Strain gauges

Abstract

To provide a strain gauge with improved strain resistance.SOLUTION: A strain gauge provided herein comprises a substrate and a resistor formed on the substrate, the resistor comprising sensing sections and connecting sections connected in series with the sensing sections, where the connecting sections are made of a material having an elastic modulus lower than that of the sensing sections and are arranged to be in direct contact with the sensing sections.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 a measurement object to detect the strain of the measurement object. The strain gauge includes a resistor that detects the strain, and the resistor is formed on, for example, an insulating resin. The resistor is connected to an electrode via, for example, a wiring (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-74934 A Summary of the Invention [Problem to be solved by the invention]

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

[0005] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a strain gauge capable of improving strain resistance. [Means for solving the problem]

[0006] The strain gauge includes a substrate and a resistor formed on the substrate, the resistor comprising: Multiple A detection unit and the Multiple Detection Unit At least one of connected in series with Multiple a connection portion, the connection portion being formed from a material having a lower elastic modulus than the detection portion and being disposed so as to be in direct contact with the detection portion. The resistor includes a plurality of elongated portions arranged in parallel, each including the detection portion, and a folded portion connecting ends of the adjacent elongated portions, and one or more of the connection portions are arranged on each of the elongated portions. . Effect of the Invention

[0007] According to the disclosed technique, a strain gauge capable of improving strain resistance can be provided. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Diagram 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Diagram 3] 4 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. [Figure 4] 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment. FIG. [Diagram 5] FIG. 2 is a plan view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 6] 4 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. FIG. [Figure 7] 11 is a plan view illustrating a strain gauge according to a second modified example of the first embodiment. FIG. [Figure 8] 10 is a cross-sectional view illustrating a strain gauge according to a second modified example of the first embodiment. FIG. [Figure 9] 11 is a plan view illustrating a strain gauge according to a third modified example of the first embodiment. FIG. [Figure 10] 11 is a cross-sectional view illustrating a strain gauge according to a third modified example of the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] First embodiment [Structure of strain gauge] Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1. Fig. 3 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in Fig. 1.

[0011] 1 to 3, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. For convenience, only the outer edge of the cover layer 60 is shown by a dashed line in Fig. 1 to 3. The cover layer 60 may be provided as needed.

[0012] In this embodiment, for convenience, in the strain gauge 1, the side of the substrate 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. In addition, the surface on which the resistor 30 is provided in each part is referred to as one side or upper surface, and the surface on which the resistor 30 is not provided is referred to as the other side or lower surface. However, the strain gauge 1 can be used upside down or placed at any angle. In addition, the planar view refers to the object being viewed from the normal direction of the upper surface 10a of the substrate 10, and the planar shape refers to the shape of the object being viewed from the normal direction of the upper surface 10a of the substrate 10.

[0013] 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, and 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.

[0014] 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, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0015] 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.

[0016] Examples of materials other than resin for the substrate 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. In this case, for example, an insulating film is formed on the metal substrate 10.

[0017] 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. The resistor 30 includes a detection part 31 and a connection part 32 connected in series with the detection part 31.

[0018] The resistor 30 has a structure in which a plurality of elongated portions are arranged at a predetermined interval with their longitudinal direction in the same direction (the direction of line AA in FIG. 1), and the ends of adjacent elongated portions are alternately connected to form a zigzag fold as a whole. That is, the resistor 30 includes a plurality of elongated portions arranged in parallel and a folded portion that connects the ends of adjacent elongated portions. The longitudinal direction of the plurality of elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction perpendicular to line AA in FIG. 1).

[0019] One end in the longitudinal direction of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction to form terminal ends 30e1 and 30e2 in the grid width direction of the resistor 30. The terminal ends 30e1 and 30e2 in the grid width direction of the resistor 30 are electrically connected to the electrodes 50 via the wiring 40. In other words, the wiring 40 electrically connects the terminal ends 30e1 and 30e2 in the grid width direction of the resistor 30 to the electrodes 50.

[0020] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrode 50. The wiring 40 is not limited to being linear, and may have any pattern. In addition, the wiring 40 may have any width and any length.

[0021] The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40, and are formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting to the outside a change in resistance value of the resistor 30 caused by distortion, and for example, lead wires for external connection are joined to the electrodes 50.

[0022] The electrode 50 has a pair of metal layers 51 and a metal layer 52 laminated on the upper surface of each of the metal layers 51. The metal layers 51 are electrically connected to the ends 30e1 and 30e2 of the resistor 30 via the wiring 40. The metal layer 51 is formed in a substantially rectangular shape in a plan view. The metal layer 51 may be formed to have the same width as the wiring 40.

[0023] Although the detection unit 31, the wiring 40, and the metal layer 51 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the detection unit 31, the wiring 40, and the metal layer 51 have approximately the same thickness.

[0024] The metal layer 52 is formed of a material having a lower resistance than the detection section 31. The material of the metal layer 52 is not particularly limited as long as it is a material having a lower resistance than the detection section 31, and can be appropriately selected depending on the purpose. For example, when the detection section 31 is a Cr mixed phase film described later, the material of the metal layer 52 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, and compounds are appropriately laminated. The thickness of the metal layer 52 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 3 μm to 5 μm.

[0025] One or more other metal layers may be laminated on the upper surface of metal layer 52. For example, metal layer 52 may be a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be laminated in this order on the upper surface of the copper layer. By forming the top layer of electrode 50 as a gold layer, the solder wettability of electrode 50 can be improved.

[0026] The cover layer 60 is formed on the substrate 10, covers the resistor 30 and the wiring 40, and exposes the electrodes 50. A part of the wiring 40 may be exposed from the cover layer 60. By providing the cover layer 60 that covers the resistor 30 and the wiring 40, it is possible to prevent mechanical damage, etc. from occurring to the resistor 30 and the wiring 40. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 and the wiring 40 from moisture, etc. The cover layer 60 may be provided so as to cover the entire portion except for the electrodes 50.

[0027] 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, composite resin (e.g., silicone resin, polyolefin resin), etc. The cover layer 60 may contain a filler or a pigment. There is no particular limit to 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.

[0028] [Detailed structure of resistor] In the resistor 30, the connection portion 32 is disposed so as to be in direct contact with the detection portion 31. The length of one connection portion 32 in the grid direction is, for example, about 50 μm. In the resistor 30, the detection of strain is mainly performed by the detection portion 31.

[0029] For example, the connection parts 32 can be disposed one by one on each of the elongated portions constituting the resistor 30. Furthermore, the connection parts 32 can be disposed, for example, at the same position in the grid direction on each of the elongated portions constituting the resistor 30. Here, "disposed at the same position in the grid direction" refers to a state in which a single straight line perpendicular to the grid direction can be drawn to pass through the connection parts 32 disposed on each of the elongated portions.

[0030] The connection portion 32 is disposed, for example, between adjacent detection portions 31, and conducts the adjacent detection portions 31. Each detection portion 31 and each connection portion 32 are connected in series, and as a whole form one resistor 30. Note that the connection portion 32 may be disposed only at a portion that contacts the terminations 30e1 and / or 30e2. In this case, the connection portion 32 conducts one end and / or both ends of one zigzag-shaped detection portion 31 with the wiring 40.

[0031] It is preferable that the width and thickness of the connection portion 32 are equal to the width and thickness of the detection portion 31. This allows adjacent detection portions 31 to be reliably conductive via the connection portion 32 to form one resistor 30, allowing the strain gauge 1 to function normally. Here, the width and thickness of the connection portion 32 are considered to be equal to the width and thickness of the detection portion 31 when the width and thickness of the connection portion 32 are within ±10% or less, respectively.

[0032] The detection unit 31 can be formed, for example, from a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the detection unit 31 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).

[0033] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0034] The thickness of the detection section 31 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 0.05 μm to 2 μm. In particular, it is preferable that the thickness of the detection section 31 is 0.1 μm or more in order to improve the crystallinity of the crystals constituting the detection section 31 (for example, the crystallinity of α-Cr). It is further preferable that the thickness of the detection section 31 is 1 μm or less in order to reduce film cracks and warping from the substrate 10 caused by the internal stress of the film constituting the detection section 31. The width of the detection section 31 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be, for example, about 10 μm to 100 μm in consideration of measures against disconnection.

[0035] For example, when the detection section 31 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making α-Cr the main component of the detection section 31, 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 in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the detection section, but from the viewpoint of improving the gauge characteristics, the detection section 31 preferably contains α-Cr at 80% by weight or more, and more preferably contains 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0036] When the detection unit 31 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr2N. By containing 20% ​​by weight or less of CrN and Cr2N in the Cr mixed-phase film, a decrease in the gauge factor can be suppressed.

[0037] In addition, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant due to the Cr2N having semiconductor properties. Furthermore, by reducing the formation of ceramics, brittle fracture is reduced.

[0038] On the other hand, if a small amount of N2 or atomic N is mixed into the film, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in the film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[0039] The connection part 32 is formed from a material having a lower elastic modulus than the detection part 31. The elastic modulus of the connection part 32 is preferably ½ or less, more preferably ⅓ or less, and particularly preferably ¼ or less, of the elastic modulus of the detection part 31.

[0040] The connection portion 32 is preferably formed from a material having a higher electrical conductivity than the detection portion 31. This is to make it difficult for the connection portion 32 to contribute to the detection of strain. Examples of materials for the connection portion 32 include Au, Ag, Cu, Al, Pt, and Fe. These metals have a relatively low elastic modulus and a relatively high electrical conductivity. Note that materials with a low elastic modulus have high ductility and are less likely to break.

[0041] For example, when a Cr mixed phase film is used as the detection unit 31, the elastic modulus is about 400 GPa. In this case, for example, Pt with an elastic modulus of about 200 GPa or Fe with an elastic modulus of about 170 GPa can be used as the material of the connection unit 32. Also, when nickel chromium is used as the detection unit 31, the elastic modulus is about 214 GPa. In this case, for example, Au with an elastic modulus of about 80 GPa or Al with an elastic modulus of about 70 GPa can be used as the material of the connection unit 32.

[0042] Thus, in the strain gauge 1, the resistor 30 includes the detection portion 31 and the connection portion 32 connected in series with the detection portion 31. The connection portion 32 is formed of a material having a lower elastic modulus than the detection portion 31 and is arranged so as to be in direct contact with the detection portion 31. Since the detection portion 31 has a high elastic modulus, if no measures are taken, brittle fracture may occur and cracks may occur when a strong force is applied due to an external factor. However, in the strain gauge 1, by arranging the connection portion 32 having a lower elastic modulus than the detection portion 31 in series with the detection portion 31, even if a strong force is applied due to an external factor, the connection portion 32 behaves as if it were a spring, so that cracks are unlikely to occur in the detection portion 31. In other words, by arranging the connection portion 32 having a lower elastic modulus than the detection portion 31 in series with the detection portion 31, it is possible to realize an improvement in the strain limit (improvement in strain resistance).

[0043] Providing the connection portion 32 is particularly effective when the detection portion 31 has a thickness of 0.05 μm or more and 2 μm or less, and is extremely effective when the detection portion 31 has a thickness of 0.05 μm or more and 1 μm or less.

[0044] [Strain gauge manufacturing method] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, metal layer A) is formed on an upper surface 10a of the base material 10. The metal layer A is a layer that is finally patterned to become the detection unit 31, the wiring 40, and the metal layer 51. Therefore, the material and thickness of the metal layer A are the same as the material and thickness of the detection unit 31, the wiring 40, and the metal layer 51 described above.

[0045] The metal layer A can be formed by, for example, a magnetron sputtering method using a target made of a raw material capable of forming the metal layer A. The metal layer A may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulsed laser deposition method, or the like instead of the magnetron sputtering method.

[0046] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the base material 10 by, for example, conventional sputtering, before depositing the metal layer A.

[0047] In the present application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper layer, the metal layer A (detection unit 31). The functional layer preferably further has a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and a function of improving adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0048] Since the insulating resin film that constitutes the substrate 10 contains oxygen and moisture, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, particularly when the metal layer A contains Cr, since Cr forms a self-oxidized film.

[0049] 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 A (detection unit 31), 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), and the like can be used. Examples of the metal include one or more metals selected from the group consisting of ruthenium (Ru), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0050] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compound include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0051] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the detection section. In this range, the crystal growth of α-Cr can be promoted, and a decrease in the detection sensitivity of strain due to a part of the current flowing through the detection section flowing through the functional layer can be prevented.

[0052] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the detection section. In this range, the crystal growth of α-Cr can be promoted, and the strain detection sensitivity can be further prevented from decreasing due to a part of the current flowing through the detection section flowing through the functional layer.

[0053] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 100 or less of the thickness of the detection section, which can further prevent a part of the current flowing through the detection section from flowing through the functional layer, thereby preventing a decrease in the detection sensitivity of strain.

[0054] When the functional layer is made of an insulating material such as an oxide or a nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0055] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0056] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm, which can promote the crystal growth of α-Cr and can be more easily formed without cracking the functional layer.

[0057] The planar shape of the functional layer is patterned to be substantially the same as the planar shapes of the detection unit 31, the wiring 40, and the metal layer 51 shown in FIG. 1. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shapes of the detection unit 31, the wiring 40, and the metal layer 51. When the functional layer is made of an insulating material, it does not have to be patterned to be the same as the planar shapes of the detection unit 31, the wiring 40, and the metal layer 51. In this case, the functional layer may be formed in a solid shape at least in the region where the detection unit 31 is formed. Alternatively, the functional layer may be formed in a solid shape on the entire upper surface of the substrate 10.

[0058] Furthermore, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, so that the thickness and surface area of ​​the functional layer are increased, and the heat generated by the resistor can be dissipated to the substrate 10. As a result, the deterioration of the measurement accuracy of the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0059] The functional layer can be formed in vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target 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, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0060] 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 a 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.

[0061] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A and can be selected appropriately depending on the purpose. For example, it is possible to use Ti for the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component for the metal layer A.

[0062] In this case, for example, the metal layer A 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 A 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. In this case, the ratio of CrN and Cr2N contained in the Cr mixed phase film, and the ratio of Cr2N in CrN and Cr2N can be adjusted by changing the amount and pressure of the nitrogen gas introduced (nitrogen partial pressure) or by adjusting the heating temperature by providing a heating process.

[0063] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film containing α-Cr, which has a stable crystal structure, as a main component, can be formed. Furthermore, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

[0064] When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and improving the adhesion between the base material 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0065] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystal phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0066] Next, the metal layer A is patterned into the planar shape of Fig. 1 by photolithography to form the detection section 31, the wiring 40, and the metal layer 51. Then, the connection section 32 is formed in series with the detection section 31 so as to be in direct contact with the detection section 31, forming a single resistor 30. The connection section 32 can be formed by, for example, a vapor deposition method, a sputtering method, or the like. The connection section 32 may also be formed by using a coating technique such as a sol-gel method or an inkjet method.

[0067] Next, the metal layer 52 is formed on the upper surface of the metal layer 51. The metal layer 52 can be formed by, for example, a well-known semi-additive method. The material and thickness of the metal layer 52 are as described above.

[0068] Thereafter, as necessary, a cover layer 60 that covers the resistor 30 and the wiring 40 and exposes the electrodes 50 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 wiring 40 and expose the electrodes 50, 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 wiring 40 and expose the electrodes 50, and then heating and curing the resin.

[0069] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the detection unit 31, the wiring 40, and the metal layer 51, the strain gauge 1 has a cross-sectional shape as shown in Fig. 4. The layer indicated by reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is similar to, for example, the detection unit 31, the wiring 40, and the metal layer 51 in Fig. 1. However, as described above, the functional layer 20 may be formed solidly on a part or all of the upper surface 10a of the substrate 10.

[0070] First Modification of the First Embodiment In the first modification of the first embodiment, an example of a strain gauge in which a region where a connection portion is provided is different will be described. Note that in the first modification of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

[0071] Fig. 5 is a plan view illustrating a strain gauge according to Modification 1 of the first embodiment. Fig. 6 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the first embodiment, showing a cross section along line CC in Fig. 5. Referring to Figs. 5 and 6, the strain gauge 1A is similar to the strain gauge 1 in that the connection parts 32 are arranged one by one on each of the elongated parts constituting the resistor 30. However, the strain gauge 1A differs from the strain gauge 1 in that the connection parts 32 are also arranged on the folded-back parts of the resistor 30.

[0072] In this way, the connection parts 32 are not limited to each elongated part constituting the resistor 30, but can also be arranged at the folded-back part of the resistor 30. This increases the number of parts that behave like a spring when a strong force is applied due to an external factor, thereby further improving the strain resistance of the detection part 31.

[0073] Second Modification of the First Embodiment In the second modification of the first embodiment, another example of a strain gauge in which a region where a connection portion is provided is different will be described. Note that in the second modification of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

[0074] Fig. 7 is a plan view illustrating a strain gauge according to Modification 2 of the first embodiment. Fig. 8 is a cross-sectional view illustrating the strain gauge according to Modification 2 of the first embodiment, taken along line DD in Fig. 7. With reference to Figs. 7 and 8, strain gauge 1B differs from strain gauge 1 in that wiring 40 is replaced with wiring 40B.

[0075] The wiring 40B includes a plurality of conductive portions 41 and a connection portion 42 connected in series with the conductive portions 41. The connection portion 42 is formed so as to be in direct contact with the conductive portion 41. For example, one connection portion 42 may be disposed on each of the wirings 40. Also, the connection portion 42 may be disposed, for example, at the same position as the connection portion 32 in the grid direction. Also, the connection portion 42 may be disposed at a portion where the resistor 30 is folded back from its end.

[0076] The connection portion 42 is disposed between adjacent conductive portions 41, and provides electrical continuity between the adjacent conductive portions 41. The connection portion 42 is also disposed between adjacent conductive portions 41 and the detection portion 31, and provides electrical continuity between the adjacent conductive portions 41 and the detection portion 31. The resistor 30, each conductive portion 41, and each connection portion 42 are connected in series.

[0077] The width and thickness of the connection portion 42 are preferably equal to the width and thickness of the conductive portion 41. This allows the connection portion 42 to reliably conduct electricity between adjacent conductive portions 41. Here, the width and thickness of the connection portion 42 are considered to be equal to the width and thickness of the conductive portion 41 when the width and thickness of the connection portion 42 are within ±10% or less of the width and thickness of the conductive portion 41, respectively.

[0078] In the strain gauge 1B, disconnection is not limited to the detection part 31, and there is a risk of disconnection in the conductive part 41, which is made of the same material as the detection part 31. Therefore, by arranging the connection part 42 on each wiring 40B, the connection part 42 behaves like a spring when a strong force is applied due to an external factor, thereby reducing the risk of the conductive part 41 disconnecting.

[0079] <Modification 3 of the First Embodiment> In the third modification of the first embodiment, another example of a strain gauge in which a region where a connection portion is provided is different will be described. Note that in the third modification of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0080] Fig. 9 is a plan view illustrating a strain gauge according to Modification 3 of the first embodiment. Fig. 10 is a cross-sectional view illustrating the strain gauge according to Modification 3 of the first embodiment, showing a cross section along line EE in Fig. 9. Referring to Figs. 9 and 10, strain gauge 1C differs from strain gauge 1B in that the number of connection parts 32 in resistor 30 is increased and wiring 40B is replaced with wiring 40C. Wiring 40C differs from wiring 40B in that the number of connection parts 42 is increased.

[0081] In this way, in the resistor 30, one or more connection parts 32 can be arranged on each of the elongated portions, and the number of connection parts 32 can be determined arbitrarily. Also, one or more connection parts 42 can be arranged on each of the wirings 40C, and the number of connection parts 42 can be determined arbitrarily. By increasing the number of connection parts 32 and 42, the number of parts that behave like a spring when a strong force is applied due to an external factor increases, so that the risk of disconnection of the detection part 31 and the conductive part 41 can be further reduced. However, it is preferable to determine the number of connection parts 32 and 42 within a range that does not increase the area of ​​the entire strain gauge 1C.

[0082] Although the preferred embodiments have been described in detail above, 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]

[0083] 1, 1A, 1B, 1C strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 termination, 31 detection portion, 32, 42 connection portion, 40, 40B, 40C wiring, 41 conductive portion, 51, 52 metal layer, 50 electrode, 60 cover layer

Claims

1. A substrate; a resistor formed on the substrate, The resistor includes a plurality of detection portions and a plurality of connection portions connected in series with at least one of the plurality of detection portions, the connection portion is formed from a material having a lower elastic modulus than the detection portion and is disposed so as to be in direct contact with the detection portion; The resistor includes a plurality of elongated portions arranged in parallel, each including the detection portion, and a folded portion connecting ends of the adjacent elongated portions, The strain gauge, wherein one or more of the connection portions are disposed on each of the elongated portions.

2. The strain gauge according to claim 1 , wherein the connection portion is disposed between adjacent detection portions.

3. The strain gauge according to claim 2 , wherein the connection portions are arranged at the same positions in the grid direction on each of the elongated portions.

4. The strain gauge according to claim 1 , wherein the connection portion is disposed at the folded portion.

5. a pair of electrodes formed on the base material and electrically connected to the resistor via wiring; The strain gauge according to claim 1 , wherein one or more of the connection parts are arranged on the wiring.

6. The strain gauge according to claim 1 , wherein the elastic modulus of the connection portion is equal to or less than half the elastic modulus of the detection portion.

7. The strain gauge according to claim 1 , wherein a width and a thickness of the connection portion are equal to a width and a thickness of the detection portion.

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

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