JPH0677120B2 - Liquid crystal element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device or a liquid crystal device such as a liquid crystal-optical shutter array, and more specifically, to a display device by improving an initial alignment state of liquid crystal molecules. The present invention relates to a ferroelectric liquid crystal element whose driving characteristics are improved.

[Summary of Disclosure] The present specification and drawings show a ferroelectric liquid crystal device used in a liquid crystal display device, a liquid crystal-optical shutter array, or the like, in which a color filter of each pixel is a dye and a transparent resin, or a dye and a transparent inorganic compound. And a flattening layer made of an insulating material are formed in the depressions between the color filters so that a uniform monodomain liquid crystal phase without alignment defects can be obtained.

[Prior Art] Examples of conventional liquid crystal elements include M.Sc.
hadt) and W. Helfrich's "Applied Physics Letters"("Applied
Physics Letters ") Volume 18, Issue 4 (Published February 15, 1971), pages 127-128," Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal ". (“Volt
age Dependent Optical Activity of a Twisted Nemati
c Liquid Crystal ") is known, which uses twisted nemetic liquid crystal. This TN liquid crystal is a cross-type liquid crystal that is driven by a time division drive using a matrix electrode structure with high pixel density. The number of pixels is limited because of the problem of generating talk.

In addition, a display element of a type in which a switching element using a thin film transistor is connected to each pixel and switching is performed for each pixel is known, but a step of forming a thin film transistor on a substrate is extremely complicated, and a large area display element is used. There are problems that are difficult to create.

As a solution to these problems, Clark et al. Proposed a ferroelectric liquid crystal device in US Pat. No. 4,367,924.

FIG. 2 schematically shows an example of a cell for explaining the operation of the ferroelectric liquid crystal. 21 and 21 ′ are In ₂ O ₂ and SnO ₂
Alternatively, it is a substrate (glass plate) covered with a transparent electrode composed of a thin film of ITO (Indium-Tin-Oxide) or the like, in which the liquid crystal molecular layer 22 is oriented so that the liquid crystal molecular layer 22 is perpendicular to the glass surface ^.
Phase or SmH ^* phase liquid crystal is enclosed. Lines shown in bold
Reference numeral 23 represents a liquid crystal molecule, and the liquid crystal molecule 23 has a dipole moment (P _⊥ ) 24 in a direction orthogonal to the molecule. When a voltage above a certain threshold is applied between the electrodes on the substrates 21 and 21 ', the helical structure of the liquid crystal molecules 23 is unraveled, and the dipole moment (P _⊥ ) 24 is oriented in the direction of the electric field. You can change direction. Liquid crystal molecule 23
Has an elongated shape, and exhibits refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if crossed Nicols polarizers are placed above and below the glass surface, the optical characteristics will change depending on the voltage applied polarity. It will be easily understood that the liquid crystal optical modulation element changes.

The liquid crystal cell preferably used in the liquid crystal element of the present invention can be made sufficiently thin (for example, 10 μm or less). As shown in FIG. 3, as the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure even when no electric field is applied, and its dipole moment P or P ′ is upward ( 24) or downward (2
Either of 4 '). As shown in FIG. 3, 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 26 and 26 ', the dipole moment is the electric field vector of the electric field E or E'. The liquid crystal molecules are oriented in either the first stable state 25 or the second stable state 25 'in response to the upward 24 or downward 24'.

As described above, there are two advantages of using such ferroelectricity as a liquid crystal 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 explained with reference to FIG. 3, for example.
The stable state 25 is oriented, but this state is stable even when the electric field is cut off. When a reverse electric field E'is applied, the liquid crystal molecules are oriented in the second stable state 25 'to change the orientation of the molecules, but they remain in this state even when the electric field is cut off. Further, as long as the applied electric field E does not exceed a certain threshold value, the respective alignment states are also maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible.

[Problems to be Solved by the Invention] In order for this ferroelectric liquid crystal element to exhibit a predetermined driving characteristic, a ferroelectric liquid crystal disposed between a pair of parallel substrates must be
Regardless of the applied state of the electric field, it is necessary that the molecular arrangement is such that conversion between the two stable states described above effectively occurs. 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 thus a region (monodomain) in which the liquid crystal molecular axes are arranged substantially parallel to the substrate surface is formed. Need to However, in the conventional ferroelectric liquid crystal device, the alignment state of the liquid crystal having such a mono-domain structure was not always formed satisfactorily, and therefore, in reality, sufficient characteristics were not obtained.

FIG. 4 is a sectional view of a conventional ferroelectric liquid crystal device, and FIG. 5 is a diagram showing a state of alignment defects appearing in the conventional ferroelectric liquid crystal device.

That is, the conventional ferroelectric liquid crystal element 40 shown in FIG.
It has a pair of parallel substrates 41 and 42, and each of the substrates 41 and 42 has a striped electrode wire forming a matrix electrode structure.
43 and 44 are provided (the electrode wire 43 is provided via the protective layer 48). The color filter consists of red (R), green (G), and blue (B) dyes, but the film thickness of each dye is different regardless of its formation method.
A step A of about Å to 1 μ is formed. As a result, when the alignment control is performed by utilizing the temperature lowering process, the above-mentioned step A causes the alignment defect in the ferroelectric liquid crystal 47 with the step A as a boundary. Further, when the orientation control films 45 and 46 are respectively provided on the substrates 41 and 42 where the step A exists,
A step B formed corresponding to the step A also occurs in this orientation control film in a thickness of the pixel, and the ferroelectric liquid crystal 47 is formed in the same manner as described above.
Had an alignment defect.

FIG. 5 is a sketch of the ferroelectric liquid crystal device observed with a crossed Nicols polarization microscope. White lines 51 in the drawing correspond to the lines of the spacer (not shown) used for the liquid crystal device, and the line 52 And 53 are observed correspondingly to the step B on the substrate 41 in FIG. Further, a portion 54 in the figure is a ferroelectric liquid crystal sandwiched between opposed electrodes. A large number of blade lines 55 appearing in the polarization microscope represent alignment defects of the ferroelectric liquid crystal.

If there is a step of 1000 Å or more on the surface in contact with the ferroelectric liquid crystal as described above, an alignment defect is generated from the step and the monodomain formation of the ferroelectric liquid crystal is hindered.

The present inventors have made experiments to clarify that such a step on the substrate causes an alignment defect with respect to the ferroelectric liquid crystal.

An object of the present invention is to provide a ferroelectric liquid crystal device capable of preventing the occurrence of the above-mentioned alignment defects and sufficiently exhibiting the high-speed response and the memory effect characteristics which the ferroelectric liquid crystal device originally has. .

[Means for Solving Problems] The present inventors have paid particular attention to the initial orientation in the temperature decreasing process in which the liquid crystal transitions from the isotropic phase (high temperature state) to the liquid crystal phase (low temperature state), and the bistability of the liquid crystal is considered. A liquid crystal element having a structure capable of satisfying both the operating characteristics of the element based on the property and the monodomain property of the liquid crystal layer. 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, that is, by not causing a sudden change in the film thickness of the liquid crystal layer, It is characterized in that the initial alignment property in (3) is kept in a good state and a monodomain without alignment defects is formed.

That is, the present invention relates to a ferroelectric liquid crystal device in which a ferroelectric liquid crystal is sandwiched between a pair of parallel substrates on which transparent electrodes are formed, and a color filter is provided between at least one of the transparent electrodes and the substrate. Is formed of a dye and a transparent resin, or a dye and a transparent inorganic compound, and a protective layer is provided over the entire surface, and the dents on the protective layer generated based on the intervals between the color filter units are flattened. This is a ferroelectric liquid crystal element characterized by being provided with a color filter gap material for realizing the same.

Particularly suitable as the liquid crystal material used in the present invention is a liquid crystal having bistability, which has ferroelectricity. Specifically, a chiral smectic C phase (SmC
^* Phase), H phase (SmH ^* ), I phase (SmI ^* phase), J phase (SmJ
^* Phase), K phase (SmK ^* phase), G phase (SmG ^* phase) or F phase (SmF)
^* Phase) liquid crystal can be used.

For this ferroelectric liquid crystal, please refer to "LE JOURNAL DE PHYSIQUE L
ETTERS ") 1975, 36 (L-69)," Ferroelectric Liquid Crystals "(" Ferroelectricliq
uid Crystals ”);“ Applied physics Letters ”1980, 36 (1
1), "Sub-micro second bistable electro-optical switching in liquid
Crystals ("Submicro Second Bistable Electroop
tic Switching in Liquid Crystals ”);“ Solid physics ”1
981, 16 (141), "Liquid crystal" and the like, 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-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-p′-amino-2-chloropropylcinnamate (HOBACPC), 4 -o
-(2-Methyl) -butylresorcylidene-4'-octylaniline (MBRA8).

When an element is formed using these materials, the element is supported by a block or the like in which a heater is embedded, if necessary, because the element is held in a temperature state where the liquid crystal compound is in a chiral smectic phase.

Examples of the material of the alignment control film used in the present invention include polyvinyl alcohol, polyimide, polyamideimide, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, and urea resin. , Resins such as acrylic resin, photosensitive polyimide, photosensitive polyamide, cyclized rubber photoresist, phenol novolac photoresist or electron beam photoresist (polymethylmethacrylate, epoxidized-1,4-polybutadiene, etc.), etc. It can be selected and formed.

Examples of the dye material used in the present invention include azo-based, anthraquinone-based, phthalocyanine-based, quinacridone-based, isoindolinone-based, dioxazine-based, perylene-based, perinone-based, thioindigo-based, pyrocholine-based, fluorobin-based, and quinophthalone-based. To be

Examples of the transparent resin used in the present invention include polyparaxylylene (trade name; Parylene, Union Carbide Co.), polyethylene, polystyrene, polycarbonate and the like. As a coating method for these, a spinner coating method can be used.

The transparent inorganic compound used in the present invention includes SiO ₂ ,
_{Al 2 O 3, TiO 2,} ZrO 2, MgF 2, SiO , and the like.

The color filter gap material used in the present invention may be a mixture of the above-mentioned R, G and B dyes as an organic pigment, iron black (Fe ₃ O ₄ or FeOFe ₂ O ₃ ) as an inorganic pigment, or the like. Inorganic substances include PrMnO ₃ in addition to graphite.

[Operation] The liquid crystal layer sandwiched between the substrates having good flatness is gradually cooled in the temperature decreasing process of transitioning from the isotropic phase to the liquid crystal phase, so that the liquid crystal phase region gradually expands to form a uniform monodomain liquid crystal phase. Come to do.

For example, the above-mentioned DOBAMBC showing a ferroelectric liquid crystal phase as liquid crystal
As an example, when gradually cooling from the isobaric phase of DOBAMBC, it undergoes a phase transition to a smectic A phase (SmA phase) at about 115 ° C. At this time, if the substrate is subjected to an alignment treatment such as rubbing or SiO ₂ oblique vapor deposition, a monodomain in which the molecular axes of liquid crystal molecules are parallel to the substrate and aligned in one direction is formed. Further, as the cooling proceeds, the phase transitions to the chiral smectic C phase (SmC ^* phase) at a specific temperature of about 90 to 75 ° C. depending on the thickness of the liquid crystal layer. When the thickness of the liquid crystal layer is about 2 μm or less, the spiral of the SmC ^* phase is unraveled, and bistability is exhibited.

Furthermore, in the present invention, a protective layer for the color filter is provided so that a compound that lowers the resistance value of the liquid crystal by directly contacting the color filter with the liquid crystal is not mixed into the liquid crystal from the color filter. It is positioned between the filter and the filter so that the capacitance based on the protective layer does not occur between the opposing electrodes. When the capacity occurs,
The voltage applied to the liquid crystal shifts to the opposite polarity side, and when the capacitance is large, it exceeds the inversion threshold value and is inverted. In the present invention, since the position of the protective layer is located outside the transparent electrode, the generation of the capacitance is prevented, and the above switching failure does not occur.

[Embodiment] FIG. 1 is a sectional view showing the basic structure of a ferroelectric liquid crystal device according to the present invention. In FIG. 1, a ferroelectric liquid crystal device 1
Has substrates 2 and 3 made of a transparent plate such as a glass plate or a plastic plate, and a ferroelectric liquid crystal 4 is sandwiched between them. Stripe-shaped transparent electrodes 5 and 6 forming a matrix electrode structure are arranged on each of the substrates 2 and 3, and alignment control films 7 and 8 are formed on the transparent electrodes. Each of the R, G, and B color filters is formed of a pigment and a transparent resin, or a pigment and a transparent inorganic compound so that the color filters have almost the same film thickness. On the other hand, depressions are formed on the protective film 9 based on the intervals between the color filter units, and a color filter gap material 10 is provided to flatten the depressions. This color filter gap material 10
Can also function as a light shielding layer.

In the substrate having the above structure, since the thickness of the color filter and the step due to the depression between the pixels are corrected, the substrate surface can be kept substantially flat even if the transparent electrode and the alignment film are sequentially formed on the pixel. .

In the present invention, the step of the color filter substrate can be set to 1000 Å or less by the above-mentioned flattening, but it is preferably set to 500 Å or less. A liquid crystal element formed with a step of 1000 Å or more, particularly 1200 Å or more, and not using a color filter gap material will cause the alignment defect of the edge line shown in FIG. 5 described above.

Although the orientation control film 7 depends on the film thickness of the ferroelectric liquid crystal, it is generally set in the range of 10Å to 1 μ, preferably 100Å to 3000Å. Further, the film thickness of the protective film 9 can determine the film thickness of the ferroelectric liquid crystal 4, and therefore varies depending on the type of liquid crystal material and the required response speed.
Generally, it is set in the range of 0.2 μ to 20 μ, preferably 0.5 μ to 10 μ.

Hereinafter, examples of the present invention will be described more specifically.

FIGS. 6A to 6F are diagrams showing a process of forming color pixels of R, G, and B colors. First, a positive type resist (trade name; OFPR 77, manufactured by Tokyo Ohka Co., Ltd.) was applied on a ^# 7059 glass substrate 61 made by Corning Co., Ltd. using a spinner to a layer thickness of 1.0 μm to form a resist layer 62 (see FIG. 6). a)). Next, this is exposed using a predetermined pattern mask 63 (see FIG. 6b),
It was developed with a developer for ODUR 1010 series to form a lift-off pattern 62a having a predetermined stripe shape (see FIG. 6c).

Next, the entire surface of the pattern formation surface of the glass substrate 61 is exposed,
Further, the resist residue other than the unnecessary pattern portion was removed from the glass substrate 61 by oxygen plasma ashing treatment.

In this way, the glass substrate 61 on which the lift-off pattern 62a is formed is arranged at a predetermined position in the vacuum vapor deposition apparatus, and nickel phthalocyanine as a blue pigment for vapor deposition is provided on one of the two molybdenum boats as an evaporation source. Parylene (manufactured by Union Carbide Co., Ltd.) is put into another boat as resin, the former evaporation temperature is adjusted to 470 ° C and the latter temperature is adjusted to 250 ° C. First, nickel phthalocyanine 4500Å, then parylene 1000Å substrate 61 The colored layer 64 was formed by vapor deposition on the lift-off pattern forming surface of FIG.
reference). The layer thickness of the deposited colored layer 64 was 5500Å.

The substrate 61 on which the lift-off pattern 62a and the colored layer 64 are formed is immersed and stirred in a developer exclusively for OFPR 77 series for 5 minutes to remove the colored layer 64a deposited on the resist pattern 62a and the resist pattern 62a from the substrate. A blue stripe filter was prepared (see FIG. 6e).

On the other hand, the green and red stripe filters can be obtained by repeating the steps (a) to (e) of FIG.

First, as a vapor deposition dye for green, 5,000 liters of namariphthalocyanine and then 500 liters of parylene were deposited in this order to form a green layer. The layer thickness of this green colored layer was set to 5500Å.

Next, anthraquinone was first used as a red vapor deposition dye.
3000 Å and then parylene were deposited in the order of 2500 Å to form a red layer. The layer thickness of the red colored layer was 5500Å.

As described above, as shown in FIG. 6 (f), it was possible to form a color filter having almost the same thickness for B, G and R.

Next, a negative resist (ODUR Tokyo Oka) was applied and formed as the protective film 9 in FIG.

Next, a color filter interstitial material 10 was applied and formed in order to fill the depressions formed between the dyes. First, the same OFPR as that of the photoresist was applied on the protective film 9, exposed so that only the depressions were exposed to light, and developed. Thereafter, graphite was applied and formed as the color filter gap material 10. After that, remove the unnecessary photoresist
Lift off in MIBK solvent and color filter gap material 10
Left. Therefore, at this stage, the color filter substrates are formed on the same plane.

Next, as shown in FIG. 1, ITO was formed into a film with a thickness of 500 Å by a sputtering method to form a transparent electrode 5. A polyimide forming solution (Hitachi Chemical Co., Ltd. “PI
Q ”) is applied with a spinner rotating at 3000 rpm and 150 ° C.
Was heated for 30 minutes to form a 2000 Å polyimide film. Then, the surface of this polyimide coating film was rubbed.

The color filter substrate thus formed and the opposing substrate 3 were attached to each other to form a cell set, and a ferroelectric liquid crystal was injected and sealed to obtain a liquid crystal element. When this liquid crystal element was observed with a crossed Nicols polarization microscope, it was confirmed that the liquid crystal molecules inside did not have alignment defects.

[Effects of the Invention] As described above, according to the present invention, by providing a color filter gap material in the depressions between the color filters on the substrate to eliminate the difference in the thickness of the color filters, the occurrence of alignment defects can be prevented. It is possible to provide a ferroelectric liquid crystal element that can be prevented and can fully exhibit the characteristics of the ferroelectric liquid crystal.

Further, in the present invention, switching failure due to the capacitance of the protective layer is prevented, so that good switching characteristics are exhibited.

[Brief description of drawings]

FIG. 1 is a sectional view showing the basic structure of a ferroelectric liquid crystal device according to the present invention, FIGS. 2 and 3 are perspective views schematically showing a ferroelectric liquid crystal used in the present invention, and FIG. 4 is a conventional view. 5 is a cross-sectional view of the ferroelectric liquid crystal device of FIG. 5, FIG. 5 is a diagram showing a state of alignment defects appearing in a conventional ferroelectric liquid crystal device, and FIG.
(F) is a figure which shows the formation process of the color pixel of this invention. 1 ... Ferroelectric liquid crystal element, 2, 3 ... Substrate, 4 ... Ferroelectric liquid crystal, 5, 6 ... Transparent electrode, 7, 8 ... Alignment control film, 9 ... Protective film, 10 ... Color filter gap material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideaki Takao 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuko Motoi 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non-Incorporated (72) Inventor Tatsuo Murata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP-A-60-237403 (JP, A) JP-A-59-137931 ( JP, A)

Claims (3)

[Claims] 1. A liquid crystal device comprising a pair of substrates and a chiral smectic liquid crystal, wherein a distance between the pair of substrates is set to be sufficiently small so as to suppress formation of a helical arrangement structure of the chiral smectic liquid crystal. At least one of the substrates has a plurality of color filter units arranged on the substrate to form a color filter layer, and a protective layer is provided on the entire surface of the color filter unit. A liquid crystal element, characterized in that a color filter gap material is provided in the depression on the protective layer, and the depression is flattened. 2. The liquid crystal device according to claim 1, wherein a transparent electrode and an alignment control film are sequentially laminated on the protective layer. 3. The liquid crystal device according to claim 1, wherein the color filter gap material also has a function as a light shielding layer.