JP2010016260A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic sensor which is particularly excellent in DC voltage resistance, ESD resistance, and the voltage dependency of a change rate of magnetic resistance and has a change rate of magnetic resistance higher than 100%. <P>SOLUTION: The magnetic sensor 1 has a TMR element 3 whose electric resistance value varies with respect to an outside magnetic field. The TMR element 3 is formed in such a manner that an antiferromagnetic layer 11, a fixed magnetic layer 23, an insulating barrier layer 16, and a free magnetic layer 24 are laminated in this order. The insulating barrier layer 16 is characterized by a film thickness which is formed at Mg-O of 16 Å-40 Å. A parallel surface to an interface of each layer constituting the TMR element is almost circular, and its diameter is preferable to be in a range of 5 μm-100 μm. The number of TMR elements 3 is preferable to be 8 or more and to be connected in series. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic sensor using a tunnel type magnetoresistive effect element.

  The TMR element (tunnel magnetoresistive effect element) can increase the magnetoresistance change rate as compared with the Hall element, the AMR element (anisotropic magnetoresistive effect element), and the GMR element (giant magnetoresistive effect element). The TMR element is known to be used for a magnetic head of a hard disk drive device, for example.

  However, in the use of the magnetic head, in order to obtain good head characteristics, it is necessary to reduce the element resistance even at the sacrifice of the magnetoresistance change rate.

  On the other hand, the following patent documents disclose the use of TMR elements for magnetic sensors such as encoders and switches. Unlike the magnetic head, the magnetic sensor is considered to be more advantageous for detection accuracy and circuit design if the magnetoresistance change rate is increased regardless of the element resistance.

  However, these documents do not make any improvements to the configuration of the TMR element in order to increase the magnetoresistance change rate.

Further, the TMR element has a problem that it is inferior in DC pressure resistance and ESD resistance.
Further, the TMR element has a property that the rate of change in magnetoresistance deteriorates with an increase in applied voltage.
Japanese Patent Laid-Open No. 11-112054 JP-A-11-108689

  Therefore, the present invention is to solve the above-described conventional problems, and in particular, a magnetic sensor having a high magnetoresistance change rate of 100% or more, which is excellent in DC voltage resistance, ESD resistance, and voltage dependency characteristics of magnetoresistance change rate. The purpose is to provide.

The present invention is a magnetic sensor including a tunnel type magnetoresistive effect element whose electric resistance value varies with respect to an external magnetic field,
The tunnel magnetoresistive element is formed by sequentially stacking an antiferromagnetic layer, a pinned magnetic layer, an insulating barrier layer, and a free magnetic layer,
The insulating barrier layer is formed of Mg-O having a thickness of 16 to 40 mm.

  According to the present invention, the magnetoresistive change rate (ΔR / Rmin) of the tunnel type magnetoresistive effect element can be 100% or more, and the BDV (breakdown voltage) can be 1V or more. According to the present invention, it is possible to realize a magnetic sensor capable of obtaining a high output without using an amplifying means (amplifying circuit).

In the present invention, it is preferable that the plane parallel to the interface of each layer constituting the tunnel type magnetoresistive effect element has a shape with no corners and the area is in the range of 19.6 μm ^{2 to} 7850 μm ² . In particular, the parallel surfaces are preferably circular and have a diameter in the range of 5 μm to 100 μm. Thereby, ESD tolerance can be improved.

  In the present invention, it is preferable that eight or more tunnel type magnetoresistive effect elements are connected in series. By connecting eight or more tunnel-type magnetoresistive elements having high BDV and high ESD resistance in series, the DC withstand voltage can be improved more effectively and the voltage dependence coefficient (VCΔR / R) and the voltage dependency coefficient (VCR) of the resistance value can be reduced. Specifically, both the voltage dependence coefficient (VCΔR / R) of the magnetoresistance change rate and the voltage dependence coefficient (VCR) of the resistance value can be suppressed to 20 ppm / mV or less in absolute value, and excellent voltage dependence characteristics can be obtained. I can do it.

  According to the present invention, a TMR element having a high magnetoresistance change rate of 100% or more excellent in DC voltage resistance, ESD resistance, and voltage dependence characteristics of magnetoresistance change rate is provided, and an amplifying means (amplifier circuit) is not used. In addition, a magnetic sensor capable of obtaining a high output can be realized.

  1 is a partial plan view of a magnetic sensor according to the present embodiment, FIG. 2 is a partial cross-sectional view taken along the line AA shown in FIG. 1 and viewed from the direction of the arrow, and FIG. 3 is the present embodiment. FIG. 4 is an enlarged cross-sectional view showing the tunnel type magnetoresistive effect element (TMR element) in FIG. 4 cut from the film thickness direction, FIG. 4 is a circuit diagram of a two-wire switch configured using the magnetic sensor of this embodiment, and FIG. FIG. 2 is a circuit diagram of an encoder configured using the magnetic sensor of the present embodiment.

  As shown in FIGS. 1 and 2, the magnetic sensor 1 includes a lower electrode 2, a TMR element 3, and an upper electrode 4. In FIG. 1, the insulating layer shown in FIG. 2 is not shown. As shown in FIG. 2, the lower electrode 2 is formed on the substrate 6. As shown in FIG. 1, in this embodiment, a plurality of lower electrodes 2 are arranged at predetermined intervals in the X direction. The lower electrode 2 is formed in a vertically long shape in which the length dimension in the Y direction is longer than the length dimension in the X direction. The lower electrode 2 is made of a nonmagnetic conductive material by sputtering or plating.

As shown in FIG. 2, the periphery of the lower electrode 2 is filled with an insulating layer 5. The upper surface 2a of the lower electrode 2 and the upper surface 5a of the insulating layer 5 are formed on the same flat surface using a CMP technique or the like. The insulating layer 5 is formed of an insulating material such as Al ₂ O ₃ or SiO ₂ .

  As shown in FIGS. 1 and 2, two TMR elements 3 are formed on each lower electrode 2. The film configuration of the TMR element 3 will be described later. The two TMR elements 3 formed on each lower electrode 2 are arranged at intervals in the Y direction.

  As shown in FIG. 2, the periphery of the TMR element 3 is filled with an insulating layer 7. As shown in FIG. 2, the upper surface 3a of the TMR element 3 and the upper surface 7a of the insulating layer 7 are preferably formed on the same flat surface, but may be an uneven surface.

  As shown in FIGS. 1 and 2, the upper electrodes 4 are electrically connected between the upper surfaces of the TMR elements 3 formed on the adjacent lower electrodes 2 and opposed in the X direction. The upper electrode 4 is formed in a horizontally long shape in which the length dimension in the X direction is longer than the length dimension in the Y direction. As shown in FIG. 1, there are an upper electrode 4 formed on the Y1 side and an upper electrode 4 formed on the Y2 side, and these are alternately arranged in the X direction, whereby a plurality of TMR elements 3 are arranged. Are connected in series via the lower electrode 2 and the upper electrode 4. The current flows in the TMR element 3 in the film thickness direction (Z direction).

  The film configuration of the TMR element 3 will be described with reference to FIG. As shown in FIG. 3, the TMR element 3 provided between the lower electrode 2 and the upper electrode 4 has a seed layer 10, an antiferromagnetic layer 11, a fixed magnetic layer 23, an insulating barrier layer 16, a free magnetic layer 24, and The protective layer 21 is laminated in this order.

  The seed layer 10 is used to adjust the crystal orientation of each layer formed thereon, and is formed of Ru, Ni—Fe—Cr, or the like.

The antiferromagnetic layer 11 is formed of Ir—Mn, Pt—Mn, or the like.
As shown in FIG. 3, the pinned magnetic layer 23 has a laminated ferrimagnetic structure in which the first pinned magnetic layer 12, the nonmagnetic intermediate layer 13, and the second pinned magnetic layer 22 are laminated in this order from the bottom. The first pinned magnetic layer 12 is caused by an exchange coupling magnetic field (Hex) generated between the antiferromagnetic layer 11 and the RKKY interaction generated between the first pinned magnetic layer 12 and the second pinned magnetic layer 22 by annealing in a magnetic field. , The magnetization is fixed in one direction. On the other hand, the magnetization of the second pinned magnetic layer 22 is pinned in the direction opposite to the magnetization direction of the first pinned magnetic layer 12. The first pinned magnetic layer 12 is made of, for example, Co—Fe. The nonmagnetic intermediate layer 13 is made of, for example, Ru. The second pinned magnetic layer 22 is formed with a stacked structure of, for example, a Co—Fe—B layer 14 and a Co—Fe layer 15.

In the present embodiment, the insulating barrier layer 16 is formed of Mg—O. The composition ratio of Mg is preferably in the range of 40 at% to 60 at%. Most preferred is Mg _{50 at%} O _{50 at%} .

  In the embodiment of FIG. 3, the free magnetic layer 24 is formed with a laminated structure of, for example, a Co—Fe layer 17 / Co—Fe—B layer 18 / Ta layer 19 / Ni—Fe layer 20.

The protective layer 21 is made of Ta, for example.
The layer configuration and material of the TMR element 3 described above are examples. For example, the free magnetic layer 24, the insulating barrier layer 16, the pinned magnetic layer 23, and the antiferromagnetic layer 11 may be stacked in this order from the bottom. The pinned magnetic layer 23 and the free magnetic layer 24 may have a single layer structure or a laminated structure of magnetic layers.

A characteristic configuration of the present embodiment will be described below.
In the present embodiment, the insulating barrier layer 16 of the TMR element 3 is formed of Mg—O, and the film thickness H1 of the insulating barrier layer 16 is in the range of 16 to 40 mm. The film thickness H1 is preferably 20 mm or more. The film thickness H1 is preferably 30 mm or less.

  Here, as shown in an experiment described later, RA is increased by setting the thickness H1 of the insulating barrier layer 16 to 16 mm or more. For example, R is Rmin, and A is the area (average value) of the XY plane of the TMR element 3. Although adjustment of RA was important in the use of a magnetic head, in the use of a sensor, the film thickness H1 of the insulating barrier layer 16 can be adjusted from the viewpoint of the magnetoresistance change rate (ΔR / Rmin) regardless of RA. I can do it.

  And, by setting the film thickness H1 of the insulating barrier layer 16 formed of Mg-O as described above within the range of 16 to 40 mm, the magnetoresistance change rate (ΔR / Rmin) of the TMR element is 100% or more, Preferably it can be 150% or more, more preferably 200% or more. Here, ΔR is Rmax−Rmin, and Rmax is an electric resistance value when the magnetization direction of the second pinned magnetic layer 22 and the magnetization direction of the free magnetic layer 24 shown in FIG. 3 are antiparallel. , Rmin are electrical resistance values when the magnetization direction of the second pinned magnetic layer 22 shown in FIG. 3 and the magnetization direction of the free magnetic layer 24 are parallel to each other.

  In the present embodiment, the BDV (breakdown voltage) of one TMR element can be 1 V or more.

  Next, in the present embodiment, as shown in FIG. 1, a plane (XY plane) parallel to the interface of each layer constituting the TMR element 3 is circular. For this reason, the shape anisotropy is small, and the free magnetic layer 24 constituting the TMR element 3 reacts with high sensitivity to detect any direction from which direction the external magnetic field extends (for example, even when a rotating magnetic field of 360 degrees acts). The accuracy can be improved.

  The diameter Φ (average value) of the XY plane formed in a circular shape of the TMR element 3 is preferably in the range of 5 μm to 100 μm. Thereby, ESD tolerance can be improved. More preferably, the diameter Φ is 10 μm or more.

As described above, the XY plane of the TMR element 3 is preferably circular, but may be other than circular in this embodiment. However, like a circular shape, it is preferable to have a shape with no corners. For example, an elliptical shape or a polygonal corner having an R shape. In such a case, the area A (average value) of the XY plane of the TMR element 3 is preferably in the range of 19.6 μm ^{2 to} 7850 μm ² . This numerical range corresponds to the area A of the circular XY plane having a diameter Φ of 5 to 100 μm. The area A of the XY plane of the TMR element 3 is more preferably 78.5 μm ² or more. This numerical value corresponds to the area of a circular XY plane having a diameter Φ of 10 μm.

  Next, in this embodiment, eight or more TMR elements 3 having high BDV and high ESD tolerance are connected in series. In FIG. 1, twelve TMR elements 3 are connected in series. As a result, the DC withstand voltage can be improved more effectively, and the voltage dependency coefficient (VCΔR / R) of the magnetoresistance change rate and the voltage dependency coefficient (VCR) of the resistance value can be reduced. Specifically, both the voltage dependence coefficient (VCΔR / R) of the magnetoresistance change rate and the voltage dependence coefficient (VCR) of the resistance value can be suppressed to 20 ppm / mV or less in absolute value, and excellent voltage dependence characteristics can be obtained. I can do it.

  By obtaining such excellent voltage dependency, it is possible to suppress the deterioration of the magnetoresistance change rate accompanying the increase in applied voltage. In other words, by increasing the number of TMR elements 3 in series, the applied voltage per element can be reduced, and the magnetoresistance change rate can be increased more effectively.

  FIG. 4 is a circuit diagram of a two-wire switch configured using the magnetic sensor of this embodiment. 4 has a configuration in which a plurality of TMR elements 3 are connected in series as shown in FIG. For example, the applied voltage is 5v. In the configuration in which the XY plane of each TMR element 3 (magnetoresistivity change rate = 162%) is formed in a circular shape with a diameter Φ = 5 μm and 32 TMR elements 3 are connected in series, the DC withstand voltage can be 45V. . The current value when the magnetization directions of the pinned magnetic layer (second pinned magnetic layer 22) and the free magnetic layer 24 are parallel is 11 mA (ON state). The pinned magnetic layer (second pinned magnetic layer 22) and the free magnetic layer The current value when the magnetization direction of 24 was antiparallel was 4.2 mA (OFF state). Thus, it was found that the current value in the ON state can be more than double the current value in the OFF state, and the magnetic sensor 1 of this embodiment can be preferably applied to a two-wire switch.

FIG. 5 is a circuit diagram of an encoder configured using the magnetic sensor of this embodiment.
The four element parts 31 to 34 constitute a bridge circuit. The element unit 31 and the element unit 32 are connected in series via the first output terminal (OUTA). The element unit 33 and the element unit 34 are connected in series via the second output terminal (OUTB). Each element part 31-34 is comprised by the TMR element 3 shown in FIG. 5 indicate the magnetization directions of the pinned magnetic layer (second pinned magnetic layer 22) of the TMR element 3. With the configuration of FIG. 5, a sin wave is output from the first output terminal (OUTA), and a cosine wave is output from the second output terminal (OUTB). For example, the applied voltage is 5V.

  Here, the XY plane of each TMR element 3 (magnetic resistance change rate = 182%) constituting each element part 31 to 34 shown in FIG. 5 is formed in a circular shape with a diameter Φ = 5 μm, and each element part 31 is formed. In the configuration in which 32 TMR elements 3 are connected in series (total 128), the DC withstand voltage can be reduced to 45V. Moreover, Vpp (difference between the maximum output and the minimum output of the output waveform) could be 2.38V (applied voltage was 5V).

  Thus, if the magnetic sensor 1 of this embodiment is used, a high output can be obtained without using an amplifying means (amplifying circuit). Therefore, the circuit configuration can be simplified, the magnetic sensor 1 can be downsized, and the cost can be reduced.

(Mg-O film thickness experiment)
The TMR element 3 was formed with the following layer configuration.
From the bottom, a seed layer 10; Ta (30) / Ru (40) / antiferromagnetic layer _{11; Ir 20at% Mn 80at%} (80) / pinned magnetic layer 23 [first pinned magnetic layer 12; Co _70at% Fe _{30at %} (14) / nonmagnetic intermediate layer 13; Ru (9.1) / second pinned magnetic layer 22; [{Co—Fe} _{70 at%} B _{30 at%} (7) / Co _{50 at%} Fe _{50 at%} (6)] ] / insulating barrier layer _{16; Mg 50at% O 50at%} / free magnetic layer _{24 [Co 50at% Fe 50at%} (10) / {Co-Fe} 70at% B 30at% (15) / Ta (3) / Ni 88at _% Fe _12at% (120)] / protective layer 21; Ru (20) / Ta (280) were laminated in this order. The numerical values in parentheses for each layer indicate the film thickness and the unit is Å.

  In addition, a plane parallel to the interface of each layer (XY plane) was formed in a circular shape, and the diameter Φ was set to 10 to 20 μm.

  In the experiment, RA, magnetoresistance effect change rate (ΔR / Rmin), and BDV were measured while changing the film thickness H1 of the insulating barrier layer 16 formed of Mg—O. Here, RA is (minimum resistance value Rmin) × (area XY plane A).

  FIG. 6 shows the relationship between the film thickness of the insulating barrier layer 16 and RA. FIG. 7 shows the relationship between the film thickness of the insulating barrier layer 16 and the magnetoresistance effect change rate (ΔR / Rmin). FIG. 8 shows the relationship between the thickness of the insulating barrier layer 16 and BDV.

  As shown in FIG. 6, it was found that RA increases as the thickness of the insulating barrier layer 16 increases. Note that RA depends on the film configuration (in particular, the film thickness H1 of the insulating barrier layer 16), and does not depend on the diameter Φ or the number of series elements.

  As shown in FIG. 7, when the thickness of the insulating barrier layer 16 is increased, the rate of change in magnetoresistance (ΔR / Rmin) gradually increases, but the rate of change in magnetoresistance (ΔR / Rmin) increases from the middle. ) Was not seen.

  Further, as shown in FIG. 8, it was found that the BDV can be increased as the thickness of the insulating barrier layer 16 increases.

  For magnetic sensor applications, the resistance value may be large. Therefore, from the above experimental results, the film thickness H1 of the insulating barrier layer 16 made of Mg-O was set to 16 to 40 mm. As a result, it was found that the magnetoresistance effect change rate (ΔR / Rmin) of the TMR element can be 100% or more, preferably 150% or more, and the BDV of one TMR element can be 1V or more. It was also found that the film thickness H1 is preferably 20 mm or more. Moreover, it turned out that it is preferable to make film thickness H1 into 30 mm or less. Thereby, it was found that the magnetoresistance effect change rate (ΔR / Rmin) can be increased to 200% or more.

(Experiment of area A (diameter Φ))
The TMR element 3 having the above-described layer configuration was used. In the experiment, the film thickness H1 of the insulating barrier layer 16 made of Mg—O was set to 22 mm. The Rmin · A of the TMR element 3 was 1000Ω · μm ² . Eight TMR elements 3 were connected in series.

  In the experiment, a plane parallel to the interface of each layer (XY plane) was formed in a circular shape, and the diameter Φ was changed to 3, 5, and 10 μm, and ESD resistance based on HBM (Human Body Model) was measured.

  FIG. 9 shows experimental results when the HBM conditions are 1500Ω, 100 pF, and 200V. As shown in FIG. 9, it was found that by setting the diameter Φ to 5 μm and 10 μm, the ESD resistance of 200 V can be realized under the conditions of 1500Ω and 100 pF without changing the minimum resistance value Rmin before and after stress application.

  FIG. 10 shows the experimental results when the HBM conditions are 330Ω and 150 pF, which are stricter than those in FIG. As shown in FIG. 10, it was found that by setting the diameter Φ to 10 μm, the ESD resistance of 200 V can be realized under the conditions of 330Ω and 150 pF without changing the minimum resistance value Rmin before and after the stress application.

From the above experimental results, it was found that the ESD resistance can be improved by setting the diameter Φ to 5 μm or more (the XY plane area A is 19.6 μm ² or more). It was also found that the ESD resistance can be improved more effectively by setting the diameter Φ to 10 μm or more (the area A of the XY plane is 78.5 μm ² or more).

(Experiment on the number of TMR elements 3 in series)
The layer configuration of the TMR element 3 described above was used. In the experiment, the film thickness H1 of the insulating barrier layer 16 made of Mg—O was set to 21 mm. In addition, a plane parallel to the interface of each layer (XY plane) was formed in a circular shape, and the diameter was set to 15 μm. The Rmin · A of the TMR element 3 was 500Ω · μm ² .

  A plurality of TMR elements 3 having high BDV and high ESD resistance were connected in series, and the relationship between the number of series elements and the voltage dependence coefficient (VCΔR / R) of the magnetoresistance change rate was examined. The experimental results are shown in FIG.

  Subsequently, the number of series elements of the TMR element 3 was set to 8, 12, and 20, and the relationship between the number of series elements and the normalized Vpp and the relationship between the applied voltage per element and the normalized Vpp were examined. The experimental results are shown in FIGS. The standardized Vpp is calculated by setting Vpp of a sample having 8 serial connections as 1.

  By making the number of series connection of the TMR elements 3 having high BDV and high ESD resistance preferably 8 or more, the DC withstand voltage can be improved more effectively and the voltage dependency coefficient (VCΔR) of the magnetoresistance change rate can be improved. / R) (absolute value) and the voltage dependence coefficient (VCR) (absolute value) of the resistance value can be reduced. Specifically, the voltage dependence coefficient (VCΔR / R) of the magnetoresistance change rate and the voltage dependence coefficient (VCR) of the resistance value can be suppressed to 20 ppm / mV or less in absolute values, and excellent voltage dependence characteristics can be obtained. I knew that I could do it.

  By obtaining such excellent voltage dependency, it is possible to suppress the deterioration of the magnetoresistance change rate accompanying the increase in applied voltage. In other words, it can be seen that by increasing the number of TMR elements 3 in series, the applied voltage per element can be reduced, and the magnetoresistance change rate (ΔR / Rmin) and Vpp of the output waveform can be increased more effectively. It was.

The partial top view of the magnetic sensor in this embodiment, The fragmentary sectional view which cut | disconnected in the height direction along the AA line shown in FIG. The expanded sectional view which cut and showed the tunnel type magnetoresistive effect element (TMR element) in this embodiment from the film thickness direction, A circuit diagram of a two-wire switch configured using the magnetic sensor of the present embodiment, Circuit diagram of an encoder configured using the magnetic sensor of the present embodiment, A graph showing the relationship between RA and the film thickness of an insulating barrier layer formed of Mg-O constituting a TMR element; A graph showing the relationship between the film thickness of an insulating barrier layer made of Mg—O constituting a TMR element and the magnetoresistance effect change rate (ΔR / Rmin), A graph showing the relationship between the thickness of an insulating barrier layer made of Mg-O constituting a TMR element and BDV; Experimental results of ESD resistance based on HBM (Human Body Model) under the conditions of 1500Ω, 100 pF, and 200 V, which was performed on the TMR element with the area A on the XY plane changed, Experimental results of ESD resistance based on HBM (Human Body Model) under the conditions of 330Ω, 150 pF, 200 V, performed on a TMR element with the area A on the XY plane changed, A graph showing the relationship between the number of TMR elements in series and the voltage dependence coefficient (VCΔR / R) of the magnetoresistance change rate; A graph showing the relationship between the number of TMR elements in series and the normalized Vpp; A graph showing the relationship between the applied voltage per element and the normalized Vpp;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 2 Lower electrode 3 TMR element 4 Upper electrode 11 Antiferromagnetic layer 12 1st pinned magnetic layer 13 Nonmagnetic intermediate layer 16 Insulating barrier layer 22 Second pinned magnetic layer 23 Pinned magnetic layer 24 Free magnetic layers 30-34 Element Part

Claims (4)

A magnetic sensor comprising a tunnel-type magnetoresistive effect element whose electric resistance value varies with respect to an external magnetic field,
The tunnel magnetoresistive element is formed by sequentially stacking an antiferromagnetic layer, a pinned magnetic layer, an insulating barrier layer, and a free magnetic layer,
The magnetic sensor according to claim 1, wherein the insulating barrier layer is made of Mg-O having a thickness of 16 to 40 mm. ^2. The magnetic sensor according to claim 1, wherein a plane parallel to the interface of each layer constituting the tunnel type magnetoresistive effect element has a cornerless shape and an area in a range of 19.6 μm ^{2 to} 7850 μm ² .   The magnetic sensor according to claim 2, wherein the parallel surfaces are circular and have a diameter in a range of 5 μm to 100 μm.   The magnetic sensor according to claim 2 or 3, wherein eight or more tunnel type magnetoresistive effect elements are connected in series.

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