Strain gauge

Abstract

To provide a strain gauge that can output information on the temperature at the periphery of a resistor.SOLUTION: A strain gauge comprises a strain detection unit and a temperature detection unit formed on a resin substrate with flexibility. The strain detection unit has a functional layer formed from metal, an alloy, or a compound of metal directly on one face of the substrate, and a resistor including α-Cr as a main component on one face of the functional layer. The resistor includes a plurality of resistance patterns, and a folding portion connecting the ends of the adjacent resistance patterns to each other. The functional layer accelerates the crystal growth of α-Cr and deposits 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. A first metal layer formed from a material with a lower gauge factor than the resistor is laminated on the folding portion, and the value of resistance of the first metal layer is lower than the value of resistance of the folding portion. The temperature detection unit is a thermocouple having, on the substrate, a second metal layer formed of the same material as the resistor, and a third metal layer formed of the same material as the first metal layer.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 in the object. The strain gauge has a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni) (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, the resistance value of the resistor changes with temperature, and if the resistance temperature coefficient varies, it is not possible to detect strain with high accuracy.

[0005] The present invention has been made in view of the above points, and has an object to provide a strain gauge that can output ambient temperature information of a resistor. [Means for solving the problem]

[0006] The strain gauge comprises a strain detection unit and a temperature detection unit formed on a flexible resin substrate, the strain detection unit having a functional layer formed from a metal, alloy, or metal compound directly on one surface of the substrate, and a resistor having α-Cr as its main component, formed from a film containing Cr, CrN, and CrN directly on one surface of the functional layer, the resistor including a plurality of juxtaposed resistor patterns and a folded portion connecting ends of the adjacent resistor patterns, the functional layer promoting crystal growth of the α-Cr and The thermocouple has a function of forming a film containing r as a main component, the resistor has a thickness of 0.05 μm or more and 2 μm or less, the functional layer has a thickness of 1 nm or more and 100 nm or less, a first metal layer made of a material having a lower gauge factor than the resistor is laminated on the folded portion, the resistance value of the first metal layer on the folded portion is lower than the resistance value of the folded portion, and the temperature detection unit is a thermocouple having a second metal layer formed on the base material from the same material as the resistor, and a third metal layer formed on the second metal layer from the same material as the first metal layer. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge that can output ambient temperature information of a resistor. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a plan view (part 1) illustrating a strain gauge according to a first embodiment; [Figure 2] FIG. 2 is a second plan view illustrating the strain gauge according to the first embodiment. [Figure 3] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 4] 3A to 3C are diagrams illustrating a manufacturing process of the strain gauge according to the first embodiment. [Figure 5] FIG. 10 is a plan view illustrating a strain detector according to a first 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 plan view illustrating a strain gauge according to the first embodiment, showing only the first layer. Fig. 3 is a cross-sectional view illustrating the strain gauge according to the first embodiment, where Fig. 3(a) shows a cross-section along line AA in Fig. 1, Fig. 3(b) shows a cross-section along line BB in Fig. 1, and Fig. 3(c) shows a cross-section along line CC in Fig. 1.

[0011] 1 to 3, the strain gauge 1 includes a strain detection unit 1S, a humidity detection unit 1H, and a temperature detection unit 1T, which are formed on the same substrate 10. The strain detection unit 1S, the humidity detection unit 1H, and the temperature detection unit 1T are arranged independently of each other and are not electrically connected.

[0012] In Figures 1 and 2, the humidity detection unit 1H, strain detection unit 1S, and temperature detection unit 1T are arranged from the top of the paper, but this is not limited to this and the humidity detection unit 1H, strain detection unit 1S, and temperature detection unit 1T can be arranged in any manner.

[0013] The strain detector 1S has a resistor 301, an electrode 40A, and a metal layer 431 formed on a substrate 10.

[0014] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 301 of the substrate 10 is provided is referred to as the upper side or one side, and the side on which the resistor 301 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 301 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 301 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.

[0015] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 301 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.

[0016] 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.

[0017] 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.

[0018] The resistor 301 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 301 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.

[0019] The resistor 301 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 301 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).

[0020] 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.

[0021] The thickness of resistor 301 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 301 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 301 (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 301 and warpage from substrate 10 caused by internal stress in the film.

[0022] For example, when the resistor 301 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 301, the gauge factor of the strain detection unit 1S can be 10 or more, and the temperature coefficient of gauge factor TCS and the 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 301 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0023] The electrodes 40A extend from both ends of the resistor 301 and are formed in a generally rectangular shape wider than the resistor 301 in a plan view. The electrodes 40A are a pair of electrodes for outputting a change in the resistance value of the resistor 301 caused by strain to the outside, and are joined to, for example, a lead wire for external connection. The resistor 301 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.

[0024] The electrode 40A can have a laminated structure in which multiple metal layers are stacked. Specifically, the electrode 40A has terminal portions 411 extending from both ends of the resistor 301 and a metal layer 421 formed on the upper surface of the terminal portion 411. Although the resistor 301 and the terminal portion 411 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0025] The material of the metal layer 421 can be selected from materials with better solder wettability than the terminal portion 411. For example, when the resistor 301 is a Cr mixed-phase film, the material of the metal layer 421 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 laminated film in which any of these metals, alloys, or compounds are appropriately laminated. The thickness of the metal layer 421 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 421 is preferably 1 μm or more, more preferably 3 μm or more. Note that when the metal layer 421 is formed by electroplating, the thickness of the metal layer 421 is preferably 30 μm or less in view of the ease of electroplating.

[0026] However, if solder wettability and solder erosion are not a problem, the terminal portion 411 itself may be used as an electrode without laminating the metal layer 421.

[0027] The resistor 301 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.

[0028] A metal layer 431 made of a material having a lower gauge factor than the resistor 301 is laminated on the folded portion 33. The material and thickness of the metal layer 431 are selected so that the resistance value of the metal layer 431 on the folded portion 33 is lower than the resistance value of the folded portion 33.

[0029] 1, the folded portion 33 of the resistor 301 is linear, but the folded portion of the resistor 301 is not limited to being linear and may have any shape. For example, the folded portion of the resistor 301 may be curved, or may have a mixture of linear and curved portions.

[0030] The material of the metal layer 431 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 301. For example, when the resistor 301 is a Cr mixed-phase film, the material of the metal layer 431 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 431 is not particularly limited and can be appropriately selected depending on the purpose as long as the resistance value of the metal layer 431 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.

[0031] The metal layer 431 may be formed using the same material as the metal layer 421 in the same process as the metal layer 421. Alternatively, the metal layer 431 may be formed using a different material from the metal layer 421 in a process different from the metal layer 421. In this case, the thickness of the metal layer 431 does not need to be the same as the thickness of the metal layer 421. For convenience, the resistor pattern 31, the metal layer 421, and the metal layer 431 are shown in a matte finish in FIG. 1.

[0032] A cover layer 601 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 301 and the metal layer 431 and expose the electrode 40A. By providing the cover layer 601, it is possible to prevent mechanical damage, etc. from occurring to the resistor 301 and the metal layer 431. Furthermore, by providing the cover layer 601, it is possible to protect the resistor 301 and the metal layer 431 from moisture, etc. Note that the cover layer 601 may be provided so as to cover a wider area excluding the electrode 40A.

[0033] The cover layer 601 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 601 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 601 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0034] The humidity detection unit 1H has a metal layer 302, a metal layer 432, an electrode 40B, and a moisture-sensitive layer 602 formed on the substrate 10.

[0035] The metal layer 302 includes two interdigitated comb patterns formed on the substrate 10 so as not to contact each other. The metal layer 302 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. The material and thickness of the metal layer 302 may be the same as those of the resistor 301, for example.

[0036] The metal layer 432 is laminated on the metal layer 302 and has a pattern with the same planar shape as the metal layer 302. The material and thickness of the metal layer 432 can be the same as those of the metal layer 431, for example.

[0037] The electrode 40B can have a layered structure in which a metal layer 422 is layered on a terminal portion 412. The terminal portion 412 extends from both ends of the metal layer 302 and is formed in a substantially rectangular shape in a plan view. The metal layer 422 extends from both ends of the metal layer 432 and is formed on the terminal portion 412 in a substantially rectangular shape in a plan view.

[0038] In other words, electrode 40B includes a pair of terminal portions 412 extending from the ends of metal layers 302 constituting each comb pattern, and metal layers 422 extending from the ends of metal layers 432 constituting each comb pattern onto each terminal portion 412.

[0039] The metal layer 302 and the terminal portion 412 are formed so as to overlap with the metal layers 432 and 422 in a plan view.

[0040] The metal layers 302 and 432 constituting one comb pattern connected to one of the electrodes 40B are not directly electrically connected to the metal layers 302 and 432 constituting the other comb pattern connected to the other electrode 40B. One comb pattern and the other comb pattern are electrically connected via a moisture-sensitive layer 602 that fills the gap between at least two comb patterns. The moisture-sensitive layer 602 may be formed on the two comb patterns and fills the gap between the two comb patterns.

[0041] The moisture-sensitive layer 602 is made of a material whose resistance changes with moisture absorption and desorption (the resistance decreases as humidity increases). The material of the moisture-sensitive layer 602 is not particularly limited and can be appropriately selected depending on the purpose, as long as the resistance changes with moisture absorption and desorption. Examples of the material include lithium chloride (LiCl), sulfonated polystyrene, potassium metaphosphate (KPO), phosphorus pentoxide (PO), carbon (C), selenium (Se), germanium (Ge), silicon (Si), aluminum oxide (AlO), chromium oxide (CrO), nickel oxide (NiO), iron oxide (FeO), zinc oxide (ZnO), magnesiochromite (MgCrO), magnesium aluminate (MgAlO), and magnesioferrite (MgFeO). The thickness of the moisture-sensitive layer 602 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, approximately 1 μm to 30 μm.

[0042] The electrodes 40B are a pair of electrodes for outputting to the outside a change in the resistance value of the moisture-sensitive layer 602 in response to a change in the ambient humidity of the strain detection unit 1S, and are connected to, for example, lead wires for external connection.

[0043] The temperature detection unit 1T has a metal layer 303, a metal layer 433, and an electrode 40C formed on the substrate 10.

[0044] The metal layer 303 is a thin film formed in a solid state on the substrate 10. The metal layer 303 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. The material and thickness of the metal layer 303 may be the same as those of the resistor 301 and the metal layer 302, for example.

[0045] Metal layer 433 is a solid thin film laminated on metal layer 303. The material and thickness of metal layer 433 can be the same as, for example, metal layers 431 and 432. Because metal layer 303 and metal layer 433 are made of different materials, they can function as a thermocouple. By making metal layers 303 and 433 solid thin films, the influence of distortion can be reduced, enabling accurate temperature detection.

[0046] The electrode 40C can have a laminated structure in which a metal layer 423 is laminated on a terminal portion 413. The terminal portion 413 extends from both end portions of the metal layer 303 and is formed in a substantially rectangular shape in a plan view. One side of the metal layer 423 extends from one end portion of the metal layer 433 and is formed in a substantially rectangular shape on one side of the terminal portion 413 in a plan view. The other side of the metal layer 423 is formed in a substantially rectangular shape on the other side of the terminal portion 413, but is not electrically connected to the metal layer 433.

[0047] The electrodes 40C are a pair of electrodes for outputting to the outside the potential difference (thermoelectric power) that occurs between the metal layer 303 and the metal layer 433 in response to changes in the ambient temperature of the strain detection unit 1S, and are connected to, for example, a lead wire for external connection.

[0048] A moisture-proof layer 603 may be provided on the upper surface 10a of the substrate 10 so as to cover the metal layers 303 and 433 and expose the electrode 40C. By providing the moisture-proof layer 603, the influence of moisture on the metal layers 303 and 433 can be reduced, enabling accurate temperature detection. The moisture-proof layer 603 may also be provided so as to cover a wider area excluding the electrode 40C.

[0049] The material of moisture-proof layer 603 is not particularly limited and can be selected appropriately depending on the purpose as long as it can reduce the effects of moisture on metal layers 303 and 433, and examples thereof include high-density polyethylene, polyvinylidene chloride, polytetrafluoroethylene, polypropylene, butyl rubber, etc. The thickness of moisture-proof layer 603 is not particularly limited and can be selected appropriately depending on the purpose, and can be, for example, about 2 μm to 30 μm.

[0050] Although resistor 301, terminal portion 411, metal layer 302, terminal portion 412, metal layer 303, and terminal portion 413 are designated by different reference numerals for convenience, they can be integrally formed from the same material in the same process. Also, although metal layer 421, metal layer 431, metal layer 422, metal layer 432, metal layer 423, and metal layer 433 are designated by different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0051] 4 is a diagram illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section of the strain detection unit 1S corresponding to FIG. 3(b). The layer structures of the humidity detection unit 1H and the temperature detection unit 1T are the same as those of the strain detection unit 1S, so cross-sectional views and the like are omitted.

[0052] To manufacture the strain gauge 1, first, in the step shown in Figure 4(a), a substrate 10 is prepared, a metal layer 300 is formed on the upper surface 10a of the substrate 10, and then a metal layer 310 is formed on the metal layer 300.

[0053] Metal layer 300 is a layer that is ultimately patterned to become resistor 301, terminal portion 411, metal layer 302, terminal portion 412, metal layer 303, and terminal portion 413. Therefore, the material and thickness of metal layer 300 are the same as the material and thickness of resistor 301 and the like described above. Metal layer 310 is a layer that is ultimately patterned to become metal layer 421, metal layer 431, metal layer 422, metal layer 432, metal layer 423, and metal layer 433. Therefore, the material and thickness of metal layer 310 are the same as the material and thickness of metal layer 421 and the like described above.

[0054] 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.

[0055] 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.

[0056] 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 301). 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.

[0057] 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.

[0058] 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 301), 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 (biphenyl), Examples of the metal include one or more metals selected from the group consisting of aluminum (spherical), 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.

[0059] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 strain detection unit 1S can have a gauge factor of 10 or more, and the gauge factor temperature coefficient TCS and temperature coefficient of resistance TCR 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).

[0065] 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.

[0066] 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, the stability of the gauge characteristics of the strain detection unit 1S can be improved. Furthermore, the material constituting the functional layer diffuses into the metal layer 300, thereby improving the gauge characteristics of the strain detection unit 1S.

[0067] 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.

[0068] Next, in a step shown in Fig. 4(b), the metal layer 310 is patterned by photolithography to form metal layers 421, 431, 422, 432, 423, and 433, each having the planar shape shown in Fig. 1. Next, in a step shown in Fig. 4(c), the metal layer 300 is patterned by photolithography to form resistor 301, terminal portion 411, metal layer 302, terminal portion 412, metal layer 303, and terminal portion 413, each having the planar shape shown in Fig. 2.

[0069] As a result, in the strain detection unit 1S, a metal layer 431 is laminated on the folded portion 33 of the resistor 301. Also, in the strain detection unit 1S, a metal layer 421 is laminated on the terminal portion 411 to form an electrode 40A. Also, in the humidity detection unit 1H, a metal layer 432 is laminated on the metal layer 302. Also, in the humidity detection unit 1H, a metal layer 422 is laminated on the terminal portion 412 to form an electrode 40B. Also, in the temperature detection unit 1T, a metal layer 433 is laminated on the metal layer 303. Also, in the temperature detection unit 1T, a metal layer 423 is laminated on the terminal portion 413 to form an electrode 40C.

[0070] 4(c), a cover layer 601 is provided on the upper surface 10a of the substrate 10 to cover the resistor 301 and the metal layer 431 and expose the electrode 40A, a moisture-sensitive layer 602 is provided on the upper surface 10a of the substrate 10 to cover the metal layer 302 and the metal layer 432 and expose the electrode 40B, and a moisture-proof layer 603 is provided on the upper surface 10a of the substrate 10 to cover the metal layer 303 and the metal layer 433 and expose the electrode 40C, thereby completing the strain gauge 1. However, the cover layer 601 and the moisture-proof layer 603 may be provided as needed.

[0071] The cover layer 601 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 301 and the metal layer 431 and expose the electrode 40A, and then heating and curing the film. The cover layer 601 may also be produced by applying a liquid or paste thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 301 and the metal layer 431 and expose the electrode 40A, and then heating and curing the resin. The moisture-sensitive layer 602 and the moisture-proof layer 603 can be produced by the same method as the cover layer 601.

[0072] In the above steps, an example has been shown in which metal layer 421, metal layer 431, metal layer 422, metal layer 432, metal layer 423, and metal layer 433 are formed using the same material, but this is just one example, and as described above, metal layer 421, metal layer 422, and metal layer 423 may be formed in different steps using different materials from metal layer 431, metal layer 432, and metal layer 433. Also, metal layer 421, metal layer 422, and metal layer 423 may not be provided.

[0073] In this way, the strain gauge 1 has the temperature detection unit 1T disposed near the strain detection unit 1S on the same substrate 10. This allows the temperature detection unit 1T to detect the ambient temperature of the resistor 301 and output information about the ambient temperature of the resistor 301 to the outside of the strain gauge 1. As a result, even if the TCR of the resistor 301 varies, the effect of temperature changes can be reduced and strain can be calculated accurately by performing a correction calculation on the detection result of the strain detection unit 1S in an external circuit based on the detection result of the temperature detection unit 1T.

[0074] Furthermore, changes in TCR due to humidity can be a problem depending on the materials used for the base material and resistor. In this case, the effects of temperature and humidity changes can be reduced and strain can be calculated with high accuracy by performing correction calculations in an external circuit using the detection results of the temperature detection unit 1T and the humidity detection unit 1H.

[0075] Furthermore, in the strain detection unit 1S, by laminating a metal layer 431 made of a material with a lower gauge factor than the resistor 301 on the folded portion 33 of the resistor 301 and making the resistance value of the metal layer 431 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 detection unit 1S.

[0076] That is, at the folded portion 33 of the resistor 301, a larger amount of current flows toward the metal layer 431, which has a lower resistance than the folded portion 33. Therefore, even if strain occurs in the misdetection direction (the Y direction in this case) along which the folded portion 33 of the resistor 301 extends, the output is mainly from the metal layer 431, which has a lower gauge factor than the resistor 301, and therefore a large output is not obtained from the electrode 40A. On the other hand, except for the folded portion 33 of the resistor 301, all of the current flows through the resistor 301, which has a high gauge factor. Therefore, when strain occurs in the grid direction of the resistor 301 (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. However, if a change in resistance due to strain in the misdetection direction is not a problem, the metal layer 431 need not be stacked.

[0077] This effect is obtained regardless of the material of the resistor 301, but is particularly noticeable when the resistor 301 is made of a Cr mixed phase film having a large gauge factor.

[0078] <Modification 1 of the First Embodiment> In the first modification of the first embodiment, an example is shown in which the structure near the folded portion of the strain detector is different. 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.

[0079] The strain detection unit 1S shown in the first embodiment can be modified to the following strain detection units 2S, 3S, and 4S. In the first modification of the first embodiment, the humidity detection unit 1H and the temperature detection unit 1T have the same configurations as those in the first embodiment.

[0080] Fig. 5(a) is a plan view (part 1) illustrating a strain detection unit according to Modification 1 of the first embodiment. Referring to Fig. 5(a), strain detection unit 2S differs from strain detection unit 1S (see Fig. 1, etc.) in that folded portion 33 is replaced with folded portion 34 and metal layer 431 is replaced with metal layer 441.

[0081] The resistor 301 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions in the same direction (the X direction in the example of Figure 5(a)), and a folded portion 34 connecting the opposing sides of the ends of adjacent resistor patterns 31.

[0082] A metal layer 441 made of a material having a lower gauge factor than the resistor 301 is laminated on the folded portion 34. The material and thickness of the metal layer 441 are selected so that the resistance value of the metal layer 441 on the folded portion 34 is lower than the resistance value of the folded portion 34. The material and thickness of the metal layer 441 can be the same as those of the metal layer 431, for example.

[0083] The folded portion of the resistor 301 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 301 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 5(a).

[0084] In either of the above cases, by laminating a metal layer made of a material with a lower gauge factor than resistor 301 on the folded portion of resistor 301 and making the resistance value of the metal layer on the folded portion lower than the resistance value of the folded portion, it is possible to reduce the sensitivity in the erroneous detection direction and improve the strain detection accuracy of the strain detection unit.

[0085] Fig. 5(b) is a plan view (part 2) illustrating a strain detection unit according to Modification 1 of the first embodiment. Referring to Fig. 5(b), strain detection unit 3S differs from strain detection unit 1S (see Fig. 1 etc.) in that metal layer 431 is replaced with metal layer 451.

[0086] The metal layer 451 is laminated on the folded portion 33 of the resistor element 301, and further extends from above the folded portion 33 to a part of the resistor pattern 31, and is formed into an overall U-shape. The material and thickness of the metal layer 451 can be the same as those of the metal layer 431, for example.

[0087] In this way, a part of the metal layer 451 may extend from on the folded portion 33 to a part of the resistor pattern 31. In this case, even when manufacturing variations are taken into consideration, the metal layer 451 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 detection unit 3S can be reliably improved.

[0088] However, in the strain detection unit 3S, the length in the grid direction of the resistance pattern 31 (the length of the portion where the metal layer 451 is not laminated) is slightly shorter than in the strain detection unit 1S, so a slight decrease in detection sensitivity is expected.

[0089] Fig. 5(c) is a plan view (part 3) illustrating a strain detection unit according to the first modification of the first embodiment. Referring to Fig. 5(c), the strain detection unit 4S differs from the strain detection unit 1S (see Fig. 1, etc.) in that the folded portion 33 is replaced with the folded portion 36 and the metal layer 431 is replaced with the metal layer 461.

[0090] The resistor 301 includes a plurality of resistor patterns 31 arranged side by side with their longitudinal directions in the same direction (the X direction in the example of Figure 5(c)), and a folded portion 36 connecting the outer ends of adjacent resistor patterns 31.

[0091] A metal layer 461 made of a material having a lower gauge factor than the resistor 301 is laminated on the folded portion 36. The material and thickness of the metal layer 461 are selected so that the resistance value of the metal layer 461 on the folded portion 36 is lower than the resistance value of the folded portion 36. The material and thickness of the metal layer 461 can be the same as those of the metal layer 431, for example.

[0092] Unlike the folded portion 33 (see FIG. 1), the folded portion 36 is formed in a curved shape (for example, a U-shape). In this case, too, by laminating a metal layer 461 made of a material having a lower gauge factor than the resistor 301 on the folded portion 36 of the resistor 301 and by making the resistance value of the metal layer 461 on the folded portion 36 lower than the resistance value of the folded portion 36, it is possible to reduce the sensitivity in the erroneous detection direction and improve the strain detection accuracy of the strain detection unit 4S.

[0093] In the strain detection unit 4S, as in the strain detection unit 3S, a portion of the metal layer 461 may extend from the folded portion 36 onto a portion of the resistor pattern 31. In this case, the metal layer 461 can be reliably laminated on the folded portion 36 even taking into account manufacturing variations. As a result, the sensitivity in the erroneous detection direction can be reliably reduced, and the strain detection accuracy of the strain detection unit 4S can be reliably improved. However, since the length of the resistor pattern 31 in the grid direction (the length of the portion where the metal layer 461 is not laminated) is slightly shortened, a slight decrease in detection sensitivity is expected.

[0094] 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.

[0095] For example, if the change in TCR due to humidity is not a problem due to the materials of the substrate or resistor, the strain gauge may be configured only with a strain detection section and a temperature detection section, without providing a humidity detection section. [Explanation of symbols]

[0096] 1 strain gauge, 1S, 2S, 3S, 4S strain detection section, 1H humidity detection section, 1T temperature detection section, 10 substrate, 10a upper surface, 301 resistor, 302, 303, 421, 422, 423, 431, 432, 433, 441, 451, 461 metal layer, 31 resistor pattern, 33, 34, 36 folded portion, 40A, 40B, 40C electrodes, 411, 412, 413 terminal section, 601 cover layer, 602 moisture-sensitive layer, 603 moisture-proof layer

Claims

1. The device includes a strain detection unit and a temperature detection unit formed on a flexible resin base material, The strain detection unit 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 resistor includes a plurality of resistor patterns arranged in parallel and a folded portion connecting ends of adjacent resistor patterns, 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, a first metal layer made of a material having a lower gauge factor than the resistor is laminated on the folded portion, and a resistance value of the first metal layer on the folded portion is lower than a resistance value of the folded portion; The temperature detection unit a second metal layer formed on the substrate from the same material as the resistor; a third metal layer formed on the second metal layer from the same material as the first metal layer; and a strain gauge that is a thermocouple.

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.

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

4. a second electrode electrically connected to the second metal layer; the second electrode includes a pair of second terminals extending from both ends of the second metal layer, and a fifth metal layer formed on each of the second terminals; the fifth metal layer formed on one of the second terminals is electrically connected to the third metal layer; the fifth metal layer formed on the other second terminal portion is not electrically connected to the third metal layer, 4. The strain gauge according to claim 1, wherein the third metal layer and the fifth metal layer are made of the same material.

5. Further comprising a humidity detection unit, The humidity detection unit Two interdigitated patterns that do not touch each other, a moisture-sensitive layer filling the gaps between at least two of the comb-shaped patterns; The two comb patterns are: a sixth metal layer formed on the substrate from the same material as the resistor; 5. The strain gauge according to claim 1, further comprising: a seventh metal layer formed on the sixth metal layer and made of the same material as the first metal layer.

6. a third electrode electrically connected to the sixth metal layer; 6. The strain gauge according to claim 5, wherein the third electrode includes a pair of third terminal portions extending from ends of the sixth metal layer constituting each of the comb-shaped patterns, and an eighth metal layer extending from ends of the seventh metal layer constituting each of the comb-shaped patterns onto each of the third terminal portions.

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

8. The strain gauge according to claim 1 , further comprising a moisture-proof layer covering the second metal layer and the third metal layer.

Images