strain gauges

Abstract

The strain gauge includes: a flexible substrate; a functional layer formed on one surface of the substrate and made of a metal, an alloy, or a metal compound; and a resistor formed on one surface of the functional layer and made of a material containing at least one of chromium and nickel.

Description

[0001] This application is a divisional application of the following application:

[0002] Invention Name: Strain Gauge International Filing Date: September 26, 2018 International Application Number: PCT / JP2018 / 035706

[0003] National application number: 201880076750.3 Technical Field

[0004] The present invention relates to a strain gauge. Background Art

[0005] A strain gauge is known that is attached to an object to be measured to detect the object's strain. The strain gauge includes a resistor for detecting strain. The resistor is made of, for example, Cr (chromium) or Ni (nickel). The resistor is formed on a substrate made of, for example, an insulating resin (see, for example, Patent Document 1).

[0006] <Prior Art Literature>

[0007] <Patent Document>

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention

[0009] <Problems to be Solved by the Invention>

[0010] However, when a flexible substrate is used, it is difficult to form a stable resistor on the substrate, and there is a problem that the stability of strain characteristics (strain rate, temperature coefficient of strain rate TCS, and temperature coefficient of resistance TCR) is insufficient.

[0011] In view of the above-mentioned problems, an object of the present invention is to improve the stability of strain characteristics in a strain gauge including a resistor formed on a flexible substrate.

[0012] <Methods used to solve the problem>

[0013] The strain gauge includes: a flexible substrate; a functional layer formed on one surface of the substrate and made of a metal, an alloy, or a metal compound; and a resistor formed on one surface of the functional layer and made of a material containing at least one of chromium and nickel.

[0014] <Effects of the Invention>

[0015] According to the disclosed technology, it is possible to improve the stability of strain characteristics in a strain gauge including a resistor formed on a flexible substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a plan view showing the strain gauge according to the first embodiment.

[0017] Figure 2 This is a cross-sectional view showing a strain gauge according to the first embodiment.

[0018] Figure 3A This is a diagram (part 1) showing a manufacturing process of a strain gauge according to the first embodiment.

[0019] Figure 3B This is a diagram (part 2) showing the manufacturing process of the strain gauge according to the first embodiment.

[0020] Figure 4 It is a diagram showing the results of fluorescent X-ray analysis of the functional layer.

[0021] Figure 5 It is a figure which shows the result of X-ray diffraction of a resistor. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and overlapping descriptions may be omitted.

[0023] <First embodiment>

[0024] Figure 1 This is a plan view showing the strain gauge according to the first embodiment. Figure 2 is a cross-sectional view showing a strain gauge according to the first embodiment, showing the strain gauge along Figure 1 The cross section of line AA. Figure 1 and Figure 2 As shown, the strain gauge 1 includes a substrate 10 , a functional layer 20 , a resistor 30 , and a terminal portion 41 .

[0025] It should be noted that in this embodiment, for convenience, in the strain gauge 1, the side of the substrate 10 on which the resistor 30 is provided is the upper side or one side, and the side on which the resistor 30 is not provided is the lower side or the other side. In addition, the surface of the side on which the resistor 30 is provided at each location is one surface or the upper surface, and the surface of the side on which the resistor 30 is not provided is the other surface or the lower surface. However, the strain gauge 1 can also be used in an upside-down state, or can be arranged at any angle. In addition, a plan view refers to a view of an object observed from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object when observed from the normal direction of the upper surface 10a of the substrate 10.

[0026] Substrate 10 is a flexible component that serves as a base layer for forming resistors 30 and other components. The thickness of substrate 10 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, it can be approximately 5 μm to 500 μm. In particular, from the perspectives of strain transfer from the strain-bearing surface bonded to the lower surface of substrate 10 via an adhesive layer or the like, and dimensional stability against the environment, the thickness of substrate 10 is preferably 5 μm to 200 μm. From the perspective of insulation properties, a thickness of 10 μm or greater is more preferred.

[0027] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, or polyolefin resin. The term "film" refers to a flexible member having a thickness of approximately 500 μm or less.

[0028] Here, “formed from an insulating resin film” does not prevent the insulating resin film of the base 10 from containing fillers, impurities, etc. The base 10 may be formed from an insulating resin film containing a filler such as silica or alumina.

[0029] The functional layer 20 is formed on the upper surface 10a of the substrate 10 as the lower layer of the resistor 30. That is, the planar shape of the functional layer 20 is the same as that of the resistor 30. Figure 1 The resistors 30 shown have substantially the same planar shape. The thickness of the functional layer 20 may be, for example, approximately 1 nm to 100 nm.

[0030] In this application, a functional layer refers to a layer that has at least the function of promoting crystal growth of the resistor 30 serving as the upper layer. The functional layer 20 preferably also has the function of preventing oxidation of the resistor 30 due to oxygen or moisture contained in the substrate 10 and improving the adhesion between the substrate 10 and the resistor 30. The functional layer 20 may also have other functions.

[0031] Since the insulating resin film constituting the base material 10 contains oxygen or moisture, particularly when the resistor 30 contains Cr (chromium), Cr forms a self-oxidation film. Therefore, it is effective to provide the functional layer 20 with a function of preventing the resistor 30 from oxidizing.

[0032] Regarding the material of the functional layer 20, there is no particular limitation as long as it is a material that has at least the function of promoting the crystal growth of the resistor 30 as the upper layer. It can be appropriately selected according to the purpose. For example, it can include one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any metal in the group, or a compound of any metal in the group.

[0033] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compound include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0034] The resistor 30 is a thin film formed on the upper surface of the functional layer 20 in a predetermined pattern and is a sensing portion that generates a resistance change when subjected to strain. Figure 1 , for convenience, the resistor 30 is shown in a hatched pattern.

[0035] The resistor 30 can be formed, for example, from a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. Examples of materials containing Cr include Cr mixed-phase films. Examples of materials containing Ni include Cu-Ni (copper nickel). Examples of materials containing both Cr and Ni include Ni-Cr (nickel chromium).

[0036] Here, the Cr mixed-phase film is a film formed by mixing Cr, CrN, Cr2N, etc. The Cr mixed-phase film may contain unavoidable impurities such as chromium oxide. In addition, a portion of the material constituting the functional layer 20 may diffuse into the Cr mixed-phase film. In this case, the material constituting the functional layer 20 and nitrogen may form a compound. For example, when the functional layer 20 is formed of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0037] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, it can be approximately 0.05 μm to 2 μm. In particular, from the perspective of improving the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr), the thickness of the resistor 30 is preferably 0.1 μm or greater. From the perspective of reducing cracking of the film constituting the resistor 30 due to internal stress or warping from the substrate 10, the thickness is more preferably 1 μm or less.

[0038] By forming the resistor 30 on the functional layer 20 , the resistor 30 can be formed using a stable crystal phase, thereby improving the stability of strain characteristics (strain rate, temperature coefficient of strain rate TCS, and temperature coefficient of resistance TCR).

[0039] For example, when the resistor 30 is a Cr mixed phase film, the resistor 30 can be formed with α-Cr (α-chromium) as the main component by providing the functional layer 20. Since α-Cr is a stable crystal phase, the stability of the strain characteristics can be improved.

[0040] Here, the term "main component" refers to a substance that accounts for at least 50% by weight of the total material constituting the resistor. If resistor 30 is a Cr mixed-phase film, it is preferred that resistor 30 contain at least 80% by weight of α-Cr to improve strain characteristics. α-Cr is Cr with a bcc (body-centered cubic) structure.

[0041] Furthermore, by diffusing the metal (e.g., Ti) that constitutes the functional layer 20 into the Cr mixed-phase film, the strain characteristics can be improved. Specifically, the strain rate of the strain gauge 1 can be set to 10 or higher, and the temperature coefficient of strain rate (TCS) and temperature coefficient of resistance (TCR) can be set within the range of -1000 ppm / °C to +1000 ppm / °C.

[0042] The terminal portion 41 extends from both ends of the resistor 30 and is formed into a roughly rectangular shape that is wider than the resistor 30 in a plan view. The terminal portion 41 is a pair of electrodes for outputting the change in the resistance value of the resistor 30 caused by strain to the outside, for example, for connection to a lead wire for external connection. The resistor 30 extends in a zigzag shape from one terminal portion 41 and folds back to connect to the other terminal portion 41. The upper surface of the terminal portion 41 can be covered with a metal that has better weldability than the terminal portion 41. It should be noted that although different symbols are given to the resistor 30 and the terminal portion 41 for convenience, the two can be formed integrally from the same material in the same process.

[0043] A cover layer 60 (insulating resin layer) can be provided on the upper surface 10a of the substrate 10 to cover the resistor 30 and expose the terminal portion 41. The provision of the cover layer 60 can prevent mechanical damage to the resistor 30. Furthermore, the provision of the cover layer 60 can protect the resistor 30 from moisture and other effects. It should be noted that the cover layer 60 can be provided to cover the entire portion except for the terminal portion 41.

[0044] Cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or a composite resin (e.g., silicone resin or polyolefin resin). Cover layer 60 may contain a filler or pigment. The thickness of cover layer 60 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, it can be approximately 2 μm to 30 μm.

[0045] Figure 3A and Figure 3B is a diagram showing a manufacturing process of a strain gauge according to the first embodiment, showing Figure 2 To manufacture the strain gauge 1, first, Figure 3A In the steps shown, a substrate 10 is prepared, and a functional layer 20 is formed on the upper surface 10a of the substrate 10. The materials and thicknesses of the substrate 10 and the functional layer 20 are as described above.

[0046] The functional layer 20 can be formed in a vacuum film using, for example, a conventional sputtering method. In this conventional sputtering method, a raw material capable of forming the functional layer 20 is used as a target, and Ar (argon) gas is introduced into a chamber. By using the conventional sputtering method, the functional layer 20 can be formed while the upper surface 10a of the substrate 10 is etched with Ar gas. This minimizes the amount of functional layer 20 formed, thereby improving adhesion.

[0047] However, this is only one example of a method for forming the functional layer 20, and other methods may be used to form the functional layer 20. For example, before forming the functional layer 20, the upper surface 10a of the substrate 10 may be activated by plasma treatment using Ar or the like to improve adhesion, and then the functional layer 20 may be vacuum-formed by magnetron sputtering.

[0048] Then, in Figure 3B In the process shown, after the resistor 30 and the terminal portion 41 are formed on the entire upper surface of the functional layer 20, the functional layer 20, the resistor 30 and the terminal portion 41 are patterned by photolithography. Figure 1The planar shape shown. The materials and thicknesses of the resistor 30 and the terminal portion 41 are as described above. The resistor 30 and the terminal portion 41 can be integrally formed from the same material. For example, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering using a target made of a material capable of forming the resistor 30 and the terminal portion 41. Instead of magnetron sputtering, the resistor 30 and the terminal portion 41 can be formed by reactive sputtering, vapor deposition, arc ion plating, or pulsed laser deposition.

[0049] There is no particular restriction on the combination of the material of the functional layer 20 and the materials of the resistor body 30 and the terminal portion 41, and they can be appropriately selected according to the purpose. For example, Ti can be used as the functional layer 20, and a Cr mixed phase film with α-Cr (α-chromium) as the main component can be formed as the resistor body 30 and the terminal portion 41.

[0050] In this case, for example, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the resistor 30 and the terminal portion 41 can be formed by reactive sputtering using pure Cr as a target and introducing Ar gas and an appropriate amount of nitrogen gas into a chamber.

[0051] These methods can restrict the growth plane of the Cr mixed-phase film starting with the Ti functional layer 20, thereby forming a Cr mixed-phase film primarily composed of α-Cr, a stable crystal structure. Furthermore, by diffusing the Ti that constitutes the functional layer 20 into the Cr mixed-phase film, strain characteristics are improved. For example, the strain rate of the strain gauge 1 can be increased to 10 or higher, while the temperature coefficient of strain (TCS) and temperature coefficient of resistance (TCR) can be within the range of -1000 ppm / °C to +1000 ppm / °C.

[0052] It should be noted that, when the resistor 30 is a Cr mixed-phase film, the functional layer 20 composed of Ti has all the functions of promoting crystal growth of the resistor 30, preventing oxidation of the resistor 30 due to oxygen or moisture contained in the substrate 10, and improving the adhesion between the substrate 10 and the resistor 30. The same applies when Ta, Si, Al, or Fe is used instead of Ti for the functional layer 20.

[0053] exist Figure 3BAfter the steps shown, a cover layer 60 is formed on the upper surface 10a of the substrate 10, as needed, to cover the resistor 30 and expose the terminal portion 41. This completes the strain gauge 1. The cover layer 60 can be formed, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portion 41, and then heating and curing it. Alternatively, the cover layer 60 can be formed by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portion 41, and then heating and curing it.

[0054] By providing the functional layer 20 below the resistor 30, crystal growth of the resistor 30 can be promoted, allowing the resistor 30 to be formed from a stable crystal phase. Consequently, the stability of the strain characteristics of the strain gauge 1 can be improved. Furthermore, by diffusing the material constituting the functional layer 20 into the resistor 30, the strain characteristics of the strain gauge 1 can be improved.

[0055] [Example 1]

[0056] First, as a preliminary experiment, a Ti film was vacuum-deposited on the upper surface 10a of a 25 μm thick polyimide resin substrate 10 by conventional sputtering as the functional layer 20. Five Ti film-deposited samples were prepared with various target film thicknesses.

[0057] Then, X-ray fluorescence (XRF) analysis was performed on the five samples and the Figure 4 The results shown. Figure 4 The presence of Ti was confirmed from the X-ray peak in , and the X-ray intensity of each sample at the X-ray peak confirmed that the film thickness of the Ti film could be controlled within the range of 1 nm to 100 nm.

[0058] Next, as Example 1, a Ti film with a thickness of 3 nm was vacuum-deposited as the functional layer 20 on the upper surface 10 a of the substrate 10 made of a polyimide resin with a thickness of 25 μm by a conventional sputtering method.

[0059] Next, a Cr mixed phase film is formed on the entire upper surface of the functional layer 20 by magnetron sputtering as the resistor 30 and the terminal portion 41, and then the Cr mixed phase film is formed by photolithography as shown in FIG. Figure 1 As shown, the functional layer 20 , the resistor 30 , and the terminal portion 41 are patterned.

[0060] In addition, as a comparative example 1, the functional layer 20 was not formed on the upper surface 10a of the substrate 10 made of polyimide resin with a thickness of 25 μm, but a Cr mixed phase film was formed as the resistor 30 and the terminal portion 41 by magnetron sputtering, and the Cr mixed phase film was formed by photolithography as shown in FIG. Figure 1 It should be noted that the film forming conditions of the resistor 30 and the terminal portion 41 in the sample of Example 1 and the sample of Comparative Example 1 are exactly the same.

[0061] Next, X-ray diffraction (XRD) evaluation was performed on the samples of Example 1 and Comparative Example 1, and the results were as follows: Figure 5 The results shown. Figure 5 The X-ray diffraction pattern with a 2θ diffraction angle within the range of 36 to 48 degrees shows that the diffraction peak of Example 1 is shifted to the right of the diffraction peak of Comparative Example 1. In addition, the diffraction peak of Example 1 is higher than the diffraction peak of Comparative Example 1.

[0062] The diffraction peak of Example 1 is located near the diffraction line of α-Cr (110), and it is believed that the provision of the functional layer 20 composed of Ti promotes the crystal growth of α-Cr, thereby forming a Cr mixed phase film containing α-Cr as a main component.

[0063] Next, multiple samples of Example 1 and Comparative Example 1 were prepared and their strain characteristics were measured. The results showed that the strain rate of each sample of Example 1 was 14 to 16, while the strain rate of each sample of Comparative Example 1 was less than 10.

[0064] In addition, the strain rate temperature coefficient TCS and the resistance temperature coefficient TCR of each sample in Example 1 are within the range of -1000 ppm / °C to +1000 ppm / °C. In contrast, the strain rate temperature coefficient TCS and the resistance temperature coefficient TCR of each sample in Comparative Example 1 are not within the range of -1000 ppm / °C to +1000 ppm / °C.

[0065] In this way, by providing the functional layer 20 composed of Ti, a strain gauge is produced that promotes the crystal growth of α-Cr, forming a Cr mixed-phase film with α-Cr as the main component. The strain rate is 10 or higher, and the temperature coefficient of strain rate (TCS) and temperature coefficient of resistance (TCR) are within the range of -1000 ppm / °C to +1000 ppm / °C. It is believed that the diffusion of Ti into the Cr mixed-phase film contributes to the improvement of strain characteristics.

[0066] Preferred embodiments have been described in detail above, but the present invention is not limited to the above embodiments and various modifications and substitutions may be made to the above embodiments without departing from the scope of the claims.

[0067] This international application claims priority based on Japanese Patent Application No. 2017-191820, filed on September 29, 2017, and incorporates the entire contents of Japanese Patent Application No. 2017-191820 by reference.

[0068] Explanation of symbols

[0069] 1 strain gauge; 10 substrate; 10a upper surface; 20 functional layer; 30 resistor;

[0070] 41 terminal portion; 60 covering layer.

Claims

1. A strain gauge comprising: The substrate is flexible; a functional layer formed directly on one surface of the substrate from a metal, an alloy, or a metal compound; as well as A resistor body, wherein a Cr mixed phase film formed by mixing Cr, CrN, and Cr2N and diffused with elements other than Cr contained in the functional layer is directly formed on one surface of the functional layer, wherein: The resistor body has α-Cr as the main component. The functional layer limits the growth surface of the Cr mixed phase film and promotes the crystal growth of the Cr mixed phase film. The strain rate is 10 or more.

2. A strain gauge comprising: The substrate is flexible; a functional layer formed directly on one surface of the substrate from a metal, an alloy, or a metal compound; as well as A resistor body, wherein a Cr mixed phase film formed by mixing Cr, CrN, and Cr2N and diffused with elements other than Cr contained in the functional layer is directly formed on one surface of the functional layer, wherein: The resistor body has α-Cr as the main component. The functional layer limits the growth surface of the Cr mixed phase film and promotes the crystal growth of the Cr mixed phase film. The temperature coefficient of resistance is within the range of -1000ppm / ℃ to +1000ppm / ℃.

3. A strain gauge comprising: The substrate is flexible; a functional layer formed directly on one surface of the substrate from a metal, an alloy, or a metal compound; as well as The resistor body is formed by mixing Cr, CrN and Cr2N into a Cr mixed phase film directly on one surface of the functional layer, wherein: The resistor body has α-Cr as the main component. The functional layer limits the growth surface of the Cr mixed phase film and promotes the crystal growth of the Cr mixed phase film.

4. The strain gauge according to any one of claims 1 to 3, wherein: The functional layer comprises one or more metals selected from the group consisting of Cr, Ti, V, Nb, Ta, Ni, Y, Zr, Hf, Si, C, Zn, Cu, Bi, Fe, Mo, W, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, Mn, and Al, an alloy of any metal in the group, or a compound of any metal in the group.

5. The strain gauge according to claim 4, wherein: The functional layer comprises one or more metals selected from the group consisting of Cr, V, Nb, Ta, Ni, Y, Hf, C, Zn, Bi, Fe, Mo, W, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, and Mn, an alloy of any metal in the group, or a compound of any metal in the group.

6. The strain gauge according to claim 4, wherein: The functional layer includes any one of TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

7. The strain gauge according to claim 6, wherein: The functional layer includes a metal compound selected from the group consisting of TiN, TaN, Si3N4, and Ta2O5.

8. The strain gauge according to claim 4, wherein: The functional layer includes an alloy selected from the group consisting of FeCr, TiAl, FeNi, NiCr, and CrCu.

9. The strain gauge according to any one of claims 1 to 3, wherein: The functional layer has a function of preventing the resistor from being oxidized by oxygen and moisture contained in the base material and / or a function of improving adhesion between the base material and the resistor.

10. The strain gauge according to any one of claims 1 to 3, wherein: The functional layer is patterned into the same planar shape as the resistor.

11. The strain gauge according to any one of claims 1 to 3, wherein: The thickness of the functional layer is 1 nm to 100 nm.

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