JP4548431B2 - Thermistor composition and thermistor element - Google Patents

Description

  The present invention relates to a thermistor element and a thermistor element including an element body including the thermistor composition.

As this type of thermistor element, a so-called NTC (Negative Temperature Coefficient) thermistor element having a characteristic that the resistance decreases as the temperature increases is known (see, for example, Patent Document 1).
JP-A-5-251209

  By the way, this NTC thermistor element generally has a non-linear characteristic in which an output voltage changes in a curve with respect to temperature. For this reason, when temperature detection or measurement is performed using a conventional NTC thermistor element, a compensation circuit for correcting the nonlinearity of the output voltage of the NTC thermistor element is required. The problem is that the circuit becomes complicated and expensive.

  Then, an object of this invention is to provide the thermistor composition and thermistor element which have the characteristic that an output voltage can change linearly with respect to temperature.

The inventors of the present invention have also intensively studied a thermistor composition having a characteristic that the output voltage can change linearly with respect to temperature. As a result, the present inventors have included Ca (MnTi) O ₃ in which a part of Mn in CaMnO ₃ having a perovskite structure is substituted with Ti, and Co, the output voltage with respect to temperature. I came up with a new phenomenon that sometimes changes linearly.

Based on such research results, the thermistor composition according to the present invention includes Ca (MnTi) O ₃ in which a part of Mn in CaMnO ₃ having a perovskite structure is substituted with Ti, and Co. content ratio, Ca in Ca (MnTi) _{O 3,} relative to the total amount of Ti and Mn, in the range of 0.1 to 10 atomic%, the Ca (MnTi) _{O 3,} the composition ratio x of Ti for Mn It is characterized by 0.33 ≦ x ≦ 0.7.

The thermistor element according to the present invention is a thermistor including an element body and a terminal electrode disposed on the outer surface of the element body, and the element body includes a part of Mn in CaMnO ₃ having a perovskite structure. Ca (MnTi) O ₃ substituted with Ti and Co are contained, and the content ratio of Co is 0.1 to 10 with respect to the total amount of Ca, Ti and Mn in Ca (MnTi) O ₃ . It is in the range of atomic%, and the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ is 0.33 ≦ x ≦ 0.7.

In these inventions, since the thermistor composition or element contains Ca (MnTi) O ₃ and Co, the output voltage varies linearly with temperature. This event is thought to be due to the following reasons.

Ca (MnTi) O ₃ having a perovskite structure can hardly dissolve Co. Ca (MnTi) not dissolved in the _{O 3} Co is constitutes the different phases and Ca (MnTi) _{O 3,} reacts with Mn contained in the Ca (MnTi) _{O 3,} oxides of Mn (For example, Mn ₂ CoO ₄ or the like). Therefore, the thermistor composition containing Ca (MnTi) O ₃ and Co includes a region mainly composed of Ca (MnTi) O ₃ and a region mainly composed of an oxide of Co and Mn. It becomes. At this time, Ca (MnTi) O ₃ and the oxide of Co and Mn have different B constants (degree of change in resistance value with respect to temperature change), and the oxide of Co and Mn is Ca It has a higher B constant than (MnTi) O ₃ . Thus, regions having different B constants are connected in series and in parallel, and as a result, the output voltage varies linearly with respect to temperature.

By setting the Co content ratio to 0.1 atomic% or more and setting the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ to 0.33 ≦ x ≦ 0.7, output relative to temperature The voltage can be changed linearly, and the amount of change in output voltage per unit temperature (the slope in the change in output voltage with respect to temperature) can be increased. That is, when the content ratio of Co is less than 0.1 atomic% and the composition ratio x of Ti to Mn is outside the above numerical range, the region mainly composed of an oxide of Co and Mn decreases and Ca ( The B constant of the region containing MnTi) O ₃ as a main component does not increase, the output voltage hardly changes linearly with respect to temperature, and the amount of change in output voltage per unit temperature also decreases.

  By setting the Co content to 10 atomic% or less, the characteristics (B constant, resistance, etc.) can be stabilized. That is, when the content ratio of Co is larger than 10 atomic%, there are too many regions mainly composed of an oxide of Co and Mn, and the connection state of the above-described regions having different B constants is not stable, resulting in variations in characteristics. Occurs.

  ADVANTAGE OF THE INVENTION According to this invention, the thermistor composition and thermistor element which have the characteristic that an output voltage can change linearly with respect to temperature can be provided. In addition, according to the present invention, it is possible to provide a thermistor composition and a thermistor element having a large amount of change in output voltage per unit temperature.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  The thermistor element 1 is a so-called NTC thermistor element. As shown in FIGS. 1 and 2, the thermistor element 1 includes a substantially disk-shaped element body 3 and terminal electrodes 5 and 7 arranged on the outer surface of the element body 3. I have. FIG. 1 is a perspective view of the thermistor element according to this embodiment. FIG. 2 is a cross-sectional view of the thermistor element shown in FIG.

  The terminal electrode 5 is arranged on one main surface of the element body 3, and the terminal electrode 7 is arranged on the other main surface opposite to one main surface of the element body 3. The terminal electrode 5 and the terminal electrode 7 are opposed to each other with the element body 3 interposed therebetween. The terminal electrodes 5 and 7 have a three-layer structure including first metal electrode layers 5a and 7a, second metal electrode layers 5b and 7b, and third metal electrode layers 5c and 7c in this order from the outer surface side of the element body 3. It has become.

  The first metal electrode layers 5a and 7a contain, for example, Ag as a main component. The first metal electrode layers 5a and 7a can be formed by applying and baking a conductive paste containing conductive metal powder (Ag powder) and glass frit on the outer surface of the element body 3.

  The second metal electrode layers 5b and 7b contain, for example, Ni as a main component. The second metal electrode layers 5b and 7b are formed on the first metal electrode layers 5a and 7a so as to cover the first metal electrode layers 5a and 7a. The second metal electrode layers 5b and 7b are formed by plating the outer surfaces of the first metal electrode layers 5a and 7a with Ni.

  The third metal electrode layers 5c and 7c contain, for example, Sn or Sn alloy as a main component. The third metal electrode layers 5c and 7c are formed on the second metal electrode layers 5b and 7b so as to cover the second metal electrode layers 5b and 7b. The third metal electrode layers 5c and 7c are formed by plating the outer surfaces of the second metal electrode layers 5b and 7b with Sn or an Sn alloy.

The element body 3 contains Ca (MnTi) O ₃ in which a part of Mn in CaMnO ₃ having a perovskite structure is substituted with Ti, and Co. The content ratio of Co is in the range of 0.1 to 10 atomic% with respect to the total amount of Ca, Ti and Mn in Ca (MnTi) O ₃ . Further, the composition ratio x of Ti to Mn (Ca (Mn _x Ti _1-x ) O ₃ ) in Ca (MnTi) O ₃ is 0.33 ≦ x ≦ 0.7. The element body 3 may further contain inevitable impurities in addition to Ca (MnTi) O ₃ and Co. Examples of such impurities include metal elements such as Si, K, Na, and Ca. .

  Next, a method for manufacturing the thermistor element 1 having the above configuration will be described.

First, the element body 3 (thermistor composition) is prepared. Here, Mn ₃ O ₄ , CaCO ₃ , TiO ₂ and Co ₃ O ₄ were used as raw materials for the element body 3, and these were wet mixed by a ball mill or the like, and the raw materials were mixed at a desired composition ratio. A raw material mixture is prepared. In addition, in the raw material mixture, inevitable impurities as described above may be included. After drying this raw material mixture, temporary baking is performed at about 800 to 1200 ° C. to obtain a temporary baking product. The obtained calcined product is wet-pulverized again with a ball mill or the like. And after adding a binder (for example, polyvinyl alcohol (PVA) etc.) to this pulverized material and granulating it into granules, it is pressure-molded into a disk shape. Next, the disk-shaped molded body is subjected to binder removal and main firing to obtain an element body 3.

  Thereafter, Ag paste or the like for forming the first metal electrode layers 5a and 7a is baked on both end faces of the obtained element body 3 to form the first metal electrode layers 5a and 7a. Further, the second metal electrode layers 5b and 7b and the third metal electrode layers 5c and 7c are formed by electroplating or the like so as to cover the first metal electrode layers 5a and 7a. The thermistor element 1 having the configuration shown in FIG.

As described above, in the present embodiment, the element body 3 contains Ca (MnTi) O ₃ and Co. Therefore, as shown in FIG. 3, the element body 3 is composed of Ca (MnTi). This includes a region P1 mainly composed of O ₃ and a region P2 mainly composed of an oxide of Co and Mn. This is because Ca (MnTi) O ₃ having a perovskite structure can hardly dissolve Co. That, Co not solid-dissolved Ca (MnTi) _{O 3} becomes a configuring a different phase and Ca (MnTi) _{O 3,} reacts with Mn contained in the Ca (MnTi) _{O 3,} oxides of Mn Is generated.

By the way, as shown in FIG. 3, in the element body 3, a region P <b> 2 mainly composed of an oxide of Co and Mn is surrounded by a region P <b> 1 mainly composed of Ca (MnTi) O _3. Exist. The region P1 made of Ca (MnTi) O ₃ and the region P2 made of an oxide of Co and Mn have different B constants, and the region P2 made of an oxide of Co and Mn is Ca (MnTi ) It has a higher B constant than the region P1 made of O ₃ . Therefore, in the element body 3, as shown in FIG. 4, the regions P1 and P2 having different B constants are connected in series and in parallel, and the output voltage changes linearly with respect to the temperature.

In the element body 3, the Co content is set to 0.1 atomic% or more, and the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ is set to 0.33 ≦ x ≦ 0.7, The output voltage can be changed linearly with respect to the temperature, and the change amount of the output voltage per unit temperature can be increased. That is, when the Co content is less than 0.1 atomic% and the composition ratio x of Ti to Mn is out of the above numerical range, the region P2 mainly composed of an oxide of Co and Mn is reduced and the Ca is reduced. The B constant of the region P1 containing (MnTi) O ₃ as a main component does not become high, the output voltage hardly changes linearly with respect to the temperature, and the change amount of the output voltage per unit temperature becomes small.

  In the element body 3, the characteristics (B constant, resistance, etc.) can be stabilized by setting the Co content to 10 atomic% or less. That is, when the content ratio of Co is larger than 10 atomic%, there are too many regions mainly composed of an oxide of Co and Mn, and the connection state of the above-described regions having different B constants is not stable, resulting in variations in characteristics. Occurs.

  In this embodiment, the element body 3 is configured to include regions P1 and P2 having different B constants, and a thermistor element having a characteristic that the output voltage changes linearly with respect to temperature is realized as one element. Can be

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  The element body 3 is not limited to the disk shape described above, but may be a polyhedron shape or a spherical shape. Further, the thermistor element 1 may include an internal electrode electrically connected to the terminal electrodes 5 and 7 inside the element body 3.

  Hereinafter, the thermistor composition and the thermistor element according to the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a present Example.

(Manufacture of thermistor elements)
First, as the raw material (starting material) of the thermistor composition, commercially available Mn ₃ O ₄ , CaCO ₃ , TiO ₂ and Co ₃ O ₄ are prepared, and the composition after sintering these becomes the composition ratio shown in FIG. Weighed and blended as follows. Next, these raw materials were wet mixed by a ball mill for 16 hours to obtain a raw material mixture. This raw material mixture contained a slight amount of metal elements such as Si, K, Na, and Ca.

  Next, the obtained raw material mixture was dehydrated and dried, and powdered using a mortar and pestle. Furthermore, this powder was put into an alumina pot and pre-baked at 800 to 1200 ° C. for 2 hours. Next, the calcined product is finely pulverized with a ball mill and Zr beads, dehydrated and dried, added with polyvinyl alcohol (PVA) as a binder, granulated into granules with a mortar and pestle, and then 16 mm in diameter and 2.5 mm in thickness. It was press-molded into a disk shape.

  Next, this disc-shaped molded body is heated in the atmosphere at 600 ° C. for 2 hours to remove the binder, and then subjected to main firing at 1100 to 1500 ° C. in the atmosphere for 2 hours to obtain the element body. Obtained. Silver paste was screen-printed on both sides of the obtained element body and baked at 800 ° C. to form terminal electrodes. As a result, various thermistor elements (samples 1 to 56) having a structure including an element body between a pair of terminal electrodes were obtained.

(Characteristic evaluation)
First, 20 thermistor elements of Samples 1 to 56 are used, respectively, and resistance values under each temperature condition are obtained by the following method, and B constants in the low temperature side and high temperature side temperature ranges are obtained based on these values. It was.

  That is, the resistance value (R25) (Ω) at 25 ° C. and the resistance value (R85) (Ω) at 85 ° C. were measured by a direct current four-terminal method. Then, these values were substituted into the following formula (1) to calculate the B constant (B25 / 85) (K). Further, the coefficient of variation (Bcv) (%) of the B constant in each sample 1 to 56 was calculated.

B25 / 85 = 2.3026 × Log (R25 / R85) /
{1 / (273.15 + 25) -1 / (273.15 + 85)} (1)

  Next, samples 1, 3, 5, 8, 9, 13, 16, 18, 20, 23, 24, 25, 26, 27, 30, 32, 34, 36, 37, 38, 40, 41, 44, Using the thermistor elements 46, 48, 50, 52, and 54, the change characteristics of the output voltage with respect to temperature were obtained by the following method.

That is, as shown in FIG. 6, samples 1, 3, 5, 8, 9, 13, 16, 18, 20, 23, 24, 25, 26, 27, 30, 32, 34, 36, 37, 38 , 40, 41, 44, 46, 48, 50, 52, and 54, a measurement circuit in which each thermistor element S1 is connected in series with the fixed resistor R1 is manufactured, and this measurement circuit is placed in a thermostatic bath, and the temperature in the thermostatic bath is set. While changing, the output voltage (Eout) with respect to the input voltage (Ein) of 1 V was measured. The temperature was changed in the range of −40 ° C. to 150 ° C. From the measurement results, the amount of change in output voltage per unit temperature (ΔE) and the coefficient of determination (R ² ) were calculated.

  FIG. 5 shows the B constant (B25 / 85) and coefficient of variation (Bcv) of the B constant obtained for the thermistor elements of Samples 1 to 56, together with the composition of the thermistor composition in each sample.

Samples 1, 3, 5, 8, 9, 13, 16, 18, 20, 23, 24, 25, 26, 27, 30, 32, 34, 36, 37, 38, 40, 41, 44, 46, 48 , 50, 52, and 54, the change amount (ΔE) of the output voltage per unit temperature and the determination coefficient (R ² ) obtained for the thermistor elements are shown in FIG. 8 to 13 show the relationship between temperature and output voltage as a diagram.

As can be seen from the measurement results shown in FIGS. 7 to 13, the Co content is 0.1 atomic% or more, and the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ is 0.33 ≦ x ≦. When 0.7, ΔE is 1.5 mV / ° C. or more, and the output voltage changes linearly with respect to temperature. Further, R ² is 0.995 or more, and the change amount of the output voltage per unit temperature is large.

The reason why the quality criterion for ΔE is 1.5 mV / ° C. is that when ΔE is less than 1.5 mV / ° C., the amount of change in voltage with respect to temperature is small, and the sensitivity as a sensor becomes insufficient. The reason for the quality criteria of R ² and 0.995, when R ² is less than 0.995, can not substantially be regarded as a straight line the output voltage, because the correction circuit or the like is required.

  As can be seen from the measurement results shown in FIG. 5, when the Co content is 10 atomic% or less, Bcv is less than 1, and the characteristic variation is extremely small.

  From the above, the effectiveness of the present invention was confirmed.

It is a perspective view of the thermistor element concerning this embodiment. FIG. 2 is a cross-sectional view of the thermistor element shown in FIG. 1. It is a schematic diagram for demonstrating the structure of an element body. This is an equivalent circuit of a prime field. It is a graph which shows the measurement result of the composition of a sample, and the B constant (B25 / 85) and the coefficient of variation (Bcv) of B constant. It is a figure which shows a measurement circuit. Variation of the output voltage per unit temperature of the sample (Delta] E) and coefficient of determination (R ²⁾ measurements is a table showing. It is a diagram which shows the relationship between temperature and an output voltage. It is a diagram which shows the relationship between temperature and an output voltage. It is a diagram which shows the relationship between temperature and an output voltage. It is a diagram which shows the relationship between temperature and an output voltage. It is a diagram which shows the relationship between temperature and an output voltage. It is a diagram which shows the relationship between temperature and an output voltage.

Explanation of symbols

1 ... thermistor element 1, 3 ... body, 5,7 ... terminal electrodes, a region mainly composed of _{P1 ... Ca (MnTi) O 3} , a region mainly composed of oxide of P2 ... Co and Mn.

Claims (2)

Ca (MnTi) O ₃ in which a part of Mn in CaMnO ₃ having a perovskite structure is substituted with Ti, and Co,
The content ratio of Co is in the range of 0.1 to 10 atomic% with respect to the total amount of Ca, Ti and Mn in Ca (MnTi) O ₃ ,
A thermistor composition, wherein the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ is 0.33 ≦ x ≦ 0.7. A thermistor element comprising an element body and a terminal electrode disposed on the outer surface of the element body,
The element body includes Ca (MnTi) O ₃ in which a part of Mn in CaMnO ₃ having a perovskite structure is substituted with Ti, and Co.
The content ratio of Co is in the range of 0.1 to 10 atomic% with respect to the total amount of Ca, Ti and Mn in Ca (MnTi) O ₃ ,
A thermistor element, wherein the composition ratio x of Ti to Mn in Ca (MnTi) O ₃ is 0.33 ≦ x ≦ 0.7.

Images