Strain gauge

Abstract

To provide a strain gauge with improved strain resistance.SOLUTION: A strain gauge provided herein comprises a flexible base material, a resistor formed on the base material, and a pair of electrodes formed on the base material and electrically connected to the resistor via wiring, the resistor having a width in a range of 10-100 μm, inclusive, and the wiring includes a portion with a width in a range of 5-100 μm, inclusive.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] A strain gauge that is attached to a measurement object to detect the strain of the measurement object is known. The strain gauge includes a resistor that detects strain, and the resistor is formed, for example, on an insulating resin. The resistor is connected to an electrode via a wiring (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a strain gauge capable of improving strain resistance.

Means for Solving the Problems

[0006] This strain gauge has a flexible base material, a resistor formed on the base material, , Cr, CrN, and Cr 2 is composed of a Cr mixed-phase film in which CrN is in a mixed phase and a pair of electrodes formed on the base material and electrically connected to the resistor via a wiring, and the width of the resistor is 10 μm or more and 100 μm or less. a plurality of Among the plurality of the wirings, two or more of them electrically connect one of the ends in the grid width direction of the resistor and one of the pair of the electrodes, and the other two or more of the plurality of the wirings electrically connect the other of the ends in the grid width direction of the resistor and the other of the pair of the electrodes. Each ​The wiring includes a portion with a width of 5 μm or more and 100 μm or less. mi , Each of the wirings is composed of the same Cr mixed-phase film as the resistor and is formed integrally with the resistor. The thickness of each of the wirings is 0.05 μm or more and 2 μm or less.

Advantages of the Invention

[0007] According to the disclosed technology, a strain gauge capable of improving strain resistance can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0009] Hereinafter, modes for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant descriptions 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 illustrating a strain gauge according to the first embodiment, showing a cross-section along line A-A in FIG. 1. Referring to FIGS. 1 and 2, the strain gauge 1 has a base material 10, a resistor 30, wirings 41 and 42, and electrodes 51 and 52.

[0011] In this embodiment, for convenience, in the strain gauge 1, the side where the resistor 30 of the base material 10 is provided is defined as the upper side or one side, and the side where the resistor 30 is not provided is defined as the lower side or the other side. Also, the surface on the side where the resistor 30 of each part is provided is defined as one surface or the upper surface, and the surface on the side where the resistor 30 is not provided is defined as the other surface or the lower surface. However, the strain gauge 1 can be used in an upside-down state or arranged at an arbitrary angle. Also, the plan view means viewing the object from the normal direction of the upper surface 10a of the base material 10, and the planar shape means the shape of the object viewed from the normal direction of the upper surface 10a of the base material 10.

[0012] The base material 10 is a member serving as a base layer for forming the resistor 30 and the like, and has flexibility. The thickness of the base material 10 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 5 μm to 500 μm. In particular, when the thickness of the base material 10 is 5 μm to 200 μm, it is preferable in terms of the transmissibility of strain from the surface of the strain-generating body joined to the lower surface of the base material 10 via an adhesive layer or the like and the dimensional stability against the environment. When it is 10 μm or more, it is more preferable in terms of insulation.

[0013] The base material 10 can be formed from an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, an LCP (liquid crystal polymer) resin, or a polyolefin resin. Here, the film refers to a member having a thickness of about 500 μm or less and having flexibility.

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

[0015] Examples of materials other than the resin of the base material 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3), and in addition, amorphous glass and the like can be mentioned. Further, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), and titanium may be used. In this case, for example, an insulating film is formed on the metal base material 10.

[0016] The resistor 30 is a thin film formed on the base material 10 in a predetermined pattern, and is a sensing part that undergoes strain and causes a resistance change. The resistor 30 may be formed directly on the upper surface 10a of the base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for convenience, the resistor 30 is shown as a dark matte pattern.

[0017] The resistor 30 has a structure in which a plurality of elongated portions are arranged at a predetermined interval with their longitudinal directions facing the same direction (the direction of line A-A in FIG. 1), and the ends of adjacent elongated portions are alternately connected to form a zigzag fold as a whole. The longitudinal direction of the plurality of elongated portions becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction.

[0018] One end portion in the longitudinal direction of the two outermost elongated portions in the grid width direction is bent in the grid width direction to form respective ends 30e1 and 30e2 of the resistor 30 in the grid width direction. The end 30e1 of the resistor 30 in the grid width direction and the electrode 51 are electrically connected by a single wiring 41, and the end 30e2 of the resistor 30 in the grid width direction and the electrode 52 are electrically connected by a single wiring 42. Note that the wiring 41 is a typical example of the first wiring according to the present invention, and the wiring 42 is a typical example of the second wiring according to the present invention.

[0019] The resistor 30 can be formed of, 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 of a material containing at least one of Cr and Ni. Examples of the material containing Cr include a Cr mixed-phase film. Examples of the material containing Ni include Cu-Ni (copper nickel). Examples of the material containing both Cr and Ni include Ni-Cr (nickel chromium).

[0020] Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr2N, etc. are in a mixed phase. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

[0021] The thickness of the resistor 30 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, it is preferable in that the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 30 is 1 μm or less, it is more preferable in that cracks in the film due to internal stress of the film constituting the resistor 30 and warping from the base material 10 can be reduced. Considering the requirements such as resistance value and lateral sensitivity and taking measures against disconnection, the width of the resistor 30 is preferably 10 μm or more and 100 μm or less.

[0022] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. Also, when the resistor 30 has α-Cr as the main component, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance occupies 50% by weight or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. Note that α-Cr is Cr having a bcc structure (body-centered cubic lattice structure).

[0023] Further, when the resistor 30 is a Cr mixed-phase film, it is preferable that CrN and Cr2N contained in the Cr mixed-phase film are 20% by weight or less. By having CrN and Cr2N contained in the Cr mixed-phase film be 20% by weight or less, a decrease in the gauge factor can be suppressed.

[0024] Moreover, the proportion 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. By having the proportion of Cr2N in CrN and Cr2N be 90% by weight or more and less than 95% by weight, due to Cr2N having semiconductor-like properties, a decrease in TCR (negative TCR) becomes even more prominent. Furthermore, by reducing ceramization, brittle fracture is reduced.

[0025] On the other hand, when a small amount of N2 or atomic N is mixed and present in the film, due to them escaping outside the film by an external environment (for example, under a high-temperature environment), a change in film stress occurs. By creating chemically stable CrN, the generation of the above-mentioned unstable N can be avoided, and a stable strain gauge can be obtained.

[0026] Wiring 41 and 42 are formed on the base material 10. Electrodes 51 and 52 are formed on the base material 10 and are electrically connected to the resistor 30 via the wiring 41 and 42. For example, they are formed in a substantially rectangular shape with a width wider than that of the wiring 41 and 42. Electrodes 51 and 52 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain. For example, lead wires for external connection or the like are joined thereto. In FIG. 1, for the sake of convenience, the wiring 41 and 42 and the electrodes 51 and 52 are shown in a matte pattern thinner than the resistor 30.

[0027] Note that although the resistor 30, the wiring 41 and 42, and the electrodes 51 and 52 are given different reference signs for the sake of convenience, they can be integrally formed of the same material in the same process. Therefore, the resistor 30, the wiring 41 and 42, and the electrodes 51 and 52 have substantially the same thickness.

[0028] The upper surfaces of the wirings 41 and 42 and the electrodes 51 and 52 may be coated with a metal formed from a material having a lower resistance than the wirings 41 and 42 and the electrodes 51 and 52. For example, when the resistor 30, the wirings 41 and 42, and the electrodes 51 and 52 are Cr mixed-phase films, examples of the metal material having a lower resistance than the Cr mixed-phase film include 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 formed by appropriately laminating any of these metals, alloys, and compounds.

[0029] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the base material 10 so as to cover the resistor 30 and the wirings 41 and 42 and expose the electrodes 51 and 52. By providing the cover layer 60, it is possible to prevent mechanical damage or the like from occurring in the resistor 30 and the wirings 41 and 42. Also, by providing the cover layer 60, the resistor 30 and the wirings 41 and 42 can be protected from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion excluding the electrodes 51 and 52.

[0030] The cover layer 60 can be formed from an insulating resin such as, for example, PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (for example, silicone resin, polyolefin resin), etc. The cover layer 60 may contain a filler or a pigment. The thickness of the cover layer 60 is not particularly limited and can be appropriately selected according to the purpose, but for example, it can be about 2 μm to 30 μm.

[0031] Here, the strain resistance of the strain gauge 1 will be described. According to the study by the inventors, it was found that when the widths of the wirings 41 and 42 are narrower, cracks and disconnections are less likely to occur when the wirings 41 and 42 are subjected to strain. Specifically, the inventors produced a plurality of test strain gauges of four types with widths of 10 μm, 100 μm, 345 μm, and 560 μm for the wirings 41 and 42, applied strain to each of them, and examined the occurrence of cracks and disconnections. In this experiment, the wirings 41 and 42 were Cr mixed-phase films with a thickness of 0.2 μm.

[0032] As a result of the experiment, it was confirmed that as the widths of wirings 41 and 42 decreased, cracks and disconnections tended to decrease, and it was found that the strain limit depends on the widths of wirings 41 and 42. Note that the strain limit is the value of mechanical strain at which cracks or disconnections begin to occur when strain is applied to a strain gauge.

[0033] Figure 3 is a diagram showing the experimental results of the strain limit, and plots the minimum values of the strain limit in a plurality of test strain gauges. As shown in Figure 3, in the experimental results of the inventors, the strain limit was 5500 με or more when the widths of wirings 41 and 42 were 560 μm, whereas the strain limit was 8500 με or more when the widths of wirings 41 and 42 were 10 μm. That is, the strain limit is about 1.5 times when the widths of wirings 41 and 42 are 10 μm compared to when the widths of wirings 41 and 42 are 560 μm. Also, between the widths of wirings 41 and 42 being 560 μm and 10 μm, the strain limit improves almost linearly. Further, from the results of Figure 3, it is expected that the strain limit will further improve almost linearly even when the widths of wirings 41 and 42 are less than 10 μm.

[0034] This result is considered to be obtained because brittle fracture is likely to occur when the widths of wirings 41 and 42 made of a Cr mixed-phase film with a high elastic modulus are wide, and the apparent fracture resistance increases by narrowing the widths of wirings 41 and 42. When actually using strain gauge 1, since a strain limit of about 8000 με is required, the widths of wirings 41 and 42 are preferably 100 μm or less. On the other hand, it is difficult to make the widths of wirings 41 and 42 less than 5 μm in terms of the manufacturing process. Considering this point, it can be said that the widths of wirings 41 and 42 are preferably 5 μm or more and 100 μm or less. Also, from Figure 3, it can be said that when a strain limit of 8500 με or more is required, the widths of wirings 41 and 42 are preferably 5 μm or more and 10 μm or less.

[0035] In addition, when stress concentrates on wirings 41 and 42, it may cause the wirings 41 and 42 to break. However, when the resistor 30 and the wirings 41 and 42 are formed of the same material (for example, in the case of a Cr mixed-phase film), by making the widths of the wirings 41 and 42 equal to or less than the width of the resistor 30, stress concentration on the wirings 41 and 42 can be reduced. Thereby, even when a large strain is applied to the strain gauge 1, disconnection of the wirings 41 and 42 is suppressed.

[0036] The strain gauge 1 is attached to the strained body and detects the amount of strain of the strained body by expanding and contracting following the movement of the strained body. Therefore, in order to detect a larger amount of strain, the strain gauge 1 itself must not be damaged (such as disconnected) during the expansion and contraction process, and higher strain resistance is required. In the strain gauge 1, by making the widths of the wirings 41 and 42 be 5 μm or more and 100 μm or less, it is possible to improve the strain limit (improve the strain resistance).

[0037] Note that it is preferable that the widths of all parts of the wiring 41 and all parts of the wiring 42 are 5 μm or more and 100 μm or less. However, for example, even if there are partially wider parts than 100 μm as in the thick line parts 451 and 461 shown in FIG. 6 described later, as long as the wirings 41 and 42 include parts with widths of 5 μm or more and 100 μm or less, it has a certain effect on improving the strain limit (improving the strain resistance).

[0038] To manufacture the strain gauge 1, first, the base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 10. The metal layer A is a layer that is finally patterned into the resistor 30, the wirings 41 and 42, and the electrodes 51 and 52. Therefore, the material and thickness of the metal layer A are the same as those of the aforementioned resistor 30, the wirings 41 and 42, and the electrodes 51 and 52.

[0039] The metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming the metal layer A as a target. Instead of the magnetron sputtering method, the metal layer A may be formed using a reactive sputtering method, an evaporation method, an arc ion plating method, a pulsed laser deposition method, or the like.

[0040] From the viewpoint of stabilizing the gauge characteristics, before forming the metal layer A, it is preferable to vacuum deposit a functional layer with a predetermined film thickness on the upper surface 10a of the base material 10 as an underlayer, for example, by a conventional sputtering method.

[0041] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper metal layer A (resistor 30). The functional layer preferably further has a function of preventing the oxidation of the metal layer A by oxygen or moisture contained in the base material 10 and a function of improving the adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0042] Since the insulating resin film constituting the base material 10 contains oxygen and moisture, especially when the metal layer A contains Cr, Cr forms a self-oxidized film, so it is effective for the functional layer to have a function of preventing the oxidation of the metal layer A.

[0043] 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 (resistor 30), and can be appropriately selected according to the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), 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), Al (aluminum), one or more metals selected from the group consisting of, an alloy of any metal in this group, or a compound of any metal in this group can be mentioned.

[0044] Examples of the above alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the above compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0045] When the functional layer is formed of a conductive material such as a metal or an alloy, the film thickness of the functional layer is preferably 1 / 20 or less of the film thickness of the resistor. In such a range, the crystal growth of α-Cr can be promoted, and at the same time, a part of the current flowing through the resistor can flow into the functional layer, preventing the detection sensitivity of strain from decreasing.

[0046] When the functional layer is formed of a conductive material such as a metal or an alloy, the film thickness of the functional layer is more preferably 1 / 50 or less of the film thickness of the resistor. In such a range, the crystal growth of α-Cr can be promoted, and at the same time, a part of the current flowing through the resistor can flow into the functional layer, further preventing the detection sensitivity of strain from decreasing.

[0047] When the functional layer is formed of a conductive material such as a metal or an alloy, it is more preferable that the film thickness of the functional layer is 1 / 100 or less of the film thickness of the resistor. When it is within such a range, a part of the current flowing through the resistor can flow into the functional layer, and it is possible to further prevent the detection sensitivity of strain from decreasing.

[0048] When the functional layer is formed of an insulating material such as an oxide or a nitride, it is preferable that the film thickness of the functional layer is 1 nm to 1 μm. When it is within such a range, the crystal growth of α-Cr can be promoted, and a film can be easily formed without cracks in the functional layer.

[0049] When the functional layer is formed of an insulating material such as an oxide or a nitride, it is more preferable that the film thickness of the functional layer is 1 nm to 0.8 μm. When it is within such a range, the crystal growth of α-Cr can be promoted, and a film can be more easily formed without cracks in the functional layer.

[0050] When the functional layer is formed of an insulating material such as an oxide or a nitride, it is still more preferable that the film thickness of the functional layer is 1 nm to 0.5 μm. When it is within such a range, the crystal growth of α-Cr can be promoted, and a film can be even more easily formed without cracks in the functional layer.

[0051] Note that 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 the case where it is substantially the same as the planar shape of the resistor. When the functional layer is formed of an insulating material, it does not have to be patterned into the same shape as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape over the entire upper surface of the base material 10.

[0052] Further, when the functional layer is formed of an insulating material, by forming the functional layer relatively thick so that the thickness of the functional layer is 50 nm or more and 1 μm or less and forming it in a solid state, the thickness and surface area of the functional layer increase, so that heat generated when the resistor generates heat can be dissipated to the substrate 10 side. As a result, in the strain gauge 1, it is possible to suppress a decrease in measurement accuracy due to self-heating of the resistor.

[0053] The functional layer can be formed by vacuum deposition, for example, by a conventional sputtering method in which a raw material capable of forming the functional layer is used as a target and Ar (argon) gas is introduced into the chamber. By using the conventional sputtering method, since the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, it is possible to obtain an effect of improving adhesion with a minimum film formation amount of the functional layer.

[0054] However, this is an example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, an adhesion improvement effect may be obtained by activating the upper surface 10a of the substrate 10 by plasma treatment using Ar or the like before forming the functional layer, and then a method of forming the functional layer by vacuum deposition by magnetron sputtering may be used.

[0055] The combination of the material of the functional layer and the material of the metal layer A is not particularly limited and can be appropriately selected according to the purpose. For example, Ti can be used as the functional layer, and a Cr mixed-phase film mainly composed of α-Cr (alpha chromium) can be formed as the metal layer A.

[0056] In this case, for example, the metal layer A can be formed by magnetron sputtering in which a raw material capable of forming a Cr mixed-phase film is used as a target and Ar gas is introduced into the chamber. Alternatively, pure Cr may be used as a target, an appropriate amount of nitrogen gas may be introduced together with Ar gas into the chamber, and the metal layer A may be formed by reactive sputtering. At this time, by changing the introduction amount and pressure (nitrogen partial pressure) of nitrogen gas or providing a heating step to adjust the heating temperature, 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.

[0057] In these methods, the growth surface of the Cr mixed-phase film is defined by the functional layer made of Ti, and a Cr mixed-phase film mainly composed of α-Cr with a stable crystal structure can be formed. Also, by the diffusion of Ti constituting the functional layer into the Cr mixed-phase film, the gauge characteristics are improved. For example, 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. Note that when the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0058] Note that when the metal layer A is a Cr mixed-phase film, the functional layer made of Ti has all of the functions of promoting the crystal growth of the metal layer A, preventing the oxidation of the metal layer A by 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 instead of Ti as the functional layer.

[0059] In this way, by providing the functional layer under the metal layer A, it becomes possible to promote the crystal growth of the metal layer A, and a metal layer A composed of a stable crystal phase can be produced. As a result, in the strain gauge 1, the stability of the gauge characteristics can be improved. Also, by the diffusion of the material constituting the functional layer into the metal layer A, the gauge characteristics can be improved in the strain gauge 1.

[0060] Next, the metal layer A is patterned by photolithography to form the resistor 30, wirings 41 and 42, and electrodes 51 and 52 having the planar shape shown in FIG. 1.

[0061] Thereafter, if necessary, a cover layer that covers the resistor 30 and the wirings 41 and 42 and exposes the electrodes 51 and 52 is provided on the upper surface 10a of the base material 10, thereby completing the strain gauge 1. The cover layer can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the base material 10 so as to cover the resistor 30 and the wirings 41 and 42 and expose the electrodes 51 and 52, and then heating and curing it. The cover layer may be produced by applying a liquid or paste-like thermosetting insulating resin on the upper surface 10a of the base material 10 so as to cover the resistor 30 and the wirings 41 and 42 and expose the electrodes 51 and 52, and then heating and curing it.

[0062] In addition, when a functional layer is provided on the upper surface 10a of the base material 10 as an underlayer for the resistor 30, the wirings 41 and 42, and the electrodes 51 and 52, the strain gauge 1 has the cross-sectional shape shown in FIG. 4. The layer indicated by reference numeral 20 is the functional layer. The planar shape of the strain gauge 1 when the functional layer 20 is provided is the same as that in FIG. 1, for example. However, as described above, the functional layer 20 may be formed in a solid state on a part or all of the upper surface of the base material 10. Since the functional layer 20 is extremely thin with respect to the resistor 30 and the wirings 41 and 42, it is considered that the presence or absence of the functional layer 20 has no influence on the strain limits of the resistor 30 and the wirings 41 and 42.

[0063] <Modification Example of the First Embodiment> In the modification example of the first embodiment, an example of a strain gauge with a different routing of the wiring is shown. In the modification example of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

[0064] FIG. 5 is a plan view illustrating a strain gauge according to Modification Example 1 of the first embodiment. Referring to FIG. 5, the strain gauge 1A is different from the strain gauge 1 (see FIGS. 1 and 2, etc.) in that the wirings 41 and 42 are replaced by the wirings 43 and 44. The wiring 43 is a typical example of the third wiring according to the present invention, and the wiring 44 is a typical example of the fourth wiring according to the present invention.

[0065] In the strain gauge 1A, the terminal 30e1 in the grid width direction of the resistor 30 and the electrode 51 are electrically connected by three wires 43 connected in parallel. Also, the terminal 30e2 in the grid width direction of the resistor 30 and the electrode 52 are electrically connected by three wires 44 connected in parallel. In all parts of each wire 43 and all parts of each wire 44, the width is 5 μm or more and 100 μm or less.

[0066] Thus, the wires connecting the resistor 30 and the electrodes 51 and 52 may be made into multiple wires. Also in this case, by setting the widths of each wire 43 and each wire 44 to 5 μm or more and 100 μm or less, it is possible to realize an improvement in the strain limit (improvement in strain resistance), similar to the case of the wires 41 and 42.

[0067] Also, even if some of the multiple wires 43 and 44 are damaged (such as broken wires), as long as at least one wire 43 and wire 44 are connected, the strain gauge 1A can operate. Note that the number of multiple wires may be two or more, and is not limited to the three wires illustrated in FIG. 5.

[0068] FIG. 6 is a plan view illustrating a strain gauge according to Modification 2 of the first embodiment. Referring to FIG. 6, the strain gauge 1B differs from the strain gauge 1 (see FIGS. 1, 2, etc.) in that the wires 41 and 42 are replaced by wires 45 and 46. Note that the wire 45 is a typical example of a fifth wire according to the present invention, and the wire 46 is a typical example of a sixth wire according to the present invention.

[0069] In the strain gauge 1B, the terminal 30e1 in the grid width direction of the resistor 30 and the electrode 51 are electrically connected by the wire 45. Also, the terminal 30e2 in the grid width direction of the resistor 30 and the electrode 52 are electrically connected by the wire 46.

[0070] The wiring 45 includes a single thick line portion 451 whose one end is electrically connected to the terminal 30e1 in the grid width direction of the resistor 30, and three thin line portions 452 branched from the other end of the thick line portion 451 and electrically connected to the electrode 51. Further, the wiring 46 includes a single thick line portion 461 whose one end is electrically connected to the terminal 30e2 in the grid width direction of the resistor 30, and three thin line portions 462 branched from the other end of the thick line portion 461 and electrically connected to the electrode 52.

[0071] In all portions of each thin line portion 452 and all portions of each thin line portion 462, the width is 5 μm or more and 100 μm or less. The thick line portion 451 is wider than each thin line portion 452, and the width in all portions of the thick line portion 451 may be wider than 100 μm. Also, the thick line portion 461 is wider than each thin line portion 462, and the width in all portions of the thick line portion 461 may be wider than 100 μm.

[0072] Thus, it is not necessary to perform the multiplexing of the wiring for all portions from the resistor 30 to the electrodes 51 and 52, and it may be performed only for a part. Also in this case, by setting the width of each thin line portion 452 and each thin line portion 462 to 5 μm or more and 100 μm or less, it is possible to realize an improvement in strain limit (improvement in strain resistance), similar to the case of the wirings 41 and 42.

[0073] Also, even if any of the plurality of thin line portions 452 and 462 are damaged (such as open-circuited), as long as at least one thin line portion 452 and 462 are connected, it can operate as the strain gauge 1B. Note that the number of multiplexed lines (the number of thin line portions) may be two or more, and is not limited to the three shown in FIG. 6.

[0074] Although the preferred embodiments etc. have been described in detail above, it is not limited to the above-described embodiments etc., and various modifications and substitutions can be made to the above-described embodiments etc. without departing from the scope described in the claims.

[0075] For example, the present invention is also applicable to a strain gauge in which a plurality of resistors are formed on a substrate. The present invention is also applicable to, for example, a strain gauge that constitutes a half-bridge circuit with two resistors formed on a substrate. Alternatively, the present invention is also applicable to, for example, a strain gauge that constitutes a full-bridge circuit with four resistors formed on a substrate.

Explanation of Reference Signs

[0076] 1, 1A, 1B strain gauges, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 terminals, 41, 42, 43, 44, 45, 46 wirings, 51, 52 electrodes, 60 cover layer, 451, 461 thick wire portions, 452, 462 thin wire portions

Claims

1. A flexible substrate, A resistor formed on the substrate and composed of a Cr mixed-phase film in which Cr, CrN, and Cr₂N are in a mixed phase, A pair of electrodes formed on the substrate and electrically connected to the resistor via a plurality of wirings, and having, The width of the resistor is 10 μm or more and 100 μm or less, Two or more of the plurality of wirings electrically connect one end of the grid width direction of the resistor to one of the pair of electrodes, The other two or more of the plurality of wirings electrically connect the other end of the grid width direction of the resistor to the other of the pair of electrodes, Each of the wirings includes a portion having a width of 5 μm or more and 100 μm or less, Each of the wirings is composed of the same Cr mixed-phase film as the resistor and is formed integrally with the resistor, The thickness of each of the wirings is 0.05 μm or more and 2 μm or less, A strain gauge.

2. A flexible substrate, A resistor formed on the substrate and composed of a Cr mixed-phase film in which Cr, CrN, and Cr₂N are in a mixed phase, A pair of electrodes formed on the substrate and electrically connected to the resistor via a plurality of wirings, and having, The width of the resistor is 10 μm or more and 100 μm or less, One of the plurality of wirings electrically connects one end of the grid width direction of the resistor to one of the pair of electrodes, and includes one thick wire portion whose one end is electrically connected to one end of the grid width direction of the resistor, and two or more thin wire portions branched from the other end of the thick wire portion and electrically connected to one of the electrodes, The other one of the plurality of wirings electrically connects the other end of the grid width direction of the resistor to the other of the pair of electrodes, and includes one thick wire portion whose one end is electrically connected to the other end of the grid width direction of the resistor, and two or more thin wire portions branched from the other end of the thick wire portion and electrically connected to the other of the electrodes, Each of the thin wire portions included in each of the wirings includes a portion having a width of 5 μm or more and 100 μm or less, Each of the wirings is composed of the same Cr mixed-phase film as the resistor and is formed integrally with the resistor, The thickness of each of the wirings is 0.05 μm or more and 2 μm or less, A strain gauge.

3. The strain gauge according to claim 1 or 2, wherein the strain limit is 8000 με or more.

4. The strain gauge according to claim 1, wherein, in all portions of each of the wirings, the width is 5 μm or more and 100 μm or less.

5. The strain gauge according to claim 2, wherein, in all portions of each of the thin wire portions, the width is 5 μm or more and 100 μm or less.

6. The strain gauge according to claim 5, wherein, in all portions of each of the thick wire portions, the width is wider than 100 μm.

7. The strain gauge according to any one of claims 1 to 6, wherein the gauge factor is 10 or more.

8. CrN and Cr contained in the resistor ２ The strain gauge according to any one of claims 1 to 7, wherein N is 20% by weight or less.

9. The CrN and the Cr ２ Cr in the N ２ The strain gauge according to claim 8, wherein the proportion of N is 80% by weight or more and less than 90% by weight.

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