JP6940369B2 - Thin film strain sensor material and thin film strain sensor - Google Patents

Description

The present invention relates to thin film strain sensor materials and thin film strain sensors.

A strain sensor is an element or the like that measures the strain generated in an object, and is also called a strain gauge. Generally, the sensitivity that the strain gauge has in the direction perpendicular to the gauge axis (the direction in which the current flows in the main sensing part), which is the normal measurement direction, is called the lateral sensitivity, and the lateral sensitivity coincides with the strain direction of the gauge axis. It has been reported that it is 2 to 3% or less of the spindle sensitivity (vertical sensitivity), which is the sensitivity when measured by the force (Non-Patent Documents 1 and 2). Therefore, a conventional general strain gauge hardly produces an output due to strain in the direction perpendicular to the gauge axis.

Taking advantage of this feature, when a 2-active 4-gauge type Wheatstone bridge circuit configuration is formed, a method is adopted in which a dummy gauge is formed in the vicinity of the active gauge in a direction perpendicular to the gauge direction (= strain direction). This method has been widely used in thin film strain sensors in recent years. The reason why the dummy gauge is placed near the active gauge is that there is no other place including the limitation of the film formation area, so the wiring is shortened to reduce the noise picked up there, and the influence of the temperature distribution is reduced. For the reason. Since the two dummy gauges in the bridge circuit are oriented in the direction perpendicular to the strain, they can play a role as dummies with almost no resistance change due to the strain.

However, in reality, the strain to be measured causes deformation based on the Poisson's ratio of the target measurement substance in the direction perpendicular to the strain direction (lateral direction), and strain (transverse strain) occurs in that direction. Then, since the direction of the lateral strain coincides with the gauge shaft of the dummy gauge, the output is generated at the spindle sensitivity, and a loss is caused in the bridge output. That is, the function as a dummy becomes insufficient. Also, in the case of a multi-axis (rosette) strain gauge in which multiple uniaxial strain gauges are stacked or arranged in different directions to form a single gauge element, or a group of strain gauges for multi-axis mechanical quantity detection. Even when arranged, lateral strain may cause noise components such as interference with other axes.

As a strain gauge arranged in the direction perpendicular to the strain to be measured as in the vertically arranged sample of FIG. 1 described later, for example, in the case of a commercially available strain gauge (strain gauge) made of CuNi alloy foil, the output value is , The apparent gauge ratio is reported to be -0.4 (Patent Document 1). The value is a little smaller than the gauge ratio 2.1 when the direction of strain (strain application direction), which is the original measurement target, and the main axis direction of the gauge are matched, but it is smaller than the lateral sensitivity. Is about 10 times larger, which is a problem.

Further, Cr thin films and Cr—N thin films are known as materials having a large gauge ratio and suitable as strain gauges (Patent Documents 2 and 3), but they are also known to have high lateral sensitivity (Patent Document 1). ). Conventional general strain gauges have almost no lateral sensitivity, so they have anisotropy and can specify the magnitude and direction of strain in a multiaxial stress field, whereas Cr thin films and Cr-N thin films can be specified. The strain sensor using is almost isotropic in sensitivity and is affected by strain in all directions regardless of the direction of the installed gauge shaft. Therefore, it is not possible to specify the strain direction and form a multi-axis strain gauge.

On the other hand, in Patent Document 4, the conventional Pd-Cr alloy and Ni-Cr-Al alloy have problems that the temperature coefficient of resistance is large and the strain sensitivity (longitudinal direction) is small and the lateral sensitivity is large. In order to solve the problem, we have proposed a Pd-Cr alloy (Cr content: 14 to 25% by mass) having a composition different from the conventional one, and the Pd-Cr alloy having that composition has a lateral sensitivity of -0.3 to 0. .3, strain sensitivity (gauge ratio) is 1.75 to 1.83, TCR is 39 to 60 ppm / ° C, resistance temperature coefficient is small, lateral sensitivity is small, and strain sensitivity in the vertical direction is large, which is better than before. It is said that a strain sensor with different characteristics can be obtained. The value of the lateral sensitivity in Patent Document 4 is not the pure lateral sensitivity, but the apparent gauge ratio obtained when the strain gauge is arranged (vertically arranged) in the horizontal direction, that is, in the direction perpendicular to the vertical direction. It seems to represent.

However, in Patent Document 4, although it is possible to set the gauge ratio to zero in the case of vertical arrangement, the sensitivity in the vertical direction, that is, the gauge ratio in the case of arrangement parallel to the strain direction is about 1.8. The value is even smaller than 2.1 of a general commercially available strain gauge (strain gauge). In measurements such as multi-axis, high accuracy, and high-speed response, lateral sensitivity and vertical placement sensitivity cannot be ignored, and a larger gauge ratio for parallel placement is required.

Japanese Unexamined Patent Publication No. 2014-305239 Japanese Unexamined Patent Publication No. 10-270201 Japanese Unexamined Patent Publication No. 2015-031633 Japanese Unexamined Patent Publication No. 2013-217763

Takahashi Award, Masayasu Kawai: "Introduction to Strain Measurement with Strain Gauge", Taiseisha, pp. 46-47 (2007) Akira Kanno, Takahashi Award, Toshio Yoshino: "Stress-Strain Analysis", Asakura Shoten, p. 31 (1986)

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a thin film strain sensor material and a thin film strain sensor having a gauge ratio of almost zero in a vertical arrangement and a large gauge ratio in a parallel arrangement. ..

As a result of repeated studies to solve the above problems, the present inventor uses a Cr-based thin film or a Cr—N-based thin film represented by a Cr—Ni thin film having a predetermined composition, so that the gauge ratio in the vertical arrangement can be increased. We have found that a thin film strain sensor with almost zero and a large gauge ratio in parallel arrangement can be obtained.

The present invention has been made based on such findings, and provides the following (1) to (8).

(1) _{A thin film strain sensor material represented by the general formula Cr 100-x Mx} , in which the thin film of the material is arranged in a direction perpendicular to the strain direction of the measurement target on the high temperature side of the nail temperature of the material. A thin film strain sensor material, characterized in that the second element M is added in the range of 0 ≦ x ≦ 30 in composition ratio x in atomic% so that the gauge ratio is within 0 ± 0.3.

(2) A thin film strain sensor material represented by the general formula _{(Cr 100-x M x)} 100-y N y, composition ratio y is in the range of 0.0001 ≦ y ≦ 30 in atomic percent, The composition ratio x is atomic so that the gauge ratio is within 0 ± 0.3 when the thin film of the material is arranged in the direction perpendicular to the strain direction to be measured on the high temperature side of the nail temperature of the material. A thin film strain sensor material, characterized in that the third element M is added in the range of 0 ≦ x ≦ 30 in%.

(3) The thin film strain sensor material according to (1) above, wherein the second element M is Ni and the composition ratio x is 5 ≦ x ≦ 22 in atomic%.

(4) The thin film strain sensor material according to (1) above, wherein the second element M is Fe and the composition ratio x is 17 ≦ x ≦ 28 in atomic%.

(5) a thin film of material represented by the general formula Cr _100-x M _x A thin film strain sensor having a sensing part, the high-temperature side of the Neel temperature of the material, the strain thin film of said material to be measured The second element M should be added in the range of 0 ≦ x ≦ 30 with a composition ratio x of atomic% so that the gauge ratio when arranged in the direction perpendicular to the direction of is within 0 ± 0.3. A featured thin film strain sensor.

(6) The general formula _{(Cr 100-x M x)} thin film of a material represented by _{100-y N y} thin film strain sensor having a sensing part, the composition ratio y is, 0.0001 ≦ with atomic% It is in the range of y ≦ 30, and the gauge ratio is within 0 ± 0.3 when the thin film of the material is arranged in the direction perpendicular to the strain direction of the measurement target on the high temperature side of the nail temperature of the material. As described above, the thin film strain sensor is characterized in that the third element M is added in the range where the composition ratio x is atomic% and 0 ≦ x ≦ 30.

(7) The thin film strain sensor according to (5) above, wherein the second element M is Ni and the composition ratio x is 5 ≦ x ≦ 22 in atomic%.

(8) The thin film strain sensor according to (5) above, wherein the second element M is Fe and the composition ratio x is 17 ≦ x ≦ 28 in atomic%.

According to the present invention, there are provided a thin film strain sensor material and a thin film strain sensor having a gauge ratio of almost zero in a vertical arrangement and a large gauge ratio in a parallel arrangement.

It is a figure for demonstrating the parallel arrangement sample and the vertical arrangement sample in a thin film element pattern. It is a figure which shows the relationship between the Ni addition amount in a Cr—Ni thin film, the gauge ratio of a parallel arrangement, and the gauge ratio of a vertical arrangement. It is a figure which shows the relationship between the Fe addition amount in a Cr—Fe thin film, the gauge ratio of a parallel arrangement, and the gauge ratio of a vertical arrangement. It is a figure which shows the relationship between the temperature and the gauge ratio, and the relationship between the temperature and a resistance value in a Cr thin film. It is a figure described on page 40 of Non-Patent Document 3. It is a figure described on page 39 of Non-Patent Document 3. It is a figure which shows the relationship between the amount of Ni of a Cr—Ni thin film, and the temperature coefficient of resistance (TCR). It is a figure which shows the relationship between the amount of Ni of a Cr—Ni thin film, and the temperature coefficient of sensitivity (TCS). It is a figure which shows the relationship between the Fe amount of Cr—Fe thin film, and the sensitivity temperature coefficient (TCS).

Hereinafter, embodiments of the present invention will be described in detail.
First, in the following description, the parallel arrangement sample and the vertically arrangement sample in the thin film element pattern will be described with reference to FIG. FIG. 1 shows an I-shaped sample in which the direction of the thin film element pattern is matched with the strain application direction in the parallel arrangement sample, and the direction of the thin film element pattern is perpendicular to the strain application direction in the vertical arrangement sample. If. The gauge ratio of the parallel arrangement sample (gauge ratio in the parallel arrangement) is the gauge ratio in the spindle direction, and the gauge ratio of the vertically arranged sample (gauge ratio in the vertical arrangement) is the gauge ratio related to the lateral sensitivity.

The present inventor has studied various Cr-based alloy thin films in order to obtain a thin film strain sensor material having a gauge ratio of almost zero in a vertical arrangement and a large gauge ratio in a parallel arrangement. As a result, the results shown in FIGS. 2 and 3 were obtained for the Cr—Ni thin film and the Cr—Fe thin film, respectively. That is, as the Ni content increases, both the gauge ratio in the parallel arrangement and the gauge ratio in the vertical arrangement decrease, and the gauge ratio in the parallel arrangement is about 2.6 with 8.4 at% of Ni, and the gauge ratio in the vertical arrangement is For the first time, it was found that the gauge ratio was zero, and that the gauge ratio of the parallel arrangement was about 3.3 with Fe of 20 at% and the gauge ratio of the vertical arrangement was zero.

On the other hand, the present inventor has previously clarified that in a Cr thin film or a Cr—N thin film, the lateral sensitivity shows a value as large as the longitudinal sensitivity (Patent Document 3 above). In addition, the present inventor further clarified from the measurement of the gauge ratio up to the high temperature region that the gauge ratio of the large parallel arrangement of the Cr thin film appears on the low temperature side of the Néel temperature observed in the antiferromagnet. Eiji Niwa: "Effect of Addition of Second Element to Cr Thin Film on Gauge Ratio in High Temperature Region", Institute of Electrical Engineers of Japan Physical Sensor Study Group Sample, PHS-17-005 (2017)).

Based on these findings, the contents of considering the behavior of the Cr—Ni thin film and the Cr—Fe thin film will be described with reference to FIG. FIG. 4 is a diagram showing the relationship between the temperature and the gauge ratio and the relationship between the temperature and the resistance value in the Cr thin film. As shown in FIG. 4, with respect to the Cr thin film, since it becomes an antiferromagnetic phase below the Néel temperature, the piezoresistive effect greatly acts and the lateral sensitivity also increases, and not only in the case of parallel arrangement but also in the case of vertical arrangement. It is considered that the gauge rate will take a large positive value.

On the other hand, since it is a paramagnetic phase above the Néel temperature, the piezoresistive effect does not work, so the lateral sensitivity becomes almost zero, and it is considered that the gauge ratio takes a small negative value due to the Poisson's ratio due to the shape effect alone. .. Then, it was considered that there is a temperature at which the gauge ratio of the vertical arrangement becomes zero in the transition region between the two, that is, in the vicinity of the Néel temperature. Then, it was confirmed that the gauge ratio of the parallel arrangement at that time was larger than 2 in the Cr—Ni thin film and the Cr—Fe thin film. In FIG. 4, the measured values were used as the gauge ratio and the resistance value of the Cr thin film with respect to the measured temperature.

The figure described on page 40 of Non-Patent Document 3 (E. Fawcett et al .: "Spin-density-wave antiferromagnetism in chromium alloys", Rev. Mod. Phys., 66 (1), (1994)). 5 is shown in FIG. 5, and the figure shown on page 39 is shown in FIG. 6. As shown in these figures, in the case of a thin film in which the second element M is added to Cr, the type and amount of the second element M to be added. It can be seen that it is possible to change the nail temperature of the thin film to the high temperature side or the low temperature side. Specifically, when the second element M is Mn, Os, Ir, Pt, Ru, Rh, Ge, As, Sn, Ga, Sb, Re or the like, the Néel temperature can be changed to the higher temperature side. When the two elements M are Au, Fe, Co, Mo, W, Ti, Ni, V, Er, Yb, Be, Si and the like, the Neel temperature can be changed to the lower temperature side. When the second element M is Al, it can be changed to either the low temperature side or the high temperature side depending on the amount.

From the data in FIGS. 5 and 6 and the above consideration results, by adjusting the type and amount of the second element M, the gauge ratio of the vertical arrangement is near zero (within 0 to ± 0.3) at an arbitrary temperature. It has been found that the properties can be manifested.

In FIGS. 2 and 3, the Cr—Ni thin film and the Cr—Fe thin film have a composition in which the gauge ratios at room temperature are about 2.6 and 3.3 in the parallel arrangement and 0 in the vertical arrangement, respectively. confirmed. It is considered that the Néel temperature around 170 ° C of the Cr thin film (the Néel temperature of Cr bulk is 35 ° C, but it seems that it was shifted because it is a thin film) was reduced by adding Ni or Fe and shifted to near room temperature. Be done. Similar results can be obtained with elements other than Ni and Fe that reduce the Néel temperature, and conversely, similar characteristics can be obtained at higher temperatures with elements that increase the Néel temperature.

The experimental results using various elements other than Ni and Fe were also in good agreement with the above discussion results, and the phenomenon could be explained logically.

The present invention includes a result many of these experiments, which the present inventors is based on the experience of stacked far, is represented by the general formula Cr _100-x M _x, Neel temperature vicinity of the material, and Neel temperature When the thin film of the material is arranged in the direction perpendicular to the strain direction of the measurement target on the high temperature side of, the composition ratio x is 0 in atomic% so that the gauge ratio is within 0 ± 0.3. The present invention provides a thin film strain sensor material to which the second element M is added in the range of ≦ x ≦ 30, and a thin film strain sensor having a thin film of the material as a sensitive portion. As a result, it is possible to obtain a thin film strain sensor in which the gauge ratio of the parallel arrangement is large and the gauge ratio of the vertical arrangement is almost zero.

The second element M includes the above-mentioned Mn, Os, Ir, Pt, Ru, Rh, Ge, As, Sn, Ga, Sb, Re, Au, Fe, Co, Mo, W, Ti, Ni, V, Er. , Yb, Be, Si, Al and the like can be used. The reason why the composition ratio x is set in the range of 0 ≦ x ≦ 30 in atomic% is that if it exceeds this range, the sensitivity in the spindle direction becomes small. Further, the reason why the gauge ratio in the vertical arrangement is set to 0 ± 0.3 or less is that if the gauge ratio is out of this range, noise components such as interference with other axes become remarkable. Inevitable impurities other than Cr and the second element M are allowed.

When the second element M is Ni, as shown in FIG. 2, the gauge ratio of the parallel arrangement is as large as 2.1 or more in the range of the Ni content (composition ratio x) of 5 to 22 at%, and the vertical arrangement is performed. The gauge rate becomes almost zero. Therefore, when the second element M is Ni, the composition ratio x is preferably in the range of 5 to 22 at%. More preferably, it is in the range of 6.8 to 10 atomic%.

In the Cr—Ni thin film, the temperature coefficient of resistance (TCR) at the Ni content is as large as about 500 ppm / ° C. as shown in FIG. However, by forming the four elements of the bridge in a narrow region, it is possible to eliminate the temperature difference in the bridge, so that the point that the TCR is large does not matter.

On the other hand, it is important that the sensitivity temperature coefficient (TCS) (degree of change of gauge rate with temperature) has no such compensation method and its value itself is small. As shown in FIG. 8, the TCS of the Cr—Ni thin film is small and good at about 400 ppm / ° C.

When the second element M is Fe, as shown in FIG. 3, the gauge ratio of the parallel arrangement is as large as 3.3 or more at the Fe content (composition ratio x) of 17 to 28 at%, and the gauge of the vertical arrangement is vertically arranged. The rate is almost zero. The TCS at the Fe content is very good at almost zero (<± 500 ppm / ° C.) as shown in FIG. Therefore, when the second element M is Fe, the composition ratio x is preferably in the range of 17 to 28 at%. More preferably, it is in the range of 17 to 23 atomic%.

Note that TCS is not mentioned in Patent Document 4 above.

The thin film to which the second element is added based on Cr has been described above, but as shown in Patent Document 2, the Cr-N thin film also has a large gauge ratio like the Cr thin film, and is based on Cr-N. By using the second element to be added to Cr as a third element equivalent thereto, it is possible to make adjustments with exactly the same amount of addition as when the second element is added based on Cr, and the same result. Can be obtained.

Here, when Cr-N is used as a base, the thin film strain sensor material can be represented by the general formula (Cr _100-x M _x ) _100-y N _y , and the addition amount x of the third element M is Similarly, the atomic% is in the range of 0 ≦ x ≦ 30, and the amount y of N added is in the range of 0.0001 ≦ y ≦ 30, as in Patent Document 2.

By adding N and using Cr-N as a base, the gauge ratio may decrease slightly compared to the case where N is not added, but TCR can be adjusted by the amount of N and the heat treatment temperature, and not only TCS but also TCS A thin film strain sensor having a TCR of almost 0 can be obtained. The reason why the composition ratio y is set in the range of 0.0001 ≦ y ≦ 30 in terms of atomic% is that if the composition ratio is out of this range, the TCR value becomes large in absolute value.

As described above, according to the present invention, it is possible to obtain a thin film strain sensor having a gauge ratio of 2.1 or more indicating general strain sensitivity in parallel arrangement and an apparent gauge ratio of 0 ± 0.3 or less in the case of vertical arrangement. Can be done. At the same time, it is possible to obtain excellent characteristics in which TCS is within 0 ± 500 ppm / ° C.

Claims (8)

A thin film strain sensor material represented by the general formula Cr _100-x M _x , in which the thin film of the material is arranged in a direction perpendicular to the direction of the strain to be measured on the high temperature side of the nail temperature of the material. A thin film strain sensor material, wherein the second element M is added in a range of 0 ≦ x ≦ 30 in a composition ratio x of atomic% so that the gauge ratio of the above is within 0 ± 0.3. A thin film strain sensor material represented by the general formula _{(Cr 100-x M x)} 100-y N y, composition ratio y is in the range of 0.0001 ≦ y ≦ 30 in atomic percent, of the material The composition ratio x is 0 in atomic% so that the gauge ratio is within 0 ± 0.3 when the thin film of the material is arranged in the direction perpendicular to the strain direction to be measured on the high temperature side of the nail temperature. A thin film strain sensor material, characterized in that the third element M is added in the range of ≦ x ≦ 30. The thin film strain sensor material according to claim 1, wherein the second element M is Ni and the composition ratio x is 5 ≦ x ≦ 22 in atomic%. The thin film strain sensor material according to claim 1, wherein the second element M is Fe and the composition ratio x is 17 ≦ x ≦ 28 in atomic%. A thin film of material represented by the general formula Cr _100-x M _x A thin film strain sensor having a sensing part, the high-temperature side of the Neel temperature of the material in the direction of the strain thin film of said material to be measured The second element M is added in the range of 0 ≦ x ≦ 30 with a composition ratio x of atomic% so that the gauge ratio when arranged in the vertical direction is within 0 ± 0.3. Thin film strain sensor. A general thin-film strain sensor having a _{(Cr 100-x M x)} thin film of a material represented by _{100-y N y} as a sensing part, the composition ratio y is, 0.0001 ≦ y ≦ 30 at% The gauge ratio is within 0 ± 0.3 when the thin film of the material is arranged in the direction perpendicular to the strain direction of the measurement target on the high temperature side of the nail temperature of the material. A thin film strain sensor characterized in that the third element M is added in the range of 0 ≦ x ≦ 30 with a composition ratio x of atomic%. The thin film strain sensor according to claim 5, wherein the second element M is Ni and the composition ratio x is 5 ≦ x ≦ 22 in atomic%. The thin film strain sensor according to claim 5, wherein the second element M is Fe and the composition ratio x is 17 ≦ x ≦ 28 in atomic%.

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