JP2013105825A - Biomagnetic sensor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high sensitivity of a tunnel magnetoresistive element in a biomagnetic sensor using the tunnel magnetoresistive element and measure biomagnetism with high accuracy by the sensor.SOLUTION: In a zero magnetic field, an easy magnetization axis 4a of a ferromagnetic metal magnetization free layer 4 is at a twisted position with respect to an easy magnetization axis 6a of a ferromagnetic metal magnetization fixed layer 6. Preferably, the twist angle is between 45 degrees and 135 degrees. The fixed layer is laminated at a position upper than the free layer, and the area of the fixed layer is arranged smaller than the area of the free layer. The free layer and the fixed layer each comprise three layers -- a first ferromagnetic body, an ultra thin non-magnetic metal layer, and a second ferromagnetic body -- and have an anti-parallel coupling film structure having exchange coupling force, in the structure the magnetization direction of the first ferromagnetic body and the magnetization direction of the second ferromagnetic body with the ultra thin non-magnetic metal layer interposed therebetween becoming anti-parallel. MgO and Ru are used as for an insulation layer and the ultra thin non-magnetic metal layer respectively.

Description

  The present invention relates to a biomagnetic sensor for sensing a magnetic field generated from a living body and a method for manufacturing the same.

Conventionally, as a device for measuring a magnetic field generated from a living body, a biomagnetic measuring device using a SQUID (Superconducting Quantum Interference Device) sensor has been studied (Patent Documents 1-5). Two-dimensional biomagnetic information such as magnetoencephalogram and magnetocardiogram can be obtained by arranging a large number of SQUID sensors and using them for measurement of biomagnetism.
In order to perform biomagnetism measurement with the SQUID sensor, it is necessary to keep the SQUID sensor in a superconducting state with a refrigerant such as liquid helium. For this reason, the SQUID sensor is incorporated in a dewar in which the refrigerant is stored, and is used for measurement in a state immersed in the refrigerant.
A part of the outer wall portion of the refrigerant tank of this Dewar is formed into a shape corresponding to a measurement target part of a living body, for example, the skull, and a number of SQUID sensors are arranged inside the outer wall portion and immersed in the refrigerant. A biomagnetic measurement apparatus has been proposed that can measure a large number of SQUID sensors in close proximity to a living body by contacting the outside of the body with the living body to obtain a magnetoencephalogram or the like.

  On the other hand, Patent Document 6 discloses an ultrathin body that exists between a first ferromagnetic body, a second ferromagnetic body, and the first ferromagnetic body and the second ferromagnetic body. An antiparallel coupling film structure having a nonmagnetic metal layer and having an exchange coupling force in which the magnetization direction of the first ferromagnetic material and the magnetization direction of the second ferromagnetic material are antiparallel, In addition, a tunnel magnetoresistive element and a magnetic device in which the antiparallel coupling film structure is applied to a magnetization free layer or a magnetization fixed layer are described, and the antiparallel coupling film structure increases thermal fluctuation of magnetization and increase of a write current. It is explained that this problem can be solved.

JP-A-2-40578 Japanese Patent Laid-Open No. 3-1839 JP 2000-193364 A JP 2004-65605 A JP 2007-17248 A JP 2010-10233 A

In a biomagnetic measuring device using a SQUID sensor, a refrigerant that keeps the sensor at a low temperature is required, which increases the size of the device and allows the sensor to be flexibly accommodated close to the test part. There is a problem that it is difficult to arrange them at high density.
Therefore, the present inventors apply a tunnel magnetoresistive element (TMR (Tunnel Magneto Resistive) element) to biomagnetism measurement as a sensor device that can be used at room temperature and can be reduced in size, weight, thickness, and density. think of.

However, since the biomagnetic signal is very weak, in order to detect the biomagnetic signal with the tunnel magnetoresistive element, the sensitivity of the ferromagnetic metal magnetization free layer of the tunnel magnetoresistive element must be increased to the limit.
In the prior art, since the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer are simultaneously heat-treated in a magnetic field during the manufacturing process, the easy magnetization directions of the two layers are the same.
Although the magnetization direction of the ferromagnetic magnetization free layer basically changes depending on the external magnetic field, the study by the present inventors has shown that the easy magnetization axis of the ferromagnetic metal magnetization free layer and the easy magnetization axis of the ferromagnetic magnetization fixed layer are In the case of the same direction, the ferromagnetic metal magnetization free layer is considered to be in an unstable state from the viewpoint of magnetic energy due to the influence of the leakage magnetic field from each other, which can be a hindrance to sensitivity improvement and noise increase. It came to obtain the knowledge of.

  The present invention has been made in view of the above-described problems in the prior art. In a biomagnetic sensor using a tunnel magnetoresistive element, the sensitivity of the tunnel magnetoresistive element is increased, and biomagnetism is measured with high accuracy. It is an object of the present invention to provide a biomagnetic sensor that can be used and a manufacturing method thereof.

The invention described in claim 1 for solving the above-mentioned problems is a ferromagnetic metal magnetization fixed layer in which the magnetization direction is fixed, and the ferromagnetic metal magnetization free in which the magnetization direction changes under the influence of an external magnetic field. And an insulating layer disposed between the ferromagnetic metal magnetization fixed layer and the ferromagnetic metal magnetization free layer, the magnetization direction of the ferromagnetic metal magnetization fixed layer and the ferromagnetic metal magnetization free In a biomagnetic sensor including a tunnel magnetoresistive element that changes the resistance of the insulating layer by a tunnel effect according to an angle difference with the magnetization direction of the layer,
In the biomagnetic sensor, the easy magnetization axis of the ferromagnetic metal magnetization free layer in a zero magnetic field is in a position twisted with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer.
Here, the “twisted position” refers to a positional relationship in which two straight lines in the space are not parallel and do not intersect, that is, a positional relationship between two straight lines that cannot exist on the same plane. A straight line perpendicular to the two straight lines at the position of twist is called “twist axis”, and the relative angle of the other straight line to one straight line around the twist axis is called “twist angle”.

  The invention according to claim 2 is the biomagnetic sensor according to claim 1, wherein an area of the ferromagnetic metal magnetization fixed layer is smaller than an area of the ferromagnetic metal magnetization free layer.

  According to a third aspect of the present invention, each of the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer includes a first ferromagnet, a second ferromagnet, and the first ferromagnet. An ultrathin nonmagnetic metal layer sandwiched between the second ferromagnetic material, and the magnetization direction of the first ferromagnetic material and the magnetization direction of the second ferromagnetic material 3. The biomagnetic sensor according to claim 1, wherein the biomagnetic sensor is an antiparallel coupling film structure having an exchange coupling force that becomes antiparallel to each other.

  According to a fourth aspect of the present invention, the ferromagnetic metal magnetization fixed layer is the ferromagnetic metal magnetization free layer as viewed from the substrate supporting the laminated body including the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer. The biomagnetic sensor according to claim 1, wherein the biomagnetic sensor is formed in an upper layer.

  The invention according to claim 5 is the biomagnetic sensor according to any one of claims 1 to 4, wherein the insulating layer is made of MgO.

  The invention according to claim 6 is the biomagnetic sensor according to claim 3, wherein the ultrathin nonmagnetic metal layer is made of Ru.

  According to a seventh aspect of the present invention, the angle of twist between the easy magnetization axis of the ferromagnetic metal magnetization free layer and the easy magnetization axis of the ferromagnetic metal magnetization fixed layer in a zero magnetic field is 45 degrees to 135 degrees. The biomagnetic sensor according to any one of claims 1 to 6, wherein the biomagnetic sensor is provided.

The invention according to claim 8 is a ferromagnetic metal magnetization fixed layer whose magnetization direction is fixed, a ferromagnetic metal magnetization free layer whose magnetization direction changes under the influence of an external magnetic field, and the ferromagnetic metal An angle between a magnetization direction of the ferromagnetic metal magnetization fixed layer and a magnetization direction of the ferromagnetic metal magnetization free layer having an insulating layer disposed between the magnetization fixed layer and the ferromagnetic metal magnetization free layer; Fabricate a tunnel magnetoresistive element that changes the resistance of the insulating layer by the tunnel effect according to the difference,
A first heat treatment is performed on the magnetoresistive element at a first temperature while an external magnetic field is applied, and the external temperature is lower than the first heat treatment and the direction is different from that of the first heat treatment. By performing the second heat treatment while applying a magnetic field, the easy magnetization axis of the ferromagnetic metal magnetization free layer in a zero magnetic field is twisted with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer. This is a method of manufacturing a biomagnetic sensor.

  The invention according to claim 9 is characterized in that the area of the ferromagnetic metal magnetization fixed layer is formed smaller than the area of the ferromagnetic metal magnetization free layer. Is the method.

  According to a tenth aspect of the present invention, the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer are respectively formed of a first ferromagnet, a second ferromagnet, and the first ferromagnet. And an ultrathin nonmagnetic metal layer sandwiched between the first ferromagnetic material and the second ferromagnetic material, the magnetization direction of the first ferromagnetic material and the magnetization of the second ferromagnetic material. 10. The biomagnetic sensor manufacturing method according to claim 8, wherein the biomagnetic sensor is manufactured as an antiparallel coupling film structure having an exchange coupling force whose direction is antiparallel.

  The invention according to claim 11 is the ferromagnetic metal magnetization free layer as viewed from the substrate supporting the laminated body including the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer. The biomagnetic sensor manufacturing method according to claim 8, wherein the biomagnetic sensor is formed in an upper layer.

  According to the present invention, the easy magnetization axis of the ferromagnetic metal magnetization free layer and the easy magnetization axis of the ferromagnetic metal magnetization fixed layer are already in different directions in a zero magnetic field, When a magnetic field is applied, the influence of the leakage magnetic field generated from the ferromagnetic metal magnetization fixed layer is suppressed, and the sensitivity of the ferromagnetic metal magnetization free layer to the external magnetic field is improved. High sensitivity can be achieved and biomagnetism can be measured with high accuracy.

It is a block diagram of the biomagnetic sensor which concerns on one Embodiment of this invention. 1 is a schematic perspective view of a tunnel magnetoresistive element according to an embodiment of the present invention, in which an insulating layer is omitted. It is a graph which shows transition of the temperature in a furnace in the heat treatment process in a magnetic field of the tunnel magnetoresistive element concerning one embodiment of the present invention. It is a graph which showed the change rate (MR (%), vertical axis | shaft) of the resistance of the tunnel magnetoresistive element with respect to the external magnetic field (H (Oe), horizontal axis) concerning a comparative example. FIG. 5 is a graph showing a rate of change in resistance (MR (%), vertical axis) of a tunneling magnetoresistive element with respect to an external magnetic field (H (Oe), horizontal axis) according to a comparative example, and a horizontal axis relative to the graph of FIG. Is expanding. 6 is a graph showing a rate of change (MR (%), vertical axis) of resistance of a tunnel magnetoresistive element with respect to an external magnetic field (H (Oe), horizontal axis) according to an example of the present invention. FIG. 7 is a graph showing a rate of change in resistance (MR (%), vertical axis) of a tunnel magnetoresistive element with respect to an external magnetic field (H (Oe), horizontal axis) according to an embodiment of the present invention. On the other hand, the horizontal axis is enlarged.

  An embodiment of the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention.

  As a typical example, the biomagnetic sensor of the present embodiment is used for biomagnetic measurement in which a magnetoencephalogram is obtained by measuring a magnetic field emitted from a human skull. Various biomagnetism measurement systems are built in and a magnetic field emitted from the living body is measured.

As shown in FIG. 1, the biomagnetic sensor 1 includes a tunnel magnetoresistive element (hereinafter referred to as “TMR element”) 10.
As shown in FIG. 1, the biomagnetic sensor 1 includes a lower electrode layer 3, a ferromagnetic metal magnetization free layer 4, an insulating layer 5, a ferromagnetic metal magnetization fixed layer 6, an immobilization promoting layer 7, an upper portion on a substrate 2. It has a stacked structure in which the electrode layers 8 are sequentially stacked.
The TMR element 10 changes the resistance of the insulating layer 5 by the tunnel effect according to the angle difference between the magnetization direction of the ferromagnetic metal magnetization fixed layer 6 and the magnetization direction of the ferromagnetic metal magnetization free layer 4.
A power supply 11 for inputting current and a constant resistance 12 are connected in series between the upper electrode layer 8 and the lower electrode layer 3, and a change in resistance value of the insulating layer 5 is detected as a change in voltage value. The biomagnetic sensor 1 is mounted by being connected to the voltmeter 13. Note that a change in the resistance value of the insulating layer 5 may be detected by applying a voltage to the TMR element 10 and detecting a current flowing through the insulating layer 5 of the TMR element 10.

The substrate 2 is not particularly limited as long as it can withstand the formation of each layer, but a substrate having both heat resistance and insulation that can withstand film formation and heat treatment is preferable. Moreover, it is preferable that it is non-magnetic to prevent the magnetic flux from being sucked and the surface is formed relatively smoothly. From such a viewpoint, for example, Si, SiO ₂ or the like can be used.

  The lower electrode layer 3 includes three layers 31, 32, and 33. The layer 31 is for adjusting the roughness of the substrate 2, and for example, Ta can be used. The layer thickness of the layer 31 is preferably about 2 nm to 10 nm. Ru can be used as the layer 32 and Ta can be used as the layer 33.

The ferromagnetic metal magnetization free layer 4 is a ferromagnetic metal magnetization layer whose magnetization direction changes under the influence of an external magnetic flux, and includes a first ferromagnetic layer 41, an ultrathin nonmagnetic metal layer 42, and the like. And the second ferromagnetic layer 43.
For example, Ni ₇₉ Fe ₂₁ can be used as the first ferromagnetic layer 41. The thickness of the first ferromagnetic layer 41 is preferably about 10 nm to 200 nm.
The ultrathin nonmagnetic metal layer 42 is for magnetically coupling the first ferromagnetic layer 41 and the second ferromagnetic layer 43, and for separating the latter from the former crystal structure, It is desirable to use a thin film layer having no crystal structure. Specific examples of the material include Ru. The layer thickness of the ultrathin nonmagnetic metal layer 42 is preferably about 0.5 to 1 nm.
As the second ferromagnetic layer 43, various types can be used. As a typical example, a layer obtained by heat-treating Co ₄₀ Fe ₄₀ B ₂₀ from an amorphous structure to exhibit ferromagnetism can be used. . The crystal structure of this layer is, for example, a body-centered cubic crystal. Fe-rich materials such as Co ₁₆ Fe ₆₄ B ₂₀ can also be used. The layer thickness of the second ferromagnetic layer 43 is preferably about 1 to 10 nm. The second ferromagnetic layer 43 is bonded to the lower surface of the insulating layer 5.
The ferromagnetic metal magnetization free layer 4 is the same as the first ferromagnetic layer 41 as described above. A second ferromagnetic layer 43 and an ultrathin nonmagnetic metal layer 42 sandwiched between them are provided, and the magnetization direction of the first ferromagnetic layer 41 and the second ferromagnetic layer An antiparallel coupling film structure having an exchange coupling force in which the magnetization direction of 43 is antiparallel is formed. Here, “anti-parallel” means that the direction of the magnetic field is substantially parallel and opposite, and the range in which the direction of the magnetic field can be regarded as substantially parallel (for example, tilted 10 degrees forward and backward). In the range).

  The insulating layer 5 is disposed between the ferromagnetic metal magnetization fixed layer 6 and the ferromagnetic metal magnetization free layer 4. As the insulating layer 5, various insulating materials can be used. For example, MgO, AlOx, or the like can be used. MgO is preferable from the viewpoint of improving the sensitivity of the element, and in particular, an MgO film is preferably used as the insulating layer 5 in order to detect a weak magnetic field such as a biomagnetic signal with a tunnel magnetoresistive element. The thickness of the insulating layer 5 is desirably about 1 nm to 10 nm.

The ferromagnetic metal magnetization fixed layer 6 is a ferromagnetic metal magnetization layer whose magnetization direction is fixed. The first ferromagnetic layer 61, the ultrathin nonmagnetic metal layer 62, and the second ferromagnetic layer. 63.
As the first ferromagnetic layer 61, the same material as the first ferromagnetic layer 43 of the free layer 4, for example, Co ₄₀ Fe ₄₀ B ₂₀ can be used. The thickness of the first ferromagnetic layer 61 is preferably about 1 to 10 nm. The second ferromagnetic layer 61 is bonded to the upper surface of the insulating layer 5.
The ultra-thin nonmagnetic metal layer 62 is for magnetically coupling the first ferromagnetic layer 41 and the second ferromagnetic layer 43 and separating the latter from the former crystal structure, It is desirable to use a thin film layer having no crystal structure. Specific examples of the material include Ru. The layer thickness of the ultrathin nonmagnetic metal layer 62 is preferably about 0.5 to 1 nm.
As the second ferromagnetic layer 63, for example, CoFe can be used. The composition ratio of Co and Fe can be arbitrarily set, but typically, Co: Fe = 75: 25 or Co: Fe = 50: 50 can be set. The crystal structure of the second ferromagnetic layer 63 is, for example, a face centered cubic crystal. The thickness of the second ferromagnetic layer 63 is preferably about 0.5 nm to 5 nm.
As described above, the ferromagnetic metal magnetization fixed layer 6 includes the first ferromagnetic layer 61, the second ferromagnetic layer 63, and the ultrathin nonmagnetic metal layer 62 that is sandwiched therebetween. And an antiparallel coupling film structure having an exchange coupling force that makes the magnetization direction of the first ferromagnetic layer 61 and the magnetization direction of the second ferromagnetic layer 63 antiparallel.

  The immobilization promoting layer 7 is for promoting the immobilization of the second ferromagnetic layer 63, and an antiferromagnetic film such as IrMn or platinum manganese is preferably used. The crystal structure of the second ferromagnetic layer 63 is, for example, a face centered cubic crystal. The thickness of the immobilization promoting layer 7 is preferably about 5 nm to 20 nm.

  The upper electrode layer 8 is composed of two layers 81 and 82. The layer 81 is a base layer of the layer 82 for adjusting the roughness of the immobilization promoting layer 7, and for example, Ta can be used. The layer 81 preferably has a thickness of about 2 nm to 10 nm. The layer 82 is an upper layer to which an electrode is connected, and for example, Au can be used. The layer 82 preferably has a thickness of about 20 nm to 40 nm.

Each layer can be formed by, for example, a magnetron sputtering method. In addition, for the purpose of obtaining a desired crystal structure, heat treatment may be performed as necessary. In the present embodiment, as shown in FIG. 2, the easy magnetization axis 4 a of the ferromagnetic metal magnetization free layer 4 in the zero magnetic field is twisted with respect to the easy magnetization axis 6 a of the ferromagnetic metal magnetization fixed layer 6. In position. In order to obtain the easy magnetization axes 4a and 6a having such a relationship, the substrate 2 on which the respective layers are stacked is placed in a furnace and placed in a magnetic field, and two heat treatments with different temperature conditions are performed as shown in FIG.
First, the easy heat axis 4a of the ferromagnetic metal magnetization free layer 4 is formed by performing the first heat treatment. The vertex temperature in the temperature transition graph A2 of the second heat treatment is lower than the vertex temperature in the temperature transition graph A1 of the first heat treatment (preferably lower by 10 ° C. or more), and after the first heat treatment, preferably after cooling to near room temperature By performing the second heat treatment, the easy magnetization axis 6a of the ferromagnetic metal magnetization fixed layer 6 is formed. The easy magnetization axis 4a is formed along the magnetic field direction during the first heat treatment. The easy magnetization axis 6a is formed along the magnetic field direction during the second heat treatment. Therefore, by changing the magnetic field direction during the second heat treatment relative to the magnetic field direction during the first heat treatment, the easy magnetization axis 6a can be twisted with respect to the easy magnetization axis 4a. The magnetic field direction during the first heat treatment and the magnetic field direction during the second heat treatment are parallel to the layer. Therefore, the easy magnetization axis 6a can be in a twisted position with respect to the easy magnetization axis 4a by rotating the magnetic field direction around an axis in the stacking direction on the substrate 2 (= an axis perpendicular to the substrate 2). There is no restriction | limiting in particular in heat processing time, for example, what is necessary is just to carry out for about 10 minutes-2 hours, and it is preferable to shorten time of 2nd heat processing rather than 1st heat processing. There is no restriction | limiting in particular also in the magnetic field in the case of heat processing, for example, it may carry out in the range of 0.01-2 [T], and it is preferable to make the external magnetic field in 2nd heat processing smaller than 1st heat processing.

  As shown in FIG. 2 (a), it is sufficient that the twist angle φ between the easy magnetization axis 4a and the easy magnetization axis 6a is 90 degrees. If the easy magnetization axis 4a and the easy magnetization axis 6a are not parallel as shown in FIG. 2 (b), the effect of improving the sensitivity is obtained even if the twist φ formed by the two is not 90 degrees, but the twist angle φ Is preferably in the range of 45 degrees to 135 degrees.

  Further, the area of the ferromagnetic metal magnetization fixed layer 6 is equal to the area of the ferromagnetic metal magnetization free layer 4 or smaller than the area of the ferromagnetic metal magnetization free layer 4 as shown in FIG. By making the area of the ferromagnetic metal magnetization fixed layer 6 relatively small, the influence of the leakage magnetic field from the fixed layer 6 to the free layer 4 is reduced, and the sensitivity of magnetic detection can be further improved. The ratio of the area of the ferromagnetic metal magnetization fixed layer 6 to the area of the ferromagnetic metal magnetization free layer 4 is not limited to this, but is preferably set in the range of 1: 1 to 1:10.

  Further, as described with reference to FIG. 1, the ferromagnetic metal magnetization fixed layer 6 is strong when viewed from the substrate 2 supporting the laminated body including the ferromagnetic metal magnetization free layer 4 and the ferromagnetic metal magnetization fixed layer 6. It is formed above the magnetic metal magnetization free layer 4 (that is, on the side farther from the substrate 2). By having such a vertical relationship, the area of the ferromagnetic metal magnetization fixed layer 6 is reduced by the selective etching from the substrate surface on which the ferromagnetic metal magnetization fixed layer 6 and the like are laminated. It is easy to form small with respect to the area.

According to the biomagnetic sensor 1 of the present embodiment described above, the easy magnetization axis 4a of the ferromagnetic metal magnetization free layer 4 and the easy magnetization axis 6a of the ferromagnetic metal magnetization fixed layer 6 are already different in a zero magnetic field. When an external magnetic field is generated from this state, adverse effects such as a leakage magnetic field generated from the ferromagnetic metal magnetization fixed layer 6 are suppressed to be small, and the magnetization of the ferromagnetic metal magnetization free layer 4 is changed to an external magnetic field. Changes to high sensitivity.
In addition, according to the biomagnetic sensor 1 of the present embodiment, the area of the ferromagnetic metal magnetization fixed layer 6 is smaller than the area of the ferromagnetic metal magnetization free layer 4. The influence of the leakage magnetic field on is suppressed.
Furthermore, according to the biomagnetic sensor 1 of the present embodiment, since the ferromagnetic metal magnetization fixed layer 6 is an antiparallel coupling film structure, the leakage magnetic field is reduced, and this also causes the fixed layer 6 to the free layer 4. The influence of the leakage magnetic field can be kept small.
Moreover, according to the biomagnetic sensor 1 of this embodiment, since the ferromagnetic metal magnetization free layer 4 is similarly an antiparallel coupling film structure, a stable magnetization film free from leakage magnetic flux can be formed.
By combining the above technical elements, high sensitivity of the TMR element can be achieved, and biomagnetism can be measured with high accuracy.
In particular, a biomagnetic sensor suitable for highly sensitive biomagnetic measurement in the vicinity of zero magnetic field can be obtained.

  Since the biomagnetic sensor 1 uses a TMR element, the biomagnetic sensor 1 is a magnetic sensor that can be used at room temperature, and neither a refrigerant for cooling nor a heat insulating material for cutting off heat from the outside is required. The sensor unit on which the sensor 1 is mounted can be configured to be lighter and thinner. And since the sensor unit can be configured to be lighter and thinner, it can be configured in a simple and flexible form that can be handled manually and applied to the subject's measurement target site, or can be attached to the subject. Regardless of the size and shape of the body, the TMR element is arranged at a fixed distance from the test part, and accurate measurement can be performed. Further, it can be configured at a lower cost than the SQUID and has low power consumption.

The above-described biomagnetic sensor 1 having the configuration shown in FIG. 1 in which the easy magnetization axis 4a of the ferromagnetic metal magnetization free layer 4 and the easy magnetization axis 6a of the ferromagnetic metal magnetization fixed layer 6 are in a twisted positional relationship. The magnetic detection sensitivity was compared with a biomagnetic sensor in which the easy magnetization axis is not in a torsional positional relationship.
Specifically, biomagnetic sensors of the examples of the present invention and comparative examples were produced by the following procedure.
Using a magnetron sputtering apparatus, on the SiO ₂ substrate, Ta is 5 nm as the layer 31, Ru is 10 nm as the layer 32, Ta is 5 nm as the layer 33, and Ni ₇₉ Fe ₂₁ is 10, ₂₀ , 70, 150 as the layer 41. , 200 nm, Ru as layer 42 0.85 nm, Layer 43 as Co ₄₀ Fe ₄₀ B ₂₀ as 3 nm, Layer 5 as MgO as 2.5 nm, Layer 61 as Co ₄₀ Fe ₄₀ B ₂₀ as 3 nm, Layer 62 as Ru 0.85 nm, Co ₇₅ Fe ₂₅ as layer 63, IrMn as layer 7, 10 nm as layer 7, Ta as 5 nm as layer 81, Au as 30 nm as layer 82, were sequentially laminated. The film thickness was calculated from the film formation speed and the film formation time. Next, after resist patterning is performed on the layer 82 by a photolithography process, Ar ion milling is performed until the layer 43 is reached, whereby the area of the ferromagnetic metal magnetization fixed layer 6 and the area of the ferromagnetic metal magnetization free layer 4 are increased. The resist film was removed by processing to a ratio of 1: 3.5.
The thus obtained laminate was heat-treated at 325 ° C. for 50 minutes while applying an external magnetic field 1 [T] as the first heat treatment. After cooling to room temperature, by changing the arrangement direction of this laminate, an external magnetic field of 0.1 [T] intersecting the magnetic field direction of the magnetic field at the time of the first heat treatment by 90 degrees is applied at 300 ° C. Heat treatment was performed for 20 minutes (second heat treatment). After cooling to room temperature, a resistor, a power source, and a voltmeter were electrically connected to obtain a biomagnetic sensor of the example of the present invention. In the comparative example, the same procedure as in the above example was performed except that the magnetic field direction in the second heat treatment was not changed from the magnetic field direction in the first heat treatment. A biomagnetic sensor was prepared in which the easy magnetization axis and the easy magnetization axis of the ferromagnetic metal magnetization fixed layer were in the same direction.

The magnetic detection performance of the sensors of Examples and Comparative Examples thus obtained was measured. Specifically, a sensor to be measured is placed in a Helmholtz coil, and a constant current of several μA is passed through the sensor, and the magnetic field of the coil is changed from −1800 [Oe] to +1800 [Oe] and then −1800 [Oe The sensor resistance change rate with respect to the external magnetic field was measured by detecting the output voltage of the sensor.
4 to 7 are graphs showing the change rate (MR (%), vertical axis) of the resistance of the TMR element with respect to the external magnetic field (H (Oe), horizontal axis) thus obtained. 4 and 5 relate to a comparative example, and FIGS. 6 and 7 relate to an example of the present invention. 5 and 7 are enlarged views in the vicinity of the zero magnetic field in FIGS. 4 and 6, respectively. Note that the horizontal scale is different. In these graphs, biomagnetism is detected by a change in a linear portion including a zero magnetic field. As can be seen by comparing the graph of the comparative example and the graph of the embodiment of the present invention, the linear portion including the zero magnetic field has a steeper slope in the embodiment of the present invention than the comparative example, and the external magnetic field The resistance of the TMR element changes greatly with respect to the change, that is, it is highly sensitive and advantageous in measuring weak biomagnetism with high accuracy.

Regardless of the above embodiment, when the antiparallel coupling film structure is applied to the ferromagnetic metal magnetization layer, only one of the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer is used. An anti-parallel coupling film structure may be applied to the structure, and the effect of making the ferromagnetic metal magnetization free layer an anti-parallel coupling film structure and the effect of making the ferromagnetic metal magnetization fixed layer an anti-parallel coupling film structure are obtained. It is done.
In addition, in the case where no condition is set for the size relationship between the area of the ferromagnetic metal magnetization fixed layer and the area of the ferromagnetic metal magnetization free layer, the vertical relationship in the lamination of these layers is also arbitrary. As described above, it is advantageous to make the fixed layer an upper layer and to have a small area.

DESCRIPTION OF SYMBOLS 1 Biomagnetic sensor 2 Substrate 3 Lower electrode layer 4 Ferromagnetic metal magnetization free layer 4a Easy magnetization axis 5 Insulating layer 6 Ferromagnetic metal magnetization fixed layer 6a Easy magnetization axis 7 Immobilization promoting layer 8 Upper electrode layer 10 Tunnel magnetoresistive element 13 Voltmeter 41 First ferromagnetic layer 42 Ultrathin nonmagnetic metal layer 43 Second ferromagnetic layer 61 First ferromagnetic layer 62 Ultrathin nonmagnetic metal layer 63 Second ferromagnetic layer φ Twist corner

Claims (11)

A ferromagnetic metal magnetization fixed layer whose magnetization direction is fixed, a ferromagnetic metal magnetization free layer whose magnetization direction changes under the influence of an external magnetic field, and the ferromagnetic metal magnetization fixed layer and the ferromagnetic metal An insulating layer disposed between the magnetization free layer and the tunneling effect according to an angular difference between a magnetization direction of the ferromagnetic metal magnetization fixed layer and a magnetization direction of the ferromagnetic metal magnetization free layer; In a biomagnetic sensor including a tunnel magnetoresistive element that changes the resistance of
A biomagnetic sensor, wherein an easy magnetization axis of the ferromagnetic metal magnetization free layer in a zero magnetic field is in a twisted position with respect to an easy magnetization axis of the ferromagnetic metal magnetization fixed layer.   The biomagnetic sensor according to claim 1, wherein an area of the ferromagnetic metal magnetization fixed layer is smaller than an area of the ferromagnetic metal magnetization free layer.   The ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer include a first ferromagnet, a second ferromagnet, the first ferromagnet, and the second ferromagnet, respectively. Exchange coupling in which the magnetization direction of the first ferromagnet and the magnetization direction of the second ferromagnet are antiparallel to each other. The biomagnetic sensor according to claim 1, wherein the biomagnetic sensor is an antiparallel coupling membrane structure having a force.   The ferromagnetic metal magnetization fixed layer is formed in an upper layer than the ferromagnetic metal magnetization free layer when viewed from the substrate supporting the laminated body including the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer. The biomagnetic sensor according to claim 1, 2, or 3.   The biomagnetic sensor according to any one of claims 1 to 4, wherein the insulating layer is made of MgO.   The biomagnetic sensor according to claim 3, wherein the ultrathin nonmagnetic metal layer is made of Ru.   The twist angle between the easy magnetization axis of the ferromagnetic metal magnetization free layer and the easy magnetization axis of the ferromagnetic metal magnetization fixed layer in a zero magnetic field is 45 degrees to 135 degrees. The biomagnetic sensor according to claim 6. A ferromagnetic metal magnetization fixed layer whose magnetization direction is fixed, a ferromagnetic metal magnetization free layer whose magnetization direction changes under the influence of an external magnetic field, and the ferromagnetic metal magnetization fixed layer and the ferromagnetic metal An insulating layer disposed between the magnetization free layer and the tunneling effect according to an angular difference between a magnetization direction of the ferromagnetic metal magnetization fixed layer and a magnetization direction of the ferromagnetic metal magnetization free layer; Fabricate a tunnel magnetoresistive element that changes the resistance of
A first heat treatment is performed on the magnetoresistive element at a first temperature while an external magnetic field is applied, and the external temperature is lower than the first heat treatment and the direction is different from that of the first heat treatment. By performing the second heat treatment while applying a magnetic field, the easy magnetization axis of the ferromagnetic metal magnetization free layer in a zero magnetic field is twisted with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer. A method for producing a biomagnetic sensor.   9. The method of manufacturing a biomagnetic sensor according to claim 8, wherein the area of the ferromagnetic metal magnetization fixed layer is formed smaller than the area of the ferromagnetic metal magnetization free layer.   The ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer are respectively formed of a first ferromagnet, a second ferromagnet, the first ferromagnet, and the second ferromagnet. And an ultrathin non-magnetic metal layer sandwiched between the first ferromagnetic material and the second ferromagnetic material in which the magnetization direction is antiparallel. 10. The method of manufacturing a biomagnetic sensor according to claim 8, wherein the biomagnetic sensor is manufactured as an antiparallel coupling film structure having a binding force.   The ferromagnetic metal magnetization fixed layer is formed above the ferromagnetic metal magnetization free layer when viewed from the substrate supporting the laminated body including the ferromagnetic metal magnetization free layer and the ferromagnetic metal magnetization fixed layer. The biomagnetic sensor manufacturing method according to claim 8, claim 9, or claim 10.

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