JP2001201754A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which an in-plane switching method (IPS) can be realized without decreasing the picture quality while suppressing the power consumption. SOLUTION: The liquid crystal display device has a liquid crystal composition layer in which liquid crystal molecules can be twisted and rotated, a first substrate and a second substrate to hold the liquid crystal composition layer, a plurality of pixels formed into a matrix between the first substrate face and the liquid crystal composition layer face, and thin film transistors formed for each pixel. The device is provided with pixel electrodes on which video signals are applied on each pixel and with a counter electrode on which a counter voltage is applied. The twist of the liquid crystal molecules is controlled by the electric field generating between the pixel electrode and the counter electrode and having a component parallel to the substrate face. In the device, the counter electrode is formed from the same light-transmitting material as the semiconductor layer including the source drain region of the thin film transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal display device which can be used as a flat display of AV / OA equipment. In particular, an active matrix type liquid crystal display device using a thin film transistor (Liquid C)
crystal Display: Hereinafter, "LCD". ).

[0002]

2. Description of the Related Art At present, LCDs have been actively employed in various fields such as viewfinders of video cameras, pocket televisions, high-definition projection televisions, and information display terminals such as personal computers and word processors. And is being actively developed and commercialized.

[0003] In particular, a thin film transistor (Thin Film Transistor:
Hereinafter, it is referred to as “TFT”. ) Using active matrix type TN (Twisted Nemati)
In recent years, in the development of c) type LCDs, polycrystalline silicon thin films (Polycrystallin) have been used as semiconductor materials.
e Silicon: Hereinafter, referred to as “p-Si”. ), A method of incorporating a driver circuit for a pixel on the same substrate has been often adopted.

[0004] Above all, a low-temperature p-Si process which can be used even for a large-area and low-quality glass substrate by controlling the heating temperature at the time of forming a p-Si film to a relatively low temperature of 450 ° C. or less is particularly preferred. -TFT-LCD technology is being actively developed and has already been put to practical use.

In general, p-Si.TFT is made of amorphous silicon (hereinafter, referred to as “a”).
-Si ". ) ・ High-speed driver circuit because carrier mobility is higher than TFT and source / drain regions are formed in a self-aligned manner with the gate electrode, so that miniaturization and reduction of parasitic capacitance between the gate and drain can be achieved. Can be formed. Therefore, the pixel and the driver circuit can be integrally formed, and cost reduction and high definition of the LCD can be realized at the same time.

On the other hand, there are two types of display systems used in active matrix type LCDs which are currently spread on the market. One is TN (Twiste
dNematic) type NW (Normally W)
white) mode.

In this method, electrodes formed on each of two substrates sandwiching a liquid crystal composition layer (one electrode is a transparent electrode)
In this method, the liquid crystal is operated by an electric field perpendicular to the substrate surface generated between the electrodes, and the light transmitted through the electrodes and incident on the liquid crystal is modulated for display. In the NW mode, white display is performed when no voltage is applied or when the voltage is equal to or lower than the threshold voltage. When a voltage higher than that is applied, the light transmittance gradually decreases, and black display is performed. Such display characteristics utilize the property that liquid crystal molecules tend to be arranged in the direction of an electric field while applying a voltage to the LCD while eliminating the twisted structure. Therefore, the deflection state of the light transmitted through the LCD changes according to the change in the arrangement state of the liquid crystal molecules, and the light transmittance is modulated.

However, even in the same molecular arrangement state, the polarization state of the transmitted light changes depending on the incident direction of the light incident on the LCD, so that the light transmittance differs depending on the incident direction. That is, the characteristics of the LCD have strong viewing angle dependence.

Due to such visual characteristics, if the viewpoint is inclined obliquely to the main viewing angle direction (the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal), a luminance inversion phenomenon is caused depending on the viewpoint. That is, in the display method, a phenomenon that the display luminance at a predetermined voltage becomes brighter than the display luminance at a lower voltage may occur. Since the occurrence of the reversal phenomenon significantly impairs the image quality of the LCD, it is an important issue in maintaining the image quality.

In order to solve such a problem, an electric field is not applied in a direction perpendicular to the substrate as in the TN type liquid crystal display system, but is applied to a plane substantially parallel to a substrate surface generated between two electrodes formed on the same substrate. A method of operating a liquid crystal by an electric field and modulating light incident on the liquid crystal from a gap between two electrodes for display (horizontal electric field method or In Plane Switch method)
ng: Hereinafter, referred to as “IPS”. ) Has been devised,
The lateral electric field method has a feature that the viewing angle is extremely wide.

[0011]

As described above, instead of applying an electric field in the direction perpendicular to the substrate as in the TN type liquid crystal display system, the direction in which the liquid crystal is applied is substantially parallel to the substrate. By using the electric field method, the viewing angle characteristics can be improved. However, as shown in FIG. 1, the pixel area, the counter electrode, and the counter electrode wiring are formed in the pixel region, so that the aperture ratio (the ratio of the effective display area to one pixel) is the conventional. Inevitably, the size becomes smaller than that of the TN type liquid crystal display system. Therefore, it is difficult to obtain a bright image, which is a major problem in improving the display image quality.

In order to solve such a problem, a method of actually increasing the aperture ratio by reducing the thickness of the wiring itself or increasing the brightness of the backlight is used. However, when the wiring is made thinner, it is necessary to increase the film thickness of the counter electrode in order to lower the wiring resistance, and the etching residue on the side wall of the gate electrode or the source / drain electrode formed simultaneously with the counter electrode, There is a high possibility that a step coverage defect or the like occurs. In addition, when the brightness of the backlight is increased, a new problem arises in that power consumption is significantly increased.

An object of the present invention is to provide a liquid crystal display device capable of realizing a horizontal electrolysis method without deteriorating image quality and suppressing power consumption in order to solve the above problems.

[0014]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a liquid crystal composition layer capable of twisting and rotating liquid crystal molecules, a first substrate sandwiching the liquid crystal composition layer, and A second substrate, a plurality of pixels formed in a matrix between the first substrate surface and the surface of the liquid crystal composition layer,
And a thin film transistor formed for each pixel,
A pixel electrode to which a video signal is applied and a counter electrode to which a counter voltage is applied are provided for each pixel, and liquid crystal molecules are generated by an electric field generated between the pixel electrode and the counter electrode, the component being parallel to the first substrate surface. Wherein the counter electrode is formed of the same translucent material as the semiconductor layer including the source / drain regions of the thin film transistor.

With this configuration, the counter electrode, which was conventionally formed of a non-translucent material, can be formed of a translucent material.
The rate at which the pixel region is shielded by the non-translucent material is reduced, and the lateral electric field method can be adopted without any reduction in the aperture ratio. Conventionally, the resistance of the opposing electrode had to be reduced for the purpose of sufficiently supplying the opposing voltage to each pixel. Since the rate is reduced, the only way to deal with this is to increase the film thickness, and the etching residue on the side walls of the gate electrode and the source / drain electrodes, and poor step coverage have occurred. However, according to the present invention, it is possible to increase the line width, and the yield is greatly improved. Further, since the counter electrode (translucent material) can be formed simultaneously with the semiconductor layer including the source / drain regions of the thin film transistor, a conventional transparent type transparent electrode (ITO) is used.
), And the number of steps does not increase due to the use of a light-transmitting material.

In the liquid crystal display device according to the present invention, it is preferable that impurity ions are implanted into the semiconductor layer including the source / drain regions by an ion doping method. This is because the resistance value of the counter electrode formed simultaneously with the semiconductor layer including the source / drain regions can be set to a desired value by the amount of impurity ions implanted during ion doping, the acceleration voltage, and the like.

Next, in order to achieve the above object, a liquid crystal display device according to the present invention comprises a liquid crystal composition layer capable of twisting and rotating liquid crystal molecules, a first substrate sandwiching the liquid crystal composition layer, and a second liquid crystal composition layer. A video signal is applied to each pixel including a substrate, a plurality of pixels formed in a matrix between the first substrate surface and the surface of the liquid crystal composition layer, and a thin film transistor formed for each pixel. A pixel electrode and a counter electrode to which a counter voltage is applied. The liquid crystal controls the amount of twist of liquid crystal molecules by an electric field generated between the pixel electrode and the counter electrode and including a component parallel to the first substrate surface. In a display device, the counter electrode is formed using the same light-transmitting material as the gate electrode of the thin film transistor.

According to this structure, as in the case where the counter electrode is formed of the same light-transmitting material as the semiconductor layer including the source / drain regions of the thin-film transistor, the rate at which the pixel region is blocked by the non-light-transmitting material is reduced. The lateral electric field method can be realized without reducing the aperture ratio at all. Also, by increasing the line width, it becomes possible to lower the wiring resistance of the counter electrode, so that etching residue on the side walls of the gate electrode and source / drain electrodes and defective step coverage can be suppressed, and the yield can be greatly reduced. It can be expected to improve. Further, since the counter electrode can be formed simultaneously with the gate electrode of the thin film transistor, which is a light-transmitting material, it is not necessary to use a conventional transmission-type transparent electrode (such as ITO), and the number of steps is increased by using a light-transmitting material. Nothing to do.

Further, in the liquid crystal display device according to the present invention, it is preferable that impurity ions are implanted into the gate electrode by an ion doping method. This is because the resistance value of the counter electrode formed simultaneously with the gate electrode can be set to a desired value by the amount of implanted impurity ions during ion doping, the acceleration voltage, and the like.

In the liquid crystal display device according to the present invention, it is preferable that the same translucent material is a polycrystalline silicon thin film. This is because the carrier mobility of the thin film transistor is dramatically improved, and a high-performance liquid crystal display device can be obtained.

Further, in the liquid crystal display device according to the present invention, it is preferable that a storage capacitor is formed between the pixel electrode and the counter electrode via at least one insulating film. This is because the storage capacitor can be easily formed by using the overlapping region of the pixel electrode and the counter electrode.

[0022]

Embodiment 1 Hereinafter, a liquid crystal display device according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 shows an active matrix type L including a TFT which is a switching element according to the present invention.
FIG. 2 is a plan view showing one pixel of a CD and its periphery. FIG. 2 is a cross-sectional structure diagram of a pixel taken along a line AA ′, FIG. 3 is a cross-sectional structure diagram of a TFT taken along a line BB ′, and FIG. It is sectional drawing of a part.

1 to 4, reference numeral 101 denotes a distortion point 5
A # 7059 glass substrate (thickness: 1.1 mm) manufactured by Corning Corporation at 90 ° C.
A base insulating film layer 102 made of iO ₂ is deposited.

On the base insulating film 102, a semiconductor layer 1 made of a 50-nm-thick p-Si thin film, which is a light-transmitting material, is formed.
The opposing electrode 104a and the opposing voltage signal line 104b, each of which has a comb shape with the reference numeral 03, are patterned into a predetermined shape. The p-Si semiconductor layer 103, the counter electrode 104a and the counter voltage signal line 104b are formed by laser crystallization.

The p-Si semiconductor layer 103 has a source region 103 on both sides of the channel region 103a.
b and the drain region 103c are formed. This p
-Si 103, counter electrode 104a and counter voltage signal line 1
04b contains impurity ions such as phosphorus and boron implanted by an ion doping method. If it is desired to set the resistance of the counter electrode 104a and the counter voltage signal line 104b to desired values, It can be controlled by the amount of implanted impurity ions, acceleration voltage, and the like.

On the p-Si 103, the counter electrode 104a and the counter voltage signal line 104b, a 100 nm thick S
consisting iO ₂ insulating film - is (gate gate insulating film) 105 is deposited further thereon, gate made of Al with a thickness of 300 nm - gate electrode 106a and the scanning signal line 106b is pattern in a predetermined shape - the training ing.

The gate electrode 106a and the scanning signal line 1
An interlayer insulating film 107 made of SiO ₂ having a thickness of 400 nm is deposited on 06b, and the gate electrode 106a and the scanning signal line 106b are covered with the interlayer insulating film 107.

Gate insulating film 105 and interlayer insulating film 107
The contact hole 108 is a p-Si 103 source.
The drain region 103c and the drain region 103b are formed respectively. On the interlayer insulating film 107,
A Ti film and an Al film having a film thickness of 100 nm and 700 nm are patterned into a predetermined shape, and the contact hole 108 is filled with the Ti film and the Al film to form a source film.
Source electrode 109a and drain electrode 109 for making contact with the source region 103b and the drain region 103c.
b, and a video signal line 109d and a comb-shaped pixel electrode 110 are formed of the same material.

The pixel electrode 110 is provided so as to engage with the opposing electrode 104a also having a comb shape.
The amount of twist of liquid crystal molecules is controlled by an electric field including a component parallel to the substrate surface generated between the counter electrode 10 and the counter electrode 104a.

The counter electrode 104a and the pixel electrode 110
The storage capacitor 111 is formed using the superimposed portion of. In the lateral electric field method in which an electric field is applied in parallel with the substrate surface, unlike the method in which the electric field is applied perpendicular to the substrate surface, there is almost no liquid crystal capacitance formed by the pixel electrode and the counter electrode. It is a component. Source electrode 109a, drain electrode 109b, video signal line 109d
A passivation protection film made of SiNx is formed on the pixel electrode 110. One pixel is configured by the above configuration.

FIG. 5 is an illustration of an active matrix type LCD in which the above-mentioned pixels are arranged in a matrix. As shown in FIG. 5, the active matrix type L
The CD has a configuration in which a pair of glass substrates 101 and 401 are arranged so as to face each other, and a liquid crystal composition layer 402 is sealed in a gap therebetween. A pair of glass substrates 101, 4
01 (on the side of the liquid crystal composition layer 402), alignment films 403a and 403b for controlling the initial alignment of the liquid crystal are provided, and the outer surfaces of the pair of glass substrates 101 and 401 are provided on the respective outer surfaces. Deflection plates 404a and 404b whose axes are arranged orthogonally are provided.

Glass substrate 101 serving as TFT array substrate
The scanning signal lines 106 arranged in a matrix are
b, a video signal line 109b, a counter voltage signal line 104b for applying a voltage to the counter electrode 104a, and a T disposed at the intersection of the scanning signal line 106b and the video signal line 109b.
FT 405 and scanning line driving circuit 40 which is a peripheral driving circuit
6 and a signal line drive circuit 407 are formed.

The TFT 405 functions as a switching element for connecting the pixel electrode 110 and writing a pixel signal to the pixel electrode 110. Further, the scanning line driving circuit 406 and the signal line driving circuit 407 which are peripheral driving circuits
It is composed of a CMOS inverter or the like formed by combining TFTs, and is built on the same substrate as a driver circuit.

On the other hand, on a glass substrate 401 serving as a color filter substrate, a color filter 408 and a light-shielding film (black matrix) pattern 409 are formed on the liquid crystal composition layer 402 side. The color filter 408 is divided into red (R), green (G), and blue (B) segments corresponding to each pixel electrode 108d. The active matrix type LCD having the above configuration is connected to two polarizing plates 404a,
A desired image display can be obtained by sandwiching the light at 404b and allowing light to enter.

According to the first embodiment as described above, the counter electrode, which is conventionally formed of a non-light-transmitting material, is formed of a light-transmitting material. Greatly reduces the rate of shielding. Therefore, it is possible to realize a horizontal electric field method in which the liquid crystal is operated by an electric field substantially parallel to the substrate surface generated between two electrodes formed on the same substrate without lowering the aperture ratio at all.

Even when the resistance of the counter electrode must be reduced, the resistance can be reduced by increasing the line width since the counter electrode is formed of a light-transmitting material. By increasing the film thickness, it is possible to suppress the remaining of the etching on the side walls of the gate electrode and the source / drain electrodes, the step coverage defect, and the like, which are caused by lowering the resistance, and the yield is greatly improved.

Further, since the counter electrode can be formed simultaneously with the semiconductor layer including the source / drain regions of the thin film transistor which is a light transmitting material, there is no increase in the number of steps due to the use of the light transmitting material.

Further, since the aperture ratio does not decrease as compared with the conventional case, it is not necessary to increase the luminance of the backlight, and the power consumption can be suppressed to the same level as the conventional TN type liquid crystal display system.

Embodiment 2 Hereinafter, a liquid crystal display device according to Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 6 is a sectional structural view showing one pixel of an active matrix type LCD including a TFT which is a switching element according to the present invention and its periphery. The structure of the TFT shown in the second embodiment is almost the same as the structure of the TFT shown in the first embodiment, except for the steps of forming the counter electrode and the counter voltage signal line.

In FIG. 6, reference numeral 114a denotes a counter electrode, for example, a 300 nm-thick p-Si film which is a light-transmitting material.
The gate electrode 113 is formed at the same time as patterning into a predetermined shape.

Although not shown in the figure, the counter electrode 114a is also provided for the counter voltage signal line and the scanning signal line.
And the gate electrode 113a. The gate electrode 113a, the scanning signal line and the counter electrode 114a
And the counter voltage signal line contain impurity ions such as phosphorus and boron implanted by the ion doping method, and the gate electrode 113a, the scanning signal line and the counter electrode 11
A desired value can be set by controlling the resistance of the counter voltage signal line 4a and the counter voltage signal by controlling the amount of impurity ions implanted during ion doping, the acceleration voltage, and the like.

According to the second embodiment, similarly to the first embodiment, the counter electrode conventionally formed of a non-light-transmitting material can be formed of a light-transmitting material. The rate of shielding by the conductive material is greatly reduced. Therefore, it is possible to realize a horizontal electric field method in which the liquid crystal is operated by an electric field substantially parallel to the substrate surface generated between two electrodes formed on the same substrate without lowering the aperture ratio at all.

As in the first embodiment, even when the resistance of the counter electrode needs to be reduced, the resistance can be reduced by increasing the line width, and the gate electrode and the source / drain can be reduced. Etching residue on the electrode side wall,
Step coverage failure can be suppressed, and the yield can be greatly improved.

Further, since the counter electrode can be formed simultaneously with the gate electrode of the thin film transistor which is a light transmitting material, there is no increase in the number of steps due to the use of the light transmitting material.

In this embodiment, for example, a p-Si.TFT is used as an active element. However, the present invention is not limited to this.
The present invention can be applied to a MOS type TFT or an MIM diode on an i-wafer.

[0046]

As described above, according to the liquid crystal display device of the present invention, the counter electrode, which was conventionally formed of a non-light-transmitting material, can be formed of a light-transmitting material. In the horizontal electric field method, in which the liquid crystal is operated by an electric field that is substantially parallel to the substrate surface generated between two electrodes formed on the same substrate, the aperture ratio is greatly reduced. It can be realized without.

Further, even when the resistance of the counter electrode must be reduced, the resistance can be reduced by increasing the line width, and the resistance is reduced by increasing the film thickness. The etching residue on the side walls of the gate electrode and the source / drain electrodes, the poor step coverage, and the like can be suppressed, and the yield is greatly improved.

Further, since the counter electrode can be formed simultaneously with the semiconductor layer including the source / drain region of the thin film transistor which is a light-transmitting material or the gate electrode, it is not necessary to use a conventional transmission type transparent electrode (ITO or the like). An increase in the number of steps due to the use of a light-transmitting material can be avoided.

Further, since the aperture ratio does not decrease as compared with the conventional case, there is no need to increase the luminance of the backlight, and the power consumption can be suppressed to the same level as the conventional TN type liquid crystal display system.

[Brief description of the drawings]

FIG. 1 is a plan view showing one pixel of an active matrix type LCD and its periphery in a liquid crystal display device according to a first embodiment of the present invention;

FIG. 2 is a sectional structural view of a pixel in the liquid crystal display device according to the first embodiment of the present invention (section line AA ′);

FIG. 3 is a sectional structural view of a TFT in the liquid crystal display device according to the first embodiment of the present invention (section line BB ′);

FIG. 4 is a cross-sectional structural view of a storage capacitor section in the liquid crystal display device according to the first embodiment of the present invention (section taken along line CC ′);

FIG. 5 is an exemplary view of a liquid crystal display device according to the first embodiment of the present invention.

FIG. 6 is a sectional structural view of a TFT in a liquid crystal display device according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 101 glass substrate (TFT array substrate) 103 semiconductor layer (p-Si) 103a semiconductor layer (channel region) 103b semiconductor layer (source region) 103c semiconductor layer (drain region) 104a counter electrode (p-Si) 104b counter voltage signal line (P-Si) 110 pixel electrode 111 storage capacitor 113a gate electrode (p-Si) 114a counter electrode (p-Si) 401 glass substrate (color filter substrate) 402 liquid crystal composition layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsuya Otomo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 2H092 GA14 HA03 JA26 JA46 JB16 JB65 KA04 KA10 MA30 NA07 NA26 QA06

Claims (6)

[Claims] A liquid crystal composition layer capable of twisting and rotating liquid crystal molecules; a first substrate and a second substrate sandwiching the liquid crystal composition layer; a first substrate surface and a liquid crystal composition layer; A plurality of pixels formed in a matrix between the pixel and a surface; a thin film transistor formed for each pixel; a pixel electrode to which a video signal is applied to each pixel; and a counter electrode to which a counter voltage is applied to each pixel A liquid crystal display device that controls the amount of twist of liquid crystal molecules by an electric field generated between the pixel electrode and the counter electrode and including a component parallel to the first substrate surface, wherein the counter electrode is A liquid crystal display device comprising the same light-transmitting material as a semiconductor layer including a source / drain region of the thin film transistor. 2. The liquid crystal display device according to claim 1, wherein impurity ions are implanted into the semiconductor layer including the source / drain regions by an ion doping method. 3. A liquid crystal composition layer in which liquid crystal molecules can be twisted and rotated; a first substrate and a second substrate sandwiching the liquid crystal composition layer; and a first substrate surface and the liquid crystal composition layer. A plurality of pixels formed in a matrix between the pixel and a surface; a thin film transistor formed for each pixel; a pixel electrode to which a video signal is applied to each pixel; and a counter electrode to which a counter voltage is applied to each pixel A liquid crystal display device that controls the amount of twist of liquid crystal molecules by an electric field generated between the pixel electrode and the counter electrode and including a component parallel to the first substrate surface, wherein the counter electrode is A liquid crystal display device, comprising: a same light-transmitting material as a gate electrode of the thin film transistor. 4. The liquid crystal display device according to claim 3, wherein impurity ions are implanted into said gate electrode by an ion doping method. 5. The liquid crystal display device according to claim 1, wherein the same light transmitting material is a polycrystalline silicon thin film. 6. The liquid crystal display device according to claim 1, wherein a storage capacitor is formed between the pixel electrode and the counter electrode via at least one insulating film.