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] This invention relates to strain gauges. [Background technology]

[0002] A strain gauge is known that is attached to an object to be measured to detect its strain. The strain gauge is equipped with a resistor that detects strain, and the material used for the resistor is, for example, a material containing Cr (chromium) or Ni (nickel). The resistor is formed into a predetermined pattern by etching a metal foil, for example (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-74934 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, when using a flexible substrate, it is difficult to form a stable resistor on the substrate, resulting in problems with the stability of gauge characteristics, particularly the temperature coefficient of resistance (TCR).

[0005] The present invention has been made in view of the above points, and aims to improve the stability of the temperature coefficient of resistance TCR in strain gauges. [Means for solving the problem]

[0006] This strain gauge consists of a flexible resin base material and a direct connection on one side of the base material. From metals, alloys, or compounds of metalsThe device comprises a formed functional layer, a resistor mainly composed of α-Cr formed directly on one surface of the functional layer from a film containing Cr, CrN, and Cr2N, and an oxidation-inhibiting layer formed on the non-oxidizing surface that is the upper surface of the resistor, wherein the functional layer has the function of promoting the crystal growth of α-Cr and forming a film mainly composed of 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. be . [Effects of the Invention]

[0007] According to the disclosed technology, the stability of the temperature coefficient of resistance (TCR) in strain gauges can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 2] This is a cross-sectional view illustrating a strain gauge according to the first embodiment. [Figure 3] This is a schematic diagram (part 1) illustrating the interior of a resistor when the resistor is a Cr multiphase film. [Figure 4] This is a schematic diagram (part 2) illustrating the interior of a resistor when the resistor is a Cr multiphase film. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> Figure 1 is a plan view illustrating a strain gauge according to the first embodiment. Figure 2 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1. Referring to Figures 1 and 2, the strain gauge 1 includes a base material 10, a resistor 30, a terminal portion 41, and an oxidation-inhibiting layer 50. However, in Figure 1, the oxidation-inhibiting layer 50 is omitted from the illustration for convenience in order to show the positional relationship between the resistor 30 and the terminal portion 41.

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

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

[0013] The base material 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, or polyolefin resin. The term "film" refers to a flexible material with a thickness of approximately 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, for example, an insulating resin film containing fillers such as silica and alumina.

[0015] The resistor 30 is a thin film formed in a predetermined pattern on the base material 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 base material 10 or may be formed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown as a matte pattern.

[0016] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. Examples of the material containing Cr include, for example, a Cr mixed-phase film. Examples of the material containing Ni include, for example, Ni-Cu (nickel copper). Examples of the material containing both Cr and Ni include, for example, Ni-Cr (nickel chromium).

[0017] Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr2N, etc. are mixed-phase. The Cr mixed-phase film may contain unavoidable 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 set to 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 film cracks caused by internal stress of the film constituting the resistor 30 and warping from the base material 10.

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

[0020] The terminal portion 41 extends from both ends of the resistor 30 and, in a plan view, is wider than the resistor 30 and is formed in a substantially rectangular shape. The terminal portion 41 is a pair of electrodes for outputting the change in the resistance value of the resistor 30 caused by strain to the outside, and for example, lead wires for external connection are joined to it. The resistor 30 extends from one terminal portion 41 in a zigzag pattern and is connected to the other terminal portion 41. The upper surface of the terminal portion 41 may be covered with a metal that has better solderability than the terminal portion 41. Although the resistor 30 and the terminal portion 41 are given different reference numerals for convenience, both can be formed integrally from the same material in the same process.

[0021] The oxidation-inhibiting layer 50 is formed on the upper surfaces of the resistor 30 and the terminal portion 41, for example, in the same planar shape as the resistor 30 and the terminal portion 41. The resistance and gauge factor of a Cr-based thin film are affected by the oxidation state. Therefore, controlling the oxidation of Cr is important, but since the Cr oxide layer is generally called a passivation layer and is easily formed, controlling oxidation is difficult. Therefore, in this embodiment, an oxidation-inhibiting 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-inhibiting layer 50, the oxidation-inhibiting layer 50 on the upper surface of the terminal portion 41 may be removed.

[0022] 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, but examples include Ti, TiN, TaN, Si3O4, Si, SiO2, ZrO2, etc. Multiple substances selected from this group may be mixed together.

[0023] For example, if the resistor 30 is a Cr multiphase 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 multiphase film. Also, if the resistor 30 is a Cr multiphase 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 TCR stability of the Cr multiphase film.

[0024] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the oxidation-inhibiting layer 50 on the resistor 30 and expose the oxidation-inhibiting layer 50 on the terminal portion 41. Providing the cover layer 60 prevents mechanical damage to the resistor 30. In addition, providing the cover layer 60 protects the resistor 30 from moisture and other elements. The cover layer 60 may be provided so as to cover the entire portion of the terminal portion 41 excluding the oxidation-inhibiting layer 50.

[0025] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 60 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 60, and it can be appropriately selected depending on the purpose, but 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 terminal portion 41 in the planar shape shown in Figure 1 are formed on the upper surface 10a of the base material 10. The material and thickness of the resistor 30 and terminal portion 41 are as described above. The resistor 30 and terminal portion 41 can be formed integrally from the same material.

[0027] The resistor 30 and terminal portion 41 can be formed, for example, by depositing a film using a magnetron sputtering method targeting a raw material capable of forming the resistor 30 and terminal portion 41. Alternatively, the resistor 30 and terminal portion 41 may be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0028] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer with a thickness of approximately 1 nm to 100 nm on the upper surface 10a of the substrate 10 as a base layer, for example by conventional sputtering, before depositing the resistor 30 and terminal portion 41. The functional layer is then patterned by photolithography into the planar shape shown in Figure 1, after forming the resistor 30 and terminal portion 41 on the entire upper surface of the functional layer and forming an oxidation-inhibiting layer 50 on the entire upper surface of the resistor 30 and terminal portion 41.

[0029] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of the resistor 30, which is at least the upper layer. Preferably, the functional layer also has the function of preventing oxidation of the resistor 30 by oxygen and moisture contained in the substrate 10, and the function of improving the adhesion between the substrate 10 and the resistor 30. The functional layer may also have other functions.

[0030] Since the insulating resin film that makes up the base material 10 contains oxygen and moisture, and especially when the resistor 30 contains Cr, the Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the resistor 30.

[0031] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of the upper layer resistor 30, and can be appropriately selected according to the purpose, but 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 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 these metals, or a compound of any of these metals.

[0032] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0033] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 10a of the substrate 10 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0034] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 10a of the substrate 10 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

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

[0036] This promotes crystal growth in the resistor 30, enabling the production of a resistor 30 consisting of a stable crystalline phase, thereby improving the stability of the gauge characteristics. Furthermore, the diffusion of the material constituting the functional layer into the resistor 30 improves the gauge characteristics. Moreover, the functional layer acts as a barrier layer, suppressing 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 ratio of the strain gauge 1. In addition, the stability of the TCR of the strain gauge 1 can be further improved.

[0037] As a functional layer that promotes crystal growth and functions as a barrier layer, for example, when the resistor 30 is a Cr multiphase film, Ti or TiN can be used, but it is particularly preferable to use TiN. When Ti is diffused into the Cr multiphase film, the gauge characteristics improve, but variations in gauge characteristics occur depending on the degree of diffusion. However, when TiN is diffused into the Cr multiphase film, the diffusion in the Cr multiphase film is small, so variations in gauge characteristics due to the degree of diffusion are less likely to occur, and the stability of gauge characteristics with respect to temperature is improved.

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

[0039] In these methods, a functional layer made of TiN initiates the growth surface of the Cr multiphase film, enabling the deposition of a Cr multiphase film mainly composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of TiN constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C.

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

[0041] In this way, by providing a functional layer beneath the resistor 30, it becomes possible to promote crystal growth in the resistor 30, and a resistor 30 consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the resistor 30 can improve the gauge characteristics in the strain gauge 1.

[0042] To form the oxidation-inhibiting layer 50 on the upper surfaces of the resistor 30 and terminal portion 41, after the resistor 30 and terminal portion 41 are deposited, for example, a raw material capable of forming the oxidation-inhibiting layer 50 is targeted, and the entire upper surface of the resistor 30 and terminal portion 41 is vacuum deposited using a conventional sputtering method with Ar (argon) gas introduced into the chamber. Subsequently, the functional layer, resistor 30, terminal portion 41, and oxidation-inhibiting layer 50 are patterned into the planar shape shown in Figure 1. Then, if necessary, the oxidation-inhibiting layer 50 on the upper surface of the terminal portion 41 is removed.

[0043] By performing the deposition of the resistor 30 and terminal portion 41 and the deposition of the oxidation-inhibiting layer 50 as a series of steps in a vacuum chamber, the oxidation-inhibiting layer 50 can be deposited directly on the upper surface of the resistor 30 without the formation of an oxide layer on the upper surface of the resistor 30 and terminal portion 41. In other words, the oxidation-inhibiting layer 50 can be deposited on the non-oxidized surface that forms the upper surface of the resistor 30 and terminal portion 41.

[0044] Although the patterning exposes the sides of the resistor 30 and terminal portion 41 from the oxidation-inhibiting layer 50, oxidation from the sides is not a problem because the resistor 30 and terminal portion 41 are thin and have a small surface area.

[0045] After forming the oxidation-inhibiting layer 50, the strain gauge 1 is completed by providing a cover layer 60 on the upper surface 10a of the substrate 10, if necessary, which covers the oxidation-inhibiting layer 50 on the resistor 30 and exposes the oxidation-inhibiting layer 50 on the terminal portion 41. The cover layer 60 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the substrate 10 so as to cover the oxidation-inhibiting layer 50 on the resistor 30 and expose the oxidation-inhibiting layer 50 on the terminal portion 41, and then heating and curing it. Alternatively, the cover layer 60 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the oxidation-inhibiting layer 50 on the resistor 30 and expose the oxidation-inhibiting layer 50 on the terminal portion 41, and then heating and curing it.

[0046] In this way, by forming an oxidation-inhibiting layer 50 on the non-oxidized surface that forms the upper surface of the resistor 30, the resistor 30 will not be oxidized even if the resistor 30 is a thin film with Cr as the base material. Therefore, the stability of the resistance value of the resistor 30 and the gauge factor of the strain gauge 1 can be improved. In addition, the stability of the TCR of the strain gauge 1 can be improved.

[0047] The above explanation used a Cr-based thin film as an example, but the same effects can be obtained with Ni-Cu thin films and Ni-Cr thin films by providing an oxidation-inhibiting layer 50 on the upper surface of the resistor 30. Furthermore, the same effects can be obtained with Ni-Cu thin films and Ni-Cr thin films by providing a functional layer below the resistor 30 that promotes crystal growth and acts as a barrier layer.

[0048] <Second Embodiment> The second embodiment shows an example of improving the TCR stability of a strain gauge using a method different from that of the first embodiment. In the second embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0049] Figure 3 is a schematic diagram illustrating the interior of a resistor when the resistor is a Cr multiphase film. As shown in Figure 3, the resistor 30, which is a Cr multiphase film, contains α-Cr crystal grains 301 and chromium nitride 302 (either CrN, Cr2N, or both), but in this embodiment, a further substance 303 is added.

[0050] The TCR of the Cr multiphase film before heating, without the addition of substance 303, shows a negative value. This is thought to be because, although Cr crystal grains are a positive component of TCR, deposition in a nitrogen atmosphere, for example, causes chromium nitride (either CrN, Cr2N, or both), which is a negative component of TCR, to form at the grain boundaries of Cr, and the influence of chromium nitride, a negative component of TCR, becomes significant.

[0051] In Cr multiphase films without added substance 303, heating significantly alters the TCR, resulting in a lower TCR value. This is thought to be because the residual stress in the Cr multiphase film is relieved, bringing the Cr crystal grains closer together, which increases the tunneling current at the grain boundaries and reduces the influence of chromium nitride, the negative component of TCR.

[0052] In this embodiment, a substance 303 that has the function of preventing α-Cr crystal grains 301 from coming close together is added to the Cr multiphase film, and the substance 303 is dispersed in the Cr multiphase film and exists at the grain boundaries of the α-Cr crystal grains 301.

[0053] Material 303 is not particularly limited as long as it has the function of preventing α-Cr crystal grains 301 from coming close together, and can be appropriately selected according to the purpose. Material 303 has a TCR of -30000 ppm / ℃ or higher and +1000 ppm / ℃ or lower, and an electrical conductivity of 10 -6 The ratio is preferably S / m or less, and examples include insulators such as AlN, BN, TiO2, ZrO2, SiO2, and Si3N4. Multiple substances selected from this group may be mixed together.

[0054] The reason why a TCR between -30000 ppm / °C and +1000 ppm / °C is preferable is as follows: For example, if a substance with a TCR greater than +1000 ppm / °C is present at the grain boundary, the behavior of the conductor becomes dominant, causing the overall TCR value of the film to exceed +1000 ppm / °C. Also, if a substance with a TCR less than -30000 ppm / °C is present at the grain boundary, thermally activated hopping conduction due to structural defects contributes, resulting in an unstable TCR value. In contrast, if substance 303 with a TCR between -30000 ppm / °C and +1000 ppm / °C is present at the grain boundary, the above problems do not occur, and the overall TCR of the Cr multiphase film can be stably controlled to a low value.

[0055] Also, the electrical conductivity is 10 -6 The reason why it is preferable for the electrical conductivity to be 10 S / m or less is as follows: For example, in a Cr multiphase film, the electrical conductivity is 10 7 When a metal is added as a substance with a S / m ratio greater than 10, heating causes the metal to diffuse into the Cr multiphase film, resulting in a significant change in TCR. Also, when the electrical conductivity of the Cr multiphase film is 10 -6 Larger than S / m, 10 7When adding a metal compound with higher electrical properties than an insulator as a substance with a conductivity of 10 S / m or less, diffusion is suppressed, unlike with metals, but it changes the electrical properties of the Cr multiphase film. In contrast to these, when adding a metal compound with an electrical conductivity of 10 S / m or less to a Cr multiphase film, -6 When substance 303, which has a S / m or less, is added, unlike metals, diffusion is suppressed and the distance between Cr particles can be controlled, so the TCR can be kept low both before and after heating.

[0056] The amount of substance 303 added can be appropriately selected depending on the film formation conditions of the resistor 30, but can be between 1% and 25% by weight. In particular, an amount of substance 303 added to the resistor 30 of 2% to 10% by weight is preferable because it improves the crystallinity of α-Cr.

[0057] By adding a substance 303, which has the function of preventing α-Cr crystal grains 301 from coming close together, to the resistor 30, which is a Cr multiphase film, the presence of substance 303 at the grain boundaries suppresses the bonding between crystal grains of Cr, which is the positive component of TCR, and thus the TCR of the strain gauge can be reduced to a low value.

[0058] In other words, the material 303 present at the grain boundaries prevents the α-Cr crystal grains 301 from coming closer together due to residual stress relaxation during heating. As a result, the internal state of the resistor 30 does not change significantly after heating, and the TCR of the strain gauge 1 can be maintained at a low value.

[0059] As a result, it becomes possible to keep the TCR of the Cr multiphase film low both before and after heating, thereby suppressing changes in TCR before and after heating. In other words, the stability of the TCR of strain gauge 1 can be improved. Furthermore, the degree to which the α-Cr crystal grains 301 come close together can be controlled by the amount of substance 303 added to the Cr multiphase film, and as a result, the TCR of strain gauge 1 can be controlled.

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

[0061] In these methods, the functional layer made of Al (Al) defines the growth surface of the Cr multiphase film, allowing for the formation of a Cr multiphase film mainly composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Al (Al) constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that if the functional layer is formed from Al, the Cr multiphase film may contain Al or AlN. In other words, AlN can be added to the Cr multiphase film from the functional layer made of Al.

[0062] Alternatively, in order to form a Cr multiphase film with added AlN, the resistor 30 and terminal portion 41 may be formed by reactive sputtering, with Cr and Al as targets, and an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, Al is formed as AlN in the Cr multiphase film, and a Cr multiphase film with added AlN can be formed.

[0063] Furthermore, with this method, a Cr multiphase film with added AlN can be formed even if the Cr multiphase film is deposited on a functional layer other than Al. Also, with this method, a Cr multiphase film with added AlN can be formed even if the Cr multiphase film is deposited directly on the upper surface 10a of the substrate 10 without forming a functional layer.

[0064] The first and second embodiments can be combined. For example, if the resistor 30 is a Cr multiphase film, a Ti film can be formed on the upper surface of the resistor 30 as an oxidation-inhibiting layer 50, and AlN can be added to the resistor 30 as substance 303. Furthermore, a functional layer having the function of promoting crystal growth of the resistor 30 and the function of preventing oxidation of the resistor 30 may be provided in the lower layer of the resistor 30. This makes it possible to obtain both the effects shown in the first and second embodiments.

[0065] The above explanation used a Cr multiphase film as an example, but the same effect can be obtained with 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 components of the resistor, from coming close together.

[0066] <Third Embodiment> The third embodiment shows an example in which a substance with different properties from that of the second embodiment is added to the resistor. In the third embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0067] Figure 4 is a schematic diagram illustrating the interior of a resistor when the resistor is a Cr multiphase film, schematically showing the state before and after heating. As shown in Figure 4, the resistor 30, which is a Cr multiphase film, contains α-Cr crystal grains 301 and chromium nitride 302 (either CrN, Cr2N, or both), but in this embodiment, substance 304 is further added.

[0068] In Cr multiphase films without substance 304 added, heating significantly alters the TCR, with the TCR increasing in the positive direction as the heating time increases. This is thought to be because heating causes the Cr crystal grains, which are the positive component of TCR, to gradually grow, and the chromium nitride, which is the negative component of TCR present at the grain boundaries, is either incorporated into the Cr film or pushed out, thus reducing the amount of chromium nitride present at the grain boundaries. Therefore, the TCR continues to increase in the positive direction as the heating time increases.

[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 the 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 or more and 10 7 S / m or less. For example, metal compounds such as TiN, TaN, SiTiN, and CrSiO, and semiconductors such as Si can be mentioned. 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 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 a 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 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 more than 10 -6 S / m and 10 7 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 due to heating, so the TCR changes greatly. Also, when a substance of 10 -6 S / m or less is added, the electrical characteristics in the Cr mixed-phase film cannot be controlled because almost no electricity passes through. In contrast, when the electrical conductivity in the Cr mixed-phase film is 10-6 Larger than S / m, 10 7 When adding substance 304, which has a S / m or less, diffusion is suppressed, unlike with metals. Furthermore, it is possible to add materials with electrical properties corresponding to the characteristics of the Cr multiphase film, thus keeping the TCR low both before and after heating.

[0073] The amount of substance 304 added can be appropriately selected depending on the film formation conditions of the resistor 30, but can be between 1% and 25% by weight. In particular, an amount of substance 304 added to the resistor 30 of 2% to 10% by weight is preferable because it improves the crystallinity of α-Cr.

[0074] By adding a substance 304, which has the function of suppressing the growth of α-Cr crystal grains 301, to the resistor 30, which is a Cr multiphase film, it is possible to suppress the TCR from continuously increasing to a positive value due to heating and keep the TCR at a low value. In other words, the stability of the TCR of the strain gauge 1 can be improved. Furthermore, the degree of growth of the α-Cr crystal grains 301 can be controlled by the amount of substance 304 added to the Cr multiphase film, and as a result, the TCR of the strain gauge 1 can be controlled.

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

[0076] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, allowing for the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that if the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN. In other words, TiN can be added to the Cr multiphase film from the functional layer made of Ti.

[0077] Alternatively, in order to form a Cr multiphase film with added TiN, the resistor 30 and terminal portion 41 may be formed by reactive sputtering, with Cr and Ti as targets, and an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, Ti is formed as TiN in the Cr multiphase film, and a Cr multiphase film with added TiN can be formed.

[0078] Furthermore, this method allows for the formation of a Cr multiphase film with added TiN even when a Cr multiphase film is deposited on a functional layer other than Ti. Additionally, this method allows for the formation of a Cr multiphase film with added TiN even when a Cr multiphase film is deposited directly on the upper surface 10a of the substrate 10 without forming a functional layer.

[0079] The first and third embodiments can be combined. For example, if the resistor 30 is a Cr multiphase film, a Ti film can be formed on the upper surface of the resistor 30 as an oxidation-inhibiting layer 50, and TiN can be added to the resistor 30 as substance 304. Furthermore, a functional layer having the function of promoting crystal growth of the resistor 30 and the function of preventing oxidation of the resistor 30 may be provided in the lower layer of the resistor 30. This makes it possible to obtain all the effects shown in the first and third embodiments.

[0080] Furthermore, the second and third embodiments can be combined. For example, if the resistor 30 is a Cr multiphase film, AlN can be added as substance 303 and TiN as substance 304 to the resistor 30. This makes it possible to obtain both the effects shown in the second and third embodiments.

[0081] Furthermore, the first, second, and third embodiments can be combined. For example, if the resistor 30 is a Cr multiphase film, a Ti film can be formed on the upper surface of the resistor 30 as an oxidation-inhibiting layer 50, and AlN can be added to the resistor 30 as substance 303, and TiN as substance 304. In addition, a functional layer having the function of promoting crystal growth of the resistor 30 and the function of preventing oxidation of the resistor 30 may be provided in the lower layer of the resistor 30. This makes it possible to obtain all the effects shown in the first, second, and third embodiments.

[0082] The above explanation used a Cr multiphase film as an example, but the same effects can be obtained with Ni-Cu thin films and Ni-Cr thin films by adding metal compounds, semiconductors, or insulators to the resistor 30.

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

[0084] 1 Strain gauge, 10 Substrate, 10a Top surface, 30 Resistor, 41 Terminal section, 50 Oxidation inhibitor layer, 60 Cover layer, 301 α-Cr crystal grains, 302 Chromium nitride, 303, 304 Substance

Claims

1. A flexible resin base material, A functional layer formed directly on one surface of the aforementioned substrate from a metal, alloy, or metal compound, On one side of the functional layer, Cr, CrN, and Cr ２ A resistor mainly composed of α-Cr, formed from a film containing N, The resistor has an oxidation-inhibiting layer formed on the non-oxidized surface which is the upper surface of the resistor, The functional layer has the function of promoting the crystal growth of α-Cr and forming a film mainly composed of α-Cr. The thickness of the resistor is 0.05 μm or more and 2 μm or less. A strain gauge having a functional layer thickness of 1 nm or more and 100 nm or less.

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

3. The strain gauge according to claim 1 or 2, wherein one or more first substances selected from the group consisting of AlN, BN, TiO2, ZrO2, SiO2, and Si3N4 are added to the resistor.

4. The first substance has a temperature coefficient of resistance of -30,000 ppm / °C or higher and +1,000 ppm / °C or lower, and an electrical conductivity of 10 －６ The strain gauge according to claim 3, wherein the strain ratio is S / m or less.

5. The strain gauge according to any one of claims 1 to 4, wherein the resistor is given one or more second substances selected from the group consisting of TiN, TaN, SiTiN, CrSiO, and Si.

6. The second substance has a temperature coefficient of resistance of -30,000 ppm / °C or higher and +1,000 ppm / °C or lower, and an electrical conductivity of 10 －６ Greater than S / m, 10 ７ The strain gauge according to claim 5, wherein the strain ratio is S / m or less.

7. A strain gauge according to any one of claims 1 to 6, comprising an insulating resin layer covering the resistor.

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