JPH0553115A - Ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a stable memory characteristic and responsiveness by constituting oriented layers holding a liquid crystal layer of inorg. oriented films obtd. by diagonal vapor deposition of inorg. matter having a prescribed dielectric constant, such as aluminum nitride. CONSTITUTION:The oriented films 2, 2' are constituted of the inorg. oriented films obtd. by the diagonal vapor deposition of the inorg. matter having 7 to 15, more preferably 8 to 10 dielectric constant. Namely, a degradation in the memory characteristic of the liquid crystal, a malfunction, etc., arise if the dielectric constant of the inorg. matter constituting the oriented films 2, 2' is smaller than 7. A short circuiting arises between the oriented films 2 and 2' facing each other on both sides of the liquid crystal at the time of voltage impression if the dielectric constant is larger than 15. Not only the driving of the liquid crystal is then affected but also a failure in driving equipment is resulted. Then, the good memory characteristic is obtd. by constituting the oriented films 2, 2' of the inorg. oriented films obtd. by the diagonal vapor deposition of the inorg. matter having 7 to 15 dielectric constant at 1MHz. In addition, the malfunctions are eliminated and the excellent characteristics to exhibit the good responsiveness are obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel ferroelectric liquid crystal display device. More specifically, the present invention provides a ferroelectric liquid crystal display device having a stable memory property and responsiveness.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been developed for the purpose of increasing the display area and increasing the operation speed. However, the drive resistance is reduced due to the lead resistance of the transparent electrode during image display, which has been a barrier to the increase in size of the liquid crystal display element. With respect to such a problem, a ferroelectric liquid crystal display element having a memory property at the time of displaying an image has attracted attention. This ferroelectric liquid crystal display element provides a memory property by using a liquid crystal having bistability, and can be driven even if the duty ratio is small, thereby enabling an increase in size.
The above-mentioned ferroelectric liquid crystal display element is generally constructed by sequentially laminating an alignment film, an electrode layer and a transparent insulating substrate with a liquid crystal layer interposed therebetween.

In the above ferroelectric liquid crystal, in order to realize uniform display, it is required to obtain a uniform alignment state of the liquid crystal over the entire surface of the display element.
It is necessary to form an alignment film having uniform alignment and thickness.

Conventionally, silica (S
An orthorhombic vapor deposited film of iO ₂ ) is known.

[0005]

However, the ferroelectric liquid crystal display device using the oblique vapor deposition film of silica as the alignment film has a problem in the memory property of the liquid crystal. That is, in the alignment film formed by obliquely depositing silica, the liquid crystal may partially lose the memory property or malfunction even though the uniform alignment is obtained. Therefore, although the silica alignment film can obtain a good shape, it has a problem in practical use.

[0006]

The inventors of the present invention have conducted extensive research to solve the above problems, and as a result, an alignment film obtained by obliquely vapor-depositing an inorganic material having a specific dielectric constant as an alignment film on the electrode surface. By using, it is possible to arrange the ferroelectric liquid crystal molecules with a pretilt angle of a desired angle, and due to the action of the inorganic substance having the specific dielectric constant, it is only possible to use the oblique deposition film of silica. The inventors have found that it is possible to almost completely prevent the phenomenon that the liquid crystal partly loses its memory property or malfunctions, and has completed the present invention.

According to the present invention, the alignment film sandwiching the liquid crystal layer is 1 MH.
Dielectric constant at z (hereinafter simply referred to as "dielectric constant") 7-
A ferroelectric liquid crystal display device comprising an inorganic alignment film obtained by obliquely depositing 15 inorganic substances.

In the ferroelectric liquid crystal display device of the present invention, the alignment film is composed of an inorganic alignment film obtained by oblique vapor deposition of an inorganic substance having a dielectric constant of 7 to 15, preferably 8 to 10. That is, when the dielectric constant of the inorganic material forming the alignment film is smaller than 7, the memory property of the liquid crystal is deteriorated, malfunction occurs, and the object of the present invention cannot be achieved. When the dielectric constant is higher than 15, a short circuit occurs between the alignment films facing each other with the liquid crystal sandwiched when a voltage is applied, which not only affects the liquid crystal driving but also damages the driving device.

As the inorganic material having the above-mentioned specific dielectric constant, known ones can be used without particular limitation. Examples thereof include aluminum nitride, alumina, silicon nitride and zircon. Among them, aluminum nitride is most preferable because it can stably form a film and has excellent reliability as a thin film.
In particular, in the oblique vapor deposition described below, as the aluminum nitride raw material, it is preferable to use oxygen and impurities combined with oxygen other than aluminum as 0.01 wt% or less.

The inorganic alignment film obtained by the above oblique vapor deposition is provided so as to sandwich the liquid crystal. Generally, it is formed on the liquid layer side of the electrode layer. The thickness of the alignment film is better as it is thinner so as not to affect the optical characteristics.
0.01 to 0.1 μm is suitable. Further, the angle of the groove in the alignment film is preferably 30 ° to 5 ° with respect to the electrode surface.

The oblique vapor deposition for forming the above-mentioned inorganic alignment layer may be carried out according to a known method. Generally, as the evaporation source, the inorganic particles are used, and the particles are dissolved and evaporated by irradiating with an ion beam. In vapor deposition, the glass substrate is installed at a desired angle with respect to the evaporation beam to form an alignment film. For example, if vapor deposition is performed at an angle of 60 degrees from the normal line of the electrode layer, a parallel orientation structure in which the pretilt angle is zero and the orientation vector is orthogonal to the vapor deposition direction is obtained. Further, if the vapor deposition is performed at an angle of 85 degrees from the normal direction, a pretilt angle of several degrees can be obtained.

The above vapor deposition is 10 ⁻⁶ to 10 ⁻⁵ mmTorr.
It is preferable to carry out under a high vacuum.

In the present invention, the structure of a known ferroelectric liquid crystal display device is adopted as the other structure without particular limitation. Figure 1
FIG. 3 is a schematic view showing a typical structure of a ferroelectric liquid crystal display element. As shown in the figure, the liquid crystal layer 1 is sandwiched between the orientation films 2 and 2 ′, which are oblique vapor deposition films of inorganic materials, the electrode layers 3 and 3 ′, and the transparent insulating substrates 4 and 4 ′, which are sequentially stacked. ..
Further, a spacer 5 is provided in the liquid crystal layer, and a sealing material 7 is provided to seal the liquid crystal layer.

In the ferroelectric liquid crystal display device of the present invention having the above structure, as the liquid crystal, a known ferroelectric liquid crystal can be used without particular limitation. For example, chiral smectic C-phase liquid crystal and the like can be mentioned. Further, the gap between the alignment films provided so as to sandwich the ferroelectric liquid crystal display element is suitably 1 to 2 μm. In addition, an electrode layer 3 on which the inorganic alignment films 2 and 2'are laminated,
As the material of 3 ', a known material is used without particular limitation.
For example, a transparent conductive material such as In ₂ O ₃ —SnO ₂ (ITO) is suitable.

The material of the glass substrates 4 and 4'laminated on the outer side of the electrode layer is not particularly limited to a known material. For example, soda lime glass, non-alkali glass and the like can be mentioned. When the glass material is alkali-eluting, it is preferable to form barrier layers 6, 6'of SiO ₂ or the like between the glass and the electrode layer in order to prevent corrosion of the electrode layer.

Further, as the spacer 5 for keeping the thickness of the ferroelectric liquid crystal layer uniform, known spacers may be used without particular limitation, but inorganic spherical particles such as silica are preferable.

[0017]

[Effect] The ferroelectric liquid crystal display device of the present invention has an alignment film of 1M.
By having an inorganic alignment film obtained by obliquely depositing an inorganic material having a dielectric constant of 7 to 15 at Hz, it has a good memory property, no malfunction, and exhibits good responsiveness. It has excellent characteristics.

Although it is not clear that the above-mentioned structure of the present invention exerts the above-mentioned effects, the present inventor estimates as follows. That is, the above memory effect and malfunction are
It is caused by the polarization phenomenon induced on the surface of the alignment layer by applying a driving voltage, and the easiness of the polarization phenomenon is caused by the interaction between the property of the inorganic material having a specific dielectric constant and the shape of the alignment film brought about by the oblique deposition. It is estimated that this is due to the extremely effective suppression.

[0019]

EXAMPLES In order to more specifically describe the present invention,
Examples are shown, but the present invention is not limited to these examples.

In the examples and comparative examples, various tests were carried out by the following methods.

(1) Memory property After a voltage was applied to the liquid crystal display element to display an image, the application of the voltage was reversed, and it was observed whether or not abnormality appeared in the image display.

(2) Responsiveness The responsiveness was shown by the polarization reversal current when a voltage was applied to the liquid crystal display element and then reversed.

Example 1, Comparative Example 1 On the glass substrates of the transparent insulating substrates 4 and 4 ′, wiring patterns that cross in a grid pattern when they were laminated facing each other were formed of ITO to form the electrode layers 3 and 3. 'Stacked. Then, as a material for the alignment film on the surface of the electrode layer, 1 MHz
Ta ₂ O ₅ (ε ₁ = 2 with dielectric constant in ()
5), SiO ₂ (ε ₁ = 2) Al ₂ O ₃ (ε ₁ = 6) AlN
(Ε ₁ = 9), the deposition angle is 85 ° from the substrate normal,
Oblique vapor deposition was performed at a vacuum degree of 10 ⁻⁶ mmTorr for 5 minutes, and orientation films 2 and 2 ′ each having an oblique vapor deposition layer having a thickness shown in Table 1 were laminated. As the liquid crystal, a chiral smectic C-phase liquid crystal (dielectric constant = 2) is used, and the diameter between the alignment films is 1.5.
A liquid crystal cell having the structure of FIG. 1 was prepared in which spherical silica particles of μm were present at a dispersion density of 10 particles / mm ² and the periphery was sealed with a sealing material. In the liquid crystal display device, one polarizing plate is arranged on each of the upper and lower sides of the panel in crossed Nicols.

Table 1 shows various test results of the above ferroelectric liquid crystal display device.

[0025]

[Table 1]

In the sample using the Ta ₂ O ₅ alignment film, a short circuit occurred and normal operation was impossible. It seems that the permittivity was too high. In the sample using the SiO ₂ alignment film, a large polarization reversal current was observed, and the phenomenon of impairing the memory property was observed. Only the most normal charge current of AlN was observed, and the memory property was stable. The Al ₂ O ₃ alignment film sample obtained almost normal operation, but lacked memory stability. Examples 2 and 3 Ferroelectric liquid crystal display elements were produced in the same manner as in Example 1, except that the inorganic material forming the alignment film was changed to the material shown in Table 2 and the thickness was changed to the thickness shown in Table 2.

Table 2 shows the results of various tests on the above ferroelectric liquid crystal display device.

[0028]

[Table 2]

[Brief description of drawings]

FIG. 1 is a schematic view showing a typical structure of a ferroelectric liquid crystal display element.

[Simple explanation of symbols]

 1 liquid crystal layer 2, 2'alignment film 3, 3'electrode layer 4, 4'transparent insulating substrate 5 spacer 7 sealant

Claims (1)

[Claims] 1. A ferroelectric liquid crystal display device characterized in that an alignment film sandwiching a liquid crystal layer is composed of an inorganic alignment film obtained by oblique vapor deposition of an inorganic material having a dielectric constant of 7 to 15 at 1 MHz.