JP2008145500A - Liquid crystal device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal device capable of performing high quality display having high transmittance and free from an alignment defect (disclination) by eliminating occurrence of an alignment defect due to a lateral electric field in a twisted nematic type liquid crystal, and to provide an image display device provided with the liquid crystal device. <P>SOLUTION: In the liquid crystal device provided with a plurality of pixel electrodes 9 provided on a liquid crystal layer side of a TFT array substrate 10 and a counter electrode provided on the liquid crystal layer side of a counter substrate, the pixel electrode 9 has a side parallel to an alignment direction of a nematic liquid crystal molecule 21 on the pixel electrode 9 and upper and lower sides a and b which are not parallel to the alignment direction of the nematic liquid crystal molecule 21, the upper and the lower sides a and b of the pixel electrode 9 which are not parallel to the alignment direction of the nematic liquid crystal molecule 21 are inclined at a prescribed angle to a direction vertical to the alignment direction of the nematic liquid crystal molecule 21 and the upper sides a and the lower sides b which are not parallel to the alignment direction of the nematic liquid crystal molecule 21 of the plurality of pixel electrodes 9 are inclined in the same direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal device and an electronic apparatus.

  There is a liquid crystal projector as a device for displaying an image on a large screen using a liquid crystal display element. In projectors, it is important to have high brightness and high contrast. In recent years, even in projectors, high aperture ratio and high definition have progressed, and the distance between pixels has become smaller and smaller. As a result, when black and white is switched and displayed in units of pixels on the liquid crystal display element, a horizontal electric field is generated between adjacent pixel electrodes. There is a problem that the vertical electric field for controlling the alignment of the liquid crystal generated between the opposing substrates and the pixel electrodes is affected by the horizontal electric field, thereby causing a liquid crystal alignment defect.

  As an alignment method of a liquid crystal projector, a TN type (twisted nematic type) liquid crystal device is currently widely used from the viewpoint of high transmittance. However, a reverse twist state occurs in which the twisted nematic alignment mode liquid crystal is aligned in a direction (reverse direction) different from the original twist direction due to a lateral electric field generated when different voltages are applied to adjacent pixel electrodes. Is a problem.

  When such an orientation failure occurs, a normal twist domain and a reverse twist domain are opposed to each other. Then, disclination (line defect) is observed between the normal alignment portion and the abnormal alignment portion of the liquid crystal layer, and there is a possibility that display defects may occur.

In order to solve such problems, the following techniques are disclosed.
As a technique for preventing this phenomenon and obtaining a stable orientation in a TN (Twist Nematic) -TFT type liquid crystal display device, Patent Documents 1 and 2 have a convex portion formed in a gap between adjacent pixel electrodes. An electro-optical device is disclosed. Accordingly, it is possible to reduce the disturbance of the alignment state of the liquid crystal due to the lateral electric field generated between the pixel electrodes adjacent to each other having different polarities of the applied voltage.
JP 2002-40455 A JP 2005-121805 A

  In the above Patent Documents 1 and 2, it is possible to reduce liquid crystal alignment failure due to the influence of a lateral electric field generated between pixel electrodes adjacent to each other in a direction perpendicular to the liquid crystal alignment direction on the pixel electrode. There is still a lateral electric field generated between adjacent pixel electrodes in the direction along the alignment direction of the liquid crystal, and the effect of preventing the occurrence of reverse twist due to the influence of the lateral electric field has not been sufficiently solved.

  The present invention has been made in view of the above problems, and its object is to eliminate the occurrence of alignment failure due to a transverse electric field in a twisted nematic type liquid crystal, and to achieve high transmittance and no alignment defects (disclination). An object of the present invention is to provide a liquid crystal device capable of displaying quality and an image display device including the same.

  In order to solve the above problems, the liquid crystal device of the present invention is a twist nematic type liquid crystal device in which a liquid crystal layer made of a liquid crystal having positive dielectric anisotropy is sandwiched between a pair of substrates, A plurality of pixel electrodes provided on the liquid crystal layer side of one of the pair of substrates, and a counter electrode provided on the liquid crystal layer side of the other substrate of the pair of substrates, The pixel electrode has a pair of sides parallel to the alignment direction of the liquid crystal on the pixel electrode and a pair of sides not parallel to the alignment direction of the liquid crystal, and the pixel not parallel to the alignment direction of the liquid crystal A pair of sides of the electrode are inclined at a predetermined angle with respect to a direction perpendicular to the alignment direction of the liquid crystal, and sides of the plurality of pixel electrodes that are not parallel to the alignment direction of the liquid crystal are inclined in the same direction. It is characterized by being.

  According to such a configuration, when different voltages are applied to pixel electrodes adjacent to each other in the liquid crystal alignment direction on the pixel electrodes among adjacent pixel electrodes, an electric field oblique to the liquid crystal alignment direction can be generated. it can. By generating such an electric field between the pixels, when the liquid crystal is changed from the vertical alignment to the twist horizontal alignment in the pixel electrode group from the voltage application state to the no-voltage application state, the rotation is reversed (reverse). It can be guided to be oriented in a desired direction without being twisted. As a result, alignment failure of the liquid crystal when the voltage is OFF can be prevented, high transmittance can be realized, and the occurrence of disclination can be prevented and suppressed.

  In this way, by preventing the occurrence of reverse twist of the liquid crystal, it is possible to eliminate display problems caused by poor alignment of the liquid crystal. Therefore, according to the present embodiment, it is possible to provide a liquid crystal device having high contrast, bright and uniform display quality without display defects.

In addition, the pair of sides of the pixel electrode not parallel to the alignment direction of the liquid crystal is opposite to the alignment direction of the liquid crystal molecules positioned in the middle of the liquid crystal layer when no voltage is applied to the alignment direction of the liquid crystal on the pixel electrode. It is preferable to incline in the direction.
With such a configuration, the rotation direction of the liquid crystal can be reliably guided to a predetermined direction, so that the reverse twist of the liquid crystal can be prevented from occurring.

In addition, a switching element and a wiring connected to the pixel electrode through the switching element are formed on the substrate having the pixel electrode, and the scanning line is not parallel to the alignment direction of the liquid crystal of the pixel electrode It is preferable that a part of the sides overlap.
According to such a configuration, the pixel electrodes adjacent in the alignment direction of the liquid crystal can be arranged closer to each other, so that the area of the light shielding film provided between the pixels can be reduced. Thereby, an aperture ratio can be improved. When the pixel electrodes adjacent to each other in the liquid crystal alignment direction are closer to each other, the intensity of the electric field generated in the oblique direction with respect to the liquid crystal alignment direction can be increased. As a result, the liquid crystal can be reliably guided in the original rotation direction, and the occurrence of alignment failure of the liquid crystal can be further reduced.

It is also preferable that the scanning line is formed along a side of the pixel electrode that is not parallel to the alignment direction of the liquid crystal on the pixel electrode.
According to such a configuration, an electric field can be generated in a direction inclined at a predetermined angle with respect to the alignment direction of the liquid crystal between the pixel electrodes without reducing the aperture ratio of the liquid crystal device.

An electronic apparatus according to the present invention includes the above-described liquid crystal device.
According to the electric device of the present invention, the above-described liquid crystal device can be used as a light modulation device for a display screen of an electronic device such as a liquid crystal television or a mobile phone, a monitor of a personal computer, or a liquid crystal projector (projection display device). By using the liquid crystal device for such a purpose, an electronic device excellent in a display device can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the film thicknesses and dimensional ratios of the respective components are appropriately changed in order to make the drawings easy to see.

[Liquid Crystal Device]
The liquid crystal device of the present embodiment described below is an active matrix liquid crystal device 1 using a TFT (Thin-Film Transistor) element as a switching element. In the present embodiment, a transmissive liquid crystal device will be described as an example of a display method for displaying an image by generating an electric field in a desired direction with respect to the liquid crystal to control the alignment of the liquid crystal.

Hereinafter, the structure of the liquid crystal device of the present embodiment will be described in more detail with reference to the drawings. FIG. 1 is a plan view of a TFT array substrate for explaining a schematic configuration of the liquid crystal device, FIG. 2 is a cross-sectional view taken along line HH ′ of FIG. 1, and FIG. FIG. 4 is a plan view showing the arrangement state of the pixel electrodes on the TFT array substrate.
In the following description, an xyz orthogonal coordinate system is set, and the positional relationship of each member will be described with reference to this xyz orthogonal coordinate system. A predetermined direction in the horizontal plane is an x direction, a direction orthogonal to the x direction in the horizontal plane is a y direction, and a direction orthogonal to each of the x direction and the y direction is a z direction.

  As shown in FIGS. 1 and 2, the liquid crystal device 1 has a positive dielectric anisotropy between the TFT array substrate 10 and the counter substrate 20 bonded via the sealing material 52 via the alignment films 13 and 14. The liquid crystal layer 50 is composed of nematic liquid crystal molecules 21 (hereinafter sometimes simply referred to as nematic liquid crystal or liquid crystal). The alignment film 13 provided on the TFT array substrate 10 and the alignment film 14 provided on the counter substrate 20 cause the nematic liquid crystal 21 to have an orientation in which the molecular long axis direction is twisted about 90 °, and a TN (twisted nematic) type liquid crystal. The apparatus 1 is configured. The alignment films 13 and 14 are tilted (pretilted) by a predetermined angle with respect to the long axis direction of the nematic liquid crystal molecules 21 with respect to the substrate surface.

Next, each component formed on the TFT array substrate 10 will be described in detail.
In FIG. 1, a sealing material 52 is provided on the TFT array substrate 10 along the edge of the counter substrate 20, and a second light shielding film 53 is provided in parallel to the inside thereof. An area surrounded by the second light shielding film 53 is an image display area A of the liquid crystal device 1. A data line driving circuit 101 and an external circuit connection terminal 102 are provided along one side of the TFT array substrate 10 in a region outside the sealing material 52, and the scanning line driving circuit 104 is adjacent to the one side. It is provided along two sides.

  Furthermore, a plurality of wirings 105 are provided on the remaining side of the TFT array substrate 10 for connecting the scanning line driving circuits 104 provided on both sides of the image display area A. Here, the second light shielding film A precharge circuit may be provided hidden under 53. In addition, at least one of the four corners of the counter substrate 20 is provided with a conductive material 106 for electrical conduction between the TFT array substrate 10 and the counter substrate 20. In this embodiment, it is provided in all four places.

A plurality of pixel electrodes 9 are formed in a matrix in the TFT array substrate 10. As shown in FIG. 2, a common electrode 28 common to the plurality of pixel electrodes 9 is formed inside the common substrate 20 disposed to face the TFT array substrate 10.

Hereinafter, the pixel electrode of this embodiment will be described in detail.
In the present embodiment, as the pixel electrode 9, a pixel electrode 9 having an oblique side as shown in FIG. FIG. 3A is a plan view seen from the TFT array substrate side, and FIG. 3B is an enlarged view of the pixel switching TFT element.
As shown in FIG. 3A, the pixel electrode 9 has a pair of opposing sides (upper side a and lower side b) among the four sides of the pixel electrode body 9a. Specifically, as shown in FIG. 3B, the upper side a and the lower side b are at a predetermined angle with respect to a direction perpendicular to the initial alignment direction of liquid crystal on the pixel electrode 9 (shown by a solid line arrow in the figure). It is inclined at θ. The upper side a and the lower side b are preferably inclined with an inclination of, for example, about 45 ° with respect to a direction perpendicular to the alignment direction of the nematic liquid crystal on the pixel electrode 9. However, in reality, it is necessary to maintain the aperture ratio for the convenience of display. Therefore, the opening is formed so as to form an angle θ of, for example, 45 ° or less with respect to a direction perpendicular to the alignment direction of the nematic liquid crystal. Since the inclination directions of the upper side a and the lower side b are the same direction, the shape is like a substantially rhombus in plan view.

(Planar structure)
Next, the planar structure in the image display area of the TFT array substrate will be described in detail with reference to FIG. In FIG. 4, the vertical direction of the drawing coincides with the vertical direction of the display screen.
As shown in FIG. 4, in the image display area A (see FIG. 1) on the TFT array substrate 10 of the liquid crystal device 1, the plurality of transparent pixel electrodes 9 described above are provided in a matrix.

  At that time, the inclination direction of the upper side a (lower side b) of each pixel electrode 9 is unified, and the upper side a and the lower side b in one pixel electrode 9 are the initial alignment directions of liquid crystal on the pixel electrode 9 (hereinafter simply referred to as liquid crystal alignment). It is arranged in a line. In the present embodiment, as shown in FIG. 5, each upper side a and lower side b are gradually inclined downward from the left side to the right side in the drawing. Specifically, for example, the end portions q of the upper side a and the lower side b facing the scanning line 3a are inclined so that they are most separated from the scanning line 3a and the end portion r is closest to the scanning line 3a.

As a result, the upper side a of one pixel electrode 9 and the lower side b of the other pixel electrode 9 which are adjacent in the liquid crystal alignment direction face each other at equal intervals in the extending direction.
As shown in FIG. 4, the pixel electrodes 9 adjacent to each other in the direction perpendicular to the alignment direction of the liquid crystal are aligned with the position of the end q (end r) of the upper side a (lower side b). Match the direction.

  With such an arrangement, when different voltages are applied to the pixel electrodes 9 adjacent in the liquid crystal alignment direction, the upper side a between the upper side a and the lower side b of the pixel electrode 9 adjacent in the liquid crystal alignment direction. In addition, an electric field G (indicated by a dashed-dotted arrow in the figure) is generated in a direction perpendicular to the lower side b.

  A data line 6a is provided along the vertical boundary of the pixel electrode body 9a of each pixel electrode 9, and a scanning line 3a is provided orthogonal to the data line 6a.

  On the TFT array substrate 10, as shown in FIG. 3, a plurality of data lines 6 a extending in the vertical direction (y direction in the figure) of the image display area A are arranged in the horizontal direction ( They are provided at predetermined intervals in the x direction in the figure. Further, a plurality of scanning lines 3a intersecting these data lines 6a and extending in the left-right direction (x direction in the figure) of the image display area A have a predetermined interval in the vertical direction (y direction in the figure) of the image display area A. Is provided. A region surrounded by two adjacent data lines 6a and scanning lines 3a is a pixel region C (a region indicated by a one-dot chain line 9 'in the drawing). Such pixel regions C are formed in a matrix on the TFT array substrate 10.

  In each pixel region C, a pixel electrode 9 made of a transparent conductive material such as indium tin oxide (hereinafter abbreviated as “ITO”) is located. The pixel electrode body 9a in each pixel region C functions as an image display unit.

  As shown in FIG. 3A, the pixel switching TFT element 30 is provided in the vicinity of the intersection of the data line 6a and the scanning line 3a. More specifically, as shown in FIG. 3B, for example, the gate electrode 26 branched from the scanning line 3a in the y direction, the semiconductor layer 1a made of amorphous silicon, the semiconductor layer 1a, and the scanning line 3a And a source electrode 25 that is partially overlapped in a plane area. The source electrode 25 is formed to branch from the data line 6a in the left-right direction (x direction) of the image display area A.

  The pixel electrode 9 is electrically connected to the drain region 1d described later of the semiconductor layer 1a made of, for example, a polysilicon film constituting the pixel switching TFT element 30 through the contact hole 8, and the data line 6a is The semiconductor layer 1a is electrically connected to a source region 1e described later via a contact hole 5.

(Cross-section structure)
Next, the cross-sectional structure of the liquid crystal device of the present embodiment will be described in detail with reference to FIG. In FIG. 6, some components such as a pixel switching TFT element are omitted in view of the visibility of the drawing.

  In the liquid crystal device 1 of the present embodiment, as shown in FIG. 6, a liquid crystal layer 50 is sandwiched between the TFT array substrate 10 and a counter substrate 20 disposed to face the TFT array substrate 10. The liquid crystal layer 50 is composed of nematic liquid crystal molecules 21 having a positive dielectric anisotropy aligned along the electric field, and the liquid crystal device 1 is a twisted nematic display device. The TFT array substrate 10 and the counter substrate 20 are made of a translucent material such as glass, quartz, or plastic.

  In the TFT array substrate 10, the TFT array substrate 10 is transmitted on the surface of the substrate body 10 </ b> A on the liquid crystal layer 50 side, and is reflected by the lower surface of the TFT array substrate 10 (interface between the TFT array substrate 10 and air). A first light-shielding film 11a for partially shielding the return light returning to the liquid crystal layer 50 side is provided. The first light shielding film 11 a is provided to prevent the above-described return light from entering the pixel switching TFT element 30, and is provided in a range where the light shielding effect on the pixel switching TFT element 30 can be obtained.

  Further, a pixel switching TFT element 30 that controls switching of the pixel electrode 9 is provided on the surface of the substrate body 10A via a first interlayer insulating film 12 formed on the substantially entire surface so as to cover the first light shielding film 11a. Is arranged. The first interlayer insulating film 12 is made of silicon oxide or the like, and is electrically insulated by being interposed between the first light shielding film 11 a and the pixel switching TFT element 30.

  The pixel switching TFT element 30 includes a semiconductor layer 1a formed on the first interlayer insulating film 12, a gate electrode 26, and a data line 6a. The semiconductor layer 1a is composed of a channel region 1a ′ of the semiconductor layer 1a in which a channel is formed by an electric field from the gate electrode 26, a drain region 1d and a source region 1e of the semiconductor layer 1a, and a gate insulating film 2 covering the surface. It is insulated from the gate electrode 26.

  In addition, a gate electrode 26 is disposed in the semiconductor layer 1a so as to face the channel region 1a '.

  On the substrate body 10A including the gate electrode 26 and the gate insulating film 2, a second interlayer insulating film 4 having a contact hole 8 leading to the drain region 1d and a contact hole 5 leading to the source region 1e is formed. Has been. That is, the data line 6 a is electrically connected to the source region 1 e through the contact hole 5 that penetrates the second interlayer insulating film 4.

  Further, a third interlayer insulating film 7 having a contact hole 8 leading to the drain region 1d is formed on the data line 6a and the second interlayer insulating film 4. That is, the drain region 1 d is electrically connected to the pixel electrode 9 formed on the third interlayer insulating film 7 through the contact hole 8 that penetrates the second interlayer insulating film 4 and the third interlayer insulating film 7. ing.

  An alignment film 13 made of polyimide or the like is formed on the substrate body 10A so as to cover the pixel electrode 9. The alignment film 13 is subjected to a rubbing process along the extending direction of the data line 6a (the direction indicated by the arrow O in FIG. 4). As the rubbing method, a method of rubbing with a rubbing machine in which a cloth made of rayon, nylon, polyester or the like is attached to a roller is often used. Note that the alignment film 13 may be formed by a technique such as vapor deposition or sputtering using polyimide, SiO2, or the like.

  On the other hand, the counter substrate 20 has a data line 6a, a scanning line 3a (not shown), a channel region 1a ′ and a drain region 1d of the semiconductor layer 1a of the pixel switching TFT element 30 on the inner surface side (liquid crystal layer 50 side). A second light shielding film 19 is provided to prevent incident light from entering the source region 1e.

  Furthermore, a counter electrode 28 common to all the pixel electrodes 9 provided on the TFT array substrate 10 is provided on substantially the entire surface of the second light shielding film 19 (surface on the liquid crystal layer 50 side). The counter electrode 28 functions to drive the nematic liquid crystal molecules 21 so as to face the pixel electrode 9.

  Further, an alignment film 14 is formed on the substrate main body 20 </ b> A provided with the counter electrode 28 on the liquid crystal layer 50 side so as to cover the counter electrode 28. The alignment film 14 is rubbed along the extending direction of the scanning lines 3a (the direction indicated by the arrow P in FIG. 4).

  The alignment films 13 and 14 are for twisting nematic alignment of the nematic liquid crystal molecules 21 with respect to the film surface when no voltage is applied by rubbing formed on each of the alignment films 13 and 14. The rubbing directions of the alignment films 13 and 14 are orthogonal to each other and are shifted by 90 ° in plan view. From the above, the nematic liquid crystal molecules 21 on the pixel electrode 9 are aligned along the data line 6a.

  In the present embodiment, the pretilt angle given to the nematic liquid crystal molecules 21 by the alignment films 13 and 14 is, for example, 8 °. By providing the pretilt angle and slightly tilting the nematic liquid crystal molecules 21 with respect to the substrate surface, the direction in which the nematic liquid crystal molecules 21 rise (the alignment direction of the nematic liquid crystal molecules 21) can be stabilized in one direction.

  When the alignment films 13 and 14 are formed, a method of forming a film such as polyimide by a liquid phase method such as a spin coating method can be employed. Further, depending on the material (such as SiO 2), a film may be formed using a known vapor deposition method, and may have a columnar microstructure standing upright on the surface.

  Although the TFT array substrate 10 and the counter substrate 20 are not shown in FIG. 6, the dielectric anisotropy is positive from the liquid crystal injection port formed on the seal material, which are bonded to each other via the seal material. The liquid crystal panel 40 is obtained by injecting nematic liquid crystal molecules 21 (positive type nematic liquid crystal material).

  The nematic liquid crystal molecules 21 modulate light by changing the alignment state of the molecular assembly according to the applied voltage level, thereby enabling gradation display. In addition to nematic liquid crystal molecules 21 having positive dielectric anisotropy, chiral nematic liquid crystal materials and the like can be mentioned.

  The liquid crystal panel 40 is provided with polarizing plates 22 and 23 on the outer surface sides of the counter substrate 20 and the TFT array substrate 10, respectively, so that the light transmission axes L and N are orthogonal to each other as shown in FIG. Is arranged. The polarizing plates 22 and 23 scan the light transmission axes L and N so that the light transmittance of the liquid crystal device 1 when no voltage is applied is 0% and the light transmittance of the liquid crystal device 1 when voltage is applied is 100%. They are arranged in a direction along the line 3a and the data line 6a. As described above, the polarizing plates 22 and 23 are bonded in a crossed Nicol state so that the TFT array substrate 10 and the counter substrate 20 are sandwiched between both sides of the TFT array substrate 10 and the counter substrate 20, and the liquid crystal device 1 of the present embodiment. It is said.

Next, a method for producing the TFT array substrate of this embodiment will be described.
FIG. 7 is an explanatory view schematically showing a method for producing a TFT array substrate.

  First, as shown in FIG. 7A, a translucent substrate body 10A made of glass or the like is prepared, and a first interlayer insulating film, a second interlayer insulating film, a semiconductor layer, various wirings (not shown) ). Then, a third interlayer insulating film 7 is formed on the second interlayer insulating film including the data line 6a. The third interlayer insulating film 7 can be formed by a film forming method such as a plasma chemical vapor deposition method (PECVD method), a low pressure chemical vapor deposition method (LPCVD method), or a sputtering method.

  Next, as shown in FIG. 7B, cylindrical fine holes are formed as contact holes 8 in the third interlayer insulating film 7. The contact hole 8 is a hole that leads to a drain region (not shown). The fine holes of the contact hole 8 may be formed with a predetermined hole diameter and may have a shape other than a cylindrical shape (for example, a prismatic shape).

  Next, as shown in FIG. 7C, the pixel electrode 9 is formed on the third interlayer insulating film 7 by a known method. The pixel electrodes 9 are formed at a predetermined interval from each other. In the figure, the pixel electrode 9 is connected to the drain region of the pixel switching TFT element (not shown) through the contact hole 8.

  Next, as illustrated in FIG. 7D, the alignment film 13 is formed on the substrate body 10 </ b> A so as to cover the pixel electrode 9. The alignment film 13 is formed by depositing polyimide, SiO 2 or the like using a spin coating method. The TFT array substrate 10 is formed through the above steps.

  Next, it will be described in detail how the alignment state of the liquid crystal shows the alignment method when an electric signal for display is input to the liquid crystal device of the present embodiment. FIG. 4 shows the alignment state of the liquid crystal before and after applying the voltage.

  As shown in FIG. 4, pixel electrodes 9 are arranged in a matrix on the TFT array substrate 10.

  As described above, the liquid crystal device 1 of the present embodiment uses nematic liquid crystal molecules 21 having positive dielectric anisotropy. The nematic liquid crystal molecules 21 having a positive dielectric anisotropy have the property of aligning the major axis direction along the direction of the electric field.

  In a conventional TN liquid crystal device using nematic liquid crystal molecules 21 having a positive dielectric anisotropy, for example, a voltage is applied to all pixels so that the liquid crystal molecules are aligned so as to be substantially perpendicular to the substrate surface. Then, as shown in FIG. 12, when the pixel electrodes 9A and 9B having substantially square shapes adjacent to each other provided on the TFT array substrate 10 are changed to a state where different voltages are applied, the orientation of the liquid crystal molecules is An attempt is made to shift from a state in which the long axis of the molecule stands perpendicular to the substrate surface to a state in which the molecule is twisted in a direction parallel to the substrate surface. At this time, an alignment failure occurs in which the liquid crystal molecules 21 are aligned in the direction opposite to the predetermined twist direction due to the electric field generated at each electrode end (particularly, the transverse electric field E generated in the alignment direction of the liquid crystal). As described above, many alignment defects tend to occur at the ends of the pixel electrodes 9A and 9B because the alignment direction of the nematic liquid crystal molecules 21 on the pixel electrode 9A is different from the alignment direction of the nematic liquid crystal molecules 21 on the pixel electrode 9B. It is in. Details are described below.

  As shown in FIG. 13, when no voltage is applied, the nematic liquid crystal molecules 21 on the pixel electrode 9 have a predetermined tilt angle so that one end thereof rises to the counter substrate 20 side by rubbing the alignment film on the TFT array substrate 10. Standing up. However, after a voltage is applied to a pixel group in a certain region (for example, the pixel electrode 9B ′ shown in the drawing) and the nematic liquid crystal molecules 21 are oriented so as to stand perpendicular to the substrate surface of the TFT array substrate 10. When the voltage of a certain pixel is turned off, the nematic liquid crystal molecules 21 return to the original state, and the liquid crystal molecules have their major axes returning to the twisted state in a plane substantially parallel to the substrate surface of the TFT array substrate 10. . At this time, a voltage is still applied to the surrounding pixel electrodes, and along the initial alignment direction of the nematic liquid crystal molecules 21 between the pixel electrodes to which no voltage is applied (for example, the pixel electrode 9A ′ in the figure). A lateral electric field E (indicated by a dashed line in the figure) is generated. For this reason, the rising edge of the nematic liquid crystal molecules 21 in the inter-pixel region D is reversed (reverse tilt) due to the influence of the lateral electric field E described above. Then, due to the alignment state of the nematic liquid crystal molecules 21 that are reverse-tilted under the influence of the lateral electric field E, when the voltage application is turned off, the liquid crystal layer is returned from the vertical alignment state to the original twisted horizontal alignment state. The twist direction may be opposite to the original direction so that the free energy is minimized (reverse twist). As described above, most of the nematic liquid crystal molecules 21 that are reverse twisted under the influence of the transverse electric field E exist between the TFT array substrate 10 side and the vicinity of the center of the liquid crystal layer in the thickness direction.

In FIG. 12, the alignment direction of the liquid crystal on the TFT array substrate 10 is indicated by an arrow O in the drawing, and the alignment direction of the liquid crystal on the counter substrate is indicated by an arrow P in the drawing.
Since the nematic liquid crystal molecules 21 constituting the liquid crystal layer are twisted nematically aligned, in the vicinity of the center of the liquid crystal layer in the thickness direction, as shown in FIG. 12, the liquid crystal layer 21 rotates clockwise with respect to the orientation direction of the liquid crystal on the surface of the pixel electrode. Twist about 45 degrees. The lateral electric field E generated between the pixel electrodes 9A and 9B when the voltage is applied to the electric field OFF causes a reverse tilt in which the tilt angle is apparently reversed on the TFT array substrate 10, thereby causing a liquid crystal layer in the thickness direction. There is a possibility that the nematic liquid crystal molecules 21 located in the vicinity of the center may be reverse twist aligned to rotate in a direction opposite to the twist direction of the main body. In FIG. 12, the reverse twisted liquid crystal molecules 21 are indicated by a one-dot chain line.
As described above, the nematic liquid crystal molecules 21 existing in the inter-pixel region D are reverse twisted due to the influence of the lateral electric field E due to the tilt angle, so that there is a normal twist domain near the center of the liquid crystal layer in the thickness direction. There is a possibility that the reverse twist domain is mixed temporarily (see the portion surrounded by a two-dot chain line in FIG. 13).

  As shown in FIG. 13, the nematic liquid crystal molecules 21 on the pixel electrode 9 </ b> A ′ are reverse-tilted by the lateral electric field E in the vicinity of the boundary between the pixel electrodes 9 </ b> A ′ and 9 </ b> B ′ to which different voltages are applied. For this reason, a reverse twist of the nematic liquid crystal molecules 21 is generated near the center in the thickness direction of the liquid crystal layer 50 where the reverse tilt has occurred, and an alignment conflict occurs with the nematic liquid crystal molecules 21 that are normally twisted in the adjacent liquid crystal layer region. . Then, a disclination S (line defect) as shown in FIG. 12 due to the conflict between the liquid crystal molecules 21 occurs. This disclination S is particularly confirmed at the end of the pixel electrode 9A. In the pixel electrode 9A, the disclination S is conspicuous for white display. Since the occurrence and disappearance of the disclination S is accompanied by hysteresis, for example, there is a possibility that an afterimage or the like is generated and the display quality of the image is deteriorated.

  The alignment failure of the nematic liquid crystal molecules 21 that are not originally in the desired alignment state is caused by the fact that two polarizing plates (a polarizing plate is arranged in a crossed Nicols state on the liquid crystal panel and the TFT array is aligned with the rubbing direction of the alignment film on the pixel electrode 9. Arranged so that the light transmission axis L of the polarizing plate on the substrate side is parallel, and arranged so that the light transmission axis N of the polarizing plate on the counter substrate side is parallel to the rubbing direction of the alignment film on the counter electrode. When it is arranged), it appears that the transmittance change changes significantly locally.

The present embodiment effectively solves such a problem.
As shown in FIG. 5, the liquid crystal device according to the present embodiment has the reverse twist orientation of nematic liquid crystal molecules located at the boundary of the inter-pixel region D on the TFT array substrate, so that the upper side a of the pixel electrode 9A and the pixel electrode 9B described above are aligned. It can be suppressed to some extent by the electric field G generated between the lower sides b. Details are described below.

  In FIG. 4, the alignment direction of the liquid crystal on the TFT array substrate 10 is indicated by an arrow O in the drawing, the alignment direction of the liquid crystal on the counter substrate is indicated by an arrow P in the drawing, and the normal twist direction of the liquid crystal when a voltage is applied. Is clockwise. The liquid crystal device 1 has a configuration in which the upper side a of the adjacent pixel electrode 9A and the lower side b of the pixel electrode 9B are opposed to each other in the liquid crystal alignment direction in an inter-pixel region D that is a boundary between the pixel regions C adjacent in the liquid crystal alignment direction. It has become. Therefore, when different voltages are applied to the pixel electrodes 9 adjacent in the alignment direction of the nematic liquid crystal molecules 21, the upper side a and the pixel electrode 9B of the pixel electrode 9A are perpendicular to the upper side a and the lower side b. An electric field G is generated. This electric field G is an electric field inclined at a predetermined angle with respect to the initial alignment direction of the liquid crystal, and can regulate the twist direction of the nematic liquid crystal molecules 21 on the pixel electrode 9 to an arbitrary direction (clockwise in this case). it can.

  That is, when the voltage G is turned off by applying the electric field G, the nematic liquid crystal molecules 21 try to return to the original alignment state. However, in the case of the twisted nematic alignment, the chiral nematic liquid crystal that defines the twist rotation direction is not mixed. And has the possibility of rotating in either direction. Further, in order to stabilize the elastic free energy of the liquid crystal layer itself as small as possible, the rotation direction is also affected by the tilt angle of the substrate surface. That is, in the conventional configuration as shown in FIGS. 12 and 13, the tilt direction is reversed between the pixels due to the lateral electric field generated between the two pixels having different voltages. Therefore, reverse tilt is likely to occur. On the other hand, in the configuration of the present embodiment, if the nematic liquid crystal molecules 21 are controlled in a predetermined twist (rotation) direction by an electric field G generated between the pixels as shown in FIGS. It becomes possible to align the rotation direction of the nematic liquid crystal molecules 21 when the is released. Thereby, it is possible to realize high transmittance due to the liquid crystal 21 rotating in the same direction, and it is possible to prevent and suppress the occurrence of disclination due to the reverse twist.

  In order to regulate the alignment direction of the liquid crystal, any one of the liquid crystal 21 having the twisted nematic alignment is twisted except for the initial alignment direction of the liquid crystal and the direction perpendicular to the initial alignment direction of the liquid crystal. The inclination angles of the upper side a and the lower side b of the pixel electrode 9 may be set so that the direction in which the electric field G is generated is substantially parallel to the alignment direction of the nematic liquid crystal molecules 21. That is, at least the liquid crystal molecules twisted in the same direction as the rotation direction of the nematic liquid crystal molecules 21 on the pixel electrode 9 need only be regulated, so that the liquid crystal layer inherently rotates the liquid crystal 21 in the inter-pixel region D. The angles at which the pixel electrodes 9A and 9B are tilted on the upper side a and the lower side b of the pixel electrodes 9A and 9B are set so as to generate an electric field G necessary for guiding the predetermined direction of rotation.

  As described above, the alignment regulating force due to the action of the electric field G allows the nematic liquid crystal molecules 21 to be aligned in a desired direction without causing alignment failure. In the conventional inter-pixel region D shown in FIG. 13, a nematic liquid crystal is used as a boundary between a liquid crystal group in an initial alignment state on the pixel electrode 9A and a liquid crystal group vertically aligned on the pixel electrode 9B in the intermediate region of the liquid crystal layer. There was a conflict between the molecules 21. However, in this embodiment, the alignment defect of the nematic liquid crystal molecules 21 does not occur in the inter-pixel region D as shown in FIG. Therefore, the entire pixel region C can be fully utilized for display.

  Further, the inter-pixel region D is a boundary at which the alignment direction of the nematic liquid crystal molecules 21 is switched, and corresponds to a light-shielding portion between the pixels. That is, noise light generated above the upper side a of the pixel electrode 9A and the pixel electrode 9B is shut out by providing a first light-shielding film 11a and a second light-shielding film 19 as shown in FIG. 3 between the pixels. Is done. Therefore, the light transmittance of the inter-pixel region D does not affect the display, and the first light shielding film 11a and the second light shielding film 19 can further improve the contrast of the image. Further, since the alignment defects of the liquid crystal molecules 21 are much smaller than those of the conventional liquid crystal device, the area where the first light shielding film 11a and the second light shielding film 19 are provided can be reduced. Thereby, an aperture ratio can be improved.

  Note that the second light shielding film 19 may be provided so as to cover a part of the pixel electrodes 9A and 9B so as to include the upper side a of the pixel electrode 9A and the lower side b of the pixel electrode 9B.

  In this way, by controlling the twist direction of the nematic liquid crystal molecules 21, the occurrence of alignment failure can be prevented, and almost all nematic liquid crystal molecules 21 in the pixel region C can be normally aligned. Therefore, the alignment of the nematic liquid crystal molecules 21 in the pixel region C is stabilized, the interference between the liquid crystal molecules 21 is prevented, and the occurrence of disclination can be prevented and suppressed. Therefore, a high transmittance can be realized, and the liquid crystal device 1 having high contrast, bright and uniform display quality can be obtained.

  In the present embodiment, the normal twist direction of the nematic liquid crystal molecules 21 is clockwise, but it may be counterclockwise. In this case, in order to generate an electric field G that induces the liquid crystal molecules 21 counterclockwise, the inclination direction of the upper side a and the lower side b of the pixel electrode 9 is set to be opposite to the inclination direction of the present embodiment. In other words, the inclination directions of the upper side a and the lower side b are described with reference to FIG. 5. The end portions q of the upper side a and the lower side b in the pixel electrode 9B are the most with respect to the scanning line 3a facing the upper side a and the lower side b. The direction of inclination is such that the ends r of the upper side a and the lower side b are farthest from the scanning line.

  As described above, the inclination direction and the angle of the upper side a and the lower side b are appropriately set so that the electric field G generated between the pixel electrodes 9A and 9B is generated in a direction in which the nematic liquid crystal molecules 21 can be guided in a desired rotation direction. To do.

  The liquid crystal device 1 as one embodiment of the present invention has been described above, but the present embodiment is not limited to this, and the wording of each claim does not depart from the scope described in each claim. The present invention is not limited, and the scope of the present invention can be easily replaced by those skilled in the art, and improvements based on knowledge that the person skilled in the art normally has can be added as appropriate.

For example, when the pixel electrodes 9 are arranged as shown in FIG. 4, the scanning lines 3a may be formed along the gaps between the pixel electrodes 9 adjacent in the liquid crystal alignment direction. Since the scanning line 3a is formed along the upper side a (lower side b) of the adjacent pixel electrode 9, it has a zigzag shape.
Thus, the partition shape of the pixel region C may be a shape along the outer shape of the pixel electrode 9.

Further, the shape and arrangement position of the pixel electrode 9 are not limited to the above-described form and can be changed as appropriate.
For example, by setting the inclination angles of the upper side a and the lower side b of the pixel electrode 9 to a minimum angle for inducing the alignment direction of the liquid crystal when a voltage is applied, the pixel region C having a substantially square shape in plan view is formed. The shape of the pixel electrode 9 can be brought close to the shape. As a result, the pixel area C can be effectively used without being covered as a display area.

  In the above embodiment, the pixel electrode 9 is arranged in the pixel region C surrounded by the two adjacent data lines 6a and the scanning lines 3a. However, as shown in FIG. A part of the upper side a and the lower side b of the pixel electrode 9 is placed in the pixel region C so that the upper side a of the pixel electrode 9A and a part of the lower side b of the pixel electrode 9B overlap with the scanning line 3a extending perpendicular to the direction. You may form so that it may protrude outside.

  By configuring in this way, the pixel region 9 having a substantially rhombic shape in plan view can be used for display even in the pixel region C having a substantially square shape in plan view. . In addition, the arrangement interval between the pixel electrodes 9A and 9B adjacent in the liquid crystal alignment direction is narrowed, and the upper side a and the lower side b of the pixel electrode 9B that face each other approach each other. Then, since the electric field G generated between the two becomes stronger, the reverse twist of the liquid crystal molecules 21 can be more reliably prevented. In addition, by allowing the pixel electrodes 9 to be arranged close to each other, it is possible to further reduce the area where the first light shielding film 11a and the second light shielding film 19 are provided, and to further improve the aperture ratio.

  Further, as shown in FIG. 9, the pixel electrodes 9 adjacent in the direction perpendicular to the alignment direction of the liquid crystal are arranged so that the extending directions of the upper side a or the lower side b coincide with each other on a straight line. Also good. Specifically, it is arranged such that the upper side a (lower side b) of the adjacent pixel electrode 9B extends on the extension of the upper side a (lower side b) of the pixel electrode 9A. As a result, the pixel electrodes 9 are aligned on the TFT array substrate 10 in a direction inclined by a predetermined angle with respect to the alignment direction of the liquid crystal. With the arrangement of the pixel electrodes 9, the scanning line 3a also extends in a direction inclined at a predetermined angle with respect to the liquid crystal alignment direction.

  Furthermore, in the present embodiment, only the active matrix liquid crystal device using the image display switching TFT element 30 has been described. However, the present embodiment is not limited to this, and a TFD (Thin-Film Diode) element is used. The present invention can also be applied to the used active matrix liquid crystal device. In the present embodiment, only the transmissive liquid crystal device has been described. However, the present embodiment is not limited to this, and can be applied to a reflective or transflective liquid crystal device. Thus, the present embodiment can be applied to a liquid crystal device having any structure.

[Electronics]
Examples of electronic devices including the liquid crystal device of the above embodiment will be described.
FIG. 10A is a perspective view showing an example of a mobile phone. In FIG. 10A, reference numeral 500 denotes a mobile phone body, and reference numeral 501 denotes a liquid crystal display unit using the liquid crystal device of the above embodiment.

  FIG. 10B is a perspective view illustrating an example of a portable information processing apparatus such as a word processor or a personal computer. In FIG. 10B, reference numeral 600 denotes an information processing apparatus, reference numeral 601 denotes an input unit such as a keyboard, reference numeral 603 denotes an information processing apparatus body, and reference numeral 602 denotes a liquid crystal display unit using the liquid crystal device of the above embodiment. .

  FIG. 10C is a perspective view illustrating an example of a wristwatch type electronic device. In FIG. 10C, reference numeral 700 denotes a watch body, and reference numeral 701 denotes a liquid crystal display unit using the liquid crystal device of the above embodiment.

  As described above, since the electronic apparatus shown in FIG. 10 uses the above-described liquid crystal device as an example of the present embodiment for the display unit, there is a problem that rubbing streaks are displayed, for example, when a rubbing process is performed. In addition, the display device can maintain a high-contrast, bright and high-quality display over a long period of time.

[Projection type display device]
Next, a configuration of a projection display device (projector) including the liquid crystal device of the above embodiment as a light modulation unit will be described with reference to FIG. FIG. 11 is a schematic configuration diagram showing a main part of a projection display device using the liquid crystal device of the above embodiment as a light modulation device. 11, 810 is a light source, 813 and 814 are dichroic mirrors, 815, 816 and 817 are reflection mirrors, 818 is an incident lens, 819 is a relay lens, 820 is an exit lens, 822, 823 and 824 are liquid crystal light modulators, Reference numeral 825 denotes a cross dichroic prism, and reference numeral 826 denotes a projection lens.

  The light source 810 includes a lamp 811 such as a metal halide and a reflector 812 that reflects the light of the lamp. The dichroic mirror 813 that reflects blue light and green light transmits red light out of the light flux from the light source 810 and reflects blue light and green light. The transmitted red light is reflected by the reflection mirror 817 and enters the liquid crystal light modulation device 822 for red light including the liquid crystal device as an example of the above-described embodiment.

  On the other hand, green light out of the color light reflected by the dichroic mirror 813 is reflected by the dichroic mirror 814 that reflects green light, and enters the liquid crystal light modulation device 823 for green light including the liquid crystal device according to the above-described embodiment. The Note that the blue light also passes through the second dichroic mirror 814. For blue light, light guide means 821 comprising a relay lens system including an incident lens 818, a relay lens 819, and an exit lens 820 is provided in order to compensate for the difference in optical path length from green light and red light. Through this, the blue light enters the liquid crystal light modulation device 824 for blue light including the liquid crystal device as an example of the above-described embodiment.

  The three color lights modulated by the respective light modulation devices are incident on the cross dichroic prism 825. In this prism, four right-angle prisms are bonded together, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in a cross shape on the inner surface. These dielectric multilayer films combine the three color lights to form light representing a color image. The synthesized light is projected onto the screen 827 by the projection lens 826 which is a projection optical system, and the image is enlarged and displayed.

It is a top view which shows schematic structure of a liquid crystal device. It is H-H 'sectional drawing of FIG. It is a top view which shows the form of a pixel electrode. It is a top view which shows the arrangement | positioning state of each pixel electrode on a TFT array substrate. It is a top view which shows the arrangement state of the pixel electrodes adjacent to the initial orientation direction of a liquid crystal. It is NN sectional drawing of Fig.3 (a). It is explanatory drawing which shows one manufacturing process of the TFT array substrate in a liquid crystal device. It is a top view which shows the modification of this embodiment. It is a top view which shows the modification of this embodiment. It is a perspective view which shows some examples about the electronic device which concerns on this embodiment. It is a figure which shows an example about the projection type display apparatus which concerns on this embodiment. It is explanatory drawing which shows the orientation state of the liquid crystal molecule in the conventional liquid crystal device. It is explanatory drawing which shows the orientation state of the liquid crystal influenced by the horizontal electric field E. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal device, 9 ... Pixel electrode, 10 ... TFT array substrate, 13 ... Orientation film, 14 ... Orientation film, 28 ... Counter electrode, 20 ... Counter substrate, 21 ... Nematic liquid crystal, nematic liquid crystal molecule, 50 ... Liquid crystal layer, A: Image display area, C: Pixel area, D: Inter-pixel area, G: Electric field, L: Transmission axis, N: Transmission axis

Claims (5)

A liquid crystal device of a twisted nematic type in which a liquid crystal layer made of a liquid crystal having positive dielectric anisotropy is sandwiched between a pair of substrates,
A plurality of pixel electrodes provided on the liquid crystal layer side of one of the pair of substrates, and a counter electrode provided on the liquid crystal layer side of the other substrate of the pair of substrates,
The pixel electrode has a pair of sides parallel to the alignment direction of the liquid crystal on the pixel electrode and a pair of sides not parallel to the alignment direction of the liquid crystal,
A pair of sides of the pixel electrode that are not parallel to the alignment direction of the liquid crystal are inclined at a predetermined angle with respect to a direction perpendicular to the alignment direction of the liquid crystal;
A side of the plurality of pixel electrodes that is not parallel to the alignment direction of the liquid crystal is inclined in the same direction.     The pair of sides of the pixel electrode that are not parallel to the alignment direction of the liquid crystal is the alignment direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer when no voltage is applied to the alignment direction of the liquid crystal on the pixel electrode. The liquid crystal device according to claim 1, wherein the liquid crystal device is inclined in a reverse direction.     A switching element and a wiring connected to the pixel electrode via the switching element are formed on the substrate having the pixel electrode, and the scanning line has a side that is not parallel to the alignment direction of the liquid crystal of the pixel electrode. 3. The liquid crystal device according to claim 1, wherein a part thereof overlaps.     4. The liquid crystal device according to claim 1, wherein the wiring is formed along a side of the pixel electrode that is not parallel to an alignment direction of the liquid crystal on the pixel electrode. 5.     An electronic apparatus comprising the liquid crystal device according to claim 1.

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