Magnetoresistive element for sensing a magnetic field in a Z-axis
Magnetoresistive element including a reference layer having a fixed reference magnetization, a sense layer having a free sense magnetization and a tunnel barrier layer between the reference layer and the sense layer; the magnetoresistive element being configured to measure an external magnetic field oriented substantially perpendicular to the plane of the layers. The reference magnetization being oriented substantially perpendicular to the plane of the reference layer. The sense magnetization including a vortex configuration in the absence of an external magnetic field, the vortex configuration being substantially parallel to the plane of the sense layer and having a vortex core magnetization along an out-of-plane axis substantially perpendicular to the plane of the sense layer.
1. Magnetoresistive element comprising:
a reference layer having a fixed reference magnetization, a sense layer having a free sense magnetization and a tunnel barrier layer between the reference layer and the sense layer;
the magnetoresistive element being configured to measure an external magnetic field oriented substantially perpendicular to the plane of the layers;
wherein the reference magnetization is oriented substantially perpendicular to the plane of the reference layer; and
wherein the sense magnetization comprises a vortex configuration in the absence of an external magnetic field, the vortex configuration being substantially parallel to the plane of the sense layer and having a vortex core magnetization along an out-of-plane axis substantially perpendicular to the plane of the sense layer;
wherein the sense layer has a thickness that is greater than 60 nm, and
wherein the sense layer comprises a first soft ferromagnetic material having a sense magnetization between 300-600 kA/m (kiloamperes per meter).
2. Magnetoresistive element according to claim 1 , having a lateral dimension being smaller than 450 nm (nanometer), and preferably smaller than 300 nm, 250 nm.
3. Magnetoresistive element according to claim 1 , wherein the sense layer has a thickness being greater than 80 nm or greater than 100 nm.
4. Magnetoresistive element according to claim 1 , wherein the sense magnetization is between 300-600 kA/m at room temperature.
5. Magnetoresistive element according to claim 1 , wherein the sense layer comprises a first sense layer comprising a first soft ferromagnetic material and a second sense layer comprising a second soft ferromagnetic material, the second sense layer being between the first sense layer and the tunnel barrier layer and in contact with the latter.
6. Magnetoresistive element according to claim 5 , wherein second sense layer comprises a single layer having a thickness between 1 nm and 5 nm.
7. Magnetoresistive element according to claim 5 , wherein the second sense layer comprises a plurality of ferromagnetic sublayers, each ferromagnetic sublayers having a thickness between 0.5 nm and 3 nm.
8. Magnetoresistive element according to claim 6 , wherein the second soft ferromagnetic material comprises a CoFeB (Cobalt-Iron-Boron) or a NiFeB (Nickel-Iron-Boron) alloy.
9. Magnetoresistive element according to claim 8 , wherein the CoFeB alloy comprises Co=20-80 at %, Fe=20-80 at %, and B=0-30 at %.
10. Magnetoresistive element according to claim 7 , wherein the second sense layer further comprises an insertion sublayer of Ta, W or Ti comprised between adjacent ferromagnetic sublayers, the insertion sublayer having a thickness between 0.1 nm and 0.5 nm.
11. Magnetoresistive element according to claim 5 , wherein the sense layer comprises an insertion layer of Ta (Tantalum), W (Tungsten) or Ti (Titanium) and of thickness between 0.1 nm and 0.5 nm, between the second sense layer and the first sense layer.
12. Magnetoresistive element according to claim 5 ,
wherein the first sense layer comprises a plurality of first ferromagnetic sublayers, each first ferromagnetic sublayer being between 0.5 nm and 3 nm in thickness; and
wherein the first ferromagnetic sublayers are separated by a first insertion sublayer comprising Ta, Ti, W or Ru (Ruthenium) and having a thickness between 0.05 nm and 0.2 nm.
13. Magnetoresistive element according to claim 4 , wherein the first soft ferromagnetic material comprises an alloy of Ni (Nickel), Fe (Iron) and/or Co (Cobalt).
14. Magnetoresistive element according to claim 13 , wherein the alloy comprises Ni80Fe20 at %.
15. Magnetoresistive element according to claim 4 , wherein the first soft ferromagnetic material contains between 0 at % and 30 at % of one of: Ta, Ti, W or Ru.
16. Magnetoresistive element according to claim 1 , wherein the reference layer comprises a synthetic antiferromagnetic (SAF) structure including a first reference sublayer in contact with the tunnel barrier layer and a second reference sublayer separated from the first reference sublayer by a coupling layer antiferromagnetically coupling the first reference sublayer to the second reference sublayer.
17. Magnetoresistive element according to claim 16 , wherein each of the first and second reference sublayer comprises a plurality of alternating first metallic layers and second metallic layers.
18. Magnetoresistive element according to claim 17 , wherein the first metallic layer has a thickness between 0.4 nm and 0.6 nm and the second metallic layer has a thickness between 0.2 nm and 0.4 nm and the second metallic layer.
19. Method for operating the magnetoresistive element according to claim 1 , comprising:
selecting the direction of the vortex core magnetization by applying an initialization magnetic field until a vortex expulsion field is reached and reducing the initialization magnetic field below a nucleation field at which vortex re-forms; wherein the vortex core direction is determined by the polarity of the vortex expulsion field and the nucleation field; and
measuring an external magnetic field.
20. Method according to claim 19 , wherein said measuring an external magnetic field is performed for external magnetic field below the vortex expulsion field.