JP2003279423A - Strain sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate highly sensitively a fine generated force or a torque, and to perform stress adjustment of a magnetostrictive film corresponding to the using state easily with excellent reproducibility over a wide range. <P>SOLUTION: This strain sensor has a structure wherein at least one coil 16 is formed through an insulating layer 14, on the surface of the magnetostrictive film 12 formed on a substrate 10. The insulating layer is formed from a heat-shrinkable material, and the stress adjustment of the magnetostrictive film is performed by using the heat-shrinkable property. As another example, a constitution may be adopted, wherein the magnetostrictive film is formed on the coil through the second insulating layer, and either or both insulating layers are formed from the heat-shrinkable material, to thereby perform the stress adjustment of the magnetostrictive films. The insulating layer comprising the heat-shrinkable material is formed from, for example, a polyimide-based resin, and is heat-cured at 200-350°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain sensor using a magnetostrictive film, and more specifically, it has a structure in which a coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer, The present invention relates to a strain sensor in which the stress of a magnetostrictive film is adjusted by forming an insulating layer with a heat-shrinkable material. This strain sensor is useful for measuring a minute force / torque in the field of micromachines, for example.

[0002]

2. Description of the Related Art In recent years, there has been an increasing need for micro-force measurement for evaluation of forces and torques generated by microactuators, and evaluation of frictional forces and interactions between materials in the field of microtribology. However, in these micro system fields, the micro force measurement range and measurement site are much smaller than conventional measurement targets, so it is difficult to evaluate with existing sensors such as metal strain gauges and semiconductor gauges. There were many problems in the interface such as Ma.

Therefore, recently, a strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer has been developed. This strain sensor is configured to measure the impedance change of the coil and obtain the strain by utilizing the fact that the magnetic permeability of the magnetostrictive film changes due to a small external force.

[0004]

In order to react to a small external force in this type of strain sensor, it is important that the stress of the magnetostrictive film is small in the absence of the external force. Further, when a strain sensor is attached to a curved surface having a certain radius of curvature, the operating point needs to be moved while maintaining high strain sensitivity, so that the stress adjustment of the magnetostrictive film can be performed over a wide range. Is important.

Conventionally, the stress adjustment of the magnetostrictive film has been performed by a method of utilizing the difference in thermal expansion between the substrate and the magnetostrictive film when forming the magnetostrictive film. However, in reality, in addition to the coil being formed on the magnetostrictive film, it may have a complicated structure in which various films are further laminated thereon, and it is difficult to adjust the stress of the magnetostrictive film by the above method. is there.

An object of the present invention is to provide a strain sensor which can evaluate a minute generated force or torque with high sensitivity and reproducibility. Another object of the present invention is to provide a strain sensor having a structure in which the stress of the magnetostrictive film can be easily adjusted over a wide range and with good reproducibility in accordance with the situation of use.

[0007]

The present invention provides a strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate through an insulating layer, wherein the insulating layer is heat-shrinkable. A strain sensor using a magnetostrictive film, characterized in that the stress of the magnetostrictive film is adjusted by utilizing the heat shrinkability of the insulating layer.

Further, according to the present invention, in a strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer, a magnetic sensor is formed on the coil via a second insulating layer. A film is formed, one or both insulating layers are formed of a heat-shrinkable material, and the stress of the magnetostrictive film is adjusted by utilizing the heat-shrinkability of the insulating layer. It was a strain sensor. The magnetic film is, for example, a high-permeability magnetic film and is preferably formed over substantially the entire surface of the coil portion by electroless plating or electrolytic plating.

In these, the magnetostrictive film is formed to be slightly smaller than the substrate area so that the substrate surface is exposed only in the entire circumference, and the insulating layer is formed so as to completely cover the magnetostrictive film including the peripheral edges. The structure is preferable.

As the insulating layer made of a heat-shrinkable material,
Polyimide resin is the most suitable, and in that case 200-
Heat cure at a temperature in the range of 350 ° C. The stress of the magnetostrictive film can be adjusted by adjusting the film thickness and the heat treatment temperature during or after hardening.

Magnetostrictive films are typically vapor phase grown RTs.
-Based magnetostrictive material (however, rare earth elements including R: Y, T: Fe
Transition metal whose main component is). In that case, the composition ratio of the rare earth element R is preferably 37 to 43 at%. For example, a Tb-Fe based magnetostrictive material is preferable.

[0012]

1 is a basic configuration diagram of a strain sensor according to the present invention, in which A is a plane and B is a longitudinal section taken along the line bb. In this structure, a magnetostrictive film 12 is formed on a thin substrate 10 made of glass or polyimide resin, and a coil 16 is formed on the magnetostrictive film 12 via an insulating layer 14. The magnetostrictive film 12 is, for example, a vapor phase grown RT.
-Based magnetostrictive material (however, rare earth elements including R: Y, T: Fe
Is a transition metal whose main component is R, and its rare earth element R
The composition ratio is about 37 to 43 at%. Coil 16
Is a meandering shape (see A in FIG. 1) or a spiral shape (not shown) that can be easily formed on a thin substrate. Form.

Here, the insulating layer 14 is formed of a heat-shrinkable material, by which the stress of the magnetostrictive film is adjusted. The insulating layer 14 needs to have good heat resistance and corrosion resistance, and a polyimide resin is optimal from this viewpoint. This resin is heat-cured at a desired temperature within a temperature range of 200 to 350 ° C. The degree of shrinkage can be controlled and the stress of the magnetostrictive film can be adjusted by controlling the film thickness to an optimum value or by adjusting the heat hardening temperature or the heat treatment temperature after hardening.

The magnetostrictive film 12 is formed to be slightly smaller than the substrate area so that the surface of the substrate 10 is exposed over the entire circumference, and the insulating layer 14 completely covers the magnetostrictive film 12 including the peripheral edges. A formed structure is desirable. In this type of sensor, usually, sensor units are regularly formed in a matrix on a wafer (a large substrate), and the sensor units are cut in the vertical and horizontal directions to obtain a large number of strain sensors. It is manufactured by the individual picking method. Therefore, by forming the sensor element parts on the wafer in an island shape and cutting the substrate with a dicing saw or the like at a position between the sensor element parts, each strain is generated without damaging the film or the like at the time of cutting. Can be separated into sensors.
In addition, even after cutting, the magnetostrictive film 12 including the edges is the insulating layer 1.
Since it is covered with 4, it is completely protected from the external environment.

The operating principle of this type of strain sensor is as follows. When the substrate 10 made of thin glass having a thickness of about 0.1 mm is distorted by a small external force, the magnetostrictive film 1 is thereby distorted.
2 is also distorted. Then, since the magnetic permeability changes, the impedance of the coil 16 also changes. By utilizing this fact, a minute strain (hence force or torque) can be measured by measuring the impedance change between both ends of the coil 16.

From such an operating principle, in order for the strain sensor to react to a minute external force, it is important that the stress of the magnetostrictive film is small in the absence of the external force. When a strain sensor is attached to a curved surface having a certain radius of curvature, the operating point is moved while maintaining high strain sensitivity, so it is important to be able to adjust the stress of the magnetostrictive film over a wide range. .

Therefore, the stress applied to the magnetostrictive film is adjusted by heat-treating the insulating layer during or after manufacturing the strain sensor to shrink the insulating layer. At that time, the stress applied to the magnetostrictive film also changes depending on the film thickness of the insulating layer, so that the film thickness of the insulating layer also needs to be appropriately controlled. When a strain sensor is attached to a curved surface with a certain radius of curvature, the stress of the magnetostrictive film must be largely moved to the compression side in order to move the operating point while maintaining high strain sensitivity. It is effective to use a heat-compressible material, especially to use a polyimide resin. This is because the polyimide resin also has an advantage that stress can be easily adjusted. When using polyimide-based resin, 200 ° C for sufficient curing
As described above, it is necessary to perform heat treatment within a temperature range of 350 ° C. or lower so that the resin does not deteriorate. Since the more the heat is applied, the more it moves toward the compression side due to hardening, so the compression stress can be adjusted by selecting the heating conditions. The stress adjustment is performed so that the stress of the magnetostrictive film becomes substantially zero when the strain sensor is actually used.

In order to improve the characteristics of the strain sensor, it is desirable to use a material exhibiting large magnetostriction characteristics as the magnetostrictive film. Therefore, as described above, a vapor-phase grown RT-based (for example, Tb-Fe-based) magnetostrictive material having a large magnetostrictive characteristic is used, and the composition ratio of the rare earth element is 37 to 4 in particular.
3 at%. As a result, a low magnetic field (80 kA /
In the case of m), the magnetostriction is 700 ppm or more, and extremely good magnetostrictive characteristics not found in conventional magnetostrictive films are obtained (see Japanese Patent Application No. 2001-137294). By using the thin film made of this magnetostrictive material, it is possible to enhance the sensor sensitivity even for a small measurement area and a minute distortion.

2A to 2C are vertical cross-sectional views showing another structural example of the present invention. Both have a structure in which the coil 16 is formed on the surface of the magnetostrictive film 12 formed on the substrate 10 with the insulating layer 14 interposed therebetween. In the example shown in A, the second insulating layer 20 is formed on almost the entire surface of the coil 16, and the magnetic film 22 is formed only on the portion corresponding to the second insulating layer 20. This configuration may be applicable only when the coil width is large, but a good magnetic film 22 can be formed by a vapor deposition method or a sputtering method. In the example shown in B, the second insulating layer 20 is formed on almost the entire surface of the coil 16, and the magnetic film 24 is formed on the almost entire surface of the second insulating layer 20. This configuration is the simplest in terms of manufacturing process. The example shown in C is the coil 16
The second insulating layer 26 is formed only on the periphery of the above, and the magnetic film 24 is formed on almost the entire surface thereof. This configuration
It may be applicable only when the coil spacing is wide, but it is most effective on the magnetic circuit.

In any case, in these configurations, when the coil is sandwiched between the magnetostrictive film and the magnetic film and magnetically approaches a closed magnetic circuit, when the magnetic permeability of the magnetostrictive film changes due to a small external force. The sensitivity of the impedance change of the coil can be increased. As the magnetic film, a high-permeability magnetic film such as Ni-Fe alloy is preferable. In addition, by using a magnetostrictive film as the magnetic film to form a sandwich structure,
The sensitivity of the strain sensor can be improved.

Since the coil is preferably made relatively thick (for example, about 10 μm in thickness) in order to reduce the electric resistance, the second insulating layer formed on the coil is undulated according to the shape of the coil. Such unevenness occurs. Therefore, if a magnetic film is formed thereon by a vapor deposition method, a sputtering method, or the like, it may happen that the film is not formed because it partially shades the coil. Then, strong anisotropy may occur due to the influence of the step shape. This problem can be solved by using a patterned magnetic film as shown in A, but it is not always satisfactory in terms of magnetic efficiency. However, the problem of unevenness due to the coil can be solved by forming a magnetic film by a wet method such as electroless plating or electrolytic plating, and thereby a sufficiently good (required film thickness) magnetic film can be formed. . The magnetic film covering the entire surface can also function as a magnetic shield.

By the way, the film formed by the plating method is
Usually related to hydrogen (related to the entry and exit of hydrogen ions)
It is said that tensile stress occurs. In the present invention,
Since a heat-shrinkable material is used for the insulating layer, the tensile stress of the magnetic layer due to plating can be canceled out by the shrinking of the insulating layer, and even with a structure in which the magnetic film is formed on top by plating, good characteristics are achieved. Is obtained.

[0023]

EXAMPLE A magnetostrictive film was made of a binary system of Tb and Fe, and was produced by vapor phase growth on a glass substrate having a thickness of 0.1 mm by DC magnetron sputtering. T on Fe target
The composition of the magnetostrictive film was adjusted by arranging b chips and adjusting the number of Tb chips. Here, a Tb-Fe binary system magnetostrictive film having a Tb composition ratio of about 40 at% is used in an amount of about 1%.
The film was formed to have a film thickness of μm.

Subsequently, a polyimide resin was applied onto the magnetostrictive film by a spin coating method and heat-cured at 250 ° C. for 1 hour in the atmosphere to form an insulating layer. The thickness of the insulating layer is 1μ
m, 3 μm, and 6 μm, and the stress of the magnetostrictive film was controlled by the film thickness of the insulating layer. 10 μm thick on the insulating layer
A zigzag folded Cu coil was formed by electrolytic plating. In this way, a strain sensor having a structure as shown in FIG. 1 was manufactured.

To evaluate the characteristics of the strain sensor, as shown in FIG. 3, the strain sensor 30 is fixed at one end of the glass substrate 32 to the fixing portion 34.
Fixed in a cantilever shape to the micrometer head 36
Was applied to the glass substrate 32 to measure the impedance at a frequency near the resonance point. The load applied to the glass substrate 32 is the glass substrate 32.
The displacement (deflection amount) x was calculated. The impedance change was measured with an impedance analyzer. The maximum amount of deflection given to the glass substrate 32 was 500 μm.

When the thickness of the insulating layer is 3 μm, the displacement (deflection amount) x-impedance change (ΔZ / when the measurement frequency is near the resonance point (195 to 203 MHz))
The relationship of Z) is shown in FIG. In the strain sensor in which the insulating layer having a film thickness of 3 μm is formed in this way, a maximum impedance change of about 7% was obtained by applying strain to the glass substrate 30. However, in the strain sensor in which the insulating layers having the film thicknesses of 1 μm and 6 μm are formed, the impedance change cannot be measured even if the same strain is applied to the glass substrate 30. From this, it is understood that the stress of the magnetostrictive film can be adjusted by controlling the film thickness of the insulating layer even if the heat treatment is performed at the same heating temperature.

[0027]

As described above, the present invention is a strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer, and therefore, a minute force or torque is generated. Can be evaluated with high sensitivity and reproducibility. In particular, when the magnetic film is formed on the coil via the second insulating layer, the coil is sandwiched by the magnetostrictive film and the magnetic film and approaches a closed magnetic circuit, so that the strain detection sensitivity is further improved.

Further, according to the present invention, since the insulating layer is formed of a heat-shrinkable material, the stress adjustment of the magnetostrictive film can be easily performed over a wide range and with good reproducibility according to the use situation.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a strain sensor according to the present invention.

FIG. 2 is a vertical cross-sectional view showing another configuration example of the strain sensor according to the present invention.

FIG. 3 is an explanatory diagram of a measurement state of a strain sensor.

FIG. 4 is a graph showing an example of displacement-impedance change.

[Explanation of symbols]

10 substrates 12 Magnetostrictive film 14 Insulation layer 16 coils

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Teruo Kiyomiya             F-de, 5-36-1 Shimbashi, Minato-ku, Tokyo             K.K Co., Ltd. (72) Inventor Yoshiyuki Umemoto             F-de, 5-36-1 Shimbashi, Minato-ku, Tokyo             K.K Co., Ltd. (72) Inventor Hiroyuki Wakiwaka             Wakasato inn, 5-16-3 Wakasato, Nagano City, Nagano Prefecture             Building 3-5 (72) Inventor Yoji Yamada             191-2 Inaba Kami-Senta, Nagano City, Nagano Prefecture             Uchida Annex 301 (72) Inventor Mika Makimura             1-1-18 Wakasato Nagano City, Nagano Prefecture Nagano Prefecture             Inside the industrial testing ground

Claims (7)

[Claims] 1. A strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer, wherein the insulating layer is formed of a heat-shrinkable material, A strain sensor characterized in that the stress of a magnetostrictive film is adjusted by utilizing contractility. 2. A strain sensor having a structure in which at least one coil is formed on the surface of a magnetostrictive film formed on a substrate via an insulating layer, wherein a magnetic film is formed on the coil via a second insulating layer. A strain sensor, wherein one or both insulating layers are formed of a heat-shrinkable material, and the stress of the magnetostrictive film is adjusted by utilizing the heat-shrinkability. 3. The strain sensor according to claim 2, wherein the magnetic film is a high magnetic permeability magnetic film formed over substantially the entire surface of the coil portion by electroless plating or electrolytic plating. 4. The magnetostrictive film is formed smaller than the substrate area so that the surface of the substrate is exposed over the entire circumference, and the insulating layer is formed so as to completely cover the magnetostrictive film including the peripheral edges. The strain sensor according to any one of 1 to 3. 5. The strain sensor according to claim 1, wherein the insulating layer made of a heat-shrinkable material is made of a polyimide resin and is heat-cured at a temperature of 200 to 350 ° C. 6. The magnetostrictive film is formed of a vapor-grown RT-based magnetostrictive material (however, a rare earth element containing R: Y and a transition metal containing T: Fe as a main component). The strain sensor described in. 7. The composition ratio of the rare earth element R is 37 to 43.
The strain sensor according to claim 6, wherein the strain sensor is at%.