Strain gauge

Abstract

To provide a strain gauge with improved strain detection accuracy.SOLUTION: The strain gauge has: a base material made of resin having flexibility; a functional layer formed of metal, an alloy, or a compound of metal directly on one face of the base material; and a resistor including α-Cr as a main component, and formed of a film including Cr, CrN, and Cr2N directly on one face of the functional layer. The functional layer has a function to accelerate crystal growth of the α-Cr, and deposit a film including the α-Cr as a main component. The thickness of the resistor is 0.05 μm or more and 2 μm or less. The thickness of the functional layer is 1 nm or more and 100 nm or less. the resistor includes a plurality of resistance patterns arranged in parallel to each other, and a folded portion connecting the ends of the adjacent resistance patterns to each other. A first metal layer formed of a material with a lower gauge factor than the resistor is laminated on the folded portion. The value of resistance of the first metal layer on the folded portion is lower than the value of resistance of the folded portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain on the object. The strain gauge includes a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni). The resistor is formed in a zigzag folded pattern, 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] However, when resistors are formed in a zigzag folded pattern, patterns facing the desired detection direction (hereinafter referred to as the detection direction) and patterns facing a direction different from the desired detection direction (hereinafter referred to as the erroneous detection direction) are mixed together. As a result, it is not possible to detect strain in only one axis (detection direction), and the total strain in the detection direction and the erroneous detection direction is detected, which reduces the strain detection accuracy.

[0005] The present invention has been made in view of the above points, and has an object to provide a strain gauge with improved strain detection accuracy. [Means for solving the problem]

[0006] This strain gauge has a flexible resin substrate, a functional layer formed from a metal, alloy, or metal compound directly on one side of the substrate, and an α-Cr-based resistor formed from a film containing Cr, CrN, and CrN directly on one side of the functional layer, wherein the functional layer has the function of promoting crystal growth of the α-Cr and forming the film mainly composed of α-Cr, the resistor has a thickness of 0.05 μm to 2 μm, and the functional layer has a thickness of 1 nm to 100 nm, the resistor includes a plurality of juxtaposed resistance patterns and a folded portion connecting ends of adjacent resistance patterns, and a first metal layer made of a material with a lower gauge factor than the resistor is laminated on the folded portion, and the resistance value of the first metal layer on the folded portion is lower than the resistance value of the folded portion. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge with improved strain detection accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 3] 3A to 3C are diagrams illustrating a manufacturing process of the strain gauge according to the first embodiment. [Figure 4] FIG. 2 is a plan view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 5] FIG. 10 is a plan view illustrating a strain gauge according to a second modification of the first embodiment. [Figure 6] FIG. 10 is a plan view illustrating a strain gauge according to a third modification of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment Fig. 1 is a plan view illustrating a strain gauge according to a first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, taken along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, an electrode 40A, and a metal layer 43.

[0011] 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 or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0012] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[0013] The substrate 10 can be 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, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0014] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0015] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strained. 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.

[0016] 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).

[0017] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0019] 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, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0020] The electrodes 40A extend from both ends of the resistor 30 and are formed in a generally rectangular shape in plan view, wider than the resistor 30. The electrodes 40A are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and are joined to, for example, lead wires for external connection. The resistor 30 extends from one of the electrodes 40A while folding back in a zigzag pattern and is electrically connected to the other electrode 40A, for example.

[0021] The electrode 40A can have a laminated structure in which multiple metal layers are stacked. Specifically, the electrode 40A has terminal portions 41 extending from both ends of the resistor 30 and a metal layer 42 formed on the upper surface of the terminal portions 41. Although the resistor 30 and the terminal portions 41 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0022] The material of the metal layer 42 can be selected from materials with better solder wettability than the terminal portion 41. For example, when the resistor 30 is a Cr mixed-phase film, the material of the metal layer 42 can be Cu, Ni, Al, Ag, Au, Pt, or the like, or an alloy of any of these metals, a compound of any of these metals, or a laminate film in which any of these metals, alloys, or compounds are appropriately laminated. The thickness of the metal layer 42 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, approximately 0.01 μm to 30 μm. In consideration of solder erosion, the thickness of the metal layer 42 is preferably 1 μm or more, more preferably 3 μm or more. Note that when the metal layer 42 is formed by electroplating, the thickness of the metal layer 42 is preferably 30 μm or less in view of the ease of electroplating.

[0023] However, if solder wettability and solder erosion are not a problem, the terminal portion 41 itself may be used as an electrode without laminating the metal layer 42.

[0024] The resistor 30 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions directed in the same direction (the X direction in the example of FIG. 1), and a folded portion 33 connecting the outer ends of adjacent resistor patterns 31.

[0025] A metal layer 43 made of a material having a lower gauge factor than the resistor 30 is laminated on the folded portion 33. The material and thickness of the metal layer 43 are selected so that the resistance value of the metal layer 43 on the folded portion 33 is lower than the resistance value of the folded portion 33.

[0026] 1, the folded portion 33 of the resistor 30 is linear, but the folded portion of the resistor 30 is not limited to being linear and may have any shape. For example, the folded portion of the resistor 30 may be curved, or may have a mixture of linear and curved portions.

[0027] The material of the metal layer 43 is not particularly limited and can be appropriately selected depending on the purpose as long as it has a lower gauge factor than the resistor 30. For example, when the resistor 30 is a Cr mixed-phase film, the material of the metal layer 43 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminate film in which any of these metals, alloys, or compounds are appropriately laminated. The thickness of the metal layer 43 is not particularly limited and can be appropriately selected depending on the purpose as long as the resistance value of the metal layer 43 on the folded portion 33 can be lower than the resistance value of the folded portion 33 itself, and can be, for example, about 0.01 μm to 30 μm.

[0028] The metal layer 43 may be formed using the same material as the metal layer 42 in the same process as the metal layer 42. Alternatively, the metal layer 43 may be formed using a different material from the metal layer 42 in a process separate from the metal layer 42. In this case, the thickness of the metal layer 43 does not need to be the same as the thickness of the metal layer 42. For convenience, the resistor pattern 31, the metal layer 42, and the metal layer 43 are shown in FIG. 1 with different matte finishes.

[0029] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the metal layer 43 and expose the electrodes 40A. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30 and the metal layer 43. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 and the metal layer 43 from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the electrodes 40A.

[0030] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0031] Fig. 3 is a diagram illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section corresponding to Fig. 2. To manufacture the strain gauge 1, first, in the step shown in Fig. 3(a), a substrate 10 is prepared, a metal layer 300 is formed on the upper surface 10a of the substrate 10, and a metal layer 310 is further formed on the metal layer 300.

[0032] The metal layer 300 is a layer that is ultimately patterned to become the resistor 30 and the terminal portion 41. Therefore, the material and thickness of the metal layer 300 are the same as the material and thickness of the resistor 30 and the terminal portion 41 described above. The metal layer 310 is a layer that is ultimately patterned to become the metal layers 42 and 43. Therefore, the material and thickness of the metal layer 310 are the same as the material and thickness of the metal layers 42 and 43 described above.

[0033] The metal layer 300 can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer 300. Instead of magnetron sputtering, the metal layer 300 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0034] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer having a thickness of about 1 nm to 100 nm on the upper surface 10a of the substrate 10 as a base layer by, for example, conventional sputtering before depositing the metal layer 300.

[0035] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the metal layer 300 (resistor 30). The functional layer preferably also has a function of preventing oxidation of the metal layer 300 due to oxygen and moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the metal layer 300. The functional layer may also have other functions.

[0036] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the metal layer 300, especially when the metal layer 300 contains Cr.

[0037] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper metal layer 300 (resistor 30), and can be appropriately selected depending on the purpose. For example, 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), Examples of the metals include one or more metals selected from the group consisting of copper (iron), iron (Fe), molybdenum (Mo), tungsten (W), ruthenium (Ru), rhodium (Rh), re (rhenium), osmium (Os), iridium (Ir), platinum (Pt), palladium (Pd), silver (Ag), gold (Au), cobalt (Co), manganese (Mn), and aluminum (Al), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0038] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0039] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0040] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0041] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer 300, and they can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer 300.

[0042] In this case, for example, the metal layer 300 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer 300 can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber.

[0043] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0044] When the metal layer 300 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the metal layer 300, preventing oxidation of the metal layer 300 due to oxygen and moisture contained in the base material 10, and improving adhesion between the base material 10 and the metal layer 300. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0045] In this way, by providing a functional layer below the metal layer 300, it is possible to promote crystal growth in the metal layer 300, and to produce a metal layer 300 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material that constitutes the functional layer into the metal layer 300, it is possible to improve the gauge characteristics of the strain gauge 1.

[0046] The metal layer 310 can be formed by, for example, magnetron sputtering using a target made of a material capable of forming the metal layer 310. Instead of magnetron sputtering, the metal layer 310 may be formed by reactive sputtering, vapor deposition, plating, arc ion plating, pulsed laser deposition, or the like. When the metal layer 310 is to be formed thick, it is preferable to select plating.

[0047] Next, in the step shown in Fig. 3(b), the metal layer 310 is patterned by photolithography to form metal layers 42 and 43 having the planar shape shown in Fig. 1. Next, in the step shown in Fig. 3(c), the metal layer 300 is patterned by photolithography to form the resistor 30 and terminal portion 41 having the planar shape shown in Fig. 1. As a result, the metal layer 43 is laminated on the folded portion 33 of the resistor 30. Furthermore, the metal layer 42 is laminated on the terminal portion 41 to form the electrode 40A.

[0048] 3(c), if necessary, a cover layer 60 that covers the resistor 30 and the metal layer 43 and exposes the electrodes 40A is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, 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 the metal layer 43 and expose the electrodes 40A, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the metal layer 43 and expose the electrodes 40A, and then heating and curing the resin.

[0049] In the above steps, an example has been shown in which the metal layers 42 and 43 are formed using the same material, but this is just one example, and as mentioned above, the metal layers 42 and 43 may be formed using different materials in different steps. Also, the metal layer 42 may not be provided.

[0050] In this way, by laminating a metal layer 43 made of a material with a lower gauge factor than the resistor 30 on the folded portion 33 of the resistor 30 and making the resistance value of the metal layer 43 on the folded portion 33 lower than the resistance value of the folded portion 33, it is possible to reduce the sensitivity in the erroneous detection direction and improve the strain detection accuracy of the strain gauge 1.

[0051] That is, at the folded portion 33 of the resistor 30, a larger amount of current flows toward the metal layer 43, which has a lower resistance than the folded portion 33. Therefore, even if strain occurs in the erroneous detection direction (the Y direction in this case) along which the folded portion 33 of the resistor 30 extends, the output is mainly from the metal layer 43, which has a lower gauge factor than the resistor 30, and therefore no large output is obtained from the electrode 40A. On the other hand, except for the folded portion 33 of the resistor 30, all of the current flows through the resistor 30, which has a high gauge factor. Therefore, when strain occurs in the grid direction of the resistor 30 (the X direction in this case), a large output is obtained from the electrode 40A. As a result, the strain detection accuracy in the grid direction (the X direction in this case) can be improved.

[0052] This effect is obtained regardless of the material of the resistor 30, but is particularly noticeable when the resistor 30 is made of a Cr mixed phase film having a large gauge factor.

[0053] <Modification 1 of the First Embodiment> In the first modification of the first embodiment, an example is shown in which the shape of the folded portion and the metal layer is different from that of the first embodiment. Note that in the first modification of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0054] Fig. 4 is a plan view illustrating a strain gauge according to Modification 1 of the first embodiment. Referring to Fig. 4, strain gauge 1A differs from strain gauge 1 (see Fig. 1 etc.) in that folded portion 33 is replaced with folded portion 34 and metal layer 43 is replaced with metal layer 44.

[0055] The resistor 30 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions directed in the same direction (the X direction in the example of Figure 4), and a folded portion 34 connecting the opposing sides of the ends of adjacent resistor patterns 31.

[0056] A metal layer 44 made of a material having a lower gauge factor than the resistor 30 is laminated on the folded portion 34. The material and thickness of the metal layer 44 are selected so that the resistance value of the metal layer 44 on the folded portion 34 is lower than the resistance value of the folded portion 34. The material and thickness of the metal layer 44 can be the same as those of the metal layer 43, for example.

[0057] The folded portion of the resistor 30 may be the portion connecting the outer ends of adjacent resistor patterns 31, such as the folded portion 33 shown in Figure 1, or the folded portion of the resistor 30 may be the portion connecting the opposing sides of the ends of adjacent resistor patterns 31, such as the folded portion 34 shown in Figure 4.

[0058] In either case, by laminating a metal layer made of a material with a lower gauge factor than resistor 30 on the folded portion of resistor 30 and making the resistance value of the metal layer on the folded portion lower than the resistance value of the folded portion, the sensitivity in the erroneous detection direction can be reduced and the strain detection accuracy of the strain gauge can be improved.

[0059] <Modification 2 of the First Embodiment> In the second modification of the first embodiment, the position of the metal layer on the folded portion is different from that of the first embodiment. Note that in the second modification of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0060] 5 is a plan view illustrating a strain gauge according to Modification 2 of the first embodiment. Referring to FIG. 5, strain gauge 1B differs from strain gauge 1 (see FIG. 1, etc.) in that metal layer 43 is replaced with metal layer 45.

[0061] The metal layer 45 is laminated on the folded portion 33 of the resistor element 30, and further extends from above the folded portion 33 to a part of the resistor pattern 31, forming an overall U-shape. The material and thickness of the metal layer 45 may be the same as those of the metal layer 43, for example.

[0062] In this way, a portion of the metal layer 45 may extend from the folded portion 33 onto a portion of the resistor pattern 31. In this case, even when manufacturing variations are taken into consideration, the metal layer 45 can be reliably laminated on the folded portion 33. As a result, the sensitivity in the erroneous detection direction can be reliably reduced, and the strain detection accuracy of the strain gauge 1B can be reliably improved.

[0063] However, in the strain gauge 1B, the length in the grid direction of the resistance pattern 31 (the length of the portion where the metal layer 45 is not laminated) is slightly shorter than that of the strain gauge 1, so a slight decrease in detection sensitivity is expected.

[0064] <Third Modification of the First Embodiment> In the third modification of the first embodiment, an example is shown in which the shape of the folded portion is different from that of the first embodiment. Note that in the third modification of the first embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0065] Fig. 6 is a plan view illustrating a strain gauge according to Modification 3 of the first embodiment. Referring to Fig. 6, strain gauge 1C differs from strain gauge 1 (see Fig. 1 etc.) in that folded portion 33 is replaced with folded portion 36 and metal layer 43 is replaced with metal layer 46.

[0066] The resistor 30 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions directed in the same direction (the X direction in the example of FIG. 6), and a folded portion 36 connecting the outer ends of adjacent resistor patterns 31.

[0067] A metal layer 46 made of a material having a lower gauge factor than the resistor 30 is laminated on the folded portion 36. The material and thickness of the metal layer 46 are selected so that the resistance value of the metal layer 46 on the folded portion 36 is lower than the resistance value of the folded portion 36. The material and thickness of the metal layer 46 can be the same as those of the metal layer 43, for example.

[0068] Unlike folded portion 33 (see FIG. 1), folded portion 36 is formed in a curved shape (for example, a U-shape). In this case, too, by laminating a metal layer 46 made of a material with a lower gauge factor than resistor 30 on folded portion 36 of resistor 30 and making the resistance value of metal layer 46 on folded portion 36 lower than the resistance value of folded portion 36, it is possible to reduce sensitivity in the erroneous detection direction and improve the strain detection accuracy of strain gauge 1C.

[0069] In strain gauge 1C, as in strain gauge 1B, a portion of metal layer 46 may extend from on folded portion 36 onto a portion of resistor pattern 31. In this case, metal layer 46 can be reliably laminated on folded portion 36 even taking into account manufacturing variations. As a result, sensitivity in the erroneous detection direction can be reliably reduced, and the strain detection accuracy of strain gauge 1C can be reliably improved. However, since the length of resistor pattern 31 in the grid direction (the length of the portion where metal layer 46 is not laminated) is slightly shortened, a slight decrease in detection sensitivity is expected.

[0070] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0071] 1, 1A, 1B, 1C strain gauge, 10 substrate, 10a upper surface, 30 resistor, 31 resistor pattern, 33, 34, 36 folded portion, 40A electrode, 41 terminal portion, 42, 43, 44, 45, 46 metal layer, 60 cover layer

Claims

1. a flexible resin substrate; a functional layer formed of a metal, an alloy, or a metal compound directly on one surface of the substrate; Cr, CrN, and Cr are directly applied to one surface of the functional layer. ２ a resistor formed from a film containing N and containing α-Cr as a main component; the functional layer has a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; The resistor has a thickness of 0.05 μm or more and 2 μm or less, the thickness of the functional layer is 1 nm or more and 100 nm or less; the resistor includes a plurality of resistor patterns arranged in parallel and a folded portion connecting ends of adjacent resistor patterns, A strain gauge in which a first metal layer made of a material having a lower gauge factor than the resistor is laminated on the folded portion, and the resistance value of the first metal layer on the folded portion is lower than the resistance value of the folded portion.

2. 2. The strain gauge according to claim 1, wherein the first metal layer extends from above the folded portion onto a part of the resistor pattern, and is formed into a U-shape as a whole.

3. an electrode electrically connected to the resistor; the electrode includes a terminal portion extending from an end of the resistor and a second metal layer formed on the terminal portion; 3. The strain gauge according to claim 1, wherein the first metal layer and the second metal layer are made of the same material.

4. 4. The strain gauge according to claim 1, further comprising an insulating resin layer that covers the resistor and the first metal layer.

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