Strain gauge

Abstract

To improve the strain limit of a strain gauge.SOLUTION: The strain gauge has a base, a resistor formed on the base, and wiring formed on the base and connected to a terminal end portion of the resistor, wherein the wiring includes a first portion juxtaposed with the resistor with a gap in the grid width direction in a plan view, and, the wiring includes a first metal layer and a second metal layer laminated on the first metal layer, and the second metal layer in the first portion of the wiring protrudes toward a side where the resistive element is disposed in a grid direction as compared with an end portion of the gap.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, strain gauges that are attached to an object to be measured have been known. The strain gauges have resistors that detect strain, and the resistors are formed on, for example, an insulating resin. The resistors are connected to electrodes via wiring, for example (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0004] Strain gauges are attached to a strain-generating body and detect the amount of strain in the body by expanding and contracting in response to the body's movement. Therefore, in order to detect larger amounts of strain, the strain gauge itself must not be damaged in the process of expansion and contraction, and a higher strain limit is required.

[0005] The present invention has been made in view of the above points, and has as its object to improve the strain limit of a strain gauge. [Means for solving the problem]

[0006] A strain gauge according to one embodiment of the present disclosure includes a substrate, a resistor formed on the substrate, and wiring formed on the substrate and connected to an end portion of the resistor, the wiring including a first portion juxtaposed to the resistor in a grid width direction with a gap therebetween in a plan view, the wiring including a first metal layer and a second metal layer stacked on the first metal layer, and the second metal layer in the first portion of the wiring protruding toward the side where the resistor is located in the grid direction compared to the end of the gap. [Effects of the Invention]

[0007] According to the disclosed technology, the strain limit of the strain gauge can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 3] 10A and 10B are diagrams illustrating a state in which cracks occur in a resistor and wiring. [Figure 4] 2 is a partially enlarged plan view of the vicinity of the connection portion between the resistor and the wiring in FIG. 1. [Figure 5] FIG. 10 is a partially enlarged plan view of the vicinity of a connection portion between a resistor and a wire in a strain gauge according to a comparative example. [Figure 6] FIG. 10 is a diagram showing experimental results of strain limits. [Figure 7] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the invention will be described with reference to the drawings. In each drawing, the same components may be assigned the same reference numerals. Furthermore, in the description of each drawing, descriptions of components that are the same as components already described may be omitted. Furthermore, in each drawing, mutually orthogonal X-, Y-, and Z-axes may be defined. In this case, in the X-axis direction, the side of the starting point (base) of the arrow may be referred to as the X-side, and the side of the ending point (arrowhead) of the arrow may be referred to as the X+ side. The same applies to the Y-axis and Z-axis directions. Furthermore, the direction parallel to the X-axis may be referred to as the first direction X, and the direction parallel to the Y-axis may be referred to as the second direction Y.

[0010] First Embodiment Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1.

[0011] 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. The cover layer 60 can be provided as needed. For convenience, only the outer edge of the cover layer 60 is shown by a dashed line in FIGS. 1 and 2. First, each part of the strain gauge 1 will be described in detail.

[0012] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 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." The surface located on the upper side of each portion is referred to as the "upper surface," and the surface located on the lower side of each portion is referred to as the "lower surface." However, the strain gauge 1 can also be used upside down. The strain gauge 1 can also be positioned at any angle. A planar view refers to viewing an object in a normal direction from above to below the upper surface 10a of the substrate 10. A planar shape refers to the shape of the object when viewed in the normal direction.

[0013] The substrate 10 is a member that serves as a base layer for forming the resistor 30 and the like. The substrate 10 is flexible. There are no particular limitations on the thickness of the substrate 10, and it may be determined appropriately depending on the intended use of the strain gauge 1, etc. For example, the thickness of the substrate 10 may be approximately 5 μm to 500 μm. A flexure element may be bonded to the underside of the strain gauge 1 via an adhesive layer or the like. From the standpoints of strain transmission from the surface of the flexure element to the sensing part and dimensional stability against environmental changes, the thickness of the substrate 10 is preferably within the range of 5 μm to 200 μm. From the standpoint of insulation, the thickness of the substrate 10 is preferably 10 μm or more.

[0014] The substrate 10 is formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0015] When the substrate 10 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the substrate 10 may be formed from an insulating resin film containing a filler such as silica or alumina.

[0016] Materials other than resin for the substrate 10 include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3). In addition to the crystalline materials described above, amorphous glass or the like may also be used as the material for the substrate 10. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. When a metal is used, an insulating film is provided on the metallic substrate 10.

[0017] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10. In the strain gauge 1, the resistor 30 is a sensing part that receives strain and generates a resistance change. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 as having a dense matte finish.

[0018] The resistor 30 includes a plurality of elongated portions 31 and a plurality of folded portions 32. In the example of Fig. 1, the resistor 30 includes six elongated portions 31 and seven folded portions 32, but the number of elongated portions 31 and folded portions 32 is not limited to that in the example of Fig. 1.

[0019] In the resistor 30, the multiple elongated portions 31 are arranged side by side with their longitudinal directions aligned in a first direction X. The multiple folded portions 32 alternately connect the ends of adjacent elongated portions 31 among the multiple elongated portions 31, connecting the individual elongated portions 31 in series. This gives the resistor 30 a zigzag folded structure as a whole. The first direction X, which is the longitudinal direction of the multiple elongated portions 31, is the grid direction, and the second direction Y, which is perpendicular to the grid direction, is the grid width direction.

[0020] In the resistor 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 bends in the Y- direction and reaches one end 30e1 of the resistor 30 in the grid width direction. Furthermore, one end (X-side end) of the elongated portion 31 located at the other end (Y+side end) in the second direction Y bends in the Y+ direction and reaches the other end 30e2 of the resistor 30 in the grid direction. Each end 30e1 and 30e2 are electrically connected to the electrode 50 via the wiring 40. In other words, the wiring 40 electrically connects each end 30e1 and 30e2 of the resistor 30 in the grid width direction to each electrode 50. While the ends 30e1 and 30e2 are shown by dashed lines in FIG. 1 for convenience, the resistor 30 and a first metal layer 41 (described later) of the wiring 40 can be integrally formed.

[0021] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0022] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed together. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0023] The thickness of the resistor 30 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1, etc. For example, the thickness of the resistor 30 may be approximately 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. Furthermore, 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 internal stress of the film constituting the resistor 30 are reduced.

[0024] In order to prevent lateral sensitivity and to prevent 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, and more preferably 5 μm to 50 μm.

[0025] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, when the resistor 30 is a Cr mixed-phase film, the resistor 30 can have an α-Cr main component, thereby enabling the gauge factor of the strain gauge 1 to be 10 or more, and the temperature coefficient of gauge factor (TCS) and the temperature coefficient of resistance (TCR) to be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, the term “main component” refers to a component that accounts for 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, the resistor 30 more preferably contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0026] Furthermore, 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, which can suppress a decrease in the gauge factor of the strain gauge 1.

[0027] Furthermore, the ratio of CrN to Cr2N in the Cr mixed phase film is preferably 80 wt% or more but less than 90 wt% of the total weight of CrN and Cr2N. More preferably, the ratio is 90 wt% or more but less than 95 wt% of the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the Cr2N ratio to 90 wt% or more but less than 95 wt%, the decrease in TCR (negative TCR) becomes even more pronounced. Furthermore, by setting the Cr2N ratio to 90 wt% or more but less than 95 wt%, the resistor 30 is less likely to become ceramic, making it less susceptible to brittle fracture.

[0028] 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 unstable N being generated can be reduced, resulting in a stable strain gauge. Here, "unstable N" refers to trace amounts of N2 or atomic N that can exist in the Cr mixed-phase film. This unstable N can escape from the film depending on the external environment (e.g., high-temperature environment). When unstable N escapes from the film, the film stress of the Cr mixed-phase film can change.

[0029] In the strain gauge 1, when a Cr mixed-phase film is used as the material for the resistor 30, high sensitivity and miniaturization can be achieved. For example, while the output of a conventional strain gauge was approximately 0.04 mV / 2 V, an output of 0.3 mV / 2 V or more can be obtained when a Cr mixed-phase film is used as the material for the resistor 30. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was approximately 3 mm × 3 mm, when a Cr mixed-phase film is used as the material for the resistor 30, the size (gauge length × gauge width) can be reduced to approximately 0.3 mm × 0.3 mm.

[0030] Two wirings 40 are formed on the substrate 10. One of the wirings 40 is juxtaposed to the elongated portion 31 located 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 of the elongated portion 31 (the end on the X- side) via a folded portion 32. The other of the wirings 40 is juxtaposed to the elongated portion 31 located 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 of the elongated portion 31 (the end on the X- side) via a folded portion 32.

[0031] The wiring 40 only needs to be juxtaposed to 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 juxtaposed to the elongated portion 31. In other words, the wiring 40 is not limited to being linear, and can have any pattern in which it is juxtaposed to the elongated portion 31 at least on one end side in the first direction X. Furthermore, the wiring 40 can have any length.

[0032] The electrodes 50 are formed on the substrate 10 and electrically connected to the resistor 30 via the wiring 40, and are formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain, and are connected, for example, to lead wires for external connection.

[0033] Each wiring 40 has a first metal layer 41 and a second metal layer 42 laminated on the first metal layer 41. 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 terminations 30e1 and 30e2 of the resistor 30 via the first metal layer 41 of the wiring 40. The first metal layer 51 is formed in a substantially rectangular shape in a plan view. The first metal layer 51 may be formed to have the same width as the wiring 40. Note that, for convenience, in FIG. 1, the first metal layers 41 and 51 are shown with a matte pattern having the same density as the resistor 30, and the second metal layers 42 and 52 are shown with a matte pattern having a lower density than the resistor 30.

[0034] 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 excluding 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. Furthermore, in a plan view, the outer edge of the first metal layer 51 is exposed from the second metal layer 52.

[0035] The second metal layer 42 and the second metal layer 52 may be formed integrally using the same material, or may be formed using different materials. The material of the second metal layers 42 and 52 may be selected from materials having a lower volume resistivity than the resistor 30 (the first metal layers 41 and 51). Examples of such materials include Cu, Ni, Al, Ag, Au, Pt, etc., alloys of any of these metals, compounds of any of these metals, and laminated films of any of these metals, alloys, and compounds. It is particularly preferable to use Cu, Cu alloys, Al, 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 depending on the purpose. The thickness of the second metal layers 42 and 52 may be, for example, approximately 0.5 μm to 5 μm.

[0036] One or more other metal layers may be laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be 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 a copper layer, and a palladium layer and a gold layer may be laminated in this order on the upper surface of the copper layer. By using a gold layer as the uppermost layer of the electrode 50, the solder wettability of the electrode 50 can be improved.

[0037] Although the resistor 30, the first metal layer 41, and the first metal layer 51 are given different reference numerals for convenience, they can be integrally formed in the same process using the same material. Therefore, the resistor 30, the first metal layer 41, and the first metal layer 51 may have approximately the same thickness. Furthermore, although the second metal layer 42 and the second metal layer 52 are given different reference numerals for convenience, they can be integrally formed in the same process using the same material. Therefore, the second metal layer 42 and the second metal layer 52 may have approximately the same thickness.

[0038] In this way, the wiring 40 has a structure in which a second metal layer 42 formed from a material having a lower volume resistivity than the first metal layer 41 is stacked on a first metal layer 41 made of the same material as the resistor 30. Therefore, the resistance of the wiring 40 is lower than that of the resistor 30, and the wiring 40 can be prevented from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

[0039] In other words, by forming the wiring 40 using a material with a volume resistivity lower than that of the resistor 30, the actual sensitive part of the strain gauge 1 can be limited to the local area where the resistor 30 is formed, thereby improving the accuracy of strain detection by the resistor 30.

[0040] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed-phase film as the resistor 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensitive part to the local region where the resistor 30 is formed has a significant effect on improving strain detection accuracy. Also, making the wiring 40 lower in resistance than the resistor 30 has the effect of reducing lateral sensitivity.

[0041] The cover layer 60 is provided, as necessary, on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50. Examples of materials for the cover layer 60 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin and polyolefin resin). The cover layer 60 may contain a filler or a pigment. The thickness of the cover layer 60 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the cover layer 60 can be approximately 2 μm to 30 μm. The provision of the cover layer 60 can prevent mechanical damage to the resistor 30. The provision of the cover layer 60 can also protect the resistor 30 from moisture and the like.

[0042] 3 is a diagram showing a schematic diagram of cracks occurring in the resistor and wiring. As the strain applied to the strain gauge 1 increases, cracks occur in the resistor 30 and the first metal layer 41. According to the inventors' investigation, as shown in FIG. 3, cracks C tend to occur near the end of the second metal layer 42 constituting the wiring 40 in the first direction X, and extend approximately in the second direction Y.

[0043] 4 is a partially enlarged plan view of the vicinity of the connection between the resistor and the wiring in FIG. 1. As shown in FIG. 4, in the strain gauge 1, in a plan view, the end portion on one end side (X-side) in the first direction X of the second metal layer 42 protrudes toward the one end side (X-side) in the first direction X further than the end portion on 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. In other words, when the length of the end portion on one end side of the second metal layer 42 protruding toward the one end side in the first direction X from the end portion on one end side of the gap S in the first direction X is L1, the length L1 is greater than 0. Note that in the strain gauge 1, the positional relationship between the end portion on one end side in the first direction X of the second metal layer 42 and the end portion on one end side in the first direction X of the gap between adjacent elongated portions 31 may be arbitrary in a plan view.

[0044] Fig. 5 is a partially enlarged plan view of the vicinity of the connection between the resistor and the wiring in a strain gauge according to a comparative example. In the comparative example of Fig. 5, the length L1 shown in Fig. 4 is 0. That is, in the comparative example of Fig. 5, the end of the second metal layer 42 on one side in the first direction X is at the same position as the end of the gap S on one side in the first direction X. In this case, if a crack C as shown in Fig. 3 occurs, the wire 40 and the elongated portion 31 adjacent to the wire 40 will be disconnected, preventing current from flowing, and the strain gauge according to the comparative example will no longer function as a strain gauge.

[0045] In contrast, in the strain gauge 1 shown in Fig. 4, since the length L1 is greater than 0, even if a crack C as shown in Fig. 3 occurs, the electrical connection between the wiring 40 and the elongated portion 31 adjacent to the wiring 40 is maintained without disconnection, and the strain gauge 1 can continue to function as a strain gauge. In Fig. 4, the length L1 is preferably 1 µm or more. This ensures a sufficient electrical width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40, making it easier to maintain the electrical connection.

[0046] 4, it is more preferable that the length L1 is equal to or greater than the length L2 of the elongated portion 31 in the second direction Y (i.e., the width of the elongated portion 31). It is preferable that the length of the elongated portion 31 in the second direction Y is equal to or greater than 5 μm. That is, it is more preferable that the length L1 is equal to or greater than 5 μm. This further ensures a sufficient electrical width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40, making it easier to maintain electrical connection.

[0047] In addition, in FIG. 4, the length L3 in the first direction X between the end portion on one end side in the first direction X of the first metal layer 41 and the end portion on 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.

[0048] In the manufacturing process of the strain gauge 1, the first metal layer 41 and the second metal layer 42 are etched and patterned. However, during etching, the first metal layer 41 may be over-etched relative to the second metal layer 42. If the end of the second metal layer 42 protrudes horizontally beyond the end of the first metal layer 41 due to over-etching, when a cover layer 60 is provided to cover the wiring 40, the adhesion between the wiring 40 and the cover layer 60 may be reduced. For example, if the first metal layer 41 of the wiring 40 is formed of a Cr mixed-phase film and the second metal layer 42 is formed of copper, the Cr mixed-phase film may be over-etched by approximately 1 to 2 μm relative to the copper during etching in the manufacturing process of the strain gauge 1. Furthermore, if the end of the second metal layer 42 protrudes horizontally beyond the end of the first metal layer 41 due to over-etching, for example, if the second metal layer 42 is formed of copper, the protruding portion of the copper may oxidize, degrading the copper and reducing the reliability of the strain gauge 1.

[0049] Therefore, in plan view, it is preferable that the outer edge of the first metal layer 41 is exposed from the second metal layer 42, and the length L3 is preferably 5 μm or more, and more preferably 10 μm or more. This makes it possible to prevent the first metal layer 41 from being over-etched relative to the second metal layer 42, thereby maintaining adhesion between the wiring 40 and the cover layer 60. Furthermore, even if the second metal layer 42 is made of copper, it is possible to prevent the copper from oxidizing and deteriorating.

[0050] Fig. 6 is a diagram showing the experimental results of strain limits, plotting the minimum strain limits of multiple test strain gauges. In Fig. 4, L1 = 0 μm indicates the experimental results of the strain gauge according to the comparative example. On the other hand, L1 = 1 μm indicates the experimental results of the strain gauge 1 according to the first embodiment.

[0051] In Figure 6, the vertical axis shows the strain limit [μST]. The strain limit is the mechanical strain value at which applying strain to a strain gauge causes wire breakage and the gauge is no longer able to function as a strain gauge. The results in Figure 6 confirm that when L1 = 5 μm, the strain limit is approximately 1.4 times higher than when L1 = 0 μm.

[0052] According to another study by the inventors, it is not preferable not to laminate the second metal layer 42 on the first metal layer 41. When the second metal layer 42 is not laminated on the first metal layer 41, the strain limit is further reduced compared to the case where L1 = 0 μm shown in FIG. 6. For example, when the first metal layer 41 is a Cr mixed-phase film, the Cr mixed-phase film has poor elasticity, so it is thought that the strain limit will be lower if the wiring 40 is formed only from the Cr mixed-phase film. The strain limit can be improved by laminating the second metal layer 42 made of a material, such as copper, that has better elasticity than the Cr mixed-phase film on the first metal layer 41 made of the Cr mixed-phase film.

[0053] That is, from the viewpoint of improving the strain limit, it is preferable that the wiring 40 has a laminated structure of a first metal layer 41 and a second metal layer 42, and it is preferable that the second metal layer 42 is formed from a material that is more elastic than the first metal layer 41. That is, it is preferable that the second metal layer is formed from a material that has a lower volume resistivity than the first metal layer and more elastic than the first metal layer 41. When the first metal layer is a Cr mixed phase film, examples of materials that have a lower volume resistivity than the first metal layer and more elastic than the first metal layer 41 include gold, silver, and aluminum in addition to copper.

[0054] [Strain gauge manufacturing method] In the strain gauge 1 according to this embodiment, a resistor 30, wiring 40, electrodes 50, and a cover layer 60 are formed on a substrate 10. Note that another layer (such as a functional layer described below) may be formed between the substrate 10 and these layers of components.

[0055] The following describes a method for manufacturing the strain gauge 1. To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30 and the like described above.

[0056] The metal layer A can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, the metal layer A may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0057] Alternatively, a base layer may be formed on the upper surface 10a of the substrate 10 before the metal layer A is formed. For example, a functional layer having a predetermined thickness may be vacuum-deposited on the upper surface 10a of the substrate 10 by conventional sputtering. By providing a base layer in this manner, the gauge characteristics of the strain gauge 1 can be stabilized.

[0058] In the present application, the functional layer refers to a layer having the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen or moisture contained in substrate 10 and / or the function of improving adhesion between substrate 10 and metal layer A. The functional layer may also have other functions.

[0059] The insulating resin film constituting the substrate 10 may contain oxygen and moisture, and Cr may form a self-oxidized film. Therefore, when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing oxidation of the metal layer A.

[0060] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 is improved. Furthermore, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0061] Examples of materials for the functional layer include one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0062] 7 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. Fig. 7 shows the cross-sectional shape of the strain gauge 1 when a functional layer 20 is provided as an underlying layer for the resistor 30, the wiring 40, and the electrodes 50.

[0063] The planar shape of the functional layer 20 may be patterned to be substantially the same as the planar shapes of the resistor 30, the wiring 40, and the electrodes 50, for example. However, the planar shapes of the functional layer 20 and the resistor 30, the wiring 40, and the electrodes 50 do not have to be substantially the same. For example, when the functional layer 20 is formed from an insulating material, the functional layer 20 may be patterned to be different from the planar shapes of the resistor 30, the wiring 40, and the electrodes 50. In this case, the functional layer 20 may be formed in a solid shape in the region where the resistor 30, the wiring 40, and the electrodes 50 are formed, for example. Alternatively, the functional layer 20 may be formed in a solid shape over the entire upper surface of the substrate 10.

[0064] 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 well-known photolithography method.

[0065] Next, a photosensitive resist is formed on the upper surfaces of the metal layer A, the second metal layer 42, and the second metal layer 52, and the resist is exposed and developed to be patterned into a planar shape similar to the resistor 30, wiring 40, and electrode 50 in FIG. 1. Then, using the resist as an etching mask, the metal layer A exposed from the resist is removed by wet etching or the like. Next, the resist is removed, thereby forming the resistor 30, wiring 40, and electrode 50 in the planar shape shown in FIG. 1. At this time, the shape of the resist is controlled so that the first metal layer 41 is not over-etched relative to the second metal layer 42.

[0066] After forming the resistor 30, wiring 40, and electrodes 50, a 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 wiring 40, but the electrodes 50 may be exposed from the cover layer 60. For example, the cover layer 60 can be formed by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and wiring 40 and expose the electrodes 50, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 1 is completed.

[0067] The preferred embodiments have been described above in detail. However, the strain gauge according to the present disclosure is not limited to the above-described embodiments. For example, various modifications and substitutions can be made to the strain gauge according to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0068] 1 strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 termination, 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 substrate; a resistor formed on the substrate; a wiring formed on the substrate and connected to a terminal portion of the resistor; the wiring includes a first portion that is juxtaposed to the resistor with a gap in a grid width direction in a plan view, the wiring includes a first metal layer and a second metal layer stacked on the first metal layer; A strain gauge, wherein the second metal layer in the first portion of the wiring protrudes toward the side where the resistor is arranged in the grid direction compared to the end of the gap.

2. A substrate; a resistor formed on the substrate; a wiring formed on the substrate and connected to an end of the resistor; the resistor includes a plurality of elongated portions that are arranged side by side with their longitudinal directions in a first direction and are connected in series with each other; the wiring is juxtaposed to the elongated portion located at one end in a second direction perpendicular to the first direction, and is connected to the elongated portion at one end in the first direction; the wiring includes a first metal layer and a second metal layer stacked on the first metal layer; A strain gauge, wherein one end of the second metal layer in the first direction protrudes toward the one end in the first direction beyond one end in the first direction of a gap between the wiring and the elongated portion adjacent to the wiring.

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

4. 3. The strain gauge according to claim 1, wherein the second metal layer is made 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 from a material having greater elasticity than the first metal layer.

6. 3. The strain gauge according to claim 1, wherein the first metal layer is made of the same material as the resistor and is integral with the resistor.

7. The resistor is made of Cr, CrN, and Cr ２ 3. The strain gauge according to claim 1, which is formed from a film containing N.

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