Strain detection system

Abstract

To provide a strain gauge for improving strain tolerance.SOLUTION: A strain gauge includes a flexible substrate and a resistor made of a film containing Cr, CrN, and Cr2N formed on the substrate. The strain gauge is attached to a measuring object so that the grid direction of the resistor is perpendicular to the strain direction of the measuring object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain of the object. The strain gauge includes a resistor that detects 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, 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] Strain gauges are attached to a strain-generating body and detect the amount of strain in the body by expanding and contracting in response to the body's movements. 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 view of the above points, and has an object to provide a strain gauge that can improve strain resistance. [Means for solving the problem]

[0006] This strain detection system includes a strain gauge and a measurement object to which the strain gauge is attached. The strain gauge includes a flexible substrate, a resistor formed on the substrate from a film containing Cr, CrN, and CrN, and a pair of electrodes formed on the substrate and electrically connected to the resistor via wiring. The grid direction of the resistor is perpendicular to the strain direction of the measurement object, and the pair of electrodes are arranged on both sides of the resistor in a direction perpendicular to the strain direction and on both sides of the strain direction. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge that can improve strain resistance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 3] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 4] FIG. 1 is a diagram (part 1) for explaining the attachment direction of a strain gauge. [Figure 5] FIG. 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 2 is a plan view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 7] FIG. 2 is a diagram (part 2) for explaining the attachment direction of the strain gauge. [Figure 8] 10 is a plan view (part 1) illustrating a strain gauge according to a second modification of the first embodiment. FIG. [Figure 9] 10 is a second plan view illustrating a strain gauge according to Modification 2 of the first embodiment. FIG. 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 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. Note that arrow E in Fig. 1 indicates the strain direction (expansion / contraction direction) of the measurement object to which strain gauge 1 is attached.

[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 Figs. 1 to 3. The cover layer 60 may be provided as needed.

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

[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, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[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 with 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, for example.

[0016] Materials other than resin for the substrate 10 include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Alternatively, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 10. In this case, an insulating film, for example, 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 element that generates a resistance change when strain is applied. 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. For convenience, the resistor 30 is shown in FIG. 1 with a dark matte pattern.

[0018] The resistor 30 has a structure in which multiple elongated portions are arranged at predetermined intervals with their longitudinal direction in the same direction (the direction of line AA in Figure 1), and the ends of adjacent elongated portions are connected alternately, resulting in a zigzag folded structure as a whole. The longitudinal direction of the multiple elongated portions forms the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction of line BB in Figure 1). The strain gauge 1 is attached to the object to be measured so that the grid direction of the resistor 30 is perpendicular to the strain direction E of the object to be measured.

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

[0020] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0021] 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.

[0022] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, approximately 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting the resistor 30 (e.g., the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less is even more preferable because it reduces film cracks and warpage from the substrate 10 caused by internal stress in the film constituting the resistor 30. The width of the resistor 30 can be optimized for required specifications such as resistance value and lateral sensitivity, and can be set to, for example, approximately 10 μm to 100 μm, taking into consideration measures against disconnection.

[0023] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50% by weight or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] Furthermore, when the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0025] Furthermore, 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 Cr2N has semiconducting properties, which leads to a more significant decrease in TCR (negative TCR). Furthermore, by reducing the amount of ceramic formation, brittle fracture is reduced.

[0026] On the other hand, if trace amounts of N2 or atomic N are mixed into or present in the film, they will escape to the outside of the film due to external conditions (such as high temperature environments), causing changes in film stress.By creating chemically stable CrN, the unstable N mentioned above will not be generated, and a stable strain gauge can be obtained.

[0027] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrodes 50. The wiring 40 is not limited to being linear and can have any pattern. The wiring 40 can have any width and any length. For convenience, in FIG. 1, the wiring 40 and the electrodes 50 are shown with a matte finish that is thinner than the resistor 30.

[0028] The electrodes 50 are formed on the substrate 10 and 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. In the example of FIGS. 1 to 3, the electrodes 50 are arranged on both sides of the resistor 30 in a direction (grid direction) perpendicular to the strain direction E. The electrodes 50 are a pair of electrodes for outputting to the outside a change in resistance value of the resistor 30 caused by strain, and are connected, for example, to lead wires for external connection.

[0029] Although the resistor 30, the wiring 40, and the electrode 50 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, the wiring 40, and the electrode 50 have approximately the same thickness.

[0030] A conductive layer made of a material having a lower resistance than the resistor 30 may be laminated on the wiring 40 and the electrode 50. The material of the laminated conductive layer is not particularly limited as long as it has a lower resistance than the resistor 30, and can be appropriately selected depending on the purpose. For example, when the resistor 30 is a Cr mixed phase film, examples of the material include Cu, Ni, Al, Ag, Au, Pt, etc., alloys of any of these metals, compounds of any of these metals, and laminated films in which any of these metals, alloys, or compounds are appropriately laminated. The thickness of the conductive layer is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 3 μm to 5 μm.

[0031] In this way, by laminating a conductive layer made of a material with a lower resistance than the resistor 30 on the wiring 40 and the electrode 50, the wiring 40 has a lower resistance than the resistor 30, and therefore, it is possible to prevent the wiring 40 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

[0032] In other words, by providing the wiring 40 with a lower resistance than the resistor 30, the actual sensitive part of the strain gauge 1 can be limited to the local area where the resistor 30 is formed, thereby improving the accuracy of strain detection by the resistor 30.

[0033] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed-phase film as the resistor 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensitive part to the local region where the resistor 30 is formed has a significant effect on improving strain detection accuracy. Also, making the wiring 40 lower in resistance than the resistor 30 has the effect of reducing lateral sensitivity.

[0034] The cover layer 60 is formed on the substrate 10, covers the resistor 30 and the wiring 40, and exposes the electrodes 50. A portion 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 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 and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the electrodes 50.

[0035] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0036] Strain Limit The strain gauge 1 is attached to an object to be measured, either via a strain element or directly without a strain element, and detects strain in the object. In order for the strain gauge 1 to detect a larger amount of strain, it is preferable to improve the strain limit (strain resistance) as much as possible, since the resistor 30 itself must not be damaged (such as broken) as it expands and contracts. The strain limit is the value of mechanical strain at which cracks or breaks begin to occur when strain is applied to the strain gauge.

[0037] 1 to 3, the strain limit varies greatly depending on the positional relationship between the strain direction of the object to be measured and the grid direction of the resistor 30 when the strain gauge 1 is attached to the object to be measured. In the study, a polyimide resin film with a film thickness of 25 μm was used as the substrate 10 in the strain gauge 1. A Cr mixed phase film was used for the resistor 30.

[0038] Specifically, the inventors prepared multiple samples in which strain gauges 1 were attached to objects to be measured so that the grid direction of resistor 30 was perpendicular to the strain direction E (expansion / contraction direction) of the objects to be measured, as shown in Figure 1. Then, strain was applied to each sample to check for the occurrence of cracks or breakage, and the strain limit was measured. As a result, with the arrangement shown in Figure 1, the strain limit of each sample was 10,900 με or more.

[0039] On the other hand, the inventors prepared several comparative samples in which strain gauges 1 were attached to objects to be measured so that the grid direction of resistor 30 was parallel to the strain direction E of the object, as shown in Fig. 4. Then, strain was applied to each sample to check for the occurrence of cracks or breakages, and the strain limit was measured. As a result, with the arrangement shown in Fig. 4, the strain limit of each sample was 2300 με or more.

[0040] That is, by attaching the strain gauge 1 so that the grid direction of the resistor 30 is perpendicular to the strain direction E of the object to be measured, the strain limit can be improved by more than four times compared to when the grid direction of the resistor 30 is attached so that it is parallel to the strain direction E of the object to be measured. Note that when actually using the strain gauge 1, a strain limit of approximately 5000 με or more is required.

[0041] In this way, by attaching the resistor 30 so that the grid direction is perpendicular to the strain direction E of the object to be measured, it is believed that even if the object to be measured expands and contracts in the strain direction E, the resistor 30 will be less susceptible to expansion and contraction. In other words, the substrate 10 has the characteristic of being less likely to expand and contract in the longitudinal direction of the substrate 10 but more likely to expand and contract in the lateral direction. As shown in FIG. 1, when the grid direction of the resistor 30 (the longitudinal direction of the substrate 10) is perpendicular to the strain direction E, the substrate 10 expands and contracts in the lateral direction of the substrate 10, which is more likely to expand and contract. On the other hand, as shown in FIG. 4, when the grid direction of the resistor 30 (the longitudinal direction of the substrate 10) is parallel to the strain direction E, the substrate 10 expands and contracts in the longitudinal direction of the substrate 10, which is less likely to expand and contract. In this case, it is believed that the substrate 10 cannot follow the expansion and contraction, which is likely to cause fracture of the substrate 10 and the resulting disconnection of the resistor 30.

[0042] [Strain gauge manufacturing method] Here, a method for manufacturing the strain gauge 1 will be described. To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of metal layer A are the same as the material and thickness of the resistor 30, wiring 40, and electrodes 50 described above.

[0043] The metal layer A can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, the metal layer A may also be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0044] 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 substrate 10 by, for example, conventional sputtering before depositing the metal layer A.

[0045] In the present application, the functional layer refers to a layer having the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and the function of improving adhesion between the substrate 10 and metal layer A. The functional layer may also have other functions.

[0046] 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 A, especially when the metal layer A contains Cr.

[0047] 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 layer, the metal layer A (resistor 30), and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Examples of the metals include one or more metals selected from the group consisting of copper (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, and a compound of any of the metals in this group.

[0048] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0049] 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 resistor, which can promote the crystal growth of α-Cr and prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[0050] 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 resistor, which can promote the crystal growth of α-Cr and further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[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 / 100 or less of the thickness of the resistor, which further prevents a portion of the current flowing through the resistor from flowing through the functional layer, thereby further preventing a decrease in strain detection sensitivity.

[0052] 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 1 μm, which promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracks.

[0053] 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 not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0054] 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 0.5 μm, which not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0055] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. If the functional layer is made of an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid state at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the substrate 10.

[0056] Furthermore, when the functional layer is made of an insulating material, the thickness of the functional layer is made relatively thick, between 50 nm and 1 μm, and the functional layer is made solid. This increases the thickness and surface area of ​​the functional layer, allowing heat generated by the resistor to be dissipated to the substrate 10. As a result, the deterioration of measurement accuracy in the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0057] 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.

[0058] 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.

[0059] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and it 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 A.

[0060] In this case, for example, the metal layer A can be formed by magnetron sputtering using a target made of a material capable of forming a Cr mixed-phase film and introducing Ar gas into the chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as the target and introducing an appropriate amount of nitrogen gas into the chamber together with Ar gas. In this case, the proportions of CrN and CrN contained in the Cr mixed-phase film, and the proportion of CrN in CrN and CrN can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the nitrogen gas introduced or by adjusting the heating temperature in a heating step.

[0061] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0062] 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 substrate 10, and improving adhesion between the substrate 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0063] 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 crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 can be improved. Furthermore, the material that constitutes the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0064] Next, the metal layer A is patterned by photolithography to form the resistor 30, the wiring 40, and the electrode 50.

[0065] Thereafter, if 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.

[0066] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlying layer for the resistor 30, the wiring 40, and the electrodes 50, the strain gauge 1 has a cross-sectional shape as shown in FIG. 5. The layer indicated by the reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 will be the same as that shown in FIG. 1, for example. However, as mentioned above, the functional layer 20 may be formed solidly on part or all of the upper surface 10a of the substrate 10.

[0067] <Modification of the first embodiment> In the modified example of the first embodiment, an example of a strain gauge is shown in which the wiring layout, the electrode arrangement, etc. are different. Note that in the modified example of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

[0068] Fig. 6 is a plan view illustrating a strain gauge according to Modification 1 of the first embodiment. Referring to Fig. 6, the strain gauge 1A is, like the strain gauge 1, attached so that the grid direction of the resistor 30 is perpendicular to the strain direction E of the object to be measured. However, the routing of the wiring 40A and the arrangement of the electrodes 50 differ from those of the strain gauge 1 (see Figs. 1 to 3, etc.).

[0069] In the strain gauge 1A, each wire 40A, unlike the wires 40, has one bent portion and includes a portion that extends perpendicular to the grid direction of the resistor 30. However, the direction is not limited to perpendicular, and the wire 40A may include a portion that is inclined with respect to the grid direction of the resistor 30. In the strain gauge 1A, the electrodes 50 are arranged on both sides of the resistor 30 in the strain direction E. Note that when the wire 40A includes a portion that extends perpendicular to the grid direction of the resistor 30, this is an example of when the wire 40A includes a portion that is inclined with respect to the grid direction of the resistor 30, and the inclination angle is 90 degrees. The same applies to the other wires.

[0070] The inventors investigated the strain limit of strain gauge 1A using the same method as for strain gauge 1, and found that the strain limit of each sample was 7200 με or more in the arrangement shown in Fig. 6. This result is significantly better than the arrangement in Fig. 4 (2300 με or more) and is a value that is sufficiently practical, but it falls short of the arrangement in Fig. 1 (10900 με or more).

[0071] This is because, in the arrangement shown in Figure 6, by attaching the strain gauge 1A so that the grid direction of the resistor 30 is perpendicular to the strain direction E of the object to be measured, even if the object to be measured expands and contracts in the strain direction E, the resistor 30 is less affected by the expansion and contraction, but it is thought that the resistor 30 is affected by the stress of the electrode 50.

[0072] That is, when the object to be measured expands or contracts in the strain direction E, stress is generated in the electrode 50 in the strain direction E. In the arrangement of Fig. 6, the electrodes 50 are arranged on both sides of the resistor 30 in the strain direction E, so the stress generated in the electrode 50 is transmitted linearly to the resistor 30, which is thought to have reduced the strain limit of the resistor 30. On the other hand, in the arrangement of Fig. 1, the electrodes 50 are arranged on both sides of the resistor 30 in the direction perpendicular to the strain direction E, so the electrodes 50 are less affected by the stress of the electrodes 50, and therefore the strain limit is thought to be higher than that of the arrangement of Fig. 6.

[0073] Furthermore, according to the inventors' investigations, the strain limit of each sample was 6900 με or more in the arrangement shown in Fig. 7. This result is slightly lower than the arrangement in Fig. 6 (7200 με or more), but is almost the same value and is sufficiently practical.

[0074] The arrangement of Figure 7 is less advantageous than the arrangement of Figure 6 in that the grid direction of resistor 30 is parallel to strain direction E. However, since electrodes 50 are arranged on both sides of resistor 30 in a direction perpendicular to strain direction E, it is less susceptible to the stress of electrodes 50, which is an advantage and is thought to be why such results were obtained.

[0075] It is also possible to route the wiring 40B and arrange the electrodes 50 as in the strain gauge 1B shown in Figures 8 and 9. When the strain gauge 1B is arranged as shown in Figure 8, a strain limit similar to that obtained when the strain gauge 1 is arranged as shown in Figure 1 can be obtained. Furthermore, when the strain gauge 1B is arranged as shown in Figure 9, a strain limit similar to that obtained when the strain gauge 1A is arranged as shown in Figure 7 can be obtained.

[0076] The wire 40B of the strain gauge 1B has three bent portions. That is, the wire 40B has a folded portion at the portion connected to the electrode 50, including a wire bent in a direction away from the resistor 30, a wire extending parallel to the resistor 30, and a wire bent in a direction toward the resistor 30. The spring effect of this folded portion relieves stress generated in the electrode 50 and makes it less likely to be transmitted to the resistor 30, which is advantageous for improving the strain limit. The folded portion may have four or more bent portions, and in this case, the spring effect is also exerted. The wire 40B may also include a portion inclined with respect to the grid direction of the resistor 30.

[0077] 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]

[0078] 1, 1A, 1B strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 termination, 40, 40A, 40B wiring, 50 electrode, 60 cover layer

Claims

1. A strain gauge and a measurement object to which the strain gauge is attached, The strain gauge comprises: a flexible substrate; On the substrate, Cr, CrN, and Cr ２ a resistor formed from a film containing N; a pair of electrodes formed on the substrate and electrically connected to the resistor via wiring; The grid direction of the resistor is perpendicular to the strain direction of the object to be measured, A strain detection system, wherein the pair of electrodes are arranged on both sides of the resistor in a direction perpendicular to the strain direction and on both sides of the strain direction.

2. The strain detection system according to claim 1 , wherein the pair of electrodes are arranged at positions that are point symmetric with respect to the resistor.

3. The strain detection system according to claim 1 or 2, wherein the resistor has a plurality of elongated portions arranged with their longitudinal directions oriented in the same direction.

4. The strain detection system according to claim 1 , wherein the wiring includes a portion that is inclined with respect to a grid direction of the resistor.

5. The strain detection system according to claim 1 , wherein the wiring includes a portion extending in a direction perpendicular to a grid direction of the resistors.

6. CrN and Cr contained in the resistor ２ The strain detection system according to claim 1 , wherein the proportion of N is 20% by weight or less.

7. The CrN and the Cr ２ The Cr in N ２ The strain detection system according to claim 6 , wherein the proportion of N is equal to or greater than 80% by weight and less than 90% by weight.

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