JP2017096627A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor using a tunnel magneto-resistance (TMR) element in which detection errors are corrected due to magnetic field resistance characteristics, temperature changes of the TMR element, or the like.SOLUTION: Individual differences between ohmic values of a TMR element (1) are eliminated by stabilizing a voltage applied to the TMR element incorporated in a Wheatstone bridge circuit at a reference value. A correspondence between a magnetic field acting on the TMR element and a signal inherent to the TMR element according to magnetic field resistance characteristics of the TMR element is stored, in the correspondence, a magnetic field acting on the TMR element corresponding to the inherent signal (voltage value) outputted from the TMR element is identified and outputted. A reference magnetic field acts on the TMR element based on a reference signal, a signal derived from the reference signal is detected from an output signal of the TMR element, while the detected detection signal is compared with the reference signal outputted from a reference transmitter, to calculate a sensitivity correction value and multiply the sensitivity correction value by an output signal of a tunnel magneto-resistance element.SELECTED DRAWING: Figure 4

Description

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

Conventionally, a magnetic sensor using a magnetoresistive element has been proposed as thinning, flaw detection, and defect detection for nondestructive inspection, as shown in Patent Document 1.
However, there are only examples of AMR (anisotropic magnetoresistance) elements as magnetoresistive elements (MR) in nondestructive inspection. Specifically, a means for non-destructively inspecting piping CUI (corrosion under thermal insulation) using an AMR element has been proposed, but the resistance change rate against a magnetic field is as small as several percent, output is small, noise There is a problem that it is weak. For this reason, when the heat insulating material is thick, no output is obtained.
A measurement method using an AMR element has also been proposed for flaw detection and defect inspection of iron plates, but since the output is small and it is sensitive to noise, scratches and defects in the deep layer cannot be measured.

As magnetoresistive elements, there are GMR elements (giant magnetoresistive elements) and tunnel magnetoresistive elements (TMR (Tunnel Magneto Resistive) elements) in addition to AMR elements. .
The TMR 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 that is strongly An insulating layer disposed between the magnetic metal magnetization free layer and the tunneling 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.
In order to use the magnetoresistive 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). The property (linearity) to cause is required.
In a normal TMR element, the magnetization direction of the fixed layer and the magnetization direction of the free layer are stable in parallel or anti-parallel, so that the state of zero detection magnetic field cannot be created. Moreover, even if a neutral position could be created physically, the variation was large, and the performance as a magnetic measuring device was not realized.

However, Patent Document 2 proposes that the TMR element is applied to biomagnetic measurement.
In the biomagnetic sensor including a tunneling magnetoresistive element, the easy magnetization axis of the ferromagnetic metal magnetization free layer in the detection magnetic field zero is fixed to the ferromagnetic metal magnetization fixed in the biomagnetic sensor including the tunnel magnetoresistive element. It is characterized by being in a twisted position with respect to the easy magnetization axis of the layer.
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.

Japanese Patent No. 4487082 JP2013-105825A

However, using a TMR element that detects an external magnetic field from the state in which the magnetization direction of the fixed layer and the magnetic direction of the free layer are twisted as described above, a material to be inspected in biomagnetic measurement or nondestructive inspection When performing leakage magnetic measurement from the following, there are further problems as follows.
For the measurement, it is necessary to form a sensor array with a large number of magnetic sensors, arrange this on the surface of a living body or the surface of a material to be inspected, and configure a measurement system that can map the measurement values.
When the above-described twist angle of the TMR element, that is, the twist angle is different for each element, the resistance change characteristic with respect to the magnetic field is different for each element. That is, there are individual differences in magnetic field resistance characteristics. If there is an individual difference in the magnetic resistance characteristics, for example, even if the voltage value output from one TMR magnetic sensor is the same as the voltage value output from another TMR magnetic sensor, it acts on the one TMR magnetic sensor. Therefore, the external magnetic field acting on the other TMR magnetic sensor is different. Conversely, even if the external magnetic field acting on one TMR magnetic sensor is the same as the external magnetic field acting on another TMR magnetic sensor, the voltage value output from the one TMR magnetic sensor, The voltage value output from the other TMR magnetic sensor is different. Therefore, there is a problem that accurate measurement cannot be performed and the reliability of the mapped measurement data is lowered.
Further, the magnetic field resistance characteristic of the TMR element has a temperature characteristic. That is, there is a temperature characteristic in which a voltage value output from the TMR magnetic sensor varies depending on the element temperature in a state where a constant external magnetic field acts on the TMR magnetic sensor. If there is an individual difference in this temperature characteristic, for example, when a constant external magnetic field is acting on two TMR magnetic sensors, the voltage value output from one TMR magnetic sensor and the other TMR magnetic sensor Even if the output voltage value is the same at a certain temperature, it is different at other temperatures. Therefore, there is a problem that accurate measurement cannot be performed due to temperature change, and the reliability of the mapped measurement data is lowered. Of course, there is a problem that the values measured by the same TMR magnetic sensor differ depending on the temperature at the time of measurement.
In addition, even if the temperature is constant, the magnetic resistance characteristics of the TMR element may change with time, so that a problem that the value varies depending on the measurement may occur.
In addition, since TMR uses a tunnel effect, 1 / f noise is larger at a lower frequency than AMR and GMR. However, it is desired to improve the S / N ratio by reducing the 1 / f noise.

  The present invention has been made in view of the above-described problems in the prior art, and corrects detection errors that may occur due to magnetic field resistance characteristics of the tunnel magnetoresistive element, temperature changes, and the like in the magnetic sensor using the tunnel magnetoresistive element. This is the issue.

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,
A Wheatstone bridge circuit incorporating the tunnel magnetoresistive element;
A feedback circuit for stabilizing a voltage applied to the tunnel magnetoresistive element to a reference value,
The magnetic sensor is characterized in that a fluctuating detected magnetic signal is output from the feedback circuit.

The invention according to claim 2 stabilizes the feedback circuit so that the voltage 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 change in the voltage in a fluctuation frequency region of the detection magnetic signal is output as the detection magnetic signal.

In the invention according to claim 3, the feedback circuit is stabilized so that the voltage 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 voltage and is output as the detected magnetic signal.

According to a fourth aspect of the present invention, there is provided 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; In a magnetic sensor including a tunnel magnetoresistive element that changes the resistance of the insulating layer by a tunnel effect according to a difference,
A storage device storing a correspondence relationship between a magnetic field acting on the tunnel magnetoresistive element and a signal unique to the tunnel magnetoresistive element according to a magnetic field resistance characteristic of the tunnel magnetoresistive element;
In the correspondence, an arithmetic device that specifies a magnetic field acting on the tunnel magnetoresistive element corresponding to the specific signal output from the tunnel magnetoresistive element and outputs it as a detected magnetic signal;
It is a magnetic sensor characterized by comprising.

The invention according to claim 5 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; In a magnetic sensor including a tunnel magnetoresistive element that changes the resistance of the insulating layer by a tunnel effect according to a difference,
A reference transmitter for outputting a reference signal;
A magnetic field generator for applying a reference magnetic field to the tunnel magnetoresistive element based on the reference signal output from the reference transmitter;
A reference signal detector for detecting a signal derived from the reference signal from an output signal of the tunnel magnetoresistive element on which the reference magnetic field acts;
A comparison circuit that calculates a sensitivity correction value by comparing the detection signal detected by the reference signal detector with the reference signal output from the reference transmitter;
A multiplier for multiplying the sensitivity correction value calculated by the comparison circuit by the output signal of the tunnel magnetoresistive element on which the reference magnetic field acts to calculate a detection magnetic signal;
The magnetic sensor according to claim 4, further comprising:

  The invention according to claim 6 includes a tunnel magnetoresistive module in which two or more tunnel magnetoresistive elements are connected in series, and an external magnetic field is applied to the tunnel magnetoresistive module to detect the external magnetic field. It is a magnetic sensor as described in any one of Claims 1-5.

  The invention according to claim 7 is characterized in that the ferromagnetic metal magnetization free layer includes a soft magnetic layer formed in a layer thickness of 10 nm or more and 100 nm or less. It is a magnetic sensor as described in.

  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.

  The invention according to claim 9 is characterized in that the easy magnetization axis of the ferromagnetic metal magnetization free layer is in a twisted position with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer. Item 9. The magnetic sensor according to any one of Items 8 above.

According to the first aspect of the present invention, the detection signal at the zero detection magnetic field is corrected to the zero reference value and the detection magnetic signal is correctly calculated regardless of the resistance value at the zero detection magnetic field of the tunnel magnetoresistive element. Can do.
According to the fourth aspect of the present invention, the detected magnetic signal can be calculated correctly regardless of the magnetic field resistance characteristics of the tunnel magnetoresistive element.
According to the fifth aspect of the present invention, the detected magnetic signal can be correctly calculated regardless of the sensitivity change of the tunnel magnetoresistive element.

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 sectional drawing of the laminated structure of the TMR module in which six TMR elements were comprised concerning one Embodiment of this 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 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. 1 is a configuration block diagram of a magnetic sensor according to an embodiment of the present invention. It is a circuit block diagram of the magnetic sensor which concerns on one Embodiment of this invention.

  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. The thickness of the soft magnetic layer 41 is preferably 10 nm or more and 100 nm or less. By setting the layer thickness of the soft magnetic layer 41 to 10 nm or more, preferably 30 nm or more, it is possible to form a TMR element having good linearity of magnetic field resistance characteristics. On the other hand, when the layer thickness of the soft magnetic layer 41 exceeds 100 nm, linearity is hardly improved. Therefore, the layer thickness of the soft magnetic layer 41 is preferably formed to 100 nm or less.

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, a plurality of configurations shown in FIG. 1 are arranged, and as shown in FIG. 2, a TMR module 1 in which four or more TMR elements are connected in series by connecting them in series with conductors 13 at adjacent upper electrode layers 9. Can be configured and used. FIG. 2 shows a configuration in which six TMR elements are connected in series.
As more TMR elements are connected in series, 1 / f noise can be reduced. In order to reduce 1 / f noise to 1/10, for example, 100 TMR elements are connected in series.

  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.

When the easy magnetization axis of the free layer 4 is parallel to the easy magnetization axis of the fixed layer 6, the magnetization direction c2 of the fixed layer 6 and the magnetization direction c6 of the free layer 4 are in a parallel state or an antiparallel state. . When an external magnetic field is detected using this state as a zero point in magnetic field measurement, the relationship between the magnetic field H and the resistance R is non-linear near the resistance lower limit value Rb and the resistance upper limit value Ra, and the magnetic field cannot be quantified.
Therefore, the state (H = 0) in which there is no detected magnetic field H as shown in FIG. 3 is made to correspond to the intermediate value of the resistance and set as the zero point in the magnetic field measurement.
As one method for enabling this, as described in Patent Document 2, heat treatment in a magnetic field is performed twice, first, heat treatment is performed at a temperature that determines the easy magnetization axis of the free layer 4, and the second heat treatment is performed first. The heat treatment is performed by changing the applied magnetic field to the twisted position at a temperature lower than the heat treatment temperature. As a result, the easy magnetization axis of the free layer 4 is twisted with respect to the easy magnetization axis of the fixed layer 6.
At this time, it is necessary to have a structure in which the free layer 4 is laminated before the fixed layer 6. This is because the area of the fixed layer 6 is made smaller than the area of the free layer 4. By making the area of the 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.

In the above method, the state without the detection magnetic field H is made to correspond to the intermediate value of the resistance. However, when the intermediate position is set by the heat treatment in the magnetic field twice, the intermediate resistance value varies depending on the variation of the torsion angle. .
Therefore, in order to make the intermediate resistance value corresponding to the state without the detection magnetic field H constant, the magnetic sensor 10A shown in FIG. 4 or the magnetic sensor 10B shown in FIG. 5 is configured.

That is, the TMR module 1 is used to form a bridge as shown in FIG. 4 or FIG. 5 to form a magnetic center 10A or 10B having a feedback circuit.
As shown in FIGS. 4 and 5, a Wheatstone bridge circuit is configured by the constant resistances R1, R2, R3 and the TMR module 1 between the electrodes to which the reference voltage V1 is applied. However, one end of the TMR module 1 is connected to the voltage control unit a5, and the voltage applied to the R3 and the TMR module 1 is controlled.
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 TMR module 1, the instrumentation amplifier a1, the voltage amplifier a2, and the voltage control unit a5 are included to constitute a feedback circuit that stabilizes the voltage applied to the TMR module 1 to a reference value. The reference value is set so that the potential difference becomes a constant value (for example, zero) under the condition that the detected magnetic field is zero. As a result, the intermediate value of the resistance becomes constant regardless of the TMR element when there is no detection magnetic field H.

The magnetic center 10A shown in FIG. 4 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 voltage control unit a5.
The voltage control unit a5 controls the voltage applied to the bridge composed of the constant resistance R3 and the TMR module 1 based on the control signal.

The magnetic center 10B shown in FIG. 5 further has the following configuration.
The output signal of the voltage amplifier a2 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 voltage control unit a5.
Based on the control signal, the voltage control unit a5 controls the voltage applied to the bridge composed of the constant resistance R3 and the TMR module 1 based on the control signal.

The magnetic sensors 10A and 10B measure a biomagnetic signal such as brain magnetism, or a magnetic signal that forms a pulse waveform of a predetermined frequency that is applied to an inspection object and leaks from the inspection object in a nondestructive inspection apparatus. Can do.
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. 4, the magnetic field fluctuation that gradually changes due to a disturbance such as a temperature change becomes a signal that passes through the low-pass filter a3 even if the TMR element resistance is changed. Stabilize by feedback control.
The relatively high frequency magnetic fluctuations that do not pass through the low-pass filter a3 are not fed back to the voltage control unit a5. Therefore, the TMR element resistance is allowed to change, and signals corresponding to the change are instrumentation amplifier a1, voltage amplifier a2, and buffer. The detected magnetic signal is output via the 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 voltage applied to the TMR element so as not to be affected by the disturbance outside the fluctuation frequency range of the detected magnetic signal. And 10 A of magnetic sensors output the signal according to the fluctuation | variation of the said voltage in the fluctuation | variation frequency range of a detection magnetic signal as a detection magnetic signal.

In the magnetic sensor 10B shown in FIG. 5, since no filter is provided between the TMR module 1 and the comparator a4, the voltage applied to the TMR element due to disturbance including the fluctuation frequency range of the detected magnetic signal. Is stabilized by the above-described feedback control so as not to be affected.
Further, the magnetic sensor 10B passes a relatively high-frequency signal component from the control signal for controlling the voltage applied to the TMR element 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 voltage applied to the TMR element by the disturbance including the fluctuation frequency range of the detected magnetic signal so as not to be affected. 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 voltage applied to the TMR element, and outputs it as a detected magnetic signal.

Next, the magnetic sensor J shown in FIG. 6 will be described.
The magnetic sensor J shown in FIG. 6 includes a TMR basic circuit J1, an arithmetic device J2, and a storage device J3.
The TMR basic circuit J1 is a circuit including a TMR element as means for sensing an external magnetic field. Here, it is assumed that the above-described TMR module 1 is applied. Depending on the magnetic resistance characteristics of the individual TMR elements configured in the TMR module 1, individuality also occurs in the magnetic resistance characteristics of the entire TMR module 1. As the TMR basic circuit J1, for example, the low-pass filter a3, the comparator a4, and the voltage control unit a5 are excluded from the circuit shown in FIG. 4, and a bridge composed of the constant resistance R3 and the TMR module 1 is applied between the reference voltage V1. Is.

Therefore, the TMR basic circuit J1 outputs a signal (voltage value) J11 unique to the TMR module 1 corresponding to the magnetic field resistance characteristics of the TMR module 1 to the arithmetic unit J2.
The storage device J3 stores a correspondence relationship between the magnetic field acting on the TMR module 1 and the signal J11 unique to the TMR module 1 according to the magnetic field resistance characteristics of the TMR element. This correspondence is created by placing the TMR module 1 in a known magnetic field in advance and obtaining the output from the TMR basic circuit J1 while changing the magnetic field.
The arithmetic device J2 specifies the magnetic field corresponding to the unique signal J11 in the correspondence relationship J31 read from the storage device J3, and outputs it as the detected magnetic signal J21.
Further, in the magnetic measurement system that handles the detection values of a plurality of sensors as in the case of performing the mapping described above, since there are a plurality of TMR basic circuits J1, identification information is given to each TMR basic circuit J1. The unique correspondence relationship is stored in the storage device J2 in association with the identification information.

Next, the magnetic sensor K shown in FIG. 7 will be described.
7 includes a TMR basic circuit K1, a voltage amplifier K2, a “reference signal detector and comparison circuit” K3, an “amplifier and low-pass filter” K4, a multiplier K5, and a buffer circuit K6. And a reference transmitter K7 and a magnetic field generator K8.
As the TMR basic circuit K1, for example, the voltage amplifier a2, the low-pass filter a3, the comparator a4, the voltage control unit a5, and the buffer circuit a7 are eliminated from the circuit shown in FIG. 4, and a bridge composed of the constant resistor R3 and the TMR module 1 is used. Is multiplied by the reference voltage V1, and the output of the instrumentation amplifier a1 is connected to the voltage amplifier K2.

The reference signal K9 is output from the reference transmitter K7 to the magnetic field generator K8 and the “reference signal detector and comparison circuit” K3.
The magnetic field generator K8 includes a coil that generates a magnetic field as shown in FIG. The magnetic field generator K8 amplifies the reference signal K9 output from the reference transmitter K7, generates electric power for flowing a current through the included coil, flows the current through the coil, and the TMR basic circuit K1 from the coil. A reference magnetic field K9 is applied to the TMR element inside.
A voltage signal K12 including a component in response to the reference magnetic field K10 is output from the TMR basic circuit K1 and input to the voltage amplifier K2.
The voltage signal K12 is sufficiently amplified so that the detection error is reduced by the voltage amplifier K2, and then input to the “reference signal detector and comparison circuit” K3. The “reference signal detector and comparison circuit” K3 receives the input signal. To detect the reference signal.
Next, the “reference signal detector and comparison circuit” K3 compares the reference signal detected from the signal K13 input from the voltage amplifier K2 with the reference signal K9 input directly from the reference transmitter K7, and determines the sensitivity. A correction value is calculated.

The reference magnetic field K10 is always constant, and if the sensitivity of the TMR element is constant, the detected reference signal is also constant.
However, the sensitivity of the TMR element changes due to a temperature change or the like, and appears in the above comparison result.
For example, when the ratio of the detected reference signal to the input reference signal K9 is higher at a higher temperature than at a low temperature, this is a result of the sensitivity of the TMR element being increased at a higher temperature than at a low temperature. In this case, the detection signal of the external magnetic field K11 is excessive. It is also conceivable that the sensitivity of the TMR element changes due to aging.
Therefore, this change in sensitivity is corrected by the sensitivity correction value so that a detection magnetic signal equivalent to that detected with a constant sensitivity is output.
That is, the multiplier K5 multiplies and corrects the signal K13 output from the voltage amplifier K2 by the sensitivity correction value K14 calculated by the “reference signal detector and comparison circuit” K3, and corrects the detected magnetism from the buffer circuit K6. Output a signal. The sensitivity correction value K14 is amplified by the “amplifier and low-pass filter” K4, and a relatively high frequency change component is cut.

  A certain temperature is set as a reference temperature, the TMR element is placed under the reference temperature at the initial setting, and the sensitivity correction value is set to “1” with respect to the reference signal detected by the “reference signal detector and comparison circuit” K3. If there is an increase or decrease in the reference signal detected by the “reference signal detector and comparison circuit” K3 in the subsequent magnetic measurement with respect to the reference signal detected at the initial setting, the reciprocal of the increase / decrease rate is set as the sensitivity correction value. Thereby, in the subsequent magnetic measurement, a detected magnetic signal when there is no change in the sensitivity of the TMR element is output from the buffer circuit K6. After correction by the sensitivity correction value, the reference signal detected at the initial setting may be subtracted.

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 J Magnetic center K Magnetic center 41 Soft Magnetic layer 42 Barrier layer 43 Ferromagnetic layer 61 Ferromagnetic layer 62 Barrier layer 63 Ferromagnetic layer R1 Constant resistance R2 Constant resistance R3 Constant resistance

Claims (9)

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
A Wheatstone bridge circuit incorporating the tunnel magnetoresistive element;
A feedback circuit for stabilizing a voltage applied to the tunnel magnetoresistive element to a reference value,
A magnetic sensor, wherein a fluctuating detected magnetic signal is output from the feedback circuit. The feedback circuit is stabilized so that the voltage 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 voltage in a fluctuation frequency range of the detection magnetic signal is output as the detection magnetic signal. The feedback circuit is stabilized so that the voltage 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 voltage and is output as the detected magnetic signal. 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
A storage device storing a correspondence relationship between a magnetic field acting on the tunnel magnetoresistive element and a signal unique to the tunnel magnetoresistive element according to a magnetic field resistance characteristic of the tunnel magnetoresistive element;
In the correspondence, an arithmetic device that specifies a magnetic field acting on the tunnel magnetoresistive element corresponding to the specific signal output from the tunnel magnetoresistive element and outputs it as a detected magnetic signal;
A magnetic sensor characterized by comprising: 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
A reference transmitter for outputting a reference signal;
A magnetic field generator for applying a reference magnetic field to the tunnel magnetoresistive element based on the reference signal output from the reference transmitter;
A reference signal detector for detecting a signal derived from the reference signal from an output signal of the tunnel magnetoresistive element on which the reference magnetic field acts;
A comparison circuit that calculates a sensitivity correction value by comparing the detection signal detected by the reference signal detector with the reference signal output from the reference transmitter;
A multiplier for multiplying the sensitivity correction value calculated by the comparison circuit by the output signal of the tunnel magnetoresistive element on which the reference magnetic field acts to calculate a detection magnetic signal;
The magnetic sensor according to claim 4, further comprising:   6. A tunnel magnetoresistive module in which two or more tunnel magnetoresistive elements are connected in series is included, and an external magnetic field is applied to the tunnel magnetoresistive module to detect the external magnetic field. Magnetic sensor as described in any one of them.   The magnetic sensor according to any one of claims 1 to 6, wherein the ferromagnetic metal magnetization free layer includes a soft magnetic layer formed to have a layer thickness of 10 nm or more and 100 nm or less.   The magnetic sensor according to claim 1, wherein the insulating layer is made of MgO.   The easy magnetization axis of the ferromagnetic metal magnetization free layer is in a position twisted with respect to the easy magnetization axis of the ferromagnetic metal magnetization fixed layer. The described magnetic sensor.

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