
`dmin. The value of dmax—dmin of a TFT array substrate, Which
`difference in height of the convex portions on the TFT
`portions 3 and the depth of the concave portions on the pixel
`electrodes 2 Was approximately 1 pm, Was approximately
`0.8 pm.
`In a general IPS mode, the retardation (An)~d is set to be
`275 nm. In our studies, it has been found that display
`de?ciencies occurred in case retardation (An)~(dmax—dmin)
`Was different by not less than 20 nm. The An of liquid crystal
`generally used in an IPS mode is 0.05 to 0.15. That is, in case
`dmax-duh, is not less than 0.8 pm, (An)~(dmax—dmin) is in the
`range betWeen 40 to 120 nm and thus causes display
`de?ciencies as already described. Thus, dmax—dmin is
`required to be not more than 0.4 pm in order to make
`(An)~(dmax—dmin) to be not more than 20 nm.
`As described, variations in thickness of liquid crystal 7
`caused irregularities in colors in conventional arrangements
`of IPS panels, and thus caused de?ciencies in display
`property of display.
`Further, since difference in height of the convex portion of
`the TFT array substrate and the depth of the pixel electrode
`Was approximately 1 pm in a conventional arrangements of
`TFT array substrates 1 Which Was formed on the TFT array
`substrate 1 Which Was due to arrangements of the TFT
`portions or pixel electrodes. Thus, the spherical shape of
`secondary spacers 10 contained in the seal member 9 and the
`diameter of primary spacers 8 dispersed Within the display
`surface could not be accurately set. Therefore, variations in
`dispersing processes of secondary spacers 10 and primary
`spacers 8 caused differences in the thickness dmin of the
`liquid crystal 7 in the proximity of the seal member 9 and in
`the thickness dmax of the liquid crystal 7 in the central
`portion of the display surface, Whereby display de?ciencies
`Were generated.
`The present invention has been made With the aim of
`solving the above described problems, and it is an object of
`the present invention to provide an IPS panel of favorable
`display property by eliminating variations in colors Which
`Were due to unevenness in thickness of the liquid crystal
`layer Which existed in conventional arrangements of IPS
`panels.
`
`SUMMARY OF THE INVENTION
`The liquid crystal display apparatus according to Claim 1
`of he present invention is a liquid crystal display apparatus
`comprised of a FT array substrate on Which there are formed
`on a substrate scanning signal lines, image signal lines, thin
`?lm transistors formed at each intersection of the scanning
`signal lines and image signal lines, liquid crystal driving
`electrodes connected to the thin ?lm transistors, common
`electrodes formed such that at least a part of them are
`opposing the liquid crystal driving electrodes, and common
`signal lines for Writing in signals to the common electrodes,
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`contact With one side of the TFTs and comb-like electrodes.
`Comb-like electrodes on the other side are provided With
`contact holes for contact With the common electrodes. That
`is, by providing the comb-like electrodes on the organic ?lm
`for ?atting, voltage loss due to the organic ?lm can be
`prevented and an even greater electric ?eld can be applied to
`the liquid crystal.
`In the liquid crystal display apparatus according to Claim
`5 of the present invention, in case uneveness of an in-plane
`?lm of the organic ?lm that is parallel to the TFT array
`substrate are expressed as concave portions/convex portions,
`an absolute value for a height obtained by subtracting the
`concave portion from the convex portion is not more than
`0.4 pm, Whereby the retardation can be made to be not less
`than 0 nm and not more than 20 nm, and is thus favorable.
`In the liquid crystal display apparatus according to Claim
`6 of the present invention, the primary spacers are of
`spherical shape, and the secondary spacers are of columnar
`shape, Whereby they are easily available and present desired
`dimensional accuracy, and is thus favorable.
`In the liquid crystal display apparatus according to Claim
`7 of the present invention, a diameter of the secondary
`spacers is a sum of a thickness of a coloring layer provided
`on the opposing substrate and of a diameter of the primary
`spacers, Whereby the gap betWeen the TFT array substrate
`and opposing substrate can be made constant, and is thus
`favorable.
`In manufacturing the TFT array substrate as employed in
`the liquid crystal display apparatus according to Claim 8 of
`the present invention, the organic ?lm is formed as a ?atting
`?lm by applying organic resin having a viscosity of not less
`than 15 cP and not more than 50 cP onto the surface of the
`TFT array substrate by spin coat method at a rotational speed
`of not less than 500 rpm and not more than 2,000 rpm,
`Whereby the ?lm thickness of the ?atting ?lm can be easily
`set to be not less than 3 pm and not more than 10 pm, and
`is thus favorable.
`In manufacturing the TFT array substrate as employed in
`the liquid crystal display apparatus according to Claim 9 of
`the present invention, the organic resin is one selected from
`photosensitive acrylic resin and acrylic resin, Whereby ?lm
`forming can be performed When the TFT array is
`manufactured, and is thus favorable.
`In manufacturing the TFT array substrate as employed in
`the liquid crystal display apparatus according to Claim 10 of
`the present invention, the thickness of the ?atting ?lm is set
`to be not less than 3 pm and not more than 10 pm, Whereby
`variations in thickness of the ?lm can be made to be not
`more than 0.4 pm.
`The arrangement and manufacturing method of the liquid
`crystal display apparatus according to the present invention
`Will noW be explained in details With reference to the
`draWings.
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`a counter substrate Which opposes the TFT array
`substrate,
`a plurality of primary spacers for maintaining a gap
`betWeen the TFT array substrate and the opposing
`substrate constant,
`a plurality of secondary spacers for maintaining a gap
`betWeen peripheral portions of the TFT array substrate
`and the counter substrate constant,
`a sealing agent Which is interposed in the gap betWeen the
`TFT array substrate and counter substrate together With
`the secondary spacers and Which adhere the TFT array
`substrate and counter substrate at the peripheral
`portions, and
`a liquid crystal layer pinched and held betWeen the array
`substrate and counter substrate,
`the liquid crystal layer presenting bifringence effects,
`Wherein an in-plane retardation of the display apparatus
`(An)~(dmax—dmin) is not less than 0 nm and not more
`than 20 nm in case the largest gap of gaps betWeen
`the liquid crystal driving electrodes and opposing
`substrates Within the display surface of the liquid
`crystal display is denoted dmax, and the smallest gap
`Within the display surface of the liquid crystal dis
`play dmin.
`In the liquid crystal display apparatus according to Claim
`2 of the present invention, the primary spacers is of spherical
`shape, and the secondary spacers is of columnar shape,
`Whereby they are easily available and present desired dimen
`sional accuracy, and is thus favorable.
`The liquid crystal display apparatus according to Claim 3
`of the present invention is a liquid crystal display apparatus
`comprised of a TFT array substrate on Which there are
`formed on a substrate scanning signal lines, image signal
`lines, thin ?lm transistors formed at each intersection of the
`scanning signal lines and image signal lines, liquid crystal
`driving electrodes connected to the thin ?lm transistors,
`common electrodes formed such that at least a part of them
`are opposing the liquid crystal driving electrodes, and com
`mon signal lines for Writing in signals to the common
`electrodes,
`a counter substrate Which opposes the TFT array
`substrate,
`a plurality of primary spacers for maintaining a gap
`betWeen the TFT array substrate and the counter sub
`strate constant,
`a plurality of secondary spacers for maintaining a gap
`betWeen peripheral portions of the TFT array substrate
`and the counter substrate constant,
`a sealing agent Which is interposed in the gap betWeen the
`TFT array substrate and counter substrate together With
`the secondary spacers and Which adhere the TFT array
`substrate and counter substrate at the peripheral
`portions, and
`a liquid crystal layer pinched and held betWeen the array
`substrate and counter substrate,
`the liquid crystal layer presenting bifringence effects,
`Wherein an organic ?lm is provided on the TFT array
`substrate having a thickness of not less than 3 pm and
`not more than 10 pm.
`In the liquid crystal display apparatus according to Claim
`4 of the present invention, the liquid crystal driving elec
`trodes and common electrodes are formed on the organic
`?lm, Whereby driving voltages for the liquid crystal panel
`can be made loW, and is thus favorable. That is, While
`planation ?lms are arranged on conventional TFT array
`substrates, contact holes are formed on the planation ?lm for
`
`55
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a graph according to EMBODIMENT 1 of the
`present invention shoWing dependency of transmittance on
`Wavelength in IPS modes;
`FIG. 2 is a sectional explanatory vieW shoWing an IPS
`panel of EMBODIMENT 1 of the present invention;
`FIGS. 3(a) and 3(b) are sectional explanatory vieWs
`shoWing, as a ?oWchart, manufacturing process of a TFT
`array substrate employed in the IPS panel of EMBODI
`MENT 1 of the present invention;
`FIGS. 4(a) and 4(b) are sectional explanatory vieWs
`shoWing, as a ?oWchart, manufacturing process of a TFT
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`65
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`Page 18 of 23
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`

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`6,141,078
`
`7
`array substrate employed in the IPS panel of EMBODI
`MENT 1 of the present invention;
`FIGS. 5(a) to 5(c) are sectional explanatory views
`showing, as a ?owchart, manufacturing process of a TFT
`array substrate employed in the IPS panel of EMBODI
`MENT 1 of the present invention;
`FIG. 6 is a sectional explanatory view showing an IPS
`panel of EMBODIMENT 2 of the present invention;
`FIG. 7 is a plan explanatory view showing a single pixel
`of IPS panel of EMBODIMENT 2 of the present invention;
`FIGS. 8(a) and 8(b) are sectional explanatory views
`showing, as a ?owchart, manufacturing process of a TFT
`array substrate employed in the IPS panel of EMBODI
`MENT 2 of the present invention;
`FIG. 9 is a sectional explanatory view showing an IPS
`panel of EMBODIMENT 2 of the present invention;
`FIG. 10 is a sectional explanatory view showing IPS panel
`of the present invention;
`FIG. 11 is a sectional explanatory view showing a con
`ventional IPS panel;
`FIG. 12 is a plan explanatory view showing a single pixel
`of conventional IPS panel;
`FIG. 13 is a sectional explanatory view taken along line
`X—X in FIG. 11; and
`FIG. 14 is a sectional explanatory view showing a prob
`lem of the conventional IPS panel.
`
`DETAILED DESCRIPTION
`Embodiments of the liquid crystal display apparatus of the
`present invention will now be explained.
`
`EMBODIMENT 1
`The arrangement of the IPS liquid crystal display appa
`ratus according to the present embodiment will ?rst be
`explained. The IPS liquid crystal display apparatus accord
`ing to the present embodiment is mainly comprised of,
`similarly to conventional ones, a TFT array substrate, a
`counter substrate, a sealing agent, spacers (secondary
`spacers) and a liquid crystal layer. Spacers will be discussed
`in details later. The TFT array substrate is a substrate made,
`for instance, of glass provided with scanning signal lines,
`image signal lines, TFTs and liquid crystal driving elec
`trodes which are arranged in a form of an, and there are
`further arranged common electrodes and common signal
`lines. The scanning signal lines are arranged in that a
`plurality thereof are arranged at equal intervals and in a
`parallel manner, and the image signal lines in that a plurality
`thereof are arranged at equal intervals and in a parallel
`manner and further as to be orthogonal to the scanning signal
`lines via an insulating ?lm. TFTs are respectively arranged
`at each intersection at which the scanning signal lines and
`image signal lines intersect, to each of which a liquid crystal
`driving electrode is connected. The common electrodes are
`arranged in that at least a part thereof are formed to oppose
`and to be parallel with respect to the liquid crystal driving
`electrodes, and common signal lines for writing in signals to
`the common electrodes are disposed vertical with respect to
`the common electrodes. It should be noted that at least a part
`of the common electrodes and common signal lines
`intersect, and are arranged in that signals may be written in
`through these intersections. The counter substrate is dis
`posed as to oppose the TFT array substrate, and the counter
`substrate is formed with coloring layers of red, green and
`blue as well as a protecting ?lm for preventing these
`coloring layers from melting to the liquid crystal layer.
`
`10
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`15
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`25
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`35
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`45
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`55
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`65
`
`8
`For maintaining a predetermined gap between the TFT
`array substrate and the counter substrate in regions formed
`with liquid crystal driving electrodes constant, there are
`interposed primary spacers in these regions between the TFT
`array substrate and the counter substrate.
`The primary spacers are of spherical shape having a
`diameter of approximately 5 pm, and a plurality of these are
`used which are made of synthetic resin. The reason for using
`those made of plastic is that spacers of plastic are compara
`tively soft and do not damage the TFT elements.
`Alternatively, materials of the silica (SiO2) may be selected.
`Dimensional variations are approximately 0.3 pm (average
`deviation), whereby the gap between the TFT array substrate
`and opposing substrate can be maintained constant. The
`amount of primary spacers that is to be dispersed into the
`gap between the TFT array substrate and counter substrate
`is suitably selected for achieving a desired uniformity for the
`gap. Such spherical spacers are easily available and are
`effective in achieving a desired dimensional accuracy.
`Aplurality of secondary spacers are employed which may
`be of columnar, strip-like or spherical shape. In view of costs
`thereof, it is often the case that spacers of glass are
`employed. In any case, they are easily available and are
`effective in achieving a desired dimensional accuracy. While
`materials for the primary spacers are selected from materials
`which are soft and do not damage the TFT elements, those
`for the secondary spacers are selected from hard ones.
`The sealing agent is for adhering the TFT array substrate
`and counter substrate together at their peripheral portions
`while maintaining a predetermined gap therebetween, and
`secondary spacers are interposed in the seal member for
`maintaining a predetermined gap between the TFT array
`substrate and counter substrate at their peripheral portions
`constant, and the TFT array substrate and counter substrate
`are adhered together. In this gap of a predetermined interval,
`a liquid crystal layer characteristics of liquid crystal having
`bifringence is interposed and held. PolariZers are arranged in
`the upper side of the TFT array substrate and in the lower
`side of the counter substrate.
`Considerations of a relationship between visual recogni
`tion of irregularities in colors and transmittance of light
`correspondi