Strain gauges, strain sensors

Abstract

To improve the moisture resistance of strain gauges. [Solution] This strain gauge comprises a resin base material, a first metal layer disposed on one side of the base material, a first ceramic layer disposed on the opposite side of the first metal layer from the base material, and a resistor disposed on the opposite side of the first ceramic layer from the base material.

Description

Technical Field

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

Background Art

[0002] A strain gauge that is attached to a measurement object to detect the strain of the measurement object is known. The strain gauge includes a resistor that detects strain. The resistor is disposed, for example, on a resin base material (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The resin base material is likely to change in dimensions due to moisture absorption and desorption, and apparent strain occurs along with this dimensional change. This apparent strain is superimposed on the strain of the measurement object to be detected by the resistor and becomes a noise component, so the measurement accuracy of the strain of the measurement object decreases. Therefore, in the strain gauge, improvement in moisture resistance is required to suppress the decrease in measurement accuracy.

[0005] The present disclosure aims to improve the moisture resistance of a strain gauge.

Means for Solving the Problems

[0006] A strain gauge according to an embodiment of the present disclosure includes a resin base material, a first metal layer disposed on one side of the base material, a first ceramic layer disposed on the opposite side of the first metal layer from the base material, and a resistor disposed on the opposite side of the first ceramic layer from the base material.

Effects of the Invention

[0007] According to this disclosure, the moisture resistance of strain gauges can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 2] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 3] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 4] This is a cross-sectional view illustrating a strain gauge according to the second embodiment. [Figure 5] This is a cross-sectional view illustrating a strain gauge according to a modified example 1 of the second embodiment. [Figure 6] This is a cross-sectional view illustrating a strain gauge according to the third embodiment. [Figure 7] This is a cross-sectional view illustrating a strain gauge according to the fourth embodiment. [Figure 8] This is a cross-sectional view illustrating a strain gauge according to the fifth embodiment. [Figure 9] This is a cross-sectional view illustrating a strain gauge according to the sixth embodiment. [Figure 10] This is a cross-sectional view illustrating a strain gauge according to the seventh embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same components may be denoted by the same reference numeral. Also, in the description of each drawing, the description of components that have already been described may be omitted.

[0010] <First Embodiment> Figure 1 is a plan view illustrating a strain gauge according to the first embodiment. Figure 2 is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1. In Figures 1 and 2 and subsequent drawings, the strain generating body 110 on which the strain gauge 1 is placed is also shown as needed.

[0011] Referring to Figures 1 and 2, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, an electrode 50, a metal layer 61, a ceramic layer 62, and an adhesive layer 120. The adhesive layer 120 can be provided as needed. The strain gauge 1 is placed on the strain generating body 110. In this specification, a unit including one or more strain gauges 1 and a strain generating body 110 is also referred to as a "strain sensor". First, the parts constituting the strain gauge 1 will be described in detail.

[0012] In each embodiment, including this embodiment, for convenience, the side of the strain gauge that is in the same direction as the side on which the resistor 30 is provided when viewed from the base material 10 is referred to as the "upper side," and the side that is in the same direction as the side on which the resistor 30 is not provided when viewed from the base material 10 is referred to as the "lower side." For example, in the strain gauge 1 of Figure 1, the upper side is the positive Z-axis direction side, and the lower side is the negative Z-axis direction side. Also, the surface located above each part of the strain gauge according to each embodiment is referred to as the "upper surface," and the surface located below each part is referred to as the "lower surface." However, these definitions of upper and lower are for convenience only, and the strain gauge according to each embodiment can also be used upside down. Also, the strain gauge can be placed at any angle. Furthermore, a plan view refers to viewing the object in the normal direction from the top to the bottom with respect to the upper surface 10a of the base material 10. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0013] The base material 10 is a member serving as a base layer for forming a resistor 30 or the like. In this specification, when it is described that a certain member "forms" another member, unless otherwise specified, it may include both the case where the certain member directly forms the other member and the case where the certain member indirectly forms the other member via other components. Similarly, in this specification, when it is described that a certain member "disposes" another member, unless otherwise specified, it may include both the case where the certain member directly disposes the other member and the case where the certain member disposes the other member via other components. The base material 10 has flexibility. The thickness of the base material 10 is not particularly limited and may be appropriately determined according to the use purpose of the strain gauge 1 or the like. For example, the thickness of the base material 10 may be about 5 μm to 500 μm. From the viewpoints of the strain transmission property from the first main surface 110a of the strain generating body 110 to the resistor 30 which is the sensing part and the dimensional stability against environmental changes, the thickness of the base material 10 is preferably within the range of 5 μm to 200 μm. Further, from the viewpoint of insulation, the thickness of the base material 10 is preferably 10 μm or more.

[0014] The base material 10 is made of resin. The base material 10 is formed from an insulating resin film such as, for example, a PI (polyimide) resin, an epoxy resin, a PEEK (polyether ether ketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, an LCP (liquid crystal polymer) resin, or a polyolefin resin. Here, a film refers to a member having a thickness of about 500 μm or less and having flexibility.

[0015] When the base material 10 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, or the like. For example, the base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0016] The resistor 30 is disposed on one side of the base material 10. The resistor 30 is a thin film formed in a predetermined pattern. In the strain gauge 1, the resistor 30 is a sensing portion that receives strain and causes a resistance change. The resistor 30 may be directly disposed on the upper surface 10a of the base material 10, or may be disposed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown in a dense matte finish pattern.

[0017] The resistor 30 has a structure in which a plurality of elongated portions are arranged at a predetermined interval with their longitudinal directions facing the same direction (the direction of the line A-A in the example of FIG. 1), and the end portions of adjacent elongated portions are alternately connected to form a zigzag fold as a whole. The longitudinal direction of the plurality of elongated portions becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the direction perpendicular to the line A-A in the example of FIG. 1).

[0018] One end portions in the longitudinal direction of the two outermost elongated portions located in the grid width direction are bent in the grid width direction to form respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction. The respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction are electrically connected to the electrodes 50 via the wirings 40. In other words, the wirings 40 electrically connect the respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction to the respective electrodes 50.

[0019] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. 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).

[0020] 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.

[0021] The thickness of the resistor 30 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1. For example, the thickness of the resistor 30 may be approximately 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 30 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 10, caused by internal stress in the film constituting the resistor 30, are reduced.

[0022] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of the resistor 30 is preferably 10 μm or more and 100 μm or less. More specifically, the width of the resistor 30 is preferably 10 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0023] For example, if the resistor 30 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Also, for example, if the resistor 30 is a Cr multiphase film, by making α-Cr the main component of the resistor 30, the gauge factor of strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means a component that accounts for 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 30 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is even more preferable that the resistor 30 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] Furthermore, if the resistor 30 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less, the decrease in the gauge factor of the strain gauge 1 can be suppressed.

[0025] Furthermore, in the Cr multiphase film, it is preferable that the ratio of CrN to Cr2N is such that the proportion of Cr2N is 80% or more and less than 90% by weight relative to the total weight of CrN and Cr2N. More preferably, the ratio is such that the proportion of Cr2N is 90% or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the decrease in TCR (negative TCR) becomes even more pronounced. Moreover, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the ceramicization of the resistor 30 is reduced, making brittle fracture of the resistor 30 less likely to occur.

[0026] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of unstable nitrogen generation can be reduced, thus enabling the creation of a stable strain gauge. Here, "unstable nitrogen" refers to trace amounts of N2 or atomic nitrogen that may be present in the Cr multiphase film. These unstable nitrogen atoms may escape from the film depending on the external environment (e.g., high temperature environment). When unstable nitrogen atoms escape from the film, the film stress of the Cr multiphase film may change.

[0027] In strain gauge 1, using a Cr multiphase film as the material for the resistor 30 enables higher sensitivity and miniaturization. For example, while the output of a conventional strain gauge was approximately 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 30 allows for an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was approximately 3mm × 3mm, using a Cr multiphase film as the material for the resistor 30 allows for miniaturization to approximately 0.3mm × 0.3mm.

[0028] The wiring 40 is provided on the base material 10. The wiring 40 is electrically connected to the resistor 30 and the electrode 50. The wiring 40 is not limited to being linear and can be in any pattern. Also, the wiring 40 can have any width and any length. In Figure 1, for convenience, the wiring 40 is shown with a matte pattern that is less dense than the resistor 30. The wiring 40 may have a multilayer structure. For example, the wiring 40 can have a structure in which a metal layer made of a material with lower resistance than the lower layer is laminated on top of a lower metal layer.

[0029] The electrode 50 is provided on the substrate 10. The electrode 50 is electrically connected to the resistor 30 via the wiring 40. In a plan view, the electrode 50 is wider than the wiring 40 and is formed in a substantially rectangular shape. The electrode 50 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 30 caused by strain. For example, lead wires for external connection are joined to the electrode 50. The electrode 50 may have a multilayer structure. For example, the electrode 50 can have a structure in which a metal layer made of a material with lower resistance than the lower layer and / or a metal layer made of a material with good solderability are laminated on top of a lower metal layer. The resistor 30, wiring 40 and electrode 50 are given different reference numerals for convenience, but both can be formed integrally from the same material in the same process. In Figure 1, for convenience, the electrode 50 is shown with a matte pattern of the same density as the wiring 40.

[0030] The metal layer 61 can be placed on the other side of the substrate 10. In the example in Figure 2, the metal layer 61 is placed on the lower surface 10b of the substrate 10. The metal layer 61 is a protective layer that protects the substrate 10 and the resistor 30, etc., placed on the substrate 10. The metal layer 61 may be placed on a part of the lower surface 10b of the substrate 10, but in order to enhance its effectiveness as a protective layer, it is preferable to place it on the entire lower surface 10b of the substrate 10.

[0031] Generally, resins have the property of absorbing and releasing moisture. Therefore, when detecting the strain of the strain-generating body 110 with the strain gauge 1, if the base material 10 absorbs or releases moisture, the base material 10 expands or contracts, causing strain. The strain caused by the absorption or release of moisture by the base material 10 becomes a noise component in relation to the strain of the strain-generating body 110 that is being detected, thus reducing the measurement accuracy of the strain gauge 1.

[0032] In strain gauge 1, by placing a metal layer 61 on the lower surface 10b of the base material 10, moisture absorption and release from the lower surface 10b of the base material 10 can be suppressed. Therefore, the moisture resistance of strain gauge 1 can be improved. As a result, even when measuring strain in a high-humidity environment, noise components caused by humidity are reduced in strain gauge 1, so the strain of the strain generating body 110 can be measured with high accuracy.

[0033] Furthermore, electrical noise (such as static electricity noise) superimposed on the resistor 30 reduces the measurement accuracy of the strain gauge 1. By placing the metal layer 61 on the lower surface 10b of the base material 10, the electrical noise superimposed on the resistor 30 can be reduced. As a result, even when measuring strain in an environment with a lot of electrical noise, the strain gauge 1 reduces the electrical noise component, allowing for accurate measurement of the strain of the strain generating body 110.

[0034] In particular, highly sensitive strain gauges with a gauge factor of 10 or higher using a Cr multiphase film are prone to noise components being generated due to the effects of humidity and static electricity, which can easily reduce the measurement accuracy of the strain gauge 1. Therefore, the effect of placing a metal layer 61 is especially significant in highly sensitive strain gauges 1 with a gauge factor of 10 or higher using a Cr multiphase film.

[0035] Furthermore, by placing the metal layer 61 on the lower surface 10b of the base material 10, it is possible to prevent static charge buildup on the base material 10 and to equalize the heat distribution of the strain gauge 1.

[0036] Examples of materials for the metal layer 61 include alloys of any of the following metals: Cu, Ni, Al, Ag, Au, Pt, Pd, Sn, Cr, etc. A multilayer film formed by appropriately stacking any of these metals or alloys may be used as the metal layer 61. The same material as the resistor 30 (for example, a Cr multiphase film) may also be used as the material for the metal layer 61.

[0037] The thickness of the metal layer 61 can be, for example, 0.001 μm or more and 5 μm or less. By setting the thickness of the metal layer 61 to 0.001 μm or more, sufficient moisture-proofing and noise reduction effects can be obtained. By setting the thickness of the metal layer 61 to 5 μm or less, the flexibility of the substrate 10 can be maintained, and as a result, a decrease in gauge modulus can be suppressed. Furthermore, by setting the thickness of the metal layer 61 to 5 μm or less, the metal layer 61 can be easily formed without cracking. For example, when an aluminum thin film is used as the metal layer 61, a metal layer 61 with a thickness of approximately 0.03 μm or more and 0.1 μm or less can be formed. Also, when a nickel thin film is used as the metal layer 61, a metal layer 61 with a thickness of approximately 0.002 μm or more and 3 μm or less can be realized. The elastic modulus of the metal layer 61 is, for example, approximately 50 GPa or more and 500 GPa or less.

[0038] The ceramic layer 62 can be positioned on the opposite side of the metal layer 61 from the base material 10. "Opposite side from the base material 10" means the side opposite to where the base material 10 is located. In the example in Figure 2, the ceramic layer 62 is positioned on the underside of the metal layer 61. The ceramic layer 62 is insulating. Together with the metal layer 61, the ceramic layer 62 forms a protective layer. While the ceramic layer 62 may be positioned on a portion of the underside of the metal layer 61, it is preferable to position it across the entire underside of the metal layer 61 to enhance its protective effect.

[0039] In strain gauge 1, by making the protective layer a laminated structure of a metal layer 61 and a ceramic layer 62, moisture absorption and release from the base material 10 from the bottom surface 10b can be further suppressed compared to when the protective layer is composed of only a metal layer 61. Therefore, the moisture resistance of strain gauge 1 can be further improved. In addition, by using ceramics as the material laminated on the metal layer 61 and providing a ceramic layer 62, there is the advantage of improved heat resistance compared to when general resins or the like are laminated on the metal layer 61.

[0040] Examples of materials for the ceramic layer 62 include SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3).

[0041] The thickness of the ceramic layer 62 can be, for example, 0.001 μm or more and 5 μm or less. A thickness of 0.001 μm or more of the ceramic layer 62 provides sufficient moisture resistance. A thickness of 5 μm or less of the ceramic layer 62 maintains the flexibility of the substrate 10, thereby suppressing a decrease in gauge modulus. For example, when SiO2 is used as the material for the ceramic layer 62, a ceramic layer 62 with a thickness of approximately 0.01 μm or more and 0.5 μm or less can be realized. The elastic modulus of the ceramic layer 62 is, for example, approximately 50 GPa or more and 500 GPa or less.

[0042] The side of the ceramic layer 62 opposite to the substrate 10 can be bonded to the first main surface 110a of the strain-generating body 110 via the adhesive layer 120. In the example shown in Figure 2, the lower surface of the ceramic layer 62 is bonded to the first main surface 110a of the strain-generating body 110 via the adhesive layer 120.

[0043] The strain generating body 110 is a member that generates strain when subjected to a load. The strain generating body 110 is, for example, rectangular in shape in plan view. The outer peripheral region of the first main surface 110a of the strain generating body 110 is, for example, exposed in an annular shape on the outside of the base material 10 in plan view. As the material of the strain generating body 110, for example, stainless steel (SUS), copper, aluminum, etc. can be used. The strain generating body 110 can be formed, for example, by a press working method. Inorganic materials such as ceramics may also be used as the material of the strain generating body 110.

[0044] The adhesive layer 120 is not particularly limited as long as it is made of a material that has the function of bonding the first main surface 110a of the strain-generating body 110 to the lower surface of the ceramic layer 62. For example, the adhesive layer 120 may be a layer formed by using epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc., to bond the ceramic layer 62 to the strain-generating body 110. Alternatively, the adhesive layer 120 may be a layer such as a bonding sheet used to bond the ceramic layer 62 to the strain-generating body 110. If the adhesive layer 120 is a bonding sheet layer, the adhesive layer 120 may include not only an adhesive but also an intermediate layer containing glass and / or resin, etc. The thickness of the adhesive layer 120 is not particularly limited. For example, the thickness of the adhesive layer 120 can be about 0.1 μm to 50 μm.

[0045] [Manufacturing method for strain gauge 1] In the strain gauge 1 according to this embodiment, a resistor 30, wiring 40, and electrodes 50 are formed on the upper surface 10a of the base material 10. Another layer (such as a functional layer, described later) may be formed between the upper surface 10a of the base material 10 and the layers of these components. Furthermore, a metal layer 61 and a ceramic layer 62 are formed on the lower surface 10b of the base material 10. If necessary, the lower surface of the ceramic layer 62 is bonded to the first main surface 110a of the strain generating body 110 by an adhesive layer 120.

[0046] The manufacturing method of the strain gauge 1 is described below. To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 10. Metal layer A is the layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrode 50. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, wiring 40, and electrode 50 described above.

[0047] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, or pulsed laser deposition instead of magnetron sputtering.

[0048] Next, the metal layer 61 and the ceramic layer 62 are sequentially laminated on the lower surface 10b of the substrate 10. The metal layer 61 and the ceramic layer 62 can be formed, for example, by magnetron sputtering. Instead of magnetron sputtering, any of the above-mentioned film formation methods exemplified as methods for forming the metal layer A may be used to form the metal layer 61 and the ceramic layer 62.

[0049] Next, using a well-known photolithography method, the metal layer A is patterned into a planar shape similar to the resistor 30, wiring 40, and electrode 50 in Figure 1. At this time, since the ceramic layer 62 is present beneath the metal layer 61, etching of the metal layer 61 by the etching solution used for patterning can be prevented. In other words, the ceramic layer 62 also functions as an etching barrier layer for the metal layer 61.

[0050] Alternatively, a base layer may be formed on the upper surface 10a of the substrate 10 before forming the metal layer A. For example, a functional layer of a predetermined thickness may be vacuum-deposited on the upper surface 10a of the substrate 10 by conventional sputtering. By providing a base layer in this way, the gauge characteristics of the strain gauge 1 can be stabilized.

[0051] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 30). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen or moisture contained in the substrate 10, and / or the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer may further have other functions.

[0052] The insulating resin film constituting the base material 10 may contain oxygen and moisture, and Cr may form an oxidized film. Therefore, especially when metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of metal layer A.

[0053] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 is improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A improves the gauge characteristics in the strain gauge 1.

[0054] 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 these metals, or a compound of any of these metals.

[0055] Figure 3 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 3 shows the cross-sectional shape of the strain gauge 1 when a functional layer 20 is provided as a base layer for the resistor 30, wiring 40, and electrode 50.

[0056] The planar shape of the functional layer 20 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 30, the wiring 40, and the electrodes 50. However, the planar shapes of the functional layer 20 and the resistor 30, the wiring 40, and the electrodes 50 do not have to be substantially the same. For example, if the functional layer 20 is formed from an insulating material, the functional layer 20 may be patterned to be different from the planar shapes of the resistor 30, the wiring 40, and the electrodes 50. In this case, the functional layer 20 may be formed as a solid in the region where the resistor 30, the wiring 40, and the electrodes 50 are formed. Alternatively, the functional layer 20 may be formed as a solid over the entire upper surface of the substrate 10.

[0057] Through the above process, strain gauge 1 is completed. If necessary, a strain sensor may be fabricated by bonding the lower surface of the ceramic layer 62 of one or more strain gauges 1 to the first main surface 110a of the strain generating body 110 using the adhesive layer 120.

[0058] <Second Embodiment> The second embodiment shows an example of a strain gauge in which the position of the protective layer differs from that of the first embodiment. In the second embodiment, descriptions of components identical to those already described in the previously described embodiments may be omitted. Similarly, in the subsequent embodiments, descriptions of components identical to those already described in the previously described embodiments will not be repeated.

[0059] Figure 4 is a cross-sectional view illustrating a strain gauge according to the second embodiment. Referring to Figure 4, the strain gauge 2 includes a base material 10, a resistor 30, wiring 40, an electrode 50, a metal layer 71, a ceramic layer 72, an adhesive layer 73, a metal layer 74, a resin layer 75, and an adhesive layer 120. The adhesive layers 73 and 120 can be provided as needed. Although the wiring 40 is not shown in Figure 4, it can be placed in the same position as in Figure 1. The same applies to the following figures.

[0060] In other words, strain gauge 2 has a structure in which the metal layer 61 and ceramic layer 62 are removed from strain gauge 1, and a metal layer 71, ceramic layer 72, adhesive layer 73, metal layer 74, and resin layer 75 are added. The other side of the base material 10 can be bonded to the first main surface 110a of the strain generating body 110, for example, via the adhesive layer 120. In the example in Figure 4, the lower surface 10b of the base material 10 is bonded to the first main surface 110a of the strain generating body 110 via the adhesive layer 120.

[0061] The metal layer 71 can be placed on one side of the base material 10. In the example shown in Figure 4, the metal layer 71 is placed on the upper surface 10a of the base material 10. That is, the metal layer 71 is placed on the upper side of the base material 10 when viewed from the entire strain gauge 2. The metal layer 71 is a protective layer that protects the base material 10 and the resistor 30 etc. placed on it. The metal layer 71 may be placed on a part of the upper surface 10a of the base material 10, but in order to enhance its effectiveness as a protective layer, it is preferable to place it on the entire upper surface 10a of the base material 10.

[0062] In strain gauge 2, by placing a metal layer 71 on the upper surface 10a of the base material 10, moisture absorption and release from the upper surface 10a of the base material 10 can be suppressed. Therefore, the moisture resistance of strain gauge 2 can be improved. As a result, even when measuring strain in a high-humidity environment, noise components caused by humidity are reduced in strain gauge 2, so the strain of the strain generating body 110 can be measured with high accuracy.

[0063] Furthermore, by placing the metal layer 71 on the upper surface 10a of the base material 10, electrical noise superimposed on the resistor 30 can be reduced. As a result, the strain gauge 2 can accurately measure the strain of the strain generating body 110 because the electrical noise component is reduced even when measuring strain in an environment with a lot of electrical noise.

[0064] In particular, highly sensitive strain gauges with a gauge factor of 10 or higher using a Cr multiphase film are prone to noise components due to the influence of humidity and static electricity, which can easily reduce the measurement accuracy of the strain gauge 2. Therefore, the effect of placing a metal layer 71 is especially significant in highly sensitive strain gauges 2 with a gauge factor of 10 or higher using a Cr multiphase film.

[0065] Furthermore, by placing the metal layer 71 on the upper surface 10a of the base material 10, it is possible to prevent static charge buildup on the base material 10 and to equalize the heat distribution of the strain gauge 2.

[0066] The material of the metal layer 71 can be appropriately selected from the materials exemplified for the metal layer 61. The thickness of the metal layer 71 can be within the same range as that of the metal layer 61. The elastic modulus of the metal layer 71 is also within the same range as that of the metal layer 61. The metal layer 71 can be formed using the various film deposition methods exemplified for the metal layer 61. The material, thickness, elastic modulus, and other physical properties of the metal layer 61 and the metal layer 71 may be different or the same.

[0067] The ceramic layer 72 can be positioned on the opposite side of the metal layer 71 from the base material 10. That is, the ceramic layer 72 is positioned above the metal layer 71 when viewed from the entire strain gauge 2. In the example in Figure 4, the ceramic layer 72 is positioned on the upper surface of the metal layer 71. The ceramic layer 72 is insulating. The ceramic layer 72, together with the metal layer 71, constitutes a protective layer. The ceramic layer 72 may be positioned on a portion of the upper surface of the metal layer 71, but to enhance its protective effect, it is preferable to position it on the entire upper surface of the metal layer 71.

[0068] The material of the ceramic layer 72 can be appropriately selected from the materials exemplified for the ceramic layer 62. The thickness of the ceramic layer 72 can be within the same range as that of the ceramic layer 62. The elastic modulus of the ceramic layer 72 is also within the same range as that of the ceramic layer 62. The ceramic layer 72 can be formed using the various film deposition methods exemplified for the ceramic layer 62. The material, thickness, elastic modulus, and other physical properties of the ceramic layer 62 and the ceramic layer 72 may be different or the same.

[0069] In strain gauge 2, by making the protective layer a laminated structure of a metal layer 71 and a ceramic layer 72, moisture absorption and release from the upper surface 10a of the base material 10 can be further suppressed compared to when the protective layer is composed of only a metal layer 71. Therefore, the moisture resistance of strain gauge 2 can be further improved. In addition, in strain gauge 2, by placing an insulating ceramic layer 72 between the metal layer 71 and the resistor 30, wiring 40, and electrode 50, short circuits between the metal layer 71 and the resistor 30, wiring 40, and electrode 50 can be prevented.

[0070] The resistor 30, wiring 40, and electrode 50 can be positioned on the opposite side of the ceramic layer 72 from the base material 10. That is, the resistor 30, wiring 40, and electrode 50 are positioned on the upper side of the ceramic layer 72 when viewed from the entire strain gauge 2. In the example in Figure 4, the resistor 30, wiring 40, and electrode 50 are positioned on the upper surface of the ceramic layer 72. The aforementioned functional layer may be placed between the resistor 30, wiring 40, and electrode 50 of the strain gauge 2 and the ceramic layer 72.

[0071] The metal layer 74 is positioned on the opposite side of the ceramic layer 72 from the substrate 10 and can cover the resistor 30. In the example in Figure 4, the adhesive layer 73 is positioned on the upper surface of the ceramic layer 72, and the metal layer 74 is positioned on the upper surface of the adhesive layer 73. The metal layer 74 is bonded to the upper surface of the ceramic layer 72 by the adhesive layer 73 and indirectly covers the resistor 30, wiring 40, and electrode 50 via the adhesive layer 73. That is, the metal layer 74 is positioned above the ceramic layer 72 and the resistor 30 (and wiring 40) when viewed from the entire strain gauge 2 and covers at least the upper side of the resistor (and wiring 40). The material of the adhesive layer 73 can be appropriately selected from the materials exemplified as the material of the adhesive layer 120, as an insulating material.

[0072] The metal layer 74 is a protective layer that protects the substrate 10 and the resistor 30 placed thereon. The metal layer 74 may be placed together with the adhesive layer 73 on a part of the upper surface of the ceramic layer 72, but in order to enhance its protective effect, it is preferable to place it together with the adhesive layer 73 on the entire exposed portion of the upper surface of the ceramic layer 72 and the resistor 30.

[0073] The material of the metal layer 74 can be appropriately selected from the materials exemplified for the material of the metal layer 61. The thickness of the metal layer 74 can be within the same range as that of the metal layers 61 and 71. The elastic modulus of the metal layer 71 is also within the same range as that of the metal layer 61. By arranging the metal layer 71 and the ceramic layer 72 on the upper surface 10a of the substrate 10, and further arranging the metal layer 74 that covers the resistor 30 via the adhesive layer 73, the moisture-proof effect and noise reduction effect can be further enhanced. Note that the materials, thickness, elastic modulus, and other physical properties of the metal layers 61 and 71 and the metal layer 74 may be different or the same.

[0074] The resin layer 75 can be positioned on the opposite side of the metal layer 74 from the base material 10. That is, the resin layer 75 is positioned above the metal layer 74 when viewed from the entire strain gauge 2. In the example in Figure 4, the resin layer 75 is positioned on the upper surface of the metal layer 74. The resin layer 75 can prevent corrosion and scratches of the metal layer 74. The resin layer 75 may be positioned on a portion of the upper surface of the metal layer 74, but to enhance the protective effect of the metal layer 74, it is preferable to position it on the entire upper surface of the metal layer 74.

[0075] Examples of materials for the resin layer 75 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The thickness of the resin layer 75 can be, for example, about 2 μm to 50 μm. The material of the resin layer 75 may be the same as or different from the material of the base material 10.

[0076] To arrange the adhesive layer 73, the metal layer 74, and the resin layer 75, for example, a film is prepared in which the resin layer 75 is laminated on one side of the metal layer 74 and the adhesive layer 73 is laminated on the other side of the metal layer 74. Then, with the adhesive layer 73 facing the resistor 30, the wiring 40, and the electrode 50, the film is attached to the upper surface of the ceramic layer 72.

[0077] Alternatively, a film may be prepared in which a resin layer 75 is laminated on one side of a metal layer 74. In this case, an uncured adhesive, which will become an adhesive layer 73, is applied to the upper surface of the ceramic layer 72 so as to cover the resistor 30, wiring 40, and electrode 50. Then, with the metal layer 74 facing the adhesive, the film is placed on top of the adhesive, and the adhesive is cured to form the adhesive layer 73.

[0078] Alternatively, a first film may be prepared in which an adhesive layer 73 is laminated on one side of the metal layer 74, and a second film may be prepared in which an adhesive layer is laminated on one side of the resin layer 75. In this case, the first film is attached to the upper surface of the ceramic layer 72 with the adhesive layer 73 facing the resistor 30, wiring 40, and electrode 50. Furthermore, the second film is attached to the upper surface of the metal layer 74 with the adhesive layer facing the metal layer 74.

[0079] Furthermore, the adhesive layer 73, the metal layer 74, and the resin layer 75 are provided with openings 73x that expose at least a portion of the electrode 50. Lead wires are connected to the electrode 50 exposed within the openings 73x, for example, by solder.

[0080] Figure 5 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the second embodiment. Referring to Figure 5, in strain gauge 2A, the adhesive layer 73, metal layer 74, and resin layer 75 extend from the upper surface 10a of the substrate 10 to the side surface of the substrate 10. The adhesive layer 73, metal layer 74, and resin layer 75 cover the ceramic layer 72, metal layer 71, and each side surface of the substrate 10. It is preferable that the adhesive layer 73, metal layer 74, and resin layer 75, which are positioned on the side surface of the substrate 10, reach the first main surface 110a of the strain generating body 110. That is, it is preferable that there are no portions exposed from the laminated structure of the adhesive layer 73, metal layer 74, and resin layer 75 on each side surface of the ceramic layer 72, metal layer 71, and substrate 10.

[0081] In this way, the metal layer 74 covers the upper surface 10a and side surfaces of the substrate 10 via the adhesive layer 73, thereby suppressing moisture absorption and release from the upper surface 10a and side surfaces of the substrate 10, and thus the moisture resistance of the strain gauge 2A can be further improved compared to the strain gauge 2.

[0082] <Third Embodiment> In the third embodiment, an example of a strain gauge with an additional protective layer compared to the first embodiment is shown.

[0083] Figure 6 is a cross-sectional view illustrating a strain gauge according to the third embodiment. Referring to Figure 6, the strain gauge 3 is obtained by adding an adhesive layer 73, a metal layer 74, and a resin layer 75 similar to those of the strain gauge 2A shown in Figure 5 to the strain gauge 1 shown in Figure 2, etc.

[0084] The metal layer 74 is positioned on one side of the substrate 10 via the adhesive layer 73, and the resistor 30 can be covered via the adhesive layer 73. In the example in Figure 6, the adhesive layer 73, the metal layer 74, and the resin layer 75 cover the upper surface 10a of the substrate 10, and further extend from the side of the upper surface 10a of the substrate 10 to the side of the substrate 10, covering the respective sides of the substrate 10, the metal layer 61, and the ceramic layer 62.

[0085] In this way, the metal layer 74 covers the upper surface 10a and side surfaces of the substrate 10 via the adhesive layer 73, thereby suppressing moisture absorption and release from the upper surface 10a and side surfaces of the substrate 10, and thus further improving the moisture resistance of the strain gauge 3 compared to the strain gauge 1.

[0086] Furthermore, the strain gauge 3 may have a structure in which the side surface of the base material 10 is exposed from the metal layer 74, similar to the strain gauge 2 shown in Figure 4. That is, in the strain gauge 3, the metal layer 74 may be placed only on the upper surface 10a of the base material 10 via the adhesive layer 73. In this case, since the metal layer 74 covers the upper surface 10a of the base material 10 via the adhesive layer 73, moisture absorption and release from the upper surface 10a of the base material 10 can be suppressed, and the moisture resistance of the strain gauge 3 can be further improved compared to the strain gauge 1.

[0087] <Fourth Embodiment> The fourth embodiment shows another example of a strain gauge with an additional protective layer compared to the first embodiment.

[0088] Figure 7 is a cross-sectional view illustrating a strain gauge according to the fourth embodiment. Referring to Figure 7, the strain gauge 4 is obtained by adding the metal layer 71 and ceramic layer 72 shown in Figure 4 as protective layers to the strain gauge 1 shown in Figure 2, etc. In other words, in addition to the configuration of the strain gauge 1, the strain gauge 4 has a metal layer 71 positioned on the side of the upper surface 10a of the base material 10, and a ceramic layer 72 positioned on the opposite side of the metal layer 71 from the base material 10. In the strain gauge 4, the resistor 30 is positioned on the opposite side of the ceramic layer 72 from the base material 10.

[0089] In this way, by covering the upper surface 10a of the substrate 10 with the metal layer 71 and the ceramic layer 72, moisture absorption and release from the upper surface 10a of the substrate 10 can be suppressed, thereby further improving the moisture resistance of the strain gauge 4 compared to the strain gauge 1.

[0090] <Fifth Embodiment> The fifth embodiment shows an example of a strain gauge in which an additional protective layer is added compared to the fourth embodiment.

[0091] Figure 8 is a cross-sectional view illustrating a strain gauge according to the fifth embodiment. Referring to Figure 8, strain gauge 5 is obtained by adding an adhesive layer 73, a metal layer 74, and a resin layer 75 similar to those of strain gauge 2A shown in Figure 5 to strain gauge 4 shown in Figure 7. In other words, strain gauge 5 is a combination of the configuration of strain gauge 1 shown in Figure 2, etc., and the configuration of strain gauge 2A shown in Figure 5. In the example in Figure 8, the adhesive layer 73, metal layer 74, and resin layer 75 cover the upper surface of ceramic layer 72 and further extend from the upper surface 10a side of the substrate 10 to the side side of the substrate 10, covering the respective side surfaces of ceramic layer 72, metal layer 71, substrate 10, metal layer 61, and ceramic layer 62.

[0092] In this way, the metal layer 74 covers the upper surface 10a and side surfaces of the substrate 10 via the adhesive layer 73, thereby suppressing moisture absorption and release from the upper surface 10a and side surfaces of the substrate 10, and thus further improving the moisture resistance of the strain gauge 5 compared to the strain gauge 4.

[0093] Furthermore, the strain gauge 5 may have a structure in which the side surface of the base material 10 is exposed from the metal layer 74, similar to the strain gauge 2 shown in Figure 4. That is, in the strain gauge 5, the metal layer 74 may be placed only on the upper surface 10a of the base material 10 via the adhesive layer 73. In this case, since the metal layer 74 covers the upper surface 10a of the base material 10 via the adhesive layer 73, moisture absorption and release from the upper surface 10a of the base material 10 can be suppressed, and the moisture resistance of the strain gauge 5 can be further improved compared to the strain gauge 4.

[0094] <Sixth Embodiment> In the sixth embodiment, an example of a strain gauge is shown in which the metal layers 61 and 71 are not provided in the strain gauge 4 of the fourth embodiment.

[0095] Figure 9 is a cross-sectional view illustrating a strain gauge 6 according to the sixth embodiment. Referring to Figure 9, the strain gauge 6 has a configuration in which the metal layers 61 and 71 are removed from the strain gauge 4 shown in Figure 7. That is, the strain gauge 6 has a base material 10, a ceramic layer 72 (third ceramic layer) disposed on one side of the base material 10, a resistor 30 disposed on the opposite side of the ceramic layer 72 from the base material 10, and a ceramic layer 62 (fourth ceramic layer) disposed on the other side of the base material 10.

[0096] In this way, by covering both the upper and lower surfaces of the substrate 10 with ceramic layers 62 and 72, moisture absorption and release from the upper and lower surfaces of the substrate 10 can be suppressed, thereby improving the moisture resistance of the strain gauge.

[0097] Furthermore, the sides of the base material 10 may be covered with the ceramic layers 62 and / or 72. By covering the sides of the base material 10 with the ceramic layers 62 and / or 72, moisture absorption and release from the sides of the base material 10 can be suppressed, thereby further improving the moisture resistance of the strain gauge.

[0098] <Seventh Embodiment> The seventh embodiment shows an example of a strain gauge in which an additional protective layer is added compared to the sixth embodiment. However, the protective layer in this embodiment differs from the protective layer shown in the fifth embodiment and the like in that it has a ceramic layer and a resin layer.

[0099] Figure 10 is a cross-sectional view illustrating a strain gauge 7 according to the seventh embodiment. Referring to Figure 10, the strain gauge 7 is the strain gauge 6 shown in Figure 9 with the addition of an adhesive layer 73, a ceramic layer 76, and a resin layer 75. The adhesive layer 73 and the resin layer 75 may be made of the same materials and have the same configuration as the strain gauge 2A shown in Figure 5. The ceramic layer 76 (fifth ceramic layer) has the same configuration as the metal layer 74 shown in Figure 5, except that the material of the metal layer 74 is changed from metal to ceramic. The material of the ceramic layer 76 may be selected from the same materials as the ceramic layers 62 and 72. The thickness of the ceramic layer 76 can be within the same range as the ceramic layers 62 and 72. The elastic modulus of the ceramic layer 76 is also within the same range as the ceramic layers 62 and 72. The ceramic layer 76 can be arranged using the various film deposition methods exemplified for the ceramic layers 62 and 72. Furthermore, the materials, thickness, elastic modulus, and other physical properties of the ceramic layer 76, ceramic layer 62, and ceramic layer 72 may be different or the same.

[0100] The strain gauge 7, in addition to the configuration of the strain gauge 6, includes a ceramic layer 76 positioned on one side of the base material 10 and covering the resistor 30, and a resin layer 75 positioned on the opposite side of the ceramic layer 76 from the base material 10. The ceramic layer 76 extends from one side of the base material 10 to the side surface of the base material 10, covering the sides of the base material 10, the ceramic layer 62, and the ceramic layer 72.

[0101] Furthermore, the strain gauge 7 may have a configuration in which the metal layer 74 of the strain gauge 2 shown in Figure 4 is replaced with a ceramic layer 76, that is, a structure in which the side surface of the base material 10 is exposed from the ceramic layer 76. In other words, in the strain gauge 7, the ceramic layer 76 may be placed only on the upper surface 10a of the base material 10 via the adhesive layer 73. In this case, by covering the upper surface 10a of the base material 10 with the ceramic layer 76 via the adhesive layer 73, moisture absorption and release from the upper surface 10a of the base material 10 can be suppressed.

[0102] <Variation 1> The strain gauge according to this disclosure may have a configuration in which the ceramic layer 62 or ceramic layer 72 is omitted from the strain gauge 6 shown in the sixth embodiment or the strain gauge 7 shown in the seventh embodiment. That is, the ceramic layer may be placed on either one side or the other side of the base material 10. By placing the ceramic layer on either the upper or lower side of the base material 10 in this way, the number of layers of the strain gauge can be reduced compared to the case where ceramic layers are placed on both sides, while suppressing moisture absorption and release of the base material 10 to some extent. In other words, a strain gauge can be realized that balances the simplification of the manufacturing process with the effect of preventing moisture absorption and release.

[0103] <Variation 2> The protective layer (protective layer including the ceramic layer 76) shown in the seventh embodiment may be implemented in combination with the strain gauge 1 according to the first embodiment, rather than the strain gauge 6 according to the sixth embodiment. In this case as well, it is possible to suppress moisture absorption and release from the upper surface 10a of the substrate 10.

[0104] Furthermore, the strain gauge 7 may be a strain gauge obtained by adding the protective layer shown in Figure 4 or Figure 5 to the strain gauge 6 according to the sixth embodiment. When a metal layer 74 (fourth metal layer) is used, similar to the case of the ceramic layer 76, moisture absorption and release from the upper surface 10a of the substrate 10 can be suppressed. Alternatively, the strain gauge 7 may include both the metal layer 74 and the ceramic layer 76 as protective layers. In this case, the order in which the metal layer 74 and the ceramic layer 76 are laminated does not matter, as long as the resistor 30, wiring 40, and electrode 50 are insulated from the metal layer 74 and the ceramic layer 76 by means of an adhesive layer 73 or the like.

[0105] Although preferred embodiments have been described in detail above, the strain gauge according to the present invention is not limited to the embodiments described above, and can be realized by making various modifications and substitutions to the embodiments described above without departing from the scope of the claims. [Explanation of symbols]

[0106] 1, 2, 2A, 3, 4, 5, 6, 7 Strain gauge, 10 Substrate, 10a Top surface, 10b Bottom surface, 20 Functional layer, 30 Resistor, 40 Wiring, 50 Electrode, 61, 71, 74 Metal layer, 62, 72, 76 Ceramic layer, 73, 120 Adhesive layer, 75 Resin layer, 110 Strain generating body, 110a First main surface

Claims

1. A resin base material, A first metal layer disposed on one side of the substrate, A first ceramic layer is disposed on the opposite side of the first metal layer from the substrate, A strain gauge comprising a resistor disposed on the opposite side of the first ceramic layer from the substrate.

2. A second metal layer is disposed on the opposite side of the first ceramic layer from the substrate and covers the resistor, The strain gauge according to claim 1, comprising a resin layer disposed on the opposite side of the second metal layer from the substrate.

3. The strain gauge according to claim 2, wherein the second metal layer extends from one side of the substrate to the side surface of the substrate, covering the first ceramic layer, the first metal layer, and each of the sides of the substrate.

4. A second ceramic layer is disposed on the opposite side of the first ceramic layer from the substrate and covers the resistor, The strain gauge according to claim 1, comprising a resin layer disposed on the opposite side of the second ceramic layer from the substrate.

5. The strain gauge according to claim 4, wherein the second ceramic layer extends from one side of the substrate to the side surface of the substrate, covering the first ceramic layer, the first metal layer, and each of the sides of the substrate.

6. A strain gauge according to any one of claims 1 to 5, It has a strain-generating body having a first main surface, A strain sensor in which the other side of the substrate is bonded to the first main surface.

Images