JPH09325340A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a moving picture of excellent display quality by making the visual field wide and operation fast as to the liquid crystal display element which has high contrast and superior gradations and shock resistance and is low in driving voltage. SOLUTION: On an array substrate 12, a common electrode 18 and pixel electrodes 27 are formed, and liquid crystal molecules 14a are switched with a lateral electric field which is parallel to the array substrate 12 to obtain a wide field angle; and an orientation film is processed for circular orientation as shown by 32a-32c; and the liquid crystal molecules 14a when switched are rotated from the initial state of the circular orientation shown by 32a-32c to the electric field direction to shorten a response time and make the response fast.

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 element, and more particularly to a liquid crystal display element formed by switching nematic liquid crystal sealed between substrates in a lateral direction parallel to the substrates.

[0002]

2. Description of the Related Art In recent years, because of the advantages of thinness, light weight and low power consumption, small items such as wrist watches and calculators are
2. Description of the Related Art A liquid crystal display element (hereinafter abbreviated as LCD) is often used as a display unit of a display device such as a personal OA device such as a word processor or a desktop personal computer, a large-sized device such as a projection television, a small television.

In general, these liquid crystal display elements are active matrix type liquid crystal display elements in which twisted nematic liquid crystal is driven by a thin film transistor (hereinafter abbreviated as TFT) to rotate light in the layer thickness direction, or nematic liquid crystal with twisted orientation of 270 ° is XY. It was roughly classified into a simple matrix type liquid crystal display element which is driven by electrodes in the direction of rotation and rotates in the layer thickness direction. However, all of these liquid crystal display elements utilize the optical rotatory power of liquid crystal molecules, and since the response time is slow because they are driven by transitioning from the twist nematic state to the homeotropic state, the display quality when displaying a moving image is poor,
Moreover, there is a problem that the viewing angle is narrow.

Therefore, a liquid crystal display element using a ferroelectric liquid crystal or an antiferroelectric liquid crystal, which obtains a wide viewing angle due to a switching characteristic in a lateral direction parallel to the substrate, is also under study. However, among such liquid crystal display devices, the former is not suitable for gradation display and has a low impact resistance, and the latter requires a high driving voltage and thus has a problem that it is difficult to obtain contrast. In order to realize the same effects as these with nematic liquid crystals in recent years, as shown in FIG. 13, stripe-shaped first electrodes 2 having different polarities are formed on an array substrate 1.
And a second electrode 3 is installed, and a voltage is applied between the electrodes 2 and 3 to cause the liquid crystal molecules 4 to move in a horizontal electric field E parallel to the array substrate 1 to move the liquid crystal molecules 4 to a homogeneous state in the initial state shown in FIG. As shown in FIG. 14B, a liquid crystal display element has been developed which is gradually rotated in the direction of the electric field E on the plane parallel to the array substrate 1 from the orientation and switches.

[0005]

However, in the liquid crystal display device in which the liquid crystal molecules of the nematic liquid crystal composition are rotated in parallel with the array substrate to perform switching, the switching is not in the layer thickness direction but in the array substrate. Since the liquid crystal molecules do not change in the layer thickness direction, the wide viewing angle can be obtained without much change in retardation even when viewed obliquely, but as shown in FIG. The liquid crystal molecules 4 homogeneously aligned substantially parallel to the electrodes 2 and 3 of No. 2 in the direction of the electric field E as shown in FIG.
° It took a long time to rotate, and the response time was slow.

Therefore, the present invention eliminates the above problems. In a liquid crystal display device using a nematic liquid crystal composition, the liquid crystal molecules are switched in the lateral direction parallel to the substrate to obtain a wide viewing angle and the liquid crystal molecules. It is an object of the present invention to provide a liquid crystal display element which can obtain a high response speed and can obtain a good display quality even in a moving image by reducing the switching time in the electric field direction.

[0007]

Means for Solving the Problems As a means for solving the above problems, the present invention provides a liquid crystal display device in which a nematic liquid crystal composition is sealed between a pair of substrates provided facing each other. A comb-shaped pixel electrode formed on any of the substrates, and provided on any of the pair of substrates,
When viewed from the normal direction of the pair of substrates, a slit-shaped common electrode that is alternately arranged with the pixel electrode with a gap, and an alignment film that is alignment-treated to align the nematic liquid crystal composition in an arc shape. Is provided.

With the above structure, according to the present invention, like a hybrid arrangement in the layer thickness direction, the liquid crystal molecules are oriented in an arc shape in the lateral direction parallel to the substrate and are oriented obliquely with respect to the electrodes, so that the electric field is changed from the initial state. The rotation time of liquid crystal molecules before switching to the direction is shortened, the response is speeded up,
A liquid crystal display device capable of displaying a moving image with high display quality at high speed and wide viewing angle.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. Reference numeral 10 denotes a liquid crystal display element, and an array substrate 12 using a TFT 11 as a driving element for driving one pixel of size 150 μm × 50 μm
Further, between the pair of substrates composed of the counter substrate 13, Z having a positive dielectric anisotropy as the nematic liquid crystal composition 14 is formed.
LI-3926 (Δn = 0.030) (manufactured by Merck Japan Co., Ltd.) is enclosed. 15 and 16 are shown in FIG.
It is a polarizing plate that is combined in a crossed Nicols as shown in.

Here, the array substrate 12 is formed by forming an indium tin oxide (hereinafter, I) on an insulating substrate 17 made of transparent glass.
Abbreviated as TO. A common electrode 18 made of
A TFT 11 is formed on top of this with an electrode insulating film 20 made of a silicon oxide (SiO ₂ ) film interposed therebetween. That is, the gate electrode 2 made of thallium (Ta) on the electrode insulating film 20.
A semiconductor layer 23 made of amorphous silicon (a-Si) and a protective layer 24 made of silicon nitride (SiNx) are formed on the substrate 1 via a gate insulating film 22 made of silicon oxide (SiO ₂ ). Protective layer 2
The source electrode 28 made of aluminum (Al) connected to the pixel electrode 27 through the ohmic layer 26 made of amorphous silicon (a-Si) and the drain electrode 31 integrated with the signal line 30. Is provided.

Here, the pixel electrode 27 is made of ITO and is formed in a comb shape on the gate insulating film 22, and further, the common electrode 18 and the pixel electrode 27 are made of polyimide which can be oriented by ultraviolet irradiation. An alignment film 33 in which three circular alignments 32a to 32c are formed in one pixel is printed. As a result, the liquid crystal molecules 14a in the nematic liquid crystal composition 14 are aligned in parallel with the array substrate 12 and form a circle along the circular alignments 32a to 32c. The liquid crystal molecules 14a are oriented parallel to the array substrate in the layer thickness direction.

On the other hand, the counter substrate 13 has red (R), green (G), and blue (B) stripe color filters 36 on an insulating substrate 34 made of transparent glass.

Next, a method of manufacturing the liquid crystal display element 10 will be described. First, in the array substrate 12, the insulating substrate 17
An ITO film is formed thereon by a sputtering method, and the electrode insulating film 20 is entirely covered on the ITO film. Next, a gate electrode 21 and a scanning line 21a integrated with the gate electrode 21 are formed by using a photolithography technique in which a film of thallium (Ta) is formed by a sputtering method and a photoresist (not shown) is used as a mask for etching.
Is patterned.

Next, a silicon oxide (SiO ₂ ) film and amorphous silicon (a-Si) are formed by the plasma CVD method.
A film and a silicon nitride (SiNx) film are sequentially laminated to form a silicon nitride (SiNx) film and amorphous silicon (a
The -Si) film is patterned by the photolithography technique to form the semiconductor layer 23 and the protective layer 24. Then, an amorphous silicon (a-Si) film is formed on the semiconductor layer 23 by a plasma CVD method, an ohmic layer 26 is patterned by etching, and an aluminum (Al) film is further formed by a vapor deposition method. The source electrode 28, the signal line 30, and the drain electrode 31 are processed by photo etching.
Is patterned to form the TFT 11.

After that, an ITO film is formed on the gate insulating film 22 by a sputtering method, and photo-etching is performed to form a comb-shaped pixel electrode 27 in a pattern. Further, the gate insulating film 22 and the electrode insulating film 20 are etched into a slit shape and exposed so that the common electrode 18 is interposed between the comb-shaped pixel electrodes 27, and then polyimide is printed to form the alignment film 33. To film.

Further, the alignment film 33 is irradiated with ultraviolet rays through a mask (not shown) capable of polarizing three circles for each pixel so that three circular alignments 32a to 32c are formed. , Orientation treatment.

Next, in the counter substrate 13, the insulating substrate 3
After the pigments are spin-coated on the surface 4 in the order of red (R), green (G), and blue (B), pattern exposure and development are repeated to form a stripe-shaped color filter 36.

Then, a dry type silica (Catalyst Kasei Co., Ltd.) 35 having a particle size of 2.2 μm is formed on the array substrate 12 so that the liquid crystal layer thickness is 2.5 μm so that the dispersion density is 50 particles / mm ^2. After spraying by the spraying method, the array substrate 12 and the counter substrate 13 are opposed to each other to form an assembled cell, and the nematic liquid crystal composition 14 is injected into the gap and sealed. Then, polarizing plates 15 and 16 having polarization axes in the arrow r direction and the arrow s direction are attached to both substrates 12 and 13 to complete the liquid crystal display element 10.
In this liquid crystal display element 10, since the liquid crystal layer is thin and the Δn of the nematic liquid crystal composition 14 is large, the transmittance due to the birefringence of the liquid crystal layer is increased.

Next, the operation will be described. Liquid crystal display element 1
At the time of 0, when the voltage is not applied to the common electrode 18 and the pixel electrode 27, the alignment film 33 is circularly aligned at the time of OFF, so that the liquid crystal molecules 14 of the nematic liquid crystal composition 14 are aligned.
a is three circular orientations 32a in one pixel as shown in FIG.
32c and are obliquely arranged with respect to both electrodes 18 and 27, and the light incident from the polarizing plate 15 side is circularly polarized by the birefringence effect as it advances in the layer thickness direction,
The light passes through the liquid crystal display element 10 and is emitted from the polarizing plate 16 side. On the other hand, when a voltage is applied between the common electrode 18 and the pixel electrode 27, the liquid crystal molecules 14a of the nematic liquid crystal composition 14 are aligned in the electric field direction as shown in FIG. Since the light is directed in the same direction as, the incident light from the polarizing plate 15 side is not modulated and absorbed by the polarizing plate 16 and is not emitted.

Then, when a moving image is displayed on the liquid crystal display device 10 and the response time is measured, the rise time is 8 msec.
The fall was 20 msec, which was an extremely fast value.
As for the viewing angle characteristics, a wide viewing angle with a contrast of 10: 1 or more was obtained in the vertical and horizontal directions of 60 ° or more.

According to this structure, when the nematic liquid crystal composition 14 is switched in the direction parallel to the array substrate 12 in order to obtain a wide viewing angle, the liquid crystal molecules 14 are initially formed.
Since a is arranged along the circular alignments 32a to 32c that are oblique to the common electrode 18 and the pixel electrode 27, the liquid crystal molecules 14a can rotate in the electric field direction in a shorter time than in the conventional case during switching, The display speed is increased due to the shortened response time, and a good display quality can be obtained even in a moving image while having a wide viewing angle. Further, compared to the ferroelectric liquid crystal and the anti-ferroelectric liquid crystal, a high contrast can be obtained, the shock resistance and the gradation are excellent, and the driving voltage is reduced.

[Comparative Example] Compared with this, the alignment film 33 in the first embodiment is parallel to the common electrode 18 and the pixel electrode 27 as shown in FIG. 12 so that the liquid crystal molecules 14a have a 90 ° twist. [Comparative example]
Then, when a response time was measured by displaying a moving image, the rising edge was 80 msec and the falling edge was 120 msec, which was slower than the television frame frequency of 30 Hz, and the image was blurred.

Next, a second embodiment of the present invention will be described with reference to FIG. Although the present embodiment is different from the first embodiment in the alignment direction of the initial state of the liquid crystal molecules 14a, the other parts are the same as the first embodiment, and therefore, the same parts are denoted by the same reference numerals. The description is omitted.

That is, the alignment film 37 printed on the upper surface of the array substrate 12 is a mask capable of forming a closed small circular alignment 38 for each gap between the adjacent common electrode 18 and pixel electrode 27 during the alignment process. Both electrodes are irradiated with ultraviolet rays through 1
It is formed to have a small circular orientation 38 in the gap of 8, 27.

As a result, in the initial state of the liquid crystal display element 10, since the alignment film 37 is subjected to the alignment treatment so as to have the small circular alignment 38, the liquid crystal molecules 14a of the nematic liquid crystal composition 14 are shown in FIG. Common electrode 1 as shown in
8 and the pixel electrode 27 are arranged along a small circular orientation 38 and are obliquely arranged with respect to both electrodes 18 and 27, and incident light is transmitted through the layer thickness direction by a birefringence effect.
On the other hand, when a voltage is applied between the common electrode 18 and the pixel electrode 27, the liquid crystal molecules 14a are aligned in the direction of the electric field by the electric field in the direction of the arrow s as in the first embodiment shown in FIG. Since it is oriented in the same direction as the polarization axis of, the incident light is not modulated and is absorbed by the polarizing plate 16 and does not pass therethrough.

Then, when a moving image is displayed on the liquid crystal display element 10 and the response time is measured, the rise time is 10 mse.
c, the fall was 25 msec, which was an extremely fast value. As for the viewing angle characteristics, a wide viewing angle with a contrast of 10: 1 or more was obtained in the vertical and horizontal directions of 60 ° or more.

With this structure, as in the first embodiment, the nematic liquid crystal composition 14 is used which can obtain high contrast and is excellent in gradation and impact resistance and capable of reducing driving voltage. In the liquid crystal display element 10, a wide viewing angle can be obtained, and in the initial state, the liquid crystal molecules 14a are arranged along the small circular alignment 38 so as to be inclined with respect to the common electrode 18 and the pixel electrode 27. The response time is shortened, the response speed is increased, and good display quality can be obtained even in a moving image with a wide viewing angle.

Next, a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, liquid crystal molecules are switched laterally by an electric field in the lateral direction parallel to the array substrate 12 in the first embodiment. Therefore, the slit-shaped common electrode 18 is provided not on the array substrate 12 but on the opposite substrate 13 side. Since the other parts are the same as those of the first embodiment, the same parts are designated by the same reference numerals and the description thereof will be omitted. That is, the insulating substrate 1 of the array substrate 40
The common electrode 18 and the electrode insulating film 20 according to the first embodiment are not formed on the gate electrode 2 on the gate electrode 2
1. The TFT 11 having the semiconductor layer 23 made of amorphous silicon (a-Si) and the like and the comb-shaped pixel electrode 27 are formed, and further, three circular orientations 32a to 32c are formed in one pixel by ultraviolet irradiation. The alignment film 33 to be subjected to the alignment treatment is printed.

On the other hand, the counter substrate 41 is formed on the insulating substrate 34 on the red (R), green (G), and blue (B) stripe-shaped color filters 36 via the insulating film 39 by the sputtering method. A common electrode 42 is formed by photo-etching the ITO film in a stripe shape so as to be adjacent to the pixel electrodes 27 alternately and in parallel when viewed from the normal line direction of the insulating substrate 34. Similarly 1
An alignment film 43 is printed so that three circular alignments 32a to 32c are formed in each pixel. The array substrate 40 and the counter substrate 41 as described above are arranged so as to face each other as in the first embodiment, and the nematic liquid crystal composition 14 is sealed in the gap to form a liquid crystal display element 44 in which one pixel is 300 μm × 100 μm.

As a result, in the initial state of the liquid crystal display element 44, the liquid crystal molecules 14a of the nematic liquid crystal composition 14 due to the alignment films 33 and 43 have three circles in one pixel as in the first embodiment. The light is arranged along the orientations 32a to 32c and obliquely arranged with respect to the pixel electrode 27 and the common electrode 42, and the incident light is transmitted and emitted in the layer thickness direction by the birefringence effect. On the other hand, when a voltage is applied between the common electrode 42 and the pixel electrode 27, the liquid crystal molecules 14a are aligned in the electric field direction by the electric field in the direction of the arrow s as in the first embodiment shown in FIG. Since it is oriented in the same direction as the polarization axis in the direction of arrow s, the incident light is not modulated and is absorbed by the polarizing plate 16 and is not emitted.

Then, when a moving image is displayed on the liquid crystal display element 42 and the response time is measured, the rise time is 6 msec.
The fall was 16 msec, which was an extremely fast value.
As for the viewing angle characteristics, a wide viewing angle with a contrast of 10: 1 or more was obtained in the vertical and horizontal directions of 60 ° or more.

According to this structure, as in the first embodiment, the nematic liquid crystal composition 14 having high contrast, excellent impact resistance and gradation, and capable of reducing driving voltage is obtained.
In the liquid crystal display element 44 using, a wide viewing angle can be obtained, the response time at the time of switching can be shortened, the response speed can be increased, and good display quality can be obtained even in a moving image.

The present invention is not limited to the above-described embodiment, and modifications can be made without departing from the spirit of the invention. For example, a common electrode and a pixel for generating a lateral electric field parallel to the substrate. The size and number of electrodes are arbitrary, but in order to improve the aperture ratio, it is desirable that the electrodes are thinner and smaller, and the ratio of the common electrode and the pixel electrode when viewed from the normal direction of the substrate is It is desirable that it is 2/3 or less. Further, the cell thickness of the liquid crystal display element, the material of the nematic liquid crystal composition, etc. are arbitrary, and the dielectric anisotropy is positive,
It may be either negative or a guest-host liquid crystal composition in which a dye is mixed with a nematic liquid crystal composition.

Further, the orientation direction of the liquid crystal molecules in the initial state is not limited to the circular shape, and the liquid crystal molecules 48 are semicircular in the gap between the common electrode 46 and the pixel electrode 47 as in the first modification shown in FIG. Alternatively, as in the second modification shown in FIG. 11, the liquid crystal molecules 52 may be aligned in a quarter circle in the gap between the common electrode 50 and the pixel electrode 51. Also, the liquid crystal display element is driven by MIM regardless of the TFT.
It may be an active matrix liquid crystal display element using (metal / insulating film / metal), a simple matrix liquid crystal display element, or the like.

[0035]

As described above, according to the present invention, since the nematic liquid crystal composition is switched in the lateral direction parallel to the substrate, a wide viewing angle can be obtained, and the initial phase of liquid crystal molecules at the time of switching is obtained. The state is oriented in an arc shape oblique to the electrode, it is easy to rotate in the direction of the electric field by applying a voltage, the switching response time is shortened, the response speed can be increased, and a good display is displayed even in a moving image. You can get dignity. Moreover, good contrast can be obtained, and gradation and impact resistance are excellent. Further, since the driving voltage is low, economic efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an array substrate according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the liquid crystal display element taken along the line AA ′ in FIG. 1 according to the first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of the liquid crystal display element taken along the line BB ′ in FIG. 1 according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an alignment state of an alignment film according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing liquid crystal molecules when a voltage is applied according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an alignment state of an alignment film according to a second embodiment of the present invention.

FIG. 7 is a schematic plan view showing an array substrate according to a third embodiment of the present invention.

FIG. 8 is a schematic plan view showing a counter substrate according to a third embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing a liquid crystal display element of a third embodiment of the present invention.

FIG. 10 is an explanatory diagram showing an alignment state of a first modified example of the present invention.

FIG. 11 is an explanatory diagram showing an alignment state of a second modified example of the present invention.

FIG. 12 is an explanatory diagram showing an alignment direction of a comparative example.

13A is a schematic cross-sectional view showing an initial state of a conventional device, and FIG. 13B is a schematic cross-sectional view showing a voltage application thereof.

14A and 14B show a conventional device, and FIG. 14A is an explanatory diagram showing liquid crystal molecules in an initial state thereof, and FIG. 14B is an explanatory diagram showing liquid crystal molecules when a voltage is applied thereto.

[Explanation of symbols]

 10 ... Liquid crystal display element 11 ... TFT 12 ... Array substrate 13 ... Counter substrate 14 ... Nematic liquid crystal composition 15, 16 ... Polarizing plate 18 ... Common electrode 27 ... Pixel electrodes 32a to 32c ... Circular alignment 33 ... Alignment film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toshihiro Ninomiya Toshihiro Ninomiya 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Incorporated company Toshiba Yokohama Works (72) Inventor Masumi Okamoto 8-story, Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Ceremony Company Toshiba Yokohama Works (72) Inventor Masahito Ishikawa 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Yokohama Office (72) Inventor Yasuharu Tanaka 8-Shin-Sugita-cho, Isogo-ku, Yokohama Kanagawa Toshiba Yokohama office (72) Inventor Hitoshi Hato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama office (72) Inventor Masato Shoko 8-Shin-Sugita-cho, Isogo-ku, Yokohama, Kanagawa stock company Toshiba Yokohama In the office

Claims (9)

[Claims] 1. A liquid crystal display device comprising a nematic liquid crystal composition enclosed between a pair of substrates provided facing each other, comprising: a comb-shaped pixel electrode formed on one of the pair of substrates; A slit-shaped common electrode which is provided on any one of the substrates and which is alternately arranged with the pixel electrode with a gap, when viewed from the normal direction of the pair of substrates, and the nematic liquid crystal composition is aligned in an arc shape. A liquid crystal display device, comprising: 2. The pixel electrode and the common electrode are formed on the same substrate, and an electric field parallel to the substrate is generated in a gap between the pixel electrode and the common electrode adjacent to the arbitrary pixel electrode. The liquid crystal display element according to claim 1. 3. The liquid crystal display element according to claim 1, wherein the alignment film is subjected to alignment treatment so as to align the nematic liquid crystal composition in a circular shape. 4. The alignment film is subjected to an alignment treatment so as to align the nematic liquid crystal composition in a circular shape in the gap between the pixel electrode and the common electrode adjacent to the pixel electrode. 3. The liquid crystal display element according to any one of 3 above. 5. The alignment film is subjected to an alignment treatment so as to align the nematic liquid crystal composition in a semicircular shape in the gap between the pixel electrode and the common electrode adjacent to the pixel electrode. Item 3. The liquid crystal display device according to item 2. 6. The liquid crystal display device according to claim 1, wherein the pixel electrode and the common electrode are formed on different substrates. 7. The liquid crystal display device according to claim 6, wherein the alignment film is subjected to alignment treatment so as to align the nematic liquid crystal composition in a circular shape. 8. The alignment film is subjected to an alignment treatment so as to align the nematic liquid crystal composition in a circular shape within the gap between the pixel electrode and the common electrode adjacent to the pixel electrode when viewed in the normal direction of the pair of substrates. The liquid crystal display element according to claim 6, wherein the liquid crystal display element is a liquid crystal display element. 9. The alignment film is subjected to an alignment treatment so as to align the nematic liquid crystal composition in a semicircular shape in the gap between the pixel electrode and the common electrode adjacent to the pixel electrode when viewed from the normal direction of the pixel electrode. The liquid crystal display device according to claim 6, wherein the liquid crystal display device is a liquid crystal display device.