JPH0368924A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To control the uniformity of non-picture element parts and to obtain the liquid crystal device having a good display grade by setting the average layer normal direction of a smectic phase nearly parallel with substrates in the picture element parts where the electrodes of a pair of the substrates intersect and setting the above-mentioned direction in the non-picture elements nearly perpendicular to the substrates. CONSTITUTION:The stripe-shaped parallel transparent electrode 2a, a protective film 3a consisting of SiO2 and an oriented film 4a consisting of polyimide are superposed on the glass substrate 1 and the film 4a is rubbed and is thereby uniaxially oriented. A resist mask 5 is applied thereon and is ion-etched to eliminate the rubbing effect of the surface. The mask 5 is then removed. The substrate 11 is formed in the same manner as for the glass substrate 10. The oriented films are disposed to face each other and the rubbing directions where the transparent electrodes intersect orthogonally with each other are nearly matched. The substrates are sealed by an epoxy resin 6 via silica spacers 7. A ferroelectric liquid crystal 8 of a chiral smectic phase C is packed between the substrates. The parts corresponding to the picture elements of the oriented film 4a of the substrate 10 are uniaxially oriented and the parts corresponding to the non-picture element parts are etched to remove the rubbing effect; therefore, the layer normal of the liquid crystal is nearly parallel with the substrates in the picture element parts and is nearly perpendicular in the non-picture element parts. The good display grade is obtd. via two sheets of the polarizers having the deflection directions orthogonal with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device using ferroelectric liquid crystal.

Prior art A typical prior art liquid crystal display device using a nematic liquid crystal is the twisted nematic type (Tuii
sLed NenaLie, abbreviated as TN type> liquid crystal display device, super twisted type (Supertwisted type)
isted Birefringence Effec
There is a type of liquid crystal display (abbreviated as type SB E).

However, twisted nematic liquid crystal display devices have the disadvantage that as the driving method becomes more multiplexed, the driving margin becomes narrower and sufficient contrast cannot be obtained. In addition, the super twisted liquid crystal display device, which is an improved version of the twisted nematic liquid crystal display device and uses a large twist angle, has disadvantages such as reduced contrast and slow response speed when used for large capacity displays. ing.

Therefore, in 1980, Clark (N
, ^, CIark) Lallerwall
) has proposed a liquid crystal display device using a smectic liquid crystal, that is, a ferroelectric liquid crystal.

This liquid crystal display device differs from the above-mentioned liquid crystal display device which uses an electric field effect utilizing the dielectric anisotropy of liquid crystal molecules, in that this liquid crystal display device uses a rotational force that changes the polarity of the spontaneous polarization of the ferroelectric liquid crystal and the polarity of the electric field. This is the liquid crystal display device used. Characteristics of this liquid crystal display device include bistability, memory performance, and high-speed response. In other words, when a ferroelectric liquid crystal is injected into a cell with a thin gap, the helical structure of the ferroelectric liquid crystal unwinds due to the influence of the interface, and the liquid crystal molecules stabilize by tilting at an angle θ with respect to the normal to the smectic layer. A region in which the liquid crystal molecules are tilted in the opposite direction by a tilt angle of −θ coexists and has bistability.

By applying a voltage to the ferroelectric liquid crystal in this cell, the orientation of the liquid crystal molecules and their spontaneous polarization can be uniformly changed, and by switching the polarity of the applied voltage, the orientation of the liquid crystal molecules can be changed. It becomes possible to perform switching drive to switch from one certain state to another certain state. With this switching drive, birefringent light changes in the ferroelectric liquid crystal within the cell, so by sandwiching the cell between two polarizers, transmitted light can be controlled. Furthermore, even if the voltage application is stopped, the alignment of the liquid crystal molecules is maintained in the state before the voltage application was stopped by the alignment regulating force of the interface, so that a memory effect can also be obtained.

In addition, the time required for switching drive is 1/1000 or less of that of a twisted nematic liquid crystal display device because the spontaneous polarization of the liquid crystal and the electric field act directly, so the device has high-speed response and can perform high-speed display.

Therefore, by utilizing the memory effect and high-speed response of ferroelectric liquid crystals, it is possible to construct a high-duty liquid crystal display device with a large number of scanning lines using a multi-layer class driving method as shown in the cross-sectional view in Figure 4. This has been attempted in the past.

In the liquid crystal display device shown in FIG. 4, two glass substrates 1a are arranged parallel to each other and facing each other.

Transparent electrodes 2a, 2a and 2b are respectively provided on opposing surfaces of 1b.
A plurality of transparent electrodes 2b are arranged parallel to each other in a stripe shape, and the transparent electrode 2a on one glass substrate 1a,
The transparent electrodes 2b on the other glass substrate 1b are arranged perpendicular to each other.

The transparent electrodes 2a, 2b formation side surface of each glass substrate 1a, lb is further provided with an alignment film 11i via an electrode protective film 3a, 3b.
4a and 4b are respectively formed, and a ferroelectric liquid crystal 8 is interposed between these two glass substrates 1a and lb.

Problems to be Solved by the Invention However, in the conventional liquid crystal display device using the above-mentioned ferroelectric liquid crystal, since the liquid crystal has bistability and has two optically stable states, there are two Two optical axes exist in a chaotic manner. An electric field can be applied to the pixel part where the transparent electrodes 2a and 2b intersect to align the direction to the required optical axis, but an electric field cannot be applied to the non-pixel part where the transparent electrodes 2a and 2b do not intersect. Therefore, the optical axis remains in a disordered manner. For this reason, there is a problem that the brightness of non-picture element areas is not uniform, resulting in a decrease in display quality.

Furthermore, when applying an electric field to a pixel, if the optically stable state in the same direction is continued, the display will seep into the non-pixel areas around the pixel, resulting in an afterimage of the display. There was a problem in that the display quality deteriorated.

Therefore, an object of the present invention is to provide a liquid crystal display device that has good display quality by controlling the uniformity of non-picture element areas.

Means for Solving the Problems The present invention involves arranging a pair of substrates on which electrodes are selectively formed and alignment films formed thereon so that the alignment films face each other; In a liquid crystal display device in which a liquid crystal is interposed between two substrates, and the liquid crystal is driven by selectively applying a voltage to the electrodes, the electrodes of the pair of substrates are connected to each other among the alignment films of the pair of substrates. In pixel areas where the electrodes intersect, the direction of the average layer normal of the smectic phase approaches parallel to the substrate, while in non-pixel areas where the electrodes of a pair of substrates do not intersect, the smectic phase This is a liquid crystal display device characterized in that the direction of the average layer normal is approximately perpendicular to the substrate.

According to the present invention, the non-pixel portion where the electrodes of a pair of substrates do not intersect is formed such that the direction of the average layer normal of the smectic phase having a layered structure approaches perpendicular to the substrate. Therefore, the alignment state of the liquid crystal molecules in this part is aligned in one state. Furthermore, the direction of the average layer normal of the picture element part is made to approach parallel to the substrate, and the direction of the average layer normal of the non-picture element part is made to approach perpendicular to the substrate. Therefore, the display does not leak from the picture element part to the non-picture element part around the picture element part'.

Embodiment FIG. 1 is a sectional view showing the manufacturing process of a liquid crystal display device according to a first embodiment of the present invention.

In this liquid crystal display device, as shown in FIG. 1 (a), first, a plurality of transparent electrodes 2a having a thickness of 300 to 5000, preferably 1000 to 2000, are arranged parallel to each other on a glass substrate l furnace. 300 to 5,000 people, preferably 500 to 500 people
An electrode protection 11J3a of 1000 sins is formed by sputtering, and a polyimide film (Nissan Chemical Co., Ltd., RN715) with orientation 1 is further formed on this electrode protection ill3a.
1i4a is formed with a spin coater to a thickness of 500 mm,
After this, uniaxial alignment treatment is performed by rubbing.

Next, as shown in FIG. 1(b), a photoresist 5 (manufactured by Tokyo Ohka Co., Ltd., 0FF800) is coated on the alignment film 4a using a spin coater at 300 rpm for 30 seconds.

Next, as shown in FIG. 1C, portions of the photoresist 5 corresponding to non-picture element portions during the formation of the liquid crystal display device are removed by a photolithography process.

Next, as shown in FIG. 1(d), the surface of the orientation 11i4a in the exposed non-pixel area is treated with an ultraviolet cleaner (UV cleaner) or ion etching (rea).
ion etching (abbreviated as RIE). This etching may be performed by several tens to several hundreds of people to the extent that it takes away the effect of rubbing applied to the surface of orientation 1 [i4a.

Next, as shown in FIG. 1(e), the photoresist 5 is peeled off. In this way, the substrate 10 is formed.

On the other hand, as shown in FIG. 1(f'), a plurality of transparent electrodes 2b are also formed on the glass substrate lb in the same manner as above, arranged in a stripe pattern parallel to each other, and on top of the transparent electrodes 2b, electrode protection is provided. An alignment film 4b is formed via the film 3b, and then a uniaxial alignment process is performed by rubbing to form a substrate 11.

Next, as shown in FIG. 1(g), this substrate 11 and the other substrate 10 are placed on the alignment film 4a.

4b face each other, the transparent molds f[+2a and 2b are orthogonal to each other, and are arranged with a silica spacer 7 interposed at an interval of 2°0 μm so that the rubbing directions are almost the same, and a seal made of epoxy resin is installed. It is sealed with member 6. Since they are arranged so that the rubbing directions are almost the same, the asymmetry of the alignment regulating force between the front substrates is reduced, and a bistable memory effect can be obtained. Between these substrates 10 and 11, while heating the liquid crystal, a ferroelectric liquid crystal 8 (manufactured by Merck & Co., Ltd.), which is a chiral smectic C phase liquid crystal, is inserted from the injection port using a vacuum injection method.
ZLI4237000) is injected.

By sandwiching the liquid crystal display element thus obtained between two polarizers, a liquid crystal display device in which picture elements are arranged in a matrix is constructed.

In this liquid crystal display device, a portion of the alignment film 4a of one substrate 10 corresponding to a picture element portion is subjected to uniaxial alignment treatment, whereas a portion of the same alignment film 4a corresponding to a non-picture element portion is subjected to a uniaxial alignment treatment. The effect of rubbing has been removed by etching. Therefore, the direction of the average layer normal of the smectic phase of the liquid crystal is approximately parallel to the substrate in the portion corresponding to the pixel portion, while it is approximately perpendicular to the portion corresponding to the valve pixel portion.

As a result, non-uniformity of display in non-pixel areas is eliminated, and the display of the pixel area does not seep into the non-pixel areas.In addition, the polarization directions of the two polarizers are orthogonal to each other. Since the non-pixel area always has a high light shielding effect with respect to the setting, high contrast can be obtained.

FIG. 2 is a sectional view showing the manufacturing process of a liquid crystal display device according to a second embodiment of the present invention.

In this embodiment, the liquid crystal display device is constructed almost the same as in the first embodiment, except that the alignment film 4a is used here.

The types of 4b and the process of processing the alignment film in non-picture element areas are different.

In this embodiment, as shown in FIG.
After the tFi protective film 3a is formed, the orientation M4a is 1.
ffi amount% m-cresol solvent nylon 6 is 3000
The alignment film 4a is coated for 30 seconds using a spin coater at rpm, and uniaxial alignment treatment is performed on the alignment film 4a by rubbing.

Next, as shown in FIG. 2(b), a photoresist 5 is formed, and as shown in FIG. Figure 2 ((1)
As shown in FIG. 3, the portion corresponding to the non-picture element portion is etched, and the orientation wA4a of the portion corresponding to the non-picture element portion is removed.

Next, as shown in FIG. 2(e), the substrate 1a is immersed in a 0.05% solution of vertical alignment material 9 (AY-43, manufactured by Toshisha Co., Ltd.), and by a pulling method, the vertical alignment material 9 becomes electrode protective fliB.
It is applied to the part corresponding to the non-picture element part on a. Vertical alignment agents include n-dodecyltriethoxysilane, 3-aminopropyltriethoxysilane, rl-hexyltrimethoxysilane, n-hexadecyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and octadecyltrimethoxysilane. Silane etc. can be used.

Next, as shown in FIG. 1(f), after baking at 100° C. for 30 minutes, the photoresist 5 is peeled off, and a substrate 10 is formed.

Similarly to the substrate 10 thus formed, a substrate 11 is formed through the steps shown in FIGS. 2(a) to 2(f).

Next, as shown in FIG. 2(g), the substrates 10 and 11 are
They are arranged with a silica spacer 7 interposed at an interval of 2.0 μm so that the orientations 1114a and 4b face each other, the transparent electrodes 2a and 2b are orthogonal to each other, and the rubbing directions are almost the same. It is sealed with a sealing member 6 made of. Since they are arranged so that the rubbing directions are almost the same, the asymmetry of the alignment regulating force between both substrates is reduced, and a bistable memory effect can be obtained. A ferroelectric liquid crystal 8, which is a chiral smectic C-phase liquid crystal, is injected between these substrates 10 and 11. By sandwiching the liquid crystal display element obtained in this way between two polarizers,
A liquid crystal display device is configured in which picture element parts are arranged in a matrix.

In this liquid crystal display device, uniaxial alignment treatment is applied to the portions corresponding to picture element portions of the alignment film 4a of the substrate 10 and the alignment 114b of the substrate 11, while the portions corresponding to non-picture element portions are subjected to uniaxial alignment treatment. A vertical alignment agent 9 is applied. Therefore, in the portion corresponding to the picture element portion, the direction of the average layer normal of the smectic phase of the liquid crystal is approximately parallel to the substrate, whereas in the portion corresponding to the valve pixel portion, it is approximately perpendicular. As a result,
As in the first embodiment, the non-uniformity of the display in the non-picture element area is eliminated, and the seepage of the non-picture element area l\ in the display of the picture element area is also eliminated. Further, since the non-picture element portion always has a high light shielding effect with respect to the setting of a pair of polarizers whose polarization directions are perpendicular to each other, high contrast can be obtained.

Although the embodiments have been described above, the present invention is not limited to the above embodiments. Any method may be used for orientation as long as it forms an angle, for example, a method of rubbing an organic alignment film such as polyimide, polyimide amide, polyamide, polyvinyl alcohol, etc., an oblique deposition method of Sin, an LB film. The present invention also includes a liquid crystal display device in which liquid crystal is oriented using a method using a method such as the above.

In addition, in the non-picture element part, the liquid crystal may be oriented using any method as long as the average layer normal angle of the smectic phase forms an angle of 80' to 90' with respect to the substrate. For example, the present invention also includes a liquid crystal display device in which liquid crystal is oriented using a method using a surface treatment agent of silane or chromium compound, which has been established for conventional twisted nematic liquid crystals, or an oblique evaporation method of 5i02.

Note that the average layer normal angle of the above-mentioned smectic phase is expressed by the following equation 1.

The average layer normal angle of the smectic phase (in the first equation, θα is the angle between the layer normal and the substrate, ■ α is θ
The average layer normal angle, which indicates the abundance at α, is the absolute value of the acute angle side of the angle between the layer normal and the substrate. ) The smectic phase often has layer bending, and in this case, the normal direction of the layer is not unidirectional, so the average layer normal angle is determined using the first equation.

This average layer normal angle is calculated as the average of the diffraction intensity and diffraction angle by performing X-ray diffraction (Ferroele
ctrics, 1988. vol, 85. pp79-9
7. N, ^.

C1ark).

FIG. 3 is an explanatory diagram that defines the average layer normal angle of the smectic phase 12. FIG. 3(a) shows that when the layer normal direction is one direction, When the line directions are bidirectional, FIG. 3(c) shows the case where the layer normal directions are multidirectional.

In FIG. 3(a), the layer normal angle of the smectic phase is the angle θ between the straight line l indicating the direction of the layer normal and the substrate.
It is.

In FIG. 3(b), the smectic phase consists of a slope <71 A from the top right to the bottom left and a slope <Ni B from the top left to the bottom right. The layer normal direction of layer A is shown as a straight line, the layer normal angle is θ2, and the abundance at θ2 is I2.0 layer B
The normal direction of is shown by the straight line l, the normal angle of the layer is θ, and the abundance at θ is I.

Therefore, the average layer normal angle of the smectic phase is (θ2I2+θsI*)/(zz+x3). Expressing this as a vector using the third Vl(c), A in layer A and A in layer B The angle θ between C and the substrate, which is a composite vector with B, is the average layer normal angle.

In FIG. 3(d), the smectic phase is bent in multiple directions, although only four directions are shown in the figure. In this case as well, the average layer normal angle is determined using the first equation described above in the same manner as in 3rd [J(b).

Effects of the Invention As described above, according to the liquid crystal display device of the present invention, the layer normal of the smectic phase of the liquid crystal is approximately parallel to the substrate in the pixel portion, while it is approximately perpendicular to the non-pixel portion. Therefore, non-uniformity of display in non-picture element areas is eliminated, and display seepage into non-picture element areas is also eliminated. Furthermore, the directions of the two optical axes present in the pixel area vary depending on the liquid crystal material and the configuration conditions of the liquid crystal display device, but in the non-pixel area, when two polarizers are set so that the polarization directions are orthogonal, Regardless of these factors, it exhibits a high light-shielding effect, so when performing black-and-white display, a blacker display is possible, and a liquid crystal display device with high contrast can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the manufacturing process of a liquid crystal display device according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the manufacturing process of a liquid crystal display device according to the second example of the present invention. Section 3 is an explanatory diagram defining the average layer normal angle of the smectic phase, and FIG. 4 is a sectional view showing the main part of a prior art liquid crystal display device.

Claims (1)

[Claims] A pair of substrates having electrodes selectively formed on their surfaces and an alignment film formed thereon are arranged so that the alignment films face each other, and a liquid crystal is placed between these substrates. In a liquid crystal display device in which a liquid crystal is driven by selectively applying a voltage to the electrodes, the picture element where the electrodes of the pair of substrates intersect with each other among the alignment films of the pair of substrates. In the non-pixel part, the direction of the average layer normal of the smectic phase approaches parallel to the substrate, while in the non-pixel part, where the electrodes of a pair of substrates do not intersect with each other, the direction of the average layer normal of the smectic phase approaches parallel to the substrate. A liquid crystal display device characterized in that the lines are formed so that the direction of the lines approaches perpendicular to the substrate.