WO2016042871A1 - Magnetic field sensor - Google Patents

Abstract

According to an embodiment of the present invention, a magnetic field sensor is provided with: a magnetic field sense circuit (11) that is provided with a ferromagnetic element (15) wherein a resistance value changes due to a magnetic field and an electric field, and an electrode (31) to which a control voltage (Vcontrol) for generating the electric field is applied; a resistance detection circuit (12) that detects the resistance value of the ferromagnetic element (15); and a control voltage generation circuit (10) that generates the control voltage. The control voltage generation circuit (10) generates the control voltage (Vcontrol) that makes the resistance value of the ferromagnetic element (15) at a predetermined value when the magnetic field is zero.

Description

Magnetic field sensor

Embodiment relates to a magnetic field sensor.

In recent years, magnetic field sensors are widely used for medical purposes such as HDD read heads, electronic compasses, and magnetocardiographs, magnetomyographs, and magnetoencephalographs. However, the conventional magnetic field sensor has a trade-off between sense sensitivity and cost, and it is difficult to provide a high-sensitivity magnetic field sensor at low cost.

For example, if the sense sensitivity of the magnetic field sensor is increased, the structure of the magnetic field sensor becomes complicated and the power consumption increases, resulting in an increase in cost. On the other hand, if it is going to realize cost reduction (miniaturization), since the structure of a magnetic field sensor must be simplified, sense sensitivity falls.

Special table 2003-519780 gazette JP 2001-91612 A JP 2007-235119 A

Embodiment proposes a magnetic field sensor with high sensitivity and low cost.

According to the embodiment, the magnetic field sensor includes: a first element including a ferromagnetic element whose resistance value varies depending on a magnetic field and an electric field; an electrode to which a voltage for generating the electric field is applied; and the magnetic field is zero And a second circuit for applying a voltage at which the resistance value of the ferromagnetic element becomes a predetermined value to the electrode.

The block diagram which shows the magnetic field sensor concerning a 1st Example. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the sense sensitivity of the magnetic field sensor of FIG. The figure which shows the sense sensitivity of the magnetic field sensor as a comparative example. The block diagram which shows the magnetic field sensor concerning a 2nd Example. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the sense sensitivity of the magnetic field sensor of FIG. The block diagram which shows the magnetic field sensor concerning a 3rd Example. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the structural example of the magnetic field sensor of FIG. The figure which shows the sense sensitivity of the magnetic field sensor of FIG. The figure which shows the magnetic field sensor concerning a 4th Example.

Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
In the first embodiment, the resistance value of the ferromagnetic element when the external magnetic field is zero (zero point) is shifted to a high-sensitivity region in which the ratio of change in resistance value to the change in external magnetic field (magnetoresistivity change rate) is large. It is related with the technique which improves the sense sensitivity when the value of an external magnetic field is low.

FIG. 1 shows a magnetic field sensor according to the first embodiment.

The magnetic field sense circuit 11 is a circuit for sensing the external magnetic field Hext. The magnetic field sense circuit 11 includes, for example, a ferromagnetic element 15 whose resistance value is changed by an external magnetic field Hext. That is, since the magnetization direction of the ferromagnetic element 15 is changed by the external magnetic field Hext, the resistance value Rx of the ferromagnetic element 15 is also changed according to the magnitude of the external magnetic field Hext.

In this example, the resistance value Rx of the ferromagnetic element 15 can be controlled by the control voltage Vcontrol generated by the control voltage generation circuit 10.

For example, if an electrode for applying the control voltage Vcontrol is provided in the magnetic field sense circuit 11, the carrier density in the ferromagnetic element 15 can be changed by the electric field generated by the control voltage Vcontrol. Since the change in the carrier density causes a change in the anisotropic magnetic field of the ferromagnetic element 15, the magnetization direction of the ferromagnetic element 15 changes. As a result, the resistance value Rx of the ferromagnetic element 15 can be changed.

Note that the control voltage generation circuit 10 includes, for example, a constant voltage source.

The resistance detection circuit 12 detects the resistance value Rx of the ferromagnetic element 15 in the magnetic field sensing circuit 11. The resistance detection circuit 12 may be a voltage detection type that detects a voltage applied to the ferromagnetic element 15 or may be a current detection type that detects a current flowing through the ferromagnetic element 15. The resistance detection circuit 12 includes, for example, an operational amplifier. The resistance value Rx of the ferromagnetic element 15 is output as the output voltage Vout.

2 and 3 show a configuration example of the magnetic field sensor of FIG.

In the example of FIG. 2, the magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 on the insulating layer 32. The ferromagnetic element 15 is an anisotropic magnetoresistive effect element, for example, and has a thin wire structure.

3, the magnetic field sense circuit 11 includes the electrode 31 to which the control voltage Vcontrol is applied, the insulating layer 32 on the electrode 31, and the ferromagnetic element 15 on the insulating layer 32. However, the ferromagnetic element 15 is a tunnel magnetoresistive effect element, for example.

The tunnel magnetoresistive effect element includes a first ferromagnetic layer 21, a second ferromagnetic layer 23, and a nonmagnetic insulating layer (tunnel barrier layer) 22 between them. One of the first and second ferromagnetic layers 21 and 23 is a reference layer having a permanent magnetization, and the other is a storage layer having a variable magnetization.

In the tunnel magnetoresistive effect element, each of the first and second ferromagnetic layers 21 and 23 may be of a perpendicular magnetization type having remanent magnetization in the perpendicular direction in which the first and second ferromagnetic layers 21 and 23 are laminated. Each of the ferromagnetic layers 21 and 23 may be an in-plane magnetization type having a remanent magnetization in the in-plane direction perpendicular to the direction in which they are laminated.

The magnetoresistive effect element is not limited to an anisotropic magnetoresistive effect element or a tunnel magnetoresistive effect element, and may be a giant magnetoresistive effect element or a super magnetoresistive effect element. If there is a structure in which a magnetic film whose resistance is changed by an external magnetic field and whose direction of magnetization is changed by a change in the external magnetic field or electric field is formed on the insulating layer 32, the following principle is given. A highly sensitive sensor can be configured using

Here, sensing of the external magnetic field Hext is performed by detecting a change in the resistance value Rx of the ferromagnetic element 15 due to the external magnetic field Hext.

For example, in the example of FIG. 3, the external magnetic field Hext can be detected by a change in the magnetization direction of the storage layer. This is because the magnetization direction of the storage layer changes due to the external magnetic field Hext, and the resistance value Rx of the magnetoresistive element changes.

The resistance value Rx of the ferromagnetic element 15 can be detected by, for example, sensing a voltage generated between the ferromagnetic elements 15 when a current I is passed through the ferromagnetic element 15. In this example, the resistance detection circuit 12 outputs the resistance value Rx of the ferromagnetic element 15 as an output voltage Vout by an operational amplifier.

Therefore, a change in the external magnetic field Hext appears as a change in the output voltage Vout.

In the magnetic field sensor of this example, the resistance value Rx of the ferromagnetic element 15 is shifted by the control voltage Vcontrol instead of the magnetic field when the external magnetic field Hext is zero (zero point). This has the following significance.

When the zero point is shifted using a magnetic field, for example, a magnetic field from a permanent magnet, the magnetization of the permanent magnet may change due to an external influence. For this reason, the strength of the magnetic field from the permanent magnet may also change. In this case, since the zero point changes, the sensitivity of the magnetic field sensor decreases. Further, when a permanent magnet is incorporated in the magnetic field sensor, the structure of the magnetic field sensor becomes complicated and the cost increases. On the other hand, if the zero point is set by the control voltage Vcontrol, the change of the zero point due to the influence from the outside or the complicated structure does not occur. That is, high sensitivity and low cost of the magnetic field sensor can be realized.

FIG. 4 shows the sense sensitivity of the magnetic field sensor of FIGS. FIG. 5 shows the sense sensitivity of a magnetic field sensor as a comparative example.

The magnetic field sensor of FIGS. 1 to 3 uses the resistance value Rx of the ferromagnetic element 15 when the external magnetic field Hext is zero (zero point) as the ratio of change in the resistance value Rx to the change in the external magnetic field Hext (magnetic resistance change rate). Shift to a high-sensitivity region where becomes large.

For example, when the magnetoresistance curve of the ferromagnetic element 15 is expressed as shown in FIGS. 4 and 5, when the zero point is set at the center (control voltage Vcontrol is zero) A of this magnetoresistance curve (FIG. 5), The magnetoresistance change rate of the ferromagnetic element 15 decreases near the zero point. This means that the sense sensitivity when detecting a small external magnetic field Hext is reduced.

Therefore, in the magnetic field sensor of FIGS. 1 to 3, the zero point is set at a position shifted from the center of the magnetoresistance curve by the control voltage Vcontrol (FIG. 4). In this case, the magnetoresistance change rate of the ferromagnetic element 15 increases in the vicinity of the zero point. This means that the sense sensitivity when detecting a small external magnetic field Hext is increased.

Further, the magnitude of the control voltage Vcontrol for determining the zero point depends on the principle of the magnetoresistance effect in the ferromagnetic element 15. However, regardless of which principle is applied, for example, if the zero point is shifted to a position where the rate of change in magnetoresistance is maximized by the control voltage Vcontrol, a magnetic field sensor with high sensitivity and low cost can be provided. .

(Second embodiment)
In the second embodiment, when the external magnetic field changes, the feedback control is performed so as to cancel the change in the resistance value of the ferromagnetic element, that is, the resistance value of the ferromagnetic element is always constant. (Zero method) and a technique for increasing the sensitivity of a magnetic field sensor.

FIG. 6 shows a magnetic field sensor according to the second embodiment.

The magnetic field sense circuit 11 is a circuit for sensing the external magnetic field Hext. The magnetic field sense circuit 11 includes, for example, a ferromagnetic element 15 whose resistance value is changed by an external magnetic field Hext. The resistance detection circuit 12 detects the resistance value Rx of the ferromagnetic element 15 in the magnetic field sense circuit 11.

The magnetic field sense circuit 11 and the resistance detection circuit 12 are the same as the magnetic field sense circuit 11 and the resistance detection circuit 12 in the first embodiment (FIGS. 1 to 5), respectively, and thus detailed description thereof is omitted here. .

The feedback voltage generation circuit 14, generated when the external magnetic field Hext is changed, based on a feedback voltage to generate an electric field to cancel the change in the resistance value Rx of the ferromagnetic element 15, the output voltage V _R of the resistance detection circuit 12 To do. For example, the feedback voltage is output as the output voltage Vout of the magnetic field sensor, is fed back to the magnetic field sense circuit 11 as the control voltage Vcontrol, and is applied to the electrodes in the magnetic field sense circuit 11.

7 and 8 show a configuration example of the magnetic field sensor of FIG.

7, the magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 on the insulating layer 32. The ferromagnetic element 15 is a domain wall motion element, for example, and has a fine wire structure.

8, the magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 on the insulating layer 32. However, the ferromagnetic element 15 is, for example, a magnetoresistive effect element.

The resistance value Rx of the ferromagnetic element 15 can be detected by, for example, sensing a voltage generated between the ferromagnetic elements 15 when a current I is passed through the ferromagnetic element 15. In this example, the resistance detection circuit 12, an operational amplifier, and outputs the resistance value Rx of the ferromagnetic element 15, as an output voltage V _R.

The configuration examples of the magnetic field sense circuit 11 and the resistance detection circuit 12 are also the same as the magnetic field sense circuit 11 and the resistance detection circuit 12 in the first embodiment (FIGS. 1 to 5), respectively. Is omitted.

Changes in the external magnetic field Hext is manifested as a change in the output voltage V _R. The output voltage V _R, for example, via a feedback voltage generating circuit 14 is output as the output voltage Vout. That is, a change in the external magnetic field Hext is detected as a change in the output voltage Vout (change in the control voltage Vcontrol).

The feedback voltage generation circuit 14 cancels the change in the resistance value Rx of the ferromagnetic element 15 when the external magnetic field Hext changes, that is, the feedback such that the resistance value Rx of the ferromagnetic element 15 is always constant. voltage, a circuit for generating on the basis of the output voltage V _R of the resistance detection circuit 12.

For example, the feedback voltage generation circuit 14 includes an operational amplifier (voltage follower). In this case, the feedback voltage generation circuit 14 reduces the impedance of the output of the magnetic sensor. That is, the feedback loop in the operational amplifier, the output voltage V _R of the resistance detection circuit 12 as an output voltage Vout of the feedback voltage generation circuit 14, is output correctly. For this reason, sense sensitivity can be improved.

In addition, the output voltage Vout of the feedback voltage generation circuit 14 also functions as a feedback voltage. That is, the feedback voltage is applied to the electrode 31 in the magnetic field sense circuit 11 as the control voltage Vcontrol.

In the magnetic field sensor of this example, the feedback voltage generated by the feedback generation circuit 14 is fed back to the magnetic field sense circuit 11 as the control voltage Vcontrol. In this case, regardless of the current flowing through the output of the magnetic field sensor, the output voltage V _R of the resistance detection circuit 12, as a feedback voltage, it is possible to properly feedback.

Further, when the external magnetic field Hext changes, the feedback voltage is controlled so as to cancel the change in the resistance value Rx of the ferromagnetic element 15, that is, so that the resistance value Rx of the ferromagnetic element 15 is always constant. By feeding back the voltage Vcontrol, the external magnetic field Hext can be detected by the null method.

Thus, in this example, a magnetic field sensor with higher sensitivity can be realized as compared with the detection by the displacement method that directly reads the resistance fluctuation of the ferromagnetic element 15.

FIG. 9 shows the sense sensitivity of the magnetic field sensor of FIGS.

6 to 8, the feedback voltage generated by the feedback generation circuit 14 is fed back to the magnetic field sense circuit 11, and the resistance value Rx of the ferromagnetic element 15 is always constant even when the external magnetic field Hext changes. Feedback control is performed so that

For example, the magnetoresistance curve of the ferromagnetic element 15, when expressed as in FIG. 9, a change in the resistance value Rx of the ferromagnetic element 15 due to changes in the external magnetic field Hext (change in the output voltage V _R), the feedback voltage A change in the feedback voltage (change in the control voltage Vcontrol) generated by the generation circuit 14 is compared with each other, and feedback control is performed so that both are equal.

That is, the magnetic field sensor of this example, applying a control voltage Vcontrol and an output voltage V _R to the balance, the resistance value Rx of the ferromagnetic element 15 is always controlled to be in the A point.

(Third embodiment)
The third embodiment relates to a combination of the first and second embodiments.

FIG. 10 shows a magnetic field sensor according to the third embodiment.

The magnetic field sense circuit 11 is a circuit for sensing the external magnetic field Hext. The magnetic field sense circuit 11 includes, for example, a ferromagnetic element 15 whose resistance value is changed by an external magnetic field Hext. The resistance detection circuit 12 detects the resistance value Rx of the ferromagnetic element 15 in the magnetic field sense circuit 11.

The bias voltage generation circuit 13 generates a bias voltage for setting the resistance value Rx of the ferromagnetic element 15 to a predetermined value based on the output voltage of the feedback voltage generation circuit 14 when the external magnetic field Hext is zero.

The output voltage of the bias voltage generation circuit 13 is output as, for example, the output voltage Vout of the magnetic field sensor, fed back to the magnetic field sense circuit 11 as the control voltage Vcontrol, and applied to the electrodes in the magnetic field sense circuit 11.

The feedback voltage generation circuit 14 cancels the change in the resistance value Rx of the ferromagnetic element 15 when the external magnetic field Hext changes when the bias voltage is applied to the electrode in the magnetic field sense circuit 11 as the control voltage Vcontrol. the feedback voltage for, based on the output signal voltage V _R of the resistance detection circuit 12.

11 and 12 show a configuration example of the magnetic field sensor of FIG.

In the example of FIG. 11, the magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 on the insulating layer 32. The ferromagnetic element 15 is a domain wall motion element, for example, and has a fine wire structure.

12, the magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 on the insulating layer 32. However, the ferromagnetic element 15 is, for example, a magnetoresistive effect element.

The resistance value Rx of the ferromagnetic element 15 can be detected by, for example, sensing a voltage generated between the ferromagnetic elements 15 when a current I is passed through the ferromagnetic element 15. In this example, the resistance detection circuit 12, an operational amplifier, and outputs the resistance value Rx of the ferromagnetic element 15, as an output voltage V _R.

Changes in the external magnetic field Hext is manifested as a change in the output voltage V _R. The output voltage V _R, for example, via a bias voltage generating circuit 13 and a feedback voltage generating circuit 14 is output as the output voltage Vout. That is, a change in the external magnetic field Hext is detected as a change in the output voltage Vout (change in the control voltage Vcontrol).

In the magnetic field sensor of this example, high sensitivity sensing of the external magnetic field Hext is possible by combining the zero shift by the bias voltage generation circuit 13 and the sensing by the zero method by the feedback generation circuit 14. In addition, the magnetic field sensor of this example can realize highly sensitive sensing only by adding two operational amplifiers, for example.

FIG. 13 shows the sense sensitivity of the magnetic field sensor of FIGS.

10 to 12, the bias voltage generation circuit 13 causes the resistance value Rx of the ferromagnetic element 15 when the external magnetic field Hext is zero (zero point) to be a high sensitivity region (B Shift to point). In addition, the magnetic field sensors of FIGS. 10 to 12 perform feedback control by the feedback generation circuit 14 so that the resistance value Rx of the ferromagnetic element 15 is always constant even when the external magnetic field Hext changes.

Therefore, a highly sensitive and low-cost magnetic field sensor can be realized.

(Fourth embodiment)
The fourth embodiment relates to a modification of the magnetic field sense circuit in the first to third embodiments.

FIG. 14 shows a magnetic field sensor according to the fourth embodiment.

The magnetic field sensor of this example is an example in which a so-called bridge circuit is used to detect the resistance value Rx of the ferromagnetic element 15.

The magnetic field sense circuit 11 includes an electrode 31 to which a control voltage Vcontrol is applied, an insulating layer 32 on the electrode 31, and a ferromagnetic element 15 and resistance elements 16, 17, and 18 on the insulating layer 32. Resistance elements 16, 17, and 18 have resistance values R1, R2, and R3, respectively, and these resistance values R1, R2, and R3 are known.

The resistance elements 16 and 17 are connected in series between the two nodes N1 and N2, and the ferromagnetic element 15 and the resistance element 18 are also connected in series between the two nodes N1 and N2. The connection point between the resistance elements 16 and 17 is connected to the power supply terminal Vdd, and the connection point between the ferromagnetic element 15 and the resistance element 18 is connected to the power supply terminal Vss. However, the potential of the power supply terminal Vdd is higher than the potential of the power supply terminal Vss.

The resistance detection circuit 12 is connected between the two nodes N1 and N2.

The resistance detection circuit 12, the bias voltage generation circuit 13, and the feedback voltage generation circuit 14 are respectively the resistance detection circuit 12 and the bias voltage generation circuit 13 in the first to third embodiments (FIGS. 1 to 13). , And the feedback voltage generation circuit 14 is the same, and a detailed description thereof is omitted here.

In this case, utilizing the fact that the ratio of the resistance values of the resistance elements 16 and 17 (R1 / R2) and the ratio of the resistance values of the ferromagnetic element 15 and the resistance element 18 (Rx / R3) are equal to each other, The resistance value Rx of the ferromagnetic element 15 can be detected.

In this example, the bridge circuit includes one variable resistance element (ferromagnetic element 15) and three fixed resistance elements (resistance elements 16 to 18), but at least one of the plurality of resistance elements in the bridge circuit is variable. Any resistive element may be used. For example, two, three, or all resistance elements in the bridge circuit may be variable resistance elements.

According to the detection of the resistance value Rx of the ferromagnetic element 15 using such a bridge circuit, the resistance value Rx of the ferromagnetic element 15 can be detected with higher accuracy. This contributes to further improvement in the sense sensitivity of the magnetic field sensor.

(Musubi)
According to the embodiment, a magnetic field sensor with high sensitivity and low cost can be realized.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10: control voltage generation circuit, 11: magnetic field sense circuit, 12: resistance detection circuit, 13: bias voltage generation circuit, 14: feedback voltage generation circuit, 15: ferromagnetic element (resistance change element), 16, 17, 18: Resistance element, 21 and 23: ferromagnetic layer, 22: nonmagnetic insulating layer, and I: current source.

Claims (10)

A first circuit comprising: a ferromagnetic element whose resistance value changes according to a magnetic field and an electric field; and an electrode to which a voltage for generating the electric field is applied;
A second circuit for applying a voltage at which the resistance value of the ferromagnetic element becomes a predetermined value to the electrode when the magnetic field is zero,
Magnetic field sensor. A first circuit comprising: a ferromagnetic element whose resistance value changes according to a magnetic field and an electric field; and an electrode to which a voltage for generating the electric field is applied;
A second circuit that applies a voltage to the electrode that generates the electric field that reduces a change in the resistance value of the ferromagnetic element when the magnetic field changes.
Magnetic field sensor. A first circuit comprising: a ferromagnetic element whose resistance value changes according to a magnetic field and an electric field; and an electrode to which a voltage for generating the electric field is applied;
Applying a first voltage to the electrode that generates the electric field at which the resistance value of the ferromagnetic element is a predetermined value when the magnetic field is zero;
In a state where the first voltage is applied to the electrode, when the magnetic field is changed, the second voltage is set to generate the electric field that reduces a change in the resistance value of the ferromagnetic element. A second circuit applied to the electrode,
Magnetic field sensor. The magnetic field sensor according to claim 1, further comprising a third circuit that detects the resistance value of the ferromagnetic element. The magnetic field sensor according to any one of claims 1 to 4, wherein the change in the magnetic field is detected as a change in the resistance value of the ferromagnetic element. The magnetic field sensor according to claim 1, wherein the first circuit further includes an insulating layer between the ferromagnetic element and the electrode. The magnetic field sensor according to any one of claims 1 to 6, wherein the ferromagnetic element is a magnetoresistive effect element. The magnetic field sensor according to any one of claims 1 to 6, wherein the ferromagnetic element is a domain wall motion element. The first circuit further includes first, second, and third resistance elements, and the first and second resistance elements are connected in series between the first and second nodes, and the strong circuit The magnetic element and the third resistance element are connected in series between the first and second nodes, and a connection point of the first and second resistance elements is connected to a first power supply terminal, The connection point of the magnetic element and the third resistance element is connected to a second power supply terminal, and the third circuit is connected between the first and second nodes. Magnetic field sensor. 10. The magnetic field sensor according to claim 9, wherein at least one of the first to third resistance elements is a ferromagnetic element.

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