JP5141736B2 - Multilayer thermistor element - Google Patents

Description

  The present invention relates to a laminated thermistor element.

  Conventionally, a thermistor element for measuring the temperature of automobile exhaust gas or the like has been mainly capable of detecting temperatures up to 800 ° C. However, recently, it has been desired to develop a thermistor element capable of measuring a high temperature up to 1100 ° C., for example.

  Since platinum has high temperature resistance, a thermistor element that contains platinum in the external electrode layer and can be used at high temperatures up to 1000 ° C. is known. However, in a continuous use environment at a higher temperature near 1100 ° C., the phenomenon that the external electrode layer containing platinum aggregates and the area of the external electrode layer in the plane decreases may occur, and the resistance value of the thermistor element varies. May occur.

  In order to improve the adhesion to the element body, a thermistor element is known in which the external electrode layer is composed of a metal layer and a layer containing metal and ceramic (see Patent Document 1).

  The thermistor element shown in Patent Document 1 is not a laminated thermistor element, and it is not necessary to consider contact with the internal electrode layer. Since the external electrode layer shown in Patent Document 1 has too much ceramic content, when the external electrode layer is applied to a laminated thermistor element, electrical connection between the external electrode layer and the internal electrode layer is insufficient. Therefore, there is a possibility that the resistance value of the laminated thermistor element varies.

Japanese Patent Laid-Open No. 4-322401

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a highly reliable stacked thermistor element in which the resistance value does not vary even during continuous use at high temperatures.

In order to achieve the above object, the laminated thermistor element according to the present invention is:
An element body having at least a pair of internal electrode layers and a thermistor layer sandwiched between the internal electrode layers;
A laminated thermistor element formed on the surface of the element body and having an external electrode layer electrically connected to the internal electrode layer,
The external electrode layer is
A first external electrode layer formed directly on the surface of the element body;
A second external electrode layer formed on the surface of the first external electrode layer,
The first external electrode layer includes platinum particles and ceramic particles, and the second external electrode layer is composed of platinum particles;
When the total of the platinum particles and the ceramic particles in the first external electrode layer is 100 vol%, the ceramic particles are 30 to 50 vol%.

  In the present invention, since the first external electrode layer contains 30 vol% or more of ceramic particles, the external electrode layer is not likely to aggregate even during continuous use at around 1100 ° C. Therefore, the area of the external electrode layer in the plane is constant during high temperature use, and the resistance value of the laminated thermistor element does not vary. Further, since the insulating ceramic particles contained in the first external electrode layer is 50 vol% or less, it is possible to ensure good electrical connection between the external electrode layer including the first external electrode layer and the internal electrode layer. Thus, it is possible to prevent variation in the resistance value of the laminated thermistor element. As described above, even in a relatively high temperature use environment around 1100 ° C., the resistance value of the laminated thermistor element does not vary, so that the reliability can be improved.

  Further, since the second external electrode layer is composed of platinum particles, the structure of the second external electrode layer is dense, and there is little possibility of moisture or the like entering the internal electrode in the manufacturing process of the laminated thermistor element.

  Preferably, the ceramic particles are the same as the ceramic particles constituting the thermistor layer. By making the ceramic particles in the first external electrode layer the same as the ceramic particles in the thermistor layer, the adhesion between the first external electrode layer and the element body is improved, and the external particles are continuously used at around 1100 ° C. Aggregation of the electrode layer can be effectively prevented. Moreover, the manufacturing process can be simplified by using the same ceramic particles for the thermistor layer and the first external electrode layer.

  Preferably, the first external electrode layer is a fired body of a paste film containing the platinum particles and the ceramic particles, and the second external electrode layer is a fired body of a paste film containing the platinum particles. Preferably, the internal electrode layer, the thermistor layer, and the external electrode layer are formed by simultaneous firing.

  Even if it is formed by simultaneous firing, it is possible to prevent the occurrence of delamination or the like based on the difference in shrinkage ratio between the element body and the external electrode layer (first external electrode layer + second external electrode layer) as much as possible. Further, simplification of the manufacturing process can be achieved by simultaneous firing.

FIG. 1 is a longitudinal sectional view of an essential part of a multilayer thermistor element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the laminated thermistor element taken along line II-II shown in FIG. FIG. 3A is an explanatory diagram showing a manufacturing process of the multilayer thermistor element shown in FIG. FIG. 3B is an explanatory diagram showing a manufacturing process of the multilayer thermistor element shown in FIG. 1. FIG. 4 is a longitudinal sectional view of a main part of a laminated thermistor element according to another embodiment of the present invention. FIG. 5 is a cross-sectional view of the laminated thermistor element taken along line VV shown in FIG. FIG. 6 is a cross-sectional view of a stacked thermistor element after a high temperature experiment in a comparative example.

First Embodiment As shown in FIGS. 1 and 2, a laminated thermistor element 2 according to an embodiment of the present invention includes an element body 4, a pair of external electrode layers 10, and a pair of lead terminals 12 extending in parallel. And an insulating layer 14. A direction parallel to a line connecting the pair of lead terminals 12 is defined as an X axis, a direction in which the lead terminals 12 extend is defined as a Y axis, and a direction perpendicular to the X axis and the Y axis is defined as a Z axis.

  The element body 4 has a rectangular parallelepiped shape. A pair of external electrode layers 10 are formed on two surfaces constituting both end surfaces in the X-axis direction of the element body 4 so as to be connected to an internal electrode layer 8 described later. Each external electrode layer 10 is formed on the entire surface of both end surfaces of the element body 4 in the X-axis direction, but it is not necessarily formed on the entire surface.

  Each external electrode layer 10 includes a first external electrode layer 10a directly formed on both end faces in the X-axis direction of the element body 4, and a second external electrode formed on the surface of each first external electrode layer 10a. Layer 10b. A pair of lead terminals 12 are connected to the external electrode layer 10 by a Pt connection layer 16 so as to sandwich the element body 4 on which the external electrode layer 10 is formed.

  Internal electrode layers 8 are alternately stacked inside the element body 4 so as to sandwich the thermistor layers 6 having NTC characteristics. In this embodiment, the plane of the internal electrode layer 8 is a direction parallel to the plane including the X axis and the Y axis. One internal electrode layer 8 sandwiching the thermistor layer 6 is connected to one external electrode layer 10, and the other internal electrode layer 8 is connected to the other external electrode layer 10. The thermistor layer 6 sandwiched between the electrode layers 8 serves as a sensor portion.

  As shown in FIG. 2, the internal electrode layers 8 stacked alternately via the thermistor layers 6 are respectively connected to a pair of external electrode layers 10 formed on both end surfaces in the X-axis direction of the element body 4. A thermistor layer 6a that does not function as a sensor portion is laminated at both ends of the element body 4 in the lamination direction (Z-axis direction).

  The material of the NTC characteristic thermistor layer 6 (including the thermistor layer 6a) is not particularly limited as long as it is a semiconductor ceramic. For example, yttrium (Y), calcium (Ca), chromium (Cr), aluminum (Al), etc. It is composed of a material containing an elemental oxide as a main component. In addition, an auxiliary component may be contained for improving characteristics. As a subcomponent, tin (Sn), cobalt (Co), or the like may be contained. What is necessary is just to determine suitably a composition and content of a main component and a subcomponent according to a desired characteristic. The particle size of the ceramic particles in the thermistor layer 6 (including the thermistor layer 6a) is preferably 0.5 to 2.0 μm.

  The thickness of the thermistor layer 6 is not particularly limited, but is preferably about 10 to 100 μm in this embodiment. Moreover, the thickness of the thermistor layer 6a laminated | stacked on the outer side is although it does not specifically limit, Preferably it is 40-600 micrometers.

  The conductive material constituting the internal electrode layer 8 is preferably composed of Pt, but may be composed of a noble metal such as Ag, Pd, Au, Pt, and alloys thereof (such as Pt—Pd alloy). . In the present embodiment, the internal electrode layer 8 is formed by co-firing Pt paste together with the green sheets constituting the thermistor layers 6 and 6a. The thickness of the internal electrode layer 8 is preferably 0.5 to 3.0 μm.

  The thickness of the external electrode layer 10 is not particularly limited, but is preferably 2 to 15 μm. The first external electrode layer 10a is composed of Pt particles and ceramic particles. The material and particle size of the ceramic particles in the first external electrode layer 10a are preferably the same as the ceramic particles in the thermistor layer 6, but may be somewhat different.

  When the total of Pt particles and ceramic particles in the first external electrode layer 10a is 100 vol%, the ceramic particles are 30 to 50 vol%. The first external electrode layer 10 a is formed by applying a paste film containing Pt particles and ceramic particles and simultaneously firing the element body 4. The second external electrode layer 10 b is formed by applying a paste film containing Pt particles and simultaneously firing the element body 4.

  In the present embodiment, the lead terminal 12 is formed of a wire having an elliptical cross section, and the length of the elliptical minor axis is not particularly limited, but is preferably 0.1 to 0.4 μm. In this embodiment, the lead terminal 12 is made of Pt, but may be made of a heat-resistant alloy based on Fe (for example, stainless steel) or a heat-resistant alloy based on Ni. The Pt connection layer 16 is formed by applying and baking a Pt paste 16A as shown in FIG. 3B when the lead terminal 12 is connected to the external electrode layer 10 after firing. The internal electrode layer 8, the second external electrode layer 10b, and the Pt connection layer 16 are preferably formed from the same Pt paste 16A. Materials can be shared and manufacturing costs can be reduced.

  The leading end of the lead terminal 12 covers at least the portion connected to the external electrode layer 10 (second external electrode layer 10b), covers the entire circumference of the element body 4, and exposes the rear end portion of the lead terminal 12. The insulating layer 14 covers the periphery of the element body 4.

  The insulating layer 14 preferably has a heat resistance of 1100 ° C. or higher. The stacked thermistor element 2 is disposed inside the metal case 18. The metal case 18 is made of stainless steel, for example.

  Next, an example of a method for manufacturing the laminated thermistor 2 according to this embodiment will be described. A method for manufacturing the laminated thermistor according to the present embodiment is not particularly limited, and a known method may be used. However, in the following description, a case where a sheet method is used is illustrated.

  First, a Pt paste is prepared. The internal electrode layer 8, the second external electrode layer 10b, and the Pt connection layer 16 are formed using this Pt paste.

  Next, a green sheet is prepared. The raw materials of the material constituting the thermistor layer are uniformly mixed by means such as wet mixing and then dried. As a raw material for the thermistor layer, oxides, carbonates, nitrates, etc. of Y, Ca, Cr, Al, Co, Sn are used. This type of material may contain inevitable impurities such as Si, K, Na, Ni and the like in an amount of about 0.1% by weight or less.

  Next, the material constituting the thermistor layer is temporarily fired, and the calcined powder is wet pulverized. The pre-baking condition is preferably 1100 to 1300 ° C. Part of the wet-pulverized ceramic particles is used later as a material for the first external electrode layer paste. Then, a binder or a solvent is added to the pulverized calcined powder to form a slurry. Next, the slurry is formed into a sheet by means such as a doctor blade method or a screen printing method, and then dried to obtain a green sheet. In addition, it is preferable that the particle size of the ceramic particle at this time is 0.5-2.0 micrometers.

  By performing screen printing using the Pt paste on the green sheet thus obtained, a green sheet on which a Pt paste film having a predetermined pattern is formed is obtained. This Pt paste film becomes the internal electrode layer 8 later. A green sheet on which a Pt paste film having a predetermined pattern is formed on a surface and a green sheet on which no Pt paste film is formed are prepared.

  Next, these green sheets are overlapped, pressure is applied and pressure-bonded, and after necessary steps such as a drying step, the green sheets are cut to obtain the element body 4 in a green state.

  Next, a first external electrode layer paste to be the first external electrode layer 10a is applied to the two surfaces where the internal electrode layer 8 of the element body 4 in the green state is exposed. The first external electrode layer paste includes Pt particles, the above-described ceramic particles, a binder, and a solvent. The ratio of the Pt particles and the ceramic particles in the first external electrode layer paste is 30 to 50 vol%, preferably 40 to 50 vol%, when the total of the Pt particles and the ceramic particles is 100 vol%. .

  The above-described Pt paste is applied to the surface of the first external electrode layer paste formed on the element body 4 as the second external electrode layer paste that becomes the second external electrode layer 10b. Thereafter, the element body 4 on which the first external electrode layer paste and the second external electrode layer paste are formed is dried and integrally fired together with the element body 4 (shown in FIG. 3A). As firing conditions, firing is preferably performed at 1500 ° C. to 1600 ° C. In this way, the element body 4 in which the external electrode layer 10 is formed is obtained.

  Next, the tip of the lead terminal 12 is bonded to the external electrode layer 10 (second external electrode layer 10b) formed on the element body 4 using a Pt paste 16A (shown in FIG. 3B). That is, the lead terminal 12 is brought into contact with the second external electrode layer 10b via the Pt paste 16A and dried, and the leading end portion of the lead terminal 12 is baked on the external electrode layer 10. As a condition for the baking treatment, baking is preferably performed at 1100 to 1300 ° C.

Next, an insulating layer 14 is formed around the element body 4 to which the lead terminals 12 are bonded. As a material for the insulating layer 14, it is preferable to use glass or ceramic having heat resistance of 1100 ° C. or higher. As a preferred ceramic, for example, Al ₂ O ₃ , MgO, SiO ₂ or a mixture thereof is used.

  The element body 4 to which the tip of the lead terminal 12 is bonded is coated with a paste to be the insulating layer 14 by dipping or the like. Thereafter, firing is performed. As firing conditions, firing is preferably performed at 1000 to 1200 ° C. In this way, the desired thermistor element 2 in which the element body 4 is covered with the insulating layer 14 is obtained.

  Although the description has been made so that the element body 4 is covered with the single insulating layer 14, the insulating layer may be a multilayer. The element body 4 covered with the insulating layer may not be placed in the metal case 18.

  In the present embodiment, since the first external electrode layer 10a contains 30 vol% or more of ceramic particles, the external electrode layer 10 is not likely to aggregate even during continuous use near 1100 ° C. Therefore, the area of the external electrode layer 10 in the plane is constant during high temperature use, and the resistance value of the laminated thermistor element 2 does not vary. Further, since the insulating ceramic particles contained in the first external electrode layer 10a is 50 vol% or less, good electrical connection between the external electrode layer 10 including the first external electrode layer 10a and the internal electrode layer 8 is ensured. It is possible to prevent variation in the resistance value of the laminated thermistor element 2. As described above, even in a relatively high temperature use environment around 1100 ° C., the resistance value of the multilayer thermistor element 2 does not vary, so that the reliability can be improved.

  Further, since the second external electrode layer 10b is composed of Pt particles, the structure of the second external electrode layer 10b is dense, and moisture and the like enter the internal electrode 8 in the manufacturing process of the multilayer thermistor element 2. There is little possibility to do.

  By making the ceramic particles in the first external electrode layer 10a the same as the ceramic particles in the thermistor layers 6 and 6a, the adhesion between the first external electrode layer 10a and the element body 4 becomes better, and at around 1100 ° C. During continuous use, the aggregation of the external electrode layer 10 can be effectively prevented. Further, by using the same ceramic particles for the thermistor layers 6 and 6a and the first external electrode layer 10a, the manufacturing process can be simplified.

  Even if the element body 4 and the external electrode layer 10 are formed by simultaneous firing, delamination based on the difference in shrinkage between the element body 4 and the external electrode layer 10 (first external electrode layer 10a + second external electrode layer 10b), etc. Can be prevented as much as possible. Further, simplification of the manufacturing process can be achieved by simultaneous firing.

The second embodiment is the same as the above-described first embodiment except for the following, and redundant description is omitted. As shown in FIGS. 4 and 5, in the present embodiment, at the tip end side of the lead terminal 12, at least the tip end portion 12 a connected to the second external electrode layer 10 b has a flat plate shape with a rectangular cross section. The vertical and horizontal dimensions of the cross section of the distal end portion 12a of the lead terminal 12 are preferably 0.1 to 0.4 mm × 0.2 to 0.5 mm. The lead terminal 12 of the present embodiment is formed by pressing the tip portion 12a of a wire having a circular cross section. The lead terminal 12 may have a flat plate shape from the front end to the rear end.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.
Example 1
First, a green sheet was prepared. Y, Ca, Cr, Al, Co, Sn oxides, carbonates and nitrates were uniformly mixed by wet mixing and then dried. Next, it was calcined under firing conditions of 1100 to 1300 ° C., and the calcined powder was wet pulverized to obtain ceramic particles. A binder and a solvent were added to the obtained ceramic particles to form a slurry. Next, the slurry was formed into a sheet by a doctor blade method and then dried to obtain a green sheet.

  A Pt paste (internal electrode layer paste) containing Pt particles, a binder, and a solvent was prepared, and a Pt paste film was formed on the surface of the green sheet by screen printing. A green sheet having a Pt paste film formed on the surface and a green sheet having no Pt paste film formed on the surface were prepared.

  Next, these green sheets were superposed, pressure was applied and pressure-bonded, and after a drying step, the green sheets were cut to obtain a green element body 4.

  Next, a first external electrode layer paste was prepared, and the first external electrode layer paste was applied to the two surfaces where the internal electrode layer 8 of the element body 4 in the green state was exposed. As the first external electrode layer paste, a paste containing Pt particles, ceramic particles after wet pulverization, a binder, and a solvent was used. The ratio of Pt particles and ceramic particles in the first external electrode layer paste was 30 vol% of ceramic particles when the total of Pt particles and ceramic particles was 100 vol%.

  Next, the same Pt paste as the internal electrode layer paste was applied as a second external electrode layer paste to the surface of the first external electrode layer paste. Thereafter, the element body 4 to which the first external electrode layer paste and the second external electrode layer paste were applied was dried and integrally co-fired under firing conditions of 1600 ° C. (shown in FIG. 3A). Thus, the element body 4 in which the external electrode layer 10 (first external electrode layer 10a + second external electrode layer 10b) was formed was obtained. The ratio of Pt particles and ceramic particles in the first external electrode layer 10a after firing was 30 vol% when the total of Pt particles and ceramic particles was 100 vol%.

  In this way, 20 of the element bodies 4 on which the external electrodes 10 were formed were sampled, and whether or not the external electrode layer 10 was in contact with the internal electrode layer 8 was evaluated. In addition, since the resistance value increases when the contact becomes defective, the contact evaluation was performed based on the resistance value variation. Coefficient of variation CV (%) = standard deviation / average value × 100. The results are shown in Table 1.

  Next, 20 of the element bodies 4 on which the external electrodes 10 were formed as described above were sampled, and these were exposed to a high temperature of 1100 ° C. for 1000 hours to perform electrode aggregation evaluation. Since the resistance value increases when the external electrode layer 10 is aggregated as in the element body 4 shown in FIG. Coefficient of variation CV (%) = standard deviation / average value × 100. The results are shown in Table 1.

Examples 2-5
The element body 4 was manufactured in the same manner as in Example 1 except that the ratio of the ceramic particles in the first external electrode layer 10a after firing was 35 vol%, 40 vol%, 45 vol%, and 50 vol%. 10 was formed, and contact evaluation and electrode aggregation evaluation were performed. The results are shown in Table 1.

Comparative Example 1
Except that the ratio of the ceramic particles in the first external electrode layer 10a after firing was set to 25 vol%, the element body 4 was manufactured in the same manner as in Example 1 described above, the external electrode 10 was formed, contact evaluation and electrode Aggregation evaluation was performed. The results are shown in Table 1. In Comparative Example 1, as shown in Table 1, the resistance value variation in the electrode aggregation evaluation was large. That is, the external electrode layer 10 was agglomerated like the element body 4 shown in FIG.

Comparative Example 2
Except that the ratio of the ceramic particles in the first external electrode layer 10a after firing was 53 vol%, the element body 4 was manufactured in the same manner as in Example 1 described above, the external electrode 10 was formed, contact evaluation and electrode Aggregation evaluation was performed. The results are shown in Table 1. In Comparative Example 2, the variation in resistance value in the contact evaluation was large.

As shown in Evaluation Table 1, compared with Comparative Examples 1 and 2, Examples 1 to 3 were superior in both resistance value variation in aggregation evaluation and resistance value variation in contact evaluation. From these results, when the ratio of the ceramic particles in the first external electrode layer 10a after firing is 30 to 50 vol%, preferably 40 to 50 vol%, the external electrode It has been found that the phenomenon that the layer 10 aggregates is hardly observed, and that the contact between the external electrode layer 10 and the internal electrode layer 8 is good.

2 ... stacked thermistor element 4 ... element body 6 ... thermistor layer 8 ... internal electrode layer 10 ... external electrode layer 10a ... first external electrode layer 10b ... second external electrode layer

Claims (4)

An element body having at least a pair of internal electrode layers and a thermistor layer sandwiched between the internal electrode layers;
A laminated thermistor element formed on the surface of the element body and having an external electrode layer electrically connected to the internal electrode layer,
The external electrode layer is
A first external electrode layer formed directly on the surface of the element body;
A second external electrode layer formed on the surface of the first external electrode layer,
The first external electrode layer includes platinum particles and ceramic particles, and the second external electrode layer is composed of platinum particles;
The multilayer thermistor element, wherein the ceramic particles are 30 to 50 vol% when the total of the platinum particles and the ceramic particles in the first external electrode layer is 100 vol%.   The multilayer thermistor element according to claim 1, wherein the ceramic particles are the same as the ceramic particles constituting the thermistor layer. The first external electrode layer is a fired body of a paste film containing the platinum particles and the ceramic particles,
The multilayer thermistor element according to claim 1, wherein the second external electrode layer is a fired body of a paste film containing the platinum particles.   The multilayer thermistor element according to claim 1, wherein the internal electrode layer, the thermistor layer, and the external electrode layer are formed by simultaneous firing.

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