(12) United States Patent
`Tomioka et al.
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 8,758,871 B2
`Jun. 24, 2014
`
`US008758871B2
`
`(54)
`
`LIQUID CRYSTAL DISPLAY AND METHOD
`FOR MANUFACTURING SAME
`
`(75)
`
`(73)
`
`(*)
`
`Inventors: Yasushi Tomioka, Hitachinaka (JP);
`Hidetoshi Abe, Hitachinaka (JP);
`Katsumi Kondo, Mito (JP)
`
`Assignees: Japan Display Inc., Tokyo (JP);
`Panasonic Liquid Crystal Display Co.,
`Ltd., Hyogo-ken (JP)
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. l54(b) by 0 days.
`
`13/212,072
`
`Aug. 17, 2011
`
`Prior Publication Data
`
`US 201 1/0301324 Al
`
`Dec. 8, 2011
`
`Related U.S. Application Data
`
`Division of application No. 12/781,815, filed on May
`18, 2010, now Pat. No. 8,025,939, which is a
`continuation of application No. 10/537,825, filed as
`application No. PCT/JP03/15658 on Dec. 8, 2003,
`now Pat. No. 7,718,234.
`
`(30)
`
`Foreign Application Priority Data
`
`7,718,234 B2
`7,935,396 B2
`8,025,939 132*
`2001/0048498 A1
`2004/0012725 A1
`2005/0271833 A1
`2007/0160778 A1
`
`5/2010
`5/2011
`9/2011
`12/2001
`1/2004
`12/2005
`7/2007
`
`"omioka et al.
`Matsumori et al.
`"omioka et al.
`............. .. 428/1.2
`"omioka et al.
`"omioka et al.
`Matsumori et al.
`Matsumori et al.
`
`FOREIGN PATENT DOCUMENTS
`
`850975
`1037092
`63-21907
`6-160878
`6-202127
`7-36047
`7-209650
`7-209653
`07-287235
`8-36183
`9-73101
`9-297313
`10-307295
`11-218765
`11-264982
`2000-080164
`2000-319510
`2001-281671
`2001-517317
`2002-131751
`3303766
`2002-258262
`2002-258303
`2003-73471
`2003-255349
`473497
`WO 91/10936
`
`7/1998
`9/2000
`5/1988
`6/1994
`7/1994
`2/1995
`8/1995
`8/1995
`10/1995
`2/1996
`3/1997
`11/1997
`11/1998
`8/1999
`9/1999
`3/2000
`11/2000
`10/2001
`10/2001
`5/2002
`5/2002
`9/2002
`9/2002
`3/2003
`9/2003
`1/2002
`7/1991
`
`
`
`/1gnawututututututututututmutututmututmmmmfnfn5€"U"U"d"U"d"U"U"U"U"U"U"U*U"U"U"U*U"U*U"U*U"U*U>-U»-g
`
`Dec. 9, 2002
`
`(JP) ............................... .. 2002-356461
`
`OTHER PUBLICATIONS
`
`(51)
`
`(52)
`
`(58)
`
`Int. Cl.
`C09K 19/56
`G02F1/1337
`U.S. Cl.
`
`(2006.01)
`(2006.01)
`
`USPC ....... .. 428/1.2; 428/1.25; 428/1.26; 428/1.27;
`252/299.4; 349/123; 349/135
`Field of Classification Search
`
`USPC ........... .. 428/1.2, 1.25, 1.26, 1.27; 252/299.4;
`349/123, 135; 525/425; 528/343.344
`See application file for complete search history.
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
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`Togashi
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`2003-408382.
`
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`
`* cited by examiner
`
`Primary Examiner — Shean C Wu
`(74) Attorney, Agent, or Firm —Ant0nelli, Terry, Stout &
`Kraus, LLP.
`
`(57)
`
`ABSTRACT
`
`A liquid crystal display is provided which is capable ofreduc-
`ing the occurrence ofdefective display due to variations in the
`initial alignment direction of a liquid crystal alignment con-
`trol film in a liquid crystal display of an IPS scheme, realizing
`the stable liquid crystal alignment, providing excellent mass
`productivity, and having
`image quality with a higher
`contrast ratio. The liquid crystal display has a liquid crystal
`layer disposed between a pair of substrates, at least one ofthe
`substrates being transparent, and an alignment control film
`formed between the liquid crystal layer and the substrate. At
`least one of the alignment control films 109 comprises pho-
`toreactive polyimide and/or polyamic acid provided with an
`alignment control ability by irradiation of substantially lin-
`early polarized light.
`
`14 Claims, 8 Drawing Sheets
`
`Page 1 of 29
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`US 8,758,871 B2
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`1
`LIQUID CRYSTAL DISPLAY AND METHOD
`FOR MANUFACTURING SAME
`
`This application is a Divisional application of application
`Ser. No. 12/781,815, filed May 18, 2010, now U.S. Pat. No.
`8,025,939 which is a Continuation application of application
`Ser. No. 10/537,825, filed Jun. 8, 2005, now U.S. Pat. No.
`7,718,234 the contents of which are incorporated herein by
`reference in their entirety. Ser. No. 10/537,825 is a National
`Stage application, filed under 35 USC 371, of International
`(PCT) Application No. PCT/JP03/15658, filed Dec. 8, 2003.
`
`'
`
`TECHNICAL FIELD
`
`The present invention relates to a liquid crystal display of a
`so-called IPS (In-Plane Switching) scheme in which an elec-
`tric field substantially in parallel with a substrate is applied to
`a liquid crystal layer for operation, and to a production pro-
`cess thereof.
`
`BACKGROUND ART
`
`In general, display of a liquid crystal display is realized by
`applying an electric field to liquid crystal molecules in a
`liquid crystal layer sandwiched between a pair ofsub strates to
`change the alignment direction ofthe liquid crystal molecules
`and utilizing the resulting change in the optical property ofthe
`liquid crystal layer. Conventionally, a liquid crystal display of
`a so-called active drive type having a switching device such as
`a thin-film transistor for each pixel is represented by a TN
`(Twisted Nematic) display scheme in which an electrode is
`provided for each of a pair of substrates sandwiching a liquid
`crystal layer between them, the direction of an electric field
`applied to the liquid crystal layer is set to be substantially
`perpendicular to the interface between the substrates, and the
`optical rotatory power of the liquid crystal molecules consti-
`tuting the liquid crystal layer is utilized to achieve display. In
`the liquid crystal display of the TN scheme, a small viewing
`angle is regarded as the greatest problem.
`On the other hand, “Patent Document 1,” “Patent Docu-
`ment 2,” “Patent Document 3,” “Patent Document 4,” “Patent
`Document 5” and the like have disclosed an IPS scheme in
`
`which an inter-digital electrode formed on one of a pair of
`substrates is used to produce an electric field having a com-
`ponent substantially in parallel with the substrate surface to
`rotate liquid crystal molecules constituting a liquid crystal
`layer in a plane substantially in parallel with the substrate and
`the birefringence of the liquid crystal layer is used to realize
`display. The IPS scheme has advantages such as a wider
`viewing angle and a lower load capacity due to the in-plane
`switching of the liquid crystal molecules as compared with
`the conventional TN scheme. The IPS scheme is considered
`
`as a new and promising liquid crystal display which will
`replace the TN scheme and has made rapid advances in recent
`years. In addition, another type of the IPS scheme has been 55
`disclosed in “Patent Document 6” in which at least one of
`
`paired electrodes for applying an electric field to a liquid
`crystal layer is made of a transparent conductive film to
`improve transmittance.
`The liquid crystal display of the IPS scheme (abbreviated
`as IPS-TFT-LCD) with favorable viewing angle characteris-
`tics (luminance contrast ratio, tone and color reversal) and
`bright display represents prospective technology for monitors
`or televisions with a large display area. In the liquid crystal
`display, an alignment control film provided with a liquid
`crystal alignment control ability is formed on the interface
`between a liquid crystal layer and each of a pair of substrates
`
`2
`
`sandwiching the liquid crystal layerbetween them. However,
`to put IPS-TFT-LCDs for supporting large screens of 20
`inches or more into practice use in the future, it is necessary to
`develop a new structure and process for large-size displays
`(large panels).
`In particular, for an IPS-TFT-LCD having many stepped
`structures on a surface opposite to a liquid crystal layer, it is
`diflicult to perform uniform alignment processing on an
`alignment control film over a large screen. A margin in per-
`forming the alignment processing on the alignment control
`film is significantly smaller than that of the conventional TN
`scheme, especially a normally open type TN scheme which is
`predominant at present (bright display at low voltage and dark
`display at high voltage). The reasons for the small margin
`include three points described below as (1) to (3).
`(1) Stepped Structure
`In the IPS-TFT-LCD, it is necessary to provide a number of
`elongated electrodes (which may be referred to as inter digital
`electrodes) having a width of approximately several microns
`in principle. This causes minute stepped structures to be
`formed therein. The height of the step depends on the thick-
`ness of the electrodes or the shapes of various films formed
`thereon, and typically is equal to 0.1 micron (mu) or larger. An
`alignment control film (also referred to as an alignment film)
`made of a polymer film such as polyimide is formed in the
`uppermost layer of those films.
`In conventional mass production technology, the align-
`ment control film is subjected to rubbing processing to pro-
`vide a liquid crystal alignment ability (initial alignment).
`Meanwhile, a cloth for the rubbing is formed by binding thin
`fibers with a thickness of approximately 10 to 30 microns.
`Essentially, each of the thin fibers provides shearing force in
`a predetermined direction for a local portion of the alignment
`film to perform the processing of giving the liquid crystal
`alignment ability. While very thin fibers of approximately
`several microns are present as the fibers, such very thin fibers
`have not been put into practical use since rigidity for provid-
`ing certain frictional force is required for the rubbing. The
`interval between the electrodes in the IPS scheme is approxi-
`mately 10 to 30 microns which is substantially the same as the
`diameter of the fibers, so that sufficient rubbing is not per-
`formed near the steps and misalignment tends to occur. The
`misalignment leads to reduced image quality such as a higher
`black level, an associated lower contrast ratio, and uneven
`luminance.
`
`(2) Alignment Angle
`In the IPS-TFT-LCD, the initial alignment direction needs
`to be set inprinciple at a certain angle or more shifted from the
`direction in which the electrode extends or the direction per-
`pendicular thereto. The electrode refers to a signal wiring
`electrode, a common electrode in pixels, and a pixel elec-
`trode. The definition ofthe initial alignment direction through
`the rubbing requires the fibers of approximately 10 to 30
`microns to rub in a predetermined angular direction as
`described above. However, the step of the wire such as the
`signal wiring electrode, the common electrode in pixels, or
`the pixel electrode extending in a certain direction at their
`ends draws the fibers toward the step from the set angle to
`produce misalignment, thereby reducing image quality such
`as a higher black level.
`(3) Expression of Dark Level
`One ofthe characteristics of the IPS-TFT-LCD is excellent
`
`expression of a dark level (black display). Thus, misalign-
`ment is easily noticeable as compared with the other schemes.
`In the conventionally normally open type TN scheme, the
`dark level is provided while a high voltage is applied. In this
`case, most of liquid crystal molecules align in the direction of
`
`Page 10 of 29
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`US 8,758,871 B2
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`3
`
`4
`
`the electric field which is one direction perpendicular to the
`substrate surface at a high voltage, and the dark level is
`provided from the relationship between the arrangement of
`the liquid crystal molecules and the placement of a polarizing
`plate. Thus, the uniformity ofthe dark level hardly depends on
`the initial alignment state at a low voltage in principle. In
`addition, since human eyes recognize uneven luminance as a
`relative ratio of luminance and make response close to a
`logarithmic scale, they are sensitive to variations in the dark
`level. From this viewpoint, the conventional normally open
`type TN scheme in which the liquid crystal molecules are
`forcedly arranged in one direction at a high voltage is advan-
`tageous in that it is not sensitive to the initial alignment state.
`On the other hand, in the IPS scheme, display of a dark
`level is performed at a low voltage or no voltage, so that it is
`sensitive to disturbance of the initial alignment state. In par-
`ticular, when homogeneous alignment is used in which the
`alignment directions of liquid crystal molecules are in paral-
`lel with each other on an upper substrate and a lower sub-
`strate, and the light transmission axis of one of polarizing
`plates is set in parallel with the alignment direction of the
`liquid crystal molecules and the light transmission axis of
`other polarizing plate is set orthogonally thereto (called a
`birefringence mode), polarized light incident on the liquid
`crystal layer is transmitted with almost no disturbance of
`lineal polarization. This is effective in providing excellent
`expression of the dark level.
`The transmittance T in the birefringence mode is expressed
`by the following equation:
`
`5
`
`10
`
`15
`
`25
`
`T=T0-sin2{20(E)}-sin2{(n-d?fAn)/A}
`
`where To represents a coefiicient which is a numerical value
`determined mainly by the transmittance of the polarizing
`plate for use in the liquid crystal panel, 6(E) represents an
`angle between the alignment direction of liquid molecules
`(the effective optical axis of the liquid crystal layer) and the
`polarized light transmission axis, E represents an applied
`electric field intensity, dej,-represent the effective thickness of
`the liquid crystal layer, An represents the refractive index 40
`anisotropy of liquid crystal, and X represents the wavelength
`oflight. The product ofthe effective thickness dgflofthe liquid
`crystal layer and the refractive index anisotropy An of the
`liquid crystal, that is, defAn is called retardation. The thick-
`ness defof the liquid crystal layer does not refer to the thick-
`ness of the whole liquid crystal layer but corresponds to the
`thickness ofthe liquid crystal layer which actually changes in
`the alignment direction when a voltage is applied thereto.
`This is because the liquid crystal molecules near the interface
`of the liquid crystal layer do not change in the alignment
`direction due to the influence of anchoring at the interface
`even when a voltage is applied thereto. Thus, assuming the
`thickness of the whole liquid crystal
`layer sandwiched
`between the substrates is dLC, the relationship def<dLC is
`always found between the thicknesses dLC and dgf. The dif-
`ference between them can be estimated at approximately 20
`nm to 40 nm, although it depends on the liquid crystal mate-
`rial used in the liquid crystal panel and the type of the inter-
`face in contact with the liquid crystal layer, for example the
`material of the alignment film.
`As apparent from the above equation, the term sin2{26(E)}
`depends on the electric field intensity, and the luminance can
`be adjusted by changing the angle 6 in accordance with the
`electric field intensity E. For the normally close type, polar-
`izing plates are set to satisfy 6:0 when no voltage is applied,
`and it is sensitive to disturbance of the initial alignment direc-
`tion.
`
`In this manner, the uniformity of alignment is a very impor-
`tant factor in the IPS scheme, and problems in the currently
`used rubbing technique have become apparent. In general, the
`rubbing alignment processing includes many problems asso-
`ciated with the rubbing processing technique such as TFT
`breakage due to static electricity produced by friction, unfa-
`vorable display due to misalignment from disordered fiber
`ends of a rubbing cloth or dust, and the need for frequent
`exchanges of rubbing cloths. For the purpose of solving the
`problems associated with the rubbing alignment processing, a
`so-called “rubbing-less” alignment technique for aligning
`liquid crystal molecules without the rubbing has been studied
`and various processes thereof have been proposed. Among
`other things, a process has been proposed in which polarized
`ultraviolet rays or the like are irradiated to the surface of a
`polymer film to align liquid crystal molecules without the
`rubbing.
`As an example, a process disclosed in “Non-Patent Docu-
`ment 1” is characterized in that it does not require the con-
`ventional rubbing processing and realizes the alignment of
`liquid crystal molecules in a predetermined direction through
`irradiation of polarized light. The process is advantageous in
`presenting no problems such as damages on the film surface
`and static electricity associated with the rubbing technique
`and providing a simpler production process in view of indus-
`trial production. The process has attracted attention as a new
`liquid crystal alignment processing process without using the
`rubbing processing.
`As a material ofthe liquid crystal alignment film used in the
`previous reports, the use of a polymer compound having a
`photoreactive group in the side chain of a polymer has been
`proposed for the need to provide photochemical sensitivity to
`polarized light. A representative example thereof is polyvi-
`nylcinnamate, in which case it is thought that dimerization in
`the side chain through light irradiation develops anisotropy in
`a polymer film to align the liquid crystal. Another proposal
`involves dispersing low-molecular dichroic azo dye in a poly-
`mer material and irradiating a film surface with polarized
`light to allow the alignment of liquid crystal molecules in a
`predetermined direction. In addition, the alignment of liquid
`crystal molecules achieved by irradiating a particular poly-
`imide film with polarized ultraviolet rays or the like has been
`reported. In this case, it is contemplated that the light irradia-
`tion decomposes the polyimide main chain in a certain direc-
`tion to develop the liquid crystal alignment.
`Patent Document 1: JP-B-63-21907
`
`Patent Document 2: U.S. Pat. No. 4,345,249
`Patent Document 3: WO9l/ 10936
`Patent Document 4: JP-A-6-22739
`Patent Document 5: JP-A-6-160878
`Patent Document 6: JP-A-9-73101
`
`Patent Document 7: Japanese Patent No. 3303766
`Patent Document 8: JP-A-1 l-218765
`Non-Patent Document 1: W. M. Gibbons et al.,
`Nature, 351, 49 (1991)
`
`DISCLOSURE OF THE INVENTION
`
`In this manner, the photo -alignment process through light
`irradiation has been proposed and studied as the rubbing-less
`alignment technique for solving the problems in the rubbing
`alignment technique, but it has the following problems from
`a practical standpoint. In a polymeric material obtained by
`introducing a photoreactive group in the side chain of a poly-
`mer represented by polyvinylcinnamate, the heat stability of
`alignment is insufficient and satisfactory reliability is not
`ensured from a practical viewpoint. In this case, since it is
`
`Page 11 of 29
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`US 8,758,871 B2
`
`5
`
`where R1, R2, R3, R4 each represent a hydrogen atom, a
`fluorine atom, an alkyl group or alkoxyl group with a carbon
`number of l to 6.
`
`On the other hand, the aromatic diamine compound con-
`tains at least one of compounds selected from a group of
`compounds consisting of ones represented by formulas [18]
`to [32]:
`
`_
`
`thought that the side chain of the polymer corresponds to the
`site of the structure which develops the aligmnent of liquid
`crystal, it is difiicult to say that the technique is preferable in
`providing more uniform alignment of liquid crystal mol-
`ecules and more resistant alignment. When low-molecular
`dichroic dye is dispersed in a polymer, the dye itself for
`aligning liquid crystal is the low molecular substance, and
`from the viewpoint ofpractical use, problems remain in terms
`of reliability for heat and light.
`In addition, in the process of irradiating particular polyim-
`ide with polarized ultraviolet rays, the polyimide itself is
`reliable in heat resistance or the like, but it is thought that the
`alignment mechanism is caused by decomposition through
`the light, and it is thus difficult to ensure sufficient reliability
`for practical use. Specifically, when the liquid crystal align-
`ment with the polarized light irradiation is applied in the
`future, it is necessary not only to initially align the liquid
`crystal but also to develop more stable alignment from the
`viewpoint of reliability. In view of actual industrial applica-
`tion, selection of a thermally stable polymer structure is
`desired. From those points, the polymer material proposed
`conventionally for the liquid crystal alignment through light
`irradiation is not sufficient in the alignment property and the
`stability, which actually presents a significant problem in
`realizing the rubbing-less alignment through light irradiation.
`Thus, it is an object of the present invention to provide,
`particularly, a large-sized liquid crystal display capable of
`solving the inherent problem of the small production margin
`in the alignment processing in the IPS-TFT-LCD described
`above, reducing the occurrence of defective display due to
`variations in the initial alignment direction, realizing the
`stable liquid crystal alignment, and having high image quality
`with a higher contrast ratio. It is another object of the present
`invention to provide a process ofproducing a high-quality and
`high-definition liquid crystal display with excellent mass pro-
`ductivity.
`To achieve the abovementioned objects, the present inven-
`tion provides a liquid crystal display comprising: a pair of 40
`substrates, at least one of the substrates being transparent; a
`liquid crystal layer disposed between the pair of substrates; a
`group ofelectrodes formed on one ofthe pair of substrates for
`applying an electric field having a component substantially in
`parallel with a surface of the substrate to the liquid crystal 45
`layer; a plurality of active devices connected to the group of
`electrodes; an alignment control film disposed between the
`liquid crystal layer and at least one of the pair of substrates;
`and optical means fonned on at least one of the pair of sub-
`strates for changing the optical property of the liquid crystal 50
`layer in accordance with an alignment state of molecules of
`said liquid crystal layer, wherein at least one of the alignment
`control films is an alignment control film comprising photo-
`reactive polyimide and/or polyamic acid provided with an
`alignment control ability by irradiation of substantially lin-
`early polarized light.
`The present invention is characterized in that liquid crystal
`molecules in the liquid crystal layer on the alignment control
`film have a long axis in a direction orthogonal to a polariza-
`tion axis of the substantially linearly polarized light for irra-
`diation. In particular, it is desirable that the photoreactive
`alignment control film is polyamic acid or polyimide com-
`prising at least cyclobutanetetracarboxylic acid dianhydride
`as acid anhydride and at least aromatic diamine as diamine.
`The present invention is characterized in that the cyclobu-
`tanetetracarboxylic acid dianhydride and its derivative are a
`compound represented by a formula [l7]:
`
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`US 8,758,871 B2
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`7
`-continued
`
`8
`-continued
`
`R4
`
`where R1, R2, R3, R4 each represent a hydrogen atom, a
`fluorine atom, an alkyl group or alkoxyl group with a carbon
`number of l to 6, or a vinyl group {—(CH2)m—CH:CH2,
`m:0, l, 2} or an acetyl group {—(CH2)n—CECH, n:0, l,
`2}, and in the formula [5], X represents a bond group —S—,
`%O—, —NH—.
`When the alignment control film is formed as a thin film
`having a thickness from 1 nm to 100 nm, the light transmit-
`tance is improved and the efficiency of light reaction with
`polarized light irradiation is effectively improved. In addi-
`tion, when the liquid crystal display is produced, the voltage
`for driving the liquid crystal is effectively applied to the liquid
`crystal layer. Furthermore, when the alignment control film
`on the electrode is fonned as a thin film having a thickness
`from 1 nm to 50 nm, and even from 1 nm to 30 nm, it is
`possible to reduce a direct current voltage component (a
`so-called residual DC voltage) remaining between the elec-
`trode/alignment control film/liquid crystal layer/alignment
`control film/electrode in each pixel of the liquid crystal dis-
`play, and after-image and persistence characteristics are
`effectively enhanced.
`In addition, the present invention is characterized in that
`the liquid crystal layer ofthe liquid crystal display has a pretilt
`angle equal to or smaller than one degree. In the conventional
`rubbing alignment technique, the end of the electrode step
`acts as a guide for the fibers of a rubbing cloth to draw the
`fibers in the direction in which the step extends, and the fibers
`do not extend to the comer ofthe step, which may prevent the
`alignment processing to cause misalignment. In particular,
`when at least one of a pixel electrode, a common electrode,
`and a common electrode wire is formed of a transparent
`electrode, the alignment state near the electrode step is easily
`recognized, and the present invention is effective. Especially,
`when the transparent electrode is formed of an ion-doped
`titanium oxide film or an ion-doped zinc oxide film (ZnO), the
`present invention effectively works. When the pixel electrode
`and the common electrode opposite thereto are arranged in
`parallel with each other and formed of zigzag bending struc-
`tures, the adhesion of the liquid crystal alignment film to an
`underlying organic insulating film may be poor, and the con-
`ventional rubbing alignment processing may cause defective
`display such as stripping ofthe alignment film. In such a case,
`the present invention is effective.
`The present invention is particularly effective when the
`common electrode and/or the pixel electrode is formed on the
`organic insulating film and the liquid crystal alignment film is
`formed on the organic insulating film and the electrodes. In
`addition, the present invention is characterized in that the
`liquid crystal molecules have substantially the same align-
`ment control directions at two interfaces between the liquid
`crystal layer and the alignment control film formed on each of
`the paired substrates.
`The present invention is characterized in that the liquid
`crystal alignment processing is performed by irradiating the
`liquid crystal alignment film with polarized light. The present
`invention is characterized in that the polarized light used in
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`9
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`10
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`the alignment processing has a wavelength range from 200 to
`400 nm. In addition, the present invention is more effective
`when polarized light with at least two wavelengths, that is,
`substantially linearly polarized light with a first wavelength
`and light with a second wavelength are used in the alignment
`processing.
`The present invention is also characterized in that the liquid
`crystal alignment film has a glass transition temperature equal
`to or higher than 250° C. The present invention more effec-
`tively fianctions by applying at least one processing of heat-
`ing, irradiation of infrared rays, irradiation of far infrared
`rays, irradiation of electron beams, and irradiation of radio-
`active rays when the irradiation ofthe liquid crystal alignment
`film with the polarized light is performed to provide the liquid
`crystal alignment ability. When the liquid crystal alignment
`ability is provided by irradiating the liquid crystal alignment
`film with the polarized light, the heating, irradiation of infra-
`red rays, irradiation offar infrared rays, irradiation ofelectron
`beams, or irradiation of radioactive rays is performed to
`accelerate the provision ofthe liquid crystal alignment ability
`through the polarized light irradiation and induce cross-link
`reaction or the like, thereby effectively promoting and stabi-
`lizing the liquid crystal alignment ability. Especially, at least
`one processing of heating, irradiation of infrared rays, irra-
`diation of far infrared rays, irradiation of electron beams, and
`irradiation ofradioactive rays is perfonned to overlap in time
`with the irradiation of polarized light, so that the present
`invention more effectively fimctions.
`The present invention effectively works by performing
`imidation calcination processing of the alignment control
`film to overlap in time with the irradiation of polarized light.
`In particular, when at least one processing of heating, irradia-
`tion of infrared rays, irradiation of far infrared rays, irradia-
`tion of electron beams, and irradiation of radioactive rays is
`performed in addition to the polarized light irradiation of the
`liquid crystal alignment film, it is desirable to set the tem-
`perature of the alignment control film in a range from 100 to
`400° C., and more preferably, from 150 to 300° C. It is
`possible and effective that the processing of heating, irradia-
`tion ofinfrared rays, irradiation of far infrared rays also serves
`as the imidation calcination (firing) processing.
`In the present invention, the target contrast ratio is equal to
`or higher than 500:1, and the target time for eliminating
`after-image is equal to or shorter than five minutes. The time
`for eliminating after-image is determined by a process
`defined in the following embodiments.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`FIG. 1 is a section view showing a pixel portion for explain-
`ing the pixel structure of Embodiment 1 of a liquid crystal
`display according to the present invention.
`FIG. 2a is a plan view and FIGS. 2b and 2c are sectional
`views, respectively, showing a pixel portion for explaining
`the pixel structure of Embodiment 1 of the liquid crystal
`display according to the present invention.
`FIG. 3 is a section view showing a pixel portion for explain-
`ing the pixel structure of Embodiment 2 of the liquid crystal
`display according to the present invention.
`FIG. 4a is a plan view and FIGS. 4b and 4c are sectional
`views, respectively, showing a pixel portion for explaining
`the pixel structure of the liquid crystal display which is
`Embodiment 2 of the liquid crystal display according to the
`present invention.
`FIG. 5 is a section view showing the structure of a pixel of
`the liquid crystal display for explaining Example of the
`present invention.
`
`’
`
`FIG. 6 is a section view showing the structure of a pixel of
`the liquid crystal display for explaining Example of the
`present invention.
`FIG. 7 is a section view showing apixel portion for explain-
`ing the pixel structure of the liquid crystal display which is
`Embodiment 4 of the liquid crystal display according to the
`present invention.
`FIG. 8 is a plan view showing a pixel portion for explaining
`the pixel structure of the liquid crystal display which is
`Embodiment 4 of the liquid crystal display according to the
`present invention.
`
`BEST MODE FOR CARRYING OUT TH:
`INVENTION
`
`Embodiments of the present invention will hereinafter be
`described in detail with reference to the drawings. In the
`following, a substrate which has active devices such as thin
`fihn transistors formed thereon is referred to as an active
`
`matrix substrate. When an opposite substrate has a color filter
`thereon, this is referred to as a color filter substrate.
`FIG. 1 is a schematic section view showing almost one
`pixel for explaining Embodiment 1 of a liquid crystal display
`according to the present invention. FIGS. 2(a) to 2(c) are
`schematic diagrams ofthe active matrix substrate for explain-
`ing the structure of almost one pixel for describing Embodi-
`ment 1 of the liquid crystal display according to the present
`invention, in which FIG. 2(a) is a plan view, FIG. 2(b) is a
`section view taken along an A-A‘ line of FIG. 2(a), and FIG.
`2(c) is a section View taken along a B-B‘ line of FIG. 2(a).
`FIG. 1 corre