JP4301446B2 - Magnetic sensor - Google Patents

Description

  The present invention relates to a magnetic sensor for detecting a weak magnetic field used in the fields of automobiles, home appliances, communication equipment, ships, aircraft, medical equipment, and the like, and more particularly to the structure of a magnetic impedance sensor.

  The magnetic impedance sensor is such that the skin depth of the skin effect produced when a high frequency current of several MHz or more is applied to a magnetic material is proportional to the reciprocal of the square of the magnetic permeability, and the magnetic permeability of the magnetic material depends on an external magnetic field. Due to the large fluctuation, the impedance of the magnetic substance is fluctuated by an external magnetic field, and this is a magnetic sensor using this property.

  In the patent document 1, the applicant of the present application provided a configuration in which a bridge circuit in which two sides of a magnetic detection core are incorporated on a substrate of a magnetic impedance sensor element is incorporated, and the impedance of the resistance side and the magnetic detection core are made substantially equal. By doing so, we succeeded in detecting the impedance fluctuation of the magnetic detection core as a voltage fluctuation and improving the magnetic detection sensitivity and providing the offset reduction function.

  Further, Patent Document 2 provides a magnetic bias means using a spiral coil, a thin film coil, and a magnetic film, with a resistance side made nonmagnetic and miniaturized. Patented is an element that is constructed by forming a high-permeability magnetic film on a non-magnetic substrate and has magnetic anisotropy so that the straight line is folded back several times in the middle to be perpendicular to the longitudinal direction. Provided in document 3. In this way, the entire element can be shortened and miniaturized even if the total extension of the magnetic film is lengthened by turning back multiple times. Moreover, it becomes a high impedance and easy-to-use element. Patent Document 4 provides a multilayer structure of a high magnetic permeability magnetic film.

  In this method of manufacturing a magneto-impedance sensor, a photoresist is used for a dielectric substrate, exposure is performed to form a resist mask having an element shape, and a magnetic film is formed by sputtering. Thereafter, magnetic film patterning is performed by a lift-off method to form a plurality of high-permeability magnetic thin films having an element shape. Further, resist masking of a conductor film connecting a plurality of magnetic films in series is produced in the same process as described above, and the conductor film is patterned.

  Further, after patterning, a general manufacturing method is performed in which heat treatment in a magnetic field is performed in vacuum, anisotropy at the time of sputtering is removed, and uniaxial anisotropy is imparted in the width direction of the patterned magnetic film.

JP-A-10-270774 JP 2000-206217 A JP 09-127218 A JP 2002-027182 A

  Like conventional elements, it was possible to some extent to arrange impedance elements with the same width in parallel and control the sensitivity by changing the width at the same time, and to control the peak point of impedance with respect to the applied magnetic field. There is a problem that the controllable range is coarse and the sensitivity decreases when the linear range is widened.

  Further, in the case of the conventional single layer film, there is a problem that discontinuous domain wall movement is likely to occur due to defects and impurities inside the magnetic body during domain wall movement, and there is a problem that linearity is deteriorated. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic sensor with good linearity in which the linear range is expanded and the impedance change is smooth due to the magnetic film laminated structure.

  According to the present invention, in a magnetic sensor using an impedance element made of a magnetic material whose impedance when a high-frequency current is applied as a carrier varies with an external magnetic field, the impedance element is a plate-like magnetic thin film, A plurality of impedance elements having different lengths and widths are arranged in parallel to obtain a magnetic sensor connected in series.

  Further, according to the present invention, a magnetic sensor can be obtained in which the width of one impedance element is 5 to 50 μm and the maximum difference in the width of the impedance elements between a plurality of impedance elements is 5 μm or more.

  In addition, according to the present invention, it is possible to obtain a magnetic sensor in which the length of one impedance element is 0.5 mm to 5 mm and the maximum difference between the lengths of the impedance elements is 10% or more.

  Further, according to the present invention, a magnetic sensor is obtained in which the impedance element is a plate-like magnetic thin film having a multilayer structure composed of a magnetic film and a nonmagnetic film.

  According to the present invention, by changing the width and length of a plurality of impedance elements in a magnetic sensor, the linear range is expanded while varying the peak point of impedance change with respect to an external magnetic field, and the impedance is improved by the magnetic film laminated structure. A magnetic sensor with smooth linearity and good linearity can be provided.

  The magnetic sensor according to the embodiment of the present invention will be described below.

(Embodiment 1)
FIG. 1 is an explanatory diagram of a patterning shape of a high permeability magnetic film. Moreover, FIG. 2 is explanatory drawing of a high magnetic permeability magnetic film and conductor film pattern shape.

As shown in FIG. 1, five magnetic thin film impedance elements 11, 12, 13, 14, and 15 having a thickness of 2 μm and a length of 1 mm are arranged in parallel. Further, as shown in FIG. 2, the magnetic thin film impedance elements 11 to 15 are connected in series with the conductor films 62, 63, 64 and 65 having a thickness of 0.6 μm. Conductive films 61 and 66 are connected to both ends thereof and connected to the electrode pads 100 and 200. A high-frequency probe is connected between the electrode pads 100 and 200, a high-frequency current of 10 MHz to 60 MHz is applied by a network analyzer, and an external magnetic field of -20 to 20 × 10 ³ / 4πA / m is applied in the longitudinal direction of the element. And observe the change in impedance.

  FIG. 3 is an explanatory diagram of an impedance change with respect to an external magnetic field when the element width is changed. Here, the element width is 40 μm, the inside is 30 μm, and the narrow is 20 μm. As shown in FIG. 3, when the width of the magnetic thin film impedance elements 11 to 15 is reduced to 20 μm, the peak point of the impedance is low with respect to the applied magnetic field, and the peak point is increased by increasing the width to 40 μm. Is obtained.

  When the width of the magnetic thin film impedance elements 11 to 15 is narrowed, the demagnetizing field against the external magnetic field in the width direction becomes stronger, and the magnetic field when uniaxial anisotropy is imparted by the heat treatment in the magnetic field is the same as that of the wide magnetic thin film impedance element. The magnetic domain cannot be provided completely in the width direction, and the magnetic domain is provided obliquely. A magnetic film having magnetic domains given obliquely has a weak uniaxial anisotropy and a low impedance peak point.

  Based on this principle, characteristics when impedance elements having different widths are arranged will be described. The characteristic indicated by the broken line in FIG. 4 is a diagram showing the impedance characteristic with respect to the application of an external magnetic field in the case where five magnetic thin film impedance elements 11 to 15 having a length of 1 mm and a width of 40 μm are arranged in parallel. The characteristic indicated by the broken line in FIG. 5 is a diagram showing the impedance characteristic with respect to application of an external magnetic field when five magnetic thin film impedance elements 11 to 15 having a length of 1 mm and a width of 30 μm are arranged in parallel. FIG. 6 is an explanatory diagram of the shape when the width of a part of the elements according to the present invention is changed (the center width is 30 μm). FIG. 7 is an explanatory diagram of the shape of (center width 20 μm) when the partial element width is changed according to the present invention.

  The solid line in FIG. 4 shows two magnetic thin film impedance elements 1 and 2 having a length of 1 mm and a width of 40 μm arranged in parallel, and next to the magnetic thin film impedance elements 1, 2, 4 and 5 by 10 μm in width. Narrow magnetic thin film impedance elements 3 having a length of 1 mm and a width of 30 μm are arranged in parallel. Furthermore, it is an impedance characteristic with respect to the application of an external magnetic field when two magnetic thin film impedance elements 4 and 5 having a length of 1 mm and a width of 40 μm are arranged in parallel, and a total of five magnetic film impedance elements have a line-symmetric configuration.

  The solid line in FIG. 5 shows two magnetic thin film impedance elements 1 and 2 having a length of 1 mm and a width of 30 μm arranged in parallel, and next to the magnetic thin film impedance elements 1, 2, 4 and 5 by 10 μm in width. This is an impedance characteristic for application of an external magnetic field when two thin magnetic film impedance elements 4 and 5 having a narrow length of 1 mm and a width of 20 μm are arranged in parallel, and a total of five magnetic film impedance elements have a line-symmetric configuration.

  In the case of the width configuration of the magnetic thin film impedance elements having the same width dimension, the impedance change with respect to the externally applied magnetic field changes so as to draw an arc, which is a non-linear change. The tendency is the same even if the width of the magnetic thin-film impedance element is reduced to 30 μm.

  Next, in the case of the line-symmetric configuration shown in FIGS. 6 and 7, as shown in the characteristics of FIGS. 4 and 5, by reducing the width of the magnetic film impedance element at the center, elements having different uniaxial anisotropies are used. Since the characteristics of each element are added to each other, the nonlinear characteristics can be compensated to change linearly, the linear area can be increased, and the linearity can be improved.

(Embodiment 2)
The magnetic sensor of the second embodiment was manufactured by the same manufacturing method as that of the first embodiment. The shape of the magnetic sensor of the second embodiment is the same as the shape of the high permeability magnetic film and the conductor pattern shown in FIG. 2, and the width of the element was changed. Patterning by lift-off using a resist is characterized in that patterning can be performed relatively easily. However, the patterning width is limited to about 5 μm in manufacturing, and if the absolute value of impedance is low, the amount of change is small. Since the absolute value is also low, the device is difficult to handle.

  FIG. 8 is an explanatory diagram of a difference in impedance absolute value when the element width is changed. As shown in FIG. 8, the impedance value decreases in the order of the element width of 20 μm, 30 μm, and 40 μm. Further, by limiting the absolute value of the impedance to 50 μm, it is possible to obtain the magnetic sensor of the second embodiment that is easy to handle without causing an extreme decrease in sensitivity.

(Embodiment 3 )
The magnetic sensor according to the third embodiment using the magneto-impedance effect was manufactured as follows. In the magnetic sensor of the third embodiment, a dielectric substrate is washed, a photoresist is applied, and exposure is performed with a mask having a magnetic thin film impedance element shape, thereby producing resist masking of the impedance element having a multilayer structure.

The magnetic thin films 2c, 3c, and 4c are sputtered from 0.1 μm to 5 μm on the resist mask. After sputtering the magnetic thin films 2c, 3c and 4c, several hundred nonmagnetic intermediate layers 71, 81 and 91 such as Ti and SiO ₂ are sputtered, and after the nonmagnetic intermediate layers 71, 81 and 91, the first magnetic thin film 2c is sputtered. , 3c, 4c are sputtered on the magnetic thin films 2b, 3b, 4b having the same thickness.

  In this case, there are two layers, but a multilayer is also possible, and the total thickness is determined by the applied current frequency. Therefore, when the magnetic film is an even number stack, the magnetic thin films 2c, 3c, 4c to be stacked are A thickness equal to that of the magnetic thin films 2b, 3b, 4b is desirable. In the case of an odd-numbered laminate, the magnetic film corresponding to the central portion may be made twice as thick as the upper and lower layers.

  Patterning can be performed by performing lift-off to remove the laminated magnetic film and resist masking, and a plurality of high permeability laminated magnetic thin films having the shape of FIG. 10 are formed.

Thereafter, in the same process as described above, masking of a conductor film connecting a plurality of laminated magnetic films is produced, and the conductor film is patterned. After patterning, heat treatment in a magnetic field is performed in vacuum, the anisotropy during sputtering is removed, and uniaxial anisotropy is applied in the width direction of the patterned magnetic film to obtain the magnetic sensor of the third embodiment. be able to.

  FIG. 11 shows the characteristics of the impedance change with respect to the external magnetic field of the magnetic thin film impedance element in the single layer film produced by the method of the first embodiment. FIG. 12 shows the characteristic of impedance change with respect to the external magnetic field of the magnetic thin film impedance element produced by the laminated structure of the above method.

  An element made of a single layer has an abnormal change with a hysteresis (a bump-like impedance change) in the so-called dead zone where there is no change in impedance, and the impedance change rising part has a jagged, discontinuous characteristic. Change (Barkhausen movement) is seen.

  As shown in the schematic explanatory diagram of the magnetic domain of the conventional single layer film shown in FIG. 13, this phenomenon is presumed that the magnetic domain becomes fine because only the magnetic dipole interaction in the film surface direction works in the case of the single layer. Is done. Also in the experiment, it can be confirmed from the magnetic domain observation by the optical Kerr effect microscope that the magnetic domains are finely formed as shown in the explanatory diagram in the plane of the magnetic domain of the conventional single layer film shown in FIG.

  The end of the magnetic domain shown in FIG. 14 that is an observation photograph is rounded because of the reflux magnetic domain, which is a part where the magnetic domain desired to be applied in the width direction is obstructed and the magnetic domain is formed in the longitudinal direction.

  Accordingly, it is considered that the domain wall is moved from the width direction of the element to the longitudinal direction of the element by an external magnetic field, and discontinuous domain wall movement occurs due to defects and impurities inside the magnetic body when the magnetization is rotated.

FIG. 15 is a schematic explanatory view of magnetic domains of the magnetic laminated film according to the present invention. FIG. 16 is an explanatory view in a plane of the magnetic laminated film according to the present invention. In the element manufactured in the third embodiment, since the magnetic film has a relationship between the upper and lower layers as shown in FIG. 15, the magnetic dipole interaction acts in the direction perpendicular to the film, and the action in the film surface direction is weakened. Is estimated to increase. Also in the experiment, it can be confirmed from the magnetic domain observation by the optical Kerr effect microscope that the magnetic domain is enlarged as shown in FIG.

  FIG. 17 is an explanatory diagram of domain wall motion of a conventional single layer film. Moreover, FIG. 18 is explanatory drawing of the domain wall movement of the magnetic laminated film by this invention. It can be presumed that the probability of catching at the time of domain wall movement and magnetization rotation is reduced by reducing the number of domain walls in the same shape element. In the case of a single layer film, as shown in FIG. 17, during the domain wall movement process, the domain wall moves while rotating a domain such as a magnetic domain in the domain wall in the direction perpendicular to the film. It is estimated to be large.

However, in the third embodiment, the energy in moving the domain wall is small because of rotation in the film surface direction as shown in FIG. Therefore, it is considered that even if a defect or impurity inside the magnetic material is caught, it does not appear as a large change due to the small energy. For this reason, the discontinuity of the straight line portion is improved and a wide linear range is obtained.

Explanatory drawing of the patterning shape of a high magnetic permeability magnetic film. Explanatory drawing of the pattern shape of a high magnetic permeability magnetic film and a conductor film. Explanatory drawing of the impedance change with respect to an external magnetic field at the time of changing element width. Explanatory drawing of the impedance change with respect to an external magnetic field at the time of arranging the several element width and changing the partial element width by this invention (30 micrometers). Explanatory drawing of the impedance change with respect to an external magnetic field at the time of arranging the several element width, and changing the partial element width by this invention (20 micrometers). Explanatory drawing of the shape when the partial element width by this invention is changed (central width 30 micrometers). Explanatory drawing of the shape when the partial element width by this invention is changed (central width 20 micrometers). Explanatory drawing of an impedance absolute value difference at the time of changing element width. Explanatory drawing of the impedance change when changing the length of the element by this invention. Explanatory drawing of the shape of a magnetic laminated film when changing the partial element width by this invention. Explanatory drawing of the impedance change by the conventional single layer film. Explanatory drawing of the impedance change by the magnetic laminated film by this invention. The schematic explanatory drawing of the magnetic domain of the conventional single layer film. Explanatory drawing in the plane of the magnetic domain of the conventional single layer film. The schematic explanatory drawing of the magnetic domain of the magnetic laminated film by this invention. Explanatory drawing in the plane of the magnetic domain of the magnetic laminated film by this invention. Explanatory drawing of the domain wall motion of the conventional single layer film. Explanatory drawing of the domain wall movement of the magnetic laminated film by this invention.

Explanation of symbols

1,2,4,5 Magnetic thin film impedance element (40μm width)
1a, 2a, 4a, 5a Magnetic thin film impedance element (30 μm width)
3 Magnetic thin film impedance element (30μm width)
3a Magnetic thin film impedance element (20μm width)
2b, 3b, 4b Magnetic thin film (upper layer)
2c, 3c, 4c Magnetic thin film (lower layer)
11, 12, 13, 14, 15 Magnetic thin film impedance elements 61, 66 Conductor film (edge-pad)
62, 63, 64, 65 Conductor film (series connection)
71, 81, 91 Nonmagnetic intermediate layer 100, 200 Electrode pad

Claims (3)

In a magnetic sensor using an impedance element made of a magnetic material whose impedance when a high frequency current is applied as a carrier varies with an external magnetic field, the impedance element is a plate-shaped magnetic thin film, and the length and width of the magnetic thin film A plurality of impedance elements different from each other are arranged in parallel and connected in series ,
A magnetic sensor characterized in that the impedance elements are line-symmetrically arranged, and the width of the impedance element in the center is narrower by 5 μm or more than the width of other impedance elements . The magnetic sensor according to claim 1, wherein the impedance element has a length in a range of 0.5 mm to 5 mm. 3. The magnetic sensor according to claim 1, wherein the impedance element is a plate-like magnetic thin film having a multilayer structure including a magnetic film and a nonmagnetic film.

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