JPS62141517A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain the titled element having a complete ON-OFF operation of the liquid crystal by comprising plural transparent electrode segments between parallel substrates, and by inserting a flat film composed of an insulating film between adjacent transparent electrode segments. CONSTITUTION:The titled element 30 comprises the substrates 31 and 32 made of the transparent plate such as a glass plate or a plastic plate etc. The ferroelectric liquid crystal 33 is inserted between said substrates. The transparent electrode segments 34 and 35 which have a stripe shape and are composed of the matrix electrode structure are provided with each substrates 31 and 32 respectively. The flated film 38 composed of the insulating film is imposed between the adjacent stripe shaped transparent electrode segments 34a and 34b in the substrate 31. The flated film composed of said insulating film is imposed between the adjacent stripe shaped transparent electrode segments 35 in the substrate 32.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal display device such as a liquid crystal optical shutter array, and more particularly, to a method for improving the initial alignment state of liquid crystal molecules. This invention relates to a liquid crystal element with improved display and driving characteristics.

[Conventional technology]

As a conventional liquid crystal element, for example, M-Shut (M,
8chadt) and double knee, hell 7ritto ('if,
H.1frich) "IF" Ryo Bride Physics Letters Goliame 18, Number 4 (197
1゜2.15), pages 127-128 (“Muppli
・dPhysics Lett@rs' To, 18
．． 44 (1971, 2°15)? , 127-128) 1 voltage dependent 1st tical activity.

DepeM@ntOp
Laalmu atlvity of a TwistM
Nemati.

Liquil Crysta1'') K shown tee,
znu ('rN) (twisted nematic (twi)
ateLnematta)) Those using liquid crystal are known.

TN liquid crystals have problems such as rounding, which can cause crosstalk when time-division driving is performed using a matrix electrode structure with high pixel density, and the number of pixels is limited.

Furthermore, a display element is known in which a switching element using a thin film transistor is connected to each pixel, and each pixel is switched. However, the process of forming the thin film transistor on the substrate is extremely complicated, and it is difficult to use a display element with a large area. There are some problems that make it difficult to create.

In order to solve these problems, a ferroelectric liquid crystal device was disclosed by Clark et al. in US Pat. No. 4,340,7924. However, in order for this ferroelectric liquid crystal element to exhibit predetermined driving characteristics, the ferroelectric liquid crystal placed between a pair of parallel substrates must be placed between a pair of parallel substrates, regardless of the state of application of an electric field.

It is necessary that the molecules be in such a state that conversion between the above two stable states occurs effectively.

For example, in a ferroelectric liquid crystal having a chiral smectic phase, the liquid crystal molecular layer of the chiral smectic phase is perpendicular to the substrate surface, and therefore the liquid crystal molecular axes are aligned approximately 1,000 times along the substrate surface, forming nine domains (monodomains). need to be done.

[Problem that the invention seeks to solve]

However, in the conventional ferroelectric liquid crystal elements, the alignment state of the liquid crystal having such a monodomain structure was not always formed satisfactorily, so that sufficient characteristics could not be obtained.

! #, when the matrix electrodes formed on the substrate are wired with high density as described below, the resistance of the electrode wires is reduced and the IC
, [Polar lines are relatively thick (e.g. 5ooX to soooX)
Since the thickness is IIg, there is a gap between the surface of the substrate itself and the electrode surface.
It has become clear through experiments by Akira Moto that a large step larger than 00 is formed, and that this step is the cause of alignment defects in the ferroelectric liquid crystal.

[Means for Solving the Problems] and [Operation] Accordingly, an object of the present invention is to provide a ferroelectric liquid crystal element in which the occurrence of alignment defects is prevented.

Another object of the present invention is to provide a liquid crystal device with high chirality by forming pixels at high density.

Furthermore, another object of the present invention has hitherto been a problem in ferroelectric liquid crystal devices. By improving the monodomain formation property or the initial phase orientation, the T4 dielectric liquid and crystal can exhibit the high-speed response and mesori effect characteristics inherent in the ferroelectric liquid crystal element. The purpose is to provide devices.

As a result of further research for the above-mentioned purpose, the present inventors found that the liquid crystal phase (low temperature state tl!4
), it is possible to provide a liquid crystal element having a structure that can achieve both the operating characteristics of an element based on a bistable IC and the monodomain property of a liquid crystal layer. became. That is, the liquid crystal element of the present invention is based on such knowledge, and more specifically, there is no step on the surface in contact with the liquid crystal layer, and the liquid crystal element of the present invention does not cause a sudden change in the thickness of the liquid crystal layer. If it is eliminated, the initial orientation during the leakage process will be in good condition.
It is characterized by the formation of domains without orientation defects.

Therefore, the present invention provides a liquid crystal element having a ferroelectric liquid crystal between a pair of parallel substrates, in which at least one of the pair of parallel substrates has a plurality of transparent electrode segments, and the adjacent transparent The liquid crystal element is characterized by having a flattening film formed of an insulating film between electrode segments.

In this way, the liquid crystal layer sandwiched between substrates with good planarity is gradually cooled (0.1°C/hour to 5°C/hour) during the transition period from the uniform phase to the liquid crystal phase. , the liquid crystal phase region gradually expands to form a monodomain liquid crystal phase.

〔Example〕

For example, DOBA shown below exhibits a ferroelectric liquid crystal phase as a liquid crystal.
Taking MBO as an example, when slowly cooling the DOBAMBO phase, it undergoes a phase transition to a smectic human phase (8 mA phase) at about 115°C. At this time, the substrate is rubbed or 810. When alignment treatment such as oblique vapor deposition is performed, monodomains are formed in which the molecular axes of liquid crystal molecules are parallel to the substrate and aligned in one direction. When the cooling is further progressed, a phase transition occurs to a chiral smectic C phase (8 mO' phase) at a specific temperature between about 90 and 75° C., which depends on the thickness of the liquid crystal layer. Further, when the thickness of the liquid crystal layer is about 2 μm or less, the helix of the 8 mO' phase is unraveled and exhibits bistability.

A particularly suitable liquid crystal material for use in the present invention is a liquid crystal having bistability and ferroelectricity, specifically, the above-mentioned 8mC! 'In addition to chiral smectic H phase (8 mH"),
Town, K phase (8mK”), G phase (8mG*) or ? phase (8
mF") liquid crystal can be used.

For more information on ferroelectric liquid crystals, see, for example, Le Gernard de Fissique L'Etre (L!Ii, TOUR
NAL DI P)IY81Q,UICLITTffi
R) 36 (L-69) 1975. r Ferroelectric Liquid Crystals J (Farr
oelectric Liked 0ryatalsJ
) ; “Applied Physics Letters (
”Applied Physics Letter”
) 315 (11), 1980 r Zabumiku O, Second Bistiple Electro-Optic Switching in Liquid Crysta A/SJ (Snb
micro 8eaond B15table n1e
at-rooptic Switching Li
Quii Crystals J); “Solid State Physics”
16 (141) 1981 "Liquid Crystal" etc.
In the present invention, the ferroelectric liquid crystal disclosed in these documents can be used.

Specific examples of ferroelectric liquid crystal compounds include decyloxybenzylidene-y-minor 2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-y-
y-amino-2-chloroprovir cinname) (HO
BACPC, 4-O-(2-methyl)-butyl resol cylidene-4'-octylaniline (MBRA 8'
).

When constructing an element using these materials, the element can be supported by a block with a heater embedded, etc., if necessary, in order to maintain the temperature at which the liquid crystal compound enters the chiral smectate phase. .

The present invention will be explained below with reference to the drawings.

Figure 1 shows a cross-sectional view of a conventional ferroelectric liquid crystal element.
Figure g2 is a diagram showing the state of alignment defects that appear in a conventional ferroelectric liquid crystal element.

That is, the conventional ferroelectric liquid crystal device 10 shown in FIG. 1 has a pair of parallel substrates 11 and 12, and each of the substrates 11 and 12 has strip-shaped transparent electrode segments forming a matrix electrode structure. 13 and 14 are provided.

These striped transparent electrode segments 13 and 14 are
Generally used (Indium Tin Oxide)
For example, when wiring electrode wires at 16 Pe/(16 wires/mm), the line width of the electrode wires becomes extremely thin and the resistance becomes high.
Thicker than the segment electrodes used in regular calculators and watches, specifically 800X~! l O00
It is necessary to set it to about X, preferably 10G0Å to 1sooX, in order to lower the resistance.

Therefore, in a liquid crystal device with high-density pixels, the thickness of the transparent electrode segment between the substrate surface and the electrode surface (aooX~5
When a step gap (oOar) is formed and orientation control is performed using temperature cooling, the above-mentioned difference gap becomes the cause.
This causes alignment defects in the ferroelectric liquid crystal 17 due to the unevenness. Furthermore, if the alignment control films 15 and 16 are provided on the substrates 11 and 12, respectively, where the step exists,
Also in the alignment control film of the ferroelectric liquid crystal 1, a step B formed in accordance with the step difference occurs almost outside the film thickness of the electrode.
7iC orientation defects were produced.

Figure 2 is a sketch of the ferroelectric liquid crystal element shown in the comparative example below when observed with a crossed Nicol (one-source microscope). ), and @22 is the step BK on the substrate 11 in FIG.

Line 23 is observed corresponding to step B on substrate 12 in FIG. Also, the portion 24 in Figure 1 is 111 between the opposing electrodes.
! It is a rare ferroelectric liquid crystal. A large number of edge-like lines 25 appearing in the polarizing microscope represent alignment defects of the strongly electrostatic liquid crystal.

If a step of 8ooX or more exists on the surface in contact with the ferroelectric liquid crystal as described above, alignment defects will occur from the step and the formation of monodomains of the ferroelectric liquid crystal will be inhibited.

FIG. 3 is a cross-sectional view of a preferred ferroelectric liquid crystal element of the present invention.

The device 30 shown in FIG. 3 has substrates 31 and 32 made of transparent plates such as glass plates or plastic plates, and a ferroelectric liquid crystal 33 is sandwiched between them. Each board 31 and 3
28C, stripe-shaped transparent electrode segments 34 and 35 forming a matrix electrode structure are wired, respectively.

A flattening film 38 made of an insulating film is disposed on the substrate 31 between adjacent striped transparent electrode segments 34a and sab. A flattening film (not shown) made of the same insulating film as described above can also be provided between adjacent strip-shaped transparent electrode segments 350 on the substrate 32.

The above-mentioned leveled membrane water 8 can be prepared as follows.゛ ′ □ ″First, a CZTO film was formed on the glass plate or Plastyref film, which will become the substrate s1, by a metal puttering deposition method or an ion plating deposition method.
A metal film such as an iK chromium film is formed □ to a thickness approximately 3 to 5 times that of ZTO@, and then a patterned fTo film as shown in M4 (a) K is formed by ordinary photolithography and etching techniques. 34 and a metal film 41 are formed.

Next, on the substrate 31 on which the patterned KTO film 34 shown in FIG.
0@, Ti01, ra! oI, gro,
+A/! A vapor deposited layer 42 of a solid insulating material such as O@ is formed to have a thickness similar to that of the ZTOIj 134 described above, and then the gold JI1@41 is etched as shown in FIG. [The evaporated layer 42m of an inorganic insulating material which has been formed in contact is removed at the same time, and the evaporated R film 42a of a non-contacted insulating material, which becomes the flattened film 38, is brought together.
It is formed during S4.

In the liquid crystal element of the present invention, the thickness of the transparent electrode segment 34 (tlA) and the thickness of the flattening film 380 formed of an insulating film (
tta) 1500mm≦11-1. It is necessary to satisfy the relationship of ≦50 OA, preferably 1300 MB,
, =-tj≦300; That is, according to the findings of the present inventors, when the ferroelectric liquid crystal 33 in the device comes into contact with the substrate 31 or 32, if the step difference generated on the substrate 31 or 32 is 500A or less, an alignment defect as shown in the M2 diagram occurs. The occurrence of this can be suppressed to within a reasonable range. Therefore, in the present invention, 1 m-1 is -5ooX~5
The second feature is that it is set to ooX, preferably -3ooX to 300X.

When the values of 1t, -t, and 1 exceed 5ooX, a large number of orientation defects as shown in FIG. 2 occur as shown in the comparative example below, and the monodomain 8mO* is not formed.

Although it can be obtained by forming a film by a rating vapor deposition method, a vapor deposited film formed by covering an organic insulating material by a vapor deposition method can also be used. Polyfluorinated olefins such as poly7tethylene are suitable as organic insulating materials that can be used in this method.

In the liquid crystal element of the present invention, it is preferable that an alignment control film 36 is provided on the transparent electrode segment 34 and the planarization film 38. Further, the alignment control film 3 is similarly formed on the other substrate 32 side.
7, but the orientation control @h156 and 37
It is also possible to omit one of the alignment control films.

#, when the ferroelectric liquid crystal 33 is a chiral smectic liquid crystal having at least two stable orientation states, especially a bistable chiral smectic liquid crystal, the first stable orientation state and the second stable orientation state
Equalize the stabilization energies of the stable orientation states (first
In order to reduce the difference between the threshold voltage of the stable orientation state and the threshold voltage of the second stable orientation state, it is preferable to provide one orientation control film on only one substrate.

Materials for this orientation control@36 and 37 include, for example, polyvinyl alcohol, polyimide II, polyamideimide, polyesterimide, polyvaraxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, Resins such as cellulose resin, melamine resin, urea resin, acrylic resin, or photosensitive polyimide,
Photosensitive polyamide, weakened rubber photoresist, phenol novolak photoresist or electron beam photoresist (polymethyl methacrylate, epoxidized-1)
, 4-polybutadiene, etc.). Then, by subjecting this film to uniaxial alignment treatment such as rubbing treatment in one direction, the substrate 3
The smectic molecular layer formed perpendicular to 1 and 52 can be preferentially oriented in one direction.

FIG. 5 schematically depicts an example of a cell for explaining the operation of a ferroelectric liquid crystal. 51a and 51b are /n
, O! , SnO, or ndium-Ti
A substrate (glass plate) coated with a transparent electrode made of a thin film such as nOxle') is used, and a liquid crystal of 8 mO" phase or 8 mH' phase in which the smectic molecular layer 52 is oriented perpendicular to the glass surface is sealed between the substrates (glass plates). A thick line 53 represents a liquid crystal molecule, and this liquid crystal molecule 53 has a dipole moment (P) 54 in the optical direction perpendicular to the molecule.
have.

When a voltage higher than a certain threshold is applied between the electrodes on the substrates 51a and 511), the helical structure of the liquid crystal molecules 53 is unraveled.
The alignment direction of the liquid crystal molecules 53 can be changed so that all of the liquid crystal molecules 54 are oriented in the direction of the electric field. The liquid crystal molecules 53 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface,
It is easily understood that the electronic mark 710 is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity.

The liquid crystal cell preferably used in the liquid crystal element of the present invention can have a sufficiently thin thickness (for example, 10 μm or less). As the liquid crystal layer becomes thinner, the 6th M
As shown in Figure 3, even when no electric field is applied, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure.The dipole moment (Pa or PI) is either upward (64a) or downward (64b). take a state. Voltage applying means 61a and 61b are applied to such cells with electric fields ga or g'b having different polarities of a constant 1:threshold value or more as shown in FIG.
When the force is applied, the dipole moment changes its direction upward 64a or downward 641) in response to the electric field ga or the electric field vector of Etll, and accordingly, the liquid crystal molecules
Either the first stable state 65a or the second stable state 63
Orient in either direction of +.

As mentioned above, there are two advantages to using such triferroelectricity as a liquid crystal element. 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 point @2 using, for example, FIG. 6, the electric field 11! When a is applied, the liquid crystal molecules are oriented in a first stable state 65a, and this state remains stable even when the electric field is turned off. When an electric field ib in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 65b and change their orientation, but they remain in this state even after the spot field is turned off. Further, as long as the applied electric field E& exceeds 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.

Hereinafter, the present invention will be explained according to examples.

Example 1 On glass substrate &C, 3+1 by high frequency sputtering method
A TO film of o'aoX was deposited. After that, the same deposited film f! tK change the target ↑0 while chromium (
A chromium film of υ% 3000X was formed by vapor deposition.

Next, a positive resist ("AZ-1") was placed on this glass substrate.
370" (manufactured by Hoechat) was applied using a spinner to a film thickness of 1 μm and prebaked. On this resist layer, a mask width of 80 μm and a mask part pitch of 100 were applied.
Exposure was performed using a μm striped i-screen. Then,
Develop and wash with water to form a striped pattern mask. After post-etching, the chromium film was etched with a mixture of ceric ammonium nitrate, perchloric acid, and water, and then the XTO film was buttered by etching with a mixture of ferric chloride, hydrochloric acid, and water. .

Next, the positive type resist is peeled off to form the embodiment shown in FIG. 1ooo
Vapor deposited with a film thickness of X, 81o! A vapor-deposited film was formed (FIG. 4(b)). Thereafter, it was immersed in the same etching solution for chromium as described above, and the remaining chromium film and the slo layer on it were removed between the films, resulting in the embodiment shown in FIG. 4(c).

Further, after coating polyide ζ No. 1oooX on the ζ-sheet, rubbing treatment with a cloth was performed along the stripe longitudinal direction of the striped ZTO film that had been patterned. Next, alumina beads having a diameter of 1 μm were uniformly applied to the entire surface of this substrate to prepare an electrode plate (A) 11.

In addition, the polyimide film is made of pyromellitic dianhydride 4,4I
After applying an N-methylpyrrolidone solution of polyamic acid, which is a dehydrated condensate with -diaminodiphenyl ether, a cypolyimide compound was formed by a dehydration ring-closing reaction by heating at 180°C.

Separately, an electrode plate (B) was prepared in exactly the same manner except that the rubbing direction used when creating the AI electrode plate was set perpendicular to the stripe longitudinal direction of the striped ITO film. Spraying was omitted.

Assemble K cells with the ri+ electrode plate (so that the striped pattern electrodes of the Bl electrode plate are perpendicular (so that their rubbing directions are parallel), and apply DOBAMBO ia.

Heat it until it reaches the tropio phase and seal it in the cell. The temperature of the cell was gradually cooled (0.5° C./hour) to produce a monodomain liquid crystal device.

When this liquid crystal element was observed with a crossed Nicol polarizing microscope, it was found that there was no alignment defect of edge lines that appeared in the comparative example below.

Comparative Example 1 White 00 was deposited on a glass substrate by high frequency sputtering method.
A positive resist film similar to that in Example 1 was formed on this by vapor deposition, and the resist film was exposed using the same mask, developed, and washed with water. The To film was etched and patterned. Next, a polyimide film similar to that in Example 1 was applied to a film thickness of 1000 μm, and then subjected to a scratching process along the longitudinal direction of the patterned striped fTo film to form (C) an electrode plate. Create nine.

Separately, the rubbing direction used when creating the electrode plate (C) was changed to the WI:W direction with respect to the stripe longitudinal direction of the striped TO film, but in exactly the same manner as the above (Konden wafer plate was created).

After assembling the rat electrode plate and the C-cut electrode plate into a cell in the same manner as in Example 1, the same liquid crystal was injected in the same manner to form a liquid crystal element, and the same evaluation was performed. It was found that many alignment defects of the edge-like lines were formed as shown in the figure.

Examples 2 to 7 and Comparative Examples 2 to 5 The liquid crystal device of Example 1 was prepared in exactly the same manner as in Example 1, except that the 9810 was used and the film thickness was changed as shown in Table 1 below. A liquid crystal device was created and evaluated in the same way. The results are shown in Table 1.

Table 1 Example 2 1500 0u
5 1soo OII 4
1100 OII 5
900 ◎” 6 70
0 Qn 7 soo
O Comparative Example 2 1800
X#S 1600
Δ# 4 400 Δ#
5 200
X (In the table, ◎ indicates a state in which there are no orientation defects, O indicates a state in which a few orientation defects are observed but does not pose a practical problem, and Δ indicates a state in which an orientation defect occurs between the electrodes, which poses a practical problem. (X indicates a state in which a large number of alignment defects have occurred.) Example 8 Used when creating the liquid crystal element of Example 1 (Using the polyimide film formed on the Bl electrode plate and its rubbing treatment) A liquid crystal element was fabricated and evaluated in exactly the same manner as in 5J! Example 1, except that 5J! was omitted, and no alignment defects were observed. ) K, good bistability was observed.

〔Effect of the invention〕

According to the present invention, it has become possible to control uniform alignment over the entire surface of a strongly conductive liquid crystal element, and it has become possible to perform complete ON-OFF operation of the liquid crystal. In addition, not only the appearance was improved, but also the apparent contrast was improved compared to the conventional one with alignment defects due to steps.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional ferroelectric liquid crystal element. FIG. 2 is an explanatory diagram showing a sketch of a conventional ferroelectric liquid crystal element observed under a crossed Nicol polarization microscope. FIG. 3 is a cross-sectional view of the ferroelectric liquid crystal element of the present invention. Fourth
Figures (al to (cl) are cross-sectional views showing the process of forming the flattened film used in the present invention. Figures 5 and 6 schematically represent the ferroelectric liquid crystal element used in the present invention. It is an explanatory diagram.

Claims (10)

[Claims] (1) In a liquid crystal element having a ferroelectric liquid crystal between a pair of parallel substrates, at least one of the pair of parallel substrates has a plurality of transparent electrode segments, and between the adjacent transparent electrode segments A liquid crystal element characterized by having a flattening film formed of an insulating film. (2) If the thickness of the transparent electrode segment (t_1 Å) and the thickness of the insulating film (t_2 Å) are -500 Å≦t_
The liquid crystal element according to claim 1, which has a relationship of 1-t_2≦500 Å. (3) The film thickness (t_1 Å) of the transparent electrode segment is 8
The liquid crystal element according to claim 2, which has a thickness of 00 Å to 3000 Å. (4) The film thickness of the transparent electrode segment is 1000 Å to 1
The liquid crystal element according to claim 2, which has a thickness of 500 Å. (5) The liquid crystal element according to claim 1, wherein the insulating film is a film obtained by forming a film of an inorganic insulating material. (6) The inorganic insulating material is SiO, SiO_2, TiO
_2, Ta_2O_5, Al_2O_3 and ZrO_2
6. The liquid crystal element according to claim 5, which is at least one substance selected from the group consisting of: (7) The liquid crystal element according to claim 1, wherein the insulating film is a vapor deposited film of an inorganic insulating material. (8) The liquid crystal element according to claim 7, wherein the inorganic insulating material is SiO_2. (9) The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (10) The liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal having at least two stable orientation states.