Current sensor

1. A current sensor comprising:

a conductor through which a current to be measured flows; and

a magnetic detecting bridge circuit formed of four magneto-resistance effect elements with a resistance value varied by application of an induced magnetic field from the current to be measured, the four magneto-resistance effect elements having a same resistance change rate, each of the four magneto-resistance effect elements having a laminated structure including:

a self-pinned type ferromagnetic fixed layer formed of a first ferromagnetic film and a second ferromagnetic film anti-ferromagnetically coupled to each other;

a nonmagnetic intermediate layer; and

a soft magnetic free layer,

wherein the laminated structure does not include any layer made of antiferromangnetic material,

wherein the magneto detecting bridge circuit has an output between two of the four magneto-resistance effect elements, magnetization directions of the ferromagnetic fixed layers of the two magneto-resistance effect elements being different from each other by 180°,

wherein the magnetic detecting bridge circuit has a wiring symmetrical to a power supply point,

wherein the magnetic detecting bridge circuit measures the current to be measured by the outputs of the four magneto-resistance effect elements which are in proportion to the induced magnetic field,

wherein each of the magneto-resistance effect elements has a meandering shape including a plurality of stripes, each of the plurality of stripes being perpendicular to the induced magnetic field extended from the conductor,

and wherein the magnetization direction, which is a pin-direction, of each of the ferromagnetic fixed layers is perpendicular to the stripes in each of the magneto-resistance effect elements.

2. The current sensor according to claim 1 , wherein the first ferromagnetic film is made of a CoFe alloy containing Fe of 40 atomic percent to 80 atomic percent, and the second ferromagnetic film is made of a CoFe alloy containing Fe of more than 0 atomic percent up to 40 atomic percent.

3. The current sensor according to claim 1 , further comprising:

a magnetic shield configured to attenuate the induced magnetic field and to enhance the cancelling magnetic field.

4. The current sensor according to claim 3 , wherein the magnetic shield is made of a high permeability material selected from a group consisting of an amorphous magnetic material, a permalloy-based magnetic material, and an iron-based microcrystalline material.

5. The current sensor according to claim 1 , wherein the first ferromagnetic film and the second ferromagnetic film are anti-ferromagnetically coupled to each other via an antiparallel coupling film interposed therebetween.

6. The current sensor according to claim 1 , wherein the first ferromagnetic film has a magnetization Ms 1 per volume and a thickness t 1 , the second ferromagnetic film has a magnetization Ms 2 per volume and a thickness t 2 , a magnetization amount (Ms 1 ·t 1 ) of the first ferromagnetic film and a magnetization amount (Ms 2 ·t 2 ) of the second ferromagnetic film are substantially equal to each other.

7. The current sensor according to claim 1 , wherein the first ferromagnetic film has a first coercive force, and the second ferromagnetic film has a second coercive force smaller than the first coercive force.

8. The current sensor according to claim 1 , wherein the first ferromagnetic film and the second ferromagnetic film in one of the magneto-resistance effect elements are magnetized by applying a magnetic field thereto in a first direction along a width direction of the stripes, while the first ferromagnetic film and the second ferromagnetic film in another of the magneto-resistance effect elements are magnetized by applying the magnetic field thereto in a second direction different from the first direction.

9. The current sensor according to claim 8 , wherein the second direction is opposite to the first direction.

10. The current sensor according to claim 3 , further comprising:

an insulating layer formed between the magnetic shield and the magneto-resistance effect elements, the insulating layer formed by a heating process after the magneto-resistance effect elements are formed.

11. The current sensor according to claim 1 , wherein the self-pined type ferromagnetic fixed layer consists of:

the first ferromagnetic film;

the second ferromagnetic film; and

an antiparallel coupling film interposed therebetween.