WO2012120940A1

WO2012120940A1 - Current sensor

Info

Publication number: WO2012120940A1
Application number: PCT/JP2012/051850
Authority: WO
Inventors: 井出　洋介; 斎藤　正路
Original assignee: アルプス電気株式会社
Priority date: 2011-03-07
Filing date: 2012-01-27
Publication date: 2012-09-13
Also published as: JP5597305B2; JPWO2012120940A1

Abstract

Provided is a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection precision. The current sensor is provided with magnetic-resistance effect elements (12a, 12b), and is characterized in that each of the magnetic-resistance effect elements (12a, 12b) comprises a self-pinning type ferromagnetic fixed layer, a nonmagnetic intermediate layer on top of the ferromagnetic fixed layer, and a soft magnetic free layer on top of the nonmagnetic intermediate layer, in that the soft magnetic free layer is composed of a laminated structure of a CoFe alloy film on top of the nonmagnetic intermediate layer, a NiFe alloy film on top of the CoFe alloy film, and a NiFeM alloy film (wherein M is an element selected from among Ta, Cr, Nb, Rh, Zr, Mo, Al, Au, Pd, Pt, and Si) on top of the NiFe alloy film, and in that the thickness of the CoFe alloy film is 0.5 nm to 1.5 nm, the thickness of the NiFe alloy film is 0.5 nm to 2.0 nm, and the thickness of the NiFeM alloy film is 6 nm to 17 nm.

Description

Current sensor

The present invention relates to a current sensor using a magnetoresistive effect element.

In an electric vehicle, a motor is driven using electricity generated by an engine or a regenerative brake. The magnitude of the current used for driving the motor is detected by, for example, a non-contact current sensor. As such a current sensor, a sensor in which a magnetic core having a notch (core gap) is arranged around a conductor through which a current to be measured flows and a magnetic detection element is arranged in the core gap is known.

The magnetic sensor of the current sensor described above has a laminated structure of a fixed magnetic layer whose magnetization direction is fixed, a nonmagnetic layer, and a free magnetic layer (soft magnetic free layer) whose magnetization direction varies with respect to an external magnetic field. A magnetoresistive element or the like is used. Moreover, the current sensor using a magnetoresistive effect element includes a bridge circuit including a magnetoresistive effect element and a fixed resistance element as a magnetic field detection circuit (see, for example, Patent Document 1).

In a current sensor using such a magnetoresistive effect element, various characteristics such as dynamic range (current measurement range) and linearity (output linearity) greatly depend on the characteristics of the magnetoresistive effect element constituting the current sensor. For example, when a GMR element using a giant magnetoresistive effect (GMR: Giant Magneto Resistive effect) is used as the magnetoresistive element, the dynamic range of the current sensor depends on the linearity of the magnetic field-resistance change rate curve of the GMR element. . That is, if the linear region of the magnetic field-resistance change rate curve of the GMR element becomes wider, the dynamic range of the current sensor becomes wider.

In order to realize a GMR element having a wide linear region as described above and a current sensor having a wide dynamic range, for example, a thick free magnetic layer in the GMR element may be formed. By increasing the shape anisotropy by forming a thick free magnetic layer, the slope of the magnetic field-resistance change rate curve is reduced, so that the resistance change rate can be made linear over a wide magnetic field range.

Further, in order to realize a GMR element having a wide linear region, there is a technique for canceling the AMR effect (anisotropic magnetoresistive effect) by setting the thickness of the free magnetic layer to 5 nm or less and suppressing the linearity deterioration of the GMR element. It is known (see, for example, Patent Document 2).

JP 2007-248054 A JP-A-9-36455

However, when the free magnetic layer is formed thick in order to realize a GMR element having a wide linear region, there arises a problem that the MR ratio (magnetoresistance ratio) of the GMR element is lowered. A decrease in MR ratio in the GMR element causes a decrease in current detection accuracy in the current sensor. For this reason, it has been difficult to realize a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy by the above-described method of thickening the free magnetic layer.

Further, as disclosed in Patent Document 2, the method of canceling the AMR effect by setting the thickness of the free magnetic layer to 5 nm or less can obtain a GMR element suitable for the use of the magnetic head. Since the anisotropy is small, it is impossible to achieve both high linearity and low magnetic hysteresis. In particular, since the thickness of the free magnetic layer is as thin as 5 nm or less, it is difficult to keep the magnetic hysteresis low. For this reason, even if the GMR element is used as a current sensor, it is difficult to realize a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy.

The present invention has been made in view of such a point, and an object thereof is to provide a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy.

The current sensor of the present invention is a current sensor including a magnetoresistive effect element whose resistance value is changed by application of an induced magnetic field from a current to be measured, and the magnetoresistive effect element is inserted through an antiparallel coupling film. A self-pinned ferromagnetic pinned layer formed by antiferromagnetically coupling the first ferromagnetic film and the second ferromagnetic film, a nonmagnetic intermediate layer on the ferromagnetic pinned layer, and the nonmagnetic intermediate layer A soft magnetic free layer (free magnetic layer) on the layer, and the soft magnetic free layer includes a CoFe alloy film on the nonmagnetic intermediate layer, a NiFe alloy film on the CoFe alloy film, and the NiFe alloy. And a NiFeM alloy film (M is an element selected from Ta, Cr, Nb, Rh, Zr, Mo, Al, Au, Pd, Pt, and Si), and the CoFe alloy film The thickness is 0.5 nm to 1.5 nm, The thickness of the iFe alloy film is 0.5 nm ~ 2.0 nm, and the thickness of NiFeM alloy film is 6 nm ~ 17 nm.

According to this configuration, since the soft magnetic free layer in the magnetoresistive effect element has a laminated structure of a relatively thin CoFe alloy film and NiFe alloy film and a relatively thick NiFeM alloy film, linearity is improved. Thus, a magnetoresistive element with improved MR ratio and reduced coercive force is realized. This is because the MR ratio is increased by the NiFe alloy film having a predetermined thickness disposed on the CoFe alloy film, and the coercive force is maintained while maintaining the MR ratio by the NiFeM alloy film having the predetermined thickness disposed on the NiFe alloy film. This is because it can be suppressed. Further, the linearity can be improved by increasing the thickness of the NiFeM alloy film having a small AMR effect and reducing the thickness of the NiFe alloy film having a large AMR effect. Also, by setting the CoFe alloy film to the above thickness, while suppressing magnetostriction and magnetic hysteresis, the thermal diffusion of the film constituting the laminated structure of the magnetoresistive effect element is prevented, and the spin-dependent interface scattering effect is enhanced. This is because the ratio can be increased. As a result of realizing a magnetic sensor element suitable for the current sensor as described above, a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy is realized.

In the current sensor of the present invention, the CoFe alloy film may be made of a CoFe alloy containing 0 atomic% to 20 atomic% of Fe. That is, the CoFe alloy film may be a Co film. According to this configuration, since the CoFe alloy has a face-centered cubic structure (fcc) or a hexagonal close-packed structure (hcp), magnetic hysteresis can be further suppressed.

In the current sensor of the present invention, the NiFe alloy film may be composed of a NiFe alloy containing 16 atomic% to 22 atomic% of Fe. According to this configuration, since the linear magnetostriction constant of the NiFe alloy is close to zero, dispersion of magnetic anisotropy due to the magnetoelastic effect can be suppressed.

In the current sensor of the present invention, the NiFeM alloy film may be composed of a NiFeM alloy containing 10 atomic% to 15 atomic% Fe and 2 atomic% to 8 atomic% M. According to this configuration, since the linear magnetostriction constant of the NiFeM alloy is close to zero, dispersion of magnetic anisotropy due to the magnetoelastic effect can be suppressed.

In the current sensor of the present invention, a magnetic field detection bridge circuit including the magnetoresistive effect element and the fixed resistance element may be provided.

According to this configuration, since the magnetic field detection bridge circuit is configured using the magnetoresistive effect element and the fixed resistance element as described above, a current having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy. The sensor is realized.

According to the present invention, a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy can be provided.

It is a schematic diagram which shows the current sensor which concerns on embodiment. It is a schematic diagram which shows the current sensor which concerns on embodiment. It is sectional drawing which shows the current sensor which concerns on embodiment. It is sectional drawing which shows the film | membrane structure of the magnetoresistive effect element in the current sensor which concerns on embodiment. It is a graph which shows the RH waveform (magnetic field-resistance change rate curve) of a magnetoresistive effect element. It is a graph which shows the relationship between the film thickness of a NiFe alloy film, and MR ratio ((DELTA) R / R) in a magnetoresistive effect element. It is a graph which shows the relationship between the magnetization amount (Ms * t) of a soft-magnetic free layer, and a coercive force (Hc) in a magnetoresistive effect element. It is a graph which shows the relationship between the magnetization amount (Ms * t) of a soft-magnetic free layer, and MR ratio ((DELTA) R / R) in a magnetoresistive effect element. It is a graph which shows the relationship between the film thickness of a CoFe alloy film, and a magnetostriction constant ((lambda) s) in a magnetoresistive effect element. It is a graph which shows the output waveform (magnetic field-output voltage) of the half bridge circuit comprised with the magnetoresistive effect element and the fixed resistance element. It is a figure for demonstrating the manufacturing method of the magnetoresistive effect element in the magnetic proportional type current sensor which concerns on this Embodiment. It is a figure for demonstrating the manufacturing method of the magnetoresistive effect element in the magnetic proportional type current sensor which concerns on this Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 and 2 are schematic views showing an example of a current sensor according to an embodiment of the present invention. The current sensor shown in FIGS. 1 and 2 is a magnetic proportional current sensor and is disposed in the vicinity of the conductor 11 through which the current I to be measured flows. Hereinafter, a magnetic proportional current sensor will be described, but the current sensor is not limited thereto. For example, a magnetic balance equation that generates a canceling magnetic field that cancels the induced magnetic field by the feedback coil and calculates the magnitude of the current to be measured from the current flowing through the feedback coil may be applied.

The current sensor shown in FIG. 1 and FIG. 2 has a magnetic field detection bridge circuit 12 that detects an induced magnetic field due to the current I to be measured flowing through the conductor 11. The magnetic field detection bridge circuit 12 includes two

magnetoresistive effect elements

12a and 12b whose resistance values are changed by applying an induction magnetic field from the current I to be measured, and two

fixed resistance elements

12c and 12d whose resistance values are not changed by the induction magnetic field. Have By using the magnetic field detection bridge circuit 12 having the magnetoresistive effect element as described above, a highly sensitive current sensor can be realized. The magnetic field detection bridge circuit 12 is not limited to a full bridge circuit composed of four elements. A half-bridge circuit composed of two elements may be used.

The magnetic field detection bridge circuit 12 includes two output terminals Out1 and Out2 that generate a voltage difference corresponding to the induced magnetic field caused by the current I to be measured. In the magnetic field detection bridge circuit 12 shown in FIG. 2, a power source Vdd is connected to one end of the magnetoresistive effect element 12a and one end of the fixed resistance element 12d, and one end of the magnetoresistive effect element 12b and one end of the fixed resistance element 12c. Is connected to the ground GND. The other end of the magnetoresistive effect element 12a and the other end of the fixed resistance element 12c are connected to form an output end Out1, and the other end of the magnetoresistive effect element 12b and the other end of the fixed resistance element 12d Are connected to form an output terminal Out2. Based on the voltage difference output from the output terminals Out1 and Out2, the current sensor calculates the current value of the current I to be measured.

FIG. 3 is a cross-sectional view showing the current sensor shown in FIG. As shown in FIG. 3, in the current sensor according to the present embodiment,

magnetoresistive elements

12 a and 12 b constituting the magnetic field detection bridge circuit 12 are formed on the substrate 21. A magnetic shield that attenuates the induced magnetic field A caused by the current I to be measured may be disposed on the

magnetoresistive effect elements

12a and 12b. By arranging the magnetic shield, the induced magnetic field A applied to the

magnetoresistive effect elements

12a and 12b is weakened, so that the substantial current measurement range of the current sensor can be expanded. The magnetic shield can be configured using a high magnetic permeability material such as an amorphous magnetic material, a permalloy magnetic material, or an iron microcrystalline material.

The layer structure shown in FIG. 3 will be described in detail. 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,

magnetoresistive effect elements

12a and 12b and fixed

resistance elements

12c and 12d (not shown) are formed, and the magnetic field detection bridge circuit 12 described above is formed. As shown in the enlarged view of FIG. 2, the

magnetoresistive effect elements

12a and 12b are formed by folding back a plurality of strip-like long patterns (stripes) arranged so that their longitudinal directions are parallel to each other (meander shape). It is preferable that the GMR element has The film configuration of the

magnetoresistive effect elements

12a and 12b will be described later.

The sensitivity axis direction (Pin direction) of the

magnetoresistive effect elements

12a and 12b is a direction (stripe width direction) orthogonal to the longitudinal direction (stripe longitudinal direction) of the long pattern in the meander shape described above. That is, from the viewpoint of improving linearity, it is preferable that the meandering shape is configured such that the induced magnetic field A faces in the direction perpendicular to the stripe longitudinal direction (stripe width direction). In consideration of linearity, the width in the meander-shaped pin direction is preferably 1 μm to 10 μm.

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

12a and 12b, the fixed

resistance elements

12c and 12d, and the electrode 24 are formed. The polyimide layer 25 can be formed by applying and curing a polyimide material.

A silicon oxide film 31 is formed on the polyimide layer 25. The silicon oxide film 31 can be formed by a method such as sputtering. A contact hole is formed in a predetermined region of the polyimide layer 25 and the silicon oxide film 31 (region where the electrode 24 exists), and an electrode pad 26 is formed in the contact hole. Photolithography, etching, and the like are used for forming the contact holes. The electrode pad 26 can be formed by photolithography and plating after the electrode material is deposited.

Next, the film configuration of the

magnetoresistive effect elements

12a and 12b will be described. FIG. 4 is a schematic cross-sectional view showing the film configuration of the magnetoresistive effect element 12a. That is, the magnetoresistive effect element 12a has a laminated structure provided on the substrate 21, as shown in FIG. In FIG. 4, the configuration other than the substrate 21 and the magnetoresistive effect element 12a is omitted for the sake of simplicity. Further, since the film configuration of the magnetoresistive effect element 12b is the same as that of the magnetoresistive effect element 12a except for the Pin direction, the film configuration of the magnetoresistive effect element 12a will be described here.

The magnetoresistive effect element 12a includes a seed layer 42, a first ferromagnetic film 43, an antiparallel coupling film 44, a second ferromagnetic film 45, a nonmagnetic intermediate layer 46, a soft magnetic free layer (free magnetic layer) 47, And a protective layer 48. In this magnetoresistive effect element, the first ferromagnetic film 43 and the second ferromagnetic film 45 are antiferromagnetically coupled via the antiparallel coupling film 44, so-called self-pinning type ferromagnetic. A fixed layer (SFP layer: Synthetic Ferri Pinned layer) is configured. Thus, the magnetoresistive effect element 12 a is a spin valve type element using the ferromagnetic pinned layer, the nonmagnetic intermediate layer 46 and the soft magnetic free layer 47.

The seed layer 42 is made of NiFeCr or Cr. A base layer made of a nonmagnetic material containing at least one element of Ta, Hf, Nb, Zr, Ti, Mo, and W is provided between the substrate 21 and the seed layer 42, for example. Also good.

The first ferromagnetic film 43 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 first ferromagnetic film 43 is provided with induced magnetic anisotropy by applying a magnetic field in the meander-shaped stripe width direction during the film formation. The direction of the applied magnetic field is the direction from the back side to the near side.

The antiparallel coupling film 44 is made of Ru or the like. The antiparallel coupling film 44 is desirably formed with a thickness of 0.3 nm to 0.45 nm or 0.75 nm to 0.95 nm. This is because by setting the antiparallel coupling film 44 to such a thickness, strong antiferromagnetic coupling can be provided between the first ferromagnetic film 43 and the second ferromagnetic film 45.

The second ferromagnetic film 45 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 a direction antiparallel to the direction in which the first ferromagnetic film 43 is preferentially magnetized (direction different by 180 °). is there. The second ferromagnetic film 45 has a magnetic field similar to that during the film formation of the first ferromagnetic film 43 (a magnetic field in the meander stripe width direction, a direction from the back side to the front side of the drawing). Is applied), induced magnetic anisotropy is imparted. By forming the film while applying such a magnetic field, the first ferromagnetic film 43 is preferentially magnetized in the direction of the applied magnetic field, and the second ferromagnetic film 45 is magnetized by the first ferromagnetic film 43. The direction is magnetized in an antiparallel direction (a direction different by 180 °).

The nonmagnetic intermediate layer 46 is made of Cu or the like.

The soft magnetic free layer (free magnetic layer) 47 is composed of a laminated structure of films made of a magnetic material. Specifically, it has a three-layer structure of a CoFe alloy film 471, a NiFe alloy film 472, and a NiFeM alloy film 473. Here, M represents an element selected from Ta, Cr, Nb, Rh, Zr, Mo, Al, Au, Pd, Pt, and Si. Further, the thickness of the CoFe alloy film 471 is 0.5 nm to 1.5 nm, more preferably 0.8 nm to 1.2 nm, and the thickness of the NiFe alloy film 472 is 0.5 nm to 2.0 nm, more preferably The thickness of the NiFeM alloy film 473 is 6 nm to 17 nm, more preferably 9 nm to 14 nm. By configuring the soft magnetic free layer 47 with such a configuration, the magnetoresistive effect element 12a with improved linearity, improved MR ratio, and suppressed coercive force is realized. This is because the MR ratio is increased by the NiFe alloy film 472 disposed on the CoFe alloy film 471, and the coercive force can be suppressed while maintaining the MR ratio by the NiFeM alloy film 473 disposed on the NiFe alloy film 472. is there. Further, the linearity can be improved by increasing the thickness of the NiFeM alloy film having a small AMR effect and reducing the thickness of the NiFe alloy film having a large AMR effect. In order to sufficiently increase the linearity, it is desirable that the ratio t1 / t2 between the thickness t1 of the NiFe alloy film and the thickness t2 of the NiFeM alloy film is 3 to 30.

The CoFe alloy film 471 is preferably composed of a CoFe alloy containing 0 atomic% to 20 atomic% of Fe. That is, the CoFe alloy film may be a Co film. With such a composition, since the CoFe alloy has a face-centered cubic structure (fcc) or a hexagonal close-packed structure (hcp), magnetic hysteresis can be further suppressed. Further, the NiFe alloy film 472 is preferably composed of a NiFe alloy containing 16 atomic% to 22 atomic% of Fe, and the NiFeM alloy film 473 is composed of 10 atomic% to 15 atomic% Fe and 2 atomic% to 8 atomic%. It is desirable to be composed of a NiFeM alloy containing atomic% M. In such a composition, since the linear magnetostriction constants of the NiFe alloy and the NiFeM alloy are close to zero, dispersion of magnetic anisotropy due to the magnetoelastic effect can be suppressed.

The soft magnetic free layer 47 is preferably provided with induced magnetic anisotropy by applying a magnetic field in the longitudinal direction of the meander-shaped stripe during film formation. Thereby, a resistance change linearly with respect to the external magnetic field in the stripe width direction and a magnetoresistive effect element 12a having a small magnetic hysteresis can be realized.

The protective layer 48 is made of Ta or the like.

As described above, by making the soft magnetic free layer 47 a laminated structure of layers having a predetermined thickness and made of a magnetic material, the linearity is improved, the MR ratio is improved, and the coercive force is suppressed. The resistance effect element 12a is realized. The improvement of the linearity of the magnetoresistive effect element 12a contributes to the expansion of the dynamic range and the current detection accuracy in the current sensor, and the improvement of the MR ratio of the magnetoresistive effect element 12a improves the current detection accuracy in the current sensor. Contributing to the improvement, the suppression of the coercive force of the magnetoresistive effect element 12a contributes to the reduction of magnetic hysteresis in the current sensor. For this reason, the magnetoresistive effect element 12a is suitable for a current sensor. By using the magnetoresistive effect element 12a, a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy is realized.

In the magnetoresistive element 12a, it is desirable that the magnetization amount (Ms · t) of the first ferromagnetic film 43 and the magnetization amount (Ms · t) of the second ferromagnetic film 45 are substantially the same. . When the difference in magnetization between the first ferromagnetic film 43 and the second ferromagnetic film 45 is substantially zero, the effective anisotropic magnetic field of the ferromagnetic fixed layer is increased. This is because the magnetization stability of the ferromagnetic pinned layer can be sufficiently secured without using an antiferromagnetic material. Further, it is desirable that the Curie temperature (Tc) of the first ferromagnetic film 43 and the Curie temperature (Tc) of the second ferromagnetic film 45 are substantially the same. Thereby, even in a high temperature environment, the difference in magnetization (Ms · t) between the first ferromagnetic film 43 and the second ferromagnetic film 45 becomes substantially zero, and high magnetization stability can be maintained. It is.

FIG. 5 is a graph showing an RH waveform (magnetic field-resistance change rate curve) of the magnetoresistive effect element. In FIG. 5, the solid line shows the RH waveform of the magnetoresistive effect element (implementing element) in the present embodiment, and the broken line shows the RH waveform of the conventional magnetoresistive effect element (comparative element). . Here, as an implementation element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: 1 nm) / Ni ₈₂ A magnetoresistive element having a film configuration of Fe ₁₃ Nb ₅ (soft magnetic free layer: 10 nm) / Ta (protective layer: 10 nm) was used.

As a comparative element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ ( Second ferromagnetic film: 2.4 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 (protection) A magnetoresistive element having a film configuration of (layer: 10 nm) was used. That is, only the configuration of the soft magnetic free layer is different between the implementation element and the comparison element. Note that the RH waveform shown in FIG. 5 was obtained under conditions that are normally measured.

FIG. 5 confirms that the linearity of the graph of the implementation element in the present embodiment is higher than that of the comparison element, and the linearity is enhanced. The improvement of the linearity brings about the effect of increasing the dynamic range and improving the current detection accuracy in the current sensor.

FIG. 6 is a graph showing the relationship between the film thickness of the NiFe alloy film 472 and the MR ratio (ΔR / R) in the magnetoresistive effect element (implementing element). Here, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (second Ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: X ₁ nm) / Ni ₈₂ Fe ₁₃ In a magnetoresistive effect element having a film configuration of Nb ₅ (soft magnetic free layer: 9 nm) / Ta (protective layer: 10 nm), a NiFe alloy film having a film thickness X ₁ different between 0 nm and 3 nm can be obtained. The relationship between the film thickness of the film 472 and the MR ratio was obtained.

From FIG. 6, it is confirmed that in the magnetoresistive effect element (implementing element) in the present embodiment, a relatively high MR ratio can be obtained when the NiFe alloy film is as thin as 0.5 nm to 2.5 nm. it can. In order to obtain a sufficiently high MR ratio, it is desirable that the thickness of the NiFe alloy film be 0.5 nm to 2.0 nm. A high MR ratio in the magnetoresistive effect element brings about an effect of improving current detection accuracy in the current sensor.

FIG. 7 is a graph showing the relationship between the amount of magnetization (Ms · t) of the soft magnetic free layer and the coercive force (Hc) in the magnetoresistive effect element. In FIG. 7, the solid line indicates the relationship in the magnetoresistive effect element (implementing element) of the present embodiment, and the broken line indicates the relationship in the conventional magnetoresistive effect element (comparative element). Here, as an implementation element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: 2 nm) / Ni ₈₂ Using a magnetoresistive element having a film structure of Fe ₁₃ Nb ₅ (soft magnetic free layer: X ₂ nm) / Ta (protective layer: 10 nm) and changing the film thickness X ₂ of the NiFeNb alloy film, the amount of magnetization is changed. And the relationship with the coercive force was obtained. In the characteristic shown by the solid line in FIG. 7, the film thickness X ₂ values at the measurement points (unit nm) are also shown.

As a comparative element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ ( Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: Y ₂ nm) / Ta (protective layer: 10 nm) using a magnetoresistive element of a membrane structure that, similarly changing the magnetization by varying the thickness Y ₂ of the NiFe alloy film, obtained relation between the coercive force. That is, only the configuration of the soft magnetic free layer is different between the implementation element and the comparison element. In the characteristic shown by the broken line in FIG. 7, the thickness Y ₂ of the values at the measurement points (unit nm) are also shown.

From FIG. 7, in the magnetoresistive effect element (implementing element) in the present embodiment, the coercive force hardly changes even when the value of the magnetization amount changes, but in the comparison element, the coercive force increases as the magnetization amount increases. I can confirm that. A large coercive force means that the magnetic hysteresis is large. Therefore, the magnetoresistive effect element in which the coercive force is suppressed brings about an effect of reducing the magnetic hysteresis in the current sensor.

FIG. 8 is a graph showing the relationship between the magnetization amount (Ms · t) of the soft magnetic free layer and the MR ratio (ΔR / R) in the magnetoresistive effect element. In FIG. 8, the solid line indicates the relationship in the magnetoresistive effect element (implementing element) of the present embodiment, the broken line indicates the relationship in the conventional magnetoresistive effect element (comparative element), and the alternate long and short dash line is for reference. The relationship in the magnetoresistive element (reference element) is shown. Here, as an implementation element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: 2 nm) / Ni ₈₂ Using a magnetoresistive element having a film structure of Fe ₁₃ Nb ₅ (soft magnetic free layer: X ₃ nm) / Ta (protective layer: 10 nm) and changing the film thickness X ₃ of the NiFeNb alloy film, the amount of magnetization is changed. The relationship with the MR ratio was obtained. The thickness _{X 3} of NiFeNb alloy film was varied between 3 nm ~ 15 nm. In the characteristic shown by the solid line in FIG. 8, the film thickness X ₃ value at the measurement point (in nm) shown together.

As a comparative element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ ( Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / NiFe (soft magnetic free layer: Y ₃ nm) / Ta (protective layer: 10 nm) using a magnetoresistive element of a membrane structure that, similarly changing the magnetization by varying the thickness Y ₃ of the NiFe alloy film, obtained relation between MR ratio. As a reference element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ ( Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / Ni ₈₂ Fe ₁₃ Nb ₅ (soft magnetic free layer: Z ₃ nm) / Ta (protective layer: 10 nm) using a magnetoresistive effect element, and similarly changing the film thickness Z ₃ of the NiFeNb alloy film to change the amount of magnetization and obtaining the relationship with the MR ratio. It was. That is, only the configuration of the soft magnetic free layer is different between the implementation element, the comparison element, and the reference element. In the characteristics indicated by the broken line and the alternate long and short dash line in FIG. 8, the value of the film thickness Y _{3 and} the value of the film thickness Z ₃ (unit: nm) at the measurement point are shown together.

FIG. 8 confirms that the magnetoresistive effect element (implementing element) according to the present embodiment has a relatively large MR ratio even when the amount of magnetization increases. On the other hand, in order to ensure the same MR ratio in the comparison element and the reference element, the amount of magnetization must be sufficiently reduced. When the amount of magnetization is reduced, the shape anisotropy is reduced and the slope of the RH waveform is increased, so that the range in which linearity can be ensured is narrowed. As described above, in the magnetoresistive effect element 12a in the present embodiment, a relatively large MR ratio can be obtained even when the amount of magnetization is large, so that high linearity and high MR ratio are realized. From the relationship with other characteristics, the thickness of the NiFeNb alloy film in the magnetoresistive effect element 12a is preferably 6 nm to 17 nm.

FIG. 9 is a graph showing the relationship between the thickness of the CoFe alloy film 471 and the magnetostriction constant (λs) in the magnetoresistive effect element. Here, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (second Ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: X ₄ nm) / Ni _81.5 Fe _18.5 (soft magnetic free layer: 2 nm) / Ni ₈₂ Fe ₁₃ Nb ₅ (soft magnetic free layer: 9 nm) / Ta (protective layer: 10 nm), the magnetoresistive effect element has a film thickness X ₄ of 0.4 nm to 2 nm. Thus, the relationship between the film thickness of the CoFe alloy film 471 and the MR ratio was determined.

From FIG. 9, in the magnetoresistive effect element (implementing element) in the present embodiment, when the thickness of the CoFe alloy film is in the range of 0.5 nm to 1.5 nm, the magnetostriction constant λs becomes λs ≦ ± 1 ppm. I understand that If the absolute value of the magnetostriction constant λs is greater than 1, the magnetic anisotropy of the soft magnetic free layer is dispersed due to the magnetoelastic effect, and magnetic hysteresis is likely to occur. It is desirable to be 5 nm to 1.5 nm.

FIG. 10 is a graph showing an output waveform (magnetic field-output voltage) of a half bridge circuit composed of a magnetoresistive effect element and a fixed resistance element. In FIG. 10, the solid line shows the output waveform of the half bridge circuit using the magnetoresistive effect element (implementing element) in the present embodiment, and the broken line shows the half bridge using the conventional magnetoresistive effect element (comparative element). The output waveform of the circuit is shown. Here, as an implementation element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ (Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / Ni _81.5 Fe _18.5 (soft magnetic free Layer: 1 nm) / Ni ₈₂ Fe ₁₃ Nb ₅ (soft magnetic free layer: 10 nm) / Ta (protective layer: 10 nm).

As a comparative element, NiFeCr (seed layer: 4.2 nm) / Fe ₆₀ Co ₄₀ (first ferromagnetic film: 1.8 nm) / Ru (anti-parallel coupling film: 0.36 nm) / Co ₉₀ Fe ₁₀ ( Second ferromagnetic film: 2.4 nm) / Cu (nonmagnetic intermediate layer: 2.2 nm) / Co ₉₀ Fe ₁₀ (soft magnetic free layer: 1 nm) / Ni _81.5 Fe _18.5 (soft magnetic free layer) : 7 nm) / Ta (protective layer: 10 nm) was used. That is, only the configuration of the soft magnetic free layer is different between the implementation element and the comparison element.

From FIG. 10, the linear region of the output waveform of the half-bridge circuit using the comparison element is about ± 20 Oe, whereas the linear region of the output waveform of the half-bridge circuit using the implementation element in the present embodiment is ± It can be confirmed that it is about 70 Oe. The output of the half bridge circuit corresponds to the output of the current sensor, and it can be seen that the linearity of the output of the current sensor can be enhanced by using the implementation element.

FIGS. 11A to 11C and FIGS. 12A to 12C are views for explaining a method of manufacturing the

magnetoresistive effect elements

12a and 12b according to the present embodiment.

As shown in FIG. 11A, first, 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 magnetic free layer are formed on a substrate 21. A layer (free magnetic layer) 47a and a protective layer 48a are sequentially formed.

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. 11, both the direction of the magnetic field applied during the formation of the first ferromagnetic film 43a and the direction of the magnetic field applied during the formation of the second ferromagnetic film 45a are from the front side of the drawing. It is a direction toward the side. Thereby, the first ferromagnetic film 43a is preferentially magnetized in the applied magnetic field direction, and the second ferromagnetic film 45a is antiparallel to the magnetization direction of the first ferromagnetic film 43a (a direction different by 180 °). ) Is magnetized.

The soft magnetic free layer (free magnetic layer) 47a is formed with a three-layer structure of a CoFe alloy film 471a, a NiFe alloy film 472a, and a NiFeM alloy film 473a. Further, during the formation of the soft magnetic free layer (free magnetic layer) 47a, a magnetic field is applied in the longitudinal direction of the meander stripe.

Next, as shown in FIG. 11B, a resist layer is formed on the protective layer 48a, and the resist layer 50a is left on the region where the magnetoresistive effect element 12a is formed by photolithography and etching. Then, as shown in FIG. 11C, the exposed laminated film is removed by ion milling or the like to expose the surface on which the magnetoresistive effect element 12b is formed.

Next, as shown in FIG. 12A, on the exposed surface, the seed layer 42b, the first ferromagnetic film 43b, the antiparallel coupling film 44b, the second ferromagnetic film 45b, the nonmagnetic intermediate layer 46b, the soft magnetic layer. A free layer (free magnetic layer) 47b and a protective layer 48b are sequentially formed.

Again, a magnetic field is applied in the meander-shaped stripe width direction during the formation of the first ferromagnetic film 43b and the second ferromagnetic film 45b. However, the direction of the applied magnetic field is the direction from the front side to the back side in FIG. Accordingly, the first ferromagnetic film 43a and the second ferromagnetic film 45a are magnetized in the antiparallel direction (direction different by 180 °).

Further, the soft magnetic free layer (free magnetic layer) 47b is formed of a three-layered structure of a CoFe alloy film, a NiFe alloy film, and a NiFeM alloy film. During the formation of the soft magnetic free layer (free magnetic layer) 47b, a magnetic field is applied in the longitudinal direction of the meander stripe.

Next, as shown in FIG. 12B, a resist is formed on the

protective layers

48a and 48b, and the resist

layers

51a and 51b are left on the formation regions of the

magnetoresistive elements

12a and 12b by photolithography and etching. Then, as shown in FIG. 12C, the exposed laminated film is removed by ion milling or the like to obtain

magnetoresistance effect elements

12a and 12b.

As described above, in the present invention, the soft magnetic free layer of the magnetoresistive effect element is composed of a laminated structure of a relatively thin CoFe alloy film and NiFe alloy film and a relatively thick NiFeM alloy film. Thus, a magnetoresistive element with enhanced MR ratio and reduced coercive force is realized. This is because the MR ratio is increased by the NiFe alloy film having a predetermined thickness disposed on the CoFe alloy film, and the coercive force is maintained while maintaining the MR ratio by the NiFeM alloy film having the predetermined thickness disposed on the NiFe alloy film. This is because it can be suppressed. Further, the linearity can be improved by increasing the thickness of the NiFeM alloy film having a small AMR effect and reducing the thickness of the NiFe alloy film having a large AMR effect. Further, by setting the thickness of the CoFe alloy film to the above-mentioned thickness, it is possible to prevent thermal diffusion of the film constituting the laminated structure of the magnetoresistive effect element (for example, Cu layer, NiFe layer, etc.) while suppressing magnetostriction and magnetic hysteresis. This is because the spin-dependent interface scattering effect can be enhanced and the MR ratio can be increased. As a result of realizing a magnetic sensor element suitable for the current sensor as described above, a current sensor having a wide dynamic range, low magnetic hysteresis, and high current detection accuracy is realized.

Note that 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, for example, 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. 2011-049163 filed on March 7, 2011. All this content is included here.

Claims

A current sensor comprising a magnetoresistive element whose resistance value changes by application of an induced magnetic field from a current to be measured,
The magnetoresistive effect element includes a self-pinned ferromagnetic fixed layer formed by antiferromagnetically coupling a first ferromagnetic film and a second ferromagnetic film via an antiparallel coupling film, and the strong A nonmagnetic intermediate layer on the magnetic pinned layer, and a soft magnetic free layer on the nonmagnetic intermediate layer,
The soft magnetic free layer includes a CoFe alloy film on the nonmagnetic intermediate layer, a NiFe alloy film on the CoFe alloy film, and a NiFeM alloy film on the NiFe alloy film (M is Ta, Cr, Nb, Rh) , Zr, Mo, Al, Au, Pd, Pt, Si))
The CoFe alloy film has a thickness of 0.5 nm to 1.5 nm, the NiFe alloy film has a thickness of 0.5 nm to 2.0 nm, and the NiFeM alloy film has a thickness of 6 nm to 17 nm. Characteristic current sensor.
2. The current sensor according to claim 1, wherein the CoFe alloy film is made of a CoFe alloy containing 10 atomic% to 20 atomic% of Fe.
3. The current sensor according to claim 1, wherein the NiFe alloy film is made of a NiFe alloy containing 16 atomic% to 22 atomic% of Fe.
4. The NiFeM alloy film according to claim 1, wherein the NiFeM alloy film is composed of a NiFeM alloy containing 10 atomic% to 15 atomic% of Fe and 2 atomic% to 8 atomic% of M. Current sensor.
The current sensor according to any one of claims 1 to 4, further comprising a magnetic field detection bridge circuit including the magnetoresistive effect element and a fixed resistance element.