HK1086890A - Liquid crystal display unit - Google Patents

Description

Liquid crystal display device having a plurality of pixel electrodes

Technical Field

The present invention relates to a liquid crystal display device capable of performing both reflective display using external light as light of a use environment and transmissive display using illumination light such as backlight. A liquid crystal display element used in a liquid crystal display device is a non-self-luminous display element and has features of a thin type and low power consumption. Therefore, the present invention has been widely applied to OA devices such as clocks, word processors, and personal computers, portable devices such as electronic notebooks and mobile phones, and electronic devices such as AV devices.

Background

In recent years, in order to observe display in both bright and dark places, a liquid crystal display device that can observe both in a reflective display mode using external light such as natural light and indoor light and in a transmissive display mode using illumination light from a backlight is preferable. A structure in which a colored layer is provided on a reflective film having a hole formed therein has been known as such a transflective color liquid crystal display device (see, for example, japanese unexamined patent application publication No. h 11-052366). In such a structure, in the case of observing the transmissive display, the illumination light passing through the hole portion (transmissive area) of the non-reflective film reaches the observer. In this case, the illumination light from the backlight can be displayed brightly by the colored layer only once. On the other hand, in such a structure, in the case of observing the reflective display, the external light reflected by a part (reflective region) of the reflective film reaches the observer. At this time, the light once having passed through the colored layer is reflected by the reflective film and returns to pass through the colored layer again. That is, the display becomes dark because the colored layer having a low transmittance is passed 2 times.

Therefore, in order to improve the brightness of the dark display screen during reflection, a structure has been disclosed in which a colored layer in a part of the reflective region is removed and a portion not passing through the colored layer is provided (see, for example, japanese patent laid-open No. 2000-111902). In the case of such a structure, since the colored layer is not provided in a part of the reflective region, loss of light by the colored layer is eliminated. Therefore, the incident light on the part without the colored layer is reflected on the reflective film and then returned to the viewer side with little darkening, and the effect of making the display bright when reflected is obtained.

In the conventional transflective color liquid crystal display device, as described above, a structure is used in which a hole is formed in the colored layer to expose the reflective film, thereby ensuring brightness in reflective display, and therefore, a step difference occurs in the film thickness of the colored layer between the region where the colored layer is present and the region where the colored layer is absent. In general, in a liquid crystal display device, in order to planarize the surface of a color filter substrate, a coating step of providing a planarization film after providing a color layer is required. However, since the film thickness of the colored layer is usually about 1 μm, it is difficult to obtain a surface with high flatness even if a coating step of a planarizing film is provided, and a step difference (unevenness) of about 0.2 μm remains.

In this way, when there is a step difference on the surface of the color filter substrate, a difference in cell gap occurs between the substrate and the counter substrate depending on the position. When the cell gaps are different, the alignment of the liquid crystal molecules injected into the cell gaps also differs, causing a reduction in display quality such as a deterioration in contrast. In particular, in a color liquid crystal display device using STN liquid crystal, the step difference becomes a factor of reducing display quality.

Accordingly, an object of the present invention is to provide a liquid crystal display device which can perform bright reflective display, has no display unevenness, and has high display quality.

Disclosure of the invention

Therefore, in the liquid crystal display device of the present invention, a reflective film having an area smaller than that of the colored layer is provided between the colored layer and the liquid crystal layer constituting the color filter layer. Alternatively, a color filter substrate on which a color filter layer is formed and a counter substrate facing the color filter substrate via a liquid crystal layer are provided, and a reflective film having an area smaller than that of a colored layer constituting the color filter layer is provided on the colored layer. With this configuration, since the color display is performed in the transmissive display mode, the black-and-white display is performed in the reflective display mode, and the light that does not pass through the colored layer is observed in the reflective display mode, the brightness in the reflective display mode is improved as compared with the conventional technology.

In addition, in order to improve close contact between the colored layer and the reflective film, a transparent insulating film is provided between the colored layer and the reflective film.

Or, provided with: a color filter layer substrate on which a color filter layer is formed; a planarization film provided on the color filter layer; a reflective film formed on the planarization film in an area smaller than a colored layer constituting the color filter layer; and a counter substrate provided so as to face the color filter substrate with a liquid crystal layer interposed therebetween.

In addition, in the above structure, the thickness of the reflection film is easily made to be 0.1 to 0.2 μm, so that the flatness of the surface of the color filter substrate can be improved.

Brief description of the drawings

Fig. 1 is a diagram schematically showing the outline of the structure of a liquid crystal display device of the present invention.

Fig. 2 is a diagram schematically showing another structure of the present invention.

Best mode for carrying out the invention

The following describes embodiments of the present invention.

In the liquid crystal display device of the present invention, the colored layer is provided in the transmissive region, and the colored layer is not provided on the reflective film which is the reflective region. Therefore, a reflective film having an area smaller than that of the colored layer is provided between the colored layer and the liquid crystal layer constituting the color filter layer. That is, in a liquid crystal display device in which a color filter substrate on which a color filter layer is formed and a counter substrate are opposed to each other with a liquid crystal layer interposed therebetween, a reflective film having an area smaller than that of a colored layer constituting the color filter layer is provided on the colored layer.

With this configuration, the color display is performed in the transmissive display mode, the black-and-white display is performed in the reflective display mode, and the light that does not pass through the colored layer is observed in the reflective display mode, so that the brightness in the reflective display mode can be ensured. Here, a metal film containing Al or silver may be used as the reflective film 4. The thickness is preferably about 1000 to 2000 angstroms. If the thickness is too small, the light transmitted through the reflective film increases, and the reflectance decreases, so a film thickness of 1000 angstroms or more is preferable. Further, if the thickness is too large, the flatness of the surface is impaired, so that a film thickness of 2000 angstrom or less is preferable. In addition, in order to improve close contact between the colored layer and the reflective film, a transparent insulating film may be provided between the colored layer and the reflective film. The transparent insulating film can be made of SiO₂Or TiO₂And the like.

In addition, conventionally, the surface unevenness (flatness) associated with the thickness of the colored layer of about 1 μm is associated with the thickness of the reflective film above the colored layer which can be thinly formed to about 0.1 to 0.2 μm, and the flatness of the surface of the color filter substrate is improved.

The reflective film is provided in an arbitrary shape at an appropriate position on the surface of the colored layer. In this case, the shape of the reflective film does not need to be uniform between the pixels.

In addition, as a region where the reflective film is provided, a region other than the surface of the colored layer is also considered. For example, a structure is formed which is provided with: a color filter layer substrate on which a color filter layer is formed; a planarization film provided on the color filter layer; a reflective film formed on the planarization film in a smaller area than a colored layer forming the color filter layer; and a counter substrate provided so as to face the color filter substrate with a liquid crystal layer interposed therebetween.

The liquid crystal display device of the present invention can be manufactured by forming a color layer by a general method for manufacturing a color filter substrate and then providing a reflective film in an arbitrary shape at an appropriate position on the surface of the color layer. Thereafter, a planarization film for planarizing the surface of the color filter layer substrate is formed. In this case, since the reflective film can be formed thin, high surface flatness can be easily achieved by the planarizing film coating process.

Alternatively, after the planarization film is formed by a general method for manufacturing a color filter substrate, the reflective film may be formed in an arbitrary shape at an appropriate position on the surface of the planarization film. In addition, since the reflective film can be formed thinly, high surface flatness can be maintained even if the planarization film is not provided any more.

In any case, the liquid crystal display device of the present invention can be manufactured without increasing the number of steps as compared with a method for manufacturing a general reflective or semi-transmissive liquid crystal display device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(example 1)

Fig. 1 schematically shows an outline of a liquid crystal display element used in the liquid crystal display device of the present embodiment. In this embodiment, a case of a passive color liquid crystal display device will be described. Fig. 1(a) is a diagram showing a cross-sectional structure of the present embodiment. As shown in the figure, the color filter layer substrate 1 and the transparent substrate 9 face each other with the liquid crystal layer 8 interposed therebetween. On one surface of each substrate, a transparent electrode 6 having a desired pattern is provided. The color filter substrate has a structure in which a colored layer for forming a color filter on a glass substrate is provided. Specifically, a light-shielding film (black matrix) 2 having a desired pattern and colored layers of red (3R), green (3G), and blue (3B) which are three primary colors of light are provided on the surface of the color filter layer substrate at a thickness of about 1 μm. Then. A reflective film 4 is provided on a part of the surface of the colored layer. Since the reflective film 4 is provided on the surface (viewer side) of the colored layer in this way, light incident on the reflective region during reflective display is observed as black-and-white display without being reflected to the front of the display unit by the colored layer. At this time, the light absorbed by the conventional colored layers (3R, 3G, 3B) returns to the observer side as it is, and thus bright display is obtained. On the other hand, in the case of transmissive display, incident light from the side opposite to the observation direction passes through the colored layer in the portion where the reflective film 4 is not provided, reaches the observer, and color display is observed.

Fig. 1(B) is a schematic view of the liquid crystal display element shown in fig. 1(a) as viewed from the viewing direction, and is a view of extracting one pixel portion. Here, one pixel portion of red is enlarged and illustrated. In the figure, a portion to be the colored layer 3R is a transmissive region, and a portion provided with the reflective film 4 is a reflective region. In this embodiment, the colored layer is constituted by 100 μm × 300 μm, and a reflective layer is formed thereon in an area of 10% to 50% of the colored layer. By changing the area of the reflective film 4, the color density in the transmissive display and the brightness in the reflective display can be adjusted. In order to have both the characteristics of color display in transmission and black-and-white display in reflection, the reflective layer is preferably 10 to 50% of the area of the colored layer. That is, in the present invention, since observation light does not pass through the colored layer in the reflective mode, a high reflectance (ratio of reflected light to incident light to the LCD) can be obtained even if the area of the reflective film is reduced as compared with the conventional art, and the amount of light passing through the colored layer increases in the transmissive mode in a portion where the area of the reflective film is reduced. Therefore, if the reflective film is 10% or more of the area of the colored layer, sufficient reflection characteristics are obtained. If the area of the reflective film is further reduced, brightness at the time of reflection is not obtained, which is not preferable. On the other hand, if the area of the reflective film is increased, although the brightness at the time of reflection is improved, when the transmissive mode (color display) is observed in an environment where external light enters from the observer side, the external light reaches the observer due to the reflective film, and affects the display color. Therefore, the reflective film is preferably 50% or less of the area of the colored layer.

In this embodiment, the respective colored layers are formed in the same size as the size of the pixel formed by the electrode of the color filter substrate and the electrode of the counter substrate, but there is substantially no problem even if the sizes are slightly different. Therefore, if the size of one pixel is the same as that of the colored layer, the area of the reflective film can be made 10% to 50% of the size of the pixel electrode.

In fig. 1(B), the reflective film is provided at a position corresponding to the substantially central portion of the colored layer, but the position of the reflective film on the colored layer, that is, at which position on the colored layer the reflective film is provided, can be set arbitrarily.

In this embodiment, an Al — Nd film having a thickness of 1500 angstroms is used as the reflective film. In addition, in order to improve the close contact between the colored layers (3R, 3G, 3B) and the reflective film 4, SiO may be provided between the colored layers and the reflective film with a thickness of 150 to 200 angstroms₂Or TiO₂And the like.

Further, a planarization film 5 is formed so as to cover the color filter substrate, and a transparent electrode 6 for applying a voltage to the liquid crystal layer is provided thereon. Since the transparent electrode is formed on the surface of the planarization film, flatness and insulation are required. Since the planarizing film is formed to have a thickness of about 2 μm and the metal film 4 is formed to be very thin, the planarity is easily improved.

Next, a method for manufacturing a liquid crystal display device of the present invention will be described. Initially, a colored layer constituting a color filter layer was formed on a glass substrate. Specifically, a light-shielding film (black matrix) 2 having a desired pattern and colored layers (3R, 3G, 3B) of red, green, and blue, which are three primary colors of light, are provided on the surface of the color filter layer substrate at a thickness of about 1 μm. All of these are formed by a manufacturing method called a pigment dispersion method obtained by photolithography.

Thereafter, the reflective film 4 is formed in an arbitrary shape, and the colored layers (3R, 3G, 3B) are formedThe surface forms a suitable area. Generally, a metal film of Al or silver is used as the reflective film 4, and the metal film is formed by sputtering or the like to a thickness of about 1000 to 1500 angstroms. In order to improve the close contact between the colored layer and the reflective film 4, SiO may be provided between the colored layer and the reflective film₂Or TiO₂And the like. Since the transparent insulating film and the reflective film 4 can be formed continuously, it is not necessary to add a step for moving a workpiece or changing a reaction chamber.

Next, in order to planarize the surfaces of the black matrix 2, the colored layers (3R, 3G, 3B), and the reflective film 4, the planarizing film 5 is applied to a thickness of about 2 μm. As described above, since the metal film can be formed very thinly, the planarization of the planarization film is easily improved in the planarization film application step.

Further, a transparent electrode 6 is provided on the planarization film 5. Photolithography may be used to form a desired pattern of the transparent electrode 6. The transparent electrode 6 is a transparent conductive film called ITO obtained by oxidizing In containing Sn as an impurity, and can be set to have a desired resistance value. Since ITO is a semiconductor substance having a low resistance, its resistance value is on the most widely used order of 10 Ω/□ to 100 Ω/□ in terms of sheet resistance. Generally, ITO is formed by a vacuum deposition method called a sputtering method or a vapor deposition method. In addition, a transparent electrode was formed on the counter glass substrate 9 in the same manner.

Then, spacers for setting the cell thickness to a target value are spread, and alignment films for aligning the liquid crystal 8 are provided on the surfaces of the color filter substrate 1 and the counter glass substrate 9. Next, a sealant 7 is applied to one of the color filter substrate 1 and the counter glass substrate 9, and both substrates are bonded to each other, thereby forming a liquid crystal cell structure. Generally, the sealing material 7 is formed by thermocompression bonding using a thermosetting resin. Then, liquid crystal is injected into the cell gap, thereby obtaining a liquid crystal display element.

(example 2)

Fig. 2 schematically shows an outline of a liquid crystal display element used in the liquid crystal display device of the present embodiment. The present embodiment is different from embodiment 1 in that the reflective film 4 is provided on the planarization film 5. The description overlapping with embodiment 1 is appropriately omitted. Fig. 2(a) is a diagram showing a cross-sectional structure of the liquid crystal display element of the present embodiment. Fig. 2(B) is a schematic view of the display element shown in fig. 2(a) as viewed from the viewing direction, and is a view of extracting one pixel portion. Here, one pixel portion of red is enlarged and illustrated. That is, the color filter substrate 1 has a structure in which a color filter layer composed of a light shielding film (black matrix) 2 and colored layers (3R, 3G, 3B) is formed on a glass substrate. The color filter layer is usually provided to have a thickness of about 1 μm. A planarization film 5 is provided on the color filter layer, and a reflection film 4 is formed on the planarization film 5. If necessary, a transparent insulating film is formed on the planarization film 5, and the reflection film 4 is provided thereon. Here, the reflective film 4 is provided so as to correspond to the positions of the colored layers (3R, 3G, 3B). Fig. 2(B) shows an example in which the reflective film 4 is provided at a position corresponding to the center position of the colored layer. Therefore, similarly to example 1, light incident on the reflective region provided with the reflective film is not reflected to the front surface of the display unit by the colored layer, and the light returns to the viewer side without being absorbed by the colored layer. Therefore, a bright display can be obtained. That is, bright display can be realized when viewed in the reflective mode.

In this way, a transparent electrode for applying a voltage to the liquid crystal layer is formed on the color filter layer substrate provided with the reflective film. If it is intended to further improve the flatness, a flattening film may be further provided on the reflective film, and a transparent electrode may be formed thereon.

As described above, according to the liquid crystal display device of the present invention, since incident light does not pass through the coloring layers (3R, 3G, 3B) at the time of reflective display, bright display can be obtained.

Further, since the reflective film 4 can be formed very thinly to 1000 to 2000 angstroms, high flatness can be obtained when a planarizing film is applied thereafter. In addition, even when the planarization film is not applied thereafter, the reflection film itself is thin, and thus the unevenness on the surface is reduced. Therefore, the display quality can be prevented from being degraded.

Industrial applicability

As described above, the transflective liquid crystal display device of the present invention can perform bright reflective display and is suitable for realizing high display quality without display unevenness.

Claims (10)

1. A liquid crystal display device, characterized in that:

the method comprises the following steps: a color filter layer substrate on which a color filter layer is formed; and a counter substrate facing the color filter substrate with a liquid crystal layer interposed therebetween, wherein a reflective film having an area smaller than that of a colored layer constituting the color filter layer is provided between the colored layer and the liquid crystal layer.

2. The liquid crystal display device according to claim 1, wherein:

the reflective film is provided on the colored layer.

3. The liquid crystal display device according to claim 2, wherein:

a transparent insulating film is provided between the colored layer and the reflective film.

4. A liquid crystal display device as claimed in claim 3, characterized in that:

the reflective film is a metal reflective film, and the transparent insulating film is silicon oxide or titanium oxide.

5. The liquid crystal display device according to claim 4, wherein:

the metal reflective film contains aluminum or silver.

6. The liquid crystal display device according to any one of claims 2 to 5, wherein:

a planarization film is provided so as to cover the reflective film.

7. The liquid crystal display device according to claim 1, wherein:

a planarization film is provided on the color filter layer, and the reflective film is provided on the planarization film.

8. The liquid crystal display device as claimed in any one of claims 1 to 7, wherein:

the area of the reflective film is 10% to 50% of the area of the colored layer.

9. The liquid crystal display device as claimed in any one of claims 1 to 7, wherein:

the area of the reflective film is 10% to 50% of the area of a pixel electrode formed of a transparent electrode formed on the color filter layer substrate and a counter electrode formed on the counter substrate.

10. The liquid crystal display device according to any one of claims 1 to 9, wherein:

the thickness of the reflective film is 0.1 to 0.2 μm.