Strain gauge

Abstract

Provided is a strain gauge that is capable of suppressing corrosion of a resistor and is thus stabilized.　A strain gauge according to an aspect of the present invention is characterized by comprising a base material, a resistor formed in a predetermined pattern on a surface of the base material, a corrosion prevention film formed on an upper surface of the resistor, and an electrode electrically connected to the resistor, wherein the corrosion prevention film comprises: a base region formed on the upper surface of the resistor; and a surface region formed on an upper surface of the base region and containing a compound based on a material constituting the base region.

Description

strain gauge

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

[0002] A known strain gauge includes, for example, a substrate, a resistor formed in a predetermined pattern on the upper surface of the substrate, and electrodes electrically connected to the resistor. When an object to which the strain gauge is attached is strained, the strain gauge also strains. When the strain gauge is strained, the resistance value of the resistor changes. As a result, when a constant voltage is applied to the strain gauge, the current value output from the strain gauge fluctuates. In other words, the strain gauge can output the strain of the object as an electrical signal (see, for example, Patent Document 1).

[0003] JP 2016-085088 A

[0004] The resistor in a strain gauge is susceptible to corrosion depending on the environment in which the strain gauge is used. Examples of corrosion include oxidation and sulfurization. Examples of environments in which resistors are susceptible to corrosion include high temperatures and high humidity. When the resistor corrodes, the electrical characteristics of the strain gauge change. For example, the magnitude of the electrical signal output changes even if the degree of strain remains the same. This reduces the stability of the strain gauge. This problem becomes particularly pronounced when strain gauges are used for long periods of time.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a strain gauge that can suppress corrosion of the resistor and thereby stabilize the output characteristics of the strain gauge.

[0006] (1): A strain gauge according to one aspect of the present disclosure is a strain gauge comprising a substrate, a resistor formed in a predetermined pattern on the surface of the substrate, a corrosion prevention film formed on the upper surface of the resistor, and an electrode electrically connected to the resistor, wherein the corrosion prevention film comprises a base region formed on the upper surface of the resistor, and a surface region formed on the upper surface of the base region and containing a compound based on the material constituting the base region.

[0007] FIG. 1 is a perspective view showing the structure of a strain gauge according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA' in FIG. 1. FIG. 3 is a cross-sectional view taken along line BB' in FIG. 1. FIG. 4 is a cross-sectional view of a strain gauge according to a second embodiment of the present invention. FIG. 5 is a cross-sectional view of a strain gauge according to a third embodiment of the present invention. FIG. 6 is a cross-sectional view of a strain gauge according to a fourth embodiment of the present invention. FIG. 7 is a cross-sectional view of a strain gauge according to a fifth embodiment of the present invention. FIG. 8 is a perspective view of a strain gauge according to a sixth embodiment of the present invention.

[0008] Below, embodiments for carrying out the strain gauge according to the present invention are illustrated with reference to the drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be modified or improved from the following embodiments without departing from the spirit of the present invention. Furthermore, in the drawings, the dimensions of each component may be exaggerated or reduced, and hatching may be omitted, in order to facilitate understanding.

[0009] First Embodiment First, the configuration of a strain gauge 1a according to a first embodiment of the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is a perspective view showing the structure of the strain gauge 1a according to the first embodiment of the present disclosure. Figure 2 is a cross-sectional view taken along line AA' in Figure 1, and Figure 3 is a cross-sectional view taken along line BB' in Figure 1.

[0010] The strain gauge 1 a includes a substrate 10 , an insulating layer 10 a , a resistor 20 , a corrosion prevention film 30 , electrodes 40 , and a cover layer 50 .

[0011] In the following description, in each of the strain gauges 1a to 1f, the direction in which the resistor 20 is provided as viewed from the substrate 10 is referred to as "upper," and the direction opposite to the upper direction is referred to as "lower." Furthermore, the surface located on the upper side of each portion is referred to as the "upper surface," and the surface located on the lower side of each portion is referred to as the "lower surface." However, this definition of upper and lower is for convenience, and the strain gauges 1a to 1f can also be used upside down. Furthermore, the strain gauges 1a to 1f can be positioned at any angle relative to the object (detection target) whose strain is to be detected. Furthermore, a planar view refers to viewing the object in the normal direction from above to below the top surface of the substrate 10. Furthermore, a planar shape refers to the shape of the object when viewed in the normal direction.

[0012] (Substrate) The substrate 10 is a member that serves as a base layer for forming the resistor 20 and the like. The substrate 10 is, for example, flat and has an upper surface and a lower surface. The substrate 10 is also flexible. The Young's modulus of the substrate 10 may be, for example, approximately 2.4 to 23.1 GPa at room temperature (approximately 23°C). The thickness of the substrate 10 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1a. For example, the thickness of the substrate 10 may be approximately 5 to 500 μm. A strain generator may be bonded to the lower surface of the substrate 10 by any method, either directly or via another member. From the perspectives of strain transmission from the surface of the strain generator to the sensing part (described below) and / or dimensional stability against environmental changes, the thickness of the substrate 10 is preferably within the range of 5 to 200 μm. From the perspective of insulation, the thickness of the substrate 10 is preferably 10 μm or greater. The shape of the substrate 10 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1a, and may be elongated, for example.

[0013] Examples of materials for the substrate 10 include PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, and polyolefin resin. More preferably, the substrate 10 is formed from an insulating resin film. Note that a film refers to a flexible material with a thickness of approximately 500 μm or less. When the substrate 10 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, and the like. For example, the substrate 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0014] Examples of materials other than resin for the substrate 10 include SiO ２ , ZrO ２ (including YSZ), Si, Si ２ N ３ , Al ２ O ３ (including sapphire), ZnO, perovskite ceramics (CaTiO ３ , BaTiO ３ Examples of the material for the substrate 10 include crystalline materials such as aluminum, aluminum alloy (duralumin), stainless steel, and titanium. In addition to the crystalline materials described above, amorphous glass or the like may also be used as the material for the substrate 10. The material for the substrate 10 may also be a metal such as aluminum, an aluminum alloy (duralumin), stainless steel, or titanium.

[0015] The thermal expansion coefficient of the substrate 10 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1a, etc. The thermal expansion coefficient of the substrate 10 can be adjusted to any value by adjusting the material of the substrate 10. For example, if the substrate 10 is made of PI resin, the thermal expansion coefficient of the substrate 10 is 1 to 40 ppm / K. If the substrate 10 is made of PEEK resin, the thermal expansion coefficient of the substrate 10 is 1 to 115 ppm / K. If the substrate 10 is made of PET resin, the thermal expansion coefficient of the substrate 10 is 15 to 92 ppm / K.

[0016] (Insulating Layer) The insulating layer 10a is formed on the upper surface of the substrate 10. The insulating layer 10a may have any configuration and may be omitted. For example, when the substrate 10 is made of a metal, the insulating layer 10a is formed on the upper surface of the substrate 10 by natural oxidation of the metal. The insulating layer 10a may also be intentionally formed on the upper surface of the substrate 10. In this case, the material of the insulating layer 10a may be a compound of Si, Al, Cr, Ti, or the like. In particular, the insulating layer 10a may be made of SiO ２ , SiN, Al ２ O ３ As a method for forming the insulating layer 10a on the upper surface of the base material 10, for example, in addition to the natural oxidation described above, metal may be corroded (e.g., oxidized) using a method such as chemicals, heating, plasma oxidation, reactive sputtering, a sol-gel method, and / or a CVD method.

[0017] (Resistor) The resistor 20 is a thin film formed in a predetermined pattern on the surface (upper surface) of the substrate 10, and is a sensing part that generates a change in resistance value when the strain gauge 1a is strained. The resistor 20 may be formed directly on the surface (upper surface) of the substrate 10, or may be formed on the surface (upper surface) of the substrate 10 via another layer (for example, the above-mentioned insulating layer 10a).

[0018] The resistor 20 includes a plurality of elongated portions and a plurality of folded portions (three in the example of FIG. 1 ). In the resistor 20, the plurality of elongated portions are arranged side by side with their longitudinal directions oriented in the same direction. The folded portions alternately connect the ends of adjacent elongated portions among the plurality of elongated portions, connecting the elongated portions in series. This gives the resistor 20 a zigzag folded structure as a whole. The longitudinal direction of the plurality of elongated portions corresponds to the grid direction, and the direction perpendicular to the grid direction corresponds to the grid width direction.

[0019] One longitudinal end of each of the two elongated portions located at the outermost sides in the grid width direction is electrically connected to the electrode 40. In the example shown in Fig. 1, the electrode 40 is formed on the upper surface of the resistor 20 via the corrosion prevention film 30, but it may also be electrically connected to the resistor 20 via wiring (not shown). The pattern of the resistor 20 is not limited to the above and can be set as appropriate depending on the characteristics required of the strain gauge 1a.

[0020] Examples of materials that constitute the resistor 20 include transition metals (Ni, Cr, Fe), noble metals (Cu, Pd, Pt), alloys of these, and materials that optionally contain compounds of these. For example, the resistor 20 can be made of a material that contains Cr (chromium), a material that contains Ni (nickel), or a material that contains both Cr and Ni. That is, the resistor 20 can be made of a material that contains at least one of Cr and Ni. Examples of materials that contain Cr include Cr mixed phase films. The Cr mixed phase film is a film made of Cr, CrN, and Cr. ２ It is a film containing a mixed phase of N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium). Of these, Cu-Ni and Ni-Cr are particularly preferred.

[0021] Furthermore, when the resistor 20 is made of Cu—Ni, the resistor 20 may further contain another element M. In this case, the composition of the material that makes up the resistor 20 is shown below.

[0022] Cu １００－ｘ－ｙ Ni ｘ M ｙ (25≦x≦75, 0≦y≦27.5, 25≦x+y<100 (wt %)) When the resistor 20 contains Cu—Ni, the Cu—Ni contained in the resistor 20 mainly has a face-centered cubic structure or an Al-type structure. However, the resistor 20 may contain Cu—Ni with other crystal structures. In other words, the resistor 20 is made of polycrystal and may contain amorphous.

[0023] Other materials that can be used for the resistor 20 include Ge, Si, C, Ti, and materials containing these, such as Cr—N, Ge, Ge—In, Ge—Ga, Ge—P, Pt, Pt—In, Cu, Ni—C, Si, and Ti—C—O.

[0024] The resistivity of the resistor 20 is not particularly limited.

[0025] The thickness of the resistor 20 is not particularly limited and can be selected appropriately depending on the intended use of the strain gauge 1a, etc. For example, the thickness of the resistor 20 can be about 30 to 500 nm. The width of the resistor 20 can be optimized for required specifications such as resistance value and lateral sensitivity, and can be about 1 to 200 nm, for example, taking into consideration measures against wire breakage.

[0026] The gauge factor of the strain gauge 1 is preferably 5 or less, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR are preferably within the range of -500 ppm / °C to +500 ppm / °C.

[0027] There are no particular limitations on the method for manufacturing the resistor 20, and any known manufacturing method can be applied. For example, the resistor 20 is formed on the surface (upper surface) of the substrate 10 by sputtering, wet etching, or the like.

[0028] (Wiring) The resistor 20 and the electrode 40 may be electrically connected by wiring. The wiring is provided on the upper surface of the substrate 10 (or the insulating layer 10a). One end of the wiring is electrically connected to both ends of the resistor 20 (i.e., both ends of the resistor 20), and the other end is electrically connected to the electrode 40. The resistor 20 and the wiring may be integrally formed from the same material. The wiring is not limited to being linear and can have any pattern. The wiring can have any width and any length. The wiring may also have a multi-layer structure. The wiring is formed on the upper surface of the substrate 10 by the same manufacturing method as the resistor 20.

[0029] (Corrosion-preventing film) The corrosion-preventing film 30 is formed on the upper surface of the resistor 20. The corrosion-preventing film 30 suppresses corrosion of the resistor 20 by the surface region 30b. This stabilizes the strain gauge 1a. Examples of corrosion include oxidation and sulfidation. The corrosion-preventing film 30 includes a substrate region 30a formed on the upper surface of the resistor 20, and a surface region 30b formed on the upper surface of the substrate region 30a and containing a compound based on the material that constitutes the substrate region 30a.

[0030] Materials constituting the substrate region 30a include metals, alloys of those metals, and compounds thereof. The substrate region 30a contains at least one of these materials as a primary material. As described below, the surface region 30b contains a compound based on the material constituting the substrate region 30a. By forming the corrosion-resistant film 30 from such a material, the corrosion-resistant film 30 can be formed using a process substantially similar to the pattern formation of the resistor 20. This improves the degree of freedom in the shape of the corrosion-resistant film 30. Furthermore, the corrosion-resistant film 30 can be formed on the upper surface of the resistor 20 without complicating the manufacturing process of the strain gauge 1a. The substrate region 30a may be crystalline or amorphous.

[0031] The material constituting the substrate region 30a is preferably capable of forming a passivation state. Examples of such materials include Al, Fe, Ni, Ti, Cr, Co, Mo, and alloys thereof. By forming the substrate region 30a from these materials, the surface region 30b can be easily formed on the upper surface of the substrate region 30a. The material constituting the substrate region 30a is preferably one that naturally bonds with oxygen in the air (i.e., naturally oxidizes) to form a passivation state. By forming the substrate region 30a from these materials, the substrate region 30a can naturally form a passivation state, i.e., a surface region 30b. In other words, even if the surface region 30b is damaged, as long as the substrate region 30a remains, the substrate region 30a exposed to the air can naturally oxidize and form the surface region 30b (i.e., self-repair). This more effectively suppresses corrosion of the resistor 20.

[0032] Furthermore, it is preferable that the material constituting the substrate region 30a has the same ionization tendency as the material constituting the resistor, or is more noble than the material constituting the resistor (i.e., has a more negative ionization energy). This allows the substrate region 30a to corrode preferentially over the resistor 20, thereby more effectively suppressing corrosion of the resistor 20. For example, if the resistor 20 is made of Cu-Ni, it is preferable that the substrate region 30a be made of Cr, Al, or the like, which is more noble than Cu and Ni.

[0033] Furthermore, it is preferable that the resistance value of the substrate region 30a is equal to or greater than the resistance value of the resistor 20. This allows a larger current to flow through the resistor 20, thereby making the strain gauge 1a more stable.

[0034] As described above, the surface region 30b includes a compound based on the material constituting the substrate region 30a. That is, the surface region 30b includes a compound formed by combining the material constituting the substrate region 30a (preferably the main material) with other substances. The surface region 30b preferably includes a compound based on the material constituting the substrate region 30a as its main component (50 wt% or more of the total mass of the surface region 30b). Examples of such compounds include oxides, sulfides, nitrides, hydroxides, etc. Among these, oxides are preferred because they are dense (amorphous) and stable. The surface region 30b may be composed of multiple types of compounds. This can more effectively suppress corrosion of the resistor 20. Furthermore, the method of forming the surface region 30b is not limited to natural oxidation of the substrate region 30a, but may also include heat treatment, chemical treatment, or electrochemical treatment of the substrate region 30a. For example, if the substrate region 30a contains Ti, electrochemical treatment of the Ti in an acidic solution can form a Ti compound, i.e., the surface region 30b, on the upper surface of the substrate region 30a. Furthermore, if the substrate region 30a contains Al, anodizing can form an Al compound, i.e., the surface region 30b, on the upper surface of the substrate region 30a. Treatments other than natural oxidation can be used to form a thicker surface region 30b. These treatments may also be combined. This may result in the surface region 30b having a multilayer structure composed of multiple types of compounds.

[0035] If the corrosion prevention film 30 is not formed on the upper surface of the resistor 20, the resistor 20 will corrode from its upper surface. The corrosion of the resistor 20 will then progress in the thickness direction. When the resistor 20 corrodes, the electrical characteristics of the strain gauge will change. On the other hand, as shown in FIG. 1 , by forming the corrosion prevention film 30 on the upper surface of the resistor 20, the resistor 20 can be isolated from environmental factors and corrosion of the resistor 20 can be suppressed. Specifically, the substrate region 30a corrodes instead of the resistor 20, and the thickness of the surface region 30b increases, but once the surface region 30b reaches a certain thickness, corrosion will no longer progress. This suppresses corrosion of the resistor 20.

[0036] The corrosion prevention film 30 is formed on all or part of the upper surface of the resistor 20. When the corrosion prevention film 30 is formed on part of the upper surface of the resistor 20, it is preferable to form the corrosion prevention film 30 on the folded portion 20a of the resistor 20 where corrosion is likely to occur.

[0037] The corrosion prevention film 30 may also be formed on the wiring or the electrode 40. However, as shown in Fig. 3, when forming the corrosion prevention film 30 on the electrode 40, it is preferable to first provide the electrode 40 on the substrate region 30a, and then corrode the upper surface of the substrate region 30a to form the surface region 30b. This is to avoid inhibiting the flow of electricity between the resistor 20 and the electrode 40.

[0038] The substrate region 30a and the surface region 30b may or may not have a layered structure. The boundary between the substrate region 30a and the surface region 30b can be identified, for example, by the following method. That is, a cross section of the corrosion prevention film 30 is observed using SEM-EDS or the like, and the composition of the cross section is observed. Then, the portion where the compound that makes up the surface region 30b is 50 wt % or more is determined to be the boundary between the substrate region 30a and the surface region 30b. The boundary does not necessarily have to be flat.

[0039] It is preferable that the modulus of elasticity of the substrate region 30a is approximately equal to the modulus of elasticity of the resistor 20, and the modulus of elasticity of the surface region 30b is equal to or greater than the modulus of elasticity of the substrate region 30a. The modulus of elasticity here is, for example, the modulus of elasticity at room temperature (approximately 23°C).

[0040] The thickness of the corrosion-preventing film 30 may be set appropriately depending on the specifications of each part of the strain gauge 1a, such as the composition of the corrosion-preventing film 30, the composition of the resistor 20, the shape of the resistor 20, and the thickness of the resistor. For example, the thickness of the corrosion-preventing film 30 may be greater than 0 and less than or equal to 100 μm. Here, in order to maintain the self-repair function of the corrosion-preventing film 30, the lower limit of the thickness of the corrosion-preventing film 30 is preferably 1 nm or more. The upper limit of the thickness of the corrosion-preventing film 30 is preferably 25 nm.

[0041] The thickness of the surface region 30b is determined depending on the composition of the base region 30a, the method for forming the surface region 30b, etc. If the boundary between the base region 30a and the surface region 30b is not flat, the thickness of the surface region 30b can be measured at multiple locations and averaged. For example, if the base region 30a is composed of Fe, Ni, Cr, or an alloy thereof, the thickness of the surface region 30b will be 1 to 20 nm. Furthermore, if the base region 30a is composed of Al, Ti, or an alloy thereof and the surface region 30b is formed by electrochemical treatment (more specifically, anodization), the thickness of the surface region 30b will be approximately 50 μm. In this case, the base region 30a must be formed to a sufficient thickness.

[0042] The ratio of the thickness of the substrate region 30a to the thickness of the resistor 20 is preferably within a range of 1:100 to 1:5, in order not to impair the characteristics of the resistor 20. The thickness of the substrate region 30a may be measured in the same manner as the thickness of the surface region 30b.

[0043] 1 to 3, the side surfaces of the corrosion prevention film 30 are preferably substantially flush with the side surfaces of the resistor 20. This more reliably suppresses corrosion of the resistor 20, particularly corrosion from the upper surface of the resistor 20. Here, "side surfaces" refers to surfaces extending upward from the surface of the substrate 10.

[0044] As described above, the electrodes 40 are provided at one end in the longitudinal direction of the two elongated portions located on the outermost sides in the grid width direction. Of course, the installation position of the electrodes 40 is not limited to this.

[0045] The electrode 40 is provided on the upper surface of the corrosion prevention film 30. The electrode 40 is electrically connected to the resistor 20. The electrode 40 may be electrically connected to the resistor 20 via wiring. The electrode 40 is wider than the wiring in a plan view and is formed in any shape, such as a substantially rectangular or substantially circular shape. The electrodes 40 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 20 caused by strain. For example, a lead wire for external connection is joined to the electrode 40. The joining method is not particularly limited, and the lead wire may be joined to the upper surface of the electrode 40 by soldering, for example.

[0046] The electrode 40 may be formed integrally with the resistor 20 using the same material. Alternatively, a metal layer having low electrical resistivity such as copper or a metal layer having good solderability such as gold may be laminated on the upper surface of the electrode 40.

[0047] (Cover Layer) The cover layer 50 is provided so as to cover the upper surface of the substrate 10 (or the insulating layer 10a), the upper surface of the wiring, and the upper surface of the corrosion prevention film 30. The cover layer 50 has an optional configuration and may be omitted. In the first embodiment, the cover layer 50 does not cover the electrode 40 and its surrounding area. The material of the cover layer 50 may be selected appropriately depending on the protection purpose, such as preventing dust adhesion, scratches, and moisture.

[0048] More specifically, the cover layer 50 is provided as needed to cover the upper surface of the substrate 10 and the upper surface of the corrosion-resistant film 30, exposing the electrodes 40. Examples of materials for the cover layer 50 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). Alternatively, the cover layer 50 may be a metal layer or a ceramic layer. The cover layer 50 may contain a filler and / or a pigment. The provision of the cover layer 50 can prevent mechanical damage, etc., from occurring to the substrate 10, resistor 20, wiring, and corrosion-resistant film 30. Furthermore, the provision of the cover layer 50 can protect the substrate 10, insulating layer 10a, resistor 20, wiring, and corrosion-resistant film 30 from moisture, etc.

[0049] The thickness of the cover layer 50 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the cover layer 50 can be about 2 to 30 μm. By providing the cover layer 50, it is possible to prevent mechanical damage to the resistor 20 and the like. Furthermore, by providing the cover layer 50, it is possible to protect the resistor 20 and the like from moisture and the like.

[0050] As described above, according to the first embodiment, the corrosion prevention film 30 can suppress oxidation of the resistor 20 (i.e., protect the resistor 20), thereby stabilizing the strain gauge 1a. In other words, the electrical characteristics of the strain gauge 1a are less likely to change. Therefore, even if the strain gauge 1a is used for a long period of time, for example, it is possible to reduce measurement errors due to deterioration over time.

[0051] Second Embodiment Next, the configuration of a strain gauge 1b according to a second embodiment of the present invention will be described with reference to FIG. 4. Note that a description of the same configuration as in the first embodiment will be omitted. FIG. 4 is a cross-sectional view (corresponding to the AA′ cross section in FIG. 1) of the strain gauge 1b according to the second embodiment. As shown in FIG. 4, the corrosion prevention film 30 may be formed so as to cover the side surface of the resistor 20 (and the side surface of the portion where the electrode 40 is provided). If the strain gauge 1b has wiring, the corrosion prevention film 30 may be formed so as to cover the side surface of the wiring. According to the second embodiment, the corrosion prevention film 30 can also protect the side surface of the resistor 20, thereby more reliably suppressing corrosion of the resistor 20.

[0052] Third Embodiment Next, the configuration of a strain gauge 1c according to a third embodiment of the present invention will be described with reference to FIG. 5 . Note that a description of the same configuration as in the first embodiment will be omitted. FIG. 5 is a cross-sectional view (corresponding to the AA′ cross section in FIG. 1 ) of the strain gauge 1c according to the third embodiment. As shown in FIG. 5 , the substrate region 30a of the corrosion-preventing film 30 may collectively cover the upper and side surfaces of the multiple elongated portions of the resistor 20, and the surface region 30b may be formed on the upper and side surfaces of the substrate region 30a. According to the third embodiment, the substrate region 30a is collectively formed on the upper and side surfaces of the multiple elongated portions, which facilitates the manufacture of the corrosion-preventing film 30. Furthermore, the corrosion-preventing film 30 can also protect the side surfaces of the resistor 20, thereby more reliably suppressing corrosion of the resistor 20.

[0053] Fourth Embodiment Next, the configuration of a strain gauge 1d according to a fourth embodiment of the present invention will be described with reference to FIG. 6. Note that a description of the same configuration as in the first embodiment will be omitted. FIG. 6 is a cross-sectional view (corresponding to cross section AA' in FIG. 1) of the strain gauge 1d according to the fourth embodiment. As shown in FIG. 6, the strain gauge 1d is the strain gauge 1b according to the second embodiment, in which adjacent corrosion prevention films 30 are integrated. According to the fourth embodiment, the corrosion prevention film 30 can also protect the side surface of the resistor 20, thereby more reliably suppressing corrosion of the resistor 20.

[0054] Fifth Embodiment Next, the configuration of a strain gauge 1e according to a fifth embodiment of the present invention will be described with reference to FIG. 7 . Description of the same configuration as in the first embodiment will be omitted. FIG. 7 is a cross-sectional view (corresponding to the AA′ cross section in FIG. 1 ) of the strain gauge 1e according to the fifth embodiment. As shown in FIG. 7 , the strain gauge 1e differs from the strain gauge 1b according to the second embodiment in that the side surface of the corrosion-preventing film 30 covering the outermost elongated portion (the surface of the portion covering the side surface of the resistor 20) is flush with the side surface of the substrate 10 (and the insulating layer 10a). According to the fifth embodiment, the corrosion-preventing film 30 can also protect the side surface of the resistor 20, thereby more reliably suppressing corrosion of the resistor 20.

[0055] Sixth Embodiment Next, the configuration of a strain gauge 1f according to a sixth embodiment of the present invention will be described with reference to FIG. 8 . Note that a description of the same configuration as in the first embodiment will be omitted. FIG. 8 is a perspective view of the strain gauge 1f according to the sixth embodiment. As shown in FIG. 8 , in the strain gauge 1f, the cover layer 50 is provided to cover the entire upper surface except for the upper surfaces of the electrodes 40. The electrodes 40 may be thicker than the cover layer 50 (i.e., protruding from the cover layer 50) or thinner (i.e., disposed within the cover layer 50). Protruding the electrodes 40 from the cover layer 50 facilitates electrical connection of the strain gauge 1f to other components. The shape of the opening in the cover layer 50 through which the electrodes 40 are exposed is not particularly limited and may be any shape, such as circular or rectangular. According to the sixth embodiment, the cover layer 50 is provided to cover the entire upper surface except for the upper surfaces of the electrodes 40, thereby more reliably protecting each component of the strain gauge 1f.

[0056] Although the present invention has been described above using the above embodiment as an example, the present invention is not limited to this.

[0057] For example, any of the configurations shown in Figures 1 to 8 may be combined. An example of such a combination is to form a corrosion prevention film 30 as shown in any of Figures 4 to 7, and then form a cover layer 50 as shown in Figure 8.

[0058] Those skilled in the art can modify the strain gauge of the present invention as appropriate in accordance with conventionally known knowledge. As long as the configuration of the present invention is still maintained even after such modification, it is of course included in the scope of the present invention.

[0059] 1a to 1f: strain gauge, 10: substrate, 10a: insulating layer, 20: resistor, 30: corrosion prevention film, 30a: substrate region, 30b: surface region, 40: electrode, 50: cover layer

Claims

1. A strain gauge comprising: a substrate; a resistor formed in a predetermined pattern on the surface of the substrate; a corrosion-resistant film formed on the upper surface of the resistor; and an electrode electrically connected to the resistor, wherein the corrosion-resistant film comprises a base region formed on the upper surface of the resistor; and a surface region formed on the upper surface of the base region and containing a compound based on the material that constitutes the base region.

2. A strain gauge according to claim 1, characterized in that the material constituting the base region is at least one selected from the group consisting of metals, alloys of said metals, and compounds thereof.

3. The strain gauge according to claim 2, wherein the material constituting the substrate region is capable of forming a passivation state.

4. A strain gauge according to claim 1 or 2, characterized in that the material constituting said substrate region is more base-based than the material constituting said resistor.

5. A strain gauge according to claim 1 or 2, characterized in that the resistance value of said substrate region is equal to or greater than the resistance value of said resistor.

6. A strain gauge according to claim 1 or 2, characterized in that the surface region contains a plurality of types of compounds.

7. A strain gauge according to claim 1 or 2, characterized in that the modulus of elasticity of said substrate region is approximately equal to the modulus of elasticity of said resistor, and the modulus of elasticity of said surface region is equal to or greater than the modulus of elasticity of said substrate region.

8. A strain gauge according to claim 1 or 2, wherein the side surface of the corrosion prevention film is substantially flush with the side surface of the resistor.

9. The strain gauge according to claim 1 or 2, wherein the corrosion prevention film further covers the side surface of the resistor.

10. A strain gauge as described in claim 9, wherein the surface of the portion of the corrosion prevention film covering the side surface of the resistor is substantially flush with the side surface of the substrate.

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