JP2762946B2 - Reflective liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display.

[0002]

2. Description of the Related Art A reflection type liquid crystal display uses light reflected from a reflection plate located inside the liquid crystal display as a display light source, thereby eliminating the need for a backlight in the light source. This is considered as an effective method that can achieve lower power consumption, thinner, and lighter than the transmissive liquid crystal display device. The basic structure of a current reflection type liquid crystal display device is a liquid crystal using a TN (twisted nematic) mode, an STN (super twisted nematic) mode, a GH (guest host) mode, etc., and an element (thin film transistor, diode) for switching the liquid crystal. And the like, and a reflector provided inside or outside thereof.

[0003] The display performance of a reflection type liquid crystal display device is required to provide a bright and white display in a liquid crystal transmission state. In order to realize this display performance, it is important to control the reflection performance of the reflector.

[0004] Since the current reflector reflects incident light from all angles with respect to the reflection surface in a desired direction (display direction), the surface of the reflector has an uneven shape. It is known that this reflector is mainly manufactured by the following method.

A reflector is manufactured by polishing an acrylic or glass substrate or the like and covering the rough upper surface with irregularities with a highly efficient reflective metal such as aluminum or silver (To).
hru Koizumi and Tatsuo Uc
hida, Proceedings of the
SID, Vol. 29, 157, 1988). And
The reflection plate obtained by this manufacturing method is provided outside the panel.

Further, a reflector is manufactured by forming irregularities on a polyimide film formed on a flat glass substrate using photolithography and etching, and covering the surface with aluminum (see, for example, Japanese Patent Application Laid-open No. 5-28
No. 1533, a reflection type liquid crystal display device and a manufacturing method thereof). The reflector is provided inside the panel.

[0007]

When a substrate having a roughened surface by the conventional polishing and sandblasting method is used as a reflector-side substrate of a reflection type liquid crystal display device, the active matrix is formed on the upper surface because of the unevenness. A switching element, a wiring, and the like for driving cannot be formed. In addition, when the unevenness is manufactured by the above-described method, the physical damage received during the manufacturing is large, so that the reflection plate cannot be provided above the switching element and the wiring. For this purpose, the reflection plate is provided outside the glass substrate having the switching element. This causes display parallax caused by a difference in film thickness of the glass substrate, and a favorable panel display cannot be obtained. Further, as a method of forming a reflection plate inside the panel, there is a method of applying a concavo-convex forming film for forming concavities and convexities on a flat glass substrate and forming the concavities and convexities by etching, but since the number of process steps is large, There are problems that it is costly and that it is difficult to obtain a desired uneven shape.

Therefore, in the present invention, in order to solve the conventional drawbacks, a reflection film formed by a simple method is provided inside a liquid crystal cell, and the structure and manufacturing for realizing the improvement of the display performance of the reflection type liquid crystal display device are realized. The purpose is to provide a method.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a polishing method and a polishing method for a reflection type active matrix drive liquid crystal display device having a reflection plate having projections and depressions and comprising pixels composed of switching elements and liquid crystal arranged in a matrix. By sandblasting, irregularities are formed on the insulating substrate, a reflective film is provided on the irregularities, a transparent flattening film is formed on the reflective film, and a switching element, a wiring, and a transparent film are formed on the flattening film. The pixel electrode is formed.

According to the present invention, in the above structure, a film having an intermediate value between the refractive index of the flattening film and the transparent pixel electrode is located between the flattening film and the transparent pixel electrode. .

According to the present invention, in the above structure, a film having a refractive index gradient distribution which continuously changes between the flattening film and the refractive index of the transparent pixel electrode is provided between the flattening film and the transparent pixel electrode. It is characterized by being located in.

The present invention is characterized in that, in the above structure, the upper surface of the flattening film has a refractive index gradient distribution so as to have the same refractive index as that of the transparent pixel electrode.

According to the present invention, in the above structure, the thickness of the flattening film is 200 μm or less.

According to the present invention, in a structure of a reflection type active matrix drive liquid crystal display device having a reflection plate having projections and depressions and pixels composed of switching elements and liquid crystal arranged in a matrix, an insulating substrate is polished or sandblasted. Irregularities are formed on the upper surface, a part of the irregularities is etched to be flattened, a switching element and a wiring are formed in the flattened portion, and a reflective film is formed in an uneven region other than the flattened portion. It is characterized by.

[0015]

FIG. 1 is a sectional view of a reflection type liquid crystal display device for explaining the principle of the present invention. FIG. 2 is a sectional view of a conventional reflection type liquid crystal display device in which a reflection plate is located outside a glass substrate. In the liquid crystal display device of the present invention, the pixel electrode 4, the switching element and the wiring 5 are provided on the reflection plate 8 in which the aluminum layer 2 is provided on the surface of the roughened glass substrate 1.
Is formed to provide a flattening film 3. By providing the flattening film 3, the upper surface of the uneven reflection plate can be flattened, and the pixel electrode 4, the switching element, and the wiring 5 can be formed. As a result, the reflection plate can be provided inside the liquid crystal panel using the substrate having irregularities.

As shown in FIG. 3, when the refractive indexes of the planarizing film 3 and the transparent electrode 4 of the present invention have different refractive indices of N1 and N2, the incident light 11 passes through the liquid crystal cell, After being scattered by the reflection plate 8, in the process of being emitted to the outside 12 again, reflection occurs at the boundary D <b> 1 between the transparent electrode and the flattening film. The reflected lights 13 and 14 at the boundary D1 cause a loss of the intensity of the reflected light 12 (the refractive index distribution of the above structure is shown in FIG. 3A).

A film 15 (refractive index N3: N1 <N3 <N2) corresponding between the two refractive indexes is provided on the flattening film. As a result, the reflection components occurring at different refractive index boundaries D1 show a decrease (FIG. 3B).

By forming a film having a refractive index gradient distribution which continuously changes between the two refractive indexes on the flattening film (refractive index distribution: FIG. 3 (c)), the film is continuously refracted. Since the rate has changed, the reflection components 13, 14 are further reduced. Thus, a reflective liquid crystal display device that is brighter and has excellent display performance can be obtained. On the other hand, when the refractive index gradient distribution is provided inside the flattening film, the same effect can be obtained.

In the reflection type liquid crystal display device of the present invention,
The thickness D1 of the flattening layer is 200 μm or less. As a result, the parallax (floating characters) caused by the optical path difference caused by the film thickness becomes a level that cannot be detected by human eyes.

In the reflection type liquid crystal display device of the present invention,
In order to form pixel electrodes, switching elements, wiring, etc. on part of the roughened substrate, the surface of the substrate is flattened by etching, and the remaining area is provided with a reflector having irregularities. I have. Thus, a reflection type active matrix driving liquid crystal display device in which a reflection film is provided inside a liquid crystal cell using a substrate having irregularities without providing a flattening film can be obtained. This simplifies the process and provides a high-quality panel display without parallax.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIGS. 4A to 4I show the manufacturing steps of the first embodiment of the present invention. A glass substrate (OM-2 made by NEC Glass) 16 was used as the substrate (FIG. 4A), and the surface was roughened with abrasive # 1000. Thereafter, the polished surface is wet-etched with a hydrofluoric acid aqueous solution, and the angle of irregularity of the surface is controlled by the etching time.
Thereby, a target reflection performance is obtained. The size of the irregularities on the surface of the obtained reflector is 30 μm or less in pitch and 2 μ in height
m or less. An aluminum layer 17 (or silver), which is a metal film having a high reflection efficiency, was formed on the upper portion as a reflection layer to form a reflection plate 18 (FIG. 4B). Further, an organic insulating film was used as the flattening film 19.
In this embodiment, a polyimide film (Nissan Chemical: RN-81) is used.
2, Japanese synthetic rubber: HRC series, etc.). This film thickness was about 8 μm in order to eliminate parallax (FIG. 4).
(C)). However, in this embodiment, the reflectance reducing layer 20 is not provided.

On top of this, a gate electrode 21 made of chromium
Is formed (FIG. 4E). Next, the silicon nitride film 22
Was formed (FIG. 4F). Thereafter, n + amorphous silicon 23 doped with amorphous silicon and phosphorus was continuously formed by plasma CVD and patterned (FIGS. 4 (g) and 4 (h)). Further, by forming source / drain electrodes and pixel electrodes, a TFT substrate having a reflector is manufactured (FIG. 4 (i)). The process temperature at this time is determined by the heat resistant temperature of the flattening film and the switching element process. The CVD temperature is 2
The temperature was set to 50 ° C. Thereafter, liquid crystal was sandwiched between the TFT substrate and the opposing substrate having ITO and a color filter, whereby a liquid crystal display device was manufactured.

Next, a second embodiment of the present invention will be described. On the reflection plate obtained by the same manufacturing method as in the first embodiment, an antireflection film 20 is provided between a flattening film having a refractive index of n = 1.5 and a transparent electrode (ITO film) having a refractive index of 2.0. As an inorganic film having a refractive index of 1.7 (silicon oxynitride film)
Was formed. In the manufacturing process, a process shown in FIG.
Thereafter, a liquid crystal display device can be manufactured by the same manufacturing steps as in the first embodiment.

Next, a third embodiment of the present invention will be described. On the reflection plate obtained by the same manufacturing method as in the first embodiment, a flattening film (organic film) 19 having a refractive index of n = 1.4 and a transparent electrode 24 (ITO film) having a refractive index of 2.0 are provided. Then, an inorganic film (silicon oxynitride film) having a refractive index gradient distribution of 1.4 to 2.0 was formed as an antireflection film. At this time, the refractive index can be changed by changing the film composition ratio of nitrogen atoms and oxygen atoms in the silicon oxynitride film. As a method for producing this film, the supply amount of monosilane as a source gas is kept constant by a plasma CVD method, and the flow rate ratio between oxygen (or N20) and ammonia is changed to freely from 1.38 to about 2.1. Could control. FIG. 5 shows the relationship between the gas flow ratio and the refractive index of the film. Note that the refractive index gradient distribution film is not limited to the silicon oxynitride film, but any film that can change the refractive index continuously in the thickness direction, such as amorphous silicon, various oxide films, or organic films. good. Further, a film having a gradient refractive index distribution can be used as the flattening film itself.

FIGS. 6 (a) to 6 (f) are views showing a process of manufacturing a switching element side substrate according to a fourth embodiment of the present invention. Irregularities are formed on the glass substrate surface by a polishing method, and target irregularities are obtained by etching (FIG. 6A). Thereafter, patterning is performed by applying, exposing, and developing (OMD-3) a resist (manufactured by Tokyo Ohka: OFPR-800C) (FIG. 6).
(B)). Next, etching is performed using a hydrofluoric acid aqueous solution. In the case of irregularities polished with the abrasive # 1000, a flat surface of 500 nm or less is formed on the etched surface in 5 minutes or more (FIG. 6C). After the resist is stripped, the reflection plate forming region 30 has unevenness, and the other element forming regions 29 are flattened (FIG. 6D). A switching element and a wiring are formed in a flat region in the same manner as in the first embodiment. However, the pixel electrode also serves as a reflector. Thereafter, an aluminum layer 28 is formed on the top and bottom of the uneven region 30 (FIG.
(F)). The switching elements include TFT,
MIM diodes can be used.

In this embodiment, since the process does not use a flattening layer, there is no problem with the process constraint temperature up to the device fabrication constraint temperature. As a result, a reflective liquid crystal display device having good display performance without parallax was obtained.

In the above embodiment, the reflection type LCD for driving an active matrix having switching elements such as TFTs and MIMs has been described.
It can be applied to any reflective LCD such as a simple matrix. In the above-described embodiment, the setting position of the reflection plate is provided on the element substrate side. Furthermore, the present invention can be applied to a transflective / reflective liquid crystal display device in which the reflectance is reduced by adjusting the film thickness and film quality of the material used for the reflective layer.

[0028]

According to the present invention, by providing a flattening film on an insulating substrate having irregularities, it is possible to form switching elements and wiring for driving an active matrix on the irregular substrate, thereby forming a reflection plate on a liquid crystal. The liquid crystal display device can be provided inside the cell and has excellent panel display performance without parallax. Further, in the present invention, a simple method for forming unevenness such as a polishing method or a sandblast method can be used, so that the cost of the reflector manufacturing process can be reduced.

When the refractive index of the flat layer and the transparent pixel electrode located on the flat layer are different, a film having a refractive index between these films is provided between them, or the transparent pixel electrode is determined based on the refractive index of the flat film. By providing a film having a refractive index gradient distribution that changes continuously to the refractive index of the liquid crystal display device, the reflection component occurring at the boundary between the flat film and the transparent pixel electrode can be reduced. Is improved.

Further, according to the present invention, a flat area and an uneven area are formed on an insulating substrate having unevenness by using a photolithography technique and an etching technique, and the switching element for active matrix driving and the wiring are formed in the flat area. In addition, a reflection plate serving also as a pixel electrode can be manufactured in the uneven area. Thus, a reflective active matrix driven liquid crystal display device having no parallax and excellent in display performance without providing a flat layer can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining the principle of the present invention.

FIG. 2 is an explanatory view of a conventional reflective panel structure having a reflector outside a liquid crystal cell.

FIGS. 3A to 3C are explanatory diagrams when the transparent electrode and the planarizing film have different refractive indexes.

FIGS. 4 (a) to 4 (i) are explanatory views of the manufacturing process of the reflective panel according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a refractive index of a silicon oxynitride film and a flow rate ratio of a reaction gas.

FIGS. 6 (a) to 6 (f) are explanatory views of a manufacturing process of a reflective panel according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1,25 Uneven glass substrate 2,17,28 Aluminum layer 3,19 Flattening film 4 Transparent electrode 5,27 Switching element and wiring 6 Liquid crystal layer 7 Opposite substrate 8,9,18 Reflector 10 Glass substrate 11 Incident light 12 Outgoing light 13,14 Reflected light 15,20 Antireflection film 16 Glass substrate 21 Gate electrode 22 Insulating layer 23 Semiconductor layer 24 Pixel electrode 26 Resist layer 29 Flat area 30 Uneven area

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-205181 (JP, A) JP-A-4-212931 (JP, A) JP-A-5-181126 (JP, A) JP-A-58-181126 75118 (JP, A) JP-A-53-47298 (JP, A) JP-A-4-305625 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/1335 520 G02F 1/136-1/136 510 G02F 1/1333-1/1333 505

Claims (1)

(57) [Claims] In a structure of a reflection type active matrix drive liquid crystal display device having a reflection plate having projections and depressions and comprising switching elements and liquid crystal pixels arranged in a matrix, an insulated substrate is formed by a polishing method or a sandblast method. Irregularities are formed, flattening is performed by etching a part of the irregularities, switching elements and wirings are formed in the flattened portions, and a reflection film is formed in an uneven region other than the flattened portions. Reflective liquid crystal display device.