WO2011111537A1 - Current sensor - Google Patents

Abstract

The disclosed current sensor can measure a current with high precision as a midpoint potential difference output changes proportionally to an induced magnetic field generated by the current being measured. Said current sensor has a magnetic-field detection bridge circuit comprising two magnetoresistive elements, the resistances of which change due to the application of the induced magnetic field from the current being measured, and two fixed-resistance elements. The outputs of the magnetic-field detection bridge circuit are taken from between the two magnetoresistive elements and between the two fixed-resistance elements. Both magnetoresistive elements have the same resistance change rate, and each magnetoresistive element has: a self-pinned ferromagnetic fixed layer comprising a first ferromagnetic film and a second ferromagnetic film coupled antiferromagnetically with an antiparallel coupling film interposed therebetween; a nonmagnetic interlayer; and a soft-magnetic free layer. The magnetization directions of the ferromagnetic fixed layers in the magnetoresistive elements are in 180° opposition to each other.

Description

Current sensor

The present invention relates to a current sensor using a magnetoresistive effect element (TMR element, GMR element).

In an electric vehicle, a motor is driven using electricity generated by an engine, and the magnitude of the current for driving the motor is detected by, for example, a current sensor. As this current sensor, a magnetic core having a notch (core gap) in part is arranged around a conductor, and a magnetic detection element is arranged in the core gap.

As a magnetic sensing element of a current sensor, a magnetoresistive effect element (GMR element, TMR) having a laminated structure of a fixed magnetic layer whose magnetization direction is fixed, a nonmagnetic layer, and a free magnetic layer whose magnetization direction varies with respect to an external magnetic field. Element) or the like. In such a current sensor, a magnetoresistive effect element and a fixed resistance element constitute a full bridge circuit (Patent Document 1).

As a current sensor in which a magnetic detection bridge circuit is configured by a magnetoresistive effect element and a fixed resistance element, for example, there are magnetic balanced current sensors shown in FIGS. In the magnetic balanced current sensor, the feedback coil is energized by the voltage difference obtained by the magnetic detection bridge circuit 2, and the induction magnetic field generated by the measured current I energizing the conductor 1 and the cancellation magnetic field generated by the feedback coil cancel each other. The current to be measured is measured based on the current flowing through the feedback coil when the equilibrium state is reached.

The magnetic detection bridge circuit 2 of the current sensor shown in FIG. 9 includes one magnetoresistive effect element 201 and three fixed resistance elements 202a to 202c. In the magnetic detection bridge circuit 2, the resistance value of the magnetoresistive effect element 201 in the zero magnetic field and the resistance values of the fixed resistance elements 202a to 202c are the same (R _com ). The output between the fixed resistance elements 202b and 202c is Out1, and the output between the magnetoresistance effect element 201 and the fixed resistance element 202a is Out2. The resistance value of the fixed resistance element 202b is R1, the resistance value of the fixed resistance element 202a is R2, the resistance value of the fixed resistance element 202c is R3, and the resistance value of the magnetoresistive effect element 201 is R4.

Here, when the resistance change amount of the magnetoresistive effect element 21 due to the induced magnetic field generated by the measured current I is ΔR, the bridge midpoint potential difference (Out1-Out2) is obtained as follows.
Resistance between Vdd and Gnd1 = R1 + R3 = 2 × R _com
Resistance between Vdd and Gnd2 = R2 + (R4−ΔR) = 2 × R _com −ΔR
Out1 potential = (R _com ) / (2 × R _com ) × Vdd
Out2 potential = (R _com −ΔR) / (2 × R _com −ΔR) × Vdd
Out1-Out2 potential difference = ΔR / {2 × (2 × R _com −ΔR)} × Vdd

The magnetic detection bridge circuit 2 of the current sensor shown in FIG. 10 includes two magnetoresistive effect elements 201a and 201b and two fixed resistance elements 202a and 202b. In the magnetic detection bridge circuit 2, the resistance values of the magnetoresistive effect elements 201a and 201b in the zero magnetic field and the resistance values of the fixed resistance elements 202a and 201b are the same (R _com ). The resistance change rates of the magnetoresistive effect elements 201a and 201b are the same. Further, the output between the magnetoresistive effect element 201b and the fixed resistance element 202b is set as Out1, and the output between the magnetoresistive effect element 201a and the fixed resistance element 202a is set as Out2. The resistance value of the magnetoresistive effect element 201b is R1, the resistance value of the fixed resistance element 202a is R2, the resistance value of the fixed resistance element 202b is R3, and the resistance value of the magnetoresistive effect element 201a is R4.

Here, when the resistance change amount of the magnetoresistive effect elements 201a and 201b due to the induced magnetic field generated by the current I to be measured is ΔR, the bridge midpoint potential difference (Out1−Out2) is obtained as follows.
Resistance between Vdd and Gnd1 = (R1−ΔR) + R3 = 2 × R _com −ΔR
Resistance between Vdd and Gnd2 = R2 + (R4−ΔR) = 2 × R _com −ΔR
Out1 potential = (R _com ) / (2 × R _com −ΔR) × Vdd
Out2 potential = (R _com −ΔR) / (2 × R _com −ΔR) × Vdd
Out1-Out2 potential difference = ΔR / (2 × R _com −ΔR) × Vdd

JP 2007-248054 A

However, in the configuration of the magnetic detection bridge circuit shown in FIG. 9 and FIG. 10, the term of ΔR is included in the denominator of the bridge midpoint potential difference equation. For this reason, there is a problem that the output of the midpoint potential difference does not show a complete proportional change with respect to the induced magnetic field generated by the current I to be measured, and the measurement accuracy is lowered.

The present invention has been made in view of the above points, and provides a current sensor capable of performing current measurement with high accuracy by showing a proportional change in the output of the midpoint potential difference with respect to the induced magnetic field generated by the current to be measured. The purpose is to do.

The current sensor according to the present invention includes two magnetoresistive elements and resistance elements that change in resistance value when an induction magnetic field is applied from a current to be measured, and outputs between the two magnetoresistive elements and A current sensor having a magnetic field detection bridge circuit having an output between two fixed resistance elements, wherein the two magnetoresistive effect elements have the same rate of change in resistance, and have a first strong resistance through an antiparallel coupling film. A self-pinned ferromagnetic pinned layer formed by antiferromagnetically coupling the magnetic film and the second ferromagnetic film, a nonmagnetic intermediate layer, and a soft magnetic free layer; The magnetization direction of the ferromagnetic pinned layer of the effect element is different from each other by 180 °.

According to this configuration, the magnetization directions of the self-pinned ferromagnetic pinned layers of the two magnetoresistive effect elements that output the midpoint potential in the magnetic detection bridge circuit are different from each other by 180 °, and thus are generated by the current to be measured. The output of the midpoint potential difference shows a proportional change with respect to the induced magnetic field, and current measurement can be performed with high accuracy.

In the current sensor of the present invention, a feedback coil that is disposed in the vicinity of the magnetoresistive effect element and generates a canceling magnetic field that cancels the induced magnetic field, and a magnetic shield that attenuates the induced magnetic field and enhances the canceling magnetic field. And a current flowing in the feedback coil when the feedback coil is energized by a voltage difference obtained by the magnetic detection bridge circuit to achieve an equilibrium state in which the induction magnetic field and the cancellation magnetic field cancel each other. Preferably, the current to be measured is measured based on the measured current.

In the current sensor of the present invention, the two magnetoresistive elements have a shape formed by folding a plurality of strip-like long patterns arranged so that their longitudinal directions are parallel to each other, and the induced magnetic field and It is preferable that the cancel magnetic field is applied so as to be along a direction orthogonal to the longitudinal direction.

In the current sensor of the present invention, it is preferable that the current to be measured is measured by the magnetic field detection bridge circuit based on outputs of the two magnetoresistive elements proportional to the induced magnetic field.

In the current sensor of the present invention, the first ferromagnetic film is made of a CoFe alloy containing 40 atomic% to 80 atomic% of Fe, and the second ferromagnetic film is made of 0 atomic% to 40 atomic% of Fe. It is preferable to be comprised with the CoFe alloy containing.

In the current sensor of the present invention, the magnetic shield is preferably made of a high permeability material selected from the group consisting of an amorphous magnetic material, a permalloy magnetic material, and an iron microcrystalline material.

The current sensor according to the present invention includes two magnetoresistive elements and resistance elements that change in resistance value when an induction magnetic field is applied from a current to be measured, and outputs between the two magnetoresistive elements and A magnetic field detection bridge circuit having an output between two fixed resistance elements, the two magnetoresistive effect elements have the same resistance change rate, and the first ferromagnetic film and the first ferromagnetic film through an antiparallel coupling film; A ferromagnetic pinned layer formed by antiferromagnetically coupling the two ferromagnetic films, a nonmagnetic intermediate layer, and a soft magnetic free layer. Since the magnetization directions of the magnetic pinned layers are 180 ° different from each other, the output of the midpoint potential difference shows a proportional change with respect to the induced magnetic field generated by the current to be measured, and current measurement can be performed with high accuracy.

It is a figure which shows the magnetic balance type current sensor which concerns on embodiment of this invention. It is a figure which shows the magnetic balance type current sensor which concerns on embodiment of this invention. It is sectional drawing which shows the magnetic balance type current sensor shown in FIG. It is a figure which shows the magnetic detection bridge circuit in the magnetic balance type current sensor which concerns on embodiment of this invention. It is a figure which shows the relationship between a midpoint potential difference and the induced magnetic field by a to-be-measured electric current. It is a figure which shows the magnetic detection bridge circuit in the magnetic proportional type current sensor which concerns on embodiment of this invention. (A)-(c) is a figure for demonstrating the manufacturing method of the magnetoresistive effect element in the magnetic balance type current sensor which concerns on embodiment of this invention. (A)-(c) is a figure for demonstrating the manufacturing method of the magnetoresistive effect element in the magnetic balance type current sensor which concerns on embodiment of this invention. It is a figure which shows the magnetic detection bridge circuit in the conventional magnetic balance type current sensor. It is a figure which shows the magnetic detection bridge circuit in the conventional magnetic balance type current sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, the case where the current sensor according to the present invention is a magnetic balance type current sensor will be described.

1 and 2 are diagrams showing a magnetic balance type current sensor according to an embodiment of the present invention. In the present embodiment, the magnetic balance type current sensor shown in FIGS. 1 and 2 is disposed in the vicinity of the conductor 11 through which the measured current I flows. This magnetic balance type current sensor includes a feedback circuit 12 that generates a magnetic field (cancellation magnetic field) that cancels the induced magnetic field caused by the current I to be measured flowing through the conductor 11. The feedback circuit 12 includes a feedback coil 121 wound in a direction to cancel the magnetic field generated by the current I to be measured, two magnetoresistive elements 122a and 122b, and two fixed resistance elements 123a and 123b.

The feedback coil 121 is a planar coil. In this configuration, since there is no magnetic core, the feedback coil can be manufactured at low cost. Further, as compared with the case of the toroidal coil, it is possible to prevent the canceling magnetic field generated from the feedback coil from spreading over a wide range and to avoid affecting the peripheral circuits. Furthermore, compared to the toroidal coil, when the current to be measured is an alternating current, the cancellation magnetic field can be easily controlled by the feedback coil, and the current flowing for the control is not so large. About these effects, it becomes so large that a to-be-measured electric current becomes a high frequency by alternating current. When the feedback coil 121 is configured by a planar coil, the planar coil is preferably provided so that both an induction magnetic field and a cancellation magnetic field are generated in a plane parallel to the plane of the planar coil.

The resistance values of the magnetoresistive effect elements 122a and 122b are changed by applying an induction magnetic field from the current I to be measured. The two magnetoresistance effect elements 122a and 122b and the fixed resistance elements 123a and 123b constitute a magnetic field detection bridge circuit. By using a magnetic field detection bridge circuit having a magnetoresistive effect element as described above, a highly sensitive magnetic balance type current sensor can be realized.

This magnetic field detection bridge circuit has two outputs that generate a voltage difference corresponding to the induced magnetic field generated by the current I to be measured. In the magnetic field detection bridge circuit shown in FIG. 2, a power source Vdd is connected to a connection point between the magnetoresistive effect element 122a and the fixed resistance element 123a, and between the magnetoresistive effect element 122b and the fixed resistance element 123b. A ground (GND) is connected to the connection point. Further, in this magnetic field detection bridge circuit, one output (Out1) is taken out from the connection point between the fixed resistance elements 123a and 123b, and the other output (Out2) is outputted from the connection point between the magnetoresistance effect elements 122a and 122b. I'm taking it out. These two outputs are amplified by the amplifier 124 and supplied to the feedback coil 121 as a current (feedback current). This feedback current corresponds to a voltage difference according to the induced magnetic field. At this time, a cancellation magnetic field that cancels the induction magnetic field is generated in the feedback coil 121. Then, the current to be measured is measured by the detection unit (detection resistor R) based on the current flowing through the feedback coil 121 when the induced magnetic field and the canceling magnetic field cancel each other.

FIG. 3 is a sectional view showing the magnetic balance type current sensor shown in FIG. As shown in FIG. 3, in the magnetic balanced current sensor according to the present embodiment, a feedback coil, a magnetic shield, and a magnetic field detection bridge circuit are formed on the same substrate 21. In the configuration shown in FIG. 3, the feedback coil is arranged between the magnetic shield and the magnetic field detection bridge circuit, and the magnetic shield is arranged on the side close to the current I to be measured. That is, the magnetic shield, the feedback coil, and the magnetoresistive element are arranged in this order from the side close to the conductor 11. Thereby, the magnetoresistive effect element can be furthest away from the conductor 11, and the induction magnetic field applied to the magnetoresistive effect element from the current I to be measured can be reduced. Moreover, since the magnetic shield can be brought closest to the conductor 11, the attenuation effect of the induced magnetic field can be further enhanced. Therefore, the cancellation magnetic field from the feedback coil can be reduced.

The layer structure shown in FIG. 3 will be described in detail. In the magnetic balance type current sensor shown in FIG. 3, a thermal silicon oxide film 22 that is an insulating layer is formed on a substrate 21. An aluminum oxide film 23 is formed on the thermal silicon oxide film 22. The aluminum oxide film 23 can be formed by a method such as sputtering. Further, a silicon substrate or the like is used as the substrate 21.

On the aluminum oxide film 23, magnetoresistance effect elements 122a and 122b and fixed resistance elements 123a and 123b are formed, and a magnetic field detection bridge circuit is formed. As the magnetoresistive elements 122a and 122b, TMR elements (tunnel magnetoresistive elements), GMR elements (giant magnetoresistive elements), and the like can be used. The film configuration of the magnetoresistive element used in the magnetic balance type current sensor according to the present invention will be described later.

As shown in the enlarged view of FIG. 2, the magnetoresistive effect element has a shape (a meander shape) formed by folding a plurality of strip-like long patterns (stripes) arranged so that their longitudinal directions are parallel to each other. The GMR element is preferably included. In this meander shape, the sensitivity axis direction (Pin direction) is a direction (stripe width direction) orthogonal to the longitudinal direction (stripe longitudinal direction) of the long pattern. In this meander shape, an induced magnetic field and a cancel magnetic field are applied along a direction (stripe width direction) orthogonal to the stripe longitudinal direction.

In this meander shape, in consideration of linearity, the width in the pin direction is preferably 1 μm to 10 μm. In this case, in consideration of linearity, it is desirable that the longitudinal direction is both perpendicular to the direction of the induction magnetic field and the direction of the cancellation magnetic field. By adopting such a meander shape, the output of the magnetoresistive effect element can be taken with a smaller number of terminals (two terminals) than the Hall element.

Further, an electrode 24 is formed on the aluminum oxide film 23. The electrode 24 can be formed by photolithography and etching after forming an electrode material.

A polyimide layer 25 is formed as an insulating layer on the aluminum oxide film 23 on which the magnetoresistive effect elements 122a and 122b, the fixed resistance elements 123a and 123b, and the electrode 24 are formed. The polyimide layer 25 can be formed by applying and curing a polyimide material.

A silicon oxide film 27 is formed on the polyimide layer 25. The silicon oxide film 27 can be formed by a method such as sputtering.

A feedback coil 121 is formed on the silicon oxide film 27. The feedback coil 121 can be formed by photolithography and etching after the coil material is deposited. Alternatively, the feedback coil 121 can be formed by photolithography and plating after forming a base material.

Further, a coil electrode 28 is formed on the silicon oxide film 27 in the vicinity of the feedback coil 121. The coil electrode 28 can be formed by photolithography and etching after forming an electrode material.

A polyimide layer 29 is formed as an insulating layer on the silicon oxide film 27 on which the feedback coil 121 and the coil electrode 28 are formed. The polyimide layer 29 can be formed by applying and curing a polyimide material.

A magnetic shield 30 is formed on the polyimide layer 29. As a material constituting the magnetic shield 30, a high magnetic permeability material such as an amorphous magnetic material, a permalloy magnetic material, or an iron microcrystalline material can be used.

A silicon oxide film 31 is formed on the polyimide layer 29. The silicon oxide film 31 can be formed by a method such as sputtering. Contact holes are formed in predetermined regions of the polyimide layer 29 and the silicon oxide film 31 (the region of the coil electrode 28 and the region of the electrode 24), and electrode pads 32 and 26 are formed in the contact holes, respectively. Photolithography and etching are used for forming the contact holes. The electrode pads 32 and 26 can be formed by photolithography and plating after forming an electrode material.

In the magnetic balance type current sensor having such a configuration, as shown in FIG. 3, the induced magnetic field A generated from the current I to be measured is received by the magnetoresistive element, and the induced magnetic field is fed back from the feedback coil 121. The cancel magnetic field B is generated, and the two magnetic fields (the induction magnetic field A and the cancel magnetic field B) are canceled and adjusted appropriately so that the magnetic field applied to the magnetoresistive effect element 121 becomes zero.

The magnetic balanced current sensor of the present invention has a magnetic shield 30 adjacent to the feedback coil 121 as shown in FIG. The magnetic shield 30 attenuates the induced magnetic field generated from the current I to be measured and applied to the magnetoresistive effect element (in the magnetoresistive effect element, the direction of the induced magnetic field A and the direction of the canceling magnetic field B is opposite), and the feedback coil The cancellation magnetic field B from 121 can be enhanced (in the magnetic shield, the direction of the induction magnetic field A and the direction of the cancellation magnetic field B are the same). Therefore, since the magnetic shield 30 functions as a magnetic yoke, the current flowing through the feedback coil 121 can be reduced, and power saving can be achieved. Further, the magnetic shield 30 can reduce the influence of an external magnetic field.

The magnetic balance type current sensor having the above configuration uses a magnetic field detection bridge circuit having a magnetoresistive effect element, particularly a GMR element or a TMR element, as a magnetic detection element. Thereby, a highly sensitive magnetic balance type current sensor can be realized. In addition, this magnetic balance type current sensor is composed of two magnetoresistive effect elements having the same magnetic film detection bridge circuit. In addition, the magnetic balanced current sensor having the above-described configuration can be reduced in size because the feedback coil 121, the magnetic shield 30, and the magnetic field detection bridge circuit are formed on the same substrate. Furthermore, since this magnetic balance type current sensor has no magnetic core, it can be reduced in size and cost.

The film configuration of the magnetoresistive effect element used in the present invention is, for example, as shown in FIG. That is, the magnetoresistive effect element has a laminated structure provided on the substrate 41 as shown in FIG. In FIG. 7A, for simplicity of explanation, the substrate 41 is shown with the base layer other than the magnetoresistive effect element omitted. The magnetoresistive effect element includes a seed layer 42a, a first ferromagnetic film 43a, an antiparallel coupling film 44a, a second ferromagnetic film 45a, a nonmagnetic intermediate layer 46a, soft magnetic free layers (free magnetic layers) 47a and 48a. And a protective layer 49a.

The seed layer 15 is made of NiFeCr or Cr. The protective layer 20 is made of Ta or the like. In the laminated structure, an underlayer composed of a nonmagnetic material such as at least one element of Ta, Hf, Nb, Zr, Ti, Mo, and W, for example, between the substrate 41 and the seed layer 42a. May be provided.

In this magnetoresistive effect element, the first ferromagnetic film 43a and the second ferromagnetic film 45a are antiferromagnetically coupled via the antiparallel coupling film 44a, so-called self-pinned ferromagnetic A fixed layer (SFP: Synthetic Ferri Pinned layer) is configured.

In this ferromagnetic pinned layer, the thickness of the antiparallel coupling film 44a is set to 0.3 nm to 0.45 nm, or 0.75 nm to 0.95 nm, so that the first ferromagnetic film 43a and the second strong film can be strengthened. Strong antiferromagnetic coupling can be brought about between the magnetic film 45a.

Further, the magnetization amount (Ms · t) of the first ferromagnetic film 43a and the magnetization amount (Ms · t) of the second ferromagnetic film 45a are substantially the same. That is, the difference in magnetization between the first ferromagnetic film 43a and the second ferromagnetic film 45a is substantially zero. For this reason, the effective anisotropic magnetic field of the SFP layer is large. Therefore, the magnetization stability of the ferromagnetic pinned layer (Pin layer) can be sufficiently ensured without using an antiferromagnetic material. This is because the film thickness of the first ferromagnetic film is t ₁ , the film thickness of the second ferromagnetic film is t _2, and the magnetization per unit volume of both layers and the induced magnetic anisotropy constant are Ms, This is because the effective anisotropic magnetic field of the SFP layer is represented by the following expression (1) when K is assumed.
Formula (1)
eff Hk = 2 (K · t ₁ + K · t ₂ ) / (Ms · t ₁ −Ms · t ₂ )
Therefore, the magnetoresistive effect element used for the magnetic balance type current sensor of the present invention has a film configuration that does not have an antiferromagnetic layer.

The Curie temperature (Tc) of the first ferromagnetic film 43a and the Curie temperature (Tc) of the second ferromagnetic film 45a are substantially the same. Thereby, even in a high temperature environment, the difference in magnetization (Ms · t) between the films 43a and 45a becomes substantially zero, and high magnetization stability can be maintained.

The first ferromagnetic film 43a is preferably made of a CoFe alloy containing 40 atomic% to 80 atomic% of Fe. This is because a CoFe alloy having this composition range has a large coercive force and can stably maintain magnetization with respect to an external magnetic field. The second ferromagnetic film 45a is preferably made of a CoFe alloy containing 0 atomic% to 40 atomic% of Fe. This is because a CoFe alloy having this composition range has a small coercive force, and is easily magnetized in an antiparallel direction (a direction different by 180 °) with respect to the direction in which the first ferromagnetic film 43a is preferentially magnetized. is there. As a result, it is possible to further increase Hk represented by the above formula (1). Further, by limiting the second ferromagnetic film 45a to this composition range, it is possible to increase the resistance change rate of the magnetoresistive effect element.

A magnetic field is applied to the first ferromagnetic film 43a and the second ferromagnetic film 45a in the meandering stripe width direction during the film formation, and the first ferromagnetic film 43a and the second strong film 43a after the film formation are applied. It is preferable that induced magnetic anisotropy is imparted to the magnetic film 45a. As a result, both films 43a and 45a are magnetized antiparallel to the stripe width direction. Further, since the magnetization directions of the first ferromagnetic film 43a and the second ferromagnetic film 45a are determined by the magnetic field application direction during the formation of the first ferromagnetic film 43a, the first ferromagnetic film 43a is formed. It is possible to form a plurality of magnetoresistive elements having ferromagnetic pinned layers with different magnetization directions on the same substrate by changing the magnetic field application direction during film formation.

The antiparallel coupling film 44a of the ferromagnetic fixed layer is made of Ru or the like. The soft magnetic free layers (free layers) 47a and 48a are made of a magnetic material such as a CoFe alloy, a NiFe alloy, or a CoFeNi alloy. The nonmagnetic intermediate layer 46a is made of Cu or the like. In addition, a magnetic field is applied to the soft magnetic free layers 47a and 48a in the longitudinal direction of the meander-shaped stripe during film formation, and induced magnetic anisotropy is imparted to the soft magnetic free layers 47a and 48a after film formation. It is preferable. Thereby, in the magnetoresistive effect element, the resistance is linearly changed with respect to the external magnetic field (magnetic field from the current to be measured) in the stripe width direction, and the hysteresis can be reduced. In such a magnetoresistive effect element, a spin valve configuration is adopted by a ferromagnetic fixed layer, a nonmagnetic intermediate layer, and a soft magnetic free layer.

As an example of the film configuration of the magnetoresistive effect element used in the magnetic balance type current sensor of the present invention, for example, NiFeCr (seed layer: 5 nm) / Fe ₇₀ Co ₃₀ (first ferromagnetic film: 1.65 nm) / Ru (Anti-parallel coupling film: 0.4 nm) / Co ₉₀ Fe ₁₀ (second ferromagnetic film: 2 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: 7 nm) / Ta (protective layer: 5 nm).

In the magnetic balanced current sensor of the present invention, as shown in FIG. 4, the magnetization directions (second ferromagnetic properties) of the ferromagnetic pinned layers of the two magnetoresistive effect elements 122a and 122b that output the midpoint potential (Out2). The magnetization directions of the films (Pin 2) are 180 ° different from each other (anti-parallel). Further, the resistance change rates of the two magnetoresistive elements 122a and 122b are the same. The magnetoresistive elements 122a and 122b preferably exhibit the same rate of change in resistance at the same magnetic field strength when the angle of the applied magnetic field with respect to the ferromagnetic fixed layer is the same.

In the magnetic balanced current sensor having the two magnetoresistive effect elements 122a and 122b and the two fixed resistance elements 123a and 123b arranged in this manner, the voltage difference between the two outputs (Out1, Out2) of the magnetic detection bridge circuit is A canceling magnetic field is applied from the feedback coil 121 to the magnetoresistive effect element so as to be zero, and the current value flowing through the feedback coil 121 at that time is detected, thereby measuring the current to be measured. That is, as shown in FIG. 4, when the current to be measured flows in the direction of the arrow, the induced magnetic field A and the cancel magnetic field B are applied to the two magnetoresistive effect elements 122a and 122b (Out2 side), respectively. At this time, when the combined magnetic field intensity of the induced magnetic field generated by the measured current and the canceling magnetic field becomes zero, the midpoint potential difference of the magnetic detection bridge circuit becomes zero.

In such a magnetic detection bridge circuit, the resistance values of the fixed resistance elements 123a and 123b in the zero magnetic field and the resistance values of the magnetoresistance effect elements 122a and 122b are the same (R _com ). Further, the resistance change rates of the magnetoresistive effect elements 122a and 122b are the same. Also, the output between the fixed resistance element 123a and the fixed resistance element 123b is Out1, and the output between the magnetoresistance effect element 122a and the magnetoresistance effect element 122b is Out2. The resistance value of the fixed resistance element 123a is R1, the resistance value of the magnetoresistance effect element 122a is R2, the resistance value of the fixed resistance element 123b is R3, and the resistance value of the magnetoresistance effect element 122b is R4.

Here, when the resistance change amount of the magnetoresistive effect elements 122a and 122b due to the induced magnetic field generated by the current I to be measured is ΔR, the bridge midpoint potential difference (Out1-Out2) is obtained as follows.
Resistance between Vdd and Gnd1 = R1 + R3 = 2 × R _com
Resistance between Vdd and Gnd2 = (R2 + ΔR) + (R4−ΔR) = 2 × R _com
Out1 potential = R3 / (R1 + R3) × Vdd = (R _com ) / (2 × R _com ) × Vdd
Out2 potential = (R4-ΔR) / (R2 + R4) × Vdd
= (R _com -ΔR) / (2 × R _com ) × Vdd
Out1-Out2 potential difference = ΔR / (2 × R _com ) × Vdd

As described above, the magnetic balanced current sensor of the present invention does not include the term ΔR in the denominator of the bridge midpoint potential difference equation. For this reason, the output of the midpoint potential difference shows a proportional change with respect to the induced magnetic field generated by the current I to be measured. As a result, current measurement can be performed with high accuracy.

A magnetic balance type current sensor using two magnetoresistive effect elements can also be manufactured by a type of magnetoresistive effect element in which the magnetization of the fixed magnetic layer is fixed by an antiferromagnetic film. In this case, the exchange coupling direction of the pinned magnetic layer (Pin layer) of one of the two magnetoresistive effect elements is antiparallel to the exchange coupling direction of the pinned magnetic layer of the other magnetoresistive effect element. Therefore, it is necessary to apply laser local annealing or install a magnetic field application coil adjacent to the magnetoresistive effect element. Such a method can be applied to manufacture a sensor or device having a magnetoresistive element near the outermost surface of the chip. However, as in the case of the magnetic balanced current sensor of the present invention, It cannot be applied to the fabrication of a device having a thick organic insulating film, a thick feedback coil, and a thick magnetic shield film. For this reason, the configuration of the present invention is particularly useful in the magnetic balanced current sensor according to the present invention.

When the magnetic detection bridge circuit and the feedback coil are integrally formed on the same substrate as in the magnetic balance type current sensor according to the present invention, it is necessary to completely insulate both of them, so that an organic insulating film such as a polyimide film is used. Will separate them. The organic insulating film is generally formed by applying a heat treatment at 200 ° C. or higher after being applied by spin coating or the like. Since the organic insulating film is formed in a subsequent process of forming the magnetic detection bridge circuit, the magnetoresistive element is also heated together. In the manufacturing process of a magnetoresistive effect element that fixes the magnetization of the pinned magnetic layer with an antiferromagnetic film, a magnetic field is applied so that the characteristics of the pinned magnetic layer do not deteriorate due to the thermal history of the organic insulating film formation process. It is necessary to heat-treat it. In the magnetic balance type current sensor according to the present invention, since the antiferromagnetic film is not used, it is possible to maintain the characteristics of the fixed magnetic layer without performing a heat treatment while applying a magnetic field. Therefore, deterioration of the hysteresis of the soft magnetic free layer can be suppressed.

Further, since the magnetoresistive effect element of the magnetic balance type current sensor according to the present invention does not contain an antiferromagnetic material, the material cost and the manufacturing cost can be suppressed.

Here, examples carried out to clarify the effects of the present invention will be described. For the magnetically balanced current sensor (invention) having the magnetic detection bridge circuit shown in FIG. 4, the relationship between the induced magnetic field (measured current magnetic field) due to the current to be measured and the midpoint potential difference of the magnetic detection bridge circuit was examined. . The result is shown in FIG. Further, a magnetic balance type current sensor (conventional (GMR × 1)) having a magnetic detection bridge circuit shown in FIG. 9 and a magnetic balance type current sensor (conventional (GMR × 2)) having a magnetic detection bridge circuit shown in FIG. Similarly, the relationship between the induced magnetic field due to the current to be measured (current magnetic field to be measured) and the midpoint potential difference of the magnetic detection bridge circuit was examined. The results are also shown in FIG.

As can be seen from FIG. 5, the magnetic balanced current sensor of the present invention (the present invention) has a midpoint potential difference that changes linearly with respect to the induced magnetic field caused by the current to be measured, and performs current measurement with high accuracy. Can do. On the other hand, in the conventional magnetic balance type current sensor (conventional (GMR × 1), conventional (GMR × 2)), the midpoint potential difference changes in a curved line with respect to the induced magnetic field due to the current to be measured, and the accuracy is high. Current measurement cannot be performed.

The present invention can be applied not only to a magnetic balance type current sensor, but also to a magnetic proportional type current sensor that measures a current to be measured by outputs of two magnetoresistive elements proportional to an induced magnetic field. This magnetic proportional current sensor has a configuration excluding the feedback coil 121 and the magnetic shield film 30 in the configuration shown in FIG. Further, as shown in FIG. 6, the magnetic detection bridge circuit of the magnetic proportional current sensor has two magnetoresistance effect elements 122a and 122b and two fixed resistance elements 123a and 123b. Further, the magnetization directions of the ferromagnetic pinned layers (magnetization direction of the second ferromagnetic film: Pin2) of the two magnetoresistive effect elements 122a and 122b that output the midpoint potential (Out2) are 180 ° different from each other (reversely). parallel). The resistance change rates of the two magnetoresistive elements 122a and 122b are the same.

Even in a magnetic proportional current sensor having such a magnetic detection bridge circuit, the equation for obtaining the Out1-Out2 potential difference does not include the term ΔR in the denominator of the bridge midpoint potential difference equation. For this reason, the output of the midpoint potential difference shows a proportional change with respect to the induced magnetic field generated by the current I to be measured. As a result, current measurement can be performed with high accuracy. The present invention is particularly useful in a magnetic proportional current sensor.

7 (a) to (c) and FIGS. 8 (a) to (c) are views for explaining a method of manufacturing a magnetoresistive element in the current sensor according to the embodiment of the present invention. First, as shown in FIG. 7A, a seed layer 42a, a first ferromagnetic film 43a, an antiparallel coupling film 44a, a second ferromagnetic film 45a, a nonmagnetic intermediate layer 46a, a soft layer are formed on a substrate 41. Magnetic free layers (free magnetic layers) 47a and 48a and a protective layer 49a are formed in sequence. During the formation of the first ferromagnetic film 43a and the second ferromagnetic film 45a, a magnetic field is applied in the meander-shaped stripe width direction. In FIG. 7, for the first ferromagnetic film 43a, the applied magnetic field direction is the direction from the back side to the front side of the paper, and for the second ferromagnetic film 45a, the applied magnetic field direction is the front side to the back side of the paper. It is the direction toward. Further, during the formation of the soft magnetic free layers (free magnetic layers) 47a and 48a, a magnetic field is applied in the longitudinal direction of the meander stripe.

Next, as shown in FIG. 7B, a resist layer 50 is formed on the protective layer 49a, and the resist layer 50 is left on the region on the magnetoresistive effect element 122a side by photolithography and etching. Next, as shown in FIG. 7C, the exposed laminated film is removed by ion milling or the like to expose the substrate 41 in the region where the magnetoresistive effect element 122b is provided.

Next, as shown in FIG. 8A, on the exposed substrate 41, the seed layer 42b, the first ferromagnetic film 43b, the antiparallel coupling film 44b, the second ferromagnetic film 45b, and the nonmagnetic intermediate film 46b. Then, a soft magnetic free layer (free magnetic layer) 47b, 48b and a protective layer 49b are sequentially formed. During the formation of the first ferromagnetic film 43b and the second ferromagnetic film 45b, a magnetic field is applied in the meander-shaped stripe width direction. In FIG. 8, for the first ferromagnetic film 43b, the applied magnetic field direction is from the front side to the back side of the paper, and for the second ferromagnetic film 45b, the applied magnetic field direction is from the back side of the paper to the front side. It is the direction toward. Further, during the formation of the soft magnetic free layers (free magnetic layers) 47b and 48b, a magnetic field is applied in the longitudinal direction of the meander stripe.

Next, as shown in FIG. 8B, a resist layer 50 is formed on the protective layers 49a and 49b, and the resist layer 50 is formed on the formation regions of the magnetoresistive elements 122a to 122c and 123 by photolithography and etching. Remain. Next, as shown in FIG. 8C, the exposed laminated film is removed by ion milling or the like to form magnetoresistive elements 122a and 122b.

As described above, according to the current sensor of the present invention, the magnetization directions of the self-pinned ferromagnetic fixed layers of the two magnetoresistive effect elements that output the midpoint potential in the magnetic detection bridge circuit are different from each other by 180 °. Therefore, the output of the midpoint potential difference shows a proportional change with respect to the induced magnetic field generated by the current to be measured, and current measurement can be performed with high accuracy.

The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the materials, connection relations, thicknesses, sizes, manufacturing methods, and the like in the above embodiments can be changed as appropriate. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

The present invention can be applied to a current sensor that detects the magnitude of a current for driving a motor of an electric vehicle.

This application is based on Japanese Patent Application No. 2010-056155 filed on Mar. 12, 2010. All this content is included here.

Claims (6)

1. The magnetoresistive element includes two magnetoresistive elements whose resistance value changes by application of an induced magnetic field from a current to be measured and two fixed resistive elements, and outputs between the two magnetoresistive elements and between the two fixed resistive elements. A current sensor having a magnetic field detection bridge circuit having an output, wherein the two magnetoresistive elements have the same rate of change in resistance, and the first ferromagnetic film and the second strong film are interposed through an antiparallel coupling film. A ferromagnetic pinned layer of the two magnetoresistive effect elements having a self-pinned type ferromagnetic pinned layer formed by antiferromagnetically coupling the magnetic film, a nonmagnetic intermediate layer, and a soft magnetic free layer The current sensors are characterized in that their magnetization directions are different from each other by 180 °.
2. A feedback coil that is disposed in the vicinity of the magnetoresistive element and generates a canceling magnetic field that cancels the induced magnetic field; and a magnetic shield that attenuates the induced magnetic field and enhances the canceling magnetic field. The current to be measured is measured based on the current flowing through the feedback coil when the feedback coil is energized by the voltage difference obtained by the detection bridge circuit and the induced magnetic field cancels the canceling magnetic field. The current sensor according to claim 1.
3. The two magnetoresistive elements have a shape formed by folding a plurality of strip-like long patterns arranged so that their longitudinal directions are parallel to each other, and the induced magnetic field and the canceling magnetic field are in the longitudinal direction. The current sensor according to claim 2, wherein the current sensor is applied along a direction orthogonal to each other.
4. 2. The current sensor according to claim 1, wherein the current to be measured is measured by the magnetic field detection bridge circuit based on outputs of the two magnetoresistive effect elements proportional to the induced magnetic field.
5. The first ferromagnetic film is made of a CoFe alloy containing 40 atomic% to 80 atomic% of Fe, and the second ferromagnetic film is made of a CoFe alloy containing 0 atomic% to 40 atomic% of Fe. The current sensor according to claim 1.
6. 6. The magnetic shield according to claim 1, wherein the magnetic shield is made of a high magnetic permeability material selected from the group consisting of an amorphous magnetic material, a permalloy magnetic material, and an iron microcrystalline material. The current sensor according to Crab.

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