JPH11160703A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve display contrast by suppressing unwanted reflection on a display device. SOLUTION: This display device is composed of a light transmissive front side substrate 1 opposed to a observer 100, a rear side substrate 2 bonded through a prescribed gap to the front side substrate 1, and an electro-optic material 3 such as a liquid crystal held in the gap between both the substrates. The front side substrate 1 is divided into an outer layer part 4 and an inner layer part 5. The outer later part 4 contains a transparent substrate 6 composed of glass or the like and its refractive index is relatively low. The inner layer part 5 contains a transparent electrode 10 for impressing voltage to the electro- optic material 3 and its refractive index is relatively high. Then, a reflection- proof film 15 is interposed between the outer layer part 4 and the inner layer part 5 and has a refractive index just between the outer and inner layer parts 4 and 5 for suppressing the unwanted reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using an electro-optical material such as a liquid crystal as a display medium. More specifically, the present invention relates to an anti-reflection structure for external light incident on a display device.

[0002]

2. Description of the Related Art Conventionally, liquid crystal displays have been widely used as thin and lightweight display devices. 2. Description of the Related Art In recent years, information display devices for personal digital assistants (PDAs) and mobile personal computers have been required to be lightweight, have low power consumption, and also have high color, high definition, and high image quality. . A reflective color liquid crystal display is most suitable as a display device that meets these requirements, and is being actively developed at present. A conventional monochrome reflective liquid crystal display device generally uses two polarizing plates. In order to colorize this, it is necessary to attach a color filter to the display device in addition to the two polarizing plates. However, when a color filter is used, the utilization efficiency of external light is reduced to several percent, so that the display screen becomes dark and cannot be put to practical use. At present, the development of a liquid crystal display device using a single polarizing plate or a method using no polarizing plate is being conducted. However, a display device having sufficiently satisfactory characteristics has not yet been obtained. At present, STN, R-TN, and R-OCB utilizing the birefringence of liquid crystal are used as driving methods using one polarizing plate.
It has been known. However, the STN mode or the like has an advantage that simple matrix driving can be performed, but is inferior in image quality and response speed. On the other hand, various guest-host (GH) modes have been proposed as methods without a polarizing plate. The guest host mode is generally excellent in brightness but not reliable. As mentioned above, each mode has its advantages and disadvantages,
It can be said that the reflection type liquid crystal display device is under development.

[0003]

FIG. 9 is a schematic sectional view showing a conventional display device of a single-polarizer type. This display device is a light-transmitting front substrate 1 facing an observer 100.
And a rear substrate 2 joined to the front substrate 1 via a predetermined gap, and an electro-optical material 3 such as a liquid crystal held in the gap between the two.
Consists of The front substrate 1 is divided into an outer layer 4 and an inner layer 5. The outer layer portion 4 includes a transparent substrate 6 such as glass and has a relatively small refractive index. A retardation plate 7 and a polarizer 8 are mounted on the upper surface of the transparent substrate 6. A color filter 9 is formed on the lower surface of the transparent substrate 6. The inner layer portion 5 includes a transparent electrode 10 for applying a voltage to the electro-optical material 3, and has a relatively large refractive index. The surface of the transparent electrode 10 is covered with an alignment film 11. The rear substrate 2 has a structure in which a light reflection layer 22, an electrode 20, and an alignment film 21 are sequentially stacked on a glass plate or the like from below.

In the reflective display device having such a configuration, there is a problem in particular that unnecessary reflection occurs at the interface between the layers of the front substrate 1. In order to efficiently use external light in the reflection type display device, it is necessary to minimize reflection other than reflection on the light reflection layer 22 of the rear substrate 2. As shown in the figure, the light incident on the front substrate 1 enters the electro-optical material 3 such as a liquid crystal through a polarizer 8, a retardation plate 7, a transparent substrate 6, a color filter 9, a transparent electrode 10, and an alignment film 11. I do. In this case, when light enters from a medium having a small refractive index to a medium having a large refractive index, unnecessary reflection occurs at an interface. This unnecessary reflection is determined by the refractive index of each medium.
In particular, the reflection at the interface between the air layer and the polarizer 8 and the interface between the color filter 9 and the transparent electrode 10 is large, and when evaluated as a display device, the contrast is lowered and the image quality is reduced. Regarding the reflection at the interface between the air layer and the polarizer 8, a polarizing plate provided with an antireflection film (AR coating) is commercially available, and the use of this plate solves the problem. However, at present, no measures are taken against reflection at the interface between the color filter 9 and the transparent electrode 10, and this is a problem to be solved. In addition,
Since the monochrome reflective display device does not have the color filter 9, unnecessary reflection at the interface between the transparent substrate 6 and the transparent electrode 10 becomes a problem.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the display device according to the present invention has, as a basic configuration, a light-transmitting front substrate facing an observer, a rear substrate joined to the front substrate via a predetermined gap, and held in the gap. Electro-optic material. The front substrate is divided into an outer layer portion and an inner layer portion. The outer layer portion includes a transparent substrate and has a relatively small refractive index. The inner layer portion includes a transparent electrode for applying a voltage to the electro-optical material and has a relatively large refractive index. As a characteristic feature, an antireflection film is interposed between the outer layer portion and the inner layer portion. The antireflection film has an intermediate refractive index between the outer layer and the inner layer in order to suppress unnecessary reflection.

[0006] Preferably, the antireflection film is an inorganic dielectric thin film having a refractive index of 1.6 to 1.8. The thickness of the inorganic dielectric thin film is set, for example, in the range of 75 nm to 90 nm. Alternatively, an organic resin film having a refractive index of 1.6 to 1.7 can be used as the antireflection film. The organic resin film has a thickness of, for example, 80 nm to 9 nm.
It is set to 0 nm.

In one embodiment of the present invention, the outer layer portion includes a color filter formed on the transparent substrate, and the antireflection film is interposed between the color filter and the transparent electrode and is in contact with both. I agree. Preferably, the outer layer portion includes a light scattering layer supported on the transparent substrate. Also preferably, the rear substrate has a light reflecting layer for reflecting light incident from the front substrate. In some cases, a reflection enhancing film in which at least two dielectric thin films having different refractive indices are stacked on the surface of the light reflecting layer may be arranged. Preferably,
The light reflection layer has a diffuse reflection surface that diffusely reflects light incident from the front substrate. In one embodiment of the present invention, a pixel electrode and a switching element for driving the pixel electrode are integrally formed on the rear substrate, and the transparent electrode formed on the front substrate is formed through the electro-optical material. It becomes a counter electrode facing the pixel electrode.

According to the present invention, an antireflection film is provided as an intermediate layer between an outer layer having a relatively low refractive index and an inner layer having a relatively high refractive index on the front substrate facing the observer.
The reflection occurring at the interface is suppressed. With such a configuration, the display device of the present invention can efficiently use external light.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing a basic configuration of a display device according to the present invention. As shown in the drawing, the display device includes a light-transmitting front substrate 1 facing an observer 100, a rear substrate 2 bonded to the front substrate 1 through a predetermined gap, and a liquid crystal held in the gap between the two. And a flat panel structure including the electro-optical material 3. The front substrate 1 is divided into an outer layer 4 and an inner layer 5. The outer layer portion 4 includes a transparent substrate 6 made of glass or the like, and has a relatively small refractive index. A retardation plate 7 and a polarizer 8 are mounted on the outer surface of the transparent base 6. A color filter 9 is formed on the lower surface of the transparent substrate 6. The inner layer portion 5 includes a transparent electrode 10 for applying a voltage to the electro-optical material 3, and has a relatively large refractive index.
The surface of the transparent electrode 10 is covered with an alignment film 11. On the other hand, the rear substrate 2 is made of a glass plate or the like, and has electrodes 20 formed thereon. The surface of the electrode 20 is covered with an alignment film 21. As a characteristic feature, an antireflection film 15 is interposed between the outer layer 4 and the inner layer 5 of the front substrate 1. The antireflection film 15 has an intermediate refractive index between the outer layer portion 4 having a small refractive index and the inner layer portion 5 having a large refractive index, and can suppress unnecessary reflection Z.

In one embodiment, the anti-reflection film 15 can be an inorganic dielectric thin film having a refractive index of 1.6 to 1.8. In this case, the thickness of the inorganic dielectric thin film is preferably set to 75 nm to 90 nm. With this value, the optical optical path n · d in the thickness direction of the dielectric thin film is about λ / 4. Here, n is the refractive index of the dielectric thin film, d is the physical thickness of the dielectric thin film, and λ is the wavelength of the incident light. In another embodiment of the present invention, the anti-reflection film 15 uses an organic resin film having a refractive index of 1.6 to 1.7. For the same reason as described above, the thickness of the organic resin film is set to 80 nm to 90 nm.

Preferably, the outer layer portion 4 includes a color filter 9 formed on the transparent substrate 6, so that a color display device can be obtained. In this case, the antireflection film 15 is interposed between the color filter 9 having a small refractive index and the transparent electrode 10 having a large refractive index, and is surface-bonded to both. Preferably,
The rear substrate 2 has a light reflection layer that reflects light incident from the front substrate 1, and a reflective display device is obtained. In the illustrated example, the electrode 20 is formed of a metal film or the like, and can also serve as a light reflection layer. In some cases, a reflection enhancing film in which at least two dielectric thin films having different refractive indexes are stacked on the surface of the light reflecting layer can be arranged. Antireflection film 1 of front substrate 1
By providing an antireflection film on the rear substrate 2 in addition to 5, the utilization efficiency of incident light can be further improved. In one embodiment, the light reflection layer has a diffuse reflection surface that diffusely reflects light incident from the front substrate 1, and can exhibit the appearance of a so-called white paper. In some cases, a specular reflection surface may be used instead of the diffuse reflection surface. At this time, it is preferable to dispose a light scattering layer on the transparent substrate 6 of the front substrate 1. When the present display device is of an active matrix type, the electrode 20 on the rear substrate is patterned to be processed into a pixel electrode, and a switching element such as a thin film transistor for driving the electrode is integrally formed. In this case, the transparent electrode 10 formed on the front substrate 1 becomes a counter electrode facing the pixel electrode via the electro-optical material 3.

The color filter 9 is obtained by dispersing dyes of the three primary colors RGB in a transparent resin in a pixel-division manner, and has a refractive index n0 of, for example, 1.54. The transparent electrode 10 is made of ITO
, And the refractive index n2 is about 1.84. The antireflection film 15 interposed between the color filter 9 and the transparent electrode 10 has a refractive index n1 and a physical film thickness d. The reflectance at the interface between the color filter 9 and the transparent electrode 10 is n1 · d = λ / 4 for vertically incident light.
Or it is the minimum when it becomes an odd multiple of this. Here, λ represents the wavelength of the vertically incident light. That is, when the optical path n1 · d of the antireflection film 15 substantially corresponds to a quarter wavelength of the incident light, the reflectance of the incident light becomes minimum due to the multiple interference.
The reflectance R in this case is represented by the following equation.

(Equation 1) As is apparent from the above equation, the refractive index n of the antireflection film 15
When 1 becomes equal to the square root of the product of the refractive index n0 of the color filter 9 and the refractive index n2 of the transparent electrode 10, the reflectance R becomes substantially 0, and almost unnecessary interface reflection can be suppressed. By calculating by substituting n0 = 1.54 and n2 = 1.84, an almost non-reflective state can be obtained by setting the refractive index n1 of the antireflection film 15 to 1.68. Generally, when n1 is between n0 and n2, the reflectivity is always lower than without the anti-reflection coating. As described above, by providing the antireflection film 15 between the color filter 9 and the transparent electrode 10, unnecessary reflection of external light can be eliminated. When the color filter 9 is not provided, an antireflection film 15 having an intermediate refractive index may be interposed between the transparent substrate 6 made of glass or the like and the transparent electrode 10. If the wavelength λ is represented by 555 nm having high visibility, it can be understood that the antireflection film 15 is ideally formed by forming an optical material having a thickness d of about 80 nm and a refractive index n1 of 1.68. As the antireflection film 15, an inorganic dielectric thin film or an organic resin film can be used. Si as the inorganic dielectric thin film
O, CeF ₃ , Al ₂ O ₃ , MgO, ThO _{2 and the} like can be selected.

FIG. 2 is a schematic partial sectional view showing a first embodiment of the display device according to the present invention. This embodiment is a one-polarizer type liquid crystal display using a liquid crystal as an electro-optical material. This liquid crystal display is of a reflection type capable of color display and employs an active matrix system. The same applies to all other examples and comparative examples. A liquid crystal 3 is provided between the front substrate 1 and the rear substrate 2 as an electro-optical material.
a is held. The front substrate 1 uses a transparent substrate 6 made of glass or the like, and a polarizing plate 8, a retardation film (retardation film) 7, and a light scattering layer (light scattering film) 12 are laminated on the upper surface thereof. The surface of the polarizer (polarizing plate) 8 is covered with an anti-reflection coat (AR). On the lower surface of the transparent substrate 6, a color filter 9 divided into three primary colors of RGB is formed. Each of the above layers is included in the outer layer portion 4. The front substrate 1 further includes an inner layer portion 5, on which a transparent electrode (counter electrode) 10 made of ITO or the like and an alignment film 11 made of a polyimide film or the like are formed. Rear substrate 2
Is formed of a glass plate or the like, on the surface of which a thin film transistor 24 is integrally formed as a switching element. Each thin film transistor 24 is covered with an insulating film 23, and a pixel electrode 20a is formed thereon. Each pixel electrode 2
Reference numeral 0a is also covered with an alignment film 21 made of polyimide or the like. A liquid crystal 3a is held between the front substrate 1 and the rear substrate 2.

As described above, the front substrate 1 is formed using the transparent substrate 6 such as glass, and is disposed on the light incident side. On the liquid crystal 3a side of the transparent base material 6, a micro color filter 9, a counter electrode 1 made of a transparent conductive film such as ITO,
0, an alignment film 11 made of polyimide or the like is formed. On the viewer side of the transparent substrate 6, a polarizer 8, a retardation plate 7, and a light scattering layer 12 are arranged. As a feature, an antireflection film 15 is interposed between the color filter 9 and the transparent electrode 10. In this embodiment, the antireflection film 15 uses an inorganic dielectric thin film formed by vapor deposition or sputtering. Specifically, SiO was used as the inorganic material.

On the rear substrate 2, an alignment film 21 and a pixel electrode 20a are formed in this order from the liquid crystal 3a side. In this embodiment, the pixel electrode 20a is formed of a vapor-deposited film of aluminum or the like and also serves as a light reflection layer. Since this light reflection layer is almost specularly reflected, the light scattering layer 12
Is arranged. Each pixel electrode 20a is electrically connected to a corresponding drain electrode of the thin film transistor 24 via an insulating film 23 such as silicon dioxide. Thin film transistor 24
Has a bottom gate structure, for example, and has a laminated structure in which a gate electrode, a gate insulating film, and a semiconductor thin film are stacked in order from the bottom. The semiconductor thin film is made of, for example, polycrystalline silicon or the like, and a channel region matching the gate electrode is protected from above by a stopper. A pair of contact holes are formed in the insulating film 23 covering the thin film transistor, and communicate with the source electrode and the drain electrode. The drain electrode is connected to the pixel electrode 20a via a contact hole. Thus, the drain electrode of the thin film transistor 24 and the pixel electrode 20a have the same potential. A signal voltage such as a video signal is supplied to the source electrode.

The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and the gap between them is, for example, 3 μm.
Is controlled. As the liquid crystal 3a, a p-type nematic liquid crystal having a small refractive index anisotropy (Δn = 0.0074) is used. The nematic liquid crystal 3a is twist-aligned by the upper and lower alignment films 11 and 21. Upper and lower electrodes 1
When a voltage is applied between 0 and 20a, the twisted nematic liquid crystal 3a shifts to vertical alignment. In this display device, when no voltage is applied, the liquid crystal 3a is parallel to the substrate and displays black. In the voltage application state, the liquid crystal 3a is in a birefringence mode in which the liquid crystal 3a is oriented perpendicular to the substrate and displays white. In this method, after the incident light is converted into linearly polarized light by the polarizer 8, a phase difference of a quarter wavelength is generated at the time of incidence and at the time of emission, respectively, by the combination of the phase difference plate 7 and the liquid crystal 3a. Sometimes polarizing plate 8
Absorb light. Normally, the wavelength difference is compensated by the phase difference plate 7 so that the phase difference becomes a quarter wavelength in the entire visible wavelength range.

Next, a second embodiment of the present invention will be described. The second embodiment has basically the same structure as the first embodiment described above, and will be described with reference to FIG. Although the inorganic dielectric thin film is used as the antireflection film 15 in the second embodiment, Al ₂ O ₃ is used instead of SiO in the first embodiment. Al ₂ O ₃ was formed on the color filter 9 by vacuum evaporation or sputtering. Its thickness is between 70 nm and 90 nm.

A third embodiment of the present invention will be described with reference to FIG. Basically, it is the same as the first embodiment shown in FIG. 2, and corresponding parts are denoted by corresponding reference numerals to facilitate understanding. As a characteristic matter, a reflection enhancing film 25 is provided on the rear substrate 2. The pixel electrode 20a is made of, for example, aluminum and has a reflectance of about 90%. By overlaying the reflection enhancing film 25 thereon, the reflectance increases to 97%. The reflection enhancing film 25 has a structure in which at least two dielectric thin films having different refractive indexes are stacked.
Hereinafter, the third embodiment will be specifically described. The front substrate 1 uses a transparent substrate 6 such as a glass plate and is disposed on the light incident side. A color filter 9 is provided on the liquid crystal 3a side of the transparent substrate 6.
Anti-reflection film 15 for reducing reflection of incident light, ITO
A transparent electrode 10 made of a transparent conductive film such as a polyimide film, and an alignment film 11 made of a polyimide or the like are formed. A polarizing plate 8, a retardation plate 7, and a light scattering layer 12 are arranged on the incident side of the transparent substrate 6. The anti-reflection film 15 is made of Si as in the first embodiment.
O was used. The rear substrate 2 has an alignment film 21 on the liquid crystal 3a side.
And a light reflection type pixel electrode 20a. The pixel electrode 20a is connected to the thin film transistor 24 via the insulating film 23.
Connected to the drain electrode. On the pixel electrode 20a,
The reflection enhancement film 25 is formed by coating two layers of a λ / 4 film of ZnS and MgF ₂ . Spacers are scattered between the front substrate 1 and the rear substrate 2 and are joined to each other with a predetermined gap. This gap size is, for example, 3 μm. A p-type nematic liquid crystal 3a is held in the gap.

FIG. 4 is a schematic partial sectional view showing a first comparative example. Basically, it is the same as the first embodiment shown in FIG. 2, and corresponding parts are denoted by corresponding reference numerals. In this first comparative example, a color filter 9 and a transparent electrode 10 were used.
Are in direct contact with each other, and no antireflection film is interposed at the interface between them. Hereinafter, the first comparative example will be specifically described. The front substrate 1 is made of a transparent substrate 6 such as a glass plate and is arranged on the light incident side. On the liquid crystal 3a side of the transparent substrate 6, a color filter 9, a transparent electrode 10 made of a transparent conductive film such as ITO, and an alignment film 11 made of polyimide or the like are formed. A polarizing plate 8, a retardation plate 7, and a light scattering layer 12 are arranged on the incident side of the transparent substrate 6. The rear substrate 2 has an alignment film 21 and a light-reflective pixel electrode 20a on the liquid crystal 3a side.
Is arranged. The pixel electrode 20a is connected to the drain electrode of the thin film transistor 24 via the insulating film 23. The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and the gap between them is set to 3 μm. In this gap, a nematic liquid crystal 3a that is twist-oriented is held.

FIG. 5 is a schematic partial sectional view showing a fourth embodiment of the display device according to the present invention. Basically, it has a structure similar to that of the first embodiment shown in FIG. 2, and corresponding parts are denoted by corresponding reference numerals to facilitate understanding. The first embodiment is different from the first embodiment in that the light scattering layer 1
In contrast to the forward-scattering type in which the second substrate 2 is disposed, the present embodiment is a back-scattering type in which a diffuse reflection surface is provided on the rear substrate 2. Hereinafter, the fourth embodiment will be described in detail. The front substrate 1 is a transparent substrate 6
And is arranged on the light incident side. On the liquid crystal 3a side of the transparent substrate 6, a color filter 9, an antireflection film 15 for reducing the reflection of incident light, a transparent electrode 10 made of a transparent conductive film such as ITO, and an alignment film 11 made of polyimide or the like are formed. I have. As the antireflection film 15, an SiO vapor deposition film or a sputtered film was used as in the first embodiment. On the rear substrate 2, a light reflection layer 22 is formed on a thin film transistor 24 via an insulating film 23. The light reflection layer 22 is made of a deposited film of aluminum or the like. The insulating film 23 is made of an acrylic resin or the like, and has irregularities formed by photolithography. For this reason, the light reflection layer 22 is also uneven, forming a light diffusion surface. The light reflection layer 22 is subdivided for each pixel, and is electrically connected to the drain electrode of the thin film transistor 24 via the insulating film 23. A flattening film 26 made of acrylic resin or the like is applied on the light reflection layer 22 having the unevenness. The pixel electrode 20a is formed on the flattening film 26. The pixel electrode 20a is electrically connected to the drain electrode of the corresponding thin film transistor 24 via a contact hole opened in the planarizing film 26 and the insulating film 23. The pixel electrode 20a is covered with an alignment film 21 such as polyimide. Front substrate 1 and rear substrate 2
Are connected to each other via a spacer, and a p-type nematic liquid crystal 3a having a small refractive index anisotropy is held in a gap between the two. The gap size is about 3 μm. As described above, in this embodiment, the light scattering layer 12 is removed from the front substrate 1 while the light diffusion surface is provided on the rear substrate 2. In the first to fourth embodiments described above, the inorganic dielectric thin film constituting the antireflection film 15 has a thickness of 80 nm.
Is set to

FIG. 6 is a schematic partial sectional view showing a second comparative example. Basically, the second comparative example is the same as the fourth embodiment shown in FIG. 5, and corresponding portions are denoted by corresponding reference numerals to facilitate understanding. The difference is that the antireflection film is not used and the color filter 9 and the transparent electrode 10 are in direct contact. Hereinafter, this comparative example will be described. The front substrate 1 is made of a transparent substrate 6 such as glass and is disposed on the light incident side. On the liquid crystal 3a side of the transparent base 6, a color filter 9, a transparent electrode 10, and an alignment film 11 are formed. On the rear substrate 2, a light reflection layer 22 is formed on a thin film transistor 24 via an insulating film 23.
Since the surface of the insulating film 23 is uneven, the light reflecting layer 22
Is a light diffusion surface. The light reflection layer 22 is subdivided for each pixel, and is connected to the drain electrode of the corresponding thin film transistor 24. A flattening film 26 for flattening irregularities is formed on the light reflection layer 22, and a transparent pixel electrode 20a made of ITO or the like is formed thereon. The pixel electrode 20a is connected to the corresponding light reflection layer 22 via the flattening film 26 and to the corresponding drain electrode of the thin film transistor 24. An alignment film 21 made of polyimide or the like is formed on the pixel electrode 20a. The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and a p-type nematic liquid crystal 3a having a small refractive index anisotropy is held between them.
The gap between the two substrates is 3 μm.

FIG. 7 is a schematic partial sectional view showing a fifth embodiment of the display device according to the present invention. Basically, it is the same as the first embodiment shown in FIG. 2, and the corresponding parts are denoted by the corresponding reference numerals. The difference is that the anti-reflection film 15
"a" is not an inorganic dielectric thin film but an organic resin film. Although the inorganic dielectric thin film exhibits excellent properties as an antireflection film, a sputtering step is required for film formation, and the number of processes is increased, which is not suitable for equal mass production in some cases. Since the sputtering process is a batch process, it deviates from online processing. Therefore, in this embodiment, the antireflection film 15a is formed by applying an organic resin film having excellent mass productivity and productivity. Hereinafter, this embodiment will be described. The front substrate 1 is made of a transparent substrate 6 such as glass and is disposed on the light incident side. On the liquid crystal 3a side of the transparent substrate 6, a micro color filter 9, an antireflection film 15a for reducing unnecessary reflection of incident light, IXO
And an alignment film 11 made of polyimide or the like. The anti-reflection film 15a is made of an organic resin film, and is coated with polyimide in this embodiment. The coating method includes spin coating, printing, dipping and the like. The thickness of the organic resin film is set to 87 nm. This film thickness is the same in the following examples. Basically, the film thickness of the antireflection film 15a is set so that its optical path is λ / 4. As λ, for example, 560 nm is selected. Actually, since the oblique incidence component needs to be considered, the optical path is longer than the film thickness d. Therefore, in this embodiment, the actual thickness d of the organic resin film is set to 87 nm. On the other hand, a polyimide alignment film 21 and a reflective pixel electrode 20a are formed on the rear substrate 2 so as to face the liquid crystal 3a. The reflective pixel electrode 20 a made of aluminum or the like is connected to the corresponding drain electrode of the thin film transistor 24 via the insulating film 23.
The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and a p-type nematic liquid crystal 3a is sealed in a gap between the two. The gap between the two substrates is 3 μm.

Next, a sixth embodiment of the present invention will be described. This is basically the same as the fifth embodiment shown in FIG. 7, and the sixth embodiment will be described with reference to FIG. The difference from the fifth embodiment is that an ultraviolet-curable acrylic resin is used instead of polyimide as the organic resin film constituting the antireflection film 15a. The front substrate 1 is made of a transparent substrate 6 such as glass and is disposed on the light incident side. On the liquid crystal 3a side of the transparent substrate 6, a color filter 9, an antireflection film 15a for reducing unnecessary reflection of incident light, a transparent electrode 1 made of IXO, etc.
0, an alignment film 11 made of polyimide is formed.
On the incident side of the transparent substrate 6, a polarizing plate 8, a retardation film 7,
The light scattering layer 12 is provided. Therefore, it is a forward scattering type. The thickness of the ultraviolet curable acrylic resin used as the antireflection film 15a is 87 nm. On the rear substrate 2, an alignment film 21 made of polyimide and a pixel electrode 20a made of aluminum are formed facing the liquid crystal 3a.
The pixel electrode 20a is connected to the drain electrode of the thin film transistor 24 via the insulating film 23. The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and a p-type nematic liquid crystal is sealed in a gap between the two. The gap size is 3 μm.

FIG. 8 is a schematic partial sectional view showing a seventh embodiment of the present invention. While the fifth and sixth embodiments shown in FIG. 7 are of the forward scattering type, this embodiment is of the back scattering type. The front substrate 1 uses a transparent substrate 6 such as glass and is disposed on the light incident side. The transparent substrate 6 has a liquid crystal 3a
, A color filter 9, an antireflection film 15 a for reducing reflection of incident light, a transparent electrode 10 made of ITO,
An alignment film 11 made of polyimide or the like is formed. The antireflection film 15a is made of an ultraviolet curable acrylic resin. On the rear substrate 2, a light reflection layer 22 is formed on a thin film transistor 24 via an insulating film 23. Insulating film 2
Reference numeral 3 is made of an acrylic resin, and its surface is processed into irregularities by photolithography. Therefore, the light reflection layer 22 made of aluminum forms a light diffusion surface. The light reflection layer 22 is subdivided corresponding to the pixel, and is connected to the drain electrode of the corresponding thin film transistor 24 via the insulating film 23. The unevenness of the light reflection layer 22 is flattened by the flattening film 26. A pixel electrode 20a made of ITO or the like is arranged on the flattening film 26. Pixel electrode 20
“a” is connected to the corresponding light reflection layer 22 via the flattening film 26, and is further electrically connected to the drain electrode of the corresponding thin film transistor 24 via the contact hole opened in the insulating film 23. The surface of the pixel electrode 20a is covered with an alignment film 21 made of polyimide. The front substrate 1 and the rear substrate 2 are bonded to each other with a predetermined gap therebetween, and a p-type nematic liquid crystal 3a having a small refractive index anisotropy is held between the two. The gap size is 3 μm.

Finally, an eighth embodiment of the present invention will be described. This is basically the same as the seventh embodiment shown in FIG. 8, and will be described with reference to FIG. The difference is that a polyimide resin is used as the organic resin film constituting the antireflection film 15a instead of the ultraviolet-curable acrylic resin. Front substrate 1
Uses a transparent substrate 6 made of glass or the like, and is disposed on the light incident side. On the liquid crystal 3a side of the transparent substrate 6, a color filter 9 and an antireflection film 1 for reducing reflection of incident light are provided.
5a, a transparent electrode 10 made of ITO, and an alignment film 11 made of polyimide or the like are formed. As described above, the antireflection film 15a is made of a polyimide coating and has a thickness of 87 mm.
nm. On the rear substrate 2, a light reflection layer 2 made of aluminum is formed on a thin film transistor 24 via an insulating film 23.
2 are provided. Since the surface of the insulating film 23 made of an acrylic resin is processed into irregularities by photolithography, the light reflecting layer 22 forms a light diffusing surface. The light reflection layer 22 is subdivided for each pixel, and is connected to the corresponding drain electrode of the thin film transistor 24 via the insulating film 23. A flattening film 26 is formed on the light reflection layer 22, and a pixel electrode 20a made of ITO or the like is formed thereon. Pixel electrode 20a and corresponding light reflection layer 2
2 has the same potential, and both are connected to the drain electrode of the corresponding thin film transistor 24. Pixel electrode 20a
Is covered with an alignment film 21 made of polyimide. The front substrate 1 and the rear substrate 2 are joined to each other via a spacer, and a p-type nematic liquid crystal having a small refractive index anisotropy is sealed in a gap between the two. The gap size is 3
It is set to μm.

The display contrast of the first to eighth embodiments, the first comparative example, and the second comparative example was measured to make a relative evaluation. The results are shown in Table 1 below.

[Table 1]

The display contrast was represented by the ratio of the brightness of white display to the brightness of black display. The corresponding figure numbers for each example and each comparative example are shown in the table. The first comparative example is a forward scattering type and does not use an antireflection film. First
The embodiment uses a forward scattering type inorganic thin film made of SiO as an antireflection film. The second embodiment is also of a forward scattering type, and uses an inorganic dielectric thin film made of Al ₂ O ₃ as an antireflection film. The third embodiment is also of the forward scattering type, uses an inorganic dielectric thin film made of SiO as an antireflection film, and adds a reflection enhancing film. The second comparative example is a back scattering type and does not use an antireflection film. The fourth embodiment is of a backscattering type and uses an inorganic dielectric thin film made of SiO as an antireflection film. The fifth embodiment is of a forward scattering type and uses an organic resin film made of polyimide as an antireflection film. The sixth embodiment is also of a forward scattering type and uses an ultraviolet-curable acrylic organic resin film as an antireflection film. The seventh embodiment is of a back scattering type, in which an ultraviolet curable acrylic organic resin film is used as an antireflection film. The eighth embodiment is also a back scattering type, and uses an organic resin film made of polyimide as an antireflection film.

As is clear from the comparison between the first comparative example and the first to third embodiments, the display contrast is remarkably improved in the forward scattering type by providing an antireflection film. When an inorganic dielectric thin film is used as an antireflection film,
As is apparent from the difference between the embodiment and the second embodiment, SiO is superior to Al ₂ O ₃ as a material. As is clear from the comparison between the first embodiment and the third embodiment, the display contrast is further improved by providing the reflection enhancing film on the rear substrate in addition to the antireflection film on the front substrate. As is clear from the comparison between the second comparative example and the fourth embodiment, the display contrast is improved by providing the antireflection film even in the back scattering type. However, the degree of improvement is smaller in the backscattering type than in the forward scattering type. Comparing the group of the first to fourth embodiments with the group of the fifth to eighth embodiments, the inorganic dielectric thin film has slightly better characteristics as the antireflection film than the organic resin film. I have. However, from the viewpoint of productivity, the organic resin film is superior to the inorganic dielectric thin film.

[0029]

In the reflection type display device, a high contrast (1) between the whiteness of the paper and the blackness of the characters printed thereon is obtained.
0) is desired. For that purpose, a bright white display and a dark black display are required. That is, a high reflectance in white display and a low reflectance in black display are desired. For this purpose, it is necessary to increase the utilization efficiency of incident light. The display device has a multilayer structure and has many interfaces. In particular, the interface exhibits relatively large reflection at the interface between the air layer and the polarizing plate and at the interface between the transparent substrate layer or the color filter layer and the transparent electrode layer. The present invention particularly provides an anti-reflection film at the interface of the transparent electrode on the incident side to realize a high-contrast, high-quality display image of black display. As the antireflection film, an inorganic dielectric thin film is used, and excellent characteristics are obtained. However, an organic resin film can be used instead of the inorganic dielectric thin film from the viewpoint of mass productivity and manufacturing cost. Unnecessary reflection at the interface between the transparent substrate or the color filter and the transparent electrode is not limited to the reflection type display device but always exists in the transmission type display device.
The present invention can be widely applied as a method for tightening black display. In particular, an antireflection film is effective in a forward scattering type in which a light diffusion layer is provided on a front substrate of a display device, because obliquely incident light increases.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a basic configuration of a display device according to the present invention.

FIG. 2 is a sectional view showing a first embodiment and a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

FIG. 4 is a sectional view showing a first comparative example.

FIG. 5 is a sectional view showing a fourth embodiment.

FIG. 6 is a sectional view showing a second comparative example.

FIG. 7 is a sectional view showing a fifth embodiment and a sixth embodiment.

FIG. 8 is a sectional view showing a seventh embodiment and an eighth embodiment.

FIG. 9 is a cross-sectional view illustrating a conventional display device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 front substrate, 2 rear substrate, 3 electro-optical material, 3 a liquid crystal, 4 outer layer portion, 5 inner layer portion, 6 transparent substrate, 7 ... Phase plate, 8 ...
Polarizer, 9 ... color filter, 10 ... transparent electrode, 11 ... alignment film, 12 ... light scattering layer, 15 ...
・ Anti-reflection film, 15a: an anti-reflection film, 20: an electrode, 20a: a pixel electrode, 21: an alignment film, 22 ・
..Light reflecting layer, 23 ... insulating film, 24 ... thin film transistor, 25 ... reflection enhancing film, 26 ... planarizing film

Claims (11)

[Claims] 1. A display device comprising: a light-transmitting front substrate facing an observer; a rear substrate joined to the front substrate via a predetermined gap; and an electro-optical material held in the gap. The front substrate includes an outer layer portion having a relatively small refractive index including a transparent substrate, an inner layer portion having a relatively large refractive index including a transparent electrode for applying power to the electro-optical material, and the outer layer portion and the inner layer. A display device having an antireflection film having a refractive index intermediate between the two so as to intervene between the portions to suppress unnecessary reflection. 2. The display device according to claim 1, wherein the antireflection film is an inorganic dielectric thin film having a refractive index of 1.6 to 1.8. 3. The display device according to claim 2, wherein said inorganic dielectric thin film has a thickness of 75 nm to 90 nm. 4. The display device according to claim 1, wherein the anti-reflection film is an organic resin film having a refractive index of 1.6 to 1.7. 5. The display device according to claim 4, wherein said organic resin film has a thickness of 80 nm to 90 nm. 6. The method according to claim 1, wherein the outer layer portion includes a color filter formed on the transparent substrate, and the antireflection film is interposed between the color filter and the transparent electrode and is surface-bonded to both. The display device according to claim 1, wherein: 7. The display device according to claim 1, wherein the outer layer portion includes a light scattering layer supported on the transparent substrate. 8. The display device according to claim 1, wherein the rear substrate has a light reflection layer for reflecting light incident from the front substrate. 9. The display device according to claim 8, wherein a reflection enhancing film in which at least two dielectric thin films having different refractive indexes are laminated is disposed on a surface of the light reflecting layer. 10. The display device according to claim 8, wherein the light reflection layer has a diffuse reflection surface that diffusely reflects light incident from the front substrate. 11. A pixel electrode and a switching element for driving the pixel electrode are integrally formed on the rear substrate.
2. The display device according to claim 1, wherein the transparent electrode formed on the front substrate forms a counter electrode facing the pixel electrode via the electro-optical material.