Strain gauge

Abstract

To miniaturize a plane shape of a strain gauge having four resistance parts constituting a Wheatstone bridge circuit.SOLUTION: A strain gauge includes a resin flexible base material, and a resistor, wherein the resistor includes a first functional layer formed from metal, an alloy or a metallic compound directly on one surface of the base material, a first resistance part and a second resistance part which are formed from a film containing Cr, CrN and Cr2N and contain α-Cr as a main component, directly on one surface of the first functional layer, a second functional layer formed from metal, an alloy or a metallic compound directly on the other surface of the base material, and a third resistance part and a fourth resistance part which are formed from a film containing Cr, CrN and Cr2N and contain α-Cr as a main component, directly on one surface of the second functional layer, wherein the first functional layer and the second functional layer have a function for promoting crystal growth of α-Cr and film-forming the film containing α-Cr as a main component, and the first resistance part, the second resistance part, the third resistance part and the fourth resistance part constitute a Wheatstone bridge circuit.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] There is known a strain gauge that is attached to an object to be measured to detect strain of the object. The strain gauge has a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni). The resistor is formed on a substrate made of insulating resin, for example (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, there are cases where a Wheatstone bridge circuit is constructed by forming four resistive elements on the same plane of a substrate, but forming four resistive elements on one layer poses the problem of the planar shape of the strain gauge becoming larger.

[0005] The present invention has been made in view of the above points, and has an object to reduce the planar shape of a strain gauge having four resistive elements that constitute a Wheatstone bridge circuit. [Means for solving the problem]

[0006] This strain gauge has a flexible resin substrate and a resistor, and the resistor comprises a first functional layer formed directly on one surface of the substrate from a metal, alloy, or metal compound, a first resistive portion and a second resistive portion formed directly on one surface of the first functional layer from a film containing Cr, CrN, and Cr2N, the first resistive portion and the second resistive portion having α-Cr as the main component, the second functional layer formed directly on the other surface of the substrate from a metal, alloy, or metal compound, and the second resistive portion formed directly on one surface of the second functional layer from a film containing Cr, CrN, and Cr2N. a third resistor portion and a fourth resistor portion having α-Cr as a main component, wherein the first functional layer and the second functional layer have the function of promoting crystal growth of the α-Cr and forming a film having the α-Cr as a main component, the first resistor portion, the second resistor portion, the third resistor portion, and the fourth resistor portion each having a thickness of 0.05 μm or more and 2 μm or less, the first functional layer and the second functional layer each having a thickness of 1 nm or more and 100 nm or less, and the first resistor portion, the second resistor portion, the third resistor portion, and the fourth resistor portion forming a Wheatstone bridge circuit. [Effects of the Invention]

[0007] According to the disclosed technique, it is possible to reduce the size of the planar shape of a strain gauge having four resistive elements that form a Wheatstone bridge circuit. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Figure 2] 2 is a plan view illustrating an example of the pattern of resistor portions 31 and 32 in the strain gauge according to the first embodiment. FIG. [Figure 3] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 4] FIG. 10 is a circuit diagram illustrating the connection of four resistor sections. [Figure 5] 3A to 3C are diagrams illustrating a manufacturing process of 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 plan view illustrating the pattern of resistor portions 31 and 32 in the strain gauge according to the first embodiment. Fig. 3 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in Figs. 1 and 2. Referring to Figs. 1 to 3, the strain gauge 1 has a substrate 10, a resistor 30 (resistor portions 31 to 34), terminal portions 41 to 44, and cover layers 61 and 62.

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistance portions 33 and 34 of the substrate 10 are provided will be referred to as the upper side or one side, and the side on which the resistance portions 31 and 32 are provided will be referred to as the lower side or other side. Furthermore, the side on which the resistance portions 33 and 34 of each portion are provided will be referred to as the one side or upper side, and the side on which the resistance portions 31 and 32 are provided will be referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing the object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[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 the substrate 10 of 5 μm to 200 μm is preferable in that it can reduce strain sensitivity errors of the resistor portions 31 to 34.

[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, polyolefin resin, etc. The film refers to a flexible member having 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] The resistor 30 is formed on the substrate 10 and is a sensitive part that changes resistance when strained. The resistor 30 includes resistance sections 31 and 32, and resistance sections 33 and 34, which are laminated via the substrate 10. In other words, the resistor 30 is a general term for the resistance sections 31 to 34, and will be referred to as resistor 30 when there is no need to particularly distinguish between the resistance sections 31 to 34. For convenience, the resistance sections 31 to 34 are shown with a matte finish in FIGS. 1 and 2.

[0016] The resistor portions 31 and 32 are thin films formed in a predetermined pattern on the lower surface 10b side of the substrate 10. The resistor portions 31 and 32 may be formed directly on the lower surface 10b side of the substrate 10, or may be formed on the lower surface 10b side of the substrate 10 via another layer. The resistor portions 31 and 32 may be arranged, for example, so that their grid directions are the same.

[0017] A via receiving pad 31A is formed at one end of the resistor portion 31, and a via receiving pad 31B is formed at the other end of the resistor portion 31. The pads 31A and 31B extend from both ends of the resistor portion 31 and are formed in a generally rectangular shape wider than the resistor portion 31 in plan view.

[0018] A via receiving pad 32A is formed at one end of the resistor portion 32, and a via receiving pad 32B is formed at the other end of the resistor portion 32. The pads 32A and 32B extend from both ends of the resistor portion 32 and are formed in a generally rectangular shape wider than the resistor portion 32 in plan view.

[0019] The resistor portions 33 and 34 are thin films formed in a predetermined pattern on the upper surface 10a of the substrate 10. The resistor portions 33 and 34 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. The resistor portions 33 and 34 may be arranged, for example, so that their grid directions are the same. Furthermore, the resistor portions 33 and 34 may be arranged, for example, so that their grid directions are perpendicular to those of the resistor portions 31 and 32.

[0020] The resistor 30 (resistance portions 31 to 34) 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 Ni-Cu (nickel copper). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0021] 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.

[0022] 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.

[0023] 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 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] The terminal portions 41, 42, 43, and 44 are formed on the substrate 10. The terminal portions 41 to 44 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. The terminal portions 41 to 44 are input or output electrodes, and are connected to, for example, lead wires for external connection.

[0025] The terminal portions 41 and 42 extend from both ends of the resistor portion 33 and are formed in a generally rectangular shape in plan view, wider than the resistor portion 33. For example, the resistor portion 33 extends from the terminal portion 41 while folding back in a zigzag pattern and is connected to the terminal portion 42. The upper surfaces of the terminal portions 41 and 42 may be coated with a metal that has better solderability than the terminal portions 41 and 42.

[0026] The terminal portions 43 and 44 extend from both ends of the resistor portion 34 and are formed in a generally rectangular shape in plan view, wider than the resistor portion 34. For example, the resistor portion 34 extends from the terminal portion 43 while folding back in a zigzag pattern and is connected to the terminal portion 44. The upper surfaces of the terminal portions 43 and 44 may be coated with a metal that has better solderability than the terminal portions 43 and 44.

[0027] The terminal portion 41 is electrically connected to the pad 31A exposed in the via hole 10x through the substrate 10. For example, the terminal portion 41 is continuously formed from the upper surface 10a of the substrate 10 to the side wall of the via hole 10x and the upper surface of the pad 31A exposed in the via hole 10x, and is electrically connected to the pad 31A.

[0028] A recess 10y is formed in the via hole 10x by the portion of the terminal portion 41 formed on the side wall of the via hole 10x and on one upper surface of the pad 31A exposed in the via hole 10x. However, the terminal portion 41 may fill the via hole 10x (the recess 10y may not be formed).

[0029] The terminal portion 42 is electrically connected to the pad 32A exposed in the via hole 10x through the substrate 10. The terminal portion 42 is formed, for example, continuously from the upper surface 10a of the substrate 10 to the side wall of the via hole 10x and the upper surface of the pad 32A exposed in the via hole 10x, and is electrically connected to the pad 32A.

[0030] A recess 10y is formed in the via hole 10x by the portion of the terminal 42 formed on the side wall of the via hole 10x and on one upper surface of the pad 32A exposed in the via hole 10x. However, the terminal 42 may fill the via hole 10x (the recess 10y may not be formed).

[0031] The terminal portion 43 is electrically connected to the pad 32B exposed in the via hole 10x through the substrate 10. The terminal portion 43 is formed, for example, continuously from the upper surface 10a of the substrate 10 to the side wall of the via hole 10x and the upper surface of the pad 32B exposed in the via hole 10x, and is electrically connected to the pad 32B.

[0032] A recess 10y is formed in the via hole 10x by the portion of the terminal portion 43 formed on the side wall of the via hole 10x and on one upper surface of the pad 32B exposed in the via hole 10x. However, the terminal portion 43 may fill the via hole 10x (the recess 10y may not be formed).

[0033] The terminal portion 44 is electrically connected to the pad 31B exposed in the via hole 10x through the substrate 10. The terminal portion 44 is formed, for example, continuously from the upper surface 10a of the substrate 10 to the side wall of the via hole 10x and the upper surface of the pad 31B exposed in the via hole 10x, and is electrically connected to the pad 31B.

[0034] A recess 10y is formed in the via hole 10x by the portion of the terminal portion 44 formed on the side wall of the via hole 10x and on one upper surface of the pad 31B exposed in the via hole 10x. However, the terminal portion 44 may fill the via hole 10x (the recess 10y may not be formed).

[0035] Although the resistor portions 33 and 34 and the terminal portions 41 to 44 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0036] Fig. 4 is a circuit diagram illustrating the connection of four resistors. As shown in Fig. 4, resistors 31 to 34 are electrically connected to one another to form a Wheatstone bridge circuit. In the Wheatstone bridge circuit shown in Fig. 4, for example, an input voltage is applied between terminals 41 and 43, and an output voltage can be obtained between terminals 42 and 44. By amplifying this output voltage, strain can be detected.

[0037] Returning to the explanation of FIGS. 1 to 3, the cover layer 61 is an insulating resin layer provided on the upper surface 10a of the substrate 10 so as to cover the resistor portions 33 and 34 and expose the terminal portions 41 to 44. By providing the cover layer 61, it is possible to prevent mechanical damage and the like from occurring to the resistor portions 33 and 34. Furthermore, by providing the cover layer 61, it is possible to protect the resistor portions 33 and 34 from moisture and the like. Note that the cover layer 61 may be provided so as to cover the entire portion excluding the terminal portions 41 to 44.

[0038] The cover layer 62 is an insulating resin layer provided on the lower surface 10b of the base material 10 so as to cover the resistor portions 31 and 32, the pads 31A and 31B, and the pads 32A and 32B. The provision of the cover layer 62 can prevent mechanical damage and the like from occurring to the resistor portions 31 and 32, the pads 31A and 31B, and the pads 32A and 32B. The provision of the cover layer 62 can also protect the resistor portions 31 and 32, the pads 31A and 31B, and the pads 32A and 32B from moisture and the like.

[0039] The cover layers 61 and 62 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 layers 61 and 62 may contain a filler or a pigment. The thickness of the cover layers 61 and 62 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, approximately 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm for the cover layer 62 is preferable in terms of the transmission of strain from the surface of the strain generator bonded to the lower surface of the cover layer 62 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. The cover layers 61 and 62 may be formed from different materials, or may be formed to different thicknesses.

[0040] FIG. 5 is a diagram illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section corresponding to FIG.

[0041] 5(a), a substrate 10 is prepared, and a metal layer 310 is formed over the entire lower surface 10b of the substrate 10. The metal layer 310 will eventually be patterned to form the resistor portions 31 and 32, the pads 31A and 31B, and the pads 32A and 32B. The material and thickness of the metal layer 310 are the same as those of the resistor 30 (resistor portions 31 and 32) described above.

[0042] The metal layer 310 can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer 310. Instead of magnetron sputtering, the metal layer 310 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0043] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer having a thickness of about 1 nm to 100 nm on the lower surface 10b of the substrate 10 by, for example, conventional sputtering as a base layer before depositing the metal layer 310.

[0044] In this application, the functional layer refers to a layer having the function of promoting crystal growth of at least the upper layer, the resistor portion (patterned metal layer 310). The functional layer preferably also has the function of preventing oxidation of the upper layer, the resistor portion, due to oxygen or moisture contained in the substrate 10, etc., and the function of improving adhesion between the substrate 10, etc. and the upper layer, the resistor portion. The functional layer may also have other functions.

[0045] 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 upper resistive layer, particularly when the upper resistive layer contains Cr.

[0046] 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 resistor portion, 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), F Examples of suitable metals include one or more metals selected from the group consisting of 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.

[0047] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0048] 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 lower surface 10b of the substrate 10 with Ar, which minimizes the amount of functional layer formed and improves adhesion.

[0049] 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 lower surface 10b 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.

[0050] There are no particular restrictions on the combination of the material of the functional layer and the material of the upper resistive layer, and it 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 upper resistive layer.

[0051] In this case, the upper layer, i.e., the resistor portion, 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 upper layer, i.e., the resistor portion, 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.

[0052] 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).

[0053] When the upper resistive layer is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the upper resistive layer, preventing oxidation of the upper resistive layer due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the upper resistive layer. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0054] In this way, by providing a functional layer below the resistor section, it is possible to promote crystal growth in the resistor section, which is the upper layer, and to create a resistor section 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 makes up the functional layer diffuses into the resistor section, which is the upper layer, and the gauge characteristics of the strain gauge 1 can be improved.

[0055] 4(b), via holes 10x are formed through the substrate 10 to expose the upper surface of the metal layer 310. The via holes 10x can be formed, for example, by laser processing. The via holes 10x are formed in areas where the metal layer 310 is patterned to become the pads 31A and 31B and the pads 32A and 32B.

[0056] 4(c), a metal layer 320 is formed over the entire upper surface 10a of the base material 10. The metal layer 320 will eventually be patterned to form the resistor portions 33 and 34 and the terminal portions 41 to 44. The metal layer 320 is continuously formed from the upper surface 10a of the base material 10 to the sidewalls of the via holes 10x and the upper surface of the metal layer 310 exposed within the via holes 10x, and is electrically connected to the metal layer 310.

[0057] A recess 10y is formed in the via hole 10x by a portion of the metal layer 320 formed on the sidewall of the via hole 10x and on the upper surface of the metal layer 310 exposed in the via hole 10x. However, the metal layer 310 may fill the via hole 10x (the recess 10y may not be formed).

[0058] The material and thickness of the metal layer 320 can be, for example, the same as those of the metal layer 310. The metal layer 320 can be formed, for example, by the same method as that of the metal layer 310. For the same reasons as those for the metal layer 310, before depositing the metal layer 320, it is preferable to vacuum deposit a functional layer having a thickness of about 1 nm to 100 nm on the upper surface 10a of the base material 10 by, for example, conventional sputtering, as a base layer.

[0059] 4(d), the functional layer and metal layer 310 formed on the lower surface 10b of the substrate 10 and the functional layer and metal layer 320 formed on the upper surface 10a of the substrate 10 are patterned by photolithography. As a result, the resistor portions 31 and 32, pads 31A and 31B, and pads 32A and 32B having the shapes shown in FIG. 2 are formed on the lower surface 10b of the substrate 10, and the resistor portions 33 and 34 and terminal portions 41 to 44 having the shapes shown in FIG. 1 are formed on the upper surface 10a of the substrate 10. By simultaneously patterning the metal layer 310 and the metal layer 320 by photolithography, the relative positional accuracy of the resistor portions 31 and 32 and the resistor portions 33 and 34 can be improved.

[0060] 4(d), a cover layer 61 that covers the resistor portions 33 and 34 and exposes the terminal portions 41 to 44 is formed on the upper surface 10a of the substrate 10. A cover layer 62 that covers the resistor portions 31 and 32, the pads 31A and 31B, and the pads 32A and 32B is formed on the lower surface 10b of the substrate 10. The material and thickness of the cover layers 61 and 62 are as described above.

[0061] The cover layer 61 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 portions 33 and 34 and expose the terminal portions 41 to 44, and then heating and curing the film. The cover layer 61 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 portions 33 and 34 and expose the terminal portions 41 to 44, and then heating and curing the resin. The cover layer 62 can also be produced by the same method as the cover layer 61. The strain gauge 1 is completed by the above steps.

[0062] Thus, in the strain gauge 1, the resistor portions 31 and 32 are formed on the lower surface 10b of the substrate 10, and the resistor portions 33 and 34 are formed on the upper surface 10a of the substrate 10, and the resistor portions 31, 32, 33, and 34 are connected to each other to form a Wheatstone bridge circuit. This allows the planar shape of the strain gauge to be more compact than a conventional structure in which four resistor portions are formed on the same plane of the substrate to form a Wheatstone bridge circuit.

[0063] Furthermore, the resistor portions 31 and 32 and the resistor portions 33 and 34 can be formed by simultaneously patterning metal layers formed on both sides of the substrate 10 by photolithography. As a result, it is possible to improve the relative positional accuracy of the resistor portions 31 and 32 and the resistor portions 33 and 34.

[0064] The strain gauge 1 has a laminated structure in which the top and bottom of the substrate 10 are approximately symmetrical. That is, the resistors 31 and 32 and the cover layer 62 are laminated on the bottom surface 10b of the substrate 10, and the resistors 33 and 34 and the cover layer 61 are laminated on the top surface 10a of the substrate 10. This structure makes it possible to reduce warping of the strain gauge 1.

[0065] Furthermore, in the strain gauge 1, the resistor 30 has a multilayer structure in which multiple resistive portions are stacked, thereby reducing the planar shape, and therefore it is possible to measure strain in a relatively narrow range of the object to be measured.

[0066] Furthermore, since the strain gauge 1 is small, it is possible to increase the number of gauges that can be taken from the same sheet, thereby improving productivity.

[0067] The above describes in detail preferred embodiments, but 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]

[0068] 1 strain gauge, 10 substrate, 10a upper surface, 10b lower surface, 10x via hole, 10y recess, 30 resistor, 31, 32, 33, 34 resistor portion, 41, 42, 43, 44 terminal portion, 61, 62 cover layer

Claims

1. a flexible resin substrate; a resistor; The resistor has a first functional layer formed of a metal, an alloy, or a metal compound directly on one surface of the substrate, and a first functional layer formed of Cr, CrN, and CrN directly on one surface of the first functional layer. ２ A first resistor portion and a second resistor portion mainly composed of α-Cr formed from a film containing N, a second functional layer formed from a metal, an alloy, or a metal compound directly on the other surface of the substrate, and a second functional layer formed from Cr, CrN, and CrN directly on one surface of the second functional layer. ２ a third resistor portion and a fourth resistor portion formed from a film containing N and containing α-Cr as a main component, the first functional layer and the second functional layer have a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; the first resistor portion, the second resistor portion, the third resistor portion, and the fourth resistor portion each have a thickness of 0.05 μm or more and 2 μm or less; the thickness of the first functional layer and the second functional layer is 1 nm or more and 100 nm or less; The first resistor portion, the second resistor portion, the third resistor portion, and the fourth resistor portion form a Wheatstone bridge circuit.

2. two electrodes for applying an input voltage to the Wheatstone bridge circuit and two other electrodes for obtaining an output voltage from the Wheatstone bridge circuit; 2. The strain gauge according to claim 1, wherein the two electrodes and the other two electrodes are formed on one side of the substrate.

3. the two electrodes and the other two electrodes are electrically connected to any one of pads extending from both ends of the third resistor portion and the fourth resistor portion through via holes provided in the base material; 3. The strain gauge according to claim 2, wherein the two electrodes and the other two electrodes are continuously formed from one side of the substrate to the sidewall of the via hole and the surface of the pad exposed in the via hole, forming a recess in the via hole.

4. a first insulating resin layer is formed on one side of the base material to cover the first resistor portion and the second resistor portion; 4. The strain gauge according to claim 1, wherein a second insulating resin layer is formed on the other side of the substrate to cover the third resistor portion and the fourth resistor portion.

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