Strain gauge

Abstract

To provide a strain gauge capable of increasing signal to noise ratio (S / N).SOLUTION: A strain gauge includes: a base material 10 made of resin having flexibility; a functional layer formed from metal, alloy, or a metal compound directly on both the surfaces of the base material 10; and a resistor 30. The resistor 30 is formed from a film containing Cr, CrN, and Cr2 N, and includes sensing sections 31S, 32S for causing a resistance change by receiving strain with α-Cr as a main constituent. The functional layer has a function of forming a film with the α-Cr as the main constituent while accelerating crystal growth of the α-Cr. The thickness of the resistor 30 is equal to or more than 0.05 μm and is equal to or less than 2 μm. The thickness of the functional layer is equal to or more than 1 nm and is equal to or less than 100 nm. The functional layer is in nearly the same pattern as that of the sensing sections 31S, 32S and is disposed in an opposing position while sandwiching the base material 10.SELECTED DRAWING: Figure 3

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. Also, for example, one resistor is formed on one surface of a base material made of 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] By the way, when the strain gauge is adhered to a strained body to detect a change in the resistance value of the resistor, external disturbance noise such as electromagnetic waves or power supply noise may be superimposed on the output of the strain gauge. In this case, in the strain gauge, the signal-to-noise ratio (S / N) decreases, and the sensor sensitivity decreases.

[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 improving the signal-to-noise ratio (S / N).

Means for Solving the Problems

[0006] This strain gauge comprises a flexible resin base material, a first functional layer formed directly on one surface of the base material from a metal, alloy, or metal compound, a second functional layer formed directly on the other surface of the base material from a metal, alloy, or metal compound, and a resistor. The resistor is formed directly on one surface of the first functional layer from a film containing Cr, CrN, and Cr2N, and has a first sensitive portion mainly composed of α-Cr that changes resistance when strained, and has a first sensitive portion formed directly on the other surface of the second functional layer from a film containing Cr, CrN, and Cr2N. The resistor comprises a second sensitive portion formed from a film containing 2N and mainly composed of α-Cr, which undergoes a change in resistance upon strain, wherein the first functional layer and the second 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 resistor is 0.05 μm or more and 2 μm or less, the thickness of the first functional layer and the second functional layer is 1 nm or more and 100 nm or less, the first sensitive portion and the second sensitive portion have substantially the same pattern and are arranged at opposing positions with the substrate in between. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge capable of improving the signal-to-noise ratio (S / N). [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 bottom view illustrating a strain gauge according to the first embodiment. [Figure 3] This is a cross-sectional view illustrating a strain gauge according to 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 plan view illustrating a strain gauge according to the first embodiment, showing the strain gauge as viewed from the top side of the base material. Figure 2 is a bottom view illustrating a strain gauge according to the first embodiment, showing the strain gauge as viewed from the bottom side of the base material. Figure 3 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 to 3, the strain gauge 1 includes a base material 10, a resistor 30 (resistance parts 31 and 32), and terminal parts 41 and 42.

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistance portion 31 is provided is referred to as the upper side or one side, and the side on which the resistance portion 32 is provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistance portion 31 is provided in each part is referred to as one surface or the upper surface, and the surface on which the resistance portion 32 is 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, 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 substrate 10 is a base layer component for forming the resistor 30 and the like, and is flexible. The thickness of the substrate 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 substrate thickness of 5 μm to 200 μm is preferable because it can reduce the strain sensitivity error of the resistive parts 31 and 32.

[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. The resistor 30 includes resistive parts 31 and 32 laminated via the substrate 10. In other words, the resistor 30 is a collective term for the resistive parts 31 and 32, and is referred to as the resistor 30 when there is no need to distinguish between the resistive parts 31 and 32. For convenience, in Figures 1 and 2, the resistive parts 31 and 32 are shown with a textured surface.

[0016] The resistive portion 31 is a thin film formed in a predetermined pattern on the upper surface 10a of the substrate 10. The resistive portion 31 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 31 includes a sensing portion 31S that changes resistance when subjected to strain. The portion of the resistive portion 31 other than the sensing portion 31S functions as a wiring pattern connected to the terminal portion 41.

[0017] The resistive portion 32 is a thin film formed in a predetermined pattern on the lower surface 10b side of the substrate 10. The resistive portion 32 may be formed directly on the lower surface 10b of the substrate 10, or it may be formed on the lower surface 10b of the substrate 10 via another layer. The resistive portion 32 includes a sensing portion 32S that changes resistance when subjected to strain. The portion of the resistive portion 32 other than the sensing portion 32S functions as a wiring pattern connected to the terminal portion 42.

[0018] The sensing parts 31S and 32S have substantially the same pattern and are positioned opposite each other with the base material 10 in between. In other words, the sensing parts 31S and 32S have substantially the same pattern and are positioned in overlapping locations in a plan view.

[0019] Here, the fact that the sensing units 31S and 32S have substantially the same pattern means that as a result of being manufactured based on the same design, the patterns of both are almost the same, and it means that the degree of manufacturing error is acceptable.

[0020] Note that the wiring pattern portion of the resistor 31 and the wiring pattern portion of the resistor 32 may be arranged at positions facing each other with the base material 10 interposed therebetween, or may not be arranged at positions facing each other with the base material 10 interposed therebetween. Also, the terminal portions 41 and 42 may be arranged at positions facing each other with the base material 10 interposed therebetween, or may not be arranged at positions facing each other with the base material 10 interposed therebetween.

[0021] The resistor 30 (resistor portions 31 and 32) 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 a Cr mixed-phase film. Examples of the material containing Ni include Cu-Ni (copper nickel). Examples of the material containing both Cr and Ni include Ni-Cr (nickel chromium).

[0022] Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr2N, etc. are in a mixed phase. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide.

[0023] 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 cracks in the film caused by internal stress of the film constituting the resistor 30 and warping from the base material 10.

[0024] 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).

[0025] The terminal portion 41 extends from both ends of the resistive portion 31 on the upper surface 10a of the base material 10, and in a plan view, it is wider than the resistive portion 31 and formed in a substantially rectangular shape. The terminal portion 41 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistive portion 31 caused by strain, and for example, lead wires for external connection are joined to it. The resistive portion 31 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 resistive portion 31 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.

[0026] The terminal portion 42 extends from both ends of the resistive portion 32 on the lower surface 10b of the base material 10, and in a plan view, it is wider than the resistive portion 32 and formed in a substantially rectangular shape. The terminal portion 42 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistive portion 32 caused by strain, and for example, lead wires for external connection are joined to it. The resistive portion 32 extends from one terminal portion 42 in a zigzag pattern and is connected to the other terminal portion 42. The upper surface of the terminal portion 42 may be covered with a metal that has better solderability than the terminal portion 42. Although the resistive portion 32 and the terminal portion 42 are given different reference numerals for convenience, both can be formed integrally from the same material in the same process.

[0027] Alternatively, through-holes (through wiring) may be provided to penetrate the base material 10, and terminals 41 and 42 may be concentrated on the upper surface 10a or lower surface 10b of the base material 10.

[0028] A cover layer 61 (insulating resin layer) may be provided on the upper surface 10a of the base material 10 so as to cover the resistor portion 31 and expose the terminal portion 41. Alternatively, a cover layer 62 (insulating resin layer) may be provided on the lower surface 10b of the base material 10 so as to cover the resistor portion 32 and expose the terminal portion 42. Providing cover layers 61 and 62 prevents mechanical damage to the resistor portions 31 and 32. Furthermore, providing cover layers 61 and 62 protects the resistor portions 31 and 32 from moisture and other elements. Note that cover layers 61 and 62 may be provided so as to cover the entire portion excluding the terminal portions 41 and 42.

[0029] The cover layers 61 and 62 can be formed from insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resins (e.g., silicone resin, polyolefin resin). The cover layers 61 and 62 may also contain fillers or pigments.

[0030] The thickness of the cover layers 61 and 62 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 for the cover layer 62 is preferable in terms of the transmission of strain from the surface of the strain-generating body joined to the lower surface of the cover layer 62 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. The cover layer 61 and the cover layer 62 may be formed from different materials, or the cover layer 61 and the cover layer 62 may be formed with different thicknesses.

[0031] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a resistance portion 31 and a 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 resistance portion 31 and the terminal portion 41 are as described above. The resistance portion 31 and the terminal portion 41 can be formed integrally from the same material.

[0032] The resistor portion 31 and the 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 portion 31 and the terminal portion 41, and then patterning it by photolithography. The resistor portion 31 and the terminal portion 41 may also be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0033] 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 an underlayer, for example by conventional sputtering, before depositing the resistive portion 31 and the terminal portion 41. After forming the resistive portion 31 and the terminal portion 41 on the entire upper surface of the functional layer, the functional layer is patterned together with the resistive portion 31 and the terminal portion 41 into the planar shape shown in Figure 1 by photolithography.

[0034] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of the resistive portion 31, which is at least the upper layer. Preferably, the functional layer also has the function of preventing oxidation of the resistive portion 31 by oxygen and moisture contained in the substrate 10, and the function of improving the adhesion between the substrate 10 and the resistive portion 31. The functional layer may also have other functions.

[0035] Since the insulating resin film that makes up the base material 10 contains oxygen and moisture, and especially when the resistive portion 31 contains Cr, the Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the resistive portion 31.

[0036] 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 in at least the upper layer, the resistive part 31, 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] There are no particular restrictions on the combination of materials for the functional layer and the resistive portion 31 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 to deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the resistive portion 31 and terminal portion 41.

[0041] In this case, for example, the resistive portion 31 and terminal portion 41 can be formed 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 resistive portion 31 and terminal portion 41 may be formed by reactive sputtering with pure Cr as the target, using an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas.

[0042] 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).

[0043] Furthermore, when the resistive portion 31 is a Cr multiphase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the resistive portion 31, preventing oxidation of the resistive portion 31 by oxygen and moisture contained in the substrate 10, and improving the adhesion between the substrate 10 and the resistive portion 31. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0044] In this way, by providing a functional layer beneath the resistive portion 31, it becomes possible to promote crystal growth in the resistive portion 31, and a resistive portion 31 made of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the strain gauge 1 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the resistive portion 31 can improve the gauge characteristics of the strain gauge 1.

[0045] Next, a planar resistor 32 and a terminal 42, as shown in Figure 2, are formed on the lower surface 10b of the substrate 10. The resistor 32 and terminal 42 can be formed in the same manner as the resistor 31 and terminal 41. It is also preferable to form a functional layer on the lower surface 10b of the substrate 10 as an underlayer before forming the resistor 32 and terminal 42.

[0046] After forming the resistance portion 31 and terminal portion 41, and the resistance portion 32 and terminal portion 42, a cover layer 61 covering the resistance portion 31 and exposing the terminal portion 41 may be provided on the upper surface 10a of the base material 10, and a cover layer 62 covering the resistance portion 32 and exposing the terminal portion 42 may be provided on the lower surface 10b of the base material 10, if necessary. This completes the strain gauge 1.

[0047] The cover layer 61 can be manufactured, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the base material 10 so as to cover the resistor portion 31 and expose the terminal portion 41, and then heating and curing it. The cover layer 62 can also be manufactured, for example, by laminating a semi-cured thermosetting insulating resin film onto the lower surface 10b of the base material 10 so as to cover the resistor portion 32 and expose the terminal portion 42, and then heating and curing it. Instead of laminating the insulating resin film, the cover layers 61 and 62 may also be manufactured by applying a liquid or paste-like thermosetting insulating resin and heating and curing it.

[0048] Thus, in the strain gauge 1, the sensing parts 31S and 32S have substantially identical patterns and are positioned opposite each other across the base material 10. Therefore, for example, when bending stress occurs such that the sensing part 31S is on the tensile side and the sensing part 32S is on the compression side, the output of the terminal 41 connected to the sensing part 31S and the output of the terminal 42 connected to the sensing part 32S have substantially equal absolute values ​​but opposite signs. In contrast, external noise such as electromagnetic waves and power supply noise are applied substantially equally to both the sensing part 31S and the sensing part 32S. Therefore, by taking the difference signal between the output of the terminal 41 and the output of the terminal 42, the output is approximately doubled and the noise is reduced. As a result, it is possible to improve the signal-to-noise ratio (S / N) in the strain gauge 1 and improve the sensor sensitivity.

[0049] While it is possible to separately manufacture two strain gauges, each with a nearly identical pattern of sensing element, and attach them to opposing positions on either side of the strain-generating body, this process is inefficient and makes it difficult to ensure attachment accuracy. This problem can be solved by using a single strain gauge 1 in which two nearly identical sensing elements are positioned opposite each other on the base material 10.

[0050] 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]

[0051] 1 Strain gauge, 10 Base material, 10a Top surface, 10b Bottom surface, 30 Resistor, 31, 32 Resistor section, 31S, 32S Sensing section, 41, 42 Terminal section, 61, 62 Cover layer

Claims

1. A flexible resin base material, A first functional layer formed directly on one surface of the substrate from a metal, alloy, or metal compound, A second functional layer formed directly on the other surface of the aforementioned substrate from a metal, alloy, or metal compound, It has a resistor, The resistor is On one side of the first functional layer, Cr, CrN, and Cr ２ A first sensitive part formed from a film containing N, with α-Cr as the main component, which undergoes a change in resistance when strained, On the other side of the second functional layer, Cr, CrN, and Cr ２ It comprises a second sensitive part formed from a film containing N, with α-Cr as the main component, which undergoes a change in resistance when strained, The first functional layer and the second 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 resistor is 0.05 μm or more and 2 μm or less. The thickness of the first functional layer and the second functional layer is 1 nm or more and 100 nm or less. The first sensing portion and the second sensing portion have substantially the same pattern and are arranged at opposing positions with the substrate in between.

2. The strain gauge according to claim 1, further comprising an insulating resin layer covering at least one of the first sensing portion and the second sensing portion.

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