JP4047955B2 - Magnetic impedance sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor, and more particularly to a magnetic impedance sensor that is a highly sensitive magnetic sensor.
[0002]
[Prior art]
With the recent rapid development of information equipment and measurement / control equipment, there is an increasing demand for small, low-cost, high-sensitivity, high-speed response magnetic sensors. For example, hard disk drives for computer external storage devices have been improved in performance from bulk type inductive magnetic heads to thin film magnetic heads and magnetoresistive effect (MR) heads. As the number of magnetic poles in the ring increases, a magnetic sensor capable of detecting a weak surface magnetic flux with high sensitivity is required instead of the conventionally used magnetoresistive effect (MR) sensor. In addition, there is an increasing demand for high-sensitivity sensors that can be used for nondestructive inspection and banknote inspection. In addition, there is a growing demand for compact and lightweight automobile orientation sensors, high-definition color televisions, and active magnetic shield sensors for display tubes of personal computers.
[0003]
Typical magnetic detection elements currently used include an inductive reproducing magnetic head, a magnetoresistive effect (MR) element, a fluxgate sensor, and a Hall element. Recently, the magneto-impedance effect of amorphous wires (see JP-A-6-176930, JP-A-7-181239, JP-A-7-333305) and the magnetic impedance effect of a magnetic thin film (JP-A-8-75835). A high-sensitivity magnetic sensor using a gazette, Journal of Japan Society of Applied Magnetics, vol.20, 553 (1996)) has been proposed.
[0004]
The induction type reproducing magnetic head requires a coil winding, so that the size of the magnetic head itself is increased. Further, when the disk is reduced in size, the relative speed between the magnetic head and the medium is decreased, and the detection sensitivity is significantly decreased. On the other hand, a magnetoresistive effect (MR) element using a ferromagnetic film has been used. The MR element detects not the time change of the magnetic flux but the magnetic flux itself, and the miniaturization of the magnetic head has been promoted. However, the current MR element has an electrical resistance change rate of about 2%, and even an MR element using a spin valve element has a small electrical resistance change rate of 6% or less and obtains a resistance change of several percent. The external magnetic field required for this is as large as 20 Oe or more. Therefore, the magnetoresistive sensitivity is as low as 0.1% / Oe or less. Recently, a giant magnetoresistance effect (GMR) using an artificial lattice having a magnetoresistance change rate of several tens of percent has been found. However, in order to obtain a resistance change of several tens of percent, an external magnetic field of several hundred Oe is required, and it has not been put into practical use as a magnetic sensor.
[0005]
A fluxgate sensor, which is a conventional high-sensitivity magnetic sensor, measures magnetism by utilizing the fact that the symmetrical BH characteristic of a high-permeability magnetic core such as Permalloy is changed by an external magnetic field. ^-6 High resolution of Oe and high directivity of ± 1 °. However, in order to increase the detection sensitivity, a large magnetic core with a small demagnetizing field is required, and it is difficult to reduce the overall size of the sensor and increase the response speed, and the power consumption is high.
[0006]
A magnetic field sensor using a Hall element utilizes a phenomenon in which, when a magnetic field is applied perpendicularly to the plane of current flow, an electric field is generated in a direction perpendicular to both the current and applied magnetic fields, and an electromotive force is induced in the Hall element. It is a sensor. Although the Hall element is advantageous in terms of cost, the magnetic field detection sensitivity is low, and since it is composed of a semiconductor such as Si or GaAs, electrons or holes are scattered by scattering due to thermal oscillation of the lattice in the semiconductor against temperature changes. Since the mobility changes, the temperature characteristic of the magnetic field sensitivity is bad.
[0007]
As described in JP-A-6-176930, JP-A-7-181239, and JP-A-7-333305, a magneto-impedance element has been proposed, which greatly improves magnetic field sensitivity, is miniaturized, and has high-speed response. Is realized. The basic principle of this magneto-impedance element is to detect only the voltage against the time change of the circumferential magnetic flux using the skin effect generated by applying a current that changes rapidly with time to the magnetic wire as a change due to the externally applied magnetic field. It is a magnetic impedance element. FIG. 16 shows an example of the magneto-impedance element. As this magnetic wire, an amorphous wire having a diameter of about 30 μm with a zero magnetostriction such as FeCoSiB (wire subjected to tension annealing after drawing) is used. FIG. 17 shows the applied magnetic field dependence of the impedance change of the wire. . Even if a wire with a minute dimension of about 1 mm in length is applied with a high frequency current of about 1 MHz, the amplitude of the wire voltage changes with a high sensitivity of about 100% / Oe, which is 1000 times or more that of the MR element.
[0008]
[Problems to be solved by the invention]
As a magnetic sensor, there is a demand for a high-sensitivity magnetic sensor that is small, low-cost, excellent in output linearity with respect to the detected magnetic field, and excellent in temperature characteristics. A magnetic sensor that uses the magneto-impedance effect of amorphous wire is a highly sensitive magnetic field. The detection characteristics are shown. In addition, in the ones disclosed in Japanese Patent Laid-Open Nos. 6-176930 and 6-347490, the linearity of the applied magnetic field dependency of the impedance change is improved by applying a bias magnetic field, and the amorphous wire is negatively affected. By winding a feedback coil and applying negative feedback by applying a current proportional to the voltage across the amorphous wire to the coil, the linearity and response speed are excellent, and the magnetic field detection sensitivity is invariant to changes in the sensor temperature. It shows that the sensor can provide.
[0009]
However, since this high-sensitivity magneto-impedance element is made of an amorphous wire having a diameter of about 30 μm, it is not suitable for fine processing, and it has been difficult to provide an ultra-small magnetic detection element. Moreover, it is not easy to form electrodes by soldering, and special measures have been taken. Further, both the bias coil and the negative feedback coil have to be manufactured by winding a thin copper wire, and there is a limit to miniaturization, and there is a problem in productivity.
[0010]
On the other hand, what is described in Japanese Patent Application Laid-Open No. 8-75835 proposes a magnetic impedance element using a magnetic thin film to reduce the size of the element, but a bias magnetic field for improving the linearity of sensor sensitivity. A method using a hard magnet and a method using a single-plate conductor are proposed as an application method. A method using a hard magnet for the bias is difficult to manufacture, and it is not easy to control the bias magnetic field due to the change of the magnet over time. In addition, the method of applying a bias using a single-plate conductor is structurally simple, and the bias magnetic field can be controlled by the amount of current, but since it is a single-plate conductor, in order to obtain a practically necessary bias magnetic field. In this case, a very large current must be passed, which causes problems such as heat generation and disconnection of the element. Also, no consideration is given to adding a negative feedback function.
[0011]
Journal of Japan Society of Applied Magnetics vol. 21, 649-652 (1997), a thin film coil is wound around a thin film magnetic core to form a bias coil, but this structure is a structure having a bias coil and a negative feedback coil at the same time. Absent. Moreover, since Au is used for the thin film coil, there is a problem in terms of cost. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a high-sensitivity magnetic sensor that is small in size and low in cost and excellent in output linearity, temperature characteristics, and mass productivity with respect to a detection magnetic field.
[0012]
[Means for Solving the Problems]
According to one aspect of the present invention, the substrate comprises a substrate made of a non-magnetic material, a thin film magnetic core formed on the substrate, and a first electrode and a second electrode provided at both longitudinal ends of the thin film magnetic core. A magneto-impedance sensor having a structure in which a bias coil and a negative feedback coil are alternately wound at regular intervals in the same direction through an insulator around the thin-film magnetic core. Provided. Further, the bias coil and the negative feedback coil are constituted by thin film coils, and the number of turns can be the same. When forming a magneto-impedance sensor, a plurality of thin film conductors arranged in parallel and insulated from the thin film magnetic core on the lower surface of the thin film magnetic core and arranged in parallel and insulated from the thin film magnetic core on the upper surface of the thin film magnetic core The bias coil and the negative feedback coil are formed by electrically connecting the tip portions of the thin film conductors on the upper surface and the lower surface of the thin film magnetic core, respectively. The thin film magnetic core is formed of a NiFe, CoFeNi, FeP, FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB, CoFe plated film, or a CoZrNb, FeSiB, CoSiB amorphous sputtered film or a NiFe sputtered film. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 is a front view schematically showing the structure of a thin film MI sensor using a magneto-impedance (MI) element according to the present invention, and FIG. 2 is a cross-sectional view taken along line AB in FIG. 3 is a cross-sectional view taken along line CD in FIG. The actual thin film MI sensor as a whole is formed on a plate-like body such as a thin film ceramic plate or glass plate, but this is omitted in FIG. 1, 2, and 3, reference numeral 1 denotes an MI sensor plate that is a thin-film magnetic core formed in a thin plate shape having a rectangular planar shape. The thin film magnetic core as the MI sensor plate has a width of 20 μm, a thickness of 5 μm, and a length of 500 μm. A bias coil 4 and a negative feedback coil 5 are wound around the MI sensor plate 1 alternately in the same direction via insulator layers 2 and 3. Although not shown correctly in the figure, each of these coils has 20 turns. Bias coil terminals 6 and 7 are connected to both ends of the bias coil 4, and negative feedback coil terminals 8 and 9 are connected to both ends of the negative feedback coil 5. MI sensor terminals 10 and 11 are connected to both ends of the MI sensor plate 1. These terminals are made of an Au metal thin film, and the wide portion at the tip serves as a pad for external wiring. Reference numeral 12 denotes an insulating protective film that covers the entire MI sensor.
[0014]
Next, a manufacturing process of the thin film MI sensor according to the present invention will be described in detail with reference to FIG. Note that FIG. 4 is described in a state viewed from the cross-sectional direction of AB in FIG.
4A is a coil lower layer part constituting a bias coil and a negative feedback coil, and is connected to the coil end part of the coil upper layer part pattern shown in FIG. 4E at the end part of each coil part pattern. Thus, the continuous bias coil 4 and negative feedback coil 5 shown in FIG. 1 are configured.
[0015]
As shown in FIG. 4A, the coil lower layer is made of Al. ₂ O _Three A Cu sputtered film with a thickness of about 50 nm is formed on a non-magnetic substrate 20 with improved surface smoothness such as a ceramic wafer, Si wafer, glass wafer or the like to serve as a seed layer for plating. After forming a photoresist pattern with an inverted pattern of a predetermined coil shape, Cu plating is embedded in the photoresist pattern to a thickness of about 3 μm, and after removing the photoresist pattern with an organic solvent, etc., a Cu sputtered film seed The coil pattern 21 is formed by removing the layer by etching. On the other hand, a Cu sputtered film is formed to a thickness of about 3 μm, and then a predetermined coil-shaped photoresist pattern is formed. Using the photoresist pattern as an etching mask, etching is performed by an etching means such as ion milling. The lower coil part can also be produced by removing the photoresist pattern with an organic solvent or the like. The Cu coil production method described above can reduce the size of the coil itself and bring the coil closer to the magnetic core compared to the method of producing a coil by winding a conductor wire or the method of producing a coil by winding a conductor ribbon. Therefore, coil efficiency can be increased.
[0016]
As shown in FIG. 4B, the insulator layer 3 is deposited on the formed coil lower layer. In FIG. 4C, a thin film magnetic core is formed on the insulator layer 3. For this thin film magnetic core, a plated film such as NiFe or CoFeNi, an amorphous sputtered film such as CoZrNb, FeSiB or CoSiB, or a soft magnetic film such as a NiFe sputtered film is used. Here, an example of creation when a NiFe plating film is used as a thin film magnetic core is shown. First, a NiFe sputtered film having a thickness of about 50 nm is formed to serve as a seed layer for plating. On the seed layer, an inverted pattern of a photoresist pattern with a predetermined coil shape is formed. After that, NiFe plating is embedded in the photoresist pattern to a thickness of about 5 μm, and the photoresist pattern is removed with an organic solvent or the like. Thereafter, the NiFe sputtered film is formed by removing the seed layer by etching. The same process is used when a CoFeNi plating film is used as a thin film magnetic core. In addition, when a thin film magnetic core is formed and then heat treatment is performed in a rotating magnetic field and in a static magnetic field, the magnetic properties are improved.
[0017]
Next, a production process when an amorphous sputtered film such as CoZrNb, FeSib, or CoFeB or a soft magnetic film such as a NiFe sputtered film is used as a thin film magnetic core will be described. For example, a CoZrNb sputtered film is formed to a thickness of about 5 μm, and then a photoresist pattern having a predetermined magnetic core shape is formed. Using the photoresist pattern as an etching mask, etching is performed by etching means such as ion milling, Further, the lower layer coil portion can be produced by removing the photoresist pattern with an organic solvent or the like. On the other hand, there is a metal mask method in which a reverse shape of a predetermined thin film magnetic core is produced on a thin metal plate and used as a sputtering mask. However, this method makes it difficult to obtain a magnetic core with a fine shape, and its dimensional accuracy is poor. It is not preferable.
[0018]
As shown in FIG. 4D, the insulator layer 2 is formed on the thin film magnetic core. The insulator layer 2 is an insulating film for electrically insulating a coil upper layer portion to be formed next and the thin film magnetic core. The forming method is the same as in the case of the insulator layer 3 shown in FIG.
Next, as shown in FIG. 4E, a coil upper layer portion constituting a bias coil and a negative feedback coil is formed on the surface of the insulating layer 2. As shown in the explanation of FIG. 4A, the end of each coil portion is connected to the coil end of the lower coil portion shown in FIG. A coil 5 is configured. The manufacturing method is the same as in the case of forming the coil upper layer portion shown in FIG.
[0019]
After completion of the step shown in FIG. 4 (e), a wire for obtaining an electrical connection between the insulating protective film 12 for protecting the manufactured magnetic sensor portion and a peripheral circuit for driving and detecting the magnetic sensor. Bonding pads (bias coil terminal 7, MI sensor terminals 10, 11 etc.) are provided to obtain the state shown in FIG. The insulating protective film 12 is exposed to light and developed in the same manner as the insulating layer 3 shown in FIG. 4B to form a predetermined insulating layer shape, and then heat-treated at 270 ° C. for 10 hours. Use hardened material. Also, a cured resin such as polyimide or Si0 ₂ For example, an inorganic film formed in a predetermined shape may be used. A bonding pad for wire bonding is made of an Au plating film or an Au sputtered film. The manufacturing process is substantially the same as that of the Cu coil.
As described above, the thin film processes are stacked in order from FIG. 4A to FIG. 4E and FIG. 2 to produce a thin film MI sensor.
[0020]
The magneto-impedance effect (MI effect) is a phenomenon in which when a high-frequency magnetic material is energized with a high-frequency current, the impedance at both ends thereof is changed by an external magnetic field applied in the energizing direction. That is, the impedance due to the internal inductance Li of the magnetic material and the resistance Rw that increases with the current frequency f due to the skin effect.
Z = Rw (μθ) + jωLi (μθ) (1)
However, it is because it changes as a function of the magnetic permeability μ in the width direction of the magnetic material, which changes by applying a magnetic field from the outside.
In the case of a thin film, the resistance Rw of the thin film in the high frequency region where the skin effect is remarkable (film thickness d> 2δ) is DC resistance Rdc.
Rw = Rdc (d / 2 δ)
It can be expressed as.
On the other hand, when d> 2δ, the inductance is
L = Li (2 δ / d)
It can be expressed as.
Here, δ indicates the depth of the skin, which is the value shown in FIG.
Therefore, the impedance Z of the thin film is
Z = Rdc (d / 2δ) + jωLi (2δ / d)
It becomes.
Here, when the thickness of the thin film is d = 2a, and the width W and the length 1 are given, the absolute value of the impedance Z of the thin film is as shown in FIG.
Here, since the depth δ of the skin is as shown in FIG. 5, the absolute value of the impedance Z of the thin film is a function of the permeability μθ.
[0021]
As shown in FIG. 7A, when uniaxial anisotropy is imparted in the width direction of the thin film pattern, the magnetization vector faces the width direction, and the magnetic domain structure has a 180 ° domain wall. By the way, when a high-frequency current is passed in the length direction of this thin film, a high-frequency magnetic field is generated in the width direction, but the movement of the 180 ° domain wall is hindered by eddy current braking. Further, since the direction of the high-frequency magnetic field and the direction of the magnetization vector are the same, rotational magnetization is unlikely to occur. For this reason, the change in magnetic flux is small and μθ is small.
[0022]
On the other hand, when the external magnetic field Hex is applied in the length direction of the thin film pattern, the direction of the magnetization vector is tilted from the width direction. Therefore, the magnetization vector is rotated by the magnetic field generated by the high-frequency current (rotational magnetization). growing. When the external magnetic field Hex becomes the same as the anisotropic magnetic field Hk of the pattern, μθ becomes maximum, and at this time, the impedance Ζ becomes maximum. Further, when Hex increases (Hex> Hk), the magnetization vector is fixed to Hex, so that rotation of the magnetization vector is suppressed, μθ decreases, and Z decreases accordingly.
These phenomena are verified using FIG. 7B based on the rotational magnetization model. Rotation angle θ when H θ = 0 ₀ Is determined by the energy minimum condition of equation (3) shown in FIG.
Therefore,
Using Hk = 2Ku / Ms,
θ ₀ = Hex / Hk is obtained.
Here, change of rotation angle by H θ | Δθ |> θ ₀ Then, the magnetization change Δ 変 化 in the width direction is expressed by the following equation.
ΔM = Ms COSθ ₀ Δθ (4)
The total energy including the term due to Hθ is expressed by the following equation.
E = −Ms (Hθ + Hk) COS [π / 2− (θ ₀ + Δθ)] − Ms Hex COS (θ ₀ + Δθ) (5)
When Δθ is obtained from the equation (7) shown in FIG. 9 using the equation (5) and substituted into the equation (4), the equation (6) shown in FIG. 9 is obtained.
Therefore, when Hex <Hk, μθ, that is, Ζ increases as the magnetic field increases, and after Hex = Hk reaches the maximum value, it decreases as the magnetic field increases.
Also, when the magnetization vector is oriented in the length direction of the thin film pattern, the MI effect is very small because μθ in the width direction due to Hex hardly changes.
[0023]
Next, the characteristics of the prepared thin film MI sensor are described. Here, the dimensions of the thin film magnetic core are a width of 20 μm, a thickness of 5 μm, a length of 500 μm, and an energization current of 10 mA. The bias and negative feedback coils are alternately wound on the same surface, and the number of turns is 20 turns. Bias and negative feedback coils are wound around a thin film magnetic core alternately on the same surface, so that a bias magnetic field and a negative feedback magnetic field can be applied uniformly to each part of the magnetic core, and the characteristics as a magnetic sensor are stabilized. . Fig. 10 shows the energization of the sensor electrode Ε (Ε = Ζ * I) when a magnetic field (Hex) of 0 and 30 Oe is applied to the thin film magnetic sensor when the thin film magnetic core is made of NiFe plating. It is a current frequency characteristic. The difference ΔΕ between Hex = 0 and Hex = 30 Oe was the maximum at a current flow frequency of 20 MHz. FIG. 11 shows the dependence of the impedance change rate on the applied magnetic field (Hex) when the energization current frequency is constant at 20 MHz (10 mA). As the applied magnetic field is increased, the impedance change rate Δ イ ン ピ ー ダ ン ス / Z _o Becomes larger, and ΔΖ / Z at the element's anisotropic magnetic field HK _o Becomes the maximum, and ΔΖ / Z for Hex> Hk _o Is getting smaller. These results were the characteristics shown by the above theoretical formula. Further, the amount of change in impedance per unit applied magnetic field (magnetic field sensitivity) was maximum around Hex = 20 Oe, indicating a magnetic field sensitivity of 1.5% / Oe.
[0024]
When used as a magnetic sensor, sensor sensitivity can be improved by bringing the operating point to the maximum sensitivity. FIG. 12 shows the rate of change in impedance ΔΖ / Z when the operating point is changed by applying a bias magnetic field of 20 Oe to the thin film magnetic material by passing a current through the bias coil. _o This shows the dependence on the applied magnetic field (Hex). As can be seen from this figure, by applying a bias magnetic field of 20 Oe to the magnetic core using a thin film coil, an MI characteristic that maximizes the magnetic field sensitivity at a magnetic field of 0 Oe was obtained.
[0025]
FIG. 13 shows the relationship between the coil magnetomotive force (product of current and number of turns) and the bias magnetic field. When a thin film coil is used as a bias coil, the slope of the graph is 28 (Oe / AT). When a bias coil in which a copper wire is wound around an amorphous wire having a diameter of 30 μm examined as a comparison is 2 (Oe / AT). / AT). The thin-film coil is close to the NiFe thin-film core and can form the coil densely, so that the coil efficiency for converting the current into the magnetic flux is more than 10 times higher than that of the bias coil wound with the copper wire.
[0026]
On the other hand, when the operating point is moved so as to bring the maximum sensitivity to the applied magnetic field 0 using a bias coil, the linearity of the impedance change (output change) with respect to the magnetic field is not very good as shown in FIG. It has become. As a method of improving this linearity, the output signal is fed back to the thin film magnetic core as a negative feedback magnetic field by feeding back the output signal and correcting the nonlinearity of the output with respect to the magnetic field using a negative feedback coil. A way to get sex is taken. FIG. 14 shows a block diagram of an electronic circuit of the linear magnetic field MI sensor. This circuit moves the operating point to the point of maximum sensitivity, feeds back the output signal, and adds a negative feedback magnetic field to the thin film core to improve the linearity of the sensitivity characteristic.
[0027]
FIG. 15 shows the relationship of the output voltage to the applied magnetic field when negative feedback with a bias coil magnetic field of 20 Oe and a negative feedback rate of 50% is applied using the circuit of FIG. Here, the frequency of the energization current is 20 MHz, and the amplification factor of the output is 500 times. As shown in the figure, it exhibits excellent linearity within a measuring magnetic field of ± 3 Oe, and 10 ^-Five The magnetic field resolution of Oe is shown. These results are good characteristics as a linear magnetic field sensor. In addition, in the case of an element using a negative feedback coil in which a copper wire is wound around a comparative amorphous wire, about 300% negative feedback had to be applied in order to obtain a straight line equivalent to the figure. Compared to the negative feedback coil in which the copper wire is wound around the amorphous wire, the thin film coil can obtain the same linearity with a negative feedback factor of about 1/6. This is due to the high efficiency.
The above is an example of measurement, and it is also possible to use a pulse excitation type MI effect using a C-MOS IC capable of driving with low power consumption as another MI sensor driving method. Furthermore, a bias magnetic field application method can also apply a pulse in conjunction with pulse excitation, whereby a necessary bias magnetic field can be obtained.
[0028]
As mentioned above, although this invention was demonstrated by the above-mentioned embodiment, a various deformation | transformation is possible within the range of the meaning of this invention. For example, the bias coil 4 and the negative feedback coil 5 do not have the same number of turns, and as shown in FIG. 18, the negative feedback coil 5 is partially short-circuited by a connecting line 5 ′ across the bias coil 4. The number of turns with the negative feedback coil 5 may be changed. Of course, a part of the bias coil 4 may be connected by a connecting line to change the number of turns of the bias coil and the negative feedback coil. These modifications and applications are not excluded from the scope of the present invention.
[0029]
【The invention's effect】
The thin-film MI sensor structure in which a thin film coil for bias and negative feedback is formed through an insulator around the thin-film magnetic core enables the magnetic sensor to be downsized, highly reliable, and mass-produced. Since the thin film coil manufactured in such a structure has good coil efficiency, a necessary bias magnetic field can be obtained with a small current, and the output linearity with respect to the magnetic field can be improved with a small negative feedback amount. Therefore, a thin film linear magnetic field sensor with high sensitivity, good sensitivity linearity, and excellent temperature characteristics can be provided.
Further, by alternately winding the thin film coil for bias and the thin film coil for negative feedback, a bias magnetic field and a negative feedback magnetic field can be applied uniformly to each part of the thin film magnetic core, and the characteristics as a magnetic sensor are stabilized. .
[Brief description of the drawings]
FIG. 1 is a front view schematically showing the structure of a thin film MI sensor using a magnetic impedance (MI) element according to the present invention.
FIG. 2 is a cross-sectional view taken along line AB in FIG.
FIG. 3 is a cross-sectional view taken along the line CD in FIG. 1;
FIG. 4 is a cross-sectional view showing a manufacturing process of the magneto-impedance sensor according to the present invention.
FIG. 5 is an equation diagram showing the value of δ.
FIG. 6 is an equation diagram showing an absolute value of impedance.
FIG. 7 is a magnetic domain structure model diagram of a magnetic core part of a thin film MI sensor.
FIG. 8 is an equation showing the value of EO.
FIG. 9 is an equation diagram showing the value of ΔM0.
FIG. 10 is a characteristic diagram showing the dependence of the output on the current-carrying current frequency.
FIG. 11 is a characteristic diagram showing the magnetic field dependence of the impedance change rate.
FIG. 12 is a characteristic diagram showing the magnetic field dependence of the impedance change rate when a bias magnetic field of 20 Oe is applied.
FIG. 13 is a characteristic diagram showing the bias coil magnetomotive force dependence of the bias magnetic field strength.
FIG. 14 is a circuit block diagram using a magneto-impedance sensor according to the present invention.
FIG. 15 is a characteristic diagram showing linear sensing characteristics of the magneto-impedance sensor according to the present invention.
FIG. 16 is a circuit block diagram using a magnetic impedance sensor.
FIG. 17 is a characteristic diagram showing the MI effect of an amorphous wire.
FIG. 18 is a front view showing another embodiment.
[Explanation of symbols]
1 ... MI sensor plate
2 ... Insulator layer
3. Insulator layer
4 ... Bias coil
5 ... Negative feedback coil
6 ... Bias coil terminal
7: Bias coil terminal
8 ... Negative feedback coil terminal
9: Negative feedback coil terminal
10 ... MI sensor terminal
11 ... MI sensor terminal
12 ... Insulating protective film
20 ... Non-magnetic substrate
21 ... Coil pattern

Claims (6)

A magnetic impedance sensor comprising a nonmagnetic substrate, a thin film magnetic core formed on the substrate, a first electrode and a second electrode provided at both longitudinal ends of the thin film magnetic core, wherein the thin film magnetic core A magnetic impedance sensor having a structure in which a bias coil and a negative feedback coil are alternately wound at regular intervals in the same direction with an insulator interposed therebetween .   2. The magneto-impedance sensor according to claim 1, wherein the bias coil and the negative feedback coil are formed of thin film coils.   2. The magneto-impedance sensor according to claim 1, wherein the bias coil and the negative feedback coil are respectively wound the same number of times around the thin film magnetic core.   A plurality of thin film conductors arranged in parallel and insulated from the thin film magnetic core on the lower surface of the thin film magnetic core, and a plurality of thin film conductors arranged in parallel and insulated from the thin film magnetic core on the upper surface of the thin film magnetic core. 3. The magnetic impedance sensor according to claim 2, wherein the bias coil and the negative feedback coil are formed by electrically connecting the tip portions of the thin film conductors on the upper surface and the lower surface of the thin film magnetic core.   The thin film magnetic core is formed of a NiFe, CoFeNi, FeP, FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB, CoFe plated film, or a CoZrNb, FeSiB, CoSiB amorphous sputtered film or a NiFe sputtered film. The magneto-impedance sensor according to claim 1.   2. The magnetic impedance sensor according to claim 1, wherein the thin film magnetic core is heat-treated in a magnetic field.

Images