JP3922441B2 - Magneto-impedance element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor that performs magnetic detection, and more particularly to a high-sensitivity magneto-impedance element that uses the magneto-impedance effect.
[0002]
[Prior art]
In recent years, high performance, downsizing, thinning, and low cost of information equipment and measurement / control equipment have rapidly progressed. With these rapid developments, magnetic sensors and current sensors used in them have become small and low cost. Demand for high sensitivity is increasing.
[0003]
Known magnetic sensors include Hall elements, magnetoresistive effect elements (MR elements), giant magnetoresistive effect elements (GMR elements), and fluxgate sensors. Current sensors include current transformers. Etc. are known. For example, the performance of magnetic heads used in hard disk drives for computer external storage devices is increasing from conventional bulk-type induction magnetic heads to MR heads, and currently uses the giant magnetoresistive effect (GMR). There are many active studies. Further, in a rotary encoder which is a rotation sensor of a motor, the magnetic flux leaking to the outside becomes weak with the miniaturization of the magnet ring, and a highly sensitive magnetic sensor that replaces the current MR element is required. Development of electronic breakers and thermal relays that use current sensors instead of conventional mechanical types is also progressing with breakers, etc., but it is difficult to reduce the size with conventional current transformers, and sensitivity and detection There is a need to increase the sensitivity and range of magnetic sensors in terms of range.
[0004]
In order to satisfy these requirements, a magneto-impedance sensor using the magneto-impedance effect (also referred to as MI effect) of an amorphous wire has been proposed (Japanese Patent Laid-Open No. 6-281712, Journal of Japan Society of Applied Magnetics, vol. 18, p493, 1994 etc.). The magnetic impedance effect means that when an external magnetic field changes in a state where a high frequency current is applied to a magnetic material, the magnetic permeability of the magnetic material changes, and accordingly, the impedance of the magnetic material is several tens to several times that when the magnetic field is zero. It is a phenomenon that changes by 100%. By measuring the voltage across the magnetic body due to this phenomenon, a minute external magnetic field change of about several Gauss is detected.
[0005]
The above-mentioned magneto-impedance effect is similarly observed not only with amorphous wires, but also with magnetic ribbons and magnetic thin films. Especially, thin films can be made small and thin, and are excellent in reliability and mass productivity. Structures have been proposed (see IEEJ Magnetics Study Group Material MAG-94-75, 1994, IEEJ Transactions A, 115, 10, p949, 1995, JP-A-8-75835, etc.).
[0006]
A magneto-impedance element using a thin film is provided with magnetic anisotropy, and is composed of a magnetic thin film pattern obtained by processing a high permeability soft magnetic film in which uniaxial anisotropy is induced into a strip shape. The magnetic anisotropy is performed while applying a magnetic field when forming the magnetic film, and is further induced by heat treatment at about 150 to 400 ° C. in a rotating magnetic field or a static magnetic field. The direction of the easy axis of magnetization is generally the short axis (line width) direction of the strip structure. The magneto-impedance element has a characteristic that the impedance is changed by the magnetic field of the longitudinal component. In this case, when the easy axis of magnetization is a line width, the magnetoimpedance characteristic shows a characteristic that takes a peak of impedance depending on whether the magnetic field is positive or negative and is symmetric when the magnetic field is positive or negative. Moreover, the change rate shows a very large change of several tens to several hundreds%.
[0007]
Even when magnetic anisotropy is imparted in the length direction, magnetic impedance characteristics are exhibited. The characteristic at that time has the highest impedance when the magnetic field is zero, and decreases as the absolute value of the magnetic field increases. In this case as well, the impedance is symmetric with respect to the positive and negative magnetic fields. The direction of the detected magnetic field in this case is also a component in the length direction of the magnetic thin film pattern.
[0008]
The change in impedance in these magnetic impedance characteristics is caused by a change in magnetic permeability while a high frequency current is applied to the magnetic thin film pattern. When the impedance is separated into a resistance component and an inductance component, both change due to a change in magnetic permeability, but a resistance component having a large absolute value is dominant in the change. The resistance change due to the permeability change is basically caused by the skin effect that occurs when a high-frequency current flows in the magnetic material. To increase the skin effect, the frequency of the high-frequency current is increased or the magnetic thin film is increased. A method of increasing the thickness of the film becomes effective.
[0009]
As described above, the magneto-impedance element is characterized in that the impedance greatly changes with respect to the magnetic field. However, by applying a bias magnetic field to the element and operating it at a point where the impedance changes greatly with respect to the magnetic field, The sensor responds with high sensitivity to the magnetic field. In order to apply this bias magnetic field, it is necessary to form a coil (bias coil) around the element and generate a magnetic field by applying a current to the coil. A coil is also required when applying a negative feedback magnetic field for the purpose of improving sensitivity linearity. When an amorphous wire is used, a structure in which a coil is formed by winding a Cu wire or the like directly around the wire is used. However, a structure in which a coil is formed in a thin film on the same substrate as a magnetic impedance element formed in a thin film is also available. (See Journal of Japan Society of Applied Magnetics, vol. 21, p649, 1997, Japanese Patent Laid-Open No. 9-269084, etc.).
[0010]
[Problems to be solved by the invention]
As described above, there are two types of magneto-impedance elements, one using an amorphous wire and the other using a thin film. In terms of reproducibility (stability), reliability, and mass productivity, it is better to use a thin film. It can be said that it is advantageous. In the case of using a thin film, conventionally, a film is formed on a hard nonmagnetic substrate such as glass by sputtering, a fine pattern is formed using a photosensitive material such as a resist, and wet etching, ion beam etching, etc. It is processed into a fine pattern using dry etching.
[0011]
By the way, when a magnetic field generated from a linear conductor through which a current flows is measured using a magneto-impedance element for magnetic detection produced by a hard substrate, the intensity distribution of the magnetic field is concentric around the linear conductor. It is not a plane. Therefore, since the magneto-impedance element conventionally produced on the glass substrate has a finite size, the magnetic field intensity received by the magneto-impedance element varies depending on the location of the magnetic thin film pattern. In particular, when measuring a very small current, it is necessary to make it as close as possible to the object to be measured. However, the magnetic field distribution received by the magneto-impedance element becomes larger as the object gets closer, causing a problem that high-precision magnetic field measurement cannot be performed.
[0012]
Accordingly, an object of the present invention is to solve the problem of magnetic field distribution received by a magneto-impedance element and provide a highly sensitive and highly accurate magnetic detector.
[0013]
[Means for Solving the Problems]
In order to solve such a problem, in the invention of claim 1, a magnetic film is formed by an external magnetic field by applying a high frequency current to a magnetic thin film formed by forming a high permeability magnetic film on a substrate and processing it into a strip shape. A magneto-impedance element using a magneto-impedance effect in which body impedance changes, and using a flexible substrate as a substrate for supporting a strip-shaped magnetic thin film composed of one or more strip-shaped magnetic films In
A flexible substrate that supports a magnetic thin film formed in a strip shape is formed by spirally or spirally winding a magnetic field generation source made of a linear conductor .
[0014]
In the invention of claim 1, one or more magnetic field generation sources comprising the linear conductor can be provided (invention of claim 2).
[0015]
In the first or second aspect of the present invention, an organic material different from the substrate can be applied linearly on the same surface as the magnetic thin film formed into a strip shape on the substrate or the reverse surface thereof (invoice). Item 3 ).
[0016]
In the invention of claim 3 above, when the organic material is applied in a straight line, it is made to be parallel to the length direction of the strip-shaped magnetic thin film, or crossed at right angles or at an angle, Or these can be combined (invention of Claim 4 ).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing the principle of the present invention.
[0018]
As shown in the figure, in a magneto-impedance element composed of an elongated strip-shaped magnetic thin film 2 on a flexible substrate (thickness: about 50 μm) 1 of an aramid film, it is passed through a linear conductor 3 so that both ends thereof are in contact with each other. And arranged so as to coincide with the circular magnetic field 5 generated by the measured current 4. At this time, since both ends of the flexible substrate 1 are in contact, the strip-shaped magnetic thin film 2 is formed in advance slightly shorter than the length of the flexible substrate 1 to the extent that they do not contact each other, or the strip-shaped magnetic thin film 2 is formed in the flexible substrate 1. When the length is the same, the strip-shaped magnetic thin films 2 are arranged so as not to contact each other. FIG. 1 is an example of the former. Reference numeral 6 denotes an electrode.
[0019]
The elongated strip-shaped magnetic thin film 2 is formed by forming an amorphous magnetic film on the flexible substrate 1 using, for example, a magnetron sputtering method, forming a fine pattern using a photosensitive material such as a resist, and ion beam etching after magnetic field heat treatment. Is produced. Although an aramid film is used as the flexible substrate, a plastic plate used in other organic films, non-magnetic metal ribbons, cash cards and the like may be used.
[0020]
By doing so, it becomes a very thin magnetic detection element, and since the circuit 5 circulates around the magnetic field 5, it is not affected by the place and has high sensitivity and high accuracy. Although the elongated strip-shaped magnetic thin film 2 is one here, it may be two or more. In addition, the bias coil and the negative feedback coil can be formed as a thin film on the same flexible substrate 1 as the strip-shaped magnetic thin film 2.
[0021]
FIG. 2 is a block diagram showing an embodiment of the present invention.
[0022]
In FIG. 1, a magnetic detection element configured in a ring shape by contacting both ends of the flexible substrate 1 is used. However, here, a magnetic material composed of an elongated strip-shaped magnetic thin film 2 around a linear conductor 3 as a magnetic field generation source. The impedance element is formed by spiraling as in (a) or spiraling as in (b). When winding in a spiral shape as shown in (b), the flexible substrate 1 is shown in FIG. 2 (c), for example, so that the inner electrode 6 is partially exposed (or can be electrically connected from the outside). It is good to form longer than this width. The elongated strip-shaped magnetic thin film 2 can also be two or more here.
[0023]
FIG. 3 is a block diagram showing another embodiment of the present invention.
As in FIG. 1, for example, three linear conductors 3 are arranged in a magnetic impedance element configured in a ring shape by contacting both ends of the flexible substrate 1. When, for example, a three-phase alternating current is passed through the three conductors 3, the sum of the currents to be measured 4 becomes zero. In other words, no magnetic field is received by the ring-shaped magneto-impedance element. From this, a magnetic field is generated when an abnormality occurs in one of the three conductors, and this is detected by the magneto-impedance element. Note that this also applies to a structure in which a magneto-impedance element composed of an elongated strip-shaped magnetic thin film 2 as shown in FIG. 2 is spirally wound as shown in (a) or spiral as shown in (b). Can do. Further, the number of conductors 3 may be one or any number of two or more.
[0024]
4A and 4B are configuration diagrams showing still another embodiment of the present invention, in which FIG. 4A is a plan view and FIG. 4B is a cross-sectional view.
[0025]
For example, an aramid film flexible substrate 1 is used, and an organic film 7 such as polyimide is linearly applied to the back surface opposite to the surface having the strip-shaped magnetic thin film 2 made of an amorphous magnetic film, for example, and cured. It has been made. After production of the strip-shaped magnetic thin film 2, an organic film 7 such as polyimide was applied to the back surface of the flexible substrate 1 and cured. When the film thickness of the strip-shaped magnetic thin film 2 and the organic material film 7 such as polyimide are both 4 μm, the film becomes flat. By adjusting the film thickness of the organic film 7 such as polyimide, the flatness or warpage of the element can be adjusted. Fine adjustments can be made. The organic film 7 such as polyimide may be formed on the same surface as the surface where the strip-shaped magnetic thin film 2 is present. In addition, the strip-shaped magnetic thin film 2 is one here, but may be two or more.
[0026]
FIG. 5 and FIG. 6 show modifications of FIG. 5A and 6A are plan views, FIG. 5B is a sectional view in the longitudinal direction, and FIG. 5C is a sectional view in a direction orthogonal to the longitudinal direction.
[0027]
Using an aramid film flexible substrate 1, for example, an organic film 7 such as polyimide is linearly applied to the back surface (which may be the same surface) opposite to the surface having the strip-shaped magnetic thin film 2 made of an amorphous magnetic film, In the curing, FIG. 5 patterns the organic film 7 such as polyimide parallel to the strip-shaped magnetic thin film 2, whereas FIG. 6 patterns the organic film 7 such as polyimide perpendicular to the strip-shaped magnetic thin film 2. This is an example of patterning.
[0028]
In either case, the number of the strip-shaped magnetic thin films 2 is one, but two or more may be used. The pattern of the organic film 7 may or may not be evenly spaced depending on how the sample is wound or bent. By doing so, the degree of warping of the flexible substrate 1 can be finely adjusted.
[0029]
【The invention's effect】
According to the present invention, since the magneto-impedance element for magnetic detection is fabricated on the flexible substrate, the magneto-impedance element can receive a uniform magnetic field, and high-precision and high-sensitivity magnetic detection is possible. The advantage is obtained.
[0030]
In addition, since the stress of the magnetic thin film formed into a strip shape by the flexible substrate is relieved, the influence of magnetic anisotropy due to the stress is reduced, and a highly sensitive magnetic detector can be manufactured.
[0031]
Furthermore, by winding a band-shaped magneto-impedance element around the magnetic field generation source in a spiral or spiral shape, it is possible not only to receive at least one round of the circular magnetic field but to increase the sensitivity, but also to form a spiral or spiral band-shaped magneto-impedance element. It is possible to detect a change in the magnetic field using the fact that the balance of the magnetic field generation source in the element is lost.
[Brief description of the drawings]
FIG. 1 is a principle configuration diagram of the present invention.
FIG. 2 is a configuration diagram showing an embodiment of the present invention.
FIG. 3 is a block diagram showing another embodiment of the present invention.
FIG. 4 is a block diagram showing still another embodiment of the present invention.
FIG. 5 is a configuration diagram showing a first modification of FIG. 4;
6 is a configuration diagram showing a second modification of FIG. 4; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Flexible substrate, 2 ... Strip-shaped magnetic thin film, 3 ... Linear conductor, 4 ... Current to be measured, 5 ... Circulating magnetic field, 6 ... Electrode, 7 ... Organic substance film | membrane.

Claims (4)

It is an element that uses the magnetic impedance effect, in which the impedance of a magnetic material is changed by an external magnetic field by applying a high-frequency current to a magnetic thin film formed by forming a high permeability magnetic film on a substrate and processing it into a strip shape. In a magneto-impedance element using a flexible substrate as a substrate for supporting a strip-shaped magnetic thin film composed of one or more strip-shaped magnetic films,
A magneto-impedance element, wherein a flexible substrate supporting a magnetic thin film formed into a strip is wound around a magnetic field generation source made of a linear conductor in a spiral shape or a spiral shape . 2. The magneto-impedance element according to claim 1, wherein one or more magnetic field generation sources comprising the linear conductor are provided . 3. The magneto-impedance element according to claim 1, wherein an organic material different from the substrate is applied linearly on the back surface opposite to or opposite to the magnetic thin film formed into a strip shape on the substrate. . When the organic material is applied in a straight line, it is made to be parallel to the length direction of the magnetic thin film formed into the strip shape, crossed at right angles or at an angle, or a combination thereof. The magneto-impedance element according to claim 3 , wherein:

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