TWI416547B - Rheostat and its manufacturing method - Google Patents

Abstract

The invention provides a rheostat, solving the problems that the voltage of the rheostat is changed due to the inhibition of the change of the baking temperature of the rheostat electrode and the adhesiveness of the rheostat electrode is improved. The inventive rheostat comprises a semiconductor porcelain 11 with the rheostat characteristic, and an electrode 15 configured on the surface of the semiconductor porcelain 11. The electrode 15 comprises a first conductor body 12' formed by a first electrode material containing silver powder, zincum powder, aluminium powder and frit, and a second conductor body 14 configured on the first conductor layer and formed by a second electrode material containing silver powder and frit.

Description

Rheostat and manufacturing method thereof

The present invention relates to a varistor which is a voltage non-linear resistance element having a structure in which an ohmic electrode is formed on a semiconductor ceramic having a varistor characteristic, and a method of manufacturing the same.

The ceramic itself has a varistor characteristic, such as a titanium oxide (TiO ₂ )-based semiconductor ceramic, a barium titanate (SrTiO ₃ )-based semiconductor ceramic, and a zinc oxide (ZnO)-based semiconductor ceramic. When a varistor is constructed using such a semiconductor ceramic having a varistor characteristic, in order to obtain good varistor characteristics, it is desirable to form an ohmic electrode on the surface of the semiconductor ceramic.

In the prior art, a method of forming a semiconductor ceramic electrode having a varistor characteristic, as disclosed in Japanese Laid-Open Patent Publication No. Hei 2-304909 (Patent Document 1), includes the step of coating a surface of a semiconductor ceramic with silver. a slurry of (Ag) and zinc (Zn) is dried to form a first electrode material coating film (ohmic electrode layer), and a silver (Ag) paste is applied onto the first electrode material coating film. And drying to form a second electrode material coating film (non-ohmic electrode layer); and thereafter, the first electrode material coating film and the second electrode material coating film are baked in the air, thereby forming the first conductor layer ( The ohmic electrode layer) and the second conductor layer (non-ohmic electrode layer). Since the first conductor layer contains zinc (Zn) which is easily oxidized, the weldability is poor. However, by covering the first conductor layer containing zinc (Zn) with the second conductor layer not containing zinc (Zn), the weldability of the varistor electrode is improved.

Further, the above Patent Document 1 further discloses that in order to solve the problem of zinc (Zn) oxidation of the first conductor layer (ohmic electrode layer), it is added to the silver paste forming the second conductor layer (non-ohmic electrode layer). A substance that is more susceptible to oxidation than zinc (Zn) (Si, B, W).

However, it has been difficult to form a first conductor layer (ohmic electrode layer) having excellent flatness, smoothness, and compactness by the ohmic electrode material containing silver (Ag) and zinc (Zn). 1 shows a state in which an ohmic electrode material containing silver (Ag), zinc (Zn), and glass frit is coated on the surface of a barium titanate (SrTiO ₃ )-based semiconductor ceramic 1 in accordance with Comparative Example 3 to be described later. The slurry is dried to form a first electrode material coating film 2. In addition, FIG. 1 and FIG. 5 are based on a photograph obtained by photographing a cross section of a coating film on which a first electrode material is formed on a surface of a semiconductor ceramic by a scanning electron microscope (FE-SEM Hitachi), and FIG. 2 And Fig. 6 is based on a photograph obtained by photographing a cross section of the first and second conductor layers formed on the surface of the semiconductor ceramic by a scanning electron microscope (FE-SEM Hitachi).

In FIG. 1, the Zn particles 3 having a relatively large particle diameter are present on 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 has a relatively large height difference H1, and the maximum thickness T1 of the first electrode material coating film 2 becomes large. Further, in the case where the slurry of the non-ohmic electrode material containing silver (Ag) is applied onto the surface of the first electrode material coating film 2 of FIG. 1 and baked, as shown in FIG. When the second conductor layer 4 is formed on the first conductor layer 2', when the varistor electrode 5 is completed, the surface of the second conductor layer 4 becomes non-flat with a relatively large height difference H2. Further, a large gap 6 is formed in the second conductor layer 4. As a result, the maximum thickness T2 of the total of the first conductor layer 2' and the second conductor layer 4 after the electrode is baked becomes large.

Further, although not clearly shown in FIG. 2, zinc is segregated in a layered manner 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 lowered.

Further, since the first conductor layer 2' and the second conductor layer 4 are formed without good reproducibility, the difference in electrical characteristics of the varistor becomes large. In particular, the change in the varistor voltage due to the change in the firing temperature of the varistor electrode increases.

In addition, with the miniaturization and thinning of electronic devices and the like in recent years, the varistor is also required to be thinned. However, as shown in Fig. 2, if the maximum thickness T2 of the varistor electrode 5 becomes larger, the maximum thickness of the varistor also becomes large, so that the required thinner varistor cannot be provided.

As the other ohmic electrode of the semiconductor ceramic, for example, it is known that the surface of the semiconductor ceramic is coated with silver (Ag) and aluminum (Al as disclosed in Japanese Patent Publication No. Sho 58-201201 (Patent Document 2). The slurry is baked and baked. However, the above ohmic electrode cannot be made to make good ohmic contact to the semiconductor ceramic.

[Patent Document 1] Japanese Patent Laid-Open No. Hei 2-304909

[Patent Document 2] Japanese Patent Laid-Open No. SHO 58-201201

The problem to be solved by the present invention is that a change in the varistor voltage is greatly caused by a change in the firing temperature of the varistor electrode, and a difference in adhesion between the second conductor layer and the first conductor layer is provided, and an object of the present invention is to provide a A varistor and a method of manufacturing the same that can solve the problem.

The present invention for solving the above problems is a varistor (voltage non-linear resistance element) comprising: a semiconductor ceramic having a varistor characteristic; and an electrode disposed on a surface of the semiconductor ceramic, wherein the electrode comprises: a first conductive a body layer disposed on a surface of the semiconductor ceramic and formed of a first electrode material containing silver powder, zinc powder, aluminum powder, and glass frit; and a second conductor layer disposed on the first conductor layer And formed of a second electrode material containing silver powder.

Preferably, the varistor is formed by coating a first electrode material slurry containing silver powder, zinc powder, aluminum powder, glass frit, and carrier on the surface of the semiconductor ceramic having varistor characteristics. And drying to form a first electrode material coating film; applying a second electrode material slurry containing silver powder and a carrier onto the first electrode material coating film to form a second electrode material coating film; 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.

Further, it is preferable that the first electrode material slurry is a glass frit and a carrier added to 100 parts by weight of the silver powder, 20 to 80 parts by weight of the zinc powder, and 0.1 to 5.0 parts by weight of the aluminum powder, and the first electrode The baking temperature of the material coating film and the second electrode material coating film is 540 ° C to 620 ° C.

Further, it is preferable that the zinc powder has a median diameter D50 of 1.2 to 2.7 μm as the first electrode material slurry.

Further, it is preferable that the aluminum powder of the first electrode material slurry contains particles having an average particle diameter smaller than the zinc powder.

The present invention has the following effects.

(a) According to the present invention, when aluminum powder is further added to the slurry of the first electrode material containing the silver powder, the zinc powder, and the glass frit, the distribution of the zinc particles in the first conductor layer after the baking is uniform. Thereby, a small electrode for ohmic contact with the semiconductor ceramic can be formed. In other words, when the small or thin varistor is produced equivalently, the difference in characteristics is reduced.

(b) The change in the varistor voltage due to the change in the firing temperature of the varistor electrode becomes small, so that the characteristic difference is reduced when the varistor is produced.

(c) Since the distribution of the zinc particles in the first conductor layer after the 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.

[Example 1]

In order to manufacture a toroidal varistor for protecting an electronic component from an abnormally high voltage, an annular semiconductor ceramic 11 as shown in FIGS. 3 and 4 is formed. The semiconductor ceramic 11 can be selected from titanium oxide (TiO ₂ )-based semiconductor ceramics having a varistor property, a barium titanate (SrTiO ₃ )-based semiconductor ceramic, and a zinc oxide (ZnO)-based semiconductor ceramic. In this embodiment, a well-known varistor ceramic material is prepared, and the varistor ceramic material is micro-mixed with a main component containing barium titanate (SrTiO ₃ ) and calcium titanate (CaTiO ₃ ) and contains niobium oxide (Nb ₂ O ₅ ). And a component (additive) of yttrium oxide (Y ₂ O ₃ ), and further adding PVA (Polyvinyl Alcohol, polyvinyl alcohol) as an organic binder to the varistor ceramic material to be granulated, thereby obtaining a semiconductor for forming Ceramic material powder of ceramic 11. Next, the ceramic material powder is filled in a ring-shaped template and press-formed into a ring shape by a pressing device. Then, the annular ceramic material molded body is subjected to a known reduction calcination and reoxidation calcination to obtain a surface reoxidation type varistor element, that is, a semiconductor ceramic 11 having a varistor characteristic.

Next, three varistor electrodes 15 including a first conductor layer 12' (ohmic electrode layer) and a second conductor layer 14 (non-ohmic electrode layer) are formed on one main surface of the annular semiconductor ceramic 11.

Next, a method of forming the varistor electrode 15 according to the present invention will be described in detail.

First, as the first electrode material slurry for obtaining the first conductor layer 12' of the varistor electrode 15, that is, the 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, and glass are prepared. A slurry of a mixture of 1 part by weight and 57 parts by weight of a carrier.

As the silver powder, a spherical powder having a median diameter D50 of 1.2 μm to 2.7 μm is preferably measured by a laser light diffraction scattering particle size analyzer. In the first embodiment, a spherical powder having a median diameter D50 of 1.0 μm was used as the silver powder. When the median diameter D50 of the silver powder is less than 1.2 μm, the conductivity of the formed conductor layer is lowered, and when it is more 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, and is preferably 20 to 80 parts by weight, more preferably 30 to 70 parts by weight. When the amount of 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, and the adhesion of the first conductor layer 12' to the semiconductor ceramic 11 is deteriorated, so that the element having a low varistor voltage is fabricated. Will become difficult. On the other hand, when the zinc powder exceeds 80 parts by weight, the adhesion of the first conductor layer 12' to the semiconductor ceramic 11 and the adhesion between the first conductor layer 12' and the second conductor layer 14 are deteriorated, and further 1 The conductor layer 12' becomes brittle.

For the zinc powder, the median diameter D50 of the laser light diffraction scattering particle size analyzer is preferably from 1.2 μm to 2.7 μm, more preferably from 1.5 μm to 2.5 μm. The zinc powder is preferably a spherical powder. The zinc powder of Example 1 had a median diameter D50 of 1.6 μm. When the median diameter D50 of the zinc powder is less than 1.2 μm, aggregation tends to be easy, and the pot life of the electrode material slurry is reduced, and the amount of the metal zinc component is also lowered. In addition, when the zinc powder median diameter D50 is more than 2.7 μm, the printability of the first electrode material slurry is deteriorated, and the film thickness is uneven, and the sintered first conductor layer 12' is applied to the semiconductor ceramic 11 The adhesiveness is deteriorated, and the flatness and compactness of the first conductor layer 12' are deteriorated, and the maximum thickness Tb of the varistor electrode 15 is increased.

For the zinc powder, it is desirable that it has a particle diameter in the range of 0.6 μm to 3.5 μm in an amount of 80% by volume or more, and has a sharp particle size distribution. By making the particle size distribution of the zinc powder sharp and the zinc powder is uniformly distributed in the first electrode material slurry, the flatness and compactness of the first conductor layer 12' are improved.

Further, as for the zinc powder, it is preferable that the content of Pb (lead) and Cd (cadmium) as impurities is less than 50 ppm. If the impurities of the zinc powder become large, it will be detrimental to the environment.

The ratio of the aluminum powder to 100 parts by weight of the silver powder is not limited to 0.25 parts by weight, and is 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 oxidizing zinc in the first electrode material is delayed, the effect of uniformly distributing zinc in the first conductor layer after baking, and the varistor voltage E ₁₀ value are stabilized. The effect will be reduced. On the other hand, when the amount of 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.

For the aluminum powder, it is desirable to use a spherical powder having a median diameter D50 smaller than that of the zinc powder and a median diameter D50 by a laser light diffraction scattering particle size analyzer. It is preferably 0.1 μm to 3.0 μm, more preferably 0.2 μm to 2.0 μm. The aluminum powder of the first embodiment had a median diameter D50 of 1.0 μm. When the median diameter D50 of the aluminum powder is less than 0.1 μm, the treatment becomes troublesome, and if it is more than 3.0 μm, the original effect of the aluminum powder cannot be satisfactorily obtained, and zinc is generated in the first conductor layer. Segregation.

For the glass frit, Bi-B-Si system, Ba-Si system, Na-Si-Al system, Zn-Bi-Si system without Pb (lead), and glass having environmental factors are considered. material. In the first embodiment, a Bi-B-Si-based glass frit was used.

The ratio of the glass frit to 100 parts by weight of the silver powder is not limited to 1 part by weight, and may be an appropriate amount required for the first electrode material slurry, preferably 0.1 to 5.0 parts by weight, more preferably 0.2 to 2. 2.0 parts by weight. If the ratio of the glass frit to the silver powder of less than 100 parts by weight is less than 0.1 part by weight, the subsequent strength of the first conductor layer after firing may be lowered, and if it is more than 5 parts by weight, the electrical properties may be deteriorated.

The carrier component of the first electrode material slurry of the carrier preferably contains an organic binder (resin) and an organic solvent.

For the resin used in the carrier, a thermoplastic, a thermosetting resin or the like can be used. Further, as the resin, since the residual amount of the resin or the decomposition product thereof in the conductor layer after baking is small, a thermoplastic resin is more preferable.

Examples of the thermoplastic resin include acrylic resin, ethyl cellulose, nitrocellulose, polyester, polyfluorene, phenoxy resin, and polyimine.

As the thermosetting resin, an amine resin such as a urea resin, a melamine resin or a melamine resin; an epoxy resin such as a bisphenol A type, a bisphenol F type, a phenol type or an alicyclic type is preferable. An oxetane resin; a phenolic resin such as a novolac type or a novolak type. In the case of an epoxy resin, even when a self-curing resin is used, a hardener or a hardening accelerator such as an amine, an imidazole, an acid anhydride or a barium salt may be used, or an amine resin or a phenol resin may be used as the epoxy resin. It functions as a hardener for epoxy resin.

The resins may be used singly or in combination of two or more.

The organic solvent used in the carrier is not particularly limited, and it is preferred to select it depending on the kind of the resin. Examples of the organic solvent include aromatic hydrocarbons; ketones; lactones; ether alcohols; acetate-like esters corresponding to the above; and diesters of dicarboxylic acids. The organic solvents may be used singly or in combination of two or more.

The carrier of this Example 1 contained 4 parts by weight of ethyl cellulose and 53 parts by weight of butyl carbitol with respect to 100 parts by weight of the silver powder.

The ratio of the carrier (total of the organic solvent and the organic binder) to 100 parts by weight of the silver powder is not limited to 57 parts by weight, and may be an appropriate amount required for the first electrode material slurry, preferably 20~. 80 parts by weight, more preferably 30 to 70 parts by weight.

The first electrode material slurry can be obtained by uniformly kneading silver powder, zinc powder, aluminum powder, glass frit, and a carrier, for example, in a roll mill. Further, a plasticizer or an additive or the like described later may be added to the first electrode material slurry as needed.

Examples of the additive include a dispersing aid, a leveling agent, a thixotropic agent, an antifoaming agent, a decane coupling agent, and the like.

As the dispersing aid, an aliphatic polycarboxylic acid ester; an unsaturated fatty acid amine salt; a surfactant such as sorbitan monooleate; and a polyesteramine salt; a polymer compound such as polyamine Wait. Examples of the decane coupling agent include a substituted propyltrialkoxydecane, a substituted propylmethyldialkoxydecane, and the like, and can be selected depending on the type of the electrode material, the resin, and the semiconductor ceramic to be bonded to the electrode.

Next, the first electrode material slurry is applied to one main surface of the semiconductor ceramic 11 in a specific pattern by a screen printing method, and dried at 150 ° C to obtain a first electrode before baking shown in FIG. 5 . Material coating film 12. 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 first 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 previous first electrode material coating film 2 of Fig. 1 . Further, when observed by a scanning electron microscope, the Zn particles 13 are uniformly distributed in the first electrode material coating film 12, and there is no large Zn particles as shown in FIG. The particle size distribution and the median diameter D50 of the Zn particles 13 were measured using a laser light scattering scattering particle size analyzer Microtrack HRA MODEL 9320-X100 manufactured by Microtrack.

Further, the drying temperature of the first electrode material slurry is not limited to 150 ° C, and may 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 in accordance with the requirements of the varistor.

Next, a non-ohmic electrode material slurry which is a second electrode material slurry for forming a coating film of the second electrode material on the first electrode material coating film 12 is obtained by dispersing silver powder in a carrier. The known silver paste is applied onto the first electrode material coating film 12 by a screen printing method. Further, the second electrode material slurry is applied so as not to cover the upper surface of the first electrode material coating film 12 and also to cover the side surface. The silver powder of the second electrode material slurry is a spherical powder having a distribution of a particle diameter of 0.05 to 3.0 μm measured by the above-described laser light diffraction scattering particle size analyzer. Of course, the particle diameter of the silver powder of the second electrode material slurry can be changed in the same manner as the first electrode material slurry. As the carrier of the second electrode material slurry, ethyl cellulose and butyl carbitol were used similarly to the first electrode material slurry. However, the organic solvent used as the carrier of the second electrode material slurry is selected from the group consisting of α-terpineol, BCA (Butyl Carbitol Acetate, butyl carbitol acetate), butyl cellosolve (Butyl Cellusolve), and the like. As the organic binder (resin), those selected from the group consisting of methyl cellulose, butyl cellulose, and PVA (polyvinyl alcohol) can also be used. The ratio of the carrier in the second electrode material slurry to 100 parts by weight of the silver powder is preferably from 20 to 80 parts by weight.

Next, the semiconductor ceramic 11 having the first electrode material coating film 12 and the second electrode material coating film is placed in a baking furnace (tunnel kiln), kept in an air atmosphere, and fired at a temperature of 580 ° C for 60 minutes. With the treatment, the first conductor layer 12' and the second conductor layer 14 after the baking treatment shown in FIGS. 4 and 6 are obtained. The first conductor layer 12' is formed based on the first electrode material slurry, and the second conductor layer 14 is formed based on the second electrode material slurry. The baking temperature of the first and second electrode material coating films is preferably set in the range of 540 ° C to 620 ° C, and more preferably in the range of 560 ° C to 600 ° C. Moreover, it is preferable that the above-mentioned baking time is set in the range of 30 to 120 minutes. Further, when there is a temperature change in the above-mentioned baking time, it is desirable to maintain the peak temperature for 3 to 5 minutes. Further, the atmosphere at the time of firing is not limited to the atmospheric atmosphere, and may be changed to an oxidizing atmosphere similar to the atmospheric atmosphere, or a non-oxidizing atmosphere.

Fig. 6 is a cross-sectional view showing a photograph obtained by photographing a part of a varistor manufactured in accordance with Example 1 by a scanning electron microscope (FE-SEM Hitachi). The maximum thickness Tb of the varistor electrode 15 including 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 fabricated in accordance with Embodiment 1 of FIG. 6 is thinner than the maximum thickness T2 of the previous varistor electrode 5 shown in FIG. Moreover, the maximum height difference Hb of the surface of the varistor electrode 15 fabricated in accordance with Embodiment 1 of FIG. 6 is smaller than the maximum height difference H2 of the previous varistor electrode 5 shown in FIG. Further, in the second conductor layer 14 of the varistor electrode 15 of Fig. 6, there is no gap corresponding to the larger gap 6 in the previous second conductor layer 4 shown in Fig. 2 . Therefore, the electrode 15 of FIG. 6 is superior to the previous varistor electrode 5 of FIG. 2 in terms of compactness and smoothness (flatness). If the maximum thickness Tb of the varistor electrode 15 is thin, the varistor can be made thinner or smaller. When the smoothness (flatness) of the varistor electrode 15 is excellent, the connection of the external circuit to the varistor electrode 15 can be easily and satisfactorily achieved.

The varistor voltage E ₁₀ of the varistor according to Embodiment 1 is 5.1V. In addition, the varistor voltage E ₁₀ is a voltage between the terminals of one of the varistor when the current of 10 mA flows through the varistor.

The voltage nonlinear coefficient (α) of the varistor according to Embodiment 1 was 4.0. In addition, the voltage nonlinear coefficient (α) represents 1/log (E ₁₀ /E ₁ ). Here, E ₁₀ represents the varistor voltage when the varistor current is 10 mA, and E1 represents the varistor voltage when the varistor current is 1 mA.

The direction of the arrow 20 of FIG. 4 of the first conductor layer 12', that is, the direction perpendicular to the main surface of the semiconductor ceramic 11, is determined by a method called a peeling test, in which the second conductor layer 14 of the varistor according to the first embodiment is applied to the first conductor layer 12'. Then the intensity. When the measurement of the adhesion strength is further described in detail, the stretched sheet is welded to the second conductor layer 14, and the second conductor layer 14 is stretched in the direction of the arrow 20 of FIG. 4 via the stretched sheet, and the measurement is performed. 2 The force at which the conductor layer 14 is peeled off from the first conductor layer 12', and this force is taken as the bonding strength. A varistor having a strength equal to or higher than a specific value (for example, 2.5 kg) is used as a good product. The adhesion strength of the second conductor layer 14 of the varistor according to the first embodiment to the first conductor layer 12' is a specific value or more.

In order to investigate the relationship between the firing temperature of the varistor electrode 15 and the varistor voltage E ₁₀ , the conditions other than the firing temperature were set to be the same as in Example 1, and only the firing temperature was changed to 580 ° C, 600 ° C, and 620 ° C. The sample was measured for the varistor voltage E ₁₀ to obtain the following results.

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).

Further, as described above, as the varistor voltage E of Example ₁₀ i.e. 1 560 ℃ varistor voltage E of Example ₁₀ is 5.10 (V). The relationship between the firing temperature T of the sample of Example 1 and a sample similar thereto and the varistor voltage E ₁₀ is as shown by line A of FIG. Here, for convenience of explanation, the samples of 580 ° C, 600 ° C, and 620 ° C are all referred to as Embodiment 1. Line B in Fig. 7 shows the relationship between the sintering temperature T of the varistor electrode and the varistor voltage E ₁₀ according to the second embodiment to be described later, and the lines C, D, E, and F indicate the comparative examples 1, 2, and 3, which will be described later. 4 of the previous relationship of a varistor electrodes sticking temperature T of the varistor voltage E _10.

The line A in FIG. 7 of the apparent, in accordance with the varistor Example of 1, changes due to changes in the sticking temperature of the varistor electrodes caused varistor voltage E ₁₀ of less than lines C, D, E, F of the antecedent varistor. The above-mentioned case means that the difference of the varistor voltage E ₁₀ due to the difference in the sintering temperature of the varistor electrode can be reduced by using the first electrode material slurry according to the first embodiment in which Al is further added to Ag and Zn. . Thereby, the varistor having the varistor voltage E ₁₀ of the desired range can be easily mass-produced.

According to the above, the varistor according to the first embodiment and the method of manufacturing the same have the following effects.

(1) The aluminum powder added to the first electrode material slurry for obtaining the ohmic electrode layer contributes to the uniform distribution of the respective distributions of silver, zinc, and aluminum in the first conductor layer after the sintering. Thereby, even in the case where the area of the varistor electrode 15 is small, the varistor electrode 15 having the desired characteristics and having the desired bonding strength can be obtained. Moreover, miniaturization or thinning of the varistor electrode 15 can be achieved. In other words, when the small or thin varistor is produced equivalently, the difference in characteristics is reduced.

(2) When the aluminum powder of the first electrode material slurry is sintered, the sintered state of Ag and Zn is good, and the oxidation of Zn is delayed. Thereby, the varistor voltage E _{10 is} stabilized. Further, the adhesion strength of the second conductor layer 14 to the first conductor layer 12' is improved. Moreover, when the varistor is produced equivalently, the difference in characteristics is reduced.

(3) Since the particle diameter of the aluminum powder is smaller than the particle diameter of the zinc powder, the effect of the aluminum powder can be better obtained.

[Embodiment 2]

The same as in Example 1 except that 1 part by weight of the Bi-B-Si-based glass frit of the first electrode material slurry of the varistor of Example 1 was changed to 1 part by weight of the Zn—Bi—Si-based glass frit. The varistor of Example 2 was produced by the method, and the same evaluation as in Example 1 was carried out. The bonding strength, smoothness, and compactness of the varistor electrode of the second embodiment were substantially the same as those of the first embodiment. Further, the varistor voltage E ₁₀ and the voltage nonlinear coefficient (α) of the varistor of the second embodiment are also substantially the same as those of the first embodiment. Further, the relationship between the baking temperature T and the varistor voltage E _{10 in} the second embodiment is as shown in the line B of FIG. 7, and is substantially the same as the relationship of the first embodiment.

In addition, when a Ba-Si-based glass frit and a Na-Si-Al-based glass frit are used instead of the Bi-B-Si-based glass frit of the first electrode material slurry of the varistor of the first embodiment, the same can be obtained as in the first embodiment. And 2 the same effect.

[Example 3]

The varistor of Example 3 was produced in the same manner as in Example 1 except that the zinc powder of the first electrode material slurry of the varistor of Example 1 was changed to 20 parts by weight, and the same evaluation as in Example 1 was carried out. According to the third embodiment, substantially the same effects as those of the first embodiment can be obtained.

[Example 4]

The varistor of Example 4 was produced in the same manner as in Example 1 except that the zinc powder of the first electrode material slurry of Example 1 was changed to 80 parts by weight, and the same evaluation as in Example 1 was carried out. According to the fourth embodiment, substantially the same effects as those of the first embodiment can be obtained.

[Example 5]

The varistor of Example 5 was produced in the same manner as in Example 1 except that the zinc powder median diameter D50 of the first electrode material slurry of Example 1 was changed to 1.2 μm, and the same procedure as in Example 1 was carried out. Evaluation. According to the fifth embodiment, substantially the same effects as those of the first embodiment can be obtained.

[Embodiment 6]

The varistor of Example 6 was produced in the same manner as in Example 1 except that the zinc powder median diameter D50 of the first electrode material slurry of Example 1 was changed to 2.7 μm, and the same procedure as in Example 1 was carried out. Evaluation. According to the sixth embodiment, substantially the same effects as those of the first embodiment can be obtained.

[Embodiment 7]

The varistor of Example 7 was produced in the same manner as in Example 1 except that the aluminum powder of the first electrode material slurry of Example 1 was changed to 0.1 part by weight, and the same evaluation as in Example 1 was carried out. According to the seventh embodiment, substantially the same effects as those of the first embodiment can be obtained. However, the change of the varistor voltage E ₁₀ due to the change in the firing temperature T of the varistor electrode is greater than the line A of FIG.

[Embodiment 8]

The varistor of Example 8 was produced in the same manner as in Example 1 except that the aluminum powder of the first electrode material slurry of Example 1 was changed to 3.0 parts by weight, and the same evaluation as in Example 1 was carried out. According to the eighth embodiment, substantially the same effects as those of the first embodiment can be obtained.

Further, in Examples 1 to 8, even if the sintering temperature of the varistor electrode was changed in the range of 540 ° C to 620 ° C, a varistor having desired characteristics can be obtained.

(Comparative Example 1)

For comparison, a varistor of Comparative Example 1 was produced in the same manner as in Example 1 except that the aluminum powder was omitted from the first electrode material slurry of Example 1, and the same evaluation as in Example 1 was carried out. The varistor voltage E ₁₀ of the comparative example 1 is 5.2 V, the voltage nonlinear coefficient (α) is 4.1, and the subsequent strength, smoothness, and compactness of the varistor electrode are substantially the same as those of the first embodiment, but the stability of the varistor voltage E _{10 is obtained} . Slightly lower than Example 1. The change of the varistor voltage E ₁₀ due to the change in the firing temperature of the varistor electrode of Comparative Example 1 is shown by the line C of FIG.

(Comparative Example 2)

For comparison, the varistor of Comparative Example 2 was produced in the same manner as in Example 1 except that the aluminum powder of the first electrode material slurry of Example 1 was changed to 5.0 parts by weight, and the same procedure as in Example 1 was carried out. Evaluation. The varistor voltage E ₁₀ of the comparative example 2 is lower than 4.8 V of the first embodiment, and the voltage nonlinear coefficient (α) is lower than 3.5 of the first embodiment, and the smoothness and compactness of the varistor electrode are substantially the same as those of the first embodiment. However, the subsequent strength of the varistor electrode and the varistor voltage E _{10 were} slightly lower than those of Example 1. The change of the varistor voltage E ₁₀ due to the change in the firing temperature of the varistor electrode of Comparative Example 2 is shown by the line D of FIG.

(Comparative Example 3)

For comparison, a comparative example was produced in the same manner as in Example 1 except that the aluminum powder was omitted from the first electrode material slurry of Example 1, and the zinc powder median diameter D50 was changed to 4.5 μm. The varistor of 3 was subjected to the same evaluation as in Example 1. The varistor voltage E ₁₀ of the comparative example 3 is 5.0 V, the voltage nonlinear coefficient (α) is 4.0, and the susceptor electrode has a lower bonding strength than that of the first embodiment, and the smoothness, compactness, and varistor voltage E ₁₀ stability of the varistor electrode Both are inferior to Example 1. The change of the varistor voltage E ₁₀ due to the change in the firing temperature of the varistor electrode of Comparative Example 3 is shown by the line E of FIG.

(Comparative Example 4)

For comparison, a varistor of Comparative Example 4 was produced in the same manner as in Example 2 except that the Zn—Bi—Si-based glass frit of the first electrode material slurry of Example 2 was changed to 6.0 parts by weight. The same evaluation as in Example 2. The varistor voltage E ₁₀ of the comparative example 4 is 4.7 V, the voltage nonlinear coefficient (α) is 3.5, and the varistor electrode has a lower bonding strength than that of the first embodiment, and the smoothness and compactness of the varistor electrode are substantially the same as those of the first and second embodiments. The same, but the stability of the varistor voltage E ₁₀ is inferior to that of Embodiments 1 and 2. The change of the varistor voltage E ₁₀ due to the change in the firing temperature of the varistor electrode of Comparative Example 4 is shown by the line F of FIG.

(Comparative Example 5)

For comparison, a varistor of Comparative Example 5 was produced in the same manner as in Example 2 except that the aluminum powder was omitted from the first electrode material slurry of Example 2, and the same evaluation as in Example 2 was carried out. 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 inferior to those of Examples 1 and 2.

For the sake of easy understanding, the characteristics of the varistor of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in the following table. Further, in the following table, ○ indicates the same or substantially the same characteristics as in the first embodiment, Δ indicates that the characteristics are slightly inferior to those of the first embodiment, and × indicates that the characteristics of the first embodiment are significantly deteriorated.

According to the above Table and FIG. 7, investigated the content of Al and the diameter of the first electrode material paste of the Effect of Zn E _10, α, smoothness of varistor electrodes, and the denseness of the resulting adhesive strength.

In Comparative Example 1 using Zn having a median diameter D50 of 1.6 μm, compared with Comparative Example 3 using Zn having a median diameter D50 of 4.5 μm, the electrode had high bonding strength and was excellent in smoothness and compactness.

It is understood that Comparative Example 2 containing 40 parts by weight of Zn and 0.25 parts by weight of Al per 100 parts by weight of Ag, compared with Comparative Example 2 containing 5 parts by weight of Al, has no decrease in E ₁₀ and α, and the strength is high, and E _{10 is} relatively The variation in the firing temperature is small and appears to be relatively stable. Further, in Comparative Example 1 containing no Al, it was found that the strength and the denseness were good, but the variation of E ₁₀ with respect to the baking temperature was increased.

In 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-based glass frit, 100 parts by weight of Ag was used, and the strength was higher than that of Comparative Example 3, and the smoothness and compactness were good. Further, in Comparative Example 4 containing 6 parts by weight of the Zn—Bi—Si-based glass frit, although smoothness and compactness were good, it was found that E ₁₀ and α were lowered, and the strength was also lowered. Further, in Comparative Example 5 which does not contain Al and which uses a Zn—Bi—Si-based glass frit, the strength is high and the smoothness and compactness are good, but the stability of E ₁₀ with respect to the variation of the baking temperature is poor, and thus May cause a decrease in yield.

It is understood that Example 2 in which the average particle diameter of Zn is 1.6 μm and contains 0.25 parts by weight of Al and contains 1 part by weight of the Zn—Bi—Si-based glass frit, compared with Comparative Example 4 in which the glass frit is 6 parts by weight. There is no decrease in E ₁₀ and α, and E ₁₀ is stable with a small variation with respect to the baking temperature.

The present invention is not limited to the above embodiments, and for example, the following modifications are possible.

(1) As shown by the broken line in Fig. 4, an annular auxiliary electrode 21 may be provided under the annular semiconductor ceramic.

(2) The present invention can also be applied to a plate-shaped varistor in which an electrode is provided on one main surface and the other main surface of a semiconductor ceramic.

(3) The glass frit and the carrier may be replaced by those having the same functions as 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 can be a titanium oxide (TiO ₂ )-based semiconductor ceramic, a barium titanate (SrTiO ₃ )-based semiconductor ceramic, or a zinc oxide (ZnO)-based semiconductor ceramic other than the examples.

(6) Other metals may be added to the first and second electrode material pastes without departing from the object of the present invention.

(7) A glass frit may be added to the second electrode material slurry. As the composition of the glass frit, Si-B-based glass such as Bi-B-Si-based glass and Si-B-Zn-based glass is preferable.

The amount of the glass frit is usually 0.01 to 20 parts by weight based on 100 parts by weight of the metal powder, and the conductor layer obtained by the baking of the electrode material coating film does not exhibit interfacial peeling, and the glass component does not occur. The segregation near the surface of the second conductor layer or the welding failure therewith is preferably 0.01 to 5.0 parts by weight, more preferably 0.01 to 3.0 parts by weight.

11. . . Semiconductor ceramic

12. . . First electrode material coating film

12'. . . First conductor layer

14. . . Second conductor layer

15. . . Rheostat electrode

1 is a cross-sectional view showing a state in which a slurry of a first electrode material is applied onto a semiconductor ceramic according to Comparative Example 3 and dried;

2 is a cross-sectional view showing a state in which the first and second electrode material pastes are applied onto a semiconductor ceramic according to Comparative Example 3 and baked;

Figure 3 is a plan view showing the varistor of Embodiment 1;

Figure 4 is a cross-sectional view taken along line A-A of Figure 3;

5 is a cross-sectional view showing a state in which a slurry of a first electrode material is applied onto a semiconductor ceramic according to Example 1 and dried;

6 is a cross-sectional view showing a state in which a first and a second electrode material slurry is applied onto a semiconductor ceramic and baked in accordance with Example 1;

Fig. 7 is a graph showing the relationship between the baking temperature of the electrodes of Examples 1, 2 and Comparative Examples 1, 2, 3, and 4 and the varistor voltage.

11. . . Semiconductor ceramic

15. . . Rheostat electrode

Claims (6)

A varistor comprising: a semiconductor ceramic having a varistor characteristic; and an electrode disposed on a surface of the semiconductor ceramic; the electrode comprising: a first conductor layer disposed on a surface of the semiconductor ceramic, and A first electrode material containing silver powder, zinc powder, aluminum powder, and glass frit; and a second conductor layer disposed on the first conductor layer and formed of a second electrode material containing silver powder. A method of manufacturing a varistor, comprising: coating a first electrode material slurry containing silver powder, zinc powder, aluminum powder, glass frit, and carrier on a surface of a semiconductor ceramic having varistor characteristics, followed by drying And forming a first electrode material coating film; applying a second electrode material slurry containing silver powder and a carrier onto the first electrode material coating film to form a second electrode material coating film; and performing the first The electrode material coating film and the second electrode material coating film are baked to form a first conductor layer and a second conductor layer. The method of producing a varistor according to claim 2, wherein the first electrode material slurry is a glass frit and a carrier added to 100 parts by weight of the silver powder, 20 to 80 parts by weight of the zinc powder, and 0.1 to 5.0 parts by weight of the aluminum powder; The baking temperature of the first electrode material coating film and the second electrode material coating film is 540 ° C to 620 ° C. The method of producing a varistor according to claim 2, wherein the zinc powder of the first electrode material slurry is a laser light diffraction scattering particle size analyzer having a median diameter D50 of 1.2 to 2.7 μm. The method of manufacturing a varistor according to claim 2 or 3, wherein the aluminum powder of the first electrode material slurry is determined by a laser light diffraction scattering particle size analyzer to have a median diameter D50 smaller than a value of the zinc powder. Particle size D50. The method of manufacturing a varistor according to claim 4, wherein the aluminum powder of the first electrode material slurry is determined by a laser light diffraction scattering particle size analyzer to have a median diameter D50 smaller than a median diameter of the zinc powder. D50.