JPH0442505A - Manufacture of sintered body varistor element - Google Patents

Abstract

PURPOSE:To manufacture coated varistor particles efficiently and to obtain a sintered body varistor element of high performance by adding a metal oxide to single crystal particles of zinc oxide and heating them to make them a paste. CONSTITUTION:A minute powder of zinc oxide is made and is sintered by heating so as to crystallize it into a polycrystal-line body including single crystal grains. Next, it is ground into a single crystal powder. By using an air classify ing machine, ZnO single crystal particles whose diameter is 5 - 10mum are obtained. These are heated to fuse only their surface, thereby forming them into balls. Next, a metal oxide is added and is calcined, resulting in that a varistor paticle 13a covered with a uniform thickness of an insulating film 132 of MnO2 and Co2O3 is formed on a surface of a ZnO single crystal particle 131. Consequently, a glass frit, an organic binder and an organic solvent are added and these are mixed to be made pasty. This is applied by printing on a glass substrate previously provided with a line electrode 11 and a picture element electrode 12 consisting of indium oxide - tin oxide and a sintered body varistor element can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a sintered varistor element suitable for use as a nonlinear element in, for example, a two-terminal element type liquid crystal display device.

[Prior Art] Currently, for example, image display bags for LCD TVs! There are two main types of methods: simple matrix method and active matrix method. In the simple matrix method, a plurality of liquid crystal pixels are arranged in a matrix and connected between two sets of band-shaped electrode groups (row electrode group and column electrode group) arranged at right angles. A predetermined voltage is applied by a drive circuit to operate the liquid crystal pixels. This method has the advantage of being able to implement a system at a low cost due to its simple structure, but due to crosstalk occurring in each LCD pixel, the pixel's pixel resistance is low, resulting in poor image quality when displaying images on an LCD TV. The decline was inevitable. On the other hand, in the active matrix method, a switching element 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 can maintain the voltage at the time of selection. , it is possible to increase the display capacity, have good image quality characteristics such as contrast, and realize high-quality image display on a liquid crystal television. However, the active matrix method has the drawback that the structure is complicated and the manufacturing cost is high. For example, in the TFT type, which uses thin film transistors as switching elements,
In the manufacturing process, five or more photomasks are used to stack five or more thin films, making it difficult to increase product yield.

For the above reasons, there is a desire to realize a liquid crystal display device that has good image quality characteristics such as contrast, has a simple structure, and is low cost. Sintered varistor elements are a method that can meet these requirements. A two-terminal element type liquid crystal display device using a 2-terminal device is attracting attention.

A two-terminal element type liquid crystal display device is a simple matrix (IJ) method with improvements, and as shown in FIG. The sintered varistor element 3 is electrically connected in series with a sintered varistor element that conducts, as shown in FIG.
This utilizes the nonlinear current-voltage characteristics of In other words, in time-division driving using the simple matrix method, as shown in Figure 9, the liquid crystal pixels are turned on (light transmittance is 90%).
voltage V,. and the voltage V at which it turns off (light transmittance is 10%)
The ratio T ("V*o/V'++=(V+o+A
V)/V,. ), the maximum allowable number of scanning lines N■ax without causing crosstalk between each liquid crystal pixel is N
IIax - ((y"+ 1)/D"-1))", and the smaller the value of T, the greater the number of scanning lines, which is advantageous for LCD television display.On the other hand, the two-terminal element type Now, by applying a voltage exceeding the threshold voltage Vv to the liquid crystal pixel 4 by the sintered body varistor element 3, the operating voltage of the liquid crystal pixel without the sintered body varistor element (
(see FIG. 10(a)) is increased by its threshold voltage Vv by providing a sintered body varistor element (see FIG. 10(b)). As a result, the γΦ value is . /
'VI.

to (VV+VI.)/(Vv+V+.), the maximum number of scanning lines N1ax is increased by decreasing the T value, and a high-quality liquid crystal display can be realized.

2 to 6 show general two-terminal element type liquid crystal display devices.

As shown in FIG. 2, a large number of pixel electrodes 12 are provided for each row electrode 11 at a constant interval d, and the row electrodes 11 and pixel electrodes 12 are arranged at a constant threshold in each sintered varistor element 13. It is connected with a value voltage Vv. Regarding a liquid crystal pixel, as shown in FIGS. 3 and 4, row electrodes 11 and pixel electrodes 12 are arranged on a lower glass substrate 10.
The row electrodes 11 and the pixel electrodes 12 are connected to each other by a sintered varistor element made of zinc oxide (ZnO). Then, the upper parts of these are filled with liquid crystal 14, and column electrodes 15 and color filters 1 are further filled.
6. An upper glass substrate 17 is provided. As shown in detail in FIG. 6, the sintered varistor element 13 has a ZnO single crystal particle 131 covered with an inorganic insulating film 1 made of Mn, Co oxide, etc.
As shown in detail in FIG. 5, these varistor particles 13a are sintered with glass frit 13b. In such a sintered varistor element 13, a threshold voltage of about 3 .mu.m can be obtained per 5 .mu.m varistor particle. Therefore, the distance d between the row electrode 11 and the pixel electrode 12 is set to 25
If it is set to μm, the row electrode 11 and the pixel electrode 12 are connected through substantially five varistor grains 13a in series existing within this interval d, and there are five varistor grains 13a between the cholera electrodes 11 and 12. A threshold voltage of 15V is obtained.

[Problem B to be solved by the invention] In particular, in order to realize a two-terminal element type liquid crystal display device with good image quality, it is necessary that the sintered varistor element 13 has high performance, high stability, and high performance. It must be constant between elements. For this purpose, the varistor particles 13 shown in FIG.
When forming a, it is necessary to coat the surface of the ZnO single crystal particle 131 with an inorganic insulating film 132 to a certain thickness.

Conventionally, the sintered body varistor element 13 is made by heating and sintering fine zinc oxide powder to polycrystallize it, and then crushing and classifying the sintered polycrystalline body to obtain zinc oxide single crystal particle powder. After the zinc oxide single crystal particles are heat-treated and cornered, the surface of the zinc oxide single crystal particles is coated with an inorganic insulating film such as a Mn or Co# compound insulating film to form a varistor particle powder, and the varistor particles are It was obtained by adding glass frit and an organic binder to powder to form a paste, printing the paste on an insulating substrate, and then firing it.

However, such conventional techniques have a problem in that varistor particles having a film of a certain thickness cannot be manufactured with good yield, making it difficult to reduce the cost and improve the performance of liquid crystal display devices.

The present invention was made in view of the above-mentioned conventional circumstances, and it is possible to efficiently manufacture varistor particles coated with an inorganic insulating film to a certain thickness, and to easily produce sintered varistor elements with high performance and whose performance is constant from element to element. The aim is to mass produce it.

[Means for Solving the Problems] The method for manufacturing a sintered varistor element of the present invention involves heating and sintering a fine powder of zinc oxide, and then crushing and classifying the sintered body to form a single zinc oxide. After obtaining crystal grain powder and spheroidizing the zinc oxide single crystal particles, a metal oxide was added to the zinc oxide single crystal particles and mixed,
By heating at ℃ to 1300℃ for 30 minutes or more, the surface of the zinc oxide single crystal particles is coated with an inorganic insulating film to form varistor particle powder, and a glass frit and an organic binder are added to the varistor particle powder. Make it into a paste,
The method is characterized in that the paste is printed and coated on an insulating substrate and then fired to obtain a sintered varistor element.

[Function] In the present invention, in the step of coating zinc oxide single crystal particles with an inorganic insulating film, a metal oxide is added to zinc oxide single crystal particles, mixed, and then heated and baked at 1250 to 1300 ° C. for 30 minutes or more. As a result, varistor particles coated with an inorganic insulating film to a certain thickness can be efficiently manufactured, making it easy to produce sintered varistor elements with high performance and whose performance is constant from element to element.

[Example] A method for manufacturing a sintered varistor element according to the present invention will be specifically described based on an example.

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

First, in a granulation step 101, commercially available zinc oxide (ZnO) fine powder (particle size of about 0.5 μm), which is a raw material, is granulated.

Next, in a sintering step 102, this ZnO 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 crystal grains with an average grain size of 7 μm to 8 μm. 0 Next, in the crushing step 103,
The polycrystal is ground using a mortar or the like to obtain a ZnO single crystal powder. Next, in the classification step 1°4, ZnO single crystal particles with a particle size of 5 μm to 10 μm are separated using an air classifier.
Obtained at 0%.

Then, in the corner firing step 105, 950″C ~
Heating is performed at 1,050° C. for 1 to 3 hours to melt only the surface portion of the ZnO single crystal grains and round the corners of the ZnO single crystal grains to make them spheroidal.

Next, in the metal oxide addition and firing step 106, Z
Add 0°5 each of MnCO5 and Co*os to nO single crystal powder.
Add 1% of ++O and bake at 1250-13ooC for 30 minutes or more. As a result, as shown in FIG.
Varistor particles 13a are formed by coating the surfaces of single crystal particles 131 with MnO2, Co, O, and an insulating film 132 with a constant thickness. In addition, since the varistor particles are somewhat fused to each other during baking, they are lightly dissolved in a mortar or the like in a powder removing step 107 to form a varistor particle powder.Next, in an ink forming step 108, glass flift, ethyl cellulose as an organic binder, etc. Calpitol is then added as an organic solvent and mixed to form a paste.

Next, in a printing step 109, the pasted varistor particle powder is applied to row electrodes 11 and pixel electrodes 1 made of indium oxide and tin oxide (ITO), as shown in FIG.
This paste is printed and applied in a predetermined shape onto a glass substrate on which No. 2 has been previously provided using a 250-mesh screen printing plate, and is dried and solidified by heating at 420° C. for 1 hour in air. As a result, as shown in FIG. 5, the varistor particles 13a in contact with each other are
A solidified sintered varistor element is obtained in step b.

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.

1 = KV" Here, ■ is the current flowing through the varistor element, ■ 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, The larger this voltage nonlinearity index α (usually called the α value), the more
In this example, the varistor characteristics are excellent.
The α value was calculated from the slope at I = 10-'' (A) and ! = 10-' (A). This is what is shown.

As shown, when the firing temperature was set to 1200° C. or lower, an appropriate α value could not be obtained. 1350
If the temperature exceeds ℃, zinc oxide particles begin to sublimate, which is not preferable. However, when the present invention is used, it is possible to obtain an α value of 12 to 22, so it is possible to obtain a sintered body varistor element with high performance and whose performance is constant from element to element.

In the above example, MnCO3, co! The explanation has been given using O8 as an example, but Sr can be used as an example of other metals.

Of course, metal oxides containing Nb, Ge, etc. may also be used.

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.

[Effects of the Invention] As explained in detail above, according to the present invention, in the step of coating zinc oxide single crystal particles with an inorganic insulating film,
Since a metal oxide is added to zinc oxide single crystal particles, mixed and then heated and fired at 1250 to 1300°C for 30 minutes or more, it is possible to efficiently produce varistor particles coated with an inorganic insulating film to a certain thickness. It is possible to easily mass-produce sintered varistor elements with high performance and whose performance is constant from element to element. Therefore, it is possible to obtain a liquid crystal display device that achieves an even and clear image display. 3 is an enlarged plan view of one pixel of a general liquid crystal display device, FIG. 4 is a sectional view showing an example of a liquid crystal display device using varistor elements, and FIG. An enlarged view of the essential parts of the varistor element, Figure 6 is a cross-sectional view of the varistor particles, Figure 7 is an equivalent circuit diagram of a two-terminal element type liquid crystal display device, and Figure 8 shows the voltage-current characteristics of the sintered varistor element. Graph, Figure 9 is a graph showing the operating characteristics of a simple matrix type liquid crystal pixel, Figure 1θ (a)
, (b) are graphs showing the operating characteristics of a liquid crystal pixel when a sintered body varistor element is not used and when it is used, respectively.

11... Row electrode 12... Pixel electrode 13...
・Sintered body varistor element 13a...Paris particle
13b...Glass frit 14...Liquid crystal 15.
...Column electrode 131...ZnO single crystal particles 132.
...Inorganic insulating film Figure 1 shows how to manufacture the sintered varistor element of the present invention (2nO irradiation powder) ↓ Lower mouth 11 102 ↓ [1 Upper 110 Figure 1 Figure 3 Figure 4 Figure 5 Figure 2 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] (1) Fine zinc oxide powder is heated to form a sintered body, the sintered body is crushed and classified to obtain zinc oxide single crystal particles with a particle size of 5 μm to 10 μm, and the zinc oxide single crystal particles are sintered. After adding and mixing the metal oxide that forms the insulating film, 125
By heating at 0°C to 1300°C for 30 minutes or more, the surface of the zinc oxide single crystal particles is coated with an inorganic insulating film to form varistor particle powder, and a glass frit and an organic binder are added to the varistor particle powder. and paste it.
A method for manufacturing a sintered varistor element, which comprises printing and applying the paste on an insulating substrate and then firing it to obtain a sintered varistor element.