JPH04367829A - Production of sintered-body varistor element - Google Patents

Abstract

PURPOSE:To produce a high-performance varistor element with the performance constant between the elements. CONSTITUTION:A varistor element 13a for connecting a line electrode 11 and a picture-element electrode 12 is formed on a glass board 10 by printing to produce a sintered-body varistor element 13. In this case, the powder of the varistor grains obtained by coating the surface of a zinc oxide single crystal grain with an inorg. insulating film is made into a paste with an org. binder, the paste is printed between the line electrode 11 and the picture-element electrode 12, and a paste consisting essentially of a glass frit 13b is printed on the element and sintered. Consequently, a high-performance sintered-body varistor element with the packing density of the varistor grains increased and with the performance constant between the elements is obtained, and a liq. crystal display capable of displaying a high-definition picture is obtained.

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 using a sintered varistor element as a nonlinear element.

0002

2. Description of the Related Art Currently, image display devices for, for example, liquid crystal televisions are broadly classified into simple matrix type and active matrix type.

[0003] In the simple matrix method, a plurality of liquid crystal pixels are arranged in a matrix and connected between a set of band-shaped electrode groups (row electrode group and column electrode group) arranged at right angles. A predetermined voltage is applied between the strip electrodes by a drive circuit to operate the liquid crystal pixels.

[0004] This method has the advantage of being able to realize a system at a low cost due to its simple structure, but since crosstalk occurs in each liquid crystal pixel, the pixel contrast is low, and when displaying images on a liquid crystal television, Deterioration in image quality was inevitable.

On the other hand, in the active matrix method, a switch is provided for each liquid crystal pixel to maintain the voltage, and even if the liquid crystal display device is time-divisionally driven, the liquid crystal pixel does not maintain the voltage at the time of selection. As a result, display capacity can be increased, and characteristics related to image quality such as contrast are good, and high-quality image display on liquid crystal televisions can be realized.

However, the active matrix method has the disadvantage that the structure is complicated and the manufacturing cost is high. For example, in a TFT type device that uses a thin film transistor as a switching element, it is difficult to increase the product yield because five or more photomasks are used in the manufacturing process to stack five or more thin film layers.

[0007] For the above reasons, it is desired to realize a liquid crystal display device that has good image quality characteristics such as contrast, has a simple structure, and is low in cost. Two-terminal element type liquid crystal display devices using body varistor elements are attracting attention.

The two-terminal element type liquid crystal display device is an improvement on the simple matrix method, and as shown in FIG. The sintered varistor elements 3 are electrically connected in series, and the nonlinear current-voltage characteristics of the sintered varistor elements 3 as shown in FIG. 8 are utilized.

That is, in time-division driving using a simple matrix method, as shown in FIG.
%) to the voltage V10 (=V90/V10=(
V10+ΔV) /V10), the maximum number of scanning lines N allowed without causing crosstalk between each liquid crystal pixel
max is Nmax = ((γ2 +1)/(γ2
-1))2, and the smaller the value of γ, the greater the number of scanning lines, which is advantageous for liquid crystal television display.

On the other hand, in the two-terminal element type, by providing the sintered varistor element 3, the threshold voltage Vv
so that the voltage exceeding the voltage is applied to the liquid crystal pixel 4,
The operating voltage is set to be higher than the operating voltage of the liquid crystal pixel when no sintered body varistor element is provided (see FIG. 10) by a threshold voltage Vv (see FIG. 11).

As a result, the value of γ is improved from V90/V10 to (Vv + V90)/(Vv + V10), and by decreasing the γ value, the maximum number of scanning lines Nmax is increased, realizing a high-quality liquid crystal display. can do.

A two-terminal element type liquid crystal display device using a conventional varistor is shown in FIGS. 2 to 6.

As shown in FIG. 2, a large number of pixel electrodes 12 are provided on the lower glass substrate at a constant interval d for each row electrode 11, and the row electrodes 11 and pixel electrodes 12
and are connected by each sintered varistor element 13 having a constant threshold voltage Vv.

Regarding one liquid crystal pixel, as shown in FIG. 3 and FIG. 4, which is a cross-sectional view of FIG.
These row electrodes 11 and pixel electrodes 12
A sintered varistor element 13 made of zinc oxide (ZnO) is connected between the two. There is a layer of liquid crystal 14 injected to cover these, and an upper glass substrate 17 on which column electrodes 15 and color filters 16 are provided is disposed above the layer.

The liquid crystal 14 used here is usually TN (
Twisted nematic) type liquid crystals are common, and liquid crystals are used as optical shutters. In this case, the alignment film layer 18 for aligning the liquid crystal is in contact with the layer of the liquid crystal 14 from above and below, and the lower glass substrate 10, the row electrodes 11, the pixel electrodes 12, and the sintered The body varistor element 13 is separated from an upper glass substrate 17 on which column electrodes 15 and color filters 16 are provided on the other upper side.

Note that a polarizing plate 19 is installed outside the lower glass substrate 10 and the upper glass substrate 17.

The sintered varistor element 13 switches the liquid crystal 14 based on the voltage applied to the row electrode 11.
As shown in FIG. 6, the varistor particles 13a are composed of ZnO single crystal particles 131 whose surfaces are coated with an inorganic insulating film 132 such as Co or Mn oxide, and as shown in FIG. It is sintered with

In such a sintered varistor element 13, a threshold voltage of about 3 V can be obtained per varistor particle having a particle size of about 5 μm.

Therefore, if the distance d between the row electrode 11 and the pixel electrode 12 is set to 25 μm, the row electrode 11 and the pixel electrode 12 are are connected, and these electrodes 11
, 12, a threshold voltage of 5×3V=15V is obtained.

That is, when a voltage exceeding this threshold voltage is applied, the liquid crystal 14 is driven, eliminating the influence of the applied voltage on other liquid crystal elements and preventing the occurrence of crosstalk. I can do that.

Conventionally, the sintered varistor element 13a is made by heating and sintering fine powder of zinc oxide to polycrystallize it, and then
The sintered body is crushed and classified to obtain a zinc oxide single crystal particle powder, and after the zinc oxide single crystal particle is heat-treated and cornered, Co and Mn oxide powders are added to the zinc oxide single crystal particle. In addition, varistor particles were obtained by firing after mixing to form an inorganic insulating film.

Glass frit and an organic binder are added to the varistor particle powder to form a paste, and the paste is printed and coated on an insulating substrate and then fired to obtain a sintered varistor element.

However, in the method for manufacturing a sintered varistor element as described above, the varistor particles and glass frit are pasted together and the varistor element is formed by printing, so the packing density of the varistor particles is low, and there are gaps between the particles. This results in a state in which many gaps exist, resulting in low stability and non-uniform performance among elements, resulting in a problem of variations in image quality when used in a liquid crystal display device.

[0024]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and it is an object of the present invention to bind sintered varistor particles to an organic binder when forming a sintered varistor element on a lower glass substrate. By making a paste, printing the paste between the row electrode and pixel electrode, and printing and firing a paste mainly composed of glass frit on the element, a sintered varistor with high performance and uniform performance between elements can be created. The purpose is to obtain an element.

[0025]

[Means for Solving the Problems] A method for manufacturing a sintered varistor element according to the present invention is to form a powder of varistor particles whose surfaces are coated with an inorganic insulating film on the surface of zinc oxide single crystal particles into a paste with an organic binder, and to form a paste with an organic binder. is printed between the row electrode and the pixel electrode, and a paste containing glass frit as the main component is printed on the paste, followed by firing.

[0026]

[Operation] In the present invention, the varistor particle powder is made into a paste with an organic binder, and after printing the paste, a paste containing glass frit as the main component is printed and fired, so the packing density of the varistor particles is high and the performance is high. Moreover, it is possible to obtain a sintered body varistor element whose performance is constant between elements.

[0027]

EXAMPLES The method for manufacturing a sintered varistor element according to the present invention will be specifically explained based on examples.

FIG. 1 is a process diagram of a manufacturing method according to an embodiment of the present invention.

First, in the granulation step 101, commercially available zinc oxide (ZnO) fine powder (particle size 0.5 μm) is used as a raw material.
m) is granulated.

Next, in the sintering step 102, this Z
The nO fine powder is heated and sintered at 1150° C. to 1250° C. for 2 hours or more to crystallize it into a polycrystalline body containing single crystals with an average particle size of 7 μm to 8 μm.

Next, in a grinding step 103, the polycrystal is ground into ZnO single crystal powder using a mortar or the like.

Next, in a classification step 104, ZnO single crystal particles having a particle size of 5 μm to 10 μm were obtained at a yield of 20% using an air classifier.

[0033] Then, in the corner firing step 105, the Z
Only the surface portion of the nO single crystal grain is melted, and the corners of the ZnO single crystal grain are rounded to form a sphere.

Next, in the additive addition/calcination step 106, cobalt and manganese nitrates are added as additives.
(NO3)2 ・6H2 O, Mn(NO3)2
・Dissolve 0.5 mol% of each in water in terms of 5H2O, add and mix ZnO single crystal particles to the aqueous solution,
After heating to .degree. C., cobalt oxide and manganese oxide particles are precipitated on the surface of the zinc oxide single crystal particles by pre-calcining at 180.degree. C. to 260.degree. C. for 1 hour.

[0035] Then, this zinc oxide single crystal covered with cobalt and manganese oxide particles was heated to 1100°C to 1200°C.
Bake for 1 hour.

As a result, as shown in FIG. 6, Co2 O3 and MnO2 are formed on the surface of the ZnO single crystal particles 131.
Varistor particles 13a uniformly coated with an insulating film 132 at a constant thickness are formed.

[0037] Since the varistor particles are somewhat fused to each other during firing, they are lightly loosened in a mortar or the like in the powder removing step 107 to form varistor particle powder.

In the ink forming step 108, 75% by weight of varistor particles, 2% by weight of ethyl cellulose as an organic binder, and 23% by weight of carbitol as a solvent.
An ink containing varistor particles as the main component is prepared by mixing the varistor particles.

[0039] Also, an ink whose main component is glass frit mixed with 75% by weight of glass frit, 2% by weight of ethyl cellulose as an organic binder, and 23% of carbitol as a solvent is also prepared.

[0040] Then, a printing process 109 and a baking process 11
0, as shown in FIG. 4, a paste containing the varistor particles as a main component is spread over a 325-mesh screen on a glass substrate on which row electrodes and pixel electrodes 12 made of indium oxide/tin oxide (ITO) have been provided in advance. Print and coat in a predetermined shape using a printing plate.

After drying this at 120° C. for 10 minutes, a paste containing the glass frit as a main component is printed and applied thereon. Then, it is heated in air at 420° C. for 1 hour to dry and solidify.

As a result, as shown in FIG. 5, a sintered varistor element is obtained in which the varistor particles 13a that are in contact with each other are hardened by the glass frit 13b.

The electrical characteristics of the varistor element of the present invention obtained as described above will be described. As is well known, the current-voltage characteristics of a varistor are expressed by the following equation.

[0044]

[Math 1]

Here, I is the current flowing through the varistor element, V is the voltage between the electrodes of the varistor element, K is a constant corresponding to the resistance value of the specific resistance, and α is the exponent of the voltage nonlinear characteristic. This voltage nonlinearity index α (usually called α value)
The larger the value, the better the varistor characteristics. In this example, I=10-9(A) and I=10-6
The α value was determined from the slope in (A).

[0046]

[Table 1]

Table 1 compares the results of the present invention and the conventional method in terms of varistor voltage (voltage at 10 -6 (A)), α value, and variation in varistor voltage.

From this table, in the present invention, after printing a paste containing varistor particles as a main component, a paste containing glass frit as a main component was printed on the element, so the filling rate of varistor particles in each varistor element was improved. do. Therefore, it was possible to obtain an element with better varistor voltage and α value than with the conventional method, and with reduced variation.

From this fact, by using the present invention, it is possible to obtain a sintered varistor element with high performance and whose performance is constant from element to element. Furthermore, the present invention can of course be applied not only to sintered varistor elements for liquid crystal display devices, but also to commonly used sintered varistor elements.

[0050]

[Effects of the Invention] As explained in detail above, according to the present invention, varistor particle powder is made into a paste with an organic binder, and after printing the paste, a paste containing glass frit as a main component is printed and fired on the element. Therefore, it is possible to obtain a sintered varistor element with a high packing density of varistor particles, high performance, and whose performance is constant from element to element. Therefore, it is possible to obtain a liquid crystal display device that achieves clear image display without unevenness.

[0051]

[Brief explanation of drawings]

FIG. 1 is a process diagram of a method for manufacturing a varistor element according to an embodiment of the present invention.

FIG. 2 is a plan view showing an example of an electrode shape of a general liquid crystal display device.

FIG. 3 is an enlarged plan view of one pixel of the liquid crystal display device of FIG. 2;

FIG. 4 is a cross-sectional view showing an example of a liquid crystal display device using a varistor element.

FIG. 5 is an enlarged view of the main part of the varistor in FIG. 1.

FIG. 6 is a cross-sectional view of a varistor particle.

FIG. 7 is an equivalent circuit of a two-terminal element type liquid crystal display device.

FIG. 8 is a graph diagram showing voltage-current characteristics of a sintered varistor element.

FIG. 9 is a graph diagram showing operating characteristics of a simple matrix type liquid crystal pixel.

FIG. 10 is a graph diagram showing operating characteristics of a liquid crystal pixel when a sintered body varistor element is not used.

FIG. 11 is a graph diagram showing operating characteristics of a liquid crystal pixel when a sintered body varistor element is used.

[Explanation of symbols]

10...Lower glass substrate 11...row electrode 12...Pixel electrode 13...Sintered varistor element 13a...varistor element 13b...Glass frit 14...Liquid crystal 15...Column electrode 16...Color filter 17...Lower glass substrate 18...Alignment film 19...Polarizing plate 20...Spacer glass beads 131...ZnO single crystal particles 132...Inorganic insulating film

Claims (1)

[Claims] 1. A method for manufacturing a sintered varistor element substrate in which a varistor element connecting a row electrode and a pixel electrode on a glass substrate is formed by a printing method, in which the surface of zinc oxide single crystal particles is coated with an inorganic insulating film. This method is characterized in that the powder of varistor particles obtained by the process is made into a paste with an organic binder, the paste is printed between the row electrode and the pixel electrode, a paste containing glass frit as the main component is printed on top of the paste, and then it is fired. A method for manufacturing a solid varistor element.