JP4780306B2 - Multilayer thermistor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer thermistor that uses a Ni-based metal for an internal electrode and has positive resistance temperature characteristics.

As the thermistor, there is a thermistor that has a positive resistance temperature characteristic, that is, a resistance that increases with an increase in temperature. This thermistor is called a PTC (Positive Temperature Coefficient) thermistor. The PTC thermistor is configured to include a semiconductor ceramic and an electrode made of barium titanate (BaTiO ₃ ) as a main component and added with a trace amount of rare earth elements to provide conductivity. For example, as an overcurrent protection element of a circuit, Alternatively, it is widely used as a temperature sensor or the like.

  In recent years, there has been a strong demand for lower resistance of PTC thermistors in order to reduce power consumption as much as possible. Since the resistance is inversely proportional to the electrode area, the larger the electrode area, the more the resistance can be reduced. However, there is a limit to increasing the electrode area in the conventional single-plate type semiconductor porcelain. I can't respond. For this reason, a laminated PTC thermistor has been proposed as an alternative to the single plate type (see, for example, Patent Document 1). A multilayer PTC thermistor is formed by forming an external electrode on a sintered body obtained by integrally firing a laminate formed by alternately laminating semiconductor ceramic layers and internal electrodes. According to this multilayer PTC thermistor, For example, the electrode area of the internal electrode can be greatly increased, the resistance can be lowered accordingly, and the above requirement can be met.

For the internal electrode, it is necessary to employ a metal having excellent ohmic properties and heat resistance during firing. As such a metal, Ni or a Ni-based alloy (hereinafter collectively referred to as “Ni-based metal”) is effective. However, when this Ni-based metal is employed as the internal electrode, there is a problem that the electrode is oxidized when fired in the atmosphere as in the case of a normal single plate type. For this reason, in order to avoid oxidation of the Ni-based metal, the ceramic layer and the internal electrode made of the Ni-based metal are simultaneously fired in a reducing atmosphere. However, if the oxygen partial pressure during firing is too low, the adsorbed oxygen at the grain boundaries of the PTC thermistor will be insufficient and the PTC characteristics will deteriorate rapidly. For this reason, after firing in a reducing atmosphere, PTC characteristics are improved by performing oxidation treatment at a low temperature that does not oxidize the internal electrode. For example, in Patent Document 1, (Ba _0.998-x Ca _x La _0.002 ) _m TiO ₃ + yMnO ₂ +0.01 SiO ₂ , x = 0.02 to 0.45, y = 0.00002 to A composition of 0.015, m = 0.98 to 1.06 was adopted, and after baking at 1350 ° C. for 2 hours in a reducing atmosphere, an oxidation treatment was performed in which heating was performed at 800 ° C. for 2 hours in air. Yes.

JP-A-6-151103 (Example)

According to the multilayer PTC thermistor described in Patent Document 1, it is possible to reduce the resistance. However, as a result of the inventor performing firing and oxidation treatment in a reducing atmosphere under the conditions described in Patent Document 1 on the composition described in Patent Document 1, a multilayer thermistor having sufficient PTC characteristics is obtained. I couldn't.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide a technique for improving the PTC characteristics after oxidation treatment while reducing resistance.

In order to improve the PTC characteristics after the oxidation treatment, the present inventor has made various studies from the viewpoints of composition and manufacturing conditions. As a result, SiO ₂ previously considered as a mere sintering aid has a correlation with the ratio of Ti / Ba sites, and when both have a specific relationship, it has both low resistivity and high PTC characteristics. I found out that I can do it. That is, the present invention is a multilayer thermistor having a positive resistance temperature characteristic, in which semiconductor ceramic layers and internal electrodes are alternately stacked and has external electrodes electrically connected to the internal electrodes. The internal electrode is made of a Ni-based metal, and the semiconductor ceramic layer is made of a sintered body containing a compound represented by the general formula (Ba _1-xy Sr _x Re _y ) _α TiO ₃ + βSiO ₂ + zMn. Is represented by at least one selected from the group consisting of Y, La, Ce, Sm, Er, Nd, and Dy, and x, y, and α are respectively molar ratios, 0 ≦ x ≦ 0.3, 0 0.002 ≦ y ≦ 0.008, 1.02 ≦ α ≦ 1.1, z is 0 ≦ z [mol] ≦ 0.0015, and β is 2 in the range of 1.02 ≦ α ≦ 1.1. .35α-2.39 <β [mol] <2.35α- A laminated thermistor satisfying 2.32 and having a porosity of 5 to 25% is provided.
In the above general formula, x is preferably 0.05 ≦ x ≦ 0.3, and z is preferably 0.0002 ≦ z ≦ 0.0013. By setting x and / or z within this range, higher PTC characteristics can be obtained.

Moreover, it turned out that 1180-1280 degreeC is preferable for the calcination temperature in a reducing atmosphere from a viewpoint of manufacturing conditions. When it is fired at 1300 ° C. as in Patent Document 1, a high-density one is obtained, but the PTC characteristic does not show a desired value.
The oxidation treatment temperature after firing may be 500 to 850 ° C, more preferably 550 to 650 ° C.

  According to the present invention, it is possible to provide a laminated thermistor having low resistance and high PTC characteristics.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a cross-sectional view showing the configuration of the stacked thermistor according to the present embodiment.
The laminated thermistor 1 has a rectangular parallelepiped shape. The laminated body is formed by alternately laminating the semiconductor ceramic layers 2 and the internal electrodes 3 made of Ni-based metal, and the laminated body is integrally fired to form a sintered body 4. It is configured. This sintered body 4 is formed by baking the above-mentioned laminated body at a high temperature in a reducing atmosphere and then subjecting it to a low-temperature oxidation treatment in the atmosphere.

  Only one end face 3a of each internal electrode 3 is alternately exposed on the left end face 4a and the right end face 4b of the sintered body 4, and the other end face 3b is located inside the ceramic layer 2 and is located inside the sintered body 4. It is buried in. An external electrode 5 is formed on the left end surface 4 a and the right end surface 4 b of the sintered body 4, and the external electrode 5 is electrically connected to one end surface 3 a of the internal electrode 3. For example, Ag or an Ag—Pd alloy can be baked to form the external electrode 5.

In the present invention, the semiconductor ceramic layer 2 contains a compound represented by the following general formula.
(Ba _1-xy Sr _x Re _y ) _α TiO ₃ + βSiO ₂ + zMn Formula (1)
Here, Re is represented by at least one selected from the group consisting of Y, La, Ce, Sm, Er, Nd, and Dy,
x, y and α are each in molar ratio,
0 ≦ x ≦ 0.3,
0.002 ≦ y ≦ 0.008,
1.02 ≦ α ≦ 1.1,
z is 0 ≦ z [mol] ≦ 0.0015,
β satisfies 2.35α-2.39 <β [mol] <2.35α-2.32 in a range of 1.02 ≦ α ≦ 1.1.

The reasons for limiting x, y and z in the general formula are as follows.
X indicating the amount of Sr is in the range of 0 ≦ x ≦ 0.3. The Curie temperature can be changed by adding Sr. However, as x increases, the Curie temperature decreases, and when x exceeds 0.3, the difference between the Curie temperature and room temperature decreases, so the upper limit of x is set to 0.3. In the present application, the temperature at which the resistivity becomes twice the room temperature resistivity is called the Curie temperature. The Curie temperature needs to be adjusted according to the use of the PTC thermistor. For example, a PTC thermistor may be placed in the battery pack to detect the temperature of the battery cell. The Curie temperature required for the battery pack is 80 to 90 ° C. Therefore, when the PTC thermistor of the present invention is used for a battery pack, x may be in the range of 0.05 ≦ x ≦ 0.075.
Moreover, as shown in the Example mentioned later, a PTC characteristic can be improved by containing predetermined amount Sr rather than the case where Sr is not contained. When it is desired to obtain a high Curie temperature, x is preferably in the range of 0 ≦ x ≦ 0.25, and more preferably 0.05 ≦ x ≦ 0.15. When emphasizing PTC characteristics, x is preferably in the range of 0.05 ≦ x ≦ 0.3, and more preferably 0.1 ≦ x ≦ 0.3.

Re is represented by at least one selected from the group consisting of Y, La, Ce, Sm, Er, Nd, and Dy. Re functions as a semiconducting agent, and y indicating the amount is in the range of 0.002 ≦ y ≦ 0.008. Within this range, high PTC characteristics can be obtained. On the other hand, if y is less than 0.002, it is difficult to make the porcelain constituting the semiconductor ceramic layer 2 into a semiconductor. On the other hand, if y exceeds 0.008, the resistivity at room temperature (25 ° C.) (hereinafter referred to as “room temperature resistivity”) increases, and the PTC characteristics deteriorate.
y is preferably in the range of 0.002 ≦ y ≦ 0.006, more preferably 0.003 ≦ y ≦ 0.005. Among Re, Y and Sm are particularly preferred because of low room temperature resistivity and high PTC characteristics.

Z indicating the amount of Mn is in a range of 0 ≦ z ≦ 0.0015. The addition of Mn is effective in improving the PTC characteristics. However, if z becomes too large (for example, 0.1 mol), the room temperature resistivity becomes too high to obtain the PTC characteristic, and the NTC (Negative Temperature Coefficient) characteristic in which the resistance decreases with increasing temperature. Indicates.
z is preferably in the range of 0.0002 ≦ z ≦ 0.0013, more preferably 0.0005 ≦ z ≦ 0.001.

Here, a PTC thermistor (sample No. 1) prepared by performing reduction firing and oxidation treatment under the following conditions in the composition of (Ba _0.772 Sr _0.223 Y _0.005 ) _α TiO ₃ + βSiO ₂ +0.001 Mn. Table 1 shows the room temperature resistivity, PTC jump, and porosity of -26). The PTC jump is an index for determining the PTC characteristic, and was calculated as Log ₁₀ (resistivity at 200 ° C./resistivity at room temperature). As the PTC jump value is larger, it can be determined that the PTC characteristic is higher, and as described above, the lower the room temperature resistivity is preferable in terms of suppressing the power consumption of the PTC thermistor. Note that a pure Ni electrode was used as the internal electrode, and the reduction firing conditions and the oxidation treatment conditions were as follows.

Sample No. 1 to 26 reduction firing conditions:
Atmosphere: Mixed atmosphere of hydrogen and nitrogen (ratio of hydrogen and nitrogen is 1.2: 98.8 by volume)
Firing time: 2 hours Firing temperature: As shown in Table 1.
Sample No. 1 to 26 oxidation treatment conditions:
Atmosphere: Oxygen concentration 20% (in air)
Oxidation treatment time: 2 hours Oxidation treatment temperature: 600 ° C

As shown in Table 1, when α is fixed and β is varied, the room temperature resistivity, the PTC characteristic, and the porosity are varied. If β is too small or too large with respect to α, the room temperature resistivity and / or the PTC characteristics are deteriorated. For example, the sample No. with the same β value as 0.05 mol. 3 and sample no. 7 is compared with sample No. 7 in which α is 1.02. No. 3 shows a high PTC characteristic in which the room temperature resistivity is as low as 2.0 × 10 ⁴ [Ωcm] or less and the PTC jump is as high as 1.6 or more. No. 7 has insufficient PTC characteristics. That is, the SiO ₂ addition amount of 0.05 mol is an appropriate amount when α is 1.02, but is too small when α is 1.04.
Similarly, sample No. with the same β value as 0.24 mol. 18 and sample no. As compared with sample No. 21, sample No. Sample No. 21 having a low room temperature resistivity and high PTC characteristics, but α of 1.08. For room temperature 18, the room temperature resistivity was too high, indicating NTC characteristics instead of PTC characteristics. That is, the SiO ₂ addition amount of 0.24 mol is too large when α is 1.08, but it is an appropriate amount when the molar ratio Ba site / Ti site is 1.10.

FIG. It is the graph which plotted (alpha) and (beta) of 1-22. In FIG. 2, a sample having a PTC characteristic having a room temperature resistivity of 2 × 10 ⁴ [Ωcm] or less and a PTC jump of 1.6 or more is plotted with a square, and the room temperature resistivity or the PTC characteristic is outside the above range. Plotted with diamonds. As a result, 2.35α-2.39 <β <2.35α-2.32 (provided that 1.02 ≦ α ≦ 1.1) is satisfied for the sample having the desired room temperature resistivity and PTC characteristics. I was able to confirm. In other words, by controlling α and β within the above ranges, the room temperature resistivity and the PTC characteristic can be made preferable for the multilayer thermistor 1. Therefore, β should not be determined alone, but should be determined according to α.

  Sample No. As in 23 to 26, when α is less than 1.02 or α exceeds 1.10, the room temperature resistivity is increased and the PTC characteristics are deteriorated. Therefore, in the present invention, α is set to 1.02 ≦ α ≦ 1.10. α is preferably in the range of 1.02 ≦ α ≦ 1.08, and more preferably 1.02 ≦ α ≦ 1.05.

In the present invention, the porosity of the sintered body 4 is 5 to 25%. The porosity has a correlation with the room temperature resistivity and the PTC characteristics, and when the porosity is too low as less than 5%, the PTC characteristics deteriorate. On the other hand, if the porosity is higher than 25%, the room temperature resistivity increases and the PTC characteristics also deteriorate. For example, sample no. The porosity of 18 is 25.8%, which is outside the range recommended by the present invention. Sample No. No. 18 has a very high room temperature resistivity of 4.6 × 10 ⁹ and a PTC jump of −0.2, indicating no PTC characteristics.
A preferable porosity is 10 to 25%, and more preferably 10 to 23%. As shown in Table 1, α and β are within the range recommended in the present invention, and the sample No. in which the porosity is 10 to 25%. Nos. 2 to ^4, 8, 9, 14, and 15 have particularly preferable characteristics as the laminated thermistor 1 having a low room temperature resistivity of 1.0 × 10 ⁴ or less and a PTC jump of 2.0 or more.

Further, as a factor for changing the porosity, reduction firing conditions can also be mentioned. Even when the composition is within the range of the present invention, the sample No. Nos. 27 and 29 have a high room temperature resistivity of 1.0 × 10 ⁹ and insufficient PTC characteristics. Further, although the composition is within the range of the present invention, the sample No. 28 and 30 have low room temperature resistivity, but PTC characteristics are insufficient.

  In order to produce the laminated thermistor 1 described above, the raw materials are blended and calcined, and the obtained calcined body is pulverized to produce a slurry. And after producing the green sheet for semiconductor ceramic layers using the slurry, the internal electrode 3 is formed by printing the paste for internal electrodes on the upper surface of the green sheet. Subsequently, the laminated body obtained by laminating the green sheets is sintered, and the obtained sintered body 4 is subjected to oxidation treatment (heat treatment). Hereinafter, each process is explained in full detail.

As the main component material, an oxide or a compound that becomes an oxide by heating is used. Specifically, BaCO ₃ , TiO ₂ , SrCO ₃ , SiO ₂ , Mn (NO ₃ ) ₂ 6H ₂ O, and an oxide of Re (for example, Y ₂ O ₃ ) can be used. In addition, not only the raw material powder mentioned above but it is good also considering the powder of the complex oxide containing 2 or more types of metals as raw material powder. What is necessary is just to select suitably the average particle diameter of each raw material powder in the range of 0.1-3.0 micrometers.

After each raw material powder is weighed so as to have the composition of the above formula (1), the raw material powder is put into a nylon pot together with pure water and a grinding ball, pulverized and mixed for 4 to 8 hours, and then dried to obtain a mixed powder. obtain. This mixed powder is temporarily molded and calcined by holding it within a range of 1000 to 1200 ° C. for a predetermined time. The atmosphere at this time may be N ₂ or air. What is necessary is just to select suitably the holding time of calcination in the range of 0.5 to 5 hours.
Next, the calcined powder obtained by pulverizing this calcined body is put into a nylon pot together with pure water and grinding balls, and a solvent, a binder and a plasticizer are added thereto and mixed for 10 to 20 hours. A slurry of viscosity is obtained. The content of the solvent, binder, and plasticizer in the semiconductor ceramic layer slurry is not limited. For example, the content of the solvent is 10 to 50% by weight, and the content of the binder is in the range of about 1 to 10% by weight. Can be set. Moreover, in a slurry, a dispersing agent etc. can be contained in the range of 10 weight% or less as needed.

  The obtained slurry is applied onto a polyester film or the like by a doctor blade method or the like, and dried to produce a green sheet having a thickness of 10 to 100 μm. The green sheet is punched into strips to obtain a large number of semiconductor ceramic layer green sheets, and then an internal electrode paste is printed on the upper surface of the green sheet by screen printing or the like to form the internal electrodes 3. The internal electrode 3 is formed so that only one end surface 3a thereof extends to the edge of the green sheet and the other end surface 3b is positioned inside the green sheet. The internal electrode paste can be prepared by mixing Ni powder or Ni alloy powder and an electrical insulating material (varnish). As the Ni alloy powder, for example, Ni-Pd powder can be used.

  Next, the green sheets are laminated so that the semiconductor ceramic layers 2 and the internal electrodes 3 are alternately overlapped, and one end surfaces 3a of the internal electrodes 3 are alternately exposed at the left and right edges of the semiconductor ceramic layer 2, The semiconductor ceramic layer 2 on which the internal electrode 3 is not formed is overlaid on the lower surface. This is pressed and pressed in the laminating direction with a press. The pressure-bonded body is cut into a desired size with a cutter or the like to obtain a laminate. As a result, only one end face 3a of each internal electrode 3 is exposed on the left end face or right end face of the laminate, and the remaining end face 3b is sealed inside the laminate.

  The laminate is heated and held at 400 to 600 ° C. for 1 to 2 hours in the air to remove the binder. Thereafter, the laminated body is sintered in a reducing atmosphere at 1180 to 1280 ° C. for 0.5 to 4 hours to obtain a sintered body 4. The reducing atmosphere can be, for example, a mixed atmosphere of hydrogen and nitrogen, and the reason why sintering is performed in the reducing atmosphere is to prevent oxidation of the Ni-based metal electrode as the internal electrode 3.

Subsequently, the sintered body 4 is subjected to oxidation treatment (heat treatment) in an oxidizing atmosphere. The conditions for the oxidation treatment must be capable of improving the PTC characteristics of the semiconductor ceramic layer 2 while preventing oxidation of the Ni-based metal electrode. For example, the oxidation treatment can be performed by heating and holding the sintered body 4 at 500 to 850 ° C. for 0.5 to 6 hours in the atmosphere. When the oxidation treatment temperature is less than 500 ° C., the oxidation treatment does not proceed sufficiently. Further, when the oxidation treatment temperature exceeds 850 ° C., the internal electrode 3 is oxidized. The temperature of the oxidation treatment is preferably 550 to 650 ° C., and the oxidation treatment time is preferably 0.4 to 6 hours, more preferably 0.4 to 3 hours. During the oxidation treatment, the room temperature resistivity and the PTC characteristics can be changed by changing the oxygen concentration. The oxygen concentration must be set according to the oxidation treatment temperature and the oxidation treatment time. When the oxidation treatment temperature is 550 to 650 ° C. and the oxidation treatment time is 2 hours, the oxygen concentration may be about 10 to 30%. Even if the treatment time is 2 hours, the oxygen concentration is preferably 1.0% or less, more preferably about 0.1 to 0.5% when the oxidation treatment temperature is higher. In addition, it is necessary to set the temperature and time of an oxidation process suitably according to the dimension of the sintered compact 4. FIG.
After the external electrode paste is applied to the left end surface 4a and the right end surface 4b of the sintered body 4 after the oxidation treatment, the external electrode 5 is formed by baking at 550 to 650 ° C. in the atmosphere to form the external electrode 5 and the internal electrode 3. By electrically connecting the one end surface 3a, the laminated thermistor 1 shown in FIG. 1 can be obtained. As the external electrode paste, for example, an Ag paste or an Ag—Pd paste can be used.

Hereinafter, the present invention will be described based on specific examples.
_{BaCO 3, TiO 2, SrCO 3} , Y 2 O 3, SiO 2, Mn (NO 3) 2 · 6H 2 O and were weighed respectively so as to obtain the composition shown in Table 3, nylon with deionized water and milling balls After putting in a pot and mixing for 6 hours, it was dried and mixed powder was obtained. This mixed powder was temporarily molded and calcined at 1100 ° C. for 4 hours. The atmosphere at this time was air. Next, the calcined powder (average particle size 1 μm) obtained by pulverizing this calcined body is put in a nylon pot together with pure water and grinding balls, and a solvent, a binder and a plasticizer are added thereto to add 3 The slurry was mixed for 20 hours to obtain a slurry for forming a semiconductor ceramic layer. The mixing ratio of the solvent, binder and plasticizer was as follows.
Solvent: 50 parts by weight was blended with 100 parts by weight of the powder.
Binder: 5 parts by weight was blended with 100 parts by weight of the powder.
Plasticizer: 2.5 parts by weight was blended with 100 parts by weight of the powder.

The obtained semiconductor ceramic layer forming slurry was applied onto a polyester film by a doctor blade method and dried to prepare a green sheet having a thickness of 80 μm. The green sheet was punched to a size of 50 mm × 50 mm to obtain a large number of ceramic layer green sheets, and then an internal electrode paste was printed on the upper surface of the green sheet by screen printing to form internal electrodes. The internal electrode paste was prepared by adding 10 parts by weight of BaTiO ₃ as an electrical insulating material to 100 parts by weight of Ni powder having an average particle size of 0.2 μm and kneading.
Laminate green sheets so that one end face of the internal electrode is alternately exposed at the left end and right end of the ceramic layer. Overlay the green sheet on which the internal electrode is not formed on the top and bottom surfaces of the green sheet. Pressurized and pressure bonded. The pressure-bonded body was cut with a cutter to obtain a laminate of 2 mm × 1.2 mm × 1.2 mm.
The laminate was heated and held at 600 ° C. for 2 hours in the air to remove the binder, and then the laminate was sintered at 1200 ° C. for 2 hours in a reducing atmosphere to obtain a sintered body. The reducing atmosphere was a mixed atmosphere of hydrogen and nitrogen, and the ratio of hydrogen to nitrogen was 1:99.
Subsequently, the sintered body was heated and held at 800 ° C. for 2 hours in the atmosphere to carry out an oxidation treatment. The oxygen concentration was 0.2%. An Ag paste was applied to the left end surface and the right end surface of the sintered body after the oxidation treatment, and then baked at 650 ° C. in the atmosphere to form external electrodes. Thus, a multilayer thermistor having the configuration shown in FIG. 1 was obtained. About the obtained lamination type thermistor, the resistivity in 25-200 degreeC was measured. The result is shown in FIG. Further, the Curie temperature and PTC jump of the laminated thermistor were obtained. The results are shown in Table 3.

  As shown in Table 3 and FIG. 3, the Curie temperature and the PTC characteristic can be changed by adding Sr. PTC characteristics improve as x increases, but on the other hand, since the Curie temperature decreases, x is preferably 0 ≦ x ≦ 0.3, more preferably 0 ≦ x ≦ 0.25. When it is desired to obtain a PTC jump of 2.2 or more, x is preferably in the range of 0.05 ≦ x ≦ 0.3, more preferably 0.1 ≦ x ≦ 0.3. .

BaCO ₃ , TiO ₂ , SrCO ₃ , SiO ₂ , Mn (NO ₃ ) ₂ .6H ₂ O, Re oxide (Ba _0.777-y Sr _0.223 Re _y ) _1.00 TiO ₃ + 0.05SiO ₂ +0.001 Mn or (Ba _0.777-y Sr _0.223 Re _y ) _1.02 TiO ₃ + 0.05SiO ₂ +0.001 Mn, and the value of y is 0.003 mol, 0 A laminate was produced under the same conditions as in Example 1 except that the amount was 0.005 mol or 0.010 mol. As Re, Yb was used as a comparative example in addition to La, Nd, Sm, and Y recommended by the present invention.
Next, after removing the binder from the laminate under the same conditions as in Example 1, the laminate was sintered at each temperature shown in Table 4 for 2 hours in a reducing atmosphere to obtain a sintered body. The reducing atmosphere was a mixed atmosphere of hydrogen and nitrogen, and the ratio of hydrogen to nitrogen was 1:99. Subsequently, the sintered body was heated and held at 600 ° C. for 2 hours in the atmosphere to perform an oxidation treatment.
After applying an Ag paste to the left end surface and right end surface of the sintered body after the oxidation treatment, it was baked at 600 ° C. in the atmosphere to form an external electrode, thereby obtaining a multilayer thermistor having the configuration shown in FIG. About the obtained laminated thermistor, the resistivity (room temperature resistivity) at 25 ° C., the PTC jump, and the density were measured. Further, the Curie temperature and PTC jump of the laminated thermistor were obtained. The results are shown in Table 4. Note that “high” is displayed in the room temperature resistivity column if the room temperature resistivity is 1 × 10 ⁹ Ωcm or more.

As shown in Table 4, when Yb was used as Re, desired PTC characteristics could not be obtained even when the values of A / B and y and the reduction firing temperature were varied. On the other hand, when La, Nd, Sm, and Y were used as Re and A / B was 1.02, it was possible to combine low room temperature and low efficiency and high PTC characteristics. However, when A / B is 1.02, the YTC is preferably 0.002 to 0.008 mol because the PTC characteristics are deteriorated when y is 0.010 mol.
In addition, when reduced firing at 1300 ° C., each sample showed a high density, but a PTC jump of 0.5 or more could not be obtained. In the case of reduction firing at 1300 ° C., since the sintered body is dense, even if an oxidation treatment is performed thereafter, oxygen hardly penetrates into the sintered body and the oxidation treatment does not proceed sufficiently. It is assumed that there is.

Under the same conditions as in Example 1, except that BaCO ₃ , TiO ₂ , SrCO ₃ , SiO ₂ , Mn (NO ₃ ) ₂ .6H ₂ O, and Y ₂ O ₃ were each weighed to have the composition shown in Table 5. A laminated thermistor was produced. About the obtained lamination type thermistor, the resistivity in 25-200 degreeC was measured. The result is shown in FIG. The PTC jump was calculated. The results are shown in Table 5.

As shown in Table 5, when the amount of Mn was 0 to 0.002 mol, a PTC jump of 2.5 or more was shown, but when the amount was 0.1 mol, not PTC characteristics but NTC characteristics were shown.
As shown in FIG. 4, when the amount of Mn is 0.001 mol, the room temperature resistivity is the same as when the amount of Mn is 0 mol, but when the amount of Mn is 0.002 mol, the room temperature resistivity is greatly increased. Increased.
Therefore, in order to combine low room temperature resistivity and high PTC characteristics, the amount of Mn, that is, z is preferably 0 ≦ z ≦ 0.0015, more preferably 0.0005 ≦ z ≦ 0.001.

Under the same conditions as in Example 1, except that the oxides of BaCO ₃ , TiO ₂ , SrCO ₃ , SiO ₂ , Mn (NO ₃ ) ₂ .6H ₂ O, and Re were each weighed to have the composition shown in Table 6. A laminated thermistor was produced. About the obtained laminated thermistor, room temperature resistivity, PTC jump, and porosity were measured. The results are shown in Table 6.

  As shown in Table 6, even when Sm, La, Ce, Er, Nd, and Dy are used as Re, by setting the composition and porosity within the range recommended by the present invention, the room temperature resistivity is low, A PTC thermistor with high PTC characteristics could be obtained. In particular, when Sm was used as Re, it was confirmed that the room temperature resistivity was low and the PTC characteristics were high.

  A raw material powder was weighed so as to have the composition shown in Table 7, and a laminated thermistor was produced under the same conditions as in Example 1 except that the sintered body after reduction firing was oxidized under the conditions shown in Table 7. did. About the obtained lamination | stacking type | mold thermistor (sample No. 31-40), the resistivity in 25-200 degreeC was measured. The results are shown in FIGS. The PTC jump was calculated. The results are shown in Table 7.

FIG. 5 shows a sample No. with an oxidation treatment temperature of 800 ° C. The result of having measured the resistivity in each temperature about 31-33 is shown. 6 shows a sample No. having an oxidation treatment temperature of 700 ° C. FIG. The result of having measured the resistivity in each temperature about 34-36 is shown. As shown in FIGS. 5 and 6, if the oxidation treatment temperature is the same, the higher the oxygen concentration, the higher the room temperature resistivity.
As shown in Table 7, when the oxidation treatment temperature is 800 ° C., the PTC jump is large when the oxygen concentration is 2%, and when the oxidation treatment temperature is 700 ° C., the PTC jump is large when the oxygen concentration is 20%. Become. Therefore, the oxygen concentration during the oxidation treatment needs to be appropriately set according to the oxidation treatment temperature.
From the viewpoint of low room temperature resistivity and good PTC characteristics, the oxygen concentration is 0.2 to 2% when the oxidation treatment temperature is 800 ° C., and the oxygen concentration is 0.2 to 0.2 when the oxidation treatment temperature is 700 ° C. 20% is preferable.

7 shows a sample No. with an oxidation treatment temperature of 600 ° C. or 500 ° C. The result of having measured the resistivity in each temperature about 37-40 is shown. Sample No. having an oxidation treatment temperature of 600 ° C. 37 and sample no. No. 38 shows the same PTC characteristics even when the oxidation treatment time is different as shown in Table 7, and the room temperature resistivity is also equivalent as shown in FIG.
Sample No. having an oxidation treatment temperature of 500 ° C. 39 (oxidation treatment time: 2 h) and sample no. 40 (oxidation treatment time: 5h), sample No. No. 40 shows better PTC characteristics. 37 and sample no. 38. In consideration of productivity, sample No. An oxidation treatment condition of 38 is preferred.

  FIG. For 33, 36, 37, and 39, the results of measuring the resistivity at each temperature are shown. Sample No. 33, 36, 37 and 39 are oxidized under the same conditions except that the oxidation treatment temperatures are different. Since the room temperature resistivity is small and the PTC characteristics are good, it has been found that the oxidation treatment at around 600 ° C. is preferable.

  A raw material powder was weighed so as to have the composition shown in Table 8, and a laminated thermistor was produced under the same conditions as in Example 1 except that the sintered body after reduction firing was oxidized under the conditions shown in Table 8. did. The end portion of the obtained laminated thermistor was blasted to expose the Ni internal electrode, and then an Ag paste was applied to measure the resistivity of the Ni internal electrode. The results are shown in Table 8 and FIG.

As shown in Table 8 and FIG. 9, it can be said that the resistivity of the Ni internal electrode increases as the oxygen concentration increases to 0.2%, 2.0%, and 20.8%, and the oxidation of the Ni internal electrode proceeds. . However, when the oxidation treatment temperature was 500 ° C. or 600 ° C., the increase in resistivity could be suppressed even if the oxygen concentration was as high as 20.8%. Therefore, in order to prevent oxidation of the Ni internal electrode, it was confirmed that the oxidation treatment temperature is preferably 500 to 650 ° C., more preferably 550 to 600 ° C. From the viewpoint of preventing the Ni internal electrode from being oxidized and greatly improving the PTC characteristics, it is preferable to perform the oxidation treatment at 550 to 650 ° C.
When the oxidation treatment temperature is 800 ° C. or 700 ° C., the resistance rapidly increases when the oxygen concentration is changed from 0.2% to 2.0%, so that the oxygen concentration is 1.0% or less, and further 0.1 to 0 0.5% is preferable.

It is sectional drawing for demonstrating the laminated type thermistor in this Embodiment. Sample No. It is the graph which plotted (alpha) and (beta) of 1-22. 3 is a graph showing the resistivity at 25 to 200 ° C. of the laminated thermistor produced in Example 1. FIG. 6 is a graph showing the resistivity at 25 to 200 ° C. of the laminated thermistor produced in Example 3. It is a graph which shows the resistivity in 25-200 degreeC of the laminated | stacked thermistor (sample No. 31-33) produced in Example 5. FIG. It is a graph which shows the resistivity in 25-200 degreeC of the laminated | stacked thermistor (sample No. 34-36) produced in Example 5. FIG. It is a graph which shows the resistivity in 25-200 degreeC of the laminated | stacked thermistor (sample No. 37-40) produced in Example 5. FIG. It is a graph which shows the resistivity in 25-200 degreeC of the laminated | stacked thermistor produced in Example 5 (sample No. 33, 36, 37, 39). 10 is a graph showing the electrode resistivity of the laminated thermistor produced in Example 6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Multilayer thermistor, 2 ... Semiconductor ceramic layer, 3 ... Internal electrode, 4 ... Sintered body, 5 ... External electrode

Claims (6)

A laminated thermistor having semiconductor ceramic layers and internal electrodes alternately stacked and having an external electrode electrically connected to the internal electrode and having a positive resistance temperature characteristic,
The internal electrode is made of a Ni-based metal,
The semiconductor ceramic layer is composed of a sintered body containing a compound represented by the general formula (Ba _1-xy Sr _x Re _y ) _α TiO ₃ + βSiO ₂ + zMn, where Re is Y, La, Ce, Sm, Er. And at least one selected from the group consisting of Nd, Dy,
x, y and α are each in molar ratio,
0 ≦ x ≦ 0.3,
0.002 ≦ y ≦ 0.008,
1.02 ≦ α ≦ 1.1,
z is 0 ≦ z [mol] ≦ 0.0015,
β satisfies 2.35α-2.39 <β [mol] <2.35α-2.32 in the range of 1.02 ≦ α ≦ 1.1,
A laminated thermistor, wherein the sintered body has a porosity of 5 to 25%.   The multilayer thermistor according to claim 1, wherein 0.05 ≦ x ≦ 0.3.   The stacked thermistor according to claim 1, wherein 0.0002 ≦ z ≦ 0.0013.   The laminated thermistor according to claim 1, wherein 1.02 ≦ α ≦ 1.08. A laminated thermistor having positive resistance temperature characteristics, wherein semiconductor ceramic layers and internal electrodes made of Ni-based metal are alternately laminated, and have external electrodes electrically connected to the internal electrodes. A manufacturing method comprising:
Obtaining a laminate in which the semiconductor ceramic layer forming sheet and the internal electrode material are alternately laminated; and
Sintering the laminate at 1180-1280 ° C. in a reducing atmosphere to obtain a sintered body;
Heat-treating the sintered body at 500 to 850 ° C. in an oxidizing atmosphere,
The semiconductor ceramic layer is composed of a sintered body containing a compound represented by the general formula (Ba _1-xy Sr _x Re _y ) _α TiO ₃ + βSiO ₂ + zMn, where Re is Y, La, Ce, Sm, Er. And at least one selected from the group consisting of Nd, Dy,
x, y and α are each in molar ratio,
0 ≦ x ≦ 0.3,
0.002 ≦ y ≦ 0.008,
1.02 ≦ α ≦ 1.1,
z is 0 ≦ z [mol] ≦ 0.0015,
β satisfies 2.35α-2.39 <β [mol] <2.35α-2.32 in the range of 1.02 ≦ α ≦ 1.1.   The method for manufacturing a laminated thermistor according to claim 5, wherein the sintered body is heat-treated at 550 to 650 ° C.

Images