JP4812064B2 - Magnetic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor for detecting magnetism with high sensitivity and high accuracy, and more particularly to a magnetic impedance sensor utilizing impedance change.
[0002]
[Prior art]
In this type of magnetic sensor, the skin depth of the skin effect that occurs when a high frequency voltage of several MHz or more is applied to a magnetic material is proportional to the inverse of the square of the magnetic permeability, and the magnetic permeability of this magnetic material is Since it fluctuates greatly depending on the magnetic field, it utilizes the property that the impedance of the magnetic material fluctuates with an external magnetic field.
[0003]
Since the impedance fluctuation due to the external magnetic field of the magnetic material having high permeability is detected by a high frequency drive current of 1 MHz or more, the magnetic sensor using the above effect is also called a magnetic impedance sensor.
[0004]
By the way, an attempt of application as a magnetic sensor using impedance variation of a magnetic material is disclosed in Japanese Patent Laid-Open No. 59-2204.
[0005]
Furthermore, in 1989, at the 13th Japan Society of Applied Magnetics, Yoshikazu Kamo and Hiroshi Shimada disclosed changes in the high-frequency electrical resistance due to an external magnetic field when a magnetic material was formed into a thin film and a wire. Yes.
[0006]
Thereafter, Toshio Mohri et al. At the Institute of Electrical Engineers of Japan in 1992 disclosed a wire-shaped element having an impedance change rate 10 times that of a conventional MR element.
[0007]
Development in the form of a thin film is also underway, and Japanese Patent Application Laid-Open No. 8-75835 discloses that a fixed magnetic bias is applied by a magnetic film to linearly detect impedance fluctuations due to fluctuations in the detected magnetic field.
[0008]
In Japanese Patent Application Laid-Open No. 10-270774, the present applicant proposes a configuration in which a bridge circuit incorporating two sides of a magnetic detection core is incorporated on a magnetic impedance sensor element substrate, and the impedances of the resistance side and the magnetic detection core are substantially equal. did. By adopting such a configuration, it was possible to detect the impedance fluctuation of the magnetic detection core as a voltage fluctuation, and to provide the functions of improving the magnetic detection sensitivity and reducing the offset.
[0009]
Furthermore, in Japanese Patent Application Laid-Open No. 2000-206217, a magnetic bias means using a spiral coil, a thin film coil, and a magnetic film was proposed by reducing the size by making the resistance side nonmagnetic.
[0010]
Also, an element formed by forming a high-permeability magnetic film on a non-magnetic substrate and giving magnetic anisotropy so that a straight line is folded back several times in the middle to be perpendicular to the longitudinal direction. Is disclosed in JP-A-9-127218. In this way, by turning back multiple times, the entire element can be shortened and downsized even if the total extension of the magnetic film is lengthened. In addition, the impedance becomes high and the device is easy to use.
[0011]
[Problems to be solved by the invention]
However, these conventional devices have a problem that an extra processing circuit for detecting a magnetic field is required because the linear range is narrow and the low sensitivity region is wide.
[0012]
An object of the present invention is to solve the above problems and provide a magnetic sensor having a wide linear range and a wide high sensitivity region.
[0013]
[Means for Solving the Problems]
In order to solve the above-described problems, according to the present invention, the skin depth of the skin effect that occurs when a high frequency voltage is applied to a magnetic material changes with respect to an external magnetic field, whereby the impedance of the magnetic material varies. In the magnetic sensor using the effect, the magnetic sensor includes a magnetic core in which a plurality of magnetic films having different lengths and widths are connected in series with a zigzag folded structure, and the impedance values of the plurality of magnetic films are equal to each other. A magnetic sensor is obtained. By making the impedance values of the respective magnetic films substantially equal, the effect of adding the magnetic characteristics is increased.
[0014]
In addition, according to the present invention, in the above magnetic sensor, a magnetic sensor is obtained in which the width of each of the plurality of magnetic films is different by 30% or more.
[0016]
Moreover, according to the present invention, in the above magnetic sensor, a magnetic sensor having a length ratio to the width of the magnetic core in the range of 600 or less and 10 or more can be obtained. When the ratio of the length to the width of the magnetic core is smaller than this, the sensitivity is lowered, and when the ratio is larger, the influence of the demagnetizing field is increased, and the magnetic domain formation becomes difficult.
[0017]
In the present invention, the length of the magnetic core is preferably within a few millimeters in order to reduce the size of the magnetic sensor.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0019]
(Embodiment 1)
The magnetic sensor of the first embodiment using the MI (magnetic impedance) effect was manufactured as follows. First, the dielectric substrate is washed, masked with a photoresist, and a magnetic film is sputtered. Next, patterning is performed by lift-off to form the magnetic core 1 made of an amorphous magnetic thin film having the shape shown in FIG. Next, heat treatment is performed in a vacuum. By this heat treatment, an easy axis of magnetization is formed in the lateral direction of the magnetic film, and the sensitivity as a magnetic sensor is improved. Thereafter, the magnetic sensor of the first embodiment is obtained by similarly forming the electrodes by lift-off.
[0020]
The characteristics of the magnetic core produced by the above method will be described with reference to FIGS. FIG. 2 shows the magnetic characteristics when the width of the magnetic core is changed by 30%. When changing the width of the magnetic core, if the width is narrow, a characteristic having a low bias point (external magnetic field (Oe) when the amount of change in impedance is maximum) is obtained. As the width becomes wider, the bias point becomes the higher magnetic field side. When the width of the magnetic core is narrow, as shown in FIG. 3, the ratio of the return magnetic domain is larger than that of the wide element (FIG. 4). When an external magnetic field is generated in the longitudinal direction of the element, which is the direction of magnetic detection, since there are few regions where magnetization rotation occurs, it is considered that magnetization rotation occurs easily and the magnetization directions are aligned in a low magnetic field. Further, even if the width of the magnetic core is changed by less than 30%, the effect is small. FIG. 5 shows the magnetic characteristics when the length of the magnetic core is changed. When the length of the magnetic core changes, if the width is the same, the longer the magnetic core, the higher the impedance, and the shorter, the lower the impedance. The bias point appears in a slightly higher magnetic field when the element length is shorter.
[0021]
Next, the characteristics of the magnetic core in the magnetic sensor of the present invention shown in FIG. 1 when magnetic films having different widths are connected in series in a spelling shape will be described. By magnetically folding the magnetic cores having different widths and connecting them in series, the magnetic characteristics obtained by adding the characteristics of the single magnetic cores described above can be obtained. FIG. 6 shows magnetic characteristics obtained by adding the respective characteristics. When the width is narrow, the length is shortened, and when the width is wide, the length of the core is lengthened, so that the impedance of each magnetic core can be made substantially equal. Since the greater the impedance, the greater the contribution to the magnetic properties, it is preferable that all the magnetic cores have the same impedance.
[0022]
FIG. 7 shows the magnetic characteristics of a conventional magnetic core having a zigzag structure composed of magnetic films having the same width. There are several Oe insensitive areas and the linear range tends to be narrow. When the impedance characteristics are designed by changing the length and width of the magnetic core, as shown in FIG. 6, the linear range is widened and an insensitive region can be eliminated. In this way, the magnetic characteristics can be controlled in the element design.
[0023]
(Embodiment 2)
The magnetic sensor of Embodiment 2 was produced as follows. First, the dielectric substrate is cleaned and a magnetic film is sputtered. Next, masking with a photoresist and patterning with an ion milling apparatus and other types of wet etching form the magnetic core 1 made of an amorphous magnetic thin film having the shape shown in FIG. Next, heat treatment is performed in a vacuum. By this heat treatment, an easy axis of magnetization is formed in the lateral direction of the magnetic film, and the sensitivity as a magnetic sensor is improved. Thereafter, the non-magnetic conductor film is sputtered by masking with a photoresist. Electrodes are formed by patterning by lift-off to obtain a magnetic sensor. As in the first embodiment, this magnetic sensor has a wide linear range and can eliminate an insensitive region.
[0024]
(Embodiment 3)
The magnetic sensor according to the third embodiment was manufactured as follows. First, the dielectric substrate is cleaned, masked with a photoresist, and a magnetic film is formed by electroless plating. Next, patterning is performed by lift-off to form the magnetic core 1 made of an amorphous magnetic thin film having the shape shown in FIG. Next, heat treatment is performed in a vacuum. By this heat treatment, an easy axis of magnetization is formed in the transverse direction of the magnetic film, and the sensitivity as a magnetic sensor is improved. Thereafter, the non-magnetic conductor film is sputtered by masking with a photoresist. Electrodes are formed by patterning by lift-off to obtain a magnetic sensor. As in the first embodiment, this magnetic sensor has a wide linear range and can eliminate an insensitive region.
[0025]
【The invention's effect】
As described above, according to the present invention, a magnetic sensor having a wide linear range and a wide high sensitivity region can be provided.
[Brief description of the drawings]
FIG. 1 is a plan view showing the shape of a magnetic core in a magnetic sensor of the present invention.
FIG. 2 is a diagram showing impedance change and magnetic sensitivity with respect to an external magnetic field when the width of a magnetic core is changed. FIG. 2A is a diagram showing a change in impedance. FIG. 2B shows the magnetic sensitivity.
FIG. 3 is a diagram showing a magnetic domain structure of a narrow element and how a magnetic domain changes when an external magnetic field is received. FIG. 3A shows a magnetic domain structure. FIG. 3B is a diagram showing a state of change of magnetic domains.
FIG. 4 is a diagram showing a magnetic domain structure of a wide element and how the magnetic domain changes when receiving an external magnetic field. FIG. 4A shows a magnetic domain structure. FIG. 4B is a diagram showing a change in the magnetic domain.
FIG. 5 is a diagram showing changes in impedance and magnetic sensitivity with respect to an external magnetic field when the length of a magnetic core is changed. FIG. 5A is a diagram showing a change in impedance. FIG. 5B shows magnetic sensitivity.
FIG. 6 is a diagram showing an impedance change and magnetic sensitivity with respect to an external magnetic field in the magnetic sensor of the present invention having a spelling element in which magnetic cores having different shapes are connected in series. FIG. 6A shows a change in impedance. FIG. 6B shows magnetic sensitivity.
FIG. 7 is a diagram showing impedance change and magnetic sensitivity with respect to an external magnetic field in a conventional magnetic sensor having spelled elements having equal magnetic core widths. FIG. 7A shows a change in impedance. FIG. 7B shows the magnetic sensitivity.
[Explanation of symbols]
1 Magnetic core

Claims (3)

In the magnetic sensor using the effect that the impedance of the magnetic material varies due to the change in the skin depth of the skin effect caused by the application of high-frequency voltage to the magnetic material with respect to the external magnetic field, A magnetic sensor comprising a magnetic core in which a plurality of magnetic films having different widths are connected in series, and the impedance values of the plurality of magnetic films are equal . 2. The magnetic sensor according to claim 1, wherein the width of each of the plurality of magnetic films differs by 30% or more. 3. The magnetic sensor according to claim 1 , wherein a ratio of a length to a width of the magnetic core is in a range of 600 or less and 10 or more.

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