JP2018044789A - Magnetic field detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field detector with which it is possible to reduce a measurement error due to the temperature dependency of an electric resistance value of a GMR element while suppressing an increase in cost.SOLUTION: Provided is a magnetic field detector 1, equipped with a plurality of GMR elements 2 having a giant magnetoresistance effect and a magnetic field generation unit 3 for applying bias magnetic fields Bb1-Bb4 to the plurality of GMR elements 2, for detecting the strength of a magnetic field Bm to be detected that is in a direction orthogonal to the bias magnetic fields Bb1-Bb4 by a change in the electrical resistance of the GMR elements 2. The magnetic field generation unit 3 includes a coil 31 for generating the bias magnetic fields Bb1-Bb4 and a power supply 32 for supplying an excitation current to the coil 31, the strength of the bias magnetic fields Bb1-Bb4 declining due to a reduction in the excitation current when the temperatures of the GMR elements 2 rise and a change rate of electrical resistance to a change in the strength of the magnetic field Bm to be detected drops.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic field detection apparatus using a GMR (Giant Magneto Resistive effect) element having a giant magnetoresistance effect.

  Conventionally, a magnetic field detection device using a GMR element is used for various applications such as measurement of the amount of current flowing through a conductor. Some of such magnetic field detection devices include a plurality of GMR elements, and a bridge circuit is configured by the plurality of GMR elements (see, for example, Patent Documents 1 and 2).

  The magnetic field detection device (current detection device) described in Patent Document 1 includes a plate-like bias magnet that generates a bias magnetic field in a direction orthogonal to a magnetic field to be detected (detected magnetic field). The intensity of the magnetic field to be detected is detected based on the change in electrical resistance accompanying the change in the direction of the combined magnetic field with the magnetic field depending on the intensity of the magnetic field to be detected.

  In addition, the magnetic field detection device (magnetic sensor) described in Patent Document 2 compensates for a measurement error caused by a change in the electrical resistance of the GMR element depending on the temperature, so that the temperature dependence obtained by heating and cooling the element. It has a control circuit unit (LSI) that corrects the output value based on characteristic compensation data (ratio of change in resistance value with respect to temperature change of the element). The GMR element and the control circuit portion (LSI region) are formed by being stacked on a substrate made of quartz glass or the like.

JP-A-2016-99291 International Publication No. 2004/051298

  When a control circuit unit that compensates for an error due to a temperature change of the GMR element is provided as in the magnetic field detection device described in Patent Document 2, the cost increases.

  Therefore, an object of the present invention is to provide a magnetic field detection apparatus capable of reducing a measurement error due to temperature dependency of an electrical resistance value of a GMR element while suppressing an increase in cost.

  In order to solve the above problems, the present invention includes a GMR element having a giant magnetoresistive effect, and a magnetic field generation unit that applies a bias magnetic field to the GMR element, and changes the electrical resistance of the GMR element to A magnetic field detection apparatus for detecting the intensity of a detected magnetic field in a direction orthogonal to a bias magnetic field, wherein the magnetic field generator includes a coil that generates the bias magnetic field and a power source that supplies an excitation current to the coil. When the temperature of the GMR element rises and the rate of change of the electrical resistance with respect to the change in the intensity of the detected magnetic field decreases, the magnetic field detection device reduces the intensity of the bias magnetic field due to the decrease in the excitation current To do.

  According to the magnetic field detection apparatus of the present invention, it is possible to reduce a measurement error due to the temperature dependence of the electrical resistance value of the GMR element while suppressing an increase in cost.

It is a schematic block diagram which shows typically the structure of the magnetic field detection apparatus which concerns on embodiment of this invention. It is sectional drawing of the magnetic field detection apparatus in the AA of FIG. It is explanatory drawing shown in order to demonstrate operation | movement of the bridge circuit comprised by the 1st thru | or 4th GMR element. (A) is a graph which shows the relationship between the intensity | strength of the to-be-detected magnetic field at the time of normal temperature and high temperature, and an output voltage when a bias magnetic field is constant irrespective of temperature. (B) is a graph showing the relationship between the intensity of the detected magnetic field and the output voltage at normal temperature and at high temperature when the saturation voltage of the sensor chip is assumed to be constant regardless of temperature. (C) is a graph showing the relationship between the intensity of the detected magnetic field and the output voltage. It is a schematic block diagram which shows typically the structure of the magnetic field detection apparatus which concerns on the modification of embodiment.

[Embodiment]
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram schematically showing a configuration of a magnetic field detection apparatus according to an embodiment of the present invention. 2 is a cross-sectional view of the magnetic field detection apparatus taken along line AA in FIG.

  This magnetic field detection device 1 seals a plurality of GMR elements 2 having a giant magnetoresistive effect, a magnetic field generator 3 that applies a bias magnetic field to the GMR elements 2, and a plurality of GMR elements 2 and coils 31 of the magnetic field generator 3. And a sealing material 4 to be stopped. In FIG. 1, the outer edge of the sealing material 4 is shown and the internal structure is illustrated. In FIG. 1, the coil 31 on the back side of the GMR element 2 is indicated by a broken line. The sealing material 4 has electrical insulation and is made of a resin material such as an epoxy resin.

  The plurality of GMR elements 2 and the coil 31 are sealed and integrated by a sealing material 4 to constitute a single sensor chip 10. The magnetic field detection device 1 is used to detect a magnetic field generated when a sensor chip 10 is disposed in the vicinity of a conductive path such as a bus bar and a current flows through the conductive path.

  The magnetic field generation unit 3 includes a coil 31 that generates a bias magnetic field and a power supply 32 that supplies an excitation current to the coil 31. The coil 31 is formed of a linear conductor in a spiral shape, and generates a bias magnetic field by an excitation current supplied from a power supply 32. In FIG. 2, this bias magnetic field is indicated by a broken line. The power supply 32 is a constant voltage source that outputs a constant voltage regardless of the magnitude of the excitation current.

  The coil 31 includes first and second linear portions 31a and 31b in which a conductor is formed in a linear shape, and first and second arc portions 31c and 31d in which a conductor is formed in a semicircular shape. doing. The first straight line portion 31a and the second straight line portion 31b are parallel to each other, and the first and second arc portions 31c and 31d are located between the first straight line portion 31a and the second straight line portion 31b. Is formed. In the present embodiment, the conductor makes six rounds around the central portion 310 of the coil 31 in a planar shape. That is, the number of turns of the coil 31 is six. As a material of the conductor, for example, copper (Cu), aluminum (Al), silver (Ag), alloy (CuAl), or the like can be used.

  The GMR element 2 is known per se, and the magnetization direction is changed by a fixed layer 201 whose magnetization direction is fixed, a bias magnetic field applied in a direction orthogonal to the magnetization direction of the fixed layer, and a detected magnetic field. And a nonmagnetic intermediate layer 203 interposed between the fixed layer 201 and the free layer 202 are laminated. The magnetic field detection device 1 detects the strength of the detected magnetic field in the direction orthogonal to the bias magnetic field by the change in the electrical resistance of the GMR element 2.

  In the present embodiment, the magnetic field detection device 1 has four GMR elements 2 having common electrical characteristics, and a bridge circuit 20 is configured by these GMR elements 2. Hereinafter, these four GMR elements 2 are referred to as first to fourth GMR elements 21 to 24, respectively.

  The first GMR element 21 and the second GMR element 22 are connected in series by a wiring 51 to constitute a half bridge circuit. The third GMR element 23 and the fourth GMR element 24 are connected in series by a wiring 52 to constitute a half bridge circuit. The first GMR element 21 and the third GMR element 23 are connected by a wiring 53. The second GMR element 22 and the fourth GMR element 24 are connected by a wiring 54.

  The first GMR element 21 and the second GMR element 22 are arranged so as to overlap the first straight line portion 31a. The third GMR element 23 and the fourth GMR element 24 are arranged so as to overlap the second straight line portion 31b. As shown in FIG. 2, since the direction of the current flowing through the first straight line portion 31a and the direction of the current flowing through the second straight line portion 31b are opposite to each other, the first GMR element 21 and the second GMR The direction of the bias magnetic field acting on the element 22 and the direction of the bias magnetic field acting on the third GMR element 23 and the fourth GMR element 24 are opposite to each other.

  The sensor chip 10 includes a power supply terminal 101, a ground terminal 102, first and second output terminals 103 and 104, and first and second power supply terminals 105 and 106 for supplying an excitation current to the coil 31. These terminals are exposed to the outside of the sealing material 4. A wiring 53 is connected to the power supply terminal 101, and a wiring 54 is connected to the ground terminal 102. A wiring 51 is connected to the first output terminal 103, and a wiring 52 is connected to the second output terminal 104. One end of the coil 31 is connected to the first power supply terminal 105, and the other end of the coil 31 is connected to the second power supply terminal 106.

  A DC voltage for operating the bridge circuit 20 is applied between the power supply terminal 101 and the ground terminal 102. The first power supply terminal 105 is connected to the positive terminal of the power supply 32, and the second power supply terminal 106 is connected to the negative terminal of the power supply 32.

  FIG. 3 is an explanatory diagram shown for explaining the operation of the bridge circuit 20 constituted by the first to fourth GMR elements 21 to 24.

  In FIG. 3, the detected magnetic fields in the first to fourth GMR elements 21 to 24 are denoted by reference numeral Bm, and the magnetization directions of the fixed layers 201 of the first to fourth GMR elements 21 to 24 are denoted by reference numerals Mp1 to Mp4. Is shown. Bias magnetic fields acting on the first to fourth GMR elements 21 to 24 are denoted by reference numerals Bb1 to Bb4, and a combined magnetic field of the detected magnetic field Bm and the bias magnetic fields Bb1 to Bb4 is denoted by reference numerals B1 to B4, respectively. .

  The application direction of the detected magnetic field Bm is parallel to the magnetization directions Mp1 to Mp4 of the fixed layer 201 of the first to fourth GMR elements 21 to 24 and orthogonal to the bias magnetic fields Bb1 to Bb4. The first to fourth GMR elements 21 to 24 are arranged side by side with the coil 31 in a direction orthogonal to the bias magnetic fields Bb1 to Bb4 and the detected magnetic field Bm.

  The magnetization directions Mp1 and Mp4 of the fixed layer 201 of the first and fourth GMR elements 21 and 24 are opposite to the magnetization directions Mp2 and Mp3 of the fixed layer 201 of the second and third GMR elements 32 and 33. In the example shown in FIG. 3, the direction of the detected magnetic field Bm is the same as the magnetization directions Mp1 and Mp4 of the fixed layer 201 of the first and fourth GMR elements 21 and 24, and the second and third GMR elements 32 , 23 are opposite to the magnetization directions Mp2, Mp3 of the fixed layer 201.

  The bias magnetic field Bb1 acting on the first GMR element 21 and the bias magnetic field Bb2 acting on the second GMR element 22 have the same direction and magnitude. The bias magnetic field Bb3 acting on the third GMR element 23 and the bias magnetic field Bb4 acting on the fourth GMR element 24 have the same direction and magnitude. The bias magnetic fields Bb1 and Bp4 and the bias magnetic fields Bb2 and Bp3 are the same in magnitude and opposite to each other.

  The intensity of the combined magnetic fields B1 to B4 of the bias magnetic fields Bb1 to Bb4 acting on the first to fourth GMR elements 21 to 24 and the detected magnetic field Bm is the square value of the intensity of the bias magnetic fields Bb1 to Bb4 and the detected magnetic field Bm. It is obtained by the square root of the square value of the intensity.

Further, in FIG. 3, the angles of the magnetization directions of the free layer 202 (the directions of the combined magnetic fields B1 to B2) with respect to the magnetization directions Mp1 to Mp4 of the fixed layers 201 of the first to fourth GMR elements 21 to 24, respectively. This is indicated by θ _{1 to} θ ₄ . When these angles θ _{1 to} θ ₄ are decreased, the current density distribution in the stacking direction of the fixed layer 201, the intermediate layer 203, and the free layer 202 is increased, and the electric resistance value is decreased. Conversely, when the angles θ _{1 to} θ ₄ are increased, the current density distribution in the stacking direction of the fixed layer 201, the intermediate layer 203, and the free layer 202 is narrowed, and the electrical resistance value is increased.

In the illustrated example of FIG. 3, when the detected magnetic field Bm increases, θ ₁ and θ ₄ decrease, the electrical resistance of the first and fourth GMR elements 21 and 24 decreases, and θ ₂ and θ ₃ increase. Thus, the electrical resistance of the second and third GMR elements 22 and 23 is increased. As a result, the potential difference between the wiring 51 and the wiring 52, which is the output voltage of the sensor chip 10, changes according to the magnitude and direction of the detected magnetic field Bm.

  By the way, the sensitivity of the first to fourth GMR elements 21 to 24 (the ratio of the change in electrical resistance to the change in the intensity of the detected magnetic field Bm) is the case where the intensity (magnetic flux density) of the detected magnetic field Bm is relatively small. The output voltage of the sensor chip 10 changes linearly as the strength of the detected magnetic field Bm increases or decreases. On the other hand, when the intensity of the detected magnetic field Bm increases, the output voltage of the sensor chip 10 is saturated and becomes a substantially constant value.

  In general, the sensitivity and saturation output of the GMR element decrease as the temperature increases. For this reason, the output voltage of the sensor chip 10 decreases as the temperature of the sensor chip 10 increases even if the detected magnetic field Bm and the bias magnetic fields Bb1 to Bb4 have constant intensities.

ここで、温度係数Ksatは負値である。 The saturated output when the output voltage of the sensor chip 10 is saturated is Vsat, the temperature coefficient is Ksat, the saturated output when the temperature of the sensor chip 10 is the reference temperature, Vsat0, and the difference between the temperature of the sensor chip 10 and the reference temperature is T Assuming that T = actual temperature of sensor chip 10−reference temperature, the saturation output Vsat can be expressed by the following approximate expression (1).

Here, the temperature coefficient Ksat is a negative value.

  FIG. 4A shows the intensity of the detected magnetic field Bm and the output voltage of the sensor chip 10 at normal temperature (for example, 25 ° C.) and high temperature (for example, 150 ° C.) when the bias magnetic fields Bb1 to Bb4 are constant. It is a graph which shows the relationship. As shown in FIG. 4A, the output voltage of the sensor chip 10 is lower and the saturation voltage is lower at high temperatures than at normal temperatures. Variation in the output voltage of the sensor chip 10 due to the change in sensitivity of the first to fourth GMR elements 21 to 24 accompanying such a temperature change becomes a measurement error. Note that, in FIG. 4A, fluctuations in the output voltage of the sensor chip 10 due to changes in temperature are exaggerated for clarity of explanation. The same applies to FIGS. 4B and 4C described below.

  In this embodiment, in order to suppress this measurement error, the temperature of the sensor chip 10 (specifically, the temperature of the first to fourth GMR elements 21 to 24) rises and the intensity of the detected magnetic field Bm changes. The magnetic field detection device 1 is configured so that the strength of the bias magnetic fields Bb1 to Bb4 decreases when the rate of change in electrical resistance of the first to fourth GMR elements 21 to 24 decreases.

Here, the principle that the measurement error is suppressed when the strength of the bias magnetic fields Bb1 to Bb4 decreases when the temperature rises will be described with reference to FIG. As described above, the electrical resistances of the first to fourth GMR elements 21 to 24 change according to the angles θ _{1 to} θ ₄ of the magnetization direction of the free layer 202 with respect to the magnetization directions Mp _{1 to} Mp ₄ of the fixed layer 201, and the angle θ _{1 to} θ ₄ vary depending on the relative relationship between the intensity of the bias magnetic fields Bb1 to Bb4 and the intensity of the detected magnetic field Bm. Therefore, if the intensity of the bias magnetic fields Bb1 to Bb4 is reduced, the angles θ ₁ to θ ₄ are likely to change according to the intensity of the detected magnetic field Bm, and apparently the first to fourth GMR elements 21 to 24 are apparent. The sensitivity to the detected magnetic field Bm increases. And the fall of the sensitivity by temperature rise and the raise of the sensitivity by the strength fall of bias magnetic field Bb1-Bb4 are offset, and the measurement error of the sensor chip 10 is suppressed.

  In the present embodiment, since the power source 32 is a constant voltage source, when the resistance value (DC resistance value) of the coil 31 increases due to temperature rise, the exciting current flowing through the coil 31 decreases. For this reason, the intensity | strength of bias magnetic field Bb1-Bb4 falls.

Assuming that the resistance value of the coil 31 is R, the temperature coefficient is α, the resistance value of the coil 31 at the reference temperature is R0, and the temperature difference between the coil 31 and the reference temperature is T, the resistance value R of the coil 31 is It can be represented by (2).

Further, assuming that the output voltage of the power supply 32 is Vb, the number of turns of the coil 31 is n, and the distance between the coil 31 and the free layer 202 of the first to fourth GMR elements 21 to 24 is r, the intensity of the bias magnetic fields Bb1 to Bb4. Bb can be expressed by the following formula (3).

When the above equation (2) is applied to this equation (3), the following equation (4) is obtained.

Here, assuming that the intensity Bb0 of the bias magnetic fields Bb1 to Bb4 at the reference temperature, the intensity Bb0 is expressed by the following equation (5).

すなわち、バイアス磁界Ｂｂ１〜Ｂｂ４の強度Ｂｂは、温度差Ｔの変数として表すことができる。 When this equation (5) is applied to the above equation (4), the following equation (6) is obtained.

That is, the intensity Bb of the bias magnetic fields Bb1 to Bb4 can be expressed as a variable of the temperature difference T.

  FIG. 4B shows the intensity of the detected magnetic field Bm at normal temperature (for example, 25 ° C.) and high temperature (for example, 70 ° C.), assuming that the saturation voltage of the sensor chip 10 is constant regardless of temperature. 4 is a graph showing a relationship with an output voltage of the sensor chip 10. As shown in FIG. 4B, the strength of the bias magnetic fields Bb1 to Bb4 decreases due to the temperature rise, so that the sensor chip 10 has a higher temperature at a higher temperature than at a normal temperature, contrary to the graph shown in FIG. The output voltage increases.

  FIG. 4C is a graph showing the relationship between the intensity of the detected magnetic field Bm and the output voltage of the sensor chip 10 according to the present embodiment. As shown in FIG. 4C, in this embodiment, the sensitivity decreases due to the temperature increase of the first to fourth GMR elements 21 to 24, and the strength of the bias magnetic fields Bb1 to Bb4 decreases due to the temperature increase of the coil 31. This offsets the increase in sensitivity due to the above, and the measurement error of the sensor chip 10 is suppressed.

  The magnetic field detection device 1 is accurate in that the sensitivity decreases due to the temperature increase of the first to fourth GMR elements 21 to 24 and the sensitivity increases due to the intensity decrease of the bias magnetic fields Bb1 to Bb4 due to the temperature increase of the coil 31. The number n of turns of the coil 31, the distance r between the coil 31 and the free layer 202, the temperature coefficient α of the coil 31, the resistance value R 0 of the coil 31 at the reference temperature, and the output voltage Vb of the power source 32 are adjusted so as to cancel each other. ing. Of the elements related to the intensity of these bias magnetic fields Bb1 to Bb4, the output voltage Vb of the power supply 32 is particularly easy to adjust.

(Modification)
FIG. 5 is a schematic configuration diagram schematically illustrating a configuration of a magnetic field detection device 1A according to a modification of the embodiment. This modification is different from the embodiment described with reference to FIG. 1 and the like in that the magnetic field generation unit 3 includes a thermal element 33 whose electric resistance increases as the temperature rises. The thermal element 33 is connected in series with the coil 31. In the illustrated example of FIG. 5, the thermal element 33 is connected between the − (minus) terminal of the power supply 32 and the second power supply terminal 106. According to this configuration, the exciting current flowing through the coil 31 is also reduced by the thermal element 33 when the temperature rises. For this reason, even if the strength of the bias magnetic fields Bb1 to Bb4 is not sufficiently reduced at the time of temperature rise only by the increase in electrical resistance accompanying the temperature rise of the coil 31, the temperature rise of the first to fourth GMR elements 21 to 24 is increased. It is possible to accurately offset the decrease in sensitivity due to the above and the increase in sensitivity due to the decrease in the intensity of the bias magnetic fields Bb1 to Bb4 due to the temperature increase of the coil 31.

(Summary of embodiment)
Next, the technical idea grasped from the embodiment described above will be described with reference to the reference numerals in the embodiment. However, each reference numeral in the following description does not limit the constituent elements in the claims to members or the like specifically shown in the embodiment.

[1] A GMR element (2) having a giant magnetoresistive effect, and a magnetic field generation unit (3) for applying a bias magnetic field (Bb1 to Bb4) to the GMR element (2). A magnetic field detection device (1) for detecting the intensity of a detected magnetic field in a direction orthogonal to the bias magnetic field (Bb1 to Bb4) by a change in electrical resistance, wherein the magnetic field generation unit (3) includes the bias magnetic field (Bb1). To Bb4) and a power source (32) for supplying an exciting current to the coil (31), and the temperature of the GMR element (2) rises to increase the intensity of the detected magnetic field. The magnetic field detector (1), wherein when the rate of change of the electrical resistance with respect to the change of the current decreases, the intensity of the bias magnetic field (Bb1 to Bb4) decreases due to the decrease of the excitation current.

[2] The magnetic field detection device (1) according to [1], wherein the power source (32) is a constant voltage source that outputs a constant voltage.

[3] First to fourth GMR elements (21 to 24) are provided, and the first to fourth GMR elements (21 to 24) constitute a bridge circuit (20), and the first [1], wherein the fourth to fourth GMR elements (21 to 24) are arranged side by side with the coil (31) in a direction perpendicular to the bias magnetic fields (Bb1 to Bb4) and the detected magnetic field. Or the magnetic field detection apparatus (1) as described in [2].

[4] The magnetic field generator (3) has a thermal element (33) whose electrical resistance increases with an increase in temperature, and the coil (31) and the thermal element (33) are connected in series. The magnetic field detection device (1A) according to any one of [1] to [3].

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1,1A ... Magnetic field detection apparatus 2 ... GMR element 20 ... Bridge circuit 21-24 ... 1st thru | or 4th GMR element 3 ... Magnetic field generation part 31 ... Coil 32 ... Power source 33 ... Thermal element Bb1-Bb4 ... Bias magnetic field Bm ... Detected magnetic field

Claims (4)

A GMR element having a giant magnetoresistive effect and a magnetic field generator for applying a bias magnetic field to the GMR element, and detecting the strength of the detected magnetic field in a direction perpendicular to the bias magnetic field by a change in electrical resistance of the GMR element A magnetic field detection device
The magnetic field generation unit includes a coil that generates the bias magnetic field, and a power source that supplies an excitation current to the coil.
When the temperature of the GMR element rises and the rate of change of the electrical resistance with respect to the change in the intensity of the detected magnetic field decreases, the intensity of the bias magnetic field decreases due to the decrease in the excitation current.
Magnetic field detection device. The power source is a constant voltage source that outputs a constant voltage.
The magnetic field detection apparatus according to claim 1. First to fourth GMR elements are provided, a bridge circuit is constituted by the first to fourth GMR elements, and the first to fourth GMR elements include the bias magnetic field and the detection target. Arranged alongside the coil in a direction perpendicular to the magnetic field,
The magnetic field detection apparatus according to claim 1 or 2. The magnetic field generator has a thermal element whose electrical resistance increases with a rise in temperature, and the coil and the thermal element are connected in series.
The magnetic field detection apparatus according to any one of claims 1 to 3.

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