JP2022186395A - strain gauge - Google Patents

Abstract

To provide a strain gauge which can be used for scales.SOLUTION: A strain gauge disclosed herein comprises a flexible base material and multiple resistors formed of films containing Cr, CrN, and Cr2N provided on the base material, the resistors being arranged to have grid directions thereof pointing in the same direction and connected in parallel. The resistors connected in parallel have resistance in a range of 160-600 Ω, inclusive.SELECTED DRAWING: Figure 5

Description

The present invention relates to strain gauges.

A strain gauge is known that has a resistor on a base material, is attached to an object to be measured, and detects the characteristics of the object to be measured. BACKGROUND ART Strain gauges are used, for example, as sensors that detect strain in materials and sensors that detect ambient temperature (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2001-221696

However, strain gauges are sometimes used for weighing applications in addition to being used for sensors, and in such cases, it is necessary to satisfy a stricter creep standard than for sensor applications. Therefore, even strain gauges that can be used for sensors cannot be used for scales in some cases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a strain gauge that can be used for weighing scales.

The strain gauge has a flexible base material, and a plurality of resistors formed on the base material from films containing Cr, CrN, and _Cr2N , each of the resistors are arranged with the grid direction facing the same direction and connected in parallel with each other, and the resistance value of the resistors connected in parallel is 160 Ω or more and 600 Ω or less.

According to the technology disclosed, it is possible to provide a strain gauge that can be used for scales.

1 is a plan view illustrating a strain gauge according to a first embodiment; FIG. 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment; FIG. FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment; It is a figure explaining the measuring method of the amount of creeps, and the amount of creep recovery. It is a figure which shows the examination result of the resistance value, the amount of creep, and the amount of creep recovery. FIG. 3 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First embodiment>
1 is a plan view illustrating a strain gauge according to a first embodiment; FIG. FIG. 2 is a cross-sectional view (Part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in FIG. FIG. 3 is a cross-sectional view (No. 2) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in FIG.

Referring to FIGS. 1 to 3, the strain gauge 1 has a three-layer structure in which a _{second layer 1-2 and} a third layer _1-3 are sequentially laminated on a first layer 1-1. In each of the first layer 1 ₁ , the second layer 1 ₂ , and the third layer 1 ₃ , resistors for detecting strain are arranged with the grid direction facing the same direction. A detailed description will be given below.

The first layer _1-1 has a substrate _10-1 , and a resistor 30-1 and _a wiring 40-1 formed on the _upper surface 10a of the substrate _10-1 . The _second layer _1-2 has a substrate _10-2 and a resistor _30-2 and a wiring 40-2 formed on the upper surface 10b of the substrate _10-2 . _The substrate _10-2 is laminated on the substrate _10-1 by covering the resistor 30-1. The _third layer _1-3 has a substrate 10-3 _, and a resistor 30-3 _, a wiring 40-3 _, and an electrode 50-3 formed _on the upper surface 10c of the substrate 10-3. _The substrate _10-3 is laminated on the substrate _10-2 by covering the resistor 30-2. A cover layer 60 is formed on the _third layer 13 if necessary. 1 to 3, only the outer edge of the cover layer 60 is indicated by broken lines for the sake of convenience.

In the present embodiment, for the sake of convenience, in the strain gauge 1, the side of each substrate on which the resistor is provided is the upper side or one side, and the side on which the resistor is not provided is the lower side or the other side. . The surface of each substrate on which the resistor is provided is defined as one surface or upper surface, and the surface on which the resistor is not provided is defined as the other surface or lower surface. However, the strain gauge 1 can be used upside down or arranged at any angle. Further, the term “planar view” refers to viewing an object from the direction normal to the upper surface 10c of the substrate 103 _, and the term “planar shape” refers to the shape of the object viewed from the direction normal to the upper surface 10c of the substrate ₁₀₃ . shall point to

Although the planar shapes of the resistors _30-1 and 30-2 _are not shown, they _are similar to the resistor 30-3. The resistors _30-1 and 30-2 _are formed, for example, at positions overlapping the resistor _30-3 in plan view. Although the planar shapes of the wirings _40-1 and 40-2 _are not shown, they _are similar to the wiring 40-3. The wirings _40-1 and 40-2 _are formed, for example, at positions overlapping with the wiring _40-3 in plan view.

The base material _10-3 is a member that serves as a base layer for forming the resistor _30-3 and the like, and has flexibility. The film thickness of the base material ₁₀₃ is not particularly limited and can be appropriately selected according to the purpose. _In particular, the film thickness of the substrate 103 is preferably 5 μm to 200 μm from the viewpoint of strain transmission and dimensional stability against the environment, and more preferably 10 μm or more from the viewpoint of insulation.

The base material 103 is made of _, for example, PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP ( It can be formed from an insulating resin film such as a liquid crystal polymer) resin, polyolefin resin, or the like. Note that the film refers to a flexible member having a film thickness of about 500 μm or less.

Here, "formed from an insulating resin film" does not prevent the base material 103 from containing fillers _, impurities, etc. in the insulating resin film. The substrate 103 may be formed from an insulating resin film containing filler such as silica or alumina _, for example.

Materials other than the resin of the substrate 103 include, for example, SiO ₂ , ZrO ₂ (including YSZ), Si, Si ₂ N ₃ , Al ₂ O ₃ (including sapphire), ZnO, perovskite ceramics ₍ CaTiO ₃ , BaTiO ₃ ) and the like, and also amorphous glass and the like. Also, as the material of the base material 103 _, a metal such as aluminum, an aluminum alloy (duralumin), or titanium may be used. In this case, for example, an insulating film is formed _on the base material 103 made of metal.

The resistor 30-3 is a thin film formed in a predetermined pattern _on the base material 10-3 _, and is a sensing part that undergoes a change in resistance when subjected to strain. The resistor 30-3 may be formed directly _on the upper surface 10c of the base material 10-3 _, or may be formed _on the upper surface 10c of the base material 10-3 via another layer. In addition, in FIG. 1, the resistor ₃₀₃ is shown with a dark pear-skin pattern for the sake of convenience.

The resistor ₃₀₃ has a plurality of elongated portions oriented in the same longitudinal direction (the direction of line AA in FIG. 1) and arranged at predetermined intervals, and the ends of adjacent elongated portions are alternately connected. It has a zigzag folding structure as a whole. The longitudinal direction of the elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction of line BB in FIG. 1).

One ends in the longitudinal direction of the two elongated portions located on the outermost side in the grid width direction are bent in the grid width direction, and terminate at respective ends 30 ₃ e ₁ and 30 ₃ e ₂ of the resistor 30 ₃ in the grid width direction. to form _Each end _30-3e1 and _303e2 of the resistor _30-3 in the _grid width direction is electrically connected to the electrode _50-3 via the wiring _40-3 . _In other words, the wiring _40-3 electrically connects the ends _30-3e1 and _303e2 of the resistor _30-3 in the grid width direction and _each electrode _50-3 .

The resistor ₃₀₃ can be made of, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor ₃₀₃ can be made of a material containing at least one of Cr and Ni. Materials containing Cr include, for example, a Cr mixed phase film. Materials containing Ni include, for example, Cu—Ni (copper nickel). Materials containing both Cr and Ni include, for example, Ni—Cr (nickel chromium).

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N, or the like is mixed. The Cr mixed phase film may contain unavoidable impurities such as chromium oxide.

The thickness of the resistor ₃₀₃ is not particularly limited, and can be appropriately selected according to the purpose. In particular, it is preferable that the thickness of the resistor ₃₀₃ is 0.1 μm or more because the crystallinity of the crystal forming the resistor ₃₀₃ (for example, the crystallinity of α-Cr) is improved. Further, if the thickness of the resistor ₃₀₃ is ₁ μm or less, cracks in the film and warping from the substrate 103 due to internal stress of the film forming the resistor ₃₀₃ can be reduced.

The width of the resistor ₃₀₃ is preferably 10 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less, and even more preferably 10 μm or more and 50 μm or less, in order to make the lateral sensitivity less likely to occur and to prevent disconnection.

For example, when the resistor ₃₀₃ is a Cr mixed phase film, the stability of 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 the resistor ₃₀₃ , the gauge factor of the strain gauge 1 is 10 or more, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR are in the range of -1000 ppm/°C to +1000 ppm/°C. can be within Here _, the term “main component” means that the target substance accounts for 50% by weight or more of all substances constituting the resistor. % or more, more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

Further, when the resistor ₃₀₃ is a Cr mixed phase film, CrN and Cr ₂ N contained in the Cr mixed phase film are preferably 20% by weight or less. When CrN and Cr ₂ N contained in the Cr mixed phase film are 20% by weight or less, a decrease in gauge factor can be suppressed.

Also, the ratio of Cr ₂ N in CrN and Cr ₂ N is preferably 80% by weight or more and less than 90% by weight, more preferably 90% by weight or more and less than 95% by weight. When the ratio of Cr ₂ N in CrN and Cr ₂ N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more pronounced due to Cr ₂ N having semiconducting properties. . Furthermore, by reducing ceramicization, brittle fracture is reduced.

On the other hand, when a small amount of N ₂ or atomic N is mixed in the film and is present, the external environment (for example, high temperature environment) causes a change in the film stress by escaping from the film. By creating chemically stable CrN, a stable strain gauge can be obtained without generating unstable N.

The wiring _40-3 is formed _on the base material _10-3 and electrically connected to the resistor _30-3 and the electrode 50-3. The wiring ₄₀₃ is not limited to a straight line, and can have any pattern. Also _, the wiring 403 can be of any width and any length. _In FIG. ₁ , for convenience, the wiring 40-3 and the electrode 50-3 are shown in a pear _- skin pattern that is thinner than the resistor 30-3.

The electrode _50-3 is formed _on the base material _10-3 and electrically connected to the resistor _30-3 through the wiring _40-3 . there is The electrodes 50 ₃ are a pair of electrodes for outputting to the outside the change in resistance value caused by the strain of the resistors 30 ₁ , 30 ₂ , and 30 ₃ . For example, lead wires for external connection are connected. be.

Although the resistor ₃₀₃ , the wiring 403 _, and the electrode 503 _are given different symbols for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30-3 _, the wiring _40-3 and the electrode _50-3 have substantially the same thickness.

A conductive layer made of a material having a resistance lower than that of the resistor _30-3 may be stacked over the wiring _40-3 and the electrode _50-3 . The material of the conductive layer to be laminated is not particularly limited as long as it has a lower resistance than that of the resistor ₃₀₃ , and can be appropriately selected according to the purpose. For example, when the resistor ₃₀₃ is a Cr mixed phase film, Cu, Ni, Al, Ag, Au, Pt, etc., alloys of any of these metals, compounds of any of these metals, or any of these Laminated films obtained by appropriately laminating metals, alloys, and compounds of the above. The thickness of the conductive layer is not particularly limited and can be appropriately selected according to the purpose, and can be, for example, about 3 μm to 5 μm.

When a conductive layer made of a material having a lower resistance than that of the resistor 30-3 is laminated _on the wiring _40-3 and the electrode 50-3 in this way _, the wiring _40-3 has a lower resistance than the resistor _30-3 . It is possible to suppress the wiring ₄₀₃ from functioning as a resistor. As a result, the accuracy of strain detection by the resistor ₃₀₃ can be improved.

_In other words, by providing the wiring 40-3 having a resistance lower than that of the resistor 30-3 _, it is possible to limit the substantial sensing portion of the strain gauge ₁ to the local region where the resistor 30-3 is formed. Therefore, the strain detection accuracy by the resistor ₃₀₃ can be improved.

_In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more using a Cr mixed phase film as the resistor ₃₀₃ , the resistance of the wiring 403 is made lower than that of the resistor ₃₀₃ so that the substantial sensing part is replaced by the resistor ₃₀₃ . Restricting to the local region where is formed exhibits a significant effect in improving strain detection accuracy. Further _, making the resistance of the wiring _40-3 lower than that of the resistor 30-3 also has the effect of reducing the lateral sensitivity.

The base material _{10 3} , the resistor 30 ₃ , the wiring 40 ₃ and the electrode _{50 3} of the third layer _{1 3} have been described above. 40 ₁ , the base material 10 ₂ , the resistor 30 ₂ and the wiring 40 ₂ of the second layer 1 ₂ are the same as the base material 10 ₃ , the resistor 30 ₃ and the wiring 40 ₃ of the third layer 1 ₃ is. However _, the portion corresponding to the electrode 50-3 is not provided in the first layer _1-1 and the _second layer 1-2.

A cover layer ₆₀ may be provided _on the upper surface 10c of the substrate 10-3 so as to cover the resistor _30-3 and expose the electrode 50-3. By providing the cover layer ₆₀ , the resistor 303 can be prevented from being mechanically damaged. Also, by providing the cover layer 60, the resistor ₃₀₃ can be protected from moisture and the like. Note that the cover layer ₆₀ may be provided so as to cover the entire portion excluding the electrode 503 .

The cover layer 60 can be made of insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (eg, silicone resin, polyolefin resin). The cover layer 60 may contain fillers or pigments. The thickness of the cover layer 60 is not particularly limited, and can be appropriately selected according to the purpose.

[Low resistance]
In the strain gauge ₁ , the wiring 40-1, the wiring 40-2, and the wiring 40-3 are connected to each other by _two through holes 70 provided in the vicinity of _each of the _two electrodes 50-3. As _a result, resistors 30-1 _, 30-2, and 30-3 _are connected in parallel with each other. _The resistors 30-1 _, 30-2, and 30-3 _are formed, for example, to have substantially the same resistance value, and are connected in parallel. As a result, the overall resistance value is reduced by about one- _third for _each of resistors 30-1 _, 30-2, and 30-3. _The resistance value between the _pair of electrodes _50-3 is the resistance value of the resistors 30-1 _, 30-2 and 30-3 connected in parallel.

The through hole 70 is provided in a through hole penetrating at _least the base materials _10-2 and 10-3. The through hole 70 may be formed using the same material as the resistor ₃₀₃ or the like, or may be formed using a low resistance material such as copper. Also, the position of the through _- hole 70 may be arbitrary as long as the resistors _{30-1 ,} 30-2 and 30-3 can be connected in parallel. For example, resistors 30 ₁ , 30 ₂ and 30 ₃ may be connected in parallel by providing through holes 70 in the vicinity of the termination of each resistor in each layer without providing the wirings 40 ₁ and 40 ₂ . Alternatively _, dummy electrodes corresponding to the electrodes 50-3 may be formed on the substrates _10-1 and _10-2 , and the electrodes _50-3 and the respective dummy electrodes may be connected through the through holes 70. FIG. The number of through _- holes may be arbitrary as long as resistors _{30-1 ,} 30-2 and 30-3 can be connected in parallel. For example, if the resistance value of through holes is a problem, the number of through holes may be increased as appropriate.

When using the strain gauge 1 for weighing applications, it is necessary to satisfy the standard for creep. Standards related to creep include, for example, accuracy grade C1 based on OIML R60 (hereinafter referred to as C1 standard) and accuracy grade C2 based on OIML R60 (hereinafter referred to as C2 standard).

The C1 standard requires that the creep amount and creep recovery amount be ±0.0735% or less. In addition, the C2 standard requires that the amount of creep and the amount of creep recovery be ±0.0368% or less. When the strain gauge 1 is used as a sensor, the standard for creep amount and creep recovery amount is about ±0.5%.

As a result of intensive studies by the inventors, creep is highly dependent on the resistance value of the resistor connected between the pair of electrodes 503 _, and in order to satisfy the C1 standard and the C2 standard _, It has been found that the resistance value of the resistor connected to is required to be relatively low.

Therefore, the inventors studied the resistance value of the resistor connected between the pair of electrodes 503 _, which is necessary for reducing the amount of creep and the amount of creep recovery. Specifically, a plurality of strain gauges 1 with different resistance values of resistors connected between a pair of electrodes 503 _are produced, and each strain gauge 1 is attached on a strain-generating body made of SUS304, and creeping is performed. Quantity and creep recovery were measured. As the substrates 10 ₁ , 10 ₂ , and 10 ₃ , polyimide resin films having a film thickness of 25 μm were used. Cr mixed-phase films were used for the resistors 30 ₁ , 30 ₂ , and 30 ₃ .

Since the creep amount and the creep recovery amount are the amount of elastic deformation (strain amount) of the surface on which the resistors 30 ₁ , 30 ₂ , and 30 ₃ are provided in the strain gauge 1, change over time, can be measured by monitoring the strain voltage calculated based _on the output between the electrodes 503. A detailed description will be given with reference to FIG.

FIG. 4 is a diagram explaining a method of measuring the creep amount and the creep recovery amount. In FIG. 4, the horizontal axis is time, and the vertical axis is strain voltage [mV].

First, 10 seconds after turning on the power to the measuring device, a 150% load is applied to the strain gauge 1 attached to the strain generating body for 10 seconds, and then the load is removed. When 20 minutes have passed after the unloading, a 100% load is applied to the strain gauge 1 attached to the strain generating body for 20 minutes, and then the load is unloaded. Then, wait for 20 minutes after unloading.

The strain voltage changes, for example, as shown in FIG. In FIG. 4, the absolute value B of the strain voltage difference is measured 20 minutes after the 150% load is removed and immediately after the 100% load is applied. In addition, the absolute value ΔA of the difference in strain voltage immediately after application of 100% load and 20 minutes after the start of application of 100% load is measured. At this time, ΔA/B is the amount of creep. Next, the absolute value ΔC of the difference in strain voltage immediately after the 100% load is removed and 20 minutes after the 100% load is removed is measured. At this time, ΔC/B is the amount of creep recovery.

The 100% load is 3 kg, and the 150% load is 1.5 times the 100% load.

FIG. ₅ is a diagram showing the results of examination of the resistance value, creep amount, and creep recovery amount. It summarizes the results of measuring the amount of recovery by the measuring method of FIG.

As shown in FIG. 5, when the resistance value of the resistor connected between the pair of electrodes 503 is _160Ω or more and 600Ω or less, the C1 standard creep amount and creep recovery amount can be satisfied. Further, as shown in FIG. 5, if the resistance value of the resistor connected between the pair of electrodes 503 is _210Ω or more and 400Ω or less, the C2 standard creep amount and creep recovery amount can be satisfied. That is, by controlling the resistance value of the resistor connected between the pair of electrodes ₅₀₃ within a predetermined range, the amount of creep and the amount of creep recovery are improved, so that the strain gauge 1 can be used for weighing purposes.

In order to obtain a resistance value that satisfies the C1 standard or C2 standard, it is conceivable to widen the width of the resistor. In this case, widening the width of the resistor causes an effect of lateral sensitivity due to the high sensitivity, which is not preferable. On the other hand, if the resistance is reduced by connecting multiple resistors in parallel like the strain gauge 1, a resistance value that satisfies the C1 or C2 standard can be achieved without exposing the problem of lateral sensitivity. can.

In the above example, the strain gauge 1 has a three-layer structure in which the _{second layer 1-2 and} the third layer _1-3 are sequentially laminated on the first layer 1-1. The gauge 1 may have a two-layer structure, or may have a structure of four or more layers.

Moreover, the method of lowering the resistance is not necessarily limited to the method of stacking a plurality of resistors and connecting the respective resistors in parallel with each other through through holes. For example, a plurality of resistors are arranged on the upper surface of one base material with the grid direction oriented in the same direction, and each resistor is connected in parallel with each other by wiring provided on the upper surface of the base material to reduce the resistance. good too. However, when multiple resistors are placed on the top surface of one substrate, the area of the top surface of the substrate becomes large. A structure in which the resistors are connected in parallel with each other by means of through-holes is more advantageous.

[Manufacturing method of strain gauge]
Here, a method for manufacturing the strain gauge 1 will be described. In order to manufacture the strain gauge 1, _first , the substrate _10-1 is prepared, and a metal layer (referred to as a metal layer A for convenience) is formed on the upper surface 10a of the substrate 10-1. The metal layer _A is a layer that is finally patterned to become the resistor _30-1 and the wiring 40-1. Therefore, the material and thickness of the metal layer _A are the same as those of the resistor _30-1 and the wiring 40-1.

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

From the viewpoint of stabilizing the gauge characteristics, before forming the metal layer A, a functional layer having a predetermined thickness is vacuum-formed on the _upper surface 10a of the base material 101 as a base layer by conventional sputtering, for example. is preferred.

In the present application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper metal layer A (resistor 30 ₁ ). The functional layer may further have a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material _10-1 and a function of improving adhesion between the base material _10-1 and the metal layer A. preferable. The functional layer may also have other functions.

Since the insulating resin film constituting the base material 101 contains oxygen and moisture, especially when the metal layer _A contains Cr, Cr forms a self-oxidizing film, so the functional layer prevents the metal layer A from being oxidized. Having functions is effective.

The material of the functional layer is not particularly limited as long as it has a function of promoting the crystal growth of at least the upper metal layer A (resistor 30 ₁ ), and can be appropriately selected according to the purpose. (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), Al (aluminum) Mention may be made of one or more metals, alloys of any metal of this group, or compounds of any metal of this group.

Examples of the above alloy include FeCr, TiAl, FeNi, NiCr, CrCu, and the like. Examples of the above compounds include TiN, _TaN , _Si3N4 , _TiO2 , _Ta2O5 , _{SiO2 and} the like.

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. Within this range, it is possible to promote the crystal growth of α-Cr, and to prevent a part of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in strain detection sensitivity.

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. Within this range, it is possible to promote the crystal growth of α-Cr, and further prevent the deterioration of the strain detection sensitivity due to part of the current flowing through the resistor flowing through the functional layer.

When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is more preferably 1/100 or less of the thickness of the resistor. Within such a range, it is possible to further prevent a decrease in strain detection sensitivity due to part of the current flowing through the resistor flowing through the functional layer.

When the functional layer is made of an insulating material such as oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within such a range, the crystal growth of α-Cr can be promoted, and the film can be easily formed without causing cracks in the functional layer.

When the functional layer is made of an insulating material such as oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within such a range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracks.

When the functional layer is made of an insulating material such as oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm. Within such a range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracks.

The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. If the functional layer is made of an insulating material, it may not be patterned in the same planar shape as the resistor. In this case, the functional layer may be solidly formed at least in the region where the resistor is formed. Alternatively, the functional layer may be formed all over the _top surface of the substrate 101 .

Further, when the functional layer is formed of an insulating material, the thickness and surface area of the functional layer can be increased by forming the functional layer relatively thick such that the thickness is 50 nm or more and 1 μm or less and forming the functional layer in a solid manner. Since the resistance increases, the heat generated by the resistor can be dissipated to the substrate 101 _side . As a result, in the strain gauge 1, deterioration in measurement accuracy due to self-heating of the resistor can be suppressed.

The functional layer can be formed, for example, by conventional sputtering using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into the chamber in a vacuum. By using the conventional sputtering method, the functional layer is formed while etching the _upper surface 10a of the substrate 101 with Ar, so that the amount of film formation of the functional layer can be minimized and the effect of improving adhesion can be obtained. .

However, this is an example of the method of forming the functional layer, and the functional layer may be formed by another method. For example, before forming the functional layer, the _upper surface 10a of the base material 101 is activated by plasma treatment using Ar or the like to obtain the adhesion improvement effect, and then the functional layer is vacuum-formed by magnetron sputtering. You may use the method of film|membrane.

The combination of the material of the functional layer and the material of the metal layer A is not particularly limited and can be appropriately selected according to the purpose. It is possible to form a Cr mixed phase film as a main component.

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 the chamber. Alternatively, the metal layer A may be formed by reactive sputtering using pure Cr as a target, introducing an appropriate amount of nitrogen gas into the chamber together with Ar gas. At this time, by changing the introduction amount and pressure (nitrogen partial pressure) of nitrogen gas and adjusting the heating temperature by providing a heating process, the ratio of CrN and Cr ₂ N contained in the Cr mixed phase film, and the ratio of CrN and Cr _The proportion of _Cr2N in 2N can be adjusted.

In these methods, the growth surface of the Cr mixed phase film is defined by the functional layer made of Ti, and a Cr mixed phase film containing α-Cr, which has a stable crystal structure, as a main component can be formed. In addition, the diffusion of Ti constituting the functional layer into the Cr mixed phase film improves the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. When the functional layer is made of Ti, the Cr mixed phase film may contain Ti or TiN (titanium nitride).

When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has the function of promoting the crystal growth of the metal layer A and preventing the metal layer _A from being oxidized by oxygen and moisture contained in the base material 101. It has all of the function and the function of improving the adhesion between the base material ₁₀₁ and the metal layer A. The same is true when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

In this way, by providing the functional layer under the metal layer A, the crystal growth of the metal layer A can be promoted, and the metal layer A having a stable crystal phase can be produced. As a result, in the strain gauge 1, the stability of gauge characteristics can be improved. Further, by diffusing the material forming the functional layer into the metal layer A, the gauge characteristics of the strain gauge 1 can be improved.

Next, the metal layer _A is patterned by photolithography to form the resistor _30-1 and the wiring 40-1. Thereby, the _first layer 11 is completed.

Next, a _second layer 12 and a _third layer 13 are produced in the same manner as above. However, in the case of the _third layer _1-3 , a pair of electrodes 50-3 _are formed in addition to the resistor _30-3 and the wiring 40-3 in the step of patterning the metal layer A by photolithography.

Next, the _second layer 12 and the _third layer 13 are sequentially laminated on the _first layer 11, through holes for forming the through holes 70 are formed by a laser processing method or the like, and the through holes are formed by a plating method or the like. A through hole 70 is formed. After the first layer _1-1 is completed, the substrate _10-2 is subsequently laminated on the _first layer 1-1, the resistor 30-2 and the wiring 40-2 _are formed on the substrate _10-2 , and the _second layer is further formed. _A substrate 10-3 may be laminated _{on 12} to form a resistor 30-3 _, a wiring 40-3 _, and an electrode 50-3 _on the substrate 10-3. In this case, after providing a through hole for forming the through hole 70, the resistor 30 ₃ , the wiring 40 ₃ , and the electrode 50 ₃ are formed on the substrate 10 ₃ , and the through hole 70 and the resistor 30 ₃ etc. are formed. They may be integrally formed from the same material.

After that, the strain gauge 1 is completed by providing a cover layer ₆₀ covering the resistor _30-3 and the wiring _40-3 and exposing the electrodes 50-3 on the upper surface 10c of the base material 10-3 _, if necessary. For the cover layer 60 _, for example, a semi-cured thermosetting insulating resin film is laminated _on the upper surface 10c of the base material 103 so as to cover the resistors ₃₀₃ and the wirings 403 and expose the electrodes 503 _, It can be produced by heating and curing. The cover layer ₆₀ is formed by coating the upper surface 10c of the base material 103 with a liquid or paste thermosetting insulating resin so as to cover the resistors ₃₀₃ and the wirings ₄₀₃ and expose the electrodes 503 _, followed by heating. It may be produced by curing with

In addition, when a functional layer is provided on the upper surface of each base material as a base layer for the resistors 30 ₁ , 30 ₂ , 30 ₃ and the like, the strain gauge 1 has a cross-sectional shape as shown in FIG. Layers denoted by reference numerals 20 ₁ , 20 ₂ and 20 ₃ are functional layers. The planar shape of the strain gauge 1 when the functional layers 20 ₁ , 20 ₂ and 20 ₃ are provided is, for example, the same as that shown in FIG. However, as described above, the functional layers 20 ₁ , 20 ₂ , and 20 ₃ may be solidly formed on part or all of the top surface of each substrate.

Although the preferred embodiments and the like have been described in detail above, the present invention is not limited to the above-described embodiments and the like, and various modifications and substitutions can be made to the above-described embodiments and the like without departing from the scope of the claims. can be added.

1 strain gauge, 1 ₁ first layer, 1 ₂ second layer, 1 ₃ third layer, 10 ₁ , 10 ₂ , 10 ₃ substrate, 10a, 10b, 10c upper surface, 20 ₁ , 20 ₂ , 20 ₃ functional layer , 30 ₁ , 30 ₂ , 30 ₃ resistors, 30 ₃ e ₁ , 30 ₃ e ₂ terminations, 40 ₁ , 40 ₂ , 40 ₃ wirings, 50 ₃ electrodes, 60 cover layers, 70 through holes

Claims (7)

a flexible substrate;
a plurality of resistors formed from films containing Cr, CrN, and _Cr2N on the substrate;
each of the resistors is arranged in the same grid direction and connected in parallel to each other;
The strain gauge, wherein the resistor connected in parallel has a resistance value of 160Ω or more and 600Ω or less. 2. The strain gauge according to claim 1, wherein the resistors connected in parallel have a resistance value of 210[Omega] or more and 400[Omega] or less. The base material includes a first base material and a second base material,
the plurality of resistors includes a first resistor formed on the first substrate and a second resistor formed on the second substrate;
The second base is laminated on the first base by covering the first resistor,
3. The strain gauge according to claim 1, wherein said first resistor and said second resistor are connected in parallel with each other through a through-hole penetrating said second substrate. 4. The strain gauge according to any one of claims 1 to 3, wherein the width of each said resistor is between 10 [mu]m and 100 [mu]m. 5. The strain gauge according to any one of claims 1 to 4, having a gauge factor of 10 or more. 6. The strain gauge according to any one of claims 1 to 5, wherein the proportion of CrN and _Cr2N contained in each said resistor is 20% by weight or less. 7. The strain gauge according to any one of claims 1 to 6, wherein the _Cr2N content in the CrN and the _Cr2N is 80% by weight or more and less than 90% by weight.

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