Strain gauge

Abstract

To provide a strain gauge capable of detecting distortion in the surface of an object to be measured and distortion except the surface.SOLUTION: A strain gauge includes a resin base material 10 having flexibility and a resistance 30 formed of a material containing at least one of chromium and nickel on the base material. The resistance 30 includes: a first functional layer directly formed of metal, alloy or a metal compound on a predetermined surface of the base material; a first resistance part; a second functional layer; a second resistance part; a third functional layer; and a third resistance part. The first, second and third functional layers promoting α-Cr crystal growth have a function for depositing a film using α-Cr as a main component; the thicknesses of the first, second and third resistance parts are more than 0.05 μm or more and 2 μm or less; and the thicknesses of the first, second and third functional layers are 1 nm or more and 100 nm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A strain gauge that is attached to a measurement object to detect the strain of the measurement object is known. The strain gauge includes a resistor that detects 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 on one surface of a base material made of, for example, an insulating resin (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] Conventional strain gauges could only detect the strain on the surface of the measurement object, but there is also a need to detect strain other than the surface.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a strain gauge capable of detecting not only the strain on the surface of the measurement object but also the strain other than the surface.

Means for Solving the Problems

[0006] This strain gauge comprises a flexible resin substrate and a resistor formed on the substrate from a material containing at least one of chromium and nickel. The resistor comprises a first functional layer formed directly on a predetermined surface of the substrate from a metal, alloy, or metal compound, a first resistance portion mainly composed of α-Cr formed directly on one surface of the first functional layer from a film containing Cr, CrN, and Cr2N, a second functional layer formed directly on the predetermined surface of the substrate from a metal, alloy, or metal compound, and a second resistance portion mainly composed of α-Cr formed directly on one surface of the second functional layer from a film containing Cr, CrN, and Cr2N, with the grid direction aligned with the first resistance portion. The material includes a second resistive portion formed in a direction different from the first resistive portion, a third functional layer formed directly from a metal, alloy, or metal compound on a surface adjacent to the predetermined surface of the substrate, and a third resistive portion mainly composed of α-Cr, formed directly from a film containing Cr, CrN, and Cr2N on one surface of the third functional layer, wherein the first functional layer, the second functional layer, and the third functional layer have the function of promoting the crystal growth of α-Cr and forming a film mainly composed of α-Cr, the thickness of the first resistive portion, the second resistive portion, and the third resistive portion is 0.05 μm or more and 2 μm or less, and the thickness of the first functional layer, the second functional layer, and the third functional layer is 1 nm or more and 100 nm or less. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge capable of detecting not only surface strain but also strain on surfaces other than the surface of the object being measured. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective 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 perspective view illustrating a strain gauge according to Modification 1 of the First Embodiment. [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 perspective 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 cut along line AA in Figure 1 in a direction parallel to the YZ plane. Referring to Figures 1 and 2, the strain gauge 1 includes a base material 10, a resistor 30 (resistance parts 30x, 30y, and 30z), and a terminal part 41 (terminal parts 41x, 41y, and 41z).

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistance portion 30x is provided is referred to as the upper side or one side, and the side opposite to the side on which the resistance portion 30x is provided is referred to as the lower side or the other side. Furthermore, the side of each part on which the resistance portion 30x is provided is referred to as one side or the upper surface, and the side opposite to the side on which the resistance portion 30x is provided is referred to as the other side or the lower surface. However, the strain gauge 1 can be used upside down or positioned at any angle. Moreover, a plan view refers to viewing the object from the direction normal to the upper surface 10a of the base material 10, and a 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 resistive portion 30x, 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 1000 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 or impurities in the insulating resin film. For example, the base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0015] The resistor 30 is formed on the substrate 10 and is a sensitive part that undergoes a change in resistance when subjected to strain. The resistor 30 includes resistance parts 30x, 30y, and 30z. In other words, the resistor 30 is a collective term for the resistance parts 30x, 30y, and 30z, and is referred to as the resistor 30 when there is no need to distinguish between the resistance parts 30x, 30y, and 30z. For convenience, in Figure 1, the resistance parts 30x, 30y, and 30z are shown with a textured surface.

[0016] The resistive portion 30x is a thin film formed on the substrate 10 in a predetermined pattern, and is a sensitive portion that generates a change in resistance when strain is applied. The resistive portion 30x may be formed directly on the upper surface 10a of the substrate 10, or it may be formed on the upper surface 10a of the substrate 10 via another layer. Figure 1 is a three-dimensional Cartesian coordinate system in which the grid direction of the resistive portion 30x is the X direction. Therefore, the resistive portion 30x can detect strain in the X direction.

[0017] The resistive portion 30y is a thin film formed on the substrate 10 in a predetermined pattern, and is a sensitive portion that undergoes a change in resistance when subjected to strain. The resistive portion 30y may be formed directly on the upper surface 10a of the substrate 10, or it may be formed on the upper surface 10a of the substrate 10 via another layer. The resistive portion 30y is arranged so that its grid direction is the Y direction, and it can detect strain in the Y direction.

[0018] The resistance portion 30z is a thin film formed in a predetermined pattern on the side surface 10b adjacent to the upper surface 10a of the base material 10, and is a sensing portion that receives strain and causes a resistance change. The resistance portion 30z may be formed directly on the side surface 10b of the base material 10, or may be formed on the side surface 10b of the base material 10 via another layer. In the base material 10, the side surface 10b is substantially orthogonal to the upper surface 10a. The resistance portion 30z is arranged such that the grid direction is the Z direction, and can detect strain in the Z direction.

[0019] Thus, the resistance portions 30x, 30y, and 30z are arranged such that the grid directions are orthogonal to each other.

[0020] The resistor body 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 body 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).

[0021] 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 inevitable impurities such as chromium oxide.

[0022] The thickness of the resistor body 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 body 30 is 0.1 μm or more, it is preferable in terms of improving the crystallinity of the crystal constituting the resistor body 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 body 30 and warping from the base material​​​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).

[0024] The terminal portion 41x extends from both ends of the resistor portion 30x via the wiring pattern 40, and in a plan view, it is wider than the resistor portion 30x and is formed in a roughly rectangular shape. The terminal portion 41x is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor portion 30x caused by strain in the X direction, and for example, lead wires for external connection are joined to it. The resistor portion 30x extends from one terminal portion 41x via the wiring pattern 40 in a zigzag pattern and is connected to the other terminal portion 41x via the wiring pattern 40.

[0025] The terminal portion 41y extends from both ends of the resistor portion 30y via the wiring pattern 40, and in a plan view, it is wider than the resistor portion 30y and is formed in a roughly rectangular shape. The terminal portion 41y is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor portion 30y caused by strain in the Y direction, and for example, lead wires for external connection are joined to it. The resistor portion 30y extends from one end of the terminal portion 41y via the wiring pattern 40, folding back in a zigzag pattern, and is connected to the other end of the terminal portion 41y via the wiring pattern 40.

[0026] The terminal portion 41z extends from both ends of the resistor portion 30z via the wiring pattern 40, and in a plan view, it is wider than the resistor portion 30z and is formed in a roughly rectangular shape. The terminal portion 41z is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor portion 30z caused by strain in the Z direction, and for example, lead wires for external connection are joined to it. The resistor portion 30z extends from one terminal portion 41z via the wiring pattern 40 in a zigzag pattern and is connected to the other terminal portion 41z via the wiring pattern 40.

[0027] In the example shown in Figure 1, the terminal portions 41x, 41y, and 41z are formed on the upper surface 10a of the base material 10, but the design is not limited to this, and the terminal portions 41x, 41y, and 41z can be formed on any surface of the base material 10. The terminal portions 41x, 41y, and 41z do not have to be formed on the same surface of the base material 10.

[0028] The upper surfaces of terminal portions 41x, 41y, and 41z may be covered with a metal that has better solderability than terminal portions 41x, 41y, and 41z. Although resistor portions 30x, 30y, terminal portions 41x, 41y, and 41z are given different reference numerals for convenience, they can be formed integrally from the same material in the same process.

[0029] In addition, when there is no need to distinguish between terminal sections 41x, 41y, and 41z, they are collectively referred to as terminal section 41.

[0030] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a and side surface 10b of the base material 10 so as to cover the resistor 30 and expose 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 to cover the entire portion excluding the terminal portion 41. In Figure 1, the cover layer 60 is not shown.

[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, 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.

[0032] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as the metal layer 300) is formed on the entire upper surface 10a and side surface 10b of the base material 10, which will ultimately be patterned to form the resistor 30 and terminal portion 41. The material and thickness of the metal layer 300 are the same as those of the resistor 30 and terminal portion 41 described above.

[0033] The metal layer 300 can be formed, for example, by depositing it using a magnetron sputtering method targeting a raw material capable of forming the metal layer 300. Alternatively, the metal layer 300 may be deposited using reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0034] 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 and side surface 10b of the substrate 10 as an underlayer, for example, by conventional sputtering, before depositing the metal layer 300.

[0035] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of the resistor 30 (a patterned metal layer 300), 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 and side surface 10b of the substrate 10 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0040] 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 and side surface 10b 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.

[0041] There are no particular restrictions on the combination of materials for the functional layer and the metal layer 300 which will form the resistor 30 and terminal portion 41, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer 300.

[0042] In this case, for example, the metal layer 300 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 metal layer 300 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.

[0043] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling 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 when the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0044] Furthermore, when the resistor 30 is a Cr multiphase 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 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 Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0045] 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.

[0046] After forming the functional layer and metal layer 300 on the entire upper surface 10a and side surface 10b of the substrate 10, the functional layer and metal layer 300 formed on the upper surface 10a and the functional layer and metal layer 300 formed on the side surface 10b of the substrate 10 are patterned to the shape shown in Figure 1 by photolithography. This forms the resistor 30 and the terminal portion 41.

[0047] After forming the resistor 30 and terminal portion 41, the strain gauge 1 is completed by providing a cover layer 60 on the upper surface 10a and side surface 10b of the base material 10, if necessary, to cover the resistor 30 and expose the terminal portion 41. The cover layer 60 can be made, for example, by laminating a semi-cured thermosetting insulating resin film to the upper surface 10a and side surface 10b of the base material 10 so as to cover the resistor 30 and expose 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 and side surface 10b of the base material 10 so as to cover the resistor 30 and expose the terminal portion 41, and then heating and curing it.

[0048] Thus, a resistance section 30x with the grid direction facing the X direction and a resistance section 30y with the grid direction facing the Y direction are formed on the upper surface 10a of the substrate 10, and a resistance section 30z with the grid direction facing the Z direction is formed on the side surface 10b of the substrate 10. This makes it possible to simultaneously detect strain in the X, Y, and Z directions.

[0049] <Modification 1 of the first embodiment> Modification 1 of the first embodiment shows an example of a strain gauge with a different base material shape from that of the first embodiment. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0050] Figure 3 is a perspective view illustrating a strain gauge according to modification 1 of the first embodiment. Referring to Figure 3, strain gauge 1A differs from strain gauge 1 (see Figures 1, 2, etc.) in that the side surface 10b of the base material 10 is not substantially perpendicular to the top surface 10a.

[0051] The angle θ between the side surface 10b of the base material 10 and the top surface 10a is obtuse, and can be, for example, θ = 135 degrees. The side surface 10b of the base material 10 can be made inclined with respect to the top surface 10a by, for example, buff polishing.

[0052] In this way, by making the angle θ between the side surface 10b of the substrate 10 and the top surface 10a obtuse, exposure can be easily performed when patterning the resistive portion 30z from the metal layer 300 deposited on the side surface 10b of the substrate 10 by photolithography.

[0053] In strain gauge 1A, since the grid direction of the resistance section 30z is not oriented in the Z direction, the change in the resistance value of the resistance section 30z includes strain in the Y direction and strain in the Z direction, and therefore, strain in the Z direction cannot be directly detected. To detect strain in the Z direction, for example, the change in the resistance value of the resistance section 30z can be corrected using the change in the resistance value of the resistance section 30y. Alternatively, the change in the resistance value of the resistance section 30z can be corrected based on the inclination angle (=180-θ) of the side surface 10b. However, correction is not necessary when detecting strain in the direction of the side surface 10b of the base material 10.

[0054] 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.

[0055] For example, in the first embodiment and its modification 1, the resistive portion 30x is formed with the grid direction being the X direction, and the resistive portion 30y is formed with the grid direction being the Y direction, but it is not limited to this. The resistive portion 30y can be formed on a predetermined surface of the base material 10 with the grid direction facing a different direction from that of the resistive portion 30x. For example, the resistive portion 30y can be formed on a predetermined surface of the base material 10 with the grid direction facing a direction 45 degrees different from that of the resistive portion 30x.

[0056] Furthermore, it is not necessary to form the resistive portion 30x and the resistive portion 30y on the same surface of the base material 10; the resistive portion 30x and the resistive portion 30y may be formed on surfaces of the base material 10 that are parallel to each other. For example, the resistive portion 30x can be formed on the upper surface 10a of the base material 10, and the resistive portion 30y can be formed on the lower surface 10c of the base material 10 that is parallel to the upper surface 10a.

[0057] Furthermore, if necessary, resistors may be formed on surfaces where resistors were not formed in the first embodiment and its modified example 1. For example, resistors may be formed on all six surfaces of the substrate 10. [Explanation of Symbols]

[0058] 1, 1A Strain gauge, 10 Base material, 10a Top surface, 10b Side surface, 10c Bottom surface, 30 Resistor, 30x, 30y, 30z Resistor section, 40 Wiring pattern, 41, 41x, 41y, 41z Terminal section, 60 Cover layer

Claims

1. A flexible resin base material, The substrate has a resistor formed from a material containing at least one of chromium and nickel, The resistor is A first functional layer formed directly on a predetermined surface of the substrate from a metal, alloy, or metal compound, and Cr, CrN, and Cr ２ A first resistive element, mainly composed of α-Cr, is formed from a film containing N, A second functional layer formed directly from a metal, alloy, or metal compound on the predetermined surface or a surface parallel to the predetermined surface of the substrate, and Cr, CrN, and Cr directly on one surface of the second functional layer. ２ A second resistive section formed from a film containing N, with α-Cr as the main component, and with its grid direction oriented in a direction different from that of the first resistive section, A third functional layer formed directly from a metal, alloy, or metal compound on the predetermined surface and adjacent surface of the substrate, and Cr, CrN, and Cr directly on one surface of the third functional layer. ２ It includes a third resistive portion mainly composed of α-Cr, formed from a film containing N, The first functional layer, the second functional layer, and the third functional layer have the function of promoting the crystal growth of α-Cr and forming a film mainly composed of α-Cr. The thickness of the first resistor, the second resistor, and the third resistor is 0.05 μm or more and 2 μm or less. A strain gauge in which the thickness of the first functional layer, the second functional layer, and the third functional layer is 1 nm or more and 100 nm or less.

2. The strain gauge according to claim 1, wherein the angle between the predetermined surface and the adjacent surface is an obtuse angle.

3. The strain gauge according to claim 1, wherein the first resistance section, the second resistance section, and the third resistance section are arranged such that their grid directions are orthogonal to each other.

4. A strain gauge according to any one of claims 1 to 3, further comprising an insulating resin layer covering the resistor.

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