JPH07244142A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To obtain the magnetic sensor whose sensitivity can be made high in a very small magnetic field by a method wherein the direction of spontaneous magnetization is changed forcibly from an easy direction of magnetization to a hard direction of magnetization by properly combining the direction of the strain of a magnetic substance with the positive/the negative of the magnetization constant of the magnetic substance. CONSTITUTION:A meander shaped sensor pattern 21 which uses a ferromagnetic-metal thin film is formed on the surface of a substrate 22. When, e.g. an iron-nickel alloy is used for the ferromagnetic-metal thin film, an easy direction of magnetization in its strainless state is the lengthwise direction of the pattern, and a hard direction of magnetization is the short direction of the pattern. Then, since a magnetization constant is positive, the spontaneous magnetization of the sensor pattern 21 is directed to the hard direction of magnetization when a tensile stress is applied to the short direction of the sensor pattern 21, i.e., to the hard direction of magnetization. As a result, when a magnetic field Hex is applied to the lengthwise direction of the sensor pattern 21 in this state, the direction of magnetization is changed into the easy direction of magnetization. As a result, a change in magnetization in a very small magnetic field is made smooth, and the high sensitivity of the magnetic sensor can be achieved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic field (also called a magnetic field).
Magnetic sensor whose electric resistance changes according to the strength of the magnetic field. Specifically, the magnetoresistive effect of a ferromagnetic metal thin film (typical example is a permalloy thin film or amorphous rare earth iron-based alloy film) is used to detect or displace a magnetic field. The present invention relates to a technique for increasing the sensitivity of a so-called ferromagnetic magnetic sensor used for various purposes such as position detection and position detection.

[0002]

2. Description of the Related Art First Conventional Example FIGS. 12A and 12B are two examples showing a planar layout of a conventional ferromagnetic magnetic sensor. In the figure, 1 and 2 are sensor patterns using a ferromagnetic metal thin film, and these sensor patterns 1 and 2 have a shape in which the whole is folded back although not particularly limited, and terminals 3a and 3b are provided at both ends. 4a, 4b are provided. Between terminals 3a and 3b (or terminals 4a and 4b)
When voltage E is applied to (between) sensor pattern 1 (or 2)
A current I corresponding to the electric resistance R of the current flows.

In general, the electric resistance of a ferromagnetic metal thin film (hereinafter, also simply referred to as "magnetic material") has a direction of current and a direction of magnetization (magnetization moment per unit area) parallel to each other due to a magnetoresistive effect. When it is orthogonal, it becomes the maximum, and when it is orthogonal, it becomes the minimum, and since it has a magnitude according to the crossing angle, the electric resistance R has a value according to the strength of the magnetic field Hex in which the sensor pattern 1 (or 2) is placed. .

Here, the longitudinal directions of the sensor patterns 1 and 2 are the directions of spontaneous magnetization with the lowest internal energy due to magnetic anisotropy, that is, the easy magnetization direction,
The short-side direction orthogonal to that is a difficult-to-magnetize direction. The difference between the sensor patterns 1 and 2 lies in the width in the lateral direction. Sensor pattern 2 for sensor pattern 1
The short width of is large. If the width is increased, the demagnetizing field Hd (the magnetic field in the opposite direction to the magnetization) created inside the magnetic body by the magnetic charge generated on the surface of the magnetic body can be reduced when the magnetic body is magnetized. The rotation can be smoothed to increase the detection sensitivity. The demagnetizing field Hd can be reduced by thinning the sensor pattern.

FIG. 13 is a characteristic diagram of FIG. 12, in which the characteristic line indicated by the solid line (a) is large when the demagnetizing field Hd is large (that is, the sensor pattern 1), and the characteristic line indicated by broken line (b) is when the demagnetizing field Hd is small (that is, the sensor). Pattern 2). The broken line B (the demagnetizing field Hd is smaller) has a larger rate of change in electric resistance (ΔR / R) with respect to the change in the magnetic field Hex.
Subtle changes in ex can be detected with high sensitivity.

However, as can be understood from the characteristic diagram of FIG. 13, the detection sensitivity in the vicinity of the zero point of the magnetic field Hex, that is, in the minute magnetic field cannot be improved by only decreasing the demagnetizing field Hd. Has the disadvantage that it cannot detect extremely small magnetic fields. Second Conventional Example FIG. 14 shows an example in which the drawback of FIG. 12 is eliminated, and the sensor pattern 5 is formed into a so-called barber pole type. According to this, it is possible to obtain a linear characteristic line c passing through the vicinity of the zero point of the magnetic field Hex as shown in FIG. 15 by using it together with an external bias magnetic field (indispensable for preventing reversal of internal magnetization). It is possible to realize high sensitivity in a minute magnetic field.

Third Conventional Example FIG. 16 is an example in which the drawbacks of FIG. 12 are also eliminated.
Contrary to 2, the lateral direction of the sensor sensor pattern 6 is the direction of easy magnetization. According to this, as shown in FIG. 17, it is possible to obtain a characteristic line D that sharply rises at the zero point of the magnetic field Hex, and it is possible to achieve high sensitivity in a minute magnetic field.

[0008]

However, the second or third conventional example is effective in that it can solve the drawback of the first conventional example, that is, the lack of sensitivity in a minute magnetic field. In the conventional example, an external bias magnetic field is required, so that there is a disadvantage that the configuration is complicated and the cost is disadvantageous. In addition, in the third conventional example,
Since the demagnetizing field Hd is large and the spontaneous magnetization is difficult to be aligned, the amount of resistance change at full scale is small, and the dynamic range (see symbol D in FIG. 17) cannot be widened. [Purpose] Therefore, the present invention has been made in view of the above technical problems, and aims to improve the sensitivity in a minute magnetic field without complicating the configuration and while ensuring a sufficient dynamic range. The purpose is to

[0009]

The invention according to claim 1 is
In a magnetic sensor including a sensor pattern 10 using a ferromagnetic metal thin film whose direction of magnetization changes between an easy magnetization direction and a difficult magnetization direction according to the strength of a magnetic field as shown in FIG. When the ferromagnetic metal thin film has a positive magnetostriction constant, continuous tensile stress was applied in the direction of hard magnetization of the sensor pattern, or continuous compressive stress was applied in the direction of easy magnetization of the sensor pattern. It is characterized by

The invention according to claim 2 is the principle diagram of FIG.
As shown in FIG. 3, in a magnetic sensor including a sensor pattern 11 using a ferromagnetic metal thin film whose magnetization direction changes between an easy magnetization direction and a difficult magnetization direction according to the strength of a magnetic field, Has a negative magnetostriction constant, it is characterized in that a continuous compressive stress is applied in the direction of hard magnetization of the sensor pattern or a continuous tensile stress is applied in the direction of easy magnetization of the sensor pattern.

[0011]

[Operation] The magnetization (spontaneous magnetization) of the ferromagnetic metal thin film when the magnetic field is zero is oriented in the easy magnetization direction. This is the case where no strain is applied to the magnetic substance, and when strain is applied. By appropriately combining the direction of the strain and the positive / negative of the magnetostriction constant of the magnetic material, the direction of spontaneous magnetization can be forcibly changed from the easy magnetization direction to the difficult magnetization direction.

That is, in a magnetic material having a magnetostriction constant of "positive", spontaneous magnetization is oriented in the direction of tensile stress (or in a direction orthogonal to the direction of compressive stress), or in a magnetic material having a magnetostriction constant of "negative", Spontaneous magnetization is oriented in the direction of compressive stress (or the direction orthogonal to the direction of tensile stress). Therefore, according to claim 1 or claim 2, the direction of magnetization when the magnetic field is zero can be changed from the easy magnetization direction to the difficult magnetization direction, and the magnetization direction when the magnetic field is other than zero can be changed. Since the direction can be changed to the opposite easy magnetization direction, it is possible to smoothly change the magnetization in an extremely minute magnetic field and achieve high sensitivity.

Incidentally, FIG. 3 is a characteristic diagram of FIG. 1, in which the change rate (ΔR / R) of the electric resistance near the zero point of the magnetic field Hex is large and the dynamic range D is wide.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIGS. 4 and 5 are views showing a first embodiment of the magnetic sensor according to the present invention. In FIG. 4, reference numeral 20 denotes a substrate (for example, a silicon substrate), and the surface of the substrate 20 is a so-called meander-shaped sensor pattern 21 (hereinafter simply referred to as “sensor pattern”) that is formed by using a ferromagnetic metal thin film. Are formed. Note that 22a and 22b are terminals formed at both ends of the sensor pattern 21.

An iron (Fe) -nickel (Ni) alloy (Ni 76%, film thickness 2000 Å) is used for the ferromagnetic metal thin film, and the easy magnetization direction in the unstrained state is the longitudinal direction of the pattern and the magnetization. The difficult direction is the lateral direction of the pattern. Magnetostriction constant of iron-nickel alloy thin film is "positive"
Therefore, in this example, a tensile stress (preferably a stress that causes a strain of about 0.1%) is applied in the short-side direction of the sensor pattern 21, that is, in the direction of hard magnetization (or in the longitudinal direction of the sensor pattern 21). That is, a similar compressive stress may be applied in the easy magnetization direction).

By doing so, the spontaneous magnetization of the sensor pattern 21 is oriented in the difficult magnetization direction.
When the magnetic field Hex is applied in the longitudinal direction of the sensor pattern 21, the direction of magnetization changes to the direction of easy magnetization, and the change of magnetization in a minute magnetic field can be smoothed to achieve high sensitivity. FIG. 5 is a characteristic diagram of FIG. 4, in which the solid line E gives only stress, and the broken line F shows the direction of the magnetic anisotropy of the magnetic material aligned with the longitudinal direction of the pattern. All of them have been able to achieve increased sensitivity and expanded dynamic range near the zero point of the magnetic field Hex.
Looking at the magnitude of the change rate (ΔR / R) of the electric resistance with respect to the change of, the change rate (ΔR / R) to the broken line is larger, which is desirable.

Second Embodiment FIGS. 6 and 7 are views showing a second embodiment of the magnetic sensor according to the present invention. In FIG. 6, reference numeral 30 denotes a substrate (for example, a silicon substrate), and on the surface of the substrate 30, first to fourth meander-shaped sensor patterns 31 to 34 using the same ferromagnetic metal thin film as in the first embodiment. (Hereinafter, simply referred to as “first to fourth sensor patterns”) are formed. Note that 35a to 35d are first to fourth sensor patterns 31.
These terminals are terminals formed at connection points of ~ 34, and a constant current is applied between a pair of terminals located on a diagonal line to measure a voltage between the other pair of terminals.

First to fourth sensor patterns 31 to 34
The lengthwise direction (which is illustrated as a single line for convenience, but actually has a predetermined width) has an inclination of about 45 degrees with respect to each side of the substrate 30. When a tensile stress or a compressive stress (preferably a stress that causes a strain of about 0.1%) is applied in the direction of any one side, about 45 degrees in the longitudinal direction of all patterns 31 to 34. The above stress is applied in the direction of.

With such a structure as well, it is possible to direct the spontaneous magnetization in the direction of the tensile stress (or the direction orthogonal to the direction of the compressive stress), that is, the difficult magnetization direction, and the direction of change of the magnetization when a magnetic field is applied. The direction of easy magnetization can be used. Therefore, as in the first embodiment, it is possible to achieve high sensitivity in a minute magnetic field, and as shown in the characteristic diagram of FIG. 7, the output linearly changes at the zero point of the magnetic field Hex. Thus, it is possible to provide a highly convenient magnetic sensor capable of detecting whether the applied magnetic field is positive or negative.

Third Embodiment FIGS. 8 and 9 are views showing a third embodiment of the magnetic sensor according to the present invention, and a preferred stress application technique is disclosed for use in the first embodiment or the second embodiment. It is a thing. In FIG. 8, reference numeral 40 denotes a flexible substrate on which wiring patterns 41a and 41b are formed. On the flexible substrate 40, the substrate 20 of the first embodiment (or the substrate 3 of the second embodiment) is provided.
0; hereinafter, the substrate 20 is representatively bonded and fixed. Note that 42a and 42b are terminals 22a and 22b of the sensor pattern 21 formed on the substrate 20 and a wiring pattern 41a,
41b is a bonding wire for connecting to 41b.

Reference numerals 43 and 44 denote mold members, respectively, and one mold member 43 is provided with a convex portion 43a having an arcuate surface having a constant curvature at least in an area larger than the area of the flexible substrate 40. Further, the other mold member 44 is formed with a recess 44a having a predetermined shape, and when these two mold members 43, 44 are overlapped, the projection 43a fits inside the recess 44a with a margin. Has become.

Now, when the back surface of the flexible substrate 40 on which the substrate 20 is mounted and fixed is attached to the front surface of the convex portion 43a, the flexible substrate 40 has a predetermined curvature according to the surface shape of the convex portion 43a, as shown in FIG. Since the substrate 20 fixed to the surface of the flexible substrate 40 can be similarly bent, the sensor pattern 21 on the substrate 20 is subjected to a tensile stress of a magnitude corresponding to the bending degree. Can be given.

Therefore, by adjusting the surface curvature of the convex portion 43a, the magnitude of the stress can be adjusted and the adhesion between the substrate 20 and the flexible substrate 40 and between the flexible substrate 40 and the convex portion 43a can be achieved. As long as the above is maintained, the stress can be continuously applied, and the high sensitivity in a minute magnetic field can be maintained for a long time.

The mold member 44 in which the recess 44a is formed serves as a lid of the package and is not essential for applying stress. By the way, the thickness of the flexible substrate 40 is 50 μm, and the thickness of the substrate 20 is 250 μm.
The sensor pattern 21 is a Ni-Fe thin film having a film thickness of 2000 angstrom, and the pattern width is about 30.
The meandering pattern of μm is used, and a thermosetting adhesive is used to fix the flexible substrate 40 and the convex portion 43a between the substrate 20 and the flexible substrate 40, and to reduce the curvature of the convex portion 43a to about 100 μm. When the magnetic field was detected at 200 mm, the external magnetic field range was 10 to 20O.
A change in resistance of about 2% was obtained at e. Moreover, in this magnetic field range, the linearity of the resistance change with respect to the change of the external magnetic field is good,
It was confirmed that high sensitivity was achieved in a minute magnetic field.

Fourth Embodiment FIGS. 10 and 11 are views showing a fourth embodiment of the magnetic sensor according to the present invention, which is used in the first embodiment or the second embodiment as in the third embodiment. The preferred technique of applying stress is disclosed. In FIG. 10, 50 is a wiring pattern 51.
a resin substrate on which a and 51b are formed.
0, the substrate 20 of the first embodiment (or the substrate 30 of the second embodiment; hereinafter, represented by the substrate 20) is coated with the predetermined adhesive 5
2 is used for adhesion.

Here, the resin substrate 50 and the adhesive 52 are
A substrate having a coefficient of thermal expansion larger than that of the substrate 20 should be used. When the resin substrate 50 and the substrate 20 are bonded at a high temperature, the resin substrate 50 and the adhesive 53 are fixed in a state in which the resin substrate 50 and the adhesive 53 are largely expanded as compared with the substrate 20, so that after the temperature is lowered to about room temperature, A strain having a magnitude corresponding to the difference in expansion between the two remains, and stress due to this strain is applied to the sensor pattern on the substrate 20.

For example, silicon (coefficient of thermal expansion is 2.6 × 10 ⁻⁶ / ° C.) is used for the substrate 20, and epoxy resin (coefficient of thermal expansion is 30 to 90 × 1) for the resin substrate 50 and the adhesive 52.
0 ^-6 / ° C) and the adhesive 52 at a high temperature of about 150 ° C.
After the resin is cured and then returned to room temperature, the resin substrate 50 and the adhesive 52, which have a thermal expansion coefficient of one order of magnitude, greatly contract, so that the resin substrate 50 becomes the substrate 20 as shown by an arrow 53 in FIG.
Will be curved downwards on the opposite side, and as a result,
A tensile stress having a magnitude corresponding to the degree of curvature is applied to the sensor pattern (not shown) on the substrate 20.

In FIG. 11, 54 is a bonding wire and 55 is a sealing resin. Incidentally, also in the fourth embodiment, a resistance change of about 2% was obtained in the external magnetic field range of 10 to 20 Oe. Moreover, the linearity of the resistance change with respect to the change of the external magnetic field was good in this magnetic field range, and it was confirmed that the high sensitivity was achieved in the minute magnetic field.

[0029]

According to the first or second aspect of the present invention, the direction of magnetization when the magnetic field is zero can be changed from the easy magnetization direction to the difficult magnetization direction, and the magnetization when the magnetic field is other than zero. Since the direction of can be changed to the opposite direction of easy magnetization, it is possible to smoothly change the magnetization in an extremely minute magnetic field and achieve high sensitivity.

[Brief description of drawings]

FIG. 1 is a principle diagram of the invention according to claim 1;

FIG. 2 is a principle diagram of the invention according to claim 2;

FIG. 3 is a characteristic diagram of the invention according to claim 1.

FIG. 4 is a configuration diagram of a first embodiment.

FIG. 5 is a characteristic diagram of the first embodiment.

FIG. 6 is a configuration diagram of a second embodiment.

FIG. 7 is a characteristic diagram of the second embodiment.

FIG. 8 is a configuration diagram of a third embodiment.

FIG. 9 is a sectional view of a third embodiment.

FIG. 10 is a configuration diagram of a fourth embodiment.

FIG. 11 is a sectional view of a fourth embodiment.

FIG. 12 is a configuration diagram of a first conventional example.

FIG. 13 is a characteristic diagram of a first conventional example.

FIG. 14 is a configuration diagram of a second conventional example.

FIG. 15 is a characteristic diagram of a second conventional example.

FIG. 16 is a configuration diagram of a third conventional example.

FIG. 17 is a characteristic diagram of a third conventional example.

[Explanation of symbols]

 10, 11, 21, 31-34: Sensor pattern

Continued Front Page (72) Inventor Miyoko Kawamoto 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (2)

[Claims] 1. A magnetic sensor comprising a sensor pattern using a ferromagnetic metal thin film in which the direction of magnetization changes depending on the strength of a magnetic field between an easy magnetization direction and a difficult magnetization direction. In the case of having a positive magnetostriction constant, a continuous tensile stress is applied in the direction of hard magnetization of the sensor pattern, or a continuous compressive stress is applied in the direction of easy magnetization of the sensor pattern. . 2. A magnetic sensor having a sensor pattern using a ferromagnetic metal thin film, the direction of magnetization of which changes between an easy magnetization direction and a difficult magnetization direction according to the strength of a magnetic field. When having a negative magnetostriction constant, a continuous compressive stress is applied in the direction of hard magnetization of the sensor pattern,
Alternatively, the magnetic sensor is characterized in that a continuous tensile stress is applied in the direction of easy magnetization of the sensor pattern.