MAGNETIC MEMORY WITH A THERMALLY ASSISTED WRITING PROCEDURE

• US 20100246254A1
• Filed: 06/11/2010
• Published: 09/30/2010
• Est. Priority Date: 12/13/2007
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Crocus Technology S.A.
• Inventors: Nozieres, Jean-Pierre, Prejbeanu, Ioan Lucian
• Granted Patent: US 8,102,701 B2
• Time in Patent Office: Days
• US Class Current: 365/171
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods

Abstract

A magnetic memory device of MRAM type with a thermally-assisted writing procedure, the magnetic memory device being formed from a plurality of memory cells, each memory cell comprising a magnetic tunnel junction, the magnetic tunnel junction comprising a magnetic storage layer in which data can be written in a writing process; a reference layer, having a magnetization being always substantially in the same direction at any time of the writing process; an insulating layer between the reference layer and the storage layer; wherein the magnetic tunnel junction further comprises a writing layer made of a ferrimagnetic 3d-4f amorphous alloy, and comprising a net magnetization containing a first magnetization contribution originating from the sub-lattice of 3d transition elements and a second magnetization contribution originating from the sub-lattice of 4f rare-earth elements. The magnetic memory device has a low power consumption.

Claims

1. A magnetic memory device of MRAM type with a thermally-assisted writing procedure, the magnetic memory device being formed from a plurality of memory cells, each memory cell comprising a magnetic tunnel junction formed from:

a magnetic storage layer in which data can be written in a writing process;

a reference layer, having a magnetization being always substantially in the same direction at any time of the writing process;

an insulating layer between the reference layer and the storage layer;

wherein

the magnetic tunnel junction further comprises a writing layer made of a ferrimagnetic 3d-4f amorphous alloy and comprising a net magnetization containing a first magnetization contribution originating from the sub-lattice of 3d transition elements and a second magnetization contribution originating from the sub-lattice of 4f rare-earth elements.

2. A magnetic memory device according to claim 1, wherein

the net magnetization of the writing layer is dominated by the second magnetization contribution at a temperature below a compensation temperature T_COMP of the writing layer, and dominated by the first magnetization contribution at a temperature above T_COMP.

3. A magnetic memory device according to claim 1, wherein

the writing layer is made of an alloy containing Co or Fe with Gd, Sm, or Tb.

4. A magnetic memory device according to claim 1, wherein

the writing layer is composed of GdCo, SmCo or TbFeCo.

5. A magnetic memory device according to claim 1, wherein

the magnetic tunnel junction further comprises a non-magnetic spacer layer between the writing layer and the storage layer.

6. A magnetic memory according to claim 1, wherein the storage layer comprises a ferromagnetic storage layer and an antiferromagnetic storage layer, the antiferromagnetic storage layer having a blocking temperature T_BS

7. A magnetic memory according to claim 6, wherein the blocking temperature T_BS is in a range comprised between 120°

C. and 220°

C.

8. A magnetic memory device according to claim 6, wherein

the reference layer comprises an antiferromagnetic reference layer having a blocking temperature T_BR higher than T_BS.

9. A magnetic memory device according to claim 8, wherein

the compensation temperature T_COMP of the writing layer is higher than the blocking temperature T_BS of the antiferromagnetic storage layer and lower than the blocking temperature T_BR of the antiferromagnetic reference layer.

10. A method for writing a magnetic memory device comprising a plurality of memory cells, each memory cell comprising a magnetic tunnel junction formed from a magnetic storage layer containing a ferromagnetic storage layer having a magnetization that can be reversed during the writing process, a reference layer having a magnetization being always substantially in the same direction during the writing process, and an insulating layer between the reference layer and the storage layer;

the magnetic tunnel junction further comprising a writing layer made of a ferrimagnetic 3d-4f amorphous alloy comprising a net magnetization containing a first magnetization contribution originating from the sub-lattice of 3d transition elements and a second magnetization contribution originating from the sub-lattice of 4f rare-earth elements;

the method comprising;

orienting the net magnetization of the writing layer substantially antiparallel to the magnetization of the ferromagnetic storage layer;

reversing the magnetization of the first magnetization contribution of the writing layer substantially antiparallel with the magnetization of the ferromagnetic layer;

reversing the magnetization of the second magnetization contribution of the writing layer substantially antiparallel with the first magnetization contribution; and

reversing the magnetization of the ferromagnetic storage layer substantially antiparallel in respect to the net magnetization of the writing layer.

11. A method according to claim 10, wherein the antiferromagnetic storage layer has a blocking temperature T_BS, and wherein orienting the net magnetization of the writing layer is performed with the magnetic tunnel junction being at a temperature T₁ below T_BS.

12. A method according to claim 11, wherein the net magnetization being dominated by the first and second magnetization contribution at a temperature respectively above and below a compensation temperature T_COMP of the writing layer, and wherein

reversing the magnetization of the first magnetization contribution is performed with the magnetic tunnel junction being heated at a temperature T₂, above T_BS and T_COMP, but below the Curie temperature of the writing and antiferromagnetic storage layers.

13. A method according to claim 12, wherein reversing the magnetization of the second magnetization contribution is performed with the magnetic tunnel junction being at a temperature T₃, lower than T_COMP but higher than T_BS.

14. A method according to claim 10, wherein reversing the magnetization of the ferromagnetic storage layer is performed at a temperature T₅ below T_BS where the magnetization of the ferromagnetic layer becomes frozen.

15. A method according to claim 13, wherein the magnetic tunnel junction being heated at the temperature T₂ by passing a junction current pulse through the junction.

16. A method for writing a magnetic memory device comprising a plurality of memory cells, each memory cell comprising a magnetic tunnel junction formed from a magnetic storage layer containing a ferromagnetic storage layer having a magnetization that can be reversed during the writing process, a reference layer having a magnetization being always substantially in the same direction during the writing process, and an insulating layer between the reference layer and the storage layer;

the magnetic tunnel junction further comprising a writing layer made of a ferrimagnetic 3d-4f amorphous alloy comprising a net magnetization containing a first magnetization contribution originating from the sub-lattice of 3d transition elements and a second magnetization contribution originating from the sub-lattice of 4f rare-earth elements;

the method comprising;

an initial step where the net magnetization of the writing layer is oriented antiparallel in respect to the magnetization of the ferromagnetic storage layer due to magnetostatic interactions between the two layers;

a second step where the magnetization of the first magnetization contribution of the writing layer is reversed by 180°

compared to its orientation in the initial step;

a third step where the magnetization of the second magnetization contribution of the writing layer is reversed by 180°

compared to its direction in the initial state;

a fourth step where the magnetization of the ferromagnetic storage layer is reversed by 180°

compared to its direction in the initial state due to magnetostatic interactions between the ferromagnetic storage layer and the writing layer;

a final step where the magnetization of the ferromagnetic storage layer and the net magnetization of the writing layer is reversed by 180°

in respect to their respective orientations in the initial step.