JPH05241202A - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] The wiring resistance value of the scanning electrode is reduced, and the varistor gap, which is one of the factors that greatly influences the electrical characteristics of the varistor element, is formed with high accuracy and little variation, thereby providing a display. Provide a liquid crystal display device with high image quality without unevenness. [Structure] The pixel electrode provided on the lower glass substrate 10 is divided into a varistor element forming portion side 19 and a liquid crystal display portion side 20, and the varistor element forming portion side 19 is made of the same material as the scanning electrode 11. Is formed by a thin metal film that is
A liquid crystal display device is characterized in that 20 is formed of a transparent electrode, and the varistor element formation portion side 19 and the liquid crystal display portion side 20 are electrically connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to a liquid crystal display device in which a sintered body varistor element formed by a printing method is used as a two-terminal element.

[0002]

2. Description of the Related Art The structure of a liquid crystal display device is roughly classified into a simple matrix system and an active matrix system. In the simple matrix system, pixel electrodes are formed at the intersections of a pair of strip-shaped electrode groups (scan electrode group and signal electrode group) provided at right angles, and a predetermined voltage is applied to these electrode groups by a drive circuit. The liquid crystal in the pixel portion is operated by applying the voltage. This method has the advantage that the system can be realized at a low price because of its simple structure, but since crosstalk occurs between each pixel, the contrast is low,
When displaying a high-definition image on a liquid crystal television or the like, deterioration in image quality is unavoidable.

On the other hand, in the active matrix system, a switching element is provided for each pixel to hold the voltage, and the liquid crystal in the pixel section holds the voltage when the liquid crystal display device is driven in a time division manner. Therefore, the display capacity can be increased, the characteristics relating to image quality such as contrast are excellent, and high image quality display of a liquid crystal television can be realized. However, the active matrix method has a drawback that the structure is complicated, the yield is low, and the manufacturing cost is high. For example, in the TFT type using a thin film transistor as a switching element, it is difficult to increase the product yield because it is necessary to stack five or more thin films in the manufacturing process and finely process the thin film into a predetermined shape. There is a definite disadvantage in increasing the size of.

From the above reasons, it is desired to realize a liquid crystal display device of a system which has good characteristics relating to image quality such as contrast and has a simple structure and low cost, and as a method for realizing such requirements. A two-terminal element type liquid crystal display device using a sintered varistor element is promising.

The two-terminal element type liquid crystal display device is an improvement of the simple matrix system, and as shown in FIG. 5, liquid crystal 14 and a predetermined threshold value are provided between the scanning electrode 11 and the signal electrode 16. A sintered body varistor element 13 that conducts with a voltage is electrically connected in series, and uses the non-linear current-voltage characteristics of the sintered body varistor element 13 as shown in FIG. is there.

FIG. 8 shows the structure of a general two-terminal element type active matrix. As shown here, a large number of pixel electrodes 12 are provided for each scanning electrode 11 with a constant distance d (varistor gap), and the scanning electrodes 11 and the pixel electrodes 12 are fixed in each sintered body varistor element 13. They are connected with a threshold voltage V _V. As shown in detail in (FIG. 4), the sintered varistor element 13 is made of Zn.
The varistor particles 13a are formed by coating the surface of the O single crystal particles 131 with an inorganic insulating film 132 such as Mn or Co oxide.
As shown in detail in FIG. 3, these varistor particles 13a are fused with a glass frit 13b.

An example of a conventional two-terminal element type active matrix liquid crystal display device is shown in FIGS. 7 and 8. As shown in FIG. 7, the pixel electrode 12 and the scanning electrode 11 made of a transparent conductive film such as ITO are formed on the lower glass substrate 10 by a photofabrication method. Furthermore,
25 parts by weight of glass frit and 10 parts by weight of ethyl cellulose (viscosity 50 cps) were added to varistor particles classified so as to be as monodisperse as possible within a particle size range of 2 to 10 μm, and carbitol was used as a solvent to form a paste. A sintered body varistor element is printed on the glass substrate 10 by silk screen printing so as to span the gap between the scanning electrode 11 and the pixel electrode 12, and is baked at 480 ° C. for 30 minutes. 13

On the other hand, ITO is formed on the upper glass substrate 17.
The signal electrode 16 is formed of a transparent conductive film such as. Next, an alignment film 15 made of alignment-treated polyimide is formed on the lower glass substrate 10 and the upper glass substrate 17.
In addition, the upper glass substrate 17 and the lower glass substrate 10 are bonded to each other with a predetermined gap by using a spacer so that the cell gap value matches the characteristics of the liquid crystal, and the liquid crystal 14 is filled between them. ing. Polarizing plates 18 are provided on both outer surfaces of the cell. In addition, here, the one using the TN liquid crystal has been described as a typical example.

In the conventional liquid crystal display device, the scanning electrode 1
1 and the pixel electrode 12 are accurately formed by a photofabrication method using a transparent electrode such as ITO. However, the transparent conductive film has a higher electric resistance value than the metal thin film, and even the best one has a sheet resistance value of about 10Ω / □. Therefore, for example, a liquid crystal display device (6
When used for a scanning electrode of 40 × 400 dots), the size of the scanning electrode is about 300 mm and the line width is about 50 μm, and the wiring resistance is a sheet resistance of about 60 kΩ / □. At the tip of the scanning electrode, due to the wiring resistance of the scanning electrode, the voltage drops in proportion to the distance and the transmittance of the liquid crystal changes, so that the resistance of the scanning electrode causes distortion of the signal waveform (delay time), Furthermore, it was also a cause of display unevenness.

Generally, the delay time is represented by the product of the resistance value of the electrode and the capacitance. In order to prevent display unevenness, the delay time needs to be sufficiently shorter than the time required to charge one pixel of the liquid crystal, and also for this purpose, it is desired to reduce the wiring resistance. In addition, the display screen is enlarged.
In order to achieve finer definition, the length of the scanning electrode is increased and the line width is reduced, so that the reduction of the wiring resistance is very important.

Conventionally, in order to reduce the wiring resistance of the scan electrode, a metal thin film such as Al or Cr having a resistance value lower than that of the ITO transparent conductive film is used as the material of the scan electrode. In this case, a glass substrate on which a metal thin film such as Cr is formed is formed into a predetermined scan electrode pattern by photoetching, and then a vacuum process such as a sputtering method is used.
The transparent conductive film made of ITO is formed, and the pixel electrode is formed again using the photofabrication method. At this time, the varistor gap is generally formed by the gap between the scanning electrode and the pixel electrode.

Since the varistor gap is a large factor that determines the threshold voltage of the varistor element, the dimensional accuracy of this varistor gap is important. Generally, the threshold voltage of a varistor element depends on the number of varistor particles present between the varistor gaps. Therefore, when the dimensional error of the varistor gap is equal to or larger than the average particle size of the varistor particles, it appears as a variation in the threshold voltage and is observed as display unevenness of the liquid crystal display device. For example, if the average particle size of the varistor particles is 5 μm, 20 ± 2.5 μm
Accuracy of m or less is required.

However, as the size of the glass substrate becomes larger in accordance with the tendency of the display screen to become larger in accordance with the demands from the market, the conventional method requires a more accurate alignment of the scanning electrode pattern and the pixel electrode pattern. I'm starting to run out. That is, in a 14-inch diagonal glass substrate, since the alignment error is generally ± 5 μm or more, the threshold voltage of the varistor element varies due to the uneven dimensional value of the varistor gap. This variation in the threshold voltage of the varistor element is one of the main causes of display quality deterioration such as display unevenness, and has been a serious problem.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the above-mentioned conventional liquid crystal display device, and reduces the wiring resistance value of the scanning electrode and has a great influence on the electrical characteristics of the varistor element. By forming the varistor gap, which is one of the factors that affects it, with high precision and little variation,
It is intended to provide a high-quality liquid crystal display device without display unevenness.

[0015]

Means for Solving the Problems The means provided by the present invention for solving the above-mentioned problems are as follows: a varistor element is used as an active matrix element to connect a scanning electrode and a pixel electrode on a lower glass substrate. In the liquid crystal display device driven by the varistor element, the liquid crystal layer is formed between the upper glass substrate and the lower glass substrate facing each other. The pixel electrode provided on the liquid crystal display portion is divided into a varistor element forming portion side and a liquid crystal display portion side, and the varistor element forming portion side is formed of a metal thin film made of the same material as the scanning electrode. In the liquid crystal display device, the side is formed of a transparent electrode, and the varistor element forming portion side and the liquid crystal display portion side are electrically connected. That.

[0016]

In the present invention, each pixel electrode on the lower glass substrate is composed of the varistor element forming portion side and the liquid crystal display portion side, and is formed in a state in which electrical connection is maintained between them. There is. The scanning electrode and the pixel electrode on the side of the varistor element forming portion are made of the same metal material and are simultaneously formed from the same thin film formed on the lower glass substrate by using a photofabrication method. The pattern of the transparent conductive film forming the liquid crystal display portion side of the pixel electrode is formed by the photofabrication method from the state of the thin film, and at this time, the pattern that can be electrically connected to the varistor element forming portion side. Shaped and arranged. This makes it possible not only to sufficiently reduce the delay time by reducing the wiring resistance value of the scan electrodes, but also to simultaneously improve the accuracy of varistor gap formation and reduce the variation. still,
It is also preferable to use a lift-off method in particular for forming the scan electrodes, the varistor element formation portion side and the liquid crystal display portion side.

[0017]

Embodiments of the liquid crystal display device according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a sectional view showing a liquid crystal display device according to the present invention, and FIG. 2 is a plan view of the varistor element part thereof. As shown in FIG. 1, a Cr film as a metal thin film having a thickness of 1000 Å is formed on a lower glass substrate 10 made of soda glass coated with SiO ₂ as a base material using a magnetron sputtering apparatus. The type of metal thin film is not limited to Cr, but Al, Ta, Ni, C
Various metals such as u can be used. The sheet resistance at this time was 2Ω / □. A resist pattern is formed by applying a photofabrication method to the scan electrode 11 using an cerium ammonium nitrate-based etching solution.
And the varistor element forming portion side 19 of the pixel electrode are formed at the same time. At this time, the line width of the scan electrode 11 is 50 μm, and the scan electrode 11 and the pixel electrode 1 on the varistor element formation portion side 1
The varistor gap d formed in No. 9 was 20 ± 1 μm.

Next, an ITO transparent conductive film was formed using a magnetron sputtering device. At this time, the film thickness is 100
It was 0Å, and the sheet resistance of the film was 40Ω / □. Further, a resist pattern is formed by using the photofabrication method, and the liquid crystal display portion side 20 of the pixel electrode is formed.
To form. At this time, the transparent conductive film on the liquid crystal display section side 20 is formed on the varistor element side 20 so that the previously formed varistor element formation section side 19 of the pixel electrode and the liquid crystal display section side 20 of the pixel electrode are electrically connected. It is laminated on a part of the part side 19.

Next, after the raw material ZnO powder was calcined at 1200 ° C. for 1 hour, it was crushed by a ball mill and air classified to obtain a ZnO single crystal powder of 3 to 5 μm, and further Co ₂ O ₃ was added thereto. Of 0.5 mol% and MnCO ₃ of 0.
5 mol% was added and fired at 1150 ° C. for 1 hour to obtain varistor powder having varistor characteristics. To this varistor powder, 25 parts by weight of glass frit and ethyl cellulose (viscosity 5
0 cps) is added to form a paste using carbitol as a solvent, and the paste is sintered on the lower glass substrate 10 by a silk screen printing method.
Print in the pattern of 3. Further, after printing, firing is performed at 470 ° C. for 1 hour to complete the sintered body varistor element 13.

Next, an ITO film (thickness 1100Å) was formed on the upper glass substrate 17 made of soda glass coated with SiO ₂ as a base material by using a magnetron sputtering device.
A film is formed using an O target. At this time, the sheet resistance value is preferably 30Ω / □ or less. Further, this ITO film is patterned by a wet etching method to form a signal electrode 16
And

Thereafter, an aligning agent (manufactured by Hitachi Chemical Co., Ltd.) is applied to both the upper glass substrate 17 and the lower glass substrate 10.
Apply the product name HL1110) to a film thickness of approximately 700Å,
The alignment film 15 is formed by rubbing using a roller rubbing device so that the rubbing directions form an angle of about 90 °.

Then, a sealing epoxy resin mixed with a spacer (diameter of 10 μm) having a predetermined gap value is printed on the upper glass substrate 17 by a silk screen printing method to form a sealing portion. At the same time, spacers are scattered in the center of the cell. Next, after accurately aligning the lower glass substrate 10, this cell is uniformly pressed and heated using a pressing jig to cure the sealing material. The pressure applied at this time is generally about 1 kg / cm ² .

Finally, TN liquid crystal is injected, and polarizing plates 19 are attached to both outer surfaces of the cell to complete the liquid crystal display device. The liquid crystal used is not limited to TN liquid crystal, but guest-host liquid crystal, polymer dispersed liquid crystal, and the like can also be used.

When the completed liquid crystal display device was evaluated, the accuracy of the varistor gap was 20 ± 5 μm of the conventional method.
To 20 ± 1 μm, the defective rate due to display unevenness of the liquid crystal display device is 10% from 60% of the conventional method.
Decreased to.

[0025]

According to the liquid crystal display device of the present invention, the pixel electrode on the lower glass substrate is divided into the varistor element forming portion side and the liquid crystal display portion side, and the varistor is applied by applying the photofabrication method. The element formation part side and the scanning electrode are simultaneously formed from the same metal thin film, and the liquid crystal display part side which is the main part of the pixel electrode and is made of a transparent conductive film is electrically connected to the varistor element formation part side formed previously. Is formed. This makes it possible not only to sufficiently shorten the delay time by lowering the resistance value of the scan electrode, but also to easily improve the accuracy of forming the varistor gap and reduce the variation thereof, and to improve the threshold voltage of the varistor element. I was able to reduce the variation. As a result, a high-quality liquid crystal display device without display unevenness can be easily obtained.

[0026]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a cross-sectional view of an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory view showing a plan view of a two-terminal element of one embodiment of the liquid crystal display device according to the present invention.

FIG. 3 is an explanatory diagram showing an enlarged view of a main part of a varistor element of an embodiment of a liquid crystal display device according to the present invention.

FIG. 4 is an explanatory view showing an enlarged cross-sectional view of a main part of a varistor element of an embodiment of a liquid crystal display device according to the present invention.

FIG. 5 is an equivalent circuit diagram of an embodiment of a (two-terminal element type) liquid crystal display device according to the present invention.

FIG. 6 is a graph showing voltage-current characteristics of a sintered varistor element of an example of the liquid crystal display device according to the present invention.

FIG. 7 is an explanatory diagram showing a cross-sectional view of an example of a liquid crystal display device according to a conventional method.

FIG. 8 is an explanatory diagram showing a plan view of an example of a (two-terminal element type) liquid crystal display device according to a conventional method.

[Explanation of symbols]

 10 ... Lower glass substrate 11 ... Scan electrode 12 ... Pixel electrode 13 ... Sintered varistor element 14 ... Liquid crystal 15 ... Alignment film 16 ... Signal electrode 17 ... Upper glass substrate 18 ... Polarizing plate 19 ... Varistor element forming part side 20 ... Liquid crystal display part side

Claims (1)

[Claims] 1. A varistor element is formed as an active matrix element in a structure for connecting a scanning electrode and a pixel electrode on a lower glass substrate, and a liquid crystal layer is opposed to an upper glass substrate and the lower glass substrate. In a liquid crystal display device provided between the glass substrate and the varistor element, the pixel electrode provided on the lower glass substrate is
It is divided into a varistor element forming portion side and a liquid crystal display portion side, the varistor element forming portion side is formed of a metal thin film made of the same material as the scanning electrode, the liquid crystal display portion side is formed of a transparent electrode, and A liquid crystal display device, wherein the varistor element forming portion side and the liquid crystal display portion side are electrically connected.