Strain gauge

Abstract

To improve a strain limit of a strain gauge.SOLUTION: A strain gauge includes: a base material; a resistor formed on the base material; and two wires formed on the base material and connected in series across both the ends of the resistor. The resistor includes multiple slender parts that are juxtaposed while a longer direction faces a first direction and are connected in series mutually. One of the wires is juxtaposed in the slender part positioned in one end in a second direction orthogonal to the first direction and is connected to one end in the first direction of the slender part, the other of the wires is juxtaposed in the slender part positioned in the other end in the second direction and is connected to one end in the first direction of the slender part, and the respective wires include a first metal layer, and a second metal layer that is laminated on the first metal layer and is formed from a material having smaller volume resistivity than the first metal layer. An outer edge of the first metal layer is exposed from the second metal layer in a plan view, and an end in one end side in the first direction of the second metal layer projects toward one end side in the first direction relative to an end in one end side in the first direction of a gap between the first metal layer, and the slender parts adjacent to the first metal layer in a plan view.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The strain gauge is attached to a strained body and detects the amount of strain of the strained body by expanding and contracting following the movement of the strained body. Therefore, in order to detect a larger amount of strain, the strain gauge itself must not be damaged during the expansion and contraction process, and a higher strain limit is required.

[0005] The present invention has been made in view of the above points, and an object thereof is to improve the strain limit of the strain gauge.

Means for Solving the Problems

[0006] A strain gauge according to one embodiment of the present disclosure comprises a base material, a resistor formed on the base material, and two wires formed on the base material and connected in series to both ends of the resistor, wherein the resistor includes a plurality of elongated portions arranged side by side with their longitudinal direction oriented in a first direction and connected in series to one another, one of the wires is arranged side by side with the elongated portion located at one end in a second direction perpendicular to the first direction and connected to one end of the elongated portion in the first direction, and the other of the wires is arranged side by side with the elongated portion located at the other end in the second direction The wiring is arranged side by side and connected to one end of the elongated portion in the first direction, and each wiring comprises a first metal layer and a second metal layer laminated on the first metal layer and made of a material having a lower volume resistivity than the first metal layer, wherein in plan view, the outer edge of the first metal layer is exposed from the second metal layer, and in plan view, the end of the second metal layer on the first end in the first direction protrudes on the first end side of the gap between the first metal layer and the elongated portion adjacent to the first metal layer. [Effects of the Invention]

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

[0008] [Figure 1] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 2] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 3] This diagram schematically illustrates how cracks can occur in resistors and wiring. [Figure 4] This is a partially enlarged plan view of the vicinity of the connection point between the resistor and the wiring in Figure 1. [Figure 5] This is a partially enlarged plan view of the vicinity of the connection between the resistor and the wiring in a strain gauge relating to a comparative example. [Figure 6] This figure shows the experimental results of the strain limit. [Figure 7] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same components may be denoted by the same reference numeral. Also, in the description of each drawing, the description of components that have already been described may be omitted. In addition, in each drawing, mutually orthogonal X, Y, and Z axes may be defined. In this case, in the X-axis direction, the starting point (root) of the arrow may be referred to as the X- side, and 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. Also, 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> Figure 1 is a plan view illustrating a strain gauge according to the first embodiment. Figure 2 is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1.

[0011] Referring to Figures 1 and 2, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. The cover layer 60 can be provided as needed. For convenience, in Figures 1 and 2, only the outer edge of the cover layer 60 is shown with a dashed line. First, the various parts constituting the strain gauge 1 will be described in detail.

[0012] In this embodiment, for convenience, the side of the base material 10 on which the resistor 30 is provided in the strain gauge 1 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." Furthermore, the surface located above each part is referred to as the "upper surface," and the surface located below each part is referred to as the "lower surface." However, the strain gauge 1 can also be used upside down. Furthermore, the strain gauge 1 can be positioned at any angle. Moreover, a planar view refers to viewing the object in the direction normal to the upper surface 10a of the base material 10 from top to bottom. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0013] The base material 10 is a component that serves as a base layer for forming the resistor 30, etc. The base material 10 is flexible. The thickness of the base material 10 is not particularly limited and may be appropriately determined according to the intended use of the strain gauge 1, etc. For example, the thickness of the base material 10 may be about 5 μm to 500 μm. A strain generating body may be joined to the lower surface of the strain gauge 1 via an adhesive layer or the like. From the viewpoint of strain transmission from the surface of the strain generating body to the sensing part and dimensional stability against environmental changes, the thickness of the base material 10 is preferably in the range of 5 μm to 200 μm. Also, from the viewpoint of insulation, the thickness of the base material 10 is preferably 10 μm or more.

[0014] The base material 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, or polyolefin resin. Note that "film" refers to a flexible material with a thickness of approximately 500 μm or less.

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

[0016] Examples of materials other than the resin of the base material 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO3, BaTiO3), etc. In addition to the above-mentioned crystalline materials, amorphous glass or the like may also be used as the material of the base material 10. Further, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), titanium, etc. may be used. When using a metal, an insulating film is provided on the metal base material 10.

[0017] The resistor 30 is a thin film formed in a predetermined pattern on the base material 10. In the strain gauge 1, the resistor 30 is a sensing portion that receives strain and causes a resistance change. The resistor 30 may be formed directly on the upper surface 10a of the base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown in a high-density matte pattern.

[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 the elongated portions 31 and the folded portions 32 is not limited to the example of FIG. 1.

[0019] In the resistor 30, the plurality of elongated portions 31 are juxtaposed with their longitudinal directions facing the first direction X. And the plurality of folded portions 32 connect the ends of the adjacent elongated portions 31 among the plurality of elongated portions 31 alternately to connect each elongated portion 31 in series with each other. Thereby, the resistor 30 has a structure that folds back in a zigzag as a whole. The first direction X, which is the longitudinal direction of the plurality of elongated portions 31, becomes the grid direction, and the second direction Y, which is the direction perpendicular to the grid direction, becomes the grid width direction.

[0020] In the resistor 30, one end (X - side end) 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 terminal 30e1 in the grid width direction of the resistor 30. Also, one end (X - side end) 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 terminal 30e2 in the grid direction of the resistor 30. Each of the terminals 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 terminals 30e1 and 30e2 in the grid width direction of the resistor 30 and each electrode 50. In FIG. 1, for the sake of convenience, the terminals 30e1 and 30e2 are shown by broken lines, but the resistor 30 and the 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. Examples of the material containing Cr include, for example, a Cr mixed - phase film. Examples of the material containing Ni include, for example, Cu - Ni (copper nickel). Examples of the material containing both Cr and Ni include, for example, Ni - Cr (nickel chromium).

[0022] Here, the Cr mixed - phase film is a film in which Cr, CrN, Cr2N, etc. are mixed - phase. 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 appropriately determined according to the purpose of use of the strain gauge 1, etc. For example, the thickness of the resistor 30 may be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α - Cr) is improved. Also, when the thickness of the resistor 30 is 1 μm or less, (i) cracks in the film and (ii) warpage of the film from the base material 10 due to the internal stress of the film constituting the resistor 30 are reduced.

[0024] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of each elongated portion 31 of the resistor 30 is preferably 5 μm or more and 100 μm or less. More specifically, the width of each elongated portion 31 of the resistor 30 is preferably 5 μm or more and 70 μm or less, and more preferably 5 μm or more and 50 μm or less.

[0025] For example, if the resistor 30 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Also, for example, if the resistor 30 is a Cr multiphase film, by making α-Cr the main component of the resistor 30, the gauge factor of strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means a component that accounts for 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 30 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is even more preferable that the resistor 30 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, if the resistor 30 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less, the decrease in the gauge factor of the strain gauge 1 can be suppressed.

[0027] Furthermore, in the Cr multiphase film, it is preferable that the ratio of CrN to Cr2N is such that the proportion of Cr2N is 80% or more and less than 90% by weight relative to the total weight of CrN and Cr2N. More preferably, the ratio is such that the proportion of Cr2N is 90% or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the decrease in TCR (negative TCR) becomes even more pronounced. Moreover, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the ceramicization of the resistor 30 is reduced, making brittle fracture of the resistor 30 less likely to occur.

[0028] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of unstable nitrogen generation can be reduced, thus enabling the creation of a stable strain gauge. Here, "unstable nitrogen" refers to trace amounts of N2 or atomic nitrogen that may be present in the Cr multiphase film. These unstable nitrogen atoms may escape from the film depending on the external environment (e.g., high temperature environment). When unstable nitrogen atoms escape from the film, the film stress of the Cr multiphase film may change.

[0029] In strain gauge 1, using a Cr multiphase film as the material for the resistor 30 enables higher sensitivity and miniaturization. For example, while the output of a conventional strain gauge was approximately 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 30 allows for an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was approximately 3mm × 3mm, using a Cr multiphase film as the material for the resistor 30 allows for miniaturization to approximately 0.3mm × 0.3mm.

[0030] Two wirings 40 are formed on the base material 10. One end of the wiring 40 is positioned alongside an elongated portion 31 located at one end (the Y-side end) of the second direction Y, and is connected via a folded portion 32 to one end (the X-side end) of the elongated portion 31 in the first direction X. The other end of the wiring 40 is positioned alongside an elongated portion 31 located at the other end (the Y+side end) of the second direction Y, and is connected via a folded portion 32 to one end (the X-side end) of the elongated portion 31 in the first direction X.

[0031] The wiring 40 only needs to be arranged alongside the elongated portion 31 at least at one end in the first direction X, and the entire wiring 40 does not need to be arranged alongside the elongated portion 31. In other words, the wiring 40 is not limited to a straight line, and can be any pattern arranged alongside the elongated portion 31 at least at one end in the first direction X. Also, the wiring 40 can be of any length.

[0032] The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40. For example, they are wider than the wiring 40 and are formed in a roughly 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 for example, lead wires for external connection are attached to them.

[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 also 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 30 via the first metal layer 41 of the wiring 40. In plan view, the first metal layer 51 is formed in a substantially rectangular shape. The first metal layer 51 may be formed to the same width as the wiring 40. In Figure 1, for convenience, the first metal layers 41 and 51 are shown with a textured surface of the same density as the resistor 30, and the second metal layers 42 and 52 are shown with a textured surface of lower density than the resistor 30.

[0034] The second metal layers 42 and 52 are formed on a portion of the upper surface of the first metal layers 41 and 51. Specifically, the second metal layers 42 and 52 are formed in the region of the upper surface of the first metal layers 41 and 51, excluding the outer edges. Therefore, in a plan view, the outer edge of the first metal layer 41 is exposed from the second metal layer 42. Also, 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 from the same material, or they may be formed from different materials. For the materials of the second metal layers 42 and 52, a material with a lower volume resistivity than the resistor 30 (first metal layers 41 and 51) can be selected. Examples of such materials include Cu, Ni, Al, Ag, Au, Pt, alloys of any of these metals, compounds of any of these metals, or laminated films formed by appropriately stacking any of these metals, alloys, or compounds. In particular, it is preferable to use Cu, Cu alloys, Al, Ag, Au, CrMn, etc., as the material for 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. For example, the thickness of the second metal layers 42 and 52 can be about 0.5 μm to 5 μm.

[0036] One or more additional 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 sequentially laminated on the upper surface of the copper layer. By making the uppermost layer of the electrode 50 a gold layer, 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 from the same material in the same process. Therefore, the resistor 30, the first metal layer 41, and the first metal layer 51 may have approximately the same thickness. Similarly, although the second metal layer 42 and the second metal layer 52 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 42 and the second metal layer 52 may have approximately the same thickness.

[0038] Thus, the wiring 40 has a structure in which a second metal layer 42, made of a material with a lower volume resistivity than the first metal layer 41, is laminated on a first metal layer 41 made of the same material as the resistor 30. Therefore, the wiring 40 has lower resistance than the resistor 30, which prevents the wiring 40 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 lower volume resistivity than the resistor 30, the effective sensing area of ​​the strain gauge 1 can be limited to the local region where the resistor 30 is formed. Therefore, the accuracy of strain detection by the resistor 30 can be improved.

[0040] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 30, reducing the resistance of the wiring 40 to that of the resistor 30 and limiting the effective sensing area to the local region where the resistor 30 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 40 to that of the resistor 30 also has the effect of reducing lateral sensitivity.

[0041] The cover layer 60 is provided on the upper surface 10a of the substrate 10 as needed, covering the resistor 30 and wiring 40 and exposing 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, polyolefin resin). The cover layer 60 may also contain fillers and pigments. The thickness of the cover layer 60 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 60 can be about 2 μm to 30 μm. By providing the cover layer 60, mechanical damage to the resistor 30 can be suppressed. In addition, by providing the cover layer 60, the resistor 30 can be protected from moisture and other elements.

[0042] Figure 3 schematically shows how cracks occur in the resistor and wiring. As the strain applied to the strain gauge 1 is increased, cracks occur in the resistor 30 and the first metal layer 41. According to the inventors' studies, as shown in Figure 3, crack C tends to occur near the end in the first direction X of the second metal layer 42 constituting the wiring 40, extending approximately in the second direction Y.

[0043] Figure 4 is a partially enlarged plan view of the vicinity of the connection between the resistor and the wiring in Figure 1. As shown in Figure 4, in strain gauge 1, in plan view, one end of the second metal layer 42 in the first direction X (X-side) protrudes further in the first direction X (X-side) than one end 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, if L1 is the length that the end of one end of the second metal layer 42 in the first direction X protrudes toward one end of the gap S in the first direction X, then length L1 > 0. Note that in strain gauge 1, in plan view, the positional relationship between one end of the second metal layer 42 in the first direction X and one end of the gap between adjacent elongated portions 31 in the first direction X can be arbitrary.

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

[0045] In contrast, in the strain gauge 1 shown in Figure 4, since length L1 > 0, even if a crack C as shown in Figure 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 can continue to function. In Figure 4, it is preferable that length L1 is 1 μm or more. This makes it easier to maintain the electrical connection by ensuring sufficient current-carrying width between the wiring 40 and the elongated portion 31 adjacent to the wiring 40.

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

[0047] Furthermore, in Figure 4, the length L3 in the first direction X between one end of the first metal layer 41 and one end of the second metal layer 42 in the first direction X is preferably 5 μm or more, and more preferably 10 μm or more.

[0048] In the manufacturing process of strain gauge 1, the first metal layer 41 and the second metal layer 42 are etched and patterned, but in some cases the first metal layer 41 may be over-etched compared to the second metal layer 42. If the edge of the second metal layer 42 protrudes horizontally beyond the edge of the first metal layer 41 due to over-etching, the adhesion between the wiring 40 and the cover layer 60 will decrease when a cover layer 60 is provided to cover the wiring 40. For example, if the first metal layer 41 of the wiring 40 is formed from a Cr multiphase film and the second metal layer 42 is formed from copper, the Cr multiphase film will be over-etched by about 1 to 2 μm more than the copper during the etching process in the manufacturing process of strain gauge 1. Also, if the edge of the second metal layer 42 protrudes horizontally beyond the edge of the first metal layer 41 due to over-etching, for example, if the second metal layer 42 is formed from copper, the protruding portion of the copper will oxidize and the copper will deteriorate, reducing the reliability of strain gauge 1.

[0049] Therefore, in a 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 suppresses over-etching of the first metal layer 41 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 formed from copper, oxidation and degradation of the copper can be prevented.

[0050] Figure 6 shows the experimental results of the strain limit, plotting the minimum strain limit values ​​for multiple test strain gauges. In Figure 4, L1=0μm represents the experimental results for the strain gauge related to the comparative example. On the other hand, L1=1μm represents the experimental results for strain gauge 1 according to the first embodiment.

[0051] In Figure 6, the vertical axis represents the strain limit [μST]. The strain limit is the mechanical strain value at which the strain gauge breaks and ceases to function as a strain gauge when strain is applied. From the results in Figure 6, it was confirmed that when L1 = 5 μm, the strain limit is improved by approximately 1.4 times compared to when L1 = 0 μm.

[0052] Furthermore, according to another study by the inventors, it is undesirable not to laminate the second metal layer 42 onto the first metal layer 41. When the second metal layer 42 is not laminated onto the first metal layer 41, the strain limit is further reduced compared to the case where L1 = 0 μm as shown in Figure 6. For example, if the first metal layer 41 is a Cr multiphase film, the Cr multiphase film has poor elasticity, so if the wiring 40 is formed only from the Cr multiphase film, the strain limit is expected to be low. By laminating a second metal layer 42 made of a material with better elasticity than the Cr multiphase film, such as copper, onto the first metal layer 41 made of a Cr multiphase film, the strain limit can be improved.

[0053] In other words, from the viewpoint of improving the strain limit, the wiring 40 is preferably a laminated structure of a first metal layer 41 and a second metal layer 42, and the second metal layer 42 is preferably made of a material with better elasticity than the first metal layer 41. That is, the second metal layer is preferably made of a material with lower volume resistivity than the first metal layer and better elasticity than the first metal layer 41. When the first metal layer is a Cr multiphase film, materials that have lower volume resistivity than the first metal layer and better elasticity than the first metal layer 41 include, in addition to copper, gold, silver, and aluminum.

[0054] [Method of manufacturing strain gauges] 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 base material 10. Note that another layer (such as a functional layer, described later) may be formed between the base material 10 and these layers.

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

[0056] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, or pulsed laser deposition instead of magnetron sputtering.

[0057] Alternatively, a base layer may be formed on the upper surface 10a of the substrate 10 before forming the metal layer A. For example, a functional layer of 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 way, the gauge characteristics of the strain gauge 1 can be stabilized.

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

[0059] The insulating resin film constituting the base material 10 may contain oxygen and moisture, and Cr may form an oxidized film. Therefore, especially when metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of metal layer A.

[0060] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 is improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A improves the gauge characteristics in 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 these metals, or a compound of any of these metals.

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

[0063] The planar shape of the functional layer 20 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 30, the wiring 40, and the electrodes 50. 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, if 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 as a solid in the region where the resistor 30, the wiring 40, and the electrodes 50 are formed. Alternatively, the functional layer 20 may be formed as a solid over the entire upper surface of the substrate 10.

[0064] Next, a second metal layer 42 and a second metal layer 52 are formed on the upper surface of metal layer A. The second metal layer 42 and the second metal layer 52 can be formed in a predetermined pattern, for example, by a well-known photolithography method.

[0065] Next, a photosensitive resist is formed on the upper surface of metal layer A, the upper surface of the second metal layer 42, and the upper surface of the second metal layer 52. The resist is then exposed and developed to pattern it into a planar shape similar to the resistor 30, wiring 40, and electrode 50 shown in Figure 1. The resist is then used as an etching mask, and metal layer A exposed from the resist is removed by wet etching or the like. Next, by removing the resist, the resistor 30, wiring 40, and electrode 50 with the planar shape shown in Figure 1 can be formed. 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 electrode 50, a cover layer 60 is formed on the upper surface 10a of the base material 10 as needed. The cover layer 60 covers the resistor 30 and wiring 40, but the electrode 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 onto the upper surface 10a of the base material 10 so as to cover the resistor 30 and wiring 40 and expose the electrode 50, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 1 is completed.

[0067] Preferred embodiments have been described in detail above. However, the strain gauges according to this disclosure are not limited to the embodiments described above. For example, various modifications and substitutions can be made to the strain gauges according to the embodiments described above without departing from the scope described in the claims. [Explanation of Symbols]

[0068] 1 Strain gauge, 10 Substrate, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1, 30e2 Termination, 31 Elongated section, 32 Folded section, 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; two wirings formed on the substrate and connected in series to both ends of the resistor; The resistor includes a plurality of elongated portions that are arranged in parallel with each other and connected in series with each other, the elongated portions being arranged in a first direction, one of the wirings is juxtaposed to the elongated portion located at one end in a second direction perpendicular to the first direction and is connected to one end of the elongated portion in the first direction; the other of the wirings is juxtaposed to the elongated portion located at the other end in the second direction and 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; In a plan view, an outer edge of the first metal layer is exposed from the second metal layer; A strain gauge, wherein, in a planar view, an end portion of the second metal layer on one end side in the first direction protrudes toward the one end side in the first direction further than an end portion of the gap between the first metal layer and the elongated portion adjacent to the first metal layer on one end side in the first direction.

2. 2. The strain gauge according to claim 1, wherein a length of an end of the second metal layer protruding toward one end in the first direction from an end of the gap on the one end in the first direction is 1 μm or more.

3. The strain gauge according to claim 2 , wherein the protruding length is equal to or greater than 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. 5. The strain gauge according to claim 1 , wherein a length in the first direction between an end portion of the first metal layer on one end side in the first direction and an end portion of the second metal layer on one end side in the first direction is 5 μm or more.

6. The strain gauge according to claim 1 , wherein the second metal layer is made of a material having a higher elasticity than the first metal layer.

7. The strain gauge according to claim 1 , wherein the first metal layer is made of the same material as the resistor and is formed integrally with the resistor.

8. The resistor is made of Cr, CrN, and Cr. ２ 5. The strain gauge according to claim 1, which is formed from a film containing N.

Images