JPH07104514B2 - Ferroelectric liquid crystal panel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a display device and a panel for an optical shutter, and more particularly to a ferroelectric liquid crystal panel.

Conventional Technology Conventional technology will be described below with reference to the drawings.

Currently, a TN (Twisted Nematic) type display system is most widely used as a liquid crystal display device. However, compared to other displays (plasma display, electroluminescence display, etc.), it is inferior in response speed, and no significant improvement has been seen so far.

Recently, a display method using a ferroelectric liquid crystal has been announced, and it has attracted much attention because it has a high matrix property in addition to its fast response speed. References:
N. A. Clark, S. tea. Lager Bar;
AP pl. P.H. Wyeth. LTT Tea., 36,899 (1980) and Tea. Harada, Ether, SID 85 digest
16 131 (1985) (NAClerk, STLagerwall; Appl.Phys.
Lett., 36,899 (1980) and T. Harada, et al, SID 85 DI.
GEST 16 131 (1985)) First, the ferroelectric liquid crystal will be described with reference to the drawings.

Ferroelectric liquid crystal refers to liquid crystal exhibiting ferroelectricity. In order to show ferroelectricity from the theory of crystal symmetry, the liquid crystal molecule must first have an asymmetric center. Further, it is necessary to have a layered structure and to tilt the molecules in the layer. As liquid crystal phases satisfying such symmetry, smectic C chiral phase, smectic I chiral phase, smectic G chiral phase and the like have been discovered up to now and recognized as ferroelectric liquid crystal phases. In this specification, the properties will be described by using the smectic C chiral phase having the highest symmetry among the ferroelectric liquid crystal phases. FIG. 2 is a schematic diagram of a ferroelectric liquid crystal molecule. Ferroelectric liquid crystals are usually liquid crystals having a layered structure called smectic liquid crystals. The molecules are tilted by θ with respect to the normal to the layer.

Ferroelectric liquid crystals have asymmetric centers and are therefore composed of optically active liquid crystal molecules that are not racemic. As shown in FIG. 2 as a molecular structure, the ferroelectric liquid crystal molecule has a permanent dipole moment that is a spontaneous polarization in the direction perpendicular to the long axis of the molecule. In the chiral smectic C phase, It is free to move outside the cone. The vector dropped from the center point O of the cone to the liquid crystal molecules is called the C director.

In FIG. 2, 21 is a liquid crystal molecule, 22 is a permanent dipole, and 23 is C.
A director, 24 is a cone, 25 is a layer structure, 26 is a layer normal direction, and 27 is a tilt angle θ.

Ferroelectric liquid crystal molecules usually have a twisted structure because they have asymmetric atoms. This twisted structure is shown in FIG. As shown in FIG. 3, a twist structure may exist in the normal direction of the layer.

In FIG. 3, 31 is a liquid crystal molecule, 32 is a permanent dipole moment, 33 is a pitch (L) representing a twist period, 34 is a layer structure, 35 is a normal direction of the layer, and 36 is an inclination angle θ.

Next, the operation principle of the ferroelectric liquid crystal will be described with reference to the drawings. When the cell thickness (d) of the ferroelectric liquid crystal panel is thicker than the pitch (d> L), the influence of the cell substrate surface does not extend to the center of the cell, so that the cell usually has a twisted structure. However, when the cell thickness is smaller than the pitch (d <L)
The twisted structure is unwound by the force of the substrate surface, and two regions (domains) in which molecules as shown in Fig. 4a are parallel to the substrate surface.
Appears. In these two regions, the permanent dipole moments of the molecule are pointing in opposite directions,
One is from the front side to the front side of the paper and the other is from the front side to the back side of the paper. This corresponds to the tilt angle of the molecule with respect to the layer normal.

At this time, when an electric field is applied from the back side to the front side of the paper, all the permanent dipole moments are oriented in the direction of the electric field, and all the molecules have a tilt angle of + θ as shown in FIG. 4b. In such a state, when the polarization axis direction of the polarizer (P) of the polarizing plate is made parallel to the long axis direction of the molecule, the polarization axis direction of the analyzer (A) is made parallel to the short axis direction of the molecule (see FIG. 4b). The linearly polarized light that has passed through the polarizer (P) is transmitted without being subjected to birefringence and is blocked by the analyzer (A) to obtain a dark state. Further, when an electric field is applied in the opposite direction, all the molecules have a tilt of −θ as shown in FIG. 4c, and linearly polarized light that has passed through the polarizer passes through the analyzer due to the birefringence effect to obtain a bright state.

In FIG. 4 abc, 41 is the direction of the electric field, 42 is the permanent dipole moment of the molecule, 43 is the layer structure, 44 is the tilt angle θ, 45 is the polarization axis of the polarizer (P) and the analyzer (A), respectively. ing.

As described above, bright and dark states can be obtained depending on whether the electric field is positive or negative.

(Reference: Fukuda, Takezoe, Kondo ,: High-speed display using ferroelectric liquid crystal, Optronics, 9th page, 64 pages, 1983
In addition, cells with a cell thickness smaller than the pitch (d>
In L), the twisted structure is usually unraveled, so the molecule remains stable after removing the electric field.
It is said that a so-called memory effect occurs.

Problems to be Solved by the Invention As shown in the preceding sentence, the ferroelectric liquid crystal panel has two brightness (bright and dark) because stable states exist only at both ends (+ θ, −θ) of the cone due to its display principle. However, there was a problem that half tone could not be produced.

Means for Solving the Problems In order to solve the problems described above, halftone display is made possible by obliquely vapor deposition (oblique vapor deposition) with a spacer provided on the substrate.

Action Diagonal vapor deposition with spacers on the substrate creates a portion with and without a vapor deposition film as an alignment layer on the substrate, and confirms that the electro-optical characteristics of each are different. You can use it as a ferroelectric liquid crystal panel that can display halftones. This will be briefly described with reference to the drawings. FIG. 1 is a schematic diagram when vapor deposition is performed obliquely on a substrate provided with a spacer. Here, 11 is a vapor deposition direction, 12 is a glass substrate, 13 is a spacer, 14 is an angle formed by the substrate vertical direction and the vapor deposition direction, 15 is an ITO layer, and 16 is a portion which is shaded by the spacer by oblique vapor deposition. When the spacer 13 is obliquely vapor-deposited, a shadow 16 is formed, and due to the height of the spacer (h) and the angle of the vapor deposition direction 11 (90 ° -θ),
The length (L) of the shadow that is not vapor-deposited is determined by the following equation.

L = h × tan (90−θ) (1) At this time, when θ is 85 °, L becomes about 11h.

EXAMPLE An example of the ferroelectric liquid crystal panel of the present invention will be described below with reference to the drawings. In this embodiment, a line spacer is provided on the substrate, and oblique vapor deposition is performed perpendicularly to the line spacer to generate a portion where the vapor deposition film exists and a portion where the vapor deposition film does not exist.

The line spacer is a glass substrate 51 as shown in FIG.
A line spacer 53 with a width of 40 μm and a pitch of 0.4 mm is formed by a photo process using a photosensitive polyimide on a transparent electrode 52 of ITO (indium tin oxide) provided on the above.
Was formed.

Next, the method of oblique vapor deposition will be described. The actual method of the oblique deposition method is shown in FIG.

There is a vapor deposition source in a vapor deposition vessel (bell jar) that is in a vacuum state, and heating can be performed by resistance heating or irradiation with an electron beam. The cell substrate is set at an angle of θ with respect to the vapor deposition direction from the substrate normal direction.

61 is a bell jar, 62 is a cell substrate, 63 is a vapor deposition source, and 64 is a tilt angle θ.

○ Bibliographic reference of oblique deposition method: W. ULVAC, M. Boyx, E. Guyon; Orientation of nematic and smectic phases on vapor-deposited film, Applied Physics Letters, Vol. 25, No. 9, (1) 479, 1974 (W. Urbac
h, M.Boix, and E.Guyon; Alignment of nematics and sme
c-ticson evaporated films, Applied Physics Letter
s, Vol.25, No.9,1 P.479 November 1974) Tsutomu Uemoto, Yasuo Iwasaki, Katsumi Yoshino, Yoshio Inuishi; Electro-optical properties of smectic ferroelectric liquid crystals (2), 4th liquid crystal study Proceedings of the Meeting (1978) Lecture No. 3R13 The composition of the orthorhombic vapor deposition method used in the examples is described in detail. FIG. 1 shows the structure of the vapor deposition method which is the main feature of the present invention. The arrow 11 indicates the vapor deposition direction, and the line spacers 13 are arranged on the glass substrate 12 with TIO as described above. At this time, the line spacer and the vapor deposition direction were arranged at right angles.

Reference numeral 14 represents the vapor deposition angle (θ).

Silicon monoxide (SiO) was used as the vapor deposition material.

The vapor deposition angle was 85 degrees.

The deposition rate was about 20Å / sec, and the film thickness was about 300Å in the direction perpendicular to the substrate.

A ferroelectric liquid crystal panel was prepared using the ITO substrate thus obliquely vapor-deposited. Figure 1 shows the panel structure. In FIG. 7, 71 is a polarizing plate, 72 is a glass substrate, and 73 is TIO.
A layer, 74 is an oblique SiO vapor deposition layer, 75 is a ferroelectric liquid crystal layer, 76 is a line spacer for adjusting the cell thickness, and 77 is a combination of vapor deposition directions.

The vapor deposition directions of the upper and lower substrates were set to be antiparallel to each other.

As the ferroelectric liquid crystal material used in the experiment, a liquid crystal material having a ferroelectric property in the temperature range of 0 ° C. to 58 ° C. was used. The phase transition temperature of the ferroelectric liquid crystal used below is shown.

Here, Cr: crystalline phase SmC *: smectic C chiral phase SmA: smectic A phase Ch: cholesteric phase Iso: isotropic liquid After heating the panel to 100 ° C to make it an isotropic liquid, slowly cool it ( 0.6 ° C / min) allows smectic C
We obtained a chiral phase monodomain.

Next, using this panel, a voltage-transmittance curve (hereinafter, B-
V curve) was measured.

The optical experimental system used for the measurement of the BV curve is shown in FIG.
In FIG. 8, the white light emitted from the light source 81 is the polarizer 82.
After entering the liquid crystal cell 83 as linearly polarized light through the
A photomultiplier tube which is condensed by a condenser lens 85 through 84.
It is sensed at 86 and measured by the storage oscilloscope 87 as a BV curve. An arbitrary waveform can be added to the liquid crystal cell by the programmable pulse generator 88.

In such an experimental system, the BV curve of the ferroelectric liquid crystal panel having the above configuration was measured.

The voltage waveform used in the measurement of the BV curve of the threshold characteristic is shown in FIG. In FIG. 9, after a constant reset pulse 91 is applied, a reverse polarity variable pulse 92 for measuring the threshold characteristic is applied. This series of pulses is applied every certain time 93 (frame frequency). First, FIG. 10 shows an example of the BV curve of the threshold characteristic obtained by measuring only the vapor-deposited portions of both the upper and lower substrates. In FIG. 10, the horizontal axis represents time (t), and the vertical axis represents voltage (V) or brightness (B). The upper diagram is the applied voltage waveform and the lower diagram is the corresponding brightness curve. When the variable pulse 101 for measuring the threshold value is gradually increased, the 10th
In the figure, the dark state caused by the reset pulse gradually becomes bright. FIG. 11 ab shows a plot of the luminance at the point where the variable pulse was applied and the light amount changed most with respect to the variable pulse voltage. In the 11th ab, the horizontal axis represents voltage and the vertical axis represents luminance. Fig. 11 ab
The reset pulse voltage is 25V and the variable pulse voltage is 0V.
To 25 V, and the pulse widths were both 1 ms. Figure 11a
11b shows that the polarity of the variable pulse is positive and changes from dark to dark state. FIG. 11b shows that the polarity of the variable pulse is negative and changes from bright to bright state. The results of measuring the threshold value characteristics are shown in FIG. 12 ab.
It can be seen from FIGS. 11 ab and 12 ab that the threshold value is higher in the portion deposited on both sides than in the portion deposited on one side.

Also, FIG. 13 ab shows the threshold characteristics of both double-sided vapor deposition and single-sided vapor deposition measured simultaneously. 13 ab is shown in FIG. 11 ab,
The threshold characteristic is similar to that of Fig. 12 ab, and it is easy to produce two-stage halftone.

EFFECTS OF THE INVENTION The present invention is that the threshold characteristics are gentle because the vapor deposition is performed obliquely in the state where the spacer is provided on the substrate to form a portion where the vapor deposition film as the orientation film layer exists and a portion where the vapor deposition film does not exist on the substrate. Alternatively, we have advanced to realize a ferroelectric liquid crystal panel capable of half-tone display.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the constitution of the vapor deposition method of the present invention, FIG. 2 is a schematic diagram showing the structure of ferroelectric liquid crystal, FIG. 3 is a schematic diagram showing the twisted structure of ferroelectric liquid crystal, and FIG. (A) (b)
(C) is a schematic view showing a twisted structure in a thin cell thickness panel of a ferroelectric liquid crystal and a schematic view showing an operation principle in a ferroelectric liquid crystal panel of a thin cell thickness, and FIG. 5 is a glass substrate. Structure diagram showing line spacer type using photosensitive polyimide on ITO transparent electrode provided above, 6th
FIG. 7 is a schematic diagram showing a vapor deposition apparatus and a vapor deposition method, FIG. 7 is a schematic diagram of a ferroelectric liquid crystal panel used in the present invention, and FIG. 8 is an optical system used for BV curve measurement of conventional examples and examples. Fig. 9 is a graph of the voltage waveform when measuring the threshold characteristics of the ferroelectric liquid crystal panel, and Fig. 10 is a graph showing the BV curve against the applied voltage for measuring the threshold characteristics. FIGS. 11 (a) and (b) are graphs showing the threshold characteristics of the double-sided evaporated portion, and FIGS. 12 (a) and (b) are graphs showing the threshold characteristics of the single-sided evaporated portion. Figure 13 (a)
(B) is a graph showing the threshold characteristics when both the double-sided and single-sided evaporated portions are measured. 11 …… Vapor deposition direction, 12 …… Glass substrate, 13 …… Spacer, 15 …… ITO layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Onishi, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. 56) References JP-A-61-203427 (JP, A) JP-A-61-166590 (JP, A) JP-A-56-62228 (JP, A) JP-A-56-59220 (JP, A) JP-A Sho 61-235814 (JP, A)

Claims (4)

[Claims] 1. A liquid crystal layer and a plurality of substrates, at least one of which is disposed so as to sandwich the liquid crystal layer, is transparent, and a voltage applying means attached to the substrate so that a voltage can be applied to the liquid crystal layer. In addition, in a panel in which a spacer that defines the cell thickness is attached to at least one of the substrates, the spacer has at least a line-shaped portion, and an inorganic substance is obliquely vapor-deposited from a direction perpendicular to the line. By doing so, a ferroelectric liquid crystal panel characterized by controlling the alignment of the ferroelectric liquid crystal. 2. The ferroelectric material according to claim 1, wherein a region where the orientation control layer exists and a region where the orientation control layer does not exist are mixed in at least one of the plurality of substrates. Liquid crystal panel. 3. The ferroelectric liquid crystal panel according to claim 1, characterized in that the inorganic substance is silicon oxide. 4. A ferroelectric liquid crystal panel according to any one of claims (1) to (3), characterized in that the spacer is made of an insulating material and is made by a printing method. .