Thin film thermocouple element and method for manufacturing thin film thermocouple element

Abstract

To provide a small thin film thermocouple element with small difference of temperature characteristics, and a method for manufacturing a thin film thermocouple element.SOLUTION: A thermocouple element comprises: a substrate 10; and a thermocouple that is formed by a first conductive thin film 11 made of Cu and a second conductive thin film 12 made of a Cu-Ni alloy on the substrate, has a temperature measurement contact 18 on one end side, and comprises external connection points 20, 21 for each thin film on the other end side. In a range of -40°C to 200°C, a characteristic value, which is a value obtained by dividing an electromotive force by an electromotive force of a T-type thermocouple according to JIS C 1602-1995, is 0.95 or more and 1.05 or less. A composition of the Cu-Ni alloy shows Cu:Ni=59.3 at%:40.7 at% to 54.6 at%:45.4 at%.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a thin film thermocouple element and a method for manufacturing a thin film thermocouple element. [Background technology]

[0002] An element made of a combination of two types of metal for the purpose of temperature measurement is called a thermocouple, and is a technology that has long been used as a temperature measurement element that utilizes the Seebeck effect. Conventionally used general-purpose bulk thermocouple elements are thermocouples that use metal wire with a wire diameter of approximately 0.50 to 3.20 mm, and an example is the K thermocouple that conforms to the Japanese Industrial Standards (JIS) standard (JIS C 1602-1995).

[0003] Thin-film thermocouple elements are made by forming a thin film of thermocouple material on a substrate such as a polymer film, and are used as temperature sensors for measuring the temperature in small, narrow areas. Thin-film thermocouple elements have the advantage of being thinner and more flexible than bulk thermocouple elements, but the thermoelectromotive force generated in thin-film thermocouple elements is several tens of percent lower than that generated in general bulk thermocouple elements.

[0004] It is difficult to make the temperature-thermoelectric power characteristics of a thin-film thermocouple element match those of a bulk thermocouple element. Although it is possible to make the temperature-thermoelectric power characteristics of a thin-film thermocouple element as close as possible to those of a bulk thermocouple element, this is not realistic from the viewpoint of productivity.

[0005] Patent Document 1 describes a temperature calibration device connected to a thin-film thermocouple element made of dissimilar metals, connected to each other at a temperature measurement contact on one end, and having at least one pair of thin films with a pair of external contacts on the other end. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-190884 Summary of the Invention [Problem to be solved by the invention]

[0007] To make thin-film thermocouple elements replaceable, it is essential that there is little variation in the temperature characteristics between each element, but with conventional technology, the temperature characteristics between each element exceeded the allowable range, and calibration had to be performed using a temperature measuring device every time the thin-film thermocouple element was replaced.In particular, in the case of K-type thin-film thermocouples made of a combination of chromel and alumel, a problem was found in that there was large variation in the temperature characteristics between each element.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a thin-film thermocouple element with small differences in temperature characteristics and a method for manufacturing the thin-film thermocouple element. [Means for solving the problem]

[0009] As a result of extensive research, the inventors have found that by adopting a combination of Cu and a Cu-Ni alloy, which are the materials used in T-type thermocouples, it is possible to reduce the variation in temperature characteristics between elements compared to K-type thin-film thermocouples and to achieve thermoelectric power characteristics equivalent to the temperature-thermoelectric power characteristics of bulk thermocouple elements.

[0010] The above-mentioned problems are solved by a thin-film thermocouple element of the present invention, which comprises a substrate and a thermocouple formed on the substrate from a first conductive thin film made of Cu and a second conductive thin film made of a Cu-Ni alloy, with a temperature measurement junction at one end and an external connection point for each thin film at the other end, wherein the thin-film thermocouple element has a characteristic value of 0.95 or more and 1.05 or less, which is a value obtained by dividing the electromotive force by the electromotive force of a T-type thermocouple according to JIS C 1602-1995, at temperatures from -40°C to 200°C, and the composition of the Cu-Ni alloy is Cu:Ni=59.3 at %:40.7 at % to 54.6 at %:45.4 at %. In this case, it is preferable that the composition of the Cu-Ni alloy is Cu:Ni=54.6 at %:45.4 at %. In this case, it is preferable that the characteristic value at 0°C to 200°C is 0.95 or more and 1.05 or less.

[0011] The above-mentioned object can be achieved by the method for manufacturing a thin-film thermocouple element of the present invention, which includes the steps of: preparing a substrate; and depositing on the substrate a first conductive thin film made of Cu and a second conductive thin film made of a Cu-Ni alloy to form a thermocouple having a temperature measurement junction at one end and an external connection point for each thin film at the other end; and in the step of forming the thermocouple, depositing the second conductive thin film so that the composition of the Cu-Ni alloy is Cu:Ni=59.3 at%:40.7 at% to 54.6 at%:45.4 at%. In this case, it is preferable to form the second conductive film so that the composition of the Cu—Ni alloy is Cu:Ni=59.3 at %:40.7 at %. [Effects of the Invention]

[0012] According to the thin-film thermocouple element and the method for manufacturing a thin-film thermocouple element of the present invention, the difference in temperature characteristics between thin-film thermocouple elements is reduced, and the characteristic value becomes approximately 1, eliminating the need for complicated two-point measurement and temperature calibration, and making it possible to measure temperature simply by connecting to a commercially available temperature measuring instrument. [Brief explanation of the drawings]

[0013] [Figure 1A] 1 is a schematic diagram illustrating a thin-film thermocouple element according to an embodiment of the present invention. [Figure 1B] 1B is a cross-sectional view taken along the line AA in FIG. 1A. [Figure 2] FIG. 2 is a schematic diagram of a temperature measuring element according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram showing a state in which a temperature measuring element is connected to a temperature display. [Figure 4] 1 is a list of film formation conditions. [Figure 5] 1 is a graph showing the resistivity of each sample. [Figure 6] 10 is a graph comparing measured temperatures. [Figure 7]1 is a graph showing characteristic values ​​(0 to 200° C.). [Figure 8] 1 is a graph enlarging the characteristic value (0 to 200° C.) in the vicinity of 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] A thin-film thermocouple element according to an embodiment (present embodiment) of the present invention will be described with reference to the drawings. Note that the materials, arrangement, configuration, etc. described below do not limit the present invention and can be modified in various ways within the scope of the present invention.

[0015] <Thin film thermocouple element 1> Figure 1 is a schematic diagram of a thin-film thermocouple element 1 according to an embodiment of the present invention. In Figure 1, a first conductive thin film 11 and a second conductive thin film 12 are made of different materials and are joined at a temperature measuring junction 18 of the thin-film thermocouple element 1. The temperature measuring junction 18 of the thin-film thermocouple element 1 is joined so that the first conductive thin film 11 and the second conductive thin film 12 overlap.

[0016] The thin-film thermocouple element 1 is a replaceable element, and is configured to be detachable from the connector 2. The temperature measuring element H is configured by combining the thin-film thermocouple element 1 with the connector 2 (Fig. 2). The connector 2 to be combined with the thin-film thermocouple element 1 is not particularly limited in terms of the method of attaching the element, as long as it allows the thin-film thermocouple element 1 to be detachably attached.

[0017] 3, the first conductive thin film 11 and the second conductive thin film 12 are joined to the same metal wire as the first conductive thin film 11 and the second conductive thin film 12 at external connection points 20 and 21 located at the connection end 10a opposite the temperature measuring junction 18. The thin-film thermocouple element 1 has the first conductive thin film 11 and the second conductive thin film 12 on a substrate 10, with the temperature measuring junction 18 for measuring the temperature of the object at one end and the external connection points 20 and 21 of each thin-film pattern at the other end, which are open ends. A first compensation lead wire 13 and a second compensation lead wire 14 are connected to the external connection points 20 and 21 of the thin-film thermocouple element 1.

[0018] In the temperature measuring element H, it is preferable that the materials of the first conductive thin film 11 and the second conductive thin film 12 of the thin-film thermocouple element 1 are the same as the materials of the first compensation lead wire 13 and the second compensation lead wire 14. The first compensation lead wire 13 and the second compensation lead wire 14 are connected to a calculation unit 17a equipped with a CPU (calculation circuit) and a calculation result display unit 17b connected by a connection line 17c.

[0019] Glass, film, metal, etc. can be used as the substrate 10 on which the thin-film thermocouple element 1 is formed. However, if the substrate 10 is made of a conductive material such as metal, it is necessary to form an insulating film such as SiO2 or Al2O3 on the metal surface beforehand to form the thin-film thermocouple. Therefore, it is preferable to use a film. Unlike conductive substrates such as metals, glass and film do not require pretreatment, making operation less complicated and suitable. Furthermore, film's flexibility can increase the strength of the temperature-sensing element. It is even more preferable to use a polyimide film. Polyimide film is a suitable material for the substrate of a thin-film thermocouple because it can be bent, is difficult to break even when the substrate is several tens of microns thick, and is easy to handle, and is relatively stable even at temperatures exceeding 200°C.

[0020] The thickness of the substrate 10 is preferably 1 μm or more and 150 μm or less, more preferably 1 μm or more and 50 μm or less, and particularly preferably 1 μm or more and 18 μm or less.

[0021] The combination of different metals constituting the first conductive thin film 11 and the second conductive thin film 12 of the thin-film thermocouple element 1 is Cu and a Cu-Ni alloy. Specifically, the first conductive thin film 11 is Cu, and the second conductive thin film 12 is a Cu-Ni alloy. Here, the composition of the Cu-Ni alloy forming the second conductive thin film 12 is preferably Cu:Ni=59.3 at %:40.7 at % to 54.6 at %:45.4 at %, and particularly preferably Cu:Ni=59.3 at %:40.7 at %.

[0022] The thickness of the first conductive thin film 11 and the second conductive thin film 12 is preferably 10 nm or more and 1 μm or less, more preferably 100 nm or more and 700 nm or less, and even more preferably 150 nm or more and 550 nm or less.

[0023] The first conductive thin film 11 and the second conductive thin film 12 can be formed by vacuum deposition methods such as sputtering, electron beam evaporation, and thermal evaporation, or by coating. Preferably, a vacuum deposition method is used, which can form a thinner and more uniform thin film. More preferably, a sputtering method is used, which can form a uniform film with little deviation in atomic composition from the deposition material.

[0024] The thin-film thermocouple element 1 is preferably covered with a protective film P. This is because the protective film P not only improves the environmental resistance of the thin-film thermocouple element 1, but also has the effect of preventing cracks, which may occur when the thin-film thermocouple element 1 is deformed by an external force. Applicable protective films P include insulating films formed by vapor deposition, sputtering, dipping, or the like using SiO2, Al2O3, or the like, and polyimide films formed by screen printing. Preferably, a polyimide film is used, which has high heat resistance, chemical resistance, and adhesiveness.

[0025] It is preferable that a reinforcing member G is provided on the connection end 10a of the substrate 10 opposite the external connection points 20 and 21. The material of the reinforcing member G is not particularly limited, and epoxy glass, for example, can be used. The reinforcing member G improves the strength of the thin-film thermocouple element 1 and improves the connectability with the connector 2.

[0026] In the thin-film thermocouple element 1 of this embodiment, the composition of the Cu-Ni alloy forming the second conductive thin film 12 is Cu:Ni=59.3 at %:40.7 at % to 54.6 at %:45.4 at %, and therefore, at temperatures from -40°C to 200°C, the characteristic value obtained by dividing the electromotive force by the electromotive force of a T-type thermocouple according to JIS C 1602-1995 is 0.95 or more and 1.05 or less.

[0027] Furthermore, the thin-film thermocouple element 1 of this embodiment has a simple composition of Cu and Cu-Ni alloy, so that the characteristic value in the high temperature range of 0°C to 200°C is 0.95 or more and 1.05 or less, and is less affected by heat.

[0028] <Method for manufacturing thin-film thermocouple elements> The method for manufacturing a thin-film thermocouple element according to this embodiment includes the steps of: preparing a substrate 10 (step S1); and forming a thermocouple (step S2) on the substrate 10, a first conductive thin film 11 made of Cu and a second conductive thin film 12 made of a Cu-Ni alloy, to form a thermocouple having a temperature measuring junction 18 at one end and external connection points 20, 21 for each thin film at the other end. In the step of forming the thermocouple, the second conductive thin film 12 is formed so that the composition of the Cu-Ni alloy is preferably Cu:Ni=59.3 at%:40.7 at% to 54.6 at%:45.4 at%, and particularly preferably Cu:Ni=59.3 at%:40.7 at%.

[0029] The step of forming the thermocouple (step S2) is preferably carried out by sputtering, which minimizes deviation in atomic composition from the deposition material and allows for uniform film formation. In this case, it is preferable to use a polyimide film as the substrate. The film is formed by heating at a temperature higher than 100°C, preferably 120°C or higher, more preferably 130°C or higher, even more preferably 140°C or higher, and particularly preferably 150°C or higher. The upper limit of the heating temperature for the substrate depends on the substrate material and the quality of the Cu thin film or Cu-Ni alloy thin film to be formed, but is preferably 250°C or lower, preferably 230°C or lower, more preferably 210°C or lower, and even more preferably 200°C or lower.

[0030] According to the manufacturing method of the thin-film thermocouple element of this embodiment, the obtained thin-film thermocouple element has a characteristic value of 0.95 or more and 1.05 or less, which is the value obtained by dividing the electromotive force by the electromotive force of a T-type thermocouple according to JIS C 1602-1995, at temperatures from -40°C to 200°C, and the characteristic value is 0.95 or more and 1.05 or less at temperatures from 0°C to 200°C. [Example]

[0031] Hereinafter, specific examples of the thin-film thermocouple element and the method for manufacturing the thin-film thermocouple element of the present invention will be described, but the present invention is not limited thereto.

[0032] <A. Fabrication of Thin-Film Thermocouple Element> Under the following conditions, a conductive thin film was laminated on a polyimide substrate as a substrate, using a combination of Cu and Cu-Ni alloy (Fig. 4). Sputtering apparatus: carousel-type batch sputtering apparatus Target: 5 inches × 25 inches, chromel-alumel Sputtering method: DC magnetron sputtering Exhaust device: turbo molecular pump Reached vacuum degree: 2 - 5×10 -4 Pa Substrate temperature: 25°C (room temperature) or 150°C (set value) Sputtering power: 7.5 kW Film thickness of conductive thin film: 300 - 500 ± 10 nm Ar flow rate: 250 sccm Substrate used: polyimide (PI) film substrate (50 μm thick)

[0033] <B. Measurement of Temperature Characteristics> Using chromel-alumel as the material constituting the conductive thin film of the thin-film thermocouple element, with the substrate temperature being unheated (room temperature 25°C) or heated (150°C), a thin-film thermocouple was formed on a polyimide film as a substrate by sputtering based on the above conditions. Further, a polyimide film different from the substrate was adhered to the formed thin-film thermocouple and used as a protective film.

[0034] Fig. 5 shows a graph comparing the resistivity values of each sample. It can be seen that the resistivity of Cu and Cu-Ni alloy is smaller than that of the K-type thermocouple (chromel or alumel).

[0035] Figure 6 shows a graph comparing the temperature characteristic values ​​of a thin-film thermocouple element with a Cu-Ni alloy containing 40.7 at% Ni, with a normal K-type thermocouple element as the reference. It was found that the temperature indicated by the thin-film thermocouple element was approximately the same as that of the K-type thermocouple element (within a range of ±1°C on the vertical axis of Figure 6) without any correction.

[0036] Figures 7 and 8 show plots of the characteristic values, which are the electromotive force divided by the electromotive force of a T-type thermocouple according to JIS C 1602-1995, for each element at temperatures between 0°C and 200°C. The characteristic values ​​also changed when the composition ratio of the Cu-Ni alloy was changed. The value was highest for an element with a Ni content of 40.7 at%. The characteristic values ​​were very stable regardless of whether heating was performed. Furthermore, no significant changes in the characteristic values ​​were observed depending on whether heating was performed. It was found that the characteristic values ​​were between 0.95 and 1.05 when the composition of the Cu-Ni alloy was Cu:Ni = 59.3 at%:40.7 at% to 54.6 at%:45.4 at%.

[0037] <C.まとめ> It was found that the combination of Cu and Cu-Ni alloy has several advantages over K-type thin-film thermocouples, which are a combination of chromel and alumel. First, the characteristic values ​​are larger and closer to 1 compared to K-type materials. Also, there is less variation between elements (compared to K-type thin-film thermocouples). Furthermore, there is less influence from heating during film formation (compared to K-type thin-film thermocouples).

[0038] It is necessary to consider the thin film composition to match the characteristics of the bulk material (wire material), but with a K-type thermocouple, both wires are made of an alloy (three or more components), making it difficult to consider the thin film composition.On the other hand, the thin film thermocouple of this embodiment is made of Cu and a Cu-Ni alloy, so it is possible to consider the composition by considering the alloy (two components) composition of one pole.

[0039] Conventional K-type thin-film thermocouples do not have a characteristic value of 1; even with optimized processing conditions, the characteristic value is only around 0.8. This requires two-point measurement for correction during temperature measurement, and targeting the characteristic value is cumbersome. Furthermore, conventional K-type thin-film thermocouples have variations between sheets, which requires suppressing variations within a single film sheet by heating the film, making process management cumbersome and limiting the sensor layout. Furthermore, the large difference in characteristic values ​​between heated and unheated thermocouples makes process management strict. Furthermore, the high resistance of the sensor causes noise during measurement, making it impossible to extend the length. Regarding flexibility, while thicker films could be considered to eliminate noise, this poses challenges, such as impaired flexibility and increased risk of pattern cracking.

[0040] In the thin-film thermocouple element of this embodiment, by changing to a T-type thermocouple material and appropriately selecting the composition of the copper-nickel alloy, it was possible to create a thin-film thermocouple with a characteristic value of 1. By changing to a T-type with a material configuration with a low resistance value, it became more advantageous in terms of flexibility.

[0041] As described above, the thin-film thermocouple element of this embodiment, with a characteristic value of 1, eliminates the need for complicated two-point measurements and corrections, and can be used simply by connecting it to a commercially available measuring instrument. Furthermore, the low sensor resistance reduces noise during measurements and allows for longer lengths. Furthermore, the soft material improves flex resistance. Furthermore, while the creation of a K-type thin-film thermocouple requires management of processes such as thermal deposition, pre-deposition treatment (plasma ashing), and the time from dehydration baking to loading into the equipment, these processes can be eliminated or alleviated. Furthermore, since heating is not required, temperature management can be relaxed. Because it is made of Cu and a Cu-Ni alloy, the material structure is simple and the alloy composition is not complicated, making it easy to control conditions such as deposition, and the effects of heat are minimal. [Industrial Applicability]

[0042] The thin-film thermocouple element of the present invention has small differences in temperature characteristics between thin-film thermocouple elements and a characteristic value of approximately 1, eliminating the need for complicated two-point measurements and temperature calibration, making it possible to measure temperature simply by connecting it to a commercially available temperature measuring device. While the application fields for temperature measurement using thin-film thermocouple elements are not particularly limited, they can be used to suitably measure temperatures at extremely small locations, such as fuel cells, heating rollers, heat presses, heat generation temperatures of electronic circuit components, chemical reaction temperatures, and instantaneous heating temperatures. Furthermore, they enable relatively low-temperature temperature measurement (below 100°C), making them suitable for applications in healthcare, food processing, and biotechnology. [Explanation of symbols]

[0043] H Temperature measuring element 1 Thin-film thermocouple element P protective film G Reinforcement member 2 connectors 10 Substrate 10a Connection end 11 First conductive thin film 12 Second conductive thin film 13 1st compensation conductor 14 2nd compensation conductor 17 Temperature display 17a Arithmetic unit 17b Operation result display section 17c connecting wire 18 Temperature measuring junction 20 External Connection Points 21 External connection points

Claims

1. A substrate; a thermocouple formed on the substrate by a first conductive thin film made of Cu and a second conductive thin film made of a Cu-Ni alloy, the thermocouple having a temperature measuring junction at one end and an external connection point of each thin film at the other end; a characteristic value, which is the value obtained by dividing the electromotive force by the electromotive force of a T-type thermocouple in accordance with JIS C 1602-1995, is 0.95 or more and 1.05 or less at temperatures between -40°C and 200°C; The thin-film thermocouple element has a composition of the Cu—Ni alloy of Cu:Ni=59.3 at %:40.7 at % to 54.6 at %:45.4 at %.

2. 2. The thin film thermocouple element according to claim 1, wherein the composition of said Cu--Ni alloy is Cu:Ni=59.3 at %:40.7 at %.

3. 2. The thin film thermocouple element according to claim 1, wherein the characteristic value at 0° C. to 200° C. is 0.95 or more and 1.05 or less.

4. providing a substrate; forming a first conductive thin film made of Cu and a second conductive thin film made of a Cu-Ni alloy on the substrate to form a thermocouple having a temperature measuring contact on one end and an external connection point of each thin film on the other end; A method for manufacturing a thin-film thermocouple element, wherein in the step of forming the thermocouple, the second conductive film is formed so that the composition of the Cu-Ni alloy is Cu:Ni = 59.3 at%:40.7 at% to 54.6 at%:45.4 at%.

5. 5. The method for manufacturing a thin-film thermocouple element according to claim 4, wherein the second conductive film is formed so that the composition of the Cu--Ni alloy is Cu:Ni=59.3 at %:40.7 at %.

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