JPH0618874A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the utilization efficiency of an external light by providing a metallic reflecting layer on a liquid crystal layer side of a substrate. CONSTITUTION:Two pieces of substrates 2, 9 are provided by inserting and holding a liquid crystal layer 5. One substrate 2 of the substrates is a transparent substrate. In the substrates 2, 9, transparent electrodes 3, 6 are provided, and by applying a voltage between the electrodes, light transmittivity of the liquid crystal layer 5 is controlled. A metallic reflecting layer 8 having a granular undulation in the horizontal direction against the substrate, and having prescribed surface roughness in the vertical direction is provided on the liquid crystal layer side of the other substrate 9.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reflective liquid crystal display device, and more particularly to a reflective liquid crystal display device in which a metal reflective layer having fine irregularities on its surface is provided on the liquid crystal layer side of a substrate.

[0002]

2. Description of the Related Art A conventional reflective liquid crystal display device is shown in FIG.
In the figure, 21 is an upper polarizing plate, 22 is an upper transparent substrate, 23 is an upper transparent electrode, 24 is an alignment film, 25 is a liquid crystal layer, 26 is a lower transparent electrode, 27 is a lower transparent substrate, 28 is a lower polarizing plate, 29. Is a reflector. Generally, in a reflective liquid crystal display device, external light that has passed through a liquid crystal cell is reflected by a reflector, and then passes through the liquid crystal cell again before being recognized by an observer. It is necessary that the reflection plate has a high reflectance and is a diffuse reflection surface that reflects incident light in various directions. Since a metal film deposited on a flat substrate has only a specular reflection component, it cannot be used as a reflection plate as it is. Therefore, a reflection plate in which a filler of about 10 to 100 μm is added to a polyethylene terephthalate (PET) film and the film surface is provided with irregularities having a height of several μm and aluminum is vapor-deposited is widely used. In addition to this, there is a method of forming aluminum on the back surface of the liquid crystal cell substrate and then depositing aluminum.

For example, as in JP-A-2-83537,
There has been an attempt to use a reflection plate as an electrode for applying a voltage to the liquid crystal layer, but the flat metal reflection surface cannot fulfill the function of the reflection plate as described above. There is also an attempt to form a diffusive reflection surface by providing irregularities of 1 to 2 μm on the surface of the substrate or the metal electrodes like a reflection plate, but since the distance between the substrates can be different depending on the location in the liquid crystal panel, display unevenness is caused. There is a problem that it ends up.

Since the liquid crystal display device is lightweight and thin, it has been attracting attention as a display device replacing the CRT.
Further, since the liquid crystal display device is a non-luminous type, it is necessary to provide a backlight or a reflector on the back surface of the liquid crystal panel. Many segment display types such as desktop calculators and wristwatches are reflective, while many dot display types such as word processors and personal computers are transmissive with a backlight. Especially in a color display, the light transmittance of the liquid crystal panel is as low as a few percent, so that the backlight is indispensable. However, the addition of a backlight increases power consumption and limits the continuous use time when the battery is driven. In order to take advantage of the portability, which is an inherent feature of liquid crystal display devices, bright reflective liquid crystal display devices that do not require a backlight are required.

Further, in order to improve the utilization efficiency of external light, it is necessary to increase the light transmittance of the liquid crystal layer and use a reflector having high reflection efficiency. Recently, research and development of polymer-scattering type liquid crystal that does not use a polarizing plate as a liquid crystal display device having a high light transmittance have been actively conducted, but there are few new proposals regarding a reflector.

In the conventional reflection type liquid crystal display device, a plastic film is mixed with a filler having a thickness of 10 to 100 μm, or physical or chemical etching is carried out to form an unevenness of a few μm on the surface of the substrate and then aluminum is vapor deposited. A method of making a diffused reflection plate that has been prepared and set it on the back surface of the liquid crystal panel to assemble the unit, or a method of attaching it to the back surface of the panel using an adhesive, and a method of depositing aluminum after making the back surface of the panel substrate uneven Etc. are used. In such a configuration, there is a liquid crystal panel substrate, an adhesive layer, an air layer, etc. between the liquid crystal layer and the light reflecting surface, and the reflection efficiency decreases due to reflection at a plurality of interfaces and absorption at each layer. In addition, since the distance between the liquid crystal layer that controls the light transmittance and the reflection surface is long, the light incident from one pixel is reflected to another adjacent pixel, resulting in a decrease in contrast, and in the case of color, color Purity will be reduced. This phenomenon becomes more remarkable as the pixel pitch becomes smaller in high-definition display devices and full-color display devices.

[0007]

[Object] The present invention has been made in view of the above-mentioned circumstances, and a metal reflective layer having fine irregularities on the surface thereof is provided on the liquid crystal layer side of a substrate to improve the utilization efficiency of external light. The present invention has been made for the purpose of providing the reflective liquid crystal display device.

[0008]

In order to achieve the above object, the present invention provides (1)
A guest-host type in which at least one substrate sandwiches a layer containing a liquid crystal between a plurality of substrates, and a voltage is applied between electrodes provided on the substrates to control the light transmittance of the liquid crystal layer to display information. In the polymer dispersion type liquid crystal display device,
A metal reflective layer having a granular undulation of a predetermined size in the horizontal direction with respect to the substrate and having a predetermined surface roughness in the vertical direction is provided on the liquid crystal layer side of one of the substrates, and further,
(2) A structure in which a colored resin is superposed on the patterned metal reflection layer, and (3) the metal reflection layer also serves as an electrode for applying an electric field to the liquid crystal layer, and (4) The metal reflection layer also serves as a pixel electrode for applying an electric field to the liquid crystal layer, and an MIM element for switching each of the pixel electrodes is added, further,
(5) It is characterized in that the unevenness of the particles is 400 to 800 nm and the surface roughness is 10 to 100 nm. Hereinafter, description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining one embodiment of a reflective liquid crystal display device according to the present invention. In the figure, 1 is a polarizing plate, 2 is an upper transparent substrate, 3 is an upper transparent electrode, and 4 is a transparent electrode. Alignment film, 5
Is a liquid crystal layer, 6 is a lower transparent electrode, 7 is an insulating film, 8 is a reflective layer,
Reference numeral 9 is a lower substrate. The two substrates 2, with the liquid crystal layer 5 in between.
9 is provided. One of the substrates 2 is a transparent substrate. Transparent electrodes 3 and 6 are provided on the substrates 2 and 9, and a voltage is applied between the electrodes to control the light transmittance of the liquid crystal layer 5. A metal reflective layer 8 having granular undulations in the horizontal direction and having a predetermined surface roughness in the vertical direction with respect to the substrate is provided on the liquid crystal layer side of the other substrate 9.

In the reflection type liquid crystal display device, in order to improve the utilization efficiency of external light, it is of course necessary to use a light reflecting surface having a high reflectance, as well as to circulate light to other pixels, reflection at an interface, Alternatively, light absorption by the substrate or the like should be minimized. For this purpose, it is better to make the distance between the liquid crystal layer and the light reflecting surface as short as possible. However, if the thickness (cell gap) of the liquid crystal layer varies, display unevenness occurs. 1 to the surface
It was not possible to provide a substrate having large irregularities of 5 μm on the liquid crystal layer side of the substrate. On the other hand, when fine irregularities are formed on the metal surface with particles as small as the wavelength of visible light, the metal reflection surface can be used as a diffuse reflection surface.

However, when such a fine pattern is formed, it cannot be formed by a conventional method such as photolithography or dispersion of fine particles. There is a method of utilizing light interference as a method of forming a pattern smaller than visible light, but the pattern due to interference exhibits an interference color depending on the viewing angle, and therefore cannot be used as a reflector. Aluminum, silver, platinum, iridium and the like are used as the metal having a high reflectance, but an aluminum vapor deposition film which is excellent in stability and inexpensive is widely used for the reflector. The film itself of the aluminum vapor deposition film used as the reflector has a very smooth surface, and the reflected light of the film formed on the smooth substrate has almost no diffuse reflection component.

However, the film surface has the same 400
When fine irregularities are formed on the film surface by depositing crystal grains having a size of up to 800 nm, a diffused reflection component is generated in the reflected light. The ratio between the specular reflection component and the diffuse reflection component of the reflected light can be controlled by the density of the crystal grains to be deposited, and the higher the density, the greater the diffuse reflection component. By providing the diffuse reflection surface having fine irregularities on the liquid crystal layer side of the substrate as described above, the distance between the liquid crystal layer and the light reflection surface can be shortened. In addition to this, there is also a method of etching the metal surface or oxidizing it to roughen the surface, and the surface shape can be controlled by etching and oxidizing conditions.

Since the metal film can be patterned by etching, the film can be left as a reflective layer only on a necessary portion of the entire surface of the substrate. Since only the portion where the pattern of the metal film remains reflects light, a light shielding layer (black mask) which has been conventionally required for preventing light leakage is not required. The surface of the substrate where the metal film is etched remains flat, so that TFT (Thin Film Transistor) and MIM (Metal Insulato) are formed on the same substrate.
A switching element for driving an active matrix such as r Metal) can also be manufactured. Further, the metal film is also a material for electric wiring, and this can be used as a pixel electrode. Since the light reflection layer is provided on the liquid crystal layer side of the substrate, the substrate used does not need to be transparent or have optical isotropy, so engineering plastics, etc. that could not be used as substrates for liquid crystal display devices so far Can also be used.

An aluminum film having a thickness of 0.5 μm is formed on the entire surface of the optically-polished alkali-free glass by DC magnetron sputtering.
Was formed into a film. The film forming conditions are a pressure of 5 × 10 ⁻³ torr, an Ar flow rate of 20 sccm, a substrate temperature of 120 ° C., and a substrate bias of −100.
v, the film forming rate is 250Å / min. On the surface of this aluminum film, crystal grains of about 0.5 μm are grown in the plane direction, and irregularities of about 50 nm are formed in the direction perpendicular to the substrate.
The specular reflectance was about 20%. A thermosetting epoxy resin was coated to 1 μm and cured at 170 ° C., and then a transparent conductive film of 0.1 μm was formed by sputtering.

190 μm by photolithography
After forming a line pattern with a width of 210 μm, a soluble polyimide film was applied, baked, and subjected to orientation treatment by rotary rubbing. It has a transparent electrode having a line pattern with a width of 190 μm and a pitch of 210 μm, and is bonded to another transparent substrate that has been subjected to an alignment treatment to form a cell gap 10
A guest-host type liquid crystal display device of μm was manufactured. In this liquid crystal display device, since the distance between the light reflecting surface and the liquid crystal layer is short,
Good contrast could be obtained.

FIG. 2 is a view showing another embodiment of the reflection type liquid crystal display device according to the present invention, in which 10 is a flattening layer and 11 is a flattening layer.
Is a color filter, and other parts having the same functions as those in FIG. 1 are denoted by the same reference numerals. An aluminum film having a thickness of 0.5 μm was deposited on a polyphenylene sulfide (PPS) film having a thickness of 100 μm by vacuum vapor deposition using resistance wire heating. The vapor deposition conditions are a pressure of 5 × 10 ⁻⁶ torr, a substrate temperature of 150 ° C., and a vapor deposition rate of 1200 Å / min. Crystal grains of about 0.3 μm are grown on the surface of this aluminum film and have irregularities of about 30 nm. The specular reflectance was about 40%.

90 μm wide by photolithography,
It was etched into a line pattern having a pitch of 110 μm.
A colored photosensitive resin in which a red pigment was dispersed in a photosensitive acrylic resin was applied in an amount of 1 μm, and a pattern having a width of 100 μm and a pitch of 330 μm was formed by photolithography in accordance with the aluminum stripe pattern. Similarly, RGB color reflective substrates were prepared using green and blue color photosensitive resins. A thermosetting epoxy resin was coated to 2 μm and cured at 150 ° C., and then a transparent conductive film of 0.1 μm was formed by sputtering. PPS is a high heat-resistant engineering plastic, but since it is not transparent, it cannot be used as a substrate for a liquid crystal panel until now. Further, by patterning the metal reflection layer, the black mask of the color filter is not required.

90 μm wide by photolithography,
A line pattern with a pitch of 110 μm was prepared by aligning the line pattern with an aluminum pattern, a soluble polyimide film was applied, and an orientation treatment was performed by rotary rubbing. Thickness 10
After a transparent conductive film of 0.1 μm was formed on a 0 μm polyethylene terephthalate (PET) film by sputtering, a stripe pattern with a width of 280 μm and a pitch of 330 μm was produced, and after alignment treatment, it was attached to a color reflection substrate to form a cell gap of 10 μm. A guest-host type color simple matrix liquid crystal display device was manufactured.

FIG. 3 is a view showing still another embodiment of the reflection type liquid crystal display device according to the present invention, in which 12 is a lower electrode and reflection layer,
Reference numeral 13 is a transparent electrode, and other parts having the same functions as those in FIG. An aluminum film of 0.5 μm was vapor-deposited on the optically-polished alkali-free glass by vacuum vapor deposition with resistance wire heating. The vapor deposition conditions are a pressure of 5 × 10 ⁻⁶ torr, a substrate temperature of 50 ° C., and a vapor deposition rate of 100 Å / min. The surface of this aluminum film is almost a mirror surface, but a phosphoric acid-based etching solution (phosphoric acid: nitric acid: acetic acid: water = 16: 1: 2: 1, 40
By light etching at (° C.) for 10 seconds, irregularities of about 0.5 μm are formed on the surface in the vertical direction of the substrate of about 50 nm. The specular reflectance of this aluminum surface is 40
It was about%.

190 μm by photolithography
Form a stripe pattern with a width of 210 μm,
It also serves as a reflective layer and an electrode. Indium tin oxide (ITO) is widely used as a transparent electrode, and it has a problem that it has a higher resistance than other metals, but by using a reflective layer as an electrode, a low resistance electrode is formed. be able to. 190 μm after applying soluble polyimide film to this substrate and performing orientation treatment by rotary rubbing
A guest-host liquid crystal display device having a cell gap of 10 μm was produced by bonding a transparent electrode having a line pattern with a width of 210 μm pitch and having been subjected to an alignment treatment.

FIGS. 4A to 4C are views showing still another embodiment of the reflection type liquid crystal display device according to the present invention.
FIG. 3B is a plan view of the MIM element, FIG. 6B is a sectional view taken along line BB of FIG. 3A, and FIG. 14 in the figure
Is a chromium electrode, 15 is a substrate, 16 is a hard carbon film, 17 is a pixel electrode / reflecting layer, and other parts having the same functions as in FIG. Chromium on a 100 μm thick polyether sulfone (PES) film with 0.1
Then, the lower electrode (signal electrode) of the MIM element was formed by vapor deposition of μm and patterning. Other than the above, platinum, gold, silver, nickel, tungsten, tantalum, titanium, aluminum and the like can be used as the material of the lower electrode. A hard carbon film (also called a diamond thin film, an amorphous diamond film, or an i-C film) was formed to a thickness of 0.2 μm by plasma CVD. Subsequently, an aluminum film of 0.5 μm was formed by DC magnetron sputtering. Film forming conditions are pressure 5 × 10 ^-3 torr, A
r flow rate 10 sccm, substrate temperature 80 ° C., substrate bias −10
It is 0 v and the film forming rate is 150 Å / min.

The surface of this aluminum film is almost a mirror surface,
By anodizing, irregularities of about 50 nm can be formed on the surface. An aqueous solution of tartaric acid (5
%) To which aqueous ammonia (2%) was added was used.
The specular reflectance of the aluminum film after oxidation was about 20%.
Aluminum oxide formed by anodic oxidation is porous, and its surface property can be controlled by the type of electrolytic solution. Large irregularities are formed by those having strong oxidizing ability such as phosphoric acid and chromic acid, and small irregularities are formed by those having weak oxidizing ability such as oxalic acid and tartaric acid. This aluminum film is patterned to serve as a light reflector and pixel electrode, and
A MIM element of chromium / hard carbon film / aluminum as shown in FIGS. A thickness of 10μ consisting of a mixture of nematic liquid crystal / polymer resin / dye on this substrate
m liquid crystal layer is formed by a casting method, and then has a transparent electrode patterned in a stripe shape and has a thickness of 100 μm.
m PES film was stuck together to produce a reflective polymer dispersed liquid crystal display device.

[0023]

As is apparent from the above description, the present invention has the following effects. (1) Effect on claim 1: By providing a metal reflective layer having fine irregularities on the liquid crystal layer side of the substrate, the utilization efficiency of external light is increased, and an opaque substrate that could not be used until now is also used. We were able to. (2) Effect on Claim 2: By producing a color filter on the patterned metal reflection layer, a bright color reflection substrate which does not require a black mask can be produced. (3) Effect on Claim 3: By using the metal reflective layer as an electrode for image display, the resistance of the electrode can be reduced and the manufacturing process can be shortened. (4) Effect on Claim 4: Since the metal reflective layer also serves as an electrode for image display, and the MIM element is configured, the manufacturing process of the liquid crystal display panel driven by the active matrix can be shortened. (5) Effect on Claim 5: Since the granular undulations and the surface roughness are optimized, the utilization efficiency of external light can be further enhanced.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of a reflective liquid crystal display device according to the present invention.

FIG. 2 is a configuration diagram for explaining another embodiment of the reflective liquid crystal display device according to the present invention.

FIG. 3 is a configuration diagram for explaining still another embodiment of the reflective liquid crystal display device according to the present invention.

FIG. 4 is a configuration diagram for explaining yet another embodiment of the reflective liquid crystal display device according to the present invention.

FIG. 5 is a diagram showing a conventional reflective liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polarizing plate, 2 ... Upper transparent substrate, 3 ... Upper transparent electrode, 4 ... Alignment film, 5 ... Liquid crystal layer, 6 ... Lower transparent electrode, 7 ... Insulating film, 8 ...
Reflective layer, 9 ... Lower substrate.

Claims (5)

[Claims] 1. A liquid crystal-containing layer is sandwiched between a plurality of substrates, at least one of which is transparent, and a voltage is applied between electrodes provided on the substrates to control the light transmittance of the liquid crystal layer to display information. In the guest-host-type or polymer-dispersion-type liquid crystal display device, a metal reflection layer having a predetermined level of granular undulations in the horizontal direction and a predetermined surface roughness in the vertical direction is formed on one side of the substrate. A reflective liquid crystal display device, which is provided on the liquid crystal layer side of the substrate. 2. The reflective liquid crystal display device according to claim 1, wherein a colored resin is laminated on the patterned metal reflective layer. 3. The reflective liquid crystal display device according to claim 1, wherein the metal reflective layer also serves as an electrode for applying an electric field to the liquid crystal layer. 4. The reflection type liquid crystal display device according to claim 1, wherein the metal reflection layer also serves as a pixel electrode for applying an electric field to the liquid crystal layer, and an MIM element for switching each of the pixel electrodes is added. . 5. The reflection type liquid crystal display device according to claim 1, wherein the granular undulations are 400 to 800 nm and the surface roughness is 10 to 100 nm.