Strain gauge and manufacturing method thereof, and strain detector

Abstract

To provide a strain gauge that can reduce the effect of creep on an output voltage of a bridge circuit.SOLUTION: This strain gauge has a substrate and a resistor provided on the substrate, and the resistor includes a first resistance part and a second resistance part connected in series with the first resistance part, and the first resistance part and the second resistance part have the same sign and the same value of creep, and the first resistance part and the second resistance part have different line widths.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a strain gauge, a manufacturing method thereof, and a strain detection device. [Background technology]

[0002] Conventionally, strain gauges that are attached to a measurement target are known. For example, strain gauges are sometimes used as sensors that detect the strain of a material or the ambient temperature (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-221696 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned strain gauges may experience creep. In strain gauges, "creep" refers to the phenomenon in which the strain changes over time when a constant load acts on the strain gauge under constant temperature conditions. Strain gauges are used in connection with a bridge circuit, and creep can cause measurement errors, so it is preferable that creep has little effect on the output voltage of the bridge circuit.

[0005] The present invention has been made in view of the above-mentioned points, and has an object to provide a strain gauge that can reduce the effect of creep on the output voltage of a bridge circuit. [Means for solving the problem]

[0006] A strain gauge according to one embodiment of the present disclosure has a substrate and a resistor provided on the substrate, the resistor including a first resistor portion and a second resistor portion connected in series with the first resistor portion, the first resistor portion and the second resistor portion having creep amounts of the same sign and value, and the first resistor portion and the second resistor portion having different line widths. Effect of the Invention

[0007] According to the disclosed technique, it is possible to provide a strain gauge that can reduce the effect of creep on the output voltage of a bridge circuit. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Diagram 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Diagram 3] 2 is an enlarged partial plan view of a first resistor portion and a second resistor portion of FIG. 1. [Figure 4] FIG. 1 is a diagram illustrating an example of a bridge circuit. [Diagram 5] FIG. 13 is a diagram (part 1) illustrating a method for adjusting the line width of a resistor portion. [Figure 6] FIG. 2 is a diagram (part 2) illustrating a method for adjusting the line width of a resistor portion. [Figure 7] FIG. 11 is a diagram (part 3) illustrating a method for adjusting the line width of a resistor portion. [Figure 8] 4 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. [Figure 9] 13 is a simulation result showing the relationship between the line widths WA and WB of the resistor portion and the amount of creep. [Figure 10] 13 is a simulation result showing the relationship between the film thickness and line width WB of the resistor portion and the amount of creep. [Figure 11] FIG. 4 is a plan view illustrating a strain gauge according to a modified example of the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a mode for carrying out the invention will be described with reference to the drawings. In each drawing, the same components may be given the same reference numerals. In addition, in each drawing, an X direction, a Y direction, and a Z direction that are perpendicular to each other may be defined. In this case, in the X direction, the starting point (root) side of the arrow may be referred to as the X- side, and the ending point (arrowhead) side of the arrow may be referred to as the X+ side. The same applies to the Y direction and the Z direction. In addition, in the description of each drawing, a description of components that are the same as components already described may be omitted.

[0010] First Embodiment Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1.

[0011] 1 and 2, the strain gauge 1 has a substrate 110, a resistor 130, wiring 140A, wiring 140B, wiring 140C, electrodes 150A, 150B, 150C, and a cover layer 160. The cover layer 160 can be provided as necessary. The strain gauge 1 may also have dummy wiring 140E formed in the same manner as each of the wiring 140A, wiring 140B, and wiring 140C. First, each part constituting the strain gauge 1 will be described in detail.

[0012] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 130 of the substrate 110 is provided is referred to as the "upper side", and the side on which the resistor 130 is not provided is referred to as the "lower side". The surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". However, the strain gauge 1 can also be used upside down. The strain gauge 1 can also be arranged at any angle. The planar view refers to viewing the object in a normal direction from the upper side to the lower side with respect to the upper surface 110a of the substrate 110. The planar shape refers to the shape of the object when the object is viewed in the normal direction.

[0013] The substrate 110 is a member that serves as a base layer for forming the resistor 130 and the like. The substrate 110 has flexibility. The thickness of the substrate 110 is not particularly limited and may be appropriately determined depending on the intended use of the strain gauge 1 and the like. For example, the thickness of the substrate 110 may be about 5 μm to 500 μm. A strain generator may be bonded to the lower surface side of the strain gauge 1 via an adhesive layer or the like. From the viewpoint of the transferability of strain from the surface of the strain generator to the sensing part and dimensional stability against environmental changes, the thickness of the substrate 110 is preferably within the range of 5 μm to 200 μm. From the viewpoint of insulation, the thickness of the substrate 110 is preferably 10 μm or more.

[0014] The substrate 110 is made of, for example, resin. The substrate 110 is formed of, for example, 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 member having a thickness of about 500 μm or less and having flexibility.

[0015] When the base material 110 is formed from an insulating resin film, the insulating resin film may contain a filler, impurities, etc. For example, the base material 110 may be formed from an insulating resin film containing a filler such as silica or alumina.

[0016] The resistor 130 is a thin film provided in a predetermined pattern on the substrate 110. In the strain gauge 1, the resistor 130 is a sensing part that receives strain and generates a resistance change. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or may be formed on the upper surface 110a of the substrate 110 via another layer. For convenience, the resistor 130 is shown in FIG. 1 as having a high-density matte pattern.

[0017] The resistor 130 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 130 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).

[0018] 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.

[0019] The thickness of the resistor 130 is not particularly limited and may be appropriately determined depending on the intended use of the strain gauge 1, etc. For example, the thickness of the resistor 130 may be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 130 is 0.1 μm or more, the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr) is improved. Furthermore, when the thickness of the resistor 130 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 110 caused by the internal stress of the film constituting the resistor 130 are reduced.

[0020] For example, when the resistor 130 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. For example, when the resistor 130 is a Cr mixed-phase film, the resistor 130 can make α-Cr the main component, so that the gauge factor of the strain gauge 1 is 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 a component which occupies 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 130 preferably contains 80% by weight or more of α-Cr. More specifically, from the same viewpoint, the resistor 130 more preferably contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0021] Moreover, when the resistor 130 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 of the strain gauge 1 can be suppressed.

[0022] In addition, the ratio of CrN and Cr2N in the Cr mixed phase film is preferably such that the ratio of Cr2N is 80% by weight or more and less than 90% by weight with respect to the total weight of CrN and Cr2N. More specifically, the ratio is more preferably such that the ratio of Cr2N is 90% by weight or more and less than 95% by weight with respect to the total weight of CrN and Cr2N. Cr2N has semiconductor properties. Therefore, by setting the ratio of Cr2N to 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant. Furthermore, by setting the ratio of Cr2N to 90% by weight or more and less than 95% by weight, the resistor 130 is less likely to become ceramic, and the resistor 130 is less likely to be brittle fractured.

[0023] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr mixed-phase film, the possibility of unstable N being generated can be reduced, resulting in a stable strain gauge. Here, "unstable N" refers to trace amounts of N2 or atomic N that may be present in the Cr mixed-phase film. This unstable N may escape to the outside of the film depending on the external environment (e.g., high-temperature environment). When unstable N escapes to the outside of the film, the film stress of the Cr mixed-phase film may change.

[0024] In the strain gauge 1, when a Cr mixed-phase film is used as the material of the resistor 130, high sensitivity and miniaturization can be achieved. For example, while the output of a conventional strain gauge was about 0.04 mV / 2 V, an output of 0.3 mV / 2 V or more can be obtained when a Cr mixed-phase film is used as the material of the resistor 130. In addition, while the size (gauge length x gauge width) of a conventional strain gauge was about 3 mm x 3 mm, when a Cr mixed-phase film is used as the material of the resistor 130, the size (gauge length x gauge width) can be miniaturized to about 0.3 mm x 0.3 mm.

[0025] The resistor 130 includes a plurality of resistive portions. In the present embodiment, the resistor 130 includes a first resistive portion 130A and a second resistive portion 130B connected in series with the first resistive portion 130A. Each of the first resistive portion 130A and the second resistive portion 130B includes a plurality of elongated portions and a plurality of folded portions.

[0026] In the first resistor 130A, the multiple elongated portions are arranged side by side with their longitudinal directions facing a first direction (the Y-axis direction in the example of FIG. 1). The multiple folded back portions alternately join the ends of adjacent elongated portions among the multiple elongated portions to connect the elongated portions in series. This results in the first resistor 130A having a structure folded back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the X-axis direction in the example of FIG. 1).

[0027] In the second resistor 130B, the multiple elongated portions are arranged side by side with their longitudinal directions facing the second direction (the X-axis direction in the example of FIG. 1). The multiple folded back portions alternately join the ends of adjacent elongated portions among the multiple elongated portions to connect the elongated portions in series. This results in the second resistor 130B having a structure folded back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the Y-axis direction in the example of FIG. 1).

[0028] In the present embodiment, as an example, the grid directions of the first resistor section 130A and the second resistor section 130B are orthogonal to each other, but this is not limiting. The grid directions of the first resistor section 130A and the second resistor section 130B may intersect at any angle, or may be parallel. In this specification, the term "orthogonal grid directions" includes a case where the angle between the grid directions is within 90±5 degrees.

[0029] The wirings 140A, 140B, and 140C are provided on the base material 110 and spaced apart from each other. The wiring 140A has a first metal layer 141A and a second metal layer 142A laminated on the upper surface of the first metal layer 141A. The wiring 140B has a first metal layer 141B and a second metal layer 142B laminated on the upper surface of the first metal layer 141B. The wiring 140C has a first metal layer 141C and a second metal layer 142C laminated on the upper surface of the first metal layer 141C.

[0030] Each of the wirings 140A, 140B, and 140C is not limited to being linear, and may be any pattern including linear and curved portions in accordance with the arrangement of the resistor 130. Each of the wirings 140A, 140B, and 140C may be any length. For convenience, in FIG. 1, the first metal layer 141A, the first metal layer 141B, and the first metal layer 141C are shown with the same dark matte pattern as the resistor 130. Also, the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C are shown with a matte pattern that is less dense than the resistor 130.

[0031] Although the resistor 130, the first metal layer 141A, the first metal layer 141B, and the first metal layer 141C are given different reference numbers for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 130, the first metal layer 141A, the first metal layer 141B, and the first metal layer 141C have approximately the same thickness. Moreover, the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C are given different reference numbers for convenience, but they can be integrally formed from the same material in the same process. Therefore, the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C have approximately the same thickness.

[0032] Each of the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C is formed of a material having a lower resistance than the resistor 130 (the first metal layer 141A, the first metal layer 141B, and the first metal layer 141C). The material of each of the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C is not particularly limited as long as it is a material having a lower resistance than the resistor 130, and can be appropriately selected according to the purpose. For example, when the resistor 130 is a Cr mixed phase film, the material of each of the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C 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. There are no particular limitations on the thickness of each of second metal layer 142A, second metal layer 142B, and second metal layer 142C and the thickness can be appropriately selected depending on the purpose, but it can be, for example, about 3 μm to 5 μm.

[0033] The second metal layer 142A may be formed on a part of the first metal layer 141A, or may be formed on the entire first metal layer 141A. The second metal layer 142B may be formed on a part of the first metal layer 141B, or may be formed on the entire first metal layer 141B. The second metal layer 142C may be formed on a part of the first metal layer 141C, or may be formed on the entire first metal layer 141C.

[0034] When the strain gauge 1 has the dummy wiring 140E, the dummy wiring 140E has a first metal layer 141E and a second metal layer 142E laminated on the upper surface of the first metal layer 141E. The material and thickness of the first metal layer 141E and the second metal layer 142E can be, for example, the same as the material and thickness of the first metal layer 141A and the second metal layer 142A.

[0035] The electrode 150A is defined at an end of the wiring 140A. The electrode 150A is a part of the wiring 140A. The electrode 150B is defined at an end of the wiring 140B. The electrode 150B is a part of the wiring 140B. The electrode 150C is defined at an end of the wiring 140C. The electrode 150C is a part of the wiring 140C. Each of the electrodes 150A, 150B, and 150C is a terminal for outputting to the outside a change in resistance value caused in the resistor by strain. For example, a lead wire for external connection is joined to each of the electrodes 150A, 150B, and 150C.

[0036] The electrode 150A is connected to one end of the first resistor portion 130A via the wiring 140A. The electrode 150C is connected to the other end of the first resistor portion 130A via the wiring 140C. The electrode 150B is connected to one end of the second resistor portion 130B via the wiring 140B. The electrode 150C is connected to the other end of the second resistor portion 130B via the wiring 140C.

[0037] The other end of the first resistor portion 130A and the other end of the second resistor portion 130B are connected via the wiring 140C. In other words, the first resistor portion 130A and the second resistor portion 130B are connected in series between the electrodes 150A and 150B. The electrode 150C is connected to the connection portion between the first resistor portion 130A and the second resistor portion 130B.

[0038] One or more other metal layers may be laminated on the upper surfaces of the electrodes 150A, 150B, and 150C. For example, the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C may be copper layers, and a gold layer may be laminated on the upper surfaces of the copper layers. Alternatively, the second metal layer 142A, the second metal layer 142B, and the second metal layer 142C may be copper layers, and a palladium layer and a gold layer may be laminated in this order on the upper surfaces of the copper layers. By making the top layers of the electrodes 150A, 150B, and 150C gold layers, the solder wettability of the upper surfaces of the electrodes 150A, 150B, and 150C can be improved.

[0039] A cover layer 160 (insulating resin layer) may be provided on the upper surface 110a of the base material 110 so as to cover the resistor 130 and the wirings 140A, 140B, and 140C and expose the electrodes 150A, 150B, and 150C. In the example of Fig. 1, the electrodes 150A, 150B, and 150C are exposed in circular openings provided in the cover layer 160. Note that the openings in the cover layer 160 exposing the electrodes 150A, 150B, and 150C are not limited to being circular, and may be any shape such as rectangular.

[0040] By providing the cover layer 160, it is possible to prevent mechanical damage and the like from occurring to the resistor 130 and the wirings 140A, 140B, and 140C. In addition, by providing the cover layer 160, it is possible to protect the resistor 130 and the wirings 140A, 140B, and 140C from moisture and the like. Note that the cover layer 160 may be provided so as to cover the entire upper surface 110a of the base material 110 except for the electrodes 150A, 150B, and 150C.

[0041] The cover layer 160 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, polyolefin resin). The cover layer 160 may contain a filler or a pigment. There is no particular limit to the thickness of the cover layer 160 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0042] [Resistor line width] 3 is an enlarged partial plan view of the first resistor portion and the second resistor portion of FIG. 1. As shown in FIG. 3, the line width of the first resistor portion 130A is W A and the line width of the second resistor portion 130B is W B (≠W A Here, the line width of the resistor portion is the average value of the line widths of the elongated portions constituting the resistor portion in the short direction. In the example of FIG. 3, the line width W B is the line width W of the first resistor portion 130A. A Thinner than.

[0043] It is known that the creep characteristics of a strain gauge depend on the line width of the resistance portion. Therefore, in the strain gauge 1, the line width W A and the line width W of the second resistor portion 130B B are adjusted so that the first resistor portion 130A and the second resistor portion 130B have the same sign and the same value of creep amount.

[0044] Fig. 4 is a diagram showing an example of a bridge circuit. In the bridge circuit shown in Fig. 4, a resistor R1 is connected to the upper left side, and a resistor R2 is connected to the lower left side. In addition, a resistor R3 is connected to the lower right side, and a resistor R4 is connected to the upper right side. In the bridge circuit shown in Fig. 4, a DC voltage E is supplied between the connection part of the upper left side and the lower left side, and the connection part of the upper right side and the lower right side. As a result, an analog output voltage e0 can be obtained from between the connection part of the upper left side and the upper right side, and the connection part of the lower left side and the lower right side.

[0045] A strain detector can be configured by the strain gauge 1 and a bridge circuit. That is, a strain detector can be configured by connecting the first resistor portion 130A and the second resistor portion 130B of the strain gauge 1 in place of the resistors of the bridge circuit shown in Fig. 4. In the strain detector, the amount of strain of the strain body to which the strain gauge 1 is attached can be detected as an output voltage e0.

[0046] As described above, the first resistor section 130A and the second resistor section 130B are adjusted to have the same sign and the same creep amount. Therefore, by connecting the first resistor section 130A and the second resistor section 130B to adjacent sides of the bridge circuit, it is possible to obtain an output voltage e0 in which the creep amounts of the first resistor section 130A and the second resistor section 130B are offset, without reducing the absolute values ​​of the creep amounts of the first resistor section 130A and the second resistor section 130B. In other words, by having the first resistor section 130A and the second resistor section 130B have the same sign and the same creep amount, it is possible to realize a strain gauge 1 that can reduce the effect of creep on the output voltage e0 of the bridge circuit.

[0047] The adjacent sides of the bridge circuit can be arbitrarily selected, for example, the side connected to resistor R1 and the side connected to resistor R2 in FIG. 4, or the side connected to resistor R1 and the side connected to resistor R4.

[0048] [How to adjust the line width of the resistor] As an example of a method for adjusting the line width of the resistor portion, a method using laser light irradiation will be described. A The line width of the second resistor portion 130B is changed to W B An example of adjusting the

[0049] First, a strain gauge is prepared, which includes a substrate 110 and a resistor 130 provided on the substrate 110, the resistor 130 including a first resistor portion 130A and a second resistor portion 130B connected in series with the first resistor portion 130A. Then, the resistor 130 is irradiated with a laser beam. It is also possible to prepare a strain gauge in which a cover layer 160 is provided on the upper surface 110a of the substrate 110. In this case, since the laser beam can remove only the metallic resistor 130, the resistor 130 can be irradiated with the laser beam from above the resin cover layer 160.

[0050] Specifically, as shown above the arrow in FIG. 5, the line width W AThe laser light L is irradiated to one end of the second resistor 130B in the short direction. Before the laser light L is irradiated, the side of the second resistor 130B is, for example, approximately perpendicular to the upper surface 110a of the base material 110. In the region irradiated with the laser light L, as shown below the arrow in FIG. 5, a part of the second resistor 130B is removed and the line width of the second resistor 130B becomes narrower. In addition, the side of the second resistor 130B irradiated with the laser light L becomes an inclined surface inclined with respect to the upper surface 110a of the base material 110. The inclination angle with respect to the upper surface 110a of the base material 110 is about 0°<θ1≦70°. In addition, when a functional layer 120 described later exists under the second resistor 130B, the functional layer 120 irradiated with the laser light L is also removed.

[0051] In addition, since the laser light L is also irradiated onto the upper surface 110a of the base material 110, a carbonized layer 110c may be formed at the boundary between the base material 110 and the resistor 130, where the resin constituting the base material 110 is carbonized by the thermal energy of the laser light L. The carbonized layer 110c is formed in a shallow region on the upper surface 110a side of the base material 110. The carbonized layer 110c is visually recognized as being, for example, a dark color (black, brown, etc.). The laser light L is irradiated sequentially over the entire length of the second resistive portion 130B. The carbonized layer 110c may be formed over the entire length of the second resistive portion 130B along the longitudinal direction, or may be formed only in a portion of the second resistive portion 130B.

[0052] Next, as shown in the upper arrow of FIG. 6, the other end of the second resistive portion 130B in the short direction is irradiated with laser light L. In the region irradiated with the laser light L, as shown in the lower arrow of FIG. 6, a part of the second resistive portion 130B is removed, and the line width of the second resistive portion 130B becomes narrower. In addition, the side surface of the second resistive portion 130B irradiated with the laser light L becomes an inclined surface inclined with respect to the upper surface 110a of the base material 110, and the cross section of the resistor 130 becomes trapezoidal. The inclination angle with respect to the upper surface 110a of the base material 110 is about 0°<θ2≦70°.

[0053] In addition, since the laser light L is also irradiated onto the upper surface 110a of the base material 110, a carbonized layer 110c may be formed at the boundary between the base material 110 and the resistor 130, where the resin constituting the base material 110 is carbonized by the thermal energy of the laser light L. The carbonized layer 110c is formed in a shallow region on the upper surface 110a side of the base material 110. The carbonized layer 110c is visually recognized as being, for example, a dark color (black, brown, etc.). The laser light L is irradiated sequentially over the entire length of the second resistive portion 130B. The carbonized layer 110c may be formed over the entire length of the second resistive portion 130B along the longitudinal direction, or may be formed only in a portion of the second resistive portion 130B.

[0054] In the lower part of the arrow in FIG. 6, the laser light L is irradiated so that the line width of the second resistor portion 130B becomes the desired line width W B Repeat until the line width W B is defined at a position where the thickness of the second resistor portion 130B is half of the maximum thickness.

[0055] In the manufacturing process of the strain gauge 1, the line width of the resistor 130 may be adjusted by the method shown in Fig. 5 and Fig. 6, or only one of Fig. 5 and Fig. 6 may be performed to adjust the line width of the resistor 130. That is, the line width of the second resistor 130B may be narrowed by removing a part of the second resistor 130B only on one side of the side surface of the second resistor 130B. In this case, only one side of the side surface of the second resistor 130B becomes an inclined surface that is inclined with respect to the upper surface 110a of the substrate 110.

[0056] That is, when the line width is adjusted by irradiating the resistor 130 with a laser beam, the cross section of the resistor 130 in the short side direction has a shape having at least one inclined surface. Note that when the line width is adjusted by a method other than irradiating the laser beam, the cross section of the resistor 130 in the short side direction may not have a shape having an inclined surface.

[0057] In the manufacturing process of the strain gauge 1, the desired line width W B Alternatively, instead of determining the creep characteristic in advance, irradiation with the laser light L and measurement of the creep characteristic may be repeated alternately until the desired creep characteristic is obtained.

[0058] The line width may be adjusted for only some or all of the multiple resistor portions. That is, the step of irradiating with laser light includes a step of narrowing the line width of the first resistor portion 130A and / or the second resistor portion 130B by irradiating with laser light so that the first resistor portion 130A and / or the second resistor portion 130B have the same sign and the same value of creep amount and have different line widths.

[0059] The step of irradiating the laser light may further include a step of thinning the film thickness of the first resistive portion 130A and / or the second resistive portion 130B. Since the amount of creep varies depending on the film thickness of the resistive portion, the adjustable range of the amount of creep can be increased by adjusting not only the line width but also the film thickness. When the laser light is used to adjust the film thickness of the first resistive portion 130A and / or the second resistive portion 130B, the portion of the first resistive portion 130A and / or the second resistive portion 130B irradiated with the laser light has a rougher surface than the portion of the first resistive portion 130A and / or the second resistive portion 130B not irradiated with the laser light.

[0060] Specifically, as shown in the upper arrow of FIG. 7, the laser beam L is irradiated onto the upper surface of the second resistor portion 130B while the irradiation position of the laser beam L is moved in the Y direction. As a result, as shown in the lower arrow of FIG. 7, a part of the upper surface side of the second resistor portion 130B is removed, and the film thickness of the second resistor portion 130B is reduced. By sequentially performing the same operation on the entire second resistor portion 130B in the longitudinal direction, the entire film thickness of the second resistor portion 130B can be uniformly reduced. The film thickness of the first resistor portion 130A may be adjusted.

[0061] In addition, in the case of a high-sensitivity strain gauge with a gauge factor of 10 or more (for example, when a Cr mixed phase film is used for the resistor 130), the high sensitivity makes it sensitive to the influence of the material properties, and the creep characteristics may also be significantly reduced. Therefore, in a high-sensitivity strain gauge with a gauge factor of 10 or more, it is extremely important to improve the creep characteristics by adjusting the line width and film thickness of the resistor part.

[0062] [Strain gauge manufacturing method] In the strain gauge 1 according to this embodiment, a resistor 130 including a first resistor portion 130A and a second resistor portion 130B, a wiring 140A, a wiring 140B, a wiring 140C, an electrode 150A, an electrode 150B, an electrode 150C, and a cover layer 160 are formed on a substrate 110. Another layer (such as a functional layer described later) may be formed between the substrate 110 and the layers of these members. In the following description, the wiring 140A, the wiring 140B, and the wiring 140C are collectively referred to as wiring 140. Also, the electrodes 150A, 150B, and 150C are collectively referred to as electrodes 150.

[0063] A method for manufacturing the strain gauge 1 will be described below. To manufacture the strain gauge 1, first, a base material 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on an upper surface 110a of the base material 110. Metal layer A is a layer that is ultimately patterned to become resistor 130, wiring 140, and electrode 150. Therefore, the material and thickness of metal layer A are the same as those of resistor 130 and the like described above.

[0064] 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. Instead of the magnetron sputtering method, 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.

[0065] After forming a metal layer A on the upper surface 110a of the substrate 110, the metal layer A is patterned by a well-known photolithography method into a planar shape similar to that of the resistor 130, the wiring 140, and the electrode 150 in Fig. 1. Each of the first resistive portion 130A and the second resistive portion 130B of the resistor 130 includes a plurality of juxtaposed elongated portions and a folded portion that alternately links ends of adjacent elongated portions among the plurality of elongated portions to connect the elongated portions in series, and the plurality of elongated portions includes two or more types of elongated portions having different widths.

[0066] Alternatively, a base layer may be formed on the upper surface 110a of the substrate 110, and then the metal layer A may be formed. For example, a functional layer of a predetermined thickness may be vacuum-formed by conventional sputtering on the upper surface 110a of the substrate 110. By providing a base layer in this manner, the gauge characteristics of the strain gauge 1 can be stabilized.

[0067] 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, metal layer A (resistor 130). The functional layer preferably further has a function of preventing oxidation of metal layer A due to oxygen or moisture contained in base material 110, and / or a function of improving adhesion between base material 110 and metal layer A. The functional layer may further have other functions.

[0068] The insulating resin film constituting the base material 110 may contain oxygen or 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 having a function of preventing the oxidation of the metal layer A.

[0069] 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, the stability of the gauge characteristics of the strain gauge 1 is improved. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0070] Examples of materials for the functional layer include 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.

[0071] 8 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. Fig. 8 shows the cross-sectional shape of the strain gauge 1 when a functional layer 120 is provided as an underlying layer for the resistor 130, the wiring 140, and the electrodes 150.

[0072] The planar shape of the functional layer 120 may be patterned to be substantially the same as the planar shapes of the resistor 130, the wiring 140, and the electrode 150, for example. However, the planar shapes of the functional layer 120, the resistor 130, the wiring 140, and the electrode 150 may not be substantially the same. For example, when the functional layer 120 is formed from an insulating material, the functional layer 120 may be patterned to a shape different from the planar shapes of the resistor 130, etc. In this case, the functional layer 120 may be formed in a solid shape in the region where the resistor 130, etc. are formed, for example. Alternatively, the functional layer 120 may be formed in a solid shape on the entire upper surface of the substrate 110.

[0073] After forming the resistor 130, the wiring 140, and the electrodes 150, a cover layer 160 is formed on the upper surface 110a of the base material 110 as necessary. The cover layer 160 covers the resistor 130 and the wiring 140, but the electrodes 150 may be exposed from the cover layer 160. For example, the cover layer 160 can be formed by laminating a semi-cured thermosetting insulating resin film on the upper surface 110a of the base material 110 so as to cover the resistor 130 and the wiring 140 and expose the electrodes 150, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 1 is completed.

[0074] [simulation] Figure 9 shows the line width W A and W B The figure shows the simulation results showing the relationship between the thickness and the creep amount. The material of the resistor part is a Cr mixed phase film. The thickness of the resistor part is fixed at 220 nm. Table 1 shows the creep amount values ​​for the main line widths in Figure 9.

[0075] [Table 1] From FIG. 9 and Table 1, when the film thickness of the resistor part is 220 nm, the line width W A is 100 μm or less, and the line width W B If the line width W is 10 μm or less, the creep amount can be kept at 3% FS or less. A is 100 μm or less, and the line width W B If the thickness is 5 μm or less, the creep amount can be kept at 1% FS or less.

[0076] Figure 10 shows the film thickness and line width W B The material of the resistor is a Cr mixed phase film. A is fixed at 10 μm. Table 2 shows the creep amount values ​​for the main line widths in FIG.

[0077] [Table 2] From Figure 10 and Table 2, when the film thickness of the resistor part is thin, the line width W B For example, when the film thickness is 50 nm, the line width W B If the line width W is 100 μm, the creep amount can be kept below 1% FS. When the film thickness is 220 nm, as can be seen from the results in FIG. B If the line width W is 10 μm or less, the creep amount can be kept at 3% FS or less. B If the line width W is 5 μm or less, the creep amount can be kept at 1% FS or less. B The line width W is preferably 5 μm or more and 15 μm or less, and more preferably 10 μm or more and 15 μm or less. B If the thickness is 15 μm, the creep amount can be kept below 1% FS.

[0078] As can be seen from FIG. 9 and Table 1, and FIG. 10 and Table 2, the optimal line width W A and W B varies depending on the film thickness of the resistor part. Therefore, the film thickness and line width W A and W B It is preferable to determine approximate design values ​​for the resistor and then adjust the line width and film thickness of the resistor while monitoring the amount of creep as described above.

[0079] Modification of the First Embodiment In the modified example of the first embodiment, an example of a strain gauge having four resistance parts is shown. Note that in the modified example of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

[0080] Fig. 11 is a plan view illustrating a strain gauge according to a modified example of the first embodiment. The strain gauge 1A shown in Fig. 11 differs from the strain gauge 1 in that a third resistor 130C, a fourth resistor 130D, a wiring 140D, and an electrode 150D are added.

[0081] In the strain gauge 1A, the resistor 130 further includes a third resistor portion 130C and a fourth resistor portion 130D connected in series with the first resistor portion 130A and the second resistor portion 130B. The third resistor portion 130C and the fourth resistor portion 130D have the same sign and the same creep amount. The third resistor portion 130C and the fourth resistor portion 130D have different line widths.

[0082] In the third resistor 130C, the multiple elongated portions are arranged side by side with their longitudinal directions facing a first direction (the Y-axis direction in the example of FIG. 1). The multiple folded portions alternately join the ends of adjacent elongated portions among the multiple elongated portions to connect the elongated portions in series. This results in the third resistor 130C having a structure folded back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the X-axis direction in the example of FIG. 1).

[0083] In the fourth resistor section 130D, the multiple elongated portions are arranged side by side with their longitudinal directions facing the second direction (the X-axis direction in the example of FIG. 1). The multiple folded back portions alternately join the ends of adjacent elongated portions among the multiple elongated portions to connect the elongated portions in series. This results in the fourth resistor section 130D having a structure folded back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the Y-axis direction in the example of FIG. 1).

[0084] In this embodiment, as an example, the grid directions of the third resistor section 130C and the fourth resistor section 130D are orthogonal to each other, but this is not limited thereto. The grid directions of the third resistor section 130C and the fourth resistor section 130D may cross at any angle, or may be parallel. In this embodiment, as an example, the grid directions of the first resistor section 130A and the fourth resistor section 130D, and the second resistor section 130B and the third resistor section 130C are orthogonal to each other, but this is not limited thereto. The grid directions of the first resistor section 130A and the fourth resistor section 130D, and the second resistor section 130B and the third resistor section 130C may cross at any angle, or may be parallel.

[0085] The wiring 140D is provided on the base material 110 and spaced apart from the wirings 140A, 140B, and 140C. The wiring 140D has a first metal layer 141D and a second metal layer 142D laminated on an upper surface of the first metal layer 141D. The material and thickness of the first metal layer 141D and the second metal layer 142D can be, for example, similar to the material and thickness of the first metal layer 141A and the second metal layer 142A.

[0086] The wiring 140D is not limited to being linear, and may have any pattern including linear and curved portions in accordance with the arrangement of the resistor 130. The wiring 140D may have any length. The patterns of the wirings 140A, 140B, and 140C are different from those of the strain gauge 1.

[0087] The electrode 150D is defined at the end of the wiring 140D. The electrode 150D is exposed in a circular opening provided in the cover layer 160. The electrode 150D is a part of the wiring 140D. The electrode 150D, together with the electrodes 150A, 150B, and 150C, is a terminal for outputting to the outside a change in resistance value caused in the resistor by strain. For example, a lead wire for external connection is joined to the electrode 150D.

[0088] The electrode 150A is connected to one end of the first resistor portion 130A via the wiring 140A. The electrode 150C is connected to the other end of the first resistor portion 130A via the wiring 140C. The electrode 150B is connected to one end of the second resistor portion 130B via the wiring 140B. The electrode 150C is connected to the other end of the second resistor portion 130B via the wiring 140C.

[0089] The electrode 150B is connected to one end of the third resistor section 130C via the wiring 140B. The electrode 150D is connected to the other end of the third resistor section 130C via the wiring 140D. The electrode 150A is connected to one end of the fourth resistor section 130D via the wiring 140A. The electrode 150D is connected to the other end of the fourth resistor section 130D via the wiring 140D.

[0090] The other end of the third resistor section 130C and the other end of the fourth resistor section 130D are connected via a wiring 140D. In other words, the third resistor section 130C and the fourth resistor section 130D are connected in series between the electrodes 150A and 150B. The electrode 150D is connected to the connection section between the third resistor section 130C and the fourth resistor section 130D.

[0091] A strain detector can be configured by the strain gauge 1A and a bridge circuit. That is, a strain detector can be configured by connecting the first resistor portion 130A, the second resistor portion 130B, the third resistor portion 130C, and the fourth resistor portion 130D of the strain gauge 1A in place of the resistors of the bridge circuit shown in Fig. 4. In the strain detector, the amount of strain of the strain body to which the strain gauge 1A is attached can be detected as an output voltage e0.

[0092] As described above, the first resistor section 130A and the second resistor section 130B are adjusted to have the same sign and the same creep amount. The third resistor section 130C and the fourth resistor section 130D are adjusted to have the same sign and the same creep amount. Therefore, the first resistor section 130A and the second resistor section 130B are connected to adjacent sides of the bridge circuit, and the third resistor section 130C and the fourth resistor section 130D are connected to adjacent sides of the bridge circuit. For example, the first resistor section 130A and the fourth resistor section 130D are connected to adjacent sides of the bridge circuit.

[0093] This makes it possible to obtain an output voltage e0 in which the creep amounts of the first resistor section 130A and the second resistor section 130B and the creep amounts of the third resistor section 130C and the fourth resistor section 130D are offset, without reducing the absolute values ​​of the creep amounts of the first resistor section 130A and the second resistor section 130B and the creep amounts of the third resistor section 130C and the fourth resistor section 130D.

[0094] The method for adjusting the line width of the third resistor section 130C and / or the fourth resistor section 130D is as described above. In the third resistor section 130C and / or the fourth resistor section 130D, the film thickness may be adjusted together with the line width. When a laser beam is used to adjust the film thickness of the third resistor section 130C and / or the fourth resistor section 130D, the portion of the third resistor section 130C and / or the fourth resistor section 130D irradiated with the laser beam has a rougher surface than the portion of the third resistor section 130C and / or the fourth resistor section 130D not irradiated with the laser beam.

[0095] That is, the step of applying the laser light may include a step of narrowing the line width of the third resistor portion 130C and / or the fourth resistor portion 130D by applying the laser light so that the third resistor portion 130C and / or the fourth resistor portion 130D have creep amounts of the same sign and value and are different from each other in line width. The step of applying the laser light may further include a step of thinning the film thickness of the third resistor portion 130C and / or the fourth resistor portion 130D.

[0096] The preferred embodiments and the like have been described above in detail. However, the strain gauge according to the present disclosure is not limited to the above-described embodiments and modifications. For example, various modifications and substitutions can be made to the strain gauge according to the above-described embodiments and the like without departing from the scope of the claims.

[0097] For example, in a strain gauge having a first resistance portion and a second resistance portion whose grid directions are perpendicular to each other, the first resistance portion and the second resistance portion may be made to have creep amounts of the same sign and value by a method other than the line width or film thickness of the resistance portion. [Explanation of symbols]

[0098] 1, 1A strain gauge, 110 substrate, 110a upper surface, 120 functional layer, 130 resistor, 130A first resistor section, 130B second resistor section, 130C third resistor section, 130D fourth resistor section, 140A, 140B, 140C, 140D wiring, 141A, 141B, 141C, 141D, 141E first metal layer, 142A, 142B, 142C, 142D, 142E second metal layer, 150A, 150B, 150C, 150D electrode, 160 cover layer

Claims

1. Substrate and The substrate has a resistor provided on it, The resistor includes a first resistive section and a second resistive section connected in series with the first resistive section. The first resistor and the second resistor have the same sign and the same creep amount. The first and second resistance sections are strain gauges with different wire widths.

2. The strain gauge according to claim 1, wherein the first resistance section and the second resistance section have grid directions perpendicular to each other.

3. The strain gauge according to claim 1 or 2, wherein a carbonized layer is formed at the boundary portion of the substrate with the resistor.

4. The strain gauge according to claim 3, wherein the cross-section of the resistor in the short direction has at least one inclined surface.

5. The resistor further includes a third resistor and a fourth resistor connected in series with the first resistor and the second resistor, The third resistor and the fourth resistor have the same sign and the same creep amount. The strain gauge according to claim 1 or 2, wherein the third resistance section and the fourth resistance section have different line widths.

6. The strain gauge according to claim 5, wherein the third resistance section and the fourth resistance section, and the first resistance section and the fourth resistance section, have grid directions that are orthogonal.

7. A strain gauge according to either claim 1 or 2, It has a bridge circuit, A strain detection device in which the first resistor and the second resistor are connected to adjacent sides of the bridge circuit.

8. The strain gauge described in claim 5, It has a bridge circuit, The first resistor and the second resistor are connected to adjacent sides of the bridge circuit. A strain detection device in which the third resistor and the fourth resistor are connected to adjacent sides of the bridge circuit.

9. The strain detection device according to claim 8, wherein the first resistor and the fourth resistor are connected to adjacent sides of the bridge circuit.

10. A step of preparing a strain gauge comprising a base material and a resistor provided on the base material, wherein the resistor includes a first resistive portion and a second resistive portion connected in series with the first resistive portion, The step includes irradiating the resistor with laser light, A method for manufacturing a strain gauge, comprising the step of irradiating with laser light, which includes the step of narrowing the line width of the first resistance portion and / or the second resistance portion by irradiation with laser light such that they have the same sign and the same creep amount and different line widths from each other.

11. The method for manufacturing a strain gauge according to claim 10, wherein the step of irradiating with laser light further includes a step of thinning the film thickness of the first resistive portion and / or the second resistive portion.

12. The method for manufacturing a strain gauge according to claim 11, wherein in the first resistive portion and / or the second resistive portion, the portion irradiated with the laser light has a rougher surface roughness than the portion not irradiated with the laser light.

13. The resistor further includes a third resistor and a fourth resistor connected in series with the first resistor and the second resistor, A method for manufacturing a strain gauge according to any one of claims 10 to 12, wherein the step of irradiating with laser light further includes a step of narrowing the line width of the third resistance portion and / or the fourth resistance portion by irradiation with laser light such that they have the same symbol and the same creep amount and different line widths.

14. The method for manufacturing a strain gauge according to claim 13, wherein the step of irradiating with laser light further includes a step of thinning the film thickness of the third resistive portion and / or the fourth resistive portion.

15. The method for manufacturing a strain gauge according to claim 14, wherein in the third resistance portion and / or the fourth resistance portion, the portion irradiated with the laser light has a rougher surface roughness than the portion not irradiated with the laser light.

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