JP5286037B2 - Varistor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a voltage nonlinear resistance element, that is, a varistor having a structure in which an ohmic electrode is formed on a semiconductor ceramic having varistor characteristics, and a method for manufacturing the same.

  Titanium oxide (TiO2) -based semiconductor ceramics, strontium titanate (SrTiO3) -based semiconductor ceramics, zinc oxide (ZnO) -based semiconductor ceramics, and the like have varistor characteristics. When a varistor is formed using a semiconductor ceramic having this kind of varistor characteristics, it is desirable to form an ohmic electrode on the surface of the semiconductor ceramic in order to obtain good varistor characteristics.

A conventional typical method for forming an electrode of a semiconductor ceramic having varistor characteristics is disclosed in, for example, Japanese Unexamined Patent Publication No. 2-304909 (Patent Document 1) with silver (Ag) on the surface of a semiconductor ceramic. Applying a paste containing zinc (Zn) and drying to form a first electrode material coating film (ohmic electrode layer), and applying a silver (Ag) paste on the first electrode material coating film And forming the second electrode material coating film (non-ohmic electrode layer) by drying, and then baking the first electrode material coating film and the second electrode material coating film in the atmosphere to form the first electrode material coating film. Forming a conductor layer (ohmic electrode layer) and a second conductor layer (non-ohmic electrode layer). Since the first conductor layer contains zinc (Zn) that is easily oxidized, the solderability is poor. However, the solderability with respect to the varistor electrode is improved by covering the first conductor layer containing zinc (Zn) with the second conductor layer not containing zinc (Zn).
In Patent Document 1, a silver paste for forming a second conductor layer (non-ohmic electrode layer) is used to solve the problem of oxidation of zinc (Zn) in the first conductor layer (ohmic electrode layer). It is disclosed that a substance (Si, B, W) that is more easily oxidized than zinc (Zn) is added.

By the way, it has been difficult to form a first conductor layer (ohmic electrode layer) having good flatness, smoothness and denseness by using an ohmic electrode material made of conventional silver (Ag) and zinc (Zn). In FIG. 1, a paste of ohmic electrode material containing conventional silver (Ag), zinc (Zn) and glass frit is applied on the surface of a strontium titanate (SrTiO ₃ ) -based semiconductor ceramic 1 according to Comparative Example 3 described later. And the state which dried and formed the 1st electrode material coating film 2 is shown. FIGS. 1 and 5 show the case where the first electrode material coating film is formed on the surface of the semiconductor porcelain, and FIGS. 2 and 6 show the first and second conductor layers on the surface of the semiconductor porcelain. Each of the formed ones is created based on a photograph taken with a scanning electron microscope (FE-SEM manufactured by Hitachi).
In FIG. 1, Zn particles 3 having a relatively large particle size are present in the first electrode material coating film 2, and the dispersibility of the Zn particles 3 is poor. As a result, the surface of the first electrode material coating film 2 becomes non-flat with a relatively large height difference H1, and the maximum thickness T1 of the first electrode material coating film 2 becomes relatively large. Further, a paste of non-ohmic electrode material containing silver (Ag) is applied on the surface of the first electrode material coating 2 in FIG. 1 and baked to form on the first conductor layer 2 ′ as shown in FIG. When the second conductor layer 4 is formed and the varistor electrode 5 is completed, the surface of the second conductor layer 4 becomes non-flat with a relatively large height difference H2. In addition, a relatively large gap 6 is generated in the second conductor layer 4. As a result, the total maximum thickness T2 of the first conductor layer 2 ′ and the second conductor layer 4 after electrode baking is relatively large.
Although not clearly shown in FIG. 2, zinc segregates in the vicinity of the surface of the first conductor layer 2 ′, and the adhesion strength of the second conductor layer 4 to the first conductor layer 2 ′ is increased. A decrease occurs.
In addition, since the first conductor layer 2 ′ and the second conductor layer 4 cannot be formed with good reproducibility, the variation in the electrical characteristics of the varistor becomes relatively large. In particular, the varistor voltage changes greatly due to changes in the baking temperature of the varistor electrode.

In addition, with the recent miniaturization and thinning of electronic devices and the like, the varistors are also required to be thin. However, as shown in FIG. 2, when the maximum thickness T2 of the varistor electrode 5 is relatively large, the maximum thickness of the varistor also increases, and the required thin varistor cannot be provided.

As another ohmic electrode of semiconductor porcelain, for example, as disclosed in Japanese Patent Publication No. 58-20201 (Patent Document 2), a paste containing silver (Ag) and aluminum (Al) on the surface of the semiconductor porcelain is used. Those that have been applied and baked are known. However, it cannot make good ohmic contact with the semiconductor ceramic.
JP-A-2-304909 JP 58-20201 A

The problem to be solved by the present invention is that the varistor voltage changes relatively greatly due to the change in the baking temperature of the varistor electrode, and the adhesion of the second conductor layer to the first conductor layer is poor. An object of the present invention is to provide a varistor and a method for manufacturing the same that can solve this problem.

The present invention for solving the above problems comprises a semiconductor ceramic having varistor characteristics, and an electrode disposed on the surface of the semiconductor ceramic,
The electrodes, Ri formed of a first conductive layer disposed on a surface of said semiconductor ceramic, a second conductive layer containing the disposed and silver powder on said first conductive layer,
The first conductor layer includes 100 parts by weight of spherical silver powder, 20 to 80 parts by weight of zinc powder with respect to 100 parts by weight of the silver powder, and 0.1 to 5 parts with respect to 100 parts by weight of the silver powder. 0.0 part by weight of aluminum powder and 0.1 to 5.0 parts by weight of glass frit with respect to 100 parts by weight of the silver powder ,
The median diameter D50 of the silver powder is 1.2 μm to 2.7 μm,
The median diameter D50 of the zinc powder is 1.2 μm to 2.7 μm ,
The aluminum powder has a median diameter D50 of 0.1 μm to 3.0 μm and relates to a varistor (voltage nonlinear resistance element).

The varistor is composed of 100 parts by weight of spherical silver powder, 20 to 80 parts by weight of zinc powder, 0.1 to 5.0 parts by weight of aluminum powder, and 0.1 to 5 on the surface of a semiconductor ceramic having varistor characteristics. .0 containing glass frit of parts, the silver powder of median diameter D50 of 1.2Myuemu～2.7Myuemu, the median diameter D50 of the zinc powder is 1.2Myuemu～2.7Myuemu, the median diameter of the aluminum powder Applying a first electrode material paste having a D50 of 0.1 μm to 3.0 μm and then drying to form a first electrode material coating;
Forming a second electrode material coating the second electrode material paste containing silver powder is coated on the first electrode material coating,
Preferably, the first electrode material coating film and the second electrode material coating film are baked to form a first conductor layer and a second conductor layer.
Also, the baking temperature of the first electrode material coating and the second electrode material coating, have to want to be 540 ° C. - 620 ° C..
Also, the aluminum powder of the first electrode material paste is preferably comprised of particles of smaller average particle size than said zinc powder.

The present invention has the following effects.
(A) According to the present invention, when aluminum powder is further added to the first electrode material paste containing silver powder, zinc powder and glass frit, the distribution of zinc particles in the first conductor layer after baking is uniform. become. This makes it possible to form a small electrode that is in ohmic contact with the semiconductor ceramic. In other words, the characteristic variation becomes small when a small or thin varistor is mass-produced.
(A) Since the change in the varistor voltage due to the change in the baking temperature of the varistor electrode is relatively small, the characteristic variation is small when the varistor is mass-produced.
(C) Since the distribution of zinc particles in the first conductor layer after baking is uniform, the adhesion of the second conductor layer to the first conductor layer is improved.

Next, examples and comparative examples of the present invention will be described.

In order to manufacture a ring type varistor for protecting electronic components from abnormally high voltages, a ring type semiconductor ceramic 11 shown in FIGS. 3 and 4 was formed. The semiconductor ceramic 11 can be selected from a titanium oxide (TiO ₂ ) -based semiconductor ceramic, a strontium titanate (SrTiO ₃ ) -based semiconductor ceramic, a zinc oxide (ZnO) -based semiconductor ceramic, and the like that have varistor characteristics. In this embodiment, the main component consisting of strontium titanate (SrTiO ₃ ) and calcium titanate (CaTiO ₃ ) is added to the subcomponent (addition) consisting of niobium oxide (Nb ₂ O ₅ ) and yttrium oxide (Y ₂ O ₃ ). A well-known varistor porcelain material mixed with a small amount of (agent) was prepared, and PVA (polyvinyl alcohol) as an organic binder was further added thereto and granulated to obtain a porcelain material powder for forming the semiconductor porcelain 11. Next, the porcelain material powder was filled into a ring-shaped mold, and was pressed into a ring shape by a press device. Next, a well-known reduction firing and reoxidation firing were performed on the ring-shaped ceramic material molded body to obtain a surface-reoxidized varistor element body, that is, a semiconductor ceramic 11 having varistor characteristics.

Next, on one main surface of the semiconductor porcelain 11 having a ring shape, three layers each composed of a first conductor layer 12 ′ (ohmic electrode layer) and a second conductor layer 14 (non-ohmic electrode layer) are formed. A varistor electrode 15 was formed.

Next, a method for forming the varistor electrode 15 according to the present invention will be described in detail.
First, as a first electrode material paste for obtaining a first conductor layer 12 ′ of the varistor electrode 15, that is, an ohmic electrode layer,
100 parts by weight of silver powder,
40 parts by weight of zinc powder 0.25 parts by weight of aluminum powder,
1 part by weight of glass frit,
Vehicle A paste consisting of 57 parts by weight of a mixture was prepared.

The silver powder is preferably a spherical powder having a median diameter D50 of 1.2 μm to 2.7 μm measured with a laser light diffraction / scattering particle size analyzer. In Example 1, a spherical powder having a median diameter D50 of 1.0 μm is used as the silver powder. When the median diameter D50 of the silver powder is smaller than 1.2 μm, the conductivity of the formed conductor layer is lowered, and when it is larger than 2.7 μm, the flatness of the surface of the electrode material coating film is lowered.

The ratio of the zinc powder to 100 parts by weight of the silver powder is not limited to 40 parts by weight, preferably 20 to 80 parts by weight, and more preferably 30 to 70 parts by weight. When the zinc powder is less than 20 parts by weight, the ohmic property of the first conductor layer 12 ′ to the semiconductor ceramic 11 is deteriorated, the adhesion of the first conductor layer 12 ′ to the semiconductor ceramic 11 is deteriorated, and the varistor voltage is low. It becomes difficult to create an element. On the other hand, if the zinc powder exceeds 80 parts by weight, the adhesion of the first conductor layer 12 'to the semiconductor porcelain 11 and the adhesion between the first conductor layer 12' and the second conductor layer 14 are poor. Further, the first conductor layer 12 ′ becomes brittle.
The zinc powder preferably has a median diameter D50 measured by a laser light diffraction / scattering particle size analyzer of 1.2 μm to 2.7 μm, more preferably 1.5 μm to 2.5 μm. The zinc powder is preferably a spherical powder. The median diameter D50 of the zinc powder of Example 1 is a spherical powder of 1.6 μm. When the median diameter D50 of the zinc powder is smaller than 1.2 μm, aggregation tends to occur and the pot life of the electrode material paste is reduced, and the amount of metallic zinc component is also reduced. If it is larger than 2.7 μm, the printability of the first electrode material paste is poor and the film thickness becomes non-uniform, and the adhesion of the first conductor layer 12 ′ after baking to the semiconductor ceramic 11 is deteriorated, and The flatness and denseness of the first conductor layer 12 ′ are deteriorated, and the maximum thickness Tb of the varistor electrode 15 is increased.
It is desirable that 80% by volume or more of the zinc powder has a particle size in the range of 0.6 μm to 3.5 μm and has a sharp particle size distribution. By sharpening the particle size distribution of the zinc powder, the zinc powder is uniformly distributed in the first electrode material paste, so that the flatness and denseness of the first conductor layer 12 ′ are improved.
The zinc powder preferably has a content of Pb (lead) and Cd (cadmium) as impurities of less than 50 ppm. When the impurity of zinc powder increases, it is not preferable in an environmental aspect.

The ratio of the aluminum powder to 100 parts by weight of silver powder is not limited to 0.25 parts by weight, preferably 0.1 to 5.0 parts by weight, more preferably 0.2 to 2.0 parts by weight. . When the aluminum powder is less than 0.1 parts by weight, the effect of delaying the oxidation of zinc in the first electrode material, the effect of uniformly distributing zinc in the first conductor layer after baking, the varistor voltage E ₁₀ value The effect of stabilizing the content is reduced. On the other hand, when the aluminum powder exceeds 5.0 parts by weight, the adhesion of the first conductor layer 12 ′ to the semiconductor ceramic 11 is lowered and the voltage nonlinear coefficient (α) of the varistor is lowered.
The aluminum powder has a median diameter D50 measured by a laser light diffraction / scattering particle size analyzer smaller than the median diameter D50 of the zinc powder, preferably the median diameter D50 is 0.1 μm to 3.0 μm, more preferably 0.2 μm to A spherical powder of 2.0 μm is desirable. The median diameter D50 of the aluminum powder of Example 1 is 1.0 μm. When the median diameter D50 of the aluminum powder is smaller than 0.1 μm, this handling becomes troublesome. When the median diameter D50 is larger than 3.0 μm, the original effect of the aluminum powder cannot be obtained satisfactorily. Segregation of zinc occurs in the layer.

The glass frit is desirably an environment-friendly Pb (lead) -less glass frit of Bi—B—Si, Ba—Si, Na—Si—Al, and Zn—Bi—Si. In Example 1, Bi—B—Si glass frit is used.
The ratio of the glass frit to 100 parts by weight of silver powder is not limited to 1 part by weight, but can be an appropriate amount required by the first electrode material paste, preferably 0.1 to 5.0 parts by weight, more preferably 0.2 to 2.0 parts by weight. If the ratio of the glass frit to 100 parts by weight of silver powder is less than 0.1 parts by weight, the adhesive strength of the first conductor layer after baking is lowered, and if it is more than 5 parts by weight, the electrical characteristics are deteriorated.

The vehicle is a paste component of the first electrode material paste, and preferably contains an organic binder (resin) and an organic solvent.
As the resin used for the vehicle, thermoplastic, thermosetting resin, or the like can be used. Further, as the resin, a thermoplastic resin is more preferable because the amount of the resin or its decomposition product remaining in the conductor layer after baking is small.
Examples of the thermoplastic resin include acrylic resin, ethyl cellulose, nitrocellulose, polyester, polysulfone, phenoxy resin, and polyimide.
Examples of thermosetting resins include amino resins such as urea resins, melamine resins, and guanamine resins; epoxy resins such as bisphenol A type, bisphenol F type, phenol novolac type, and alicyclic type; oxetane resins; resol type, novolac type Such phenol resins are preferred. In the case of an epoxy resin, even when a self-curing resin is used, a curing agent or curing accelerator such as amines, imidazoles, acid anhydrides or onium salts can be used. It can also function as a curing agent for epoxy resins.
The resins can be used alone or in combination of two or more.
The organic solvent used in the vehicle is not particularly limited, but is preferably selected according to the type of resin. Examples of the organic solvent include aromatic hydrocarbons; ketones; lactones; ether alcohols; corresponding esters such as acetate ester; and diesters of dicarboxylic acid. An organic solvent can be used individually or in combination of 2 or more types.
The vehicle of Example 1 consists of 4 parts by weight ethylcellulose and 53 parts by weight butyl carbitol per 100 parts by weight silver powder.
The ratio of the vehicle (the total of the organic solvent and the organic binder) to 100 parts by weight of silver powder is not limited to 57 parts by weight, and may be an appropriate amount required by the first electrode material paste, preferably 20 to 80 weights. Parts, more preferably 30 to 70 parts by weight.

The first electrode material paste is obtained by uniformly kneading silver powder, zinc powder, aluminum powder, glass frit, and vehicle, for example, with a roll mill. In addition, a plasticizer, the additive mentioned later, etc. can be added to a 1st electrode material paste as needed.
Examples of the additive include a dispersion aid, a leveling agent, a thixotropic agent, an antifoaming agent, and a silane coupling agent.
Examples of the dispersion aid include aliphatic polyvalent carboxylic acid esters; unsaturated fatty acid amine salts; surfactants such as sorbitan monooleate; and polyesteramine salts; polymer compounds such as polyamide. Examples of the silane coupling agent include substituted propyltrialkoxysilane, substituted propylmethyl dialkoxysilane, and the like, and can be selected according to the type of electrode material, resin, and semiconductor ceramic to which the electrode is bonded.

Next, the first electrode material paste is applied on one main surface of the semiconductor ceramic 11 in a predetermined pattern by a screen printing method, dried at 150 ° C., and the first electrode material coating film 12 before baking shown in FIG. Got. The maximum thickness Ta of the first electrode material coating film 12 is 20 μm, which is thinner than the maximum thickness T1 of the conventional first electrode material coating film 2 of FIG. The height difference Ha of the surface of the first electrode material coating film 12 is 2 μm, which is smaller than the height difference H1 of the conventional first electrode material coating film 2 of FIG. Further, when observed with a scanning electron microscope, the Zn particles 13 were uniformly distributed in the first electrode material coating film 12, and there were no large Zn particles as shown in FIG. The particle size distribution and median diameter D50 of the Zn particles 13 were measured using a Microtrack HRA MODEL 9320-X100 laser beam diffraction / scattering particle size analyzer manufactured by Microtrack.
Note that the drying temperature of the first electrode material paste is not limited to 150 ° C., and can be changed, for example, in the range of 100 ° C. to 300 ° C. Further, the maximum thickness Ta of the first electrode material coating film 12 can be changed according to the requirements of the varistor.

Next, as a second electrode material paste for forming a second electrode material coating film on the first electrode material coating film 12, that is, a non-ohmic electrode material paste, silver powder dispersed in a vehicle The known silver paste was applied on the first electrode material coating film 12 by a screen printing method. The second electrode material paste was applied so as to cover not only the upper surface of the first electrode material coating film 12 but also the side surfaces. As the silver powder of the second electrode material paste, a spherical powder having a distribution with a particle size of 0.05 to 3.0 μm measured by the laser light diffraction / scattering particle size analyzer was used. Of course, the particle size of the silver powder of the second electrode material paste can be changed in the same manner as the first electrode material paste. As the vehicle for the second electrode material paste, ethyl cellulose and butyl carbitol were used in the same manner as the first electrode material paste. However, as the organic solvent for the vehicle of the second electrode material paste, an organic solvent selected from α-terpineol, BCA (butyl carbitol acetate), butyl cellosolve, etc. is used, and methyl cellulose, butyl cellulose, PVA (polyvinyl) are used as the organic binder (resin). What was selected from alcohol etc. can also be used. The vehicle ratio with respect to 100 parts by weight of silver powder in the second electrode material paste is preferably 20 to 80 parts by weight.

Next, the semiconductor porcelain 11 having the first electrode material coating film 12 and the second electrode material coating film is put in a baking furnace (tunnel furnace) and kept in an air atmosphere and subjected to a baking process at a temperature of 580 ° C. for 60 minutes. 4 and 6, the first conductor layer 12 ′ and the second conductor layer 14 after the baking treatment were obtained. The first conductor layer 12 'is formed based on the first electrode material paste, and the second conductor layer 14 is formed based on the second electrode material paste. The baking temperature of the first and second electrode material coatings is preferably set in the range of 540 ° C to 620 ° C, more preferably 560 ° C to 600 ° C. The baking time is preferably set in the range of 30 to 120 minutes. In addition, when there exists a temperature change during the said baking time, it is desirable to hold | maintain a peak temperature for 3 to 5 minutes. Further, the atmosphere at the time of baking is not limited to the air atmosphere, but can be changed to an oxidizing atmosphere similar to the air atmosphere or a non-oxidizing atmosphere.

FIG. 6 is a cross-sectional view created based on a photograph of a part of the varistor manufactured according to Example 1 taken with a scanning electron microscope (FE-SEM manufactured by Hitachi). The maximum thickness Tb of the varistor electrode 15 composed of the first conductor layer 12 ′ and the second conductor layer 14 is 35 μm, and the maximum height difference Hb of the surface of the second conductor layer 14 is 2 μm. Therefore, the maximum thickness Tb of the varistor electrode 15 manufactured according to Example 1 of FIG. 6 is thinner than the maximum thickness T2 of the conventional varistor electrode 5 shown in FIG. Further, the maximum height difference Hb of the surface of the varistor electrode 15 manufactured according to Example 1 of FIG. 6 is smaller than the maximum height difference H2 of the conventional varistor electrode 5 shown in FIG. Further, the second conductor layer 14 of the varistor electrode 15 shown in FIG. 6 does not have a portion corresponding to the relatively large gap 6 in the conventional second conductor layer 4 shown in FIG. Therefore, the electrode 15 of FIG. 6 is superior to the conventional varistor electrode 5 of FIG. 2 in terms of denseness and smoothness (flatness). When the maximum thickness Tb of the varistor electrode 15 is thin, the varistor can be thinned or miniaturized. When the smoothness (flatness) of the varistor electrode 15 is good, connection of an external circuit to the varistor electrode 15 can be achieved easily and satisfactorily.

The varistor voltage E ₁₀ of the varistor according to Example 1 was 5.1V. The varistor voltage E ₁₀ is a voltage between the terminals of the varistor pair when a current of 10 mA is passed through the varistor.

The voltage nonlinear coefficient (α) of the varistor according to Example 1 was 4.0. The voltage nonlinear coefficient (α) indicates 1 / log (E ₁₀ / E ₁ ). Here, E ₁₀ represents the varistor voltage when the varistor current is 10 mA, and E 1 represents the varistor voltage when the varistor current is 1 mA.

The adhesion strength in the direction of the arrow 20 in FIG. 4 of the second conductor layer 14 with respect to the first conductor layer 12 ′ of the varistor according to the first embodiment, that is, the direction perpendicular to the main surface of the semiconductor ceramic 11 is measured by a method called a peeling test did. The measurement of the adhesive strength will be described in more detail. A tensile piece is soldered to the second conductive layer 14, and the second conductive layer 14 is pulled through the tensile piece in the direction of the arrow 20 in FIG. The force when the body layer 14 was peeled from the first conductor layer 12 ′ was measured, and this force was defined as the adhesive strength. A varistor having an adhesive strength of a predetermined value (for example, 2.5 kg) or more was regarded as an acceptable product. The adhesion strength of the second conductor layer 14 to the first conductor layer 12 'of the varistor according to Example 1 was not less than a predetermined value.

In order to investigate the relationship between the baking temperature of the varistor electrode 15 and the varistor voltage E ₁₀ , the conditions other than the baking temperature were the same as in Example 1, and only three baking temperatures were changed to 580 ° C., 600 ° C., and 620 ° C. create a sample was measured for this varistor voltage E _10, the following results were obtained.
The varistor voltage E ₁₀ of the sample at 580 ° C. is 5.10 (V).
The varistor voltage E ₁₀ of the sample at 600 ° C. is 5.15 (V).
The varistor voltage E ₁₀ of the sample at 620 ° C. was 5.20 (V).
As already described, the varistor voltage E _{10 of} Example 1, that is, the varistor voltage E _{10 at} 560 ° C. is 5.10 (V). The relationship between the baking temperature T and the varistor voltage E _{10 of} Example 1 and similar samples is shown by line A in FIG. Here, for ease of explanation, samples at 580 ° C., 600 ° C., and 620 ° C. also belong to Example 1. In FIG. 7, the line B shows the relationship between the baking temperature T of the varistor electrode according to Example 2 described later and the varistor voltage E _10, and the lines C, D, E, and F follow Comparative Examples 1, 2, 3, and 4 described later. It shows the relationship between the baking temperature T and the varistor voltage E ₁₀ of a conventional varistor electrodes.
As apparent from the line A in FIG. 7, in the varistor according to the first embodiment, the change in the varistor voltage E ₁₀ due to the change in the baking temperature of the varistor electrode is smaller than that in the conventional varistors in the lines C, D, E, and F. . This means that by using the first electrode material paste according to Example 1 in which Al is further added to Ag and Zn, variation in the varistor voltage E ₁₀ due to variation in the baking temperature of the varistor electrode can be reduced. ing. Thus, it is possible to easily mass-produced varistor having a varistor voltage E ₁₀ of the desired range.

As is clear from the above, the varistor according to the first embodiment and the manufacturing method thereof have the following effects.
(1) The aluminum powder added to the first electrode material paste for obtaining the ohmic electrode layer helps to homogenize the distribution of silver, zinc, and aluminum in the first conductor layer after baking. Thereby, even when the area of the varistor electrode 15 is small, it is possible to obtain the varistor electrode 15 having desired characteristics and having desired adhesive strength. Further, the varistor electrode 15 can be reduced in size or thickness. In other words, when the small or thin varistor is mass-produced, the variation in characteristics becomes small.
(2) The aluminum powder of the first electrode material paste improves the sintered state of Ag and Zn during baking and delays the oxidation of Zn. Thereby, the varistor voltage E ₁₀ is stabilized. Further, the adhesive strength of the second conductor layer 14 to the first conductor layer 12 ′ is improved. Also, when the varistor is mass-produced, the variation in characteristics is reduced.
(3) Since the particle size of the aluminum powder is made smaller than the particle size of the zinc powder, the effect of the aluminum powder can be obtained better.

The same method as in Example 1 except that 1 part by weight of the Bi-B-Si glass frit of the first electrode material paste of the varistor of Example 1 was changed to 1 part by weight of Zn-Bi-Si glass frit. Thus, the varistor of Example 2 was prepared, and the same evaluation as in Example 1 was performed. The adhesive strength, smoothness, and denseness of the varistor electrode of Example 2 were almost the same as those of Example 1. Further, the varistor voltage E ₁₀ and the voltage nonlinear coefficient (α) of the varistor of Example 2 were almost the same as those of Example 1. Further, the relationship between the baking temperature T and the varistor voltage E ₁₀ in Example 2 is as shown by the line B in FIG. 7, and was almost the same as that in Example 1.
In addition, when the Ba-Si glass frit and the Na-Si-Al glass frit were used instead of the Bi-B-Si glass frit of the first electrode material paste of the varistor of the example 1, the examples 1 and The same effect as 2 was obtained.

  The varistor of Example 3 was prepared by the same method as in Example 1 except that the zinc powder of the first electrode material paste of the varistor of Example 1 was changed to 20 parts by weight, and the same evaluation as in Example 1 was performed. It was. In Example 3, the same effect as in Example 1 was obtained.

    A varistor of Example 4 was prepared by the same method as in Example 1 except that the zinc powder of the first electrode material paste of Example 1 was changed to 80 parts by weight, and the same evaluation as in Example 1 was performed. Also in Example 4, the same effect as in Example 1 was obtained.

The varistor of Example 5 was created in the same manner as in Example 1 except that the median diameter D50 of the zinc powder of the first electrode material paste of Example 1 was changed to 1.2 μm, and the same evaluation as in Example 1 was made. Was done. In Example 5, the same effect as in Example 1 was obtained.

The varistor of Example 6 was created in the same manner as in Example 1 except that the median diameter D50 of the zinc powder of the first electrode material paste of Example 1 was changed to 2.7 μm, and the same evaluation as in Example 1 was made. Was done. In Example 6, the same effect as that of Example 1 was obtained.

A varistor of Example 7 was prepared by the same method as in Example 1 except that the aluminum powder of the first electrode material paste of Example 1 was changed to 0.1 part by weight, and the same evaluation as in Example 1 was performed. It was. In Example 7, the same effect as in Example 1 was obtained. However, the change in the varistor voltage E ₁₀ due to the change in the baking temperature T of the varistor electrode was larger than the line A in FIG.

A varistor of Example 8 was prepared by the same method as in Example 1 except that the aluminum powder of the first electrode material paste of Example 1 was changed to 3.0 parts by weight, and the same evaluation as in Example 1 was performed. It was. Also in Example 8, almost the same effect as Example 1 was obtained.
In Examples 1 to 8, a varistor having desired characteristics could be obtained even when the baking temperature of the varistor electrode was changed in the range of 540 ° C to 620 ° C.

(Comparative Example 1)
For comparison, a varistor of Comparative Example 1 was prepared in the same manner as in Example 1 except that the aluminum powder was omitted from the first electrode material paste of Example 1, and the same evaluation as in Example 1 was performed. The varistor voltage E ₁₀ of this comparative example 1 is 5.2 V, the voltage nonlinear coefficient (α) is 4.1, and the adhesive strength, smoothness and denseness of the varistor electrode are almost the same as those of the first embodiment. However, the stability of the varistor voltage E ₁₀ was slightly lower than that in Example 1. The change in the varistor voltage E ₁₀ due to the change in the baking temperature of the varistor electrode of Comparative Example 1 is shown by line C in FIG.

(Comparative Example 2)
For comparison, the varistor of Comparative Example 2 was prepared in the same direction as Example 1 except that the aluminum powder of the first electrode material paste of Example 1 was changed to 5.0 parts by weight. Was evaluated. The varistor voltage E ₁₀ of Comparative Example 2 is 4.8 V, which is lower than that of Example 1, the voltage nonlinear coefficient (α) is 3.5, which is lower than that of Example 1, and the smoothness and denseness of the varistor electrode. Although were almost the same as those in example 1, the stability of the adhesive strength and the varistor voltage E ₁₀ of varistor electrodes was slightly lower than in example 1. The change in the varistor voltage E ₁₀ due to the change in the baking temperature of the varistor electrode of Comparative Example 2 is shown by line D in FIG.

(Comparative Example 3)
For comparison, a varistor of Comparative Example 3 was prepared in the same manner as in Example 1 except that the aluminum powder was omitted from the first electrode material paste of Example 1 and the median diameter D50 of the zinc powder was changed to 4.5 μm. The same evaluation as in Example 1 was performed. Varistor voltage E ₁₀ of this Comparative Example 3 is 5.0V, a voltage non-linear coefficient (alpha) is 4.0, the adhesive strength of the varistor electrodes is lower than in Example 1, the smoothness of the varistor electrodes, and The density and the stability of the varistor voltage E ₁₀ were worse than in Example 1. The change in the varistor voltage E ₁₀ due to the change in the baking temperature of the varistor electrode of Comparative Example 3 is shown by line E in FIG.

(Comparative Example 4)
For comparison, a varistor of Comparative Example 4 was prepared in the same manner as in Example 2 except that the Zn—Bi—Si-based glass frit of the first electrode material paste of Example 2 was changed to 6.0 parts by weight. The same evaluation as in Example 2 was performed. Varistor voltage E ₁₀ of this Comparative Example 4 is 4.7V, the voltage non-linear coefficient (alpha) is 3.5, the adhesive strength of the varistor electrodes is lower than in Example 1, smoothness and dense varistor electrode The stability of the varistor voltage E ₁₀ was worse than that of Examples 1 and 2. The change in the varistor voltage E ₁₀ due to the change in the baking temperature of the varistor electrode of Comparative Example 4 is shown by line F in FIG.

(Comparative Example 5)
For comparison, a varistor of Comparative Example 5 was prepared in the same manner as in Example 2 except that the aluminum powder was omitted from the first electrode material paste of Example 2, and the same evaluation as in Example 2 was performed. The varistor voltage E ₁₀ of Comparative Example 5 was 5.2 V, the voltage nonlinear coefficient (α) was 4.1, and the stability of the varistor voltage E ₁₀ was worse than that of Examples 1 and 2.

In order to facilitate understanding, various characteristics of the varistors of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in the following table. In the table below, ◯ indicates the same or almost the same characteristics as Example 1, Δ indicates a slightly worse characteristic than Example 1, and x indicates a significantly worse characteristic than Example 1.
table
E ₁₀ (V) α Adhesive strength Smoothness / denseness E ₁₀ Stability
Example 1 5.1 4.0 ○ ○ ○
Example 2 5.1 4.0 ○ ○ ○
Comparative Example 1 5.2 4.1 ○ ○ ×
Comparative Example 2 4.8 3.5 △ ○ △
Comparative Example 3 5.0 4.0 Δ × ×
Comparative Example 4 4.7 3.5 △ ○ △
Comparative Example 5 5.2 4.1 ○ ○ Δ

From the above table and FIG. 7, the influence of the Zn particle size and Al content in the first electrode material paste on E ₁₀ , α, smoothness, denseness, and adhesive strength of the varistor electrode will be considered.
Comparative Example 1 using Zn having a median diameter D50 of 1.6 μm has higher electrode adhesion strength and smoothness and denseness than Comparative Example 3 using Zn having a median diameter D50 of 4.5 μm.
In Example 1 containing 40 parts by weight of Zn and 0.25 parts by weight of Al with respect to 100 parts by weight of Ag, there is no decrease in E ₁₀ and α as compared with Comparative Example 2 containing 5 parts by weight of Al. high, it can be seen that the fluctuation range of the E ₁₀ is less stable to baking temperature. Further, Comparative Example 1 not containing Al is the adhesive strength and denseness is good, it can be seen that the E ₁₀ varies with respect to the baking temperature increases.
Example 2 containing 40 parts by weight of Zn, 0.25 parts by weight of Al, and 1 part by weight of Zn-Bi-Si glass frit with respect to 100 parts by weight of Ag has higher adhesive strength than that of Comparative Example 3, and is smooth and dense. Property is improved. Further, Comparative Example 4 containing 6 parts by weight of Zn—Bi—Si glass frit can improve the smoothness and denseness, but shows a decrease in E ₁₀ and α, and the adhesive strength. Has also declined. Furthermore, Comparative Example 5 and Zn-Bi-Si-based glass frit containing no Al is used, although the high and smoothness and denseness adhesive strength becomes good, E ₁₀ varies with respect to the baking temperature It is inferior in stability, and there is a risk that yield will be reduced.
Example 2 in which the average particle size of Zn is 1.6 μm, 0.25 part by weight of Al, and 1 part by weight of Zn—Bi—Si-based glass frit is 6 parts by weight of glass frit It can be seen that E ₁₀ and α do not decrease as compared with Comparative Example 4 in FIG. 4, and the fluctuation range of E ₁₀ is small and stable with respect to the baking temperature.

The present invention is not limited to the above-described embodiments, and for example, the following modifications are possible.
(1) As shown by the dotted line in FIG. 4, the ring-shaped auxiliary electrode 21 can be provided on the lower surface of the ring-shaped semiconductor ceramic.
(2) The present invention can also be applied to a plate-like varistor in which electrodes are respectively provided on one main surface and the other main surface of a semiconductor ceramic.
(3) The glass frit and the vehicle can be replaced with those having the same function other than those shown in the examples.
(4) The second conductor layer 14 can be provided only on the first conductor layer 12 ′.
(5) The semiconductor ceramic 11 may be a titanium oxide (TiO 2) -based semiconductor ceramic, a strontium titanate (SrTiO ₃ ) -based semiconductor ceramic, or a zinc oxide (ZnO) -based semiconductor ceramic other than the examples.
(6) Another metal can be added to the 1st and 2nd electrode material paste in the range which does not inhibit the objective of this invention.
(7) Glass frit can be added to the second electrode material paste. As the composition of the glass frit, Si—B glass such as Bi—B—Si glass and Si—B—Zn glass is preferable.
The blending amount of the glass frit is usually 0.01 to 20 parts by weight with respect to 100 parts by weight of the metal powder, the conductor layer obtained by baking the electrode material coating film does not show interfacial peeling, and the second conductive In order not to cause the segregation of the glass component near the surface of the body layer and the soldering defect associated therewith, 0.01 to 5.0 parts by weight is preferable, and 0.01 to 3.0 parts by weight is more preferable.

It is sectional drawing which shows the state which apply | coated the 1st electrode material paste according to the comparative example 3 to a semiconductor ceramic, and dried. It is sectional drawing which shows the state which apply | coated and baked the 1st and 2nd electrode material paste according to the comparative example 3 to a semiconductor ceramic. 1 is a plan view showing a varistor of Example 1. FIG. FIG. 4 is a sectional view taken along line AA in FIG. 3. It is sectional drawing which shows the state which apply | coated the 1st electrode material paste according to Example 1 to the semiconductor ceramic, and dried. It is sectional drawing which shows the state which apply | coated and baked the 1st and 2nd electrode material paste according to Example 1 to a semiconductor ceramic. It is a figure which shows the relationship between the baking temperature and varistor voltage of the electrodes of Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor porcelain 12 1st electrode material coating film 12 '1st conductor layer 14 2nd conductor layer 15 Varistor electrode

Claims (4)

A semiconductor ceramic having varistor characteristics, and an electrode disposed on the surface of the semiconductor ceramic,
The electrodes, Ri formed of a first conductive layer disposed on a surface of said semiconductor ceramic, a second conductive layer containing the disposed and silver powder on said first conductive layer,
The first conductor layer includes 100 parts by weight of spherical silver powder, 20 to 80 parts by weight of zinc powder with respect to 100 parts by weight of the silver powder, and 0.1 to 5 parts with respect to 100 parts by weight of the silver powder. 0.0 part by weight of aluminum powder and 0.1 to 5.0 parts by weight of glass frit with respect to 100 parts by weight of the silver powder ,
The median diameter D50 of the silver powder is 1.2 μm to 2.7 μm,
The median diameter D50 of the zinc powder is 1.2 μm to 2.7 μm ,
The varistor characterized in that the median diameter D50 of the aluminum powder is 0.1 μm to 3.0 μm . 100 parts by weight of spherical silver powder, 20 to 80 parts by weight of zinc powder, 0.1 to 5.0 parts by weight of aluminum powder, and 0.1 to 5.0 parts by weight on the surface of the semiconductor porcelain having varistor characteristics of containing the glass frit, the silver median diameter D50 of the powder 1.2Myuemu～2.7Myuemu, the median diameter D50 of the zinc powder is 1.2Myuemu～2.7Myuemu, the median diameter D50 of the aluminum powder is 0. Applying a first electrode material paste of 1 μm to 3.0 μm and then drying to form a first electrode material coating;
Forming a second electrode material coating the second electrode material paste containing silver powder is coated on the first electrode material coating,
Forming a first conductor layer and a second conductor layer by baking the first electrode material coating film and the second electrode material coating film. The baking temperature of the first electrode material coating and the second electrode material coating method according to claim 2 Symbol mounting varistors characterized in that it is a 540 ° C. - 620 ° C.. Wherein said aluminum powder of the first electrode material paste method according to claim 2 or 3 Symbol placement of the varistor, characterized in that it consists of particles of smaller average particle size than said zinc powder.

Images