JPS5842030A - Display element - Google Patents

Abstract

PURPOSE:To drive a liquid crystal display element with a low voltage and make the high-speed response possible, by providing a minute material, which enhances the electric field in a liquid crystal layer, in the liquid crystal layer. CONSTITUTION:Particles 9 of minute materials having an outside diameter D are scattered on electrode faces of a liquid crystal layer 4 held between substrates 1 where electrodes 2 are formed on faces facing to each other. A particle dielectric constant epsilonM is higher than a liquid crystal dielectric constant epsiloni for non- application. Equipotential lines 10 in the liquid crystal layer are dense near a potential line 10 in the liquid crystal layer are dense near a position A of a particle 9, and the electric field is enhanced there. Consequently, the rise time is shortened, and the liquid crystal display element is driven with a low voltage, and the high-speed response is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display element, and particularly to a display element that is excellent in low voltage and high-speed response.

Normally, a display element has a pair of substrates that face each other with a slight gap between them, electrodes are provided on the opposing surfaces of the side substrates, the display body +1 is held between the side substrates, and the opposing portions of the electrodes and the space between them. A pixel 1 is formed on the display body located at . and,
The display element is driven by changing the magnitude (effective value) of the voltage applied between both electrodes.

As an example, FIG. 1 shows a display element using a phase change guest-host type liquid crystal as a display material.

Electrodes 2 are formed on opposing surfaces of a pair of transparent substrates 1, and a horizontally aligned film 3 is formed thereon.

As shown in Fig. 1(a), the liquid crystal is a chiral nematic liquid crystal 4 which has a cholesteric structure (helical structure) in which cholesteric liquid crystal is completely mixed in Np (positive nematic) liquid crystal.
In this case, dichroic dye 5 was mixed. The dye molecules 5 are arranged along the helical structure of the liquid crystal molecules, and the long axis direction (light absorption direction) of the dye molecules is parallel to the surface of the substrate 1, so the incident light 7 is absorbed and colored (the color of the dye). It looks like it does. When the electric field E applied between the upper and lower electrodes 2 exceeds the critical voltage Ec, the first
The phase changes to a TJ structure, and the liquid crystal molecules and dye molecules are attached to the substrate,
1, the incident light 7 is not absorbed by the liquid crystal layer and exits as transmitted light 8. That is, the pixel changes from a colored state to a colorless state by applying a voltage.

°The critical electric field Ec is from Leslie's paper (Molec.

CrySt, 1iquid, Cryst, yot1
2.1970), the pitch of the emission line of the cholesteric structure is P. Then, we have the following relationship.

K here, 1 + K 22 is 5 plays each,
It is Bend's elastic constant.

Further, when the gap length d of the element is constant, the smaller the pitch Po of the bright lines, the more light in all vibration directions is absorbed by the dye, so the contrast ratio improves. The relationship between the critical electric field Ec, the contrast ratio CC, and the bright line pitch P0 is as shown in Figure 2. If the contrast ratio CC is increased, the critical Narita becomes higher, which means that it is necessary to raise the driving Narita. . Also, the response time when voltage is applied (
The rise time tr, the fall time 1f,) are given by the following equation.

Here, η is the viscosity of the liquid crystal, Δε is the alignment anisotropy of the liquid crystal molecules, and K is the elastic constant of the liquid crystal material. In order to obtain a display element with a high contrast ratio, the amount of cholesteric liquid crystal added to nematic liquid crystal is increased to increase # and line pitch P.
. However, as shown in Figure 2 and Equation (3), the drive voltage of the display element becomes higher1, and P in Equation (3) increases.
As o becomes smaller, the rise time t also becomes longer. That is, there is a problem that the response speed of the display element becomes slow.

Furthermore, although TN type liquid crystal display elements are superior in low voltage driving and responsiveness compared to phase change type liquid crystal display elements, their responsiveness is inferior to other display systems such as fluorescent display tubes and CRTs. When considering the application of liquid crystal elements to TVs and automobile instrument panels, it is necessary to achieve high-speed response.

The response time t・, tf of a TN liquid crystal display element is determined by the following formula % Formula % Formula (3) 9 From formula (5), as the electric field Et applied between the electrodes is increased, the rise time t becomes shorter and the contrast ratio improves. I know what to do.

Means for increasing the electric field E applied between the electrodes include increasing the driving voltage or shortening the gear length d'ff: between the electrodes.

Increasing the drive voltage increases power consumption, which negates the advantages of low voltage drive and low power consumption of the liquid crystal display element. Also, if the gear length d6 between the electrodes is shortened,
There is a problem in that it is technically difficult to make d uniformly constant, and color unevenness is likely to occur.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a display element that can be driven at a low voltage, has a high-speed response, and has a high contrast ratio even if it has a certain gap length. be.

The display element of the present invention that achieves the above goals is characterized by providing a dielectric constant greater than the dielectric constant of the display body when no driving voltage is applied between the opposing electrodes.

Here, the "display" refers to a field-effect display, and is preferably a liquid crystal, but is not limited thereto. In addition, "fine IP objects" include metals, organic materials, inorganic materials, and materials made of two or more of these materials, and are not limited to other materials as long as the dielectric constant is greater than that of the display material before voltage is applied. .

Furthermore, the display device of the present invention is characterized in that when the display body is a gold phase change liquid crystal, the length in the direction of the opposite electrodes is the thickness of the phase change liquid crystal layer between the opposite electrodes. The purpose is to provide a container for minute objects smaller than the above.

FIG. 3 is a diagram showing the main points of the present invention. There is a liquid crystal layer 4 which is a display body sandwiched between substrates 1 having electrodes 2 formed on opposing surfaces, and particles ±9 which are minute objects having an outer diameter are dispersed on the electrode surfaces.

The dielectric constant of the liquid crystal is ε11, and the dielectric constant of the particles is εMakoto.

(b) When ε〉ε, 11.91
010. (7) As shown in FIG. 3(a), the equipotential [10] in the liquid crystal layer becomes dense in the vicinity A of the particle 9, and the electric field becomes high.

(b) When εM: εi...
(8) As shown in FIG. 3(b), the equipotential lines 10 in the liquid crystal layer are uniform regardless of the presence of particles 9,
The presence of particles does not affect the electric field distribution within the liquid crystal layer.

(c) ε store〈When ε1...
(9) As shown in FIG. 3(C), the equipotential line 1° in the liquid crystal layer becomes rough in the vicinity A of the particle 9, and the electric field is relaxed.

Therefore, by providing at least one minute object between opposing electrodes with a dielectric constant higher than the dielectric constant of the liquid crystal when no driving voltage is applied, the center field can be concentrated as shown in Fig. 3(a). As a result, the electric field on the surface becomes higher, the start-up time becomes shorter, the liquid crystal display element can be driven with a lower voltage, and high-speed response becomes possible.

Furthermore, when the display material is, for example, a cholesteric nematic phase change liquid crystal or a guest-host type phase change liquid crystal obtained by adding a dichroic dye to a chiral nematic liquid crystal, a hysteresis phenomenon occurs. This phenomenon is shown in FIG. The change in the amount of light transmission B differs between when the effective value v of the voltage applied to the display element is completely raised (2) and when it is lowered (2). Unless this hysteresis phenomenon is actively utilized, time-division driving of the display element becomes difficult.

Therefore, in Fig. 3, on the dielectric constant of the particles, the dielectric constant of the liquid crystal when the driving voltage εv1 is not applied is 61, and the dielectric constant of the liquid crystal when the driving voltage is applied is ε8, and ε1〈εV〈 εS・・・・・・・・・
1101.

When the effective value of the voltage applied to the display element is increased, since ε is εV, electric field concentration occurs in the liquid crystal layer, and the apparent electric field becomes stronger. It becomes like this. Furthermore, when the effective value of the voltage applied to the display element is lowered, the electric field in the liquid crystal layer is relaxed because ε is <ε8, and the apparent electric field becomes weaker.
′, the hysteresis loop becomes smaller, and
Time-division driving is possible with low voltage.

In addition, when the display is a liquid crystal, as can be seen from equations (4) and (6), the falling time is 1. is almost determined by the physical property values of the liquid crystal material. However, as a result of experiments conducted by the present inventors, it has been found that, in the case of a phase change type liquid crystal element, there are other controlling factors in addition to the above-mentioned parameters for the rise and fall times. This is caused by dust particles existing in the liquid crystal layer and discs left behind from the cholesteric-nematic phase transition.
ination1inete8ru. Ko (7) discli
Nation 1ine is basically a liquid crystal! − Exists around dust particles within. Therefore, by artificially providing foreign particles in the liquid crystal layer, the same effects as described above can be brought about. E, P, aAYNEs literature
tic, Display, 1975), these defects behave as "nucleus points" during the cholesteric-nematic phase transition when voltage is applied, and the presence of these defects shortens the response time of the liquid crystal display element. Says.

Conventionally, the first condition for manufacturing has been to avoid foreign matter within the liquid crystal. This is because there is a fear that the presence of foreign matter may cause conductive ions to be mixed in, resulting in a shortened lifespan or a deterioration in display quality. However, it has been confirmed through experiments that the above problem can be avoided if the type of foreign matter and the amount of contamination are considered.

Therefore, by providing a minute object in the liquid crystal layer that increases the electric field within the liquid crystal layer, it becomes possible to drive the liquid crystal display element at a low voltage and achieve high-speed response for the reasons stated above.

FIG. 5 is a diagram showing a first embodiment of the present invention.

Organic solvent for polyamide resin (cyclohexanone, DM
Titanium oxide ('riot, dielectric constant 113) in solution
particles are mixed in and applied onto the substrate 1. Next 1
After drying the solvent at a temperature around 20C, approximately 700 particles, which are "microscopic objects", are integrated with the resin film and formed on the electrode.
distributed at the rate of crn2. In this case, it is sufficient that at least one minute object is provided. Thereafter, this film surface is subjected to an orientation treatment to provide an orientation film 3. Spacers 12 are dispersed in the surrounding sealing material 11 to create a gap between the elements, and liquid crystal 4 is sealed between the substrates. In this case, the gap length d is 10 μm, but is not limited to this.

The liquid crystal 4 which is a display body is, for example, E, P of MerCk.
CH-based liquid crystal ZLI-1132, cholesteric liquid crystal C
This is a guest-host type phase change liquid crystal with a helical structure containing 3% B-15 and 3% dichroic dye GB-10. The pitch of the spiral is 10 μm and d/P0210. The dielectric constant ε of this liquid crystal layer in its initial alignment state is 4.5.1 [The dielectric constant εB of the liquid crystal layer when the pressure is sufficiently high and it is in a nematic state is 17.5. ε−9εs < T iOt
satisfies the condition of Equation (7) that the dielectric constant ε wrinkles. The potential distribution in the liquid crystal layer when voltage is applied to the display element is as shown in FIG. 3(a), and the electric field near the TiO2 powder is strengthened. The grain size of Ti01 was set to 3 μm (the alignment film thickness was 0).
．． 1 μm), the electric field near the TiO2 particle 9 is about three times the uniform electric field. Therefore, it can be driven with a low voltage and the rise time is shortened.

In addition, since the display body is a phase change liquid crystal, the TiO2 particles 9 are
They behave as the aforementioned dust particles and shorten the response time of the display element.

Furthermore, since ε is smaller than εy, the hysteresis effect can be reduced and time-division driving becomes easier.

Table 1 is a table showing the effects of the first embodiment of the present invention confirmed by the inventors. Operating voltage is approximately 1V compared to conventional elements
The start-up and fall times are reduced to less than 1/2.

Although particles with a diameter of 3 μm were used in the examples of the present invention, the electric field near the particles is influenced by the distance between the particles.

As shown in FIG. 6, the electric field near the particles 13 is higher in the figure (b) where the distance between particles is shorter than in the figure (a) where the distance between particles is larger, and the effect of the present invention is increased.

A typical material with a high dielectric constant is a metal, and the dielectric constant is theoretically infinite. Therefore, Cu, Fe, A
Powders of all metal materials such as T, SUS, etc. can be used.

FIG. 7 is a diagram showing a second embodiment of the present invention.

In FIG. 7, the minute object in FIG. 5 is 9 instead of Attos, and the other structures are the same as in FIG. 5.

Since the dielectric constant εV of A t t Os is 9.7, ε
The dielectric constant εw (t B) of + < A At Os satisfies the condition 2〇〇.

In this example, when voltage is applied to the display element, the electric field in the liquid crystal layer is strengthened as shown in Figure 3(a) because the permittivity of the particles is larger than that of the liquid crystal layer. Therefore, as in the first embodiment, the driving voltage is low and the response time is also shortened.

Furthermore, in this example, a cholesteric-nematic phase transition occurs, and when the liquid crystal layer becomes a nematic phase, the dielectric constant of the liquid crystal layer becomes larger than that of the particles, as shown in FIG. 3(e). On the contrary, the electric field is weakened. the result,
The hysteresis loop becomes smaller. Table 2 shows the effects. Vl, Vt and Vr defined in FIG.
Comparing Vt, the voltage applied to the liquid crystal layer Vt
Vt is reduced to about 172.

The above explanation relates to a display element using a negative guest-host type phase change liquid crystal using a cholesteric liquid crystal with positive dielectric anisotropy. Needless to say, the present invention can be applied to display elements using positive guest-host type phase and transition liquid crystals, and can also be applied to phase transition liquid crystals in which dichroic dyes are added to chiral nematic liquid crystals. Furthermore, the present invention can also be applied to smectic liquid crystals having a hysteresis phenomenon.

FIG. 8 is a diagram showing the temperature characteristics of the rise time (driving voltage 6V) when the present invention is applied to a TN liquid crystal display element.

The alignment film is a rubbed polyamide resin film, and the liquid crystal is biphenyl liquid crystal E7. Further, the device gap was 10 μm, and Tie powder with a diameter of 3 μm was used as the particles. As shown in FIG. 8, when the temperature of the crystalline layer decreases, the response time of the display element increases rapidly. However, in the display element of the present invention, the electric field strength in the liquid/crystal layer is increased due to the presence of TiO□ particles, which are minute objects, so as shown in Figure 8 (■), as supported by equation (5), Even at low temperatures, a considerably faster response can be obtained compared to the conventional example shown in FIG.

FIG. 9 is a diagram showing another embodiment of the present invention.

The minute object is not limited to the electrode surface, but as shown in FIG. 9(a), a solvent (such as isopropyl alcohol) containing particles as the minute object is placed on the surface of the oriented resin film 3 formed on the substrate 1. may be provided on the alignment film 3 by known means such as dispersing it with a spinner and drying the solvent. It's fine even if you don't have it.

Mae, fine! ', O. The shape is not limited to actual strength, but may be any shape such as fiber, prismatic, etc., and the size of the minute object is determined by the length in the direction of the opposing electrodes.
It is arbitrary as long as it is smaller than the thickness of the display body between the opposing electrodes, and the shape shown in FIG. 9(b) is C□. However, if the minute object has an 8° property, in order to prevent a short circuit between the upper and lower electrodes, either provide a material with a diameter smaller than the gap length d only on one substrate, or provide a material with a diameter smaller than half of the gap length d. It is desirable to provide a small writing object on the side substrate.

Further, as shown in FIG. 9(C), a spacer 11 for keeping the gap length d constant and a microshape object may be provided in combination.

Furthermore, "providing a minute object" is a concept that includes the case where a part of the electrode 2 is provided with a convex (the shape of the convex is arbitrary) as shown in FIG. 9(d). Any means that locally reduces the thickness of the display body in the area facing the electrodes may be used.

In the embodiments of the present invention, liquid crystals such as guest-host type phase change liquid crystals and TN type liquid crystals are used as examples of display bodies, but the present invention can be applied to any field effect type display body. .

As described above, according to the present invention, it is possible to obtain a display element that can be driven at a low voltage, has a high-speed response, and has a high contrast ratio even if it has a certain gap length.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the structure of a conventional display element, Fig. 2 is a diagram showing the characteristics of a conventional liquid crystal element, Fig. 3 is a diagram showing the main points of the present invention, and Fig. 4 is a diagram showing the phenomenon of hysteresis. FIG. 5 is a sectional view of the first embodiment of the present invention, Table 1 shows the effects of the first embodiment, FIG. 6 is a diagram showing the influence of particle size, and FIG. Table 2 is a cross-sectional view of the second embodiment, Table 2 is a diagram showing the effects of the second embodiment, FIG. 8 is a diagram showing the effects of the present invention applied to a TNW'tL crystal element, and FIG. 9 is a diagram showing the effects of the present invention It is a figure which shows another Example. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Electrode, 3...Alignment treatment film, 4
...Liquid crystal, 5...Dichroic dye, 7...Incident light, 8
...Transmitted light, 9...Particle, -10...Equipotential line,
11...Sealing material, 12...1st 2nd figure 0 Pip+P. Table 2 4 degrees (0C) Figure 9 (α)
(4-procedural amendment (method) % formula % Relationship between the person making the amendment 1 and 1 Patent applicant IC office Marunouchi, Moyota-ku, Tokyo - Name of lower number 5-1
Koma 15111) Representative of Hitachi, Ltd.
3 1) Detailed explanation of the invention in the subject specification of the amendment by Shigeyo Katsu, 1, "Table 1 is...
・It will be shortened. ” is corrected as follows. "The effects of the @l embodiment of the present invention confirmed by the inventors are shown in the following table. Compared to conventional elements, the operating voltage is approximately IV lower, and the rise and fall times are shortened to 172 or less." 2. In the first line of page 15 of the specification of the present application, "become... in" is amended as follows. "The effect is shown in the table below. In Figure 4." 3. The column for the brief explanation of the drawings in this JiA specification is amended as follows. "Figure 1 is a diagram showing the structure of a conventional display element, Figure 2 is a diagram showing the characteristics of a conventional liquid crystal element, Figure 3 is a diagram showing the main points of the present invention, and Figure 4 is a diagram showing the phenomenon of hysteresis. , FIG. 5 is a cross-sectional view of the first embodiment of the present invention, FIG. 6 is a diagram showing the influence of particle size, and FIG. 7 is a cross-sectional view of the embodiment of the present invention shown in FIG. 2.
FIG. 8 is a diagram showing the effect of applying the present invention to a TNall liquid crystal element, and FIG. 9 is a diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Electrode, 3...Alignment treatment film, 4
...Liquid crystal, 5...Dichroic dye, 7...Incident light, 8
...Transmitted light, 9...particles, 10...! potential line, 1
DESCRIPTION OF SYMBOLS 1...Sealing material, 12...Spacer, 13...Particle vicinity. 4. Amend the preliminary drawings as shown in the attached drawings. Above Figure 1 Figure 2 Pitch 20 Figure 4 Figure 5 Figure 6 Mouth 7 Mouth 8 Figure Shi Star Cliff (1-)

Claims (1)

[Claims] 1. A display body is held between a pair of substrates each having electrodes on opposing surfaces, a pixel is formed by the opposing portions of the electrodes and the display body located between them, and the opposing electrodes having a dielectric constant greater than the dielectric constant of the display body when no driving voltage is applied between the opposing electrodes, in which the brightness and darkness of the pixel is controlled by a driving voltage selectively applied between the electrodes; A display element characterized in that a minute object is provided whose length in the direction of the opposing electrodes is smaller than the thickness of the display body between the opposing electrodes. 2. A display element according to claim 1, characterized in that the display body is a liquid crystal. 3. In claim 1, the display body is a liquid crystal having a hysteresis phenomenon, and the dielectric constant of the minute object is equal to the dielectric constant of the liquid crystal having the hysteresis phenomenon when no driving voltage is applied. 1. A display element characterized in that the dielectric constant is larger than that of a liquid crystal and has a dielectric constant smaller than that of a liquid crystal having the above-mentioned hysteresis phenomenon when a voltage is applied. 4. A phase change liquid crystal is held between a pair of substrates each having electrodes on opposing surfaces, and a pixel is formed by the opposing portions of the electrodes and the phase change liquid crystal located between them. The brightness of the pixel is controlled by the driving voltage applied to the pixel, and the length between the opposing electrodes in the direction of the opposing electrodes is greater than the thickness of the small phase transition liquid crystal layer between the opposing electrodes. A display element characterized by providing a small minute object. 5.1# A display element according to claim 1 or 4, wherein the minute object is TtOt. 6. A display element according to claim 1, 3, or 4, wherein the J object is A t20s.