JPH0862592A - Liquid crystal display element - Google Patents

Abstract

PURPOSE: To make liquid crystal orientation uniform by absorbing the differences in level of a black mask film. CONSTITUTION: This liquid crystal display element has a panel structure consisting of a lower substrate 1, a transparent upper substrate 2 to be joined thereto via a prescribed spacing and liquid crystals 3 held in this spacing. Numerous matrix-form pixels 4 are formed in this panel structure. Light shieldable black mask films 5 patterned along the boundaries of the respective pixels 4 and transparent electrode films 6 arranged in superposition thereon are formed on the inside surface, in contact with the liquid crystals 3, of the upper substrate 2. Transparent flattening films 6 are interposed between the black mask films 5 and the transparent electrode films 6 to fill the differences in the level of the black mask films 5. On the other hand, electrode films 8 patterned to prescribed shapes are formed on the inside surface, in contact with the liquid crystals 3, of the lower substrate 1 and face the transparent electrode films 6 trimmed by the black mask films 5, by which the matrix-form pixels 4 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having pixels arranged in a matrix. More specifically, the present invention relates to a surface flattening technique for a substrate on a side where a black mask that borders individual pixels is formed.

[0002]

2. Description of the Related Art A conventional liquid crystal display device has a panel structure including a lower substrate, a transparent upper substrate bonded to the lower substrate through a predetermined gap, and liquid crystal held in the gap. . An innumerable matrix of pixels is formed in this panel structure. On the inner surface of the upper substrate in contact with the liquid crystal, a light-shielding black mask film that is patterned along the boundary of each pixel and a transparent electrode film that is arranged so as to overlap the black mask film are formed. This transparent electrode film becomes, for example, a common electrode.
On the other hand, an electrode film patterned in a predetermined shape is formed on the inner surface of the lower substrate which is in contact with the liquid crystal, and constitutes, for example, a pixel electrode. The pixel electrode faces a common electrode bordered by the black mask film to form a matrix of pixels.

[0003]

The black mask film formed on the upper substrate is made of a light-shielding metal film or the like, and the portion matching the pixel is removed in advance by etching.
In other words, the metal film is patterned so as to frame each pixel. Therefore, a step is formed in the pixel by the thickness of the metal film. In the conventional structure, the transparent electrode film is directly formed on the black mask film, and the surface thereof is affected by the step difference of the underlying black mask film and rises in a convex shape around the pixel. . In general, the inner surfaces of the upper and lower substrates are subjected to alignment treatment to control the liquid crystal in a predetermined aligned state. However, in the conventional structure, since the convex portion exists on the inner surface of the upper substrate along the periphery of each pixel, the alignment process is not uniform, and the step is disturbed. Therefore, there is a problem that reverse tilt or reverse twist of liquid crystal molecules is generated, which adversely affects image quality. In addition, when rubbing is performed as the alignment process, the pixel edge portion becomes a shadow due to the influence of the peripheral convex portion,
There is a problem that sufficient rubbing cannot be performed, which causes disorder of liquid crystal alignment.

[0004]

In view of the above-mentioned problems of the prior art, the present invention provides a structure of a substrate for a liquid crystal display device capable of removing the influence of the step of the black mask film and performing a uniform alignment process. To aim for things. The following measures have been taken in order to achieve this object. That is, the liquid crystal display element according to the present invention has, as a basic structure, a panel structure including a lower substrate, a transparent upper substrate bonded to the lower substrate through a predetermined gap, and liquid crystal held in the gap. Have An innumerable matrix of pixels is formed in this panel structure. On the inner surface of the upper substrate in contact with the liquid crystal, a light-shielding black mask patterned along the boundaries of each pixel,
A transparent electrode film disposed so as to overlap this is formed.
A feature of the present invention is that a transparent flattening film is interposed between the two so as to fill the step of the black mask film. An electrode film patterned in a predetermined shape is formed on the inner surface of the lower substrate which is in contact with the liquid crystal, and a matrix-like pixel is formed facing the transparent electrode framed by the black mask film. .

Preferably, the flattening film is made of a transparent polymer film. The electrode film formed on the inner surface of the lower substrate is a pixel electrode film patterned in a matrix, and a thin film switching element for driving each pixel electrode film is formed below the electrode film. In such a structure, another flattening film is interposed between the pixel electrode film and the thin film switching element. That is, the flattening film is applied not only to the upper substrate but also to the lower substrate. In addition, a color filter film having three primary color segments matching each pixel is formed on the inner surface of the lower substrate.

[0006]

According to the present invention, the black mask film and the transparent electrode film for framing the pixels are formed on the upper substrate of the pair of substrates constituting the matrix type liquid crystal display element. As a feature of the present invention, a transparent flattening film made of, for example, a polymer film is interposed between the both, and the peripheral step difference of the pixel bordered by the black mask film is reduced. As a result, the inner surface of the upper substrate is flattened, and alignment treatment such as rubbing can be performed uniformly. In particular,
Since the step around the pixel is filled, reverse tilt and reverse twist can be suppressed. Further, since the substrate surface is sufficiently flattened, dust generation can be suppressed even when rubbing or the like is performed. Further, since the generated dust does not remain around the pixels, it is possible to suppress the image quality deterioration due to the inclusion of foreign matter. In addition, when a thin film switching element or the like is formed on the lower substrate in an integrated manner, it is preferable to interpose a flattening film as with the upper substrate in order to eliminate the influence of the step. Generally, the flattening film reduces the unevenness of the substrate surface to 0.
If the thickness can be suppressed to 1 μm or less, the function can be sufficiently exhibited.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial sectional view showing a first embodiment of a liquid crystal display element according to the present invention. The present liquid crystal display device has a panel structure including a lower substrate 1, a transparent upper substrate 2 bonded to the lower substrate 1 through a predetermined gap, and a liquid crystal 3 held in the gap between the two. The liquid crystal 3 is, for example, twisted nematically aligned. Innumerable pixels 4 are formed in this panel structure, and only two are shown in the figure for simplicity. On the inner surface of the upper substrate 2 in contact with the liquid crystal 3, a light-shielding black mask film 5 patterned along the boundaries of the pixels 4 is formed. Further, the transparent electrode film 6 is arranged so as to overlap with this. As a characteristic feature, a transparent flattening film 7 is interposed between the black mask film 5 and the transparent electrode film 6 to fill the step of the black mask film 5. Therefore, the inner surface of the upper substrate 2 is substantially flattened, and alignment treatment such as rubbing is performed on the inner surface of the liquid crystal 3
Achieves twisted nematic alignment.

On the other hand, an electrode film 8 patterned in a predetermined shape is formed on the inner surface of the lower substrate 1 which is in contact with the liquid crystal 3 and faces the transparent electrode film 6 bordered by the black mask film 5. At the intersection of the two
Stipulate. Electrode film 8 formed on the inner surface of lower substrate 1
Are patterned in a matrix to form pixel electrodes. On the other hand, the transparent electrode film 6 formed on the upper substrate 2 constitutes a common electrode. The pixel 4 is defined in a portion where the common electrode and the individual pixel electrodes overlap. The present invention is not limited to this, and the upper electrode film 6 may be patterned in rows, the lower electrode film may be patterned in columns, and a simple matrix structure in which pixels are provided at the intersections of the two is also used. good. When the pixel electrode is formed on the lower substrate 1 as in this embodiment, the thin film switching element (not shown) such as a thin film transistor for driving the pixel electrode and the wiring 9 are also provided on the lower substrate 1.
To form an active matrix type liquid crystal display element. In this case, another flattening film 10 is interposed between the upper region including the electrode film 8 and the lower region including the thin film switching element and the wiring 9, so that the surface of the lower substrate 1 is also flattened. ing. A first interlayer insulating film 11 and a second interlayer insulating film 12 are also formed on the inner surface of the lower substrate 1.

Continuing to refer to FIG. 1, each component of the present liquid crystal display device will be described in detail. The upper substrate 2 is made of a transparent material such as glass. The black mask film 5 is formed by patterning a light-shielding metal film (for example, chromium or aluminum) by etching or the like, and has a thickness of about 0.15 μm to 0.2 μm in order to secure sufficient light-shielding property. There is. In order to absorb this step, a flattening film 7 is formed between the transparent electrode film 6 made of ITO or the like and the black mask film 5.
Is intervening. As the flattening film 7, for example, a transparent polymer film can be used, and a step difference of 0.1 μm to
It is reduced to 0.01 μm or less. The minimum step required for stable alignment of the liquid crystal 3 differs depending on the type of liquid crystal material and alignment film. With such a structure, the alignment treatment around the pixels 4 becomes uniform over the entire surface, and stable twisted nematic alignment of the liquid crystal 3 can be obtained. As the transparent polymer film used as the flattening film 7, for example, acrylic resin, epoxy resin, or polycarbonate resin can be selected. As a film forming method, these polymer resins are dissolved in a solvent and applied by spin coating or offset printing.
Then, the resin is cured by ultraviolet irradiation or heat treatment to obtain a desired polymer film. As the flattening film 7, it is possible to use an inorganic material in addition to the polymer film.
A representative example is iO ₂ . Alternatively, PSG, B
SG, BPSG, etc. can be used. These inorganic materials are formed on the flattening film by sputtering, vacuum deposition, CVD or the like.

On the other hand, the lower substrate 1 is also made of a transparent material such as quartz glass, and as described above, the thin film switching element and the wiring 9 are integratedly formed on the inner surface thereof in addition to the pixel electrode. Since the wiring 9 also includes a step, like the upper substrate 2, the flattening film 10 is interposed between the electrode film 8 (pixel electrode) and the wiring 9 or the thin film switching element. For this flattening film 10, the same material and film forming method as for the flattening film 7 formed on the upper substrate 2 can be adopted. The flattening film is required on the lower substrate 1 when a step is generated due to the wiring 9 or the switching element in the active matrix type or the like, and the step is generated particularly in the case of the simple matrix type liquid crystal display element. Since it does not exist, the flattening film 10 on the lower substrate 1 may not be provided.

FIG. 2 is a schematic partial sectional view showing a second embodiment of the liquid crystal display element according to the present invention, and basically has the same structure as the first embodiment shown in FIG. ing. Therefore, corresponding parts are provided with corresponding reference numerals to facilitate understanding. The first embodiment is, for example, a normally white mode monochrome display element, whereas the second embodiment has a structure capable of color display. That is, on the inner surface of the lower substrate 1, the color filter film CF having the three primary color segments R, G, and B that match each pixel 4 is formed. The surface of the color filter film CF is a flattening film 10.
And the surface of the lower substrate 1 is flattened. The color filter film CF can be formed by, for example, a printing method. Alternatively, a film containing pigments of three primary colors may be sequentially patterned into a predetermined shape by photolithography. In this embodiment, the flattening film 10 is superposed on the color filter film CF, but the present invention is not limited to this. For example, the flattening film 10 itself has three primary colors corresponding to the individual pixels 4. It may be colored.

FIG. 3 is a schematic partial sectional view showing a reference example of a liquid crystal display element. Unlike the liquid crystal display element according to the present invention, a black mask film 5 and a transparent electrode film 6 are directly laminated on each other. There is no flattening film between them. Therefore, the step of the black mask film 5 is directly exposed on the inner surface of the upper substrate 2 which is in contact with the liquid crystal 3. Flat area F
In contrast, while the liquid crystal molecules 3a are in a normal tilt state, in the step region S, the alignment of the liquid crystal molecules 3a is disturbed, and for example, the reverse tilt state is set. For this reason, the continuity of liquid crystal alignment is lost in the regions F and S, so that disclination appears at the boundary and becomes a display defect. Further, since the tilt of the liquid crystal molecules 3a is reversed, the twist direction is also reversed and a reverse twist region is generated. As a result, the display quality is impaired.

FIG. 4 is a schematic perspective view of the liquid crystal display element according to the first embodiment shown in FIG. 1, and shows only four pixels. As shown in the figure, the present liquid crystal display element has a structure in which a pair of glass substrates 1 and 2 are arranged so as to face each other, and a liquid crystal 3 is held in the gap. On the inner surface of the lower substrate 1, there are formed data wirings 9d and gate wirings 9g arranged in a matrix, and thin film transistors 13 and pixel electrodes 8a arranged at their intersections. The thin film transistor 13 is a specific example of the thin film switching element described above. The gate electrode of the thin film transistor 13 is connected to the corresponding gate wiring 9g, the source electrode is connected to the corresponding data wiring 9d, and the drain electrode is connected to the corresponding pixel electrode 8a. The pixel electrode 8a corresponds to the electrode film 8 shown in FIG. 1 and is patterned in a matrix. The thin film transistors 13 are sequentially selected by the gate wiring 9g, and the image signal supplied from the data wiring 9d is written in the corresponding pixel electrode 8a. On the other hand, a black mask film 5 and a common electrode 6c are formed on the inner surface of the upper substrate 2. The common electrode 6c corresponds to the transparent electrode film 6 shown in FIG. The black mask film 5 is provided with openings 5a corresponding to the pixel electrodes 8a. The flattening film 7 is interposed between the black mask film 5 and the common electrode 6c, and the opening 5
A is filled in for flattening. By sandwiching the active matrix type liquid crystal display device having such a structure between two polarizing plates and allowing white light to enter, a desired monochrome image display can be obtained.

Finally, a concrete example of the structure of the lower substrate 1 shown in FIG. 4 will be described with reference to FIG. The lower substrate 1 is made of a transparent insulating material such as quartz and has a pixel electrode 8a on its surface.
And the lower region including the thin film transistor 13 that drives each pixel electrode 8a are integrally formed. The thin film transistor 13 is configured by using a polycrystalline silicon thin film 14 patterned in a predetermined shape as an element region, and a gate electrode G is patterned on the thin film transistor 13 via a three-layer gate insulating film. The gate electrode G is made of, for example, a polycrystalline silicon thin film having a low resistance.
It is continuous with the gate wiring shown in. An auxiliary capacitor 15 is also formed on the polycrystalline silicon thin film 14 at the same time.
The thin film transistor 13 and the storage capacitor 15 are covered with the first interlayer insulating film 11. First interlayer insulating film 11
Is made of, for example, phosphorus-doped glass (PSG). A data wiring 9d made of metal aluminum or the like is formed on the first interlayer insulating film 11, and is electrically connected to the source region S of the thin film transistor 13 through a contact hole. The data wiring 9d is covered with a second interlayer insulating film 12 also made of PSG or the like.

The flattening film 10 is interposed between the lower region to which the thin film transistor 13 and the like described above belong and the upper region to which the pixel electrode 8a belongs. The flattening film 10 covers the lower region to fill the irregularities thereof, and the transparent pixel electrode 8a is formed on the flattened upper face. As can be seen from the figure, since the pixel electrode 8a has an extremely flat surface, the rubbing treatment for aligning the liquid crystal can be uniformly performed, and the display quality can be greatly improved. The pixel electrode 8a is electrically connected to the drain region D of the lower thin film transistor 13 via a contact hole opened in the flattening film 10. In order to open this contact hole, the planarizing film 10
Is made of, for example, a material that can be photo-etched. In this example, a transparent acrylic resin containing a light absorber is used.

[0016]

As described above, according to the present invention, the flattening film is provided between the light-shielding black mask film which is patterned along the boundary of each pixel and the transparent electrode film which is arranged on the black mask film. Is interposed to fill the step of the black mask film. With this configuration, there is an effect that the alignment process of the pixel portion is stabilized and the image quality can be improved. In particular,
There is an effect that the reverse tilt domain and the reverse twist domain, which have been conventionally generated at the step portion of the black mask film, can be reduced and the uniformity of the displayed image can be improved.
Further, there is an effect that the rubbing process can be performed uniformly over the entire substrate. As described above, the effect that the high aperture ratio and the high definition of the matrix type liquid crystal display element can be realized can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of a liquid crystal display element according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the liquid crystal display element according to the present invention.

FIG. 3 is a schematic partial cross-sectional view showing a reference example of a liquid crystal display element.

FIG. 4 is a schematic perspective view of the first embodiment shown in FIG.

FIG. 5 is a schematic cross-sectional view showing a specific configuration example of a lower substrate that constitutes a liquid crystal display element.

[Explanation of symbols]

 1 Lower Substrate 2 Upper Substrate 3 Liquid Crystal 4 Pixel 5 Black Mask Film 6 Transparent Electrode Film 7 Flattening Film 8 Electrode Film 9 Wiring 10 Flattening Film 13 Thin Film Transistor CF Color Filter Film

Claims (4)

[Claims] 1. A liquid crystal display device comprising: a lower substrate; a transparent upper substrate bonded to the lower substrate via a predetermined gap; and liquid crystals held in the gap, wherein a matrix of pixels is formed. Then, on the inner surface of the upper substrate in contact with the liquid crystal, a light-shielding black mask film that is patterned along the boundaries of each pixel, a transparent electrode film that is laid over the black mask film, and an intervening film A transparent flattening film for filling the step of the black mask film is formed, and an electrode film patterned in a predetermined shape is formed on the inner surface of the lower substrate in contact with the liquid crystal. A liquid crystal display element that constitutes a matrix of pixels facing the transparent electrode film bordered by a black mask film. 2. The liquid crystal display device according to claim 1, wherein the flattening film is a transparent polymer film. 3. The electrode film formed on the inner surface of the lower substrate is a pixel electrode film patterned in a matrix, and a thin film switching element for driving each pixel electrode film is formed under the electrode film. The liquid crystal display element according to claim 1, wherein another flattening film is interposed between the pixel electrode film and the thin film switching element. 4. The liquid crystal display element according to claim 1, wherein a color filter film having three primary color segments matching each pixel is formed on an inner surface of the lower substrate.