NTC thermistor composition and thermistor element

Abstract

To provide an NTC thermistor composition capable of realizing an NTC thermistor element having excellent thermal stability against heat during reflow treatment and small variation in resistance value, and a thermistor element having the composition.SOLUTION: An NTC thermistor composition contains 40 to 63 mol% Mn, 10 to 30 mol% Co, and 15 to 35 mol% Ni, Al is 5.9 mol% or less (including 0).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an NTC thermistor composition and a thermistor element having a thermistor layer composed of the composition.

Background Art

[0002] An NTC (negative temperature coefficient) thermistor element has the property that its resistance value decreases as the temperature rises, and is used for applications such as temperature sensors and temperature compensation elements in various devices such as electronic devices. Since devices on which such thermistor elements are mounted are used in various environments, the thermistor elements are required to have high reliability. Specifically, even in a high-temperature and high-humidity atmosphere of 120°C or higher, a thermistor element with a small resistance change rate is required. For example, a thermistor element having the composition shown in Patent Document 1 below has been developed.

[0003] A thermistor element having the composition shown in Patent Document 1 is suitable as a thermistor composition used for, for example, a glass diode type thermistor, a glass bead type thermistor, and a resin bead type thermistor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Recently, multilayer chip type thermistor elements have also been developed. However, in the case of multilayer thermistor elements, the present inventors have found that the characteristics change greatly depending on the composition before and after mounting the thermistor element on a circuit board of various electronic devices.

[0006] The present invention has been made in view of such a situation, and an object thereof is to provide an NTC thermistor composition capable of realizing an NTC thermistor element having excellent thermal stability against heat during reflow processing and small variation in resistance value, a thermistor element having the composition, and to provide.

Means for Solving the Problems

[0007] In order to achieve the above object, the NTC thermistor composition according to one aspect of the present invention is When the total of Mn, Co, Ni, and Al is 100 mol%, Mn is 40 to 63 mol%, Co is 10 to 30 mol%, and Ni is 15 to 35 mol%, and Al is 5.9 mol% or less (including 0).

[0008] As a result of intensive studies on the NTC thermistor composition, the present inventors have found that by including Mn, Co, and Ni within a predetermined range, it is possible to realize an NTC thermistor element having excellent thermal stability against heat during reflow processing and small variation in resistance value, and have completed the present invention.

[0009] Zr may be contained in an amount of 0 to 2.5 mol%.

[0010] Preferably, it contains more Ni than Co. By configuring in this way, the thermal stability is improved and, moreover, the variation in resistance value becomes even smaller.

[0011] Preferably, it does not substantially contain Fe or Cu. If either is substantially contained in the composition, the thermal stability tends to decrease and, moreover, the variation in resistance value tends to increase. Note that not being substantially contained means that it may be contained within a range that does not significantly inhibit the thermal stability and does not significantly increase the variation in resistance value. For example, Fe or Cu may be contained in the composition in an amount within 0.5 mol%.

[0012] Preferably, the composition has spinel-type metal oxide particles with an average particle diameter of 10 μm or less. By configuring it in this way, the density of the composition is improved, the thermal stability is further improved, the variation in resistance values is further reduced, and the firing temperature can be lowered, making it easier to control the shrinkage of the internal electrodes and reducing the variation in resistance values.

[0013] The NTC thermistor element according to one aspect of the present invention has the NTC thermistor composition described in any of the above. According to this NTC thermistor element, when this element is mounted on a circuit board or the like, even if a plurality of reflow processes are performed, the change in characteristics is small, the thermal stability is excellent, and the variation in resistance values is also small.

[0014] Preferably, the size of the element is 0.6 mm or less in the first axial direction and 0.3 mm or less in the second axial direction.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments will be described with reference to the drawings. In the figures, the X-axis, Y-axis, and Z-axis are perpendicular to each other.

[0017] Thermistor element As shown in FIG. 1, the NTC thermistor element 1 according to the present embodiment has an element body 2 and external electrodes 4, 4 provided at both ends of the element body 2 in the X-axis direction. Inside the element body 2, internal electrode layers 3 are laminated at predetermined intervals along the Z-axis direction so as to sandwich a thermistor layer 2a, and protective layers 2b are laminated outside the internal electrode layer located most outside along the Z-axis.

[0018] The internal electrode layer 3 has a pair of first internal electrode layers 3a of a first predetermined pattern and a second internal electrode 3b of a second predetermined pattern positioned therebetween, and both are continuous in the pattern shown in FIG. 1 along the Y axis, and are intermittent in part along the X axis. The first internal electrode layer 3a has an intermittent portion 3a1 formed at a substantially central portion along the X axis so as to block electrical conduction between the first internal electrode layers 3a positioned on both sides. The first internal electrode layers 3a positioned on both sides of the intermittent portion 3a1 along the X axis are respectively connected to separate external electrodes 4, 4. At the intermittent portion 3a1, the thermistor layer 2a and the protective layer 2b are continuous.

[0019] The second internal electrode layer 3b positioned between the pair of first internal electrode layers 3a, 3a along the Z axis has a pair of intermittent portions 3b1 formed at positions close to the external electrodes 4, 4 respectively along the X axis and at a substantially central position so as to block electrical conduction with both the second internal electrode layer 3b of the isolated pattern positioned at the center and the external electrodes 4, 4. At the intermittent portion 3b1, two thermistor layers 2a are continuous.

[0020] The width of the second internal electrode layer 3b of the isolated pattern positioned at the center along the X axis is larger than the width of the intermittent portion 3a1 of the first internal electrode layer 3a. Moreover, when viewed from the direction along the Z axis, the second internal electrode layer 3b of the isolated pattern positioned at the center along the X axis overlaps with the first internal electrode layers 3a positioned on both sides along the X axis, and the portion of the thermistor layer 2a positioned at the overlapping portion becomes the active layer of the thermistor layer. Note that the number of stacked layers and the pattern shape of the internal electrode layers 3a, 3b are not limited to the example shown in FIG. 1, and are not particularly limited as long as they are the number of layers and the pattern shape in which the thermistor circuit is formed.

[0021] In the present embodiment, it is preferable that the thermistor layer 2a and the protective layer 2b are composed of a thermistor composition of the same material. However, since the protective layer 2b hardly affects the characteristics of the thermistor element, it may be composed of an insulating material composition different from that of the thermistor layer 2a. The thermistor layer 2a is composed of an NTC thermistor composition described later in the present embodiment.

[0022] The first internal electrode layer 3a and the second internal electrode layer 3b preferably contain a noble metal element as a conductive component. The noble metal element contained in the internal electrode is not particularly limited, and may contain one or more elements selected from the group consisting of Pd, Ag, and Pt. The internal electrode layers 3a and 3b may contain base metal elements such as Ni and Cu in addition to the above-mentioned noble metal element as a conductive component.

[0023] The external electrode 4 preferably contains a noble metal element as a conductive component. The noble metal element contained in the external electrode 4 is not particularly limited, and may contain one or more elements selected from the group consisting of Pd, Ag, and Pt. The external electrode 4 may contain base metal elements such as Ni and Cu in addition to the above-mentioned noble metal element as a conductive component. The external electrode 4 may contain a glass component in addition to the above metal elements. The glass component is added to promote the sintering of the external electrode 4 and to impart mechanical strength to the external electrode. The composition of the external electrode 4 is not particularly limited. For example, it may contain 60% to 95% by volume of a metal component and 5% to 40% by volume of a glass component. The composition of the glass component contained in the external electrode is not particularly limited and can be appropriately set according to the intended use. The glass component contained in the external electrode may contain, for example, at least one selected from the group consisting of alkaline earth metals, Cu, Si, Ti, Zn, alkali metals, Sr, Al, and Bi.

[0024] The size of the NTC thermistor element 1 of the present embodiment is not particularly limited, but is preferably 0.6 mm or less along the X-axis direction, 0.3 mm or less along the Y-axis, and 0.3 mm or less along the Z-axis. Further, the thickness of the thermistor layer 2a is not particularly limited, but is preferably 5 to 100 μm.

[0025] In this embodiment, the thermistor layer 2a is composed of an NTC thermistor composition, preferably has spinel-type metal oxide particles with an average particle diameter of 10 μm or less, and these particles are arranged in the thermistor layer 2a at a predetermined density. By setting the particle diameter of the oxide particles to 10 μm or less, the fired body density is improved and the thermal stability is enhanced. Note that the control method for setting the particle diameter of the oxide particles to 10 μm or less is not particularly limited. For example, it may be sized by passing a ceramic slurry through a mesh.

[0026] Whether the thermistor layer 2a has spinel-type metal oxide particles can be determined, for example, by analyzing the thermistor layer 2a using X-ray diffraction. Also, the average particle diameter of the metal oxide particles can be obtained by observing the cross-section of the thermistor layer 2a with, for example, a scanning electron microscope and averaging over 100 or more particles. Also, by observing the cross-section of the thermistor layer 2a in a similar manner, the density of the metal oxide, for example, the number ratio of particles per 100 square μm can be analyzed. In the thermistor layer 2a, there may be segregation particles or the like in addition to the metal oxide particles, but it is preferably 5% or less in terms of the area ratio of the cross-section.

[0027] In this embodiment, the metals contained in the NTC thermistor composition constituting the thermistor layer 2a include at least Mn, Co, and Ni, and may contain Al and Zr as necessary, and preferably do not substantially contain Fe or Cu.

[0028] In this embodiment, when the total of Mn, Co, Ni, and Al is 100 mol%, the content of Mn is 40 to 63 mol%, preferably 47 to 60 mol%. By setting the content of Mn within a predetermined range, both the resistance change rate and the resistance value fluctuation coefficient become small. The reason is considered to be that if the content of Mn is too small, self-heating increases and it tends to be difficult to use as an NTC thermistor element, and if it is too large, the structural stability decreases and the thermal stability tends to be low.

[0029] Note that the resistance change rate indicates the change rate of the resistance of the NTC thermistor element having the NTC thermistor composition according to the present embodiment before and after passing through the reflow furnace several times. Further, the resistance value variation coefficient indicates the variation between individuals of the resistance values at 25°C of a plurality of NTC thermistor elements having the NTC thermistor composition according to the present embodiment, and the smaller the coefficient, the less the variation between individuals.

[0030] The content of Co is 10 to 30 mol%, preferably 13 to 25 mol%, and more preferably 15 to 23 mol%. By setting the content of Co within a predetermined range, both the resistance change rate and the resistance value variation coefficient become small. The reason is considered to be that if the content of Co is too small, the structural stability decreases and the thermal stability tends to be low, and if it is too large, it tends not to be solid-solved and easily precipitates as a heterogeneous phase, and the resistance value variation tends to increase.

[0031] Also, the content of Ni is 15 to 35 mol%, preferably 17 to 31 mol%, and more preferably 21 to 27 mol%. By setting the content of Ni within a predetermined range, both the resistance change rate and the resistance value variation coefficient become small. The reason is considered to be that if the content of Ni is too small, the structural stability decreases and the thermal stability tends to be low, and if it is too large, it tends not to be solid-solved and easily precipitates as a heterogeneous phase, and the resistance value variation tends to increase.

[0032] Regarding Al, it may or may not be contained in the composition. When it is contained, it is 5.9 mol% or less. By setting the content of Al within a predetermined range, both the resistance change rate and the resistance value variation coefficient become small. The reason is considered to be that if the content of Al is too large, it tends not to be solid-solved and precipitates as a heterogeneous phase, and the variation of the resistance value tends to increase. Note that compared with the case where Al is not contained, it is advantageous in that the structural stability is improved and the thermal stability tends to be high when Al is contained. In that regard, the content of Al is preferably 1.9 to 4.8 mol%.

[0033] Preferably, the content of Ni is more than the content of Co. By configuring in this way, both the resistance change rate and the resistance value variation coefficient become small. The reason is considered to be that the valence fluctuation is reduced and the thermal stability is improved. In addition, by making the content of Ni more than the content of Co, reduction of the manufacturing cost can be expected.

[0034] Regarding Zr, it may not be contained in the composition, but it may be contained. When it is contained, it is 2.5 mol% or less. By setting the content of Zr within a predetermined range, both the resistance change rate and the resistance value variation coefficient become small. The reason is considered to be that the valence fluctuation is reduced and the thermal stability is improved.

[0035] It is preferable that the NTC thermistor composition according to this embodiment does not substantially contain Fe. By not substantially containing Fe, both the resistance change rate and the resistance value variation coefficient are small. The reason is that when Fe is substantially contained, the variation in the resistance value becomes large. Note that "not substantially contained" means that Fe may be contained as long as it does not inhibit the original characteristics of the NTC thermistor composition according to this embodiment, and it may be contained if it is about 0.5 mol% or less.

[0036] It is preferable that the NTC thermistor composition according to this embodiment does not substantially contain Cu. By not substantially containing Cu, both the resistance change rate and the resistance value variation coefficient are small. The reason is that when Cu is substantially contained, the variation in the resistance value tends to increase. Note that "not substantially contained" means that Cu may be contained as long as it does not inhibit the original characteristics of the NTC thermistor composition according to this embodiment, and it may be contained if it is about 0.5 mol% or less.

[0037] The NTC thermistor composition according to this embodiment may contain metals such as Ba, Ca, Mo, Nb, Sn, Ti, V, W, and Y as other metal components, as long as the content is about 0.5 mol% or less. Other metals may be included as long as the original characteristics of the NTC thermistor composition according to this embodiment are not inhibited.

[0038] Since the thermistor layer 2a of the thermistor element 1 of this embodiment is composed of the above-described composition, even if the element 1 is miniaturized, it has excellent thermal stability against heat during the reflow process, and moreover, the variation in resistance value is small. As the heat during the reflow process, for example, a temperature of 200°C or higher is considered, and as the number of times of the reflow process applied to the element 1, for example, 2 times or more is considered. The thickness W of the thermistor layer 2a is not particularly limited, but is preferably 5 to 100 μm. By setting it within this range, particularly the variation in resistance becomes small and the thermal stability is improved.

[0039] The thermistor element 1 of this embodiment is formed, for example, by applying a conductive paste (external electrode paste) containing Pd particles to both end faces of an element body 2 made of a ceramic body and performing a baking process. The element body 2 can be manufactured by preparing ceramic pastes that respectively constitute the thermistor layer 2a and the protective layer 2b, preparing electrode pastes that constitute the internal electrode layers 3a and 3b, laminating the paste layers by a printing method or the like, drying, and sintering.

[0040] Specifically, the thermistor element 1 is manufactured as follows.

[0041] First, raw materials of metals contained in the metal oxide particles of the thermistor composition are prepared. In this embodiment, as raw materials, manganese oxide, nickel oxide, cobalt oxide, aluminum oxide, zirconium oxide, or raw materials that become these oxides after firing are prepared. Examples of the compounds that become oxides after firing include carbonates, halogen compounds, oxalates, nitrates, hydroxides, and organometallic compounds containing these metals.

[0042] Next, the above raw materials are weighed and mixed to prepare a mixed powder. The mixing method is not particularly limited. For example, it may be carried out by dry mixing, or water, an organic solvent, etc. may be added to the mixed powder, and a ball mill or the like may be used for wet mixing.

[0043] Next, the prepared mixed powder is granulated. Granulation is carried out to make the mixed powder into agglomerated particles of an appropriate size and convert it into a form suitable for molding. Examples of the granulation method include a pressure granulation method and a spray drying method. The spray drying method is a method in which a commonly used binder such as polyvinyl alcohol is added to the mixed powder, then atomized in a spray dryer, and dried. The average particle size of the mixed powder (raw material for the thermistor composition) as granules is preferably 50 μm or less.

[0044] Then, water and a dispersant are added to the obtained granules and mixed with a ball mill, and a binder resin is further added to obtain a ceramic slurry. This ceramic slurry is formed by the doctor blade method to obtain a green sheet having a thickness of about 5 to 100 μm.

[0045] An internal electrode paste is prepared by mixing a noble metal powder and an organic vehicle. The average particle size of the noble metal powder is preferably 0.1 μm or more and 5.0 μm or less. The internal electrode paste preferably contains a powder of a noble metal in a predetermined weight percentage and an organic vehicle in a predetermined weight percentage. The organic vehicle can be prepared, for example, by dissolving ethyl cellulose in terpineol.

[0046] The internal electrode paste is printed on the green sheet in a predetermined shape to form an internal electrode pattern. The green sheet on which the internal electrode pattern is formed and the green sheet on which the internal electrode pattern is not formed are stacked in a predetermined order and a predetermined number of sheets, and pressed to obtain a mother laminate. This mother laminate is cut into a predetermined size to obtain a chip-shaped laminate.

[0047] Next, or in parallel with the above steps, an external electrode paste is prepared by kneading Pd powder, glass frit, and an organic vehicle. As the Pd powder, a mixture of spherical Pd powder and flat Pd powder may be used. As the glass frit, for example, a glass frit containing B is used. The glass frit preferably has a transition point of 400°C or higher and 650°C or lower, and a softening point of 500°C or higher and 750°C or lower.

[0048] The organic vehicle can be prepared, for example, by dissolving an acrylic resin in terpineol. The content of the acrylic resin in the organic vehicle may be, for example, 5% by weight or more and 40% by weight or less.

[0049] The external electrode paste is applied to one end face and the other end face of the element body 2 as a sintered body in a predetermined shape. The applied external electrode may be dried. The coating thickness of the external electrode paste can be appropriately set according to the thickness of the target external electrode.

[0050] The external electrode paste applied to one end face and the other end face of the ceramic element body is baked to form a first external electrode 4 provided on one end face and a second external electrode 4 provided on the other end face.

[0051] If necessary, a plating layer may be formed on the surface of the external electrode 4 by electrolytic plating. The plating layer has a function of improving the solder wetting property and heat resistance during mounting. The composition of the plating layer can be appropriately selected according to the composition of the external electrode, etc. For example, an Ni plating layer may be formed on the surface of the external electrode 4, and an Sn plating layer may be formed thereon.

[0052] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0053] For example, the NTC thermistor composition according to the above-described embodiment is suitable for use as the thermistor layer 2a of a laminated chip-type thermistor element, but it can also be used as the composition of other types of thermistor elements. The NTC thermistor composition of the above-described embodiment can be used as other types of elements, for example, in NTC thermistor elements such as glass diode type thermistors, glass bead type thermistors, and resin bead type thermistors.

Examples

[0054] Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

[0055] Examples 1 to 6 First, as starting materials, commercially available manganese sesquioxide (Mn 3 O 4 ), nickel oxide, cobalt oxide, and aluminum oxide were weighed and prepared so that the composition after firing would be the composition ratio shown in Table 1. However, in Table 1, the mol% of Mn, Ni, Co, and Al is based on a total of 100 mol% of Mn, Ni, Co, and Al. These raw materials were blended and wet-mixed in a ball mill for 16 hours. Note that these starting raw materials may contain inevitable impurities in an amount of about 0.1 wt% or less.

[0056] Next, the starting raw materials after wet mixing were dehydrated and dried, and then made into a powder using a mortar and pestle. Then, the obtained powder was placed in an alumina crucible and calcined at 800 to 1200 °C for 2 hours.

[0057] Next, the obtained calcined powder was finely pulverized by a ball mill and then dehydrated and dried to obtain granules of the thermistor composition raw material. Water and a dispersant were added to the obtained granules and mixed in a ball mill, and then a binder resin was added to obtain a ceramic slurry. This ceramic slurry was formed by the doctor blade method to obtain a green sheet having a predetermined thickness.

[0058] An internal electrode paste was prepared by mixing Pd powder as a precious metal powder and an organic vehicle. The average particle size of the precious metal powder was 0.5 μm. The internal electrode paste was formed by dispersing the precious metal powder in the organic vehicle. The organic vehicle was prepared by dissolving ethyl cellulose in terpineol.

[0059] The internal electrode paste was printed on the green sheet in a predetermined shape to form an internal electrode pattern. The green sheet with the internal electrode pattern formed thereon and the green sheet without the internal electrode pattern formed thereon were laminated in a predetermined order and a predetermined number of sheets, and pressed to obtain a mother laminate. This mother laminate was cut into a predetermined size to obtain a chip-shaped laminate.

[0060] Next, or in parallel with the above steps, an external electrode paste was prepared by kneading Pd powder, glass frit, and an organic vehicle. As the Pd powder, a mixture of spherical Pd powder and flat Pd powder was used. As the glass frit, for example, a glass frit containing B was used. The transition point of the glass frit was 520 °C, and the softening point was 580 °C.

[0061] The organic vehicle was prepared by dissolving an acrylic resin in terpineol, for example. The content of the acrylic resin in the organic vehicle was 30% by weight.

[0062] The external electrode paste was applied to one end face and the other end face of the element body 2 as a sintered body in a predetermined shape. The applied external electrode was dried. The external electrode paste applied to one end face and the other end face of the ceramic body was baked to form a first external electrode 4 provided on one end face and a second external electrode 4 provided on the other end face. A Ni plating layer was formed on the surface of the external electrode 4 by electrolytic plating, and an Sn plating layer was formed thereon. Thus, a sample of the NTC thermistor element 1 was manufactured.

[0063] For each sample, the evaluations shown in Table 1 were performed. The resistance change rate was obtained by repeating the process of putting a sample of the NTC thermistor element 1 into a reflow furnace at a temperature of 260 °C for about 10 minutes and then cooling it 6 times, and showing the change rate of the resistance value of the sample after 6 reflow treatments with respect to the resistance value of the sample before being put into the reflow furnace. The symbol A for the resistance change rate in Table 1 indicates that the change rate of the resistance value of the sample after 6 reflow treatments is within ±0.5% with respect to the resistance value of the sample before being put into the first reflow furnace.

[0064] Also, the coefficient of variation of the resistance value was obtained by preparing 30 samples of each of the NTC thermistor elements of Examples 1 to 6, measuring the variation (CV value) between the resistance values of these samples at 25 °C, and examining how much it changed compared to the CV value of Example 1. The symbol F indicates that the CV value became 2.0 or more larger compared to Example 1, the symbol A indicates that the CV value was 1.4 or more and less than 2.0, the symbol A2 indicates that the CV value was 1.1 or more and less than 1.4, and the symbol A3 indicates that the CV value was less than 1.1.

[0065] Also, in the determination, when the resistance change rate is A and moreover the coefficient of variation of the resistance value is A3, it is judged as A3, when the resistance change rate is A and moreover the coefficient of variation of the resistance value is A2, it is judged as A2, when the resistance change rate is A and moreover the coefficient of variation of the resistance value is A, it is judged as A, and when the resistance change rate is F or the coefficient of variation of the resistance value is F, it is judged as F and indicated.

[0066] These results are shown in Table 1. Also, regarding the thermistor layer of the samples of Element 1 according to Examples 1 to 6, cross-sectional photographs were taken with a scanning electron microscope and the particles were analyzed by X-ray diffraction method. As a result, it was confirmed that these particles are spinel-type oxide particles. Also, when the average particle diameter of the particles was determined, it was 10 μm or less.

[0067] Comparative Example 1 An element sample was fabricated in the same manner as in Example 1, except that the starting materials were prepared such that the Al content was 7.3 mol%, exceeding 5.9 mol% as shown in Table 1. The same tests and evaluations as in Example 1 were conducted. The results are shown in Table 1.

[0068] Evaluation 1 As shown in Table 1, it was confirmed that in Examples 1 to 6, good results were obtained for both the resistance change rate and the resistance value variation coefficient, as compared with the sample according to Comparative Example 1 in which the Al content exceeded 5.9 mol%.

[0069]

Table 1

[0070] Examples 7 to 12, Comparative Examples 2 and 3 The starting materials were prepared such that the Al content was 2.6 mol% and the Mn content was varied in the range of 36.5 to 66.1 mol%, and accordingly, the Co and Ni contents were varied. An element sample was fabricated in the same manner as in Example 3. The same tests and evaluations as in Example 3 were conducted. The results are shown in Table 2.

[0071] Evaluation 2 As shown in Table 2, it was confirmed that in Examples 7 to 12 in which the Mn content was in the range of 40 to 63 mol%, good results were obtained for both the resistance change rate and the resistance value variation coefficient, as compared with the samples according to Comparative Examples 2 and 3 in which the Mn content was outside the range of 40 to 63 mol%. Further, it was confirmed that in Examples 9 to 11 in which the Mn content was in the range of 47 to 60 mol%, even better results were obtained for the resistance value variation coefficient.

[0072]

Table 2

[0073] Examples 13 to 18, Comparative Examples 4 and 5 The starting materials were prepared in the same manner as in Example 5, except that the Al content was set to 4.9 mol% as shown in Table 3, the Ni content was varied in the range of 12.0 to 39.0 mol%, and the Mn and Co contents were varied accordingly. Samples of the device were fabricated and the same tests and evaluations as in Example 5 were performed. The results are shown in Table 3.

[0074] Evaluation 3 As shown in Table 3, compared with the samples according to Comparative Examples 4 and 5 in which the Ni content is outside the range of 15 to 35 mol%, in Examples 13 to 18 where the Ni content is in the range of 15 to 35 mol%, it was confirmed that good results were obtained for both the resistance change rate and the resistance value variation coefficient. Also, in Examples 14 to 17 where the Ni content is in the range of 17 to 31 mol%, it was confirmed that better results were obtained for the resistance value variation coefficient. Furthermore, in Examples 15 to 16 where the Ni content is in the range of 21 to 27 mol%, it was confirmed that better results were obtained for the resistance value variation coefficient.

[0075]

Table 3

[0076] Examples 19 to 25, Comparative Examples 6 and 7 The starting materials were prepared in the same manner as in Example 4, except that the Al content was set to 3.7 mol% as shown in Table 4, the Co content was varied in the range of 8.1 to 32.3 mol%, and the Mn and Ni contents were varied accordingly. Samples of the device were fabricated and the same tests and evaluations as in Example 4 were performed. The results are shown in Table 4.

[0077] Evaluation 4 As shown in Table 4, compared with the samples according to Comparative Examples 6 and 7 in which the Co content is outside the range of 10 to 30 mol%, in Examples 19 to 25 in which the Co content is in the range of 10 to 30 mol%, it was confirmed that good results were obtained for both the resistance change rate and the resistance value variation coefficient. Further, in Examples 20 to 23 in which the Co content is in the range of 13 to 25 mol%, it was confirmed that better results were obtained for the resistance value variation coefficient. Furthermore, in Examples 4 and 21 to 22 in which the Co content is in the range of 15 to 23 mol%, it was confirmed that better results were obtained for the resistance value variation coefficient.

[0078] Also, as shown in Tables 1 to 4, it was confirmed that the resistance value variation coefficient is better in the examples in which the Ni content is larger than the Co content, compared with the examples in which the Ni content is smaller than the Co content.

[0079]

Table 4

[0080] Examples 2a to 2b and 6a to 6b As shown in Table 5, the Al content was changed, and starting materials were prepared so as to include Fe or Cu. Except for this, samples of the element were produced in the same manner as in Example 2 or 6, and the same tests and evaluations as in Example 2 or 6 were performed. The results are shown in Table 5.

[0081] Evaluation 5 As shown in Table 5, it was confirmed that when Fe or Cu is included, the resistance value variation coefficient deteriorates as compared with the case where Fe or Cu is not included.

[0082]

Table 5

[0083] Comparative Examples 8 to 9 The starting materials were prepared by changing the contents of Mn, Co, Ni, and Al as shown in Table 6, and adding or not adding Fe and Cu. Then, samples of the device were fabricated in the same manner as in Example 3, and the same tests and evaluations as in Example 3 were conducted. The results are shown in Table 6.

[0084] Evaluation 6 As shown in Table 6, when Co was not included, it was confirmed that whether Fe and Cu were included or not, the resistance change rate deteriorated and the resistance value fluctuation coefficient deteriorated. In addition, Fig. 2 shows graphs showing the relationship between the number of furnace passes and the resistance change rate in the samples of Comparative Examples 8 and 9. Also, Fig. 2 shows a graph showing the relationship between the number of passes and the resistance change rate in the sample of Example 3.

[0085]

Table 6

[0086] Examples 26 to 29 The starting materials were prepared by changing the content of Al as shown in Table 7 and including Zr instead. Then, samples of the device were fabricated in the same manner as in Example 3, and the same tests and evaluations as in Example 3 were conducted. The results are shown in Table 7.

[0087] Evaluation 7 As shown in Table 7, when Zr was included, it was confirmed that the resistance value fluctuation coefficient was equivalent compared to the case where Zr was not included, and Zr may be added up to 2.5 mol%.

[0088]

Table 7

Description of Signs

[0089] 1… NTC thermistor element 2… Element body 2a… Thermistor layer 2b… Protection layer 3… Inner electrode layer 3a… First inner electrode layer 3a1… Intermittent part 3b… Second inner electrode layer 3b1… Intermittent part 4… External electrode

Claims

1. When the total of Mn, Co, Ni, and Al is 100 mol%, Mn is 40 to 63 mol%, Co is 10 to 30 mol%, and Ni is 15 to 35 mol%, and Al is 5.9 mol% or less (including 0), an NTC thermistor composition.

2. The NTC thermistor composition according to Claim 1, containing Zr in an amount of 0 to 2.5 mol%.

3. The NTC thermistor composition according to Claim 1, containing more Ni than Co.

4. The NTC thermistor composition according to Claim 1, substantially free of Fe or Cu.

5. The NTC thermistor composition according to Claim 1, having spinel-type metal oxide particles with an average particle diameter of 10 μm or less.

6. An NTC thermistor element having the NTC thermistor composition according to any one of Claims 1 to 5.

7. The NTC thermistor element according to Claim 6, being 0.6 mm or less in the first axial direction and 0.3 mm or less in the second axial direction.

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