Magnetic memory with a thermally assisted spin transfer torque writing procedure using a low writing current

1. A spin transfer torque (STT)-based magnetic random access memory (MRAM) cell with a thermally assisted switching (TAS) writing procedure, comprising:

a magnetic tunnel junction formed from a ferromagnetic storage layer having a first magnetization adjustable at a high temperature threshold, an antiferromagnetic storage layer which pins the first magnetization of the ferromagnetic storage, a ferromagnetic reference layer having a fixed second magnetization, and an insulating layer, said insulating layer being disposed between the ferromagnetic storage and reference layers, wherein the magnetocrystalline anisotropy of the ferromagnetic storage layer is substantially orthogonal to the magnetocrystalline anisotropy of the ferromagnetic reference layer and the magnetocrystalline anisotropy of the antiferromagnetic storage layer such that the first magnetization is oriented substantially orthogonal to the direction of the second magnetization of the ferromagnetic reference layer when the magnetic tunnel junction is heated to the high temperature threshold;

a select transistor being electrically connected to said magnetic tunnel junction and controllable via a word line; and

a current line, electrically connected to said magnetic tunnel junction, passing at least a write current.

2. The STT-based TAS-MRAM cell according to claim 1 , wherein the cell ( 100 ) is writable by the write current passing through the junction via the current line, the write current having:

a first intensity for heating the junction at the high temperature threshold; and

a second intensity, lower than the first intensity, for switching the first magnetization of the storage layer and cooling the magnetic tunnel junction at a low temperature threshold at which the first magnetization becomes fixed.

3. The STT-based TAS-MRAM cell according to claim 1 , wherein the write current is a spin polarized current for switching the first magnetization in a direction determined by the spin polarized current.

4. The STT-based TAS-MRAM cell according to claim 1 , wherein said magnetic tunnel junction further comprises an antiferromagnetic reference layer pinning said second magnetization of the ferromagnetic reference layer below a blocking temperature of the antiferromagnetic reference layer.

5. A magnetic memory device formed from an array comprising a plurality of STT-based TAS-MRAM cells comprising:

a magnetic tunnel junction formed from:

a ferromagnetic storage layer having a first magnetization adjustable at a high temperature threshold;

an antiferromagnetic storage layer that pins said first magnetization of the ferromagnetic storage layer;

a ferromagnetic reference layer having a fixed second magnetization and

an insulating layer, said insulating layer being disposed between the ferromagnetic storage and reference layers,

wherein the magnetocrystalline anisotropy of the ferromagnetic storage layer is essentially orthogonal to the magnetocrystalline anisotropy of the ferromagnetic reference layer and the magnetocrystalline anisotropy of the antiferromagnetic layer;

a select transistor being electrically connected to said magnetic tunnel junction and controllable via a word line; and

a current line, electrically connected to said magnetic tunnel junction, passing at least a write current.

6. A method of writing data in a spin transfer torque (STT)-based magnetic random access memory (MRAM) cell with a thermally assisted switching (TAS) writing procedure, wherein the STT-based TAS-MRAM cell comprises a magnetic tunnel junction formed from a storage layer having a first magnetization that is adjustable at a high temperature threshold, an antiferromagnetic layer which pins the first magnetization of the storage layer, a reference layer having a fixed second magnetization, an insulating layer disposed between the storage and reference layers, a select transistor connected to said magnetic tunnel junction and controllable via a word line, and a current line electrically connected to said magnetic tunnel junction, wherein the magnetocrystalline anisotropy of the storage layer is substantially orthogonal to the magnetocrystalline anisotropy of the reference layer and the magnetocrystalline anisotropy of the antiferromagnetic layer, the method comprising the steps of:

passing a heating current through the magnetic tunnel junction via the current line to heat the magnetic tunnel junction;

passing a field current through the field line to switch the first magnetization of the storage layer;

turning off the heating current to cool the magnetic tunnel junction after the magnetic tunnel junction has reached a high temperature threshold; and

turning off the field current after the magnetic tunnel junction has cooled down to a low temperature threshold.

7. The method according to claim 6 , wherein said write current is a spin polarized current switching the first magnetization in a direction according to the spin orientation of the spin-polarized current.

8. The method according to claim 6 , wherein said switching the first magnetization is performed from an orientation, substantially orthogonal to the direction of the second magnetization, to a switched direction, substantially parallel or antiparallel with the direction of the second magnetization.

9. A method of manufacturing a spin transfer torque (STT)-based magnetic random access memory (MRAM) cell with a thermally assisted switching (TAS) writing procedure, the STT-based TAS-MRAM cell comprising a magnetic tunnel junction formed from a storage layer having a first magnetization that is adjustable at a high temperature threshold, an antiferromagnetic layer which pins the first magnetization of the storage layer, a reference layer having a fixed second magnetization, and an insulating layer, said insulating layer being disposed between the storage and reference layers; wherein the magnetocrystalline anisotropy of the storage layer is substantially orthogonal to the magnetocrystalline anisotropy of the reference layer and the magnetocrystalline anisotropy of the antiferromagnetic layer; the method comprising the steps of:

depositing said reference layer with an applied external magnetic field having a first field direction;

depositing said storage layer with the applied external magnetic field having a second field direction, substantially perpendicular to said first field direction; and

annealing said magnetic tunnel junction with the applied external magnetic field having a third field direction substantially parallel or antiparallel to the first field direction.

10. The STT-based TAS-MRAM cell according to claim 1 , wherein

the antiferromagnetic storage layer pins said first magnetization of the ferromagnetic storage layer at a low temperature threshold and unpins the first magnetization at the high temperature threshold.