JPS63163424A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To prevent the generation of an orientation defect of a ferroelectric liquid crystal element by providing a specific relation between each thickness of a protective film on a color filter layer, a transparent conductive film on the protective film, and an oriented film on the transparent film, and a distance extending from the uppermost end of the convex surface of a light scattering surface to the lowest end of the concave surface. CONSTITUTION:On a color filter layer 13, a protective film 12 of thickness d1, a transparent conductive film 5 of thickness d2 on the protective film, and an oriented film 7 of thickness d3 on the transparent conductive film are provided, and the surface of a spacer for controlling the thickness of a liquid crystal layer between a substrate 2 having a color filter, and other opposed substrate 3 is formed to a light scattering surface of an uneven shape. Also, when a distance extending from the uppermost end of the convex surface of the light scattering surface to the lowest end of the concave surface is denoted as (d), the spacer 9 is allowed to sink into a film which comes into contact with the liquid crystal layer so as to become d<d1+d2+d3. In such a way, no step difference is generated in the liquid crystal layer, an orientation defect of a liquid crystal molecule is not generated, and also, since the surface of the spacer is the light scattering surface, the transmittivity can be improved, and the element which is bright and excellent in its contrast is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to liquid crystal elements such as liquid crystal display elements and liquid crystal-light shutter arrays. The present invention relates to a ferroelectric liquid crystal element that improves the display quality by improving the utilization efficiency of liquid crystal molecules and eliminating alignment defects of liquid crystal molecules.

(Prior Art) As a conventional liquid crystal element, for example, M-Shut (M
, 5chadt) and W. Helfrich (W,H
, Elfrich) “Applied Physics Letters”
ers”) Volume 18, No. 4 (February 15, 1971), P, 127-+28 “Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal”
'("Voltage Dependent Op
t, 1cal 8activity of aTw
isted Nematic Liquid Crys
Twisted nematic (tw
There are known devices that use liquid crystals.

This TN liquid crystal has a problem in that crosstalk occurs when a matrix electrode structure with high pixel density is used or when split driving is performed, so 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 the display element has a large area. The problem is that it is difficult to create.

To solve these storage problems, Clark et al. proposed a ferroelectric liquid crystal element in US Pat. No. 4,367,924.

The example shown in the second diagram schematically shows an example of a cell for explaining the operation of a ferroelectric liquid crystal element, and 21 and 2 in the diagram are
1' is In2o3.5no2 or ITO (Indiu
A substrate (e.g., a glass plate) coated with a transparent electrode such as m-Tin Oxide), and an insulating layer, an alignment film, etc. (none of which are shown) are provided on these pair of substrates,
Between these alignment films, etc., a liquid crystal layer 22 having a 5 lll phase is sealed so as to be oriented perpendicularly to the surface of the substrate.

A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P±) 24 in a direction perpendicular to the molecule.

When a voltage higher than a certain threshold is applied between the electrodes on the substrates 21 and 21' of such a ferroelectric liquid crystal element, the liquid crystal molecules 2
The helical structure of 3 unravels and the dipole moment (P±)24
The alignment direction of the liquid crystal molecules 23 can be changed so that all of the liquid crystal molecules are oriented in the direction of the electric field.

The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction, and therefore, for example,
It is easily understood that by placing polarizers disposed above and below the surfaces of the substrates 21 and 21'' in a cross Nicol positional relationship, a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage is obtained.

More preferably, when the thickness of the liquid crystal element is made sufficiently thin (for example, 10 μm or less), the helical structure of the liquid crystal molecules is unraveled (non-helical structure) even when no electric field is applied, as shown in FIG. , its dipole moment P or P' is either upward (24) or downward (24').

As shown in FIG. 3, voltage applying means 26 and 26' apply an electric field E or E' of different polarity above a certain threshold value to such an element.
When given for a predetermined period of time, the dipole moment P or P
′ is an upward direction 2 corresponding to the electric field E or the electric field vector of E′.
4 or downward 24', and accordingly the liquid crystal molecules 23 are in the first alignment state 25 or in the second alignment state 2.
5'.

As mentioned above, there are two advantages to using such a ferroelectric liquid crystal element as an optical modulation element.

Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability.

To explain the second point with reference to FIG. 3, for example, when the electric field E is applied, the liquid crystal molecules are aligned in the first alignment state 25, and in this state they are stable even when the electric field is turned off. Furthermore, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are aligned to the second orientation state 25' and change their orientation, but they remain in this state even after the electric field is turned off. 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 element be as thin as possible, and generally 0.5 to 20 μm,
Particularly suitable is 1 to 5 μm.

(Problem to be Solved by the Invention) 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 Regardless, it is necessary that the molecules be in such a state that conversion between the two stable states can occur 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, thus forming a region (monodomain) in which the liquid crystal molecular axes are aligned almost parallel to the substrate surface. need to be done. However, in the conventional ferroelectric liquid crystal elements, the alignment state of the liquid crystal having such a monodomain structure was not necessarily formed satisfactorily, so that sufficient characteristics could not be obtained.

FIG. 4 shows a cross-sectional view of a conventional ferroelectric liquid crystal element 40, and FIG. 5 shows a state of alignment defects that appear in the conventional ferroelectric liquid crystal element.

That is, the conventional ferroelectric liquid crystal element 40 shown in FIG. 4 has a pair of parallel substrates 42 and 43.
and 43 are provided with strip-shaped electrode wires 45 and 46, which form matrix electrodes, respectively.

The color filter 413 consists of red (R), green (G), and blue (B) pigments.

Bead spacers 49 made of alumina or the like are used to control the thickness of the liquid crystal layer 44, and a large pressure is applied to the substrates 43 and 42 to control the thickness of the liquid crystal layer. At this time, since the surface of the spacer is smooth, when pressure is applied, a dent occurs in the film in contact with the liquid crystal layer, resulting in a step A as shown in Figure 4.
occurs. The size of these steps is 2,000 people ~ 1μ
It is about m. As a result, when the alignment of liquid crystal molecules is controlled using the temperature decreasing process, alignment defects occur in the ferroelectric liquid crystal layer 44 with the step A as a boundary due to the step A described above.

FIG. 5 is a sketch of the ferroelectric liquid crystal element observed under a crossed Nicol polarizing microscope, and lines 52 and 53 are observed corresponding to the step A in FIG. 4. Further, a portion 54 in the figure is a ferroelectric liquid crystal sandwiched between opposing electrodes. A large number of edge-like lines 55 appearing in the polarizing microscope represent alignment defects in the ferroelectric liquid crystal.

If a step of 1,000 Å or more exists in the contacting surface of the ferroelectric liquid crystal as described above, alignment defects will occur from the step, and the formation of monodomains in the ferroelectric liquid crystal layer will be inhibited.

The present inventors have clarified through experiments that such a step difference causes alignment defects in the ferroelectric liquid crystal layer.

Another problem is that since the thickness of the liquid crystal is controlled by spacers, alignment defects will occur if there are large variations in the thickness of the spacers. In order to prevent alignment defects, for example, if the thickness of the liquid crystal is 2 μm, the spacer size should be 2 μm.
m±0.2 μm, and in order to realize this, it is necessary to manufacture the spacer with high precision, which poses a problem that the manufacturing cost of the spacer is high.

In addition, the spacer blocks the light entering the liquid crystal element,
There was a problem that the spacer itself was black and conspicuous.

Another problem is that the transmittance is reduced by the color filter used when colorizing the ferroelectric liquid crystal element. In other words, the method for creating a color filter is
There are dyeing methods, vapor deposition methods, electrodeposition methods, colored resin methods, etc., but in any case, a color filter is a light absorption film, and by providing a color filter on a ferroelectric liquid crystal element, it is possible to improve the ferroelectric liquid crystal element. Transmittance decreases.

As a result, the entire screen of the liquid crystal display element becomes dark, resulting in a color ferroelectric liquid crystal element with poor color reproducibility and poor contrast.

Therefore, an object of the present invention is to prevent the occurrence of alignment defects in the above-mentioned conventional ferroelectric liquid crystal elements, and to fully utilize the high-speed response and memory effect characteristics inherent in ferroelectric liquid crystal elements. Another object of the present invention is to provide a ferroelectric liquid crystal element that is bright, has good contrast, and has excellent display quality.

(Means for Solving the Problems) As a result of intensive research in order to achieve the above object of the present invention, the present inventors have discovered that the surface of a spacer used to control the thickness of the liquid crystal layer of a ferroelectric liquid crystal element has been improved. A light-scattering surface with an uneven shape,
By sinking the convex part of this spacer into the film in contact with the liquid crystal (alignment film, transparent conductive film, protective film), steps on the surface in contact with the ferroelectric liquid crystal layer and uneven thickness of the liquid crystal can be reduced, making it possible to reduce the uneven thickness of the liquid crystal. In addition to forming a monodomain that eliminates alignment defects, which are a drawback of ferroelectric liquid crystal elements, the spacer scatters the light incident on the ferroelectric liquid crystal element, making the spacer itself inconspicuous, and efficiently transmitting light to pixels. We have discovered that the brightness of ferroelectric liquid crystal devices can be improved by guiding

That is, the present invention provides a ferroelectric liquid crystal element in which a ferroelectric liquid crystal layer is disposed 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. On the filtration layer there is a thickness d
o protective film, a transparent conductive film with a thickness of d2 on the protective film, and an alignment film with a thickness of d3 on the transparent conductive film, and between the substrate having the color filter and another substrate facing the substrate. When the surface of the spacer that controls the thickness of the liquid crystal layer is an uneven light scattering surface, and the distance from the top end of the convex surface to the bottom end of the concave surface of the light scattering surface is d, d < d r + d This is a ferroelectric liquid crystal element characterized in that a spacer is sunk into a film in contact with a liquid crystal layer so that 2 + d 3.

(Function) Next, the present invention will be described in more detail with reference to the accompanying drawings that schematically show one embodiment of the present invention.

FIG. 1(a) is a sectional view showing the structure of a color ferroelectric liquid crystal device according to the present invention. In addition, Fig. 1(b) is similar to Fig. 1(b).
It is an enlarged view of the spacer periphery of (a).

In FIG. 1(a), a color ferroelectric liquid crystal device 1 of the present invention has substrates 2 and 3 using transparent plates such as glass plates or plastic plates, and a ferroelectric liquid crystal layer 4 is disposed between them. It is arranged in the space provided by the spacer 9.

As shown in FIG. 1(b), the spacer 9 has an uneven surface, and the convex portion of the spacer surface is a film (alignment film 7, transparent electrode 5, protective film 12) in contact with the liquid crystal layer by a distance d. It's stuck inside. Since the convex portion of the spacer 9 sinks into the film in contact with the liquid crystal layer, the film does not warp and the flatness of the film can be maintained, and as a result, no alignment defects occur in the liquid crystal layer 4.

Strip-shaped transparent electrodes 5 and 6 forming a matrix electrode structure are arranged on each substrate 2 and 3, and alignment films 7 and 8 are formed on the transparent electrodes.

The R, G, and H color filters that form each pixel are
It is formed of R, G, and B using an organic dye or organic pigment having desired color characteristics of R, G, and H, or a dichroic mirror using optical interference.

Furthermore, in order to protect each of these pixels, a protective film 12 is formed on each pixel. Furthermore, in order to use these cells as display elements, the cells are arranged between linear polarizing plates 10 and 11.

The thickness of the alignment films 7 and 8 depends on the thickness of the ferroelectric liquid crystal layer 4, but is generally set to a thickness of 10 to 1 μm, preferably 100 to 3,000. The thickness of the protective film 12 is generally 0.2 μm to 20 μm, preferably 0.2 μm to 20 μm.
．． It is set in the range of 5 μm to 2 μm.

The size of the spacer 9 used in the ferroelectric liquid crystal element 1 of the present invention is as shown in FIG. 1(b).
The amount of penetration (e) and the amount that determines the thickness of the liquid crystal layer 4 (fi
). In order for the ferroelectric liquid crystal element 1 to exhibit high-speed response and memory performance, the thickness of the liquid crystal layer 4 needs to be 2 μm or less, and the spacer 9 L is set to 2 μm or less.

Further, the amount of penetration (e) of the spacer 9 needs to be smaller than the total thickness of the films 5.7 and 12 covering the color filter layer 13. If it is large, the convex portion of the spacer 9 will come into contact with the color filter layer 13, causing contamination of the liquid crystal layer 4 by the color filter.

That is, the depth (e) of the spacer 9 is generally 4 μm or less, preferably 2 μm or less.

Therefore, the size of the spacer 9 is Il, +e, which is generally 6 μm or less, preferably 4 μm or less.

Further, the distance d from the uppermost end of the convex surface to the lowermost end of the concave surface of the light scattering surface of the spacer 9 is generally 4 μm or less, preferably 2 μm or less.

Various materials can be used for the spacer 9 as described above, such as inorganic materials such as carbon beads, glass beads, alumina beads, or metal aluminum beads,
Metal materials such as metallic nickel beads, iron-cobalt alloy beads, or organic materials such as plastic beads can be used.

Particularly suitable liquid crystal materials for use in the present invention are liquid crystals with bistability and ferroelectricity, specifically chiral smectic C phase (SmCIl).
phase), H phase (SmH7), I phase (Sn+I” phase), J phase (SmJ” phase), K phase (SmK’ phase), G phase (SmG”
It is possible to use a liquid crystal of phase (SmF phase) or phase F (SmF phase).

Regarding this ferroelectric liquid crystal, please refer to “Le Journal
PHYSIQUE LETTER5”) 197
5th year, No. 36 (L-69), “Ferroelectric
Liquid Crystals J ('Ferroelect
ric 1quid CrystalSj) ; “
Applied Physics Letters
physics Letters'') 1980, 3
6(11), [Submicro Second Bistiple Electro-Optic Switching in Liquid Crystals ('Submicr.

5econd B15table Electroop
tic Switching 1nLiquid Cr
ystals J); “Solid State Physics” 1981,
16 (141), "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

Specific examples of ferroelectric liquid crystal compounds include desiloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC) and hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate ().
IOBAcPc), 4-o-(2-methyl)-butylresolsiliten-4'-octylaniline (MBRA8
) etc.

When constructing an element using these materials, the element can be supported by a block or the like in which a heater is embedded, if necessary, in order to maintain the temperature at which the liquid crystal compound becomes a chiral smectic phase.

Examples of materials for the alignment film used in the present invention include polyvinyl alcohol, polyimide, polyamideimide,
Resins such as polyester, polycarbonate polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, Yuria resin, acrylic resin, or photosensitive polyimide, photosensitive polyamide, cyclized rubber photoresist, phenol Novolak photoresist or electron beam photoresist (polymethyl methacrylate, epoxidized-1,4
-polybutadiene, etc.).

Examples of the pigment materials used in the present invention include azo, anthraquinone, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, pyrocholine, fluorobin, and quinophthalone. It will be done.

(Example) The present invention will be explained in more detail below by giving examples.

FIGS. 6(a) to 6(f) are diagrams showing the process of forming color pixels of 83 colors of R, G, and R. First, Corning's '70
59 Positive resist (product name; 0
FPR77, manufactured by Tokyo Ohka) using a spinner to 1.0μ
A resist layer 62 was formed by applying the coating to a layer thickness of m (FIG. 6C).
reference). Next, this was exposed using a predetermined pattern mask 63 (see Fig. 6) and developed with a developer exclusively for the Kano PR series to form a lift-off pattern 62a having a predetermined stripe shape (see Fig. 6). (See Figure C).

Next, the entire pattern-forming surface of the glass substrate 61 was exposed to light, and resist residue other than unnecessary pattern portions was removed from the glass substrate 61 by oxygen plasma ashing.

In this way, the glass substrate 61 on which the lift-off pattern 62a has been formed is placed at a predetermined position in the vacuum evaporation apparatus, and nickel phthalocyanine is placed as a blue pigment for evaporation into a molybdenum boat as an evaporation source, and the former is evaporated. Adjust the temperature to 470°C and add 4,000 nickel phthalocyanine.
A colored layer 64 was formed by vapor deposition on the lift-off pattern forming surface of the substrate 61 to a thickness of 500 mm (see FIG. 6d).

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 the Kano PR series for 5 minutes, and the colored layer 64a deposited on this pattern along with the resist pattern 62a is removed from the substrate. A blue stripe filter was produced (see Figure 6e).

On the other hand, the green and red striped filters are shown in Figure 6 (
It can be obtained by repeating steps a) to (e).

First, 4 lead phthalocyanine was added as a green vapor deposition pigment.
, 500 layers to form a line layer.

Next, as a red dye for deposition, a red anthraquinone dye was first deposited to a thickness of 4,500 mm to form a red layer.

As shown in FIG. 6(f), B, G, R
It was possible to form a color filter.

Next, a negative resist (
0DOR (Tokyo Ohka) was applied and formed.

Next, as shown in FIG. 1(a), a transparent electrode 5 was formed by forming an ITO film to a thickness of 500 mm by sputtering.

A polyimide forming solution (Hitachi Chemical's PIQJ) was applied thereon as an alignment film 7 using a spinner rotating at 3.00 Orpm, and heated at 150°C for 30 minutes.
,000 polyimide coatings were formed. After that,
The surface of this polyimide film was subjected to a rubbing treatment. Furthermore, the transparent electrode 6 and alignment film 8 of the glass substrate 3 were also formed in the same manner as described above.

The color filter substrate 2 thus formed and the opposing substrate 3 are stacked, and k is set to 1.0 as shown in FIG. 1(b).
Alumina bead spacers with a light scattering surface of 0 μm and d of 0.23 μm were arranged as shown in Figure 1(a), the inner substrates were bonded together to form a cell, and ferroelectric liquid crystal was injected and sealed. A liquid crystal element was obtained.

Then, the polarizing plates 10 and 11 were bonded together to form a ferroelectric liquid crystal element of the present invention. When this ferroelectric liquid crystal element was observed using a crossed Nicol polarizing microscope, it was confirmed that the internal liquid crystal molecules had no alignment defects.

When a fluorescent lamp was irradiated from the opposite side of the color filter and the transmittance of this ferroelectric liquid crystal element to the viewer was measured, it was 16%, indicating that the ferroelectric liquid crystal element was bright and had good contrast.

(Comparative Example) A ferroelectric liquid crystal element for comparison was obtained in the same manner as in the example except that an alumina bead spacer with a diameter of 1.5 μm was arranged as a spacer whose surface was not a light-scattering surface.

When this ferroelectric liquid crystal element was observed using a crossed Nicol polarizing microscope, it was observed that the internal liquid crystal molecules had alignment defects as shown in FIG. In addition, when the transmittance of this ferroelectric liquid crystal element was measured in the same manner as in the example, the transmittance was 10.
%, it was dark and the contrast was poor.

As explained above, if a spacer having a light-scattering surface according to the present invention is used in a ferroelectric liquid crystal element, there will be no alignment defects compared to a spacer without a light-scattering surface, the spacer will be less noticeable, the transmittance will be high, and the display will be bright and contrasty. A ferroelectric liquid crystal element with good properties is provided.

(Effects) As explained above, by forming the surface of the spacer used in the ferroelectric liquid crystal element into an uneven light scattering surface, the following effects can be achieved.

(1) Since the convex portion of the spacer sinks into the film in contact with the liquid crystal layer, no steps are created in the liquid crystal layer, and no alignment defects of liquid crystal molecules occur.

(2) Since a spacer larger than the thickness of the liquid crystal layer can be used, the particle size can be easily made uniform, and manufacturing costs can be reduced.

(3) Since the spacer surface is a light-scattering surface, the light incident on the ferroelectric liquid crystal element can be effectively used and the transmittance can be improved, resulting in brightness and excellent contrast.

(4) Since light is scattered on the spacer surface, the spacer itself is not noticeable.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view schematically showing the basic structure of a ferroelectric liquid crystal element according to the present invention, and FIG. 1(b) is a sectional view of FIG. 1(a).
FIGS. 2 and 3 are perspective views schematically representing the ferroelectric liquid crystal used in the present invention, FIG. 4 is a cross-sectional view of a conventional ferroelectric liquid crystal element, and FIG. 5 is an enlarged view of the area around the spacer. 6A to 6F are diagrams showing the state of alignment defects appearing in a conventional ferroelectric liquid crystal element, and FIGS. 6(a) to 6(f) are diagrams illustrating the process of forming color pixels of the ferroelectric liquid crystal element of the present invention. 1.40... Color ferroelectric liquid crystal element 2.3.42.
43... Substrate 4.44... Ferroelectric liquid crystal 5.6.45.46-... Transparent electrode 7.8.47.48... Alignment film 9.49-... Spacer 10.11. 410.411--Polarizing plate 12.412
-...Protective film 13.413-...Color filter layer Patent applicant
Canon Corporation Figure 1a Figure 1b Figure 2 Figure 3 Figure 6a

Claims (1)

[Claims] A ferroelectric liquid crystal element in which a ferroelectric liquid crystal layer is arranged 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,
A protective film with a thickness of d_1 is provided on the color filter layer, a transparent conductive film with a thickness of d_2 is provided on the protective film, and an alignment film with a thickness of d_3 is provided on the transparent conductive film. The surface of the spacer that controls the thickness of the liquid crystal layer between the opposing substrate and another substrate is made into an uneven light scattering surface,
The spacer is embedded into the film in contact with the liquid crystal layer so that, where d is the distance from the top end of the convex surface to the bottom end of the concave surface of the light scattering surface, d<d_1+d_2+d_3. Dielectric liquid crystal element.