Magnetoresistive sensor and manufacturing method thereof

A manufacturing method of a magnetoresistive sensor, comprising:

• forming an initial reference layer in an annular shape, wherein the initial reference layer includes an antiferromagnetic layer with only a single side in contact with a ferromagnetic layer;
• subjecting the initial reference layer to a heat treatment, wherein the ferromagnetic layer is magnetized and has a magnetization direction oriented along a vortex path during a heating step of the heat treatment, and an exchange bias oriented along the vortex path is generated at an interface between the antiferromagnetic layer and the ferromagnetic layer during a cooling step of the heat treatment;
• patterning the initial reference layer to form separate reference layers, wherein the reference layers are respectively in an annular sector shape, and the reference layers are arranged along the vortex path;
• forming spacer layers and free layers, to form magnetoresistive devices, wherein the magnetoresistive devices respectively comprise one of the reference layers and one of the free layers separated from each other by one of the spacer layers;
• and
• routing the magnetoresistive device to form the magnetoresistive sensor,
• wherein the initial reference layer is not applied with an external magnetic field in the cooling step during the heat treatment,
• wherein the spacer layers and the free layers are formed after formation of the reference layers.