JPS6345571B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the alignment of chiral smect liquid crystal used in producing chiral smect liquid crystal elements such as liquid crystal display elements and liquid crystal-optical shutter arrays.

Conventionally, liquid crystal display elements are well known in which a scanning electrode group and a signal electrode group are configured in a matrix, and a liquid crystal compound is filled between the electrodes to form a large number of pixels to display images or information. There is. The driving method for this display element is time-division driving, in which an address signal is selectively and periodically applied to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. However, this display element and its driving method have major and fatal drawbacks as described below.

That is, it is difficult to increase the pixel density or enlarge the screen. Among conventional liquid crystals, most of them are used practically as display elements because they have a relatively high response speed and low power consumption. Vo.18, No.4 (1971,
2, 15), “Voltage-.” on P.127-128.
Dependent Optical Activity of a Twisted
TN shown in “Nematic Liquid Crystal”
This type of liquid crystal has a structure (helical structure) in which the molecules of the nematic liquid crystal, which has positive dielectric anisotropy in the absence of an electric field, are twisted in the thickness direction of the liquid crystal layer. The liquid crystal molecules form a structure in which they are arranged in parallel on both electrode surfaces. On the other hand, when an electric field is applied, nematic liquid crystals with positive dielectric anisotropy are aligned in the direction of the electric field, resulting in optical modulation. When a display element is constructed using this type of liquid crystal with a matrix electrode structure, in the region where both the scanning electrode and the signal electrode are selected (selected point), there is a A voltage higher than the threshold is applied, and no voltage is applied to areas where neither the scanning electrode nor the signal electrode is selected (non-selected points), so the liquid crystal molecules maintain a stable alignment parallel to the electrode surface. . By arranging linear polarizers above and below a liquid crystal cell in a cross-Nicol relationship with each other, light does not pass through selected points, but light passes through non-selected points, making it possible to use it as an image element. Become. However, when a matrix electrode structure is configured, there is a possibility that the scan electrodes are selected and the signal electrodes are not selected, or the scan electrodes are not selected and the signal electrodes are selected (so-called "half-selected points"). The electric field becomes finite. If the difference between the voltage applied to the selected point and the voltage applied to the half-selected point is sufficiently large, and the voltage threshold required to align the liquid crystal molecules perpendicular to the electric field is set to an intermediate voltage value, the display element will It works normally, but if you increase the number of scanning lines (N), the time that an effective electric field is applied to one selected point while scanning the entire screen (1 frame) (duty ratio) is 1/
It decreases at a rate of N. For this reason, when repeated scanning is performed, the effective voltage difference between selected points and non-selected points becomes smaller as the number of scanning lines increases, resulting in a decrease in image contrast and crosstalk. It has become an unavoidable drawback. This phenomenon is caused by a liquid crystal that does not have bistability (the stable state is when the liquid crystal molecules are aligned horizontally with respect to the electrode surface, and the liquid crystal molecules are aligned vertically only while an electric field is effectively applied). This is essentially an unavoidable problem that arises when driving (i.e., repeatedly scanning) using the temporal accumulation effect. In order to improve this point, voltage averaging method, dual-frequency driving method, multiple matrix method, etc. have already been proposed, but all of these methods are insufficient, and it is necessary to increase the screen size and density of display elements. Currently, the number of scanning lines has reached a plateau due to the inability to increase the number of scanning lines sufficiently.

On the other hand, looking at the field of printers, laser beam printers provide electrical image signals in the form of light to electrophotographic photoreceptors in terms of both pixel density and speed, as a means of obtaining hard copies using electrical signals as input. (LBP) is currently the best.
However, LBP has the following drawbacks: 1. The printer is large; 2. It has a high-speed moving part like a polygon scanner, which generates noise, and requires strict mechanical precision. In order to overcome these drawbacks, a liquid crystal shutter array has been proposed as an element that converts electrical signals into optical signals. However, when providing pixel signals using a liquid crystal shutter array, for example, in order to write pixel signals at a rate of 16 dots/mm within a length of 210 mm, it is necessary to have more than 3000 signal generating sections. In order to provide independent signals to each, it was originally necessary to wire lead wires to send signals to all of the signal generating parts, which was difficult to manufacture.

For this reason, attempts have been made to provide pixel signals for one line in a time-division manner using a signal generating section divided into several lines. This is because the electrode for applying a signal can be shared by a plurality of signal generating sections, and the amount of wiring can be substantially reduced. However, if the number of lines (N) is increased by using a liquid crystal that does not have bistability, as is usually done in this case, the signal ON time becomes essentially 1/N, and the amount of time that can be obtained on the photoreceptor is reduced. There are disadvantages in that the amount of light emitted is reduced and crosstalk problems occur.

To improve the drawbacks of conventional liquid crystal devices, the use of bistable liquid crystal devices has been proposed by Clark and Lagerwall (Japanese Patent Laid-Open No. 56-107216, U.S. Patent No.
4367924 specification, etc.). As a liquid crystal having bistability, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is generally used. This liquid crystal has a first response to the electric field.
It has a bistable state consisting of an optically stable state of The liquid crystal is aligned in one optically stable state, and the liquid crystal is aligned in a second optically stable state for the other electric field vector. Furthermore, this type of liquid crystal has the property of very quickly taking one of the above two stable states in response to an applied electric field, and maintaining that state when no electric field is applied. By utilizing these properties, many of the problems of the conventional TN type devices mentioned above can be significantly improved.
This point will be explained in more detail below in connection with the present invention. However, in order for an optical modulation element using this bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal disposed between a pair of parallel substrates must be
It is necessary that the molecules be in such a state that conversion between two stable states can occur effectively. for example
For ferroelectric liquid crystals with SmC ^* or SmH ^* phase, the liquid crystal molecular layer with SmC ^* or SmH ^* phase is perpendicular to the substrate surface, and therefore the liquid crystal molecular axes are aligned approximately parallel to the substrate surface. A region (monodomain) needs to be formed. however,
The reality is that in conventional optical modulation elements using liquid crystals with bistable properties, the alignment state of the liquid crystals having such a monodomain structure was not always formed satisfactorily, and therefore sufficient characteristics could not be obtained. It is.

For example, methods of applying a magnetic field, methods of applying shear force, etc. have been proposed in order to provide such an orientation state. However, none of these methods necessarily gave satisfactory results. For example, the method of applying a magnetic field requires large-scale equipment and is incompatible with thin-layer cells with good operating characteristics. This method has the disadvantage that it is incompatible with the method of injecting liquid crystal.

By the way, in the device using the TN type liquid crystal as described above, methods for forming monodomains of liquid crystal molecules in a state parallel to the substrate surface include, for example, rubbing the substrate surface with something like cloth, A method such as diagonal vapor deposition is used. For example, the liquid crystal in contact with the rubbed substrate surface is given a directionality, and the liquid crystal molecules preferentially align in that direction, resulting in the lowest energy (that is, the most stable) state. Such a rubbed surface has the effect of preferentially arranging liquid crystal molecules in one direction. A structure with a plane to which this orientation effect is applied is described, for example, by W. Helfrich and M.
This is shown in Schadt's Canadian Patent No. 1010136, etc. In addition to the method of creating an alignment effect using this rubbing method, a structure with a plane formed by obliquely vapor depositing SiO or SiO ₂ on a substrate is used, and this SiO
Alternatively, the uniaxially anisotropic plane of SiO ₂ has the effect of preferentially aligning liquid crystal molecules in one direction.

In this way, alignment control methods such as rubbing and oblique evaporation are one of the preferred methods for producing liquid crystal elements, but these methods cannot be used to control alignment for liquid crystals that have bistability. When applied,
A plane having a wall effect that preferentially orients the liquid crystal in only one direction is formed, which has the drawback of inhibiting bistability to electric fields, high-speed response, and monodomain formation.

In view of the above-mentioned circumstances, the main object of the present invention is to
Conventional problems have been solved in optical modulators using bistable liquid crystals, which have potential suitability as display devices with high-speed response, high-density pixels, and large areas, or optical shutters with high shutter speeds. The object of the present invention is to provide a method for controlling the alignment of a chiral smect liquid crystal, which can fully exhibit its properties by improving the monodomain formation property or initial alignment.

As a result of further research by the present inventors for the above-mentioned purpose,
In particular, we focused on the orientation during the cooling process in which the liquid crystal material transitions from another phase (for example, a high temperature state such as an isotropic phase) to a uniaxial anisotropic phase (for example, a low temperature state such as SmA (Smectic A)). When a phase transition occurs from a phase (high temperature phase) to a uniaxial anisotropic phase, a new phase transition occurs at the spatial phase interface between another phase region and the uniaxial anisotropic phase region. The molecular axes of the anisotropic phase are oriented parallel to the orientation direction of liquid crystal molecules in the uniaxial anisotropic phase that has already been formed, and are also parallel to the direction in which the uniaxial anisotropic phase region grows and the orientation direction of the liquid crystal molecules. It was found that a monodomain uniaxially anisotropic phase grows extremely stably when the relationships are orthogonal. Furthermore, the present inventors have developed a structure that has horizontally aligned sidewall surfaces as a nucleation member (meaning a member that promotes the generation of liquid crystal nuclei in a uniaxially anisotropic phase). It is now possible to form the anisotropic phase nucleus as a uniaxially anisotropic phase of monodomains in which liquid crystal molecules are aligned parallel to the nucleation member.
As a result, it has been found that a liquid crystal element can be obtained with a structure that is compatible with the operating characteristics of the element based on the bistability of the liquid crystal and the monodomain nature of the liquid crystal layer.

The present invention is based on the above-mentioned knowledge, that is, the liquid crystal alignment control method according to the present invention has been made based on the above-mentioned knowledge, and is based on the uniaxially anisotropic phase of liquid crystal aligned in one direction between a pair of substrates. A uniaxially anisotropic liquid crystal is formed by forming a phase interface between the phase and another phase on the higher temperature side than the above phase, and arranging the other phase near the phase interface in a direction parallel to the liquid crystal alignment direction of the uniaxially anisotropic phase as the temperature decreases. It is characterized by a liquid crystal alignment control method in which a liquid crystal monodomain aligned in one direction is formed by causing a phase change in a phase and causing the phase change to occur continuously from the phase interface in a direction perpendicular to the phase interface. ing.

Hereinafter, the present invention will be described in further detail with reference to the drawings as necessary.

Particularly suitable liquid crystal materials for use in the present invention are those having bistability and ferroelectricity, specifically chiral smectate C phase (SmC ^* ) or H Phase (SmH ^* )
A liquid crystal having the following characteristics can be used.

For more information on ferroelectric liquid crystals, see e.g. LE
JOURNAL DE PHYSIQUE LETTERS” 36
(L-69) 1975, “Ferroelecric Liquid
Crystals”; “Applied Physics Letters” 36 (L
―69) 1975, “Ferroelectric Liquid Crystals”;
“Applied Letter Physics” 36 (11) 1980,
“Submicro Second Bistable Electrooptic
Switching in Liquid Crystals”; “Solid State Physics” 16
(141) 1981 "Liquid Crystal" etc., and the ferroelectric liquid crystal disclosed in these can be used in the present invention.

Specific examples of ferroelectric liquid crystal compounds include decyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate (HOBACPC), -o-(2-
Methyl)-butylresolcylidene-4'-octylaniline (MBRA8).

When constructing an element using these materials, the element is supported by a copper block with a heater embedded, etc., as necessary, in order to maintain the temperature state such that the liquid crystal compound becomes the SmC ^* phase or SmH ^* phase. be able to.

Figure 1 is for explaining the operation of ferroelectric liquid crystal.
This is a schematic drawing of an example of a cell. 11 and
11′ is In ₂ O ₃ , SnO ₂ or ITO (Indium-
A substrate (glass plate) coated with a transparent electrode made of a thin film such as Tin Oxide, etc., between which a liquid crystal molecular layer 12 is oriented perpendicular to the glass surface.
Enclosed is SmC ^* phase or SmH ^* phase liquid crystal.
The thick line 13 represents liquid crystal molecules,
This liquid crystal molecule 13 has a dipole moment (P⊥) 14 in a direction perpendicular to the molecule. When a voltage higher than 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 the dipole moments (P⊥) 14 are oriented in the direction of the electric field. You can change direction. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, voltage can be applied. It is easily understood that this results in a liquid crystal optical modulation element whose optical properties change depending on the polarity.

The liquid crystal cell preferably used in the liquid crystal element of the present invention has a sufficiently thin thickness (for example, 10μ or less).
can do. As the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unravels even when no electric field is applied, as shown in Figure 2.
It becomes a non-helical structure, and its dipole moment P or P' takes either an upward direction 24 or a downward direction 24'. When an electric field E or E' with a different polarity above 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 is The direction changes depending on the vector, upward 24 or downward 24', and accordingly the liquid crystal molecules are either in the first stable state 23 or the second stable state 23'.
Orient towards.

As mentioned earlier, there are two advantages to using such ferroelectricity as a liquid crystal element. The first
The first is that the response speed is extremely fast, and the second is that the alignment of liquid crystal molecules has bistability. To further explain the second point with reference to FIG. 2, for example, when the electric field E is applied, the liquid crystal molecules are oriented in a first stable state 23, and this state remains stable even when the electric field is turned off. Also, when applying an electric field E′ in the opposite direction,
The liquid crystal molecules change their orientation by aligning into a second stable state 23', but remain in this state even when the electric field is removed. Further, as long as the applied electric field E does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable that the cell be as thin as possible.

The biggest problem in forming devices using liquid crystals with such ferroelectricity is, as mentioned earlier, that the layer containing the SmC ^* phase or SmH ^* is perpendicular to the substrate surface. It is difficult to form a highly monodomain cell in which the liquid crystal molecules are aligned and oriented substantially parallel to the substrate surface, and it is the main purpose of the present invention to provide a solution to this problem.

FIG. 3A is a partial plan view of an embodiment of a liquid crystal element obtained by the liquid crystal alignment control method of the present invention, and FIG. 3B is a cross-sectional view taken along line AA'.
In order to make the cell structure easier to understand, the drawings are not drawn to an exact scale. In this example, a configuration example of a printer shutter array is shown.
The liquid crystal cell 100 shown in FIG. 3 includes a pair of substrates 101 made of glass plates, plastic plates, etc.
101' are held at a predetermined distance by a spacer (not shown), and has a cell structure in which the pair of substrates are bonded with an adhesive 106, and furthermore, a plurality of transparent electrodes 102 are formed on the substrate 101. An electrode group (for example, an electrode group for applying a scanning voltage in a matrix electrode structure) is formed in a predetermined pattern such as a strip pattern. On the substrate 101', a plurality of transparent electrodes 1 are arranged to intersect with the transparent electrode 102 described above.
02' (for example, a signal voltage applying electrode group in a matrix electrode structure) is formed in a segment pattern connected in a staggered manner by leads 107', as shown. The transparent electrode 102 is connected to the lead 107, and the transparent electrode 102' is connected to the lead 107'', so that signals from the external circuit are connected to the leads 107 and 107'', respectively.
input to the terminal.

Such substrates 101 and 101' include, for example,
Silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide,
Cerium fluoride, silicon nitride, silicon carbide, boron nitride, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine An insulating film (not shown) made of resin, urea resin, acrylic resin, or the like can be provided. This insulating film is the liquid crystal layer 103.
It also has the advantage of being able to prevent the generation of current caused by impurities etc. contained in trace amounts in the liquid crystal compound, so that even if the operation is repeated, the liquid crystal compound will not deteriorate.

The cell structure in this specific example includes a liquid crystal layer 103 that exhibits ferroelectricity at a predetermined temperature as described above, a nucleation member 104, and a heating element 105 such as a heater.

The nucleating member 104 is made of, for example, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal,
polyvinyl chloride, polyvinyl acetate, polyamide,
polystyrene, cellulose resin, melamine resin,
Resins such as urea resin and acrylic resin or
After forming a film with an inorganic compound such as SiO, SiO ₂ or TiO ₂ , it is formed into a band-like shape by a normal photolithography method. Further, the nucleation member 104 can also be made of the same material as the substrate 101 or 101'.

Further, as the heating element 105, it is suitable to use a thin film resistor such as indium oxide, tin oxide, or ITO (Indium Tin Oxide).

Such a liquid crystal cell 100 includes substrates 101 and 10.
Polarizers 108 and 108' in a crossed Nicol state or a parallel Nicol state are arranged on both sides of electrode 1', respectively, and optical modulation occurs when a voltage is applied between electrodes 102 and 102'.

To give a more specific example of the liquid crystal cell 100 shown in FIG. 3, for example, the transparent electrode 102 has a width
A band-shaped scanning electrode group with a diameter of 62.5 μm is used, while a transparent electrode 102′ forms one pixel and has a width of 26.5 μm×62.5 μm.
The signal electrode group can be made into a group of signal electrodes. Also, heating element 1
05 is an ITO thin film with an average width of 0.6 mm and a film thickness of 1000 Å.
It is preferable that the liquid crystal layer 103 is maintained at a thickness of approximately 2 μm.

Such a liquid crystal cell 100 is housed in a heating case (not shown), and polarizers 1 are arranged vertically orthogonally to each other.
08 and 108' can be arranged to operate as a liquid crystal shutter array for an electrophotographic printer. In this case, arrow B in FIG. 3A is the direction of rotation of the electrophotographic photosensitive drum.

For example, the nucleation member 104 is prepared by applying a polyimide forming solution ("PIQ" manufactured by Hitachi Chemical Co., Ltd.; non-volatile content concentration 14.5 wt%) onto the substrate 101 for 10 seconds using a spinner coating machine rotating at 3000 rpm, at °C
Heating was performed for 30 minutes to form a 2μ film. Next, a positive resist solution ("AZ1350" manufactured by Shipley) was applied using a spinner and prebaked.
This resist layer was exposed using a band-shaped mask with a mask width of 0.5 mm. Next, developer solution “MF312” containing tetramethylammonium hydroxide
The resist film in the exposed areas and the underlying polyimide film were etched to form through-holes by development, and after washing and drying, the resist film in the last exposed areas was removed using methyl ethyl ketone. After that, at 200℃ for 60 minutes,
Cured by heating at 350℃ for 30 minutes, PIQ
(polyimide) nucleation member can be formed.

The following is a liquid crystal material that exhibits ferroelectric properties at a given temperature.
Taking the case of DOBAMBC as an example, the liquid crystal layer 103
The orientation control method will be specifically explained using FIG. 3.

First, the liquid crystal cell 100 containing DOBAMBC is set in a heating case (not shown) that uniformly heats the entire cell. Next, the temperature of the heating case is controlled so that the average temperature of the cell is, for example, 90°C. At this time, DOBAMBC is in the SmC ^* phase or SmA phase state as a liquid crystal phase. Here, when a current is applied to the heating element (heater) 105 and the current value is gradually increased, only the vicinity of the heating element 105 exceeds approximately 118°C, which is the transition temperature of SmA → isotropic phase, and isotropic. A phase transition occurs from phase to liquid state.
Further, as the current is increased, the isotropic phase region expands while remaining substantially parallel to the heating element 105, and eventually the entire liquid crystal layer 103 becomes an isotropic phase.

In this state, the temperature in the longitudinal direction (direction C in FIG. 3A) of the liquid crystal cell 100 is uniform, and the temperature is uniform in the longitudinal direction (direction B in FIG. 3A) from the nucleation member 104 to the heating element 105. A temperature gradient is formed in which the temperature gradually increases in the direction. For example, the vicinity of the side wall surface 104' of the nucleation member 104 is
.degree. C., and the temperature near the heating element 105, which is about 1.5 mm away from the temperature, is set to about 140.degree. C., thereby forming a temperature gradient.

Next, if the temperature of the case in which the cell 100 is set is controlled to be gradually lowered from 90°C at a rate of 10°C/h, for example, with the temperature gradient described above applied to the cell 100, as shown in Fig. 3. In B, first, the temperature near the side wall surface 104' of the nucleation member 104 becomes lower than the isotropic phase→SmA phase transition temperature (approximately 116°C), and in this region
Nuclei of SmA phase are formed. At this time, the side wall surface 104' of the nucleation member 104 and the surface 1 of the substrate 101
09 has the effect of aligning liquid crystal molecules in the horizontal direction, so in the vicinity of the side wall surface 104'
When the SmA phase is formed, the liquid crystal molecular axis is
01 and parallel to the longitudinal direction of the side wall surface 104';
Therefore, the nucleus of the SmA phase formed is located on the side wall surface 10.
4' and a monodomain oriented horizontally with respect to the surface 109 of the substrate 101. If the temperature of the case is further lowered, it is already formed.
A phase transition occurs in SmA such that the isotropic phase near the phase interface between SmA and the isotropic phase becomes parallel to the alignment direction of SmA near the phase interface, and as a result, as the temperature continues to decrease under the temperature gradient, SmA The monodomain region of the phase expands continuously. At this time, SmA
It is desirable that the growth rate of the phase interface between the monodomain region and the isotropic phase region is the same in the longitudinal direction of the liquid crystal cell 100 (direction of arrow C in FIG. 3A). When the temperature of the case reaches, for example, about 70° C., almost the entire area of the liquid crystal, except for the vicinity of the heating element 105, undergoes a phase transition to the SmA phase.

Next, when the current flowing through the heating element 105 is gradually lowered to eliminate the temperature gradient, the liquid crystal cell 10
The temperature at 0 is 70°C uniformly throughout, and the liquid crystal is
Phase transition to SmC ^* phase. At this time, the heating element 105
Although the molecular arrangement of the liquid crystal in the vicinity of the electrodes 102 and 102' may be in a random state, it is a uniform monodomain in the region where the electrodes 102 and 102' are formed.

Regarding the orientation direction of the liquid crystal described above, the important point is that it is desirable to provide as large a temperature gradient as possible in the B direction in FIG. 3A, but it is desirable that the temperature be uniform in the C direction. It is.
This point will be explained using FIGS. 4A to 4D. That is, in FIG. 4A, an element is formed by making the heating element 105 into a band shape, and this element is formed by the method described above.
During the temperature decreasing process due to slow cooling when forming the SmA phase,
The growth process of the SmA phase region is schematically shown.

In the figure, 201 represents the phase interface between the SmA phase region 202 and the isotropic phase region 203. Heating element 105
When the liquid crystal cell 100 is set in a case (not shown) and the liquid crystal cell 100 has a linear shape with a uniform width as shown in the figure, unless the case is specially designed, the central part D of the liquid crystal cell 100 in the longitudinal direction is Since the temperature is lower at the end E than at the phase interface 2
01 grows almost parallel to the side wall surface 104' of the nucleation member 104 near the center D, but grows at an angle at the end E as shown in the figure. The alignment state of liquid crystal molecules in the edge E region and the center D region shown in FIG.
Figures B and 4C are schematically shown.

As shown in FIG. 4B, in the region of end E.
The SmA phase 202 has a long axis direction 202' of liquid crystal molecules. As can be seen from the figure, the side wall surface 10
4' and the phase interface 201 are tilted to a greater extent than parallel (the tilt angle is θ ₁ ), the liquid crystal molecules 20
The orientation direction of 2' is not parallel to the side wall surface 104', but is inclined by an angle θ ₂ (θ ₂ ≈θ ₁ ). this is,
This is presumed to be because when the SmA phase grows near the phase interface 201, the liquid crystal molecules 202 tend to align in a direction perpendicular to the growth direction of the SmA phase. Furthermore, in a region where the tilt angle θ ₁ of the phase interface 201 changes rapidly, the liquid crystal molecules are unable to align and are separated into different domains with greatly different alignment directions, resulting in the appearance of defect lines as shown in 204. do. On the other hand, as shown in FIG. 4C, in the SmA phase 202 in the central region D, the side wall surface 104' and the phase interface 201 are parallel to each other in the liquid crystal molecule axis direction 202.
2', the liquid crystal molecules are parallel and a uniform monodomain SmA phase 202 is formed.

FIG. 4D shows the shape of the heating element 105 that has been improved in view of the above points. As shown in the figure, by narrowing the width of the heater pattern at the end of the heating element 105, the resistance value of the heating element at that end is increased, and the amount of heat generated at that end is increased. Therefore, the temperature in the longitudinal direction of the alignment cell 100 can be made uniform. For this reason,
Phase interface 201 between SmA phase 202 and isotropic phase 203
is parallel to the side wall surface 201, and a uniform monodomain is obtained as a whole.

Now, the alignment is completed through the steps described above, but even though the monodomains appear to be uniformly perfect, in reality, the electrodes 102-10
When a voltage is applied between 2' and the switching characteristics as a liquid crystal optical modulation element are investigated, non-uniformity may occur depending on the region of optical contrast or response speed. This phenomenon is thought to be due to structural distortion caused by the temperature gradient set during orientation. To deal with this, after the alignment process is completed, the temperature of the case is raised and the liquid crystal is SmC ^*
One phase transition from phase to SmA phase, and then again
Gradually lowering the temperature of the case to the SmC ^* state has the effect of eliminating the aforementioned distortion due to structural relaxation.

FIG. 5 shows another embodiment based on the present invention, in which a heating element 105' is provided on the back side of the substrate 101.
is provided separately. The heating element 105' is the liquid crystal cell 1
For example, when actually used as a liquid crystal optical modulation element, if the orientation of the liquid crystal is disturbed due to some trouble, it can be used together with the heating element 105 to perform a predetermined process. It is possible to reorient by stepping on it. Of course, this heating element 105' can also be provided on the back side of the substrate 101'. That is, the SmC ^* phase formed by the method described above is used as the heating element 105'.
is heated to cause the entire liquid crystal cell 100 to undergo a phase transition to the SmA phase, and then slowly cooled to the SmC ^* phase to form a uniform monodomain again.

The liquid crystal cell 100 shown in FIG. 6 has ITO or Ni on the outside of the substrate 101' instead of the heating element 105 described above.
-Represents a specific example in which a heating element 110 made of a Cr alloy thin film is provided. The shape of this heating element 110 is preferably the shape shown in FIG. 4D described above.

In forming the liquid crystal element of the present invention, spacers can be used to control the thickness of the liquid crystal layer to a predetermined value. FIG. 7 shows an example of the structure of a liquid crystal element of the present invention having such a spacer structure. That is, the liquid crystal element shown in FIG.
A spacer member 113 is formed between a substrate 101 having an electrode 102 having a transparent conductive pattern and a substrate 101' disposed opposite to this substrate 101, and thereby a liquid crystal disposed between the substrates 101 and 101'. The uniformity of the film thickness of 103 can be made stable. The spacer member 113 is
It is obtained by applying an electrically insulating material to a predetermined thickness on one of the substrates, and then forming it into the shape shown in the figure by photolithography.

In producing this liquid crystal element, the heating element 105 is heated in the manner described above to obtain an isotropic phase of DOBMBC with a temperature gradient, and then the temperature is lowered while maintaining the temperature gradient. and from the side wall surface 104' of the nucleation member 104.
A monodomain of the SmA phase grows toward the side wall surface 113' of the spacer 113, and furthermore, the spacer 1
The other side wall surface 113'' of No. 13 can have a liquid crystal nucleation effect similarly to the aforementioned side wall surface 104', and therefore SmA can be similarly generated from this side wall surface 113''.
monodomain grows. This spacer 113
can be made in a plurality of belt-shaped pieces at the same time during a photolithography process using the same material as the nucleation member 104 described above.

8 to 10 show examples of driving the liquid crystal element of the present invention.

FIG. 8 is a schematic diagram of a cell 41 having a matrix electrode structure in which a ferroelectric liquid crystal compound is sandwiched between. 42 is a scanning electrode group, and 43 is a signal electrode group. FIGS. 9a and 9b show the electrical signals applied to the selected scan electrode 42(s) and the other scan electrodes (unselected scan electrodes) 42, respectively.
(n), and FIGS. 9c and 9d show the electrical signals applied to the selected signal electrode 43(s) and the unselected signal electrode 43, respectively.
(n) represents an electrical signal given to Figure 9a
-d, the horizontal axis represents time and the vertical axis represents voltage. For example, when displaying a moving image, the scanning electrode groups 42 are sequentially and periodically selected. Now, if the threshold voltage is Vth ₁ to provide the first stable state of the liquid crystal cell having bistability, and the threshold voltage is -Vth ₂ to provide the second stable state, then the selected scanning electrode 42 ( The electrical signal applied to s) is an alternating voltage such that it is V at phase (time) t ₁ and -V at phase (time) t _2, as shown in FIG. 9a. Further, the other scanning electrodes 42(n) are in a grounded state as shown in FIG. 9b, and have an electrical signal O. on the other hand,
The electrical signal given to the selected signal electrode 43(s) is V as shown in FIG. 9c, and the electrical signal given to the unselected signal electrode 43(n) is V as shown in FIG. 9d. -V. In the above, the voltage V is set to a desired value that satisfies V<Vth ₁ <2V and -V>-Vth ₂ >-2V. FIG. 10 shows the voltage waveform applied to each pixel when such an electric signal is applied. 10a to 10d correspond to pixels A, B, C, and D in FIG. 8, respectively. In other words, as is clear from Figure 10,
A voltage of 2V exceeding the threshold value _Vth1 is applied to the pixel A on the selected scanning line at phase _t2 . Further, to the pixel B existing on the same scanning line, a voltage of -2V exceeding the threshold value _-Vth2 is applied at phase _t1 . Therefore,
Depending on whether or not a signal electrode is selected on the selected scanning electrode line, if selected, the liquid crystal molecules are aligned in the first stable state, and if not selected, the liquid crystal molecules are aligned in the second stable state. Align the orientation. In any case, it has nothing to do with the previous history of each pixel.

On the other hand, as shown in pixels C and D, on unselected scanning lines, the voltages applied to all pixels C and D are +V or -V, neither of which exceeds the threshold voltage. Therefore, the liquid crystal molecules in each pixel C and D maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state. That is, when a scanning electrode is selected, signals for one line are written, and from the end of one frame until the next selection,
This means that the signal state can be maintained. Therefore,
Even if the number of scanning electrodes increases, the actual duty ratio remains the same, and there is no reduction in contrast or crosstalk. At this time, the value of the voltage value V and the value of the phase (t ₁ + t ₂ )=T depend on the liquid crystal material used and the thickness of the cell, but are usually 3 volts to 70 volts.
A range of 0.1 μsec to 2 msec in volts is used.
Therefore, in this case, the electrical signal applied to the selected scanning electrode changes from the first stable state (assumed to be in the "bright" state when converted to an optical signal) to the second stable state (assumed to be a "bright" state when converted to an optical signal). The change can occur either to the "dark" state when the dark state is reached or vice versa.

[Brief explanation of drawings]

1 and 2 are perspective views showing a liquid crystal cell used in the present invention. FIG. 3A is a plan view of a liquid crystal element used in the present invention, and FIG. 3B is a plan view of the liquid crystal element used in the present invention.
It is an A′ cross-sectional view. FIG. 4A, FIG. 4B, and FIG. 4C are plan views schematically showing the growth process of liquid crystal. FIG. 4D is a plan view showing another embodiment of the liquid crystal cell used in the present invention. FIG. 5, FIG. 6, and FIG. 7 are cross-sectional views showing preferred embodiments of the liquid crystal cell of the present invention. FIG. 8 is a plan view schematically showing the electrode structure of the optical modulation element used in the present invention. FIGS. 9a to 9d are explanatory diagrams showing signals for driving the optical modulation element of the present invention. FIGS. 10a to 10d are explanatory diagrams showing voltage waveforms applied to each pixel. 100; liquid crystal cell, 101, 101'; substrate,
102, 102′; electrode, 103; liquid crystal layer, 10
4; nucleation member, 104'; side wall surface of nucleation member,
105, 105', 110; heating element, 106; adhesive, 107, 107', 107''; lead wire, 1
08, 108';polarizer;109; surface of substrate 101; 112; insulating film; 113; spacer member.

Claims (1)

[Claims] 1. A liquid crystal that produces a uniaxially anisotropic phase and a nucleation member are arranged between a pair of substrates, and the amount of heat generated near the end in the longitudinal direction of a band-shaped heating element placed at a distance from the nucleation member is calculated from the center of the nucleation member. By setting the calorific value to be larger than that near the nucleation member, a temperature gradient is formed that increases the temperature from the nucleation member to the band-shaped heating element, and the uniaxially anisotropic phase and another phase on the higher temperature side than the nucleation member are formed. A method for controlling the alignment of a chiral smect liquid crystal, comprising lowering the temperature of the liquid crystal while maintaining the temperature gradient so that the phase interface is parallel to a nucleation member.