Strain guage and strain sensor

Abstract

To realize a strain gauge that indicates a more appropriate creep characteristic.SOLUTION: A strain gauge comprises a substrate, a pair of electrodes formed on the substrate, and a plurality of grids formed on the substrate. Each of the plurality of grids includes a resistive element. The resistive elements of the plurality of grids are connected in series to the pair of electrodes, respectively, and are mutually connected in parallel. The resistive element has a shape of slender parts juxtaposed with their longitudinal direction in a first direction in a plan view. The width in the lateral direction of the slender parts of the resistive element included in each of the plurality of grids differs for each grid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to strain gauges and strain sensors. [Background technology]

[0002] Patent Document 1 discloses a strain gauge including a diaphragm and first, second, third and fourth resistors formed on the diaphragm so as to form a bridge circuit using a resistor thin film. Patent Document 1 discloses that the strain gauge includes a ladder-shaped first adjustment resistor formed between the first and third resistors and a ladder-shaped second adjustment resistor formed between the second and fourth resistors.

[0003] Patent Document 2 discloses a strain gauge that is disposed on a strain generating body and includes a folded pattern portion for detecting strain formed by a resistor and a resistance adjustment pattern portion for adjusting resistance by laser trimming. Patent Document 2 discloses that the resistance adjustment pattern portion includes a continuous adjustment pattern portion for adjusting the resistance value by the trimming length, and a short-circuit adjustment pattern portion made of resistance wiring that changes the resistance value by selectively cutting the resistance value by trimming. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 04-133401 [Patent Document 2] JP 2017-173029 A Summary of the Invention [Problem to be solved by the invention]

[0005] In strain gauges, creep can be a cause of measurement errors. Therefore, there is a demand for improving the creep characteristics of strain gauges. There is also a demand for obtaining strain gauges with more suitable creep characteristics, for example, in a specific operating environment.

[0006] The present disclosure provides strain gauges that exhibit more suitable creep characteristics. [Means for solving the problem]

[0007] In one aspect of the present disclosure, a strain gauge is provided which includes a substrate, a pair of electrodes formed on the substrate, and a plurality of grid portions formed on the substrate, each of the plurality of grid portions including a resistor, the resistors of the plurality of grid portions being connected in series with the pair of electrodes and connected in parallel with each other, the resistors having a shape in which elongated portions are connected in series in a plan view and arranged side by side with their longitudinal directions facing a first direction, and the width of the elongated portions of the resistors included in each of the plurality of grid portions in the short direction differs for each of the grid portions. Effect of the Invention

[0008] According to the present disclosure, a strain gauge exhibiting more suitable creep characteristics can be realized. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment. [Diagram 3] FIG. 3 is an enlarged view illustrating the strain gauge according to the first embodiment. [Figure 4] FIG. 4 is an enlarged view for explaining a process performed before mounting the strain gauge according to the first embodiment. [Diagram 5] FIG. 5 is a cross-sectional view illustrating the strain gauge according to the first embodiment. [Figure 6] FIG. 6 is a plan view illustrating the strain sensor according to the second embodiment. [Figure 7] FIG. 7 is a plan view illustrating the strain sensor according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0011] In the directions of parallel, right-angle, orthogonal, horizontal, vertical, up-down, left-right, front-back, etc., deviations are permitted to the extent that they do not impair the effects of the embodiment. The shape of the corners is not limited to right angles and may be rounded. Parallel, right-angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angle, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0012] For example, "approximately parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as parallel to each other as long as it is within the range of manufacturing tolerance. As with "approximately parallel," "approximately right angle," "approximately perpendicular," "approximately horizontal," and "approximately vertical" are also intended to correspond to the respective terms as long as the relative positional relationship between the two lines or two surfaces is within the range of manufacturing tolerance.

[0013] First embodiment Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment. Specifically, Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. Fig. 3 is an enlarged view illustrating the strain gauge according to the first embodiment. Specifically, Fig. 3 is an enlarged view of the vicinity of strain detection unit 30 in Fig. 1.

[0014] For ease of explanation, an XYZ orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other may be set in the drawings. Note that this coordinate system is defined for the purpose of explanation, and does not limit the orientation of the strain sensor and the like according to this embodiment.

[0015] The strain gauge 1, which is an example of a strain gauge according to the first embodiment, has a substrate 10, a strain detection unit 30, a pair of wirings 40, a pair of electrodes 50, and a cover layer 60. Note that the cover layer 60 is not an essential structure. The cover layer 60 is indicated by a dotted line in FIG. 1. Also, the cover layer 60 is omitted in FIG. 3. As shown in FIG. 3, the strain detection unit 30 includes three grid portions (grid portion 31, grid portion 32, and grid portion 33).

[0016] The number of grid portions in the strain gauge according to the present disclosure may be any number equal to or greater than 2. In other words, the strain gauge according to the present disclosure may have a plurality of grid portions.

[0017] In this embodiment, for convenience, the Z-axis positive side of the strain gauge 1 is referred to as the upper side or one side, and the Z-axis negative side is referred to as the lower side or the other side. Also, the surface of each part on the Z-axis positive side is referred to as one side or upper side, and the surface on the Z-axis negative side is referred to as the other side or lower side. However, the strain gauge 1 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.

[0018] The substrate 10 is a flexible member that serves as a base layer for forming resistors (resistors 31r, 32r, and 33r described below). The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

[0019] 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.

[0020] 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.

[0021] 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, perovskite ceramics (CaTiO3, BaTiO3), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. In this case, for example, an insulating film is formed on the metal substrate 10.

[0022] Grid portion 31, grid portion 32, and grid portion 33 are sensing portions of strain gauge 1, each including a resistor. In strain gauge 1, all grid portions have the same creep sign. In the example of FIG. 3, grid portion 31 includes resistor 31r, grid portion 32 includes resistor 32r, and grid portion 33 includes resistor 33r. In strain gauge 1, resistors included in each of the plurality of grid portions (i.e., resistor 31r, resistor 32r, and resistor 33r) are each connected in series to a pair of electrodes 50, and are also connected in parallel to each other.

[0023] The resistors 31r, 32r, and 33r are each a thin film formed in a predetermined pattern on the substrate 10, and are sensing parts that undergo a resistance change when strained. The resistors 31r, 32r, and 33r 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. For convenience, the resistors 31r, 32r, and 33r are shown in FIG. 1 with a dark matte pattern.

[0024] The resistor 31r, resistor 32r, and resistor 33r 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 31r, resistor 32r, and resistor 33r 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).

[0025] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0026] The thickness of each of the resistors 31r, 32r, and 33r is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of each of the resistors 31r, 32r, and 33r can be about 0.05 μm to 2 μm. In particular, it is preferable that the thickness of the resistors 31r, 32r, and 33r is 0.1 μm or more in order to improve the crystallinity (for example, the crystallinity of α-Cr) of the crystals constituting each of the resistors 31r, 32r, and 33r, and it is more preferable that the thickness is 1 μm or less in order to reduce cracks in the film caused by the internal stress of the film constituting each of the resistors 31r, 32r, and 33r and warping from the substrate 10. The width of each of resistors 31r, 32r, and 33r can be optimized for required specifications such as resistance value and lateral sensitivity, and can be set to, for example, about 10 μm to 100 μm while taking into consideration measures against disconnection.

[0027] For example, when each of the resistors 31r, 32r, and 33r is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. In addition, by using α-Cr as the main component of each of the resistors 31r, 32r, and 33r, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be within the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, each of the resistors 31r, 32r, and 33r preferably contains α-Cr at 80% by weight or more, and more preferably contains 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0028] In addition, when the resistors 31r, 32r, and 33r are each a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr2N, which can suppress a decrease in the gauge factor.

[0029] In addition, the ratio of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant due to the Cr2N having semiconductor properties. Furthermore, by reducing the formation of ceramics, brittle fracture is reduced.

[0030] On the other hand, if a small amount of N2 or atomic N is mixed into the film, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in the film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[0031] The resistor 31r includes a plurality of elongated portions 31re. The elongated portions 31re of the resistor 31r are arranged in parallel in the short-side direction (X-axis direction) with a predetermined interval, with the longitudinal direction facing the same direction (Y-axis direction). The ends of adjacent elongated portions 31re are connected in a staggered manner. That is, the resistor 31r has a structure in which the resistor 31r is folded back in a zigzag pattern as a whole. In other words, the resistor 31r has a shape in which elongated portions 31re arranged in parallel in the long-side direction facing the Y-axis direction in a plan view are connected in series. The longitudinal direction of the elongated portions 31re is the grid direction, and the direction perpendicular to the grid direction is the grid width direction. As shown in FIG. 3, the width of the elongated portions 31re is WL1. In this specification, the "width of the elongated portions" refers to the length of the elongated portions in the short-side direction. As shown in FIG. 3, the interval between the elongated portions 31re is WS1.

[0032] The resistor 32r includes a plurality of elongated portions 32re. The elongated portions 32re of the resistor 32r are arranged side by side at a predetermined interval in the short direction (X-axis direction) with their longitudinal direction facing the same direction (Y-axis direction). The ends of adjacent elongated portions 32re are connected in a staggered manner. That is, the resistor 32r has a structure in which the resistor 32r is folded back in a zigzag pattern as a whole. In other words, the resistor 32r has a shape in which elongated portions 32re arranged side by side with their longitudinal direction facing the Y-axis direction in a plan view are connected in series. The longitudinal direction of the elongated portions 32re is the grid direction, and the direction perpendicular to the grid direction is the grid width direction. The width of the elongated portions 32re is WL2. The elongated portions 32re are arranged side by side at an interval of WS2.

[0033] The resistor 33r includes a plurality of elongated portions 33re. The elongated portions 33re of the resistor 33r are arranged side by side at a predetermined interval in the short direction (X-axis direction) with their longitudinal direction facing the same direction (Y-axis direction). The ends of adjacent elongated portions 33re are connected in a staggered manner. That is, the resistor 33r has a structure in which the resistor 33r is folded back in a zigzag pattern as a whole. In other words, the resistor 33r has a shape in which elongated portions 33re arranged side by side with their longitudinal direction facing the Y-axis direction in a plan view are connected in series. The longitudinal direction of the elongated portions 33re is the grid direction, and the direction perpendicular to the grid direction is the grid width direction. The width of the elongated portions 33re is WL3. The elongated portions 33re are arranged side by side at an interval of WS3.

[0034] In the strain gauge 1, the width of the elongated portion of the resistor included in each of the multiple grid portions (i.e., grid portion 31, grid portion 32, and grid portion 33) is different for each grid portion. That is, width WL1, width WL2, and width WL3 are different values.

[0035] In this embodiment, the elongated portions (elongated portions 31re, 32re, and 33re) are shown as substantially rectangular, but the shape of the elongated portions is not limited to this. For example, the elongated portions of each grid portion may have different widths depending on the location. In this case, widths WL1, WL2, and WL3 may be the average values ​​of the widths of elongated portions 31re, 32re, and 33re, respectively.

[0036] In the strain gauge 1, the spacing between the juxtaposed elongated portions of the resistors included in each of the multiple grid portions (i.e., each of grid portions 31, 32, and 33) may be different for each grid portion, or the spacing between the elongated portions of some or all of the grid portions may be the same. For example, as shown in FIG. 3, the spacing WS1, spacing WS2, and spacing WS3 may each be different values. However, the relationship between the size and similarity of the spacing between the juxtaposed elongated portions in each grid portion is not limited to this example. For example, WS1 and WS2 may be the same value and WS3 may be a different value, or WS1, WS2, and WS3 may all be the same value.

[0037] In other words, in the strain gauge 1, the number of elongated portions of the resistor included in each of the multiple grid portions (i.e., grid portion 31, grid portion 32, and grid portion 33) may be different for each grid portion, or the number of elongated portions of some or all of the grid portions may be the same.

[0038] The wiring 40 is formed on the substrate 10 and connects each resistor (resistance element 31r, resistance element 32r, and resistance element 33r) to the electrode 50. Each wiring 40 is not limited to a straight line and can have any pattern. Also, each wiring 40 can have any length. Each wiring 40 is composed of a first metal layer 41 and a second metal layer 42 laminated on the upper surface of the first metal layer 41. Note that in FIG. 1, for convenience, the first metal layer 41 is shown with the same dark matte pattern as the resistance elements 31r, resistance element 32r, and resistance element 33r, and the second metal layer 42 is shown with a matte pattern that is lighter than the resistance elements 31r, resistance element 32r, and resistance element 33r.

[0039] In the example of this embodiment, each of the wirings 40 extends along the Y-axis direction. In other words, each of the wirings 40 has a longitudinal direction in the Y-axis direction. In this embodiment, for convenience, a specific portion of the wiring 40 is named and described, but each portion of the wiring 40 described below is formed integrally. In the strain gauge 1 according to this embodiment, each of the pair of wirings 40 is bent toward the X-axis direction at the end opposite the electrode 50 to form a convex portion 40p. In the strain gauge 1, the convex portions 40p of each of the wirings 40 extend substantially parallel to each other as shown in FIG. 3. In the strain gauge 1, the resistors 31r, 32r, and 33r are provided to bridge between the opposing convex portions 40p. As a result, the grid portion 31, the grid portion 32, and the grid portion 33 are provided between the pair of wirings 40.

[0040] One end (e.g., one end on the Y positive direction side) of the resistor 31r, resistor 32r, and resistor 33r is electrically connected to one of the two electrodes 50 (e.g., the electrode 50 on the X negative direction side) via a wiring 40. The other end (e.g., one end on the Y negative direction side) of the resistors is also electrically connected to the other electrode 50 (e.g., the electrode 50 on the X positive direction side) via the wiring 40. That is, the resistor 31r, resistor 32r, and resistor 33r are electrically connected to a pair of electrodes 50 via a pair of wirings 40.

[0041] The electrodes 50 are a pair of electrodes for outputting a change in resistance value caused in the resistor due to strain to the outside. For example, a lead wire for external connection is joined to the electrodes 50. Each electrode 50 is formed on the substrate 10. The electrodes 50 are electrically connected to the resistors 31r, 32r, and 33r via the wiring 40. The electrodes 50 may be, for example, substantially circular or substantially rectangular in plan view as shown in FIG. 1. The electrodes 50 may be formed to be wider than the wiring 40.

[0042] Although the resistors 31r, 32r, and 33r are designated by different reference numerals from the first metal layer 41 for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistors 31r, 32r, and 33r have approximately the same thickness as the first metal layer 41. Although the second metal layer 42 is designated by a different reference numeral for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 42 has approximately the same thickness.

[0043] The second metal layer 42 may be formed of a material having a lower resistance than each of the resistors 31r, 32r, and 33r (as well as the first metal layer 41). The material of the second metal layer 42 is not particularly limited as long as it is a material having a lower resistance than the resistors 31r, 32r, and 33r, and can be appropriately selected according to the purpose. For example, when the resistors 31r, 32r, and 33r are Cr mixed phase films, the material of the second metal layer 42 may be Cu, Ni, Al, Ag, Au, Pt, or the like, 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, and compounds are appropriately laminated. The thickness of the second metal layer 42 is not particularly limited, and can be appropriately selected according to the purpose. For example, the thickness of the second metal layer 42 may be about 3 μm to 5 μm.

[0044] The second metal layer 42 may be formed on a part of the first metal layer 41, or may be formed on the entire first metal layer 41. One or more other metal layers may be laminated on the upper surface of the second metal layer 42 that becomes the electrode 50. For example, the second metal layer 42 may be a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, the second metal layer 42 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on the upper surface of the copper layer. By forming the top layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 can be improved.

[0045] A cover layer 60 may be provided on the upper surface 10a of the substrate 10 so as to cover the resistors 31r, 32r, 33r, and the wiring 40 and expose the electrodes 50. By providing the cover layer 60, mechanical damage to the resistors 31r, 32r, 33r, and the wiring 40 can be prevented. Furthermore, by providing the cover layer 60, the resistors 31r, 32r, 33r, 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.

[0046] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 60 may contain a filler or a pigment. There is no particular limit to the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0047] In this way, the wiring 40 has a structure in which the second metal layer 42 is laminated on the first metal layer 41 made of the same material as the resistors 31r, 32r, and 33r. Therefore, the resistance of each wiring 40 is lower than that of the resistors 31r, 32r, and 33r, and therefore it is possible to prevent each wiring 40 from functioning as a resistor. As a result, it is possible to improve the strain detection accuracy by the resistors 31r, 32r, and 33r.

[0048] In other words, by providing the wiring 40 having a lower resistance than the resistors 31r, 32r, and 33r, the actual sensing portion of the strain gauge 1 can be limited to the local region in which the resistors 31r, 32r, and 33r are formed, thereby improving the accuracy of strain detection by the resistors 31r, 32r, and 33r.

[0049] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses Cr mixed-phase films as the resistors 31r, 32r, and 33r, making the wiring 40 lower in resistance than the resistors 31r, 32r, and 33r and limiting the actual sensing area to the local area where the resistors 31r, 32r, and 33r are formed is significantly effective in improving the strain detection accuracy. Also, making the wiring 40 lower in resistance than the resistors 31r, 32r, and 33r is effective in reducing the lateral sensitivity.

[0050] The length of the wiring 40 connecting the resistors 31r, 32r, and 33r to the electrodes 50 is preferably 5 mm or more along each of the wirings 40, regardless of whether the wiring 40 is linear or not. By making the length 5 mm or more, heat generated when soldering a lead wire or the like to the electrodes 50 is less likely to be transmitted to the resistors 31r, 32r, and 33r, or the cover layer 60 covering them, and the thermal load on the gauge characteristics can be reduced.

[0051] Next, the process performed before mounting the strain gauge 1 will be described. FIG. 4 is an enlarged view for explaining the process performed before mounting the strain gauge according to the first embodiment. It is known that the creep characteristics of a strain gauge depend on the line width of the elongated portion of the resistor. Therefore, by dividing the area (sensing area) receiving tensile or compressive stress in the strain gauge into multiple grids (for example, grid portion 31, grid portion 32, and grid portion 33) and creating a strain gauge in which the line width of the resistor included in each grid portion is different, it is possible to create a strain gauge provided with "multiple grid portions with different creep characteristics" as shown in FIG. 1 to FIG. 3.

[0052] In the strain gauge 1 produced as described above, in any step before mounting, the resistor in one of the grid parts is left, and the connection portion between the resistor in the other grid parts and the wiring 40 is cut by laser trimming or the like (cutting step). This makes it possible to produce a strain gauge 1 in which only the resistor in the desired grid part is conductive. For example, as shown in FIG. 4, when using the grid part 33 (i.e., resistor 33r), resistor 31r and resistor 32r are each cut at the portion indicated by the arrow CL to break resistor 31r and resistor 32r. By breaking resistor 31r and resistor 32r, the strain gauge 1 becomes a strain gauge with resistor 33r as its sensitive region.

[0053] In this way, since it is possible to select one resistor for the strain gauge 1 later, it is possible to create a strain gauge that only has resistors with the desired creep characteristics by measuring the creep characteristics of each grid part in advance. Therefore, by creating the strain gauge 1 by setting the line width of the resistors in each grid part so that the creep characteristics (e.g., the amount of creep and the amount of creep recovery) of each grid part correspond to various conditions of use of the strain gauge 1 (e.g., the material of the strain gauge, and the temperature and humidity during use), it is possible to later (e.g., immediately before the installation process of the strain gauge 1) make the strain gauge 1 into a strain gauge that has the desired creep characteristics.

[0054] The portion to be cut in order to disconnect the resistor is not limited to the above example. For example, the resistor may be cut at a location other than the portion indicated by the arrow CL as long as the resistor can be disconnected between the pair of electrodes 50.

[0055] In this way, the strain gauge according to the first embodiment has multiple grid parts, and when attaching the strain gauge, the grid parts with good creep characteristics are selected and the others are disconnected, making it possible to create a strain gauge that exhibits appropriate creep characteristics under the conditions of use. Therefore, according to the first embodiment, it is possible to realize a strain gauge that exhibits more appropriate creep characteristics.

[0056] (Manufacturing method of strain gauge 1) A method for manufacturing the strain gauge 1 according to this embodiment will be described below. 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 resistors 31r, 32r, 33r, and the first metal layer 41. Therefore, the material and thickness of the metal layer A are the same as the material and thickness of the resistors 31r, 32r, 33r, and the first metal layer 41 described above.

[0057] The metal layer A can be formed by, for example, a magnetron sputtering method using a target made of a raw material capable of forming the metal layer A. The metal layer A may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulsed laser deposition method, or the like instead of the magnetron sputtering method.

[0058] From the viewpoint of stabilizing the gauge characteristics, before forming the metal layer A, a functional layer of a predetermined thickness may be vacuum-deposited as a base layer on the upper surface 10a of the base material 10 by, for example, conventional sputtering.

[0059] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 31r, resistor 32r, and resistor 33r). The functional layer preferably further has a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and a function of improving adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0060] Since the insulating resin film that constitutes the substrate 10 contains oxygen and moisture, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A, particularly when the metal layer A contains Cr, since Cr forms a self-oxidized film.

[0061] 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 metal layer A, and can be appropriately selected depending on the purpose. For example, the material of the functional layer 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.

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

[0063] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which reduces the detection sensitivity of strain.

[0064] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and the strain detection sensitivity can be further prevented from being reduced due to a part of the current flowing through the resistor flowing through the functional layer.

[0065] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 100 or less of the thickness of the resistor, which can further prevent a part of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

[0066] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0067] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0068] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm, which can promote the crystal growth of α-Cr and can be more easily formed without cracking the functional layer.

[0069] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is made of an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape on the entire upper surface of the substrate 10.

[0070] Furthermore, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, so that the thickness and surface area of ​​the functional layer are increased, and the heat generated by the resistor can be dissipated to the substrate 10. As a result, the deterioration of the measurement accuracy of the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0071] The functional layer can be formed in 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 the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0072] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by a plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0073] There is no particular limitation on the combination of the material of the functional layer and the material of the metal layer A, and it can be appropriately selected according to 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.

[0074] 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 Cr2N contained in the Cr mixed phase film, and the ratio of Cr2N in CrN and Cr2N can be adjusted by changing the amount and pressure of the nitrogen gas introduced (nitrogen partial pressure) or by adjusting the heating temperature by providing a heating process.

[0075] 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 containing α-Cr, which has a stable crystal structure, as the main component, can be formed. Furthermore, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby 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. When the functional layer is formed of Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

[0076] When metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of 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.

[0077] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystal phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0078] Next, the second metal layer 42 and the electrode 50 are formed on the upper surface of the metal layer A. The second metal layer 42 and the electrode 50 can be formed by, for example, a photolithography method.

[0079] Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of the metal layer A. Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to form openings that expose the regions in which the second metal layer 42 and the electrode 50 are to be formed. At this time, the shape of the openings in the resist can be adjusted to give the second metal layer 42 and the electrode 50 any shape. For example, a dry film resist can be used as the resist.

[0080] Next, for example, the second metal layer 42 and the electrode 50 are formed on the seed layer exposed in the opening by electrolytic plating using the seed layer as a power supply path. The electrolytic plating method is preferable in that it has high tact and can form low-stress electrolytic plating layers as the second metal layer 42 and the electrode 50. By making the electrolytic plating layer thick and low-stress, it is possible to prevent warping of the strain gauge 1. The second metal layer 42 and the electrode 50 may also be formed by electroless plating.

[0081] Next, the resist is removed. For example, the resist can be removed by immersing the resist in a solution that can dissolve the resist material.

[0082] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to be patterned into a planar shape similar to the resistors 31r to 33r, the wiring 40, and the electrode 50 in Fig. 1. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and the seed layer exposed from the resist, thereby forming the resistors 31r to 33r, the wiring 40, and the electrode 50 in the planar shape of Fig. 1.

[0083] For example, unnecessary portions of the metal layer A and the seed layer can be removed by wet etching. If a functional layer is formed below the metal layer A, the functional layer is patterned by etching into the planar shape shown in Fig. 1, similar to the resistors 31r-33r, the wiring 40, and the electrode 50. At this point, a seed layer is formed on the resistors 31r-33r and the first metal layer 41.

[0084] Next, the second metal layer 42 and the electrode 50 are used as an etching mask to remove unnecessary seed layer exposed from the second metal layer 42 and the electrode 50, thereby forming the second metal layer 42 and the electrode 50. Note that the seed layer directly below the second metal layer 42 and the electrode 50 remains. For example, the unnecessary seed layer can be removed by wet etching using an etching solution that etches the seed layer but does not etch the functional layer, resistors 31r to 33r, wiring 40, and electrode 50.

[0085] Thereafter, as necessary, a cover layer 60 that covers the resistors 31r to 33r and the wiring 40 and exposes the electrodes 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistors 31r to 33r and the wiring 40 and expose the electrodes 50, and then heating and curing the film. The cover layer 60 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 resistors 31r to 33r and the wiring 40 and expose the electrodes 50, and then heating and curing the resin. The opening that exposes the electrodes 50 can be formed, for example, by photolithography.

[0086] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the resistors 31r-33r and the first metal layer 41, the strain gauge 1 has a cross-sectional shape as shown in Fig. 5. The layer indicated by reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is, for example, the same as that shown in Fig. 1. However, as described above, the functional layer 20 may be formed solidly on a part or all of the upper surface 10a of the substrate 10.

[0087] Second Embodiment In the second embodiment, an example of a strain sensor including a plurality of strain gauges, specifically two strain gauges, will be described. When configuring the strain sensor, the plurality of strain gauges may be connected to each other by sharing at least one of their electrodes to form a bridge circuit.

[0088] 6 is a plan view illustrating the strain sensor 2 according to the second embodiment. The strain sensor 2 includes a substrate 110, a strain detection unit 130A, a strain detection unit 130B, a wiring 140A, a wiring 140B, a wiring 140C, an electrode 150A, an electrode 150B, a wiring 150C, and a cover layer 160. The strain detection unit 130A, the strain detection unit 130B, the wiring 140A, the wiring 140B, and the wiring 140C are formed on a surface 110a of the substrate 110. The strain sensor 2 may also have a dummy wiring 140E formed in the same manner as the wiring 140A, the wiring 140B, and the wiring 140C.

[0089] The wiring 140A has an electrode 150A on its upper surface. The wiring 140B has an electrode 150B on its upper surface. The wiring 140C has an electrode 150C on its upper surface. In the strain sensor 2, the electrodes 150A and 150B form a pair of electrodes, and the electrodes 150B and 150C form yet another pair of electrodes.

[0090] Since the strain detection unit 130A and the strain detection unit 130B are formed in the same manner as the strain detection unit 30, the description of the first embodiment is to be referred to and detailed description is omitted here. Note that the thin body portion of the resistor in the strain detection unit 130A has a longitudinal direction in the Y-axis direction, and the thin body portion of the resistor in the strain detection unit 130B has a longitudinal direction in the X-axis direction.

[0091] The strain detector 130A is connected to the wiring 140A and the wiring 140B. The strain detector 130B is connected to the wiring 140B and the wiring 140C.

[0092] The wiring 140A has a first metal layer 141A and a second metal layer 142A laminated on the upper surface of the first metal layer 141A. The wiring 140B has a first metal layer 141B and a second metal layer 142B laminated on the upper surface of the first metal layer 141B. The wiring 140C has a first metal layer 141C and a second metal layer 142C laminated on the upper surface of the first metal layer 141C. The dummy wiring 140E has a first metal layer 141E and a second metal layer 142E laminated on the upper surface of the first metal layer 141E.

[0093] For details of the first metal layer 141A etc., please refer to the description of the first metal layer 41 having a similar configuration. Also, for details of the second metal layer 142A etc., please refer to the description of the second metal layer 42 having a similar configuration.

[0094] The strain sensor according to the second embodiment includes at least one strain gauge having a plurality of grid portions. As with the strain gauge according to the first embodiment, when attaching the strain sensor, the strain gauge having the plurality of grid portions can be made to have appropriate creep characteristics under the conditions of use by selecting grid portions with good creep characteristics and disconnecting the others. Therefore, it can be said that the strain sensor according to the second embodiment as a whole has more appropriate creep characteristics. Therefore, the strain sensor according to the second embodiment can realize a strain gauge that has more appropriate creep characteristics.

[0095] In the strain sensor 2, each of the strain detection unit 130A and the strain detection unit 130B includes a plurality of grid portions, but either one of the strain detection unit 130A or the strain detection unit 130B may include a plurality of grid portions.

[0096] Third Embodiment In the third embodiment, an example of a strain sensor including a plurality of strain gauges, specifically, four strain gauges, will be described. When configuring the strain sensor, the plurality of strain gauges may be connected to each other by sharing at least one of their electrodes to form a bridge circuit.

[0097] 7 is a plan view illustrating a strain sensor 3 according to a third embodiment. The strain sensor 3 includes a substrate 210, a strain detection unit 230A, a strain detection unit 230B, a strain detection unit 230C, and a strain detection unit 230D, a wiring 240A, a wiring 240B, a wiring 240C, and a wiring 240D, an electrode 250A, an electrode 250B, an electrode 250C, and an electrode 250D, and a cover layer 260. The strain detection unit 230A, the strain detection unit 230B, the strain detection unit 230C, the strain detection unit 230D, the wiring 240A, the wiring 240B, the wiring 240C, and the wiring 240D are formed on a surface 210a of the substrate 210. The strain sensor 3 may also have a dummy wiring 240E formed in the same manner as each of the wiring 240A, the wiring 240B, the wiring 240C, and the wiring 240D.

[0098] The wiring 240A has an electrode 250A on its upper surface. The wiring 240B has an electrode 250B on its upper surface. The wiring 240C has an electrode 250C on its upper surface. The wiring 240D has an electrode 250D on its upper surface. The electrodes 250A and 250B, the electrodes 250B and 250C, the electrodes 250C and 250D, and the electrodes 250D and 250A each form a pair of electrodes.

[0099] Since each of the strain detection units 230A, 230B, 230C, and 230D is formed in the same manner as the strain detection unit 30, the description of the first embodiment is to be referred to and detailed description is omitted here. Note that the thin body portion of the resistor in each of the strain detection units 230A and 230C has a longitudinal direction in the X-axis direction, and the thin body portion of the resistor in each of the strain detection units 230B and 230D has a longitudinal direction in the Y-axis direction.

[0100] The strain detection unit 230A connects to the wiring 240A and the wiring 240B. The strain detection unit 230B connects to the wiring 240B and the wiring 240C. The strain detection unit 230C connects to the wiring 240C and the wiring 240D. The strain detection unit 230D connects to the wiring 240D and the wiring 240A.

[0101] The wiring 240A has a first metal layer 241A and a second metal layer 242A laminated on the upper surface of the first metal layer 241A. The wiring 240B has a first metal layer 241B and a second metal layer 242B laminated on the upper surface of the first metal layer 241B. The wiring 240C has a first metal layer 241C and a second metal layer 242C laminated on the upper surface of the first metal layer 241C. The wiring 240D has a first metal layer 241D and a second metal layer 242D laminated on the upper surface of the first metal layer 241D. The dummy wiring 240E has a first metal layer 241E and a second metal layer 242E laminated on the upper surface of the first metal layer 241E.

[0102] For details of the first metal layer 241A etc., please refer to the description of the first metal layer 41 having a similar configuration. Also, for details of the second metal layer 242A etc., please refer to the description of the second metal layer 42 having a similar configuration.

[0103] The strain sensor according to the third embodiment includes at least one strain gauge having a plurality of grid portions. As with the strain gauge according to the first embodiment, when attaching the strain sensor, the strain gauge having the plurality of grid portions can be made to have appropriate creep characteristics under the conditions of use by selecting grid portions with good creep characteristics and disconnecting the others. Therefore, it can be said that the strain sensor according to the third embodiment as a whole has more appropriate creep characteristics. Therefore, the strain sensor according to the third embodiment can realize a strain gauge that has more appropriate creep characteristics.

[0104] In the strain sensor 3, each of the strain detection unit 230A, the strain detection unit 230B, the strain detection unit 230C and the strain detection unit 230D has a plurality of grid portions, but at least one of the strain detection unit 230A, the strain detection unit 230B, the strain detection unit 230C and the strain detection unit 230D may have a plurality of grid portions.

[0105] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims. [Explanation of symbols]

[0106] 1 strain gauge, 2, 3 strain sensor, 10, 110, 210 substrate, 31, 32, 33 grid portion, 31r, 32r, 33r resistor, 31re, 32re, 33re elongated portion, 40, 140A, 140B, 140C, 240A, 240B, 240C, 240D wiring, 41, 141A, 141B, 141C, 241A, 241B, 241C, 241D first metal layer, 42, 142A, 142B, 142C, 242A, 242B, 242C, 242D second metal layer, 50, 50, 150A, 150B, 150C, 250A, 250B, 250C, 250D Electrode, 60, 160, 260 Cover layer

Claims

1. Substrate and A pair of electrodes formed on the substrate, The substrate has a plurality of grid portions formed on it, Each of the aforementioned grid sections includes a resistor. Each of the resistors in the plurality of grid sections is connected in series with the pair of electrodes, and is connected in parallel with each other. The resistor has a shape in which elongated parts are connected in series, with their longitudinal direction facing the first direction when viewed from above. A strain gauge in which the width in the short direction of the elongated portion of the resistor included in each of the plurality of grid sections differs for each grid section.

2. The strain gauge according to claim 1, wherein the spacing between the elongated portions of the resistors included in each of the plurality of grid sections is different for each grid section.

3. The strain gauge according to claim 1 or 2, wherein the number of elongated portions of the resistor included in each of the plurality of grid portions differs for each grid portion.

4. The resistor is made of Cr, CrN, and Cr ２ A strain gauge according to claim 1 or 2, formed from a film containing N.

5. A strain sensor comprising a plurality of strain gauges according to claim 1 or 2, A strain sensor in which the plurality of strain gauges are connected by sharing at least one of their respective pairs of electrodes to form a bridge circuit.

Images