JP6708538B2 - Thin film alloy for strain sensors with excellent thermal stability - Google Patents
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- 229910002070 thin film alloy Inorganic materials 0.000 title claims description 56
- 239000000203 mixture Substances 0.000 description 28
- 239000011651 chromium Substances 0.000 description 23
- 239000010409 thin film Substances 0.000 description 16
- 238000010438 heat treatment Methods 0.000 description 9
- 229910019590 Cr-N Inorganic materials 0.000 description 8
- 229910019588 Cr—N Inorganic materials 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 239000010408 film Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- 230000002123 temporal effect Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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Description
本発明は、熱安定性に優れた歪センサ用薄膜合金に関する。 The present invention relates to a thin film alloy for a strain sensor having excellent thermal stability.
歪センサは、薄膜、細線または箔形状のセンサ材の電気抵抗が弾性歪によって変化する現象を利用するものであり、その抵抗変化を測定することにより、歪や応力の計測ならびに変換に用いられる。 The strain sensor utilizes 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 measuring and converting strain and stress by measuring the resistance change.
歪センサの感度は、ゲージ率Ｋによって決まり、Ｋの値は一般に以下の（１）式で与えられる。
Ｋ＝（ΔＲ／Ｒ）／（Δｌ／ｌ）＝１＋２σ＋（Δρ／ρ）／（Δｌ／ｌ） （１）
ここで、Ｒ、σおよびρは、それぞれセンサ材である薄膜、細線または箔の全抵抗、ポアソン比および比電気抵抗である。またｌは被測定体の全長であり、よってΔｌ／ｌは被測定体に生じる歪を表す。一般に、金属・合金におけるσはほぼ０．３であるから、前記の式における右辺第１項と第２項の合計は約１．６でほぼ一定の値となる。したがってゲージ率を大きくするためには、前記の式における第３項が大きいことが必須条件である。すなわち、材料に引っ張り変形を与えたとき材料の長さ方向の電子構造が大幅に変化し、比電気抵抗の変化量Δρ／ρが増加することによる。
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 of the thin film, the thin wire or the foil which is the sensor material, the Poisson's ratio and the specific electric resistance, respectively. 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, σ in metals and alloys is about 0.3, so the sum of the first term and the second term on the right side of the above equation is about 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 the material is subjected to tensile deformation, the electronic structure in the longitudinal direction of the material changes significantly, and the amount of change in specific electric resistance Δρ/ρ increases.
そこで近年になって注目されたのが、バルクのゲージ率として２６〜２８という非常に大きい値が報告されていたクロミウム（Ｃｒ）である。Ｃｒは加工が非常に困難であるが、加工を必要としない薄膜化によって歪センサに応用することができ、薄膜化してもゲージ率が約１５と依然として大きいため、Ｃｒ薄膜が歪センサとして注目されている（例えば特許文献１）。 Therefore, in recent years, attention has been paid to chromium (Cr), which has been reported to have a very large bulk gauge ratio of 26 to 28. Although Cr is very difficult to process, it can be applied to a strain sensor by thinning it without the need for processing. Even if it is thinned, the gauge factor is still high at about 15, so the Cr thin film attracts attention as a strain sensor. (For example, Patent Document 1).
一方、歪センサは、高いゲージ率を有するとともに温度に対する安定性が高いことが要求されるが、Ｃｒ薄膜では、温度安定性の指標である抵抗温度係数（ＴＣＲ）が正の大きな値を示し、安定性の点で問題がある。これに対して、ゲージ率が高く、ＴＣＲが小さい薄膜材料としてＣｒ−Ｎ膜が提案されている（例えば特許文献２）。また、温度安定性の指標としてはゲージ率の温度係数（感度温度係数）（ＴＣＳ）も重要であり、ＴＣＲおよびＴＣＳが低いＣｒ−Ｎ薄膜も提案されている（特許文献３）。 On the other hand, the strain sensor is required to have a high gauge factor and high stability against temperature, but in the Cr thin film, the temperature coefficient of resistance (TCR), which is an index of temperature stability, shows a large positive value. There is a problem with 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). Further, 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 been proposed (Patent Document 3).
ところで、Ｃｒ−Ｎ膜は、状態図より、単相ではなく複数の相が準安定相として存在するため、熱処理温度でその特性が著しく変化する。このためＴＣＲおよびＴＣＳの双方を小さくするため、非常に限られた温度、時間で熱処理する必要がある。したがって、そのような限られた条件が崩れる条件下では非常に熱的に不安定となり例えば２５０℃程度において抵抗の時間変化が大きく十分な熱安定性が得られないことが判明した。 By the way, according to the phase diagram, the Cr-N film has a plurality of phases as metastable phases rather than a single phase, and therefore its characteristics change significantly at the heat treatment temperature. Therefore, in order to reduce both TCR and TCS, it is necessary to perform heat treatment at a very limited temperature and time. Therefore, it was found that under such a condition that the limited condition collapses, it becomes very thermally unstable, and the resistance varies with time at, for example, about 250° C., and sufficient thermal stability cannot be obtained.
したがって、本発明は、ＴＣＲおよびＴＣＳが小さいとともに２５０℃で抵抗の時間的変化が小さい、熱安定性に優れた歪センサ用薄膜合金を提供することを課題とする。 Accordingly, the present invention aims to provide a TCR and TCS is less temporal change in the resistance at 250 ° C. with small, thermostable excellent thin alloying strain sensor.
本発明者らは、上記課題を解決すべく検討を重ねた結果、所定組成のＣｒ−Ａｌ系薄膜、および所定組成のＣｒ−Ａｌにさらに適量のＢを加えたＣｒ−Ａｌ−Ｂ系薄膜合金は、単相として存在し、高温領域において優れた熱的安定性を示すことを見出した。 As a result of repeated studies to solve the above-mentioned problems, the present inventors have made a Cr-Al-based thin film having a predetermined composition and a Cr-Al-B-based thin film alloy in which a proper amount of B is added to Cr-Al having a predetermined composition Have been found to exist as a single phase and exhibit excellent thermal stability in the high temperature region.
本発明は、このような知見に基づいてなされたものであり、以下の（１）、（２）を提供する。 The present invention has been made based on such findings, and provides the following (1) and (2) .
（１）一般式Ｃｒ１００−ｘ−ｙＡｌｘＢｙ
（ただし、ｘ、ｙは原子比率（ａｔ．％）である）で表され、ｙが０≦ｙ≦５であり、ｙ＝０のとき１２≦ｘ≦１６、０＜ｙ≦５のとき１２≦ｘ≦１４であり、２５０℃において熱安定性に優れた歪センサ用薄膜合金。
(1) In formula Cr 100-x-y Al x B y
(However, x, y is the atomic ratio (at.%) Der Ru) is represented by, y is 0 ≦ y ≦ 5, 12 ≦ x ≦ 16,0 when y = 0 <a y ≦ 5 When 12≦x≦14, a thin film alloy for strain sensor having excellent thermal stability at 250° C.
（２）２５０℃での抵抗の時間変化が、２０ｐｐｍ／Ｈ以下であることを特徴とする、（１）に記載の熱安定性に優れた歪センサ用薄膜合金。 (2) The thin film alloy for a strain sensor having excellent thermal stability according to (1) , wherein the change in resistance with time at 250° C. is 20 ppm/H or less.
本発明によれば、ＴＣＲおよびＴＣＳが小さいとともに２５０℃で抵抗の時間的変化が小さい、熱安定性に優れた歪センサ用薄膜合金が提供される。 According to the present invention, the temporal change of the resistance at 250 ° C. with TCR and TCS is small is less, the thin film alloy for strain sensor excellent in thermal stability is provided.
以下、本発明の実施の形態について詳細に説明する。
まず、従来歪センサ用合金として用いられているＣｒ−Ｎ系薄膜について特性を把握した。その結果を図１〜３に示す。図１は、Ｃｒ−Ｎ系薄膜合金としてＣｒ−４．４ａｔ．％Ｎを用い、２４０〜６００℃の各温度で１時間の熱処理を行った後のゲージ率の温度変化を示す図である。また、図２は、成膜後の熱処理温度を２００℃にした場合の、Ｃｒ−Ｎ薄膜合金のＮ含有量と、ＴＣＲおよびＴＣＳとの関係を示す図である。さらに、図３は、Ｃｒ−４．４ａｔ．％Ｎ薄膜について、３００℃で１時間真空熱処理した後、２５０℃に保持したときの抵抗の時間変化を示す図である。
Hereinafter, embodiments of the present invention will be described in detail.
First, the characteristics of a Cr-N-based thin film that has been conventionally used as an alloy for a strain sensor were understood. The results are shown in FIGS. FIG. 1 shows Cr-4.4 at. It is a figure which shows the temperature change of the gauge rate after heat-processing for 1 hour at each temperature of 240-600 degreeC using %N. FIG. 2 is a diagram showing the relationship between the N content of the Cr—N thin film alloy and the TCR and TCS when the heat treatment temperature after film formation is set to 200° C. Furthermore, FIG. 3 shows Cr-4.4 at. It is a figure which shows the time change of resistance when it hold|maintains at 250 degreeC after vacuum-heat-treating about %N thin film at 300 degreeC for 1 hour.
図１に示すように、熱処理温度によって、−６０〜１１０℃の温度範囲におけるゲージ率の温度変化のパターンが変化し、図２に示すように、熱処理温度を最適化した上でＮ含有量を最適化することにより、ＴＣＲおよびＴＣＳを小さくできることが確認された。しかし、図３に示すように、Ｃｒ−Ｎ系薄膜合金は、３００℃で１時間真空熱処理後、２５０℃で保持しても抵抗の時間変化が大きく、また、熱処理およびＮ含有量の最適化でＴＣＲとＴＣＳを小さくすることができるものの、双方を零近傍にすることまでは困難であることが判明した。 As shown in FIG. 1, the pattern of the temperature change of the gauge factor in the temperature range of −60 to 110° C. changes depending on the heat treatment temperature, and as shown in FIG. It was confirmed that TCR and TCS can be reduced by optimization. However, as shown in FIG. 3, the Cr—N-based thin film alloy has a large change in resistance with time even after being subjected to vacuum heat treatment at 300° C. for 1 hour and then held at 250° C. Further, the heat treatment and optimization of the N content are performed. Although it was possible to reduce TCR and TCS, it was found that it was difficult to bring both to near zero.
そこで、Ｃｒと単相を形成し、抵抗の時間変化が小さく、ＴＣＲおよびＴＣＳも小さい、熱安定性に優れた薄膜合金を見出すべく、種々の二元系Ｃｒ系薄膜合金について検討した。
図４は、Ｃｒ薄膜および種々のＣｒ系薄膜合金について、３００℃で１時間真空熱処理した後、２５０℃に保持したときの抵抗の時間変化を示す図、図５は、Ｃｒ薄膜および種々のＣｒ系薄膜合金におけるゲージ率の温度変化を示す図である。ここでは、Ｃｒ薄膜合金として、従来のＣｒ−４．４ａｔ％Ｎの他、Ｃｒ−１．６ａｔ．％Ａｌ、Ｃｒ−３．８ａｔ．％Ｂ、Ｃｒ−２．９ａｔ．％Ｃ、Ｃｒ−９．８ａｔ．％Ｏを用いた。
Therefore, various binary Cr-based thin film alloys were studied in order to find a thin-film alloy that forms a single phase with Cr, has a small resistance change with time, and has a small TCR and TCS and is excellent in thermal stability.
FIG. 4 is a diagram showing a change with time in resistance of a Cr thin film and various Cr-based thin film alloys when vacuum heat-treated at 300° C. for 1 hour and then kept at 250° C. FIG. 5 shows Cr thin films and various Cr It is a figure which shows the temperature change of the gauge factor in a system type thin film alloy. Here, as the Cr thin film alloy, in addition to the conventional Cr-4.4 at% N, Cr-1.6 at. % Al, Cr-3.8 at. % B, Cr-2.9 at. % C, Cr-9.8 at. % O was used.
その結果、抵抗の時間変化は、Ｃｒ−１．６ａｔ．％Ａｌが最も小さく、その値は２０ｐｐｍ以下であり、Ｃｒ−４．４ａｔ．％Ｎの約１／２０であった。また、Ｃｒ−３．８ａｔ．％Ｂが次に小さく、その値はＣｒ−４．４ａｔ．％Ｎの約１／１０であった。また、Ｃｒ−２．９ａｔ．％ＣおよびＣｒ−９．８ａｔ．％Ｏの抵抗の時間変化は、Ｃｒ−４．４ａｔ．％Ｎよりも小さいが、Ｃｒ−１．６ａｔ．％ＡｌおよびＣｒ−３．８ａｔ．％Ｂよりも大きな値となり、Ｃｒと同程度であった。 As a result, the change in resistance with time is Cr-1.6 at. %Al is the smallest, the value is 20 ppm or less, and Cr-4.4 at. It was about 1/20 of %N. In addition, Cr-3.8 at. % B is next smaller, and the value is Cr-4.4 at. It was about 1/10 of% N. In addition, Cr-2.9 at. % C and Cr-9.8 at. % O resistance changes with time with respect to Cr-4.4 at. %-N, but Cr-1.6 at. % Al and Cr-3.8 at. The value was larger than %B and was about the same as Cr.
図４の測定後のＣｒ系合金で行ったゲージ率の温度変化については、Ｃｒ−１．６ａｔ．％Ａｌ、Ｃｒ−３．８ａｔ．％Ｂ、Ｃｒ−２．９ａｔ．％Ｃ、Ｃｒ−９．８ａｔ．％Ｏのいずれも、ＣｒやＣｒ−４．４ａｔ．％Ｎよりも小さく、特に、Ｃｒ−１．６ａｔ．％ＡｌおよびＣｒ−９．８ａｔ．％Ｏが小さい値となった。また、ゲージ率についてはいずれも５以上と使用可能なレベルであった。 Regarding the temperature change of the gauge factor performed on the Cr-based alloy after the measurement in FIG. 4, as for Cr-1.6 at. % Al, Cr-3.8 at. % B, Cr-2.9 at. % C, Cr-9.8 at. % O, Cr and Cr-4.4 at. % N, especially Cr-1.6 at. % Al and Cr-9.8 at. %O became a small value. In addition, the gauge ratio was 5 or more, which was a usable level.
以上の結果から、２５０℃程度の高温で保持した場合の抵抗の時間変化は、Ｃｒ−Ａｌ系薄膜合金が最も良好であり、次いでＣｒ−Ｂ系薄膜合金が良好であり、これらはいずれもゲージ率が実用的な値であることがわかった。 From the above results, the temporal change in resistance when kept at a high temperature of about 250° C. is best in the Cr-Al thin film alloy, and next in the Cr-B thin film alloy, both of which are gauges. The rate was found to be a practical value.
これらの結果に基づいて、Ｃｒ−Ａｌ系薄膜合金およびＣｒ−Ａｌ−Ｂ系薄膜合金についてさらに検討を重ねた。その結果を図６〜１４に示す。 Based on these results, the Cr-Al-based thin film alloy and the Cr-Al-B-based thin film alloy were further studied. The results are shown in FIGS.
図６〜９は、それぞれＣｒ−Ａｌ系薄膜合金の抵抗値（０℃）、ＴＣＲ（０〜５０℃）、ゲージ率（０℃）、ＴＣＳ（０〜５０℃）の組成（Ａｌ含有量）依存性を示す図である。図６〜９には、Ｂを３．３〜５ａｔ．％含有させたＣｒ−Ａｌ−Ｂ系薄膜合金の結果も併記する。また、図１０〜１３は、それぞれ抵抗値（０℃）、ＴＣＲ（０〜５０℃）、ゲージ率（０℃）、ＴＣＳ（０〜５０℃）の組成依存性を示すＣｒ−Ａｌ−Ｂ三元系組成図である。 6 to 9 show the compositions (Al content) of the resistance value (0° C.), TCR (0 to 50° C.), gauge ratio (0° C.), and TCS (0 to 50° C.) of the Cr—Al-based thin film alloy, respectively. It is a figure which shows a dependency. 6-9, B is 3.3-5 at. %, the results of the Cr-Al-B based thin film alloy contained are also shown. In addition, FIGS. 10 to 13 show Cr-Al-B3 compositions showing composition dependence of resistance value (0° C.), TCR (0 to 50° C.), gauge ratio (0° C.), and TCS (0 to 50° C.), respectively. FIG.
図６および図８に示すように、抵抗値はＡｌ含有量の増加にともなって増加し、ゲージ率はほぼ５〜１０の範囲である。この傾向は、図１０および図１２にも示すように、Ｂを添加したＣｒ−Ａｌ−Ｂ系薄膜合金でも同様である。 As shown in FIGS. 6 and 8, the resistance value increases as the Al content increases, and the gauge factor is in the range of approximately 5 to 10. This tendency is the same as in the Cr-Al-B based thin film alloy containing B as shown in FIGS. 10 and 12.
一方、図７および図９に示すように、Ｃｒ−Ａｌ系薄膜合金のＴＣＲおよびＴＣＳは、いずれもＡｌ含有量を調整することにより０近傍の値にすることができるが、さらにＢを添加することにより、ＴＣＲおよびＴＣＳをより０に近づけることができる。特に、ＴＣＳに対するＢ添加の効果が大きい。詳細には、図１１、図１３から、Ｃｒ−Ａｌ−Ｂ系の組成範囲内に、それぞれＴＣＲ＝０、ＴＣＳ＝０になる組成が存在し、その周囲にそれぞれＴＣＲ、ＴＣＳが−２００〜＋２００ｐｐｍ／℃の範囲内という非常に小さい値の範囲が存在していることがわかる。 On the other hand, as shown in FIGS. 7 and 9, the TCR and TCS of the Cr—Al-based thin film alloy can both be brought to a value near 0 by adjusting the Al content, but B is further added. As a result, TCR and TCS can be brought closer to zero. In particular, the effect of adding B to TCS is great. In detail, from FIG. 11 and FIG. 13, compositions having TCR=0 and TCS=0 exist in the composition range of the Cr—Al—B system, respectively, and TCR and TCS are −200 to +200 ppm around them. It can be seen that there is a very small range of values within the range of /°C.
図１４は、ＴＣＲとＴＣＳの両方を示すＣｒ−Ａｌ−Ｂ三元系組成図であるが、この図から、Ｃｒ−Ａｌ−Ｂ系組成を一般式Ｃｒ１００−ｘ−ｙＡｌｘＢｙで表した場合に、１＜ｘ（ａｔ．％）＜２０、０≦ｙ（ａｔ．％）＜１０の範囲内において、ＴＣＲおよびＴＣＳの双方、またはいずれか一方が−２００〜＋２００ｐｐｍ／℃の範囲内となる組成範囲が存在することがわかる。 Figure 14 is a ternary composition diagram Cr-Al-B showing both the TCR and TCS, from this figure, a Cr-Al-B-based composition in the general formula Cr 100-x-y Al x B y When expressed, in the range of 1<x (at.%)<20 and 0≦y (at.%)<10, both or one of TCR and TCS is in the range of −200 to +200 ppm/° C. It can be seen that there is a composition range within.
そこで、本発明では、２５０℃程度に保持した際の抵抗の時間変化が小さく、ＴＣＲおよびＴＣＳが小さく、かつ実用的なゲージ率を有する薄膜合金として、一般式Ｃｒ１００−ｘ−ｙＡｌｘＢｙ（ただし、１＜ｘ（ａｔ．％）＜２０、０≦ｙ（ａｔ．％）＜１０）で表される組成から選択したものとした。図７および図９から、実際にＴＣＲ＝０およびＴＣＳ＝０をほぼ満たすのは、Ａｌが１２〜１６ａｔ．％の範囲のＣｒ−Ａｌ薄膜合金およびＡｌが１２〜１４ａｔ．％の範囲のＢを５ａｔ．％まで添加したＣｒ−Ａｌ−Ｂ薄膜合金であり、また、図８からこれらの範囲ではゲージ率も６〜８と高い。これらの点から、より好ましい組成範囲は、一般式ＣｒＡｌｘＢｙにおいて、ｙ（ａｔ．％）＝０および１２≦ｘ（ａｔ．％）≦１６で表される範囲、０＜ｙ（ａｔ．％）≦５および１２≦ｘ（ａｔ．％）≦１４で表される範囲である。 Therefore, in the present invention, as a thin film alloy having a small change with time in resistance at about 250° C., a small TCR and TCS, and a practical gauge factor, a general formula Cr 100-xy Al x B is used. y (provided that, 1 <x (at.% ) <20,0 ≦ y (at.%) <10) was assumed to be selected from the composition represented by. From FIGS. 7 and 9, the fact that Al substantially satisfies TCR=0 and TCS=0 is that Al is 12 to 16 at. % Cr-Al thin film alloy and Al at 12 to 14 at. % Of B at 5 at. %, it is a Cr-Al-B thin film alloy added up to %, and the gauge factor is as high as 6 to 8 in these ranges from FIG. From these points, more preferred composition range are the compounds of formula CrAl x B y, y (at .%) = 0 and 12 ≦ x (at.%) Ranges represented by ≦ 16, 0 <y (at . %)≦5 and 12≦x (at. %)≦14 .
２５０℃程度の高温に保持した際の抵抗の時間変化は、２０ｐｐｍ／Ｈ以下とすることができる。これは、上述した図４では、Ｃｒ−Ａｌ薄膜合金を３００℃で熱処理して２５０℃で保持したときに１００時間で０．２％変化しており、さらに高い温度で熱処理して２５０℃で保持すれば、変化量はさらに小さくなると推察できるからである。また、本発明の範囲内のＣｒ−Ａｌ薄膜合金およびＣｒ−Ａｌ−Ｂ薄膜合金についても、同様に２０ｐｐｍ／Ｈ以下とすることができる。 The change with time in resistance when kept at a high temperature of about 250° C. can be 20 ppm/H or less. This is because in FIG. 4 described above, when the Cr—Al thin film alloy was heat-treated at 300° C. and held at 250° C., it changed by 0.2% in 100 hours, and further heat-treated at a higher temperature at 250° C. This is because it can be inferred that the amount of change will become even smaller if held. Further, the Cr-Al thin film alloy and the Cr-Al-B thin film alloy within the scope of the present invention can also be set to 20 ppm/H or less.
また、ＴＣＲおよびＴＣＳの双方、またはこれらのいずれか一方が、−２００〜＋２００ｐｐｍ／℃の範囲内であることが好ましい。これは、ＴＣＲおよびＴＣＳは極力小さい方が好ましく、特に、ブリッジを組むことで調整することができないＴＣＳは、２００ｐｐｍ／℃程度が必要だからである。 Further, it is preferable that both of TCR and TCS or one of them is within a range of -200 to +200 ppm/°C. This is because it is preferable that TCR and TCS are as small as possible, and in particular, about 200 ppm/° C. is required for TCS that cannot be adjusted by building a bridge.
また、比抵抗率は２５０μΩ・ｃｍ以上が好ましい。Ｃｒ−Ａｌ−Ｂ系において、図１４に示すＴＣＲおよびＴＣＳがほぼ零となる範囲と、図１０に示す抵抗値が４０００Ω以上と高い値となる範囲がほぼ一致しており、４０００Ωを比抵抗率に換算すると２５０μΩ・ｃｍとなる。歪センサを回路に組むときに高抵抗ほど小電流ですむため、比抵抗率の好ましい範囲を２５０μΩ・ｃｍ以上とした。 Further, the specific resistance is preferably 250 μΩ·cm or more. In the Cr-Al-B system, the range where TCR and TCS shown in FIG. 14 are almost zero and the range where the resistance value shown in FIG. When converted to, it becomes 250 μΩ·cm. Since a higher resistance requires a smaller current when a strain sensor is assembled in a circuit, the preferred range of the specific resistance is set to 250 μΩ·cm or more.
本発明の薄膜合金を成膜する手法は特に限定されないがスパッタリング、特に高周波スパッタリングが好ましい。歪センサの歪抵抗膜として用いる薄膜のパターンとしては、歪センサとして通常用いるパターンでよく、例えば格子状パターンを用いることができる。 The method for forming the thin film alloy of the present invention is not particularly limited, but sputtering, particularly high frequency sputtering is preferable. The thin film pattern used as the strain resistance film of the strain sensor may be a pattern normally used as the strain sensor, and for example, a lattice pattern can be used.
また、本発明の薄膜合金は、成膜後、所定温度で熱処理する必要があるが、その熱処理の温度は、高温領域で所望の特性を得るためには、その高温領域の温度よりも５０〜１００℃程度高い温度で熱処理することが好ましい。 Further, the thin film alloy of the present invention needs to be heat-treated at a predetermined temperature after film formation, but the temperature of the heat treatment is 50 to 50° C. higher than the temperature in the high temperature region in order to obtain desired characteristics in the high temperature region. It is preferable to perform heat treatment at a temperature as high as about 100°C.
（実施例１）
以下、本発明の実施例について説明する。
ここでは、基板上に、高周波スパッタリングにより所定パターンでＣｒ−１４．４ａｔ．％Ａｌ組成の薄膜を形成した後、３００℃、４５０℃で熱処理して試料を作製した。
(Example 1)
Examples of the present invention will be described below.
Here, Cr-14.4 at. After forming a thin film having a% Al composition, heat treatment was performed at 300° C. and 450° C. to prepare a sample.
各試料について、−５０〜１００℃の範囲の複数の温度で抵抗およびゲージ率を求めた。その結果を図１５および図１６に示す。また、これら試料について、２５０℃で保持して抵抗の時間変化を求めた。 For each sample, resistance and gauge factor were determined at multiple temperatures ranging from -50 to 100°C. The results are shown in FIGS. 15 and 16. Further, with respect to these samples, the change with time of the resistance was obtained by holding at 250°C.
各試料の、抵抗（０℃）、ＴＣＲ、ゲージ率Ｇｆ（０℃）、ＴＣＳ、抵抗の時間変化を表１に示す。
（実施例２）
ここでは、基板上に、高周波スパッタリングにより所定パターンで表２に示す組成のＣｒ−Ａｌ−Ｂ薄膜合金を形成した後、３００℃で熱処理して試料を作製した。
(Example 2)
Here, a Cr-Al-B thin film alloy having the composition shown in Table 2 was formed on the substrate by high frequency sputtering in a predetermined pattern, and then heat-treated at 300°C to prepare a sample.
各試料について、ゲージ率（１００℃）、ＴＣＳ（０〜５０℃）、抵抗値（０℃）、ＴＣＲ（０〜５０℃）を求めた。その際の各組成におけるゲージ率、およびＴＣＳ、抵抗、ＴＣＲを表２に示す。 For each sample, the gauge factor (100° C.), TCS (0 to 50° C.), resistance value (0° C.), and TCR (0 to 50° C.) were obtained. Table 2 shows the gauge ratio, TCS, resistance, and TCR in each composition at that time.
Claims (2)
（ただし、ｘ、ｙは原子比率（ａｔ．％）である）で表され、ｙが０≦ｙ≦５であり、ｙ＝０のとき１２≦ｘ≦１６、０＜ｙ≦５のとき１２≦ｘ≦１４であり、２５０℃において熱安定性に優れた歪センサ用薄膜合金。(Where x and y are atomic ratios (at. %)), y is 0≦y≦5, 12 when y=0, 12≦x≦16, and 0<y≦5, 12 A thin film alloy for a strain sensor having ≦x≦14 and excellent thermal stability at 250° C.
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