Magnetic sensor, method of manufacturing magnetic sensor, and sensitive element assembly

1. A magnetic sensor comprising:

a substrate; and

at least one sensitive portion disposed on the substrate and having a longitudinal direction and a transverse direction, the sensitive portion sensing a magnetic field by a magnetic impedance effect, wherein

the sensitive portion includes a soft magnetic material layer composed of a soft magnetic material having uniaxial magnetic anisotropy in a direction intersecting the longitudinal direction, the soft magnetic material layer sensing the magnetic field, and a secondary soft magnetic material layer laminated between the substrate and the soft magnetic material layer, the secondary soft magnetic material layer being composed of a soft magnetic material with large saturation magnetization compared to the soft magnetic material constituting the soft magnetic material layer, and

the secondary soft magnetic material layer contacts the soft magnetic material layer.

2. The magnetic sensor according to claim 1 , wherein the secondary soft magnetic material layer has a thickness less than or equal to 30% of a thickness of the soft magnetic material layer.

3. The magnetic sensor according to claim 2 , wherein the secondary soft magnetic material layer has a thickness greater than or equal to 5 nm.

4. The magnetic sensor according to claim 1 , wherein at least one sensitive element includes a plurality of sensitive portions arranged in the transverse direction with a gap between adjacent two of the sensitive portions, each of the sensitive portions including the soft magnetic material layer and the secondary soft magnetic material layer.

5. The magnetic sensor according to claim 1 , wherein

the at least one sensitive portion includes a plurality of the soft magnetic material layers laminated, adjacent two of the soft magnetic material layers sandwiching a conductor layer with conductivity higher than the soft magnetic material layer, and

the secondary soft magnetic material layer is laminated between the substrate and one of the plurality of the soft magnetic material layers nearest the substrate.

6. The magnetic sensor according to claim 5 , wherein the at least one sensitive portion includes another secondary soft magnetic material layer between the conductor layer and one of the plurality of the soft magnetic material layers above and nearest the conductor layer, the another secondary soft magnetic material layer composed of a soft magnetic material with large saturation magnetization compared to the soft magnetic material constituting the soft magnetic material layer.

7. The magnetic sensor according to claim 1 , wherein

the at least one sensitive portion includes a plurality of the soft magnetic material layers and a magnetic domain suppression layer between adjacent two of the plurality of the soft magnetic material layers, the magnetic domain suppression layer suppressing generation of a closure magnetic domain in the soft magnetic material layers, and

the secondary soft magnetic material layer is laminated between the substrate and one of the plurality of the soft magnetic material layers nearest the substrate.

8. The magnetic sensor according to claim 1 , wherein

the soft magnetic material layer is composed of an amorphous alloy containing Co, Nb and Zr, and

the secondary soft magnetic material layer is composed of an amorphous alloy containing Co, Nb and Zr, the amorphous alloy for the secondary soft magnetic material layer having a small Nb ratio compared to the amorphous alloy constituting the soft magnetic material layer.

9. The magnetic sensor according to claim 1 , wherein

the soft magnetic material layer is composed of an amorphous alloy based on Co, and

the secondary soft magnetic material layer is composed of an amorphous alloy based on Co with large saturation magnetization compared to the amorphous alloy constituting the soft magnetic material layer.

10. The magnetic sensor according to claim 7 , wherein the magnetic domain suppression layer is composed of any one of Ru, CrTi, AlTi, CrB, CrTa, CoW, NiP, and SiO 2 .

11. A method of manufacturing a magnetic sensor comprising:

forming an underlayer by laminating a soft magnetic material with a predetermined saturation magnetization on a surface of a substrate by magnetron sputtering;

forming a soft magnetic material layer with uniaxial magnetic anisotropy in a predetermined direction by laminating a soft magnetic material on the underlayer, the soft magnetic material for the soft magnetic material layer having small saturation magnetization compared to the soft magnetic material constituting the underlayer by magnetron sputtering, the soft magnetic material layer contacting the underlayer; and

forming a plurality of sensitive elements at a portion of the soft magnetic material layer where the uniaxial magnetic anisotropy is imparted, the plurality of sensitive elements sensing a magnetic field.

12. A sensitive element assembly comprising:

a substrate; and

a plurality of sensitive elements each having at least one sensitive portion formed on a surface of the substrate and having a longitudinal direction and a transverse direction, the sensitive portion sensing a magnetic field by a magnetic impedance effect, wherein

the sensitive portion in each of the sensitive elements includes a soft magnetic material layer composed of a soft magnetic material having uniaxial magnetic anisotropy in a direction intersecting the longitudinal direction and sensing the magnetic field, and a secondary soft magnetic material layer laminated between the substrate and the soft magnetic material layer, the secondary soft magnetic material layer being composed of a soft magnetic material with large saturation magnetization compared to the soft magnetic material constituting the soft magnetic material layer, and

the secondary soft magnetic material layer contacts the soft magnetic material layer.