JP2018112481A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor capable of directing the magnetization direction of a free magnetic layer in a GMR element to the extending direction of the GMR element without using a reset coil. SOLUTION: A pair of magnetic resistance effect elements 122a and 122b constituting a half bridge circuit 111A and a pair of magnetic resistance effect elements 122c and 122d forming a half bridge circuit 111B are formed on a substrate, and the magnetic resistance effect elements 122a are formed. Each of ~ 122d has a fixed magnetic layer having a fixed magnetization direction and a free magnetic layer whose magnetization direction changes due to an external magnetic field, and a bias magnetic field B is applied to each free magnetic layer, and the oscillator 140. By passing an AC current through the feedback coil 121, an alternating magnetic field is applied to the free magnetic layer to which the bias magnetic field is applied, and the free magnetic layer is reset to the initial magnetized state. [Selection diagram] Fig. 1

Description

  The present invention relates to a magnetic sensor having a magnetoresistive effect element, and more particularly to a magnetic sensor having a magnetoresistive effect element in which a bias magnetic field is applied to a free magnetic layer.

  A GMR (Giant Magneto Resistive effect) element has a problem that when a magnetic field is applied, the free magnetic layer is multi-domained and does not return to a predetermined initial state even after the magnetic field is removed. As countermeasures, GMR elements having a configuration in which a hard bias layer for applying a bias magnetic field is provided, or a configuration in which an antiferromagnetic material layer adjacent to the free magnetic layer is provided have been proposed. In the GMR element having these structures, the application of a bias magnetic field along the extending direction (stripe direction) of the GMR element suppresses the free magnetic layer from being multi-domained.

  By applying a bias magnetic field, it is possible to prevent the free magnetic layer from becoming multi-domained, but when a large magnetic field is applied, there arises a problem that the offset of the magnetic sensor provided with the GMR element varies. By increasing the strength of the bias magnetic field, it is possible to suppress the variation in offset due to the multi-domain of the free magnetic layer. However, if the bias magnetic field is increased, there is a problem that the output of the magnetic sensor decreases and the response speed decreases.

  There has been proposed a magnetic sensor including a reset coil for initializing the magnetization state of a free magnetic layer in a non-biased GMR element to which no bias magnetic field is applied. For example, in Patent Document 1, a reset magnetic field is applied so that the magnetization direction of the free magnetic layer is directed in a direction orthogonal to the sensitivity axis direction of the GMR element, that is, in the extending direction of the GMR element (longitudinal direction of the stripe). A magnetic sensor with a reset coil is described.

International Publication WO2015 / 125699

  In the magnetic sensor described in Patent Document 1, it is necessary to form a sufficiently large reset coil for the GMR element in order to apply a uniform reset magnetic field in the extending direction of the GMR element, that is, in the longitudinal direction of the stripe. is there. Further, when configuring a magnetic balance type magnetic sensor, in addition to the reset coil, it is necessary to form a feedback coil that generates a canceling magnetic field that cancels the induced magnetic field from the current to be measured. Therefore, there is a problem that the size of the current sensor is increased.

Accordingly, an object of the present invention is to provide a magnetic sensor that can efficiently reset the magnetization state of a free magnetic layer.
Another object of the present invention is to provide a magnetic sensor that can reset the magnetization state of a free magnetic layer without providing a reset coil or the like.

  As a result of studies by the present inventors in order to solve the above problem, by applying an alternating magnetic field in the sensitivity direction (direction perpendicular to the bias magnetic field) of the GMR element in which the bias magnetic field is applied to the free magnetic layer, The knowledge that the magnetization state of the free magnetic layer was reset and approached the initial magnetization state was obtained. The present invention based on this finding has the following configuration.

The present invention relates to a magnetic sensor provided with a plurality of magnetoresistive elements constituting a bridge circuit.
Each of the magnetoresistive elements includes a pinned magnetic layer whose magnetization direction is fixed, a free magnetic layer whose magnetization direction varies due to an external magnetic field, and a nonmagnetic material positioned between the pinned magnetic layer and the free magnetic layer And having a layer
A bias magnetic field application unit for applying a bias magnetic field to the free magnetic layer;
The free magnetic layer includes an alternating magnetic field applying unit that applies an alternating magnetic field in a direction crossing the bias magnetic field.

In the magnetic sensor of the present invention, the magnetoresistive effect element has a plurality of element portions extending in a strip shape connected in a meander shape,
The bias magnetic field application unit applies the bias magnetic field in the extending direction of the element unit,
The alternating magnetic field application unit may apply the alternating magnetic field in a sensitivity axis direction of the magnetoresistive effect element perpendicular to an extending direction of the element unit.
The magnetic sensor of the present invention can efficiently reset the free magnetic layer to the initial magnetization state by applying an alternating magnetic field in a direction orthogonal to the direction in which the bias magnetic field is applied to the element portion.

  In the magnetic sensor of the present invention, the bridge circuit can be configured as a full bridge circuit having a first half bridge circuit and a second half bridge circuit.

  The bias magnetic field is a hard bias magnetic field or an exchange bias magnetic field.

The magnetic sensor of the present invention controls, for example, a feedback coil that generates a canceling magnetic field that cancels a magnetic field to be measured applied to the magnetoresistive element, a canceling current applied to the feedback coil, and detects the canceling current. With a detection circuit,
The feedback coil is used as the alternating magnetic field applying unit.
By using the feedback coil as the alternating magnetic field application unit, it is not necessary to provide another coil for applying the alternating magnetic field, and the size of the magnetic sensor can be reduced.

  For example, the feedback coil is used as an alternating magnetic field application unit that generates the alternating magnetic field at a time when the cancel current is not applied.

The magnetic sensor of the present invention further includes a magnetic shield,
The magnetic shield preferably attenuates the magnetic field to be measured and enhances the cancellation magnetic field and the alternating magnetic field.

In the present invention, the free magnetic layer can be reset to the initial magnetization state by applying an alternating magnetic field in a direction crossing the bias magnetic field to the free magnetic layer to which the bias magnetic field is applied. Therefore, a highly accurate magnetic sensor in which the offset value is kept constant can be obtained.
In addition, the present invention includes a feedback coil, and using this feedback coil as an alternating magnetic field application unit eliminates the need for a separate reset coil or the like.

The conceptual diagram which shows the outline of a structure of the magnetic balance type magnetic sensor which concerns on embodiment of this invention. Explanatory drawing which shows the magnetic balance type magnetic sensor which concerns on embodiment of this invention Explanatory drawing which shows the magnetic balance type magnetic sensor which concerns on embodiment of this invention Sectional drawing which shows the magnetic balance type magnetic sensor shown in FIG. Explanatory drawing which shows the magnetic detection bridge circuit in the magnetic balance type magnetic sensor which concerns on embodiment of this invention Explanatory drawing which shows the film | membrane structure of the magnetoresistive effect element in the magnetic balance type magnetic sensor which concerns on embodiment of this invention Explanatory drawing which shows the other film structure of the magnetoresistive effect element in the magnetic balance type magnetic sensor which concerns on embodiment of this invention (A) The figure which shows the structure of the bias magnetic field application part which applies a hard bias to a magnetoresistive effect element, (B) The figure which shows the structure of the bias magnetic field application part which applies an exchange bias to a magnetoresistive effect element The graph which shows the RH curve of the direction orthogonal to the sensitivity axis of the GMR element which is a magnetoresistive effect element which comprises the magnetic sensor of an Example. A graph showing the transition of the offset fluctuation amount relative to the initial value when the offset evaluation of the proportional output is repeated 10 times after applying the magnetic field that completely reverses the free magnetic layer in the direction opposite to the bias magnetic field.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a conceptual diagram showing an outline of a configuration of a magnetic sensor according to an embodiment of the present invention. The magnetic sensor 1 includes a full bridge circuit 110 and a feedback coil 121. The full bridge circuit 110 has a configuration in which a half bridge circuit 111A including a magnetoresistive effect element 122b and a magnetoresistive effect element 122a and a half bridge circuit 111B including a magnetoresistive effect element 122c and a magnetoresistive effect element 122d are connected in parallel. It is. Each of half-bridge circuit 111A and half-bridge circuit 111B has one end connected to power supply voltage Vdd and the other end connected to ground potential GND. The Pin direction (X1 direction) of the magnetoresistive effect element 122a and the magnetoresistive effect element 122c is 180 degrees different from the Pin direction (X2 direction) of the magnetoresistive effect element 122b and the magnetoresistive effect element 122d.

  When the external magnetic field H is applied to the full bridge circuit 110, the direction of the free magnetic layer 44 (see FIGS. 6 and 7) of the magnetoresistive elements 122a to 122d changes so as to follow the direction of the external magnetic field H. At this time, the resistance values of the magnetoresistive effect elements 122 a to 122 d change according to the relative angle between the fixed magnetization direction of the fixed magnetic layer (second magnetic layer) 42 c and the magnetization direction of the free magnetic layer 44. Therefore, the differential output (Out1)-(Out2) between the output potential (Out1) of the midpoint terminal 131 of the half-bridge circuit 111B and the output potential (Out2) of the midpoint terminal 132 of the half-bridge circuit 111A is shown in FIG. It is obtained as a detection output (detection output voltage) Vs of a magnetic field in the arrow direction (sensitivity axis direction, X1-X2 axis direction) indicated by H. The detection output Vs is amplified by the amplifier 124 and supplied to the feedback coil 121.

  Each of the magnetoresistive effect elements 122a to 122d constituting the full bridge circuit 110 has an arrow direction (bias magnetic field direction, Y2 direction) indicated by B in the figure orthogonal to the sensitivity axis direction (X1-X2 direction) described above. ) Is applied with a bias magnetic field. When a bias magnetic field is applied to the free magnetic layers of the magnetoresistive effect elements 122a to 122d, the magnetization of the free magnetic layer is aligned in the Y direction, and preferably the magnetization of the free magnetic layer is made into a single domain and an external magnetic field is applied. In addition, the magnetization of the free magnetic layer tends to be directed in the direction of the external magnetic field.

  However, when an unexpected large external magnetic field is applied to the free magnetic layer and the magnetization of the free magnetic layer is forced to the direction of the external magnetic field, the external magnetic field subsequently becomes zero (no magnetic field), Hysteresis may not return to the initial magnetization state of the free magnetic layer, that is, the state aligned with the direction of the bias magnetic field. In this case, the differential output (Out1) − (Out2) when the external magnetic field is zero (no magnetic field) is not 0, and the detection output Vs is offset, so that the measurement accuracy of the magnetic sensor 1 is lowered.

  Therefore, the magnetic sensor 1 applies an alternating magnetic field in the sensitivity axis direction from the feedback coil 121 to the magnetoresistive effect elements 122a to 122d in order to initialize the magnetization state of the free magnetic layer. By applying an alternating magnetic field in the sensitivity axis direction (X1-X2 direction) while the bias magnetic field B is applied in the Y2 direction, the magnetization state of the free magnetic layer can be initialized. At this time, since the bias magnetic field B is applied, it is possible to prevent the magnetization direction of the free magnetic layer from being opposite to the initial direction after applying the alternating magnetic field. This eliminates the offset of the detection output Vs that occurs when a large external magnetic field is applied to the free magnetic layer, thereby increasing the measurement accuracy.

  Even if the alternating magnetic field at this time has a smaller absolute value than the external magnetic field, which is a disturbance applied to the free layer, the magnetic field having different directions in the sensitivity axis direction is repeatedly applied to the free magnetic layer. A reset process for initializing the magnetization state of the layer is possible.

  As shown in FIG. 1, an oscillator 140 is connected to the feedback coil 121 in parallel. When the oscillator 140 applies an alternating current to the feedback coil 121, an alternating magnetic field can be applied from the feedback coil 121 to the magnetoresistive elements 122a to 122d. The timing at which the oscillator 140 applies an alternating current to the feedback coil 121 includes, for example, when an abnormality of the magnetic sensor 1 is detected, at regular intervals, or periodically during magnetic field detection. If an alternating magnetic field is generated during magnetic field detection, the magnetic field cannot be detected while the alternating magnetic field is being generated, but it is possible to perform highly accurate measurements after the free magnetic layer has been initialized. It becomes. The magnetic sensor 1 is controlled by a CPU or the like (not shown). Abnormality detection is performed based on, for example, comparison with a normal process stored in advance in a memory holding unit or the like.

  The magnetic sensor 1 according to the present embodiment uses a feedback coil 121 that generates a feedback magnetic field as an alternating magnetic field application unit. For this reason, compared with the thing provided with the alternating magnetic field application part separately from the feedback coil 121, the size of the magnetic sensor 1 can be made small.

  2 and 3 are explanatory views showing a magnetic balance type magnetic sensor according to an embodiment of the present invention. In the present embodiment, the magnetic sensor 1 is disposed in the vicinity of the conductor 11 through which the current I to be measured flows. The magnetic sensor 1 includes a feedback circuit 12 that generates a magnetic field (cancel magnetic field) that cancels an induced magnetic field (measured magnetic field) due to the measured current I flowing in the conductor 11. The feedback circuit 12 includes a feedback coil 121 wound in a direction that cancels a magnetic field generated by the current I to be measured, and four magnetoresistive elements 122a to 122d.

  The feedback coil 121 is a planar coil. The feedback coil 121 is preferably provided so that both an induced magnetic field and a cancel magnetic field are generated in a plane parallel to the plane on which the planar coil is formed.

  The resistance values of the magnetoresistive elements 122a to 122d change due to application of an induced magnetic field (measured magnetic field) from the measured current I. The four magnetoresistive effect elements 122a to 122d constitute a magnetic field detection bridge circuit. Thus, a magnetic sensor with high sensitivity can be realized by using a magnetic field detection bridge circuit having a magnetoresistive effect element. From the viewpoint of improving detection sensitivity, a full bridge circuit is preferable as shown in FIG. 2 and FIG. 3, but it can also be implemented as a magnetic sensor having one half bridge circuit instead of the full bridge circuit. .

  This magnetic field detection bridge circuit includes two outputs that generate a voltage difference according 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 122b and the magnetoresistive effect element 122c, and the magnetoresistive effect element 122a and the magnetoresistive effect element 122d are connected. A ground (GND) is connected to a connection point between them. Further, in this magnetic field detection bridge circuit, one output (Out1) is taken out from the connection point between the magnetoresistive effect elements 122a and 122b, and another output (Out2) from the connection point between the magnetoresistive effect elements 122c and 122d. Take out.

  These two outputs are sent to a control circuit including an amplifier 124 and supplied to the feedback coil 121 as a current (feedback current). This feedback current is set so that the voltage difference between the output (Out1) and the output (Out2) corresponding to the induced magnetic field becomes zero. Then, the current to be measured is measured by the detection circuit (detection resistor R) based on the current flowing through the feedback coil 121 when the equilibrium state in which the induction magnetic field and the cancellation magnetic field cancel each other is achieved.

  4 is a cross-sectional view showing the magnetic sensor shown in FIG. As shown in FIG. 4, in the magnetic sensor according to the present embodiment, the feedback coil 121, the magnetic shield 30, and the magnetic field detection bridge circuit are formed on the same substrate 21. In the configuration shown in FIG. 4, the feedback coil 121 is disposed between the magnetic shield 30 and the magnetic field detection bridge circuit 110, and the magnetic shield 30 is disposed on the side close to the current I to be measured. That is, the magnetic shield 30, the feedback coil 121, and the magnetoresistive elements 122a to 122d are arranged in this order from the side close to the conductor 11. Thereby, the magnetoresistive effect elements 122a to 122d can be most distant from the conductor 11, and the induced magnetic field applied to the magnetoresistive effect element from the current I to be measured can be reduced. Moreover, since the magnetic shield 30 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, and the dynamic range of the detection operation can be expanded.

  The layer configuration shown in FIG. 4 will be described in detail. In the magnetic sensor shown in FIG. 4, 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.

  Magnetoresistive elements 122a to 122d are formed on the aluminum oxide film 23, and the magnetic field detection bridge circuit 110 is built in. As the magnetoresistive elements 122a to 122d, GMR elements (giant magnetoresistive elements) can be used. The film configuration of the magnetoresistive effect element used in the magnetic sensor according to the present invention will be described later.

  As shown in the enlarged view of FIG. 3, the magnetoresistive effect element has a shape in which a plurality of strip-like long patterns (stripes) arranged so that their longitudinal directions are parallel to each other (a meander shape) It is preferable that the GMR element has 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 (measured magnetic field) and a canceling magnetic field are applied along a direction (stripe width direction) perpendicular to the stripe longitudinal direction. An alternating magnetic field for initializing the magnetization of the free magnetic layer is also applied in a 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.

  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 elements 122a to 122d 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.

  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 sensor having such a configuration, as shown in FIG. 4, an induced magnetic field (measured magnetic field) A generated from the current I to be measured is received by the magnetoresistive effect elements 122a to 122d, and the induced magnetic field is fed back. Thus, the canceling magnetic field B is generated from the feedback coil 121, and the two magnetic fields (induction magnetic field A and canceling magnetic field B) are canceled, and the magnetic field applied to the magnetoresistive effect elements 122a to 122d is adjusted as appropriate.

  The magnetic 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 an induced magnetic field generated from the current I to be measured and applied to the magnetoresistive elements 122a to 122d (in the magnetoresistive elements 122a to 122d, the direction of the induced magnetic field A is opposite to the direction of the canceling magnetic field B). Direction) and the cancellation magnetic field B from the feedback coil 121 can be enhanced (in the magnetic shield 30, 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. In addition, the dynamic range of the measurement operation can be expanded. Further, the magnetic shield 30 can reduce the influence of an external magnetic field.

  Furthermore, when performing a reset process for generating an alternating magnetic field from the feedback coil 121 and initializing the magnetization of the free magnetic layer, the magnetic shield 30 can exert an effect of enhancing the alternating magnetic field, The free magnetic layer can be initialized by applying an alternating magnetic field having a large absolute value in the sensitivity axis direction.

  The magnetic 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 sensor can be realized. In addition, this magnetic sensor is composed of four magnetoresistive effect elements having the same magnetic film detection bridge circuit. In addition, the magnetic 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 sensor has a configuration that does not have a magnetic core, it can be reduced in size and cost.

  In the magnetic sensor of the present invention, as shown in FIG. 5, the magnetization directions of the ferromagnetic fixed layers of the two magnetoresistive elements 122b and 122a that output the midpoint potential (Out1) (the magnetization of the second ferromagnetic film). Direction) are 180 ° different from each other (antiparallel), and the magnetization directions of the ferromagnetic fixed layers of the two magnetoresistive elements 122c and 122d that output the midpoint potential (Out2) (the magnetization direction of the second ferromagnetic film) ) Are 180 ° different from each other (anti-parallel). The resistance change rates of the four magnetoresistive elements 122a to 122d are the same. The magnetoresistive effect elements 122a to 122d preferably exhibit the same rate of change in resistance at the same magnetic field strength when the angle of the applied magnetic field to the ferromagnetic fixed layer is the same.

  In the magnetic balance type current sensor having the four magnetoresistive effect elements 122a to 122d arranged in this way, the feedback coil 121 causes the voltage difference between the two outputs (Out1, Out2) of the magnetic detection bridge circuit to be zero. By applying a cancel magnetic field to the magnetoresistive element and detecting the value of the current flowing through the feedback coil 121 at that time, the induced magnetic field generated by the current to be measured is measured.

  As shown in FIG. 5, when the current I to be measured flows in the direction of the arrow, the induction magnetic field A and the cancellation magnetic field B are applied to the four magnetoresistive effect elements 122a to 122d, 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.

  FIG. 6 is a diagram showing a film configuration of the magnetoresistive effect element in the magnetic sensor according to the embodiment of the present invention. As shown in FIG. 6, the magnetic detection elements 122 a to 122 d (see FIGS. 1 to 3) include a base layer 41, a fixed magnetic layer 42, a nonmagnetic material layer 43, a free magnetic layer 44, and It can be set as the structure laminated | stacked in order of the protective layer 45. FIG. These layers are formed by, for example, a sputtering process.

  The underlayer 41 is made of NiFeCr alloy (nickel / iron / chromium alloy) or Cr.

  The pinned magnetic layer 42 has a self-pinning structure including a first magnetic layer 42a and a second magnetic layer 42c, and a nonmagnetic intermediate layer 42b positioned between the first magnetic layer 42a and the second magnetic layer 42c. It has become. The fixed magnetization direction of the first magnetic layer 42a and the fixed magnetization direction of the second magnetic layer 42c are antiparallel due to interaction. The pinned magnetization direction of the second magnetic layer 42 c adjacent to the nonmagnetic material layer 43 is the pinned magnetization direction of the pinned magnetic layer 42. The direction in which the fixed magnetization direction extends is the sensitivity axis direction of the magnetic detection elements 122a to 122d.

  The first magnetic layer 42a and the second magnetic layer 42c are formed of an FeCo alloy (iron / cobalt alloy). The FeCo alloy has a high coercive force by increasing the Fe content. The second magnetic layer 42c in contact with the nonmagnetic material layer 43 is a layer that contributes to a spin valve type giant magnetoresistance effect (GMR effect). The nonmagnetic intermediate layer 42b is made of Ru (ruthenium) or the like. The film thickness of the nonmagnetic intermediate layer 42b made of Ru is preferably 3 to 5 mm or 8 to 10 mm.

The nonmagnetic material layer 43 is made of Cu (copper) or the like.
The material and structure of the free magnetic layer 44 are not limited. For example, using a CoFe alloy (cobalt / iron alloy), a NiFe alloy (nickel / iron alloy), or the like as a material, a single layer structure, a laminated structure, a laminated ferri structure, or the like can be formed.
The protective layer 45 is made of Ta (tantalum) or the like.

  FIG. 7 is a diagram showing another film configuration of the magnetoresistive effect element in the magnetic sensor according to the embodiment of the present invention. The magnetic detection elements 122a to 122d (see FIGS. 1 to 3) shown in FIG. 6 are similar to FIG. 6 in that an antiferromagnetic layer 46 is provided between the free magnetic layer 44 and the protective layer 45. It differs from the film configuration shown.

  The antiferromagnetic layer 46 includes an x-Mn alloy (x-manganese alloy, x = Pt, Ir, Ru, Rh, Pd, Fe, Ni), an x-Cr alloy (x-chromium alloy, x = Al, Pt, Mn) and x-O (x oxide, x = Fe, Co, Ni) can be used. Among these, a PtMn alloy (platinum / manganese alloy) and an IrMn alloy (iridium / manganese alloy) are preferable.

  The antiferromagnetic layer 46 is ordered by annealing in a non-magnetic field or a weak magnetic field, and exchange coupling is generated between the antiferromagnetic layer 46 and the free magnetic layer 44 (interface). A bias magnetic field can be applied to the free magnetic layer 44 by this exchange coupling.

  Next, a bias magnetic field application unit that applies a bias magnetic field to the free magnetic layer of the magnetoresistive effect element will be described. Examples of the bias magnetic field applying unit include a hard bias configuration in which a hard bias is applied by a hard bias layer and an exchange bias configuration in which an exchange bias is applied by an antiferromagnetic layer.

  In the hard bias configuration shown in FIG. 8A, a pair of magnetoresistive elements 122a and 122b and hard bias layers (bias magnetic field application units) 53 are alternately arranged. The magnetoresistive effect elements 122a and 122b have a plurality of element portions 57 extending in a band shape from one hard bias layer 53 side toward the other hard bias layer 53 side. The plurality of element portions 57 are arranged in parallel between the pair of hard bias layers 53, and the adjacent element portions 57 are connected in a meander shape by the conductive portion 58. In each of the magnetoresistive elements 122a and 122b, the direction orthogonal to the extending direction of the element portion 57 is the Pin direction in plan view.

  In this hard bias configuration, each hard bias layer 53 is magnetized in one direction parallel to the extending direction of the element portion 57. Therefore, a bias magnetic field in the same direction is applied to the magnetoresistive effect elements 122a and 122b.

  In the hard bias configuration, the other pair of magnetoresistive elements 122c and 122d are alternately arranged with the hard bias layer 53, similarly to the magnetoresistive elements 122a and 122b.

  In the configuration for applying the exchange bias shown in FIG. 8B, a bias magnetic field opposite to each other is applied to the pair of magnetoresistive elements 122a and 122b without forming a hard bias layer. Also in this exchange bias configuration, like the hard bias configuration, a plurality of element portions 66 extending in a strip shape are arranged in parallel, and the plurality of element portions 66 are connected in a meander shape by a conductive portion 67. In each of the magnetoresistive elements 122a and 122b, the direction orthogonal to the extending direction of the element portion 66 is the Pin direction in plan view.

  In the exchange bias configuration, exchange coupling at the interface between the free magnetic layer 44 and the antiferromagnetic layer 46 (see FIG. 7) causes the element portion 66 to extend from the antiferromagnetic layer 46 to the free magnetic layer 44. A bias magnetic field is applied.

  In the pair of magnetoresistive elements 122a and 122b, the bias magnetic field along the extending direction of the element portion 66 from the antiferromagnetic layer to the free magnetic layer by exchange coupling at the interface between the free magnetic layer and the antiferromagnetic layer. Is applied. The free magnetic layer and the antiferromagnetic layer are formed while applying a magnetic field in the manufacturing process of the pair of magnetoresistive elements 122a and 122b. At this time, by applying a magnetic field reverse to the pair of magnetoresistive elements 122a and 122b to form a free magnetic layer and an antiferromagnetic layer, the magnetoresistive elements 122a and 122b have bias magnetic fields that are opposite to each other. Can be applied. Similarly, a bias magnetic field along the extending direction of the element portion 66 is applied to the other pair of magnetoresistance effect elements 122c and 122d.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, the scope of the present invention is not limited to these Examples etc.

  FIG. 9 is a graph showing an RH curve in a direction perpendicular to the sensitivity axis of the GMR element which is a magnetoresistive effect element constituting the magnetic sensor of this example. As shown in the figure, due to the hysteresis of the GMR element, its resistance value varies depending on the direction in which the strength of the magnetic field changes. For example, in the GMR element of the RH curve shown in FIG. 9, the resistance value in the zero magnetic field has a difference of about 10Ω depending on the direction in which the magnetic field changes. The difference in resistance value of the GMR element in the zero magnetic field causes a difference in the offset of the magnetic sensor 1, that is, a difference in output from the middle point 131 and the middle point 132 in the zero magnetic field (see FIG. 1). Thus, by applying a bias magnetic field (Hex) having a predetermined resistance value regardless of the direction in which the magnetic field changes, the offset of the magnetic sensor due to the hysteresis of the GMR element can be reduced.

  However, when a large magnetic field is applied to the GMR element, the magnetization state of the free magnetic layer of the GMR element changes from the initial state. Even when the large magnetic field is removed and the bias magnetic field (Hex) is applied, the magnetization state may not return to the initial state due to the influence of the applied large magnetic field. In this way, when a large magnetic field is applied, if the magnetization state of the free magnetic layer of the GMR element does not return to the initial state and the resistance deviates from a predetermined value, an offset occurs in the magnetic sensor.

  If the bias magnetic field applied to the free magnetic layer of the GMR element is sufficiently increased, the magnetization state of the free magnetic layer can be maintained in the initial state even when a large magnetic field is applied to the GMR element. However, increasing the bias magnetic field applied to the GMR element is not preferable because the output of the magnetic sensor decreases and the response speed decreases.

Therefore, in order to investigate the change caused by applying an alternating magnetic field in the sensitivity axis direction after applying a large magnetic field to the magnetic sensor to cause an offset, the following measurement was performed.
<Measurement conditions>
Vdd: 5V
Applied large magnetic field: 20 mT in the opposite direction to the bias magnetic field
Magnetic field repeatedly measured (alternating magnetic field for initializing the free magnetic layer): ± 2 mT in the direction of the sensitivity axis, that is, the direction intersecting the bias magnetic field
<Film structure of GMR element (Å)>
Underlayer: NiFeCr (42Å) / first magnetic layer: 60FeCo (19Å) / nonmagnetic intermediate layer: Ru (3.6Å) / second magnetic layer: 90CoFe (24Å) / nonmagnetic material layer: Cu (20Å) / Free magnetic layer: 90CoFe (10Å) /82.5NiFe (70Å) / antiferromagnetic layer: IrMn (80Å) / protective layer: Ta (100Å)
<Shape>
4 μm width × 80 μm length × 9 meander shape The magnetic shield 30 is not provided.

FIG. 10 shows a direction that intersects the direction of the bias magnetic field after an external magnetic field having a large intensity that completely reverses the free magnetic layer in the opposite direction to the bias magnetic field is applied to reach a state where an offset occurs in the detection output. The evaluation when an alternating magnetic field of ± 2 mT is repeatedly applied in the sensitivity axis direction is shown. The horizontal axis was measured once when an alternating magnetic field of +2 mT and − + 2 mT was applied for one cycle.
As shown in the figure, when the alternating magnetic field is applied once, the offset fluctuation amount is large due to the influence of hysteresis after the free magnetic layer is inverted. However, when the alternating magnetic field was applied twice or more, the offset fluctuation amount decreased rapidly, and after the third time, the offset fluctuation amount was stabilized near zero.

  From this result, even when ExBias is applied to the free magnetic layer and a large disturbance magnetic field in the direction opposite to the bias direction is applied, an alternating magnetic field is applied multiple times in the sensitivity direction, so that It is possible to return the magnetization direction to the initial state.

1: Magnetic sensor 110: Full bridge circuit 111A, 111B: Half bridge circuit 12: Feedback circuit 121: Feedback coils 122a to 122d: Magnetoresistive effect elements (element part)
131, 132: Midpoint terminal 140: Oscillator 21: Substrate 22: Thermal silicon oxide film 23: Aluminum oxide film 24: Electrode 25, 29: Polyimide layer 26, 32: Electrode pad 27, 31: Silicon oxide film 28: Coil electrode 30: Magnetic shield 40: Substrate 41: Underlayer 42: Fixed magnetic layer 42a: First magnetic layer 42c: Second magnetic layer 42b: Nonmagnetic intermediate layer 43: Nonmagnetic material layer 44: Free magnetic layer 45: Protective layer 46: antiferromagnetic layer (bias magnetic field application unit)
53: Hard bias layer (bias magnetic field application unit)
57, 66: element portions 58, 67: conductive portion A: induction magnetic field B: cancel magnetic field Vdd: power supply voltage GND: ground potential H: external magnetic field

Claims (7)

In a magnetic sensor in which a plurality of magnetoresistive elements constituting a bridge circuit are provided on a substrate,
Each of the magnetoresistive elements includes a pinned magnetic layer whose magnetization direction is fixed, a free magnetic layer whose magnetization direction varies due to an external magnetic field, and a nonmagnetic material positioned between the pinned magnetic layer and the free magnetic layer And having a layer
A bias magnetic field application unit for applying a bias magnetic field to the free magnetic layer;
An alternating magnetic field applying unit that applies an alternating magnetic field in a direction crossing the bias magnetic field to the free magnetic layer. In the magnetoresistive effect element, a plurality of element portions extending in a band shape are connected in a meander shape,
The bias magnetic field application unit applies the bias magnetic field in the extending direction of the element unit,
The magnetic sensor according to claim 1, wherein the alternating magnetic field applying unit applies the alternating magnetic field in a sensitivity axis direction of the magnetoresistive effect element orthogonal to an extending direction of the element unit.   3. The magnetic sensor according to claim 1, wherein the bridge circuit is a full bridge circuit having a first half bridge circuit and a second half bridge circuit.   The magnetic sensor according to claim 1, wherein the bias magnetic field is a hard bias magnetic field or an exchange bias magnetic field. A feedback coil that generates a canceling magnetic field that cancels the magnetic field to be measured applied to the magnetoresistive element, and a detection circuit that controls the canceling current applied to the feedback coil and detects the canceling current,
The magnetic sensor according to claim 1, wherein the feedback coil is used as the alternating magnetic field applying unit.   The magnetic sensor according to claim 5, wherein the feedback coil is used as an alternating magnetic field applying unit that generates the alternating magnetic field at a time when the cancel current is not applied. It is further equipped with a magnetic shield,
The magnetic sensor according to claim 3, wherein the magnetic shield attenuates the magnetic field to be measured and enhances the cancellation magnetic field and the alternating magnetic field.