Strain gauge

Abstract

To improve the stability of a resistance temperature coefficient TCR in a strain gauge.SOLUTION: A strain gauge includes: a substrate made of resin that has flexibility; a functional layer formed of metal, an alloy, or a metal compound directly on one surface of the substrate; a resistor which is formed of film containing Cr, CrN, and Cr2 N directly on one surface of the functional layer, and which contains α-Cr as its main constituent; and an oxidation inhibition layer formed on a non-oxidation surface being an upper face of the resistor. The functional layer has a function of promoting crystal growth of the α-Cr and growing a film having the α-Cr as its main constituent. A thickness of the resistor is 0.05 μm to 2 μm, and a thickness of the functional layer is 1 nm to 100 nm.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A strain gauge is known which is attached to a measurement object to detect the strain of the measurement object. The strain gauge includes a resistor for detecting strain, and as the material of the resistor, for example, a material containing Cr (chromium) or Ni (nickel) is used. Further, the resistor is formed in a predetermined pattern, for example, by etching a metal foil (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] The present invention has been made in view of the above points, and an object thereof is to improve the stability of the resistance temperature coefficient TCR in a strain gauge.

Means for Solving the Problems

[0006] This strain gauge includes a flexible resin base material, a functional layer formed directly on one surface of the base material from a metal, an alloy, or a metal compound, and directly on one surface of the functional layer, Cr, CrN, and Cr 2A resistor mainly composed of α-Cr formed from a film containing N, and an oxidation inhibition layer formed on a non-oxidized surface that becomes the upper surface of the resistor, and the functional layer has a function of promoting crystal growth of the α-Cr and forming a film of the film mainly composed of the α-Cr. The thickness of the resistor is 0.05 μm or more and 2 μm or less, and the thickness of the functional layer is 1 nm or more and 100 nm or less.

Advantages of the Invention

[0007] According to the disclosed technology, the stability of the resistance temperature coefficient TCR in the strain gauge can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, 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 A-A in FIG. 1. Referring to FIGS. 1 and 2, the strain gauge 1 has a base material 10, a resistor 30, a terminal portion 41, and an oxidation inhibition layer 50. However, in FIG. 1, for the sake of showing the positional relationship between the resistor 30 and the terminal portion 41, the illustration of the oxidation inhibition layer 50 is omitted for convenience.

[0011] In this embodiment, for the sake of convenience, in the strain gauge 1, the side where the resistor 30 of the base material 10 is provided is defined as the upper side or one side, and the side where the resistor 30 is not provided is defined as the lower side or the other side. Also, the surface on the side where the resistor 30 of each part is provided is defined as one surface or the upper surface, and the surface on the side where the resistor 30 is not provided is defined as the other surface or the lower surface. However, the strain gauge 1 can be used in an upside-down state or can be arranged at an arbitrary angle. Also, the plan view means viewing the object from the normal direction of the upper surface 10a of the base material 10, and the planar shape means the shape of the object viewed from the normal direction of the upper surface 10a of the base material 10.

[0012] The base material 10 is a member serving as a base layer for forming the resistor 30 and the like, and has flexibility. The thickness of the base material 10 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 5 μm to 500 μm. In particular, when the thickness of the base material 10 is 5 μm to 200 μm, it is preferable in terms of the transmissibility of strain from the surface of the strain-generating body joined to the lower surface of the base material 10 through an adhesive layer or the like and the dimensional stability against the environment. When it is 10 μm or more, it is more preferable in terms of insulation.

[0013] The base material 10 can be formed from an insulating resin film such as a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, or a polyolefin resin. Here, the film refers to a member having a thickness of about 500 μm or less and having flexibility.

[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 portion that undergoes strain and causes a resistance change. 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. In FIG. 1, for the sake of convenience, the resistor 30 is shown in a matte finish 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. Examples of the material containing Cr include a Cr mixed-phase film. Examples of the material containing Ni include Ni-Cu (nickel copper). Examples of the material containing both Cr and Ni include Ni-Cr (nickel chromium).

[0017] Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr 2 N, etc. are in a mixed phase. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of the resistor 30 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, it is preferable in terms of improving the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr), and when it is 1 μm or less, it is more preferable in terms of reducing cracks in the film caused by internal stress of the film constituting the resistor 30 and warping from the substrate 10.

[0019] For example, when the resistor 30 is a Cr mixed-phase film, by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component, the stability of the gauge characteristics can be improved. Also, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be made 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance occupies 50 mass% or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, it is preferable that the resistor 30 contains 80 wt% or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0020] The terminal portions 41 extend from both ends of the resistor 30 and are formed in a substantially rectangular shape that is wider than the resistor 30 in a plan view. The terminal portions 41 are a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 30 caused by strain. For example, lead wires for external connection or the like are joined thereto. The resistor 30 extends, for example, while being folded back in a zigzag manner from one of the terminal portions 41 and is connected to the other terminal portion 41. The upper surface of the terminal portion 41 may be coated with a metal having better solderability than the terminal portion 41. Note that although the resistor 30 and the terminal portions 41 are given different reference numerals for convenience, both can be integrally formed of the same material in the same process.

[0021] The oxidation inhibition layer 50 is formed, for example, in the same planar shape as the resistor 30 and the terminal portions 41 on the upper surfaces of the resistor 30 and the terminal portions 41. The resistance value and the gauge factor of a thin film based on Cr are affected by the oxidation state. Therefore, control of the oxidation of Cr is important. However, since the oxidation layer of Cr is generally called a passive layer and it is difficult to perform oxidation control because it is easy to form an oxidation layer, in this embodiment, the oxidation inhibition layer 50 is provided on the upper surfaces of the resistor 30 and the terminal portions 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.

[0022] The material of the oxidation inhibition layer 50 is not particularly limited as long as it can prevent the oxidation of the resistor 30, and can be appropriately selected according to the purpose. For example, Ti, TiN, TaN, Si 3 O 4 , Si, SiO 2 , ZrO 2 etc. may be mentioned. A plurality of substances selected from these groups may be mixed.

[0023] 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 on the gauge characteristics of the Cr mixed-phase film. 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.

[0024] 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 oxidation inhibition layer 50 on the resistor 30 and expose the oxidation inhibition layer 50 on the terminal portion 41. By providing the cover layer 60, it is possible to prevent mechanical damage or the like from occurring to the resistor 30. Also, by providing the cover layer 60, the resistor 30 can be protected from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except the oxidation inhibition layer 50 on the terminal portion 41.

[0025] The cover layer 60 can be formed from an insulating resin such as, for example, a PI resin, an epoxy resin, a PEEK resin, a PEN resin, a PET resin, a PPS resin, a composite resin (for example, a silicone resin, a polyolefin resin), etc. The cover layer 60 may contain a filler or a pigment. The thickness of the cover layer 60 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 2 μm to 30 μm.

[0026] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a resistor 30 and a terminal portion 41 having the planar shape shown in FIG. 1 are formed on the upper surface 10a of the base material 10. The materials and thicknesses 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 of the same material.

[0027] The resistor 30 and the terminal portion 41 can be formed, for example, by forming a film by a magnetron sputtering method using a raw material capable of forming the resistor 30 and the terminal portion 41 as a target. Instead of the magnetron sputtering method, the resistor 30 and the terminal portion 41 may be formed by film formation using a reactive sputtering method, an evaporation method, an arc ion plating method, a pulsed laser deposition method, or the like.

[0028] From the viewpoint of stabilizing the gauge characteristics, before forming the resistor 30 and the terminal portion 41, as an underlayer, a functional layer having a film thickness of about 1 nm to 100 nm is vacuum-deposited on the upper surface 10a of the base material 10 by, for example, a conventional sputtering method. Note that the functional layer forms the resistor 30 and the terminal portion 41 over the entire upper surface of the functional layer, forms an oxidation inhibition layer 50 over the entire upper surface of the resistor 30 and the terminal portion 41, and then is patterned into the planar shape shown in FIG. 1 together with the resistor 30, the terminal portion 41, and the oxidation inhibition layer 50 by photolithography.

[0029] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer resistor 30. The functional layer preferably further has a function of preventing oxidation of the resistor 30 by oxygen or moisture contained in the base material 10 and a function of improving the adhesion between the base material 10 and the resistor 30. The functional layer may further have other functions.

[0030] Since the insulating resin film constituting the base material 10 contains oxygen and moisture, particularly when the resistor 30 contains Cr, Cr forms a self-oxidation film, so it is effective for the functional layer to have a function of preventing oxidation of the resistor 30.

[0031] The material of the functional layer is not particularly limited as long as it has a function of promoting the crystal growth of at least the upper resistor 30, and can be appropriately selected according to 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), 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), Al (aluminum), one or more metals selected from the group consisting of, alloys of any of these metals, or compounds of any of these metals can be mentioned.

[0032] Examples of the above alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the above compounds include TiN, TaN, Si 3 N 4 、TiO 2 、Ta 2 O 5 、SiO 2 etc.

[0033] For example, the functional layer can be formed by vacuum deposition by a conventional sputtering method using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into the chamber. By using the conventional sputtering method, the upper surface 10a of the substrate 10 is etched with Ar while the functional layer is formed, so that the film formation amount of the functional layer can be minimized and the adhesion improvement effect can be obtained.

[0034] However, this is an example of the method for forming the functional layer, and the functional layer may be formed by other methods. For example, an adhesion improvement effect can be obtained by activating the upper surface 10a of the substrate 10 by plasma treatment using Ar or the like before forming the functional layer, and then a method of forming the functional layer by vacuum deposition by the magnetron sputtering method may be used.

[0035] There are no particular restrictions on the combination of the material of the functional layer, the resistor 30, and the material of the terminal portion 41, and they can be appropriately selected according to the purpose. However, it is preferable to use a layer having a function of promoting the crystal growth of the upper resistor 30 and a function of preventing the oxidation of the resistor 30 by oxygen and moisture contained in the base material 10.

[0036] As a result, it becomes possible to promote the crystal growth of the resistor 30 and produce a resistor 30 composed of a stable crystal phase, and the stability of the gauge characteristics can be improved. Also, the gauge characteristics can be improved by the diffusion of the material constituting the functional layer into the resistor 30. Furthermore, since the functional layer serves as a barrier layer and suppresses the oxidation of the resistor 30 from the base material 10 side, the stability of the resistance value of the resistor 30 and the gauge factor of the strain gauge 1 can be further improved. Also, the stability of the TCR of the strain gauge 1 can be further improved.

[0037] Examples of the functional layer having the function of promoting crystal growth and the function as a barrier layer include Ti and TiN when the resistor 30 is a Cr mixed-phase film. In particular, it is preferable to use TiN. When Ti is diffused into the Cr mixed-phase film, the gauge characteristics are improved, but variations in the gauge characteristics occur 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 variations in the gauge characteristics due to the degree of diffusion are less likely to occur, and the stability of the gauge characteristics with respect to temperature is improved.

[0038] When TiN is used as the functional layer, for example, the resistor 30 and the terminal portion 41 can be formed by a magnetron sputtering method in which a raw material capable of forming a Cr mixed-phase film is used as a target and Ar gas is introduced into the chamber. Alternatively, pure Cr may be used as a target, and an appropriate amount of nitrogen gas may be introduced into the chamber together with Ar gas, and the resistor 30 and the terminal portion 41 may be formed by a reactive sputtering method.

[0039] In these methods, the growth surface of the Cr mixed-phase film is defined by the functional layer made of TiN, and a Cr mixed-phase film mainly composed of α-Cr with a stable crystal structure can be formed. Also, since the TiN constituting the functional layer diffuses into the Cr mixed-phase film, the gauge characteristics are improved. For example, 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.

[0040] When the resistor 30 is a Cr mixed-phase film, the functional layer made of TiN has all of the functions of promoting the crystal growth of the resistor 30, preventing the oxidation of the resistor 30 by oxygen and moisture contained in the base material 10, and improving the adhesion between the base material 10 and the resistor 30. The same applies when Ti, Ta, Si, Al, or Fe is used instead of TiN as the functional layer.

[0041] Thus, by providing a functional layer under the resistor 30, it becomes possible to promote the crystal growth of the resistor 30, and a resistor 30 composed of a stable crystal phase can be produced. As a result, in the strain gauge 1, the stability of the gauge characteristics can be improved. Also, since the material constituting the functional layer diffuses into the resistor 30, the gauge characteristics can be improved in the strain gauge 1.

[0042] In order to form the oxidation-inhibiting layer 50 on the upper surfaces of the resistor 30 and the terminal portion 41, after forming the resistor 30 and the terminal portion 41, for example, using a conventional sputtering method in which a raw material capable of forming the oxidation-inhibiting layer 50 is used as a target and Ar (argon) gas is introduced into the chamber, vacuum deposition is performed on the entire upper surfaces of the resistor 30 and the terminal portion 41. Then, the functional layer, the resistor 30, the terminal portion 41, and the oxidation-inhibiting layer 50 are patterned into the planar shape shown in FIG. 1. Then, if necessary, the oxidation-inhibiting layer 50 on the upper surface of the terminal portion 41 is removed.

[0043] By performing the film formation of the resistor 30 and the terminal portion 41 and the film formation of the oxidation inhibition layer 50 as a series of steps in a vacuum chamber, the oxidation inhibition layer 50 can be directly formed on the upper surface of the resistor 30 without forming an oxide layer on the upper surfaces of the resistor 30 and the terminal portion 41. That is, the oxidation inhibition layer 50 can be formed on the non-oxidized surface that becomes the upper surfaces of the resistor 30 and the terminal portion 41.

[0044] Note that although the side surfaces of the resistor 30 and the terminal portion 41 are exposed from the oxidation inhibition layer 50 by patterning, since the resistor 30 and the terminal portion 41 are thin and the side surface area is small, oxidation from the side surfaces does not pose a problem.

[0045] After forming the oxidation inhibition layer 50, if necessary, a cover layer 60 that covers the oxidation inhibition layer 50 on the resistor 30 and exposes the oxidation inhibition layer 50 on the terminal portion 41 is provided on the upper surface 10a of the base material 10, 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 base material 10 so as to cover the oxidation inhibition layer 50 on the resistor 30 and expose the oxidation inhibition layer 50 on the terminal portion 41, and then heating and curing it. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin on the upper surface 10a of the base material 10 so as to cover the oxidation inhibition layer 50 on the resistor 30 and expose the oxidation inhibition layer 50 on the terminal portion 41, and then heating and curing it.

[0046] In this way, by forming the oxidation inhibition layer 50 on the non-oxidized surface that becomes the upper surface of the resistor 30, even when the resistor 30 is a thin film based on Cr, the resistor 30 is not oxidized, so the resistance value of the resistor 30 and the stability of the gauge factor of the strain gauge 1 can be improved. Also, the stability of the TCR of the strain gauge 1 can be improved.

[0047] The above has been described by taking a thin film based on Cr as an example. However, for Ni-Cu thin films and Ni-Cr thin films as well, by providing an oxidation inhibition layer 50 on the upper surface of the resistor 30, the same effects as in the case of the thin film based on Cr can be obtained. Also, for Ni-Cu thin films and Ni-Cr thin films, by providing a functional layer having a function of promoting crystal growth and serving as a barrier layer in the lower layer of the resistor 30, the same effects as in the case of the thin film based on Cr can be obtained.

[0048] 〈Second Embodiment〉 In the second embodiment, an example of improving the stability of the TCR of the strain gauge is shown by a method different from that of the first embodiment. Note that in the second embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0049] FIG. 3 is a schematic diagram illustrating the inside of a resistor when the resistor is a Cr mixed-phase film. As shown in FIG. 3, the resistor 30 which is a Cr mixed-phase film includes α-Cr crystal grains 301 and chromium nitride 302 (CrN, Cr 2 N or both), and in this embodiment, a substance 303 is further added.

[0050] The TCR of the Cr mixed-phase film before heating without the addition of the substance 303 shows a negative value. This is because although the crystal grains of Cr are the positive component of the TCR, for example, by film formation in a nitrogen atmosphere, chromium nitride which is the negative component of the TCR is formed (CrN, Cr 2 N or both) at the grain boundaries of Cr, and the influence of chromium nitride which is the negative component of the TCR is greatly manifested.

[0051] In the Cr mixed-phase film without the addition of the substance 303, the TCR changes greatly due to heating, and the TCR of the Cr mixed-phase film becomes a low value. This is considered to be because the residual stress in the Cr mixed-phase film is relaxed and the Cr crystal grains approach each other, so that the tunnel current at the grain boundaries becomes larger and the influence of chromium nitride which is the negative component of the TCR is reduced.

[0052] In this embodiment, a substance 303 having a function of preventing α-Cr crystal grains 301 from approaching each other is added to the Cr mixed-phase film, and the substance 303 is dispersed in the Cr mixed-phase film and exists at the grain boundaries of the α-Cr crystal grains 301.

[0053] The substance 303 is not particularly limited as long as it has a function of preventing the α-Cr crystal grains 301 from approaching each other, and can be appropriately selected according to the purpose. The substance 303 has a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less, and an electrical conductivity of 10 -6 S / m or less is preferable. For example, insulating materials such as AlN, BN, TiO 2 , ZrO 2 , SiO 2 , Si 3 N 4 etc. may be mentioned. A plurality of substances selected from these groups may be mixed.

[0054] Here, the reason why it is preferable that the TCR is -30000 ppm / °C or more and +1000 ppm / °C or less is as follows. For example, when a substance having a TCR greater than +1000 ppm / °C exists at the grain boundary, the behavior of the conductor becomes dominant, so that the TCR value of the entire film becomes greater than +1000 ppm / °C. Also, when a substance having a TCR less than -30000 ppm / °C exists at the grain boundary, hopping conduction thermally activated by structural defects contributes, resulting in an unstable TCR value. On the other hand, when the substance 303 having a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less exists at the grain boundary, there is no such problem, so that the TCR of the entire Cr mixed-phase film can be stably controlled to a low value.

[0055] Also, the reason why it is preferable that the electrical conductivity is 10 -6 S / m or less is as follows. For example, when a metal is added as a substance having an electrical conductivity greater than 10 7 S / m in the Cr mixed-phase film, the metal diffuses into the Cr mixed-phase film by heating, so that the TCR changes greatly. Also, when the electrical conductivity in the Cr mixed-phase film is greater than 10 -6 S / m and less than 10 7When adding a metal compound having higher electrical properties than an insulator as a substance of 0 S / m or less, although diffusion is suppressed unlike a metal, the electrical properties of the Cr mixed-phase film are changed. On the other hand, when adding a substance 303 having an electrical conductivity of 10 -6 S / m or less to the Cr mixed-phase film, unlike a metal, diffusion is suppressed and the distance between Cr particles can be controlled, so that the TCR can be suppressed to a low value both before and after heating.

[0056] The addition amount of the substance 303 can be appropriately selected according to the film formation conditions of the resistor 30, but it can be 1 wt% to 25 wt%. In particular, when the addition amount of the substance 303 in the resistor 30 is 2 wt% to 10 wt%, it is preferable in terms of improving the crystallinity of α-Cr.

[0057] By adding a substance 303 having a function of preventing α-Cr crystal grains 301 from approaching each other to the resistor 30 which is a Cr mixed-phase film and the substance 303 existing at the grain boundaries, the bonding between the Cr crystal grains which is a positive component of the TCR is suppressed, and the TCR of the strain gauge can be made low.

[0058] That is, the substance 303 existing at the grain boundaries prevents the α-Cr crystal grains 301 from approaching each other due to relaxation of the residual stress during heating, so that the internal state of the resistor 30 hardly changes after heating compared with before heating, and the TCR of the strain gauge 1 can be maintained at a low value.

[0059] As a result, it is possible to make both the TCR before and after heating of the Cr mixed-phase film low, and suppress the change in the TCR before and after heating. That is, the stability of the TCR of the strain gauge 1 can be improved. Note that the degree of approach of the α-Cr crystal grains 301 can be controlled by the amount of the substance 303 added to the Cr mixed-phase film, and as a result, the TCR of the strain gauge 1 can be controlled.

[0060] In order to form a Cr mixed-phase film with AlN added, for example, a functional layer made of Al is formed on the upper surface 10a of the substrate 10. Then, using a raw material capable of forming a Cr mixed-phase film as a target, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering in which Ar gas is introduced into the chamber. Alternatively, using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into the chamber, the resistor 30 and the terminal portion 41 may be formed by reactive sputtering.

[0061] In these methods, the growth surface of the Cr mixed-phase film is defined by the functional layer made of Al, and a Cr mixed-phase film mainly composed of α-Cr having a stable crystal structure can be formed. Also, since Al constituting the functional layer diffuses into the Cr mixed-phase film, the gauge characteristics are improved. For example, 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. When the functional layer is formed of Al, the Cr mixed-phase film may contain Al or AlN. That is, AlN can be added from the functional layer made of Al into the Cr mixed-phase film.

[0062] Also, in order to form a Cr mixed-phase film with AlN added, Cr and Al may be used as targets respectively, and an appropriate amount of nitrogen gas may be introduced together with Ar gas into the chamber, 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.

[0063] Note that in this method, a Cr mixed-phase film with AlN added can be formed even if the Cr mixed-phase film is formed on a functional layer other than Al. Also, in this method, a Cr mixed-phase film with AlN added can be formed by directly forming a Cr mixed-phase film on the upper surface 10a of the substrate 10 without forming a functional layer.

[0064] The first embodiment and the second embodiment can be combined. For example, when the resistor 30 is a Cr mixed-phase film, Ti can be deposited as the oxidation inhibition layer 50 on the upper surface of the resistor 30, and AlN can be added as the substance 303 to the resistor 30. Further, a functional layer having a function of promoting crystal growth of the resistor 30 and a function of preventing oxidation of the resistor 30 may be provided under the resistor 30. Thereby, both effects shown in the first embodiment and the second embodiment can be obtained.

[0065] The above has been described by taking the Cr mixed-phase film as an example. However, for Ni-Cu thin films and Ni-Cr thin films as well, by adding a substance having a function of preventing crystal grains, which are the main components of the resistor, from approaching each other to the resistor, the same effects as in the case of the Cr mixed-phase film can be obtained.

[0066] 〈Third Embodiment〉 In the third embodiment, an example of adding a substance having characteristics different from those of the second embodiment to the resistor is shown. In the third embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0067] FIG. 4 is a schematic diagram illustrating the inside of a resistor when the resistor is a Cr mixed-phase film, schematically showing the states before and after heating. As shown in FIG. 4, the resistor 30 which is a Cr mixed-phase film includes α-Cr crystal grains 301 and chromium nitride 302 (CrN, one or both of Cr 2 N), and in this embodiment, a substance 304 is further added.

[0068] In a Cr mixed-phase film to which the substance 304 is not added, the TCR changes greatly due to heating, and the longer the heating time, the greater the TCR becomes in the positive direction. This is considered to be because, due to heating, the crystal grains of Cr, which are the positive components of the TCR, gradually grow, and the chromium nitride, which is the negative component of the TCR existing at the grain boundaries, is taken into the Cr film interior or pushed out to the outside, resulting in a decrease in the chromium nitride existing at the grain boundaries. Therefore, the longer the heating time, the continuously larger the TCR becomes with a positive value.

[0069] Therefore, in the present embodiment, a substance 304 having a function of suppressing the growth of α-Cr crystal grains 301 is added to the Cr mixed-phase film, and the substance 304 is dispersed in the Cr mixed-phase film.

[0070] The substance 304 is not particularly limited as long as it has a function of suppressing the growth of α-Cr crystal grains 301, and can be appropriately selected according to the purpose. The substance 304 has a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less, and an electrical conductivity of 10 -6 S / m greater than 10 7 S / m or less, and examples thereof include metal compounds such as TiN, TaN, SiTiN, and CrSiO, and semiconductors such as Si. A plurality of substances selected from these groups may be mixed.

[0071] Here, the reason why it is preferable that the TCR is -30000 ppm / °C or more and +1000 ppm / °C or less is as follows. For example, when a substance having a TCR greater than +1000 ppm / °C exists at the grain boundaries, the behavior of the conductor becomes dominant, so that the TCR value of the entire film becomes greater than +1000 ppm / °C. Also, when a substance having a TCR less than -30000 ppm / °C exists at the grain boundaries, hopping conduction thermally activated by structural defects contributes, resulting in an unstable TCR value. In contrast, when the substance 303 having a TCR of -30000 ppm / °C or more and +1000 ppm / °C or less exists at the grain boundaries, there is no such problem, so that the TCR of the entire Cr mixed-phase film can be stably controlled to a low value.

[0072] Also, the reason why it is preferable that the electrical conductivity is greater than 10 -6 S / m and less than 10 7 S / m is as follows. For example, when a metal is added as a substance having an electrical conductivity greater than 10 7 S / m in the Cr mixed-phase film, the metal diffuses into the Cr mixed-phase film by heating, so that the TCR changes greatly. Also, 10 -6When adding a substance with a conductivity of 1 S / m or less, it is impossible to control the electrical properties in the Cr mixed-phase film because almost no electricity can pass through. In contrast, when adding Substance 304 with an electrical conductivity greater than 10 -6 S / m and less than or equal to 10 7 S / m to the Cr mixed-phase film, not only is diffusion suppressed unlike in the case of a metal, but also a material with electrical properties corresponding to the characteristics of the Cr mixed-phase film can be added. Therefore, the TCR can be suppressed to a low value both before and after heating.

[0073] The addition amount of Substance 304 can be appropriately selected according to the film formation conditions of the resistor 30, but it can be set to 1 wt% to 25 wt%. In particular, when the addition amount of Substance 304 in the resistor 30 is 2 wt% to 10 wt%, it is preferable in terms of improving the crystallinity of α-Cr.

[0074] By adding Substance 304, which has 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 continuous increase in the TCR to a positive value due to heating and suppress the TCR to a low value. That is, the stability of the TCR of the strain gauge 1 can be improved. Note that the growth degree of the α-Cr crystal grains 301 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.

[0075] To form a Cr mixed-phase film to which TiN is added, for example, a functional layer made of Ti is formed on the upper surface 10a of the base material 10. Then, using a raw material capable of forming a Cr mixed-phase film as a target, the resistor 30 and the terminal portion 41 can be formed by magnetron sputtering with Ar gas introduced into the chamber. Alternatively, using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into the chamber, the resistor 30 and the terminal portion 41 may be formed by reactive sputtering.

[0076] In these methods, the growth surface of the Cr mixed-phase film is defined by the functional layer made of Ti, and a Cr mixed-phase film mainly composed of α-Cr with a stable crystal structure can be formed. Also, by the diffusion of Ti constituting the functional layer into the Cr mixed-phase film, the gauge characteristics are improved. For example, 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. When the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti or TiN. That is, TiN can be added to the Cr mixed-phase film from the functional layer made of Ti.

[0077] Also, in order to form a Cr mixed-phase film added with TiN, Cr and Ti are used as targets respectively, an appropriate amount of nitrogen gas is introduced into the 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 added with TiN can be formed.

[0078] Note that in this method, a Cr mixed-phase film added with 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 added with TiN can be formed even if the Cr mixed-phase film is directly formed on the upper surface 10a of the base material 10 without forming a functional layer.

[0079] The first embodiment and the third embodiment can be combined. For example, when the resistor 30 is a Cr mixed-phase film, Ti can be formed as an oxidation inhibition layer 50 on the upper surface of the resistor 30, and TiN can be added as the substance 304 to the resistor 30. Further, 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 may be provided under the resistor 30. Thereby, all the effects shown in the first embodiment and the third embodiment can be obtained.

[0080] Furthermore, 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 as the substance 303 and TiN can be added as the substance 304 to the resistor 30. Thereby, both effects shown in the second embodiment and the third embodiment can be obtained.

[0081] Moreover, 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, Ti can be formed as the oxidation-inhibiting layer 50 on the upper surface of the resistor 30, and AlN can be added as the substance 303 and TiN can be added as the substance 304 to the resistor 30. Further, a functional layer having a function of promoting crystal growth of the resistor 30 and a function of preventing oxidation of the resistor 30 may be provided under the resistor 30. Thereby, all effects shown in the first embodiment, the second embodiment, and the third embodiment can be obtained.

[0082] Although the above has been described by taking the Cr mixed-phase film as an example, for Ni-Cu thin films and Ni-Cr thin films as well, by adding metal compounds, semiconductors, or insulators to the resistor 30, the same effects as in the case of the Cr mixed-phase film can be obtained.

[0083] Although the preferred embodiments and the like have been described in detail above, the present invention is not limited to the above-described embodiments and the like, and various modifications and substitutions can be made to the above-described embodiments and the like without departing from the scope described in the claims.

Explanation of Reference Numerals

[0084] 1 Strain gauge, 10 Base material, 10a Upper surface, 30 Resistor, 41 Terminal portion, 50 Oxidation-inhibiting layer, 60 Cover layer, 301 α-Cr crystal grains, 302 Chromium nitride, 303, 304 Substances

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; an oxidation-inhibiting layer formed on a non-oxidized surface that is the upper surface of the resistor; 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, A strain gauge, wherein the functional layer has a thickness of 1 nm or more and 100 nm or less.

2. The oxidation inhibition layer is made of Ti, TiN, TaN, Si ３ O ４ , Si, SiO ２ , ZrO ２ 2. The strain gauge according to claim 1, which is formed from one or more materials selected from the group consisting of:

3. The resistor is made of AlN, BN, TiO ２ , ZrO ２ , SiO ２ , Si ３ N ４ 3. The strain gauge according to claim 1 or 2, further comprising one or more first substances selected from the group consisting of:

4. 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 4. The strain gauge according to claim 3, wherein the strain gage has a strain coefficient of 100 S / m or less.

5. 5. The strain gauge according to claim 1, wherein the resistor is doped with one or more second substances selected from the group consisting of TiN, TaN, SiTiN, CrSiO, and Si.

6. The second material 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 6. The strain gauge according to claim 5, wherein the strain gage has a strain coefficient of 100 S / m or less.

7. 7. The strain gauge according to claim 1, further comprising an insulating resin layer that covers the resistor.

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