Magnetoresistive sensor

1. A magnetoresistive sensor, comprising a magnetic sensing layer;

a magnetic reference layer;

a tunnel barrier layer between the magnetic sensing layer and the magnetic reference layer;

a sensing exchange layer having a layer of anti-ferromagnetic material, the sensing exchange layer exchange coupled with the magnetic sensing layer; and

a reference exchange layer having a layer of anti-ferromagnetic material, the reference exchange layer exchange coupled with the magnetic reference layer;

wherein, in the absence of an external magnetic field:

an exchange bias pinning the magnetic reference layer es along a reference direction;

an exchange bias pinning the magnetic sensing layer lies along a first direction that is orthogonal to the reference direction; and

a magnetic anisotropy of the magnetic sensing layer is parallel to the first direction.

2. The magnetoresistive sensor according to claim 1 , wherein:

the magnetic sensing layer has a dimension defined by an aspect ratio that can be as small as 1:1.

3. The magnetoresistive sensor according to claim 1 , wherein:

the magnetic reference layer is implemented with a synthetic anti-ferromagnetic material.

4. The magnetoresistive sensor according to claim 1 , wherein:

the magnetic sensing layer is made of two ferromagnetic materials separated by a thin non-magnetic material with thickness <1 nm.

5. The magnetoresistive sensor according to claim 1 , wherein:

a thin non-magnetic layer with thickness <1 nm is positioned between the magnetic sensing layer and the sensing exchange layer.

6. A method of fabricating a magnetoresistive sensor, comprising:

forming a magnetoresistive stack by:

depositing a reference exchange layer having a layer of anti-ferromagnetic material;

depositing a magnetic reference layer over the reference exchange layer such that the reference exchange layer is exchange coupled with the magnetic reference layer;

depositing a tunnel barrier layer over the magnetic sensing layer;

depositing a magnetic sensing layer over the tunnel barrier layer; and

depositing a sensing exchange layer having a layer of anti-ferromagnetic material over the magnetic sensing layer such that the sensing exchange layer is exchange coupled with the magnetic sensing layer;

setting an exchange bias pinning the magnetic reference layer along a reference direction;

setting an exchange bias pinning the magnetic sensing layer to lie along a first direction that is orthogonal to the reference direction; and

setting a magnetic anisotropy of the magnetic sensing layer to lie parallel to the first direction.

7. The method according to claim 6 , wherein:

setting a magnetic anisotropy of the magnetic sensing layer to lie parallel to the first direction, comprises:

performing a first annealing process by exposing the magnetoresistive stack to a temperature that is sufficient to reset any anisotropy induced during deposition; and

exposing the magnetoresistive stack to an external magnetic field in the first direction during a cool down associated with the first annealing process.

8. The method according to claim 7 , wherein:

the magnetic sensing layer comprises CoFeB, the tunnel barrier layer comprises MgO, and the magnetic reference layer comprises CoFeB;

performing a first annealing process by exposing the magnetoresistive stack to a temperature that is sufficient to reset any anisotropy induced during deposition, comprises:

setting the temperature in excess of 320 degrees Celsius during the first annealing process; and

exposing the magnetoresistive stack to an external magnetic field, comprises:

applying the external magnetic field at a field value greater than or equal to One Tesla.

9. The method according to claim 7 , wherein:

setting an exchange bias pinning the magnetic reference layer along a reference direction, comprises:

performing a second annealing process after e first annealing process by exposing the magnetoresistive stack to a temperature that is insufficient to reset the magnetic anisotropy of the magnetic sensing layer, but sufficient to reset the exchange bias pinning the magnetic reference layer; and

exposing the magnetoresistive stack to an external magnetic field in the reference direction during a cool down associated with the second annealing process.

10. The method according to claim 9 , wherein:

performing a second annealing process after the first annealing process by exposing the magnetoresistive stack to a temperature that is insufficient to reset the magnetic anisotropy of the magnetic sensing layer, but sufficient to reset the exchange bias pinning the magnetic reference layer, comprises:

setting the temperature up to 280 degrees Celsius during the second annealing process; and

exposing the magnetoresistive stack to an external magnetic field, comprises:

applying the external magnetic field at a field value greater than or equal to one Tesla.

11. The method according to claim 8 , wherein:

setting an exchange bias pinning the magnetic sensing layer to lie along a first direction that is orthogonal to the reference direction, comprises:

performing a third annealing process after the second annealing process by exposing the magnetoresistive stack to a temperature that is insufficient to reset the exchange bias pinning the magnetic reference layer, but is sufficient reset the exchange bias pinning the magnetic sensing layer; and

exposing the magnetoresistive stack to an external magnetic field in the first direction during a cool down associated with the third annealing process.

12. The method of claim 11 , wherein:

performing a third annealing process after the second annealing process by exposing the magnetoresistive stack to a temperature that is insufficient to reset the exchange bias pinning the magnetic reference layer, but is sufficient to reset the exchange bias pinning the magnetic sensing layer, comprises:

setting the temperature during the third annealing process to a temperature less than 250 degrees Celsius.