JP2644757B2 - Displacement detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a displacement detection device that utilizes the fact that the resistance value of a magnetoresistive stripe changes when it is displaced by a physical stress.

(Prior Art) Conventionally, a pressure sensor or an acceleration sensor is known as a physical displacement detecting device.

FIGS. 21 and 22 show examples of a conventionally known pressure sensor, in which a diaphragm is formed by anisotropic etching of silicon single crystal, and impurities are selectively diffused into the diaphragm to partially deform the surface of the diaphragm. It is a gauge.
In FIGS. 21 and 22, reference numeral 13 denotes a silicon wafer having a diaphragm portion formed by processing only a sensor portion to a thickness of about 20 μm by anisotropic etching, and a piezoresistor 11 as a strain gauge is provided on the diaphragm portion. Is formed. Reference numeral 12 denotes electrodes formed on both ends of the piezoresistor 11, and reference numeral 14 denotes glass bonding. When the pressure applied to the surface of the piezoresistor 11 changes and the diaphragm portion is displaced, the resistance value of the piezoresistor 11 changes in accordance with the amount of displacement, so that the pressure can be measured by measuring the resistance value. .

23 and 24 show a conventionally known acceleration sensor, in which a piezoresistor as a strain gauge is provided on a silicon wafer 23 formed cantileverly on a glass cover 26.
21 is formed. Reference numeral 22 denotes an electrode of the piezoresistor 21, reference numeral 24 denotes a glass cover, and reference numeral 25 denotes a weight fixed to the tip of the silicon wafer 23. When the entire sensor fluctuates rapidly, a bending stress acts on the silicon wafer 23, and a tensile force or a compressive force is applied to the piezoresistor 21, and the resistance value changes. The acceleration can be detected from the rate of change of the resistance value.

(Problems to be Solved by the Invention) According to the conventional displacement detecting devices such as the pressure sensor and the acceleration sensor, selective diffusion and etching of impurities are performed several times to form a piezo resistor on a silicon wafer. Because of the necessity, it is difficult and expensive to manufacture, and the sensor itself cannot correct the temperature coefficient of resistance. The pressure sensor cannot detect the direction of the pressure, that is, whether the pressure is positive or negative.

The present invention has been made to solve such a conventional problem, is easy to manufacture and inexpensive, and can detect the direction of pressure and the direction of acceleration as necessary, Further, it is another object of the present invention to provide a displacement detecting device which can easily perform temperature compensation if necessary.

(Means for Solving the Problems) According to the present invention, a folded magnetoresistive stripe whose resistance value changes by being displaced by a physical stress is not applied to a position on a substrate where a physical stress is applied. And a magnet for applying a bias magnetic field to the magnetoresistive stripe, and a resistance value of the magnetoresistive stripe provided at a position where physical stress is not applied and a resistance value of the magnetoresistive stripe provided at a position where physical stress is applied. Based on the resistance value that changes due to compression or tensile stress,
The method is characterized in that a displacement amount applied to a magnetoresistive stripe provided at a position where a physical stress is applied is obtained.

(Operation) In a normal state where no physical stress is applied, the resistance value of the magnetoresistive stripe is determined by the bias magnetic field generated by the magnet. When the physical resistance is applied to the magnetoresistive stripe provided at the position where the physical stress is applied and the magnetic resistance is displaced, the folded magnetoresistive stripe receives a compressive or tensile stress and changes its resistance value. The displacement amount can be determined from the resistance value of the magnetoresistive stripe to which no physical stress is applied and the resistance value of the magnetoresistive stripe to which no physical stress is applied.

(Example) Hereinafter, an example of a displacement amount detection device according to the present invention will be described with reference to the drawings.

1 to 5, the substrate 32 is, for example, a silicon wafer, and a part of the substrate 32 is removed by anisotropic etching or the like to form a thin film portion 32a. On the substrate 32, a magnetoresistive stripe 31a is formed in a thick portion thereof, and a magnetoresistive stripe 31b is formed on the thin film portion 32a. The magnetoresistive stripes 31a and 31b are made of Ni-Fe or Ni
-An alloy thin film having a magnetoresistance effect such as -Co. Each of the magnetoresistive stripes 31 and 31b is folded in a U-shape to form a secondary parallel current path, and each of the magnetoresistive stripes 31a and 31b is formed so as to extend in parallel in the same direction. I have. Electrodes A, B, and C are also formed on the substrate 32, the magnetoresistive stripes 31 and 31b are connected in series by an electrode B, and the other ends of the magnetoresistive stripes 31a and 31b are connected to electrodes A and C, respectively. It is connected to the. FIG. 5 shows the connection relationship between each magnetoresistive stripe and each electrode. A protective film 33 is formed on the magnetoresistive stripes 31a and 31b so as to cover the magnetoresistive stripes and the upper surface of the substrate 32 except for the electrodes A, B and C. The protective film 33 can be formed of an inorganic substance such as SiO2 or polysilicon or an organic substance such as polyimide. On this protective film 33, magnets 34 for applying a bias magnetic field to the magnetoresistive stripes 31a and 31b are arranged in parallel with a predetermined distance between the protective film 33 and the spacers 36, with the spacers 36 interposed therebetween. . Magnet 34
Are arranged in parallel to the surfaces of the magnetoresistive stripes 31a and 31b, and are magnetized from an oblique direction as shown in FIG.
By using a pole and an S pole formed obliquely, the magnetic flux crosses the magnetoresistive stripes 31a and 31b obliquely.

 Next, a displacement amount detecting operation according to the above embodiment will be described.

Now, as shown in FIG. 6, when a physical stress is applied from the back side of the substrate 32, the thin film portion 32a of the substrate 32 warps upward. Here, assuming that the longitudinal direction of the magnetoresistive stripe 31b is the Y direction and the width direction perpendicular thereto is the X direction, as shown in FIG. 9, the thin film portion 32a of the substrate 32 warps upward, so that the magnetoresistive stripe 31b Applies tensile stress in the X direction. On the other hand, as shown in FIG.
Assuming that physical stress is applied from the front side of the substrate 32,
The thin film portion 32a of 32 warps downward, and a compressive stress in the X direction is applied to the magnetoresistive stripe as shown in FIG. On the other hand, even if a physical stress is applied to the thick portion of the substrate 32, the substrate 32 does not displace in this portion, so that both the tensile stress and the compressive stress are applied to the magnetoresistive stripe 31a formed in this portion. Absent.

FIG. 8 shows the hysteresis characteristics of the resistance change rate of the magnetoresistive stripe when the substrate is displaced by applying a tensile stress and a compressive stress to the magnetoresistive stripe on the thin substrate in the X direction, which is the width direction thereof. Here, as shown in FIG. 10, a magnetic field having a strength of Hb emitted from the bias magnet is linked at an angle θ with respect to the longitudinal direction of the magnetoresistive stripe, and a magnetic field Ha orthogonal to the magnetoresistive stripe is formed. In addition, the intensity of the orthogonal magnetic field was changed from -Ha to + Ha. Curve A shows the resistance change rate of the magnetoresistive stripe to which no physical stress is applied, that is, the magnetoresistive stripe corresponding to the magnetoresistive stripe 31a in the above embodiment, and curve B shows the magnetoresistive stripe affected by the tensile stress, that is, in the above embodiment. The resistance change rate of the magnetoresistive stripe 31b is shown, and the curve C shows the resistance change rate of the magnetoresistive stripe affected by the compressive stress, that is, the magnetoresistive stripe 31b in the above embodiment.

The magnetoresistive stripe 31b in the above embodiment is
6 is easily affected by the physical stress formed in the thin film portion 22a, and when a tensile stress is applied as shown in FIG. 6, the energy of the magnetoresistive stripe 31b before the stress is applied. The balance between a certain magnetostatic energy, anisotropic energy, elastic energy, and the domain wall energy of the magnetic domain formed to minimize these energies is lost, and the sum of these energies changes in proportion to the stress, and the magnetoresistance The sensitivity of the stripe decreases. Therefore, the hysteresis characteristic of the magnetoresistive stripe is represented by curve B in FIG.
become that way. Conversely, when the magnetoresistive stripe receives a compressive stress as in the case of FIG. 7, the sensitivity of the magnetoresistive stripe increases, and the hysteresis characteristic of the magnetoresistive stripe becomes as shown by a curve C in FIG.

The characteristic curve shown in FIG. 8 is obtained by applying a tensile stress and a compressive stress to the magnetoresistive stripe on the 0.7 mm thick substrate in the X direction, which is the width direction, to displace the substrate by 0.5 μm. . In the above embodiment, since the magnetic field applied to the magnetoresistive stripe is only the magnetic field of the bias magnet 34, the resistance value changes at the point Ha = 0. As is clear from FIG. 8, the resistance change rate in a normal state is about 1.75%, whereas the resistance change rate when a tensile stress is applied is reduced to about 1.1%, and when a compressive stress is applied. The rate of resistance change has increased to about 2.6%.
Therefore, if the rate of change in resistance of the magnetoresistive stripe 31b is obtained, the amount of displacement based on physical stress can be detected.

FIG. 10 shows an example of a circuit for extracting a signal corresponding to such a displacement amount.
Rb indicates the resistance value of the magnetoresistive stripe 31b. The power supply voltage Vcc is applied between the terminals A and C, and the output voltage Vout is taken out between the terminals B and C. When the thin film portion 32a of the substrate 32 is displaced by physical stress, the resistance value Rb of the magnetoresistive stripe 31b becomes Δ
If it changes by Rb, the output Vout is as follows: Vout = Ra · Vcc / (Ra + Rb−ΔRb). Therefore, by measuring the output Vout, the change ΔRb in the resistance value can be known, and the displacement can be obtained.

The output sensitivity can be increased by increasing the magnetic field strength Hb of the bias magnet 34. Further, if the angle θ between the magnetoresistive stripe and the direction of the magnetic field is made variable, the parallel component Hby and the orthogonal component Hby of the magnetic field with respect to the magnetoresistive stripe can be obtained.
bx changes, and the sensitivity of the magnetoresistive stripe can be changed. However, the sensitivity becomes maximum when θ = 30 °, and the sensitivity is attenuated even if θ is changed to increase the parallel component Hby of the magnetic field or to increase the orthogonal component Hbx.

In the case of a configuration in which the output is taken out from the midpoint between the two magnetoresistive stripes 31a and 31b as shown in FIG. 10, the resistance value of both magnetoresistive stripes changes in the same manner in accordance with the temperature change. The coefficients can be offset, and it is not necessary to provide a temperature compensation circuit or the like. However, in the method of taking output from the midpoint of two magnetoresistive stripes,
Either one of the magnetoresistive stripes needs to be configured to easily cause displacement, or one of the magnetoresistive stripes needs to be configured to prevent displacement easily.

According to the embodiment described above, not only the magnetoresistive effect of the magnetoresistive stripe but also the displacement is detected by utilizing the reverse magnetostrictive effect in which a resistance value changes when a physical stress is applied to the magnetoresistive stripe. In addition, a substrate for forming a magnetoresistive stripe and a magnet for applying a bias magnetic field to the magnetoresistive stripe are sufficient, and a displacement amount detecting device with a simpler configuration and lower cost than in the related art can be provided. Further, an output of 1.5% or more in resistance change rate can be obtained, and an output can be obtained as a quantitative value.

The protective film 33 is for preventing the magnetoresistive stripe from being damaged, and may be omitted depending on the use or the like. Further, the spacer 36 can be omitted.

Next, various application examples and various modification examples related to the displacement amount detection device according to the present invention will be described.

11 and 12 show an example in which the displacement detecting device is constituted by only one magnetoresistive stripe 41. The magnetoresistive stripe 41 is formed by folding one stripe in a folded shape. Note that this example departs from the technical scope described in the claims. Reference numeral 42 is a substrate, 43 is a protective film, 44 is a bias magnet, 45 is an electrode, 46
Is a spacer.

13 and 14, the displacement detecting device is constituted by only one magnetoresistive stripe 51, and the magnetoresistive stripe 51 is formed by forming one stripe in a straight line. Reference numeral 52 denotes a substrate, 53 denotes a protective film, 54 denotes a bias magnet, 55 denotes an electrode, and 56 denotes a spacer. This example also departs from the technical scope described in the claims.

In the examples of FIGS. 11 to 14, in the initial magnetoresistive stripe 41 where no displacement occurs, the resistance value of 51 is measured, and then the resistance values of the magnetoresistive stripes 41 and 51 during displacement are measured. The displacement amount can be obtained by comparing the displacement amount with the initial value.This example can be used as a displacement sensor for measuring, for example, a tensile stress at the time of adhesion of paint, and has an extremely simple configuration. Since there is no need for a power supply, it can be disposable.

The embodiment shown in FIGS. 14 to 16 is such that the component in the X direction and the component in the Y direction of the displacement due to the physical stress can be measured. In the example of FIG. 15, a magnetoresistive stripe 61 is provided on a portion of the substrate 62 which is not displaced by physical stress.
is formed, and two magnetoresistive stripes 61 are arranged in a direction orthogonal to each other on a portion of the substrate 62 which is easily displaced by physical stress.
b, 61c. Each stripe 61a, 61b, 61c
Are formed in a folded shape and connected in series through the electrode 65. The power supply voltage Vcc is applied between the outer electrodes of the stripes 61a and 61c at both ends, and the stripe 61a and the stripe
The output Vout is extracted from the electrode 65 between 61b. The resistance value of the stripe 61b changes due to the stress in the X direction, and the resistance value of the stripe 61c changes due to the stress in the Y direction. These changes can be detected by measuring the output Vout.

In the embodiment shown in FIG. 16, a magnetoresistive stripe 71a and a magnetoresistive stripe 71b in a direction orthogonal to the
The magneto-resistive stripes 71c and the magneto-resistive stripes 7 in the direction perpendicular to the portions where the physical stress is easily displaced by the physical stress 2
1d. Each stripe is folded twice, but may be folded once or may be formed linearly one by one. Sign
75 is an electrode. As shown in FIG. 17, stripe 71
a, 71b are connected in series by electrodes, and stripes 71c, 7
1d is also connected in series by an electrode. These serially connected stripes are connected in parallel to the power supply voltage Vcc, and the output Va of the X-direction component is output between the stripes 71a and 71b.
Is extracted, and an output Vb of the Y-direction component is extracted from between the stripes 71c and 71d. These outputs Va, Vb may be measured separately as they are, or the differential output
Vout may be taken out and measured.

The embodiment of FIG. 18 is an embodiment in which the embodiment described earlier is developed, and two magnetoresistive stripes 81a, 81a,
81b is formed in parallel, connected in series by electrodes,
The two magnetoresistive stripes 81c and 81d are formed in parallel at a portion which is easily displaced by the physical stress, and are connected in series by electrodes. Reference numeral 85 denotes an electrode formed at the end of each magnetoresistive stripe. Stripes 81a connected in series,
The power supply voltage Vcc is applied to both the other series stripes 81c and 81d connected in series with 81b, the output Va is taken out from the connection point of the stripes 81a and 81b, and the output Vb is obtained from the connection point of the stripes 81c and 81d. Is taken out. As shown in FIG. 19, the differential amplifier 86 outputs a differential output Vout of each output Va and Vb.
In this case, an output twice as high as that of the first embodiment can be obtained.

The embodiment shown in FIG. 20 differs from the previous embodiments in the configuration for deforming the substrate by physical stress. In FIG. 20, the substrate 92 is bent from the center thereof and the right half is lifted, and the left half is fixed to a predetermined object so as not to be displaced even when a physical stress is applied. The half part is displaced by physical stress, and the magnetoresistive stripes 91a and 91b are formed on the left half and the right half, respectively. Reference numeral 95 denotes an electrode. Also in this embodiment, the displacement can be obtained by comparing the resistance value of the stripe 91b with the resistance value of the stripe 91a.

(Effects of the Invention) According to the present invention, not only the magnetoresistive effect of the magnetoresistive stripe is used, but also the inverse magnetostrictive effect in which the resistance value changes when a physical stress is applied is used to reduce the physical stress. Since the amount of displacement is detected based on the resistance value of the applied magnetoresistive stripe and the resistance value of the magnetoresistive stripe to which no physical stress is applied, a bias magnetic field is applied to the substrate on which the magnetoresistive stripe is formed and the magnetoresistive stripe. A magnet is sufficient, and it is possible to provide an inexpensive displacement amount detecting device having a simpler configuration than a conventional displacement amount detecting device. In addition, a magnetoresistive stripe is formed in a portion that is not displaced even when a physical stress is applied, and the resistance value of the magnetoresistive stripe is compared with the resistance value of the magnetoresistive stripe displaced by the stress to determine a displacement amount. Compensation is also possible.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the displacement detecting device according to the present invention, FIG. 2 is a sectional view taken along line II-II in FIG.
FIG. 4 is an enlarged sectional view of a main part of the embodiment, FIG. 4 is a perspective view showing a bias magnet in the embodiment, FIG. 5 is a circuit diagram showing a connection example of magnetoresistive stripes in the embodiment, and FIG. The figure is an enlarged sectional view showing the operation mode of the above embodiment,
FIG. 7 is an enlarged sectional view showing another operation mode, FIG. 8 is a diagram showing hysteresis characteristics of the magnetoresistive stripe, and FIG. 9 is a perspective view showing an example of stress applied to the magnetoresistive stripe in the above embodiment. FIG. 10 is a circuit diagram showing the relationship between the input and output and the state of the bias magnetic field in the above embodiment, and FIG. 11 is a plan view showing another embodiment of the displacement detection device according to the present invention.
12 is a sectional view of the same, FIG. 13 is a plan view showing still another embodiment of the device of the present invention, FIG. 14 is a sectional view of the same, and FIG. 15 is a plan view of still another embodiment of the device of the present invention. FIG. 16 is a plan view showing still another embodiment of the device of the present invention, FIG. 17 is a circuit diagram showing a circuit example used in the above embodiment, and FIG. 18 is a diagram showing still another embodiment of the device of the present invention. FIG. 19 is a circuit diagram showing an example of a circuit used in the above embodiment, FIG. 20 is a perspective view showing still another embodiment of the device of the present invention, and FIG. 21 is an example of a conventional pressure sensor. Cross-sectional view shown, FIG. 22 is a bottom view of the same,
FIG. 23 is a plan view showing an example of a conventional acceleration sensor, and FIG. 24 is an upper side view of the same. 31a, 31b, 41,51 …… Magnetoresistance stripe, 61a, 61b, 61c, 71a …… Magnetoresistance stripe, 71b, 71c, 71d, 81a …… Magnetoresistance stripe, 81b, 81c, 81d, 91a, 91b …… Magneto-resistive stripe, 32,42,52,62,72,82,92 …… Substrate, 34,44,54 …… Magnet.

Claims (1)

(57) [Claims] A folded magnetoresistive stripe whose resistance value changes by being displaced by a physical stress is provided on a substrate at a position where a physical stress is applied and a position where a physical stress is not applied, respectively. A magnet that applies a bias magnetic field to the stripe is also provided, and changes depending on the resistance value of the magnetoresistive stripe provided at the position where the physical stress is not applied and the compression or tensile stress of the magnetoresistive stripe provided at the position where the physical stress is applied. A displacement amount detecting device, wherein a displacement amount applied to a magnetoresistive stripe provided at a position where the physical stress is applied is obtained based on a resistance value.