Thermistor element, temperature sensor provided with same, and thermistor element manufacturing method

Abstract

Provided are a thermistor element with minimal characteristic variation over time in a high temperature environment and during a heat resistance test, a temperature sensor including the thermistor element, and a thermistor element manufacturing method. This thermistor element comprises: a thermistor element body 2 having a crystal structure which includes a perovskite-type oxide thermistor material; and a pair of electrodes 3 on which the thermistor element body is formed. The electrodes comprise a Pt electrode layer 3a formed on the surface of the thermistor element body, and an intermetallic compound layer 3b including Pt, Sn, and M formed on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.

Description

Thermistor element, temperature sensor including the same, and method of manufacturing thermistor element

[0001] The present invention relates to a thermistor element whose characteristics change little over time even in heat resistance tests or in high-temperature environments, a temperature sensor including the thermistor element, and a method for manufacturing the thermistor element.

[0002] Generally, the resistance value of a thermistor element changes with temperature, and because the change is very sensitive to temperature, the thermistor element is widely used in temperature sensors, protection circuits for electronic devices, etc. To improve the environmental resistance of the thermistor element, for example, a sensor in which the thermistor element is sealed with resin has been known (for example, see Patent Document 1).

[0003] Patent No. 3152352

[0004] The above-mentioned conventional technologies still have the following problems. In recent years, with the improvement of motor output, extension of driving range, and high-speed charging in electric vehicles, the characteristics of thermistor elements change over time in heat resistance tests that assume higher temperatures in the driving environment of the motor, battery, etc. This problem is more pronounced in perovskite-based thermistor elements. In particular, in the case of thermistor elements provided with electrodes formed of Pt, if the thickness of the electrodes is less than 4 μm, there is a problem that the increase in resistance value becomes significant in high-temperature environments or during heat resistance tests. One possible solution to this problem is to thicken the Pt electrodes, but this has the disadvantage of increasing material costs.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a thermistor element whose characteristics change little over time in high-temperature environments or during heat resistance tests, a temperature sensor including the same, and a method for manufacturing the thermistor element.

[0006] The present inventors conducted research into the changes in the characteristics of perovskite thermistor elements over time in high-temperature environments and during heat resistance tests, and discovered that the cause of this is that when the thermistor element is mounted with a solder material, oxidation of Sn, a main component of solder, causes the thermistor element body to be exposed to a low-oxygen environment, resulting in oxygen defects due to reduction in the thermistor material. Therefore, the present invention was developed based on the above findings and employs the following configuration to solve the above problem. Specifically, a thermistor element according to a first aspect of the present invention comprises a thermistor element body containing an oxide thermistor material having a perovskite crystal structure, and a pair of electrodes on which the thermistor element body is formed, the electrodes comprising a Pt electrode layer formed on the surface of the thermistor element body and an intermetallic compound layer formed on the outside of the Pt electrode layer and containing Pt, Sn, and M, wherein M is at least one of Ag, Ni, Co, and Mn, and the intermetallic compound layer has a thickness of 50 nm or more.

[0007] In this thermistor element, M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more. Therefore, the thick intermetallic compound layer, which is a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, thereby suppressing the formation of oxygen defects in the thermistor element due to oxidation of Sn, the main component of the solder, even if the Pt electrode layer is thin. This invention is particularly effective when the Pt electrode layer is less than 4 μm thick.

[0008] A thermistor element according to a second aspect of the present invention is the thermistor element according to the first aspect of the present invention, characterized in that the thickness of the intermetallic compound layer is 190 nm or more and the concentration of M in the intermetallic compound layer is 3.0 to 7.6 wt %. That is, in this thermistor element, the thickness of the intermetallic compound layer is 190 nm or more and the concentration of M in the intermetallic compound layer is 3.0 to 7.6 wt %, so that it is possible to suppress the rate of change in resistance value in a heat resistance test to 1.6% or less.

[0009] The thermistor element according to the third invention is the thermistor element according to the first or second invention, characterized in that a solder material mainly composed of Sn is joined to at least one of the pair of electrodes. That is, in this thermistor element, since a solder material mainly composed of Sn is joined to at least one of the pair of electrodes, even if the Sn in the solder material oxidizes when the thermistor element is soldered at high temperatures or used in a high-temperature environment, the formation of oxygen defects in the thermistor element can be suppressed, and the rate of change in resistance can be reduced.

[0010] A thermistor element according to a fourth invention is the third invention, characterized in that the intermetallic compound layer has a high-concentration M region containing more M on the solder material side than on the Pt electrode layer side. That is, in this thermistor element, the intermetallic compound layer has a high-concentration M region containing more M on the solder material side than on the Pt electrode layer side, and the M-rich region enhances the oxygen barrier effect.

[0011] A temperature sensor according to a fifth aspect of the present invention is characterized by comprising the thermistor element of the third aspect of the present invention, a pair of lead wires having one end connected to the pair of electrodes by the solder material, and a resin sealing portion that seals the entire thermistor element with resin, including the one ends of the pair of lead wires. That is, since this temperature sensor comprises a resin sealing portion that seals the entire thermistor element with resin, including the one ends of the pair of lead wires, a resin-sealed temperature sensor with a low rate of change in resistance value during a heat resistance test can be obtained.

[0012] A temperature sensor according to a sixth aspect of the present invention comprises the thermistor element of the third aspect of the present invention and a mounting substrate on which the thermistor element is mounted, the mounting substrate having wiring formed on its surface, and the thermistor element being joined to the wiring with the solder material. That is, in this temperature sensor, the thermistor element of the above aspect of the present invention is joined to the wiring of the mounting substrate with the solder material, so that even when the thermistor element is mounted on the substrate, changes in resistance value can be suppressed in high-temperature environments and during heat resistance tests, etc.

[0013] A seventh aspect of the present invention provides a method for manufacturing a thermistor element, comprising: an electrode forming step of forming a pair of electrodes on a thermistor body containing an oxide thermistor material having a perovskite crystal structure; and a soldering step of joining a solder material containing Sn as a main component to at least one of the pair of electrodes, wherein the electrode forming step comprises a Pt electrode layer step of forming a Pt electrode layer on the surface of the thermistor body; and an intermetallic compound layer forming step of forming an intermetallic compound layer containing Pt, Sn, and M on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the intermetallic compound layer has a thickness of 50 nm or more.

[0014] An eighth aspect of the present invention relates to a method for manufacturing a thermistor element according to the seventh aspect, characterized in that, in the soldering step, when the molten solder material containing M is attached to the Pt electrode layer and then solidified, an intermetallic compound layer forming step is performed to form an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer between the solder material and the Pt electrode layer.In this method for manufacturing a thermistor element, when the molten solder material containing M is attached to the Pt electrode layer and then solidified, an intermetallic compound layer forming step is performed to form an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer between the solder material and the Pt electrode layer, so that the intermetallic compound layer forming step can be performed during the soldering step.

[0015] A ninth aspect of the present invention relates to a method for manufacturing a thermistor element according to the eighth aspect, characterized in that in the soldering step, the solder material is bonded at a bonding temperature of 280°C or higher. In other words, in this method for manufacturing a thermistor element, the solder material is bonded at a bonding temperature of 280°C or higher in the soldering step, making it possible to suppress the rate of resistance change in a heat resistance test to 1.6% or less. In particular, when the solder material is bonded at a bonding temperature of 380°C or higher, an intermetallic compound layer containing more M on the solder material side than on the Pt electrode layer side is obtained, further enhancing the oxygen barrier effect and reducing the rate of resistance change.

[0016] The tenth aspect of the present invention is a method for manufacturing a thermistor element according to the seventh aspect, wherein the intermetallic compound layer forming step comprises an M sputtering step of forming an M layer by adhering the M to the surface of the Pt electrode layer by a sputtering method, and an M solid solution step of forming the intermetallic compound layer containing the M in the M layer, the Pt in the Pt electrode layer, and the Sn in the solder material between the solder material and the Pt electrode layer when the solder material melted in the solder joining step is adhered to the M layer and then solidified. That is, in this method for manufacturing a thermistor element, the intermetallic compound layer forming step includes an M sputtering step in which the M is attached to the surface of the Pt electrode layer by sputtering to form an M layer, and an M solidification step in which, when the solder material molten in the solder joining step is attached to the M layer and then solidified, an intermetallic compound layer containing the M in the M layer, the Pt in the Pt electrode layer, and the Sn in the solder material is formed between the solder material and the Pt electrode layer.Therefore, even if the solder material does not contain the M, it is possible to easily obtain an intermetallic compound layer containing a sufficient amount of the M by solidifying the M in the M layer formed by sputtering.

[0017] The present invention has the following advantages. Specifically, in the thermistor element, temperature sensor including the same, and method for manufacturing the thermistor element according to the present invention, M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more. Therefore, the thick intermetallic compound layer, which is a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, thereby suppressing the formation of oxygen defects in the thermistor element due to oxidation of Sn, the main component of the solder, even if the Pt electrode layer is thin. Therefore, it is possible to suppress changes in thermistor characteristics over time in high-temperature environments or during heat resistance tests, and a highly reliable thermistor element and temperature sensor can be obtained.

[0018] 1 is a conceptual cross-sectional view of a main portion of a thermistor element in one embodiment of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing thermistor element according to the present invention. FIG. 1 is a cross-sectional view of a resin-sealed temperature sensor in the present embodiment. FIG. 2 is a cross-sectional view of a temperature sensor including the thermistor element in the present embodiment. FIG. 3 is a cross-sectional view of another example of a temperature sensor including the thermistor element in the present embodiment. FIG. 4 is a schematic cross-sectional view showing a method for manufacturing a thermistor element in the order of manufacturing steps in the present embodiment. FIG. 5 is a schematic cross-sectional view showing a method for manufacturing a thermistor element in the order of manufacturing steps in the present embodiment. FIG. 6 is a schematic cross-sectional view showing a method for manufacturing a thermistor element in the order of manufacturing steps in the present embodiment. FIG. 7 is a schematic cross-sectional view showing a method for manufacturing a thermistor element in the order of manufacturing steps in the present embodiment. FIG. 8 is a composition distribution image of each element (Ni, Sn, Pt) in a cross-section of a thermistor element at a bonding temperature of 280°C in an example of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing a thermistor element according to the present invention. FIG. 9 is a composition distribution image of each element (Ni, Sn, Pt) in a cross-section of a thermistor element at a bonding temperature of 380°C in an example of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing a thermistor element according to the present invention.

[0019] An embodiment of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing the thermistor element according to the present invention will be described below with reference to Figures 1 to 5D. Note that in the drawings used in the following description, the scale has been appropriately changed as necessary to make each component recognizable or easily recognizable.

[0020] As shown in Fig. 1, the thermistor element 1 of this embodiment comprises a thermistor body 2 containing an oxide thermistor material having a perovskite crystal structure, and a pair of electrodes 3 formed on the thermistor body 2. Note that the thermistor element 1 of this embodiment has electrodes 3 formed on both the top and bottom surfaces of the flake-shaped thermistor body 2, but Fig. 1 only shows the top surface. The electrodes 3 comprise a Pt electrode layer 3a formed on the surface of the thermistor body 2, and an intermetallic compound layer 3b containing Pt, Sn, and M formed on the outside of the Pt electrode layer 3a. M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer 3b is 50 nm or more.

[0021] In particular, it is preferable that the thickness of the intermetallic compound layer 3b is 190 nm or more and the concentration of M in the intermetallic compound layer 3b is 3.0 to 7.6 wt %. A solder material 4 containing Sn as a main component is joined to at least one of the pair of electrodes 3. The intermetallic compound layer 3b has a high-M-concentration region 3c containing more M on the solder material 4 side than on the Pt electrode layer 3a side. For example, when M is Ni, the high-M-concentration region 3c is a high-Ni-concentration region.

[0022] The concentration of M in the intermetallic compound layer 3b (M / (Sn+Pt+M) wt%) is preferably 0.5 to 10 wt% for Ni, 3.0 to 15 wt% for Ag, 0.5 to 10 wt% for Co, and 0.5 to 10 wt% for Mn. The intermetallic compound layer 3b is preferably disposed continuously over the entire surface between the Pt electrode layer 3a and the solder material 4, but may be discontinuously disposed in a plurality of locations. The Pt electrode layer 3a is formed by printing and baking a Pt paste on the thermistor element 2. The thickness of the Pt electrode layer 3a is, for example, 1 μm. The present invention is able to effectively obtain an oxygen barrier effect even with a thin Pt electrode layer 3a of less than 4 μm. The thermistor material of the thermistor element 2 is, for example, 0.5 (La ０．８ Ca ０．２ ) (Cr ０．４５ Mn ０．５５ ) O ３ +0.5Y２ O ３ etc.

[0023] 2, the temperature sensor 10A of this embodiment includes a pair of lead wires 5, one end of which is connected to a pair of electrodes 3 by solder material 4, and a resin sealing portion 6 that seals the entire thermistor element 1, including the one ends of the pair of lead wires 5, with resin. The resin sealing portion 6 is made of, for example, epoxy resin. In other words, the temperature sensor 10A of this embodiment is a resin-sealed temperature sensor.

[0024] As another example, a temperature sensor 10B according to this embodiment includes a thermistor element 1 and a mounting substrate 8 on which the thermistor element 1 is mounted, as shown in FIG. 3 . The mounting substrate 8 includes wiring 7 formed on its surface. The thermistor element 1 is bonded to the wiring 7 with solder material 4. The mounting substrate 8 is an insulating substrate, such as an FPC, made of resin. The wiring 7 is a pattern wiring formed of copper foil or the like on the mounting substrate 8, and at least two wirings 7 are provided in the form of mounting pads. Note that only the electrode 3 on the bottom surface of the thermistor element 1 is bonded to one of the wirings 7 on the mounting substrate 8 with solder material 4, and the electrode 3 on the top surface and the other wiring 7 are connected with Au wires 9 by wire bonding.

[0025] As another example, a temperature sensor 10C of this embodiment, as shown in Fig. 4, includes a thermistor element 1C having Pt electrode layers 3a formed on both ends of a cubic thermistor body 2, and a mounting substrate 8 on which the thermistor element 1C is surface-mounted. In other words, the thermistor element 1C is a chip thermistor. In this temperature sensor 10C, the lower portions of the pair of Pt electrode layers 3a are joined to a pair of wirings 7 on the mounting substrate 8 with solder material 4. Therefore, an intermetallic compound layer 3b is formed between the lower portions of the Pt electrode layers 3a and the solder material 4.

[0026] The method for manufacturing the thermistor element 1 of this embodiment includes an electrode formation step of forming a pair of electrodes 3 on a thermistor body 2 containing an oxide thermistor material having a perovskite crystal structure, and a solder bonding step of bonding a solder material 4 containing Sn as a main component to at least one of the pair of electrodes 3. The electrode formation step includes a Pt electrode layer step of forming a Pt electrode layer 3a on the surface of the thermistor body 2, as shown in Fig. 5A, and an intermetallic compound layer formation step of forming an intermetallic compound layer 3b containing Pt, Sn, and the above-mentioned M on the outer side of the Pt electrode layer 3a, as shown in Fig. 5D. The above-mentioned M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer 3b is set to be 50 nm or more.

[0027] In the soldering step, when the molten solder material 4 containing M is attached to the Pt electrode layer 3a and then solidified, an intermetallic compound layer forming step may be performed in which an intermetallic compound layer 3b containing M and Sn in the solder material 4 and Pt in the Pt electrode layer 3a is formed between the solder material 4 and the Pt electrode layer 3a. In the soldering step, the solder material 4 is preferably joined at a joining temperature of 280°C or higher.

[0028] The intermetallic compound layer forming process may include an M sputtering process in which the M is deposited on the surface of the Pt electrode layer 3a by sputtering to form an M layer 3d, as shown in Fig. 5B, and an M solid solution process in which, when the solder material 4 melted in the solder bonding process is deposited on the M layer 3d and then solidified, an intermetallic compound layer 3b containing the M in the M layer 3d, the Pt in the Pt electrode layer 3a, and the Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a, as shown in Fig. 5D. For example, when Ni is used as the M, Ni is deposited on the Pt electrode layer 3a by sputtering to form the Ni M layer 3d, and when the solder material 4 melted by heating is deposited on this M layer 3d and solidified, an intermetallic compound layer 3b containing the Ni in the M layer 3d, the Pt in the Pt electrode layer 3a, and the Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a.

[0029] As described above, in the thermistor element 1 of this embodiment, the M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer 3b is 50 nm or more, so that the thick intermetallic compound layer 3b, which is a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, thereby suppressing the formation of oxygen defects in the thermistor element 2 due to oxidation of Sn, the main solder component, even if the Pt electrode layer 3a is thin. Furthermore, since the thickness of the intermetallic compound layer 3b is 190 nm or more and the concentration of M in the intermetallic compound layer 3b is 3.0 to 7.6 wt %, it is possible to suppress the rate of change in resistance value in a heat resistance test to 1.6% or less.

[0030] Furthermore, since the solder material 4 containing Sn as a main component is joined to at least one of the pair of electrodes 3, even if the Sn in the solder material 4 oxidizes when soldered at high temperatures or when used in a high-temperature environment, it is possible to suppress the formation of oxygen defects in the thermistor body 2 and reduce the rate of change in resistance. Furthermore, the intermetallic compound layer 3b has a high-M concentration region 3c containing more M on the solder material 4 side than on the Pt electrode layer 3a side, and this region with a high M concentration further enhances the oxygen barrier effect.

[0031] The temperature sensor 10A of this embodiment is provided with a resin sealing portion 6 that seals the entire thermistor element 1 with resin, including one end of the pair of lead wires 5, resulting in a resin-sealed temperature sensor with a low rate of change in resistance during a heat resistance test. Furthermore, in the temperature sensors 10B and 10C of this embodiment, the thermistor element 1 is joined with solder to the wiring 7 of the mounting substrate 8, so that changes in resistance during high-temperature environments and heat resistance tests can be suppressed even when the thermistor element 1 is mounted on a substrate.

[0032] In the manufacturing method of the thermistor element of this embodiment, when the molten solder material 4 containing the above M is attached to the Pt electrode layer 3a and then solidified in the soldering step, an intermetallic compound layer formation step is performed to form an intermetallic compound layer 3b containing the above M and Sn in the solder material 4 and Pt in the Pt electrode layer 3a between the solder material 4 and the Pt electrode layer 3a, so the intermetallic compound layer formation step can be performed during the soldering step.

[0033] Furthermore, by joining the solder material 4 at a joining temperature of 280° C. or higher in the solder joining process, it is possible to suppress the rate of change in resistance value in a heat resistance test to 1.6% or less, and by joining the solder material 4 at a joining temperature of 320° C. or higher, it is possible to suppress the rate of change in resistance value in a heat resistance test to 0.8% or less. In particular, when the solder material 4 is joined at a joining temperature of 380° C. or higher, an intermetallic compound layer 3b containing more M on the solder material 4 side than on the Pt electrode layer 3a side is obtained, which further enhances the oxygen barrier effect and reduces the rate of change in resistance value.

[0034] Furthermore, the intermetallic compound layer forming step includes an M sputtering step in which the M is attached to the surface of the Pt electrode layer 3a by a sputtering method to form an M layer 3d, and an M solid solution step in which, when the solder material 4 melted in the solder joining step is attached to the M layer 3d and then solidified, an intermetallic compound layer 3b containing the M in the M layer 3d, the Pt in the Pt electrode layer 3a, and the Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a.As a result, even if the solder material 4 does not contain the M, it is possible to easily obtain an intermetallic compound layer 3b containing a sufficient amount of M by solid-solubilizing the M in the M layer 3d formed by sputtering.

[0035] Example 1: First, a Pt paste was printed on a 0.35 mm-thick thermistor wafer, which served as the thermistor element, and then baked to form a Pt electrode layer. This was then cut into 0.5 mm squares to produce flake thermistor chips. Ni was sputtered onto the Pt electrode layer surface of the flake thermistor chip to form a 20 nm-thick M layer. Lead wires were then joined using a solder material in a solder bath at 230°C. The solder material used was PF04 (Sn / Cu0.7) manufactured by Nihon Handa. Subsequently, Epiform (registered trademark: manufactured by Somar Co., Ltd.) was dipped into the wafer and cured at 120°C for 60 minutes to form an intermetallic compound layer composed of Sn, Pt, and Ni (the M) between the Pt electrode layer and the solder material. A thermistor element and temperature sensor with lead wires connected was produced as Example 1 of the present invention.

[0036] Example 2 A flake thermistor chip was produced in the same manner as in Example 1, and then soldered at 280°C using a Ni-containing solder material (SN100C: manufactured by Nippon Superior, Sn / 0.7Cu / 0.05Ni / Ge) to produce an intermetallic compound layer composed of Sn, Pt, and Ni (the above-mentioned M) at the interface between the Pt electrode layer and the solder material. The remaining steps were the same as in Example 1. This was used as Example 2 of the present invention.

[0037] Example 3 Example 3 of the present invention was prepared in the same manner as in Example 1 except that the soldering temperature in Example 2 was changed to 380°C to vary the Ni proportion in the intermetallic compound layer. Example 4 Example 4 of the present invention was prepared in the same manner as in Example 1 except that an intermetallic compound layer composed of Sn, Pt, and Ag (the above M) was formed by soldering M731 (Senju Metal Co., Ltd., Sn / 3.9Ag / 0.6Cu / 3.0Sb) as the solder material.

[0038] Example 5: Using Sn992 (manufactured by Tomoe Engineering, 99.2Sn / 0.5Cu+Bi+Co) as the solder material, soldering was performed at 400°C to form an intermetallic compound layer composed of Sn, Pt, and Co (M above), and the rest of the process was the same as in Example 1. This was taken as Example 5 of the present invention. Example 6: The soldering temperature of Example 1 was changed to 400°C, and the rest of the process was the same as in Example 1.

[0039] Example 7: Using SACm (manufactured by Tomoe Engineering, 98.5Sn / 0.5Ag / 1.0Cu+Mn) as the solder material, soldering was performed at 400°C to form an intermetallic compound layer composed of Sn, Pt, Ag (the above M) and Mn (the above M), and the rest of the sample was prepared in the same manner as in Example 1, which was designated Example 7 of the present invention. Example 8: The soldering temperature of Example 2 was changed to 320°C, thereby varying the Ni proportion in the intermetallic compound layer, and the rest of the sample was prepared in the same manner as in Example 1, which was designated Example 8 of the present invention. Example 9: The soldering temperature of Example 2 was changed to 350°C, thereby varying the Ni proportion in the intermetallic compound layer, and the rest of the sample was prepared in the same manner as in Example 1, which was designated Example 9 of the present invention.

[0040] Comparative Example 1: A sample prepared in the same manner as in Example 1, except that the step of forming the M layer (Ni) by sputtering in Example 1 was omitted, and no intermetallic compound layer containing M was formed. Comparative Example 2: A sample prepared in the same manner as in Example 1, except that the M layer in Example 1 was set to a thickness of 2 nm and the intermetallic compound layer was set to a thickness of 4 nm, was prepared as Comparative Example 2 of the present invention.

[0041] For these examples and comparative examples of the present invention, the M solid solution ratio (M / (Sn+Pt+M) wt %) and thickness of the intermetallic compound layer composed of Sn, Pt, and the above M are shown in Table 1. Furthermore, for these examples and comparative examples of the present invention, the initial resistance value at 25° C. was measured, and then a heat resistance test was carried out at 150° C. for 1,000 hours, and the resistance value at that time was measured. The rate of change in resistance value between the initial value and that after the heat resistance test was taken as ΔR and is shown in Table 1.

[0042]

[0043] As can be seen from these results, in Comparative Example 1, the intermetallic compound layer containing M was not formed, so there was no oxygen barrier effect, and the resistance change rate after the heat resistance test was large at 6.6%, whereas in each of the Examples of the present invention in which the intermetallic compound layer containing M was formed, the resistance change rate after the heat resistance test was small at 1.6% or less. In Comparative Example 2, although an intermetallic compound layer was formed, its thickness was only 40 nm, so a sufficient oxygen barrier effect was not obtained, and the resistance change rate was large at 5.7%. In each of the Examples of the present invention, the intermetallic compound layer was thick, at 190 nm or more, so as mentioned above, the resistance change rate was significantly reduced to 1.6% or less. In particular, when the solder material was joined at a joining temperature of 320°C or higher, the intermetallic compound layer became even thicker, and the resistance change rate was suppressed to 0.8% or less.

[0044] Next, images of the composition distribution of each element (Ni, Sn, Pt) in the cross section of the thermistor element for Example 2, in which the soldering temperature was 280°C, and Example 3, in which the soldering temperature was 380°C, are shown in Figures 6A and 6B. In Example 2, in which the soldering temperature was 280°C, as shown in Figure 6A, an intermetallic compound layer consisting of Sn, Pt, and Ni is formed between the Sn of the solder material and the Pt of the Pt electrode layer. In Example 3, in which the soldering temperature was 380°C, as shown in Figure 6B, an intermetallic compound layer consisting of Sn, Pt, and Ni is formed between the Sn of the solder material and the Pt of the Pt electrode layer, and a region where Ni, the M, is concentrated (high-concentration M region) is formed on the solder material side within the intermetallic compound layer. As shown in Table 1, as the intermetallic compound layer becomes thicker, the M (Ni)-rich region is formed, and as shown in Table 1, the resistance change rate is significantly reduced to 0.4%. In addition, although it appears that Ni is distributed in the Pt electrode layer in FIGS. 6A and 6B, this is merely a sample of the tail of the detected Pt spectrum, and is not actually a reaction of Ni.

[0045] The technical scope of the present invention is not limited to the above-described embodiment and examples, and various modifications can be made without departing from the spirit of the present invention.

[0046] 1, 1C... thermistor element, 2... thermistor element body, 3... electrode, 3a... Pt electrode layer, 3b... intermetallic compound layer, 3d... M layer, 4... solder material, 5... lead wire, 6... resin sealing portion, 7... wiring, 8... mounting board drawing number change, 10A, 10B, 10C... temperature sensor

Claims

1. A thermistor element comprising: a thermistor body containing an oxide thermistor material having a perovskite crystal structure; and a pair of electrodes formed on the thermistor body, wherein the electrodes comprise a Pt electrode layer formed on the surface of the thermistor body; and an intermetallic compound layer containing Pt, Sn, and M formed on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.

2. A thermistor element according to claim 1, wherein the thickness of said intermetallic compound layer is 190 nm or more, and the concentration of said M in said intermetallic compound layer is 3.0 to 7.6 wt %.

3. A thermistor element according to claim 1, wherein a solder material containing Sn as a main component is joined to at least one of the pair of electrodes.

4. A thermistor element according to claim 3, wherein the intermetallic compound layer has a high-concentration M region containing a larger amount of M on the solder material side than on the Pt electrode layer side.

5. A temperature sensor comprising: the thermistor element according to claim 3; a pair of lead wires, one end of which is connected to the pair of electrodes by the solder material; and a resin sealing portion that seals the entire thermistor element, including the one end of the pair of lead wires, with resin.

6. A temperature sensor comprising: the thermistor element according to claim 3; and a mounting substrate on which said thermistor element is mounted; said mounting substrate having wiring formed on its surface; and said thermistor element being joined onto said wiring with said solder material.

7. A method for manufacturing a thermistor element, comprising: an electrode formation step of forming a pair of electrodes on a thermistor body containing an oxide thermistor material having a perovskite crystal structure; and a solder joining step of joining a solder material mainly composed of Sn to at least one of the pair of electrodes, wherein the electrode formation step comprises: a Pt electrode layer step of forming a Pt electrode layer on the surface of the thermistor body; and an intermetallic compound layer formation step of forming an intermetallic compound layer containing Pt, Sn, and M on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.

8. A method for manufacturing a thermistor element as defined in claim 7, characterized in that in the soldering step, when the molten solder material containing M is attached to the Pt electrode layer and then solidified, an intermetallic compound layer forming step is carried out to form an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer between the solder material and the Pt electrode layer.

9. A method for manufacturing a thermistor element according to claim 8, wherein in the soldering step, the solder material is bonded at a bonding temperature of 280°C or higher.

10. A method for manufacturing a thermistor element as defined in claim 7, wherein the intermetallic compound layer forming step comprises: an M sputtering step in which M is deposited on the surface of the Pt electrode layer by sputtering to form an M layer; and an M solid solution step in which, when the solder material melted in the solder joining step is deposited on the M layer and then solidified, an intermetallic compound layer containing M in the M layer, Pt in the Pt electrode layer, and Sn in the solder material is formed between the solder material and the Pt electrode layer.

Images