JP4985995B2 - Thermistor element - Google Patents

Description

  The present invention relates to a thermistor element, and more particularly to a thermistor element capable of detecting a relatively high temperature.

  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, there is an increasing demand for measuring the temperature of exhaust gas on the side closer to the engine, and the development of a thermistor element capable of measuring high temperatures up to 1000 ° C. is desired.

  As a high-temperature heat-resistant type thermistor element, for example, as shown in Patent Document 1, a thermistor element having improved heat resistance has been developed by devising the material of a covering material that covers the periphery of the element body. However, the thermistor element shown in Patent Document 1 is a single plate type thermistor element that does not have an internal electrode layer, and the surface of the element body constituting the sensor unit is deteriorated by high heat, and the sensor characteristics are deteriorated. Has a problem.

  Thus, it has been proposed that a laminated thermistor element in which the surface of the element body is laminated with an internal electrode layer and a thermistor layer that do not constitute a sensor part is used for high heat applications. However, in the conventional laminated thermistor element, as shown in Patent Document 2, leads are provided at both ends of the longest side in the element body for the purpose of increasing the area of the laminated internal conductor layer as much as possible. The terminals are connected and the distance between the lead terminals is increased.

  When such a conventional laminated thermistor element is used as it is for a thermistor element for high heat use at about 1000 ° C., the element body between the lead terminals increases due to thermal expansion, and the element located at the center between the lead terminals. There is a problem that cracks are likely to occur in the main body portion (or insulating coating portion).

  As shown in Patent Document 3, a thermistor element is known in which a lead terminal is drawn out in a direction parallel to the plane of the internal electrode layer laminated inside the element body via a thermistor layer. In such a thermistor element, the lead terminal is directly connected to the internal electrode layer, and is also in direct contact with the ceramic element body.

  For this reason, when such a thermistor element is used for high-temperature applications, heat can easily escape to the outside through a lead terminal directly connected to an internal electrode layer arranged so as to sandwich a thermistor layer exhibiting sensor characteristics. There is a problem that accuracy decreases. Further, since the lead terminal is directly joined to the ceramic element body, there is a problem that when the external force is applied to the lead terminal, the element body is easily cracked by the movement of the lead terminal.

JP 2006-54258 A JP 2007-180523 A JP-A-6-251907

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a thermistor element that operates stably even at high temperatures and can effectively prevent cracks in the element body.

In order to achieve the above object, the thermistor element according to the present invention includes:
A thermistor element having an element body in which two or more internal electrode layers are embedded so as to sandwich the thermistor layer,
The element body is formed with a pair of connection holes that reach at least one of the internal electrode layers and extend in a direction intersecting the plane of the internal electrode layer,
A buffer electrode film is formed on the inner wall of each connection hole,
One end of each lead terminal is inserted in each connection hole,
The lead terminal inserted in each connection hole is connected to the different internal electrode layer through the buffer electrode film.

  In the thermistor element according to the present invention, since the internal electrode layer is laminated so as to sandwich the thermistor layer inside the element body, the sensor portion that affects the sensor characteristics is inside the element body. Therefore, even if the surface of the element body is affected by high heat, the sensor portion existing inside the element body is not affected, and the sensor characteristics are good. That is, the thermistor element of the present invention has a structure that is not easily affected by the environment such as temperature and atmosphere.

  Further, in the thermistor element according to the present invention, since one end of the lead terminal is inserted into the connection hole arranged in the direction intersecting the internal electrode layer, the cross connection area between the internal electrode layer and the lead terminal is small, The heat transferred from the internal electrode layer to the outside through the lead terminal is small. Therefore, the accuracy of temperature measurement is improved.

  Furthermore, in the thermistor element according to the present invention, the lead terminal is not directly in contact with the ceramic element body but is bonded via the buffer electrode film at the outlet of the connection hole in the element body. Therefore, even when an external force is applied to the lead terminal, the external force is relaxed by the buffer electrode film, and it is possible to effectively prevent the element body from cracking due to the movement of the lead terminal.

  Furthermore, in the thermistor element of the present invention, the lead terminal is not connected to the outer surface of the element body, and the lead terminal is inserted into the connection hole, so that the insulation between the case for housing the thermistor element and the lead terminal is easy. At the same time, the case can be made thinner.

  Preferably, the connection hole is formed in the internal electrode layer in a direction perpendicular to the plane of the internal electrode layer. The end of the lead terminal is inserted into the connection hole, and by making the crossing angle between the lead terminal and the internal electrode layer vertical, heat transferred from the internal electrode layer to the outside through the lead terminal can be minimized. In particular, the accuracy of temperature measurement is improved. Also, the thermistor element can be easily designed.

  Preferably, the thickness of the buffer electrode film is greater than 0 and 200 μm or less, more preferably 10 to 100 μm. By making the buffer electrode film in such a thickness range, the crack prevention function of the element body due to the stress relaxation effect is improved.

  Preferably, the buffer electrode film has pores therein. The buffer electrode film is formed by, for example, a paste film baking method, and is required to have conductivity, but since the film is formed inside the connection hole, mechanical strength is not required. Rather, it is preferable that the buffer electrode film is soft enough to have pores or the like in order to function as a buffer film.

  The paste film is made of a metal and an organic material, and when the paste film is baked, the organic material is scattered to form a small hole inside, so that the obtained buffer electrode film has a cushioning property. In addition, the lead terminal is made of a metal with few defects in the manufacturing process, but the electrode film obtained by sintering the paste film has many microscopic defects in the metal itself (crystal or grain boundary). It is considered that the rigidity is small and soft. Therefore, the buffer electrode film formed by the paste film baking method is liable to cause defects such as vacancies in the inside thereof, and the crack prevention function of the element body due to the stress relaxation effect is improved.

  Preferably, the first metal is platinum (Pt), the second metal is at least one of palladium (Pd), rhodium (Rh), and iridium (Ir), and the internal electrode layer and the buffer electrode film And the other includes the first metal and the second metal, and the other includes the first metal and the second metal, but the content of the second metal is relatively low or includes the first metal. Does not contain second metal.

  The edge of the internal electrode layer exposed on the inner wall of the connection hole formed in the element body tends to be recessed from the inner wall of the connection hole, and the connection with the buffer electrode film tends to be insufficient. The second metal such as palladium, rhodium or iridium is likely to diffuse at the connection portion between the internal electrode layer and the buffer electrode film, and diffuses from the higher concentration side to the lower side. Therefore, the connection between the internal electrode layer and the buffer electrode film is improved.

  The connection hole may be a hole that does not penetrate the element body or a through hole, but is preferably a hole that does not penetrate the element body (non-through hole). By attaching the end of the lead terminal to the non-through hole, the end of the lead terminal is embedded inside the element body and is not exposed to the outside of the element body. However, it is easy to ensure insulation between the lead terminal and the case. In addition, heat dissipation through the lead terminal is suppressed to be smaller than that of the lead terminal mounted in the through hole, and the accuracy of temperature measurement is improved. In addition, the thermistor element in which the penetration type connection hole is formed has an advantage that it is easy to manufacture.

  Preferably, a float electrode not connected to the lead terminal is laminated via the thermistor layer between the internal electrode layers connected to the lead terminal in the element body. By forming the float electrode, even if the pattern of the internal electrode layer is displaced, the overlapping area between the internal electrode layers can be made substantially constant, and variation in thermistor characteristics can be reduced.

FIG. 1 is a longitudinal sectional view of a main part of a thermistor element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the thermistor element taken along line II-II shown in FIG. FIG. 3 is a cross-sectional view of a main part of the thermistor element shown in FIG. FIG. 4 is a longitudinal sectional view of a thermistor element according to another embodiment of the present invention. FIG. 5 is a longitudinal sectional view of a thermistor element according to still another embodiment of the present invention.

First embodiment

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
As shown in FIGS. 1 to 3, the laminated thermistor element 2 according to one embodiment of the present invention includes an element body 4 and a pair of lead terminals 12 a and 12 b. The element body 4 has a rectangular parallelepiped shape having sides parallel to the X axis, the Y axis, and the Z axis that are perpendicular to each other.

  As shown in FIGS. 1 and 2, internal electrode layers 8 a to 8 c are laminated inside the element body 4 so as to sandwich a thermistor layer 6 having NTC characteristics. In this embodiment, the planes of the internal electrode layers 8a to 8c are directions parallel to the plane including the Y axis and the Z axis. One internal electrode layer 8a and 8b sandwiching the thermistor layer 6 is formed in a rectangular shape so as to exist on the same plane parallel to the Y axis and the Z axis, and is separated and insulated in the Z axis direction.

  One internal electrode layer 8a existing in the same plane has a lead terminal 12a in which the tip in the X-axis direction is inserted into one connection hole 10a of the pair of connection holes 10a, 10b formed in the element body 4. In contrast, it is connected via a buffer electrode film 14. The other internal electrode layer 8b existing in the same plane is connected via a buffer electrode film 14 to a lead terminal 12b whose tip in the X-axis direction is inserted into the other connection hole 10b.

  The pair of connection holes 10a and 10b formed in the element body 4 are non-through holes that do not penetrate the element body 4 in the X-axis direction. In the illustrated example, one internal hole is stacked in the X-axis direction. It is formed so as to penetrate all of the electrode layers 8a and all of the other internal electrode layers 8b. An internal electrode layer 8c serving as a float electrode that is not connected to any of the lead terminals 12a and 12b is disposed between the internal electrode layers 8a and 8a along the X-axis direction and between the internal electrode layers 8b and 8b. The internal electrode layers 8a and 8b are arranged so as to overlap with each other when viewed from the X-axis direction (see FIG. 2).

  The thermistor layer 6 located at the overlapping portion of the internal electrode layer 8c and the internal electrode layers 8a and 8b serves as a sensor portion. A thermistor layer 6a that does not function as a sensor portion is laminated on both ends of the element body 4 in the lamination direction (Y-axis) of the internal electrode layers 8a and 8b.

  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, oxides of elements such as manganese (Mn), calcium (Ca), titanium (Ti), etc. It is comprised with the material containing as a main component. In addition, an auxiliary component may be contained for improving characteristics. 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 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 layers 8a to 8c is not particularly limited. For example, noble metals such as Ag, Pd, Au, and Pt and alloys thereof (such as Pt—Pd alloy), or base metals such as Cu and Ni are used. And these alloys. In the present embodiment, the internal electrode layers 8a to 8c are preferably made of any one of Pt, Pt—Pd alloy, Pt—Rh alloy, and Pt—Ir alloy. The thickness of the internal electrode layers 8a to 8c is preferably 0.5 to 2.0 μm.

  As shown in FIG. 3, the buffer electrode film 14 is formed in a gap between the inner wall surfaces of the connection holes 10a and 10b and the lead terminals 12a and 12b, and is formed, for example, by a paste baking method. The thickness c1 of the buffer electrode film 14 corresponds to a gap that is halved by subtracting the outer diameter d2 of the lead terminals 12a and 12b from the inner diameter d1 of the connection holes 10a and 10b, preferably greater than 0 and 200 μm or less. Is 10 to 100 μm. By making the buffer electrode film 14 in such a thickness range, the crack prevention function of the element body 4 due to the stress relaxation effect described later is improved. In FIG. 3, the internal electrode layer is not shown.

  The material of the buffer electrode film 14 is not particularly limited, and the same material as the conductive material constituting the internal electrode layers 8a to 8c can be used. However, in this embodiment, when the first metal is platinum (Pt) and the second metal is at least one of palladium (Pd), rhodium (Rh), and iridium (Ir), the internal electrode layers 8a, Either one of 8b and buffer electrode film 14 includes the first metal and the second metal, and the other includes the first metal and the second metal, but the content of the second metal is relatively low. The first metal is included and the second metal is not included. For example, one of the internal electrode layers 8a and 8b and the buffer electrode film 14 is made of a Pt—Pd alloy (Pt: Pd = 80: 20 weight ratio), and the other is made of a Pt—Pd alloy (Pt: Pd = 90: 10). (Weight ratio) or Pt metal.

  The buffer electrode film 14 is formed by, for example, paste application and baking process. Specifically, an electrode paste for forming the buffer electrode film 14 is poured into the connection holes 10a and 10b, and then the tips of the lead terminals 12a and 12b are inserted into the connection holes 10a and 10b, followed by baking. Good.

  In this embodiment, the lead terminals 12a and 12b are made of a wire having a circular cross section, and the outer diameter d2 (see FIG. 3) of the wire is preferably 200 to 500 μm. In the present embodiment, the lead terminals 12a and 12b are made of the same material as the buffer electrode film 14 and have heat resistance. For example, the lead terminals 12a and 12b are made of Pt, Pt—Pd alloy, Pt—Rh alloy, or Pt—Ir alloy. Consists of either.

  As shown in FIG. 3, in each connection hole 10a, 10b, the buffer electrode film 14 does not completely fill the gap between the connection hole 10a, 10b and the lead terminal 12a, 12b. It is preferable that the inside of each connection hole 10a, 10 is recessed and filled with a gap c2 from the opening outlet 10c.

The gap c2 is preferably larger than 0 and not larger than 300 μm. By providing such a gap c2, as will be described later, the stress generated by the movement of the lead terminals 12a and 12b can be easily relaxed, which contributes to the prevention of cracks in the element body 4. However, the buffer electrode film 14 may be provided so as to protrude slightly from the opening outlet 10c of each connection hole 10a, 10. Even in that case, the effect of relieving the stress generated by the movement of the lead terminals 12a and 12b is sufficient.
Next, an example of a method for manufacturing the laminated thermistor 2 according to this embodiment will be described. A method for manufacturing the 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 green sheet on which an internal electrode layer paste film having a predetermined pattern for forming the internal electrode layers 8a to 8c on the surface and a green sheet having no internal electrode layers 8a to 8c are prepared. The green sheet is formed of a material constituting the above-described NTC thermistor layer. 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.

  And a green sheet is manufactured by a well-known technique using such a material. Specifically, for example, first, a raw material of the material constituting the thermistor layer (for example, commercially available manganese trioxide, calcium carbonate, titanium oxide, etc.) is uniformly mixed by means such as wet mixing and then dried. Next, it is calcined (preferably 1000 to 1200 ° C.) under appropriately selected calcining conditions, and the calcined powder is wet pulverized. Then, a binder or an organic 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.

  The internal electrode layer paste contains the various metals described above. By applying the internal electrode layer paste onto the green sheet by means such as a printing method, a green sheet on which an internal electrode layer paste film having a predetermined pattern is formed is obtained.

  Next, these green sheets are overlapped, pressure is applied to form a laminated body, and the laminated body is subjected to necessary steps such as a drying step, and then corresponds to each element in the laminated body. A pair of connection holes 10a and 10b are formed in each portion. The connection holes 10a and 10b are formed using a laser, a drill, a punch, etc., for example. Thereafter, the laminate is cut and the element body 4 in the green chip state is taken out. Cutting can be performed using a dicing saw or the like.

  When both the thermistor layer and the internal electrode layer are formed by a printing method, they may be formed by a pattern printing method corresponding to the connection holes 10a and 10b at the time of printing. In any case, an electrode paste that becomes the buffer electrode film 14 after firing is injected into the connection holes 10a and 10b formed in the element body 4 in the green chip state by a dispenser or the like. As the electrode paste, for example, an electrode paste mainly composed of Pt such as Pt, Pt / Pd, Pt / Rh, Pt / Ir is used.

  Thereafter, the tip ends of the lead terminals 12a and 12b are inserted into the connection holes 10a and 10b. Thereafter, the element body 4 in the green chip state to which the lead terminals 12a and 12b are attached is dried and subjected to a binder removal treatment, and then fired at appropriately selected firing conditions, preferably 1250 to 1450 ° C. Element 2 is obtained.

  According to the thermistor element 2 according to the present embodiment, since the internal electrode layers 8a to 8c are laminated so as to sandwich the thermistor layer 6 inside the element body 4, the sensor unit that affects the sensor characteristics is the element body. 4 inside. Therefore, even if the surface of the element body 4 is affected by high heat, the sensor portion existing inside the element body 4 is not affected, and the sensor characteristics are good. That is, the thermistor element 2 of the present embodiment has a structure that is not easily affected by the environment such as temperature and atmosphere.

  Further, in the thermistor element 2 according to the present embodiment, one end of each of the lead terminals 12a and 12b is inserted into the connection holes 10a and 10b that are arranged in a direction substantially perpendicular to the internal electrode layers 8a and 8b. Therefore, the cross connection area between the internal electrode layers 8a and 8b and the lead terminals 12a and 12b is small, and the heat transmitted from the internal electrode layers 8a and 8b to the outside through the lead terminals 12a and 12b is small. Therefore, the accuracy of temperature measurement is improved.

  Furthermore, in the thermistor element 2 according to the present embodiment, the lead terminals 12a and 12b do not directly contact the ceramic element body 4 at the outlets of the connection holes 10a and 10b in the element body 4, and the buffer electrode film 14 is formed. Are joined together. Therefore, even when an external force is applied to the lead terminals 12a and 12b, the external force is relaxed by the buffer electrode film 14 and effectively prevents the element body 4 from cracking due to the movement of the lead terminals 12a and 12b. can do.

  Furthermore, in the thermistor element 2 of the present embodiment, the lead terminals 12a and 12b are not connected to the outer surface of the element body 4, and the lead terminals 12a and 12b are inserted into the connection holes 10a and 10b. Therefore, the case 16 can be easily insulated from the lead terminals 12a and 12b, and the case 16 can be made thinner. Case 16 is made of a heat-resistant metal such as stainless steel.

  Moreover, in this embodiment, since the thickness of the buffer electrode film 14 is larger than 0 and 200 micrometers or less, More preferably, it is 10-100 micrometers, The crack prevention function of the element main body 4 by a stress relaxation effect improves. In addition, the buffer electrode film 14 is formed by, for example, a paste film baking method, and voids are generated therein, and is softer than the lead terminals 12a and 12b.

  The paste film is made of a metal and an organic material, and when the paste film is baked, the organic material is scattered to form a small hole in the inside, so that the obtained buffer electrode film 14 has a cushioning property. The lead terminals 12a and 12b are made of a metal having few defects in the manufacturing process, but the buffer electrode film 14 obtained by sintering the paste film has many microscopic defects in the metal itself (crystals and grain boundaries). Therefore, it is thought that hardness and rigidity are small and soft. Therefore, in the buffer electrode film 14 formed by the paste film baking method, defects such as vacancies are easily generated inside, and the crack prevention function of the element body 4 by the stress relaxation effect is improved.

  In this embodiment, when the first metal is platinum (Pt) and the second metal is at least one of palladium (Pd), rhodium (Rh), and iridium (Ir), the internal electrode layers 8a and 8b Either one of the buffer electrode films 4 includes a first metal and a second metal, and either one includes a first metal and a second metal, but the content of the second metal is relatively low, Contains one metal and no second metal.

  The edges of the internal electrode layers 8a, 8b exposed on the inner walls of the connection holes 10a, 10b formed in the element body 4 tend to be recessed from the inner walls of the connection holes, and the connection with the buffer electrode film 14 is insufficient. Prone. However, the second metal such as palladium, rhodium or iridium is likely to diffuse at the connection portion between the internal electrode layers 8a and 8b and the buffer electrode film 14, and diffuses from the higher concentration side to the lower side. Therefore, in this embodiment, the connection between the internal electrode layers 8a and 8b and the buffer electrode film 14 is improved.

  Furthermore, in this embodiment, the connection holes 10a and 10b are holes that do not penetrate the element body 4 (non-through holes), and the end portions of the lead terminals 12a and 12b are attached to the connection holes 10a and 10b that are non-through holes. Thus, the end portions of the lead terminals 12 a and 12 b are embedded in the element body 4 and are not exposed to the outside of the element body 4. For this reason, even if the element body 4 is mounted inside the case 16, it is easy to ensure insulation between the lead terminals 12 a and 12 b and the case 16. In addition, heat dissipation through the lead terminals 12a and 12b is suppressed to be smaller than that of the lead terminal mounted in the through hole, and the accuracy of temperature measurement is improved.

Further, in the present embodiment, inside the element main body 4, an internal electrode layer 8 c serving as a float electrode not connected to the lead terminals 12 a and 12 b is interposed between the internal electrode layers 8 a and 8 b connected to the lead terminals 12 a and 12 b, respectively. Are stacked via the thermistor layer 6. By forming the internal electrode layer 8c to be a float electrode, for example, even if the pattern between the internal electrode layers 8a and 8b and the internal electrode layer 8c is displaced in the Z-axis direction, the internal electrode layers 8a and 8b and the internal electrode layer The total overlapping area with 8c does not change and can be made substantially constant. Therefore, variation in the thermistor characteristics of the thermistor element 2 can be reduced.
Second embodiment

In the thermistor element 2A according to the present embodiment, as shown in FIG. 4, the connection holes 10A and 10B are holes that penetrate the element body 4 in the X-axis direction, and lead terminals 12a and 10B are connected to the connection holes 10A and 10B. Except for being inserted so that the tip of 12b is exposed from the element main body 4, it is the same as the thermistor element 2 according to the first embodiment, and a duplicate description is omitted. The thermistor element 2 </ b> A according to the present embodiment also has the same effects as the thermistor element 2 according to the first embodiment. Moreover, in this embodiment, since the through-type connection holes 10A and 10B are formed, there is an advantage that the thermistor element can be easily manufactured.
Third embodiment

  In the thermistor element 2B according to the present embodiment, as shown in FIG. 5, the internal electrode layers 8A and 8B stacked with the thermistor layer 6 interposed therebetween are alternately connected to the lead terminals 12a and 12b via the buffer electrode film 14, respectively. Except for being connected, the thermistor element 2 is the same as the thermistor element 2 according to the first embodiment, and a duplicate description is omitted.

  The thermistor element 2B according to the third embodiment has the same effects as the thermistor element 2 according to the first embodiment, except that the internal electrode layer to be a float electrode is not formed.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

2, 2A, 2B ... Thermistor element 4 ... Element body 6 ... Thermistor layers 8a, 8b, 8c, 8A, 8B ... Internal electrode layers 10a, 10b, 10A, 10B ... Connection holes 12a, 12b ... Lead terminals 14 ... Buffer electrode film 16 ... Case

Claims (6)

A thermistor element having an element body in which two or more internal electrode layers are embedded so as to sandwich the thermistor layer,
The element body is formed with a pair of connection holes that reach at least one of the internal electrode layers and extend in a direction intersecting the plane of the internal electrode layer,
A buffer electrode film is formed on the inner wall of each connection hole,
One end of each lead terminal is inserted in each connection hole,
Lead terminals are inserted into respective connection holes, said via a buffer electrode film, Ri connected to different said internal electrode layer Thea,
The first metal is platinum, the second metal is at least one of palladium, rhodium, and iridium;
One of the internal electrode layer and the buffer electrode film includes a first metal and a second metal, and the other includes a first metal and a second metal, but the content of the second metal is relative. A thermistor element comprising a first metal and no second metal .   The thermistor element according to claim 1, wherein the connection hole is formed in the internal electrode layer in a direction perpendicular to a plane of the internal electrode layer.   The thermistor element according to claim 1, wherein a thickness of the buffer electrode film is greater than 0 and equal to or less than 200 μm.   The thermistor element according to claim 1, wherein the buffer electrode film has pores therein. The connection hole does not penetrate the device body bore or thermistor element according to any one of claims 1 to 4, which is a through hole. Inside the element body between the internal electrode layers are connected to the lead terminals, it claims 1-5 wherein not connected to the lead terminal float electrodes are laminated through the thermistor layer Thermistor element described in 1.

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