Low power magnetic random access memory cell
View Patent ↗The present disclosure concerns a magnetic random access memory (MRAM) cell suitable for performing a thermally assisted write operation or a spin torque transfer (STT) based write operation, comprising a magnetic tunnel junction comprising a top electrode; a tunnel barrier layer comprised between a first ferromagnetic layer having a first magnetization direction, and a second ferromagnetic layer having a second magnetization direction adjustable with respect to the first magnetization direction; a front-end layer; and a magnetic or metallic layer on which the second ferromagnetic layer is deposited; the second ferromagnetic layer being comprised between the front-end layer and the tunnel barrier layer and having a thickness comprised between about 0.5 nm and about 2 nm, such that magnetic tunnel junction has a magnetoresistance larger than about 100%. The MRAM cell disclosed herein has lower power consumption compared to conventional MRAM cells.
1. A magnetic random access memory (MRAM) cell suitable for performing a thermally assisted write operation or a spin torque transfer (STT) based write operation, comprising:
a magnetic tunnel junction comprising a top electrode; a first ferromagnetic layer having a first magnetization direction; a second ferromagnetic layer having a second magnetization direction that can be adjusted with respect to the first magnetization direction;
a tunnel barrier layer between the first ferromagnetic layer and the second ferromagnetic layer; a front-end layer, the second ferromagnetic layer being between the front-end layer and the tunnel barrier layer;
the magnetic tunnel junction further comprising a magnetic or metallic layer, and an underlayer, on which the second ferromagnetic layer is deposited such that the second ferromagnetic layer has a roughness of less than about 0.2 nm RMS and a grain size of less than about 15nm, the underlayer having a crystallographic structure that matches a crystallographic structure of the second ferromagnetic layer; and
the second ferromagnetic layer has a thickness comprised between about 0.5 nm and about 2 nm and the magnetic tunnel junction has a magnetoresistance larger than about 100%.
2. MRAM cell according to claim 1 , wherein the second magnetization direction of the second ferromagnetic layer can be adjusted in a reversible manner by passing a spin polarized current in the magnetic tunnel junction.
3. MRAM cell according to claim 1 , wherein the second ferromagnetic magnetic layer is made from an alloy comprising one of Fe, Ni, Co, Cr, V, Si and B, or a combination of any one of them.
4. MRAM cell according to claim 1 , wherein said magnetic or metallic layer comprises an underlayer in contact with the second ferromagnetic layer.
5. MRAM cell according to claim 4 , wherein the underlayer is made of a metallic polycrystalline alloy comprising one of Ta, Ti, Cu, Ru, NiFe, TiW, NiFeCr, CoSi, or comprising one of TaN, TiN, CuN, TiWN, CoSiN.
6. MRAM cell according to claim 4 , wherein the underlayer has a thickness in the range comprised between about 1 nm and about 100 nm.
7. MRAM cell according to claim 1 , wherein said magnetic or metallic layer comprises an antiferromagnetic storage layer.
8. MRAM cell according to claim 1 , wherein said magnetic or metallic layer comprises a bottom electrode.
9. MRAM cell according to claim 1 , wherein said second ferromagnetic layer is configured to provide the magnetic tunnel junction with the magnetoresistance that is larger than about 100% by having been annealed at a temperature between about 280° C. and about 360° C. for between about 30 minutes and 2 hours 30 minutes under an applied magnetic field of between about 0.5 Tesla and about 2 Tesla.
10. Method for forming the MRAM cell of claim 1 , the method comprising:
depositing the second ferromagnetic layer on the magnetic or metallic layer;
depositing the tunnel barrier layer on the second ferromagnetic layer; and
depositing the first ferromagnetic layer on the tunnel barrier layer;
the second ferromagnetic layer being deposited with the thickness comprised between about 0.5 nm and about 2 nm.
11. Method according to claim 10 , wherein the magnetic tunnel junction further comprises a bottom electrode, and wherein the method further includes depositing the bottom electrode, and depositing the second ferromagnetic layer on the bottom electrode.
12. Method according to claim 11 , wherein the magnetic tunnel junction further comprises an antiferromagnetic storage layer, and wherein the method further comprises depositing the antiferromagnetic storage layer between the bottom electrode and the second ferromagnetic layer.
13. Method according to claim from 10 , further comprising depositing the underlayer made of a metallic polycrystalline alloy, said depositing the second ferromagnetic layer comprises depositing the second ferromagnetic layer on the underlayer.
14. Method according to claim 13 , wherein the underlayer is deposited with a thickness being comprises between about 1 nm and about 100 nm.
15. A magnetic memory device comprising a plurality of MRAM cells, each MRAM cell comprising
a magnetic tunnel junction comprising a top electrode;
a tunnel barrier layer comprised between a first ferromagnetic layer having a first magnetization direction, and a second ferromagnetic layer having a second magnetization direction adjustable with respect to the first magnetization direction;
a front-end layer; and
a magnetic or metallic layer, and an underlayer, on which the second ferromagnetic layer is deposited such that the second ferromagnetic layer has a roughness of less than about 0.2 nm RMS and a grain size of less than about 15 nm, the underlayer having a crystallographic structure that matches a crystallographic structure of the second ferromagnetic layer, and
the second ferromagnetic layer being comprised between the front-end layer and the tunnel barrier layer and having a thickness comprised between about 0.5 nm and about 2 nm, such that magnetic tunnel junction has a magnetoresistance larger than about 100%.