Strain gauge

Abstract

To mitigate stress concentration in the vicinity of the wiring and / or a strain electrode of a strain gauge.SOLUTION: The strain gauge comprises: a flexible substrate 10; a resistor 30 formed on the substrate 10; an electrode 50 formed on the substrate 10; and a wiring 40 for connecting the resistor 30 and the electrode 50 and formed on the substrate 10. At least one of the wiring 40 and the electrode 50 includes a first metal layer 41, 51 formed with the same material as the resistor 30, a second metal layer 42, 52 formed on the first metal layer 41, 51 and having lower resistance than the first metal layer 41, 51; and a third metal layer 43, 53 formed on top of the second metal layer 42, 52. The third metal layer 43, 53 is formed so as to be in contact with the circumference of the second metal layer 42, 52 in a plan view.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain of the object. The strain gauge includes, for example, a flat substrate and a resistor formed on the substrate. The resistor deforms in response to strain of the object to be measured. The strain sensor described in Patent Document 1 includes a sensor unit, a terminal unit (i.e., an electrode), and wiring that connects the sensor unit and the terminal unit. The wiring includes a metal layer formed on a resistive layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-72606 Summary of the Invention [Problem to be solved by the invention]

[0004] In the strain gauge described in Patent Document 1, stress concentration may occur in the terminals and parts of the wiring. When stress concentration occurs in the terminals or wiring, microcracks may occur.

[0005] The present disclosure aims to alleviate stress concentrations near the wiring and / or electrodes of a strain gauge. [Means for solving the problem]

[0006] A strain gauge according to one embodiment of the present disclosure comprises a flexible substrate, a resistor formed on the substrate, electrodes formed on the substrate, and wiring formed on the substrate and connecting the resistor and the electrodes, wherein at least one of the wiring and the electrode has a first metal layer formed of the same material as the resistor, a second metal layer formed on the first metal layer and having a lower resistance than the first metal layer, and a third metal layer formed on an upper surface of the second metal layer, wherein the third metal layer is formed so as to be in contact with the periphery of the second metal layer in a planar view. [Effects of the Invention]

[0007] The present disclosure can provide a strain gauge that can alleviate stress concentrations near the wiring and / or strain electrodes of the strain gauge. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 2] 2 is a cross-sectional view illustrating a wiring portion of the strain gauge according to the first embodiment, taken along line II-II in FIG. 1. FIG. [Figure 3] 3 is a cross-sectional view illustrating an electrode portion of the strain gauge according to the first embodiment, taken along line III-III in FIG. 1. FIG. [Figure 4] FIG. 2 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 5] 5 is a cross-sectional view illustrating a wiring portion of a strain gauge according to a first modified example of the first embodiment, and is a view showing a cross section along line VV in FIG. 4. FIG. [Figure 6] FIG. 10 is a cross-sectional view illustrating a strain gauge according to a second modification of the first embodiment. [Figure 7] 7 is a cross-sectional view illustrating a wiring portion of a strain gauge according to a second modification of the first embodiment, taken along line VII-VII in FIG. 6. FIG. [Figure 8] FIG. 10 is a cross-sectional view illustrating a strain gauge according to a third modified example of the first embodiment. [Figure 9] 9 is a cross-sectional view illustrating a wiring portion of a strain gauge according to a third modification of the first embodiment, taken along line IX-IX in FIG. 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] [First embodiment] Fig. 1 is a plan view illustrating a strain gauge according to a first embodiment. Fig. 2 is a cross-sectional view illustrating a wiring portion of the strain gauge according to the first embodiment, taken along line II-II in Fig. 1. Fig. 3 is a cross-sectional view illustrating an electrode portion of the strain gauge according to the first embodiment, taken along line III-III in Fig. 1.

[0011] 1 to 3, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 70. For convenience, the outer edge of the cover layer 70 is indicated by a dashed line in Fig. 1. The cover layer 70 is not an essential component and may be provided as needed.

[0012] For ease of explanation, an XYZ Cartesian coordinate system consisting of mutually orthogonal X, Y, and Z axes may be set in the drawings. Note that this coordinate system is defined for the purpose of explanation and does not limit the orientation of the strain gauge 1 according to this embodiment.

[0013] The X-axis direction includes the positive X-axis direction and the negative X-axis direction. The Y-axis direction includes the positive Y-axis direction and the negative Y-axis direction. The Z-axis direction includes the positive Z-axis direction and the negative Z-axis direction. In addition, in cross-sectional views, the direction along the cutting surface is the W-axis direction, and an arrow indicating the W-axis direction may be illustrated.

[0014] In this embodiment, for convenience, the side of the strain gauge 1 facing the substrate 10 on the same side as the side on which the resistor 30 is provided (the positive side of the Z axis in each figure in this specification) is referred to as the upper side, and the side facing the substrate 10 on the same side as the side on which the resistor 30 is not provided (the negative side of the Z axis in each figure in this specification) is referred to as the lower side. The upper surface of each part is referred to as the upper surface, and the lower surface is referred to as the lower surface. However, the strain gauge 1 can be used upside down or positioned at any angle. The planar view refers to viewing the object from the normal direction of the upper surface 10a of the substrate 10, and the planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0015] [Base material 10] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. There are no particular restrictions on 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 approximately 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, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member with a thickness of about 500 μm or less.

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

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

[0019] [Resistor 30] The resistor 30 undergoes a resistance change when subjected to strain. The resistor 30 is formed in a predetermined pattern on the substrate 10. 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.

[0020] The resistor 30 includes a plurality of elongated portions. These elongated portions are arranged at predetermined intervals, for example, with their longitudinal directions in the same direction (the X-axis direction in FIG. 1), and the ends of adjacent elongated portions are alternately connected in series. In other words, the resistor 30 has a structure in which it is folded back in a zigzag pattern as a whole. The longitudinal direction of the elongated portions is the grid direction (the X-axis direction), and the direction perpendicular to the grid direction is the grid width direction (the Y-axis direction).

[0021] One longitudinal end of each of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction. This bent portion, i.e., the terminal ends at both ends of the resistor 30, is electrically connected to the electrodes 50 via wiring 40. In other words, the wiring 40 electrically connects the resistor 30 to each electrode 50. Note that while FIG. 1 shows a single-gauge strain gauge, the strain gauge 1 may also be a two-gauge and / or four-gauge unit. In this case, the resistor of each gauge is connected directly or indirectly (for example, via the resistor of another gauge) to the wiring and electrode.

[0022] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0023] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0024] 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 approximately 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting the resistor 30 (e.g., the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less is even more preferable because it reduces film cracks and warpage from the substrate 10 caused by internal stress in the film constituting the resistor 30. The width of the resistor 30 can be optimized for required specifications such as resistance value and lateral sensitivity, and can be set to, for example, approximately 10 μm to 100 μm, taking into consideration measures against disconnection.

[0025] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50% by weight or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0026] Furthermore, when the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0027] Furthermore, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the Cr2N has semiconducting properties, which leads to a more significant decrease in TCR (negative TCR). Furthermore, by reducing the amount of ceramic formation, brittle fracture is reduced.

[0028] On the other hand, if trace amounts of N2 or atomic N are mixed into or present in the film, they will escape to the outside of the film due to external conditions (such as high temperature environments), causing changes in film stress.By creating chemically stable CrN, the unstable N mentioned above will not be generated, and a stable strain gauge can be obtained.

[0029] [Wiring 40] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrode 50. The wiring 40 has a first metal layer 41, a second metal layer 42 laminated on an upper surface 41a of the first metal layer 41, and a third metal layer 43 laminated on an upper surface 42a of the second metal layer 42.

[0030] The wiring 40 may be formed to form a substantially triangular shape in a plan view, for example, as shown in FIG. 1. In this case, the portion of the wiring 40 closer to the resistor 30 may be formed to form an acute angle, for example. The shape of the wiring 40 is not limited to a substantially triangular shape, and may be any shape. For example, the wiring 40 may be linear. Details of the first metal layer 41, the second metal layer 42, and the third metal layer 43, which are components of the wiring 40, will be described later.

[0031] [Electrode 50] The electrodes 50 are electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain. The strain gauge 1 has a pair of electrodes 50 connected to both ends of the resistor 30 via wiring 40. For example, a lead wire for external connection is joined to the electrodes 50. The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40.

[0032] Although the resistor 30, the first metal layer 41 of the wiring 40, and the first metal layer 51 are designated by different reference numerals for convenience, they are layers made of the same material. The resistor 30, the first metal layer 41, and the first metal layer 51 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 may have approximately the same thickness.

[0033] Although the second metal layer 42 and the second metal layer 52 are given different reference numerals for convenience, they are actually layers made of the same material. The second metal layer 42 and the second metal layer 52 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.

[0034] Although the third metal layer 43 and the third metal layer 53 are given different reference numerals for convenience, they are actually layers made of the same material. The third metal layer 43 and the third metal layer 53 can be integrally formed from the same material in the same process. Therefore, the third metal layer 43 and the third metal layer 53 may have approximately the same thickness.

[0035] The shape of the electrode 50 may be any shape such as a substantially circular, substantially semicircular, or substantially rectangular shape in plan view. Furthermore, when the electrode 50 is made up of multiple layers as described above, the shapes of the electrodes 50 in each layer may be the same or different.

[0036] Each figure of this embodiment shows, as an example, a case in which the electrode 50 and the wiring 40 are formed continuously. More specifically, in the strain gauge 1, the electrode 50 is approximately circular and the wiring 40 is approximately triangular in plan view, and the wiring 40 and the electrode 50 are formed continuously. As a result, the wiring 40 and the electrode 50 as a whole form a teardrop shape in plan view. For convenience, in FIG. 1, the boundary L1 between the wiring 40 and the electrode 50 is shown by a two-dot chain line. However, the position and shape of the boundary L1 of the electrode 50 are not necessarily determined as shown, but are indirectly determined by the shapes of the wiring 40 and the electrode 50. Therefore, the boundary L1 may not be a straight line as shown, but may be a curved line, or may consist of both a straight line and a curved line.

[0037] [First metal layers 41 and 51] The first metal layers 41 and 51 are layers made of the same material as the resistor 30. The thickness of the first metal layers 41 and 51 may be the same as that of the resistor 30, or may be a predetermined thickness determined from the same viewpoint as the thickness of the resistor 30.

[0038] [Second metal layers 42 and 52] The second metal layers 42 and 52 are formed of a material with lower resistance than the resistor 30 (the first metal layers 41 and 51). For example, if the resistor 30 is a Cr mixed-phase film, the second metal layers 42 and 52 may be made of Cu, Ni, Al, Ag, Au, Pt, or the like, or an alloy of any of these metals, a compound of any of these metals, or a laminate film in which any of these metals, alloys, or compounds are appropriately laminated. The thickness of the second metal layers 42, 52, and 62 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of each of the second metal layers 42, 52, and 62 may be approximately 3 μm to 5 μm.

[0039] The second metal layer 42 may be formed on a part of the upper surface 41a of the first metal layer 41, or may be formed on the entire upper surface 41a. The second metal layer 52 may be formed on a part of the upper surface 51a of the first metal layer 51, or may be formed on the entire upper surface 51a.

[0040] The wiring 40 of the strain gauge 1 according to this embodiment has a second metal layer 42 laminated on a first metal layer 41. As described above, the second metal layer 42 of the wiring 40 has a lower resistance than the resistor 30, and therefore laminating the second metal layer 42 can prevent the wiring 40 from functioning as a resistor. In other words, by providing the second metal layer 42 of the wiring 40, which has a lower resistance than the resistor 30, the actual sensitive part of the strain gauge 1 can be limited to the local region where the resistor 30 is formed. As a result, the strain gauge 1 can improve the accuracy of strain detection by the resistor 30.

[0041] In particular, in a highly sensitive strain gauge (e.g., a gauge factor of 10 or more) that uses a Cr mixed-phase film or the like as the resistor 30, making the second metal layer 42 lower in resistance than the resistor 30 and limiting the actual sensitive part to the local region where the resistor 30 is formed has a significant effect on improving strain detection accuracy. Also, making the second metal layer 42 lower in resistance than the resistor 30 has the effect of reducing lateral sensitivity.

[0042] [Third metal layers 43 and 53] As shown in FIGS. 1 to 3, the third metal layer 43 is formed so as to contact the periphery 42c of the second metal layer 42 in a plan view. Also, as shown in FIGS. 1 to 3, the third metal layer 53 is formed so as to contact the periphery 52c of the second metal layer 52 in a plan view. In other words, the periphery 42c of the second metal layer 42 can be said to be an edge portion of the second metal layer 42. Similarly, the periphery 52c of the second metal layer 52 can be said to be an edge portion of the second metal layer 52. Note that "formed so as to contact the periphery of the second metal layer" includes being disposed inside the periphery (e.g., 42c or 52c) in a plan view.

[0043] As shown in FIGS. 1 and 2, the third metal layer 43 is formed so as to be in contact with the entire periphery 42c of the second metal layer 42 in plan view (that is, so as to be continuous along the entire periphery 42c).

[0044] 1 and 3, the third metal layer 53 is formed so as to be in contact with the entire periphery 52c of the second metal layer 52 in a plan view (i.e., continuous along the entire periphery 52c). In other words, the third metal layer 43 is formed so as to cover the entire edge portion of the second metal layer 42 when the second metal layer 42 is viewed in a plan view. Similarly, the third metal layer 53 is formed so as to cover the entire edge portion of the second metal layer 52 when the second metal layer 52 is viewed in a plan view.

[0045] The Young's modulus of the third metal layers 43 and 53 may be, for example, 80% to 120% of the Young's modulus of the first metal layers 41 and 51. The thickness of the third metal layer 43 may be, for example, 80% to 120% of the thickness of the first metal layer 41. The thickness of the third metal layer 53 may be, for example, 80% to 120% of the thickness of the first metal layer 51.

[0046] Furthermore, the thickness of the third metal layers 43 and 53 may be, for example, 80% or more and 120% or less of the thickness of the second metal layers 42 and 52. The thicknesses of the second metal layers 42, 52 and the third metal layers 43, 53 are thicknesses along the Z-axis direction.

[0047] [Cover layer 70] The cover layer 70 (insulating resin layer) is formed on the substrate 10 and covers the resistor 30 and the wiring 40. At least a portion of the electrode 50 is exposed from the cover layer 70. The portion of the electrode 50 that is not covered by the cover layer 70 (the portion of the opening 70a in FIG. 1) is exposed to the outside of the strain gauge 1. The aforementioned lead wires or the like can be joined to this exposed portion of the opening 70a. Note that a portion of the wiring 40 may also be exposed from the cover layer 70.

[0048] In the strain gauge 1, by providing a cover layer 70 that covers the resistor 30 and the wiring 40, it is possible to prevent mechanical damage and the like from occurring to the resistor 30 and the wiring 40. Furthermore, by providing the cover layer 70, it is possible to protect the resistor 30 and the wiring 40 from moisture and the like. Note that the cover layer 70 may be formed so as to cover the entire portion of the strain gauge 1 except for the electrodes 50.

[0049] The cover layer 70 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 70 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 70 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0050] [Dummy wiring 80] The strain gauge 1 may also have dummy wiring 80 formed in the same manner as the wiring 40. The dummy wiring 80 may have, for example, a first metal layer 81, a second metal layer 82 laminated on the upper surface of the first metal layer 81, and a third metal layer 83 laminated on the upper surface 82a of the second metal layer 82. The first metal layer 81 may have the same material and thickness as the first metal layers 41 and 51, the second metal layer 82 may have the same material and thickness as the second metal layers 42 and 52, and the third metal layer 83 may have the same material and thickness as the third metal layers 43 and 53. The dummy gauge may also be made of a single layer rather than having the three-layer structure described above.

[0051] [Manufacturing method of strain gauge 1] Next, a method for manufacturing the strain gauge 1 according to this embodiment will be described. First, a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, first metal layer 41, and first metal layer 51. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, first metal layer 41, and first metal layer 51 described above.

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

[0053] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the substrate 10 before depositing the metal layer A. The functional layer can be deposited by, for example, conventional sputtering.

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

[0055] The insulating resin film that constitutes the substrate 10 may contain oxygen and moisture, and Cr may form a self-oxidized film. Therefore, particularly when the metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of the metal layer A. 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 produce a metal layer A consisting of a stable crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 is improved. Furthermore, the material that constitutes the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[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 alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds 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, which can promote the crystal growth of α-Cr and prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

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

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

[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 promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracks.

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

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

[0064] The planar shape of the functional layer may be patterned to be substantially the same as the planar shape of the resistor 30 shown in FIG. 1, for example. However, the planar shape of the functional layer does not have to be substantially the same as the planar shape of the resistor. For example, if the functional layer is made of an insulating material, it may be patterned to be a shape different from the planar shape of the resistor. In this case, the functional layer may be formed solidly at least in the region where the resistor 30 is formed. Alternatively, the functional layer may be formed solidly over the entire upper surface of the substrate 10.

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

[0066] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

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

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

[0070] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

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

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

[0073] Next, the second metal layer 42 and the second metal layer 52 are formed on the upper surface of the metal layer A (more specifically, the upper surface 41a of the first metal layer 41 and the upper surface 51a of the first metal layer 51). The second metal layer 42 and the second metal layer 52 can be formed by, for example, photolithography.

[0074] Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of 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 where second metal layer 42 and second metal layer 52 will be formed. At this time, by adjusting the shape of the openings in the resist, second metal layer 42 and second metal layer 52 can be formed into any shape. As the resist, for example, a dry film resist or the like can be used.

[0075] Next, for example, by electrolytic plating using the seed layer as a power supply path, the second metal layer 42 and the second metal layer 52 are formed on the seed layer exposed in the opening. Electrolytic plating is advantageous in that it has high tact time and can form low-stress electroplated layers as the second metal layer 42 and the second metal layer 52. By forming a thick electroplated layer with low stress, warping of the strain gauge 1 can be prevented. Note that the second metal layer 42 and the second metal layer 52 may also be formed by electroless plating.

[0076] Next, the resist is removed by, for example, 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, wiring 40, and electrode 50 in Fig. 1. For example, a dry film resist or the like can be used as the resist. Then, using the resist as an etching mask, the metal layer A and the seed layer exposed from the resist are removed to form the resistor 30, wiring 40, and 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, the 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, resistor 30, wiring 40, electrode 50, and wiring 60.

[0080] Next, third metal layers 43, 53 are formed on the upper surfaces 42a, 52a of the second metal layers 42, 52. The third metal layers 43, 53 can be formed, for example, in the same manner as the metal layer A described above. The third metal layers 43, 53 can be formed by magnetron sputtering using a target made of a material capable of forming the third metal layers 43, 53. The third metal layers 43, 53 may also be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like instead of magnetron sputtering.

[0081] Thereafter, a cover layer 70 may be provided on the upper surface 10a of the substrate 10, if necessary. The cover layer 70 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 70 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 openings 70a can be formed, for example, by photolithography.

[0082] [Actions and Effects of the Strain Gauge 1 According to the First Embodiment] The strain gauge 1 of the first embodiment comprises a flexible substrate 10, a resistor 30 formed on the substrate 10, an electrode 50 formed on the substrate 10, and wiring 40 formed on the substrate 10 and connecting the resistor 30 and the electrode 50, wherein at least one of the wiring 40 and the electrode 50 has a first metal layer 41, 51 formed from the same material as the resistor 30, a second metal layer 42, 52 formed on the first metal layer 41, 51 and having a lower resistance than the first metal layer 41, 51, and a third metal layer 43, 53 formed on the upper surfaces 42a, 52a of the second metal layer 42, 52, and the third metal layer 43, 53 is formed so as to contact the peripheries 42c, 52c of the second metal layer 42, 52 in a planar view.

[0083] In this strain gauge 1, the third metal layers 43, 53 formed on the upper surfaces 42a, 52a of the second metal layers 42, 52 are in contact with the peripheries 42c, 52c of the second metal layers 42, 52. In the strain gauge 1, the peripheries 42c, 52c of the second metal layers 42, 52 are sandwiched between the first metal layers 41, 51 and the third metal layers 43, 53 in the Z-axis direction. This reduces stress concentration near the peripheries 42c, 52c of the second metal layers 42, 52. This suppresses the occurrence of microcracks in the first metal layers 41, 51 near the peripheries 42c, 52c.

[0084] As described above, the strain gauge 1 can reduce stress concentration near the wiring 40 and / or the electrode 50. As a result, the strain gauge 1 can suppress the occurrence of cracks, thereby suppressing a decrease in strain detection accuracy due to cracks. Therefore, the strain gauge 1 can improve the reliability of strain measurement.

[0085] Furthermore, in the strain gauge 1, the third metal layers 43, 53 are formed so as to contact, in plan view, the entire circumferences 42c, 52cb of the second metal layers 42, 52. In this way, in the strain gauge 1, the third metal layers 43, 53 are formed on the entire circumferences 42c, 52cb, thereby preventing stress from concentrating on a portion of the circumferences 42c, 52cb.

[0086] [Modification 1 of the First Embodiment] Next, a strain gauge 1B according to a first modification of the first embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a cross-sectional view illustrating the strain gauge 1B according to the first modification of the first embodiment. FIG. 5 is a cross-sectional view illustrating the wiring 40B portion of the strain gauge 1B according to the first modification of the first embodiment. FIG. 5 shows a cross section taken along line VV in FIG. 4. The strain gauge 1B according to the first modification differs from the above-described strain gauge 1 in the arrangement of the third metal layers 43B and 53B. Note that in the description of the strain gauge 1B, explanations similar to those of the above-described strain gauge 1 may be omitted.

[0087] The strain gauge 1B includes a wiring 40B. The wiring 40B includes a first metal layer 41, a second metal layer 42, and a third metal layer 43B. The third metal layer 43B is formed on an upper surface 42a of the second metal layer 42. The third metal layer 43B is formed so as to cover the entire upper surface 42a of the second metal layer 42. The second metal layer 42 is formed below the third metal layer 43B. In FIG. 4, the lead line of the reference numeral 42 is indicated by a dashed line.

[0088] The strain gauge 1B includes an electrode 50B. The electrode 50B includes a first metal layer 51, a second metal layer 52, and a third metal layer 53B. The third metal layer 53B is formed on an upper surface 52a of the second metal layer 52. The third metal layer 53B is formed so as to cover the entire upper surface 52a of the second metal layer 52. The second metal layer 52 is formed below the third metal layer 53B. In FIG. 4, the lead line of the reference numeral 52 is indicated by a dashed line.

[0089] The strain gauge 1B may include a dummy wiring 80B. The dummy wiring 80B includes a first metal layer 81, a second metal layer 82, and a third metal layer 83B. The third metal layer 83B is formed on the upper surface of the second metal layer 82. The third metal layer 83B is formed so as to cover the entire upper surface of the second metal layer 82. The second metal layer 82 is formed below the third metal layer 83B. In FIG. 4, the lead line of the reference numeral 82 is indicated by a dashed line.

[0090] In this way, the strain gauge 1B may include third metal layers 43B, 53B that cover all surfaces of the second metal layers 42, 52. This makes it possible to further reduce stress concentration near the wiring and / or electrodes compared to the strain gauge 1 according to the first embodiment.

[0091] [Modification 2 of the First Embodiment] Next, a strain gauge 1C according to a second modification of the first embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a cross-sectional view illustrating the strain gauge 1C according to the second modification of the first embodiment. FIG. 7 is a cross-sectional view illustrating the wiring 40C portion of the strain gauge 1C according to the second modification of the first embodiment. FIG. 7 shows a cross section taken along line VII-VII in FIG. 6. The strain gauge 1C according to the second modification differs from the above-described strain gauge 1 in the arrangement of the third metal layers 43C and 53C. Note that in the description of the strain gauge 1C, explanations similar to those of the above-described strain gauges 1 and 1B will be omitted.

[0092] The strain gauge 1C includes a wiring 40C. The wiring 40C includes a first metal layer 41, a second metal layer 42, and a third metal layer 43C. The third metal layer 43C is formed on the upper surface 42a and side surface 42d of the second metal layer 42 and on the upper surface 41a of the first metal layer 41. The third metal layer 43C is formed to extend from the upper surface 42a of the second metal layer 42, across the side surface 42d of the second metal layer 42, to the upper surface 41a of the first metal layer 41. The third metal layer 43C is formed to cover the entire side surface 42d of the second metal layer 42. The third metal layer 43C is formed to cover a portion of the upper surface 41a of the first metal layer 41 that is adjacent to the side surface 42d.

[0093] The strain gauge 1C includes an electrode 50C. The electrode 50C includes a first metal layer 51, a second metal layer 52, and a third metal layer 53C. The third metal layer 53C is formed on the top surface and side surfaces of the second metal layer 52 and on the top surface of the first metal layer 51. The third metal layer 53C is formed to extend from the top surface of the second metal layer 52, across the side surfaces of the second metal layer 52, to the top surface of the first metal layer 51. The third metal layer 53C is formed to cover the entire side surfaces of the second metal layer 52. The third metal layer 53C is formed to cover the portion of the top surface of the first metal layer 51 that is adjacent to the side surfaces of the second metal layer 52.

[0094] The strain gauge 1C may include a dummy wiring 80C. The dummy wiring 80C includes a first metal layer 81, a second metal layer 82, and a third metal layer 83C. The third metal layer 83C is formed on the upper surface and side surfaces of the second metal layer 82 and on the upper surface of the first metal layer 81. The third metal layer 83C is formed to extend from the upper surface of the second metal layer 82, across the side surfaces of the second metal layer 82, to the upper surface of the first metal layer 81. The third metal layer 83C is formed to cover the entire side surfaces of the second metal layer 82. The third metal layer 83C is formed to cover the portion of the upper surface of the first metal layer 81 that is adjacent to the side surfaces of the second metal layer 82.

[0095] In this way, the third metal layers 43C, 53C of the strain gauge 1C may be formed so as to cover the side surfaces of the second metal layers 42, 52. The third metal layers 43C, 53C of the strain gauge 1C may be formed so as to cover the portions of the upper surfaces of the first metal layers 41, 51 that are close to the side surfaces of the second metal layers 42, 52. This makes it possible to further reduce stress concentration near the wiring and / or electrodes compared to the strain gauge 1 according to the first embodiment.

[0096] [Modification 3 of the First Embodiment] Next, a strain gauge 1D according to Modification 3 of the first embodiment will be described with reference to FIGS. 8 and 9. FIG. 8 is a cross-sectional view illustrating the strain gauge 1D according to Modification 3 of the first embodiment. FIG. 9 is a cross-sectional view illustrating the wiring 40D portion of the strain gauge 1D according to Modification 3 of the first embodiment. FIG. 9 shows a cross section taken along line IX-IX in FIG. 8. The strain gauge 1D according to Modification 3 differs from the above-described strain gauge 1 in the arrangement of the third metal layers 43D and 53D. Note that in the description of the strain gauge 1D, explanations similar to those of the above-described strain gauges 1, 1B, and 1C will be omitted.

[0097] The strain gauge 1D includes a wiring 40D. The wiring 40D includes a first metal layer 41, a second metal layer 42, and a third metal layer 43D. The third metal layer 43D differs from the third metal layer 43C in that it is formed to cover the entire upper surface 42a of the second metal layer 42. The second metal layer 42 is formed below the third metal layer 43D. In FIG. 8, the lead line of the reference numeral 42 is indicated by a dashed line. Like the third metal layer 43C, the third metal layer 43D covers the entire side surface 42d of the second metal layer 42. Also, like the third metal layer 43C, the third metal layer 43D is formed to cover the portion of the upper surface 41a of the first metal layer 41 adjacent to the side surface 42d.

[0098] The strain gauge 1D includes an electrode 50D. The electrode 50D includes a first metal layer 51, a second metal layer 52, and a third metal layer 53D. The third metal layer 53D differs from the third metal layer 53C in that it is formed so as to cover the entire upper surface of the second metal layer 52. The second metal layer 52 is formed below the third metal layer 53D. In FIG. 8, the lead line of the reference numeral 52 is indicated by a dashed line. Like the third metal layer 53C, the third metal layer 53D covers the entire side surface 52d of the second metal layer 52. Also, like the third metal layer 53C, the third metal layer 53D is formed so as to cover the portion of the upper surface 51a of the first metal layer 51 adjacent to the side surface 52d.

[0099] The strain gauge 1D may include a dummy wiring 80D. The dummy wiring 80D includes a first metal layer 81, a second metal layer 82, and a third metal layer 83D. The third metal layer 83D is formed on the upper surface and side surfaces of the second metal layer 82 and on the upper surface of the first metal layer 81. The third metal layer 83D is formed to extend from the upper surface of the second metal layer 82, across the side surfaces of the second metal layer 82, to the upper surface of the first metal layer 81. The third metal layer 83D is formed to cover the entire side surfaces of the second metal layer 82. The third metal layer 83D is formed to cover the portion of the upper surface of the first metal layer 81 that is adjacent to the side surfaces of the second metal layer 82.

[0100] In this way, the third metal layers 43D, 53D of the strain gauge 1D may be formed so as to cover the entire upper surfaces of the second metal layers 42, 52. The third metal layers 43D, 53D may be formed so as to cover the side surfaces of the second metal layers 42, 52. The third metal layers 43D, 53D may be formed so as to cover the portions of the upper surfaces of the first metal layers 41, 51 that are close to the side surfaces of the second metal layers 42, 52. This makes it possible to further reduce stress concentration near the wiring and / or electrodes compared to the strain gauge 1 according to the first embodiment.

[0101] It should be noted that the embodiments and modifications disclosed in this specification should be considered to be illustrative in all respects and not restrictive. The above-described embodiments and modifications may be omitted, substituted, or changed in various forms without departing from the scope and spirit of the appended claims.

[0102] In the above embodiment and modified examples, the strain gauge 1 has been described in which the third metal layer 43 is formed on the wiring 40 and the third metal layer 53 is formed on the electrode 50. However, the strain gauges according to the above embodiment and modified examples are not limited to this configuration. For example, the strain gauge 1 may have a configuration in which the third metal layer 43 is formed on the wiring 40, but the third metal layer 53 is not formed on the electrode 50. Alternatively, the strain gauge 1 may have a configuration in which the third metal layer 53 is formed on the electrode 50, but the third metal layer 43 is not formed on the wiring 40.

[0103] In the above embodiment and modified examples, the third metal layer is formed continuously around the entire periphery of the second metal layer. However, the third metal layer may be formed along only a portion of the periphery of the second metal layer, rather than the entire periphery.

[0104] Note that the above-mentioned "entire periphery" may or may not include the boundary L1 between the wiring 40 and the electrode 50. For example, if the third metal layer 43 is formed only on the wiring 40 and not on the electrode 50, the third metal layer 43 may be formed along the wiring 40 side of the boundary L1. [Explanation of symbols]

[0105] 1, 1B, 1C, 1D... strain gauge, 10... substrate, 30... resistor, 40, 40B, 40C, 40D... wiring, 41... first metal layer, 41a... top surface, 42... second metal layer, 42a... top surface, 42c... periphery, 43, 43B, 43C, 43D... third metal layer, 50, 50B, 50C, 50D... electrodes, 51... first metal layer, 51a... top surface, 52... second metal layer, 52a... top surface, 52c... periphery, 53, 53B, 53C, 53D... third metal layer, X... X-axis direction, Y... Y-axis direction, Z... Z-axis direction

Claims

1. a flexible substrate; a resistor formed on the substrate; an electrode formed on the substrate; a wiring formed on the base material and connecting the resistor and the electrode; At least one of the wiring and the electrode is a first metal layer formed of the same material as the resistor; a second metal layer formed on the first metal layer and having a lower resistance than the first metal layer; a third metal layer formed on an upper surface of the second metal layer; The third metal layer is formed so as to be in contact with the periphery of the second metal layer in a plan view.

2. The strain gauge according to claim 1 , wherein the third metal layer is formed so as to be in contact with the entire periphery of the second metal layer in the plan view.

3. The strain gauge according to claim 1 , wherein the third metal layer is formed so as to cover the entire upper surface of the second metal layer.

4. 4. The strain gauge according to claim 1, wherein the third metal layer is formed so as to extend from an upper surface of the second metal layer, via a side surface of the second metal layer, to an upper surface of the first metal layer.

5. a flexible substrate; a resistor formed on the substrate; an electrode formed on the substrate; a wiring formed on the base material and connecting the resistor and the electrode; At least one of the wiring and the electrode is a first metal layer formed of the same material as the resistor; a second metal layer formed on the first metal layer and having a lower resistance than the first metal layer; a third metal layer formed on the upper surface of the first metal layer so as to be adjacent to a side surface of the second metal layer;

6. The strain gauge according to claim 5 , wherein the third metal layer is formed so as to be in contact with the entire periphery of the second metal layer in a plan view.

Images