strain gauge

Abstract

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

Description

[Technical Field]

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

[0002] 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 strain gauge that can be used for weighing purposes. [Means for solving the problem]

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

[0007] According to the disclosed technology, it is possible to provide 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 strain gauge according to the first embodiment. [Figure 2] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 3] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 4] FIG. 2 is a diagram illustrating a method for measuring the amount of creep and the amount of creep recovery. [Figure 5] FIG. 10 is a diagram showing the results of an investigation into the resistance value, the amount of creep, and the amount of creep recovery. [Figure 6] 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 Fig. 1 is a plan view illustrating a strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1. Fig. 3 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in Fig. 1.

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

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

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

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

[0015] The substrate 103 is a flexible member that serves as a base layer for forming the resistor 303 and the like. There are no particular restrictions on the thickness of the substrate 103 and it can be appropriately selected depending on the purpose, but it can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of strain transmission and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

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

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

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

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

[0020] The resistor 303 has a structure in which multiple elongated portions are arranged at predetermined intervals with their longitudinal direction in the same direction (the direction of line AA in Figure 1), 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 1).

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

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

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

[0024] The thickness of the resistor 303 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting the resistor 303 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less is even more preferable because it reduces film cracks and warpage from the substrate 103 caused by internal stress in the film constituting the resistor 303.

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

[0026] For example, when the resistor 303 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 303, 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 303 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).

[0027] Furthermore, when the resistor 303 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.

[0028] 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.

[0029] 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.

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

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

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

[0033] A conductive layer made of a material having a lower resistance than the resistor 303 may be laminated on the wiring 403 and the electrode 503. The material of the laminated conductive layer is not particularly limited as long as it is a material having a lower resistance than the resistor 303, and can be appropriately selected depending on the purpose. For example, when the resistor 303 is a Cr mixed phase film, examples of the material 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 depending on the purpose, and can be, for example, about 3 μm to 5 μm.

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

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

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

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

[0038] A cover layer 60 may be provided on the upper surface 10c of the substrate 103 so as to cover the resistor 303 and expose the electrodes 503. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 303. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 303 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 503.

[0039] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, 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.

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

[0041] The through holes 70 are provided in through holes that penetrate at least the substrates 102 and 103. The through holes 70 may be formed using the same material as the resistors 303 and the like, or may be formed using a low-resistance material such as copper. Furthermore, the positions of the through holes 70 may be arbitrary as long as the resistors 301, 302, and 303 can be connected in parallel. For example, instead of providing the wirings 401 and 402, the through holes 70 may be provided near the ends of the resistors on each layer to connect the resistors 301, 302, and 303 in parallel. Furthermore, dummy electrodes corresponding to the electrodes 503 may be formed on the substrates 101 and 102, and the electrodes 503 may be connected to the respective dummy electrodes via the through holes 70. Furthermore, the number of through holes may be arbitrary as long as the resistors 301, 302, and 303 can be connected in parallel. For example, if the resistance value of the through holes is an issue, the number of through holes may be increased appropriately.

[0042] 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.

[0043] 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%.

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

[0045] Therefore, the inventors investigated the resistance value of the resistor connected between the pair of electrodes 503, which is necessary to reduce the amount of creep and the amount of creep recovery. Specifically, multiple strain gauges 1 were fabricated with resistors connected between the pair of electrodes 503 with different resistance values, and each strain gauge 1 was attached to a strain generator made of SUS304, and the amount of creep and the amount of creep recovery were measured. The substrates 101, 102, and 103 were made of a polyimide resin film with a thickness of 25 μm. The resistors 301, 302, and 303 were made of a Cr mixed-phase film.

[0046] The amount of creep and the amount of creep recovery are amounts that change over time in the amount of elastic deformation (amount of strain) of the surface of the strain gauge 1 on which the resistors 301, 302, and 303 are provided, and can therefore be measured by monitoring the strain voltage calculated based on the output between the pair of electrodes 503. A detailed description will be given with reference to FIG. 4.

[0047] Fig. 4 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].

[0048] 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.

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

[0050] Note that 100% load is 3 kg, and 150% load is 1.5 times the 100% load.

[0051] FIG. 5 shows the results of an investigation into the relationship between resistance value, 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 resistance values ​​of the resistor connected between a pair of electrodes 503 using the measurement method shown in FIG.

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

[0053] One method of achieving a resistance value that satisfies the C1 or C2 standard is to widen the resistor, but this is not suitable, particularly in the case of highly sensitive strain gauges that use a Cr mixed-phase film as the resistor and have a gauge factor of 10 or more, because widening the resistor width would affect the transverse sensitivity due to the high sensitivity. On the other hand, if the resistance is reduced by connecting multiple resistors in parallel, as in strain gauge 1, it is possible to achieve a resistance value that satisfies the C1 or C2 standard without exposing the problem of transverse sensitivity.

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

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

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

[0057] The metal layer A can be formed by, for example, 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.

[0058] 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 101 by, for example, conventional sputtering before depositing the metal layer A.

[0059] In this 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 301). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in base material 101, and the function of improving adhesion between base material 101 and metal layer A. The functional layer may also have other functions.

[0060] The insulating resin film that constitutes the substrate 101 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.

[0061] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 301), and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), and the like can be used. Examples of the metals include one or more metals selected from the group consisting of copper (iron), iron (Fe), molybdenum (Mo), tungsten (W), ruthenium (Ru), rhodium (Rh), re (rhenium), osmium (Os), iridium (Ir), platinum (Pt), palladium (Pd), silver (Ag), gold (Au), cobalt (Co), manganese (Mn), and aluminum (Al), alloys of any of the metals in this group, and compounds of any of the metals in this group.

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

[0063] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor, 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.

[0064] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the resistor, 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.

[0065] 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.

[0066] 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.

[0067] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0068] 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.

[0069] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. If 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 state at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the substrate 101.

[0070] 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 101. As a result, it is possible to suppress a decrease in measurement accuracy in the strain gauge 1 due to self-heating of the resistor.

[0071] 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 101 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0072] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 101 is activated by 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.

[0073] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and 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.

[0074] 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.

[0075] 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).

[0076] 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 101, and improving adhesion between the substrate 101 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0077] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable 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.

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

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

[0080] Next, the second layer 12 and the third layer 13 are sequentially laminated on the first layer 11, and through holes for forming the through holes 70 are formed by laser processing or the like, and the through holes 70 are then formed by plating or the like. After the first layer 11 is completed, the substrate 102 may be laminated on the first layer 11, and the resistor 302 and the wiring 402 may be formed on the substrate 102, and the substrate 103 may be laminated on the second layer 12, and the resistor 303, the wiring 403, and the electrode 503 may be formed on the substrate 103. In this case, after the through holes for forming the through holes 70 are formed, the resistor 303, the wiring 403, and the electrode 503 may be formed on the substrate 103, and the through holes 70 may be integrally formed from the same material as the resistor 303, etc.

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

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

[0083] 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. [Explanation of symbols]

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

Claims

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

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

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

4. 4. The strain gauge according to claim 1, wherein the width of each of the resistors is 10 μm or more and 100 μm or less.

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

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