Strain gauge

Abstract

To provide a strain gauge that features improved stability of its Temperature Coefficient of Resistance (TCR).SOLUTION: A strain gauge provided herein comprises a flexible resin substrate, a functional layer formed of a metal, alloy, or metal compound directly on one surface of the substrate, and a resistor principally made from α-Cr and formed of a film containing Cr, CrN, and Cr2N directly on one surface of the functional layer, where the functional layer features a function of promoting α-Cr crystal growth to form a film principally made from α-Cr. The resistor has a thickness of 0.05 to 2 μm, inclusive, and the functional layer has a thickness of 1 to 100 nm, inclusive. The resistor is added with one or more first substances selected from a group consisting of TiN, TaN, SiTiN, CrSiO, and Si.SELECTED DRAWING: Figure 3

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 a measurement object to detect the strain of the measurement object. The strain gauge has a resistor that detects the strain, and the resistor is made of a material that contains, for example, Cr (chromium) or Ni (nickel). The resistor is formed into a predetermined pattern by, for example, etching a metal foil (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-74934 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a flexible substrate is used, it is difficult to form a stable resistor on the substrate, and there is a problem in that the gauge characteristics, particularly the temperature coefficient of resistance TCR, lack stability.

[0005] The present invention has been made in consideration of the above-mentioned points, and has an object to improve the stability of the temperature coefficient of resistance TCR in a strain gauge. [Means for solving the problem]

[0006] This strain gauge comprises a flexible resin substrate, a functional layer formed of a metal, an alloy, or a metal compound directly on one side of the substrate, and a CrN, CrN, or CrN-based functional layer directly on one side of the functional layer. 2and a resistor formed from a film containing N and having α-Cr as a main component, the functional layer having a function of promoting crystal growth of the α-Cr and forming a film having the α-Cr as a main component, the resistor having a thickness of 0.05 μm or more and 2 μm or less, the functional layer having a thickness of 1 nm or more and 100 nm or less, and the resistor having one or more first substances selected from the group consisting of TiN, TaN, SiTiN, CrSiO, and Si added thereto. Effect of the Invention

[0007] According to the disclosed technique, it is possible to improve the stability of the temperature coefficient of resistance TCR in a strain gauge. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Diagram 3] FIG. 1 is a schematic diagram (part 1) illustrating the inside of a resistor that is a Cr mixed phase film. [Figure 4] FIG. 2 is a schematic diagram (part 2) illustrating the inside of a resistor when the resistor is a Cr mixed phase film. [Diagram 5] FIG. 11 is a cross-sectional view illustrating a strain gauge according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] First embodiment Fig. 1 is a plan view illustrating a strain gauge according to a 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, and a terminal portion 41.

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

[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, polyolefin resin, etc. The film refers to a flexible member having 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.

[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 strained. 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 pattern.

[0016] The resistor 30 can be formed, for example, from 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 Ni-Cu (nickel copper). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0017] Here, the Cr mixed phase film is composed of Cr, CrN, Cr 2 It is a film containing a mixed phase of N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, and 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 in that the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr) is improved, and a thickness of 1 μm or less is even more preferable in that film cracks and warping from substrate 10 caused by internal stress of the film constituting resistor 30 can be reduced.

[0019] For example, when the resistor 30 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making α-Cr the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance accounts for 50 mass% or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, it is preferable that the resistor 30 contains α-Cr at 80 weight% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0020] FIG. 3 is a schematic diagram illustrating the inside of a resistor made of a Cr mixed-phase film, and shows the state before and after heating. As shown in FIG. 3, a resistor 30 made of a Cr mixed-phase film is composed of α-Cr crystal grains 301 and chromium nitride 302 (CrN, Cr 2 N) and, in this embodiment, a substance 303 is further added.

[0021] In the Cr mixed-phase film without the addition of substance 303, the TCR changes significantly upon heating, and the longer the heating time, the larger the TCR becomes in the positive direction. This is thought to be because the Cr crystal grains, which are the positive component of the TCR, gradually grow upon heating, and the chromium nitride, which is the negative component of the TCR present at the grain boundaries, is either taken into the Cr film or pushed out, decreasing the amount of chromium nitride present at the grain boundaries. Therefore, the longer the heating time, the larger the TCR becomes, and the larger the positive value becomes.

[0022] Therefore, in this embodiment, a substance 303 having a function of suppressing the growth of the α-Cr crystal grains 301 is added to the Cr mixed phase film, and the substance 303 is dispersed in the Cr mixed phase film.

[0023] The substance 303 is not particularly limited and can be appropriately selected depending on the purpose as long as it has a function of suppressing the growth of the α-Cr crystal grains 301. The substance 303 has a TCR of −30000 ppm / ° C. or more and a TCR of +1000 ppm / ° C. or less and an electrical conductivity of 10 -6 S / m greater than 10 7 Examples of the material include metal compounds such as TiN, TaN, SiTiN, and CrSiO, and semiconductors such as Si. A mixture of a plurality of materials selected from these groups may be used.

[0024] Here, the reason why the TCR is preferably -30000 ppm / °C or more and +1000 ppm / °C or less is as follows. For example, when a substance with a TCR of more than +1000 ppm / °C exists at the grain boundary, the behavior of the conductor becomes dominant, and the TCR value of the entire film becomes larger than +1000 ppm / °C. Also, when a substance with a TCR of less than -30000 ppm / °C exists at the grain boundary, the hopping conduction thermally activated by structural defects contributes, resulting in an unstable TCR value. In contrast, when a substance 303 with a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less exists at the grain boundary, the above problem does not occur, and the TCR of the entire Cr mixed phase film can be stably controlled to a low value.

[0025] In addition, the electrical conductivity is 10 -6 S / m greater than 10 7 The reason why the electrical conductivity is preferably 10 S / m or less is as follows. 7 When a metal is added as a substance with a larger S / m, the metal diffuses into the Cr mixed phase film by heating, causing a large change in TCR. -6 When a substance with a conductivity of 10 S / m or less is added, it hardly conducts electricity, so the electrical properties of the Cr mixed phase film cannot be controlled. -6 S / m greater than 10 7When a substance 303 with a TCR of S / m or less is added, not only is diffusion suppressed, unlike metals, but it is also possible to add a material with electrical properties that correspond to the properties of the Cr mixed phase film, so that the TCR can be kept low both before and after heating.

[0026] The amount of the substance 303 added can be appropriately selected depending on the film formation conditions of the resistor 30, and can be 1 to 25% by weight. In particular, it is preferable that the amount of the substance 303 added in the resistor 30 is 2 to 10% by weight, in terms of improving the crystallinity of α-Cr.

[0027] By adding a substance 303 having a function of suppressing the growth of α-Cr crystal grains 301 to the resistor 30, which is a Cr mixed-phase film, it is possible to suppress the TCR from continuing to increase to a positive value due to heating, and to suppress the TCR to a low value. In other words, it is possible to improve the stability of the TCR of the strain gauge 1. Note that the degree of growth of the α-Cr crystal grains 301 can be controlled by the amount of substance 303 added to the Cr mixed-phase film, and as a result, the TCR of the strain gauge 1 can be controlled.

[0028] The above explanation has been given using a Cr mixed-phase film as an example, but the same effect as in the case of the Cr mixed-phase film can also be obtained for Ni-Cu thin film or Ni-Cr thin film by adding a substance that has the function of suppressing the growth of the crystal grains, which are the main component of the resistor, to the resistor.

[0029] Returning to the explanation of Figs. 1 and 2, the terminal portion 41 extends from both ends of the resistor 30 and is formed in a substantially rectangular shape wider than the resistor 30 in a plan view. The terminal portion 41 is a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and is connected to, for example, a lead wire for external connection. For example, the resistor 30 extends from one of the terminal portions 41 while folding back in a zigzag manner and is connected to the other terminal portion 41. The upper surface of the terminal portion 41 may be covered with a metal having 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.

[0030] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the terminal portion 41. By providing the cover layer 60, mechanical damage to the resistor 30 can be prevented. Furthermore, by providing the cover layer 60, the resistor 30 can be protected from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the terminal portion 41.

[0031] 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, composite resin (e.g., silicone resin, polyolefin resin), etc. The cover layer 60 may contain a filler or a pigment. There is no particular limit to 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.

[0032] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and the resistor 30 and the terminal portion 41 having a planar shape as shown in Fig. 1 are formed on the upper surface 10a of the substrate 10. The material and thickness of the resistor 30 and the terminal portion 41 are as described above. The resistor 30 and the terminal portion 41 can be integrally formed from the same material.

[0033] The resistor 30 and the terminal portion 41 can be formed, for example, by forming a film by magnetron sputtering using a raw material capable of forming the resistor 30 and the terminal portion 41 as a target, and patterning the film by photolithography. The resistor 30 and the terminal portion 41 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like instead of magnetron sputtering.

[0034] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-form a functional layer having a thickness of about 1 nm to 100 nm on the upper surface 10a of the substrate 10 by, for example, a conventional sputtering method as a base layer before forming the resistor 30 and the terminal portion 41. After forming the resistor 30 and the terminal portion 41 on the entire upper surface of the functional layer, the functional layer is patterned by photolithography together with the resistor 30 and the terminal portion 41 into the planar shape shown in FIG.

[0035] In the present 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 further has a function of preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer may further have other functions.

[0036] Since the insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, particularly when the resistor 30 contains Cr, it is effective for the functional layer to have the function of preventing oxidation of the resistor 30.

[0037] 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 the metal 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), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0038] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compound include TiN, TaN, Si 3 N 4 , TiO 2 , Ta 2 O 5 , SiO 2 etc.

[0039] The functional layer can be formed in vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target 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, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0040] 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 a 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.

[0041] The combination of the material of the functional layer with the materials of the resistor 30 and the terminal portion 41 is not particularly limited and 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.

[0042] In this case, for example, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the resistor 30 and the terminal portion 41 may be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber.

[0043] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film mainly composed of α-Cr, which has a stable crystal structure, can be formed. In addition, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of −1000 ppm / ° C. to +1000 ppm / ° C. In addition, when the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti and TiN. In other words, TiN can be added to the Cr mixed-phase film from the functional layer made of Ti.

[0044] 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.

[0045] In this way, by providing a functional layer under the resistor 30, it is possible to promote crystal growth of the resistor 30, and a resistor 30 consisting of a stable crystal phase can be fabricated. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the resistor 30, thereby improving the gauge characteristics of the strain gauge 1.

[0046] Also, in order to form a Cr mixed-phase film with TiN added, Cr and Ti may be used as targets, an appropriate amount of nitrogen gas may be introduced into a chamber together with Ar gas, and the resistor 30 and the terminal portion 41 may be formed by reactive sputtering. In this case, Ti is formed as TiN in the Cr mixed-phase film, and a Cr mixed-phase film with TiN added can be formed.

[0047] In this method, a Cr mixed-phase film containing TiN can be formed even if the Cr mixed-phase film is formed on a functional layer other than Ti. Also, in this method, a Cr mixed-phase film containing TiN can be formed even if the Cr mixed-phase film is formed directly on the upper surface 10a of the substrate 10 without forming a functional layer.

[0048] After forming the resistor 30 and the terminal portion 41, a cover layer 60 that covers the resistor 30 and exposes the terminal portion 41 is provided on the upper surface 10a of the substrate 10 as necessary, 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 portion 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 portion 41, and then heating and curing the film.

[0049] Second embodiment In the second embodiment, an example is shown in which a substance having different characteristics from those in the first embodiment is added to the resistor. Note that in the second embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0050] 4 is a schematic diagram illustrating the inside of a resistor made of a Cr mixed-phase film. As shown in FIG. 4, a resistor 30 made of a Cr mixed-phase film is composed of α-Cr crystal grains 301 and chromium nitride 302 (CrN, Cr 2 N) and, in this embodiment, a substance 304 is further added.

[0051] The TCR of the Cr mixed phase film before heating, to which no substance 304 is added, shows a negative value. This is because the Cr crystal grains have a positive TCR component, but when the film is formed in a nitrogen atmosphere, for example, chromium nitride (CrN, Cr), which has a negative TCR component, appears at the Cr crystal grain boundaries. 2 This is thought to be because the formation of chromium nitride (chromium nitride or both), which is a negative component of TCR, significantly affected the properties of the alloy.

[0052] In the Cr mixed-phase film without the addition of substance 304, the TCR changes significantly upon heating, and the TCR of the Cr mixed-phase film becomes low. This is thought to be because the residual stress in the Cr mixed-phase film is relaxed, bringing the Cr crystal grains closer to each other, which increases the tunnel current at the grain boundaries and reduces the effect of chromium nitride, which is a negative component of the TCR.

[0053] In this embodiment, a substance 304 having the function of preventing the α-Cr crystal grains 301 from approaching each other is added to the Cr mixed phase film, and the substance 304 is dispersed in the Cr mixed phase film and present at the grain boundaries of the α-Cr crystal grains 301.

[0054] The material 304 is not particularly limited as long as it has the function of preventing the α-Cr crystal grains 301 from approaching each other, and can be appropriately selected according to the purpose. The material 304 has a TCR of −30000 ppm / ° C. or more and a TCR of +1000 ppm / ° C. or less and an electrical conductivity of 10 -6 S / m or less, for example, AlN, BN, TiO 2 , ZrO 2 , SiO 2 , Si 3 N 4 The insulating materials include the following: A plurality of materials selected from these groups may be mixed.

[0055] Here, the reason why the TCR is preferably -30000 ppm / °C or more and +1000 ppm / °C or less is as follows. For example, when a substance with a TCR of more than +1000 ppm / °C exists at the grain boundary, the behavior of the conductor becomes dominant, and the TCR value of the entire film becomes larger than +1000 ppm / °C. Also, when a substance with a TCR of less than -30000 ppm / °C exists at the grain boundary, the TCR value becomes unstable because of the contribution of hopping conduction thermally activated by structural defects. In contrast, when a substance 304 with a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less exists at the grain boundary, the above problem does not occur, and the TCR of the entire Cr mixed phase film can be stably controlled to a low value.

[0056] In addition, the electrical conductivity is 10 -6 The reason why the electrical conductivity is preferably 10 S / m or less is as follows. 7 When a metal is added as a substance with a larger S / m, the metal diffuses into the Cr mixed phase film by heating, causing a large change in TCR. -6 S / m greater than 10 7 When metal compounds with higher electrical properties than insulators are added as substances with S / m or less, the diffusion is suppressed unlike metals, but the electrical properties of the Cr mixed phase film are changed. -6 When a material 304 having a TCR of S / m or less is added, diffusion is suppressed unlike metals, and the distance between Cr particles can be controlled, so that the TCR can be kept low both before and after heating.

[0057] The amount of the substance 304 added can be appropriately selected depending on the film formation conditions of the resistor 30, and can be 1 to 25% by weight. In particular, it is preferable that the amount of the substance 304 added in the resistor 30 is 2 to 10% by weight, in terms of improving the crystallinity of α-Cr.

[0058] A substance 304 that has the function of preventing α-Cr crystal grains 301 from approaching each other is added to the resistor 30, which is a Cr mixed phase film. The presence of the substance 304 at the grain boundaries suppresses the bonding between Cr crystal grains, which is a positive component of the TCR, and the TCR of the strain gauge can be reduced.

[0059] In other words, the substance 304 present at the grain boundaries prevents the α-Cr crystal grains 301 from approaching each other due to residual stress relaxation during heating, so that the internal state of the resistor 30 does not change significantly even after heating compared to before heating, and the TCR of the strain gauge 1 can be maintained at a low value.

[0060] As a result, it is possible to reduce the TCR of the Cr mixed phase film both before and after heating, and suppress the change in TCR before and after heating. In other words, it is possible to improve the stability of the TCR of the strain gauge 1. In addition, the degree to which the α-Cr crystal grains 301 approach each other can be controlled by the amount of substance 304 added to the Cr mixed phase film, and as a result, the TCR of the strain gauge 1 can be controlled.

[0061] To form a Cr mixed-phase film with added AlN, for example, a functional layer made of Al is formed on the upper surface 10a of the substrate 10. Then, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed-phase film as a target and introducing Ar gas into a chamber. Alternatively, the resistor 30 and the terminal portion 41 may be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber.

[0062] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Al, and a Cr mixed-phase film containing α-Cr, which has a stable crystal structure, as a main component, can be formed. Furthermore, the Al constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of −1000 ppm / ° C. to +1000 ppm / ° C. In addition, when the functional layer is made of Al, the Cr mixed-phase film may contain Al or AlN. In other words, AlN can be added to the Cr mixed-phase film from the functional layer made of Al.

[0063] Also, in order to form a Cr mixed phase film with AlN added, Cr and Al may be used as targets, an appropriate amount of nitrogen gas may be introduced into a chamber together with Ar gas, and the resistor 30 and the terminal portion 41 may be formed by reactive sputtering. In this case, Al is formed as AlN in the Cr mixed phase film, and a Cr mixed phase film with AlN added can be formed.

[0064] In this method, the Cr mixed phase film doped with AlN can be formed even if the Cr mixed phase film is formed on a functional layer other than Al. Also, in this method, the Cr mixed phase film doped with AlN can be formed even if the Cr mixed phase film is formed directly on the upper surface 10a of the substrate 10 without forming a functional layer.

[0065] The first and second embodiments can be combined. For example, when the resistor 30 is a Cr mixed phase film, TiN can be added to the resistor 30 as the material 303 and AlN can be added to the resistor 30 as the material 304. This makes it possible to obtain the effects of both the first and second embodiments.

[0066] The above explanation has been given using a Cr mixed-phase film as an example, but the same effect as in the case of the Cr mixed-phase film can also be obtained for Ni-Cu thin films and Ni-Cr thin films by adding a substance to the resistor that has the function of preventing the crystal grains, which are the main component of the resistor, from approaching each other.

[0067] Third embodiment In the third embodiment, an example of improving the stability of the TCR of a strain gauge by a method different from that of the first and second embodiments is shown. Note that in the third embodiment, the description of the same components as those of the already described embodiments may be omitted.

[0068] Fig. 5 is a cross-sectional view illustrating a strain gauge according to the third embodiment, showing a cross section corresponding to Fig. 2. Referring to Fig. 5, the strain gauge 1A differs from the strain gauge 1 (see Figs. 1, 2, etc.) in that an oxidation inhibition layer 50 is provided on the upper surfaces of the resistor 30 and the terminal portion 41.

[0069] The resistance value and gauge factor of a thin film based on Cr depend on the oxidation state. Therefore, it is important to control the oxidation of Cr. However, since the oxidized layer of Cr is easily formed, which is generally called a passive layer, it is difficult to control the oxidation. Therefore, in this embodiment, as shown in FIG. 5, an oxidation inhibition layer 50 is provided on the upper surfaces of the resistor 30 and the terminal portion 41. However, depending on the conductivity of the oxidation inhibition layer 50, the oxidation inhibition layer 50 on the upper surface of the terminal portion 41 may be removed.

[0070] The material of the oxidation-inhibiting layer 50 is not particularly limited as long as it can prevent oxidation of the resistor 30 and can be appropriately selected depending on the purpose. 3 O 4 , Si, SiO 2 , ZrO 2 A mixture of a plurality of substances selected from these groups may be used.

[0071] For example, when the resistor 30 is a Cr mixed-phase film and the material of the oxidation inhibition layer 50 is Ti, the thickness of the oxidation inhibition layer 50 is preferably about 1 nm to 100 nm from the viewpoint of reducing the influence of the Cr mixed-phase film on the gauge characteristics. Also, when the resistor 30 is a Cr mixed-phase film and the material of the oxidation inhibition layer 50 is TiN, the thickness of the oxidation inhibition layer 50 is preferably about 1 nm to 10 nm from the viewpoint of improving the stability of the TCR of the Cr mixed-phase film.

[0072] In order to form the oxidation inhibition layer 50 on the upper surfaces of the resistor 30 and the terminal portion 41, after the resistor 30 and the terminal portion 41 are formed, for example, a raw material capable of forming the oxidation inhibition layer 50 is used as a target and a vacuum film is formed on the entire upper surfaces of the resistor 30 and the terminal portion 41 by conventional sputtering in which Ar (argon) gas is introduced into a chamber. Thereafter, the resistor 30, the terminal portion 41, and the oxidation inhibition layer 50 are patterned into the planar shape shown in Fig. 1. Thereafter, the oxidation inhibition layer 50 on the upper surface of the terminal portion 41 is removed as necessary.

[0073] By performing the deposition of the resistor 30 and the terminal portion 41 and the deposition of the oxidation-inhibiting layer 50 as a series of steps in a vacuum chamber, it is possible to deposit the oxidation-inhibiting layer 50 directly on the upper surface of the resistor 30 without forming an oxidation layer on the upper surfaces of the resistor 30 and the terminal portion 41. In other words, it is possible to deposit the oxidation-inhibiting layer 50 on the non-oxidized surfaces that are the upper surfaces of the resistor 30 and the terminal portion 41.

[0074] Although the side surfaces of resistor 30 and terminal portion 41 are exposed from oxidation-inhibiting layer 50 due to patterning, oxidation from the side surfaces does not pose a problem because resistor 30 and terminal portion 41 are thin and have small side surface areas.

[0075] In this way, by forming the oxidation-inhibiting layer 50 on the non-oxidized surface that is the upper surface of the resistor 30, even if the resistor 30 is a thin film whose base material is Cr, the resistor 30 is not oxidized, and therefore the stability of the resistance value of the resistor 30 and the gauge factor of the strain gauge 1A can be improved. Also, the stability of the TCR of the strain gauge 1A can be improved.

[0076] As in the first and second embodiments, it is preferable to provide a functional layer under the resistor 30. In this embodiment, it is preferable to use, as the functional layer, a layer having a function of promoting crystal growth of the resistor 30 which is the upper layer, and a function of preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10.

[0077] This promotes crystal growth of the resistor 30, making it possible to fabricate a resistor 30 made of a stable crystalline phase, and improves the stability of the gauge characteristics. Also, the material constituting the functional layer diffuses into the resistor 30, improving the gauge characteristics. Furthermore, the functional layer acts as a barrier layer to suppress oxidation of the resistor 30 from the substrate 10 side, further improving the stability of the resistance value of the resistor 30 and the gauge factor of the strain gauge 1A. Also, the stability of the TCR of the strain gauge 1A can be further improved.

[0078] For example, when the resistor 30 is a Cr mixed-phase film, the functional layer having the functions of promoting crystal growth and acting as a barrier layer may be Ti or TiN, but it is particularly preferable to use TiN. When Ti is diffused into the Cr mixed-phase film, the gauge characteristics are improved, but the gauge characteristics vary depending on the degree of diffusion. However, when TiN is diffused into the Cr mixed-phase film, the diffusion in the Cr mixed-phase film is small, so the gauge characteristics are less likely to vary depending on the degree of diffusion, and the stability of the gauge characteristics depending on temperature is improved.

[0079] The first and third embodiments can be combined. For example, when the resistor 30 is a Cr mixed phase film, TiN can be added to the resistor 30 as the substance 303, and Ti can be formed as an oxidation inhibition layer 50 on the upper surface of the resistor 30. Furthermore, TiN or the like can be provided in the lower layer of the resistor 30 as a functional layer having a function of promoting the crystal growth of the resistor 30 and a function of preventing the oxidation of the resistor 30. This makes it possible to obtain both the effects shown in the first and third embodiments.

[0080] Moreover, the second embodiment and the third embodiment can be combined. For example, when the resistor 30 is a Cr mixed phase film, AlN can be added to the resistor 30 as the substance 304, and Ti can be formed as an oxidation inhibition layer 50 on the upper surface of the resistor 30. Furthermore, TiN or the like can be provided in the lower layer of the resistor 30 as a functional layer having a function of promoting the crystal growth of the resistor 30 and a function of preventing the oxidation of the resistor 30. This makes it possible to obtain both the effects shown in the second embodiment and the third embodiment.

[0081] Also, the first embodiment, the second embodiment, and the third embodiment can be combined. For example, when the resistor 30 is a Cr mixed phase film, TiN can be added to the resistor 30 as the material 303 and AlN can be added as the material 304, and Ti can be formed as the oxidation inhibition layer 50 on the upper surface of the resistor 30. Furthermore, TiN or the like can be provided in the lower layer of the resistor 30 as a functional layer having a function of promoting the crystal growth of the resistor 30 and a function of preventing the oxidation of the resistor 30. This makes it possible to obtain all the effects shown in the first embodiment, the second embodiment, and the third embodiment.

[0082] Although the above has been explained using a thin film having a Cr base as an example, the same effect as in the case of a thin film having a Cr base can also be obtained for a Ni-Cu thin film or a Ni-Cr thin film by providing an oxidation inhibition layer 50 on the upper surface of the resistor 30. Moreover, for a Ni-Cu thin film or a Ni-Cr thin film, by providing a functional layer having the functions of promoting crystal growth and acting as a barrier layer below the resistor 30, the same effect as in the case of a thin film having a Cr base can also be obtained.

[0083] 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]

[0084] 1, 1A strain gauge, 10 substrate, 10a upper surface, 30 resistor, 41 terminal portion, 50 oxidation inhibition layer, 60 cover layer, 301 α-Cr crystal grains, 302 chromium nitride, 303, 304 material

Claims

1. A flexible resin base material; A functional layer formed of a metal, an alloy, or a metal compound directly on one surface of the substrate; Cr, CrN, and Cr are directly attached to one surface of the functional layer. ２ A resistor mainly composed of α-Cr and formed from a film containing N, the functional layer has a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component, The resistor has a thickness of 0.05 μm or more and 2 μm or less, The thickness of the functional layer is 1 nm or more and 100 nm or less, A strain gauge in which one or more first substances selected from the group consisting of TiN, TaN, SiTiN, CrSiO, and Si are added to the resistor.

2. The first substance has a temperature coefficient of resistance of −30,000 ppm / ° C. or more and +1,000 ppm / ° C. or less and an electrical conductivity of 10 －６ S / m greater than 10 ７ 2. The strain gauge according to claim 1, wherein the strain gage has a strain coefficient of 1.5 S / m or less.

3. 3. The strain gauge according to claim 1, further comprising an insulating resin layer covering the resistor.

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