Load cell

Abstract

To provide a load cell which is usable for a scale and which includes a strain gauge.SOLUTION: A load cell includes a Roberval-type elastic body and strain gauges mounted on the elastic body. The strain gauge includes a flexible base material, and a resistor which is positioned on the base material and which is formed of a material containing at least one of chromium and nickel. The resistor has a film thickness of 6 nm or more and 100 nm or less and the creep amount and the creep recovery amount of ±0.0735% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a load cell. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-221696 Summary of the Invention [Problem to be solved by the invention]

[0004] However, strain gauges are sometimes used not only as sensors but also as scales, which require them to meet stricter creep standards than those for sensors. As a result, strain gauges that can be used for sensors sometimes cannot be used for scales.

[0005] The present invention has been made in view of the above points, and has as its object to provide a load cell equipped with a strain gauge that can be used for weighing purposes. [Means for solving the problem]

[0006] This load cell comprises a Roberval-type strain element and a strain gauge mounted on the strain element. The strain gauge has a flexible substrate and a resistor formed on the substrate from a material containing at least one of chromium and nickel. The resistor has a film thickness of 6 nm or more and 100 nm or less, thereby achieving creep amounts and creep recovery amounts of ±0.0735% or less. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a load cell equipped with a strain gauge that can be used for weighing purposes. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the load cell according to the first embodiment. [Figure 2] FIG. 2 is a side view illustrating the load cell according to the first embodiment. [Figure 3] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 4] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 5] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 2 is a diagram illustrating a method for measuring the amount of creep and the amount of creep recovery. [Figure 7] FIG. 10 is a diagram showing the results of examining the relationship between the film thickness of a resistor and the amount of creep and creep recovery. [Figure 8] FIG. 10 is a diagram showing experimental results of strain limits. [Figure 9] FIG. 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] First Embodiment [Load cell] Fig. 1 is a plan view illustrating a load cell according to the first embodiment. Fig. 2 is a side view illustrating the load cell according to the first embodiment. Referring to Fig. 1 and Fig. 2, a load cell 100 has a strain element 110 and a strain gauge 1.

[0011] The flexure element 110 is a Roberval type flexure element having a substantially rectangular parallelepiped metal block with a through hole 120, a groove 131, and a groove 132. The flexure element 110 is made of a metal such as SUS304, an aluminum alloy, or iron.

[0012] The through-hole 120 penetrates from one side surface to the other side surface of the flexure element 110. For example, the through-hole 120 is formed in a eyeglass shape in a side view, in which two circular holes spaced apart from each other are partially connected to each other at opposing portions.

[0013] Grooves 131 and 132 are arranged in the vertical direction of flexure body 110 so as to face each other across through hole 120. Groove 131 is recessed from the upper surface of flexure body 110 toward through hole 120, and groove 132 is recessed from the lower surface of flexure body 110 toward through hole 120.

[0014] The portions sandwiched between the through hole 120 and each of the grooves 131 and 132 are thin-walled portions 141 to 144. The thin-walled portions 141 to 144 are strain-generating portions where strain occurs due to an external force. Four strain gauges 1 are arranged in a matrix on the thin-walled portions 141 and 142 in the groove 131. In each strain gauge 1, the grid direction of the resistor faces, for example, in the longitudinal direction of the strain-generating body 110.

[0015] Each strain gauge 1 is attached to the thin-walled portions 141 and 142 in the groove 131, for example, via an adhesive layer. The adhesive layer is not particularly limited and can be selected appropriately depending on the purpose as long as it has the function of fastening the strain gauge 1 and the flexure element 110 together. For example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used. A material such as a bonding sheet can also be used. The thickness of the adhesive layer is not particularly limited and can be selected appropriately depending on the purpose, for example, about 0.1 μm to 50 μm.

[0016] When the load cell 100 is subjected to an external load, stress is generated in the thin-walled portions 141 to 144, which are strain-generating portions, causing strain. The strain gauge 1 detects changes in resistance caused by strain in the thin-walled portions 141 to 144. For example, by connecting four strain gauges 1 in a full bridge configuration and processing the changes in resistance, the external load can be calculated.

[0017] [Strain gauge] Fig. 3 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 4 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. 3. Fig. 5 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. 3.

[0018] 3 to 5, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. For convenience, only the outer edge of the cover layer 60 is shown by a dashed line in Figs. 3 to 5. The cover layer 60 may be provided as needed.

[0019] 3 to 5, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 of each part is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing the object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0020] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of the substrate 10 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 properties.

[0021] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member with a thickness of about 500 μm or less.

[0022] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0023] Materials other than resin for the substrate 10 include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Alternatively, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 10. In this case, an insulating film, for example, is formed on the metal substrate 10.

[0024] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing element that generates a resistance change when strain is applied. 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. For convenience, the resistor 30 is shown in FIG. 3 with a dark matte finish.

[0025] The resistor 30 has a structure in which multiple elongated portions are arranged at predetermined intervals with their longitudinal directions in the same direction (the direction of line AA in Figure 3), and the ends of adjacent elongated portions are alternately connected, resulting in a zigzag folded structure as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction of line BB in Figure 3).

[0026] One longitudinal end of each of the two elongated portions located outermost in the grid width direction is bent in the grid width direction to form terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction. Each of the terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction is electrically connected to an electrode 50 via a wiring 40. In other words, the wiring 40 electrically connects each of the terminal ends 30e1 and 30e2 of the resistor 30 in the grid width direction to each of the electrodes 50.

[0027] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0028] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0029] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50% by weight or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0030] Furthermore, when the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0031] Furthermore, 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 Cr2N has semiconducting properties, which leads to a more significant decrease in TCR (negative TCR). Furthermore, by reducing the amount of ceramic formation, brittle fracture is reduced.

[0032] On the other hand, if trace amounts of N2 or atomic N are mixed into or present in the film, they will escape to the outside of the film due to external conditions (such as high temperature environments), causing changes in film stress.By creating chemically stable CrN, the unstable N mentioned above will not be generated, and a stable strain gauge can be obtained.

[0033] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrodes 50. The wiring 40 is not limited to being linear and can have any pattern. The wiring 40 can have any width and any length. For convenience, in FIG. 3, the wiring 40 and the electrodes 50 are shown with a matte finish that is thinner than the resistor 30.

[0034] The electrodes 50 are formed on the substrate 10 and electrically connected to the resistor 30 via the wiring 40, and are formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting to the outside a change in resistance value of the resistor 30 caused by strain, and are connected, for example, to lead wires for external connection.

[0035] Although the resistor 30, the wiring 40, and the electrode 50 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, the wiring 40, and the electrode 50 have approximately the same thickness.

[0036] A conductive layer made of a material having a lower resistance than the resistor 30 may be laminated on the wiring 40 and the electrode 50. The material of the laminated conductive layer is not particularly limited as long as it has a lower resistance than the resistor 30, and can be appropriately selected depending on the purpose. For example, when the resistor 30 is a Cr mixed phase film, examples of the material include Cu, Ni, Al, Ag, Au, Pt, etc., alloys of any of these metals, compounds of any of these metals, and laminated films in which any of these metals, alloys, or compounds are appropriately laminated. 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.

[0037] In this way, by laminating a conductive layer made of a material with a lower resistance than the resistor 30 on the wiring 40 and the electrode 50, the wiring 40 has a lower resistance than the resistor 30, and therefore, it is possible to prevent the wiring 40 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

[0038] In other words, by providing the wiring 40 with a lower resistance than the resistor 30, the actual sensitive part of the strain gauge 1 can be limited to the local area where the resistor 30 is formed, thereby improving the accuracy of strain detection by the resistor 30.

[0039] 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 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensitive part to the local region where the resistor 30 is formed has a significant effect on improving strain detection accuracy. Also, making the wiring 40 lower in resistance than the resistor 30 has the effect of reducing lateral sensitivity.

[0040] The cover layer 60 is formed on the substrate 10, covers the resistor 30 and the wiring 40, and exposes the electrodes 50. A portion of the wiring 40 may be exposed from the cover layer 60. By providing the cover layer 60 that covers the resistor 30 and the wiring 40, it is possible to prevent mechanical damage to the resistor 30 and the wiring 40. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 and the wiring 40 from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the electrodes 50.

[0041] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0042] [Resistor film thickness (1)] Here, a suitable film thickness of the resistor 30 when the strain gauge 1 is used for weighing purposes will be described.

[0043] When using the strain gauge 1 for weighing purposes, it is necessary for it to satisfy creep standards, such as precision class C1 (hereinafter referred to as C1 standard) based on OIML R60 and precision class C2 (hereinafter referred to as C2 standard) based on OIML R60.

[0044] The C1 standard requires that the creep amount and creep recovery amount be within ±0.0735%. The C2 standard requires that the creep amount and creep recovery amount be within ±0.0368%. When using strain gauge 1 for sensor applications, the standard for creep amount and creep recovery amount is approximately ±0.5%.

[0045] After careful consideration, the inventors have come to the conclusion that creep is highly dependent on the film thickness of the resistor 30, and that in order to mount the strain gauge 1 on a Roberval-type strain element and satisfy the C1 and C2 standards, the film thickness of the resistor 30 needs to be relatively thin.

[0046] Therefore, the inventors investigated the film thickness of the resistor 30 necessary to reduce the amount of creep and the amount of creep recovery. Specifically, a MinebeaMitsumi FSU-15K equipped with a Roberval-type strain element was used to prepare multiple samples of strain gauges 1 with different film thicknesses of the resistor 30 (the film thickness of each resistor 30 was the same in all four strain gauges 1), and the amount of creep and the amount of creep recovery of each sample were measured. In the strain gauges 1, a polyimide resin film with a film thickness of 25 μm was used as the substrate 10. A Cr mixed-phase film was used for the resistor 30. The FSU-15K is a load cell equipped with a Roberval-type strain element made of SUS304 and has a rated capacity of 15 kgf.

[0047] The amount of creep and the amount of creep recovery are amounts that change over time as the amount of elastic deformation (amount of strain) of the surface of the strain gauge 1 where the resistor 30 is provided changes, so they can be measured by connecting four strain gauges 1 in a full bridge and performing arithmetic processing. A detailed explanation will be given with reference to FIG. 6.

[0048] Fig. 6 is a diagram illustrating a method for measuring the creep amount and the creep recovery amount, in which the horizontal axis represents time and the vertical axis represents strain voltage [mV].

[0049] First, 10 seconds after powering on 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.

[0050] The strain voltage changes, for example, as shown in Figure 6. In Figure 6, 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 is 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.

[0051] Note that 100% load is 2 kg, and 150% load is 1.5 times the 100% load.

[0052] FIG. 7 shows the results of an investigation into the relationship between the film thickness of the resistor and the amount of creep and creep recovery. It summarizes the results of measuring the amount of creep and creep recovery of multiple strain gauges 1 with different film thicknesses of the resistor 30 using the measurement method shown in FIG.

[0053] As shown in FIG. 7, if the film thickness of the resistor 30 is 6 nm or more and 100 nm or less, the creep amount and creep recovery amount of the C1 standard can be satisfied. Also, as shown in FIG. 7, if the film thickness of the resistor 30 is 11 nm or more and 50 nm or less, the creep amount and creep recovery amount of the C2 standard can be satisfied. That is, in a strain gauge 1 mounted on a Roberval-type strain element, controlling the film thickness of the resistor 30 within a predetermined range improves the creep amount and creep recovery amount, making the strain gauge 1 usable for weighing purposes. Furthermore, the inventors have confirmed that the above film thickness range of the resistor 30 that satisfies the C1 or C2 standard is established at least when the width of the resistor 30 is in the range of 50 μm or more and 500 μm or less.

[0054] According to the inventors' investigations, the film thickness of the resistor 30 that satisfies the creep amount and creep recovery amount of the C1 or C2 standard also depends on the structure of the strain element. That is, the suitable film thickness range of the resistor 30 when a Roberval type strain element is used is as described above, but when a column type, ring type, diaphragm type, or other type of strain element is used, the suitable film thickness range of the resistor 30 may differ from the above.

[0055] [Resistor film thickness (2)] In order for the strain gauge 1 attached to the strain element to detect a larger amount of strain, it is preferable to improve the strain limit (strain resistance) as much as possible, since the resistor 30 itself must not be damaged (such as broken wire) during the process of expansion and contraction of the resistor 30. The strain limit is the value of mechanical strain at which cracks or breakage begin to occur when strain is applied to the strain gauge.

[0056] After careful investigation, the inventors have found that the thickness of resistor 30 not only affects creep but also influences the strain limit. In other words, it has been found that the thinner the resistor 30, the less likely cracks or breaks will occur when resistor 30 is subjected to strain.

[0057] Therefore, the inventors investigated the film thickness of the resistor 30 necessary to improve the strain limit. Specifically, the inventors fabricated three types of strain gauges 1, each with a resistor 30 film thickness of 50 nm, 220 nm, and 800 nm, and applied strain to each to examine the occurrence of cracks and breakage. In the strain gauges 1, a polyimide resin film with a film thickness of 25 μm was used as the substrate 10. Furthermore, a Cr mixed-phase film was used for the resistor 30.

[0058] As a result of the investigation, it was confirmed that when the thickness of the resistor 30 becomes thinner than a certain point, the cracks and breaks tend to decrease as the thickness becomes thinner, and it was found that the strain limit depends on the thickness of the resistor 30.

[0059] Fig. 8 shows the results of strain limit experiments, plotting the minimum strain limit values ​​for multiple strain gauges. As shown in Fig. 8, the inventors' experimental results showed that the strain limit was approximately constant at 7000 με or more when the resistor 30 film thickness was 220 nm and 800 nm, while the strain limit was 10000 με or more when the resistor 30 film thickness was 50 nm.

[0060] That is, it was confirmed that cracks and breaks tend to decrease as the thickness of resistor 30 becomes thinner than 220 nm. It was also confirmed that when the thickness of resistor 30 is 50 nm, the strain limit is improved by approximately 30% compared to when the thickness of resistor 30 is 220 nm or 800 nm.

[0061] Considering this result together with the result of [Resistor Film Thickness (1)], in a strain gauge mounted on a Roberval-type strain element, if the film thickness of the resistor 30 is 6 nm or more and 100 nm or less, the creep amount and creep recovery amount of the C1 standard can be satisfied. If the film thickness of the resistor 30 is 6 nm or more and 50 nm or less, the creep amount and creep recovery amount of the C1 standard can be satisfied and the strain limit can be improved.

[0062] Furthermore, if the film thickness of resistor 30 is 11 nm or more and 50 nm or less, the creep amount and creep recovery amount of the C2 standard can be satisfied. In this case, it can be said that the strain limit of 10,000 με or more is sufficient regardless of the film thickness of resistor 30.

[0063] [Strain gauge manufacturing method] Here, a method for manufacturing the strain gauge 1 will be described. To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of metal layer A are the same as the material and thickness of the resistor 30, wiring 40, and electrodes 50 described above.

[0064] The metal layer A can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, the metal layer A may also be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0065] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the substrate 10 by, for example, conventional sputtering before depositing the metal layer A.

[0066] In the present application, the functional layer refers to a layer having the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and the function of improving adhesion between the substrate 10 and metal layer A. The functional layer may also have other functions.

[0067] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, especially when the metal layer A contains Cr.

[0068] 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 30), and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Examples of the metals include one or more metals selected from the group consisting of copper (Ru), 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 this group, and a compound of any of the metals in this group.

[0069] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0070] 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, which can promote the crystal growth of α-Cr and prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[0071] 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, which can promote the crystal growth of α-Cr and further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

[0072] 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 / 100 or less of the thickness of the resistor, which further prevents a portion of the current flowing through the resistor from flowing through the functional layer, thereby further preventing a decrease in strain detection sensitivity.

[0073] 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 1 μm, which promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracks.

[0074] 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 not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0075] 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 0.5 μm, which promotes the crystal growth of α-Cr and allows the functional layer to be formed more easily without cracks.

[0076] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 3, 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. If the functional layer is made of an insulating material, it does not need 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 state at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the substrate 10.

[0077] Furthermore, when the functional layer is made of an insulating material, the thickness of the functional layer is made relatively thick, between 50 nm and 1 μm, and the functional layer is made solid. This increases the thickness and surface area of ​​the functional layer, allowing heat generated by the resistor to be dissipated to the substrate 10. As a result, the deterioration of measurement accuracy in the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0078] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0079] 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 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0080] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and it can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer A.

[0081] In this case, for example, the metal layer A can be formed by magnetron sputtering using a target made of a material capable of forming a Cr mixed-phase film and introducing Ar gas into the chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as the target and introducing an appropriate amount of nitrogen gas into the chamber together with Ar gas. In this case, the proportions of CrN and CrN contained in the Cr mixed-phase film, and the proportion of CrN in CrN and CrN can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the nitrogen gas introduced or by adjusting the heating temperature in a heating step.

[0082] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0083] When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0084] 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 crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 can be improved. Furthermore, the material that constitutes the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0085] Next, the metal layer A is patterned by photolithography to form the resistor 30, the wiring 40, and the electrode 50.

[0086] Thereafter, if necessary, a cover layer 60 that covers the resistor 30 and the wiring 40 and exposes the electrodes 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrodes 50, and then heating and curing the resin.

[0087] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlying layer for the resistor 30, the wiring 40, and the electrodes 50, the strain gauge 1 has a cross-sectional shape as shown in FIG. 9. The layer indicated by the reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 will be the same as that shown in FIG. 3, for example. However, as mentioned above, the functional layer 20 may be formed solidly on part or all of the upper surface 10a of the substrate 10.

[0088] Although the preferred embodiments have been described in detail above, 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.

[0089] For example, although Fig. 1 etc. shows an example in which four strain gauges 1 are mounted on the load cell 100, it is also possible to mount one strain gauge with four resistors formed on one substrate. In that case, the resistors may be connected by wiring provided on the substrate for convenient bridge connection.

[0090] Furthermore, two resistors may be mounted on the load cell 100. In this case, each resistor can be connected in a half-bridge configuration.

[0091] Furthermore, the resistors mounted on the load cell 100 are not limited to being mounted on either the top or bottom surface of the load cell 100, but may be mounted on both the top and bottom surfaces of the load cell 100. For example, two resistors may be mounted on the top surface of the load cell 100, and two more resistors may be mounted on the bottom surface. [Explanation of symbols]

[0092] 1 strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e1, 30e2 termination, 40 wiring, 50 electrode, 60 cover layer, 100 load cell, 110 strain element, 120 through hole, 131, 132 groove, 141 to 144 thin-walled portion

Claims

1. A Roberval-type strain body, a strain gauge mounted on the strain generating body, The strain gauge includes a flexible substrate and a resistor formed on the substrate and made of a material containing at least one of chromium and nickel, A load cell, wherein the film thickness of the resistor is 6 nm or more and 100 nm or less, so that the creep amount and creep recovery amount are ±0.0735% or less.

2. the strain gauge includes wiring that electrically connects the resistor and an electrode; 2. The load cell according to claim 1, wherein a conductive layer made of a material having a lower resistance than the resistor is laminated on the wiring.

3. The resistor is made of Cr, CrN, and Cr ２ 3. The load cell of claim 2 formed from a film containing N.

4. 4. The load cell according to claim 1, wherein the resistor has a film thickness of 6 nm to 50 nm so that the strain limit is 10,000 με or more.

5. 5. The load cell according to claim 4, wherein the resistor has a film thickness of 11 nm or more and 50 nm or less, so that the creep amount and creep recovery amount are ±0.0368% or less.

6. The load cell according to claim 1 , wherein the strain gauge has a plurality of the resistors.

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