Sensor module

Abstract

To suppress the increase of a sensor module cost.SOLUTION: The present sensor module comprises: a strain gauge provided with a flexible substrate made of resin, a functional layer formed directly on one side of the substrate and made from metal, alloy, or a metal compound, and a resistive body formed directly on one side of the functional layer and formed from a film including Cr, CrN, and Cr2 N, and composed mainly of α-Cr; and an elastic body propagating strain to the strain gauge. The functional layer has the function of promoting the crystal growth of the α-Cr and depositing a film composed mainly of the α-Cr. The thickness of the resistive body is 0.05 μm to 2 μm inclusive, and the thickness of the functional layer is 1 nm to 100 nm inclusive, and the strain gauge is adhered to the elastic body in such a manner that the resistive body is oriented toward the elastic body side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sensor module. [Background technology]

[0002] There is known a strain gauge that is attached to a measurement object to detect strain of the measurement 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 and covered with a protective film (see, for example, Patent Document 1).

[0003] This strain gauge can be used as a sensor module by, for example, bonding the substrate side to a strain generator via an adhesive layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above strain gauge requires a protective film to protect the resistor from moisture, etc., which requires a process of covering the resistor with the protective film in addition to a process of forming the resistor on the substrate. Therefore, when the above strain gauge is used in a sensor module, there is a problem that the cost of the entire sensor module increases.

[0006] The present invention has been made in view of the above points, and has an object to suppress an increase in the cost of a sensor module. [Means for solving the problem]

[0007] This sensor module comprises a flexible resin substrate, a functional layer formed directly on one side of the substrate from a metal, alloy, or metal compound, and a strain gauge having an α-Cr-based resistor formed directly on one side of the functional layer from a film containing Cr, CrN, and CrN, and a flexural element that transmits strain to the strain gauge, wherein the functional layer has the function of promoting crystal growth of the α-Cr and forming a film mainly composed of α-Cr, the resistor having a thickness of 0.05 μm or more and 2 μm or less, the functional layer having a thickness of 1 nm or more and 100 nm or less, and the strain gauge is adhered to the flexural element with the resistor facing the flexural element. [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to suppress an increase in the cost of the sensor module. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view illustrating a sensor module according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a sensor module according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] First Embodiment Fig. 1 is a plan view illustrating a sensor module according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the sensor module according to the first embodiment, taken along line AA in Fig. 1. Referring to Figs. 1 and 2, a sensor module 5 has a strain gauge 1, a strain element 110, and an adhesive layer 120. The strain gauge 1 has a substrate 10, a resistor 30, and terminal portions 41.

[0012] In this embodiment, for convenience, the substrate 10 side of the sensor module 5 is referred to as the upper side or one side, and the flexure body 110 side is referred to as the lower side or the other side. Also, the surface of each part facing the substrate 10 is referred to as one side or the upper side, and the surface facing the flexure body 110 is referred to as the other side or the lower side. However, the sensor module 5 can be used upside down or placed at any angle. Also, 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.

[0013] In the strain gauge 1, the substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The substrate 10 has an upper surface 10a and a lower surface 10b. The thickness of the substrate 10 is not particularly limited and can be selected appropriately 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 is preferable in terms of the transferability of strain from the surface of the strain element 110 joined to the lower surface 10b of the substrate 10 via the adhesive layer 120 and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

[0014] 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.

[0015] 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.

[0016] The resistor 30 is a thin film formed in a predetermined pattern on the lower surface 10b of the substrate 10, and is a sensing part that generates a resistance change when strained. The resistor 30 may be formed directly on the lower surface 10b of the substrate 10, or may be formed on the lower surface 10b of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 with a matte finish.

[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 Ni-Cu (nickel copper). 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 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).

[0021] The terminal portions 41 extend from both ends of the resistor 30 and are formed in a generally rectangular shape in plan view, wider than the resistor 30. The terminal portions 41 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain.

[0022] For example, a portion of the side surface of each terminal portion 41 is exposed to the outside of the strain gauge 1, and a lead wire or the like for external connection is joined to the exposed portion. However, as long as a portion of each terminal portion 41 is exposed to the outside of the strain gauge 1, the exposed portion does not have to be the side surface of each terminal portion 41. For example, a through hole or a notch may be provided in the substrate 10, and part or all of the top surface of each terminal portion 41 may be exposed.

[0023] For example, the resistor 30 extends from one of the terminal portions 41 while folding back in a zigzag pattern and is connected to the other terminal portion 41. The top and side surfaces of the terminal portion 41 may be covered with a metal that has better solderability than the terminal portion 41. Although the resistor 30 and the terminal portion 41 are given different reference numerals for convenience, they can be formed integrally from the same material in the same process.

[0024] In the sensor module 5, the lower surface 10b side of the substrate 10 is bonded to the upper surface 110a of the flexure element 110 via an adhesive layer 120. That is, the strain gauge 1 is bonded to the flexure element 110 with the resistor 30 facing the flexure element 110 side.

[0025] The strain element 110 is an object formed from, for example, a metal such as Fe, SUS (stainless steel), or Al, or a resin such as PEEK, and deforms in response to an applied force, transmitting the generated strain to the strain gauge 1. The strain gauge 1 can detect the strain generated in the strain element 110 as a change in the resistance value of the resistor 30.

[0026] The adhesive layer 120 is sandwiched between the strain gauge 1 and the flexure element 110, and covers the resistor 30. The adhesive layer 120 is not particularly limited and can be made of any material that functions to bond the strain gauge 1 and the flexure element 110, and can be appropriately selected depending on the purpose. For example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used. A material such as a bonding sheet can also be used. However, if the flexure element 110 is a conductor, an insulating material must be selected for the adhesive layer 120. The thickness of the adhesive layer 120 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, approximately 0.1 μm to 50 μm.

[0027] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and then the resistor 30 and terminal portion 41 having the planar shape shown in Fig. 1 are formed on the lower surface 10b of the substrate 10. The material and thickness of the resistor 30 and terminal portion 41 are as described above. The resistor 30 and terminal portion 41 can be integrally formed from the same material.

[0028] The resistor 30 and the terminal portion 41 can be formed, for example, by depositing a film by magnetron sputtering using a target made of a material capable of forming the resistor 30 and the terminal portion 41, and then patterning the film by photolithography. Instead of magnetron sputtering, the resistor 30 and the terminal portion 41 may also be deposited by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0029] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-form a functional layer having a film thickness of about 1 nm to 100 nm by, for example, conventional sputtering as a base layer on the lower surface 10b of the substrate 10 before forming the resistor 30 and the terminal portion 41. After the resistor 30 and the terminal portion 41 are formed on the entire lower surface of the functional layer, the functional layer is patterned together with the resistor 30 and the terminal portion 41 into the planar shape shown in FIG.

[0030] In this application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper layer, the resistor 30. The functional layer preferably also has a function of preventing oxidation of the resistor 30 due to oxygen or moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer may also have other functions.

[0031] 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 resistor 30, especially when the resistor 30 contains Cr.

[0032] 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 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 suitable metals include one or more metals selected from the group consisting of 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), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0033] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0034] 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.

[0035] 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.

[0036] There are no particular restrictions on the combination of the material of the functional layer with the material of the resistor 30 and the terminal portion 41, 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 resistor 30 and the terminal portion 41.

[0037] In this case, for example, the resistor 30 and the terminal portion 41 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 a chamber. Alternatively, the resistor 30 and the terminal portion 41 can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas into a chamber together with Ar gas.

[0038] 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).

[0039] When the resistor 30 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the resistor 30, preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the resistor 30. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0040] In this way, by providing a functional layer below the resistor 30, it is possible to promote crystal growth of the resistor 30, and to produce a resistor 30 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 constituting the functional layer into the resistor 30, it is possible to improve the gauge characteristics of the strain gauge 1.

[0041] To manufacture the sensor module 5, after fabricating the strain gauge 1, for example, one of the above materials to become the adhesive layer 120 is applied to the lower surface 10b of the substrate 10 and / or the upper surface 110a of the flexure element 110. Then, the lower surface 10b of the substrate 10 is placed opposite the upper surface 110a of the flexure element 110, and the strain gauge 1 is placed on the flexure element 110 with the applied material sandwiched between them. Alternatively, a bonding sheet may be sandwiched between the flexure element 110 and the substrate 10.

[0042] Next, the strain gauge 1 is heated to a predetermined temperature while being pressed against the flexure element 110, and the applied material is cured to form the adhesive layer 120. This bonds the upper surface 110a of the flexure element 110 to the lower surface 10b of the substrate 10 via the adhesive layer 120, completing the sensor module 5. The sensor module 5 can be used to measure, for example, load, pressure, torque, acceleration, etc.

[0043] Thus, in the sensor module 5, the strain gauge 1 is adhered to the strain element 110 with the resistor 30 facing the strain element 110. In other words, the upper surface of the resistor 30 is covered with the substrate 10. By covering the upper surface of the resistor 30 with the substrate 10, it is possible to prevent mechanical damage and the like from occurring to the resistor 30. Furthermore, by covering the upper surface of the resistor 30 with the substrate 10, it is possible to protect the resistor 30 from moisture and the like.

[0044] As mentioned above, conventional sensor modules have a structure in which a strain gauge is fabricated with a resistor and a protective film formed on a substrate, and the substrate side of the strain gauge is attached to a flexure element via an adhesive layer. In this case, in addition to the process of forming a resistor on the substrate, a process of covering the resistor with a protective film is required, which poses a problem of increased costs for sensor modules using strain gauges.

[0045] In contrast, in the sensor module 5, the strain gauge 1 is bonded to the strain element 110 with the resistor 30 facing the strain element 110, and the upper surface of the resistor 30 is covered with the base material 10. That is, in the sensor module 5, the base material 10 also serves the role of the protective film in conventional sensor modules, so the process of covering the resistor with a protective film is unnecessary, and the time required for manufacturing is shortened. This makes it possible to suppress an increase in the cost of the sensor module 5.

[0046] 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]

[0047] 1 strain gauge, 5 sensor module, 10 substrate, 10a upper surface, 10b lower surface, 30 resistor, 41 terminal portion, 110 strain element, 110a upper surface, 120 adhesive layer

Claims

1. A substrate made of a flexible resin, a functional layer formed of a metal, an alloy, or a metal compound directly on one surface of the substrate, and a layer of Cr, CrN, or Cr directly on one surface of the functional layer. ２ a strain gauge including a resistor formed from a film containing N and containing α-Cr as a main component; a strain generating body that transmits strain to the strain gauge, the functional layer has a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; The resistor has a thickness of 0.05 μm or more and 2 μm or less, The thickness of the functional layer is 1 nm or more and 100 nm or less, The strain gauge is a sensor module in which the resistor is bonded to the strain element with the resistor facing the strain element.

2. the strain gauge includes a pair of electrodes electrically connected to the resistor; The sensor module according to claim 1 , wherein a part or all of the surfaces of the pair of electrodes opposite to the strain generating body are exposed in an opening provided in the base material.

3. an adhesive layer sandwiched between the strain gauge and the strain element; The sensor module according to claim 1 or 2, wherein the adhesive layer covers the resistor.

4. 4. The sensor module according to claim 3, wherein the adhesive layer is formed from an epoxy resin, a modified epoxy resin, a silicone resin, a modified silicone resin, a urethane resin, or a modified urethane resin.

5. 5. The sensor module according to claim 3, wherein the adhesive layer has a thickness of 0.1 μm or more and 50 μm or less.

Images