Strain gauge

Abstract

To provide a strain gauge capable of reducing noise superimposed on a resistor.SOLUTION: The gauge has a flexible base material, a resistor formed on one side of the base material directly or through another layer, a conductive layer formed on the other side of the base material, and an insulation layer formed on the opposite side of the conductive layer from the base material. The resistor is formed from a material containing at least one of chromium and nickel.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain of the object. The strain gauge has a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni). The resistor is formed on a substrate made of insulating resin, for example (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional strain gauges, the noise superimposed on the resistor is relatively large, which leads to a decrease in measurement accuracy.

[0005] The present invention has been made in view of the above points, and has an object to provide a strain gauge that can reduce noise superimposed on a resistor. [Means for solving the problem]

[0006] This strain gauge has a flexible substrate, a resistor formed on one side of the substrate directly or via another layer, a conductive layer formed on the other side of the substrate, and an insulating layer formed on the conductive layer on the side opposite the substrate, wherein the resistor is formed from a material containing at least one of chromium and nickel, and the insulating layer is formed from a material different from that of the substrate. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge that can reduce noise superimposed on a resistor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 3] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment. [Figure 5] FIG. 2 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 6] FIG. 10 is a cross-sectional view illustrating a strain gauge according to a second modification of the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view illustrating a strain gauge according to a third modified example of the first embodiment. [Figure 8] FIG. 10 is a cross-sectional view illustrating a strain gauge according to a fourth modified example of the first embodiment. [Figure 9] FIG. 10 is a diagram showing the results of noise measurement in an example and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment Fig. 1 is a plan view illustrating a strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, a terminal portion 41, and a conductive layer 50.

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0012] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[0013] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member with a thickness of about 500 μm or less.

[0014] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0015] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strain is applied. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 with a matte finish.

[0016] 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. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0017] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0019] By forming the resistor 30 on the functional layer 20, the resistor 30 can be formed using a stable crystalline phase, thereby improving the stability of the gauge characteristics (gauge factor, temperature coefficient of gauge factor TCS, and temperature coefficient of resistance TCR).

[0020] For example, when the resistor 30 is a Cr mixed-phase film, providing the functional layer 20 allows the resistor 30 to be formed with α-Cr (alpha chromium) as the main component. α-Cr has a stable crystalline phase, which can improve the stability of the gauge characteristics. Here, "main component" means that the target substance accounts for 50% by mass or more of all materials constituting the resistor. When the resistor 30 is a Cr mixed-phase film, from the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0021] Furthermore, when the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0022] Furthermore, the ratio of Cr2N in CrN and Cr2N is preferably 80% or more and less than 90%, and more preferably 90% or more and less than 95%. When the ratio of Cr2N in CrN and Cr2N is 90% or more and less than 95%, the Cr2N has semiconducting properties, which leads to a more significant decrease in TCR (negative TCR). Furthermore, by reducing ceramic formation, brittle fracture is reduced.

[0023] On the other hand, if trace amounts of N2 or atomic N are mixed into or present in the film, they will escape to the outside of the film due to external conditions (such as high temperature environments), causing changes in film stress.By creating chemically stable CrN, the unstable N mentioned above will not be generated, and a stable strain gauge can be obtained.

[0024] The terminal portions 41 extend from both ends of the resistor 30 and are formed in a generally rectangular shape wider than the resistor 30 in a plan view. The terminal portions 41 are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and are connected to, for example, lead wires for external connection. For example, the resistor 30 extends from one of the terminal portions 41 while folding back in a zigzag pattern and is connected to the other terminal portion 41. The upper surface of the terminal portion 41 may be coated with a metal that has better solderability than the terminal portion 41. Although the resistor 30 and the terminal portion 41 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0025] The conductive layer 50 is formed on the lower surface 10b of the substrate 10. The conductive layer 50 is a layer formed to reduce noise superimposed on the resistor, and is made of a material with higher electrical conductivity than the substrate 10. By forming the conductive layer 50 on the lower surface 10b of the substrate 10 and reducing the noise superimposed on the resistor, it is possible to suppress a decrease in the measurement accuracy of the strain gauge 1.

[0026] Forming the conductive layer 50 on the lower surface 10b of the substrate 10 provides the advantage of reducing variations in the TCR value and the output voltage when strain is applied, for example, when measuring in an environment where static electricity or other noise is likely to occur (e.g., low humidity). In particular, highly sensitive strain gauges using Cr mixed-phase films and having a gauge factor of 10 or more are susceptible to static electricity generated from the object being measured, such as a motor, due to their high sensitivity, and static electricity accumulation in the substrate can easily cause measurement errors and variations in the output voltage. Therefore, the effect of forming the conductive layer 50 is particularly pronounced in highly sensitive strain gauges using Cr mixed-phase films and having a gauge factor of 10 or more.

[0027] It is preferable that the conductive layer 50 is electrically connected to the reference potential (GND). Alternatively, when the strain gauge 1 is attached to the flexure element, the conductive layer 50 may be set to the same potential as the flexure element. Either case is advantageous for noise reduction.

[0028] The conductive layer 50 can be formed of, for example, a metal, an alloy, or a laminated film of a metal and / or an alloy. More specifically, examples of the material for the conductive layer 50 include Cu, Ni, Al, Ag, Au, Pt, Pd, Sn, Cr, and the like, an alloy of any of these metals, or a laminated film in which any of these metals or alloys are appropriately laminated. The material for the conductive layer 50 may be the same as that for the resistor 30 (for example, a Cr mixed-phase film).

[0029] Alternatively, as long as the material is conductive, the material of the conductive layer 50 may be an oxide film such as tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), or antimony-doped tin oxide (ATO), or a resin film containing a conductive filler.

[0030] The thickness of the conductive layer 50 can be, for example, 0.1 μm or more and 5 μm or less. By making the thickness of the conductive layer 50 0.1 μm or more, a sufficient noise reduction effect can be obtained. By making the thickness of the conductive layer 50 5 μm or less, the conductive layer 50 can be easily formed without cracking.

[0031] Furthermore, by forming a conductive layer 50 on the lower surface 10b of the substrate 10, the effects of preventing the substrate 10 from becoming charged, the effects of uniforming the heat distribution of the strain gauge 1, and the effects of preventing the substrate 10 from absorbing water are obtained.

[0032] For example, a process may be performed in which an insulating resin film that will become the substrate 10 is unwound from a roll and subjected to a predetermined treatment. In this case, if the conductive layer 50 is not formed, when the insulating resin film is unwound from the roll, the inside and outside of the roll of the insulating resin film will peel off, generating static electricity and charging the surface of the insulating resin film. This charging of the surface of the insulating resin film will cause contaminants to adhere to the surface of the insulating resin film, resulting in a decrease in yield. By forming the conductive layer 50 on the lower surface 10b of the substrate 10, it is possible to prevent the substrate 10 from becoming charged, thereby suppressing the adhesion of contaminants to the surface of the substrate 10. Note that the upper surface 10a of the substrate 10 is prevented from becoming charged by the resistor 30.

[0033] The sheet resistance of the conductive layer 50 is 10 4At [Ω / □] or less, it will no longer be charged, and 10 8 ~10 4 [Ω / □] makes it difficult to charge, and 10 11 ~10 8 At [Ω / □], the conductive layer 50 will be charged, but the charge can be attenuated. To obtain an anti-static effect, it is preferable to take these points into consideration and appropriately select the sheet resistance of the conductive layer 50 depending on the handling environment, etc. The sheet resistance can be adjusted by changing the film thickness of the conductive layer 50.

[0034] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the terminal portions 41.

[0035] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0036] To manufacture the strain gauge 1, first, the substrate 10 is prepared, and the conductive layer 50 is formed on the lower surface 10b of the substrate 10. The material and thickness of the conductive layer 50 are as described above. The conductive layer 50 can be formed on the lower surface 10b of the substrate 10, for example, by laminating rolled foil. The conductive layer 50 may also be formed on the lower surface 10b of the substrate 10 by sputtering, plating, or other methods. By first forming the conductive layer 50 on the lower surface 10b of the substrate 10 in this way, it is possible to prevent the substrate 10 from becoming charged, even if a roll is used in a later process, and the adhesion of contaminants to the surface of the substrate 10 can be suppressed.

[0037] Next, the resistor 30 and terminal portion 41 having the planar shape shown in Fig. 1 are formed on the upper surface 10a of the substrate 10. The material and thickness of the resistor 30 and terminal portion 41 are as described above. The resistor 30 and terminal portion 41 can be integrally formed from the same material.

[0038] The resistor 30 and the terminal portion 41 can be formed, for example, by depositing a film by magnetron sputtering using a target made of a material capable of forming the resistor 30 and the terminal portion 41, and then patterning the film by photolithography. Instead of magnetron sputtering, the resistor 30 and the terminal portion 41 may also be deposited by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0039] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-form a functional layer having a film thickness of about 1 nm to 100 nm by, for example, conventional sputtering as a base layer on the upper surface 10a of the substrate 10 before forming the resistor 30 and the terminal portion 41. After the resistor 30 and the terminal portion 41 are formed on the entire upper surface of the functional layer, the functional layer is patterned together with the resistor 30 and the terminal portion 41 into the planar shape shown in FIG.

[0040] In this application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper layer, the resistor 30. The functional layer preferably also has a function of preventing oxidation of the resistor 30 due to oxygen or moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer may also have other functions.

[0041] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the resistor 30, especially when the resistor 30 contains Cr.

[0042] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the resistor 30, and can be appropriately selected depending on the purpose. For example, 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), Examples of suitable metals include one or more metals selected from the group consisting of 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), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0043] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2. 2、 Examples include Cr2O3, CrN, and Cr2N.

[0044] Among the above metals and metal compounds, it is particularly preferable to use Cr2O3, CrN, Cr2N, Ti, TiO2, Ta2O5, NiCr, Ni, SiO2, and Si3N4, because the use of these materials has the effect of promoting uniform crystal growth of the resistor 30.

[0045] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 5 or less of the thickness of the resistor, which can promote the crystal growth of α-Cr and prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[0046] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 10 or less of the thickness of the resistor, which can promote the crystal growth of α-Cr and further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[0047] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 100 or less of the thickness of the resistor, which further prevents a portion of the current flowing through the resistor from flowing through the functional layer, thereby further preventing a decrease in strain detection sensitivity.

[0048] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracks.

[0049] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0050] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.5 μm, which promotes the crystal growth of α-Cr and allows for easier film formation without cracking.

[0051] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. If the functional layer is made of an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid state at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the substrate 10.

[0052] Furthermore, when the functional layer is made of an insulating material, the thickness of the functional layer is made relatively thick, between 0.05 μm and 1 μm, and the functional layer is made solid. This increases the thickness and surface area of ​​the functional layer, allowing heat generated by the resistor to be dissipated to the substrate 10. As a result, the deterioration of measurement accuracy in the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0053] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0054] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0055] There are no particular restrictions on the combination of the material of the functional layer with the material of the resistor 30 and the terminal portion 41, and it can be selected appropriately depending on the purpose. For example, it is possible to use Ti for the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component for the resistor 30 and the terminal portion 41.

[0056] In this case, for example, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering using a target made of a material capable of forming a Cr mixed phase film and introducing Ar gas into a chamber. Alternatively, the resistor 30 and the terminal portion 41 can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas into a chamber together with Ar gas. In this case, the ratios of CrN and CrN contained in the Cr mixed phase film and the ratio of CrN in CrN and CrN can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the nitrogen gas introduced or by adjusting the heating temperature in a heating step.

[0057] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0058] When the resistor 30 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the resistor 30, preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the resistor 30. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0059] In this way, by providing a functional layer below the resistor 30, it is possible to promote crystal growth of the resistor 30, and to produce a resistor 30 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material that constitutes the functional layer into the resistor 30, it is possible to improve the gauge characteristics of the strain gauge 1.

[0060] After forming the resistor 30 and the terminal portions 41, a cover layer 60 that covers the resistor 30 and exposes the terminal portions 41 is provided on the upper surface 10a of the substrate 10 as needed, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41, and then heating and curing the resin.

[0061] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlying layer for the resistor 30 and the terminal portion 41, the strain gauge 1 has a cross-sectional shape as shown in Fig. 3. The layer indicated by the reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is the same as that shown in Fig. 1.

[0062] 4, a functional layer 20 may be provided on the upper surface 10a of the substrate 10, and a functional layer 21 may be provided on the lower surface 10b of the substrate 10. In this case, the functional layers 20 and 21 may be formed to the same thickness from the same material, and the resistor 30, the terminal portion 41, and the conductive layer 50 may be formed to the same thickness from the same material. With this structure, the layer structures above and below the substrate 10 are approximately symmetrical, thereby reducing warping of the strain gauge 1.

[0063] The term "same thickness" used here refers to the same thickness by design, and includes cases where the thickness varies due to manufacturing variations. Even in such cases, the effect of reducing warpage of the strain gauge 1 can be obtained.

[0064] <Modification 1 of the First Embodiment> Modification 1 of the first embodiment shows an example of a strain gauge having a layer structure different from that of Embodiment 1. Note that in Modification 1 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0065] Fig. 5 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the first embodiment. Referring to Fig. 5, strain gauge 1A differs from strain gauge 1 (see Figs. 1, 2, etc.) in that it has an insulating layer 70 made of an inorganic material on the lower surface 10b side of the substrate 10, and a conductive layer 50 is laminated on the insulating layer 70 on the side opposite to the substrate 10.

[0066] The insulating layer 70 is formed directly on the lower surface 10b of the substrate 10. Examples of materials for the insulating layer 70 include oxides, nitrides, and oxynitrides of metals such as Cu, Cr, Ni, Al, Fe, W, Ti, and Ta, and alloys containing these metals. Oxides, nitrides, and oxynitrides of semiconductors such as Si and Ge may also be used as materials for the insulating layer 70. The thickness of the insulating layer 70 can be, for example, about 0.01 μm to 2 μm.

[0067] The method for forming the insulating layer 70 is not particularly limited and can be selected appropriately depending on the purpose, but examples include vacuum processes such as sputtering, plating, and chemical vapor deposition (CVD), and solution processes such as spin coating and sol-gel.

[0068] By forming the insulating layer 70, current flows through the resistor 30, generating heat, and the heat transferred to the substrate 10 can be efficiently transferred to the conductive layer 50 and dissipated from the conductive layer 50. As a result, it is possible to suppress a decrease in measurement accuracy in the strain gauge due to self-heating of the resistor 30.

[0069] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows another example of a strain gauge having a layer structure different from that of Embodiment 1. Note that in Modification 2 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0070] Fig. 6 is a cross-sectional view illustrating a strain gauge according to Modification 2 of the first embodiment. Referring to Fig. 6, strain gauge 1B differs from strain gauge 1 (see Figs. 1, 2, etc.) in that conductive layers are formed on both sides of substrate 10.

[0071] The strain gauge 1B has a conductive layer 50 formed on the lower surface 10b of the substrate 10, a conductive layer 51 formed on the upper surface 10a of the substrate 10, and an insulating layer 71 laminated on the conductive layer 51 on the side opposite the substrate 10. The resistor 30 and the terminal portion 41 are laminated on the insulating layer 71 on the side opposite the conductive layer 51.

[0072] The material and thickness of the conductive layer 51 can be appropriately selected from the range of materials and thicknesses exemplified for the conductive layer 50 in the first embodiment. However, the material and thickness of the conductive layer 51 may be the same as or different from the material and thickness of the conductive layer 50. The material and thickness of the insulating layer 71 can be appropriately selected from the range of materials and thicknesses exemplified for the insulating layer 70 in Modification 1 of the first embodiment.

[0073] In this way, conductive layers may be formed on both sides of the substrate 10. This can improve the effects of reducing noise generated between the terminal portions 41, preventing static buildup on the substrate 10, uniforming the heat distribution of the strain gauge 1B, and preventing water absorption by the substrate 10 compared to when a conductive layer is provided on one side of the substrate 10.

[0074] In strain gauge 1B, insulating layer 70 may be formed between lower surface 10b of substrate 10 and the upper surface of conductive layer 50, similar to strain gauge 1A.

[0075] <Modification 3 of the First Embodiment> Modification 3 of the first embodiment shows yet another example of a strain gauge having a layer structure different from that of Embodiment 1. Note that in Modification 3 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0076] Fig. 7 is a cross-sectional view illustrating a strain gauge according to Modification 3 of the first embodiment. Referring to Fig. 7, strain gauge 1C differs from strain gauge 1B (see Fig. 6) in that it has an insulating layer 72 formed on the upper surface 10a of substrate 10, and a conductive layer 51 is laminated on the side of insulating layer 72 opposite to substrate 10. Strain gauge 1C also differs from strain gauge 1B (see Fig. 6) in that it has an insulating layer 70 on the lower surface 10b of substrate 10, and a conductive layer 50 is laminated on the side of insulating layer 70 opposite to substrate 10.

[0077] The material and thickness of the insulating layer 72 can be appropriately selected from the range of materials and thicknesses exemplified for the insulating layer 70 in Modification 1 of the first embodiment. However, the materials and thicknesses of the insulating layers 70, 71, and 72 may be the same or different.

[0078] In this way, insulating layers may be formed on both sides of the substrate 10. This provides the effect of improving the shape stability of the substrate.

[0079] <Fourth Modification of the First Embodiment> Modification 4 of the first embodiment shows yet another example of a strain gauge having a layer structure different from that of Embodiment 1. Note that in Modification 4 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0080] Fig. 8 is a cross-sectional view illustrating a strain gauge according to Modification 4 of the first embodiment. Referring to Fig. 8, strain gauge 1D differs from strain gauge 1B (see Fig. 6) in that an insulating layer 73 is laminated on the conductive layer 50 on the side opposite to the substrate 10.

[0081] The material and thickness of the insulating layer 73 can be appropriately selected from the range of materials and thicknesses exemplified for the insulating layer 70 in Modification 1 of the first embodiment. However, the materials and thicknesses of the insulating layers 71 and 73 may be the same or different.

[0082] For example, the conductive layers 50 and 51 may be formed from the same metal, and the insulating layers 71 and 73 may be formed from an oxide of the metal that constitutes the conductive layers 50 and 51. Specifically, the conductive layers 50 and 51 may be formed from Al, and the insulating layers 71 and 73 may be formed from an oxide of Al. In this case, the conductive layer 51 made of Al is formed on the upper surface 10a of the substrate 10, the conductive layer 50 made of Al is formed on the lower surface 10b of the substrate 10, and then heat treatment is performed to form the insulating layer 71 made of Al2O3 on the upper surface side of the conductive layer 51 and the insulating layer 73 made of Al2O3 on the lower surface side of the conductive layer 50. Because the conductive layers 50 and 51 are made of the same material, the insulating layers 71 and 73 formed by heat treatment have the same thickness.

[0083] For example, if the conductive layers 50 and 51 are formed of Al to the same thickness, the combined thickness of the conductive layer 51 and the insulating layer 71 will be the same as the combined thickness of the conductive layer 50 and the insulating layer 73, and the layer structures above and below the substrate 10 will be approximately symmetrical, thereby reducing warping of the strain gauge 1D.

[0084] The conductive layers 50 and 51 may be formed by laminating rolled foil or by sputtering or plating. However, when using Al, a thin film formed by sputtering or plating is preferable to rolling. When Al is rolled, it becomes anisotropic, which makes the gauge characteristics unstable in highly sensitive strain gauges using Cr mixed-phase films. In contrast, Al formed as a thin film has increased isotropy, which alleviates longitudinal and lateral stresses, reducing the variation in gauge characteristics between samples and improving yield.

[0085] [Example 1] First, a full bridge circuit was fabricated using the strain gauge 1 shown in Figure 1. A polyimide film with a thickness of approximately 25 μm was used as the substrate 10, a Cr mixed phase film with a thickness of approximately 0.2 μm was used as the resistor 30, and an Al film with a thickness of approximately 0.5 μm was used as the conductive layer 50. No cover layer 60 was formed.

[0086] As a comparative example, a strain gauge was fabricated by removing the conductive layer 50 from the strain gauge 1 shown in Fig. 1 (for convenience, referred to as strain gauge 1X). In strain gauge 1X, the materials and thicknesses of the substrate 10 and resistor 30 were the same as those of the above-mentioned strain gauge 1.

[0087] Next, for strain gauges 1 and 1X, a constant voltage source and a voltmeter were used as measuring instruments to measure noise at the terminals of the output terminals of the bridge circuit.

[0088] The results of noise measurement are shown in Figure 9. Figure 9(a) shows the measurement results for strain gauge 1X, and Figure 9(b) shows the measurement results for strain gauge 1. From Figure 9, it was confirmed that the strain gauge 1 on which the conductive layer 50 is formed has a significantly reduced noise peak level compared to the strain gauge 1X on which the conductive layer 50 is not formed.

[0089] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0090] For example, the strain gauges 1A, 1B, and 1C may be provided with functional layers 20 and 21. [Explanation of symbols]

[0091] 1, 1A, 1B, 1C, 1D strain gauge, 10 substrate, 10a upper surface, 10b lower surface, 20, 21 functional layer, 30 resistor, 41 terminal portion, 50, 51 conductive layer, 60 cover layer, 70, 71, 72, 73 insulating layer

Claims

1. a flexible substrate; a resistor formed on one side of the substrate directly or via another layer; a conductive layer formed on the other side of the substrate; an insulating layer formed on the conductive layer opposite to the substrate, the resistor is formed from a material containing at least one of chromium and nickel, The strain gauge, wherein the insulating layer is formed from a material different from that of the substrate.

2. The strain gage of claim 1 , further comprising a second conductive layer formed between the substrate and the resistor.

3. 3. The strain gauge of claim 2, further comprising a second insulating layer formed between the second conductive layer and the resistor.

4. the conductive layer is made of any one of a metal, an alloy, and a laminated film of a metal and / or an alloy; 4. The strain gauge according to claim 1, wherein the insulating layer is made of any one of an oxide of a metal, an alloy, or a semiconductor, a nitride of a metal, an alloy, or a semiconductor, and an oxynitride of a metal, an alloy, or a semiconductor.

5. a flexible substrate; a resistor formed on one side of the substrate directly or via another layer; a second conductive layer formed between the substrate and the resistor; a second insulating layer formed between the second conductive layer and the resistor; the resistor is formed from a material containing at least one of chromium and nickel, The second insulating layer is formed from a material different from that of the substrate.

6. The strain gage of claim 5 further comprising a conductive layer formed on the other side of the substrate.

7. the second conductive layer is made of any one of a metal, an alloy, and a laminated film in which a metal and / or an alloy are laminated; 7. The strain gauge according to claim 5, wherein the second insulating layer is made of any of an oxide of a metal, an alloy, or a semiconductor, a nitride of a metal, an alloy, or a semiconductor, or an oxynitride of a metal, an alloy, or a semiconductor.

8. a functional layer formed in contact with a surface of the resistor on the substrate side; The strain gauge according to claim 1 , wherein the functional layer is made of a metal, an alloy, or a compound of a metal.

9. 9. The strain gauge according to claim 1, wherein the resistor is formed from a Cr mixed phase film.

10. The Cr mixed phase film is composed of Cr, CrN, and Cr ２ Contains N, CrN and Cr contained in the Cr mixed phase film ２ 10. The strain gauge according to claim 9, wherein N is 20% by weight or less.

11. The CrN and the Cr ２ The Cr in N ２ 11. The strain gauge according to claim 10, wherein the proportion of N is equal to or greater than 80% and less than 90%.

12. a flexible substrate; a resistor formed on one side of the substrate via another layer; a conductive layer formed on the other side of the substrate; an insulating layer formed on the conductive layer on the opposite side of the substrate; a second conductive layer formed between the substrate and the resistor; a second insulating layer formed between the second conductive layer and the resistor; the resistor is formed from a material containing at least one of chromium and nickel, The strain gauge, wherein the insulating layer and the second insulating layer are each formed from an inorganic material.

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