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 Art

[0002] A strain gauge that is attached to a measurement object to detect the strain of the measurement object is known. The strain gauge includes a resistor for detecting strain, and as the material of the resistor, for example, a material containing Cr (chromium) or Ni (nickel) is used. Further, the resistor is formed, for example, in a pattern that folds back in a zigzag manner (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] However, when the resistor is formed in a pattern that folds back in a zigzag manner, a pattern facing the direction to be detected (hereinafter referred to as the detection direction) and a pattern facing a direction different from the direction to be detected (hereinafter referred to as the false detection direction) are mixed. As a result, it is not possible to detect only the strain in one axis (detection direction), and the sum of the strain in the detection direction and the strain in the false detection direction is detected, resulting in a decrease in strain detection accuracy.

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

Means for Solving the Problems

[0006] This strain gauge comprises a flexible resin substrate, a functional layer formed directly on one surface of the substrate from a metal, alloy, or metal compound, and a resistor mainly composed of α-Cr, formed directly on one surface of the functional layer from a film containing Cr, CrN, and Cr2N. The functional layer has the function of promoting the crystal growth of α-Cr and forming a film mainly composed of α-Cr. The thickness of the resistor is 0.05 μm to 2 μm, and the thickness of the functional layer is 1 nm to 100 nm. The resistor includes a plurality of juxtaposed resistance patterns and folded portions connecting the ends of adjacent resistance patterns. 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 strain gauges with improved strain detection accuracy. [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 illustrating a strain gauge according to the first embodiment. [Figure 3] This figure illustrates the manufacturing process of a strain gauge according to the first embodiment. [Figure 4] This is a plan view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 5] This is a plan view illustrating a strain gauge according to a modified example 2 of the first embodiment. [Figure 6] This is a plan view illustrating a strain gauge according to a modified example 3 of 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 reference numerals are used for identical components, and redundant explanations may be omitted.

[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 illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1. Referring to Figures 1 and 2, the strain gauge 1 includes a base material 10, a resistor 30, an electrode 40A, and a metal layer 43.

[0011] In this embodiment, for convenience, the side of the base material 10 on which the resistor 30 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 is provided at each part is referred to as one surface or the upper surface, and the surface on which the resistor 30 is not provided is referred to as the other surface or the lower surface. However, the strain gauge 1 can be used upside down or positioned at any angle. Moreover, "plan view" refers to viewing the object from the direction normal to the upper surface 10a of the base material 10, and "planar shape" refers to the shape of the object when viewed from the direction normal to the upper surface 10a of the base material 10.

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

[0013] The base material 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, or polyolefin resin. The term "film" refers to a flexible material with a thickness of approximately 500 μm or less.

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

[0015] The resistor 30 is a thin film formed on the substrate 10 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or it 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 multiphase 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, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0018] The thickness of the resistor 30 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, it is preferable in terms of improving the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α-Cr), and when it is 1 μm or less, it is more preferable in terms of reducing film cracks caused by internal stress of the film constituting the resistor 30 and warping from the base material 10.

[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 is a stable crystal phase, as the main component. Also, when the resistor 30 has α-Cr as the main component, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance occupies 50 mass% or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80 wt% or more of α-Cr. 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 substantially rectangular shape that is wider than the resistor 30 in plan view. The electrodes 40A are a pair of electrodes for outputting the change in the resistance value of the resistor 30 caused by strain to the outside. For example, lead wires for external connection are joined thereto. The resistor 30 extends, for example, while being folded back in a zigzag manner from one of the electrodes 40A and is electrically connected to the other electrode 40A.

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

[0022] As the material for the metal layer 42, a material with better solder wettability than the terminal portion 41 can be selected. For example, if the resistor 30 is a Cr multiphase film, the material for the metal layer 42 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 laminated 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 according to the purpose, but for example it can be about 0.01 μm to 30 μm. Considering solder erosion, the thickness of the metal layer 42 is preferably 1 μm or more, more preferably 3 μm or more. When the metal layer 42 is formed by electroplating, the thickness of the metal layer 42 is preferably 30 μm or less due to the ease of electroplating.

[0023] However, if solder wettability or solder corrosion is 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 oriented in the same direction (the X direction in the example of Figure 1), and folded portions 33 that connect the outer edges of adjacent resistor patterns 31.

[0025] A metal layer 43 made of a material with 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] In Figure 1, the folded portion 33 of the resistor 30 is straight, but the folded portion of the resistor 30 is not limited to being straight and can have any shape. For example, the folded portion of the resistor 30 may be curved, or a mixture of straight and curved portions may be present.

[0027] The material of the metal layer 43 is not particularly limited as long as it is a material with a lower gauge factor than the resistor 30, and can be appropriately selected according to the purpose. For example, if the resistor 30 is a Cr multiphase 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 laminated film obtained by appropriately stacking any of these metals, alloys, or compounds. The thickness of the metal layer 43 is not particularly limited 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, and can be appropriately selected according to the purpose, but for example it can be about 0.01 μm to 30 μm.

[0028] The metal layer 43 may be formed using the same material as the metal layer 42 and in the same process as the metal layer 42. Alternatively, the metal layer 43 may be formed using a different material than the metal layer 42 and in a separate process. 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, in Figure 1, the resistance pattern 31, the metal layer 42, and the metal layer 43 are shown with different textured patterns.

[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 electrode 40A. Providing the cover layer 60 prevents mechanical damage to the resistor 30 and the metal layer 43. In addition, providing the cover layer 60 protects the resistor 30 and the metal layer 43 from moisture and other elements. The cover layer 60 may be provided so as to cover the entire portion excluding the electrode 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, polyolefin resin). The cover layer 60 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 60, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0031] Figure 3 is a diagram illustrating the manufacturing process of a strain gauge according to the first embodiment, and shows a cross-section corresponding to Figure 2. In order to manufacture the strain gauge 1, first, in the process shown in Figure 3(a), a base material 10 is prepared, a metal layer 300 is formed on the upper surface 10a of the base material 10, and then a metal layer 310 is formed on the metal layer 300.

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

[0033] The metal layer 300 can be formed, for example, by a magnetron sputtering method targeting a raw material capable of forming the metal layer 300. Alternatively, the metal layer 300 may be formed using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

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

[0035] 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 300 (resistor 30). Preferably, the functional layer further has the function of preventing oxidation of the metal layer 300 by oxygen and moisture contained in the substrate 10, and the function of improving the adhesion between the substrate 10 and the metal layer 300. The functional layer may further have other functions.

[0036] Since the insulating resin film that makes up the base material 10 contains oxygen and moisture, and especially when the metal layer 300 contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer 300.

[0037] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth in at least the upper metal layer 300 (resistor 30), and can be appropriately selected according to 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 (bisulfite). Examples include one or more metals selected from the group consisting of M(Os), 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.

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

[0039] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 10a of the substrate 10 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

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

[0041] There are no particular restrictions on the combination of materials for the functional layer and the metal layer 300, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer 300.

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

[0043] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that when the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0044] Furthermore, if the metal layer 300 is a Cr multiphase 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 by oxygen and moisture contained in the substrate 10, and improving the adhesion between the substrate 10 and the metal layer 300. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0045] In this way, by providing a functional layer beneath the metal layer 300, it becomes 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, the stability of the gauge characteristics in the strain gauge 1 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer 300 can improve the gauge characteristics in the strain gauge 1.

[0046] The metal layer 310 can be formed, for example, by a magnetron sputtering method targeting a raw material capable of forming the metal layer 310. Alternatively, the metal layer 310 may be formed using reactive sputtering, vapor deposition, plating, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering. When forming a thicker metal layer 310, plating is preferable.

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

[0048] After the process shown in Figure 3(c), the strain gauge 1 is completed by providing a cover layer 60 on the upper surface 10a of the base material 10, if necessary, which covers the resistor 30 and the metal layer 43 and exposes the electrode 40A. The cover layer 60 can be made, for example, 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 the metal layer 43 and expose the electrode 40A, and then heating and curing it. Alternatively, the cover layer 60 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the base material 10 so as to cover the resistor 30 and the metal layer 43 and expose the electrode 40A, and then heating and curing it.

[0049] In the above process, an example was shown in which metal layer 42 and metal layer 43 are formed using the same material. However, this is just one example, and as mentioned above, metal layer 42 and metal layer 43 may be formed using different materials in separate processes. Furthermore, metal layer 42 may be omitted entirely.

[0050] In this way, by laminating a metal layer 43 made of a material with a lower gauge factor than the resistor 30 onto the folded portion 33 of the resistor 30, and by making the resistance value of the metal layer 43 on the folded portion 33 lower than the resistance value of the folded portion 33, the sensitivity in the direction of false detection can be reduced, and the strain detection accuracy of the strain gauge 1 can be improved.

[0051] In other words, at the folded portion 33 of the resistor 30, a large amount of current flows to the metal layer 43, which has a lower resistance than the folded portion 33. Therefore, even if strain occurs in the direction of false detection (in this case, the Y direction) where the folded portion 33 of the resistor 30 extends, the output mainly comes from the metal layer 43, which has a lower gauge factor than the resistor 30, and a large output cannot be obtained from electrode 40A. On the other hand, outside the folded portion 33 of the resistor 30, all the current flows to the resistor 30, which has a higher gauge factor, so if strain occurs in the grid direction (in this case, the X direction) of the resistor 30, a large output can be obtained from electrode 40A. As a result, the accuracy of strain detection in the grid direction (in this case, the X direction) can be improved.

[0052] This effect can be obtained regardless of the material of the resistor 30, but a particularly significant effect is obtained when a Cr multiphase film with a high gauge factor is used as the resistor 30.

[0053] <Modification 1 of the first embodiment> Modification 1 of the first embodiment shows an example in which the folded portion and the shape of the metal layer differ from those of the first embodiment. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

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

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

[0056] A metal layer 44 made of a material with 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, for example, the metal layer 43.

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

[0058] In all of the above cases, by laminating a metal layer made of a material with a lower gauge factor than the resistor 30 onto the folded portion of the resistor 30, and by 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 direction of false detection can be reduced, and the strain detection accuracy of the strain gauge can be improved.

[0059] <Modification 2 of the first embodiment> Modification 2 of the first embodiment shows an example in which the formation position of the metal layer on the folded portion differs from that of the first embodiment. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

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

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

[0062] Thus, a portion of the metal layer 45 may extend from the folded portion 33 to a portion of the resistance pattern 31. In this case, even considering manufacturing variations, the metal layer 45 can be reliably laminated on the folded portion 33. As a result, the sensitivity to false detection directions can be reliably reduced, and the strain detection accuracy of the strain gauge 1B can be reliably improved.

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

[0064] <Modification 3 of the first embodiment> Modification 3 of the first embodiment shows an example in which the shape of the folded portion differs from that of the first embodiment. In Modification 3 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

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

[0066] The resistor 30 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions oriented in the same direction (the X direction in the example of Figure 6), and folded portions 36 that connect the outer edges of adjacent resistor patterns 31.

[0067] A metal layer 46 made of a material with 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, for example, the metal layer 43.

[0068] Unlike the folded portion 33 (see Figure 1), the folded portion 36 is formed in a curved shape (for example, U-shape). In this case as well, by laminating a metal layer 46 made of a material with a lower gauge factor than the resistor 30 onto the folded portion 36 of the resistor 30, and by making the resistance value of the metal layer 46 on the folded portion 36 lower than the resistance value of the folded portion 36, the sensitivity in the direction of false detection can be reduced, and the strain detection accuracy of the strain gauge 1C can be improved.

[0069] In addition, in strain gauge 1C, similar to strain gauge 1B, a portion of the metal layer 46 may extend from the folded portion 36 to a portion of the resistance pattern 31. In this case, even considering manufacturing variations, the metal layer 46 can be reliably laminated on the folded portion 36. As a result, the sensitivity in the false detection direction can be reliably reduced, and the strain detection accuracy of strain gauge 1C can be reliably improved. However, since the length of the resistance pattern 31 in the grid direction (the length of the portion where the metal layer 46 is not laminated) will be slightly shorter, a slight decrease in detection sensitivity can be expected.

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

[0071] 1, 1A, 1B, 1C Strain gauge, 10 Base material, 10a Top 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 base material, A functional layer formed directly on one surface of the aforementioned substrate from a metal, alloy, or metal compound, On one side of the functional layer, Cr, CrN, and Cr ２ It comprises a resistor mainly composed of α-Cr, formed from a film containing N, The functional layer has the function of promoting the crystal growth of α-Cr and forming a film mainly composed of α-Cr. 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 juxtaposed resistor patterns and folded portions connecting the ends of adjacent resistor patterns, A strain gauge is formed in which 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.

2. The strain gauge according to claim 1, wherein the first metal layer extends from the folded portion to a part of the resistance pattern and is formed in a U-shape overall.

3. Having an electrode electrically connected to the resistor, The electrode includes a terminal portion extending from the end of the resistor and a second metal layer formed on the terminal portion. The strain gauge according to claim 1 or 2, wherein the first metal layer and the second metal layer are made of the same material.

4. A strain gauge according to any one of claims 1 to 3, comprising the resistor and an insulating resin layer covering the first metal layer.

Images