JP2502481B2 - Liquid crystal device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display device and a liquid crystal display.
The present invention relates to a liquid crystal device used for an optical shutter and the like, and more particularly to a gradation display liquid crystal device in which display and driving characteristics are improved by improving an initial alignment state of liquid crystal molecules.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element for displaying an image or information by forming scanning electrodes and signal electrodes in a matrix and filling a liquid crystal compound between the electrodes to form a large number of pixels has been known. ,well known. The grayscale driving method of this display element is a time division in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied in parallel to the signal electrode group in synchronization with the address signal. Although driving is adopted, this display element and its gradation driving method have major drawbacks that can be said to be fatal as described below.

That is, it is difficult to increase the pixel density or enlarge the screen. Among the conventional liquid crystals, most of them are practically used as a display element because of their relatively high response speed and low power consumption. Schadt and W. "Appl" by Helfrich
ied Physics Letters "Vo.1
8, No. 4 (1971.2.15), P.I. 127-1
28 "Voltage-Dependent Opt
iCal Activity of a Twist
d Nematic Liquid Crystal ”
The TN (twisted nematic) type liquid crystal shown in Fig. 2 is used, and this type of liquid crystal has a structure in which molecules of a nematic liquid crystal having a positive dielectric anisotropy in a non-electric field state are twisted in a liquid crystal layer thickness direction. (Helical structure) is formed, and the liquid crystal molecules are arranged in parallel on both electrode surfaces. On the other hand, when an electric field is applied, nematic liquid crystals having positive dielectric anisotropy are aligned in the direction of the electric field, and as a result, optical modulation can occur. When a display element is constructed with a matrix electrode structure using this type of liquid crystal, in a region (selection point) in which both the scanning electrode and the signal electrode are selected, the liquid crystal molecules are equal to or more than the threshold value required to be aligned perpendicularly to the electrode surface. The voltage is applied, and no voltage is applied to a region (non-selection point) in which neither the scanning electrode nor the signal electrode is selected, so that the liquid crystal molecules maintain a stable alignment parallel to the electrode surface. By arranging linear polarizers having a crossed Nicol relationship above and below such a liquid crystal cell, light does not pass at selected points and light passes at non-selected points, so that it can be used as an image element. Become. However, in the case where the matrix electrode structure is formed, the scan electrode is selected and the signal electrode is not selected, or the scan electrode is not selected and the signal electrode is selected (so-called “half-selected point”). A finite electric field is applied. If the difference between the voltage applied to the selection point and the voltage applied to the semi-selection point is sufficiently large and the voltage threshold value required to align the liquid crystal molecules perpendicularly to the electric field is set to the intermediate voltage value, the display element is Although it operates normally, when the number of scanning lines (N) is increased, the time (duty ratio) during which an effective electric field is applied to one selection point while scanning the entire screen (one frame) Will decrease at a rate of 1 / N. For this reason, the voltage difference as an effective value applied to the selected point and the non-selected point when the repeated search is performed becomes smaller as the number of scanning lines increases, and as a result, the decrease in image contrast and crosstalk occur. It is an unavoidable drawback. Such a phenomenon is caused by a liquid crystal having no bistability (a stable state in which liquid crystal molecules are horizontally aligned with respect to an electrode surface, and vertically aligned only when an electric field is effectively applied. Is an inherently unavoidable problem that occurs when (1) is driven by utilizing the temporal accumulation effect (that is, repeated scanning). In order to improve this point, a voltage averaging method, a two-frequency driving method, a multiple matrix method, etc. have already been proposed, but none of them is sufficient, and the display element has a large screen and high density. The current situation is that the number of scanning lines has reached a ceiling because the number of scanning lines cannot be increased sufficiently.

On the other hand, looking at the field of printers, as a means for obtaining a hard copy by receiving an electric signal as an input, an electric image signal is applied to the electrophotographic photosensitive member in the form of light in terms of pixel density and speed. The laser beam printer (LBP) is currently the best. However, for LBP, 1. The device as a printer becomes large in size; There are drawbacks such as a high-speed driving part such as a polygon scanner, noise is generated, and severe mechanical accuracy is required. A liquid crystal shutter array has been proposed as an element for converting an electric signal into an optical signal in order to eliminate such a defect. However, in the case of providing a pixel signal using the liquid crystal shutter array, for example, in order to write the pixel signal at a rate of 16 dots / mm within a length of 210 mm, it is necessary to have 3000 or more signal generation units. However, in order to give independent signals to each of them, it is originally difficult to manufacture because lead wires for sending signals have to be wired to all of the respective signal generators.

Therefore, an attempt has been made to give a pixel signal for 1 LINE (line) in a time-division manner by a signal generation unit divided into several lines. This is because the electrodes for applying a signal can be shared by a plurality of signal generating portions, and the wiring can be substantially reduced. However, in this case, if the number of rows (N) is increased by using a liquid crystal that does not have bistability as is usually done, the signal ON time becomes substantially 1 / N, and the signal is obtained on the photoreceptor. However, there is a problem in that the amount of light emitted is reduced and a problem of crosstalk occurs.

As a solution to the above-mentioned drawbacks of conventional liquid crystal elements, the use of bistable liquid crystal elements is
proposed by Lark and Lagerwall (JP-A-56-107216, U.S. Pat. No. 43).
67924, etc.). Ferroelectric liquid crystals having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) are generally used as the bistable liquid crystal. This liquid crystal has a bistable state consisting of a first optically stable state and a second optically stable state with respect to an electric field, and thus the above-mentioned T
Unlike the optical modulation element used in the N-type liquid crystal, for example, the liquid crystal is aligned in the first optical stable state with respect to one electric field vector and the second optical stable with respect to the other electric field vector. The liquid crystal is aligned in the state. In addition, this type of liquid crystal responds to an applied electric field very quickly in accordance with the above-mentioned 2
It has the property of taking one of the two stable states and maintaining that state when no electric field is applied. By utilizing such a property, a considerable substantial improvement can be obtained with respect to many of the problems of the above-mentioned conventional TN type element. This will be explained in more detail below in connection with the present invention. However, 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 effectively converted between the two stable states. It is necessary to be in a state of molecular alignment that occurs in a specific way. For example SmC ^* or S
For the ferroelectric liquid crystal having the mH ^* phase, the liquid crystal molecular layer having the SmC ^* or SmH ^* phase is perpendicular to the substrate surface, and therefore the liquid crystal molecular axis is aligned substantially parallel to the substrate surface (monodomain). Need to be formed. However, in the conventional optical modulation element using the liquid crystal having bistability, the alignment state of the liquid crystal having the monodomain structure is not always formed satisfactorily, so that sufficient characteristics cannot be obtained. Is the reality.

For example, in order to give such an orientation state, a method of applying a magnetic field, a method of applying a shearing force,
Have been proposed. However, none of these gave necessarily satisfactory results. For example, the method of applying a magnetic field has a drawback in that it requires a large-scale device and is incompatible with a thin layer cell having good operating characteristics. There is a drawback that it is not compatible with the method of injecting liquid crystal.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to achieve a gear shift response by achieving a bistable state with good productivity and combining the bistable state with a polarizer, as will be described later. Another object of the present invention is to provide a liquid crystal optical device that realizes a gradation display by realizing a display element having a variable pixel density and a large area or a high-speed shutter element.

[0009]

MEANS FOR SOLVING THE PROBLEMS AND ACTION The present invention comprises: a. A matrix electrode and a helix composed of at least one polarizer, a pair of substrates in which at least one is uniaxially oriented, and a first electrode group and a second electrode group which are provided so as to intersect with the pair of substrates, respectively. A liquid crystal cell having a chiral smectic liquid crystal that produces a uniaxial anisotropic phase and that is arranged at a sufficient inter-substrate spacing to suppress the formation of a structure; and b. A one-polarity pulse is applied to the selected at least one first electrode of the first electrode group in a first phase with reference to a voltage applied to the first electrode when not selected, The other polarity pulse is applied in two phases, and in the first phase, the chiral smectic liquid crystal in the entire region of the intersection of the selected at least one first electrode and all the electrodes of the second electrode group is generated. A first voltage signal is applied to all the electrodes of the second electrode group so as to generate one alignment state, and the selected at least one first electrode and the first voltage signal are applied in the second phase. The chiral smectic liquid crystal at the intersection with the second electrode group has a second state for all electrodes of the second electrode group so that a mixed state of one alignment state and the other alignment state depending on gradation information is generated. Having a voltage applying means for applying the voltage signal of It is a device.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings as necessary.

A particularly suitable liquid crystal material used in the present invention is a chiral smectic liquid crystal having ferroelectricity. Specifically, the chiral smectic C phase (SmC ^* ), the chiral smectic G phase (SmG ^* ), the chiral smectic F phase (SmF)
^* ), Chiral smectic I phase (SmI ^* ) or chiral smectic H phase (SmH ^* ) liquid crystal can be used.

For details of the ferroelectric liquid crystal, for example, LEJOURNAL DE PHYSIQUE LET.
TERS "36 (L-69) 1975," Ferroe
"lectric Liquid Crystal"";
"Applied Physics Letters"
36 (11) 1980 "Submicro Secon
d Bi-stable Electrooptic
Switching in Liquid Crystal
Is ”;“ Solid State Physics ”16 (141) 1981“ Liquid Crystal ”
Etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

Specific examples of the ferroelectric liquid crystal compound include desiloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate (HOBACPC), 4-o- (2-methyl)
-Butylresorcilidene-4'-octylaniline (M
BRA8). Particularly preferable ferroelectric liquid crystals are those which exhibit a cholesteric phase on the higher temperature side, and for example, biphenyl ester liquid crystals having the phase transition temperatures listed in the examples below can be used.

When a device is formed using these materials, the device is supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the temperature state in which the liquid crystal compound is in a desired phase. You can

FIG. 1 schematically shows an example of a cell for explaining the operation of the ferroelectric liquid crystal. Hereinafter, SmC ^* will be described as an example of the desired phase.

11 and 11 'are substrates (glass plates) covered with transparent electrodes made of a thin film of In ₂ O ₃ , SnO ₂ or ITO (Indium-Tin Oxide).
In the meantime, SmC ^* phase liquid crystal oriented so that the liquid crystal molecular layer 12 is perpendicular to the glass surface is enclosed. The thick line 13 represents liquid crystal molecules, and the liquid crystal molecules 13 continuously form a spiral structure in the surface direction of the substrate. The angle formed by the central axis 15 of this helical structure and the axial direction of the liquid crystal molecules 13 is represented as Θ. This liquid crystal molecule 13
Is the dipole moment (P
⊥) 14. When a voltage above a certain threshold is applied between the electrodes on the substrates 11 and 11 ', the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 are oriented so that all dipole moments (P⊥) 14 are oriented in the electric field direction. You can change direction. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the voltage application polarity is It is easy to understand that the liquid crystal optical element changes its optical characteristics depending on the situation.

The liquid crystal cell preferably used in the liquid crystal optical element of the present invention can be made sufficiently thin (for example, 10 μm or less). As the liquid crystal layer becomes thinner in this way, as shown in FIG. 2, the helical structure of the liquid crystal molecules is unwound and becomes a non-helical structure even when no electric field is applied, and the dipole moment P or P ′ thereof is directed upward (2
4) or downward (24 '). 1/2 of the angle between the molecular axis of the liquid crystal molecular axis 23 and 23 '
Is called a tilt angle (θ), and this tilt angle (θ) is equal to the apex angle made by the cone when the helical structure is adopted. When an electric field E or E'having a polarity different from a certain threshold value is applied to such a cell by the voltage applying means 21 and 21 'as shown in FIG. 2, the dipole moment becomes the electric field vector of the electric field E or E'. Correspondingly, the liquid crystal molecules are turned upward 24 or downward 24 ', and the liquid crystal molecules are aligned in either the first stable state 23 or the second stable state 23' accordingly.

As described above, there are two advantages of using such a ferroelectric substance as a liquid crystal optical element. The first is that the response speed is extremely fast, and the second is that the alignment of the liquid crystal molecules has bistability. The second point will be further described with reference to FIG. 2, for example. When an electric field E is applied, the liquid crystal molecules are aligned in the first stable state 23, which is stable even when the electric field is cut off. When an electric field E'in the opposite direction is applied, the liquid crystal molecules are oriented in the second stable state 23 'to change the orientation of the molecules, but they remain in this state even when the electric field is cut off.

In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible.

The most problematic point in forming an element from such a liquid crystal having ferroelectricity is that the layer having the SmC ^* phase is arranged perpendicularly to the substrate surface, as described above. It is difficult to form a cell with high monodomain property in which liquid crystal molecules are aligned substantially parallel to the substrate surface.

By the way, there has been known a method of subjecting a substrate surface to a uniaxial alignment treatment in manufacturing a liquid crystal cell having a large area. Examples of this uniaxial orientation treatment method include a method of velveting the surface of the substrate in one direction with cloth or paper, a method of oblique vapor deposition of SiO or SiO ₂ on the surface of the substrate, and the like.

However, even if such a rubbing method or an oblique vapor deposition method is applied to the ferroelectric liquid crystal, the alignment treatment itself hinders the bistability of the liquid crystal molecules. It has been considered that the uniaxial alignment treatment is not suitable when a driving method utilizing the so-called memory property is adopted.

However, as a result of diligent studies by the present inventors, it is possible to achieve a specific bistable state by subjecting the substrate surface to an appropriate uniaxial orientation treatment, as will be described in detail below. It is possible, and it has been revealed that by making the polarizer coincide with the specified axial direction, the driving utilizing the memory property can be achieved.

3 and 4 show an embodiment of the liquid crystal element of the present invention. FIG. 3 is a plan view of the liquid crystal device of the present invention, and FIG. 4 is a sectional view taken along line AA ′ of FIG.

The cell structure 100 shown in FIGS. 3 and 4 comprises a pair of substrates 10 made of a glass plate, a plastic plate or the like.
1 and 101 'are held at a predetermined interval by a spacer 104, and an adhesive 10 is used to seal the pair of substrates.
6 has a cell structure adhered at 6, and further has a substrate 101
An electrode group including a plurality of transparent electrodes 102 (for example, a scanning voltage applying electrode group in the matrix electrode structure) is formed on the upper surface of the electrode in a predetermined pattern such as a strip pattern. The transparent electrode 102 is formed on the substrate 101 '.
An electrode group (for example, a signal voltage applying electrode group in the matrix electrode structure) is formed of a plurality of transparent electrodes 102 ′ intersecting with each other.

The substrate 101 'provided with such a transparent electrode 102' is, for example, silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide. , Inorganic insulating materials such as boron nitride, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, urea resin and The orientation control film 105 formed by using an organic insulating material such as acrylic resin can be provided.

The orientation control film 105 is obtained by forming a film of the above-mentioned inorganic insulating material or organic insulating material and then rubbing the surface in one direction with velvet, cloth or paper.

In another preferred embodiment of the invention, SiO
The orientation control film 105 can be obtained by forming a film of an inorganic insulating material such as SiO ₂ or SiO ₂ on the substrate 101 ′ by the oblique vapor deposition method.

In the device shown in FIG. 9, a bell jar 80 is used.
1 is placed on an insulating substrate 803 having a suction port 805 and extends from the suction port 805 (not shown)
The bell jar 801 is evacuated by the vacuum pump. A crucible 807 made of tungsten or molybdenum is disposed inside and at the bottom of the bell jar 801 and the crucible 807 has a few grams of crystals 8 such as SiO, SiO ₂ , MgF _2.
08 is placed. The crucible 807 has two lower arms 807a and 807b, each of which is a conductor 80.
9, 810 connected. Power supply 806 and switch 80
4 is connected in series between the outer conductors 809 and 810 of the bell jar 801. The substrate 802 is disposed inside the bell jar 801 directly above the crucible 807 at an angle of K with respect to the vertical axis of the bell jar 801.

When the switch 804 is opened, the bell jar 801 is first evacuated to a pressure of about 10 ^-5 mmHg,
The switch 804 is then closed and the power source 806 is adjusted to provide power until the crucible 807 is incandescent at the proper temperature and the crystals 808 are evaporated. Optimum temperature range (700-1000
The current required for C) is about 100 amps. The crystals 808 are then evaporated to form an upward molecular flow, indicated by S in the figure, and the fluid S is incident on the substrate 802 at an angle K with respect to the substrate 802, which results in the substrate 802.
Are coated. The angle K is the “incident angle” described above, and the direction of the fluid S is the “oblique vapor deposition direction” described above. The thickness of this coating is determined by the device thickness calibration over time before inserting the substrate 802 into the bell jar 801. When a film having an appropriate thickness is formed, the power from the power source 806 is reduced and the switch 804 is opened to cool the bell jar 801 and its inside. Next, the pressure is raised to atmospheric pressure, and the substrate 802 is removed from the bell jar 801.

In another embodiment, the surface of the substrate 101 'made of glass or plastic or the substrate 101'.
After the above-mentioned inorganic insulating material or organic insulating material is formed as a film on the surface of the film, the surface of the film is etched by the oblique etching method, whereby the orientation control effect can be imparted to the surface.

It is preferable that the orientation control film 105 described above also functions as an insulating film at the same time. Therefore, the film thickness of the orientation control film 105 is generally set in the range of 100Å to 1 μ, preferably 500Å to 5000Å. You can This insulating film also has an advantage of being able to prevent the generation of a current caused by a small amount of impurities contained in the liquid crystal layer 103, and therefore does not deteriorate the liquid crystal compound even if the operation is repeated.

In the liquid crystal element of the present invention, the same material as the above-mentioned alignment control film 105 can be provided on the other substrate 101.

The liquid crystal layer 103 in the cell structure 100 shown in FIGS. 3 and 4 can be SmC ^* . The thickness of the liquid crystal layer 103 is sufficiently thin that the liquid crystal molecules do not have a spiral structure.

FIG. 5 shows another specific example of the liquid crystal element of the present invention. The liquid crystal element shown in FIG.
A plurality of spacer members 203 are arranged between 1 and 101 '. The spacer member 203 is formed by, for example, SiO 2 on the substrate 101 on which the orientation control film 105 is not provided.
Inorganic compounds such as SiO ₂ , Al ₂ O ₃ and TiO ₂ , or polyvinyl alcohol, polyimide, polyamide imide, polyester imide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal,
Polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, urea resin,
It can be obtained by forming a film of a resin such as an acrylic resin or a photoresist resin by an appropriate method and then etching the spacer member 203 so that the spacer member 203 is arranged at a predetermined position.

The cell structure 100 as described above is formed on the substrate 10
Polarizers 107 and 108 in a crossed Nicol state are arranged on both sides of the electrodes 1 and 101 ', respectively.
Optical modulation will occur when a voltage is applied between 02 '.

Next, a method for manufacturing the liquid crystal element of the present invention will be described with reference to FIGS. 3, 4 and 6 by taking biphenyl ester liquid crystal as an example of the liquid crystal material. This biphenyl ester compound exhibits the phase transition state shown below.

[0038]

[Outside 1]

When the liquid crystal layer is thick enough (up to 100 μ),
SmC ^* has a helical structure with a pitch of about 4μ.

First, the cell structure 100 in which the above-mentioned biphenyl ester liquid crystal is encapsulated is set in a heating case (not shown) that uniformly heats the entire cell 100.

Next, the compound in the cell 100 is heated to a temperature (about 75 ° C.) at which it isotropic. After that, the temperature of the heating case is lowered, and the compound in the isotropic phase in the cell 100 is transferred to the temperature lowering process. During this temperature lowering process, the isotropic phase compound undergoes a phase transition to the cholesteric phase of the Grange-Yuan structure at about 72 ° C, and if the temperature lowering process is continued, the temperature changes to about 60 ° C.
Thus, a phase transition can occur from the cholesteric phase to SmA, which is a uniaxial anisotropic phase. At this time, the liquid crystal molecular axes of SmA are aligned with the rubbing direction.

After that, SmA is used in the temperature lowering process than SmA.
By making a phase transition to mC ^* , for example, a cell thickness of 3μ
When it is about m or less, a monodomain SmC ^* having a non-helical structure can be obtained.

FIG. 6 schematically shows the alignment state of liquid crystal molecules, and is a view seen from above the substrate surface 505.

In the figure, 500 corresponds to the direction of the uniaxial alignment treatment, that is, the rubbing direction in this embodiment. SmA
In the phase, the liquid crystal molecules are aligned with the average molecular axis direction 501 of the liquid crystal, which coincides with the rubbing direction 500. In the SmC ^* phase, the average molecular axis direction of the liquid crystal molecules is tilted in the direction 502, and the rubbing direction 500 and the average molecular axis direction 502 of the SmC ^{* form} an angle θ with the first stable alignment state. Become. If voltage is applied to the upper and lower substrates in this state, SmC ^*
The average molecular axis direction of the liquid crystal molecules changes to an angle larger than the angle θ and assumes the third stable alignment state saturated at the angle θ. The average molecular axis direction at this time is 503.

Next, when the voltage is returned to zero, the liquid crystal molecules return to the original state of the first molecular axis direction 502. Therefore,
The liquid crystal molecules have a memory property in the state of the first molecular axis direction 502. When a voltage in the opposite direction is applied in the state of the molecular axis direction 502, when the voltage is sufficiently high, the average molecular axis direction of the liquid crystal molecules is saturated to form the fourth stable orientation forming the angle Θ. Average molecular axis direction 50
Transfer to 3 '. Then, when the voltage is returned to zero again, the liquid crystal molecules settle in the state of the average stable molecular axis direction 502 ′ of the second stable alignment state forming the angle θ. Therefore, as shown in the figure, by aligning one polarization axis direction 504 of the polarizer with the molecular axis direction 502 forming the angle θ, between the first and second stable alignment states by the electric field as described below. The optical contrast in the on-state and the off-state can be improved by using the driving method that causes the orientation transition and the memory property.

FIG. 7 shows the angle (θ) formed by the uniaxial processing direction and the average molecular axis direction in the SmC ^* phase of the above-mentioned biphenyl ester compound liquid crystal, and the state of the molecular axis 502 and 50.
An example of the dependence of the optical contrast ratio in the 2'state depending on the thickness of the liquid crystal layer is shown. According to the curve 61, the value of the angle θ decreases as the thickness of the liquid crystal layer decreases, but the contrast increases according to the curve 62. still,
These measurements are based on the phase transition temperature of SmA → SmC ^*.
It was carried out at a temperature as low as 0 ° C. The value of the average molecular axis direction (Θ) when a sufficient electric field (for example, about 20 V to 30 V) is applied is Θ = when the thickness of the liquid crystal layer is 1.2 μ.
When 25 ° and 2.0μ, Θ = 27 ° When 2.6μ, Θ =
28 ° and the liquid crystal layer is sufficiently thick (about 10
0 μ) was Θ = 30 °.

FIG. 8 shows the state of the molecular axis 502 and the angle (θ) formed by the uniaxial processing direction and the average molecular axis direction in the SmC ^* phase of the azomethine compound as a liquid crystal material.
It is the measurement data showing the thickness dependency of the liquid crystal layer of the contrast ratio in the 2'state. This liquid crystal exhibits the following phase transition.

[0048]

[Outside 2] The helical pitch was about 2μ. In the case of this material, the angle θ increases as the thickness of the liquid crystal layer decreases, as shown by the curve 71, but the optical contrast is still the curve 7.
It increases as shown in 2. These measurements are SmA → Sm
It is measured at a temperature lower by 15 ° C. than the C ^* phase transition temperature.

The value of the average molecular axis direction (Θ) when a sufficient electric field (about 20 V to 30 V) is applied is Θ = 14 ° when the thickness of the liquid crystal layer is 1 μ, and Θ = 15 when it is 2 μ. °
And when the liquid crystal layer is thick enough (about 100μ)
Was 18 °. Symbols indicated by crosses in the figure are given for reference, and K. Kondo et al. J.
J. This is a rewrite of the data described in AP 22 (1983) L294. In the data described in the same magazine, the substrate is not subjected to any alignment treatment, and the value of the angle θ is larger than the data of the inventors of the present invention in which the substrate is subjected to the alignment treatment. Therefore, it is clear that the alignment treatment has a great influence on the alignment state of the liquid crystal molecules.

As can be seen from the feature of the present invention, which gives the liquid crystal molecules a specific stable state having an angle θ by the orientation treatment of the substrate surface, the value of the angle θ depends on the degree of treatment of the substrate surface. If the value changes and the processing method has a stronger binding force to the liquid crystal molecules, the angle θ becomes smaller, and
If the processing method is weaker, the angle θ becomes larger. When the degree of restraint force is too strong, the angle θ becomes extremely small, and it becomes practically impossible to perform the drive utilizing the memory property of SmC ^* . Therefore, the value of the angle θ is preferably

[0051]

[Outside 3] It is desirable to set the conditions for the alignment treatment.

The following method is suitable as a driving method used in the liquid crystal optical element of the present invention. That is, FIG.
(A) is a schematic diagram of a cell 91 having a matrix electrode structure in which a ferroelectric liquid crystal compound is sandwiched in the middle. Reference numeral 92 is a scanning electrode group, and 93 is a signal electrode group. FIG.
(B) and FIG. 10 (c) show selected scan electrodes 9 respectively.
2 (s) and electrical signals applied to the other scan electrodes (scan electrodes not selected) 92 (n) are shown in FIGS. 10 (d) and 10 (e), respectively. Electric signal applied to signal electrode 93 (s) (with information) and signal electrode 93 not selected (without information)
It represents the electrical signal applied to (n). FIG.
In FIG. 10E, the horizontal axis represents time and the vertical axis represents voltage. For example, when displaying a moving image, the scan electrode group 92 is sequentially and cyclically selected. Now, assuming that the threshold voltage for giving the first stable state of the liquid crystal cell having bistability is Vth ₁ and the threshold voltage for giving the second stable state is −Vth ₂ , the selected scan electrode 92. (S)
As the electric signal applied to is shown in Figure 10 (b) phase (time) in t _1, 2V phase (time) in t ₂ -V
Alternating voltage such that The other scanning electrodes 92 (n) are in the ground state as shown in FIG. On the other hand, the electric signal given to the selected signal electrode 93 (s) is O at the phase t ₁ and V at the phase t ₂ as shown in FIG. The electric signal given to () is O as shown in FIG.

In the above, the voltage value V is V <Vth ₁ <2
It is set to a desired value which satisfies V and -V> -Vth _2> -2V. FIG. 11 shows the voltage waveform applied to each pixel when such an electric signal is applied.

11 (a), (b), (c) and (d) correspond to the pixels A, B, C and D in FIG. 10 (a), respectively. That is, as is apparent from FIG. 11, since all the pixels on the selected scan line are applied with the voltage −2V exceeding the threshold voltage −Vth ₂ at the first phase t ₁ , first of all, one of the pixels is taken. Optically stable state (second stable state)
Aligned to. Of these, the pixel A corresponding to the presence of the information signal
Then, at the second phase t ₂ , the voltage 2V exceeding the threshold voltage Vth ₁ is applied, and therefore the optical phase shifts to the other optically stable state (first stable state). Further, in the pixel B existing on the same scanning line and corresponding to no information signal, the applied voltage in the second phase t ₂ is the voltage V which does not exceed the threshold voltage Vth ₁ , so that one optically stable state is obtained. Remains on.

On the other hand, on the scan line which is not selected as shown in the pixels C and D, the voltage applied to all the pixels C and D is + V or O, and neither exceeds the threshold voltage. Therefore, the liquid crystal molecules in each of the pixels C and D maintain the alignment corresponding to the signal state of the previous scan without changing the alignment state. That is, when the scan electrode is selected, first, in the first phase t ₁ , one of the optically stable states is aligned, and in the second phase t ₂ , a signal for one line is written, The signal state can be maintained until the end of one frame and the next selection.

Therefore, even if the number of scanning electrodes is increased, the substantial duty ratio remains unchanged, and the deterioration of contrast and crosstalk are not caused at all.

At this time, the value of the voltage value V and the phase (t ₁ + t
The value of ₂ ) = T depends on the liquid crystal material used and the thickness of the cell, but is usually 3 to 70 volts, and 0.
It is used in the range of 1 μsec to 2 msec.

In order to effectively achieve the driving method of the present invention, the electric signal applied to the scan electrode or the signal electrode is not necessarily a simple rectangular wave signal as described with reference to FIGS. It is self-evident that it need not be. For example, driving with a sine wave or a triangular wave is also possible.

12 and 13 show another modified embodiment. The difference from the embodiment shown in FIGS.
Voltage in the phase t ₁ of the scanning signal 92 (s) shown in (b) is a half and V, the phase t ₁ the correspondingly all information signals
, -V is applied. The advantage of this method is that the maximum voltage value of the signal applied to each electrode is shown in FIGS.
It is half that in the embodiment shown in FIG.

At this time, FIG. 12A shows the waveform of the voltage applied to the selected scan electrode 92 (s), while the unselected scan electrode 92 (n) is shown in FIG. 12B. Similarly, it is grounded, and the electric signal is O volt. 12C shows the waveform of the voltage applied to the selected signal electrode 93 (s), and FIG. 12D shows the voltage waveform applied to the unselected signal electrode 93 (n). . FIG. 13 shows the waveform of the voltage applied to each pixel A, B, C and D. That is, in FIG.
(B), (c) and (d) correspond to pixels A, B, C and D in FIG. 10 (a), respectively.

In the above description of the present invention, the liquid crystal compound layer corresponding to one pixel is uniform, and the alignment is aligned in either stable state over the entire area of one pixel. Came as being. However, since the alignment state of the ferroelectric liquid crystal is very delicately affected by the interaction with the surface of the substrate, the applied voltage and the threshold voltage Vth ₁ or −Vt.
When the difference in h ₂ is small, a situation in which stable alignment states in opposite directions are mixed in one pixel may occur due to a local slight difference in the substrate surface. By utilizing this, it is possible to add a signal that imparts gradation in the second phase of the information signal. For example, the driving method and the scanning signal described with reference to FIGS.
It is possible to obtain a gradation image by changing the number of pulses in the phase t ₂ of the information signal applied to the signal electrode according to the gradation as shown in (d).

The present invention will be described below with reference to examples.

Example 1 A pitch of 100 μm and a width of 62.
A square glass substrate provided with a 5 μm stripe ITO film as an electrode is prepared, and the ITO serving as the electrode is prepared.
The side provided with the film is faced downward and set in the oblique vapor deposition apparatus shown in FIG. 9, and then Si is placed in a molybdenum crucible.
A crystal of O ₂ was set. After that, the inside of the vapor deposition device is changed to 10
^After a vacuum state of about ⁻⁵ Torr, SiO ₂ was obliquely vapor-deposited on a glass substrate by a predetermined method to form an oblique vapor-deposited film of 800 Å (A electrode plate).

On the other hand, a polyimide forming solution (“PIQ” manufactured by Hitachi Chemical Co., Ltd .; non-volatile content concentration: 14.5 wt.%) Was formed on a glass substrate on which a similar striped ITO film was formed.
%) Was applied by a spinner coater and heated at 120 ° C. for 30 minutes to form an 800 Å coating (B electrode plate).

Next, a thermosetting epoxy adhesive was applied to the peripheral portion of the A electrode plate by screen printing except the injection port, and then the striped pattern electrodes of the A electrode plate and the B electrode plate were orthogonal to each other. The two electrode plates were held by a polyimide spacer so that the distance between the two electrode plates was 2 μm.

The above-mentioned biphenyl ester liquid crystal compound in the isotropic phase was injected from the injection port into the cell thus prepared, and the injection port was sealed. When the cell was cooled by gradual cooling and the temperature was maintained at about 30 ° C., a pair of polarizers were provided in a crossed Nicol state and then microscopic observation showed that SmC ^* having a non-helical structure was formed.
It was found that the angle θ≈10 °. A two-liquid crystal element was prepared by matching the axial direction of one of the crossed Nicols polarizers with this direction, and when this liquid crystal element was driven by the driving method shown in FIGS. 10 and 11, good memory driving was possible. It turned out to be.

[0067]

According to the present invention, an extremely great effect is brought about in that the matrix driving which enables the high contrast display is realized.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a liquid crystal element used in the present invention.

FIG. 2 is a perspective view schematically showing another liquid crystal element used in the present invention.

FIG. 3 is a plan view of a liquid crystal element used in the present invention.

4 is a sectional view taken along line AA of FIG.

FIG. 5 is a cross-sectional view of another liquid crystal element used in the present invention.

FIG. 6 is a plan view schematically showing an alignment state of liquid crystal molecules in the present invention.

FIG. 7 is an explanatory diagram showing the relationship between the angle θ formed by the uniaxial processing direction and the average molecular axis direction, the optical contrast, and the thickness of the liquid crystal layer.

FIG. 8 is an explanatory diagram showing the relationship between the angle θ formed by the uniaxial processing direction and the average molecular axis direction, the optical contrast, and the thickness of the liquid crystal layer.

FIG. 9 is a cross-sectional view of an apparatus used in the oblique vapor deposition method.

FIG. 10A is a plan view of a matrix electrode used in the present invention. FIG. 6B is an explanatory diagram showing signals of selected scan electrodes. FIG. 6C is an explanatory diagram showing signals of unselected scan electrodes. (D) Explanatory drawing which shows the information signal of the selected signal electrode. (E) is an explanatory view showing an information signal of a signal electrode which is not selected.

11A is a waveform diagram of a voltage applied to the liquid crystal of the pixel A. FIG. (B) is a waveform diagram of the voltage applied to the liquid crystal of the pixel B. (C) is a waveform diagram of the voltage applied to the liquid crystal of the pixel C.
(D) is a waveform diagram of the voltage applied to the liquid crystal of the pixel D.

FIG. 12A is an explanatory diagram showing signals of selected scan electrodes in another specific example. FIG. 9B is an explanatory diagram showing signals of unselected scan electrodes in another specific example. FIG. 6C is an explanatory diagram showing an information signal of a selected signal electrode in another specific example. (D) Explanatory drawing which shows the information signal of the signal electrode which is not selected in another specific example.

FIG. 13A is a waveform diagram of a voltage applied to the liquid crystal of the pixel A in another specific example. FIG. 6B is a waveform diagram of a voltage applied to the liquid crystal of the pixel B in another specific example. FIG. 6C is a waveform diagram of a voltage applied to the liquid crystal of the pixel C in another specific example. FIG. 6D is a waveform diagram of a voltage applied to the liquid crystal of the pixel D in another specific example.

FIG. 14A is an explanatory diagram showing a waveform example of a voltage applied to a signal electrode. FIG. 6B is an explanatory diagram showing a waveform example of the voltage applied to the signal electrode. (C) is explanatory drawing which shows the waveform example of the voltage applied to a signal electrode. (D) Explanatory drawing which shows the waveform example of the voltage applied to a signal electrode.

[Explanation of symbols]

500 rubbing direction 501 rubbing direction average molecular axis direction 502 in SmA phase are parallel SmC ^* first average molecular axis direction 502 in phase 'SmC ^* phase at a second average molecular axis direction 503 SmC ^* Saturated third average molecular axis direction when voltage is applied in phase 503 ′ SmC ^* Saturated fourth average molecular axis direction when voltage is applied in phase 504 Cross Polarization axis direction of one polarizer of Nicole 506 Cross Polarization axis direction of the other polarizer of Nicole 505 Substrate surface θ First average molecular axis direction 502 in SmC ^* and average molecular axis direction 50 in SmA phase when voltage between electrodes is zero
The angle between the third average molecular axis direction 503 in the SmC ^* phase and the average molecular axis direction 501 in the SmA phase when a voltage is applied.

Claims (8)

(57) [Claims] 1. A method comprising: a. A matrix electrode and a helix composed of at least one polarizer, a pair of substrates in which at least one is uniaxially oriented, and a first electrode group and a second electrode group which are provided so as to intersect with the pair of substrates, respectively. A liquid crystal cell having a chiral smectic liquid crystal that produces a uniaxial anisotropic phase and that is arranged at a sufficient inter-substrate spacing to suppress the formation of a structure; and b. A one-polarity pulse is applied to the selected at least one first electrode of the first electrode group in a first phase with reference to a voltage applied to the first electrode when not selected, The other polarity pulse is applied in two phases, and in the first phase, the chiral smectic liquid crystal in the entire region of the intersection of the selected at least one first electrode and all the electrodes of the second electrode group is generated. A first voltage signal is applied to all the electrodes of the second electrode group so as to generate one alignment state, and the selected at least one first electrode and the first voltage signal are applied in the second phase. The chiral smectic liquid crystal at the intersection with the second electrode group has a second state for all electrodes of the second electrode group so that a mixed state of one alignment state and the other alignment state depending on gradation information is generated. Liquid crystal having voltage applying means for applying the voltage signal of Location. 2. The first electrode group is a scanning electrode group, and the second electrode group is a scanning electrode group.
The liquid crystal device according to claim 1, wherein the electrode group is a signal electrode group. 3. The liquid crystal device according to claim 1, wherein the liquid crystal molecular axes in the uniaxial anisotropic phase are aligned in the direction of the uniaxial alignment treatment. 4. The liquid crystal device according to claim 1, wherein the uniaxial anisotropic phase is a smectic A phase. 5. The liquid crystal device according to claim 1, wherein the uniaxial alignment treatment is a rubbing treatment. 6. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a liquid crystal that produces a cholesteric phase at a temperature higher than a chiral smectic phase. 7. The chiral smectic liquid crystal is a liquid crystal that produces a cholesteric phase and a smectic A phase at a temperature higher than a chiral smectic phase, and is a liquid crystal formed by lowering the temperature of the cholesteric phase and the smectic A phase. The liquid crystal device according to claim 1. 8. The liquid crystal device according to claim 7, wherein the liquid crystal in the cholesteric phase is a liquid crystal having a Granduan structure.