Strain gauge

Abstract

To provide a strain gauge superimposed on a resistor and capable of reducing noise.SOLUTION: A strain gauge has a flexible substrate, a resistor formed from a film containing Cr, CrN, and Cr2N on one surface of the substrate, an insulating layer covering the resistor, and a conductive barrier layer that covers the insulating layer.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 includes a resistor that detects strain, and the resistor is formed on, for example, an insulating resin. The resistor is connected to an electrode via, for example, a wiring (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] In strain gauges like the one described above, if noise is superimposed on the resistor, it will appear in the output voltage, leading to a decrease in measurement accuracy. The effect of noise is particularly noticeable in strain gauges with a high gauge factor.

[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 comprises a flexible substrate, a resistor formed on one surface of the substrate from a film containing Cr, CrN, and CrN, an insulating layer covering the resistor, and a conductive barrier layer covering the insulating layer, and the barrier layer continuously covers the top and side surfaces of the resistor via the insulating layer. [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] This is the first experimental result confirming the noise reduction effect of the barrier layer. [Figure 4] This is the second experimental result confirming the noise reduction effect of the barrier layer. [Figure 5] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 2 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. 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, wiring 40, electrodes 50, an insulating layer 60, and a barrier layer 70.

[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] Materials other than resin for the substrate 10 include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Alternatively, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 10. In this case, an insulating film, for example, is formed on the metal substrate 10.

[0016] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing element 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 dark matte pattern.

[0017] The resistor 30 has a structure in which multiple elongated portions are arranged at predetermined intervals with their longitudinal direction in the same direction (the direction of line AA in Figure 1), and the ends of adjacent elongated portions are connected alternately, resulting in a zigzag folded structure as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction.

[0018] One longitudinal end of each of the two elongated portions located outermost in the grid width direction is bent in the grid width direction to form terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction. Each of the terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction is electrically connected to an electrode 50 via a wiring 40. In other words, the wiring 40 electrically connects each of the terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction to each of the electrodes 50.

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

[0020] 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.

[0021] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, approximately 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting the resistor 30 (e.g., the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less is even more preferable because it reduces film cracks and warpage from the substrate 10 caused by internal stress in the film constituting the resistor 30. The width of the resistor 30 is preferably 10 μm to 100 μm, in order to optimize it for required specifications such as resistance value and lateral sensitivity, and also take into consideration measures against disconnection.

[0022] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50% by weight or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0023] 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.

[0024] Furthermore, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the Cr2N has semiconducting properties, which leads to a more significant decrease in TCR (negative TCR). Furthermore, by reducing the amount of ceramic formation, brittle fracture is reduced.

[0025] 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.

[0026] The wiring 40 is formed on the substrate 10. The electrode 50 is formed on the substrate 10 and electrically connected to the resistor 30 via the wiring 40, and is formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain, and are connected, for example, to lead wires for external connection. In FIG. 1, for convenience, the wiring 40 and the electrode 50 are shown with a matte finish that is thinner than the resistor 30.

[0027] Although the resistor 30, wiring 40, and electrode 50 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, wiring 40, and electrode 50 have approximately the same thickness.

[0028] The upper surfaces of the wiring 40 and the electrodes 50 may be covered with a metal formed from a material having a lower resistance than the wiring 40 and the electrodes 50. For example, when the resistor 30, the wiring 40, and the electrodes 50 are Cr mixed-phase films, examples of metal materials having a lower resistance than the Cr mixed-phase film include Cu, Ni, Al, Ag, Au, Pt, etc., alloys of any of these metals, compounds of any of these metals, and laminated films in which any of these metals, alloys, and compounds are appropriately laminated.

[0029] The insulating layer 60 is provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrodes 50. The insulating layer 60 may also cover part or all of the wiring 40 as long as it covers at least the resistor 30. The insulating layer 60 is preferably provided so as to continuously cover the upper and side surfaces of the resistor 30.

[0030] The insulating layer 60 is formed of, for example, an insulating organic material. Examples of materials for the insulating layer 60 include PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, PE (polyethylene) resin, PVDC (polyvinylidene chloride) resin, PVDF (polyvinylidene fluoride) resin, PTFE (polytetrafluoroethylene) resin, PP (polypropylene) resin, butyl rubber, silicone rubber, and composite resins (e.g., silicone resin and polyolefin resin). The insulating layer 60 may contain a filler or a pigment. The thickness of the insulating layer 60 is not particularly limited and can be appropriately selected depending on the purpose, but may be, for example, approximately 0.1 μm to 30 μm. By setting the insulating layer 60 to such a thickness, the upper surface is flat, making it easy to form the barrier layer 70 on the insulating layer 60. Furthermore, the flatter the upper surface of the insulating layer 60, the more stress is alleviated in various bending directions, and peeling of the barrier layer 70 can be prevented.

[0031] The insulating layer 60 may be formed from an insulating inorganic material. In this case, examples of the material for the insulating layer 60 include metals such as Cu, Cr, Ni, Al, Fe, W, Ti, and Ta, and oxides, nitrides, and oxynitrides of alloys containing these metals. The insulating layer 60 may also be made of semiconductors such as Si and Ge, and oxides, nitrides, and oxynitrides of these semiconductors. The thickness of the insulating layer 60 is not particularly limited and can be appropriately selected depending on the purpose, but may be, for example, about 0.01 μm to 2 μm.

[0032] Note that a high Young's modulus of the insulating layer 60 may reduce the gauge factor of the strain gauge 1. In general, organic materials such as PI resin have a lower Young's modulus than inorganic materials such as SiO2. Therefore, from the viewpoint of suppressing a decrease in the gauge factor of the strain gauge 1, it is preferable to select an organic material with a low Young's modulus as the material for the insulating layer 60. From the viewpoint of suppressing a decrease in the gauge factor, it is preferable that the Young's modulus of the insulating layer 60 be 0.1 GPa or more and 10 GPa or less.

[0033] Furthermore, it is preferable that the linear expansion coefficient of the insulating layer 60 is close to that of the substrate 10. If the difference between the linear expansion coefficients of the insulating layer 60 and the substrate 10 becomes large, strain due to the difference in expansion in response to temperature changes is amplified, resulting in a larger change in the resistance value of the resistor 30. On the other hand, by making the linear expansion coefficient of the insulating layer 60 close to that of the substrate 10, the effect of reducing the TCR can be obtained. For example, the material of the insulating layer 60 may be the same as the material of the substrate 10. Furthermore, the thickness of the insulating layer 60 may be the same as that of the substrate 10.

[0034] The barrier layer 70 is provided to cover the insulating layer 60. The barrier layer 70 is a layer formed to reduce noise superimposed on the resistor 30, and is made of a conductive material. The barrier layer 70 is insulated from the resistor 30 by the insulating layer 60. In this application, a conductive material refers to a material with a resistivity of 10 Ω·cm or less. With a material with a resistivity of 1 Ω·cm or more and 10 Ω·cm or less, electromagnetic waves that reach the surface of the conductor change into eddy currents on the surface, and this current is released by grounding, thereby achieving a shielding effect.

[0035] The barrier layer 70 can be formed, for example, from a metal, an alloy, or a laminated film of a metal and / or an alloy. More specifically, a typical material for the barrier layer 70 is Al, but Cu, Ni, Ag, Au, Pt, Pd, Sn, Cr, or an alloy of any of these metals, or a laminated film of any of these metals or alloys, may also be used. However, the barrier layer 70 is not limited to metals as long as it is made of a conductive material, and may be made of ceramics containing a conductive material such as nanocarbon. Examples of ceramics containing a conductive material include ceramics (such as ZrO2 or InO2) that contain a conductive material such as nanocarbon inside, and composite oxides (complex compounds of insulating and conductive materials) such as Al2O3-MoSi2 and BN-TiB2.

[0036] In this way, in the strain gauge 1, the conductive barrier layer 70 is formed so as to cover the resistor 30 via the insulating layer 60. As a result, when noise occurs around the strain gauge 1, the noise flows through the barrier layer 70 made of a conductive material, thereby reducing the noise superimposed on the resistor 30. As a result, a decrease in the measurement accuracy of the strain gauge 1 can be suppressed. Note that the noise referred to here refers to, for example, electromagnetic noise from the object being measured, such as a motor, or noise due to static electricity.

[0037] In particular, highly sensitive strain gauges that use a Cr mixed-phase film as the resistor 30 and have a gauge factor of 10 or more are more susceptible to the influence of external noise due to their higher sensitivity than conventional strain gauges with a gauge factor of less than 10, and are therefore more susceptible to measurement errors and variations in the output voltage. Therefore, forming a barrier layer 70 so as to cover the resistor 30 via the insulating layer 60 is particularly effective for highly sensitive strain gauges that use a Cr mixed-phase film as the resistor 30 and have a gauge factor of 10 or more.

[0038] The barrier layer 70 is preferably provided so as to continuously cover the top and side surfaces of the resistor 30 via the insulating layer 60. This provides a greater noise reduction effect than when the barrier layer 70 covers only the top surface of the resistor 30 via the insulating layer 60. However, if the barrier layer 70 covers at least a portion of the resistor 30 via the insulating layer 60, a certain level of noise reduction effect can be achieved.

[0039] The thickness of the barrier layer 70 is preferably 0.1 μm or more. By making the thickness of the barrier layer 70 0.1 μm or more, a sufficient noise reduction effect can be obtained. Furthermore, by making the thickness of the barrier layer 70 0.1 μm or more, a decrease in the gauge factor of the resistor 30 can be suppressed. Furthermore, the thickness of the barrier layer 70 is preferably less than the thickness at which cracks or defects occur at the strain limit value of the resistor 30. For example, when the resistor 30 is a Cr mixed phase film and the material of the barrier layer 70 is Al, the thickness of the barrier layer 70 is preferably less than 1 mm.

[0040] Figures 3 and 4 show the results of an experiment confirming the noise reduction effect of the barrier layer. Note that Figure 4 shows an enlarged view of the time axis near the noise in Figure 3. In Figures 3 and 4, test sample A is a strain gauge with the structure shown in Figures 1 and 2 that does not have a barrier layer 70, while test sample B is a strain gauge with the structure shown in Figures 1 and 2 that has a barrier layer 70.

[0041] In test samples A and B, a 200 nm thick Cr mixed phase film was used as the resistor 30. In test sample B, a 100 μm thick Al film was used as the barrier layer 70. Static electricity of approximately 10 kV was used as the noise source. In order to eliminate the influence of the temperature coefficient of resistance (TCR) on the noise, a pair of electrodes 50 was connected to a half-bridge circuit and the output voltage was measured.

[0042] 3 and 4, at least two steep noises can be observed between 0.38 and 0.40 seconds for test sample A, which does not have barrier layer 70. In contrast, no steep noises can be observed between 0.38 and 0.40 seconds for test sample B, which does have barrier layer 70. Thus, by forming barrier layer 70 so as to cover resistor 30 via insulating layer 60, noise superimposed on the output voltage obtained via the pair of electrodes 50 is reduced, and a decrease in the measurement accuracy of strain gauge 1 can be suppressed.

[0043] According to the inventors' investigations, when the resistor 30 is not a Cr mixed phase film (for example, when it is a conventionally used Cu-Ni or Ni-Cr film), no noise was superimposed on the output voltage in a similar experiment, even without providing a barrier layer. Therefore, the problem that electromagnetic noise and static electricity noise are easily superimposed on the output voltage, and the effect that this noise can be solved by providing a barrier layer, are unique to highly sensitive strain gauges with a gauge factor of 10 or more, and are new findings by the inventors.

[0044] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, wiring 40, and electrodes 50 described above.

[0045] The metal layer A can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, the metal layer A may also be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0046] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the substrate 10 by, for example, conventional sputtering before depositing the metal layer A.

[0047] In the present application, the functional layer refers to a layer having the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and the function of improving adhesion between the substrate 10 and metal layer A. The functional layer may also have other functions.

[0048] 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 metal layer A, especially when the metal layer A contains Cr.

[0049] 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 metal layer A (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 the metals include one or more metals selected from the group consisting of copper (Ru), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, and a compound of any of the metals in this group.

[0050] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0051] 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 / 20 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.

[0052] 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 / 50 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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 not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0057] 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.

[0058] Furthermore, when the functional layer is made of an insulating material, the thickness of the functional layer is made relatively thick, between 50 nm 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.

[0059] 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.

[0060] 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.

[0061] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and it can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer A.

[0062] In this case, for example, the metal layer A 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 the chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as the target and introducing an appropriate amount of nitrogen gas into the 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.

[0063] 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).

[0064] When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0065] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A 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 metal layer A, it is possible to improve the gauge characteristics of the strain gauge 1.

[0066] Next, the metal layer A is patterned by photolithography to form the resistor 30, wiring 40, and electrode 50 in the planar shape shown in FIG.

[0067] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlying layer for the resistor 30, the wiring 40, and the electrodes 50, the strain gauge 1 has a cross-sectional shape as shown in FIG. 5. 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 will be the same as that shown in FIG. 1, for example. However, as mentioned above, the functional layer 20 may be formed solidly on part or all of the upper surface of the substrate 10.

[0068] Next, an insulating layer 60 is formed on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrodes 50. The insulating layer 60 may also cover part or all of the wiring 40 as long as it covers at least the resistor 30. The material and thickness of the insulating layer 60 are as described above.

[0069] When the insulating layer 60 is made of an organic material, the method for forming the insulating layer 60 is not particularly limited and can be appropriately selected depending on the purpose, but for example, the insulating layer 60 can be produced by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the electrodes 50, and then heating and curing the resin. The insulating layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the electrodes 50, and then heating and curing the resin.

[0070] When the insulating layer 60 is made of an inorganic material, the method for forming the insulating layer 60 is not particularly limited and can be selected appropriately depending on the purpose. For example, a method of forming a film by a vacuum process such as a sputtering method, a plating method, or a chemical vapor deposition (CVD) method, or a solution process such as a spin coating method or a sol-gel method, followed by patterning by photolithography, can be mentioned.

[0071] Next, the barrier layer 70 is formed to cover the insulating layer 60. The material and thickness of the barrier layer 70 are as described above. The barrier layer 70 can be formed on the insulating layer 60 by, for example, sputtering or plating. Through the above steps, the strain gauge 1 is completed.

[0072] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example is shown in which a conductive layer is provided on the lower surface side of the substrate 10. 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.

[0073] 6 is a cross-sectional view illustrating a strain gauge according to Modification 1 of Embodiment 1. Note that the plan view of the strain gauge according to Modification 1 of Embodiment 1 is the same as FIG.

[0074] Referring to FIG. 6, strain gauge 1A differs from strain gauge 1 (see FIGS. 1, 2, etc.) in that it has a conductive layer 80.

[0075] In the strain gauge 1A, the conductive layer 80 is formed on the lower surface 10b of the substrate 10. Examples of materials for the conductive layer 80 include Cr, Ti, Cu, Al, C, Si, and conductive resins. Among these, metals are preferred, and Cr is particularly preferred because it has a high Young's modulus. The thickness of the conductive layer 80 can be, for example, 0.01 μm or more and 1 mm or less. The conductive layer 80 can be formed on the lower surface 10b of the substrate 10 by, for example, sputtering or plating.

[0076] By forming the conductive layer 80 on the lower surface 10b of the substrate 10, it is possible to increase the hardness of the entire strain gauge 1A, improving the shape stability of the strain gauge 1A. This protects the strain gauge 1A from mechanical noise, thereby achieving higher measurement accuracy. The conductive layer 80 is preferably formed on the entire lower surface 10b of the substrate 10. By forming the conductive layer 80 on the entire lower surface 10b of the substrate 10, the effect of protecting it from mechanical noise is enhanced.

[0077] 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. [Explanation of symbols]

[0078] 1, 1A strain gauge, 10 substrate, 10a upper surface, 10b lower surface, 20 functional layer, 30 resistor, 30e1, 30e2 termination, 40 wiring, 50 electrode, 60 insulating layer, 70 barrier layer, 80 conductive layer

Claims

1. a flexible substrate; Cr, CrN, and Cr ２ a resistor formed from a film containing N; an insulating layer covering the resistor; a conductive barrier layer covering the insulating layer, The barrier layer continuously covers the top and side surfaces of the resistor via the insulating layer.

2. The strain gauge according to claim 1 , wherein the barrier layer continuously covers the top and side surfaces of the resistor via the insulating layer, but does not cover the side surfaces of the substrate.

3. The strain gauge according to claim 1 or 2, wherein the insulating layer is made of an organic material.

4. 4. The strain gauge according to claim 1, wherein the barrier layer is formed from a laminated film of a metal, an alloy, or a metal and / or an alloy.

5. The strain gauge according to claim 1 , further comprising a conductive layer formed on the other surface of the substrate.

6. 6. The strain gauge according to claim 1, wherein the gauge factor is 10 or more.

7. CrN and Cr contained in the resistor ２ 7. The strain gauge according to claim 1, wherein N is 20% by weight or less.

8. The CrN and the Cr ２ The Cr in N ２ 8. The strain gauge according to claim 7, wherein the proportion of N is equal to or greater than 80% by weight and less than 90% by weight.

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