Strain gauge

Abstract

To provide a strain gauge that can suppress corrosion of the resistor and, consequently, stabilize the strain gauge. [Solution] A strain gauge according to one aspect of the present invention comprises a base material, a resistor formed in a predetermined pattern on the surface of the base material, a corrosion-preventive film formed on the upper surface of the resistor, and an electrode electrically connected to the resistor, wherein the corrosion-preventive film comprises a base material region formed on the upper surface of the resistor, and a surface region formed on the upper surface of the base material region and containing a compound based on the material constituting the base material region.

Description

Technical Field

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

Background Art

[0002] As a strain gauge, for example, a strain gauge including a base material, a resistor formed on the upper surface of the base material in a predetermined pattern, and an electrode electrically connected to the resistor is known. When an article to which the strain gauge is attached is strained, the strain gauge is also strained. 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. That is, the strain gauge can output the strain of the article as an electrical signal (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] By the way, the resistor of the strain gauge is likely to be corroded depending on the environment in which the strain gauge is used. Examples of corrosion include oxidation, sulfidation, etc. Examples of the environment in which the resistor is likely to be corroded include high temperature, high humidity, etc. When the resistor is corroded, the electrical characteristics of the strain gauge change. For example, even when the degree of strain is the same, the magnitude of the output electrical signal changes. Therefore, the stability of the strain gauge is impaired. Such a problem becomes particularly prominent when the strain gauge is used for a long time.

[0005] The present invention was made to solve the above problems, and its objective is to provide a strain gauge that can suppress corrosion of the resistor and, consequently, stabilize the output characteristics of the strain gauge. [Means for solving the problem]

[0006] (1) A strain gauge according to one aspect of the present disclosure comprises a base material, a resistor formed in a predetermined pattern on the surface of the base material, a corrosion-preventive film formed on the upper surface of the resistor, and an electrode electrically connected to the resistor, wherein the corrosion-preventive 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. [Brief explanation of the drawing]

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

[0008] The following examples illustrate embodiments for implementing the strain gauge according to the present invention, along with the drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments without departing from its spirit. In addition, in the above drawings, the dimensions of each component may be exaggerated or reduced, or hatching may be omitted, in order to facilitate understanding.

[0009] <First Embodiment> First, the configuration of the strain gauge 1a according to the first embodiment of this disclosure will be described based on Figures 1 to 3. Figure 1 is a perspective view showing the structure of the strain gauge 1a according to the first embodiment of this disclosure. Figure 2 is a cross-sectional view AA' of Figure 1, and Figure 3 is a cross-sectional view BB' of Figure 1.

[0010] The strain gauge 1a comprises a base material 10, an insulating layer 10a, a resistor 20, a corrosion-preventive film 30, an electrode 40, and a cover layer 50.

[0011] In the following explanation, for each part of strain gauges 1a to 1f, the direction in which the resistor 20 is provided, as viewed from the base material 10, will be referred to as "up," and the direction opposite to the up direction will be referred to as "down." Furthermore, the surface located above each part will be referred to as the "top surface," and the surface located below each part will be referred to as the "bottom surface." However, this definition of up and down is for convenience only, and strain gauges 1a to 1f can also be used upside down. Also, strain gauges 1a to 1f can be positioned at any angle to the object (detection target) for which strain is to be detected. Furthermore, a planar view refers to viewing the object in the direction normal to the top and bottom of the top surface of the base material 10. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0012] (base material) The base material 10 is a component that serves as a base layer for forming the resistor 20, etc. The base material 10 is, for example, a flat plate and has an upper surface and a lower surface. The base material 10 is also flexible. The Young's modulus of the base material 10 may be, for example, about 2.4 to 23.1 GPa at room temperature (about 23°C). The thickness of the base material 10 is not particularly limited and may be appropriately determined according to the intended use of the strain gauge 1a, etc. For example, the thickness of the base material 10 may be about 5 to 500 μm. A strain generating body may be joined to the lower surface of the base material 10 directly or via another component in any way. From the viewpoint of strain transmission from the surface of the strain generating body to the sensing part (described later) and / or dimensional stability against environmental changes, the thickness of the base material 10 is preferably in the range of 5 to 200 μm. From the viewpoint of insulation, the thickness of the base material 10 is preferably 10 μm or more. Furthermore, the shape of the base material 10 is not particularly limited and can be determined appropriately according to the intended use of the strain gauge 1a, for example, it may be a long shape.

[0013] Examples of materials for the base material 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 base material 10 is formed from an insulating resin film. The term "film" refers to a flexible material with a thickness of approximately 500 μm or less. When the base material 10 is formed from an insulating resin film, the insulating resin film may contain fillers and impurities. For example, the base material 10 may be formed from an insulating resin film containing fillers such as silica and alumina.

[0014] Examples of materials other than the resin of the base material 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO3, BaTiO3), etc. In addition to the above-mentioned crystalline materials, amorphous glass or the like may be used as the material of the base material 10. Further, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), stainless steel, titanium, etc. may be used.

[0015] Note that the coefficient of thermal expansion of the base material 10 is not particularly limited and may be appropriately determined according to the purpose of use of the strain gauge 1a, etc. The coefficient of thermal expansion of the base material 10 can be adjusted to an arbitrary value by adjusting the material of the base material 10. For example, when the base material 10 is made of PI resin, the coefficient of thermal expansion of the base material 10 is 1 to 40 ppm / K. When the base material 10 is made of PEEK resin, the coefficient of thermal expansion of the base material 10 is 1 to 115 ppm / K. When the base material 10 is made of PET resin, the coefficient of thermal expansion of the base material 10 is 15 to 92 ppm / K.

[0016] (Insulating layer) The insulating layer 10a is formed on the upper surface of the base material 10. The insulating layer 10a has an arbitrary configuration and may be omitted. For example, when the base material 10 is made of metal, the insulating layer 10a is formed on the upper surface of the base material 10 by natural oxidation of the metal. The insulating layer 10a may be intentionally formed on the upper surface of the base material 10. As the material of the insulating layer 10a at this time, compounds such as Si, Al, Cr, Ti, etc. may be used. In particular, the insulating layer 10a is preferably made of SiO2, SiN, Al2O3, etc. As a method of forming the insulating layer 10a on the upper surface of the base material 10, for example, in addition to the above-mentioned natural oxidation, methods such as chemical agents, heating, plasma oxidation, reactive sputtering, sol-gel method, and / or CVD method may be used to corrode (for example, oxidize) the metal.

[0017] (Resistor) The resistor 20 is a thin film formed in a predetermined pattern on the surface (upper surface) of the base material 10, and is a sensing part that causes 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 base material 10, or may be formed on the surface (upper surface) of the base material 10 via another layer (for example, the insulating layer 10a described above).

[0018] The resistor 20 includes a plurality of elongated portions and a plurality of folded-back portions (three in the example of FIG. 1). In the resistor 20, the plurality of elongated portions are juxtaposed with their longitudinal directions facing the same direction. And the plurality of folded-back portions connect the ends of adjacent elongated portions among the plurality of elongated portions alternately to connect each elongated portion in series. Thereby, the resistor 20 has a structure that is folded back in a zigzag 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.

[0019] One end portion in the longitudinal direction of the two outermost elongated portions 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 may be electrically connected to the resistor 20 via a wiring not shown. Note that the pattern of the resistor 20 is not limited to the above, and can be appropriately set according to the characteristics required for the strain gauge 1a and the like.

[0020] Examples of materials constituting the resistor 20 include transition metals (Ni, Cr, Fe), noble metals (Cu, Pd, Pt), alloys thereof, and materials optionally containing compounds thereof. For example, the resistor 20 can be formed from a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 20 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. A Cr multiphase film is a film in which Cr, CrN, and Cr2N are mixed. The Cr multiphase film may contain unavoidable 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, if the resistor 20 is composed of Cu-Ni, the resistor 20 may also contain other elements M, in which case the composition of the material constituting 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%)) Furthermore, if 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 also contain Cu-Ni with other crystalline structures. That is, the resistor 20 is composed of polycrystalline material and may also contain amorphous material.

[0023] Other materials applicable to the resistor 20 include Ge, Si, C, Ti, or materials containing these. Specifically, these include Cr-N, Ge, Ge-In, Ge-Ga, Ge-P, Pt, Pt-In, Cu, Ni-C, Si, Ti-CO, etc.

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

[0025] There are no particular restrictions on the thickness of the resistor 20, and it can be appropriately selected depending on the intended use of the strain gauge 1a. For example, the thickness of the resistor 20 can be approximately 30 to 500 nm. The width of the resistor 20 can be optimized to meet the required specifications such as resistance value and lateral sensitivity, and also take into account measures to prevent wire breakage, for example, it can be approximately 1 to 200 nm.

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

[0027] The method for manufacturing the resistor 20 is not particularly limited, 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 base material 10 (or 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 a straight line and can be in any pattern. The wiring can also have any width and length. Furthermore, the wiring may have a multilayer structure. The wiring is formed on the upper surface of the base material 10 by the same manufacturing method as the resistor 20.

[0029] (Corrosion-preventive coating) The corrosion-preventive film 30 is formed on the upper surface of the resistor 20. The corrosion-preventive film 30 suppresses corrosion of the resistor 20 through its surface region 30b. This stabilizes the strain gauge 1a. Examples of corrosion include oxidation and sulfidation. The corrosion-preventive film 30 includes a base region 30a formed on the upper surface of the resistor 20, and a surface region 30b formed on the upper surface of the base region 30a and containing a compound based on the material constituting the base region 30a.

[0030] Materials constituting the base region 30a include metals, alloys of the metal, and compounds thereof. The base region 30a contains at least one of these materials as the main material. Furthermore, as will be described later, the surface region 30b contains compounds based on the materials constituting the base region 30a. By constructing the corrosion prevention film 30 from such materials, the corrosion prevention film 30 can be formed in a process substantially similar to the pattern formation of the resistor 20. Therefore, the degree of freedom in the shape of the corrosion prevention film 30 is improved. Moreover, the corrosion prevention film 30 can be formed on the upper surface of the resistor 20 without complicating the manufacturing process of the strain gauge 1a. The base region 30a may be crystalline or amorphous.

[0031] The material constituting the base region 30a is preferably capable of forming a passivation layer. Examples of such materials include Al, Fe, Ni, Ti, Cr, Co, Mo, and their alloys. By constituting the base region 30a with these materials, a surface region 30b can be easily formed on the upper surface of the base region 30a. The material constituting the base region 30a is particularly preferably one that spontaneously combines with oxygen in the air (i.e., spontaneously oxidizes) and forms a passivation layer. By constituting the base region 30a with these materials, the base region 30a can spontaneously form a passivation layer, i.e., a surface region 30b. That is, even if the surface region 30b is damaged, if the base region 30a remains, the base region 30a exposed to the atmosphere can spontaneously oxidize and form a surface region 30b (i.e., it can self-repair). This makes it possible to more effectively suppress 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 less noble (i.e., has a larger negative ionization energy) than the material constituting the resistor. As a result, the substrate region 30a is corroded preferentially over the resistor 20, thereby more effectively suppressing the corrosion of the resistor 20. For example, if the resistor 20 is composed of Cu-Ni, it is preferable that the substrate region 30a is composed of Cr, Al, etc., which are less noble than Cu and Ni.

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

[0034] As described above, the surface region 30b contains compounds based on the material constituting the base region 30a. That is, the surface region 30b contains compounds formed by the combination of the material constituting the base region 30a (preferably the main material) and other substances. It is preferable that the surface region 30b contains compounds based on the material constituting the base 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. Of these, oxides are preferred because they are dense (amorphous) and stable. The surface region 30b may be composed of multiple types of compounds. This makes it possible to more effectively suppress corrosion of the resistor 20. Furthermore, the method for forming the surface region 30b is not limited to the natural oxidation of the base region 30a, but also includes heat treatment, chemical treatment, or electrochemical treatment of the base region 30a. For example, if the substrate region 30a contains Ti, a Ti compound, i.e., a surface region 30b, can be formed on the upper surface of the substrate region 30a by electrochemical treatment of the Ti in an acidic solution. Furthermore, if the substrate region 30a contains Al, an Al compound, i.e., a surface region 30b, can be formed on the upper surface of the substrate region 30a by anodizing treatment. By performing treatments other than natural oxidation, the surface region 30b can be made thicker. These treatments may also be performed in combination. This may result in a multilayer structure of the surface region 30b consisting of multiple types of compounds.

[0035] If a corrosion-preventive film 30 is not formed on the upper surface of the resistor 20, the resistor 20 will corrode from its upper surface upwards. The corrosion of the resistor 20 progresses in the thickness direction. When the resistor 20 corrodes, the electrical characteristics of the strain gauge change. On the other hand, as shown in Figure 1, by forming a corrosion-preventive 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 base material region 30a corrodes instead of the resistor 20, increasing the thickness of the surface region 30b, but once the surface region 30b reaches a certain thickness, the corrosion stops progressing further. This suppresses the corrosion of the resistor 20.

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

[0037] The corrosion-preventive film 30 may also be formed on the wiring and electrodes 40. However, as shown in Figure 3, when forming the corrosion-preventive film 30 on the electrodes 40, it is preferable to first place the electrodes 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 suppressing the current flow between the resistor 20 and the electrodes 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: Observe the cross-section of the corrosion-preventive film 30 using SEM-EDS or the like, and observe the composition of the cross-section. Then, define the boundary between the substrate region 30a and the surface region 30b as the portion where the compound constituting the surface region 30b is 50 wt% or more. The boundary does not necessarily have to be flat.

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

[0040] The thickness of the corrosion-preventive film 30 can be appropriately set according to the specifications of each part of the strain gauge 1a, such as the composition of the corrosion-preventive 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-preventive film 30 may be greater than 0 and 100 μm or less. In order to maintain the self-healing function of the corrosion-preventive film 30, it is preferable that the lower limit of the thickness of the corrosion-preventive film 30 be 1 nm or more. It is preferable that the upper limit of the thickness of the corrosion-preventive film 30 be 25 nm.

[0041] The thickness of the surface region 30b is determined according to the composition of the base region 30a or the method of forming the surface region 30b. 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, anodic oxidation), the thickness of the surface region 30b can increase to about 50 μm. In this case, it is necessary to form a base region 30a of sufficient thickness.

[0042] The ratio of the thickness of the substrate region 30a to the thickness of the resistor 20 is preferably within the range of 1:100 to 1:5. This is to avoid impairing the properties of the resistor 20. The thickness of the substrate region 30a can be measured in the same way as the thickness of the surface region 30b.

[0043] Furthermore, as shown in Figures 1 to 3, it is preferable that the side surface of the corrosion-preventive film 30 is substantially flush with the side surface of the resistor 20. This makes it possible to more reliably suppress corrosion of the resistor 20, especially corrosion from the upper surface of the resistor 20. Here, "side surface" refers to the surface that extends upward from the surface of the base material 10.

[0044] (electrode) As described above, the electrode 40 is provided at one end of the longitudinal direction of the two elongated portions located on the outermost side in the grid width direction. Of course, the placement of the electrode 40 is not limited to this.

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

[0046] The electrode 40 may be integrally formed from the same material as the resistor 20. Alternatively, a layer of a metal with low electrical resistivity, such as copper, or a layer of a metal with 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 insulating layer 10a), the upper surface of the wiring, and the upper surface of the corrosion-preventive 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 appropriately selected according to the protective purpose, such as preventing dust adhesion, preventing scratches, and providing moisture protection.

[0048] More specifically, the cover layer 50 is provided to cover the upper surface of the substrate 10 and the upper surface of the corrosion-preventive film 30 as needed, while 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, polyolefin resin). In addition, the cover layer 50 may be a metal layer or a ceramic layer. The cover layer 50 may also contain fillers and / or pigments. By providing the cover layer 50, mechanical damage to the substrate 10, resistor 20, wiring, and corrosion-preventive film 30 can be prevented. Furthermore, by providing the cover layer 50, the substrate 10, insulating layer 10a, resistor 20, wiring, and corrosion-preventive film 30 can be protected from moisture and other elements.

[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, mechanical damage to the resistor 20 and the like can be suppressed. In addition, by providing the cover layer 50, the resistor 20 and the like can be protected from moisture and the like.

[0050] As described above, according to the first embodiment, the corrosion-preventive film 30 can suppress the 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 become less prone to change. Therefore, even if the strain gauge 1a is used for a long period of time, for example, measurement errors due to aging can be reduced.

[0051] <Second Embodiment> Next, the configuration of the strain gauge 1b according to the second embodiment of the present invention will be described based on Figure 4. Note that the configuration similar to that of the first embodiment will not be described. Figure 4 is a cross-sectional view of the strain gauge 1b according to the second embodiment (corresponding to the AA' cross-section in Figure 1). As shown in Figure 4, the corrosion prevention film 30 may be formed to cover the sides of the resistor 20 (and the sides of the portion where the electrode 40 is provided). If the strain gauge 1b has wiring, the corrosion prevention film 30 may also be formed to cover the sides of the wiring. According to the second embodiment, since the corrosion prevention film 30 can also protect the sides of the resistor 20, corrosion of the resistor 20 can be suppressed more reliably.

[0052] <Third Embodiment> Next, the configuration of the strain gauge 1c according to the third embodiment of the present invention will be described based on Figure 5. Note that the configuration similar to that of the first embodiment will not be described. Figure 5 is a cross-sectional view of the strain gauge 1c according to the third embodiment (corresponding to the AA' cross-section in Figure 1). As shown in Figure 5, the base material region 30a of the corrosion prevention film 30 covers the upper and side surfaces of multiple elongated parts of the resistor 20 collectively, and the surface region 30b may be formed on the upper and side surfaces of the base material region 30a. According to the third embodiment, since the base material region 30a is formed collectively on the upper and side surfaces of multiple elongated parts, the manufacturing of the corrosion prevention film 30 becomes easier. Furthermore, since the corrosion prevention film 30 can also protect the side surfaces of the resistor 20, corrosion of the resistor 20 can be suppressed more reliably.

[0053] <Fourth Embodiment> Next, the configuration of the strain gauge 1d according to the fourth embodiment of the present invention will be described based on Figure 6. Note that the configuration similar to that of the first embodiment will not be described. Figure 6 is a cross-sectional view of the strain gauge 1d according to the fourth embodiment (corresponding to the AA' cross-section in Figure 1). As shown in Figure 6, the strain gauge 1d is an integral form of the strain gauge 1b according to the second embodiment, with adjacent corrosion-preventive films 30 integrated together. According to the fourth embodiment, the corrosion-preventive film 30 can also protect the sides of the resistor 20, thus more reliably suppressing corrosion of the resistor 20.

[0054] <Fifth Embodiment> Next, the configuration of the strain gauge 1e according to the fifth embodiment of the present invention will be described with reference to Figure 7. Note that the configuration similar to that of the first embodiment will not be described. Figure 7 is a cross-sectional view of the strain gauge 1e according to the fifth embodiment (corresponding to the AA' cross-section in Figure 1). As shown in Figure 7, in the strain gauge 1e, compared to the strain gauge 1b according to the second embodiment, the side surface of the corrosion-preventive 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 base material 10 (and insulating layer 10a). According to the fifth embodiment, since the corrosion-preventive film 30 can also protect the side surface of the resistor 20, corrosion of the resistor 20 can be suppressed more reliably.

[0055] <Sixth Embodiment> Next, the configuration of the strain gauge 1f according to the sixth embodiment of the present invention will be described based on Figure 8. Note that the configuration similar to that of the first embodiment will not be described. Figure 8 is a perspective view of the strain gauge 1f according to the sixth embodiment. As shown in Figure 8, in the strain gauge 1f, the cover layer 50 is provided to cover the entire upper surface except for the upper surface of the electrode 40. The thickness of the electrode 40 may be thicker than the cover layer 50 (i.e., protruding from the cover layer 50) or thinner (i.e., placed within the cover layer 50). Note that by making the electrode 40 protrude from the cover layer 50, it becomes easier to electrically connect the strain gauge 1f to other members. Note that there are no particular limitations on the shape of the opening in the cover layer 50 that exposes the electrode 40; it may be any shape such as a circle or a rectangle. According to the sixth embodiment, since the cover layer 50 is provided to cover the entire upper surface except for the upper surface of the electrode 40, each component of the strain gauge 1f can be protected more reliably.

[0056] Although the present invention has been described above with reference to the above embodiments, the present invention is not limited thereto.

[0057] For example, the configurations shown in Figures 1 to 8 may be combined in any way. An example of such a combination is to form a corrosion-preventive film 30 as shown in any of Figures 4 to 7, and then to 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. Such modifications, insofar as they still possess the configuration of the present invention, are of course included within the scope of the present invention. [Explanation of symbols]

[0059] 1a-1f Strain gauge, 10 Substrate, 10a Insulating layer, 20 Resistor, 30 Corrosion prevention film, 30a Substrate area, 30b Surface area, 40 Electrode, 50 Cover layer

Claims

1. Substrate and A resistor formed in a predetermined pattern on the surface of the substrate, A corrosion-preventive film formed on the upper surface of the resistor, The resistor comprises an electrode electrically connected to the resistor, The strain gauge is characterized in that the corrosion-preventive 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.

2. The strain gauge according to claim 1, characterized in that the material constituting the base region is one or more selected from metals, alloys of the metals, and compounds thereof.

3. The strain gauge according to claim 2, characterized in that the material constituting the base region is capable of forming a passivation layer.

4. The strain gauge according to claim 1 or 2, characterized in that the material constituting the base region is less noble than the material constituting the resistor.

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

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

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

8. The strain gauge according to claim 1 or 2, characterized in that the side surface of the corrosion-preventive film is substantially flush with the side surface of the resistor.

9. The strain gauge according to claim 1 or 2, characterized in that the corrosion-preventive film further covers the side surface of the resistor.

10. The strain gauge according to claim 9, characterized in that the surface of the portion of the corrosion-preventive film that covers the side surface of the resistor is substantially flush with the side surface of the base material.

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