Strain gauge

Abstract

The strain gauge includes a base material, a resistor formed on the base material, and two wirings formed on the base material and connected in series to both ends of the resistor. The resistor includes a plurality of elongated portions, the plurality of elongated portions are arranged side by side with their longitudinal directions along a first direction and are connected in series to each other. One of the wirings is arranged side by side with the elongated portion located at one end in a second direction orthogonal to the first direction and is connected to one end of the elongated portion in the first direction. The other one of the wirings is arranged side by side with the elongated portion located 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 formed of a material having a volume resistivity lower than that of the first metal layer and laminated on 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 portion on the one end side in the first direction of the second metal layer protrudes toward the one end side in the first direction more than the end portion on the one end side in the first direction of the gap, and the gap refers to the gap between the first metal layer and the adjacent elongated portion.

Description

Technical Field

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

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

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

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

[0005] The strain gauge is pasted on a strain body, and expands and contracts by tracking the movement of the strain body to detect the amount of strain of the strain body. Therefore, in order to detect a larger amount of 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 improve the strain limit of the strain gauge.

[0007] <Means for Solving the Problems>

[0008] A strain gauge according to an embodiment of the present invention includes: a base material; a resistor formed on the base material; and two wirings formed on the base material and connected in series to both end portions of the resistor. The resistor includes a plurality of elongated portions, the plurality of elongated portions are arranged side by side in such a manner that the length direction is along a first direction, and are connected in series to each other. One of the wirings is arranged side by side with the elongated portion located at one end in a second direction orthogonal to the first direction, and is connected to one end of the elongated portion in the first direction. The other of the wirings is arranged side by side with the elongated portion located 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 laminated on the first metal layer. The second metal layer is formed of a material having a volume resistivity lower than that of 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 portion on the one end side in the first direction of the second metal layer protrudes toward the one end side in the first direction more than the end portion on the one end side in the first direction of the gap. The gap refers to the gap between the first metal layer and the adjacent elongated portion.

[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 showing the strain gauge of the first embodiment.

[0012] Figure 2 It is a cross-sectional view (one of them) showing the strain gauge of the first embodiment.

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

[0014] Figure 4 It is Figure 1 A partial enlarged top view of the vicinity of the connection portion between the resistor body and the wiring in

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

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

[0017] Figure 7 It is a cross-sectional view (the second one) showing the strain gauge of the first embodiment. Detailed implementation manners

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

[0019] <First Embodiment>

[0020] Figure 1 It is a top view showing the strain gauge of the first embodiment. Figure 2 It is a cross-sectional view (one of them) showing the strain gauge of the first embodiment, which shows the cross-section along Figure 1 the A-A line in

[0021] Referring to Figure 1 and Figure 2 , the strain gauge 1 includes a base material 10, a resistor body 30, a wiring 40, electrodes 50, and a cover layer 60. The cover layer 60 can be provided as needed. It should be noted that Figure 1 and Figure 2In this case, for convenience, only the outer edge of the cover layer 60 is indicated by a dashed line. First, each part 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 base material 10 where the resistor body 30 is provided is referred to as the "upper side", and the side where the resistor body 30 is not provided is referred to as the "lower side". In addition, the surface on the upper side of each part is referred to as the "upper surface", and the surface 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 with respect to the upper surface 10a of the base material 10. And the planar shape refers to the shape of the object when observing the object in the normal direction.

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

[0024] The base material 10 is formed of an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyether ether ketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, an LCP (liquid crystal polymer) resin, and a polyolefin resin. It should be noted that a film refers to a component 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 fillers such as silica or alumina.

[0026] As materials other than the resin of the base material 10, SiO 2 , ZrO 2 (including YSZ), Si, Si 2 N 3 , Al 2 O 3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO 3 , 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, 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 (the end on the X-side) of the elongated portion 31 in the first direction X located at one end (the end on the Y-side) in the second direction Y is bent in the Y-direction to reach one end 30e in the grid width direction of the resistor 30. 1 In addition, one end (the end on the X- side) of the elongated portion 31 located at the other end (the end on the Y+ side) in the second direction Y is bent in the Y+ direction to reach the other end 30e in the grid direction of the resistor 30. 2 . Each end 30e 1 and 30e 2 The electrodes 50 are electrically connected via the wiring 40. In other words, the wiring 40 electrically connects the ends 30e of the resistor 30 in the grid width direction. 1 and 30e 2 With each electrode 50. It should be noted that, although for the sake of convenience, Figure 1 The end of 30e 1 and 30e 2It is represented by a dashed line, but the first metal layer 41 (described later) of the resistor body 30 and the wiring 40 can be integrally formed.

[0031] The resistor body 30 can be formed of, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor body 30 can be formed of a material containing at least one of Cr and Ni. Examples of the material containing Cr include a Cr mixed-phase film. Examples of the material containing Ni include Cu-Ni (copper-nickel). Examples of the material containing Cr and Ni include Ni-Cr (nickel-chromium).

[0032] Here, the Cr mixed-phase film is a film formed by mixing Cr, CrN, and Cr 2 N, etc. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

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

[0034] In consideration of the difficulty in generating transverse sensitivity and measures against wire breakage, the width of each elongated portion 31 of the resistor body 30 is preferably 5 μm or more and 100 μm or less. Further, the width of each elongated portion 31 of the resistor body 30 is preferably 5 μm or more and 70 μm or less, and more preferably 5 μm or more and 50 μm or less.

[0035] For example, when the resistor body 30 is a Cr mixed-phase film, by using α-Cr (α-chromium) as the main component, which is a stable crystal phase, the stability of the strain characteristics can be improved. Also, for example, when the resistor body 30 is a Cr mixed-phase film, by making the main component of the resistor body 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 -1000 ppm / °C to +1000 ppm / °C. Here, the "main component" means a component that accounts for 50% by weight or more of all the substances constituting the resistor body. From the viewpoint of improving the strain characteristics, the resistor body 30 preferably contains 80% by weight or more of α-Cr. Further, from the same viewpoint, the resistor body 30 more preferably contains 90% by weight or more of α-Cr. It should be noted that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0036] In addition, in the case where the resistor body 30 is a Cr mixed-phase film, CrN and Cr contained in the Cr mixed-phase film 2 N is preferably 20% by weight or less. Since CrN and Cr contained in the Cr mixed-phase film 2 N is 20% by weight or less, a decrease in the strain rate of the strain gauge 1 can be suppressed.

[0037] In addition, the ratio of CrN and Cr in the Cr mixed-phase film 2 N is preferably such that the ratio of Cr 2 N to the total weight of CrN and Cr 2 N is 80% by weight or more and less than 90% by weight. Further, this ratio is more preferably such that the ratio of Cr 2 N to the total weight of CrN and Cr 2 N is 90% by weight or more and less than 95% by weight. Cr 2 N has semiconductor properties. Therefore, by setting the ratio of the above-mentioned Cr 2 N to be greater than 90% by weight and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant. Furthermore, by making the ratio of the above-mentioned Cr 2 N be greater than 90% by weight and less than 95% by weight, the ceramization of the resistor body 30 can be reduced, so that the resistor body 30 is less likely to undergo brittle fracture.

[0038] On the other hand, CrN has the advantage of chemical stability. By including more CrN in the Cr heterogeneous film, the possibility of generating unstable N can be reduced, and thus a stable strain gauge can be obtained. Here, "unstable N" refers to trace amounts of N 2 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 the unstable N escapes from the film, the film stress of the Cr mixed-phase film may change.

[0039] In the strain gauge 1, when a Cr mixed-phase film is used as the material of the resistor body 30, high sensitivity and miniaturization can be achieved. For example, compared with the case where the output of a conventional strain gauge is about 0.04 mV / 2V, when a Cr mixed-phase film is used as the material of the resistor body 30, an output of 0.3 mV / 2V or more can be obtained. In addition, compared with the case where the size (strain length × strain width) of a conventional strain gauge is about 3 mm × 3 mm, the size (strain length × strain width) in the case of using a Cr mixed-phase film as the material of the resistor body 30 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 at one end in the second direction Y (the end on the Y - side), and is connected to one end in the first direction X (the end on the X - side) of the elongated portion 31 via the turning portion 32. The other wiring 40 is arranged side by side with the elongated portion 31 at the other end in the second direction Y (the end on the Y+ side), and is connected to one end in the first direction X (the end on the X - side) of the elongated portion 31 via the turning 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 does not have to be arranged side by side with the elongated portion 31. That is, the wiring 40 is not limited to a straight - line shape, and can be any pattern that is 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 can have any length.

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

[0043] Each wiring 40 includes a first metal layer 41 and a second metal layer 42 laminated on the first metal layer 41. In addition, each electrode 50 has a first metal layer 51 and a second metal layer 52 laminated on the first metal layer 51. The first metal layer 51 is electrically connected to the ends 30e 1 and 30e 2 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, for convenience, the first metal layers 41 and 51 are represented by a dimpled pattern with the same density as the resistor 30, and the second metal layers 42 and 52 are represented by a dimpled pattern with a density lower than that of the resistor 30.

[0044] The second metal layers 42 and 52 are formed on a part of the upper surface of the first metal layers 41 and 51. Specifically, the second metal layers 42 and 52 are formed in a region except for the outer edges of the upper surfaces of the first metal layers 41 and 51. Therefore, when viewed from above, the outer edges of the first metal layer 41 are exposed from the second metal layer 42. In addition, when viewed from above, the outer edges of the first metal layer 51 are exposed from the second metal layer 52.

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

[0046] One or more other metal layers can also be further laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 can be configured as a copper layer, and a gold layer can be laminated on the upper surface of the copper layer. Alternatively, the second metal layer 52 can be configured as a copper layer, and a palladium layer and a gold layer can be sequentially laminated on the upper surface of the copper layer. By configuring the uppermost layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 can be improved.

[0047] It should be noted that, for convenience, the resistor body 30, the first metal layer 41, and the first metal layer 51 are given different reference numerals, but they can be integrally formed of the same material in the same process. Therefore, the thicknesses of the resistor body 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 second metal layer 42 and the second metal layer 52 for convenience, they can be integrally formed of the same material in the same process. Therefore, the thicknesses of the second metal layer 42 and the second metal layer 52 can be substantially the same.

[0048] Therefore, the wiring 40 has such a structure that on the first metal layer 41 formed of the same material as the resistor body 30, a second metal layer 42 formed of a material having a volume resistivity lower than that of the first metal layer 41 is laminated. Therefore, the resistance of the wiring 40 is lower than the resistance of the resistor body 30 and the wiring 40 can be prevented from being used as a resistor body. As a result, the strain detection accuracy of the resistor body 30 can be improved.

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

[0050] In particular, in a highly sensitive strain gauge with a Cr mixed-phase film as the resistor body 30 and a strain rate of 10 or more, by making the resistance of the wiring 40 lower than that of the resistor body 30, the substantial sensing portion is restricted to a local area where the resistor body 30 is formed, which has a remarkable effect in improving the strain detection accuracy. In addition, by making the resistance of the wiring 40 lower than that of the resistor body 30, the effect of reducing the transverse sensitivity can also be achieved.

[0051] As needed, the covering layer 60 is provided on the upper surface 10a of the base material 10 so as to cover the resistor body 30 and the wiring 40 and expose the electrodes 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 resins (e.g., silicone resin, polyolefin resin). It should be noted that the covering layer 60 can 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 2 μm to 30 μm. By providing the covering layer 60, the generation of mechanical damage in the resistor body 30 can be suppressed. In addition, by providing the covering layer 60, the resistor body 30 can be protected from the influence of moisture and the like.

[0052] Figure 3 is a diagram schematically showing the occurrence of cracks in the resistor body and the wiring. When the strain applied to the strain gauge 1 increases, cracks are generated in the resistor body 30 and the first metal layer 41. According to the research of the inventor, as Figure 3 shown, the crack C tends to extend substantially along 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 is Figure 1 a partially enlarged top view of the vicinity of the connection portion between the resistor body and the wiring in Figure 4 shown, in the strain gauge 1, in a top view, the end of the second metal layer 42 on the 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 one end side (X-side) in the first direction X of the gap S between the first metal layer 41 and the elongated portion 31 adjacent to the first metal layer 41. That is, if the length by which the end of the second metal layer 42 on the one end side in the first direction X protrudes toward the one end side in the first direction X with respect to the end of the one end side in the first direction X of the gap S is set as L1, then the length L1 > 0. It should be noted that in the strain gauge 1, in a top view, the positional relationship between the end of the second metal layer 42 on the one end side in the first direction X and the end of the one end side in the first direction X of the gap between the adjacent elongated portion 31 can be arbitrary.

[0054] Figure 5It is a partially enlarged top view near the connection part between the resistor body and the wiring in the strain gauge of the comparative example. In Figure 5 the comparative example of Figure 4 the length L1 shown is 0. That is, in Figure 5 the comparative example of Figure 3 in the first direction X, the end on the one - end side of the second metal layer 42 in the first direction X and the end on the one - end side of the gap S in the first direction X are located at the same position. In this case, when the crack C shown in

[0055] occurs, since the wire 40 and the elongated portion 31 adjacent to the wire 40 are disconnected and current does not flow, the strain gauge according to the comparative example cannot be used as a strain gauge. Figure 4 In contrast, in the strain gauge 1 shown in Figure 3 since the length L1 > 0, when the crack C shown in Figure 4 occurs, the wire 40 and the elongated portion 31 adjacent to the wire 40 remain electrically connected without disconnection. Therefore, the strain gauge can continue to be used as a strain gauge. In

[0056] In Figure 4 the length L1 is preferably 1 μm or more. Thereby, by ensuring the current - conducting width between the wire 40 and the elongated portion 31 adjacent to the wire 40, it is easy to maintain the electrical connection.

[0057] In addition, in Figure 4 the length L3 in the first direction X between the end on the one - end side of the first metal layer 41 in the first direction X and the end on the one - end side of the second metal layer 42 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, over-etching of the first metal layer 41 sometimes exceeds that of the second metal layer 42. If, due to over-etching, the end of the second metal layer 42 protrudes horizontally from the end of the first metal layer 41, the adhesion between the wiring 40 and the covering layer 60 provided thereon will be 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, during etching in the manufacturing process of the strain gauge 1, the degree of over-etching of the Cr mixed-phase film is about 1 to 2 μm higher than that of copper. In addition, if, due to over-etching, the end of the second metal layer 42 protrudes horizontally from the end of the first metal layer 41, then when the second metal layer 42 is formed of copper, for example, the protruding part of the copper is oxidized and the copper deteriorates, reducing the reliability of the strain gauge 1.

[0059] Therefore, in a plan view, the outer edge of the first metal layer 41 is preferably exposed from the second metal layer 42, the length L3 is preferably 5 μm or more, and more preferably 10 μm or more. Thereby, over-etching of the first metal layer 41 with respect to the second metal layer 42 can be suppressed, and thus the adhesion between the wiring 40 and the covering layer 60 can be maintained. In addition, even if the second metal layer 42 is formed of copper, oxidation deterioration of the copper can be prevented.

[0060] Figure 6 is a graph showing the experimental results of the strain limit, depicting the minimum value of the strain limits of a plurality of test strain gauges. In Figure 4 L1 = 0 μm represents the experimental results of the strain gauge of the comparative example. On the other hand, L1 = 1 μm represents the experimental results of the strain gauge 1 of the first embodiment.

[0061] In Figure 6 the vertical axis represents the strain limit [μST]. The strain limit refers to the value of the mechanical strain at which, when a strain is applied to the strain gauge, a wire break occurs and the strain gauge can no longer function as a strain gauge. From Figure 6 the results, it is confirmed that when L1 = 5 μm, the strain limit is increased by about 1.4 times compared to when L1 = 0 μm.

[0062] It should be noted that according to other research by the inventors and the like, it is not desirable for the second metal layer 42 to be laminated on the first metal layer 41. When the second metal layer 42 is not laminated on the first metal layer 41, compared with Figure 6Compared with the case where L1 = 0 μm shown, 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 stretchability, when the wiring 40 is formed only of the Cr mixed-phase film, the strain limit can be reduced. By laminating a second metal layer 42 made of a material with better stretchability than the Cr mixed-phase film such as copper on the first metal layer 41 made of the Cr mixed-phase film, the strain limit can be increased.

[0063] That is, from the viewpoint of increasing 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 with better stretchability than the first metal layer 41. That is to say, the second metal layer is preferably formed of a material with a volume resistivity lower than that of the first metal layer and better stretchability than the first metal layer 41. When the first metal layer is a Cr mixed-phase film, materials with a volume resistivity lower than that of the first metal layer and better stretchability than the first metal layer 41 include, in addition to copper, gold, silver, and aluminum.

[0064] [Manufacturing method of strain gauge]

[0065] In the strain gauge 1 according to the present embodiment, a resistor 30, a wiring 40, an electrode 50, and a cover layer 60 are formed on the substrate 10. In addition, another layer (such as a functional layer described later) can be formed between the substrate 10 and the layers of these components.

[0066] Next, the manufacturing method of the strain gauge 1 will be described. To manufacture the strain gauge 1, first, the substrate 10 is prepared to form a metal layer (referred to as metal layer A for convenience) on the upper surface 10a of the substrate 10. The metal layer A is the 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 a target of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, a reactive sputtering method, an evaporation method, an arc ion plating method, a pulsed laser deposition method, etc. can also be used to form the metal layer A.

[0068] It should be noted that a lower layer can also be formed on the upper surface 10a of the substrate 10 before forming the metal layer A. For example, a functional layer with a predetermined film thickness can be vacuum-deposited on the upper surface 10a of the substrate 10 by a conventional sputtering method. By providing such a lower layer, the strain characteristics of the strain gauge 1 can be stabilized.

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

[0070] The insulating resin film constituting the base material 10 sometimes contains oxygen or moisture, and Cr sometimes forms a self-oxidized film. Therefore, especially when the metal layer A contains Cr, it is preferable to form a functional layer having the function of preventing the oxidation of the metal layer A.

[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, and thus the metal layer A composed of a stable crystal phase can be manufactured. As a result, in the strain gauge 1, the stability of the strain characteristics is improved. In addition, by the material constituting the functional layer diffusing 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), an alloy of any metal in this group, or a compound of any metal in this group.

[0073] Figure 7 is a cross-sectional view (part two) showing the strain gauge of the first embodiment. Figure 7 Shows the cross-sectional shape of the strain gauge 1 when the functional layer 20 is provided under the resistive body 30, the wiring 40, and the electrode 50.

[0074] The pattern of the planar shape of the functional layer 20 can be substantially the same as the planar shapes of the resistive body 30, the wiring 40, and the electrode 50. However, the planar shapes of the functional layer 20 and the resistive body 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 can be different from the planar shapes of the resistive body 30, the wiring 40, and the electrode 50. In this case, the functional layer 20 can be formed in a uniform and flat manner, for example, in the regions where the resistive body 30, the wiring 40, and the electrode 50 are formed. Alternatively, the functional layer 20 can be formed in a uniform and flat manner on the entire upper surface of the base material 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; 30e 1 , 30e 2 Terminal; 31 elongated portion; 32 return portion; 40 wiring; 41, 51 first metal layer; 42, 52 second metal layer; 50 electrode; 60 cover layer.

Claims

1. A strain gauge, comprising: a base material; a resistor body formed on the base material; and two wirings formed on the base material and serially connected to both end portions of the resistor body, the resistor body includes a plurality of elongated portions, the plurality of elongated portions are arranged side by side in such a manner that the length direction is along a first direction, and are serially connected to each other, one of the wirings is arranged side by side with the elongated portion located at one end in a second direction orthogonal to the first direction, and is connected to one end of the elongated portion in the first direction, the other one of the wirings is arranged side by side with the elongated portion located 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 laminated on the first metal layer, and the second metal layer is formed of a material having a volume resistivity lower than that of the first metal layer, when viewed from above, the outer edge of the first metal layer exposes from the second metal layer, when viewed from above, the end portion on the one end side in the first direction of the second metal layer protrudes toward the one end side in the first direction more than the end portion on the one end side in the first direction of a gap, and the gap refers to the gap between the first metal layer and the adjacent elongated portion in the first direction.

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

3. The strain gauge according to claim 2, wherein, the protruding length 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, the length in the first direction between the end portion on the one end side in the first direction of the first metal layer and the end portion on the one end side in the first direction of the second metal layer is 5 μm or more.

6. The strain gauge according to any one of claims 1 to 4, wherein, the second metal layer is formed of a material having better stretchability than the first metal layer.

7. The strain gauge according to any one of claims 1 to 4, wherein, the first metal layer is integrally formed of the same material as the resistor body.

8. The strain gauge according to any one of claims 1 to 4, wherein, The resistor body is formed of a film containing Cr, CrN, and Cr 2 N.

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