JP2010217523A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal panel which has improved responsiveness. <P>SOLUTION: In an alignment layer 34 on the side of an array substrate 13, a plurality of linear grooves 34a are formed in a predetermined direction by nanoimprint. The grooves 34a is polymerized with a polymerizable compound contained in a liquid crystal layer 16 to set director directions of liquid crystal molecules LC of the liquid crystal layer 16. The liquid crystal molecules LC can be pretilted, so that the responsiveness can be improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including a liquid crystal layer interposed between alignment films.

  In the liquid crystal display element, the performance as a display element such as light transmittance, response time, viewing angle, and contrast is determined according to the alignment characteristics of the liquid crystal molecules. Therefore, it is very important to control the alignment of liquid crystal molecules uniformly.

  In recent years, as a liquid crystal display device using an active matrix, a TN mode liquid crystal in which a liquid crystal material having a positive dielectric anisotropy is aligned so as to be twisted by 90 degrees horizontally between substrates facing each other. Display devices are widely used. However, this TN mode has a problem that the viewing angle is narrow and the response is slow.

  As an alternative method, a vertical alignment (VA) mode using a liquid crystal material having negative dielectric anisotropy and a vertical alignment film has been proposed in order to satisfy high performance requirements.

  Usually, the alignment of liquid crystal molecules is defined by a slit provided on a protrusion (rib) or a transparent electrode (for example, an ITO electrode). Furthermore, by forming the grooves in a certain direction in the alignment film, the director direction of the liquid crystal molecules is aligned in a certain direction, so that the light transmittance is improved. A method for forming a fine structure in an alignment film by a photolithography method or a nanoimprint method has been proposed (see, for example, Patent Document 1).

JP-A-9-152612

  However, the method described above has the advantage of improving the transmittance because the director direction of the liquid crystal molecules is aligned in a certain direction, but the direction in which the liquid crystal molecules fall is not fixed, and it takes time until the liquid crystal molecules stabilize, so the response time Has the problem of being slow.

  The present invention has been made in view of these points, and an object thereof is to provide a liquid crystal display element with improved responsiveness.

  The present invention comprises a pair of substrates, an alignment film formed on each of these substrates, and a liquid crystal layer that includes vertically aligned liquid crystal molecules and is interposed between the alignment films. At least one of them has a linear groove portion nanoimprinted along a predetermined direction on the surface, and the liquid crystal layer has a director direction of the liquid crystal molecules by polymerization of a polymerizable compound and the groove portion of the alignment film. Is set.

  According to the present invention, since the director direction of the liquid crystal molecules is set, the responsiveness can be improved.

It is sectional drawing which shows the principal part of the liquid crystal display element of the 1st Embodiment of this invention. It is an equivalent circuit diagram which shows a liquid crystal display element same as the above. It is a perspective view which shows arrangement | positioning of the groove part and liquid crystal molecule of a liquid crystal display element same as the above. It is explanatory sectional drawing which shows the manufacturing method of a liquid crystal display element same as the above in order of (a) thru | or (c). It is sectional drawing which shows the principal part of the liquid crystal display element of the 2nd Embodiment of this invention. It is sectional drawing which shows the groove part of the liquid crystal display element of the 3rd Embodiment of this invention. It is sectional drawing which shows the groove part of the liquid crystal display element of the 4th Embodiment of this invention. It is a table | surface which shows the relationship between the direction of the groove part of Examples 1 thru | or 6 of a liquid crystal display element, and Comparative Examples 1 and 2, the shape of a projection part, the presence or absence of a polymeric compound, and each response time.

  Hereinafter, the configuration of the liquid crystal display element according to the first embodiment of the present invention will be described with reference to FIGS.

  In FIG. 1 and FIG. 2, 11 is a liquid crystal display element, that is, a liquid crystal panel which is an LCD (Liquid Crystal Display), and this liquid crystal panel 11 is, for example, a white surface from a backlight which is a surface light source device (not shown). A transmissive type that modulates and transmits light to display an image. Needless to say, a reflective type in which incident light is reflected to display an image or a transflective type in which a transmissive type and a reflective type are combined can be used.

  The liquid crystal panel 11 is, for example, an active matrix type capable of color display, and an array substrate 13 as a (first) substrate and a counter substrate 14 as a (second) substrate are illustrated as gap holding members. The liquid crystal layer 16 that is a light modulation layer is interposed between the substrates 13 and 14 and the polarizing plates 17 and 18 are attached to the substrates 13 and 14, respectively. The sub-pixels P, which are pixels for displaying images, are bonded to each other in a matrix along the vertical (V) direction and the horizontal (H) direction. Arranged in a shape.

  The array substrate 13 includes, for example, a glass substrate 25 that is a light-transmitting (first) substrate body. A thin film is formed on the main surface of the glass substrate 25 on the liquid crystal layer 16 side by a conductor such as a metal member. The scanning lines (gate wirings) 31 and the signal lines (source wirings) 32, which are a plurality of wirings formed in a grid, are arranged in a lattice pattern so as to be substantially orthogonal to each other, and the scanning lines 31 and the signal lines 32 A pixel driving thin film transistor (TFT) 33, which is a switching element, is disposed at each crossing position, and an alignment film 34 for aligning the liquid crystal molecules LC of the liquid crystal layer 16 is provided thereon.

  The scanning line 31 is electrically connected to a gate driver 36 which is a scanning line driving circuit as a driving circuit, and the signal line 32 is electrically connected to a source driver 37 which is a signal line driving circuit as a driving circuit. Has been.

  Each thin film transistor 33 has a gate electrode as a control electrode electrically connected to the scanning line 31, a source electrode as an input electrode electrically connected to the signal line 32, and a drain electrode as an output electrode. The pixel electrode 39 constituting the sub-pixel P is electrically connected. Each thin film transistor 33 is subjected to switching control by applying a signal from the gate driver 36 to the gate electrode via the scanning line 31, and corresponds to a signal input from the source driver 37 via the signal line 32. By applying a voltage to the pixel electrode 39, each sub-pixel P can be independently driven on / off.

  The gate driver 36 and the source driver 37 are electrically connected to a controller (not shown) that is formed on the glass substrate 25 and includes a data processing circuit, a clock generation circuit, and the like. Here, the data processing circuit processes RGB data input from an external device or the like and outputs it as a video signal to the source driver 37. The clock generation circuit operates in each of the drivers 36 and 37. A clock signal for controlling the timing is generated and output.

  Each pixel electrode 39 is formed in a thin film shape using a transparent conductive material such as ITO. Each pixel electrode 39 is formed in a rectangular shape in plan view that is long in the vertical (V) direction.

  The alignment film 34 is formed in a thin film shape so as to cover all the pixel electrodes 39 with an organic polymer material such as polyimide or polyamide, and is linear in a predetermined direction on the surface on the liquid crystal layer 16 side. The plurality of groove portions 34a are each formed in a longitudinal shape. Therefore, a fine concavo-convex structure is formed on the surface of the alignment film 34 by the groove 34a.

  As shown in FIG. 1 and FIG. 3, each groove 34a is for setting and controlling only the director direction of the liquid crystal molecules LC, and is formed by a nanoimprint method and is separated from each other at substantially equal intervals. Each groove 34a is formed with inclined side walls 34b so that the width gradually decreases toward the bottom. Furthermore, the width dimension of each groove 34a is set to, for example, 50 to 1000 nm, preferably 100 to 500 nm, and the depth of each groove 34a is set to 1 to 200 nm, preferably 5 to 50 nm. . Each groove portion 34a cannot be controlled in the director direction of the liquid crystal molecules LC if both the width and the depth are too narrow or too wide. Therefore, it is necessary to control the dimension within the setting. Here, the width dimension of the groove 34a refers to the maximum width dimension of the groove 34a, that is, the width dimension between the opening edges on both sides.

  The predetermined direction for forming each groove 34a is, for example, the vertical (V) direction (the direction along the longitudinal direction of the pixel electrode 39 (subpixel P)) or the horizontal (H) direction (the pixel electrode 39 (subpixel P)). (The direction along the width direction), or an oblique direction intersecting with the vertical (V) direction and the horizontal (H) direction, respectively. It shall be.

  On the other hand, as shown in FIG. 1, the counter substrate 14 includes a glass substrate 55 that is a light-transmitting (second) substrate body. On the glass substrate 55, a color filter layer 56, a counter electrode 57, and An alignment film 58 is sequentially stacked.

  The color filter layer 56 includes colored layers 56r, 56g, and 56b formed in a thin film shape with synthetic resin or the like corresponding to RGB, for example. These colored layers 56r, 56g, and 56b are formed, for example, along the vertical (V) direction and have, for example, a stripe shape in plan view. The colored layers 56r, 56g, and 56b are formed corresponding to the sub-pixels P (pixel electrodes 39) arranged in the vertical (V) direction. The color filter layer 56 may be formed on the array substrate 13 side. A light shielding layer 59 that is a black matrix is formed on the glass substrate 55 between the colored layers 56r, 56g, and 56b.

  The light shielding layer 59 is for preventing color mixing caused by a positional shift between the pixel electrode 39 and the colored layers 56r, 56g, and 56b when the substrates 13 and 14 are bonded together by a seal portion. For example, it is formed in a longitudinal shape along the vertical (V) direction with a black synthetic resin having light impermeability.

  The counter electrode 57 sets a common potential of the pixel electrodes 39, and is formed by a sputtering method or the like with a transparent conductive material such as ITO, for example, facing the entire pixel electrode 39.

  The alignment film 58 is for setting the director direction of the liquid crystal molecules LC with the alignment film 34 on the array substrate 13 side. The alignment film 58 covers the entire counter electrode 57 and is made of an organic polymer material such as polyimide or polyamide. It is formed as a thin film.

  Since the alignment film 58 linearly sets the director direction of the liquid crystal molecules LC, not only circularly polarizing plates but also linearly polarizing plates can be used as the polarizing plates 17 and 18. Since the director direction of the liquid crystal molecules LC is set to a linear shape, the contrast can be improved while maintaining the light transmittance that is a concern with the linear polarizing plate.

  The liquid crystal layer 16 is a light modulation layer formed of a predetermined liquid crystal composition having negative dielectric anisotropy. The liquid crystal molecules LC of the liquid crystal layer 16 are vertically (homeotropic) aligned and, as shown in FIG. 4, a polymerizable compound (polymerizable monomer) contained (dissolved) in the liquid crystal composition of the liquid crystal layer 16. ) 61, the tilt (pretilt) is set and controlled in advance.

  Here, the polymerizable compound 61 is polymerized by, for example, ultraviolet rays, heat, or both, to form a polymer network structure 62, thereby stably stabilizing the liquid crystal molecules LC in a predetermined tilted state. It is comprised so that it may arrange.

  Furthermore, the seal portion is formed in a rectangular frame shape (frame shape) with a predetermined adhesive or the like.

  Next, the operation of the first embodiment will be described.

  When manufacturing the liquid crystal panel 11 shown in FIG. 1, first, the array substrate 13 and the counter substrate 14 are separately formed.

  The array substrate 13 is formed by repeatedly repeating a normal film forming process and a patterning process to form the scanning line 31, the signal line 32, the thin film transistor 33, the pixel electrode 39, and the like, and after applying the alignment film 34, the nanoimprint method. A groove 34 a is formed in the alignment film 34.

  The counter substrate 14 is coated with the alignment film 58 after forming the color filter layer 56, the counter electrode 57, and the like by appropriately repeating a normal film forming process and a patterning process.

  Next, as shown in FIG. 4A, the array substrate 13 and the counter substrate 14 are bonded together by a seal portion, and the liquid crystal layer 16 is interposed between the array substrate 13 and the counter substrate 14. The liquid crystal composition constituting the liquid crystal layer 16 includes a polymerizable compound 61 in addition to the liquid crystal molecules LC, and is disposed between the substrates 13 and 14 by a liquid crystal dropping method or a vacuum injection method.

  In this state, when a voltage higher than the threshold voltage of the thin film transistor 33 is applied between the pixel electrode 39 and the counter electrode 57 (FIG. 1) by the power source E, as shown in FIGS. The LCs are lined up in a predetermined direction along the groove 34a. The tilt direction of the liquid crystal molecules LC is defined by the edge portion of the pixel electrode 39.

Moreover, after stable thus fall down the liquid crystal molecules LC, the irradiation of ultraviolet rays (e.g. 500~5000mJ / cm ^2), or heat treatment, or (arrow ex in the figure), the polymerizable compound by performing them both Since 61 is polymerized to form a polymer network structure 62, as shown in FIG. 4 (c), the liquid crystal molecules LC are stable in a state of being slightly tilted along the direction of the groove 34a even when the voltage application is canceled. Retained.

  Here, the threshold voltage refers to a gate-source voltage at which carriers (electrons or holes) start to be induced at the interface of the active layer of the thin film transistor 33.

  Further, the ultraviolet irradiation and heat treatment may be performed from the array substrate 13 side or from the counter substrate 14 side, that is, from one side, or from both sides.

  In this way, a plurality of linear grooves 34a are formed in a predetermined direction along the alignment film 34 on the array substrate 13 side by nanoimprinting, and the vertical alignment of the liquid crystal layer 16 is performed by polymerization of the grooves 34a and the polymerizable compound 61. By setting the director direction of the aligned liquid crystal molecules LC, the tilt can be set in advance for the liquid crystal molecules LC, so that the responsiveness can be improved.

  That is, in the conventional configuration in which a fine uneven structure such as a groove is formed in the alignment film, liquid crystal molecules are aligned along the groove when a voltage is applied between the electrodes 39 and 57, in other words, the director direction is controlled. Although the tilting direction (pretilt) of the liquid crystal molecules is not determined (imaginary line in FIG. 3), it takes time for the liquid crystal molecules to stabilize and the response time is not good. The direction in which the liquid crystal molecules LC are tilted can be defined by forming the groove 34a in the alignment film 34 and polymerizing the polymerizable compound 61 in a stable state by applying a voltage, thereby improving the response time. it can.

  Further, by forming the plurality of groove portions 34a along the same direction, the director directions of the liquid crystal molecules LC are aligned in a certain direction, the transmittance is improved, and multi-direction formation is not required in one subpixel P. Therefore, the groove 34a can be formed without requiring an alignment mechanism.

  Furthermore, in this embodiment, since rubbing is not used for the alignment film 58, there is no occurrence of pinholes, damage or peeling of the organic polymer film due to rubbing, contamination such as dust generation from the rubbing cloth, and organic matter. Static electricity generated by rubbing the alignment film 58 formed by rubbing with a rubbing cloth can be prevented. Therefore, when the thin film transistor 33 is used as a switching element, there is no occurrence of display defects due to electrostatic breakdown of the thin film transistor 33. In addition, it is possible to obtain the liquid crystal panel 11 having excellent display quality while suppressing defects.

  Next, a second embodiment will be described with reference to FIG. In addition, about the structure and effect | action similar to the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the second embodiment, the alignment film of the substrates 13 and 14 in the first embodiment is formed on the side where the groove is not formed, in this embodiment, on the alignment film 58 on the counter substrate 14 side. A rib 64 which is a protrusion is formed.

  The rib 64 is formed in a hook shape along the direction intersecting the groove 34a. That is, the rib 64 extends along the width direction of the pixel electrode 39 along the horizontal (H) direction, the vertical (V) direction, or an oblique direction intersecting the horizontal (H) direction and the vertical (V) direction. Here, for example, the pixel electrode 39 is formed at a substantially central position in the longitudinal direction along the horizontal (H) direction. Each of the ribs 64 has a triangular cross section, and a vertex 64a in a cross-sectional view protrudes toward the array substrate 13, and the inclined surfaces 64b and 64b forming the vertex 64a are substantially equiangular and mutually It is formed to be inclined in line symmetry.

  When the liquid crystal panel 11 is manufactured in the same manner as in the first embodiment, when a voltage higher than the threshold voltage of the thin film transistor 33 is applied between the pixel electrode 39 and the counter electrode 57, the liquid crystal molecules LC are Lined up in a predetermined direction along the groove 34a. At this time, the liquid crystal molecules LC are inclined so as to be substantially orthogonal to the inclined surfaces 64b of the ribs 64, whereby the direction in which the liquid crystal molecules LC are tilted is defined.

  In addition, after the liquid crystal molecules LC are stabilized, the polymer compound 61 is polymerized to form the polymer network structure 62 by performing ultraviolet irradiation, heat treatment, or both, so that the application of voltage is released. Even in this state, the liquid crystal molecules LC are stably held in a state of being slightly tilted along the direction of the groove 34a.

  That is, of the alignment films 34 and 58, the liquid crystal molecules LC are tilted by forming the ribs 64 along the direction intersecting (orthogonal) with the groove 34a in the alignment film 58 where the groove 34a is not formed. Since the direction can be controlled more reliably, the responsiveness becomes better.

  In the second embodiment, the cross section of the rib 64 can be arbitrarily set as long as the tilt direction of the liquid crystal molecules LC can be defined.

  Further, in each of the above embodiments, each groove 34a may be formed without inclining both side walls 34b as in the third embodiment shown in FIG. 6, and the fourth side shown in FIG. As in the embodiment, each edge portion 34c may be rounded.

  Further, the groove portion may be formed not in the alignment film 34 on the array substrate 13 side but in the alignment film 58 on the counter substrate 14 side, or may be formed in each of the alignment films 34 and 58. In this case, the rib 64 is formed on the alignment film 34 when the groove is formed on the alignment film opposite to the groove, that is, when the groove is formed on the alignment film 58, and when the groove is formed on each of the alignment films 34 and 58, the alignment film is formed. 58 and 34 may be formed.

  Examples 1 to 3 corresponding to the first embodiment, Examples 4 to 6 corresponding to the second embodiment, and Comparative Example 1 corresponding to the conventional example and For Comparative Example 2, the response time was measured.

  In the first embodiment, the groove 34 a of the alignment film 34 on the array substrate 13 side is nanoimprinted along the longitudinal direction of the pixel electrode 39.

  In the second embodiment, the groove 34 a of the alignment film 34 on the array substrate 13 side is nanoimprinted along the width direction of the pixel electrode 39.

  In the third embodiment, the groove 34a of the alignment film 34 on the array substrate 13 side is nanoimprinted with respect to the pixel electrode 39 so as to be inclined.

  In the fourth embodiment, a rib 64 is formed along the width direction of the pixel electrode 39 in the alignment film 58 on the counter substrate 14 side in the first embodiment.

  In the fifth embodiment, ribs 64 are formed along the longitudinal direction of the pixel electrode 39 in the alignment film 58 on the counter substrate 14 side in the second embodiment.

  In the sixth embodiment, in the third embodiment, the pixel is formed on the alignment film 58 on the counter substrate 14 side along one side of the pixel electrode 39 on one end side in the longitudinal direction of the pixel electrode 39 and in the center area in the longitudinal direction of the pixel electrode 39. A crank-shaped rib 64 is formed along the width direction of the electrode 39 and along the other side of the pixel electrode 39 at the other end in the longitudinal direction of the pixel electrode 39.

  On the other hand, in Comparative Example 1, ribs are formed along the width direction of the pixel electrodes 39 in the alignment film 58 on the counter substrate 14 side, nothing is applied to the alignment film 34 on the array substrate 13 side, and the liquid crystal layer 16 does not include the polymerizable compound 61.

  In Comparative Example 2, a groove portion 34a along the longitudinal direction of the pixel electrode 39 is nanoimprinted on the alignment film 34 on the array substrate 13 side, and the liquid crystal layer 16 does not include the polymerizable compound 61.

  And as shown in the table | surface of FIG. 8, as a result of measuring response time with respect to the said Examples 1-6 and Comparative Examples 1-2, respectively, in Examples 1-3, favorable responsiveness with a short response time is shown. In Examples 4-6, the response time was shorter than in Examples 1-3, whereas in Comparative Example 1, the responsiveness was longer than in Examples 1-6, and Comparative Example 2 Then, the response time was longer than that of Comparative Example 1, and the responsiveness was not sufficient.

  In this way, the response can be improved by nanoimprinting the groove 34a in the alignment film 34, and the response can be achieved by forming the rib 64 in the alignment film 58 along the direction intersecting (orthogonal) the groove 34a. It was found that the sex could be further improved.

11 Liquid crystal panel as a liquid crystal display element
13 Array substrate
14 Counter substrate, which is a substrate
16 Liquid crystal layer
34, 58 Alignment film
34a Groove
61 Polymerizable compounds
64 Ribs that are protrusions
LC liquid crystal molecules

Claims (2)

A pair of substrates,
An alignment film formed on each of these substrates;
Comprising vertically aligned liquid crystal molecules, comprising a liquid crystal layer interposed between the alignment films,
At least one of the alignment films has a linear groove on the surface that is nanoimprinted along a predetermined direction.
In the liquid crystal layer, a director direction of the liquid crystal molecules is set by polymerization of the groove and a polymerizable compound. 2. A projection formed on the other side of the alignment film along a direction intersecting with the groove and setting a director direction of the liquid crystal molecules together with polymerization of the polymerizable compound and the groove. The liquid crystal display element as described.

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