JPH04315129A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the reflection type liquid crystal display device provided with a reflection plate having good reproducibility and reflection characteristics. CONSTITUTION:A thin film 18 having ruggedness 14 is formed by using an electron beam vapor deposition method, chemical vapor reaction method, plasma CVD method, etc., on one surface of a substrate 11. A reflection film 16 consisting of a metallic thin film is formed on this thin film 18 and further, an oriented film 27 is formed thereon to obtain the reflection plate 17. An active matrix substrate 20 is disposed to face the reflection plate 27. Picture element electrodes 23, thin-film transistors 22 and the oriented film 24 are formed on the active matrix substrate 20. A liquid crystal layer 25 of a phase transition type guest-host mode is sealed between the active matrix substrate 20 and the reflection plate 17. The reflection characteristics of the reflection plate are controlled by properly selecting the conditions for forming the thin film in this way.

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 that does not use a backlight.

0002

2. Description of the Related Art In recent years, the application of liquid crystal display devices to word processors, laptop computers, pocket televisions, etc. has rapidly progressed. In particular, reflective display devices that perform display by reflecting light incident from the outside are attracting attention because they do not require a backlight, consume less power, and can be made thinner and lighter.

Conventionally, reflective liquid crystal display devices have adopted the twisted nematic method (hereinafter abbreviated as TN method) and the super twisted nematic method (hereinafter abbreviated as STN method). In both types, about 1/2 of the incident natural light is inevitably not used for display due to the linear polarizer, resulting in a dark display. To address these problems, a display mode has been proposed that attempts to effectively utilize all rays of natural light. An example of such a display mode is the phase change guest-host method (D.L. White an
dG. N. Taylor: J. Appl. Phys.
45 p. 47181974). This display mode utilizes the cholesteric-nematic phase transition phenomenon caused by an electric field. This method is further combined with a micro color filter to create a reflective multicolor display (Proceedings of the
SID Vol. 29 p. 157 1988) has also been proposed.

In order to obtain a brighter display in such a display mode that does not require a polarizing plate, it is necessary to increase the intensity of light scattered in the direction perpendicular to the display screen with respect to incident light from all angles. There is. To this end, it is necessary to control the formation of the reflective film on the reflective plate so that it has optimal reflective properties. In the above literature, the surface of a glass substrate is roughened with an abrasive, the surface unevenness is controlled by changing the etching time with hydrofluoric acid, and a thin film of silver Ag is formed on the unevenness. A reflector is disclosed.

[0005]

[Problem to be Solved by the Invention] However, in the reflecting plate described in the above-mentioned document, irregularities are formed by scratching the glass substrate with an abrasive, so it is difficult to form irregularities with a uniform shape. is not possible. Also,
There is a problem that the reproducibility of the shape of the uneven portion is poor. Therefore, it is not possible to obtain a reflective liquid crystal display device having uniformly shaped uneven portions and good reflection characteristics with good reproducibility.

The present invention is intended to solve these problems, and an object of the present invention is to provide a reflective liquid crystal display device equipped with a reflective plate having uniform and highly reproducible reflective characteristics, and a method for manufacturing the same. It is to be.

[0007]

[Means for Solving the Problems] A reflective liquid crystal display device of the present invention comprises: an insulating substrate on which a transparent electrode is formed; a reflecting plate having a reflective film formed on a thin film having an uneven surface; A liquid crystal layer is included between the substrate and the reflector, thereby achieving the above object.

[0008] Furthermore, the surface of the reflecting plate on which the reflecting film is formed may be adjacent to the liquid crystal layer side.

[0009] Furthermore, the reflective film of the reflective plate may also have the function of a counter electrode facing the transparent electrode of the insulating substrate.

Furthermore, the thin film may be formed by electron beam evaporation.

[0011] Furthermore, the thin film may be formed by a chemical vapor phase reaction method.

[0012] Furthermore, the thin film may be formed by a plasma CVD method.

[0013]

[Function] In the reflective liquid crystal display device of the present invention, the pitch and height of the unevenness can be optimally set by changing the conditions for forming the thin film, and therefore the reflective characteristics of the reflective plate can be freely controlled. Can be done. Furthermore, the reproducibility of reflection characteristics is also good.

[0014] If the surface of the reflective plate on which the reflective film is formed is adjacent to the liquid crystal layer, the distance between the reflective film and the liquid crystal layer can be shortened, and the parallax of the display device can be reduced. can. Furthermore, the reflective film can be used as a counter electrode facing the transparent electrode on the insulating substrate.

[0015]

[Examples] Examples of the present invention will be described below. FIG. 1 shows a sectional view of a reflecting plate 17 used in an embodiment of the reflective liquid crystal display device of the present invention. This example will be explained according to the manufacturing process. First, a thin film 18 made of ITO (indium tin oxide) is formed on one surface of an insulating substrate 11 such as a glass substrate. In this embodiment, the substrate 11 has a thickness of 1
．． A 1 mm one (trade name 7059, manufactured by Corning Inc.) was used. The thin film 18 was formed by electron beam evaporation using In2O3 pellets containing 1 to 10% by weight of SnO2. It is preferable that the temperature of the substrate 11 is 50 to 450° C., the oxygen partial pressure is 1×10 −5 to 8×10 −4 Torr, and the film formation rate is 0.3 nm/sec or more. In this example, using In2O3 pellets to which 5% by weight of SnO2 has been added, the temperature of the substrate 11 is 100°C, and the oxygen partial pressure is 1×
The thin film 18 was produced under conditions of 10 −4 Torr and a film formation rate of 1.5 nm/sec. The thickness of the thin film 18 is 1.8 μm. If the thin film 18 is formed under the above conditions, minute irregularities 14 will be formed on the surface of the thin film 18.

On the thin film 18 on which the minute irregularities 14 are formed,
A reflective film 16 having a uniform thickness was formed. As the material of the reflective film 16, metals such as Al, Ni, Cr, and Ag can be used, but an insulating thin film of a notch type filter using a dielectric mirror or cholesteric liquid crystal can also be used. The thickness of the reflective film 16 is preferably about 0.01 to 0.4 μm. In this example, the reflective film 16 with a thickness of 0.1 μm was formed by vacuum evaporating Ag. Through the above steps, the reflecting plate 17 is obtained.

Further, in the above embodiment, using In2O3 pellets to which 8% by weight of SnO2 was added, the temperature of the substrate 11 was 50° C., the oxygen partial pressure was 5×10 −4 Torr, and the film forming rate was 2.5 nm/sec. A reflecting plate 17a having a thin film 18a produced under the same conditions was also produced. In the reflection plate 17a, the reflection film 16 is manufactured under the same conditions as in the case of the reflection plate 17.

Reflector plate 17 (1) produced as described above
The method for measuring the reflection characteristics of 7a) is shown in FIG. In FIG. 2, assuming that the reflector 17 (17a) is used in an actual liquid crystal display device, the reflectance measurement model 1 reproduces the state in which the reflector is in contact with the liquid crystal layer. ing. In the reflectance measurement model 1, a dummy substrate 2 made of glass with a refractive index of about 1.5 is superimposed on a reflector plate 17 (17a), and the refractive index is approximately 1.5 and the refractive index of an actual liquid crystal layer is approximately the same as that of an actual liquid crystal layer. The same ultraviolet curable adhesive 3 is used to adhere tightly.

The reflectance characteristics using such a reflectance measurement model 1 are determined by measuring the incident light 5 entering the reflectance measurement model 1 using a photomultimeter 4 fixed above the dummy substrate 2. This is done by detecting the scattered light 6. The incident light 5 is incident at an angle of incidence θ with respect to the normal to the reflectance measurement model 1. The photomultimeter 4 is disposed in the normal direction of the reflecting plate 17 (17a) through which the incident light 5 passes through the point on the reflecting film 16 of the reflecting plate 17 (17a). In the state shown in FIG. 2, the reflection characteristics of the reflector are measured by measuring the scattered light 6 from the reflector 17 while changing the incident angle θ of the incident light 5. It has been confirmed that the reflectance measurement model 1 has reflection characteristics similar to those of an actual liquid crystal display device.

FIG. 3 shows the reflection characteristics of a reflectance measurement model using the reflection plates 17 and 17a. In FIG. 3, the reflection intensity of light incident at an incident angle θ is expressed as a distance from the origin O in the direction of the incident angle θ. A solid line 31 (black dots) in FIG. 3 represents the reflection characteristics of the reflection plate 17, and a solid line 32 (white dots) represents the reflection characteristics of the reflection plate 17a. A broken line 31 in FIG. 3 indicates the characteristics measured on a standard white plate (magnesium oxide).

As can be seen from FIG. 3, the reflectance (solid line 31) of the reflector 17 is small in the normal direction in areas where the incident angle θ is small, and large in the normal direction in areas where the incident angle θ is large. On the other hand, it can be seen that the reflectance of the reflecting plate 17a (solid line 32) is almost the same as the reflectance of the standard white plate (broken line 30).

In this manner, by selecting the conditions for forming the thin film 18, it becomes possible to control the reflection characteristics of the reflector with good reproducibility. When a reflective liquid crystal display device is constructed using the reflective plate 17 whose reflection characteristics are controlled in this manner, reflected light can be effectively extracted at a desired angle.

Next, a reflective liquid crystal display device using a reflective plate 17 is shown in FIG. In FIG. 4, an active matrix substrate 20 is placed opposite to a reflection plate 17 with a predetermined distance therebetween, and the periphery of the reflection plate 17 and the active matrix substrate 20 is sealed with a sealing layer 26, and a liquid crystal is placed inside the active matrix substrate 20. Layer 25 is encapsulated. The active matrix substrate 20 includes:
A thin film transistor 22 is mounted on an insulating substrate 21 such as a glass substrate.
(hereinafter referred to as "TFT"), and the TFT2
The pixel electrode 23 is connected to the pixel electrode 2. Further, the substrate 2 is placed so as to cover the TFT 22 and the picture element electrode 23.
An alignment film 24 is formed on the entire surface of 1. Further, the entire surface of the reflection plate 17 is coated with an alignment film 27 so as to cover the reflection film 16 of the reflection plate 17 . Therefore, the surface of the reflective plate 17 on which the reflective film 16 is formed is adjacent to the liquid crystal layer 25. Further, the reflective film 16 is connected to the opposing active matrix substrate 2.
It also functions as a counter electrode that faces the 0-side picture element electrode 23 with the liquid crystal layer 25 in between.

In this embodiment, the sealing layer 26 has a thickness of 9 μm.
It is formed by screen printing an adhesive sealant mixed with a spacer of size m on the peripheral edge of the reflective plate 17 and the active matrix substrate 20. A liquid crystal layer 25 is sealed inside this sealing layer 26 by vacuum degassing. In this embodiment, the liquid crystal layer 25 is a guest-host liquid crystal mixed with a black dye (product name: ZLI23).
27, manufactured by Merck & Co., Ltd.), an optically active substance (trade name S811)
A mixture containing 4.5% of mercury (manufactured by Merck & Co.) was used.

The voltage of the reflective liquid crystal display device as described above (
V)-reflectance characteristics are shown in FIG. The reflectance was measured by placing the reflective liquid crystal display device shown in FIG. 4 at the position of the reflectance measurement model 1 shown in FIG. 2 described above. The voltage (V) on the horizontal axis in FIG. 5 is the voltage applied between the picture element electrode 23 and the reflective film 16, and the reflectance on the vertical axis is the reflectance of light incident at an incident angle θ=30°. The reflectance is obtained by determining the ratio of the intensity of the light diffused in the normal direction of the reflective liquid crystal display device to be measured to the light diffused in the normal direction from the standard white plate. From FIG. 5, when a voltage is applied between the picture element electrode 23 and the reflective film 16, which is the counter electrode, the reflectance in the normal direction of the display device for light incident at θ=30° is approximately 50%. It turns out that it is quite large. Further, the contrast ratio of the display device of this example was 4.6. In this way, the display device of this example has a very bright screen.

In this embodiment, the pitch of the unevenness 14 of the reflecting plate 17 was 1 μm and the height was 0.4 μm, but the pitch of the unevenness 14 of the reflecting plate 17 was within 100 μm and the height was 10 μm.
It has been confirmed that the reflection characteristics of the liquid crystal display device can be controlled in the same manner as described above if the reflection plate has the unevenness 14 within μm. In addition, when the reflective film 16 of the reflective plate 17 is arranged facing the liquid crystal layer 25 as in the liquid crystal display device of FIG. 4 described above, the height of the unevenness 14 of the reflective plate 17 is It is preferable to set the thickness to be smaller than the cell thickness of the device, and to set the angle of the inclined portion of the unevenness 14 to be gentle so as not to disturb the alignment of the liquid crystal layer 25.

In the liquid crystal display device of this embodiment, the reflection plate 17
Since the surface on which the reflective film 16 is formed is adjacent to the liquid crystal layer 25, the distance between the reflective film 16 and the liquid crystal layer 25 is shortened, and this shortened distance reduces parallax and provides a good display image. . Further, since the reflective film 16 of the reflective plate 17 also functions as a counter electrode facing the picture element electrode 23 of the active matrix substrate 20, the structure of the liquid crystal display device is simplified and its manufacture is also facilitated. .

Next, an embodiment will be described in which tin oxide (hereinafter referred to as "SnO2") formed by a chemical vapor phase reaction method (CVD method) is used for the thin film 18 having the unevenness 14 of the reflecting plate 17. In this case, the thin film 1 made of Sn02
8 is, for example, tetramethyltin ((CH3)
4Sn) and oxygen (O2), and argon (
Ar) is introduced into the reaction chamber together with a carrier gas, and the substrate 11
The thermal decomposition reaction is carried out at a temperature of 400 to 600°C. As a result, a thin film 18 having minute irregularities 14 is obtained. In this example, the temperature of the substrate 11 is 450°C, and the thickness of the substrate 11 is 1.2 μm.
A thin film with a thickness of . A reflective film was formed on this thin film in the same manner as described above to obtain a reflective plate, and a reflective display device similar to that shown in FIG. 4 was manufactured using this reflective plate. This display device also has reflectance characteristics similar to those of the previous embodiment, and has a very bright screen.

In this example, tetramethyltin was used as a raw material, but other materials such as (CH3)2SnCl2,
Organic tin such as Sn(CH3COO)2, SnCl4, etc. can be used.

Next, an example will be described in which amorphous silicon hydride (hereinafter referred to as "a-Si:H") formed by a plasma CVD method is used for the thin film 18 having the unevenness 14 of the reflection plate 17. . In this case, the thin film 18 made of a-Si:H is produced using silane (SiH4), hydrogen (H2), and diborane (B2H6) as raw material gases, which are introduced into the reaction chamber and the temperature of the substrate 11 is 100 to 100. 300°C, pressure 2 Torr or less, B2H6/SiH4 gas ratio 0.
It is produced under conditions of 1 to 15%. When the B2H6/SiH4 gas ratio increases, the unevenness 14 on the surface of the thin film 18 obtained can be increased. In this example, the temperature of the substrate 11 is 200°C, the pressure is 0.5 Torr, and the B2H6/
The thin film 18 was produced under conditions of a SiH4 gas ratio of 4%. This display device also has reflectance characteristics similar to those of the previous embodiment, and has a very bright screen.

In this example, the thin film 18 was produced by an electron beam evaporation method, a chemical vapor phase reaction method, and a plasma CVD method, but other methods such as a spray method, a coating method, a sputtering method, a vacuum evaporation method, etc. You may also create one.

Furthermore, although a transparent glass substrate was used as the substrate 11 of the reflector 17, a similar effect can be achieved with an opaque substrate such as a Si substrate, and in this case, circuits can be integrated on the substrate. There is an advantage.

In each of the above-mentioned embodiments, the phase change type guest-host mode was adopted as the display mode, but the present invention is not limited to this, and for example, a light absorption mode such as a two-layer type guest-host mode, a polymer dispersion type LCD, etc. It is also possible to adopt a display mode such as a light scattering display mode, a birefringence display mode used in a ferroelectric LCD, or the like.

[0034]

In the reflective liquid crystal display device of the present invention, a thin film having minute irregularities is formed below the reflective film. By selecting the conditions for forming this thin film, the reflective properties of the reflective film can be easily controlled, and a reflective film having uniform reflective properties can be obtained with good reproducibility. When the reflective properties of the reflective film are well controlled, the reflective properties of the reflective plate are improved and a display device with a bright screen can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a reflector that constitutes a reflective liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a state in which the reflection characteristics of a reflection plate are measured.

FIG. 3 is a diagram showing measurement results of the reflection characteristics of FIG. 2;

4 is a sectional view of a reflective liquid crystal display device of the present invention using the reflector of FIG. 1. FIG.

FIG. 5 is a characteristic diagram showing applied voltage-reflectance characteristics of the reflective liquid crystal display device of the present invention.

[Explanation of symbols]

1 Reflectance measurement model 2 Dummy board 3. Ultraviolet curing adhesive 11, 21 Insulating substrate 14 Unevenness 16 Reflective film 17, 17a Reflector plate 18, 18a Thin film 20 Active matrix substrate 22 Thin film transistor 23 Picture element electrode 24, 27 Alignment film 25 Liquid crystal layer

Claims (1)

[Claims] 1. An insulating substrate on which a transparent electrode is formed, a reflecting plate having a reflective film formed on a thin film having an uneven surface, and a liquid crystal layer sealed between the insulating substrate and the reflecting plate. A reflective liquid crystal display device equipped with and.