Strain gauge

Abstract

To provide a strain gauge capable of reducing a difference in a resistance temperature coefficient as the entire strain gauge.SOLUTION: A strain gauge comprises: a first resistor; a first base material having a first surface in which the first resistor is formed and a second surface that opposes the first surface in a thickness direction; and a second base material having a third surface adhered to the second surface directly or indirectly and a fourth surface that opposes the third surface in a thickness direction. The first base material and the second base material are different each in terms of a first coefficient of linear expansion relative to a first direction orthogonal to a thickness direction and a second coefficient of linear expansion relative to a second direction orthogonal to a thickness direction and orthogonal to the first direction, and the first base material and the second base material are adhered overlappingly such that the first coefficient of linear expansion is larger than the second coefficient of linear expansion in the first base material and the second coefficient of linear expansion is larger than the first coefficient of linear expansion in the second base material.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] A strain gauge is known that is attached to an object to be measured to detect the strain of the object to be measured. The strain gauge includes a flat base material and a resistor formed on the base material. The resistor deforms according to the strain of the object to be measured. In the strain sensor of Patent Document 1, a sensor structure portion 6 is disclosed that is configured by bonding a gauge base 4 to which a plurality of resistive strain gauges are attached to the back surface of a flexible substrate, and further bonding a sheet-like insulating member (cover film) to the surface of the flexible substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of a flat base material, the linear expansion coefficient of the base material with respect to a certain direction on the plane and the linear expansion coefficient with respect to a direction orthogonal to the certain direction on the plane may be different. Depending on the configuration, arrangement, and / or electrical connection relationship of the strain gauge, the anisotropy of the linear expansion coefficient of the base material may affect the detection of strain by the strain gauge. For example, when forming a plurality of grids on the same base material, if the grid directions are different, there will be a difference in the temperature coefficient of resistance (TCR) for each grid, which may affect the strain detection result.

[0005] An object of the present disclosure is to provide a strain gauge capable of suppressing a decrease in detection accuracy due to expansion or contraction of a base material.

Means for Solving the Problems

[0006] The strain gauge according to one aspect of the present disclosure includes a first base material having a first resistor, a first surface on which the first resistor is formed, and a second surface facing the first surface in the thickness direction, a second base material having a third surface directly or indirectly adhered to the second surface, and a fourth surface facing the third surface in the thickness direction. The first base material and the second base material each have a first linear expansion coefficient with respect to a first direction orthogonal to the thickness direction and a second linear expansion coefficient with respect to a second direction orthogonal to the thickness direction and orthogonal to the first direction, and the first base material and the second base material are different. The first base material and the second base material are overlapped and adhered such that the first linear expansion coefficient is larger than the second linear expansion coefficient in the first base material and the second linear expansion coefficient is larger than the first linear expansion coefficient in the second base material.

[0007] The strain gauge according to one aspect of the present disclosure includes a first resistor and a second resistor, a first base material having a first surface on which the first resistor is formed, and a second surface facing the first surface in the thickness direction, a second base material having a third surface on which the second resistor is formed and directly or indirectly adhered to the second surface, and a fourth surface facing the third surface in the thickness direction. The first base material and the second base material each have a first linear expansion coefficient with respect to a first direction orthogonal to the thickness direction and a second linear expansion coefficient with respect to a second direction orthogonal to the thickness direction and orthogonal to the first direction, and the first base material and the second base material are different. The first base material and the second base material are overlapped and adhered such that the first linear expansion coefficient is larger than the second linear expansion coefficient in the first base material and the second linear expansion coefficient is larger than the first linear expansion coefficient in the second base material.

[0008] A strain gauge according to one embodiment of the present disclosure comprises a first substrate having a first resistor, a first surface, and a second surface opposite the first surface in a thickness direction; a second substrate having a third surface on which the first resistor is formed and directly or indirectly bonded to the second surface, and a fourth surface opposite the third surface in the thickness direction; the first substrate and the second substrate each have a first linear expansion coefficient in a first direction orthogonal to the thickness direction and a second linear expansion coefficient in a second direction orthogonal to the thickness direction and orthogonal to the first direction, which are different from each other; and the first substrate and the second substrate are overlapped and bonded together such that the first linear expansion coefficient is greater than the second linear expansion coefficient in the first substrate, and the second linear expansion coefficient is greater than the first linear expansion coefficient in the second substrate. [Effects of the Invention]

[0009] According to the strain gauge of the present disclosure, it is possible to suppress a decrease in detection accuracy due to expansion or contraction of the base material. [Brief explanation of the drawings]

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0011] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant descriptions may be omitted.

[0012] In the present disclosure, in directions such as parallel, right angle, orthogonal, horizontal, vertical, up and down, left and right, and front and back, a deviation within a range that does not impair the effects of the embodiment is allowed. Also, the shape of the corners of each member shown in the drawings is not limited to a right angle and may be rounded. Parallel, right angle, orthogonal, horizontal, and vertical may each include substantially parallel, substantially right angle, substantially orthogonal, substantially horizontal, and substantially vertical.

[0013] For example, "parallel" means that even if two lines or two planes are not completely parallel to each other, they can be treated as parallel to each other within a range acceptable in manufacturing. Similarly, for each of "right angle", "orthogonal", "horizontal", and "vertical", it is intended that the mutual positional relationship between two lines or two planes corresponds to each of them within a range acceptable in manufacturing.

[0014] Also, in the drawings, for the sake of convenience of explanation, an XYZ orthogonal coordinate system composed of an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other may be set. Note that the coordinate system is defined for the purpose of explanation and does not limit the posture of the strain gauge according to the present disclosure. When the XYZ orthogonal coordinate system is set, the terms in the X-axis direction, Y-axis direction, and Z-axis direction may be used. 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. Hereinafter, for the sake of convenience of explanation, the positive Z-axis direction may be referred to as "up", and the negative Z-axis direction may be referred to as "down". Also, the surface located in the upward direction of a certain member may be referred to as the upper surface, and the surface located in the downward direction may be referred to as the lower surface.

[0015] [First Embodiment] Hereinafter, with reference to FIGS. 1 to 6, the strain gauge 100A according to the first embodiment will be described. The strain gauge 100A is an example of the strain gauge in the present disclosure.

[0016] FIG. 1 is a drawing showing each part of the strain gauge 100A according to the first embodiment and its laminated relationship. The strain gauge 100A according to the present embodiment includes at least a first resistor 60, a first base material 50, and a second base material 30.

[0017] The first resistor 60 is a sensing portion of the strain gauge 100A formed on the first base material 50. The first base material 50 has a first surface on which the first resistor 60 is formed and a second surface facing the first surface in the thickness direction. In the example of FIG. 1, the upper surface of the first base material 50 is the first surface, and the lower surface is the second surface.

[0018] The second surface of the first base material 50 is adhered to the second base material 30. The second base material 30 has a third surface directly or indirectly adhered to the second surface of the first base material 50 and a fourth surface facing the third surface in the thickness direction. In the example of FIG. 1, the upper surface of the second base material 30 is the third surface, and the lower surface is the fourth surface. When using the strain gauge 100A, the fourth surface of the second base material 30 is attached to the strained body 10. Therefore, in the example of FIG. 1, the strain gauge 100A is laminated in the order of the first resistor 60, the first base material 50, and the second base material 30 from top to bottom, and the lower surface of the second base material 30 is attached to the strained body 10.

[0019] In FIG. 1, C11X and C12Y schematically show the coefficient of linear expansion of the first substrate 50. In FIG. 1, C21X and C22Y schematically show the coefficient of linear expansion of the second substrate 30. In the strain gauge 100A according to the present disclosure, the first substrate 50 and the second substrate 30 have anisotropy with respect to the coefficient of linear expansion. For example, when the first substrate 50 and the second substrate 30 are rectangular, these substrates have different coefficients of linear expansion in the longitudinal direction and the transverse direction, respectively. As shown in FIG. 1, the strain gauge 100A according to the present disclosure is characterized in that when the first substrate 50 and the second substrate 30 are laminated, the coefficients of linear expansion in two directions of both are overlapped so as to have a specific magnitude relationship. Although the detailed principle will be described later, since the strain gauge 100A has such a feature, the difference in the coefficients of linear expansion in the two directions can be reduced as a whole of the strain gauge 100A. Therefore, the strain gauge 100 can suppress a decrease in detection accuracy due to expansion or contraction of the substrate.

[0020] FIG. 2 is a plan view illustrating the strain gauge 100A. Specifically, FIG. 2 is a plan view of the upper surface of the first substrate 50 of the strain gauge 100A shown in FIG. 1, viewed from above. As described above, the first resistor 60 is formed on the upper surface of the first substrate 50. The first resistor 60 includes four resistor portions. In FIG. 2, as an example, the case where the strain gauge 100A is a four-gauge strain gauge is shown. That is, in the example of FIG. 2, four resistor portions 60A to 60D are formed on the upper surface. The strain gauge 100A includes wiring 80 and electrodes 90A to 90D. In the following description, the electrodes 90A to 90D are also collectively referred to as "electrodes 90". The resistor portions 60A to 60D are each connected to two electrodes 90 via a pair of wirings 80. The connection relationship between the resistor portions 60A to 60D and the electrodes will be described in detail later.

[0021] [Resistor portions 60A to 60D] The resistance portions 60A to 60D are each a sensing portion that receives strain in the strain gauge 100A and causes a resistance change. The resistance portions 60A to 60D are resistors in the form of a thin film formed in a predetermined pattern on the first base material 50. The resistance portions 60A to 60D may be formed directly on the upper surface of the first base material 50, or may be formed on the upper surface of the first base material 50 via another layer. In FIG. 2, for the sake of convenience, the resistance portions 60A to 60D are shown as a dark textured pattern.

[0022] Each of the resistance portions 60A to 60D includes a plurality of elongated portions. The elongated portions included in one resistance portion are arranged with their longitudinal directions aligned in the same direction and are alternately connected in series. That is, each resistance portion has a structure that folds back in a zigzag as a whole. Specifically, for example, the elongated portions included in the resistance portions 60A and 60C are arranged at predetermined intervals along the X-axis direction. Also, the elongated portions included in the resistance portions 60B and 60D are arranged at predetermined intervals along the Y-axis direction. Further, the ends of adjacent elongated portions are alternately connected. That is, each of the resistance portions 60A to 60D has a structure that folds back in a zigzag as a whole.

[0023] In a resistance portion having such a zigzag structure, the longitudinal direction of the elongated portions arranged in a certain direction is the grid direction. Also, the direction perpendicular to the grid direction in the XY plane is the grid width direction. For example, in the case of the resistance portion 60A, the grid direction is the X-axis direction and the grid width direction is the Y-axis direction.

[0024] The thicknesses of the resistance portions 60A to 60D are not particularly limited and may be appropriately determined according to the purpose of use of the strain gauge 100A or the like. For example, the film thicknesses of the resistance portions 60A to 60D may each be in the range of 0.05 μm to 2 μm. In particular, when the thickness of the resistance portions 60A to 60D is 0.1 μm or more, the crystallinity of the crystals constituting the resistance portions 60A to 60D (for example, the crystallinity of α-Cr) is improved. Further, when the thickness of the resistance portions 60A to 60D is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the first base material 50 due to internal stress of the film constituting the resistance portions 60A to 60D are reduced. When the resistance portions 60A to 60D are each formed of a material mainly composed of Cr, it is still better if the film thickness of the resistor is 200 nm or more so that the "lateral sensitivity ratio is 70% or less and the gauge factor is 5 or more".

[0025] The widths of the resistance portions 60A to 60D can each be optimized for the required specifications such as resistance value and lateral sensitivity, and in consideration of measures against disconnection, for example, can be about 10 μm to 100 μm. Note that the "width of the resistance portions 60A to 60D" is the length in the direction orthogonal to the longitudinal direction in the resistance portions 60A to 60D.

[0026] The resistance portions 60A to 60D can be formed of, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistance portions 60A to 60D can each be formed of a material containing at least one of Cr and Ni. Examples of the material containing Cr include a Cr mixed-phase film. Examples of the material containing Ni include Cu-Ni (copper nickel). Examples of the material containing both Cr and Ni include Ni-Cr (nickel chromium).

[0027] Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr2N, etc. are in a mixed phase. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

[0028] For example, when the resistance parts 60A to 60D are Cr mixed-phase films, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. Also, for example, when the resistance parts 60A to 60D are Cr mixed-phase films, by using α-Cr as the main component of the resistance parts 60A to 60D, the gauge factor of the strain gauge 100A can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000 ppm / °C to +1000 ppm / °C. Here, the "main component" means a component that occupies 50% by weight or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, it is preferable that the resistance parts 60A to 60D contain 80% by weight or more of α-Cr. Further, from the same viewpoint, it is more preferable that the resistance parts 60A to 60D contain 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0029] Also, when the resistance parts 60A to 60D are Cr mixed-phase films, it is preferable that CrN and Cr2N contained in the Cr mixed-phase film are 20% by weight or less. By CrN and Cr2N contained in the Cr mixed-phase film being 20% by weight or less, a decrease in the gauge factor of the strain gauge 100A can be suppressed.

[0030] Also, the ratio of CrN to Cr2N in the Cr mixed-phase film is preferably such that the proportion of Cr2N is 80% by weight or more and less than 90% with respect to the total weight of CrN and Cr2N. Further, more preferably, the same ratio is such that the proportion of Cr2N is 90% by weight or more and less than 95% with respect to the total weight of CrN and Cr2N. Cr2N has semiconductor-like properties. Therefore, by setting the proportion of Cr2N as described above to 90% by weight or more and less than 95%, a decrease in TCR (negative TCR) becomes more prominent. Further, by setting the proportion of Cr2N as described above to 90% by weight or more and less than 95%, the ceramization of the resistance parts 60A to 60D can be reduced, and brittle fracture of the resistance parts 60A to 60D can be made less likely to occur.

[0031] On the one hand, CrN has the advantage of being chemically stable. By increasing the content of CrN in the Cr mixed-phase film, the possibility of generating unstable N can be reduced, so a stable strain gauge can be obtained. Here, "unstable N" means trace amounts of N₂ or atomic N that may exist in the film of the Cr mixed-phase film. These unstable Ns may escape outside the film depending on the external environment (for example, a high-temperature environment). When the unstable N escapes outside the film, the film stress of the Cr mixed-phase film may change.

[0032] [Wiring 80] The wiring 80 electrically connects each of the resistance parts 60A to 60D to the electrode 90. The length of the wiring 80 is preferably 5 mm or more regardless of whether the wiring 80 is linear. By setting the length of the wiring 80 to 5 mm or more, the heat generated when soldering a lead wire or the like to the electrode 90 is less likely to be transmitted to the first resistor 60 or the cover layer 102 covering it, and the heat load on the gauge characteristics can be reduced.

[0033] [Electrode 90] The electrode 90 outputs to the outside the change in the resistance value generated in each resistance part of the first resistor 60 due to strain. For example, a lead wire for external connection or the like is joined to the electrode 90. Each electrode 90 is formed on the first base material 50. The electrode 90 may be, for example, substantially circular in plan view as shown in FIG. 2, or may be substantially rectangular. Also, the electrode 90 may be formed to have a wider width than the wiring 80.

[0034] Note that if the strain gauge 100A can obtain an output as a four-gauge strain gauge, the connection method between the first resistor 60, the wiring 80, and the electrode 90 is not limited to the example shown in FIG. 2. Also, the materials, structures, shapes, lengths, and sizes of the wiring 80 and the electrode 90 are not particularly limited. For example, the wiring 80 is not limited to a linear shape and may be in any pattern.

[0035] For example, each wiring 80 may be composed of a first metal layer 81 and a second metal layer 82 laminated on the top surface of the first metal layer 81. Although the first resistor 60 and the first metal layer 81 are denoted by different reference numerals for convenience, they may be integrally formed using the same material in the same process. The second metal layer 82 may be formed of a material with lower resistance than the first metal layer 81. The second metal layer 82 may be formed of a material with lower resistance than each resistive portion of the first resistor 60. For example, when the first resistor 60 is a Cr mixed-phase film, the second metal layer 82 may be made of Cu, Ni, Al, Ag, Au, Pt, etc., 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 second metal layer 82 may be formed on a portion of the first metal layer 81 or on the entire first metal layer 81. Further, for example, the strain gauge 100A may have dummy wirings 80E formed in the same manner as the wirings 80.

[0036] The strain gauge 100A may also include a cover layer 102. The cover layer 102 is indicated by a dashed line in FIG. 2. The cover layer 102 is provided on the upper surface of the first substrate 50 so as to cover the first resistor 60 and the wiring 80 and expose the electrodes 90. By providing the cover layer 102, the strain gauge 100A prevents mechanical damage and the like from occurring to the first resistor 60 and the wiring 80. By providing the cover layer 102, the strain gauge 100A protects the first resistor 60 and the wiring 80 from moisture and the like. The cover layer 102 may also be provided so as to cover the entire portion excluding the electrodes 90.

[0037] Examples of materials for the cover layer 102 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin and polyolefin resin). The cover layer 102 may contain a filler or a pigment. The thickness of the cover layer 102 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the cover layer 102 can be approximately 2 μm to 30 μm. By providing the cover layer 102, it is possible to prevent mechanical damage and the like from occurring to the first resistor 60. Furthermore, by providing the cover layer 102, it is possible to protect the first resistor 60 from moisture and the like.

[0038] [Bridge circuit] Next, a bridge circuit formed by the resistance portions 60A to 60D of the first resistor 60 will be described. FIG. 3 is a diagram showing an example of a bridge circuit. FIG. 3 shows an example of wiring when a full bridge circuit is formed by the resistance portions 60A to 60D. The full bridge circuit 120 includes the resistance portions 60A to 60D, which are connected in series as shown. More specifically, the full bridge circuit 120 has connection portions P12, P23, P34, and P41 connected to the resistance portions 60A to 60D, and four electrodes 90 connected to the connection portions P12, P23, P34, and P41. Wiring 80 connects each resistance portion to each connection portion, and each connection portion to each electrode 90. Note that the connection portions P12, P23, P34, and P41 each represent a portion where the circuit branches or connects, and they do not need to be independent components.

[0039] The resistance part 60A and the resistance part 60B are connected via the connection part P12, the resistance part 60B and the resistance part 60C are connected via the connection part P23, the resistance part 60C and the resistance part 60D are connected via the connection part P34, and the resistance part 60D and the resistance part 60A are connected via the connection part P41. The electrode 90B is connected to the resistance parts 60A and 60B via the connection part P12, the electrode 90C is connected to the resistance parts 60B and 60C via the connection part P23, the electrode 90D is connected to the resistance parts 60C and 60D via the connection part P34, and the electrode 90A is connected to the resistance parts 60A and 60D via the connection part P41. A DC voltage E is supplied between the electrode 90B and the electrode 90D. The voltage between the electrode 90C and the electrode 90A is the analog output voltage e0. In the full-bridge circuit 120, the output voltage e0 is obtained. The strain gauge 100A can detect the amount of strain of the strained body 10 as the output voltage e0.

[0040] [Cross-section of the strain gauge 100A] FIG. 4 is a diagram schematically showing an example of the cross-section of the strain gauge 100A. Note that FIG. 4 is a cross-sectional view in which a part of the strain gauge 100A shown in FIGS. 1 and 2 is cut out. Specifically, FIG. 4 shows the cross-section when the strain gauge 100A is cut in the Z-axis direction at a location where any one of the resistance parts 60A to 60D shown in FIG. 2 is formed. In FIG. 4, the illustration of the cover layer 102 is omitted. The same applies to the cross-sectional views in the following embodiments.

[0041] [The strained body 10 and the adhesive layer 20] The distortion body 10 is a member that transmits distortion to the strain gauge 100A. The size, shape, material, and form of the distortion body 10 are not particularly limited as long as the strain gauge 100A can be attached thereto. For example, the distortion body 10 may be plate-shaped. The strain gauge 100A is attached to the distortion body 10 by, for example, an adhesive. When an adhesive is used, an adhesive layer 20, which is a layer of the adhesive, is formed between the lower surface of the strain gauge 100A (more specifically, the lower surface of the second base material 30) and the distortion body 10. Note that since the strain gauge 100A may be attached to the distortion body 10 by a method other than an adhesive, the adhesive layer 20 may not be formed. For example, the strain gauge 100A may be attached to the distortion body 10 using a double-sided tape or the like.

[0042] [Second base material 30] The second base material 30 is adhered to the upper surface of the distortion body 10. The second base material 30 has flexibility. The second base material 30 is, for example, plate-shaped. The second base material 30 has a predetermined thickness in the Z-axis direction. The lower surface of the second base material 30 is attached to the distortion body 10. The first base material 50 is attached to the upper surface of the second base material 30. Note that the thickness and material of the second base material 30 are not particularly limited. The second base material 30 is formed from, for example, an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, or a polyolefin resin. Note that a film refers to a member having a thickness of about 500 μm or less and having flexibility. The second base material 30 may be formed from the same material as the first base material 50 and may have the same thickness.

[0043] [Adhesive layer 40 and first base material 50] The first base material 50 is attached to the upper surface of the second base material 30 with an adhesive, for example. When using an adhesive, an adhesive layer 40, which is a layer of the adhesive, is formed between the lower surface of the first base material 50 and the upper surface of the second base material 30. Note that since the first base material 50 may be attached to the second base material 30 by a method other than an adhesive, the adhesive layer 40 may not be formed. For example, the first base material 50 and the second base material 30 may be attached to the strain generating body 10 using a double-sided tape or the like. Also, the adhesive for adhering the strain generating body 10 and the second base material 30 and the adhesive for adhering the second base material 30 and the first base material 50 may be of different types.

[0044] The first base material 50 is a member that serves as a base layer for forming the first resistor 60 and the like. The first base material 50 is, for example, plate-shaped. The thickness direction of the first base material 50 is along the Z-axis direction. The first base material 50 has flexibility. The thickness of the first base material 50 is not particularly limited and may be appropriately determined according to the purpose of use of the strain gauge 100A and the like. For example, the thickness of the first base material 50 may be about 5 μm to 500 μm. From the viewpoints of the transmission of strain from the strain generating body 10 to each resistance portion of the first resistor 60 and the dimensional stability against environmental changes, the thickness of the first base material 50 is preferably within the range of 5 μm to 200 μm. Also, from the viewpoint of insulation, the thickness of the first base material 50 is preferably 10 μm or more.

[0045] The first base material 50 is formed from an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, or a polyolefin resin.

[0046] Specific product names include, for example, Upilex (registered trademark) 25S, Zenomax (registered trademark) F38, Kapton (registered trademark) 100EN-Z, Upilex 50S, Kapton 140EN-Z, Zenomax F15, etc., which can be used as the material of the first base material 50.

[0047] When the first substrate 50 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the first substrate 50 may be formed from an insulating resin film containing fillers such as silica and alumina.

[0048] Examples of materials other than the resin of the first substrate 50 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO3, BaTiO3), etc. In addition to the aforementioned crystalline materials, amorphous glass or the like may also be used as the material of the first substrate 50. Also, metals such as aluminum, aluminum alloy (duralumin), and titanium may be used as the material of the first substrate 50. When a metal first substrate 50 is used, an insulating film is provided so as to cover the upper surface of the first substrate 50. Note that the specific materials of the first substrate 50 and the second substrate 30 are not limited to those described above.

[0049] [First Resistor 60] As described above, the first resistor 60 is formed on the upper surface of the first substrate 50. The material and thickness of the first resistor 60 are also as described above.

[0050] The first substrate 50 and the second substrate 30 each have the property that the first linear expansion coefficient with respect to the first direction orthogonal to the thickness direction is different from the second linear expansion coefficient with respect to the second direction orthogonal to the thickness direction and orthogonal to the first direction. Also, the first substrate 50 and the second substrate 30 are adhesively overlapped such that the first linear expansion coefficient is larger than the second linear expansion coefficient in the first substrate 50, and the second linear expansion coefficient is larger than the first linear expansion coefficient in the second substrate 30.

[0051] Note that the specific values of the first linear expansion coefficient and the second linear expansion coefficient of the first base material 50, and the first linear expansion coefficient and the second linear expansion coefficient of the second base material 30 are not particularly limited. These linear expansion coefficients are determined by the material, shape, size, and thickness of the base material, respectively. For example, when the base material is made of an insulating resin film, the linear expansion coefficients in the longitudinal direction and the lateral direction of the base material are often about -1 to 20 ppm / °C, respectively.

[0052] In this embodiment, for the sake of clarity, the case where the first direction is the X-axis direction and the second direction is the Y-axis direction will be taken as an example to explain the magnitude of this linear expansion coefficient. However, the first direction and the second direction do not have to be along the sides of the first base material 50 and the second base material 30. In this embodiment, as shown in FIG. 1, the "thickness direction" of the first base material 50 and the second base material 30 corresponds to the Z-axis direction.

[0053] [The first linear expansion coefficient C11X and the second linear expansion coefficient C12Y of the first base material 50] FIG. 5 is a plan view illustrating the first base material 50. In FIG. 5, the first base material 50 before the temperature rise is shown by a solid line, and the first base material 50 after the temperature rise is shown by a two-dot chain line. In the first base material 50, the first linear expansion coefficient C11X with respect to the X-axis direction (i.e., the first direction) is different from the second linear expansion coefficient C12Y with respect to the Y-axis direction (i.e., the second direction), and C11X > C12Y.

[0054] The first linear expansion coefficient C11X can be calculated by the following formula (1).

[0055] C11X = ΔLX11 / LX10…(1) Here, ΔLX11 is the elongation of the first base material 50 in the X-axis direction when the temperature of the first base material 50 rises by 1 K. LX10 is the length of the first base material 50 in the X-axis direction before the temperature rise. ΔLX11 is the difference between the length LX11 of the first base material 50 in the X-axis direction after the temperature rise and the length LX10 of the first base material 50 in the X-axis direction before the temperature rise.

[0056] The second linear expansion coefficient C12Y can be calculated by the following formula (2).

[0057] C12Y = ΔLY11 / LY10…(2) Here, ΔLY11 is the elongation of the first substrate 50 in the Y-axis direction when the temperature of the first substrate 50 rises by 1K. LY10 is the length of the first substrate 50 in the Y-axis direction before the temperature rise. ΔLY11 is the difference between the length LY11 of the first substrate 50 in the Y-axis direction after the temperature rise and the length LY10 of the first substrate 50 in the Y-axis direction before the temperature rise.

[0058] [The first linear expansion coefficient C21X and the second linear expansion coefficient C22Y of the second substrate 30] FIG. 6 is a plan view illustrating the second substrate 30. In FIG. 6, the second substrate 30 before the temperature rise is shown by a solid line, and the second substrate 30 after the temperature rise is shown by a two-dot chain line. In the second substrate 30, the first linear expansion coefficient C21X with respect to the X-axis direction (i.e., the first direction) and the second linear expansion coefficient C22Y with respect to the Y-axis direction (i.e., the second direction) are different, and C22Y > C21X.

[0059] The first linear expansion coefficient C21X can be expressed by the following formula (3).

[0060] C21X = ΔLX21 / LX20…(3) Here, ΔLX21 is the elongation of the second substrate 30 in the X-axis direction when the temperature of the second substrate 30 rises by 1K. LX20 is the length of the first substrate 50 in the X-axis direction before the temperature rise. ΔLX21 is the difference between the length LX21 of the second substrate 30 in the X-axis direction after the temperature rise and the length LX20 of the second substrate 30 in the X-axis direction before the temperature rise.

[0061] The second linear expansion coefficient C22Y can be expressed by the following formula (4).

[0062] C22Y = ΔLY21 / LY20…(4) Here, ΔLY21 is the elongation of the second substrate 30 in the Y-axis direction when the temperature of the second substrate 30 rises by 1K. LY20 is the length of the second substrate 30 in the Y-axis direction before the temperature rise. ΔLY21 is the difference between the length LY21 of the second substrate 30 in the Y-axis direction after the temperature rise and the length LY20 of the second substrate 30 in the Y-axis direction before the temperature rise.

[0063] [Laminating relationship between the first substrate 50 and the second substrate 30] Referring to FIG. 1 again for explanation. The first substrate 50 of the strain gauge 100A has a first linear expansion coefficient C11X that is greater than the second linear expansion coefficient C12Y. For such a first substrate 50, the second substrate 30 is laminated and attached in a direction such that the second linear expansion coefficient C22Y is greater than the first linear expansion coefficient C21X. By overlapping the first substrate 50 and the second substrate 30 in such a direction, as a whole of the two substrates combined, the difference in the values of the first linear expansion coefficient and the second linear expansion coefficient can be reduced. For example, the directions of the first substrate 50 and the second substrate 30 on the XY plane may be orthogonal as shown in FIG. 1. Further, when the first substrate 50 and the second substrate 30 are the same member (i.e., substrates made of the same material with the same shape, size, and thickness), when viewed from the Z-axis direction, the two substrates may be rotated by 90 degrees and bonded together.

[0064] Thus, the strain gauge 100A according to the present embodiment can reduce the difference in the linear expansion coefficients of the substrates as a whole. Therefore, the strain gauge 100A can reduce the noise caused by the difference in the linear expansion coefficients of the substrates.

[0065] To explain in more detail, first, when the substrate expands, the length of the resistor formed thereon also changes to some extent. At this time, the amount of change in the length of the resistor in the direction with a high linear expansion coefficient is larger than the amount of change in the resistor in the direction with a low linear expansion coefficient. For example, comparing the resistor portions 60A and 60B in FIGS. 1 to 2, the resistor portion 60B whose grid direction is parallel to the X-axis direction extends more than the resistor portion 60A whose grid direction is orthogonal to the X-axis direction, so the resistance value of the resistor portion 60B is higher.

[0066] Thus, if the base material has anisotropy in the coefficient of linear expansion, even in the same resistance portion, the resistance value varies depending on the arrangement direction (i.e., the grid direction). Although the base material expands due to moisture absorption, temperature rise, etc., particularly in the case of expansion due to temperature rise, if the above-described variation in resistance value occurs, the temperature coefficient of resistance (TCR) also differs for each resistance portion, so that the temperature compensation performance of the entire strain gauge 100A deteriorates.

[0067] On the other hand, according to the strain gauge 100A according to the present embodiment, as the entire strain gauge 100A, the difference (i.e., anisotropy) between the coefficient of linear expansion in the first direction and the coefficient of linear expansion in the second direction can be reduced. Thereby, the difference in TCR between a plurality of resistance portions (for example, resistance portions 60A and 60B, 60C and 60D, etc.) having different grid directions can be made small. As a result, the effect that the decrease in detection accuracy due to expansion or contraction of the base material can be suppressed as the entire strain gauge 100A is achieved.

[0068] Note that the first base material 50 and the second base material 30 may be base materials made of the same material or base materials made of different materials. Also, the first base material 50 and the second base material 30 may have the same shape and size, or may have different shapes and sizes. Further, the first base material 50 and the second base material 30 may have the same thickness or may have different thicknesses. In particular, when the first base material 50 and the second base material 30 are made of the same material, according to FIGS. 5 and 6, C11X + C21X = C12Y + C22Y. Therefore, since the difference in the coefficient of linear expansion of the base material can be made smaller, the decrease in strain detection accuracy due to expansion or contraction of the base material can be suppressed. Further, the first base material 50 and the second base material 30 may be the same base material (same material, shape, size, and thickness). In this case, by stacking the same two base materials on top of each other so as to be orthogonal to each other on the XY plane, the difference in the amount of expansion of the base material in the first direction and the second direction can be substantially offset. Therefore, since the difference in the coefficient of linear expansion of the base material can be made even smaller, the decrease in strain detection accuracy due to expansion or contraction of the base material can be suppressed more.

[0069] In addition, as described above, if the same base materials (same material, shape, size, and thickness) are stacked and bonded together, the strain gauge 100A may be a gauge formed by bonding two or more and an even number of base materials one on top of the other. In this case, two base materials are stacked one on top of the other so as to be orthogonal in plan view as one set, and a plurality of such sets of units are stacked one on top of the other. [[ID=XX]] [[ID=XX]]

[0070] [[ID=XX]] [[ID=XX]] [Manufacturing Method of Strain Gauge 100A][[ID=XX]] Next, the manufacturing method of the strain gauge 100A according to the present embodiment will be described. [[ID=XX]]

[0071] [[ID=XX]] [[ID=XX]] First, a metal layer is formed on the upper surface of the first base material 50. Here, for convenience, it is referred to as metal layer A. Metal layer A is ultimately patterned to become the first resistor 60 and wiring 80 (when the wiring 80 consists of two layers, the first metal layer 81). The material and thickness of metal layer A are the same as those of the above-described first resistor 60 and wiring 80 (or the first metal layer 81). [[ID=XX]]

[0072] [[ID=XX]] Metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming metal layer A as a target. Instead of the magnetron sputtering method, metal layer A may be formed by a reactive sputtering method, an evaporation method, an arc ion plating method, a pulsed laser deposition method, or the like. After forming metal layer A on the upper surface of the first base material 50, metal layer A is patterned into the same planar shape as the resistor portions 60A to 60D in FIG. 2 and the like by a well-known photolithography method.[[ID=XX]] [[ID=XX]]

[0073] [[ID=XX]] Note that a base layer may be formed on the upper surface of the first base material 50 and then metal layer A may be formed. For example, a functional layer with a predetermined film thickness may be vacuum-deposited on the upper surface of the first base material 50 by a conventional sputtering method. By providing such a base layer, the gauge characteristics of the strain gauge 100A can be stabilized. [[ID=XX]] [[ID=XX]]

[0074] [[ID=XX]] In the present disclosure, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper metal layer A (resistive portions 60A to 60D). The functional layer preferably further has a function of preventing oxidation of the metal layer A by oxygen or moisture contained in the first substrate 50 and / or a function of improving the adhesion between the first substrate 50 and the metal layer A. The functional layer may further have other functions.

[0075] The insulating resin film constituting the first substrate 50 may contain oxygen and moisture, and Cr may form a self-oxidizing film. Therefore, particularly when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing oxidation of the metal layer A.

[0076] Thus, by providing the functional layer under the metal layer A, it becomes possible to promote crystal growth of the metal layer A, and a metal layer A composed of a stable crystal phase can be produced. As a result, in the strain gauge 100A, the stability of the gauge characteristics is improved. Also, when the material constituting the functional layer diffuses into the metal layer A, the gauge characteristics are improved in the strain gauge 100A.

[0077] Examples of the material of 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), Al (aluminum), alloys of any of these metals, or compounds of any of these metals.

[0078] The planar shape of the functional layer may be patterned to be substantially the same as the planar shapes of the resistance portions 60A to 60D shown in FIG. 2, for example. However, the planar shapes of the functional layer and the resistance portions 60A to 60D do not have to be substantially the same. For example, when the functional layer is formed of an insulating material, the functional layer may be patterned into a shape different from the planar shapes of the resistance portions 60A to 60D. In this case, the functional layer may be formed in a solid state, for example, in the regions where the resistance portions 60A to 60D are formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the first base material 50.

[0079] Next, an electrode 90 (and the second metal layer 82) is formed on the upper surface of the metal layer A. The electrode 90 (and the second metal layer 82) can be formed, for example, by a photolithography method or a semi-additive method. Thereby, the resistance portions 60A to 60D, the wiring 80, and the electrode 90 are formed on the upper surface of the first base material 50.

[0080] Next, the lower surface of the first base material 50 on which the first resistor 60 (the resistance portions 60A to 60D in the present embodiment), the wiring 80, and the electrode 90 are formed as described above is attached to the second base material 30. Thereby, the strain gauge 100A is completed. The attachment direction of the first base material 50 and the second base material 30 is as described above.

[0081] Note that, if necessary, a cover layer 102 may be provided on the upper surface of the first base material 50. The cover layer 102 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface of the first base material 50 so as to cover the first resistor 60 and the wiring 80 and expose the electrode 90, and then heating and curing it. The cover layer 102 may be produced by applying a liquid or paste-like thermosetting insulating resin on the upper surface of the first base material 50 so as to cover the first resistor 60 and the wiring 80 and expose the electrode 90, and then heating and curing it. The opening for exposing the electrode 90 can be formed, for example, by a photolithography method.

[0082] [Second Embodiment] The strain gauge according to the present disclosure may be provided with a second resistor between the first base material and the second base material. Hereinafter, the strain gauge 100B according to the second embodiment will be described. Note that descriptions that are the same as those in the first embodiment in the second embodiment will not be repeated. The same applies to the following embodiments.

[0083] FIG. 7 is a diagram schematically showing an example of a cross section of the strain gauge 100B according to the second embodiment. Note that FIG. 7 shows a cross section of the strain gauge 100B when cut in the Z-axis direction at a location where the resistance portion is formed.

[0084] The strain gauge 100B according to the second embodiment includes at least a first resistor 60, a first base material 50, a second resistor 62, and a second base material 30. As can be seen by comparing FIGS. 4 and 7, the strain gauge 100B is different from the strain gauge 100A according to the first embodiment in that the second resistor 62 is formed on the upper surface of the second base material 30.

[0085] More specifically, the first base material 50 of the strain gauge 100B has a first surface on which the first resistor 60 is formed and a second surface that is in direct or indirect contact with the second resistor 62. Further, the second base material 30 of the strain gauge 100B has a third surface on which the second resistor 62 is formed and is directly or indirectly adhered to the second surface, and a fourth surface that is adhered to the strain generating body 10. The relationship between the first linear expansion coefficient and the second linear expansion coefficient of the first base material 50 and the second base material 30 is the same as that of the strain gauge 100A described in the first embodiment.

[0086] In addition, the configuration formed on the upper surface of the first base material 50 in the strain gauge 100B (for example, the arrangement and connection relationship of the first resistor 60, the wiring 80, and the electrode 90, etc.) is the same as that in the strain gauge 100A. Also, on the upper surface of the second base material 30, a second resistor 62 (its four resistor portions), wiring 80, and an electrode 90 may be formed with the same configuration and connection relationship as the upper surface of the first base material 50, and these may be connected to form a full-bridge circuit. Note that in the strain gauge 100B, the second resistor 62 may or may not be used for strain detection. When the second resistor 62 is not used for strain detection, the wiring 80 and the electrode 90 may or may not be formed on the upper surface of the second base material 30.

[0087] The strain gauge 100B exhibits the same operational effects as the strain gauge 100A of the first embodiment. When the first base material 50 and the second base material 30 are made of the same material, two base materials on which resistors (more specifically, four resistor portions) are formed may be prepared and combined to fabricate the strain gauge 100B. That is, the two base materials are stacked one on top of the other such that the first linear expansion coefficient of the upper base material is greater than the second linear expansion coefficient, and the second linear expansion coefficient of the lower base material is greater than the first linear expansion coefficient, and then they are adhered. Thereby, the upper base material and the resistor function as the first base material 50 and the first resistor 60 respectively, and the lower base material and the resistor function as the second base material 30 and the second resistor 62 respectively.

[0088] [Third Embodiment] The strain gauge according to the present disclosure may be configured such that no first resistor is provided on the upper surface of the first base material, and a first resistor is provided on the upper surface of the second base material. Hereinafter, the strain gauge 100C according to the third embodiment will be described. FIG. 8 is a diagram schematically showing an example of a cross-section of the strain gauge 100C according to the third embodiment. Note that FIG. 8 shows a cross-section of the strain gauge 100C when cut in the Z-axis direction at the location where the resistor portion is formed.

[0089] The strain gauge 100C according to the third embodiment includes at least a first base material 50, a first resistor 60, and a second base material 30. As can be seen by comparing FIGS. 4 and 8, the strain gauge 100C is different from the strain gauge 100A according to the first embodiment in that the first resistor 60 is formed on the upper surface of the second base material 30 instead of the upper surface of the first base material 50.

[0090] More specifically, the first base material 50 of the strain gauge 100C has a first surface and a second surface facing the first surface in the thickness direction. The second base material 30 of the strain gauge 100C has a third surface on which the first resistor 60 is formed and which is directly or indirectly adhered to the second surface of the first base material 50, and a fourth surface facing the third surface in the thickness direction. The relationship between the first linear expansion coefficient and the second linear expansion coefficient of the first base material 50 and the second base material 30 is the same as that of the strain gauge 100A described in the first embodiment.

[0091] In the strain gauge 100C, on the upper surface of the second base material 30, the first resistor 60 (its four resistor portions 60A to 60D), the wiring 80, and the electrode 90 are formed with the same configuration and connection relationship as the upper surface of the first base material 50, and these may be connected so as to form a full-bridge circuit. That is, in the strain gauge 100C, the first resistor 60 formed on the second base material 30 serves as the sensing portion of the strain gauge 100C. The electrode of the strain gauge 100C may be connected to the outside of the strain gauge 100C through the side surface of the strain gauge 100C or through a through hole provided in the first base material 50 and / or the second base material 30. The strain gauge 100C has the same effects as the strain gauge 100A of the first embodiment and the strain gauge 100B of the second embodiment.

[0092] [Modification 2] The strain gauge according to the present disclosure may be realized by a half-bridge circuit. For example, the first resistor 60 of the strain gauge 100A according to the first embodiment includes two resistor portions, and the two resistor portions and the electrodes may be connected by wiring so as to form a half-bridge circuit. Also, for example, the first resistor 60 and / or the second resistor 62 of the strain gauge 100B according to the second embodiment includes two resistor portions, and the two resistor portions may be connected so as to form a half-bridge circuit as described above. Also, for example, in the strain gauge 100C according to the third embodiment, the first resistor 60 has two resistors, and the two resistors may form a half-bridge circuit. In any case, the same effects as those of the strain gauge according to each embodiment can be obtained.

[0093] It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The above embodiments may be omitted, substituted, or changed in various forms without departing from the scope and gist of the appended claims.

Description of Reference Numerals

[0094] 100A, 100B, 100C... Strain gauges, 30... Second base material, 50... First base material, 60... First resistor, 60A to 60D... Resistor portions, 62... Second resistor, 120... Full-bridge circuit

Claims

1. a first resistor, a first substrate having a first surface on which the first resistor is formed, and a second surface facing the first surface in the thickness direction, a second substrate having a third surface directly or indirectly adhered to the second surface, and a fourth surface facing the third surface in the thickness direction, wherein the first substrate and the second substrate each have a first linear expansion coefficient with respect to a first direction orthogonal to the thickness direction, and a second linear expansion coefficient with respect to a second direction orthogonal to the thickness direction and orthogonal to the first direction, and the first and second linear expansion coefficients are different, and the first substrate and the second substrate are superposed and adhered such that in the first substrate, the first linear expansion coefficient is greater than the second linear expansion coefficient, and in the second substrate, the second linear expansion coefficient is greater than the first linear expansion coefficient; a strain gauge.

2. a first resistor and a second resistor, a first substrate having a first surface on which the first resistor is formed, and a second surface facing the first surface in the thickness direction, a second substrate having a third surface on which the second resistor is formed and directly or indirectly adhered to the second surface, and a fourth surface facing the third surface in the thickness direction, wherein the first substrate and the second substrate each have a first linear expansion coefficient with respect to a first direction orthogonal to the thickness direction, and a second linear expansion coefficient with respect to a second direction orthogonal to the thickness direction and orthogonal to the first direction, and the first and second linear expansion coefficients are different, and the first substrate and the second substrate are superposed and adhered such that in the first substrate, the first linear expansion coefficient is greater than the second linear expansion coefficient, and in the second substrate, the second linear expansion coefficient is greater than the first linear expansion coefficient; a strain gauge.

3. a first resistor, a first substrate having a first surface and a second surface facing the first surface in the thickness direction, a second substrate having a third surface on which the first resistor is formed and directly or indirectly adhered to the second surface, and a fourth surface facing the third surface in the thickness direction, wherein the first substrate and the second substrate each have a first linear expansion coefficient with respect to a first direction orthogonal to the thickness direction, and a second linear expansion coefficient with respect to a second direction orthogonal to the thickness direction and orthogonal to the first direction, and the first and second linear expansion coefficients are different, and the first substrate and the second substrate are superposed and adhered such that in the first substrate, the first linear expansion coefficient is greater than the second linear expansion coefficient, and in the second substrate, the second linear expansion coefficient is greater than the first linear expansion coefficient; a strain gauge.

4. The strain gauge according to any one of claims 1 to 3, wherein the first base material and the second base material are made of the same material.

5. The strain gauge according to any one of claims 1 to 4, wherein the first base material and the second base material are of the same size and shape.

6. The strain gauge according to any one of claims 1 to 5, wherein the first base material and the second base material have the same thickness.

7. The strain gauge according to any one of claims 1 to 6, wherein the first resistor includes four resistor portions, and the four resistor portions are connected so as to form a full-bridge circuit.

8. The strain gauge according to any one of claims 1 to 6, wherein the first resistor includes two resistor portions, and the two resistor portions are connected so as to form a half-bridge circuit.

Images