JP2017083173A - Magnetometric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a higher sensitivity and measure a minute magnetic change with high accuracy in a magnetometric sensor utilizing a tunnel magnetic resistance element.SOLUTION: The magnetometric sensor includes a feedback circuit for controlling a magnetic field generation source a61 that gives a change to the direction of magnetization of a ferromagnetic metal magnetization free layer 4, rotating the direction of magnetization of the ferromagnetic metal magnetization free layer from an easy magnetization axis c4 of the ferromagnetic metal magnetization free layer, and stabilizing it at a torsion position having a prescribed angle of torsion to the easy magnetization axis of a ferromagnetic metal magnetization fixed layer 6. For example, the easy magnetization axis of the ferromagnetic metal magnetization free layer is parallel to the easy magnetization axis c1 of the ferromagnetic metal magnetization fixed layer, and the prescribed angle of torsion is 90 degrees. When this torsion position is set to a neutral position (zero point in measurement) for detecting magnetism and there is a change in a magnetic signal, it is expelled from the loop of the feedback circuit or extracted from a control signal for controlling the magnetic field generation source of the feedback circuit, whereby a detection magnetic signal is outputted.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a magnetic sensor suitable for sensing a weak magnetic field.

As described in Patent Document 1, a tunnel magnetoresistive element (TMR (Tunnel Magneto Resistive) element) is used as a sensor device that can be used at room temperature and can be reduced in size, weight, thickness, and density. It has been proposed to apply to.
The tunnel magnetoresistive element includes 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 a ferromagnetic metal magnetization fixed layer And an insulating layer disposed between the ferromagnetic metal magnetization free layer and insulating by a tunnel effect according to the angular difference between the magnetization direction of the ferromagnetic metal magnetization fixed layer and the magnetization direction of the ferromagnetic metal magnetization free layer Change the resistance of the layer.
In the biomagnetic sensor including such a tunneling magnetoresistive element, the invention described in Patent Document 1 has an easy magnetization axis of a ferromagnetic metal magnetization free layer with a detection magnetic field of zero in order to achieve high sensitivity. It is characterized by being in a twisted position with respect to the easy magnetization axis of the metal magnetization fixed layer.

JP2013-105825A

In order to use the TMR element as a magnetic sensor that accurately measures the strength of the magnetic field, the resistance changes proportionally up and down according to changes in the positive magnetic field and the negative magnetic field from the zero detection magnetic field (neutral position). It is required to wake up.
According to the invention described in Patent Document 1, the easy magnetization axis of the free layer at zero detection magnetic field is in a twisted position with respect to the easy magnetization axis of the fixed layer. In accordance with the change of the magnetic field, the resistance can be changed proportionally up and down.
In this case, as shown in FIG. 9, the TMR element exhibits a resistance change according to the strength of the magnetic field in the direction Y2 orthogonal to the direction Y1 of the magnetization of the free layer 104 in a state where the detection magnetic field is zero. Used to detect the magnetic field in the direction Y2.
When the TMR element is used to detect a magnetic field in the direction of the hard magnetization axis of the free layer as described above, the sensitivity can be expressed as a resistance change rate of the TMR element / 2Hk. Here, 2Hk corresponds to a magnetic field necessary for reversing the magnetization direction of the free layer in the difficult magnetization axis direction.
Therefore, it has been considered to increase the sensitivity by reducing 2Hk and increasing the resistance change rate of the TMR element.
However, when the magnetic field in the hard magnetization axis direction Y2 of the free layer is detected by the TMR element, the state in which the magnetization direction Y1 is oriented in the easy magnetization axis direction (G3 in FIG. 9) and the resistance change with respect to the magnetic field before and after that Shows a linear change characteristic, but shows a non-linear change in the vicinity of the state (G2 or G4 in FIG. 9) in which the magnetization direction Y1 is oriented in the direction of the difficult magnetization axis, which is a reliable magnetic field measurement. There is a problem that is not suitable.
When the magnetic field of the easy magnetization axis of the free layer is detected by the TMR element, the resistance value at the detection magnetic field zero is stable at the upper limit value or the lower limit value of the resistance, and the magnetic field from the detection magnetic field zero is It was thought that the change could not be measured (see G1 in FIG. 8).

  The present invention has been made in view of the above problems in the prior art, and in a magnetic sensor using a tunnel magnetoresistive element, it is possible to achieve high sensitivity and to measure a weak magnetic change with high accuracy. An object is to provide a magnetic sensor.

The invention described in claim 1 for solving the above-described 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 magnetic sensor including a tunnel magnetoresistive element that changes a resistance of the insulating layer by a tunnel effect according to an angle difference with a magnetization direction of the layer,
By controlling a magnetic field generation source that changes the magnetization direction of the ferromagnetic metal magnetization free layer, the magnetization direction of the ferromagnetic metal magnetization free layer is rotated from the easy magnetization axis of the ferromagnetic metal magnetization free layer. A feedback circuit that stabilizes the ferromagnetic metal magnetization fixed layer at a twist position having a predetermined twist angle with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer,
The magnetic sensor is characterized in that a fluctuating detected magnetic signal is output from the feedback circuit.
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 stabilizes the feedback circuit so that the torsion angle is not affected by disturbance outside the fluctuation frequency range of the detected magnetic signal,
2. The magnetic sensor according to claim 1, wherein a signal corresponding to a variation in the twist angle in a variation frequency range of the detected magnetic signal is output as the detected magnetic signal.

According to a third aspect of the present invention, the feedback circuit is stabilized so that the torsion angle is not affected by disturbance including a fluctuation frequency range of the detected magnetic signal,
2. The magnetic sensor according to claim 1, wherein a signal in a fluctuation frequency range of the detected magnetic signal is extracted from a control signal for controlling the magnetic field generation source and output as the detected magnetic signal.

  The invention according to claim 4 is characterized in that the easy magnetization axis of the ferromagnetic metal magnetization free layer is parallel to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer. It is a magnetic sensor as described in any one of these.

  According to a fifth aspect of the present invention, the feedback circuit applies a magnetic field from the magnetic field generation source in the direction of the hard magnetization axis of the ferromagnetic metal magnetization free layer to change the magnetization direction of the ferromagnetic metal magnetization free layer. The magnetic sensor according to claim 4, wherein the magnetic sensor is stabilized at a twisted position having the predetermined twist angle.

  According to a sixth aspect of the present invention, the feedback circuit applies a magnetic field from the magnetic field generation source in the direction of the easy magnetization axis of the ferromagnetic metal magnetization free layer to change the magnetization direction of the ferromagnetic metal magnetization free layer. The magnetic sensor according to claim 4, wherein the magnetic sensor is stabilized at a twisted position having the predetermined twist angle.

  The invention according to claim 7 is the magnetic sensor according to any one of claims 1 to 6, wherein the predetermined twist angle is between 45 degrees and 135 degrees.

  The invention according to claim 8 is the magnetic sensor according to any one of claims 1 to 7, wherein the insulating layer is made of MgO.

According to the present invention, the magnetic field generation source that changes the magnetization direction of the free layer is controlled, and the magnetization direction of the free layer is rotated from the easy magnetization axis of the free layer so as to be the easy magnetization axis of the fixed layer. On the other hand, by stabilizing the position of the torsion having a predetermined torsion angle, a neutral position for detecting magnetism (zero point in measurement) is set, and if there is a fluctuation in the magnetic signal, this is looped in the feedback circuit. The detection magnetic signal can be output by extracting from a control signal for controlling the magnetic field generation source of the feedback circuit.
At the neutral position for detecting magnetism, the direction of magnetization of the free layer and the easy magnetization axis of the fixed layer have a predetermined twist angle, so that the resistance change of the tunnel magnetoresistive element with respect to the magnetic field shows a linear change characteristic Magnetism can be measured in the region, high sensitivity is achieved, and weak magnetic changes can be measured with high accuracy.
In particular, when a magnetic field from a magnetic field generation source is applied in the direction of the easy magnetization axis of the free layer to stabilize the magnetization direction of the free layer at a twisted position having a predetermined twist angle and to be in a neutral position. The resistance change with respect to the magnetic field of the tunnel magnetoresistive element becomes remarkable, and the sensitivity can be remarkably increased.

It is sectional drawing of the laminated structure of the TMR module in which two TMR elements were comprised concerning one Embodiment of this invention. It is a circuit block diagram of the magnetic sensor which concerns on one Embodiment of this invention. It is a circuit block diagram of the magnetic sensor which concerns on one Embodiment of this invention. It is a typical perspective view which shows a mode that it concerns on one Embodiment of this invention and controls the direction of magnetization of a free layer. It is a typical perspective view which shows a mode that it concerns on one Embodiment of this invention and controls the direction of magnetization of a free layer. It is a perspective view which shows each form of the magnetic field generation source which concerns on one Embodiment of this invention and generates a magnetic field for controlling the direction of the magnetization of a free layer. FIG. 5 is a schematic perspective view showing an HR characteristic curve of a TMR element and a state of magnetization direction of the TMR element at three points on the characteristic curve according to one embodiment of the present invention. FIG. 5 is a schematic perspective view showing an HR characteristic curve of a TMR element and a state of magnetization direction of the TMR element at three points on the characteristic curve according to one embodiment of the present invention. It is a typical perspective view which shows the mode of the magnetization direction of the TMR element in three points on this characteristic curve concerning the example of the past, and the HR characteristic curve of a TMR element.

  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.

  First, FIG. 1 shows an example of a laminated structure of a TMR module 1 in which two TMR elements are configured. As shown in FIG. 1, the TMR module 1 includes a base layer 3, a ferromagnetic metal magnetization free layer 4, an insulating layer 5, a ferromagnetic metal magnetization fixed layer 6, a pinned layer 7, a buffer layer 8, an upper part on a silicon substrate 2. It has a laminated structure in which the electrode layers 9 are sequentially laminated. The ferromagnetic metal magnetization free layer 4 includes a soft magnetic layer 41, a barrier layer 42, and a ferromagnetic layer 43. The ferromagnetic metal magnetization fixed layer 6 includes a ferromagnetic layer 61, a barrier layer 62, and a ferromagnetic layer 63.

As shown in FIG. 1, the ferromagnetic metal magnetization fixed layer 6, the pinned layer 7, the buffer layer 8, and the upper electrode layer constitute two upper stacked bodies 11 and 12 that are independent of each other. The ferromagnetic metal magnetization fixed layer 6 formed in one upper laminate 11, the insulating layer 5 therebelow, and the ferromagnetic metal magnetization free layer 4 constitute one TMR element. Similarly, one TMR element is constituted by the ferromagnetic metal magnetization fixed layer 6 formed in the other upper laminated body 12, the insulating layer 5 therebelow, and the ferromagnetic metal magnetization free layer 4.
By connecting one of the anode side and the cathode side of the applied voltage to the upper electrode layer 9 configured in the upper laminate 11 and connecting the other to the upper electrode layer 9 configured in the upper laminate 12, These two TMR elements are used in series.
Further, by connecting a plurality of TMR modules 1 in series, four or more TMR elements can be used in series.
However, the structure of the TMR module 1 described above is merely an example, and by providing the lower electrode layer on the base of the ferromagnetic metal magnetization free layer 4, it can be applied from one TMR element as a minimum unit.

  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. From the viewpoint of improving the sensitivity of the element, MgO is preferable. In particular, in order to detect a weak magnetic field such as a biomagnetic signal by the TMR element, it is preferable to use an MgO film as the insulating layer 5. The thickness of the insulating layer 5 is desirably about 1 nm to 10 nm.

Using the TMR module 1 as described above, a bridge is configured as shown in FIG. 2 or FIG. 3, and a magnetic center 10A or 10B including a feedback circuit is configured.
As shown in FIGS. 2 and 3, the constant resistance R1 and the constant resistance R2 are connected in series, and the constant resistance R3 and the TMR module 1 are connected in series between the electrodes to which the reference voltage V1 is applied.
An electrode between the constant resistance R1 and the constant resistance R2 and an electrode between the constant resistance R3 and the TMR module 1 are taken out by the instrumentation amplifier a1, and the instrumentation amplifier a1 detects a potential difference between these electrodes, and a voltage amplifier Output to a2.

The magnetic center 10A shown in FIG. 2 further has the following configuration.
The output signal of the voltage amplifier a2 is output to the low pass filter a3 and the buffer circuit a7. The output signal of the low-pass filter a3 is compared with the reference value by the comparator a4, and a control signal corresponding to the comparison result with the reference value is output to the power amplifier a5.
Based on the control signal, the power amplifying unit a5 generates electric power for causing a current to flow through the magnetic field generating coil a6, and applies a magnetic field to the TMR module 1 by the magnetic field generating coil a6.

The magnetic center 10B shown in FIG. 3 further has the following configuration.
The output signal of the voltage amplifier a2 is compared with a reference value by the comparator a4, and a control signal corresponding to the comparison result with the reference value is output to the power amplifier a5.
Based on the control signal, the power amplifying unit a5 generates electric power for causing a current to flow through the magnetic field generating coil a6, and applies a magnetic field to the TMR module 1 by the magnetic field generating coil a6.
The magnetic field generating coil a6 is a magnetic field generating source that changes the magnetization direction of the ferromagnetic metal magnetization free layer 4.

Next, with reference to FIGS. 4 and 5, the relationship between the magnetization direction at the neutral position for detecting magnetism and the reference value will be described.
FIG. 4 schematically shows the free layer 4 and the fixed layer 6. The illustration of the insulating layer between the free layer 4 and the fixed layer 6 is omitted.
As shown in FIG. 4, in the fixed layer 6, the magnetization direction c2 coincides with the easy magnetization axis c1 direction, and the magnetization direction c2 is fixed. A TMR element in which the easy magnetization axis c4 of the free layer 4 is parallel to the easy magnetization axis c1 is applied.
In the free layer 4, the magnetization direction c5 before application of the control magnetic field c3 coincides with the easy magnetization axis c4. However, the free layer 4 rotates from the easy magnetization axis c4 by application of the control magnetic field c3 substantially orthogonal to the easy magnetization axis c4. The magnetization direction c6 is in a direction substantially perpendicular to the easy magnetization axis c4. The position of this twist is a neutral position for detecting magnetism. The control magnetic field c3 is a magnetic field generated by the above-described magnetic field generation coil a6, and is controlled by a feedback circuit including a comparator a4 with a reference value.

  The magnetic field generating coil a6 is denoted by reference numeral a61 in FIGS. 4, 5, and 6A. As a form of the magnetic field generation source, a configuration in which the free layer 4 is sandwiched between coils a61 and a61 arranged coaxially as shown in FIG. 6 (a), parallel conductors a62 and a62 through which reverse current flows as shown in FIG. 6 (b). And a configuration in which the free layer 4 is sandwiched by a coil a63 shown in FIG. 6C. Each magnetic field line is indicated by a line with an arrow.

A reference value is set to form the neutral position as described above. That is, the reference value is set so that the difference between the signal input to the comparator a4 and the reference value becomes zero in the neutral position. If a difference occurs between the signal input to the comparator a4 and the reference value, feedback control is performed so that the difference converges to zero, that is, the magnetization direction c6 of the free layer 4 is stabilized at the neutral position.
In FIG. 4, the direction (c7) perpendicular to the magnetization direction c6 at the neutral position is the direction of the detected magnetic field. That is, the magnetic sensors 10A and 10B detect the strength of the magnetic field in the direction of the detection axis c7. As can be seen from FIG. 4, in this configuration, the fluctuation of the external magnetic field in the direction parallel to the easy magnetization axis c4 is detected.
As described above, in the configuration shown in FIG. 4, the feedback circuit of the magnetic sensors 10 </ b> A and 10 </ b> B applies the magnetic field c <b> 3 from the magnetic field generating coil a <b> 61 in the direction of the hard magnetization axis of the free layer 4. The direction c6 is stabilized at a twisted position having a predetermined twist angle.
For clarity of explanation, the neutral position shown in FIG. 4 is referred to as “neutral position forced by a control magnetic field in the direction of the hard magnetization axis”.

Unlike the configuration shown in FIG. 4, the feedback circuits of the magnetic sensors 10 </ b> A and 10 </ b> B cause the magnetic field c <b> 3 from the magnetic field generating coil a <b> 61 to act in the direction of the easy magnetization axis c <b> 4 of the free layer 4. FIG. 5 shows a configuration in which the is stabilized at a twisted position having a predetermined twist angle.
That is, in FIG. 4, the easy magnetization axes c1 and c4 are orthogonal to the control magnetic field c3, but in FIG. 5, the easy magnetization axes c1 and c4 are arranged so as to coincide with the direction of the control magnetic field c3.
For clarity of explanation, the neutral position shown in FIG. 5 is referred to as a “neutral position forced by a control magnetic field in the direction of the easy magnetization axis”.

The state (FIG. 4) in the “neutral position forced by the control magnetic field in the direction of the difficult magnetization axis” is a point (H ₀ , R ₀ ) on the HR characteristic curve G1 of the TMR element shown in FIG. It corresponds to a certain state. H ₀ is a magnetic field generated by the magnetic field generating coil a61.
When the external magnetic field to be detected fluctuates about the detection axis c7 (FIG. 4), the magnetization direction c6 of the free layer 4 swings as indicated by arc arrows d1 and d2 in G3 of FIG. The fact that the magnetization direction c6 of the free layer 4 oscillates in the direction of the arc arrow d1 is from the point (H ₀ , R ₀ ) on the HR characteristic curve G1 of the TMR element shown in FIG. This corresponds to increasing the slope, and if it swings greatly, it corresponds to approaching the state shown in the inset G4 from the state shown in the inset G3. Conversely, the magnetization direction c6 free layer 4 in an arcuate arrow d2 direction swing is on H-R characteristic curve G1 of the TMR element shown in FIG. 7, the point as indicated by the straight arrows d2 (H _0, R ₀ ) from the state shown in the inset G2 to the state shown in the inset G2.

The state (FIG. 5) in the “neutral position forced by the control magnetic field in the direction of the easy magnetization axis” is the point (H ₀ , R ₀ ) on the HR characteristic curve G1 of the TMR element shown in FIG. It corresponds to a certain state. H ₀ is a magnetic field generated by the magnetic field generating coil a61.
When the external magnetic field to be detected fluctuates about the detection axis c7 (FIG. 5), the magnetization direction c6 of the free layer 4 swings as indicated by arc arrows d1 and d2 in G3 of FIG. The fact that the magnetization direction c6 of the free layer 4 fluctuates in the direction of the circular arc arrow d1 from the point (H ₀ , R ₀ ) as shown by the straight arrow d1 on the HR characteristic curve G1 of the TMR element shown in FIG. This corresponds to increasing the slope, and if it swings greatly, it corresponds to approaching the state shown in the inset G4 from the state shown in the inset G3. On the other hand, the magnetization direction c6 of the free layer 4 fluctuates in the direction of the circular arc arrow d2 on the HR characteristic curve G1 of the TMR element shown in FIG. 8 as indicated by the straight arrow d2 (H ₀ , R ₀ ) from the state shown in the inset G2 to the state shown in the inset G2.

  7 and 8, the vertical axis R represents the resistance of the TMR element, and the horizontal axis H represents the external magnetic field acting on the TMR element. Inset G2 shows magnetization directions C2 and C6 in a parallel state, inset G4 shows magnetization directions C2 and C6 in an antiparallel state, and inset G3 shows a state in which magnetization directions C2 and C6 are twisted to a neutral position. The resistance R is the lower limit Rb when the magnetization directions C2 and C6 are parallel, and the resistance R is the upper limit Ra when the magnetization directions C2 and C6 are antiparallel.

Using the HR characteristics of the TMR element described above, the magnetic sensors 10A and 10B are applied to the inspection object in a biomagnetic signal such as brain magnetism or a nondestructive inspection apparatus and leak from the inspection object. A magnetic signal forming a pulse waveform of a predetermined frequency can be measured.
On the other hand, magnetic field fluctuations that gradually change due to disturbances such as temperature changes are removed so as not to be detected.
A large number of magnetic sensors 10A and 10B are arranged on the outer surface of a living body such as a cranium to be measured and the outer surface of an object to be inspected in a nondestructive inspection apparatus such as a pipe or a wall so that the detection values of each sensor can be mapped. Configure and implement the measurement system.

In the magnetic sensor 10A shown in FIG. 2, with respect to the magnetic field fluctuation that gradually changes due to a disturbance such as a temperature change, magnetization is performed from the neutral position indicated by the point (H ₀ , R ₀ ) as indicated by arrows d1 and d2. Even if the torsion angle between the directions C2 and C6 and thus the resistance of the TMR element changes, the signal passes through the low-pass filter a3, so that the neutral position indicated by the point (H ₀ , R ₀ ) is obtained by the feedback control described above. Stabilize.
The relatively high-frequency magnetic fluctuations that do not pass through the low-pass filter a3 are not fed back to the magnetic field generating coil a6. Therefore, the change in the twist angle between the magnetization directions C2 and C6, and thus the TMR element resistance, is allowed. The signal is output as a detected magnetic signal via the instrumentation amplifier a1, the voltage amplifier a2, and the buffer circuit a7.
By setting the cut-off frequency of the low-pass filter a3, it is possible to detect a magnetic signal to be measured by removing disturbances such as temperature changes.
As described above, the feedback circuit of the magnetic sensor 10A stabilizes the twist angle between the magnetization directions C2 and C6 so that the twist angle between the magnetization directions C2 and C6 is not affected by the disturbance outside the fluctuation frequency range of the detected magnetic signal. Then, the magnetic sensor 10A outputs a signal corresponding to the fluctuation of the twist angle in the fluctuation frequency range of the detection magnetic signal as the detection magnetic signal.

In the magnetic sensor 10B shown in FIG. 3, since no filter is provided between the TMR module 1 and the comparator a4, the magnetization directions C2 and C6 are caused by disturbance including the fluctuation frequency range of the detected magnetic signal. By the above-described feedback control, the torsion angle is stabilized at the neutral position indicated by the point (H ₀ , R ₀ ).
Further, the magnetic sensor 10B passes a relatively high-frequency signal component from the control signal for controlling the magnetic field generating coil a6 through the high-pass filter b1, and outputs it as a detected magnetic signal via the buffer circuit b2.
By setting the cut-off frequency of the high-pass filter b1, it is possible to detect a magnetic signal to be measured by excluding a signal component due to a disturbance such as a temperature change.
As described above, the feedback circuit of the magnetic sensor 10B stabilizes the twist angle between the magnetization directions C2 and C6 so as not to be affected by the disturbance including the fluctuation frequency range of the detected magnetic signal. Then, the magnetic sensor 10B extracts a signal in the fluctuation frequency range of the detected magnetic signal from the control signal for controlling the magnetic field generation source, and outputs it as a detected magnetic signal.

As described above, according to the magnetic sensor of the present embodiment, the linear change characteristic including the point (H ₀ , R ₀ ) among the HR characteristics of the TMR element shown in FIG. 7 or FIG. The magnetism can be measured using the region shown, high sensitivity is achieved, and a weak magnetic change can be measured with high accuracy. In order to use a region exhibiting a linear change characteristic, the predetermined twist angle with respect to the easy magnetization axis of the fixed layer in the magnetization direction of the free layer at the neutral position may be between 45 degrees and 135 degrees. preferable. More preferably, it is 60 to 120 degrees.
In particular, as shown in FIG. 5, a magnetic field from a magnetic field generation source is applied in the direction of the easy magnetization axis c4 of the free layer 4 to stabilize the magnetization direction of the free layer 4 at a twisted position having a predetermined twist angle. In the case of the neutral position, the resistance change with respect to the magnetic field of the TMR element becomes significant as shown in FIG. 8, and the sensitivity can be significantly increased. That is, in the HR characteristic with high hysteresis as shown in FIG. 8, the change in the magnetization direction of the free layer, and hence the resistance change is very abrupt, and by applying the control magnetic field H ₀ , the detected magnetic field is zero (measured). The upper zero point) can be brought to the point (H ₀ , R ₀ ) in the torsion state indicated by G3 in FIG. 8 and on the steep slope indicated by G1 in FIG. Accordingly, the magnetization reversal, and hence the resistance, can be changed more steeply, so that the sensitivity can be remarkably increased.
Note that the measurement using the HR characteristic shown in FIG. 9 and the measurement using the HR characteristic in the vicinity of the point (H ₀ , R ₀ ) shown in FIG. 7 require a dynamic range of the magnetic field. For such a non-destructive inspection, measurement using the point (H ₀ , R ₀ ) and the HR characteristics in the vicinity thereof shown in FIG. 8 is suitable for detection of an extremely weak magnetic field such as a brain magnetic field.

The magnetic sensor 10A shown in FIG. 2, the point shown in FIG. 7 configured to form a state in which the "neutral position forced by the control magnetic field in the direction of hard magnetization axis" shown in FIG. 4 (H ₀ , R ₀ ) and the HR characteristics in the vicinity thereof, or a state in a “neutral position forced by a control magnetic field in the direction of the easy magnetization axis” shown in FIG. 5 is formed. Thus, the point (H ₀ , R ₀ ) shown in FIG. 8 and the HR characteristics in the vicinity thereof may be measured.
Further, the magnetic sensor 10B shown in FIG. 3 is configured to form a state in the “neutral position forced by the control magnetic field in the direction of the difficult magnetization axis” shown in FIG. H ₀ , R ₀ ) and HR characteristics in the vicinity thereof may be used for measurement, or in a “neutral position forced by a control magnetic field in the direction of the easy magnetization axis” shown in FIG. May be measured using the point (H ₀ , R ₀ ) shown in FIG. 8 and the HR characteristics in the vicinity thereof.

DESCRIPTION OF SYMBOLS 1 TMR module 2 Silicon substrate 3 Underlayer 4 Ferromagnetic metal magnetization free layer 5 Insulating layer 6 Ferromagnetic metal magnetization fixed layer 7 Pinned layer 8 Buffer layer 9 Upper electrode layer 10A Magnetic center 10B Magnetic center 41 Soft magnetic layer 42 Barrier layer 43 Ferromagnetic layer 61 Ferromagnetic layer 62 Barrier layer 63 Ferromagnetic layer a6 Magnetic field generating coil c1 Easy magnetization axis c3 Control magnetic field c4 Easy magnetization axis c7 Detection axis R1 Constant resistance R2 Constant resistance R3 Constant resistance

Claims (8)

Ferromagnetic metal magnetization fixed layer with fixed magnetization direction, 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 magnetic sensor including a tunnel magnetoresistive element that changes the resistance of
By controlling a magnetic field generation source that changes the magnetization direction of the ferromagnetic metal magnetization free layer, the magnetization direction of the ferromagnetic metal magnetization free layer is rotated from the easy magnetization axis of the ferromagnetic metal magnetization free layer. A feedback circuit that stabilizes the ferromagnetic metal magnetization fixed layer at a twist position having a predetermined twist angle with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer,
A magnetic sensor, wherein a fluctuating detected magnetic signal is output from the feedback circuit. The feedback circuit is stabilized so that the twist angle is not affected by disturbance outside the fluctuation frequency range of the detected magnetic signal,
The magnetic sensor according to claim 1, wherein a signal corresponding to a change in the torsion angle in a change frequency range of the detection magnetic signal is output as the detection magnetic signal. The feedback circuit is stabilized so that the twist angle is not affected by disturbance including a fluctuation frequency range of the detected magnetic signal,
The magnetic sensor according to claim 1, wherein a signal in a fluctuation frequency range of the detected magnetic signal is extracted from a control signal for controlling the magnetic field generation source and output as the detected magnetic signal.   The easy magnetization axis of the ferromagnetic metal magnetization free layer is in a relationship parallel to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer, according to any one of claims 1 to 3. Magnetic sensor.   The feedback circuit has a predetermined twist angle with respect to the magnetization direction of the ferromagnetic metal magnetization free layer by applying a magnetic field from the magnetic field generation source in the direction of the hard magnetization axis of the ferromagnetic metal magnetization free layer. The magnetic sensor according to claim 4, wherein the magnetic sensor is stabilized at a twisted position.   The feedback circuit has a magnetic field from the magnetic field generation source acting in the direction of the easy magnetization axis of the ferromagnetic metal magnetization free layer so that the magnetization direction of the ferromagnetic metal magnetization free layer has the predetermined twist angle. The magnetic sensor according to claim 4, wherein the magnetic sensor is stabilized at a twisted position.   The magnetic sensor according to claim 1, wherein the predetermined twist angle is between 45 degrees and 135 degrees.   The magnetic sensor according to claim 1, wherein the insulating layer is made of MgO.

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