strain gauge

Abstract

To provide a strain gauge whose creep characteristics have been improved.SOLUTION: A strain gage includes: a substrate, a resistor formed of a film containing Cr, CrN, and Cr2 N on the substrate: and an insulating resin layer formed on the substrate and covering the resistor. A groove which is open to the upper surface side and not open to the lateral side is provided in the insulating resin layer.SELECTED DRAWING: Figure 1

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] In addition to being used as sensors, strain gauges can also be used as scales. Creep properties are important whether the strain gauge is used as a sensor or a scale, and when used as a scale, the strain gauge must meet particularly strict standards regarding creep properties.

[0005] The present invention has been made in view of the above points, and has as its object to provide a strain gauge with improved creep characteristics. [Means for solving the problem]

[0006] This strain gauge is Made of polyimide resin A substrate, a resistor formed on the substrate from a film containing Cr, CrN, and CrN, and an insulating resin layer formed on the substrate and covering the resistor. The insulating resin layer is made of a polyimide resin. and the insulating resin layer is provided with a groove that opens to the upper surface side and does not open to the side surface side. The resistor includes a plurality of elongated portions arranged at predetermined intervals with their longitudinal directions directed in the same direction, and in a direction perpendicular to the grid direction of the resistor, when the line of the resistor is L and the space of the resistor is S, L / (L+S) is 96.5% or more, the grid direction is the longitudinal direction of the elongated portions, the line is the width of one of the elongated portions in the direction perpendicular to the grid direction, and the space is the width of the insulating resin layer between adjacent elongated portions in the direction perpendicular to the grid direction. . [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a strain gauge with improved creep characteristics. [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 diagram illustrating a method for measuring the amount of creep and the amount of creep recovery. [Figure 4] FIG. 10 is a diagram showing the results of investigation into the amount of creep and the amount of creep recovery. [Figure 5] FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 2 is a plan view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 7] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 8] 10 is a cross-sectional view (part 2) illustrating a strain gauge according to Modification 2 of the first embodiment. FIG. 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 illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60.

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0012] 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 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[0013] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member with a thickness of about 500 μm or less.

[0014] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0015] Materials other than resin for the substrate 10 include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Alternatively, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 10. In this case, an insulating film, for example, is formed on the metal substrate 10.

[0016] 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.

[0017] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0018] 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.

[0019] The thickness of resistor 30 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 resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0020] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50% by weight or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0021] Furthermore, when the resistor 30 is a Cr mixed phase film, the Cr mixed phase film preferably contains 20 wt % or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0022] 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.

[0023] 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.

[0024] The electrodes 50 are electrically connected to both ends of the resistor 30 via the wiring 40 and are formed in a generally rectangular shape in plan view, wider than the resistor 30 and the wiring 40. The wiring 40 may be wider than the resistor 30. The electrodes 50 are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and are connected to, for example, lead wires for external connection. The resistor 30 extends, for example, from one side of the electrode 50, zigzag-folding back via the wiring 40, and reaches the other side of the electrode 50 via the wiring 40. A low-resistance metal layer, such as copper, may be laminated on the upper surface of the wiring 40. A low-resistance metal layer, such as copper, or a metal layer with good solderability, such as gold, may be laminated on the upper surface of the electrode 50. Although the resistor 30, the wiring 40, and the electrode 50 are denoted by different reference numerals for convenience, they may be integrally formed from the same material in the same process.

[0025] A cover layer 60 (insulating resin layer) is provided 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. 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 a composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular limitations 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.

[0026] By providing the cover layer 60, it is possible to prevent mechanical damage and the like 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 and the like.

[0027] The cover layer 60 is provided with a plurality of grooves 60x that open to the upper surface side of the cover layer 60. The grooves 60x are provided so as to penetrate the cover layer 60 and expose the upper surface 10a of the substrate 10. The inner surfaces of the grooves 60x are formed by the cover layer 60, and the bottom surfaces of the grooves 60x are formed by the upper surface 10a of the substrate 10. The grooves 60x do not open to the side surfaces of the cover layer 60. Since the grooves 60x do not open to the side surfaces of the cover layer 60, the strength of the cover layer 60 can be maintained.

[0028] The resistor 30 has a structure in which multiple elongated portions of approximately the same length are arranged at predetermined intervals with their longitudinal direction in the same direction (the direction perpendicular to line AA in Figure 1), and the ends of adjacent elongated portions are connected in order, folding back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions forms the grid direction.

[0029] In the example of FIG. 1 , in a plan view, the grooves 60x are arranged along the elongated portions of the cover layer 60 in all regions between adjacent elongated portions and in regions outside the elongated portions arranged on both sides of the resistor 30 in a direction perpendicular to the grid direction. Grooves 60x may be arranged in the regions outside the elongated portions arranged on both sides of the resistor 30 in a direction perpendicular to the grid direction, as needed. The grooves 60x preferably have a length that faces substantially the entire longitudinal length of each elongated portion. The inner surfaces of the grooves 60x preferably do not reach the side surfaces of the resistor 30, but may reach them if necessary. The technical significance of the grooves 60x will be described later.

[0030] [Creep reduction] 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.

[0031] 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%.

[0032] The creep characteristics of a strain gauge are affected by the viscoelasticity of the constituent materials. Generally, creep does not occur in metal materials, which are elastic materials, but creep does occur in resin, which is a viscous material. Since the strain gauge 1 is provided with a cover layer 60 made of resin, the viscosity of the cover layer 60 cannot be ignored.

[0033] As a result of extensive research, the inventors have discovered that, where the line of resistor 30 is L and the space is S, the creep value depends on the value of L / (L+S), and that a larger value of L / (L+S) is preferable. Here, line L of resistor 30 is the width of one elongated portion constituting resistor 30 in a direction perpendicular to the grid direction (the direction of line AA in FIG. 1). Space S is the width of cover layer 60 between adjacent elongated portions in a direction perpendicular to the grid direction (the direction of line AA in FIG. 1).

[0034] The amount of creep and the amount of creep recovery are amounts in which the amount of elastic deformation (amount of strain) of the surface of the strain gauge 1 on which the resistor 30 is provided changes over time, and can therefore be measured by monitoring the strain voltage calculated based on the output between the pair of electrodes 50. A detailed description will be given with reference to FIG.

[0035] Fig. 3 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].

[0036] 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.

[0037] The strain voltage changes, for example, as shown in Figure 3. In Figure 3, 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.

[0038] Note that 100% load is 3 kg, and 150% load is 1.5 times the 100% load.

[0039] FIG. 4 shows the results of an investigation into the amount of creep and the amount of creep recovery, and summarizes the results of measuring the amount of creep and the amount of creep recovery of multiple strain gauges 1 with different values ​​of L / (L+S) using the measurement method shown in FIG. 3. Specifically, the amount of creep and the amount of creep recovery were measured by attaching each strain gauge 1 to a strain generator made of SUS304. The substrate 10 was a polyimide resin film with a thickness of 25 μm. The resistor 30 was a Cr mixed phase film. The cover layer 60 was a polyimide resin film with a thickness of 15 μm.

[0040] As shown in Figure 4, as L / (L+S) increases, the creep amount and creep recovery amount decrease. For example, if L / (L+S) is 96.5% or higher, the creep amount and creep recovery amount of the C1 standard can be met. Furthermore, if L / (L+S) is 98.5% or higher, the creep amount and creep recovery amount of the C2 standard can be met. In other words, by controlling L / (L+S) within a specified range, the creep amount and creep recovery amount can be improved, making the strain gauge 1 usable for weighing purposes. Furthermore, by controlling L / (L+S) to a certain extent and using other creep countermeasures in combination, the creep-related standards can be met. Of course, the strain gauge 1 can also be used for sensors.

[0041] L / (L+S) can be increased by increasing the width of each elongated portion of the resistor 30 and decreasing the spacing between adjacent elongated portions. However, even if the spacing between adjacent elongated portions is relatively wide, it can also be increased by reducing the space S by providing grooves 60x in the cover layer 60 as shown in Figure 1. That is, by providing grooves 60x along the elongated portions in the region between the adjacent elongated portions of the cover layer 60, L / (L+S) can be increased, thereby reducing the viscosity of the cover layer 60 and improving the creep characteristics.

[0042] In the case of a highly sensitive strain gauge with a gauge factor of 10 or more (for example, when a Cr mixed phase film is used for the resistor 30), the high sensitivity makes it susceptible to the influence of material properties, and creep characteristics may also be significantly reduced. Therefore, in a highly sensitive strain gauge with a gauge factor of 10 or more, it is extremely important to control L / (L+S) within a predetermined range to improve creep characteristics.

[0043] [Strain gauge manufacturing method] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrodes 50. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, wiring 40, and electrodes 50 described above.

[0044] 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.

[0045] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the substrate 10 by, for example, conventional sputtering before depositing the metal layer A.

[0046] In the present application, the functional layer refers to a layer having the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and the function of improving adhesion between the substrate 10 and metal layer A. The functional layer may also have other functions.

[0047] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, especially when the metal layer A contains Cr.

[0048] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 30), and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Examples of the metals include one or more metals selected from the group consisting of copper (Ru), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, and a compound of any of the metals in this group.

[0049] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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 not only promotes the crystal growth of α-Cr but also makes it easier to form the functional layer without cracking.

[0056] 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 need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid state at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid state over the entire upper surface of the substrate 10.

[0057] Furthermore, when the functional layer is made of an insulating material, the thickness of the functional layer is made relatively thick, between 50 nm and 1 μm, and the functional layer is made solid. This increases the thickness and surface area of ​​the functional layer, allowing heat generated by the resistor to be dissipated to the substrate 10. As a result, the deterioration of measurement accuracy in the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0058] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0059] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0060] 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.

[0061] 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 ratios of CrN and CrN contained in the Cr mixed-phase film, and the ratio 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.

[0062] 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).

[0063] When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0064] 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, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material that constitutes the functional layer into the metal layer A, it is possible to improve the gauge characteristics of the strain gauge 1.

[0065] Next, the metal layer A is patterned by photolithography to form the resistor 30, wiring 40, and electrode 50 in the planar shape shown in FIG.

[0066] Thereafter, a cover layer 60 having grooves 60x that cover the resistors 30 and the wiring 40 and expose the electrodes 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1.

[0067] To form the cover layer 60 having the grooves 60x, for example, a semi-cured thermosetting insulating resin film is laminated on the upper surface 10a of the base material 10 so as to cover the resistors 30 and the wiring 40 and expose the electrodes 50, and then the insulating resin film is heated and cured. Then, for example, the cover layer 60 is irradiated with laser light to form the grooves 60x.

[0068] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlying layer for the resistor 30, the wiring 40, and the electrodes 50, the strain gauge 1 has a cross-sectional shape as shown in FIG. 5. The layer indicated by the reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 will be the same as that shown in FIG. 1, for example. However, as mentioned above, the functional layer 20 may be formed solidly on part or all of the upper surface of the substrate 10.

[0069] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example is shown in which the number and shape of grooves formed in the cover layer are different. Note that in Modification 1 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0070] FIG. 6 is a plan view illustrating a strain gauge according to Modification 1 of the first embodiment. FIG. 7 is a cross-sectional view illustrating the strain gauge according to Modification 1 of the first embodiment, taken along line BB in FIG. 6. Referring to FIGS. 6 and 7, the strain gauge 1A differs from the strain gauge 1 (see FIG. 1, etc.) in that one groove 60x is formed in the cover layer 60. In plan view, the groove 60x is arranged along the elongated portion in one region between adjacent elongated portions of the cover layer 60. Note that, in plan view, the groove 60x may be arranged along the elongated portion in one or more regions between adjacent elongated portions of the cover layer 60.

[0071] As mentioned above, increasing the value of L / (L+S) allows the strain gauge to be used for weighing purposes. However, even when the strain gauge is not used for weighing purposes, there may be cases where it is desired to reduce the creep amount and creep recovery amount to some extent. In such cases, one or more grooves 60x may be formed in the cover layer 60. The number of grooves 60x can be determined appropriately depending on the desired values ​​of the creep amount and creep recovery amount.

[0072] In this way, by forming one or more grooves 60x in the cover layer 60, the viscosity of the cover layer 60 can be reduced, thereby improving the creep characteristics.

[0073] As shown in Fig. 8, the grooves 60x do not have to penetrate the cover layer 60. In the example of Fig. 8, the inner side and bottom surfaces of the grooves 60x are formed by the cover layer 60. In the case of Fig. 8 as well, the viscosity of the cover layer 60 can be reduced, thereby improving the creep characteristics.

[0074] If the creep amount and creep recovery amount satisfy the C1 or C2 standard, the grooves 60x do not need to penetrate the cover layer 60 when the strain gauge 1 shown in FIG.

[0075] 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]

[0076] 1, 1A strain gauge, 10 substrate, 10a top surface, 20 functional layer, 30 resistor, 40 wiring, 50 electrode, 60 cover layer, 60x groove

Claims

1. A substrate made of polyimide resin; Cr, CrN, and Cr on the substrate ２ a resistor formed from a film containing N; an insulating resin layer formed on the base material and covering the resistor, the insulating resin layer being made of polyimide resin; The insulating resin layer has a groove that is open to the top surface side and not open to the side surface side, The resistor includes a plurality of elongated portions arranged at predetermined intervals with their longitudinal directions oriented in the same direction, In a direction perpendicular to the grid direction of the resistor, when the line of the resistor is L and the space of the resistor is S, L / (L+S) is 96.5% or more; the grid direction is the longitudinal direction of the elongated portion, the line is the width of one of the elongated portions in a direction perpendicular to the grid direction, The space is the width of the insulating resin layer between adjacent elongated portions in a direction perpendicular to the grid direction.

2. The resistor has a structure in which ends of adjacent elongated portions are connected in sequence and folded back in a zigzag pattern as a whole, 2. The strain gauge according to claim 1, wherein, in a plan view, the groove is arranged along the elongated portion in one or more regions between adjacent elongated portions of the insulating resin layer.

3. 3. The strain gauge according to claim 2, wherein, in a plan view, the grooves are arranged along the elongated portions in all regions of the insulating resin layer between adjacent elongated portions and in regions outside the elongated portions arranged on both outside sides of the resistor in a direction perpendicular to the grid direction.

4. The strain gauge according to claim 1 , wherein the groove is provided so as to expose an upper surface of the substrate.

5. A strain gauge described in any one of claims 1 to 4, wherein L / (L+S) is 98.5% or more.

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

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