JPH07134300A - Reflective liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a reflective liquid crystal display device capable of displaying a bright screen, hardly causing a display defect, and excellent in reliability. [Structure] Back electrode plate 1 having light-reflecting metal electrode 12
And the transparent electrode 22 which is arranged facing the back electrode plate.
1. A reflective liquid crystal display device comprising an observer-side electrode plate 2 having: and a liquid crystal substance 4 enclosed between these electrode plates, wherein the metal electrode 12 is a metal that is more easily oxidized than silver (for example, Mg. ) Containing a silver alloy thin film. And the thin film of the silver alloy has better adhesion to the glass substrate that constitutes the back electrode plate than the thin film of silver alone,
In addition, since the agglomeration is less likely to occur due to the heating action and the hardness is high, it is possible to prevent damage to the metal electrode and peeling from the substrate during the assembly process of the reflective liquid crystal display device and the driving of the device. Therefore, the target reflective liquid crystal display device can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device having a light-reflective metal electrode on a back electrode plate located on the side opposite to a screen observer, and particularly capable of displaying a bright screen. The present invention relates to a reflective liquid crystal display device which is less likely to cause defects and has excellent reliability.

[0002]

2. Description of the Related Art Generally, a liquid crystal display device comprises a pair of electrode plates on which electrodes are arranged and a liquid crystal substance enclosed between the electrode plates, the main part of which is used to apply a voltage between the electrodes. By applying the voltage, the alignment state of the liquid crystal substance is changed to control the plane of polarization of the light transmitted through the liquid crystal substance, and at the same time, the polarizing film controls the transmission / non-transmission of the liquid crystal substance to perform screen display. As a liquid crystal display device of this type, a light source (lamp) is arranged on the back surface or the side surface of the back electrode plate, and a backlight type or light guide type transmissive type with a built-in lamp in which light rays are incident from the back electrode plate side. Liquid crystal display devices are widely used.

However, in a transmissive liquid crystal display device with a built-in lamp, the power consumption of the lamp is large and the CRT is large.
Since it consumes almost the same amount of power as other types of displays such as a plasma display and a plasma display, it has the drawback that the original low power consumption of the liquid crystal display device is impaired and that it becomes difficult to use it for a long time at the destination. Was.

On the other hand, without incorporating such a lamp, outside light such as room light or natural light is made incident from an electrode plate (referred to as an observer-side electrode plate) located on the observer side of the apparatus, and There is also known a reflection type liquid crystal display device in which incident light is reflected by a light reflecting material provided on the back electrode plate and a screen is displayed by this reflected light. In addition, this reflective liquid crystal display device has advantages that it consumes less power because it does not use a lamp and can withstand long-time driving at a portable location.

As such a reflection type liquid crystal display device, for example, as shown in FIG. 4, a metal reflection plate a3 is provided on the back surface of the back electrode plate a, or as shown in FIG. It is known that the electrode a2 is made of a light-reflective metal thin film and incident light is reflected by the electrode a2 to display a screen. In the reflection type liquid crystal display device shown in FIG. The display screen constituted by the above has a drawback that it is reflected on the metal reflection plate a3 to form a virtual image and is double observed.
The reflection type liquid crystal display device shown in FIG.
4 to 5, b is a viewer-side electrode plate, c is a liquid crystal substance,
Reference numeral d denotes a polarizing film, and reference numeral e denotes a sealing material that integrates the back electrode plate a and the observer-side electrode plate b in the peripheral portion.

[0006]

By the way, as the light-reflective metal electrode a2 incorporated in the reflection type liquid crystal display device of FIG. 5, an aluminum thin film which is inexpensive and has excellent light reflectance has been widely used. However, the aluminum thin film is easily oxidized by moisture or a base, and the light reflection performance is deteriorated due to this oxidation, and a display defect is likely to occur with time. It is used as the electrode a2.

However, even when a silver thin film is applied instead of the aluminum thin film, there are the following problems and there is still room for improvement.

First, the adhesion of the silver thin film to the substrate constituting the back electrode plate is not good, and there is a problem that the silver thin film easily peels off from the substrate during the process of assembling the liquid crystal display device or driving the device, and However, since the hardness of the silver thin film is not so high, there is a problem that the surface of the silver thin film is easily damaged when a physical force acts on its surface during the assembly process of the liquid crystal display.

Further, a heat treatment step in assembling the liquid crystal display device (for example, a back electrode plate a and an observer side electrode plate b are overlapped with each other with a sealing material e interposed therebetween, and heated and pressurized at 200 to 300 ° C. to be integrated. During the heating step, or in the step of heat-treating the alignment film at 200 to 300 ° C. to stably align the liquid crystal), the silver thin film is likely to be spherically aggregated by the heating action, and this aggregation causes unevenness on the silver thin film surface. It has a problem that it is easily formed and impairs its reflection performance.

The present invention has been made by paying attention to such a problem, and its problem is that the metal electrode is less likely to be peeled off or damaged during the assembly process of the liquid crystal display device or during the driving of the device. It is an object of the present invention to provide a reflective liquid crystal display device capable of displaying a bright screen over the entire length and in which display defects hardly occur.

[0011]

That is, the invention according to claim 1 is a back electrode plate having a light-reflecting metal electrode,
An observer-side electrode plate having a transparent electrode arranged opposite to the back electrode plate and a liquid crystal substance enclosed between the two electrode plates are provided, and a voltage is applied between the metal electrode and the transparent electrode. On the premise of a reflective liquid crystal display device in which a liquid crystal substance is applied to drive a liquid crystal substance to display a screen, the light reflective metal electrode is composed of a thin film of a silver alloy containing a metal that is more easily oxidized than silver. It is a feature.

A thin film of a silver alloy containing a metal that is more easily oxidized than silver has better adhesion to a substrate than a thin film of silver alone, and is less likely to aggregate due to heating.
Moreover, since the light-reflecting metal electrode is made of the above silver alloy, the metal electrode is less likely to be peeled off or damaged during the assembly process of the liquid crystal display device or during the driving of the device because of its high hardness.

Therefore, it is possible to provide a reflective liquid crystal display device capable of displaying a bright screen, hardly causing a display defect, and excellent in reliability.

The metal that is more easily oxidized than silver in such technical means is a metal that is more likely to bond with an oxygen atom and has a higher binding energy than silver, and therefore such a metal is generally a metal. It can be judged by the electron affinity (the smaller the electron affinity is, the more easily it becomes a cation and the more easily it binds to the oxygen anion), electronegativity, work function, ionization potential and the like. Further, since the binding energy between the metal atom and the oxygen atom is high, the melting point of the metal oxide is high. And a silver alloy containing such a metal,
The metal oxide and metal ions contained in a small amount in this alloy exert a strong bonding force with respect to the substrate. For example, when the substrate is made of glass, the oxygen anion on the surface of the glass substrate and the metal oxide or metal ion are bonded with a strong bonding force. Examples of such a metal include magnesium, aluminum, titanium, zirconium, and
Hafnium can be used, and two or more kinds of these metals may be contained in the thin film. The invention according to claim 2 relates to the invention in which the above metal is specified.

That is, the invention according to claim 2 is premised on the reflective liquid crystal display device according to claim 1, and the metal that is more easily oxidized than silver is selected from magnesium, aluminum, titanium, zirconium and hafnium. It is characterized by being composed of one or more selected metals.

In order to sufficiently improve the adhesion with the substrate, it is preferable that the silver alloy forming the metal electrode contains 0.5 atm% or more of the above-mentioned metal which is more easily oxidized than silver. In order to more surely prevent the agglomeration in (2), it is preferable to contain 2 atm% or more. Also,
When the metal is magnesium, aluminum, or both of them, the resistance of the silver alloy decreases with an increase in the amount of addition of these metals, and oxidation due to water or a base easily occurs. It is desirable that the content of the above metal in the silver alloy is 30 atm% or less. On the other hand, when the metal is titanium or two or more kinds of metals containing titanium, the corrosion resistance of the silver alloy becomes too high with the increase of the addition amount of these metals, which makes etching difficult, and Since the processing accuracy may be deteriorated, it is desirable that the metal content in the silver alloy forming the metal electrode is 50 atm% or less. Claim 3
The inventions according to 4 and 4 have been made based on such technical reasons.

That is, the invention according to claim 3 is premised on the reflective liquid crystal display device according to claim 2, and the metal that is more easily oxidized than silver is one or two kinds selected from magnesium and aluminum. Made of metal, and
The light-reflective metal electrode is composed of a thin film of a silver alloy containing 0.5 to 30 atm% of the metal, and the invention according to claim 4 is the invention according to claim 2. On the premise of the reflective liquid crystal display device according to the present invention, the metal that is more easily oxidized than silver is titanium or two or more kinds of metals containing titanium, and the light-reflective metal electrode has the above-mentioned metal.
It is characterized by being composed of a thin film of a silver alloy containing 5 to 50 atm%.

In order to further improve the hardness of the light-reflecting metal electrode and prevent scratches, a small amount of another element may be contained in the silver alloy. Examples of such elements include V, Nb, Ta, Cr, Mo, W, Mn,
Metal elements such as Fe, Ni, Co, Cu, and Zn are listed. Moreover, you may add nonmetallic elements, such as Si, P, Bi, and Sb.

Next, for the light-reflecting metal electrode, a thin film of a silver alloy having the same composition as the metal electrode is formed on the substrate of the back electrode plate, and the thin film is patterned by a well-known photolithography process. Can be formed. Examples of the method of forming the thin film include a method of sputtering a silver alloy having the same composition as the thin film as a target, a method of vacuum vapor deposition using the silver alloy as a vapor deposition source, and the like. Further, by alternately arranging silver and a metal that is more easily oxidized than that (for example, in a stripe shape or a concentric circle), or by placing the above-mentioned metal that is partially oxidized more easily than silver on silver. It is possible to form a thin film of the above silver alloy by partially exposing both the silver and the above metal on the surface and using them as targets for sputtering. In this case, the composition of the formed thin film depends on the ratio of the exposed area of silver to the exposed area of the metal. It is also possible to form a film by ion plating.

The substrate on which the thin film of silver alloy is formed and which constitutes the back electrode plate is, for example, a glass substrate. In addition to these, it is also possible to apply a plastic film, a plastic board, or the like. This substrate is not limited to being transparent, but may be colored in black, white, or another color. When using the black one as the substrate,
Liquid crystal display device pixel-to-pixel gap area (inter-pixel area)
It is possible to improve the contrast of the display screen by preventing the reflection of the light rays incident on the portion where the metal electrode does not exist without forming the light shielding film. Further, when the liquid crystal display device is used in a bright room with a lot of room light, the above-mentioned room light is used for screen display, and a lamp is provided inside the device for use in a dark room where the room light is insufficient. In the case of a built-in transflective liquid crystal display device, it is desirable to use a transparent substrate.

Prior to forming the silver alloy thin film on the substrate, a treatment for improving the adhesion between the thin film and the substrate may be performed on the substrate surface. Examples of such surface treatment include ultraviolet irradiation and plasma treatment. In addition, in order to improve the adhesion, a chromium thin film or an IT film is formed on the substrate before forming the silver alloy thin film.
It is also possible to form an O thin film. When the ITO thin film is formed, since the ITO thin film is transparent and has conductivity, the ITO thin film is patterned into a stripe shape and the thin film is patterned into a rectangular pixel pattern. It is possible to improve the contrast of the display screen by preventing light reflection at this portion without providing a light shielding layer on the portion other than the pixel.

On the other hand, a transparent substrate such as a glass substrate, a plastic film or a plastic board can be applied as the substrate constituting the observer side electrode plate, and a transparent conductive film such as ITO or a Nesa film can be applied as the transparent electrode. it can. It is also possible to provide a light-scattering layer on the observer-side electrode plate to scatter the display light to expand the viewing angle of the display screen, or to provide a color filter layer to color the display light for color display. . The light-scattering layer may be provided either on the inside of the substrate, which is in contact with the liquid crystal substance, or on the outside thereof, which is in contact with the polarizing film. As such a light scattering layer, for example,
A transparent resin binder in which fine particles having a refractive index different from that of the transparent resin binder is dispersed can be applied. Examples of such fine particles include MgF ₂ , CaF ₂ , LiF, NaF, and Ba.
F ₂ , SiO ₂ , TiO ₂ , HfO ₂ , MgO, CaO, A
l ₂ O ₃ , SnO ₂ , PbO, Sb ₂ O ₅ , ZrO ₂ , CeO
Inorganic fine powder such as ₂ or fluororesin fine powder such as PTFE (polytetrafluoroethylene), amorphous polyolefin fine powder, polydivinylbenzene beads, polystyrene hollow beads, polysulfone fine powder, fused silica fine powder, FK Fine powder of fluoride-containing silicate glass such as -6 can be used. It is also possible to roughen the surface of the substrate and use this surface instead of the light scattering layer.

As the color filter layer,
A color filter layer formed by printing an ink containing a colorant on a pixel pattern by a printing method, a color filter layer formed by dyeing a transparent resin on a pixel pattern by a dyeing method, or a photosensitive transparent resin containing a colorant A color filter layer by a pigment dispersion method formed by exposing and developing a pixel pattern according to a photolithography process after applying the above, and a color filter layer by an electrodeposition method formed by electrodeposition of an electrodeposition coating material containing a coloring material on the pixel pattern A well-known color filter layer such as an electrophotographic color filter layer formed by adhering a toner containing a coloring material to a pixel pattern according to the electrophotography can be used.

Since the metal electrode according to the present invention has a smaller electric resistance than the transparent electrode of the observer-side electrode plate, the liquid crystal display device uses a simple matrix driving method (the liquid crystal substance or its alignment state is STN, ECB, (Mainly applied in the case of homeotropic or antiferroelectric liquid crystal), it is possible to use the above metal electrode as the scanning side electrode and the transparent electrode of the observer side electrode plate as the signal electrode. preferable.
In addition, a driving element (TFT that drives a liquid crystal substance for each pixel)
In the case of the active matrix driving system including the above), the driving element may be provided on either the back electrode plate or the viewer side electrode plate.

[0025]

According to the present invention, the light-reflective metal electrode provided on the back electrode plate of the reflective liquid crystal display device is a thin film of a silver alloy containing a metal that is more easily oxidized than silver. The thin film of the silver alloy has better adhesion to the substrate forming the back electrode plate than the thin film of silver alone,
Moreover, the aggregation is less likely to occur due to the heating action, and moreover,
Since the hardness is high, it is possible to prevent damage to the metal electrodes and peeling from the substrate during the assembly process of the reflective liquid crystal display device and the driving of the device.

[0026]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[First Embodiment] As shown in FIG. 1, a reflective liquid crystal display device according to this embodiment includes a back electrode plate 1 and an observer-side electrode plate 2 arranged so as to face the back electrode plate 1. When,
A sealing material 3 that integrates these two electrode plates 1 and 2 in the peripheral portion, a liquid crystal substance 4 enclosed between these two electrode plates 1 and 2, and is laminated on the outer surface of the observer-side electrode plate 2. The polarized film 5 thus formed constitutes a main part thereof. The back electrode plate 1 includes a glass substrate 11 having a thickness of 0.7 μm,
315 μm wide and 330 μm pitch on this glass substrate 11.
m striped pattern and a metal electrode 12 made of a silver alloy thin film (0.2 μm thick) containing 4 atm% of magnesium, while the observer-side electrode plate 2 has a thickness of 0.7 μm. And a transparent electrode composed of a transparent conductive film having a thickness of 0.24 μm and provided on the glass substrate 21 in a stripe pattern (stripe pattern in a direction orthogonal to the metal electrode 12) having a width of 315 μm and a pitch of 330 μm. 22 and 22.

The liquid crystal display device is manufactured by the following steps.

First, using a silver alloy containing 4 atm% of magnesium as a target, a thin film having the same composition as this is formed on the glass substrate 11 by sputtering, processed into a stripe pattern according to a well-known photolithography process, and the back electrode plate 1 is formed. Was manufactured.

Next, the glass substrate 21 kept at room temperature.
After a transparent conductive film was vacuum-deposited on it and processed into a stripe pattern according to a photolithography process, the transparent conductive film was subjected to heat treatment to increase its conductivity, whereby an observer side substrate 2 was manufactured. Then, the back electrode plate 1 and the observer-side electrode plate 2 were overlapped with each other with the sealant 3 interposed therebetween, and heated and pressed at a temperature of 200 to 300 ° C. to be integrated with each other to manufacture the reflection type liquid crystal display device.

Observation of the shape of the metal electrode 12 of the reflection type liquid crystal display device manufactured in this manner confirmed that no change in appearance was observed and no agglomeration phenomenon occurred compared to when a thin film of silver alloy was formed. did it. In addition, the light reflectance was measured and found to be 95%, which confirmed that the material had excellent light reflecting performance. In addition, the cellophane tape was adhered on the metal electrode 12 and then peeled off, and the adhesion between the metal electrode 12 and the glass substrate 11 was evaluated by the presence or absence of the silver alloy thin film peeled off along with the separation of the cellophane tape. However, no silver alloy thin film adhered to the cellophane tape and peeled off was observed, and it was confirmed that the silver alloy thin film had high adhesion.

Comparative Example A reflective liquid crystal display device was manufactured in the same manner as in Example 1 except that a thin film of silver alone was used in place of the silver alloy thin film containing 4 atm% of magnesium.

When the shape of the metal electrode 12 of the reflection type liquid crystal display device manufactured as described above was observed, a silver thin film in which a part of the metal electrode 12 was destroyed and spherically aggregated was observed.

When a cellophane tape was adhered onto the metal electrode 12 and then peeled off, almost all of the silver thin film was peeled off along with the peeling of the cellophane tape.

[Example 2] A silver alloy thin film containing 4 atm% magnesium and 1 atm% titanium was used in place of the silver alloy thin film containing 4 atm% magnesium, except that a silver alloy thin film containing 4 atm% magnesium and 1 atm% titanium was used.
A reflective liquid crystal display device was manufactured in the same manner as in Example 1.

No aggregation phenomenon was observed in the metal electrode of the obtained reflection type liquid crystal display device, and high light reflection performance was exhibited.
Further, in the peeling test using the above-mentioned cellophane tape, no silver alloy thin film adhered to the cellophane tape and peeled off was observed, and it was confirmed to have high adhesion.

[Embodiment 3] In the reflection type liquid crystal display device according to this embodiment, as shown in FIG. 2, a back electrode plate 1 and an observer side electrode plate 2 arranged so as to face the back electrode plate 1. When,
A sealing material 3 that integrates these two electrode plates 1 and 2 in the peripheral portion, a liquid crystal substance 4 enclosed between these two electrode plates 1 and 2, and is laminated on the outer surface of the observer-side electrode plate 2. The polarized film 5 thus formed and a lamp (not shown) arranged behind the rear electrode plate 1 and used by being turned on in a darkened room constitute a main part. The back electrode plate 1 includes a glass substrate 11 having a thickness of 0.7 μm, and indium oxide which is provided on the glass substrate 11 in a stripe pattern having a width of 195 μm and a pitch of 210 μm and which contains 7.5 wt% of tin oxide. ITO thin film consisting of (thickness 0.1μ
m) 13 and a pixel portion on the ITO thin film 13 in a pattern (a rectangular pattern having a circular perforated pattern 14a with a diameter of 70 μm in the central portion as shown in FIG. 3 and a side of 195 μm) and aluminum. The observer-side electrode plate 2 is composed of a glass electrode 21 having a thickness of 0.7 μm, a width of 195 μm, and a pitch of 210 μm on the glass substrate 21. And a transparent electrode 22 formed of a transparent conductive film having a thickness of 0.2 μm and provided in a stripe pattern (a stripe pattern in a direction orthogonal to the metal electrode 14).

The perforated pattern 14a provided in the central portion of the metal electrode 14 guides the light beam of the lamp, which is turned on when the liquid crystal display device is driven in a dark room, to the pixel portion. is there.

The reflective liquid crystal display device is manufactured by the following steps.

First, an ITO thin film made of indium oxide containing 7.5% by weight of tin oxide and a silver alloy thin film containing 8 atm% of aluminum were formed by sputtering on a glass substrate 11 kept at room temperature. After processing the silver alloy thin film into the rectangular pattern having a perforated pattern according to the photolithographic process of 1., the ITO thin film was processed into the stripe pattern to manufacture the back electrode plate 1.

Next, the glass substrate 21 kept at room temperature.
A transparent conductive film was vacuum-deposited thereon, processed into the above stripe pattern according to a photolithography process, and then heat treatment was applied to the transparent conductive film to increase the conductivity thereof, whereby the viewer-side substrate 2 was manufactured. Then, the back electrode plate 1 and the observer-side electrode plate 2 were overlapped with each other with the sealant 3 interposed therebetween, and heated and pressed at a temperature of 200 to 300 ° C. to be integrated with each other to manufacture the reflection type liquid crystal display device.

Metal electrode 1 of the obtained reflection type liquid crystal display device
No aggregation phenomenon was observed in No. 4, and high light reflection performance was exhibited. Further, in the peeling test using the above-mentioned cellophane tape, no silver alloy thin film adhered to the cellophane tape and peeled off was observed, and it was confirmed to have high adhesion.

[0043]

According to the present invention, the light-reflective metal electrode provided on the back electrode plate of the reflective liquid crystal display device contains a silver alloy thin film containing a metal that is more easily oxidized than silver. The thin film of the silver alloy has better adhesion to the substrate forming the back electrode plate than the thin film of silver alone, and its aggregation is less likely to occur due to the heating action, and the hardness is Since the cost is high, it is possible to prevent damage to the metal electrode and peeling from the substrate during the assembly process of the reflective liquid crystal display device and the driving of the device.

Therefore, there is an effect that it is possible to provide a reflective liquid crystal display device capable of displaying a bright screen, hardly causing a display defect, and excellent in reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reflective liquid crystal display device according to a first embodiment.

FIG. 2 is a cross-sectional view of a reflective liquid crystal display device according to a third embodiment.

FIG. 3 is a plan view of a principal part showing a pattern of a metal electrode according to a third embodiment.

FIG. 4 is a cross-sectional view of a reflective liquid crystal display device according to a conventional example.

FIG. 5 is a cross-sectional view of a reflective liquid crystal display device according to a conventional example.

[Explanation of symbols]

 1 Rear Electrode Plate 2 Observer Side Electrode Plate 3 Sealing Material 4 Liquid Crystal Material 5 Polarizing Film 11 Glass Substrate 12 Metal Electrode 21 Glass Substrate 22 Transparent Electrode

Claims (4)

[Claims] 1. A back electrode plate having a light-reflecting metal electrode, an observer-side electrode plate which is arranged so as to face the back electrode plate and has a transparent electrode, and is enclosed between these two electrode plates. In a reflective liquid crystal display device comprising a liquid crystal substance and driving a liquid crystal substance by applying a voltage between the metal electrode and the transparent electrode to display a screen, the light reflective metal electrode is more easily oxidized than silver. A reflective liquid crystal display device comprising a thin film of a silver alloy containing a metal. 2. The reflective liquid crystal display according to claim 1, wherein the metal that is more easily oxidized than silver is one or more kinds of metals selected from magnesium, aluminum, titanium, zirconium and hafnium. apparatus. 3. A metal that is more easily oxidized than silver is composed of one or two kinds of metals selected from magnesium and aluminum, and a light-reflecting metal electrode is formed of 0.5 or more of the above metals.
3. The reflection type liquid crystal display device according to claim 2, wherein the reflection type liquid crystal display device is constituted by a thin film of a silver alloy containing about 30 atm%. 4. A metal which is more easily oxidized than silver is composed of titanium or two or more kinds of metals containing titanium, and a light-reflecting metal electrode is a thin film of a silver alloy containing 0.5 to 50 atm% of the above metal. The reflective liquid crystal display device according to claim 2, which is configured.