KR101887473B1 - Liquid Crystal Element, Liquid Crystal Display - Google Patents

Abstract

It is an object of the present invention to provide a novel reflective liquid crystal device that utilizes a transition between two alignment states.
A liquid crystal layer provided between the first substrate and the second substrate; a polarizing means arranged on the outside of at least the first substrate; and a liquid crystal layer disposed between the first and second substrates, 2 light diffusing means disposed at either one of the one surface side of the substrate or the outside of the second substrate, the light diffusing means disposed at any place between the polarizing means and the first substrate or between the second substrate and the reflector, And a voltage applying means for applying a voltage to the gate electrode. The first substrate and the second substrate are arranged so that the liquid crystal molecules of the liquid crystal layer are twisted in the first direction, and the liquid crystal layer is a key having a property of biting the liquid crystal molecules in the second direction opposite to the first direction It contains lard. The voltage applying means includes a first electrode provided on the first substrate, a second electrode provided on the second substrate and opposed to the first electrode, and a comb-shaped member provided on the second electrode of the second substrate via the insulating layer Three electrodes.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device and a technique for improving electro-optical characteristics in a liquid crystal display device.

Japanese Patent Registration No. 2510150 discloses a liquid crystal display device in which liquid crystal molecules are twisted and aligned in a turning direction opposite to the turning direction restricted by a combination of alignment treatment directions respectively performed on a pair of substrates arranged opposite to each other, (Prior Art 1).

Japanese Patent Application Laid-Open No. 2007-293278 discloses a method of manufacturing a semiconductor device in which a pair of substrates arranged opposite to each other is arranged in a turning direction (second turning direction) opposite to the turning direction (first turning direction) It is possible to increase the distortion in the liquid crystal layer by twisting the liquid crystal molecules in the above-described first pivot direction while adding a twisted chiral agent, thereby lowering the threshold value voltage, thereby enabling the low voltage driving (Prior Art 2).

Japanese Patent Application Laid-Open No. 2010-186045 discloses a technology relating to a reverse twisted nematic (TN) type liquid crystal device which is spray-twisted in the initial state but is stabilized in a reverse twist orientation by applying a vertical electric field once (Prior Example 3).

However, in the liquid crystal display device of Japanese Patent Publication No. 2510150, an orientation state of reverse twist is unstable and an orientation state of reverse twist can be obtained by applying a relatively high voltage to the liquid crystal layer. However, There arises a problem of transition to a state of twist alignment. The liquid crystal device of Japanese Patent Application Laid-Open No. 2007-293278 has an advantage of lowering the threshold voltage as described above. However, when the voltage is turned off, the liquid crystal device transitions to the net twist alignment state immediately (for example, several seconds) Conversely, there is a problem that the threshold voltage is increased. Also, in all the prior arts, it is not assumed that two orientation states of net torsion and reverse torsion are actively used as display or the like. That is, there is no disclosure or suggestion on the technical ideas such as the configuration, the driving method and the like necessary for positively utilizing the bistability. Particularly, in a reflection type liquid crystal device which does not normally use a backlight or a front light which consumes the most power, it is not considered to utilize the above-mentioned bistability. On the contrary, the inventors of the present application have found that a display having a high reflectance or contrast can not be obtained simply by placing a reflector on the rear side of the liquid crystal cell.

A specific form according to the present invention aims at providing a novel reflective liquid crystal device that utilizes a transition between two alignment states.

It is still another object of the present invention to provide a liquid crystal display device capable of driving with low power consumption using a novel reflective liquid crystal device.

One aspect of the liquid crystal device according to the present invention includes: (b) a liquid crystal layer provided between one surface of the first substrate and one surface of the second substrate; (c) a liquid crystal layer provided between at least one of the first substrate and the second substrate, (D) a reflection plate disposed on one side of the second substrate or on the outside of the second substrate; (e) a reflection plate disposed between the polarization means and the first substrate; (H) a voltage applying unit for applying a voltage to the liquid crystal layer; and (h) a first substrate and a second substrate, Wherein the substrate has the alignment treatment direction so as to twist the liquid crystal molecules of the liquid crystal layer in the first direction, and (i) the liquid crystal layer has a property of biting the liquid crystal molecules in a second direction opposite to the first direction (J) a voltage, which is the voltage, A first electrode provided on the first substrate, a second electrode provided on the second substrate and opposed to the first electrode, and a comb-shaped electrode provided above the second electrode of the second substrate through an insulating layer And a third electrode.

According to the above-described configuration, by using the transition between the alignment state determined by the setting of the alignment treatment direction and the alignment state generated by the action of the chiral agent, the reflection characteristic, Device can be realized.

In the liquid crystal device, it is preferable that the pretilt angle generated by the alignment treatment is 20 degrees or more.

In the liquid crystal device, it is preferable that the twist angle of the liquid crystal molecules in the liquid crystal layer determined by the alignment treatment is 45 deg. Or more and 110 deg. Or less, more preferably 70 deg. 5 deg..

In the liquid crystal device, it is preferable that the chiral agent is added in such an amount that the ratio of the thickness of the liquid crystal layer to the chiral pitch is 0.1 or more and less than 0.25.

It is also preferable that the light diffusion means in the liquid crystal element has, for example, a plurality of overlapping diffusion plates. Further, it is more preferable that such light diffusing means is disposed between the polarizing means and the first substrate.

In the above-mentioned liquid crystal device, the flat pipe means is, for example, a flat plate or a circular polarizer.

In the liquid crystal element, for example, a reflector may be disposed on one surface of the second substrate and may also serve as a second electrode.

One aspect of the liquid crystal display device according to the present invention is a liquid crystal display device comprising a plurality of pixel portions, each of which is configured by using the liquid crystal device according to the present invention.

According to the above configuration, by using the bistability (memory property) of the liquid crystal element, basically no power is required except for the display conversion, and neither a backlight nor a front light is basically required, A possible liquid crystal display device can be obtained.

1 is a schematic diagram schematically showing the operation of a reverse TN type liquid crystal device.
2 is a cross-sectional view showing a configuration example of a reverse-TN liquid crystal device.
3 is a schematic cross-sectional view illustrating an electric field that can be applied to each liquid crystal layer using each electrode.
4 is a schematic diagram for explaining the relationship between the rubbing direction and the horizontal electric field direction.
5 is a diagram schematically showing a configuration example of a liquid crystal display device.
Fig. 6 is a diagram showing the relationship between the conditions at the time of rubbing and the pretilt angle. Fig.
7 is a view showing an observation image of the liquid crystal device of Example 1. Fig.
8 is a diagram showing a method of measuring the optical characteristics (reflection characteristics) of the liquid crystal device of Example 1. Fig.
9 is a diagram showing the arrangement state of a polarizing plate or the like when measuring the optical characteristics (reflection characteristics) of the liquid crystal device of Example 1. Fig.
10 is a diagram showing the measurement results of the reflection characteristics of the liquid crystal device of Example 1. Fig.
11 is a diagram summarizing the measurement results of the reflection characteristics of the liquid crystal device of Example 2. Fig.
12 is a diagram showing the relationship between the reflectance, the contrast ratio, and the twist angle of the liquid crystal device of Example 3. Fig.
13 is a diagram showing the relationship between the reflectance, the contrast ratio, and the twist angle of the liquid crystal device according to the third embodiment.
14 is a diagram showing the relationship between the reflectance, the contrast ratio, and the twist angle of the liquid crystal device of Example 3. Fig.

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described with reference to the drawings.

1 is a schematic diagram schematically showing the operation of a reverse TN type liquid crystal device. The reverse-type TN liquid crystal device has a basic configuration of an upper substrate 1 and a lower substrate 2 arranged opposite to each other, and a liquid crystal layer 3 provided therebetween. The surfaces of the upper substrate 1 and the lower substrate 2 are subjected to alignment treatment such as rubbing treatment. The upper substrate 1 and the lower substrate 2 are relatively arranged such that their alignment treatment directions (indicated by arrows in the drawing) cross each other at an angle of about 90 deg. The liquid crystal layer 3 is formed by injecting a nematic liquid crystal material between the upper substrate 1 and the lower substrate 2. [ In this liquid crystal layer 3, there is used a liquid crystal material to which a chiral agent is added to cause the liquid crystal molecules to act in a specific direction (rightward turning direction in the example of Fig. 1) in the azimuthal direction thereof. If the interval (cell thickness) between the upper substrate 1 and the lower substrate 2 is d and the chiral pitch of the chiral agent is p, the ratio d / p is set to, for example, about 0.4. Such a reverse TN type liquid crystal device becomes a spray twist state in which the liquid crystal layer 3 is twisted while spraying orientation in the initial state due to the action of the chiral agent. When a voltage exceeding the saturation voltage is applied to the liquid crystal layer 3 in the spray twist state, the liquid crystal molecules transit to the reverse twist state (uniform twist state) in which the liquid crystal molecules are twisted in the leftward turning direction. Since the liquid crystal molecules 3 in the reverse twisted state are inclined in the bulk, the effect of reducing the driving voltage of the liquid crystal element appears.

2 is a cross-sectional view showing a configuration example of a reverse-TN liquid crystal device. The liquid crystal device shown in Fig. 2A has a basic structure in which a liquid crystal layer 60 is interposed between a first substrate (upper substrate) 51 and a second substrate (lower substrate) A first polarizing plate 61, a 1/4 wave plate 63 and a scattering plate 64 are disposed outside the first substrate 51. A second polarizing plate 62 and a reflection plate 65 are disposed. Next, the structure of the liquid crystal device will be described in more detail. On the other hand, the members such as the sealing member sealing the periphery of the liquid crystal layer 60 are not shown and described.

Each of the first substrate 51 and the second substrate 54 is a transparent substrate such as a glass substrate or a plastic substrate, for example. As shown in the drawing, the first substrate 51 and the second substrate 54 are attached to each other with a predetermined gap (for example, several 탆) therebetween so as to face each other. Although not shown, a switching element such as a thin film transistor may be formed on all the substrates.

The first electrode (52) is provided on one side of the first substrate (51). The second electrode 55 is provided on one side of the second substrate 54. The first electrode 52 and the second electrode 55 are each formed by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example.

The insulating film (insulating layer) 56 is provided so as to cover the second electrode 55 on the second substrate 54. The insulating film 56 is, for example, an inorganic insulating film such as a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof, or an organic insulating film (for example, an acrylic organic insulating film).

The third electrode 58 and the fourth electrode 59 are provided on the insulating film 56 on the second substrate 54, respectively. The third electrode 58 and the fourth electrode 59 in this embodiment are comb-shaped electrodes each having a plurality of electrode branches, and are arranged so that the electrode branches of the electrodes alternate with each other (see Fig. 4 ). The third electrode 58 and the fourth electrode 59 are each formed by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. The third electrode 58 and the fourth electrode 59 are arranged with a width of 20 μm and an electrode interval of 20 μm, for example.

 The alignment film 53 is provided so as to cover the first electrode 52 on one side of the first substrate 51. The alignment film 57 is provided on one surface of the second substrate 54 so as to cover the third electrode 58 and the fourth electrode 59. Each of the alignment films 53 and 57 is subjected to a predetermined alignment treatment (for example, rubbing treatment), and the angle formed by the respective alignment treatment directions is set to, for example, about 90 degrees.

The liquid crystal layer 60 is provided between the first substrate 51 and the second substrate 54. The dielectric anisotropy?? Of the liquid crystal material constituting the liquid crystal layer 60 is positive (??> 0). A thick line in the liquid crystal layer 60 schematically shows the alignment direction of the liquid crystal molecules in an initial state in which no voltage is applied to the liquid crystal layer 60. [

The first polarizing plate 61 is disposed outside the first substrate 51. In this embodiment, the first polarizing plate 61 side is viewed by the user. The second polarizing plate 62 is disposed outside the second substrate 54. The first polarizing plate 61 and the second polarizing plate 62 are arranged, for example, so that the transmission axes of the first polarizing plate 61 and the second polarizing plate 62 are substantially perpendicular to each other (cross-Nicol arrangement). On the other hand, the second polarizing plate 62 may be omitted.

A 1/4 wavelength plate (phase difference plate) 63 is disposed between the first polarizing plate 61 and the first substrate 51. By combining this 1/4 wave plate 63 and the first polarizing plate 61, the whole functions as a circularly polarizing plate. On the other hand, the 1/4 wave plate 63 may be omitted.

The scattering plate (diffusing plate) 64 is for making the light incident on the liquid crystal element uniform. 2 (A), the scattering plate 64 is disposed between the first polarizing plate 61 and the first substrate 51, and the scattering plate 64 is disposed between the first polarizing plate 61 and the first substrate 51, And is arranged on the side closer to the substrate 51. 2 (B), the scattering plate 64 may be disposed on the outer side of the second substrate 54. Further, as shown in Fig. In the illustrated example, the scattering plate 64 is disposed outside the second substrate 54 with the second polarizing plate 62 sandwiched therebetween. On the other hand, the scattering plate 64 is formed by stacking a plurality of scattering plates .

The reflection plate 65 is disposed outside the second substrate 54 with the second polarizing plate 62 sandwiched therebetween. When the scattering plate 64 is provided on the side of the second substrate 54, the reflection plate 65 sandwiches the scattering plate 64 and the second polarizing plate 62, .

3 is a schematic cross-sectional view illustrating an electric field that can be applied to each liquid crystal layer using each electrode. Fig. 3 (A) is a schematic diagram showing the arrangement of the first to fourth electrodes seen from a plane. Figs. 3 (B) to 3 (D) are schematic views showing the arrangement of the first to fourth electrodes in cross section. Fig. As shown in the drawing, the first electrode 52 and the second electrode 55 are disposed opposite to each other, and the third electrode 58 and the fourth electrode 59 are disposed in a region where the first electrode 52 and the second electrode 55 overlap each other. In addition, the plurality of electrode branches of the third electrode 58 and the electrodes of the fourth electrode 59 are alternately arranged one after the other.

As shown in Fig. 3 (B), by applying a voltage between the first electrode 52 and the second electrode 55, an electric field can be generated between both electrodes. The electric field in this case becomes an electric field along the thickness direction (cell thickness direction) of the first substrate 51 and the second substrate 54 as shown. Such an electric field may be referred to as a "vertical electric field" hereinafter.

As shown in Fig. 3C, by applying a voltage between the third electrode 58 and the fourth electrode 59, an electric field can be generated between both electrodes. The electric field in this case becomes an electric field in a direction substantially parallel to one surface of each of the first substrate 51 and the second substrate 54, as shown in the figure. Such an electric field may hereinafter be referred to as a " horizontal electric field ", and a mode using such an electric field may be referred to as an " IPS mode ".

3 (D), a voltage is applied between the second electrode 55, the third electrode 58 and the fourth electrode 59, which are disposed opposite to each other with the insulating film 56 sandwiched therebetween An electric field can be generated between both electrodes. The electric field in this case becomes an electric field along a direction substantially parallel to one surface of each of the first substrate 51 and the second substrate 54 as shown in the figure. Such an electric field may be referred to as a " horizontal electric field " hereinafter, and a mode using such an electric field may be referred to as an " FFS mode ".

In the liquid crystal element, the liquid crystal molecules of the liquid crystal layer 60 are aligned in the spray twisted state in the initial state. On the other hand, when the vertical electric field is generated by using the first electrode 52 and the second electrode 55 as described above, the alignment state of the liquid crystal layer 60 transits to the reverse twist state. Thereafter, when a horizontal electric field is generated by using the third electrode 58 and the fourth electrode 59 (IPS mode), the alignment state of the liquid crystal layer 60 transits to the spray twist state. Similarly, when the horizontal electric field is generated by using the second electrode 55, the third electrode 58, and the fourth electrode 59 (FFS mode), the alignment state of the liquid crystal layer 60 is reversed to the reverse twist state To the spray twist state. Compared with the IPS mode, the FFS mode allows more uniform transition of the alignment state of the liquid crystal layer 60. [ This is because a transverse electric field is also applied to each electrode of the third electrode 58 and the fourth electrode 59. Therefore, the FFS mode is suitable for the aperture ratio (transmittance, contrast ratio).

The reason why the switching of the alignment state is possible is considered as follows. In the spray twist state, the liquid crystal molecules in the liquid crystal layer 60 substantially in the center of the layer thickness direction are laid laterally, but the liquid crystal molecules in the substantially twisted state are reversely twisted by the vertical electric field. Thereafter, a transverse electric field is applied to the liquid crystal molecules at substantially the center in the layer thickness direction of the liquid crystal layer 60 in the reverse twist state by the transverse electric field in the IPS mode or FFS mode, and the liquid crystal layer 60 ), The liquid crystal molecules in the liquid crystal molecules are directed to the direction of the director in which liquid crystal molecules are to be present. Thus, it is considered that the spray twist state and the reverse twist state are switched by utilizing the vertical electric field and the horizontal electric field.

4 is a schematic diagram for explaining the relationship between the rubbing direction and the horizontal electric field direction. In each drawing, the direction of the electric field generated by the combination of the third electrode 58 and the fourth electrode 59 of the liquid crystal element or the second electrode 55 and the direction of the electric field generated by the combination of the first substrate 51 and the second substrate 54 And the direction of rubbing in each of the above-described regions. 4A and 4B show a case where the electric field direction and the rubbing direction intersect at approximately 45 DEG. 4C and 4D show a case in which one rubbing direction is substantially orthogonal to the electric field direction and the other rubbing direction is substantially parallel to the electric field direction.

Next, an example of a method of manufacturing a liquid crystal element will be described in detail.

The first substrate 51 having the first electrode 52 is manufactured by patterning the ITO film of the glass substrate to which the ITO film is attached. Here, the ITO film was patterned by a general photolithography technique. As the ITO etching method, wet etching (ferric chloride) is used. Here, the shape pattern of the first electrode 52 allows the ITO film to remain in the portion corresponding to the extraction electrode portion and the display pixel. Similarly, the second substrate 54 having the second electrode 55 is formed by patterning the ITO film of the glass substrate to which the ITO film is attached.

Then, an insulating film 56 is formed on the second electrode 55 of the second substrate 54. At this time, it is necessary to investigate that the insulating film 56 is not formed on the extraction electrode portion. In such a method, a resist is formed in advance on the extraction electrode portion to form a lift-off after the insulating film 56 is formed, or a method in which an insulating film 56 is formed through a sputtering method or the like with the extraction electrode portion hidden by a metal mask or the like And the like. As the insulating film 56, an organic insulating film, an inorganic insulating film such as a silicon oxide film or a silicon nitride film, and a combination thereof can be given. Here, a laminated film of an acrylic organic insulating film and a silicon oxide film (SiO ₂ film) is used as the insulating film 56.

A heat resistant film (polyimide tape) is attached to the extraction electrode portion (terminal portion), and the material solution of the organic insulation film is spin-coated in this state. For example, a film thickness of 1 mu m is obtained under the condition of rotating at 2000 rpm for 30 seconds. This is baked in a clean oven (for example, 220 DEG C, 1 hour). A SiO ₂ film is formed by a sputtering method (alternating current discharge) while a heat resistant film is attached. For example, the substrate is heated at 80 占 폚 to form a film of 1000 占 퐉. When the heat-resistant film is peeled off, the organic insulating film and the SiO ₂ film can be peeled off cleanly. Thereafter, it is baked in a clean oven (for example, 220 DEG C for 1 hour). This is to improve the insulating property and transparency of the SiO ₂ film. It is not always necessary to form the SiO ₂ film, but it is preferable to form the SiO ₂ film because the adhesion and the patterning property of the ITO film formed thereon are improved. Also, the insulating property is improved. On the other hand, a method of obtaining an insulating property with only the SiO ₂ film without forming an organic insulating film can be considered. In such a case, the SiO ₂ film tends to become porous, and therefore it is preferable to secure the film thickness to about 4000 to 8000 Å. A laminated film of SiNx may also be used. On the other hand, although the sputtering method is described as a method of forming the inorganic insulating film, a forming method such as a vacuum deposition method, an ion beam method, or a CVD (chemical vapor deposition) method may be used.

Next, a third electrode 58 and a fourth electrode 59 are formed on the insulating film 56. Specifically, an ITO film is first formed on the insulating film 56 by sputtering (alternating-current discharge). The substrate is heated to 100 DEG C, for example, and an ITO film of about 1200 ANGSTROM is formed on the entire surface. The ITO film is patterned by a general photolithography technique. As the photomask at this time, those having a shielding portion corresponding to the comb-like electrode as shown in Fig. 4 are used. The comb-shaped electrodes are classified into two types having a width of electrode branches of 20 占 퐉 or 30 占 퐉 and five electrode spacings of 20 占 퐉, 30 占 퐉, 50 占 퐉, 100 占 퐉 and 200 占 퐉. On the other hand, if there is no pattern on the extraction electrode portion as well, the lower ITO film is also removed by etching, so that a photomask having a pattern formed on the extraction electrode portion is also used.

The first substrate 51 and the second substrate 54 fabricated as described above are cleaned. Specifically, first, water washing (brush cleaning or spray cleaning, pure water cleaning) is performed, water is removed, UV cleaning is performed, and finally IR drying is performed.

Then, alignment films 53 and 57 are formed on the first substrate 51 and the second substrate 54, respectively. As the orientation films 53 and 57, a polyimide film in which the side chain density of a material normally used as a vertical alignment film is lowered is used. (Alignment material) of the alignment film is applied to each of the first substrate 51 and the second substrate 54, and these are baked in a clean oven (for example, at 180 DEG C for one hour). Flexographic, inkjet printing, or spin coating is used as a method for applying the material solution of the alignment layer. Although spin coating is used here, the same result is obtained by using another method. The film thickness of the alignment films 53 and 57 is, for example, 500 to 800 angstroms. Next, each of the alignment films 53 and 57 is subjected to rubbing treatment as alignment treatment. The removal amount at the time of rubbing is set to, for example, 0.4 to 0.8 mm.

Then, the first substrate 51 and the second substrate 54 are attached to each other. On the first substrate 51, a spacer material is dispersed in advance, and a sealing material is printed again. As the spacer material, for example, a material having a particle diameter of 4 탆 is used. When the first substrate 51 and the second substrate 54 are bonded to each other, the rubbing direction of each substrate is made to intersect at an angle of about 45 to 110 degrees with respect to each other. As the liquid crystal material, for example, ZLI-2293 manufactured by Merck Co., Ltd. is used. To such a liquid crystal material, CB15 is added as a chiral agent. The addition amount of the chiral agent is set so that the ratio (d / p) of the cell thickness (d) to the chiral pitch (p) is 0.1 or more and less than 0.25.

Thereafter, the first polarizing plate 61, the second polarizing plate 62, the 1/4 wavelength plate 63, the scattering plate 64, and the reflection plate 65 are provided. The first polarizing plate (61) and the second polarizing plate (62) are arranged such that the transmission axes thereof are parallel or orthogonal to the rubbing direction so that both are cross-Nicol arrangement. Thus, the liquid crystal device of the present embodiment is completed.

Next, a configuration example of a liquid crystal display device capable of driving with low power consumption using the memory property of the liquid crystal device will be described.

5 is a diagram schematically showing a configuration example of a liquid crystal display device. The liquid crystal display device shown in Fig. 5 is a simple matrix type liquid crystal display device in which a plurality of pixel portions 74 are arranged in a matrix, and each liquid crystal element is used as each pixel portion 74. Fig. Specifically, the liquid crystal display device includes m control lines B1 to Bm extending in the X direction, a driver 71 for giving control signals to the control lines B1 to Bm, N control lines A1 to An extending in the Y direction intersecting the control lines B1 to Bm and a driver 72 for giving control signals to the control lines A1 to An, B1 to Bm and extending in the Y direction and a driver 73 for giving a control signal to the control lines C1 to Cn and D1 to Dn, And a pixel portion 74 provided at each intersection of the control lines B1 to Bm and the control lines A1 to An.

Each of the control lines B1 to Bm, A1 to An, C1 to Cn and D1 to Dn is formed of, for example, a transparent conductive film of ITO or the like formed in a stripe shape. A portion where the control lines B1 to Bm intersect with the control lines A1 to An functions as the first electrode 52 and the second electrode 55 (see FIG. 3). The control lines C1 to Cn are connected to a comb-like electrode branch (not shown in Fig. 5) provided in a region corresponding to each pixel portion 74 and serving as a third electrode 58. [ Similarly, the control lines D1 to Dn are connected to a comb-shaped electrode branch (not shown in Fig. 5) provided as a fourth electrode 59 in a region corresponding to each pixel portion 74. [

Various methods are conceivable as the driving method of the liquid crystal display device having the structure shown in Fig. For example, the control lines B1, B2, B3 ... (Line-sequential driving method) in which the display is changed line by line in the following manner. In this method, a vertical electric field may be applied to the pixel portion 74 to be relatively brightly displayed, and a horizontal electric field may be applied to the pixel portion 74 to be relatively darkly displayed.

For example, a short-circuit voltage (for example, about 5 V at 150 Hz) is applied to the control line B1 to such an extent that no transition of the alignment state occurs and the control lines A1 to An, C1 to Cn, D1 to Dn ) Applies a short-wave voltage (for example, about 150 V at about 5 V) in synchronism therewith or about half of a threshold voltage delayed by half a period.

Specifically, a short-wave voltage applied to the control line B1 and a short-wave voltage delayed by half a period are applied to the control line corresponding to the pixel portion 74 to be brightly displayed among the control lines A1 to An. At this time, no voltage is applied to the control lines C1 to Cn and D1 to Dn. As a result, a voltage (vertical electric field) of about 10 V is effectively applied to the liquid crystal element of the pixel portion 74. When this voltage is equal to or higher than the saturation voltage, it is possible to cause the liquid crystal layer 60 to undergo the transition of the alignment state to change the light transmittance of the pixel portion 74. On the other hand, a short-wave voltage synchronized with the short-circuit voltage applied to the control line B1 is applied to the control line corresponding to the pixel portion 74 which does not need to change the display among the control lines A1 to An. At this time, no voltage is applied to the control lines C1 to Cn and D1 to Dn. As a result, the voltage is not effectively applied to the pixel portion 74. Therefore, the liquid crystal layer 60 does not undergo transition in the aligned state, and the light transmittance does not change.

A short wave voltage applied to the control line B1 and a short wave voltage delayed by half a period are applied to the control line corresponding to the pixel portion 74 to be brightly displayed among the control lines C1 to Cn and D1 to Dn . At this time, no voltage is applied to the control lines A1 to An. As a result, a voltage (horizontal electric field) of about 10 V is effectively applied to the liquid crystal element of the pixel portion 74. When this voltage is equal to or higher than the saturation voltage, it is possible to cause the liquid crystal layer 60 to undergo the transition of the alignment state to change the light transmittance of the pixel portion 74. On the other hand, a control line corresponding to the pixel portion 74 which does not need to change the display among the control lines C1 to Cn and D1 to Dn is supplied with a short-wave voltage . At this time, no voltage is applied to the control lines A1 to An. As a result, the voltage is not effectively applied to the pixel portion 74. Therefore, the liquid crystal layer 60 does not undergo transition in the aligned state, and the light transmittance does not change.

The driving as described above is performed by the control lines B2, B3 ... , The dot matrix display can be performed. The display state changed by such driving can be maintained semi-permanently. In order to change such a display, the control described above may be executed again from the control line B1. On the other hand, an example in which the present invention is applied to a so-called simple matrix type liquid crystal display device has been described. However, the present invention can also be applied to an active matrix type liquid crystal display device using a thin film transistor or the like. In the case of the active matrix type liquid crystal display device, it is not necessary to change every line of the control line B1 or the like, so that the conversion time can be shortened. In addition, since it is possible to apply a voltage twice or more higher than the threshold value, the voltage can be changed at a higher speed. However, since one substrate has electrodes for a horizontal electric field and a vertical electric field, two thin film transistors or the like are required per pixel.

Next, some embodiments will be described.

(Example 1)

The dependency of the optical characteristics of the liquid crystal device on the pretilt angle was verified. Fig. 6 shows the relationship between the rubbing condition and the pre-tilt angle. The manufacturing method of the liquid crystal device is basically the same as described above, and the annealing temp at the time of forming the alignment film and the clearance in rubbing treatment at the rubbing are used as the variable parameters. The firing temperature was set at 180 캜 or 200 캜, and the amount of removal at the time of rubbing was set to 0.4 mm or 0.8 mm (in the drawings, the removal amount of 0.4 mm is indicated as "-0.4" and the removal amount of 0.8 mm is indicated as "-0.8" ). When the firing temperature was 200 ° C and the removal amount was 0.8 mm, a pretilt angle of 10 ° was obtained. When the firing temperature was 180 ° C and the removal amount was 0.8 mm, a pretilt angle of 35 ° was obtained. When the firing temperature was 180 ° C and the removal amount was 0.4 mm, a pretilt angle of 62 ° was obtained. The angle formed by the rubbing direction of each of the first substrate 51 and the second substrate 54 (twist angle?) Was set at 70 ° or 90 °. The term "twist angle" as used herein refers to a twist angle in the spray twist state, and a practical twist angle in the reverse twist state is "180 ° -Ø" (the same applies to the following embodiments). The amount of the chiral agent added was such that the amount of d / p = 0.182 (when? = 90) or d / p = 0.143 (when? = 70). When the twist angle? Is 90 °, the first polarizing plate 61 and the second polarizing plate 62 are arranged so that the transmission axes thereof are substantially parallel to the rubbing direction, and both are arranged in a crossed Nicol arrangement. In the case where the twist angle? Is 70 °, the first polarizing plate 61 and the second polarizing plate 62 are arranged so that their transmission axes are located at positions 10 ° out of the rubbing direction, and both are arranged in a crossed Nicol arrangement .

7 is a view showing an observation image of the liquid crystal device of Example 1. Fig. FIG. 7A is an observation view of a liquid crystal device manufactured under the condition of high pretilt (62 DEG) in FIG. Such a liquid crystal device was dark in appearance even in the initial state (spray twist state). It is considered that the alignment state of the liquid crystal layer 60 is close to the vertical alignment because the removal amount at the time of rubbing is small and a high pretilt angle is obtained. 7B is an observation view of a liquid crystal device manufactured under the intermediate pre-tilt (35 DEG) condition shown in Fig. Such a liquid crystal device exhibited a very dark black display in the reverse twisted state. FIG. 7C is an observation view of a liquid crystal device manufactured under the low pre-tilt (10 DEG) condition shown in FIG. There was no significant difference in transmittance between the spray twist state and the reverse twist state.

As a result of further study on the intermediate pre-tilt liquid crystal device shown in Fig. 7 (B), it was found that when the firing conditions were 150 to 180 캜 and the removal amount was 0.4 to 0.8 mm, Could know. At this time, when the pretilt angle was measured, it was found that the pretilt angle was about 23 to 35 degrees. On the other hand, it was found that the pretilt angle was about 8 to 15 degrees as a result of further examination of a liquid crystal device showing a light dark blue display condition (low pretilt condition) without showing a comparatively dark black display. Therefore, in order to display a relatively dark black display in the off state in the reverse twist orientation, it may be said that the pretilt angle is preferably 20 degrees or more. On the other hand, in high-tilt liquid crystal devices, alignment defects tend to occur easily. Therefore, it can be said that it is not preferable to make the pre-tilt angle too high.

The reasons for the above characteristics can not be completely clarified. However, in the case of the reverse TN type liquid crystal device, the threshold value at the time of falling (reverse twist state) is lower than that at the time of rising (spray twist orientation) And the threshold value is lower than 0 V by the threshold voltage. Generally, it is considered that, in the reverse twist state, a large distortion occurs due to the relationship between the pre-tilt angle of the interface and the bit force of the chiral agent in the liquid crystal layer. This distortion causes the liquid crystal molecules near the center of the liquid crystal layer in the layer thickness direction to be inclined with respect to the substrate plane even in the voltage off state. Generally, in the reverse twist state, the inclination angle at the bulk becomes higher than the pretilt angle at the interface. This is confirmed in the liquid crystal molecule orientation simulation based on the continuous pair theory. In the liquid crystal device of this embodiment, by making the pretilt angle extremely high, it is presumed that the liquid crystal molecules are elevated to a state close to the vertical alignment by making the inclination angle of the liquid crystal molecules near the center of the liquid crystal layer relatively high. Thus, it is considered that a relatively dark black display can be obtained even in the voltage off state.

8 is a diagram showing a method of measuring the optical characteristics (reflection characteristics) of the liquid crystal element. As shown in Fig. 8A, when measuring the dependence of the reflection characteristic on the viewing angle, it is preferable that the 12 o'clock direction is the reference (0 deg.) When viewed from the front (viewing side) of the liquid crystal element, Direction. 8B, the normal direction of the substrate surface of the liquid crystal element is set as a reference (0 DEG), light irradiation is performed by a light source in a direction tilted by 30 DEG, The direction of tilting).

9 is a diagram showing the arrangement state of a polarizing plate and the like in measuring the optical characteristics (reflection characteristics) of the liquid crystal device of Example 1. Fig. A 1/4 wavelength plate (? / 4 plate), a light source (not shown), a liquid crystal layer Plate and a polarizing plate were disposed, and a reflection plate was disposed on the rear side of the liquid crystal cell. The reflection plate used here was a silver film, the scattering plate had a haze value of 43 to 45%, and the retardation plate had a retardation of about 137 nm. The light source was arranged at a position 30 ° from the substrate plane normal and the photo detector was arranged in the normal direction of the substrate plane. On the other hand, the arrangement of the quarter-wave plate or the scattering plate is an example, and is not limited thereto.

10 is a diagram showing the measurement results of the reflection characteristics of the liquid crystal device of Example 1. Fig. As shown in the figure, the contrast ratio tends to increase as the pretilt angle increases. On the other hand, in the comparison of the reflectance itself (absolute value), the liquid crystal device of the intermediate pre-tilt condition shows a good value. The liquid crystal device under the high pre-tilt condition is not preferable because the alignment defect (rubbing line) is observed as described above.

(Example 2)

Next, the relationship between the optical characteristics of the liquid crystal device and the scattering plate position was verified. The manufacturing method of the liquid crystal device was basically the same as described above, and the firing temperature at the time of forming the alignment film and the removal amount at the time of rubbing were set to the conditions of the intermediate pretilt angle in Example 1 described above. The twist angle (Ø) was set to 90 ° and 70 °. The amount of chiral agent added was changed according to the twist angle. More specifically, when the twist angle is Ø = 90 °, d / p is 0.15, and when the twist angle is Ø = 70 °, d / p is 0.125.

11 is a diagram summarizing the measurement results of the reflection characteristics of the liquid crystal device of Example 2. Fig. 11 (A) shows the relationship between the number of sheets (2 to 4 sheets) of the scattering plate and the reflectance and the contrast ratio. As shown in the figure, the reflectance and the contrast ratio differ due to the number of scattered plates. From the viewpoint of the reflectance, the reflectance tends to increase as the number of scattering plates increases. As shown in the figure, the contrast ratio was the best when the scattering plates were three in this condition. 11 (B) shows the relationship between the position of the scattering plate and the reflection characteristic. In this condition, when the scattering plate is disposed on the upper side (disposed on the side of the first substrate: see FIG. 2A), the visual dependency is small but the contrast is lowered. Conversely, Arrangement: see Fig. 2 (B)), the viewing angle dependency is large, but the contrast ratio tends to be high. Therefore, the number and position of the scattering plate may be appropriately determined in consideration of the product characteristics and the like required for the liquid crystal device.

(Example 3)

On the basis of Examples 1 and 2, a liquid crystal device was produced under the condition that satisfactory optical characteristics were obtained in the conditions thus verified. Specifically, an intermediate pre-tilt condition was adopted for the pre-tilt angle (refer to Example 1), and three sheets for the scattering plate were used to arrange the upper portion (see Example 2). On the other hand, the twist angle? Is set to 45 to 110 °.

12 is a diagram showing the twist angle dependency of reflectance and contrast ratio. On the other hand, the liquid crystal element here used? N = 0.13 liquid crystal material, and three scattering plates were arranged on the upper side, and the polarizing plates were arranged on the upper and lower sides, respectively, without using the quarter wave plate. As shown in FIG. 12, the reflectance (denoted by "R-t" in the drawing) in the reverse twisted state is highly dependent on the twist angle, and the twist angle in FIG. The reflectance tends to increase from the vicinity of 110 DEG in terms of the twist angle in the reverse twist state). On the other hand, the reflectance in the spray twist state (denoted by 'S-t' in the drawing) has a weak dependence on the twist angle. Therefore, the contrast ratio shows dependence on the twist angle, and the contrast ratio shows the best value when the twist angle is in the vicinity of 70 ° ± 5 °.

13 is a diagram showing the twist angle dependency of reflectance and contrast ratio. On the other hand, the liquid crystal device used here was made of a liquid crystal material of? N = 0.066, and three scattering plates were arranged on the upper side, and the polarizing plate was disposed only on the upper side and the 1/4 wave plate was disposed adjacent to the polarizing plate That is, it functions as a circularly polarizing plate). 13, there is a sufficient difference in reflectance value between the reflectance in the reverse twist state (denoted by 'R-t' in the drawing) and the reflectance in the spray twist state (denoted by 'S-t' have. From the results of the twist angle dependency, it can be seen that when the twist angle of Fig. 13 is 70 °, the contrast ratio is the highest and the reflectance of the spray twist state (white display) is also high, so that bright and clear reflection display can be realized. Even when Δn is 0.066, excellent reflection display can be achieved by optimizing the configuration (scattering plate, polarizing plate condition).

14 is a diagram showing the twist angle dependency of reflectance and contrast ratio. On the other hand, the liquid crystal device here used? N = 0.080 liquid crystal material, and three scattering plates were arranged on the upper side, and the polarizing plate was disposed only on the upper side and the 1/4 wave plate was disposed adjacent to the polarizing plate That is, it functions as a circularly polarizing plate). As shown in Fig. 14, the reflectance (denoted by "R-t" in the drawing) in the reverse twisted state has a strong dependency on the twist angle, and the rise of the twist angle (the twist angle in the substantial reverse twist state is small And reflectance increased with the increase of reflectivity. On the other hand, the reflectance in the spray twist state (denoted by "S-t" in the drawings) is weak in dependence on the twist angle. Therefore, the contrast ratio showed a dependence on the twist angle, and the contrast ratio showed the best value when the twist angle was in the vicinity of 60 to 65 degrees.

As described above, according to the present embodiment and the embodiments, it is possible to realize a reflective type bistable reverse TN type liquid crystal device having a high reflectance of bright display and a high contrast. In particular, there is an advantage that a dark display is dark and easy to display clearly. In addition, since power is not required except for switching between bright display and dark display, it is possible to drive with very low power consumption.

In addition, since the driving method using the memory property (line sequential switching method or the like) can be applied, a large-capacity dot matrix display can be performed by a simple matrix display without using a switching element such as a TFT. Therefore, it is possible to display a large capacity at low cost.

Since the manufacturing process of such a bistable reverse-TN liquid crystal device is basically the same as the manufacturing process of a general TN liquid crystal device, the manufacturing cost of the bistable reverse-TN liquid crystal device is low, .

The present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the present invention. For example, the reflection plate may be used also as the second electrode. In such a case, the second electrode may be constituted by a metal film such as an aluminum film. In this case, the polarizing plate may be formed by only the first polarizing plate on the first substrate side, and the second polarizing plate may be omitted, and the scattering plate may be disposed on the first substrate side. With such a configuration, there is an advantage that the parallax of the reflective display is reduced. Further, although not particularly mentioned in the above-described embodiment, a front light may be combined for night display. Alternatively, the backlight may be disposed by using the reflector as a transflective reflector.

1: upper substrate 2: lower substrate
3: liquid crystal layer 51: first substrate
52: first electrode 53, 57: alignment film
54: second substrate 55: second electrode
56: insulating film 60: liquid crystal layer
61: first polarizing plate 62: second polarizing plate
63: quarter wave plate 64: scatter plate
65: reflector 71, 72, 73: driver
74: pixel portions A1 to An, B1 to Bm, C1 to Cn, D1 to Dn:

Claims (9)

A first substrate and a second substrate on which respective orientations are formed,
A liquid crystal layer provided between one surface of the first substrate and one surface of the second substrate;
A polarizing means disposed at least outside the first substrate,
A reflection plate disposed on one side of the second substrate or on the outside of the second substrate,
Light diffusing means disposed between the polarizing means and the first substrate or between the second substrate and the reflector,
And voltage applying means for applying a voltage to the liquid crystal layer,
Wherein the first substrate and the second substrate are arranged such that the liquid crystal molecules of the liquid crystal layer are twisted in a first direction, and the liquid crystal molecules in the liquid crystal layer, which is determined by the alignment treatment, The twist angle ϕ in one direction is not less than 45 DEG and not more than 110 DEG,
Wherein the liquid crystal layer contains a chiral agent which has a property of biting the liquid crystal molecules in a second direction opposite to the first direction and has a twist angle in the second direction of 180 DEG-
The voltage applying means may include a first electrode provided on the first substrate, a second electrode provided on the second substrate and facing the first electrode, and a second electrode on the second substrate through an insulating layer And a third electrode having a comb-like shape. The method according to claim 1,
Wherein the pretilt angle generated by the alignment treatment is 20 DEG or more. delete The method according to claim 1,
Wherein the chiral agent is added in such an amount that the ratio of the thickness of the liquid crystal layer to the chiral pitch is 0.1 or more and less than 0.25. The method according to claim 1,
And a plurality of diffusion plates in which the light diffusion means are stacked. The method according to claim 1,
And the light diffusion means is disposed between the polarizing means and the first substrate. The method according to claim 1,
Wherein the polarizing means is a polarizing plate or a circular polarizing plate. The method according to claim 1,
Wherein the reflection plate is disposed on one side of the second substrate and also serves as the second electrode. A liquid crystal display device comprising a plurality of pixel portions, each of the plurality of pixel portions comprising the liquid crystal device according to any one of claims 1, 2 and 4 to 8.

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