Patent Application
20120120346
The present invention relates to a liquid crystal display device and a method for producing the same, and specifically a liquid crystal display device having a wide viewing angle characteristic and a method for producing the same.
Liquid crystal display devices have been improved in terms of display characteristics, and are now used for TV receivers and the like more and more widely. The viewing angle characteristics of the liquid crystal display devices have been improved but are desired to be further improved. Especially, the viewing angle characteristics of liquid crystal display devices using a vertical alignment type liquid crystal layer (also referred to as the “VA-mode liquid crystal display devices”) are strongly desired to be improved.
VA-mode liquid crystal display devices currently used for large display devices of TVs and the like adopt a multi-domain structure in which a plurality of liquid crystal domains are formed in one picture element in order to improve the viewing angle characteristics. A mainly used method for forming the multi-domain structure is an MVA mode. The MVA mode is disclosed in, for example, Patent Document 1.
According to the MVA mode, a pair of substrates facing each other with a vertical alignment type liquid crystal layer interposed therebetween each include an alignment regulation structure on a surface thereof on the liquid crystal layer side. Owing to such alignment regulation structures, a plurality of domains having different alignment directions (tilt directions) of liquid crystal molecules (typically, there are four types of alignment directions) are formed in each picture element. As the alignment regulation structures, slits (openings) or ribs (protrusion structures) provided in or on electrodes are used, and an alignment regulation force is exerted from both sides of the liquid crystal layer.
However, in the case where the slits or ribs are used, unlike in the case where pretilt directions are defined by alignment films used in the conventional TN mode, the alignment regulation force on the liquid crystal molecules is nonuniform in the picture element because the slits and ribs are linear. This causes a problem that there occurs a response speed distribution. There is another problem that since the light transmittance of an area where the slits or ribs are provided is lowered, the display luminance is decreased.
In order to avoid the above-described problems, it is preferable that even in a VA-mode liquid crystal display device, the multi-domain structure is formed by defining the pretilt direction by means of alignment films. The present applicant has proposed a VA-mode liquid crystal display device having such a multi-domain structure in Patent Document 2.
In the liquid crystal display device disclosed in Patent Document 2, the pretilt directions are defined by alignment films to form a 4-domain alignment structure. Namely, when a voltage is applied to the liquid crystal layer, four liquid crystal domains are formed in one picture element. Such a 4-domain alignment structure is occasionally referred simply as the “4D structure”.
In the liquid crystal display device disclosed in Patent Document 2, the pretilt direction defined by one of a pair of alignment films facing each other with the liquid crystal layer interposed therebetween and the pretilt direction defined by the other alignment film are different from each other by about 90°. Therefore, in the presence of an applied voltage, liquid crystal molecules are twist-aligned. A VA-mode in which the liquid crystal molecules are twist-aligned by use of a pair of vertical alignment films provided such that the pretilt directions (alignment directions) are perpendicular to each other is occasionally referred to also as the “VAIN (Vertical Alignment Twisted Nematic) mode” or the “RTN (Reverse Twisted Nematic) mode”. As described above, since the liquid crystal display device disclosed in Patent Document 2 forms the 4D structure, the present applicant refers the display mode of the liquid crystal display device disclosed in Patent Document 2 as the “4D-RTN mode”.
As a specific technique for causing the alignment films to define the pretilt directions of the liquid crystal molecules, as described in Patent Document 2, optical alignment processing is considered prospective. Optical alignment, which can be performed in a non-contact manner, does not generate static electricity due to friction unlike rubbing and thus can improve the yield.
Recently, for the purpose of further improving the viewing angle characteristics of VA-mode liquid crystal display devices, a picture element division driving technology have been put into practice (e.g., Patent Documents 3 and 4). According to the picture element division driving technology, the problem that the γ characteristic (gamma characteristic) as observed in a front direction and the γ characteristic as observed in an oblique direction are different from each other is alleviated; namely, the viewing angle dependence of the γ characteristic is improved. The “γ characteristic” is a gray scale dependence of the display luminance. According to the picture element division driving technology, one picture element is formed of a plurality of sub picture elements which can display different levels of luminance from each other, so that a prescribed luminance for a display signal voltage which is input to the picture element is displayed. Namely, the picture element division driving technology is a technology for improving the viewing angle dependence of the γ characteristic of a picture element by synthesizing different γ characteristics of a plurality of sub picture elements included in the picture element.
Recently, it is desired to enlarge a color reproduction range of a liquid crystal display device (range of displayable colors) in addition to the above-described improvement of the viewing angle characteristics. In a general liquid crystal display device, one pixel is formed of three picture elements respectively for displaying three primary colors of light, i.e., red, green and blue. Owing to this, color display is realized. By contrast, a technique of enlarging the color reproduction range of a liquid crystal display device by using four or more colors for display has been proposed as disclosed in Patent Document 5.
For example, in a liquid crystal display device 900 shown in
Patent Document 1: Japanese Laid-Open Patent Publication No. 11-242225
Patent Document 2: WO2006/132369
Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-62146
Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-78157
Patent Document 5: PCT Japanese National-Phase Laid-Open Patent Publication No. 2004-529396
As a result of making studies on adopting the 4D-RTN mode to a multiple primary color liquid crystal display device, the present inventors found that in the case where pixels have a certain structure, a problem occurs in terms of production when the 4D-RTN mode is adopted. Specifically, in the case where one pixel includes a picture element of a different size from that of another picture element, “shifted exposure” cannot be performed for the optical alignment processing as described in detail later. This increases the cost and time required for the optical alignment processing. As a result of making studies on adopting the 4D-RTN mode to a liquid crystal display device using the picture element division driving technology, the present inventors found that substantially the same problem occurs in the case where one picture element includes a sub picture element of a different size from that of another sub picture element.
The present invention, made in light of the above-described problems, has an object of suppressing the increase of the cost and time required for optical alignment processing when the 4D-RTN mode is adopted to a multiple primary color liquid crystal display device or a liquid crystal display device using the picture element division driving technology.
A liquid crystal display device according to the present invention includes a vertical alignment type liquid crystal layer; a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween; a first electrode provided on the liquid crystal layer side of the first substrate and a second electrode provided on the liquid crystal layer side of the second substrate; and a pair of optical alignment films provided between the first electrode and the liquid crystal layer and between the second electrode and the liquid crystal layer. There are pixels which are each defined by a plurality of picture elements each having a shape including a side parallel to a prescribed first direction and a side parallel to a second direction crossing the first direction; each of the plurality of picture elements includes a first liquid crystal domain in which a tilt direction of liquid crystal molecules at a center and in the vicinity thereof in a layer plane and in a thickness direction of the liquid crystal layer when a voltage is applied between the first electrode and the second electrode is a predetermined first tilt direction, a second liquid crystal domain in which the tilt direction is a predetermined second tilt direction, a third liquid crystal domain in which the tilt direction is a predetermined third tilt direction, and a fourth liquid crystal domain in which the tilt direction is a predetermined fourth tilt direction; the first, second, third and fourth tilt directions are such that a difference between any two these four directions is approximately equal to an integral multiple of 90°; and the first, second, third and fourth liquid crystal domains are arranged in a matrix of 2 rows×2 columns; the plurality of picture elements are an even number of picture elements including at least four picture elements for displaying different colors from each other; the even number of picture elements include a first picture element of which the side parallel to the first direction has a prescribed first length L1 and a second picture element of which the side parallel to the first direction has a second length L2 which is different from the first length L1; in the first picture element, the first, second, third and fourth liquid crystal domains are arranged in a first pattern; and in the second picture element, the first, second, third and fourth liquid crystal domains are arranged in a second pattern which is different from the first pattern.
In a preferable embodiment, in each of the even number of picture elements, when a gray scale is displayed, a dark area darker than the gray scale appears; the dark area appearing in the first picture element is generally gammadion-shaped; and the dark area appearing in the second picture element is generally shaped like the letter “8”.
In a preferable embodiment, the first, second, third and fourth liquid crystal domains are located such that the tilt directions of two adjacent liquid crystal domains thereamong are different by 90° from each other; the first tilt direction and the third tilt direction have an angle of about 180° with respect to each other. In the first picture element, a portion of edges of the first electrode close to the first liquid crystal domain includes a first edge portion such that an azimuthal angle direction perpendicular to the first edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the first tilt direction; a portion of edges of the first electrode close to the second liquid crystal domain includes a second edge portion such that an azimuthal angle direction perpendicular to the second edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the second tilt direction; a portion of edges of the first electrode close to the third liquid crystal domain includes a third edge portion such that an azimuthal angle direction perpendicular to the third edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the third tilt direction; a portion of edges of the first electrode close to the fourth liquid crystal domain includes a fourth edge portion such that an azimuthal angle direction perpendicular to the fourth edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the fourth tilt direction; and the first edge portion and the third edge portion are generally parallel to one of a horizontal direction and a vertical direction of a display plane, and the second edge portion and the fourth edge portion are generally parallel to the other of the horizontal direction and the vertical direction of the display plane. In the second picture element, a portion of edges of the first electrode close to a first liquid crystal domain includes a first edge portion such that an azimuthal angle direction perpendicular to the first edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the first tilt direction; a portion of edges of the first electrode close to the third liquid crystal domain includes a third edge portion such that an azimuthal angle direction perpendicular to the third edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the third tilt direction; and the first edge portion and the third edge portion each include a first portion generally parallel to the horizontal direction of the display plane and a second portion generally parallel to the vertical direction of the display plane.
In a preferable embodiment, the side of each of the first picture element and the second picture element which is parallel to the second direction has a prescribed third length L3; and the even number of picture elements further include a third picture element of which the side parallel to the second direction has a fourth length L4 which is different from the third length L3, and a fourth picture element of which the side parallel to the second direction has the fourth length L4.
In a preferable embodiment, in the third picture element, the first, second, third and fourth liquid crystal domains are arranged in a third pattern which is different from the first and second patterns; and in the fourth picture element, the first, second, third and fourth liquid crystal domains are arranged in a fourth pattern which is different from the first, second and third patterns.
In a preferable embodiment, the at least four picture elements for displaying different colors from each other include a red picture element for displaying red, a green picture element for displaying green, a blue picture element for displaying blue, and a yellow picture element for displaying yellow.
In a preferable embodiment, the at least four picture elements further include a cyan picture element for displaying cyan, and a magenta picture element for displaying magenta.
Alternatively, a liquid crystal display device according to the present invention includes a vertical alignment type liquid crystal layer; a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween; a first electrode provided on the liquid crystal layer side of the first substrate and a second electrode provided on the liquid crystal layer side of the second substrate; and a pair of optical alignment films provided between the first electrode and the liquid crystal layer and between the second electrode and the liquid crystal layer. There are pixels which are each defined by a plurality of picture elements; each of the plurality of picture elements includes a plurality of sub picture elements capable of applying different voltages to parts of the liquid crystal layer corresponding to the respective sub picture elements; each of the plurality of sub picture elements includes a first liquid crystal domain in which a tilt direction of liquid crystal molecules at a center and in the vicinity thereof in a layer plane and in a thickness direction of the liquid crystal layer when a voltage is applied between the first electrode and the second electrode is a predetermined first tilt direction, a second liquid crystal domain in which the tilt direction is a predetermined second tilt direction, a third liquid crystal domain in which the tilt direction is a predetermined third tilt direction, and a fourth liquid crystal domain in which the tilt direction is a predetermined fourth tilt direction; the first, second, third and fourth tilt directions are such that a difference between any two of these four directions is approximately equal to an integral multiple of 90°; and the first, second, third and fourth liquid crystal domains are arranged in a matrix of 2 rows×2 columns; the plurality of sub picture elements are an even number of sub picture elements each having a shape including a side parallel to a prescribed first direction and a side parallel to a second direction crossing the first direction; the even number of sub picture elements include a first sub picture element of which the side parallel to the first direction has a prescribed first length L1 and a second sub picture element of which the side parallel to the first direction has a second length L2 which is different from the first length L1; in the first sub picture element, the first, second, third and fourth liquid crystal domains are arranged in a first pattern; and in the second sub picture element, the first, second, third and fourth liquid crystal domains are arranged in a second pattern which is different from the first pattern.
In a preferable embodiment, in each of the even number of sub picture elements, when a gray scale is displayed, a dark area darker than the gray scale appears; the dark area appearing in the first sub picture element is generally gammadion-shaped; and the dark area appearing in the second sub picture element is generally shaped like the letter “8”.
In a preferable embodiment, the first, second, third and fourth liquid crystal domains are located such that the tilt directions of two adjacent liquid crystal domains thereamong are different by 90° from each other; the first tilt direction and the third tilt direction have an angle of about 180° with respect to each other. In the first sub picture element, a portion of edges of the first electrode close to the first liquid crystal domain includes a first edge portion such that an azimuthal angle direction perpendicular to the first edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the first tilt direction; a portion of edges of the first electrode close to the second liquid crystal domain includes a second edge portion such that an azimuthal angle direction perpendicular to the second edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the second tilt direction; a portion of edges of the first electrode close to the third liquid crystal domain includes a third edge portion such that an azimuthal angle direction perpendicular to the third edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the third tilt direction; a portion of edges of the first electrode close to the fourth liquid crystal domain includes a fourth edge portion such that an azimuthal angle direction perpendicular to the fourth edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the fourth tilt direction; and the first edge portion and the third edge portion are generally parallel to one of a horizontal direction and a vertical direction of a display plane, and the second edge portion and the fourth edge portion are generally parallel to the other of the horizontal direction and the vertical direction of the display plane. In the second sub picture element, a portion of edges of the first electrode close to a first liquid crystal domain includes a first edge portion such that an azimuthal angle direction perpendicular to the first edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the first tilt direction; a portion of edges of the first electrode close to the third liquid crystal domain includes a third edge portion such that an azimuthal angle direction perpendicular to the third edge portion and directed to the inside of the first electrode has an angle exceeding 90° with respect to the third tilt direction; and the first edge portion and the third edge portion each include a first portion generally parallel to the horizontal direction of the display plane and a second portion generally parallel to the vertical direction of the display plane.
In a preferable embodiment, the liquid crystal display device according to the present invention further includes a pair of polarizing plates facing each other with the liquid crystal layer interposed therebetween and located such that transmission axes thereof are generally perpendicular to each other. The tilt directions of the first, second, third and fourth liquid crystal domains have an angle of about 45° with respect to the transmission axes of the pair of polarizing plates.
In a preferable embodiment, the liquid crystal layer contains the liquid crystal molecules having a negative dielectric anisotropy; and a pretilt direction defined by one of the pair of optical alignment films and a pretilt direction defined by the other of the pair of optical alignment films are different by 90° from each other.
A method for producing a liquid crystal display device according to the present invention is a method for producing a liquid crystal display device including a vertical alignment type liquid crystal layer; a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween; a first electrode provided on the liquid crystal layer side of the first substrate and a second electrode provided on the liquid crystal layer side of the second substrate; and a first optical alignment film provided between the first electrode and the liquid crystal layer and a second optical alignment film provided between the second electrode and the liquid crystal layer; wherein there are pixels which are each defined by a plurality of picture elements each having a shape including a side parallel to a prescribed first direction and a side parallel to a second direction crossing the first direction; each of the plurality of picture elements includes a first liquid crystal domain in which a tilt direction of liquid crystal molecules at a center and in the vicinity thereof in a layer plane and in a thickness direction of the liquid crystal layer when a voltage is applied between the first electrode and the second electrode is a predetermined first tilt direction, a second liquid crystal domain in which the tilt direction is a predetermined second tilt direction, a third liquid crystal domain in which the tilt direction is a predetermined third tilt direction, and a fourth liquid crystal domain in which the tilt direction is a predetermined fourth tilt direction; the first, second, third and fourth tilt directions are such that a difference between any two of these four directions is approximately equal to an integral multiple of 90°; and the first, second, third and fourth liquid crystal domains are arranged in a matrix of 2 rows×2 columns; the plurality of picture elements are an even number of picture elements including at least four picture elements for displaying different colors from each other; and the even number of picture elements include a first picture element of which the side parallel to the first direction has a prescribed first length L1 and a second picture element of which the side parallel to the first direction has a second length L2 which is different from the first length L1. The method includes a step (A) of forming a first area having a first pretilt direction and a second area having a second pretilt direction which is antiparallel to the first pretilt direction, in an area of the first optical alignment film corresponding to each of the even number of picture elements by optical alignment processing; and a step (B) of forming a third area having a third pretilt direction and a fourth area having a fourth pretilt direction which is antiparallel to the third pretilt direction, in an area of the second optical alignment film corresponding to each of the even number of picture elements by optical alignment processing. The step (A) of forming the first area and the second area includes a first exposure step of directing light to a part of the first optical alignment film which is to be the first area; and a second exposure step of directing light to a part of the first optical alignment film which is to be the second area, after the first exposure step. The first exposure step and the second exposure step are performed by use of one, common first photomask including a plurality of light shielding parts extending like stripes parallel to the second direction and a plurality of light transmitting parts located between the plurality of light shielding parts; and each of the plurality of light transmitting parts of the first photomask has a width W1 which is equal to a sum of half of the first length L1 and half of the second length L2.
In a preferable embodiment, the step (A) of forming the first area and the second area further includes a first photomask locating step of, before the first exposure step, locating the first photomask such that a part of the first optical alignment film corresponding to about half of the first picture element and about half of the second picture element overlaps each of the plurality of light transmitting parts; and a first photomask moving step of, between the first exposure step and the second exposure step, shifting the first photomask in the first direction by a prescribed distance D1.
In a preferable embodiment, the prescribed distance D1 is about 1/m (m is an even number of 2 or greater) of a width PW1 of the pixel in the first direction.
In a preferable embodiment, the width W1 of each of the plurality of light transmitting parts, a width W2 of each of the plurality of light shielding parts, the first length L1 and the second L2 fulfill the following relationship expression:
W1=W2=(L1+L2)/2.
In a preferable embodiment, the width W1 (μm) of each of the plurality of light transmitting parts, a width W2 (μm) of each of the plurality of light shielding parts, the first length L1 (μm) and the second length L2 (μm) fulfill the following relationship expressions:
W1=(L1+L2)/2+Δ
W2=(L1+L2)/2−Δ
0<Δ≦10.
In a preferable embodiment, the side of each of the first picture element and the second picture element which is parallel to the second direction has a prescribed third length L3; and the even number of picture elements further include a third picture element of which the side parallel to the second direction has a fourth length L4 which is different from the third length L3, and a fourth picture element of which the side parallel to the second direction has the fourth length L4. The step (B) of forming the third area and the fourth area includes a third exposure step of directing light to a part of the second optical alignment film which is to be the third area; and a fourth exposure step of directing light to a part of the second optical alignment film which is to be the fourth area, after the third exposure step. The third exposure step and the fourth exposure step are performed by use of one, common second photomask including a plurality of light shielding parts extending like stripes parallel to the first direction and a plurality of light transmitting parts located between the plurality of light shielding parts; and each of the plurality of light transmitting parts of the second photomask has a width W3 which is equal to a sum of half of the third length L3 and half of the fourth length L4.
In a preferable embodiment, the step (B) of forming the third area and the fourth area further includes a second photomask locating step of, before the third exposure step, locating the second photomask such that a part of the second optical alignment film corresponding to about half of the third picture element and about half of the fourth picture element overlaps each of the plurality of light transmitting parts; and a second photomask moving step of, between the third exposure step and the fourth exposure step, shifting the second photomask in the second direction by a prescribed distance D2.
In a preferable embodiment, the prescribed distance D2 is about 1/n (n is an even number of 2 or greater) of a width PW2 of the pixel in the second direction.
In a preferable embodiment, the width W3 of each of the plurality of light transmitting parts of the second photomask, a width W4 of each of the plurality of light shielding parts of the second photomask, the third length L3 and the fourth length L4 fulfill the following relationship expression:
W3=W4=(L3+L4)/2.
In a preferable embodiment, the width W3 (μm) of each of the plurality of light transmitting parts of the second photomask, a width W4 (μm) of each of the plurality of light shielding parts of the second photomask, the third length L3 (μm) and the fourth length L4 (μm) fulfill the following relationship expressions:
W3=(L3+L4)/2+Δ′
W4=(L3+L4)/2−Δ′
0<Δ′≦10.
Alternatively, a method for producing a liquid crystal display device is a method for producing a liquid crystal display device including a vertical alignment type liquid crystal layer; a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween; a first electrode provided on the liquid crystal layer side of the first substrate and a second electrode provided on the liquid crystal layer side of the second substrate; and a first of optical alignment film provided between the first electrode and the liquid crystal layer and a second optical alignment film provided between the second electrode and the liquid crystal layer; wherein: there are pixels which are each defined by a plurality of picture elements; each of the plurality of picture elements includes a plurality of sub picture elements capable of applying different voltages to parts of the liquid crystal layer corresponding to the respective sub picture elements; each of the plurality of sub picture elements includes a first liquid crystal domain in which a tilt direction of liquid crystal molecules at a center and in the vicinity thereof in a layer plane and in a thickness direction of the liquid crystal layer when a voltage is applied between the first electrode and the second electrode is a predetermined first tilt direction, a second liquid crystal domain in which the tilt direction is a predetermined second tilt direction, a third liquid crystal domain in which the tilt direction is a predetermined third tilt direction, and a fourth liquid crystal domain in which the tilt direction is a predetermined fourth tilt direction; the first, second, third and fourth tilt directions are such that a difference between any two of these four directions is approximately equal to an integral multiple of 90°; and the first, second, third and fourth liquid crystal domains are arranged in a matrix of 2 rows×2 columns; the plurality of sub picture elements are an even number of sub picture elements each having a shape including a side parallel to a prescribed first direction and a side parallel to a second direction crossing the first direction; and the even number of sub picture elements include a first sub picture element of which the side parallel to the first direction has a prescribed first length L1 and a second sub picture element of which the side parallel to the first direction has a second length L2 which is different from the first length L1. The method includes a step (A) of forming a first area having a first pretilt direction and a second area having a second pretilt direction which is antiparallel to the first pretilt direction, in an area of the first optical alignment film corresponding to each of the even number of sub picture elements by optical alignment processing; and a step (B) of forming a third area having a third pretilt direction and a fourth area having a fourth pretilt direction which is antiparallel to the third pretilt direction, in an area of the second optical alignment film corresponding to each of the even number of sub picture elements by optical alignment processing. The step (A) of forming the first area and the second area includes a first exposure step of directing light to a part of the first optical alignment film which is to be the first area; and a second exposure step of directing light to a part of the first optical alignment film which is to be the second area, after the first exposure step. The first exposure step and the second exposure step are performed by use of one, common first photomask including a plurality of light shielding parts extending like stripes parallel to the second direction and a plurality of light transmitting parts located between the plurality of light shielding parts; and each of the plurality of light transmitting parts of the first photomask has a width W1 which is equal to a sum of half of the first length L1 and half of the second length L2.
In a preferable embodiment, the step (A) of forming the first area and the second area further includes a first photomask locating step of, before the first exposure step, locating the first photomask such that a part of the first optical alignment film corresponding to about half of the first sub picture element and about half of the second sub picture element overlaps each of the plurality of light transmitting parts; and a first photomask moving step of, between the first exposure step and the second exposure step, shifting the first photomask in the first direction by a prescribed distance D1.
In a preferable embodiment, the prescribed distance D1 is about 1/m (m is an even number of 2 or greater) of a width PW1 of the picture element in the first direction.
In a preferable embodiment, the width W1 of each of the plurality of light transmitting parts, a width W2 of each of the plurality of light shielding parts, the first length L1 and the second L2 fulfill the following relationship expression:
W1=W2=(L1+L2)/2.
In a preferable embodiment, the width W1 (μm) of each of the plurality of light transmitting parts, a width W2 (μm) of each of the plurality of light shielding parts, the first length L1 (μm) and the second length L2 (μm) fulfill the following relationship expressions:
W1=(L1+L2)/2+Δ
W2=(L1+L2)/2−Δ
0<Δ≦10.
According to the present invention, the increase of the cost and time required for optical alignment processing can be suppressed even when the 4D-RTN mode is adopted to a multiple primary color liquid crystal display device or a liquid crystal display device using the picture element division driving technology.
a), (b) and (c) show optical alignment processing for realizing the structure shown in
a), (b) and (c) show the optical alignment processing for realizing the structure shown in
a), (b) and (c) show exposure steps performed in the optical alignment processing on the optical alignment film of the TFT substrate.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 100.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 200.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 200.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 200.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 200.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 300.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 300.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 300.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 300.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 400.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 400.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 400.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 400.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 500.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 500.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 500.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 500.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 600.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 600.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 600.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 600.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 700.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 700.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 700.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 700.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 800.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the CF substrate included in the liquid crystal display device 800.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 800.
a), (b) and (c) show the optical alignment processing performed on the optical alignment film of the TFT substrate included in the liquid crystal display device 800.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and is widely applicable to a multiple primary color liquid crystal display device adopting the 4D-RTN mode, or a liquid crystal display device using the picture element division driving technology and adopting the 4D-RTN mode. The 4D-RTN mode is, as described above, the RTN mode in which each picture element has a 4-domain alignment structure (4D structure) (VAIN mode). A liquid crystal display device adopting the 4D-RTN mode includes a vertical alignment type liquid crystal layer.
In this specification, the term “vertical alignment type liquid crystal layer” refers to a liquid crystal layer in which liquid crystal molecules are aligned at an angle of about 85° or greater with respect to surfaces of vertical alignment films. The liquid crystal molecules contained in the vertical alignment type liquid crystal layer have a negative dielectric anisotropy. By a combination of the vertical alignment type liquid crystal layer and a pair of polarizing plates facing each other with the liquid crystal layer interposed therebetween and located in crossed Nicols (i.e., located such that transmission axes thereof are generally perpendicular to each other), normally black mode display is provided.
In this specification, the term “picture element” refers to the minimum unit which represents a particular gray scale level in display, and corresponds to a unit representing a gray scale level of each of primary colors used for display (red, green, blue and the like) (a “picture element” is also referred to as a “dot”). A combination of a plurality of picture elements forms (defines) one “pixel”, which is the minimum unit for providing color display. The term “sub picture element” refers to a unit for displaying a level of luminance. A plurality of sub picture elements are included in one picture element and are capable of displaying different levels of luminance from each other. Such a plurality of sub picture elements display a prescribed level of luminance (gray scale) for a display signal voltage which is input to one picture element.
The term “pretilt direction” refers to an alignment direction of a liquid crystal molecule defined by an alignment film and is an azimuthal angle direction in a display plane. An angle of the liquid crystal molecule with respect to the surface of the alignment film when the liquid crystal molecule is aligned in the pretilt direction is referred to as the “pretilt angle”. In this specification, performing processing on the alignment film to allow the alignment film to exert a capability of defining a prescribed pretilt direction is expressed as “giving a pretilt direction to the alignment film”. The pretilt direction defined by the alignment film is occasionally referred to simply as the “pretilt direction of the alignment film”.
By changing the combination of the pretilt directions given by a pair of alignment films facing each other with the liquid crystal layer interposed therebetween, a 4-domain alignment structure can be formed. A picture element divided into four has four liquid crystal domains.
Each liquid crystal domain is characterized by the tilt direction (also referred to as the “reference alignment direction”) of the liquid crystal molecules at a center and in the vicinity thereof in a layer plane and in a thickness direction of the liquid crystal layer when a voltage is applied to the liquid crystal layer. This tilt direction (reference alignment direction) has a dominant influence on the viewing angle dependence of each domain. This tilt direction is also an azimuthal angle direction. The reference based on which the azimuthal angle direction is measured is a horizontal direction of the display plane, and the counterclockwise direction is the forward direction (assuming that the display plane is the face of a clock, the o'clock direction is an azimuthal angle of 0° and the counterclockwise direction is the forward direction). Where the tilt directions of the four liquid crystal domains are set such that a difference between any two tilt directions among the four tilt directions is approximately equal to an integral multiple of 90° (e.g., 12 o'clock direction, 9 o'clock direction, 6 o'clock direction and 3 o'clock direction), the viewing angle characteristics are averaged and thus good display can be provided. From the viewpoint of uniformizing the viewing angle characteristics, it is preferable that the area sizes of the four liquid crystal domains in the picture element are approximately equal to each other. Specifically, it is preferable that a difference between the area size of the largest liquid crystal domain and the area size of the smallest liquid crystal domain among the four liquid crystal domains is 25% or less of the area size of the largest liquid crystal domain.
A vertical alignment type liquid crystal layer shown as an example in the following embodiments contains liquid crystal molecules having a negative dielectric anisotropy (a nematic liquid crystal material having a negative dielectric anisotropy). The pretilt direction defined by one of the alignment films and the pretilt direction defined by the other alignment film are different by about 90° from each other. A direction at the middle between these two pretilt directions is defined as the tilt direction (reference alignment direction). When a voltage is applied to the liquid crystal layer, the liquid crystal molecules are twist-aligned in accordance with the alignment regulation forces of the alignment films. When necessary, a chiral agent may be incorporated into the liquid crystal layer.
It is preferable that the pretilt angles respectively defined by the pair of alignment films are approximately equal to each other. When the pretilt angles are approximately equal to each other, there is an advantage that the display luminance characteristic can be improved. Especially where the difference between the pretilt angles is 1° or less, the tilt direction (reference alignment direction) of the liquid crystal molecules at the center and in the vicinity thereof of the liquid crystal layer can be controlled to be stable and thus the display luminance characteristic can be improved. A conceivable reason for this is that when the difference between the pretilt angles exceeds 1°, the tilt direction is dispersed in accordance with the position in the liquid crystal layer, and as a result, the transmittance is dispersed (i.e., an area having a transmittance lower than a desired transmittance is formed).
A pretilt direction is given to each alignment film by optical alignment processing. When an optical alignment film containing a photosensitive group is used, the variance in the pretilt angle can be controlled to be 1° or less. It is preferable that the optical alignment film contains, as the photosensitive group, at least one selected from the group consisting of 4-chalcone group, 4′-chalcone group, coumarin group and cinnamoyl group.
In the following embodiments, an active matrix driving type liquid crystal display device including thin film transistors (TFTs) will be shown as a typical example, but the present invention is applicable to any other system of liquid crystal display device, needless to say.
Before Describing this Embodiment, a Method for dividing one picture element of a general 4D-RTN mode into domains having different alignment directions, and a problem occurring when the 4D-RTN mode is adopted to a multiple primary color liquid crystal display device, will be described.
As shown in
The tilt directions (reference alignment directions) of the liquid crystal domains D1, D2, D3 and D4 are respectively represented as t1, t2, t3 and t4. A difference between any two among these four directions is approximately equal to an integral multiple of 90°. Where the azimuthal angle of the horizontal direction of the display plane (3 o'clock direction) is 0°, the tilt direction t1 of the liquid crystal domain D1 is a direction of about 225°, the tilt direction t2 of the liquid crystal domain D2 is a direction of about 315°, the tilt direction t3 of the liquid crystal domain D3 is a direction of about 45°, and tilt direction t4 of the liquid crystal domain D4 is a direction of about 135°. Namely, the liquid crystal domains D1, D2, D3 and D4 are located such that the tilt directions thereof are different by about 90° between adjacent domains among the liquid crystal domains D1, D2, D3 and D4.
A pair of polarizing plates facing each other with a liquid crystal layer interposed therebetween are located such that transmission axes (polarization axes) thereof are generally perpendicular to each other. More specifically, the transmission axis of one of the polarizing plates is generally parallel to the horizontal direction of the display plane, and the transmission axis of the other polarizing plate is generally parallel to a vertical direction of the display plane. Accordingly, the tilt directions t1, t2, t3 and t4 have an angle of about 45° with respect to the transmission axes of the pair of polarizing plates. Hereinafter, unless otherwise specified, the transmission axes of the polarizing plates are located as described above.
The 4D structure of the picture element 10 shown in
As shown in
As shown in
By bringing together the TFT substrate and the CF substrate alignment-processed as shown in
In the picture element 10 of the 4D-RTN mode, when a gray scale is displayed, as shown in
The cross-shaped dark line CL is formed when the liquid crystal molecules are aligned to be parallel or perpendicular to the transmission axes of the polarizing plates at the borders between adjacent liquid crystal domains and thus the alignment of the liquid crystal molecules is continuous between adjacent liquid crystal domains. Each of straight dark lines SL, which is formed in the vicinity of an edge of the picture element electrode which is close to the corresponding liquid crystal domain, is formed when the respective edge includes an edge portion such that an azimuthal angle direction perpendicular to the edge portion and directed to the inside of the picture element electrode has an angle exceeding 90° with respect to the tilt direction (reference alignment direction) of the corresponding liquid crystal domain. This is conceived to occur because the tilt direction of the liquid crystal domain and the direction of the alignment regulation force caused by the oblique electric field generated at the edge of the picture element electrode have components facing each other and therefore the liquid crystal molecules are aligned to be parallel or perpendicular to the transmission axes of the polarizing plates in this area. Hereinafter, a reason why the dark lines SL appear in the vicinity of the edges will be specifically described regarding the picture element 10 of the 4D structure shown in
As shown in
Each of the four liquid crystal domains D1, D2, D3 and D4 is close to two among the four edges SD1, SD2, SD3 and SD4 of the picture element electrode, and in the presence of a voltage, receives alignment regulation forces caused by the oblique electric fields generated along the respective edges.
Regarding an edge portion EG1 at the edges of the picture element electrode close to the liquid crystal domain D1, the azimuthal angle direction e1 perpendicular to the edge portion EG1 and directed to the inside of the picture element electrode makes an angle exceeding 90° with respect to the tilt direction t1 of the liquid crystal domain A. As a result, in the liquid crystal domain D1, a dark line SL1 appears generally parallel to the edge portion EG1 when a voltage is applied.
Similarly, regarding an edge portion EG2 at the edges of the picture element electrode close to the liquid crystal domain D2, the azimuthal angle direction e2 perpendicular to the edge portion EG2 and directed to the inside of the picture element electrode makes an angle exceeding 90° with respect to the tilt direction t2 of the liquid crystal domain D2. As a result, in the liquid crystal domain D2, a dark line SL2 appears generally parallel to the edge portion EG2 when a voltage is applied.
Similarly, regarding an edge portion EG3 at the edges of the picture element electrode close to the liquid crystal domain D3, the azimuthal angle direction e3 perpendicular to the edge portion EG3 and directed to the inside of the picture element electrode makes an angle exceeding 90° with respect to the tilt direction t3 of the liquid crystal domain D3. As a result, in the liquid crystal domain D3, a dark line SL3 appears generally parallel to the edge portion EG3 when a voltage is applied.
Similarly, regarding an edge portion EG4 at the edges of the picture element electrode close to the liquid crystal domain D4, the azimuthal angle direction e4 perpendicular to the edge portion EG4 and directed to the inside of the picture element electrode makes an angle exceeding 90° with respect to the tilt direction t4 of the liquid crystal domain D4. As a result, in the liquid crystal domain D4, a dark line SL4 appears generally parallel to the edge portion EG4 when a voltage is applied.
The angles made between the tilt directions t1, t2, t3 and t4 of the liquid crystal domains D1, D2, D3 and D4 and the azimuthal angle components e1, e2, e3 and e4 of the alignment regulation forces caused by the oblique electric fields generated in the edge portions EG1, EG2, EG3 and EG4 close to the liquid crystal domains D1, D2, D3 and D4, respectively, are all about 135°.
As described above, in the liquid crystal domain D1, the dark line SL1 appears generally parallel to the edge portion EG1. In the liquid crystal domain D2, the dark line SL2 appears generally parallel to the edge portion EG2. In the liquid crystal domain D3, the dark line SL3 appears generally parallel to the edge portion EG3. In the liquid crystal domain D4, the dark line SL4 appears generally parallel to the edge portion EG4. The dark line SL1 and the dark line SL3 are generally parallel to the vertical direction of the display plane, and the dark line SL2 and the dark line SL4 are generally parallel to the horizontal direction of the display plane. Namely, the edge portion EG1 and the edge portion EG3 are generally parallel to the vertical direction, and the edge portion EG2 and the edge portion EG4 are generally parallel to the horizontal direction.
The method for dividing one picture element into four liquid crystal domains D1 through D4 (i.e., the method for determining the positions of the liquid crystal domains D1 through D4 in the picture element) is not limited to the example shown in
For example, by bringing together the TFT substrate and the CF substrate alignment-processed as shown in
It should be noted that in the picture element 10, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left); whereas in the picture element 20, the liquid crystal domains D1 through D4 are located in the order of bottom right, top right, top left and bottom left (i.e., counterclockwise from bottom right). A reason for this is that the pretilt directions of the left area and the right area on the TFT substrate side are opposite, and the pretilt directions of the top area and the bottom area on the CF substrate side are opposite, between the picture element 10 and the picture element 20. The dark lines SL1 and SL3 appearing in the liquid crystal domains D1 and D3 are generally parallel to the horizontal direction of the display plane, and the dark lines SL2 and SL4 appearing in the liquid crystal domains D2 and D4 are generally parallel to the vertical direction of the display plane. Namely, the edge portions EG1 and EG3 are generally parallel to the horizontal direction of the display plane, and the edge portions EG2 and EG4 are generally parallel to the vertical direction of the display plane.
Alternatively, by bringing together the TFT substrate and the CF substrate alignment-processed as shown in
It should be noted that in the picture element 30, the liquid crystal domains D1 through D4 are located in the order of top right, bottom right, bottom left and top left (i.e., clockwise from top right). A reason for this is that the pretilt directions of the left area and the right area on the TFT substrate side are opposite between the picture element 10 and the picture element 30.
In the picture element 30, no dark line appears in the liquid crystal domains D1 and D3. A reason for this is that the edges of the picture element electrode close to the liquid crystal domains D1 and D3 does not have an edge portion such that the azimuthal angle direction perpendicular to the edge portion and directed to the inside of the picture element electrode has an angle exceeding 90° with respect to the corresponding tilt direction. By contrast, the dark lines SL2 and SL4 appear in the liquid crystal domains D2 and D4. A reason for this is that the edges of the picture element electrode close to the liquid crystal domains D2 and D4 has an edge portion such that the azimuthal angle direction perpendicular to the edge portion and directed to the inside of the picture element electrode has an angle exceeding 90° with respect to the corresponding tilt direction. The dark lines SL2 and SL4 respectively include portions SL2(H) and SL4(H) parallel to the horizontal direction and portions SL2(V) and SL4(V) parallel to the vertical direction. A reason for this is that the tilt direction of each of the liquid crystal domains D2 and D4 has an angle exceeding 90° with respect to both of an azimuthal angle direction perpendicular to the horizontal edge and directed to the inside of the picture element electrode and an azimuthal angle direction perpendicular to the vertical edge and directed to the inside of the picture element electrode.
By bringing together the TFT substrate and the CF substrate alignment-processed as shown in
It should be noted that in the picture element 40, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and top bottom (i.e., clockwise from bottom left). A reason for this is that the pretilt directions of the top area and the bottom area on the CF substrate side are opposite between the picture element 10 and the picture element 40.
In the picture element 40, no dark line appears in the liquid crystal domains D2 and D4. A reason for this is that the edges of the picture element electrode close to the liquid crystal domains D2 and D4 does not have an edge portion such that the azimuthal angle direction perpendicular to the edge portion and directed to the inside of the picture element electrode has an angle exceeding 90° with respect to the corresponding tilt direction. By contrast, the dark lines SL1 and SL3 appear in the liquid crystal domains D1 and D3. A reason for this is that the edges of the picture element electrode close to the liquid crystal domains D1 and D3 has an edge portion such that the azimuthal angle direction perpendicular to the edge portion and directed to the inside of the picture element electrode has an angle exceeding 90° with respect to the corresponding tilt direction. The dark lines SL1 and SL3 respectively include portions SL1(H) and SL3(H) parallel to the horizontal direction and portions SL1(V) and SL3(V) parallel to the vertical direction. A reason for this is that the tilt direction of each of the liquid crystal domains D1 and D3 has an angle exceeding 90° with respect to both of an azimuthal angle direction perpendicular to the horizontal edge and directed to the inside of the picture element electrode and an azimuthal angle direction perpendicular to the vertical edge and directed to the inside of the picture element electrode.
As described above, the liquid crystal domains D1 through D4 may be arranged in any of various manners in a picture element. As shown in
As described above, the shape of the dark area DR varies in accordance with the arrangement of the liquid crystal domains D1 through D4. Thus, the shape of the dark area DR is considered to characterize the arrangement of the liquid crystal domains D1 through D4. Therefore, in the figures referred to below, a dark area DR may be occasionally shown instead of (or in addition to) the liquid crystal domains D1 through D4.
Now, optical alignment processing performed in the case where the 4D-RTN mode is adopted to a multiple primary color liquid crystal display device 900 shown in
On the alignment film on the TFT substrate side, the optical alignment processing is performed as shown in
As shown in
Next, the photomask 901 is shifted in the row direction by half of the width L1 of the picture element such that as shown in
On the alignment film on the CF substrate side, the optical alignment processing is performed as shown in
As shown in
Next, the photomask 902 is shifted in the column direction by half of the width L2 of the picture element such that as shown in
As described above, for the optical alignment processing performed on the alignment film on the TFT substrate side, the photomask 901 used in the first exposure step is shifted before the second exposure step and used as it is for the second exposure step. Also for the optical alignment processing performed on the alignment film on the CF substrate side, the photomask 902 used in the first exposure step is shifted before the second exposure step and used as it is for the second exposure step. In this specification, such a technique of exposure is referred to as the “shifted exposure”.
However, when one pixel includes a picture element having a different size from that of another picture element, the shifted exposure cannot be performed on the alignment film on the TFT substrate side and/or the alignment film on the CF substrate side. For example, in a multiple primary color liquid crystal display device 900′ shown in
A liquid crystal display device in which the size of the red picture element R is larger than the yellow picture element Y like the liquid crystal display device 900′ shown in
When the optical alignment processing is to be performed on this liquid crystal display device 900′ to realize the liquid crystal arrangement as shown in the right half of
For performing the optical alignment processing on the alignment film on the TFT substrate side of the liquid crystal display device 900′, first, a photomask 903 as shown in
A width W1 of the light transmitting part 903b1, among the two types of light transmitting parts 903b1 and 903b2, is half of the length L1 of the sides of the red picture element R and the blue picture element B parallel to the row direction (see
A width W2 of the light shielding part 903a1, among the two types of light shielding parts 903a1 and 903a2, is half of the length L1 of the sides of the red picture element R and the blue picture element B parallel to the row direction (i.e., W2=L1/2; W1+W2=L1). By contrast, a width W4 of the other light shielding part 903a2 is half of the length L2 of the sides of the green picture element G and the yellow picture element Y parallel to the row direction (i.e., W4=L2/2; W3+W4=L2).
The wider light transmitting part 903b1, the wider light shielding part 903a1, the narrower light transmitting part 903b2 and the narrower light shielding part 903a2 described above are arranged cyclically in this order. The photomask 903 is located such that as shown in
The shifted exposure, which would be performed to give a prescribed pretilt direction to the remaining parts (right half) of the alignment film, cannot be performed with the photomask 903 shown in
For example, it is assumed that from the state shown in
It is assumed that from the state shown in
As described above, when one pixel includes a picture element having a different size from that of another picture element, the shifted exposure cannot be performed. Specifically, the shifted exposure cannot be performed in the direction in which there are two types of width of the picture elements (row direction in the above example). By contrast, according to the present invention, even when one pixel includes a picture element having a different size from that of another picture element, the shifted exposure can be performed. Hereinafter, a liquid crystal display device and a method for producing the same according to the present invention will be specifically described.
As shown in
The liquid crystal layer 3 contains liquid crystal molecules 3a having a negative dielectric anisotropy (i.e., Δ∈<0). When no voltage is applied to the liquid crystal layer 3 (i.e., when no voltage is applied between the picture element electrode 11 and the counter electrode 21), as shown in
The liquid crystal display device 100 further includes a pair of optical alignment films 12 and 22 and a pair of polarizing plates 13 and 23. Among the pair of optical alignment films 12 and 22, one optical alignment film 12 is provided between the picture element electrode 11 and the liquid crystal layer 3, and the other optical alignment film 22 is provided between the counter electrode 21 and the liquid crystal layer 3. The pair of polarizing plates 13 and 23 face each other with the liquid crystal layer 3 interposed therebetween, and are located, as shown in
Although not shown, the TFT substrate S1 further includes thin film transistors (TFTs), scanning lines for supplying a scanning signal to the TFTs, signal lines for supplying a video signal to the TFTs and the like. The CF substrate S2 further includes color filters and a black matrix (light shielding layer).
As shown in
Each of the plurality of pixels P is defined by a plurality of picture elements. Each of the plurality of picture elements has a shape including a side parallel to a prescribed first direction and a side parallel to a second direction crossing the first direction. More specifically, each picture element has a shape of a rectangle (encompassing a square) including sides parallel to the row direction and sides parallel to the column direction (perpendicular to the row direction).
The plurality of picture elements which define one pixel P are an even number of picture elements including at least four picture elements for displaying different colors from each other. In this embodiment, the plurality of picture elements which define one pixel P are a red picture element R, a green picture element G, a blue picture element B and a yellow picture element Y. The red picture element R, the green picture element G, the blue picture element B and the yellow picture element Y are arranged in a matrix of 2 rows×2 columns in the pixel P.
The red picture element R, the green picture element G, the blue picture element B and the yellow picture element Y are each divided into four areas having different alignment directions. Specifically, each picture element includes four liquid crystal domain D1 through D4 respectively having tilt directions of about 225°, about 315°, about 45° and about 135° when a voltage is applied between the picture element electrode 11 and the counter electrode 21. As described above, the transmission axis P1 of one of the pair of polarizing plates 13 and 23 is generally parallel to the horizontal direction of the display plane, and the transmission axis P2 of the other polarizing plate is generally parallel to the vertical direction of the display plane. Accordingly, the tilt directions of the liquid crystal domains D1 through D4 each have an angle of about 45° with respect to the transmission axes P1 and P2 of the polarizing plates 13 and 23.
In the right pixel P of
As shown in
In each of the red picture element R and the blue picture element B, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the red picture element R and the blue picture element B is generally gammadion-shaped. By contrast, in each of the green picture element G and the yellow picture element Y, the liquid crystal domains D1 through D4 are located in the order of top right, bottom right, bottom left and top left (i.e., clockwise from top right). Therefore, the dark area DR appearing in each of the green picture element G and the yellow picture element Y is generally shaped like the letter “8”.
As described above, in the liquid crystal display device 100 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 in the red picture element R and the blue picture element B is different from that in the green picture element G and the yellow picture element Y. In the liquid crystal display device 100 having such a structure, the shifted exposure can be performed on the optical alignment film 12 of the TFT substrate S1 and the optical alignment film 22 of the CF substrate S2. Hereinafter, a method for producing the liquid crystal display device 100 will be described. The steps of producing the liquid crystal display device 100 except for the optical alignment processing on the optical alignment films 12 and 22 can be carried out by a known technique. Hence, the optical alignment processing on the optical alignment film 12 of the TFT substrate S1 and the optical alignment processing on the optical alignment film 22 of the CF substrate S2 will be described below. The exposure steps in the optical alignment processing may be carried out by using, for example, a proximity exposure device produced by Ushio Inc.
First, with reference to
First, a photomask 1 shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film 12 corresponding to each picture element, an area having the first pretilt direction and an area having the second pretilt direction antiparallel to the first pretilt direction are formed. Hereinafter, the area having the first pretilt direction will be referred to as the “first area” for the sake of convenience, and the area having the second pretilt direction will be referred to as the “second area” for the sake of convenience. In each of the exposure step of directing the light toward the part of the optical alignment film 12 which is to be the first area and the exposure step of directing the light toward the part of the optical alignment film 12 which is to be the second area, light (typically, ultraviolet rays as in this example) is directed in a direction inclining at, for example, 30° to 50° with respect to the normal direction to the substrate. The pretilt angle defined by the optical alignment film 12 is, for example, 88.5° to 89°.
Now, with reference to
First, a photomask 2 shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film 22 corresponding to each picture element, an area having the third pretilt direction and an area having the fourth pretilt direction antiparallel to the third pretilt direction are formed. Hereinafter, the area having the third pretilt direction will be referred to as the “third area” for the sake of convenience, and the area having the fourth pretilt direction will be referred to as the “fourth area” for the sake of convenience. In each of the exposure step of directing the light toward the part of the optical alignment film 22 which is to be the third area and the exposure step of directing the light toward the part of the optical alignment film 22 which is to be the fourth area, light (typically, ultraviolet rays as in this example) is directed in a direction inclining at, for example, 30° to 50° with respect to the normal direction to the substrate. The pretilt angle defined by the optical alignment film 22 is, for example, 88.5° to 89°.
By bringing together the TFT substrate S1 and the CF substrate S2 processed with the optical alignment in the above-described manner, the liquid crystal display device 100 shown in
In the above-described production method, in the step of forming the first area and the second area (step of performing the optical alignment processing on the optical alignment film 12 of the TFT substrate S1), two exposure steps are performed by use of one, common photomask 1. In the step of forming the third area and the fourth area (step of performing the optical alignment processing on the optical alignment film 22 of the CF substrate S2), two exposure steps are performed by use of one, common photomask 2. Namely, according to the production method in this embodiment, the shifted exposure can be performed in the row direction in which there are two widths of the picture elements in addition to the column direction in which there is one width of the picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. Inversely describing, because one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), the liquid crystal display device 100 in this embodiment can be produced by the method in which the shifted exposure is used for the optical alignment processing. By contrast, in the case where the 4D-RTN mode is merely adopted to a multiple primary color liquid crystal display device, as in the liquid crystal display device 900 shown in
As described above, according to the present invention, even when the 4D-RTN mode is adopted to a multiple primary color liquid crystal display device, increase of the cost and time required for the optical alignment processing can be suppressed. As described above, in the photomask 1 used for the shifted exposure in the row direction (direction in which there are two widths of the picture elements) in the production method in this embodiment, the width W1 of the light transmitting part 1b is equal to the sum of half of the length L1 of the sides of the red picture element R and the blue picture element B which are parallel to the row direction and half of the length L2 of the sides of the green picture element G and the yellow picture element Y which are parallel to the row direction. Namely, the width W1 of the light transmitting part 1b is equal to the sum of half of the larger width among the two widths of the picture elements (i.e., the length L1) and half of the smaller width (length L2). By contrast, in the photomask 903 shown in
In this embodiment, in the red picture element R and the blue picture element B, the generally gammadion-shaped dark area DR appears; and in the green picture element G and the yellow picture element Y, the dark area DR generally shaped like the letter “8” appears. However, the present invention is not limited to this. As shown in
In this embodiment, the width W1 of the light transmitting part 1b and the width W2 of the light shielding part 1a of the photomask 1 are equal to each other, and are equal to the sum of half of the length L1 of the sides of the red picture element R and the blue picture element B which are parallel to the row direction and half of the length L2 of the sides of the green picture element G and the yellow picture element Y which are parallel to the row direction (i.e., W1=W2=(L1+L2)/2). It is sufficient that the width W1 of the light transmitting part 1b and the width W2 of the light shielding part 1a are generally equal to (L1+L2)/2, and the width W1 and the width W2 do not need to be precisely equal to (L1+L2)/2. For example, the width W1 of the light transmitting part 1b may be increased by a prescribed amount Δ (i.e., W1=(L1+L2)/2+Δ) and the width W2 of the light shielding part 1a may be decreased by the same amount (i.e., W2=(L1+L2)/2−Δ).
Regarding the case where the width W1 of the light transmitting part 1b of the photomask 1, the width W2 of the light shielding part 1a of the photomask 1, the length L1 of the sides of the red picture element R and the blue picture element B which are parallel to the row direction, and the length L2 of the sides of the green picture element G and the yellow picture element Y which are parallel to the row direction fulfill the relationships of W1=(L1+L2)/2+Δ and W2=(L1+L2)/2−Δ, the optical alignment processing on the optical alignment film 12 of the TFT substrate S1 will be described with reference to
First, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
In the case where the optical alignment processing is performed as described above, as shown in
The double-exposed area DE is an area for obtaining a margin against an alignment divergence which is caused when the photomask 1 is shifted for exposure. The alignment precision of the exposure device is about ±several micrometers at the maximum. Therefore, it is preferable from the viewpoint of reliability that no unexposed area is formed in a picture element even if the alignment divergence occurs. When there is an unexposed area, ion components, which are impurities in the liquid crystal layer 3 and the alignment films 12 and 22, are attracted to the unexposed area, which may cause faults such as DC divergence (divergence of the DC level between the signal voltage and the counter voltage), stains or the like.
When the conditions under which the double-exposed area DE is formed, namely, the relationships of W1=(L1+L2)/2+Δ and W2=(L1+L2)/2−Δ, are fulfilled, formation of an unexposed area can be prevented even if an alignment divergence occurs. From the viewpoint of preventing the formation of the unexposed area with more certainty, it is preferable that the increasing amount Δ of the width W1 of the transmitting part 1b is larger. However, when the increasing amount Δ is too large, namely, when the width of the double-exposed area is too large, the width of the dark line at or in the vicinity of the center of the picture element (part of the cross-shaped dark line CL which extends in the vertical direction) is increased and thus the transmittance is decreased. From the viewpoint of suppressing the decrease of the transmittance, it is preferable that the increasing amount Δ of the width W1 of the light transmitting part 1b is equal to or smaller than 10 μm (i.e., 0<Δ≦10). From the viewpoint of further suppressing the decrease of the transmittance and preventing the formation of an unexposed area with more certainty, it is preferable that the increasing amount Δ is equal to or larger than 1 μm and equal to or smaller than 5 μm (i.e., 1≦Δ5).
In this embodiment, an area of the optical alignment film 12 of the TFT substrate S1 corresponding to each picture element is divided into the left part and the right part and an area of the optical alignment film 22 of the CF substrate S2 corresponding to each picture element is divided into the top part and the bottom part. The present invention is not limited to this structure. An area of the optical alignment film 12 of the TFT substrate S1 corresponding to each picture element may be divided into the top part and the bottom part and an area of the optical alignment film 22 of the CF substrate S2 corresponding to each picture element may be divided into the left part and the right part. In this case, for performing the optical alignment processing on the optical alignment film 12 of the TFT substrate S1, the photomask 2 shown in
In the liquid crystal display device 100 shown in ”. By contrast, in the liquid crystal display device 200 in this embodiment, as shown in
A length L1 of the sides of the red picture element R and the blue picture element B which are parallel to the row direction is different from a length L2 of the sides of the green picture element G and the yellow picture element Y which are parallel to the row direction. Specifically, the length L1 is longer than the length L2 (i.e., L1>L2). By contrast, the sides of all the picture elements which are parallel to the column direction have an equal length L3. As can be seen from the above, in the pixel P of the liquid crystal display device 200 in this embodiment also, there is one width of the picture elements in the column direction, whereas there are two widths of the picture elements in the row direction.
In the pixel P, the red picture element R, the blue picture element B, the green picture element G and the yellow picture element Y are arranged in this order from the left. Namely, in the pixel P, the relatively wider picture elements and the relatively narrower picture elements are arranged alternately in the row direction.
In each of the red picture element R and the blue picture element B, the liquid crystal domains D1 through D4 are located in the order of top right, bottom right, bottom left and top left (i.e., clockwise from top right). Therefore, the dark area DR appearing in each of the red picture element R and the blue picture element B is generally shaped like the letter “8”. By contrast, in each of the green picture element G and the yellow picture element Y, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the green picture element G and the yellow picture element Y is generally gammadion-shaped.
As described above, in the liquid crystal display device 200 in this embodiment also, the arrangement pattern of the liquid crystal domains D1 through D4 in the red picture element R and the blue picture element B is different from that in the green picture element G and the yellow picture element Y. Since one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), the shifted exposure can be performed in the row direction in addition to the column direction. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 200 will be described.
First, with reference to
First, a photomask 1A shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2A shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 200 shown in
In the production method of the liquid crystal display device 200 also, in the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 1A. In the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 2A. Namely, the shifted exposure can be performed in the row direction in which there are two widths of the picture elements in addition to the column direction in which there is one width of the picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. As can be seen from the above, in the liquid crystal display device 200 in this embodiment also, because one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), increase of the cost and time required for the optical alignment processing can be suppressed.
In the production method of the liquid crystal display device 100 in Embodiment 1, the moving distance D1 of the photomask 1 in the row direction is ½ of the width PW1 of the pixel P in the row direction (see
As shown in
As shown in
In each of the red picture element R, the green picture element G and the blue picture element B, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in each of the red picture element R, the green picture element G and the blue picture element B is generally shaped like the letter “8”. By contrast, in each of the yellow picture element Y, the cyan picture element C and the magenta picture element M, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the yellow picture element Y, the cyan picture element C and the magenta picture element M is generally gammadion-shaped.
As described above, in the liquid crystal display device 300 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 in the red picture element R, the green picture element G and the blue picture element B is different from that in the yellow picture element Y, the cyan picture element C and the magenta picture element M. Since one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), the shifted exposure can be performed in the column direction in addition to the row direction in which there is one width of the picture elements. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 300 will be described.
First, with reference to
First, a photomask 1B shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2B shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 300 shown in
In the production method of the liquid crystal display device 300, in the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 1B. In the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 2B. Namely, the shifted exposure can be performed in the column direction in which there are two widths of the picture elements in addition to the row direction in which there is one width of the picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. As can be seen from the above, in the liquid crystal display device 300 in this embodiment also, because one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), increase of the cost and time required for the optical alignment processing can be suppressed.
In the example shown in
As shown in
In the liquid crystal display device 300 in Embodiment 3, the size of the red picture element R, the green picture element G and the blue picture element B is larger than the size of the yellow picture element Y, the cyan picture element C and the magenta picture element M; whereas in the liquid crystal display device 400 in this embodiment, the size of the yellow picture element Y, the cyan picture element C and the magenta picture element M is larger than the size of the red picture element R, the green picture element G and the blue picture element B. As shown in
In each of the yellow picture element Y, the cyan picture element C and the magenta picture element M, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in each of the yellow picture element Y, the cyan picture element C and the magenta picture element M is generally shaped like the letter “8”. By contrast, in each of the red picture element R, the green picture element G and the blue picture element B, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the red picture element R, the green picture element G and the blue picture element B is generally gammadion-shaped.
As described above, in the liquid crystal display device 400 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 in the red picture element R, the green picture element G and the blue picture element B is different from that in the yellow picture element Y, the cyan picture element C and the magenta picture element M. Since one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), the shifted exposure can be performed in the column direction in addition to the row direction in which there is one width of the picture elements. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 400 will be described.
First, with reference to
First, a photomask 1C shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2C shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
The pretilt direction given at this point is the same as the pretilt direction PA2 shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 400 shown in
In the production method of the liquid crystal display device 400, in the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 1C. In the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 2C. Namely, the shifted exposure can be performed in the column direction in which there are two widths of the picture elements in addition to the row direction in which there is one width of the picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. As can be seen from the above, in the liquid crystal display device 400 in this embodiment also, because one pixel P includes picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), increase of the cost and time required for the optical alignment processing can be suppressed.
As shown in
A length L1 of the sides of the red picture element R and the blue picture element B which are parallel to the row direction is different from a length L2 of the sides of the green picture element G and the yellow picture element Y which are parallel to the row direction. Specifically, the length L1 is longer than the length L2 (i.e., L1>L2). A length L3 of the sides of the red picture element R and the green picture element G which are parallel to the column direction is different from a length L4 of the sides of the blue picture element B and the yellow picture element Y which are parallel to the column direction. Specifically, the length L3 is longer than the length L4 (i.e., L3>L4). As can be seen from the above, in the liquid crystal display device 500 in this embodiment, there are two widths of the picture elements in the row direction, and there are two widths of the picture elements also in the column direction.
In the red picture element R, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in the red picture element R is generally gammadion-shaped, and more specifically, is right gammadion-shaped.
In the blue picture element B, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in the blue picture element B is generally shaped like the letter “8”, and more specifically, is shaped like the letter “8” inclined rightward from the vertical direction (rotated clockwise).
In the green picture element G, the liquid crystal domains D1 through D4 are located in the order of top right, bottom right, bottom left and top left (i.e., clockwise from top right). Therefore, the dark area DR appearing in the green picture element G is generally shaped like the letter “8”, and more specifically, is shaped like the letter “8” inclined leftward from the vertical direction (rotated counterclockwise).
In the yellow picture element Y, the liquid crystal domains D1 through D4 are located in the order of bottom right, top right, top left and bottom left (i.e., counterclockwise from bottom right). Therefore, the dark area DR appearing in the yellow picture element Y is generally gammadion-shaped, and more specifically, is left gammadion-shaped.
As described above, in the liquid crystal display device 500 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 is different among in the red picture element R, the blue picture element B, the green picture element G and the yellow picture element Y. In the liquid crystal display device 500, there are two widths of the picture elements in both of the row direction and the column direction. Since one pixel P includes four arrangement patterns as described above, the shifted exposure can be performed in the row direction and the column direction. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 500 will be described.
First, with reference to
First, a photomask 1D shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2D shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 500 shown in
In the production method of the liquid crystal display device 500, in the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 1D. In the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 2D. Namely, the shifted exposure can be performed in both of the row direction and the column direction in which there are two widths of the picture elements. As can be seen from the above, in the liquid crystal display device 500 in this embodiment, because one pixel P includes four arrangement patterns of the liquid crystal domains D1 through D4, increase of the cost and time required for the optical alignment processing can be suppressed although there are two widths of the picture elements in both of the row direction and the column direction.
In this embodiment, there are two widths of the picture elements in the row direction and also in the column direction. The moving distance D2 of the photomask 2D in the column direction is about 1/n of the width PW2 of the pixel P in the column direction (n is an even number of 2 or greater). n is equal to the number of picture elements (in this example, 2) in the pixel P.
As described above, from the viewpoint of reliability it is preferable that as a result of the optical alignment processing on an optical alignment film, a double-exposed area DE is formed than an unexposed area is formed. Accordingly, as described above with reference to
The same is true with the column direction. Namely, the width W3 of the light transmitting part 2b of the photomask 2D may be increased by a prescribed increasing amount Δ′ (i.e., W3=(L3+L4)/2+Δ′) and the width W4 of the light shielding part 2a may be decreased by the same amount (i.e., W4=(L3+L4)/2−Δ′). From the viewpoint of suppressing the decrease of the transmittance, it is preferable that the increasing amount Δ′ of the width W3 of the light transmitting part 2b is equal to or smaller than 10 μm (i.e., 0<Δ′≦10). From the viewpoint of further suppressing the decrease of the transmittance and preventing the formation of an unexposed area with more certainty, it is preferable that the increasing amount Δ′ is equal to or larger than 1 μm and equal to or smaller than 5 μm (i.e., 1≦Δ′≦5).
As shown in
As described above, the plurality of pixels P of the liquid crystal display device 600 include pixels P each defined by the red picture element R, the green picture element G, the blue picture element B and the yellow picture element Y and pixels P each defined by the red picture element R, the green picture element G, the cyan picture element C and the yellow picture element Y. The pixels P each including the blue picture element B and the pixels P each including the cyan picture element C are located alternately in the row direction and also in the column direction. Namely, the pixels P each including the blue picture element B and the pixels P each including the cyan picture element C are located in a checkered pattern.
In each pixel P including the blue picture element B, a length L1 of the sides of the red picture element R and the green picture element G which are parallel to the row direction is different from a length L2 of the sides of the blue picture element B and the yellow picture element Y which are parallel to the row direction. Specifically, the length L1 is shorter than the length L2 (i.e., L1<L2). A length L3 of the sides of the red picture element R and the yellow picture element Y which are parallel to the column direction is different from a length L4 of the sides of the green picture element G and the blue picture element B which are parallel to the column direction. Specifically, the length L3 is shorter than the length L4 (i.e., L3<L4). As can be seen from the above, in the pixel P including the blue picture element B, there are two widths of the picture elements in both of the row direction and the column direction.
In each pixel P including the cyan picture element C, the length L1 of the sides of the red picture element R and the green picture element G which are parallel to the row direction is different from the length L2 of the sides of the cyan picture element C and the yellow picture element Y which are parallel to the row direction. Specifically, the length L1 is shorter than the length L2 (i.e., L1<L2). The length L3 of the sides of the red picture element R and the yellow picture element Y which are parallel to the column direction is different from the length L4 of the sides of the green picture element G and the cyan picture element C which are parallel to the column direction. Specifically, the length L3 is shorter than the length L4 (i.e., L3<L4). As can be seen from the above, in the pixel P including the cyan picture element C also, there are two widths of the picture elements in both of the row direction and the column direction.
In the red picture element R, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in the red picture element R is generally gammadion-shaped, and more specifically, is right gammadion-shaped.
In the green picture element G, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in the green picture element G is generally shaped like the letter “8”, and more specifically, is shaped like the letter “8” inclined rightward from the vertical direction (rotated clockwise).
In the yellow picture element Y, the liquid crystal domains D1 through D4 are located in the order of top right, bottom right, bottom left and top left (i.e., clockwise from top right). Therefore, the dark area DR appearing in the yellow picture element Y is generally shaped like the letter “8”, and more specifically, is shaped like the letter “8” inclined leftward from the vertical direction (rotated counterclockwise).
In each of the blue picture element B and the cyan picture element C, the liquid crystal domains D1 through D4 are located in the order of bottom right, top right, top left and bottom left (i.e., counterclockwise from bottom right). Therefore, the dark area DR appearing in each of the blue picture element B and the cyan picture element C is generally gammadion-shaped, and more specifically, is left gammadion-shaped.
As described above, in the liquid crystal display device 600 in this embodiment, the pixel P including the blue picture element B and the pixel P including the cyan picture element C each include four arrangement patterns of the liquid crystal domains D1 through D4. Therefore, the shifted exposure can be performed in both of the row direction and the column direction. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 600 will be described.
First, with reference to
First, a photomask 1E shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2E shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 600 shown in
In the production method of the liquid crystal display device 600, in the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 1E. In the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 2E. Namely, the shifted exposure can be performed in both of the row direction and the column direction in which there are two widths of the picture elements. As can be seen from the above, in the liquid crystal display device 600 in this embodiment also, because one pixel P includes four arrangement patterns of the liquid crystal domains D1 through D4, increase of the cost and time required for the optical alignment processing can be suppressed although there are two widths of the picture elements in both of the row direction and the column direction.
In Embodiments 1 through 6 described above, a plurality of picture elements which define one pixel P display different primary colors from each other. Alternatively, one pixel P may include two or more picture elements for displaying the same primary color. For example, one pixel P may include two red picture elements R for displaying red, or two blue picture elements B for displaying blue. A multiple primary color liquid crystal display device in which one pixel P includes two red picture elements R is disclosed in WO2007/034770. When one pixel P includes two red picture elements R, brighter red (red having a higher lightness) can be displayed.
As shown in
Specifically, the red picture element R includes a dark sub picture element RsL for providing a relatively low luminance and a bright sub picture element RsH for providing a relatively high luminance. Similarly, the green picture element G includes a dark sub picture element GsL for providing a relatively low luminance and a bright sub picture element GsH for providing a relatively high luminance. The blue picture element B includes a dark sub picture element BsL for providing a relatively low luminance and a bright sub picture element BsH for providing a relatively high luminance. In each picture element, the dark sub picture element and the bright picture element are arranged in the column direction (i.e., in one line). As a specific structure for realizing the picture element division driving, any of various structures as disclosed in Patent Documents 3 and 4 is usable.
The dark sub picture element and the bright sub picture element included in each picture element are each divided into four domains having different alignment directions. Specifically, each sub picture element includes four liquid crystal domains D1 through D4 respectively having tilt directions of about 225°, about 315°, about 45° and about 135° when a voltage is applied. The tilt directions of the liquid crystal domains D1 through D4 have an angle of about 45° with respect to transmission axes P1 and P2 of a pair of polarizing plates located in crossed Nicols. The liquid crystal domains D1 through D4 are arranged in a matrix of 2 rows×2 columns.
In the liquid crystal display devices 100 through 600 in Embodiments 1 through 6, four liquid crystal domains D1 through D4 are formed in one picture element. By contrast, in the liquid crystal display device 700 in this embodiment, one picture element includes a plurality of sub picture elements, and four liquid crystal domains D1 through D4 are formed in one sub picture element as described above. In the case where four liquid crystal domains D1 through D4 are formed in one sub picture element also, a dark area DR appears which has a different shape in accordance with the arrangement of the liquid crystal domains D1 through D4 in the sub picture element.
A length L1 of sides of the dark sub picture elements RsL, GsL and BsL which are parallel to the column direction is different from a length L2 of sides of the bright sub picture elements RsH, GsH and BsH which are parallel to the column direction. Specifically, the length L1 is N times the length L2 (i.e., L1=N·L2). N is an integer of 2 or greater. By contrast, sides of all the sub picture elements which are parallel to the row direction have an equal length L3. As can be seen from the above, in the picture element of the liquid crystal display device 700 in this embodiment, there is one width of the sub picture elements in the row direction, whereas there are two widths of the sub picture elements in the column direction.
In each of the dark sub picture elements RsL, GsL, and BsL, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in each of the dark sub picture elements RsL, GsL and BsL is generally shaped like the letter “8”. By contrast, in each of the bright sub picture elements RsH, GsH and BsH, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the bright sub picture elements RsH, GsH and BsH is generally gammadion-shaped.
As described above, in the liquid crystal display device 700 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 in the dark sub picture elements RsL, GsL and BsL is different from that in the bright sub picture elements RsH, GsH and BsH. One picture element includes sub picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR). Therefore, the shifted exposure can be performed in the column direction in which there are two widths of the sub picture elements in addition to the row direction in which there is one width of the sub picture elements. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 700 will be described.
First, with reference to
First, a photomask 1F shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2F shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 700 shown in
In the production method of the liquid crystal display device 700, in the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 1F. In the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 2F. Namely, the shifted exposure can be performed in the column direction in which there are two widths of the sub picture elements in addition to the row direction in which there is one width of the sub picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. As can be seen from the above, in the liquid crystal display device 700 in this embodiment, because one picture element includes sub picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), increase of the cost and time required for the optical alignment processing can be suppressed.
In this embodiment, the moving distance D1 of the photomask 1F in the column direction is half (½) of the width PW1 of the picture element in the column direction. A reason for this is that in the picture element of the liquid crystal display device 700, the sub picture elements are arranged in two rows. In the case where there are two widths of the sub picture elements in the column direction, the moving distance D1 of the photomask 1F in the column direction is about 1/m of the width PW1 of the picture element in the column direction (m is an even number of 2 or greater). m is equal to the number of rows of the picture elements in the picture element. In the meantime, the moving distance D2 of the photomask 1F in the row direction in which there is one width of the sub picture elements is about half (about ½) of the length L3 of the sides of each sub picture element which are parallel to the row direction.
For dividing one sub picture element into four areas having different alignment directions, like for dividing one picture element into four areas having different alignment directions, it is preferable that as a result of the optical alignment processing on an optical alignment film, a double-exposed area DE is formed than an unexposed area is formed from the viewpoint of reliability. Accordingly, it is preferable that the width W1 of the light transmitting part 1b of the photomask 1F, the width W2 of the light shielding part 1a of the photomask 1F, the length L1 of the sides of the dark sub picture elements RsL, GsL and BsL which are parallel to the column direction, and the length L2 of the sides of the bright sub picture elements RsH, GsH and BsH which are parallel to the column direction fulfill the relationships of W1=(L1+L2)/2+Δ and W2=(L1+L2)/2−Δ. It is preferable that 0<Δ≦10.
Now, a specific structure for performing picture element division driving will be described.
When a picture element is divided into a plurality of sub picture elements, for example, the sub picture element s1 and the sub picture element s2, which can provide different levels of luminance from each other, the picture element is observed in the state where different characteristics are present in a mixed state. Therefore, the viewing angle dependence of the γ characteristic (the problem that the γ characteristic as observed in a front direction and the γ characteristic as observed in an oblique direction are different from each other) is alleviated. The γ characteristic is gray scale dependence of the display luminance. The γ characteristic as observed in the front direction being different from the γ characteristic as observed in an oblique direction means that the display gray scale is different in accordance with the direction of observation.
A structure for applying different effective voltages to the parts of the liquid crystal layer corresponding to the first sub picture element s1 and the second sub picture element s2 may be any of the structures disclosed in, for example, Patent Documents 3 and 4.
For example, a structure shown in
The first sub picture element s1 and the second sub picture element s2 form one picture element. Therefore, gate electrodes of the TFTs 17a and 17b are connected to a common scanning line (gate line) 15 and are controlled to be turned on or off by the same scanning signal. Signal lines (source lines) 16a and 16b are supplied with signal voltages (gray scale voltages) such that the first sub picture element s1 and the second sub picture element s2 provide different levels of luminance. The signal voltages supplied to the signal lines 16a and 16b are adjusted such that an average luminance of the first sub picture element s1 and the second sub picture element s2 matches the picture element luminance indicated by a display signal (video signal) input from an external device.
Alternatively, a structure shown in
In the structure shown in
By contrast, in the structure shown in
As shown in
Specifically, the red picture element R includes a dark sub picture element RsL and a bright sub picture element RSH. The green picture element G includes a dark sub picture element GsL and a bright sub picture element GsH. The blue picture element B includes a dark sub picture element BsL and a bright sub picture element BsH. The cyan picture element C includes a dark sub picture element CsL and a bright sub picture element CsH. The magenta picture element M includes a dark sub picture element MsL and a bright sub picture element MsH. The yellow picture element Y includes a dark sub picture element YsL and a bright sub picture element YsH. In each picture element, the dark sub picture element and the bright picture element are arranged in the column direction (i.e., in one line).
A length L1 of sides of the dark sub picture elements RsL, GsL, BsL, CsL, MsL and YsL which are parallel to the column direction is different from a length L2 of sides of the bright sub picture elements RsH, GsH, BsH, CsH, MsH and YsH which are parallel to the column direction. Specifically, the length L1 is N times the length L2 (i.e., L1=N·L2). N is an integer of 2 or greater. By contrast, sides of all the sub picture elements which are parallel to the row direction have an equal length L3. As can be seen from the above, in the picture element of the liquid crystal display device 800 in this embodiment, there is one width of the sub picture elements in the row direction, whereas there are two widths of the sub picture elements in the column direction.
In each of the dark sub picture elements RsL, GsL, BsL, CsL, MsL and YsL, the liquid crystal domains D1 through D4 are located in the order of bottom left, top left, top right and bottom right (i.e., clockwise from bottom left). Therefore, the dark area DR appearing in each of dark sub picture elements RsL, GsL, BsL, CsL, MsL and YsL is generally shaped like the letter “8”. By contrast, in each of the bright sub picture elements RsH, GsH, BsH, CsH, MsH and YsH, the liquid crystal domains D1 through D4 are located in the order of top left, bottom left, bottom right and top right (i.e., counterclockwise from top left). Therefore, the dark area DR appearing in each of the bright sub picture elements RsH, GsH, BsH, CsH, MsH and YsH is generally gammadion-shaped.
As described above, in the liquid crystal display device 800 in this embodiment, the arrangement pattern of the liquid crystal domains D1 through D4 in the dark sub picture elements RsL, GsL, BsL, CsL, MsL and YsL is different from that in the bright sub picture elements RsH, GsH, BsH, CsH, MsH and YsH. One picture element includes sub picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR). Therefore, the shifted exposure can be performed in the column direction in addition to the row direction in which there is one width of the sub picture elements. Hereinafter, the optical alignment processing on a pair of optical alignment films included in the liquid crystal display device 800 will be described.
First, with reference to
First, a photomask 1G shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the CF substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. Now, with reference to
First, a photomask 2G shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
As a result of the above-described optical alignment processing, in an area of the optical alignment film of the TFT substrate corresponding to each picture element, two areas having pretilt directions antiparallel to each other are formed. By bringing together the TFT substrate and the CF substrate processed with the optical alignment in the above-described manner, the liquid crystal display device 800 shown in
In the production method of the liquid crystal display device 800, in the step of performing the optical alignment processing on the optical alignment film of the CF substrate, two exposure steps are performed by use of one, common photomask 1G. In the step of performing the optical alignment processing on the optical alignment film of the TFT substrate, two exposure steps are performed by use of one, common photomask 2G. Namely, the shifted exposure can be performed in the column direction in which there are two widths of the sub picture elements in addition to the row direction in which there is one width of the sub picture elements. Therefore, the optical alignment processing can be realized at low cost and in a short takt time. As can be seen from the above, in the liquid crystal display device 800 in this embodiment, because one picture element includes sub picture elements having different arrangement patterns of the liquid crystal domains D1 through D4 (having different shapes of the dark area DR), increase of the cost and time required for the optical alignment processing can be suppressed.
A liquid crystal display device according to the present invention is preferably usable for uses of TV receivers and other devices required to provide a high quality of display.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009175742 | Jul 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/062585 | 7/27/2010 | WO | 00 | 1/27/2012 |
