NL1025924C2 - Liquid crystal colour light switch for e.g. low power colour liquid crystal displays, comprises liquid crystal cell with substrates coated with electrodes and controlled voltage applied to electrodes to change critical reflection wavelength - Google Patents

Abstract

The switch comprises a liquid crystal cell with upper and lower transparent substrates (101) which are sealed on all sides, transparent electrodes (103) and alignment layers (104) with an angle of inclination of 0- 90[deg] formed by coatings on the substrates and a cholesteric liquid crystal layer (105) in a focal conical state between the two electrodes. The symmetry axes (106) for all the domains of the liquid crystal layer have the same direction extending parallel to the electrodes. A control voltage is applied to the electrodes in order to alter the crystal reflection wavelength. An independent claim is also included for a method for preparing the switch, comprising the following steps:preparing a cholesteric liquid crystal composition with a nematic/chiral component ratio of 0.67:1-10:1; #applying transparent electrodes to the substrates by vapour deposition; #coating the electrodes with an organic material or applying an inorganic material (e.g. SiOx) by vapour deposition to form the alignment layers; #polishing the alignment layer material in one direction, the rubbing directions for the two layers being parallel to each other; #filling the cell with the liquid crystal composition using vacuum suction or capillary forces and sealing the cell on all sides; #cleaning the outsides of the substrates and gluing two trapezoidal prisms onto the cleaned surfaces, taking care not to form any air bubbles; and #heating the cell in an oven to a temperature above the clean point and slowly cooling in order to obtain a good ! one-dimensional focal conical state at 70-100[deg]C.

Description

Liquid crystal color switch and method of manufacture

Reference to related applications

This application is for this invention and claims the filing date of Chinese application # 02128839.9 filed August 15, 2002, entitled 5

Declaration on federally sponsored research or development

Not applicable Background of the invention

Better and better quality is constantly being demanded for liquid crystal color displays of low power. In certain special applications, for example for LCOS (Liquid Crystal On Silicon) projection displays with large screen, the requirements include photo-realistic images, fast and accurate colors, and a high light output. So far there is no color light switch that accepts strong lighting and absorbs virtually no light during the process.

20 Two major technologies currently dominate with the use of liquid crystal displays to display color. The most common is STN-LCD and TFT-LCD, which use color filters to determine its basic colors, which cannot be changed by external means. Another is Electrically Controlled Birefringence (ECB) liquid crystal display technology, where the basic colors are obtained by controlling the voltages applied to the liquid crystal layer to change the delay. The light concentrates most in the center, and is therefore not as bright at the edges, and the light output is low. None of these technologies is able to change colors quickly. Both technologies also use polarizers and color filters that absorb light. When strong light is allowed to shine on the imagers 35 used for projection displays, the temperature will rise to a point where it exceeds the normal operating range of the imager. Therefore, color displays based on current liquid crystal technologies cannot fulfill the needs for color projection.

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Brief summary of the invention

The present invention relates to a color light switch and the method for manufacturing it. By controlling an applied voltage, the color light switch can change its critical reflection wavelength, so that the incident light reflects at an oblique angle red and then green and then blue in rapid succession, in response to the applied voltage, and thus a color display system realize.

It is an object of the invention to provide a liquid crystal color light switch, with a cell of liquid crystals, which are provided with upper and lower transparent substrates, sealed on all sides, the corresponding inner surfaces of the transparent substrates being covered with transparent electrodes. The inner surfaces of the transparent electrodes are further coated with alignment layers, with the preset oblique angle ranging from about 1 ° to about 89 °. A layer of cholesterically liquid crystals in a focally conical state is located between the two transparent electrodes, with the axis of symmetry of all regions in the same direction, parallel to the two transparent electrodes. The controlled voltage is applied to change the critical reflection wavelength.

It is another object of the invention to provide a method of manufacturing a cholesteric liquid crystal color light switch with liquid crystal, which is a mixture of nematic liquid crystal and chiral components, in a weight ratio of about 0, 67: 1 to about 10: 1.

Transparent electrodes are vapor-deposited on the upper and lower substrates, which are further coated with organic material or on which inorganic material has been deposited as alignment layers. The prepared liquid crystal cell is placed in an oven, heated above the purification point of the liquid crystal mixture, and then cooled slowly until a good one-dimensional focal conical state is achieved, the associated temperature being 70 ° C to 10 ° C.

A normal liquid crystal cell is filled with cholesteric liquid crystals that include both flat and focal conical states. In the flat state, the axis of symmetry is perpendicular to or almost perpendicular to the substrate. If light falls on it, only that light with the same direction of rotation as cholesteric liquid crystal structure will produce Bragg reflection, while the rest will be led out of the liquid crystal layer.

In the rest state, when no voltage is applied, the wavelength of the reflected light and the bandwidth are respectively: (formula, etc.)

In the normal focal conical state, the symmetry axis is parallel or approximately parallel to the substrate and the regions are two-dimensionally distributed randomly. When illuminated with incident light, a small amount is reflected, while the rest is guided through the device.

In the rest state there are two different structures / states and numerous gray-tinted middle states, all of which are stable. There are numerous small areas whose axes of symmetry have different directions. At a certain electric field, two different states 30 can change back and forth in the same phase.

The present invention uses special surface treatments and control technology to achieve a stable one-dimensional aligned focal conical state within all or part of the liquid crystal layer. The striking light and the reflected light are located on opposite sides of the liquid crystal cell.

According to formula (1), the critical reflection wavelength is determined by the height P, the incident angle theta, and 162.56-24, the average refractive index of the liquid crystal material.

The height P of the cholesteric liquid crystal can be changed by changing the applied voltage. In other words, P is a function of V. When the applied electromagnetic field is strong enough, the height P becomes infinitely long.

This liquid crystal color light switch operates when P is within limited values, so that the liquid crystal maintains its focal conical state and no flat state occurs. With a different electromagnetic field, the corresponding height P (V) corresponds to different reflection wavelength. When the reflection wavelength is within the visible light spectrum, it will match different colors. As a result, the center of the reflection wavelength is continuously adjustable.

The present invention has the following advantages over the existing technologies: 1. The present invention uses the electro-optical characteristics of cholesteric liquid crystals, by applying the applied voltage to the liquid crystal layer to the wavelength of the reflected light so that the voltage can quickly change the reflected colors.

2. The present invention is not constructed with layers that absorb light (e.g., polarizers, color filters) that would increase the operating temperature of the device under strong lighting, and reduce the light output of the device. The present device allows the use of strong illumination, and is suitable for use with LCOS, DMD and other displays and other telecommunication devices.

3. The present invention produces very little light scattering. The transmitted light and the reflected light have no scattering effects.

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Brief description of the drawings

Figure 1 shows a block diagram of the invention (color light switch).

Figure 2 shows the interaction of light with the color light switch.

Figure 3 shows the color spectrum of the reflected light under differently applied control voltages.

Detailed description of the invention

Figure 1 illustrates an example of a liquid crystal color light switch. In this example we have a liquid crystal cell consisting of upper and lower transparent substrates (101) made of glass or other materials, sealed on all sides (102), with corresponding inner surfaces of the transparent substrates coated with transparent electrodes ( 103), wherein transparent conductive coatings are typically made with ITO (indium tin oxide, which is indium oxide contaminated with tin oxide), wherein the inner surface of the transparent electrodes is coated with alignment layers (104), with the slanted angle between 1 ° and 89 °, wherein a larger slanted angle (> 30 °) gives a more stable focal conical state and the alignment layer helps align the liquid crystals with proper alignment and tilt angle. In this example, the pretension angle is approximately 60 °.

There is a layer of cholesterically liquid crystals (105) between the two transparent substrates, the liquid crystals being in a one dimensionally aligned focal conical state, the axes of symmetry (106) of all domains being in the same direction, and parallel to the two transparent substrates. The applied voltage is controlled to change the critical reflection wavelength. The cholesteric liquid crystal material that is used is a mixture of nematic liquid crystal and a chiral component, wherein their weight ratio is from 2: 3 to 10: 1. The best ratio is around 1: 1 or up to 4: 1. Other inactive ingredients, such as coagulants and surfactants, can also be added, not exceeding 5% by weight of the mixture.

The key to a successful liquid crystal color light switch is the construction of the liquid crystal cell and the choice of the liquid crystal mixture. The thickness of the liquid crystal should be small. In our example, the thickness is 1 to 10 microns. The liquid crystal cell measures 0.8 inches by 0.8 inches, without the use of spacers.

10 (formula for height, etc.)

In Figure 2, the present invention is integrated with two supporting trapezoidal prisms (200, 202). To simplify manufacture for mass production, it is best to use material with compatible refractive indices, such as Canadian Balm or vulcanized resin, to glue the transparent prisms to the substrates of the liquid crystal cell. Within the liquid crystal cell, the dimensionally aligned cholesteric liquid crystal material (201) is in a focal conical state, the axes of symmetry (206) being parallel to each other and to the substrates. Striking light (203) and reflected light (205) are located on opposite sides of the liquid crystal cell, and in the same plane with the axis of symmetry. Considering the striking white light as left and right circularly polarized light, only the light with the same polarity as the cholesteric liquid crystal at a certain wavelength is reflected, the remainder will be transmitted and form the transmitted light (204). The transmitted light is the complement of the reflected light, which is the incident light minus the reflected light.

The middle wavelength of the reflected light is: (formula, etc.) 35

In Figure 3, when a voltage of v0 is applied to the liquid crystal cell, curve 301 shows that the reflected light spectrum is centered at a wavelength of 1,025,924, 7 of 400 nm. When a voltage of Vi is applied to the liquid crystal cell, curve 302 shows the reflected light spectrum centered at a wavelength of 450 nm. When a voltage of Va is applied to the liquid crystal cell, curve 303 shows that the reflected light spectrum is centered at a wavelength of 550 nm. When a voltage of V3 is applied to the liquid crystal cell, curve 304 shows that the reflected light spectrum is centered at a wavelength of 610 nm.

In this example, the applied voltage is a pulsed voltage that has no DC component when averaged over time

Example 1 of the method used in manufacturing the color light switch: a. Preparing the liquid crystal mixture using EM-provided chemicals. The weight part of ZLI-5400-100: R1011: CB-15: R- 811 »76: 5: 12: 7.

b. depositing the thin film layers of the upper and lower substrates of ITO by vapor deposition to form transparent electrodes, on which SiOx is deposited on top, the prediction angles being approximately 60 °.

c. the inclination angles of the alignment layer on the upper and lower electrodes are parallel but in opposite directions.

d. construct a liquid crystal cell with a thickness of 2.3 micrometers, and a dimension of 0.8 inches by 0.8 inches. By vacuum suction or capillary action, the cell is filled with the prepared liquid crystal mixture, and all sides are sealed with a sealant; e. the outer surfaces of the upper and lower glass substrates are thoroughly cleaned, Canadian balm is applied, and two trapezoidal prisms are glued to the cleaned surfaces, ensuring that no bubbles are trapped during this process; f. the prepared liquid crystal cell is placed inside an oven, heated to or above the cleaning point of the liquid crystal mixture and then cooled slowly until a good single domain focal conical state is reached, with the associated temperature of 70 ° C to 100 ° C. (80 ° is the best).

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Example 2 of the method used in manufacturing the color light switch: a. Preparing the liquid crystal mixture using EM-provided chemicals. The weight ratio of ZLI-5400-100: R1011: CB-15: R-811 = 76: 5: 12: 7.

b. the vapor deposition on the transparent electrodes on the upper and lower glass substrates is SiOx, with an inclination angle of 65 °; C. rubbing in a single direction applied to the organic alignment material on the surface; d. by vacuum suction or capillary action, filling the cell with the prepared liquid crystal mixture, and sealing on all sides; 20 e. thoroughly cleaning the outer surfaces of the upper and lower glass substrates, applying Canadian balm, and gluing two trapezoidal prisms glued to the cleaned surfaces, ensuring that no bubbles are trapped in the process; and f. applying a voltage greater than the disentanglement voltage between the two substrates, the alternating frequency being 1 kHz, the voltage approximately 25 V and the duration greater than 10 microseconds, and thereafter the voltage 30 gradually drops to 10 V in approximately 2 seconds or longer to allow the liquid crystals to get into field-induced nematic state, and then the voltage is slowly lowered further until a good one-dimensional focal conical state is achieved.

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Claims (6)

A liquid crystal color light switch, comprising: a cell of liquid crystals with upper and lower transparent substrates sealed on all sides, wherein; associated inner surfaces of said upper and lower transparent substrates are coated with transparent electrodes and alignment layers with a prediction angle that is between 0 and 90 °; and a cholesteric liquid crystal layer in a focal conical state is contained between two said transparent electrodes; wherein the axes of symmetry of all domains of said cholesteric liquid crystals have the same direction parallel to the two transparent electrodes; and the provision includes that a control voltage can be applied to said transparent electrodes to change the critical reflection wavelength. The liquid crystal color light switch according to claim 1, wherein the thickness of the liquid crystal cell is 1-10 micrometers without a spacer. 3. Liquid crystal color light switch according to claim 2, further comprising: liquid crystal in a cholesteric phase, which is a mixture of nematic liquid crystal and chiral components, their weight ratio being from about 0.67: 1 to 10: 1 . The liquid crystal color light switch according to claim 2, wherein further the prediction angle is between 30 and 65 °. 5. A method for manufacturing a liquid crystal color light switch, comprising: a. Preparing the cholesteric phase liquid crystal mixture containing the desired ratio of thermal and chiral components between 0.67: 1 and 10: 1; b. depositing transparent electrodes on the upper and 10 2 5924. · Lower substrates, c. further coating the transparent electrodes with organic material or depositing inorganic material such as SiOx as alignment layers; 5 d. rubbing in a single direction applied to the organic alignment material on the surface, e. filling the cell by vacuum suction or capillary action with the prepared liquid crystal mixture and sealing on all sides, 10 f. thoroughly cleaning the outer surfaces of the upper and lower glass substrates, and gluing two trapezoidal prisms to the cleaned surfaces, ensuring that no bubbles are formed in the process; 15 g. placing the prepared liquid crystal cell inside an oven, heating it above the cleaning point of the liquid crystal mixture and then cooling slowly until a good one-dimensional focal conical state is achieved at a temperature of 70 ° C to 100 ° C. A method of manufacturing a flow bar crystal color light switch, comprising: a. Preparing the liquid crystal mixture of the cholesteric phase containing the desired ratio of thermal and chiral components between 0.67: 1 and 10: 1, 25 b. depositing transparent electrodes on the upper and lower substrates, c. further coating the transparent electrodes with organic material or depositing with inorganic material such as SiOx as alignment layers with a prediction angle of 65 ° d. rubbing in a single direction applied to the organic alignment material on the surface, e. filling the cell by vacuum suction or capillary action with the prepared liquid crystal mixture and sealing, f. thoroughly cleaning the outer surfaces of the upper and lower glass substrates, and gluing two trapezoidal prisms to the cleaned surfaces, ensuring that no bubbles are formed in the process; g. applying a voltage greater than the disentanglement voltage between the two substrates, to enable the liquid crystals to enter the field-induced nematic state and then slowly reduce the voltage until a good one-dimensional focal conical state. 1025924