JPH0478970B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to a liquid crystal device using chiral smectic liquid crystal, which is a ferroelectric liquid crystal. [Prior Art] Recently, ferroelectric liquid crystals are often used in liquid crystal display elements, liquid crystal light shutters, and the like. This liquid crystal exhibits a first optically stable state and a second optically stable state in response to an electric field.
It has a bistable state consisting of an optically stable state of The liquid crystal is aligned in a stable state, and the liquid crystal is aligned in a second optically stable state with respect to the other electric field vector. In addition, this type of liquid crystal very quickly takes one of the two stable states mentioned above in response to an applied electric field.
In addition, it has the property of maintaining that state when no electric field is applied. [Problems to be solved by the invention] The chiral smectic liquid crystal molecules constituting the ferroelectric liquid crystal have a uniform monodomain layer structure, but the monodomain nature of this layer structure makes it difficult for external shock to occur. Another problem was that the cell itself collapsed due to the bending caused by the force, and it was difficult to restore the collapsed monodomain layer structure to a uniform monodomain structure. In particular, the U.S. patent published by Clark et al.
According to Publication No. 4367924, in order to exhibit bistability that produces a first stable orientation state and a second stable orientation state, the film thickness of the chiral smectic liquid crystal must be made thin enough to eliminate the helical structure. Thickness (approximately 1~5μ
m), and in the case of large display panels (diagonal size: 15 cm or more), it is necessary to form the above-mentioned thin chiral smect liquid crystal in a uniform thin film over the front panel. In large display panels using chiral smectic liquid crystals, the glass substrates that make up the cells are thin (generally less than 2 mm). The liquid crystal cell injected with the above-mentioned chiral smectic liquid crystal must be electrically connected, for example, to the electrodes provided on the liquid crystal cell and the external circuit before being applied to the display surfaces of word processors, personal computers, TVs, etc. In order to connect to
The TAB (Tape Automated Bonding) method is used, and it also goes through many processes such as quality control. During handling operations during these steps, the liquid crystal cell was bent, and alignment defects appeared to be caused by displacement due to this bending. In particular, in chiral smectic liquid crystal cells using rectangular glass or plastic substrates, displacement due to bending occurs in the longitudinal direction of the rectangle, making it difficult to form a uniform monodomain layer structure. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a chiral smectic liquid crystal device that solves the above-mentioned problems. [Means for Solving the Problems] The present invention provides for the uniaxial alignment treatment to be performed between a pair of rectangular substrates whose facing surfaces are rectangular and face each other, and at least one of which is provided with a uniaxial alignment treatment axis. In a liquid crystal element in which a chiral smectic liquid crystal is arranged to form a layered structure of liquid crystal molecules oriented according _to In the liquid crystal element, the angle θ _A between the normal line of the layer structure and the transverse axis of the rectangular substrate has a relationship of 0≦θ _A <θ _a with the angle θ _a . There are characteristics. [Function] Through experiments conducted by the present inventors, it was found that when an external force is applied to a liquid crystal cell filled with chiral smectic liquid crystal in a direction perpendicular to the display surface of the cell, the above-mentioned disturbance of the alignment state becomes chiral. It has been found through microscopic observation that the defect appears as an elongated needle-like defect in the direction perpendicular to the vertical molecular layer of the smectic liquid crystal, and is difficult to appear in the normal direction to the vertical molecular layer. [Example] FIG. 1 is a plan view of a liquid crystal element of the present invention.
In the figure, 11 is the upper rectangular substrate (glass substrate,
12 is the lower rectangular substrate (glass substrate, plastic substrate), 13 is the substrate 1
The normal to the chiral smectic liquid crystal molecular layer (referred to as the vertical molecular layer) is perpendicular to 1 and 12, 14 is an axis parallel to the short direction of the upper rectangular substrate, and 15 is the diagonal of the upper rectangular substrate. ing. Angle θ _a
represents the angle formed between the axis 14 parallel to the transverse direction and the diagonal 15, and the angle θ _A represents the angle formed between the axis 14 parallel to the transverse direction and the normal 13 of the vertical layer. This angle θ _A has a relationship of 0≦θ _A <θ _a , and preferably has a relationship of 0≦θ _A ≦1/2θ _a . In particular, when the angle θ _A exceeds the angle 1/2 θ _a , the risk of occurrence of the above-mentioned alignment defect increases as the angle increases. The normal 13 of the vertical molecular layer is the upper rectangular substrate 1
It is parallel to the uniaxial orientation treatment axis given to 1, for example, the rubbing treatment axis, the oblique vapor deposition treatment axis, and the oblique etching treatment axis. Figure 2 shows the chiral smectic C phase (SmC ^*
This figure shows the orientation state of ferroelectric liquid crystal molecules in phase), where 21 is an oriented liquid crystal molecule, and 13 is
The normal of the molecular layer 22 perpendicular to the substrate of SmC ^* ,
23 is an axis perpendicular to the normal line 13. Now, if a force is applied to the substrate from a direction perpendicular to the plane of the paper in FIG. 2 and the substrate is bent, the orientation order of the liquid crystal molecules 21 will be
3 is parallel to the lateral direction of the substrate 11, it acts on the axis 23 like a nematic liquid crystal, and the liquid crystal molecules 21 act against the force acting on the axis 23.
exhibits flexible movement and is less prone to orientation defects.
On the other hand, since the liquid crystal molecules 21 have a crystalline structure with respect to the normal line 13, the force in the direction of the normal line 13 destroys the structure of the vertical molecular layer 22, and the normal line of the vertical molecular layer 22 It is thought that elongated needle-like defects along the direction perpendicular to the above-mentioned phenomenon appear. Therefore, when a large rectangular panel is deflected during handling, a large force will be applied in the direction of the axis 23. However, in the present invention, when the normal line 13 of the vertical molecular layer 22 is , is perpendicular to the above-mentioned axis 23, so that alignment defects caused by bending can be prevented. Also, the size of the rectangular plate to which a large force is applied to the shaft 23 is as follows:
When the length in the longitudinal direction is L and the length in the transverse direction is S, S/L≦5/6, especially 1/6≦S/L≦
It turned out to be the case in 5/6. Also, at this time, the size of the diagonal line 15 of the rectangular substrate 11 is 15 in the case of a glass substrate whose wall thickness is 2 mm or less.
cm or more, alignment defects caused by deflection are likely to occur. FIGS. 3a and 3b are cross-sectional views showing embodiments of the liquid crystal element of the present invention, respectively. The liquid crystal element shown in FIG. 3a includes a pair of upper rectangular substrates 31a and lower rectangular substrates 31b arranged in parallel, and transparent electrodes 32a and 32b wired to each substrate. Between the upper substrate 31a and the lower substrate 31b is a ferroelectric liquid crystal, preferably a non-helical ferroelectric liquid crystal 33 having at least two stable states.
is located. The transparent electrodes 32a and 32b described above are used to multiplex drive the ferroelectric liquid crystal 33.
It is preferable that the wires are wired in a stripe shape, and the stripe shapes are arranged to intersect with each other. In the liquid crystal element shown in FIG. 3a, the substrates 31a and 3
Orientation control films 34a and 34b are arranged at 1b. Further, one of the alignment control films 34a and 34b used in the liquid crystal element shown in FIG. 3a can be omitted. In the present invention, the above-mentioned alignment control films 34a and 34
b can be given a uniaxial orientation axis. This uniaxial orientation axis can be imparted preferably by a rubbing treatment. At this time, the aforementioned uniaxial orientation axes can be parallel to each other, but they can also be alternated. At this time, the alignment control film 34a that can be used
As the and 34b, a polyimide film, a polyamide film, a polyvinyl alcohol film, a polyethylene oxide film, a polyethylene film, a cellulose resin film, etc. can be used. In another preferred embodiment of the invention, SiO or SiO ₂
The rectangular substrates 11a and 11 are made of inorganic insulating materials such as
By forming a film on b by an oblique vapor deposition method, an orientation control film imparted with a uniaxial orientation processing axis can be obtained. In the apparatus shown in FIG.
1 is placed on an insulating substrate 403 having a suction port 405, and the bell jar 401 is evacuated by a vacuum pump (not shown) extending from the suction port 405. A crucible 407 made of tungsten or molybdenum is placed inside and at the bottom of the bell jar 401, and the crucible 407 contains several grams of
A crystal 408 of SiO, SiO ₂ , MgF ₂ or the like is placed. The crucible 407 has two lower arms 407
a, 407b, and each arm has a conducting wire 40
Connected to 9,410. The power supply 406 and the switch 404 are connected to the external conductor 409 of the bell gear 401,
410 are connected in series. Substrate 402 is positioned inside bell gear 401 directly above crucible 407 at an angle K to the vertical axis of bell gear 401 . When the switch 404 is opened, the bell gear 4
01 is first evacuated to approximately 10 ^-5 mmHg, then switch 404 is closed and power source 4 is turned on until crucible 407 becomes incandescent at a suitable temperature and crystal 408 evaporates.
Power is supplied by adjusting 06. The current required for the appropriate temperature range (700-1000℃) is approximately 100amps
It is. The crystal 408 is then evaporated to form an upward molecular stream indicated by S in the figure, and the fluid S is directed toward the substrate 4.
02 onto the substrate 402, resulting in coating of the substrate 402. The angle K is the above-mentioned "incident angle", and the direction of the fluid S is the above-mentioned "oblique deposition direction". The thickness of this coating is determined by a time-to-thickness calibration of the apparatus prior to inserting the substrate 402 into the bell gear 401. When a coating of appropriate thickness is formed, the power from power source 406 is reduced and switch 404 is opened to cool bell jar 401 and its interior. Next, the pressure is increased to atmospheric pressure and the substrate 4
02 from the bell jar 401. By adjusting the angle K corresponding to the above-mentioned incident angle, it is possible to obtain an inclined alignment state in which liquid crystal molecules adjacent to the substrate subjected to the oblique vapor deposition treatment are aligned at an inclination angle (pre-tilt angle), The orientation state can be such that the orientation is substantially parallel to the orientation. In another specific example, after forming a film of the above-mentioned inorganic insulating material or organic insulating material on the surface of the substrate 11a or the substrate 11b made of glass or plastic, the surface of the film is etched by an oblique etching method. Accordingly, an orientation control effect can be imparted to the surface. The above-mentioned alignment control film preferably functions as an insulating film at the same time, and for this purpose, the thickness of this alignment control film is generally 100 Å to 1 μ, preferably 500 Å to 1 μm.
It can be set in the range of Å to 5000 Å. This insulating film also has the advantage of being able to prevent the generation of current caused by trace amounts of impurities contained in the liquid crystal layer, and therefore does not deteriorate the liquid crystal compound even if the operation is repeated. FIG. 5 schematically depicts an example of a cell for explaining the operation of the ferroelectric liquid crystal of the present invention.
Hereinafter, explanation will be given using SmC ^* as an example of the desired layer. 51a and 51b are IN ₂ O ₃ or ITO
It is a substrate (glass plate) coated with a transparent electrode made of a thin film such as (Indium-Tin Oxide), and a SmC ^* phase liquid crystal with vertical molecular layers 52 oriented on the glass surface is sealed between the substrates (glass plates). A thick line 53 represents liquid crystal molecules, and the liquid crystal molecules 53 continuously form a helical structure in the plane direction of the substrate, and the vertical molecular layer 52 is uniformly aligned along the normal line 55. , forming a monodomain. This liquid crystal molecule 53 has a dipole moment (P⊥) 54 in a direction perpendicular to the molecule.
When a voltage higher than a certain threshold is applied between the electrodes on the substrates 51a and 51b, the helical structure of the liquid crystal molecules 53 is unraveled so that all the dipoles are oriented in the direction of the electric field.
Liquid crystal molecules 53 can change direction. The liquid crystal molecules 53 have an elongated shape and exhibit refractive index anisotropy in the major and minor axis directions. Therefore, if crossed Nicol polarizers are placed above and below the glass surface, voltage can be applied. It is easily understood that the liquid crystal optical element is a liquid crystal optical element whose optical properties change depending on the polarity. The liquid crystal cell preferably used in the liquid crystal element of the present invention can be, for example, 10 μm or less. As the liquid crystal layer becomes thinner in this way, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure even when no electric field is applied, as shown in FIG.
or downward 64b. Even in this case, the vertical molecular layer 52 is uniformly oriented along its Y normal 55, forming a monodomain. When an electric field Ea or Eb of different polarity above a certain threshold value is applied to such a cell by voltage applying means 61a and 61b as shown in FIG. 6, the dipole moment corresponds to the electric field vector of the electric field Ea or Eb. The liquid crystal molecules change direction to upward direction 64a or downward direction 64b, and accordingly the liquid crystal molecules have one stable orientation 64a.
3a or another stable orientation 63b. As mentioned earlier, there are two advantages to using such ferroelectricity as a liquid crystal optical element. The first is that the response speed is extremely fast, and the second is that the alignment of liquid crystal molecules has bistability. The second point will be further explained with reference to FIG. 6, for example. When the electric field Ea is applied, the liquid crystal molecules are aligned in one stable orientation 63a, and this state remains stable even when the electric field is turned off. Also, the electric field in the opposite direction
When Eb is applied, the liquid crystal molecules change to other stable orientations 63
The molecules change their orientation by aligning to b, but they remain in this state even when the electric field is turned off. In order to effectively realize such fast response speed and bistability, it is preferable that the cell thickness be as thin as possible. Example 1 Two glass substrates with a substrate size of 200 mm (longitudinal direction) x 70 mm (lateral direction) x 1.1 mm (thickness) were prepared. 1000Å thick on each glass substrate
A SiO ₂ film was formed by sputtering, a 500 Å thick polyvinyl alcohol film was formed on top of the SiO 2 film, and then the surface was rubbed in one direction with an acetate cloth. The rubbing axis at this time is the angle θ _A = 0
It was set parallel to the transverse direction corresponding to . Next, on one glass substrate, the average grain size was 1.2 μm.
After scattering silica beads, the other glass substrate was placed on top of the other glass substrate, and the surrounding area was sealed with epoxy adhesive. In the cell created in this way, CS− under the isotropic phase
1013 (Chiral Smectic C liquid crystal manufactured by Chitso Corporation)
was injected and then slowly cooled (0.5°C/hour) to create a chiral smectic liquid crystal cell. In addition, the phase transition point of "CS-1013" manufactured by Chitsuso is
It was as follows. SmC ^* 62.9℃ ---→ SmA (Smectic A) 70.2℃ ---→ Ch (Cholesteric) 80.2℃ ---→ Is _p (Isotropic phase) Furthermore, as another sample, the above-mentioned chiral smectic liquid crystal The angle θ _A when the cell was created is
10°, 30°, 60°, 75° (outside the invention) and 80° (outside the invention)
A sample of a chiral smectic liquid crystal cell was prepared using exactly the same method, except that . When we observed the initial orientation states of these five types of samples using a polarizing microscope, we found that the normal to the vertical molecular layer was along the rubbing direction, and that they were uniform monodomains with no orientation defects. It has been found. After that, connect the terminals of the flexible board connected to the drive IC to the sample cell mentioned above (400 electrodes are provided in the vertical direction and 800 electrodes are provided in the horizontal direction).
The terminals were electrically connected using an anisotropic conductive adhesive, ``Anisolm AC5052'' (trade name) manufactured by Hitachi Chemical, and then lifted by hand for an external inspection. The orientation state of the sample was observed using a polarizing microscope.The results are shown below.

[Table] A defect had occurred.
Furthermore, sample cells 5 and 6 were subjected to reorientation treatment. That is, cells 5 and 6 are included in the sample.
After heating SmC ^* until it became an isotropic phase and slowly cooling it to SmC ^* (0.5°C/hour), observation using a polarizing microscope was performed, but orientation defects still occurred. Also, the connection between the sample cell and the flexible board mentioned above.
The TAB method was used to obtain the same results as described above, and in addition, it was possible to directly drive the sample cell as described above.
Similar results were obtained when an IC was provided. (Effects of the Invention) According to the present invention, in the process of incorporating a large rectangular panel as a display medium in a word processor, personal computer, TV, etc., bending of the panel that occurs when handling the large panel can be avoided. Orientation defects can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the liquid crystal element of the present invention.
FIG. 2 is a plan view schematically showing the molecular orientation state of the liquid crystal element of the present invention. Figure 3a and Figure 3b
1 is a cross-sectional view of a liquid crystal element of the present invention. FIG. 4 is a schematic diagram of the oblique evaporation apparatus used in the present invention. 5 and 6 are perspective views schematically showing the chiral smectic liquid crystal used in the present invention.

Claims (1)

[Scope of Claims] 1. A pair of rectangular substrates whose facing surfaces are rectangular and face each other, and at least one of which is provided with a uniaxial alignment treatment axis, between which liquid crystal molecules are aligned according to the uniaxial alignment treatment. In a liquid crystal element in which chiral smectic liquid crystals are _arranged with a layered structure organized in A liquid crystal element characterized in that an angle θ _A between a line and an axis in a transverse direction of the rectangular substrate has a relationship of 0≦θ _A <θ _a with the angle θ _a . 2. The liquid crystal element according to claim 1, wherein the length L in the longitudinal direction and the length S in the lateral direction of the rectangular substrate have a relationship of S/L≦5/6. 3. The liquid crystal element according to claim 1, wherein the length L in the longitudinal direction and the length S in the lateral direction of the rectangular substrate have a relationship of 1/6≦S/L≦5/6. . 4. The liquid crystal element according to claim 1, comprising a connection structure in which a drive circuit and an electrode formed on a rectangular substrate are electrically connected by the TAB method.