JP6576175B2 - Thin film magnetic field sensor and array type thin film magnetic field sensor - Google Patents

Description

  The present invention relates to a thin film magnetic field sensor using a magnetoresistive effect, and more particularly to a thin film magnetic field sensor having a thin film magnet as a magnetic bias mechanism and an array type thin film magnetic field sensor using the same.

  A magnetoresistive element has higher sensitivity to a minute magnetic field than a Hall element or a semiconductor type magnetoresistive element, and a thin film magnetic field sensor using this is widely used. As such a thin film magnetic field sensor, what was proposed by patent documents 1 and patent documents 2 is known.

  FIG. 9 is a perspective view showing the structure of the thin film magnetic field sensor described in Patent Document 1. As shown in FIG. The thin film magnetic field sensor is provided below a magnetoresistive thin film 31 whose electric resistance changes with respect to an external magnetic field, a pair of soft magnetic thin films 32 disposed on both sides of the magnetoresistive thin film 31, and a soft magnetic thin film 32. And a pair of hard magnetic thin films 33 which are thin film magnets. The hard magnetic thin film 33 and the soft magnetic thin film 32 are laminated on the substrate, and the magnetoresistive thin film 31 is interposed between the pair of soft magnetic thin films 32 and between the pair of hard magnetic thin films 33. Formed on top.

  In the thin film magnetic field sensor of FIG. 9, the soft magnetic thin film 32 has a function of converging an external magnetic field and increasing the magnetic sensitivity of the magnetoresistive thin film 31, and the hard magnetic thin film 33 applies a magnetic bias to the magnetoresistive thin film 31. As a magnetic field generation source. By applying a magnetic bias from the hard magnetic thin film 33, not only the magnitude of the magnetic field but also the direction of the magnetic field can be detected.

  Patent Document 1 describes that the hard magnetic thin film may be in contact with or away from the soft magnetic thin film, and that any one of the pair of hard magnetic thin films can provide a magnetic bias. .

  FIG. 10 is a diagram showing the structure of the thin film magnetic field sensor described in Patent Document 2. As shown in FIG. In this thin film magnetic field sensor, a magnetoresistive element 41 and two thin film magnets 42 and 43 are formed on the same chip, and the thin film magnets 42 and 43 have opposite polarities on both sides with the magnetoresistive element 41 interposed therebetween. Is arranged. In this way, since the magnetoresistive element 41 and the two thin film magnets 42 and 43 are formed on the same substrate, the positioning accuracy is high, and the poles of the two thin film magnets 42 and 43 arranged at intervals are provided. Since the parallel magnetic field generated between the two is used as the bias magnetic field, positive and negative magnetic field detection can be performed with high symmetry and high accuracy.

JP 2003-078187 A Japanese Patent Laid-Open No. 06-148301

  However, in the conventional thin film magnetic field sensor, there is a considerable leakage magnetic field from the thin film magnet that is a magnetic field generation source to the outside, and measurement of a minute magnetic field may be difficult due to the influence. For example, when a structure with high electrical conductivity such as metal is moving and measuring a minute magnetic field generated from the moving structure, there is a leakage magnetic field from the thin film magnet of the thin film magnetic field sensor. Then, an induced current is generated in the structure, and the influence of the magnetic field generated thereby cannot be ignored.

  Moreover, in an array type thin film magnetic field sensor in which a plurality of thin film magnetic field sensors having thin film magnets are arranged on the same substrate, there is a risk that the leakage magnetic field of the thin film magnet may interfere with other thin film magnetic field sensors in proximity. is there.

  Accordingly, an object of the present invention is to provide a thin film magnetic field sensor having a very small leakage magnetic field from a thin film magnet as a magnetic bias mechanism and an array type thin film magnetic field sensor having a plurality of such thin film magnetic field sensors.

In order to solve the above problems, the present invention provides the following (1) to (5).
(1) a magnetoresistive thin film whose electrical resistance changes with respect to an external magnetic field;
A pair of soft magnetic thin films disposed without gaps on both sides of the magnetoresistive thin film; and
A thin film magnet that provides a magnetic bias to the magnetoresistive thin film;
The thin film magnet is formed on a substrate, and the soft magnetic thin film is formed on the thin film magnet and is provided so as to cover at least a portion including the magnetic pole of the thin film magnet. Magnetic field sensor.

  (2) At least one of the soft magnetic thin film and the thin film magnet is made of an insulating material, and the soft magnetic thin film is provided so as to be in direct contact with the thin film magnet. Thin film magnetic field sensor.

  (3) The soft magnetic thin film and the thin film magnet are both made of a conductive material, and an electrical insulating film is interposed between the soft magnetic thin film and the thin film magnet (1). ) Thin film magnetic field sensor.

  (4) The thickness of the soft magnetic thin film is not less than the thickness of the thin film magnet, and the width of the region of the soft magnetic thin film that protrudes from the magnetic pole end of the thin film magnet is not more than 10 times the thickness of the soft magnetic thin film. The thin film magnetic field sensor according to any one of (1) to (3), wherein

  (5) An array type thin film magnetic field sensor, wherein a plurality of thin film magnetic field sensors according to any one of (1) to (4) are periodically or aperiodically arranged on a substrate.

  According to the present invention, a thin film magnetic field sensor having a very small leakage magnetic field from a thin film magnet as a magnetic bias mechanism and an array type thin film magnetic field sensor having a plurality of such thin film magnetic field sensors are provided.

It is the top view and sectional drawing which show the thin film magnetic field sensor which concerns on one Embodiment of this invention. It is sectional drawing which shows the thin film magnetic field sensor which concerns on other embodiment of this invention. It is a figure which shows the external magnetic field dependence of the electrical resistance of a thin film magnetic field sensor. It is sectional drawing which expands and shows a part of thin film magnetic field sensor which concerns on one Embodiment of this invention. It is sectional drawing which expands and shows a part of thin film magnetic field sensor which concerns on other embodiment of this invention. FIG. 3 is a cross-sectional view showing an example in which a gradient is provided at the edge of a thin film magnet in the thin film magnetic field sensor of FIG. 2. It is a figure which shows the leakage magnetic field characteristic of the thin film magnetic field sensor of this invention. It is a top view which shows the array type thin film magnetic field sensor which formed the thin film magnetic field sensor collectively on the same board | substrate collectively. It is a perspective view which shows the structure of the thin film magnetic field sensor described in patent document 1. FIG. It is a figure which shows the structure of the thin film magnetic field sensor described in patent document 2. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a plan view and a sectional view showing a thin film magnetic field sensor according to an embodiment of the present invention. The thin film magnetic field sensor 10 includes a magnetoresistive thin film 1 whose electric resistance changes with respect to an external magnetic field, a pair of soft magnetic thin films 2 disposed on both sides of the magnetoresistive thin film 1, and a magnetic bias applied to the magnetoresistive thin film 1. And a thin film magnet 3 to be provided.

  The thin film magnet 3 is formed on the substrate 4, and the soft magnetic thin film 2 is formed on the thin film magnet 3. At this time, the soft magnetic thin film 2 is provided so as to cover at least a portion including the magnetic pole of the thin film magnet 3. That is, the soft magnetic thin film 2 is provided so as to cover the upper surface, the side surface, and the end surface of the portion including at least the magnetic pole of the thin film magnet 3.

  Specifically, the thin-film magnet 3 is formed in a strip shape so as to extend in the Y direction on the substrate 4, and magnetic poles are formed at substantially both ends in the longitudinal direction. A magnetoresistive thin film 1 is formed at the center above the thin film magnet 3 so as to extend in the X direction. The length of the magnetoresistive thin film 1 in the X direction is shorter than the length of the thin film magnet 3 in the X direction. In this example, the soft magnetic thin film 2 is formed on both sides of the magnetoresistive thin film 1 so as to cover most of the upper surface and side surfaces of the thin film magnet 3 and the entire end surface, so that at least the magnetic poles of the thin film magnet 3 are soft. The magnetic thin film 2 is covered.

  In the example of FIG. 1, at least one of the soft magnetic thin film 2 and the thin film magnet 3 is an insulating material. Therefore, as shown in FIG. Provided in direct contact.

  On the other hand, when both the soft magnetic thin film 2 and the thin film magnet 3 are conductive materials (metal materials), an electrically insulating film is interposed between the soft magnetic thin film 2 and the thin film magnet 3 as shown in FIG. 5 is interposed.

  As the substrate 4, glass having an appropriate thickness (for example, about 0.5 mm) and mirror-polished on the surface can be used. In the case where the substrate 4 is formed integrally with a semiconductor IC circuit, silicon, a silicon on insulator (SOI), SiC, sapphire, a compound semiconductor, or the like having a thermal oxide film formed on the surface is suitable as the substrate 4.

  The thin film magnet 3 has an ability to generate a large magnetic field outside in order to give a magnetic bias to the magnetoresistive thin film 1. Therefore, as the material of the thin film magnet 3, one having a large maximum magnetic flux density and a high coercive force is selected, and a metallic SmCo, Nd—Fe—B, Sm—Fe—N, Nd—Fe—N based magnet, Alternatively, an iron oxide hard ferrite magnet can be suitably used.

  The soft magnetic thin film 2 has a high magnetic permeability of about several thousand, and has a function of converging many lines of magnetic force and applying a strong magnetic field to both sides of the magnetoresistive thin film 1. The thickness of the soft magnetic thin film 2 is preferably equal to or greater than the thickness of the thin film magnet 3. As a material for the soft magnetic thin film 2, a metal alloy such as FeNi, CoFeSiB, FeSiAl, FeNiNb or the like having high magnetic permeability, or oxide soft ferrite can be preferably used.

The thin film magnet 3 is a metal system such as SmCo, Nd—Fe—B, Sm—Fe—N, Nd—Fe—N magnet, and the soft magnetic thin film 2 is a metal such as FeNi, CoFeSiB, FeSiAl, FeNiNb. In the case of the system, as shown in FIG. 2 described above, an electrical insulating film 5 is formed between them. As the electrical insulating film 5, an SiO ₂ film, an Al ₂ O ₃ film, or the like can be used.

  The magnetoresistive thin film 1 exhibits a high electric resistance change with respect to an external magnetic field, and the thickness thereof is, for example, about 0.5 μm. The material of the magnetoresistive thin film 1 is preferably a material that exhibits a high electrical resistance change of several tens of percent or more depending on the external magnetic field due to the giant magnetoresistive effect or the tunnel magnetoresistive effect, such as CoAlO, CoYO, FeMgF, FeCoMgF-based, FeCoAlF-based nanogranular alloys, and the like can be preferably used.

  The magnetoresistive thin film 1, the soft magnetic thin film 2, and the thin film magnet 3 are formed in a desired fine pattern by a known thin film forming technique such as vacuum deposition and sputtering, and a known fine processing technique such as photolithography and etching. Can do.

  In the case of this example, after the thin film magnet 3 is formed on the substrate 4 and processed into a strip shape, the soft magnetism is applied directly or via the electrical insulating film 5 to the region of the thin film magnet 3 and the substrate 4 outside thereof. After forming the thin film 2, the soft magnetic thin film 2 is processed into a predetermined shape, and the magnetoresistive thin film 1 is formed in the gap between the pair of soft magnetic thin films 2. Thus, the pattern shown in FIG. A thin film magnetic field sensor 10 is obtained.

  Further, the thin film magnet 3 and the soft magnetic thin film 2 can be provided with an arbitrary uniaxial anisotropic magnetic field and coercive force by heat treatment in a magnetic field in a predetermined process.

  Next, the operation of the thin film magnetic field sensor 10 configured as described above will be described including the operating principle.

  As described above, the magnetoresistive thin film 1 exhibits a high electrical resistance change of several tens of percent or more depending on the external magnetic field due to the giant magnetoresistive effect or the tunnel magnetoresistive effect. Further, the pair of soft magnetic thin films 2 provided on both sides of the magnetoresistive thin film 1 has a high magnetic permeability of about several thousand and is strong against the magnetoresistive thin film 1 because it converges many lines of magnetic force. A magnetic field is applied. Therefore, the combination of the magnetoresistive thin film 1 and the soft magnetic thin film 2 can provide a larger magnetoresistance change with respect to a small external magnetic field change.

  On the other hand, the thin film magnet 3 has an ability to generate a large magnetic field outside, and applies a magnetic bias to both sides of the magnetoresistive thin film 1. Originally, the magnetoresistive thin film 1 has an even function magnetic characteristic with respect to an external magnetic field, and the direction of the magnetic field cannot be specified. However, when a magnetic bias is applied, the magnetoresistive film 1 is implicit in the vicinity of the zero magnetic field. Therefore, the direction of the magnetic field can be specified. The magnetic bias can be arbitrarily adjusted according to the material composition, size, and particularly thickness of the thin film magnet.

  FIG. 3 is a diagram showing the external magnetic field dependence of the electrical resistance of the thin film magnetic field sensor. As shown by the dotted line in the figure, the thin film magnetic sensor without the thin film magnet shows an even function magnetic characteristic with respect to the external magnetic field, but when a magnetic bias is given by the thin film magnet, As indicated by the solid line, the characteristic is converted to an implicit characteristic in the vicinity of the zero magnetic field. For example, a magnetic field bias of about several Oe or more is applied to the magnetoresistive thin film by an SmCo-based thin film magnet having a thickness of 1 μm.

  By the way, since the magnetic field generated from the thin film magnet 3 also affects a measurement object outside the thin film magnetic field sensor, the magnetic field leaking to the outside must be minimized. Conventionally, this point has not been taken into account, and the thin film magnetic field sensors of Patent Documents 1 and 2 generate a leakage magnetic field of about 1 Oe, which sometimes makes it difficult to measure a minute magnetic field.

  Therefore, in this embodiment, the soft magnetic thin film 2 is provided so as to cover at least a portion including the magnetic pole of the thin film magnet 3. That is, the soft magnetic thin film 2 is provided so as to cover the upper surface, side surfaces, and end surfaces of the thin film magnet 3 including at least the magnetic poles. Specifically, most of the upper surface, most of the side surfaces, and all of the end surfaces of the thin film magnet 3 are covered with the soft magnetic thin film 2. Since the leakage magnetic field from the thin film magnet 3 is emitted from the magnetic pole of the thin film magnet 3, the leakage magnetic field leaking to the outside from the thin film magnet 3 can be made extremely small by covering at least that portion with the soft magnetic thin film 2. .

  In order to make the leakage magnetic field smaller, the soft magnetic thin film 2 preferably has a low magnetic resistance. From the viewpoint of obtaining such a low magnetic resistance and the manufacturing viewpoint, the thickness of the soft magnetic thin film 2 is reduced to a thin film magnet. It is desirable that the thickness be 3 or more. Further, in order to sufficiently reduce the magnetic resistance of the soft magnetic thin film 2 itself, the relative permeability is preferably 500 or more.

FIG. 4 is an enlarged view of a part of the thin film magnetic field sensor of FIG. 1B. As described above, in order to reduce the leakage magnetic field, the thickness t _sm of the soft magnetic thin film 2 is thin. The thickness of the magnet 3 is preferably equal to or greater than _hm , and the width of the area where the soft magnetic thin film 2 is in contact with the substrate 4 outside the magnetic pole of the thin film magnet 3, that is, protrudes from the magnetic pole end of the thin film magnet 3 of the soft magnetic thin film 2. The width W _{sm of} the region is preferably 10 times or less the thickness t _sm of the soft magnetic thin film 2. If W _sm exceeds 10 times t _sm , the magnetic field toward the magnetoresistive thin film 1 via the soft magnetic thin film 2 becomes small.

FIG. 5 is an enlarged view of a part of the thin film magnetic field sensor in which the electrical insulating film 5 is provided between the soft magnetic thin film 2 and the thin film magnet 3 of FIG. It is preferable that the thickness t _sm of the thin film magnet 3 is equal to or greater than the thickness t _hm of the thin film magnet 3, and the width W _sm-s of the soft magnetic thin film 2 protruding from the magnetic pole end of the thin film magnet 3 is the thickness of the soft magnetic thin film 2. It is desirable that it is 10 times or less of t _sm .

  As shown in FIGS. 4 and 5, the soft magnetic thin film 2 is likely to be thin in the vicinity of the edge of the thin film magnet 3 in manufacturing, which may increase the magnetic resistance. In order to suppress this, when the soft magnetic thin film 2 is formed, for example, an additional film formation by oblique incident sputtering is performed on the substrate, or the thin film magnet 3 is formed on the edge portion as shown in FIG. It is effective to provide a gradient in advance. 6 shows an example in which a gradient 3a is provided at the edge portion of the thin film magnet 3 in the thin film magnetic field sensor in which the electrically insulating film 5 is provided between the soft magnetic thin film 2 and the thin film magnet 3 of FIG. It can be seen that the thickness of the soft magnetic thin film 2 in the vicinity of the edge of the thin film magnet 3 is thicker than that of the thin film magnet 3.

  FIG. 7 is a diagram showing the leakage magnetic field characteristics of the thin film magnetic field sensor of the present invention. For example, in the longitudinal direction of the strip-shaped thin film magnet of the thin film magnetic field sensor, the leakage magnetic field represented by ΔH was an extremely small value of about 0.1 Oe or less.

  Furthermore, by optimizing the shape, film forming method, material, etc., it is expected that the leakage magnetic field will be an extremely small value of 0.01 Oe or less.

  The thin film magnetic field sensor 10 itself has been described above. However, as shown in FIG. 8, a plurality of the thin film magnetic field sensors 10 as described above are collectively put on the same substrate 15 by a known thin film formation technique and fine processing technique. The array type thin film magnetic field sensor 20 may be formed. Although the thin film magnetic field sensor 10 is formed periodically in FIG. 8, it may be formed aperiodically.

  As described above, since the thin film magnetic field sensor 10 can reduce the leakage magnetic field of the thin film magnet, in the array type thin film magnetic field sensor 20, the leakage magnetic field of the thin film magnet of one thin film magnetic field sensor 10 is different from other thin films. Magnetic interference with the magnetic field sensor 10 can be effectively prevented.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical idea of the present invention. In the above embodiment, most of the upper surface, most of the side surfaces, and all of the end surface of the thin film magnet are covered with the soft magnetic thin film, so that at least the portion including the magnetic pole of the thin film magnet is covered with the soft magnetic thin film. If the magnetic pole of a thin film magnet is coat | covered, it will not restrict to it. In the above embodiment, the constituent elements of the thin film magnetic field sensor are shown in a simplified manner. However, the shape and arrangement of the magnetoresistive thin film, soft magnetic thin film, and thin film magnet can take various forms. It is permissible to add a thin film magnetic field sensor element.

DESCRIPTION OF SYMBOLS 1; Magnetoresistive thin film 2; Soft magnetic thin film 3; Thin film magnet 4; Substrate 5; Electrical insulation film 10; Thin film magnetic field sensor 15;

Claims (5)

A magnetoresistive thin film whose electrical resistance changes with respect to an external magnetic field;
A pair of soft magnetic thin films disposed without gaps on both sides of the magnetoresistive thin film; and
A thin film magnet that provides a magnetic bias to the magnetoresistive thin film;
The thin film magnet is formed on a substrate, and the soft magnetic thin film is formed on the thin film magnet and is provided so as to cover at least a portion including the magnetic pole of the thin film magnet. Thin film magnetic field sensor.   The thin film magnetic field according to claim 1, wherein at least one of the soft magnetic thin film and the thin film magnet is made of an insulating material, and the soft magnetic thin film is provided so as to be in direct contact with the thin film magnet. Sensor.   The soft magnetic thin film and the thin film magnet are both made of a conductive material, and an electrically insulating film is interposed between the soft magnetic thin film and the thin film magnet. Thin film magnetic field sensor.   The thickness of the soft magnetic thin film is not less than the thickness of the thin film magnet, and the width of the region of the soft magnetic thin film protruding from the magnetic pole end of the thin film magnet is not more than 10 times the thickness of the soft magnetic thin film. The thin film magnetic field sensor according to any one of claims 1 to 3, wherein:   An array type thin film magnetic field sensor comprising a plurality of thin film magnetic field sensors according to any one of claims 1 to 4 arranged periodically or aperiodically on a substrate.

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