Strain gauge and strain sensor

Abstract

To provide a strain gauge for suppressing the occurrence of wiring breakage.SOLUTION: The strain gauge is provided with a base material, a resistor formed on the base material, a pair of electrodes formed on the base material, a first wiring for electrically connecting one end of the resistor to one electrode, and a second wiring for electrically connecting the other end of the resistor to the other electrode. Each of the first wiring and the second wiring has a terminal on the side opposite to the side connected to the electrode, and the first wiring and / or the second wiring are connected to one end of the resistor at a position separated from the terminal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to strain gauges and strain sensors. [Background technology]

[0002] Patent Document 1 discloses a strain gauge having a flexible substrate, a resistor formed on the substrate, and a pair of electrodes formed on the substrate and electrically connected to the resistor via wiring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-008026 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if stress is concentrated in one part of a strain gauge, it may break.

[0005] The present disclosure provides a strain gauge that suppresses the occurrence of wire breakage. [Means for solving the problem]

[0006] In one aspect 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 to one of the electrodes, and a second wiring electrically connecting the other end of the resistor to the other electrode, wherein the first wiring and the second wiring each have a termination portion on the side opposite to the side connected to the electrode, and the first wiring and / or the second wiring connects to one end of the resistor at a position spaced apart from the termination portion. Effect of the Invention

[0007] According to the strain gauge of the present disclosure, the occurrence of wire breakage can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment. [Diagram 3] FIG. 3 is a diagram illustrating a strain gauge of a comparative example. [Figure 4] FIG. 4 is a diagram illustrating the strain gauge according to this embodiment. [Diagram 5] FIG. 5 is a cross-sectional view illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 6 is a plan view illustrating the strain gauge according to the second embodiment. [Figure 7] FIG. 7 is a plan view illustrating the strain gauge according to the third embodiment. [Figure 8] FIG. 8 is a plan view illustrating the strain sensor according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] In the following description and drawings, deviations in directions such as parallel, right-angled, orthogonal, horizontal, vertical, up-down, left-right, and front-back directions are permitted to a degree that does not impair the effects of the embodiments. The shape of the corners is not limited to right angles and may be rounded. Parallel, right-angled, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angled, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0011] For example, "approximately parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as being parallel to each other as long as it is within the range of manufacturing tolerance. As with "approximately parallel," "approximately right angle," "approximately perpendicular," "approximately horizontal," and "approximately vertical" are also intended to correspond to the respective terms as long as the relative positional relationship between the two lines or two surfaces is within the range of manufacturing tolerance.

[0012] 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. Specifically, Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. For ease of explanation, an XY orthogonal coordinate system consisting of an X-axis and a Y-axis perpendicular to each other may be set in the drawings. Note that this coordinate system is defined for the sake of explanation, and does not limit the attitude of the strain sensor and the like according to this embodiment.

[0013] The strain gauge 1 has a substrate 10, a resistor 30, a pair of wires 40 (a first wire and a second wire), and a pair of electrodes 50.

[0014] In this embodiment, for convenience, in the strain gauge 1, the side of the substrate 10 on which the resistor 30 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Also, the surface on which the resistor 30 is provided in each portion is referred to as the one side or the upper surface, and the surface on which the resistor 30 is not provided is referred to as the other side or the lower surface. However, the strain gauge 1 can be used upside down or placed at any angle. Also, the planar view refers to the object being viewed from the normal direction of the upper surface 10a of the substrate 10, and the planar shape refers to the shape of the object being viewed from the normal direction of the upper surface 10a of the substrate 10.

[0015] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. There is no particular limit to the thickness of the substrate 10, and it can be appropriately selected depending on the purpose. For example, the thickness of the substrate 10 can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like, and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

[0016] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0017] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0018] Examples of materials other than resin for the substrate 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. In this case, for example, an insulating film is formed on the metal substrate 10.

[0019] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strained. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 with a dark matte pattern.

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

[0021] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0022] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the resistor 30 can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable in terms of improving the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is more preferable in terms of reducing breakage of the film and warping from the substrate 10 caused by the internal stress of the film constituting the resistor 30. The width of the resistor 30 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be set to, for example, about 10 μm to 100 μm, taking into consideration measures against breakage.

[0023] For example, when the resistor 30 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making the resistor 30 mainly of α-Cr, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor. Furthermore, in order to further improve the gauge characteristics, the resistor 30 preferably contains 80% by weight or more of α-Cr, and more preferably contains 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] When the resistor 30 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr2N. By containing 20% ​​by weight or less of CrN and Cr2N in the Cr mixed-phase film, a decrease in the gauge factor can be suppressed.

[0025] In addition, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant due to the Cr2N having semiconductor properties. Furthermore, by reducing the formation of ceramics, brittle fracture is reduced.

[0026] On the other hand, if a small amount of N2 or atomic N is mixed into the film, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in the film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[0027] The resistor 30 has a structure in which a plurality of elongated portions 31 are arranged at a predetermined interval with their longitudinal direction in the same direction (the Y-axis direction in the example of FIG. 1), and the ends of adjacent elongated portions 31 are alternately connected, so that the resistor 30 is folded back in a zigzag pattern as a whole. In the example of FIG. 1, the longitudinal direction of the plurality of elongated portions 31 is the grid direction, and the direction perpendicular to the grid direction (the X-axis direction in the example of FIG. 1) is the grid width direction. Note that, although the outer periphery of the connecting portion between the elongated portions 31 is curved in the example of FIG. 1, the shape of the connecting portion is not limited to this. This also applies to the subsequent drawings.

[0028] Of the elongated portions 31 of the resistor 30, the ends of the two elongated portions 31 located at both ends are bent toward the adjacent wiring 40 (the X-axis direction in the example of FIG. 1 ). These bent ends (hereinafter also simply referred to as "resistor ends") are made of the same material as the elongated portions 31, and are extensions of the elongated portions 31.

[0029] The wiring 40 is formed on the substrate 10 and connects the resistor 30 and the electrode 50. Each wiring 40 is not limited to being linear and can be in any pattern. Also, each wiring 40 can be any length. Each wiring 40 is composed of a first metal layer 41 and a second metal layer 42 laminated on the upper surface of the first metal layer 41. For convenience, in FIG. 1, the first metal layer 41 is shown with the same dark matte pattern as the resistor 30. Also, the second metal layer 42 is shown with a matte pattern that is lighter than that of the resistor 30.

[0030] 1, each of the wirings 40 extends along the Y-axis direction. In other words, each of the wirings 40 has a longitudinal direction in the Y-axis direction. In this embodiment, for convenience, specific parts of the wirings 40 are named, but each part of the wirings 40 described below is formed integrally with each other.

[0031] Each of the wirings 40 includes a side portion 40h, a side portion 40g, a terminal portion 40e, and a connection portion 40a. The side portion 40h indicates the side of the wiring 40 on which the resistor 30 is formed in a plan view. The side portion 40g indicates the side of the wiring 40 on which the resistor 30 is not formed in a plan view. The terminal portion 40e indicates the end portion of the wiring 40 on the opposite side to the side connected to the electrode 50 (the Y-axis positive side in the example of FIG. 1). At least one of the pair of wirings 40 has a connection portion 40a on the side portion 40h at a position separated from the terminal portion 40e. In the example of FIG. 1, both of the two wirings 40 have a connection portion 40a at a position separated from the terminal portion 40e. The connection portion 40a is connected to an end of the resistor 30.

[0032] The shape of each of the wirings 40 is not limited to the above. For example, each of the wirings 40 does not have to be parallel to the Y-axis direction. Furthermore, for example, the positional relationship between the two wirings 40 does not have to be parallel. Furthermore, for example, the side of each of the wirings 40 may be inclined toward the Y-axis direction or may be curved.

[0033] One end of the resistor 30 (e.g., one end on the X-negative side) and one of the two electrodes 50 (e.g., the electrode 50 on the X-negative side) are electrically connected via a wiring 40 (first wiring). The other end of the resistor (e.g., one end on the X-positive side) and the other electrode 50 (e.g., the electrode 50 on the X-positive side) are also electrically connected via a wiring 40 (second wiring). That is, the resistor 30 is electrically connected to a pair of electrodes 50 via a pair of wirings 40.

[0034] The electrodes 50 are electrodes for outputting a change in resistance value of the resistor 30 caused by strain to the outside. For example, a lead wire for external connection is joined to the electrodes 50. Each electrode 50 is formed on the substrate 10. The electrodes 50 are electrically connected to the resistor 30 via the wiring 40. The electrodes 50 may be formed, for example, in a substantially rectangular shape wider than the wiring 40.

[0035] The electrode 50 has a first metal layer 51 and a second metal layer 52 laminated on an upper surface of the first metal layer 51. The first metal layer 51 is electrically connected to an end of the resistor 30 via the first metal layer 41 of the wiring 40. The first metal layer 51 is formed in a substantially rectangular shape in a plan view. The first metal layer 51 may be formed to have the same width as the wiring 40.

[0036] Although the resistor 30, the first metal layer 41, and the first metal layer 51 are given different reference numbers for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, the first metal layer 41, and the first metal layer 51 each have approximately the same thickness. Moreover, although the second metal layer 42 and the second metal layer 52 are given different reference numbers for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 42 and the second metal layer 52 may have approximately the same thickness.

[0037] The second metal layer 42 and the second metal layer 52 may be formed of a material having a lower resistance than the resistor 30 (and the first metal layer 41 and the first metal layer 51). The material of the second metal layer 42 and the second metal layer 52 is not particularly limited as long as it is a material having a lower resistance than the resistor 30, and can be appropriately selected according to the purpose. For example, when the resistor 30 is a Cr mixed phase film, the material of the second metal layer 42 and the second metal layer 52 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, and compounds are appropriately laminated. The thickness of the second metal layer 42 and the second metal layer 52 is not particularly limited, and 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 3 μm to 5 μm.

[0038] The second metal layer 42 may be formed on a part of the first metal layer 41, or may be formed on the entire first metal layer 41. The second metal layer 52 may be formed on a part of the first metal layer 51, or may be formed on the entire first metal layer 51. One or more other metal layers may be laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, the second metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on the upper surface of the copper layer. By forming the top layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 can be improved.

[0039] A cover layer may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50. By providing the cover layer, mechanical damage to the resistor 30 and the wiring 40 can be prevented. Furthermore, by providing the cover layer, the resistor 30 and the wiring 40 can be protected from moisture and the like. The cover layer may be provided so as to cover the entire portion except for the electrodes 50.

[0040] The cover layer can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (e.g., silicone resin, polyolefin resin), etc. The cover layer may contain a filler or a pigment. There is no particular limit to the thickness of the cover layer, and it can be appropriately selected depending on the purpose. For example, the thickness of the cover layer can be about 2 μm to 30 μm.

[0041] In this way, the wiring 40 has a structure in which the second metal layer 42 is laminated on the first metal layer 41 made of the same material as the resistor 30. Therefore, the resistance of each wiring 40 is lower than that of the resistor 30, and therefore it is possible to prevent each wiring 40 from functioning as a resistor. As a result, it is possible to improve the accuracy of strain detection by the resistor 30.

[0042] 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 region where the resistor 30 is formed. Therefore, the accuracy of strain detection by the resistor 30 can be improved.

[0043] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed phase film as the resistor 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensing part to the local region where the resistor 30 is formed has a significant effect on improving the strain detection accuracy. Also, making the wiring 40 lower in resistance than the resistor 30 has the effect of reducing the lateral sensitivity.

[0044] The length of the wiring 40 connecting the resistor 30 and each electrode 50 is preferably 5 mm or more along the wiring 40, regardless of whether the wiring 40 is linear or not. By making the length 5 mm or more, heat generated when soldering a lead wire or the like to the electrode 50 is less likely to be transmitted to the resistor 30 or the cover layer that covers the resistor 30, and the thermal load on the gauge characteristics can be reduced.

[0045] Fig. 3 is a diagram for explaining a strain gauge 1z of a comparative example. Fig. 3 shows an enlarged view of the vicinity of the end portion of the wiring. The strain gauge 1z has the same configuration as the strain gauge 1 shown in Figs. 1 and 2, except that the connection position between the resistor and the wiring is different from that of the strain gauge 1, and the shape of the wiring is different from that of the strain gauge 1.

[0046] In the strain gauge 1z shown in Fig. 3, the wiring is connected to the resistor near the end. In a strain gauge having such a shape, the connection part of the wiring and / or the resistor may break, for example, as shown in Fig. 3.

[0047] 4 is a diagram for explaining a case where a break occurs in the strain gauge 1 according to the first embodiment. Note that, although Fig. 4 explains the vicinity of the terminal end 40e of the wiring 40 on the negative X-axis side in the strain gauge 1 as an example, the same explanation also applies to the wiring 40 and terminal end 40e on the positive X-axis side.

[0048] For example, suppose that a strong stress is applied to the vicinity of the end 40e of the wiring 40 for some reason, and a break occurs at the portion indicated by the curve CL in FIG. 4. However, as shown in FIG. 4, in the strain gauge 1, the resistor 30 and the wiring 40 are connected at a position separated from the end 40e. Therefore, even if a break occurs at the portion indicated by the curve CL and a part of the wiring 40 becomes non-conductive, the break does not extend to the connection portion between the wiring 40 and the resistor 30. Therefore, there is no problem with the electrical conduction between the electrode 50 and the wiring 40, and between the wiring 40 and the resistor 30. In this way, by providing the connection portion between the wiring 40 and the resistor 30 at a position separated from the end 40e, a strain gauge that is less likely to break can be realized.

[0049] For example, the distance L between the connection portion 40a and the terminal end 42e may be 30 micrometers or more. By setting the distance L to 30 micrometers or more, the above-mentioned disconnection can be suppressed with a higher probability. In other words, it is preferable that the wiring 40 is connected to the resistor 30 at a position separated from the terminal end 42e of the second metal layer 42 by 30 micrometers or more.

[0050] Furthermore, in the strain gauge 1, the width W of the end of the second metal layer 42 at the end portion 42e is wider than that of the comparative example. For example, it is more preferable that the width W is 50 micrometers or more in plan view. Disconnections often occur at thinned portions of the peripheral ends of the wiring, power supply, resistor, etc. of the strain gauge. Therefore, by widening the width W, it is possible to suppress the occurrence of disconnections. In addition, at least one of the corners 42c of the second metal layer 42 may be formed as a right angle or an obtuse angle in plan view. By making at least one of the corners 42c a right angle or an obtuse angle, it is possible to prevent the corner of the end portion 40e from protruding thinly. Therefore, it is possible to suppress the occurrence of disconnections at the corner portion of the end portion of the wiring 40.

[0051] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on an upper surface 10a of the base material 10. Metal layer A is a layer that is finally patterned to become resistor 30, first metal layer 41, and first metal layer 51. Therefore, the material and thickness of metal layer A are similar to those of resistor 30, first metal layer 41, and first metal layer 51 described above.

[0052] The metal layer A can be formed by, for example, a magnetron sputtering method using a target made of a raw material capable of forming the metal layer A. The metal layer A may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulsed laser deposition method, or the like instead of the magnetron sputtering method.

[0053] From the viewpoint of stabilizing the gauge characteristics, before forming the metal layer A, a functional layer of a predetermined thickness may be vacuum-deposited as a base layer on the upper surface 10a of the base material 10 by, for example, conventional sputtering.

[0054] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 30). The functional layer preferably further has a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and a function of improving adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0055] Since the insulating resin film that constitutes the substrate 10 contains oxygen and moisture, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, particularly when the metal layer A contains Cr, since Cr forms a self-oxidized film.

[0056] The material of the functional layer is not particularly limited as long as it has the function of promoting crystal growth of at least the upper layer, metal layer A (resistor 30), and can be appropriately selected depending on the purpose. For example, the material of the functional layer may be 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 of the metals in this group, or a compound of any of the metals in this group.

[0057] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compound include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0058] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which reduces the detection sensitivity of strain.

[0059] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and the strain detection sensitivity can be further prevented from being reduced due to a part of the current flowing through the resistor flowing through the functional layer.

[0060] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is more preferably 1 / 100 or less of the thickness of the resistor, which can further prevent a part of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

[0061] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0062] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0063] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm, which can promote the crystal growth of α-Cr and can be more easily formed without cracking the functional layer.

[0064] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is made of an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape on the entire upper surface of the substrate 10.

[0065] Furthermore, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, so that the thickness and surface area of ​​the functional layer are increased, and the heat generated by the resistor can be dissipated to the substrate 10. As a result, the deterioration of the measurement accuracy of the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0066] The functional layer can be formed in vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0067] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by a plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0068] There is no particular limitation on the combination of the material of the functional layer and the material of the metal layer A, and it can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film containing α-Cr (alpha chromium) as the metal layer A.

[0069] In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber. In this case, the ratio of CrN and Cr2N contained in the Cr mixed phase film, and the ratio of Cr2N in CrN and Cr2N can be adjusted by changing the amount and pressure of the nitrogen gas introduced (nitrogen partial pressure) or by adjusting the heating temperature by providing a heating process.

[0070] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film containing α-Cr, which has a stable crystal structure, as the main component, can be formed. Furthermore, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

[0071] When metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of metal layer A, preventing oxidation of metal layer A due to oxygen and moisture contained in substrate 10, and improving adhesion between substrate 10 and metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0072] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystal phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0073] 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, a photolithography method.

[0074] Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of the metal layer A. Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to form openings that expose the regions in which the second metal layer 42 and the second metal layer 52 are to be formed. At this time, the shape of the openings in the resist can be adjusted to give the second metal layer 42 and the second metal layer 52 any shape. For example, a dry film resist can be used as the resist.

[0075] Next, for example, the second metal layer 42 and the second metal layer 52 are formed on the seed layer exposed in the opening by electrolytic plating using the seed layer as a power supply path. The electrolytic plating method is preferable in that it has high tact and can form low-stress electrolytic plating layers as the second metal layer 42 and the second metal layer 52. By making the electrolytic plating layer thick and low-stress, it is possible to prevent warping of the strain gauge 1. The second metal layer 42 and the second metal layer 52 may be formed by electroless plating.

[0076] Next, the resist is removed. For example, the resist can be removed by immersing the resist in a solution that can dissolve the resist material.

[0077] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to be patterned into a planar shape similar to that of the resistor 30, the wiring 40, and the electrode 50 in Fig. 1. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and the seed layer exposed from the resist, thereby forming the resistor 30, the wiring 40, and the electrode 50 in the planar shape of Fig. 1.

[0078] For example, unnecessary portions of the metal layer A and the seed layer can be removed by wet etching. If a functional layer is formed below the metal layer A, the functional layer is patterned by etching into the planar shape shown in Fig. 1, similar to the resistor 30, the wiring 40, and the electrode 50. At this point, a seed layer is formed on the resistor 30, the first metal layer 41, and the first metal layer 51.

[0079] Next, the second metal layer 42 and the second metal layer 52 are used as an etching mask to remove unnecessary seed layer exposed from the second metal layer 42 and the second metal layer 52, thereby forming the second metal layer 42 and the second metal layer 52. Note that the seed layer directly below the second metal layer 42 and the second metal layer 52 remains. 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, the resistor 30, the wiring 40, and the electrodes 50.

[0080] Thereafter, as necessary, a cover layer that covers the resistor 30 and the wiring 40 and exposes the electrodes 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50, and then heating and curing the film. The cover layer can also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50, and then heating and curing the resin. The opening that exposes the electrodes 50 can be formed, for example, by photolithography.

[0081] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the resistor 30, the first metal layer 41, and the first metal layer 51, the strain gauge 1 has a cross-sectional shape as shown in Fig. 5. The layer indicated by reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is, for example, the same as that shown in Fig. 1. However, as described above, the functional layer 20 may be formed solidly on a part or all of the upper surface 10a of the substrate 10.

[0082] Second Embodiment The resistor of the strain gauge according to the present disclosure may have a configuration having a plurality of sensing parts and a joint part arranged between the plurality of sensing parts. Fig. 6 is a plan view illustrating a strain gauge 2 according to a second embodiment. The strain gauge 2 differs from the strain gauge 1 in that the resistor 130 includes a first sensing part 131 and a second sensing part 132, and a joint part 133 arranged between them.

[0083] The strain gauge 2 has a substrate 110, a resistor 130, wiring 40, and electrodes 50. The resistor 130 and wiring 40 are formed on a surface 110a of the substrate 110.

[0084] Since the base material 110 has the same configuration as the base material 10 except for its size, the explanation of the base material 110 is to be referred to the explanation of the base material 10 and will not be repeated here. The explanation of the wiring 40 and the electrodes 50 is to be referred to the explanation of the first embodiment and will not be repeated here.

[0085] The resistor 130 includes a first sensing part 131, a second sensing part 132, and a joint part 133. The first sensing part 131 has a structure in which a plurality of elongated parts 31 are arranged at predetermined intervals in the same longitudinal direction (Y-axis direction), and the ends of adjacent elongated parts 31 are alternately connected to each other, folding back in a zigzag pattern as a whole. One end 131e1 of the first sensing part 131 is electrically connected to the electrode 50 via the wiring 40. The end 131e1 is also connected to the wiring 40 at the connection part 40a. As shown in the figure, the connection part 40a is separated from the end part 40e of the wiring 40. The other end 131e2 of the first sensing part 131 is electrically connected to the joint part 133.

[0086] The second sensing part 132 has the same configuration as the first sensing part. That is, the second sensing part 132 has a structure in which a plurality of elongated parts 31 are arranged at a predetermined interval with their longitudinal directions facing the same direction (Y-axis direction), and the ends of adjacent elongated parts 31 are alternately connected to each other, folding back in a zigzag pattern as a whole. One end 132e1 of the second sensing part 132 is electrically connected to the electrode 50 via the wiring 40. In addition, the end 132e1 is connected to the wiring 40 at the connection part 40a, and the connection part 40a is separated from the end part 40e of the wiring 40. The other end 132e2 of the second sensing part 132 is electrically connected to the joint part 133.

[0087] The joint 133 is disposed between the first sensing portion 131 and the second sensing portion 132. The joint 133 is a member made of the same material as the wiring 40. The joint 133 may be formed on the base material 110 in the same manner as the wiring 40. In addition, the shape and size of the joint 133 are not particularly limited.

[0088] 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 (i.e., end portion 131e2 and / or end portion 132e2) at a position spaced apart from each of the end portions 133e and 133f.

[0089] In the above example, the strain gauge 2 has two sensing parts. However, the number of sensing parts is not limited to two, and the strain gauge 2 may have three or more sensing parts. In this case, the resistor has three or more sensing parts connected in series as a whole, and a joint is provided between each of the three or more sensing parts.

[0090] In the strain gauge 2 according to the second embodiment, the resistor 130 is connected to the wiring 40 at a position separated from the terminal end 40e, similar to the strain gauge 1 according to the first embodiment. Therefore, for the same reason as the strain gauge 1, the strain gauge 2 can be said to be a strain gauge that is less likely to break. Furthermore, in the strain gauge 2, the sensing part (the first sensing part 131 and / or the second sensing part 132) of the resistor 130 is connected to the joint 133 at a position separated from the terminal end 133e and the terminal end 133f of the joint 133. Therefore, according to the strain gauge 2, it is possible to realize a strain gauge that is less likely to break even in the vicinity of the joint 133 (for example, at a corner portion of the terminal end of the joint 133).

[0091] <Third embodiment> The third embodiment shows an example in which a third metal layer is disposed around the resistor 30. Note that in the third embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0092] Fig. 7 is a plan view illustrating a strain gauge 3 according to a third embodiment. Referring to Fig. 7, the strain gauge 3 differs from the strain gauge 1 in that the strain gauge 3 has a third metal layer 90 disposed around the resistor 30 and spaced apart from the resistor 30, the wiring 40, and the electrode 50.

[0093] The third metal layer 90 is formed of the same material as the resistor 30. The third metal layer 90 can be formed in the same process as the resistor 30 and the first metal layer 41. The third metal layer 90 is preferably disposed in the excess space around the resistor 30 so as to occupy as large an area as possible. A metal layer made of the same material as the second metal layer 42 etc. may be laminated on the third metal layer 90.

[0094] In this manner, by disposing the third metal layer 90 around the resistor 30, the rigidity of the strain gauge 3 can be made even higher than that of the strain gauge 1. By increasing the rigidity of the strain gauge 3, breakage of the strain gauge 3 can be suppressed.

[0095] The strain gauge according to the third embodiment can prevent breakage of the strain gauge even when stress is concentrated around the wiring end and the resistor (for example, near the joint 133). Furthermore, the strain gauge according to the third embodiment includes a third metal layer, which increases the rigidity of the strain gauge and thereby prevents breakage of the strain gauge 3.

[0096] <Fourth embodiment> 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 to each other by sharing at least one of their electrodes and at least one of their wirings to form a bridge circuit.

[0097] Fig. 8 is a plan view illustrating a strain sensor 4 according to a fourth embodiment. Referring to Fig. 8, the strain sensor 4 includes a base material 210, resistors 230A, 230B, 230C, and 230D, and wiring 240A, 240B, 240C, and 240D. Resistors 230A, 230B, 230C, and 230D, wiring 240A, 240B, 240C, and 240D are formed on a surface 210a of the base material 210.

[0098] Each of the wiring 240A and the wiring 240C extends along the Y-axis direction. In other words, each of the wiring 240A and the wiring 240C has a longitudinal direction in the Y-axis direction. Each of the wiring 240B and the wiring 240D extends along the X-axis direction. In other words, each of the wiring 240B and the wiring 240D has a longitudinal direction in the X-axis direction.

[0099] In the example of FIG. 8, the electrodes of the strain sensor 4 are not explicitly shown, but in the example of the same figure, part of the wiring acts as the electrodes of the strain sensor 4.

[0100] Each of the resistors 230A, 230B, 230C, and 230D may be formed of the same material as the resistor 30 according to the first embodiment. Similarly, the wiring 240A, 240B, 240C, and 240D may be formed of the same material as the wiring 40 according to the first embodiment.

[0101] 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.

[0102] The wiring 240A has a first metal layer 241A and a second metal layer 242A laminated on the upper surface of the first metal layer 241A. The wiring 240B has a first metal layer 241B and a second metal layer 242B laminated on the upper surface of the first metal layer 241B. The wiring 240C has a first metal layer 241C and a second metal layer 242C laminated on the upper surface of the first metal layer 241c. The wiring 240D has a first metal layer 241D and a second metal layer 242D laminated on the upper surface of the first metal layer 241D.

[0103] The first metal layer 241A, the first metal layer 241B, the first metal layer 241C, and the first metal layer 241D may be formed of a similar 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 may be formed of a similar material as the second metal layer 42.

[0104] Although the wiring 240B, wiring 240C, and wiring 240D are different in direction, they are similar in shape and connection with the resistor to the wiring 240A. Therefore, the following will use the wiring 240A to explain the connection between each wiring and the resistor according to the fourth embodiment.

[0105] The wiring 240A has a substantially L-shape in plan view. The wiring 240A has, in order from an end 240Ae, a side 240Ai, an end 240Aj, a side 240Ah, an end 240Af, and a side 240Ag.

[0106] The resistor 230A is connected to the end 240Ae. The resistor 230A is connected to a position at the end 240Ae that is spaced apart from the side 240Ag and the side 240Ai. The resistor 230D is connected to the side 240Ah. The resistor 230D is connected to a position at the side 240Ah that is spaced apart from the end 240Aj and the end 240Af.

[0107] Also, for example, when an electrode is provided near the end 240Aj, the position to which the resistor 230D is connected is a position at the side 240Ah away from the end 240Ae (terminal end). In other words, the wiring 240A is an example of a configuration in which the plurality of strain gauges share at least one of the electrodes and at least one of the wiring and the second wiring, and thus share the electrodes, wiring, and at least one of the wiring.

[0108] According to the strain gauge of the fourth embodiment, the occurrence of disconnection can be suppressed. According to the strain sensor of the fourth embodiment, even if stress is concentrated at the wiring end, disconnection of the strain gauge can be suppressed.

[0109] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims. [Explanation of symbols]

[0110] 1, 2, 3 strain gauge, 4 strain sensor, 10, 110, 210 substrate, 30, 130 resistor, 40 wiring, 40a connection portion, 40e termination 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 joint portion, 230A, 230B, 230C, 230D resistor, 240A, 240B, 240C, 240D wiring

Claims

1. A substrate; a resistor formed on the substrate; a pair of electrodes formed on the substrate; a first wiring that electrically connects one end of the resistor to one electrode; a second wiring electrically connecting the other end of the resistor and the other electrode, each of the first wiring and the second wiring has a terminal end on the side opposite to the side connected to the electrode; A strain gauge, wherein the first wiring and / or the second wiring is connected to one end of the resistor at a position spaced apart from the termination portion.

2. the first wiring and the second wiring include a first metal layer integrally formed with the resistor and made of the same material, and a second metal layer formed on the first metal layer and made of a material having a lower resistance than the first metal layer; The strain gage of claim 1 , wherein the first metal layer and the second metal layer each have the termination portion.

3. The strain gauge according to claim 2 , wherein the end 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 end portion of the second metal layer of the first wiring and / or the second wiring has a right angle in plan view.

5. The strain gauge according to any one of claims 2 to 4, wherein the end portion of the second metal layer has an edge width of 50 micrometers or more in a plan view.

6. The strain gauge according to any one of claims 2 to 4, wherein the first wiring and / or the second wiring is connected to the resistor at a position spaced apart from the end portion of the second metal layer by 30 micrometers or more.

7. 5. The strain gauge according to claim 1, further comprising a third metal layer disposed around the resistor and spaced apart from the resistor, the first wiring, and the second wiring.

8. The resistor is A plurality of sensory parts; 5. The strain gauge according to claim 1, further comprising: a joint portion that is arranged between the sensing portions and is made of the same material as the first wiring and the second wiring.

9. The strain gauge according to claim 8 , wherein the sensitive part and the joint part are connected at a position spaced apart from an end of the joint part.

10. A strain sensor including a plurality of strain gauges according to any one of claims 1 to 4, A strain sensor in which the plurality of strain gauges are connected to each other, sharing at least one of the electrodes and at least one of the first wiring and second wiring, thereby forming a bridge circuit.

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