Laminated film, method for producing the same, and strain sensor

Abstract

To provide a laminated film which includes an insulative base material resin film and yet exhibits a temperature coefficient of resistance of 300 ppm / °C or less in absolute terms, and to provide a strain sensor and a method of manufacturing the same.SOLUTION: A laminated film is provided, comprising a base material resin film 2 and a resistance layer 3 arranged in the described order in the thickness direction. The resistance layer 3 contains chromium nitride. The resistance layer 3 contains 3.0-7.0 pts.mol, inclusive, of nitrogen atoms with respect to 100 pts.mol of chromium atoms.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated film, a method for manufacturing the same, and a strain sensor.

Background Art

[0002] Conventionally, a strain sensor including an insulating substrate and a patterned Cr-N thin film disposed on the surface thereof has been known (see, for example, Patent Document 1 below).

[0003] In Patent Document 1, first, a Cr-N thin film is formed on the surface of an insulating substrate to produce a thin film laminated film, and then heat treatment is performed at 300° C. to pattern the Cr-N thin film, thereby manufacturing a strain sensor. In Patent Document 1, by the heat treatment at 300° C., the absolute value of the temperature coefficient of resistance (TCR) of the Cr-N thin film is reduced, and the stability of the strain sensor is improved.

[0004] In addition, a hard silicon substrate is used as the insulating substrate that can withstand the above-described high-temperature heat treatment.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, depending on the application and purpose, a resin substrate made of resin may be used. However, if such a resin substrate is heat-treated at the above-described temperature, the resin substrate will be damaged. Therefore, the resin substrate cannot be heat-treated at a high temperature. In this case, since the absolute value of the temperature coefficient of resistance of the Cr-N thin film cannot be made close to 0, there is a problem that the strain sensor becomes unstable.

[0007] Further, from the viewpoint of improving the sensitivity of the strain sensor, a high gauge factor is required for the Cr-N thin film of the strain sensor.

[0008] The present invention provides a laminated film including an insulating base resin film and a resistance layer having a small absolute value of the temperature coefficient of resistance and a high gauge factor, a method for manufacturing the same, and a strain sensor.

Means for Solving the Problems

[0009] The present invention (1) includes a laminated film including an insulating base resin film and a resistance layer provided in order in the thickness direction, wherein the resistance layer contains chromium nitride, and the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is 3.0 molar parts or more and 7.0 molar parts or less.

[0010] Since this laminated film includes a base resin film and a resistance layer in which the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is 3.0 molar parts or more and 7.0 molar parts or less, by heating the laminated film at a relatively low temperature, the absolute value of the temperature coefficient of resistance of the resistance layer can be reduced while the gauge factor can be increased. Therefore, the strain sensor obtained from this laminated film has excellent stability and good sensitivity.

[0011] The present invention (2) includes the laminated film according to (1), wherein the material of the base resin film is polyimide.

[0012] The present invention (3) includes the laminated film according to (1) or (2), wherein the thickness of the base resin film is 10 μm or more and 200 μm or less.

[0013] The present invention (4) includes the laminated film according to any one of (1) to (3), wherein the thickness of the resistance layer is 10 nm or more and 150 nm or less.

[0014] The present invention (5) includes the laminated film according to any one of (1) to (4), wherein the gauge factor of the resistance layer is 10 or more.

[0015] In this laminated film, since the gauge factor of the resistance layer is 10 or more, a strain sensor with good sensitivity can be obtained.

[0016] The present invention (7) includes the laminated film according to any one of (1) to (6), wherein the absolute value of the temperature coefficient of resistance of the resistance layer is 300 ppm / °C or less.

[0017] In this laminated film, since the absolute value of the temperature coefficient of resistance of the resistance layer is 300 ppm / °C or less, a strain sensor with excellent stability can be obtained.

[0018] The present invention (7) includes a method for manufacturing a laminated film, comprising a step of preparing the laminated film according to any one of (1) to (6), and a step of heating the laminated film at 200°C or lower.

[0019] In this method for manufacturing a laminated film, since the laminated film is heated at 200°C or lower, damage caused by heating of the base resin film can be reduced.

[0020] The present invention (8) includes a strain sensor including an insulating base resin film and a strain sensor portion provided in order in the thickness direction, wherein the strain sensor portion includes patterned chromium nitride, and the molar portion of nitrogen atoms with respect to 100 molar portions of chromium atoms is 3.0 molar portions or more and 7.0 molar portions or less.

[0021] In this strain sensor, by heating at a relatively low temperature, the absolute value of the temperature coefficient of resistance of the strain sensor portion can be reduced while increasing the gauge factor. Therefore, this strain sensor has excellent stability and good sensitivity.

Advantages of the Invention

[0022] According to the laminated film of the present invention, a strain sensor with excellent stability and good sensitivity can be obtained.

[0023] The method for manufacturing the laminated film of the present invention can reduce damage caused by heating of the base resin film.

[0024] The strain sensor of the present invention is excellent in stability and has good sensitivity.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0026] An embodiment of the laminated film and the strain sensor of the present invention will be described with reference to FIGS. 1 to 2B.

[0027] [Laminated Film] The laminated film 1 is a film for a strain sensor used for manufacturing a strain sensor 15 (see FIGS. 2A to 2B) described later. This laminated film 1 has a flat plate shape extending in a plane direction orthogonal to the thickness direction. Specifically, the laminated film 1 includes a base resin film 2 and a resistance layer 3 in this order toward one side in the thickness direction.

[0028] [Base Resin Film] The base resin film 2 is insulating. The base resin film 2 forms the other surface in the thickness direction of the laminated film 1. The base resin film 2 has a flat plate shape extending in the plane direction.

[0029] Examples of the material of the base resin film 2 include resins such as polyimide, for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate. Preferably, polyimide is mentioned as the material of the base resin film 2. If the base resin film 2 is polyimide, it can be heated up to about 200°C.

[0030] The thickness of the base resin film 2 is not particularly limited. For example, it is 2 μm or more, preferably 10 μm or more, more preferably 20 μm or more. Also, for example, it is 500 μm or less, preferably 300 μm or less, more preferably 200 μm or less. If the thickness of the base resin film 2 is equal to or greater than the above-described lower limit, the occurrence of wrinkles can be suppressed. If the thickness of the base resin film 2 is equal to or less than the above-described upper limit, it can be conveyed in a roll-to-roll manner.

[0031] On one surface in the thickness direction of the base resin film 2, in order to improve the adhesion with the resistance layer 3, for example, treatments such as corona discharge treatment, ultraviolet irradiation treatment, plasma treatment, sputter etching treatment can be performed.

[0032] [Resistance layer] The resistance layer 3 is a layer that is patterned when the strain sensor 15 (see FIGS. 2A to 2B) is manufactured from the laminated film 1. The resistance layer 3 is disposed on one surface in the thickness direction of the base resin film 2. The resistance layer 3 forms one surface in the thickness direction of the laminated film 1. Specifically, the resistance layer 3 is in contact with the entire one surface in the thickness direction of the base resin film 2.

[0033] The resistance layer 3 contains chromium nitride. Specifically, the material of the resistance layer 3 contains chromium nitride as a main component. On the other hand, the incorporation of unavoidable impurities, for example, is allowed in the material of the resistance layer 3. The proportion of unavoidable impurities in the resistance layer 3 is, for example, 1 atomic % or less, preferably 0.1 atomic % or less, more preferably 0.05 atomic % or less. Preferably, the resistance layer 3 is made of chromium nitride.

[0034] In chromium nitride, the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is 3.0 molar parts or more and 7.0 molar parts or less.

[0035] If the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is less than 3.0 molar parts, the absolute value of the temperature coefficient of resistance (TCR) (described later) becomes excessively high. If the absolute value of the temperature coefficient of resistance becomes high, the stability of the strain sensor 15 decreases.

[0036] On the other hand, if the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms exceeds 7.0 molar parts, the absolute value of the temperature coefficient of resistance becomes excessively high, or the gauge factor becomes low. If the absolute value of the temperature coefficient of resistance becomes high, the stability of the strain sensor 15 decreases. If the gauge factor becomes low, the sensitivity of the strain sensor 15 decreases.

[0037] Also, the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is preferably 3.5 or more, more preferably 4.0 or more, and still more preferably 4.5 or more. If the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is equal to or more than the above-described lower limit, it is possible to suppress the absolute value of the temperature coefficient of resistance from becoming excessively high.

[0038] The molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is preferably 6.0 or less, more preferably 5.25 or less, and still more preferably 5.0 or less. If the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is equal to or less than the above-described upper limit, it is possible to suppress the absolute value of the temperature coefficient of resistance from becoming excessively high, and also to increase the gauge factor.

[0039] The method for obtaining the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is measured by the Rutherford backscattering spectrometry (RBS). The conditions of the RBS will be described in detail in the examples below.

[0040] The gauge factor of the resistance layer 3 is, for example, 10 or more, preferably 11 or more, and more preferably 12 or more. If the gauge factor of the resistance layer 3 is equal to or more than the above-described lower limit, the sensitivity of the strain sensor 15 can be improved. On the other hand, since the gauge factor of bulk chromium nitride is 26 to 28, the gauge factor of the resistance layer 3 is, for example, 25 or less, and also 20 or less. The method for obtaining the gauge factor of the resistance layer 3 will be described in detail in the examples below.

[0041] The thickness of the resistance layer 3 is, for example, 5 nm or more, preferably 10 nm or more, and, for example, 150 nm or less, preferably 120 nm or less. If the thickness of the resistance layer 3 is equal to or greater than the above-mentioned lower limit, the gauge factor of the resistance layer 3 can be increased. If the thickness of the resistance layer 3 is equal to or less than the above-mentioned upper limit, the occurrence of cracks in the resistance layer 3 can be suppressed.

[0042] [Manufacturing Method of Laminated Film and Strain Sensor] The manufacturing method of the laminated film 1 forms the laminated film 1, for example, by a roll-to-roll method.

[0043] For example, while transporting the long base resin film 2, the resistance layer 3 is formed on one surface in the thickness direction of the base resin film 2. Examples of the film forming method include a sputtering method, a vacuum evaporation method, an ion plating method, etc. Preferably, a sputtering method, more preferably, reactive sputtering can be mentioned.

[0044] In reactive sputtering, the target is made of chromium, and as the sputtering gas, a mixed gas of an inert gas such as argon and nitrogen is used. The volume part number of nitrogen with respect to 100 volume parts of the inert gas is, for example, 0.5 to 15 volume parts.

[0045] Thereby, the laminated film 1 including the base resin film 2 and the resistance layer 3 is produced.

[0046] Thereafter, the laminated film 1 is heated at 200°C or lower. If the heating temperature of the laminated film 1 exceeds 200°C, the base resin film 2 will be damaged.

[0047] The heating temperature is preferably 180°C or lower, and, for example, 80°C or higher, preferably 100°C or higher, more preferably 120°C or higher. The heating time is, for example, 1 minute or more, preferably 5 minutes or more, and, for example, 1 hour or less, preferably 45 minutes or less.

[0048] By the above heating, the absolute value of the temperature coefficient of resistance of the resistance layer 3 is reduced. Specifically, the absolute value of the temperature coefficient of resistance of the resistance layer 3 after heating is, for example, 300 ppm / °C or less, preferably 200 ppm / °C or less, more preferably 160 ppm / °C or less, still more preferably, especially 150 ppm / °C or less, most preferably 100 ppm / °C or less, preferably 50 ppm / °C or less. If the absolute value of the temperature coefficient of resistance of the resistance layer 3 is below the above-mentioned upper limit, the change in the resistance of the resistance layer 3 due to temperature change can be reduced, and the strain sensor 15 has excellent stability. Also, if the absolute value of the temperature coefficient of resistance of the resistance layer 3 is below the above-mentioned upper limit, the gauge factor can be increased. The method for obtaining the temperature coefficient of resistance of the resistance layer 3 will be described in detail in the following examples.

[0049] Thereby, a laminated film 1 including a base resin film 2 and a resistance layer 3 having a small absolute value of the temperature coefficient of resistance (300 ppm / °C or less) and a high gauge factor (10 or more) is obtained.

[0050] As shown in FIG. 2A, thereafter, the resistance layer 3 in the laminated film 1 is patterned to form a resistance pattern 4. Examples of the patterning of the resistance layer 3 include, for example, etching, specifically, dry etching, wet etching, preferably dry etching, more preferably laser etching.

[0051] The resistance pattern 4 integrally includes a strain sensor portion 5, a terminal 6, and a wiring 7.

[0052] As shown in FIG. 2B, the strain sensor portion 5 has a substantially zigzag shape in plan view. Specifically, the strain sensor portion 5 has a plurality of first lines 8, a plurality of first connection lines 9, and a plurality of second connection lines 10.

[0053] Each of the plurality of first lines 8 extends along a first direction (a direction included in the plane direction). The plurality of first lines 8 are arranged in alignment with a space therebetween in a second direction (a direction included in the plane direction and orthogonal to the first direction).

[0054] A plurality of first connection lines 9 connect one end portions of the first lines 8 adjacent to each other in the second direction in the first direction.

[0055] A plurality of second connection lines 10 connect the other end portions of the first lines 8 adjacent to each other in the second direction in the first direction. When projected in the first direction, the first connection lines 9 and the second connection lines 10 are alternately arranged.

[0056] The terminal 6 is spaced apart from the strain sensor unit 5 in the plane direction. The terminal 6 has, for example, a land shape that is substantially rectangular in plan view. Two terminals 6 are provided at intervals.

[0057] The wiring 7 connects the two terminals 6 and both ends of the strain sensor unit 5.

[0058] In the strain sensor unit 5, one conductive path is formed that extends from one terminal 6, passes through one wiring 7, the strain sensor unit 5, and the other wiring 7, and reaches the other terminal 6.

[0059] The dimensions of the strain sensor unit 5 are appropriately set according to the use and purpose. The widths of the first lines 8, the first connection lines 9, and the second connection lines 10 are, for example, 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and also, for example, 150 μm or less, preferably 100 μm or less, more preferably 70 μm or less.

[0060] Also, the shape of the base resin film 2 is appropriately set according to the use and purpose of the strain sensor 15, and becomes a desired dimension by, for example, external shaping.

[0061] Next, a method of measuring the amount of strain (deformation amount) of the specimen 20 by disposing the strain sensor 15 on the specimen 20 will be described.

[0062] As shown in FIG. 2A, the laminated film 1 of the strain sensor 15 is adhered to the surface of the specimen 20 via the adhesive layer 21. Also, lead wires 23 are connected to the two terminals 6 via the conductive adhesive layer 22. The lead wires 23 are electrically connected to an external resistance measurement circuit (not shown).

[0063] When the subject 20 is distorted, the resistance value of the strain sensor unit 5 changes. Based on this, the amount of strain is calculated in the resistance measurement circuit.

[0064] Specifically, when the subject 20 extends in the first direction, tensile strain is applied to the first wire 8, the cross-sectional area of the first wire 8 decreases, and the resistance of the strain sensor unit 5 increases. On the other hand, when the subject 20 contracts, compressive strain is applied to the first wire 8, the cross-sectional area of the first wire 8 increases, and the resistance of the strain sensor unit 5 decreases. From such a change amount of resistance, the amount of strain of the subject 20 is calculated.

[0065] [Operational Effects of One Embodiment] And since this laminated film 1 includes the base resin film 2 and the resistance layer 3 in which the molar part of the nitrogen atom with respect to 100 molar parts of the chromium atom is 3.0 molar parts or more and 7.0 molar parts or less, if the base resin film 2 is heated at a relatively low temperature, while the absolute value of the temperature coefficient of resistance of the resistance layer 3 can be made small, the gauge factor can be made high. Therefore, the strain sensor 15 obtained from this laminated film 1 is excellent in stability and has good sensitivity.

[0066] In this laminated film 1, if the gauge factor of the resistance layer 3 is 10 or more, a strain sensor 15 with good sensitivity can be obtained.

[0067] In this laminated film 1, if the absolute value of the temperature coefficient of resistance of the resistance layer 3 is 300 ppm / °C or less, a strain sensor 15 excellent in stability can be obtained.

[0068] In the manufacturing method of this laminated film 1, since the laminated film 1 is heated at 200°C or less, damage caused by heating of the base resin film 2 can be reduced.

[0069] In this strain sensor 15, by heating at a relatively low temperature, while the absolute value of the temperature coefficient of resistance of the strain sensor unit 5 can be made small, the gauge factor can be made high. Therefore, this strain sensor 15 is excellent in stability and has good sensitivity.

[0070] [Modified Example] In each of the following modified examples, for members and steps similar to those in the above-described embodiment, the same reference numerals are given, and detailed descriptions thereof are omitted. Further, each modified example can achieve the same operational effects as the embodiment, unless otherwise specified. Furthermore, the embodiment and its modified examples can be combined as appropriate.

[0071] In one embodiment, the timing of heating is before the patterning of the resistive layer 3, but it may be, for example, after the patterning of the resistive layer 3.

[0072] The base resin film 2 can include functional layers (not shown), such as a hard coat layer, an easy adhesion layer, and an antistatic layer, on one surface in its thickness direction.

[0073] Further, the strain sensor 15 can cover the strain sensor portion 5 and further include a cover layer 12 (dashed line) made of resin.

Examples

[0074] Examples and comparative examples are shown below to explain the present invention more specifically. Note that the present invention is not limited to any examples and comparative examples. Further, specific numerical values such as blending ratios (content ratios), physical property values, and parameters used in the following description can be replaced with the upper limit values (numerical values defined as "below" and "less than") or lower limit values (numerical values defined as "above" and "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the above "Mode for Carrying Out the Invention".

[0075] Example 1 A base resin film 2 with a thickness of 38 μm made of polyimide (150EN manufactured by Toray DuPont) was prepared.

[0076] The base resin film 2 was set on the roll-to-roll unwind roll and winding roll, and also set in the sputtering apparatus disposed therebetween.

[0077] Subsequently, after evacuating the inside of the sputtering apparatus until the degree of vacuum became 1×10 -3 Pa or less, a resistance layer 3 made of chromium nitride was formed by reactive pulsed DC sputtering (pulse width: 1 μs, frequency: 100 kHz) under the following conditions. The thickness of the resistance layer 3 was 60 nm.

[0078] Target: metallic chromium, flat plate shape of 500 mm×150 mm Power: 5 kW (power density: 6.7 W / cm 2 ) Magnetic flux density (target surface): 30 mT to 100 mT Substrate temperature: 150°C Sputtering gas: mixed gas of argon and nitrogen Film formation pressure: 0.085 Pa

[0079] Note that the ratio of nitrogen gas was adjusted so that the ratio of the number of moles of nitrogen atoms to the number of moles of chromium atoms was as shown in Table 1.

[0080] Thereby, a laminated film 1 including the base resin film 2 and the resistance layer 3 was manufactured.

[0081] Next, the laminated film 1 was heated at 150°C for 30 minutes (annealing treatment).

[0082] Thereafter, the laminated film 1 was cut into a size of 10 mm×200 mm, and a resistance pattern 4 including a zigzag strain sensor portion 5, a terminal 6, and a wiring 7 was formed from the resistance layer 3 by laser patterning. The line width of the strain sensor portion 5 was 30 μm. At this time, the resistance of the resistance pattern 4 was adjusted to be about 10 kΩ, and the resistance of the strain sensor portion 5 was adjusted to be 30 times the resistance of the wiring 7. Thereby, a strain sensor 15 was obtained.

[0083] Examples 2 to Comparative Example 3 The laminated film 1 and further the strain sensor 15 were obtained in the same manner as in Example 1, except that the ratio of the number of moles of nitrogen atoms to the number of moles of chromium atoms was changed according to Table 1. Specifically, the ratio of nitrogen in the sputtering gas was adjusted.

[0084] [Evaluation] The following items were evaluated. The results are shown in Table 1. [Ratio of nitrogen atoms] Regarding the resistance layer 3 of each example and comparative example, the number of moles of nitrogen atoms relative to 100 mole parts of chromium atoms was determined by Rutherford backscattering spectrometry (RBS). The details of RBS are shown below.

[0085] Apparatus: Pelletron 3SDH manufactured by National Electrostatics Corporation Measurement conditions: Incident ion: 4 He ++ Incident energy: 2300 keV Incident angle: 0 deg Scattering angle: 160 deg Sample current: 4 nA Beam diameter: 2 mm Φ In-plane rotation: None Irradiation dose: 40 μC

[0086] [Temperature coefficient of resistance] The temperature of the strain sensor part 5 of the strain sensor 15 of each example and comparative example was set to 5°C. A tester was connected to each of the two terminals 6, and a constant current was passed to measure the two-terminal resistance at 5°C by reading the voltage. Similarly, the two-terminal resistances at 25°C and 45°C were measured.

[0087] Then, the average value of the temperature coefficient of resistance calculated from the resistance values at 5°C and 25°C and the temperature coefficient of resistance calculated from the resistance values at 25°C and 45°C was determined as the temperature coefficient of resistance of the strain sensor part 5 (resistance layer 3).

[0088] [Gauge factor] A tester was connected to each of the two terminals 6 of each of the examples and comparative examples, and while flowing a constant current and reading the voltage, the base resin film 2 was pulled with an INSTRON 5967 universal material testing machine, and the gauge factor was obtained from the change amount of the measured wiring resistance value and the amount of pulling at that time.

[0089] [Table 1]

Explanation of Signs

[0090] 1 Laminated film 2 Base resin film 3 Resistance layer 4 Resistance pattern 5 Strain sensor section 15 Strain sensor

Claims

1. An insulating base resin film and a resistance layer are provided in order in the thickness direction, wherein the thickness of the base resin film is 10 μm or more and 200 μm or less, the resistance layer contains chromium nitride, and the molar part of nitrogen atoms with respect to 100 molar parts of chromium atoms is 3.0 molar parts or more and 7.0 molar parts or less, and the thickness of the resistance layer is 10 nm or more and 150 nm or less. A laminated film characterized by this.

2. The laminated film according to claim 1, wherein the material of the base resin film is polyimide.

3. The laminated film according to any one of claims 1 to 2, wherein the gauge factor of the resistance layer is 10 or more.

4. The laminated film according to any one of claims 1 to 3, wherein the absolute value of the temperature coefficient of resistance of the resistance layer is 300 ppm / °C or less.

5. A step of preparing the laminated film according to any one of claims 1 to 4, and a step of heating the laminated film at 200°C or lower A method for manufacturing a laminated film, characterized by comprising this.

6. An insulating base resin film and a strain sensor part formed of a resistance layer are provided in order in the thickness direction, wherein the thickness of the base resin film is 10 μm or more and 200 μm or less, the thickness of the resistance layer is 10 nm or more and 150 nm or less, the strain sensor part contains chromium nitride, and 100 moles of chromium atoms A strain sensor, characterized in that the molar part of nitrogen atoms with respect to the part is 3.0 molar parts or more and 7.0 molar parts or less.

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