JP2005308871A - Interference color filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a light reflection type display device which has high color purity and a reflection type color filter with which microfabrication is possible and which has high light resistance as a new reflection type interference color filter which is useful to make pixel intervals fine and improve light resistance. <P>SOLUTION: On a reflective metal film 1, an optical interference film is arranged which comprises at least a pair of a transparent material thin film 2b and an absorber translucent film 2a. Consequently, the light resistance is high and microfabrication by etching becomes possible, so the reflection type color filter is usable as a micro color filter for micro liquid crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color filter for a display device such as a liquid crystal display device, and more particularly to a novel reflective interference color filter that contributes to a finer pixel pitch and improved light resistance.

JP-A-8-122766 JP 10-115704 A JP-A-8-313898 JP-A-9-222512 JP2002-23149A JP 2002-341126 A

  In recent years, with the widespread use of portable terminals, a decrease in contrast of display devices under ambient light has become a problem. For example, when direct sunlight enters a display device such as a mobile phone, there is a phenomenon in which the light is scattered and the display becomes invisible. In addition, there is a strong demand for reducing power consumption, and expectations for display devices that do not require lighting are increasing.

  Since the reflective liquid crystal panel does not require illumination with a backlight, it is a device that can make full use of the advantages of low power consumption inherent to liquid crystal. However, there is a problem that the display luminance is very low due to the structure. The causes of darkness can be broadly divided into the problem of reflectance and the problem of aperture ratio. In terms of reflectance, phase transition type guest-host liquid crystal that does not use a polarizing plate is advantageous, but in terms of response speed, twisted nematic (TN) liquid crystal, vertical light distribution nematic liquid crystal, ferroelectric liquid crystal, etc. are advantageous, and cost, etc. Therefore, improvement of the reflective TN liquid crystal and the like is strongly desired.

  As a method for producing a color filter, a dyeing method, a pigment dispersion method, a colored light-sensitive material method, and a printing method are known. Generally, the pigment dispersion method is widely used. In the pigment dispersion method, for example, a photosensitive resin containing a red pigment is applied on a substrate, prebaked, exposed and developed, and then a red colored layer is formed through a drying process. Next, the same process is repeated twice to form a green colored layer and a blue colored layer, and a color filter having three colored layers is manufactured.

  Since an ordinary reflective liquid crystal color filter is provided on the viewer side substrate, incident light is reflected by the reflective metal film and passes through the color filter twice. Therefore, although priority is given to brightness by reducing the absorbance and color purity of the color filter, the wavelength of light transmitted by the filter is less than that of the cold-cathode tube light. It is dark at present.

  In the active matrix method, a method for improving the aperture ratio by forming a color filter on the reflective metal film on the TFT substrate side has been proposed, but a transparent electrode is formed on the color filter of 1 μm or more to provide a contact hole. In general, it is not often used.

  In addition, due to the progress of semiconductor technology, a display device using a micro liquid crystal such as an LCOS (Liquid Crystal on Silicon) device that forms a liquid crystal layer on a semiconductor circuit or a digital micro mirror device (DMD) is drawing attention. In these display devices, the pixel pitch is very narrow, and it is extremely difficult to form a color filter. A color filter based on a normal pigment dispersion method requires a film thickness of 1 μm or more, and a micro liquid crystal using LCOS or the like has a very small pixel pitch of about 10 μm, so the aspect ratio becomes high. For this reason, it is difficult to process, the aperture ratio is sacrificed, and it is difficult to ensure reflectivity and maintain polarization. In addition, since it is necessary to reflect very high intensity light, color filters using a dyeing method or a pigment dispersion method have poor light resistance, and there is also a problem that seizure occurs. In addition, parallax becomes a problem due to pixel miniaturization.

  In order to solve such a problem, a reflection type color filter using a dichroic filter as shown in Patent Document 1 or Patent Document 2 has been proposed. The dichroic filter is formed by laminating a high refractive index dielectric and a low refractive index dielectric, and transmits light in a specific wavelength range by light interference, and reflects light that is a complementary color. What is commonly referred to as an interference type color filter is this dichroic filter, which is characterized by no absorption.

In such a thin film filter made of a transparent multilayer film, the refractive index and film thickness of two types of thin films are defined, so it may be difficult to find a material having a predetermined refractive index. Usually, Ta ₂ O ₅ or TiO ₂ is used as the high refractive index material, and SiO ₂ or MgF ₂ is used as the low refractive index material. In a dichroic filter, these dielectrics need to be laminated to form a film thickness of several μm. Since these dielectrics have high chemical resistance and wet etching cannot be performed, when fine processing is performed, a pattern is formed with a photosensitive resist before forming a dichroic filter. Then, it is necessary to form a pattern by a lift-off method in which an excessive portion of the film is removed together with the resist. Therefore, there is a problem that the yield is poor and the cost is high.

  In addition, a proposal using a reflection hologram shown in Patent Document 3 and Patent Document 4 has been proposed. However, the reflection hologram is disadvantageous in terms of cost because the manufacturing apparatus is large. Patent Documents 5 and 6 also propose a type in which a cholestic liquid crystal is solidified, but a color filter in which a cholestic liquid crystal is solidified needs to have a step of about 0.1 μm in the solidified liquid crystal layer. There are problems in terms of process stability and cost.

  As described above, since the micro color filter cannot be practically realized in the conventional method, a three-plate method or a time division method is adopted. In the three-plate type device, one liquid crystal display device is used for each primary color of red, green, and blue, and these images are combined into one image, so that the device is large and expensive. It was. In addition, the single-plate type apparatus has a problem that there is a limit to miniaturization accompanied by a color braking phenomenon in order to perform time-division driving through a color wheel or the like.

  The present invention relates to a technique for realizing a reflective display device that is bright and has high color purity. Further, the present invention relates to a technique for realizing a micro color filter by forming a structure that can be finely processed and has high light resistance.

  In the present invention, the red, green, and blue of the color filter are formed by a reflective metal film made of a metal such as Al, and a light interference film formed of at least a pair of transparent thin films and an absorber semi-transmissive film formed on the reflective metal film. Configure each subpixel. Red, green, and blue colors can be achieved by changing the combination of film thickness of the transparent thin film and the absorber semi-transmissive film. Moreover, a cheaper and easier-to-handle process can be realized by using a transparent film in which absorber fine particles are dispersed instead of the absorber semipermeable film.

  The interference color filter according to the present invention enables a bright reflective display device with high color purity. Moreover, since it has high light resistance and can be finely processed by etching, it can be used as a micro color filter for micro liquid crystal.

  Hereinafter, specific description will be given based on the drawings. FIG. 1 is a diagram showing the configuration of the present invention. 1 is a reflective metal film, 2 is an optical interference film, and 3 is an overcoat film. The optical interference film 2 is composed of an absorber semi-transmissive film 2 a and a transparent thin film 2 b, and at least a pair of optical interference films are disposed between the reflective metal film 1 and the overcoat film 3. The overcoat film 3 may be omitted.

  The absorber semipermeable membrane is, for example, a vacuum deposited film having a mass thickness of Mo of about several tens of nm. The metal vapor deposition film of this thickness is a stage where an island-like structure grown around the nucleus formed at the initial stage of vapor deposition is changing to a network structure where islands are connected to each other. Since the portion permeates, it becomes a semi-permeable membrane. The microstructure of the semi-transmissive film is sufficiently small with respect to the wavelength, and can be viewed as homogeneous throughout the semi-transmissive film. The film forming method is not limited to the vacuum evaporation method, and many film forming methods such as a sputtering method and a vapor phase growth method can be applied.

Now, the refractive index of the overcoat film is n ₀ , the complex refractive index of the absorber semi-transmissive film of the first layer is n ₁ ^* = n ₁ −ik ₁ , the film thickness is d ₁ , and the transparent thin film of the second layer is The refractive index is n ₂ , the film thickness is d ₂ , and the complex refractive index of the reflective metal film is n _b ^* = n _b −ik _b . Incident light passes through the overcoat film and enters the absorber semi-transmissive film as the first layer, and part of the incident light is reflected, part is absorbed, and part is transmitted. The light that has passed through the absorber semi-transmissive film that is the first layer passes through the transparent thin film that is the second layer, enters the reflective metal film, and is partially absorbed and partially reflected. The light reflected by the reflective metal film again passes through the transparent thin film that is the second layer and reaches the absorber semi-transmissive film that is the first layer, and is again partially reflected, partially absorbed, and partially To Penetrate.

In order to simulate optical interference due to repetitive reflection in a multilayer thin film composed of such an overcoat film / absorber semi-transmissive film / transparent thin film / reflective metal film, the optical constants n ₀ , n ₁ , k ₁ , d _{1, n 2, d 2,} n b, it is necessary to know exactly _{k b.} Each optical constant varies depending on the incident wavelength, and the refractive index n ₁ and the absorption coefficient k ₁ of the absorber semi-transmissive film as the first layer greatly vary depending on the film thickness, the film forming method, and the state of the base.

  In general, a very thin metal vapor-deposited film grows from nuclei generated at the initial stage of vapor deposition, and thus takes an island-like structure or a net-like structure depending on the growth stage to become a semi-permeable film. In such a semi-permeable membrane, it is known that abnormal absorption in the visible region due to surface plasma vibration or the like, which is not found in bulk metal, exists. As a result, it is considered that the optical constant varies greatly depending on the film thickness. Therefore, it is necessary to perform optical calculations while measuring the optical constants according to the respective conditions such as the vapor deposition conditions, the state of the substrate, the film thickness, and the wavelength, and grasping the dispersion state.

When the reflectance simulation of the overcoat film / absorber semi-transparent film / transparent thin film / reflective metal film is performed based on the optical constants thus obtained, it matches well with the actually produced sample. By combining the optical constants, a low reflectance can be realized for light in a specific wavelength range. In the structure of Mo semi-permeable film / Al ₂ O ₃ transparent thin film / Al reflective metal film, the film thickness d _{1 of} the first-layer absorber semi-transmissive film and the film thickness d ₂ of the second-layer transparent thin film are changed. Thus, it was found that strong coloration such as red, blue, and yellow was exhibited.

  As a result of examining many materials by experiment, in addition to the Mo absorber semi-permeable film, Au, Ag, Al, Au, Co, Cr, Cu, Fe, Ge, Nb, Ni, Pb, Pd, Pt, Sb , Se, Si, Sn, Ta, Ti, W, Zn, Zr, and many other metals and metalloids have been found to exhibit strong coloration. As such a semi-transmissive film grows from an island-like film to a net-like thin film as the film thickness increases, the light absorption mechanism changes and the optical constant also changes. However, since all optical constants are not independent and change in relation to each other, the movement of the absorption band is insensitive to the change in the thickness of the absorber semipermeable membrane, and the transmittance of many absorber semipermeable membranes is low. Coloration was recognized in the range of about 10 to 90%.

The transparent thin film of the second layer is transparent such as Y ₂ O ₃ , In ₂ O ₃ , Al ₂ O ₃ , Si ₃ N ₄ and other metals, metalloid oxides, nitrides, fluorides, and transparent resins. If so, most materials can be used. In addition, oxides or nitrides of metals or metalloids such as In ₂ O ₃ and Si ₃ N ₄ may have some absorption due to deviation from the stoichiometric ratio depending on the film formation conditions. Even a certain film can be used without any problem although it slightly affects the color purity. In addition, Al, Au, Ag, Au, Cr, Co, Cu, Fe, Mo, Nb, Ni, Pb, Pd, Pt, Sn, Ta, Ti, W, Zn, and many other metals are used as the reflective metal film material. It is effective against.

  In a multilayer thin film made of such an overcoat film / absorber semi-transparent film / transparent thin film / reflective metal film, the thickness of the first layer of the absorber semi-transmissive film affects the reflectance, but the center wavelength of the absorption band. Since the intensity of the reflected light is mainly adjusted, the thickness of the transparent thin film of the second layer is largely shifted by the center wavelength of the absorption band. It is determined by the thickness of the transparent thin film of the layer. It is considered that an absorption band is generated by balancing the reflected light from the absorber surface and the reflected light from the optical interference film and adjusting the wavelength of interference.

  In the experiment, good color development is seen when the mass thickness of the absorber semi-permeable membrane is 200 nm or less, particularly 50 to 100 nm, and the central wavelength of the absorption band is changed by adjusting the thickness of the transparent thin film of the second layer. As a result, various colors can be developed. When the film thickness of the absorber semi-permeable film of the first layer is increased from several tens of nanometers, the reflectance gradually decreases and color development with high color purity is exhibited. When the thickness is a predetermined film thickness, for example, 200 nm or more, a continuous film is formed and light is not transmitted, so that color is not generated. Further, as the thickness of the transparent thin film as the second layer is increased, the center wavelength of the light absorption band gradually moves to the long wavelength side. The effective range for the colored film is 1 nm to 200 nm in which the first layer can maintain an island-like or network structure, and the second layer is generally 1 nm to 1 μm in general.

  The sample thus produced develops a specific color depending on the range of the absorption band. For example, when the long wavelength side is absorbed and short wavelength light is reflected, it looks blue. Conversely, when the short wavelength side is absorbed and long wavelength light is reflected, it appears red. The color exhibited by the reflected light varies depending on the combination of the reflective metal film material and the absorber semi-transmissive film material and the combination of the thickness of the absorber semi-transmissive film and the transparent thin film.

  Also, a plurality of absorption bands can be formed by arranging a plurality of combinations of the absorber semipermeable membrane and the transparent thin film. Each absorption band absorbs light in a specific wavelength range, and light outside the absorbed wavelength range is reflected, so that a reflective color filter pixel with high color purity can be formed.

  The characteristics of the optical interference film composed of the absorber semi-transmissive film and the transparent thin film are that the entire film thickness is thin and the range of materials that can be selected is wide. Since a transparent material such as ITO (Indium Tin Oxide) can be used as the transparent thin film, the entire color filter including the reflective metal film can be formed of a conductive material. Therefore, for example, when a color filter is formed on a TFT substrate as a color filter on array, it is not necessary to form a transparent conductive film on the surface and provide a contact hole, and a color filter electrode can be formed with a simple configuration.

In addition, the interference color filter according to the present invention can select a material that has a small film thickness and can be etched. For example, by using Y ₂ O ₃ or the above-mentioned ITO as the transparent thin film, for example, an interference color filter made of Mo / Y ₂ O ₃ / Al can be etched using a phosphoric Al etching solution. it can.

  In the second invention according to the present invention, a transparent film in which absorber fine particles are dispersed is used instead of the island-like or net-like absorber semipermeable membrane of the first layer. Absorber fine particles are fine particles having a particle diameter of 300 nm or less, are sufficiently small with respect to the wavelength of visible light, and can be seen as homogeneous throughout the transparent film in which the absorber fine particles are dispersed. Nano-sized ultrafine metal particles have strong absorption in the visible light region due to surface plasmons, etc., as well as metal island-like films and network films, transparent film in which absorber fine particles are dispersed, and reflective metal film side An absorption band similar to that of the first invention can be realized by configuring the optical interference film with two layers of transparent thin films disposed on the surface.

  Further, according to this structure, the absorber semipermeable membrane of the first invention can be used in a thick region where the continuous membrane is used, and the thickness of the first layer and the second layer is slightly increased. Even if there is variation, the shape of the absorption band does not change so much, so that the stability of the manufacturing process can be improved. The transparent film in which the absorber fine particles are dispersed is obtained by co-evaporation of the absorber and the transparent body, or by dispersing the separately prepared absorber ultrafine particles in a transparent resin or the like and spin-coating on the reflective metal film. Can be formed

  The reflective interference color filter according to the present invention can be applied to various liquid crystal panels having color filters. The linearly polarized light that has passed through the polarizing plate is reflected by the interference color filter according to the present invention and becomes circularly polarized light. Therefore, when applied to a TN type liquid crystal of a single polarizing plate, a phase adjusting plate is disposed to reflect the reflected light. Return to linearly polarized light and pass through the polarizing plate again. In this case, coloration due to birefringence of the liquid crystal or phase shift due to the optical interference film may occur in each of the red, green, and blue sub-pixels, so the overcoat film thickness is optimal for each sub-pixel. This problem can be solved.

  The reflective interference color filter according to the present invention includes a reflective metal film and a light interference film, and has a structure that serves as both a reflective electrode and a color filter of a normal reflective liquid crystal. By constructing the reflective metal film and the optical interference film as a flat film such as a vapor-deposited film, there is no scattering of light by the pigment, which is a problem with pigment-dispersed color filters, and clear reflected video light without stray light can be obtained. .

  Further, by forming irregularities on the reflective metal film and the optical interference film, it is possible to provide light distribution and a wide viewing angle. In particular, it is possible to distribute light uniformly by forming the reflective interface with a set of concave or convex parts formed of a part of a spheroid, and to reach a critical angle when the light is emitted from the display device to the outside. An efficient bright reflective color filter can be configured by setting an inclination angle of no concave portion or convex portion.

The optical constants n ₂ and d ₂ of the transparent thin film constituting the optical interference film are factors that determine the interference condition. By making the optical distance n ₂ d ₂ variable, many colors can be obtained in one pixel. Can develop color. Therefore, full color display is realized by coloring the three primary colors in a time division manner without dividing into sub-pixels. In such a configuration, the transparent thin film is made of a variable optical distance transparent film made of a ferroelectric material such as lithium niobate, and a conductive transparent film is further disposed on the absorber semi-transmissive film. Can be realized.

  That is, by applying a voltage between the conductive transparent film and the reflective metal film, the refractive index of the optical distance variable transparent film made of a ferroelectric or the like, that is, the optical distance is changed, and the interference condition of the optical interference film is changed. By changing, different colors are developed. In addition to this, the color change can be constituted by a substance that changes in film thickness or refractive index by electromagnetic waves such as heat, pressure, electric field, magnetic field, and light.

  In addition, the optical distance variable transparent film is made of a material whose optical distance is irreversibly changed by an external stimulus such as heat, and the optical distance variable transparent film is partially processed by a technique such as laser annealing, thereby enabling photolithography. An interference color filter can be produced by a simple method that does not depend.

  Embodiments of the present invention will be specifically described below.

  FIG. 2 is a sectional structural view of a reflective color liquid crystal display device using the interference color filter of the present invention. 4 is a glass substrate on the segment side, 5 is a base layer formed with a recess made of resin, 6 is a reflective metal film, 7 is an optical interference film, Mo absorber semi-transmissive film 7a and ITO conductive transparent body It consists of a thin film 7b. 8 is a light distribution film also serving as an overcoat film, 9 is a sealing member, 10 is a liquid crystal layer, 11 is a light distribution film, 12 is a transparent electrode, 13 is a common side glass substrate, 14 is a retardation plate, and 15 is a polarizing plate. It is. The color filter electrode 100 is constituted by the reflective metal film 3 and the light interference film 4. Further, the glass substrate 4 on the segment side may be a TFT substrate or a silicon backplane including a driving circuit, and the base layer 5 in which the recesses are formed can be omitted. The liquid crystal layer 7 is, for example, 45 ° twisted nematic liquid crystal, and after being flattened by the overcoat film 8, the liquid crystal layer is injected.

  The color filter electrode 100 includes three regions that are finely divided so as to reflect light in different wavelength ranges, and reflects blue, green, and red wavelengths, respectively. Such a difference in reflection characteristics can be realized by the film thickness configuration of the optical interference film 7 formed on the reflective metal film 6.

Such a structure can be formed by the following manufacturing method. A thermosetting resin containing acrylic resin as a main component is spin-coated on the glass substrate 1 to form a base layer having a thickness of about 3 μm. After pre-baking this sample, a large number of recesses are formed in the underlayer by a stamping method using a micro mold having an interface in which a large number of spheroids are juxtaposed. After further post-baking, this sample is mounted on an electron beam vapor deposition apparatus, and Al is deposited by about 200 nm. Further, ITO is deposited in a thickness of about 60 nm in an O ₂ atmosphere, and then a Mo film is deposited in a thickness of about 40 nm.

  A spin filter is applied to the sample thus prepared, and after exposure and development with an appropriate pattern, etching with a phosphoric acid-based Al etching solution can form a color filter pattern. Color filter electrode. By changing the thickness of the ITO film and repeating the film formation and etching a total of three times, three color filter electrodes could be formed. A light distribution film 8 made of polyimide resin was formed on the segment side substrate thus produced, and a rubbing treatment was performed.

  As the common substrate, a transparent electrode made of ITO is formed on a glass substrate 13, and a light distribution film 11 made of a rubbed polyimide resin is formed. Then, the segment side substrate and the common side substrate were bonded to each other via the liquid crystal layer 10 and the seal member 9, and the retardation plate 14 made of polycarbonate and the polarizing plate 15 were sequentially bonded to the outside of the glass substrate 13.

  The reflection type liquid crystal display device thus produced had high color purity and reflectance, and had no parallax. The interference color filter of the present invention has high light resistance and can be finely processed, and can form a color filter pattern with a width of several μm.

  FIG. 3 shows an example in which the optical distance of the transparent thin film constituting the optical interference film is variable. 16a is a Mo absorber semi-transmissive film, and 16b is an optical distance variable transparent thin film formed of a ferroelectric material such as lithium niobate. The optical interference film 16 having a variable optical distance is constituted by these two layers. . The reflective metal film 6 and the optical interference film 16 with a variable optical distance constitute a variable color filter electrode 200. Reference numeral 17 denotes a conductive transparent film formed of an ITO vapor deposition film or the like. When a voltage is applied between the reflective metal film 6 and the conductive transparent film 17, the refractive index of the ferroelectric film between them changes, and the interference condition of the optical interference film 16 changes due to the change in optical distance. Depending on the applied voltage, red, green, blue and their intermediate colors can be developed.

It is a cross-section figure of the interference color filter of the present invention. 1 is a cross-sectional structure diagram of a reflective liquid crystal panel to which an interference color filter of the present invention is applied. 1 is a cross-sectional structure diagram of a reflective liquid crystal panel to which a variable color interference color filter of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reflective metal film 2 Optical interference film 2a Absorber semi-transmissive film 2b Transparent thin film 3 Overcoat film 4 Segment side glass substrate 5 Underlayer 6 Reflective metal film 7 Optical interference film 7a Absorber semi-transmissive film 7b Conductive transparent body Thin film 8 Light distribution film 9 also serving as overcoat film Seal member 10 Liquid crystal layer 11 Light distribution film 12 Transparent electrode 13 Common side glass substrate 14 Phase difference plate 15 Polarizing plate 16 Optical distance variable optical interference film 16a Absorber semi-transmission film 16b Optical distance variable transparent thin film 17 Conductive transparent film 100 Color filter electrode 200 Variable color filter electrode

Claims (11)

  An interference color filter comprising: a reflective metal film; and an optical interference film comprising at least a pair of transparent thin films and an absorber semi-transmissive film formed on the reflective metal film.   An interference color filter comprising: a reflective metal film; a transparent thin film formed on the reflective metal film; and a light interference film made of a transparent film in which absorber fine particles are dispersed.   The said absorber semipermeable membrane or said absorber fine particle is comprised with 1 or more types of metals or metalloid elements selected from a transition metal element, a typical metal element, and a metalloid element, and 2. The interference color filter according to 2.   3. The interference color filter according to claim 1, wherein the transparent thin film constituting the optical interference film is formed of a conductive transparent body.   The interference color filter according to claim 1 or 2, wherein the transparent thin film constituting the optical interference film is formed of an optical distance variable material.   2. The interference color filter according to claim 1, wherein the thickness of the absorber semi-transmissive film constituting the optical interference film is in the range of 1 nm to 200 nm.   The interference color filter according to claim 2, wherein a particle diameter of the absorber fine particles constituting the optical interference film is 300 nm or less.   3. The interference color filter according to claim 1, wherein the transparent thin film constituting the optical interference film has a thickness in a range of 1 nm to 1 [mu] m.   3. The reflective metal film having the optical interference film is divided and arranged in parallel to form a subpixel, and overcoat films having different thicknesses are arranged on the subpixel, respectively. The interference color filter described.   3. The interference color filter according to claim 1, wherein the light incident interface of the reflective metal film is configured by a set of curved surfaces formed by a part of a spheroid. 3. The interference color filter according to claim 1, wherein a conductive transparent film is disposed adjacent to the absorber semi-transmissive film constituting the optical interference film.

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