JPH05297402A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain an afterimage-free display of superior display quality which has a small difference in rise and fall characteristics by compensating a polarization state caused by the liquid crystal cell of a 1st layer by the liquid crystal cell of a 2nd layer. CONSTITUTION:The angle formed by the axis of polarization of an incidenceside polarizing plate 6 and the liquid crystal molecule long axis of the 1st liquid crystal layer is denoted as phi1 and the angle formed by the axis of polarization of the incidence-side polarizing plate 6 and the liquid crystal molecule long axis of the 2nd liquid crystal layer is denoted as phi2. Then a complete dark visual field is obtained in an initial state by setting phi1 and phi2 so that the polarization state caused by the incidence-side polarizing plate 6 and 1st liquid crystal layer is canceled by the 2nd liquid crystal layer and linear polarized light is cut by a projection-side polarizing plate 6, Then when liquid crystal molecules are oriented perpendicularly to a substrate by applying an electric field to the 2nd liquid crystal layer, the 2nd liquid crystal layer becomes isotropic in the travel direction of light, so the light reaches the projection-side polarizing plate 6 by passing through the 1st liquid crystal layer while maintaining the polarization state, and consequently a light visual field can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. More specifically, it relates to a display device using a nematic liquid crystal.

[0002]

2. Description of the Related Art As a typical liquid crystal display device using nematic liquid crystal, a twisted nematic type (Twist
ed Nematic, TN) Liquid crystal display device, super twisted type (abbreviated as SBE)
Liquid crystal display, electric field controlled birefringence type
lled Birefrengence, ECB) There is a liquid crystal display device. All of these display modes utilize the fact that when an electric field is applied to a liquid crystal cell, the liquid crystal molecular alignment changes due to the dielectric anisotropy of the liquid crystal, and as a result, the birefringence in the cell changes. . When these liquid crystal cells are placed between two polarizing plates, this change in birefringence appears as a change in light transmittance, and display can be performed by this effect. The TN type and SBE type liquid crystals use Np type nematic liquid crystals with positive dielectric anisotropy, while the ECB type liquid crystals use Nn type nematic liquid crystals with negative dielectric anisotropy with respect to the substrate with the long axis of the liquid crystal molecules. DAP type that uses homeotropically aligned cells that are vertically aligned with each other, homogeneous type that uses cells that have Np type nematic liquid crystals aligned with their long axes parallel to the substrate, and liquid crystal molecules are aligned vertically on one substrate surface. On the other hand, there is a HAN type that uses a hybrid array cell which is parallel on the other hand and whose molecular array continuously changes between both substrates. H
Either AN type or Np type can be used as the AN type.

Although it is very difficult to completely explain analytically the operation effects of TN type and SBE type liquid crystals, it is possible to analytically explain ECB type liquid crystals, particularly homogeneous type and DAP type. As shown in FIG. 1, a cell with a thickness d having a uniform refractive index anisotropy Δn with respect to the traveling direction of light is
The angles formed by the polarizing plates are ψ and χ, respectively. The retardation R of the extraordinary light and the normal light generated while the light passes through the cell, and the phase difference δ are
When the wavelength of light is λ, R = Δn · d (1) δ = 2πR / λ = 2πΔn · d / λ (2) The transmitted light intensity of light vertically incident on the cell is expressed by J = A ² {COS ² (ψ-χ) -sin2χsin ² (δ / 2)} (3). Two polarizing plates are orthogonal to each other (χ
-Ψ = π / 2) and ψ = π / 4, the transmitted light intensity J⊥ is J⊥ = A ² sin ² (δ / 2) = A ² sin ² (πΔnd / λ) (4 ). If the refractive index anisotropy Δn of the cell is the refractive index of the liquid crystal molecules in the long axis direction n‖ and in the vertical direction n⊥, Is determined by. However, θ is an angle formed by the long axis of the liquid crystal molecule and the substrate. From these relationships, homogeneous type and D
It is possible to describe the change in transmitted light intensity due to application of an AP type electric field.

A display device using these nematic liquid crystals is widely used because it can be realized with a simple cell structure by using a commonly used liquid crystal material and an ordinary alignment treatment method such as a rubbing method or an oblique evaporation method. Has been done.

[0005]

However, since the liquid crystal display device using these nematic liquid crystals utilizes the motion based on the dielectric anisotropy of liquid crystal molecules, an electric field is applied to the initial alignment state to change the optical state. There are problems such as steepness of so-called optical rising characteristics and lowering of threshold voltage, which are changed. In fact, these characteristics are important because they greatly affect the expansion of the driving margin and the reduction of power consumption. However, the fall characteristic is also important in determining the performance of the display device. In particular, if the fall time is too long, the image of the display picture element is not rapidly erased even after the electric field is removed, resulting in an afterimage.

In order to solve this problem, a liquid crystal whose dielectric anisotropy is inverted from positive to negative depending on a certain frequency is used, and at the time of falling, a high frequency electric field higher than a certain frequency is applied to improve the falling characteristic. A dual frequency drive system is being considered (K. Saitoh, H. Aoki, K. Fujimuro, and A. Ma.
watare: Digest SID'86, 17 (1986) 262.). However, the dual-frequency drive method has a drawback that it is difficult to control the temperature because it consumes a large amount of power because it is driven by high frequency and the frequency characteristics greatly change with temperature.
At present, it has not been practically used except for some applications ("Liquid Crystal Device Handbook" edited by Japan Society for the Promotion of Science, 142nd Committee, p410 Nikkan Kogyo Shimbun (1989).).

Further, a liquid crystal display device using a ferroelectric liquid crystal is mentioned in the sense that there is no difference between the rising characteristics and the falling characteristics (Japanese Patent Laid-Open No. 56-107216;
U.S. Patent No. 4,367,924). Since this liquid crystal display device uses the electric field response of spontaneous polarization, it has a high-speed response of about 1000 times or more compared with the conventional nematic liquid crystal, and also has a memory effect. Is expected as a liquid crystal display device. However, this device has not yet been put into full-scale practical use due to various problems such as difficulty in uniformly aligning liquid crystals and difficulty in obtaining ideal characteristics. Further, since this element is basically a binary display, there is a problem that gradation display is difficult unless a method such as pixel division or frequency division is used and infinite gradation is very difficult. ..

Under such circumstances, the present invention provides a liquid crystal display device having an improved fall characteristic and excellent display quality by using a nematic liquid crystal which is generally widely used.

[0009]

Thus, according to the present invention, a pair of substrates, on which electrodes are selectively formed on at least the surface and on which an alignment control layer is formed, are arranged so as to face each other. A liquid crystal having a positive dielectric anisotropy showing a nematic phase is interposed between the substrates, and a driving means for switching the optical axis of the liquid crystal by selectively applying a voltage to the electrode, and an optical axis for optically switching the optical axis. In a liquid crystal cell having a means for identifying, the alignment control layer is subjected to a uniaxial alignment treatment, and the direction of the treatment is substantially parallel or antiparallel to the counter substrate, or one of the alignment control layers is uniaxial. A structure in which the liquid crystal cell is aligned in two layers and the other is not, and the polarization state caused by the liquid crystal cell in the first layer is compensated by the liquid crystal cell in the second layer. Special to To provide a liquid crystal display device according to.

Further, by driving the liquid crystal cell of the first layer and / or the liquid crystal cell of the second layer, there is provided a liquid crystal display device which displays without causing a delay between the rising characteristic and the falling characteristic of the optical change. provide. FIG. 2 shows a sectional view for explaining the structure of the liquid crystal display device 9 of the present invention. Reference numeral 1 is a substrate, 2 is a transparent electrode, 3 is an orientation control layer, 4 is an Np type nematic liquid crystal having a positive dielectric anisotropy, and these have a two-layer structure as shown in the figure. Reference numeral 6 is a polarizing plate. The polarizers are arranged in crossed Nicols.

Further, 7 is a liquid crystal cell of the first layer and 8 is a liquid crystal cell of the second layer, and the constitution thereof is as follows. A transparent substrate is used as the substrate, and a glass substrate is usually used. InO _3, SnO _{2, and} ITO are used for the substrate, respectively.
A predetermined transparent electrode made of a conductive thin film such as (Indium Tin Oxide) is formed.

An insulating film is usually formed thereon,
This can be omitted in some cases. The insulating film is, for example,
Inorganic thin films such as SiO _2, SiNx and Al ₂ O ₃ , organic thin films such as polyimide, photoresist resin and polymer liquid crystal can be used. When the insulating film is an inorganic thin film, vapor deposition, sputtering, CVD (Chemical Vapor)
It can be formed by the Deposition method or the solution coating method. When the insulating film is an organic thin film, a solution in which an organic substance is dissolved or a precursor solution thereof is used and applied by a spinner coating method, a dip coating method, a screen printing method, a roll coating method, or the like. Curing method (heating, light irradiation, etc.) to form, or evaporation method, sputtering method, CVD method, or LB (Langumui
It can also be formed by the r-Blodgett method or the like.

An orientation control layer is formed on the insulating film. However, when the insulating film is omitted, the orientation control layer is directly formed on the transparent electrode. The orientation control layer may be an inorganic layer or an organic layer. When an inorganic orientation control layer is used, a method often used is oblique vapor deposition of silicon oxide. A method such as rotary evaporation can also be used. When using an organic orientation control layer, nylon, polyvinyl alcohol,
Polyimide, polyurea, or the like can be used, and usually, rubbing is performed thereon. Further, alignment using a polymer liquid crystal or LB film, alignment by a magnetic field, alignment by a spacer edge method, and the like are also possible. Further, it is also possible to use a vapor deposition method of SiO _2, SiNx or the like and a method of rubbing the same.

The orientation control layer needs to be uniaxially oriented. When both the pair of substrates are subjected to the uniaxial orientation treatment, the pair of substrates are bonded so that the directions of the uniaxial orientation treatment are parallel or antiparallel. FIG. 7 (a) shows the molecular arrangement state in the parallel state, and FIG. 7 (b) shows the molecular arrangement state in the anti-parallel state. In addition, FIG. 7C shows the molecular alignment state when the uniaxial orientation treatment is applied to only one of the pair of substrates.
Shown in. In any of these cases, homogeneous orientation is obtained.

The periphery is sealed with an ultraviolet curable resin and bonded together, and a liquid crystal material is injected between the alignment films and then sealed. The p-type (positive dielectric anisotropy) nematic liquid crystal applied to the present invention is a known liquid crystal such as biphenyl-based or PCH.
System, CCH system, etc., and preferably commercially available ZLI-
1565 (manufactured by Merck Ltd.) and ZLI-2788 (manufactured by Merck Ltd.) are used. The liquid crystal is homogeneously aligned.

Thus, the first layer liquid crystal cell 7 and the second layer liquid crystal cell 8 in FIG. 2 are produced. A polarizing plate is arranged at the outermost part of these liquid crystal cells to form a liquid crystal display device. A polarizing glass, a polarizing plastic film, or the like is used as the polarizing plate, and the polarizing plates are arranged so as to form a crossed Nicols.

Next, when the two layers are stacked, the first
A method of compensating for the polarization state caused by the liquid crystal cell of the layer by the liquid crystal cell of the second layer will be described. Incident light that has passed through the liquid crystal cell of the first layer is polarized by the liquid crystal layer, and is passed through the liquid crystal cell of the second layer to cancel and become linearly polarized light. This will be described with reference to the drawings.

In the invention, as shown in FIG. 3, the angle formed by the polarization axis of the incident side polarization plate and the long axis of the liquid crystal molecules of the first liquid crystal layer is φ _1, and the polarization axis of the incidence side polarization plate and the second axis The angle formed by the liquid crystal molecule major axis of the liquid crystal layer is φ ₂ . Here, the ellipse schematically shows liquid crystal molecules. If the polarization state generated by the incident side polarization plate and the first liquid crystal layer is canceled by the second liquid crystal layer to make linearly polarized light, and φ ₁ and φ ₂ are arranged so as to be cut by the emission side polarization plate, it will be perfect in the initial state. A dark field is obtained (FIG. 4 (a)).

Next, as shown in FIG. 4B, when an electric field is applied only to the second liquid crystal layer so that the liquid crystal molecules are vertically aligned with the substrate, the second liquid crystal layer is formed.
Since the liquid crystal layer is isotropic with respect to the traveling direction of light, the light reaches the polarizing plate on the emission side while maintaining the polarization state after passing through the first liquid crystal layer, and as a result, a bright field can be obtained. In this case, by controlling the applied voltage to be equal to or higher than the threshold voltage and equal to or lower than the saturation voltage, the molecular orientation of the second-layer liquid crystal can be brought into an intermediate state between the initial homogeneous orientation and the vertical orientation,
In this way, infinite gradation display is possible.

Next, as shown in FIG. 5A, when an electric field is applied to the first liquid crystal layer while the second liquid crystal layer is vertically aligned and liquid crystal molecules are vertically aligned with the substrate, the incident light undergoes any modulation. Without passing, it becomes a dark field. In this case as well, infinite gradation display is possible by the same method as described with reference to FIG. If gradation display is performed in the state of FIG. 4B, it is sufficient to drive the first-layer liquid crystal and simultaneously make the second-layer liquid crystal have a completely vertical alignment.

Further, even if the electric fields of both liquid crystal layers are removed in this state (FIG. 5 (b)), if the liquid crystal has the same elastic characteristics and refractive index anisotropy, it is regarded as the liquid crystal of the first liquid crystal layer. The liquid crystal of the second liquid crystal layer deforms after the same time elapses and always compensates for the polarization state, so that it always has a dark field as in the initial state of FIG. In addition, in FIG. 5B, θ ₁ (t), θ
₂ (t), φ ₁ (t) and φ ₂ (t) are the angles formed by the liquid crystal molecules of the first liquid crystal layer and the second liquid crystal layer with the substrate and the polarization axis of the incident side polarization plate at an arbitrary time t. It is a horn.
Also in this case, if gradation display is performed in the state of FIG. 5A, until the compensation relationship of the polarization states of the first liquid crystal layer and the second liquid crystal layer is maintained, that is, the first liquid crystal layer is completely The gradation is maintained until the initial orientation is restored. In general, the fall characteristic of nematic liquid crystal is very slow, so that it is practically sufficient (FIG. 5B). In order to perform further writing from this state at an arbitrary time, if the alignment of the first liquid crystal layer is completely returned to the initial state, the driving can be performed in the same manner as described in FIG. 4B (FIG. 6). .. If the orientation of the first liquid crystal layer is not completely returned to the initial state, the slowness of the falling characteristic of the liquid crystal with respect to the rising characteristic is used to return to the initial aligned state in time with the falling characteristic of the first liquid crystal layer. Until then, the second liquid crystal layer is activated until the first liquid crystal layer returns to the initial alignment state so that the same compensation effect and gradation effect as in FIG. 4B can be obtained (FIG. 6).

By repeating the above cycle, it is possible to perform a sharp display with no difference between the rising characteristic and the falling characteristic. Even if the driving of the first liquid crystal layer and the driving of the second liquid crystal layer are reversed, the same optical effect can be obtained. The angles φ ₁ and φ ₂ formed by the long axis of the liquid crystal molecule and the polarizer are determined by the optical compensation relationship between the first liquid crystal layer and the second liquid crystal layer, and especially when φ ₁ and φ ₂ = π / 4, it is clear. It is preferable because the transmitted light in the state becomes maximum.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the embodiments shown in the drawings. The present invention is not limited to this.

Example 1 A liquid crystal display device shown in FIG. 2 was produced. A 2000 Å ITO film 2 is formed on a pair of substrates 1 by sputtering and has a thickness of 3
00 Å PVA film 3 was applied, and uniaxial orientation treatment was performed by rubbing using a rayon-based cloth. Then, these two substrates were attached to each other with a sealing member 5 made of an epoxy resin at a distance of 5 μm with a silica spacer interposed therebetween. A liquid crystal cell 7 was prepared by injecting a commercially available nematic liquid crystal 4 [E-7 (manufactured by Merck)] between these substrates by a vacuum injection method and then curing the injection port with an acrylic UV curable resin. .. Cell 8 made in the same manner as cell 7
O-electrodes overlap each other, and the uniaxial orientation directions are 90 ° to each other.
The two layers of cells were aligned and bonded to each other so as to form an angle, and polarizing plates 6 having polarization axes orthogonal to each other were arranged above and below the two-layer cell. The liquid crystal display device 9 of the present invention was prepared by arranging one polarization axis of the polarizing plate and the liquid crystal optical axis of the cell at an angle of 45 °.

As a result of driving this liquid crystal display device 9 by the method described above, a sharp display with no afterimage was obtained with the rising and falling characteristics shown in FIG.

Example 2 A liquid crystal display device 10 shown in FIG. 8 was produced. The overall structure is the same as that of the liquid crystal display device 9 of Example 1, but the number of substrates is three, and the ITO film 3 is formed on both surfaces of the substrate separating the first liquid crystal layer and the second liquid crystal layer. This liquid crystal display device 1
As a result of driving 0 by the method described above, a characteristic that there is no difference between the rising edge and the falling edge shown in FIG. 9 and a sharp display without an afterimage was obtained. Furthermore, by forming the transparent electrode with one substrate separating the first liquid crystal layer and the second liquid crystal layer, the positional deviation and the viewing angle characteristics were improved, and the display quality could be further improved.

Comparative Example As a comparative example, an ECB liquid crystal display device having a conventional structure was prepared with the same alignment film, alignment treatment, liquid crystal material, and cell thickness as those of the examples.
When the rising and falling characteristics were measured, the results shown in Fig. 10 were obtained, and the delay of the falling time was noticeable. As a result, only a conspicuous display of afterimage was obtained.

The response speed in FIGS. 9 and 10 is E-7.
When using 30V, 10% of the amount of transmitted light-9%
With 0% change, the faster one was 25 msec and the slower one was 310 msec.

Example 3 A liquid crystal display device 11 shown in FIG. 11 was produced. The overall structure is the same as that of the first embodiment, but each transparent electrode has a plurality of lines patterned by photolithography into stripes, and each liquid crystal layer forms a dot matrix. As a result of driving this liquid crystal display device 11 by the method described above, it was possible to display a sharp image with no afterimage.

Example 4 A liquid crystal display device 12 shown in FIG. 12 was produced. The overall structure is the same as that of the third embodiment, but the number of substrates is three, and the ITO electrode 2 is used for the substrate separating the first liquid crystal layer and the second liquid crystal layer.
Was formed on both sides. As a result of driving this liquid crystal display device 12 by the method described above, it was possible to display a sharp image with no afterimage. Furthermore, by using only one substrate that separates the first-layer liquid crystal and the second-layer liquid crystal, the position shift
The viewing angle characteristics were improved, and the display quality could be further improved.

Example 5 A liquid crystal display device 13 shown in FIG. 13 was produced. The entire structure is similar to that of Example 4, but the ITO electrodes 2 having the same pattern on both surfaces were formed on the substrate separating the first liquid crystal layer and the second liquid crystal layer. As a result of driving this liquid crystal display device 13 by the method described above, it was possible to display a sharp image with no afterimage. Furthermore, by using a single substrate that separates the first-layer liquid crystal and the second-layer liquid crystal, the positional deviation and the viewing angle characteristics were improved, and the display quality could be further improved. Further, this structure has an advantage that it can be formed by one-time photolithography since the transparent electrode patterns are formed on both sides and have the same shape on both sides.

[0032]

According to the present invention, it is possible to realize a liquid crystal display device having a small difference in rising and falling characteristics by using a nematic liquid crystal which is generally widely used, and is excellent in display quality with no afterimage. The display could be achieved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of an electric field control birefringence type liquid crystal display.

FIG. 2 is a sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating optical curing of the liquid crystal display device of the present invention.

4A and 4B are diagrams illustrating a driving method of a liquid crystal display device of the present invention.

5A and 5B are diagrams illustrating a driving method of another liquid crystal display device of the present invention.

FIG. 6 is a diagram illustrating a driving method of another liquid crystal display device of the present invention.

7A, 7B, and 7C are views for explaining liquid crystal molecule alignment in the liquid crystal display device of the present invention.

FIG. 8 is a sectional view of a liquid crystal display device according to another embodiment of the present invention.

FIG. 9 shows the rise of the liquid crystal display device according to the embodiment of the present invention.
The figure which shows a fall characteristic.

FIG. 10 is a diagram showing rising and falling characteristics of a liquid crystal display device of a conventional example (comparative example).

FIG. 11 is a sectional view of a liquid crystal display device according to another embodiment of the present invention.

FIG. 12 is a cross-sectional view of a liquid crystal display device according to another embodiment of the present invention.

FIG. 13 is a sectional view of a liquid crystal display device according to another embodiment of the present invention.

[Explanation of symbols]

 1 Glass Substrate 2 Transparent Electrode 3 Alignment Film 4 Nematic Liquid Crystal 5 Sealing Member 6 Polarizing Plate 7, 8, 9, 10, 11, 12, 13, Liquid Crystal Cell

Claims (3)

[Claims] 1. A pair of substrates are arranged so as to face each other, an electrode is formed on at least a surface thereof, an orientation control layer is formed thereon, and the orientation control layer is subjected to a uniaxial orientation treatment. On the opposite substrate, a liquid crystal having a substantially parallel or anti-parallel structure and having a positive dielectric anisotropy exhibiting a nematic phase is interposed between these substrates, and a voltage is selectively applied to the electrodes to cause the light of the liquid crystal to be emitted. In a liquid crystal cell having a driving means for switching the axes and a means for optically discriminating the switching of the optical axes, the cells of the liquid crystal are arranged in two layers, and the polarization state caused by the liquid crystal cell of the first layer is A liquid crystal display device having a structure in which compensation is performed by a liquid crystal cell of the second layer. 2. A pair of substrates are arranged so as to face each other, an electrode is formed on at least a surface thereof, an alignment control layer is formed thereon, one of the alignment control layers is subjected to a uniaxial alignment treatment, and the other is A liquid crystal having a positive dielectric anisotropy exhibiting a nematic phase is interposed between these substrates without being processed, and a driving means for switching the optical axis of the liquid crystal by selectively applying a voltage to the electrode, In a liquid crystal cell having means for optically discriminating optical axis switching, the liquid crystal cells are arranged in two layers, and the polarization state caused by the first layer liquid crystal cell is changed by the second layer liquid crystal cell. A liquid crystal display device having a compensation structure. 3. The display is performed by driving the liquid crystal cell of the first layer and / or the liquid crystal cell of the second layer without causing a delay between the rising characteristic and the falling characteristic of the optical change. The liquid crystal display device according to any one of item 2.