Strain gauge

Abstract

The strain gauge of the present invention comprises: a base material; the resistor body is formed on the base material; and a wiring formed on the base material and connected to a terminal portion of the resistor, the wiring including a first portion, the first portion of the wiring being disposed side by side with the resistor in a grid width direction with a gap therebetween in a plan view, and the first portion of the wiring being disposed side by side with the resistor in a grid width direction. The wiring includes a first metal layer and a second metal layer laminated on the first metal layer, and the second metal layer at the first portion of the wiring protrudes further toward the side where the resistor is disposed in the grid direction than an end portion of the void. According to the invention, the strain limit of the strain gauge can be improved.

Description

[0001] This application is a divisional application of the application with application number "202380037897.2 (International Application No. PCT / JP2023 / 016698)", application date "April 27, 2023", and invention name "Strain Gauge". Technical Field

[0002] The present invention relates to a strain gauge. Background Art

[0003] Strain gauges for attaching to a measurement object are conventionally known. These strain gauges include a resistor for detecting strain, formed, for example, on an insulating resin. The resistor is connected to electrodes via wiring, for example (see, for example, Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention

[0005] <Problems to be Solved by the Invention>

[0006] Strain gauges are attached to a strained object and expand and contract as it tracks its movement, detecting the amount of strain. Therefore, to detect larger strains, the strain gauges themselves must be protected from damage during expansion and contraction, requiring a higher strain limit.

[0007] An object of the present invention is to increase the strain limit of a strain gauge.

[0008] <Methods of solving the problem>

[0009] A strain gauge according to one embodiment of the present invention includes:

[0010] substrate;

[0011] a resistor formed on the substrate; and

[0012] wiring formed on the substrate and connected to the terminal portion of the resistor,

[0013] The wiring includes a first portion, and when viewed from above, the first portion of the wiring is arranged side by side with the resistor with a gap therebetween in the grid width direction.

[0014] The wiring includes a first metal layer and a second metal layer stacked on the first metal layer.

[0015] The second metal layer at the first portion of the wiring protrudes further toward the side where the resistor is arranged in the grid direction than an end portion of the gap.

[0016] A strain gauge according to another embodiment of the present invention includes:

[0017] A base material;

[0018] A resistor body formed on the base material; and

[0019] A wiring formed on the base material and connected to an end of the resistor body,

[0020] 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 connected in series with each other,

[0021] The wiring is arranged side by side with the elongated portion at one end in a second direction orthogonal to the first direction, and is connected to the one end of the elongated portion in the first direction,

[0022] The wiring includes a first metal layer and a second metal layer laminated on the first metal layer,

[0023] One end of the second metal layer in the first direction protrudes toward the one end side in the first direction compared to one end of a gap between the wiring and the elongated portion adjacent to the wiring.

[0024] <Effects of the present invention>

[0025] According to the disclosed technology, the strain limit of the strain gauge can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a top view illustrating a strain gauge according to the first embodiment.

[0027] Figure 2 is a cross-sectional view (one) illustrating a strain gauge according to the first embodiment.

[0028] Figure 3 is a diagram schematically showing a situation where cracks are generated in the resistor body and the wiring.

[0029] 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

[0030] Figure 5 is a partially enlarged top view of the vicinity of the connection portion between the resistor body and the wiring in a strain gauge of a comparative example.

[0031] Figure 6 is a diagram showing the experimental results of the strain limit.

[0032] Figure 7 is a cross-sectional view (two) illustrating a strain gauge according to the first embodiment. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments for implementing the present invention will be described with reference to the accompanying 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 may be omitted. In addition, in each figure, sometimes the X-axis, Y-axis, and Z-axis that are 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.

[0034] <First Embodiment>

[0035] Figure 1 is a top view showing the strain gauge of the first embodiment. Figure 2 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

[0036] 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 covering layer 60. The covering layer 60 can be provided as needed. It should be noted that, Figure 1 and Figure 2 in

[0037] 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, a top view means 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 means the shape of the object when observing the object in the normal direction.

[0038] 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 usage 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.

[0039] The base material 10 is formed of an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) 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.

[0040] 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 can be formed of an insulating resin film containing fillers such as silica or alumina.

[0041] As materials other than the resin of the base material 10, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite-based ceramics (CaTiO3, BaTiO3) can be cited. In addition, in addition to the above-mentioned crystalline materials, amorphous glass and the like can also be used as the material of the base material 10. In addition, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), and titanium can also be used. When using a metal, an insulating film is provided on the metal base material 10.

[0042] The resistor body 30 is a film formed on the base material 10 in a prescribed pattern. In the strain gauge 1, the resistor body 30 is a sensing portion that generates a resistance change when strained. The resistor body 30 can be formed directly on the upper surface 10a of the base material 10 or can be formed on the upper surface 10a of the base material 10 with another layer interposed therebetween. It should be noted that in Figure 1 , for convenience, the resistor body 30 is represented by a deep orange peel pattern.

[0043] The resistor body 30 includes a plurality of elongated portions 31 and a plurality of folded-back portions 32. In Figure 1 's example, the resistor body 30 includes 6 elongated portions 31 and 7 folded-back portions 32, but the number of the elongated portions 31 and the folded-back portions 32 is not limited to Figure 1 's example.

[0044] In the resistor body 30, a plurality of elongated portions 31 are arranged side by side with their longitudinal directions along the first direction X. Further, a plurality of bent portions 32 cross-connect the ends of adjacent elongated portions 31 among the plurality of elongated portions 31, thereby connecting the respective elongated portions 31 in series with each other. Thus, the resistor body 30 is configured to have a structure that zigzags back and forth as a whole. The longitudinal direction of the plurality of elongated portions 31, that is, the first direction X, becomes the grating direction, and the direction perpendicular to the grating direction, that is, the second direction Y, becomes the grating width direction.

[0045] In the resistor body 30, one end (X-side end) in the first direction X of the elongated portion 31 located at one end (Y-side end) in the second direction Y is bent in the Y- direction and reaches one end 30e1 in the grating width direction of the resistor body 30. Further, one end (X-side end) in the first direction X of the elongated portion 31 located at the other end (Y+ side end) in the second direction Y is bent in the Y+ direction and reaches the other end 30e2 in the grating direction of the resistor body 30. Each of the ends 30e1 and 30e2 is electrically connected to the electrode 50 via the wiring 40. In other words, the wiring 40 electrically connects each of the ends 30e1 and 30e2 in the grating width direction of the resistor body 30 to each of the electrodes 50. It should be noted that, although for convenience, Figure 1 the ends 30e1 and 30e2 in are indicated by dashed lines, the resistor body 30 and the first metal layer 41 (described later) of the wiring 40 can be integrally formed.

[0046] The resistor body 30 can be formed, for example, of 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 both Cr and Ni include Ni-Cr (nickel-chromium).

[0047] Here, the Cr mixed-phase film is a film mixed with Cr, CrN, Cr2N, etc. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

[0048] 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 or the like. 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. Further, 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.

[0049] In consideration of the difficulty in generating transverse sensitivity and measures against broken wires, 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.

[0050] For example, in the case where the resistor body 30 is a Cr mixed-phase film, by using α-Cr (α-chromium), which is a stable crystalline phase, as the main component, the stability of the strain characteristics can be improved. Also, for example, in the case where the resistor body 30 is a Cr mixed-phase film, by setting the main component of the resistor body 30 to 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).

[0051] In addition, in the case where the resistor body 30 is a Cr mixed-phase film, the CrN and Cr2N contained in the Cr mixed-phase film are preferably 20% by weight or less. Since the CrN and Cr2N contained in the Cr mixed-phase film are 20% by weight or less, a decrease in the strain rate of the strain gauge 1 can be suppressed.

[0052] In addition, the ratio of CrN and Cr2N in the Cr mixed-phase film is preferably such that the ratio of Cr2N to the total weight of CrN and Cr2N is 80% by weight or more and less than 90%. Further, this ratio is more preferably such that the ratio of Cr2N to the total weight of CrN and Cr2N is 90% by weight or more and less than 95%. Cr2N has semiconductor properties. Therefore, by setting the ratio of Cr2N to be greater than 90% and less than 95%, the decrease in TCR (negative TCR) becomes more significant. Further, by setting the ratio of Cr2N to be greater than 90% and less than 95%, the ceramization of the resistor body 30 can be reduced, so that the resistor body 30 is less likely to undergo brittle fracture.

[0053] On the other hand, CrN has the advantage of chemical stability. By including more CrN in the Cr mixed-phase 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 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 Ns may escape from the film. When the unstable N escapes from the film, the film stress of the Cr mixed-phase film may change.

[0054] In the strain gauge 1, when using the Cr mixed-phase film as the material of the resistor 30, high sensitivity and miniaturization can be achieved. For example, when the output of a conventional strain gauge is about 0.04 mV / 2V, when using the Cr mixed-phase film as the material of the resistor 30, an output of 0.3 mV / 2V or more can be obtained. In addition, when the size (strain length × strain width) of a conventional strain gauge is about 3 mm × 3 mm, the size (strain length × strain width) when using the Cr mixed-phase film as the material of the resistor 30 can be miniaturized to about 0.3 mm × 0.3 mm.

[0055] 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 folding 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 folding portion 32.

[0056] 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 whole 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 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.

[0057] The electrodes 50 are formed on the substrate 10, are electrically connected to the resistor 30 via the wiring 40, are, for example, wider than the wiring 40, and are formed in a substantially rectangular shape. The electrodes 50 are a pair of electrodes for outputting the change in the resistance value of the resistor 30 caused by strain to the outside, and are, for example, joined with leads for external connection and the like.

[0058] 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 30e1 and 30e2 of the resistor body 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 may also be formed to have the same width as the wiring 40. It should be noted that Figure 1 in Figure 1 , for convenience, the first metal layers 41 and 51 are represented by a pebble-grain pattern having the same density as the resistor body 30, and the second metal layers 42 and 52 are represented by a pebble-grain pattern having a lower density than the resistor body 30.

[0059] 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.

[0060] The second metal layer 42 and the second metal layer 52 may be integrally formed of the same material or formed of different materials. A material having a lower volume resistivity than the resistor body 3( the first metal layers 41 and 51) may be selected as the material of the second metal layers 42 and 52. Such materials may be, for example, alloys obtained by appropriately laminating Cu, Ni, Al, Ag, Au, Pt, etc., or any of these metals, compounds of any of these metals, or laminated films of any of these metals, alloys, and compounds. In particular, it is preferable to use Cu or a Cu alloy, Al or Ag, Au, CrMn, etc. as the materials of the second metal layers 42 and 52. The thicknesses of the second metal layers 42 and 52 are not particularly limited and may be appropriately selected according to the purpose. The thicknesses of the second metal layers 42 and 52 may be, for example, about 0.5 μm to 5 μm.

[0061] One or more other metal layers may be further laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be configured as a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, the second metal layer 52 may be configured as a copper layer, and a palladium layer and a gold layer may 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.

[0062] Note that, although for convenience, the resistor body 30, the first metal layer 41, and the first metal layer 51 are given different reference numerals, 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.

[0063] Therefore, the wiring 40 has a structure in which a second metal layer 42 formed of a material having a volume resistivity lower than that of the first metal layer 41 is laminated on the first metal layer 41 formed of the same material as the resistor body 30. 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.

[0064] 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 a local region where the resistor body 30 is formed. Therefore, the strain detection accuracy of the resistor body 30 can be improved.

[0065] In particular, in a high-sensitivity strain gauge having a strain rate of 10 or more using a Cr mixed-phase film as the resistor body 30, by making the resistance of the wiring 40 lower than the resistance of the resistor body 30, the substantial sensing portion is limited to the local region 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.

[0066] As needed, a 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 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 (e.g., silicone resin, polyolefin resin). Note 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 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.

[0067] Figure 3 is a diagram schematically showing a case where cracks are generated 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, asFigure 3 As shown, crack C tends to extend substantially along the second direction Y near the end of the first direction X of the second metal layer 42 that constitutes the wiring 40.

[0068] Figure 4 is Figure 1 a partial enlarged top view near the connection portion between the resistor body and the wiring. As Figure 4 shown, in the strain gauge 1, in a top view, the end on the one end side (X-side) of the first direction X of the second metal layer 42 protrudes toward the one end side (X-side) of the first direction X more than the end on the one end side (X-side) of 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 on the one end side of the first direction X of the second metal layer 42 protrudes toward the one end side of the first direction X with respect to the end on the one end side of 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 on the one end side of the first direction X of the second metal layer 42 and the end on the one end side of the first direction X of the gap between the adjacent elongated portion 31 can be arbitrary.

[0069] Figure 5 is a partial enlarged top view near the connection portion between the resistor body and the wiring in the strain gauge of the comparative example. In Figure 5 the comparative example of Figure 4 shown, the length L1 is 0. That is, in Figure 5 the comparative example of Figure 3 shown, in the first direction X, the end on the one end side of the first direction X of the second metal layer 42 and the end on the one end side of the first direction X of the gap S are located at the same position. In this case, when the crack C as shown in

[0070] occurs, since the wiring 40 and the elongated portion 31 adjacent to the wiring 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 shown, the length L1 > 0, so when the crack C as shown in Figure 3 occurs, the wiring 40 and the elongated portion 31 adjacent to the wiring 40 remain electrically connected and do not get disconnected. Therefore, the strain gauge can continue to be used as a strain gauge. In Figure 4 the length L1 is preferably 1 μm or more. Thereby, 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.

[0071] In Figure 4Among them, the length L1 is preferably greater than or equal to the length L2 in the second direction Y of the elongated portion 31 (i.e., the width of the elongated portion 31). The length in the second direction Y of the elongated portion 31 is preferably 5 μm or more. That is, the length L1 is preferably 5 μm or more. This further ensures the energization width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40, making it easier to maintain the electrical connection.

[0072] In addition, in Figure 4 Among them, the length L3 in the first direction X between the end on the one - end side in the first direction X of the first metal layer 41 and the end on the one - end side in the first direction X of the second metal layer 42 is preferably 5 μm or more, and more preferably 10 μm or more.

[0073] In the manufacturing process of the strain gauge 1, the first metal layer 41 and the second metal layer 42 are etched to form patterns. 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, when providing the covering layer 60 covering the wiring 40, the adhesion between the wiring 40 and the covering layer 60 will decrease. 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 - 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 copper is oxidized and copper deteriorates, reducing the reliability of the strain gauge 1.

[0074] Therefore, in a plan view, the outer edge of the first metal layer 41 preferably protrudes 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 relative 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 copper can be prevented.

[0075] 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 Among them, 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.

[0076] In Figure 6 Among them, 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 it can no longer function as a strain gauge. From Figure 6The results are confirmed that when L1 = 5 μm, the strain limit is increased by about 1.4 times compared to when L1 = 0 μm.

[0077] It should be noted that according to other research by the inventors and others, 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, the strain limit is further reduced compared to Figure 6 as shown when L1 = 0 μm. 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 stacking 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.

[0078] That is, from the viewpoint of increasing the strain limit, the wiring 40 is preferably formed by stacking 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.

[0079] [Manufacturing method of strain gauge]

[0080] In the strain gauge 1 according to the present embodiment, a resistor 30, wiring 40, electrodes 50, and a cover layer 60 are formed on a 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 members.

[0081] Next, the manufacturing method of the strain gauge 1 will be described. To manufacture the strain gauge 1, first, a substrate 10 is prepared to form a metal layer (for convenience, referred to as metal layer A) on the upper surface 10a of the substrate 10. The metal layer A is the layer that is finally patterned into the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of the metal layer A are similar to those of the resistor 30 and the like.

[0082] For example, the metal layer A can be formed by magnetron sputtering using a target made of a raw material capable of forming the metal layer A. The reactive sputtering method, evaporation method, arc ion plating method, pulsed laser deposition method, etc. can also be used instead of the magnetron sputtering method to form the metal layer A.

[0083] Note that the 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 the lower layer in this way, the strain characteristics of the strain gauge 1 can be stabilized.

[0084] In this application, the functional layer refers to a layer that at least has the function of promoting the crystal growth of the metal layer A (resistor 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 substrate 10 and / or the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer can also have other functions.

[0085] The insulating resin film constituting the substrate 10 sometimes contains oxygen or moisture, and Cr sometimes forms a self-oxidizing film. Therefore, especially when the metal layer A contains Cr, it is preferable to form a functional layer having the function of preventing the metal layer A from being oxidized.

[0086] In this way, by providing a 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, 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.

[0087] 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.

[0088] Figure 7 It is a cross-sectional view (part two) of the strain gauge illustrating the first embodiment. Figure 7 It shows the cross-sectional shape of the strain gauge 1 when the functional layer 20 is provided as the lower layer of the resistor body 30, the wiring 40, and the electrode 50.

[0089] The pattern of the planar shape of the functional layer 20 may be substantially the same as the planar shapes of the resistor body 30, the wiring 40, and the electrode 50. However, the planar shapes of the functional layer 20 and the resistor body 30, the wiring 40, and the electrode 50 may also 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 shapes of the resistor body 30, the wiring 40, and the electrode 50. In this case, the functional layer 20 may be formed in a uniform and flat manner, for example, in the regions where the resistor body 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.

[0090] Next, a second metal layer 42 and a 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 a known photolithography method, for example.

[0091] 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 having the same planar shape as Figure 1 the resistor body 30, the wiring 40, and the electrode 50. Then, using the photoresist as an etching mask, the metal layer A exposed from the photoresist is removed by wet etching or the like. Next, by removing the photoresist, the resistor body 30, the wiring 40, and the electrode 50 having the planar shape shown in Figure 1 can be formed. At this time, the shape of the photoresist is controlled so that the first metal layer 41 is not over-etched relative to the second metal layer 42.

[0092] After forming the resistor body 30, the wiring 40, and the electrode 50, a covering layer 60 is formed on the upper surface 10a of the substrate 10 as needed. The covering layer 60 covers the resistor body 30 and the wiring 40, and the electrode 50 may be exposed from the covering layer 60. For example, a semi-cured thermosetting insulating resin film is laminated on the upper surface 10a of the substrate 10 in such a manner as to cover the resistor body 30 and the wiring 40 and expose the electrode 50, and then the insulating resin film is heated to cure it, thereby forming the covering layer 60. Through the above steps, the strain gauge 1 is completed.

[0093] The preferred embodiments and the like have been described in detail above. However, the strain gauge of the present invention is not limited to the above-described embodiments and the like. For example, various modifications and substitutions can be made to the strain gauge of the above-described embodiments and the like without departing from the scope described in the claims.

[0094] 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.

[0095] Description of Reference Numerals

[0096] 1 Strain gauge; 10 Base material; 10a Upper surface; 20 Functional layer; 30 Resistive body; 30e1, 30e2 Terminals; 31 Elongated portion; 32 Folded-back 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 a wiring formed on the base material and connected to a terminal portion of the resistor body, wherein the wiring includes a first portion, and in a plan view, the first portion of the wiring is arranged side by side with the resistor body with a gap therebetween in a grating width direction, the wiring includes a first metal layer and a second metal layer laminated on the first metal layer, at the first portion of the wiring, the second metal layer protrudes toward a side where the resistor body is disposed in a grating direction compared to an end of the gap.

2. A strain gauge, comprising: a base material; a resistor body formed on the base material; and a wiring formed on the base material and connected to an end of the resistor body, the resistor body includes a plurality of elongated portions, the plurality of elongated portions are arranged side by side with their length directions along a first direction and are connected in series with each other, the wiring is arranged side by side with the elongated portion at one end in a second direction orthogonal to the first direction and is connected to the one end of the elongated portion in the first direction, the wiring includes a first metal layer and a second metal layer laminated on the first metal layer, one end of the second metal layer in the first direction protrudes toward the one end side in the first direction compared to one end of the gap between the wiring and the adjacent elongated portion.

3. The strain gauge according to claim 1 or 2, wherein at least a part of an outer edge of the first metal layer is exposed from the second metal layer.

4. The strain gauge according to claim 1 or 2, wherein the second metal layer is formed of a material having a volume resistivity lower than that of the first metal layer.

5. The strain gauge according to claim 1 or 2, wherein the second metal layer is formed of a material having better stretchability than that of the first metal layer.

6. The strain gauge according to claim 1 or 2, wherein the first metal layer is integrally formed of the same material as the resistor body.

7. The strain gauge according to claim 1 or 2, wherein the resistor body is formed of a film containing Cr, CrN, and Cr2N.

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