JP2024088419A - Strain gauges - Google Patents

Abstract

The present invention provides a strain gauge that is resistant to breakage and cracks.
[Solution] This strain gauge has a substrate and a resistor formed on the substrate, and the resistor forms a predetermined pattern in a plan view in which a plurality of elongated portions, each of which includes a detection portion and a connection portion connected in series to the detection portion, are arranged in a juxtaposed manner, and the connection portion is formed from a material having a lower elastic modulus than the detection portion and is arranged so as to be in direct contact with the detection portion, and in the predetermined pattern, the boundary line between the detection portion and the connection portion in a certain elongated portion and the boundary line between the detection portion and the connection portion in the same certain elongated portion are not on the same straight line in the plan view.
[Selected Figure] Figure 1

Description

The present invention relates to a strain gauge.

Strain gauges are known that are attached to an object to be measured to detect strain on the object. The strain gauge has a resistor that detects strain, and the resistor is formed, for example, on an insulating resin. The strain gauge is attached to a strain body and expands and contracts following the movement (e.g., strain) of the strain body. At this time, the resistor of the strain gauge deforms, causing a change in resistance value. The amount of strain on the strain body can be determined from the amount of change in resistance value. In recent years, strain gauges that contain different materials in the resistor portion have also been developed (Patent Documents 1 and 2).

JP 2021-152523 A JP 2019-132791 A

In this way, the resistor in a strain gauge needs to expand and contract when detecting strain. Therefore, for example, if you try to create a strain gauge that can detect larger strains, the strain gauge itself will be subjected to greater stress.

The present invention was made in consideration of the above points, and aims to create a strain gauge that is less likely to break or crack.

This strain gauge has a substrate and a resistor formed on the substrate, and the resistor forms a predetermined pattern in plan view in which a plurality of elongated portions, each including a detection portion and a connection portion connected in series to the detection portion, are arranged side by side, the connection portion is made of a material having a lower elasticity than the detection portion and is arranged so as to be in direct contact with the detection portion, and in the predetermined pattern, the boundary line between the detection portion and the connection portion in a certain elongated portion and the boundary line between the detection portion and the connection portion in a certain elongated portion adjacent to the certain elongated portion are not on the same straight line in plan view.

The disclosed technology makes it possible to create a strain gauge that is less susceptible to breakage and cracking.

FIG. 2 is a plan view illustrating a strain gauge according to an embodiment. FIG. 1 is a cross-sectional view (part 1) illustrating a strain gauge according to an embodiment. FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the embodiment. FIG. 4 is a cross-sectional view showing another example of the strain gauge according to the embodiment. 10 is a partial plan view showing an example of a connection portion between a detection portion and a connection portion in a strain gauge according to a first modified example of an embodiment. FIG. FIG. 11 is a plan view illustrating a strain gauge according to a second modified example of the embodiment. FIG. 11 is a cross-sectional view illustrating a strain gauge according to a second modified example of the embodiment. FIG. 7 is an enlarged view of a connection portion of the strain gauge shown in FIG. 6 . FIG. 11 is a plan view illustrating a strain gauge according to a third modified example of the embodiment. FIG. 11 is a cross-sectional view illustrating a strain gauge according to a third modified example of the embodiment. FIG. 13 is a plan view illustrating a strain gauge according to a fourth modified example of the embodiment.

Below, an embodiment of the invention will be described with reference to the drawings. In each drawing, the same components may be given the same reference numerals. In addition, in the description of each drawing, the description of components that are the same as components already described may be omitted.

[Structure of strain gauge]
Fig. 1 is a plan view illustrating a strain gauge according to an embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the embodiment, showing a cross section along line A-A in Fig. 1. Fig. 3 is a cross-sectional view (part 2) illustrating the strain gauge according to the embodiment, showing a cross section along line B-B in Fig. 1. Note that the shapes and sizes of the parts of the strain gauge shown in Figs. 1 to 3 are merely examples, and the appearance of the strain gauge according to this embodiment is not limited to these.

Referring to Figures 1 to 3, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. For convenience, only the outer edge of the cover layer 60 is shown by a dashed line. The cover layer 60 is not a required component.

In this embodiment, 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", and the side on which the resistor 30 is not provided is referred to as the "lower side". The surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". However, the strain gauge 1 can also be used upside down. The strain gauge 1 can also be placed at any angle. In this embodiment, "planar view" refers to the case where the upper surface 10a of the substrate 10 is viewed in the normal direction from the top to the bottom. And, "planar shape" refers to the shape of the object when the object is viewed in the planar view.

(Substrate 10)
The substrate 10 is a member that serves as a base layer for forming the resistor 30 and the like. The substrate 10 has flexibility. The thickness of the substrate 10 is not particularly limited and may be appropriately determined depending on the intended use of the strain gauge 1 and the like. For example, the thickness of the substrate 10 may be about 5 μm to 500 μm. A strain generator may be bonded to the lower surface side of the strain gauge 1 via an adhesive layer or the like. From the viewpoint of the transferability of strain from the surface of the strain generator to the sensing part and dimensional stability against environmental changes, the thickness of the substrate 10 is preferably within the range of 5 μm to 200 μm. From the viewpoint of insulation, the thickness of the substrate 10 is preferably 10 μm or more.

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. Note that a film refers to a flexible material with a thickness of about 500 μm or less.

When the substrate 10 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the substrate 10 may be formed from an insulating resin film containing a filler such as silica or alumina.

Examples of materials other than resin for the substrate 10 include crystalline materials such as _SiO2 , _ZrO2 (including YSZ), Si, _Si2N3 , _Al2O3 (including _sapphire ), ZnO, and perovskite ceramics ( _CaTiO3 , _BaTiO3 ). In addition to the above-mentioned crystalline materials, amorphous glass or _the like may be used as the material for the substrate 10. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. When a metal is used, an insulating film is provided on the metallic substrate 10.

(Resistor 30)
The resistor 30 is a thin film formed on the upper side of the substrate 10. 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. The resistor 30 includes a terminal end 30e, an elongated portion 31, and a folded portion 32. For convenience of explanation, the connection portion of the resistor 30 between the elongated portion 31 and the wiring 40 is referred to as the "terminal end 30e", but the terminal end 30e may be integral with the elongated portion 31. The terminal end 30e may be formed in the same process as the detection portion 33 of the elongated portion 31 using the same material. The folded portion 32 may also be integral with the elongated portion 31, or may be formed in the same process as the detection portion 33 using the same material.

The terminations 30e are parts of the resistor 30 and are provided on both ends of the resistor 30. The terminations 30e connect the wiring 40 and the elongated portions 31. For example, in the example of FIG. 1, the terminations 30e connect the elongated portions 31 closest to the two wirings 40 to the wirings 40, respectively.

The elongated portion 31 is a part of the resistor 30. In the strain gauge 1, multiple elongated portions 31 are arranged side by side with their longitudinal directions facing a predetermined direction. In the following description, the same direction as the longitudinal direction of the elongated portion 31 (the direction of line A-A in FIG. 1) may be simply referred to as the "longitudinal direction". Also, the same direction as the lateral direction of the elongated portion 31 (the direction perpendicular to line A-A in FIG. 1) may be simply referred to as the "lateral direction". The elongated portion 31 includes a detection portion 33 and a connection portion 34. The detection portion 33 and the connection portion 34 will be described in detail later.

The folded portion 32 is a part of the resistor 30 and is a portion that connects the ends of adjacent elongated portions 31. The folded portion 32 connects the ends of adjacent elongated portions 31 in a staggered manner as shown in FIG. 1. This causes the resistor 30 as a whole to form a zigzag folded pattern.

(Detection Unit 33)
The detection unit 33 is a strain sensing portion of the elongated portion 31. The detection unit 33 can be formed, for example, from a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the detection unit 33 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).

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N, etc. are mixed together. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

For example, when the detection section 33 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by making the main component α-Cr (alpha chromium), which is a stable crystal phase. Also, for example, when the detection section 33 is a Cr mixed-phase film, the detection section 33 can make the main component α-Cr to make the gauge factor of the strain gauge 1 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR within the range of -1000 ppm/°C to +1000 ppm/°C. Here, the "main component" means a component that occupies 50% by weight or more of the total material that constitutes the detection section 33. From the viewpoint of improving the gauge characteristics, it is preferable that the detection section 33 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is more preferable that the detection section 33 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

Furthermore, when the detection unit 33 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr ₂ N. By containing 20% by weight or less of CrN and Cr ₂ N in the Cr mixed-phase film, a decrease in the gauge factor of the strain gauge 1 can be suppressed.

In addition, the ratio of CrN and Cr ₂ N in the Cr mixed phase film is preferably such that the ratio of Cr ₂ N is 80% by weight or more and less than 90% by weight with respect to the total weight of CrN and Cr _{2 N. More specifically, it is more preferable that the ratio of Cr 2 N} is 90% by weight or more and less than 95% by weight with respect to the total weight of CrN and Cr ₂ N. Cr ₂ N has a semiconductor property. Therefore, by setting the ratio of Cr ₂ N to 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant. Furthermore, by setting the ratio of Cr ₂ N to 90% by weight or more and less than 95% by weight, the ceramicization of the detection part 33 can be reduced. Therefore, the brittle fracture of the detection part 33 can be made less likely to occur.

On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr mixed-phase film, the possibility of unstable N being generated can be reduced, and a stable strain gauge can be obtained. Here, "unstable N" means a trace amount of _N2 or atomic N that may be present in the Cr mixed-phase film. These unstable N may escape to the outside of the film depending on the external environment (e.g., high temperature environment). When unstable N escapes to the outside of the film, the film stress of the Cr mixed-phase film may change.

In the strain gauge 1, when a Cr mixed-phase film is used as the material for the detection section 33, high sensitivity and miniaturization can be achieved. For example, while the output of a conventional strain gauge was about 0.04 mV/2 V, an output of 0.3 mV/2 V or more can be obtained when a Cr mixed-phase film is used as the material for the detection section 33. In addition, while the size (gauge length x gauge width) of a conventional strain gauge was about 3 mm x 3 mm, when a Cr mixed-phase film is used as the material for the detection section 33, the size (gauge length x gauge width) of the strain gauge can be miniaturized to about 0.3 mm x 0.3 mm.

The thickness of the detection section 33 is not particularly limited and may be appropriately determined depending on the intended use of the strain gauge 1. For example, the thickness of the detection section 33 may be about 0.05 μm to 2 μm. In particular, when the thickness of the detection section 33 is 0.1 μm or more, the crystallinity of the crystals constituting the detection section 33 (for example, the crystallinity of α-Cr) is improved. In addition, when the thickness of the detection section 33 is 1 μm or less, (i) film cracks and (ii) warping of the film from the substrate 10 caused by the internal stress of the film constituting the detection section 33 are reduced. The width of the detection section 33 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be set to, for example, about 10 μm to 100 μm, taking into consideration measures against breakage and cracks. As described above, the folded portion 32 and the end 30e may also be formed of the same material and thickness as the detection section 33.

(Connection portion 34)
The connection portion 34 is a structure provided on the elongated portion 31 to prevent breakage and cracks in the resistor 30. The length of one connection portion 34 in the longitudinal direction is, for example, about 50 μm. The length of one connection portion 34 in the lateral direction may be substantially the same as that of the elongated portion 31. As shown in FIGS. 1 to 3, the connection portion 34 is disposed so as to be in direct contact with the detection portion 33. The connection portion 34 is physically and electrically connected to the detection portion 33 to form one elongated portion 31.

The connection part 34 is formed from a material having a lower elastic modulus than the detection part 33. Specifically, the elastic modulus of the connection part 34 is preferably 1/2 or less than the elastic modulus of the detection part 33. Furthermore, the elastic modulus of the connection part 34 is preferably 1/3 or less than the elastic modulus of the detection part 33, and more preferably 1/4 or less.

As mentioned above, it is preferable that the connection portion 34 is formed from a material with a lower resistance than the detection portion 33. This is to reduce the influence of the connection portion 34 on the strain detection. Specifically, examples of materials for the connection portion 34 include Au, Ag, Cu, Al, Pt, and Fe. These metals have a relatively low elastic modulus and relatively low resistance (i.e., high conductivity). Note that materials with a low elastic modulus have high ductility and are less likely to break or crack. By providing a portion with a low elastic modulus such as the connection portion 34 in the elongated portion 31, it is possible to make the resistor 30 as a whole less likely to break or crack.

For example, when a Cr mixed phase film is used as the detection unit 33, the elastic modulus is about 400 GPa. In this case, for example, Pt with an elastic modulus of about 200 GPa or Fe with an elastic modulus of about 170 GPa can be used as the material for the connection unit 34. Also, when nickel chrome is used as the detection unit 33, the elastic modulus of the detection unit 33 is about 214 GPa. In this case, for example, Au with an elastic modulus of about 80 GPa or Al with an elastic modulus of about 70 GPa can be used as the material for the connection unit 34.

The width and thickness of the connection portion 34 are preferably equal to the width and thickness of the detection portion 33. This ensures that the connection portion 34 can be electrically connected to adjacent detection portions 33. Here, the two are considered to be equal when the width and thickness of the connection portion 34 are within ±10% of the width and thickness of the detection portion 33, respectively.

(Arrangement and connection of connection portion 34)
As shown in FIG. 1, the connection portion 34 is provided so as to be sandwiched between a certain detection portion 33 and another detection portion 33 in one elongated portion 31. The detection portion 33 and the connection portion 34 are connected in series. The strain gauge 1 according to the present embodiment prevents the resistor 30 from breaking and cracking by ingeniously designing the position of the connection portion 34. Specifically, in the strain gauge 1 according to the present embodiment, the connection portion 34 is disposed so that the boundary between the detection portion 33 and the connection portion 34 when the connection portion between the detection portion 33 and the connection portion 34 is viewed in plan view satisfies a specific condition. The specific condition will be described in detail below. In the following, the "boundary between the detection portion 33 and the connection portion 34 when the connection portion between the detection portion 33 and the connection portion 34 is viewed in plan view" is also simply referred to as the "boundary".

The "specific condition" is that in the pattern of the resistor 30, the boundary line of a certain elongated portion 31 (say, elongated portion 31A) and the boundary line of an elongated portion adjacent to the elongated portion 31A (say, elongated portion 31B) are not on the same line in a plan view. Note that if there are elongated portions 31B adjacent to both sides of the elongated portion 31A, the connection portion 34 is arranged such that the boundaries of the elongated portion 31A and the boundaries of one of the elongated portions 31B are not on the same line in a plan view, and the boundaries of the elongated portion 31A and the boundaries of the other elongated portion 31B are not on the same line.

Taking the example of FIG. 1 as an example, the connection portion 34 in FIG. 1 has a parallelogram shape in a plan view. With connection portion 34 of this shape, as shown in FIG. 1, by juxtaposing connection portion 34 in parallel in the short direction, it is possible to prevent each boundary line from being on the same line as adjacent boundaries in the short direction. For example, boundary lines 35a and 35c, boundary lines 35a and 35e, boundary lines 35b and 35d, and boundary lines 35b and 35f in FIG. 1 are not on the same line. Furthermore, in the resistor 30 as a whole, there is no point where two adjacent boundaries in the short direction are on the same line.

In the example of FIG. 1, one connection portion 34 is provided for each elongated portion 31, but the arrangement of the connection portions 34 in the present invention is not limited to this. In the present invention, it is sufficient that at least two of the multiple elongated portions 31 are provided with the connection portions 34. In addition, the number of connection portions 34 provided in one elongated portion 31 is not limited. For example, one elongated portion 31 may be provided with one connection portion 34, multiple connection portions 34 may be provided, or there may be an elongated portion 31 without a connection portion 34. In addition, the number of connection portions 34 of each elongated portion 31 may be different. It is preferable that the number of connection portions 34 in the resistor 30 is appropriately determined within a range that does not increase the overall area of the strain gauge 1. In addition, as long as the above-mentioned specific conditions are met, the position of the connection portion 34 in the elongated portion 31 is not particularly limited. Furthermore, the position of each connection portion 34 in the entire resistor 30 (i.e., the distribution of each connection portion 34 in the entire resistor 30 in a plan view) is not particularly limited. The connection portion 34 can also be disposed in the portion of the elongated portion 31 that contacts the terminal end 30e. In this case, both ends of the connection portion 34 are connected to the detection portion 33 and the terminal end 30e, respectively.

The provision of the connection portion 34 is particularly effective when using a detection portion 33 having a thickness of 0.05 μm or more and 2 μm or less, and is extremely effective when using a detection portion 33 having a thickness of 0.05 μm or more and 1 μm or less.

(Wiring 40)
The wiring 40 is a member for electrically connecting the resistor 30 and the electrode 50. One end of the wiring 40 is connected to the electrode 50, and the other end is connected to the end 30e of the resistor 30. The wiring 40 is not limited to being linear, and may have any shape. In addition, the wiring 40 may have any width and any length.

(Electrode 50)
The electrodes 50 output the change in resistance value of the resistor 30 caused by the strain to the outside. In this embodiment, a pair of electrodes 50 is provided on the substrate 10. The electrodes 50 are electrically connected to the resistor 30 via the wiring 40. In this embodiment, the electrodes 50 are formed in a substantially rectangular shape wider than the wiring 40 in a plan view. However, the shape of the electrodes 50 is not limited thereto. For example, the electrodes 50 may be substantially circular or substantially elliptical in a plan view. For example, a lead wire for external connection is joined to each electrode 50.

Each electrode 50 has a metal layer 51 and a metal layer 52 laminated on the upper surface of the metal layer 51. The metal layer 51 is electrically connected to the end 30e of the resistor 30 via the wiring 40. In this embodiment, the metal layer 51 is formed in a substantially rectangular shape in a plan view. The metal layer 51 may be formed to have the same width as the wiring 40.

For convenience, the detection unit 33, the wiring 40, and the metal layer 51 are given different reference numerals, but the detection unit 33, the wiring 40, and the metal layer 51 can be integrally formed from the same material in the same process. Therefore, the detection unit 33, the wiring 40, and the metal layer 51 may have approximately the same thickness.

The metal layer 52 is formed from a material with a lower resistance than the detection section 33. There are no particular restrictions on the material of the metal layer 52, so long as it is a material with a lower resistance than the detection section 33, and it can be appropriately selected depending on the purpose. For example, when the detection section 33 is a Cr mixed phase film, the material of the metal layer 52 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately laminated. There are no particular restrictions on the thickness of the metal layer 52, and it can be appropriately selected depending on the purpose, but it can be, for example, about 3 μm to 5 μm.

In addition, one or more other metal layers may be laminated on the upper surface of the metal layer 52. For example, the metal layer 52 may be a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, the metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be laminated in this order on the upper surface of the copper layer. By making the top layer of the electrode 50 a gold layer, the solder wettability of the electrode 50 can be improved.

The cover layer 60 is formed on the substrate 10, covers the resistor 30 and the wiring 40, and exposes the electrodes 50. A portion of the wiring 40 may be exposed from the cover layer 60. By providing the cover layer 60 that covers the resistor 30 and the wiring 40, mechanical damage to the resistor 30 and the wiring 40 can be prevented. Furthermore, by providing the cover layer 60, the resistor 30 and the wiring 40 can be protected from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the electrodes 50.

Examples of materials for the cover layer 60 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The cover layer 60 may contain fillers and pigments. There are no particular limitations on the thickness of the cover layer 60, and it can be appropriately selected depending on the purpose. For example, the thickness of the cover layer 60 can be about 2 μm to 30 μm. By providing the cover layer 60, it is possible to prevent mechanical damage, etc., from occurring to the resistor 30. In addition, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture, etc.

[Strain gauge manufacturing method]
To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 10. The metal layer A is a layer that is finally patterned to become the detection section 33, the termination 30e, the wiring 40, and the metal layer 51. Therefore, the material and thickness of the metal layer A are similar to the material and thickness of the detection section 33, the termination 30e, the wiring 40, and the metal layer 51 described above.

Metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming metal layer A as a target. Instead of magnetron sputtering, metal layer A may be formed using reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

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, for example, by conventional sputtering, before depositing the metal layer A.

In this application, the functional layer refers to a layer that has a function of promoting the crystal growth of at least the upper layer, metal layer A (detection unit 33). The functional layer preferably also has a function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and/or a function of improving adhesion with metal layer A. The functional layer may also have other functions.

The insulating resin film constituting the substrate 10 may contain oxygen and moisture, and Cr may form a self-oxidized film. Therefore, particularly when the metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of the metal layer A.

The material of the functional layer is not particularly limited as long as it has the function of promoting crystal growth of at least the upper layer, metal layer A (detection section 33), and can be selected appropriately depending on the purpose. For example, the metal may be one or more metals selected from the group consisting of 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), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

The functional layer can be formed in a vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, so that the amount of functional layer formed can be minimized and the effect of improving adhesion can be obtained.

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, the upper surface 10a of the substrate 10 may be activated by performing a plasma treatment using Ar or the like before forming the functional layer. This provides an adhesion improvement effect, and the functional layer may then be vacuum-formed by magnetron sputtering.

There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and they 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 containing α-Cr (alpha chromium) as the metal layer A.

In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber. In this case, the ratio of CrN and Cr 2 N contained in the Cr mixed phase film and the ratio of Cr ₂ N in CrN and Cr ₂ N can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the _nitrogen gas introduced or by adjusting the heating temperature by providing a heating process.

In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film can be formed that is mainly composed of α-Cr, which has a stable crystal structure. In addition, the Ti that constitutes 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 gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. Note that when the functional layer is formed from Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

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

In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 can be improved. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

Next, the metal layer A is patterned into the planar shape shown in FIG. 1 by photolithography to form the detection section 33, wiring 40, and metal layer 51. The resistor 30 is then formed by forming the connection section 34 in series with the detection section 33 so as to be in direct contact with the detection section 33. The connection section 34 can be formed by, for example, a vapor deposition method, a sputtering method, or the like. The connection section 34 may also be formed using a coating technique such as a sol-gel method or an inkjet method.

Next, metal layer 52 is formed on the upper surface of metal layer 51. Metal layer 52 can be formed, for example, by a well-known semi-additive method. The material and thickness of metal layer 52 are as described above.

After that, if necessary, a cover layer 60 is provided on the upper surface 10a of the substrate 10 to cover the resistor 30 and the wiring 40 and expose the electrode 50. This completes the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrode 50, and then heating and curing the film. The cover layer 60 may be produced on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the wiring 40 and expose the electrode 50. For example, the cover layer 60 can be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a and heating it (i.e., curing the resin).

When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the detection unit 33, the wiring 40, and the metal layer 51, the strain gauge 1 has a cross-sectional shape as shown in Fig. 4. Fig. 4 is a cross-sectional view showing another example of a strain gauge according to an embodiment. The layer indicated by reference numeral 20 is the functional layer. The planar shape of the strain gauge 1 when the functional layer 20 is provided is, for example, similar to the resistor 30, the wiring 40, and the metal layer 51 in Fig. 1.
(Actions and Effects of the Strain Gauge 1 According to the Present Embodiment)

In the strain gauge 1, the connection part 34, which has a relatively lower elastic modulus than the detection part 33, is arranged in series with the detection part 33. Therefore, even if a strong force is applied to the strain gauge 1 due to an external factor or the like, the connection part 34 distorts and can alleviate the force to some extent. In other words, the connection part 34 behaves like a spring in the resistor 30. In this way, the strain gauge 1 according to this embodiment can prevent breakage and cracks from occurring in the resistor 30. In other words, a strain gauge with a high strain limit (i.e., strain resistance) can be realized.

Furthermore, in the strain gauge 1 according to this embodiment, the boundary line of a certain elongated portion 31 and the boundary line of the elongated portion 31 adjacent to that elongated portion 31 are not on the same line in a plan view. In other words, since the physical connection portion between the detection portion 33 and the connection portion 34 is not on the same line in a plan view, the connection portions are not lined up in a certain direction. Therefore, according to the strain gauge 1 according to this embodiment, it is possible to make breaks and cracks less likely to occur at the physical connection portion between the detection portion 33 and the connection portion 34. Therefore, according to this embodiment, it is possible to realize a strain gauge that is less likely to break and crack.

Below, we will explain modified examples of the above-mentioned embodiment. Note that for each modified example described below, the same processing and configuration as in the embodiment may not be described repeatedly.

<Variation 1>
The connection portion 34 according to the embodiment has a parallelogram shape in a plan view. However, the shape of the connection portion is not limited to this. For example, the connection portion may have a rectangular shape in a plan view, or a shape including curved sides. Furthermore, the boundary between the detection unit 33 and the boundary line 34 may be a straight line or a curved line.

Figure 5 is a partial plan view showing an example of the connection between the detection section and the connection section in the strain gauge 1A according to the first modified example. For example, as in the connection sections 34a and 34b in Figures 5(a) and 5(b), the boundary line 35 may be recessed toward the center of the connection sections 34a and 34b in a plan view. Furthermore, the boundary line 35 may be a straight line as shown in Figure 5(a) or a curved line as shown in Figure 5(b).

<Modification 2>
The position of the connection part in the resistor is not limited to the example described in the embodiment. For example, the connection part may be disposed in one or more folded parts of the resistor. That is, a part of the folded part of the strain gauge may be replaced with the connection part.

Figure 6 is a plan view illustrating a strain gauge 1B according to a second modified embodiment of the present invention. Figure 7 is a cross-sectional view illustrating a strain gauge 1B according to a second modified embodiment of the present invention, taken along line CC in Figure 6. Figure 8 is an enlarged view of the connection portion 34c of the strain gauge 1B shown in Figure 6.

As shown in Figures 6 and 7, strain gauge 1B differs from strain gauge 1 in that a part of the folded portion 32 in strain gauge 1 according to embodiment 1 is replaced with a connection portion 34c. In addition, in the example of strain gauge 1B, as shown in Figure 6, folded portions 32 and connection portions 34c are arranged alternately in the short direction.

In this way, by providing a connection part at the position where the folded part was, even if a strong force is applied to the folded part, the connection part (particularly connection part 34c) will distort and can alleviate the force to some extent. Therefore, it is possible to prevent breakage and cracking of the resistor 30. Also, in this modified example, as shown in FIG. 6, if the connection parts 34c that replace the folded part 32 are not arranged continuously in the short direction, it is possible to prevent as much as possible the physical connection parts of the detection part 33 and the connection parts 34c from being arranged in the same direction. Therefore, the strain gauge 1B can make it difficult for breakage and cracking to occur at the physical connection parts of the resistor 30.

Furthermore, in the strain gauge 1B, it is desirable that the boundary line between the connection part 34c and the detection part 33 is not parallel to the short side direction in a plan view (i.e., it is desirable that it is an oblique line or a curve inclined at a predetermined angle to the short side direction). As shown in FIG. 8, it is desirable that the connection part 34c is formed so that its boundaries 353 and 354 are not parallel to the short side direction.

By having the detection section 33 and the connection section 34c in this shape, it is possible to prevent the boundaries 353 and 354 from being aligned on the same straight line as much as possible. Therefore, the strain gauge 1B can make it difficult for breakage or cracks to occur at the physical connection part of the resistor 30.

<Modification 3>
A connection portion may be disposed on the wiring portion of the strain gauge. Fig. 9 is a plan view illustrating a strain gauge 1C according to a third modification of the embodiment. Fig. 10 is a cross-sectional view illustrating the strain gauge 1C according to the third modification of the embodiment, showing a cross section along line D-D in Fig. 9. Referring to Figs. 9 and 10, the strain gauge 1C differs from the strain gauge 1 in that the wiring 40 is replaced with a wiring 40B.

The wiring 40B includes a plurality of conductive portions 43 and a connection portion 44 connected in series with the conductive portions 43. The connection portion 44 is formed so as to be in direct contact with the conductive portions 43. For example, as shown in FIG. 9, one connection portion 44 can be disposed on each wiring 40B. The connection portion 44 is disposed between adjacent conductive portions 43, and provides electrical continuity between the adjacent conductive portions 43. In addition, when the termination 30e is replaced with the connection portion 44, the connection portion 44 provides electrical continuity between the conductive portion 43 and the elongated portion 31.

It is preferable that the width and thickness of the connection portion 44 are equal to the width and thickness of the conductive portion 43. This ensures that the connection portion 44 is conductive to adjacent conductive portions 43. Note that "equal" does not necessarily mean that the width and thickness of the connection portion 44 are exactly the same, but rather that the width and thickness of the connection portion 44 are within ±10% of the width and thickness of the conductive portion 43.

In the strain gauge 1C, by arranging the connection part 44 on the wiring 40B, the connection part 44 behaves like a spring when a strong force is applied due to an external factor, thereby preventing breakage and cracks in the conductive part 43.

9, the connection portion 44 has a parallelogram shape in plan view, similar to the connection portion 34 according to the embodiment. If the connection portion 44 has such a shape, as shown in FIG. 9, the connection portion 44 can be juxtaposed with the connection portion 34 in the short direction so that the boundary line of each connection portion (connection portion 44 and connection portion 34) does not lie on the same line as the boundary line of the adjacent connection portion. In this way, as long as the connection portion 44 is arranged so as not to lie on the same line as the adjacent connection portion 34 in plan view, the shape, arrangement position, and number of the connection portions 44 are not particularly limited. For example, a single wiring 40B may have multiple connection portions 44. Also, the number of connection portions 44 of each wiring 40B may be different. Also, there may be a wiring 40B without a connection portion 44.

The connection portion 44 may also be disposed in place of the terminal end 30e. By disposing the connection portion 44 so that it is not on the same straight line as the adjacent connection portion 34 in a plan view, it is possible to make it less likely that breakage or cracks will occur at the physical connection portions between the connection portion 44 and the conductive portion 43, and between the connection portion 34 and the detection portion 33.

<Modification 4>
As described above, the connection parts of the strain gauge may be rectangular. Furthermore, when the connection parts are rectangular, the connection parts may be arranged so that every other connection part is at the same position in the short direction in a plan view. In other words, the connection parts may be arranged alternately in a plan view for the entire resistor of the strain gauge. Note that in this case, too, the connection parts are arranged so that the boundaries of adjacent connection parts are not on the same straight line in a plan view and in the short direction.

Figure 11 is a plan view illustrating a strain gauge 1D according to the fourth modified example of the embodiment. In the example of Figure 11, the connection parts 34 are rectangular, and two are provided on each elongated part 31. The connection parts 34 of adjacent elongated parts 31 are also located at different positions in the short direction. In other words, the strain gauge 1D is designed so that the boundaries between adjacent connection parts 34 in the short direction are not on the same straight line.

The positions of the connection parts 34 should desirably be designed so that there are as few boundary lines that line up in a straight line as possible across the entire resistor 30. For example, in the strain gauge 1D shown in FIG. 11, the connection parts 34 are arranged so that they are slightly offset in the longitudinal direction across the entire resistor 30. In other words, the strain gauge 1D is designed so that the boundary lines of one connection part 34 and the boundary lines of another connection part 34 do not line up in a straight line as much as possible.

To give a specific example, the position of the connection portion 34 is different between the elongated portion 311 and the adjacent elongated portion 312, and the boundary lines 35 of the elongated portion 311 and the elongated portion 312 are not on the same line in a plan view. In addition, the boundary lines 35 of the elongated portion 311 and the adjacent elongated portion 313 are not on the same line in a plan view. In this way, by arranging the connection portions 34 so that they are slightly shifted in the longitudinal direction, it is possible to reduce the risk of breakage or cracks occurring at the physical connection between the detection portion 33 and the connection portions 34 while still allowing the connection portions 34 to absorb impacts and external stresses.

Preferred embodiments and the like have been described above in detail. However, the strain gauge according to the present disclosure is not limited to the above-mentioned embodiments and modifications. For example, a strain gauge may be realized that combines the configurations shown in the above-mentioned embodiments and modifications. Also, for example, various modifications and substitutions can be made to each strain gauge according to the above-mentioned embodiments and modifications without departing from the scope of the claims.

1, 1A, 1B, 1C, 1D strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e end, 31 elongated portion, 32 folded portion, 33 detection portion, 34, 34a, 34b, 34c, 44 connection portion, 35 boundary line, 40, 40B wiring, 43 conductive portion, 51, 52 metal layer, 50 electrode, 60 cover layer

Claims (7)

A substrate;
A resistor formed on the substrate,
The resistor has a predetermined pattern in which a plurality of elongated portions, each of which includes a detection portion and a connection portion connected in series to the detection portion, are arranged in parallel in a plan view;
the connection portion is formed from a material having a lower elastic modulus than the detection portion and is disposed so as to be in direct contact with the detection portion;
A strain gauge in which, in the specified pattern, the boundary line between the detection portion and the connection portion in a certain elongated portion and the boundary line between the detection portion and the connection portion in an elongated portion adjacent to the certain elongated portion are not on the same straight line when viewed in the plane. The strain gauge of claim 1, wherein in the predetermined pattern, the boundary line of at least one of the elongated portions is not parallel to the short direction of the elongated portion. In the predetermined pattern, the plurality of elongated portions are arranged side by side such that their longitudinal directions are oriented in the same direction;
2. The strain gauge according to claim 1, wherein in the plurality of elongated portions, each of the boundary lines is approximately parallel to the short direction of the elongated portion, and each of the boundary lines is not on the same straight line as an adjacent boundary line when viewed in the plane. the resistor includes a folded portion connecting ends of the adjacent elongated portions,
The strain gauge according to claim 1 , wherein the connection portion is disposed in one or more of the folded portions. a pair of electrodes formed on the base material and electrically connected to the resistor via wiring;
The strain gauge according to claim 1 , wherein the connection portion is disposed on one or more of the wires. The strain gauge according to any one of claims 1 to 5, wherein the elastic modulus of the connection portion is 1/2 or less of the elastic modulus of the detection portion. The strain gauge according to claim 1 , wherein the detection portion is formed from a film containing Cr, CrN, and Cr ₂ N.

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