JPH06214236A - Liquid crystal device and information transmitter using the same - Google Patents

Abstract

PURPOSE:To prevent the sticking of the liquid crystal device using ferroelectric liquid crystal which has large spontaneous polarization and is put in a uniform orientation state. CONSTITUTION:Uneven members 10a and 10b having uneven parts 20 are provided below orientation control films 13a and 13b; and ¦alpha-beta¦ <10 deg. and beta>5 deg. hold for the tilt angle beta of the uneven parts 20 and the pretilt angle alpha of ferroelectric liquid crystal 14 measured on the border surface between the orientation control films 13a dn 13b in the opposite direction from the tilt angle beta.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device used in a liquid crystal display device, a liquid crystal shutter, etc. and an information transmission device using the same, and is particularly suitable for use as a ferroelectric liquid crystal of a chiral smectic liquid crystal, Specifically, it relates to a method for improving the alignment state of liquid crystal molecules.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal device of a type in which transmitted light rays are controlled by using a refractive index anisotropy of a ferroelectric liquid crystal in combination with a polarizing element has been proposed by Clark and Lagerwall. There is. (JP-A-56-107216, U.S. Pat. No. 4)
369924 specification). This ferroelectric liquid crystal generally has a non-helical chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range. In this state, one of the first optical stable state and the second optical stable state in response to the applied electric field, and the property of maintaining the state when the electric field is not applied, That is, it shows bistability. In addition, it responds quickly to changes in the electric field, and is expected to be widely used as a high-speed and memory type liquid crystal device. In particular, due to its characteristics, it is expected to be applied to a large-screen / high-definition display.

In order for the ferroelectric liquid crystal having bistability to exhibit a predetermined driving characteristic, the liquid crystal molecules of the ferroelectric liquid crystal sandwiched between a pair of transparent substrates must be converted to each other in a bistable state. It is necessary to arrange them so that they can be efficiently generated, and for that reason, it is necessary that the threshold values for switching between two bistable states are almost equal.

In order to arrange the liquid crystal, the liquid crystal is sandwiched between two transparent substrates provided with an alignment regulating force.

When the above-mentioned ferroelectric liquid crystal does not have a cholesteric phase, a uniform alignment state cannot be obtained even if the liquid crystal is sandwiched between transparent substrates provided with alignment control force by rubbing treatment or the like. Is known, and it has been reported that the asymmetric alignment treatment in which the rubbing treatment is performed only on the transparent substrate on one side is effective.

In the case of a liquid crystal device utilizing the birefringence of a ferroelectric liquid crystal, the transmittance under crossed Nicols is I / I ₀ = Sin ² 4 θSin ² (Δn · d π / λ) expressed. Here, I ₀ is the incident light intensity, I is the transmitted light intensity, θ is the tilt angle, Δn is the refractive index anisotropy, d is the thickness of the liquid crystal layer, and λ is the wavelength of the incident light. The tilt angle θ in the above-mentioned non-helical structure will appear as the angle in the average molecular axis direction of the twisted liquid crystal molecules in the aligned state in the first and second optically stable states. According to the above equation, the maximum transmittance is obtained when the tilt angle θ is 22.5 °, so that the tilt angle in the non-helical structure that realizes the bistability is as close as possible to 22.5 °. is necessary.

As a method of obtaining a liquid crystal device having a tilt angle as described above, it has been proposed to apply an alternating current to change the orientation (Japanese Patent Laid-Open No. 62-161123). The tilt angle θ in the non-helical structure can be increased by this technique, and the alignment of the liquid crystal can be changed from twist alignment between transparent substrates to parallel alignment (uniform alignment) having almost the same cone-director. The transmittance in the dark state can be reduced and a high contrast can be obtained.

[0008]

However, the liquid crystal device using the ferroelectric liquid crystal described above has the following problems.

[Left-standing monostable] The above-mentioned "bistability" is a unique characteristic of a ferroelectric liquid crystal, and the characteristic can be utilized by making a state transition (switching) from one stable state to the other stable state. Has been planned. Usually, this switching is performed by applying a voltage, and when the voltage reaches a predetermined voltage (threshold voltage), switching is performed. Therefore, there is a problem in that the driving characteristics of the liquid crystal device change greatly when the threshold voltage changes.

In general, a liquid crystal device using a ferroelectric liquid crystal has a problem called "surface memory". This phenomenon causes the above-mentioned fluctuation of the threshold voltage, and is an important problem that must be solved especially in order to manufacture a liquid crystal device capable of displaying gradation.

In order to prevent image sticking, it is effective to increase the pretilt angle α at the interface of the transparent substrate when the liquid crystal comes into contact, but in the case of the Book-Schierf layer structure, the pretilt is close to 0 °. In this way, the cone director at the interface becomes closer to the corner edge, and the contrast and drive margin characteristics are dramatically improved.

[Generation of Twist State] The uniform alignment state of the ferroelectric liquid crystal is a state in which liquid crystal molecules are hardly twisted between two transparent substrates. In this alignment state, a high contrast can be obtained, and there is little flickering in the image, which is an excellent alignment state. However, the ferroelectric liquid crystal has a twist alignment state other than the uniform alignment state. This twist alignment state is a state in which liquid crystal molecules are twisted between the transparent substrates, and if this alignment state is mixed with the uniform alignment state, there is a problem that the contrast is lowered and the switching characteristics in the uniform alignment are deteriorated. .

[Defective Switching] In order to realize high brightness and high speed switching characteristics, it is necessary to use a ferroelectric liquid crystal having a large spontaneous polarization. However, in the orientation state having the chevron structure, the switching speed is easily impaired by the influence of the reverse electric field generated by the spontaneous polarization, and the liquid crystal device may not function. The switching speed depends on the electric capacity and electric resistance of the alignment control film between the electrodes and the liquid crystal layer, and the smaller electric capacity and the higher electric resistance,
The effect of the reverse electric field due to spontaneous polarization becomes large and the switching speed is impaired.

[Layer Structure (AC Applying Process)] The applied voltage in the AC applying process that has been performed so far is usually ± 20 to 30 V / μm, and if the AC applying process can be performed in the vicinity of ± 10 V / μm. The AC application process cannot be performed by also using the information signal generating circuit. Therefore, it is difficult to perform the AC application process using the drive waveform generating circuit.

Therefore, it is an object of the present invention to provide a reliable liquid crystal device that solves these problems and an information transmission device using the same.

[0016]

The present invention has been made in view of the above-mentioned circumstances, and two transparent substrates having an alignment control film subjected to a uniaxial alignment treatment are opposed to each other with a predetermined gap. Further, in a liquid crystal device in which liquid crystal is sandwiched in the gap, an uneven member having a large number of sawtooth-shaped uneven portions is provided on the transparent substrate surface under the alignment control film, and the uneven portion of the uneven member is predetermined. It is characterized in that it has an inclination of and is inclined in the same direction.

For example, when the inclination angle of the uneven portion is β and the pretilt angle of the liquid crystal at the interface of the alignment control film is measured in the opposite direction of the inclination angle β to be α, the inclination angle β and the pretilt angle α is | β-α | <10 ° and β> 5
It must meet °.

Further, the liquid crystal is a ferroelectric liquid crystal of a chiral smectic liquid crystal.

Further, the ferroelectric liquid crystal has a chiral smectic C phase, and has a helical pitch of 1 μm or less and 0.1 μm or more.

Furthermore, the spontaneous polarization of the ferroelectric liquid crystal is 2
It has 5 nC / cm ² or more and 200 nC / cm ² or less.

As an information transmission device using the liquid crystal device according to the present invention, a graphic controller for outputting a data signal and a scanning method signal, a scanning signal control circuit for outputting scanning line address data and a scanning method signal, and a display. An information signal control circuit for outputting data and a scanning method signal, and the liquid crystal device according to any one of claims 1 to 5 for displaying and transmitting information.

[0022]

According to the above construction, the concavo-convex member is provided on the surface of the transparent substrate, and the inclination angle β of the concavo-convex portion and the pretilt angle α of the ferroelectric liquid crystal at the interface of the alignment control film have a relationship of β and α. −
It satisfies α | <10 ° and β> 5 °.

[0023]

1 is a schematic view showing a cross section of a liquid crystal device, and FIG. 2 is a partial cross sectional view of an essential part of the invention. The liquid crystal device is 1.1
An inclination angle formed by a method using a Ni stamper and a photo-curing resin (acrylic UV-curing resin or the like) or a column forming method by oblique vapor deposition on the glass substrates (transparent substrates) 10a and 10b having a thickness of mm. Sawtooth-shaped concavo-convex members 11a and 11b having a concavo-convex portion 20 of β are provided, on which In ₂ O ₃ and ITO (Indiu) having a thickness of 150 nm are provided.
band-shaped transparent electrode 1 made of m Tin Oxide) or the like
2a, 12b are applied. In the present embodiment, the inclination angle β of the uneven portion 20 was set as one of the sample preparation conditions (Table 1).
reference). Further, on the transparent electrodes 12a and 12b, alignment control films 13a and 13b are formed with a film thickness of 5 nm or less. As the orientation control films 13a and 13b, a fluorine-containing polyamic acid-containing NMP (N-methylpyrrolidone):
n-Putyl panel solvent: n-Putyl carbitol =
A 4: 1 mixed solvent of 5: 1: 3 was applied by printing and then baked at 270 ° C. to form a (fluorine-containing) polyimide orientation control layer having a film thickness of 5 nm. The alignment control films 13a and 13b are subjected to an alignment treatment such as rubbing in parallel with the transparent electrodes 12a and 12b. A rubbing cloth made of nylon was used for the rubbing treatment, and the substrate feeding speed of the glass substrates 10a and 10b was 50 mm.
Samples were prepared by changing the pressing amount and the roller rotation speed under / sec (see Table 1).

Transparent electrodes 12a and 12b and orientation control film 13
A low-resistance short-circuit prevention layer may be laminated between a and 13b, and the low-resistance alignment control films 13a and 13b may have a thickness of 5 nm or more.

These two glass substrates 10a and 10b
Are bonded to each other via silica beads 15 of 3 μm so that the rubbing directions are parallel to each other while holding a predetermined gap (see Table 1 for details).
Is injected, and polarizing plates 16a and 16b are provided so as to sandwich the glass substrates 11a and 11b. The ferroelectric liquid crystal 14 used below.

True tilt angle Θ = 21 ° Spontaneous polarization Ps = 30 nC / cm ² C ^* Pitch = 8.6 μm In such a configuration, by satisfying the relationship of | β-α | <10 ° and β> 5 ° between the pretilt angle α and the interface inclination angle β, there is no standing monostable (burn-in), high speed and It is possible to produce liquid crystal devices with high contrast.

The ferroelectric liquid crystal is a chiral smectic liquid crystal, and a chiral smectic C is further used.
Phase, and helical pitch is 1μm or less, 0.1μ
m or more. The spontaneous polarization may be in the range of 25 nC / cm ² or more and 200 nC / cm ² or less.

Next, a method of measuring each characteristic value will be described. [Measurement of image sticking (left-standing monostable)]
As shown in FIG. 3, evaluation areas Px1 and Px2 are used, and these evaluation areas Px1 and Px2 are normal as an initial state,
Moreover, after confirming that it has bistability, a standing test was conducted.

Bistability is confirmed by measuring the threshold voltage from one stable state A to another stable state B and the threshold voltage from stable state B to stable state A.
In the leaving test, the evaluation areas Px1 and Px2 are set to the stable state A and the stable state B, respectively, and the environmental temperature of 30 ° C.
After standing for a day, the threshold voltages of the evaluation areas Px1 and Px2 were measured and evaluated by the following formula.

P _<AB> = { _{VA <AB>} -VB _<AB> } / VI _{I <AB>} P _<BA> = {VB _<BA> -VA _<BA> } / VI _{<BA >} Where V _{A <AB>} is the threshold voltage required to invert from the stable state A to the stable state B after being left in the stable state A, V
_{B <AB>} is a threshold voltage required to invert from the stable state A to the stable state B after being left in the stable state B, and V _{I <AB>}
Is the threshold voltage from stable state A to stable state B in the initial state,
V _{I <BA>} represents the stable state B to stable state A threshold voltage in the initial state. Therefore, the smaller the values of P _<AB> and P _<BA> , the less the image sticking. [Measurement of True Tilt Angle] A bipolar pulse sufficiently larger than the threshold voltage of the liquid crystal device (for example, when the threshold voltage of a single-shot pulse is 50 μsec, 10 V, an AC pulse of 10 Hz, 10 V is used) is applied, and the crossed Nicols are applied. After that, the liquid crystal device arranged between them is rotated horizontally with the deflecting plate to search for the first extinction position, and then the pulse of the opposite polarity to the above-mentioned single-shot pulse is applied. Find At this time, the angle ½ to the first extinction position was determined as the true tilt angle θ. [Measurement of Apparent Tilt Angle] After applying a single-shot pulse equal to or higher than the threshold voltage of the liquid crystal device, the liquid crystal device disposed between them under no electric field and under crossed Nicols is rotated horizontally with the deflection plate to make the first extinction. Position, then applying a pulse of the opposite polarity to the single vapor pulse, and then searching for the second extinction position under no electric field. At this time, a tilt with an apparent half angle up to the first extinction position. The angle is θa. [Measurement of Pretilt Angle α] The pretilt angle α was measured by the crystal rotation method. The measurement method is to rotate the liquid crystal device on the glass substrate surface and
A helium-neon laser beam with a deflection surface that makes an angle of ° is emitted from a direction perpendicular to the rotation axis, and the intensity of the transmitted light is increased by a photodiode through a deflection plate that has a transmission axis parallel to the incident deflection surface on the opposite side. It was measured. Then, an angle formed by a line perpendicular to the liquid crystal device and a center angle of a hyperbolic group of transmitted light intensity generated by interference was defined as Φx, and the pretilt angle α was obtained by substituting it into the following equation.

[0031] Here, n _O is the ordinary light refractive index and n _e is the extraordinary light refractive index. For details, see J. J. Appl. Phys. Vo
l. 119 (1980) NO. 10, Short No
tes 2013.

In the present embodiment, the following two types of measurements were performed as the measured values of the pretilt angle α. (Type 1) Concavo-convex member 1 on the glass substrate 10a, 10b
1a and 11b are not formed, and transparent electrodes 12a and 12b
Are not patterned in a matrix. The pretilt angle of the liquid crystal device, which was prepared by laminating the two glass substrates 10a and 10b so that the tilts of the liquid crystal molecules at the interfaces between the upper and lower glass substrates 10a and 10b are parallel and in the same direction, is α1. (Type 2) Compared to Type 1, on glass substrate 10a, 1
The pretilt angle of the concave and convex members 11a and 11b formed on 0b is α2.

A liquid crystal for measuring the pretilt angle α (ferroelectric liquid crystal CS-1014 manufactured by Chisso Co.) was prepared by mixing a compound represented by the following structural formula in a weight ratio of 20% as a standard liquid crystal.

[0034]

[Chemical 1] The mixed liquid crystal structure had a Sm at 10 to 55 ° C.
It showed phase A. Table 1 shows the specifications and evaluation results of the samples described above.

[0035]

[Table 1] In sample 1, α1 = 12 ° and α2 = 1 °. A rectangular wave of ± 40 V / μm, 10 Hz is applied to this liquid crystal device for 5 minutes, 3
When the apparent tilt angle θα was measured by applying in an environment of 0 ° C., 9.4 ° spreads to 20.0 °. Next, the image sticking (left-sided monostable) was measured by measuring the threshold voltage with a single pulse having a pulse width ΔT = 40 μs. P _<AB> = 0.0
4, P _<BA> = 0.05, and almost no seizure was confirmed. This also applies to Samples 2, 2 and 4. In addition, the sample 5 includes two glass substrates 10
Sample 1 is the same as sample 1 except that the rubbing directions of a and 10b were bonded in antiparallel. In this sample 5, θa after AC application was 22 °, P _<AB> = 0.04, P _<BA> = 0.
It was 04, and almost no seizure was confirmed.

The sample 6 is the same as the sample 1 except that the concavo-convex members 11a and 11b are not formed and nylon is used for the orientation control films 13a and 13b. The pretilt angle α1 was α1 = 1 ° (α2 = α1). In addition, a rectangular wave of ± 40 V / μm, 10 Hz is applied to the liquid crystal device for 5 minutes, 30
When an apparent tilt angle θα was measured by applying in an environment of ℃, 8.9 ° spreads to 19.8 °. Next, as a result of measuring the image sticking (standing monostable) with a single pulse having a pulse width ΔT = 40 μs, the threshold voltage was measured, and P _<AB> = 0.2
3, P _<BA> = 0.25, and remarkable seizure was confirmed.

On the other hand, sample 7 is the same as sample 1 except that the uneven members 11a and 11b are not formed.
1 was α1 = 12 ° (α2 = α1). Then, a rectangular wave of ± 40 V / μm, 10 Hz is applied to this liquid crystal device.
When the apparent tilt angle θa was measured by applying the voltage for 30 minutes under the environment of 30 ° C., 9.0 ° spreads to 18.2 °. However, when switching between two states of uniform orientation, a light blue orientation state (twist state) having no extinction position appeared and the characteristics changed.

Further, the sample 8 is the uneven member 11a, 11b.
Sample 1 is the same as sample 1 except that the inclination angle β and the rubbing condition of were changed. The pretilt angle α1 is α1 = 20 °, α2 =
It was 12 °. ± 40 V / μm for this liquid crystal device, 10
The rectangular shape of Hz was applied for 5 minutes in an environment of 30 ° C., and the apparent tilt angle θa was measured, and 9.4 ° was 19.2 °.
Spread. However, when switching between two states of uniform orientation, a light blue orientation state (twist state) having no extinction position appeared and the characteristics changed.

Further, like the sample 8, the sample 9 is the same as the sample 1 except that the inclination angle β of the uneven members 11a and 11b and the rubbing conditions were changed. The pretilt angle is α1 = 7
And α2 = 3 °. ± 40 V / μ for this liquid crystal device
A rectangular wave of m, 10 Hz was applied for 5 minutes in an environment of 30 ° C., and when the apparent tilt angle θa was measured, 9.4 ° spreads to 20.0 °. Then, the result of measuring the threshold voltage with a single pulse having a pulse width ΔT = 40 μs for the image sticking (standing monostable) was P _<AB> = 0.34 and P _<BA> = 0.30, and a remarkable image sticking was observed. confirmed.

As the ferroelectric liquid crystal, one having a chiral smectic layer state can be used. Specifically, the chiral smectic C phase (SmC ^* ) and H phase (S
mH ^* ), I-phase (SmI ^* ), K-phase (SmK ^* ), and G-phase (SmG ^* ) liquid crystals can be used. Particularly preferred ferroelectric liquid crystals include pyrimidine-based mixed liquid crystals that exhibit a cholesteric phase on the high temperature side and exhibit the following phase transition temperatures and substance values.

[0041]

[Outer 1] This ferroelectric liquid crystal had a true tilt angle Θ = 22 ° and spontaneous polarization Ps = 30 nC / cm ² . FIG. 4 is a photograph replacing a drawing showing an alignment state (this alignment state is represented by a symbol A1) of liquid crystal molecules before application of an alternating current in a liquid crystal device using a pyrimidine-based mixed liquid crystal and a fluorine-containing polyimide (3 nm). In addition, FIG. 5 shows an AC ± 10 V. Alignment state of liquid crystal molecules when 10 Hz is applied (this alignment state is A2
(Represented by the reference sign). The tilt angle θ in the non-helical structure in the alignment state A1 was 14 °, whereas the tilt angle θ in the non-helical structure in the alignment state A2 was 22 °.

Further, the change in layer structure was measured by X-ray analysis. FIG. 6 shows the measurement result of the alignment state A1, and FIG. 7 shows the measurement result of the alignment state A2. It can be seen from FIG. 6 that the alignment state A1 is an alignment having one or more bends between the glass substrates 10a and 10b. It can be understood from the results shown in FIG. 7 that the orientation state A1 has a pseudo-bookshelf structure by the application of alternating current.

Next, an embodiment of the information transmission device using the liquid crystal device according to the present invention will be described with reference to FIG. The information transmission device includes a graphic controller 30 and a drive control circuit 3
1, a scanning signal control circuit 32, and an information signal control circuit 33
Scanning signal applying circuit 34 and information signal applying circuit 35
And a liquid crystal device 36 according to the present invention.

The data and the scanning method signal output from the graphic controller 30 are output to the scanning signal control circuit 32 and the information signal control circuit 33 by the drive control circuit 31. At this time, the data is converted into address data and display data, and the scanning method signal is directly applied to the scanning signal applying circuit 3.
4 and the information signal application circuit 35. The scanning signal application circuit 34 scans a scanning signal waveform determined by a scanning method signal with a scanning electrode (not shown) determined by address data.
Further, the information signal applying circuit 35 outputs an information signal waveform determined by the scanning method signal and the display content of white or black sent by the display data to the information electrode (not shown).
To display the information on the liquid crystal device 36.

By using the liquid crystal device of the present invention,
It has become possible to increase the reliability of the information transmission device.

[0046]

As described above, the uneven member is provided,
By setting the spontaneous polarization to 25 nC / cm ² or more, a large pretilt angle can be obtained, a uniform alignment state can be obtained, and high speed and high brightness characteristics can be exhibited. Due to this, the reliability of the liquid crystal device is significantly increased.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal device applied to the description of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a glass substrate provided with a concavo-convex member applied to the description of the embodiment of the present invention.

FIG. 3 is a diagram showing an evaluation region of standing monostability of the liquid crystal device applied to the description of the embodiments of the present invention.

FIG. 4 is a photograph instead of a drawing, which shows the structure of an alignment state A1 of ferroelectric liquid crystal molecules applied to the description of an example of the present invention.

FIG. 5 is a photograph replacing a drawing, which shows the structure of an alignment state A2 of ferroelectric liquid crystal molecules applied to the description of an example of the present invention.

FIG. 6 is an X-ray analysis diagram showing a structure of an alignment state A1 of ferroelectric liquid crystal molecules applied to the description of an example of the present invention.

FIG. 7 is an X-ray analysis diagram showing the structure of the alignment state A2 of the ferroelectric liquid crystal molecules applied to the description of the embodiments of the present invention.

FIG. 8 is a block diagram applied to the description of an information transmission device using a liquid crystal device according to the present invention.

[Explanation of symbols]

 10a, 10b Glass substrate (transparent substrate) 11a, 11b Concavo-convex member 13a, 13b Alignment control film 14 Ferroelectric liquid crystal (liquid crystal) 20 Concavo-convex part 30 Graphic controller 32 Scan signal application circuit 33 Information signal application circuit 36 Liquid crystal device

Claims (6)

[Claims] 1. A liquid crystal device in which two transparent substrates each having an alignment control film subjected to a uniaxial alignment treatment are opposed to each other with a predetermined gap therebetween, and liquid crystal is sandwiched in the gap. A concavo-convex member having a large number of sawtooth-shaped concavo-convex portions is provided on the transparent substrate surface under the film, and the concavo-convex portions of the concavo-convex member have a predetermined inclination and are inclined in the same direction. And liquid crystal device. 2. The inclination angle β and the pretilt angle when the inclination angle of the uneven portion is β, and the pretilt angle of the liquid crystal at the interface of the alignment control film is measured in the opposite direction of the inclination angle β to α. The liquid crystal device according to claim 1, wherein α satisfies | β−α | <10 ° and β> 5 °. 3. The liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal of chiral smectic liquid crystal. 4. The ferroelectric liquid crystal has a chiral smectic C phase and has a helical pitch of 1 μm or less,
The liquid crystal device according to claim 3, wherein the liquid crystal device has a thickness of 0.1 μm or more. 5. The spontaneous polarization of the ferroelectric liquid crystal is 25 nC.
The liquid crystal device according to claim 3, wherein the liquid crystal device has a density of not less than / cm ^{2 and not} more than 200 nC / cm ² . 6. A graphic controller which outputs a data signal and a scanning method signal, a scanning signal control circuit which outputs scanning line address data and a scanning method signal, and an information signal control circuit which outputs display data and a scanning method signal. An information transmission device comprising: the liquid crystal device according to claim 1; and displaying and transmitting information.