JP2009250931A - Magnetic sensor, operation method thereof, and magnetic sensor system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic sensor, capable of detecting a low magnetic field with high sensitivity, and performing low power consumption operation, and to provide an operation method thereof. <P>SOLUTION: The magnetic sensor 40 comprises magnetoresistance elements R1-R4 having full-bridge structure, and a bias magnetic field generation coil 18, disposed in parallel with the longitudinal direction of the magnetic resistance elements R1-R4, and applying two-directional opposite bias magnetic fields to the magnetoresistance elements R1-R4, in which the bias current of the bias magnetic field generation coil 18 is controlled, to vary the sensitivity and detection range. The operation method of the magnetic sensor is also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic sensor, an operation method thereof, and a magnetic sensor system, and more particularly to a magnetic sensor capable of detecting a low magnetic field such as geomagnetism with high sensitivity, an operation method thereof, and a magnetic sensor system.

  An electric field E of a ferromagnetic element that appears when a direct current I and an external magnetic field H are applied to a ferromagnetic element such as NiFe permalloy or Fe, Co alloy is known as a galvanomagnetic effect. It is shown that E = ρi + a (i × H) + bH (i · H) by L. Landau. Here, i is a current value per unit area, ρ is a resistivity, and a and b are physical constants. Of these, the third term on the right side is the magnetoresistive (MR) effect.

  According to the MR effect, when a current is applied in the easy axis direction (usually the longitudinal direction of the element) and a magnetic field is applied in a direction perpendicular thereto, the magnetic field is symmetrical with respect to the external magnetic field H as shown in FIG. The resistance value R of MR decreases. In FIG. 21, Hk represents a saturation magnetic field.

However, the sensitivity is as small as about 0.1 (% / Oe), for example. In order to detect a low magnetic field such as geomagnetism (for example, about 0.4 Oe in Japan), a bias magnetic field H _B is usually applied to an external magnetic field H as shown in FIG. On the other hand, it is necessary to increase the output sensitivity of the MR resistance value R.

  Furthermore, such an MR element has a large change due to temperature, and in order to convert a resistance value change into a voltage, as shown in FIGS. 23A and 23B, a configuration in which two elements are arranged orthogonally, Alternatively, as shown in FIGS. 24A and 24B, the sensitivity and accuracy are enhanced by a configuration in which four elements are arranged in a full bridge type.

  Therefore, in order to easily apply a bias magnetic field to the MR elements arranged orthogonally in a uniform direction, it is common to dispose the bias coil at 45 ° (see, for example, Patent Document 1 and Patent Document 2). .

  Further, since the MR element has hysteresis characteristics due to its magnetization history, a method of alternately applying saturation magnetization and bias magnetization in both positive and negative directions and reading the output when bias magnetization is applied has been proposed (for example, Patent Document 1). , Patent Document 3 and Non-Patent Document 1).

Further, since the magnetization reversal occurs, the detection magnetic field range becomes narrow.
JP 05-157565 A Japanese Patent No. 3573100 Japanese Patent No. 4006674 Osamu Shimoe, Yasunori Abe, Yukimasa Moronowaki, Shigenao Hashizume, “Orientation Sensor Using Magnetoresistive Element”, Hitachi Metals Technical Report Vo1, 18 (2002) p. 37-42

  However, when MR elements are arranged orthogonally and a bias magnetic field is applied uniformly in the 45 ° direction, the amount of change in resistance (the slope of the RH characteristic graph) that leads to the sensitivity of the magnetic sensor increases, but large bias magnetization is required. The current consumption of the sensor increases.

  The object of the present invention is to provide a wide linear approximation range of output by external magnetic field strength, limit the detectable range narrowly, and can detect low magnetic fields with high sensitivity and low power consumption even if the bias magnetic field is reduced. It is an object of the present invention to provide an operation magnetic sensor and an operation method thereof.

  The object of the present invention is to provide a wide linear approximation range of output by external magnetic field strength, limit the detectable range narrowly, and can detect low magnetic fields with high sensitivity and low power consumption even if the bias magnetic field is reduced. An object of the present invention is to provide a magnetic sensor system equipped with an operating magnetic sensor.

  According to one aspect of the present invention for achieving the above-described object, a magnetoresistive element and a bias that is arranged in parallel with the longitudinal direction of the magnetoresistive element and applies two opposite bias magnetic fields to the magnetoresistive element A magnetic sensor comprising a magnetic field generating coil is provided.

  According to another aspect of the present invention, a magnetoresistive element in which four elements connected to each other in a full-bridge configuration are arranged on two sets of substrates, and two opposite directions arranged in parallel to the longitudinal direction of the magnetoresistive element. Provided with a bias magnetic field generating planar coil for applying a bias magnetic field to the magnetoresistive element, and arranging the bias magnetic field generating planar coil on the magnetoresistive element to form a biaxial electronic compass. Is done.

  According to another aspect of the present invention, a bias magnetic field generating coil is arranged in parallel with the longitudinal direction of the magnetoresistive element, and two opposite bias magnetic fields are applied to the magnetoresistive element and saturated in the positive direction. After applying magnetization in pulses, applying bias magnetization in the same direction as the positive direction to detect the first output voltage, and applying saturation magnetization in the negative direction opposite to the positive direction in pulses Then, applying a bias magnetization in the same direction as the negative direction to detect a second output voltage, and a difference between the first output voltage and an average value of the first output voltage and the second output voltage. A method of operating a magnetic sensor is provided that includes calculating a positive external magnetic field strength.

  According to another aspect of the present invention, a magnetic sensor according to any one of claims 1 to 9, a differential amplifier connected to the output of the magnetic sensor and amplifying the differential output of the magnetic sensor; There is provided a magnetic sensor system comprising an AD converter that digitally converts an analog signal of an output voltage of the differential amplifier, and a CPU that is connected to the output of the AD converter and executes digital signal arithmetic processing.

  According to the magnetic sensor of the present invention, a wide linear approximation range of the output by the external magnetic field strength is obtained, the detectable range is limited, the low magnetic field can be detected with high sensitivity even if the bias magnetic field is reduced, and Enables low power consumption operation.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention. The technical idea of the present invention is the arrangement of each component as described below. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

[First embodiment]
As shown in FIG. 1A, the MR element applied to the magnetic sensor according to the first embodiment of the present invention includes two MR elements R1, R2 between a power supply terminal 12 and a ground (GND) terminal 14. A configuration in which the elements are arranged on the substrate 10 in series via the midpoint extraction terminal 16 is provided.

Alternatively, the MR element applied to the magnetic sensor according to the first embodiment may have a configuration in which MR elements are arranged on a substrate in a four-element full bridge configuration as shown in FIG. Good. In FIG. 1B, two elements MR elements R1 and R2 are arranged in series on the substrate 10 between the power supply terminal 12 ₁ and the GND terminal 14 ₁ via the midpoint extraction terminal 16 ₁ . FIG. 1 (a) in which two elements MR elements R3 and R4 are arranged in series via a midpoint extraction terminal 16 ₂ between a power supply terminal 12 ₂ and a GND terminal 14 ₂ in the same configuration as in a). With the same configuration as in a), the MR element is formed in a four-element full bridge configuration.

  As shown in FIG. 1C, the bias magnetic field generating coil 18 applied to the magnetic sensor according to the first embodiment has a configuration in which the winding directions are opposite to each other (the winding direction is reversed on the left and right).

  As shown by the arrow in FIG. 1 (c), the winding direction shown in FIG. 1 (c) is reversed (the left and right winding directions are reversed) in the bias magnetic field generating coil 18. By accommodating the substrate 10 on which the MR element shown in FIG. 5B is housed, a uniaxial magnetic sensor 40 is obtained.

  As described above, the uniaxial magnetic sensor 40 in which the substrate 10 on which the MR element shown in FIG. 1A or 1B is arranged in the bias magnetic field generating coil 18 shown in FIG. As shown in FIG.

  The magnetic sensor 40 according to the first embodiment includes an MR element and a bias magnetic field generating coil 18 that is arranged in parallel with the longitudinal direction of the MR element and applies opposite bias magnetic fields to the MR element. .

  The sensitivity and detection range can be varied by controlling the bias current of the bias magnetic field generating coil 18.

  A uniaxial magnetic sensor is formed by combining four MR elements in a full bridge and storing them in a coil 18 for generating a bias magnetic field of an external winding (reverse winding direction on the left and right). Further, the voltage can be divided and output by two MR elements.

[Second Embodiment]
A schematic configuration of the bias magnetic field generating planar coil 20 applied to the magnetic sensor according to the second embodiment of the present invention is expressed as shown in FIG. Further, the configuration of the MR element applied to the magnetic sensor according to the second embodiment, in which the MR element having a four-element full bridge configuration is arranged on two sets of substrates, is expressed as shown in FIG. The

  The magnetic sensor 40 according to the second embodiment is arranged in parallel with the MR element 30 in which four elements connected to each other in a full bridge configuration are arranged on two substrates and in parallel with the longitudinal direction of the MR element 30. A bias magnetic field generating planar coil 20 that applies a bias magnetic field in two directions to the MR element 30.

  In FIG. 3, A +, A− and B +, B− represent the generation directions of the opposite two bias magnetic fields. In FIG. 4, (A1, A3), (A2, A4), (B1, B3), (B2, B4) are MR elements in which four elements connected to each other in a full bridge configuration are arranged on two sets of substrates. The directions in which the bias magnetic field is generated in two opposite directions when the planar coil 20 for generating a bias magnetic field is arranged on the element 30 in parallel with the longitudinal direction of the MR element 30 are shown.

  A magnetic sensor that forms the electronic compass of a biaxial magnetic sensor by arranging the planar coil 20 for generating a bias magnetic field on the MR element 30 can be obtained.

  It is possible to make the sensitivity and the detection range variable by controlling the bias current of the planar coil 20 for generating the bias magnetic field.

  This is an example of hysteresis characteristics of an MR element. In a stripe-shaped MR element, the resistance value R of the MR element and the applied magnetic field H when the angle formed by the longitudinal direction (easy magnetization direction) and the applied magnetic field H is inclined by 90 °. The relationship is expressed as shown in FIG. When the external magnetic field H is changed from the positive direction to the negative direction and then changed from the negative direction to the positive direction, the operating point follows a path of A → B → C → D → A in FIG.

  This is an example of hysteresis characteristics of an MR element. In a stripe-shaped MR element, when the angle between the longitudinal direction (easy magnetization direction) and the applied magnetic field H is inclined by 45 °, the resistance value R of the MR element and the applied magnetic field H The relationship is expressed as shown in FIG. When the external magnetic field H is changed from the positive direction to the negative direction and then changed from the negative direction to the positive direction, the operating point follows a path of A → B → C → D → A in FIG.

(Operation method of magnetic sensor)
The magnetic sensor operating method according to the second embodiment of the present invention includes a step of arranging a bias magnetic field generating coil parallel to the longitudinal direction of the MR element, and applying two opposite bias magnetic fields to the MR element. Applying a saturation magnetization in the positive direction for a short time and then applying a bias magnetization in the same direction as the positive direction to detect the first output voltage Vout (+), and a negative direction opposite to the positive direction In addition, after applying saturation magnetization in a pulse for a short time, applying bias magnetization in the same direction as the negative direction to detect the second output voltage Vout (−), the first output voltage Vout (+), And calculating a positive external magnetic field intensity from a difference between an average value of the first output voltage Vout (+) and the second output voltage Vout (−).

As a comparative example of the present invention, when an MR element in which the angle formed between the longitudinal direction (easy magnetization direction) and the applied magnetic field H is inclined by 90 ° is used in a stripe-shaped MR element, as shown in FIG. Since it has hysteresis characteristics, a schematic diagram of a pulse current waveform conducted to a magnetic sensor to which such an MR element is applied is expressed as shown in FIG. That is, the pulse current applied to a magnetic sensor according to a comparative example of the present invention, the MR element, the bias current I _A was conducting bias magnetic field generating plane coil 20 in the reverse direction and reverse direction. Alternatively, and a bias current -I _A is made conductive bias magnetic field generating plane coil 20 in the forward and backward directions.

On the other hand, a schematic diagram of a pulse current waveform applied to the magnetic sensor according to the second embodiment of the present invention is expressed as shown in FIG. Pulse current to be applied to a magnetic sensor according to a second embodiment of the present invention is a bias current I _B to conduct a bias magnetic field generating plane coil 20 in the positive direction in the same direction. Alternatively, the bias current -I _B was conducting bias magnetic field generating plane coil 20 in the negative direction in the same direction.

After applying short saturation magnetization (a) positive pulsed, in a positive direction in the same direction as the bias current I _B is made conductive bias magnetic field generating plane coil 20, a bias magnetization, the first output voltage Vout (+) is detected.

(B) Next, in the negative direction of the direction opposite to the forward direction, after applying a short time saturation magnetization in a pulse form, the bias current -I _B into conduction bias magnetic field generating plane coil 20 in the reverse direction in the same direction Then, bias magnetization is applied, and the second output voltage Vout (−) is detected.

(C) Next, the first output voltage Vout (+) and the difference between the average value of the first output voltage Vout (+) and the second output voltage Vout (−) Calculate the external magnetic field strength in the direction.

V _out = Vout (+) − {(Vout (+) + Vout (−)) / 2} (1)

As shown in FIG. 9, the circuit configuration of the uniaxial magnetic sensor applied to the magnetic sensor according to the second embodiment is a half bridge of MR element MR1 and MR element MR2, and a half of MR element MR3 and MR element MR4. It includes the MR element MR1～MR4 full-bridge structure comprising a bridge, a bias magnetic field H _B to be applied to the external magnetic field Hex and ,, MR element MR1～MR4 applied to the MR element MR1～MR4. Arrows represent the direction of the external magnetic field Hex and bias magnetic field H _B is applied to each of the MR elements MR1～MR4.

  Between the midpoint potential extraction terminal A of the MR elements MR1 and MR2 and the midpoint potential extraction terminal B of the MR elements MR3 and MR4, a differential amplifier 44, which is connected to the input terminals, is connected. Yes.

The magnetic field applied to the MR element MR1 is H _B + Hex, the magnetic field applied to the MR element MR2 is −H _B + Hex, the magnetic field applied to the MR element MR3 is −H _B + Hex, and the magnetic field applied to the MR element MR4 is H _B + Hex.

Due to the parallel arrangement of the two-direction (forward / reverse) bias magnetic field H _B and the MR elements MR1 to MR4, the magnetization conditions for the MR elements MR1 to MR4 are in conflict with each other as shown in FIG. Is detected by the differential amplifier 44 in the detection direction (positive bias direction), and the midpoint potential extraction terminal A of the MR element MR2 and the midpoint potential extraction terminal B of the MR element MR3 and MR element MR4 are detected. The intensity of the external magnetic field Hex can be measured.

The relationship between the resistance value R of the MR element applied to the magnetic sensor according to the second embodiment and the applied magnetic field H is expressed as shown in FIG. Further, the relationship between the output voltage _{Vout of the} magnetic sensor according to the second embodiment and the externally applied magnetic field _Hex is expressed as shown in FIG.

The value of the bias magnetic field H _B (= bias coil current) (90 °) at this time is smaller than the value of the bias magnetic field H _B (45 °) at the time of 45 ° arrangement, as shown in FIG. Further, as shown in FIG. 11, in the relationship between the output voltage _Vout and the externally applied magnetic field _Hex , the linear approximation area at Vout (90 °) is larger than the linear approximation area at Vout (45 °). A wide linear approximation area is obtained.

In the relationship between the output voltage V _{out of the} magnetic sensor according to the second embodiment and the externally applied magnetic field H _ex , the bias voltage is set to V _B2 <V _B1 when the parallel arrangement (90 °) is set, and the bias magnetic field is set to An example of increasing the sensitivity by setting a smaller value is schematically represented as shown in FIG.

Even if the detectable range is narrowly limited, in the case of an application for detecting a low magnetic field with higher sensitivity, for example, an electronic compass for detecting geomagnetism, the bias magnetic field H _B is reduced to increase sensitivity (ΔV _out / ΔHex). be able to.

  A planar coil is suitable for generating opposite bias magnetic fields.

  A planar coil is formed on a magnetoresistive element, after forming an insulating layer, and then forming a conductor such as Cu or Al by film formation → photolithography patterning, which is suitable in terms of cost, but was produced in a sheet shape. A coil may be attached.

(Geomagnetic sensor)
An MR change type geomagnetic sensor formed on a ceramic substrate will be described below as a prototype of the magnetic sensor according to the second embodiment.

  In the production of the MR change type magnetic sensor, the yield is improved by adopting the thick film screen printing technique. As a prototype of the magnetic sensor according to the second embodiment, a magnetic field at a geomagnetic level is detected with a high sensitivity of 0.89 mV / V / G by a geomagnetic sensor formed on a ceramic substrate.

  The screen printing method is a method of transferring a paste on a screen plate to a substrate through an opening with a squeegee, and can form a thick film only at a necessary portion, and is a highly productive method with no material waste.

  As a prototype of the magnetic sensor according to the second embodiment, in the MR change type geomagnetic sensor formed on the ceramic substrate, the same screen printing method is applied to the ground on which several hundreds of magnetic thin films are formed by the MR method. Thus, a thick glaze (glass) film is formed and only necessary portions are extremely flattened.

  A permalloy-based thin film (Fe27% -Ni72.5% -Co0.5%) was used for the MR element. Utilizing magnetic anisotropy in which MR changes depending on the easy magnetization direction of the magnetic material and the applied magnetic field, a weak current is passed through the MR element to detect a change in resistance value.

  As a prototype example of the magnetic sensor according to the second embodiment of the present invention, an arrangement configuration example of MR elements applied to the geomagnetic sensor is schematically represented as shown in FIG. The generating planar coil 20 is schematically represented as shown in FIG. Further, a schematic bird's-eye view of the geomagnetic sensor is expressed as shown in FIG. A schematic circuit configuration of the geomagnetic sensor is expressed as shown in FIG.

  The pattern configuration of the MR element was a folded pattern as shown in FIG. 13A in order to obtain shape anisotropy and a desired resistance value. The configuration of FIG. 13A corresponds to the configuration of FIG. This pattern is configured as a full bridge with four MR elements for each of the X and Y axes, a total of eight MR elements are manufactured and arranged in different directions, and different signals are extracted in response to changes in the magnetic field, thereby detecting the XY direction. It becomes possible.

  The MR element used for the trial production has a pattern as shown in FIG. FIG. 13A shows the arrangement of MR elements. As shown in FIG. 14, the planar coil 20 for generating a bias magnetic field shown in FIG. 13B is arranged in an overlapping manner on the upper part (Z-axis direction) of the MR element after completion of the MR element. As a result, current flows between the MR element and the bias magnetic field generating planar coil 20 in directions parallel to each other (directions A to B in FIG. 14).

As shown in FIG. 15, a bias magnetic field H _B is generated from the bias magnetic field generating planar coil 20, and the resistance value R of the MR element changes when the strength of the magnetic field is adjusted. Since the MR element has a resistance value change amount with respect to the magnetic field change amount that is not constant in the whole magnetic field region due to material characteristics, the sensitivity of the magnetic sensor can be improved by fixing the bias magnetic field H _B in the magnetic field region having the largest resistance value change amount. Can be maximized.

  It can also be seen that the MR elements MR1 to MR4 have different magnetic field environments by being arranged as shown in FIG.

(Geomagnetic sensor fabrication method)
(A) A glaze layer is screen-printed on an alumina substrate and the substrate is flattened.

(B) A lift-off resist is formed on the glaze layer, and permalloy is formed by sputtering and lift-off. The film thickness t is about 300 mm, for example. The pattern width L1 is about 40 μm, for example.

(C) Thereafter, annealing treatment is performed in order to increase the sensitivity of the formed permalloy magnetic sensor. The mechanism by which the sensitivity is improved by annealing is that annealing suppresses the growth of the FeN ₃ crystal, enlarges the crystal grain size, removes residual stress and internal strain, and reduces crystal defects.

(D) Since this crystal has a structure that adversely affects the MR characteristics, the annealed sample is subjected to X-ray diffraction analysis, and more effective annealing conditions are determined using the result as an index.

In general, annealing is performed under vacuum, but in the method of manufacturing the magnetic sensor according to the second embodiment, it was performed in a reducing atmosphere as a countermeasure against oxidation. The condition is that the temperature is raised from room temperature to about 400 ° C. in about 20 minutes under a reduced pressure of about 10 ⁻⁴ Torr in a hydrogen atmosphere and held at about 400 ° C. for about 3 hours.

(E) After the heat treatment, the temperature is lowered to room temperature in about 2 hours and taken out.

(F) Next, the bias magnetic field generating planar coil 20 is fabricated. In the method of manufacturing the magnetic sensor according to the second embodiment, a simple coil was produced for evaluation. A copper wire having a wire diameter of φ 0.02 mm is put on a 21-turn plane on an insulating film. The bias magnetic field generating planar coil 20 is in close contact with the upper part of the Z axis of the MR element for measurement.

(Experimental result)
-MR characteristic measurement method-
The material property evaluation results of the prototype geomagnetic sensor will be described below.

  As a prototype of the magnetic sensor according to the second embodiment, a surface micrograph of the MR element of the geomagnetic sensor formed on the ceramic substrate is represented as shown in FIG. A current of 100 μA is passed between the terminal A and the terminal B in FIG. 16 (the MR element R3 and the MR element R4 in FIG. 13A are connected in series), and a magnetic field is applied in the range of ± 200 G. A change in resistance value was read as a potential difference between the terminals (terminals A and C are both ends of the MR element R3 in FIG. 13A), and the material characteristics of the element were evaluated.

A photograph of the state of the magnetic sensor 40 mounted with the bias magnetic field generating planar coil 20 is shown in FIG. The bias coil current I _coil flowing through the bias magnetic field generating planar coil 20 was in the range of 15 to 40 mA, and the optimum bias magnetic field conditions for measuring geomagnetism were sought.

  Furthermore, the geomagnetism was measured by rotating the magnetic sensor in a horizontal plane. In the detection sensitivity evaluation, a magnetic field was applied with a Helmholtz coil to measure the output characteristics.

-Measurement results-
FIG. 18 is a measurement result of the geomagnetic sensor according to the second embodiment, and the relationship between the rotation angle θ (deg.) With respect to geomagnetism and the output voltage V _out (mV) is expressed as shown in FIG. When the bias coil current I _coil is a constant current of 15 mA, the relationship between the rotation angle θ with respect to the geomagnetism and the output voltage V _out has a sinusoidal characteristic.

Further, the relationship between the Helmholtz coil current (applied magnetic field) and the output voltage _Vout is expressed as shown in FIG. Linearity was exhibited in the range of ± 2 G, and the sensitivity was 0.89 mV / V / G.

  From FIG. 18 and FIG. 19, it was confirmed that the magnetic sensor according to the second embodiment can be detected in a weak magnetic field environment at the geomagnetic level. Similarly, it is possible to determine the azimuth from the arc tangent function of two orthogonal outputs. Therefore, a magnetic sensor that detects the direction by geomagnetism was obtained.

  The base part of the magnetic sensor was manufactured using thick film screen printing, and the geomagnetic sensor was manufactured to obtain the following results.

  Thick film screen printing can form derivative thicknesses and glazes of several tens of μm, and the handling properties are good throughout the entire prototype.

  The geomagnetic sensor succeeded in detecting a magnetic field at the geomagnetic level in the uniaxial direction, and was able to realize a high sensitivity of 0.89 mV / V / G.

(Magnetic sensor system)
The magnetic sensor system to which the magnetic sensor according to the first or second embodiment of the present invention is applied is connected to the magnetic sensor 40 and the output of the magnetic sensor 40 as shown in FIG. A differential amplifier 44 that amplifies the dynamic output, an AD converter 46 that digitally converts the analog signal of the output voltage _Vout of the differential amplifier 44, and a central operation that is connected to the output of the AD converter 46 and executes digital signal arithmetic processing And a processing unit (CPU) 48. As shown in FIG. 20, a bias drive circuit 42 may be connected to the magnetic sensor 40 and the CPU 48.

  In FIG. 20, in addition to the integrated magnetic sensor 40, a differential amplifier 44, an AD converter 46, a CPU 48, and the like can also be integrated.

  According to the present invention, a wide linear approximation range of the output by the external magnetic field strength is obtained, the detectable range is narrowly limited, and even if the bias magnetic field is reduced, a low magnetic field can be detected with high sensitivity and low power consumption. A magnetic sensor of operation and a method of operation thereof can be provided.

  In addition, according to the present invention, a magnetic sensor system equipped with such a magnetic sensor can be provided.

[Other embodiments]
As described above, the present invention has been described according to the first to second embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  As described above, the present invention naturally includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  The magnetic sensor of the present invention can be applied to industrial control devices, and more specifically, it can be used for proximity sensors that can be used to detect the opening and closing of folding portable devices, headings for map information of mobile phones, and navigation devices. There is a wide range of industrial applicability, such as an electronic compass and a magnetic sensor capable of grasping a posture in a game machine.

The configuration of the MR element applied to the magnetic sensor according to the first embodiment of the present invention, wherein (a) a configuration example in which two MR elements are arranged on a substrate, (b) four MR elements are full. Configuration example arranged on a substrate in a bridge configuration, (c) Configuration example of a coil for generating a bias magnetic field in which the winding directions are opposite to each other (the winding direction is reversed on the left and right). FIG. 1B is a configuration example of the magnetic sensor according to the first embodiment of the present invention, and FIG. 1C or FIG. 1B is placed in a bias magnetic field generating coil whose winding directions are opposite to each other shown in FIG. The structural example of the uniaxial magnetic sensor which accommodated the board | substrate which has arrange | positioned MR element shown in FIG. The typical structural example of the planar coil for bias magnetic field generation applied to the magnetic sensor which concerns on the 2nd Embodiment of this invention. 6 is a configuration example of an MR element applied to a magnetic sensor according to a second embodiment of the present invention, in which MR elements having a four-element full bridge configuration are arranged on two sets of substrates. It is an example of hysteresis characteristics of an MR element, and in a stripe-shaped MR element, the relationship between the MR resistance value and the applied magnetic field when the angle formed by the longitudinal direction (easy magnetization direction) and the applied magnetic field is inclined by 90 °. This is an example of hysteresis characteristics of an MR element, and in a stripe-shaped MR element, the relationship between the resistance value of the MR element and the applied magnetic field when the angle between the longitudinal direction (easy magnetization direction) and the applied magnetic field is inclined by 45 ° . The schematic diagram of the pulse current waveform applied to the magnetic sensor which concerns on the comparative example of this invention. The schematic diagram of the pulse current waveform applied to the magnetic sensor which concerns on the 2nd Embodiment of this invention. It is a circuit block diagram of the magnetic sensor of the uniaxial structure applied to the magnetic sensor which concerns on the 2nd Embodiment of this invention, Comprising: The circuit block diagram which applies MR element of a 4 element full bridge structure. Explanatory drawing of the relationship between the resistance value R of the MR element applied to the magnetic sensor which concerns on the 2nd Embodiment of this invention, and the applied magnetic field H. FIG. Explanatory drawing of the relationship between the output voltage _{Vout of the} magnetic sensor which concerns on the 2nd Embodiment of this invention, and the externally applied magnetic field _Hex . Description of an example of increasing the sensitivity by reducing the bias magnetic field in the parallel arrangement (90 °) in the relationship between the output voltage _{Vout of the} magnetic sensor according to the second embodiment of the present invention and the externally applied magnetic field _Hex. Figure. As a prototype of the magnetic sensor according to the second embodiment of the present invention, it is a geomagnetic sensor formed on a ceramic substrate, and (a) a schematic arrangement configuration example of an MR element to be applied, and (b) a bias to be applied. The typical structural example of the coil for magnetic field generation. The typical bird's-eye view of the geomagnetic sensor formed on the ceramic substrate as a trial manufacture example of the magnetic sensor which concerns on the 2nd Embodiment of this invention. The typical circuit block diagram of the geomagnetic sensor formed on the ceramic substrate as a prototype of the magnetic sensor which concerns on the 2nd Embodiment of this invention. The surface micrograph of the MR element of the geomagnetic sensor formed on the ceramic substrate as a prototype of the magnetic sensor which concerns on the 2nd Embodiment of this invention. The surface micrograph which has arrange | positioned the coil on the MR element of the geomagnetic sensor formed on the ceramic substrate as a prototype of the magnetic sensor which concerns on the 2nd Embodiment of this invention. As a prototype example of the magnetic sensor according to the second embodiment of the present invention, it is a measurement result of a geomagnetic sensor formed on a ceramic substrate, and the rotation angle θ (deg.) With respect to the geomagnetism and the output voltage V _out (mV). Relationship with. FIG. 6 shows a measurement result of a geomagnetic sensor formed on a ceramic substrate as a prototype of the magnetic sensor according to the second embodiment of the present invention, and shows the relationship between Helmholtz coil current (applied magnetic field) and output voltage _Vout . The typical block block diagram of the magnetic sensor system to which the magnetic sensor which concerns on the 1st thru | or 2nd embodiment of this invention is applied. The schematic diagram of the relationship between the magnetoresistive value R of MR element, and the external magnetic field H. FIG. FIG. 5 is an explanatory diagram of an example in which a sensitivity is increased by applying a bias magnetic field in a diagram showing a relationship between a magnetoresistance value R of an MR element and an external magnetic field H. It is an example of arrangement | positioning of MR element, Comprising: (a) The structural example which arrange | positioned two MR elements orthogonally, (b) The equivalent circuit schematic of (a). It is an example of arrangement | positioning of MR element, Comprising: (a) The structural example which arrange | positioned MR element in 4 element full bridge type, (b) The equivalent circuit diagram of (a).

Explanation of symbols

10 ... substrate 12, 12 _1, 12 ₂ ... power supply terminal 14, 14 _1, 14 ₂ ... ground (GND) terminal 16, 16 _1, 16 ₂ ... midpoint potential drawing terminal 18 ... bias field generating coil 20 ... bias magnetic field Planar coil 30 for generation, R1 to R8, MR1 to MR4, MR element 40, magnetic sensor 42, bias drive circuit 44, differential amplifier 46, AD converter 48, central processing unit (CPU)

Claims (12)

A magnetoresistive element;
A magnetic sensor comprising: a bias magnetic field generating coil that is arranged in parallel with a longitudinal direction of the magnetoresistive element and applies bias magnetic fields in two opposite directions to the magnetoresistive element.   The magnetic sensor according to claim 1, wherein the sensitivity and the detection range are made variable by controlling a bias current of the bias magnetic field generating coil.   The magnetic sensor according to claim 1, wherein the magnetoresistive element includes two elements connected in series to each other on a substrate.   The magnetic sensor according to claim 1, wherein the magnetoresistive element includes four elements connected to each other in a full bridge configuration on a substrate.   2. The magnetic sensor according to claim 1, wherein the bias magnetic field generating coil is formed by connecting two coils whose winding directions are opposite to each other in series.   The magnetic sensor according to claim 5, comprising a uniaxial configuration in which the magnetoresistive element is housed in the bias magnetic field generating coil.   The magnetic sensor according to claim 1, wherein the bias magnetic field generating coil is a planar coil.   The magnetic sensor according to claim 1, wherein the magnetoresistive element includes four elements connected to each other in a full bridge configuration on a two-set substrate. A magnetoresistive element in which four elements connected to each other in a full-bridge configuration are arranged on two sets of substrates;
A bias magnetic field generating planar coil that is disposed in parallel with the longitudinal direction of the magnetoresistive element and applies bias magnetic fields in two opposite directions to the magnetoresistive element, and the bias magnetic field generating planar coil is the magnetoresistive element A magnetic sensor, characterized in that it is arranged on top to form a biaxial electronic compass.   The magnetic sensor according to claim 9, wherein the sensitivity and the detection range are made variable by controlling a bias current of the planar coil for generating the bias magnetic field. Disposing a bias magnetic field generating coil parallel to the longitudinal direction of the magnetoresistive element, and applying two opposite bias magnetic fields to the magnetoresistive element;
Applying a saturation magnetization in the positive direction in a pulsed manner and then applying a bias magnetization in the same direction as the positive direction to detect a first output voltage;
Applying a saturation magnetization in a pulsed manner in a negative direction opposite to the positive direction and then applying a bias magnetization in the same direction as the negative direction to detect a second output voltage;
A method of operating a magnetic sensor, comprising: calculating a positive external magnetic field intensity from a difference between the first output voltage and an average value of the first output voltage and the second output voltage. The magnetic sensor according to any one of claims 1 to 10,
A differential amplifier connected to the output of the magnetic sensor and amplifying the differential output of the magnetic sensor;
An AD converter for digitally converting an analog signal of the output voltage of the differential amplifier;
A magnetic sensor system comprising: a CPU that is connected to an output of the AD converter and executes digital signal arithmetic processing.