Memory cells, semiconductor device structures, memory systems, and methods of fabrication
Memory cells are disclosed. Magnetic regions within the memory cells include an alternating structure of magnetic sub-regions and coupler sub-regions. The coupler material of the coupler sub-regions antiferromagnetically couples neighboring magnetic sub-regions and effects or encourages a vertical magnetic orientation exhibited by the neighboring magnetic sub-regions. Neighboring magnetic sub-regions, spaced from one another by a coupler sub-region, exhibit oppositely-directed magnetic orientations. The magnetic and coupler sub-regions may each be of a thickness tailored to form the magnetic region in a compact structure. Interference between magnetic dipole fields emitted from the magnetic region on switching of a free region in the memory cell may be reduced or eliminated. Also disclosed are semiconductor device structures, spin torque transfer magnetic random access memory (STT-MRAM) systems, and methods of fabrication.
1. A memory cell comprising:
a free region and a fixed region each exhibiting a vertical magnetic orientation, at least one of the free region and the fixed region comprising:
magnetic sub-regions, each magnetic sub-region comprising a magnetic material and having a height of less than about four angstroms; and
coupler sub-regions alternating with the magnetic sub-regions and providing anti-parallel coupling of neighboring magnetic sub-regions of the magnetic sub-regions, each coupler sub-region comprising a coupler material and having a height of less than about six angstroms,
the free region and the fixed region disposed in a cell core through which a current is flowable to program the memory cell.
2. The memory cell of claim 1 , wherein the at least one of the free region and the fixed region comprises at least three of the magnetic sub-regions of the magnetic material and at least two of the coupler sub-regions of the coupler material.
3. The memory cell of claim 1 , wherein each of the magnetic sub-regions is spaced from another of the magnetic sub-regions by one of the coupler sub-regions.
4. The memory cell of claim 1 , wherein each of the magnetic sub-regions exhibits a vertical magnetic orientation oppositely directed to a vertical magnetic orientation exhibited by a neighboring magnetic sub-region of the magnetic sub-regions.
5. The memory cell of claim 1 , wherein each of the magnetic sub-regions defines a height less than about three angstroms.
6. The memory cell of claim 1 , wherein each of the coupler sub-regions defines a height less than about five angstroms.
7. The memory cell of claim 1 , wherein the coupler material is formulated to effect or encourage vertical magnetic orientation exhibited by the neighboring magnetic sub-regions.
8. The memory cell of claim 1 , wherein the at least one of the free region and the fixed region is free of platinum and palladium.
9. The memory cell of claim 1 , wherein the magnetic material comprises cobalt.
10. The memory cell of claim 1 , wherein the magnetic material consists essentially of cobalt.
11. The memory cell of claim 1 , wherein the coupler material comprises at least one of ruthenium and rhodium.
12. A method of forming a memory cell, the method comprising:
forming a cell core through which a programming current is flowable during operation of the memory cell, comprising
forming one of a free region and a fixed region of the memory cell, comprising:
forming a magnetic sub-region to a thickness of less than about four angstroms, the magnetic sub-region exhibiting a vertical magnetic orientation;
forming a coupler sub-region on the magnetic sub-region to a thickness of less than about six angstroms;
forming another magnetic sub-region on the coupler sub-region to a thickness of less than about four angstroms, the another magnetic sub-region exhibiting another vertical magnetic orientation oppositely directed to the vertical magnetic orientation exhibited by the magnetic sub-region;
forming another coupler sub-region on the another magnetic sub-region to a thickness of less than about six angstroms; and
forming an additional magnetic sub-region on the another coupler sub-region to a thickness of less than about four angstroms, the additional magnetic sub-region exhibiting an additional vertical magnetic orientation oppositely directed to the vertical magnetic orientation exhibited by the another magnetic sub-region; and
forming another of the free region and the fixed region of the memory cell.
13. The method of claim 12 , further comprising forming a reference region of the memory cell.
14. The method of claim 12 , wherein forming another of the free region and the fixed region of the memory cell comprises forming additional magnetic sub-regions spaced from one another by additional coupler sub-regions.
15. The method of claim 14 , further comprising forming a non-magnetic region disposed between the one and the another of the free region and the fixed region of the memory cell.
16. A memory cell comprising at least two magnetic regions in a cell core, each of the at least two magnetic regions exhibiting either a fixed magnetic orientation or a switchable magnetic orientation, the switchable magnetic orientation being switchable by a current flowing through the cell core during operation of the memory cell, at least one of the at least two magnetic regions comprising coupler sub-regions, each of the coupler sub-regions defining a height of less than about six angstroms and separated from another of the coupler sub-regions by a magnetic sub-region exhibiting a vertical magnetic orientation and having a height of less than the height of the coupler sub-regions, each of the coupler sub-regions effecting anti-parallel coupling in the magnetic sub-region and another magnetic sub-region.
17. The memory cell of claim 16 , wherein the at least two magnetic regions comprise a free region and a fixed region, the free region exhibiting the switchable magnetic orientation, and the fixed region exhibiting the fixed magnetic orientation.
18. The memory cell of claim 16 , wherein at least two of the at least two magnetic regions each comprise a plurality of the coupler sub-regions.
19. The memory cell of claim 18 , wherein the plurality of the coupler sub-regions of one of the at least two magnetic regions comprises a different number of coupler sub-regions than the plurality of the coupler sub-regions of another of the at least two magnetic regions.
20. The memory cell of claim 18 , wherein at least one of the at least two magnetic regions exhibits the switchable magnetic orientation.
21. The memory cell of claim 16 , wherein each of the coupler sub-regions is disposed adjacent to a pair of magnetic sub-regions, each of the pair of magnetic sub-regions exhibiting the vertical magnetic orientation.
22. A memory cell comprising a magnetic region exhibiting a magnetic orientation that remains fixed when a programming current flows through a cell core of the memory cell, the magnetic region comprising a plurality of magnetic sub-regions each having a height of less than about three angstroms, at least one magnetic sub-region of the plurality exhibiting a vertical magnetic orientation opposing vertical magnetic orientations exhibited by a pair of neighboring magnetic sub-regions of the plurality, the at least one magnetic sub-region of the plurality spaced from each of the pair of neighboring magnetic sub-regions by a distance of less than about five angstroms.
23. The memory cell of claim 22 , wherein the at least one magnetic sub-region of the plurality is spaced from the pair of neighboring magnetic sub-regions of the plurality by a coupler material.
24. A semiconductor device structure, comprising:
a spin torque transfer magnetic random access memory (STT-MRAM) array comprising:
a plurality of STT-MRAM cells, each STT-MRAM cell of the plurality comprising:
a cell core through which a programming current is flowable during operation of the each STT-MRAM cell, the cell core comprising a free region and a fixed region both exhibiting a vertical magnetic orientation, at least one of the free region and the fixed region comprising a plurality of spaced sub-regions of a coupler material effecting anti-parallel coupling of neighboring sub-regions of magnetic material, the sub-regions of the coupler material each defining a thickness of less than about five angstroms and spaced distance less than about four angstroms.
25. The semiconductor device structure of claim 24 , wherein each of the plurality of spaced sub-regions of the coupler material is formulated and positioned to provide Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction with the neighboring sub-regions of magnetic material, the neighboring sub-regions of the magnetic material being directly adjacent each of the plurality of spaced sub-regions of the coupler material.
26. The semiconductor device structure of claim 25 , wherein one of the neighboring sub-regions of the magnetic material exhibits a vertical magnetic orientation oppositely directed to a vertical magnetic orientation exhibited by another of the neighboring sub-regions of the magnetic material.
27. A spin torque transfer magnetic random access memory (STT-MRAM) system, comprising:
at least one magnetic memory cell programmable by applying a programming current through a cell core of the at least one magnetic memory cell, the at least one magnetic memory cell comprising:
a fixed region in the cell core and comprising a plurality of sub-regions of magnetic material, sub-regions of the plurality exhibiting oppositely directed vertical magnetic orientations relative to other vertical magnetic orientations exhibited by other sub-regions of the plurality, the sub-regions and the other sub-regions of the plurality spaced from each other by one of a plurality of coupler sub-regions having a greater height than a height of each of the sub-regions and the other sub-regions of the plurality, the height of the one of the plurality of coupler regions being less than about six angstroms; and
at least one peripheral device in operable communication with the at least one magnetic memory cell.
28. The STT-MRAM system of claim 27 , wherein the fixed region is free of platinum and palladium.