JPH06337423A - Liquid crystal display element and manufacture of this liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a defect caused by a change in a cell thickness by restraining the movement of a liquid crystal molecule when a liquid crystal display element is driven. CONSTITUTION:When a liquid crystal display element is manufactured, a transparent electrode 2 and a metallic auxiliary electrode 7 are formed on a substrate 1. An oriented film 4 is formed on these, and after orientation treatment is carried out, photosensitive resin is applied. Light is radiated from the reverse side (the side where the electrode 2 or the like is not formed) of the substrate 1, and it is exposed. Since the metallic auxiliary electrode 7 has a light untransmissive property, the photosensitive resin is patterned in the same shape with the metallic auxiliary electrode 7, and a bank 8 is formed. When the liquid crystal display element manufactured in this way is driven, though a liquid crystal molecule tends to move, the movement is restrained by the bank 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a liquid crystal display element using a chiral smectic liquid crystal in which movement of the liquid crystal element is suppressed, and a method of manufacturing the liquid crystal display element.

[0002]

2. Description of the Related Art A display device of the type in which transmitted light rays are controlled by using a refractive index anisotropy of ferroelectric liquid crystal molecules in combination with a polarizing device has been proposed by Clark and Lagerwall. (Unexamined-Japanese-Patent No. 56-107216, US Patent No. 436792.
No. 4, etc.). This ferroelectric liquid crystal generally has a non-helical chiral smectic C in a specific temperature range.
A phase (SmC ^* ) or an H phase (SmH ^* ) in which one of a first optical stable state and a second optical stable state is taken in response to an applied electric field, and It has the property of maintaining its state when no voltage is applied, that is, has bistability, and has a rapid response to changes in the electric field, and is expected to be widely used for high-speed and memory type display elements. From the function, it is expected to be applied to a large-screen, high-definition display.

In order for the optical modulation element using the liquid crystal having the bistability to exhibit a predetermined driving characteristic, the liquid crystal arranged between the pair of parallel substrates is irrespective of the applied state of the electric field, and the above-mentioned 2 It is necessary that the molecular arrangement state is such that conversion between the two stable states occurs effectively.

In the case of a liquid crystal display device utilizing the birefringence of liquid crystal, the transmittance under orthogonal Nicols is

[0005]

[Number 1] ^{_{I / I 0 = sin 2 4θsin}} 2 Δnd / λπ formula: I ₀ is the incident light intensity, I is the transmitted light intensity, theta is the tilt angle, [Delta] n is the refractive index anisotropy, d is the liquid crystal layer The film thickness, λ, is represented by the wavelength of incident light. The tilt angle θ in the non-helical structure described above appears as an angle in the average molecular axis direction of the twisted liquid crystal molecules in the first and second alignment states. According to the above equation, the tilt angle θ is 22.5 °
The maximum transmittance is obtained when the angle is, and the tilt angle θ in the non-helical structure that realizes the bistability needs to be as close as possible to 22.5 °.

As a method of aligning the ferroelectric liquid crystal,
A molecular layer composed of a plurality of molecules forming a smectic liquid crystal can be oriented uniaxially along its normal line over a large area, and the manufacturing process can be realized by a simple rubbing treatment. Is desirable.

As an alignment method for a ferroelectric liquid crystal, especially a chiral smectic liquid crystal having a non-helical structure, for example, one described in US Pat. No. 4,561,726 is known.

[0008]

By the way, Θ>θa>
The ferroelectric liquid crystal cell having the structure of Θ / 2 had the following problems.

That is, in a non-helical ferroelectric liquid crystal cell having a high pretilt alignment structure by a conventional rubbing-treated polyimide film, when a white or black fixed pattern is continuously written and driven, it corresponds to black and white. The liquid crystal molecules move in the direction of the layer in the chiral smectic C state in the direction corresponding to the molecular position (see FIG. 1). Then, due to this movement, liquid crystal is accumulated at the cell edge and the pressure in that portion is increased, which expands the cell gap and increases the thickness of the liquid crystal layer. As a result, the portion where the liquid crystal phase is expanded turns yellow (hereinafter referred to as "yellowing"), and at the opposite end, liquid crystal molecules disappear and voids are formed. This phenomenon is most prominent at the end of the cell (near the seal), and expands inside the cell with the amount of liquid crystal molecules moving. The present inventor speculates that the cause of liquid crystal molecule movement is an electrodynamic effect generated by fluctuation of the dipole moment of the liquid crystal molecule due to an alternating electric field due to the driving pulse. Further, according to the experiments conducted by the present inventors, the moving direction 22 is a rubbing direction 20 and an average molecular axis direction 21 of liquid crystal molecules, as shown in FIG.
21 '. And since the moving direction of liquid crystal molecules depends on the rubbing direction in this way,
It is speculated that this phenomenon depends on the pretilt state at the substrate interface. The average molecular axis directions 21 and 21 'indicate average molecular positions in the bistable state of the ferroelectric liquid crystal molecules. Here, for example, the average molecular axis direction is 21
When an appropriate AC electric field to such an extent that the liquid crystal does not switch is applied in the state indicated by, the liquid crystal molecules move in the direction of arrow 22 and yellowing occurs at the cell end 23 (see FIG. 2B). However, here, the case where a liquid crystal material having a negative spontaneous polarization direction is used is described. Furthermore, this liquid crystal movement phenomenon depends on the alignment state of the cell.

Here, the orientation of the smectic layer including the chevron structure will be described with reference to FIG.

This orientation can be explained by two types of orientation models of C1 and C2. In FIG. 3, 31 is a smectic layer,
Reference numeral 32 represents a C1 orientation region, and 33 represents a C2 orientation region. Smectic liquid crystals generally have a layered structure, but when the SA phase transitions to the SC layer or SC * layer, the layer spacing shrinks, so that the layers are bent at the center of the upper and lower substrates 14a and 14b (chevron structure) as shown in FIG. Take As shown in the figure, there can be two bending directions, C1 and C2. As is well known, the liquid crystal molecules at the substrate interface form an angle (pretilt) with the substrate by rubbing, and that direction is the rubbing direction. The orientation is such that the liquid crystal molecules hang their heads toward A (the tip becomes floating). Due to this pretilt, the C1 orientation and the C2 orientation are not equivalent in terms of elastic pressure energy, and a transition occurs at a certain temperature as described above. In addition, mechanical strain may cause dislocation. When the layered structure of FIG. 3 is viewed in a plan view, the C1 orientation is changed to the C orientation in the rubbing direction A.
The boundary 34 at the time of shifting to the two orientations is zigzag lightning and is called a lightning defect, and the boundary 35 at the time of shifting from C2 to C1 is a wide, gentle curved shape and is called a hairpin defect.

The ferroelectric liquid crystal is provided with a pair of substrates that are substantially parallel to each other and are uniaxially oriented in the same direction. The pretilt angle of the ferroelectric liquid crystal is α and the tilt angle (cone) angle is 1/2) of Θ, and δ of the tilt angle of the Sm * C layer
If the ferroelectric liquid crystal has an alignment state represented by the formula 1, there are four states having a Shepron structure in the C1 alignment state.

[0013]

## EQU00002 ## .THETA. <A + .delta. These four C1 orientation states are different from the conventional C1 orientation states. Among them, two of the four C1 orientation states form a bistable state (uniform state). is doing. Here, if the apparent tilt angle in the absence of an electric field is θa, of the four states in the C1 orientation state, the state showing the relationship of equation 3 is called the uniform state.

[0014]

## EQU00003 ## .THETA.>. Theta.a> .THETA. / 2 In the uniform state, it is considered that the director is not twisted between the upper and lower substrates in view of its optical properties. FIG. 4A is a schematic view showing the arrangement of directors at respective positions between the substrates in each state of C1 orientation. 5 in the figure
1 to 54 show the state in which the director is projected on the bottom surface of the cone in each state and viewed from the bottom surface direction.
1 and 52 are splayed states, and 53 and 54 are director arrangements considered to be uniform states. As can be seen from the figure, in the two states 53 and 54 of the uniform, the positions of the liquid crystal molecules on either the upper or lower substrate interface are replaced with the positions in the splay state. FIG. 4B shows the C2 orientation, and there are two states 55 and 56 due to internal switching without interface switching. The uniform state of the C1 orientation produces a larger tilt angle θa than the bistable state of the C2 orientation which has been conventionally used, and has a large luminance and a high contrast.

Therefore, it is an object of the present invention to provide a liquid crystal display device which suppresses the yellowing and the generation of voids as described above by suppressing the movement of liquid crystal molecules, and a method of manufacturing the liquid crystal display device. It is a thing.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the first invention is to provide two substrates on which electrodes are formed so as to face each other. In a liquid crystal display device in which a ferroelectric liquid crystal is held between substrates, the electrode is a transparent electrode formed on the substrate, and a non-translucent metal auxiliary electrode partially formed on the transparent electrode. And a bank is formed so as to overlap with the metal auxiliary electrode, and movement of the ferroelectric liquid crystal is suppressed by the bank.

In this case, when the cone angle is Θ and the apparent tilt angle is θa, it is preferable that the uniform orientation satisfies the relationship of Θ>θa> Θ / 2.

A second aspect of the invention is to manufacture a liquid crystal display device in which two substrates having transparent electrodes are bonded to each other and ferroelectric liquid crystal is injected into a gap formed by these two substrates. In the method, before bonding the two substrates, a non-translucent metal auxiliary electrode is formed on a part of the transparent electrode, and a photosensitive resin is applied to the side where the metal auxiliary electrode is formed, Light is irradiated from the side where the metal auxiliary electrode is not formed, and the photosensitive resin is patterned into the same shape as the metal auxiliary electrode.

In this case, the photosensitive resin is a positive type, and the photosensitive resin is applied after the alignment film is formed on the metal auxiliary electrode and the alignment film is aligned. Is preferred.

[0020]

According to the above structure, even if liquid crystal molecules try to move when the liquid crystal display element is driven, the movement of the liquid crystal molecules is suppressed by the bank.

[0021]

Embodiments of the present invention will be described below with reference to FIG.

The liquid crystal display element according to this embodiment comprises two glass substrates 1 and 1, and transparent electrodes 2 and 2 are formed on these substrates 1 and 1. Further, metal auxiliary electrodes 7, 7 are partially formed on the transparent electrodes 2, 2, and these electrodes 2, 7 are covered with insulating films 3, 3. Furthermore, alignment films 4 and 4 are formed on these insulating films 3 and 3. Furthermore, the glass substrates 1 and 1 having such a configuration are bonded together with a spacer 6 interposed therebetween, and the ferroelectric liquid crystal 5 is injected into the gap between the substrates.

By the way, the banks 8, 8 are overlaid on the portions where the above-mentioned metal auxiliary electrodes 7, 7 are formed, and the alignment films 4, 4 are formed.
Formed on the surface. A method of forming this bank 8 will be described below. Now, the alignment films 4 and 4 after the rubbing treatment are washed and dried, and a photoresist (OFPR ^# 80) as a photosensitive resin is formed on the surfaces of the alignment films 4 and 4.
0) is applied. Here, the applied thickness is half the thickness of the void in the portion where the auxiliary electrodes intersect (0.6 μm in this embodiment). Then, at a temperature of 80 ° C, 15
Prebaked for minutes. Then, the back side of the substrates 1 and 1 (the side on which the electrodes 2 and 7 are not formed) is irradiated with UV light for exposure, and further development, rinsing treatment and post bake (120 ° C., 30 minutes) are performed for patterning. . In addition, the substrate 1 after the banks 8 are formed in this way
In No. 1, cells were formed by laminating the cells in the same manner as a usual method.

As a result, even if the liquid crystal molecules are moved by driving the liquid crystal display element, the movement of the liquid crystal molecules is caused by the bank 8,
Suppressed by 8. Therefore, the occurrence of yellowing and voids as described in the above-mentioned conventional example is suppressed, and a uniform display state is enabled. Further, the banks 8 and 8 are oriented films 4 and 4.
Since it is formed after the rubbing treatment of (1) is completed, uniform alignment can be maintained. Furthermore, since the metal auxiliary electrodes 7 and 7 play the role of a photomask in photolithography, complicated operations such as setting of the photomask are not necessary, and the bank 8 can be accurately formed on the metal auxiliary electrodes 7 and 7. it can.

[0025]

As described above, according to the present invention,
Even if the liquid crystal molecules try to move when the liquid crystal display element is driven, the movement of the liquid crystal molecules is suppressed by the bank for each pixel. Therefore, the occurrence of yellowing and voids is suppressed, and the change in cell thickness is greatly suppressed, enabling a uniform display state. Further, by forming the alignment film on the electrode and forming the bank after the alignment of the alignment film is completed, uniform alignment can be maintained. Furthermore, by making the photosensitive resin a positive type and irradiating light from the side on which the metal auxiliary electrode is not formed, the metal auxiliary electrode plays a role of a photomask in photolithography, which makes setting of the photomask troublesome. The operation can be dispensed with and the bank can be formed on the metal auxiliary electrode with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional problem.

FIG. 2A and FIG. 2B are views for showing a moving direction of liquid crystal.

FIG. 3 is a diagram showing an orientation model of a smectic layer.

4A is a schematic view showing the arrangement of directors at respective positions between substrates in each state of C1 orientation, and FIG. 4B is C2.
The schematic diagram which shows orientation.

FIG. 5 is a vertical cross-sectional view showing the structure of the liquid crystal display element according to the present embodiment.

[Explanation of symbols]

 1 substrate (glass substrate) 2 electrode (transparent electrode) 3 insulating film 4 alignment film 5 ferroelectric liquid crystal 6 spacer 7 electrode (metal auxiliary electrode) 8 bank

Claims (4)

[Claims] 1. A liquid crystal display device comprising two substrates on which electrodes are formed facing each other and holding a ferroelectric liquid crystal between the two substrates, wherein the electrodes are formed on the substrates. A transparent electrode, and a non-translucent metal auxiliary electrode partially formed on the transparent electrode,
And a bank is formed so as to overlap with the metal auxiliary electrode, and movement of the ferroelectric liquid crystal is suppressed by the bank. 2. The liquid crystal display according to claim 1, which is a uniform orientation that satisfies the relationship of Θ>θa> Θ / 2, where Θ is the cone angle and θa is the apparent tilt angle. element. 3. A method for manufacturing a liquid crystal display device, comprising bonding two substrates having transparent electrodes formed thereon, and injecting a ferroelectric liquid crystal into a gap formed by the two substrates. Before bonding the substrates together, a non-translucent metal auxiliary electrode is formed on a part of the transparent electrode, and a photosensitive resin is applied to the side where the metal auxiliary electrode is formed. A method for manufacturing a liquid crystal display element, comprising irradiating light from a side not formed to pattern the photosensitive resin into the same shape as the metal auxiliary electrode. 4. The photosensitive resin is a positive type, and the photosensitive resin is applied after the alignment film is formed on the metal auxiliary electrode and the alignment film is aligned. 4. The method for manufacturing a liquid crystal display element according to claim 3, wherein