Strain gauge

Abstract

To provide a strain gauge which can be used for a scale.SOLUTION: The strain gauge includes: a base material; and resistors provided directly or indirectly on the base material. The resistors are formed of a material including Cr, a material including Ni, or a material including at least one of Cr and Ni. The resistors are arranged with their grid directions facing the same direction and are connected together in parallel to one another. The resistance values of the resistors connected in parallel to one another are in the range of 160 Ω to 600 Ω, both inclusive.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a strain gauge. [Background technology]

[0002] There is known a strain gauge that has a resistor on a substrate and is attached to an object to be measured to detect the characteristics of the object to be measured. Strain gauges are used as sensors, for example, for detecting the strain of a material or for detecting the ambient temperature (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-221696 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, strain gauges are sometimes used as scales in addition to sensors, and in such cases they must meet stricter creep standards than those for sensors, so there are cases where strain gauges that can be used for sensors cannot be used for scales.

[0005] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a strain gauge that can be used for weighing purposes. [Means for solving the problem]

[0006] This strain gauge has a substrate and a resistor provided directly or indirectly on the substrate, the resistor being formed from a material containing Cr, a material containing Ni, or a material containing at least one of Cr and Ni, each of the resistors being arranged with the grid direction facing the same direction and connected in parallel with each other, and the resistance value of the resistors connected in parallel is 160 Ω or more and 600 Ω or less. Effect of the Invention

[0007] According to the disclosed technique, a strain gauge that can be used for weighing purposes can be provided. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Diagram 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Diagram 3] 4 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. [Figure 4] FIG. 2 is a diagram illustrating a method for measuring the amount of creep and the amount of creep recovery. [Diagram 5] FIG. 13 is a diagram showing the results of an investigation into the resistance value, the amount of creep, and the amount of creep recovery. [Figure 6] 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment 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 duplicated explanations may be omitted.

[0010] First embodiment Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1. Fig. 3 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in Fig. 1.

[0011] 1 to 3, the strain gauge 1 has a three-layer structure in which a second layer 12 and a third layer 13 are laminated in this order on a first layer 11. Resistors for detecting strain are arranged in each of the first layer 11, the second layer 12, and the third layer 13 with their grid directions facing in the same direction. This will be explained in detail below.

[0012] The first layer 11 has a substrate 101, and a resistor 301 and a wiring 401 formed on the upper surface 10a of the substrate 101. The second layer 12 has a substrate 102, and a resistor 302 and a wiring 402 formed on the upper surface 10b of the substrate 102. The substrate 102 is laminated on the substrate 101 while covering the resistor 301. The third layer 13 has a substrate 103, and a resistor 303, a wiring 403, and an electrode 503 formed on the upper surface 10c of the substrate 103. The substrate 103 is laminated on the substrate 102 while covering the resistor 302. On the third layer 13, a cover layer 60 is formed as necessary. For convenience, only the outer edge of the cover layer 60 is shown by a broken line in Figs. 1 to 3.

[0013] In this embodiment, for convenience, in the strain gauge 1, the side on which the resistor of each substrate is provided is referred to as the upper side or one side, and the side on which the resistor is not provided is referred to as the lower side or the other side. In addition, the surface on which the resistor of each substrate is provided is referred to as the one side or upper surface, and the surface on which the resistor is not provided is referred to as the other side or lower surface. However, the strain gauge 1 can be used upside down or placed at any angle. In addition, the planar view refers to the object being viewed from the normal direction of the upper surface 10c of the substrate 103, and the planar shape refers to the shape of the object being viewed from the normal direction of the upper surface 10c of the substrate 103.

[0014] The planar shapes of the resistors 301 and 302 are not shown, but are similar to that of the resistor 303. The resistors 301 and 302 are formed, for example, at positions overlapping with the resistor 303 in a planar view. The planar shapes of the wirings 401 and 402 are not shown, but are similar to that of the wiring 403. The wirings 401 and 402 are formed, for example, at positions overlapping with the wiring 403 in a planar view.

[0015] The substrate 103 is a flexible member that serves as a base layer for forming the resistor 303 and the like. The thickness of the substrate 103 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of strain transmission and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

[0016] The substrate 103 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0017] Here, "formed from an insulating resin film" does not prevent the base material 103 from containing fillers, impurities, etc. in the insulating resin film. The base material 103 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0018] Examples of materials other than resin for the base material 103 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the base material 103. In this case, for example, an insulating film is formed on the metal base material 103.

[0019] The resistor 303 is a thin film formed in a predetermined pattern on the substrate 103, and is a sensing part that generates a resistance change when strained. The resistor 303 may be formed directly on the upper surface 10c of the substrate 103, or may be formed on the upper surface 10c of the substrate 103 via another layer. For convenience, the resistor 303 is shown in FIG. 1 with a dark matte pattern.

[0020] The resistor 303 has a structure in which multiple elongated parts are arranged at regular intervals with their longitudinal direction in the same direction (the direction of line AA in FIG. 1), and the ends of adjacent elongated parts are alternately connected, folding back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated parts is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction of line BB in FIG. 1).

[0021] One end in the longitudinal direction of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction to form respective ends 303e1 and 303e2 in the grid width direction of the resistor 303. Each of the ends 303e1 and 303e2 in the grid width direction of the resistor 303 is electrically connected to the electrode 503 via the wiring 403. In other words, the wiring 403 electrically connects each of the ends 303e1 and 303e2 in the grid width direction of the resistor 303 to each of the electrodes 503.

[0022] The resistor 303 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 303 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0023] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0024] The thickness of the resistor 303 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 0.05 μm to 2 μm. In particular, it is preferable that the thickness of the resistor 303 is 0.1 μm or more, since the crystallinity of the crystals constituting the resistor 303 (for example, the crystallinity of α-Cr) is improved. It is further preferable that the thickness of the resistor 303 is 1 μm or less, since it is possible to reduce cracks in the film and warping from the substrate 103 caused by the internal stress of the film constituting the resistor 303.

[0025] In order to prevent lateral sensitivity and to prevent disconnection, the width of resistor 303 is preferably 10 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 10 μm to 50 μm.

[0026] For example, when the resistor 303 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making the resistor 303 mainly of α-Cr, 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. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, the resistor 303 preferably contains α-Cr at 80% by weight or more, and more preferably contains 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0027] When the resistor 303 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr2N. By containing 20% ​​by weight or less of CrN and Cr2N in the Cr mixed-phase film, a decrease in the gauge factor can be suppressed.

[0028] In addition, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant due to the Cr2N having semiconductor properties. Furthermore, by reducing the formation of ceramics, brittle fracture is reduced.

[0029] On the other hand, if a small amount of N2 or atomic N is mixed into the film, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in the film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[0030] The wiring 403 is formed on the base material 103 and is electrically connected to the resistor 303 and the electrode 503. The wiring 403 is not limited to being linear, and may be in any pattern. The wiring 403 may have any width and any length. For convenience, the wiring 403 and the electrode 503 are shown in FIG. 1 as having a matte finish that is thinner than the resistor 303.

[0031] The electrodes 503 are formed on the base material 103 and are electrically connected to the resistor 303 via the wiring 403, and are formed, for example, in a substantially rectangular shape wider than the wiring 403. The electrodes 503 are a pair of electrodes for outputting to the outside a change in resistance value of the resistors 301, 302, and 303 caused by distortion, and for example, a lead wire for external connection is joined to the electrodes 503.

[0032] Although the resistor 303, the wiring 403, and the electrode 503 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 303, the wiring 403, and the electrode 503 have approximately the same thickness.

[0033] A conductive layer made of a material having a lower resistance than the resistor 303 may be laminated on the wiring 403 and the electrode 503. The material of the laminated conductive layer is not particularly limited as long as it is a material having a lower resistance than the resistor 303, and can be appropriately selected depending on the purpose. For example, when the resistor 303 is a Cr mixed phase film, Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, and compounds are appropriately laminated can be mentioned. The thickness of the conductive layer is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 3 μm to 5 μm.

[0034] In this manner, by stacking a conductive layer made of a material having a lower resistance than the resistor 303 over the wiring 403 and the electrode 503, the wiring 403 has a lower resistance than the resistor 303, and therefore, it is possible to prevent the wiring 403 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 303 can be improved.

[0035] In other words, by providing the wiring 403 having a lower resistance than the resistor 303, the actual sensing portion of the strain gauge 1 can be limited to the local region where the resistor 303 is formed. Therefore, the accuracy of strain detection by the resistor 303 can be improved.

[0036] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed phase film as the resistor 303, making the wiring 403 lower in resistance than the resistor 303 and limiting the actual sensing part to the local region where the resistor 303 is formed has a significant effect on improving the strain detection accuracy. Making the wiring 403 lower in resistance than the resistor 303 also has the effect of reducing the lateral sensitivity.

[0037] The substrate 103, resistor 303, wiring 403, and electrode 503 of the third layer 13 have been described above, but the substrate 101, resistor 301, and wiring 401 of the first layer 11 and the substrate 102, resistor 302, and wiring 402 of the second layer 12 are similar to the substrate 103, resistor 303, and wiring 403 of the third layer 13. However, the first layer 11 and the second layer 12 do not have a portion corresponding to the electrode 503.

[0038] A cover layer 60 may be provided on the upper surface 10c of the base material 103 so as to cover the resistor 303 and expose the electrodes 503. By providing the cover layer 60, mechanical damage to the resistor 303 can be prevented. Furthermore, by providing the cover layer 60, the resistor 303 can be protected from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the electrodes 503.

[0039] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (e.g., silicone resin, polyolefin resin), etc. The cover layer 60 may contain a filler or a pigment. There is no particular limit to the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0040] [Lower resistance] In the strain gauge 1, the wiring 401, the wiring 402, and the wiring 403 are connected to each other by two through holes 70 provided near each of the two electrodes 503. As a result, the resistors 301, 302, and 303 are connected in parallel to each other. The resistors 301, 302, and 303 are formed, for example, to have approximately the same resistance value and are connected in parallel. As a result, the overall resistance value is reduced to approximately 1 / 3 of that of each of the resistors 301, 302, and 303. The resistance value between the pair of electrodes 503 is the resistance value of the resistors 301, 302, and 303 connected in parallel.

[0041] The through-hole 70 is provided in a through-hole penetrating at least the substrates 102 and 103. The through-hole 70 may be formed using the same material as the resistor 303, etc., or may be formed from a low-resistance material such as copper. In addition, the position of the through-hole 70 may be arbitrary as long as the resistor 301, the resistor 302, and the resistor 303 can be connected in parallel. For example, the wiring 401 and 402 may not be provided, and the through-hole 70 may be provided near the end of each resistor in each layer to connect the resistors 301, 302, and 303 in parallel. In addition, dummy electrodes equivalent to the electrode 503 may be formed on the substrate 101 and the substrate 102, and the electrode 503 and each dummy electrode may be connected by the through-hole 70. In addition, the number of through-holes may be arbitrary as long as the resistor 301, the resistor 302, and the resistor 303 can be connected in parallel. For example, if the resistance value of the through-hole is a problem, the number of through-holes may be appropriately increased.

[0042] When using the strain gauge 1 for weighing purposes, it is necessary for it to satisfy standards related to creep, such as precision class C1 based on OIML R60 (hereinafter referred to as C1 standard) and precision class C2 based on OIML R60 (hereinafter referred to as C2 standard).

[0043] The C1 standard requires the creep amount and creep recovery amount to be within ±0.0735%. The C2 standard requires the creep amount and creep recovery amount to be within ±0.0368%. If strain gauge 1 is used for sensor applications, the standard for the creep amount and creep recovery amount is approximately ±0.5%.

[0044] After careful consideration, the inventors discovered that creep is highly dependent on the resistance value of the resistor connected between the pair of electrodes 503, and that in order to satisfy the C1 and C2 standards, the resistance value of the resistor connected between the pair of electrodes 503 needs to be relatively low.

[0045] Therefore, the inventors have studied the resistance value of the resistor connected between the pair of electrodes 503, which is necessary to reduce the amount of creep and the amount of creep recovery. Specifically, a plurality of strain gauges 1 with different resistance values ​​of the resistor connected between the pair of electrodes 503 were produced, and each strain gauge 1 was attached to a strain generating body made of SUS304, and the amount of creep and the amount of creep recovery were measured. Note that, as the substrates 101, 102, and 103, a polyimide resin film with a film thickness of 25 μm was used. Also, as the resistors 301, 302, and 303, a Cr mixed phase film was used.

[0046] The creep amount and creep recovery amount are amounts in which the amount of elastic deformation (amount of strain) of the surface on which resistors 301, 302, and 303 are provided in strain gauge 1 changes over time, and can therefore be measured by monitoring the strain voltage calculated based on the output between a pair of electrodes 503. A detailed description will be given with reference to FIG.

[0047] Fig. 4 is a diagram for explaining the method of measuring the creep amount and the creep recovery amount, in which the horizontal axis represents time and the vertical axis represents strain voltage [mV].

[0048] First, 10 seconds after turning on the power to the measuring device, a 150% load is applied to the strain gauge 1 attached to the flexure body for 10 seconds, and then the load is removed. After 20 minutes have passed since the load was removed, a 100% load is applied to the strain gauge 1 attached to the flexure body for 20 minutes, and then the load is removed. Then, wait for 20 minutes to pass after the load is removed.

[0049] The strain voltage changes, for example, as shown in Figure 4. In Figure 4, the absolute value B of the difference in strain voltage between 20 minutes after the 150% load is removed and immediately after the 100% load is applied is measured. Also, the absolute value ΔA of the difference in strain voltage between immediately after the 100% load is applied and 20 minutes after the 100% load started to be applied is measured. At this time, ΔA / B is the amount of creep. Next, the absolute value ΔC of the difference in strain voltage between immediately after the 100% load is removed and 20 minutes after the 100% load is removed is measured. At this time, ΔC / B is the amount of creep recovery.

[0050] It should be noted that a 100% load is 3 kg, and a 150% load is 1.5 times the 100% load.

[0051] FIG. 5 shows the results of an investigation into the relationship between resistance value and the amount of creep and the amount of creep recovery, and summarizes the results of measuring the amount of creep and the amount of creep recovery of multiple strain gauges 1 with different resistance values ​​of the resistor connected between a pair of electrodes 503, using the measurement method shown in FIG.

[0052] As shown in Fig. 5, if the resistance value of the resistor connected between the pair of electrodes 503 is 160 Ω or more and 600 Ω or less, the creep amount and creep recovery amount of the C1 standard can be satisfied. Also, as shown in Fig. 5, if the resistance value of the resistor connected between the pair of electrodes 503 is 210 Ω or more and 400 Ω or less, the creep amount and creep recovery amount of the C2 standard can be satisfied. In other words, by controlling the resistance value of the resistor connected between the pair of electrodes 503 within a predetermined range, the creep amount and creep recovery amount are improved, and the strain gauge 1 can be used for weighing purposes.

[0053] One method of achieving a resistance value that satisfies the C1 or C2 standard is to widen the resistor width, but this is not preferable, particularly in the case of a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed phase film as the resistor, because widening the resistor width would affect the transverse sensitivity due to the high sensitivity. On the other hand, if multiple resistors are connected in parallel to each other to reduce resistance, as in strain gauge 1, a resistance value that satisfies the C1 or C2 standard can be achieved without exposing the problem of transverse sensitivity.

[0054] In the above example, the strain gauge 1 has a three-layer structure in which the second layer 12 and the third layer 13 are sequentially stacked on the first layer 11, but this is not limited to this, and the strain gauge 1 may have a two-layer structure or a four or more layer structure.

[0055] In addition, the method of reducing the resistance is not necessarily limited to a method of stacking multiple resistors and connecting each resistor in parallel with each other through a through hole. For example, multiple resistors may be arranged on the upper surface of one substrate with the grid direction facing in the same direction, and each resistor may be connected in parallel with each other through wiring provided on the upper surface of the substrate to reduce the resistance. However, when multiple resistors are arranged on the upper surface of one substrate, the area of ​​the upper surface of the substrate becomes large, so that a structure in which multiple resistors are stacked and each resistor is connected in parallel with each other through a through hole is more advantageous for installation at a fine measurement point.

[0056] [Strain gauge manufacturing method] Here, a method for manufacturing the strain gauge 1 will be described. To manufacture the strain gauge 1, first, a base material 101 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 101. Metal layer A is a layer that is finally patterned to become resistor 301 and wiring 401. Therefore, the material and thickness of metal layer A are the same as the material and thickness of resistor 301 and wiring 401 described above.

[0057] The metal layer A can be formed by, for example, a magnetron sputtering method using a target made of a raw material capable of forming the metal layer A. The metal layer A may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulsed laser deposition method, or the like instead of the magnetron sputtering method.

[0058] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-form a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the base material 101 by, for example, conventional sputtering before forming the metal layer A.

[0059] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 301). The functional layer preferably further has a function of preventing oxidation of metal layer A due to oxygen and moisture contained in base material 101, and a function of improving adhesion between base material 101 and metal layer A. The functional layer may further have other functions.

[0060] Since the insulating resin film that constitutes the substrate 101 contains oxygen and moisture, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, particularly when the metal layer A contains Cr, since Cr forms a self-oxidized film.

[0061] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 301), and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), etc. Examples of the metals that can be used include one or more metals selected from the group consisting of copper (II), iron (Fe), molybdenum (Mo), tungsten (W), ruthenium (Ru), Rh (Rhodium), Re (Rhenium), Os (Osmium), Ir (Iridium), Pt (Platinum), Pd (Palladium), Ag (Silver), Au (Gold), Co (Cobalt), Mn (Manganese), and aluminum (Aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0062] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compound include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0063] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which reduces the detection sensitivity of strain.

[0064] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and the strain detection sensitivity can be further prevented from being reduced due to a part of the current flowing through the resistor flowing through the functional layer.

[0065] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is more preferably 1 / 100 or less of the thickness of the resistor, which can further prevent a part of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

[0066] When the functional layer is made of an insulating material such as an oxide or a nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0067] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0068] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm, which can promote the crystal growth of α-Cr and can be more easily formed without cracking the functional layer.

[0069] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is made of an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape on the entire upper surface of the substrate 101.

[0070] Furthermore, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, so that the thickness and surface area of ​​the functional layer are increased, and the heat generated by the resistor can be dissipated to the substrate 101. As a result, the deterioration of the measurement accuracy of the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0071] The functional layer can be formed in a vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 101 with Ar, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0072] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 101 is activated by a plasma treatment using Ar or the like before the formation of the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0073] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A and can be selected appropriately depending on the purpose. For example, it is possible to use Ti for the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component for the metal layer A.

[0074] In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber. In this case, the ratio of CrN and Cr2N contained in the Cr mixed phase film, and the ratio of Cr2N in CrN and Cr2N can be adjusted by changing the amount and pressure of the nitrogen gas introduced (nitrogen partial pressure) or by adjusting the heating temperature by providing a heating process.

[0075] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film containing α-Cr, which has a stable crystal structure, as a main component, can be formed. Furthermore, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

[0076] When metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A due to oxygen and moisture contained in the base material 101, and improving adhesion between the base material 101 and metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0077] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystal phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0078] Next, the metal layer A is patterned by photolithography to form the resistor 301 and the wiring 401. In this way, the first layer 11 is completed.

[0079] Next, the second layer 12 and the third layer 13 are produced in the same manner as above. However, in the case of the third layer 13, in addition to the resistor 303 and the wiring 403, a pair of electrodes 503 are formed in the step of patterning the metal layer A by photolithography.

[0080] Next, the second layer 12 and the third layer 13 are sequentially laminated on the first layer 11, a through hole for forming the through hole 70 is formed by a laser processing method or the like, and the through hole 70 is formed by a plating method or the like. After the first layer 11 is completed, the base material 102 may be laminated on the first layer 11 to form the resistor 302 and the wiring 402 on the base material 102, and the base material 103 may be laminated on the second layer 12 to form the resistor 303, the wiring 403, and the electrode 503 on the base material 103. In this case, after providing a through hole for forming the through hole 70, the resistor 303, the wiring 403, and the electrode 503 may be formed on the base material 103, and the through hole 70 may be integrally formed with the resistor 303 and the like using the same material.

[0081] Thereafter, as necessary, a cover layer 60 that covers the resistors 303 and the wiring 403 and exposes the electrodes 503 is provided on the upper surface 10c of the base material 103, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10c of the base material 103 so as to cover the resistors 303 and the wiring 403 and expose the electrodes 503, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste thermosetting insulating resin to the upper surface 10c of the base material 103 so as to cover the resistors 303 and the wiring 403 and expose the electrodes 503, and then heating and curing the resin.

[0082] When a functional layer is provided on the upper surface of each substrate as a base layer for resistors 301, 302, 303, etc., the strain gauge 1 has a cross-sectional shape as shown in Fig. 6. The layers indicated by the reference symbols 201, 202, and 203 are functional layers. When functional layers 201, 202, and 203 are provided, the planar shape of the strain gauge 1 is, for example, the same as that shown in Fig. 1. However, as described above, the functional layers 201, 202, and 203 may be formed solidly on a part or all of the upper surface of each substrate.

[0083] Although preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0084] 1 strain gauge, 11 first layer, 12 second layer, 13 third layer, 101, 102, 103 substrate, 10a, 10b, 10c top surface, 201, 202, 203 functional layer, 301, 302, 303 resistor, 303e1, 303e2 termination, 401, 402, 403 wiring, 503 electrode, 60 cover layer, 70 through hole

Claims

1. A substrate; A resistor provided directly or indirectly on the substrate, the resistor is formed from a material containing Cr, a material containing Ni, or a material containing at least one of Cr and Ni, The resistors are arranged with the grid direction facing the same direction and are connected in parallel to each other, A strain gauge, wherein the resistance value of the resistors connected in parallel is 160Ω or more and 600Ω or less.

2. 2. The strain gauge according to claim 1, wherein a resistance value of the resistors connected in parallel is 210 Ω or more and 400 Ω or less.

3. The substrate includes a first substrate and a second substrate, the plurality of resistors include a first resistor formed on the first substrate and a second resistor formed on the second substrate; the second base material is laminated on the first base material to cover the first resistor; The strain gauge according to claim 1 , wherein the first resistor and the second resistor are connected in parallel to each other by a through hole penetrating the second base material.

4. 4. The strain gauge according to claim 1, wherein the width of each of the resistors is not less than 10 μm and not more than 100 μm.

5. The strain gauge according to claim 1 , wherein the gauge factor is 10 or more.

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