TWI396206B - Laminated Chip Rheostat - Google Patents

Description

Multilayer wafer varistor

The present invention relates to a laminated wafer varistor.

A varistor is an element that can change a resistance value nonlinearly by a voltage. For example, if a voltage exceeding a specified voltage value (varistor voltage) is applied, the resistance of the element is greatly reduced, so that an electric current that is almost impossible to circulate is violently The characteristics of the beginning of circulation. A varistor having such characteristics is often mounted on an electronic device and used as a protective element that protects the circuit from abnormal voltages caused by static electricity or lightning strikes.

The varistor for circuit protection is, for example, connected in parallel to a power supply circuit or the like in an electronic device, and functions as an insulating element during normal operation. Moreover, when an abnormal voltage called surge and interference enters the electronic device, the varistor will rapidly reduce the resistance value according to the abnormal voltage, and therefore, it will function as an abnormal voltage caused by surge and interference. road. In this way, abnormal voltages can be prevented from entering the power supply circuit, thereby suppressing damage to electronic equipment such as surges and interference.

In recent years, demands for miniaturization of electronic devices have increased, and varistor equipped with such electronic devices has also been required to be miniaturized. As a varistor which achieves the above-described miniaturization and is excellent in the above-described characteristics, it is known that, as described in Japanese Patent Publication No. Sho 58-23921, an internal electrode and a varistor layer containing ZnO as a main component are alternately laminated. Thereby, a laminated type varistor in which an external electrode is formed on the end portion of the laminated body is obtained.

As the internal electrode of the ZnO type laminated wafer varistor, most of the internal electrodes Pt having heat resistance and excellent electrical characteristics which are resistant to the sintering temperature at the time of formation of the varistor layer. However, Pt is very expensive, and therefore, if Pt is used for the internal electrode, there is a problem that the cost of the laminated wafer varistor is increased in manufacturing. Therefore, in order to reduce the manufacturing cost, a laminated wafer varistor which is used as a material for internal electrodes than a Pd-Ag alloy which is inexpensive Pt has been proposed.

For example, Japanese Laid-Open Patent Publication No. Hei 5-283209 discloses a laminated wafer varistor comprising: an internal electrode formed of a Pd-Ag alloy; and a varistor layer containing ZnO as a main component and Pr as a subcomponent. . Japanese Laid-Open Patent Publication No. Hei 10-12406 discloses a laminated wafer varistor comprising an internal electrode formed of a Pd-Ag alloy and a varistor layer containing ZnO as a main component and containing as a subcomponent. Bi ₂ O ₃ and the like.

In the laminated wafer varistor described in the above patent documents, the internal electrode is not expensive Pt, and therefore, the manufacturing cost can be reduced, which is industrially useful. However, the laminated wafer varistor disclosed in the above-mentioned Japanese Patent Publication No. Hei 5-283209 has a difference in volume shrinkage between the internal electrode and the varistor layer during sintering at the time of production. occur.

Further, recently, a laminated wafer varistor has been mounted on a substrate by soldering, that is, a so-called surface mount type varistor has been used more and more. However, in the laminated wafer varistor disclosed in Japanese Laid-Open Patent Publication No. H10-12406, the leakage current when a voltage is applied after soldering on the substrate tends to be large, and it is difficult to obtain a desired varistor voltage. The disadvantage of the value.

Therefore, as a laminated wafer varistor capable of solving the above-described problems of the peeling of the internal electrode and the varistor layer and the leakage current after soldering, a laminated wafer varistor has been developed which has a varistor layer. ZnO is used as a main component, and Pr is contained as a subcomponent; and an internal electrode is added to the conductive material formed of Pd, and Al ₂ O ₃ is added (for example, Patent No. 3449599).

However, as one of the important indexes for exhibiting the characteristics of the laminated wafer varistor, it is known that there is resistance to electric energy. This is the value indicating the maximum electric energy when the rate of change of the initial value of the varistor voltage is within ±10% when the specified inrush current is applied, and is the reference value of the durability of the laminated wafer varistor. The greater the resistance to electric energy, the more difficult it is to cause damage due to abnormal currents such as surges, which can be regarded as the higher the reliability.

When the inventors of the present invention reviewed the electric power resistance of the laminated wafer varistor disclosed in the above-mentioned Japanese Patent No. 3449599, it was found that these varistor have sufficiently large electric power resistance at the element size previously used, but when the component size is reduced, Specifically, when the interval between the internal electrodes is 60 μm or less, the electric energy resistance is remarkably lowered.

Recently, a laminated wafer varistor has been expected to be further miniaturized. However, since the above-described miniaturization is caused, the electric power resistance is greatly reduced as described above, and therefore, there is no practicality in miniaturization and electric energy resistance. Multilayer wafer varistor.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a laminated wafer varistor capable of ensuring charging even in the case where components are miniaturized. The resistance to electric energy.

The inventors of the present invention investigated the cause of the decrease in the electric resistance of the laminated wafer varistor as described in the above-mentioned Japanese Patent No. 3449599, and found that one of the causes is that the varistor layer is added. Pr is easily reacted with Pd which is an internal electrode material because Pr in the varistor layer is absorbed to the internal electrode. As described above, when Pr in the varistor layer is absorbed to the internal electrode, the Pr concentration in the varistor layer becomes small, causing not only an abnormal decrease in the varistor voltage but also a decrease in the withstand voltage.

Further, as a result of further review of the above phenomenon, it was found that the Pr concentration in the peripheral region of the internal electrode became small, and the region where the Pr concentration became small caused a decrease in the varistor voltage, and the electrical energy resistance was caused in combination. decline.

Based on the above findings, the inventors have found that the piezoelectric energy of the laminated wafer varistor can be sufficiently ensured by suppressing the absorption of Pr in the varistor layer into the internal electrode, and the present invention has been completed.

That is, the laminated wafer varistor of the present invention is characterized by comprising: a varistor element body having a plurality of varistor layers containing ZnO as a main component and containing Pr as a subcomponent, and an internal electrode, wherein the internal electrode is in addition to Pd In addition to Ag, the Al oxide is 0.0001 to 1.0 part by mass based on 100 parts by mass of the total of the above Pd and the Ag, and is disposed approximately in parallel with each of the varistor layers; and an external electrode It is disposed at the end of the varistor body and is respectively connected to the internal electrode.

The internal electrode in the above-mentioned laminated wafer varistor contains, in addition to Pd which is generally used as an electrode material, further contains Ag as an essential component. And two components of Al oxide. When this Ag and Al oxide are used in combination, they tend to be well absorbed into Pd. Therefore, the internal electrodes containing these components are nearly saturated, making it difficult to absorb more additives. As a result, in the laminated wafer varistor, the case where Pr in the varistor layer is absorbed to the internal electrode as described above is suppressed, so that the decrease in the withstand voltage due to the decrease in the Pr concentration of the varistor layer is extremely extreme. Fewer. However, the effects of the present invention are not limited thereto.

As described above, in the laminated wafer varistor of the present invention, Pr in the varistor layer is rarely absorbed to the internal electrode, and therefore, Pr is almost uniform in the varistor layer sandwiched by the pair of internal electrodes. Concentration distribution.

Further, in the laminated wafer varistor of the present invention, since the Pr in the varistor layer migrates less toward the internal electrode, the varistor layer in the laminated varistor is hardly connected to the internal electrode as in the prior art. The region has a situation in which the concentration of Pr is decreased. In other words, in the laminated wafer varistor having the above configuration, the Pr content per fixed volume of the varistor layer sandwiched by the pair of internal electrodes is at least one of the pair of internal electrodes connected to the varistor layer. The Pr content per fixed volume in the region is approximately the same.

The varistor layer in the laminated wafer varistor has a uniform Pr concentration distribution as described above. In other words, the distribution state can be regarded as that the Pr content of each fixed volume in the specified region adjacent to the internal electrode of the varistor layer is approximately the same as the Pr content of each fixed volume in the designated region of the central portion of the varistor layer in the lamination direction. status.

According to the laminated wafer varistor having such a structure, when analyzed by an electronic microprobe analysis method, the following results can be obtained: that is, by The intensity of the X light of Pr obtained in the region of the varistor layer sandwiched by the pair of internal electrodes and the region where the internal electrode is connected, and the X-ray intensity of Pr obtained from the central position between one of the internal electrodes of the varistor layer The approximate is the same.

More specifically, in the above laminated type varistor, the interval between the internal electrodes is preferably 20 to 60 μm. When the interval between the internal electrodes is large, that is, when the thickness of the varistor layer is large (specifically, when it exceeds 80 μm), the peripheral region of the internal electrode due to the absorption of Pr as described above can be seen. The Pr concentration is lowered, but there are many regions having a sufficient Pr concentration in the varistor layer, and therefore, the situation in which the electric power resistance is lowered is not too large. However, when the interval between the internal electrodes is 60 μm or less, the region in which the Pr concentration of the varistor layer is low is increased, and thus the electric power resistance tends to be remarkably lowered. On the other hand, the laminated wafer varistor of the present invention having the above-described structure can greatly suppress the decrease in the Pr concentration as described above. Therefore, in the case where the distance between the internal electrodes is 20 to 60 μm, the electric energy is resistant. The point of view will be particularly effective.

Further, in the above laminated type varistor, the internal electrode preferably contains 1 to 95 parts by mass of Ag based on 100 parts by mass of Pd. When the internal electrode has the above-described structure, the absorption of Pr can be more remarkably suppressed, and as a result, it is easy to ensure a sufficiently large electric power resistance.

Hereinafter, embodiments of the preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same elements will be denoted by the same reference numerals and the description of the repeated description will be omitted. In addition, the relationship between the top, bottom, left, and right is based on the positional relationship of the schema.

First, a laminated wafer varistor of the present embodiment will be described with reference to Fig. 1 . 1 is a cross-sectional view schematically showing a laminated wafer varistor of a preferred embodiment. The laminated wafer varistor 1 has a varistor element composed of a plurality of varistor layers 2 and internal electrodes 4a (first internal electrodes) and internal electrodes 4b (second internal electrodes) arranged to sandwich the varistor layers 2 Body 5.

Further, a pair of external electrodes 6 electrically connected to the internal electrode 4a and the internal electrode 4b are provided at both end portions of the varistor element body 5. Further, on the outer side of the external electrode 6, a Ni plating layer 8 and a Sn plating layer 10 are sequentially formed to cover the external electrode 6. The external terminal 12 is formed by the external electrode 6, the Ni plating layer 8, and the Sn plating layer 10.

The varistor layer 2 has a thickness of about 5 to 60 μm, which is mainly composed of ZnO and contains Pr as an auxiliary component. Since the varistor layer 2 contains the above two components as an essential component, it has excellent varistor characteristics such as a large nonlinear coefficient ( α ) which is one of the indexes showing the varistor characteristics.

The varistor layer 2 may contain, in addition to the above components, a trace additive which further enhances the varistor characteristics, for example, a metal which may contain Co, Al, K, La, Si, Ca, or the like, and any combination of these oxides. . Among them, as the trace additive contained in the varistor layer 2, an Al oxide is preferred, and Al ₂ O _{3 is} particularly preferred. When the Al oxide is contained in this manner, the nonlinear index (α) tends to be further increased.

The most suitable examples of the material constituting the above-mentioned varistor layer 2 are 97.725 mol% of ZnO, 0.5 mol% of Pr, 1.5 mol% of Co, 0.05 mol% of Al, and 0.05 mol% of K. The composition of Cr was 0.1 mol%, Ca was 0.1 mol%, and Si was 0.02 mol%.

The internal electrodes 4a and 4b are formed of a conductive material containing Ag and Pd and an Al oxide added to the conductive material, and have a thickness of about 0.5 to 5 μm. The content of the Al oxide in the internal electrodes 4a and 4b is 0.0001 to 1.0 part by mass based on 100 parts by mass of the total of Pd and Ag. Further, as the Al oxide added to the conductive material, Al ₂ O _{3 is} preferred.

In the internal electrodes 4a and 4b, if the content of the Al oxide is less than 0.0001 parts by mass based on 100 parts by mass of the total of Pd and Ag, the difference in shrinkage ratio between the internal electrodes 4a and 4b and the varistor layer during the varistor layer is changed. Big, the two will be stripped. On the other hand, when the amount is more than 1.0 part by mass, the internal electrodes 4a and 4b are less likely to be sintered. Therefore, the conductivity is lowered, the conduction with the external electrode is insufficient, and the varistor characteristics tend to be lowered.

Further, it is preferable that Pd and Ag which are conductive materials in the internal electrodes 4a and 4b are contained in a ratio as follows: that is, it is preferable to contain 1 to 95 parts by mass of Ag with respect to 100 parts by mass of Pd.

When the Ag content is less than 1 part by mass with respect to 100 parts by mass of Pd, the degree of absorption of Pr in the varistor layer 2 by the internal electrodes 4a, 4b becomes large, whereby the electric resistance of the laminated varistor 1 is changed. Small tendency. On the other hand, if the content of Ag exceeds 95 parts by mass, the melting points of the internal electrodes 4a and 4b may be too low, and the internal electrodes 4a and 4b may be melted when the varistor layer is sintered, and good varistor characteristics may not be obtained. The situation.

The varistor element body 5 is formed by alternately laminating the above-described varistor layer 2 and internal electrodes 4a and 4b. A pair of external electrodes 6 having a thickness of about 10 to 50 μm are formed on the end portions of the varistor element body 5, and are electrically connected to one of the internal electrodes 4a and 4b, respectively. The external electrode 6 is made of a material that can be internally charged The poles 4a and 4b may be well connected, and are not particularly limited, and examples thereof include an alloy of Pd, Pt, Ag, and any combination of these metals. Among them, Ag which is relatively inexpensive and has good bonding properties with the internal electrodes 4a and 4b is preferable.

On the surface of the external electrode 6, a Ni plating layer 8 having a thickness of about 0.5 to 2 μm and a Sn plating layer 10 having a thickness of about 2 to 6 μm are sequentially formed to cover the external electrode 6. The above-mentioned plating layer is mainly formed by improving solder heat resistance and solder wettability when the laminated wafer varistor 1 is mounted on a substrate or the like by a reflow process. Accordingly, in the case where this object can be attained, the plating formed on the surface of the external electrode 6 is not necessarily a combination of the above materials. For example, as another material constituting the plating layer, for example, a Sn-Pb alloy or the like is used, and it is also suitable to use the above-mentioned Ni and Sn in combination. Furthermore, the associated coating may also be a layer composed of only one layer.

In the laminated wafer varistor 1 having such a structure, the varistor layer 2 interposed between the pair of internal electrodes 4a and 4b has a state in which Pr added as an auxiliary component is approximately uniformly dispersed. Since the laminated wafer varistor of the present invention has the varistor layer in this state, it has excellent varistor characteristics as compared with the prior art.

2 to 6, the difference between the laminated wafer varistor of the present invention and the conventional laminated wafer varistor will be described and compared with the state of each varistor layer.

2 to 5 are views showing the results of an electronic microanalytical method (EPMA) observed on a conventional laminated wafer varistor (an internal electrode having Pd and a varistor having a varistor layer containing ZnO and Pr) An example of a picture. In addition, in Fig. 2 and Fig. 4, the closer to white (the lighter the color) the Pr concentration is displayed. The bigger it is. Further, in Fig. 3, L1 shows the X-ray intensity of Pr, and L2 shows the X-ray intensity of Pd. Further, in Fig. 5, L3 shows the X-ray intensity of Pr, and L4 shows the X-ray intensity of Pd.

Fig. 2 is a view showing a Pr concentration distribution obtained by observing a cross section of a laminated wafer varistor having an interval of 80 μm along the internal electrodes as observed by EPMA. In addition, FIG. 3 is a graph showing the X-ray intensity of Pr obtained by microprobe analysis of the EPMA along the lamination direction in the cross section observed in FIG. 2. 2 and 3, it was confirmed that in the laminated wafer varistor having an internal electrode interval of 80 μm, each of the varistor layers had a very small Pr concentration in the region to the internal electrode. Further, it was confirmed that the central region between the pair of internal electrodes had a higher Pr concentration than the region connected to the internal electrode.

Further, FIG. 4 is a view showing a concentration distribution of Pr obtained by EPMA observation of a cross section in the lamination direction of a laminated wafer varistor having an interval of 20 μm along the internal electrodes. In addition, FIG. 5 is a graph showing the X-ray intensity of Pr obtained by microprobe analysis of the EPMA along the lamination direction in the cross section observed in FIG. 4. 4 and 5, it was confirmed that most of Pr exists at a position overlapping the region where the internal electrode exists, and the Pr concentration (Fig. 4) of each varistor layer and the X-ray intensity (Fig. 5) of Pr become extremely small.

Here, Pd which is a constituent material of the internal electrode and Pr in the varistor layer are highly susceptible to reaction. Therefore, in the conventional laminated wafer varistor having the above structure, Pr is absorbing the internal electrode in the varistor layer, and is connected to the internal electrode as shown in FIGS. 2 to 5 The concentration of Pr will become smaller.

When the concentration of Pr connected to the region of the internal electrode is reduced as described above, There is very little Pr present in the grain boundary of ZnO in the region. In general, the varistor characteristics of the varistor layer containing ZnO, particularly the characteristics of the nonlinear coefficient (α) and electric resistance, are considered to be relatively dependent on the Pr present in the grain boundary of ZnO. Therefore, when Pr is present in the crystal grain boundary of ZnO, the varistor characteristics are remarkably lowered.

The absorption of Pr by the internal electrode described above is remarkably found in the region of the varistor layer which is located from the surface facing the internal electrode to a position of about 10 μm. Therefore, the smaller the interval between the internal electrodes, specifically, in the case of 60 μm or less, the degree of reduction in the varistor characteristics of the varistor layer becomes large, and therefore, the varistor characteristics of the laminated varistor as a whole are liable to occur. The tendency to decrease. In particular, when the interval between the internal electrodes is 20 μm or less (see FIGS. 4 and 5), most of Pr in the varistor layer is absorbed by the internal electrodes.

On the other hand, Fig. 6 is a view showing an example of the result of EPMA observation of the laminated wafer varistor 1 of the embodiment of the preferred embodiment of the present invention. Further, in the laminated wafer varistor shown in Fig. 6, the interval between the internal electrodes 4a and 4b is 20 μm. In other words, FIG. 6 is a view showing a concentration distribution of Pr obtained by observing the cross section along the lamination direction of the laminated wafer varistor 1 of the embodiment.

According to Fig. 6, it was confirmed that Pr hardly exists in the region overlapping the internal electrodes 4a, 4b, but is uniformly present in the varistor layer 2. Further, since Pr is uniformly present, it is confirmed that the concentration of Pr in the region of the varistor layer 2 connected to the internal electrode is the concentration of Pr in the central region between one of the internal electrodes of the varistor layer 2 Roughly the same.

In the laminated wafer varistor 1 of the present embodiment, the internal electrodes 4a and 4b are divided In addition to Pd, it also contains Ag and Al oxides. For this reason, the internal electrodes 4a and 4b are in a state of being nearly saturated, so that the absorption of Pr in the varistor layer 2 by the above-described internal electrodes 4a and 4b is extremely difficult to occur. Further, as a result of suppressing the absorption of Pr as described above, as shown in FIG. 6, Pr is uniformly dispersed in the varistor layer 2, that is, it has an approximately fixed concentration distribution in the varistor layer 2. status.

In the varistor layer 2 having the above-described uniform distribution of Pr, there is little possibility that the Pr concentration is lowered in the region where the internal electrode is connected in the conventional laminated wafer varistor. That is, the Pr content per fixed volume of the varistor layer 2 sandwiched by the pair of internal electrodes 4a, 4b is in contact with the varistor layer 2 in at least one of the pair of internal electrodes 4a, 4b. The Pr content per fixed volume is approximately the same.

Further, the above state of the varistor layer 2, in other words, can be expressed as follows: that is, the varistor layer 2 sandwiched by the pair of internal electrodes 4a, 4b is connected to at least one of the internal electrodes 4a, 4b. The Pr content per fixed volume may be approximately the same as the Pr content per fixed volume in the central region between the pair of internal electrodes 4a, 4b in the varistor layer 2.

Here, the region of the varistor layer 2 connected to the internal electrodes 4a, 4b, in the case of preference, means that the varistor layer 2 is connected to the surface of the internal electrodes 4a, 4b by a distance of about 10 μm. The area up to the location.

Next, a method of manufacturing the laminated wafer varistor 1 having the above configuration will be described with reference to FIG. 7 is a flow chart showing a method of manufacturing a laminated wafer varistor of a preferred embodiment.

First, the ZnO of the main component of the varistor layer 2 and the gold of the Pr of the subcomponent are added. The genus or oxide and other trace additives are weighed to a predetermined ratio, and then the components are mixed to adjust the varistor material (step S11). In this case, it is preferred that the trace amount is mixed in an amount of ppm relative to the main component of ZnO. Thereafter, an organic binder, an organic solvent, an organic plasticizer, or the like is added to the varistor, and the mixture is pulverized by a ball mill or the like for about 20 hours to obtain a polishing liquid.

This polishing liquid is applied onto a polyethylene terephthalate (PET) film by a known method such as a doctor blade method, and then dried to form a film having a thickness of about 30 μm, and the obtained film is made of PET. The film is peeled off to obtain a green sheet (step S12).

Next, an internal electrode slurry in which Pd, Ag, Al ₂ O ₃ and other additives are slurried is prepared as a material for the internal electrodes 4a and 4b. After the internal electrode paste is printed in a predetermined pattern by screen printing or the like, the slurry is dried to form an internal electrode slurry layer having a predetermined pattern (step S13).

After the green sheet in which the internal electrode slurry layer is formed on the surface of the plurality of sheets is formed, the plurality of laminated green sheets and the internal electrode slurry layers are formed in a staggered manner to form a laminate (step S14). On the laminated body thus obtained, if necessary, a protective embryo sheet formed by laminating only the above-mentioned embryonic sheet is laminated, and then cut into a desired size to obtain a embryonic wafer.

Thereafter, the embryo wafer is subjected to a heat treatment at 180 to 400 ° C for about 0.5 to 24 hours to perform a debonding treatment, and further calcined at 1000 to 1400 ° C for about 0.5 to 8 hours (step S15) to obtain a varistor. Element 5. By the associated firing, the embryonic sheet in the embryonic wafer becomes the varistor layer 2, and the internal electrode paste layer becomes the internal electrodes 4a and 4b. For the varistor thus obtained Before the step of forming the external electrode 6 is carried out, the element body 5 can be placed in a polishing container or the like together with an abrasive or the like to perform smoothing of the surface of the element.

Next, at the both end portions of the varistor element body 5, the external electrode paste mainly containing Ag is applied to the internal electrodes 4a and 4b, and the slurry is applied at about 550 to 850 ° C. The heating (sintering) treatment is performed to form the external electrode 6 which is formed by a pair of Ag (step S16).

Thereafter, the Ni plating layer 8 and the Sn plating layer 10 are sequentially formed on the surface of the external electrode 6 by plating or the like to obtain a laminated wafer varistor 1 (Step S17).

According to the laminated wafer varistor 1 configured as described above, it is possible to obtain the effect that the laminated wafer varistor 1 has the varistor layer 2 in a state where Pr is dispersed at a substantially fixed concentration, and therefore, compared with A conventional laminated wafer varistor having a very small Pr concentration in a region where the internal electrode is connected has an excellent nonlinear coefficient (α) and electric power resistance.

Further, in the laminated wafer varistor 1, even when the interval between the internal electrodes 4a and 4b is 20 μm or less, almost no Pr is absorbed by the internal electrodes 4a and 4b. Therefore, even when an attempt is made to greatly reduce the size of the element, there is little reduction in the withstand electric energy generated by the conventional varistor.

[Examples]

Hereinafter, the present invention will be described in further detail by way of examples, but the invention should not be construed as limited.

<Manufacture of laminated wafer varistor>

First, in a purity of 99.9% ZnO (97.725 mol%), Pr (0.5 mol%), Co (1.5 mol%), Al (0.005 mol%), K (0.05 mol%), A varistor material was prepared by Cr (0.1 mol%), Ca (0.1 mol%), and Si (0.02 mol%).

Further, in addition to the formulation amounts shown in Tables 1 to 3, an internal electrode slurry containing at least two of Pd, Ag, and Al ₂ O ₃ was prepared.

Using the varistor material and the internal electrode paste, a varistor layer 2 formed of a varistor material, and an internal electrode 4a containing at least two kinds of Pd, Ag, and Al ₂ O ₃ are produced according to the procedure shown in FIG. 4b. The laminated electrode varistor of Nos. 1 to 47 having the outer electrode 6, the Ni plating layer 8, and the Si plating layer 10 formed of Ag and having the shape shown in FIG. Each of the laminated wafer varistor is set to have a length of 1.6 mm, a width of 0.8 mm, and a height of 0.8 mm.

Further, in the laminated wafer varistor of No. 1, ₂ , 10, 18, 26, 33, 34, and 41, the Al ₂ O ₃ content is 0%, and therefore, as a comparative example, as for No. 8, 16, In the laminated wafer varistor of 24, 32, 40, and 47, the Al ₂ O ₃ content exceeds 1.0 mass part, and thus is a comparative example.

<Feature evaluation>

Using the laminated wafer varistor, the measurement of the varistor voltage, the measurement of the nonlinearity index (α), the measurement of the withstand electric energy, and the moisture resistance load test were carried out in the following manner. The results obtained for the laminated wafer varistor of No. 1 to 18 are shown in Table 1. The results obtained for the laminated wafer varistor of Nos. 19 to 36 are shown in Table 2, and the laminated wafer of No. 37 to 47 is shown. The results obtained with the varistor are shown in Table 3.

(Measurement of varistor voltage)

A voltage is applied and gradually applied between a pair of external terminals 12 of each laminated varistor, and a voltage at which a current of 1 mA starts to flow is measured. The varistor voltage of the varistor.

(Measurement of nonlinear index (α))

The voltage flowing through the varistor was measured while the voltage applied between the pair of external terminals 12 of the laminated varistor was gradually changed, and the voltage (V _{1 mA} ) and the current of 1 mA were measured. The voltage at which the current flows (V _0.1mA ). Next, the obtained value is substituted into the following formula (1) to calculate a nonlinear index α: α = log (1/0.1) / log (V _1mA / V _0.1mA ) (1)

(Measurement of electric energy resistance)

First, between the pair of external terminals 12 of each laminated wafer varistor, 90% of the peak value is applied after 10 μsec from the rise, and after 1000 μsec from the rise after the peak is applied. The voltage of the waveform of 50% of the peak value is observed by an oscilloscope to observe a current waveform obtained by applying a voltage of the waveform.

After the obtained voltage waveform and the current waveform are multiplied to obtain a power waveform, the power waveform is integrated to calculate the electric energy value when the voltage of the waveform is applied. Further, when the electric energy value is gradually increased, when the rate of change of the varistor voltage exceeds ±10%, the laminated varistor is broken, and the maximum value of the electric quantity that has not been broken is taken as the electric power (part: joule).

(moisture resistance test)

First, 20 laminated thin film varistor Nos. 1 to 47 were fabricated, and the varistor voltage of each sample was measured. A moisture-resistant load test was carried out by applying a voltage of 0.6 times the respective varistor voltages to the samples and performing the treatment for 1000 hours under the conditions of 85 ° C and 80% RH. After that, measure resistance The varistor voltage of each sample after the wet load test was calculated from the 20 samples of the laminated wafer varistor of No. 1 to 47, and the number of samples whose rate of change of the varistor voltage exceeded ±10% was calculated. The number of defective products that occurred due to the moisture resistance load test.

According to Tables 1 to 3, the laminated electrode varistor having an internal electrode containing Pd, Ag, and Al ₂ O ₃ and having an Al ₂ O ₃ content within the scope of the present invention has an electric resistance of more than 0.1 J, which is externally affected by moisture resistance. The non-conforming product that occurred during the load test was zero. Here, the value of the electric power resistance of 0.1 J or more is generally used to determine that it has sufficient reliability in the case of a practical laminated wafer varistor.

<Observation of profile of laminated magnet varistor by EPMA>

A laminated wafer varistor of No. 1 (a laminated wafer varistor composed of only Pd; a comparative example) and a laminated wafer varistor of No. 45 (the internal electrode contains Ag/Pd in a composition of 70/30) Laminated wafer A varistor; as a laminated wafer varistor of the present invention, the concentration of each component (Pr, Co, Pd, and Ag) in the laminated wafer varistor is measured by an electron microprobe analysis method (EPMA) according to the method described below. distributed.

First, each of the laminated wafer varistor is polished from the side surface in the width direction (the horizontal direction in FIG. 1) until the cross section corresponding to the center position in the longitudinal direction (the front-rear direction in FIG. 1) is exposed. The exposed cross section was observed with EPMA, and the concentration distribution of each element on the cross section was observed. The concentration distributions of Pr, Co, Pd, and all compositions obtained by observing the laminated wafer varistor of No. 1 are shown in Figs. 8 to 11, respectively. Further, the concentration distributions of Pr, Co, Pd, Ag and all the compositions obtained by observing the laminated wafer varistor of No. 45 are shown in Figs. 12 to 16, respectively. Further, in FIGS. 8 to 16, the area where the color is lighter indicates the content of the corresponding element.

8 to 11, it is found that in the laminated wafer varistor of No. 1 corresponding to the conventional laminated wafer varistor, Pr is at a position overlapping with Pd, that is, at the position where the internal electrode exists - There are many, and Pr is present in a very small amount in the varistor layer.

On the other hand, as shown in FIG. 12 to FIG. 16, it is found that in the laminated wafer varistor of No. 45 corresponding to the laminated wafer varistor of the present invention, Pr is at a position overlapping with Pd and Ag - that is, At the position where the internal electrodes are present - almost absent, in addition, Pr is uniformly distributed in the varistor layer.

As described above, according to the present invention, even in the case where the device is miniaturized, a laminated wafer varistor capable of ensuring sufficient electric power resistance can be provided.

1‧‧‧Laminated wafer varistor

2‧‧‧variable resistance layer

4a, 4b‧‧‧ internal electrodes

5‧‧‧varistor body

6‧‧‧External electrode

8‧‧‧Ni plating

10‧‧‧Sn plating layer

12‧‧‧External terminals

1 is a stacked type wafer varistor that modally displays a preferred embodiment Sectional view.

Fig. 2 is a view showing a Pr concentration distribution obtained by observing a cross section of a laminated wafer varistor having an interval of internal electrodes of 80 μm along the lamination direction by EPMA.

Fig. 3 is a graph showing the X-ray intensity of Pr obtained by microprobe analysis of the EPMA along the lamination direction in the cross section observed in Fig. 2.

Fig. 4 is a graph showing the concentration distribution of Pr obtained by EPMA observation of the surface of the layered wafer varistor having an internal electrode interval of 20 μm along the lamination direction.

Fig. 5 is a graph showing the X-ray intensity of Pr obtained by performing line analysis of EPMA along the lamination direction in the cross section observed in Fig. 4.

FIG. 6 is a view showing a concentration distribution of Pr obtained by observing the cross section in the lamination direction of the laminated wafer varistor 1 of the embodiment.

7 is a flow chart showing a method of manufacturing a laminated wafer varistor of a preferred embodiment.

Fig. 8 is a graph showing the Pr concentration distribution on the cross section of the laminated wafer varistor of No. 1 observed by EPMA.

Fig. 9 is a view showing a Co concentration distribution on a cross section of a laminated wafer varistor of No. 1 observed by EPMA.

Fig. 10 is a graph showing the Pd concentration distribution on the cross section of the laminated wafer varistor of No. 1 observed by EPMA.

Fig. 11 is a graph showing the concentration distribution of all components on the cross section of the laminated wafer varistor of No. 1 observed by EPMA.

Figure 12 is a multilayer wafer varistor showing No. 45 observed by EPMA. A plot of the concentration of Pr concentration on the profile.

Fig. 13 is a view showing a Co concentration distribution on a cross section of a laminated wafer varistor of No. 45 observed by EPMA.

Fig. 14 is a graph showing the Pd concentration distribution on the cross section of the laminated wafer varistor of No. 45 observed by EPMA.

Fig. 15 is a graph showing the Ag concentration distribution on the cross section of the laminated wafer varistor of No. 45 observed by EPMA.

Fig. 16 is a graph showing the concentration distribution of all components on the cross section of the laminated wafer varistor of No. 45 observed by EPMA.

1‧‧‧Laminated wafer varistor

2‧‧‧variable resistance layer

4a, 4b‧‧‧ internal electrodes

5‧‧‧varistor body

6‧‧‧External electrode

8‧‧‧Ni plating

10‧‧‧Sn plating layer

Claims (8)

A laminated wafer varistor comprising: a varistor element body having: a plurality of varistor layers containing ZnO as a main component and containing Pr as a subcomponent; and an internal electrode containing Pd and Ag, And containing 0.0001 to 1.0 part by mass of the Al oxide in a total of 100 parts by mass of the above Pd and the Ag, and arranged approximately in parallel so as to sandwich the varistor layers; and an external electrode provided in the varistor The ends of the body are respectively connected to the internal electrodes. The laminated wafer varistor of claim 1, wherein the Pr has a substantially constant concentration distribution in the varistor layer sandwiched by the pair of internal electrodes. The laminated wafer varistor according to claim 1, wherein a content of said Pr per fixed volume of said varistor layer sandwiched by said pair of internal electrodes and said varistor layer are connected to at least one of said pair of internal electrodes The content of the above Pr per fixed volume of the region is substantially the same. The laminated wafer varistor according to claim 1, wherein the content of the Pr per fixed volume of the region of the varistor layer sandwiched by the pair of internal electrodes is at least one of the internal electrodes and the varistor layer The content of the Pr per fixed volume in the central region between the pair of internal electrodes is substantially the same. A multilayer wafer varistor as claimed in claim 1, wherein In the analysis by the electron beam microprobe analysis method, the X-ray intensity of the Pr obtained in the region of the varistor layer sandwiched by the pair of internal electrodes in the region connected to the internal electrode and the varistor layer are The X-ray intensity of the Pr obtained at the center position between the pair of internal electrodes is substantially the same. The laminated wafer varistor according to any one of claims 1 to 5, wherein the internal electrodes are spaced apart from each other by 20 to 60 μm. The laminated wafer varistor according to any one of claims 1 to 5, wherein the internal electrode contains 1 to 95 parts by mass of the Ag described above for 100 parts by mass of the Pd. The laminated wafer varistor of claim 6, wherein the internal electrode contains 1 to 95 parts by mass of the Ag described above for 100 parts by mass of the Pd.