JP2007258311A - Varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance surge voltage absorption effect of an annular ceramic varistor, and to enhance high frequency noise suppression effect. <P>SOLUTION: First through third main electrodes are provided on one major surface 10 of an annular varistor element 1, having a high resistance layer 1b comprising an oxide on the surface of a semiconductor layer 1a, and an annular auxiliary electrode 5 is provided on the other major surface 11. Surge voltage absorption effect and high-frequency noise suppression effect are enhanced, by setting the resistance per unit length of the auxiliary electrode 5 lower than the resistance per unit length of the main electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a varistor that is suitable for eliminating sparks in a small motor, and more particularly to a reduced reoxidation type semiconductor porcelain varistor or a similar varistor.

A conventional typical ring-shaped reductive re-oxidation type semiconductor porcelain varistor includes a ring-type reductive re-oxidation type semiconductor porcelain varistor body mainly composed of strontium titanate (SrTiO ₃ ), and 3 provided on this surface. And main electrodes.

It is disclosed in Patent Document 1 that a common electrode (auxiliary electrode) is provided on the back surface of the varistor element body in order to suppress a decrease in capacitance in a high frequency band (10 kHz or more) of the above typical ring-shaped varistor. Has been. However, the common electrode (auxiliary electrode) of the varistor is formed of the same material and the same thickness as the three main electrodes on the surface. Moreover, in this patent document 1, the relationship between the resistance value of the common electrode (auxiliary electrode) and the surge voltage suppression effect is not mentioned.
Japanese Utility Model Publication No. 3-6804

The problem to be solved by the present invention is that the surge voltage suppression effect of a conventional varistor is not necessarily sufficient.

The present invention for solving the above-described problems includes a semiconductor layer having one and the other main surfaces facing each other, a high resistance layer covering the one and the other main surfaces of the semiconductor layer, and the semiconductor A plurality of main electrodes disposed on the one main surface of the layer via the high resistance layer; and a plurality of main electrodes disposed on the other main surface of the semiconductor layer via the high resistance layer. An auxiliary electrode having a portion facing the electrode, and the auxiliary electrode has a resistance value per unit length lower than that of the main electrode.

In addition, as shown in Claim 2, it is desirable that the auxiliary electrode is formed thicker than the main electrode.
According to a third aspect of the present invention, the auxiliary electrode is preferably made of a material having a higher conductivity than the main electrode.
The high resistance layer is also formed on a side surface of the semiconductor layer, and the auxiliary electrode is disposed on at least a part of the side surface of the semiconductor layer via the high resistance layer. It is desirable that

According to the present invention, the surge voltage suppression effect can be enhanced by a simple method in which the resistance value per unit length of the auxiliary electrode is made lower than that of the main electrode.

Next, an embodiment of the present invention will be described with reference to FIGS.

The ring-shaped varistor of the first embodiment of the present invention shown in FIGS. 1 to 4 includes a ring-shaped reduced reoxidation type semiconductor ceramic varistor element body 1, first, second and third main electrodes 2, 3, 4. And the auxiliary electrode 5. The varistor element body 1 includes a low resistance semiconductor layer 1a made of a ring-shaped semiconductor ceramic, the entire outer periphery of the semiconductor layer 1a, that is, one main surface 6, the other main surface 7, the outer peripheral side surface 8, and the inner And a high resistance layer 1b covering the side surface 9 on the circumferential side. The semiconductor layer 1a has a low resistance that can be regarded as an electrical conductor. The high resistance layer 1b is made of an oxide layer of a semiconductor ceramic and has a sufficiently higher resistivity than the semiconductor layer 1a.

Next, an example of a method for forming the varistor element body 1 will be described.
First, 3 to 30 mol% of at least one of calcium titanate (CaTiO ₃ ) and barium titanate (BaTiO ₃ ), niobium (Nb) and lanthanum (La) with respect to strontium titanate (SrTiO ₃ ). And at least one of oxide powders of tantalum (Ta) and 0.05 to 0.50 mol%, and at least one oxide of copper (Cu), molybdenum (Mo), and manganese (Mn) 0.05 to 0.50 mol% of the powder was added to make a total of 100 mol%, and the mixture was mixed in a wet ball mill for 15 hours.
Next, after drying said mixture at 150 degreeC in air | atmosphere, PVA (polyvinyl alcohol) was added as a binder, and it mixed and granulated, and obtained raw material powder.
Next, the above ring-shaped molded body was fired at 1350 ° C. for 3 hours in a reducing atmosphere composed of 96% by volume of nitrogen (N ₂ ) and 4% by volume of hydrogen (H ₂ ), and then 1000 ° C. in the air. A varistor element body 1 was obtained by heat treatment (reoxidation treatment) for 3 hours.

The first, second and third main electrodes 2, 3 and 4 are made of a conductor layer, and a conductive paste comprising 77% by weight of Ag (silver) and 23% by weight of Zn (zinc) is applied to the varistor element body 1. It is formed by printing a thick film on one main surface 10 and baking it, and has a thickness of about 15 μm.

The auxiliary electrode 5 can also be called a common electrode or a back electrode, and is formed in a ring shape so as to have portions facing the first, second and third main electrodes 2, 3, 4. . The auxiliary electrode 5 is composed of a conductor layer, and is formed by printing a well-known Ag (silver) paste on the other main surface 11 of the varistor element body 1 in a ring shape and baking it. It is thicker than the second and third main electrodes 2, 3, 4, for example, 20 μm. The resistance value of the auxiliary electrode 5 between the first position P1 and the second position P2 in FIG. 4 is about 30 mΩ.

The auxiliary electrode 5 is formed of a material having higher conductivity than the first to third main electrodes 2 to 4 and is formed thicker than the first to third main electrodes 2 to 4. Therefore, the resistance value per unit length (for example, 1 mm) of the auxiliary electrode 5 in the circumferential direction of the ring-shaped varistor element body 1 is the circumferential direction of the first, second and third main electrodes 2, 3, 4. Smaller than the resistance value per unit length (for example, 1 mm).

When using the completed varistor, for example, as shown in FIG. 5, conductive connection members 23 and 24 are connected to the first and second main electrodes 2 and 3 via solder or conductive bonding materials 21 and 22. Similarly, a connection member is connected to the third main electrode 4 not shown in FIG. 5 via solder or a conductive bonding material. The connecting members 23 and 24 can be welded or bonded to the first and second main electrodes 2 and 3 without using the solder or the conductive bonding materials 21 and 22.

FIG. 6 is an equivalent circuit of the varistor of FIG. The first and second terminals T1, T2 in FIG. 5 correspond to the first and second main electrodes 2, 3 in FIG. Since the direction of current flowing through the first and second main electrodes 2 and 3 is in the thickness direction, the resistance in the thickness direction is extremely small. Therefore, in FIG. 6, the resistances of the first and second main electrodes 2 and 3 are ignored.
The first and second variable resistors R1 and R2 in FIG. 6 indicate voltage-dependent variable resistance components based on the high resistance layer 1b between the first and second main electrodes 2 and 3 and the semiconductor layer 1a. C1 and C2 indicate capacitor components existing in parallel with the first and second variable resistors R1 and R2, respectively. The third and fourth variable resistors R3, R4 are voltage dependent based on the high resistance layer 1b between the semiconductor layer 1a and the portion of the auxiliary electrode 5 facing the first and second main electrodes 2, 3. The variable resistance component is represented, and C3 and C4 represent capacitor components existing in parallel with the third and fourth variable resistors R3 and R4, respectively.
The first resistor R11 is a resistance of the semiconductor layer 1a in the first current path 25 indicated by a broken line in FIG. The second resistor R12 is a resistance of the auxiliary electrode 5 in the second current path 26 indicated by a broken line in FIG. In the present invention, the auxiliary electrode 5 is formed so that the second resistance R12 is as small as possible.

The current in the first current path 25 in FIG. 5 is equal to the first terminal T1, the first variable resistor R1 (and the capacitor C1), the first resistor R11, the second variable resistor R2 (and the capacitor C2) in FIG. ) And the second terminal T2. The current in the second current path 26 of FIG. 5 is the same as that of the first terminal T1, the first variable resistor R1 (and the capacitor C1), the third variable resistor R3 (and the capacitor C3), and the second resistor in FIG. R12, the fourth variable resistor R4 (and capacitor C4), the second variable resistor R2 (and capacitor C2), and the second terminal T1 flow.

FIG. 7 is a waveform diagram showing the surge voltage absorption effect of the varistor of Example 1 and the varistor of the comparative example shown in FIGS. The varistor voltage waveform of Example 1 when the voltage shown by the waveform A in FIG. The surge voltage absorption waveform of a conventional varistor without the auxiliary electrode 5 is C. As in Patent Document 1, the surge voltage absorption waveform of a conventional varistor in which the resistance value per unit length of the auxiliary electrode 5 is the same as that of the first to third main electrodes 2 to 4 is D. As is clear from the comparison of the waveforms B, C, and D in FIG. 7, the varistor according to Example 1 has the best surge voltage absorption effect.
In order to enhance the surge voltage absorption effect, it is important to reduce the resistance between the first and second terminals T1, T2 of the varistor. When the value of the second resistor R12 is reduced according to the present invention, the resistance between the first and second terminals T1 and T2 is effectively reduced, the surge voltage absorption effect is improved, and the noise suppression effect in the high frequency band is also achieved. improves.
When the varistor shown in Example 1 having a large surge voltage absorption effect is used for eliminating the sparks of the motor, the back electromotive force dI / dt generated from the coil in the motor can be well suppressed, and the life of the motor can be extended. It is possible to reduce the noise of the motor at a high frequency and to reduce the impulse noise generated from the motor.

Next, a varistor according to the second embodiment will be described with reference to FIG. However, in FIG. 8, parts that are substantially the same as those in FIG.

The varistor of FIG. 8 has a modified auxiliary electrode (back electrode) 5a. The auxiliary electrode 5 a is provided not only on the other main surface 11 of the varistor element body 1 but also on the outer peripheral side surface 12. Therefore, the area of the auxiliary electrode 5a in FIG. 8 is larger than the area of the auxiliary electrode 5 in FIG. As a result, the capacitance corresponding to the third and fourth capacitors C3 and C4 in FIG. 6 increases, and the value corresponding to the second resistor R12 in FIG. 6 decreases, thereby improving the surge voltage absorption effect. .

The present invention is not limited to the above-described embodiments, and for example, the following modifications are possible.
(1) In Example 1 and Example 2, the resistance value per unit length is reduced by changing both the thickness and material of the auxiliary electrodes 5 and 5a to the first to third main electrodes 2 to 4. However, the resistance value per unit length can be changed by changing only the thickness or only the material. When the resistance value is changed depending on the thickness, it is desirable that the thickness of the first to third main electrodes 2 to 4 is 3 to 10 μm, and the thickness of the auxiliary electrodes 5 and 5 a is 15 to 30 μm.
(2) In Example 1 and Example 2, the first to third main electrodes 2 to 4 are formed by printing and baking a conductive paste composed of 77% by weight of Ag (silver) and 23% by weight of Zn (zinc). At the same time, the auxiliary electrodes 5 and 5a are formed by printing and baking Ag (silver) paste, but the first to third main electrodes 2 to 4 are formed by baking Ag (silver) paste. 5,5a may be formed by printing and baking a conductive paste composed of 77% by weight of Ag (silver) and 23% by weight of Zn (zinc). In this case, by setting the thickness of the first to third main electrodes 2 to 4 to 15 μm and the thickness of the auxiliary electrodes 5 and 5 a to 50 μm, for example, the resistance value per unit length of the auxiliary electrodes 5 and 5 a can be reduced. The resistance value per unit length of the first to third main electrodes 2 to 4 is set lower than that of the first to third main electrodes 2 to 4, and the surge voltage absorbing effect is obtained as in the first and second embodiments.
(3) A mixture of 77% by weight of Ag (silver) and 23% by weight of Zn (zinc), Cu (copper), or Ag for both the first to third main electrodes 2 to 4 and the auxiliary electrodes 5 and 5a (Silver).
(4) The first to third main electrodes 2 to 4 can be Cu electrodes, and the auxiliary electrodes 5 and 5a can be Ag electrodes.
(5) The resistance value between the first and second positions P1, P2 of the auxiliary electrodes 5, 5a can be adjusted preferably in the range of 10 to 40 mΩ.
(6) The auxiliary electrode 5 can be extended to the inner peripheral side surface 13 of the varistor element body 1 shown in FIG.
(7) The high resistance layer 1b on either or both of the outer peripheral side surface 8 and the inner peripheral side surface 9 of the ring-shaped semiconductor layer 1a can be removed.
(8) Only two main electrodes or more than three main electrodes can be provided on one main surface 10 of the varistor element body 1.

It is sectional drawing which shows the ring-shaped reduction | restoration re-oxidation type semiconductor ceramic varistor according to Example 1 of this invention in the AA line part of FIG. It is sectional drawing which shows the varistor of Example 1 by the BB line of FIG. 1 is a plan view showing a varistor of Example 1. FIG. It is a bottom view of the varistor of FIG. It is sectional drawing which shows the state which connected the varistor of FIG. 1 to the external circuit. 1 is a schematic equivalent circuit diagram of a varistor of Example 1. FIG. It is a wave form diagram which shows the surge voltage absorption effect of the varistor of Example 1, and the varistor of a comparative example. It is sectional drawing which shows the varistor of Example 2 similarly to FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Varistor element | base_body 1a Semiconductor layer 1b High resistance layer 2,3,4 The 1st, 2nd and 3rd main electrode 5,5a Auxiliary electrode

Claims (4)

A semiconductor layer having one and other main surfaces facing each other; a high resistance layer covering the one and other main surfaces of the semiconductor layer; and the high layer on the one main surface of the semiconductor layer. Auxiliary having a plurality of main electrodes arranged via a resistance layer and a portion arranged via the high-resistance layer on the other main surface of the semiconductor layer and facing the plurality of main electrodes With electrodes,
The auxiliary electrode has a resistance value per unit length lower than that of the main electrode. The varistor according to claim 1, wherein the auxiliary electrode is formed thicker than the main electrode. The varistor according to claim 1, wherein the auxiliary electrode is made of a material having a higher conductivity than the main electrode. The high resistance layer is formed also on a side surface of the semiconductor layer, and the auxiliary electrode is disposed on at least a part of the side surface of the semiconductor layer via the high resistance layer. The varistor according to 1 or 2 or 3.

Images