JP2018091848A - Strain resistance film and strain sensor, and manufacturing method of them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain resistance film and strain sensor having a high gauge factor and high temperature stability in a predetermined high-temperature region, and provide manufacturing methods of them.SOLUTION: A strain resistance film is obtained which is expressed by a general formula CrAlN(here, x and y are atomic ratios (at.%), 4≤x≤25, and 0.1≤y≤20) and has a gauge factor of 3 or more in a temperature range of -50°C or more and 300°C or less. A strain sensor is obtained by forming the strain resistance film on a strain structure. At this time, the strain resistance film is manufactured by applying a heat treatment to a thin film having the above-mentioned composition at a temperature of 300°C or more and 700°C or less.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a strain resistance film and a strain sensor having excellent characteristics at high temperatures, and a method for manufacturing the same.

  The strain sensor uses a phenomenon in which the electrical resistance of a thin film, thin wire, or foil-shaped sensor material changes due to elastic strain, and is used for measurement and conversion of strain and stress by measuring the resistance change.

The sensitivity of the strain sensor is determined by the gauge factor K, and the value of K is generally given by the following equation (1).
K = (ΔR / R) / (Δl / l) = 1 + 2σ + (Δρ / ρ) / (Δl / l) (1)
Here, R, σ, and ρ are the total resistance, Poisson's ratio, and specific electrical resistance, respectively, of the thin film, thin wire, or foil that is the sensor material. Further, l is the total length of the object to be measured, and therefore Δl / l represents the strain generated in the object to be measured. In general, since σ in a metal / alloy is approximately 0.3, the sum of the first term and the second term on the right side in the above formula is approximately 1.6, which is a substantially constant value. Therefore, in order to increase the gauge factor, it is an essential condition that the third term in the above equation is large. That is, when tensile deformation is applied to the material, the electronic structure in the length direction of the material changes significantly, and the amount of change Δρ / ρ in specific electrical resistance increases.

  Therefore, in recent years, chromium (Cr), which has been noticed as a bulk gauge factor, has been reported to be a very large value of 26 to 28. Although it is very difficult to process Cr, it can be applied to a strain sensor by reducing the film thickness that does not require processing. Since Cr still has a large gauge factor of about 15 even if it is thinned, the Cr thin film is used as a strain sensor. It is attracting attention (for example, Patent Document 1).

  On the other hand, the strain sensor is required to have a high gauge factor and high temperature stability, but in the Cr thin film, the resistance temperature coefficient (TCR), which is an index of temperature stability, shows a large positive value. There is a problem in terms of stability. On the other hand, a Cr—N film has been proposed as a thin film material having a high gauge factor and a small TCR (for example, Patent Document 2). In addition, the temperature coefficient of the gauge factor (sensitivity temperature coefficient) (TCS) is also important as an index of temperature stability, and a Cr—N thin film having low TCR and TCS has also been proposed (Patent Document 3).

  On the other hand, in recent years, sensing of various mechanical quantities with high gauge factor and high sensitivity in the high temperature range of 200-700 ° C, such as internal combustion engines related to automobiles and aircraft, injection molding, geothermal power generation, oil field development, thermal power generation turbine related, etc. There is a strong demand.

JP-A-61-256233 Japanese Patent No. 3642449 Japanese Patent Laying-Open No. 2015-031633

  By the way, since the strain sensor using the Cr-N thin film shown in the Patent Documents 2 and 3 is not considered for use in a high temperature region, the gauge factor in the high temperature region is not measured and is unknown. .

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a strain resistance film and a strain sensor exhibiting a high gauge factor and temperature stability in a predetermined high temperature region, and a method for manufacturing the same. And

  The present inventor first uses a Cr thin film as a strain resistance film, and performs heat treatment for a predetermined time in the atmosphere at a temperature higher by 50 ° C. than the upper limit of the use temperature range at a predetermined high temperature. The inventors have found that a practical gauge factor can be obtained in the temperature range of use and filed a patent application (Japanese Patent Application No. 2006-169410).

  However, such a Cr thin film has a gauge factor value of about 14 at 100 ° C., but the gauge factor decreases when the temperature exceeds 100 ° C., and about 6 at 250 ° C. or higher and 4 at 350 ° C. or higher. Decrease to a degree. Although this value is a value that can be put to practical use, it is much smaller than the gauge factor from room temperature to 100 ° C. Further, the temperature stability coefficient (sensitivity temperature coefficient) (TCS) is 2000 ppm / ° C. or less, and further temperature stability is desired.

  Therefore, as a result of studying a material having a high gauge stability and excellent TCS characteristics at a high temperature of 100 ° C. or higher in a material system having high temperature stability, a Cr—Al—N thin film having a predetermined composition is -50 to 500 ° C. We found that the gauge rate at was high.

  This invention is made | formed based on such knowledge, and provides the following (1)-(10).

(1) General formula Cr _100-xy Al _x N _y
(Where x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20), and in a temperature range of −50 ° C. or more and 300 ° C. or less, A strain resistance film having a gauge factor of 3 or more.

  (2) The strain resistance film according to (1), wherein the temperature coefficient of sensitivity (TCS) is within ± 1500 ppm / ° C. in a temperature range of −50 ° C. to 200 ° C.

  (3) The strain resistance film according to (1) or (2), wherein the temperature coefficient of resistance (TCR) is within ± 500 ppm / ° C. in a temperature range of −50 ° C. to 500 ° C.

  (4) The strain resistance film according to any one of (1) to (3), wherein the resistance stability is within ± 2 ppm / h in a temperature range of 400 ° C. or lower.

  (5) A strain sensor comprising the strain resistance film according to any one of (1) to (4) above formed on a strain generating structure.

(6) General formula Cr _100-xy Al _x N _y
(However, x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20). A method for producing a strain resistance film, characterized by performing a heat treatment to form a strain resistance film having a gauge factor of 3 or more in a temperature range of −50 ° C. or more and 300 ° C. or less.

  (7) In the temperature range of −50 ° C. or more and 200 ° C. or less, the sensitivity temperature coefficient (TCS) is within ± 1000 ppm / ° C.

  (8) Manufacture of a strain resistive film according to (6) or (7), wherein the temperature coefficient of resistance (TCR) is within ± 500 ppm / ° C within a temperature range of -50 ° C to 500 ° C. Method.

  (9) The method for producing a strain resistant film according to any one of (6) to (8), wherein the resistance stability is within ± 2 ppm / h in a temperature range of 400 ° C. or lower.

(10) General formula Cr _100-xy Al _x N _y
(Where x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20) are formed on the strain-generating structure, and 300 A method for producing a strain sensor, comprising: obtaining a strain sensor by performing a heat treatment at a temperature of not lower than 700 ° C. and not higher than 700 ° C. to obtain a strain resistance film according to any one of (6) to (9).

  ADVANTAGE OF THE INVENTION According to this invention, the strain resistance film | membrane and strain sensor which show a high gauge factor and temperature stability in a predetermined | prescribed high temperature area | region, and those manufacturing methods are provided.

It is a figure which shows the relationship between the addition amount of Al of a Cr-Al alloy, and a Neel temperature. It is a figure which shows the relationship between the addition amount of Mn of a Cr-Mn alloy, and a Neel temperature. It is a schematic block diagram which shows a high temperature strain application electric resistance measuring apparatus. It is a figure which shows a bending test sequence. It is a figure which shows the relationship between the measurement temperature of a Cr-N thin film obtained on manufacturing conditions A, and a gauge factor. It is a figure which shows the relationship between the measurement temperature and gauge factor of the thin film manufactured by making Al chip number n 0-6. It is a figure which shows the relationship between the measurement temperature and gauge factor of the thin film manufactured by making Al chip number n into 8-20. It is a figure which shows the relationship between the measurement temperature (T degreeC) of the thin film manufactured by making Al chip number n 0-6, and the value of TCS of T degreeC-T + 50 degreeC. It is a figure which shows the relationship between the measurement temperature (T degreeC) of the thin film manufactured by making Al chip number n into 8-20, and the value of TCS of T degreeC-T + 50 degreeC. It is a figure which shows the relationship between the Al chip number in the room temperature vicinity of the thin film heat-processed on various conditions, after forming into a film by making Al chip number n into 0-20, and TCR. It is a figure which shows the change of resistance value with the measurement temperature of the thin film manufactured by making Al chip number n 0-20. It is a figure which shows the relationship between the number of Al chips and TCS in the room temperature vicinity of the thin film heat-processed on various conditions, after forming into a film by making Al chip number n into 0-20. It is a figure which shows the relationship between the Al chip number in the room temperature vicinity of the thin film heat-processed on various conditions, after forming into a film with Al chip number n 0-20, and a gauge factor. It is a figure which shows resistance change rate ((DELTA) R / _R0 ) in each measurement temperature of the thin film manufactured by making Al chip number n = 0. It is a figure which shows resistance change rate ((DELTA) R / _R0 ) in each measurement temperature of the thin film manufactured by Al chip number n = 2. It is a figure which shows the resistance change rate ((DELTA) R / _R0 ) in each measurement temperature of the thin film manufactured by Al chip number n = 4. It is a figure which shows resistance change rate ((DELTA) R / _R0 ) in each measurement temperature of the thin film manufactured by Al chip number n = 6. For a Cr—N: Al (20) thin film manufactured with an Al chip number n = 20, after heat treatment at 700 ° C. in the atmosphere, at each measurement temperature, the test was conducted by holding for 30 minutes including bending at each measurement temperature. It is a figure which shows resistance change rate ((DELTA) R / _R0 ). For the Cr—N: Al (20) thin film manufactured with Al chip number n = 20, the rate of change in resistance at each measurement temperature when the retention time is 100 hours at each measurement temperature after heat treatment at 700 ° C. in the atmosphere ( It is a figure which shows (DELTA / _R0 ). FIG. 7 is a diagram showing a change in resistance value when Cr—N: Al (20) thin film manufactured with Al chip number n = 20 is heat-treated at 700 ° C. in the atmosphere, and the holding time is 100 hours at each measurement temperature. is there. The resistance stability (SR) is shown for a Cr—N: Al (20) thin film manufactured with an Al chip number n = 20 after a heat treatment at 700 ° C. in the atmosphere and a holding time of 100 hours at each measurement temperature. FIG. It is a figure which shows the relationship between the number n of Al chips, and the amount of Al (at.%). It is a figure which shows the result which grasped | ascertained the change with respect to the temperature of the resistance value in the Cr-N-Mn thin film which is a comparative example. It is a figure which shows the relationship between the measurement temperature in a Cr-N-Mn thin film which is a comparative example, and a gauge factor. It is a figure which shows the relationship between the measurement temperature and resistance value in the Cr-N-Mn thin film which is a comparative example. It is a figure which shows the relationship between the measurement temperature and resistance change rate ((DELTA) R / _R0 ) in the Cr-N-Mn thin film which is a comparative example. It is a figure which shows the relationship between the number of Mn chip | tips in the room temperature vicinity of the Cr-N-Mn thin film which is a comparative example obtained by forming into a film with n number of Mn chips 0-12, and heat-processing on various conditions after that, and TCR. is there. The figure which shows the relationship between the number of Mn chips and the TCS in the vicinity of room temperature of a Cr—N—Mn thin film which is a comparative example obtained by forming a film with n number of Mn chips of 0 to 12 and then heat-treating under various conditions. is there. The figure which shows the relationship between the number of Mn chip | tips in the room temperature vicinity of the Cr-N-Mn thin film which is a comparative example obtained by forming into a film with n number of Mn chips 0-12, and heat-processing on various conditions after that, and a gauge factor It is.

Hereinafter, embodiments of the present invention will be described in detail.
The gauge rate at high temperatures was examined for Cr thin films that are known to have a high gauge factor at room temperature, and Cr—N thin films that have a large gauge factor and allow adjustment of TCR and TCS to near zero. As a result, the gauge factor rapidly decreased at 100 ° C. or higher. Further, the rate of change of the gauge factor with respect to temperature, that is, the absolute value of TCS tends to be large, and the temperature stability may be insufficient.

  Therefore, a material having a large gauge factor and excellent temperature stability at a high temperature of 100 ° C. or higher was examined. Using various devices and methods that have made various studies to enable gauge rate measurement up to 800 ° C., Cr—N—X thin films in which various third elements are added to Cr—N can be added at high temperatures. We investigated the gauge factor and its behavior in the field.

  Samples heat-treated at 300 ° C. to 700 ° C. using Al as X, particularly samples heat-treated at 500 ° C. or higher, without decreasing even when the gauge factor at room temperature exceeds 100 ° C. as the amount of Al increases. A behavior of expanding to the high temperature side up to about 300 ° C. was found. That is, the value of 3 or more was obtained without changing the gauge factor at room temperature to 300 ° C. Moreover, it discovered for the first time that the change of the value of a gauge factor was small to 200 degreeC. As a result, the TCS from −50 ° C. to 200 ° C. shows a good value within 0 ± 1500 ppm / ° C.

  On the other hand, in the sample heat-treated at 300 ° C. to 500 ° C., the TCR near room temperature decreased and showed a large negative value as the Al content increased. In addition, the sample heat-treated at 700 ° C. was found to be good with a small negative value of 0> TCR> −200 ppm / ° C. From this, it was confirmed that the TCR increases in the positive direction as the heat treatment temperature increases.

  In other words, it became clear for the first time that the TCR can be controlled by the amount of nitrogen, the amount of Al, and the heat treatment temperature in the Cr—N—Al thin film, and the Cr—N—Al film was within ± 500 ppm even in the high temperature range up to 500 ° C. It became clear that it became low TCR. From this, it has been clarified that TCR can be reduced (= 0) even when heat treatment is performed at a higher temperature, which is necessary for high temperature applications.

  Further, in the Cr—N—Al thin film, by performing a heat treatment in the atmosphere at a high temperature of about 500 ° C. or higher, in which the TCR can be adjusted to almost 0, in a temperature range of 400 ° C. or lower in the atmosphere. In addition to the above characteristics, the inventors have found that the stability of the resistance value exhibits good characteristics within ± 0.02% in 100 hours, that is, within ± 2 ppm / h. This is considered to be an effect of heat treatment in the atmosphere.

  On the other hand, in a Cr-based thin film, the electric resistance generally changes with a positive slope with respect to a temperature change over a wide temperature range as in a normal metal, but at a Neel temperature related to Cr antiferromagnetism. It is known to take a local minimum. In other words, a negative value or a decrease in the amount of increase occurs in the temperature range near the Neel temperature and the Neel temperature reaches the minimum point, and the resistance value increases again with a positive slope in the temperature range beyond the Neel temperature. The behavior is shown. Therefore, as a result of investigating the temperature dependence of the resistance value in the Cr—N—Al thin film, a minimum value considered to be the Neel temperature was found.

  In the Cr—N—Al thin film, the gauge factor shows a constant value from room temperature to a temperature just below the Neel temperature, and is confirmed to decrease near the Neel temperature. As the Al content increases, the Neel temperature Along with this, a behavior was observed in which the slope of the gauge factor reduction on the high temperature side in the constant gauge factor region shifted to the high temperature side. From this, it is considered that the factor that the Cr—N—Al thin film exhibits a large gauge factor up to the high temperature region as described above is related to the increase in the Neel temperature that follows the increase in the Al content.

  On the other hand, in past literature (E. Fawcett et al .: “Spin-density-wave antiferromagnetism in chromium alloys”, Rev. Mod. Phys., 66 (1), (1994).), Al and Mn are It has been reported that the Neel temperature can be increased to temperatures exceeding 500 ° C. depending on the amount added to Cr.

  Specifically, page 48 of this document shows the magnetic phase diagram of the Cr—Al alloy, that is, the relationship between the amount of Al added and the Neel temperature. The figure is shown in FIG. 1, and it can be seen from FIG. 1 that the Neel temperature rises to about 25 at% of the amount of Al added to Cr, and the maximum temperature is about 800 K, that is, about 530.degree.

  The relationship between the amount of Mn added and the Neel temperature is shown on page 85 of the above document. The figure is shown in FIG. 2. In this figure, 1 to 20 are different in the amount of Mn added, and 1 is Mn: 0 at. %, 2 is Mn: 0.1 at. %, 3 is Mn: 0.2 at. %, 8 is Mn: 0.7 at. %, 9 is 1.0 at. %,... 16 is Mn: 6.0 at. %, ... 19 is Mn: 30 at. %, 20 is Mn: 34 at. %. As shown in this figure, the amount of Mn added was 34 at. It can be seen that the Neel temperature rises uniformly up to 50% and its maximum temperature is about 780K, or about 510 ° C.

  The above is the result based on the Cr thin film, but as described above, almost the same behavior was obtained in the case of the Cr—N—Al thin film based on the Cr—N thin film. It is considered that the same mechanism as in the case worked, and that a relatively large gauge factor near room temperature was maintained up to 300 ° C.

  However, in the case of the Cr—N—Mn thin film, unlike the case of the Cr—N—Al thin film, the TCR value does not change as the amount of Mn increases, and TCR = 0 by heat treatment at a temperature exceeding 300 ° C. It turned out that adjustment to was impossible. Moreover, although the gauge factor of the strain sensor using the Cr—N—Mn thin film is larger than that in the case of using the conventional Cr—N thin film, it is relatively greatly reduced by addition of Mn, and near room temperature by heat treatment at 300 ° C. or higher. It was confirmed that the gauge factor was as small as about 3, and the gauge factor increased with increasing temperature up to 300 ° C., and the TCS was large. Also, TCS is considered to increase with increasing Mn content and heat treatment temperature, and difficult to reduce. Therefore, the Cr—N—Mn thin film has a large TCS in the vicinity of room temperature to 200 ° C., the TCR cannot be adjusted, and the gauge factor is small, so that there are many problems in using it as a strain sensor in a high temperature range. found.

  From the above results, in the present invention, a Cr—N—Al thin film is used as a highly sensitive and highly stable strain sensor. That is, by using a Cr—N—Al thin film having a predetermined composition, it has been found for the first time that the gauge factor is 3 or more over the temperature range of −50 ° C. to 300 ° C. and the temperature stability is high. Has been completed. In addition, TCS is 0 ± 1500ppm / ° C in the temperature range from -50 ℃ to 200 ℃, and the change in gauge factor is small. Furthermore, in the temperature range from -50 ℃ to 500 ℃, TCR can be adjusted within ± 500ppm. Furthermore, good resistance stability within ± 2 ppm / h can be obtained in a temperature range of 400 ° C. or lower.

  Due to such excellent characteristics, the strain sensor of the present invention can be applied to various mechanical quantity sensors.

In the strain sensor of the present invention, the strain resistance film is represented by the general formula Cr _100-xy Al _x N _y , where x and y are atomic ratios (at.%), 4 ≦ x ≦ 25, 0. 1 ≦ y ≦ 20. The reason why 4 ≦ x ≦ 25 is set is that when Al is added to Cr or Cr—N, an increase in the Neel temperature is observed in the range of 4 ≦ x ≦ 25. Further, 0.1 ≦ y ≦ 20 is set because the TCR becomes larger than ± 500 ppm / ° C. outside this range, and when y exceeds 20, the gauge factor becomes smaller than 3. .

Next, an apparatus and a method for measuring a gauge factor at a high temperature will be described.
As described above, the present invention provides a resistance thin film and a strain sensor having a high gauge factor in a high temperature region, and it is necessary to grasp the gauge factor at a high temperature. The measurement method was not established.

  For this reason, as a result of various studies on an apparatus and a method capable of measuring a gauge factor at high temperatures, the inventors have conceived the high-temperature strain applied electrical resistance measuring apparatus shown in FIG.

  The apparatus shown in FIG. 3 has an electric oven 1 with a temperature control function that can be heated to about 1000 ° C. in the atmosphere, and a window 2 is formed on the upper portion of the electric oven 1. The window 2 is closed by a lid member 3, and a support bar 4 extending downward into the electric oven 1 is fixed to the lid member 3. The support bar 4 supports the measurement table 5 in the electric oven 1.

  A fixing member 6 is provided on the measurement table 5, and a sample 20 on which a thin film 8 having a predetermined pattern is formed on a substrate 7 by high-frequency sputtering or the like is cantilevered. The measuring table 5 has a box shape, and a terminal block 10 having terminals 11 is provided inside. The thin film 8 and the terminal 11 are connected by a bonding wire 9.

  A heat resistant wiring cable (not shown) is connected to the terminal 11. The heat-resistant wiring cable is drawn out through the window 2 and connected to the measurement system (DMM) 14. The power source 15 is also connected by a heat resistant wiring cable.

  A micrometer 12 is fixed to the lid member 3, and a strain applying push bar 13 extends downward from the micrometer 12 and comes into contact with the vicinity of the free end of the sample 20. As a result, the strain applying push rod 13 is lowered by a predetermined length by the micrometer 12 so that a predetermined strain can be applied to the sample 20.

  When measuring the gauge factor at a high temperature by using such a high-temperature strain applied electric resistance measuring device, the temperature in the electric oven 1 is set to a predetermined temperature up to about 800 ° C., and the micrometer 12 is set from the outside of the electric oven 1. By operating the strain applying push rod 13 to apply a predetermined strain to the sample 20, the resistance of the strain resistance film is measured. Such an operation is performed at each temperature, and the resistance change rate obtained at each temperature is calibrated with a gauge factor measured separately at 100 ° C. to obtain a gauge factor at a high temperature. Thereby, the gauge factor at a high temperature can be accurately obtained.

Next, the manufacturing method of the strain sensor of the present invention will be described.
In the present invention, the Cr—N—Al thin film described above is formed as a strain resistance film on the substrate, and then heat treatment is performed at a temperature of 300 ° C. to 700 ° C. The heat treatment at this time is preferably performed in the air for a period of 30 minutes to 4 hours.

  As a result, as described above, the gauge factor is 3 or more over the temperature range from -50 ° C to 300 ° C, and the TCS is approximately constant at 0 ± 1500 ppm / ° C from -50 ° C to 200 ° C. In addition, a strain sensor capable of reducing and adjusting TCR within ± 500 ppm at −50 ° C. to 500 ° C. is obtained.

  Also, good resistance stability within ± 2 ppm / h can be obtained in a temperature range of 400 ° C. or lower.

  In the present invention, as the base material (strain generating structure) on which the Cr—N—Al thin film is formed, alumina which is an insulating ceramic having good heat resistance can be suitably used. In addition to alumina, other various ceramics can also be used. Furthermore, as the base material, various metal plates such as stainless steel (SUS) that have been coated with an insulating coating can be used. Further, a method for forming a Cr—N—Al thin film is not particularly limited, but reactive sputtering in which sputtering is performed in an atmosphere of a small amount of nitrogen gas is preferable, and high-frequency sputtering is particularly preferable as sputtering. As the high-frequency sputtering apparatus, a magnetron type apparatus is suitable. The gas pressure during high-frequency sputtering is preferably 16 mTorr (2.13 Pa) or less, for example, 5 mTorr (0.67 Pa). The thin film pattern used as the strain resistance film may be a pattern normally used as a strain sensor, and for example, a lattice pattern can be used. The target used for high-frequency sputtering may be a composite target in which a predetermined number of Al chips are bonded to a high-purity Cr disk, but an alloy target prepared in advance with a predetermined composition of Cr—Al may be used.

  The strain sensor is obtained by forming a strain resistance film made of the Cr—N—Al thin film described above on a strain generating structure as a strain material.

Examples of the present invention will be described below.
Here, a Cr—N (N: 8.5 at.%) Thin film having a lattice pattern is formed by high-frequency sputtering on an alumina substrate as a base material (strain generating structure) under the manufacturing conditions shown below. Thereafter, the sample was subjected to a heat treatment in the atmosphere at 500 ° C. for 0.5 hours by a heat treatment apparatus different from that in FIG. 3, and then the gauge factor in the temperature range up to 425 ° C. was measured by the apparatus in FIG.

<Production conditions>
1. Film forming method: reactive sputtering method in which sputtering is performed in an atmosphere of Ar gas and a small amount of nitrogen gas. Deposition equipment: Uses conventional high-frequency sputtering equipment 3. Target: Cr disk with nominal purity of 99.9% and diameter of 101.6mm 4. Substrate: Alumina plate with purity of 99.9% and thickness of 0.1mm 5. deposition conditions, deposition vacuum (the background degree of vacuum): 2 × ¹⁰ -5 Pa
-Target-substrate distance (T-S distance): 70 mm
・ Sputtering gas pressure: 20 mTorr (2.67 Pa)
・ Sputter gas total flow rate: 20sccm
Nitrogen gas flow rate ratio (N ₂ / (Ar + N ₂ )): 0.06%
・ Input power: 100W
-Substrate temperature: 20 ° C water cooling Thin film strain sensor (strain gauge) element patterning and heat treatment, etc. Sensitive part shape: Lattice shape consisting of 8 turns. Lattice line width and spacing: 0.04 mm and 0.05 mm, respectively.
・ Lattice length: 1mm
・ Thin film thickness: about 500nm
・ Pattern formation: Utilizing photolithographic technique and corrosion shaping technique using Cr etching solution ・ Heat treatment: Holding at a predetermined temperature in the atmosphere for 30 minutes Overlapping and forming-Cutting out elements for evaluation: Individually cutting out elements using a dicing machine

  When measuring the gauge factor, the sample is set at a predetermined position on the measuring table and held at each temperature, and the strain application push rod is operated by the micrometer of the apparatus shown in FIG. A bending test in which a strain of about 0.05% was applied in a sequence was performed, and resistance measurement was performed at each temperature up to 425 ° C. The rate of change in resistance obtained at each temperature was calibrated with a gauge rate measured separately at 100 ° C., and the gauge rate at each temperature was determined.

  The result is shown in FIG. As shown in this figure, in the case of the Cr—N thin film, it was confirmed that the gauge factor rapidly decreased when the temperature exceeded 100 ° C., and the gauge factor became 3 or less at 300 ° C. or higher.

Next, as a target, a composite target in which n Al chips having a size of 10 × 10 mm ² and a thickness of 1 mm were placed on a Cr disk having a nominal purity of 99.9% and a diameter of 101.6 mm was used. The Cr—N: Al (n) thin film was formed by high frequency sputtering on the alumina substrate as the base material (strain generating structure) under the above-described production conditions. Thereafter, for the sample formed with the number n of Al chips of 2 to 6, the sample was subjected to heat treatment in the atmosphere at 500 ° C. for 0.5 hours using a heat treatment apparatus different from that in FIG. The gauge factor in the temperature range was measured. For samples formed with n of 8 to 20, the samples were subjected to heat treatment at 700 ° C. in the atmosphere for 0.5 hours using a heat treatment apparatus different from that shown in FIG. 3, and then the gauge in the temperature range up to 650 ° C. The rate was measured.

  When measuring the gauge factor, the sample is set at a predetermined position on the measuring table and held at each temperature, and the strain application push rod is operated by the micrometer of the apparatus shown in FIG. A bending test in which a strain of about 0.05% was applied in a sequence was performed, and resistance measurement was performed at each temperature up to 450 ° C. or 650 ° C. The rate of change in resistance obtained at each temperature was calibrated with a gauge rate measured separately at 100 ° C., and the gauge rate at each temperature was determined.

  The results are shown in FIGS. FIG. 6 is a graph showing the relationship between the measurement temperature and the gauge factor when the Al chip number n is 0 to 6, and FIG. 7 is the measurement temperature and gauge factor when the Al chip number n is 8 to 20. However, as shown in these figures, as the Al amount increased (the number of Al chips n increased), a region with a large gauge factor tended to expand toward the high temperature side. In addition, when the Al chip number n is 4 to 16, it was confirmed that the gauge factor showed a uniform value at room temperature to 200 ° C., although the gauge factor itself decreased.

  Next, TCS in these cases was obtained. FIG. 8 is a diagram showing the relationship between the measurement temperature (T ° C.) of a thin film manufactured with an Al chip number n of 0 to 6 and the TCS value of T ° C. to T + 50 ° C. FIG. 9 shows the Al chip number n. It is a figure which shows the relationship between the measurement temperature (T degreeC) of the thin film manufactured as 8-20, and the value of TCS of T degreeC-T + 50 degreeC. Since the plot at 150 ° C. shows TCS at 150 to 200 ° C., TCS was within ± 1500 ppm / ° C. up to 200 ° C. at n = 4 and 6 in FIG. 8, but ± 1500 ppm at n = 0 and 2 / ° C. Moreover, in n = 8-29 of FIG. 9, as shown in all, TCS was within ± 1500 ppm / ° C. up to 200 ° C.

  Next, when a composite target on which n Al chips are similarly mounted is used as the target, the number of n is varied between 2 and 20, and after the film formation under the above production conditions, the heat treatment is performed under various heat treatment conditions. The TCR around room temperature was measured. FIG. 10 is a diagram showing the relationship between the number of Al chips and the TCR.

  As shown in FIG. 10, even when Al is added to the Cr—N thin film, the TCR is as-depo. It was confirmed that it took a negative value and changed in the positive direction by heat treatment. In addition, TCR decreases with increasing Al content in the sample heat-treated at 300 to 500 ° C. and shows a large negative value, whereas the sample heat-treated at 700 ° C. has 0> TCR> −200 ppm / ° C. It was confirmed to show a substantially constant TCR. This revealed that the TCR can be controlled by the composition of the Cr—N—Al thin film (N content and Al content) and the heat treatment temperature. In addition, when the heat treatment temperature was increased to 500 ° C. and 700 ° C., it was confirmed that there was a sample having a TCR of almost zero at room temperature.

  Next, in the 500 ° C. heat treatment and the 700 ° C. heat treatment in which samples having a TCR of almost zero existed at room temperature, the change in resistance value when the measurement temperature was changed was grasped. FIG. 11 is a diagram showing a change in resistance value depending on the measurement temperature at this time. FIG. 11A shows a case where the number of Al chips n is 0 to 6 and the heat treatment temperature is 500 ° C., and FIG. This is the case where the heat treatment temperature is 700 ° C. at ˜20. As shown in this figure, it was confirmed that the Neel temperature rises with the amount of Al. This substantially coincides with the tendency that the region with a large gauge factor expands to the high temperature side as the Al amount increases. Further, when the number of chips with a TCR of 0 at room temperature is 4 and the heat treatment temperature is 500 ° C., and when the number of chips is 20 and the heat treatment temperature is 700 ° C., the TCR in the temperature range where the slope is steepest up to around 500 ° C. is It can be seen that the values are as small as -178 ppm / ° C and -296 ppm / ° C. Therefore, it was confirmed that these satisfy TCR within ± 500 ppm / ° C. in the temperature range up to 500 ° C.

  Next, when a composite target on which n Al chips are similarly mounted is used as the target, the number of n is varied between 2 and 20, and after the film formation under the above production conditions, the heat treatment is performed under various heat treatment conditions. Was measured for TCS and gauge factor near room temperature. FIG. 12 is a diagram showing the relationship between the number of Al chips and TCS, and FIG. 13 is a diagram showing the relationship between the number of Al chips and the gauge factor.

  As shown in FIG. 12, it was confirmed that TCS showed a good value within −250 ± 500 ppm / ° C. by heat treatment at 300 ° C. or higher when the number of Al chips n was 4 to 20.

  Furthermore, as shown in FIG. 13, when the number of Al chips n is 4 to 20, it is confirmed that the gauge ratio is 4.5 or more, which is larger than the conventionally used strain gauge regardless of the heat treatment temperature. It was.

  From the above results, when the number n of Al chips is 4 to 20, the gauge factor (sensitivity) is 3 or more at -50 to 300 ° C, the TCS is small at -50 to 200 ° C, and at -50 to 500 ° C. It is considered that a strain resistance film and a strain sensor having a small TCR value can be provided.

Next, the resistance stability of the Cr—N—Al thin film with varying Al content was tested. 14 to 17 are diagrams showing the rate of change in resistance (ΔR / R ₀ ) at each measurement temperature. FIG. 14 shows the case where the number of Al chips n = 0, and FIG. 15 shows the case where the number of Al chips n = 2. 16 shows the case where the number of Al chips n = 4, and FIG. 17 shows the case where the number of Al chips n = 6. As shown in FIG. 4, the resistance change rate was obtained from the resistance value before and after holding for 30 minutes including bending. Note that the heat treatment after the film formation was performed in the air at 500 ° C. for 0.5 hour.

  As shown in these figures, the heat resistance for 0.5 hours at 500 ° C. in the atmosphere showed high stability with a resistance change rate within ± 0.02% up to 400 ° C. Moreover, it turns out that the one where there is much Al content exists in the tendency for resistance change rate to become low to higher temperature.

Next, the resistance stability of the Cr—N: Al (20) thin film with Al chip number n = 20 was tested. Here, the heat treatment after film formation is set to 700 ° C. in the atmosphere for 0.5 hour, and after the heat treatment, as shown in FIG. The rate was determined. FIG. 18 is a diagram showing the rate of change in resistance (ΔR / R ₀ ) at each measurement temperature. Moreover, the resistance change rate before and after holding | maintenance in each measurement temperature when holding time was 100 hours was also calculated | required. FIG. 19 is a diagram showing the rate of change in resistance (ΔR / R ₀ ) when the holding time is 100 hours. As shown in these figures, the heat treatment at 700 ° C. in the atmosphere for 0.5 hours allows high stability with a resistance change rate within ± 0.02% up to 450 ° C. for both 30 minutes and 100 hours. Indicated. FIG. 20 is a diagram showing a change in resistance value with respect to the holding time at a temperature of 250 ° C. for 100 hours, and FIG. 21 shows the resistance stability (SR at the time of holding at the temperature of 250 ° C. for 100 hours. ). As shown in these figures, it was confirmed that the resistance variation due to the holding time was small and the resistance stability at 250 ° C. was as extremely small as 0.8 ppm / h. Such a tendency was similarly observed when the number of Al chips was 4 to 16, and it was confirmed that the Cr—N—Al thin film can be stabilized for a long time.

  The relationship between the number of Al chips n and the Al amount (at.%) Under the above-described manufacturing conditions is as shown in FIG.

Next, characteristics of a Cr—N—Mn thin film as a comparative example were obtained. Here, as a target, a composite target in which eight Mn chips each having a size of 10 × 10 mm ² and a thickness of 1 mm are placed on a Cr disk having a nominal purity of 99.9% and a diameter of 101.6 mm is used. 20 mTorr film formation), a Cr—N: Mn (8) thin film having a lattice pattern is formed on an alumina substrate as a base material (strain generating structure). Heat treatment was performed for 5 hours. The Cr—N: Mn (8) thin film after this heat treatment was tested. FIG. 23 is a graph showing the temperature dependence of the resistance value, FIG. 24 is a diagram showing the gauge factor value at each measurement temperature, FIG. 25 is a diagram showing the resistance value at each measurement temperature, and FIG. 26 is the resistance at each measurement temperature. It is a figure which shows change rate ((DELTA) R / _R0 ).

  As shown in FIGS. 23 and 24, in the case of a Cr—N—Mn thin film, the addition of Mn causes the Neel temperature to shift to a high temperature as in the case of Al addition, and a region with a large gauge factor correspondingly increases to a high temperature. There is a shift. Further, as shown in FIGS. 25 and 26, the resistance stability up to 400 ° C. was the same as that of the Cr—N—Al thin film by the heat treatment in the atmosphere, but as shown in FIG. The change, i.e., TCS, was large unlike the Cr-N-Al thin film.

  Next, a composite target in which n Mn chips are placed on a Cr disk is used as a target, the number of n is changed to 0, 4, 8, and 12, and after the film formation under the above manufacturing conditions, various heat treatment conditions are set. The TCR, TCS, and gauge factor in the vicinity of room temperature were measured for the case where heat treatment was performed. 27 is a diagram showing the relationship between the number of Mn chips and the TCR, FIG. 28 is a diagram showing the relationship between the number of Mn chips and TCS, and FIG. 29 is a diagram showing the relationship between the number of Mn chips and the gauge factor. 23 to 29 also show the case where n = 0 (Cr—N thin film).

  As shown in FIG. 27, even when Mn is added to the Cr—N thin film, the TCR is as-depo. It was confirmed that it took a negative value and changed in the positive direction by heat treatment. However, unlike the case of Al addition, the TCR value did not change with an increase in the amount of Mn, and the sample heat-treated at 500 ° C. was as large as about 500 ppm / ° C. at any Mn amount. From this, it was found that the Cr—N—Mn thin film cannot be adjusted to TCR = 0 by heat treatment at a temperature exceeding 300 ° C.

  As shown in FIG. 28, it was confirmed that TCS increased to a positive value by addition of Mn, and further increased as the heat treatment temperature increased. This tendency is considered to appear in a temperature range of 100 ° C. or higher, and it was found that adjustment of TCS is difficult.

  From FIG. 29, although the gauge factor is a larger value than that of a conventionally used strain gauge, it is relatively reduced by the addition of Mn, and it is as small as around 3 in the heat treatment at 500 ° C.

  From these results, it has been found that the Cr—N—Mn thin film has a problem that the TCS is large in the vicinity of room temperature to 300 ° C., TCR adjustment cannot be performed in a temperature range exceeding 300 ° C., and the gauge factor is small. For this reason, a Cr-N-Mn thin film can be increased in temperature with a large gauge factor as well, but the Cr-N-Al thin film has better characteristics than the Cr-N-Mn thin film, and in a high temperature range. It has been confirmed that it is more suitable for use.

  DESCRIPTION OF SYMBOLS 1; Electric oven, 2; Window, 3; Lid member, 4; Support rod, 5; Measuring stand, 6; Fixing member, 7: Substrate, 8; Thin film (strain resistance film), 10; 12; Micrometer, 13; Push rod for applying strain

In the present invention, as the base material (strain generating structure) on which the Cr—N—Al thin film is formed, alumina which is an insulating ceramic having good heat resistance can be suitably used. In addition to alumina, other various ceramics can also be used. Furthermore, as the base material, various metal plates such as stainless steel (SUS) that have been coated with an insulating coating can be used. Further, a method for forming a Cr—N—Al thin film is not particularly limited, but reactive sputtering in which sputtering is performed in an atmosphere of a small amount of nitrogen gas is preferable, and high-frequency sputtering is particularly preferable as sputtering. As the high-frequency sputtering device Ru is preferred Der ones magnetron. The thin film pattern used as the strain resistance film may be a pattern normally used as a strain sensor, and for example, a lattice pattern can be used. The target used for high-frequency sputtering may be a composite target in which a predetermined number of Al chips are bonded to a high-purity Cr disk, but an alloy target prepared in advance with a predetermined composition of Cr—Al may be used.

Claims (10)

General formula Cr _100-xy Al _x N _y
(Where x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20), and in a temperature range of −50 ° C. or more and 300 ° C. or less, A strain resistance film having a gauge factor of 3 or more.   2. The strain resistance film according to claim 1, wherein the temperature coefficient of sensitivity (TCS) is within ± 1500 ppm / ° C. within a temperature range of −50 ° C. to 200 ° C. 3.   3. The strain resistance film according to claim 1, wherein the temperature coefficient of resistance (TCR) is within ± 500 ppm / ° C. in a temperature range of −50 ° C. or more and 500 ° C. or less.   4. The strain resistance film according to claim 1, wherein the resistance stability is within ± 2 ppm / h in a temperature range of 400 ° C. or lower. 5.   A strain sensor comprising the strain resistance film according to any one of claims 1 to 4 formed on a strain generating structure. General formula Cr _100-xy Al _x N _y
(However, x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20). A method for producing a strain resistance film, characterized by performing a heat treatment to form a strain resistance film having a gauge factor of 3 or more in a temperature range of −50 ° C. or more and 300 ° C. or less.   The method for producing a strain resistance film according to claim 6, wherein the temperature coefficient of sensitivity (TCS) is within ± 1500 ppm / ° C in a temperature range of -50 ° C or higher and 200 ° C or lower.   8. The method for producing a strain resistant film according to claim 6, wherein a temperature coefficient of resistance (TCR) is within ± 500 ppm / ° C. in a temperature range of −50 ° C. or more and 500 ° C. or less.   9. The method for producing a strain resistance film according to claim 6, wherein the resistance stability is within ± 2 ppm / h in a temperature range of 400 ° C. or lower. 10. General formula Cr _100-xy Al _x N _y
(Where x and y are atomic ratios (at.%), And 4 ≦ x ≦ 25 and 0.1 ≦ y ≦ 20) are formed on the strain-generating structure, and 300 A strain sensor manufacturing method comprising: obtaining a strain sensor by performing a heat treatment at a temperature of not less than 700 ° C and not more than 700 ° C to obtain a strain resistance film according to any one of claims 6 to 9.

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