Load cell

Abstract

To provide a load cell having a strain gauge which is applicable for a scale.SOLUTION: The load cell includes: a roberval strain body; and a strain gauge equipped in the strain body. The strain gauge includes: a flexible base material; and a resistor on the base material, the resistor being formed on a film including Cr, CrN, and Cr2 N. The film thickness is at least 6nm and is 100nm at a maximum and the amount of creep and the amount of creep recovery is ±0.0735% at a maximum.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a load cell. [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 has an object to provide a load cell equipped with a strain gauge that can be used for weighing purposes. [Means for solving the problem]

[0006] The load cell includes a Roberval-type strain element and a strain gauge mounted on the strain element. The strain gauge includes a flexible substrate and a CrN-based material having a thickness of 100 μm and a thickness of 100 μm. 2and a resistor formed from a film containing N, the resistor having a film thickness of 6 nm or more and 100 nm or less, whereby the creep amount and creep recovery amount are ±0.0735% or less. Effect 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 description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the load cell according to the first embodiment. [Diagram 2] FIG. 2 is a side view illustrating the load cell according to the first embodiment. [Diagram 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. [Diagram 5] 4 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. [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. 13 is a diagram showing the results of an investigation into the relationship between the film thickness of a resistor and the amount of creep and the amount of creep recovery. [Figure 8] FIG. 13 is a diagram showing experimental results of strain limits. [Figure 9] 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 designated by the same reference numerals, and duplicated 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 a load cell according to the first embodiment. Referring to Fig. 1 and Fig. 2, a load cell 100 has a strain body 110 and a strain gauge 1.

[0011] The flexure body 110 is a Roberval type flexure body having a substantially rectangular parallelepiped metal block with a through hole 120, a groove 131, and a groove 132. The flexure body 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 body 110. For example, the through hole 120 is formed in a eyeglass shape in which two circular holes spaced apart from each other are partially connected to each other when viewed from the side.

[0013] The grooves 131 and 132 are disposed in the up-down direction of the flexure body 110 so as to face each other across the through hole 120. The groove 131 is recessed from the upper surface of the flexure body 110 toward the through hole 120, and the groove 132 is recessed from the lower surface of the flexure body 110 toward the through hole 120.

[0014] The portions sandwiched between the through hole 120 and each of the grooves 131 and 132 become the thin-walled portions 141-144. The thin-walled portions 141-144 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 onto the thin wall portion 141 and the thin wall portion 142 in the groove 131, for example, via an adhesive layer. The adhesive layer is not particularly limited and can be appropriately selected depending on the purpose as long as it is a material that has the function of fixing the strain gauge 1 and the flexure body 110. For example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used. Also, a material such as a bonding sheet can be used. The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose, for example, it can be about 0.1 μm to 50 μm.

[0016] When the load cell 100 receives 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 a change in resistance value caused by the strain in the thin-walled portions 141 to 144. For example, the external load can be calculated by connecting four strain gauges 1 in a full bridge configuration and processing the change in resistance value.

[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 Fig. 3 to 5. The cover layer 60 may be provided as needed.

[0019] In addition, in Fig. 3 to Fig. 5, for convenience, in the strain gauge 1, the side of the substrate 10 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. In addition, the surface on which the resistor 30 is provided in each part is referred to as the one side or upper surface, and the surface on which the resistor 30 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 plan view refers to the object being viewed from the normal direction of the upper surface 10a of the substrate 10, and the planar shape refers to the shape of the object being 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.

[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 having 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.

[0023] Examples of materials other than resin for the substrate 10 include SiO 2 , ZrO 2 (including YSZ), Si, Si 2 N 3 , Al2 O 3 (including sapphire), ZnO, perovskite ceramics (CaTiO 3 , BaTiO 3 ) and other crystalline materials, and furthermore, amorphous glass and the like can be used. Metals such as aluminum, aluminum alloys (duralumin), and titanium can also be used as the material for the base material 10. In this case, for example, an insulating film is formed on the metal base material 10.

[0024] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strained. 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 pattern.

[0025] The resistor 30 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. 3), 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. 3).

[0026] One end of the longitudinal direction of the two elongated portions located on the outermost sides in the grid width direction is bent in the grid width direction, and each end 30e of the resistor 30 in the grid width direction is 1 and 30e 2 Each end 30e of the resistor 30 in the grid width direction is formed. 1 and 30e 2 are electrically connected to the electrodes 50 via the wiring 40. In other words, the wiring 40 is 1 and 30e 2 and each of the electrodes 50 are electrically connected.

[0027] The resistor 30 can be made of, 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 made of 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 composed of Cr, CrN, Cr 2 It is a film containing a mixed phase of N, 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 making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making the resistor 30 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 30 preferably contains 80% by weight or more of α-Cr, and more preferably contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0030] In addition, when the resistor 30 is a Cr mixed phase film, CrN and Cr contained in the Cr mixed phase film 2 The N content is preferably 20% by weight or less. 2 By controlling the N content to 20% by weight or less, the decrease in the gauge factor can be suppressed.

[0031] In addition, CrN and Cr 2 Cr in N 2 The proportion of N 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. 2 Cr in N2 The N ratio is 90% by weight or more and less than 95% by weight, so Cr has semiconducting properties. 2 The decrease in TCR (negative TCR) becomes more pronounced due to the addition of N. Furthermore, the reduction in ceramic formation reduces brittle fracture.

[0032] On the other hand, trace amounts of N 2 Or, if atomic N is mixed in or present, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[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 may be in any pattern. The wiring 40 may have any width and any length. For convenience, the wiring 40 and the electrodes 50 are shown in FIG. 3 as having a matte finish that is thinner than the resistor 30.

[0034] The electrodes 50 are formed on the substrate 10 and are 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 distortion, and for example, lead wires for external connection are joined to the electrodes 50.

[0035] Although the resistor 30, the wiring 40, and the electrodes 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 electrodes 50 have approximately the same thickness.

[0036] A conductive layer formed 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 is a material having 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, 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.

[0037] In this way, by laminating a conductive layer made of a material having 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 having a lower resistance than the resistor 30, the actual sensing portion 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 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 sensing part to the local region where the resistor 30 is formed has a significant effect on improving the strain detection accuracy. Making the wiring 40 lower in resistance than the resistor 30 also has the effect of reducing the 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 part 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, etc. from occurring 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, etc. 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, 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.

[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 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).

[0044] 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%.

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

[0046] Therefore, the inventors have studied the film thickness of the resistor 30 required to reduce the amount of creep and the amount of creep recovery. Specifically, a number of samples were produced by changing the film thickness of the resistor 30 of the strain gauge 1 in a MinebeaMitsumi FSU-15K equipped with a Roberval type strain element (the film thickness of each resistor 30 in the four strain gauges 1 is the same), and the amount of creep and the amount of creep recovery of each sample were measured. In the strain gauge 1, a polyimide resin film with a film thickness of 25 μm was used as the substrate 10. Also, 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 on which 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 for explaining a method for measuring the amount of creep and the amount of creep recovery, in which the horizontal axis represents time and the vertical axis represents strain voltage [mV].

[0049] 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.

[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 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.

[0051] It should be noted that a 100% load is 2 kg, and a 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, and 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 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 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 the strain gauge 1 mounted on the Roberval type strain element, by controlling the thickness of the resistor 30 within a predetermined range, the creep amount and creep recovery amount are improved, and the strain gauge 1 can be used for weighing purposes. Also, the inventors confirmed that the above-mentioned thickness range of the resistor 30 that satisfies the C1 standard or the 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' study, the film thickness of resistor 30 that satisfies the creep amount and creep recovery amount of the C1 or C2 standard also depends on the structure of the flexure. That is, the suitable film thickness range of resistor 30 when a Roberval type flexure is used is as described above, but when a column type, ring type, diaphragm type, or other flexure is used, the suitable film thickness range of resistor 30 may differ from the above.

[0055] [Resistor film thickness (2)] In order for the strain gauge 1 attached to the strain body to detect a larger amount of strain, it is preferable to improve the strain limit (strain resistance) as much as possible because the resistor 30 itself must not be damaged (disconnected, etc.) in the process of expanding and contracting. The strain limit is the value of mechanical strain at which cracks or disconnections begin to occur when strain is applied to the strain gauge.

[0056] As a result of extensive research, the inventors have found that the thickness of resistor 30 not only affects creep but also affects the strain limit. In other words, it has been found that the thinner the resistor 30 is, the less likely it is to crack or break when the resistor 30 is subjected to strain.

[0057] Therefore, the inventors have studied the film thickness of the resistor 30 required to improve the strain limit. Specifically, the inventors have produced 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 breaks. In the strain gauges 1, a polyimide resin film with a film thickness of 25 μm was used as the substrate 10. Also, 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 resistor 30 becomes thinner than a certain point, the occurrence of cracks and breaks tends to decrease as the thickness becomes thinner, and it was found that the strain limit depends on the thickness of resistor 30.

[0059] Fig. 8 is a diagram showing the results of an experiment on strain limits, plotting the minimum values ​​of the strain limits for multiple strain gauges. As shown in Fig. 8, the inventors' experimental results showed that the strain limit was approximately constant at 7000με or more when the film thickness of resistor 30 was 220 nm and 800 nm, whereas the strain limit was 10000με or more when the film thickness of resistor 30 was 50 nm.

[0060] In other words, it was confirmed that when the film thickness of resistor 30 was thinner than 220 nm, the cracks and breaks tended to decrease as the film thickness became thinner. It was also confirmed that when the film thickness of resistor 30 was 50 nm, the strain limit was improved by about 30% compared to when the film thickness of resistor 30 was 220 nm and 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. And 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 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 sufficient strain limit of 10,000 με or more is achieved regardless of the 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 base material 10 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 10. The metal layer A is a layer that will ultimately be patterned to become the resistor 30, the wiring 40, and the electrodes 50. Therefore, the material and thickness of the metal layer A are the same as the material and thickness of the resistor 30, the wiring 40, and the electrodes 50 described above.

[0064] 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.

[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 base material 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 a function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 30). The functional layer preferably further has a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and a function of improving adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0067] Since the insulating resin film that constitutes the substrate 10 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.

[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), and the like can be used. Examples of the metal include one or more metals selected from the group consisting of ruthenium (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, or a compound of any of the metals in this group.

[0069] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compound include TiN, TaN, and Si 3 N 4 , TiO 2 , Ta 2 O 5 , SiO 2 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. 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.

[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. 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.

[0072] 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.

[0073] 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.

[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 can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0075] 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.

[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. 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 10.

[0077] 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 10. As a result, the deterioration of the measurement accuracy of 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 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 10 with Ar, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[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 a 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 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.

[0081] 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 the 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 the chamber. In this case, the CrN and Cr contained in the Cr mixed phase film can be formed 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. 2 The proportion of N, CrN and Cr 2 Cr in N 2 The ratio of N can be adjusted.

[0082] 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).

[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 base material 10, and improving the adhesion between the base material 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 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.

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

[0086] Thereafter, as 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 underlayer 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 reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is, for example, similar to that shown in Fig. 3. However, as described above, the functional layer 20 may be formed solidly on a part or all of the upper surface 10a of the substrate 10.

[0088] 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.

[0089] For example, in Fig. 1 and other figures, an example is shown in which four strain gauges 1 are mounted on the load cell 100, but one strain gauge having four resistors formed on one substrate may be mounted. In that case, the resistors may be connected by wiring provided on the substrate for convenience of 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] Moreover, the resistors mounted on the load cell 100 are not limited to being mounted on either the upper or lower surface of the load cell 100, but may be mounted on both the upper and lower surfaces. For example, two resistors may be mounted on the upper surface of the load cell 100, and two more resistors may be mounted on the lower surface. [Explanation of symbols]

[0092] 1 strain gauge, 10 substrate, 10a top surface, 20 functional layer, 30 resistor, 30e 1 ,30e 2 Termination, 40 wiring, 50 electrode, 60 cover layer, 100 load cell, 110 strain body, 120 through hole, 131, 132 groove, 141-144 thin wall portion

Claims

1. A Roberval type strain body, A strain gauge mounted on the strain body, The strain gauge comprises a flexible substrate and a CrN layer formed on the substrate. ２ A resistor formed from a film containing N, A load cell, wherein the resistor has a film thickness of 6 nm or more and 100 nm or less, so that the creep amount and creep recovery amount are ±0.0735% or less.

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

3. 3. The load cell according to claim 2, wherein the resistor has a film thickness of 11 nm or more and 50 nm or less, so that the creep amount and the creep recovery amount are ±0.0368% or less.

4. 4. The load cell according to claim 1, wherein the strain gauge has a gauge factor of 10 or more.

5. The CrN and Cr contained in the resistor ２ 5. The load cell according to claim 1, wherein the proportion of N is 20% by weight or less.

6. The CrN and the Cr ２ The Cr in N ２ 6. The load cell according to claim 1, wherein the proportion of N is 80% by weight or more and less than 90% by weight.

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

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