Strain gauge

Abstract

In a strain gauge having a resistor formed on a flexible substrate, the performance of protecting the resistor is improved. [Solution] The device comprises a flexible resin substrate 10, a functional layer formed directly from a metal, alloy, or metal compound on one surface of the substrate, a plurality of resistors 30 mainly composed of α-Cr formed directly from a film containing Cr, CrN, and Cr2N on one surface of the functional layer, electrodes electrically connected to the resistors, an insulating layer 50 made of an inorganic material covering the resistors, and an insulating resin layer made of an organic material covering the insulating layer. Each of the plurality of resistors 30 has a thickness of 0.05 μm to 2 μm, the thickness of the functional layer is 1 nm to 100 nm, the electrodes include terminal portions 41 extending from the ends of the resistors and a metal layer formed on the terminal portions, and the insulating layer is an oxide film of the metal constituting the metal layer.

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 a base material made of, for example, an insulating resin and is covered with a protective film or the like (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there has been a problem that if the material for forming the layer that protects the resistor is not appropriately selected, the resistor cannot be sufficiently protected.

[0005] The present invention has been made in view of the above points, and an object thereof is to improve the performance of protecting a resistor in a strain gauge having a resistor formed on a flexible base material.

Means for Solving the Problems

[0006] This strain gauge comprises a flexible resin substrate, a functional layer formed directly on one surface of the substrate from a metal, alloy, or metal compound, a plurality of resistors mainly composed of α-Cr formed directly on one surface of the functional layer from a film containing Cr, CrN, and Cr2N, electrodes electrically connected to the resistors, an insulating layer made of an inorganic material covering the resistors, and an insulating resin layer made of an organic material covering the insulating layer. 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 each of the plurality of resistors is 0.05 μm to 2 μm, the thickness of the functional layer is 1 nm to 100 nm, the electrodes include terminal portions extending from the ends of the resistors and a metal layer formed on the terminal portions, and the insulating layer is an oxide film of the metal constituting the metal layer. [Effects of the Invention]

[0007] According to the disclosed technology, in a strain gauge having a resistor formed on a flexible substrate, the performance of protecting the resistor 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 figure illustrates the manufacturing process of a strain gauge according to the first embodiment. [Figure 4] This is a plan view illustrating a strain gauge according to a second embodiment. [Figure 5] This is a cross-sectional view illustrating a strain gauge according to a second embodiment. [Figure 6] This figure illustrates the manufacturing process of a strain gauge according to a second 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. 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, an insulating layer 50, and a cover layer 60.

[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 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 a thin film formed on the substrate 10 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. The resistor 30 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. For convenience, in Figure 1, the resistor 30 is shown with a textured surface.

[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. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0017] Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase 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 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 crystal 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, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. Also, when the resistor 30 has α-Cr as the main component, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance occupies 50 mass% or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80 wt% or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

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

[0021] The insulating layer 50 is provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portion 41. The insulating layer 50 is formed from an inorganic material. Examples of materials for the insulating layer 50 include oxides, nitrides, and nitrogen oxides of metals such as Cu, Cr, Ni, Al, Fe, W, Ti, and Ta, and alloys containing them. Semiconductors such as Si and Ge, and their oxides, nitrides, and nitrogen oxides may also be used as materials for the insulating layer 50. There are no particular restrictions on the thickness of the insulating layer 50, and it can be appropriately selected according to the purpose, but for example, it can be about 0.01 μm to 2 μm.

[0022] The cover layer 60 is an insulating resin layer provided on the upper surface 10a of the base material 10 so as to cover the insulating layer 50. The cover layer 60 can be provided so as to cover, for example, a part of the side surface and the upper surface of the insulating layer 50. The cover layer 60 may also be provided so as to cover the entire portion excluding the terminal portion 41.

[0023] The cover layer 60 is formed from an insulating organic material. Examples of materials for the cover layer 60 include PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, PE (polyethylene) resin, PVDC (polyvinylidene chloride) resin, PVDF (polyvinylidene fluoride) resin, PTFE (polytetrafluoroethylene) resin, PP (polypropylene) resin, butyl rubber, silicone rubber, and composite resins (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.

[0024] In this way, by covering the resistor 30 with an insulating layer 50 made of inorganic material, corrosion of the resistor 30 due to moisture and oxygen in the environment can be prevented. Furthermore, by covering the insulating layer 50 with a cover layer 60 made of flexible organic material, mechanical damage to the resistor 30 can be prevented. In addition, covering the insulating layer 50 with the cover layer 60 can further enhance the effect of preventing corrosion of the resistor 30 due to moisture and oxygen in the environment. Furthermore, covering the insulating layer 50 with the cover layer 60 can improve heat resistance.

[0025] In particular, using Si oxide as the material for the insulating layer 50 and butyl rubber as the material for the cover layer 60 is preferable because it provides a high level of moisture resistance.

[0026] Figure 3 is a diagram illustrating the manufacturing process of a strain gauge according to the first embodiment, and shows a cross-section corresponding to Figure 2.

[0027] To manufacture the strain gauge 1, first, in the process shown in Figure 3(a), 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.

[0028] 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, and then patterning it by photolithography. The resistor 30 and terminal portion 41 may also be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0029] 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 resistor 30 and terminal portion 41. After forming the resistor 30 and terminal portion 41 on the entire upper surface of the functional layer, the functional layer is patterned together with the resistor 30 and terminal portion 41 into the planar shape shown in Figure 1 by photolithography.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] There are no particular restrictions on the combination of materials for the functional layer and 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 to deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the resistor 30 and terminal portion 41.

[0037] In this case, for example, the resistor 30 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 resistor 30 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.

[0038] 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).

[0039] 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.

[0040] 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.

[0041] Next, in the process shown in Figure 3(b), an insulating layer 50 is formed on the upper surface 10a of the substrate 10, covering the resistor 30 and exposing the terminal portion 41. The material and thickness of the insulating layer 50 are as described above. There are no particular restrictions on the method of forming the insulating layer 50, and it can be appropriately selected depending on the purpose. Examples include vacuum processes such as sputtering, plating, and chemical vapor deposition (CVD), or solution processes such as spin coating and sol-gel coating, followed by patterning using photolithography.

[0042] Next, in the process shown in Figure 3(c), a cover layer 60 is formed on the upper surface 10a of the base material 10, covering the insulating layer 50 and exposing the terminal portion 41. The material and thickness of the cover layer 60 are as described above. 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 base material 10 so as to cover the insulating layer 50 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 of the base material 10 so as to cover the insulating layer 50 and expose the terminal portion 41, and then heating and curing it. Through the above process, the strain gauge 1 is completed.

[0043] <Second Embodiment> The second embodiment shows an example of a strain gauge in which the electrodes have a stacked structure. In the second embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0044] Figure 4 is a plan view illustrating a strain gauge according to the second embodiment. Figure 5 is a cross-sectional view illustrating a strain gauge according to the second embodiment, showing a cross-section along line BB in Figure 4. Referring to Figures 4 and 5, strain gauge 2 differs from strain gauge 1 (see Figure 1, etc.) in that it is equipped with an electrode 40A and an insulating layer 50A.

[0045] The electrode 40A has a laminated structure in which multiple metal layers are stacked. Specifically, the electrode 40A has terminal portions 41 extending from both ends of the resistor 30 and a metal layer 42 formed on the upper surface of the terminal portions 41. The material of the metal layer 42 is not particularly limited and can be appropriately selected depending on the purpose, but for example, a metal with better solderability than the terminal portion 41 (e.g., Cu (copper)) can be used. The thickness of the metal layer 42 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.01 μm to 1 μm. Furthermore, a layer made of a different metal from the metal layer 42, such as a nickel layer or a gold layer, may be stacked on top of the metal layer 42.

[0046] The insulating layer 50A is provided on the upper surface of the resistor 30. The insulating layer 50A is made of an inorganic material. Specifically, the insulating layer 50A is an oxide film of the metal that makes up the metal layer 42. For example, if the material of the metal layer 42 is Cu (copper), then the material of the insulating layer 50A is CuO (copper oxide). The thickness of the insulating layer 50A is approximately the same as the thickness of the metal layer 42.

[0047] Figure 6 is a diagram illustrating the manufacturing process of a strain gauge according to the second embodiment, and shows a cross-section corresponding to Figure 5. In order to manufacture the strain gauge 2, first, in the process shown in Figure 6(a), a base material 10 is prepared, and a metal layer 300, which will ultimately become the resistor 30 and terminal portion 41, is formed on the entire upper surface 10a of the base material 10. The material and thickness of the metal layer 300 are the same as those of the resistor 30 described above.

[0048] 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.

[0049] Similar to the first embodiment, from the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer with a thickness of about 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 metal layer 300.

[0050] Next, a metal layer 310, which will ultimately become the insulating layer 50A and the metal layer 42, is formed on the upper surface of the metal layer 300, for example, by sputtering or plating. The material and thickness of the metal layer 310 are the same as those of the metal layer 42 described above.

[0051] Next, in the process shown in Figure 6(b), the metal layers 300 and 310 are patterned by photolithography to achieve the planar shape shown in Figure 4. A pattern is formed in which the metal layer 42 is laminated on the resistor 30 and the terminal portion 41.

[0052] Next, in the process shown in Figure 6(c), the metal layer 42, excluding the portion constituting the electrode 40A, is heated and oxidized to form an insulating layer 50A consisting of an oxide film of the metal constituting the metal layer 42.

[0053] After the process shown in Figure 6(c), the cover layer 60 is formed in the same manner as in Figure 3(c), thereby completing the strain gauge 2 shown in Figures 4 and 5.

[0054] Thus, the insulating layer 50A may be formed from the oxide film of the metal layer 42 constituting the electrode 40A. In this case as well, the same effects as in the first embodiment are achieved.

[0055] 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]

[0056] 1, 2 Strain gauge, 10 Base material, 10a Top surface, 30 Resistor, 40A Electrode, 41 Terminal section, 42 Metal layer, 50, 50A Insulating layer, 60 Cover layer

Claims

1. A flexible resin base material, A functional layer formed directly from a metal, alloy, or metal compound is provided on one side of the aforementioned substrate. On one side of the functional layer, Cr, CrN, and Cr ２ Multiple resistors, mainly composed of α-Cr, are formed from a film containing N, The resistor and the electrode electrically connected, An insulating layer made of an inorganic material covers the resistor, The insulating layer comprises an insulating resin layer made of an organic material that covers the insulating layer, 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 each of the aforementioned plurality of resistors is 0.05 μm or more and 2 μm or less. The thickness of the functional layer is 1 nm or more and 100 nm or less. The electrode is A terminal portion extending from the end of the resistor, The terminal portion includes a metal layer formed on the terminal portion, The insulating layer is a strain gauge, which is an oxide film of the metal that constitutes the metal layer.

2. The strain gauge according to claim 1, wherein the metal layer is formed from copper and the insulating layer is formed from copper oxide.

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