The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device suitable for providing high-resolution pixels in a horizontal alignment mode.
A liquid crystal display device is a display device that uses a liquid crystal composition for display. In a typical display method for this device, a voltage is applied to a liquid crystal composition sealed between a pair of substrates, and the alignment state of the liquid crystal molecules in the liquid crystal composition is changed in accordance with the applied voltage, whereby the light transmission amount is controlled. Such a liquid crystal display device is used in a wide range of fields by taking advantages such as thinness, lightweight, and low power consumption.
As a display method of a liquid crystal display device, a horizontal alignment mode in which control is performed by mainly rotating the alignment of liquid crystal molecules in a plane parallel to the substrate surface has attracted a great deal of attention because, for example, wide viewing angle characteristics can be easily obtained. For example, in recent years, liquid crystal display devices for smartphones and tablet PCs have widely used the in-plane switching (IPS) mode and the fringe field switching (FFS) mode, each of which is one type of horizontal alignment mode.
With respect to such a horizontal alignment mode, research and development have been continued to improve the display quality by, for example, increasing the pixel resolution, improving the transmittance, and improving the response speed. As a technique for improving the response speed, for example, Patent Literature 1 discloses a liquid crystal display device using fringe electric fields, and a technique of providing a comb-tooth portion with a specific shape to a first electrode. In addition, Patent Literature 2 relates to an FFS mode liquid crystal display and discloses an electrode structure having a slit including two linear portions and a V-shaped portion formed by coupling the two linear portions in a V shape. According to this document, this technique can reduce defects caused by process variations and improve the display performance.
Although the horizontal alignment mode has an advantage of achieving a wide viewing angle, there is a problem that the response is slow as compared with the vertical alignment mode such as the multi-domain vertical alignment (MVA) mode. Although the response speed can be improved in the horizontal mode by using the technique disclosed in Patent Literature 1, the shape of the electrode is largely restricted by an ultra-high pixel resolution of 800 ppi or more. This makes it difficult to adopt a complicated electrode shape like that disclosed in Patent Literature 1.
According to Patent Literature 2, due to the influence of the V-shaped portion provided in the opening of the electrode, it is possible to improve the display performance such as transmittance by dividing the alignment of the liquid crystal molecules into two regions at the time of voltage application. However, the effect of speeding up is not great. In addition, there is still room for improvement in order to achieve further higher resolution and higher transmittance.
As a result of various studies, the present inventors have found that high speed and high resolution can be achieved in an FFS mode liquid crystal display device even in the horizontal alignment mode by using the strain force generated by the bend-shaped and splay-shaped liquid crystal alignment formed in a narrow region by rotating liquid crystal molecules within a range smaller than a certain pitch at the time of voltage application to form four liquid crystal domains and rotating the liquid crystal molecules in the adjacent liquid crystal domains in mutually opposite azimuth directions. In this case, it is ideal that the four liquid crystal domains are generated symmetrically with respect to each other. Therefore, the opening shape of the upper layer electrode preferably has a shape symmetrical with respect to the initial alignment azimuth direction of liquid crystal molecules, for example, a quadrangular shape with two rounded end portions or an elliptical shape. In this case, ideally, the liquid crystal molecules are not rotated in the central portion of the opening. However, it has been found that when a high voltage is applied, it becomes difficult to stabilize the boundaries (dark lines) between the four liquid crystal domains, and the response characteristic deteriorated.
Therefore, in order to stabilize the dark lines even at the time of applying a high voltage, the present inventors have further studied.
Actually, however, even when the symmetrical opening 15 including the pair of protruding portions 17 is provided, when a higher voltage is applied and the rotation of the liquid crystal molecules 21 becomes larger, the alignment of the liquid crystal molecules 21 in the central portion of the opening 15 becomes unstable, and the liquid crystal molecules 21 in the central portion of the opening 15 sometimes rotate depending on a unit of display 50. The reason for this is as follows. When a high voltage is applied, the electric field is slightly distorted in the central portion of the opening 15, and the balance of the alignment of the liquid crystal molecules 21 in the central portion of the opening 15 collapses under the influence of the surrounding liquid crystal molecules 21.
The present invention has been made in view of the above state of the art, and it is an object of the present invention to provide a horizontal alignment mode liquid crystal display device capable of achieving high resolution and improving transmittance.
As a result of extensive studies on a horizontal alignment mode liquid crystal display device capable of achieving high resolution and improving transmittance, the present inventors have focused attention on the shape of the opening of an electrode used for forming a fringe electric field. The present inventors have found that even if the opening shape of the electrode is not complicated, using a shape satisfying two specific conditions makes it possible to rotate the liquid crystal molecules in a predetermined azimuth direction by intentionally distorting the electric field in the central portion of the opening and to stabilize the alignment of liquid crystal molecules in the central portion of the opening. Specifically, when the contour of the opening is divided into four by a first straight line longest among lines dividing the opening in the direction parallel to the initial alignment azimuth direction of liquid crystal molecules and a second straight line longest among lines dividing the opening in the direction orthogonal to the initial alignment azimuth direction, the liquid crystal molecules can be rotated in a predetermined azimuth direction in the central portion of the opening by distorting the electric field because (condition 1) a bend-shaped and splay-shaped liquid crystal alignment can be formed in a narrow region at the time of voltage application since the sign of the average slope of each of the divided contour portions differs from the signs of the average slopes of two adjacent contour portions, and (condition 2) the shape of the opening becomes asymmetrical with respect to the initial alignment azimuth direction of the liquid crystal molecules since the average slope of the entire contour of the opening is not zero. This makes it possible to achieve high resolution and improve the transmittance. That is, the present inventors have satisfactorily achieved the above object, and have reached the present invention.
That is, one aspect of the present invention may be a liquid crystal display device sequentially including: a first substrate; a liquid crystal layer containing liquid crystal molecules; and a second substrate, wherein the first substrate includes a first electrode, a second electrode provided closer to the liquid crystal layer than the first electrode is, and an insulating film provided between the first electrode and the second electrode, an opening is formed in the second electrode, the liquid crystal molecules are aligned parallel to the first substrate in a voltage non-applied state in which no voltage is applied between the first electrode and the second electrode, and with a contour of the opening divided into four by a first straight line longest among lines dividing the opening in the direction parallel to an initial alignment azimuth direction of the liquid crystal molecules and a second straight line longest among lines dividing the opening in the direction orthogonal to the initial alignment azimuth direction, the sign of the average slope of each of the divided contour portions differs from the signs of the average slopes of two adjacent contour portions, and the average slope of the entire contour of the opening is not zero.
With the longer of the first straight line and the second straight line dividing the opening being defined as an x-axis and the shorter of the first straight line and the second straight line dividing the opening being defined as a y-axis or, with one of the first straight line and the second straight line being defined as the x-axis and the other as the y-axis in the case where the first straight line and the second straight line dividing the opening have the same length, the average slope of each of the contour portions on a first quadrant and a third quadrant may be negative, and the average slope of each of the contour portions on a second quadrant and a fourth quadrant may be positive.
The liquid crystal molecules may have positive anisotropy of dielectric constant.
The relation A>B may hold, where A represents a length of the opening on the first straight line and B represents a length of the opening on the second straight line.
The angle formed between the initial alignment azimuth direction and the longitudinal direction of the opening may be 450 or less in a plan view.
The liquid crystal molecules may have negative anisotropy of dielectric constant.
The relation A<B may hold, where A represents a length of the opening on the first straight line and B represents a length of the opening on the second straight line.
The angle formed between the initial alignment azimuth direction and the longitudinal direction of the opening may be 450 or more in a plan view.
In a voltage applied state in which a voltage is applied between the first electrode and the second electrode, the liquid crystal molecules may rotate in the same azimuth direction in a central portion of the opening.
A shape of the opening may be the same as a 180° rotated shape in a plane parallel to the first substrate.
In at least a white display state, first, second, and third liquid crystal domains may be present on the opening, the first liquid crystal domain may include two domain portions located separately in two of four regions adjacent to each other vertically and horizontally in a plan view and a coupling portion coupling the two domain portions and located in the central portion of the opening, the two regions being the upper right region and the lower left region or the lower right region and the upper left region, and the second and third liquid crystal domains may be located separately in the other two regions where the two domain portions are not located.
According to the present invention, in a horizontal alignment mode liquid crystal display device, it is possible to achieve high resolution and to improve the transmittance.
Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments, and it is possible to appropriately change the design within the scope in which the configuration of the present invention is satisfied.
In the following description, the same reference numerals denote the same parts or parts having similar functions in different drawings, and a repetitive description thereof is omitted.
The respective configurations described in the embodiments may be appropriately combined or changed within a range not deviating from the gist of the present invention.
A liquid crystal display device according to Embodiment 1 will be described with reference to
As shown in
The pixel electrode 12 is a planar electrode on which no opening is formed. The pixel electrode 12 and the counter electrode 14 are stacked with the insulating layer 13 being interposed between them, and the pixel electrode 12 exists below an opening 15 provided in the counter electrode 14. When a potential difference is generated between the pixel electrode 12 and the counter electrode 14, a fringe electric field is generated around the opening 15 of the counter electrode 14.
Because the counter electrode 14 supplies a potential common to each unit of display, the counter electrode 14 may be formed on almost the entire surface of the first substrate 10 (excluding the opening portion for forming a fringe electric field). The counter electrode 14 may be electrically connected to the external connection terminal at the outer peripheral portion (frame region) of the first substrate 10.
As the insulating layer 13 provided between the pixel electrode 12 and the counter electrode 14, for example, an organic film (dielectric constant ε=3 to 4), an inorganic film (dielectric constant ε=5 to 7) such as silicon nitride (SiNx), silicon oxide (SiO2), or a stacked film of them can be used.
The liquid crystal molecules 21 may have negative anisotropy of dielectric constant (Δε) defined by the following formula, which may have a negative or positive value. That is, the liquid crystal molecules 21 may have negative anisotropy of dielectric constant or positive anisotropy of dielectric constant. The liquid crystal material including the liquid crystal molecules 21 having negative anisotropy of dielectric constant tends to have a relatively high viscosity. Thus, from the viewpoint of obtaining high-speed response performance, a liquid crystal material containing the liquid crystal molecules 21 having positive anisotropy of dielectric constant is preferable. However, even with a liquid crystal material having negative anisotropy of dielectric constant, because it has a viscosity as low as that of a liquid crystal material having positive anisotropy of dielectric constant, the same high speed response performance can be obtained by the means of this embodiment.
Δε=(dielectric constant in major axis direction)−(dielectric constant in minor axis direction)
The alignment of liquid crystal molecules 21 in a voltage non-applied state (to be also simply referred to as “no voltage applied state” or “OFF state” hereinafter) in which no voltage is applied between the pixel electrode 12 and the counter electrode 14, that is, the first electrode and the second electrode, is controlled to be parallel to the first substrate 10. Being “parallel” includes not only being perfectly parallel but also being regarded as parallel (substantially parallel) in this technical field. The pre-tilt angle (tilt angle in the OFF state) of the liquid crystal molecules 21 is preferably less than 3° with respect to the surface of the first substrate 10, more preferably less than 1°.
In a voltage applied state (to be also simply referred to as “voltage applied state” or “ON state” hereinafter) in which a voltage is applied between the pixel electrode 12 and the counter electrode 14, that is, between the first electrode and the second electrode, a voltage is applied to the liquid crystal layer 20, and the alignment of liquid crystal molecules 21 is controlled by the multilayer structure constituted by the pixel electrode 12, the insulating layer 13, and the counter electrode 14 which are provided on the first substrate 10. In this case, the pixel electrode 12 is an electrode provided for each unit of display, and the counter electrode 14 is an electrode shared by a plurality of units of display. Note that “unit of display” means a region corresponding to one pixel electrode 12 and may be referred to as a “pixel” in the technical field of liquid crystal display devices. When one pixel is divisionally driven, each element may be referred to as a “sub-pixel”, “dot”, or “picture element”.
The second substrate 30 is not particularly limited, and a color filter substrate generally used in the field of liquid crystal display devices can be used. The overcoat layer 33 flattens the surface of the second substrate 30 which is located on the liquid crystal layer 20 side, and for example, an organic film (dielectric constant ε=3 to 4) can be used.
Usually, the first substrate 10 and the second substrate 30 are bonded together by a sealant provided so as to surround the periphery of the liquid crystal layer 20, and the first substrate 10, the second substrate 30, and the sealing material hold the liquid crystal layer 20 in a predetermined region. As a sealant, for example, an epoxy resin containing an inorganic filler or an organic filler and a hardening agent can be used.
In addition to the first substrate 10, the liquid crystal layer 20, and the second substrate 30, the liquid crystal display device 100A may include a backlight, an optical film such as a retardation film, a viewing angle expansion film, or a brightness enhancement film, an external circuit such as a tape carrier package (TCP) or a printed circuit board (PCB), and a member such as a bezel (frame). These members are not particularly limited, and because those commonly used in the field of liquid crystal display devices can be used, descriptions of them will be omitted.
The alignment mode of the liquid crystal display device 100A is a fringe field switching (FFS) mode.
Although not shown in
The positions of the counter electrode 14 and the pixel electrode 12 may be interchanged. That is, in the multilayer structure shown in
In a plan view, the initial alignment azimuth direction 22 of the liquid crystal molecules 21 is parallel to the polarization axis of one of the first polarizer and the second polarizer, and is perpendicular to the other polarization axis. Therefore, the control method of the liquid crystal display device 100A is a so-called normally black mode in which black display is performed in a voltage non-applied state where no voltage is applied to the liquid crystal layer 20.
In this specification, the initial alignment azimuth direction of liquid crystal molecules means the alignment azimuth direction of liquid crystal molecules in a voltage non-applied state in which no voltage is applied between the first electrode and the second electrode, that is, between the pixel electrode and the counter electrode. The alignment azimuth direction of liquid crystal molecules means the major-axis direction of the liquid crystal molecules.
Although
As shown in
As shown in
The shape of the opening 15 will be described with reference to
The shape of the opening 15 satisfies the following condition. When the contour of the opening 15 is divided into four by a first straight line 61 parallel to the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and having the longest length dividing the opening 15 and a second straight line 62 orthogonal to the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and having the longest length dividing the opening 15, (condition 1) the sign of the average slope of each of the divided contour portions differs from the signs of the average slopes of two adjacent contour portions, and (condition 2) the average slope of the entire contour of the opening 15 is not zero.
In this specification, the average slope of each of the divided contour portions is obtained as follows.
As shown in
However, the point where the slope becomes 0 or infinite does not contribute to alignment control and hence is excluded. Assume that the n straight lines parallel to the y-axis include a straight line on the y-axis and a straight line passing through a point farthest from the y-axis of the contour portion. The positive and negative directions of the x-axis and the y-axis can be arbitrarily determined with the intersection point between the x-axis and the y-axis being the origin. Furthermore, when the lengths of the first straight line 61 and the second straight line 62 that divide the opening 15 are equal to each other, either one of the first straight line 61 and the second straight line 62 may be set as the x-axis, and the other may be set as the y-axis regardless of whether the anisotropy of dielectric constant of the liquid crystal molecules 21 is positive or negative.
Although n is an arbitrary positive integer and ideally infinite, n is preferably an integer of 100 to 300, preferably an integer of 200 to 300. Further, condition 1 and condition 2 described above may be satisfied for all n in these numerical ranges.
When the sign of the average slope of each of the contour portions differs from the signs of the average slopes of two adjacent contour portions (condition 1), it is possible to generate an electric field for rotating the liquid crystal molecules 21 in the opposite azimuth direction in adjacent contour portions and form bend-shaped and splay-shaped liquid crystal alignments within a narrow region. When the average slope of the entire contour of the opening 15 is not zero (condition 2), the shape of the opening 15 is asymmetric with respect to the initial alignment azimuth direction 22 of the liquid crystal molecules 21, and the rotation of the liquid crystal molecules 21 in the central portion of the opening 15 can be determined in one direction. This makes it possible to reduce the occurrence of a phenomenon in which the alignment state of the liquid crystal molecules 21 differs depending on the unit of display 50 at the time of applying a high voltage and to stabilize the alignment of the liquid crystal molecules 21 even when a high voltage is applied in all units of display 50. Therefore, a sufficiently high voltage can be applied and the transmittance can be improved.
The absolute value of the average slope of each of the contour portions is preferably 0.01 to 2, more preferably 0.05 to 1.8, and even more preferably 0.1 to 1.5.
The absolute value of the average slope of the entire contour of the opening 15 is preferably 0.01 to 2, more preferably 0.02 to 1.5, and even more preferably 0.05 to 1. When the average slope of the entire contour of the opening 15 is within the above range, the balance of the liquid crystal domains generated at the time of voltage application can be effectively maintained, so that the alignment stability of the liquid crystal molecules 21 can be further enhanced. Therefore, it is possible to further improve the response speed.
When one of the first straight line 61 and the second straight line 62 which has a longer length dividing the opening 15 is defined as the x-axis and one of the first straight line 61 and the second straight line 62 which has a shorter length dividing the opening 15 is defined as the y-axis, or when the first straight line 61 and the second straight line 62 have the same length dividing the opening 15, one of the first straight line 61 and the second straight line 62 is defined as the x-axis and the other is defined as the y-axis. In this case, the contour of the opening 15 is divided into four contour portions on a first quadrant 71 to a fourth quadrant 74. Note that the positive and negative directions of the x-axis and the y-axis can be arbitrarily determined with the intersection point between the x-axis and the y-axis being the origin, and the region where x>0 and y>0 is the first quadrant 71, the region where x<0 and y>0 is the second quadrant 72, the region where x<0 and y<0 is the third quadrant 73, the region where x>0 and y<0 is the fourth quadrant 74.
The average slopes of the respective contour portions on the first quadrant 71 and the third quadrant 73 are preferably negative and the average slopes of the respective contour portions on the second quadrant 72 and the fourth quadrant 74 are preferably positive. This can further simplify the shape of the opening 15, and hence can achieve higher resolution.
Letting A be the length of the opening 15 on the first straight line 61 and B be the length of the opening 15 on the second straight line 62, when A>B, liquid crystal molecules 21 having positive anisotropy of dielectric constant are preferably used. The liquid crystal molecules 21 having positive anisotropy of dielectric constant rotate so as to be orthogonal to the slope of the contour of the opening 15 when a voltage is applied. The angle formed between the azimuth direction orthogonal to the slope of the contour of the opening 15 and the initial alignment azimuth direction 22 of the liquid crystal molecules 21 having positive anisotropy of dielectric constant is larger when A>B than when A<B. Therefore, in the case of A>B, the liquid crystal molecules 21 having positive anisotropy of dielectric constant at the time of voltage application can be more rotated from the initial alignment azimuth direction 22, and the transmittance and the alignment stability can be further improved.
On the other hand, when A<B, it is preferable to use liquid crystal molecules 21 having negative anisotropy of dielectric constant. The liquid crystal molecules 21 having negative anisotropy of dielectric constant rotate so as to become parallel to the slope of the contour of the opening 15 at the time of voltage application. The angle formed between the azimuth direction parallel to the slope of the contour of the opening 15 and the initial alignment azimuth direction 22 of the liquid crystal molecules 21 having negative anisotropy of dielectric constant is larger when A<B than when A>B. Therefore, in the case of A<B, the liquid crystal molecules 21 having negative anisotropy of dielectric constant at the time of voltage application can be more rotated from the initial alignment azimuth direction 22, and the transmittance and the alignment stability can be further improved.
The length A of the opening 15 on the first straight line 61 is the length of the divided portion of the opening 15 divided by the first straight line 61 and the length B of the opening 15 on the second straight line 62 is the length of the divided portion of the opening 15 divided by the second straight line 62.
A preferable relationship between the longitudinal direction of the opening 15 and the initial alignment azimuth direction 22 of the liquid crystal molecules 21 will be described next with reference to
A method of determining the longitudinal direction of the opening 15 will be described first. Let C be the length of the opening 15 divided by a third straight line 63 parallel to the straight line portion of the source signal line 42 (signal conductive line) and having the longest length dividing the opening 15 and D be the length of the opening 15 divided by a fourth straight line 64 parallel to the straight line portion of the gate signal line 41 (scanning conductive line) and having the longest length dividing the opening 15. In this case, the direction of the third straight line 63 or the fourth straight line 64 corresponding to the longer one of C and D is the longitudinal direction of the opening 15. Therefore, in either of the examples shown in
When the liquid crystal molecules 21 have positive anisotropy of dielectric constant, it is preferable that the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15 is 45° or less in a plan view. This can satisfy A>B, and hence rotate the liquid crystal molecules 21 having positive anisotropy of dielectric constant more greatly from the initial alignment azimuth direction 22 at the time of voltage application, so that the transmittance and the alignment stability can be further improved.
When the liquid crystal molecules 21 have negative anisotropy of dielectric constant, it is preferable that the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15 is 45° or more in a plan view. This makes it possible to satisfy A<B, and hence to rotate the liquid crystal molecules 21 having negative anisotropy of dielectric constant more greatly from the initial alignment azimuth direction 22 at the time of voltage application, so that the transmittance and the alignment stability can be further improved.
When the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15 is 45°, the same effect can be obtained regardless of whether liquid crystal molecules having positive or negative anisotropy of dielectric constant are used.
According to this embodiment, because the shape of the opening 15 is asymmetrical with respect to the initial alignment azimuth direction 22 of the liquid crystal molecules 21, the liquid crystal molecules 21 rotate in the same azimuth direction in the central portion of the opening 15 in the voltage applied state, as shown in
The shape of the opening 15 is preferably the same as the 180° rotated shape in a plane parallel to the first substrate 10. Using the opening 15 having such a shape can implement a desired alignment more efficiently. In this case, that the shape of the opening 15 is the same as the 180° rotated shape means that the shape when it is rotated by 180° remains substantially the same, and the shape of the opening 15 overlaps 75% or more of the shape when it is rotated by 180° in a plane parallel to the first substrate 10.
In at least the white (highest gray scale) display state, as shown in
That is, in at least the white display state, as shown in
This makes it possible to reliably regulate the alignment of the liquid crystal molecules in the coupling portion 81B positioned in the central portion of the opening 15 by the alignment of the liquid crystal molecules in the two domain portions 81A. That is, this can more reliably reduce the occurrence of a phenomenon in which the alignment state of the liquid crystal molecules 21 differs depending on the unit of display 50 at the time of applying a high voltage. Note that the two domain portions 81A may be located separately in two of the four regions adjacent to each other vertically and horizontally, and the two regions are the upper right region and the lower left region in a plan view. Although the first liquid crystal domain 81, the second liquid crystal domain 82, and the third liquid crystal domain 83 may occur at least in the white display state, they may occur in a high gray scale (for example, a gray scale of 240 or more and 256 or less when the number of gray scale levels of each unit of display 50 is 256) display state in which a high voltage (for example, 5.0 V or more) is applied between the pixel electrode 12 and the counter electrode 14, that is, between the first electrode and the second electrode.
The relationship between the first to third liquid crystal domains 81 to 83 and the initial alignment azimuth direction 22 of the liquid crystal molecules 21 will be studied. As the angle of the initial alignment azimuth direction 22 of the liquid crystal molecules 21 is increased toward the direction in which the liquid crystal molecules 21 forming the first liquid crystal domain 81 rotate, the regions of the second liquid crystal domain 82 and the third liquid crystal domain 83 decrease at the time of voltage application, and the balance between the liquid crystal domains is lost. As a result, distortion caused by bend-shaped or splay-shaped liquid crystal alignments becomes small, so that the effect of high-speed response decreases. As the angle of the initial alignment azimuth direction 22 of the liquid crystal molecules 21 is increased toward the azimuth direction in which the liquid crystal molecules 21 forming the second liquid crystal domain 82 and the third liquid crystal domain 83 rotate, the probability that the coupling portion 81B does not occur in the first liquid crystal domain 81 may increase. In this case, the alignment stability deteriorates.
Accordingly, in order to improve the response speed and further enhance the alignment stability, the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 having positive anisotropy of dielectric constant and the longitudinal direction of the opening 15 is preferably smaller than 30°, and more preferably smaller than 20°.
From the same point of view, the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 having negative anisotropy of dielectric constant and the longitudinal direction of the opening 15 is preferably larger than 60°, and more preferably larger than 70°.
In the case where the liquid crystal molecules 21 have positive anisotropy of dielectric constant, the lower limit of the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15 is not particularly limited, and is only required to be 0° or more. In the case where the liquid crystal molecules 21 have negative anisotropy of dielectric constant, the upper limit of the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15 is not particularly limited, and is only required to be 90° or less.
In this specification, a liquid crystal domain means a region defined by a boundary (dark line) at which the liquid crystal molecules 21 do not rotate from the initial alignment azimuth direction 22 at the time of voltage application, and the liquid crystal molecules 21 rotate in the opposite azimuth direction in the liquid crystal domains in the upper and lower or right and left regions of the four regions adjacent to each other vertically and horizontally. Further, in this specification, “vertically and horizontally” refer to the relative positional relationship of four targets (units of display, regions, and the like), and do not mean any absolute direction.
The operation of the liquid crystal display device 100A will be described below.
No electric field is formed in the liquid crystal layer 20 in the OFF state, and the liquid crystal molecules 21 are aligned parallel to the first substrate 10. Because the alignment azimuth direction of the liquid crystal molecules 21 is parallel to the absorption axis of one of the first polarizer and the second polarizer and the first polarizer and the second polarizer are in a crossed Nicols configuration relationship, the liquid crystal display device 100A in the OFF state transmits no light and performs black display.
In the ON state, an electric field corresponding to the magnitude of the voltage between the pixel electrode 12 and the counter electrode 14 is formed in the liquid crystal layer 20. Specifically, because the opening 15 is formed in the counter electrode 14 provided closer to the liquid crystal layer 20 than the pixel electrode 12, a fringe electric field is generated around the opening 15. The liquid crystal molecules 21 rotate under the influence of the electric field, and change the alignment azimuth direction from the alignment azimuth direction in the OFF state to the alignment azimuth direction in the ON state (see
Although an embodiment of the present invention has been described above, all the matters described can be applied to all the aspects of the present invention.
The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to only these examples.
A liquid crystal display device 100A according to Example 1 is a specific example of the liquid crystal display device 100A according to Embodiment 1 described above and has the following configuration.
A pixel pitch in the liquid crystal display device 100A was 10.5 μm×31.5 μm (806 ppi), and a plate-shaped pixel electrode 12 having no punched portion such as an opening was provided on the insulating substrate 11 in each unit of display 50. In addition, the counter electrode 14 having the openings 15 shown in
A liquid crystal layer 20 was provided on the counter electrode 14 through an alignment film (not shown). The refractive index anisotropy (Δn) of the liquid crystal layer 20 was set to 0.111, and the in-plane retardation (Re) was set to 330 nm. The viscosity and anisotropy of dielectric constant (Δε) of the liquid crystal molecules 21 used for the liquid crystal layer 20 were respectively set to 70 cps and 7 (positive type).
In a voltage non-applied state, the liquid crystal molecules 21 were set in horizontal alignment so as to be aligned parallel to a first substrate 10, and an initial alignment azimuth direction 22 of the liquid crystal molecules 21 was set to be parallel, in a plan view, to straight lines having angles of 90° and 270° with respect to the polarization axis shown in
The average slope of each of the contour portions of the opening 15 used in Example 1 was obtained as follows.
First, the contour of the opening 15 was divided into four contour portions by a first straight line 61 and a second straight line 62. In this case, because the liquid crystal molecules 21 used in Example 1 had positive anisotropy of dielectric constant, the first straight line 61 was defined as the x-axis, and the second straight line 62 was defined as the y-axis. Then, the first contour portion located on a first quadrant 71 was projected on the x-axis, and 221 (=n) straight lines parallel to the y-axis were drawn, which equally divided the length of the first contour portion by 220 (=n−1). That is, 221 (=n) straight lines parallel to the y-axis were drawn, which equally divided the width of the first contour portion in the x-axis direction by 220 (=n−1). At this time, a straight line was drawn on the y-axis, and a straight line parallel to the y-axis was also drawn on the point farthest from the y-axis of the first contour portion. Then, the slope at each intersection point was obtained by differentiating at the intersection points between all of these straight lines and the first contour portion (when there are a plurality of intersection points on one straight line, all intersection points). The value obtained by dividing the sum of the slopes by the total number of intersection points was taken as the average slope of the first contour portion. Note that the point where the slope became 0 or infinite did not contribute to alignment control and hence was excluded. The average slopes of the second, third, and fourth contour portions respectively located on a second quadrant 72 to a fourth quadrant 74 were calculated in the same manner as for the first contour portion. In addition, the sum of the average slopes of the first, second, third and fourth contour portions was divided by 4 to obtain the average slope of the entire contour.
Table 1 below shows the average slopes of the contour portions of the opening 15 used in Example 1 and the average slope of the entire contour.
Table 1 shows that the average slopes of the first and third contour portions on the first quadrant 71 and the third quadrant 73 had negative signs, the average slopes of the second and fourth contour portions on the second quadrant 72 and the fourth quadrant 74 had positive signs, and the sign of the average slope of each contour portion differed from the sign of the average slope of each of the two adjacent contour portions. In addition, the average slope of the entire contour was not zero.
Table 2 shows that the opening 15 used in Example 1 satisfied A>B and C>D, and the longitudinal direction of the opening 15 was a direction parallel to a third straight line 63. The angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction (the third straight line 63) of the opening 15 was 0° in a plan view and was smaller than 45°. In addition, the opening 15 used in Example 1 had a shape that overlaps 100% of the area of a shape obtained when the shape of the opening 15 is rotated by 180° in a plane parallel to the first substrate 10.
The average slopes of the contour of the opening 15 used in Example 1 were obtained in the same manner as in Example 1.
Table 3 given below shows the average slopes of the contour portions of the opening 15 used in Example 1 and the average slope of the entire contour.
Table 3 shows that the average slopes of the first and third contour portions on a first quadrant 71 and a third quadrant 73 had negative signs, the slopes of the second and fourth contour portions on a second quadrant 72 and a fourth quadrant 74 had positive signs, and the sign of the average slope of each contour portion differed from the sign of the average slope of each of the two adjacent contour portions. In addition, the average slope of the entire contour was zero.
The alignment distribution of the liquid crystal molecules 21 in the ON state of each of the liquid crystal display devices 100A according to Example 1 and Comparative Example 1 will be described with reference to
As indicated by the simulation result in
In contrast, as indicated by the simulation results in
As a result, even when high voltages of 5.5 V and 6.0 V were applied, the liquid crystal molecules 21 can assume the same alignment state in all units of display 50, and in the liquid crystal display device 100A according to Example 1, there was no problem concerning differences in transmittance depending on the unit of display 50. Therefore, the liquid crystal display device 100A according to Example 1 allowed application of a high voltage and can increase the transmittance. Specifically, at the time of white display, when a voltage of 6.0 V was applied to the liquid crystal display device 100A according to Example 1, the transmittance was 23.8%. In contrast, when a voltage of 4.5 V was applied to the liquid crystal display device 100A according to Comparative Example 1 at the time of white display, the transmittance was 21.2%. As described above, the liquid crystal display device 100A according to Example 1 could increase the transmittance by 12.3% as compared with the liquid crystal display device 100A according to Comparative Example 1.
The difference in transmittance between the liquid crystal display devices 100A according to Example 1 and Comparative Example 1 will be considered below.
As shown in
As shown in
In the case of using the counter electrode 14 according to Comparative Example 1, ideally, four liquid crystal domains are generated in four regions symmetrical with respect to the longitudinal direction and the transverse direction of the opening 15, and electric fields balance in the central portion of the opening 15 to inhibit the liquid crystal molecules 21 from rotating. However, in reality, when a high voltage is applied, an electric field in the central portion of the opening 15 is slightly distorted, the liquid crystal molecules 21 rotate to the left as shown in
The average slopes of the contour portions of the openings 15 used in Examples 2 and 3 and the average slope of the entire contours were obtained in the same manner as in Example 1. The average slopes of the contour portions and the entire contour of the opening 15 used in Example 4 were obtained in the same manner as in Example 1 except that 211 straight lines parallel to the y-axis were drawn to divide the length of each contour portion projected on the x-axis into 210 portions. Assume that when the contour portions include a portion parallel to the first straight line 61 or the second straight line 62 like the opening 15 used in Example 3, the average slopes of the contour portions except for the parallel portion is obtained. Table 4 below shows the average slopes of the contour portions of the openings 15 used in Examples 2 to 4 and the average slope of the entire contours.
Table 4 shows that the average slopes of the first and third contour portions on the first quadrant 71 and the third quadrant 73 had negative signs, the average slopes of the second and fourth contour portions on the second quadrant 72 and the fourth quadrant 74 had positive signs, and the sign of the average slope of each contour portion differed from the sign of the average slope of each of the two adjacent contour portions. In addition, the average slope of the entire contour was not zero.
Table 5 shows the lengths A to D and the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15.
Table 5 shows that the opening 15 used in Examples 2 to 4 satisfied A>B and C>D, and the longitudinal direction of the opening 15 was a direction parallel to a third straight line 63. The angle formed between the initial alignment azimuth direction 22 and the longitudinal direction of the opening 15 was 0° in a plan view and was smaller than 45°. In addition, the openings 15 used in Examples 2 to 4 each had a shape that overlaps 100% of the area of a shape obtained when the shape of the opening 15 is rotated by 180° in a plane parallel to the first substrate 10.
The alignment distribution of the liquid crystal molecules 21 in the ON state of each of the liquid crystal display devices 100A according to Examples 2 and 4 will be described with reference to
As indicated by the simulation results in
As a result, even when a high voltage of 6.0 V is applied to each of the liquid crystal display devices 100A according to Examples 2 to 4, the liquid crystal molecules 21 could assume the same alignment state in all units of display 50, and the transmittance could be improved. Specifically, at the time of white display, when a voltage of 6.0 V was applied to the liquid crystal display devices 100A according to Examples 2 to 4, the transmittances were 24.7%, 24.2%, and 23.6%, respectively. Compared to the liquid crystal display device 100A according to Comparative Example 1, the liquid crystal display devices 100A according to Examples 2 to 4 could increase the transmittance by 16%, 14% and 11%, respectively.
A liquid crystal display device 100A according to Example 5 has the same configuration as the liquid crystal display device 100A according to Example 1 except that the shape of an opening 15 of a counter electrode 14, an initial alignment azimuth direction 22 of liquid crystal molecules 21, and the polarization axis of a pair of polarizers are changed.
The average slopes of the contour portions and the entire contour of the opening 15 used in Example 5 were obtained in the same manner as in Example 1 except that 211 straight lines parallel to the y-axis were drawn to divide the length of each contour portion projected on the x-axis into 210 portions. Table 6 below shows the average slopes of the contour portions of the opening 15 used in Example 5 and the average slope of the entire contour.
Table 6 shows that the average slopes of the first and third contour portions on a first quadrant 71 and a third quadrant 73 had negative signs, the average slopes of the second and fourth contour portions on a second quadrant 72 and a fourth quadrant 74 had positive signs, and the sign of the average slope of each contour portion differed from the sign of the average slope of each of the two adjacent contour portions. In addition, the average slope of the entire contour was not zero.
Table 7 shows the lengths A to D and the angle formed between the initial alignment azimuth direction 22 of the liquid crystal molecules 21 and the longitudinal direction of the opening 15.
Table 7 shows that the opening 15 used in Example 5 satisfied A>B and C>D, and the longitudinal direction of the opening 15 was a direction parallel to a third straight line 63. The angle formed between the initial alignment azimuth direction 22 and the longitudinal direction of the opening 15 was 10° in a plan view and was smaller than 450. In addition, the opening 15 used in Example 1 had a shape that overlaps 100% of the area of a shape obtained when the shape of the opening 15 is rotated by 180° in a plane parallel to a first substrate 10.
The alignment distribution of the liquid crystal molecules 21 in the ON state of the liquid crystal display device 100A according to Example 5 will be described with reference to
As a result, even when high voltages of 5.5 V and 6.0 V are applied, the liquid crystal molecules 21 can assume the same alignment state in all the units of display 50, and in the liquid crystal display device 100A according to Example 5, there was no problem that the transmittance differed depending on the unit of display 50. Therefore, the liquid crystal display device 100A according to Example 5 allowed application of a high voltage and could increase the transmittance. Specifically, at the time of white display, when a voltage of 6.0 V was applied to the liquid crystal display device 100A according to Example 5, the transmittance was 23.9%. In contrast, when a voltage of 4.5 V was applied to the liquid crystal display device 100A according to Comparative Example 1 at the time of white display, the transmittance was 21.2%. As described above, the liquid crystal display device 100A according to Example 5 could increase the transmittance by 12.7% as compared with the liquid crystal display device 100A according to Comparative Example 1.
One aspect of the present invention may be a liquid crystal display device sequentially including: a first substrate; a liquid crystal layer containing liquid crystal molecules; and a second substrate, wherein the first substrate includes a first electrode, a second electrode provided closer to the liquid crystal layer than the first electrode is, and an insulating film provided between the first electrode and the second electrode, an opening is formed in the second electrode, the liquid crystal molecules are aligned parallel to the first substrate in a voltage non-applied state in which no voltage is applied between the first electrode and the second electrode, and with a contour of the opening divided into four by a first straight line longest among lines dividing the opening in the direction parallel to an initial alignment azimuth direction of the liquid crystal molecules and a second straight line longest among lines dividing the opening in the direction orthogonal to the initial alignment azimuth direction, the sign of the average slope of each of the divided contour portions differs from the signs of the average slopes of two adjacent contour portions, and the average slope of the entire contour of the opening is not zero.
When the sign of the average slope of each contour portion differs from the sign of the average slope of each of the two adjacent contour portions, it is possible to generate an electric field for rotating the liquid crystal molecules 21 in the opposite azimuth direction in the adjacent contour portions. When the average slope of the entire contour of the opening is not zero, the shape of the opening is asymmetric with respect to the initial alignment azimuth direction of the liquid crystal molecules, and the rotation of the liquid crystal molecules in the central portion of the opening can be determined in one azimuth direction. This makes it possible to reduce the occurrence of a phenomenon in which the alignment state of the liquid crystal molecules differs depending on the unit of display at the time of applying a high voltage and to stabilize the alignment of the liquid crystal molecules even when a high voltage is applied in all units of display. Therefore, a sufficiently high voltage can be applied and the transmittance can be improved.
Openings satisfying the above-mentioned conditions can be formed without taking particularly complicated shapes, and thus it is possible to achieve high resolution.
With the longer of the first straight line and the second straight line dividing the opening being defined as an x-axis and the shorter of the first straight line and the second straight line dividing the opening being defined as a y-axis or, with one of the first straight line and the second straight line being defined as the x-axis and the other as the y-axis in the case where the first straight line and the second straight line dividing the opening have the same length, the average slope of each of the contour portions on a first quadrant and a third quadrant may be negative, and the average slope of each of the contour portions on a second quadrant and a fourth quadrant may be positive. According to this aspect, because the shape of the opening can be further simplified, higher resolution can be achieved.
The liquid crystal molecules may have positive anisotropy of dielectric constant. According to this aspect, liquid crystal molecules having a relatively low viscosity can be used, and hence the response speed can be further improved.
The relation A>B may hold, where A represents a length of the opening on the first straight line and B represents a length of the opening on the second straight line. According to this aspect, the transmittance and the alignment stability can be further improved.
An angle formed between the initial alignment azimuth direction and a longitudinal direction of the opening may be not more than 45° in a plan view. According to this aspect, the transmittance and the alignment stability can be further improved.
The liquid crystal molecules may have negative anisotropy of dielectric constant.
The relation A<B may hold, where A represents a length of the opening on the first straight line and B represents a length of the opening on the second straight line. According to this aspect, the transmittance and the alignment stability can be further improved.
The angle formed between the initial alignment azimuth direction and the longitudinal direction of the opening may be 45° or more in a plan view. According to this aspect, the transmittance and the alignment stability can be further improved.
In a voltage applied state in which a voltage is applied between the first electrode and the second electrode, the liquid crystal molecules may rotate in the same azimuth direction in a central portion of the opening. According to this aspect, this can more reliably reduce the occurrence of a phenomenon in which the alignment state of the liquid crystal molecules differs depending on the unit of display at the time of applying a high voltage.
A shape of the opening may be the same as a 180° rotated shape in a plane parallel to the first substrate. According to this aspect, it is possible to achieve a desired alignment more efficiently.
In at least a white display state, first, second, and third liquid crystal domains may be present on the opening, the first liquid crystal domain may include two domain portions located separately in two of four regions adjacent to each other vertically and horizontally in a plan view and a coupling portion coupling the two domain portions and located in the central portion of the opening, the two regions being the upper right region and the lower left region or the lower right region and the upper left region, and the second and third liquid crystal domains may be located separately in the other two regions where the two domain portions are not located. According to this aspect, this can more reliably reduce the occurrence of a phenomenon in which the alignment state of the liquid crystal molecules differs depending on the unit of display at the time of applying a high voltage.
Number | Date | Country | Kind |
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2016-064330 | Mar 2016 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2017/011151 | 3/21/2017 | WO | 00 |