JPS62242308A - Voltage nonlinear device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a voltage nonlinear element whose resistance value changes depending on an applied voltage, and is useful for voltage stabilization, abnormal voltage control, and matrix-driven liquid crystal, EL, etc. It is used in switching elements of display devices, etc.

Conventional technology Conventional voltage nonlinear elements include zinc oxide (ZnO), bismuth oxide (Bi203), and cobalt oxide (Oozes).
, manganese oxide (Mn02), antimony oxide (5b2)
1000-1350' by adding oxides such as 05)
There are various types such as ZnO varistors sintered with carbon.

Among them, ZnO varistors are most commonly used because they have a large voltage nonlinearity index α and surge resistance. (
(Refer to Japanese Patent Publication No. 46-19472) Problems to be Solved by the Invention In such conventional voltage nonlinear elements, including ZnO varistors, there is a limit to how thin the element can be (less than several tens of μm). The varistor voltage (current 1 to the varistor)
There is a limit to lowering the voltage (expressed as v11nm) when m people are flowing through it, and it cannot be used as a protection element for low voltage ICs or a voltage stabilizing element at low voltages. Further, as mentioned above, since a high temperature process of 1000° C. or more is required during firing, there is a problem that a voltage nonlinear element cannot be directly formed on a glass substrate or a circuit board. Furthermore, conventional devices have a large parallel capacitance, making them unsuitable for use as switching elements for liquid crystals, for example.

Means for Solving the Problem In order to solve this problem, the present invention provides an insulating substrate, one electrode provided on the insulating substrate, and an electrode provided on the one electrode. The lower layer side, which is the side, is hardened with an insulating binder, and the upper layer is made of a finely powdered semiconductor material with a thin insulating coating hardened with the other electrode made of conductive paste. It is characterized by this.

Effect: According to this configuration, a large voltage nonlinearity index α can be obtained even in a low current range, and the varistor voltage can also be controlled by the amount of insulating binder, so the distance between the electrodes can be narrowed. (several tens of micrometers or less), and an element suitable for lower voltage can be obtained very easily. Furthermore, since it can be made by curing the applied paint at a low temperature, it is possible to form elements directly on a circuit board, and it is expected to have a wide range of applications unimaginable for ZnO varistors and the like. Furthermore, since the obtained device is made of solidified semiconductor material in the form of fine powder, there is point contact between the fine powders of each semiconductor material, and since the contact area is basically small, the parallel capacitance is small. Thus, it is possible to provide an element that is optimal as a switching element for devices such as liquid crystals.

Example Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 shows an example of the manufacturing process for obtaining the device of the present invention. After firing fine particulate zinc oxide with a particle size of 0.05 to 1 μm at 700 to 1300°C without crushing, the sintered ZnO is heated to a particle size of 0.5 to 50 μm (average particle size of 1 to 1 μm). 10μm), and 0.05~10m01% of cobalt oxide was added to the ZnO fine powder,
Heat treatment was performed at 350° C. for 10 to 60 minutes to form an insulating film of cobalt oxide on the surface of the ZnO fine powder. At this time,
It was observed that a thin Co2O3 insulating film was formed on the surface of the finely powdered ZnO with a thickness of approximately several tens to several reentrants. Next, since the ZnO fine powders with the Co2O3 insulating coating formed on their surfaces adhered to each other with weak force, they were loosened in a mortar or pot mill to form a fine powder. Next, Z
Low melting point glass powder and an organic binder were added to nO as an insulating binder for bonding between the fine powders and mixed.

Here, the binder is a low melting point glass powder in an amount of 5 to 2 wt% based on the fine powder of ZnO, and it is mixed with the organic binder in an equal weight, for example,
It was made into a paint form. Here, ethyl cellulose was used as the organic binder, and the solid content was diluted to 10 wt % with respect to the solvent (for example, terpineol).

Next, as shown in FIG. 2, the paint obtained as described above is applied onto a glass substrate 2 provided with an ITO (indium tin oxide) electrode 1 by, for example, screen printing, and heated to a temperature of 300 to 650°C. Heat treatment was performed in the air for 10 to 30 minutes. Next, the other electrode 3 was formed by screen printing carbon paste to obtain an element of the present invention.

FIG. 2 is an enlarged sectional view of the voltage nonlinear element 4, and 5
6 is a ZnO fine powder, 6 is a Co2O5 insulating coating applied to the surface of the ZnO fine powder 5, and 7 is an insulating binder that mechanically connects the ZnO fine powder 5 on the lower layer side, which is the ITO electrode 1 side. The fine powders 60 on the lower layer side are solidified together by the low melting point glass 7 as a binder. Further, the ZnO fine powders 5 on the upper layer side are solidified together by electrodes 3 made of the carbon paste.

Next, the voltage-current characteristics of the voltage nonlinear element created as described above will be explained. First, Figure 3 shows the second
The voltage-current characteristics of the configuration shown in the figure are compared with those of a conventional ZnO varistor.

The element of the present invention is produced by first firing zinc oxide at 700°C,
To this, 0.6 mo1% of Co2O3 was added.
-1 After heat treatment at 900"C for 60 minutes, the average particle size was 5
In a mixture of ZnO fine powder of ~10 μm and low melting point glass fine powder manufactured by Okuno Pharmaceutical Co., Ltd. (20 wt% relative to the ZnO fine powder) and the above organic binder in equal weight, the device area was set between 1 and 1 electrodes. The characteristics are shown when the distance is 30 μm. Now, the voltage of the voltage nonlinear element -
As is well known, the current characteristics are approximately expressed by the following equation.

■ -Kv Here, E is the current flowing through the element, ■ is the voltage between the electrodes of the element, K is a constant corresponding to the resistance value of the specific resistance, and α is the exponent of the voltage nonlinear characteristic mentioned above. The larger the voltage nonlinearity index α is, the better the voltage nonlinearity is.

As shown in the characteristics in Figure 3, the conventional ZnO varistor shown in characteristic B has a voltage nonlinearity index α in the low current region.
is small, and cannot function as a good voltage nonlinear element at a current of 10 A or less. On the other hand, the voltage nonlinearity index α of the device of the present invention shown by the characteristics is large even in the low current range, indicating that it can sufficiently function as a voltage nonlinearity device even in the current range of about 10 1. ing. In addition, normally, in order to express the varistor characteristics of a ZnO varistor, for example, the voltage that appears between the electrodes when a current of 1 mA is passed through the element is called the varistor voltage Vjmm, and this varistor voltage v11nm and the above voltage non-linearity The index α is used. As mentioned above, in the device of the present invention, the voltage nonlinearity index α is large even in the low current range, and the varistor voltage is, for example, v1 μA as shown in FIG.
It can be expressed as ) In this way, in the present invention, the varistor voltage can be made low because firstly, the element thickness of the voltage nonlinear element 4 can be reduced, and furthermore, as shown in FIG. Since the voltage non-linear element 4 on the lower layer side is hardened with the low melting point glass 7 as an agent, and the voltage non-linear element 4 on the upper layer side is hardened with the carbon electrode 3, the distance between the electrodes can be substantially narrowed. This is because the element can be formed by At this time, if the amount of the low melting point glass 7 is small, the degree to which the carbon electrode 3 penetrates into the voltage nonlinear element 4 on the upper layer side increases, and the distance between the electrodes is more substantially narrowed to form an element. Because you can
This allows the bias voltage to be lowered even further.

Furthermore, although the reason why the voltage nonlinearity index α is large even in the low current range in the device of the present invention is not clear at present, the low melting point of the insulating binder is Because it is hardened with glass 7,
This is thought to be due to the fact that there is point contact between the respective semiconductor materials, the contact area is small, and the bonding agent is insulating, so the leakage current is small.

Here, the characteristics shown in Fig. 3 are obtained by changing the distance between the electrodes by 3 as described above.
This is for an element with a thickness of 0 μm;
This is because the average particle size of O fine powder is relatively large, 5 to 1 μm, and cannot be made any narrower. That is, the average particle diameter of the ZnO fine powder is 0.3
The inventors have found that if a material with a diameter of ~3 μm is used, it is possible to create an element with an interelectrode distance of approximately 10 μm or less, and even in that case, good characteristics as shown in Figure 3 can be obtained. was confirmed by experiment.

FIG. 4 shows how the varistor voltage v1 μm, the voltage nonlinearity index α, and the parallel capacitance C change when the amount of cobalt oxide added is changed in the present invention. Here, other conditions such as the firing temperature of zinc oxide were the same as those in the case of FIG. 3.

As shown in FIG. 4, in the device of the present invention, the parallel capacitance of the conventional ZnO varistor is 10oo to 20,000.
Although it is a PF, it is very small.

The reason why this parallel capacitance C is small in the device of the present invention is that the contact area between the semiconductor materials is small, as described above.

In addition, Table 1 shown below shows the varistor voltage v1 when the amount of cobalt oxide added and the heat treatment temperature are changed in the present invention.
2 is a table showing how μm, voltage nonlinear index α, and parallel capacitance C change.

11''-n13.+>' As is clear from Table 1 and Figure 4 above, it can be seen that each characteristic value depends on the amount of cobalt oxide added and the heat treatment temperature. Addition amount is 0.05
Particularly good characteristics were shown at ~3 mo1%. In addition, the heat treatment temperature varies depending on the amount of cobalt oxide added, but the temperature is 600 to 13
It showed good characteristics in the range of 50'C. If the heat treatment temperature is outside the above temperature range, for example, below 600'C, it may be difficult to form a sufficient insulating film, and if the temperature exceeds 1350'C, the voltage non-linearity index α will be below the required value. This is the reason why good characteristics cannot be obtained.

In addition, in the above embodiment, the semiconductor material is
Although ZnO has been described as an example, it goes without saying that other semiconductor materials may be used. Similarly, the material constituting the insulating film is not limited to Co2O3, and may include Ad and Ti.

Metal oxides such as Sr, Mg, Ni, Cjr, Si, etc. or organometallic oxides of these metals may be used, and these may be used alone or in combination.Furthermore, a bond that solidifies the fine powder semiconductor material may be used. As a drug,
An extra insulating organic adhesive consisting of a combination of glass powder and an organic binder may also be used, as well as a thermosetting resin such as polyimide resin, phenolic resin, furan resin, urea resin, melamine resin.

Unsaturated polyester resins, diallyl phthalate resins, epoxy resins, polyurethane resins, silicone resins, etc. may also be used.

Furthermore, in Example 2, the case where glass powder alone was used as the binder was shown, but it is also possible to use a combination of glass powder and the above-mentioned insulating organic adhesive; for example, glass powder After heat-treating and bonding the ZnO fine powder, the organic adhesive is printed from the top of the element,
The element can be formed by filling the element into the element.

Furthermore, although the elements and electrodes were formed by screen printing in the above embodiments, other coating methods such as spraying, dipping, etc. may also be used.

15/\-7' First, ZnO in the form of fine particles, which is an inorganic semiconductor, was heat-treated and pulverized to form a fine powder, and then Co2O3, which is an insulating inorganic compound, was added, and then heat-treated.
This can be done by directly adding the inorganic compound to the inorganic semiconductor fine powder and omitting the processing steps of firing and pulverizing the inorganic semiconductor fine particles.

Effects of the Invention As is clear from the above explanation, the voltage nonlinear element according to the present invention has a large voltage nonlinearity index α in the low current region, and an element with small parallel capacitance can be obtained.
This makes it possible to provide an element that is optimal as a switching element for devices such as liquid crystals and devices with low current consumption. In addition, since the device can be formed by narrowing the distance between the electrodes, a device with a low varistor voltage can be obtained, and the varistor voltage can also be controlled by the amount of insulating organic adhesive or the amount of glass powder. Coupled with the large nonlinearity index α, the conventional ZnO varistor can be used as a protection element or a voltage stabilizing element at low voltages.

Furthermore, since the applied paint can be cured at low temperatures and easily manufactured, elements can be directly formed on circuit boards or glass substrates. The voltage nonlinear element of the present invention having such various characteristics can be expected to have a wide range of applications unimaginable for conventional ZnO varistors, and has great industrial potential.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the manufacturing process of a voltage non-linear element according to the present invention, FIG. 2 is an enlarged sectional view showing an embodiment of the voltage non-linear element according to the present invention, and FIG. 3 is a diagram showing an example of the manufacturing process of a voltage non-linear element according to the present invention. Figure 4 shows the voltage-current characteristics of the device and the conventional ZnO varistor, and shows the voltage nonlinearity index α, varistor voltage v1 μm, and parallel capacitance C when the amount of Co2O3 added is changed in the device according to the present invention. FIG. 3 is a diagram showing how things change. DESCRIPTION OF SYMBOLS 1...ITO electrode, 2...Glass substrate, 3...17'\-NO ZnO fine powder, 6...Co2O3 insulation coating, 7
・Old...Low melting point glass (binder). Name of agent: Patent attorney Toshio Nakao Haga 1 person No. 3
Figure Ichishi Voltage (V)

Claims (1)

[Claims] An insulating substrate, one electrode provided on the insulating substrate, a lower layer side provided on the one electrode side, which is the one electrode side, is hardened with an insulating bonding agent, and an upper layer side is solidified with an insulating bonding agent. 1. A voltage nonlinear element comprising a finely powdered semiconductor material coated with a thin insulating film and hardened by the other electrode made of conductive paste.