JP4690123B2 - Method for producing zinc oxide laminated varistor - Google Patents

Description

  The present invention relates to a zinc oxide laminated varistor used for removing steep pulse noise such as lightning induction noise, power supply noise generated in various electric and electronic devices, surge, and the like, and a method for manufacturing the same.

  With recent rapid increase in frequency and capacity of electronic devices, various electronic devices such as mobile phones are rapidly spreading. In these devices, voltage limiting elements such as zinc oxide multilayer varistors are widely used as countermeasures against various types of surges, pulse noise, ESD, as well as device circuit protection, operational stability, and noise regulation. Yes.

  A zinc oxide multilayer varistor is generally a sintered body obtained by adding various additives to a basic composition mainly composed of zinc oxide and containing bismuth oxide, and a parallel plate shape inside the sintered body. And metal internal electrodes arranged in a stacked manner. Here, in the metal electrode laminated and disposed inside the sintered body, the sintering temperature of the sintered body is generally 950 to 1300 ° C., and is co-fired with this, so silver / palladium alloy, palladium, platinum, etc. Expensive precious metals must be used. As a result, the production cost is increased, and there are many problems such as the utility cost due to high-temperature firing and the contamination of the furnace with scattered bismuth.

For this reason, a method for manufacturing a zinc oxide multilayer varistor has been proposed in which the sintering temperature of the sintered body is lowered so that inexpensive silver can be used as an internal electrode (Patent Document 1).
Japanese Patent Laid-Open No. 9-320814

  However, the melting point of silver is 960 ° C., and considering the silver migration, the firing temperature of the sintered body is desirably as low as possible, 900 ° C. or less. Moreover, it is necessary not only to be able to perform low-temperature sintering, but also to obtain good varistor electrical characteristics and reliability.

  The present invention has been made in view of the above-described circumstances, and can be fired at 900 ° C. or lower. By employing a silver internal electrode, the cost can be reduced, and good electrical characteristics and reliability can be achieved. It is an object of the present invention to provide a zinc oxide laminated varistor capable of obtaining high performance and a method for producing the same.

The zinc oxide multilayer varistor of the present invention is composed of a sintered body in which zinc oxide is a main component and bismuth oxide is added to the basic composition, and at least copper oxide is added, and is laminated inside the sintered body. And a silver electrode. Here, with respect to 100 mol% of zinc oxide, 0.1 to 1.5 mol% of bismuth oxide and 0.1 to 3.0 mol% of copper oxide are added as an outer layer, and antimony oxide is added in an amount of 0.01 to It was added in an amount of 2.0 mol%, and calcining these raw materials, is characterized in that constituting the sintered body.

  Since copper oxide has a small ionic radius and liquefies at a relatively low temperature, it is effective for promoting low-temperature sintering of a varistor sintered body having a basic composition mainly composed of zinc oxide and containing bismuth oxide. For this reason, since a varistor sintered body can be formed by firing at 900 ° C. or lower, inexpensive silver can be employed as the internal electrode, and a zinc oxide multilayer varistor can be produced at a low manufacturing cost. And by optimizing the additive of the varistor raw material, it is possible to secure good electrical characteristics and reliability while adopting an inexpensive silver electrode.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows an example of the element structure of a zinc oxide laminated varistor. This zinc oxide laminated varistor 10 is obtained by laminating and firing a green sheet 11 containing a zinc paste as a main component and containing an additive such as bismuth oxide and having an internal electrode pattern of silver paste disposed thereon. It is a laminated type sintered body element manufactured in this manner. In the sintered body 11 containing zinc oxide as a main component and containing an additive such as bismuth oxide, silver internal electrodes 12a and 12b are alternately arranged in a parallel plate shape, resulting in an electrode arrangement similar to that of a multilayer capacitor. ing.

  The silver inner electrodes 12a and 12b are connected to the left and right outer electrodes 13a and 13b, respectively. Therefore, the voltage applied between the left and right external electrodes 13 a and 13 b is applied to the varistor sintered body portion between the electrodes 12 a and 12 b arranged in a parallel plate shape inside the varistor sintered body 11. In this embodiment, the voltage limiting element is constituted by four varistor sintered body layers. The external electrodes 13a and 13b are made of silver or the like and are plated with nickel, solder, or tin so that the mountability is good. The zinc oxide multilayer varistor 10 is a surface-mount type component having a size as a standard chip component such as 3.2 mm × 1.6 mm (3216 type).

  A varistor is an element having a voltage limiting function for limiting a voltage when a voltage suddenly flows when an applied voltage exceeds a certain value. The voltage limiting function of the varistor protects the circuits and semiconductor elements of the electrical equipment from abnormal voltages such as static electricity. Conventionally, semiconductor Zener diodes have been used for such applications, but two elements are required and capacitors must be externally attached, requiring a large mounting area. If a varistor is used, the mounting area can be reduced to a half or less, and since it has a large withstand voltage, it exhibits an excellent voltage limiting function against an excessive voltage pulse such as static electricity.

  In the varistor, the resistance value of the sintered body arranged between the electrodes suddenly changes depending on the voltage, and when the voltage exceeds a certain voltage, the current that has hardly flowed until then suddenly flows out. In general, the voltage between varistor terminals when a current of 1 mA flows through the varistor is called a varistor voltage. With a slight change in the varistor voltage, the current changes by a factor of ten. The non-linearity at this time (that is, the current and voltage are linearly related in Ohm's law) is called the α value, and the α value increases as the non-linearity becomes better. The larger the α value, the smaller the standby / operation leakage current and the lower the power consumption, and the less the heat destruction caused by the self-runaway.

On the other hand, the voltage between varistor terminals when a large current (2A, 10A, etc.) flows is called a limiting voltage, and the limiting voltage decreases as the α value increases. The ratio (limit voltage / varistor voltage) to the limit voltage (V _{2A, 10A} ) with respect to the varistor voltage (V _1mA ) is called the limit voltage ratio. The limit voltage indicates how many volts the voltage between the semiconductor elements can be suppressed when a large current such as a surge current flows. The lower the voltage, the higher the circuit protection function.

  On the other hand, the surge resistance is an index that represents the magnitude of the surge current that the element can withstand by detecting whether or not the element is broken by applying a large surge current such as 100A or 1000A. The surge resistance refers to the maximum current value at which the change rate of the varistor voltage is measured within 10% or without breakdown after the surge current is applied.

  In the case of a bismuth-based zinc oxide varistor, the basic composition of the varistor material is zinc oxide as a main component and bismuth oxide added thereto. That is, bismuth, which is a low melting point metal, is used for the grain boundary forming layer of crystal grains mainly composed of zinc oxide. And in order to exhibit a varistor characteristic, generally antimony oxide, manganese oxide, and cobalt oxide which are transition metals are added.

  As described in many literatures and the like, the presence of antimony oxide covers the surface of zinc oxide (ZnO) at a relatively low temperature and inhibits sintering. However, antimony oxide greatly contributes to ensuring the electrical characteristics and reliability of the varistor electrically and physically, and no alternative material is found at present. Therefore, it is difficult to eliminate antimony oxide.

As described above, antimony oxide (Sb ₂ O ₃ ) becomes Sb ₂ O _{4 at a} low temperature, covering the surface of zinc oxide (ZnO) and inhibiting sintering. Not only the reactivity at low temperature but also spinel at high temperature prevents the grain growth. Therefore, many studies have been made and published on the means of performing heat treatment with bismuth oxide in advance so as not to become Sb ₂ O ₄ at a low temperature.

  However, in practice, no matter how much calcining is performed, it is impossible to obtain a sintered body for obtaining stable characteristics at a firing temperature of 900 ° C. or lower, and when it exceeds 900 ° C., the melting point of silver is 960 ° C. In effect, silver migration is accelerated, and deterioration of characteristics is inevitable. Therefore, in order to further promote the sintering, it is a liquid phase sintering material similar to bismuth, but a certain amount of copper oxide having a small ionic radius is added, calcined, and heat treatment is performed at 850 to 880 ° C. Sintering became possible.

  In addition, it is good by optimizing the addition amount of cobalt oxide, manganese oxide, chromium oxide, silicon oxide, boric acid, titanium oxide, germanium oxide, magnesium oxide, aluminum oxide, indium oxide, gallium oxide, rare earth elements, etc. A varistor having excellent electrical characteristics and reliability was obtained.

  Below, the varistor of the present invention will be described with respect to its constituent materials and the evaluation results of the electrical characteristics and reliability of the varistor.

ここで、酸化ビスマス（Ｂｉ_２Ｏ_３）と酸化アンチモン（Ｓｂ_２Ｏ_３）とは、予め５００℃、１時間の仮焼を行い、添加されている。 First, a conventional low-temperature sintered multilayer chip varistor will be described as a comparative example.
The composition ratio of this raw material is as follows. In addition, the addition amount numerical value is an outer mol% with respect to 100 mol% of zinc oxide (ZnO).

Here, bismuth oxide (Bi ₂ O ₃ ) and antimony oxide (Sb ₂ O ₃ ) are preliminarily calcined at 500 ° C. for 1 hour and added.

  Firing was held at a temperature of 880 ° C. for 5 hours. The product shape was 3216 size, the number of internal electrode layers was 4, the internal electrode material was a silver (Ag) 100% paste, and an electrode pattern was formed by screen printing. Three types of low-pressure varistor, medium-pressure varistor, and high-pressure varistor were produced by changing the thickness of the green sheet.

The evaluation results of the electrical characteristics of the manufactured varistor are shown below. The numerical value is the standard deviation σ representing the average value and variation, and the number of samples is 20.

The evaluation results of the reliability characteristics of the produced varistor are shown below. The numerical value of the evaluation result is the average value of the varistor voltage change rate, and the number of samples is 20.

  From the evaluation results of the electrical characteristics and the evaluation results of the reliability test, it has been clarified that baking at 880 ° C. is not sufficient, and good evaluation results cannot be obtained.

  Therefore, in the present invention, since it is premised that a good sintered body can be obtained by firing at 900 ° C. or less, a material composition that can obtain a good sintered body by firing at 900 ° C. or less was examined. Evaluation was performed using TMA which is thermal analysis. The preparation procedure of the sample is shown below.

  First, the raw materials are blended based on Table 1. However, one was not calcined, and the other was a material obtained by calcining bismuth oxide and antimony oxide, which are conventional low-temperature sintering techniques, at 500 ° C. in advance. The composition ratio of the raw materials is the same. Next, the raw material is mixed with a vehicle to produce granulated powder. The composition of the vehicle is composed of 3 wt% PVA and 97 wt% ion-exchanged water. The amount of vehicle input is 20 parts by weight per 100 g of varistor raw material. And it press-molded in the shape of 5 mmphi. The press pressure was 200 MPa for 3 seconds.

  The evaluation temperature produced by the above procedure was evaluated for the sintering temperature using TMA of thermal plus 2 manufactured by Rigaku Corporation. Sintering was evaluated by setting the point at which the shrinkage of the shrinkage curve was parallel to the horizontal axis as the sintering temperature.

この結果、仮焼により確かに低温焼結化の効果はあるが、９００℃以下での焼結化は出来ない事が確認出来た。 (Examination of significant difference in presence or absence of calcination)
It is clear that antimony oxide theoretically covers the surface of zinc oxide and inhibits sintering. Then, in order to confirm the content, the significant difference of the presence or absence of calcination was evaluated. The results are shown in the table below. In addition, calcination mixes the bismuth oxide and antimony oxide which were mix | blended with the composition based on Table 1, and is 500 degreeC and 1 hour.

As a result, it was confirmed that calcination has the effect of low-temperature sintering but cannot be sintered at 900 ° C. or lower.

(Examination of addition of copper oxide CuO, a liquid phase sintering material)
Bismuth oxide sinters at a low temperature to form a liquid phase, which contributes to oxygen transport and additive dispersion, but has a large ionic radius and is not considered to be particularly effective for low-temperature sintering. . Therefore, copper oxide CuO having a small ionic radius with the same liquid phase sintered material was added as shown in Table 6 below, and the possibility of low-temperature sintering was examined. The numerical value is the amount of CuO added in an outer mol% with respect to 100 mol% of ZnO. Similar to the above-described examination of the presence or absence of calcination, a comparison was made between a case where copper oxide was simply added as a composition and a case where calcination was previously performed at 500 ° C. together with antimony oxide and bismuth oxide. The basic composition follows the composition shown in Table 1.

  As a result, similar to the above examination results, it was confirmed that low-temperature sintering was promoted by calcination in advance, and that sintering at 900 ° C. or lower was possible by adding copper oxide. On the other hand, when calcination was performed, 3 mol% or more of copper oxide (CuO) was added. When no calcination was performed, when 2.5 mol% or more of copper oxide (CuO) was added, a liquid phase was deposited on the surface. Since a low-temperature sintered body cannot be obtained without calcining, it is essential that the upper limit of the CuO addition amount is 3.0 mol% or less and that the lower limit can be sintered at 900 ° C. or less on the premise of calcining. The calcination with 0.1 mol% or more and bismuth oxide and antimony oxide is essential.

The addition of copper can promote sintering and lower the sintering temperature because copper forms a liquid phase at a relatively low temperature (several hundreds of degrees Celsius) and easily has a valence. It is considered that there is a point that the ionic radius is small (Cu ₂ O and CuO), and it is a technique that is also used for low-temperature sintering of ferrite and the like. As a result, as shown in FIG. 2, low-temperature sintering has progressed, and in the conventional technique, the sintering start temperature is about 930 ° C., but the sintering start temperature is reduced to 870 ° C. by calcination of bismuth and antimony, Furthermore, the sintering start temperature is lowered to about 750 ° C. by calcination of bismuth, antimony and copper.

Next, the calcination temperature range was confirmed. As shown in the following table, the calcining temperature and the amount of copper oxide (CuO) added were changed, and the firing temperature was confirmed. The basic composition other than the amount of copper oxide added is as shown in Table 1.

  As a result, it was confirmed that by performing calcination at 300 ° C. or higher, a sintered body was obtained by firing at 900 ° C. or lower. However, calcination at 750 ° C. or higher results in excessive sintering, generating coarse particles, and generating particles that cannot be pulverized in the subsequent pulverization step. In addition, as described in the results of Table 5, when 3.0 mol% or more of copper oxide (CuO) is added, CuO is precipitated on the surface at any calcination temperature.

  Therefore, the addition amount of copper oxide (CuO), which is a key additive for low-temperature sintering at 900 ° C. or lower, needs to be in the range of 0.1 to 3 mol% on the basis of 100 mol% of ZnO. It is. Moreover, the calcination temperature (heat treatment conditions) of the mixture of bismuth oxide, antimony oxide, and copper oxide needs to be in the range of 300 to 750 ° C.

  From the above examination, it is confirmed that a varistor sintered body can be formed by low-temperature firing at 900 ° C. or lower by calcining a mixture of bismuth oxide, antimony oxide, and copper oxide into raw material powder, and granulating and firing the mixture. did it. However, it is meaningless to perform low-temperature sintering without considering the electrical characteristics and reliability as a varistor. Therefore, the correlation with the amount of other additives added was examined, and an optimum varistor composition capable of obtaining sufficiently good electrical characteristics and reliability and capable of low-temperature sintering was confirmed.

For the examination of the composition, the following was evaluated. However, since it provides a low temperature co Yuika possible varistor is the purpose, the amount is _{0.1～3.0Mol%} of copper oxide _{(CuO), Bi 2 O 3} -Sb 2 precalcination O 3 -CuO In response to the above experimental result that the temperature was 300 to 750 ° C., the copper oxide CuO was fixed at 1 mol%, the calcining temperature was fixed at 500 ° C., and the composition conditions were examined for the following 12 items.

1. Examination of partially calcined material composition (examination of Bi ₂ O ₃ —Sb ₂ O ₃ composition ratio)
2. Study of basic additives for grain boundary formation (CoO, MnO)
3. Investigation of reliability stabilizing materials (Cr ₂ O ₃ )
4). Examination of glass additives (H ₃ BO ₃ , SiO ₂ )
5. Study of titanium oxide (TiO ₂ )
6). Study of germanium oxide (GeO ₂ )
7). Examination of rare earth element addition (Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
8). 8. Simultaneous calcination of chromium oxide Study of simultaneous calcining of glass additives10. Examination of donor additives (Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ )
11. Study of reducing agent (magnesium oxide) (MgO)
12 Examination of simultaneous addition of oxide (Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , MgO)

(Examination of partially calcined material composition (examination of Bi ₂ O ₃ —Sb ₂ O ₃ composition ratio))
Moiety as calcined material, of a system of _{Bi 2 O 3 -Sb 2 O 3} -CuO a basic composition of low temperature co Yuika examined _the composition ratio combination of Bi _{2 O 3 -Sb 2} O 3 system. The evaluation was carried out using the α value, which is a unique electrical characteristic of non-linearity of the varistor. The evaluation standard of the α value was evaluated by considering 20 as the lower limit between 0.01 mA and 1 mA in consideration of practicality.

The evaluation results are shown below.

As a result, with respect ZnO100mol%, _Bi 2 _{O 3} added amount 0.1～1.5Mol% by outer percentage, _Sb 2 _{O 3} added amount 0.01~3.0mol%, CuO amount of 0.1 to 3. By using a raw material obtained by mixing three kinds of materials of 0 mol% and partially calcined at 300 to 750 ° C., low temperature sintering at 900 ° C. or lower is possible, and an α value that is a basic characteristic of a varistor is 20 or more. It was confirmed that a high performance varistor was obtained. In addition, with respect to the α value evaluation shown in the above table, zinc oxide, bismuth oxide, and antimony oxide alone cannot provide a large non-linear characteristic (α value), and cobalt oxide and manganese oxide are usually added as transition metal elements. For this reason, in order to obtain practicality and accurate judgment, the values are evaluated by adding 0.5 mol% of cobalt oxide in the evaluation of Table 7.

(Examination of basic additives for grain boundary formation (CoO, MnO))
As basic additives for grain boundary formation, the addition amounts of cobalt oxide (CoO) and manganese oxide (MnO) were examined. The evaluation was performed using the α value in the same manner as the above evaluation. The evaluation standard of α value was evaluated by considering 20 as a lower limit value between 0.01 mA and 1 mA in consideration of practicality. The partial calcination raw ZnO were evaluated in the above 1: was added 0.5 mol% of _Bi 2 _O 3 _-1.0mol% of _Sb 2 _O 3 _-1.5mol% of CuO in outer percentage relative to 100 mol%.

The results are shown in Tables 8 and 9 below.

As a result, it can be seen that when the addition amount of cobalt oxide (CoO) and manganese oxide (MnO) is 0.1 to 1.5 mol%, an α value of 20 or more can be achieved.
Next, cobalt and manganese, which are the same transition metals, were added in combination, and the α value was evaluated. The results are shown in Table 10 below.

この結果、酸化コバルト（ＣｏＯ）と酸化マンガン（ＭｎＯ）の添加量は一種類以上を合計０．１〜１．５ｍｏｌ％添加する事で、α値２０以上が得られた。

As a result, the addition value of cobalt oxide (CoO) and manganese oxide (MnO) was such that an α value of 20 or more was obtained by adding one or more types in a total amount of 0.1 to 1.5 mol%.

(Examination of reliability stabilizing substance (Cr ₂ O ₃ ))
The amount of chromium oxide (Cr2O3) added as a reliability stabilizing substance was examined. The evaluation was performed based on the varistor voltage change rate after applying the surge current. The applied surge current was uniformly 600 A, and the non-defective product determination was set to be within 10% of the varistor voltage change rate. The partially calcined raw material ZnO evaluated in 1 was evaluated with 0.5 mol% Bi ₂ O ₃ -1.0 mol% Sb ₂ O ₃ -1.5 mol% CuO, 2 with respect to 100 mol%. Cobalt oxide was added in an amount of 1 mol% as an outer coating with respect to ZnO: 100 mol%.

この結果、酸化クロム（Ｃｒ_２Ｏ_３）の添加量を、０．０１〜２ｍｏｌ％添加する事で信頼性の高いバリスタが得られる事を確認できた。 The results are shown in Table 11 below.

As a result, it was confirmed that a highly reliable varistor can be obtained by adding 0.01 to ₂ mol% of chromium oxide (Cr ₂ O ₃ ).

(Examination of glass additives (H ₃ BO ₃ , SiO ₂ ))
The optimization of the amount of glass additive added was examined for surge resistance, energy resistance, and leakage current tests at high temperatures. Larger surge and energy tolerances are better for large currents, and leakage currents at high temperatures are leakage currents that flow during standby, so smaller ones are better.

(Examination of boric acid addition amount (H ₃ BO ₃ ))
Partially calcined raw material ZnO evaluated in 1: Cobalt oxide evaluated with 0.5 mol% Bi ₂ O ₃ , 1.0 mol% Sb ₂ O ₃ , 1.5 mol% CuO and 2 with respect to 100 mol%. Was added to 0.5 mol% of ZnO: 100 mol% as an outer coating to obtain a basic evaluation composition. Table 12 shows the measurement results of surge withstand (ampere: A), Table 13 with energy withstand (joule: J), and Table 14 shows the leakage current (microampere μA) at high temperature.

この結果、ホウ酸（Ｈ_３ＢＯ_３）の添加量は０．０１〜２．０ｍｏｌ％が望ましい。

As a result, the addition amount of boric acid (H ₃ BO ₃ ) is desirably 0.01 to 2.0 mol%.

この結果、二酸化ケイ素（ＳｉＯ_２）の添加量は０．０１〜２．０ｍｏｌ％が望ましいことが分かる。 (Examination of silicon dioxide addition amount (SiO ₂ ))
Partially calcined raw material ZnO evaluated in 1: Cobalt oxide evaluated with 0.5 mol% Bi ₂ O ₃ , 1.0 mol% Sb ₂ O ₃ , 1.5 mol% CuO and 2 with respect to 100 mol%. Of ZnO: 100 mol% was added as an outer coating, and 1 mol% of chromium oxide evaluated at 3 was added to ZnO: 100 mol% as an outer coating of 0.5 mol% to obtain a basic evaluation composition. Table 15 shows the surge resistance (ampere: A), Table 16 shows the energy resistance (joule: J), and Table 17 shows the leakage current (microampere: μA) at high temperature.

As a result, it is understood that the amount of silicon dioxide (SiO ₂ ) added is preferably 0.01 to 2.0 mol%.

(Examination of titanium oxide (TiO ₂ ))
As evaluated in 1, the partially calcined raw material was externally coated (0.1 to 1.5 mol%) Bi ₂ O ₃ and (0.01 to ₂ mol%) Sb ₂ O _{3 with} respect to 100 mol% of ZnO. , (0.1 to 3 mol%) CuO was added so that low temperature sintering was possible and it was confirmed that a varistor having an α value of 20 or more was obtained.
As a further improvement, we examined the improvement of surge resistance and energy resistance by adding titanium oxide to the partially calcined material composition. The evaluation results are shown in Table 18 for surge resistance and Table 19 for energy resistance.
Incidentally, in response to the result of the 1 to 4, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, Cr 2} O 3: 0.5mol%, H 3 BO 3: 0.5mol%, SiO 2: After adding 0.5 mol% to make the basic composition, the partially calcined material was examined.

この結果、酸化チタン（ＴｉＯ_２）を０．０１〜０．５ｍｏｌ％添加する事で、更にサージ耐量、エネルギー耐量が向上する事が確認出来た。

As a result, it was confirmed that by adding 0.01 to 0.5 mol% of titanium oxide (TiO ₂ ), surge resistance and energy resistance were further improved.

(Examination of germanium dioxide (GeO ₂ ))
As evaluated in 1, the partially calcined raw material was externally coated with 0.1 to 1.5 mol% of Bi ₂ O ₃ and (0.01 to ₂ mol%) of Sb ₂ O _{3 with} respect to 100 mol% of ZnO. , (0.1 to 3 mol%) CuO was added so that low temperature sintering was possible and it was confirmed that a varistor having an α value of 20 or more was obtained.
As a further improvement, the improvement of the α value was examined by adding germanium oxide to the partially calcined material composition. Table 20 shows the α value measurement results.
Incidentally, in response to the result of the 1-4, similarly to the 5, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, Cr 2} O 3: 0.5mol%, H 3 BO 3: 0. 5 mol% and SiO ₂ : 0.5 mol% were added to obtain a basic composition, and then a partially calcined material was examined.

この結果、酸化ゲルマニウム（ＧｅＯ_２）を０．０１〜１．０ｍｏｌ％添加する事で非直線性（α値）が向上する事が確認出来た。

As a result, it was confirmed that non-linearity (α value) was improved by adding 0.01 to 1.0 mol% of germanium oxide (GeO ₂ ).

(Examination of rare earth element addition (Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu))
As evaluated in 1, the partially calcined raw material was externally coated with 0.1 to 1.5 mol% of Bi ₂ O ₃ and (0.01 to ₂ mol%) of Sb ₂ O _{3 with} respect to 100 mol% of ZnO. , (0.1-3 mol%) CuO was added so that low temperature sintering was possible, and it was confirmed that a varistor having an α value of 20 or more was obtained.
As a further improvement, we examined the improvement of surge and energy resistance by adding rare earth elements to the partially calcined material composition. The evaluation results are shown in Table 21 for the surge resistance and Table 22 for the energy resistance.

この結果、希土類酸化物（Ａ_２Ｂ_３）を０．０１〜０．５ｍｏｌ％添加する事で、サージ耐量、エネルギー耐量が向上する事が確認出来た。
尚、上記１〜４の結果を受けて、ＺｎＯ１００ｍｏｌ％に対して外掛けでＣｏＯ：１．０ｍｏｌ％、Ｃｒ_２Ｏ_３：０．５ｍｏｌ％、Ｈ_３ＢＯ_３：０．５ｍｏｌ％、ＳｉＯ_２：０．５ｍｏｌ％を添加し基本組成とした上で、部分仮焼材料を検討した。

As a result, it was confirmed that by adding 0.01 to 0.5 mol% of rare earth oxide (A ₂ B ₃ ), surge resistance and energy resistance were improved.
Incidentally, in response to the result of the 1 to 4, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, Cr 2} O 3: 0.5mol%, H 3 BO 3: 0.5mol%, SiO 2: After adding 0.5 mol% to obtain a basic composition, a partially calcined material was examined.

(Simultaneous calcination of chromium oxide (Cr ₂ O ₃ ))
As evaluated in 1, the partially calcined raw material was externally coated with 0.1 to 1.5 mol% of Bi ₂ O ₃ and (0.01 to ₂ mol%) of Sb ₂ O _{3 with} respect to 100 mol% of ZnO. , (0.1 to 3 mol%) CuO was added so that low temperature sintering was possible and it was confirmed that a varistor having an α value of 20 or more was obtained.
As a further improvement, high performance surge resistance and energy resistance were examined by adding chromium oxide (Cr ₂ O ₃ ) to the partially calcined material composition. Table 23 shows the evaluation results.
Incidentally, in response to the result of the 1 to 5, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, H 3} BO 3: 0.5mol%, SiO 2: 0.5mol%, TiO 2: 0. 1 mol% was added to make a basic composition, and a comparison was made with and without using chromium oxide (Cr ₂ O ₃ : 0.5 mol%) as a partially calcined material.

この結果、酸化クロム（Ｃｒ_２Ｏ_３）を部分仮焼き材に入れる事でサージ、エネルギー耐量が向上する事が確認出来た。

As a result, it was confirmed that surge and energy resistance were improved by adding chromium oxide (Cr ₂ O ₃ ) to the partially calcined material.

(Simultaneous calcining of boric acid (H ₃ BO ₃ ) and silicon dioxide (SiO ₂ ))
As evaluated in 1, the partially calcined raw material was externally coated (0.1 to 1.5 mol%) Bi ₂ O ₃ and (0.01 to ₂ mol%) Sb ₂ O _{3 with} respect to 100 mol% of ZnO. , (0.1 to 3 mol%) CuO was added so that low temperature sintering was possible and it was confirmed that a varistor having an α value of 20 or more was obtained.
As a further improvement, high performance of surge and energy resistance was examined by adding boric acid (H ₃ BO ₃ ) and silicon dioxide (SiO ₂ ) to the partially calcined material composition. Table 24 shows the evaluation results of boric acid, and Table 25 shows the evaluation results of silicon dioxide.
Incidentally, CoO in outer percentage relative ZnO100mol% receives the results of the above _{1~5: 1.0mol%, H 3 BO} 3: 0.5mol%, TiO 2: 0.1mol%, Cr 2 O 3: 0 .5 mol% was added, and comparison was made with and without boric acid (H ₃ BO ₃ ) and silicon dioxide (SiO ₂ ) as partially calcined materials.

この結果、ホウ酸、二酸化ケイ素といったガラス成分を部分仮焼材料として同時に添加する事でサージ耐量、エネルギー耐量が向上する事が確認出来た。

As a result, it was confirmed that surge resistance and energy resistance were improved by simultaneously adding glass components such as boric acid and silicon dioxide as a partially calcined material.

(Examination of donor additives (Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ ))
In order to improve the performance of zinc oxide varistors, ZnO is doped with ZnO in advance as aluminum oxide (Al ₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), and indium oxide (In ₂ O ₃ ) as a donor element. The improvement of withstand and energy tolerance was studied. Tables 26 and 27 show the examination results. As basic composition, CoO in outer percentage relative ZnO100mol% Based on the contents of the _{1~5: 1.0mol%, Cr 2 O} 3: 0.5mol%, H 3 BO 3: 0.5mol%, SiO 2: 0.5 mol% is added, and the partially calcined material is coated with 0.5 mol% Bi ₂ O ₃ , 1.0 mol% Sb ₂ O ₃ , and 1.5 mol% CuO on the basis of ZnO: 100 mol%. The donor element was examined. The amount added was shown as ppm in addition to ZnO: 100 mol%.

(Surge resistance (A))

(Energy tolerance)

As a result, it was confirmed that the surge resistance and the energy resistance were improved by adding 1 to 50 ppm of a donor element to ZnO in advance and performing calcination (heat treatment) at 600 to 900 ° C. for doping. Further, although details are not shown, with regard to Tables 26 and 27 above, the same tendency is the same for any element of Al ₂ O ₃ , Ga ₂ O ₃ , and In ₂ O ₃ as long as it is a donor element. The value is shown. Therefore, if the addition of the donor element is in the range of 1 to 50 ppm, the same result is obtained with any element or mixed composition.

(Examination of reducing agent magnesium oxide (MgO))
In order to improve the performance of zinc oxide varistors, magnesium oxide (MgO), which has a reducing action on ZnO at a high temperature, was previously doped into ZnO, and improvements in surge resistance and energy resistance were studied. The results are shown in Tables 28 and 29, respectively. As basic composition, based on the content of the 1 to 5, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, Cr 2} O 3: 0.5mol%, H 3 BO 3: 0.5mol%, SiO 2 : 0.5 mol% is added, and the partially calcined material is coated with 0.5 mol% Bi ₂ O ₃ , 1.0 mol% Sb ₂ O ₃ , and 1.5 mol% CuO on the basis of ZnO: 100 mol%. The reducing agent (MgO) was studied. The amount added was expressed as mol% over ZnO: 100 mol%.

(Surge resistance (A))

(Energy tolerance (J))

  As a result, magnesium oxide (MgO) having a reduction effect at a high temperature with respect to ZnO in advance is added in an amount of 0.1 to 2 mol% on the basis of ZnO: 100 mol%, and heat treatment is performed at 600 to 900 ° C. to dope, It was confirmed that surge resistance and energy resistance were improved.

(Consideration of simultaneous addition of donor element (Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ ) and reducing agent (ZnO))
In order to improve the performance of the zinc oxide varistor, the donor element (Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ ) and the reducing agent (ZnO) were added individually from the above results, and the same was performed at the same 600 to 900 ° C. When firing, it was confirmed that there was an effect of improving surge resistance and energy resistance as described above.
Therefore, the effect of improving surge resistance and energy resistance when added together was investigated. These are shown in Tables 30 and 31, respectively. As basic composition, based on the content of the 1 to 5, CoO in outer percentage relative _{ZnO100mol%: 1.0mol%, Cr 2} O 3: 0.5mol%, H 3 BO 3: 0.5mol%, SiO 2 : 0.5 mol% is added, and the partially calcined material is ZnO: 0.5 mol% Bi ₂ O ₃ , 1.0 mol% Sb ₂ O ₃ , 1.5 mol% CuO as an outer coating with respect to 100 mol% It added so that it might become. The added amount was expressed in terms of ZnO: 100 mol%, and the donor element was external ppm, and the reducing material was external mol%. The calcining temperature was fixed at 700 ° C.

(Surge resistance (A))

(Energy tolerance (J))

As a result, 0.1 to 2 mol% of magnesium oxide (MgO), which is preliminarily applied to ZnO and has a reducing effect at high temperatures, and aluminum oxide (Al ₂ O ₃ ) and gallium oxide (Ga ₂ O ₃ ) as donor elements. In addition, it was confirmed that surge resistance and energy resistance were improved by simultaneously adding 1-50 ppm of any one of indium oxide (In ₂ O ₃ ) and performing heat treatment at 600-900 ° C. for doping.

  As described above, by adding copper oxide as a low-temperature sintering accelerator and optimizing the composition and manufacturing conditions of the varistor raw material, sintering can be performed at a low temperature of 900 ° C. or less, thereby making an inexpensive silver electrode as an internal electrode It was confirmed that a high-performance varistor excellent in electrical characteristics such as α value, surge resistance, energy resistance, varistor voltage change rate, and reliability can be obtained.

  Next, with reference to FIG. 3, the manufacturing method of the zinc oxide lamination type varistor of this invention is demonstrated. First, bismuth oxide is 0.1 to 1.5 mol%, antimony oxide is 0.01 to 2.0 mol%, and copper oxide is 0.1 to 3.0 mol% in the range of 100 mol% of zinc oxide. Mix. And bismuth oxide, antimony oxide, and copper oxide are partially calcined in a temperature range of 300 to 750 ° C. After calcination, the mixture is pulverized with a ball mill or the like and sized.

Next, bismuth oxide, antimony oxide, and copper oxide that have been pulverized and sized after the calcination are added to zinc oxide. Further, among cobalt oxide and manganese oxide, one or more types are 0.1 to 1.5 mol%, chromium oxide is 0.01 to 2 mol%, boric acid is 0.01 to 2 mol%, and silicon oxide is 0.01 to Add 2 mol%. When performing partial calcination of bismuth oxide, antimony oxide, and copper oxide, 0.01 to 0.5 mol% of titanium oxide, 0.01 to 1 mol% of germanium oxide, or rare earth element is added. (Pr, Y, Nb, etc.) _a 2 _O 3: adding 0.01 to 0.5 mol% in the form of (a rare earth element), or the addition of boric acid or silicon oxide, or the addition of chromium oxide, Alternatively, 0.1 to 2 mol% of magnesium oxide may be added, or one or more of aluminum, gallium, and indium serving as donor elements may be added in a total of 1 to 50 ppm with respect to 100 mol% of zinc oxide.

  Next, the raw materials are thoroughly mixed with a ball mill or the like, and PVB, a phthalate ester plasticizer, a polycarboxylic acid dispersant, a release material, and an ethanol / toluene dilution solvent are added to the slurry. And it forms into a film with a doctor blade and produces about 10-100 micrometers green sheet.

  Next, an internal electrode pattern is formed on the green sheet as necessary. In this method, 100% silver paste is screen-printed to arrange a large number of internal electrode patterns. Then, the green sheets are stacked and stacked by hot pressing or the like. Then, it cut | disconnects according to a product size, and divides | segments into each green chip (dicing).

  Then, a binder removal treatment is performed by performing a heat treatment, and then baking is performed at a temperature of 900 ° C. or lower. By this firing, a varistor sintered body is formed and a silver internal electrode is formed. As described above, since firing is performed at a relatively low temperature of 900 ° C. or lower, even if the internal electrode is a silver electrode, silver migration does not proceed and a high-quality silver electrode can be formed. In addition, since the firing temperature is low, less power is used and the burden on facilities is reduced. In addition to the low material cost of silver, it is possible to produce a varistor at a low manufacturing cost.

  After firing, after annealing, and returning to room temperature, the base external electrode is formed of silver or the like, and this is subjected to nickel plating, solder or tin plating, thereby forming the external electrode connected to the internal electrode The Thereafter, the varistor is completed through processes such as measurement, marking, and inspection.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is sectional drawing of a zinc oxide lamination type varistor. It is a graph which shows the relationship between a sintering furnace temperature and shrinkage | contraction rate, and the temperature which shrinkage | contraction starts with a temperature rise is a sintering start temperature, and it is thought that sintering temperature is proportional to sintering start temperature. In the prior art, the sintering start temperature of about 930 ° C. is lowered to 870 ° C. by calcination of bismuth and antimony, and the sintering start temperature is 750 ° C. by calcination of bismuth, antimony and copper. It is shown that it has decreased to a certain extent. It is a flowchart of the manufacturing method of the zinc oxide lamination type varistor of one embodiment of the present invention.

Explanation of symbols

10 Zinc oxide multilayer varistor 11 Varistor sintered body (green sheet)
12a, 12b Internal electrodes 13a, 13b External electrodes

Claims (8)

Bismuth oxide, antimony oxide, and copper oxide are preliminarily calcined in a temperature range of 300 to 750 ° C.,
Add bismuth oxide in the range of 0.1-1.5 mol%, antimony oxide in the range of 0.01-2.0 mol%, and copper oxide in the range of 0.1-3.0 mol% with respect to 100 mol% of zinc oxide. ,
Further, among cobalt oxide and manganese oxide, one or more types are 0.1 to 1.5 mol%, chromium oxide is 0.01 to 2 mol%, boric acid is 0.01 to 2 mol%, and silicon oxide is 0.01 to 2 mol% added,
A method for producing a zinc oxide laminated varistor, comprising: forming a green sheet, forming a silver paste pattern on the green sheet, laminating the green sheet, cutting to form a green chip, and firing. When performing the partial calcination, the bismuth oxide and antimony oxide and copper oxide, the production of the zinc oxide laminated varistor according to claim 1, wherein the addition of titanium oxide 0.01 to 0.5 mol% Method. Wherein in performing the partial calcination, the bismuth oxide and antimony oxide and copper oxide, a manufacturing method of the zinc oxide laminated varistor according to claim 1, wherein the addition of germanium oxide 0.01 to 1 mol%. When the partial calcination is performed, rare earth elements (Pr, Y, Nb, etc.) are added to bismuth oxide, antimony oxide, and copper oxide in the form of A ₂ O ₃ (A: rare earth element) in a range of 0.01 to 0.00. 5. The method for producing a zinc oxide multilayer varistor according to claim 1 , wherein 5 mol% is added. Wherein in performing the partial calcination, the bismuth oxide and antimony oxide and copper oxide, a manufacturing method of the zinc oxide laminated varistor according to claim 1, wherein the addition of boric acid or silicon oxide. Wherein in performing the partial calcination, the bismuth oxide and antimony oxide and copper oxide, a manufacturing method of the zinc oxide laminated varistor according to claim 1, wherein the addition of chromium oxide. In outer percentage to zinc oxide 100 mol%, the production method of the zinc oxide laminated varistor according to claim 1, wherein the addition of magnesium oxide 0.1 to 2 mol%. The method for producing a zinc oxide multilayer varistor according to claim 1, wherein one or more of aluminum, gallium, and indium serving as donor elements are added in a total amount of 1 to 50 ppm with respect to 100 mol% of zinc oxide.

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