JP2008003072A - Thin-film magnetoresistive element and thin-film magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide thin-film magnetoresistive element which shows high isotropic response to in-plane directional magnetic field and is available as a switching device, and also practical thin film magnetic sensor using this element. <P>SOLUTION: The thin-film magnetoresistive element is designed that it has inside soft magnetic film 2 formed on an insulating substrate 1, outside soft magnetic film 3, thin-film magnetoresistive element 4 and required wiring 5, in which magnetoresistive effect film 4 is formed in regularly-spaced clearance 6 formed between outer edge section of the inside soft magnetic film 2 and the inner edge section of the outside soft magnetic film 3. The thin-film magnetic sensor is designed to build bridge circuit allowing this thin-film magnetoresistive element to be variable resistor. Radially-extending slit-shaped notch section 8 can also be formed on the outside soft magnetic film 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film magnetoresistive element and a thin film magnetic sensor, and in particular, a thin film magnetoresistive element that exhibits a response to an external magnetic field in any direction in a plane and can be used as a switch element, and a thin film using the same The present invention relates to a magnetic sensor.

  Conventionally, Hall ICs and MR elements have been widely used as magnetic sensors that perform switching operations. The Hall IC is a package in which a Hall element and a circuit that shapes the output of the Hall element are integrally packaged, and is applied to position detection or the like. On the other hand, in the MR element, the end surfaces of the first and second soft magnetic films are arranged opposite to each other with a required gap in the same plane, and the MR element is in the gap between the end surfaces of the first and second soft magnetic films. A magnetoresistive film such as a nanogranular alloy thin film is formed, and is applied to a magnetic sensor in a magnetic head, a servo motor, a rotary encoder, or the like.

  As described above, the Hall IC includes a Hall element and a circuit that shapes the output of the Hall element. Therefore, the sensor module is large and expensive, and has high sensitivity anisotropy. On the other hand, the MR element does not need an output shaping circuit and can be implemented in a small size and at a low cost. However, the MR element is similar to the Hall IC in that the anisotropy of sensitivity is high. There is a need to develop an MR element that exhibits a response to a magnetic field in any direction.

  The present invention has been made to solve such a technical problem, and an object of the present invention is to provide a thin film magnetoresistive element that exhibits a response to a magnetic field in any direction in the plane and can be used as a switching element. And a practical thin film magnetic sensor using the same.

  In order to solve the above-mentioned problems, the present invention relates to a thin film magnetoresistive element, firstly, an insulating substrate, an inner soft magnetic film formed on the insulating substrate, an outer soft magnetic film, a magnetoresistive film, and the aforementioned Wiring for detecting the resistance value of the magnetoresistive effect film, and the outer soft magnetic film surrounds the outer periphery of the inner soft magnetic film over the entire circumference, or the outer periphery of the inner soft magnetic film is covered over the most part. A gap is formed between the outer edge of the inner soft magnetic film and the inner edge of the outer soft magnetic film, and the magnetoresistive film is formed in the gap. It was configured to be formed.

  If the outer soft magnetic film is arranged over the entire outer periphery of the inner soft magnetic film and the magnetoresistive effect film, the saturation magnetic flux density of the outer soft magnetic film can be made constant regardless of the application direction of the external magnetic field. An omnidirectional thin film magnetoresistive element exhibiting an equivalent response with respect to an external magnetic field applied in the direction is obtained. Even when the outer soft magnetic film surrounds most of the outer peripheries of the inner soft magnetic film and magnetoresistive effect film, and a part that does not have the outer soft magnetic film is formed in part, the external magnetic field is applied in the entire direction. Since the saturation magnetic flux density of the corresponding outer soft magnetic film can be provided, the thin film magnetoresistive element showing a response to an external magnetic field in any direction in the plane is obtained. In this case, since the saturation magnetic flux density of the outer soft magnetic film changes according to the application direction of the external magnetic field, the MR ratio change characteristic changes according to the application direction of the external magnetic field.

  According to the present invention, secondly, in the thin film magnetoresistive element of the first configuration, the outer soft magnetic film is divided into two by a slit-like cutout portion extending in a radial direction. According to this configuration, the external magnetic field acting in any direction in the plane shows a response, and the resistance change rate characteristic with respect to the external magnetic field in the direction parallel to the notch and the resistance change rate with respect to the external magnetic field in the direction perpendicular to the notch A thin film magnetoresistive element having a large difference from the characteristics is obtained.

  According to a third aspect of the present invention, in the thin film magnetoresistive element of the first configuration, the outer soft magnetic film has a slit-shaped cutout part that does not reach the inner edge part. did. According to this configuration, the external magnetic field acting in any direction in the plane shows a response, and the resistance change rate characteristic with respect to the external magnetic field in the direction parallel to the notch and the resistance change rate with respect to the external magnetic field in the direction perpendicular to the notch A thin film magnetoresistive element having different characteristics is obtained.

  According to a fourth aspect of the present invention, in the thin film magnetoresistive element of the first configuration, the outer edge portion of the inner soft magnetic film is circular, and the inner edge portion and outer edge portion of the outer soft magnetic film are circular or arc-shaped. It was configured to be. If the inner edge portion and the outer edge portion of the outer soft magnetic film are formed in a circular shape, the width of the outer soft magnetic film can be made constant over the entire circumference, so that the uniformity of response to changes in the application direction of the external magnetic field can be maximized. Further, even when the inner and outer edges of the outer soft magnetic film are formed in an arc shape, the width of the outer soft magnetic film can be made constant, so that the uniformity of the response to the external magnetic field can be improved.

  According to the present invention, fifthly, in the thin film magnetoresistive element of the first configuration, the outer edge portion of the inner soft magnetic film and the inner edge portion of the outer soft magnetic film are square. Even with such a configuration, the saturation magnetic flux density of the outer soft magnetic film according to the direction in which the external magnetic field is applied can be provided over the entire circumference, so that the thin film magnetoresistive element exhibits a response to the external magnetic field in any direction in the plane. It can be.

  On the other hand, the present invention relates to a thin film magnetic sensor for detecting resistance values of an insulating substrate, an inner soft magnetic film, an outer soft magnetic film, a magnetoresistive film, and the magnetoresistive film formed on the insulating substrate. And the outer soft magnetic film is formed so as to surround the outer periphery of the inner soft magnetic film over the entire circumference, or to surround the outer periphery of the inner soft magnetic film over most of the outer soft magnetic film. A gap is provided between the outer edge of the magnetic film and the inner edge of the outer soft magnetic film, and the first thin film magnetoresistive element having the magnetoresistive film formed in the gap is variable. A resistance, and an insulating substrate, and an inner nonmagnetic metal film, an outer soft magnetic film, a magnetoresistive film, and a wiring for detecting a resistance value of the magnetoresistive film formed on the insulating substrate, The outer soft magnetic film is the inner non-magnetic film. Surrounding the outer circumference of the metal film over the entire circumference, or so as to surround the outer circumference of the inner nonmagnetic metal film over the most part, the outer edge of the inner nonmagnetic metal film and the inner edge of the outer soft magnetic film Is provided with a fixed gap, and the second thin film magnetoresistive element in which the magnetoresistive film is formed in the gap is used as a fixed resistor, and the outer soft magnetic film of the variable resistance portion and the A configuration is adopted in which a bridge circuit is provided so as to be separated from the outer soft magnetic film of the fixed resistance portion.

  In the first thin film magnetoresistive element, when the magnetic field acting on the outer soft magnetic film reaches the saturation magnetic flux density, magnetic flux flows from the outer soft magnetic film to the inner soft magnetic film via the magnetoresistive effect film. The change in the resistance value of the effect film can be used as a variable resistance. On the other hand, the second thin film magnetoresistive element has a nonmagnetic metal film, not a soft magnetic film, formed inside the outer soft magnetic film and the magnetoresistive film, and the magnetic field acting on the outer soft magnetic film is reduced. Even after reaching the saturation magnetic flux density, the magnetoresistive effect (MR effect) is gently expressed, so that it can be used as a fixed resistance. Therefore, when a bridge circuit is configured using these variable resistors and fixed resistors, a thin film magnetic sensor capable of detecting the magnitude of the applied magnetic field regardless of the direction of the applied magnetic field can be obtained. In addition, the bridge circuit makes it possible to detect changes in the magnetic field acting on the magnetoresistive effect film by the null method, and to eliminate influences such as fluctuations in power supply voltage, detector input impedance, or changes in film-derived characteristics. Therefore, a highly accurate thin film magnetic sensor can be obtained.

  In the thin film magnetoresistive element of the present invention, the outer soft magnetic film is formed so as to surround the outer periphery of the inner soft magnetic film over the entire circumference, or to surround the outer periphery of the inner soft magnetic film over the most part. It can be used as a switching element that responds to an external magnetic field. In particular, the one in which the outer soft magnetic film is arranged on the entire outer periphery of the inner soft magnetic film is a non-directional thin film magnetoresistive element that performs switching operation only by the magnitude of the external magnetic field regardless of the direction of the applied external magnetic field. be able to.

  The thin film magnetic sensor of the present invention includes a first thin film magnetoresistive element in which an outer soft magnetic film is formed so as to surround the outer circumference of the inner soft magnetic film over the entire circumference or to surround the outer circumference of the inner soft magnetic film over most of the circumference. Since it is used as a variable resistor, a thin film magnetic sensor having a bridge circuit having a fixed resistance of a second thin film magnetoresistive element having an inner nonmagnetic metal film instead of the inner soft magnetic film of the first thin film magnetoresistive element is provided. An external magnetic field in any direction can be detected, and a highly accurate thin film magnetic sensor can be obtained.

<First Embodiment>
Hereinafter, an example of a thin film magnetoresistive element according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view of a thin film magnetoresistive element according to the first embodiment, FIG. 2 is an enlarged cross-sectional view of the AA portion of FIG. 1, and FIG. 3 is an MR ratio of the thin film magnetoresistive element according to the first embodiment to an external magnetic field. It is a graph which shows the change of.

  As shown in FIGS. 1 and 2, the thin film magnetoresistive element of this example includes an insulating substrate 1, an inner soft magnetic film 2, an outer soft magnetic film 3, a magnetoresistive effect film 4 formed on the insulating substrate 1, and It is mainly composed of wiring 5 for detecting the resistance value of the magnetoresistive effect film 4.

  The insulating substrate 1 is formed into a required shape and size with a highly rigid nonmagnetic insulator such as an inorganic dielectric, plastics, or nonmagnetic ceramics.

The inner soft magnetic film 2 and the outer soft magnetic film 3 are formed of a soft magnetic material having a high saturation magnetic flux density, such as a Co ₇₇ Fe ₅ Si ₉ B ₈ alloy or a permalloy alloy (Fe ₆₅ Ni ₃₅ ). As a method of forming the inner soft magnetic film 2 and the outer soft magnetic film 3, sputtering can be used. As shown in FIG. 1, the inner soft magnetic film 2 has a circular planar shape, and the outer soft magnetic film 3 has an inner diameter and an outer diameter larger than the outer diameter of the inner soft magnetic film 2. They are formed in an annular shape and are arranged concentrically with each other. Therefore, an annular gap 6 having a constant width is formed between the outer edge portion of the inner soft magnetic film 2 and the inner edge portion of the outer soft magnetic film 3.

The magnetoresistive film 4 has a remarkably large MR ratio as compared to a permalloy alloy-type magnetoresistive film, and a large MR ratio can be obtained in one layer. A dispersed granular magnetic film is formed. Examples of the granular magnetic film include 32 vol% CoFe—MgF ₂ and CoYO. As shown in FIG. 2, the magnetoresistive film 4 is formed in the gap 6 between the outer edge portion of the inner soft magnetic film 2 and the inner edge portion of the outer soft magnetic film 3 by sputtering or the like. In the example of FIG. 2, the outer edge portion of the inner soft magnetic film 2 and the inner edge portion of the outer soft magnetic film 3 are formed so as to be inclined with respect to the insulating substrate 1. In order to facilitate the formation of the magnetoresistive film 4 in the gap 6, the magnetoresistive film 4 is formed in the gap 6 by devising the conditions during sputtering, for example. If densely formed, each edge can be formed perpendicular to the insulating substrate 1.

  The wiring 5 is formed of a metal material having excellent conductivity such as copper or aluminum. Sputtering can also be used as a method for forming the wiring 5.

  FIG. 3 shows a test example of the thin film magnetoresistive element according to this embodiment. The samples are the following four examples.

Sample (1): The outer diameter φ1 of the outer soft magnetic film 3 is 150 μm, the outer diameter φ2 of the inner soft magnetic film 2 is 40 μm, the size Lg of the gap 6 is 2 μm, the inner soft magnetic film 2 and the outer soft magnetic film 3 Thickness tsof is 1.5 μm
Sample (2): The outer diameter φ1 of the outer soft magnetic film 3 is 150 μm, the outer diameter φ2 of the inner soft magnetic film 2 is 20 μm, the size Lg of the gap 6 is 2 μm, the inner soft magnetic film 2 and the outer soft magnetic film 3 Thickness tsof is 1.5 μm
Sample (3): The outer diameter φ1 of the outer soft magnetic film 3 is 75 μm, the outer diameter φ2 of the inner soft magnetic film 2 is 20 μm, the size Lg of the gap 6 is 2 μm, the inner soft magnetic film 2 and the outer soft magnetic film 3 Thickness tsof is 1.5 μm
Sample (4): The outer diameter φ1 of the outer soft magnetic film 3 is 150 μm, the outer diameter φ2 of the inner soft magnetic film 2 is 40 μm, the size Lg of the gap 6 is 2 μm, the inner soft magnetic film 2 and the outer soft magnetic film 3 Thickness tsof is 2 μm.

  When the change in the MR ratio of the thin film magnetoresistive elements according to the samples (1) to (4) was measured while changing the external magnetic field Hex, the results shown in FIG. 3 were obtained. As is clear from this figure, the thin film magnetoresistive elements according to the samples (1) to (4) have the characteristic of having an external magnetic field Hex whose MR ratio changes abruptly, and can be used as a switch element. it can.

  In the thin-film magnetoresistive element of this example, the annular outer soft magnetic film 3 is concentrically disposed on the entire outer periphery of the inner soft magnetic film 2 formed in a circle, so that the outer soft magnetic film 3 is not affected by the direction of the applied external magnetic field. The magnetic flux density until the magnetic film 3 is saturated becomes constant in the circumferential direction of the outer soft magnetic film 3, and the isotropic response to the external magnetic field is the best.

Second Embodiment
As shown in FIG. 4, the thin film magnetoresistive element of this example is characterized in that the inner soft magnetic film 2 is formed in a square shape and the outer soft magnetic film 3 is formed in a rectangular frame shape. In the thin-film magnetoresistive element of this example, the saturation magnetic flux density of the outer soft magnetic film 3 differs depending on the application direction of the external magnetic field. Since the outer soft magnetic film 3 is formed over the entire circumference of the outer periphery, the response to the external magnetic field is shown over the entire circumference regardless of the direction in which the external magnetic field is applied. Therefore, according to the thin film magnetoresistive element of this example, it is possible to provide a thin film magnetoresistive element that shows a response to an external magnetic field in any direction in the plane and that can specify the application direction of the external magnetic field.

<Third Embodiment>
As shown in FIG. 5, the thin-film magnetoresistive element of this example has an outer end portion and an outer soft magnetic film of the inner soft magnetic film 2 on the upper surface on the inner end side and the upper surface on the outer end side, respectively. Each of these films 2, 3, 4 is formed so that the inner end portions of 3 overlap each other. With this configuration, the same effect as the thin film magnetoresistive element according to the first embodiment can be obtained.

<Fourth embodiment>
The thin film magnetoresistive element of this example is characterized in that slit-shaped notches 8a, 8b, and 8c are formed in the outer soft magnetic film 3, as shown in FIGS. 6 (a), 6 (b), and 7. FIG. . FIG. 6A shows a length that is ½ of the width of the outer soft magnetic film 3 (difference between outer diameter and inner diameter) from the outer peripheral edge of the outer soft magnetic film 3 in the radial direction of the outer soft magnetic film 3. This is an example in which the notch portions 8a are provided on both sides of the outer soft magnetic film 3 through the center (the center of the inner soft magnetic film 2 and the center of the magnetoresistive effect film 4) O. FIG. From the outer peripheral edge of the outer soft magnetic film 3 toward the radial direction of the outer soft magnetic film 3, a notch 8b having a length of 3/4 of the width of the outer soft magnetic film 3 is interposed through the center of the outer soft magnetic film 3. This is an example provided on both sides of the lever. FIG. 7 shows an example in which slit-shaped notches 8c extending from the outer peripheral edge to the inner peripheral edge are formed in the radial direction of the outer soft magnetic film 3, and the outer soft magnetic film 3 is divided into two semicircular parts. It is. The thin film magnetoresistive element in FIG. 6A is referred to as a sample (5), the thin film magnetoresistive element in FIG. 6B as a sample (6), and the thin film magnetoresistive element in FIG. 7 as a sample (7). The size other than the notch was the same as the sample (1) described above.

  When the change in the MR ratio of the thin film magnetoresistive element according to samples (1), (5), (6), and (7) was measured while changing the external magnetic field Hex, the results shown in FIG. 8 were obtained. The application direction of the external magnetic field Hex is the x direction in FIGS. 6 and 7, and when the external magnetic field Hex is applied in the y direction in FIGS. 6 and 7 for the samples (5), (6), and (7). The change in MR ratio was almost the same as the result of the sample (1) in FIG.

  As is clear from FIG. 8, the thin film magnetoresistive elements according to the samples (1), (5), (6), and (7) also have a characteristic having an external magnetic field Hex in which the MR ratio changes abruptly. It can be used as a switch element. As is clear from comparison between FIG. 3 and FIG. 8, the thin film magnetoresistive element according to the sample (1) and the thin film magnetoresistive element according to the samples (5), (6), and (7) And the thin film magnetoresistive elements according to the samples (5), (6), and (7) have different MR ratio change characteristics with respect to the external magnetic field Hex depending on the application direction of the external magnetic field Hex. I can see that they are different. Therefore, according to the thin film magnetoresistive element of this example, it is possible to provide a thin film magnetoresistive element that shows a response to an external magnetic field in any direction in the plane and that can specify the application direction of the external magnetic field.

  Hereinafter, the configuration of the thin film magnetic sensor using the thin film magnetoresistive element according to the first embodiment will be described with reference to FIGS. 9 is a configuration diagram of a thin film magnetic sensor according to the embodiment, FIG. 10 is an equivalent circuit diagram of the thin film magnetic sensor according to the embodiment, and FIG. 11 is a resistance of a variable resistor and a fixed resistor with respect to an external magnetic field in the thin film magnetic sensor according to the embodiment. FIG. 12 is a graph showing a change rate characteristic, and FIG. 12 is a graph showing a midpoint potential change characteristic with respect to an external magnetic field of the thin film magnetic sensor according to the embodiment.

  As shown in FIG. 9, the thin film magnetic sensor of this example connects the insulating substrate 1, the variable resistor 11 and the fixed resistor 21 formed on the insulating substrate 1, and the variable resistor 11 and the fixed resistor 21 to each other. And wiring 5 constituting the bridge circuit shown in FIG.

  As the variable resistor 11, the thin film magnetoresistive element shown in FIGS. 1 and 2 is used. On the other hand, the fixed resistor 21 is formed by forming a nonmagnetic metal film 22 in place of the inner soft magnetic film 2 of the variable resistor 11. Other portions are formed in the same manner as the variable resistor 11 in shape and size.

  As described above, the variable resistor 11 has a resistance change rate characteristic indicated by a solid line in FIG. 11 with respect to a magnetic field. On the other hand, since the fixed resistor 21 includes the nonmagnetic metal film 22, when the outer soft magnetic film 3 reaches the saturation magnetic flux density, the magnetoresistive effect is gently exhibited, and is indicated by a broken line in FIG. It has a resistance change rate. Therefore, when a bridge circuit is constituted by the variable resistor 11 and the fixed resistor 21, it is possible to detect the fluctuation of the magnetic field acting on the magnetoresistive effect film by the null method, and to change the power supply voltage, the input impedance of the detector or the non-linearity. Thus, a practical thin film magnetic sensor with high accuracy can be obtained. As the sample, the thin film magnetoresistive element according to the above-described sample (1) is used as the variable resistor 11, and has the same shape and the same size as the thin film magnetoresistive element according to the sample (1). Instead of the magnetic film 2, a non-magnetic metal film 22 is used as the fixed resistor 21.

  The thin film magnetic sensor of the present example exhibited the output characteristics shown in FIG. 12 or the output characteristics approximate to the external magnetization in any direction in the plane of the thin film magnetoresistive element.

  As the variable resistor 11, the thin film magnetoresistive element according to the second to fourth embodiments can be used instead of the thin film magnetoresistive element according to the first embodiment. Of course, in these cases, the fixed resistor 21 having the same shape and the same size as the variable resistor 11 is used.

It is a top view of the thin film magnetoresistive element concerning a 1st embodiment. It is an AA part expanded sectional view of FIG. It is a graph which shows the change characteristic of MR ratio with respect to the external magnetic field of the thin film magnetoresistive element which concerns on 1st Embodiment. It is a top view of the thin film magnetoresistive element concerning a 2nd embodiment. It is a principal part expanded sectional view of the thin film magnetoresistive element which concerns on 3rd Embodiment. It is a top view of the thin film magnetoresistive element concerning a 4th embodiment. It is a top view which shows the other example of the thin film magnetoresistive element which concerns on 4th Embodiment. It is a graph which shows the change characteristic of MR ratio with respect to the external magnetic field of the thin film magnetoresistive element concerning 4th Embodiment. It is a block diagram of the thin film magnetic sensor which concerns on embodiment. It is an equivalent circuit diagram of the thin film magnetic sensor according to the embodiment. It is a graph which shows the resistance change rate characteristic of the variable resistance and fixed resistance with respect to the external magnetic field in the thin film magnetic sensor which concerns on embodiment. It is a graph which shows the midpoint potential change characteristic with respect to the external magnetic field of the thin film magnetic sensor which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Inner soft magnetic film 3 Outer soft magnetic film 4 Magnetoresistive film 5 Wiring 6 Gap 8 Notch 11 Variable resistance 21 Fixed resistance 22 Nonmagnetic metal film

Claims (6)

  An insulating substrate; an inner soft magnetic film formed on the insulating substrate; an outer soft magnetic film; a magnetoresistive effect film; and a wiring for detecting a resistance value of the magnetoresistive effect film. Is formed so as to surround the outer periphery of the inner soft magnetic film over the entire circumference, or to surround the outer periphery of the inner soft magnetic film over most of the outer soft magnetic film. A thin film magnetoresistive element, wherein a gap having a constant interval is provided between the inner edge and the magnetoresistive film is formed in the gap.   2. The thin film magnetoresistive element according to claim 1, wherein the outer soft magnetic film is divided into two by a slit-shaped cutout portion extending in a radial direction.   2. The thin film magnetoresistive element according to claim 1, wherein the outer soft magnetic film has a slit-like cutout portion that does not reach the inner edge portion.   3. The thin film magnetoresistive element according to claim 1, wherein an outer edge portion of the inner soft magnetic film is circular, and an inner edge portion and an outer edge portion of the outer soft magnetic film are circular or arc-shaped. .   The thin film magnetoresistive element according to claim 1 or 2, wherein an outer edge portion of the inner soft magnetic film and an inner edge portion of the outer soft magnetic film are square. An insulating substrate; an inner soft magnetic film formed on the insulating substrate; an outer soft magnetic film; a magnetoresistive effect film; and a wiring for detecting a resistance value of the magnetoresistive effect film. Is formed so as to surround the outer periphery of the inner soft magnetic film over the entire circumference, or to surround the outer periphery of the inner soft magnetic film over most of the outer soft magnetic film. A gap having a constant interval is provided between the inner edge and the first thin film magnetoresistive element in which the magnetoresistive film is formed in the gap as a variable resistance.
An insulating substrate; an inner nonmagnetic metal film formed on the insulating substrate; an outer soft magnetic film; a magnetoresistive effect film; and a wiring for detecting a resistance value of the magnetoresistive effect film. The film is formed so as to surround the outer periphery of the inner nonmagnetic metal film over the entire circumference, or to surround the outer periphery of the inner nonmagnetic metal film over most of the outer nonmagnetic metal film. A gap having a constant interval is provided between the inner edge of the soft magnetic film, and the second thin film magnetoresistive element in which the magnetoresistive film is formed in the gap is used as a fixed resistance.
A thin film magnetic sensor comprising a bridge circuit in which an outer soft magnetic film of the variable resistance portion and an outer soft magnetic film of the fixed resistance portion are provided apart from each other.

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