JP3161667B2 - Magnetic field detection sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a magnetic field detection sensor, an anisotropic magnetoresistance effect (MR effect;
Many magnetoresistive sensors (MR sensors) using a resistance effect have been used. FIG. 8 shows the structure of the MR sensor. In the figure, reference numeral 10 denotes a magneto-resistive element, and electric conductors 12a and 12b are connected to both ends in the longitudinal direction. 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. Electric conductors 14a and 14b are connected to both ends of the conductor line 13 as in the element 10. The change in the resistance R due to the MR effect is expressed by the following equation.

[0003]

R = R ₀ + ΔR cos ² θ (1) where 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 the R ₀ when the, theta 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 R sensor material
Alloys and the like. FIG. 9 shows the external magnetic field dependence of the resistivity of NiFe. As shown in FIG. 9, the MR ratio of the conventional MR sensor is as low as several percent (room temperature), and ΔR itself is only a small value. Therefore,
The conventional MR sensor has a problem that signal output, SN ratio, sensitivity, and the like are low.

Recently, a phenomenon in which the MR ratio is about 50% has been discovered in a Fe / Cr multilayer film (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 a sensor having a high sensitivity and a high sensitivity, it is not suitable for practical use because its operating temperature is as low as 4.2 K and a strong magnetic field of 20 kOe needs to be applied. Furthermore, since a large hysteresis appears in the dependence of the resistance on the external magnetic field, there is a disadvantage that the signal detection accuracy is low.

As is apparent from the above equation (1), MR
Since the effect is symmetric with respect to the reversal of the magnetic field, 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 anti-symmetry. In the conventional MR sensor, therefore, it was necessary to newly install the DC bias conductor line 13 as shown in FIG. However, this method has a drawback that the number of components is increased and the design of components, the production of components, and the complexity are involved.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the signal output, the S / N ratio, the sensitivity, the signal detection accuracy, and the complexity of the components, which are problems in the conventional magnetic field detection sensor. To provide a magnetic field detection sensor that solves the above.

[0007]

According to the magnetic field detection sensor of the present invention, at least one magnetic material is disposed directly or via a non-magnetic insulator on the surface of a detection conductor having a pair of electrodes at both ends, 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 material changes according to an external magnetic field, the reflection coefficient at the electrode end changes. The external magnetic field is detected based on the above.

In the above structure, the magnetic body preferably has a closed magnetic circuit structure surrounding the detection conductor, and the magnetic body has a multilayer structure in which magnetic layers and non-magnetic insulating layers are alternately stacked. It is preferable to use a structural magnetic material.
In this case, it is important that the thickness of the magnetic layer is smaller than the skin depth of the magnetic layer, and that the thickness of the non-magnetic insulating layer is set to a thickness that can maintain electrical insulation between the magnetic layers.

Preferably, the magnetic body is formed in a strip shape, and the long side direction thereof is set to be parallel to the direction of the external magnetic field. Here, the magnetic material desirably has uniaxial magnetic anisotropy whose easy axis is 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 substance.

[0011]

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

According to the magnetic field detection 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 a change in the reflection coefficient, so that a high signal output, a high SN ratio, and a high sensitivity are obtained. . Further, since no hysteresis appears in the external magnetic field dependence, the signal detection accuracy is high. In addition, the detection conductor
Since it also serves as a direct bias conductor line, the component configuration is simplified.

[0013]

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

FIGS. 1 and 2 show a front view of an embodiment of a magnetic field detection sensor according to the present invention, and FIGS.
(B) is a figure which shows the sectional view which follows the AA 'line of FIG. 1 and FIG. 2, respectively. At least one magnetic body 4 is disposed directly (FIG. 3A) or via a non-magnetic insulator 3 (FIG. 3B) on the surface of the detection conductor 2 having a pair of electrodes 1a and 1b at both ends. A transmission line 5 is connected to the electrodes 1a and 1b.
It is connected to the. Note that reference numeral 7 in the figure denotes 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. 3 (a) shows a case where the magnetic body 4 is directly disposed on the surface of the detection conductor 2. In the case, FIG.
Is a case where the magnetic body 4 is disposed on the surface of the detection conductor 2 via the non-magnetic insulator 3.

The principle of detection will be described. Electrode 1a, the impedance Z between 1b, the impedance Z ₀ of only the detection conductor 2, as the sum of the impedance Z _m derived from the magnetic body 4,

[0017]

## EQU2 ## 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比 μ _r × f (3) Since the relative magnetic 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. In this sensor,
This change in impedance Z is measured by reflection coefficient measurement.

In order to improve the signal output, the SN ratio, and the sensitivity, it is effective to devise the following structure.

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 path structure in which the magnetic body 4 makes a round around the detection conductor 2 is necessary in that the magnetic flux leakage can be suppressed. It is effective. For example, FIGS. 1, 2 and 3 show a closed magnetic circuit structure in which the detection conductor 2 is sandwiched between the upper and lower two magnetic bodies 4.

The operating frequency of this sensor is
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 sectional structure of the magnetic body 4 is shown in FIG.
It is effective to form a multilayer structure in which magnetic layers 41 and nonmagnetic insulating layers 42 are alternately stacked as shown in FIG. On this occasion,
The thickness of the magnetic layer 41 is determined by the skin depth (ski) of the magnetic layer 41.
It is effective to set the thickness of the nonmagnetic insulating layer 42 to be smaller than n depth, for example, about one digit, and to set the layer thickness of the nonmagnetic 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 must be a rectangular shape in which the direction of the external magnetic field 7 and the long side of the magnetic body 4 are parallel as shown in FIGS. It is effective to avoid the influence of the in-plane diamagnetic field. FIG. 5 shows an experimental result of the dependence of the demagnetizing field coefficient on the magnetic material shape in the NiFe film. Film thickness 3 μm, width 5
μm, and the relationship with the length was shown. The length is 200 from the figure
It is understood that the influence of the demagnetizing field can be almost neglected at 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 4 is the circumferential direction of the detection conductor 2, the direction of the hard axis of the uniaxial magnetic anisotropy coincides with the direction of the uniaxial magnetic field with the short side direction of the magnetic body 4 as the easy axis. Give anisotropy.

In order to provide a polarity detection function, a DC bias magnetic field generated from a DC bias current flowing through the detection conductor 2 can be used. At this time, since the detection conductor 2 also serves as a DC bias conductor line, the component configuration is simplified.

A specific example will be described below. 2 and 3A, and the magnetic body 4 employs the multilayer structure shown in FIG.
NiFe was used for the magnetic layer 41, and the layer thickness was set to 50 nm, which was sufficiently smaller than the skin depth on 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 was a thickness capable of maintaining electrical insulation between the magnetic layers 41. The magnetic body 4 had a total film thickness of 1.5 μm, and the detection conductor 2 was sandwiched between two pieces. The width of the magnetic body 4 was 5 μm and the length was 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 in which the short side direction is an easy axis. Cu was used for the detection conductor 2, the width of the detection conductor 2 was 10 μm, the thickness was 2 μm, and the length was 10 μm. The film was formed by ion beam sputtering, and the processing was performed by photolithography. The film forming conditions are as follows: operating vacuum degree Ar
1 × 10 ^-4 Torr, acceleration voltage 1 kV, substrate temperature from room temperature
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.

[0026] The change of the impedance Z due to a change in relative permeability mu _r corresponding to the intensity of the external magnetic field 7 in this sensor is measured by measuring the reflection coefficient gamma. Here, for comparison with FIG. 9, a result converted to a 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]

R = Real [(1 + Γ) / (1-Γ)] × 50 (Ω) (4) FIG. 6 shows the frequency characteristics of the high-frequency resistor R. The solid line indicates the zero magnetic field state, and the broken line indicates the R in the state where a sufficiently large external magnetic field is applied.
Value. At 750 MHz, the difference between them is (5.8
−0.65) Ω, and the MR ratio is (5.8−0.65) /5.8=0.887 (89%).
And 10 times or more the size of the conventional MR effect. The reason that the R value becomes maximum around 750 MHz is that this frequency band coincides with the magnetic resonance frequency of NiFe used for the magnetic body 4 of 600 to 1000 MHz. From this, it can be seen that 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 in order to obtain a large MR ratio. Also, from the figure, the bandwidth defined by the 3 dB bandwidth is estimated to be several hundred MHz, which indicates that the bandwidth is relatively wide. For example, a high-density magnetic recording in the future requires a band of about 100 MHz, and the present sensor can sufficiently respond to 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
Greatly decreases around 3 to 5 Oe, which is a uniaxial anisotropic magnetic field, and becomes substantially constant at several Oe. Compared to FIG. 9, the sensor saturates at the same level of external magnetic field strength, but the sensor has higher sensitivity due to the higher rate of change in resistance. Further, no hysteresis appears in the characteristics of FIG. 7, and it can be confirmed that the detection accuracy is high.

As the film forming method, besides the ion beam sputtering method, a method such as an RF sputtering method, a magnetron sputtering method, or a vapor deposition method can be mentioned, and the same effect can be obtained in any case.

The magnetic material 4 and the magnetic layer 41 are made of Fe, C
o, Ni-based magnetic materials such as 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 the nonmagnetic insulator 3 and the nonmagnetic insulating layer 42 are made of SiO ₂ , AlN, Al
₂ O ₃ , BN, TiN, SiC, polyethylene naphthalate (PEN), polyethylene terephthalate (PE
T), polyimide, Kapton, photoresist, and Cu, Al, Ag, Au, Pt, S
n, Cr, Zn, In can be used, and the same effect can be obtained in any case.

As is clear from the above results, the magnetic field detection sensor of the present invention has a higher signal output and
There have been improvements in that the S / N ratio, sensitivity, and signal detection accuracy are high and the component configuration is simplified.

[0032]

As described above, according to the magnetic field detection sensor of the present invention, since the change in the magnetic permeability of the magnetic material according to the change in the external magnetic field is sensitively reflected in the change in the reflection coefficient, a high signal output and a high signal output can be obtained. High SN ratio and high sensitivity. In addition, since it has a relatively wide band, it is possible to stably detect even a high-frequency signal, and it is possible to exhibit excellent usefulness for increasing the recording density of magnetic recording. Furthermore, since the detection conductor also functions 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 in the amount of applied DC bias magnetic field, and low magnetic field response are possible, and there is no need to set a special surrounding environment for detection. Numerous excellent effects such as small hysteresis, high-precision detection, simple detection system configuration, high sensitivity, and high reliability are achieved.

[0034]

[Brief description of the drawings]

FIG. 1 is a diagram showing a front view of an embodiment of a magnetic field detection sensor according to 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 cross-sectional view of an embodiment of the magnetic field detection sensor of the present invention, and FIG. 3B is a diagram showing a cross-sectional view of another embodiment of the magnetic field detection sensor of the present invention.

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

FIG. 5 is a graph showing a magnetic material shape dependency of a demagnetizing coefficient.

FIG. 6 is a graph showing frequency characteristics of a high-frequency resistor.

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

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-123871 (JP, A) JP-A-63-73176 (JP, A) JP-A-7-5234 (JP, A) JP-A 8- 274384 (JP, A) JP-A-8-274383 (JP, A) JP-A-9-21837 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33 / 00-33 / 18 H01L 43/08

Claims (7)

(57) [Claims] At least one magnetic material is provided directly or via a non-magnetic insulator on the surface of a detection conductor having a pair of electrodes at both ends, and a transmission line is connected to the electrodes. The line is connected to the 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 circuit according to claim 1, wherein the magnetic body has a closed magnetic circuit structure surrounding the detection conductor.
2. A magnetic field detection sensor according to claim 1. 3. The magnetic field detection sensor according to claim 1, wherein the magnetic body is a multilayered magnetic body in which magnetic layers and nonmagnetic insulating layers are alternately stacked. 4. The thickness of the magnetic layer is set to be smaller than the skin depth of the magnetic layer, and the thickness of the nonmagnetic insulating layer is set to be greater than or equal to 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 a long side direction thereof is set to be parallel to an external magnetic field direction. Detection sensor. 6. The magnetic field detection sensor according to claim 5, wherein the magnetic material has a uniaxial magnetic anisotropy whose easy axis is in a short side direction. 7. The magnetic field detection sensor according to claim 1, wherein a measurement frequency of the reflection characteristic measuring device is near a magnetic resonance frequency of the magnetic body.