Strain gauge and strain sensor

Abstract

This strain gauge is provided with: a base material; a resistor body formed on the base material; a pair of electrodes formed on the base material; a first wiring electrically connecting one end of the resistor and one electrode; a second wiring electrically connecting the other end of the resistor and the other electrode; the first wiring and the second wiring are respectively provided with a terminal part on the side opposite to the side connected with the electrode. The first wiring and / or the second wiring are / is connected to one end of the resistor at a position away from the terminal portion.

Description

Technical Field

[0001] The present invention relates to a strain gauge and a strain sensor. Background Art

[0002] Patent Document 1 discloses a strain gauge including 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.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-008026 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, when stress concentrates on a part of the strain gauge, the wire may break.

[0008] The present disclosure provides a strain gauge that suppresses the occurrence of wire breakage.

[0009] Methods for solving problems

[0010] In one embodiment of the present disclosure, a strain gauge is provided, comprising: a substrate; a resistor formed on the substrate; a pair of electrodes formed on the substrate; a first wiring electrically connecting one end of the resistor and one electrode; and a second wiring electrically connecting the other end of the resistor and another electrode; the first wiring and the second wiring each having a terminal portion on the side opposite to the side connected to the electrode, and the first wiring and / or the second wiring being connected to one end of the resistor at a position away from the terminal portion.

[0011] Effects of the Invention

[0012] According to the strain gauge of the present disclosure, it is possible to suppress the occurrence of wire breakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a plan view illustrating the strain gauge according to the first embodiment.

[0014] Figure 2 This is a cross-sectional view illustrating the strain gauge according to the first embodiment.

[0015] Figure 3 It is a diagram illustrating a strain gauge of a comparative example.

[0016] Figure 4 It is a diagram for explaining the strain gauge according to the present embodiment.

[0017] Figure 5 This is a cross-sectional view illustrating the strain gauge according to the first embodiment.

[0018] Figure 6 It is a plan view illustrating a strain gauge according to the second embodiment.

[0019] Figure 7 It is a plan view illustrating a strain gauge according to a third embodiment.

[0020] Figure 8 It is a plan view illustrating a strain sensor according to a fourth embodiment. DETAILED DESCRIPTION

[0021] Hereinafter, the specific embodiment will be described with reference to the accompanying drawings. In the drawings, the same components are sometimes given the same reference numerals and repeated descriptions are omitted.

[0022] In the following description and accompanying drawings, deviations in parallel, right-angled, orthogonal, horizontal, vertical, up-down, left-right, and front-back directions are permitted to the extent that they do not affect the effects of the embodiments. The shape of corners is not limited to right angles and may also be rounded. Parallel, right-angled, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angled, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0023] For example, "approximately parallel" means that even if two lines or two surfaces are not completely parallel, they can be considered parallel as long as they are within the range allowed by manufacturing. Similarly, "approximately right angles," "approximately perpendicular," "approximately horizontal," and "approximately vertical" correspond to "approximately parallel" as long as the relative positional relationship between two lines or two surfaces is within the range allowed by manufacturing.

[0024] <First embodiment>

[0025] Figure 1 It is a plan view illustrating the strain gauge according to the first embodiment. Figure 2 : is a cross-sectional view illustrating a strain gauge according to the first embodiment. Specifically, Figure 2 yes Figure 1 AA cross-sectional view in FIG. In addition, in the drawings, for convenience of explanation, an XY orthogonal coordinate system consisting of mutually orthogonal X-axis and Y-axis is sometimes provided. This coordinate system is set for explanation purposes only and does not limit the posture of the strain sensor, etc. involved in this embodiment.

[0026] The strain gauge 1 includes a base material 10 , a resistor 30 , a pair of wirings 40 (a first wiring and a second wiring), and a pair of electrodes 50 .

[0027] In this embodiment, for convenience, the side of the substrate 10 provided with the resistor 30 is referred to as the upper side or one side, and the side not provided with the resistor 30 is referred to as the lower side or the other side. Furthermore, the surface of each portion provided with the resistor 30 is referred to as the one side or the upper side, and the surface not provided with the resistor 30 is referred to as the other side or the lower side. However, the strain gauge 1 can be used in an upside-down position or at any angle. Furthermore, the term "planar view" refers to the object as viewed from the direction normal to the upper surface 10a of the substrate 10, and the term "planar shape" refers to the shape of the object as viewed from the direction normal to the upper surface 10a of the substrate 10.

[0028] The substrate 10 is a component used as a bottom layer for forming the resistor 30 and the like, and has flexibility. The thickness of the substrate 10 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the substrate 10 can be about 5 μm to 500 μm. In particular, when the thickness of the substrate 10 is 5 μm to 200 μm, it is preferable from the perspective of strain transferability from the strain body surface bonded to the lower surface of the substrate 10 via an adhesive layer, etc., and dimensional stability to the environment. When the thickness is 10 μm or more, it is more preferable from the perspective of insulation.

[0029] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, or polyolefin resin. The term "film" refers to a flexible member having a thickness of approximately 500 μm or less.

[0030] Here, “formed from an insulating resin film” does not prevent the base material 10 from containing fillers, impurities, etc. The base material 10 may be formed from an insulating resin film containing fillers such as silica and alumina.

[0031] 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, and perovskite ceramics (CaTiO3, BaTiO3). Furthermore, amorphous glass can be used. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium can be used as the material for the substrate 10. In this case, for example, an insulating film is formed on the metal substrate 10.

[0032] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing portion that generates a resistance change when deformed. The resistor 30 can be formed directly on the upper surface 10a of the substrate 10, or can be formed on the upper surface 10a of the substrate 10 via another layer. Figure 1In the figure, for convenience, the resistor 30 is represented by a dense pear-shaped pattern.

[0033] For example, the resistor 30 may be formed of a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. Specifically, the resistor 30 may be formed of 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).

[0034] Here, the Cr mixed phase film is a film of a mixed phase of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0035] The thickness of the resistor 30 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the resistor 30 can be about 0.05μm to 2μm. In particular, if the thickness of the resistor 30 is 0.1μm 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. If it is 1μm or less, it is more preferable in that the film breakage caused by the internal stress of the film constituting the resistor 30 and the warping from the substrate 10 can be reduced. The width of the resistor 30 is optimized according to the required specifications such as the resistance value and the lateral sensitivity, and considering the countermeasures for breakage, it can be, for example, about 10μm to 100μm.

[0036] For example, in the case where the resistor 30 is a Cr mixed phase film, by using α-Cr (α chromium), which is a stable crystalline phase, as the main component, the stability of the strain characteristics can be improved. In addition, by using α-Cr as the main component of the resistor 30, the strain coefficient of the strain gauge 1 can be greater than 10, and the strain coefficient temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000ppm / °C to +1000ppm / °C. Here, the so-called main component means that the target substance accounts for more than 50% by weight of all the materials constituting the resistor. Furthermore, when the strain characteristics are to be further improved, the resistor 30 preferably contains more than 80% by weight of α-Cr, and more preferably contains more than 90% by weight of α-Cr. In addition, α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0037] When the resistor 30 is a Cr mixed phase film, the CrN and Cr2N contained in the Cr mixed phase film are preferably 20 wt% or less. 20 wt% or less of CrN and Cr2N in the Cr mixed phase film can suppress a decrease in gauge coefficient.

[0038] In addition, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, more preferably 90% by weight or more and less than 95% by weight. By setting the ratio of Cr2N in CrN and Cr2N to 90% by weight or more and less than 95% by weight, the reduction in TCR (negative TCR) becomes more significant by utilizing Cr2N having semiconductor properties. Moreover, by reducing ceramicization, brittle fracture can be reduced.

[0039] On the other hand, if trace amounts of N2 or atomic N are present in the film, they can be removed from the film due to the external environment (e.g., high temperature), causing changes in film stress. By creating chemically stable CrN, the generation of such unstable N is eliminated, resulting in a stable strain gauge.

[0040] The resistor 30 has a plurality of elongated portions 31 oriented in the same direction in the longitudinal direction (in Figure 1 In the example, the Y-axis direction is arranged at a predetermined interval, and the ends of adjacent elongated portions 31 are connected to each other in a staggered manner, forming a structure that is zigzag as a whole. Figure 1 In the example of FIG. 1 , the longitudinal direction of the plurality of elongated portions 31 becomes the gate direction, and the direction perpendicular to the gate direction (in Figure 1 In the example, the X-axis direction) becomes the gate width direction. Figure 1 In the example shown in FIG, the outer periphery of the connection portion between the elongated portions 31 is a curved line, but the shape of the connection portion is not limited thereto. This also applies to the following drawings.

[0041] Of the two elongated portions 31 located at both ends of the elongated portion 31 of the resistor 30, the ends of the elongated portion 31 extend in the direction of the adjacent wiring 40 (in the direction of the adjacent wiring 40). Figure 1 The bent end portion (hereinafter also referred to as the “end portion of the resistor”) is made of the same material as the elongated portion 31 and is an extension of the elongated portion 31.

[0042] The wiring 40 is formed on the substrate 10 and connects the resistor 30 to the electrode 50. Each wiring 40 is not limited to a straight line and can be any pattern. In addition, each wiring 40 can be of any length. Each wiring 40 includes a first metal layer 41 and a second metal layer 42 stacked on the upper surface of the first metal layer 41. Figure 1 In the figure, for convenience, the first metal layer 41 is represented by the same dark pear-shaped pattern as the resistor 30. The second metal layer 42 is represented by a lighter pear-shaped pattern than the resistor 30.

[0043] exist Figure 1In the example shown in FIG. , each wiring 40 extends in the Y-axis direction. In other words, each wiring 40 has a longitudinal direction in the Y-axis direction. In this embodiment, specific parts of the wiring 40 are named for convenience, but the various parts of the wiring 40 described below are integrally formed.

[0044] The wiring 40 includes a side portion 40h, a side portion 40g, a terminal portion 40e, and a connecting portion 40a. The side portion 40h is a side portion of the wiring 40 that forms a side of the resistor 30 when viewed in a plan view. In addition, the side portion 40g represents a side portion of the wiring 40 that does not form the resistor 30 when viewed in a plan view. In addition, the end portion 40e represents the side of the wiring 40 opposite to the side connected to the electrode 50 (in FIG. Figure 1 In the example, the terminal portion of the positive direction side of the Y axis. At least one of the other pair of wirings 40 has a connection portion 40a at a position away from the end portion 40e of the side portion 40h. Figure 1 In the example of FIG. 4 , both of the two wirings 40 have a connection portion 40 a at a position away from the terminal portion 40 e. The connection portion 40 a is connected to the end portion of the resistor 30 .

[0045] Furthermore, the shape of each wiring 40 is not limited to this. For example, each wiring 40 may be non-parallel to the Y-axis. Furthermore, for example, the positional relationship between two wirings 40 may be non-parallel. Furthermore, for example, the side of each wiring 40 may be inclined in the Y-axis direction or may be curved.

[0046] One end of the resistor 30 (e.g., the end on the negative X-direction side) is electrically connected to one of the two electrodes 50 (e.g., the electrode 50 on the negative X-direction side) via a wiring 40 (a first wiring line). The other end of the resistor 30 (e.g., the end on the positive X-direction side) is also electrically connected to the other electrode 50 (e.g., the electrode 50 on the positive X-direction side) via a wiring 40 (a second wiring line). In other words, the resistor 30 is electrically connected to the pair of electrodes 50 via a pair of wiring lines 40.

[0047] Electrodes 50 are used to output changes in the resistance value of resistor 30 caused by strain to the outside. For example, external connection wires are bonded to electrodes 50. Each electrode 50 is formed on substrate 10. Electrodes 50 are electrically connected to resistor 30 via wiring 40. For example, electrodes 50 can be wider than wiring 40 to form a generally rectangular shape.

[0048] Electrode 50 includes a first metal layer 51 and a second metal layer 52 stacked on the upper surface of first metal layer 51. First metal layer 51 is electrically connected to the end of resistor 30 via first metal layer 41 of wiring 40. First metal layer 51 is formed into a substantially rectangular shape when viewed in plan. First metal layer 51 may also be formed to the same width as wiring 40.

[0049] For convenience, the resistor 30, first metal layer 41, and first metal layer 51 are designated by different symbols, but they can be integrally formed using the same material in the same process. Therefore, the thicknesses of the resistor 30, first metal layer 41, and first metal layer 51 are substantially the same. For convenience, the second metal layer 42 and second metal layer 52 are designated by different symbols, but they can be integrally formed using the same material in the same process. Therefore, the thicknesses of the second metal layer 42 and second metal layer 52 can be substantially the same.

[0050] The second metal layer 42 and the second metal layer 52 can be respectively formed of a material with lower resistance than the resistor 30 (as well as the first metal layer 41 and the first metal layer 51). There is no particular limitation on the material of the second metal layer 42 and the second metal layer 52 as long as it is a material with lower resistance than the resistor 30, and it can be appropriately selected according to the purpose. For example, in the case where the resistor 30 is a Cr mixed-phase film, the material of the second metal layer 42 and the second metal layer 52 can include Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of the above metals, a compound of any of the above metals, or a laminated film of any of the above metals, alloys, and compounds. There is no particular limitation on the thickness of the second metal layer 42 and the second metal layer 52, and it can be appropriately selected according to the purpose. For example, the thickness of the second metal layer 42 and the second metal layer 52 can be about 3μm to 5μm.

[0051] The second metal layer 42 can be formed on a portion of the first metal layer 41 or on the entire first metal layer 41. The second metal layer 52 can be formed on a portion of the first metal layer 51 or on the entire first metal layer 51. One or more other metal layers can also be stacked on the upper surface of the second metal layer 52. For example, the second metal layer 52 can be a copper layer, and a gold layer can be stacked on the upper surface of the copper layer. Alternatively, the second metal layer 52 can be a copper layer, and a palladium layer and a gold layer can be stacked in sequence on the upper surface of the copper layer. By using a gold layer as the top layer of the electrode 50, the solder wettability of the electrode 50 can be improved.

[0052] Alternatively, a cover layer may be provided on the upper surface 10a of the substrate 10 to cover the resistor 30 and wiring 40 and expose the electrode 50. Providing the cover layer can protect the resistor 30 and wiring 40 from mechanical damage, etc. Furthermore, providing the cover layer can protect the resistor 30 and wiring 40 from moisture, etc. Alternatively, the cover layer may be provided to cover all portions except the electrode 50.

[0053] The covering layer can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or a composite resin (e.g., silicone resin, polyolefin resin). The covering layer may also contain fillers or pigments. The thickness of the covering layer is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the thickness of the covering layer can be approximately 2 μm to 30 μm.

[0054] Therefore, the wiring 40 has a structure in which a second metal layer 42 is laminated on a first metal layer 41 made of the same material as the resistor 30. Consequently, the resistance of each wiring 40 is lower than that of the resistor 30. This prevents each wiring 40 from functioning as a resistor. Consequently, the accuracy of detecting strain caused by the resistor 30 can be improved.

[0055] In other words, by providing the wiring 40 having a lower resistance than the resistor 30, the actual sensing portion of the strain gauge 1 can be limited to the local area where the resistor 30 is formed. Therefore, the accuracy of detecting the strain caused by the resistor 30 can be improved.

[0056] In particular, in high-sensitivity strain gauges with a gauge factor of 10 or greater that use a Cr mixed-phase film as the resistor 30, by making the wiring 40 have a lower resistance than the resistor 30, the actual sensing portion is limited to the local area where the resistor 30 is formed, significantly improving strain detection accuracy. Furthermore, making the wiring 40 have a lower resistance than the resistor 30 also has the effect of reducing lateral sensitivity.

[0057] Furthermore, regardless of whether or not the wiring 40 is linear, the length of the wiring 40 connecting the resistor 30 and each electrode 50 is preferably 5 mm or longer along the length of the wiring 40. When the length is 5 mm or longer, heat generated when soldering a lead wire to the electrode 50, for example, is less likely to be transferred to the resistor 30 and the covering layer covering the resistor 30, thereby reducing the thermal load on various strain characteristics.

[0058] Figure 3 1 is a diagram for explaining a strain gauge 1z of a comparative example. Figure 3 In FIG, the vicinity of the terminal end of the wiring is shown in an enlarged manner. The strain gauge 1z has the same characteristics as the strain gauge 1 except that the connection position between the resistor and the wiring and the shape of the wiring are different from those of the strain gauge 1. Figures 1 and 2 The strain gauge 1 shown has the same structure.

[0059] exist Figure 3 In the strain gauge 1z shown in FIG. 1 , the wiring is connected to the resistor near the terminal portion. In a strain gauge of this shape, for example, Figure 3 As shown, disconnection may sometimes occur at the connection portion of the wiring and / or resistor.

[0060] on the other hand, Figure 4: is a diagram for explaining a case where a wire break occurs in the strain gauge 1 of the first embodiment. Figure 4 The description is given by taking the vicinity of the end portion 40 e of the wiring 40 on the negative side of the X-axis in the strain gauge 1 as an example, but the same description applies to the wiring 40 and the terminal portion 40 e on the positive side of the X-axis.

[0061] For example, for some reason, strong stress is applied near the terminal end 40e of the wiring 40. Figure 4 The curve CL of the graph is broken. Figure 4 As shown, in the strain gauge 1, the resistor 30 and the wiring 40 are connected at a location away from the terminal portion 40e. Therefore, even if a break occurs in the portion of the curve CL and a portion of the wiring 40 becomes non-conductive, the break will not reach the connection between the wiring 40 and the resistor 30. Consequently, there is no problem with the electrical conduction between the electrode 50 and the wiring 40, or between the wiring 40 and the resistor 30. Therefore, by positioning the connection between the wiring 40 and the resistor 30 away from the terminal portion 40e, a strain gauge that is less susceptible to breakage can be realized.

[0062] For example, the distance L between the connecting portion 40a and the end portion 42e can be 30 microns or greater. By setting the distance L to 30 microns or greater, the aforementioned disconnection can be suppressed with a higher probability. In other words, the wiring 40 is preferably connected to the resistor 30 at a location 30 microns or greater away from the end portion 42e of the second metal layer 42.

[0063] Furthermore, in the strain gauge 1, the width W of the end edge of the terminal portion 42e of the second metal layer 42 is wider than that of the comparative example. For example, when viewed in plan, the width W is preferably 50 microns or more. Wire breaks typically occur at the thinner portions of the peripheral ends of the strain gauge wiring, power supply, resistor, etc. Therefore, by widening the width W, the occurrence of wire breaks can be suppressed. In addition, at least one of the corners 42c of the second metal layer 42 can be formed as a right angle or an obtuse angle when viewed in plan. By making at least one of the corners 42c a right angle or an obtuse angle, the corner of the end portion 40e can be prevented from protruding sharply. Therefore, the occurrence of wire breaks at the corner portion of the terminal portion of the wiring 40 can be suppressed.

[0064] To manufacture the strain gauge 1, a substrate 10 is first prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. The metal layer A is the layer that is ultimately patterned into the resistor 30, the first metal layer 41, and the first metal layer 51. Therefore, the material and thickness of the metal layer A are the same as those of the resistor 30, the first metal layer 41, and the first metal layer 51 described above.

[0065] For example, the metal layer A can be formed by magnetron sputtering using as a target a raw material capable of forming the metal layer A. Alternatively, the metal layer A can be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like instead of magnetron sputtering.

[0066] From the viewpoint of stabilizing the strain characteristics, before forming the metal layer A, a functional layer may be formed as an underlayer on the upper surface 10 a of the substrate 10 by vacuum deposition to a predetermined thickness, for example, by a conventional sputtering method.

[0067] In this application, the term "functional layer" refers to a layer that has the function of promoting at least the crystal growth of the upper metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of the metal layer A caused by oxygen or moisture contained in the substrate 10 and the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer may also have other functions.

[0068] Since the insulating resin film constituting the base material 10 contains oxygen and moisture, and particularly when the metal layer A contains Cr, Cr forms a self-oxidation film, it is effective for the functional layer to have a function of preventing the metal layer A from being oxidized.

[0069] The material of the functional layer is not particularly limited. As long as it has the function of promoting the crystal growth of the metal layer A (resistor 30) as the upper layer, it can be appropriately selected according to the purpose. For example, as the material of the functional layer, one or more metals selected from the group consisting of 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), and Al (aluminum), an alloy of any metal in the group, or a compound of any metal in the group can be cited.

[0070] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0071] When the functional layer is formed from a conductive material such as a metal or alloy, the thickness of the functional layer is preferably no greater than 1 / 20 of the thickness of the resistor. This range promotes the crystal growth of α-Cr and prevents some of the current flowing through the resistor from flowing through the functional layer, thereby reducing strain detection sensitivity.

[0072] When the functional layer is formed of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably no greater than 1 / 50 of the thickness of the resistor. This range promotes the crystal growth of α-Cr and further prevents a portion of the current flowing through the resistor from flowing through the functional layer, thereby reducing strain detection sensitivity.

[0073] When the functional layer is formed of a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be less than 1 / 100 of the thickness of the resistor. Within this range, a portion of the current flowing to the resistor can be prevented from flowing to the functional layer, thereby further preventing a decrease in strain detection sensitivity.

[0074] When the functional layer is formed of an insulating material such as oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted and the film can be easily formed without causing cracks in the functional layer.

[0075] When the functional layer is formed of an insulating material such as oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted and the film can be formed more easily without causing cracks in the functional layer.

[0076] When the functional layer is formed of an insulating material such as oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted and the film can be formed more easily without causing cracks in the functional layer.

[0077] In addition, the planar shape of the functional layer is formed to be, for example, Figure 1 The functional layer is formed into a pattern that is substantially identical to the planar shape of the resistor shown. However, the planar shape of the functional layer is not limited to being substantially identical to the planar shape of the resistor. When the functional layer is formed of an insulating material, the functional layer pattern may not be formed to be identical to the planar shape of the resistor. In this case, the functional layer may be formed in a bonded shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a bonded shape over the entire upper surface of the substrate 10.

[0078] Furthermore, when the functional layer is formed of an insulating material, by forming the functional layer thicker, to a thickness of 50 nm to 1 μm, and forming it in a bonded state, the thickness and surface area of ​​the functional layer are increased, thereby allowing heat generated by the resistor to be dissipated toward the substrate 10. As a result, in the strain gauge 1, a decrease in measurement accuracy due to self-heating of the resistor can be suppressed.

[0079] The functional layer can be formed in a vacuum film by, for example, a conventional sputtering method in which Ar (argon) gas is introduced into a chamber using a raw material capable of forming the functional layer as a target. By using the conventional sputtering method, the functional layer is formed while the upper surface 10a of the substrate 10 is etched with Ar gas. This minimizes the amount of functional layer formed and improves adhesion.

[0080] However, this is only one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, before forming the functional layer, the upper surface 10a of the substrate 10 may be activated by plasma treatment using Ar or the like to improve adhesion, and then the functional layer may be formed by vacuum deposition using magnetron sputtering.

[0081] There are no particular limitations on the combination of materials for the functional layer and the metal layer A. They can be appropriately selected depending on the intended purpose. For example, Ti is used as the functional layer, and a Cr mixed phase film containing α-Cr (α chromium) as the main component is formed as the metal layer A.

[0082] In this case, for example, a raw material capable of forming a Cr mixed-phase film can be used as a target, and a magnetron sputtering method can be used to introduce Ar gas into the chamber to form the metal layer A. Alternatively, pure Cr can be used as a target, and an appropriate amount of nitrogen gas can be introduced into the chamber together with the Ar gas to form the metal layer A by reactive sputtering. In this case, by changing the amount or pressure (nitrogen partial pressure) of nitrogen gas introduced, or by providing a heating step to adjust the heating temperature, the ratio of CrN and Cr2N contained in the Cr mixed-phase film, as well as the ratio of Cr2N in CrN and Cr2N, can be adjusted.

[0083] In these methods, the growth plane of the Cr mixed-phase film is defined by the functional layer composed of Ti, enabling the formation of a Cr mixed-phase film primarily composed of α-Cr, a stable crystalline structure. Furthermore, the diffusion of Ti from the functional layer into the Cr mixed-phase film improves strain characteristics. For example, the gauge factor of the strain gauge 1 can be 10 or greater, and the gauge temperature coefficient (TCS) and resistance temperature coefficient (TCR) can be within the range of -1000 ppm / °C to +1000 ppm / °C. Furthermore, when the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0084] Furthermore, when the metal layer A is a Cr mixed-phase film, the functional layer composed of Ti has the functions of promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A caused by oxygen or moisture contained in the substrate 10, and improving the adhesion between the substrate 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used instead of Ti as the functional layer.

[0085] By providing a functional layer below metal layer A in this manner, the crystal growth of metal layer A can be promoted, allowing metal layer A to be formed from a stable crystalline phase. As a result, the stability of the strain characteristics of strain gauge 1 can be improved. Furthermore, by diffusing the material constituting the functional layer into metal layer A, the strain characteristics of strain gauge 1 can be improved.

[0086] Next, the second metal layer 42 and the second metal layer 52 are formed on the upper surface of the metal layer A. The second metal layer 42 and the second metal layer 52 can be formed by, for example, photolithography.

[0087] Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating to cover the upper surface of metal layer A. Next, a photosensitive photoresist is formed on the entire upper surface of the seed layer, and exposure and development are performed to form openings that expose the areas where second metal layer 42 and second metal layer 52 are to be formed. At this time, by adjusting the shape of the openings in the photoresist, second metal layer 42 and second metal layer 52 can be formed into any shape. As the photoresist, for example, dry film photoresist can be used.

[0088] Next, for example, second metal layer 42 and second metal layer 52 are formed on the seed layer exposed within the opening by electrolytic plating, using the seed layer as a power supply path. Electrolytic plating has the advantage of providing a good rhythm and enabling the formation of low-stress electrolytic plating layers as second metal layer 42 and second metal layer 52. By providing a relatively thick electrolytic plating layer with low stress, warping of strain gauge 1 can be prevented. Alternatively, second metal layer 42 and second metal layer 52 can be formed by electroless plating.

[0089] Next, the photoresist is removed. The photoresist can be removed by, for example, immersing the photoresist material in a dissolvable solution.

[0090] Then, a photosensitive photoresist is formed on the entire surface of the upper surface of the seed layer, exposed and developed, and the pattern is formed into the same Figure 1 The resistor 30, wiring 40 and electrode 50 have the same planar shape. As the photoresist, for example, a dry film photoresist can be used. Then, the photoresist is used as an etching mask to remove the metal layer A and the seed layer exposed from the photoresist to form Figure 1 The resistor 30, wiring 40 and electrode 50 have a planar shape.

[0091] For example, by wet etching, unnecessary portions of the metal layer A and the seed layer can be removed. When a functional layer is formed under the metal layer A, the functional layer is patterned by etching in the same manner as the resistor 30, wiring 40, and electrode 50. Figure 1At this time, a seed layer is formed on the resistor 30, the first metal layer 41 and the first metal layer 51.

[0092] Next, second metal layer 42 and second metal layer 52 are used as etching masks to remove the unnecessary seed layer exposed from second metal layer 42 and second metal layer 52, thereby forming second metal layer 42 and second metal layer 52. The seed layer still remains directly below second metal layer 42 and second metal layer 52. For example, the unnecessary seed layer can be removed by wet etching using an etching solution that etches the seed layer but does not etch the functional layer, resistor 30, wiring 40, and electrode 50.

[0093] Then, as needed, a cover layer is formed on the upper surface 10a of the substrate 10, covering the resistor 30 and wiring 40 while exposing the electrode 50. This completes the strain gauge 1. The cover layer can be formed, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10, heating and curing the film so as to cover the resistor 30 and wiring 40 and expose the electrode 50. Alternatively, the cover layer can be formed by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10, heating and curing the film so as to cover the resistor 30 and wiring 40 and expose the electrode 50. The opening for exposing the electrode 50 can be formed, for example, by photolithography.

[0094] When a functional layer is provided on the upper surface 10a of the substrate 10 as a base layer of the resistor 30, the first metal layer 41, and the first metal layer 51, the strain gauge 1 becomes Figure 5 The cross-sectional shape shown in FIG. The layer indicated by reference numeral 20 is a functional layer. The planar shape of the strain gauge 1 when the functional layer 20 is provided is, for example, Figure 1 However, as described above, the functional layer 20 may be formed in an adhesive state on a part or the entirety of the upper surface 10 a of the substrate 10 .

[0095] <Second embodiment>

[0096] The resistor of the strain gauge according to the present invention may have a structure including a plurality of sensing portions and a junction portion disposed between the plurality of sensing portions. Figure 6 1 is a plan view illustrating a strain gauge 2 according to the second embodiment. The strain gauge 2 differs from the strain gauge 1 in that the resistor 130 includes a first sensing portion 131 , a second sensing portion 132 , and a junction portion 133 disposed therebetween.

[0097] The strain gauge 2 includes a substrate 110 , a resistor 130 , wiring 40 , and electrodes 50 . The resistor 130 and wiring 40 are formed on a surface 110 a of the substrate 110 .

[0098] Since the substrate 110 has the same structure as the substrate 10 except for the size difference, the description of the substrate 110 refers to the description of the substrate 10 and is omitted here. In addition, the wiring 40 and the electrode 50 refer to the description of the first embodiment and are omitted here.

[0099] The resistor 130 includes a first sensing portion 131, a second sensing portion 132, and a junction 133. The first sensing portion 131 has a plurality of elongated portions 31 arranged at predetermined intervals in the same longitudinal direction (the Y-axis direction), with the ends of adjacent elongated portions 31 interlaced and connected to each other, forming a zigzag structure as a whole. One end 131e1 of the first sensing portion 131 is electrically connected to the electrode 50 via the wiring 40. Furthermore, this end 131e1 of the connecting portion 40a is connected to the wiring 40. As shown in the figure, the connecting portion 40a is separated from the end 40e of the wiring 40. The other end 131e2 of the first sensing portion 131 is electrically connected to the junction 133.

[0100] The second sensing portion 132 has the same structure as the first sensing portion. Specifically, the second sensing portion 132 comprises a plurality of elongated portions 31 arranged at predetermined intervals along the longitudinal direction (the Y-axis), with the ends of adjacent elongated portions 31 interlaced and connected to each other, forming a zigzag structure as a whole. One end 132e1 of the second sensing portion 132 is electrically connected to the electrode 50 via the wiring 40. Furthermore, this end 132e1 is connected to the wiring 40 at a connection 40a, which is separated from the terminal end 40e of the wiring 40. The other end 132e2 of the second sensing portion 132 is electrically connected to the junction 133.

[0101] The joint portion 133 is disposed between the first sensing portion 131 and the second sensing portion 132. The joint portion 133 is made of the same material as the wiring 40. The joint portion 133 can be formed on the substrate 110 using the same method as the wiring 40. The shape and size of the joint portion 133 are not particularly limited.

[0102] The joint portion 133 may be connected to an end portion of the first sensing portion 131 and / or an end portion of the second sensing portion 132 (ie, the end portion 131e2 and / or the end portion 132e2) at a position away from the terminal portion 133e and the terminal portion 133f.

[0103] In the above example, the strain gauge 2 includes two sensing sections. However, the number of sensing sections is not limited to two, and three or more sensing sections may be included. In this case, the resistor as a whole is composed of three or more sensing sections connected in series, with joints provided between the three or more sensing sections.

[0104] Similar to the strain gauge 1 according to the first embodiment, the strain gauge 2 according to the second embodiment is connected to the wiring 40 at a location on the resistor 130 that is distant from the terminal end 40e. Therefore, for the same reason as the strain gauge 1, the strain gauge 2 is also a strain gauge that is less susceptible to wire breakage. Furthermore, in the strain gauge 2, the sensing portion (the first sensing portion 131 and / or the second sensing portion 132) of the resistor 130 is connected to the joint 133 at a location that is distant from the terminal ends 133e and 133f of the joint 133. Therefore, the strain gauge 2 achieves a strain gauge that is less susceptible to wire breakage even near the joint 133 (e.g., at a corner of the terminal end of the joint 133).

[0105] <Third embodiment>

[0106] The third embodiment shows an example in which a third metal layer is arranged around the resistor 30. In the third embodiment, description of components identical to those in the already described embodiments may be omitted.

[0107] Figure 7 3 is a plan view illustrating a strain gauge 3 according to the third embodiment. Figure 7 The strain gauge 3 differs from the strain gauge 1 in that the strain gauge 3 includes a third metal layer 90 disposed around the resistor 30 and separated from the resistor 30 , the wiring 40 , and the electrode 50 .

[0108] Third metal layer 90 is formed of the same material as resistor 30. Third metal layer 90 can be formed using the same process as resistor 30, first metal layer 41, and the like. Third metal layer 90 is preferably arranged in the remaining space around resistor 30, occupying as large an area as possible. Alternatively, a metal layer composed of the same material as second metal layer 42 and the like may be stacked on third metal layer 90.

[0109] Thus, by disposing the third metal layer 90 around the resistor 30, the rigidity of the strain gauge 3 can be made higher than that of the strain gauge 1. By increasing the rigidity of the strain gauge 3, disconnection of the strain gauge 3 can be suppressed.

[0110] The strain gauge according to the third embodiment can be made less susceptible to wire breakage even when stress concentrates on the wiring ends and the periphery of the resistor (for example, near the joint 133). Furthermore, the strain gauge according to the third embodiment, by including the third metal layer, increases its rigidity and can suppress wire breakage of the strain gauge 3.

[0111] <Fourth embodiment>

[0112] In the fourth embodiment, an example of a strain sensor including a plurality of strain gauges will be described. In the strain sensor according to the fourth embodiment, the plurality of strain gauges are connected by sharing at least one of their electrodes and at least one of their wirings to form a bridge circuit.

[0113] Figure 8 : is a top view illustrating a strain sensor 4 according to a fourth embodiment. Figure 8 The strain sensor 4 includes a substrate 210, resistors 230A, 230B, 230C, 230D, and wirings 240A, 240B, 240C, and 240D. The resistors 230A, 230B, 230C, 230D, and wirings 240A, 240B, 240C, and 240D are formed on the surface 210a of the substrate 210.

[0114] Each of the wirings 240A and 240C extends in the Y-axis direction. In other words, each of the wirings 240A and 240C has a length in the Y-axis direction. Each of the wirings 240B and 240D extends in the X-axis direction. In other words, each of the wirings 240B and 240D has a length in the X-axis direction.

[0115] In addition, Figure 8 In the example of FIG. 1 , although the electrodes included in the strain sensor 4 are not clearly described, in the example of the figure, a part of the wiring is used as the electrode of the strain sensor 4 .

[0116] The resistors 230A, 230B, 230C, and 230D can each be formed of the same material as the resistor 30 of the first embodiment. Similarly, the wirings 240A, 240B, 240C, and 240D can each be formed of the same material as the wiring 40 of the first embodiment.

[0117] The resistor 230A is connected to the wiring 240A and the wiring 240B. The resistor 230B is connected to the wiring 240B and the wiring 240C. The resistor 230C is connected to the wiring 240C and the wiring 240D. The resistor 230D is connected to the wiring 240D and the wiring 240A.

[0118] Wiring 240A includes a first metal layer 241A and a second metal layer 242A stacked on the upper surface of first metal layer 241A. Wiring 240B includes a first metal layer 241B and a second metal layer 242B stacked on the upper surface of first metal layer 241B. Wiring 240C includes a first metal layer 241C and a second metal layer 242C stacked on the upper surface of first metal layer 241C. Wiring 240D includes a first metal layer 241D and a second metal layer 242D stacked on the upper surface of first metal layer 241D.

[0119] The first metal layer 241A, the first metal layer 241B, the first metal layer 241C, and the first metal layer 241D can be formed of the same material as the first metal layer 41. In addition, the second metal layer 242A, the second metal layer 242B, the second metal layer 242C, and the second metal layer 242D can be formed of the same material as the second metal layer 42.

[0120] Although the wiring 240B, the wiring 240C, and the wiring 240D have different directions, their shapes and connection relationships with the resistor are the same as those of the wiring 240A. Therefore, the following description uses the wiring 240A to describe the connection between each wiring and the resistor according to the fourth embodiment.

[0121] The wiring 240A has a substantially L-shaped shape in a plan view. The wiring 240A has a side portion 240Ai, an end portion 240Aj, a side portion 240Ah, an end portion 240Af, and a side portion 240Ag in this order from the end portion 240Ae.

[0122] Resistor 230A is connected to end 240Ae. Resistor 230A is connected at a position away from each of side 240Ag and side 240Ai in end 240Ae. Furthermore, resistor 230D is connected to side 240Ah. Resistor 230D is connected at a position away from each of end 240Aj and end 240Af in side 240Ah.

[0123] Furthermore, for example, when an electrode is provided near end 240Aj, the connection position of resistor 230D is located away from end 240Ae (terminal end) of side portion 240Ah. In other words, wiring 240A provides an example of a configuration in which at least one of the electrodes, at least one of the wirings, and at least one of the second wirings are shared among multiple strain gauges, thereby providing a shared electrode and at least one of the wirings.

[0124] According to the strain gauge of the fourth embodiment, it is possible to suppress the occurrence of wire breakage. According to the strain sensor of the fourth embodiment, even if stress concentrates on the wiring end, it is possible to suppress the occurrence of wire breakage in the strain gauge.

[0125] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive, and may be omitted, replaced, or modified in various ways without departing from the claims and the spirit thereof.

[0126] This application claims the benefit of priority from basic patent application No. 2023-028342 filed in the Japan Patent Office on February 27, 2023, the entire contents of which are hereby incorporated by reference.

[0127] Explanation of symbols

[0128] 1, 2, 3 strain gauges, 4 strain sensor, 10, 110, 210 substrate, 30, 130 resistor, 40 wiring, 40a connecting portion, 40e terminal portion, 41 first metal layer, 42 second metal layer, 50 electrode, 51 first metal layer, 52 second metal layer, 90 third metal layer, 131 first sensing portion, 132 second sensing portion, 133 joining portion, 230A, 230B, 230C, 230D resistor, 240A, 240B, 240C, 240D wiring.

Claims

1. A strain gauge comprising: a substrate; a resistor formed on the substrate; a pair of electrodes formed on the substrate; a first wiring electrically connecting one end of the resistor and one electrode; as well as a second wiring electrically connecting the other end of the resistor and the other electrode; The first wiring and the second wiring each have a terminal portion on a side opposite to a side connected to the electrode; The first wiring and / or the second wiring is connected to one end of the resistor at a position away from the terminal portion.

2. The strain gauge according to claim 1 , wherein the first wiring and the second wiring include: a first metal layer integrally formed of the same material as the resistor; and a second metal layer formed on the first metal layer and made of a material having a lower resistance than that of the first metal layer; The first metal layer and the second metal layer each have the terminal portion. 3 . The strain gauge according to claim 2 , wherein the terminal portion of the second metal layer of the first wiring and / or the second wiring has an obtuse angle in a plan view. 4 . The strain gauge according to claim 2 , wherein the terminal portion of the second metal layer of the first wiring and / or the second wiring forms a right angle in a plan view. 5 . The strain gauge according to claim 2 , wherein the terminal portion of the second metal layer has an end side width of 50 μm or more in a plan view. 6 . The strain gauge according to claim 2 , wherein the first wiring and / or the second wiring is connected to the resistor at a position at least 30 μm away from the terminal end of the second metal layer. 7 . The strain gauge according to claim 1 , wherein the resistor, the first wiring, and a third metal layer arranged separately from the second wiring are provided around the resistor.

8. The strain gauge according to any one of claims 1 to 7, wherein: The resistor has: Multiple feeling departments; A bonding portion is disposed between the sensing portions and is formed of the same material as the first wiring and the second wiring. 9 . The strain gauge according to claim 8 , wherein the sensing portion and the joint portion are connected at a position away from an end portion of the joint portion.

10. A strain sensor comprising a plurality of strain gauges according to any one of claims 1 to 9, The plurality of strain gauges share at least one of the electrodes connected thereto and at least one of the first wiring and the second wiring, thereby forming a bridge circuit.

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