Strain gauge and strain sensor

Abstract

A strain gauge (10) according to one embodiment of the present invention is provided with: a first laminate (LB1); the first laminate (LB1) has a Cr-based strain resistance layer (13) that is provided on the resin-based substrate (30) and has a body-centered cubic structure, a first layer (11) that is provided between the resin-based substrate (30) and the strain resistance layer (13), and a second layer (12) that is provided between the strain resistance layer (13) and the first layer (11) and serves as a base layer when the strain resistance layer (13) is formed. The first layer (11) suppresses the diffusion of oxygen from the resin-based substrate (30) to the strain resistance layer (13), and the second layer (12) suppresses the crystal growth of the strain resistance layer (13) caused by the crystal structure of the first layer (11), thereby maintaining the strain coefficient and having high adhesion to the resin-based substrate.

Description

Technical Field

[0001] The invention relates to a strain gauge and a strain sensor. Background Art

[0002] Patent document 1 discloses the following strain gauge, which comprises: a flexible resin substrate, a functional layer formed directly from a metal, an alloy, or a metal compound on one surface of the substrate, and a resistor formed directly from a film containing Cr, CrN, and Cr2N on one surface of the functional layer, wherein the resistor contains α-Cr as a main component, and the functional layer promotes the crystal growth of the α-Cr and has the function of forming a film containing α-Cr as a main component.

[0003] In the invention disclosed in Patent Document 1, the functional layer is provided for stabilizing the strain characteristics of the strain gauge and has the function of promoting the crystal growth of the resistor. It is also recorded that the functional layer can also have the function of inhibiting the oxidation of the resistor caused by oxygen and moisture and the function of improving the adhesion between the substrate and the resistor.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6793103 Summary of the invention

[0007] Technical problem to be solved by the invention

[0008] The "functional layer" disclosed in Patent Document 1 is a preferred method from the perspective of improving the adhesion of the strain resistor layer to a resin-based substrate composed of a polyimide resin or the like. However, according to the research of the present inventors, it is clear that if a strain resistor layer is formed with the functional layer as a base, the strain coefficient of the strain resistor layer is reduced (described in detail later).

[0009] The present invention is based on the above situation and aims to provide a strain gauge capable of maintaining a gauge factor and improving adhesion to a resin substrate. Another object is to provide a strain sensor capable of measuring strain with high accuracy even for a small strain generating body using the strain gauge.

[0010] Means for solving technical problems

[0011] A strain gauge of one embodiment of the present invention for solving the above-mentioned technical problems comprises a first stacked body, the first stacked body comprising: a strain resistor layer, which is provided on a resin-based substrate and is Cr-based and has a body-centered cubic structure; a first layer, which is provided between the resin-based substrate and the strain resistor layer; and a second layer, which is provided between the strain resistor layer and the first layer and serves as a base layer when the strain resistor layer is formed; the strain gauge is characterized in that the first layer inhibits the diffusion of oxygen from the resin-based substrate to the strain resistor layer, and the second layer hinders the crystal growth of the strain resistor layer caused by the crystal structure of the first layer.

[0012] The present inventors have studied the reason why the “functional layer” disclosed in Patent Document 1 reduces the gauge coefficient of the strain resistor layer, and have obtained the following findings.

[0013] The diffusion of oxygen from the resin substrate to the strain resistor layer side is the cause of the decrease in adhesion. The "functional layer" disclosed in Patent Document 1 is set as a layer with a higher atomic configuration density than the strain resistor layer, thereby promoting the crystal growth of the body-centered cubic structure of the strain resistor layer and functioning as an oxygen barrier layer.

[0014] However, as disclosed in Patent Document 1, if a strain resistor layer is directly formed on a layer with a high atomic configuration density, the crystallinity of the strain resistor layer becomes higher. If the crystallinity of the strain resistor layer becomes higher, the responsiveness of the resistance change to the strain decreases, and the gauge coefficient decreases. In this way, if the strain resistor layer is formed using the "functional layer" as a base, the crystal growth of the strain resistor layer is promoted due to the crystal structure of the "functional layer".

[0015] Based on the above insights, further research was conducted, in which a layer (first layer) having an oxygen barrier function was provided between the resin-based substrate and the strain resistor layer. However, the first layer was not used as a base layer when forming the strain resistor layer. Instead, a layer (second layer) that hindered the crystal growth of the body-centered cubic structure in the strain resistor layer was used as a base layer, thereby obtaining new insights into suppressing the reduction in the gauge coefficient of the strain gauge.

[0016] In the above-described strain gauge, from the viewpoint of ensuring a gauge coefficient, the crystallinity of the strain resistor layer in the first stacked body is preferably lower than the crystallinity of the strain resistor layer in a case where the first layer is formed as a base layer.

[0017] In the above-mentioned strain gauge, the film thickness of the second layer is preferably 1.5 nm to 10 nm in some cases.

[0018] In the above-mentioned strain gauge, the second layer may be formed of a Cr-based material. In this case, the second layer may contain an element other than Cr, that is, a second element.

[0019] When the second layer contains the second element, the second element may contain a typical element or one or more elements selected from the group consisting of elements of Group 12 to Group 15. The Pauling electronegativity of the second element is preferably higher than that of Cr in some cases and is preferably 2.6 or less in some cases.

[0020] In the above-mentioned strain gauge, it is preferable that the second layer can be wet-etched using an etching solution used for wet-etching the strain resistor layer.

[0021] In the strain gauge described above, the first layer may include a first element having a Pauling electronegativity greater than that of Cr. In this case, the first layer may preferably be composed of a metal or an alloy based on the first element.

[0022] In the above-mentioned strain gauge, the first layer preferably has a composition forming a face-centred cubic lattice structure or a hexagonal closest packing structure.

[0023] In the above-mentioned strain gauge, it is preferable that the first layer can be wet-etched using an etching solution used for wet-etching the strain resistor layer.

[0024] As another aspect, the present invention provides a strain sensor including the above-mentioned strain gauge and an electrode for supplying electricity to the strain gauge.

[0025] Effects of the Invention

[0026] According to the present invention, a strain gauge capable of maintaining a gauge coefficient and improving adhesion to a resin-based substrate is provided, and further a strain sensor capable of measuring strain with high accuracy even with a small strain generating body is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a diagram showing an example of a strain sensor according to an embodiment of the present invention.

[0028] Figure 2 It means along Figure 1 Conceptual diagram of the cross section along the A-A' line.

[0029] Figure 3 This is a cross-sectional view for explaining the structure of a strain gauge according to one embodiment of the present invention.

[0030] Figure 4 It is a diagram showing an X-ray diffraction spectrum of the strain gauge of the example.

[0031] Figure 5 This is a graph showing the dependence of the gauge coefficient Gf of the strain gauge of the example on the thickness of the second layer. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same reference numerals are given to the same components, and the description of the components that have already been described will be appropriately omitted.

[0033] Figure 1 FIG. 1 is a diagram showing an example of a strain sensor according to an embodiment of the present invention. Figure 1 As shown, the strain sensor 100 of the present embodiment includes a strain gauge 10 having a meandering pattern and an electrode 20 for energizing the strain gauge 10. The strain gauge 10 and the electrode 20 are both formed on a resin-based substrate 30. Non-limiting examples of the constituent material of the electrode 20 include Cu, Au, and alloys containing Cu and Au. The electrode 20 includes a first electrode 201 connected to one end of the strain gauge 10 and a second electrode 202 connected to the other end. In order to improve the solder bonding strength, a plating layer 21 is provided on each of the first electrode 201 and the second electrode 202. The resin-based substrate 30 is not limited to a constituent material as long as it has a predetermined flexibility. As a specific example of the constituent material, a polyimide resin can be cited.

[0034] Figure 2 It means along Figure 1 Conceptual diagram of the cross section along the A-A' line. Figure 3 2 is a cross-sectional view illustrating the structure of a strain gauge according to an embodiment of the present invention. Figure 2 As shown, the strain gauge 10 includes a strain resistor layer 13 , and a first laminate LB1 including a first layer 11 provided between a resin-based substrate 30 and the strain resistor layer, and a second layer 12 provided between the strain resistor layer 13 and the first layer 11 . Figure 3 1 is a diagram for explaining the structure of the first stacked body LB1 in detail, which is equivalent to Figure 2 A partial enlarged view of .

[0035] The strain resistor layer 13 of the first stacked body LB1 is composed of a Cr-based metallic material having a body-centered cubic structure, and as a specific example, a Cr-Ta alloy that is Cr-based and contains several atomic % of Ta. The strain resistor layer 13 may also be composed of a material that contains Cr as a main component and contains non-metallic elements, specifically, typical elements (such as N).

[0036] The first layer 11 of the first stacked body LB1 is composed of a metallic material having a function of inhibiting oxygen diffusion from the resin-based substrate 30 to the strain resistor layer 13. The first layer functions as an oxygen barrier layer, thereby preventing the adhesion between the strain resistor layer 13 and the resin-based substrate 30 from being reduced. From the viewpoint of serving as the oxygen barrier layer, it is preferred that the first layer 11 has a higher atomic arrangement density than the strain resistor layer 13, and specifically, preferably has a composition that forms a face-centered cubic (fcc) structure or a hexagonal close-packed (hcp) structure.

[0037] In addition, the first layer 11 may contain a first element having a Pauling electronegativity greater than Cr (1.66) from the viewpoint of appropriately functioning as an oxygen barrier layer. In this case, the first layer may preferably be composed of a metal or alloy based on the first element.

[0038] Specific examples of materials constituting such a first layer 11 include Ni (electronegativity: 1.91) and Ni-Cr alloy and other Ni-based alloys (fcc structure), Cu (electronegativity: 1.90) and Cu-Ni alloys (fcc structure), Co (electronegativity: 1.88) and Co-Cr alloy and other Co-based alloys (hcp structure), etc.

[0039] In addition, the first layer 11 can be wet-etched using an etching solution (ammonium cerium nitrate is a specific example) used for wet-etching the strain resistor layer 13 , which may be advantageous in production.

[0040] The second layer 12 possessed by the first stack LB1 becomes the base layer when the strain resistor layer 13 is formed, and has the function of hindering the crystal growth of the strain resistor layer 13. If the strain resistor layer 13 is directly formed on the first layer 11 having the function of an oxygen barrier layer, the configuration density of the atoms of the first layer 11 is high, so the crystallinity of the strain resistor layer 13 becomes higher due to this influence. For example, in the case of a Cr-based strain resistor layer 13, the (110) orientation of the body-centered cubic structure of the strain resistor layer 13 becomes too strong. If the crystallinity of the strain resistor layer 13 becomes higher, the responsiveness of the resistance change relative to the strain of the strain resistor layer 13 decreases, and the strain coefficient Gf decreases. The reduction in the strain coefficient Gf is considered to be because the higher the configuration density of atoms, the more difficult it is to exert the magnetovolume effect (the phenomenon in which the magnetic properties and their volume change while influencing each other), which is the reason why the Cr-based material has a relatively large strain coefficient Gf.

[0041] Therefore, a layer (first layer 11) having an oxygen barrier function is provided between the resin-based substrate 30 and the strain resistor layer 13, but the first layer 11 is not used as a base layer when forming the strain resistor layer 13, but a layer (second layer 12) that inhibits excessive crystal growth of the body-centered cubic structure in the strain resistor layer 13 is used as a base layer, thereby appropriately adjusting the crystallinity of the strain resistor layer 13 and suppressing the reduction of the gauge coefficient Gf of the strain gauge 10. That is, the second layer 12 is a layer that inhibits the crystal growth of the strain resistor layer caused by the crystal structure of the first layer.

[0042] From the viewpoint of stably suppressing a decrease in the gauge coefficient Gf, the film thickness of the second layer 12 is preferably 1.5 nm to 10 nm in some cases.

[0043] The second layer 12 may also be composed of a Cr-based material, in which case the second layer 12 may also include an element other than Cr, i.e., a second element. In the case where the second layer 12 includes a second element, the second element may include a typical element or one or more elements selected from a group consisting of elements from Group 12 to Group 15. The Pauling electronegativity of the second element is sometimes preferably higher than Cr (1.66). Due to manufacturing reasons, etc., the Pauling electronegativity of the second element is sometimes preferably less than 2.6. In addition, due to the same manufacturing reasons, the second layer 12 is preferably capable of being wet-etched using an etching solution for wet-etching the strain resistor layer 13.

[0044] A specific example of a material constituting such a second layer 12 is CrB containing B (electronegativity: 2.04) as a second element. From the viewpoint of maintaining the properties of the metal, the B content is preferably 40 atomic % or less, and more preferably 30 atomic % or less.

[0045] The embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, the gist of each element disclosed in the above embodiments is to include all design changes and equivalents within the technical scope of the present invention.

[0046] Hereinafter, the present invention will be specifically described using examples.

[0047] [Example]

[0048] A strain gauge having the structure shown in Table 1 was produced. In Table 1, "NiCr" means a Ni-Cr alloy having a Cr content of 25 atomic %, "CuNi" means a Cu-Ni alloy having a Ni content of 45 atomic %, and "Co" means Co metal.

[0049]

Table 1

[0050]

[0051] Specifically, the strain gauge of Example 1 has a structure in which the strain resistor layer 13 is directly provided on the resin base material 30. The strain gauge of Example 2 has a structure in which the strain resistor layer 13 is provided with the first layer 11 provided on the resin base material 30 as a base.

[0052] In Examples 2 to 8, a first layer 11 composed of the material shown in Table 1 is formed on a resin substrate 30 composed of a polyimide film with a thickness shown in Table 1. On the first layer 11 provided on the resin substrate 30, a second layer 12 composed of CrB having a B content of 30 atomic % and having a thickness shown in Table 1 is formed. With the second layer 12 as a base, a strain gauge 10 is obtained in which a first stacked body LB1 including the first layer 11, the second layer 12, and the strain gauge 10 is formed on the resin substrate 30.

[0053] X-ray diffraction measurement was performed on the obtained strain gauge 10. Since the first layer 11 and the second layer 12 were thin, no peaks based on these layers were measured in the spectrum obtained by the X-ray diffraction measurement, and only the peak based on the strain resistor layer 13 was measured.

[0054] Figure 4 is a graph showing the X-ray diffraction spectrum of the strain gauge of the embodiment. Figure 4 As shown, in Example 4 in which the strain resistor layer 13 is provided directly on the resin-based substrate 30, the peak of the (110) orientation in the body-centered cubic structure of the strain resistor layer 13 is detected weakly, and it is confirmed that the strain resistor layer 13 of Example 4 has lower crystallinity than the strain resistor layer 13 of Example 1. On the other hand, in Example 2 in which the strain resistor layer 13 is provided on the first layer 11 as a base, the peak of the (110) orientation in the body-centered cubic structure of the strain resistor layer 13 is detected strongly, and it is confirmed that the crystallinity is higher than that of the strain resistor layer 13 of Example 2 and the strain resistor layer 13 of Example 1.

[0055] The strain sensor 100 was made based on the obtained strain gauge, and the strain coefficient Gf was measured. In addition, a high temperature and high humidity environment test (100 hours) at 85°C and 85% relative humidity was performed, and the strain gauge after the test was observed to evaluate whether the first laminate LB1 was peeled off from the resin-based substrate 30 (film peeling test). The measurement results of the strain coefficient Gf and the results of the film peeling test are shown in Tables 1 and Figure 5 Shown in. Figure 5The dashed line is shown for comparison with the gauge factor Gf (11.7) of Example 1 in which the strain resistor layer 13 is directly provided on the resin base material 30 .

[0056] As shown in Table 1 and Figure 5 As shown in FIG. 1 , by providing the second layer 12, the strain coefficient Gf becomes higher than when the second layer 12 is not provided. In particular, when the strain coefficient Gf is in the range of 1.5 nm to 10 nm in thickness, the result is equivalent to that of the case where the strain resistor layer 13 is directly provided on the resin substrate 30 (Example 1).

[0057] Description of Reference Numerals

[0058] 100: Strain sensor

[0059] 10: Strain gauge

[0060] 11: First floor

[0061] 12: Second layer

[0062] 13: Strain resistor layer

[0063] 20: Electrode

[0064] 21: Plating

[0065] 30: Resin base material

[0066] 201: First electrode

[0067] 202: Second electrode

[0068] Gf: Gauge factor

[0069] LB1: First stack

Claims

1. A strain gauge comprising a first stacked body, the first stacked body having: The strain resistor layer is provided on the resin base material, is Cr-based and has a body-centered cubic structure; A first layer is provided between the resin base material and the strain resistor layer; and A second layer is provided between the strain resistor layer and the first layer and becomes a base layer when the strain resistor layer is formed; The strain gauge is characterized in that The first layer inhibits diffusion of oxygen from the resin base material to the strain resistor layer. The second layer hinders crystal growth of the strain resistance layer caused by the crystal structure of the first layer.

2. The strain gauge according to claim 1, wherein: The crystallinity of the strained resistor layer in the first stacked body is lower than the crystallinity of the strained resistor layer in a case where the first layer is formed as a base layer.

3. The strain gauge according to claim 1, wherein: The second layer has a thickness of 1.5 nm to 10 nm.

4. The strain gauge according to claim 1, wherein: The second layer is made of a Cr-based material and contains an element other than Cr, ie, a second element.

5. The strain gauge according to claim 4, wherein: The second element includes a typical element.

6. The strain gauge according to claim 4, wherein: The second element includes one or more elements selected from the group consisting of Group 12 elements to Group 15 elements.

7. The strain gauge according to claim 5, wherein: The Pauling electronegativity of the second element is higher than that of Cr.

8. The strain gauge according to claim 7, wherein: The Pauling electronegativity of the second element is 2.6 or less.

9. The strain gauge according to claim 1, wherein: The second layer can be wet-etched using an etching solution used to wet-etch the strain resistor layer.

10. The strain gauge according to claim 1, wherein: The first layer includes a first element having a larger Pauling electronegativity than Cr.

11. The strain gauge according to claim 10, wherein: The first layer is made of a metal or an alloy based on the first element.

12. The strain gauge according to claim 1, wherein: The first layer has a composition forming a face-centered cubic lattice structure or a close-packed hexagonal structure.

13. The strain gauge of claim 1, wherein: The first layer can be wet-etched using an etching solution used to wet-etch the strain resistor layer.

14. A strain sensor, wherein: A device comprising the strain gauge according to any one of claims 1 to 13 and an electrode for supplying electricity to the strain gauge.

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