JPH07287115A - Reflection color filter and liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a reflection-type color display having not only enough contrast but enough brightness for practical use by forming a multilayer interference film comprising alternately laminated high refractive index thin films and low refractive index thin films on a substrate having a low reflectance. CONSTITUTION:Transparent dielectric films having low refractive index and transparent dielectric films having high refractive index are alternately laminated on a black substrate or a substrate 1 having low reflectance to obtain multilayer interference films 2, 3, 4 patterned as pixels. The film thickness of each layer of the multilayer interference film 2 is controlled to transmit <=600nm wavelength light and to reflect >=600nm light. Thus, the film 2 acts as a red reflection film. Also, the multilayer interference film 3 is formed by controlling the film thickness of each layer to transmit >=500nm light and reflect <=500nm light. Thus the film 3 acts as a blue reflection film. The multilayer interference film 4 is formed by controlling the film thickness of each layer to transmit <=500nm light and <=600nm light and reflect 500 to 600nm light. The film 4 acts as a green reflection film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a reflection type color filter that reflects light during color reproduction or color separation and functions as a color filter, and color display can be performed using this reflection type color filter. The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Color liquid crystal display devices are used in various display devices used in computers and the like, display devices used in office automation equipment and the like, or liquid crystal televisions which are one of flat-screen TVs and wall-mounted TVs. It is a display device having a very thin depth (a remarkable difference in depth as compared with a CRT is a simple example) and being extremely lightweight.

Direct-view liquid crystal display devices currently in use include TN (Twisted nemat-ic) type and STN.
The mainstream is of the (Super Twisted nematic) type, but in all of these liquid crystal display devices, the display is dark due to the use of a polarizing plate, which requires a backlight. This is because the direct view type liquid crystal display device uses a polarizing plate, so that the total amount of light handled is 50%.
This is because more than% has been cut. Therefore, as a reflective liquid crystal display device that does not require the backlight and can be displayed only by ambient light, polymer dispersed liquid crystal that performs display by controlling the light transmission state and the light scattering state has attracted attention. ing.

A cross-sectional structure of a reflection type color liquid crystal display device using polymer dispersed liquid crystal is schematically shown in FIG. In this reflective color liquid crystal display device, a pixel electrode is formed by dispersing a large number of liquid crystal particles 15 having a size of micron in a polymer matrix 14 or a liquid crystal containing a liquid crystal. Two boards 1
It is formed between 6 and 17. Then, in the color liquid crystal display device, when a voltage is applied to the pixel electrode, the liquid crystal is aligned along the direction of the electric field, so that the refractive indices of the polymer and the liquid crystal particles are uniform, and the liquid crystal becomes transparent (light transmitting state). become). on the other hand,
In this color liquid crystal display device, light is scattered because the liquid crystal orientation is random in a state where no voltage is applied, and as a result, it becomes an opaque state.

Substrate 17 has colored patterns 18, 19, 2
A color filter consisting of 0 is formed, and further, the substrate 1
A reflective plate 21 is provided on the outer side of 7 to realize a reflective color liquid crystal display device. In addition to this, it is also possible to form a reflective film on a substrate and then directly form a color filter on this.

[0006]

However, although there is no particular problem in the case of monochrome display, in the case of such a reflection type liquid crystal display device, the display is dark in the case of color display and is not in a sufficiently bright environment. There is a problem that it can not be used.

The reason why it is difficult to make bright display in the reflection type color liquid crystal display device is as follows: (1) 2 / of the white light incident on the color filter is caused by the color filter used as a component for colorization. 3 is absorbed, or (2) in a color filter formed by a dyeing method, a pigment dispersion method, or a printing method that is usually used, since a dye or a pigment is used as a coloring means, Since it cannot be expected that the transmittance is too high (for example, the upper limit of the transmittance of each color of red, green, and blue is 80 to 90%).
The cause is.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device capable of displaying not only contrast but also brightness of practically sufficient brightness and reflection type color display. And a reflective color filter suitable for use therein.

[0009]

[Means for Solving the Problems] Means provided by the present invention for solving the above-mentioned problems are as follows. First, a thin film made of a high refractive index material and a thin film made of a low refractive index material. A reflective color having a reflective pattern formed of a multilayer interference film in which the layers are alternately laminated in a desired shape on the substrate, and the substrate having a low reflectance. It is a filter.

Preferably, as shown in claim 2, the reflective color filter according to claim 1, wherein the reflective patterns are formed on the substrate so as to be spaced apart from each other.

Preferably, as described in claim 3, the substrate has a low reflectance for at least visible light, and the reflective color filter according to claim 1 or 2.

And, preferably, as shown in claim 4,
The reflective color filter according to claim 1, wherein the substrate has a low reflectance for light having a wavelength of 400 to 700 nm.

More preferably, as shown in claim 5,
5. The reflective color filter according to claim 1, wherein the reflectance of the substrate is 10% or less.

Further, as described in claim 6, in a liquid crystal display device which performs display by controlling a light scattering state and a light transmitting state by an electric field, one substrate has a low reflectance, and A liquid crystal display device characterized in that a reflective pattern made of a multilayer interference film in which thin films made of a high refractive index material and thin films made of a low refractive index material are alternately laminated is formed on the substrate. is there.

It is preferable that the reflective patterns are formed on the substrate so as to be spaced apart from each other.

Preferably, the substrate has a low reflectance for at least visible light, as described in claim 8 is the liquid crystal display device according to claim 6 or 7.

And preferably, as shown in claim 9,
The low reflectance of the substrate is a reflectance for light having a wavelength of 400 to 700 nm.
The liquid crystal display device according to any one of 1.

More preferably, as shown in claim 10, the low reflectance value of the substrate is 10% or less, and the liquid crystal display device according to any one of claims 6 to 7.

When the substrate area in the area where there is no reflective pattern made of the multilayer interference film is used as it is as a light-shielding pattern (a black pattern such as a so-called black matrix or black stripe), the substrate has a low reflectance. Having it is convenient. The light that reaches the substrate portion not covered by this reflective pattern has almost no reflection because the substrate has low reflectivity,
The substrate portion not covered with the reflective pattern can be used as it is as a so-called light-shielding pattern. When used as a display device for ordinary humans to see with the naked eye, it is preferable that the substrate has a low reflectance for at least visible light, and particularly, a low reflectance for light having a wavelength band of 400 to 700 nm. Preferably there is.

It is preferable that the substrate has a reflectance as low as possible, and for that purpose, it is preferable that the surface of the substrate is generally black. Also, even if the substrate itself is black,
Alternatively, the substrate itself may be non-black and a black layer may be formed on the surface of the substrate. Then, even if the substrate is not black as described above, the substrate itself has a low reflectance to some extent, or even if the substrate itself does not have a low reflectance, the surface thereof exhibits a low reflectance. If a layer is formed, a reflective color filter and a liquid crystal display device can be obtained which has no problems in practical use and can be used favorably. Incidentally, the black layer and the low reflectance layer on the surface of the substrate is preferably the side having the reflective pattern, however, when it is present on the opposite surface or the inner layer portion of the substrate, It is possible to obtain a reflective color filter and a liquid crystal display device having a certain level of performance, although the performance is lower than that on the above side.

That is, when the ratio of the reflected light which is a little due to the low reflectance and the reflected light of the pattern portion composed of the multi-layer interference thin film is above a certain level, the contrast which can be sufficiently discriminated by the naked eye is obtained. can get. It is generally difficult to determine what the limit of the contrast that can be satisfactorily discriminated by the naked eye is unequivocally because it is closely related to the sensory ability (with individual differences), but it is generally about 5: 1. For this reason, the preferred contrast in the present invention is preferably at least 5: 1, and more preferably 10: 1 or more in order to obtain a display that is easier to see. Due to these reasons, the reflectance of the portion exhibiting low reflectance is 1
It is particularly preferably 0% or less. However, as described above, even if the low-reflectance portion has a reflectance higher than this value, it is not impossible to obtain the reflective color filter and liquid crystal display device of the present invention.

In the reflection type color filter of the present invention, the multilayer interference film formed by a multilayer thin film in which high refractive index thin films and low refractive index thin films are alternately laminated transmits light in a specific wavelength region. On the other hand, the fact that the function as a color filter is exhibited by reflecting light outside the wavelength range is first applied. When the multilayer interference film is formed on a substrate whose surface is black or exhibits low reflectance, the light of the wavelength transmitted through the multilayer interference film reaches the substrate and is not reflected (or is not reflected so much). Therefore, only the light reflected by the multilayer interference film is observed and functions as a color filter. In addition, as a material of the multilayer thin film, there is a wide range of selection of refractive index as a thin film material, and high electric insulation (this portion causes a short circuit when the color filter is used in a liquid crystal display device). A dielectric is preferable for the reason such as avoiding danger). However, even if a thin film made of a conductor (a typical example is a metal material) is used, it can still be used if sufficient measures are taken against the insulating property.

Since such a multilayer interference film has a transmittance of almost 100% in the transmission wavelength region and a reflectance of almost 100% in the reflection wavelength region, the absorption of the dye is used. There is no decrease in transmittance like a color filter, and it is almost 10 for light in the desired wavelength range.
A reflective color filter having a reflectance of 0% can be obtained.

The present invention will be described in detail below with reference to (FIG. 1) and (FIG. 2). (FIG. 1) is a schematic view of a cross-sectional structure of a reflective color filter of the present invention. Multilayer interference films 2, 3, 4 by alternately laminating a transparent dielectric film having a low refractive index and a transparent dielectric film having a high refractive index on a substrate 1 having a black or low reflectance.
Are formed into a pixel shape and patterned. The multilayer interference film 2 sets the film thickness of each layer so that light of 600 nm or less is transmitted and light of 600 nm or more is reflected. This result 60
Light of 0 nm or less passes through the multilayer interference film and is hardly reflected on the surface of the substrate. On the other hand, since light having a wavelength of 600 nm or more is reflected by the multilayer interference film, this multilayer interference film 2 acts as a red reflective film.

Similarly, the thickness of each layer is set so that the multilayer interference film 3 transmits light of 500 nm or more and reflects light of 500 nm or less, and this is used as a blue reflection film, and the multilayer interference film 4 is 500 nm or less. And the light of 600 nm or more are transmitted, and the film thickness of each layer is set so as to reflect the light of 500 nm or more and 600 nm or less, and this is used as a green reflective film, and the reflective color filter is completed.

As the black or low-reflectance substrate 1, a glass or plastic substrate having a low-reflection film formed on the surface on which the multilayer interference film is formed, a metal substrate, or a glass or plastic substrate having the back surface painted black can be used. . The lower the reflectance of the substrate is, the more preferable. However, the reflectance may be within a range in which the light passing through the multilayer interference film is not reflected and the color purity of the reflected light is not deteriorated. Color display is possible.

As the dielectric thin film forming the multilayer interference film, it is common to use an inorganic thin film such as silicon oxide, titanium oxide, magnesium oxide or magnesium fluoride, but fluorocarbon, acrylic, epoxy, polyimide, etc. It is also possible to use a transparent resin thin film.

Of these, a combination of silicon oxide as the low dielectric constant film and titanium oxide as the high dielectric constant film is usually often used. In this case, a vacuum evaporation method is used for forming the multilayer film. Further, the patterning is performed by forming a lift-off material on a portion other than the portion where the multilayer interference film is formed in advance, depositing the multilayer interference film, and then simultaneously peeling off the multilayer interference film on the lift-off material and patterning it. A lift-off method or a method of forming a resist pattern by using a photoresist after depositing a multilayer interference film on the entire surface of the substrate and performing etching to form a pattern is used.

A reflective color filter is formed by repeating this process for the reflective film patterns of three colors of red, blue and green, for example. If a constant gap is provided at the boundary portion of each pattern, the reflective film does not exist in this portion, so that it functions as a black matrix. Therefore, in the color filter of the present invention, it is not necessary to newly form a light shielding pattern (for example, a black matrix).

Further, the combination of colors is not limited to the three primary colors of red, blue and green, and colors other than red, blue or green can be preferably used. For example, a reflective color filter having a combination of so-called complementary colors of yellow, cyan, and magenta may be used. In this case, the range of colors that can be displayed is inferior to the combination of red, blue, and green,
Since it reflects 2/3 of the incident light, it becomes a color filter capable of extremely bright multi-color display. Depending on the application, a combination of two colors may be used, or a reflective filter of a specific color can be formed by the same method by optimizing the film thickness and the number of layers of the multilayer interference film. It is possible. Regarding the setting method and the optimization of the film thickness and the number of layers of each layer of this multilayer interference film, publicly known literature (for example, Kazumi Murata "Science Library Physics = 9 Optics", Science Co., Ltd., 1979). The items described on pages 67 to 69 issued on the 25th of each month can be preferably used.

FIG. 2 is a schematic view showing a cross section of an example of the liquid crystal display device of the present invention. A low reflection layer made of a metal thin film is formed on the substrate 7, and a red reflection multilayer interference film 8, a blue reflection multilayer interference film 9, and a green reflection multilayer interference film 10 are formed on the substrate 7 in a pattern of pixel patterns. Has been done.

A pixel-shaped transparent conductive film 11 and a thin film transistor array connected thereto are formed on the substrate 6 on the opposite side. Polymer-dispersed liquid crystal in which liquid crystal is dispersed and held in a resin matrix is sandwiched between both substrates.
As the liquid crystal material sandwiched between the substrates, a so-called microcapsule type liquid crystal in which the liquid crystal exists as independent liquid bubbles may be used, or in addition to this, a scattering-transmission type liquid crystal may be used. It can be used.

[0033]

In the reflective color filter of the present invention, a pixel-shaped patterned multilayer interference film is formed on a black or low reflectance substrate. The thickness and the number of layers of each multilayer interference film are set so that they function as a red reflection film, a blue reflection film, and a green reflection film, respectively, and each reflection film has a reflectance of almost 100% in the reflection wavelength range. Indicates. In addition, almost 100% of light in the wavelength range other than the reflection wavelength is transmitted, but since the black substrate exists under the multilayer interference film, the transmitted light is not reflected. Therefore, each multilayer interference film acts as a red, blue, and green reflection pattern, and functions as a reflection type color filter.

By appropriately designing the structure of the multilayer interference film (refractive index, thickness and number of layers of each thin film), it can be used as a reflective pattern for colors other than red, blue and green. Then, by forming the reflective patterns on the low reflective substrate so as to be spaced apart from each other, the portion without the reflective patterns can be suitably used as a light shielding pattern (so-called black matrix or black stripe).

Further, in the liquid crystal display device of the present invention, the above-mentioned reflection type color filter is used as a substrate on one side of the liquid crystal display device for performing the transmission-scattering type display, and the liquid crystal layer is transmitted in the transmission state. Since only 100% of the white light of the color selected by the multilayer interference film is reflected,
It is possible to realize a very bright color display that is sufficiently recognizable only with ambient light.

[0036]

【Example】

<Example 1> A glass substrate was coated with a polyimide resin in which a black pigment was dispersed to a film thickness of 2 [mu] m, and baked to obtain a substrate.
On this black substrate, a titanium oxide thin film (refractive index 2.40) as a high refractive index film and a silicon oxide thin film (refractive index 1.46) as a low refractive index thin film are alternately laminated using a vacuum deposition method, and a red color is obtained. A reflective film was formed. The wavelength of 50% reflectance of this red reflecting film was 590 nm, and the reflectance of 610 nm or more showed a value of almost 100%.

The layer structure of this red reflecting film is such that the above-mentioned titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ) are alternately laminated to form a total of 7 layers, and the film thickness thereof is 940Å in order.
(TiO ₂ ) / 1240Å (SiO ₂ ) / 750Å (T
_{iO 2) / 1240Å (SiO 2} ) / 750Å (TiO
₂ ) / 1240Å (SiO ₂ ) / 940Å (TiO ₂ )
And

Next, a photoresist (manufactured by Shipley, trade name: MP-1400) having a film thickness of 2 μm is formed on the red reflective film, and mask exposure and development are performed according to a conventional method to form a resist pattern corresponding to red pixels. did. further,
After performing dry etching by a reactive ion etching method using CF ₂ Cl ₂ gas, the photoresist was stripped off to form a red reflection pattern.

Then, the same procedure was repeated to sequentially form a green reflection pattern and a blue reflection pattern to obtain a reflection type color filter. The layer structure of the green reflective film is the same as that of the red reflective film except for the film thickness.
iO ₂ ) and silicon oxide (SiO ₂ ) are alternately layered for a total of 7
It is layered. And, the film thicknesses thereof are 1 in order.
800Å (TiO ₂ ) / 350Å (SiO ₂ ) / 105
0Å (TiO ₂ ) / 350Å (SiO ₂ ) / 1050Å
(TiO ₂ ) / 350Å (SiO ₂ ) / 1800Å (T
iO ₂ ).

The layer structure of the blue reflective film is the same as the red reflective film and the green reflective film except for the film thickness and the number of layers. Titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ) are alternately laminated. It is a thing. And, the film thicknesses thereof are 30 in order.
0Å (TiO ₂ ) / 700 Å (SiO ₂ ) / 430 Å
(TiO ₂ ) / 700Å (SiO ₂ ) / 430Å (Ti
O ₂ ) / 700Å (SiO ₂ ) / 430 Å (TiO ₂ )
/ 700Å (SiO ₂ ) / 430Å (TiO ₂ ) / 70
It was set to 0Å (SiO ₂ ) / 430Å (TiO ₂ ).

The reflection type color filter obtained was red,
The reflectance of the green and blue patterns is almost 100% in the wavelength range of each color, which is 10% or more for red and blue and 20% for green as compared with the conventional color filters using pigments or dyes as coloring materials. As described above, the color filter has a high reflected light intensity.

Example 2 Copper was sputtered on a transparent glass substrate and patterned by photolithography according to a conventional method to remove only the copper in the red pattern portion by etching. Then, the others are <Example 1>.
Similarly, titanium oxide thin films and silicon oxide thin films were alternately laminated to form a red reflective film, and then the copper pattern was removed by etching to form a red reflective film pattern.

Thereafter, the same procedure is repeated to sequentially form a green reflection pattern and a blue reflection pattern,
Finally, black paint was applied to the back surface of the substrate to obtain a reflective color filter. This reflective color filter is also <Example 1
The reflectance of the patterns for red, green, and blue was almost 100% in the wavelength range of each color, as in the case of &gt;

Example 3 0.1 μm copper was sputtered on a glass substrate, and then the surface was blackened. The reflectance of this surface is 1 at 400 to 700 nm.
It was 0% or less. On this substrate, red, green and blue reflective color filters made of a multilayer interference film were formed by the same method as in <Example 1>.

A substrate having a thin film transistor array formed thereon was used as a counter substrate, and a spacer having a thickness of 20 μm was interposed between the substrates to seal the periphery to form a cell.
And 7 parts of 2-ethylhexyl acrylate and 2
-Hydroxyethyl acrylate 15 parts, acrylic oligomer (manufactured by Toagosei Chemical Co., Ltd., trade name: Aronix M-12
00) in an amount of 24 parts, a photopolymerization initiator (manufactured by Ciba-Geigy, trade name: Irgacure 651) in 0.9 part, and a liquid crystal (manufactured by BDH, trade name: E-8) in a uniform solution. Injected. Then, ultraviolet rays were irradiated to complete a polymer dispersion type reflective liquid crystal display device.

This liquid crystal display device was in a scattering state and was capable of white display when no voltage was applied to the pixels, and was in a transmissive state when voltage was applied and capable of color display by a color filter. Moreover, in the state of color display,
It was possible to display bright colors with sufficient color recognition only with ambient light in the room.

[0047]

In the reflective color filter of the present invention, a pattern having a specific color is formed on a substrate whose surface is black or has a low reflectance and which is composed of a multilayer interference film. That is, each of the multilayer interference films is designed to selectively reflect light in the red, green, and blue wavelength regions, and transmit the remaining light, for example. Since the light transmitted through the multilayer interference film is not reflected on the surface of the substrate, only the red, green and blue lights are selectively reflected from each color pattern. Since the multilayer interference film does not have absorption in the film itself, unlike the coloring by using dyes or pigments used as a conventional color filter, the reflectance is close to 100% for a desired color. And a bright reflective color filter product having a very high reflectance can be realized.

Further, the liquid crystal display device of the present invention uses the above-mentioned reflective color filter as a substrate on one side of the liquid crystal display device for performing transmission-scattering type display, and in the transmissive state, it is a white color which has passed through the liquid crystal layer. Of the light, only the light of the color selected by the multilayer interference film is reflected by almost 100%, so that a bright color display can be realized, and white display is achieved in one of the scattering states, so that only ambient light can be sufficiently recognized. It is possible to realize a product of a liquid crystal display device (reflective liquid crystal display device) which has a very high display quality and is extremely bright. After all, it was possible to provide a reflective color liquid crystal display device capable of displaying not only the contrast but also a brightness practically sufficient and a reflective color filter suitable for use in the liquid crystal display device.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a cross section of an example relating to a color filter of the present invention.

FIG. 2 is an explanatory view schematically showing the cross section of one embodiment of the liquid crystal display device of the present invention.

FIG. 3 is an explanatory view schematically showing a cross section of an example of a conventional reflection type color liquid crystal display device.

[Explanation of symbols]

 1 ... Black substrate 2 ... Red reflective multilayer interference film 3 ... Blue reflective multilayer interference film 4 ... Green reflective multilayer interference film 5 ... Color filter side substrate 6 ... Opposing side substrate 7. ..Low reflective film 8 ... Red reflective multilayer interference film 9 ... Blue reflective multilayer interference film 10 ... Green reflective multilayer interference film 11 ... Transparent conductive film 12 ... Sealant 13 ... High Molecular dispersed liquid crystal layer 14 ... Polymer matrix 15 ... Liquid crystal particles 16, 17 ... Substrate 18, 19, 20 ... Color filter 21 ... Reflector

Claims (10)

[Claims] 1. A reflective pattern formed of a multi-layer interference film in which thin films made of a high refractive index material and thin films made of a low refractive index material are alternately laminated to have a desired shape on the substrate. A reflective color filter, wherein the substrate has a low reflectance. 2. The reflective color filter according to claim 1, wherein the reflective patterns are formed on the substrate so as to be spaced apart from each other. 3. The reflective color filter according to claim 1, wherein the substrate has a low reflectance for at least visible light. 4. The substrate has a wavelength of at least 400 to 700 nm.
4. The reflective color filter according to claim 1, which has a low reflectance with respect to the light. 5. The reflective color filter according to claim 1, wherein the reflectance of the substrate is 10% or less. 6. A liquid crystal display device for displaying by controlling a light scattering state and a light transmitting state by an electric field, wherein one substrate has a low reflectance and a high refractive index on the substrate. A liquid crystal display device having a reflective pattern formed of a multilayer interference film in which a thin film made of a material and a thin film made of a low refractive index material are alternately laminated. 7. The liquid crystal display device according to claim 6, wherein the reflective patterns are formed on the substrate so as to be spaced apart from each other. 8. The liquid crystal display device according to claim 6, wherein the substrate has a low reflectance for at least visible light. 9. The liquid crystal display device according to claim 6, wherein the substrate has a low reflectance for light having a wavelength of 400 to 700 nm. 10. The liquid crystal display device according to claim 6, wherein the substrate has a reflectance of 10% or less.