JPH02184819A - Ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To form the element at a high yield without admitting the coloring of the element even if the thickness of the plural liquid crystal layers to specifying the angle of inclination of the liquid crystal layers from the normal direction of a substrate is increased. CONSTITUTION:The inclination of the liquid crystal layer is preferably >=45 deg. and <90 deg. from the normal direction of the substrate. The thickness of the liquid crystal film cannot be increased too much if the inclination of the liquid crystal layer is <45 deg.. The liquid crystal turns perpendicular to the substrate and the liquid crystal does not longer respond to electric fields at 90 deg.. Such inclination is, therefore, inadequate. The direction of the director of the liquid crystal is directed to the direction inclined by the angle beta from the substrate if the angle of inclination of the liquid crystal layer from the normal direction of the substrate is set at beta. The component which acts as an optical switch is the component projected to the substrate surface and, therefore, DELTAn cosbeta (DELTAn is the refractive index anisotropy of the liquid crystal) is obtd. and DELTAn can be effectively diminished. As a result, the increase of d (thickness of the liquid crystal layer) is possible. The liquid crystal thickness is increased to the thickness larger than the thickness when the liquid crystal layer is not inclined in this way and the yield is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a ferroelectric liquid crystal display device that utilizes birefringence.

Conventional technology In a ferroelectric liquid crystal display device that utilizes birefringence, the light intensity that passes through this system is determined by the angle 2θ between the polarization direction of the incident light and the direction of the director, and the angle 2θ between the two polarizers being parallel. Transmitted light intensity 11I when
2θ) ・5in2 (7Y dΔn/in)・ ・ ・
・(+) May it come to you. Surface stabilized ferroelectric liquid crystal (S
In SFLC) display elements, the direction of the director is switched between two states, up and down, by reversing the polarity of the electric field. If the direction of the director in the up state now matches the polarization direction, 2θ=0 and the transmitted light intensity 1 (up) at this time becomes 0. In order to maximize the contrast of the 5SFLC element, the transmitted light intensity in the down state must be maximized, that is, 20=π in equation (1).
/4 (=45 degrees), dΔ11 /λ=m/2 (m is an odd number). There are many ferroelectric liquid crystals with 2θ=45 degrees. On the other hand, regarding dΔn/λ, when using 5SFI and C elements as switching elements for medium color light sources, by optimizing the thickness of the liquid crystal layer -CdΔn/λ
= m/2 (m is an odd number). For example, Merck's ferroelectric liquid crystal ZLI-3654 (Δn =
0.13), 1le-Ne laser (λ = 632.8n
In the liquid crystal light valve using m), the thickness of the liquid crystal layer is d
=m included/2Δn=2.4, 7.3.12. ,,,(μm
). However, in the case of liquid crystal color displays, if dΔn/input is not kept constant to a certain extent over the entire visible light range (400 to 700 nm), the transmittance at a certain wavelength of visible light may become extremely low, or the wavelength dependence of the transmittance may become extremely low. As they grow larger, they begin to appear colored. Therefore, dΔn =
Generally, the thickness is 0.2 to 0.3 μm. FIG. 1 shows the transmittance spectrum calculated by changing dΔn using equation (1).

The Δn of commercially available ferroelectric liquid crystals is approximately 0.
．． 13~5] Therefore, calculating from this value, the thickness of the liquid crystal layer must be 1.3~2.3 μm.

The liquid crystal layer thickness of currently commercially available LCD color TVs is approximately 5.
It is a well-known fact that even with this liquid crystal layer thickness, gap defects occur due to dust, clumps, etc., and it is difficult to make the liquid crystal layer thinner.

Problems to be Solved by the Invention In a ferroelectric liquid crystal display element for color display, the thickness of the liquid crystal layer is reduced to 2.
It had to be on the order of μm, resulting in poor yield.

The present invention aims to solve such problems.

Means for Solving the Problems In the present invention, the liquid crystal layer is formed so that the inclination angle from the normal to the substrate is 45 degrees or more and 90 degrees.

If the tilt angle of the working liquid crystal layer from the normal to the substrate is β, then the direction of the liquid crystal director is tilted from the substrate by the angle β. What acts as an optical switch is the component projected onto the substrate surface, so Δn cos β, and Δn can be effectively reduced. As a result, it becomes possible to increase d. For example, with a ferroelectric liquid crystal material with Δn=0.13,
If the tilt angle β is 260 degrees, Δn(eff,) = 0.13
cos60' ==0.065 and dΔn ==0
．． To make it 2-0.371m, d = 3.1-4.6μ
It should be m. If there is no slope, d = 1.5~2
．． Since 311 m is the optimum value, the liquid crystal layer can be made relatively large when not tilted, and an improvement in yield can be expected.

Also, when tilted, the effective spontaneous polarization becomes smaller, but it was originally about 20nC/cm2, but it was 20cos60.
Even if ゜=10 (nC/cm2), there is no significant change in the response speed. This is because the response speed is proportional to the reciprocal of spontaneous polarization.

Example Embodiments of the present invention will be described below with reference to the drawings.

A ferroelectric liquid crystal display element is realized by sandwiching a ferroelectric liquid crystal between two substrates. The surfaces of these substrates that come into contact with the liquid crystal are subjected to at least electrode formation and alignment treatment. Methods of controlling the tilt of the liquid crystal layer from the normal to the substrate include changing the deposition angle of SiO oblique evaporation, adding long-chain alkyl groups to alignment films such as polyimide and polyvinyl alcohol, and changing their density. There are several methods, but the easiest is to change the deposition angle during oblique deposition of SiO.

As the substrate, any material such as glass or plastic can be used as long as it is colorless and transparent under visible light, but glass is best in consideration of transparency and surface uniformity.

Any electrode can be used as long as it is transparent to some extent. Indium tin oxide (ITO)
has high visible light transmittance and is optimal.

However, it is necessary to keep the surface of the electrode flat.

An alignment treatment is applied to the edge of this electrode. It is preferable to arrange the upper and lower substrates so that the directions of the alignment treatment are reversed. That is, in oblique evaporation, it is preferable to face each other so that the evaporation directions are opposite to each other. When aligning by rubbing a polymer, the rubbing direction may be reversed on the L lower substrate. With such a substrate arrangement, the layer structure of the ferroelectric liquid crystal becomes uniform (tilted uniform structure) from the bottom substrate to the first substrate, making it easy to control the tilt angle of the layers.

However, if the orientation process is performed in the same direction on the upper and lower substrates, the layer structure of the ferroelectric liquid crystal will have a flat bend at the center of the liquid crystal layer (chevron structure), so the tilt angle of the layer will change. is difficult to control.

The tilt angle of the liquid crystal layer can be measured by the magnitude of the polarization reversal current of the ferroelectric liquid crystal or the peak position of X-ray diffraction.

The inclination of the liquid crystal layer is preferably 45 degrees or more and less than 90 degrees from the normal direction of the substrate, and optimally 60 degrees to 80 degrees. If the tilt of the liquid crystal layer is less than 45 degrees, the thickness of the liquid crystal layer cannot be increased very much. Further, at 90 degrees, the liquid crystal becomes perpendicular to the substrate and the liquid crystal no longer responds to an electric field, which is not suitable. Further, if the angle is 80 degrees or more and less than 90 degrees, the response speed will be 6 to 10 times slower than when it is not tilted at all.

However, if the Δn of the liquid crystal material becomes smaller than 0.13 in the future, the thickness of the liquid crystal layer will be reduced by 5 degrees even if it is tilted from 45 degrees to 60 degrees.
It is convenient because it can be made larger than μm.

Note that when the layer is tilted, the tilt angle of the ferroelectric liquid crystal, that is, 2θ in the (+) equation, needs to be smaller than 45 degrees. If the tilt angle projected onto the substrate is α, and the tilt angle of the layer from the normal direction of the substrate (that is, the tilt angle of liquid crystal molecules from the substrate) is β, then the tilt angle γ required for the liquid crystal material is (2)
It can be calculated using the formula.

7 =cos-'(sin"β+C08213CO5α
)a11(2) The calculation method is shown below. Assume that the coordinates are taken as shown in FIG. 2, the xy plane is the substrate, and the two stable states of the ferroelectric liquid crystal are the OP position and the OQ position. Point P
is (Acosβ, O, As1nβ)・ Point Q is (Aco
sβCOS Q *AcosβS group α, As1nβ), so if we use the cosine theorem between triangle OPQ, we get ^
2cos2β(1-cosa)2+^2cos2βs
in" a = A"+A2-2A2cos7...
・(3) If we rearrange the equation (3), cos 7 = sin2β + C082β cos a, so 7 = cos-' (s in2β + cos2β
cosa) Here, if α: 45 degrees, then 7 = cos-' (sin2β+0.71cos2
β)---(4) For example, when the layer inclination angle β is 60 degrees, γ=22 degrees.

More specific examples will be described below.

Examples 1 to 4 Circular electrodes with a diameter of 20IIlaI were obtained by vapor-depositing ITO on a glass center plate 1 of type 81059 manufactured by Corning, Sui, with a thickness of 1.1. A 5iOO column was fabricated on this substrate by rotating oblique evaporation. The tilt angle of the SiO column-like structure was changed by changing the large tilt angle of the oblique evaporation onto the substrate.

Next, the two substrates were faced to each other so that the vapor deposition directions were opposite to each other, and the two substrates were bonded together using a re-boxy resin. At this time, glass fibers having a diameter corresponding to the thickness of the liquid crystal layer shown in the table were dispersed on the substrate.

Next, this cell was equipped with a ferroelectric liquid crystal C manufactured by Chisso Petrochemical Co., Ltd.
5-1013 (spontaneous polarization 16nc/cnr', Δn=0
．． 14) was injected at 100 degrees, slowly cooled, and Example 1~
A 5SFLC device of No. 4 was prepared.

Comparative Examples 1 to 4 Examples! A 5SFLC device was fabricated using the same materials and process as in -4. However, in this case, SiO
The large tilt angle of the vapor deposition was lowered to make the tilt angle of the liquid crystal layer less than 45 degrees.

5SFLC element driving results ±lO■ for the 5SFLC element created in this way
The polarization reversal current was measured, and the tilt angle of the layer was calculated from the value of the apparent spontaneous polarization. Comparative Example 1 did not respond at all to the application of an electric field, and the layer was separated by 90° from the normal direction of the substrate.
It is thought that the liquid crystal molecules are oriented almost perpendicularly to the substrate. The color change of the element was also evaluated. O means it is good, Δ means it looks a little bluish, and X means it looks magenta, so clear coloration can be observed. The results are shown in the table.

Table wood: In the examples that did not respond to the electric field, no clear discoloration was observed even when the liquid crystal layer thickness was increased to 4 Brn or more, but in the comparative examples, the discoloration was so large that it could not withstand use as a display. Met.

Effects of the Invention As described above, in the strongly electrostatic liquid crystal display element according to the present invention, the inclination angle of the layer from the normal direction of the substrate is 45 degrees or more h9
It was found that when the temperature is less than 0 degrees, no discoloration of the device is observed even if the liquid crystal layer thickness is increased, and the device can be manufactured with a high yield.

[Brief explanation of the drawing]

Figure 1 is a graph showing the transmittance spectrum when changing the product of liquid crystal layer thickness d and refractive index anisotropy Δn. Figure 2 is a graph showing the tilt angle required for the liquid crystal material when the layer is tilted. This is a graph showing the coordinates for Name of agent: Patent attorney Shigetaka Awano
m)

Claims (2)

[Claims] (1) A ferroelectric liquid crystal display element characterized in that the tilt angle of the liquid crystal layer from the normal line of the substrate is 45 degrees or more and less than 90 degrees. (2) The ferroelectric liquid crystal display element according to claim 1, wherein the ferroelectric liquid crystal display element is arranged so that the direction of alignment treatment of the upper and lower substrates is reversed.