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 Art

[0002] A strain gauge having a resistor on a base material and attached to a measurement object to detect the characteristics of the measurement object is known. The strain gauge is used, for example, as a sensor for detecting the strain of a material, a sensor for detecting the ambient temperature, etc. (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in addition to being used for sensor applications, the strain gauge may also be used for weighing applications. In that case, it is necessary to satisfy standards regarding creep that are more stringent than those for sensor applications. Therefore, even a strain gauge that can be used for sensor applications may not be usable for weighing applications.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a load cell provided with a strain gauge that can be used for weighing applications.

Means for Solving the Problems

[0006] This load cell comprises a Roberval-type strain generator and a strain gauge mounted on the strain generator. 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 thickness of the resistor is 6 nm to 100 nm, thereby achieving a creep amount and creep recovery amount of ±0.0735% or less. [Effects of the Invention]

[0007] According to the disclosed technology, a load cell equipped with strain gauges that can be used for weighing applications can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a load cell according to the first embodiment. [Figure 2] This is a side view illustrating a load cell according to the first embodiment. [Figure 3] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 4] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 5] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 6] This diagram illustrates the method for measuring creep amount and creep recovery amount. [Figure 7] This figure shows the results of the study on the film thickness of the resistor, the amount of creep, and the amount of creep recovery. [Figure 8] This figure shows the experimental results of the strain limit. [Figure 9] This is a cross-sectional view (part 3) illustrating a strain gauge according to the first embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> [Load cell] Figure 1 is a plan view illustrating a load cell according to the first embodiment. Figure 2 is a side view illustrating a load cell according to the first embodiment. Referring to Figures 1 and 2, the load cell 100 includes a strain generating body 110 and a strain gauge 1.

[0011] The strain generating body 110 is a Roberval-type strain generating body formed from a roughly rectangular parallelepiped metal block with through holes 120, grooves 131 and 132. The strain generating body 110 is formed from a metal such as SUS304, aluminum alloy, or iron.

[0012] The through-hole 120 penetrates the strain-generating body 110 from one side to the other. The through-hole 120 is formed in a spectacle shape, for example, in a side view, where parts of the opposing portions of two circular holes, which are spaced apart from each other, are connected.

[0013] Grooves 131 and 132 are arranged in the vertical direction of the strain generating body 110, facing each other with the through hole 120 in between. Groove 131 is recessed from the upper surface of the strain generating body 110 toward the through hole 120, and groove 132 is recessed from the lower surface of the strain generating body 110 toward the through hole 120.

[0014] The portions sandwiched between the through hole 120 and grooves 131 and 132 are thin-walled portions 141 to 144. These thin-walled portions 141 to 144 are strain-generating portions where strain is generated by external force. Four strain gauges 1 are arranged in a matrix on the thin-walled portions 141 and 142 within groove 131. In each strain gauge 1, the grid direction of the resistive element is, for example, oriented in the longitudinal direction of the strain-generating body 110.

[0015] Each strain gauge 1 is attached, for example, via an adhesive layer, onto the thin portions 141 and 142 in the groove 131 over the thin-walled portions. The adhesive layer is not particularly limited as long as it is a material having a function of fixing the strain gauge 1 and the strained body 110, and can be appropriately selected according to the purpose. For example, an epoxy resin, a modified epoxy resin, a silicone resin, a modified silicone resin, a urethane resin, a modified urethane resin, etc. can be used. Also, a material such as a bonding sheet may be used. The thickness of the adhesive layer is not particularly limited and can be appropriately selected according to the purpose. For example, it can be about 0.1 μm to 50 μm.

[0016] When the load cell 100 receives a load from the outside, stress is generated in the thin portions 141 to 144 which are strained portions, and strain occurs. The strain gauge 1 detects the change in the resistance value caused by the strain of the thin portions 141 to 144. For example, by connecting the four strain gauges 1 in a full-bridge configuration and performing arithmetic processing on the change in the resistance value, the load received from the outside 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 the line A-A 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 the line B-B in FIG. 3.

[0018] Referring to FIGS. 3 to 5, the strain gauge 1 has a base material 10, a resistor 30, a wiring 40, an electrode 50, and a cover layer 60. In FIGS. 3 to 5, for the sake of convenience, only the outer edge of the cover layer 60 is shown by a broken line. Note that the cover layer 60 may be provided as needed.

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

[0020] The substrate 10 is a component that serves as a base layer for forming the resistor 30, etc., and is flexible. The film thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a film thickness of 5 μm to 200 μm of the substrate 10 is preferable in terms of strain transmission and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0021] The base material 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, or polyolefin resin. Note that "film" refers to a flexible material with a film thickness of approximately 500 μm or less.

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

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

[0024] The resistor 30 is a thin film formed on the substrate 10 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or it may be formed on the upper surface 10a of the substrate 10 via another layer. In Figure 3, for convenience, the resistor 30 is shown with a dark, textured pattern.

[0025] The resistor 30 has a structure in which multiple elongated sections are arranged at predetermined intervals with their longitudinal directions aligned in the same direction (the direction of line AA in Figure 3), and the ends of adjacent elongated sections are connected alternately, resulting in an overall zigzag folding pattern. The longitudinal direction of the multiple elongated sections becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the direction of line BB in Figure 3).

[0026] The longitudinal ends of the two elongated portions located on the outermost side in the grid width direction are bent in the grid width direction, forming the respective ends 30e1 and 30e2 of the resistor 30 in the grid width direction. The respective ends 30e1 and 30e2 of the resistor 30 in the grid width direction are electrically connected to the electrodes 50 via the wiring 40. In other words, the wiring 40 electrically connects the respective ends 30e1 and 30e2 of the resistor 30 in the grid width direction to the respective 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 multiphase 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, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0029] For example, if the resistor 30 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Furthermore, by making α-Cr the main component of the resistor 30, the gauge factor of strain gauge 1 can be set to 10 or higher, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means that the substance in question accounts for 50% by weight or more of the total substances constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 30 contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0030] Furthermore, if the resistor 30 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0031] Furthermore, the proportion 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 proportion 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 even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0032] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, 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 electrode 50. The wiring 40 is not limited to a straight line and can be in any pattern. Also, the wiring 40 can have any width and length. For convenience, in Figure 3, the wiring 40 and the electrode 50 are shown with a textured surface 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. For example, they are wider than the wiring 40 and formed in a roughly rectangular shape. The electrodes 50 are a pair of electrodes for outputting the change in resistance value caused by strain in the resistor 30 to the outside, and for example, lead wires for external connection are attached to them.

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

[0036] A conductive layer formed from a material with 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 lower resistance than the resistor 30, and can be appropriately selected according to the purpose. For example, if the resistor 30 is a Cr multiphase film, examples of conductive layers include Cu, Ni, Al, Ag, Au, Pt, etc., or alloys of any of these metals, compounds of any of these metals, or 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 according to the purpose, but for example, it can be about 3 μm to 5 μm.

[0037] In this way, by laminating a conductive layer made of a material with lower resistance than the resistor 30 onto the wiring 40 and the electrode 50, the resistance of the wiring 40 becomes lower than that of the resistor 30, thus suppressing 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 wiring 40 with lower resistance than the resistor 30, the effective sensitive area of ​​the strain gauge 1 can be limited to the local region where the resistor 30 is formed. Therefore, the accuracy of strain detection by the resistor 30 can be improved.

[0039] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 30, reducing the resistance of the wiring 40 to that of the resistor 30 and limiting the effective sensing area to the local region where the resistor 30 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 40 to that of the resistor 30 also has the effect of reducing lateral sensitivity.

[0040] The cover layer 60 is formed on the substrate 10 and covers the resistor 30 and wiring 40, exposing 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 wiring 40, mechanical damage to the resistor 30 and wiring 40 can be prevented. In addition, the cover layer 60 can protect the resistor 30 and wiring 40 from moisture and other elements. The cover layer 60 may be provided to cover the entire portion excluding 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, polyolefin resin). The cover layer 60 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 60, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0042] [Thickness of the resistor (1)] Here, we will describe the preferred film thickness of the resistor 30 when the strain gauge 1 is used for weighing purposes.

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

[0044] The C1 standard requires that the creep amount and creep recovery amount be ±0.0735% or less. The C2 standard requires that the creep amount and creep recovery amount be ±0.0368% or less. Note that when strain gauge 1 is used for sensor applications, the creep amount and creep recovery amount specifications are approximately ±0.5%.

[0045] After diligent research by the inventors, they discovered 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 generator 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 creep recovery. Specifically, using the MinebeaMitsumi FSU-15K, which is equipped with a Roberval-type strain element, several samples were prepared with varying film thicknesses of the resistor 30 in the strain gauge 1 (the film thickness of each resistor 30 was the same in all four strain gauges 1), and the amount of creep and creep recovery were measured for each sample. In the strain gauge 1, a polyimide resin film with a film thickness of 25 μm was used as the base material 10. A Cr multiphase film was used for the resistor 30. The FSU-15K is a load cell with a rated capacity of 15 kgf equipped with a Roberval-type strain element made of SUS304.

[0047] The creep amount and creep recovery amount are the amounts by which the amount of elastic deformation (strain) of the surface on which the resistor 30 is provided in the strain gauge 1 changes over time. Therefore, they can be measured by connecting four strain gauges 1 in a full bridge configuration and performing calculations. Please refer to Figure 6 for a detailed explanation.

[0048] Figure 6 illustrates the method for measuring creep and creep recovery. In Figure 6, the horizontal axis represents time, and the vertical axis represents strain voltage [mV].

[0049] First, after powering on the measuring device for 10 seconds, a 150% load is applied to strain gauge 1 attached to the strain generating 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 strain gauge 1 attached to the strain generating body for 20 minutes, and then the load is removed. Then, wait for another 20 minutes to pass after the load has been 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 is measured between 20 minutes after the 150% load is removed and immediately after the 100% load is applied. Also, the absolute value ΔA of the difference in strain voltage is measured between immediately after the 100% load is applied and 20 minutes after the 100% load is applied. In this case, ΔA / B is the creep amount. Next, the absolute value ΔC of the difference in strain voltage is measured between immediately after the 100% load is removed and 20 minutes after the 100% load is removed. In this case, ΔC / B is the creep recovery amount.

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

[0052] Figure 7 shows the results of the study on the film thickness of the resistor, creep amount, and creep recovery amount. It summarizes the results of measuring the creep amount and creep recovery amount of multiple strain gauges 1 with different film thicknesses of the resistor 30 using the measurement method shown in Figure 6.

[0053] As shown in Figure 7, if the film thickness of the resistor 30 is between 6 nm and 100 nm, the creep amount and creep recovery amount of the C1 standard can be satisfied. Also, as shown in Figure 7, if the film thickness of the resistor 30 is between 11 nm and 50 nm, the creep amount and creep recovery amount of the C2 standard can be satisfied. In other words, in a strain gauge 1 mounted on a Roberval-type strain generator, 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 applications. Furthermore, the inventors have confirmed that the above film thickness range of the resistor 30 that satisfies the C1 or C2 standard is achieved when the width of the resistor 30 is at least between 50 μm and 500 μm.

[0054] Furthermore, according to the inventors' studies, 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-generating body. That is, while the preferred film thickness range for the resistor 30 when using a Roberval-type strain-generating body is as described above, the preferred film thickness range for the resistor 30 may differ from that described above when using strain-generating bodies such as column-type, ring-type, or diaphragm-type bodies.

[0055] [Thickness of the resistor (2)] In order for the strain gauge 1 attached to the strain-generating body to detect a larger amount of strain, the resistor 30 must not be damaged (e.g., break in the wire) during the process of stretching and contracting. Therefore, it is preferable to improve the strain limit (strain resistance) as much as possible. The strain limit is the value of mechanical strain at which cracks or wire breakage begin to occur when strain is applied to the strain gauge.

[0056] Through diligent research, the inventors discovered that the film thickness of the resistor 30 affects not only creep but also the strain limit. Specifically, they found that the thinner the resistor 30, the less likely cracks or disconnections are to occur when the 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 multiple strain gauges 1 of three types with resistor 30 film thicknesses of 50 nm, 220 nm, and 800 nm, applied strain to each, and investigated the occurrence of cracks and breaks. In the strain gauge 1, a polyimide resin film with a film thickness of 25 μm was used as the base material 10. In addition, a Cr multiphase film was used for the resistor 30.

[0058] The study revealed that as the film thickness of the resistor 30 decreased below a certain point, the number of cracks and disconnections tended to decrease as the thickness decreased, indicating that the strain limit depends on the film thickness of the resistor 30.

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

[0060] In other words, it was observed that as the film thickness of the resistor 30 decreased below 220 nm, the number of cracks and disconnections tended to decrease as the thickness decreased. Furthermore, it was confirmed that when the film thickness of the resistor 30 was 50 nm, the strain limit improved by approximately 30% compared to when the film thickness of the resistor 30 was 220 nm and 800 nm.

[0061] Considering these results together with the results for [resistor thickness (1)], in a strain gauge mounted on a Roberval-type strain generator, if the 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. Furthermore, if the 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 the resistor 30 is between 11 nm and 50 nm, the creep amount and creep recovery amount of the C2 standard can be satisfied. In this case, regardless of the film thickness of the resistor 30, it can be said that there is a sufficient strain limit of 10,000 με or more.

[0063] [Method of manufacturing strain gauges] Here, we will explain the manufacturing method of the strain gauge 1. To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, let's call it metal layer A) is formed on the upper surface 10a of the base material 10. Metal layer A is the layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrode 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 electrode 50 described above.

[0064] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

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

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

[0067] Since the insulating resin film that makes up the base material 10 contains oxygen and moisture, and especially when the metal layer A contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer A.

[0068] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of at least the upper metal layer A (resistor 30), and can be appropriately selected according to 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 (bismodium) Examples include one or more metals selected from the group consisting of (S), 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 these metals, or a compound of any of these metals.

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

[0070] When the functional layer is formed from 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. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor can flow into the functional layer, preventing a decrease in strain detection sensitivity.

[0071] When the functional layer is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer, further preventing a decrease in strain detection sensitivity.

[0072] When the functional layer is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to some of the current flowing through the resistor flowing into the functional layer.

[0073] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be easily formed without cracking.

[0074] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracking.

[0075] When the functional layer is formed from an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer.

[0076] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 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. When the functional layer is formed from 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 as a solid block at least in the region where the resistor is formed. Alternatively, the functional layer may be formed as a solid block over the entire upper surface of the substrate 10.

[0077] Furthermore, when the functional layer is formed from an insulating material, forming the functional layer relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer, allowing the heat generated when the resistor is heated to be dissipated towards the substrate 10. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 1.

[0078] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 10a of the substrate 10 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0079] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 10a of the substrate 10 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

[0080] There are no particular restrictions on the combination of materials for the functional layer and the metal layer A, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer A.

[0081] In this case, for example, metal layer A can be formed by targeting a raw material capable of forming a Cr multiphase film and using a magnetron sputtering method with Ar gas introduced into the chamber. Alternatively, metal layer A may be formed by targeting pure Cr and using a reactive sputtering method with an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0082] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that when the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0083] Furthermore, when metal layer A is a Cr multiphase 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 by oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and metal layer A. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0084] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A can improve the gauge characteristics in the strain gauge 1.

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

[0086] Subsequently, if necessary, a cover layer 60 is provided on the upper surface 10a of the base material 10 to cover the resistor 30 and wiring 40 and expose the electrode 50, thereby completing the strain gauge 1. The cover layer 60 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the base material 10 to cover the resistor 30 and wiring 40 and expose the electrode 50, and then heating and curing it. Alternatively, the cover layer 60 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the base material 10 to cover the resistor 30 and wiring 40 and expose the electrode 50, and then heating and curing it.

[0087] Furthermore, if a functional layer is provided on the upper surface 10a of the base material 10 as a base layer for the resistor 30, wiring 40, and electrode 50, the strain gauge 1 will have the cross-sectional shape shown in Figure 9. The layer indicated by reference numeral 20 is the functional layer. The planar shape of the strain gauge 1 when the functional layer 20 is provided will be the same as, for example, as shown in Figure 3. However, as mentioned above, the functional layer 20 may also be formed as a solid layer on part or all of the upper surface 10a of the base material 10.

[0088] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

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

[0090] Furthermore, the load cell 100 may have two resistors. 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 either the top or bottom surface of the load cell 100, but may be mounted on both the top and bottom surfaces. 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 Base material, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1, 30e2 Termination, 40 Wiring, 50 Electrode, 60 Cover layer, 100 Load cell, 110 Strain generating element, 120 Through hole, 131, 132 Grooves, 141-144 Thin-walled section

Claims

1. Roberval type strain-generating body, The strain gauge mounted on the strain generating body comprises, The strain gauge comprises a flexible base material and a resistor formed on the base material from a material containing at least one of chromium and nickel. A load cell in which the thickness of the resistor is 6 nm or more and 100 nm or less, thereby the creep amount and creep recovery amount are ±0.0735% or less.

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

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

4. A load cell according to any one of claims 1 to 3, wherein the film thickness of the resistor is set to 6 nm or more and 50 nm or less so that the strain limit is 10,000 με or more.

5. The load cell according to claim 4, wherein the thickness of the resistor is 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 any one of claims 1 to 5, wherein the strain gauge has a plurality of resistors.

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