Read out scheme for several bits in a single MRAM soft layer
View Patent ↗A magnetic tunnel junction (MTJ) device is configured to store at least two bits of data in a single cell utilizing the variable resistance characteristic of a MTJ. The MTJ includes a soft and two fixed magnetic layers with fixed field directions oriented in perpendicular directions. The soft magnetic layer is separated from the fixed layers by insulating layers preferably with different thicknesses, or with different material compositions. The resulting junction resistance can exhibit at least four distinct resistance values dependent on the magnetic orientation of the free magnetic layer. The cell is configured using a pattern with four lobes to store two bits, and eight lobes to store three bits. The resulting cell can be used to provide a fast, non-volatile magnetic random access memory (MRAM) with high density and no need to rewrite stored data after they are read, or as a fast galvanic isolator.
1. A magnetic tunnel junction (MTJ) configured to be programmed with a plurality of bits, comprising:
a soft ferromagnetic layer requiring a low coercivity to magnetize or demagnetize or to change its magnetic orientation, with magnetic anisotropy configured so that the magnetic field of the soft ferromagnetic layer has at least four stable orientations;
two hard ferromagnetic layers requiring substantial coercivity to magnetize or demagnetize or to change its magnetic orientation, formed on either side of the soft ferromagnetic layer with magnetic fields oriented in different directions;
insulating layers separating the two hard ferromagnetic layers from the soft ferromagnetic layer, each insulating layer having a distinguishable resistance that is dependent on the direction of magnetization of the soft ferromagnetic layer;
conductors configured to carry currents to produce magnetic fields to alter the orientation of the magnetic field of the soft ferromagnetic layer; and
a sense amplifier configured to sense the resistance of the MTJ.
2. The MTJ according to claim 1 , wherein the sense amplifier is configured as a current sense amplifier.
3. The MTJ according to claim 1 , wherein the soft ferromagnetic layer is formed with a pattern with at least four lobes.
4. The MTJ according to claim 1 , wherein at least four distinguishable resistances of the MTJ are produced by at least four corresponding stable orientations of the magnetic field of the soft ferromagnetic layer.
5. The MTJ according to claim 4 , wherein the insulating layers are formed with different thicknesses so as to produce the at least four distinguishable resistances for the MTJ corresponding to the stable orientations of the magnetic field of soft ferromagnetic layer.
6. The MTJ according to claim 4 , wherein the insulating layers are formed with different material compositions so as to produce the at least four distinguishable resistances for the MTJ corresponding to the stable orientations of the magnetic field of soft ferromagnetic layer.
7. The MTJ according to claim 1 , wherein the magnetic fields of the two hard ferromagnetic layers are oriented in substantially perpendicular directions.
8. The MTJ according to claim 1 , wherein an antiferromagnetic layer is formed adjacent to each hard ferromagnetic layer.
9. The MTJ according to claim 1 , wherein the soft ferromagnetic layer with magnetic anisotropy is configured as a synthetic antiferromagnetic layer.
10. The MTJ according to claim 1 , wherein the conductors formed adjacent to the MTJ span two orthogonal directions.
11. The MTJ according to claim 1 , wherein the sense amplifier is configured to sense at least four distinguishable resistances of the MTJ.
12. The MTJ according to claim 1 , wherein the MTJ is configured as a galvanic isolator to communicate a plurality of bits across a dielectric boundary.
13. The MTJ according to claim 12 , wherein the MTJ is operated in a substantially uninterrupted store-read sequence.
14. The MTJ according to claim 12 , wherein the conductors configured to carry currents to produce the magnetic fields to alter the orientation of the magnetic field of the soft ferromagnetic layer are dielectrically isolated from the sense amplifier configured to sense the resistance of the MTJ.
15. A magnetic random access memory device, comprising:
an array of a plurality of MTJ memory cells, each cell comprised of
a soft ferromagnetic layer requiring a low coercivity to magnetize or demagnetize or to change its magnetic orientation, with magnetic anisotropy configured so that the magnetic field of the soft ferromagnetic layer has at least four stable orientations;
two hard ferromagnetic layers requiring substantial coercivity to magnetize or demagnetize or to change its magnetic orientation, formed on either side of the soft ferromagnetic layer in each cell with magnetic fields oriented in different directions;
insulating layers separating the two hard ferromagnetic layers from the soft ferromagnetic layer in each cell, each insulating layer having a distinguishable resistance that is dependent on the direction of magnetization of the soft ferromagnetic layer;
conductors configured to carry currents to produce magnetic fields to selectively alter the orientation of the magnetic field of a soft ferromagnetic layer; and
a sense amplifier configured to selectively sense the resistance of an MTJ.
16. The magnetic random access memory device according to claim 15 , wherein the sense amplifier is configured as a current sense amplifier.
17. The magnetic random access memory device according to claim 15 , wherein the soft ferromagnetic layer in each cell is formed with a pattern with at least four lobes.
18. The magnetic random access memory device according to claim 15 , wherein the at least four distinguishable resistances of the cells are produced by at least four corresponding stable orientations of the magnetic field of each soft ferromagnetic layer.
19. The magnetic random access memory device according to claim 18 , wherein the insulating layers in each cell are formed with different thicknesses so as to produce the at least four distinguishable resistances for the MTJs corresponding to the stable orientations of the magnetic field of the soft ferromagnetic layer in each cell.
20. The magnetic random access memory device according to claim 18 , wherein the insulating layers in each cell are formed with different material compositions so as to produce the at least four distinguishable resistances for the MTJs corresponding to the stable orientations of the magnetic field of soft ferromagnetic layer in each cell.
21. The magnetic random access memory device according to claim 15 , wherein the soft ferromagnetic layer with magnetic anisotropy is configured as a synthetic antiferromagnetic layer.
22. The magnetic random access memory device according to claim 15 , wherein the magnetic fields of the two hard ferromagnetic layers in each cell are oriented in substantially perpendicular directions.
23. The magnetic random access memory device according to claim 15 , wherein an antiferromagnetic layer is formed adjacent to each hard ferromagnetic layer in each cell.
24. The magnetic random access memory device according to claim 15 , wherein the conductors span two orthogonal directions.
25. The magnetic random access memory device according to claim 15 , wherein the sense amplifier is configured to sense at least four distinguishable resistances of an MTJ.
26. A method of configuring an MTJ to be programmable with a plurality of bits, comprising:
forming a soft ferromagnetic layer requiring a low coercivity to magnetize or demagnetize or to change its magnetic orientation with magnetic anisotropy, and configuring the magnetic field of the soft ferromagnetic layer so that it has at least four stable orientations;
forming hard ferromagnetic layers requiring substantial coercivity to magnetize or demagnetize or to change its magnetic orientation on either side of the soft ferromagnetic layer with magnetic fields oriented in different directions;
separating the two hard ferromagnetic layers from the soft ferromagnetic layer with insulating layers, each insulating layer having a distinguishable resistance that is dependent on the direction of magnetization of the soft ferromagnetic layer;
forming conductors at right angles to each other and configuring the conductors to carry currents to produce magnetic fields that can alter the orientation of the magnetic field of the soft ferromagnetic layer; and
configuring a sense amplifier to sense the resistance of the MTJ.
27. The method according to claim 26 , including configuring the sense amplifier as a current sense amplifier.
28. The method according to claim 26 , including forming the soft ferromagnetic layer with a pattern with at least four lobes.
29. The method according to claim 26 , including producing at least four distinguishable resistances of the MTJ with at least four corresponding stable orientations of the magnetic field of the soft ferromagnetic layer.
30. The method according to claim 29 , including forming the insulating layers with different thicknesses so as to produce the at least four distinguishable resistances for the MTJ corresponding to the stable orientations of the magnetic field of soft ferromagnetic layer.
31. The method according to claim 29 , including forming the insulating layers with different material compositions so as to produce the at least four distinguishable resistances for the MTJ corresponding to the stable orientations of the magnetic field of soft ferromagnetic layer.
32. The method according to claim 26 , including orienting the magnetic fields of the two hard ferromagnetic layers in substantially perpendicular directions.
33. The method according to claim 26 , including forming an antiferromagnetic layer adjacent to each hard ferromagnetic layer.
34. The method according to claim 26 , including forming conductors adjacent to the MTJ spanning two orthogonal directions.
35. The method according to claim 26 , including configuring the sense amplifier to sense at least four distinguishable resistances of an MTJ.
36. The method according to claim 26 , including configuring the MTJ as a galvanic isolator to communicate a plurality of bits across a dielectric boundary.
37. The method according to claim 26 , including operating the MTJ in a substantially uninterrupted store-read sequence.
38. The method according to claim 36 , including configuring the conductors that carry currents to produce the magnetic fields that alter the orientation of the soft ferromagnetic layer to be dielectrically isolated from the current sense amplifier that is configured to sense the resistance of the MTJ.