Strain gauge

Abstract

The strain gauge includes a base material, a resistor formed on the base material, and two wires formed on the base material and connected in series to both end portions of the resistor, the resistor including a plurality of elongated portions arranged side by side in a first direction and connected in series to each other, one of the wirings is provided side by side with the elongated section located at one end in a second direction orthogonal to the first direction and is connected to one end in the first direction of the elongated section, and the other of the wirings is provided side by side with the elongated section located at the other end in the second direction and is connected to one end in the second direction of the elongated section. Each of the wirings includes a first metal layer and a second metal layer laminated on the first metal layer and formed of a material having a lower volume resistivity than the first metal layer, an outer edge of the first metal layer is exposed from the second metal layer in a plan view, and an outer edge of the second metal layer is exposed from the second metal layer in a plan view. In a plan view, an end portion of the second metal layer on one end side in the first direction protrudes further toward one end side in the first direction than an end portion of a gap on one end side in the first direction, the gap being a gap between the first metal layer and the elongated portion adjacent to the first metal layer.

Description

Technical Field

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

[0002] Conventionally, a strain gauge for attaching to a measurement object is known. The strain gauge includes a resistor for detecting strain, and the resistor is formed on, for example, an insulating resin. The resistor is connected to an electrode via, for example, wiring (see, for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2016-74934 Summary of the invention

[0004] <Problems to be Solved by the Invention>

[0005] The strain gauge is attached to the strain body and detects the strain of the strain body by tracking its movement and expansion. Therefore, in order to detect a larger strain, the strain gauge itself cannot be damaged during the expansion and contraction process, and a higher strain limit is required.

[0006] An object of the present invention is to increase the strain limit of a strain gauge.

[0007] <Methods of solving the problem>

[0008] A strain gauge according to an embodiment of the present invention comprises: a substrate; a resistor formed on the substrate; and two wirings formed on the substrate and connected in series with both ends of the resistor, wherein the resistor comprises a plurality of elongated portions, the plurality of elongated portions are arranged side by side in a manner that the length direction is along a first direction and are connected in series with each other, one of the wirings is arranged side by side with the elongated portion located at one end of a second direction orthogonal to the first direction and is connected to one end of the elongated portion in the first direction, and the other of the wirings is arranged side by side with the elongated portion located at the other end of the second direction. The wiring is arranged in a row and connected to one end of the slender portion in the first direction, each of the wirings includes a first metal layer and a second metal layer stacked on the first metal layer, the second metal layer is formed of a material with a lower volume resistivity than the first metal layer, and the outer edge of the first metal layer is exposed from the second metal layer when viewed from above, and the end of the second metal layer on one end side in the first direction protrudes toward one end side in the first direction more than the end of the gap on one end side in the first direction when viewed from above, and the gap refers to the gap between the first metal layer and the slender portion adjacent to the first metal layer.

[0009] <Effects of the Invention>

[0010] According to the disclosed technology, the strain limit of the strain gauge can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a top view illustrating the strain gauge according to the first embodiment.

[0012] Figure 2 This is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment.

[0013] Figure 3 This is a diagram schematically showing a situation where cracks have occurred in a resistor and wiring.

[0014] Figure 4 yes Figure 1 A partially enlarged top view of the vicinity of the connection between the resistor and the wiring.

[0015] Figure 5 It is a partially enlarged plan view of the vicinity of the connection portion between the resistor and the wiring in the strain gauge of the comparative example.

[0016] Figure 6 It is a graph showing the experimental results of strain limit.

[0017] Figure 7 This is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. DETAILED DESCRIPTION

[0018] Hereinafter, the mode for implementing the present invention will be described with reference to the accompanying drawings. In each figure, the same reference numerals are sometimes given to the same components. In addition, in the description of each figure, the description of the components that are the same as the components that have been described is sometimes omitted. In addition, in each figure, the X-axis, Y-axis and Z-axis that are orthogonal to each other are sometimes specified. In this case, in the X-axis direction, the starting point (root) side of the arrow is called the X-side, and the end point (end of the arrow) side of the arrow is called the X+ side. The same is true for the Y-axis direction and the Z-axis direction. In addition, the direction parallel to the X-axis is called the first direction X, and the direction parallel to the Y-axis is called the second direction Y.

[0019] <First embodiment>

[0020] Figure 1 It is a plan view showing the strain gauge according to the first embodiment. Figure 2 is a cross-sectional view (part 1) showing the strain gauge of the first embodiment, which shows the strain gauge along the Figure 1 The section of line AA in .

[0021] Reference Figure 1 and Figure 2 The strain gauge 1 includes a substrate 10, a resistor 30, a wiring 40, an electrode 50 and a covering layer 60. The covering layer 60 can be provided as required. It should be noted that Figure 1 and Figure 2In FIG. 1 , for convenience, only the outer edge of the cover layer 60 is indicated by a dotted line. First, each component constituting the strain gauge 1 will be described in detail.

[0022] It should be noted that in the present embodiment, for convenience, in the strain gauge 1, the side of the substrate 10 on which the resistor 30 is provided is referred to as the "upper side", and the side on which the resistor 30 is not provided is referred to as the "lower side". In addition, the surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". However, the strain gauge 1 can also be used in an upside-down state. In addition, the strain gauge 1 can be arranged at any angle. In addition, looking down refers to observing an object along the normal direction from top to bottom relative to the upper surface 10a of the substrate 10. And, the plane shape refers to the shape of the object when the object is observed in the normal direction.

[0023] The substrate 10 is a component that serves as a base layer for forming the resistor 30 and the like. The substrate 10 has flexibility. The thickness of the substrate 10 is not particularly limited and can be appropriately determined according to the purpose of use of the strain gauge 1 and the like. For example, the thickness of the substrate 10 can be about 5 μm to 500 μm. On the lower surface side of the strain gauge 1, the strain body can also be bonded via an adhesive layer or the like. It should be noted that, if the transmission of strain from the surface of the strain body to the sensing part and the dimensional stability to environmental changes are considered, the thickness of the substrate 10 is preferably in the range of 5 μm to 200 μm. In addition, if considered from the perspective of insulation, the thickness of the substrate 10 is preferably greater than 10 μm.

[0024] The substrate 10 is formed of 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, LCP (liquid crystal polymer) resin, and polyolefin resin. It should be noted that the film refers to a member having a thickness of 500 μm or less and having flexibility.

[0025] When the base material 10 is formed of an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the base material 10 may be formed of an insulating resin film containing a filler such as silica or alumina.

[0026] Examples of materials other than the resin of the substrate 10 include SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO 3)In addition to the above-mentioned crystalline materials, amorphous glass and the like can also be used as the material of the substrate 10. In addition, as the material of the substrate 10, metals such as aluminum, aluminum alloy (duralumin), and titanium can also be used. When a metal is used, an insulating film is provided on the metal substrate 10.

[0027] The resistor 30 is a thin film formed on the substrate 10 in a predetermined pattern. In the strain gauge 1, the resistor 30 is a sensing part that generates a change in resistance when it is subjected to strain. The resistor 30 can be formed directly on the upper surface 10a of the substrate 10 or on the upper surface 10a of the substrate 10 through another layer. Figure 1 In the figure, for convenience, the resistor 30 is represented by a dark pear skin pattern.

[0028] The resistor 30 includes a plurality of elongated portions 31 and a plurality of folded portions 32. Figure 1 In the example of FIG. 1 , the resistor 30 includes six elongated portions 31 and seven folded portions 32, but the number of the elongated portions 31 and the folded portions 32 is not limited to Figure 1 Example.

[0029] In the resistor 30, a plurality of elongated portions 31 are arranged side by side along the first direction X in the length direction. In addition, a plurality of folded portions 32 connect the ends of adjacent elongated portions 31 in the plurality of elongated portions 31 in an interlaced manner, thereby connecting the elongated portions 31 in series. Thus, the resistor 30 is configured as a structure that is folded back in a zigzag shape as a whole. The length direction of the plurality of elongated portions 31, i.e., the first direction X, becomes the grid direction, and the direction perpendicular to the grid direction, i.e., the second direction Y, becomes the grid width direction.

[0030] In the resistor 30, one end of the first direction X (the end on the X-side) of the slender portion 31 located at one end of the second direction Y (the end on the Y-side) is bent in the Y-direction to reach one end 30e1 in the grid width direction of the resistor 30. In addition, one end of the first direction X (the end on the X-side) of the slender portion 31 located at the other end of the second direction Y (the end on the Y+ side) is bent in the Y+ direction to reach the other end 30e2 in the grid direction of the resistor 30. The respective ends 30e1 and 30e2 are electrically connected to the electrode 50 via the wiring 40. In other words, the wiring 40 electrically connects the respective ends 30e1 and 30e2 in the grid width direction of the resistor 30 to the respective electrodes 50. It should be noted that, although for the sake of convenience, Figure 1 The ends 30e1 and 30e2 in FIG. 3 are indicated by dotted lines, but the resistor body 30 and a first metal layer 41 (described later) of the wiring 40 may be integrally formed.

[0031] The resistor 30 may be formed of a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 may be formed of 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 Cr and Ni include Ni-Cr (nickel chromium).

[0032] Here, the Cr mixed phase film is a film formed by a mixed phase of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0033] The thickness of the resistor 30 is not particularly limited and can be appropriately determined according to the purpose of use of the strain gauge 1, etc. For example, the thickness of the resistor 30 can be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. In addition, when the thickness of the resistor 30 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 10 caused by the internal stress of the film constituting the resistor 30 are reduced.

[0034] In consideration of preventing lateral sensitivity and preventing disconnection, the width of each elongated portion 31 of the resistor 30 is preferably 5 μm to 100 μm. Furthermore, the width of each elongated portion 31 of the resistor 30 is preferably 5 μm to 70 μm, more preferably 5 μm to 50 μm.

[0035] For example, in the case where the resistor 30 is a Cr mixed phase film, by using α-Cr (α chromium) as a stable crystalline phase as the main component, the stability of the strain characteristics can be improved. For another example, in the case where the resistor 30 is a Cr mixed phase film, by making the main component of the resistor 30 α-Cr, the strain rate of the strain gauge 1 can be set to 10 or more, and the strain rate temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000ppm / ℃ to +1000ppm / ℃. Here, the "main component" refers to a component that accounts for more than 50% by weight of all the materials constituting the resistor. From the viewpoint of improving the strain characteristics, the resistor 30 preferably contains more than 80% by weight of α-Cr. Furthermore, from the same viewpoint, the resistor 30 more preferably contains more than 90% by weight of α-Cr. It should be noted that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0036] When the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N. Since the Cr mixed phase film contains 20 wt % or less of CrN and Cr2N, the strain rate of the strain gauge 1 can be suppressed from decreasing.

[0037] In addition, the ratio of CrN and Cr2N in the Cr mixed phase film is preferably 80 weight % or more and less than 90 weight % of the ratio of Cr2N to the total weight of CrN and Cr2N. Further, the ratio is more preferably 90 weight % or more and less than 95 weight % of the ratio of Cr2N to the total weight of CrN and Cr2N. Cr2N has semiconductor properties. Therefore, by setting the ratio of the above-mentioned Cr2N to be greater than 90 weight % and less than 95 weight %, the reduction of TCR (negative TCR) becomes more significant. Furthermore, by setting the ratio of the above-mentioned Cr2N to be greater than 90 weight % and less than 95 weight %, the ceramicization of the resistor 30 can be reduced, so that the resistor 30 is not prone to brittle failure.

[0038] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr mixed phase film, the possibility of generating unstable N can be reduced, so a stable strain gauge can be obtained. Here, "unstable N" refers to a trace amount of N2 or atomic N that may exist in the film of the Cr mixed phase film. Depending on the external environment (such as a high temperature environment), these unstable N may escape from the film. When unstable N escapes from the film, the film stress of the Cr mixed phase film may change.

[0039] In the strain gauge 1, when the Cr mixed phase film is used as the material of the resistor 30, high sensitivity and miniaturization can be achieved. For example, compared with the output of the conventional strain gauge of about 0.04 mV / 2V, when the Cr mixed phase film is used as the material of the resistor 30, an output of 0.3 mV / 2V or more can be obtained. In addition, compared with the size of the conventional strain gauge (strain length × strain width) of about 3 mm × 3 mm, when the Cr mixed phase film is used as the material of the resistor 30, the size (strain length × strain width) can be miniaturized to about 0.3 mm × 0.3 mm.

[0040] Two wirings 40 are formed on the substrate 10. One wiring 40 is arranged side by side with the elongated portion 31 located at one end (end on the Y-side) in the second direction Y, and is connected to one end (end on the X-side) of the elongated portion 31 in the first direction X via the folded portion 32. The other wiring 40 is arranged side by side with the elongated portion 31 located at the other end (end on the Y+ side) in the second direction Y, and is connected to one end (end on the X-side) of the elongated portion 31 in the first direction X via the folded portion 32.

[0041] The wiring 40 only needs to be arranged side by side with the elongated portion 31 at least on one end side in the first direction X, and the entire wiring 40 may not be arranged side by side with the elongated portion 31. That is, the wiring 40 is not limited to a straight line, and may be any pattern arranged side by side with the elongated portion 31 at least on one end side in the first direction X. In addition, the wiring 40 may have any length.

[0042] The electrode 50 is formed on the substrate 10, electrically connected to the resistor 30 via the wiring 40, and is formed in a substantially rectangular shape, for example, wider than the wiring 40. The electrode 50 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, connected to a lead wire for external connection.

[0043] Each wiring 40 includes a first metal layer 41 and a second metal layer 42 stacked on the first metal layer 41. In addition, each electrode 50 has a first metal layer 51 and a second metal layer 52 stacked on the first metal layer 51. The first metal layer 51 is electrically connected to the ends 30e1 and 30e2 of the resistor 30 via the first metal layer 41 of the wiring 40. When viewed from above, the first metal layer 51 is formed in a substantially rectangular shape. The first metal layer 51 can also be formed to have the same width as the wiring 40. It should be noted that Figure 1 In FIG. 1 , for convenience, the first metal layers 41 and 51 are represented by a pear-skin pattern having the same density as the resistor 30 , and the second metal layers 42 and 52 are represented by a pear-skin pattern having a lower density than the resistor 30 .

[0044] The second metal layers 42 and 52 are formed on a portion of the upper surfaces of the first metal layers 41 and 51. Specifically, the second metal layers 42 and 52 are formed in regions other than the outer edges of the upper surfaces of the first metal layers 41 and 51. Therefore, in a plan view, the outer edge of the first metal layer 41 is exposed from the second metal layer 42. In addition, in a plan view, the outer edge of the first metal layer 51 is exposed from the second metal layer 52.

[0045] The second metal layer 42 and the second metal layer 52 can be formed integrally from the same material or from different materials. A material having a lower volume resistivity than the resistor 30 (the first metal layers 41 and 51) can be selected as the material of the second metal layers 42 and 52. Such a material can be, for example, a laminated film of Cu, Ni, Al, Ag, Au, Pt, etc. or an alloy of any of these metals, a compound of any of these metals, or any of these metals, alloys, and compounds appropriately stacked. In particular, it is preferred to use Cu or Cu alloys, Al or Ag, Au, CrMn, etc. as the material of the second metal layers 42 and 52. The thickness of the second metal layers 42 and 52 is not particularly limited and can be appropriately selected according to the purpose. The thickness of the second metal layers 42 and 52 can be, for example, about 0.5μm to 5μm.

[0046] It is also possible to further stack one or more other metal layers on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be formed as a copper layer, and a gold layer may be stacked on the upper surface of the copper layer. Alternatively, the second metal layer 52 may be formed as a copper layer, and a palladium layer and a gold layer may be stacked in sequence on the upper surface of the copper layer. By forming the uppermost layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 may be improved.

[0047] It should be noted that, although different reference numerals are used for the sake of convenience, the resistor 30, the first metal layer 41, and the first metal layer 51 can be integrally formed using the same material in the same process. Therefore, the thickness of the resistor 30, the first metal layer 41, and the first metal layer 51 can be substantially the same. In addition, although different reference numerals are used for the sake of convenience for the second metal layer 42 and the second metal layer 52, they can be integrally formed using the same material in the same process. Therefore, the thickness of the second metal layer 42 and the second metal layer 52 can be substantially the same.

[0048] Therefore, the wiring 40 has a structure in which a second metal layer 42 formed of a material having a lower volume resistivity than the first metal layer 41 is stacked on a first metal layer 41 formed of the same material as the resistor 30. Therefore, the resistance of the wiring 40 is lower than the resistance of the resistor 30 and the wiring 40 can be suppressed from functioning as a resistor. As a result, the strain detection accuracy of the resistor 30 can be improved.

[0049] In other words, by forming the wiring 40 using a material having a lower volume resistivity than the resistor 30, the substantial sensing portion of the strain gauge 1 can be limited to a local region where the resistor 30 is formed. Therefore, the strain detection accuracy of the resistor 30 can be improved.

[0050] In particular, in a high-sensitivity strain gauge with a strain rate of 10 or more using a Cr mixed-phase film as the resistor 30, by making the resistance of the wiring 40 lower than the resistance of the resistor 30, the actual sensing portion is limited to the local area where the resistor 30 is formed, which has a significant effect on improving the strain detection accuracy. In addition, by making the resistance of the wiring 40 lower than the resistor 30, the effect of reducing the lateral sensitivity can also be achieved.

[0051] As needed, the covering layer 60 is arranged on the upper surface 10a of the substrate 10 in a manner that covers the resistor 30 and the wiring 40 and exposes the electrode 50. The material of the covering layer 60 can be an insulating resin, such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin and composite resin (for example, silicone resin, polyolefin resin). It should be noted that the covering layer 60 may also contain fillers or pigments. The thickness of the covering layer 60 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the covering layer 60 can be about 2μm to 30μm. By providing the covering layer 60, the occurrence of mechanical damage in the resistor 30 can be suppressed. In addition, by providing the covering layer 60, the resistor 30 can be protected from the influence of moisture and the like.

[0052] Figure 3 Schematically shows the situation where cracks are generated in the resistor and the wiring. When the strain applied to the strain gauge 1 increases, cracks are generated in the resistor 30 and the first metal layer 41. According to the inventor's research, Figure 3 As shown, the crack C tends to extend substantially in the second direction Y near the end of the second metal layer 42 constituting the wiring 40 in the first direction X.

[0053] Figure 4 yes Figure 1 A partial enlarged top view of the connection between the resistor and the wiring. Figure 4 As shown, in the strain gauge 1, when viewed from above, the end of the second metal layer 42 on one end side (X-side) in the first direction X protrudes toward the one end side (X-side) in the first direction X more than the end of the gap S on one end side (X-side) in the first direction X between the first metal layer 41 and the elongated portion 31 adjacent to the first metal layer 41. That is, if the length of the end of the second metal layer 42 on one end side in the first direction X protruding toward the one end side in the first direction X with respect to the end of the gap S on one end side in the first direction X as a reference is L1, the length L1>0. It should be noted that in the strain gauge 1, when viewed from above, the positional relationship between the end of the second metal layer 42 on one end side in the first direction X and the end of the gap between the adjacent elongated portions 31 on one end side in the first direction X may be arbitrary.

[0054] Figure 5 This is a partial enlarged top view of the vicinity of the connection between the resistor and the wiring in the strain gauge of the comparative example. Figure 5 In the comparative example, Figure 4 The length L1 shown is 0. That is, Figure 5 In the comparative example of FIG. 1 , in the first direction X, the end of the second metal layer 42 on one side of the first direction X and the end of the gap S on one side of the first direction X are located at the same position. In this case, when the Figure 3In the case of the crack C shown, since disconnection occurs between the wiring 40 and the elongated portion 31 adjacent to the wiring 40 and current does not flow, the strain gauge according to the comparative example cannot be used as a strain gauge.

[0055] In contrast, due to Figure 4 In the strain gauge 1 shown, the length L1>0, so in the generation Figure 3 In the case of the crack C shown in the figure, the wiring 40 and the elongated portion 31 adjacent to the wiring 40 maintain electrical connection without disconnection, so the strain gauge can continue to function as a strain gauge. Figure 4 In this case, the length L1 is preferably 1 μm or more. Thus, by ensuring the current-carrying width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40 , it is easy to maintain the electrical connection.

[0056] exist Figure 4 In the embodiment, the length L1 is preferably greater than or equal to the length L2 of the second direction Y of the elongated portion 31 (i.e., the width of the elongated portion 31). The length of the elongated portion 31 in the second direction Y is preferably greater than 5 μm. That is, the length L1 is preferably greater than 5 μm. This further ensures the conducting width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40, making it easier to maintain electrical connection.

[0057] In addition, Figure 4 A length L3 in the first direction X between an end of the first metal layer 41 on one side in the first direction X and an end of the second metal layer 42 on one side in the first direction X is preferably 5 μm or more, more preferably 10 μm or more.

[0058] In the manufacturing process of the strain gauge 1, the first metal layer 41 and the second metal layer 42 are etched to form a pattern. However, during etching, the first metal layer 41 is sometimes overetched beyond the second metal layer 42. If the end of the second metal layer 42 protrudes horizontally from the end of the first metal layer 41 due to overetching, when the cover layer 60 covering the wiring 40 is provided, the adhesion between the wiring 40 and the cover layer 60 is reduced. For example, in the wiring 40, when the first metal layer 41 is formed of a Cr mixed phase film and the second metal layer 42 is formed of copper, when etching is performed during the manufacturing process of the strain gauge 1, the overetching degree of the Cr mixed phase film is higher than that of copper by about 1 to 2 μm. In addition, if the end of the second metal layer 42 protrudes horizontally from the end of the first metal layer 41 due to overetching, then when the second metal layer 42 is formed of copper, for example, the protruding portion of the copper is oxidized and the copper deteriorates, and the reliability of the strain gauge 1 is reduced.

[0059] Therefore, in a plan view, the outer edge of the first metal layer 41 is preferably exposed from the second metal layer 42, and the length L3 is preferably 5 μm or more, and more preferably 10 μm or more. Thus, overetching of the first metal layer 41 relative to the second metal layer 42 can be suppressed, so that the adhesion between the wiring 40 and the cover layer 60 can be maintained. In addition, even if the second metal layer 42 is formed of copper, oxidation degradation of copper can be prevented.

[0060] Figure 6 This is a graph showing the experimental results of strain limit, which plots the minimum value of strain limit of multiple experimental strain gauges. Figure 4 In FIG. 1 , L1 = 0 μm indicates the experimental result of the strain gauge of the comparative example. On the other hand, L1 = 1 μm indicates the experimental result of the strain gauge 1 of the first embodiment.

[0061] exist Figure 6 In the figure, the vertical axis represents the strain limit [μST]. The strain limit is the value of the mechanical strain at which the strain gauge breaks when strain is applied to it and cannot function as a strain gauge. Figure 6 The results confirmed that when L1 = 5μm, the strain limit increased by about 1.4 times compared with that when L1 = 0μm.

[0062] It should be noted that according to other studies by the inventors, it is not desirable for the second metal layer 42 to be stacked on the first metal layer 41. When the second metal layer 42 is not stacked on the first metal layer 41, Figure 6 Compared with L1 = 0 μm shown in the figure, the strain limit is further reduced. For example, when the first metal layer 41 is a Cr mixed phase film, since the Cr mixed phase film has poor elasticity, when the wiring 40 is formed only by the Cr mixed phase film, the strain limit can be reduced. By stacking the second metal layer 42 composed of a material having better elasticity than the Cr mixed phase film such as copper on the first metal layer 41 composed of the Cr mixed phase film, the strain limit can be increased.

[0063] That is, from the viewpoint of improving the strain limit, the wiring 40 is preferably formed by laminating the first metal layer 41 and the second metal layer 42, and the second metal layer 42 is preferably formed of a material having a higher elasticity than the first metal layer 41. That is, the second metal layer is preferably formed of a material having a lower volume resistivity than the first metal layer and a higher elasticity than the first metal layer 41. When the first metal layer is a Cr mixed phase film, as a material having a lower volume resistivity than the first metal layer and a higher elasticity than the first metal layer 41, in addition to copper, gold, silver and aluminum can also be cited.

[0064] [Method of manufacturing strain gauge]

[0065] In the strain gauge 1 according to the present embodiment, the resistor 30, the wiring 40, the electrode 50 and the cover layer 60 are formed on the base material 10. Furthermore, another layer (a functional layer described later, etc.) may be formed between the base material 10 and the layers of these members.

[0066] Next, a method for manufacturing the strain gauge 1 is described. In order to manufacture the strain gauge 1, first, a substrate 10 is prepared to form a metal layer (for convenience, referred to as a metal layer A) on the upper surface 10a of the substrate 10. The metal layer A is a layer that is finally patterned into the resistor 30, the wiring 40, and the electrode 50. Therefore, the material and thickness of the metal layer A are similar to those of the resistor 30 and the like.

[0067] For example, the metal layer A can be formed by magnetron sputtering using as a target a material capable of forming the metal layer A. The metal layer A can also be formed by reactive sputtering, vapor deposition, arc ion plating, pulse laser deposition, or the like instead of magnetron sputtering.

[0068] It should be noted that the metal layer A may be formed after the lower layer is formed on the upper surface 10a of the substrate 10. For example, a functional layer of a predetermined film thickness may be formed by vacuum deposition on the upper surface 10a of the substrate 10 by a conventional sputtering method. By providing the lower layer in this way, the strain characteristics of the strain gauge 1 can be stabilized.

[0069] In the present application, the functional layer refers to a layer having at least the function of promoting the crystal growth of the metal layer A (resistor 30). The functional layer also preferably has the function of preventing the metal layer A from being oxidized by oxygen or moisture contained in the substrate 10 and / or the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer may also have other functions.

[0070] The insulating resin film constituting the substrate 10 may contain oxygen or moisture, and Cr may form a self-oxidized film. Therefore, in particular, when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing the metal layer A from being oxidized.

[0071] In this way, by providing the functional layer under the metal layer A, the crystal growth of the metal layer A can be promoted, so that the metal layer A composed of a stable crystal phase can be manufactured. As a result, the stability of the strain characteristics is improved in the strain gauge 1. In addition, by diffusing the material constituting the functional layer into the metal layer A, the strain characteristics are improved in the strain gauge 1.

[0072] As the material of the functional layer, for example, 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), Al (aluminum), alloys of any metal in the group, or compounds of any metal in the group.

[0073] Figure 7 This is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. Figure 7 The cross-sectional shape of the strain gauge 1 is shown when the functional layer 20 is provided as a lower layer of the resistor 30 , the wiring 40 , and the electrode 50 .

[0074] The pattern of the planar shape of the functional layer 20 may be substantially the same as the planar shape of the resistor 30, the wiring 40, and the electrode 50. However, the planar shapes of the functional layer 20 and the resistor 30, the wiring 40, and the electrode 50 may not be substantially the same. For example, if the functional layer 20 is formed of an insulating material, the pattern of the functional layer 20 may be different from the planar shape of the resistor 30, the wiring 40, and the electrode 50. In this case, the functional layer 20 may be formed in a uniform and flat manner in, for example, an area where the resistor 30, the wiring 40, and the electrode 50 are formed. Alternatively, the functional layer 20 may be formed in a uniform and flat manner on the entire upper surface of the substrate 10.

[0075] Next, the second metal layer 42 and the second metal layer 52 are formed on the upper surface of the metal layer A. The second metal layer 42 and the second metal layer 52 can be formed into a predetermined pattern by, for example, a known photolithography method.

[0076] Next, a photosensitive photoresist is formed on the upper surface of the metal layer A, the upper surface of the second metal layer 42, and the upper surface of the second metal layer 52, and the photoresist is exposed and developed to form a pattern. Figure 1 The resistor 30, wiring 40 and electrode 50 have the same planar shape. Then, the metal layer A exposed from the photoresist is removed by wet etching or the like using the photoresist as an etching mask. Then, by removing the photoresist, a Figure 1 The resistor 30, the wiring 40 and the electrode 50 are shown in the planar shape. At this time, the shape of the photoresist is controlled so that the first metal layer 41 is not overetched relative to the second metal layer 42.

[0077] After forming the resistor 30, the wiring 40, and the electrode 50, the cover layer 60 is formed on the upper surface 10a of the substrate 10 as needed. The cover layer 60 covers the resistor 30 and the wiring 40, and the electrode 50 may be exposed from the cover layer 60. For example, a semi-cured thermosetting insulating resin film is laminated on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrode 50, and then the insulating resin film is heated and cured, thereby forming the cover layer 60. Through the above steps, the strain gauge 1 is completed.

[0078] Preferred embodiments, etc. have been described in detail above. However, the strain gauge of the present invention is not limited to the above embodiments, etc. For example, various modifications and substitutions may be made to the strain gauge of the above embodiments, etc. without departing from the scope described in the claims.

[0079] This international application claims the priority of Japanese Patent Application No. 2022-076117 filed on May 2, 2022, and the entire contents of Japanese Patent Application No. 2022-076117 are incorporated into this international application.

[0080] Description of Reference Numerals

[0081] 1 strain gauge; 10 substrate; 10a upper surface; 20 functional layer; 30 resistor; 30e1, 30e2 terminals; 31 elongated portion; 32 folded portion; 40 wiring; 41, 51 first metal layer; 42, 52 second metal layer; 50 electrode; 60 cover layer.

Claims

1. A strain gauge, comprising: Base material; A resistor is formed on the substrate; as well as Two wirings are formed on the substrate and connected in series with both ends of the resistor. The resistor includes a plurality of elongated portions, the plurality of elongated portions are arranged side by side in a manner that the length direction thereof is along a first direction and are connected in series with each other. One of the wirings is arranged side by side with the elongated portion located at one end of a second direction orthogonal to the first direction, and is connected to one end of the elongated portion in the first direction. Another one of the wirings is arranged side by side with the elongated portion at the other end in the second direction and is connected to one end of the elongated portion in the first direction. Each of the wirings includes a first metal layer and a second metal layer stacked on the first metal layer, the second metal layer being formed of a material having a lower volume resistivity than the first metal layer. When viewed from above, the outer edge of the first metal layer is exposed from the second metal layer. When viewed from above, the end of the second metal layer on one side in the first direction protrudes toward the one side in the first direction more than the end of the gap on one side in the first direction, and the gap refers to the gap between the first metal layer and the elongated portion adjacent to the first metal layer.

2. The strain gauge according to claim 1, wherein: The end portion of the second metal layer on the one end side in the first direction protrudes toward the one end side in the first direction with reference to the end portion of the gap on the one end side in the first direction by a length of 1 μm or more.

3. The strain gauge according to claim 2, wherein: The length of the protrusion is greater than or equal to the length of the elongated portion in the second direction.

4. The strain gauge according to claim 3, wherein: The length of the elongated portion in the second direction is 5 μm or more.

5. The strain gauge according to any one of claims 1 to 4, wherein: A length in the first direction between an end of the first metal layer on one end side in the first direction and an end of the second metal layer on one end side in the first direction is 5 μm or more.

6. The strain gauge according to any one of claims 1 to 5, wherein: The second metal layer is formed of a material having better elasticity than that of the first metal layer.

7. The strain gauge according to any one of claims 1 to 6, wherein: The first metal layer is integrally formed of the same material as the resistor.

8. The strain gauge according to any one of claims 1 to 7, wherein: The resistor is formed of a film containing Cr, CrN, and Cr2N.

Images