JP2002350522A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high sensitivity shield type magnetic sensor superior in directivity which is capable of effectively detecting only a changed component of impedance. SOLUTION: The sensor contacts a plurality of conductive magnetic films 25 arranged in mutually parallel in one direction and a shield core including a soft magnetic film 27 for magnetically shielding spaces between the conductive magnetic films. Four conductive magnetic films are used and mutually connected to form a bridge circuit and the conductive magnetic film disposed on the open end of the shield core is used for detecting a magnetic field. This cancels invariant impedance components against a signal magnetic field to thereby detect only an impedance component changed by the signal magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield-type high-sensitivity magnetic sensor having excellent directivity using a new high-frequency impedance change.

[0002]

2. Description of the Related Art FIG. 9 shows an MI (Magnetic Impedance) element using a change in magnetic impedance reported in IEICE Technical Report MR95-80. In FIG. 9, 101
Is a detection conductor film made of a conductive metal thin film, which is sandwiched between the soft magnetic cores 105 and 106 to form an MI element. As shown in the enlarged view, the soft magnetic cores 105 and 106 are formed of a laminated film of the permalloy film 103 and the SiO ₂ film 104, and have a width that extends over the track width 102. The operating principle of this MI element is as follows.

A high-frequency signal is applied from a UHF band high-frequency transmitter 107 to a detection conductor film 101 via a resistor 108, and a current 109 is passed between the terminals 110 and 111 provided at both ends of the detection conductor thin film 101. The resulting change in magnetic impedance is detected by detecting the change in voltage between its terminals 110 and 111. That is, a voltage of the UHF carrier signal corresponding to the product of the impedance of the detection conductor thin film 101 between the terminals 110 and 111 and the current 109 is generated between the terminals 110 and 111. At this time, if the MI element receives an external magnetic field, the easy magnetization direction of the magnetization of the soft magnetic cores 105 and 106 is oriented in the track width direction. , The magnetic impedance is smaller than in the case where there is no. Therefore, the UHF carrier signal is detected in a form where it is AM-modulated by the signal magnetic field of the magnetic recording medium. An external magnetic field can be detected by AM detection of this signal.

If this magnetic sensor is realized, there is a possibility that an output about 10 times that of the giant MR head currently under development is obtained. FIG. 10 is an operation curve of the MI element shown in FIG. 9, which is obtained by setting the carrier signal frequency to 1.0 GHz and applying the dc magnetic field to the center of the Helmholtz coil. As can be seen from FIG. 10, setting of the DC bias point 112 is important for reproducing a signal with high sensitivity and obtaining a waveform with small distortion. In the above-described model, a DC magnetic field is generated by using a coil from the outside and is used as a bias.

[0005]

However, in the above-mentioned method, if a magnetic sensor having a good resolution is formed in order to detect, for example, geomagnetism with high accuracy, the magnetic sensor is easily affected by noise. In this method, it is desirable to reduce the size of the detection conductor, particularly the cross-sectional area, but if the cross-sectional area is reduced, the resistance value will increase significantly. It is also desirable to reduce the thickness of the magnetic material around the detection conductor, but this has the disadvantage that the inductance, that is, the impedance, decreases. Further, in the above method, although there is some directivity of sensitivity, since it is not shielded, there is a drawback that accurate detection is not performed when a motor, a transmitter, and the like are present close to each other. Therefore, it has been desired to realize a shielded magnetic sensor having excellent directivity for detecting a magnetic field from one direction with high resolution.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a shielded magnetic sensor which can efficiently detect only a change in impedance, has excellent directivity, and has high sensitivity.

[0007]

In order to solve the above-mentioned problems, a magnetic sensor having a basic structure according to the present invention comprises a plurality of magnetic sensors arranged in parallel to each other in one direction. It has a shield type configuration including the present conductive magnetic film and a shield core including a soft magnetic film for magnetically shielding between the conductive magnetic films.

Preferably, in the above structure, the shield core is opened at a portion of the conductive magnetic film disposed at one end of the plurality of conductive magnetic films. And In this configuration, preferably, the plurality of conductive magnetic films include first to fourth conductive magnetic films, and the four conductive magnetic films are connected to each other to form a bridge. A circuit is formed, and a magnetic field is detected by a first conductive magnetic film of the four conductive magnetic films disposed on the open end side of the shield core.

In the above basic structure, preferably, the first to fourth conductive magnetic films formed as a plurality of conductive magnetic films and connected to form a bridge circuit are provided. And a pair of shielding soft films formed so as to sandwich the first to fourth conductive magnetic films via an insulator film and to magnetically shield between the first to fourth conductive magnetic films. A magnetic body, means for applying a DC magnetic field to the first to fourth conductive magnetic films, first and second electrode terminals for supplying a signal to the bridge circuit, and for detecting a signal of the bridge circuit And a high-frequency oscillator connected to the third and fourth electrode terminals, a high-frequency oscillator connected to the first and second electrode terminals, and a high-frequency amplifier connected to the third and fourth electrode terminals. As a result, the first signal changed by the signal magnetic field
Is detected as a change in the high-frequency carrier signal.

Preferably, in the above configuration,
As in the invention, the effective magnetic permeability of the shielding soft magnetic material at the high-frequency carrier signal frequency is configured to be smaller than the effective magnetic permeability of the conductive magnetic film. Also preferably, as in the invention of claim 6, the thickness of the conductive magnetic film is
It is configured to have a skin depth or less at the high frequency carrier signal frequency. Also preferably, as in the invention of claim 7,
A high-frequency carrier signal current and a DC current as a DC bias are superimposed and applied to the conductive magnetic film.

Preferably, in the above basic configuration,
A structure in which a hard magnetic film is formed adjacent to the conductive magnetic film and magnetized in the direction in which the conductive magnetic film is aligned, thereby applying a DC magnetic field to the conductive magnetic film as a DC bias. And

According to a ninth aspect of the present invention, there is provided a method of manufacturing a magnetic sensor, comprising the steps of: forming an insulating film on a magnetic substrate; Forming a conductive magnetic film on the insulating film, forming an insulating layer on the conductive magnetic film, and etching a part of each of the formed layers to the substrate surface to separate the conductive magnetic film into a plurality of pieces. And forming a soft magnetic film thereon.

A method of manufacturing a magnetic sensor according to another aspect of the present invention is a method of manufacturing a magnetic sensor according to the invention of claim 8, comprising the steps of: forming a soft magnetic film on a nonmagnetic substrate; Forming an insulating film on the soft magnetic film, forming a conductive magnetic film on the insulating film, forming a hard film in close proximity to the conductive magnetic film, and insulating on the conductive magnetic film A step of forming a layer, and a step of etching a part of each formed layer to the substrate surface to separate the conductive magnetic film into a plurality of layers,
Forming a soft magnetic film thereon.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described. The fact that the inductance is determined by the number of crossings between the magnetic flux generated at this time and the current flowing through the conductor,
It is well known electromagnetically. In such a case, the inductance determined by the current inside the conductor and the magnetic flux generated inside the conductor can be divided into an internal inductance and the external inductance determined by the current flowing inside the conductor and the magnetic flux generated outside the conductor. . Therefore, for example, the inductance when a non-magnetic conductor wire is wound around a magnetic material or the inductance when a soft magnetic material is formed around a non-magnetic conductor may be regarded as an external inductance.

As a conventional method for detecting a signal from a magnetic head, a method using a resistance change such as MR or GMR,
A method of detecting a signal by a resistance change in a skin depth that changes by a magnetic field using an eddy current as in the MI effect, and a conductive film formed by laminating a soft magnetic material and an SiO ₂ film as described in the above prior art. There is a method of detecting an impedance change due to application of a signal magnetic field by using an external impedance by forming a conductive metal film in a sandwiched state.

The detection method of the present invention mainly detects a change in the internal inductance of a ribbon-shaped conductive magnetic thin film due to a signal magnetic field. In general, it is well known that the resistance component of a conductive metal film increases as its thickness decreases. Even in the case of a conventional example in which a soft magnetic film is formed around a conductive metal film and the external impedance is used, the resistance component is related to the cross-sectional area of the conductive film penetrating the magnetic circuit, and the cross-sectional area of the metal conductor is reduced. However, it was found that when the length was increased, the resistance component that did not change due to the magnetic field became extremely large, and the change in impedance due to the signal magnetic field was largely masked. Therefore, it is necessary to cancel out the extremely large resistance component and detect only the change.

In the present invention, a simple Wheatstone bridge circuit is constituted by a plurality of conductive magnetic films that are arranged so as to be shielded from each other between shield cores of a shield type magnetic sensor. As a result, the resistance component, which greatly increases due to the thinning of the soft magnetic film, is canceled out, and only the impedance component that changes due to the signal magnetic field (external magnetic field) can be detected with high directivity and high sensitivity.

(Embodiment 1) Hereinafter, a magnetic sensor according to Embodiment 1 will be described in detail with reference to FIGS.

FIG. 1 is a perspective view showing a part of the magnetic sensor according to the first embodiment to show the principle of operation.
The effect of the shield of the present invention will be described. Arrow 1,
2, 3 indicate the longitudinal direction, the thickness direction, and the width direction of the magnetic sensor element 4, respectively. A conductive magnetic film 6 made of an FeTaN film is disposed between a soft magnetic film film 9 for a shield and a magnetic substrate 8 for a shield via an insulating layer 7 made of SiO ₂ .
The lead 5 made of a Cu conductive film is connected to the conductive magnetic film 6. The lead 5 applies a carrier signal and a DC bias, and is connected to an electrode terminal for detecting a signal. Here, the magnetic field applied from the direction of arrow 1 is Hl, the magnetic field applied from the direction of arrow 2 is Ht, and the magnetic field applied from the direction of arrow 3 is Hw. The magnetic fluxes generated by these magnetic fields flow as shown in FIGS. 2 and 3, respectively.

FIG. 2 is a cross-sectional view taken along the line (g)-(h)-(i) in FIG. When a magnetic field Hl is applied from the direction of arrow 1, the magnetic fluxes 10, 11, and 14 at the central portion pass through the conductive magnetic film 6 and pass through the shield core portion composed of the soft magnetic film 9 for shield and the magnetic substrate 8 for shield. pass. The other magnetic fluxes 12, 13, 15, 16 flow without passing through the conductive magnetic film 6, which is a sensor. Therefore,
It can be a magnetic sensor with extremely high directivity.

FIG. 3 is a diagram showing the magnetic flux generated by the magnetic field Ht applied in the direction of arrow 2 in FIG. 1 as viewed from the direction of arrow 3 in the section (g)-(h)-(i). Magnetic flux 17, 18,
19 and 20 pass through the shield core portion as they are, and magnetic fluxes 21 and 22 incident near the position of the conductive magnetic film 6 also bypass and pass as shown in the figure. Therefore, the sensor hardly responds to the magnetic flux in the thickness direction.

The sensor may respond to the magnetic field Hw applied in the direction of arrow 3, but this component is canceled by the bridge circuit and the magnetic sensor described below. The influence of this component can be suppressed sufficiently small by making the width of the shielding magnetic substrate 8 and the width of the shielding soft magnetic film 9 sufficiently larger than the width of the conductive magnetic film 6.

FIG. 4 is a side sectional view for explaining the structure of the magnetic sensor element according to the first embodiment and a method for manufacturing the same.

As shown in FIG. 4A, using a photolithographic technique, a shield magnetic substrate 2 made of MnZn ferrite is used.
An insulating film 24 made of SiO ₂ is formed on 3. Next, the first conductive magnetic film 25a, the second conductive magnetic film 25b,
Conductive magnetic material 25c and fourth conductive magnetic film 25d
Four conductive magnetic films 25 are formed. Further, after forming an insulating film 26 made of SiO ₂ on each conductive magnetic film 25, a soft magnetic film 27 for shielding made of a laminated film of CoNbZr and SiO ₂ is formed. Thus, the shielding magnetic substrate 2
3 and the shield soft magnetic film 27 of CoNbZr,
The fourth conductive magnetic films 25a to 25d are magnetically shielded from each other.

Next, the wafer is cut and polished on the cross section (j)-(k), and FIG.
As shown in (B), the first conductive magnetic film 25a is magnetically exposed so that an external magnetic field can be detected. In addition,
Even if a non-magnetic overcoat layer is provided on this end face, the performance is not affected.

FIG. 5 is a plan view of a magnetic sensor constituted by using this magnetic sensor element. FIG. 5 is a diagram in which four conductive magnetic films 25a to 25d are viewed in the thickness direction. DC power supply 2
9 supplies a DC bias, supplies a high-frequency carrier signal from a high-frequency oscillator 30, superimposes both,
1 is applied to the conductive magnetic film 25. The right ends of the first conductive magnetic film 25a and the fourth conductive magnetic film 25d are connected to the contact (a), and the right ends of the second conductive magnetic film 25b and the third conductive magnetic film 25c are the contact ( c). The high frequency signal from the high frequency signal generator 7 is
Applied between contacts (a) and (c).

The left ends of the first conductive magnetic film 25a and the second conductive magnetic film 25b are connected to the contact (b),
Conductive magnetic film 25c and fourth conductive magnetic film 25d
Is connected to the contact (d). The contacts (b) and (d) are connected to the high-frequency amplifier 34 via the electrode terminals (f) and (e), respectively.

In this configuration, the arrangement of the conductive magnetic film 25 and the contacts (a), (b), (c), and (d) allows the arrangement shown in FIG.
As shown in the figure, a Wheatstone bridge circuit is configured. That is, the first to fourth conductive magnetic films 25a to 25a
5d each constitute a bridge circuit as impedances Z1, Z2, Z3 and Z4, and a high frequency signal is applied from the high frequency signal generator 30 between the contacts (a) and (c). The output of the bridge circuit is detected between contacts (b) and (d). When the impedances Z1, Z2, Z3, Z4 are equal to each other, no voltage is generated between the contacts (b) and (d).

In the magnetic sensor configured as described above, FIG.
Is applied from the direction of arrow 33,
The magnetic flux generated from the external magnetic field is applied to the second, third, and fourth conductive magnetic films 25b to 25d in accordance with the above-described shield effect.
Instead, it flows to the shielding soft magnetic film 27 and the shielding magnetic substrate 23 only through the first conductive magnetic film 25a. Therefore, an external magnetic field is applied to the first conductive magnetic film 25a.
Only detected by. The other magnetic flux passes through the shielding soft magnetic film 27 and the shielding magnetic substrate 23 and is not reflected on the detected output.

In this shielded magnetic sensor, when there is no external magnetic field, since the impedance of the four conductive magnetic films 25 is equal, the output is provided between the electrode terminals (e) and (f) of the output of the bridge circuit. No voltage is generated. When an external magnetic field is applied, a magnetic flux flows only in the first conductive magnetic film 25a, so that only the impedance Z1 of the first conductive magnetic film 25a changes, and the impedance component not changed by the magnetic field is canceled. Further, a magnetic field such as geomagnetism applied in the width direction is one of the components canceled by the bridge because the dimensions of the sensor are small and are applied almost equally to the four conductive magnetic films 25. Therefore, only the change in impedance due to the signal magnetic field (external magnetic field) is detected between the electrode terminals (e) and (f) as the output of the bridge circuit. The signal generated by the external magnetic field is amplified by the high frequency amplifier 34 and output.

The contacts (a), (b), (c),
(D) is a material film of good conductivity, such as Cu, Al, Au, Ag, etc., which is formed as thick as possible to form a bridge circuit with good accuracy. The frequency characteristics of the effective magnetic permeability of the material of the conductive magnetic film 25 and the shield core are adjusted as shown in FIG. In FIG. 7, the effective magnetic permeability of the former is represented by μ1, and the effective magnetic permeability of the latter is represented by μc. When the high-frequency carrier signal frequency is 1 GHz, the effective magnetic permeability μ1 is configured to be larger than the effective magnetic permeability μc. As a result, the region responding to the high-frequency carrier signal and the external magnetic field is divided by the conductive magnetic film and the shield core.

In the above magnetic sensor, the FeTaN film is used as the conductive magnetic film 25, but all soft magnetic materials such as NiFe, FeCo and FeN are effective. Also, MnZn ferrite is used as the soft magnetic substrate for shielding, but it is also effective to form a magnetic thin film for shielding on a nonmagnetic substrate such as a ferrite substrate such as NiZn or ceramic or glass.

(Embodiment 2) FIG. 8 is a sectional view of a shielded magnetic sensor according to Embodiment 2. The magnetic sensor according to the second embodiment has the same basic structure and operating principle as those of the first embodiment. Therefore, the same elements are denoted by the same reference numerals, and a detailed description thereof will be omitted. The difference from the first embodiment is that the first to fourth conductive magnetic films 25 a to 25
5D, the CoPt hard films 35, 36, 3
7 and 38 are formed. These are magnetized in the longitudinal direction of the element to form a magnet, which is used instead of the DC bias current in the first embodiment. Thus, when mounted on a portable device, the power can be significantly reduced.

Although the FeTaN film is used as the conductive magnetic thin film 25 in the first and second embodiments, a magnetic material having a small specific resistance such as permalloy is more suitable. FeTaN
While the specific resistance of the film is 75 Ω · cm, the specific resistance of the permalloy film is 20 Ω · cm, for example, when the film thickness is 500
Å, When the length is 0.5 μm and the width is 0.5 μm, it can be reduced from about 15 ohms to about 4 ohms. If the resistance value that cancels out with respect to the impedance that changes due to the magnetic field is significantly large, the error that cancels out increases, so that it is effective to select a material having a small specific resistance.

Further, the insulating film 2 forming the gap
Examples in which SiO ₂ was used as ₄ , 26 were shown.
An inorganic dielectric film such as glass is effective, and as the soft magnetic film 27 for shielding, an eddy current is not generated.
Although a laminated film of CoNbZr metal magnetic material and SiO ₂ is used, other metal magnetic materials such as Fe-based and Co-based metal magnetic materials and ferrite oxide are also effective. Also, as the hard film, Ba
All hard films such as ferrite, Nb-based, and Co-based magnets are effective.

[0036]

According to the present invention, by arranging a plurality of conductive magnetic films so as to be magnetically shielded by the shield core, impedance components which are not changed by the signal magnetic field are canceled out and changed by the signal magnetic field. A high-frequency carrier-type magnetic sensor having excellent directivity, which detects only the impedance component to be changed, can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an operation principle of a magnetic sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the operation principle of the magnetic sensor according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing the operation principle of the magnetic sensor according to the first embodiment of the present invention.

FIG. 4 is a side sectional view showing the magnetic sensor element according to the first embodiment of the present invention.

FIG. 5 is a plan view showing a magnetic sensor constituted by using the magnetic sensor element of FIG. 4;

FIG. 6 is a diagram showing a bridge circuit formed by the magnetic sensor element in FIG.

FIG. 7 is a magnetic permeability characteristic diagram of a magnetic material used for the magnetic sensor of the present invention.

FIG. 8 is a sectional view of a magnetic sensor according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating the operation principle of a conventional MI element.

FIG. 10 is a diagram showing an operation curve of a conventional MI element.

[Explanation of symbols]

1 to 3 arrow 4 magnetic sensor element 5 lead 6 conductive magnetic film 7 insulating layer 8 shielding magnetic substrate 9 shielding soft magnetic film 10 to 22 magnetic flux 23 shielding magnetic substrate 24, 26 insulating film 25a to 25d conductive magnetic film 27 Soft magnetic film for shielding 29 DC power supply 30 High frequency oscillator 31 Resistance 33 Arrow 34 High frequency amplifier 35-38 Hard film 101 Detection conductor film 102 Track width 103 Permalloy 104 SiO ₂ 105, 106 Soft magnetic core 108 Resistance 109 Current 110, 111 Terminal 112 DC bias

Continued on the front page (72) Inventor Akio Murata 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 2G017 AA03 AC01 AC09 AD69 5E049 AA00 BA16 CB00 EB05

Claims (10)

[Claims] 1. A semiconductor device comprising: a plurality of conductive magnetic films arranged in parallel with each other in one direction; and a shield core including a soft magnetic film for magnetically shielding between the conductive magnetic films. A shield type magnetic sensor characterized by the above-mentioned. 2. The method according to claim 1, wherein the shield core is open at a portion of the conductive magnetic film disposed at one end of the plurality of conductive magnetic films.
A magnetic sensor as described. 3. The plurality of conductive magnetic films include first to fourth conductive magnetic films, and the four conductive magnetic films are connected to each other to form a bridge circuit. The magnetic sensor according to claim 2, wherein the magnetic field is detected by the first conductive magnetic film disposed on the open end side of the shield core among the conductive magnetic films. 4. A first to a fourth conductive magnetic film formed as the plurality of conductive magnetic films and connected to form a bridge circuit, and the first to the fourth conductive magnetic films. 1 formed so as to be sandwiched with an insulating film therebetween and to magnetically shield between the first to fourth conductive magnetic films.
A pair of soft magnetic members for shielding, means for applying a DC magnetic field to the first to fourth conductive magnetic films, first and second electrode terminals for supplying a signal to the bridge circuit, Third and fourth electrode terminals for detecting a signal of the bridge circuit, a high-frequency oscillator connected to the first and second electrode terminals, and a high-frequency oscillator connected to the third and fourth electrode terminals 2. A high-frequency amplifier, wherein an impedance of the first conductive magnetic film, which changes due to a signal magnetic field, is detected as a change in a high-frequency carrier signal.
A magnetic sensor as described. 5. The magnetic sensor according to claim 4, wherein the effective magnetic permeability of the shielding soft magnetic material at the high-frequency carrier signal frequency is smaller than the effective magnetic permeability of the conductive magnetic film. 6. The magnetic sensor according to claim 4, wherein the conductive magnetic film has a thickness equal to or less than a skin depth at the high-frequency carrier signal frequency. 7. The magnetic sensor according to claim 4, wherein the high-frequency carrier signal current and a DC current as a DC bias are applied to the conductive magnetic film in a superimposed manner. 8. A method for applying a DC magnetic field as a DC bias to the conductive magnetic film by forming a hard film adjacent to the conductive magnetic film and magnetizing the hard film in an alignment direction of the conductive magnetic film. The magnetic sensor according to claim 1, wherein: 9. A method for manufacturing a magnetic sensor according to claim 1, wherein an insulating film is formed on a magnetic substrate, and a conductive magnetic film is formed on the insulating film. A step of forming an insulating layer on the conductive magnetic film, a step of etching a part of each of the formed layers up to a substrate surface to separate the conductive magnetic film into a plurality of layers, and forming a soft magnetic film thereon. Forming a magnetic sensor. 10. A method for manufacturing a magnetic sensor according to claim 8, wherein: a step of forming a soft magnetic film on a non-magnetic substrate; a step of forming an insulating film on the soft magnetic film; Forming a conductive magnetic film on an insulating film, forming a hard film in close proximity to the conductive magnetic film, forming an insulating layer on the conductive magnetic film, and forming each of the formed layers And a step of forming a soft magnetic film on the conductive magnetic film by separating a part of the conductive magnetic film by etching a part of the conductive magnetic film to a substrate surface.