JP2019219312A - Strain gauge - Google Patents

Abstract

To provide a strain gauge which can increase a signal-to-noise ratio (S/N).SOLUTION: The strain gauge includes: a flexible base material; and a resistor made of at least one of chromium and nickel. The resistor includes a first sensitive part formed on one side of the base material, the first sensitive part generating a change in the resistance in response to strain, and a second sensitive part formed on another side of the base material, the second sensitive part generating a change in the resistance in response to strain. The first and second sensitive parts have nearly the same pattern and are arranged in opposed positions across the base material.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a strain gauge.

  2. Description of the Related Art There is known a strain gauge that is attached to a measurement target to detect a strain of the measurement target. The strain gauge includes a resistor for detecting strain, and a material containing, for example, Cr (chromium) or Ni (nickel) is used as a material of the resistor. Also, for example, one resistor is formed on one surface of a base material made of an insulating resin (for example, see Patent Document 1).

JP-A-2006-74934

  By the way, when a strain gauge is adhered to a strain generator to detect a change in the resistance value of a resistor, disturbance noise or power supply noise due to electromagnetic waves or the like 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.

  The present invention has been made in view of the above points, and has as its object to provide a strain gauge capable of improving a signal-to-noise ratio (S / N).

  The present strain gauge has a flexible base material and a resistor formed from a material containing at least one of chromium and nickel, and the resistor is formed on one side of the base material. A first sensing part that generates a resistance change by receiving a strain; and a second sensing part that is formed on the other side of the base material and that generates a resistance change by receiving a strain. The sensing section and the second sensing section have substantially the same pattern, and are arranged at positions facing each other with the base material interposed therebetween.

  According to the disclosed technology, it is possible to provide a strain gauge capable of improving a signal-to-noise ratio (S / N).

FIG. 2 is a plan view illustrating a strain gauge according to the first embodiment. FIG. 2 is a bottom view illustrating the strain gauge according to the first embodiment. FIG. 2 is a cross-sectional view illustrating a strain gauge according to the first embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First Embodiment>
FIG. 1 is a plan view illustrating the strain gauge according to the first embodiment, and shows a state where the strain gauge is viewed from the upper surface side of the base material. FIG. 2 is a bottom view illustrating the strain gauge according to the first embodiment, and shows a state in which the strain gauge is viewed from the lower surface side of the base material. FIG. 3 is a cross-sectional view illustrating the strain gauge according to the first embodiment, and shows a cross section taken along line AA of FIG. Referring to FIGS. 1 to 3, the strain gauge 1 has a base material 10, a resistor 30 (resistors 31 and 32), and terminals 41 and 42.

  In the present embodiment, for the sake of convenience, in the strain gauge 1, the side on which the resistance portion 31 of the base material 10 is provided is the upper side or one side, and the side on which the resistance portion 32 is provided is the lower side or the other side. Side. In addition, the surface on the side where the resistance portion 31 is provided is defined as one surface or upper surface, and the surface on the side where the resistance portion 32 is provided is defined as the other surface or lower surface. However, the strain gauge 1 can be used upside down, or can be arranged at any angle. The plan view refers to viewing the target from the normal direction of the upper surface 10a of the base material 10, and the planar shape refers to the shape of the target viewed from the normal direction of the upper surface 10a of the base material 10. And

  The base material 10 is a member serving as a base layer for forming the resistor 30 and the like, and has flexibility. The thickness of the base material 10 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness can be about 5 μm to 500 μm. In particular, it is preferable that the thickness of the base material 10 be 5 μm to 200 μm in that the strain sensitivity error of the resistance portions 31 and 32 can be reduced.

  The substrate 10 is made of, for example, PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, polyolefin resin, and the like. From an insulating resin film. Note that a film refers to a member having a thickness of about 500 μm or less and having flexibility.

  Here, “formed from an insulating resin film” does not prevent the base material 10 from containing fillers, impurities, and the like in the insulating resin film. The substrate 10 may be formed from, for example, an insulating resin film containing a filler such as silica or alumina.

  The resistor 30 is formed on the base material 10. The resistor 30 includes resistor portions 31 and 32 stacked with the base material 10 interposed therebetween. That is, the resistor 30 is a general term for the resistor portions 31 and 32, and is referred to as the resistor 30 when it is not necessary to particularly distinguish the resistor portions 31 and 32. In FIGS. 1 and 2, for convenience, the resistance portions 31 and 32 are shown in a satin pattern.

  The resistance part 31 is a thin film formed in a predetermined pattern on the upper surface 10a side of the base material 10. The resistance portion 31 may be formed directly on the upper surface 10a of the base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. The resistance section 31 includes a sensing section (sensing section) 31S that undergoes a strain and undergoes a resistance change. Note that portions other than the sensing portion 31S of the resistance portion 31 function as a wiring pattern connected to the terminal portion 41.

  The resistance part 32 is a thin film formed in a predetermined pattern on the lower surface 10 b side of the base material 10. The resistance portion 32 may be formed directly on the lower surface 10b of the substrate 10 or may be formed on the lower surface 10b of the substrate 10 via another layer. The resistance section 32 includes a sensing section (sensing section) 32S that undergoes strain and undergoes a resistance change. Note that portions other than the sensing portion 32S of the resistance portion 32 function as a wiring pattern connected to the terminal portion 42.

  The sensing section 31S and the sensing section 32S have substantially the same pattern, and are arranged at positions facing each other with the base material 10 therebetween. In other words, the sensing unit 31S and the sensing unit 32S have substantially the same pattern, and are arranged at overlapping positions in plan view.

  Here, a pattern in which the sensing unit 31S and the sensing unit 32S are substantially the same indicates that the two patterns are almost the same as a result of being manufactured based on the same design. Means to be done.

  The portion of the wiring pattern of the resistor portion 31 and the portion of the wiring pattern of the resistor portion 32 may be arranged at positions opposed to each other with the base material 10 interposed therebetween, or may be arranged at positions opposed to each other with the base material 10 interposed therebetween. It does not have to be. Further, the terminal portion 41 and the terminal portion 42 may be arranged at positions facing each other across the base material 10 or may not be arranged at positions facing each other across the base material 10.

  The resistor 30 (the resistors 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. As a material containing Cr, for example, a Cr mixed-phase film is given. Examples of the material containing Ni include Cu-Ni (copper nickel). As a material containing both Cr and Ni, for example, Ni-Cr (nickel chromium) is given.

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N and the like are mixed. The Cr mixed phase film may contain unavoidable impurities such as chromium oxide.

  The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness can be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. It is further preferable that cracks in the film and warpage from the base material 10 due to the internal stress of the film constituting the film 30 can be reduced.

  For example, when the resistor 30 is a Cr mixed phase film, the stability of gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as a main component. Further, since the resistor 30 contains α-Cr as a main component, the gauge factor of the strain gauge 1 is 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR are within the range of −1000 ppm / ° C. to +1000 ppm / ° C. It can be. Here, the main component means that the target substance occupies 50% by mass or more of all the substances constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 contains α-Cr at 80% by weight. It is preferable to include the above. Note that α-Cr is Cr having a bcc structure (body-centered cubic lattice structure).

  The terminal portion 41 extends from both ends of the resistor portion 31 on the upper surface 10a of the base material 10, and is formed in a substantially rectangular shape with a width wider than that of the resistor portion 31 in plan view. The terminal portion 41 is a pair of electrodes for outputting a change in the resistance value of the resistance portion 31 caused by the strain to the outside, and for example, a lead wire for external connection is joined. The resistance portion 31 is connected to the other terminal portion 41, for example, while extending in a zigzag manner from one of the terminal portions 41. The upper surface of the terminal portion 41 may be covered with a metal having better solderability than the terminal portion 41. In addition, although the resistance part 31 and the terminal part 41 are shown with different symbols for convenience, they can be integrally formed of the same material in the same step.

  The terminal portions 42 extend from both ends of the resistance portion 32 on the lower surface 10b of the base material 10, and are formed in a substantially rectangular shape with a wider width than the resistance portion 32 in a plan view. The terminal part 42 is a pair of electrodes for outputting a change in the resistance value of the resistance part 32 caused by the strain to the outside, and for example, a lead wire for external connection is joined. The resistance portion 32 extends, for example, from one of the terminal portions 42 in a zigzag manner and is connected to the other terminal portion 42. The upper surface of the terminal portion 42 may be covered with a metal having better solderability than the terminal portion 42. In addition, although the resistance part 32 and the terminal part 42 are shown with different symbols for convenience, they can be integrally formed of the same material in the same step.

  Note that a through wiring (through hole) penetrating the base material 10 may be provided, and the terminal portions 41 and 42 may be integrated on the upper surface 10a side or the lower surface 10b side of the base material 10.

  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 resistance portion 31 and expose the terminal portion 41. Further, 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 resistance portion 32 and expose the terminal portion 42. The provision of the cover layers 61 and 62 can prevent the resistance portions 31 and 32 from being mechanically damaged. Further, by providing the cover layers 61 and 62, the resistance portions 31 and 32 can be protected from moisture and the like. Note that the cover layers 61 and 62 may be provided so as to cover the entire portion except for the terminal portions 41 and 42.

  The cover layers 61 and 62 can be formed from an insulating resin such as a PI resin, an epoxy resin, a PEEK resin, a PEN resin, a PET resin, a PPS resin, and a composite resin (for example, a silicone resin or a polyolefin resin). The cover layers 61 and 62 may contain a filler or a pigment.

  The thickness of the cover layers 61 and 62 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness can be about 5 μm to 500 μm. In particular, when the thickness of the cover layer 62 is 5 μm to 200 μm, in terms of the transmission of strain from the surface of the strain generating body bonded to the lower surface of the cover layer 62 via an adhesive layer and the like, and the dimensional stability to the environment. Preferably, the thickness is 10 μm or more in view of insulating properties. Note that 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 to have different thicknesses.

  In order to manufacture the strain gauge 1, first, the base material 10 is prepared, and the resistance portion 31 and the terminal portion 41 having the planar shape shown in FIG. 1 are formed on the upper surface 10a of the base material 10. The materials and thicknesses of the resistance portion 31 and the terminal portion 41 are as described above. The resistance section 31 and the terminal section 41 can be integrally formed of the same material.

  The resistance portion 31 and the terminal portion 41 can be formed by, for example, forming a film by a magnetron sputtering method using a material capable of forming the resistance portion 31 and the terminal portion 41 as a target, and patterning the film by photolithography. The resistance portion 31 and the terminal portion 41 may be formed by a reactive sputtering method, an evaporation method, an arc ion plating method, a pulse laser deposition method, or the like instead of the magnetron sputtering method.

  From the viewpoint of stabilizing the gauge characteristics, before forming the resistance portion 31 and the terminal portion 41, a function having a film thickness of about 1 nm to 100 nm as an underlayer on the upper surface 10a of the base material 10 by, for example, a conventional sputtering method. Preferably, the layer is deposited in a vacuum. After forming the resistance portion 31 and the terminal portion 41 on the entire upper surface of the functional layer, the functional layer is patterned by photolithography together with the resistance portion 31 and the terminal portion 41 into the planar shape shown in FIG.

  In the present application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper resistive portion 31. The functional layer preferably further has a function of preventing the resistance portion 31 from being oxidized by oxygen or moisture contained in the base material 10 and a function of improving the adhesion between the base material 10 and the resistance portion 31. The functional layer may further have another function.

  Since the insulating resin film forming the base material 10 contains oxygen and moisture, especially when the resistance portion 31 contains Cr, Cr forms a self-oxidized film, so that the functional layer has a function of preventing oxidation of the resistance portion 31. Providing is effective.

  The material of the functional layer is not particularly limited and may be appropriately selected depending on the purpose as long as it has a function of promoting the crystal growth of the resistive portion 31 which is the upper layer. 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), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir ( Selected from the group consisting of iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum). One or more metals that, either metal alloys of this group, or a compound of any one of metals of this group and the like.

Examples of the above alloy include FeCr, TiAl, FeNi, NiCr, CrCu and the like. Examples of the above compound include TiN, TaN, Si ₃ N ₄ , TiO ₂ , Ta ₂ O ₅ , and SiO ₂ .

  The functional layer can be formed, for example, by a conventional sputtering method using a material capable of forming the functional layer as a target and introducing an Ar (argon) gas into the chamber. By using the conventional sputtering method, the functional layer is formed while the upper surface 10a of the substrate 10 is etched with Ar, so that the effect of improving the adhesion can be obtained by minimizing the amount of the functional layer formed.

  However, this is an example of a method for forming the functional layer, and the functional layer may be formed by another method. For example, before forming the functional layer, the upper surface 10a of the base material 10 is activated by plasma treatment using Ar or the like to obtain an adhesion improving effect, and thereafter, the functional layer is formed into a vacuum by a magnetron sputtering method. May be used.

  The combination of the material of the functional layer and the material of the resistor portion 31 and the terminal portion 41 is not particularly limited and can be appropriately selected depending on the purpose. For example, Ti is used as the functional layer, and the resistor portion 31 and the terminal portion 41 are used. It is possible to form a Cr mixed phase film containing α-Cr (alpha chromium) as a main component.

  In this case, for example, the resistance portion 31 and the terminal portion 41 can be formed by a magnetron sputtering method in which a material capable of forming a Cr mixed phase film is used as a target and Ar gas is introduced into the chamber. Alternatively, the resistance portion 31 and the terminal portion 41 may be formed by a reactive sputtering method by introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber using pure Cr as a target.

  In these methods, the growth surface of the Cr mixed phase film is defined by the functional layer made of Ti, and a Cr mixed phase film having α-Cr as a main component having a stable crystal structure can be formed. Further, the gauge characteristics are improved by diffusing Ti constituting the functional layer into the Cr mixed phase film. For example, 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 in the range of −1000 ppm / ° C. to +1000 ppm / ° C. When the functional layer is formed of Ti, the Cr mixed phase film may include Ti or TiN (titanium nitride).

  When the resistance part 31 is a Cr mixed phase film, the functional layer made of Ti has a function of promoting the crystal growth of the resistance part 31 and a function of preventing the resistance part 31 from being oxidized by oxygen or moisture contained in the base material 10. , And all the functions of improving the adhesion between the base material 10 and the resistance portion 31. The same applies when Ta, Si, Al, or Fe is used instead of Ti as the functional layer.

  As described above, by providing the functional layer below the resistor 31, the crystal growth of the resistor 31 can be promoted, and the resistor 31 having a stable crystal phase can be manufactured. As a result, in the strain gauge 1, the stability of the gauge characteristics can be improved. In addition, since the material constituting the functional layer diffuses into the resistance portion 31, the gauge characteristics of the strain gauge 1 can be improved.

  Next, on the lower surface 10b of the base material 10, the planar resistive portion 32 and the terminal portion 42 shown in FIG. 2 are formed. The resistance part 32 and the terminal part 42 can be formed in the same manner as the resistance part 31 and the terminal part 41. Similarly, it is preferable to form a functional layer on the lower surface 10b of the base material 10 as a base layer before forming the resistance section 32 and the terminal section 42.

  After forming the resistance portion 31 and the terminal portion 41 and the resistance portion 32 and the terminal portion 42, if necessary, the upper surface 10a of the base material 10 is covered with a cover layer 61 that exposes the resistance portion 31 and exposes the terminal portion 41. A cover layer 62 that covers the resistor portion 32 and exposes the terminal portion 42 may be provided on the lower surface 10b of the base. Thereby, the strain gauge 1 is completed.

  The cover layer 61 is formed, for example, by laminating a thermosetting insulating resin film in a semi-cured state so as to cover the resistance portion 31 on the upper surface 10a of the base material 10 and expose the terminal portion 41, and then heat and cure the film. can do. The cover layer 62 is formed, for example, by laminating a thermosetting insulating resin film in a semi-cured state so as to cover the resistance portion 32 on the lower surface 10 b of the base material 10 and expose the terminal portion 42, and to cure by heating. Can be manufactured. The cover layers 61 and 62 may be produced by applying a liquid or paste-like thermosetting insulating resin and heating and curing the resin instead of laminating the insulating resin film.

  As described above, in the strain gauge 1, the sensing part 31 </ b> S and the sensing part 32 </ b> S have substantially the same pattern, and are arranged at positions facing each other with the base material 10 therebetween. Therefore, for example, when a bending stress occurs in which the sensing section 31S is on the pull side and the sensing section 32S is on the compression side, the output of the terminal section 41 connected to the sensing section 31S and the connection to the sensing section 32S are generated. The output of the terminal unit 42 thus obtained has substantially the same absolute value and the opposite sign. On the other hand, disturbance noise and power supply noise due to electromagnetic waves and the like are substantially equally applied to the sensing unit 31S and the sensing unit 32S. Therefore, by obtaining a difference signal between the output of the terminal unit 41 and the output of the terminal unit 42, the output is approximately doubled and noise is reduced. As a result, in the strain gauge 1, the signal-to-noise ratio (S / N) can be improved, and the sensor sensitivity can be improved.

  In addition, it is also possible to separately manufacture two strain gauges provided with the sensing parts of substantially the same pattern and paste them at positions facing each other with the strain element interposed therebetween, but the attaching work is inefficient, It is also difficult to secure the sticking accuracy. Such a problem can be solved by using one strain gauge 1 in which two sensing parts of substantially the same pattern are arranged at positions facing each other across the base material 10.

  As described above, the preferred embodiments and the like have been described in detail. However, the present invention is not limited to the above-described embodiments and the like, and various modifications may be made to the above-described embodiments and the like without departing from the scope described in the claims. Variations and substitutions can be made.

DESCRIPTION OF SYMBOLS 1 Strain gauge, 10 base material, 10a upper surface, 10b lower surface, 30 resistor, 31, 32 resistor, 31S, 32S sensing part, 41, 42 terminal, 61, 62 cover layer

Claims (8)

A flexible substrate;
A resistor formed from a material containing at least one of chromium and nickel,
The resistor is
A first sensing portion formed on one side of the base material and receiving a strain to generate a resistance change,
A second sensing portion formed on the other side of the base material and receiving a strain to cause a change in resistance,
A strain gauge in which the first sensing section and the second sensing section have substantially the same pattern, and are arranged at positions facing each other with the base material interposed therebetween.   The strain gauge according to claim 1, wherein the first sensing section and the second sensing section are formed of a Cr mixed phase film.   The strain gauge according to claim 2, wherein the first sensing section and the second sensing section mainly include alpha chrome.   The strain gauge according to claim 3, wherein the first sensing section and the second sensing section each include 80% by weight or more of alpha chrome.   The strain gauge according to any one of claims 2 to 4, wherein the first sensing part and the second sensing part include chromium nitride.   The strain according to any one of claims 1 to 5, wherein a functional layer formed of a metal, an alloy, or a compound of a metal is provided below the first sensing section and below the second sensing section. gauge.   The strain gauge according to claim 6, wherein the functional layer has a function of promoting crystal growth of the first sensing section and the second sensing section.   The strain gauge according to any one of claims 1 to 7, further comprising an insulating resin layer covering at least one of the first sensing part and the second sensing part.

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