WO2016017490A1

WO2016017490A1 - Magnetic switch

Info

Publication number: WO2016017490A1
Application number: PCT/JP2015/070783
Authority: WO
Inventors: 井出　洋介; 斎藤　正路; 直樹坂詰
Original assignee: アルプス電気株式会社
Priority date: 2014-07-31
Filing date: 2015-07-22
Publication date: 2016-02-04

Abstract

[Problem] To provide a magnetic switch for which it is difficult for switch output switching timing to vary even when there is temperature variation. [Solution] A magnetic switch has a magneto-resistance effect element, an antiferromagnetic layer is disposed on a free magnetic layer of the magneto-resistance effect element, and an exchange coupling magnetic field is applied as a bias magnetic field from the antiferromagnetic layer to the free magnetic layer. The characteristics of the variation of the exchange coupling magnetic field caused by temperature variation are made to match the characteristics of the variation of a spin valve magnetoresistance layered device caused by temperature variation. This makes it possible to suppress variation in detection output caused by temperature variation if a magnetic field to be measured is below a reference value. As a result, if a threshold value is set at or below a standard value, it is possible to obtain unvaried switch output even if there is temperature variation.

Description

Magnetic switch

The present invention relates to a magnetic switch that uses a magnetoresistive effect element that detects a magnetic field to be measured, and switches an output depending on whether or not the magnetic field to be measured reaches a threshold value.

Patent Document 1 describes a current sensor using a magnetoresistive effect element. The magnetoresistive effect element used in this current sensor is a GMR element (giant magnetoresistive effect element) having a spin valve structure in which a fixed magnetic layer, a nonmagnetic layer, and a free magnetic layer are stacked. Due to the applied bias magnetic field, the magnetization direction of the free magnetic layer is aligned in a direction perpendicular to the Pin direction of the pinned magnetic layer.

The current sensor described in Patent Document 1 includes a magnetoresistive effect element that forms a bridge circuit. However, a pair of magnetoresistive effect elements connected in series and installed on the same chip have opposite bias magnetic fields. It has become. Accordingly, it is described that fluctuations in the output of the pair of magnetoresistive elements can be offset and the linearity of the sensor output can be improved.

In the current sensor described in Patent Document 2, a pair of magnetoresistive effect elements connected in series and located on the same chip have the bias magnetic fields opposite to each other, similar to the one described in Patent Document 1. ing. The magnetoresistive effect element uses an exchange bias instead of a hard bias.

WO2012 / 172946A1 JP 2014-063893 A

The magnetoresistive effect element using the GMR effect described in Patent Document 1 and Patent Document 2 has a spin valve structure, and when a measured magnetic field is applied, a nonmagnetic layer such as a Cu layer and a ferromagnetic layer A resistance value change (ΔR) depending on spin scattering occurs at the interface with the free magnetic layer or the pinned magnetic layer which is a layer.

However, this magnetoresistive element has a problem that the rate of change in resistance (ΔR / R) decreases as the environmental temperature in use increases. That is, when the temperature rises, the lattice vibration of atoms constituting the GMR film increases, so that electron scattering independent of electron spin increases. Therefore, the fixed resistance component (R) increases, and as a result, the rate of change in resistance (ΔR / R) decreases with increasing temperature.

For this reason, when a current sensor using a magnetoresistive element is used in a high temperature environment, the detection output fluctuates due to a decrease in the rate of change in resistance, and the temperature at which the temperature sensor is used to correct this. It becomes necessary to provide a compensation circuit, and the circuit configuration becomes complicated. In addition, if the sensitivity of the temperature sensor varies, accurate temperature compensation cannot be performed.

However, in Patent Document 1 and Patent Document 2, no consideration is given to the change in the resistance change rate of the magnetoresistive element when the temperature changes.

The present invention solves the above-described conventional problems, and an object of the present invention is to provide a magnetic switch that can suppress a fluctuation in detection output of a magnetoresistive effect element due to a temperature change and obtain a stable switch output. It is said.

The present invention comprises a magnetoresistive effect element whose resistance value changes according to the strength of a magnetic field to be measured, and a comparison unit that generates a switch output by comparing a detection output based on the change in the resistance value and a threshold value. In the magnetic switch provided,
The magnetoresistive effect element has a pinned magnetic layer, a nonmagnetic material layer, and a free magnetic layer, and an antiferromagnetic layer is superimposed on the free magnetic layer and acts from the antiferromagnetic layer to the free magnetic layer. By the exchange coupling magnetic field, the magnetization direction of the free magnetic layer is set to intersect the direction of the fixed magnetization of the fixed magnetic layer,
The magnetoresistive effect element has a variation characteristic of a rate of change in resistance with respect to a change in temperature so that a change in the detection output due to a change in temperature is not more than a predetermined ratio within a range in which the measured magnetic field rises to a predetermined reference value. And a fluctuation characteristic of the exchange coupling magnetic field with respect to a temperature change, and the threshold value is set to be equal to or less than the reference value.

In the magnetic switch of the present invention, when a plurality of change lines indicating changes in the detection output with respect to the strength of the magnetic field to be measured are obtained at different environmental temperatures, the plurality of change lines intersect and thereafter the difference in the detection output increases. As described above, the two fluctuation characteristics are set, and the intersection of the change lines can be set as the reference value.

In the present invention, it is preferable that the threshold value matches the reference value.
In the magnetic switch of the present invention, the distance between the source of the magnetic field to be measured and the magnetoresistive element is set according to the threshold value.

The magnetic switch of the present invention is a magnet in which the source of the magnetic field to be measured moves opposite to the magnetoresistive element. Alternatively, the source of the magnetic field to be measured is a current path facing the magnetoresistive effect element, and the magnetic field to be measured changes according to the amount of current flowing through the current path.

The magnetic switch of the present invention is configured such that the detection output from the magnetoresistive effect element that detects the magnetic field to be measured is compared with a threshold value, and the switch output changes when the detection output exceeds the threshold value. Yes. In the magnetoresistive effect element, an exchange coupling magnetic field is applied as a bias magnetic field from the antiferromagnetic layer to the free magnetic layer. Since the exchange coupling magnetic field using the antiferromagnetic layer decreases as the temperature increases, the detection sensitivity increases accordingly. Therefore, by combining the change characteristic of the resistance change rate due to the temperature rise of the magnetoresistive effect element and the change characteristic of the detection sensitivity due to the temperature rise, the temperature change is within a range where the measured magnetic field increases to a predetermined reference value. It is possible to reduce fluctuations in the detection output due to. The threshold value for obtaining the switch output is set to a value corresponding to the magnetic field strength equal to or less than the reference value, or a value corresponding to the magnetic field strength matching the reference value, so that the switch having less influence due to the temperature change. Output will be obtained.

The block diagram which shows the magnetic switch of embodiment of this invention, A plan view showing a structure of a magnetoresistive effect element constituting a magnetic switch, FIG. 3 is an enlarged sectional view of a magnetoresistive effect element showing a section taken along line III-III in FIG. (A) is a diagram schematically showing the temperature characteristics of the resistance change rate, (B) is a diagram schematically showing the temperature characteristics of the exchange coupling magnetic field, The block diagram which shows the structure of the switching device of the magnet movement type containing a magnetic switch, Configuration diagram of a current detection device including a magnetic switch, In Example 1, the diagram which shows the relationship between the intensity | strength change of the to-be-measured magnetic field which acts on a magnetic switch, and a midpoint voltage difference, In Example 2, the diagram which shows the relationship between the intensity | strength change of the to-be-measured magnetic field which acts on a magnetic switch, and a midpoint voltage difference, In Example 3, the diagram which shows the relationship between the intensity | strength change of the to-be-measured magnetic field which acts on a magnetic switch, and a midpoint voltage difference,

FIG. 1 shows a magnetic switch 1 according to an embodiment of the present invention.
The magnetic switch 1 has a bridge circuit 2. The bridge circuit 2 includes two first magnetoresistive elements 10a and two second magnetoresistive elements 10b. The first magnetoresistive element 10a and the second magnetoresistive element 10b are connected in series to form a series circuit, and the two series circuits are connected in parallel to form a full bridge circuit. For example, a power supply voltage of 5 V is applied to the power supply terminal 3 common to the two series circuits, and the ground terminal 4 common to the two series circuits is set to the installation potential. In the two series circuits, the order of series connection of the first magnetoresistive effect element 10a and the second magnetoresistive effect element 10b is opposite to each other.

In the first magnetoresistance effect element 10a and the second magnetoresistance effect element 10b, the S direction is the sensitivity axis direction, and the resistance value changes according to the strength of the magnetic field in the S direction. When the magnetic field strength in any one of the S directions changes, the resistance values of the first magnetoresistive effect element 10a and the second magnetoresistive effect element 10b change with opposite characteristics.

The potential of the midpoint 5a of the left series circuit constituting the full bridge circuit 2 and the potential of the midpoint 5b of the right series circuit are obtained by the differential amplifier 6, and the potential of the midpoint 5a and the potential of the midpoint 5b are Is obtained as the detection output (detection output voltage) Vs.

In the comparison unit 7, the detection output Vs obtained from the differential amplifier 6 is compared with the threshold voltage Vr set in the threshold setting unit 8. In the comparison unit 7, the switch output changes when the detection output Vs exceeds the threshold voltage Vr or coincides with the threshold voltage Vr, and this switch output is given to the processing circuit 9. The processing circuit 9 performs a predetermined processing operation when a switch output is given.

FIG. 2 is a plan view of the first magnetoresistive element 10a.
The first magnetoresistive effect element 10 a has a stripe-shaped element portion 12. A plurality of element parts 12 are formed in parallel, the right end part of the adjacent element parts 12 shown in the figure is connected via the conductive part 13, and the right end part of the adjacent element part 12 shown in the figure is connected via the conductive part 13. Has been. The conductive portions 13 are alternately connected to the right end portion and the left end portion of the element portion 12 in the drawing, and the element portion 12 is connected in a so-called meander shape. In the first magnetoresistive effect element 10a, the upper left conductive portion 13 is electrically connected to the connection terminal 14a, and the lower right conductive portion 13 is electrically connected to the connection terminal 14b.

As shown in the sectional view of FIG. 3, each element portion 12 has a structure in which a plurality of metal layers are laminated.
The element portion 12 is a GMR element having a spin valve structure, and is formed on the surface of the substrate 29. From the surface of the substrate 29, the seed layer 20, the fixed magnetic layer 21, the nonmagnetic material layer (nonmagnetic conductive layer) 22, and the free magnetism. The layer 23, the antiferromagnetic layer 24, and the protective layer 25 are stacked in this order. These layers are formed by, for example, a sputtering process.

The seed layer 20 is made of NiFeCr alloy (nickel / iron / chrome alloy) or Cr. The pinned magnetic layer 21 has a self-pinning structure including a first magnetic layer 21a and a second magnetic layer 21c, and a nonmagnetic intermediate layer 21b positioned between the first magnetic layer 21a and the second magnetic layer 21c. ing. The fixed magnetization direction of the first magnetic layer 21a and the fixed magnetization direction of the second magnetic layer 21c are antiparallel due to the RKKY interaction. The fixed magnetization direction of the second magnetic layer 21 c is the fixed magnetization direction P of the fixed magnetic layer 21. The direction in which the fixed magnetization direction P extends is the sensitivity axis direction S.

Both the first magnetic layer 21a and the second magnetic layer 21c are formed of an FeCo alloy (iron-cobalt alloy), but the first magnetic layer 21a has a higher Fe content than the second magnetic layer 21c. Magnetic force is set high. The second magnetic layer 21c in contact with the nonmagnetic material layer 22 is a layer that contributes to the spin valve type GMR effect, and the second magnetic layer 21c has a mean free path of conduction electrons having up spins and conduction electrons having down spins. The composition is determined so that the difference is larger than that of the first magnetic layer 21a. In addition, the difference in the amount of magnetization (saturation magnetization Ms · film thickness t) is substantially zero between the first magnetic layer 21a and the second magnetic layer 21c. The nonmagnetic intermediate layer 21b is formed of Ru (ruthenium) or the like.
The nonmagnetic material layer 22 is made of Cu (copper) or the like.

The free magnetic layer 23 is formed by laminating a first ferromagnetic layer 23a and a second ferromagnetic layer 23b. The first ferromagnetic layer 23a and the second ferromagnetic layer 23b are formed of a NiFe alloy (nickel / iron alloy), a CoFe alloy (cobalt / iron alloy), or the like. An antiferromagnetic layer 24 is laminated in direct contact with the second ferromagnetic layer 23b of the free magnetic layer 23. Due to the antiferromagnetic coupling at the interface between the antiferromagnetic layer 24 and the second ferromagnetic layer 23b, the exchange coupling magnetic field Hex acts as a bias magnetic field on the free magnetic layer 23. As a result, the magnetization direction F of the free magnetic layer 23 is aligned with the direction in which the bias magnetic field acts. The second ferromagnetic layer 23b has a higher iron content than the first ferromagnetic layer 23b due to antiferromagnetic coupling with the antiferromagnetic layer 24.

The antiferromagnetic layer 24 is preferably formed of an IrMn alloy (iridium / manganese alloy) capable of exchange coupling without annealing in the magnetic field with the free magnetic layer 23. In addition, although it is possible to use PtMn (platinum manganese alloy) etc. as the antiferromagnetic layer 24, in this case, annealing treatment is required for ordering of the film.

In the first magnetoresistance effect element 10a shown in FIG. 2, the fixed magnetization direction P of the fixed magnetic layer 21 has an angle of 90 degrees counterclockwise with respect to the magnetization direction F of the free magnetic layer 23 by the exchange coupling magnetic field. Is set. The element structure of the second magnetoresistive effect element 10b is the same as that of the first magnetoresistive effect element 10a. However, as shown in FIG. 1, the fixed magnetization direction P and the magnetization direction F have the first magnetoresistance effect 10b. It is 180 degrees opposite to the effect element 10a.

In the first magnetoresistive effect element 10a and the second magnetoresistive effect element 10b having the element part 12 having the spin valve structure, the S direction is the sensitivity axis direction. When a magnetic field to be measured directed in the S1 direction is applied, the magnetization direction F of the free magnetic layer 23 is rotated so as to be directed in the left direction in FIG. In the first magnetoresistive effect element 10a, the angle between the fixed magnetization direction P and the magnetization direction F is small, so that the resistance value decreases. In the second magnetoresistive effect element 10b, the fixed magnetization direction P and the magnetization direction F are reduced. As the angle increases, the resistance value increases. Conversely, when a magnetic field to be measured directed in the S2 direction is applied, the resistance value of the first magnetoresistance effect element 10a increases and the resistance value of the second magnetoresistance effect element 10b decreases.

When the magnetic field strength in the S1 direction increases, the potential at the midpoint 5a decreases and the potential at the midpoint 5b increases. Therefore, the detection output Vs from the differential amplifier 6 increases. The comparison unit 7 compares the detection output Vs with the threshold voltage Vr. When the detection output Vs exceeds the threshold voltage Vr or when the detection output Vs matches the threshold voltage Vr, the switch output is switched.

In the comparison unit 7, a positive threshold voltage + Vr and a negative threshold voltage −Vr are set, the strength of the magnetic field to be measured directed in the S1 direction is increased, and the detection output Vs is the first threshold voltage. When the threshold voltage + Vr is exceeded or coincides with the threshold voltage + Vr, the first switch output is obtained, the intensity of the magnetic field to be measured in the S2 direction is increased, and the detection output Vs is the first threshold voltage −. The second switch output may be obtained when it becomes smaller than Vr or coincides with the threshold voltage −Vr.

The degree of change in the resistance value of the element portion 12 constituting the

magnetoresistive effect elements

10a and 10b when the measured magnetic field changes is evaluated by the resistance change rate (ΔR / R). (R) is a fixed resistance component of the element section 12, and (ΔR) is a change component of the resistance value of the element section 12 caused by fluctuation of the measured magnetic field.

The element part 12 having a spin valve structure has temperature characteristics. That is, when the environmental temperature rises, the rate of change in resistance (ΔR / R) decreases. FIG. 4A is a diagram showing a decrease state of the rate of change in resistance (ΔR / R) as the temperature (T) increases. FIG. 4A schematically shows a change in the resistance change rate (ΔR / R). The resistance change rate (ΔR / R) is relatively close to a linear function as the temperature rises. It will decline due to the relationship.

The spin valve type GMR element has a change in resistance value (ΔR) depending on spin scattering at the interface between the nonmagnetic material layer 22 such as a Cu layer and the free magnetic layer 23 and the ferromagnetic layer of the pinned magnetic layer 21. Arise. However, when the temperature rises, the lattice vibration of atoms constituting the GMR film increases, so that the resistance increases without depending on the spin, the fixed resistance component (R) increases, and the resistance change rate ( ΔR / R) decreases.

On the other hand, it is known that the exchange coupling magnetic field (Hex) acting on the free magnetic layer 23 from the antiferromagnetic layer 24 decreases as the temperature increases. The reason is that as the temperature rises, Hex decreases as the temperature of the antiferromagnetic material approaches the Neel temperature (the temperature at which antiferromagnetism disappears). FIG. 4B schematically shows the change of the exchange coupling magnetic field (Hex) with an increase in temperature, but the temperature characteristic of the exchange coupling magnetic field (Hex) shows a quadratic function change.

As shown in FIG. 4A, when the temperature rises, the spin valve type GMR effect deteriorates and the resistance change rate (ΔR / R) decreases. On the other hand, when the temperature rises, the bias magnetic field due to the exchange coupling magnetic field (Hex) with respect to the free magnetic layer 23 decreases, so that the magnetization direction F of the free magnetic layer 23 becomes easy to move when a measured magnetic field is applied. That is, as the temperature increases, the sensitivity of the free magnetic layer 23 to the external magnetic field increases. Therefore, in the embodiment of the present invention, by combining the temperature characteristic of the resistance change rate (ΔR / R) and the temperature characteristic of the exchange coupling magnetic field (Hex), the external magnetic field is changed to a predetermined reference value. In the meantime, the detection output Vs is hardly affected by the temperature change.

If it is possible to realize a state in which the detection output Vs is hardly affected by the temperature change, the switch output is always accompanied by the same measured magnetic field strength without changing the threshold voltage Vr even if there is a large temperature change. Can be switched. Therefore, it is not necessary to change the threshold voltage Vr by providing a temperature compensation circuit including a temperature sensor or the like.

FIG. 5 shows a switching device 30 including the magnetic switch 1. In the switching device 30, a magnet 31 is opposed to the magnetic switch 1, and the magnet 31 is moved in the F1-F2 direction by an external operation. When the magnet 31 approaches the magnetic switch 1, the magnetic field strength of the magnetic field B to be measured in the S <b> 1 direction becomes stronger than the magnetic switch 1. When the detection output Vs shown in FIG. 1 exceeds the threshold voltage Vr or coincides with the threshold voltage Vr, the comparison unit 7 switches the switch output. In the processing circuit 9, a predetermined control process is performed in accordance with the change in the switch output.

FIG. 6 shows a current detection device 35 including the magnetic switch 1. In the current detection device 35, a current path (bus bar) 36 faces the magnetic switch 1. When the current I flowing through the current path 36 increases, the magnetic field strength of the magnetic field B to be measured in the S1 direction becomes stronger with respect to the magnetic switch 1. When the detection output Vs shown in FIG. 1 exceeds the threshold voltage Vr or coincides with the threshold voltage Vr, the comparison unit 7 switches the switch output.

In the switching device 30 shown in FIG. 5 and the current detection device 35 shown in FIG. 6, the temperature characteristics of the resistance change rate (ΔR / R) and the exchange coupling magnetic field (Hex) in the element portion 12 of the

magnetoresistive effect elements

10a and 10b. By combining with the temperature characteristics, the detection output Vs is hardly affected by the temperature change until the external magnetic field reaches the predetermined reference value, and a stable detection output Vs can always be obtained. Therefore, even if the use environment temperature becomes high, the switch output can be obtained accurately using the fixed threshold voltage Vr.

As an example, a switch element 1 having a bridge circuit 2 shown in FIG. 1 was prepared. The element part 12 of the

magnetoresistive effect elements

10a and 10b has a meander shape, the width dimension of the element part 12 is 1 μm, and the length dimension of each stripe part of the element part 12 is 120 μm.

Laminated structure of the element portion 12, a seed layer deposited by _Ni 48 _Fe 12 _{Cr 40,} was 4.2nm thickness.

In the pinned magnetic layer 21, the first magnetic layer 21a is formed of Fe ₆₀ Co ₄₀ , the second magnetic layer 21c is formed of Co ₉₀ Fe ₁₀ , and the nonmagnetic intermediate layer 21b is formed of Ru. The first magnetic layer 21a was 1.9 nm thick, the second magnetic layer 21c was 2.4 nm thick, and the nonmagnetic intermediate layer 21b was 0.36 nm thick.
The nonmagnetic material layer 22 is a Cu layer and has a thickness of 2.0 nm.

In the free layer 23, the first ferromagnetic layer 23a was formed of Co ₉₀ Fe ₁₀ and the second ferromagnetic layer 23b was formed of Co ₇₀ Fe ₃₀ . The thickness of the first ferromagnetic layer 23a was a variable Xnm, and the thickness of the second ferromagnetic layer 23b was a fixed value of 1.0 nm.

The antiferromagnetic layer 24 is made of Ir ₂₂ Mn ₇₈ , and the protective layer 25 having a thickness of 5.0 nm is a Ta layer and has a thickness of 10.0 nm.

(Example 1)
In the element unit 12 of Example 1, the thickness of the first ferromagnetic layer 23a constituting the free layer 23 was set to 5.0 nm.

(Example 2)
In the element unit 12 of Example 2, the thickness of the first ferromagnetic layer 23a was set to 4.0 nm.

(Example 3)
In the element unit 12 of Example 3, the thickness of the first ferromagnetic layer 23a was set to 3.0 nm.

FIG. 7 shows the relationship between the change in the intensity of the magnetic field to be measured (mT) acting on the magnetic switch 1 and the voltage difference between the potential at the midpoint 5a and the potential at the midpoint 5b in the first embodiment. This potential difference is expressed as a ratio (%) to the power supply voltage Vdd. FIG. 8 shows the change of the midpoint voltage difference (detected output Vs in FIG. 1) with respect to the intensity change of the magnetic field to be measured (mT) acting on the magnetic switch 1 in Example 2 in%. FIG. 9 shows the change in the midpoint voltage difference (detected output Vs in FIG. 1) with respect to the intensity change of the magnetic field to be measured (mT) acting on the magnetic switch 1 in Example 3 in%.

7, 8, and 9, in any of the examples, data (change line) when the use environment of the magnetic switch 1 is room temperature (25 ° C.), data when 85 ° C., and 150 ° C. When the data is shown.

FIG. 7, FIG. 8 and FIG. 9 show the results of experiments and actual measurements. The exchange coupling magnetic field (Hex) applied as a bias magnetic field from the antiferromagnetic layer 24 to the free magnetic layer 23 decreases in contrast to the increase in the amount of magnetization (saturation magnetization Ms · film thickness t) of the free magnetic layer 23. To do.

In this experiment, the exchange coupling magnetic field (Hex) applied to the free magnetic layer 23 was set to 15.0 mT by setting the thickness of the first ferromagnetic layer 23a to 5.0 nm in Example 1. In Example 2, since the thickness of the first ferromagnetic layer 23a was 4.0 nm, the exchange coupling magnetic field (Hex) applied to the free magnetic layer 23 was 18.0 mT. In Example 3, the exchange coupling magnetic field (Hex) applied to the free magnetic layer 23 was set to 22.0 mT by setting the thickness of the first ferromagnetic layer 23a to 3.0 nm.

From the actual measurement results of FIG. 7 to FIG. 9, the fluctuation characteristics of the resistance change rate (ΔR / R) due to temperature change and the fluctuation characteristics of the exchange coupling magnetic field (Hex) due to temperature change are combined to reach the magnetic switch 1. Difference in change in midpoint voltage difference (detection output Vs) obtained at each temperature of 25 ° C., 85 ° C., and 150 ° C. within a range in which the measured magnetic field rises from 0 (mT) to a predetermined reference value K It can be seen that can be made extremely small.

7 to 9, the reference value K of the magnetic field to be measured is shown as the position of the vertical broken line. In Example 1 of FIG. 7, the reference value K is around 16 mT, in Example 2 shown in FIG. 8, the reference value K is around 24 mT, and in Example 3 shown in FIG. 9, the reference value K is around 27 mT. is there.

As shown in FIGS. 7 to 9, when the magnetic field to be measured reaches a certain magnitude, a detection output change line at 25 ° C., a detection output change line at 85 ° C., and a change output line at 150 ° C. An intersection that matches will appear. In each figure, the measured magnetic field from which this intersection is obtained is used as a reference value K. When the magnetic field to be measured having the reference value K is applied, the detection outputs Vs substantially coincide with each other if the environmental temperature is approximately 150 ° C. or less. However, when the magnetic field to be measured exceeds the reference value K, the variation in the detection output due to temperature change increases.

Also, when the measured magnetic field is within the reference value K or less, the variation in the detection output due to the temperature change is extremely small. In Example 1 in FIG. 7, there is almost no variation in detection output due to temperature change within a range where the measured magnetic field is less than or equal to the reference value K. In Example 3 in FIG. 9, the measured magnetic field is less than or equal to the reference value K. Within the range, the variation in detection output due to temperature change is very small, less than 10% or less than 5%. However, the term “less than 10%” or “less than 5%” here is a value that does not take into account variations between elements when the measured magnetic field is about 0 to 30 mT.

From comparison of FIG. 7, FIG. 8, and FIG. 9, it can be seen that when the exchange coupling magnetic field (Hex) increases, the range of the magnetic field strength from 0 (mT) to the reference value K increases. However, as can be seen from FIG. 9, when the exchange coupling magnetic field (Hex) increases, the variation in the detection output due to the temperature change slightly increases in the region where the measured magnetic field is equal to or less than the reference value K, and is less than 10% as described above. Alternatively, a variation of less than 5% remains. It can be predicted that when the exchange coupling magnetic field (Hex) is increased, the quadratic change characteristic of the exchange coupling magnetic field (Hex) shown in FIG.

Therefore, the threshold voltage Vr set by the threshold setting unit 8 shown in FIG. 1 is set to one of the detection voltages corresponding to the measured magnetic field equal to or less than the reference value K shown in FIGS. By doing so, it is possible to obtain a switch output with very little variation due to temperature change. Preferably, when the threshold voltage Vr is made to coincide with the reference value K shown in FIGS. 7 to 9, a switch output with little variation due to temperature change can be obtained. That is, even if the temperature changes, the switch output is switched when the measured magnetic field acting on the magnetic switch 1 has the same magnitude.

Further, in the switching device 30 shown in FIG. 5, the magnet 31 and the magnetic switch 1 are arranged so that the measured magnetic field corresponding to the threshold voltage Vr acts on the magnetic switch 1 when the magnet 31 reaches a predetermined operation position. And the distance is set.

In the current detection device 35 shown in FIG. 6, when a current I that should not flow any more flows in the current path 36, the current to be measured acts on the magnetic switch 1 corresponding to the threshold voltage Vr. The distance between the path 36 and the magnetic switch 1 is set. With this setting, even if there is a temperature change in the usage environment, a switch output is obtained when a constant limit current always flows through the current path 36. The processing circuit 9 shown in FIG. It is possible to perform processing such as shutting off the power to the unit.

DESCRIPTION OF SYMBOLS 1 Magnetic switch 2 Bridge circuit 6 Differential amplifier 7 Comparison part 8 Threshold setting part 9 Processing circuit 10a 1st magnetoresistive effect element 10b 2nd magnetoresistive effect element 12 Element part 21 Fixed magnetic layer 22 Nonmagnetic material layer 23 Free magnetic layer 24 Antiferromagnetic layer 30 Switching device 31 Magnet 35 Current detection device 36 Current path F Magnetization direction P Fixed magnetization direction

Claims

A magnetoresistive element having a resistance value that changes according to the strength of the magnetic field to be measured, and a comparator that compares the detection output based on the change in the resistance value with a threshold value to generate a switch output. In the switch
The magnetoresistive effect element has a pinned magnetic layer, a nonmagnetic material layer, and a free magnetic layer, and an antiferromagnetic layer is superimposed on the free magnetic layer and acts from the antiferromagnetic layer to the free magnetic layer. By the exchange coupling magnetic field, the magnetization direction of the free magnetic layer is set to intersect the direction of the fixed magnetization of the fixed magnetic layer,
The magnetoresistive effect element has a variation characteristic of a rate of change in resistance with respect to a change in temperature so that a change in the detection output due to a change in temperature is not more than a predetermined ratio within a range in which the measured magnetic field rises to a predetermined reference value. And the fluctuation characteristics of the exchange coupling magnetic field with respect to temperature change are set.
The magnetic switch, wherein the threshold value is set to be equal to or less than the reference value.
When the plurality of change lines indicating the change in the detection output with respect to the strength of the magnetic field to be measured are obtained for each of different environmental temperatures, the two change lines intersect so that the difference in the detection output is increased thereafter. The magnetic switch according to claim 1, wherein a fluctuation characteristic is set, and an intersection of the change lines is set to the reference value.
The magnetic switch according to claim 1 or 2, wherein the threshold value is matched with the reference value.
3. A magnetic switch according to claim 1, wherein a distance between a generation source of the magnetic field to be measured and the magnetoresistive element is set in accordance with the threshold value.
5. The magnetic switch according to claim 1, wherein a source of the magnetic field to be measured is a magnet that moves to face the magnetoresistive element.
5. The magnetic switch according to claim 1, wherein a source of the magnetic field to be measured is a current path facing the magnetoresistive element, and the magnetic field to be measured changes according to an amount of current flowing through the current path. .