Strain gauge

Abstract

This strain gauge has a base material and a resistor formed on the base material, the resistor is formed from a material having Cr as the main component, and the line width W and the film thickness T of the resistor satisfy the relationship of formula (1) such that the lateral sensitivity ratio is 70% or less and the sensitivity coefficient is 5 or more. W is smaller than or equal to 0.0177 t2 + 0.1521 t + 2.9541... (1), and in the formula (1), w is equal to logW, and t is equal to logT.

Description

Technical Field

[0001] The present invention relates to strain gauges. Background Art

[0002] Conventionally, there is known a strain gauge which is attached to a measurement object and used. The sensitivity factor of a strain gauge is generally about 2, but some strain gauges having a resistor body containing Cr as a main component have a sensitivity factor of about 10 (for example, see Patent Document 1).

[0003] It is also known that in a strain gauge having a resistor whose main component is Cr, not only is the longitudinal sensitivity, which is the sensitivity in the main axis direction, large, but the lateral sensitivity, which is the sensitivity in the direction perpendicular to the main axis direction, is also large to the same extent as the longitudinal sensitivity, and this property is independent of the shape of the resistor (see non-patent document 1).

[0004] [Prior art literature]

[0005] [Patent Literature]

[0006] [Patent Document 1] Patent No. 6084393

[0007]

Non-patent literature

[0008] [Non-patent document 1] Isotropy of sensitivity coefficient in Cr-N thin film for strain sensor, Proceedings of the 2013 National Conference of the Institute of Electrical Engineering 3 (2013): 240-241 Summary of the invention

[0009] [Problems to be solved by the invention]

[0010] However, when using a strain gauge to detect strain, a large sensitivity coefficient is preferred, but if the ratio of the lateral sensitivity to the longitudinal sensitivity, i.e. the lateral sensitivity ratio, is large, detection errors will occur. Therefore, a strain gauge with a sensitivity coefficient higher than the conventional sensitivity coefficient (about 2) and a low lateral sensitivity ratio is required.

[0011] In view of the above-mentioned points, an object of the present invention is to provide a strain gauge having a higher sensitivity coefficient and a lower lateral sensitivity ratio than conventional strain gauges.

[0012]

Methods to solve the problem

[0013] A strain gauge according to one embodiment of the present invention comprises a substrate and a resistor formed on the substrate, wherein the resistor is formed of a material having Cr as a main component, and wherein a line width W and a film thickness T of the resistor satisfy the relationship of the following formula (1) so that a lateral sensitivity ratio is less than 70% and a sensitivity coefficient is greater than 5. w≤0.0177t 2 +0.1521t+2.9541···(1), where, in formula (1), w=logW, t=logT.

[0014] [Effects of the Invention]

[0015] According to the disclosed technology, a strain gauge can be provided, which has a higher sensitivity coefficient and a lower lateral sensitivity ratio than before. BRIEF DESCRIPTION OF THE DRAWINGS

[0016]

Figure 1

[0017]

Figure 2

[0018]

Figure 3

[0019]

Figure 4

[0020]

Figure 5

[0021]

Figure 6

[0022]

Figure 7

[0023]

Figure 8

[0024]

Fig. 9

[0025]

Fig.10

[0026] Hereinafter, specific embodiments will be described with reference to the drawings. In each of the drawings, the same components may be denoted by the same reference numerals.

[0027] <First embodiment>

[0028] Figure 1 It is a top view illustrating the strain gauge according to the first embodiment. Figure 2 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment, showing a cross-sectional view along Figure 1 The cross section of line AA.

[0029] Reference Figure 1 and Figure 2The strain gauge 1 has a substrate 10, a resistor 30, wiring 40, an electrode 50 and a cover layer 60. The cover layer 60 can be provided as required. Figure 1 and Figure 2 In FIG. 1 , for convenience, only the outer edge of the cover layer 60 is indicated by a dotted line. First, each component constituting the strain gauge 1 will be described in detail.

[0030] In addition, in the present embodiment, for convenience, in the strain gauge 1, the side where the resistor 30 of the substrate 10 is provided is referred to as the "upper side", and the side where the resistor 30 is not provided is referred to as the "lower side". In addition, the surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". Here, the strain gauge 1 can also be used in a state of being upside down. In addition, the strain gauge 1 can also be configured at any angle. In addition, a top view refers to observing an object in the normal direction from the upper side to the lower side relative to the upper surface 10a of the substrate 10. Then, a planar shape refers to the shape of the object when the object is observed in the normal direction.

[0031] The substrate 10 is a component for forming a base layer of the resistor 30 and the like. The substrate 10 is flexible. The thickness of the substrate 10 is not particularly limited and can be appropriately determined according to the purpose of use of the strain gauge 1 and the like. For example, the thickness of the substrate 10 can be about 5 μm to 500 μm. The lower surface side of the strain gauge 1 is bonded to the strain body through an adhesive layer and the like. In addition, based on the strain transmission from the surface of the strain body to the sensing part and the dimensional stability relative to environmental changes, the thickness of the substrate 10 is preferably in the range of 5 μm to 200 μm. In addition, based on the insulation property, the thickness of the substrate 10 is preferably greater than 10 μm.

[0032] The substrate 10 is formed of an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film is a flexible member having a thickness of 500 μm or less.

[0033] When the base material 10 is formed of an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the base material 10 may be formed of an insulating resin film containing a filler such as silica or alumina.

[0034] As materials other than the resin of the substrate 10, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3) can be cited. In addition to the aforementioned crystalline materials, amorphous glass and the like can also be used as the material of the substrate 10. In addition, as the material of the substrate 10, metals such as aluminum, aluminum alloy (duralumin), stainless steel, and titanium can be used. When a metal is used, an insulating film is provided in a manner covering the upper and lower surfaces of the metal substrate 10.

[0035] The resistor 30 is a thin film formed in a predetermined pattern on the upper side of the substrate 10. In the strain gauge 1, the resistor 30 is a sensing part that generates a change in resistance due to strain. The resistor 30 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. Figure 1 In the figure, for convenience, the resistor 30 is represented by a high-density pear-skin pattern.

[0036] The resistor body 30 includes a plurality of elongated portions and a plurality of folded portions. In the resistor body 30, the plurality of elongated portions are arranged side by side with their length directions facing the same direction. Then, the plurality of folded portions are alternately connected to the ends of the adjacent elongated portions among the plurality of elongated portions, and the elongated portions are connected in series. Thus, the resistor body 30 as a whole is a zigzag folded structure. The length direction of the plurality of elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction.

[0037] One end of the length direction of the two outermost elongated portions in the mesh width direction is bent in the mesh width direction to form respective terminals 30e1 and 30e2 in the mesh width direction of the resistor 30. The respective terminals 30e1 and 30e2 in the mesh width direction of the resistor 30 are electrically connected to the electrode 50 via the wiring 40. In other words, the wiring 40 electrically connects the respective terminals 30e1 and 30e2 in the mesh width direction of the resistor 30 to the respective electrodes 50.

[0038] In the strain gauge 1, the sensitivity factor is preferably 5 or more. The sensitivity factor of the strain gauge 1 is not dependent on the line width W of the resistor 30. Here, the sensitivity factor is not dependent on the line width W of the resistor 30, which means that the difference between the maximum and minimum values ​​of the sensitivity factor in the range of the line width W of the resistor 30 is 2 or less. In addition, the lateral sensitivity ratio of the strain gauge 1 has a positive correlation with the logarithm of the line width W of the resistor 30, and the narrower the line width W of the resistor, the lower the sensitivity ratio.

[0039] In addition, the sensitivity coefficient of the strain gauge 1 does not depend on the film thickness T of the resistor 30. Here, the sensitivity coefficient does not depend on the film thickness T of the resistor 30 means that the difference between the maximum value and the minimum value of the sensitivity coefficient in the range of the film thickness T of the resistor 30 is 2 or less. In addition, the lateral sensitivity ratio of the strain gauge 1 has a negative correlation with the film thickness T of the resistor 30, and the thicker the film thickness T of the resistor 30, the lower the sensitivity ratio.

[0040] The lateral sensitivity ratio of the strain gauge 1 is affected by both the line width W and the film thickness T of the resistor 30 and varies in value. The definition of the lateral sensitivity ratio and the relationship between the line width W and the film thickness T of the resistor 30, the sensitivity coefficient, and the lateral sensitivity ratio are described in detail separately.

[0041] In addition, the strain limit has a negative correlation with the film thickness T of the resistor 30, and the thicker the film thickness T of the resistor 30, the lower the strain limit. Here, the strain limit refers to the value of the mechanical strain that starts to occur when strain is applied to the strain gauge, and cracking or disconnection begins. In addition, the relationship between the film thickness T of the resistor 30 and the strain limit will be described in detail separately.

[0042] The resistor 30 can be formed of a material having Cr (chromium) as a main component, for example. Here, the "main component" refers to a component that accounts for 50% by weight or more of all the materials constituting the resistor 30. As a material having Cr as a main component, a Cr multiphase film can be cited. The Cr multiphase film refers to a multiphase film of Cr, CrN, Cr2N, etc. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0043] For example, when the resistor 30 is a Cr multiphase film, the stability of the sensitive characteristics can be improved by using α-Cr (alpha chromium) of a stable crystalline phase as the main component. For another example, when the resistor 30 is a Cr multiphase film, since the resistor 30 is mainly composed of α-Cr, the sensitivity coefficient of the strain gauge 1 can be greater than 10, and the sensitivity coefficient temperature coefficient TCS and the resistance temperature coefficient TCR are in the range of -1000ppm / ℃ to +1000ppm / ℃. If based on the viewpoint of improving the sensitive characteristics, the resistor 30 preferably contains more than 80 weight% of α-Cr. Further, based on the same viewpoint, the resistor 30 more preferably contains more than 90 weight% of α-Cr. In addition, α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0044] When the resistor 30 is a Cr multiphase film, the CrN and Cr2N contained in the Cr multiphase film are preferably 20 wt% or less. When the CrN and Cr2N contained in the Cr multiphase film are 20 wt% or less, the sensitivity coefficient of the strain gauge 1 can be suppressed from decreasing.

[0045] In addition, the ratio of CrN and Cr2N in the Cr multiphase film is preferably 80% by weight or more and less than 90% by weight relative to the total weight of CrN and Cr2N. Further, the ratio is more preferably 90% by weight or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has the properties of a semiconductor. Therefore, by making the ratio of the aforementioned Cr2N 90% by weight or more and less than 95% by weight, the reduction of TCR (negative TCR) is further significant. Furthermore, by making the ratio of the aforementioned Cr2N 90% by weight or more and less than 95% by weight, the ceramicization of the resistor 30 can be reduced, and it is difficult to cause brittle failure of the resistor 30.

[0046] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of generating unstable N can be reduced, and thus a stable strain gauge can be obtained. Here, "unstable N" refers to a trace amount of N2 or atomic N that may exist in the film of the Cr multiphase film. These unstable N may sometimes escape to the outside of the film due to the external environment (such as a high temperature environment). When unstable N escapes to the outside of the film, the film stress of the Cr multiphase film may change.

[0047] In the strain gauge 1, when a Cr multiphase film is used as the material of the resistor 30, high sensitivity and miniaturization can be achieved. For example, the output variation of the conventional strain gauge is about 0.04 mV / 2V, while when a Cr multiphase film is used as the material of the resistor 30, an output variation of 0.3 mV / 2V or more can be obtained. In addition, the size of the conventional strain gauge (instrument length × instrument width) is about 3 mm × 3 mm, while when a Cr multiphase film is used as the material of the resistor 30, the size (instrument length × instrument width) can be miniaturized to about 0.3 mm × 0.3 mm.

[0048] The wiring 40 is provided on the substrate 10. One end of the wiring 40 is electrically connected to both ends of the resistor 30, and the other end is electrically connected to the electrode 50. The wiring 40 is not limited to a straight line, and can be any pattern. In addition, the wiring 40 can be any width and any length. In addition, Figure 1 In the figure, for convenience, the wiring 40 is represented by a pear-skin pattern having a lower density than the resistor 30.

[0049] The electrode 50 is provided on the substrate 10. The electrode 50 is electrically connected to the resistor 30 through the wiring 40. When viewed from above, the electrode 50 is wider than the wiring 40 and forms a roughly rectangular shape. The electrode 50 is a pair of electrodes, which are used to output the change in the resistance value of the resistor 30 generated by the strain to the outside. The electrode 50 is connected to, for example, a wire for external connection. The upper surface of the electrode 50 can be stacked with a metal layer with low resistance such as copper, or a metal layer with good solderability such as gold. For convenience, the resistor 30, the wiring 40 and the electrode 50 have different symbols, but the two can be formed integrally with the same material in the same process. In addition, Figure 1 For convenience, the electrode 50 is represented by a pear-skin pattern with the same density as the wiring 40.

[0050] The covering layer 60 is provided as required to cover the resistor 30 and the wiring 40 on the upper surface 10a of the substrate 10, exposing the electrode 50. As the material of the covering layer 60, for example, insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (such as silicone resin, polyolefin resin) and the like can be cited. In addition, the covering layer 60 may also contain fillers and pigments. The thickness of the covering layer 60 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the covering layer 60 can be about 2μm to 30μm. By providing the covering layer 60, mechanical damage to the resistor 30 can be suppressed. In addition, by providing the covering layer 60, the resistor 30 can be protected from moisture and the like.

[0051] [Method of manufacturing strain gauge]

[0052] In the strain gauge 1 according to the present embodiment, the resistor 30, the wiring 40, the electrode 50, and the cover layer 60 are formed on the substrate 10. In addition, another layer (functional layer described later, etc.) may be formed between the substrate 10 and these components.

[0053] The following is a description of a method for manufacturing the strain gauge 1. To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as a metal layer A) is formed on the upper surface 10a of the substrate 10. The metal layer A is a layer that is ultimately patterned into the resistor 30, the wiring 40, and the electrode 50. Therefore, the material and thickness of the metal layer A are the same as those of the resistor 30 and the like described above.

[0054] The metal layer A can be formed by, for example, a magnetron sputtering method using a raw material that can form the metal layer A as a target. In addition to the magnetron sputtering method, the metal layer A can also be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, or a pulsed laser deposition method. When the metal layer A is formed, the film thickness of the metal layer A can be adjusted to a desired value.

[0055] After forming a metal layer A on the upper surface 10a of the substrate 10, the metal layer A is patterned into a shape similar to the metal layer 10a by a known photolithography method. Figure 1 The resistor 30, wiring 40 and electrode 50 have the same planar shape. When patterning is performed based on photolithography, the line width of the resistor 30 can be adjusted to a desired value. The resistor 30 includes a plurality of parallel elongated portions and a structure of a folded portion that connects the ends of adjacent elongated portions in the plurality of elongated portions alternately and connects the elongated portions in series.

[0056] In addition, the metal layer A may be formed after forming a base layer on the upper surface 10a of the substrate 10. For example, a functional layer of a predetermined film thickness may be formed by vacuum deposition using a conventional sputtering method on the upper surface 10a of the substrate 10. By providing the base layer in this way, the sensitivity characteristics of the strain gauge 1 can be stabilized.

[0057] In the present application, the functional layer refers to a layer having at least the following functions: promoting the crystal growth of the metal layer A (resistor 30) as the upper layer. The functional layer preferably further has the function of preventing the metal layer A from being oxidized by oxygen or moisture contained in the substrate 10, and / or the function of improving the airtightness between the substrate 10 and the metal layer A. The functional layer may further have other functions.

[0058] The insulating resin film constituting the substrate 10 may contain oxygen and moisture, and Cr may form a self-oxidized film. Therefore, when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing the metal layer A from being oxidized.

[0059] Thus, by providing the functional layer under the metal layer A, the crystal growth of the metal layer A can be promoted, and the metal layer A composed of a stable crystal phase can be produced. As a result, the stability of the sensitive characteristics is improved in the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the sensitive characteristics in the strain gauge 1.

[0060] As materials for the functional layer, for example, 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), alloys of some metals in the group, or compounds of some metals in the group.

[0061] Figure 3 This is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. Figure 3 The cross-sectional shape of the strain gauge 1 when the functional layer 20 is provided as a base layer of the resistor 30 , the wiring 40 , and the electrode 50 is shown.

[0062] The planar shape of the functional layer 20 can be patterned, for example, to be substantially the same as the planar shape of the resistor 30, the wiring 40, and the electrode 50. However, the planar shapes of the functional layer 20 and the resistor 30, the wiring 40, and the electrode 50 may not be substantially the same. For example, when the functional layer 20 is formed of an insulating material, the functional layer 20 can be patterned into a shape different from the planar shapes of the resistor 30, the wiring 40, and the electrode 50. In this case, the functional layer 20 can be formed uniformly and flatly in a region where, for example, the resistor 30, the wiring 40, and the electrode 50 are formed. Alternatively, the functional layer 20 can be formed uniformly and flatly on the entire upper surface of the substrate 10.

[0063] After forming the resistor 30, the wiring 40, and the electrode 50, the cover layer 60 is formed on the upper surface 10a of the substrate 10 as needed. The cover layer 60 covers the resistor 30 and the wiring 40, but the electrode 50 may be exposed from the cover layer 60. For example, a semi-cured thermosetting insulating resin film may be laminated on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrode 50, and then the insulating resin film may be heated and cured, thereby forming the cover layer 60. Through the above steps, the strain gauge 1 is completed.

[0064] [Reduction in lateral sensitivity ratio]

[0065] First, the lateral sensitivity ratio will be described. Figure 4 This is a diagram for explaining the lateral sensitivity ratio. Figure 4 In FIG. 8 , axis M indicates the direction in which the strain is measured. Figure 4 In the embodiment, a strain gauge 1A whose grid direction faces the axis M and a strain gauge 1B whose grid direction faces the direction perpendicular to the axis M are attached to the strain body 100. Figure 4 The x-axis, y-axis, and z-axis in the figure represent axes that intersect each other perpendicularly. Axis M is parallel to the y-axis, and the direction perpendicular to axis M is parallel to the x-axis.

[0066] Figure 4 When tensile strain is generated in the direction of the axis M, the resistor of the strain gauge 1A extends in the direction of the axis M, and the resistor of the strain gauge 1B contracts in the direction perpendicular to the axis M based on the Poisson's ratio. Figure 4 The arrow N indicates the contraction direction based on Poisson's ratio.

[0067] Here, the sensitivity corresponding to the strain generated in the direction of axis M is the longitudinal sensitivity F a The sensitivity corresponding to the strain generated in the direction perpendicular to the axis M is the lateral sensitivity F t When , equations (1) and (2) hold. In addition, the lateral sensitivity F t and longitudinal sensitivity F aThe lateral sensitivity ratio K defined by the ratio is shown in formula (3).

[0068] In addition, in equations (1) and (2), ε y is the strain in the direction of axis M, ε x is the strain generated in the direction perpendicular to the axis M. In addition, R A is the resistance value of the resistor of the strain gauge 1A when no strain occurs. B is the resistance value of the resistor of the strain gauge 1B when no strain occurs. A is the strain ε x and ε y When the strain gauge 1A is generated, the resistance value generated on the resistor changes. B is the strain ε x and ε y When it occurs, the resistance value generated in the resistor of the strain gauge 1B changes.

[0069]

Number 1

[0070] Δh A / R A =F a ε y +F t ε x …(1)

[0071]

Number 2

[0072] ΔR B / R B =F t ε y +F a ε x …(2)

[0073]

Number 3

[0074] K=F t / F a …(3)

[0075] When a bridge circuit is formed in a commercially available strain gauge, the output variation is about 0.10 mV / V. In order to achieve an output variation equal to or greater than that of a commercially available strain gauge, the lateral sensitivity ratio should be 70% or less and the sensitivity coefficient should be 5 or more.

[0076] The lateral sensitivity ratio is more preferably 50% or less, further preferably 40% or less, and particularly preferably 30% or less. In addition, the sensitivity coefficient is more preferably 8 or more, more preferably 11 or more, and particularly preferably 14 or more. The smaller the lateral sensitivity ratio and the larger the sensitivity coefficient, the greater the output change when a bridge circuit is formed in the strain gauge.

[0077] Hereinafter, examples will be described, but the present invention is not limited to the following examples at all.

[0078] [Example 1]

[0079] (Relationship between the line width of the resistor and the lateral sensitivity ratio and sensitivity coefficient)

[0080] The inventors made samples of strain gauges and studied the relationship between the line width of the resistor and the lateral sensitivity ratio and sensitivity coefficient.

[0081] First, a Ti film with a thickness of 3 nm was formed as a functional layer 20 by conventional sputtering on the upper surface 10a of the substrate 10 composed of a polyimide resin with a thickness of 25 μm. Next, a Cr multiphase film with a thickness of 200 nm was formed as a resistor 30, wiring 40, and electrode 50 on the entire upper surface of the functional layer 20 by magnetron sputtering. Then, the functional layer 20, the resistor 30, the wiring 40, and the electrode 50 were formed by photolithography, as shown in FIG. Figure 1 The strain gauge sample was produced by patterning in this manner. In this sample, the line width W of the resistor 30 was patterned to be 500 μm.

[0082] Next, the same method was used to make the line width W of the resistor 30 200μm, 100μm, 50μm, 40μm, 20μm, 10μm, and 5μm, respectively, to produce patterned strain gauge samples. Then, the lateral sensitivity ratio and sensitivity coefficient of each strain gauge sample were measured in an environment of 20°C, and the results are summarized in Figure 5 .

[0083] like Figure 5 As shown, the sensitivity coefficient of the fabricated sample does not depend on the line width W of the resistor 30 . Figure 5 In the figure, the difference between the maximum and minimum values ​​of the sensitivity coefficient when the line width W of the resistor 30 changes is about 1.5. In this regard, the lateral sensitivity ratio has a positive correlation with the logarithm of the line width W of the resistor 30, and the narrower the line width of the resistor 30, the lower the sensitivity coefficient. In addition, Figure 6 , when a sample with a sensitivity coefficient of about 9 is made by the same method, the relationship between the line width of the resistor, the lateral sensitivity ratio, and the sensitivity coefficient is shown. In this case, the sensitivity coefficient is also independent of the line width W of the resistor 30. In contrast, the lateral sensitivity ratio has a positive correlation with the logarithm of the line width W of the resistor 30, and the narrower the line width of the resistor 30, the lower the sensitivity coefficient. In addition, although the illustration is omitted, the same characteristics are shown in other samples with a sensitivity coefficient of 5 or more.

[0084] Based on these results, it can be seen that by forming the resistor 30 with a material mainly composed of Cr and reducing the line width W of the resistor 30, the lateral sensitivity ratio can be reduced while maintaining a high sensitivity coefficient. That is, it can be seen that by forming the resistor 30 with a material mainly composed of Cr and controlling the line width W of the resistor, a strain gauge with a higher sensitivity coefficient and a lower lateral sensitivity ratio than before can be realized. In this way, by reducing the lateral sensitivity ratio while maintaining a high sensitivity coefficient, the accuracy of strain detection can be improved.

[0085] Figure 7 This is a diagram showing the relationship between the line width of the resistor, the lateral sensitivity ratio, and the output change of the strain gauge. Figure 7 In the invention, for a strain gauge with a sensitivity coefficient of 5 and a strain gauge with a sensitivity coefficient of 15, the inventors have experimentally determined the relationship between the line width, the lateral sensitivity ratio and the output variation of the strain gauge. In addition, Figure 7 As a comparative example, the output change of a commercially available strain gauge with a sensitivity factor of 2 is also given. Figure 7 The output change amount shown is the output change amount when a bridge circuit is formed in the strain gauge.

[0086] like Figure 7 As shown, it can be seen that if the sensitivity coefficient is 5 and the lateral sensitivity ratio is 70% or more, an output variation equal to or greater than that of a commercially available strain gauge can be obtained. By making the line width W of the resistor 30 less than 70 μm, the lateral sensitivity ratio can be made less than 70%. Therefore, by making the line width of the resistor 30 less than 70 μm, making the lateral sensitivity ratio less than 70% and the sensitivity coefficient greater than 5, a strain gauge with an output variation equal to or greater than that of a commercially available strain gauge can be realized. For example, by making the line width of the resistor 30 70 μm, making the lateral sensitivity ratio 70% and the sensitivity coefficient 15, a strain gauge with an output variation about three times that of a commercially available strain gauge can be realized.

[0087] In addition, as mentioned above, the lateral sensitivity ratio is more preferably 50% or less, further preferably 40% or less, and particularly preferably 30% or less. Figure 5 By making the line width W of the resistor 30 less than 20 μm, the lateral sensitivity ratio can be made less than 50%. Figure 5 By making the line width W of the resistor 30 less than 10 μm, the lateral sensitivity ratio can be made less than 40%. Figure 5 By making the line width W of the resistor 30 less than 5 μm, the lateral sensitivity ratio can be made less than 30%.

[0088] In order to obtain an output variation equal to or greater than that of a commercially available strain gauge, the sensitivity factor may be 5 or greater, but the sensitivity factor of each sample using a Cr multiphase film in the resistor 30 is 14 or greater, which is a sufficiently large value. In addition, by using a Cr multiphase film in the resistor 30, the sensitivity factor can be adjusted to various values ​​of 5 or greater by changing the content of α-Cr in the resistor 30. In addition, by using a Cr multiphase film in the resistor 30 and improving the crystallinity of α-Cr, the sensitivity factor is in the range of 5 or greater and 10 or less.

[0089] In this way, a strain gauge can be realized, in which the resistor 30 is formed of a material mainly composed of Cr, the sensitivity coefficient is 5 or more, the sensitivity coefficient is independent of the line width of the resistor 30, and the lateral sensitivity ratio has a positive correlation with the logarithm of the line width of the resistor 30, and the lateral sensitivity ratio is lower as the line width of the resistor 30 is narrower. Such characteristics can be realized at least in the range of 0.1 μm to 70 μm when the line width of the resistor 30 is greater than or equal to 0.1 μm.

[0090] (Relationship between the film thickness of the resistor and the lateral sensitivity ratio and sensitivity coefficient)

[0091] Next, the inventors fabricated strain gauge samples and studied the relationship between the film thickness of the resistor and the lateral sensitivity ratio and sensitivity coefficient.

[0092] First, a 3 nm thick Ti film was formed as a functional layer 20 by conventional sputtering on the upper surface 10a of a substrate 10 made of polyimide resin with a thickness of 25 μm. Next, a 800 nm thick Cr multiphase film was formed as a resistor 30, wiring 40, and electrode 50 on the entire upper surface of the functional layer 20 by magnetron sputtering. Then, the functional layer 20, the resistor 30, the wiring 40, and the electrode 50 were patterned by photolithography. Figure 1 In this way, a strain gauge sample was produced. Furthermore, the resistor 30 was patterned so that the line width W was 50 μm.

[0093] Next, the same method was used to prepare strain gauge samples in which the film thickness T of the resistor 30 was 500nm, 200nm, 100nm, 50nm, and 30nm. Then, the lateral sensitivity ratio and sensitivity coefficient of each strain gauge sample were measured in an environment of 20°C and summarized in Figure 8 .

[0094] like Figure 8 As shown, the sensitivity coefficient of the manufactured sample does not depend on the film thickness T of the resistor 30 . Figure 8 , the difference between the maximum and minimum values ​​of the sensitivity coefficient when the film thickness T of the resistor 30 changes is about 1.5. In this regard, it can be considered that the lateral sensitivity ratio has a negative correlation with the film thickness T of the resistor 30, and as the film thickness T of the resistor 30 increases, the value of the lateral sensitivity ratio tends to decrease.

[0095] also, Figure 8 In the sample, the sensitivity factor is about 15, but in the samples with various sensitivity factors above 5, although the figure is omitted, it is confirmed that the sensitivity factor is similar to Figure 8 Same characteristics.

[0096] Based on these results, it can be seen that by forming the resistor 30 from a material mainly composed of Cr and increasing the film thickness T of the resistor 30, the lateral sensitivity ratio can be reduced while maintaining a high sensitivity coefficient. That is, it can be seen that by forming the resistor 30 from a material mainly composed of Cr and controlling the film thickness T of the resistor, a strain gauge having a higher sensitivity coefficient and a lower lateral sensitivity ratio than the conventional strain gauge can be realized. In this way, by reducing the lateral sensitivity ratio while maintaining a high sensitivity coefficient, the accuracy of strain detection can be improved.

[0097] As mentioned above, if the lateral sensitivity ratio is less than 70%, the output change can be equal to or higher than that of commercially available strain gauges. Figure 8 By setting the film thickness T of the resistor 30 to be 200 nm or more, the lateral sensitivity ratio can be set to 70% or less. That is, a strain gauge can be realized in which the film thickness of the resistor 30 is 200 nm or more, so that the lateral sensitivity ratio is 70% or less and the sensitivity coefficient is 5 or more.

[0098] In order to obtain an output variation equal to or greater than that of a commercially available strain gauge, the sensitivity factor may be 5 or greater, and the sensitivity factor of each sample using a Cr multiphase film in the resistor 30 is 14 or greater, which is a sufficiently large value. In addition, when a Cr multiphase film is used in the resistor 30, the sensitivity factor can be adjusted to various values ​​of 5 or greater by changing the content of α-Cr in the resistor 30. In addition, by using a Cr multiphase film in the resistor 30 to improve the crystallinity of α-Cr, the sensitivity factor is in the range of 5 or greater and 10 or less.

[0099] In this way, a strain gauge can be realized, in which the resistor 30 is formed of a material with Cr as the main component, the sensitivity coefficient is greater than 5, is independent of the film thickness of the resistor 30, and the lateral sensitivity ratio is negatively correlated with the film thickness of the resistor 30, and the thicker the film thickness of the resistor 30, the lower the sensitivity coefficient.

[0100] (Relationship between the line width and film thickness of the resistor, and the lateral sensitivity ratio and sensitivity coefficient)

[0101] As a result of further studies, the inventors have found that the lateral sensitivity ratio of the strain gauge 1 is affected by both the line width W and the film thickness T of the resistor 30 , and the value changes.

[0102] That is, the above experiment shows that when the film thickness T of the resistor 30 is 200 nm, in order to make the lateral sensitivity ratio less than 70%, the line width W of the resistor 30 can be made less than 70 μm. In addition, the above experiment shows that when the line width W of the resistor 30 is 50 μm, in order to make the lateral sensitivity ratio less than 70%, the film thickness T of the resistor 30 can be made greater than 200 nm.

[0103] However, the lateral sensitivity ratio of the strain gauge 1 is affected by both the line width W and the film thickness T of the resistor 30, and the value varies. Therefore, the lateral sensitivity ratio can be made 70% or less within a wider range than the line width W and the film thickness T obtained in the above-mentioned experiment. That is, even if the line width W of the resistor 30 is wider than 70μm, the lateral sensitivity ratio can be made 70% or less by adjusting the film thickness T to an appropriate value. Similarly, even if the film thickness T of the resistor 30 is thinner than 200nm, the lateral sensitivity ratio can be made 70% or less by adjusting the line width W to an appropriate value.

[0104] Fig. 9 It is a contour diagram showing the lateral sensitivity ratio with respect to line width and film thickness, and summarizes the results of experiments conducted by the inventors. Fig. 9 In the first region indicated by the high-density dot pattern, 0%≤lateral sensitivity ratio≤70%. In addition, in the second region indicated by the low-density dot pattern, 70%<lateral sensitivity ratio≤100%.

[0105] The boundary between the first region and the second region can be approximated as, w = 0.0177t 2 +0.1521t+2.9541. Here, when the line width of the resistor is W and the film thickness is T, w=logW and t=logT. That is, w=logW and t=logT satisfy w≤0.0177t. 2 +0.1521t+2.9541…(1), the lateral sensitivity ratio can be made less than 70%. In other words, a strain gauge can be realized in which the line width W and the film thickness T of the resistor 30 satisfy the relationship of the above formula (1) so that the lateral sensitivity ratio is less than 70% and the sensitivity coefficient is greater than 5.

[0106] In addition, by Fig. 9 It is understood that by setting the line width W of the resistor 30 to 40 μm or less, the lateral sensitivity ratio can be set to 70% or less, almost independently of the film thickness T.

[0107] In addition, in Example 1, a polyimide resin is used for the substrate 10, but Figures 5 to 9 The characteristics shown do not depend on the material of the substrate 10. For example, when a material other than resin is used for the substrate 10, the same Figures 5 to 9 Same characteristics.

[0108] In addition, other materials other than the Cr multiphase film can also be used to obtain a sensitivity factor of 5 or more. As materials that can obtain a sensitivity factor of 5 or more, Ge, Pt, Si, Ni, Cu, C, Ti, Cr, or materials containing them can be cited. Specifically, they are Cr-N, Ge, Ge-In, Ge-Ga, Ge-P, Pt, Pt-In, Cu, Ni-C, Si, Ti-CO, etc. In addition, by adjusting the line width W and / or film thickness T of the resistor 30 using these materials, a desired lateral sensitivity ratio can be obtained.

[0109] That is, using these materials, a strain gauge can be realized, wherein the line width W and the film thickness T of the resistor 30 satisfy the relationship of the above formula (1) so that the lateral sensitivity ratio is less than 70% and the sensitivity coefficient is greater than 5. In addition, a strain gauge can be realized, wherein the sensitivity coefficient is greater than 5, is independent of the line width of the resistor 30, and has a positive correlation with the logarithm of the line width of the resistor 30, and the narrower the line width of the resistor 30, the lower the sensitivity coefficient. Alternatively, a strain gauge can be realized, wherein the resistor 30 is formed of these materials, has a sensitivity coefficient greater than 5, is independent of the film thickness of the resistor 30, and has a negative correlation with the film thickness of the resistor 30, and the thicker the film thickness of the resistor 30, the lower the sensitivity coefficient.

[0110] [Example 2]

[0111] The inventors produced multiple samples of strain gauges of the same specifications as those used in the "Relationship between the film thickness of the resistor and the lateral sensitivity ratio and sensitivity coefficient" of Example 1, and studied the relationship between the film thickness of the resistor and the strain limit. Here, the film thickness of the resistor is 1100nm, 800nm, 500nm, 200nm, 100nm, 50nm, and 30nm. In addition, the line width of the resistor is set to 50μm, and the strain limit is almost independent of the line width of the resistor.

[0112] Fig.10 2 is a graph showing the results of the study of Example 2, in which the minimum values ​​of the strain limits of a plurality of strain gauge samples at various film thicknesses are plotted. Fig.10 As shown in FIG. 1 , the strain limit has a negative correlation with the film thickness T of the resistor 30, and it can be confirmed that the strain limit value tends to decrease as the film thickness T of the resistor 30 increases. In particular, when the film thickness T of the resistor 30 is in the range of 30 nm to 200 nm, the strain limit value decreases significantly. On the other hand, when the film thickness T of the resistor 30 exceeds 200 nm, the strain limit value decreases slowly.

[0113] When actually using strain gauge 1, sometimes 6000×10 -6 Therefore, based on Fig.10The results show that the film thickness T of the resistor 30 is preferably 6000×10 -6 Above 800nm ​​or less.

[0114] The strain gauge 1 is attached to the strain body, and expands and contracts to follow the movement of the strain body, thereby detecting the strain amount of the strain body. Therefore, in order to detect a larger strain amount, a higher strain limit is required so that the strain gauge 1 itself will not be damaged (broken wires, etc.) during expansion and contraction. In the strain gauge 1, the film thickness T of the resistor 30 is set to 800nm ​​or less, which can improve the strain limit.

[0115] In addition, according to Fig.10 Based on the strain limit, the film thickness T is preferably 600 nm or less, further preferably 400 nm or less, and particularly preferably 200 nm or less. Fig.10 It can be seen that by making the film thickness T less than 200nm, the strain limit can be greatly improved, and by making the film thickness T less than 100nm, the strain limit can be further improved. Fig. 9 It can be seen that when the film thickness T is 100nm / 200nm, the lateral sensitivity ratio can be made less than 70% by adjusting the line width W. For example, when the line width W of the resistor 30 is made less than 40μm and the film thickness T is made less than 200nm, the lateral sensitivity ratio can be made less than 70% and the strain limit can be greatly improved.

[0116] In addition, in Example 2, a polyimide resin is used in the substrate 10, but Fig.10 The properties shown do not depend on the material of the substrate 10. For example, using a material other than resin in the substrate 10 can also obtain the same Fig.10 Same characteristics.

[0117] In addition, the use of other materials besides Cr multiphase film can also obtain Fig.10 Other materials include Ge, Pt, Si, Ni, Cu, C, Ti, Cr, or materials containing them. Specifically, Cr-N, Ge, Ge-In, Ge-Ga, Ge-P, Pt, Pt-In, Cu, Ni-C, Si, Ti-CO, etc.

[0118] [Appropriate range of film thickness T of resistor 30]

[0119] Based on the results of Example 2, if the strain limit is considered, the film thickness T of the resistor 30 is preferably 800 nm or less so that the strain limit is 6000×10 -6Therefore, if the results of Example 1 are added to the results of Example 2, it can be considered that within the range of film thickness T being 800 nm or less, the line width W and film thickness T of the resistor 30 preferably satisfy the above formula (1) so that the lateral sensitivity ratio is 70% or less and the sensitivity coefficient is 5 or more.

[0120] Thus, a strain gauge can be realized in which the line width W and the film thickness T of the resistor 30 are adjusted so that the lateral sensitivity ratio is 70% or less, the sensitivity coefficient is 5 or more, and the strain limit is 6000×10 -6 Then, the strain gauge can be used to improve the accuracy of strain detection and detect a larger amount of strain.

[0121] In addition, depending on the required specifications, the strain limit may sometimes be less than 6000×10 -6 , therefore, the film thickness T of the resistor 30 does not need to be less than 800 nm.

[0122] The preferred embodiments, etc. have been described in detail above. However, the strain gauge according to the present invention is not limited to the above-mentioned embodiments and modifications, etc. For example, various modifications and substitutions may be applied to the strain gauge according to the above-mentioned embodiments, etc., without departing from the scope described in the patent claims.

[0123] This international application claims the benefit of priority based on Japanese Patent Application No. 2022-125250 filed on August 5, 2022, the entire contents of which are incorporated herein by reference.

[0124] [Description of Reference Numerals]

[0125] 1, 1A, 1B strain gauges, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 terminals, 40 wiring, 50 electrode, 60 cover layer, 100 strain body.

Claims

1. A strain gauge comprising a substrate and a resistor formed on the substrate, The resistor is formed of a material containing Cr as a main component. The line width W and the film thickness T of the resistor satisfy the relationship of the following formula (1) so that the lateral sensitivity ratio is less than 70% and the sensitivity coefficient is greater than 5. w≤0.0177t 2 +0.1521t+2.9541…(1) Here, in formula (1), w=logW, t=logT.

2. The strain gauge according to claim 1, wherein the film thickness T of the resistor is 800 nm or less, so that the lateral sensitivity ratio is 70% or less, the sensitivity coefficient is 5 or more, and the strain limit is 6000×10 -6 above. 3 . The strain gauge according to claim 2 , wherein a film thickness T of the resistor is 200 nm or less. 4 . The strain gauge according to claim 2 , wherein the strain limit has a negative correlation with a film thickness T of the resistor, and is lower as the film thickness T of the resistor is thicker.

5. The strain gauge according to any one of claims 1 to 4, wherein the sensitivity coefficient does not depend on the line width W of the resistor, and the lateral sensitivity ratio has a positive correlation with the logarithm of the line width W of the resistor, and the narrower the line width W of the resistor, the lower the lateral sensitivity ratio.

6. The strain gauge according to any one of claims 1 to 5, wherein the sensitivity coefficient does not depend on the film thickness T of the resistor, and the lateral sensitivity ratio has a negative correlation with the film thickness T of the resistor, and is lower as the film thickness T of the resistor is thicker. 7 . The strain gauge according to claim 1 , wherein a line width W of the resistor is 40 μm or less. 8 . The strain gauge according to claim 1 , wherein the resistor is formed of a film containing Cr, CrN and Cr 2 N.

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