JPH07333304A - Magnetic field detection sensor - Google Patents

Abstract

PURPOSE:To provide a magnetic field detection sensor wherein signal output, S/N ratio, sensitivity, and signal detection accuracy are high, and parts configuration is simple. CONSTITUTION:On the surface of a detection conductor 2 with a pair of electrodes 1a and 1b at both ends, at least a magnetic body 4 is assigned directly or with a non-magnetic insulator in between. A transmission line 5 is connected to the electrodes 1a and 1b. The transmission line 5 is connected to a reflection characteristic measuring instrument, and when magnetic permeability of the magnetic body 4 is changed according to an external magnetic field, based on the changes of a reflection coefficient on the ends of electrodes 1a and 1b, an external magnetic field 7 is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field detecting sensor.

[0002]

2. Description of the Related Art Conventionally, as a magnetic field detecting sensor, an anisotropic magnetoresistive effect (MR effect; Magneto-) of a ferromagnetic material has been used.
A magnetoresistive effect type sensor (MR sensor) utilizing the resistance effect has been widely used. The structure of the MR sensor is shown in FIG. In the figure, reference numeral 10 is a magnetoresistive element, and electric conductors 12a and 12b are connected to both ends in the longitudinal direction thereof. Therefore, the current flows in the longitudinal direction I of the magnetoresistive element 10 as indicated by the arrow in the figure. The element 10 is arranged so that the external magnetic field H is perpendicular to the current direction I. The inclination of the magnetization direction M with respect to the current direction I at this time is represented by θ. This conventional M
In the R sensor, a DC bias conductor line 13 is provided in parallel with the element 10. Like the element 10, the conductor line 13 is connected at both ends with electric conductors 14a and 14b. The change in the resistance R due to the MR effect is expressed by the following equation.

[0003]

## EQU1 ## R = R ₀ + ΔR cos ² θ (1) Here, R ₀ is the resistance when the magnetization direction M is perpendicular to the current direction I, and ΔR is the magnetization direction M is parallel to the current direction I. The difference between the resistance and R _{0 in} the case of the above, θ is the angle between the magnetization direction M and the current direction I as described above. The SN ratio of the MR sensor is represented by ΔR / R ₀ (MR ratio). Representative M
NiFe, NiCo, NiCu as materials for R sensor
Examples include alloys. FIG. 9 shows the external magnetic field dependence of the resistivity of NiFe. As can be seen from FIG. 9, the MR ratio of the conventional MR sensor is as low as several% (room temperature), and ΔR itself is a small value. Therefore,
The conventional MR sensor has a problem that signal output, SN ratio, sensitivity, etc. are low.

Recently, in the Fe / Cr multilayer film, a phenomenon in which the MR ratio becomes about 50% was discovered (giant MR effect:
M. N. Baibich et al. , Phys. R
ev. Lett. , 61, 472, '88), high SN
Although it was expected as a material for high-sensitivity sensors, it is not suitable for practical use because its operating temperature is 4.2K, which is extremely low, and it requires the application of a strong magnetic field of 20 kOe. Further, since a large hysteresis appears in the dependence of the resistance on the external magnetic field, there is a drawback that the signal detection accuracy is low.

As is clear from the above equation (1), the MR
Since the effect is symmetric with respect to the magnetic field reversal, in order to detect the polarity of the external magnetic field, it is necessary to apply a DC bias magnetic field to the magnetoresistive element 10 to move the operating point to have antisymmetry. Therefore, in the conventional MR sensor, it was necessary to newly install the DC bias conductor line 13 as shown in FIG. However, this method has a drawback in that the number of constituent parts is increased and complexity is involved in part designing, part manufacturing.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The problems to be solved by the present invention are low signal output, SN ratio, sensitivity, low signal detection accuracy, and complexity of parts configuration, which were problems in the conventional magnetic field detection sensor. It is to provide a magnetic field detection sensor that solves the above problem.

[0007]

In the magnetic field detection sensor of the present invention, at least one magnetic body is disposed on the surface of a detection conductor having a pair of electrodes at both ends, directly or through a non-magnetic insulator. A transmission line is connected to the electrode, and the transmission line is connected to a reflection characteristic measuring device. When the magnetic permeability of the magnetic body changes according to an external magnetic field, the reflection coefficient at the electrode end changes. Based on this, the external magnetic field is detected.

In the above structure, it is preferable that the magnetic body has a closed magnetic circuit structure that goes around the detection conductor, and the magnetic body has a multilayer structure in which magnetic layers and nonmagnetic insulating layers are alternately laminated. It is preferable to use a structural magnetic material.
In this case, it is important that the layer thickness of the magnetic layer is thinner than the skin depth of the magnetic layer, and the layer thickness of the non-magnetic insulating layer is set to a thickness equal to or more than a thickness capable of maintaining electrical insulation between the magnetic layers.

Further, it is desirable that the magnetic body is formed in a strip shape and is set so that the long side direction thereof is parallel to the external magnetic field direction. Here, the magnetic material preferably has uniaxial magnetic anisotropy with the easy axis in the short side direction.

Further, in the above structure, it is desirable that the measurement frequency of the reflection characteristic measuring device is near the magnetic resonance frequency of the magnetic material.

[0011]

The magnetic field detection sensor of the present invention differs from the conventional magnetic field detection sensor in the parts configuration and the detection principle.

According to the magnetic field detection sensor of the present invention, a change in the magnetic permeability of the magnetic material according to a change in the external magnetic field is sensitively reflected in the change in the reflection coefficient, so that a high signal output, a high SN ratio, and a high sensitivity are obtained. . Further, since hysteresis does not appear in the external magnetic field dependency, the signal detection accuracy is high. In addition, the sensing conductor
Since it also serves as the conductor line for bias directly, the component structure is simplified.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

1 and 2 are front views of an embodiment of the magnetic field detecting sensor of the present invention, FIG. 3 (a) and FIG.
FIG. 3B is a diagram showing a cross-sectional view taken along the line AA ′ of FIGS. 1 and 2. At least one magnetic body 4 is arranged on the surface of the detection conductor 2 having a pair of electrodes 1a and 1b at both ends, either directly (FIG. 3A) or via a non-magnetic insulator 3 (FIG. 3B). A transmission line 5 is connected to the electrodes 1a and 1b, and the transmission line 5 is a reflection characteristic measuring device 6
It is connected to the. Reference numeral 7 in the figure indicates an external magnetic field.

FIG. 1 shows a case where there are a plurality of magnetic bodies 4, FIG. 2 shows a case where there is one magnetic body 4, and FIG. 3A shows a case where the magnetic bodies 4 are directly arranged on the surface of the detection conductor 2. In case of Fig. 3 (b)
Shows the case where the magnetic body 4 is disposed on the surface of the detection conductor 2 via the non-magnetic insulator 3.

The detection principle will be described. The impedance Z between the electrodes 1a and 1b is the sum of the impedance Z _{0 of} only the detection conductor 2 and the impedance Z _m derived from the magnetic body 4,

[0017]

[Expression 2] Z = Z ₀ + Z _m (2) Z _m is proportional to the product of the relative permeability μ _r of the magnetic body 4 and the frequency f as in the following equation.

[0018]

Z _m ∝ μ _r × f (3) Since the relative permeability μ _r of the magnetic body 4 changes from a finite value to zero according to the strength of the external magnetic field 7, the impedance Z _m ,
Therefore, the impedance Z also changes. With this sensor,
This change in impedance Z is measured by reflection coefficient measurement.

In order to improve the signal output, SN ratio, and sensitivity, it is effective to make the following structural improvements.

In order to efficiently reflect the change in the magnetic permeability of the magnetic body 4 in the change in the reflection coefficient, a closed magnetic circuit structure in which the magnetic body 4 makes one round around the detection conductor 2 is used in order to suppress magnetic flux leakage. It is effective. For example, in FIG. 1, FIG. 2 and FIG. 3, a closed magnetic circuit structure in which the detection conductor 2 is sandwiched by two upper and lower magnetic bodies 4 is used.

The operating frequency of this sensor is as described below.
It becomes a high frequency of several hundred MHz. At high frequencies, the effective volume of the magnetic material decreases due to the well-known skin effect, and the signal output, SN ratio, and sensitivity decrease. As a method of avoiding the skin effect, the cross-sectional structure of the magnetic body 4 is shown in FIG.
It is effective to have a multilayer structure in which the magnetic layers 41 and the non-magnetic insulating layers 42 are alternately laminated as shown in FIG. On this occasion,
The layer thickness of the magnetic layer 41 is determined by the skin depth (ski
It is effective to set the thickness of the non-magnetic insulating layer 42 to be thinner than n depth), for example, by about one digit, and to set the thickness of the non-magnetic insulating layer 42 to a thickness that can maintain electrical insulation between the magnetic layers 41 or more.

In order to improve the sensitivity to the external magnetic field 7, the shape of the magnetic body 4 is a strip shape in which the direction of the external magnetic field 7 and the long side direction of the magnetic body 4 are parallel as shown in FIGS. 1, 2 and 3. Therefore, it is effective to avoid the influence of the in-plane demagnetizing field. FIG. 5 shows the experimental results of the magnetic material shape dependence of the demagnetizing factor in the NiFe film. Thickness is 3μm, width is 5
μm, and the relationship with the length is shown. 200 length from the figure
It can be seen that the effect of the demagnetizing field can be almost ignored when the thickness is μm (0.2 mm) or more.

Only a magnetization process in the hard axis direction of uniaxial magnetic anisotropy responds to a high frequency magnetic field of several hundred MHz. Detection conductor 2
Since the direction of the high-frequency magnetic field generated from the magnetic field is the circumferential direction of the detection conductor 2, the uniaxial magnetic anisotropy with the easy axis in the short side direction of the magnetic body 4 is made to coincide with the hard axis direction of the uniaxial magnetic anisotropy. Gives direction.

Further, in order to have a polarity detecting function, a DC bias magnetic field generated from the DC bias current flowing in the detecting conductor 2 can be used. At this time, since the detection conductor 2 also serves as a DC bias conductor line, the component structure is simplified.

Specific examples are shown below. The type shown in FIGS. 2 and 3A is used, and the magnetic body 4 has the multilayer structure shown in FIG.
NiFe was used for the magnetic layer 41, and the layer thickness was 50 nm, which was sufficiently thinner than the skin depth of the order of 1 μm. SiO ₂ was used for the nonmagnetic insulating layer 42, and the layer thickness was set to 50 nm, which is a thickness capable of maintaining electrical insulation between the magnetic layers 41. The magnetic substance 4 had a total film thickness of 1.5 μm, and two detection conductors 2 were sandwiched. The width of the magnetic body 4 was set to 5 μm and the length thereof was set to 200 μm so as to avoid the influence of the demagnetizing field. The magnetic body 4 was provided with a uniaxial anisotropic magnetic field of 3 to 5 Oe with the easy axis in the short side direction. Cu was used for the detection conductor 2, and the detection conductor 2 had a width of 10 μm, a thickness of 2 μm, and a length of 10 μm. Ion beam sputtering was used for film formation, and photolithography was used for processing. The film forming conditions are the operating vacuum degree Ar.
1 × 10 ⁻⁴ Torr, acceleration voltage 1 kV, substrate temperature room temperature to
The temperature was set to 160 ° C., and Corning glass was used for the substrate.
The uniaxial anisotropic magnetic field was applied by applying a static magnetic field of several hundred Oe parallel to the substrate surface during film formation. A 50Ω coaxial cable was used for the transmission line 5, and a network analyzer was used for the reflection characteristic measuring device 6. All measurements were performed at room temperature.

In this sensor, the change in the impedance Z due to the change in the relative permeability μ _r according to the strength of the external magnetic field 7 is measured by measuring the reflection coefficient Γ. Here, for comparison with FIG. 9, the result converted into the high frequency resistance value R is shown. The following relational expression holds between the reflection coefficient Γ and the high frequency resistance value R.

[0027]

## EQU00004 ## R = Real [(1 + .GAMMA.) / (1-.GAMMA.)]. Times.50 (.OMEGA.) (4) FIG. 6 shows the frequency characteristic of the high-frequency resistor R. The solid line is the zero magnetic field state, and the broken line is the R with a sufficiently large external magnetic field applied.
It is a value. At 750 MHz, the difference between the two is (5.8
It becomes the maximum value of −0.65) Ω, and at this time, the MR ratio is (5.8−0.65) /5.8=0.887 (89%).
Thus, the size is 10 times or more that of the conventional MR effect. The R value becomes maximum around 750 MHz because this frequency band matches the magnetic resonance frequency of 600 to 1000 MHz of NiFe used for the magnetic body 4. From this, it can be seen that in order to obtain a large MR ratio, it is effective to set the measurement frequency of the reflection characteristic measuring device 6 near the magnetic resonance frequency of the magnetic body 4. Further, from the figure, the bandwidth defined by the 3 dB bandwidth is estimated to be several hundred MHz, and it can be seen that the bandwidth is relatively wide. For example, a band of about 100 MHz is required for high density magnetic recording in the future, and this sensor can sufficiently meet this requirement.

FIG. 7 shows the external magnetic field dependence of the high frequency resistance value R at 750 MHz. R is NiFe used for the magnetic body 4
It greatly decreases around 3 to 5 Oe, which is a uniaxial anisotropic magnetic field, and becomes a substantially constant value at several Oe. Compared to FIG. 9, the sensor is saturated with an external magnetic field strength of the same degree, but the sensor has higher sensitivity due to the larger resistance change rate. Further, it can be confirmed that no hysteresis appears in the characteristics of FIG. 7 and the detection accuracy is high.

As the film forming method, in addition to the ion beam sputtering method, a method such as an RF sputtering method, a magnetron sputtering method, a vapor deposition method and the like can be mentioned, and the same effect can be obtained.

For the magnetic body 4 and the magnetic layer 41, Fe, C
Magnetic material based on o, Ni, for example, NiFeM
o, NiFeCu, NiFeCr, NiFeNb, Ni
FeTi, NiFeSi, FeSi, FeC, FeN,
CoFe, FeSiAl, FeB, FeBSi, CoB
Si, FeCoBSi, FeCoNiBSi, CoXa
(Xa: Y, Zr, Hf, Ti, Nb, Mo, W, R
e, Ni, Fe, Mn), CoXbXc (Xb: Y, Z
r, Hf, Ti, Nb, Mo, W, Re, Ni, Fe,
Mn, Xc: Y, Zr, Hf, Ti, Nb, Mo, W,
Re, Ni, Fe, Mn), and as the nonmagnetic insulator 3 and the nonmagnetic insulating layer 42, SiO ₂ , AlN, Al.
₂ O ₃ , BN, TiN, SiC, polyethylene naphthalate (PEN), polyethylene terephthalate (PE
T), polyimide, Kapton, and photoresist, and Cu, Al, Ag, Au, Pt, S as the detection conductor 2.
n, Cr, Zn, In can be used, and the same effect can be obtained.

As is clear from the above results, in the magnetic field detection sensor of the present invention, the signal output,
The SN ratio, sensitivity, signal detection accuracy are high, and the parts configuration is simplified.

[0032]

As described above, according to the magnetic field detecting sensor of the present invention, a change in the magnetic permeability of the magnetic material in response to a change in the external magnetic field is sensitively reflected in the change in the reflection coefficient. High SN ratio and high sensitivity. Further, since it is in a relatively wide band, it becomes possible to stably detect even a high frequency signal, and it is possible to exhibit excellent usefulness even for increasing the recording density of magnetic recording. Furthermore, since the detection conductor also serves as a DC bias conductor line, the component configuration is simplified, the number of components can be reduced, the manufacturing cost can be reduced by simplifying the configuration, and the number of manufacturing steps can be reduced. Excellent economy.

Further, when compared with the conventional giant MR effect, operation at room temperature, reduction of DC bias magnetic field application amount, and low magnetic field response are possible, and there is no need to set a special ambient environment for detection. It has a number of excellent effects such as low hysteresis, high-precision detection, simple detection system configuration, high sensitivity, and high reliability.

[0034]

[Brief description of drawings]

FIG. 1 is a diagram showing a front view of an embodiment of a magnetic field detection sensor of the present invention.

FIG. 2 is a diagram showing a front view of another embodiment of the magnetic field detection sensor of the present invention.

3A is a diagram showing a sectional view of an embodiment of a magnetic field detection sensor of the present invention, and FIG. 3B is a diagram showing a sectional view of another embodiment of the magnetic field detection sensor of the present invention.

FIG. 4 is a diagram showing an example of a cross-sectional structure of a magnetic body of the magnetic field detection sensor of the present invention.

FIG. 5 is a graph showing the dependence of a demagnetizing factor on the shape of a magnetic body.

FIG. 6 is a graph showing frequency characteristics of high frequency resistance.

FIG. 7 is a graph showing the external magnetic field dependence of the high frequency resistance.

FIG. 8 is a perspective view showing a structure of a conventional magnetoresistive sensor.

FIG. 9 is a graph showing the dependence of the resistivity of the conventional magnetoresistive sensor on the external magnetic field.

[Explanation of symbols]

 1a, 1b Electrode 2 Detection conductor 3 Non-magnetic insulator 4 Magnetic substance 5 Transmission line 6 Reflection characteristic measuring instrument 7 External magnetic field 41 Magnetic layer 42 Non-magnetic insulating layer

Claims (7)

[Claims] 1. At least one magnetic body is provided on the surface of a detection conductor having a pair of electrodes at both ends, directly or through a non-magnetic insulator, and a transmission line is connected to the electrodes, and the transmission line is connected to the transmission line. The line is connected to a reflection characteristic measuring instrument,
A magnetic field detection sensor, wherein when the magnetic permeability of the magnetic material changes according to an external magnetic field, the external magnetic field is detected based on a change in a reflection coefficient at the electrode end. 2. The magnetic body has a closed magnetic circuit structure that goes around the circumference of the detection conductor.
Magnetic field detection sensor described in. 3. The magnetic field detection sensor according to claim 1, wherein the magnetic material is a multi-layer magnetic material in which magnetic layers and nonmagnetic insulating layers are alternately laminated. 4. The layer thickness of the magnetic layer is set to be thinner than the skin depth of the magnetic layer, and the layer thickness of the non-magnetic insulating layer is set to a thickness equal to or larger than a thickness capable of maintaining electrical insulation between the magnetic layers. The magnetic field detection sensor according to claim 3, wherein: 5. The magnetic field according to claim 1, wherein the magnetic body is formed in a strip shape and its long side direction is set to be parallel to the external magnetic field direction. Detection sensor. 6. The magnetic field detection sensor according to claim 5, wherein the magnetic body has a uniaxial magnetic anisotropy with the easy axis in the short side direction. 7. The magnetic field detection sensor according to claim 1, wherein a measurement frequency of the reflection characteristic measuring device is in the vicinity of a magnetic resonance frequency of the magnetic body.