JPH0262005A - Sheet-shaped varistor - Google Patents

Abstract

PURPOSE:To obtain a sheet-shaped varistor which is suitable for a low voltage by a method wherein a varistor powder is dispersed in a thermoplastic resin or in a mixture of the thermoplastic resin and a thermoset resin and this dispersed substance is formed into a thin film on a flexible insulating film. CONSTITUTION:A varistor powder 5 is dispersed in a thermoplastic resin, in a thermosetting resin or in a mixture of these resins. This dispersed substance is formed into a thin film on a flexible insulating film 1. A fine powdery semiconductor substance whose outer periphery has been coated with a thin insulating film is used as the powder 5. Then, it is possible to obtain the powder whose voltage nonlinear index is large in a low current region and to form an element whose interelectrode distance is narrow. Thereby, it is possible to obtain the element which is suitable for a low voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sheet-like varistor whose resistance value changes depending on applied voltage, and is used for voltage stabilization, abnormal voltage control, electrostatic protection, etc.

Conventional technology Conventional varistors are made of zinc oxide (ZnO) or bis oxide.
x (Bi2O5), cobalt oxide (Co2O3), mangaf oxide (MnO2), 77 f mon (5b
1000-135 by adding oxides such as 205)
There are various types including ZnO varistors sintered at 0'C. Among them, ZnO varistors are most commonly used as semiconductor elements on circuit boards or as protection elements for electrical and communication equipment because they have a large voltage nonlinearity index α and surge resistance (Japanese Patent Publication No. 19472/1983). (see official bulletin).

Problems to be Solved by the Invention In such conventional varistors, including ZnO varistors, there is a limit to reducing the element thickness (less than several hundred μm). There is a limit to how low the voltage (expressed in V1mm) can be, and it cannot be used as a protection element for low voltage ICs or as a voltage stabilizing element at low voltages. Further, as described above, since a high temperature process of 1000° C. or higher is required for firing, there is a problem that a varisque element cannot be directly formed on a glass substrate or a circuit board.

In addition, there is a limit to the size of the shape, and there are problems in that it cannot be mounted directly on fine-pitch circuit wiring or electrode patterns of 1 mm or less, and cannot be used on high-density substrates due to space constraints. Further, conventional devices have a large capacitance and are unsuitable for use in communication equipment, which is becoming increasingly high-frequency, for example.

Means for Solving the Problems In order to solve this problem, the present invention provides that a varistor powder is dispersed in a thermoplastic resin, a thermosetting resin, or a mixture of these resins, and the powder is dispersed in a flexible insulating material. It is formed in the form of a thin film on a film. Further, the varistor powder is constructed using a finely powdered semiconductor material having a thin insulating coating applied to the outer periphery.

Effect: According to this configuration, a large voltage non-linearity index α can be obtained even in a low current range, and the device can be formed with a narrow distance between electrodes, making it extremely easy to create a device suitable for low voltage. It will be obtained. In addition, since it can be easily manufactured by pasting or crimping onto pre-formed electrodes, the varistor can be directly formed on the circuit board, allowing for a wide range of applications unimaginable with ZnO varistors. This is something to look forward to. Furthermore, since it is a solidified form of semiconductor material in the form of fine powder, there is point contact between the fine powders of each semiconductor material, and the contact area is small, resulting in a small parallel capacitance, which is useful for high-frequency communication equipment. This means that we can provide the best barista for you.

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

First, fine particulate zinc oxide with a particle size of 0.05 to 1.071 m is fired at 700 to 13 oO℃, and then the sintered ZnO is heated to a particle size of 0.6 to 50.0 μm (average particle size 1 ~10μm), and added Bi2 to the ZnO fine powder.
O,, Co2O3, MnO2 and 5b205 in a total amount of 0.05 to 10. Omo1% added, 600-1350
A heat treatment was performed at ℃ for 10 to 60 minutes to form an insulating film of these oxides on the surface of the ZnO fine powder. Here, on the surface of the fine powder ZnO, an insulating film of the above-mentioned oxide is formed on the surface of the ZnO.
It was observed that it was formed thinly, with a thickness of several hundred people.

Next, since the ZnO fine powder group with the oxide insulating film formed on its surface adhered to each other with weak force, it was loosened in a mortar or pot mill to form a fine powder.

Next, an insulating binder (resin binder) for bonding between the fine powders was added to the finely powdered ZnO with the oxide insulating film formed on the surface obtained as described above, and the mixture was mixed. . Here, the resin components as a binder include 30 parts by weight of epoxy resin (Ebicor #a2s manufactured by Shell Chemical Co., USA) as a thermosetting resin, and 30 parts by weight of pheno-μ resin (manufactured by Matsushita Electric Works Co., Ltd.). , 4 parts by weight of thermoplastic polymeric polyester resin (manufactured by Japan Synthetic Rubber Industry Co., Ltd.) was dissolved in methyl ethyl ketone to prepare a solution with a solid content of approximately 30%, and this was mixed with ZnO fine powder, for example. The mixture was mixed and dispersed by weight to form a paint. Next, as shown in FIG. 1, the paint obtained as described above is applied to a polyethylene terephthalate (hereinafter simply referred to as PET) film (or copper foil sheet) 1 as a flexible insulating film by, for example, screen printing. Apply and heat to 85℃
This was pre-dried for 60 minutes to obtain Varistor 2, and a sheet-like varistor was produced. Further, the sheet-like varistor obtained as described above was placed in a thin film form on the above-mentioned PET film 1 on a glass substrate 4 provided with an ITO (indium tin oxide) electrode 3, as shown in FIG. The formed varistor 2 is cut into an appropriate size, and the varistor 2 is cut into a suitable size.
With the surface facing ITO electrode 3, temperature 150℃, pressure 4c)k
A sheet-like varistor was formed on the glass substrate 4 by thermocompression bonding at g/- for 30 seconds.

FIG. 3 is an enlarged cross-sectional view of a sheet-like varistor, in which 5 is a ZnO fine powder, 6 is an oxide insulating coating applied to the surface of the ZnO fine powder 6, and 7 is a mechanical layer between the ZnO fine powders 5. This is an insulating binder (resin) that binds together, and the ZnO fine powders 5 are solidified together by this binder 7.

Next, the voltage-current characteristics of the sheet-like varistor produced as described above will be explained. First, Figure 4 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 1000°C,
This includes Bi2O5, CO2O5, MnO2 and 5b2
0.2mo1% each of o5, total amount of shims 0.8m
After heating the ZnO fine powder with an average particle size of 5 to IQ/1 m and the above binder in equal weights, the element area was adjusted to 1-1 between the ITO electrodes. The distance (indicated by L in Figure 2) is 3
Q 71m shows the characteristics when the element area (the total area of two adjacent electrodes including the distance between the electrodes) is set to 1-. Now, as is well known, the voltage-current characteristics of a voltage nonlinear element are approximately expressed by the following equation.

I - K V': t Here, E is the current flowing through the element, V 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. Furthermore, the larger the voltage nonlinearity index α, the better the voltage nonlinearity.

As shown in the characteristics in Figure 4, the conventional ZnO varistor shown by 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 characteristic curve 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 A. ing. Furthermore, in order to express the varistor characteristics of a ZnO varistor, for example, the voltage that appears between the electrodes when a current of 11 nAOT flows through the element is expressed as the varistor voltage vt.
This varistor voltage 'l'1mm and the voltage non-linearity index α are used. As mentioned above, in the device of the present invention, the voltage non-linearity index α is large even in the low current range, and the varistor voltage is changed to v1, for example, as shown in FIG.
It can be expressed in μm.

In this way, in the present invention, the varistor voltage can be made low because the element can be formed by narrowing the distance between the electrodes.

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, it is possible to This is thought to be due to the fact that since it is solidified, there is point contact between the respective semiconductor materials, so the contact area is small, and the bonding agent is insulating, so leakage current is small. Here, the characteristics shown in Figure 4 are for an element with an inter-electrode distance of 3071 m as described above, but this is because the average particle size of the ZnO fine powder is relatively large, 5 to 10 μm. This is because it cannot be made any narrower. That is,
If ZnO fine powder with an average particle diameter of 0.3 to 3.0 μm is used, it is possible to create an element with an inter-electrode distance of about 10 μm or less, and even in that case, as shown in Figure 4. The inventor of the present invention confirmed through experiments that excellent characteristics can be obtained.

FIG. 5 shows B-work 205 in the present invention. CO2O3゜M
It shows how the varistor voltage v1,7m, the voltage non-linearity index α, and the parallel capacitance Be change when the amount of a added to nO2 and 5b2o3 is changed. Here, other conditions such as the firing temperature of zinc oxide were the same as those in the case of FIG. 4. As shown in FIG. 5, in the device of the present invention, the parallel capacitance is 1000 to 20
00QpF, which is extremely small. The reason why this parallel capacitance 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, in the above embodiment, the semiconductor material is
Although the explanation has been made using ZnO as an example, it goes without saying that other semiconductor materials may be used. Similarly, materials constituting the insulating film include Bi2O5, C
It is not limited to only o2O3, MnO2, and 5b205, but includes all of Bi, Go, Mn, and Sb as main components, as well as Al, Ti, Sr, and Mg.
, Ni.

Metal oxides such as Or and Si, or compounds containing these metals can be used alone or in combination.

Furthermore, as an insulating binder for solidifying a finely powdered semiconductor material, there are, of course, four types of insulating binders other than the resins in the above embodiments, including thermosetting resins such as furan resin, urea resin, and melamine resin. , unsaturated polyester resin, diallyl phthalate resin, polyurethane resin, silicone resin, etc. may also be used.

In addition, in the above embodiments, a fine powder semiconductor substance with a thin insulating coating on the outer periphery is used as the varistor powder, and this is dispersed in a mixture of a thermoplastic resin and a thermosetting resin. Even if the varistor powder is dispersed in a thermoplastic resin, a thermosetting resin, or a mixture of these resins, the sheet-like varistor that is the object of the present invention can be provided.

Effects of the Invention As is clear from the above explanation, the voltage nonlinear element of the present invention has a large voltage nonlinearity index α in the low current range, and an element with small parallel capacitance can be obtained, so it is suitable for high frequency applications. This makes it possible to provide an element that is optimal for use in increasingly advanced communication equipment. In addition, since the device can be formed with a narrow distance between the electrodes, a low varistor voltage can be obtained, which, combined with the large voltage nonlinearity index α mentioned above, cannot be achieved with conventional ZnO varistors. It can be used as a protection element for low voltage ICs or a voltage stabilizing element at low voltages. Furthermore, it can be easily manufactured without requiring high-temperature processes when solidifying with a binder to form elements, and since the elements are formed on a flexible insulating film, they can be easily fabricated on circuit boards. A sheet-like varistor can be easily formed on a glass substrate. As described above, the sheet-like varistor of the present invention having the characteristics of Type 4 can be expected to have a wide range of applications that are unimaginable for conventional ZnO varistors, and has great industrial potential.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the sheet-like varistor according to the present invention, FIG. 2 is a cross-sectional view showing an example in which the sheet-like varistor of the present invention is provided on a glass substrate, and FIG. 3 is a cross-sectional view showing an example of the sheet-like varistor according to the present invention. FIG. 4 is a diagram showing the voltage-current characteristics of the sheet-like varistor of the present invention and a conventional ZnO varistor, and FIG. 5 is a diagram showing the voltage-current characteristics of the sheet-like varistor of the present invention, MnO2, 5b205
FIG. 3 is a diagram showing how the voltage non-linearity index α, the varistor voltage v1□, and the parallel capacitance C change when the total addition of the voltage is changed. 1... POET film, 2... Varistor, 3... ITO electrode, 4... Mark glass substrate, 5... ZnO fine powder, 6... ...Oxide insulation film, 7. River...Binder. Name of agent: Patent attorney Shigetaka Awano (1 person)
Figure Mubarista Figure 3 / PET Film Figure - Land and Electric Power (V)

Claims (2)

[Claims] (1) A sheet characterized by having varistor powder dispersed in a thermoplastic resin, a thermosetting resin, or a mixture of these resins, and formed into a thin film on a flexible insulating film. barista. (2) A sheet-like varistor according to claim (1), characterized in that a finely powdered semiconductor material having a thin insulating coating on the outer periphery is used as the varistor powder.