Magnetic sensor

A magnetic sensor includes a magnetization fixed layer, a magnetic field detecting layer, and an intermediate layer. The magnetization fixed layer is formed into a thin-film shape, and a magnetization direction of the magnetization fixed layer is fixed in a direction parallel to an in-plane direction. A magnetization direction of the magnetic field detecting layer changes depending on an external magnetic field. The intermediate layer is disposed between the magnetization fixed layer and the magnetic field detecting layer, and a resistance value of the intermediate layer changes depending on an angle between the magnetization direction of the magnetization fixed layer and the magnetization direction of the magnetic field detecting layer. A magnetization amount per unit area of the magnetic field detecting layer is less than 0.2 [memu/cm2].

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a U.S. national stage application of International Patent Application No. PCT/JP2015/000853 filed on Feb. 23, 2015 and is based on Japanese Patent Application No. 2014-35811 filed on Feb. 26, 2014, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a magnetic sensor.

BACKGROUND

In a conventional magnetic sensor, a magnetic resistance effect film including a fixed layer P, a spacer S, and a free layer F and a bias magnet film that applies a bias magnetic field to the free layer are disposed on the same substrate (see, for example, Patent Literature 1).

In the magnetic sensor, a magnetization direction of the free layer F is stably restored to an initial state by the bias magnetic field applied from the bias magnet film to the free layer so that a detected magnetic field range of an external magnetic field can be enlarged as the magnetic sensor.

However, the actual detected magnetic field range of the magnetic sensor in Patent Literature 1 is only about 2 [mT] (i.e., 20 [Oe]), and the magnetic sensor cannot deal with the larger detected magnetic field range.

PATENT LITERATURE

SUMMARY

An object of the present disclosure is to provide a magnetic sensor having a large detected magnetic field range of an external magnetic field.

A magnetic sensor according an aspect of the present disclosure includes a magnetization fixed layer, a magnetic field detecting layer, and an intermediate layer. The magnetization fixed layer is formed into a thin-film shape and has a magnetization direction fixed to a direction parallel to an in-plane direction. The magnetic field detecting layer has a magnetization direction that changes depending on an external magnetic field. The intermediate layer is disposed between the magnetization fixed layer and the magnetic field detecting layer and has a resistance value that changes depending on an angle between the magnetization direction of the magnetization fixed layer and the magnetization direction of the magnetic field detecting layer. A magnetization amount per unit area of the magnetic field detecting layer is less than 0.2 [memu/cm2].

The magnetic sensor can have a large detected magnetic field range of the external magnetic field.

DETAILED DESCRIPTION

The following describes a magnetic sensor1according to an embodiment of the present disclosure with reference to the drawings.

The magnetic sensor1according to the present embodiment includes a substrate10, a thermal oxidation film11, a pin layer20, an intermediate layer30, a free layer40, and a protective layer50, as shown inFIG. 1.

The substrate10is a substrate made of a Si wafer (silicon wafer). The thermal oxidation film11is made of SiO2and formed into a thin-film shape on the substrate10. The pin layer20includes a base layer11, an antiferromagnetic layer22, a ferromagnetic layer23, a nonmagnetic layer24, and a ferromagnetic layer25. The pin layer20corresponds to a magnetization fixed layer.

The base layer21is made of, for example, Ta or Ru and is formed into a thin-film shape on the thermal oxidation film11. The antiferromagnetic layer22is made of, for example, IrMn or PtMn, and is formed into a thin-film shape on the base layer21. A magnetization direction of the antiferromagnetic layer22(i.e., a magnetization direction of the pin layer20) is fixed to a predetermined direction. The magnetization direction of the antiferromagnetic layer22is parallel to an in-plane direction of the antiferromagnetic layer22(i.e., the substrate10). The in-plane direction means a planar direction in which the antiferromagnetic layer22(i.e., the substrate10) spreads flatly.

The ferromagnetic layer23is made of an alloy including Co, Fe, and Ni, and is formed into a thin-film shape on the antiferromagnetic layer22. The nonmagnetic layer24is made of, for example, Ru, and is formed into a thin-film shape on the ferromagnetic layer23. The ferromagnetic layer25is made of an alloy including Co, Fe, Ni, and B, and is formed into a thin-film shape on the ferromagnetic layer25. The ferromagnetic layer23, the nonmagnetic layer24and the ferromagnetic layer25interrupts the magnetic field from the antiferromagnetic layer22from leaking to the free layer40.

The intermediate layer30is formed into a thin-film shape on the antiferromagnetic layer25. In a case where the intermediate layer30is formed of an insulation layer made of, for example, MgO or AlO, a tunnel magneto resistance effect (TMR) element is formed as the magnetic sensor1. On the other hand, in a case where the intermediate layer30is formed of a non-ferromagnetic layer made of, for example, Cu or Ag, a giant magneto resistance (GMR) element is formed as the magnetic sensor1.

The free layer40is formed into a thin-film shape on the intermediate layer30. The free layer40forms a magnetic field detecting layer having a magnetization direction that changes depending on an external magnetic field. The free layer40according to the present embodiment is a CoFeB film made of an alloy including Co, Fe, and B. The protective film50is made of, for example, Ta or Ru, and is formed into a thin-film shape on the free layer40.

A state of the CoFeB film forming the free layer40according to the present embodiment may be crystal or amorphous.

In the magnetic sensor1according to the present embodiment having the above-described structure, the substrate10, the pin layer20, the intermediate layer30, and the free layer40are formed in parallel with each other. An electric resistance value of the pin layer20and the free layer40via the intermediate layer30(hereafter, referred to as a resistance value of the magnetic sensor1) changes depending on an intensity of the external magnetic field.

Next, an operation of the magnetic sensor1according to the present embodiment will be described with reference toFIG. 2AtoFIG. 2D.

FIG. 2Ais a graph G in which a vertical axis is the resistance value of the magnetic sensor1and a horizontal axis is the external magnetic field intensity. InFIG. 2A, a center of the horizontal axis is a reference point at which the external magnetic field intensity is 0 (zero). InFIG. 2B,FIG. 2C,FIG. 2D, arrows Da are directions of the external magnetic field, arrows Db are magnetization directions of the free layer40, and arrows Dc are magnetization directions of the pin layer20.

As shown inFIG. 2B, when the external magnetic field intensity is 0 (zero) (corresponding to IIB inFIG. 2A), the magnetization direction Db of the free layer40is a direction perpendicular to the in-plane direction of the free layer40.

As shown inFIG. 2C, in a case where the external magnetic field is applied to the magnetic sensor1in a direction same as the magnetization direction Dc of the pin layer20, the magnetization direction of the free layer40changes and an angle between the magnetization direction of the free layer40and the magnetization direction of the pin layer20decreases with increase of the external magnetic field intensity. In this case, the resistance value of the magnetic sensor1increases with increase of the external magnetic field intensity.

As shown inFIG. 2D, in a case where the external magnetic field is applied to the magnetic sensor1in a direction opposite to the magnetization direction Dc of the pin layer20(corresponding to IID inFIG. 2A), the magnetization direction of the free layer40changes and the angle between the magnetization direction of the free layer40and the magnetization direction of the pin layer20increases with increase of the external magnetic field intensity. In this case, the resistance value of the magnetic sensor1decreases with increase of the external magnetic field intensity.

As described above, the graph G inFIG. 2Aaccording to the present disclosure has inflection points h1and h2, and the resistance value of the magnetic sensor1increases with increase of the external magnetic field intensity between the inflection points h1and h2. A range of the external magnetic field intensity between the inflection points h1and h2is defined as a detected magnetic field range of the magnetic sensor1.

The inventors carried out a verification experiment of the magnetic sensor1so as to obtain a large detected magnetic field range as the detected magnetic field range of the magnetic sensor1. The following describes results of the verification experiment of the magnetic sensor1with reference toFIG. 3A,FIG. 3B, andFIG. 3C.

The verification experiment is an experiment in which a relationship between the magnetization amount per unit area of the free layer40and the detected magnetic field range of the magnetic sensor1is examined.

Each of four diamond-shaped plots inFIG. 3Ais the result of the verification experiment showing the relationship between the magnetization amount per unit area of the free layer40and the detected magnetic field range of the magnetic sensor1. The four diamond-shaped plots are the results of the verification experiment in cases where the magnetization amounts per unit area of the free layer40are set to be different values.FIG. 3Bshows the experimental result that the detected magnetic field range of the magnetic sensor1is about 0 [mT] when the magnetization amount per unit area of the free layer40is set to 0.20 [memu/cm2] (corresponding to IIIB inFIG. 3A).FIG. 3Cshows the experimental result that the detected magnetic field range of the magnetic sensor1is 300 [mT] when the magnetization amount per unit area of the free layer40is set to 0.17 [memu/cm2] (corresponding to IIIC inFIG. 3A). The detected magnetic field range inFIG. 3Chas the minimum value of −200 [mT] and the maximum value of 100 [mT]. Thus, as known from the four plots inFIG. 3A,FIG. 3B, andFIG. 3C, when the magnetization amount per unit area of the free layer40is less than 0.2 [memu/cm2], the detected magnetic field range of the magnetic sensor1is 300 [mT] or more. The magnetization amount per unit area of the free layer40is a magnitude of a magnetic moment per unit area of the free layer40.

Thus, in the magnetic sensor1according to the present embodiment, the magnetization amount per unit area of the free layer40is set to a value greater than 0 [memu/cm2] and less than 0.2 [memu/cm2].

Furthermore, according to the verification experiment, as shown inFIG. 4, the magnetization amount per unit area of the free layer40decreases and the detected magnetic field range enlarges with decrease of the thickness of the free layer40(CoFeB film thickness in the drawing). Thus, in the present embodiment, the detected magnetic field range of 300 [mT] or more is set in the magnetic sensor1by setting the thickness of the free layer40to be less than about 1.5 [nm]. Three diamond-shaped plots inFIG. 4indicate the detected magnetic field ranges of the magnetic sensor1when the thickness of the free layer40is set to be different values.

According to the present embodiment described above, the magnetic sensor1includes the pin layer20having the magnetization direction that is fixed with respect to the external magnetic field, the free layer40having the magnetization direction that changes depending on the external magnetic field, and the intermediate layer30disposed between the pin layer20and the free layer40and having the resistance value that changes depending on the angle between the magnetization direction of the pin layer20and the magnetization direction of the free layer40. The magnetization amount per unit area of the free layer40is less than 0.2 [memu/cm2] (=0.2×10−3[emu/cm2]). Accordingly, a large detected magnetic field range of 300 [mT] or more can be set in the magnetic sensor1.

In the magnetic sensor1, the magnetization amount per unit area of the free layer30is defined to be less than 0.2 [memu/cm2]. The value defining the magnetization amount is the same even when the material or the crystal state of the free layer40, or the pin layer20or the intermediate layer30is changed into the above-described contents. That is, in the magnetic sensor1, when the magnetization amount per unit area of the free layer40is defined to be less than 0.2 [memu/cm2], the large detected magnetic field range of 300 [mT] or more can be set without depending on the material or the crystal state of the free layer40, or the pin layer20or the intermediate layer30.

Other Embodiments

In the above-described embodiment, an example that the free layer40is composed of the CoFeB film is described. However, the free layer40is not limited to that and may be composed of something other than the CoFeB film. Furthermore, the pin layer20or the intermediate layer30may be composed of a something other than the above-described material.

In the above-described embodiment, the example that the free layer40is composed of the CoFeB film is described. Alternatively, the free layer40may be composed of at least one or more elements among Co, Fe, and Ni. In this case, the free layer40may be composed of an alloy including at least one or more elements among Co, Fe, and Ni, and B.

In the above-described embodiment, an example that the magnetization amount per unit area of the free layer40is decreased by decreasing the thickness of the free layer40. Alternatively, the magnetization amount per unit area of the free layer40may be decreased by increasing the content of a nonmagnetic material in the free layer40. In this case, the detected magnetic field range of the magnetic sensor1can be enlarged by adjusting the content of the nonmagnetic material in the free layer40.

The present disclosure is not limited to the above-described embodiments and may be suitably modified.