JPS63271431A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To improve the voltage characteristic of the title element by directly forming the thin film of a ferroelectric org. polymer on at least one electrode. CONSTITUTION:A liq. crystal 1 is enclosed between a couple of electrodes 3 and 4, the thin film 2 of a ferroelectric org. polymer is formed between one electrode 3 and the liq. crystal 1, and the driving is carried out by impressing a voltage between the electrodes. A film is formed from a vinylidene fluoride polymer and a polymer contg. a cyano group by the conventional process, the film is then uniaxially or biaxially oriented or a high electric field of more than several times the anti-electric field is impressed, and the film 2 can be obtained. By this method, the voltage characteristic can be remarkably improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a liquid crystal element having a novel driving principle, more specifically, to a liquid crystal element in which a ferroelectric single molecule thin film is added to the liquid crystal element. J: Threshold voltage '+'': J This relates to a liquid crystal element with improved characteristics.

<Prior art> In the case of a liquid crystal device using the 71-RIS drive method, crosstalk between pixels is a problem in the conventional Leistid nematic (abbreviated as TN) type liquid crystal element, and the number of electrodes in the scanning direction is 100. It is difficult to do more. Currently, as technologies to improve the drawbacks of the TN type and further increase the number of electrodes in the scanning direction, there are active matrix methods using thin film transistors and super twist methods in which the twist angle of the liquid crystal on the wall is 270° or 180". However, the Actiama 1-RiX method requires many steps to manufacture, and it is extremely expensive to produce large, defect-free devices, and the supertwist method is difficult to display in color. There are drawbacks such as.

In addition, we used a so-called nonlinear resistance element in which the current does not follow Ohm's law because the resistance value of the dielectric thin film changes depending on the applied voltage (Metal-InsLIIa
tOr-Metal) type liquid crystal display elements (for example, Japanese Patent Application Laid-Open No. 60-241021) have also been developed.
This method has problems such as it is difficult to achieve uniform performance, and although the manufacturing process is improved over the active matrix method, it is still complicated.

<Problems to be Solved by the Invention> It is an object of the present invention to solve the problems of the prior art.
It is an object of the present invention to solve the above-mentioned drawbacks of the M method and to provide a liquid crystal element of a new method using a ferroelectric polymer thin film. That is, it is an object of the present invention to realize a large-capacity matrix-driven liquid crystal display device with less crosstalk between pixels.

Means for Solving Problems> The present invention essentially consists of a liquid crystal, an electrode facing the liquid crystal, and a ferroelectric organic polymer thin film interposed between at least one of the electrodes and the liquid crystal. This is a liquid crystal element formed by.

The liquid crystal used in the present invention may be any of nematic liquid crystal, cholesteric liquid crystal, and ferroelectric liquid crystal.

The ferroelectric organic polymer thin film referred to in the present invention means that (1) the polymer thin film has spontaneous polarization, and (2) T:1 of a certain size or more derived from the physical properties of the film is formed on both sides of the film. By applying a field (hereinafter referred to as a coercive electric field), the spontaneous polarization rotates in the direction of the electric field, and (J) Even after the electric field is removed, the spontaneous polarization of the membrane remains as long as no electric field is applied in the opposite direction. It refers to a thin polymer film that determines the properties it retains. Therefore, as a material for producing a ferroelectric organic polymer thin film, among organic polymers containing polar groups, the above properties (1) to (3) can be obtained during film formation or by corrosion treatment. Although it is not particularly limited as long as it has
F-TrFE), vinylidene fluoride copolymers such as vinylidene fluoride and tetrafluoroethylene copolymers (hereinafter referred to as P(VDF-TEFE)), and cyanovinylidene and vinyl acetate copolymers. Polymers containing cyano groups, such as copolymers and polyacrylonitrile, are used. In addition, single polymers of vinylidene fluoride and vinylidene chloride (hereinafter abbreviated as PVDF and PVDC, respectively) can be made into the ferroelectric organic polymer thin film of the present invention by subjecting them to the following special treatment. can. In other words, with PVDF and PVDC, the polarity within the crystal is canceled out by normal film forming processes such as solution coating method, spin cord method, immersion pulling method, casting method, vacuum evaporation method, and melt film forming method. It becomes a so-called α-type crystal, and cannot generate spontaneous polarization, but it can be generated by stretching the thin film uniaxially or biaxially after film formation, or by applying a high electric field several times higher than the coercive electric field. A ferroelectric organic polymer thin film that can be changed into a crystal type (referred to as a β-type crystal) and has the properties (1) to (3) above can be obtained.

Among the above materials that can be applied to the ferroelectric organic polymer B film, vinylidene fluoride copolymer is particularly preferred in view of the size of the spontaneous polarization matrix and the good squareness ratio of the D-E hysteresis curve. . As vinylidene fluoride copolymer,
P(VDF-TrFE), P(VDF-TEFE>
(1) In addition, a copolymer of vinylidene fluoride and vinyl fluoride, or a copolymer of vinylidene fluoride and a non-fluorine-based vinyl monomer can also be applied. Each of the above copolymers may further contain other copolymerizable vinyl monomers as a copolymerization component. It is also possible to use a blend of two or more of these vinylidene fluoride copolymers, or a blend of the vinylidene fluoride copolymer and another polymer material such as polymethyl methacrylate. Among these vinylidene fluoride copolymers, P (VDF-TrFE) and P (VDF-TEF
E> is preferred.

The copolymerization ratio of vinylidene fluoride in the vinylidene fluoride copolymer is 10 to 98 mol%, particularly 55 to 95 mol%.
is preferred. In the case of P (VDF-TrFE), the copolymerization ratio of vinylidene fluoride is 65 to 90 mol%,
In addition, the same ratio is 72 for P (VDF-TEFE>)
Particularly preferred is ~87 mol%.

To form a ferroelectric thin film, when vinylidene fluoride copolymer is used, it can be dissolved in a polar solvent such as dimethylborumamide, methyl ethyl chloride, or acetone, and applied on a substrate using a coating method, or It can be formed by a melt film forming method in which a film is formed by melting with heat. Specific methods of coating include dipping and pulling method, spin cord method,
Casting methods, coating with a bar coater, printing methods, etc. are effective. In this case, in order to further improve the adhesion between the substrate and the ferroelectric organic polymer thin film, a coupling material may be added on the substrate in advance. The substrate on which the ferroelectric organic polymer thin film is applied may be a glass plate with electrodes, a plastic panel with electrodes, a flexible film such as a polymer with electrodes, etc. It may also be a semiconductor such as silicon.

There is no particular limitation on the thickness of the ferroelectric organic polymer film, but the thicker it is, the higher the driving voltage will be when used as a liquid crystal element, and a wA thickness exceeding 5 μm is not suitable for practical use. The preferred film thickness is 0.01 to 5 μm, particularly preferably 0.05 to 2 μm.

In the case of PVDF and PVDC, a ferroelectric organic polymer thin film can be formed by uniaxially or biaxially stretching the thin film in the usual way, or by applying a high electric field several times higher than the coercive electric field. can be formed.

Although the ferroelectric organic polymer film has been described above, the liquid crystal element according to the present invention has a pair of electrodes as shown in FIG. The structure is based on a structure in which a liquid crystal is sealed between the electrodes (in which electrodes are formed), and driving is performed by applying a voltage between the electrodes.

When a voltage (V) is applied between the opposing electrodes of a liquid crystal element as shown in Figure 1, in which a ferroelectric thin film is formed using the above method, the voltage (abbreviated as a dielectric film), and its equivalent circuit is shown in FIG.

In the circuit shown in FIG. 2, the voltage (Vl) applied to the liquid crystal and the voltage (Vl) applied to the ferroelectric film are determined from the following equations.

Vl =V/ (1001/C() ■Vf=V
Vl (2) Here, C1 and Cl are the capacitances Q of the liquid crystal and ferroelectric film in the liquid crystal element, respectively. In formula (2), (1) becomes smaller as cl/Cf increases, and for C1/Cy~O, (1) becomes V.

On the other hand, Cf is expressed by the formula (2) using the thickness (d), area (S), and dielectric constant (6) of the ferroelectric film.

Cf-ε0εfS/d ■ Here ε. means the permittivity of vacuum.

Since ferroelectric materials have permanent polarization, their electric displacement is generally expressed by the equation (2), and it is known that they have hysteresis characteristics with respect to the electric field E.

D=ε ε E0P, ■r Here, P is permanent polarization, and ε is the dielectric constant due to electronic polarization. By differentiating the equation (2) with respect to the electric field E, the permittivity εf of the ferroelectric material, which takes permanent polarization into consideration, is expressed by the equation (2).

εf='9D 1 E= ε ε 10 P 1 E ■ Or S ■ ε in the formula. ε is constant regardless of the electric field, but permanent polarization is due to the coercive electric field E. In order to cause rotation in the direction of the electric field due to the above electric field, EVE. In the electric field of P /alE=o
However, if E≧E, then ε. It has a sufficiently large value compared to ε. E, due to the rapid increase in Cf at the border, C1
/Cf decreases rapidly, so the voltage Vl applied to the liquid crystal becomes EC@
: It increases rapidly at the border, and as shown in Figure 3, V
becomes nonlinear for . Therefore, in v=VC, Vl=
By setting the voltage to be VTh, it is possible to make the alignment characteristics of the liquid crystal depending on the voltage steep. Here, VTh means the threshold voltage for aligning the liquid crystal used, and this is a value specific to the liquid crystal material. Therefore, the threshold characteristics of the change in light transmittance due to the voltage of the liquid crystal element can be sharpened. The type of liquid crystal used is not limited to nematic liquid crystal, and may be either cholesteric liquid crystal or ferroelectric liquid crystal. Accordingly, various alignment methods such as TN type and guest-host type can be applied. Therefore, depending on the orientation method, the upper and lower polarizing plates shown in FIG. 1 are not necessary. On the other hand, VTh is V. In addition to selecting the thickness of the ferroelectric film and the liquid crystal layer, and selecting a liquid crystal material with an appropriate threshold voltage and dielectric constant, methods for setting the ferroelectric film and liquid crystal layer in the vicinity include selecting a liquid crystal material with an appropriate threshold voltage and dielectric constant. This can also be done by adjusting the effective area ratio of the liquid crystal and the ferroelectric film by adding a transparent intermediate electrode using a metal such as ΔU, Cr, indium oxide, or tin oxide on the ferroelectric film. can.

As is clear from the above description, the present invention utilizes the non-linear characteristics of the capacitance of the ferroelectric film in addition to the equivalent circuit of the liquid crystal element shown in FIG. The objective is to improve the threshold characteristics and realize a large-capacity liquid crystal device capable of high-duty driving.

The liquid crystal element of the present invention can be applied not only to liquid crystal display means but also to various uses such as liquid crystal shutters and projectors.

Examples> The liquid crystal element of the present invention will be described in detail below using examples.

Example 1 P (V
DF-TrFE) was made into a dimethylformamide solution and spicicoated onto a glass substrate to which a metal electrode (Δ1) was added to obtain a 0.5 μm thick ferroelectric thin film. Au was roughly deposited on this ferroelectric 8V to form an intermediate electrode. The actual measured value of the relationship between the electrical displacement of this film and the electric field E is shown in Figure 5 (
Shown in a>.

Since the permanent polarization rotates around the coercive electric field (Eo = 40 MV/IrL), a hysteresis curve with a good squareness ratio was obtained. In addition, the copolymerization molar fraction of vinylidene fluoride is 6
For 5%, 75%, and 86% P (VDF-RFE), films with a thickness of 0.5 μm were made using the above method.
The DE curve was measured. In the case of P (VDF-TrFE) with a copolymerization molar fraction of vinylidene fluoride of 65%, the results are shown in Figure 5(b), and when the copolymerization molar fraction of vinylidene fluoride is 75% and 86%. In the case of the copolymer, the same results as in FIG. 5(a) were obtained.

In addition, for P (VDF-TEFE), a thin film with a thickness of 0.5 μm was made using the above method for copolymers with vinylidene fluoride copolymerization molar fractions of 72% and 82%, respectively, and the D-E As a result of measuring the curves, the results shown in Figure 5 (C) were both 1q.

The relative permittivity of these ferroelectric thin films is ε'/ε0 is 2QQl
At low frequencies below lZ, E, 10-20 when lower electric fields are applied, and 15 for electric fields above EC.
It was 0. Figure 6 shows P (VDF-
εf/ε of the TrFE) e membrane (copolymerized mole fraction of vinylidene fluoride is 80%). The actual measured value is shown.

A liquid crystal element having the structure shown in FIG. 7 was constructed using the above-mentioned ferroelectric thin film made of P (VDF-TrFE) with a copolymerized mole fraction of vinylidene fluoride of 80%.A glass substrate was used as a transparent substrate. Indium oxide/
Tin oxide was used. The liquid crystal material used was a normal P-type nematic liquid crystal (Merck ZLI2144).The electric constant is ε
,,=29, ε=8, Vlo (voltage required for 10% orientation)=1.22V, V,. (Voltage required for 90% orientation) = 1.77V.

The area ratio (Sl /Sf) of the ferroelectric film to the liquid crystal layer is 200.
Then, the alignment film of polyvinyl alcohol was subjected to rubbing treatment so that the initial alignment of the liquid crystal was TN type. A polyethylene terephthalate film was used as a spacer with a thickness of 4 μTn, and a liquid crystal was sealed in the spacer.

FIG. 8 shows the measured values of the light transmittance of the liquid crystal cell with respect to the applied voltage. In Fig. 8, the light transmittance changes sharply around 21V, and V90/V10 in this element is 1.
．． It is 13. On the other hand, the liquid crystal material used was V9o/■
Since 1o is 1.45, this means that the threshold characteristics of the liquid crystal display element have been significantly improved by the present invention.

In addition, the copolymerization molar fraction of vinylidene fluoride is 65%, 7
For 5% and 86% P (VDF-TrFE), ferroelectric thin films with a thickness of 0.5 μm were fabricated in the same manner as above, and a liquid crystal element with the structure shown in Figure 7 was fabricated using them. As a result, light transmission band characteristics similar to those shown in FIG. 8 were obtained for all three.

Ferroelectric thin films of P (VDF-TEFE) with vinylidene fluoride copolymerization molar fractions of 72% and 82% were also produced by the above method.

These are the coercive electric fields of P(VDF-T used in this example)
Considering that it is slightly higher than rFE), the film thickness was set to 0.3.
It was set to 5 μm.

As a result of fabricating a 4vi liquid crystal element shown in FIG. 7 using these materials, almost the same light transmission band characteristics as those shown in FIG. 8 were obtained in both cases.

In addition, P (VDF-T
As a result of measuring the voltage dependence of resistance of 0.5 μm thick ferroelectric thin films consisting of P (rFE) and P (VDF-TEFE), the resistance value is voltage dependent in both cases in an electric field of 100 MV/m or less. It remained almost constant.

<Effects of the Invention> Compared to conventional TN type liquid crystal elements, the liquid crystal element according to the present invention has an extremely simple structure in which a ferroelectric organic polymer thin film is directly formed on at least one electrode. Nevertheless, its threshold voltage characteristics are greatly improved compared to conventional TN type elements. In addition, ferroelectric ceramics such as dill titanate/lead monophosphate and single crystal ferroelectric materials are conceivable as ferroelectric materials used in the device, but both are U films with a thickness of 5 μyn or less. It is extremely difficult to calculate 1q. Therefore, the operating voltage of the device becomes high, making it unsuitable for practical use. Furthermore, in a liquid crystal element, if the ferroelectric material is optically transparent, the element can be easily made into either a reflective type or a transmissive type, which is a great advantage. When using a ferroelectric polymer, a thin film of several μm or less can be easily obtained by coating it on a substrate on which an electrode is formed, and since it is optically transparent, it can be coated on the entire substrate. Even if it is done, it will not be a hindrance.

Furthermore, the present invention has the effect of significantly improving the threshold voltage characteristics of a liquid crystal element while keeping the manufacturing cost of the liquid crystal element sufficiently lower than that of a conventional active drive type element.

Therefore, when the element of the present invention is used in a matrix drive type liquid crystal device, crosstalk noise between pixels can be reduced, and a large capacity liquid crystal display device capable of high duty driving can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a liquid crystal element according to the present invention. FIG. 2 does not show an equivalent circuit of the liquid crystal element according to the present invention. FIG. 3 shows the voltage characteristics applied to the liquid crystal. FIG. 4 is a schematic diagram of the liquid crystal element of the present invention in which an intermediate electrode is added. Figure 5 shows the electric displacement-electric field hysteresis characteristics of a ferroelectric organic polymer film, and (a) shows P (V
The copolymerization ratio of vinylidene fluoride in DF-TrFE> is 8
0 mol%, (b) is 65% of the same proportion of P (VDF-TrFE>, (C) is P (VDF-TEF
The same proportions of E) are shown as 72% and 82%, respectively. FIG. 6 shows the dielectric constant-voltage characteristics of a ferroelectric organic polymer thin film. FIG. 7 is a schematic diagram of an element configuration in an embodiment of the present invention. FIG. 8 shows the light transmittance-voltage characteristics in an example of the present invention. 1... Liquid crystal 2... Ferroelectric organic polymer thin film 3...
Electrode 4...Transparent electrode 5...Substrate 6...Polarizing plate 7...Intermediate electrode 8...Alignment film Patent applicant Shi Azuma Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 5 (Turtle) Figure 5 (b) Figure 5 (Figure 6 Renf1nse IxCV)

Claims (3)

[Claims] (1) A liquid crystal element essentially consisting of a liquid crystal, electrodes facing each other with the liquid crystal in between, and a ferroelectric organic polymer thin film interposed between at least one of the electrodes and the liquid crystal. (2) The liquid crystal device according to claim (1), wherein the ferroelectric organic polymer thin film is made of vinylidene fluoride copolymer. (3) The ferroelectric organic polymer thin film has a thickness of 0.01 to 5
The liquid crystal element according to claim (1), which is in the μm range.