MAGNETORESISTIVE MEMORY DEVICES INCLUDING DUAL FREE LAYERS AND METHODS FOR MAKING AND OPERATING THE SAME

1 . A magnetoresistive memory cell, comprising:

a magnetic polarizer layer having a hard magnetization along a hard magnetization direction;

a first magnetic tunnel junction located on a first side of the magnetic polarizer layer and comprising a first reference layer having a first side facing the magnetic polarizer layer, a first free layer facing a second side of the first reference layer, and a first tunnel barrier layer located between the first free layer and the first reference layer; and

a second magnetic tunnel junction located on a second side of the magnetic polarizer layer and comprising a second reference layer having a second side facing the magnetic polarizer layer, a second free layer facing a first side of the second reference layer, and a second tunnel barrier layer located between the second free layer and the second reference layer.

2 . The magnetoresistive memory cell of claim 1 , wherein:

the first reference layer faces the first side of the magnetic polarizer layer, is antiferromagnetically coupled to the magnetic polarizer layer, and has a first fixed magnetization direction that is antiparallel to the hard magnetization direction; and

the second reference layer faces the second side of the magnetic polarizer layer, antiferromagnetically coupled to the magnetic polarizer layer, and has a second fixed magnetization direction that is antiparallel to the hard magnetization direction.

3 . The magnetoresistive memory cell of claim 2 , wherein:

the first magnetic tunnel junction has a first parallel state resistance when a magnetization direction of the first free layer is parallel to the first fixed magnetization direction; and

the second magnetic tunnel junction has a second parallel state resistance when a magnetization direction of the second free layer is parallel to the second fixed magnetization direction.

4 . The magnetoresistive memory cell of claim 3 , wherein the first free layer and the second free layer both comprise a positive spin polarization material.

5 . A magnetoresistive memory device comprising the magnetoresistive memory cell of claim 4 and a programming circuit configured to program magnetization directions of the first free layer and the second free layer into two magnetic configurations comprising:

a first, relatively low resistance magnetic configuration in which the first magnetic tunnel junction is in the first parallel state and the second magnetic tunnel junction is in the second parallel state; and

a second, relatively high resistance magnetic configuration in which the first magnetic tunnel junction is in the first antiparallel state and the second magnetic tunnel junction is in the second antiparallel state, wherein the relatively high resistance is higher than the relatively low resistance.

6 . The magnetoresistive memory device of claim 5 , wherein the programing circuit is configured to program the magnetization directions of the first free layer and the second free layer into the first, relatively low resistance magnetic configuration by:

applying a relatively large first negative electron current to the magnetoresistive memory cell that flows in a first direction from the first reference layer to the first free layer, to switch the first magnetic tunnel junction into the first parallel state; and

applying a relatively small first positive electron current to the magnetoresistive memory cell that flows in a second direction from the second reference layer to the second free layer, which is opposite to the first direction, to switch the second magnetic tunnel junction into the second parallel state without disturbing the magnetization direction of the first free layer which requires a relatively large second positive electron current which is greater than the first positive electron current to switch into the first antiparallel state.

7 . The magnetoresistive memory device of claim 6 , wherein the programing circuit is configured to program the magnetization directions of the first free layer and the second free layer into the second, relatively high magnetic configuration by:

applying a relatively large second positive electron current which is larger than the first positive electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction into the first antiparallel state and to switch the second magnetic tunnel junction into the second parallel state; and

applying a relatively small second negative electron current which is smaller than the first negative current to the magnetoresistive memory cell to switch the second magnetic tunnel junction into the second antiparallel state, without disturbing the magnetization direction of the first free layer which requires the relatively large first negative current which is greater than the second negative current to switch into the first parallel state.

8 . The magnetoresistive memory cell of claim 3 , wherein the first free layer comprises a positive spin polarization material and the second free layer comprises a negative spin polarization material.

9 . A magnetoresistive memory device comprising the magnetoresistive memory cell of claim 8 and a programming circuit configured to program magnetization directions of the first free layer and the second free layer into two magnetic configurations comprising:

a first, relatively low resistance magnetic configuration in which the first magnetic tunnel junction is in the first parallel state and the second magnetic tunnel junction is in the second antiparallel state; and

a second, relatively high resistance magnetic configuration in which the first magnetic tunnel junction is in the first antiparallel state and the second magnetic tunnel junction is in the second parallel state, wherein the relatively high resistance is higher than the relatively low resistance.

10 . The magnetoresistive memory device of claim 9 , wherein the programing circuit is configured to program the magnetization directions of the first free layer and the second free layer into the first, relatively low resistance magnetic configuration by applying a negative electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction to the first parallel state and to switch the second magnetic tunnel junction to the second antiparallel state.

11 . The magnetoresistive memory device of claim 10 , wherein the programing circuit is configured to program the magnetization directions of the first free layer and the second free layer into the second, relatively high resistance magnetic configuration by applying a positive electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction to the first antiparallel state and to switch the second magnetic tunnel junction into the second parallel state.

12 . The magnetoresistive memory cell of claim 1 , wherein:

the positive spin polarization material comprises Fe, Co, Ni or an alloy thereof; and

the negative spin polarization material comprises Fe 1−x Cr x where x<0.7, a Mn 2 VGa Heusler alloy, Fe 4 N or SrRuO 3 .

13 . The magnetoresistive memory cell of claim 1 , wherein the magnetoresistive memory cell further comprises a selector element.

14 . The magnetoresistive memory cell of claim 13 , wherein the magnetoresistive memory cell further comprises:

a first antiferromagnetic coupling layer located between the magnetic polarizer layer and the first reference layer and providing the antiferromagnetic coupling therebetween; and

a second antiferromagnetic coupling layer located between the magnetic polarizer layer and the second reference layer and providing the antiferromagnetic coupling therebetween.

15 . The magnetoresistive memory cell of claim 1 , wherein the magnetic polarizer layer comprises a hard magnet layer.

16 . The magnetoresistive memory cell of claim 1 , wherein:

the first reference layer underlies the magnetic polarizer layer;

the first free layer underlies the first reference layer;

the second reference layer overlies the magnetic polarizer layer; and the second free layer overlies the second reference layer.

17 . A method, comprising programming the magnetoresistive memory cell of claim 4 into two different memory states comprising:

a first, relatively low resistance memory state in which the first magnetic tunnel junction is in a first parallel state and the second magnetic tunnel junction is in a second parallel state; and

a second, relatively high resistance memory state in which the first magnetic tunnel junction is in the first antiparallel state and the second magnetic tunnel junction is in the second antiparallel state.

18 . The method of claim 17 , comprising:

programming the magnetoresistive memory cell into the first, relatively low resistance memory state by:

applying a relatively large first negative electron current to the magnetoresistive memory cell that flows in a first direction from the first reference layer to the first free layer, to switch the first magnetic tunnel junction into the first parallel state; and

applying a relatively small first positive electron current to the magnetoresistive memory cell that flows in a second direction from the second reference layer to the second free layer, which is opposite to the first direction, to switch the second magnetic tunnel junction into the second parallel state without disturbing the magnetization direction of the first free layer which requires a relatively large second positive electron current which is greater than the first positive electron current to switch into the first antiparallel state.

programming the magnetoresistive memory cell into the second, relatively high resistance memory state by:

applying a relatively large second positive electron current which is larger than the first positive electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction into the first antiparallel state and to switch the second magnetic tunnel junction into the second parallel state; and

applying a relatively small second negative electron current which is smaller than the first negative current to the magnetoresistive memory cell to switch the second magnetic tunnel junction into the second antiparallel state, without disturbing the magnetization direction of the first free layer which requires the relatively large first negative current which is greater than the second negative current to switch into the first parallel state.

19 . A method, comprising programming the magnetoresistive memory cell of claim 8 into two different memory states comprising:

a first, relatively low resistance memory state in which the first magnetic tunnel junction is in a first parallel state and the second magnetic tunnel junction is in a second antiparallel state; and

a second, relatively high resistance memory state in which the first magnetic tunnel junction is in the first antiparallel state and the second magnetic tunnel junction is in the second parallel state.

20 . The method of claim 19 , comprising:

programming the magnetoresistive memory cell into the first, relatively low resistance memory state by applying a negative electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction to the first parallel state and to switch the second magnetic tunnel junction to the second antiparallel state; and

programming the magnetoresistive memory cell into the second, relatively high resistance memory state by applying a positive electron current to the magnetoresistive memory cell to switch the first magnetic tunnel junction to the first antiparallel state and to switch the second magnetic tunnel junction into the second parallel state.