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 technology]

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain of the object. The strain gauge has a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni). The resistor is formed on one surface of a substrate made of insulating resin (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional strain gauges can only detect strain on the surface of an object being measured, but there is also a demand for detecting strain on areas other than the surface.

[0005] The present invention has been made in view of the above points, and has as its object to provide a strain gauge that can detect strains not only on the surface of an object to be measured but also on areas other than the surface. [Means for solving the problem]

[0006] This strain gauge has a flexible resin substrate and a resistor formed on the substrate from a material containing at least one of chromium and nickel, the resistor comprising: a first functional layer formed from a metal, alloy, or metal compound directly on a predetermined surface of the substrate; a first resistance portion formed from a film containing Cr, CrN, and Cr2N directly on one surface of the first functional layer and containing α-Cr as its main component; a second functional layer formed from a metal, alloy, or metal compound directly on the predetermined surface of the substrate or on a surface parallel to the predetermined surface; and a second resistance portion formed from a film containing Cr, CrN, and Cr2N directly on one surface of the second functional layer and containing α-Cr as its main component, with the grid direction extending in the direction of the first resistance portion. the first functional layer, the second functional layer, and the third functional layer have the function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component, and the thickness of the first functional layer, the second functional layer, and the third functional layer are 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 are 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 that can detect strain not only on the surface of an object to be measured but also on areas other than the surface. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view illustrating a strain gauge according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 3] FIG. 2 is a perspective view illustrating a strain gauge according to a first modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment Fig. 1 is a perspective view illustrating a strain gauge according to a first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section taken along line AA in Fig. 1 in a direction parallel to the YZ plane. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30 (resistance portions 30x, 30y, and 30z), and terminal portions 41 (terminal portions 41x, 41y, and 41z).

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistance portion 30x of the substrate 10 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 other side. Furthermore, the surface on which the resistance portion 30x of each portion is provided is referred to as the one side or upper side, and the surface opposite to the side on which the resistance portion 30x is provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0012] The substrate 10 is a flexible member that serves as a base layer for forming the resistor portion 30x and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 1000 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[0013] The substrate 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, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 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 an insulating resin film containing fillers such as silica or alumina, for example.

[0015] The resistor 30 is formed on the substrate 10 and is a sensitive part that changes resistance when strained. The resistor 30 includes resistance portions 30x, 30y, and 30z. That is, the resistor 30 is a general term for the resistance portions 30x, 30y, and 30z, and will be referred to as resistor 30 when there is no need to particularly distinguish between the resistance portions 30x, 30y, and 30z. For convenience, the resistance portions 30x, 30y, and 30z are shown in FIG. 1 with a matte finish.

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

[0017] The resistor section 30y is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing section that generates a resistance change when strain is received. The resistor section 30y may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. The resistor section 30y is arranged so that the grid direction is the Y direction, and can detect strain in the Y direction.

[0018] The resistor section 30z is a thin film formed in a predetermined pattern on the side surface 10b adjacent to the top surface 10a of the substrate 10, and is a sensing section that generates a resistance change when strain is applied. The resistor section 30z may be formed directly on the side surface 10b of the substrate 10, or may be formed on the side surface 10b of the substrate 10 via another layer. In the substrate 10, the side surface 10b is approximately perpendicular to the top surface 10a. The resistor section 30z is arranged so that the grid direction is in the Z direction, and can detect strain in the Z direction.

[0019] In this way, the resistance portions 30x, 30y, and 30z are arranged so that the grid directions are perpendicular to each other.

[0020] 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 mixed phase film. An example of a material containing Ni is Ni-Cu (nickel copper). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0021] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0022] The thickness of resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0023] 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 has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

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

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

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

[0027] 1, the terminal portions 41x, 41y, and 41z are formed on the upper surface 10a of the substrate 10, but this is not limitative, and the terminal portions 41x, 41y, and 41z can be formed on any surface of the substrate 10. The terminal portions 41x, 41y, and 41z do not have to be formed on the same surface of the substrate 10.

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

[0029] When there is no need to particularly distinguish between the terminal portions 41x, 41y, and 41z, they will be collectively referred to as the terminal portion 41.

[0030] A cover layer 60 (insulating resin layer) may be provided on the top surface 10a and side surface 10b of the substrate 10 so as to cover the resistor 30 and expose the terminal portion 41. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the terminal portion 41. The cover layer 60 is not shown in FIG. 1.

[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 or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0032] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer 300) is formed on the entire top surface 10a and side surface 10b of the substrate 10. The metal layer 300 is ultimately patterned to become 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 by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer 300. Instead of magnetron sputtering, the metal layer 300 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0034] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer having a thickness of approximately 1 nm to 100 nm on the upper surface 10a and side surface 10b of the substrate 10 as a base layer, for example, by conventional sputtering, before depositing the metal layer 300.

[0035] In this application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the resistor 30 (having a patterned metal layer 300). The functional layer preferably also has a function of preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer may also have other functions.

[0036] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the resistor 30, especially when the resistor 30 contains Cr.

[0037] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the resistor 30, and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Examples of suitable metals 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), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0038] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0039] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the top surface 10a and side surface 10b of the substrate 10 with Ar, which minimizes the amount of functional layer formed and improves adhesion.

[0040] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a and the side surface 10b of the substrate 10 are activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0041] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer 300 that becomes the resistor 30 and the terminal portion 41, and it can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer 300.

[0042] In this case, for example, the metal layer 300 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer 300 can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber.

[0043] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0044] When the resistor 30 is a Cr mixed phase 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 due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the resistor 30. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0045] In this way, by providing a functional layer below the resistor 30, it is possible to promote crystal growth of the resistor 30, and to produce a resistor 30 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material constituting the functional layer into the resistor 30, it is possible to improve the gauge characteristics of the strain gauge 1.

[0046] After the functional layer and metal layer 300 are formed over 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 of the substrate 10 and the functional layer and metal layer 300 formed on the side surface 10b of the substrate 10 are patterned by photolithography into the shape shown in Fig. 1. This forms the resistor 30 and the terminal portion 41.

[0047] After forming the resistor 30 and the terminal portions 41, a cover layer 60 that covers the resistor 30 and exposes the terminal portions 41 is provided on the upper surface 10a and side surface 10b of the substrate 10 as needed, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a and side surface 10b of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a and side surface 10b of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41, and then heating and curing the resin.

[0048] In this way, the resistor section 30x whose grid direction faces the X direction and the resistor section 30y whose grid direction faces the Y direction are formed on the upper surface 10a of the substrate 10, and the resistor section 30z whose grid direction faces the Z direction are formed on the side surface 10b of the substrate 10. This makes it possible to simultaneously detect strain in the three directions X, Y, and Z.

[0049] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example of a strain gauge is shown in which the shape of the substrate is different from that of Embodiment 1. Note that in Modification 1 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

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

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

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

[0053] In the strain gauge 1A, since the grid direction of the resistor portion 30z does not face the Z direction, the change in the resistance value of the resistor portion 30z includes strain in both the Y and Z directions, and 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 resistor portion 30z can be corrected using the change in the resistance value of the resistor portion 30y. Alternatively, the change in the resistance value of the resistor portion 30z can be corrected based on the inclination angle (=180-θ) of the side surface 10b. However, when detecting strain in the direction of the side surface 10b of the substrate 10, correction is not necessary.

[0054] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

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

[0056] Furthermore, the resistor portion 30x and the resistor portion 30y do not need to be formed on the same surface of the substrate 10, and the resistor portion 30x and the resistor portion 30y may be formed on parallel surfaces of the substrate 10. For example, the resistor portion 30x can be formed on the upper surface 10a of the substrate 10, and the resistor portion 30y can be formed on the lower surface 10c of the substrate 10 that is parallel to the upper surface 10a.

[0057] Furthermore, if necessary, resistors may be formed on surfaces where no resistors were 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 substrate, 10a upper surface, 10b side surface, 10c lower surface, 30 resistor, 30x, 30y, 30z resistor portion, 40 wiring pattern, 41, 41x, 41y, 41z terminal portion, 60 cover layer

Claims

1. a flexible resin substrate; a resistor formed on the substrate from a material containing at least one of chromium and nickel, The resistor is A first functional layer formed of a metal, an alloy, or a metal compound is directly formed on a predetermined surface of the substrate, and a layer of Cr, CrN, and Cr is directly formed on one surface of the first functional layer. ２ a first resistor portion formed from a film containing N and containing α-Cr as a main component; A second functional layer formed of a metal, an alloy, or a metal compound is formed directly on the predetermined surface of the base material or on a surface parallel to the predetermined surface, and a second functional layer formed of Cr, CrN, and Cr is formed directly on one surface of the second functional layer. ２ a second resistor portion formed from a film containing N, containing α-Cr as a main component, and having a grid direction oriented in a direction different from that of the first resistor portion; a third functional layer formed of a metal, an alloy, or a metal compound directly on a surface of the base material adjacent to the predetermined surface; and a third functional layer formed of Cr, CrN, and Cr directly on one surface of the third functional layer. ２ a third resistor portion formed from a film containing N and containing α-Cr as a main component, the first functional layer, the second functional layer, and the third functional layer have a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; the first resistor portion, the second resistor portion, and the third resistor portion each have a thickness of 0.05 μm or more and 2 μm or less; A strain gauge, wherein 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. 2. The strain gauge according to claim 1, wherein the angle formed between the predetermined surface and the surface adjacent to the predetermined surface is an obtuse angle.

3. The strain gauge according to claim 1 , wherein the first resistor portion, the second resistor portion, and the third resistor portion are arranged so that their grid directions are perpendicular to each other.

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

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