阅读说明：本技术 应变片 (Strain gauge ) 是由 浅川寿昭 相泽祐汰 户田慎也 高田真太郎 丹羽真一 于 2018-09-26 设计创作，主要内容包括：本应变片包括：基材,具有可挠性；功能层,在所述基材的一个表面上,由金属、合金、或金属的化合物形成；以及电阻体,在所述功能层的一个表面上,由包含铬和镍中的至少一者的材料形成。(This foil gage includes: a substrate having flexibility; a functional layer formed of a metal, an alloy, or a compound of a metal on one surface of the substrate; and a resistor formed of a material containing at least one of chromium and nickel on one surface of the functional layer.)

1. A strain gage, comprising:

A substrate having flexibility;

A functional layer formed of a metal, an alloy, or a compound of a metal on one surface of the substrate; and

And a resistor formed of a material containing at least one of chromium and nickel on one surface of the functional layer.

2. The strain gage of claim 1, wherein,

The functional layer has a function of promoting crystal growth of the resistor.

3. The strain gage of claim 1 or 2,

the resistor body contains α -chromium as a main component.

4. The strain gage of claim 3, wherein,

the resistor body contains 80 wt% or more of alpha-chromium.

5. The strain gage of claim 3 or 4,

The resistor body includes chromium nitride.

6. The strain gage of claim 5, wherein,

The functional layer comprises titanium.

7. The strain gage of claim 6, wherein,

The resistor body contains titanium.

8. The strain gage of claim 6 or 7,

The resistor body includes titanium nitride.

9. The strain gage of any one of claims 1-8,

The strain gauge includes an insulating resin layer covering the resistor.

Technical Field

The invention relates to a strain gauge (strain gauge).

Background

A strain gauge is known which is attached to an object to be measured to detect strain of the object to be measured. The strain gauge has a resistor for detecting strain, and a material containing Cr (chromium) or Ni (nickel), for example, is used as a material of the resistor. The resistor is formed on a base material made of, for example, an insulating resin (see, for example, patent document 1).

< Prior Art document >

< patent document >

Patent document 1: japanese unexamined patent publication No. 2016-74934

Disclosure of Invention

< problems to be solved by the present invention >

However, when a flexible substrate is used, it is difficult to form a stable resistor on the substrate, and the stability of the strain characteristics (strain rate, strain rate temperature coefficient TCS, and resistance temperature coefficient TCR) is insufficient.

In view of the above problems, an object of the present invention is to improve the stability of strain characteristics in a strain sheet including a resistor formed on a flexible substrate.

< means for solving the problems >

This foil gage includes: a substrate having flexibility; a functional layer formed of a metal, an alloy, or a compound of a metal on one surface of the substrate; and a resistor formed of a material containing at least one of chromium and nickel on one surface of the functional layer.

< effects of the invention >

According to the disclosed technology, the stability of strain characteristics can be improved in a strain gauge including a resistor formed on a flexible substrate.

Drawings

Fig. 1 is a plan view showing a strain gauge according to embodiment 1.

Fig. 2 is a sectional view showing a strain gauge according to embodiment 1.

Fig. 3A is a view (1 thereof) showing a manufacturing process of a strain gauge according to embodiment 1.

Fig. 3B is a view (2 thereof) showing a manufacturing process of the strain gauge according to embodiment 1.

Fig. 4 is a graph showing the results of fluorescent X-ray analysis of the functional layer.

Fig. 5 is a graph showing the results of X-ray diffraction of the resistor.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and overlapping description may be omitted.

< embodiment 1 >

Fig. 1 is a plan view showing a strain gauge according to embodiment 1. 3 fig. 3 2 3 is 3 a 3 sectional 3 view 3 showing 3 a 3 strain 3 gauge 3 according 3 to 3 embodiment 3 1 3, 3 showing 3 a 3 section 3 along 3 line 3 a 3- 3 a 3 of 3 fig. 3 1 3. 3 As shown in fig. 1 and 2, the strain gauge 1 includes a substrate 10, a functional layer 20, a resistor 30, and a terminal portion 41.

In the present embodiment, for convenience, in the strain gauge 1, the side of the substrate 10 on which the resistor 30 is provided is the upper side or one side, and the side on which the resistor 30 is not provided is the lower side or the other side. The surface of each portion on the side where the resistor 30 is provided is one surface or an upper surface, and the surface on the side where the resistor 30 is not provided is the other surface or a lower surface. However, the strain gauge 1 may be used in an upside-down state, or the strain gauge 1 may be arranged at an arbitrary angle. The plan view is a view of the object viewed from the normal direction of the upper surface 10a of the base material 10, and the planar shape is a shape of the object viewed from the normal direction of the upper surface 10a of the base material 10.

The base material 10 is a member for forming a base layer of the resistor 30 and the like, and has flexibility. The thickness of the substrate 10 is not particularly limited and may be appropriately selected according to the purpose, and may be, for example, about 5 μm to 500 μm. In particular, the thickness of the substrate 10 is preferably 5 μm to 200 μm from the viewpoint of the transmission of strain from the surface of the strain body bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability with respect to the environment, and more preferably 10 μm or more from the viewpoint of the insulation property.

The substrate 10 may be formed of 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 thin film is a member having a thickness of about 500 μm or less and having flexibility.

Here, "formed of an insulating resin film" does not prevent the insulating resin film of the substrate 10 from containing a filler, impurities, or the like. The substrate 10 may be formed of an insulating resin film containing a filler such as silica or alumina.

The functional layer 20 is formed as a lower layer of the resistor 30 on the upper surface 10a of the substrate 10. That is, the planar shape of the functional layer 20 is substantially the same as the planar shape of the resistor 30 shown in fig. 1. The functional layer 20 may have a thickness of about 1nm to 100nm, for example.

In the present application, the functional layer is a layer having at least a function of promoting crystal growth of the resistor 30 as an upper layer. The functional layer 20 preferably further has a function of preventing the resistor 30 from being oxidized by oxygen or moisture contained in the substrate 10 and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer 20 may also have other functions.

Since the insulating resin film constituting the substrate 10 contains oxygen or moisture, particularly when the resistor 30 contains Cr (chromium), Cr forms an autoxidation film, and thus it is effective to provide the functional layer 20 with a function of preventing oxidation of the resistor 30.

The material of the functional layer 20 is not particularly limited as long as it has at least a function of promoting crystal growth of the resistor 30 as an upper layer, examples of the metal include one or more metals selected from the group consisting of 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 (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in the group, and a compound of any of the metals in the group.

Examples of the alloy include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compound include TiN, TaN, and Si ₃N₄、TiO₂、Ta₂O₅、SiO₂And the like.

The resistor 30 is a thin film formed on the upper surface of the functional layer 20 in a predetermined pattern, and is a sensing portion that undergoes strain to produce a change in resistance. In fig. 1, the resistor 30 is illustrated in a hatched pattern for convenience.

The resistor 30 may be formed of a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni, for example. That is, the resistor 30 may be formed of a material including 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).

The Cr mixed phase film is formed of Cr, CrN, and Cr ₂N, etc. are mixed together. The Cr mixed phase film may contain inevitable impurities such as chromium oxide. In addition, a part of the material constituting the functional layer 20 may diffuse into the Cr mixed phase film. In this case, the material constituting the functional layer 20 and nitrogen may form a compound. For example, when the functional layer 20 is formed of Ti, Ti or TiN (titanium nitride) may be contained in the Cr mixed phase film.

the thickness of the resistor 30 is not particularly limited and may be appropriately selected according to the purpose, and may be, for example, approximately 0.05 μm to 2 μm, and particularly, the thickness of the resistor 30 is preferably 0.1 μm or more from the viewpoint of improving the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α — Cr), and more preferably 1 μm or less from the viewpoint of reducing cracks of the film due to internal stress of the film constituting the resistor 30 and warpage from the substrate 10.

By forming the resistor 30 on the functional layer 20, the resistor 30 can be formed with a stable crystal phase, and therefore, the stability of the strain characteristics (strain rate, strain rate temperature coefficient TCS, and resistance temperature coefficient TCR) can be improved.

for example, when the resistor 30 is a Cr mixed phase film, the resistor 30 having α -Cr (α -Cr) as a main component can be formed by providing the functional layer 20, and the stability of the strain characteristics can be improved because α -Cr is a stable crystal phase.

here, the main component means that the target substance accounts for 50 mass% or more of the total substances constituting the resistor, and when the resistor 30 is a Cr mixed phase film, it is preferable that the resistor 30 contains 80 mass% or more of α -Cr., and α -Cr is Cr having a bcc structure (body-centered cubic lattice structure), from the viewpoint of improving the strain characteristics.

Further, the strain characteristics can be improved by diffusing the metal (for example, Ti) constituting the functional layer 20 into the Cr mixed phase film. Specifically, the strain rate of the strain gauge 1 is set to 10 or more, and the strain rate temperature coefficient TCS and the resistance temperature coefficient TCR may be set to be in the range of-1000 ppm/deg.c to +1000 ppm/deg.c.

The terminal portions 41 extend from both end portions of the resistor 30, and are formed in a substantially rectangular shape wider than the resistor 30 in a plan view. The terminal portions 41 are a pair of electrodes for outputting the change in the resistance value of the resistor 30 due to strain to the outside, and are bonded to, for example, external connection leads or the like. The resistor 30 extends, for example, in a zigzag shape from one terminal 41, is folded back, and is connected to the other terminal 41. The upper surface of the terminal portion 41 may be covered with a metal having better solderability than the terminal portion 41. Note that, although the resistor 30 and the terminal 41 are given different symbols for convenience, they may be integrally formed of the same material in the same step.

A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the terminal portions 41. By providing the cover layer 60, it is possible to prevent mechanical damage and the like from occurring on the resistor 30. Further, by providing the cover layer 60, the resistor 30 can be protected from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the terminal portion 41.

The cover layer 60 may be formed of 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 pigment. The thickness of the cover layer 60 is not particularly limited and may be appropriately selected according to the purpose, and may be, for example, about 2 μm to 30 μm.

Fig. 3A and 3B are views showing steps of manufacturing the strain gauge according to embodiment 1, and show cross sections corresponding to fig. 2. To produce the strain gauge 1, first, in the step shown in fig. 3A, the substrate 10 is prepared, and the functional layer 20 is formed on the upper surface 10a of the substrate 10. The materials and thicknesses of the substrate 10 and the functional layer 20 are as described above.

The functional layer 20 can be vacuum-deposited by, for example, a conventional sputtering method in which a raw material capable of forming the functional layer 20 is used as a target and Ar (argon) gas is introduced into a chamber. By using the conventional sputtering method, the functional layer 20 can be formed while etching the upper surface 10a of the substrate 10 with Ar, and therefore, the film formation amount of the functional layer 20 can be minimized to obtain the effect of improving the adhesion.

However, this is only one example of a method for forming the functional layer 20, and the functional layer 20 may be formed by another method. For example, a method of activating the upper surface 10a of the substrate 10 by plasma treatment using Ar or the like to obtain an effect of improving adhesion before the film formation of the functional layer 20, and then performing vacuum film formation of the functional layer 20 by a magnetron sputtering method may be used.

Next, in the step shown in fig. 3B, after the resistor 30 and the terminal portion 41 are formed on the entire upper surface of the functional layer 20, the resistor 30, and the terminal portion 41 are patterned into a planar shape shown in fig. 1 by photolithography. The material and thickness of the resistor 30 and the terminal 41 are as described above. The resistor 30 and the terminal 41 may be integrally formed of the same material. The resistor 30 and the terminal 41 can be formed by, for example, magnetron sputtering using a material capable of forming the resistor 30 and the terminal 41 as a target. The resistor 30 and the terminal portion 41 may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulse laser deposition method, or the like instead of the magnetron sputtering method.

the combination of the material of the functional layer 20 and the materials of the resistor 30 and the terminal portion 41 is not particularly limited, and may be appropriately selected according to the purpose, and for example, Ti may be used as the functional layer 20, and a Cr mixed phase film containing α -Cr (α -Cr) as a main component may be formed as the resistor 30 and the terminal portion 41.

In this case, for example, the resistor 30 and the terminal 41 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 the chamber. Alternatively, the resistor 30 and the terminal 41 may be formed by a reactive sputtering method by introducing Ar gas and an appropriate amount of nitrogen gas into a chamber using pure Cr as a target.

in these methods, the growth surface of the Cr mixed phase film can be restricted with the functional layer 20 made of Ti as an open end, and a Cr mixed phase film containing α — Cr as a main component, which is a stable crystal structure, can be formed, and the strain characteristics can be improved by diffusing Ti constituting the functional layer 20 into the Cr mixed phase film, and for example, the strain rate of the strain gauge 1 can be made to be 10 or more, and the strain rate temperature coefficient TCS and the resistance temperature coefficient TCR can be made to be in the range of-1000 ppm/° c to +1000ppm/° c.

When the resistor 30 is a Cr mixed phase film, the functional layer 20 made of Ti has all of a function of promoting crystal growth of the resistor 30, a function of preventing oxidation of the resistor 30 by oxygen or moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The same applies to the case where Ta, Si, Al, or Fe is used instead of Ti as the functional layer 20.

After the step shown in fig. 3B, if necessary, a covering layer 60 covering the resistor 30 and exposing the terminal portion 41 is formed on the upper surface 10a of the base material 10, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a thermosetting insulating resin film in a semi-cured state on the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the terminal portion 41, and heating and curing the resin film. The covering layer 60 may be prepared by applying a liquid or paste thermosetting insulating resin on the upper surface 10a of the base material 10 so as to cover the resistor 30 and expose the terminal portion 41, and heating and curing the resin.

By providing the functional layer 20 below the resistor 30 in this way, crystal growth of the resistor 30 can be promoted, and the resistor 30 having a stable crystal phase can be produced. Therefore, the strain gauge 1 can improve the stability of the strain characteristics. Further, by diffusing the material constituting the functional layer 20 into the resistor 30, the strain characteristics of the strain gauge 1 can be improved.

[ example 1]

First, as a preliminary experiment, a Ti film was vacuum-deposited as the functional layer 20 on the upper surface 10a of the base material 10 made of a polyimide resin having a thickness of 25 μm by a conventional sputtering method. At this time, 5 samples on which Ti film formation was performed were prepared for a plurality of film thicknesses.

Next, fluorescent X-ray (XRF: X-ray Fluorescence) analysis was performed on the prepared 5 samples, and the results shown in FIG. 4 were obtained. The presence of Ti was confirmed from the X-ray peak in fig. 4, and it was confirmed from the X-ray intensity of each sample at the X-ray peak that the film thickness of the Ti film could be controlled in the range of 1nm to 100 nm.

Next, as example 1, a Ti film having a film thickness of 3nm was vacuum-deposited as the functional layer 20 on the upper surface 10a of the substrate 10 made of a polyimide resin having a thickness of 25 μm by a conventional sputtering method.

Next, a Cr mixed phase film was formed as the resistor 30 and the terminal portion 41 on the entire upper surface of the functional layer 20 by magnetron sputtering, and then the functional layer 20, the resistor 30, and the terminal portion 41 were patterned by photolithography as shown in fig. 1.

In comparative example 1, a Cr mixed phase film was formed as the resistor 30 and the terminal portion 41 by magnetron sputtering without forming the functional layer 20 on the upper surface 10a of the substrate 10 made of a polyimide resin having a thickness of 25 μm, and was patterned by photolithography as shown in fig. 1. In the sample of example 1 and the sample of comparative example 1, the film formation conditions of the resistor 30 and the terminal 41 were completely the same.

Next, the sample of example 1 and the sample of comparative example 1 were evaluated by X-ray diffraction (XRD: X-ray diffraction), and the results shown in FIG. 5 were obtained. FIG. 5 shows an X-ray diffraction pattern with a diffraction angle of 36 to 48 degrees at 2 θ, wherein the diffraction peak of example 1 is shifted to the right of the diffraction peak of comparative example 1. In addition, the diffraction peak of example 1 was higher than that of comparative example 1.